7 DAY

Stratigraphy of the
Outeropping Post- agothy
Upper Cretaceous Formations
in Southern New Jersey and
Northern Delmarva Peninsula,
Delaware and Maryland .

 

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U.S.S.D.

Stratigraphy of the
Outeropping Post-Magothy
Upper Cretaceous Formations
in Southern New Jersey and
Northern Delmarva Peninsula,
Delaware and Maryland

By JAMES P. OWENS, JAMES P. MINARD, NORMAN F. SOHL, and JAMES F. MELLO

 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 674

Lit/zoxtra tz'grap/zz'c a nd fiz’on‘ra tigrap/zie

:tua’z‘ee confirm the ferriyz‘enee of four

Campanian formation: from northern New j‘errey
to northern Delaware and eaxtern Maryland

 

 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1970

UNITED STATES DEPARTMENT OF THE INTERIOR

WALTER J. HICKEL, Secretary

GEOLOGICAL SURVEY

William T. Pecora, Director

Library of Congress catalog-card No. 73—608366

 

For sale by the Superintendent of Documents,
V U. 8. Government Printing Office
'Washington, DC. 20402~Price 65 cents (paper cover)

 

CONTENTS

 

 

 

 

  
  
 

 

 

 

 

 
 
 
 

  
 
 
 

 
 
 

 

 

  
  

 

Page Page
Abstract .............. 1 Rock stratigraphic studies—Continued
Introduction ............................................................... 1 Petrologic studies .............................................................. 22
Previous investigations ............................................................ 1 Heavy—mineral analyses _ _ 23
Rock stratigraphic studies, by James P. Owens and Light-mineral analyses ____________________________________________ 23
James P. Minard ---------------------------------------------------------- 5 Glauconite—clastic ratios .......................................... 24
New Jersey -------------------------------------------------------------- 5 Clay—mineral analyses .............................................. 25
Merchantvflle Formation .............................. 5 Conclusions ________________________________________________________________________ 26
Woodbury Clay """""" 6 Biostratigraphic analysis, by Norman F. Sohl and
Enghshtown Formation ................................... 6 James F Mello 28
Marshalltown Formation ................................. 6 ' """"""""""""""""""""""""""""""""
Wenonah Formation __________ 6 Megapaleontologic studies ................................ 28
Mount Laurel Sand ___________________________________________ 6 Northern Atlantic Coastal Plain ............ 28
Navesink Formation _____________________________________________ 7 Problems of regional correlation 28
Red Bank Sand _________ 7 Revised correlations ............................. 31
Tinton Sand ______________________________________________________________ 7 Summary of Cretaceous megafauna ............ 35
Distribution of formations ______________________________________ 7 Cretaceous megafauna fossils from the Chesa-
Summary of rock stratigraphic studies in New peake and Delaware Canal ............ 35
Jersey ______________________________________________________________________ 10 Merchantville Formation ................ 35
Northern Delaware __________________________________________________________ 11 Englishtown Formation ......... 39
Distribution of formations ..................................... 11 Marshalltown Formation ............ 41
Section along Chesapeake and Delaware Mount Laurel Sand ................................ 44
Canal near Summit Bridge ________________________ 11 Navesink and younger formations ................ 49
Section 1.1 miles west of St. Georges to 1.3 Summary Of megapaleontologic studies ------ 50
miles east of St. Georges at Biggs Farm 15 Micropaleontolog‘ic studies ______________________________________________ 50
Section near Odessa ---------------------------------------- 17 Sampling procedures and sample designations .. 50
Comparison of the Upper Cretaceous forma- Taxonomic revisions ________________________________________________ 52
tions 1n northern Delaware‘and southern Age interpretations __________________________ 52
New Jersey """""""""""""""""""""""""""""""" 17 E ' t l 'nter retations 54
Eastern Maryland ....................... _ 20 nv1ronmen a .1 p , """"" , """""""
Distribution of formations _____________________________________ 20 Summary of micropaleontologic studies .............. 54
Summary of rock stratigraphic studies in east- Selected references ------------------------------------------------------------------ 55
ern Maryland ........................................................ 22 Index ............................................................................................ 57
ILLUSTRATIONS
Page
FIGURE 1. Index map of southern New Jersey and northern Delmarva Peninsula ................................................................ 2
I 2. Correlation chart showing development of stratigraphic interpretations of the pre-Miocene strata in New
Jersey ............................................................................................................................ 1. ..................................................... 3
3. Composite columnar section showing the Upper Cretaceous formations in the northern and west-central
Coastal Plain in New Jersey ........................................................................................................................................ 5
4. Stratigraphic section showing Upper Cretaceous formations from southwestern New Jersey to eastern
Maryland ........................................................................................................................................................................... 8
5 Geologic map of southern New Jersey and northern Delmarva Peninsula .................................................. 9
6. Sketch map showing localities along the Chesapeake and Delaware Canal ...................................................... 12
7. Photograph showing excavation for new railroad bridge near Summit Bridge, Del .. ..... 12
8 Columnar section for new railroad bridge near Summit Bridge, Del ...................................................................... 13
9—12 Photographs showing:
9. Contact between Marshalltown and Englishtown Formations _ ...... 14
10. Sharp contact between overlying Englishtown and Merchantville Formations .................................. 14

III

IV

FIGURE

13—15.

16—18.

TABLE

19.
20.

21.
22.

23.

25.

CONTENTS

 

 

Page
11. Large Ophiomorpha nodusa borings in the Englishtown Formation ...................................................... 15
12. Contact between sandy and clayey calcareous beds of the Mount Laurel Sand .................................. 16
Columnar sections showing:
13. Stratigraphic sequence in northern Delaware .............................................................................................. 18
14. Cyclic pattern of deposition in northern Delaware and New Jersey .. 19
15. Upper Cretaceous formations in eastern Maryland .................... 20
Photographs showing:
16. Contact of the Merchantville and Magothy at Grove Point on Chesapeake Bay ................................ 21
17. Dark massive—bedded Marshalltown Formation along north bank of Sassafras River ........................ 21
18. Contact between Mount Laurel Sand and Marshalltown Formation ........................................................ 22

Histograms showing heavy-mineral distribution from Woodstown, N.J., to the eastern shore of Maryland 26
Histograms showing light-mineral and glauconite—clastic ratio distributions from Woodstown, N.J., to the

eastern shore of Maryland ........................................................................................................................................... 27
Diagram showing ranges of molluscan species from the Upper Cretaceous rocks of New Jersey .................... 29
Graphs showing state of preservation of the described Late Cretaceous pelecypod and gastropod fauna of

New Jersey ........................................................................................................................................................................ 30
Chart showing correlation of the Upper Cretaceous post-Raritan formations .................................................... 32
Chart showing comparison of stage nomenclature as it has been applied to the Upper Cretaceous sequence

in New Jersey ................................................................................................................................................................. 33
Graph showing clustering of nine samples from the Mount Laurel Sand and Marshalltown Formation ...... 54

 

TABLES

 

 

 

 

 

 

 

 

Page
Stratigraphic interpretations of formations cropping out along or south of the Chesapeake and Delaware
Canal .................................................................................................................................................................................... 4
Heavy- and light- mineral content and glauconite-clastic ratios from Woodstown quadrangle, New Jersey,
and from eastern Maryland .......................................................... 24
Heavy- and light- mineral concentrations and glauconite-clastic ratios from localities in the vicinity of the
Chesapeake and Delaware Canal 25
Minerals in the clay—silt range in the formations discussed 1n the text 28
Megainvertebrate distribution in the Merchantville Formation in the Chesapeake and Delaware Canal area
and New Jersey ............... 36
Megainvertebrate distribution in the Englishtown Formation in the Chesapeake and Delaware Canal area
and New Jersey ............................................................ 40
Megainvertebrate distribution in the Marshalltown Formation in the Chesapeake and Delaware Canal area
and New Jersey 42
Megainvertebrate distribution in the Mount Laurel sand in the Chesapeake and Delaware Canal area and
New Jersey ........ 46

Distribution of microfauna in the Englishtown and Marshalltown Formations and Mount Laurel Sand in
southern New Jersey and northern Delaware 51

STRATIGRAPHY OF THE OUTCROPPING POST-MAGOTHY
UPPER CRETACEOUS FORMATIONS IN SOUTHERN NEW
JERSEY AND NORTHERN DELMARVA PENINSULA,
DELAWARE AND MARYLAND

By JAMES P. OWENS, JAMES P. MINARD, NORMAN F. SOHL, AND JAMES F. MELLO

ABSTRACT

Stratigraphic studies of the post-Magothy Upper Cretace-
ous Coastal Plain formations of the Delmarva Peninsula
indicate that four of the formations recognized in New Jersey
are present in northern Delaware and eastern Maryland.
These are the Merchantville, Englishtown, and Marshalltown
Formations and the Mount Laurel Sand; the Wenonah and
Navesink Formations probably either pinch out or have been
eroded away between southern New Jersey and northern
Delaware. Although the four formations persist as recog-
nizable lithostratigraphic units from New Jersey into the
Delmarva Peninsula, each shows a depletion of glauconite
sand toward the southwest.

Comparison of the faunas of the formations in the two
areas confirms the rock stratigraphic correlations. The me-
gainvertebrate fossils have proved to be, in this area, more
useful than the microfauna in stratigraphic correlation. The
Exogyra cancellata zone in the Mount Laurel Sand and the
E. ponderosa zone in the Marshalltown Formation are in
the same stratigraphic positions in southern New Jersey and
in the Delmarva Peninsula.

INTRODUCTION

The northern Atlantic Coastal Plain was one of
the earliest areas investigated geologically in North
America, and a stratigraphy of Coastal Plain forma-
tions gradually evolved from the many early investi-
gations. Much effort was devoted to the study of the
sediments of Cretaceous to early Tertiary age be-
cause of their good exposure between Raritan Bay,
N.J., and the Potomac River in northern Virginia.
North and south of this region, younger sediments
overlap and obscure the underlying Cretaceous and
lower Tertiary beds. In the northern Atlantic Coastal
Plain the most detailed stratigraphy of these beds
was established for the west-central and northern
parts of the Coastal Plain in New Jersey. In Dela-
ware and Maryland, the stratigraphy that evolved
was less detailed. One of the major reasons for the
lack of knowledge of detailed stratigraphy southwest
of New Jersey is that Delaware Bay and Chesapeake
Bay prevent tracing along the outcrop of the New

 

Jersey formations into Delaware and Maryland.
These bays divide the outcrop belt of Upper Cretace-
ous and lower Tertiary formations in the northern
Atlantic Coastal Plain into three ".larts: New Jersey,
Delmarva Peninsula (east of Chesapeake Bay), and
the western Maryland Coastal Plain (west of Chesa-
peake Bay). _

In recent years, three major attempts have been
made to extend the Upper Cretaceous-lower Tertiary
stratigraphy of New Jersey into the Delmarva
Peninsula, the flat low-lying area between the Dela-
ware and Chesapeake Bays (fig. 1) .

Since 1957 the US. Geological Survey has been
mapping the rock stratigraphic units of the Coastal
Plain in New Jersey. An area of about 600 square
miles has been mapped at a scale of 1:24,000 in
west-central New Jersey near Trenton and in the
adjacent parts of Pennsylvania. Mapping also has
been completed in the Sandy Hook quadrangle to the
northeast and in the Woodstown quadrangle to the
southwest (fig. 1), both in New Jersey. Reconnais-
sance has been done in the areas between. In addi-
tion, mapping and reconnaissance recently has been
extended into the Delmarva Peninsula.

This report is divided into two parts: (1) rock
stratigraphic studies and (2) biostratigraphic anal-
ysis. The region discussed extends from Sandy Hook,
N.J., to Chesapeake Bay, Md. (fig. 1). The main
emphasis is on the stratigraphic relationships be-
tween units of southern New Jersey and the north-
ern Delmarva Peninsula.

PREVIOUS INVESTIGATIONS

Numerous lithostratigraphic and biostratigraphic
studies have been made of Cretaceous-Tertiary rocks
in the northern part of the Atlantic Coastal Plain
during the past century. Only those that are partic-
ularly significant to the main topic of this paper will

1

2 STRATIGRAPHY OF OUTCROPPING POST-MAGOTHY UPPER CRETACEOUS FORMATIONS

 

 
      
           

 

 

 

 

 

     
 
 

   
 

I

l

Sassafras‘
River

  
  
 
 

1. Trenton West (unpublished data)

2. Trenton East, GQ—341 .501»

3. Allentown, GQ~566 a0” sandy "Wk
4. Roosevelt, GQ—340 App imat 5 d e of

. FOX 6 Inner e, /

2‘ giitrilg‘iQégzmo Coastal Plain Provifice Atlantic Highland“

7. New Egypt,GQ7161 / 5
8. Mount Holly, GQ—272

9. Pemberton5GQ—262 I

10. Browns Mills5GQ~264 / Trenton /

11. Woodstown,GQ~404 1 O 2 3 4

12. Sandy Hook, Bull. 1276

5 %y 6 7
8 9 10 j
PENNSYLVANIA ___ 7[
MARYLAND 1 1
OWogdstown
CHESAPEAKE
DEW/2“
N E W J E R S E Y

 

 

 

 

 

   
 

 

 

 

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|
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l .9
|
'I DELAWARE BAY
DELMARVA
V | \ (j/
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Q
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53 PENINSU LA 5e
55 I e
5;) Y’
s 1 3‘6
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FIGURE 1.—Index map of southern New Jersey and northern Delmarva Peninsula showing locations of 7%-
minute quadrangles that have been mapped. A—A’ is line of section for figure 4.

be discussed here. More detailed discussions of early
investigations have been given by Groot, Organist,
and Richards (1954) for Delaware and by Greacen
(1941) for New Jersey.

Detailed stratigraphic investigations of the Cre-
taceous formations for the entire region began with
the studies of W. B. Clark and his associates during
the period from 1894 to 1916. Clark, Bagg, and
Shattuck (1897) proposed a stratigraphic sequence

(fig. 2) from which most of the present divisions
evolved. Kiimmel and Knapp (1904) modified Clark’s
stratigraphy in New Jersey, particularly the Mata-
wan Formation (fig. 2). Weller and Knapp (Weller,
1907) modified the earlier stratigraphic studies and
further subdivided the basic units (fig. 2). This
stratigraphic sequence is accepted today not only in
New Jersey but also in Delaware and eastern Mary-
land. They were the first to define the relation be-

PREVIOUS INVESTIGATIONS

 

Clark, Bagg, and Shattuck (1897)

K'u'mmel and Knapp (1904)

Weller (1907)

Cooke and Stephenson (1928)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Raritan Formation

 

Ran'tan Clay Series

Cliffwood lignitic

sands and clays
Laminated Sands No.4
Amboy Stoneware Clay
Sand Bed No.3
South Amboy Fire Clay
“Feldspar” Kaolin Sand Bed
Woodbridge Clay
Fire Sand No. l
Raritan Fire and Terracotta

(Potters Clay)

(including Cliffwood Clay)

 

 

 

Raritan Clay

 

EQCENE Shark River Formation Upper marl Shark River Marl
(in part) Manasquan Marl
Manasquan Marl
Manasquan Formation
Limesand Vincentown Formation m
_ . (including yellow sand) (including yellow sand) E Q Vincentown Sand
5 V1ncentown Lime-Sands U :I
‘5 o E
g m (5
'5 Q
in Se 11 M 1 M'ddl 1 §
§ we ar 5 l e mar Hornerstown Marl E Hornerstown Marl
o (Sewell)
3
a:
Tinton Beds Tinton Sand Member
R db k S d Red Sand _ — _ _
.5 e an a“ 5 (Red Bank Sand) a
*5 Red Bank Sand =3 Red Bank Sand
5 B
S c:
e 5.
55 L l E ' /
g g Navesink Marls ower mar Navesink Formation / / 5 Navesmk Marl /
O : (Navesmk Marl) g /
Ed 0 / / /
a 2 /
E Mount Laurel Formation Mount Laurel Sand
5 Mount Laurel Sands
a Wenonah Sand
& Wenonah Sand Wenonah Sand
D s
N
E Hazlet Sands Marshalltown Bed Marshalltown Clay-Marl El) 5 Marshalltown Formation
:5 <3 3
{a F a: .
5 Columbus Sand Englishtown Sand E ‘2; Englishtown Sand
3 O .
g Woodbury Clay Woodbury Clay 1:: Woodbury Clay
2 E
Crosswicks Clays MerchantVIIIe Clay Merchantv1lle Clay-Marl g Merchantvflle Clay
Magothy Formation
Magothy Formation

 

Raritan Formation

 

 

 

tween the lithostratigraphy and the biostratigraphy
of the Upper Cretaceous beds in New Jersey (Weller,

FIGURE 2.—Development of stratigraphic interpretations of the pre-Miocene strata in New Jersey.

1907). Cooke and Stephenson (1928) showed that

the uppermost formations assigned to the Upper

Cretaceous by previous investigations were actually
lower Tertiary (fig. 2).

The stratigraphic section proposed by Clark,

Bagg, and Shattuck (1897) for the Coastal Plain of

4 STRATIGRAPHY OF OUTCROPPING POST-MAGOTHY UPPER CRETACEOUS FORMATIONS

Delaware and Maryland was similar to that of New
Jersey. However, despite the fact that Clark con-
tinued his investigations in Delaware and Maryland
well into the early 1900’s, the stratigraphic section
proposed in 1897 was not formally subdivided in
this region as it was in New Jersey.

Carter studied the strata along the Chesapeake
and DelaWare Canal during 1934 and 1935, especially
near Summit Bridge, Del. He (1937) applied some
of the New Jersey formation names to his units
(table 1). The Matawan of the area was subdivided
for the first time, and the Monmouth Group, along
the canal, contained only a single formation (table

 

1). Spangler and Peterson (1950) examined the
canal section as part of a regional study of the
northern Atlantic Coastal Plain. They also applied ,
New Jersey names to the units, but their identifica-
tion and correlation of units differed from Carter’s
(table 1). Groot, Organist, and Richards (1954)
made the most recent study of the canal section be-
fore the present report (table 1). Names of strati-
graphic units of New Jersey were assigned to the
units, but the interpretation of the section by Groot,
Organist, and Richards differed from that of Carter
and that of Spangler and Peterson (table 1). The
authors of this report first studied the canal section

TABLE 1.—Stratigraphic interpretation of the formations cropping out along or nearby to the south of the Chesapeake and
Delaware Canal

[The column by Carter and the column of this report are nearly identical and are considered, by the present authors, to be thecorrect interpretation of
the stratigraphy]

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

(19193327) (193$,a 1:9 1r245) Spatiigsighfxlidgiheison GmOt' 91%??? ifiifiucmrds This “9°“
: o E _
53 Rancocas 5 . . .E
c: , u Vmcentown (Aquia) 4; Hornerstown Sand
<3 Formatlon é a)
Q a
— -- — Unconformity Unconformity —
g; Navesink marl g
2 (presence in- 33 A
O ferred in area a g.
Monmouth g south of the S g R d B k Mount Laurel
Formation g canal) E3 Navesink g e an Sand
;: f, 4:
o 4—)
2 Mount Laurel g 3
Sand g g E
_ g 8 g
p: 0
g Marshalltown — 4% Navesink-Mount Marshalltown
g g Formation Mount Laurel 0’“ Laurel Formation
a) O) m A _
0 U) a.) s: 5"
S I“ 3‘ En lishtown ”1 E & ”1 En lishtown
2 fi 8 g :1 :6 Wenonah .3 A Wenonah g g .
o m (.5 Sand 8 S g 8 Formation
F) Matawan 3 § g E S 3
' 4) q) d)
g Formation 3 E Crosswicks Clay is 5 I: . 8 5
D E 4:73) the equivalent of a as Marshalltown, g 5..
O 2 the Woodbury & E W°°dbury’ and 3 -11 3 Merchantville
H a a M h t .11 N Merchantv1 e Q, _
& Clay and Mer- D :6 811° an Vl_ e ‘5 :3 Formation
Q chantville Clay 2 undifferentiated E
D in New Jersey
— — Unconformity— — ’
g M th
: ago Y . Ma 0th
0 - M h F0 mation Ma 0th g Y
3 Formation agot y r g y Formation
B
:- —— Unconformity — _ Unconformity—
as
'E .
g Rantan Raritan Formation Raritan
0 Formation
8
U

 

 

 

 

 

 

 

ROCK STRATIGRAPHIC STUDIES

in 1963 and mainly agree with Carter’s interpretation
(table 1).

The Upper Cretaceous stratigraphic nomenclature
in eastern Maryland has remained much as Clark
(1916) had shown. Clark’s Matawan and Monmouth
Formations were the standard for the east side of
Chesapeake Bay (Overbeck and Slaughter, 1958)
prior to this report.

In the following section, the units in New Jersey
will be described in detail in order to establish their
lithologic characteristics and to compare these units
with those in the northern Delmarva Peninsula.

ROCK STRATIGRAPHIC STUDIES
By JAMES P. OWENS and JAMES P. MINARD

The sedimentary rocks of Late Cretaceous age in
New Jersey are mostly mixed or interbedded un-
consolidated sands, silts, and clays. Both allogenic
(quartz, feldspar, mica, and carbonaceous debris)
and authigenic (glauconite, pyrite, and siderite)
minerals are abundant, although the allogenic con-
stituents predominate.

These sedimentary rocks can be divided into 11
lithostratigraphic units which are well defined in
outcrop. These have a pronounced cyclic pattern that
has not been previously recognized and that has
been a major cause for misidentifications in earlier
regional stratigraphic studies.

NEW JERSEY
MERCHANTVILLE FORMATION

The Merchantville Formation is the oldest of the
glauconite sandy units in the Coastal Plain in New
Jersey (fig. 3), but unlike most of the younger green-
sands it consists of more than one lithofacies.

In the north, the Merchantville is mainly a se-
quence of thin (2—6 in.) very fine to fine-grained
sandy and silty beds and, less commonly, thick (3—6
ft) beds of glauconite sand. Discontinuous layers of
rounded pale-gray siderite concretions are abundant
in the thin-bedded sequence. In the west-central out-
crop area, the Merchantville is a thick-bedded (5—15
ft) sequence of dark-gray clayey quartz silts and
dark-greenish-gray quartz-glauconite sands. In the
southwest, the formation is a dark-gray massive
silty fine to very fine glauconite-quartz sand. All
beds in the Merchantville are poorly sorted; So
(Trask sorting coefficient) equals 2.56 millimeters
average. Fossil casts are abundant, and locally in
the southwest, very fossiliferous siderite concretions
are common in the lower part of the formation. The
Merchantville ranges in thickness from 40 to 60
feet. The contact with the underlying Magothy is
sharp and disconformable. A bed about 1 foot thick

 

 

 

 

 

 

 

 

 

 

 

 

 

Hornerstown W
Sand ' . ‘ . . .
TERTIARY ‘- '. EXPLANATION
CRETACEOUS - . .
Tinton
Sand
Gravel
,— r» A
NA m A
A /\~ N
Regafiznk Glauconite sand
Quartz—feldspar
and sand
Silt
Navesink
Formation _ __ _
_ _.
Clay
Mount
Laurel
Sand if/ :// /
Wenonah Crossbedding
Formation

 

Marshalltown if." ‘-
Formation

 

Englishtown

 

 

 

Formation
Woodbury __—:
Clay ....._'_.....__
:...._.__' 0
,4, N l N 20
LN 0 ~ .
.—‘ _—/\/—
. IV. i,,* 40’
MerchantVIlle /
Formation ,«o _N .~.
_....._ _ 60'

 

 

.LV' N N‘L
—W 80'

FIGURE 3.——Composite columnar section showing general
thickness and lithology of Upper Cretaceous formations in
the northern and west-central Coastal Plain in New Jersey.

6 STRATIGRAPHY 0F OUTCROPPING POST-MAGOTHY UPPER CRETACEOUS FORMATIONS

containing reworked gravel and rounded woody frag-
ments is present along the contact between the two
units.

WOODBURY CLAY

The Woodbury Clay is chiefly a dark-grayish—black
unconsolidated massive very clayey silt, except in
the upper part where lentils of glauconite sand are
common. It is very poorly sorted (802262—424 mm
commonly). The silt fraction consists mainly of
quartz, feldspar, and mica; mica plates are also
common in sand sizes. Carbonaceous matter, both
finely comminuted and coarse grained, is also very
abundant. Imprints of fossil shells are abundant, and
locally in the southwest, well-preserved calcareous
shells have been collected. The unit ranges in thick-
ness from a maximum of 50 feet in the west-central
part to zero in the southwest. It is gradational into
the underlying Merchantville Formation.

ENGLISHTOWN FORMATION

The Englishtown Formation is chiefly a clastic
sand that consists of more than one lithofacies. In
the north where this unit is approximately 140 feet
thick, it is mainly a pale-gray to white cross-strati-
fied medium sand in the upper part and a dark-gray
silt with thin quartz sandy partings in the lower
part. In the west-central outcrop area, it is chiefly
an intercalated thin-bedded sand-clay sequence. The
Englishtown is approximately 90 feet thick in this
area. In the southwest, the Englishtown thins to
approximately 40 feet and is a dark-gray massive
very fine to fine sand. These beds resemble the
Wenonah Formation.

The sandy beds in the Englishtown are typically
moderately to well sorted (So=1.35—1.58 mm).
Quartz, feldspar, weathered glauconite grains, and
mica are the major sand constituents. The thin clay
beds in the intercalated sequences and the massive
dark beds are very silty and micaceous and contain
large concentrations of fine to coarse lignitized plant
matter.

Few fossils have been reported from the English-
town. Locally, fossiliferous pale-gray sideritic con-
centrations are present in the base of the intercalated
sequences. Fossil casts are also common in the
massive dark sand in the southwest.

The Englishtown grades downward into the Wood-
bury Clay throughout most of the outcrop, but in
the southwest where the Woodbury is absent, it over-
lies and grades downward into the Merchantville
Formation.

 

MARSHALLTOWN FORMATION

The Marshalltown Formation is a massive dark-
greenish-gray very fine to fine sand, which locally
contains abundant silt and clay. Small pebbles and
granules are common in the base and middle of the
formation. It is moderately to very poorly sorted
(So=1.36—4.80 mm commonly). Quartz and glau-
conite are the common sand minerals; feldspar and
mica are present in small amounts. Glauconite is
abundant in the middle and upper parts of the for-
mation; quartz and, locally, concentrations of ligni-
tized wood are common in the base. The glauconite
grains are light to dark green and very fine to fine
and include several percent of “accordion” forms.
Fossils are rare in the north and west-central part
of the Coastal Plain but are abundant in the south-
west, especially the pelecypod Exogyra ponderosa
(Roemer). The Marshalltown is remarkably constant
in outcrop thickness, ranging from 10 to 15 feet.
The contact with the underlying Englishtown For—
mation is sharp; a thin reworked bed occurs locally
along the boundary.

WENONAH FORMATION

The Wenonah Formation is an unconsolidated
massive to thick-bedded dark-gray silty very fine to
fine sand. It is very poorly to moderately sorted
(Sozl.49—2.81 mm commonly). The Wenonah is
chiefly a very micaceous, glauconite-feldspar-quartz
sand. Finely disseminated pyrite and sand- to silt-
sized carbonaceous particles are particularly abun-
dant. The formation has few fossils; only casts have
been observed. Abundant cylindrical borings indicate
that the unit ranges in thickness from a maximum
of 60 feet in the west-central part of the Coastal
Plain in New Jersey to a minimum of 15 feet in
the southwest. The contact with the underlying
Marshalltown Formation is gradational.

MOUNT LAUREL SAND

The Mount Laurel Sand is largely a clastic sand,
which weathers readily to a light gray or reddish
brown. These weathered beds strongly resemble the
upper quartz sand unit of the Red Bank Sand for
which it is commonly mistaken. The Mount Laurel
consists of more than one lithofacies along strike. In
the northeast, it is mostly a sequence of intercalated
thin (6 in. or less) dark-gray clay and light-gray
sand beds. In the west-central area, it is largely a
massive sand that locally interfingers with the inter-
calated sequence, particularly at the base of the
formation. In the southwest, the formation is mainly
a massive to thick-bedded sand. A 5- to 10-foot-thick

ROCK STRATIGRAPHIC STUDIES 7

bed of pebbly coarse sand occurs everywhere in out-
crop at the top of the formation. Most of the sandy
facies are moderately sorted (So=1.15—1.87 mm
commonly) , except in the upper coarser beds where
the sorting is poor. Characteristically, this formation
is a glauconite-feldspar-quartz sand. Locally, mica is
abundant in the base. Fossils are largely in thin to
thick layers throughout; the upper shell beds include
Exogyra cancellata (Stephenson) and Belemmtella
americana. (Morton). E. cancellata is restricted to
this formation. The Mount Laurel Sand ranges in
thickness from 20 feet in the north to 7 0 feet in the
southwest. The contact with the underlying Wenonah
is typically gradational but locally may be distinct.

NAVESINK FORMATION

The Navesink Formation is a massive unconsoli-
dated dark-greenish-gray clayey and silty medium
to coarse sand. It is moderately to very poorly sorted
(So: 1.57—3.24 mm commonly). The Navesink is pri—
marily a clayey glauconite sand (greensand); the
lower few feet contain a few percent quartz, re-
worked from the underlying Mount Laurel. The unit
is differentiated from the quartz-glauconite litho-
facies of the Red Bank Sand mainly by the lack of
sand-sized mica and by the smaller amounts of car-
bonaceous matter. However, clay- to silt-sized mica
is abundant. The N avesink is very fossiliferous,
especially the base. In the north, the middle and
upper parts of the formation contain fossil beds as
much as 5 feet thick largely consisting of mollusks.
The unit crops out along the entire inner edge of the
Coastal Plain in New Jersey. Here it ranges in thick-
ness from a maximum of 35 feet in the west-central
part to 5 feet in the southwest. The contact with the
underlying Mount Laurel Sand is sharp.

RED BANK SAND

The Red Bank Sand is restricted to the northern
and west-central parts of the Coastal Plain in New
Jersey where it forms a wedge-shaped deposit that
pinches out downdip and along strike to the south-
west. The formation consists of three major litho-
facies: an upper quartz sand, a lower silt, and a
lower glauconite sand (fig. 3).

Upper quartz sand—The upper quartz sand is an
unconsolidated massive reddish-brown fine to coarse
sand, which locally contains pebbles and which is
well to moderately sorted (So=1.17—1.83 mm com-
monly). It is a glauconite-feldspar-quartz sand.
Typically, it is weathered throughout and locally is
cemented by iron oxides. Most of the unit is un-
fossiliferous, but it contains some poorly preserved
reworked fossils in the base. The upper quartz sand

 

unit ranges from 0 to 100 feet in thickness and
grades into the underlying lithofacies, commonly
through a transitional zone several feet thick.

Lower silt—The lower silt crops out only in the
northern part of the Coastal Plain. It is an uncon-
solidated massive dark—gray silty medium sand.
Typically it is poorly to very poorly sorted (So:
2.34—3.93 mm). This lower silty unit is a moderately
to very micaceous feldspar-glauconite-quartz sand;
locally it contains much sand-sized carbonaceous
matter and pyrite. The unit is very fossiliferous, and,
locally, calcareous tests are well preserved. It is as
much as 30 feet thick.

Lower glauconite sand—The lower glauconite
sand crops out only in the west—central part of the
Coastal Plain. It is an unconsolidated dark-greenish-
gray massive fine sand containing much clay and
silt. Typically. it is very poorly sorted (8022.12
mm). The sand consists of feldspar, quartz, and
especially glauconite. Carbonaceous matter and sand-
sized mica are especially abundant in this lithofacies.
This unit is sparingly fossiliferous. It is as much as
30 feet thick, and to the north it grades laterally into
the lower silty unit and downward into underlying
Navesink with no perceptible break.

TINTON SAND

The Tinton Sand is an unconsolidated pale-
greenish-gray sand in the base to locally reddish-
brown well-indurated sandstone in the upper 8—10
feet. Induration is largely due to fine crystalline
sideritic cement. The sand is mostly fine to medium.
Near the top, however, it is coarse and pebbly and
is very poorly sorted (So=3.0 mm commonly). The
Tinton is mostly a feldspar-glauconite-quartz sand to
quartz-glauconite sand; glauconite is much more
abundant near the top of the formation. In some
areas, it contains many fossils, chiefly mollusks and
Callinassa sp. The cephalopod Sphenodiscus is fairly
common at the type locality. The unit is restricted to
the northern part of the Coastal Plain where it at-
tains a maximum thickness of about 25 feet. The
contact with the underlying Red Bank Sand is grada-
tional. The upper boundary with the Hornerstown is
sharp and unconformable.

DISTRIBUTION OF FORMATIONS

A major stratigraphic problem in New Jersey is to
determine which formations persist from the north-
east, where the Upper Cretaceous section is the
thickest, to the southwest, where the section is thin-
ner and the formations are fewer. An additional
problem is to determine what facies changes occur
within each formation. The Upper Cretaceous sec-

 

  

 

 

 

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STRATIGRAPHY 0F OUTCROPPIN G POST-MAGOTHY UPPER CRETACEOUS FORMATIONS
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120 MILES

  

 

FIGURE 4.—Stratigraphic section along the Upper Cretaceous outcrop belt from southwestern New Jersey to eastern Mary-
land. Line of section shown in figure 1.

tion, excluding the Raritan Formation, thins from
about 500 feet in the Raritan Bay area to about 250
feet at Woodstown (fig. 4). As can be seen in figure
4, major changes toward the southwest primarily
involve the uppermost Cretaceous units, the Tinton,
Red Bank, and Navesink. The absence and thinning
of these units toward the southwest can be explained
by nondeposition and (or) postdepositional erosion.

A map showing the areal distribution of the
Coastal Plain formations from New York to northern
Virginia has been published by the US. Geological
Survey (1967). Part of this map is reproduced in
figure 5 and illustrates the authors’ interpretation
of the geology of southwestern New Jersey and the
northern Delmarva Peninsula.

The section at Woodstown is discussed in more

 

detail than any other from New Jersey because it is
the closest area to the Delmarva Peninsula in which
detailed mapping was completed.

At Woodstown (figs. 4 and 5), the Tinton and Red
Bank Sands are absent, as postulated by Knapp
(Weller, 1907, p. 15) and mapped by Minard (1965).
The basal Tertiary unit, the Hornerstown, here rests
on the Navesink and locally on the Mount Laurel in
updip areas. The Navesink thins in outcrop from
about 12 feet near the east boundary of the Woods-
town quadrangle to zero at the west edge. Downdip
or southwestward, the Navesink thickens to more
than 20 feet. The wedge shape of the Navesink in
this quadrangle suggests an angular unconformity
between this unit and the overlapping Hornerstown
Sand.

ROCK STRATIGRAPHIC STUDIES

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10 STRATIGRAPHY 0F OUTCROPPING POST-MAGOTHY UPPER CRETACEOUS FORMATIONS

The Mount Laurel Sand underlying the N avesink
is approximately 80 feet thick at Woodstown. This
is the maximum outcrop thickness of this unit in
New Jersey. Weller and Knapp (Weller, 1907, p.
103) considered the thickening of the Mount Laurel
to be at the expense of the Navesink. It should be
noted, however, that the underlying Wenonah also
thins southwestward, and at Woodstown, the forma-
tion is only 15 feet thick. This fact suggests that the
thickening of the Mount Laurel may be related to
the thinning of the Wenonah because of a simple
textural change from the silt (Wenonah) to a
coarser sand (Mount Laurel). If the above explana-
tion is correct, then a radical mineralogic change is
not required as would be so for the change from the
Mount Laurel (detrital sand) to the Navesink
(authigenic sand).

The Marshalltown has virtually the same thickness
and lithology at Woodstown as to the northeast;
fossils, however, are abundant at Woodstown, but
rare to the northeast. The Marshalltown, because of
its persistent lithic characteristics, serves as an ex—
cellent stratigraphic marker in New Jersey and the
Delmarva Peninsula.

The Englishtown shows a marked change in facies
in the Woodstown area. In the north-central part of
the quadrangle, near Swedesboro, this unit is a se-
quence of intercalated thin-bedded clays and sands,
like much of the Englishtown to the northeast. Be-
tween Swedesboro and Woodstown, the formation
changes to a thick-bedded silt and sand. At the west
edge of the quadrangle, the formation is a massive
dark very micaceous silty very fine to fine sand that
strongly resembles the Wenonah, the basal Red Bank
in the northern Coastal Plain, [and the underlying
Woodbury Clay in its type area. A major strati-
graphic problem has been whether this dark very
fine sand is the Woodbury or a facies change in the
Englishtown. 0n the geologic map of New Jersey
(Lewis and Kiimmel, 1912), the Englishtown is
' shown to pinch out in the Woodstown quadrangle
and the Woodbury to continue through. However,
because the bedded clay-sand sequence of the forma-
tion laterally interfingers with the massive unit
formerly mapped as Woodbury, Minard (1965)
mapped the Englishtown continuously across the
Woodstown quadrangle. Johnson and Richards
(1952, p. 2155) reported at least 36 feet of English-
town at Layton Lakes, which is several miles west
of the Woodstown quadrangle.

The Woodbury Clay is not present in the Woods-
town quadrangle and apparently pinches out north-
east of Swedesboro (Minard, 1965).

 

The Merchantville Formation is far less glau-
conitic in the vicinity of Woodstown than it is to the
north between Trenton and Camden. However, suf-
ficient glauconite still occurs in the Merchantville at
Woodstown to help in differentiating it from the
overlying and similar but less glauconitic dark
massive Englishtown.

One of the unforeseen results of the detailed
mapping in several areas and examination of forma-
tions in the intervening areas was the detection of a
probable basement high in southern New Jersey and
northern Delaware. This conclusion was reached
partly as a result of lithologic changes in the
formations. These changes were most evident in the
greensands. In New Jersey, several units contain
glauconite in superabundance. One formation, the
Hornerstown, of early Tertiary age, is commonly 30
feet thick. The sand fraction in this unit is as much
as 95 percent glauconite. The other glauconite-rich
units of appreciable extent are the Navesink, Mar-
shalltown, and Merchantville Formations.

As these formations are traced from the northeast
to the southwest, a marked depletion of glauconite
is evident. To the northeast, these formations are
excellent marker beds because of their high glau-
conite content. To the southwest, however, their use
as stratigraphic markers is much less reliable be-
cause they have become so deficient in glauconite, or
have pinched out, or have been overlapped. Accom-
panying the depletion of glauconite is an increase in
the amount of detrital minerals, particularly quartz.

The authors believe that glauconite is primarily an
authigenic mineral and is deposited in a low-energy
environment in waters a few to several hundred feet
deep on the middle and outer continental shelf. Based
on this concept of the origin of glauconite, the glau-
conite depletion and the thinning or overlapping of
glauconite-rich beds to the southwest and the con-
comitant increase in amount of detrital minerals and
in grain size suggest a shoaling of the sea on a
possible structural high.

SUMMARY OF ROCK STRATIGRAPHIC STUDIES IN
NEW JERSEY
The important changes in the Upper Cretaceous-
lowermost Tertiary section that take place from
northern New Jersey southwestward to the Woods-
town area are:

1. The Hornerstown Sand of early Tertiary age rests
on progressively older sediments towards the
southwest (fig. 4). It lies on the Tinton in the
extreme north, the Red Bank in the west-central
part, the Navesink in the west-central to south-

ROCK STRATIGRAPHIC STUDIES 11

western part, and the Mount Laurel in the
updip section in the southwestern part.

2. The upper quartz-sand unit of the Red Bank is
absent in the southwestern part of the Coastal
Plain in New Jersey as S. Weller and G. N.
Knapp (Weller, 1907, p. 18) had postulated.
This is significant when the interpretation of
Groot, Organist, and Richards (1954, table 2)
in northern Delaware is considered.

3. As a result of the erosion of progressively lower
parts of the uppermost Cretaceous beds from
north to south, the Navesink is only 5 feet thick
in much of the updip section at Woodstown and
locally is absent.

4. Thickening of the coarse sandy Mount Laurel
southwestward and a concomitant thinning of
the underlying finer grained Wenonah suggests
shallowing of the basin of deposition during
Wenonah-Mount Laurel time.

5. The Marshalltown persists with little change in
lithology or thickness in outcrop throughout the
entire Coastal Plain in New Jersey and there-
fore serves as an excellent marker bed. Concen-
trations of Exrogym ponderosa are present
only in the southwest.

6. A significant reduction in the thickness of the
Englishtown-Woodbury interval was produced
by the pinchout of the Woodbury and by a
change to a thinner, deeper water silty sand
facies within the Englishtown, which here re-
sembles the Wenonah.

7. The Merchantville also undergoes a facies change.
It is largely a greensand in the Trenton-Camden
area, but the glauconite content decreases
markedly to the southwest, where the Mer-
chantville is a somewhat silty fine glauconite
quartz sand.

8. Within the Coastal Plain in New Jersey, the
quartz-rich sandy or silty units vary more in
thickness and lithology along outcrop than the
glauconite-rich units, which maintain remark-
able uniformity in texture, mineralogy, and
thickness for the entire outcrop distance. Facies
changes are present, but the changes from one
texture, lithology, or thickness to another are
gradual and commonly take place over many
miles.

9. The most significant feature of the stratigraphy
is the repetition of similar lithologies in the
vertical section throughout the Upper Creta-
ceous beds of New Jersey. This characteristic
requires a very detailed knowledge of the
spatial distribution of the formations before

 

any regional synthesis of the Upper Cretaceous
stratigraphy can be made.

NORTHERN DELAWARE

Although the marine Cretaceous sediments of
Delaware are lithologically similar to those of New
Jersey, the authigenic mineral glauconite is gen-
erally less abundant than in formations of the same
age in New Jersey. The outcropping Cretaceous sec-
tion continues to thin southwestward into Delaware
where the section is estimated to be only 240 feet
thick (fig. 4).

There are no exposures of the complete Cretaceous
section in Delaware. Even the more or less contin-
uous exposures along the Chesapeake and Delaware
Canal are incomplete because no basal Tertiary beds
have ever been found. In order to locate these lower
Tertiary beds and establish a top to the section, a
series of shallow holes were bored south of the canal
in the vicinity of Odessa, Del. (fig. 1), where Booth
(1841) and Johnson and Richards (1952, p. 2158-
2159) reported the early Tertiary brachiopod
Oleneothym’s harlam'. The presence of Tertiary rocks
in that area was also suggested by the fact that
glauconite mining once flourished. The bulk of the
glauconite mining in New Jersey was in the Horners-
town Sand of Paleocene age.

Studies in Delaware were concentrated at three
main localities: along the Chesapeake and Delaware
Canal from the new Summit Bridge to the new rail-
road bridge (fig. 6); from the St. Georges Bridge
east to the Biggs Farm locality of Groot, Organist,
and Richards (1954, fig. 5) ; and the general vicinity
of Odessa (fig. 5) south of the canal. These localities
are approximately 15 miles southwest along strike
from Woodstown, N.J.

DISTRIBUTION OF FORMATIONS

The areal distribution of Upper Cretaceous and
lower Tertiary beds from southern New Jersey to
northern Delaware is shown in figure 5. As can be
seen, four Cretaceous formations younger than the
Magothy extend into the canal area: the Merchant-
ville, Englishtown, and Marshalltown Formations,
and the Mount Laurel Sand.

SECTION ALONG CHESAPEAKE AND DELAWARE CANAL NEAR
SUMMIT BRIDGE

An unusually good exposure was studied in a
fresh cutbank in the footings for the new railroad
bridge on the south bank of the canal. About 65 feet
of section was exposed (fig. 7). Weathering, always
a problem in surface or near—surface studies of the
Coastal Plain formations, was perceptible to a depth

12

STRATIGRAPHY OF OUTCROPPING POST-MAGOTHY UPPER CRETACEOUS FORMATIONS

 

Present route
of canal

 

   

New railroad
bridge

? MILES

 

 
 
 

 
 
  
   

   
 
 

Biggs Farm
locality

DELA WA BE RIVER

 

 

 

FIGURE 6.—Localities along the Chesapeake and Delaware Canal described in text (modified from Groot and others, 1954,
pl. 2).

of about 50 feet. The impermeable clayey units were
the least altered, but even in the more permeable
sands, weathering did not mask the essential litho-
logic characteristics.

 

FIGURE 7.—Upper Cretaceous formations exposed in cutbank
at site of “Chesapeake and Delaware Canal railroad bridge.

 

Except for the Navesink and Wenonah Forma-
tions, the same lithologic units are recognized here as
at Woodstown, N .J . (fig. 4). The change in facies
within the Wenonah to a coarser sand southwest-
ward in New Jersey has been carried to completion
in northern Delaware where the Wenonah-Mount
Laurel interval is occupied by a Mount Laurel

lithology.
Particularly fine exposures of the Marshalltown,

Englishtown, and the upper part of the Merchant-
Ville Formations at this locality are of special inter-
est. It is also noteworthy that the placement of our
formational boundaries is nearly coincident with
those of Carter (1937) in this general area.

A measured section, which accompanies figure 8,

is given below.

Measured section in excavation for rail/road bridge footing
on south bank of the old channel of Chesapeake and
Delaware Canal 1.3 miles northeast of Summit, Del.

[Elevation of top of out about '70 feet]

Thickness
(feet)

Wicomico(?) Formation:
Sand, yellow—brown, very gravelly ........................ 0—10
Mount Laurel Sand:

Sand, yellowish- to reddish-brown, somewhat
clayey and silty; massive but extensively pene-
trated by cylindrical borings commonly etched
out by wind on dry surfaces. White to buff
soft irregular masses of apatite as much as
3 in. in diameter abundant in the lower 5 ft.
Quartz, feldspar, and glauconite the major
sand constituents (table 3) ; mica and apatite
also present in significant concentrations. De-
trital heavy minerals abundant and chiefly of
metamorphic origin (table 3). Sand moder-
ately to well sorted and mostly fine to medium

(Groot, 1955, p. 147). Unit grades down into
the Marshalltown, the transition taking place

Wicomico(?) ,. ., . . ..
formation ‘.'.

 

Mount Laurel . '..’ -' . 1'
Sand

 

Marshalltown
Formation

 

Englishtown
Formation

 

Merchantville I
Formation

 

 

 

ROCK STRATIGRAPH‘IC STUDIES

EXPLANATION

 

 

 

 

 

 

 

 

 

 

 

Crossbedding

 

/\/‘/\,’\

AAA/x

AAr-xfl

 

FossHs

 

fi/

 

Borings

 

' '

 

O o ——

 

 

Wood

10’

FxGURE 8.—Columnar section at the new railroad
bridge excavation near Summit Bridge, Del., shown

in figure 7.

Mount Laurel Sand—Continued

Thickness

in a l-ft interval. Borings filled with quartz
sand. They project downward from Mount
Laurel into underlying Marshalltown ............

Total measured Mount Laurel Sand

(feet)

H
U!
C

H
01
O

 

Marshalltown Formation:

Sand, clayey, silty, grayish—green; at top grades
downward into greenish-black, massive. Bor-
ings similar to those in Mount Laurel, but
filled with glauconite sand, common. White
masses of apatite similar to those in overlying
formation also occur in upper few feet of this
unit. Phosphatized internal molds of shells in
upper few feet, and a layer containing fairly
well preserved thick calcareous shells of
Exogym ponderosa Roemer in the middle.
Microfossils locally abundant in shell layer
and associated with numerous broken translu-
cent dark-brown bone fragments, fine quartz
gravel (maximum diameter 1/2 in.), and frag-
ments of black carbonized wood.

Glauconite is major sand constituent (table
3), although quartz and feldspar abundant in
lower few feet of this formation. Mica com-
mon throughout. Many glauconite grains have
accordian shapes similar to those described by
Galliher (1935). Heavy minerals common; the
assemblage and distribution virtually same as
in Mount Laurel Sand.

Contact with Englishtown sharp (fig. 9).
Numerous borings filled with glauconite, pro-
ject below contact into underlying quartz sand.
Gravel (as much as 2 in.) and large pieces
of carbonized wood (as much as 8 in. long)
occur locally along this boundary ....................

Total measured Marshalltown
Formation.

Englishtown Formation:

Sand, white to pale bufl" ; upper part pale gray in
lower few feet; extensively stained orange
brown by iron oxides along the bedding planes.
Many of beds less than 1 in. thick (fig. 10).
Small—scale crossbedding thicker in lower few
feet. Entire formation penetrated by excel-
lently preserved borings (Halymem'tes major
of other authors). These borings differ from
those in overlying beds both in size and com-
plexity of surface ornamentation.

Formation primarily a silty sand, fine to
very fine and well sorted (Groot, 1955, p.
149). Quartz, feldspar, and mica are the
primary constituents (table 3); glauconite
generally a minor constituent but locally
abundant. Heavy minerals abundant and
chiefly metamorphic types (table 3). Con-
tact with underlying Merchantville Formation
sharp and most evident on weathered surfaces
where dark carbonaceous matter leached from
Merchantville. A zone of reworked sediment
as much as 2 ft thick occurs locally along
this boundary. Fine gravel, carbonaceous mat-
ter, rounded black to reddish-brown iron oxide
fragments and less commonly small to large
broken calcareous and phosphatic shell frag-
ments distributed in this zone ............................

Total measured Englishtown Formation

13

Thickness
(feet)

,_.
5"
o

H
A
O

l

HH
as]?
CO

14 STRATIGRAPHY OF OUTCROPPING POST-MAGOTHY UPPER CRETACEOUS FORMATIONS

   

 

, . , h ,fi'm ' “

 
  

 

 

S'r
¢

 

fa»

FIGURE 9.——Contact between the Marshalltown (dark) and underlying Englishtown (light). Note thin zone of reworked
sediment along boundary and the numerous glauconite-filled borings in upper part of the Englishtown quartz sand.

Thickness
. . (feet)
Merchantv1lle Formation:

Sand, very fine to fine, very silty and clayey,
poorly to well—sorted; pale gray in the upper
8 ft, remainder dark grayish black; thick
bedded, but this feature is most evident on
weathered surfaces. Quartz, glauconite, feld-
spar, chlorite, and muscovite the major min-
erals. Glauconite grains have accordion shapes
similar to those in Marshalltown Formation.
Pyrite and siderite important accessory min-
erals, particularly in upper beds. Siderite oc-
curs in irregularly shaped gray masses. Heavy
minerals abundant and similar to those found
in overlying Englishtown (table 3). Fossils
abundant. Most only imprints, shell material
leached. A thin zone containing abundant crab
claws near top of formation ................................

Total measured Merchantville
Formation.

[\D N
00,9.
0 O

H-

Carter (1937, p. 271) and Groot, Organist, and
Richards (1954, p. 33—34) have also made studies at
or near this locality. All reports agree on the place-
ment of formational boundaries Within a few feet.
Except for the lower unit (Merchantville) for which
Carter used the collective name, Crosswicks Clay,
his stratigraphic assignments and those of this paper
are mainly the same, whereas those of Groot, Or-
ganist, and Richards are most like those of Spangler
and Peterson (1950).

No lower Merchantville beds were observed in this
excavation, but the engineer in charge reports an
additional 24 feet of the Merchantville lithology be-

 

 

FIGURE 10,—Sharp contact between Merchantville and over-
lying Englishtown Formations. Thin bedding in the Eng-
lishtown is emphasized by the iron oxide staining.

ROCK STRATIGRAPHIC STUDIES

low the 23 feet exposed in this cut. The total Mer-
chantville, therefore, is about 50 feet at this site.
A small section of the basal beds was temporarily
exposed on the south shore of the canal 1.4 miles to
the west. There, about 9 feet of Merchantville and
its contact with the underlying Magothy was ex-
posed in a long cutbank bench that was subsequently
removed during widening of the canal. The contact
is sharp and slightly irregular and has a 2- to 3-foot
zone of reworked sediment along the boundary. The
reworked zone is a dark-gray very silty and clayey
very fine to fine sand. Granules and small pebbles
of quartz are concentrated in this interval, as are
reworked pieces of carbonized wood and large dis-
coidal brown siderite concretions. Borings, gen-
erally filled with glauconite and quartz sand that are
coarser than the surrounding very micaceous matrix,
are abundant even in the wood and siderite concre-
tions. Above this lower bed, the amount of fine gravel
diminishes, and the sediment is much finer. Glau-
conite-filled borings are abundant even above the
basal zone.

In general, the lower Merchantville beds appear to
be more clayey and less micaceous and to have a
higher glauconite content than the upper beds ob-
served at the bridge pier.

SECTION 1.1 MILES WEST OF ST. GEORGES T0 1.3 MILES EAST
OF ST. GEORGES AT BIGGS FARM

The Englishtown and Marshalltown Formations
and the Mount Laurel Sand can be traced almost
continuously along the north side of the Chesapeake
and Delaware Canal from the railroad bridgeeast-
ward to St. Georges. The regional dip of the forma-
tions in this area is southeast, so that younger strata
are found to the east. Unfortunately, the ground
there is lower than at the railroad pier, and the out-
crops are smaller. Only short sections of the younger
Upper Cretaceous strata are exposed. Most of the
exposures are low cutbanks at water level along the
canal and are usually only a few feet high at low
tide. The sharp contact between the Marshalltown
and Englishtown is exposed at a few points on the
north bank between 0.3 and 1.1 miles west of the St.
Georges Bridge. The long distance over which this
contact is exposed suggests either a more easterly
strike of the Marshalltown than usual or local gentle
warping of the beds. Others (Groot, 1955, p. 14, for
example) have observed small folds in other beds
along the canal. The undulatory contact between the
two formations can be seen at low—tide level in this
general region.

The Englishtown in this area is typically orange
brown and semi-indurated by secondary iron oxide.

 

15

Its general lithology is similar to that of the beds
near the railroad pier except that it locally has small
concentrations of pebbles as much as one-fourth of
an inch in diameter. The Ophiomorpha borings are
large and very abundant in this formation. Because
they are better indurated than the surrounding sand,
they are etched out where the beds are exposed in
the intertidal zone (fig. 11). At a few localities, other
fossil impressions have been exposed on the washed
surfaces.

The basal beds of the overlying Marshalltown are
similar to those at the railroad pier except that they
are less weathered and much more fossiliferous.
Well-preserved shells of Exgogym ponderosa. and
Ostrea falcata. commonly litter the outcrop along the
shores of the canal.

At St. Georges Bridge, the dark-gray Marshall-
town is capped by a thin bed of orange-brown glau-
conite quartz sand identified by us as the basal
Mount Laurel. The weathered condition of the upper
bed makes it difl‘icult, however, to be certain of this
identification. If this represents the contact between
the two formations, the Marshalltown is less than 10
feet thick at this locality.

The basal unit of the Mount Laurel is exposed on
the south bank of the canal east of the St. Georges
Bridge. About 2.5 feet of unweathered pale-gray
very clayey glauconite quartz sand having composi-
tion apparently similar to that of the weathered bed
just mentioned crops out for a distance of about 100
yards. In general appearance this bed resembles the
Marshalltown because of its very clayey nature, but
it is lighter in color. This similarity is deceptive be—

 

FIGURE 11.—Large Ophiomo'rphia nodusa borings in the Eng-
lishtown Formation exposed at water level along the north
side of the Chesapeake and Delaware Canal east of the St.
Georges Bridge. Borings of this type are present in other
sandy formations but these are unusually large and well
preserved.

16

cause the cement in this unit of the Mount Laurel is
mostly clay-sized calcite rather than a complex as-
semblage of clay minerals as in the Marshalltown
(table 4). Therefore, the basal Mount Laurel at this
locality is an arenaceous calcilutite or a very calcare-
ous glauconite quartz sand, a lithology not observed
in the formation elsewhere. Lithologically, the Mount
Laurel exposed at the railroad pier could have been
the same as at this locality, except for leaching of
the fossils and calcareous cement. Fossils are abun-
dant along this south-bank exposure, but Exogym
cancellata occurs here rather than E. ponderosa. As
noted earlier, to the northeast in New Jersey, E.
cancellata is restricted to the Mount Laurel Sand.
Locally, small dark-brown phosphatized fossils of the
same types as the calcareous shells are present. The
origin of these phosphatic fossils is not known, but
they appear to be derived from a different source
than the larger calcitic shells.

Glauconite from the Exogym ponderosa bed of the
Marshalltown and the E. cancellata bed of the Mount
Laurel was dated by the potassium-argon method.
Glauconite from the Mount Laurel Sand yielded an
age of 70.3:25 m.y. (million years) ; that from the
underlying Marshalltown, 682:2.4 m.y. (J. P.
Obradovich, written commun., 1967). Although the
reported age of the glauconite in the Marshalltown
is younger than that from the overlying Mount
Laurel, both are virtually the same if the analytical
error is considered. Both determinations, however,
indicate a Late Cretaceous age for these beds.

Sporadic exposures of this lower Mount Laurel
calcareous bed were found along the south bank of
the canal from the St. Georges Bridge to the Biggs
Farm locality (fig. 6) about 1 mile to the east. A
hole augered at this locality penetrated approxi-
mately 16 feet of the light-gray fossiliferous calcare-
ous Mount Laurel. The lower contact with the
Marshalltown was difl‘icult to establish precisely be-
cause of contamination from above. Unequivocal
Marshalltown was obtained 10 feet below the 16 feet
of basal Mount Laurel, so that the thickness assigned
to the calcareous part of the Mount Laurel is a
minimum.

The Biggs Farm locality is a favorite fossil-
collecting site. It is also of special interest because
it is there that Groot, Organist, and Richards (1954,
p. 37) described a section of what they termed “Red
Bank and N avesink-Mount Laurel undifferentiated.”
The fauna from this locality was described by Rich-
ards and Shapiro (1963) and is discussed later in
this report in the section “Biostratigraphic anal-
ysis.” This is probably the locality referred to by

 

STRATIGRAPHY 0F OUTCROPPIN G POST-MAGOTHY UPPER CRETACEOUS FORMATIONS

Spangler and Peterson (1950, p. 47) in which the
Vincentown and Navesink are in contact.

The authors disagree with these formation desig-
nations and suggest instead that this entire outcrop
is Mount Laurel. At this locality, the basal 2.5 feet of
the cut is the same calcareous bed described at St.
Georges Bridge. This calcareous bed is in sharp con-
tact with the overlying yellowish-brown medium
somewhat glauconitic quartz sand (fig. 12). The con-
tact is highly irregular, apparently a reflection of
the uneven leaching of the underlying calcareous
bed.

To test our interpretation, three samples were
collected, one from the basal shell zone (Navesink-
Mount Laurel as used by Groot, Organist, and
Richards (1954)) and two approximately 6 feet
apart above this bed (Red Bank as used by Groot
and others). These were compared with each other
and with a sample from the basal Mount Laurel
exposed at the railroad excavation near Summit
Bridge.

The detrital components of the three samples were
concentrated and compared petrographically. It was
assumed that these detrital components would be
more likely to resist the effects of subaerial oxidation
than would the authigenic constituents. No signif-
icant differences were found in these samples either
in the light fractions (less than 2.80 sp gr) or in the
heavy fractions (greater than 2.80 sp gr, table 3).
No significant difference in size, shape, or total glau-
conite percentage was found between the sands.
These sands were then compared with the lower
Mount Laurel from the railroad bridge, and, except

 

FIGURE 12.——Contact between the lower light-colored very
clayey calcareous beds and the upper darker very sandy
beds of the Mount Laurel at the Biggs Farm locality.
Leaching of the calcareous beds has produced an irregular
contact.

ROCK STRATIGRAPHIC STUDIES 17

for minor variations in the percentages of the heavy
and light minerals, the samples were nearly identical.
The major difference is in the quartz-glauconite
ratio, but the sample from the railroad bridge is
from the base of the unit, and concentrations of re-
worked glauconite might be expected in this basal
interval.

Because of similarities in lithology and regional
stratigraphic position, we conclude that these local-
ities are part of a single lithologic entity, the Mount
Laurel Sand.

SECTION NEAR ODESSA

In the two previously described sections, the Cre-
taceous-Tertiary boundary was not exposed nor was
it seen anywhere eastward along the Chesapeake and
Delaware Canal. As already indicated, the section at
the Biggs Farm locality probably is basal Mount
Laurel. In southern New Jersey, the Mount Laurel is
80 feet thick, and it is reasonable to assume an equal
or greater thickness of this unit in northern Dela-
ware. In addition, in southern New Jersey, the up-
permost Cretaceous bed is the Navesink Formation,
but here it is very thin or absent in the updip areas.
The problems, therefore, in northern Delaware, are
to determine: (1) the thickness of the Mount Laurel,
(2) the presence or absence of the Navesink, (3) the
top of the Cretaceous section, and (4) the character
of the lowest Tertiary formation. As indicated previ-
ously, some older publications reported the occur-
rence in a greensand of a characteristic Paleocene
fossil, Oleneothyris harlam' (Morton), in the vicinity
of Odessa. This fossil is commonly found along or
above the Hornerstown-Vincentown contact in New
Jersey. The presence of the highly glauconitic Hor-
nerstown Sand or its lateral equivalent in Delaware
is, therefore, strongly suggested.

Groot, Jordan, and Richards (1961, p. 24) , in their
guidebook to the geology of the area, described an
outcrop at the western edge of Odessa, whose strati-
graphic placement was uncertain because of its un-
fossiliferous nature. At this locality, about 4 feet of
glauconite sand with a lithology similar to that of the
Hornerstown Sand of New Jersey overlies a pebbly
glauconite quartz sand that is similar to the upper
beds of the Mount Laurel. (See descriptions ac-
companying fig. 3.) Because of the thinness and
weathered nature of the upper glauconite sand at
this locality, a series of holes was augered east and
north of Odessa to ascertain the thickness and trend
of this unit and to obtain less weathered samples.
The thickness, about 20 feet, and lithology are nearly
identical to the Hornerstown Sand of New Jersey
(Minard and others, 1969) . In New Jersey, the

 

Hornerstown Sand consistently has a very diagnostic
green glauconite clay matrix. The green clay matrix
of the sand at Odessa is identical. Another unique
feature of the Hornerstown in New Jersey is the
abnormally high potassium oxide content of the glau-
conite grains as compared with Cretaceous glauconite
pellets. The grains from the Odessa sample were
analyzed and have a potassium oxide content of 8.1
percent (H. J. Rose, written commun., 1963). Such
high values are typical of the Hornerstown rather
than of the Cretaceous glauconite (Owens and
Minard, 1960, p. B431). Subsequent radiogenic age
determinations (potassium-argon method) of the
glauconite sand yielded an age of 63.8:21 m.y.
(J. P. Obradovich, written commun., 1967). This
date is compatible with a very early Tertiary age
(Kulp, 1961).

In summary, in the vicinity of Odessa the spatial
and lithologic relationships indiate that the Hor-
nerstown Sand rests directly on the Mount Laurel
Sand and that the Navesink Formation, which is
only 4-5 feet thick updip at Woodstown, is com-
pletely absent at Odessa and in the nearby shallow
subsurface. Certainly, if this interpretation is cor-
rect, then the quartz sand at the Biggs Farm locality
could not be the Red Bank but is the Mount Laurel.
The stripping of the upper beds of the Upper Cre-
taceous sequence and the onlap of the basal Paleocene
beds onto progressively older beds toward the south-
west has continued. If the Mount Laurel has the
same rate of dip here as at the canal, then it is
calculated that the unit is about 170 feet thick in this
part of Delaware. This is a reasonable estimate if
the regional trend of southward thickening of the
Mount Laurel continues into northern Delaware.

Figure 13 is a composite section showing our in-
terpretation of the stratigraphic sequence in the
northern Delaware coastal plain.

COMPARISON OF THE UPPER CRETACEOUS FORMATIONS
IN NORTHERN DELAWARE AND SOUTHERN NEW JERSEY

The foregoing descriptions permit a comparison of
the stratigraphic sequences of the two regions. The
stratigraphic sequence near and along the canal is as
follows:

 

 

 

 

Formation Age
Hornerstown Paleocene
Mount Laurel Late Cretaceous
Marshalltown Do.
Englishtown Do.
Merchantville ........................................................ Do.

The above sequence has a distinct cyclic sedimen-
tation pattern (fig. 14A). Cycle one consists of a

18 STRATIGRAPHY OF OUTCROPPING POST-MAGOTHY UPPER CRETACEOUS FORMATIONS

glauconite sand (basal Merchantville) overlain by a
silt (upper Merchantville) which grades up into a
quartz sand (Englishtown). Then the pattern is re-
peated and another cycle completed: glauconite sand
(Marshalltown), grading up into a calcareous silt
(basal Mount Laurel), which is overlain by a quartz
sand (upper Mount Laurel). The glauconite sands
are interpreted as representing transgressive beds,
and the quartz silts and sands are interpreted as
representing the regressive facies of the cycles. Two
cycles occur in the Upper Cretaceous sediments at
the canal; 31/2 cycles occur in the Upper Cretaceous
sediments of New Jersey (fig. 14). The fewer cycles
in Delaware are most likely the result of a more
intense early Tertiary period of erosion than oc-
curred in northern New Jersey. The uppermost beds,

EXPLANATION

Hornerstown .
Sand

TERTIARY
CRETACEOUS 1-a bow-1

 

 

 

 

 

 

 

Mount Laurel
Sand

 

I I
I I
I I
I I
I I
i I

I

E

i I
I I
l I
I i
I I

 

 

 

       

 

Marshallt0wn Calcareous sandstone

Formation

 

 

m {I 4

Crossbedding

 

Englishtownl
Formation

 

 

 

 

__~_ -0
Merchantviile __ I ~ . . ,
Formation i/K/\/\/\/\/\/\/\/\/\i
i Concealed i 20’
WW1
, Lime
Magma //////////
Formationl/\/\/\/\/\/\/\ 40,

FIGURE 13.—-Composite columnar section of Upper
Cretaceous stratigraphic relations in the northern
Delaware Coastal Plain. A, At Odessa. B, At new
railroad bridge and east to Biggs Farm. C, On
south bank of canal at the new Summit Bridge.

 

the Tinton, Red Bank, and Navesink, were stripped
away during the erosional period. In addition, the
deposits of a single cycle from New Jersey and Dela-
ware are somewhat different. A complete sedimenta-
tion cycle in New Jersey (fig. 148) consists of an
upper quartz sand, a middle very micaceous quartz
sand or silt, and a lower glauconite sand. In Dela-
ware, the middle clastic silt is present in the first
cycle but is replaced by calcareous silt in the second
cycle. An intermediate calcareous silt does not occur
in the Upper Cretaceous beds of New Jersey but is
present in the Paleocene Vincentown Formation.

Much of the confusion in correlations over long
distances in the northern Atlantic Coastal Plain is
due to the failure to recognize the cyclic nature of
these sediments. The repetition of generally similar
lithologies, coupled with poor formational descrip-
tions and lack of good maps, left most stratigraphers
dependent on biostratigraphic correlations. Unfor-
tunately, most of the outcropping units are un-
fossiliferous or lack a diagnostic fauna. Frequently
such correlations were based on widely spaced
samples.

The quartz sand units, particularly beds in the Red
Bank and Mount Laurel Sands, are most commonly
confused by regional stratigraphers. Cook (1868, p.
268) and Clark, Bagg, and Shattuck (1897, p. 335)
confused these two units in their early studies in
New Jersey. Only through the precise tracing of the
two units in the field, was Knapp (in Weller, 1907,
p. 17—20) able to demonstrate the correct spatial
distribution of the sands. The same misidentification
of the Mount Laurel as the Red Bank appears to have
been made by Groot, Organist, and Richards (1954)
in the Chesapeake and Delaware Canal section. Once
they assumed that the Mount Laurel was the Red
Bank, the underlying glauconite-rich unit (Marshall-
town) was understandably misidentified as the Nave-
sink. The same reasoning applied to the quartz sand
beneath the Marshalltown. This sand was identified
as the Wenonah rather than the Englishtown. (For
details of the stratigraphic sequence, see fig. 3.) Fur-
ther complicating the interpretation was the fact
that the geologic map of New Jersey (Lewis and
Kiimmel, 1912) shows the Englishtown pinching out
near Swedesboro in the Woodstown quadrangle.
However, mapping by Minard (1965) showed that
the Englishtown continues southwest and the Wood-
bury Clay pinches out. This mapping also showed
that the Mount Laurel thickens rapidly at the ex-
pense of the underlying Wenonah.

The interpretation of the canal section, however,
was clearly predictable and was verified by lithol-

ROCK STRATIGRAPHIC STUDIES 19

 

 

 

 

       

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

    

 

 

 

 

 

 

 

A B
- , 1 - N _ Hornerstown
Hornerstown ’-" - ' — "’
Sand 2» Paleocene . "f" Sand v A
r .' ’. . Upper Cretaceous .o- f; Tinton 'j ‘g
-. '--.%:Sand 23
Mount I p:
N Laurel j - ',' .-,' Red
I-u Sand ~_-'~1 g r Bank "3
é ‘ :Z'Sand '3’
Marshalltown ..'.‘ Navesink
Formation ' Formation
Englishtown; . 3 1". 7: l
Formation '. 1 Mount
'. 1'. Laurel
~. ‘ r Sand
5 _ : ' " g
5 Merchantvrlle i >_
Formation 3 t. _ Wenonah o
a ” Formation
4f°~~ N H Marshalltown
~ ——‘— . ~ _ Formation 1
(UM)
\\\\.\\ Englishtown
7 ' Formation
Li;_ L”
_l
" —“‘— Woodbury (>3
_ ...... Clay 0
:71 Merchantville
—;—_ Formation
FIGURE 14.—Schematic columnar sections showing differences between Upper
Cretaceous cyclic deposits in Delaware (A) and New Jersey (B). Lithic
symbols are the same as those in figure 13. Drilling by the U.S. Geological
Survey during recent investigations in Delaware has now provided complete
lithologic data for these units. (See fig. 13.)
ogies and faunal associations, the following facts the Mount Laurel in updip sections in southern
being kept in mind: New Jersey.
1. Pinchout of the Red Bank in the central Coastal . .
. . 3. Thinning of the Wenonah towards the southwest.
Plain in New Jersey.

2. Removal of the Navesink by a pre-Hornerstown 4. Continuation of the Englishtown southwestward
erosion and deposition of the Hornerstown on from Woodstown.

20 STRATIGRAPHY OF OUTCROPPING POST-MAGOTHY UPPER CRETACEOUS FORMATIONS

5. Pinchout of the Woodbury in the area northeast
of Swedesboro.

EASTERN MARYLAND

The lower formations of Late Cretaceous age are
well exposed along the Chesapeake and Delaware
Canal in northern Delaware, but the uppermost for-
mation, the Mount Laurel Sand, especially its middle
and upper beds, is poorly exposed. To better examine
the uppermost Cretaceous beds, a series of traverses
was made along the Sassafras River in eastern
Maryland.

Bluffs, some more than 60 feet high, occur along
the east-west—oriented Sassafras River, from near
Fredericktown, Md., westward to Chesapeake Bay
(fig. 5). The stratigraphic sequence exposed in these
bluffs ranges from the Vincentown Formation of
Paleocene age to the Potomac Group of Early Cre-
taceous age. Locally, deep, wide channels filled by
gravelly sand of Quaternary age have cut deeply into
the older formations and interrupt the nearly con-
tinuous sequence of formations.

Iron oxide staining and cementation is common in
many of the more sandy formations. Many of the
more soluble constituents, such as calcareous shells,
pyrite, siderite, and carbonaceous matter, have been
selectively removed or converted to other mineral
phases during weathering. In spite of these wide-
spread weathering effects, the same units noted along
the canal have retained sufficient lithologic identity
to be recognized in these bluffs. Some lithic changes,
like those in the area from Woodstown, N .J ., to
northern Delaware, have taken place in all the units
in the area between the canal and eastern Maryland.
Thus, the Upper Cretaceous sequence, the Merchant-
ville, Englishtown, Marshalltown, and Mount Laurel
can be traced as recognizable lithostratigraphic units
to the eastern shore of Chesapeake Bay. Figure 15 is
a composite stratigraphic section of the Upper Cre-
taceous-lower Tertiary sequence of this region.

The total calculated thickness of the Upper Cre-
taceous section in eastern Maryland is approximately
240 feet. A southwestward thinning of this section
from Delaware to eastern Maryland is not evident.

DISTRIBUTION OF FORMATIONS

The Merchantville is well exposed on the south
bank of the Sassafras River, west of Betterton
Beach, and also at Grove Point on Chesapeake Bay
on the north side of the mouth of the Sassafras
River. A typical section of the Merchantville Forma-
tion averages 40—60 feet in thickness in New Jersey,
whereas it is approximately 40 feet thick along the
Sassafras River. The formation overlies the Magothy

 

 

EXPLANATION

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

' ' N N ' Q '
Hornerstown ' ‘ - ' . '
f" N ' . . - .
Sand .- P'_ . ‘0'“? 'O'O'PUO'
' ' .,~./- . ‘°--0'..'
TERTIARY JVLLV :9 - ', b ‘ . '.° "2' °
CRETACEOUS . ’9 -{:'.' O H. Gravel
a]. . o. ' ‘- -‘
:'_ '."‘.'.'. ~~~~
'-,.. "’4." HNNI-vfl
I . o - ‘ . '. .... ~ ~ ~ ~
. M - . o '. Glauconite sand
I I - on . . ' I
..i c " o.
. o H - -. o ' . . . . .
' _. ‘ '1', - uartzs nd
. .. _ ‘ F,- . o Q a
Mount Laurel o ""0 . o. .' _— — ~—
Sand "V.- j .': '- — ‘__ —
124/335 Slit
- ’_ /,,-: 1,,-
2.‘ _- Clay
' '.'~.' / I I
. ‘ . . ' /// ll/l/l/V/
N . ' '- ,/ ’ // //
. N‘ 'N " Crossbedding
—. '..,;_, '__‘...F-'{ ( f/ I (
Marshalltown ~"‘Z":—'"~ / (/ / ( : /
Formation . -‘ (.. ( / k/ (f 4
.' ~ ‘. ....) .. ."-" Fossuls
73’. _~.°‘~.
- '————;__'_ 7/ I " ‘
Englishtown ///____‘____' "’ ’ o ‘ 0
Formation '. °°° ~ ° °.'.- Wood
~ '_-—.——.- : _. :
..fv..——-;..,-
-..’.:...:-:.’.'- ‘ O
Merchantville :3”? °"._.o_.:fv I
Formation '02: N '_...
_ ......... 2 '
._..._...,_, _... 20'
O
,4...” ._ _
0
Magothy _ I-’ '.I '—
Formation m 40'

FIGURE ]5.—Composite columnar section showing
Upper Cretaceous formations in eastern Maryland.

with a sharp but broadly undulatory contact in this
area (fig. 16). The basal foot of the Merchantville is
reworked sediment containing pieces of gravel as
much as 1 inch in diameter, carbonized pieces of
wood as much as several inches long and abundant
coarse sand. Overlying this basal interval is a se-
quence of thick beds (averaging 10 ft) which are
sharply differentiated from each other. These beds
consist largely of dark very micaceous silt to very
fine sand. Concentrations of very coarse sand and
fine pebbles are abundant in some of the beds, and
these tend to emphasize the bedding in this unit.
Large to small woody pieces are abundant in the
entire formation. An unusual feature in some of the
lower beds is an abundance of thin indurated,

ROCK STRATIGRAPHIC STUDIES 21

 

FIGURE 16.—Cutbank along Chesapeake Bay at Grove Point
exposing the light-colored Magothy at the base of the bluff
in sharp, flat contact with the dark-colored Merchantville
Formation. The Merchantville is unconformably overlain
by sand and gravel of the Wicomico(?) Formation. Pho-
tograph by L. C. Conant.

siderite-cemented(?) platelets. In the upper part of
the formation, intercalated thin (2—4 in.) beds of
black clay and light fine to medium sand beds inter-
finger with the dark-gray silts.

The Merchantville grades upward into about 20
feet of intercalated thin beds of black silty clay and
white micaceous sand. Many of the sandy layers
have small-scale trough cross-stratification. Most of
the sand is fine to medium. Pebbles as large as one—
fourth of an inch in diameter are common in many
of the sands. Large concentrations of coarse car-
bonaceous material commonly associated with coarse
mica grains are common in the dark clay beds. The
well-bedded character, lithology, and stratigraphic
position of this unit indicate that it is unquestionably
the Englishtown Formation. This formation is ex-

 

posed along the south bank of the Sassafras at
Betterton Beach.

The thin-bedded Englishtown is overlain by about
15 feet of massive dark-gray glauconite quartz sand,
which we have assigned to the Marshalltown. The
lower 6—8 feet of the Marshalltown is dark-gray
quartz glauconite sand that contains granules and
some small pebbles in the base. The glauconite sand
content decreases rapidly above this bed, and the
upper part of the formation is largely a dark-gray
quartz silt. Borings filled with light-gray more
clayey sediment are extensive in the upper Marshall-
town (fig. 17). Fossil casts also seen in this photo-
graph are common in the middle of the formation.
The entire thickness of the formation is well exposed
at several localities along the north side of the
Sassafras River. The formation is only exposed at
one locality on the south side of the Sassafras River
just east of Betterton.

The Marshalltown grades upward into the yel-
lowish-brown to pale-yellow quartz sand of the
Mount Laurel sand (fig. 18). The Mount Laurel is
exceptionally well exposed in the bluffs along both
banks of the Sassafras River between Betterton and
Fredericktown (fig. 5). At some localities, more than
60 feet of Mount Laurel is exposed in a single bank.
The lower 20—25 feet of the formation is a massive
fine quartz sand containing small amounts of
glauconite sand. Thin discontinuous borings filled
with glauconite sand are well developed in these beds.
Overlying this basal massive sand is a series of thick
horizontal beds (averaging 10—15 ft), which are
commonly sharply differentiated from each other.
The horizontal bedding is largely produced by varia-
tions in average grain size from bed to bed. Most of

 

FIGURE 17.—Dark massive-bedded Marshalltown Formation,
north bank of Sassafras River, 2 miles east of Grove Point.
Borings filled with lighter colored clayey sediment are ex-
tensive. Photograph by L. C. Conant.

22

    

FIGURE 18.—Gradational contact between the light-colored
Mount Laurel Sand and dark-colored Marshalltown Forma-
tion exposed at the same locality as figure 17. Upper part
of Marshalltown is weathered pale gray. Photograph by
L. C. Conant.

the beds consist of pale-gray to brown medium sand,
although beds of fine and coarse sand are common.
Granules and pebbles are present in most of these
upper beds. In general, the average grain size is
coarser in the upper beds than in the base. Most of
the beds are massive, although some, particularly in
the middle of the formation, have large-scale cross-
stratification.

The mineralogy from bed to bed is similar——
quartz, glauconite, and feldspar are the major sand
constituents. Sample Ea 4, table 2, has a typical
composition for the upper Mount Laurel in this
region. As can be seen, glauconite is abundant and
is exceptionally coarse; some beds contain large con-
centrations of coarse to very coarse glauconite
grains.

Large thick-shelled fossils replaced by iron oxides
are common in the middle and upper parts of the
Mount Laurel Sand particularly at Fredericktown
along the north side of the Sassafras River and near
Kentmore Beach along the south side of the river.
Because of the poor state of preservation of these
fossils, precise paleontologic identification is very
difficult, but they establish the marine origin of these
beds. Ophiomorphia borings are also widespread
throughout this unit.

At Gregg Neck (fig. 5), a promontory on the south
bank of the river east of Fredericktown, the
Hornerstown-Mount Laurel contact is well exposed

 

STRATIGRAPHY OF OUTCROPPING POST-M AGOTHY UPPER CRETACEOUS FORMATIONS

in a borrow pit and a nearby roadcut. The sharp
contact between the Hornerstown glauconite sand
and the underlying quartz sand of the Mount Laurel
is virtually the same here as at Odessa, Del. About
15 feet of Mount Laurel is exposed beneath the
Hornerstown at Gregg Neck. This relationship in-
dicates that throughout the northern Delmarva
Peninsula the Navesink Formation is absent and the
Hornerstown in outcrop rests directly on the Mount
Laurel. Along the eastern shore of Chesapeake Bay,
the Mount Laurel is a very thick unit, as much as
170 feet thick. The best exposures of the Mount
Laurel in the northern Delmarva Peninsula are along
the Sassafras River where most of the formation
can be seen.

SUMMARY OF ROCK STRATIGRAPHIC STUDIES IN
EASTERN MARYLAND

The section along the eastern shore of Chesapeake
Bay is similar to that at the Chesapeake and Dela-
ware Canal except that all units were apparently
deposited nearer shore. Nearshore deposition is in-
dicated by (1) decrease in the glauconite content in
the Cretaceous units, particularly in the Merchant-
Ville Formation, (2) change in the bedding charac-
teristics in most units from massive to thin through
thick bedded (Merchantville, Englishtown, and
Mount Laurel), or the development of cross-stratifi-
cation (Mount Laurel), and (3) increase in general
coarseness of clastic material (Merchantville, Mar-
shalltown, and Mount Laurel) and abundance of
carbonaceous matter, particularly large pieces of
wood (Merchantville, Englishtown, and basal Mar-
shalltown).

In interpreting the stratigraphy of the eastern
shore of Maryland, the terms Matawan and Mon-
mouth Formations are no longer useful, and it is
recommended that these terms be abandoned in east-
ern Maryland and that the New Jersey stratigraphic
nomenclature be adopted, thereby eliminating the
dual nomenclature that has prevailed for many
years. The Matawan Formation of eastern Maryland
would be replaced by (in ascending order) the Mer-
chantville, Englishtown, and Marshalltown Forma-
tions, and the Monmouth would be replaced by the
Mount Laurel Sand. The areal distribution of the
beds in eastern Maryland is shown in figure 5.

PETROLOGIC STUDIES
A general survey of the petrologic characteristics
of the Upper Cretaceous—lowermost Tertiary forma-
tions was made in order to compare the Iithologies
of all the formations from Woodstown, N.J., and
the eastern shore of Maryland.

ROCK STRATIGRAPHIC STUDIES 23

Groot (1955) and Groot and Glass (1960) ex-
amined some of the petrologic characteristics of the
Coastal Plain formations in this general region. In
the latter publication concerning the petrology of
these formations, Groot and Glass (1960) discussed
the clay minerals and heavy minerals in the forma-
tions. They noted that the marine sediments are
primarily characterized by an illite—montmorillonite
clay assemblage in association with a full suite of
heavy minerals. A full suite is defined as a mineral
assemblage that contains significant concentrations
of any two of the following minerals: epidote,
Chloritoid, garnet, and hornblende. These minerals
are presumed to be relatively susceptible to intensive
weathering conditions. The nonmarine sediments
characteristically contain kaolinite as the major clay
mineral and have a limited heavy-mineral suite. A
limited suite, therefore, is one that does not have
significant concentrations of the relatively unstable
minerals. Groot and Glass (1960) also observed that
many formation assemblages varied along strike but
that these differences could be explained by a change
in provenance or preferential segregation in the clay
fractions because of crystal-size sorting. Diagenetic
effects were considered unimportant controls on
these mineral assemblages.

In our petrologic studies of the Upper Cretaceous
and lower Tertiary formations, the techniques of
Groot and Glass were adopted and were supple-
mented by light-mineral studies and the determina-
tion of glauconite-clastic ratios.

HEAVY-MINERAL ANALYSES

Samples of all the formations of southern New
Jersey, northern Delaware, and eastern Maryland
were studied for their heavy-mineral content (tables
2 and 3, and fig. 19). The results generally agree
with those reported from northern Delaware by
Groot (1955). Groot, however, subdivided many of
the mineral groups (for example, the epidote
group); we did not. All formations examined are
characterized by full suites of heavy minerals, the
terminology of Groot and Glass (1960) being used.

Variations in heavy—mineral types and concentra-
tions, however, do occur between the formations in
a single area and in the same formations from one
area to another. In the Merchantville and Mount
Laurel, the garnet and epidote content decreases
from Woodstown to the eastern shore of Maryland
(fig. 19). In the Englishtown, epidote content also
decreases southwe‘stward, but garnet decreases only
southwest of Delaware. Epidote also shows the same
general decrease to the southwest of Delaware in the
Marshalltown, but garnet increases southwestward

 

from Woodstown, N.J. Chloritoid also appears to
vary systematically from area to area, but the trend
is the reverse from that noted for garnet and epidote.
As can be seen in figure 19, Chloritoid content in-
creases toward the southwest. None of the other
minerals show any significant trends like those cited
above.

Despite the limited number of samples studied
from the Chesapeake and Delaware Canal area, it
is apparent that detrital heavy-mineral assemblages
have little value in stratigraphic correlations. Local
source—rock variations, particularly within the meta-
morphic rocks of the nearby Piedmont province,
apparently are significant enough to produce mark—
edly different heavy-mineral assemblages in the same
stratigraphic horizons within short distances. It can
be stated, however, that the high percentages of
metamorphic minerals in the Coastal Plain forma-
tions indicate that the Piedmont was a major source
land during the Late Cretaceous.

LIGHT-MINERAL ANALYSES

Petrographic studies of the light-mineral fractions
(tables 2 and 3 and fig. 20A) reveal that four
major components are present: common quartz,
feldspar, polycrystalline quartz and rock fragments.

Common quartz is the major sand-sized light
mineral in these formations. Variations in the per-
centages within the formations are shown in tables
2 and 3, and figure 20A shows the average for each
of the formations. This mineral is at least 66 percent
to as much as 93 percent of any light-mineral com-
ponent of the sand fraction. No significant trends in
the common quartz distribution, however, were dis-
cernible in the formations of a single region or
within the regions.

Feldspar makes up 3—18 percent of the sand-sized
light—mineral fraction in the formations and aver-
ages about 10 percent. Generally, the formations in
eastern Maryland have less feldspar than the other
regions. Most of the feldspar grains are badly
altered in all formations from southern New Jersey
to eastern Maryland. Typically, all grains have re-
fractive indices of <1.54, and a large number have
microcline twinning. The bulk of this fraction, there-
fore, is potassic feldspar. Some grains, however, are
untwinned and have a cloudy appearance. The degree
of alteration in association with the low indices
tends to mask whether these are orthoclase or un-
twinned albite. An occasional grain with plagioclase
twinning was observed, but these are not common.
Although two major feldSpar families are present,
potassic feldspar is more abundant by far.

24

STRATIGRAPHY OF OUTCROPPING POST-MAGOTHY UPPER CRETACEOUS FORMATIONS

TABLE 2.——Heavy- and light-mineral content, in percent, and glauconite-clastic ratios from Woodstown quadrangle, New Jersey,
and from eastern Maryland

[Approximate sample localities are shown in fig. 5. Tr.. trace; N.d., not determined. Glauconite not counted in mineral analyses. Number in parentheses
means that more than one sample was located at that locality]

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  

 

 

Specific gravity >2.80; particle size <0.177, >0.074 mm Specific gravity GIauconite-clastic
0 <2.80;0particle ”130:2 parbticle size
paque - size < .149, < .4 .> .062 mm
minerals Nonopaque minerals > 0.074 mm
5
L4
Name of E g
formation and a) g N a ,9
field number 3-: a t g ‘5
5.5 g‘ a; g a) g g E o
s g 2 g .5 s E 2 c» t g e 3 . v s E 3
3 :8 a ea 76 w 2 M E ‘1 o m '5 '5‘ o o I: g m :8 E 'E w
._ s... e «H .o v o «5 .a 2 r: c o r: “J a W ° E' a. o u
fiaAgsééwgsg’aésssa-Esfi‘a’é2:5: as
5 ° “ 5 .s ‘5 5 'a ° 33 E s = — = .2 r "i w " — ~ ° a s
:Sgflsmfimmu£m&<52m5$a§éfifin? (so
Woodstown quadrangle, New Jersey
Hornerstown Sand:
1: 61 1 ................ 99 1
Mount Laurel Sand:
Wt 62 ...... 95 2 3 30 10 2 2 27 12 2 7 1 1 1 85 2 1 12 88
Wt 92D .. 6 17 2 3 6 10 3 40 20 3 7 3 3 N.d. N.d. Nd N.d N.d. N.d
Marshalltown
Formation:
Wt 71D ............ 76 10 14 12 4 7 12 10 29 7 7 9 2 1 85 8 7 59 41
Englishtown
Formation:
Wt 129 2 7 25 5 9 4 2 7 21 7 2 3 1 6 5 3 81 4 14 1 2 98
Wt 74 ...... 2 50 1 2 4 12 10 4 Tr. 2 1 16 22 4 9 13 83 5 12 Tr. N.d. N.d.
Merchantville
Formation:
1 13 8 7 6 21 Tr. 20 10 4 5 1 7 Tr. 1 2 8 93 2 4 1 25 75
3 11 6 6 10 27 Tr. 19 9 4 2 .. 5 2 1 9 Tr. N.d. N.d. N d. N.d. 16 84
Eastern Maryland
6 14 9 11 6 24 4 5 26 Tr. 3 3 6 3 86 3 11 70 30
21 6 5 6 4 36 12 6 9 4 6 6 84 1 15 34 66
10 9 11 20 13 .. 39 7 6 2 2 N.d. N d. N.d. N.d 6 94
2 9 21 12 12 6 1 22 2 2 11 2 4 N.d. N d. N.d. N.d 7 93
2 21 20 5 5 4 20 17 3 3 2 5 12 4 92 4 4 7 93
Sp 7 ...... 1 16 19 5 12 3 21 18 6 1 Tr. 7 1 6 1 N.d. Nd Nd Nd 16 84
Englishtown
Formation:
Bet 1A .............. 62 8 30 4 15 19 Tr 15 9 6 21 7 4 84 11 5 2 98
Merchantville
3 ‘33 1 9 8 20 11 1 Tr. 40 7 2 1 87 10 3 4 96
5 24 49 6 8 6 9 1 1 11 7 1 1 N d N.d. N d. N.d N.d. N.d.
1Too small a sample to make an analysis.
Rock fragments and polycrystalline quartz are the (Pettijohn, 1957) or subgraywackes (Krynine,

other common light components. Their distribution
is more erratic than the feldspar or common quartz.
Rock fragments and polycrystalline quartz are more
abundant in northern Delaware than in southern
New Jersey or in eastern Maryland.

A plot of the data in figure 20A showed that, in
the four categories counted, no definite trends were
evident either within a group of formations in a
single area or within a single formation from one
area to another. The data, however, do indicate a
probable metamorphic source for a large volume
of these sediments.

Because these light minerals constitute the bulk
sediment in the elastic sands (Englishtown and
Mount Laurel), they determine the composition of
the rock and hence their rock-type classification. The
relatively feldspathic nature is apparent, and these
sands can properly be classed as protoquartzites

1948). Except for variations in glauconite sand con-
tent, the Englishtown and Mount Laurel maintain a
uniform composition from southern New Jersey to
eastern Maryland. In fact, the clastic light minerals
are distributed throughout the silts and greensands
in nearly the same proportions as in the elastic sands
throughout this region.

GLAUCONITE-CLASTIC RATIOS

During field mapping a gradual decrease in glau-
conite sand content to the southwest was observed
in nearly all formations, especially those of Late
Cretaceous age. To quantify this observation, sam-
ples of the sands were electromagnetically processed
to determine glauconite-clastic ratios (tables 2 and 3
and fig. 208).

The most obvious changes occur in the Merchant-

 

ville, Marshalltown, and Hornerstown (fig. 203),

ROCK STRATIGRAPHIC STUDIES

25

TABLE 3.—Heavy- and light-mineral concentrations, in percent, and glanconite-clastic ratios from localities in the vicinity of
the Chesapeake and Delaware Canal

[Sample localities are shown in

figs. 1 and 6; number after railroad bridge pier indicates depth in feet below ground level. Samples from bridge pier are

listed in distance from upper surface. Glauconite not counted in mineral analyses. Tr. trace]

 

 

 

 

 

 

 

 

 

  

Spec1fic grav1ty >2.80, part1cle size <0.177. >0.074 mm Specific gravity <2.80; Glauconite-clastic
0 a ue _ particle size <0.149, ratio: particle size
miliiegals N°n°DWue minerals >0-074 mm <o.42. >0.062 mm
5
'u 3
Formation Locality 5 n N g m
0 0 0 '5‘
£2 a. o. ‘5 n a
5% 5 °’ 3 ° 3 o :I E 0
5:2 2.552532: £723 «“35 E s
3 ...o u an '55 w 2 ::: “1‘ 0 m 0 'g 3 a, 3 E, 5 a 3 $3 a m
'a§-=§82§§€§3§§§afsfiraagg E a: 8-3
°’ A 0 '5 5 -~ 5« r.. 5 :2 d “U .2 g *‘ 2 .: 9 1.. 2' 'C o 5 3
E °"" 5 .E :1 a 0 no -.: >. r: .s: .2 {E >. o T) 1': ..
:asfiamfimmogma<ozm5£mm8 a. in a? o o
Hornerstown Sand .............. Odessa ..... 7 20 5 6 1 6 2 19 35 7 8 6 5 Tr ......... 81 10 9 89 11
Mount Laurel Sand ................ do 2 5 10 4 2 15 2 30 19 8 4 2 4 ........................ 71 1 18 10 45 55
Biggs Farm. 6 feet
above high tide. 84 9 7 14 7 3 18 2 13 22 8 4 4 4 . 1 ................ 72 17 11 7 93
Biggs Farm,
high-tide level. ........ 979 10 11 4 4 4 18 5 26 19 3 7 l 5 3 1 76 Tr. 11 13 4 96
Marshalltown Formation ....Bridge pier. 25 .. .. 1 9 8 9 5 19 2 17 17 9 5 2 4 2 . 78 1 16 5 15 85
27 9 11 15 10 9 22 2 8 17 2 3 3 5 1 1 81 1 12 6 60 40
32 12 17 8 6 9 22 15 19 l 3 Tr. 8 3 5 81 1 10 8 58 42
39 2 13 14 7 6 30 1 15 10 2 1 1 5 2 4 66 3 13 18 15 85
Englishtown Formation ....Bridge pier, 41 _. 8 46 2 1 6 26 1 9 8 4 3 6 12 2 7 83 2 8 7 6 94
44 7 22 Tr. 9 7 10 1 18 8 1 2 2 28 5 4 81 Tr. 6 13 8 92
51.. 5 17 10 3 7 14 1 26 8 1 1 1 7 8 2 80 1 8 11 11 89
53 .. 8 21 6 7 12 20 1 17 9 3 2 2 7 4 3 86 1 9 4 20 80
Merchantville Formation ....Bridge pier, 55 .. 20 28 5 2 6 13 11 8 1 l 8 17 7 82 5 10 8 10 90
62.. 2 17 23 Tr. 8 13 .. 13 8 Tr..... Tr. 4 6 2 85 4 8 3 22 78
70 1 22 6 1 9 18 .. 13 5 Tr. lTr. 11 10 6 1 81 6 11 2 25 75
76.. 12 28 6 1 2 10 11 5 1 1 7 14 4 88 4 8 11 89

 

 

 

the formations in which glauconite sand is a major
constituent. In each of these formations glauconite
content gradually decreases between Woodstown,
N.J., and the Chesapeake and Delaware Canal, and
then there is a further abrupt decrease to the eastern
shore of Chesapeake Bay. The glauconite depletion
is less evident in the quartz sand units, the English-
town and Mount Laurel. The overall trend, however,
is toward glauconite depletion from northeast to
southwest, which suggests a nearer shore deposi-
tional site for most of these formations in the south-
west.

CLAY-MINERAL ANALYSES

Part of the study of the Coastal Plain sediments
by Groot and Glass (1960) was an analysis of the
clay minerals. In the marine Cretaceous section, to
which our study was restricted, these units, accord-
ing to Groot and Glass, should be characterized by an
illite-montmorillonite assemblage in which kaolinite
and chlorite are present, but as minor constituents.

Montmorillonite is present occasionally in the
Merchantville Formation and Mount Laurel Sand,
whereas it is common in the Marshalltown and
Englishtown Formations (table 4). Illite and (or)
muscovite are present in some but not all samples.
Kaolinite is common in most samples, nearly in the
same abundance as montmorillonite.

Groot and Glass (1960, p. 279) ascribed the lack

of kaolinite in the Marshalltown in the southwest to
deeper water deposition. The present authors found
no such relationship; in fact, kaolinite was con—
sistently present in higher concentrations than
montmorillonite in the Marshalltown in the Del-
marva Peninsula. The Marshalltown in the south-
west is probably a shallower water facies than it is
to the northeast, as shown by the general decrease in
glauconite sand.

In addition to the major clay minerals, there are
significant concentrations of clay-sized siderite in the
Merchantville and Englishtown Formations at the
Chesapeake and Delaware Canal. Sepiolite is also
present in some of the samples from the same area
but in much smaller amounts (table 4). Groot and
Glass did not discuss these two minerals in their
report.

From the analyses, it is evident that the clay-sized
assemblages are complex mixtures of many clay and
nonclay minerals. These complex clay mixtures
characterize the marine formations in the northern
Atlantic Coastal Plain. The characteristic illite-
montmorillonite assemblage suggested by Groot and
Glass for the marine formations is not consistently
present. Our study was too restricted areally to
answer the basic question whether differences in clay
mineralogy and the abundances of the various clay
minerals resulted from segregation because of crystal
size or diagenesis or both.

 

26 STRATIGRAPHY OF OUTCROPPING POST-MAGOTHY UPPER CRETACEOUS FORMATIONS

EXPLANATION 40—- woodstown quadrangle,

New Jersey

   

Hornblende

s‘

Epidote 20—

Chloritvoid

”/1

Sillimanite-kyanite

 

I
O

 

n 4Ofi Chesapeake and Delaware Canal, T
E] Delaware

Garnet

 

Staurolite

Zircon-tourmaline-
rutlle

20"

 

   

 

 

 

 

 

FREQUENCY DISTRIBUTION, IN PERCENT

 

 

 

 

 

O
801 F
Eastern Maryland
60— W_
40- ~—
3

20- _
0

3 c: c 33

L 3 C 35 : I:

= 2 g 2: z 9

SE 1n; In fig fig

H I“ 4: E _ L J: E

gm 3 5 9:0 o 8 8

o m u. “ll-L «nu.

2 E 2

FIGURE 19,—Histograms showing frequency distribution of some of the heavy minerals listed in tables 2
and 3. Number above each histogram indicates the number of samples averaged to obtain percentage of
each mineral.

CONCLUSIONS from 500 feet in the northern Coastal Plain in
The main points revealed by this rock strati- New Jersey to 240 feet in the eastern shore of
graphic analysis of the Upper Cretaceous Coastal Maryland. The thinning was accomplished in
Plain sequence of New Jersey, Delaware, and eastern two ways: (1) nondeposition and (2) erosion.
Maryland are: Erosion is largely responsible for the removal
1. Lithostratigraphic comparison shows that four of the Tinton, Red Bank, and Navesink Forma-
formations of Late Cretaceous age, the Mer- tions to the southwest.
chantville, Englishtown, Marshalltown Forma- 3. Many stratigraphic misidentifications have re-
tions, and the Mount Laurel Sand, can be sulted from failure to recognize the repetition
recognized throughout the region. of similar lithologies in cycles, especially the
2. The Upper Cretaceous section thins in outcrop more sandy units such as the upper Red Bank

 

ROCK STRATIGRAPHIC STUDIES 27

w

A Woodstown quadrangle
100[— New Jersey

1 1 1

    

No sample

No sample
w H

l—

 

 

100 Chesapeake and Delaware Canal —
and Odessa, Delaware
80
60

4o

 

2O

 

 

 

 

100

FREQUENCY DISTRIBUTION, IN PERCENT

 

 

 

 

 

 

 

 

 

 

80 -
1 1 1 1 _
60
40 —
20 —
0 m
- I: c» c - - c C 2

g E" §= :8 as 5 gr as 55 25

fig £33 £3 2% ea ‘62 figs 32% 5% ES ‘5“:

3“ 25 :35 EE 53 «MS «a? 29 =E SE

:tf) ll); Do‘ on. C :07: 5‘09 In» mo 0;.

5 as =8 as: s a v a v a: 5 L a:

I 2 “J 5 I 2 2 2 2

EXPLANATION EXPLANATION
7
a D, a .
Rock fragments Polycrystalline quartz Clastlc Glauconlte
\
§
Feldspar Common quartz

FIGURE. 20.—Frequency distribution listed in tables 2 and 3 for (A), three light minerals and rock fragments (Sp g!“
< 2.80) and (B), glauconite-clastic ratios. Clastics include all nonmagnetic components—mostly quartz, feldspar,
and muscovite. Number above each histogram indicates the number of samples averaged to obtain percentage of
each mineral.

Sand and massive Mount Laurel Sand, or the menites) mjor, of earlier authors, and the re-
silty beds of the lower Red Bank Sand and ported restriction of this form to the Wenonah
Wenonah Formation. Formation is not warranted. It is diagnostic
4. The dominantly authigenic glauconite-rich units of the sandier units (the nearer shore facies)
show a more consistent thickness and lithology such as the Mount Laurel Sand and the
along outcrop than the dominantly allogenic Englishtown and Wenonah Formations.
quartz sand units. The consistency in thickness 6. Changes of facies are gradual and for the most
and lithology of the Marshalltown is especially part are mappable.
noteworthy. 7. The Upper Cretaceous section thins gradually
5. Borings—crustacean, worm, and molluscan—are southwestward. In the same general direction,
common in all the more sandy and silty units. there is a tendency to lose the deeper water or
The dominant boring is Ophiomorpha (Haly- greensand facies.

 

28

STRATIGRAPHY OF OUTCROPPING POST-MAGOTHY UPPER CRETACEOUS FORMATIONS

TABLE 4.—Minerals in clay-silt range in the formations discussed in the text

[Determined by X-ray spectrometer. Numbers indicate peak-height ratios from X-ray traces. M, major. Tr., trace. Sample localities are shown in figs. 5 and
6. Number after railroad bridge pier indicates depth in feet below surface]

 

 

3 a:
s: ‘a
.9 In o
, :q a; 3 0
Formation Fieldlorzgflger or 32 E 33 E g 3 a, E ”E E
{3, {:1 E ‘r: g '5 5 5'5 :5 a ,, ‘g 3-:
3 3 5 :3 ’5 E "U 73 3 3.. *1 a .2
0' :4 2 o s. w (75 o 4 Ln. E > z
dornerstown Wt61A ....... .. .. 5
Sand. Odessa ........ .. Tr. .. 4
MillA ........ .. 1 .. 3
Mount Laurel Wt 62 ........ M 1+ 1— 1+
Sand. Biggs Farm, 6 M 2+ Tr. 1— Tr. 2+ Tr.
feet above
high tide.
Biggs Farm, M Tr. 6 1-—
high-tide level.
Bridge pier, 25 M Tr. ... ... ... Tr. .. . 1— 1— 1— ...
Ea4 .......... M 1 1+ 1-— 1
Wt71D ....... M 1 1— 1 5 1—
Marshalltown Bridge pier, 27 M 1 1— 1— . . . . . . Tr. . . . 1+ . . . 1 . . .
Formation. 39 M 1— 1- 1— 2 1 1—
Bet2 ......... M 2 Tr. 2 Tr.
Wt129 ........ M 3 3 1- 1— 2
Englishtown Bridge pier, 41 M 2 2 . . . . . . Tr. . . . . . . . . . Tr. 1
Formation. 44 M 1 Tr. 1
51 M 3 1—
53 M . . . ... 1 2 1— 1+ . ..
BetlA ........ M 1+ 1+ 1— 1+
Wt 66 ........ M 1 Tr. 1 1
Merchantville Bridge pier, 55 M 1— Tr. 1— . . . Tr. 3 1 . . .
Formation. 62 M 1— ... ... Tr ... 4 1— ...
70 M 1— . .. 2 1— Tr.
76 M Tr. 1— 2 1—
Bet 1 ......... M 3 . . . Tr. . . . Tr. 3

 

BIOSTRATIGRAPHIC ANALYSIS
By NORMAN F. SOHL and JAMES F. MELLO

The prime objective of this section is to integrate
the biostratigraphic interpretations with those de-
rived from the rock stratigraphy. In order to do this
it was necessary not only to evaluate the strati-
graphic distribution of faunas along the Chesapeake
and Delaware Canal but to attempt to relate them to
other parts of the Coastal Plain. To understand the
problems facing those attempting to use the available
information for purposes of correlation, one must
first realize the limitations imposed by the nature of
the record. Therefore a critical analysis of the New
Jersey Late Cretaceous larger invertebrate fauna
has been given as a necessary prelude to rational
application of the data.

Primary responsibility for the opinions expressed
in the sections dealing with the megapaleontology
and for the correlation charts rests with Sohl. The
interpretations presented in the micropaleontologic
section are those of Mello.

MEGAPALEONTOLOGIC STUDIES
NORTHERN ATLANTIC COASTAL PLAIN
PROBLEMS OF REGIONAL CORRELATION

Correlation of the Upper Cretaceous sequence of

 

the northern Atlantic Coastal Plain with other areas
has been based primarily upon the megafossils. The
main basis for correlation has been the two broad
zones of Exogym costata and Exogym ponderosa,
proposed by Stephenson in 1914, that are recognized
along the Coastal Plain from New Jersey to Mexico.
Stephenson later (1923, pl. 8) proposed another
zone, that of Exogyra cancellata, which was included
in the lower part of the E. costatar zone (fig. 23),
but it was not until 1933 that he recognized the
E. cancellata zone in the Mount Laurel Sand of New
Jersey. The confusion surrounding the relationships
of the New Jersey Cretaceous sequence to others of
the Coastal Plain was well expressed in the 1942
correlation chart (Stephenson and others, 1942, p.
436):

The absence of sharply defined faunal zones of regional ex-
tent in some parts of the series and lack of knowledge as to
the number and vertical distribution of the diastems and
unconformities have rendered diflicult the accurate vertical
placing of some of the recognized lithologic units; this dif-
ficulty has been experienced especially in the North Atlantic
Coastal Plaini“**.

Recent summaries, such as that of Richards and
others (1958, 1962), have done little to refine the
correlation, offering only such broad and undocu-

29

BIOSTRATIGRAPHIC ANALYSIS

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30 STRATIGRAPHY 0F OUTCROPPING POST-M AGOTHY UPPER CRETACEOUS FORMATIONS

mented correlations as “the Monmouth group is
roughly equivalent to the Peedee Formation of the
Carolinas, the Navarro of Texas and part of the
Maestrichtian of Europe” (Richards and others,
1958, p. 17).

That this condition exists is superficially astound-
ing. Perhaps because of the proximity of this area
to eastern centers of research, the New Jersey
Cretaceous sequence and its fauna, through the ef-
forts of such men as Morton, Gabb, Conrad, Whit-
field, Clark, and Weller was, at an early date, better
known and more thoroughly investigated than any
other area on the Coastal Plain. By 1907, Weller, in
his exhaustive monograph on the New Jersey
Cretaceous faunas, had seemingly set a firm founda-
tion for future study of the Upper Cretaceous bio-
stratigraphy of the northern Atlantic Coastal Plain.
According to the most recent summary by Richards
and others (1958, 1962), there are 428 species of
mollusks in the Upper Cretaceous sequence of New
Jersey. Figure 21 is a plot of these species, each
vertical line illustrating the total range of an individ-
ual species as cited in Richards and others (1962).
With such a large fauna and the large number of
supposed stratigraphically restricted species one
might assume that zonation would be simple. Why
then is this not so?

One reason why this seeming wealth of biostrati-
graphic information has not yielded more precise

 

correlation is that the majority of the described
species have never been reported outside New
Jersey and Delaware. For example, 99 of the 148
species of gastropods and 173 of the 249 species of
pelecypods (about 77 percent of the described
species) were erected solely for New Jersey speci-
mens. This endemic aspect is not so real as it is a
reflection of taxonomic provinciality and poor state
of preservation of the fauna.

The effect of state of preservation of the fauna is
shown in figure 22 in which the number of species
based upon internal molds or steinkerns is plotted
against the number based on well-preserved material
or mixed well-preserved and steinkern material. For
example, about 80 percent of the gastropod species
are based upon internal molds, many of which are
not determinable even at the generic level. Further
critical analysis of the gastropod fauna shows that
32 percent of the described species have been cor-
rectly identified to genus, 38 percent have been in-
correctly identified generically, and the remaining 30
percent are generically indeterminate. The biostrati-
graphic utility of the pelecypods is hampered,
furthermore, by citation of an overlong range that
comes from assignment of steinkerns to species
based upon well-preserved specimens from a dif-
ferent stratigraphic level.

When species described from other areas are cited
as occurring in New Jersey, it is difficult to reconcile

NUMBER OF SPECIES

0 50 100
l

O 50 100
I

 

 

GOOD

 

 

 

 

MIXED

 

 

 

 

 

 

STEINKERNSW

 

 

 

 

 

 

 

GASTROPODA PELECYPODA
NUMBER OF SPECIES
O 50 100 150 200 250
I l | 1
GOOD
MIXED

 

 

STEINKERNS /

 

 

 

/

 

TOTAL

FIGURE 22.—State of preservation of the described Late Cretaceous pelecypod and gastropod fauna of New Jersey. Good,
species described from well-preserved specimens. Mixed, species description based on both well-preserved and poorly
preserved specimens. Steinkerns, species descriptions based entirely upon internal molds.

BIOSTRATIGRAPHIC ANALYSIS 3].

their ranges in New Jersey with their stratigraphic
ranges elsewhere in the Coastal Plain. History plays
a part in this story. Most of the species in question
were described in the mid-1800’s by T. A. Conrad
and W. M. Gabb from the Campanian and
Maestrichtian of the Ripley, Owl Creek, and Prairie
Bluff Formations of Alabama and Mississippi. The
early paleontologists in New Jersey naturally looked
to these descriptions for comparison with their ma-
terial. Knowledge of the stratigraphy was scant, and
they can be forgiven their misidentifications, but
later workers with much more information available
have done little to rectify the situation, treating these
early identifications as inviolate.

These circumstances are sufficient to explain why
correlation based upon megainvertebrates is impre-
cise for the Cretaceous formations of the northern
Atlantic Coastal Plain, but to these impediments to
the utilization of the available biostratigraphic in-
formation, we must add the common lack of precise
geographic and stratigraphic information as to the
source of the collections. For example, Weller and
others believed that the Mount Laurel Sand and
Navesink Formation could not be distinguished on
either faunal or lithic grounds. This opinion has led
to lumping of the faunas of the two formations and
thus the unnecessary lengthening of the stated
ranges of many of the species (fig. 21). Minard and
' Owens (1962) have amply demonstrated that the
two units can be lithically differentiated and mapped,
and, as discussed herein, the faunas differ as well.

The biostratigraphic problems outlined in the pre-
ceding discussion will obviously not be solved until
there is a thorough and critical revision of the avail-
able information that involves extensive collecting of
fossils from carefully measured and precisely located
stratigraphic sections. Such investigations are in
progress by the authors and others.

REVISED CORRE LATIONS

Figure 23 is an attempt at a more refined correla-
tion of the Upper Cretaceous formations of the
northern Atlantic Coastal Plain. It is based upon
reinterpretation of existing data coupled with pre-
liminary results of investigations now in progress.
As is obvious, much reliance is placed upon the use
of ammonites as a biostratigraphic tool. Because of
the general rarity of distinctive ammonites in the
faunal assemblages of this region, other types of
mollusks have previously been used (for example,
Exogym). However, from new finds, the literature,
and information from older collections in such in-
stitutions as the Yale Peabody Museum, it was found

 

that more than 30 species of ammonites occur in
the area. The inoceramids, another useful but neg-
lected tool, are now under study, and it is hoped
that they will eventually yield additional aid in zon-
ing the stratigraphic sequence. At present, this in-
formation permits more detailed correlation than did
the three broad zones based upon Exogym. In ad-
dition, some correlations can be made between the
Coastal Plain and the western interior.

The correlation chart includes only generalized
stratigraphic columns for areas outside the northern
Atlantic Coastal Plain. The numbers included with
the formation names indicate the occurrence of cer-
tain species in that unit, the names of which are
given at the left-hand margin along with the range
of the species as represented by the vertical lines as-
sociated with the species.

Correlation of the Merchantville, Englishtown,
and Marshalltown Formations and the Mount Laurel
Sand is dealt with separately and in detail in other
parts of this paper, but some departures from the
correlation chart by Stephenson and others (1942)
need clarification.

Considering first of all the stages (fig. 24), it has
been common practice to equate the Monmouth
Group (the Mount Laurel Sand and younger
Cretaceous formations) with the Maestrichtian
Stage, and the Matawan Group (Merchantville
through the Wenonah Formations) with the
Campanian. The Mount Laurel Sand and equivalent
units of the Exogym cancellata zone in the gulf coast
have yielded ammonites (Anaklinocems, Didymo-
cems, and baculites) of the Baculites compressus
zone fauna, which strongly suggest a mid-late
Campanian age. Recent finds of scaphitid ammonites
in the Monmouth Formation of the western shore
of Maryland are, according to W. A. Cobban
(written commun., January 1965), similar to those
in the Baculz'tes clinolobatus zone of the uppermost
part of the Pierre Shale in the western interior, to
which he assigns an early Maestrichtian age. On the
Coastal Plain and the western interior, the wide-
spread discoidal ammonite Sphenodiscus first ap-
pears in beds at about the same stratigraphic level
as the Maryland ammonite. In terms of the New
Jersey sequence, this would place the Campanian-
Maestrichtian boundary in the upper part of the
Navesink Formation. The base of the Campanian lies
somewhat below but close to the base of the Mer-
chantville Formation where Scaphites hippocrepis
(DeKay) occurs.

The Upper Cretaceous formations of the northern
Atlantic Coastal Plain range in age from Ceno-

STRATIGRAPHY 0F OUTCROPPING POST-MAGOTHY UPPER CRETACEOUS FORMATIONS

32

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been applied to the Upper Cretaceous sequence in New

Jersey.

34 STRATIGRAPHY OF OUTCROPPING POST-MAGOTHY UPPER CRETACEOUS FORMATIONS

manian to Maestrichtian. The Raritan Formation
is the oldest of these. According to Stephenson
(1954), the Woodbridge clay of Kummel and Knapp
(1904) of the Raritan Formation contains a marine
fauna of Cenomanian age and most probably would
equate with the mid-Cenomanian-age faunas. The
Amboy stoneware clay of Kiimmel and Knapp
(1904), formerly considered as the uppermost unit
of the Raritan Formation, contains pollen of San-
tonian age (J. A. Wolfe, oral commun., 1968; Doyle,
1969, table 2), and is now considered the basal unit
of the Magothy Formation. On the basis of field
relationships, the Raritan appears restricted to the
Raritan Bay area of New Jersey. The white clays
exposed at the base of the Chesapeake and Delaware
Canal section belong to the Potomac Group lithologi-
cally, but may, at least in part, be of Cenomanian
age.

The next highest unit, the Magothy Formation, is
of Santonian to early Campanian age. Marine faunas
have been found only in the upper part of the forma-
tion, and these are restricted to the northernmost
outcrops in the vicinity of Cliffwood, N.J. As in-
dicated in figure 23, Baculites asper Morton ranges
from the late Santonian into the early Campanian.
Another significant species, Ostrea cretacea Morton,
has been reported from the Magothy of the Cliffwood
area by Richards and others (1958, p. 1040). This
species is a common form in the Tombigbee Sand
Member of the Eutaw Formation of the gulf coast in
units considered of late Santonian to early Cam—
panian age. On the basis of pollen and spore analysis,
J. A. Wolfe (oral commun., 1968) has assigned the
Amboy stoneware and Morgan beds to the late
Santonian, but he states that the Cliffwood flora con-
tains elements previously known only from the
Campanian. Thus, there appears to be a significant
time gap separating the Raritan and Magothy For-
mations. There are no dateable marine Turonian or
Coniacian rocks cropping out in the northern Atlan-
tic Coastal Plain or, for that matter, to the south,
until the Alabama outcrops.

The age of the Merchantville Formation is dis-
cussed later, but it is a readily correlative early
Campanian unit.

J. B. Reeside Jr. (in Richards and others, 1962,
p. 126), reported that an ammonite closely akin to
Scaphites leei Reeside occurs in the Woodbury Clay.
The specimen more likely belongs to S. hippocrepis
III of Cobban, a species that is a component of the
early Campanian faunas of the western interior and
the Coastal Plain.

The Englishtown Formation has a small fauna in

 

Delaware and virtually no fauna in New Jersey, so
that at present little can be done in terms of precise
correlation.

The Marshalltown Formation fauna is discussed in
detail later. Its fauna is of late early or early late
Campanian age.

The Wenonah Formation cannot be distinguished
with ease at present on a faunal basis. The ammonite
Placenticeras does occur in the formation, but its
lineage on the Coastal Plain is too poorly understood
to aid in correlation at present. Another ammonite,
Memu‘tes? aff. M. complexus (Hall and Meek), is
reported from the formation by Reeside (in Richards
and others, 1962, p. 122). This species occurs in the
early late Campanian Gregory Member of the Pierre
Shale in the western interior; however, Reeside ex-
pressed the opinion that the New Jersey specimen
probably represented a distinct but related species.
The only other significant form reported from the
Wenonah Formation in New Jersey is Flemingites
subspatulata (Forbes) (see Richards and others,
1958, p. 106). Sohl (1964a, fig. 12) has indicated
that this species ranges through that part of the
Exogyra costata zone above the zone of E. cancellata.
Later studies in the Cretaceous rocks of the Chat-
tahoochee River region of Georgia and Alabama
have shown that F. subspatulata is part of an evolv-
ing lineage beginning with smaller and thinner early
forms appearing in the Cusseta Sand Member of the
Ripley Formation just below the first occurrence of
E. cancellata. The normal large thick-shelled form
ranges through the E. costata zone of the Ripley
Formation and gives rise, in the basal part of the
Providence Sand, to a large but more slender, less
curved, and sharper beaked form. The specimens
figured by Weller (1907) and by Richards and others
(1958) are internal molds, but in size, shape, and
the reflection of resilifer and muscle scar they are
certainly suggestive of the early form of Flemingites
subspatulata that occurs in the upper part of the
Cusseta Sand Member. Thus, the Wenonah Forma-
tion appears to correlate with the uppermost part
of the Exogym ponderosa zone and perhaps the low-
est part of the E. cancellata zone.

As discussed more fully later, the assemblage of
ammonites and other mollusks in the Mount Laurel
Sand is of mid-late Campanian age and can be cor-
related readily with units throughout the Atlantic
and Gulf Coastal Plains.

The age limits of the Navesink Formation are at
present a problem. The presence of Bacuh’tes clavi-
formz's Stephenson in the lower part of the forma-
tion and the one specimen of Sphenodz'scus (Minard

BIOSTRATIGRAPHIC ANALYSIS 35

and others, 1969, p. H13), recovered supposedly
from the upper part of the formation, suggests a
close equivalency with the Nacatoch Sand of Texas.
A recent collection of ammonites made by H. Men—
drych of North Arlington, N.J., from the lower
part of the Navesink Formation at the classic At-
lantic Highlands section, has, according to W. A.
Cobban (written commun., 1968) , yielded specimens
that are closely related to western interior and gulf
coast species. Species of Exitelocems, Nostoceras,
and Scaphites (Hoploscaphites) are represented. In
total, they are closely related to species from late
Campanian Baculites cuneatus and B. reesidei zones
of the Pierre Shale. In summation, the Navesink
Formation appears to range in age from late
Campanian to earliest Maestrichtian.

The Tinton and Red Bank Sands of New Jersey
contain a varied assemblage, including a number of
stratigraphically restricted but widespread species
such as Baculites columna Morton which occur in
equivalent formations as far away as Texas and
the western interior. Other species such as Trigom'a,
cerulz’a Whitfield (=T. haynesensis Stephenson)
found in the Providence Sand of Georgia and in the
highest beds of the Peedee Formation are restricted
in distribution to the East Gulf and Atlantic Coastal
Plains. These formations are definitely of Maestrich-
tian age but how much of this stage is represented
is debatable. At present I (Sohl) feel that on the
outcrop, the Tinton and Red Bank represent no more
than the lower half of the Maestrichtian and that
the overlying formations rest unconformably on the
Cretaceous sequence throughout the northern At-
lantic Coastal Plain (see also Minard and others,
1969).

SUMMARY OF CRETACEOUS MEGAFAUNA

In the northern Atlantic Coastal Plain, precise
correlation based on megafossils has been hindered
by:

1. Dependence on comparison of poorly preserved
New Jersey fossils with well-preserved fossils
of other areas.

2. Misidentification of well-preserved material.

3. Taxonomic provinciality, which has erroneously
lent the New Jersey fauna an endemic aspect.

4. Poor documentation as to source of collections.

5 Lumping together of assemblages from more
than one formation.

6. Misidentification of formations.

Revised correlation based primarily on ammonite
occurrence shows that:

1. The Upper Cretaceous formations of northern

 

New Jersey range in age from the Cenomanian
Raritan Formation at its base to the early
Maestrichtian Tinton Sand at its top.

2. On the Chesapeake and Delaware Canal, the
lowermost fossiliferous Upper Cretaceous unit,
the Magothy, is of Santonian to early Cam-
panian age, and the uppermost unit, the Mount
Laurel Sand, is early late Campanian.

3. Nowhere in the region are there dateable marine
beds of Turonian or Coniacian age.

CRETACEOUS MEGAFAUNA FOSSILS FROM THE
CHESAPEAKE AND DELAWARE CANAL

The fossils from the Chesapeake and Delaware
Canal section, like those from New Jersey, are com-
monly poorly preserved. Calcitic oyster shells are,
however, well preserved in some places. Fortunately,
sideritic concretions and phosphatic nodules are
present in most rock units, and these afford external
molds of sufficient quality to allow precise deter-
mination.

In tables 5, 7, and 8, those taxa marked by an
asterisk are known only as internal molds. Except
where distinctive characters are shown, no attempt
has been made to perpetuate the illusion of certain
identification by assigning such molds to a species.
Some molds can be assigned to a group composed of
similar species. For example, some molds of the
pelecypod Nucula, can be placed in the percmssa
lineage and others in the amica lineage, but they
cannot be assigned with certainty to an individual
species. Many gastropods from the canal that are
listed only as indeterminable internal molds could
perhaps be assigned to species described from New
Jersey, but as this would be only a comparison of
similar internal molds of uncertain affinities, it
seems more a semantic exercise than a taxonomic
determination.

MERCHANTVILLE FORMATION

FAUNAL CHARACTERISTICS

The Merchantville Formation contains the largest
megainvertebrate fauna of any formation exposed
along the canal. One hundred and three genera and
subgenera of mollusks (see table 5) are represented
(56 pelecypods, 40 gastropods, 5 ammonites, 2
scaphopods). Seventy-six species are definitely as-
signed to or compared with previously described
species. The remainder are represented by material
sufl‘icient only for generic placement.

Fossils occur mainly in concretions that are con-
centrated in zones in the lower and more coarsely
clastic part of the Merchantville. Fossils are rarer

36 STRATIGRAPHY OF OUTCROPPING POST-M AGOTHY UPPER CRETACEOUS FORMATIONS

TABLE 5.—Megairwertebrate distribution in the Merchant'ville Formation in the Chesapeake and Delaware Canal area and
New Jersey

[A, Occurrence of the species outside the Merchantville Formation of the canal'area: x, rare occurrence (1—5 specimens); 0, common occurrence (5—15
specimens); I. abundant occurrenoe (15+ specimens); *, known only as internal molds]

 

Chesapeake and Delaware New Jersey

 

 

 

 

 

 

 

 
 
  
 
  
  
  
  

    
 

 

    

 

 

 

 

 

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Trigonia sp
*Trigonia sp _
Nemodon cf. N. neusensts (Stephenson) _
SD
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Glueymeris sp
*Pinna laqueata Conrad
*Pinna sp
Lithophaga sp
Pteria cf. petrosa Conrad ..................
Gervitliopsis ensifarmis (Conrad)
lnoceramus sp
Syncyelonema simplicius (Conrad)
conradi (Whitfield) ...................
Camptoneetes bellisculptus (Conrad) ..
Neithea quinqueeostata (Sowerby) of Weller ..
Plicatula n. sp
Lima 51)
Exogyra ponderosa Roemer
Ostrea mesenteriea Morton
falcata Morton
*Ostrea sp
Anemia cf. A. argentaria Morton .
cf. A. radiata Weller .
Paranomia scabra Morton
Astarte? SD
Crassatella cf. C. roodsensis Stephenson ...................................... ..
cf. C. car " «in Conrad
cf. C. newkirkensis Stephenson .............................................. ..
Crassatella sp
Vetericardia sp

 

 

 

 

 

 

       
     
   
 

   

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EN bi >>§ bi >>§

 

 

 

 

 

 

 

 

ixx: xxxg x; xxxxé x; xx;

 

 

Lucina sp

Aenona? sp r.

Linearia metast'riata Conrad ............................................................
contraeta Whitfield .-
maynoliense Stephenson .......................................................... ..

Tellina sp

*Tellina sp ‘—

Unieardium cf. U. umbonatum (Whitfield) ................................ ..

Solyma sp

Cardium (Pm-l- ‘dium) or", ' Conrad

 

(Criocardium) sp
(Granocardimn) tenuistriatum (Whitfield) ..
dumosum Conrad

 

 

 

 

n. sp
(Traehyeardium) eufaulensis Conrad
(Trachyeardium ?) uniformis Weller

longstreeti Weller ..

 

SDD
Isocardia sp
Cymbophora? sp ..
Etea cf. E. earolinensis Conrad ......................................................

 

 

 

SD
*Etea? 51') r.
Veniella conradi Weller non Conrad .............................................. ,V
Aphrodina sp
Cyprimeria sp
Legumen planulatum (Conrad) .7

concentricum Stephenson ......

 

 

 

 

 

n. sp
Anatymya sp .l
Pholadomya oeeidentalis (Morton) ................................................ .l
Pholas cithara Morton
Photos? sp

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

     

 

 

BIOSTRATIGRAPHIC ANALYSIS

37

TABLE 5.—Megairwertebrate distribution in the Merchantville Formation in the Chesapeake and Delaware Canal area and
New Jersey—Continued

[A, Occurrence of the species outside the Merchantville Formation of the canal area; ><, rare occurrence (1—5 specimens); 0, common occurrence (5»15
specimens); I, abundant occurrence (15+ specimens) ; *. known only as internal molds]

 

Chesapeake and Delaware

New J ersey

 

 

 

 

 

 

 

 

 

 

 

Canal
E In situ
5 Middle and . . .
a
E Lower Upper Posrtlon uncertaln
a
o
.3:
«“2“ .=
.h g
‘3 a
a F 2 8 g = = z
3 ‘ a = 3 ‘5‘ a 5 7';
'8 § .4 '2 g >. "E B 8 § ‘1 S
.5 a a 4;, .n 5 u g .5 Te § 3
-,: '5 t: > m <0 =9 r m w o :7: iv an u: no a: o c: H a: .— o '5 'U ;: '5 G
m x. g 06 H co u: u: m u: v co oo o a: :0 H o co as s! '5 an :- O be h = ,
=“°§5555355335355552‘;a“~°:mwa
H E E [3] H H H H H H H H H H H H H H H H H (I) S S 3 m E 3 2
Pelecypoda—Continued. .
Caesticorbula er" ,' (Gabb) A .. x x X x x x x X A A A
Caryocorbula sp
Parmicorbula sp _ ..
Corbula cf. C. swedesboroensw Weller ............................................ A, A
ED
Panopea deeisa Conrad A
Kummelia sp
Cymella belle. Conrad A

cf. C. irone'nsis Stephenson
Liopistha alternata Weller? ......
of. L. pretexta (Conrad) ..
Gastropoda:
Urceolabrum mantachiensis Sohl? ...............................
Calliomphalus (Calliomphalus) paucispirilua Sohl .
(Planolateralis) n. sp .....
Lazispira lumbricalis Gabb
Turritella merchantvillensis Weller ..
cf. T. merchantvillensis Weller
n. sp
Haustator quadrilira (Johnson) ......................................................
Cerithium cf. C. ' ‘ Wade
Cerithiella n. sp

 

 

 

Opalia (Opalia?) n. sp ....................................................................

Acrilla? n. sp

 

Graciliala johnsom'. ( Stephenson) .................................................. ..

5D ..
Arrhoyes (Latiala) cf. A. (L.) lobata (Wade) ........................ ..

 

Latiala) sp
’A'nchura'! sp
Pterocerella aft. P. poinsettiformis Stephenson
Tundora cf. T. tuberculata Stephenson
Xenophon sp
Trichotropis m, (Gabb)
cf. Vmikoropsis ambigua (Meek and Hayden) ..
GyrodfesGafi. CZ; major Wa e ......................................

c . . a

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Gabb

SDI) ..
Empira aft. E. rectilabrum (Conrad) ........................................

Sp ..
Pseudamaura lepta Sohl .................................................................. .-
‘Ecpho'ra? sp ..
Sargana cf. S. stantom’ (Weller) .................................................. ..
Canthamlus? sp
A ' fame? S .-
Dn'lluta afl'. D. dictum (Conrad) .................................................. ..
Drilluta? sp
Bellifusus n. sp
Hercorh'mchus n sp.
Pm-ifusue ' ‘ ‘ Sohl
Pyropsis sp
N , n. sp
Liapeplum cf. L. tho-r ' Sf " m
Lonaoconcha sp --
Paladmete cf. P. cancellaria Conrad ............................................ ~-
C n.I sp.

 

SD
A ' ‘ n. sp
Acteon sp
N ‘ ‘

 

 

3D
Ringicula n. sp

Anisommm cf. A. borealis (Meek and Hayden) ........................

Cephalopoda:

Bamlites cf. 3. minerensis Landes ................................................

 

SD
Seaphites hippocrepia (Dekay)
Placenticeraa placenta (Dekay) ..
Snbmartoniceras 1“ ' Young

Membites (Delawarella) delawarensis (Morton) ....................

Ammonite undet
Scapgopoda:

 

A

wbar ‘ Conrad
Cadul'us obnatus Conrad ....................................................................
Chaetopoda:
Serp’ula sp
Hamulus major Gabb
Longitubus 3p
Indeterminate echinoids

 

 

 

 

 

 

 

 

 

 

 

 

 

 

   

   

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

XX

 

 

 

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xxxx

 

 

 

 

 

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ix xxxxxx;

 

   

 

 

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38 STRATIGRAPHY OF OUTCROPPING POST-MAGOTHY UPPER CRETACEOUS FORMATIONS

TABLE 5.—Megain’uertebrate distribution in the Merchantville Formation in the Chesapeake and Delaware Canal area and

New Jersey —Continued
Merchantuille Formation

17715. Material in place at water’s edge on north side of Chesapeake and
Delaware Canal at station 56+600. Delaware. Collected by C. W.
Carter. 1935 37.

North side Chesapeake and Delaware Canal at station 53+500. Dela-
ware. Collected by C. W. Carter, 1935-37.

North side of Chesapeake and Delaware Canal at station 53+500,
about 1,300 ft west of Summit Bridge, Del. Fossils taken from
formation at water’s edge and up to 6 ft above water in the bank.
Collected by C. W. Carter, 1935—37.

South side of Chesapeake and Delaware Canal at station 53+200,
Delaware. Material taken from concretions collected in place at
water’s edge. Collected by C. W. Carter, 1935~37.

Clay lens in top of formation, south side of Chesapeake and Delaware
Canal. approx at station 65+000, Delaware. Collected by C. W.
Carter. 1935—37.

South side of Chesapeake and Delaware Canal at station 62+550.
Delaware. Material from a dry lens in top of formation. Collected
by C. W. Carter, 1935—37.

From the fossiliferous clay lens at top of Crosswicks Clay (equiva-
lent to Merchantville Formation and Woodbury Clay), north side
of Chesapeake and Delaware Canal, approx at station 61+000.
Delaware. Collected by C. W. Carter, 1935—37.

Upper Cretaceous. In sandy top of formation at water’s edge on west
side of Summit Bridge, Chesapeake and Delaware Canal. Del.
Collected by C. W. Carter, 1935—37.

Friable material in a sandy lens about 3 ft thick and 300 ft long in
top of Merchantville at the Penn Central Railroad’s Chesapeake
and Delaware Canal bridge (formerly Pennsylvania, Baltimore,

17736.

17756.

17757.

17693.

17754.

17740.

17689.

17687.

and Washington bridge) on south side of the canal, Delaware.
Collected by C W. Carter, 1935—37.

At station 63+000 (south side) about 1 mile east of Maryland-Dela-
ware line, Chesapeake and Delaware Canal, Del. Collected by C.
Carter 1935— 37.

South side of Chesapeake and Delaware Canal (in place) at station
62+500, Delaware. approx 1 mile east of Maryland-Delaware line.
Collected by C. W. Carte., 1935— 37.

South side Chesapeake and Delaware Canal at station 62+000, Dela-
ware. Collected by C. W. Carter, 1935 —3.

Station 59+850 (north side), 8,000 ft east of Maryland-Delaware
line, Chesapeake and Delaware Canal. Del. Collected by C. W.
Carter. 1935-37.

Material in place at station 59+850, north side of Chesapeake and
Delaware Canal. 1%, miles west of Summit Bridge. Del. Collected by
C. W. Carter, 1935—37.

North side Chesapeake and Delaware Canal at station 57+000, Dela-
ware. Collected by C. W. Carter, 1935—37.

South side of Chesapeake and Delaware Canal (in place) at station
62+, Delaware. Approx 1 mile east of Maryland-Delaware line.
Collected by C. W. Carter, 1935—37.

South side Chesapeake and Delaware Canal at station 55+500. Dela-
ware. Material contained in concretions in place at water’s edge.
Collected by C. W. Carter, 1935—37.

Near base of excavation for abutments of new railroad (Penn Cen-
tral) bridge over Chesapeake and Delaware Canal just west and
approx 1,600 ft south of old bridge, New Castle County. Del. Col-
lected by N. F. Sohl, R. W. Imlay. and Jack Wolfe. 1963.

17703.

17695.

17738.
17719.

17700.

17739.
17691.

17749.

28824.

Collections from spoil banks

17692. Old dump (1925 dredging) on road from Summit Bridge to Kirk-
wood, Del., 2% miles east of Summit Bridge. Collected by C. W.
Carter, 1935—37.

17696. Old disposal area on north side of Chesapeake and Delaware Canal,

at station 53+500. Delaware. Collected by C. W. Carter, 1935—37.

17698. Old dump (1925 dredging) on road from Summit Bridge to Kirk-
wood. Del., 1/é mile east of Summit Bridge. Collected by C. W
Carter, 1935—37.

Disposal area north side Chesapeake and Delaware Canal at the Penn
Central Railroad’s Chesapeake and Delaware Canal bridge, Del~

17688.

in the upper part of the formation in the finer
grained and more micaceous beds. For the most part,
fossils in these micaceous clayey silts occur as poorly
preserved impressions, but Carter, during his col-
lecting from the canal section, made several collec-
tions from “clay lenses in the top of the formation”
(see table 5, locs. 17693, 17754). No fossils from so
high a position within the Merchantville were col-
lected during this survey.

Though the specimens are devoid of shell material,
when the sideritic concretions from the lower part of
the formation are split, they yield excellent external
molds associated with the internal molds. Latex
rubber impressions of the external molds show all
the characters of sculpture and form, and when
combined with the characters of the columella and
aperture that can be learned from examination of
the internal molds, identification can be precise. In
table 5, the first three columns from left to right
list the species found in common in the Merchantville
and the other fossiliferous formations of the canal
section. In the next columns to the right, the collec-
tions from the Merchantville are arranged in
stratigraphic order. The specimens in collections
listed as “position uncertain” were found in place
but are not assignable to a specific level; they most
probably belong to the lower part of the formation.

In summary, the formation bears a larger and
more diverse fauna in its lower than in its upper
beds. Throughout the formation, gastropods are in-
dividually more abundant and diverse than the

 

aware. Collected by C. W. Carter, 1935—37.

16225. Dredgings from Chesapeake and Delaware Canal, north side, about a
mile east of Summit Bridge, New Castle County, De]. Collected by

.W. Stephenson, Sept. 17, 1932

16579. Chesapeake and Delaware Canal, Deep Cut. Del. Collected by L. W.
Stephenson.

15896. Chesapeake and Delaware Canal, from dredgings thrown out of the
canal on the north side within 2, 000 ft west of Summit Bridge.
5??? Castle County, Del. Collected by L. W. Stephenson, Sept. 2.

pelecypods. In all other formations along the canal,
pelecypods are more abundant. In addition, cephalo-
pods, primarily Placenticeras and Menabites (Dela-
warella), are more abundant here than in the
overlying formations. In some places individual con-
cretions may be composed almost wholly of a single
species. The deposit-feeding aporrhaid and filter-
feeding turritellid snails are the most abundant ele-
ments of the fauna. The algal or algal-detritus feeder
Calliomphalus and possible mucous-string feeder
Laxispira are also common snails that are abundant
in some collections. No single pelecypod is abundant,
but Pinna, Legamen, Pholadomya, and Panopea are
of common occurrence. This abundance of deeper
burrowing types of clams and the general sparcity of
epifaunal pelecypods contrasts strongly with the
faunas of the other formations along the canal in
which epifaunal clams (oysters, pectens) and shal-
low burrowers such as the cardiids predominate.

COMPARISON WITH THE New JERSEY MOLLUSCAN FAUNA

The Merchantville fauna of the Chesapeake and
Delaware Canal compares closely with that of the
Merchantville and Woodbury Formations of New
Jersey. Species common to other formations are pri—
marily those that, according to Richards and others
(1962), range through most of the section. For
instance, Geroilliopsis ensiformis (Conrad) and
Pecten (Camptonectes) bellisculptus (Conrad) range
from the Merchantville through the Mount Laurel
Sand and Navesink Formation in New Jersey. Forty-

BIOSTRATIGRAPHIC ANALYSIS 39

nine species present in the Merchantville Formation
of the Chesapeake and Delaware Canal also occur
in New Jersey. These are distributed as follows:

_ ' Number of species
Mount Laurel Sand-Navesmk Formation ........................

 

 

Wenonah Formation 17
Marshalltown Formation .................................................... 16
Englishtown Formation ........................................................ 2
Woodbury Clay ....... ..26
Merchantville Formation .................................................... 30

...13

 

Magothy Formation

The similarity of the Merchantville fauna of the
canal section to that of the Woodbury in New Jersey
is not surprising. In New Jersey, the Merchantville
has yielded 118 species of mollusks, 66 of which, or
more than 50 percent, also are reported from the
Woodbury. The common occurrence of the strati-
graphically restricted species Scaphites hippocrem's
(DeKay) and Menabites (Delawarella) delawarensis
(Morton) in the Merchantville of both States, how-
ever, is strong evidence that the Chesapeake and
Delaware Canal fauna correlates with the Merchant-
ville fauna of New Jersey rather than with that of
the Woodbury. (See fig. 23.)

AGE AND CORRELATION

The Merchantville Formation is accepted here as
early Campanian in age (fig. 23), on the basis of
the occurrence of the widespread ammonite species
Scaphites hippocrem's (DeKay). This species occurs
in rocks of this age from the western interior of
the United States to Western Europe (Cobban,
1969). Scaphites hippocrepis has long been used as
a zonal index in the western interior. A recent study
by Cobban (1969) on the Scaphites leei Reeside and
Scaphz'tes hippocrepis lineages in the western inte-
rior has special bearing on the age of the Merchant-
ville Formation. Cobban (1969, p. 6) has divided
each species into three stratigraphically restricted
types. Scaphites leei forms I and II are of late San-
tonian age. S. leei form III is basal early Campanian
and is followed in sequence by Scaphites hippocrem‘s
forms I, II and III, all, however, being early Cam-
panian. Cobban maintains that all forms illustrated
from the Merchantville Formation by Reeside (in
Richards and others, 1962, pl. 71, figs. 1—7), as well
as those assigned by Reeside to S. afi. S. leei (Ree-
side, in Richards and others, 1962, pl. 71, figs.
8—11) belong to S. hippocrepis form III. All the addi-
tional material in the Merchantville collections was
submitted to him, and these specimens he also as-
signed to S. hippocrepis 111.

Other stratigraphically important Merchantville
species are listed on the correlation chart (fig. 23).
In total, these ammonites afford strong evidence for

 

correlation with the sections in other areas.
Scaphites hippocrepis III is present in the Matawan
Group of Maryland (Gardner, 1916). This occur-
rence indicates an extension of Merchantville Forma-
tion equivalents to the western shores of Chesapeake
Bay. Units equivalent to the Merchantville Forma-
tion may be represented by certain parts of the Black
Creek Formation of North Carolina, but until more
carefully collected and stratigraphically controlled
material is available from that area, no refined
correlation should be attempted. The Scaphites
hippocrepis—Menabites (Delawarella) delawarensis
fauna is represented in the medial part of the Bluff-
town Formation of Georgia and Alabama, in the
lower part of the Coffee Sand of Mississippi (Sohl,
1964b, p. 350), and in the Brownstown Marl of
Arkansas. In Texas, the Dessau Formation of Dur-
ham (1955), the Gober Tongue of the Austin Chalk,
and the Burditt Marl of Adkins (1933) contain this
fauna plus Submortonicems uddem’ Young (1963),
which occurs also in the Merchantville Formation of
the canal section (table 5, USGS 16225). The speci-
men from the canal area is unfortunately from a
Merchantville concretion from a spoil-pile collection
and therefore cannot be precisely placed at a given
level within the formation. However, along the canal,
most of the sideritic concretions were observed to
occur near the base of the formation.

In the western interior, the Eagle Sandstone, the
Telegraph Creek Formation, and equivalent units
contain Scaphites hippocrem's.

It is obvious in view of the above discussion that
the Merchantville Formation is one of the more
easily correlated units in the Upper Cretaceous
strata of the Coastal Plain and that it is virtually
coordinate in a time sense to at least the upper part
of the Scaphites hippocrepis range zone. Evidence
that the formation may include equivalents of some-
what older units is the presence in a spoil-bank col-
lection of Submortom'cems uddeml which should
occur lower in the section than Scaphites hippocrepis
III. In essence the evidence suggests that the Mer-
chantville Formation is of early Campanian age but
that it does not include beds of earliest Campanian
age. The missing interval of earliest Campanian time
is equivalent to the ranges in the western interior of
the chronologic subspecies Scaphites leez‘ III and S.
hippocrepis I and II of Cobban. This time interval
may be represented by part of the Magothy Forma-
tion, as is suggested on the correlation chart (fig. 23) .

ENGLISHTOWN FORMATION

Throughout its extent in New Jersey, the English-
town Formation is virtually unfossiliferous. Fossils

40 STRATIGRAPHY OF OUTCROPPING POST-MAGOTHY UPPER CRETACEOUS FORMATIONS

TABLE 6,—Megaimzertebrate distribution in the Englishiflwn eI;oririatiori in the Chesapeake and Delaware Canal area and
ew ersey

[A, Occurrence of the species outside the Englishtown Formation of the caml area; X. rare occurrence (1—5 specimens); 0, common occurrence (5—15
specimens); I. abundant occurrence (15+ specimens)]

 

 

 

 

 

 

 

 

  

 

 

 

 

 

 

 

 

 

 

  
    
  
 
 
  
 
 
 

 

  
 
   
   
   

 

 

 

 

 

 

 

Chesapeake and
Delaware Canal New Jersey
1 x
.5
g
2'?
0 "' .—
E E 2 5'3 : E 1’
> 5 ‘5 B H
E g 5 i? E E" 3 g '5 .3
on —= as
J: 'E E w 00 a: N ‘5 "l g 3 .u 5 2
a? E g e s s e s: g 8 2° 5 5 a
S E E 3 3 3 3’: E 2 3 {a S 3 E
Pelecypoda:
Nucula sp. ............ X X
Nuculana afi'. N. marlboroensis (Weller) ................................. >< A
Sp ----------------- X X
Trigonia (Pterotrigonia) cf. T. (P.) bartrami Stephenson ............ X
(Scabrotrigonia) sp X
Nemodori sp X .
Glycymeris aff. G. mortoni (Gabb) ............................................... Q 0 A A
Volsella julia (Lea) ......... X A A
Pirma sp ......... ........ X
Pteria sp .............. X X ..
Inoceramus? sp X __ ..
Camptonectes bellisculptus (Conrad) .................................................. A A X X A A A A A
Camptonectes? burlingtonensis (Gabb) ................................................ X A A A
Syncyclonema conradi (Whitfield) A X X X ..
Lima reticulata Forbes ............... A X A A A
Exogyra sp .................................................................................................. X
Crassostrea tecticosta (Gabb) ......... A X X A
Lopha falcata Morton? ............................ A A A X X X X A A
Anomia argentaria Morton .................................................................... A A A X X A A A
Crassatella? sp X A
Scambula perplarza Conrad ................ X A
Vetericardia sp .................................................................................... .
Lucina sp .............................................. . X X
AenorLa afl’. A. eufaulensis Conrad .. . X . A A A
Linearia metastriata Conrad ....................................... A A A X X X A A A . A A
Tellina sp ........................ X
Cardium (Trachycardium) longstreeti Weller? ........ A O O X C A
(Granocardium) sp ........................................ X X
Cymbophora sp ............................. X X X
Etea cf. E. carolinensis Conrad A X
Legumen ellipticum Conrad? ..... X A
Leptosolen biplicatus Conrad ............... X A A A A A
Parmicorbula cf. P. bisulcata Conrad X X X A A A
Cymella bella Conrad ................................. A X A A A A
Liopistha protexta Conrad? . .. . .. ........................................ A A X X A A A
Gastropoda:
Pachymelania n. sp .................................................................................. X
Haustator quadrilira (Johnson) ............. A A X X A A A
Turritella cf. T. lorillardensis Weller ............................................ X C A
Graciliala sp .................................. X X X
Arrhoges (Latiala) sp ...... O .
Tuba afl‘. T. bella Conrad .. A X
Xenophora sp .......................................... X
Euspira aff. E. rectilabrum (Conrad) A A X X X
Gyrodes sp .................................................. X
Pseudomaura meekana (Whitfield)? _. A X A A
Morea cf. M. marylandica Gardner ...... X
Napulus sp ....................................................................... X
Volutomorpha sp ......... . ........ X
Caveola sp ......................... . X
Paladmete aff. P. cancellaria (Conrad) ................................................ X
Chaetopoda:
Hamulus sp ................................................................................................ X
Serpula sp _______ X
Echinodermata:
Hardouinea? sp X X
Cidaroid . X
Vertebrata:
Fish vertebrae .............. . ...... X

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

BIOSTRATIGRAPHIC ANALYSIS 41

TABLE 6.—Megainvertebrate distribution in the Marshalltown Formation in the Chesapeake and Delaware Canal area and

New Jersey—Continued
Englishtown Formation

16224. Chesapeake and Delaware Canal, north side, at post 40+500, about 1
mile east of the Penn Central Railroad‘s Chesapeake and Delaware
Canal bridge (formerly Pennsylvania, Baltimore, and Washington
bridge), New Castle County, Del. Collected by L. W. Stephenson.
Sept. 16, 1932.

29578. Reddish-brown sand at water level along north bank of Chesapeake
and Delaware Canal about one-fourth of a mile west of the St.
Georges Bridge, Del. Collected by Arthur H. Hopkins. May 1967.

have been recovered from few localities, and Rich-
ards and others (1962, p. 209—229) record only two
species (Cardium tenuistm‘atum Whitfield and Tur—
m'tella quadrilira Johnson) from all its outcrops. In
addition, Cymella bella has been found by the author
in the Allentown quadrangle of New Jersey. At most
localities along the Chesapeake and Delaware Canal,
the major organic remains are Ophiomorpha borings
that form an interlocking network on weathered sur-
faces. However, locally in the area west of the St.
Georges Bridge, the upper foot or so of the forma-
tion bears a dominantly molluscan fauna preserved
as impressions in a case-hardened and concretionary
sandstone. Several specimens have also been recov-
ered from Ophiomorpha burrow fillings. The total
fauna, listed in table 6, consists of representatives of
33 genera and subgenera of pelecypods and 15
genera of gastropods.

With the exception of the genus Pachymelam'a,
this assemblage is consistent with a shallow-water
sand—facies fauna. Pachymelam'a is a thiariid typical
of the types that are of upper estuarine low-brackish
to fresh—water tolerance. Because the Pachymelania
specimens show little wear or other evidences of long
transport, they further suggest that the fauna lived
not only in shallow water but near shore. The great
abundance of Ophiomorpha burrows is consistent
with such shallow-water conditions.

Although burrows are abundant in the other for—
mations along the canal, they appear to have been
made by some other organism than Ophiomorpha.
The longitudinal striations on the walls of many
suggest some type of crab; others may well have
been created by worms.

Many of the most common fossils in the English-
town fauna such as Cardiam (Trachycardium) and
Tawt'tella are also common elements in the faunas of
other formations along the canal. Glycymeris, how-
ever, is rare in other formations but common in sev-
eral collections from the Englishtown.

The lack of any significant fauna in the English-
town Formation of New Jersey precludes comparison
with the fauna along the canal. Similarly, the general
lack of stratigraphically restricted species in the
Englishtown fauna of the canal section does not
allow for regional correlation.

 

29579. Low-tide level beneath main Ophiomorpha level, north side of Chesa-
peake and Delaware Canal about 0.4 mile west of the St. Georges
Bridge, Del. Collected by N. F. Sohl and J. P. Owens, June 22, 1967.

29582. Low-tide level beneath Ophiomorpha bed in upper part of formation
on north side of Chesapeake and Delaware Canal about 0.6 mile
west of the St. Georges Bridge, Del. Collected by N. F. Sohl and
J. P. Owens, June 22, 1967.

NIARSHALLTO‘VN FORNIATION

FAUNAL CHARACTERISTICS

The Marshalltown Formation of the Chesapeake
and Delaware Canal section contains representatives
of 72 genera of mollusks (39 pelecypods, 30 gastro-
pods, 3 cephalopods) (table 7). Many of these are
represented only by internal molds and thus are not
subject to precise specific determination. Fossils oc-
cur in great abundance and are generally concen—
trated in certain beds rather than scattered through
the formation. The ostreids are generally abundant
and occur both as well-preserved calcitic shells and
as internal molds. In the excavation for the Penn
Central Railroad’s Chesapeake and Delaware Canal
bridge abutments, the Marshalltown is exposed in its
full thickness (see section, p. 13). Here, Exogyra
ponderosa Roemer is especially abundant, well pre-
served, and concentrated in a single bed. Pyncno-
donte mutabilis (Morton) is likewise very abundant
and well preserved and is found with Exogyra along
the canal at water level immediately west of St.
Georges Bridge where the contact with the Mount
Laurel Sand is seen. In these upper beds are local
concentrations of articulated valves of Lopha falcata
(Morton) that form rounded patches as much as 10
or 12 inches in diameter. The specimen orientation
suggests that these concentrations may be derived
from disintegration of a stalked plant to which the
oysters were attached.

Shell material may adhere to some of the internal
molds, or on some specimens the external molds may
be impressed upon the internal molds. These circum-
stances give sul’ficient information about the external
sculpture to indicate specific relationship.

The Marshalltown fauna of the canal section is
distinctive, especially in its abundance of Exogyra
ponderosa, Lopha falcata, large Trigonia, Cardium,
Cucallaea, and Cyprimem'a. These genera occur in
other rock units in the canal section, but not in the
abundance seen in the Marshalltown.

This characteristic assemblage extends at least 25
miles to the southwest where the Marshalltown
Formation is well exposed and where its fauna can be
collected on the north bank of the Sassafras River
in Maryland.

Although borings are abundant in the Marshall-
town, they are not of the Ophinomorpha type. This

42 STRATIGRAPHY 0F OUTCROPPING POST-MAGOTHY UPPER CRETACEOUS FORMATIONS

TABLE 7.——Megainvertebrate distribution in the Marshalltown Formation in the Chesapeake and Delaware Canal area and

New Jersey

[A, Occurrence of the species outside the Marshalltown Formation of the canal area; X. rare occurrence (1—5 specimens); 0, common occurrence (5—15

specimens): I, abundant occurrence (15+ specimens); ‘-", known only as internal molds]

 

Chesapeake and Delaware Canal

New Jersey

 

Merchantville

Englishbown

Mount Laurel
28822 Excavation

17727

17702

17718

17730

17735

17708

17731

17721

17699

17717

29511

29506

Disposal areas

Englishtown
Mount Laurel

 

l

Pelecypoda:
*Nucula. percrassa species group
Nuculana sp .....................
*Trigonia. thoracic. Morton
Nemodon Sp. (large) ...........................
*Cucullaea of. C. tippana Conrad of We e
Lithophaga, sp ..
*Inoceramus‘! sp
Camptonectes bellzsculptus (Conrad)
Chlamys n. sp. cf. C. eretosus DeFrance
Neithea. quinquecostata Sowerby of Weller
*Pecten sp .....
""Spandylus sp .
Lima lorillarden
*Lima cf. L. Icerri Stephenso
Crenella serica Conrad ...........
Exogyra ponderosa erraticosta a ..
ponderosa Roemer ............................................

 

 

”Sp
Pyncnodante mutabilis Morton
convexa Say .
*Gryphaea sp ......
Gryphaeostrea vomer Morton
*Gryphaeostrea‘.’ sp ..........
Lopha falcata (Morton)
Ostrea mesenterica Morton
"‘sp
Anomia argentaria Morton
cf. A. argentaria Morton
Paranomia scabra. Morton ........
Crassatella cf. C. vadosa Morton
Crassatellu? sp ..
*Crassatella sp
Veterioardia sp
Lucina cf. L. parva Stephenson
*Lucina sp .........................................
Linearia cf. L. metastriata Conrad
(large)
*Umbonicardium c .
Cardiurn (Granocardium) dumosum Conrad
*Cardium spp. ......................................
Brevzcardium parahillanum Wade .
"CI/mbophora sp ..................................
*Etea sp
Veniella conradi Morton of Weller .
Aphrodina. cf. A. tippana Conrad
*Cyprimeria emcavata (Morton)
*Cyprimeria SD. (large) ..............
*Tenea sp
Caesticorbula crassaplica (Gabb)
Ca'ryocorbula sp .....
*Panopea decisa Con
*Gastrochaena 5p
Martesia sp .......
Gastropoda:
Patella tentorium Morton
Margaritella sp ..................
Laxispira lumbricalis Gabb
*Laxispira sp ...........................
Turritella. marshalltownensis Weller?
Haustator quadrilira Johnson
trilira. Conrad .................
cf. H. lenolensis Weller ..
Turn'tella cf. T. tippana Cont
*Turritella sp .....................................
Melanatria? cf. M. cretacea Wade
Tuba sp
*Anchura? sp .....
Graciliala? sp
*Arrhoges (Latiala) sp
Capulus n. sp ................
*Gyrodes abyssinus (Morton) .
*Gyrodes petrosus (Morton) ..
Amauropsis meelcana Whitfield .
Euspira sp .............
Cypraea. cf. C. mor .
*Bussinid sp ....................
B ' p is sp
Bellifusus of. B. curvicostasus (Wade)
*Bellifusus sp ................................................
Ornopsis cf. 0. (Pornosis) digressa Wade.
Ripleyella sp ...........
Hercorhynchus sp .
Pyrifusus? sp
*Pyropsis sp
*Pyropsis? sp
Napulus cf. N.
*Longoconcha. sp
*Voiutomorpha sp

 
 
 
 
 
  
  
 
  
  
  
 
   
   
 
  
 
 
 
  
 
  
 
 
 
  
 
  
  
 
 
  
  
  
 
 
  
  
 
  
  
 
  
 
  
 
  
 
 
  
 
 
 

 

 

   

 

 

 

 

 

 

   
 
 
  
  
  
 
 
 
 
 
 
 

 

 

 

 

 

 

 

 

 

 

 

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BIOSTRATIGRAPHIC ANALYSIS

43

TABLE 7.—Megainvertebrate distribution in the Marshalltown Formation in the Chesapeake and Delaware Canal area and
New Jersey—Continued

ll. Occurrence of the species outside the Marshalltown Formation of the canal area; X, rare occurrence 1—5 specimens): 0, common occurrence (5—15

 

 

 

 

 
  

 

 

 

 

 

specimens): I. abundant occurrence (15+ specimens); *, known only as internal molds]
Chesapeake and Delaware Canal New Jersey
3‘ T
w E g u; T)
i
E t: T, > cu E x: H
> 3 h 5 E > >. 3 g 5
‘5. 3 i * .. >. E ‘- 3 ’3 "E A
n a A “*1 a s a 3 a 7. 2 ..
'5 :: a N b m N 00 o m 00 H H a: b H an O o '5 ”a z: '5. O I:
u be t: N N N c H co m o co N :7: H H o a. on i. o an 5.4 t: :1
°’ = 5 g E S E: E: t: E {I " {I 3 E: ‘3: “’ 3 “ °‘ ° = “ °’ °
2 m g N H H H H H H H 5 H H v—1 ' g Q E 2 a H E a S
Gastropoda—Continued
Paladmete cancellaria (Conrad)? X ...l
*Acteon cretacea Gabb ..... X >< A .. A A
*Avellana bullata (Morton A x X X x A A
Butla macrostromata Gabb . X
Cephalopoda:
Didymoceras? sp ....................... ><
AM?" '" "' ° 31)
Parapachydiscus sp ................................................
Porifera:
Clione sp .................................................................... G O I A

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Marshalltown Formation

28822. Excavation for abutments of new segment of Penn Central Rail-
road‘s Chesapeake and Delaware Canal bridge (formerly Pennsyl-
vania, Baltimore, and Washington bridge) just west and approx
1,600 ft south of old bridge, New Castle County, Del. Collected
by N. F. Sohl, R. W. Imlay, and Jack Wolfe, 1963.

Material in place 500 ft west of Penn Central Railroad's Chesapeake
and Delaware Canal bridge. south side of canal, Delaware. Col-
lected by C. W. Carter, 1935—37.

Five to 10 ft above base of formation, Chesapeake and Delaware
Canal, south side, 600 ft west of the Penn Central Railroad’s
Chesapeake and Delaware Canal bridge. opposite post 47, New
Castle County, Del. Collected by L. W. Stephenson, Sept. 15, 1932.

South side of Chesapeake and Delaware Canal, 100 yd west of Penn
Central Railroad’s Chesapeake and Delaware Canal bridge, Del.
Collected by C. W. Carter, 1935—37.

South side of Chesapeake and Delaware Canal, 50—1,000 ft west of
Penn Central Railroad’s Chesapeake and Delaware Canal bridge,
Del. Collected by C. W. Carter, 1935737.

South side of Chesapeake and Delaware Canal at station 46+700.
Delaware. Material taken from near top of bank. Collected by
C. W. Carter, 1935—37.

17727.

16223.

17702.
17718.

17730.

fact, coupled with the greater diversity of the fauna
and general lithic character, suggests that the
Marshalltown was deposited in somewhat deeper
water than the Englishtown Formation. The com—
mon concentration of fossils in beds suggests some
transportation of the fauna, but the articulated
nature of many of the bivalves would indicate that
transportation was not far. Some parts of the fauna,
for example the aforementioned concentrations of
bivalved specimens of Lopha falcata, may represent
in situ faunas.

Groot, Organist, and Richards (1954, p. 24) stated
that the Marshalltown Formation does crop out along
the canal but that,

In New Jersey the Marshalltown Formation contains the
index fossil Exogyra ponderosa. Numerous specimens of this
pelecypod were found in spoil banks and along the north shore
of the canal between the railroad bridge and station 3. Pre-
sumably these were dredged from below sea level. Similar
specimens of E. ponderosa were also found along the spoil
bank of the canal between Lorwood Grove and St. George’s.***

The authors then suggest that the Marshalltown
Formation may be present and recognizable in the
subsurface. Their interpretation that the Marshall-
town is absent on the outcrop is predicated on the

 

17735.
17708.
17731.
17721.

Station 46+500 on south side of Chesapeake and Delaware Canal,
Del. Collected by C. W. Carter. 1935—37.

North side Chesapeake and Delaware Canal at station 47+500, Dela-
ware. Collected by C. W. Carter, 1935—37.

South side Chesapeake and Delaware Canal at station 50, Delaware.
Collected by C. W. Carter, 1935—37.

South side Chesapeake and Delaware Canal at station 50+ 000, about
2,000 3th east of Summit Bridge, Del. Collected by C. W. Carter,
1935— .

Station 50, south side of Chesapeake and Delaware Canal. 2,400 ft
east of Summit Bridge, Del. Collected by C. W. Carter, 1935737.
Material in place in Marshalltown on south side of Chesapeake and
Delaware Canal, 100 ft east of Summit Bridge. Collected by C. W.

Carter, 1935-37.

South side Chesapeake and Delaware Canal, 0.8 mile west of Penn
Central Railroad bridge, 27 ft above water level. Collected by
N. F. Sohl and E. G Kaufiman. 1966.

Upper part of formation immediately below the Mount Laurel Sand
about 75—100 yds west of St. Georges Bridge, north bank of
Chesapeake and Delaware Canal. Collected by E. G. Kaufi‘man and
N. F. Sohl, 1966.

17699.
17717.

29511.

29506.

belief that there are no beds of Marshalltown lithol-
ogy between the units they picked as Merchantville
and those designated as Wenonah. They suggested
that although Carter had called some beds English-
town, the presence of “Halymenites major” indi-
cated that these beds actually belonged to the
Wenonah because the Englishtown of New Jersey
lacked these supposed diagnostic borings. Ophiomor-
pha (=Halymehites of Groot and others) ghost-
shrimp borings, however, have little age significance,
for they are common to beach or shallow near-shore
sand deposits of Cretaceous to Holocene age. Thus,
this is an ecologic and not a biostratigraphic corre-
lation. Once these so-called Wenonah sands are
accepted as Englishtown, one does not seek a
Marshalltown equivalent below them but above them,
and certainly it is there in the outcrop and not the
subsurface as was proposed by Groot, Organist, and
Richards (1954). Thus, at least the lower part of the
Mount Laurel—Navesink section they give for their
station 3 (Groot and others, 1954, p. 35) is actually
Marshalltown. Evidence for this is amply shown by
the specimen from this locality that they illustrate
on their plate 4, figure 2, as an example of Exogyra
cancellata Stephenson, a misidentification of a speci-

44 STRATIGRAPHY OF OUTCROPPING POST-M AGOTHY UPPER CRETACEOUS FORMATIONS

men that the figure clearly shows to be an example
of E. ponderosa. In their interpretation, therefore,
the Marshalltown Formation is included in their
Mount Laurel-Navesink.

COMPARISON WITH THE NEW JERSEY MOLLUSCAN FAUNA

Approximately 35 species present in the Marshall-
town Formation of the Chesapeake and Delaware
Canal section also occur in New Jersey. These are
distributed as follows:

Number of species

 

Mount Laurel Sand-Navesink Formation ........................ 14
Wenonah Formation ............................................................ 14
Marshalltown Formation .................................................... 16
Englishtown Formation ...................................................... 1
Woodbury Clay .......................... 13
Merchantville Formation .................................................... 15
Magothy Formation .............................................................. 6

There is no clear—cut correlation here, as the higher
values correspond closely to the formations contain-
ing the largest faunas. In addition, most of the
species are those that are long ranging in New
Jersey (table 7; fig. 21). Seventy percent of the
genera also occur in the Merchantville Formation,
but the Marshalltown fauna differs by being rich in
ostreid elements and by the lack of any abundance of
cephalopods and crustacean remains. Although 80
percent of the genera of the Marshalltown fauna are
also found in the Mount Laurel Sand and the fauna
of both formations contain an abundance of oysters,
the Marshalltown fauna is less diverse and lacks the
belemnites common to the Mount Laurel. The best
positive correlation of the Marshalltown fauna along
the canal with that of the Marshalltown of New
Jersey rests in the occurrence in both areas of abun-
dant Exogyra ponderosa. Although this is a longer
ranging species in the rest of the Coastal Plain, it is
apparently abundant only in the Marshalltown For-
mation in the northern Atlantic Coastal Plain. In
addition, Umbom'cardium is restricted to the Mar-
shalltown Formation in New Jersey, as are Turm'tella
marshalltownensis Weller and Cyprimem‘a excavata
(Morton).

The fauna of the Marshalltown Formation is dis-
tinctive in its composition, preservation, and in the
abundance of certain species from the overlying and
underlying units along the canal. Compared with
the younger Wenonah faunas of New Jersey, there
is little similarity, but a greater similarity with the
older faunas of New Jersey is evident.

AGE AND CORRELATION
As indicated in figure 23, the Marshalltown For—
mation is in the upper part of the Exogyra ponderosa
range zone. This is consistent with the fact that the

 

costations present on the early part of the shell of
many specimens suggest the form called Exogym
ponderosa erraticastata Stephenson which is most
common elsewhere in the upper part of the range
zone of E. ponderosa. The general lack of knowledge
of mollusks from this part of the section in other
parts of the Coastal Plain, the lack of distinctive
ammonites, and the fact that most of the well-pre-
served faunal elements present belong to long-
ranging species makes precise correlation difficult.
On the basis of the gross character of the representa-
tives of such genera as Cyprimeria, Aphrodina,
Crassatella, and Turm'tella, the Marshalltown fauna
is certainly no older than the faunas to be found in
the upper part of the Blufftown Formation of
Georgia and Alabama, the upper part of the Coffee
Sand of Mississippi, or the Wolfe City Sand and
Pecan Gap Chalk Members of the Taylor Marl of
Texas. The few heteromorph ammonites that have
been collected from the formation are too poorly
preserved to be of much aid other than to indicate
a general Campanian age. The available information
from the total fauna suggests a late but not latest
Campanian age.

MOUNT LAUREL SAND
FAUNAL CHARACTERISTICS

Along the Chesapeake and Delaware Canal, fos-
siliferous exposures of the Mount Laurel Sand occur
intermittently from immediately west of St. Georges
Bridge, where the contact with the subjacent
Marshalltown Formation is seen, to about 11/2 miles
east of St. Georges Bridge at Biggs Farm.

Preservation of the fauna in the Mount Laurel
Sand varies widely. The basal beds near St. Georges
Bridge yield well-preserved specimens of ostreids,
such as Pyncnodonte, Exogyra, Anomz’a, and Pam-
nomia, and of the pecten N eithea; all have shells of
calcite. The aragonitic-shelled clams and gastropods
are preserved only as phosphatized internal molds.
At Biggs Farm the calcitic-shelled forms are simi-
larly well preserved, but the rest of the fauna is a
mixture both of internal molds and aragonitic shells
converted to phosphate, a most unusual occurrence.
At both localities, it is common for the chambers of
the sponge borings in the shells to be phosphatized,
although the calcitic shell material is preserved.

Near the base of the formation immediately east
of St. Georges Bridge is a bed of Pyncnodonte shells
with almost no associated fauna except for a few
specimens of Exogyra cancellata. Higher in the se-
quence, the fauna becomes more diverse. The patchy
distribution of the phosphatic material, as pockets

BIOSTRATIGRAPHIC ANALYSIS 45

of concentration, shows that some transportation if
not reworking of the material is involved.

Richards and Shapiro (1963) have published on
the fauna from the Biggs Farm locality. The follow-
ing notes may help to clarify the nomenclatural dif-
ferences between their list and that included in
table 8.

Nuculana pittensis (Stephenson): Here included under N.
longifrons (Conrad).

Yoldia gabbana (Whitfield): This species appears to belong
in Nuculana and is based on indeterminate internal molds
from New Jersey.

Nemodon grandis sohli Richards and Shapiro: Indeterminate
internal molds.

Cucullaea neglecta Gabb: Long-ranging composite New J er-
sey species known only from internal molds. (= Cucullaea
sp. herein.)

Area rostellata Morton: Based on internal molds from an
unknown stratigraphic level in Alabama. This material is
better placed in Area n. sp.

Area obesa (Whitfield): Based on poor material from the
Merchantville Formation of New Jersey: here included
with the preceding in Area n. sp.

Glycymem‘s mortom' (Conrad): A “wastebasket” term for
internal molds of Glycymeris from all formations in New
Jersey.

Inoceramus proximus Tuomey: Type specimen lost, unfigured
and inadequately described, probably from the Eutaw For-
mation of Mississippi.

Ostrea monmouthensis Weller: A variant of O. mesentem‘ca
Morton.

Ostrea panda Morton: A good species, but I have not been
able to verify the report by Richards and Shapiro.

Ostrea biggsi Richards and Shapiro, 1963: Appears to be
only a variety of 0. mesente’m’ca.

G’ryphaea convexa (Say) : Pyncnodonte mutabilis of my list.

Trigonia mortom' Whitfield: Based on indeterminate internal
molds from the Marshalltown. Well—preserved specimens
from this locality are here placed in T. eufaulensis Gabb.

Pecten whitfieldi Weller: Not found.

Lima, obliqua Gardner: A misidentification. The Richards and
Shapiro specimen is an internal mold belonging in Ptem‘a.
Corimya tenm's Whitfield: Internal molds of doubtful generic

affinities.

Vetericardia crenali'rata (Conrad): Here termed V. aif. V.
subci'rcula Wade.

Cardium wenonah Weller: Internal molds of doubtful place-
ment here placed in Cardium sp.

Cardium whitfieldi Weller?: Same as preceding.

Tellina gabbi Gardner: Internal molds, may belong in Aenona.

Corbula crassiplz'ca Gabb: Belongs in genus Caesticorbula.

Weeksia deplzmata (Johnson) : Based on internal molds from
the Prairie Bluff Chalk of Alabama = Weeksia sp. of this
report.

Emarginula ladowae Eichman: Only Emarginula seen at this
locality; belongs to a new species.

Margarites abyssina (Gabb) and M. depressa Gardner:
Based on internal molds here considered to be Calliomphalus
sp. ,

Margaritella pumila Stephenson to Margaritella sp.

Polim'ces altispira (Gabb): Based on internal molds, prob-
ably equivalent to Amaurellina stephensom' (Wade) of this
report.

 

Laxispim lumbricalis Richards and Shapiro [non Gabb]: Be-
longs in L. monilife'ra Sohl (1964b, p. 361).

Turritella encrinoides Morton: Based on internal molds here
treated as Turritella sp.

Ans/mm rostrum (Gabb) : Indeterminable molds probably in
wrong order.

Anchum pennata (Morton): Molds assignable to Awhoges
(Latiala) sp. indet.

Cypraea grooti Richards and Shapiro, new species: An inter-
nal mold.

Napulus whitfieldi (Weller): Probably equals N. reesidez‘
Sohl of this report.

Pyropsis richardsom' (Tuomey)?: Based on unfigured, lost,
internal molds from an unknown locality and stratigraphic
level in Mississippi. Equal to Pyropsis sp. of this report.

Bellifusus medians (Whitfield) ?: Based on indeterminate in-
ternal molds.

Turm‘cula sp.: A Holocene and later Tertiary genus.

Cinulia naticoides (Gabb): Indeterminate internal molds.

Cylichna ’recta (Gabb): Species based on indeterminable in-
ternal molds from the Paleocene Hornerstown Formation.

Scaphites hippocrepz's (DeKay) : Misidentified; belongs in
Hoploscaphites Sp.

Menabites delawarensis (Morton): Misidentified; for if it
had been identified correctly, like the preceding, its occur-
rence in the Mount Laurel Sand would be the only place
between Mexico and New Jersey where this fossil occurs
at this stratigraphic level.

COMPARISON WITH THE NEW JERSEY MOLLUSCAN FAUNAS
Of the 99 species (table 8) here listed from the
Mount Laurel Sand of the Chesapeake and Delaware
Canal area, 36 occur in New Jersey. They are dis-
tributed as follows:

Number of species
Mount Laurel Sand-Navesink Formation ........................ 27

 
  

 

Wenonah Formation .................................................. 13
Marshalltown Formation .......................................... 12
Englishtown Formation ........................................................ 0
Woodbury Clay 11
Merchantville Formation .................................................... 15
Magothy Formation 2

 

Comparison with the Mount Laurel-Navesink
strata of New Jersey is obvious, but precise correla-
tion is difficult because of the lack of differentiation
of the faunas of the Mount Laurel Sand and the
N avesink Formation in the literature. Weller (1907)
and Richards and others (1958, 1962) have consid-
ered the formations inseparable and therefore have
listed their faunas together. The fauna of the Mount
Laurel Sand is, however, distinct from that of the
N avesink. The common association of Exogym com-
cellata Stephenson, Anomia. tellinoides Morton, and
Belemnitella americana (Morton) characterizes the
Mount Laurel fauna from New Jersey to Maryland.
These species do not occur together in the Navesink
Formation, which, in turn, characteristically bears a
fauna with the brachiopod Chorystothyris and other
restricted species. The consistent composition of the

46

STRATIGRAPHY 0F OUTCROPPING POST-MAGOTHY UPPER CRETACEOUS FORMATIONS

TABLE 8.—Megainvertebrate distribution in the Mount Laurel Sand in the Chesapeake and Delaware Canal area and New Jersey

[A, Occurrence outside the Mount Laurel Sand of the canal area; X, rare occurrence (1—5 specimens); 0, common occurrence (5—15 specimens) ' I abun-
dant occurrence (15+ specimens) ; ‘1‘, known only as internal molds] ' .

 

Chesapeake and Delaware Canal

New Jersey

 

Merchantville

Marshalltown

Biggs - lower 26634, 27749

Englishtown
Richards and Shapiro
St. Georges 29585
Biggs - lower 29507
Biggs - upper 26635
Biggs - upper 29510
Biggs - float 29508

Biggs - float 29509

Magothy

Merchantville

Woodbury

Englishtown

Marshalltown

Wenonah

Mount Laurel

 

Pelecypoda:
Nuculana longifrons (Conrad) ..................................................

Perissonata stephensoni (Richards) .
""Perissonata cf. P. protexta Gabb?
Trigonia eufaulensis Gabb ...............
*Trigonia sp ............................
Nemodon eufaulensis Gabb

 
 
  
 
   
  
  
 
 
 
 
  
 
 
 
 
 
 
 
  
 
 
  
 
  
 
 
 
  
 
   
   
 
   

 

SP
Arca cf. A. macnairyensis Wade
n. sp ..........................................
Breviarca richardsi Harbison? .
Barbatia sp ................................
Cucullaea sp
Glycymeris sp .....................
Postiligata crenata Wade
wordeni Gardner
Lithophaga sp ...........
*Gervilliopsis sp
Inoceramus sp ..................................
Neithea quinquecostata Sowerby ..........
Radiopecten mississippiensis (Conrad)
Pecten (Pecten?) venustus Morton ......
Syncyclonema simplicius Conrad
Plicatula mullicanensis Weller ........
Lima reticulata Lyell and Forbes
sp .............................................
Exogyra cancellata Stephenson ..
Pyncnodonte inutabilis Morton
Gryphacostrea vomer Morton
Lopha falcata Morton ..............
mesenterica Morton
Ostrea plumosa Morton

SP
Anomia tellinoides Morton .
argentaria Morton .............................................
Paranomia scabra Morton ......................
Vetericardia afl’. V. subeircula Wade
Lucina parva Stephenson ...................

 

sp ..........................................
Tellina cf. T. georgiana Gabb .
s ..........................................
Linearia metastriata Conrad
n. sp. (large) .................
Unicardium sp ........................................................
Cardinm (Trachyeardium) eufaulensis Conrad ..
(Granoeardium) dumosum Conrad ..........

afl". C. (G.) kummeli Weller .........
Cardium afl". C. donohuensis Stephenson
*Cardium spp ..................................................
Brevicardium parahillanum (Wade)

Cymbophora subtilis Stephenson

*Cymbophora spp ............
Etea sp .....................................
Veniella conradi Morton ....................................
Aphrodina? eufaulensis (Conrad) of Wade .

 

 
   
  
    

Cyprimeria sp

*Legumen sp
Clavagella armata Morton .......................
Caesticorbula crassiplica (Gabb) ......................

*Kumrnelia? sp .. ..
Liopistha protexia, (Conrad) ......................................................

 

 

 

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BIOSTRATIGRAPHIC ANALYSIS 47

TABLE 8.——Megatnvertebrate distribution in the Mount Laurel Sand in the Chesapeake and Delaware Canal area
and New J ersey—Continued

EA, Occurrence outside the Mount Laurel Sand of the canal area; X, rare occurrence (1,5 specimens); 0, common occurrence (5—15 specimens): I. abun-
dant occurrence (15+ specimens); *, known only as mternal molds]

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  
 
     
 

 

 

Chesapeake and Delaware Canal New Jersey
‘3:
E:
E “‘1 m c,
94 V‘ I” 93' H
a! m m S w “3 g g
a = s g N s a E 2 a a a c g ‘2
éégzfizfissé‘é Ehgagfi
Eiéahwlmgfiéfiié‘:
o m 3:“ m n O u :1 m
as as"..§§§§.§§:sssssg
E 2 F11 or. :73 m m m m m m S S 3 m S B s
Pelecypoda—Continued
Cuspidar'la cf. C. grandis Stephenson ...................................... X A . A A
sp X X .... .
Gastropoda:
*Weeksta sp . A . . X _ .
Emarginula n. sp . . X .
Calliomphalus (Calliomphalus) americanus Wade? ............ . A - X X . . X
cf. nudus Sohl . A . . X X .
*Calliomphalus (Calliomphalus) sp' .......................................... - A - - I 0 .
Calliomphalus (P‘lanolateralls) sp ............................................ - A - - X - X
*Margarz'tella sp . A . X . . X 0 .
Architectonica cf. A. voragiforrm's Stephenson ...................... . A - X . X .
Pseudomalaxis sp . A . X . .
Mathilda n. sp .. X X .
Tuba bella Conrad X .
‘ sp .... ..._ .... .. X X X . ....
Belliscala cf. B. creideri Stephenson ........................................ A - X . .. .
Nudivagus sp . . . X . .
Laxlspira monilifera Sohl . X X .
Haustator trilira Conrad A . A X C O .. A
Turritella vertebroides Morton? ................................................ A X . A
*Turritella sp O X X .
Turritella macnairyensis Wade ................................................ X . .
Cerithium weeksi Wade X . .
*Cerithz'um sp X X
Arrhoges sp X X
*Drepanochilus sp
Pterocerella cf. P. poinsettiformis Stephenson ........................ . X .
Xenophora cf. X. leprosa Morton .................... X X . . X .. A
Euspira rectilabrum Conrad ......... O . . X X .
Amaurellina stephensonz' (Wade) X . . X X
Pseudomaura lirata (Wade) ......... X
Gyrodes americanus Wade? ._ X .
*Gyrodes abyssinus (Morton) ...................................................... A .. A
*Gyrodes sp .u. "n .N. "u x .u. .u. _ "u
Tintorium? sp X
. X

Sargana sp
Bellifusus curvicostatus (Wade) ..............................................

s
Woodgella typica Wade
Remera? sp
Hercorhynchus Sp
Anomalofusus substriatus Wade?
Napulus reesidei Sohl ..
Pyropsis cf. P. perlata Conrad ..................................................

s ..........

 

 

 

 

 

 

 

   

P
*Longoconcha sp
*Volutomorpha sp

 

 

 

EXXOHE

 

 

 

 

 

 

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Beretra sp .

Caveola sp ..... . . .

Paladmete gardnerae Wade . X _ .

Acteon sp _ . X .

ancteon percultus Sohl _ . X . . ..

Parietipltcatum cf. P. conicum (Wade) ................................. . . . ..

*Avellana bullata (Morton) A . . X . .. A ..

*Ellipsoscapha sp ....... . A . . . ..

Cylzchna secalina Shumard . X . ..
Sp A X .

Anisomyon? jessuzn' Richards and Shapiro ............................ A X .

Scaphopoda:
Dentalium intercalatum Wade .................................................. A X X . . .. .

 

48

STRATIGRAPHY OF OUTCROPPING POST-MAGOTHY UPPER CRETACEOUS FORMATIONS

TABLE 8,—Megainoertebrate distribution in the Mount Laurel Sand in the Chesapeake and Delaware Canal area
and New J ersey—Continued
[A, Occurrence outside the Mount Laurel Sand of the canal area; X. rare occurrence (1—5 specimens); 0. common occurrence (5—15 specimens): I. abun-

dant occurrence (15+ specimens);

*. known only as internal molds]

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Chesapeake and Delaware Canal New Jersey
0)
E
g 5':
'a a“ v a 3 .o a.
e = q “a 3 s a s 5 31 31 s = = E
35%”3EE3§§§ Laws:
gsae~772...>53§afid
5' 5 i a g m m m m m fl —= 4: ""3 £1 5 "
B E '5}, _: ho a be an an no 8; g '8 a, ."j r. S
I» N s: .2 - .9? £9 .5.“ .29 E.“ .E.“ N w 0 e w ‘1’ c
2 2 m a: E on m m m m an 2 E B Id 2 3 S
Cephalopoda:
Eutrephoceras dekayi (Morton) .............................................. . X X . X . . A . . . .
Baculites cf. B. undatus Stephenson ........................................ . . x . . . . .
sp . . A X . .. A A . . A
Hoploscaphites sp ____ . >< . . . . _ .
Anaklinoceras sp . .. . X . . .
Didymoceras sp .. .. . . . . .
Didymoceras? sp . . X _
Belemnitella americana (Morton) ............................................ _ _ A _ _ I . _ _ . A
Porifera:
Clione sp . O X . .
Coelenterata:
Micrabacia hilgardi Stephenson ................................................ . . . . . . O X . O O .
Wadeopsamea? sp . . . . X . . . .. . . .
Bryozoa:
Cheilostomata .. . . . . X X . . X . . . ..
Brachiopoda :
Lingula? Sp . . . . X . .
Terebratulina cooperi Richards and Shapiro .......................... . A . X 0 . . X . . .
Echinodermata :
Cidaroidea (one test and spines) .............................................. ._ . X . . . .
Comatulid crinoid . . . . X . . . . . . . .
Chaetopoda:
Hamulus onyx Morton . . . . X . .
Serpula sp . . O O .. X .
Arthropoda (Decapoda) :
Crab claw . X . . X

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Mount Laurel Sand

29585. "Gryphaea" bed in bench 150—300 yd east of St. Georges Bridge.
south bank Chesapeake and Delaware Canal, Delaware. Collecte
by Buddenhagen, Sohl, Kauffman, 1966.

26634. South bank of the Chesapeake and Delaware Canal, about 300 yd
west of light 13 and 1.35 miles (airline) due east of St. George’s
Bridge. from 0 to 6.0 ft above low-tide line, New Castle County.
Del. Collected by N. F. Sohl, 1957.

27749. South bank of the Chesapeake and Delaware Canal about 300 yd
west of light 13 and 1.35 miles east of St. Georges Bridge 0~6 ft
above low tide, New Castle, Del. Collected by N. F. Sohl, 1960.

Mount Laurel fauna in this northern part of the
Atlantic Coastal Plain is not only significant but
impressive.

The following fossils from the Mount Laurel Sand
were collected along a tributary of Crosswicks Creek
about 1.2 miles east-northeast of Arneytown, NJ.
The forms marked by an asterisk are found in both
New Jersey and Delaware. Plus marks indicate oc-
currence of the species in the Exogyra cancellata

zone elsewhere in the Coastal Plain.
Pelecypoda:
+*Trigonia eufaulensis Gabb
Cucullaea sp.
Glycymeris sp.
Inoceramus sp.
Chlamys n. sp.

 

29507. Biggs Farm locality on the Chesapeake and Delaware Canal, south
bank, about 300 yds west of light 13 and 1.35 miles (airline) due
east of St. Georges Bridge. Collection near water level in place.
New Castle County, Del. Collected by Buddenhagen, Kaufiman. and
Sohl, 1966.

Locality same as above but at from about 6 to 10 ft above low-tide
level. Collected by N. F. Sohl, Aug. 22, 1957.

Locality same as for 29507 but from shell bed at base of blulf.

Locality same as for 29507 but from float on beach.

Locality same as for 29507 but from spoil pile along road.

26635.

29510.
29508.
29509.

Pelecypoda—Continued
+*Radiopecten weeksi Stephenson
+*Syncyclonema simplicius (Conrad)
Crenella sp.
Lithophaga sp.
Plicatula mullicaensis Weller?
+*Lima reticulata Forbes
Lima whitfieldi Weller
+*Lima acutilineata Conrad
+*Eocogyra cancellata Stephenson
+*Ostrea tecticosta Gabb
+ *Anomia perlineata Wade
+ *Crassatella vadosa Morton?
+ *Vetericardz’a subcircula Wade
+*Lucina cf. L. mattiformis Stephenson
+*Linear'£a metastriata Conrad
Brevicardium sp.
+ *Vem'ella conradi (Morton)
+*Panope decisa Conrad

BIOSTRATIGRAPHIC ANALYSIS 49

Pelecypoda—Continued
Parmicorbula sp.
+*Corbula cf. C. torta Stephenson
+*Caesticorbula crassiplica (Gabb)
Kummelia sp.
+ *Liopistha protexta Conrad
Gastropoda:
Emarginula n. sp.
+*Calliomphalus (C.) americanus Wade
Calliomphalus? n. sp.
+*Ma'rgam'tella pumila Stephenson?
+*Pseudomalaxis pilsbryi Harbison
Tintom’um sp.
*Nudz'vagus? sp.
+*Laxispira mom‘lifem Sohl
+ Arrhoges (Lat'iala) cf. A. (L.) lobata (Wade)
+ *Euspz’ra rectilabrum (Conrad)
+ Fusinus macnai'ryensis (Wade)
*Anomalofusus? sp.
Pyrifusus? sp.
+*Napulus of. N. reesidei Sohl
+*Bellifusus curvicostatus (Wade)
+ Paleopsephaea cf. P. mutabilis Wade
+ Lupim variabilis (Wade)
ancteon sp.
Cylichna sp.
Scaphopoda:
Dentalium sp.
Cephalopoda :
+*Eutrephocems dekayi (Morton)
*Belemnitella amen‘cana (Morton)
Porifera:
*Clione sp.
Echinodermata :
Echinoid plates
Coelenterata :
+ Micmbacea rotatalis Stephenson?
Worms:
+*Hamulus onyx Morton
Arthropoda:
Crab claws
Vertebrata:
Shark teeth
Dermal scutes

This list indicates not only the close correspond-
ence of the faunas of the Mount Laurel Sand of New
Jersey and Delaware but an equally close corre-
spondence to the faunas from equivalent units of the
Exogyra cancellata zone in other parts of the Coastal
Plain.

AGE AND CORRELATION

The age and correlation of the Mount Laurel Sand
is well documented. The fauna is a part of the char-
acteristic and widespread assemblage of the Exogym
cancellata zone that may be traced from New Jersey
to Mexico. The correlation chart (fig. 23) indicates
some of the more significant correlative fossils. As
noted on the chart, the Mount Laurel Sand can be
traced from New Jersey into Maryland, where at
Bohemia Mills (Gardner, 1916) it still carries the
same distinctive assemblage of Exogym cancellata,

 

Anemia. tellinoides, Belemm’tella. americana, and
others.

At present, this assemblage has not been definitely
identified on the western shore of Chesapeake Bay.
Farther south in North Carolina, the Mount Laurel
is correlative with the lower part of the Peedee
Formation. In the Gulf Coastal Plain, equivalents in
age are the upper part of the Cusseta Sand Member
and perhaps the lowest part of the unnamed middle
part of the Ripley Formation of the Chattahoochee
River region (Georgia-Alabama), the uppermost
part of the Demopolis Chalk (Bluffport Marl Mem-
ber) in Alabama and Mississippi, and the Coon Creek
Tongue of the Ripley Formation in Tennessee, but
not in Mississippi. In the western Gulf Coastal Plain,
the Saratoga Chalk of Arkansas and the Neyland-
ville Marl of Texas bear this same fauna. In Mexico,
the same zone is recognizable in the lower, but not
lowest, part of the Cardenas Formation of San Luis
Potosi. The presence in the Mount Laurel Sand and
its equivalents of heteromorph ammonites like
Didymoceras, Anaklmocems, and Baculites of the
Baculites compressus fauna suggests a correlation
with medial parts of the Pierre Shale of the western
interior. The assemblage is late Campanian in age.

NAVESINK AND YOUNGER FORMATIONS

There is no faunal evidence at the Biggs Farm
locality (11/2 miles east of St. Georges, Del.) of any
unit as young as the N avesink Formation. Chorysto-
thyris and other characteristic species of the Nave-
sink are absent and have not been found in collections
from spoil banks near Reedy Point east of Biggs
Farm. The citation by Groot, Organist, and Richards
(1954, p. 43) of the presence of Exogym cancellata
in both the Mount Laurel Sand and Navesink Forma-
tion along the canal is thus in error. Extensive
collections made recently from their locality 3 where
they list E. cancellata as occurring have yielded only
Exogy’ra ponder-03a and E. ponderosa erraticostata,
all derived from the Marshalltown Formation. More
convincing, is that the specimen figured in Groot,
Organist, and Richards (1954, pl. 4, fig. 2) as an
example of Exogym cancellata lacks obvious can-
cellations or costations and is in fact a young speci-
men of E. ponderosa. The same error was made by
Richards and others (1958, pl. 21, fig. 1), who
erroneously assigned to E. cancellata a specimen of
E. ponderosa that had faint costations on the early
part of the shell (as is typical of the species high in
its range zone). Similarly, there is no faunal evi-
dence for the presence of the Red Bank Sand along
the canal, as proposed by Groot, Organist, and Rich-

5O STRATIGRAPHY OF OUTCROPPING POST-MAGOTHY UPPER CRETACEOUS FORMATIONS

ards (1954). In New Jersey, the Red Bank carries a
fauna with forms such as Sphenodiscus (fig. 23)
that are diagnostic of an early Maestrichtian age.
No such forms have been found along the canal.
Recent excavations of the old Biggs Farm locality
have provided fresh exposures, and fossils collected
through the total sequence are assignable to the
Exogym cancellata range zone of late Campanian
age.

SUMMARY OF LIEGAPAIJ‘ZONTOLOGIC STUDIES

1. The Cretaceous section along the Chesapeake and
Delaware Canal has yielded four distinct mega-
faunal assemblages assignable respectively to
the Merchantville, Englishtown, and Marshall-
town Formations and the Mount Laurel Sand.

2. Along the canal no invertebrates have been found
in the basal unit—the clays of the Potomac
Group—and the overlying Magothy Formation
has produced only unidentified plants.

3. The presence of marine faunas equivalent to those
of the Raritan, Woodbury, Wenonah, or Nave-
sink Formations, or Red Bank Sand has not
been demonstrated.

4. The faunas of the fossiliferous units are charac—
terized as follows:

A. Merchantville Formation: Abundance of
gastropods—Graciliala (floods of im-
mature forms), Arrhoges, Calliompha—
lus, Laxispim, and Palademete; the
common occurrence of the ammonites
Scaphites hippocrepis and Menabites
(Delawarella) delawarensis; and an
abundance of decapod crustacean re—
mains.

B. Englishtown Formation: Abundance of
Ophiomorpha burrows and a molluscan
assemblage dominated by Cardium
(Trachycmdium), Glycyme'ris, Lopha,
and Turritella.

C. Marshalltown Formation: Abundance of
Exogyra ponderosa, Trigom'a, Cypri-
meria excavata, Crassatella, Cucullaea,
and Cardium.

D. Mount Laurel Sand: Association of Exo-
gym cancellata, Anomia tellenoides, and
Belemm’tella americana.

MICROPALEONTOLOGIC STUDIES

The status of the study of Foraminifera in the
Cretaceous of the Atlantic Coastal Plain can be con-
trasted in several respects with the status of megain-
vertebrate studies. The most important difi'erence is
the scarcity of published data on the Foraminifera,

 

which is partly due to the belated appreciation of
the value of Foraminifera in correlation and paleo-
ecologic interpretation. As a result, there are few
localities in which Foraminifera have been described
in the Coastal Plain; this makes it difficult to develop
meaningful correlation within the region on the basis
of the Foraminifera. On the other hand, when pres-
ent, foraminiferal faunas are usually well preserved
and quite diverse, often containing 50 or more spe-
cies. However, very few paleoecologic interpretations
have been made on the basis of these faunas, and
detailed morphologic and phylogenetic studies have
been limited to the planktonic Foraminifera. At
present, relatively little is known about Atlantic
Coastal Plain Cretaceous benthonic Foraminifera.

The intensive study given the planktonic forms
has resulted in their wide use in regional and espe-
cially interregional correlation. However, because of
the detailed morphologic features used in species
identification and because of the varying phylogenies
and consequent ranges that have been proposed,
there is diversity of opinion in the literature as to
the definitive characteristics of subspecies, species,
and genera, and their ranges. This increased refine-
ment of diagnostic morphologic criteria has made
many of the older generalized descriptions either
unusable or equivocal.

A complete review of the study of Cretaceous
Foraminifera reported from the Atlantic Coastal
Plain is not warranted here, but the recent work of
Olsson (1960, 1964), which is considered later, does
have direct bearing on the fauna] interpretations
made.

SAMPLING PROCEDURES AND SAMPLE DESIGNATIONS

Forty-two samples from the three Upper Creta-
ceous formations exposed in and near the Chesapeake
and Delaware Canal were examined for Foramini-
fera. The samples were washed through a ZOO-mesh
sieve, dried, and floated on carbon tetrachloride.
Thirteen samples yielded Foraminifera, and nine
contained identifiable specimens. Only one of the nine
samples that contained identifiable specimens, sam-
ple U from the Englishtown Formation, failed to
yield abundant well-preserved specimens. Only 30—35
specimens, assignable to 10 species, were recovered
from this sample. The very small size of the speci-
mens, the presence of all species in the physically
overlying Marshalltown Formation, and the incon-
gruity of a predominantly planktonic assemblage in
sediments deposited in a probable near-shore shal-
low-water environment combine to strongly suggest
that the Foraminifera in this sample are contami-
nants from the Marshalltown Formation.

TABLE 9.—Distribution of microfauna

in

BIOSTRATIGRAPHIC ANALYSIS

51

the Englishtown and Marshalltown Formations and Mount Laurel Sand in southern
New Jersey and northern Delaware

 

 

  

  
 
  
  
 
  
   
   
  

 

 

 

 

 

  

 

 

 

 

 
 

 

 

 

 

 

 

 

 

 

 
   
 
 
  
  
   

 

 
 
 
   

 

  

 

 

 

 

 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

U V W X Y Z D C B A Austin Taylor Navarro Comments
Bulimina reussi Morrow ................ X X X X X x X x X X X X
Gaudryina stephensoni Cushman .. X X X X X X X X X X X X
Globigen'rwlloides messinae Bronnimann X X X X X X X X X Late Campanian and early and late Maestrichtian in
New Jersey and Delaware.
Glabotruncana? subrugosa. Gandolfi .............. X ? X X X X X X X Late Campanian of New Jersey and Delaware
(Marshalltown Formation) .
Gyroidina depressa (Alth) ............. X X X X X X X X X X X X
Hedbergella planispira (Tappan) X X X X X X X X X X Do.
Heterohelix globulosa (Ehrenberg) X X X X X X X X X X X X Santoniainsand Coniacian of the western interior
Unite tates.
Neobulimina. canadensis Cushman and X X X X X X X X X x X Varietal form from the late Campanian Pierre Shale.
Wickenden var. A.
spinosa, Cushman and Parker .................. X X X X X X X X X X X X Early and late Maestrichtian of New Jersey (Red—
bank Sand and Navesink Formation). Campanian
of Colombia.
Rugoglobigerina macrocephala. Bronnimann X X X X X X
Anomalina nelsoni Berry .. .. X X X X X
rubiginosa Cushman X X X X x X X Maestrichtian of Europe.
Astacolus of. A. cretaceus X . .. X X X X
Bolivina watersi Cushman X , . X X
Bolivinitella elem’ (Cushman) X X Do.
Bolivinoides decoratus australzs Edgell x X X Upper Campanian or lower Maestrichtian of Aus-
Bulimina. kickapaoensis Cole ........ X X X X X X X X traua.
rudita Cushman and Parker . X X . X X X X X
Caucasina. cf. C. pusilla (Brotzen) X X X _ Upper Cretaceous of Sweden.
vitrea (Cushman and Parker) .. X . X X X X X X
Cibicides beaumontianus d’Orbigny X X X X
cf. C. harperi (Sandidge) ........... X X X X x X X X X
Citharina. cf. C. multicostata (Cushman) X X X X
Dentalina basiplanata Cushman X . X X X X X
legumen Reuss ..................... X _ X X X X
Frondicularia archiaciana. d’Orbigny X X X X X X X
Globotruneana? cretaeea. (d’Orbigny) X X X X X X X Late Campanian of Delaware (Marshalltown For-
mationl.
fornicata (Plummet) ................................ X X X X .. Late Campanian of Delaware and late Campanian
and early Maestrichtian of New Jersey (Marshall-
town Formation and Mount Laurel Sand).
linneiana (d’Orbigny) ............. X X X X X X . Do.
subcircumnodifer (Gandolfi) X X X X X X X X Late Campanian and early and late Maestrichtian of
New Jersey and Delaware (Marshalltown Forma-
tion, Mount Laurel Sand, Navesink Formation.
‘ and Redbank Sand).
tncarinato (Quereau) ---------------------------- X X X X 7 X Late Campanian 'Z and early and late Maestrichtian of
New Jersey and Delaware (Marshalltown? and
. Navesink Formations and Redbank Sand).
Globulina lacnma, Reuss s. l .......................... X X X x x X X X x x
Gy'roidina globosa (Hagenow‘) of Cushman X X x , X X X X X X
Heterohelix pulchra (Brotzen) X X X X x X X X X X Maestrichtian of New Jersey.
Loxostoma gamma (Cushman) X X X X X X >< Upper Campanian of Israel.
plaita plaita (Carsey) . _ X X X X ‘ X X X X
Marginulina sp. A ................. _ X . X X X X
N L " hm n. sp . X X X
canodensis Cushman and . X X X X X X X X Varietal form also occurs in the late Campanian
Wickenden var. B. Pierre Shale.
Nodosaria (minis Reuss . . X X X X X X X X X X
amphiotcys Reuss . X X X .. X X
obscura Reuss .. _ X X X x x X X
Nonionella austinan _ X X X X X X X X
Nuttallinella? n. sp . X X X X X - Also occurs in the late Campanian Pierre Shale.
Oolina. n. sp .. . X X X X X Do.
Planulina of. P. spzssocostata Cushman . X X X X X X X X
taylorensis Cushman ........................... ,. _ X X X X x x x x x
Pseudoguembelina. excolata costulata _ lX .. X X X .. X X X
Cushman.
Pseudouvigerina. sp. afl'. P. seliyi (Cushman) , X X X X
Pullem’a. americana Cushman .......................... , x x X x x x x x x
Sigmomorphina. semiteeta terquemiana _ X X X x X X X X x
(Fornasini) .
Stilostomella stephensoni (Cushman) x . X ? X x x 'I X X X
Textularia ripleyensis Berry _ X X .. X X X X X X X
Dentalina basitorta Cushman X . X .. X X
Dorothia, glabrella Cushman .. X . X X
Eouvigerina americana Cushm x . x x X X x X .
Fissurina marginata. (Walker and ass ) . X . X X X X Campanian of California and Tertiary of Trinidad.
Gaudryina. sp. A ........................... X . X
Glabotruncana rasetta (Carsey) . X Late Campanian of Delaware and late Campanian
and early Maestrichtian of New Jersey (Marshall-
town Formation and Mount Laurel Sand).
Hoeglundina cf. H. supracretacea (ten Dam) . X X X
Lagena. sulcata. semiinterrupta. Berry .. . X X X X X X
Marginulina taylorana Cushman .......... , X X ., X X
Pseudonadosaria. appressu (Loeblich . X? X X X X
and Tappan).
Pymlina of. P. cylindroides Roemer . _ X X X X
Bulimina. n. sp.? ................................ X X? X
Dentalina of. D. consobrina d’Orbigny X X X X X X
Eouviyerina hispida Cushman ........... . X X X X X X
Globorotalites michelinianus (d’Orbigny) X X X X x X X
Lingulirw. sp. A . x X
Neoconorbina n. sp . X X X X
Ramulina of. R. arkadelphmna Cushman X X X X
Anomalim cf. A. pseudopapillosa, Carsey __ X ><
Astacolus sp. 2 ................................. . X
Bolivinopsis rosula (Ehrenberg) . X X X X X
Clavulinoides trilatera trilatera (Cushman) X X X X X
Dentalina gracilis d’Orbigny . . X X X X X
‘Discorbis’ n. sp ......................... X X "'3 X . _
Fissurina orbignyana (Seguenza) x X X Upper Comaman of Austria.
Globotruncana area. (Cushman) X X X" Uppermost Campaman and Maestrichtian of New
.1! ersey and Santonian to Maestrichtian in Cali-
ornia.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

52

STRATIGRAPHY 0F OUTCROPPING POST-MAGOTHY UPPER CRETACEOUS FORMATIONS

TABLE 9.—Distribution of microfauna in the Englishtown and Marshalltown Formations and Mount Laurel Sand in southern
New Jersey and northern Delaware—Continued

 

 

  

 

  
 
  

 

 

 

 

 

  
  

 

 

 

 

 
 
 
     

   

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

U V W X Y Z D C B A Austin Taylor Navarrfl Comments
Globotruncana uentn‘cosa White . X ? x . x X Coniacian to Maestrichtian.
Heterohelix planata (Cushman) . x .. x .. x Maestrichtian of Egypt.
sp. afl‘. H. pulchra (Brotzen) . X x x X H. pulchm, to which this species is closely allied. also
occurs in the Maestrichtian of New Jersey.
Laaena. sp. 8.6. L. quadralata Brady .. . X x Thsih form also occurs in the late Campanian Pierre
a e.
substriata. Williamson x X X X
Lingulina sp. B. X
. m,‘ " sp. X
sp. ........... . X .. .
Pseudotextularia. elegans elegans (Rzehak) .. X x . X X Uppermost Coniacian to Maestrichtian.
Seabrookia stewurti Olsson .............................. X Only previously reported occurrence is from the
Maestrichtian of New Jersey.
Anomalinoides n. sp.? X X
Astacolus sp. 1 x
Gaudryina Cf- G. bulloules 0155011 - X X X Only previously reported occurrence is from the
Maestrichtian Redbank Sand of New Jersey.
n. sp .............................................................. x X X
. mg' " sp. B x X
Nodosaria cf. N. navarroana Cushman x x X X X
Planulirw, sp. aff. P. correcta. (Carsey) x x X x x
Plectina watersi Cushman .............. X . X X Senonian of Bulgaria.
Pleurostomella. subnodosa Reuss .. X . x X Santlfnian-Maestrichtian of New Jersey and else-
W ere.
Pr ' k ‘r‘ " ‘ '- M'e x . X Upper Campanian and Maestrichtian of New Jersey
( Voorwijk) . and elsewhere.
Schaclcoina multispinata Cushman and X x X X . Maestrichtian of Trinidad.
Wickenden.
Clavulinoides cf. C. insignia (Plummer) ...... . x X
YDentalina aculeata d’Orbigny ........ X X
Epom’des haidingen'i (d’Orbigny) .. X X Lower upper Campanian of Bavaria.
Gaudryina. cf. G. ellisorae Cushman X X
Pernen‘na n. sp. 1’ x
Anomalinoides pin X X Mqunt Laurel Sand and Navesink Formation of New
ersey.
Astacolus cf. A. ja'r'visi (Cushman) ............ . .. . X Refported with question from the Campanian of Cali-
orma.
Dorothia stephensom‘ Cushman ...................... X X X X
Quadrimorphina allomorphinoides (Reuss) X X X X ' _
Spiroplectammina. mordensis Wickenden X Santonian? and Campanian of Alaska.
A. Mount Laurel Sand, from the Chesapeake and Delaware Canal at Y. Marshalltown Formation, north side of the Chesapeake and Delaware
Biggs Farm. 6—8 ft above the top of the Marshalltown Formation. Canal. 100 yd west of the U.S. Route 13 bridge at St._ Georges. in
B. Mount Laurel Sand, from the same stratigraphic position and locality 2'“): 11:33:21“ f°°t 0f the formation and associated Wlth Exogyra
as sample A. . X. Marshalltown Formation, south side of the Chesapeake and Delaware
C. Mount Laurel Sand, south Side of the Chesapeake and Delaware Canal, Canal, 15 miles northeast of Summit Bridge, Del., from the upper
about 100 Yd 935‘: Of the bridge on U-S- Route 13: from a C°n391°u' part of the formation, in an excavation for a railroad bridge pier.
ous Pyncnodonte bed, about 3 ft above the top of the Marshalltown W. Marshalltown Formation, south bank of Oldmans Creek at Camp
Formation. . Kimble, near Auburn, southwest New Jersey (Mello and others,
D. Mount Laurel Sand, same locality as sample C, from inside a closed 1964, p, 361).
Pyncnodonte shell. V. Marshalltown Formation, same locality data as for X, but from the
Z. Marshalltown Formation, north side of the Chesapeake and Delaware middle part of the formation.
Canal, immediately west of the bridge on U.S. Route 13; within the U. Englishtown Formation, same locality as for sample X, but from the

upper 1—2 ft of the formation.

Faunas from the nine fossiliferous samples are
compared with the fauna reported from a single
sample of the Marshalltown Formation at Auburn,
N.J. (Mello and others, 1964). From these 10 sam-
ples, a total of 111 species of Foraminifera were
identified, of which 93 are positively or tentatively
assigned to previously named species. Eight species
are considered to be new or probably new, and 10
are given temporary letter or number designations.
Table 9 indicates the distribution of the species in
the samples, and shows their Cretaceous ranges.

TAXONOMIC REVISIONS

Comparisons have been made between the speci-
mens from the Marshalltown Formation at Auburn,
N.J. (Mello and others, 1964, p. 63) and specimens
from the nine Chesapeake and Delaware Canal sam-
ples included in this study. Many species are repre-
sented by better specimens in the Chesapeake and
Delaware Canal samples than in the Auburn sample,
and comparisons have shown that several species

 

base of the formation.

were incorrectly identified from the Auburn sample.
Also, several species present in the Auburn sample
but not identified previously could be identified after
comparison with the Chesapeake and Delaware Canal
faunas. Modifications and additions to the Auburn
species list are shown in the following summary.

AGE INTERPRETATIONS

Repetition of lithologies, thinness of the lithologic
units, and scarcity of good exposures has severely
hampered stratigraphic and biostratigraphic study
of the Cretaceous deposits on the Atlantic Coastal
Plain. Stratigraphic interpretations made earlier in
this report are the framework within which the
fossil evidence presented here is considered and
against which other interpretations are compared.

Olsson (1960, 1964) was the first in more than 30
years to systematically study Foraminifera from the
Cretaceous rocks in this region, and his taxonomic
work has been extensively used in this study, chiefly
for the comparison of planktonic Foraminifera.

BIOSTRATIGRAPHIC ANALYSIS

Mello, Mina/rd, and Owens, 1964
Not identified

53

- This report
.Anomalina nelsom‘ Berry

 

Do

 

Do

 

Pseudogaudryinella capitosa, (Cushman) ......................................

Not identified

Biglobigeri'nella biforaminata (Hofker) ........................................
Not identified ........................................................................................

Globotruncana cretacea Cushman ..

Globigem’na (Rugoglobigerina) mgosa Plummer? ......................

Globotmncana wilsom' Bolli ......

  

.......... Cibicides cf. C. harpem' (Sandidge)

Dorothz’a glabrella Cushman
Gaudyrina stephensom' Cushman
Gaudryina sp. A

.......... Globigerinelloides messinae Bronnimann
.......... Globotrunccma? cretacea (d’Orbigny)

Globotmmccma rosetta (Carsey)

.......... Globotruncana? submgosa Gandolfi

Globotruncama subcircumnodifer (Gandolfi)
....Lagena sulcata semiinterrupta Berry

 

Lagena cf. L. acutz’costa Reuss ......

Bolivina incmssata Reuss ..................................................................
Bulimina prolixa Cushman and Parker ..........................................
Pseudoglandulina cf. P. lagenoides (Olszewski) ..........................

Not identified ..

Olsson (1964, p. 160) reported on planktonic Fora-
minifera from one sample of the Mount Laurel Sand
and two samples of the Marshalltown Formation in
New Jersey, and on two samples of the Mount
Laurel-Navesink Formations (undifferentiated)
from the Chesapeake and Delaware Canal, Del.

Of the planktonic species identified both in this
study and by Olsson (1964), the following have
ranges that include at least part of the late Cam-
panian and at least part of the Maestrichtian: H ed-
bergella planispira, Globotrunccma cretacea, G.
submgosa, G. linneioma, G. rosetta, G. fornicata, G.
tricarmata, G. subcircumnodifer, Globigem’nelloides
messinae, and Praeglobotmncana hammensis
(=petaloidea of Olsson).

The only two planktonic species recovered in this
study which do not have ranges extending from the
late Campanian into at least the earliest Maestrich-
tian are Rugoglobigerma macrocephala and Globo-
truncana area, both of which Olsson reported only
from the Maestrichtian. Bandy (1967, p. 20) cited a
Coniacian to Maestrichtian range for G. area.
R. macrocephala, a rare species in seven samples
from both the Marshalltown Formation and Mount
Laurel Sand, was reported from the Campanian of
Colombia by Gandolfi (1955, p. 46).

The balance of evidence from the planktonic Fora-
minifera, supported by several benthonic species
with restricted ranges, indicates a late Campanian
or earliest Maestrichtian age for both the Marshall-
town and Mount Laurel samples studied. Table 9 lists
the occurrences of the identified species in the sam-
ples and shows the ranges of many through the
Austin, Taylor, and Navarro provincial stages of the
Gulf Coastal Plain, as reported by Cushman (1946).

It is noteworthy that Olsson’s (1964) usage of the
term Mount Laurel-Navesink Formation in conjunc-
tion with his two samples from the Chesapeake and
Delaware Canal is based exclusively on lithologic

 

.......... Loxostoma plaita plaita (Carsey)
.......... Neobulimina canadensis Cushman and Wickenden var. A.
.......... Pseudonodosaria appressa (Loeblich and Tappan)

..Rugoglobt’gerina macrocephala Bronnimann

character. He clearly points out the difference in age
attributed to this unit along the canal with respect
to the ages of the Mount Laurel Sand and N avesink
Formation in New Jersey. The descriptions of col-
lecting localities given by Olsson (1964, p. 160) indi-
cate that his sample, DK5, from the Mount Laurel
Sand-Navesink Formation, was taken at approxi-
mately the same stratigraphic level and within 200
feet geographically of samples C and D of this study.
His sample DK6, also from the Mount Laurel-Nave-
sink Formation, is apparently from the same strati-
graphic level and geographic position as samples A
and B of this study. Within the stratigraphic frame-
work developed in this paper, samples C and D are
from the Mount Laurel Sand, within 3 feet of the
top of the Marshalltown Formation; samples A and
B are from the Mount Laurel Sand 6—8 feet above
the top of the Marshalltown Formation.

The presence of each planktonic species in samples
from both the Mount Laurel Sand and Marshalltown
Formation makes it impossible to differentiate these
formations, on this basis, as to age. In addition, 88
out of the total of 111 species occur both in the
Mount Laurel Sand and in the Marshalltown Forma-
tion. No species represented by a large number of
specimens in any one sample fails to appear in both
formations, and nearly all the species restricted to
one or the other formation are represented by fewer
than five specimens in any sample. The persistence
of such a large percentage of species, including the
supposedly rapidly evolving planktonic species, sug-
gests that deposition of the Mount Laurel Sand
followed close upon the cessation of deposition of
the Marshalltown Formation. In light of this in-
terpretation, it is possible that the absence of the
Wenonah Formation between the Marshalltown and
Mount Laurel is due to the loss of identity of the
Wenonah by facies change within the lower part of
the Mount Laurel in the sampled area.

54 STRATIGRAPHY 0F OUTCROPPING POST—MAGOTHY UPPER CRETACEOUS FORMATIONS

Close faunal similarity, such as is found here be-
tween the Mount Laurel Sand and Marshalltown
Formation, is suggestive of secondary faunal mixing,
although this seems unlikely for these samples.
Nearly all specimens from both formations show no
abrasion or breakage which might be indicative of
transportation, and faunas from both formations
are large and diverse in addition to being largely
composed of the same species. Also, samples 8 feet
or more above and below the contact retain the same
faunal character, further suggesting that mixing is
not the cause for the similarities.

ENVIRONMENTAL INTERPRETATIONS

Although it is dangerous to attempt close defini-
tion of depositional environment in the absence of
specimen counts, sediment analysis, and complete
faunal representation, it does seem quite evident
that the faunas recovered from the Mount Laurel
Sand and Marshalltown Formation were deposited
under open marine conditions like those existing over
the middle continental shelves during the Holocene.
The chief factors favoring this interpretation are
the generally very high diversity of Foraminifera
and the frequency of occurrence of planktonic speci-
mens in the samples. The faunal similarities dis-
cussed above strongly indicate that the depositional
environments for the Marshalltown and Mount
Laurel through the stratigraphic interval and in the
area studied were identical or very closely similar.
It should be emphasized here that these interpreta-
tions pertain only to the glauconite-bearing calcare-
ous beds of the Mount Laurel and not to the medium
to coarse quartz sand beds found in the upper part
of the formation.

A simple clustering program was carried out in an
attempt to determine What, if any, differences exist
between the recovered faunas that might indicate
consistent environmental differences between the two
formations. The nature of the data itself put rigor-
ous restrictions on the coefficients of correlation that
could be used. Each of the samples was floated on
carbon tetrachloride before picking. This procedure
undoubtedly alters the faunal composition and
largely invalidates the significance of specimen
counts. The logic presented by Simpson (1960) con-
cerning the selection of coefficients of correlation is
applicable here, and Simp son’s index 2 is used. Com-
parability of samples is calculated as:

C
m X 100
where C equals the number of species common to two

samples, and N1 equals the total number of species

 

present in the smaller sample. For ease in visualiza-
tion of relationships, the values thus calculated were
clustered using the weighted pair-group method with
arithmetic averages (Mello and Buzas, 1968). The
calculated relationships between samples are shown
in figure 25. Sample U, from the Englishtown For-
mation, was deleted before clustering because of its
probable contamination.

Examination of the clustering (fig. 25) shows no
subdivision into separate Mount Laurel and Mar-
shalltown clusters. Instead, the samples are grouped
rather heterogeneously, and this indicates that, at
least on the basis of presences and absences, the
faunas from the two formations cannot be differ-
entiated. The faunas from these samples are also
similar with regard to relative abundances of spe-
cies. Although no single species is consistently domi-
nant, a small group of species is collectively dominant
in all samples, and many species are consistently
scarce in all samples. In view of these faunal simi-
larities, it seems warranted to conclude that environ-
mental factors necessary for the existence of the
foraminiferal species found in the Marshalltown
Formation persisted during the deposition of the
Mount Laurel Sand.

SUMMARY OF MICROPALEONTOLOGIC STUDIES
Eight samples were examined from the Mount
Laurel Sand and Marshalltown Formation along the
Chesapeake and Delaware Canal, Del., and one sam-
ple from the Marshalltown Formation at Auburn,
N.J. Faunas from the two formations cannot be

 

100

to

O

T
l

 

 

 

 

 

 

 

 

 

 

oo
o
l
l

 

 

 

 

 

 

 

\l
O
|
l

 

method usmg arithmetic averages)

 

 

CLUSTERED SAMPLE RELATIONSHIPS
(Calculated by the_weighted pair-group

ca

0
I
l

 

 

50

 

FIGURE 25.—Clustering of nine samples from the Mount
Laurel Sand (italicized letters) and Marshalltown
Formation.

SELECTED REFERENCES 55

distinguished from each other on the basis of species
presences and absences; they are also generally alike
with regard to commonness and scarcity of con—
stituent species. The ubiquity of most planktonic
species in the samples and the presence of all plank-
tonic species in both formations indicate that
through the intervals sampled the two formations
are of late Campanian to earliest Maestrichtian age.
The absence of the Wenonah Formation west of the
Delaware River is possibly the result of facies change
within the basal Mount Laurel Sand rather than of
erosion or nondeposition. Comparisons of the total
faunas from both formations strongly suggest a
close similarity in living environments.

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Simpson, G. G., 1960, Notes on the measurement of faunal
resemblance: Am. Jour. Sci., v. 258—A, p. 300—311.

Sohl, N. F., 1964a, Neogastropoda, Opisthobranchia, and
Basommatophora from the Ripley, Owl Creek, and
Prairie Bluff Formations: U.S. Geol. Survey Prof.
Paper 331—B, p. 154—344, pls. 19—52.

Gastropods from the Coffee Sand (Upper Cretaceous)
of Mississippi: U.S. Geol. Survey Prof. Paper 331—0,
p. 345—394, pls. 53—57.

Spangler, W. B., and Peterson, J. J., 1950, Geology of the
Atlantic Coastal Plain in New Jersey, Delaware, Mary-
land, and Virginia: Am. Assoc. Petroleum Geologists
Bull., v. 34, no. 1, p. 1—99.

Stephenson, L. W., 1914, Cretaceous deposits of the eastern
Gulf region and Species of Exogyra from the eastern
Gulf region and the Carolinas: U.S. Geol. Survey Prof.
Paper 81, 77 p., 21 pls.

1923, Cretaceous formations of North Carolina; Part

I, Invertebrate fossils of the Upper Cretaceous forma-

tions: North Carolina Geol. and Econ. Survey, v. 5, pt. 1,

604 p., 102 pls.

1933, The zone of Exogyra cancellata traced 2,500

miles: Am. Assoc. Petroleum Geologists Bull., v. 17, no.

11, p. 1351—1361.

1954, Additions to the fauna of the Raritan formation
(Cenomanian) of New Jersey: U.S. Geol. Survey Prof.
Paper 264—B, p. 25—43.

Stephenson, L. W., Cooke, C. W., and Mansfield, W. C., 1932,
Chesapeake Bay region: Internat. Geol. Cong., 16th,
Washington, D.C., 1933, Guidebook 5, Excursion A—5,
49 p., 9 pls.

Stephenson, L. W., King, P. B., Monroe, W. H., and Imlay,
R. W., 1942, Correlations of the outcropping Cretaceous
formations of the Atlantic and Gulf Coastal Plain and
Trans-Pecos, Texas: Geol. Soc. America Bull., v. 53,
no. 3, p. 435—448, chart.

U.S. Geological Survey, 1967, Engineering geology of the
Northeast Corridor, Washington, D.C., to Boston, Mass.
—Coastal Plain and surficial deposits: U.S. Geol. Sur-
vey Misc. Geol. Inv. Map I—514—B, 8 sheets.

Weller, Stuart, 1907, A report on the Cretaceous paleontol—
ogy of New Jersey, based upon the stratigraphic studies
of George N. Knapp: New Jersey Geol. Survey, Pale-
ontology Ser., v. 4, 2 v.: 1107 p.

Young, Keith, 1963, Upper Cretaceous ammonites from the
Gulf Coast of the United States: Texas Univ. Pub. 6304,
373 p., 82 pls.

 

 

 

 

 

 

A
Page
Acteon cretacea ...................................................... 43
sp ................................................................ 37, 47
Aenomz 45
sp 26
Age and correlation, Marshalltown Forma-

 
 
 
 
 

tion ..................................
Merchantville Formation .
Amaurellina stephensom' .
Amauropsis meekana
Amboy stoneware clay
Amuletum

INDEX

 

[Italic page numbers indicate major references]

 

 
 
 

minerensis .....
reesidei zone _
undatus
Barbatia. carolinensis ........................................... 36
sp 46

 

 

      

 

 

 

    
 
 
 
 
  
 
 
  

A "”' as
SD

Analyses, clay-mineral ._
heavy-mineral .
light-mineral

Ann ‘- 1' a Sp

Anatymya sp .........

Anchura pennuta .
, rostrum

 

 

 

  

 

 

 

 
 
 
 

 

 

Belemnitella americana "7, 45, 48, 49
Bellifusus ...............
curvicostatus .
11‘ g
sp ................................................................ 42, 47
B 7" ’ creideri
Beretm sp _____________

  
 

Biggs Farm locality ..................
Biglobigerinella, biforaminata
Biostratigraphic analysis ........ i.
Biostratigraphic studies ...................................... 1
Black Creek Formation of North Carolina ....39
Blufitown Formation of Georgia and
Alabama ................................................ 39, 44
Bolivim incrassata, ,.
watersi ..................

 

 

 

  

 

 

 

 
 

 

 

   

 

 

 

 

    

 

 

 

 

 

  

 

 

 

A ' ,, borealis Boliv' "0”” eleyi
jessupi .............................................................. 47 Bolivinoides decoratus uustralis
AM " 'nelsoni ’11. 53 Bolivinopsis rosula .......................
,. 4 ,, ,illosa. R1 Breviarca haddonfieldensis
rubiginosa, ........................................................ 51 richardsi
AM 1' n‘J 5p
pinguis ......................... Breviwrdium pamhillamum ........................ 42, 46
Anomalafusus substriatus sp 48
sp ...................... . Brownstown Marl of Arkansas
Anemia, argentaria . .36, 40, 42, 46 Buccinid SD ..
perlineata ........................................................ 48 Buccinopsis .sp ........................................................ 42
radium 26 Bu" ' =31
tellinoides 45, 46, 49 7 ' ' , ein 51
Aphrodina .......... 44 prolixa ..
eufuulensis reussi
tippana l mdita
sp ‘16 Build macrostromata,
Area ‘ yensis 46 Burditt Marl of Adkins ...................................... 39
obesa .................................................................. 45
rostellata .......................................................... 45 C
Si) .
Architectomca ooragiformis C aduius abmtus ____________________________________________________ 37
A'rrhoges (Latiala) lobata 37, 49 Caesticorbula
(Latiala) sp . 37, 40, 42, 45 . .
crassiplzca
sp 47 .
Calliomssa sp
Astacolus cretaceus .............................................. 51 Call' 1. 1M
jarvisi ................................................................ 52 ’
sp 1 ‘2 nudus ................................................................ 47
SD- 2 '51 (Callzomaphalus) americanus

 

Astarte sp .4
Atlantic Coastal Plain, northern

  
 
 

 

 

 

 

 

 
 

Atlantic Highlands section ............ .
A "n n L H 4 43’ 47
B

Baculites
asper .
claviformis ...................................................... 34
" ’ " “to zone ‘11
columna l
campressus .49
compressus zone fauna .. ...31
r ‘ zone ‘15

 

 

paucispirilus .......................

 

 

(Planolateralis) ..
sp ................................................................ 47
5D 45
Campanian faunas
Campanian Stage ......
Camptonectes bellisculptus
burlingtonensis ..............................................
CHM" ulus sp “7
Capulus
Cardium ..
donohuensis .
dmnosum ..
longstreeti
tenuist-riatum

 

   

 

 

 

 
  

 

wenonah
whitfieldi
(C‘riocardium) sp .
(Granocardium) dumosum
Icummeli ..........
tenuistriatum
sp ,
(Pachycardmm )
(Trachycardium)
eufaulensis ..
longstreeti
uniformis ................................................

 

 
 
 
 
 
    
  
 
 
 
 
 
 
 

spillmam .

SD
Caryocorbula sp .
Caucasina pusilla .

 

 

vitrea
C ' $1) 27, 40, 4'7
Cementation in sand formations .................... 20

Cenomanian age fauna
Cerithium weeksi ............
Sp
Chattahoochee River region of Georgia and
Alabama ...................................................... 34
Cheilostomata
Chesapeake and Delaware Canal
section near Summit Bridge
Chlamys .............
cretosus
Chlorite as minor constituent
Chloritoid .....................................
Chorystothyris .....................
Cibicides beaumontianus
harperi .
Cidaroid
Cidaroidea
Cinulia. nuticoides
Citharina, multicostata .
Clavagella armata ........
Clavulinoides insignia
trilatem trilatem
Clay-mineral analyses
Clifiwood flora
Cliane sp ........
Coffee Sand of Mississippi
Comatulid crinoid ......................................... ..
Comparison with the New Jersey molluscan
fauna
Conclusions on rock stratigraphic studies
Coniacian rocks
Corbula crassiplica
‘esbor “'0
torta ..................................................................
SD
Con'mya. tenuis ........................................................ 45
Correlation, regional problems .......................... 28
Correlation and age of Cretaceous
megafauna fossils ...................................... 39
Correlations of Upper Cretaceous formations
revised
Crab claw ......
Crassatella .......
carolinensis
mwkirkensis
roadsensis .....
J

 

 

 

  
 
  
   
  
  
 
 
 
 
 
 
 

   

 

 

 

 
 

 

 

58

Crassostrea tecticosta _
Crenella serica ..........

 

 

SD
Cretaceous formations, comparison .................. 17
Cretaceous megafauna, summary ..................... 35

Cretaceous megafauna fossils from the
Chesapeake and Delaware Canal
Crosswicks Clay
Cucullaea
neglecta
tippana
sp ........................................................ 45, 46, 48
Cusseta Sand Member of Ripley
Formation
Cylichna recta
secalina

  
 
 
  
   
 
 

Cymella bella
ironensis
Cypraea grooti

morttmi .42
Cyprimeria . 44
excavata . ".42, 44
sp .......................................................... 36, 42, 46

D

Delaware, northern, rock stratigraphic
studies
Dentalim aculeata ..
basi,’ h-
basitorta .........................................................
consobrina
gracilis .......
legumen
Dentalium intercalatum
subarctuatum
SD
Dermal scutes .......................................................
Dessau Formation of Durham ..
Didymoceras .....................................
sp
Discorbis .
Distribution of formations, Delaware .
Maryland ..
New Jersey
Dorothia glabrella
stephensom' .....
Dre, ”We sp
Drilluta distans .................................................... 37
sp 27

 
 
 

 

 

 
 
 
  
 
 
 
 
 

 

 

 

 

Eagle Sandstone .................................................... 39
Echinoid plates
Ecphora sp ...... .
EH5, pha 51) 47
Emarginula ......
ladowae
Englishtown Formatlon

 

 

 

 
 

24, 26, 34, 39, 44
ancteon peroultus ................................................ 4’7

 

SD
Eouvigerina americana
hispida ......................
Epidote content in Merchantville and
Mount Laurel
Eponides haidingerii .
Etea carolinensis

 

 

 
 
 
 
    
 
  
   

..37, 40, 47,
............. 37, 42
Eutaw Formation of gulf coast
Eutrephoceras dekayi .............

 
 

Exiteloceras .
Exoyyra ...... 31, 41
cancellata 7, 16, 28, 34, 45, 46, 48, 49

 

 

 

 

 

 
 

 

INDEX

bed ..
Zone 28, 31, 34, 48, 49
costata ...... 28
zone .28, 34
ponderosa ........................ 6, 11, 15, 16, 28, 36,
41, 42, 44, 49
erraticostata .42, 44, 49
sp 40

F

Fauna. Marshalltown Formation
Merchantville Formation
Mount Laurel Sand
state of preservation ..

Feldspar in light-mineral fraction

Fissurina marginata ..........................
orbignz/ana

Flemingites subspatulata

Formations, distributions .....

Frondicularia archiaciana

Fusinus rizacnairyensis ..

 
 
 

 

 

 

 

 

 
 

G

Garnet content in Merchantville Formation
and Mount Laurel Sand .
Gastrochaena sp .....................
Gaudryina bulloides .
ellisorae
stephensoni .
sp. A .......
Geruilliopsis ensiformis
Sp
Glaueonite ................................................................ 11
age 16
depletion
Glauconite-clastic ratios .
Glauconite sand, major constituent
Globigerintz (Rugoglobigeri'na) rugosa
Globigerinelloides messinae .....
Globorotalites michelinianus ..
Globatruncana area
cretacea
form'cam
linneiana
rosetta ..
subcircumnodifer
submgosa ..............
trican‘nata r.
ventricosa
wilsoni
Globulina lacrm’La
Glycymeris .............
mortoni

 
 
 
 
 
 
 
 

 

 
 
 
  
 
 

 

 
 
 
 
 
 
  
 

.36, 46, 48

 

Gober Tongue of Austin Chalk
Graciliala johnsoni .

 

 
 
   

37, 40, 42

 

 

 

  
 
 

sp ..
Greensand . ..24
Gregory Member of Pierre Shale . ..34
Gryphaea convexa ................................................ 45

51) 42
Gryphaeostrea vomer .................................... 42, 46

5p 42
Gyrodes abyssinus .

americanus ..47

major . 31

petrosus 42

spillmani . ..37

SD
Gyroidina depressa .

I L n

 

 

 

Hamulus major .
onyx .............
Sp 40

 

 

 

 
  
 
 
  
 
 
 
 
 

Page

Harri ' n 51) 40

Haustator lenolensis ............................................ 42
quadrilira
trilira ......

Heavy-mineral analyses
Hedbergella planispira
Hercorhynchus ..............

Hetero‘helix globulosa
planata .
pulchra .

Hoeglundina supracretacea

Hoploscaphites sp ...........

Hornerstown Formation

Hornerstown glauconite sand

Idanearca vulgaris ................................................ 36

sp ‘36
Illite—montmorillonite clay assemblage ""23, 25
Inoceramus proximus

sp ..........................
Investigations, previous
Iron oxide staining .......

 

.36, 40, 42, 46, 48

 

 

Isocardia sp ............................................................ 36
K
Kaolinite occurrence ............................................ 25
Kummelia sp ............................................ 3’7, 46, 49
L
LagerLa acuticosta ................................................ 53
quadralata .

 
  
 
 

substriata
sulcata semiinterrupta .
Laxispira ............... 38
lumbricalis .
monilifera .
5D
Legumen
concentricum
ellipticum
planulatmn
SD
Leptosolen biplicatus ............................................ 40
Light-mineral analyses
Lima acutilineata ........
kerri ...........
lorillardensis .
obliqua .
retiwlata .
whitfieldi

 

 

  
 
 
 
 
  
 
 
 
 
 
 
 
 
 
 
 
  

 

Linearia magnoliense
metastriata
Lingulina sp. A .
51). B .................................................................. 52
SD
Liopeplum thoracic-um
Liopistha alternata ......
protexta ......
Lithophaga sp .
Longitubus sp .....
Longoconcha sp ..
Lopha falcata
mesenten'ca
Lower glauconite sand of Red Bank Sand 7
Lower silt of Red Bank Sand ..................
Loxostoma gemma
plaita plaita
Lucina mattiformz‘s .
parva ....................
sp ..
Lupira variabilis .

 

 

 

46

   

 

M

 

Maestrichtian age of formations

 

 

 

Maestrichtian Stage ........................ ..

‘Magothy Formation .1 5, 34, 39, 44

Margaritella pumila .. ......... 45, 49
45, 47, 51

 

Margaritas abyssina
depressa
Marginulina taylorana

  
 
 

 

 

SD.

sp. B

sp. 0 :2
51). D ........................................................ 52

 

Marshalltown Formation 6, 10, 13. 15, 17,
24, 26, 34, 39, 41, 44

 

Martesia sp ............................................................ 42
Maryland, eastern, rock stratigraphic
studies “.20

 

Matawan Formation
Matawan Group .
Mathilda ...............
Megafauna, summary of Cretaceous
Megafauna fossils from the Chesapeake

 
 
 
 

and Delaware Canal .................................. 35
Megainvertebrate fauna from Merchantville
Formation .................................................... 35

Megapaieontoiogic studies
Melanatria cretacea ...........
Menabites delawarensis

(Delawarella)
delawarensis
Menuites complexus .....

Merchantville fauna, comparison
Merchantville Formation ............ 5, 11, 14, 1'7, 20,
24, 26, 85, 39, 44

 
 
 
  

Micrabacia hilgardi .

rotatalis .........
Micropaleontology ..
Mineral analyses, heavy

light
Molluscan fauna, comparison .
Monmouth Group ....................
Montmorillonite occurrence .
Morea marglandica .
Morgan beds

     

 

 

 

 
    
   

6‘, 12, la,

 

 

 

 

Mount Laurel Sand
18, 24, 26, 31, 34, 39, 1.4
Muscovite occurrence ............................................ 25
N
Nacatoch Sand of Texas ...................................... 35
Napulus Q7
’reesidei ,,,,, 42, 45, 47, 49
whitfieldi . ...................... 45
5D

 
 
 
 
 
  

 

Navesink Formation ..
age limits
Neithea quinquecostata
Nemodtm eufaulensis
grandis sohli

 

 

 

 

 

 

 

neusensis ........ ..
Sp .................................................. 36, 4o, 42, 46
N L 1' ' a1
canadensis 51, 53
spinosa ........... 51
N rbina 51
New Jersey molluscan fauna,
comparison ............................................ 38, 1,4
New Jersey rock stratigraphic studies ..
Nodosaria afi‘inis ............................................ .151
navarroana . x .1
obscura ......... ..51

   

Nonactaeonina sp
Nanionella austinana ..
Northern Atlantic Coastal Plain "28
Nostoceras ................................................................ 35
Nucula Q5

 

 

 

 

 

 

 

 

 

  

INDEX

amica

percrassa .. 42

1 1 ‘ 36

whitfieldi .......................................................... 36

SD 40
Nuculana .................

compressifrons

longifrons

marlboroensis . ,40

pittensis 45

Nuculana sp ..
Nudi‘uagus sp .. ..
Nuttallinella ............................................................ 51

 

0
Odessa, formations in Delaware ...................... 17
Oleneothyris harlani ...................................... 11, 17
Oolina 51

 

   
  

Ophiomorpha borings
Ornopsis (Pornosis) digressa
Ostrea biggsi ,_
cretacea
falcata ..

15, 22, 41

 

 

 

 
 

 

 
 
  
 
  
 
 
 
 
 

mesenter’ica ..... 36 42 45
monmouthensis
, 4 45
,7 46
tecticosta
5D
Owl Creek Formation of Alabama and
Mississippi .................................................. 31
P
Pac‘hymelania .................................................... 40, 41
Paladmete cancellaria ..37, 40, 43
gard’nerae
Panopea
decisa

Paranomia scabra
Parapachydiscus sp ..........
Parietiplicatum conicmn

Parmicorbula bisulcata .

Patella tenton'um
Pecten whitfieldi
(Camptonectes) bellisculptus .
SD 42

 

 
 
 
 

Peedee Formation ................................................ 35
Perissonata stephensani

protexta
Pernerina

Petrographic studies
Petrologic studies ,
Pl. 1 J yw

 

 

 

 

59

Page
Prairie Bluff Formation of Alabama and

   

 

 

Mississippi

Protoquartzites

Providence Sand of Georgia

P 1 Ta lepta
lirata ................................................................
W ’ na

 

Pseudogaudryinella capitosa ..
Pseudoglandulina lagenoides r.
Pseudoguembelina excolata costulata
Pseudomalaxis pilsbryi ............... . .........

5D
Pseudonodasaria appressa ..............
Pseudotextularia elegans elegans .

 

 

 

Pseudouvigerina seligi .......................................... 51
Pteria 45
petrosa .............................................................. 36
sp 4O

 

Pterocerella poinsettiformis
Pullem'a americana .....
Pyncnodonte convexa .
mutabilis .. ..................
Pyrifusus sinucostatus
Sp
Pyropsis perlata, ..
richardsam‘

..37, 47

  
 
  
 

 

 

Pyrulina cylindroides .

Q

Quadrimorphina allomorphinoides ..
Quartz, polycrystalline ......................

 

R

Radiopecten mississippiensis .............................. 46
weeksi
Ramulina arkadelphiana
Raritan Formation
Red Bank Sand ..... 6, 7, 8, 18, 26, 35
Regional correlation problems .,
Remera sp ......................................
Revised correlations of Upper Cretaceous
formations

 

  

 

 

 
 

 

 

 

Ringicula ................ ..37
Ripleyella sp ............................................................ 42
Ripley Formation of Alabama and
Mississippi ...31, 34
Rock fragments in light-mineral fraction ....24
Rock stratigraphic studies .............................. 1, 5
eastern Maryland, summary . ..22
New Jersey, summary ........... "10
Rugoglobigerina macrocephala .................... 51, 53

S

St. Georges Bridge ............. 11, 15, 16, 41

   

 

 

 

 

 

 
 

occidentalis ...................................................... 36 Sandy Hook quadrangle . 1
Pholas cithara ........................................................ 36 Santonian age pollen . .34
sp ‘ ‘36 Sargana stantom; ......... .37
Pierre Shale of western interior ................ 31. 34 sp 47
Pinm *8 Scambula perplana .............................................. 40
laqueata .. Scaphites hippocrepis .31, 37, 39. 45
sp ........... leei .............................
Placenticeras .. (Hoploscaphites) .
placenta 27 S 1' ' ' multhpinata .52
Planuli'na correcta .............................................. 52 Seabrookia stewarti .52
spissocostata A Section 1.1 miles west of St. Georges to
taylorensis ,. 1.3 miles east of St. Georges at Biggs

 
  
 
 

Plectina watersi .
Pleurostomella subnodosa
Plicatula
mullicanensis
Polim’nes altispira
Postiligata crenata
wordem‘
Potassium-argon dating method .1
Potomac Group ................................
Praeglobotruncana havanensis .
havanensis havanensis

 

 

 

 

 

Farm
Sedimentation cycle in New Jersey
Sepiolite occurrence
Serpula sp ..............
Shark teeth ___________
Siderite occurrence
Sigmamorphina semitecta terquemiana
Solyma sp ......
Sphenodiscus .
Spiroplectammi’na mordensis
Spondylus sp .............................

 

 
 
 
 
  
 
 
 
  
 

60

Steinkerns
Stilostomella stephensam .
Subgraywackes ..........
Submorttmiceras uddem _
Summary of Cretaceous megafauna
Summit Bridge ......................................
Syncuclonema conradi

   
 

 

 

 

 

 

 
   
 

simplicius ................
T
Telegraph Creek Formation .............................. 39
Tellina gabbi .
georgiana .
sp ...........

Tenea sp .....................
Terebratuli'rw. cooperi .
Textularia ripleyensis .
Tinton Sand ..................
Tintorium sp .................................................... 47, 49
Tombigbee Sand Member of Eutaw
Formation ....................................................

 

Trask sorting coefficient .
Trichatropis squamosus .....

 

 

 
 

 

 

Trigonia, ..
cerulia 35
eufaulenszs . .45, 46, 48
hwy ' ‘45

 

INDEX
Page
mortom' .............................. 4 5
thoracia. . .42

 
   
 
  
 
 
 
 
 

(Pterotrigonia) bartrami
(Scab'rotrigonm) sp ........

 

 

Tundora tuberculata

Turonian rocks .4

Turritella .............
encrinoides
lorillardensis
macmiryensis
marshalltownensis
merchantvillensis
quadrilira
tippana
vertebroides

 

 

 

 

 

U
Umbom'cardium .. ....44
umbonatum .V
Unicardium umbonatum ...................................... 36
51;) 46

 

Upper quartz sand of Red Bank Sand
Urceolabmm manmhiensis ..................

7. 11

 

 

Page
V

Vanilcoropsis ambiqua .......................................... 37
Veniella. conradi ................... 36, 42, 46, 48
Vetericardia crenalirata
subcircula
sp ........

 

 
 
 
 

 

Volsella julia

Volutomorpha sp .................................... 40, 42. 47
W

Wadeor - sp 48

W ’ ‘ de,’ M 45

 

 

Wenonah Formation .
Wicomico Formation
Woodbridge clay
Woodbury Clay
Woodsella typica. ............
Woodstown quadrangle

  
 

 

 

X

Xenophon; leprosa
5D

 
 

Yoldia gab band .
papyria

 
 

 

* U.S. GOVERNMENT PRINTING OFFICE: I870 O—SOB~36‘

 

7 QM”

:7?
5 ,

.. Landslides in the Vicinity of
“$757

the Fort Randall Reservoir,
South Dakota

 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 675

 

 

 

Landslides in the Vicinity of
the Fort Randall Reservoir,
South Dakota

By CHRISTOPHER F. ERSKINE

 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 675

A stuajz of some fundamental causes of landslides
in the Pierre Shale along the Missouri River trench

 

 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON 2 1973

UNITED STATES DEPARTMENT OF THE INTERIOR

ROGERS C. B. MORTON, Secretary

GEOLOGICAL SURVEY

V. E. McKelvey, Director

Library of Congress Catalog-card No. 72—60030?)

 

For sale by the Superintendent of Documents, U.S. Government Printing Office
Washington, DC. 20402 - Price $3.75 (paper cover)
Stock Number 2401—2200

CONTENTS

Abstract ___________________________________________
Introduction _______________________________________
Purpose and scope ______________________________
Fieldwork ______________________________________
Acknowledgments _______________________________
Geographic setting __________________________________
Culture ________________________________________
Physiography __________________________________
Climate _______________________________________
Vegetation _____________________________________
Geology ___________________________________________
Upper Cretaceous sedimentary rocks ______________
Niobrara Formation _________________________

Pierre Shale ________________________________

Sharon Springs Member _________________

Gregory Member _______________________

Crow Creek Member ____________________

De Grey Member _______________________

Verendrye Member _____________________

Virgin Creek Member ___________________

Mobridge Member ______________________

Elk Butte Member ______________________

Structure __________________________________
Tertiary and Quaternary deposits _________________
Ogallala Formation _________________________

Till _______________________________________
Alluvium __________________________________
Alluvium, colluvium, and loess _______________

Loess ______________________________________

Origin and development of Missouri River trench _______
Landslides-____________-________________» ___________
Types of landslides ______________________________
Rockfalls __________________________________

Soilfalls ____________________________________
Bedrock slumps and block glides ______________

Soil slumps ________________________________

Slow earthflows ____________________________
Mudflows __________________________________

Causes of landsliding in the Fort Randall Reservoir
area _________________________________________
Erosion ____________________________________

Ground water ______________________________

Weight ________________________________

Lubrication ____________________________

Hydrostatic pressure ____________________

Uniform hydrostatic pressure"--- _ _ _ _

Variations in hydrostatic pressure _____

Piping _________________________________
Miscellaneous causes of landsliding ____________
Relative importance of the landslide causes- _ _ _
Analyses of the Pierre Shale _________________________
Mechanical analyses _____________________________
Mineral composition- _ - _V ________________________
Montmorillonite __________________________________

"U
:2
"<3

CDQQDSDWWOOKIQRIOGO‘JOTUIUIAI‘FthkNWODIONNNi-l

Representative study areas __________________________
Method of selection _____________________________
Scope of investigations __________________________

Slope stability appraisal _____________________
Stable ground __________________________ ,
Stabilized landslides _____________________
Recently active landslides _______________
Reactivated landslides ___________________
Active landslides ________________________

Geologic mapping __________________________

Descriptions of individual areas ___________________

Area 1 ____________________________________

Area 2 _____________________________________

Area 3 _____________________________________

Area 4 _____________________________________

Area 5 _____________________________________

Interpretation of data ___________________________

Prereservoir slope stability ___________________

Correlation of landslides, slope angles, and

geologic materials _________________________
Preparation of data _____________________
Analysis _______________________________
Interpretation __________________________
Summary and conclusions ________________________

Ground-water investigations _________________________
Purpose _______________________________________
Method of investigations _________________________
Piezometer locations ____________________________
Results and interpretations ______________________

Relation between reservoir water level and
ground-water level ________________________
Relation between cyclic processes and ground-
water levels ______________________________
Behavior of ground water ____________________
Site A _________________________________
Site B _________________________________
Site C _________________________________
Site D _________________________________
Sites 1 and 2 ___________________________
Site 3 __________________________________
Site 4 __________________________________
Summary ______________________________

Landslide movements ________________________________
Methods of investigations ________________________
Descriptions of landslides ________________________

Highway 16 slump __________________________
Cable School earthflows _____________________
Cable School slump-earthflow ________________

Landing Creek slump-earthflow _______________

Paulson slump ______________________________

Surplus precipitation, ground water, slope stability:

corrections ______________________________________
Precipitation available for storage as ground water__

III

CONTENTS

IV
Surplus Precipitation—Continued Page Surplus Precipitation—Continued
Relation between precipitation and potential evapo- Correlation between surplus precipitation and ground-
transpiration at Pickstown _____________________ 58 water levels __________________________________
Cumulative precipitation surplus __________________ 59 Conclusion ____________________________________
Correlation between surplus precipitation and slope References ________________________________________
stability _____________________________________ 59 Index _____________________________________________

PLATE

ll.
12.
13.
14.

10.
16.
17—28.

29.
30.
31.
32.

TABLE 1.

mucuciuswp

ILLUSTRATIONS

[All plates are in pocket]

. Maps showing slope stability appraisals of areas 1, 3, 4, and 5, Fort Randall Reservoir.
. Chart showing classification of landslides.

Geologic and slope stability map and sections of area 2, Fort Randall Reservoir.

. Graph showing piezometer readings and reservoir water levels.
. Detailed geologic maps of selected slumps and earthflows in the Fort Randall Reservoir area.

. Map showing physical divisions of South Dakota ______________________________________________________
. Photograph of soilfall and slumping, left bank of Fort Randall Reservoir _________________________________
. Cross sections showing relation between slump and block glide __________________________________________
. Photograph of Landing Creek slump-earthflow ________________________________________________________
. Schematic cross section through a potential slump _____________________________________________________
. Photographs:

6. Highway 16 slump __________________________________________________________________________
7. Cable School slump-earthflow _________________________________________________________________
8. Active slump along the Fort Randall Reservoir shore ____________________________________________
9. Slumping along the face of a gravel terrace _____________________________________________________
10. Slumping in slow-draining alluvium, right bank of Fort Randall Reservoir __________________ , .......
Idealized diagram of conditions conducive to earthflows ________________________________________________
Photograph of three earthflows in colluvium and Pierre Shale, Cable School area __________________________
Diagrams showing effect of hydrostatic water pressure in fractures _______________________________________
Photograph of slump caused by highway fill placed at head of a potential landslide block ___________________
Graph showing particle-size distribution in five members of Pierre Shale __________________________________
Graph showing Pierre Shale mineral composition ______________________________________________________
Photographs:
17 . Area of Pierre Shale slopes considered stable ____________________________________________________
18. A low—level stable fill terrace at base of slopes composed of old stabilized landslides __________________
19. Recently stablized slump _____________________________________________________________________
20. Stabilized landslide terrain ___________________________________________________________________
21. Exposed slump along Fort Randall Reservoir Shore ______________________________________________
22. A recently active slump ______________________________________________________________________
23. A slump earthflow caused by reactivation of old stabilized slump block _____________________________
24. The head of an active landslide on southwest bank of Fort Randall Reservoir ______________________
25. Terrain on southwest side of area 2 ____________________________________________________________
26. Terrain west of Missouri River in area 4 _______________________________________________________
27. Blufl's along left bank of White River where river erosion causing active landslides __________________
28. East part of Cable School landslide area _______________________________________________________
Schematic diagram of piezometer installation __________________________________________________________
Photograph of Paulson slump, a reactivated slump in Pierre Shale _______________________________________
Graphs showing correlation between precipitation and potential evapotranspiration ________________________
Graphs showing correlation between piezometer water levels and cumulative precipitation surpluses __________

TABLES

A generalized stratigraphic section ____________________________________________________________________
Estimate of relative importance of agents involved in Fort Randall landslides _____________________________

. Localities of shale samples shown in figure 16 _________________________________________________________
- Percentage of total area of landslides in each class of landsude activity ___________________________________
- Slope stability conditions 0f lore-Quaternary deposits in area 2 southwest of Missouri River _________________
- Average" slope angles 0f Pierre Shale members along cross sections A—A’ to J—J’ ___________________________
. Ranking of Pierre Shale data ________________________________________________________________________
. Piezometer installations in South Dakota ___________________________________________________________ k, -

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65

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LANDSLIDES IN THE VICINITY OF THE FORT RANDALL RESERVOIR,
SOUTH DAKOTA

By CHRISTOPHER F. ERSKINE

ABSTRACT

The Fort Randall Reservoir, which first held water in 1952,
is one of the several multipurpose reservoirs created by the US
Army Corps of Engineers along the Missouri River. It is in
south-central South Dakota and extends from near the South
Dakota-Nebraska boundary upstream about 130 miles to the
northwest. The walls of the Missouri River valley and its tribu—
taries consist predominantly of Upper Cretaceous Pierre Shale,
a bentonitic claystone and shale that is subject to extensive
landsliding. Alluvium underlies terraces and comprises the flood-
plain deposits in the Missouri River trench.

The impounded water of the reservoir had little effect on
slope stability during the period of study. Emphasis was placed
on investigating the nature and causes of landslides along the
Missouri River trench above and below Fort Randall Dam.

The landslides along the trench are the following types: rock-
falls, soilfalls, bedrock slumps, soil slumps, slow earthflows,
mudflows, and slump-ea rthflows. The most common of these are
slump-earthflows, earthflows, soilfalls (along the reservoir
shore), and slumps, in that order.

All landslides are activated primarily by erosion and ground
water, which may be considered as general causes or as trigger
actions. General causes are long-term processes that decrease
overall stability of a slope and increase its potential for land-
sliding. Trigger actions are rapid, often recurring processes
that set off individual landslides in places where general causes
have already reduced stability of the slopes. The main general
cause of landslides is erosion. Ground water can act both as
general cause and trigger action where oversteep, potentially
unstable slopes exist. It can affect slope stability by increase
of weight of slope material in a potential landslide, lubrication,
hydrostatic pressure, and piping.

Analyses of the Pierre Shale indicate that it is mostly iso-
lated silt-size grains in a matrix of clay-size particles that are
predominantly montmorillonite. The silt grains do not inter-
lock; hence, the strength of the shale depends almost entirely
upon the montmorillonitic matrix.

Appraisal of slope stability in five representative areas, each
including about 25 square miles, suggests that the Missouri
River trench walls have been relatively stable during historic
time. Most of the active and recently active landslides are re-
lated to erosion by tributary streams, whereas many of the
old partially obscured landslide remnants, including most of
the larger slides, shown an apparent topographic relation to
the main river valley. Landslide activity probably was last at
a maximum during the latest glacial advance.

A statistical comparison, made for individual members of
the Pierre Shale, indicates a relation between montmorillonite
in the clay-size component and the average slope angles and

also a possible relation between slope angles and the relative
amount of landslide terrain. There is no statistical relation,
however, between montmorillonite and the relative amount of
landslide terrain. The conclusions are that all members of the
Pierre Shale along the Missouri River slide as a part of the
normal erosion process, and the angle at which individual
members develop a stable slope is a function of the montmoril-
lonite content in their clay-size portions.

The apparent relation between landslide activity and ground—
water conditions was explored in a ground-water observation
program from 1954 through 1959. Twenty porous tube piezo-
meters were installed at eight sites near the reservoir. Four of
the sites are in bedrock and four in alluvium. The observa-
tions indicate that ground water in the shale bedrock moves
primarily through fractures, and the direction and rate of
ground-water movement depends on the orientation and size
of the fractures.

Movements of control points established on five landslides—-
one earthflow, one slump, and three slump-earthflows—were
measured over a 3-year period. The resulting data indicate that
these three types of landslides have somewhat characteristic
activity patterns. Earthflows have one short period of activity
of a few days or weeks, after which they become stable. The
movement of slumps is small relative to their size. Most of the
movement probably occurs at one time, although minor move-
ments as the slump approaches equilibrium may continue for
several years. Slump-earthflows generally have a longer active
life than either earthflows or slumps, the active life of a
slump-earthflow being proportional to its size.

Possible correlations exist between (1) surplus precipitation
available for ground-water storage, (2) landslide activity, and
(3) ground-water conditions. Theoretical maximum potential
evapotranspiration values were calculated from climatic data.
The difference between actual precipitation and potential
evapotranspiration is the precipitation-surplus or deficiency
available to supplement ground-water supplies. The available
information shows a distinct correlation between surplus pre-
cipitation and landslide activity. Long-term surplus precipita-
tion values represented by a 12—month cumulafive-precipitation-
surplus curve were at a maximum in 1952 when landslide activ—
ity was at a maximum; long-term ground-water influxes, there-
fore, seem to be a general cause of unstable slopes. There are
usually precipitation-surpluses during the winter and early
spring, and most landslide activity occurs in the spring; short-
term ground-water influxes thus seem to trigger landslides. The
ground-water data from the piezometers are too limited to
either prove or disprove that the precipitation-surplus actually
affects ground-water conditions. The available data, however,
are fully compatible with the precipitation-surplus—landslide-

1

2 LANDSLIDES NEAR FORT RANDALL RESERVOIR, SOUTH DAKOTA

activity relation. It seems likely that times of maximum land-
slide activity occur when infiltration of surplus precipitation
appreciably augments the ground-water supplies. It may be
possible to predict periods of appreciable landslide activity by
appraising 12-month cumulative-precipitation-surplus curves.

INTRODUCTION

This report summarizes the results of landslide stud-
ies near the Fort Randall Reservoir in South Dakota
(pl. 1). The reservoir occupies the Missouri River valley
(Missouri River trench) and is formed behind the
Fort Randall Dam, located 5 miles above the point
where the Missouri River crosses the Nebraska-South
Dakota State line. The reservoir extends upstream
about 130 miles northwesterly nearly to Big Bend, a
large meander curve in the river about 10 miles above
Fort Thompson.

The walls of the trench in the segment containing
the Fort Randall Reservoir are composed primarily of
Pierre Shale, which here is virtually a bentonitic mud-
stone. Pierre Shale is very susceptible to landsliding
when it is saturated or nearly saturated; ground-water
conditions, therefore, have a close relation to slope
stability in the shale. Filling of the reservoir (dam
closure in 1952) has raised the free-water level in the
trench and is undoubtedly changing the ground—water
regimen in the area. The environs of the reservoir (pl.
1) are well suited to the study of the effect of chang-
ingground-water conditions on slope stability.

PURPOSE AND SCOPE

This study was undertaken to learn more about land-
sliding, particularly reasons for the failure of slopes
in bentonitic mudstone. The goal is not only to provide
general qualitative information but also to point out
specific problems for more detailed research. Factors
affecting slope stability were studied throughout a
large area, therefore, rather than exhaustive studies
made of particular landslides.

The scope is restricted to three specific problems of
landsliding. The first problem is to determine the rela—
tion between landslides and ground—water conditions.
Because the Pierre Shale is relatively impermeable, its
ground-water conditions will take many years to reach
equilibrium with. the free-water level in the reservoir.
Little can now be said, therefore, about the effect of
the reservoir on landsliding except where wave ero-
sion and saturation are causing landslides along the
reservoir shore. In this report emphasis is placed on
ground—water effects independent of the reservoir and
that result from seasonal precipitation variations as
well as short- and long—range climatic changes. The
second problem is to identify the factors that control

times and rates of movement of individual and col—
lective landslides. The third problem is to determine
whether there is a relation between composition of the
members of the Pierre Shale and their susceptibility to
landsliding. The effects on slope stability of major com-
positional variations, such as quartzite versus clay
shale, are obvious, but little is known about minor com-
positional differences between individual members of
the Pierre Shale.

The landslide investigation consisted of analysis of
the Pierre Shale, appraisal of selected study areas,
ground-water investigations, and measurement of land-
slide movements; based on these studies, correlation
was suggested between surplus precipitation available
for groundwater storage, landslide activity, and
ground-water conditions.

FIELDWORK

Most of the fieldwork was done during the summers
of 1952—55 inclusive. During 1956 about 1 month was
spent field checking and measuring landslide move-
ments. US. Geological Survey personnel at Huron, S.
Dak., made ground—water measurements during the
winters of 1954 (J an.—March) and 1954—55. They as-
sumed full responsibility for the ground-water pro—
gram in the fall of 1955 and continued to make pie-
zometer measurements intermittently through 1959.

In the field, data were plotted on maps and on aerial
photographs, and later they were transferred to base
maps. The landslide movements were measured by
periodically relocating control points on the landslides
with a transit either by triangulation or by closed
traverse. Porous tube piezometers were used to observe
ground-water levels. Subsurface samples for analyses
of the Pierre Shale were obtained with a power auger.

ACKNOWLEDGMENTS

The author was assisted in the field by W. A. Smyth
in 1952, Darrel Kroenlein for 6 weeks in 1953, J. E.
Garrison for 3 weeks and J. H. Smith for 5 weeks in
1954, and Herman Ponder in 1955. Members of the
US. Geological Survey, especially D. R. Crandell,
H. E. Simpson, and D. J. Varnes, visited the project
area and made many helpful suggestions.

The late Mrs. Helen Varnes accepted the author’s
duties when he resigned from the US. Geological Sur—
vey in 1957. Without her conscientious revision of the
original draft and later work on the manuscript, the
report could never have been completed. D. J. Varnes.
C. G. Johnson, and R. D. Miller made significant con-
tributions in further reviewing and revising the manu—
script for publication.

GEOGRAPHIC SETTING 3

The ground-water observation program is credited
to personnel in several agencies. J. R. Jones, F. C.
Koopman, and G. A. LaRocque, Jr., of the Huron,
S. Dak., office of the US. Geological Survey, were ad-
visers for the overall program. Information about por-
ous tube piezometers was furnished by W. W. Daehn,
E. E. Esmiol, and J. P. Gould of the US. Bureau of
Reclamation. W. H. Jackson of the US. Geological
Survey designed the device used to measure water
levels in the piezometers. The Omaha District, U.S.
Army Corps of Engineers, furnished a churn drill and
crew to install the piezometers.

The Omaha District, US. Army Corps of Engineers,
provided the project with maps, services, space for
field offices, and storage facilities, and their personnel
cooperated with project personnel in every way pos-
sible. A. H. Burling, J. A. Trantina, and L. B. Under-
wood, especially, gave the author many good sugges-
tions at numerous discussions and field conferences.

Many other persons and agencies contributed to the
project. Among them were theSouth Dakota State
Geological Survey and the South Dakota State High-
way Commission. The city ofiicials of Chamberlain,
S. Dak., allowed piezometers to be installed on city
land. Landowners near Fort Randall Reservoir permit-
ted landslide investigations on their land.

GEOGRAPHIC SETTING
CULTURE

The land around Fort Randall Reservoir is used en—
tirely for farming and ranching. Generally, crops are
raised on the relatively flat uplands, terraces, and
flood plains, and the valley walls are used for grazing
cattle and sheep.

The only permanent towns near the reservoir and
their 1960 populations are Chamberlain, 2,598; Fort
Thompson, 150; Oacoma, 312; and Pickstown, about
600. Pickstown, located at the Fort Randall damsite,
was built by the US. Army Corps of Engineers.

The roads are mostly in the uplands somewhat re-
mote from the reservoir. US. Highway 16 crosses the
reservoir at Chamberlain, and US. Highway 18 crosses
the Missouri River at the Fort Randall Dam. The up-
lands have a good network of State and county roads.
There are few roads along the valley walls of the Mis-
souri River and its tributaries; in most places the reser-
voir shore can be reached only on foot or by four-
wheel-drive vehicles.

The Chicago, Milwaukee, St. Paul and Pacific Rail-
road line from Mitchell, S. Dak., to Rapid City, S.
Dak., crosses the reservoir at Chamberlain. A spur
track built by the Corps of Engineers to carry con-
struction materials to the Fort Randall Dam runs

from the Chicago, Milwaukee, St. Paul and Pacific
Railroad line at Lake Andes to the damsite 7 miles to

the south. ,
PHYSIOGRAPHY

The Fort Randall Reservoir lies entirely within the
Misouri River trench (fig. 1), one of the 12 physical
divisions of South Dakota of Flint (1955), but locally
the landslide areas extend eastward into the Coteau du
Missouri and westward into the Pierre hills.

Missouri River trench—The Missouri River valley
constitutes the Missouri River trench physical division
(fig. 1). It is a broad southeast-trending trough, 300—
650 feet deep, cut into the eastward—sloping Missouri
Plateau. Between the Nebraska border and Big‘ Bend
(pl. 1), the trench is 11/2—5 miles wide, and the floor is
%—11/2 miles wide. The walls of the trench, cut in eas-
ily eroded Pierre Shale, have a rugged “badlands”
topography—alternating steep-sided gullies and spurs.
Terrace remnants are common. Where large segments
of old terraces remain, they protect the trench walls
above from direct rivererosion. As a result, in these
places the walls have not been greatly affected by post—
terrace valley cutting, and the topography is more
subdued than in unprotected parts of the trench.

Pierre hills—The Pierre hills physical division is
characterized by mature topography of low rolling hills
and a well—integrated drainage system. Downcutting by
the Missouri River has rejuvenated the drainage sys-
tem, and steep-walled youthful valleys now are en-
croaching on the rolling uplands.

Coteau du Missouri—The Coteau du Missouri is a
glaciated eastward extension of the Pierre hills. Most
of the gently rolling surface is ‘mantled by glacial drift
that masks any preglacial drainage pattern. Compara-

 

 

FIGURE 1.—Physical divisions of South Dakota. 1, Minnesota
River-Red River lowland; 2, Coteau des Prairies; 3, James
River lowland; 4, Lake Dakota plain; 5, James River high-
lands; 6, Coteau du Missouri; 7, Missouri River trench;
8, northern plateaus; 9, Pierre hills; 10, Black Hills; 11,
southern plateaus; 12, Sand Hills. From (Flint, 1955, fig. 1.)

4- LANDSLID'ES NEAR FORT RANDALL RESERVOIR, SOUTH DAKOTA

tively few youthful streams extend far beyond the lim-
its of the Missouri River trench into the Coteau; con-
sequently much of the area drains into intermittent
ponds in numerous closed depressions.

CLIMATE

South Dakota has a dry subhumid climate with hot
summers and cold winters, US. Department of Agri-
culture (1941) and Visher (1954). Within the reser-
voir area, precipitation and temperature decrease mark—
edly northwestward. Average annual precipitation is
about 23 inches at the dam and about 18 inches at
Fort Thompson. More than 7 5 percent of the precipi-
tation falls from early April through September, and
40—50 percent of the total precipitation falls in May,
June, and July. Average January temperatures range
from 20° F at Fort Randall Dam to 16° F at Fort
Thompson; average July temperatures are about 75° F
for the entire area. A temperature range of 130° F,
from —25° F minimum to 105° F maximum, can be
expected in a normal year. Winds, predominantly
northwest in winter and southeast in summer, have an
average velocity of 10—12 miles per hour.

VEGETATION

The natural plants of the uplands are drought-re-
sistant grasses. Shrubs and trees grow in the valleys
and gullies. Many good stands of trees, predominantly
cottonwoods, are along the river bottomland not flooded

by water in the reservoir. Trees growing away from
permanent streams become increasingly scarce toward
the northwest end of the reservoir area, reflecting the
regional decrease in precipitation. Cultivated are corn,
the main crop in the southeast end of the reservoir
area, Wheat, the main crop in the northwest end, and
some oats, soybeans, and sorghum.

Vegetation commonly is lusher on slopes Where land-
slides have occurred for the following reasons: the
excess water that encourages landsliding also encour-
ages vegetation; the closed depressions and fissures that
result from landsliding trap water which would nor-
mally run off a smoother stable slope.

GEOLOGY

This report is concerned with the geologic forma-
tions of the Fort Randall Reservoir area relative to
their involvement in landslides along valley walls of
the Missouri River and its tributaries. The following
geologic descriptions and the generalized stratigraphic
section (table 1) are presented primarily as back-
ground information for discussion of the landslides.
More detailed information on the regional geology is
given by Petsch (1946), Flint (1955),Crandell (1958),
Simpson (1960), and Schultz (1965).

UPPER CRETACEOUS SEDIMENTARY ROCKS

The Upper Cretaceous sedimentary rocks are virtu-
ally the only consolidated deposits in the area. They

TABLE 1.——A. generalized stratigraphic section of the Fort Randall Reservoir area

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Era System Series Group Unit Thickness (it)
Alluvium, colluvium, and loess Generally <10
>. Loess 30:1:
E
3 Slow draining
.2 g Alluvium 100:1:
g 0’ Fast draining
E
D Till Locally as much as 100
>~ S
E § Ogallala Formation 403:
a; =
E4 (14
Elk Butte Member >180
Mobridge Member > 100
3 3 Virgin Creek Member 50—100
65 _._._..
o 3 § fi Verendrye Member 90—170
s o 3 Montana Q ——
g g g E De Grey Member 20—50
8 o ._.
g 5; :5 °" Crow Creek Member 10:}:
a.
:5" Gregory Member 30—90(7)
Sharon Springs Member 35—55
Colorado Niobrara Formation 16—90 exposed (prereservoir)

 

 

 

GEOLOGY 5

include the most stable (Niobrara Formation) and the
least stable (Pierre Shale) deposits in the area.

NIOBRARA FORMATION

The Niobrara Formation, a soft impure fossiliferous
limestone, was widely exposed in the lower part of the
walls of the Missouri River trench before the dam was
built. Now, however, most of the formation in the
downstream half of the area is permanently sub-
merged.

The Niobrara crops out as nearly vertical blufl’s
bordering the river and its flood plain. Before the com-
pletion of the dam in 1952 these bluffs were from a few
feet to more than 85 feet above the river level (Petsch,
1946, fig. 12). The exposed thickness above the river
varied considerably, due to the uneven upper surface
of the formation and also to the gentle open folding
of the Cretaceous beds. Near Fort Randall Dam, the
top of the Niobrara, at an altitude of 1,310 feet, was
about 70 feet above river level (1,240-ft altitude). Up-
stream at the site of the former Wheeler Bridge, only
16 feet of Niobrara was exposed. Near Chamberlain, the
Niobrara-Pierre contact is 1,420 feet in altitude, and
about 90 feet of Niobrara was exposed above the Mis—
souri River. The formation passes below river level
near the lower end of Big Bend at an altitude of about
1,350 feet.

The Niobrara Formation, the oldest exposed bed-
rock in the area, is the uppermost formation of the
Upper Cretaceous Colorado Group. The Niobrara rocks
that crop out within the report area can be traced di-
rectly to the Niobrara type locality of Meek and Hay—
den (1861, p. 422—424) near the junction of Niobrara
Creek and the Missouri River about 35 miles southeast
of the Fort Randall Dam.

The Niobrara Formation is a dark-gray impure
chalk containing many microscopic shells of Foramini-
fera and Ostracoda. Small light-colored shell frag-
ments and elastic particles in a darker grou'ndmass
give the chalk a salt-and-pepper appearance when
closely examined. Weathering changes the color from
dark gray to pale orange. (All color terms conform
with terminology used in the ‘Rock-Color Chart” by
Goddard and others (1948).)

The rock is massive and coherent, with a toughness
and resilience that makes it difficult to fracture, al-
though it is soft enough to be scratched by a finger-
nail. The nearly horizontal bedding is best shown by
partings a few inches to 5 feet apart and by thin clay
and gypsum layers along. many of the bedding planes.
Nearly vertical joints 1 inch to several feet apart are
conspicuous in most exposures.

PIERRE SHALE

The Pierre Shale, overlying the Niobrara Forma-
tion, constitutes most of the valley walls of the Mis-
souri River and its tributaries. The Pierre underlies
a mature topography of low, gently rounded hills
slashed by recently cut steep—sided gullies and valleys,
and locally disrupted by landslides.

In this report the Pierre is divided into eight mem-
bers following Crandell’s classification (1958, p. 8—19),
although individual members are not everywhere map-
pable, either because contacts are obscured or because
the members are too similar lithologically. Because
classification changes by Schultz (1965) after recor-
relation of marl beds in the Gregory and Crow Creek
Members were (made after completion of the landslide
studies, they have not been incorporated in this report.

The maximum thickness measured was 423 feet at
the site of the former Wheeler Bridge 15 miles above
Fort Randall Dam. Although a complete section was
not compiled in the upper part of the area, the fol-
lowing figures for sections, including the lower six
members, suggest that the whole formation thickens
several hundred feet within the length of the reser—
voir. At Wheeler Bridge, the total thickness of the six
members is 228 feet; in the Vicinity of Chamberlain, it
is at least 400 feet (interpreted from Petsch, 1952).

SHARON SPRINGS MEMBER

Before the filling of the reservoir the Sharon Springs
Member of the Pierre Shale was exposed throughout
the report area. The normal operating water level of
the reservoir now covers this member south of the site
of the former Wheeler Bridge. The Sharon Springs
Member at Wheeler Bridge is 35 feet thick. The thick-
ness in the upper part of the reservoir near Chamber-
lain is uncertain: Warren and Crandell (1952, p. 4)
inferred 55 feet thickness from measurement of weath-
ered shale chips in the section, but they saw no actual
exposures of the shale more than about 15 feet thick.

The contact between the Pierre Shale and the under-
lying Niobrara Formation is sharp. The Sharon
Springs Member commonly crops out in relatively
steep slopes above the chalk, as the unweathered shale
is stable and can stand in nearly vertical slopes. As
weathering progresses, the shale breaks down into
chips which tend to ravel down the slope face until a
slope at the angle of repose, generally about 30°, is
formed.

The Sharon Springs Member is olive to brownish-
dark—gray bituminous shale. Fish scale fragments are
widely disseminated through the member, and in many
places the bituminous content is large enough to sup-

6 LANDSLID‘ES NEAR FORT RANDALL RESERVOIR, SOUTH DAKOTA

port combustion. Thin bentonite beds, generally less
than 1 inch thick, are common, and secondary gypsum,
either as disseminated selenite crystals or as inter-
growths in the bentonite beds, is plentiful. A yellow
powdery mineral, identified as a secondary hydrous
sulfate of iron (Simpson, 1954, p. 63), in places coats
the shale along parting and joint surfaces.

Partially weathered outcrops of the Sharon Springs
Member are characterized by stacks of horizontal chips
one-eighth inch or less thick and generally less than 2
inches in diameter. The rock is relatively hard (barely
marked by a fingernail) and the only member of the
Pierre Shale that does not readily weather to clay.
Bedding is not apparent in fresh exposures, but hori-
zontal fissility develop on weathered outcrops.

GREGORY MEMBER

The Gregory Member of the Pierre Shale underlies
. moderate grass-covered slopes throughout the area bor-
dering the Fort Randall Reservoir. Locally, rapid ero-
sion produces fairly steep slopes, although nearly all
slopes more than 25 feet high are flattened by subse—
quent landsliding. The unit, which is separated from
the underlying Sharon Springs by a sharp contact, is
the lowest member of the Pierre Shale that will be com-
pletely exposed when the reservoir is at minimum pool
level (1,310 ft).

Thickness of the Gregory Member increases from
about 35 feet in the lower part of the reservoir (Gries,
1942, p. 31) to 50—90 feet near Chamberlain (Warren
and Crandell, 1952, p. 5).

Near the dam, the Gregory corresponds lithologically
to the lower beds of the type section (Crandell, 1958,
p. 10) and is a dark-gray marl underlain by a basal
silty layer and overlain by a dark-gray calcerous shale.
In the upper reaches of the reservoir, the Gregory is
a predominantly noncalcareous gray bentonitic clay-
stone that closely resembles the upper part of the
Gregory in the Pierre area (Crandell, 1958, p. 10), al—
though a marl layer is locally present at or near the
base.

The appearance of the outcrops varies with the lith-
ology. The marl is a dense resistant rock that locally
forms small ledges less than 10 feet high. The shale
weathers rapidly; fresh shale alters to bentonitic clay
in a few years, passing through a partially weathered
stage of chips up to about 1 inch in diameter and one-
eighth inch thick. The claystone weathers directly to a
bentonitic clay without passing through a chip stage.
Marl beds, bentonite beds, and occasional concretionary
layers are the only depositional indications of bedding.
Unweathered shale and claystone appear to be homo-

genous, but partially altered shale develops a fissility
apparently parallel with the bedding.

CROW CREEK MEMBER

The Crow Creek Member consists of a blocky un-
bedded marl underlain by a few inches of laminated
siltstone. The Crow Creek is remarkably persistent al-
though the siltstone is only 10—15 inches thick and the
marl is generally 7—10 feet thick. The marl bed has
been recognized along the Missouri River trench for
more than 250 miles from Yankton, 70 miles down-
stream from Fort Randall Dam, to the vicinity of
Pierre, almost 200 miles upstream from the dam. The
siltstone is present upstream from the former Wheeler
Bridge site, but it has not been identified downstream.

Exposures of the Crow Creek Member become in—
creasingly distinctive from the dam toward the upper

. part of the reservoir. In the lower part of the reservoir

the member typically is covered by slope wash or soil
and is visible only where recently eroded. In the upper
part it stands out very noticeably as a light band in
the otherwise dark Pierre Shale. The contact with the
Gregory Member is sharp and disconformable, al—
though no evidence of channeling has been observed.

Crandell (1952, 1958) made a detailed study of the
Crow Creek Member, and the following brief lithologic
description is largely a summary of his data. The un—
weathered marl is light gray; upon exposure it oxi-
dizes to grayish orange. Secondary iron oxide in the
siltstone commonly gives it a yellowish-brown appear-
ance. The marl is soft and shows no indication of bed-
ding, whereas the siltstone consistently shows bedding
and breaks into thin slabs along bedding planes as it
weathers. In some outcrops secondary iron oxide has
cemented the siltstone to form ledges approximately
1 foot high; in other places it is cemented in varying
degrees by calcium carbonate.

DEGREY MEMBER

The DeGrey Member of the Pierre Shale exposed
in the valley walls bordering the reservoir is a massive
dark—olive-gray bentonitic claystone containing numer-
ous thin bentonite beds and, in the north half of the
area, abundant iron-manganese concretions. A black
band of residual concretions makes DeGrey outcrops
a striking feature of the walls of the Missouri River
trench around the upper part of the reservoir. The
basal few feet of the DeGrey generally contains no
concretions, and the contact between the Crow Creek
and DeGrey Members is a relatively sharp transition
from marl to noncalcareous claystone. The DeGrey of
the Fort Randall area closely resembles the shale and
bentonite facies described by Crandell (1958, p. 13—

GEOLOGY 7

14), but the thick basal siliceous shale facies described
by Crandell apparently is not present in the report.
area.

The member ranges in thickness from 23 feet at the
Wheeler Bridge site (Gries, 1942, p. 31) to about 50
feet near Chamberlain (Warren and Crandell, 1952,
p. 7).

In a fresh cut the claystone appears well consoli-
dated, but it weathers rapidly to gentle slopes blank-
eted by 4-8 inches of clay with a characteristic coarse,
porous crumblike structure when dry. Wherever the
more resistant bentonite beds and layers of concretions
are eroded, a steplike topography develops. Continued
weathering and erosion, however, break down these
layers and leave the concretions scattered as a lag con-
centrate on the shale.

The DeGrey is very susceptible to landsliding, espe-
cially in the southern part of the area. Most exposures
show at least minor displacements, most of which can
be attributed to landsliding.

VERENDRYE MEMBER

The Verendrye Member is present throughout the
report area. Most fresh outcrops are on active and re-
cently active landslide blocks because exposed clay—
stone weathers rapidly and is blanketed by residual
clay soil. No complete sections were measured during
the present investigation, but Petsch (1946, p. 37)
showed 80 feet of thickness at the Wheeler Bridge site
and about 170 feet at Crow Creek, 10 miles north of
Chamberlain.

The contact between the Verendrye and the underly-
ing DeGrey Member becomes less distinct southward
along the reservoir. In the northern part of the reser-
voir, the contact can readily be recognized at the top
of the iron-manganese concretion zone in the DeGrey.
In the southern part of the reservoir, landslides and
vegetation commonly obscure the contact. Moreover,
the absence here of a conspicuous concretionary zone
in the DeGrey results in a similar lithology that makes
distinction between the two members difficult in the
few good exposures available.

Lithologically, the Verendrye is a bentonitic olive-
gray claystone very similar to parts of the DeGrey
Member. In the Fort Randall area, the Verendrye has
far fewer concretions and fewer discrete bentonite beds
than the DeGrey. In the Pierre area to the northwest,
however, Crandell (1958, p. 15) reported abundant
concretions in the Verendrye and a gradational con-
tact between it and the DeGrey.

The Verendrye Member breaks down to bentonitic
clay after a few months of exposure. The material
closely resembles the weathering products of the De-

Grey except for the absence of lag concentrates.
Throughout the area the Verendrye appears to be un-
stable and susceptible to landsliding.

VIRGIN CREEK MEMBER

The Virgin Creek Member, defined by Searight
(1937, p. 35) and described by Crandell (1958, p. 15—
16), is present above the Verendrye Member through-
out the area. It consists of a noncalcareous bentonitic
shale at the base and grades into noncalcareous benton-
itic claystone at the top. In the upper half of the reser-
voir it is the highest member of the Pierre Shale ex—
tensively exposed in the walls of the Missouri River
trench.

The Virgin Creek Member is about 50 feet thick
near the dam and increases in thickness to the north-
west. Poor outcrops make direct measurement difficult
in the northern part of the reservoir, but comparison
of the Chamberlain quadrangle geologic map (Petsch,
1952) and the topographic map suggests that the mem-
ber is about 100 feet thick near Chamberlain.

Outcrops typical of the Virgin Creek Member are
rare in the smooth, grass-covered slopes. Fresh out-
crops are found only where stream erosion or landslides
have recently exposed the member. Outcrops of the
shale facies show a characteristic silvery sheen derived
from the shale chips. In outcrops weathered to a ben-
tonitic clay, it is difficult to distinguish the Virgin
Creek Member from the underlying Verendrye Mem-
ber, as apparently there is no sharp contact between
them. The contact, which is inferred to be gradational
over a vertical distance of 5—10 feet, is usually hidden
by slump blocks derived from weathered Virgin Creek
beds.

Both the shale and claystone are dark gray to gray-
ish black where fresh and brownish gray where weath-
ered. Concretionary layers and thin bentonite beds as
much as 1 inch thick are common. The basal shale,
with the exception of the Sharon Springs Member, is
the most fissile material in the Pierre Shale. It weath-
ers to small chips generally less than 1 inch in diameter
and one-eighth-inch thick. After prolonged exposure
the chips disintegrate to a bentonitic clay similar to the
soils derived from the DeGrey and Verendrye Mem-
bers.

The transition of shale to claystone is gradual. No
obvious break separates the two facies, but the upper
part of the member is less fissile and quickly weathers
to bentonitic clay.

MOBRIDGE MEMBER

The Mobridge Member of the Pierre Shale consists
of partly indurated marl and calcareous shale beds

8 LANDSLIDES NEAR FORT RANDALL RESERVOHL SOUTTT DAKOTA

very similar to those described in the Pierre area by
Crandell (1958, p. 16—17). In the south half of the
Fort Randall area, the Mobridge crops out in the Mis-
souri River trench walls bordering the reservoir; in
the north half, it crops out only in the uplands away
from the trench.

The Mobridge is about 100 feet thick near the Fort
Randall Dam (Gries, 1942, p. 25). Although it thickens
northwestward along the trench, no data are available
on thicknesses in the northern part of the report area.

The lithology has considerable lateral variation.
Along the Missouri River trench in South Dakota, the
member grades from bentonitic marl (containing
roughly 35 percent calcium carbonate) near Fort Ran-
dall Dam to calcareous bentonitic shale (containing
less than 10 percent calcium carbonate) near the North
Dakota border (Curtiss, 1950, p. 7 5). The color changes
from medium dark gray in fresh exposures to yellow—
ish gray and buff in completely weathered beds.

The rock appears massive and firm, although it is
more friable than some shale members of the Pierre.
Concretionary layers are common. As weathering pro-
gresses, partings and color bandings 1/2—1 inch thick
develop parallel to the bedding. The contact between
the calcareous Mobridge beds and the noncalcareous
Virgin Creek beds is sharp, although the two mem-
bers intertongue locally.

The Mobridge Member is more resistant to erosion
than the underlying members. Although it typically
forms grass-covered hillsides, the slopes are generally
more pronounced and, in many places, the Mobridge
crops out as fairly steep buff-colored slopes. The steep-
er slopes suggest that it is less susceptible to landslid-
ing than are most members of the Pierre.

ELK BUTTE MEMBER

The youngest unit of the Pierre Shale is the Elk
Butte Member, a locally calcareous bentonitic clay-
stone and shale. Exposures are confined to the uplands
and the upper trench walls bordering the south half
of the Fort Randall Reservoir.

The original thickness of the Elk Butte Member in
this area is unknown because the upper part was eroded
and later overlain unconformably by upper Tertiary
beds. At the Wheeler Bridge site, Gries (1942, p. 31)
recorded nearly 100 feet of Elk Butte beds overlain
by 80 feet of Fox Hills Formation. The Fox Hills as
used by Gries is now considered to be part of the Elk
Butte Member (Stevenson and Carlson, 1950), and
therefore the total thickness is now estimated to be
180 feet in this location.

Exposures of the Elk Butte Member are similar to
those of the underlying Mobridge, and the contact

between the two members is transitional. The top of
the calcareous beds is commonly considered to be the
top of the Mobridge (Crandell, 1950, p. 2338; 1958, p.
18), but because some calcareous beds occur above the
supposed base of the Elk Butte Member in the lower
part of the reservoir, color is also used to separate the
two members (Crandell, 1958, p. 18). The weathered
Elk Butte material is generally darker than the Mo-
bridge. The color ranges from olive gray where par-
tially weathered to moderate brown where fully weath-
ered; unweathered material is rarely seen. A distinctive
feature noted by Crandell is the presence of yellowish-
brown calcareous concretions throughout the Elk Butte.
In the Fort Randall area concretions are commonly
scattered throughout the member and are also concen-
trated locally in lenses and discontinuous beds.

The Elk Butte Member appears to be well consoli-
dated. As it weathers it develops slight fissility, and
partings are spaced about one-fourth inch apart paral-
lel to the bedding. Continued weathering easily alters
the material to bentonitic clay. Weathering also brings
out a conspicuous color banding in outcrops of consoli-
dated shale and claystone.

STRUCTURE

The exposed rocks of Cretaceous age are flat-lying
undisturbed sediments. Some minor open folds un-
doubtedly exist, but they are too small to affect land-
sliding in the area. The Niobrara—Pierre contact has
a vertical range of almost 150 feet within the length
of the reservoir. These fluctuations in altitude may
represent open folds.

Exposures of the Niobrara Formation and the Pierre
Shale show some faulting. Most of the faults have no
more than a few feet of displacement and rarely can
be traced between outcrops. Subsurface damsite in—
vestigations by the Corps of Engineers have revealed
intense local faulting of both formations.

Almost all the coherent outcrops show randomly
oriented near-vertical joints, which presumably are
present in all members of the Pierre Shale as well as in
the Niobrara Formation.

TERTIARY AND QUATERNARY DEPOSITS

The Tertiary and Quaternary sediments are mostly
unconsolidated terrestrial deposits. They include the
Ogallala Formation of Pliocene age, glacial till, allu-
vium, colluvium, and loess. All these deposits form
more stabe slopes than does the Pierre Shale. Only a
few of the landslides along the reservoir occur wholly
in the Tertiary and Quaternary deposits.

GEOLOGY 9

OGALLALA FORMATION

The Ogallala Formation of Pliocene age is a hetero-
geneous‘mixture of silt, sand, and fine to medium
gravel locally cemented to form orthoquartzite. The
Ogallala is restricted to the south half of the reservoir
area. Uplands and buttes protected by resistant caps
of orthoquartzite of the Ogallala rise above the gen-
eral land surface.

The original thickness of the formation is unknown
and the present thickness varies because of erosion.
The average thickness in the area is about 40 feet.
Many landslides in Pierre Shale have extended up
into the Ogallala Formation, and masses of Ogallala
material are found in landslide remnants on slopes
below their true stratigraphic locations.

The orthoquartzite is grayish olive in fresh exposures
and weathers to yellowish gray. Unconsolidated parts
of the formation generally are pale shades of gray.

TILL

Unsorted glacial deposits blanket the uplands along
much of the east side of the reservoir and are exposed
in many places along the east wall of the Missouri
trench. Till occurs chiefly in small isOlated patches on
the west side of the reservoir.

Because glacial deposits tend to fill in and smooth
out irregularities in the preglacial topography, the
thickness of these deposits varies greatly over short
distances. Generally, the deposits are less than 50 feet
thick although locally they may be at least twice as
thick.

In the Fort Randall area till is primarily silt and
clay wth some pebbles, cobbles, and boulders. Mechan-
ical analyses of the till at Chamberlain show that
about 70 percent is of silt and clay size (Warren and
Crandell, 1952, p. 44). Most of the till is partially
weathered to some shade of brown; fresh til] is gen-
erally a dark gray.

ALLUVIUM

In this report the term “alluvium” is applied to all
water-laid deposits of Quaternary age and includes
glacial outwash as well as stream and flood-plain de-
posits. The general category has been subdivided into
fast-draining alluvium and slow-draining alluvium.
Fast-draining alluvium is sufficiently permeable to
offer little resistance to the passage of water. Where it
borders the shore of a lake or reservoir, there is no
appreciable lag between fluctuations in the water level
and resulting water table fluctuations within the allu-
vium. Slow-draining alluvium has relatively low per-
meability, and the movement of water is restricted.
There is slower adjustment of the water table within

slow—draining alluvium to changes of water level in
an adjacent body of water.

Extended studies of alluvial deposits enabled the
author to use field methods to set a relatively consistent
boundary between fast- and slow-draining alluvium.
Fast-draining alluvium was predominantly composed
of particles of coarse-sand size (0.5—1.0 mm) or larger;
slow-draining alluvium was predominantly composed
of particles of medium-sand size (0.5—0.25 mm) or
smaller.

The alluvium either covers nearly flat valley bot-
toms or is exposed in terraces. The valley bottom allu-
vium is widespread and deep at least along the Mis—
souri River trench. Flint (1955, p. 147) gave a depth
of 189 feet to the bedrock floor of the Missouri River
trench at Fort Randall Dam. Because valley bottom
alluvium is comparatively unimportant as a landslide
medium, the author did not attempt to separate it into
fast- and slow-draining groups. Most is permanently
flooded by the reservoir or is too far up the tributaries
to be affected. Some minor landsliding may be antici-
pated in the zone where periodic drawdown of the
water level will expose banks of slow-draining alluvium.

The terrace alluvium is considerably more important
for the purposes of this report. Alluvial terraces are
common along the walls of the Missouri River trench
and, in places, form the reservoir shore. Locally, ero-
sion has produced a topographic reversal so that allu-
vial deposits cap uplands bordering the trench.

The thickness and composition of the terrace allu-
vium vary. In some exposures the alluvium is only a
thin veneer over bedrock; in others it forms terraces
as much as 80 feet high. Preponderance of the slow— or
fast-draining alluvium varies from one outcrop to the
next, but most terrace deposits are composed of fast-
draining alluvium overlain by a few feet to perhaps
25 feet of slow-draining alluvium.

Many landslides resulting from the combined effects
of wave erosion and changes in saturation have al-
ready developed in fast—draining and slow-draining
terrace aluvium. Continued sliding may be expected
until the slopes reach equilibrium.

ALLUVIUM, COLLUVIUM, AND LOESS

These deposits are composed of mixtures of allu-
vium, colluvium exclusive of landslide material, and
loess. Acording to Stokes and Varnes (1955), collu-
vium is earth material moved or deposited mainly
through the action of gravity. The grain size common-
ly is no coarser than fine sand, although locally there
are thin lenses of pebbly material. The material be—
haves as slow-draining alluvium. These deposits are

10 LANDSLIDES NEAR FORT RANDALL RESERVOIR, SOUTH DAKOTA

rarely more than 10 feet thick and commonly occur
as relatively small areas in the bottom of small valleys.

LOESS

Loess, a porous wind-deposited sediment composed
predominantly of silt with minor amounts of fine sand
and clay, forms a patchy blanket along the Missouri
River trench walls and on the bordering uplands. In
most of the Fort Randall area it is a few inches to a
few feet thick, although locally it is more than 30 feet
thick.

When dry, loess has sufficient strength to stand in
vertical bluffs. This characteristic apparently results
from the bonding action of clay particles that adhere
to the silt and sand grains (Holtz and Gibbs, 1951, p.
15). When the clay becomes wet, the bonding forces
are reduced and the loess loses its strength. Loess bluffs
saturated by the reservoir water soon collapse, and the
fallen material is removed by wave erosion.

ORIGIN AND DEVELOPMENT. OF MISSOURI
RIVER TRENCH

A brief discussion of the origin and development of
the Missouri River trench is pertinent because nearly
all the landslides in the area are the result of the
downcutting and widening of the trench.

History—The Missouri River trench is a compara-
tively recent feature. Until mid—Pleistocene time the
major drainage in central South Dakota was easterly
(Flint, 1955, pl. 7). During the Illinoian Glaciation
ice dammed the east—flowing streams so that they were
forced to drain southeastward along the ice front
(Warren, 1952). By the time the ice retreated, this
melt-water channel, the incipient Missouri River
trench, had become well established in the easily
eroded Pierre Shale. Most of the downcutting in the
trench probably occurred during the Sangamon Inter-
glaciation (Warren, 1952, p. 1151). Successive glacial
advances in Wisconsin time partly filled the trench
with outwash and till. Although most of these deposits
were removed by renewed downcutting after each ice
advance, numerous terraces and terrace remnants along
the trench remain from this period.

The Missouri River has reexcavated its valley in
Holocene time and now has a gradient of'about 1 foot
per mile. Until the reservoir was filled most of the
river’s energy was spent cutting laterally into the
valley walls.

.llecham'cs of erosion—In the course of its develop-
ment the Missouri River trench was excavated in the
Pierre Shale primarily by mass wasting and stream
erosion, and to a minor degree by slope wash. In this
multiple effort, landsliding probably was at least as

effective as stream cutting. Slope wash probably was
most effective on slopes where there were few if any
active landslides.

Erosion by landsliding is caused by and in many
places perpetuated by stream action. Downward and
lateral cutting by streams oversteepens and undercuts
the valley walls. Blocks of material adjacent to the
streams thereby become unstable and break loose, slid-
ing down and outward until they reach a stable posi-
tion. Movement of these blocks leaves unsupported
oversteepened slopes above, and eventually other blocks
will slide. By repetition of this process, the entire val-
ley wall slowly slides toward the stream, which in turn
makes further sliding inevitable by its removing the
landslide debris when it reaches the valley bottom.

The upslope migration of a zone of active landslides
is never as obvious in the field as it would seem from
the preceding description, because in nature many
factors other than removal of toe support affect slope
stability. At numerous places along the walls of the
Missouri River trench, nevertheless, a slide sequence
grades upslope from old, barely discernible, stabilized
landslide blocks along the riverbank, through more re-
cently stabilized slide blocks, into areas of active land-
sliding near the uplands. In some places, moreover, new
landslides are developing along the riverbank, start-
ing a new cycle of landsliding.

Over a long period of time the cumulative effect of
several landslide cycles may be considerable lateral
and vertical movement, although individual blocks are
not necessarily transported a great distance during a
single cycle. Wave erosion along the west shore of the
reservoir about 10 miles upstream from Fort Randall
Dam has exposed an old landslide containing isolated
blocks of Ogallala Formation more than 350 feet below
the outcrop level of the formation in the nearby up-
lands.

LANDSLIDES

Because landslides are the result of variable combi-
nations of material and movement, it was inevitable
that several systems of clasifying landslides were de-
vised. The Highway Research Board classification
(Varnes, 1958) based on two main variables—type of
material and type of movement—was selected as the
most satisfactory for this investigation. Plate 2 is a
graphic summary of this system, with notes added
concerning the materials involved in the most common
landslides in the Fort Randall Reservoir area.

The fundamental concepts of landslides and their
behavior are stated concisely by Varnes (1958, p. 20),
as follows:

* f * the term “landslide” denotes downward and outward
movement of slope-forming materials composed of natural rock,

LANDSLIDES ‘ 1 1

soils, artificial fills, or combinations of these materials. The
moving mass may proceed by any of three principal types of
movement; falling, sliding, or flowing, or by their combinations.
* * * Normal surficial creep is excluded. Also most types of
movement due to freezing and thawing (solifluction), together
with avalanches that are composed mostly of snow and ice,
are not considered as landslides.

TYPES OF LANDSLIDES

Most landslides in the Fort Randall Reservoir area
involve at least two types of movement and commonly
more than one type of material. One type of movement
predominates in most of the slides, and if more than
one kind of material in involved, generally only one
is responsible for the landsliding. In the slump—earth-
flow type of landslide, two kinds of movement occur,
slump and flow, and a hyphenated compound term is
used to describe them.

The various types of landslides along the reservoir
are discussed in the order they are listed on the land-
slide classification chart (pl. 2), rather than according
to their abundance or size in the Fort Randall area.

ROCKFALLS

Small rockfalls occur in the Niobrara Formation
where the chalk beds are undercut by stream and wave
erosion or are weakened by prolonged weathering. The
blocks rarely are more than a few feet in maximum
dimension and the process usually borders between
raveling and rockfall.

SOILFALLS

Soilfalls—in till, slow-draining alluvium, the allu-
vium, colluvium and loess unit, and loess—(pl. 2),
caused by stream and wave erosion, are very common
where fine-grained unconsolidated deposits crop out
along the reservoir (fig. 2) or along the tributary val-
leys. Generally the blocks are a few feet wide and no
more than 30 feet long. The overall importance of soil-
falls as a landslide process is usually overlooked be-
cause the individual blocks are relatively small. Prob—
ably more than half of the fine-grained unconsolidated
material undergoing erosion along the reservoir shore
is entering the water as soilfall blocks.

Although soilfalls are a common result of erosion,
their mechanics are relatively simple. Soilfalls result
from removal of support at the base of nearly vertical
or vertical bluffs. Slopes must be so steep that unstable
blocks tend to fall downward and outward instead of
sliding along the surface of failure. Saturation, seep-
age pressure from ground water moving toward a free
face, and unbalanced pore-water pressures may con—
tribute to soilfalls, but they are never primary causes.

 

FIGURE 2—Soilfa11 and slumping along the left bank of Fort
Randall Reservoir, Charles Mix County, S. Dak. This land-
slide consists of two distinct types of movement, soilfall at
the water’s edge and slumping upslope. The material is slow-
draining alluvium capped by a few feet of loess and underlain
a short distance below water level by Pierre Shale. Several
small overhanging blocks of loess are visible in the center
of the photograph. Photographed September 27, 1954.

BEDROCK SLUMPS AND BLOCK GLIDES

Slumps (rotational movement) and block glides
(planar movement) (pl. 2; fig. 3) represent the end
members of the series of landslide types caused by
shear failure of coherent blocks. The relation between
the two slide processes is shown in the schematic cross
sections of figure 3. If slumps have cylindrical surfaces
of shear failure, the shear surface appears in cross.
section as the arc of a circle with a radius of finite
length, r (fig. 3A). If the curvature of the shear sur-
face is reduced. the radius, r, will increase, gradually
approaching infinity. The extreme case, where the
radius, r’, is infinitely long and the shear surface is
planar, is represented by the block glide (fig. SB). Be-

 

    
    

Surface of
tension
failure

5. BLOCK GLIDE

FIGURE 3. Relation between slump (A) and block glide
(B), end members in the series of landslide types in-
volving shear failure of coherent blocks.

12 LANDSLIDES NEAR FORT RANDALL

cause of the similarity in causes and behavior, block
glides in the Pierre Shale are considered slumps.

Slumping in the Pierre Shale is the most common
type of landslide movement in the project area. In
some parts of the Missouri River trench the trench
walls are almost entirely slump blocks. These slides
vary greatly in size. One slide, the Landing Creek
slump-earthflow (fig. 4), has a scarp about 1,300 feet
long at the head of the slump section; but some slides
are no more than 30 feet across.

Although rotational movement predominates, most
slumps seem to be composite, with both rotational and
planar movement. Where the shale is relatively ho-
mogenous, the slump movement is rotational along
a concave-upward shear surface. Abundant bentonite
beds in the Pierre, however, represent zones of weak-
ness. If a shear surface encounters a bentonite bed
near the base of a slump block (fig. 5), the shear sur-
face becomes planar, and movement is translated to
glide. Sometimes there is contemporaneous glide move—
ment along several parallel shear planes at the base of
a slump. If a shear surface encounters bentonite beds
at the back of a slump block above the base, it cuts
through the beds and remains curved.

Most slumps start as movement of a single block
(fig. 6, lower half of slump). If the block is large or if
the shear surface is irregular, deformation caused by
the movement breaks the single block into several
smaller units. Where there is sufficient water, the toe
of the slump, which is commonly highly fractured and
most easily saturated, may become an earthflow (fig.
7). The original block continues to move, either as a
single unit or in pieces, until it reaches a stable posi-
tion. If the toe of a slump is removed by agency of
nature or man, the landslide will not become stable
until all or most of the slide material has been re-
moved (fig. 8).

 

FIGURE 4.—Landing Creek slump-earthflow. The upper part of
the landslide consists of slump blocks moving out on an old
terrace remnant. Where gullies had eroded the terrace, the
slump blocks received no support. and the material disin-
tegrated to form earthflows moving down the gullies.
SEJANE14 sec. 25, T. 100 N., R. 72 W., Gregory County,
S. Dak. Photographed September 12, 1953.

RESERVOIR,

SOUTH DAKOTA

   

Planar shear 27 Curved shear

FIGURE 5,—Schematic cross section through a potential slump
with a bentonite bed controlling development of the shear
surface.

Slump movements become more complex as move-
ment continues. The material in the unsupported scarp
above the initial slump block generally cannot stand
long without support on its downhill side, and soon
a second block breaks loose. If the initial slump block
continues to move, the second block follows, leaving a
new unstable scarp at the head of the landslide. By
repetition of this process, the slump area gradually
migrates upslope until the individual blocks reach
stable positions (figs. 7, 8).

SOIL SLUMPS

Soil slumps—alluvium, colluvium and loess unit,
loess, and till ?—(pl. 2) were rare before the filling of
the reservoir but they have been fairly common along
the shoreline since, and probably will continue to occur
for many years. The lower part of most of the soil
slumps is submerged, and many have been completely
inundated by the rising water. Till adjacent to the up-
lands is involved in many slumps, but failure of the
Pierre Shale underlying the till generally is respon-
sible. ’

a

.
" Presser ; recign

 

FIGURE 6.——-Highway 16 slump. A slump southwest of U.S. High-
way 16 about 1 mile south of the center of Chamberlain,
S. Dak. The lower part of the slump, with a pressure ridge
caused by forward and upward thrusting of the slump block
at the toe, is inferred to be the original slump block. The
upper part is a graben formed by collapse after the original
slump block moved and left the upslope material unsup-
ported. Photographed October 14. 1954.

LANDSLIDES 13

 

FIGURE 7.——Cab1e School stump-earthflow. NE%NE% sec. 25, T. 103 N., R. 72 W., Brule County, S. Dak. The upper part of the
slide (above points 5, 6, and 7) is numerous slump blocks. In the scarp between points 3 and 4 and points 5, 6, and 7, the
slump blocks are disintegrating to chunks of weathered shfale and clay. Water from springs near point 4 mixes with the
disintegrated slump blocks and forms an earthflow (the lower part of the slide below points 3 and 4). Numbers refer to
control stations established to measure movement. Photographed October 14, 1954.

Soil slumps now occurring along the reservoir shore
range from those caused primarily by saturation to
those caused by erosion. The slump shown in figure 9
has developed along the face of a terrace composed of

 

FIGURE 8.—Active slump along the Fort Randall Reservoir
shore in Gregory County, S. Dak. Wave erosion at the toe
of the slump is breaking up the slump blocks and removing
the material. Photographed September 27, 1954.

472-733 0 - 73 - 2

gravel (fast—draining alluvium) blanketed by loess and
colluvium. A small wave-cut bench about 8 feet above
the water surface represents the reservoir water level
before a drawdown beginning about 2 months before
the photograph was taken. The wave-cut bench on the
slide block is closely alined with wave-cut benches on
each side of the slide area, a feature indicating that
little or no movement has occurred since the drawdown.
Also, the fact that the bench is as well developed on
the landslide as it is on either side indicates that the
slump occurred before wave erosion started. These
facts indicate that neither minor wave erosion nor
drawdown noticeably affected the slump block after it
became stabilized. The slump movement apparently is
related to saturation of the materials composing the

14 LANDSLIDES NEAR FORT RANDALL RESERVOIR, SOUTH DAKOTA

 

FIGURE 9.—Slumping along the face of a gravel terrace blanketed by colluvium and loess. The limited amount of wave erosion
implies that saturation, rather than oversteepening of the shore, was the primary cause of slumping. Fort Randall Reservoir
shore, Charles Mix County, S. Dak. Photographed October 24, 1953.

slump block. Failure began after saturation destroyed
the intergranular bonding effect of capillary forces in
the gravel (see p. 18). Once the block began to settle,
part of its weight was supported by water, the inter-
granular friction in the gravel was reduced by the
buoyant effect of the water, and further settling
occurred.

A soil slump caused primarily by wave erosion is
shown in figure 10. This photograph, taken at the same
time as figure 9, shows slumping in slow-draining allu-
vium. Here also, there has been a temporary drawdown
of about 8 feet in the reservoir water level. There is
no indication of a wave-cut bench, however, despite
the fact that wave erosion is more active here than
in near the area shown in figure 9. The slump shown
in figure 10 was still moving at the time it was photo-
graphed, and the combination of landslide movement
and wave erosion apparently obliterated all evidence
of a wave-cut bench. Saturation followed by friction
from draining water and unbalanced pore-water pres-

 

FIGURE 10.——S1umping in slow-draining alluvium along the
right bank of the Fort Randall Reservoir, Gregory County,
S. Dak. The area is exposed to‘wave erosion which, by re-
moving support at the toe of the slump block, is probably
the primary cause of slumping. Photographed October 24,
1953.

sure probably decreased the stability of the slow-drain-
ing alluvium; however, the area should have become
stable after the water level dropped. A logical explana-
tion of the slump’s continuing movement is that re-
moval of support at the toe by continuing wave ero-
sion was the main cause of slumping and was still
preventing stability at the time the photograph was
taken.
SLOW EARTHFLOWS

Slow earthflo-ws—weathered Pierre Shale, till, and
colluvium—(pl. 2) (Varnes, 1958, p. 38) are the most
common type of slope failure in plastic unconsolidated
materials along the reservoir. Most of the earthflows
are small, less than 100 feet Wide by 150 feet long.
Where a larger area is involved, the upper part of the
landslide generally is a well-developed slump, and the
slide is classified as a slump-earthflow.

Earthflows form only on slopes that are composed
of a mantle of plastic, unconsolidated material under—
lain by relatively coherent impermeable material. Two
conditions are responsible for this restriction. Earth-
flows form only in material that is sufficiently porous
to hold enough water to make it sufficiently plastic to
flow as a mass or to be converted into a viscous fluid.
Generally this qualification applies only to clay-rich
colluvium or weathered shale and till. Also, earthflow
material must be saturated, or nearly saturated, before
it will flow. Where relatively impermeable material
is overlain by more permeable material, water perco-
lating downward from the surface will stop at the con-
tact and build up a saturated zone in the mantle (fig.
11). Sections of the mantle will fail by flowing if the
saturated zone is thick enough and the slope steep
enough. Blocks of unsaturated material commonly are
carried along on the surface of the earthflow.

LANDSLIDES 15

     
     

\\

\\\\ 11".:
\\\
\\\

‘\\\
\\\

\
\\.\\

\.

Arrows Indicate direction of movement of
downward percolating water

 

Zone of saturated weathered shale

FIGURE 11.—Idealized diagram of conditions conducive to
earthflows.

The three earthflows shown in figure 12 are typical
of those along the Fort Randall Reservoir. They have
formed in shale-rich gravelly colluvium and weathered
Pierre Shale, all underlain by relatively competent
shale. The small flow shown in the lower left corner
of the photograph has virtually no slump movement.
In the middle of the photograph is a flow in transition
from slump-earthflow to earthflow. The upper half of

the flow consists of many slump blocks so small that the
overall behavior of the material more closely resembles
flowage than movement of unit slump blocks. The third
flow, on the right in the photograph, is the most com-
mon type. Although there are one or two large coherent
slump blocks at the top, over three—quarters of the
area involved is a true flow.

MUDFLOWS

Mudflows characterized by the rapid flow of a satu-
rated mass of material are confined to the weathered
Pierre Shale along the Missouri River trench. Though
viscous, they are much more fluid than earthflows and,
once started, they flow on very gentle slopes. Old flows
closely resemble, and are locally incorporated in, allu-
vial fans at the mouths of gullies.

Most members of the Pierre Shale weather to benton-
itic clays that when dry develop a very coarse, porous,
crumblike structure. During heavy rainfalls this open
structure rapidly absorbs large quantities of water
before the wet bentonite expands and reduces the per-
meability. The saturated mass of weathered shale be-
comes .a mudflow when added water has increased the
weight and lessened the cohesion of the clay so much
that it is no longer stable on a slope.

 

FIGURE 12.——Oable School earthflows‘, NWIA sec. 30, T. 103 N., R. 71 W., Brule County, S. Dak. Three earthflows in gravelly
colluvium and weathered Pierre Shale. The two larger flows have numerous small slump blocks in their upper portions.
Note vehicle on top of ridge for scale. Photographed July 7, 1952.

16 LANDSLIDES NEAR FORT RANDALL RESERVOIR, SOUTH DAKOTA

CAUSES OF LANDSLIDING IN THE FORT RANDALL
RESERVOIR AREA

The causes of landslides are in two general groups:
(1) basic processes which slowly reduce the stability of
a mass of material and (2) trigger processes which in
themselves are of minor importance but which, when
added to the stresses already operating in a potential
slide area, are sufficient to set the mass in motion. The
trigger actions are more obvious and often are errone-
ously considered the dominant causes of slides. A trig-
ger process, however, can start a landslide only after
an area has become unstable through the operation of
other factors. Eliminating possible trigger actions,
nevertheless, can prevent or at least postpone many
landslides.

EROSION

Erosion, the main cause of landsl-iding along the res-
ervoir, operates both as a basic cause of movement and
as a trigger action. As a basic cause, it creates the
topography that makes the downward and outward
movement of landslides possible. Landsliding could
not continue in structurally stable South Dakota if ero-
sion did not create steep slopes. Erosion-becomes a trig-
gering process when it removes from the toe of a
potential landslide material which otherwise would
serve as a buttress (figs. 8, 10).

GROUND WATER

Ground water is the most versatile cause of land—
slides. It can affect slope stability by means of weight,
lubrication, hydrostatic pressure, and piping. Some of
these increase landslide stresses; others decrease sheer
strength in potential slides. Ground-water conditions
may be the trigger action or simply the general cause
of instability.

WEIGHT

The effect of the weight of ground water on a poten-
tial landslide is not easily evaluated. Addition of
water to earth materials increases their density because
air in the voids is replaced by water; the greater den-
sity then produces some increase in the stresses within
the earth materials. The {present studies have not fur-
nished sufficient data to determine if an increase in
stress due to greater density will necessarily be accom-
panied by a decrease in stability.

LUBRICATION

Lubrication by water is one of the oldest explana—
tions regarding the disastrous effects of ground water
on the stability of slopes. Consequently, such lubrica—
tion is often acepted as the trigger action in most land—
slides that closely followed periods of heavy ground—

water intake. The nature of the material to be lubri-
cated and its reaction to water must be considered in
order to analyze the lubricating effects of water in
landslides along the Fort Randall Reservoir. Fresh
Pierre Shale is a coherent aggregation of close-packed,
interbonded particles of silt and clay size. Its present
character is explained by the history of its deposition
and compaction.

The sediment that comprises the Pierre Shale was
deposited on the bottom of an inland sea as a mud
composed of loosely bonded aggregates of poorly ori-
ented particles that were relatively admixed with large
quantities of free and adsorbed water. As the deposits
thickened, compaction gradually broke down the poorly
bonded, unstable aggregates. The platy clay-mineral
grains probably developed the horizontal orientation
that gives fissility to the shale, and much of the free
water was squeezed out by the reduction in pore space.
At this stage the material became a soft clay.

Compaction of the Pierre Shale continued as the
overburden increased until much of the adsorbed water
was driven from between the particles. The particles
became closer packed, and molecular forces between
particles formed a relatively tight bond. In subse-
quent periods of uplift, erosion removed much of the
overburden, but molecular forces bonding the particles
apparently remain strong enough to prevent re—expan-
sion of the shale under most conditions.

The rapid weathering of exposed Pierre Shale to a
poorly bonded clay indicates, however, that the ad-
sorbed water layer was still sufficiently thick to prevent
the molecular forces between particles from developing
a bond between solids. When overburden pressures are
removed, therefore, the attractive forces between the
adsorbed water and available free water are greater
than the molecular forces between the particles. Addi-
tional water is drawn into the adsorbed water layer,
reducing the bonding forces between particles. The
effects of weathering are aggravated by the presence
in the Pierre Shale of montmorillonite, a clay capable
of swelling by adsorbing water within its molecular
structure (p. 25).

Behavior of unconsolidated material not directly
derived from Pierre Shale depends on the size of the
particles. In materials in which clay or fine silt is a
binder, the area of intergranular contacts is high in
proportion to the volume of solids. Molecular forces
are important, therefore, and the material behaves
much like Pierre Shale. In coarser grained material
the area of intergranular contacts is small in propor-
tion to the total volume of solids; the effects of molecu—
lar attraction are less and lubrication by water is a
less important factor in stability.

LANDSLIDES 17

The shear strength along the surface of contact be-
tween two solids is related to friction between the sol-
ids. If a liquid is placed so there is direct contact
between the two solids, shear will occur in the liquid,
which has much less shear strength than the solids.
Reduction of friction by allowing shear to occur in
some medium with very little shear strength is the basic
principle of lubricants.

Terzaghi’s theories (1950, p. 91) that a very thin film
of water around a particle provides full lubricating
effect and that most materials are always fully lubri-
cated do not seem entirely valid with regard to the
sediments along the Fort Randall Reservoir. Full
lubrication implies shear within the lubricant; there—
fore, the shear strength of a material should equal
that of the lubricant. Such conditions occur only locally
and intermittently in any of the materials along the
reservoir. In fact, full lubrication during movement is
approached only in the more fluid types of flows.

Lubrication in Pierre Shale slumps, though probably
never complete, is a major cause of movement. Ground-
water investigations (see section “Ground—Water In-
vestigation”) indicate that the regional water table is
high enough to saturate permanently most of the shear
surface in large slumps. In smaller slumps the shear
surface generally is saturated for at least 4 months of
each year. Even in saturated shale, lubrication is not
complete, however, because a combination of molecular
forces and overburden pressures binds the particles
(including adsorbed water layers) together at their
contacts. The pressure of the saturating water nor-
mally is not great enough to penetrate these contacts
and lubricate where friction is greatest. Although shale
is not fully lubricated even in zones of permanent or
semipermanent saturation, its lubrication is as complete
as is possible for the given conditions.

Lubrication is more complete in flows than in slumps.
An active flow is essentially an assemblage of solid
particles, or aggregates of particles, in a matrix of
water, and behaves like a viscous liquid. The shear
strength of flow material, as a result, is much less than
that of solid material in a dry state. In some mud-
flows it approaches that of water, indicating almost
complete lubrication.

The difference in the degree of lubrication in Pierre
Shale slumps and in flows is due to differences in ma-
terials and environment. Slumps occur in coherent
materials that generally have sizable overburden pres—
sures along the surface of failure. Flows occur in
near-surface unconsolidated materials where coherence
is relatively slight and overburden pressures are
negligible.

Lubrication generally has a secondary effect in
slumps in unconsolidated materials. If enough water
is present, the failure is by flowage instead of by shear.
When flow occurs in unstable material underlying co-
herent material, movement in the coherent block may
resemble a slump.

The effect of saturation on apparent cohesion prob-
ably is a common trigger action for slumps in uncon-
solidated materials. Apparent cohesion is the cohesion
developed by surface tension at air-water interfaces in
materials than contain water but are not saturated
(Terzaghi and Peck, 1948, p. 126). Saturation destroys
air-water interfaces, and the resulting loss of apparent
cohesion directly reduces stability of the material.
Saturation also reduces the cohesion between the
grains, and as a result more water can enter the ad-
sorbed water layers as a lubricant.

The effects of lubrication on soil slumps (unconsoli-
dated materials) are not as great as on slumps com-
posed of Pierre Shale. The only exception is slum-ping
in till. Being fairly compact material derived largely
from Pierre Shale, till behaves like Pierre Shale.

The effects of lubrication cannot be classified on all
landslides either as a general cause of decreased stabil-
ity or as a trigger action. In general, however, lubrica-
tion by permanent or semipermanent saturation prob-
ably results in decreased stability. Lubrication by peri-
odic or occasional inflow of ground water commonly
is a trigger action.

HYDROSTATIC PRES S URE

The effects of hydrostatic pressures in ground water
have increasingly been emphasized as landslide causes.
Terzaghi (1950), one of the chief proponents, sum-
marizes the engineering viewpoint on effects of hydro-
static pressures.

Many of the theoretical principles of hydrostatic
pressure, though not directly applicable in nature,
can be combined with empirical data to yield quanti-
tative information. For example, the theoretical dis-
cussion of hydrostatic pressures that can develop in
shale fractures cannot be used quantitatively in nature.
Water pressure changes can actually be measured,
nevertheless, and the application of theoretical reason-
ing to these data will determine the changes in forces
acting on the shale along fractures. Thus, water levels
in the standpipes of piezometers within stable shale
have been known to rise more than a foot in less than
a month. A 1-foot rise in water level represents 62.4 psf
(pounds per square foot) increase in pressure. This
increase in pressure acting on a surface 10 feet square
creates a force of more than 3 tons.

18 LANosLIDEs NEAR FORT RANDALL RESERVOIR, SOUTH DAKOTA

Hydrostatic pressures are either uniform or vari-
able. Uniform hydrostatic pressures create static
ground-water conditions. Ideally, pressure can occur
in unconfined water as a result of the weight of over-
lying ground water, in which case the pressure is di-
rectly proportional to the depth below the local water
table; or else the pressure can occur in water confined
to a permeable zone overlain and underlain by rela-
tively impermeable materials. In the latter the pressure
theoretically would have no direct relation to the over-
lying water table.

UNIFORM HYDROSTATIC PRESS URE

Independence between unconfined static ground
water and the surrounding material is a basic concept
of soil mechanics. Under static conditions the total
pressure at any point in saturated material composed
of incompressible grains is equal to the pressure exerted
by the material (effective pressure) plus the pressure
exerted by the contained water (neutral pressure). The
two component pressures act independently of each
other.

Hydrostatic pressure in confined static ground water
behaves much like a hydraulic jack; pressures in the
fluid are constant throughout any horizontal stratum
in the system, and pressure exerted anywhere on the
fluid system is transmitted through the entire system.
A small increase in pressure over a large area thus can
represent a major increase in force. A vertical rise
in the hydraulic head of a small fracture connected
with a horizontal permeable stratum can also create
a tremendous increase in the total hydraulic force in
the stratum.

Pierre Shale is the only material, with the possible
exception of till, along the Fort Randall Reservoir in
which pressure in confined static ground water may
be important. The Pierre is a generally massive shale
with very low permeability. Fractures are numerous,
however, and investigation (see p. 50) shows that
they carry most of the moving ground water. Ground
water in these fractures reacts like confined water to
pressure changes.

The effects of hydrostatic pressure in fractures
within the Pierre Shale are demonstrated schematic-
ally in figure 13A, a cross section through a shale bank
containing a horizontal permeable parting 40 feet be-
low the top. It is assumed that the parting is sealed at
the surface to permit static conditions. Another frac-
ture, a steeply dipping joint, intersects the parting and
crops out at the top of the bank. The block outlined
by the two fractures and the surface of the shale
represents a potential landslide.

When the fractures are filled with water, the pres-
sure is proportional to the height of water. The water
pressures throughout the parting shown in figure 13A
are caused by the 40-foot head of water in the joint.
Although water pressures exert force in all directions,
the water pressures acting on the potential landslide
block are the present concern. An essentially horizontal
pressure at the back of the block pushes it laterally;
an upward pressure along the base of the block reduces
friction (see below). If the total forces from these com-
bined pressures is great enough, the block becomes an
active landslide.

Reducing friction by increasing hydrostatic pres-
sures in confined ground water can renew movement in
old landslides as well as initiate movement in new
slides, the only difference being that in old landslides
the surface of failure forms the permeable fracture
(fig. 131)).

An analysis of vertical pressures on a small block
of shale (block X, fig. 13A) illustrates the potential
effect of hydrostatic pressures. When the fractures are
dry, the vertical pressures on block X are a downward
pressure from the weight of the overlying shale and
equal upward pressure transmitted to the potential
slide block from the shale below the parting (fig. 133).
If an average density of 155 lb per cu ft is assumed
for the shale, the magnitude of each force acting on
block X is about 6,200 psf.

When the fractures are filled with water (fig. 130),
the downward pressure on block X remains the same,
but about 2,500 psf of upward pressure is now exerted
by the water. Inasmuch as total upward pressure still
equals 6,200 psf. the pressure transmitted through solid
shale particle contacts now is only 3,700 psf. The re-
duction of the upward-acting solid-to-Solid pressure to
about 60 percent of its original amount correspondingly
lowers friction along the base of the block and in-
creases the chances of movement along the parting.

VARIATIONS IN HYDROSTATIC PRESSURE

One important effect of lateral changes in hydro-
static pressure results from friction created by molecu-
lar attraction between the water and the solid particles
betWeen which it passes. This drag of moving water
exerts a force on particles known as seepage pressure
(Terzaghi and Peck, 1948, p. 54; Terzaghi, 1950, p.
99). Where the pressure gradient is steep, seepage
pressures may become great enough to trigger land-
slides.

The effectiveness of seepage pressure depends on the
particle size of the material on which it acts. In coarse
gravel and other fast-draining materials, resistance to
flow is slight, and generally large seepage pressures do

LANDSLIDES 19

 

    

Water pressure

Water

 

1 6,200 lbs per 6,200 lbs per
sq ft weight sq ft weight
of shale of shale

 

 

 

 

2,500 lbs per sq ft
water pressure

3,700 lbs per sq
ft transmitted
l through shale

 

, 6,200 lbs per sq
B l ft transmitted
l through shale

 

Joint

Water pressure

Permeable parting/

 

Shale block

I/X

Water pressure/

Density of shale:155
lbs per cu ft

l

40 ft

I m

Seal/

 

 

FIGURE 13.—Effect of hydrostatic water pressure in fractures Within relatively impermeable shale. A, potential landslide block;
B, pressure exerted on block X when fractures are dry; 0, pressures exerted on block X when fractures are filled with
water; D, old landslide block where the surface of failure is the permeable fracture.

not develop. Pressures caused by seepage in clays prob-
ably can be considered minor, also. In clay, the finest-
grained of slow-draining materials, water pressure is
virtually static. Slow-draining materials in the effec-
tive size range of silt and fine sand are most affected
by seepage pressures because they are coarse enough
to permit considerable movement of water, yet fine
enough to develop large seepage pressures. Slope fail—
ures in which seepage pressures may be the trigger
action occur in silt and fine sand along many reservoirs
subject to rapid large drawdowns (Terzaghi, 1950, p.
99). Sudden drawdown of the free water level creates
a steep pressure gradient in the ground water. The re-
sulting movement in the ground water creates seepage

pressures that may be large enough to trigger land-
slides.

The effects of saturation and drainage on the bond-
ing forces of capillary water combined with the effects
of seepage pressures are responsible for marked differ-
ences in the behavior of fast-draining alluvium and
slow—draining alluvium.

Fast-draining alluvium becomes less stable as it is
saturated, and it regains its stability as it drains. As
water saturates fast—draining alluvium it quickly fills
nearly all the pores and eliminates the air-water inter-
faces. As a result, the bonding effect of surface tension
is destroyed, and the alluvium becomes less stable. As
the alluvium drains, it soon regains the original condi-

20 LANDSLIDES NEAR FORT RANDALL RESERVOIR, SOUTH DAKOTA

tion in which capillary water bonds the particles.
There is no appreciable friction between the draining
water and the alluvium, and the water drains too rap-
idly to build up significant pore-water pressure.

Several factors cause slow-draining aluvium to be
appreciably more stable when saturated than fast-
draining alluvium. When the level is raised in an
adjacent body of water, the low permeability of slow—
draining alluvium resists entrance of the water. In-
stead of rapidly filling the pores, the water becomes a
buttress against the alluvium, thus making the allu-
vium more stable. Moreover, air trapped by the Slowly
infiltrating water preserves some of the air—water in-
terfaces and so the bonding effect of surface tension
is not entirely destroyed. The adsorbed water layer on
the surface of every particle (Terzaghi and Peck,
1948, p. 10—17) also increases the stability of slow-
draining alluvium. Water in the adsorbed layer is less
fluid than normal water and as a result has greater
shear strength. The adsorbed water layer, consequently,
has little effect in coarse-grained alluvium. In the finer
materials of the slow-draining alluvium, however, the
proportion of voids smaller than 0.2 micron wide be-
comes significant and the adsorbed water layers become
important forces in helping the material resist shear.

Two forces tend to reduce the stability of slow-
draining alluvium when it is draining. If the water
level falls rapidly in a body of water in contact with
Slow-draining alluvium, the water in the alluvium can-
not escape as rapidly as the free water level drops.
Then the friction between the alluvial particles and
the escaping water creates an internal stress which
acts toward the free face of the alluvium. At the same
time the pore-water pressure in the alluvium is no
longer balanced by water pressure in the adjacent
water body, and the unbalanced pressure creates a lat-
eral stress toward the free face of the alluvium.

PIPING

Piping, internal erosion by moving ground water,
is a minor process that gradually reduces the stability
of slopes. The stability changes caused by piping are
generally impossible to determine quantitatively. In-
ternal erosion can occur by mechanical transportation
or by solution? Mechanical transportation usually in-
volves movement of particles of silt and fine sand
small enough to be easily transported but not so small
that they are held together appreciably by molecular
forces. It is most common in poorly sorted gravels in
which the coarser constituents can support the overly-
ing material while the fines are washed away.

The effect of solution on stability in the Fort Randall
area is unknown; the removal of material by solution

does not leave large cavities, and appreciable surface
deposits are not precipitated. The best evidence that
solution ocurs in this area is the ground water itself.
Searight and Meleen (1940) stated that there is hard
water in more than three-quarters of the shallow wells
in the counties along the reservoir. All these wells
are less than 200 feet deep, and most are less than 50
feet deep. The water is relatively pure when it enters
the ground; it must, therefore, dissolve minerals from
the material through which it passes.

MISCELLANEOUS CAUSES OF LANDSLIDING

Earth tremors and loading on the heads of potential
landslides can produce movement. Earth tides and
atmospheric pressure changes are possible but generally
unverified causes of landsliding. Although loading at
the head of a potential landslide is rare under natural
conditions, it occurs fairly commonly as a manmade
phenomenon associated with various engineering proj-
ects. It may be either a general cause of instability
or a trigger action. The slump pictured in figure 14
is a typical example of an earth movement produced
by artificial overloading of an unstable area. Failure
occurred after fill for a new highway was placed on
a ridge of Pierre Shale. Abnormally lush vegetation in
parts of the landslide area indicates that the shale was
already wet and unstable; the added weight of the
fill was the trigger that set the slope in motion.

In the Great Plains area the effects of earth tremors
are probably very slight. Small or infrequent trigger
actions, on the other hand, may be important comple-
ments to a larger trigger action. For example, the
eflects of saturation may not be enough to trigger a
potential slide, but a very slight earth tremor occurring
when material is saturated may produce movement.

RELATIVE IMPORTANCE OF THE LANDSLIDE CAUSES

Most landslide movement results from a combination
of causes, but the various agents involved have been
discussed separately so that their individual effects
on slope stability could be appraised.

Table 2 summarizes landslide causes and presents
estimates of their relative importance in the Fort
Randall Reservoir area. Investigations along the reser-
voir were qualitative, and at best crudely quantitative.
The interpretations presented in the table are intended
to be a guide for future detailed investigations.

ANALYSES OF THE PIERRE SHALE

All the slope failures along the Fort Randall Reser-
voir, except soil slumps and soilfalls in alluvium and
loess, involve either the Pierre Shale or material de-
rived from it.

ANALYSES

OF THE

PIERRE SHALE 21

 

FIGURE 14.——Slum.p caused by highway fill being placed at the head of a potential landslide block. Relocation of South Dakota
Highway 47, sec. 36, T. 103 N., R. 73 W., Lyman County, S. Dak. Photographed July 16, 1955.

A thorough investigation of the characteristics and
behavior of the Pierre Shale is beyond the scope of
the present study, and the data included here are only
qualitative at best and are not complete. The informa-
tion about the Crow Creek Member, which is thin and
seems to have little effect on slope stability, was taken
from Crandell’s report (1952). The samples of the
other shale members were collected from only one
locality and, in most cases, one horizon per member;
therefore they cannot show lateral and vertical vari—
ations although they give a good picture of the general
nature of the Pierre.

Investigation of the shale included mechanical anal-
yses, mineral analyses, and some clay studies. Mechan-
ical analyses were made to determine possible relation
between grain size and stability. Mineral analyses
were made to evaluate the effects of mineral composi—
tion on stability. The clay studies were made in an
attempt to correlate behavior of the clay minerals with
slope stability in the shale. /

MECHANICAL ANALYSES

The mechanical analyses were made by the hydrom- I

eter method virtually as prescribed by the American
Society for Testing Materials (1950). Interpretation
of particle size from the hydrometer readings was
based on the empirical time particle-size relation used
' by the US. Bureau of Reclamation (1951) .

The accuracy of mechanical analyses by the hydrom-
eter method is limited by certain inherent factors. It is
practically impossible to disaggregate completely fine-
grained consolidated or partly consolidated sample ma-

terial without also breaking some of the component
particles. Although maximum possible disaggregation
without excessive breakdown of the individual particles
was attempted, most of the samples used included a
small percentage of aggregates and some clay mineral
particles broken during disaggregation. Some materials
tend to flocculate even though deflocculating agents
are added to the water-sediment mixture. Therefore,
hydrometer analyses could not be made on the Mo-
bridge and Virgin Creek Members of the Pierre Shale.
Finally, errors of as much as 10 percent may result
from the US. Bureau of Reclamation’s empirical
method of correlating time with the sizes of particles
in suspension. This method does not ignore the effects
of specific gravity, but there is no correction factor
for variation in specific gravity of any particular
sample from the mean of the samples from which the
empirical curve was constructed.

Mechanical analyses of the Pierre Shale ShOW the
particle-size distribution in the shale and permit com-
parison of particle-size distribution between individual
members. A cumulative curve of data from the analyses
was plotted in figure 15 for five members analyzed:
Sharon Springs, Gregory, DeGrey, Verendrye, Elk
Butte. The data also were averaged to construct an
average cumulative curve to approximate a composition
curve for the entire formation in the Fort Randall
area.

The curves are divided into three general size classes:
greater than 0.074 mm (sand and coarser) (Truesdell
and Varnes, 1950) ; less than 0.074 mm but greater than
2 microns (0.002 mm) (silt) ; and less than 2 microns

LANDSLIDES NEAR FORT RANDALL RESERVOIR, SOUTH DAKOTA

TABLE 2.—Estimate of relative importance of agents involved in landsliding in the Fort Randall area

 

Agent Mode of operation

Relative effectiveness in Fort Randall area

Principal type of movement

 

III. Loading head of

IV. Tremors in earth’s
crust.

I. Erosion _____________ Creates slopes on which landslides

start. Triggers landslides by
oversteepening or undercutting
slopes.

II. G round water _________________________________________

A. Hydrostatic
pressure.

Increase in hydrostatic pressure in
joints and fractures, resulting
from an influx of ground water,
creates a large force acting out-
ward and upward on a potential
landslide block. A vertical rise in
the hydraulic head of a small
fracture connected with a
horizontal permeable stratum
can create a tremendous increase
in the total hydraulic force.

As a result of a steep piezometric
surface, moving ground water
creates enough pressure on soil
or rock particles to overcome
frictional resistance of the
material.

C. Lubrication- a _ _ (a) A sudden influx of ground water
lubricates normally dry surface
material and destroys its
coherence.

(b) Addition of ground water to a
shear surface failure perpetuates
movement already started by
other processes.

B. Seepage
pressure.

D. Weight ________ (a) An influx of ground water into
pores and fractures of previous
or unconsolidated materials can
produce an appreciable increase
in weight.

(b) Fractures in unweathered shale
probably cannot hold enough
water to have appreciable effect
on the weight of a potential
slide block.

E. Saturation _____ Saturation of moist weathered shale
and unconsolidated material in
which surface tension has allowed
abnormally steep slopes to
develop, destroys their apparent
coherence.

F. Piping _________ Subsurface removal of fine solids or
soluble materials by movement of
seepage water may weaken
material thus eroded.

Weight of added material increases
shearing stresses in already
unstable material to point of
failure.

Vibrations are known to set
potential slides in motion.

potential slide.

Probably the major general cause
of instability. Also a major
trigger action in shale or
unconsolidated deposits.

Various effects of ground water
combine to make it the most
common trigger agent. All
landslides in the area, except
those started by direct erosion,
occur when ground-water
conditions favor instability.

Probably one of the main
important trigger causes of
landsliding.

Probably not a major factor while
the reservoir is filled, but it is
a potentially effective agent in
silt and fine sand whenever the
reservoir is subject to rapid
drawdowns.

Effective trigger action in flow
type of movement.

Probably ineffective as a trigger
agent in most slumps, but
probably very effective in
continued movement of active
slides.

Significant in flows but probably
less significant than lubrication.

Probably only very minor
importance either as a general
cause or as trigger action.

As a reservoir fills, saturation of
steep sand and gravel banks
may trigger landslides.

No present indication that piping
is an effective force in this
area.

May be a general cause or a
trigger action. Effective only
locally.

Very minor trigger action _________

Generally slumps in shale;
some soilfalls in unconw
solidated materials;
rockfalls in Niobrara
Formation.

Predominantly slumps in
shale.

Slumps and earthflows in
weathered shale and
unconsolidated materials.

Mudflows and earthflows in
weathered shale and
surficial materials.

Predominantly slumps in
shale.

Earthflow and mudflows in
weathered shale and (or)
unconsolidated deposits.

Slumps.

May be slumps or flows in
weathered shale and
surficial materials.

Presumably produces slumps.

Mostly slumps and slump-
earthflows in fresh and
altered shale.

Slumps or flows.

 

ANALYSES OF THE PIERRE SHALE 23

 

 

 

     
   
 

 

 

100 _ l l | I l | l l f __ \ . |
‘ ___’———=—- ——’J Material >0.074 mm,
SE S”: / / mostly fibrous
_ calcite
Predominantly Material >0.074 mm,
clay minerals mostly selenite
9O - Material >0.074 mm,
mostly fibrous
calcite
Sand
f . ——>
80 _ —200 mesh +200 mesh
._ _
Z
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LIJ
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0.001 0.002 0.003 0.004 0.005 0.01 0.02 0.03 0.04 0.05 0.1

PARTICLE DIAMETER, IN MILLIMETERS

FIGURE 15.——Particle-size distribution in five members of the Pierre Shale.

(clay) (Grim, 1953, p. 1—2). The first division, 0.074
mm, is the dividing point between sieving and the
more complicated methods of mechanical analysis, such
as hydrometer analysis or elutriation. The division be-
tween silt and clay is placed between 2 and 5 microns
in various size classifications (Truesdell and Varnes,
1950). The 2-micron division, as given by Grim (1953,
p. 1—2) , is selected for this report:

Although there is no sharp universal boundary between the
particle size of the clay minerals and nonclay minerals in
argillaceous sediments, a large number of analyses have shown
that there is a general tendency for the clay minerals to be
concentrated in a size less than about 2 microns, or that
naturally occurring larger clay-mineral particles break down
easily to this size when the clay is slaked in water. Also such
analyses have shown that the nonclay minerals usually are
not present in particles much smaller than about 1 to 2 microns.

The cumulative curves ShOW the predominantly fine
grained character of the formation and similar part-
icle-size distribution among five different members of
the Pierre Shale. The average curve indicates that more
than 95 percent of the particles are silt size and smaller.
About 65 percent of the material has a particle diam-
eter smaller than 2 microns. Particle-size distribution
of the individual members shown in figure 15 is sur-
prisingly similar to the average distribution. The ma-
terial retained on the 200-mesh sieve ranges from less
than 1 to about 8 percent of the individual samples.
In several samples this material is mostly secondary

minerals formed after deposition of the shale, and in
all samples the +200-mesh material undoubtedly in-
cludes numerous aggregates of grains not separated
during disaggregation of the samples. At the 2-micron
size there is a range of about 16 percent. In the Sharon
Springs Member about 58 percent of the material was
finer than 2 microns; in the Verendrye Member about
74 percent was finer than 2 microns. Particle-size vari-
ation in the —2-micron sizes seems greater. At 1
micron, the smallest size measured, the range between
members has increased to 24 percent, and presumably
the curves continue to diverge in the smaller sizes.

The particle—size distribution is a significant factor
because it seems to control mineral distribution (fig.
16), which in turn afl'ects the strength of the material.
The predominant mineral in the —-2-micron size range
is montmorillonite clay, but in the +2—micr0n size
range the predominant mineral is quartz. The only
exceptions, the Mobridge Member and the Crow Creek
Member as described by Crandell (1952), contain large
amounts of calcite. Shear strength of consolidated
montmorillonite clay is small compared with the shear
strength of consolidated quartz grains. The problem
essentially is whether the +2-micron material, the
—-2-micron material, or the combination of both deter-
mines shear strength in the shale.

Relative effects of the two particle-size components
on shear strength of the shale are controlled by struc-

24 LANDSLIDES NEAR FORT RANDALL RESERVOIR, SOUTH DAKOTA

tural arrangement of the grains. The effects of grain
structure are considered first in theoretical homogene-
ous mixtures composed of varying ratios of two grain
sizes: large relatively strong spherical grains, and
minute relatively weak grains. The theoretical mix-
tures can then be compared with the Pierre Shale.

Two extreme types of particle or grain structure can
develop in a homogeneous mixture of coarse grains and
fine grains depending on the relative proportions of
the two components. If the volume of the interstices
between the coarse grains is the same as, or greater
than, the volume of the fine grains, the coarse grains
can develop a stable structural network. If the volume
of fines is greater than the volume of the interstices,
the fine grains can form a matrix in which coarse
grains are isolated from each other. In the first case,
shear strength of the mass is a function of the shear
strength of the coarse grains and also of the friction
between them. In the second case, shear strength of the
mass is controlled by the shear strength of the fine-
grained matrix.

The changes in shear strength from material in
which the coarse grains predominate to that in which
fine grains predominate are gradual. If the volume of
fine grains only slightly exceeds the volume of the
interstices between coarse grains, much of the shear
strength of the coarse grains is retained. Even after
the coarse grains are completely isolated from each
other, they may effectively increase friction along
shear surfaces.

The transition point at which the fine grains change
from filler to matrix is controlled by the packing of the
coarse grains. In systematically packed spheres of uni-
form size, the porosity ranges from 25.95 to 47.64 per-
cent (Graton and Fraser, 1935, table 2). The transition
point in the theoretical mixture thus should be about
26—48 percent fines, if the fines fill all the voids. In ran-
dom packed spheres, if one asumes that a stable net-
work of coarse grains exists, the transition point prob-
ably Will fall in the same range as in the theoretical
mixture.

Comparison of the +2-micron to the ~2-micron
particle- or grain-size mixture in the Pierre Shale
with the theoretical mixture shows their general be-
havior to be similar.

The +2-micron fraction of the Pierre is predom—
inantly quartz grains, which commonly are equidimen-
sional if not spherical. Mica, one of the minor coarse-
grained constituents, is platy and may increase porosity
of the packed coarse grains. The fine grains are not
without dimension as in the theoretical mixture, but
their average size is small compared to the coarse

grains. On the average cumulative curve (fig. 15) about
15 percent of the —2—micron particles occur in the 1-
to 2—micron size range; about 85 percent of the fine-
grained component has a diameter of less than half
the smallest diameter in the coarse-grained component.
The shale, moreover, consists of particle sizes undoubt-
edly mixed heterogeneously although they appear to
be homogeneous when inspected through a binocular
microscope.

These variations in the particle-size mixture of the
shale should reduce the proportion of fines necessary
to reach the transition point at which the coarse grains
no longer form a continuous structural network. The
closer packing should also counteract the tendency of
the mica to increase porosity. The —2—micron particles
in the shale cannot completely fill all voids between
coarse grains, because the shale has some porosity; the
volume of fine particles necessary to separate the
coarse grains thus is less than the total volume of
voids.

Comparison of the Pierre Shale and the theoretical
mixture implies that —2-micron particles in the Pierre
Shale become a matrix for the +2-micron grains at
some proportion of fines less than 50 percent. The per-
centages of -2-micr0n particles in the five members
of the Pierre Shale shown in figure 15 ranges from
about 58 to 73. It seems valid, therefore, to assume that
the —2-micron size fraction of the shale is a matrix
for the coarser grains and that shear strength is deter-
mined by this matrix. Because the +2-micron fraction
probably has little effect on the shear strength of the
shale, it can be ignored in the shale behavior studies.

MINERAL COMPOSITION

Although the results therefrom are approximate, X-
ray diffraction is the only feasible method of quantita-
tive mineral identification for the dominantly fine
grained Pierre Shale. Identifications for each member
except the Crow Creek were made by Dorothy Carroll,
J. C. Hathaway, C. J. Parker, and W. W. Brannock,
US. Geological Survey, August 1955, using the fol-
lowing procedure:

A portion of each sample was disaggregated and dispersed
in distilled water with sodium tetraphosphate added as a dis-
persing agent. The silt (2-62 microns) and clay (less than 2
microns) fractions were separated by repeated centrifuging
and decanting. Excess water was removed from the clay sus
pension by porcelain filter candles under vacuum, and the clay
was Ca+2 saturated by passing the concentrated suspension
through a Ca ion-exchange resin column. Oriented aggregates
were prepared by pipetting portions of the concentrated sus-
pensions on glass slides and allowing the water to evaporate
at room temperature.

ANALYSES OF THE PIERRE SHALE 25

X-ray diffractometer patterns were made on each sample
as follows:
Clay fraction
Oriented aggregate, untreated.
. Oriented aggregate, ethylene glycol treated.
. Oriented aggregate, heated to 400° C.
. Oriented aggregate, heated to 500° C.
. Randomly oriented powder.
Silt fraction
6. Randomly oriented powder.

Quantitative estimates are based on the intensity of the
lines recorded by the X-ray diffractometer and are given as
parts in 10. Inasmuch as many factors in addition to quantity
of a mineral affect diflraction intensity. these estimates are
not intended to give more than a very general indication of
the relative amounts of the various minerals present.

“sealer-l

OI

Throughout the rest of this report, 74 microns is used
for the upper limit of silt size, rather than 62 microns
as given here. An average of less than 1 percent of
the shale particles is in the 62- to 74-micron size range;
therefore, the approximate quantitative mineral data
should be equally valid for the larger silt-size limit.

Mineral compositions of the various shale members
are shown graphically in figure 16; geographic loca-
tions of the samples are given in table 3. The Virgin
Creek, Verendrye, and DeGrey Members are each rep-
resented by a set of samples, an auger sample from
depths of 25 feet or less, and a surface grab sample.
An additional auger sample was collected from 9. ben-
tonite bed in the Sharon Springs Member to check
possible variations between it and the enclosed shale.
Sets of samples from two horizons were used for the
Elk Butte and Mobridge Members. The grab samples
were collected to determine the effects of near-surface
weathering on mineral composition. Inasmuch as auger
samples were. from comparatively shallow depths, they
are all presumed to be at least slightly weathered.

TABLE 3.—-—Localities of shale samples shown in figure 16

 

Sample Locality
(fig. 16)

 

County Sec. T.N. R.W.
1 _____________ Gregory ______ SEMSWM 13-- _ _ 95 66
2 __________________ do _______ SWMSEM 13--- _ 95 66
3 _____________ Lyman _______ SWMSWV; 21- _ _ 104 72
4 __________________ do _______ SW%SE% 22- _ _ _ 104 72
5 __________________ do _______ NWMSEK 22- _ _ 104 72
6 __________________ do _______ SE%SE% 22---- 104 72
7 __________________ do _______ SWMSEM 14____ 104 72

 

The mineral composition of members of the Pierre
Shale (fig. 16) is easily summarized. The clay-size
material is predominantly mon-tmorillonite, ranging
from five parts in 10 in the Gregory Member to nine
parts in 10 in the DeGrey, Verendrye, and Virgin
Creek Members. Except in the Mobridge Member, the
major mineral in the silt-size material is quartz, which

is three to five parts in 10 of the silt-size category. In
the Mobridge Member montmorillonite does not exceed
four parts in 10 of the clay-size component, and quartz
represents only one or two parts in 10 of the silt-size
component. Calcite in the Mobridge Member, although
only two to five parts in 10 in a single grain-size com—
ponent, is an abundant mineral in both size compo-
nents. Mineral com-position of the Crow Creek Member
is similar to that of the Mobridge Member, and cal-
cium carbonate (presumably calcite) is the most abun-
dant mineral (Crandell, 1952).

One of the most interesting features of the mineral-
ogy of the Pierre Shale is the contrast in mineral com-
position between clay-size and silt-size material. Ca1-
cite in the Mobridge Member is the only nonclay min-
eral that exceeds the proportion of one part in 10 in
the clay-size portions of the samples shown in figure
16. In the silt-size portions of the same samples no
clay mineral exceeds two parts in 10, and in only four
of the 19 samples does a clay mineral comprise more
than one part in 10.

The data in figure 16 imply that near-surface weath-
ering has no profound universal effect on the Pierre
Shale. Apparently the effects of weathering are influ-
enced more by local conditions than by any regional
control.

The available data are insufficient to show the lat-
eral and vertical ranges in composition and weather-
ing effects. They suggest, however, that there is little
variation within a given member. The two sets of
samples from the Elk Butte and Mobridge Members
show little variation over a vertical distance of 10
feet, but they cannot be considered representative of
the total thicknes of each member. The Mobridge and
Elk Butte samples show that minor variations (one
part in 10) in mineral com-position between surface
and subsurface samples are not necessarily representa-
tive of the weathering conditions. Samples may show
a small change in the amount present of a mineral
between the surface and one subsurface horizon, but
another horizon a few feet above or below the first
horizon may show no difl’erence in the amount present
of the same mineral.

MONTMORILLONITE

Montmorillonite clay in the Pierre Shale apparently
is responsible for the susceptibility of the shale to
landslides. Interpretation of the data from mechanical
analyses indicates that shear strength of the shale is
determined by the shear strength of its clay—size por-
tion, and the clay—size portion of most of the shale is
dominated by montmorillonite. Slope stability of indi-
vidual members, therefore, should depend on the pro—

LANDSLIDES NEAR FORT RANDALL RESERVOIR, SOUTH DAKOTA

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ANALYSES OF THE PIERRE SHALE

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28 LANDSLIDES NEAR FORT RANDALL RESERVOIR, SOUTH DAKOTA

portion of montmorillonite in the clay-size compo-
nents. In a general way this is true: the Mobridge
Member, which contains noticeably less montmorillon-
ite than the other members (fig. 16), commonly forms
and maintains steeper slopes. Though susceptible to
landsliding, it appears to be more stable than the other
members. The following description of montmorillon-
ite is adapted from Grim (1953).

The basic structure of montmorillonite is a series
of silicate layers perpendicular to the c-axis. Unbal-
anced negative charges are on the surfaces of all sili-
cate layers attracting various exchangeable cations,
which are a necessary part of the montmorillonite
structure.

The silicate layers also attract water molecules and
other polar molecules to their interlayer surfaces. The
thickness of the adsorbed water between silicate lay-
ers is controlled by the amount of water available and
by the nature of the exchangeable cations held by the
clay. The bond between adsorbed water and the sili-
cate layers is not completely understood, but water
molecules in direct contact with the silicate layer be-
have as a solid and apparently are held rigidly in an
oriented position. Successive layers of oriented water
attach themselves to the first molecular layer, but in
each succeeding layer the orientation and degree of
bonding are less and the water is more fluid.

If only a little water is adsorbed, the montmorillonite
is held in a virtually solid state, and the clay has rela-
tively high shear strength. If a large amount of water
is adsorbed there is semifluid or fluid water held be-
tween the silicate layers and this water lubricates and
allows movement between layers. The shear strength
thus is reduced to almost nothing if sufficient water
enters between the silicate layers.

As the addition of water reduces the shear strength
of montmorillonite, it also reduces shear strength of
the shale in almost direct proportion.

Exchange of cations at a given water content can
also reduce shear strength in montmorillonite. As an
example, replacement of cations that promote a thick
layer of adsorbed water by cations that do not, can
release some of the adsorbed water, which then be-
comes free water between silicate layers. If this free
water is not expelled immediately by compaction of
the clay, the shear strength of the clay is drastically
reduced.

The stability of clay may also be reduced when ca-
tions that can adsorb only a thin layer of water are
replaced by cations that can adsorb a thicker layer.
In this case, if extra water becomes available to in-
crease the thickness of the adsorbed water, the water
in the center of the water layer is farther from the

orienting effect of the silicate layer and therefore
is not held as tightly. This water, as a result, is more
fluid and is a better lubricant.

At present, the effect of cation exchange on the
stability of Pierre Shale slopes cannot be measured.
Studies—by Dorothy Carroll, J. C.Hathaway, C. J.
Parker, and W. W. Brannock, US. Geological Survey,
August 1955—of the exchangeable cations and ion ex-
change capacities in Pierre Shale samples indicated
that near-surface weathering causes a general increase
in exchange capacity, with calcium becoming the major
exchangeable cation. These data, however, are from
samples from horizons too shallow to have any major
application to landslides. Data furnished by the Omaha
District of the US. Army Corps of Engineers (D. K.
Knight, oral commun.) show no significant contrast
between exchangeable cations in clay from unweath-
ered shale at Oahe damsite, about 100 miles upstream
from the Fort Randall Reservoir, and exchangeable
ions in the clay from shale samples along the Fort
Randall Reservoir.

REPRESENTATIVE STUDY AREAS

The two major objectives of the Fort Randall Reser—
voir landslide investigations were (1) to determine the
effect of the reservoir on slope stability along its
shores, and (2) to determine the relation between dif-
ferent materials and the potential for landsliding.
Both slope stability appraisals and geologic mapping
are needed to achieve these objectives.

Study of the present slopes also is a basis for com-
parison of current to former landslide activity along
the walls of the Missouri River trench. Correlation
between slope stability and geology, supplemented by
shale analyses and measurements of slope angles, indi-
cates the susceptibility of individual geologic units to
landsliding and makes possible estimates of the rela-
tion between geology, slope stability, and natural slope
angles.

This approach to the study of landslides was tested
in five areas representative of the reservoir environ«

ments.
METHOD OF SELECTION

There were two main factors to consider in selecting
the areas for slope stability investigations. First, ade-
quate large-scale base maps had to be available. Second,
the areas had to be as representative of conditions
along the entire reservoir as possible. At least one area
near but outside the limits of the reservoir and its
effects was needed as a control or reference area.

The areas selected are covered by sheets 23, 26, 30,
39, and 42 of the Missouri River Survey, Gavins Point
near Yankton, S. Dak., to Stanton, N. Dak., topo-

REPRESENTATIVE STUDY AREAS 29

graphic map series made in 1947 by the Omaha Dis-
trict, US. Army Corps of Engineers. These maps
were available at scales of 1 :12,000 and 1:24,000, and
each covers an average of 25 square miles along the
Missouri River trench. The maps have accurate photo-
grammetric planimetry of nearly the entire Missouri
River trench. Topography is portrayed by contours at
10-foot intervals along the lower part of the trench
from the river level to an altitude of 1,400 feet. 'For
this study, contours at 20-foot intervals above 1,400
feet were completed, by the US. Geological Survey,
on special manuscript sheets. The areas shown on map
sheets 23, 26, 30, 39, and 42 are termed areas 1, 2, 3, 4,
and 5, respectively. . _

Area 1, just below the Fort Randall Dam (pl. 1),
is the reference area, which has an environment as
similar as possible to that above the dam. Tributary
valleys between the dam and area 1 should effectively
isolate most of the control area from any near-surface
ground-water changes caused by the reservoir.

A complete geologic map was made only in area 2
(pl. 3), which includes the entire Pierre Shale section
as well as many old and new landslides. The area was
chosen because it is an ideal locality for correlating
slope stability and materials. In the other areas, only
the geology that is to be permanently submerged was
mapped as part of this project.

Areas 2 and 3 (pls. 1, 3), near the dam, were chosen
to provide a record of slope stability changes in the
part of the trench that undergoes greatest inundation.
These areas, moreover, are sufficiently close to act as
a check on each other. The general conditions control-
ling slope stability should have a similar effect in both
areas, but any local factor presumably would apply
in only one. Areas 4 and 5 (pl. 1), in the upper part
of the reservoir, include parts of the trench that will
have comparatively little inundation. These areas also
are geographically close enough to provide checks on
each other.

SCOPE OF INVESTIGATIONS

Investigations in the selected areas are in two cate—
gories: slope stability appraisals and geologic map-
ping.

SLOPE STABILITY APPRAISAL

Slope stability appraisals were made by examining
the terrain in the field and plotting the landslides on
vertical aerial photographs. This information was
transferred to the base maps with the aid of a vertical
sketchmaster.

The first purpose of these appraisals was to observe
changes caused by formation of the Fort Randall
Reservoir. The studies described in this report record
conditions at the time the dam was built. Reappraisals

472-783 0 — '73 — 3

can be made in the future to determine the slope
stability changes occurring after the reservoir was
filled and in operation. The second and more imme-
diately important purpose of the slope stability ap—
praisals is to supply data to help us better understand
landslides and factors that control them.

The first phase of the appraisals was to set up a
satisfactory group of slope stability conditions. There
are no simple, absolute criteria, and therefore the
classification developed was generalized. It includes
the major classes of stability and is designed for recon-
naissance-type observations. The classification, there-
fore, does not use core drilling to locate slide surfaces
or firmly scheduled observation of control points to
determine accurately the activity of individual land-
slides. The slope stability appraisal is only approxi-
mate, but examinations of the same area by more than
one person indicate that the results in general are
reproducible.

The slope stability classification is divided into two
basic categories: (1) areas apparently always stable,
and (2) areas that are or were subject to landsliding.
The second category is further divided into a series
of four classes of slide activity at the time of observa-
tion. The end points of this series are active landslides
and stabilized landslides, with two gradations between
—one applying to landslides that appear stable but
show signs of very recent activity, and the other
applying to landslides that were stable for a number
of years but that have been recently reactivated.

STABLE GROUND

Stable ground includes all material that appears
never to have been subject to landsliding. The only
exceptions are thin patchy deposits of stable loess,
alluvium, and colluvium that overlie but do not com-
pletely mask old landslide material. For such deposits
the stability classification depends on the underlying
material.

Stable material consists of two basic types: (1) ma-
terial that was deposited independently of the Mis-
souri River trench and (2) material deposited within
the trench and its tributary valleys.

The stable material underlying the trench comprises
the deposits into which the trench and its tributary
valleys were cut. Inasmuch as these same deposits are
also involved in most landslides, the distinction between
stable material and very old stabilized landslides often
is difficult. Material underlying uplands and gentle
slopes (fig. 17) without steep scarps probably is stable.
Evidence of stable ground is hard to find on steeper
slopes, and undoubtedly some small stable areas are

30 LANDSLIDES NEAR FORT RANDALL RESERVOIR, SOUTH DAKOTA

 

FIGURE 17.-—Area of Pierre Shale slopes considered stable. View southwest into N% sec. 4, T. 103 N., R. 72 W.. Lyman County,
S. Dak. (area 5 west of the Missouri River). Photographed August 2-1, 1956.

not recognized in large areas of old stabilized land-
slides.

Stable material deposited within the trench and its
tributary valleys can generally be recognized easily.
\Vhere it is sufficiently thick and extensive to mask the
underlying terrain, it forms relatively smooth sur-
faces, generally on flood plains or terrace remnants.
Such deposits may give a false impression of stable
conditions because they may cover older deposits with
long complex histories of landslide activity. In some
areas landslides have obviously been covered by stable
natural fill material, but it is impossible to determine
the conditions beneath the fill (fig. 18). Consequently,
it is difficult to draw an accurate contact between
stable ground and landslide areas where a stable fill
feathers out against old landslide topography.

STABILIZED LANDSLIDES

Areas of stabilized landslides include landslide ma-
terials that show no evidence of recent activity. The
surfaces of weakness are still present and the shearing
strength is probably much less than in undisturbed
material; therefore, changes in the factors controlling
stability could result in renewed movement.

Surface indications of stabilized landslides range
from slightly hummocky irregular topography to in-
dividual landslides with relatively fresh scarps and

easily distinguished boundaries. The slump shown in
figure 19 is typical of recently stabilized landslides
that are still obvious entities only slightly modified
by erosion and deposition. Although the scarp and
the outlines of the slump block are still clearly discern—
ible, deposition of loess and colluvium is beginning to
obscure the limits of the block, and erosion is cutting
gullies into the upthrust toe.

Identification of old slides is increasingly difficult
as time and geologic processes continue to alter the
slides. The characteristic older stabilized landslide ter—
rain in the Pierre Shale is shown in figure 20. It is
obvious from the photograph that any stable ground
below the ridges cannot easily be distinguished from
areas of stabilized landslides.

The hummocky topography shown in the left back—
ground of figure 20 is composed of old scarps and
slump blocks that can still be recognized. Sufficient
water from runoff and seepage has been trapped at the
break in slope between some scarps and slump blocks
to support growth of trees and shrubs. The backward
rotation of the slump blocks has produced flatter
slopes than the surrounding terrain so that they re-
semble terrace remnants. In most places, however, the
two features can be easily distinguished because ter-
race remnants along a valley occur at about the same
elevation, whereas the levels of old slump blocks rarely
coincide.

REPRESENTATIVE STUDY AREAS 31

 

FIGURE 18.—A low-level stable fill terrace (center background) at the base of slopes composed out 01d stabilized landslides
(foreground). The upper limits of the terrace seem to grade into the landslide area, which strongly suggests that the terrace
fill was deposited on and masks 01d landslide topography. View north toward Fort Randall Dam from center of boundary

between SW14 and SE% sec. 20, T. 95 N., R. 65 W., Gregory County, S. Dak. (west Side of area 1). Photographed August 16,
1956.

 

FIGURE 19.—Recently Stabilized Slump. This Slump is still a distinct entity, but erosion and deposition locally obscure its limits.
SW14SE1/4 sec. 6, T. 98 N ., R. 69 W., Charles Mix County, S. Dak. Photographed August 19, 1956.

32 LANDSLIDE'S NEAR FORT RANDALL RESERVOIR, SOUTH DAKOTA

 

FIGURE 20.——Sthbilized landslide terrain. All of the area, except some of the ridges along the skyline, probably sli‘d at some time.
The evidence of landsliding ranges from hummocky terrain to discrete slump blocks. 13.1% sec. 20, '1‘. 97 N., R. 68 W., Gregory
County, S. Dak. (area 3 west of the Missouri River). Photographed August 15, 1956.

Continual erosion and development of well-inte-
grated drainage, coupled with deposition of loess and
colluvium, modifies the landforms and reduces relief
until the stabilized landslide area looks like the sub-
dued hummocky slopes shown in the right-central part
of figure 20. Surface evidence of landslides may be
completely lost in the final stage, illustrated in figure
21 which shows loess deposition concealing a small
slump in the Pierre Shale. This slump would never
have been recognized if it had not been exposed by
later erosion.

RECENTLY ACTIVE LANDSLIDES

Landslides showing recent movement are classified
as recently active even though they were apparently
inactive at the time of study. There is no certain way
to judge Whether they are actually stable or only tem-
porarily quiet. Landslides in this category can become
active without a major change in their stability condi-
tions.

 

FIGURE 21.——Exposed slump along the Fort Randall Reservoir
shore. The slump in the Pierre Shale was completely hidden
by loess deposition. Erosion along the shore revealed the
loess-shale relation. Charles Mix County, S. Dak. Photo-
graphed September 27, 1954.

Although the slump shown in figure 22 is recent, ap-
parently it has not moved within the past few years.
The slump block is surrounded by fresh-looking frac-
tures, and at first glance it appears to be active, but
cattle trails crossing the fractures without displace-
ment and the edges of fractures not being sharp indi-
cate that it is not active.

REACTIVATED LANDSLIDES

Reactivated landslides have started to move again
after a period of stability. The term is not used for
active landslides that include a part of one or more
stabilized slides but is confined to old landslides mov-
ing again as their original entities. The significance
of a reactivated landslide is that it implies redevelop—
ment of the stress conditions that caused the original
movement.

The slump-earthflow shown in figure 23 is a typical
reactivated landslide. It apparently was a subsidiary
part of a larger slump, part of which can be seen on
the left of the reactivated area. The limits of the re—
activated area follow a topographic break that out-
lines the original slump unit. Renewed movement of
the subsidiary slump block has not affected the major
stabilized landslide beside it. This reactivation may be
complete Within itself, or it may be a forewarning of
more extensive reactivation.

ACTIVE LANDS LIDE S

All landslides that show no signs of stability are
classified as active. This negative criterion is necessary
because actual movement was observed in very few

REPRESENTATIVE STUDY AREAS 33

 

FIGURE 22.—A recently active slump. The fresh appearance of the fractures implies that this landslide moved recently, but close
examination shows no present activity. The landslide may be permanently stable or temporarily quiet. SW14 SE1/4 sec. 19,
T. 103 N., R. 71 W., Brule County, S. Dak. (area 5 east of the Fort Randall Reservoir). Photographed August 23, 1956.

landslides along the Fort Randall Reservoir. Either
landslides move too slowly for direct observation or
else the movement is in periodic surges with only minor
activity between. All unstable landslides are included
in this category whether they are in formerly stable
areas or whether they represent renewed activity in
stabilized landslide areas.

Criteria suggestive of active sliding include fresh
bare fractures and scarps, slickensides on exposed slide
surfaces, fresh jagged blocks of landslide material, and
dead or dying vegetation. Figure 24, a photograph of
the head of an active landslide, shows all these features
except slickensides.

Some landslides considered active on the basis of

 

FIGURE 23.—A slump-earthflow caused by reactivation of an old stabilized slump block. The slump-earthflow follows the outline
of an old slump block apparently subsidiary to the stabilized landslide on the left side of the active area. NWIANWJA sec. 36,
T. 95 N., R. 65 W., Charles Mix County, S. Dak. (east side of area 1). Photographed August 20, 1956.

34 LANDSLIDES NEAR FORT

RANDALL RESERVOIR, SOUTH DAKOTA

 

FIGURE 24.—The head of an active landslide on the southwest bank of the Fort Randall Reservoir, about 14 miles upstream from
the Fort Randall Dam, Gregory County, S. Dak. Photographed September 26, 1955.

appearance may be stable. Every landslide, after its'

final movement, passes through a stage when the signs
of activity are still very fresh. By observation alone it
is difficult to distinguish between a newly stabilized
landslide and one that is stil active.

GEOLOGIC MAPPING

The geologic map of area 2 (pl. 3) is intended to
show as accurately as possible the stable positions of
the various geologic units in the Fort Randall reser-
voir area. All] exposed and apparently stable geologic
contacts were plotted on 1220,000-scale vertical aerial
photographs, then transferred to the map with the
aid of a vertical sketchmaster.

Throughout much of the area, geologic contacts are
hidden by loess, colluvium, and landslide deposits;
however, sufficient reliable information was available
to show that the Cretaceous beds are horizontal and
that the thicknesses of the map units in the Pierre
Shale are virtually constant throughout the area. Con-
tacts in the Cretaceous units, therefore, are presumed
to follow contours between reliable exposures. Con-
tacts of the post-Cretaceous deposits are not necessarily

horizontal, and their locations can only be approxi-
mated in areas of poor exposures.

The descriptions of the’geologic units (p. 4) as they
occur in the lower part of the reservoir apply to plate 3,
with the few exceptions that follow.

Pierre Shale, Grow Creek Member—The Crow Creek
Member is not identified in area 2, but it may be pres-
ent beneath either landslides or surficial deposits. Pos-
sible outcrops of the Crow Creek would be displaced
downward by landslides and therefore would not be
distinguishable from the marl facies of the under-
lying Gregory Member.

Pierre Shale, DeGrey and Vererwlrye Members.—The
DeGrey and Verendrye Members have been mapped as
a single unit in area 2. The lithologic similarity between
the two members and the scarcity of stable outcrops
make it impossible to draw any contact between them.

Pierre Shale, thicknesses of map unita—Thicknesses
of the Pierre Shale map units, except for those units
having unconformable contacts at the bottom and top
of the section, are nearly constant throughout area 2.
Thicknesses of the map units are as follows:

REPRESENTATIVE

Feet
Elk Butte Member ___________________________________ 1 i140
Mobridge Member ____________________________________ 100
Virgin Creek Member ________________________________ 50
DeGrey and Verendrye Members ______________________ 100
Gregory Member _____________________________________ 30
Sharon Springs Member ______________________________ 2 +40

1 Unconformlty at top.
3 Unconformity at base.

Slow—draining terrace alluvium.—Slow-draining ter-
race alluvium is distinguished from other slow-draining
alluvium simply to aid interpretation of the geologic
map. Physical characteristics of the two materials are
similar, but the terrace alluvium was deposited when
the altitude of the Missouri River was considerably
higher than the present channel.

DESCRIPTIONS OF INDIVIDUAL AREAS

The five study areas have similar geologic settings.
The Missouri River has eroded its valley, the Missouri
River trench, through the flat-lying Pierre Shale and
into the underlying Niobrara Formation. The valley
walls in the lower part of the reservoir contain the
entire Pierre Shale section and on some of the uplands
the shale is capped by Ogallala Formation. In the up-
per part of the reservoir post—Cretaceous erosion has
removed some of the upper members of the Pierre
Shale from the Vicinity of the river valley. Water, ice,
and wind have by repeated cycles of erosion and depo-
sition during Quaternary time modified the basic geo-
logic setting.

AREA 1

Area 1 (pl. 1), immediately downstream from the
Fort Randall Reservoir, extends from lat 42°59’ to
43°03’ N. and from long 98°27’ to 98°35’ W. The
right (southwest) abutment of the Fort Randall Dam
lies in the northwest corner and the Missouri River
trench cuts diagonally southeastward through the cen-
tral part of the map. All the area east of the Missouri
River is in Charles Mix County, S. Dak. Approximate-
ly the southern one-fifth of the area on the west side
of the river is in Boyd County, Nebr; the rest is in
Gregory County, S. Dak.

This study area provides a reference or control not
affected by the reservoir in a geologic and topographic
setting similar to the other study areas.

The base of the Missouri River trench is a steep-
walled alluvium-filled valley about a mile wide incised
into an earlier floor of the trench. The river occupies
one-third to one-half of this inner valley at an altitude
of about 1,240 feet. On the east side of the river the
inner valley is walled by 50- to 100-foot-high bluffs.
The older upper slopes of the trench wall rise steeply
from the blufi's to a gently undulating surface 1,500—
1,550 feet in altitude. Farther from the trench in the

STUDY AREAS 35

northeastern part of the area, this upland gives way
to rolling hills as much as 1,800 feet in altitude.

West of the river, blufl's 80—100 feet high form the
southern part of the inner valley wall. The height of
these bluffs decreases to the northwest until they merge
with the gentle slopes bordering the junction of Ran-
dall Creek and the Missouri River. Away from the
inner trench walls, moderately sloping hills rise to an
altitude of about 1,600 feet. The slopes then steepen
abruptly and rise until they reach an upland that
averages about 1,700 feet in altitude.

Geologic setting.~—The entire pre-Quatern'ary se-
quence from the Niobrara Formation to the Ogallala
Formation is exposed in the trench walls; however,
erosion has removed the Ogallala Formation and the
top of the Pierre Shale from all but the northern part
of the area east of the Missouri River. Alluvium cov-
ers the flood plains of the river and its tributaries, and
loess forms a patchy cover on the uplands. An ice
sheet that advanced at least as far as the Missouri
River after the beginning of downcutting of the river
has left till deposits along the east wall of the trench.
Deposits of fine and coarse (slow-draining and fast-
draining, respectively) alluvium cap terrace renmanrts
west of the river. In the northern part of the area,
the terrace alluvium is thick enough to mask the Nio-
brara Formation and the lower members of the Pierre
Shale. Southward it thins to isolated patches capping
terrace remnants cut in the Cretaceous rocks.

Stability conditiona—Except for the limestone bluffs
of the Niobrara Formation along the river, most of
the steeper slopes in area 1 (pl. 1) have slid at some
time or other. There are few exceptions to this steep-
slope—lan-dslide—terrain relation on the west side of the
river. Some areas of relatively steep slopes east of the
river, however, show no signs of landslides. An expla-
nation for the seemingly anomalous stability of the
slopes is that sliding has occurred, but that its sur-
face evidence now is completely lost. The absence of
landslides on some steep hills in the north part of area
1 may be due to deposits of till, which is more stable
than Pierre Shale. Other slopes, such as those along
Seven Mile Creek, may be stable because the adjustment
of internal stresses in the underlying materials was
able to keep pace with the changes wrought by erosion.

Almost all of the landslide terrain consists of stabil-
ized landslides that long ago were reduced by erosion
to patches of hummocky ground. Many of the indivi-
dual landslides, one would infer from their remnants,
must have been enormous.

Active, reactivated, and recently active landslides
each represent a small proportion of area 1 (pl. 1). In
most areas these landslides are randomly distributed,

36 LANDSLIDES NEAR FORT RANDALL RESERVOIR, SOUTH DAKOTA

but they are concentrated in several localities, such as
the WV; sec. 19 and the NWIA sec. 31, T. 95 N., R.
64 W.

Two differences between the stabilized landslides and
the active and recently active landslides indicate that
the modern slopes are more stable than the old slopes:
the presently active slides are considerably smaller
than the old ones; current activity is not on the large
and formerly unstable slopes of the Missouri River
trench or major tributaries but in the small gullies of
minor tributaries where streams have locally out very
steep banks or have removed the supperting toe of an
old slide.

AREA 2

Area 2 (pl. 3), about 5 miles upstream from the
Fort Randall Dam, extends from lat 43°03’ to 43°07’
N., and from long 98°39’ to 98°47’ W. Land east of
the Missouri River is in Charles Mix County, S. Dak.;
land west of the river is in Gregory County, S. Dak.

The Missouri River trench in area 2, as in area 1,
has a steep-walled inner valley incised in an older
trench bottom. This inner valley trends southeastward
from the area’s north boundary; near the center of the
area it curves about 45° and heads due east. The inner
valley increases in width from about 1 mile at the

 

,fi,-.w..._t,,. V...

.:.,,l‘moud.,,,landszide ierra

 

north boundary to about 1 1/3 miles at the east bound-
ary. Before the construction of the dam, the Missouri
River occupied only one-third to one-half of the inner
valley, but water in the reservoir now completely fills
it.

The terrain northeast of the river is rather subdued,
although it contains some steep slopes. The northeast
wall of the inner valley rises steeply from the valley
bottom (altitude about 1,250 ft) or, locally, from nar—
row low terraces along the river to a broad terrace 7 5—
130 feet high. The terrace is about three-fourths mile
wide near the north edge of the area but broadens east-
ward to almost 114 miles. It slopes gently upward
from 1,350 feet altitude along the river blufl’s to an
average of 1,480 feet altitude at its outer margin. In
the northeast part the terrace grades into moderately
sloping hills that rise to an upland 1,720—1,740 feet in
altitude.

Southwest of the river (fig. 25) the terrain is much
more rugged. At altitudes of 1,300—1,4-00 feet the steep
walls of the inner valley merge with a belt of hills and
ridges whose slopes are moderately gentle to moderately
steep near the river but rise precipitously to the south
and west to an upland 1,780—1,890 feet in altitude. The
most striking feature of the slopes between the inner

 

 

 

- FIGURE 25.—Terrain on the southwest side of area 2 showing hummocky terrain characteristic of old landslides. View northwest
from SWJASWIA sec. 1, T. 95 N., R. 67 W., Gregory County, S. Dak. Photographed August 27, 1956.

REPRESENTATIVE STUDY AREAS 37

valley and the upland is the erratic hummocky appear-
ance characteristic of old landslide terrain.

Geologic setting.—The geologic setting of area 2
(pl. 3) difi'ers only in detail from that of the other
study areas.

The entire pie-Quaternary sequence from the Ogal-
lala Formation to the Niobrara Formation is present
in the southwest trench wall. Loess caps the uplands
and occurs in small patches below the upland surface.
There are also many pockets of loess, too small and
discontinuous to be map‘pa'ble. Slow-draining alluvium
in the Missouri River flood plain forms the bottom of
the trench and extends short distances up some of the
larger tributary valleys. Farther up the valleys, and in
many of the smaller valleys and depressions, the allu-
vium is mixed with colluvium and loess and is mapped
as alluvium, colluvium, and loess.

Northeast of the river, the ngallala Formation is
missing and the middle part of the Pierre Shale is ob-
scured by overlying Quaternary deposits. The Quater-
nary deposits in turn are more varied and more wide-
spread than they are southwest of the river. Loess caps
the Elk Butte Member of the Pierre Shale on the up-
lands. Loess also covers the broad terrace just above
the inner valley of the Missouri River trench. In the
eastern part of the terrace the loess is underlain suc-
cesively by slow-draining alluvium, fast-draining a1—
luvium, and Pierre Shale. At the northwest end, the
sequence below the loess descends through fast-drain-
ing alluvium to till and into more deposits of fast-
draining alluvium before reaching the unconformable
surface of the Pierre. Apparently there was a glacial
advance between deposition of the upper and lower
alluvium that was not recorded in the eastern part
of this area.

The prereservoir Missouri River flood plain and a
low terrace along the bottom of the inner valley are
composed of a younger slow-draining alluvium that
also floors the lower parts of some tributary valleys.
In most of the small valleys and gullies the alluuvium
is mixed with colluvium and loess. Alluvium, collu-
vium. and loess also blanket part of the inner-valley
wall in sec. 32, T. 96 N., R. 66 W.

Stability conditions.——The slope stability conditions
on opposite sides of the river are very different.
Southwest of the river nearly all of the Pierre Shale,
which makes up most of the steeper slopes, has been
subject to landslides. Northeast of the river, land-
sliding apparently has been largely confined to the
wall of the inner valley west of White Swan Bottom.
The Pierre Shale exposed above the terrace contains
few slides.

The difference in stability on opposite sides of the
trench is caused by the difference in terrain. The slopes
southwest of the river rise rather uniformly from
the flood plain to the uplands; therefore their erosion
and stability are controlled directly by the Missouri
River. Periods of increased downcutting or sidecut-
ting, such as have occurred several times in the recent
history of the Missouri River, would have stimulated
oversteepening of slopes and contributed to conditions
favorable to landslides or landslide cycles at numer-
ous points along the river.

Northeast of the river, only the steep inner wall of
the trench is directly influenced by the river. The broad
terrace that separates the uplands from the flood plain
acted as a buffer that protects the uplands from direct
erosion by renewed cutting by the river. The efii-
cacy of this buffer is demonstrated by the fact that
although some downcutting occurred recently in the
small stream valleys above the terrace, erosion was rela-
tively minor and only a few small landslides developed
on the steepened slopes. In contrast, landslides are
relatively common along sections of the inner valley
wall.

Most landslides in area 2 are stabilized. Northeast
of the river only three landslides are active. South-
west of the river there are more landslides that are
active or recently active, but they are still only a
fraction of the total landslide terrain.

Almost all the active and recently active landslides
southwest of the river are on the higher parts of the
older trench wall or along tributary valleys away from
the inner valley of the Missouri River. These land-
slides, moreover, are concentrated in the eastern two-
thirds of the area, where the inner valley walls are
steepest. This localization probably is linked to active
lateral erosion and downcutting by the Missouri River
in the recent past. Erosion by the main river also
accelerated downcutting along the major tributaries.
The stable Niobrara Formation maintained steep,
nearly vertical slopes at the base of the inner valley
wall. Failure of the oversteepened slopes in the less
stable Pierre Shale, however, began a cycle of land-
sliding that moved progressively up the trench walls
and upstream along the tributaries. The first products
of this cycle were removed or completely masked long
ago. Later stages are present in the large areas of
stabilized landslides and range from slides so altered
that they can be identified only with difficulty to
younger ones that are, as yet, only partly modified.

The current and recently active landslides belong
to the waning stage of the cycle. The active slides on
the main trench wall have reached the uplands. In
the tributary valleys activity now is upstream at

38 LANDSLIDES NEAR FORT RANDALL RESERVOIR, SOUTH DAKOTA

least a half mile from the valley mouths, and much
of the landsliding occurs in the valleys of secondary
tributaries.

AREA 3

Area 3 (pl. 1) is about 20 miles upstream from
the Fort Randall Dam and includes the area be-
tween lat 43°10’ and 43°14’ N. and long 98°49’ and
98°57 ’ W. East of the Missouri River the land is in
Charles Mix County, S. Dak.; west of the river it is
in Gregory County, S. Dak.

The Missouri River divides area 3 so that about two—
thirds of the land is west of the river. On the west
side, the floor of the trench consists of a flood plain
at about 1,270 feet altitude and low terrace remnants
at various heights above the flood plain. The terraces
grade upward into shale hills as much as 2,000 feet
in altitude. The slopes in general are moderate (fig.
20) except where underlain by the relatively resistant
Mobridge Member that forms a zone of steeper slopes
at altitudes between 1,700 and 1,800 feet. The shale
hills are part of a maturely dissected southward-drain-
ing upland that was established before the present
course of the Missouri River was established. This
upland surface is present on both sides of the river.
In the southwest quarter of the area, the earlier drain-
age has been bisected and modified by Whetstone
Creek.

The east side of the Missouri trench wall rises
abruptly from the river in steep bluffs 80—180 feet
above the prereservoir water level. Except for nu-
merous small terrace remnants above the bluffs, the
upper part of the trench wall continues to rise
steeply to the southward-sloping upland. The dissected
upland grades from maximum altitudes of 1,900 feet
at the north edge of the area to about 1,450 feet
where it merges with the upper part of a broad well—
developed terrace near the south edge.

Geologic setting—The geology in area 3 (pl. 1)
is virtually the same as in the other areas. The
entire pre-Quaternary section (lower part now below
reservoir level) is present, although the Ogallala
Formation occurs only in patches on the highest points
in the northwest corner of the area. The flood-plain
deposits of the Missouri River and Whetstone Creek
are slow-draining alluvium, and both slow-draining
and fast-draining alluvium underlie most of the
terrace remnants. Ground moraine caps the uplands
in the northeast corner of the area (Stevenson and
Carlson, 1950). The patchy deposits of loess and of
the alluvium, colluvium, and loess unit are widespread
throughout the area.

Stability conditions.—Landsliding has occurred on
most of the steeper slopes. Most of the landslides are
now stable and the characteristic hummocky terrain
prevails (fig. 20).

Nearly all slopes west of the reservoir show evi-
dence of landsliding. The active or very recently active
slides, except for some along Whetstone Creek, are
near the uplands. Most occur on slopes that do not
have any low-level terraces. The evidence implies
that present landslide activity west of the reservoir
is the waning phase of a cycle begun after the river
had formed the terraces.

East of the reservoir are two general classes of
slopes, west-draining and south—draining. The west-
draining slopes adjacent to the reservoir resemble
those across the river. They consist mostly of hum-
mocky stabilized-landslide topography with a few
active and recently active landslides. Much of the
current landslide activity is near the uplands, but an
appreciable amount is also on the lower slopes and
along the river. Recent erosion along the river and the
resulting renewed erosion along the tributaries appear
to be responsible for the present landslide activity.
Farther east, the south-draining slopes of the dis-
sected upland show much less evidence of landsliding.
As in area 2 (pl. 3), the terrace south of the upland
has apparently acted as a buffer to protect the slopes
above from recent direct erosion by the river; there
is no evidence of sliding in terrace and preterrace time.
In postterrace times, however, the streams crossing the
terrace have done more downcutting and oversteepen-
ing of their walls than their counterparts in area 2.
As a result, landslides, both stabilized and active, are
more common above the terrace in area 3 than in area
2.

AREA 4

The limits of area 4 (pl. 1) are lat 43°33’ to 43°37’
N. and long 99°16’ to 99°24’ W. The area is about 55
miles upstream from the Fort Randall Dam. The part
of the area west of the river is in Lyman County,
S. Dak., and the part east of the river is in Brule
County, S. Dak.

The Missouri River divides area 4 into two nearly
equal parts. The river flows due south to about lat
43°35’ N., then swings gently southeastward to the
south boundary of area 4. Flood plains and low ter-
races form a bottomland as much as three-fourths mile
wide along the west side of the river. Moderately
steep shale slopes (fig. 26) rise from the valley floor
(about 1,320-ft altitude) to uplands ranging from
about 1,750 feet to as much as 1,820 feet in altitude.
In the northwest part of the area the upland is dis-
sected by steep-walled valleys draining northwest

REPRESENTATIVE

STUDY AREAS 39

 

FIGURE 26.—'I‘errain west of the Missouri River in area 4. Typical steep slopes with hummocky stabilized landslide topography
and some small active landslides along the valley bottoms. View north from SEIASEIA sec. 6, T. 101 N., R. 71 W., Lyman
County, S. Dak. Photographed August 27, 1956.

away from the Missouri River. On the east side of the
river erosion has removed or prevented development
of an extensive flood plain. Except for isolated bits of
flood plain, bluffs from 20 feet to more than 100 feet
high rise directly from the river. In the southern third
of the area the bluffs terminate in a clearly defined,
gently sloping terrace as much as one—half mile Wide.
In the northern two-thirds of the area erosion has re-
duced the terrace to flat-topped spurs that cap the
bluffs bordering the river. Behind the terrace, rela-
tively steep slopes rise to an upland that is 1,700—
1,800 feet in altitude.

Geologic setting.—The geology in area 4 (pl 1)
differs from the areas downstream primarily in that
the Mobridge Member of the Pierre Shale is the upper-
most pre-Quaternary unit present. Much of the geo-
logic information below was summarized from Bald-
win and Baker (1952).

The flood-plain and low-terrace deposits of the
river are mostly slow-draining alluvium. Except for
exposures near the north and south edges of area 4,
the top of the Niobrara Formation is concealed by the
alluvium. Pierre Shale, from its base up through the

lower part of the Mobridge Member, is exposed on the
slopes rising from the bottomlands.

In the east half of area 4 the Niobrara Formation
is well exposed north of lat 43°35’ N.; to the south
it is found mostly in scattered exposures along small
tributaries as far south as Elm Creek. The Pierre
Shale, from the Sharon Springs through the Veren-
drye Members, overlies the Niobrara east of the river.
Till, blanketed by loess, overlies the Verendrye Mem-
ber and forms the upland surface. Alluvium com—
prises the terrace and the small flood plain at its base.
Alluvium also floors the valley of Elm Creek above
the northern limit of the terrace. Small deposits of
alluvium also cap the terrace remnants to the north.
The alluvium is mostly slow draining, but some fast-
draining alluvium is also present.

Stability conditions—Slides (fig. 26) have occurred
on nearly all of the slopes in the Missouri River trench
and in most of its tributary valleys. Landsliding is
less prevalent along valley walls of the westward-flow—
ing streams in the northwest corner of the area.

Active and recently active landslides are numerous
on both sides of the river, but most of the slides are

4:0 LANDSLIDES NEAR FORT RANDALL RESERVOIR, SOUTH DAKOTA

small and collectively they form a very small per-
centage of the total landslide area. Present landslide
activity is related almost entirely to minor erosion
and local oversteepening of slopes by the smaller
tributary streams.

The extensive areas of now-stabilized landslides
apparently were most active before the formation of
the high terraces east of the river, because there is
no evidence of landslides encroaching on the terraces.
In postterrace time, moreover, the river has partially
or completely removed the terraces north of Elm
Creek, but extensive landsliding has not followed. This
apparently anomalous erosion without landsliding may
occur because the river is incised 40—50 feet into the
Niobrara Formation, which has supported the weaker
overlying shale here.

AREA 5

Area 5 (pl. 1), the northernmost study area, is about
70 miles upstream from Fort Randall Dam at the con-
fluence of the White and Missouri River valleys (pl. 1) ,
and is bounded by lat 43°42’ and 43°46’ N. and long
99°21' and 99°29’ W. The land west of the Missouri
River is in Lyman County, S. Dak.; the land east of
the river is in Brule County, S. Dak.

The Missouri River, which flows from north to south
in a gentle S-curve, divides the area nearly in half. The
west half is further divided by the curving course of
White River which isolates the southwest quarter from
the rest of area 5.

The physiography in area 5 represents three stages
of development. The oldest is the preglacial White
River valley that crossed the area from west to east
(F lint, 1955, pl. 7). Subsequently, this valley was mod-
lfied by glaciation and the formation of the present
valleys of the White and Missouri Rivers. The upland
surface on both sides of the Missouri was originally
part of the preglacial White River valley and is gen-
erally lower than the uplands in the other study areas.
West of the Missouri River there are still remnants
of several preglacial White River terraces. East of the
river the former White River valley is filled with till
and is identified only as a broad shallow sag in the
present upland surface (Warren, 1952, fig. 2).

In the northern two-thirds of the area, vertical
bluffs 70—100 feet high border the Missouri River
(about 1,320—ft altitude). Above the bluffs, the walls
of the trench rise steeply to a gently rolling upland
that is 1,500—1,650 feet in altitude. Downstream, where
the Missouri River makes a wide swing to the south-
west, the steep trench wall gives way to gentler slopes,
and a succession of terraces descend to a flood plain
that broadens southward to the junction with the
White River.

The floor of the White River valley is characterized
by extensive flood plains, low fl-at islands, and low ter-
races. Supported by resistant outcrops of the Niobrara
Formation, the valley walls generally rise above the
floor as steep bluffs. The slopes above the Niobrara
range from gentle in places not recently eroded to
precipitous in stretches undergoing erosion by the
river.

The east side of the Missouri River is bordered by
a flood plain one-fourth to one-half mile Wide sur—
mounted by broad low terraces. The east wall of the
Missouri trench, in the northern part of the area, is
characterized by gentle multiterraced slopes. It steep-
ens southward to precipitous blufl's as much as 100 feet
high in turn surmounted by steep slopes. The upland
east of the river ranges in altitude from approximately
1,620 to 1,700 feet.

Geologic setting—Data on the geologic setting are
derived from Baldwin and Baker (1952), Petsch
(1952), Warren (1952), and Warren and Crandell
(1952), supplemented by the author’s observations.

The oldest exposed rock, the Niobrara Formation,
has its upper limit at an altitude of about 1,380 feet.
The lower five members (Sharon Springs to Veren-
drye) of the Pierre Shale overlie the Niobrara Forma—
tion and comprise most of the slopes. The Quaternary
deposits, separated from the Cretaceous by a major un-
conformity, are alluvium and till with minor amounts
of loess and of the alluvium, colluvium, and loess unit.
Fast-draining alluvium caps most of the higher ter-
races of both pre- and post-Missouri River age. Fast-
draining alluvium also crops out on the east side of the
Missouri River trench wherever erosion has exposed
the floor of the preglacial White River valley. The
lower terraces and prereservoir flood plains along the
contemporary drainage system are largely slow—drain-
ing alluvium. Till underlies the uplands east of the
Missouri River. Loess occurs as a thin blanket over-
lying the till and as small isolated patches. The allu-
vium, colluvium, and loess unit forms small deposits
in hollows and gulslies.

Stability conditiona—Landslides make up a smaller
proportion of area 5 (pl. 1) than of any other study
areas. This can be attributed to the topography created
by numerous terrace remnants left by both pregliacial
and postglacial rivers. These terrace remnants form
steps in the valley walls and therefore areas of unin-
terrupted steep slopes are limited. The terraces, more—
over, protect the slopes above them from direct river
erosion.

In only two parts of area 5 has landsliding in-
volved entire valley walls in the manner so common in
the other representative areas. The first is the northern

REPRESENTATIVE

two-thirds of the west trench wall. Here a cycle of
landsliding in the Pierre Shale apparently followed
erosion of the supporting Niobrara Formation by the
Missouri River. Most of the slides are now stable,
which indicates that the Pierre Shale slopes have read-
j usted to prereservoir condition of the underlying Nio-
brara Formation.

The second par-t of the area is at the bend of
the White River in the NE. cor. sec. 16, T. 103 N.,
R. 72 W. There the landsliding is less extensive than
along the west trench wall, but it is more spectacular
because large land-slides are still active (fig 27). In
this area also the landslides occurred after erosion of
the Niobrara Formation removed support for the
overlying shale.

Other landslides in the area are individual slides or
relatively small areas of coalesced slides. Except for
a few along the east trench wall, these slides are in
the valleys of tributary streams.

Active and recently active landslides make up a
very small part of the slides described above; more-
over, more than half of the activity is concentrated
in two areas. The first is at the bend in the White
River in the NE. cor. sec. 16, T. 103 N., R. 72 W. The
second area, which includes the 81/2 sec. 19, N1/2 sec.
30, T. 103 N., R. 71 W., east of the Missouri River
and some land south of area 5, is informally called
the Cable School landslide area for the Cable School,
located about 1 mile to the east. The Cable School
landslides (fig. 28) are along a branching tributary in
the lowest part of the buried White River valley (War—
ren, 1952, fig. 2). The sliding occurred in shales satu-

STUDY AREAS 41

rated by seeps and springs fed from water-bearing
gravels in the sediments of the preglacial valley.

INTERPRETATION OF DATA

The information derived from appraisal of slope
stability and from geologic mapping is used for two
purposes. The first is to present semiquantitative meas-
ures of prereservoir landslide distribution and activity,
and to infer from these measures and from the rela-
tion between landslides and local topography that
landslide activity was greater in the more distant past
than in the time just before filling of the reservoir.
The second purpose is to show the degree of correlation
betWeen slope stability, natural slope angles, and com—
position of geologic materials in part of the area in-
cluded in area 2 (pl. 3).

PRERESERVOIR SLOPE STABILITY

The factors considered in judging the stability of
prereservoir slopes are: the area in each landslide sta-
bility class relative to the total area of landslides, the
relative sizes of individual landslide areas in each sta-

bility class, and the relation between landslide activity
and local topography.

The area of each class of landslide stability in the
five representative study areas was measured With a
polar planimeter and the results by percentages of
total landslide area are shown in table 4. Stabilized
landslides are the predominant class in all areas. For
present purposes the three other classes are considered
current landslides in contrast with stabilized landslides

 

FIGURE 27.—Bluffs along the left bank of the White River where river erosion is causing active land-slides. The light-colored
outcrops in the lower middle part of the slopes are Niob‘rara Formation. The Niobrara Formation is eroded by the river and
leaves oversteepened shale slopes above. These shale slopes fail and the landslide debris masks the Niobrara Formation.
N E14 sec. 16, T. 103 N., R. 72 W., Lyman County, S. Dak. (west side of area 5). Photographed July 10, 1952.

42 LANDSLIDES NEAR FORT

RANDALL RESERVOIR,

SOUTH DAKOTA

 

FIGURE 28.—East part of the Cable School landslide area. View east-northeast from SW14NW14 sec. 30, T’. 103 \.. R. 71 W.,
Brule County, S. Dak. Photographed October 14, 1954.

TABLI‘. 4.~Percentage of total area of landslides in each class of
landslide activity

 

Current landslides
Stabilized

Study area

 

 

landslides Recently Reactivated Active
active
98 <1 < 1 1
92 2 3 3
97 < 1 <1 1
()9 <1 <1 < 1
95 <1 i 5
Average ________________ 06 < 1 <1 2

 

The stabilized landslide areas, large slides appar—
ently are more common than small slides (figs. 20, 25,
and 26). In current landslide areas, however, small
slides (figs. 6, 12) are much more common than large
landslides (figs. 4, 27). Large current landslide areas
are numerous only in area 2 (pl. 3).

In the past, landslides have been prevalent on most
of the steeper slopes, but many of these slopes now
seem virtually stable. therever stabilized landslide
areas are flanked by river terraces, there is no evi-
dence of renewed sliding. New activity is confined
to the valleys of streams recently entrenched into the
terraces. Most new slides are directly related to ero-

sion along the smaller tributary streams, and steep—
ness of slope is a secondary factor in determining their
location. Even in large areas of current landslide
activity (pl. 3), there is very little landsliding along
the precipitous inner trench wall.

The information summarized above indicates that
in immediately preservior time the walls of this part of
the Missouri River trench were more stable than at
any time in their preceding history. Most evidence
suggests that landslide activity was relatively small
when the reservoir began to fill.

Two other factors probably have also contributed to
the comparatively large landslide activity of the past
and the small scale of recent slope failures. First, the
change in climate that followed the vanishing ice
sheets has resulted in a sharp decrease in the amount of
water available to lubricate the potential slides. Pre—
cipitation must have been greater throughout the gla-
cial periods. During the waning stages of glaciation,
moreover, melt waters contributed appreciably to the
ground-water supply in areas bordering the ice. The
present climate must be very dry by comparison. with
attendant diminution of ground—water supplies.

REPRE SENTATIVE

Second, during glacial and much of postglacial
times, the Missouri was cutting through the easily
eroded and unstable Pierre Shale in which slope fail-
ures are common. More recently, the river has en-
trenched itself in the Niobrara Formation which is
harder and much less susceptible to failure. A de-
crease in landslide activity would predictably follow
in most areas, as the slopes in the overlying Pierre
reached equilibrium.

CORRELATION OF LANDSLIDES, SLOPE ANGLES,
AND GEOLOGIC MATERIALS

The land southwest of the Missouri River in area 2
(pl. 3) is well suited to an investigation of possible
correlations between landslides, slope angles, and geo-
logic materials. It not only has more recently active
landslides than any other study area but it also con—
tains the entire Pierre Shale section, with the possible
exception of the Crow Creek Member. The investiga-
tion was restricted to the pre—Quaternary rocks be-
cause these include the materials most prone to land-
sliding.

PREPARATION or DATA

The information on slope stability conditions of the
pre-Quaternary geologic units in area 2 (pl. 3) is
given in percent-ages. First the areas of each unit and
of each stability class in each unit were measured with
a plianimeter. Then the results were used to compute
(1) the percentage of total pre-Quaternary exposures
represented by each geologic unit, (2) the percentage
distribution of each unit among the stability classes,
and (3) the percentage of each stability class within in-
dividual units. The results are presented in table 5.

The Pierre Shale, as shown on table 5, comprises
97.4 percent of the pre-Quaternary exposures and in—
cludes all but 1—2 percent of each class of landslide.
Field observations indicate, moreover, that landslides
in the Ogallala and Niobrara Formations are usually
the result of landslides in the shale. Inasmuch as vir-
tually all the landslides are in or are controlled by the

43

STUDY AREAS

Pierre Shale, consideration of the correlation between
landsliding, slope angles, and geologic materials is
restricted to that formation.

Data for the slope angles were averaged from 10 cross
sections; three of the cross sections and location of all 10
are shown 011 plate 3.

For every pre-Quaternary geologic unit exposed along
each cross section, average slope angles were computed
according to the following formula:

thickness of unit

horizontal exposure of
umt along cross sectlon.

The angles for individual shale members in each cross
section were then averaged with the corresponding
angles along the other cross sections, and the results
are taken as representative angles for each member of
the Pierre Shale (table 6).

tan (average slope angle) =

TABLE 6.—-Auerage slope angles, in degrees, of the members of the
Pierre Shale along cross sections A—A’ to J—J’

 

 

 

 

Verendrye

Elk Virgin and Sharon

Cross section Butte Mobridge Creek De Grey Gregory Springs
6 6 3 3 11 16
18 18 8 3 15 6
5 12 10 5 2 __________
7 5 3 10 27 22
17 7 7 5 5 2
8 6 9 5 20 17
6 10 4 6 ____________________
10 13 5 3 6 ..........
17 12 8 3 ____________________
J —J ’ ________________ 17 20 7 7 3 5
Average ________ 11 11 6 5 11 11

 

Assuming that only the proportional amount of mont-
morillonite in the clay-size component of each member
affects the stability of that member, the author averaged
and incorporated quantities for the montmorillonite
content (fig. 16) in table 7 . Although some of the
samples (fig. 16) were collected as much as 60 miles
from area 2 (pl. 3), their analyses are considered to be
sufficiently accurate for this study because the mineral
composition of the Pierre Shale apparently is relatively
consistent throughout the Fort Randall area.

TABLE 5.——Slope stability conditions of pre-Quaternarg deposits in study area 2 southwest of the Missouri River

 

 

 

 

 

 

Percentage Percentage of unit Percentage of each stability class in stratigraphic
Map of total nits
Unit symbol area of
(pl. 3) exposures of Stabil- Recently Reacti- All Stabil- Recently Reacti-

pre‘Quater- Stable ized active vated Active landslide Stable ized active vated Active

nary units categories
Ogallala Formation _________________ To 2 5 53 44 <1 2 <1 47 25 1 <1 2 1

Pierre Shale:
Elk Butte Member ______________ Kpc 22. 9 12 79 2 4 3 88 56 21 14 34 24
Mobrid e Member _____ ____ Kpm 19.5 <1 90 4 3 3 100 1 20 31 20 22
Virgin reek Member ___________ vac 16. 1 0 92 3 3 2 100 0 17 19 16 11
Vegendrye and DeGrey Mem- vad 30. 2 <1 93 3 2 2 100 2 32 33 24 23
ers.

Gregory Member ................ Kpg 6.0 5 89 <1 1 4 95 6 6 2 2 11
Sharon Springs Member Kps 2. 7 15 76 0 2 7 85 8 3 0 2 8
Total Pierre Shale _______________________ 97. 4 4 88 3 3 2 96 73 99 99 98 99
Niobrara Formation ________________ Kn . 1 86 14 0 0 0 14 2 0 0 0 0

 

44 LANDSLIDES NEAR FORT RANDALL RESERVOIR, SOUTH DAKOTA

ANALYSIS

Although the data from area 2 (pl. 3) are quanti-
tative and permit statistical analysis, the selection of
a workable method for analysis was restricted by data
being limited in both quantity and quality. Some in-
formation, such as the distinction between stable
ground and landslide areas, is necessarily subjective.
Many of the geologic contacts are either approxi-
mate or inferred. The slope angles are based on a lim-
ited number of cross sections, and the proportional
values for montmoril-lonite clay are derived from scat-
tered samples collected over the entire reservoir area.

Slope stability, slope angles, and montmorillonite
clay content are interrelated, but geographic and strat—
igraphic locations are also important factors in slope
stability of exposures. Exposures along a stream-cut
bank, for example, are more susceptible to landslides
than exposures of the same material on a gentle slope.
Similarly, geologic units overlying stable strata are
less prone to sliding than similar units overlying un-
stable strata. Finally, effects of ground water on slope
stability are not taken into consideration.

Spearman’s rank correlation coefficient was used to
determine possible correlation between montmorillonite
content, slope angles, and relative amount of landslide
terrain of the members of the Pierre Shale. This
coefficient indicates the relation between two classes of
data ranked according to increasing or decreasing
values. A method using ranks instead of actual
numerical values minimizes minor discrepancies and
also simplifies correlation of dissimilar classes of data.

Spearman’s rank correlation coefficient (rmk) is
defined as:

r =1_6 ED2
rank N (N2—1)
in which,
D= difference in rank between paired item in two
series,
2D2=sum of values of D2 for all paired items in two
series,
N =the number of pairs of items in two paired
series. (Croxton and Cowden, 1955, p.
478—480.)
Values for the correlation coefficient range from 1 for
complete correlation, 0 for completely random distribu—
tion, to —1 for complete inverse correlation. Only two

series can be correlated at one time.
The first step to determine rank correlation coeffi—

cients is to assign ranks to each item (table 7). Where
two or more items are of equal value, the respective
rank numbers are averaged between them. After the
data are ranked, the rank correlation coefficient is cal-
culated between each pair of series.

TABLE 7 .—Ranking of Pierre Shale data

 

 

  

 

Average
montmoril- Average Relative
lonite slope amount of
Member content of Rank angle Rank landslide
clay -size (degrees) terrain Rank
fraction (percentage)
(parts in 10)
_ 7 3 11 4% 88 5
_ 4 6 11 4% 100 2
Virgin Cre _ 9 1% 6 2 100 2
Verendrye and DeGrey 9 l 5 1 100 2
Gregory _____________ 6 4% 11 4% 95 4
Sharon Springs _____________ 6 4% 11 4% 85 6

 

M ontmorillonite—content—slope—angle rank correlation coefl‘icient

 

 

  
 
  
 

 

 

Rank of Rank of
Member of the Pierre Shale montmoril- slope D D2
lonite content angle
Elk Butte__ 3 4% 3/2 9/4
Mobrid e__ 6 4% 3/2 9/4
Virgin reek ______ . 1% 2 % %
Verendrye and DeGrey 1.1/6 1 1/2 34
Gregory ________________ _ _ _ _ _ 4% 4% 0 0
Sharon Springs ............................. 4% 4% 0 0
ED2=5
N =6
. =1_ 1?” ,
rank N<N2-1)
_1_ fl
_ 6(36)—1)
=0. 857

M ontmorillonite-content—relatlve-amountrof-landslide-terrain rank
correlation coefl‘lcrent

 

 

   

 

 

 

   

Rank of Rank of
montmoril— relative
Member of the Pierre Shale lonite amount of D D2
content landslide
terrain
Elk Butte ______________________________ 3 5 2 4
Mobrid e ______ . 6 2 4 161
Virgin ‘reak _______________ . 1% 2 % A
Verendrye and DeGrey. 1% 2 ’2 M
Gregory ______________ 4% 4 % %
Sharon Springs ............. 4% 6 3/2 9/4
2D2=23
N =6
r _1_ 62172
unk— N(N2—1)
_1_ 6(23)
_ 6(36—1)
=0. 343
Slope-angle—relative—amount-of-landshide—terrain rank correlation
coefliczent
Rank of
Rank of relative
Member of the Pierre Shale slope amount of D D?
angle landslide
terrain
Elk Butte, ____________ 4% 5 12 %
Mobrid e 4% 2 5/2 25/4
Virgin ree _ 2 2 0 0
Verendrye and DeGrey , _ 1 2 l 11
Gregory ____________________ _ . 4% 4 V2 /4
Sharon Springs _____________________________ 4% 6 __:fl2__‘3/:
2D2=10

 

02m
"MM—1)
6(10)
6(36—1)
14

funk=l

 

=0.7

REPRESENTATIVE STUDY AREAS 45

The rank correlation coefficients indicate a large
range in the degree of correlation between the three
series. In any two series where N=6 there is only one
chance in 20 that randomly selected independent vari-
ables will have a rank correlation coefficient as high
as 0.829 (Olds, 1949, quoted from Dixon and Massey,
1951, table 17—6). It follows that the montmorillonite-
content—slope—angle coeflicient (0.857) has less than
one chance in 20 of representing random correlation be-
tween variables. There is little doubt, therefore, that
montmorillonite content and slope angles are related.
The relation is inverse; that is, the higher the mont-
morillonite content, the lower the angle of slope. The
montmorillonite-content — relative—amount-of-landslide_
terrain coefficient (0.343), on the other hand, is too low
to be significant. Between the two extremes is the co—
efficient for rank correlation between slope angles and
relative amounts of landslide terrain (0.714). This
value is not low enough to refute the possibility of
correlation, but neither is it high enough to conclu-
sively prove correlation.

INTERPRETATION

There is a correlation between montmorillonite con-
tent and slope angles if the conclusion is correct that
shear strength of the Pierre Shale is an inverse func-
tion of montmorillonite content in the clay—size portion
of the shale. The shear strength in turn largely deter-
mines the maximum natural slope angle of the shale.
The maximum possible slope angles, therefore, are
finally con-trolled by the montmorillonite content of
the shale.

The line of reasoning in the preceding paragraph
admittedly is much oversimplified. This generaliza-
tion presents only the principle that there is a correla-
tion between montmorillonite content and slope angle.
Lack of complete quantitative correlation between the
montmorillonite contents and slope angle data for the
shale members (table 7) presumably is due to various
modifying factors (p. 44). The data in table 7, and
above show that the lack of correlation between the
montmorillonite content and the relative amount of
landslide terrain may be due largely to the apparently
contradictory statitsics for the Mobridge Member. Al-
though its average slope angle is among the highest
and its montmorillonite content is the lowest in the
whole formation, the Mobridge is classified as 100 per—
cent landslides (table 7). This surprising lack of sta-
bility in the Mobridge probably arises because the
underlying members are high both in montmorillonite
content and in percentage of landslide terrain.

The only obvious correlation between slope angle
and the relative amount of landsliding is that factors

472-783 0 < '73 < 4

which permit the shale to maintain steep slopes also
tend to reduce the amount of landsliding. The amount
of landsliding, for example, seems to be controlled
partly by stratigraphic and topographic location. The
most stable members of the Pierre Shale (table 5) are
the Sharon Springs and Gregory, which overlie the
Niobrara Formation, and the Elk Butte, which is the
uppermost member and comprises part of the stable
upland surfaces (pl. 3). The relatively stable Niobrara
Formation apparently increases stability of the over-
lying Sharon Springs and Gregory Members by form-
ing a stable foundation for them. The fact that the
Gregory, separated from the Niobrara by the Sharon
Springs, has a higher percentage of landslides than
the Sharon Springs shows that the effectiveness of sup—
port diminishes with distance from the foundation.

In contrast, the Mobridge, although its low mont-
morillonite content should make it more stable than the
Sharon Springs and Gregory Members, is extremely
susceptible to landsliding. The fact that it is underlain
by the highly unstable Virgin Creek, Verendrye, and
DeGrey Members undoubtedly tends to nullify its
strength and to reduce its value as a potential support
for the Elk Butte. The Elk Butte Member, in spite
of its fairly high montmorillonite count, has fewer
slides and steeper slopes, probably because there are
no very thick overlying sediments creating stresses
within it.

SUMMARY AND CONCLUSIONS

Investigations in the representative study areas have
yielded several noteworthy results:

(1) There is a strong inference that before forma-
tion of the Fort Randall Reservoir the walls of the
Missouri River trench were comparatively stable. Prob-
ably the last period of great landslide activity was in
glacial times.

(2) Virtually all of the landslides occur in the Pierre
Shale.

(3) All members of the Pierre Shale are subject
to landslides. Relative stability of the members is
reflected in the angles at which they form stable slopes
and not by the relative number of landslides in each
member.

(4) Natural slope angles in individual shale mem—
bers, and therefore relative stability and strength of
the members, are an inverse function of montmoril-
lonite content in the clay-size fraction of the shale.

(5) Restricted landslide activity in some shale mem-
bers seems due to stratigraphic and geographic loca-
tions of the members. Apparently it is not related to
composition and behavior of the members themselves.
Where external factors restrict landsliding, the shale

46 LANDSLIDES NEAR FORT RANDALL RESERVOIR, SOUTH DAKOTA

may be stable on what otherwise would be abnormally
steep slopes.

General conclusions are that the Fort Randall Res-
ervoir should have little effect on slope stability beyond
the immediate shoreline unless wave erosion is unex-
pectedly great or unless there is an unforeseen major
rise in the ground-water table within the Pierre Shale.
A major change from the present environment would
be required to restore, or even approach, the condi-
tions of the glacial times. Slope stability is directly
related to the percentage of montmorillonite in the
clay-size fraction of the Pierre Shale, although other
factors may also influence slope stability.

GROUND-WATER INVESTIGATIONS

A continuing program was started in the winter of
1954 to investigate ground-water conditions at depths
of less than 100 feet. The ground water data in this
report are based on the first 3 years of ground—water
observations.

PURPOSE

Ground—water observations in the Fort Randall
Reservoir area were undertaken to correlate changes in
ground-water conditions with landslide activity, and
to better understand the behavior of ground water in
the Pierre Shale and alluvium along the reservoir
shores. Two general classes of factors control the
ground-water conditions: (1) those that create per-
manent or semipermanent ground-water changes and
(2) those of periodic or cyclic nature that occur either
rather regularly or randomly.

The Fort Randall Reservoir itself is a factor in the
first class. This permanent body of free water has
formed a new base level at a higher altitude than the
former Missouri River surface. The nearby water table
consequently must reach a new, higher surface to re-
develop a state of equilibrium. Such an adjustment is
a long—range process controlled by the amount of water
available and by the permeability of the ground. This
report describes only the general effects of the reservoir
water level on the table because the available records
are insufficient for more detailed consideration.

The most obvious cyclic factor is seasonal climatic
variations. Other factors are alternate periods of
drought and above-normal precipitation and the effects
of single, abnormally heavy, storms. Some of these re-
curring factors have relatively rapid effects on ground-
water conditions and can be investigated qualitatively
on available ground-water records.

METHOD OF INVESTIGATIONS

Porous tube piezometers, first described by Casa—
grande (1949), were used in the ground-water obser-

vation program. Casagrande’s method of constructing
and installing the piezometers was somewhat modified
and simplified for the purposes of the investigation.

For several reasons, porous tube piezometers were
considered suitable. Materials for their construction
are inexpensive. Several piezometers can be installed
independently at different depths in a single drill hole
to provide ground-water data for several horizons
without materially increasing installation costs. Be-
cause of their small diameter, they are sensitive to the
small pressure changes caused by minor changes in
water volume in relatively impermeable materials.
They are nonmetallic and do not corrode in the min—
eral-rich waters of the Pierre Shale.

The porous tube piezometer is fundamentally an
observation well with a well point consisting of a
porous tube and a standpipe. Standpipes used on this
project were made of %-inch—inside—diameter plastic
tubing (fig. 29). In the drill hole, the porous tube is

Porous plastic
/tubing (%-inch
Inside diameter)

W/G

EXPLANATION

m

Shale or other relatively
impervious fill

 

 

 

 

 

 

 

FIGURE 29.—Schematic diagram of piecometer
installation. Plastic tubing extends 2—3 feet
above ground surface.

GROUND-WATER

packed 111 clean sand and sealed above and below with
bentonite clay so that the water level in the standpipe
reflects piezometric pressures at the horizon of the
porous tube.

Installation of the piezometers along the reservoir
was relatively simple. Holes for installation of the
piezometers were drilled with either a power augei
or a churn drill. Then the piezometers were lowered
into the holes, which were backfilled. \Vhere more than
one piezometer was installed in a single hole, each ad-
ditional one was emplaced when the hole had been
backfilled to the desired depth.

PIEZOMETER LOCATIONS

Twenty piezometers were installed in the area at six
sites along the reservoir shore and at two sites down-
stream from the dam. General locations of the piezo-
meter sites are shown on plate 1; detailed descriptions
of the locations are given in table 8. The two sites
below the dam were selected as control installations to
determine regional ground-water changes that may
occur independently of the effects of the reservoir.

TABLE 8.—Piezometcr installations in South Dakota

 

 

 
 

County Location Altitude
(ft)

A ________ Giegory __________ NEMNEMSEV sec. 20, T. 95 N. R. 65W. 1,360

._ SEVNEVNWVsec. 28,T. 97N. R. 68W. _ 1,444

SEMSEMSEM sec. 28 T. 116N., R.66 W . 1,463

do ___________ SWMSWMSWM sec. 31, T. 95N., R 64 W.. 1,498

1 _________ Brule _____________ About 600 ft southwest of water plant in- 1,381

take building Chamberlain.

2 ______________ do _____________ About 450 {t northeast of intersection of 11th 1, 390
Ave. and Courtland St. Chambeilain

3 ______________ do _____________ SEMSWMSWM sec. 11 T. 105N. R.71W. 1,414

4 ______________ do _____________ SEMNEANWMsec.18,T103N., R 71W. 1,450

 

The piezometer sites are grouped generally about the
towns of Pickstown and Chamberlain to make them
easily accessible for periodic measurements. The piezo-
meters near Pickstown include the two control sites and
two sites in the lower part of the reservoir where
ground-water changes should be greatest. The piezo-
meters near Chamberlain are near the head of the
reservoir where the rise in free water level, and pre-
sumed corresponding rise in ground-water levels,
should be small.

Sites 1 and 2 at the town of Chamberlain were
chosen specifically to investigate seepage pressures in
a terrace of fine surficial deposits similar to landslide—
susceptible materials along the shores of Lake Roose-
velt behind Grand Coulee Dam in Washington. The
landslides along Lake Roosevelt have occurred most
frequently after a rapid major drawdown of the reser-
voir water level, and it is likely that seepage pressures
from water draining out of the saturated materials
along the shore triggered these slope failures. In the

INVESTIGATIONS 47

event of similar major drawdowns in the Fort Ran-
dall Reservoir, the piezometers at Chamberlain will
provide information about seepage pressures in the
terrace.

Four of the piezometer installations—sites 4, B, C,
and D—are in Pierre Shale; the other four—sites A,
1, 2, and 3—are in alluvium. This distribution was
selected to determine ground—water trends in a typical
variety of materials along the reservoir.

Piezometers in the shale were installed approxi-
mately 30, 60, and 90 feet below the surface so that the
piezometers would be far enough apart to avoid
ground—water migration from one horizon to another.
An additional piezometer was installed at a depth of
12 feet at site B to record ground—water conditions near
the surface. The piezometer numbers indicate site and
depth; thus, piezometers B—12 and B—8O are at depths
of 12 and 30 feet in the same hole at site B.

Distribution of piezometers in the surficial materials
was more varied; depths ranged from 14 to 81 feet, and
one to three piezometers were installed at each site.

RESULTS AND INTERPRETATIONS

Water levels for each piezometer and the drillers
log for each site are shown graphically in plate 4. The
reservoir water levels at both Pickstown and Cham-
berlain are also plotted for comparison with ground-
water levels. The following results and interpretations
refer to the data in plate 4.

Piezometric pressures were surprisingly constant
during 1954—56; water levels varied little more than 1
foot in most of the piezometers, and they varied more
than 4 feet in only three piezometers (B—92, D—92, and
1—60.

RELATION BETWEEN RESERVOIR WATER LEVEL AND
GROUND-WATER LEVEL

As of November 1956 there was little indication of
a relation between reservoir water level and ground—
water level in the piezometers located in the shale.
Only piezometer B—92 showed a gradual rise of pres-
sure followed by a relatively stable water level.

The piezometers at sites 1 and 2 on the Chamberlain
terrace are the only ones in the upper part of the
reservoir that show any response to the rising water
level. This is to be expected because the piezometers are
near the reservoir in slow—draining alluvium, one of
the relatively permeable materials along the reservoir.
Piezometer 1—60 apparently shows a direct relation
between reservoir water level and piezometric pres-
sures in the terrace. The absence of the usual seasonal
drop in water level in piezometer 1—29 during the sum-

48 LANDSLIDES NEAR FORT RANDALL RESERVOIR, SOUTH DAKOTA

mer of 1956 may be the result of ground-water changes
caused by the rising reservoir water level.

During 1954-55, the water level in piezometer 2—24
was high in the winter and low during the summer
months; in 1956, however, it rose steadily until in
November it stood about 3 feet above the former nor-
mal level. This suggests that the water table at site 2
began in 1956 to respond to the raised water level of
the reservoir. If this assumption is correct, there was
a lag of about 11/2 years from the time the reservoir
water level began to rise until the water table about
750 feet inland from the shoreline also began to rise.

Comparison between reservoir and piezometer 1—60
water levels reveals an interesting relation. The water
level in the piezometer was above the reservoir water
level until about the end of September 1954, when, until
May 1956, conditions were reversed, in that the reser-
voir water level was generally higher than the water
level in the piezometer. The prereservoir hydraulic
gradient obviously was toward the river, whereas from
fall 1954 at least to spring 1956 water was moving
from the reservoir into the terrace deposits. All the
other piezometric data indicate that the normal hy-
draulic gradient along the Missouri River trench is
toward the reservoir. The reversed hydraulic gradient
that existed for at least 11/2 years after the rise in the
reservoir water level was, therefore, a locally anomal-
ous condition that should exist only until ground-water
conditions became adjusted to the new reservoir water
level. Because ground—water adjustments in slow-drain-
ing alluvium were still incomplete less than 150 feet
from the reservoir after 11/2 years, one may assume
that the overall readjustment along the reservoir may
take at least 10 years.

RELATION BETWEEN CYCLIC PROCESSES AND
GROUND-WATER LEVELS

Observations in 1954—56 indicated that cyclic pro-
cesses had only minor effects on ground-water levels.
Variations in water levels that could be correlated with
seasonal climatic changes amounted to only a few feet
in the shallowest piezometers and was even less in the
deeper ones. There was no great change in annual pre-
cipitation during the 3 years that ground-water records
were kept and, therefore, no corresponding change in
ground—water conditions. Some small temporary rises
of water levels in the shallower piezometers were prob-
ably the result of especially heavy local storms, but
the precipitation records are not sufliciently detailed to
make a definite correlation.

Most small variations in the piezometer water levels
do not seem directly attributable to periodic or cyclic
causes and have no obvious relation to permanent

ground-water changes. Many are deviations in indi-
vidual water—level readings that may be faulty mea-
surements or temporary changes resulting from storms:
or other causes.

BEHAVIOR OF GROUND WATER

This section briefly outlines ground-water behavmi
at each piezometer installation and summarizes ground-
water behavior in alluvium and in the Pierre Shale.

SITE A

The piezometers at site A are in slow-draining alluv-
ium. Piezometers A—14 and A—30 measure pressures in
a lean clay. The porous tube of piezometer A—81 is just
below the alluvium-Niobrara Formation contact, but
the sand filter around the porous tube extends upward
about 8 feet into fine sand and clayey sand.

Piezometer A—14 is approximately at the water table.
The system rarely contains much more than 2 feet of
water, and frequently it is dry during part of the sum-
mer and early fall.

The water level in A—30 generally stands 8—10 feet
above the base of the porous tube, or about 7—9 feet
below the water table. Fluctuations in the water table
are crudely reflected on a reduced scale by the water
level in A—BO; friction between the downward migrat-
ing water and the clay and silt particles reduces the
hydrostatic pressures and dampens the effects of
changes in the water table.

Piezometric pressures in piezometer A—81 apparently
were smaller than in A—30 despite the greater depth.
The water level in A—81 rarely rose to more than 6
feet above the base of the porous tube. The water-level
fluctuations, moreover, show little correlation with
water levels in the shallower piezometers except from
December 1954 to February 1955. The water level in
piezometer A—14 rose suddenly in December 1954, fol-
lowed by a major drop in the water level in January;
a similar rise and fall of the water level occurred in
piezometer A—81 during January and February 1955.
The failure of A—30 to Show a similar response may be
due either to unknown hydrologic factors or simply to
clogging of the piezometer tube.

SITE B

The piezometers at site B are located in shale over-
lain by about 4 feet of colluvium. Piezometer B—12 is
in the weathered part of the shale near. the surface; the
others are in unweathered shale.

Unusual water-level conditions were found in the
piezometers at site B. Piezometer B-12 was dry almost
half the time it was being measured, but 14 out of 24

GROUND-WATER INVESTIGATIONS 49

measurements showed as much as 1.9 feet of water.
Piezometer 13—30, 18 feet below B—12, was dry at all
measurements. Piezometer B—59, 29 feet deeper than
B—30, consistently contained about 10 feet of water,
and the minor water—level fluctuations roughly correl-
ated with the fluctuations in B412. The water level in
B—59, moreover, was virtually at equilibrium when the
first measurement was made in February 1954. The
deepest piezometer, B-—92, did not reach equilibrium
until early in 1956 when the water level became stabil-
ized at a height of about 34 feet above the piezometer.

The water levels in the piezometers at site B would
be anomalous for normal ground-water conditions in
material of uniform permeability, but are normal for
the weathered and fractured conditions that appar—
ently exist in the Pierre Shale. Although fresh shale is
almost impermeable, weathered shale has greatly in-
creased permeability. During intervals of rapid
ground-water intake, therefore, the weathered zone can
become saturated even though fresh shale below is dry.
Piezometer B—12, located in weathered shale, records
the presence of an intermittent perched water table,
whereas piezometer B—30, in fresh shale but above the
permanent water table, record nothing.

Although piezometer B—59 is in fresh unweathered
shale, the comparatively rapid development of equili-
brium and sizable monthly water-level fluctuations
suggest that the water moves through fractures rather
than through the shale itself. The presence of water
in 13—12 and B—59 and the absence of water in B—SO
can be explained if B—59 intersects one of these frac-
tures and B—3O does not. At times of heavy intake,
some ground water would saturate the weathered shale
and the remainder would move down through the frac-
tures toward the permanent water table. An increase
in piezometric pressures would develop throughout the
entire fracture system and be reflected by piezometers
intersecting that system.

Comparison of the water levels in piezometers B—59
and B—92 supports the theory that ground—water move-
ment in the Pierre Shale is predominantly through
fractures. The extra time for piezometer B—92 to reach
equilibrium compared to the time for B—59 indicates
that the material surrounding B—92 is little fractured
and has a much lower permeability.

Field observations of the Pierre Shale further sup-
port the conclusion that fractures are the main avenues
of ground-water movement. Seeps issuing from frac-
tures in steep shale banks are common. In many shale
banks that do not have active seeps, the fractures are
coated with water—deposited secondary minerals. At
Oahe Dam near Pierre, S. Dak., the Corps of Engi-
neers also found that ground-water flow is related to

the fractures in the Pierre Shale (A. H. Burling, pro-
ject geologist, Oahe area, and L. B. Underwood, district
geologist, Omaha District, oral commun.)

SITE C

The geologic section at site C has about 11 feet of
lean clay (probably colluvium derived from the Pierre
Shale) underlain by about 28 feet of weathered Pierre
Shale, in turn underlain by fresh shale. The shallowest
piezometer, 0—29, is in the weathered shale and the
two deeper ones are in fresh shale.

Water levels in the three piezometers at site C were
relatively stable and all were within a range in eleva-
tion of about 10 feet. Piezometer 0—29 seems to be
located approximately at the water table; it never had
more than 1.4 feet of water and frequently was dry.
The depths of water in piezometers C—55 and 0—88
were about 19 feet and 51 feet respectively. Altitudes
of the water levels in these two piezometers never were
as much as 3 feet apart, whereas there was commonly
a difference of about 8 feet in the water levels in 0—55
and 0—29. The available data do not suggest a close
correlation between water-level fluctuations in the three
piezometers.

Such fluctuation of the water levels at site C may
be expected if ground-water movement in the shale
matches the movement postulated for water levels at
site B. The water level in 0—29 represents the water
table, and the water levels in 0—55 and 0—88 represent
piezometric pressures at depths of 55 and 88 feet below
the surface. The rapid water-level equilibrium reached
in both C—55 and C—88 indicates that they intersect
relatively permeable fractures. The unrelated fluctua—
tions of water levels in the two piezometers imply that
the fractures do not directly interconnect.

SITE D

The three piezometers at site D are in unweathered
Pierre Shale. lVater in the shallowest piezometer, D—32,
had an average depth of about 10 feet, which suggests
that the water table was a few feet higher, or about
20 feet below the ground surface. Although the water
level in the piezometer was relatively constant, there
was a slow unexplained rise of about 2 feet in the
3-year period, 1954—56. Small fluctuations generally of
less than a foot were superimposed on the gradual up-
ward trend of the water level.

Although minor dissimilarities were noted, the
ground-water conditions measured by piezometer D—62
apparently were closely related to the conditions at the
horizon of D—32. With the exception of one measure—

50 LANDSLIDE‘S NEAR FORT RANDALL RESERVOIR, SOUTH DAKOTA

ment, the water level in D—62 was consistently about
0.5 foot below the water level in D—32.

The water level in piezometer D—92 indicates that it
is subject to slightly difl'erent conditions than the shal-
lower piezometers. After the piezometers were in—
stalled, the water level rose more in D—92 than in D—32
and D—62 and did not reach approximate equilibrium
in D—92 until October 1954; from that time to Novem—
ber 1956 the upward movement of the water level was
slightly faster than in the two shallower tubes. The
depth of water in D—92 was about 65 feet in November
1956, and the water surface 4.5 feet below that of D—62.
This contrasts with a difference of only 0.5 feet between
water levels in piezometers D—32 and D—62.

Most of the ground-water conditions observed at site
D suggest that here also ground-water movement is
predominantly through fractures. Piezometers D—32
and D—62 apparently intersect relatively permeable
fractures. Their levels adjust to water table fluctuations
with only brief time lags, and the slight differences in
water level in the two piezometers reflect the relative
ease with which water moves along the fractures. Slow
development of equilibrium in D—92 indicates less per-
meability than at the shallower horizons. The greater
difference of water levels between D—92 and D—62 than
between D—62 and D—32 may indicate that D—92 en—
countered a small relatively closed fracture or that it
lies entirely in unfractured shale.

SITES 1 AND 2

The piezometers at sites 1 and 2 were installed to
measure water pressures in the Chamberlain terrace.
The material at both sites is slow-draining alluvium
ranging in composition from clay to clayey sand.

Apparently the Chamberlain terrace has a permanent
water table overlain by one or more perched water
bodies. The wide range in permeability in the strata
composing the Chamberlain terrace probably favors
horizontal rather than vertical ground-water move-
ment. The water level in piezometer 1—60 approximates
the permanent water table near the reservoir shoreline.
The water level in piezometer 2—24 probably repre—
sents the water table toward the back of the terrace.
The water level in piezometer 1—29 is well above the
level in 1—60 and undoubtedly is a local water table
perched on the lean clay bed 33 feet below the surface
of the terrace.

SITE 3

The single piezometer installed at site 3 measures
water pressures in a 6-foot-thick bed of fast-draining
alluvium underlain by the Niobrara Formation and
overlain by about 39 feet of slow-draining alluvium.

Measurements of one piezometer can give no data
on vertical or horizontal movement, but they do show
that the fast-draining alluvium has never been fully
saturated and that at times it has had very little, if
any, water in it. This suggests that the fast-draining
alluvium may act as an underdrain for the slow-drain—
ing alluvium.

SITE 4

The hole at site 4 was drilled through about 8 feet
of silty colluvium and about 80 feet of Pierre Shale
into the Niobrara Formation. The two shallower piezo-
meters, 4—32 and 4—57, measure water pressure in the
shale. The deepest piezometer, 4—93, measures pressures
in both the Pierre Shale and the Niobrara Formation
near their contact.

The piezometer results at site 4 indicate the possi-
bility of several separate and distinct ground-water
levels. The independence of water levels in these piezo-
meters is in direct contrast to the water levels in shale
piezometer installations, each of which showed an in—
terdependence between water pressures at different
levels. The water in 4—32 had an average depth of 16
feet, greatest of the three, and showed a maximum var-
iation in level of 1.5 feet. Piezometer 4—57, in contrast,
had a maximum water depth of 1.8 feet and was
dry periodically despite the apparently permanent
ground-water body above it. The deepest piezometer,
4—93, had a remarkably stable water depth of 2 feet.
Except for one probably erroneous measurement in
January 1955, the level varied only 0.3 feet in 1954—57.
Ground-water conditions at 4—93, therefore, show no
correlation with conditions at the shallower piezo-
meters. There is no correlation between water-level
fluctuations nor is there a rise in water level toward a
water table defined by one of the shallower piezometers.

Such varying water levels in the three piezometers
seem to indicate that most ground water there moves
horizontally through fractures in the shale. The verti-
cal permeability apparently is slight, compared to the
horizontal permeability.

SUMMARY

The following brief generalities of ground-water be-
havior at the eight piezometer installations are valu-
able only as working hypotheses inasmuch as they are
based on data from only eight piezometer installations
collected intermittently over a 3-year period.

Ground-water movement through alluvium is pre-
dominantly horizontal. Because most alluvium consists
of layers of material with different permeabilities,
ground water moves downward until it reaches a less
permeable layer than the one through which it is mov-

LANDSLIDE MOVEMENTS 51

ing. The less permeable layer deflects the ground water
from predominantly vertical to predominantly hori-
zontal movement. Water pressures at various levels in
alluvium consequently may not show any direct vertical
correlation.

Most ground-water movement in Pierre Shale ap-
parently is along fractures. The water can move either
vertically or horizontally at a rate depending on the
degree of development of fractures in any particular
direction. Where vertical fractures are well developed,
there is a vertical component of movement that pro-
motes vertical equilibrium in the water pressures.
Where horizontal fractures predominate, the relative
horizontal component of movement may be so great
that vertical water pressure equilibrium cannot de-
velop, and there will be no correlation between water
pressures, or even rates of movement, at different levels.
Behavior of the ground water in these circumstances
is similar to that of ground water in stratified al-
luvium.

Piezometer measurements were continued until
December 1959 by the US. Geological Survey, Huron,
S. Dak. These are not plotted on plate 4, nor are they
correlated with reservoir water levels and precipitation
surpluses. In general, these later measurements add
little to the preceding account except for the follow-
ing minor corrections and additions:

Site A.—The difference in water level between A—14
and A—3O through the latter part of 1957 and through
most of 1959 increasedto about 15 feet, owing mostly
to a steady drop in level of A—30.

Site B.—Conditions have remained practically the
same as before except that B—30 had as much as 1.5 feet
of water in the winter of 1958—59.

Site 0.—Minor fluctuations in C—55 and 0—88 were
apparently unrelated. C—29 became plugged in early
1959, and other tubes became plugged later in the
year.

Site 1).—“Tater levels in D—32 and D—62 were almost
the same from the spring of 1957 through 1959. They
dropped gradually about 3 feet from July 1958 to
October 1959 and rose about 1.7 feet in November and
December 1959. These changes in the higher piezom-
eters were reflected rather faithfully by similar changes
at the same times in D-92, whose water level is 3—4
feet lower.

Sites I and 2.——Piezometer 1—29 remained dry or
had less than 2 feet of water during 1957—59, similar
to ground-water conditions in 1954—56. The water level
in 1—60 rose to elevation 1,351.9 in July 1958, and
dropped gradually to 1,344.9 by December. The water
level in 2—24, at the back of the Chamberlain terrace,
remained fairly constant between elevations 1,359.1

and 1,361.6 during 1957—59 except for a rise to 1,364.9
in July 1958.

Site 5’.—Piezometer 3—46 showed little change in
1957—59. The water level ranged in elevation from
1,369.9 to 1,372.4 feet. Measurements were periodic
because the tube was occasionally plugged.

Site 4.—During 1957—59 there was little change from
previous readings. The records are discontinuous owing
to plugging of the tubes or inaccessibility of the site
during periods of poor road conditions.

LANDSLIDE MOVEMENTS
METHODS OF INVESTIGATIONS

An estimate of the time, rate, processes, and mag-
nitude of movements was made for individual land-
slides and landslide complexes in five areas (pl. 1).
A network of control points was established on and
near each landslide. These points were occupied peri-
odically and compared with previous readings to de-
termine the amount and rate of movement.

Control points on the Highway 16 slump, Landing
Creek slump—earthflow, and Paulson slump and on the
Cable School earthflows were located by transit tra-
verse. At least two reference points on each traverse
were located on presumably stable ground. The main
traverses were closed to check surveying errors, but
short open traverses to isolated points were extended
from the closed traverses.

The Cable School slump-earthflow is across a small
valley from a stable ridge; so it was possible to tri—
angulate control point locations from three stations
established along the ridge. Triangulation had the ad-
vantages of being faster than a transit traverse and
required only one man for the survey. Points on the
Cable School slump-earthflow consequently were meas-
ured more frequently than those on the other land-
slides.

The control points were 1- by 2-inch stakes 2—4 feet
long usually driven into the ground until 6 inches of
the stake was exposed. At many points, however, more
than 6 inches was exposed so the control point would
be visible from adjacent stations. Aiming targets for
triangulation were large tin—can covers nailed to the
stakes. For the traverses, headless nails were set in the
tops of the stakes for aiming points. A number of
stakes were destroyed or damaged by cattle and were
replaced or abandoned.

Horizontal control for each landslide was adjusted
to an arbitrary grid system superimposed on a map of
the landslide. The horizontal and vertical movements,
computed from the triangulation and transit traverse
data, were plotted vectorially on the individual land-
slides. Inasmuch as the two types of movement were

52 LANDSLIDES NEAR FORT RANDALL RESERVOIR, SOUTH DAKOTA

similar in general behavior, only the horizontal move-
ments are discussed in this report.

DESCRIPTIONS OF LANDSLIDES

Except in the geologic map of the Landing Creek
slump—earthflow, the mapping represents the geology
in each of the landslide areas before movement oc-
curred. At the Landing Creek slump—earthflow, land-
slide material and other shallow col'luvial deposits as
well as bedrock geology were mapped to demonstrate
the masking effects of the landslide materials. Mapping
these also showed some of the larger stratigraphically
displaced blocks of Pierre Shale that probably are rem-
nants of old landslide blocks. Landslide and colluvial
debris are not shown at the other four slide areas so
that the causes of the landslides can be clearly separated
from their effects.

HIGHWAY 16 SLUMP

The Highway 16 slump (fig. 6, pl. 5) is in NEM;
NEIAL sec. 22, T. 104 N., R. 71 W., on US. Highway
16 about 1 mile south of the center of Chamberlain.
The landslide is on the nose of a Pierre Shale ridge at
the contact between the DeGrey and Verendrye Mem-
bers and is one of the few pure slump movements near
the reservoir. Instead of disintegrating into an earth-
flow as is common, the base of the landslide has pushed
upward and forward over stable ground as a single
unit forming a pressure ridge along the toe.

The landslide is not located where exceptional quan-
tities of ground water would be expected, but during
1952 and 1953 lush vegetation near the toe of the land-
slide indicated appreciable amounts of moisture in the
ground. From 1954 to 1956 there was less evidence of
moisture, although a closed depression in front of the
landslide contained standing water each spring.

The slump (pl. 5) is a main, backward-rotated block
in front of a complex graben area composed of several
smaller blocks. Initial movement probably occurred in
the large block and the two smaller ones adjacent to it
on the south and southwest. As the mass moved down—
ward and outward, the upper parts of the blocks col-
lapsed into the open fracture behind them to form the
two smallest blacks. Then the laterally unsupported
edge of stable ground directly upslope from the frac-
ture also collapsed into the opening.

Most of the movement in the Highway 16 slump
apparently occurred in the early spring of 1952. When
the slump was first observed in June 1952, the up—
rooted vegetation was still green and all the major
fractures described above had already formed. The
only noticeable change in the slump from June 1952
to September 1956 was minor sloughing along some of

the scarps and weathering of some material exposed in
scarps and fractures.

Control points were measured annually from 1953
through 1956. Six permanent points were established
in 1953 and the rest in 1954. Control points 1 and 6
were used as stable reference points for movements
from 1953 to 1954. Points Z4, 6, and Z3 were assumed
to be stable from 1954 to 1956. The error in horizontal
closure of the closed transit traverse was 0.74 foot in
1953 and not more than 0.19 foot in the following 3
years. The minor difference in locations for point 6
between 1953 and 1954 implies that the error in the
1953 measurements was in the locations of temporary
points used to close the traverse from point 6 to point
1. None of the measurement vectors, consequently, are
assumed to have errors larger than 0.2 foot.

The vectors plotted for each point show that there
was some relatively minor movement between 1953 and
1956. Control. point 3 at the top of the lowest slump
block moved about 0.4 foot, the greatest for any of the
points. The rates of movement of all the points on
the landslide were about the same and the directions of
movement were north and northeast downslope and
toward the pressure ridge. Exceptions to this general
direction were point 2 on the lowest slump block and
point 1 below the slide which showed southeastward
movements of about 0.3 foot between the 1954 and
1955 measurements. Inasmuch as no adequate reasons
were found to explain a localized change in ground
movement, it was assumed that these two stakes prob-
ably had been disturbed by cattle. The magnitude of
movement at points 2 (excepting the presumably dis—
turbed 1954—55 lateral displacement), 3, and 4 was
greater between 1953 and 1954 than the magnitude of
movement for later measurements. The points beyond
the limits of the landslide, excepting point 1, had
neither individual nor cumulative movements as much
as 0.2 foot, which is within the limits of surveying
error.

The apparent movements of points 5, Z2, Z5, and
Z6 are the only movements outside the landslide boun—
daries that may have some significance. Although small
and within the limit of error in the survey their con-
sistent downhill component strongly suggests actual
movement that may be the result of any of three
processes: (1) natural creep of the weathered shale on
the steep slopes near the landslide, (2) slow sliding of
the laterally unsupported material upslope from the
landslide, and (3) plastic deformation of the unsup—
ported material upslope from the landslide. However,
information is too limited to assign a specific cause
to these movements.

LANDSLIDE MOVEMENTS 53

Before the first measurements in 1953, the total
amount of movement in the Highway 16 slump and in
individual blocks was probably less than 10 feet. The
relatively short distance and the high cohesion of the
shale enabled the toe of the landslide to remain fairly
intact instead of disintegrating into an earthflow.

The trend from an initial major movement in 1952
through minor movements in 1953 and 1954 to very
minor movements after 1954 implies that the landslide
was becoming stabilized under the existing climatic
conditions. If climatic conditions became more con-
ducive to landsliding they might reactivate movement.

CABLE SCHOOL EARTHFLOWS

The Cable School earthflows (fig. 12 and pl. 5 (two
larger flows)) in NVVlANWMLNWlfll sec. 30, T. 103
N., R. 71 W., Brule County (pl. 1), are part of a fairly
extensive complex of active and recently active land—
slides in the Cable School area. The larger flow is 90
by 150 feet; the smaller one is about 100 by 110 feet.
The greatest depth of disturbed material is less than
10 feet.

The two earthflows are on the side of a small ridge
composed mostly of the Sharon Springs and Gregory
Members of the Pierre Shale. The shale is overlain by
a 15-foot-thick stratum of gravel (fast-draining allu-
vium) capped by 15—20 feet of till. Several feet of
colluvium blankets all the earlier deposits. Although
much of the colluvium moved normally by slope wash
and creep, former landslides apparently also trans-
ported large quantities.

The two earthflows are similar in appearance. Below
the prominent scarp at the head of each slide is a zone
of slump block that is about half of the larger flow but
is less than one-fourth of the smaller one. The re-
mainder of each slide has moved as a true flow. The
toes have bulbous appearance where flow material
moved over the original surface. The smaller earth—
flow includes a subsidiary earthflow that behaved as a
separate entity although it is physically connected to
the main one.

A small seep was observed about 10 feet below the
gravel-shale contact (pl. 5) on the larger earthflow
when it was first examined in July 1952. The water
was probably derived from local precipitation because
a valley isolates the ridge from ground-water sources in
the nearby uplands. The seep dried up later in the sum-
mer and did not reappear during the time of observa—
tion. Accumulation of eiflorescent minerals at the seep
indicated, nevertheless, some intermittent flow of water.

When the earthflows were first examined in July
1952, the still partially saturated materials, the freshly
uprooted vegetation, and the active seep indicated that

the flows occurred in spring or early summer of that
year. From 1952 to 1956 the earthflows became drier
and lost some of their fresh appearance but otherwise
changed very little. The only indication of activity was
the growth in 1952 and 1953 of a crack from the top
of the larger slide (pl. 5) toward the smaller one; the
crack showed no change after 1953.

Eight control points were established on and near
the larger earthflow in August 1953, and three more
were added in October 1954. Control points A, Y1, and
2 were assumed to be stable, and all traverses were
run from them. The maximum error in closure was
0.20 foot; movements, therefore, are assumed to be ac-
curate to at least 0.2 foot. All movements of the control
points from 1953 to 1956 were randomly oriented and
neither single nor aggregate movement at any point
was more than 0.2 foot. These measurements indicated
that there was virtually no movement of the earthflow;
the slight shifting of the control points undoubtedly
reflects minor adjustments of the earthfiow material
as it became stabilized after the activity of 1952.

Observation of the two earthflows indicates that
nearly all of their movement occurred at one time, or
at least during a short interval of time. They now seem
stabilized and give no indication of future movement.

CABLE SCHOOL SLUMP-EARTHFLOW

The Cable School slump—earthflow in SE%NE%
NElflL sec. 25, T. 103 N., R. 72 W., Brule County ,fig.
7, pl. 5), was one of the most active landslides during
the investigations along the Fort Randall Reservoir.
The slide is about 400 by 700 feet and is divided nearly
equally between slump and earthflow movements.

The slump-earthflow is on the southwest wall of the
Cable School area directly across a small valley from
the two Cable School earthflows. The geologic setting
is similar: Sharon Springs and Gregory Members of
the Pierre Shale are overlain by gravel (fast-draining
alluvium) capped by till. Colluvium forms a thin
blanket over most of the surface and obscures much
of the underlying geology.

There is a zone of springs at and just below the
gravel-Gregory Member contact. The ground-water
source for the springs must be extensive because the
flow was continuous, though small, during the 4 years
of landslide observation. The water probably comes
from gravels in the eastward extension of the pre-
Missouri River White River valley.

The upper part of the Cable School slump-earth-
flow is a broad but relatively short area, about 400 by
250 feet, composed of numerous slump blocks. Differ-
ential settling of the slump blocks has produced a
horst-and-graben structure both in the major blocks

54 LANDSLIDES NEAR FORT RANDALL RESERVOIR, SOUTH DAKOTA

and in the subsidiary units. A steep scarp 20-30 feet
high forms the upper limit of the slump. The lower
limit is approximately at the till-gravel contact (pl.
5) near the middle of a second scarp, about halfway
down the landslide. Below this point, the slump blocks
break up and become part of the earthflow.

The earthflow part of the landslide narrows from
almost 300 feet at the gravel—till contact to less than
50 feet at the toe about 400 feet away. The earthflow
material above the line of springs, at the gravel-shale
contact (fig. 6, pl. 4), behaves more like a debris slide
than an earthflow because there is not enough moisture
to permit flowage. The springs sap the base of the
slump blocks, causing their partial disintegration and
movement of the debris downslope as semiplastic mass-
es. As the masses pass through the zone of springs,
they become saturated and continue down the slope
as an extremely viscous liquid.

The slide probably started as a predominantly slump-
type movement with failure occurring in the saturated
Pierre Shale immediately below the gravel. Aerial
photographs taken in June 1949 show the landslide as a
small slump-earthflow less than half the size it was
in 1952. By July 1952 it had grown to the approximate
size shown in plate 5. The absence of vegetation on the
earthflow and freshness of the cracks and scarps showed
that much of the movement probably occurred that
spring. Although no other large slump blocks de-
veloped, saturation from the springs kept the earth—
fiow fluid, and the entire landslide was active at least
until August 1956.

Triangulation of 10 control points was started in
August 1953. Eight points were located on the land—
slide; point 9 was established just above the upper
scarp and point 10 on the ridgetop above the land-
slide (fig. 7, pl. 5). Measurements were made approxi-
mately monthly during the fall of 1953 and the sum-
mers of 1954 and 1955.

Control point 10. on stable ground, was farthest from
the triangulation baseline, and because the angles of
the other points were of the same general magnitude,
it was assumed that the errors in measuring point 10
would be larger than those for any other point. Because
the loci of measurements of point 10 all fall within a
circle slightly less than 0.5 foot in diameter, the great-
est error in any measurement is presumed to be less
than 0.5 foot. The movements of point 9 greater than
0.5 foot are believed to represent the effects of creep
on the steep slope just above the landslide.

Control points on the slump and flow parts of the
landslide showed distinct differences in their rates of
movement. On the slump blocks, point 5 moved only
about 0.8 foot while point 6 moved about 2 feet. Move-

ments of points 7 and 8 were too random to show any
general direction of movement. On the earthflow, how-
ever, movements ranged from about 2.7 feet at point 1
to about 26 feet at point 2. Although point 3 along the
edge of the flow showed only random movements over
periods of a few months, it had a cumulative m0vement
of about 2.7 feet over a period of 2 years. The next
larger movement was at point 4 which moved about
14 feet. or five times as far as point 3.

The data show differences in the basic types of
movements in the flow and slump parts of the land-
slide. On the earthflow, movement is dominantly linear
with small lateral components. This behavior implies
that the earthflow material is moving along a rela-
tively well defined route. Movement of the slump part
of the landslide does not show a similar dominant
component. Instead, only points 5 and 6, which are at
the top of the scarp directly above the earthflow, show
any indication of a dominant linear movement. Appar-
ently the individual slump blocks are shifting difl'er—
entially in more or less random directions except for
the blocks in transition from slump to earthflow.

An interesting conclusion derived from the control
point measurements is that points on slides vary in
rates of movement. Points 3, 4, and 6 decreased in rate
of movement during the 2 years that measurements
were made. For the first year, points 1 and 2 on the
earthflow showed a corresponding decrease in rate of
movement, but during the second year, movement at
these points accelerated, and so they moved about
three times as far during the summer of 1955 as during
the summer of 1954. Because the rate of movement at
the toe of the earthflow reflects changes that occur
farther up the slide, the acceleration at the toe was
probably caused by addition of materials to the earth-
flow from the slump part of the landslide before meas-
urements were started in August 1953.

In summary, the initial failure at the Cable School
slump—earthflow probably was by slumping of large
unified blocks. As the material was displaced down-
slope, it became saturated by seepage from the springs
at the gravel-shale contact and disintegrated into an
earthflow. As the springs continue to sap the base of
the slumps above them, more material sloughs off and
is incorporated into the saturated earthflow. This proc-
ess both replenishes the earthflow and removes support
from the base of the slump blocks. The increased insta—
bility creates continual shift and probably gradual
downslope movement of the individual slump blocks.

LANDING CREEK SLUMP—EARTHFLOW

The Landing Creek slump-earthflow (fig. 4, pl. 5)
is the largest and most complex landslide on which

LANDSLIDE MOVEMENTS

movement was measured. The basic component is a
large slump about 900 feet from top to bottom and
2,000 feet across. Several smaller slumps and earthflows
are superimposed along the toe of the main slump.

The landslide is on a ridge that parallels the Fort
Randall Reservoir in SE%NE14 sec. 25, T. 100, N.,
R. 72 W., Gregory County, S. Dak. The slide developed
above an intensely dissected terrace remnant about 100
feet above the prereservoir Missouri River level, and
moved forward onto the terrace. There is no direct
connection, consequently, between river erosion and
landslide activation here.

The ridge consists of the lower five members of the
Pierre Shale and the underlying Niobrara Formation.
In prereservoir time the Niobrara Formation formed
bluffs about 35—40 feet above the river alluvium. About
35 feet of the Sharon Springs Member overlies the
Niobrara Formation, and the Gregory-Sharon Springs
contact is at an altitude of about 1,365 feet. The true
thickness of the Sharon Springs and the overlying
beds is obscured by ancient and recent landslides. A
band of the Crow Creek Member about 10 feet thick
crops out on several spurs of the terrace remnant at
altitudes ranging from 1,375 to 1,420 feet. Above the
Crow Creek, and comprising nearly all of the Landing
Creek slump—earthflow material as well as the top of
the ridge, are the undifferentiated DeGrey and Veren—
drye Members. Extraneous masses of the Virgin Creek
and Mobridge Members, probably remnants of ancient
landslides, are found with the DeGrey and Verendrye
landslide material, but only the largest masses are in-
dicated on the geologic map (pl. 5) .

The Landng Creek slide can be understood by con-
sidering its components individually. The main slump
is in itself a complex landslide. All of the recent move-
ment has been restricted to the northwest two-thirds of
the slump. The southeast third either is older or it
stabilized sooner. Though considerably modified by ero-
sion, the southeast third is a jumbled series of slump
blocks below a 30- to 40-foot—high scarp. The scarp
becomes increasingly fresh to the northwest and shows
the greatest indications of recent activity in the north-
west third, where it reaches a maximum height of about
70 feet. Immediately below the scarp, in the northwest
part of the slump, is a graben about 900 feet long and
150—200 feet wide. The northeast margin of the graben
is bounded by a second scarp as much as 20 feet high.
The graben and the slide material bordering it have
few fractures or other visible evidence of major activ-
ity, although the control points on them showed appre-
ciable movements. Farther downslope, however, the
ground surface is increasingly fractured and shows
signs of major activity.

55

The small slumps and earthflows along the toe of
the main slump make up about one-half its total
length. Earthflows predominate; slump-type movement
is dominant only in the northwest part of a subsidiary
slide at the grid location of 1,100—1,400 feet north and
1,600—2,000 feet east (pl. 5). Two prominent earth-
flows extend down small valleys to the prereservoir
Missouri River level. The largest heads in the north
corner of the main slump and is about 750 feet long.
It has a dumbbell shape, with the source area about
275 feet wide forming one bulge, and the toe about
225 feet wide forming the other. The ends are con-
nected by a central section about 100 feet wide and 300
feet long which flows down a steep gully.

The Landing Creek slump-earthflow probably started
as a large slump on the slope above the terrace rem—
nants. Causes of the original movement can only be in-
ferred, the most likely being that weathering processes
over a long time weakened the material so much that it
became unstable on the existing slopes. Ground-water
and minor gully erosion probably then triggered move—
ment in the weakened mass.

Direct erosion by the Missouri River had no effect
on the Landing Creek slump-earthflo-w, terrace rem-
nants acted as a buffer to protect the upper slopes.
The terrace surface, however, was dissected by many
small gullies in the general surface. As the slump
moved onto the terrace, some material collapsed into
these gullies and destroyed the unity of the original
slump. Where the gullies were broad and shallow, the
slump broke into fairly large blocks; where the gul—
lies were deeper, the material disintegrated and became
potential earthflows.

Excellent examples of the effect of the dissected ter-
race surface on the landslide are the earthflow in the
north corner of the landslide and the slump just south-
west of it (pl. 5). These subsidiary landslides developed
over a large deep gully cut into the original terrace.

Ground water probably has played a greater part in
perpetuating and enlarging the activity of the slide
than in launching the original movement. The pre-
slide drainage apparently was well integrated, and
there was no unusually large supply of ground water
available. The initial movement, however, created frac-
tures and closed depressions that trapped most of the
subsequent precipitation, thus appreciably increasing
the amount of ground water available.

Little is known about the movement of the landslide
before the control points were established in August
1953. A map of the area (US. Army Corps of En-
gineers, 1947, sheet 37), which was compiled photo—
grammetrically from aerial photographs taken in 1945,
shows that the landslide was already extensive with at

56 LANDSLIDES NEAR FORT RANDALL RESERVOIR, SOUTH DAKOTA

least one subsidiary earthflow that reached the river.
Aerial photographs taken in 1949 show the landslide
virtually the same size that it was from 1952 to 1956.
The largest earthflow has a larger lobe than is shown
on the earlier Corps of Engineers’ map, and the smaller
earthflow to the southeast has a small lobe that also
extends into the river. Between 1949 and 1953, there
were several small changes: both earthflow lobes in
the river grew about one-fifth larger, a small earthflow
developed along the toe at the southeast end of the
slide, and the slump—earthflow northwest of it nearly
doubled its size.

Thirty-one control points were installed on the north-
west half of the slump-earthflow in August 1953, and
they were measured annually through September 1956.
During this time several control points were either
covered by the rising reservoir or destroyed by land-
slide movements and cattle. Some of these points were
abandoned; others were replaced.

The maximum error for transit traverse closure for
1953, 1955, and 1956 was 0.33 foot, and consequently
all measurements for these years are considered ac-
curate to at least 0.33 foot. In 1954 there was an error
of closure of 1.37 feet, of which 1.36 feet is in the
north component.

The measurements indicate that there was appre-
ciable movement of all the points on the landslide
during the 3-year period, and also that the range in
amount of movement was very great. Point 4 had the
least movement, about 2 feet, over the entire 3-year
period. Measurements are available for only 2 years
at points 3 and J, but during that time their movements
were of the same order of magnitude as at point 4. The
other extreme is point 16, which moved about 100 feet
in 3 years.

The control points beyond the limits of the landslide
remained fairly stable, With the exception of point 2.
Points X, Y, and 1 at the head of the slide were as-
sumed to be stable and were used as controls for orient-
ing the annual traverses. The location of point 15,
below the slide, was within the limits of error of meas-
urement during the 3—year period. This fact indicates
not only that point 15 was stable, but also that the
assumed stability of points X, Y, and 1 was valid.
Point 2 was placed on apparently stable ground above
the top scarp in 1953, but during the following year
the area became an active slump block.

The movement of the control points on the land-
slide revealed some interesting contrasts between the
movement of the slump and the earthflows. All the
control points on slump blocks were remarkably con-
stant in their direction of movement, and lateral move-
ments resulting from differential shifting of unit

blocks were very small relative to the overall downslope
component of the entire landslide. The subsidiary
slump block above the largest earthflow showed some
exception to this trend. In general, its movement was
subparallel to and independent of the other parts of
the main slump. In contrast to the unity of the main
slump each point on the earthflows was influenced by
conditions at its particular site instead of by the con-
ditions over the entire flow.

This behavior is shown best by a comparison of the
movements of points J, 14, and 14—B with movements
of the other points on the earthflow. Point J, near
the earthflow’s edge, was at the side of the main cur-
rent of the earthflow. Its movement, consequently, was
much smaller than that of the remainder of the points.
At the site of points 14 and 14—B, the direction of flow
was deflected by local topography so that movement of
these points was at about 45° to the other points of the
earthflow.

The rate of movement on the main slump increased
from the top to the base of the mass. The material on
the lower half of the slump was not pushing a large
weight ahead of it and consequently could move farther
under the same conditions than the upper part. On the
earthflow the magnitude of movements was not so de-
pendent on the relative location of the control point.
Point 16 moved farther during the period 1953 to 1954
than did point 17 a short distance below it. Point 14
moved almost as far as point 15—A from 1954 to 19515,
and it moved farther than point 16 during the same
time. The entire flow, moreover, moved rapidly than
the slump moved.

Finally, control points everywhere on the slide had a
fairly large movement the first year and smaller,
nearly equal, movements during the succeeding years.
Apparently the conditions affecting stability had a
similar effect on all parts of the landslide despite its

complex nature.
PAULSON SLUMP

The Paulson slump (pl. 5, fig. 30) is an old landslide
that has been reactivated by the development of two
subsidiary landslides on its lower slopes. It is about
500 by 500 feet and has about 90 feet of relief. Its
shape is very irregular, largely because the lower slopes
have been extensively eroded by an intermittent stream
at their base.

The slump is on the southeast side of a Pierre Shale
ridge in NEIASWMLSWIA sec. 6, T. 98 N., R. 69 W.,
Charles Mix County, between two intermittent streams
tributary to the Missouri River. About 15 feet of the
Gregory Member is exposed above the valley-bottom
alluvium. The overlying Crow Creek Member is about

LAN DSLIDE

Sitié'bm ' Quit?” “

57

MOVEMENTS

Stream gUHy '

 

FIGURE 30.—-The Paulson slump, a reactivated slump in Pierre Shale. The two active landslides are in the toe of the main slump,
which includes the area between the two active slides and the rather flat surface just above them. Photographed August 19,

1956.

5 feet thick in this locality and is overlain by about
80 feet of undifferentiated DeGrey and Verendrye
Members.

Interrupting the general slope of the ridge, the old
slump formed a flatter area bordered by short steep-
ened slopes that were the remnants of the original
scarp. By 1956, reactivation had opened new fractures
that closely outlined the top and sides of the original
slide. There were also other fractures on the slump
itself, especially between the scarps of the subsidiary
slides.

The subsidiary landslides are slum‘p-earthflows, al-
though the earthflow parts are not very well developed
on either slide. The slide in the southeast part of the
old slump is about 225 feet long and 175 feet wide.
Although the slide in the northeast part of the old
slump was about 275 feet long and 200 feet wide,
stream erosion had cut away its northeast corner until
its total area is not much greater than that of the
southeast slide. Both subsidiary slides have well-devel-
oped scarps. The northeast slide has a prominent scarp
at its head and a second scarp on the margin of a
large active slump block.

The causes of movement in the original slide cannot
be determined. The low scarp remnants at the head of
the block (fig. 30) and the relatively undisturbed shale
exposed in the newer scarps indicate that the movement
was small and that the landslide was predominantly a
slump. After this movement, the slump became stable.
Erosion subsequently modified it until the only remain-

ing evidence of the landslide was the small scarp at
the head and the flattened slope on the surface of the
rotated slump block.

Aerial photographs show that the subsidiary slides
were almost as well developed in 1949 as when the

author first examined them in 1952, when they were
active but the main Slump was still stable. Renewed
movement of the main Paulson slump started during
1952—53 and continued to increase as long as the slide
was under observation.

Stream erosion probably was the major cause of the
subsidiary landslide activity. The normally dry
streambed may contain a swiftly flowing stream after
heavy rains or during wet seasons. Shortly after a
cloudburst in the area, the author saw a boulder more
than 1 foot in maximum dimension lodged against a
tree near the stream channel. A stream that can trans—
port boulders of this size is capable of major erosion
in the Pierre Shale. Although ground water may have
contributed to the renewed instability of the old slump,
during this study there was never evidence of appre-
ciable amounts of ground water in the landslide.

The northeast subsidiary slide was definitely acti-
vated by stream erosion. The southeast slide was prob-
ably also caused by erosion, although it is farther from
the stream chanel. After these subsidiary slides had
removed an appreciable amount of material from the
toe of the original slump, it became unstable and be-
gan to move again.

Measurements were started in 1952 and were made
annually through 1956. Points A—l to A—5 and B—1
to B—5 were installed in October 1952, and additional
points to provide a closed traverse were installed in
August 1953. The measurements in 1952 were taped
slope distances between points; these measurements
were not included with the movement vectors shown
on plate 5, because they were approximate and did
not indicate true directions of movement. Closed transit
traverses were used for measurements from 1953 to
1956. The maximum error in closure was 0.14 foot, and

58 LANDSLIDES NEAR FORT RANDALL RESERVOIR, SOUTH DAKOTA

consequently all movement vectors are assumed to be
accurate within 0.14 foot.

From 1952 to 1956 the general trend on the Paulson
slump was toward increasingly greater movement. Be—
tween 1952 and 1953 only points A—3, A—5, and B—5
moved appreciably, and the greatest movement, at A—5,
was not more than 0.5 foot. Movement of all points on
the slump between August 1953 and October 1954 in-
dicated that the entire slump was then active. The
amount of movement ranged from about 0.3 foot at
points B—2, B—3, and B—4, to about 0.8 foot at point
A—5. There was less movement from October 1954 to
July 1955: points 13—2, 13—3, and B—4 each moved about
0.1 foot, which is within the possible limits of error,
and point B1—5 moved about 0.5 foot, the most move-
ment of any point on the main slump. The greatest
movements occurred during the last year of observa-
tion, July 1955 to September 1956. All the points on
the northeast half of the slump were destroyed, either
by movement or by cattle, but on the southwest half
the movements ranged from about 0.6 foot at B—2 to
about 1.8 feet at B1—5. The appearance of new frac-
tures and small scarps on the reactivated slump also
showed that differential movement increased during
this period.

The preceding observations indicate that renewed
large-scale landsliding was developing in the Paulson
area between 1952 and 1956. Renewed activity of the
old slump began near the toe where the subsidiary
slides had recently disturbed its equilibrium. Activity,
renewed in one part of the slump, soon involved the
entire area. Development of fractures throughout the
slump block indicated that the mass was losing its
unity and the lower half, at least, might disintegrate
into an earthflow. The combination of a disintegrating
Slump unit and a potentially erosive stream at the toe
could easily cause extensive landsliding.

SURPLUS PRECIPITATION, GROUND WATER,
SLOPE STABILITY: CORRELATIONS

In this final section an attempt is made to correlate
surplus precipitation available for ground-water stor-
age, landslide activity, and ground water. Emphasis
throughout the report has been on the relation between
ground water and landslide activity, but little has been
said about the possibility of correlations between (1)
percentage of surplus precipitation available for stor—
age as ground water, (2) the ground-water levels, and
(3) slope stability. Such correlations can be valuable
for prediction and interpretation of slope stability
conditions.

PRECIPITATION AVAILABLE FOR STORAGE AS
GROUND WATER

The amount of moisture potentially available to re—
plenish and increase ground-water supplies is not
easily determined. Precipitation can be recorded, but
only a fraction of the moisture from precipitation
ever becomes ground water. The rest is lost either to
the streams and rivers as runoff or the atmosphere as
evaporation and transpiration (evapotranspiration).
Although runoff is an effective agent of erosion, it is
less than 5 percent of the normal annual precipitation
(Visher, 1954, p. 258). The average annual runoff at
Pickstown thus amounts to less than 1 inch of precipi-
tation per year. Inasmuch as runoff represents such a
small part of total precipitation, only the relation be—
tween evapotranspiration and precipitation was used
to determine the approximate amount of water avail-
able to affect ground—water supplies.

Evapotranspiration is a direct function of the cli-
mate and vegetation. It involves precipitation, temper-
ature, hours of daylight, relative humidity, types of
vegetation, and other variable factors. Adequate meth-
ods for directly measuring evapotranspiration have
not yet been developed, because there is no direct way
to satisfactorily measure the moisture that plants re-
lease to the atmosphere.

Thornthwaite (1948) has worked with basic climatic
data to determine evapotranspiration without actual
measurements of the rate of water loss from the ground
to the atmosphere. He has developed empirical methods
for computing “potential evapotranspiration,” the
amount of evapotranspiration that will occur under
given climatic conditions if there is an unlimited source
of water. Thornwaite cites evapotranspiration in a
desert where water and vegetation are limited, and in
a desert irrigation project where unlimited water is
available and vegetation consequently is plentiful, as
examples of natural and potential evapotranspiration.

Although the calculated potential evapotranspira-
tion values are only approximate (Thornthwaite, 1948,
p. 91), the basic concept is valuable in providing a
comparative method of estimating the rate at which
moisture can return to the atmosphere from the

ground.

RELATION BETWEEN PRECIPITATION AND POTENTIAL
EVAPOTRANSPIRATION AT PICKSTOWN
Pickstown is the only station along the Fort Randall
Reservoir that has climatic data available (U.S.
Weather Bureau, 1948-56) for investigation of the pre-
cipitation—potential evapotranspiration relation. Vari-
ations along the reservoir are probably fairly small,

SURPLUS PRECIPITATION, GROUND-WATER SLOPE STABILITY: CORRELATIONS 59

however, and Pickstown is assumed to be typical of
the entire area.

The potential evapotranspiration values computed by
Thornthwaite’s method and the precipitation record
at Pickstown for 1948 through 1956 are shown in a
graph at the “bottom of figure 31. Periods and amounts
of precipitation surplus, and deficiency are shown by
patterns; total annual values and surpluses or deficien-
cies are shown below the graphs. Curves for annual
averages for the entire period of record are shown at
the left side of figure 31.

The curves of annual averages show that both pre-
cipitation and potential evapotranspiration range from
minima during the winter to maxima during the sum-
mer. The potential evapotranspiration has the greatest
range, from almost no evapotranspiration during the
winter months to more than 6 inches during July. The
precipitation curve is bracketed by the evapotranspira—
tion curve and shows that evapotranspiration is less
than precipitation during the winter and greater dur-
ing the summer. Precipitation in excess of evapotrans-
piration needs, therefore, is expected during the winter
rather than during the summer.

The annual precipitation and potential evapotrans-
piration curves generally resemble the averaged annual
1948-56 precipitation curves. Annual precipitation
ranges from 12.5 to 29.8 inches, but potential evapo—
transpiration ranges from 24.1 to 30.3 inches. Simi-
larly, annual evapotranspiration curves vary less from
their average than do the precipitation curves. Occa-
sional irregularities show disparities between individ-
ual months, but variations from the 1948—56 curve for
any year are relatively uniform and reflect a generally
warm or cool year. The precipitation curves are more
erratic. Although the trend is from a winter minimum
to a summer maximum, records for individual months
often appear to reverse this pattern.

The annual precipitation—potential evapotranspira—
tion relations are similar. despite fluctuations from the
average. Every winter and spring precipitation is
greater than the amount of water used for evapotrans-
piration. The precipitation deficiency of summer, how—
ever. almost always exceeds the precipitation surplus
of winter. Only 1 year, 1951, had a precipitation sur-
plus (5.7 inches). and just 1 month, July, had an ap-
preciable deficiency. Ground-water intake probably
was continuous, therefore. for most of that year.

CUMULATIVE PRECIPITATION SURPLUS

Ground water can trigger landslide movement or
condition a potential landslide mass for trigger action
by another agent. The triggering efl’ect occurs during
or very soon after a period of excess precipitation.

Ground water, to be a general cause of landsliding,
requires an influx of ground water over an extended
period of excess precipitation and involves a slow
buildup of stresses and other factors that affect the
stability of a mass.

A 12-month cumulative precipitation surplus (cps)
curve (fig. 31, top) was constructed from monthly pre-
cipitation and potential evapotranspiration data in
order to show periods of extended precipitation that
could affect ground-water conditions. Each point on
the curve indicates the total precipitation surplus or
deficiency (negative surplus) for a 12-month period.
The 12-month period was chosen because it seemed a
reasonable time for ground water to permeate the
shale, and cumulative values for 12 months automat-
ically average the effects of normal seasonal variations
in precipitation surplus.

The curve shows that a cumulative precipitation sur—
plus for any 12-month period is rare; only 1 year of
eight had a surplus. From June 1951 to May 1952
monthly surplus was about 5 inches, which helped
provide a cumulative precipitation surplus that was
13 inches more than the average cps values for the
remainder of the time of record. Also noteworthy dur—
ing that 8—year time of record, the monthly precipita-
tion showed an average deficiency of about 8 inches.
June 1951 to May 1952 was therefore the only period
in which there was enough precipitation to cause an
appreciable increase in ground water.

CORRELATION BETWEEN SURPLUS PRECIPITATION
AND SLOPE STABILITY

The hypothesis that there is a definite relation be-
tween surplus precipitation and slope stability is based
on information in figure 31 and the assumption that
most landslides are the result of general instability,
supplemented by a trigger action that initiates move—
ment. There may actually be several causes of insta-
bility, but only the apparent effects of ground water
are considered in detail here.

Temporary increases in available ground water may
raise the water table and also cause partial saturation
of material above the water table. If such an influx of
water continues for many months, the resulting changes
in ground-water conditions may be sufficient to trigger
landslides on some slopes. On most slopes, however, it
will be a general cause of instability. Therefore, ab-
normally high peaks in the 12-month cumulative pre-
cipitation curve (for example from June 1951 to May
1952, fig. 31) may coincide with an appreciable increase
in the amount of ground water and a corresponding
decrease in general slope stability.

Periodically both general ground-water conditions,

60 LANDSLIDES NEAR FORT RANDALL RESERVOIR, SOUTH DAKOTA

 

7ITITIIIIIIIITIIII
6V

5-

SURPLUS

 

12-MONTHS CUMULATIVE PRECIPITATION, IN INCHES
DEFICIENCY
I

Potential
evapotvansplration

INCHES

 

 

 

 

I
IFMAMJJASOND JFMAMJJASONDJ
AVERAGE (1948—1956) 1948

iI III
MAMJJASOND

 

1949

Total pveciuitation:
19 7 Inches
Average annual precipitar
Hon defncuency:8.0 Inches

 

Total precmilation:
14 4 inches
Total potenilal evapo-
transpuatlon r 25 8 Inches
Preeipitatlon deflmency:
11,4 inches

 

Total pveclultatlon:
18 1 Inches
Total potential evapo-
transpvrallon 19?) Inches

Preclpllatlon deficiency:
11 5 inches

 

Total precuiitation
(estlmated>:21.2 Inches

Total potential evapo-
transpnatlon : 24 A ll'ICheS
Precipitation detucnency:

3 2 inches

 

Total precipitation
(estimated) : 29.8 Inches
TotaI pote‘nhal evapo-
transpiration :24.1 Inches
Pvecupitatxon

:5]

Surplus

FIGURE 31.———Correlation between precipitation and potential evapotranspiration at Pickstown. Precipitation data from US. Weather

at nearby stations. (2) No record at Pickstown; about average at nearby

evidenced by the 12-month cumulative precipitation
surplus curve, and temporary ground—water conditions,
shown by precipitation—potential evapotranspiration
relations, should favor landslide activity, and excep-
tional amounts of activity may occur on both new and
old landslides. Only one such period occurred from
1948, when the Pickstown climatic records were com-
menced, until 1956, and that was in the spring of
1952. The 12—m0nth cumulative precipitation surplus
curve was at a peak, and the precipitation and potential

evapotranspiration curves showed a precipitation sur-
plus.

During the first year of landslide examinations along
the Fort Randall Reservoir (1952), an outstanding
feature was the number of fresh apparently active
landslides along the walls of the Missouri River trench
and its tributaries from the streambeds to the up-
lands.

The slides described in this report either originated
in or were still active in 1956. The Highway 16' slump

SURPLUS PRECIPITATION, GROUND-WATER SLOPE STABILITY: CORRELATIONS 61

 

 

 

 

 

 

 

 

 

 

 

 

iiiiiiiiiiiiiiiiiiiiiiiiiiiiii llllllllTllllilTl|||ll|||l7
~ 6
w 5
— 4
w 3
— 2
w 1
0
- l
— 2
— 3
— 4
— 5
— 6
— 7
— 8
- 9
_ 10
—* 11
w 12
~ 13
\/\/ w 14
— 15
— '16
i— 9
-— 8
\
/ /\
lllllll Vllllllll
JFMAMJJASOND JFMAMJJAS DJFMAMJJASO
1952 1953 1954 1955
Total precipitation: Total piecipitalion: Total precipitation: Total precipitation: Total precipitation:
16.4 inches 218 inches 19.7 inches 21 6 Inches 17 5 inches
Total potential evaoo- Total potential evapo- Total potential evapo- Total potential evapo- Total potential evapo-
transpiration:301 inches transpiration229 2 Inches transpiration:27.7 inches transpiration .303 inches iraiisiiiralioii 281 inches
Precipitation deliciency: Precipitation deficiency: Freeipitaliun deficiency: Freeipitation deliciency: PreCIpiIation deliciency:
13.7 inches 74 inches 53 inches 87 inches l56inches

Bureau climatological data (1948—56) ; all data given to nearest 0.1 inch. (1) No record at Pickstown; below average
stations. (3) No record at Pickstown; well above average at nearby stations.

and the two Cable School earthflows all originated in
1952, and only minor subsequent movements occurred
up to 1956. The Cable School slulmp-earthflow had
major movement in 1952, probably greater than any
later movement up to 1956. The Landing Creek slump-
earthflow was active in 1952, but there are no data to
compare the relative amount of movement that year
with later movements. The Paulson slump alone
showed increasing activity after 1952. It also is the
only landslide in which the role of ground water ap-

4'72—783 O — '73 - 5

parently was secondary to another cause, stream ero-
sion at the toe.

After the drop in the 12-month cumulative precipi-
tation surplus curve, starting in May 1952 (fig. 31),
there was a gradual increase in overall slope stability.
The control points on all the landslides except the
Paulson slump showed either negligible movements or
a general decrease in rate of movement.

At Pierre, S. Dak., about 60 miles northwest of
Chamberlain, Crandell (1958) noted a concentration

62 LANDSLIDES NEAR FORT RANDALL RESERVOIR, SOUTH DAKOTA

of landslide activity in the spring of 1952. He stated
(1958, p. 77): “Fewer than 10 large new landslides
were observed in the Pierre area during the period
1948—51; in the spring of 1952, however, many new
slumps and flows occurred in the area and some old
slumps were. reactuated.” The increased landslide ac-
tivity in the spring of 1952 is attributed by Crandell
to an abnormally large amount of ground water.
Precipitation, potential evapotranspiration, and 12-
month cumulative precipitation curves were prepared
for the Pierre area to check the surplus precipitation-
landslide activity hypothesis with Crandell’s com-
ments on landslide activity. The curves differed in
detail from the ones at Pickstown, but the general
trends were similar. The 12—month cumulative precipi-
tation surplus curve at Pierre shows a deficiency from
1948 to the end of 1951. This period is followed by a
surplus from December 1951 through May 1952, with
a maximum of 4 inches in March. Then the curve again
shows a deficiency from June 1952 through 1956. The
precipitation and potential-evapotranspiration curves,
moreover, show a more pronounced precipitation sur-
plus at Pierre during the winter and spring of 1952
than there was at Pickstown. This agreement between
observed conditions of greater than normal precipita-
tion and landsliding at Pierre seems to validate further
the hypothesis that precipitation surpluses can be cor—
related with periods of excessive landslide activity.

CORRELATION BETWEEN SURPLUS PRECIPITATION
AND GROUND-WATER LEVELS

Available precipitation was compared with ground-
water levels in the piezometers to check the presumed
relation of precipitation surplus to ground-water con-
ditions. A qualitative analysis was made for the piezo—
meters near Pickstown that appeared to be in equilib-
rium with existing ground-water conditions. The aver—
age water level in each piezometer and the average
monthly precipitation surplus (negative values includ—
ed) were calculated first. Then the number of months
in which above-average water levels and above-average
precipitation surpluses, or below-average water levels
and below-average precipitation surpluses, coincided
was determined for each piezometer. The total number
of times that above- or below-average values coincided
was stated as a percentage of the total number of
water-level measurements at each piezometer. The cal-
culations were repeated using cumulative precipitation
surplus values for periods increasing from 2 to 12
months by 1-month increments.

The results of the analysis were plotted graphically
(fig. 32). Graphs of individual piezometers are divided
into three groups on the basis of depth: (A) 12 to 30

 

 

90— _

80— (

CORRELATION, IN PERCENTAGE OF AGREEMENT OF COMPARISON

 

 

 

 

1 2 3 4 5 6 7 8 9 10 ll 12
NUMBER OF MONTHS OF CUMULATIVE PRECIPITATION

FIGURE 32.——Corre1ation between above- or below-average piezo-
meter water levels and above- or below-average cumulative
precipitation surpluses. A. Piezometer depths 12-30 feet; B.
piezometer depths 55—59 feet; 0. piezometer depths 81—88
feet. Number following letter designation indicates depth.

feet, (B) 55 to 59 feet, and (C) 81 to 88 feet. Per-
centage values on the curves represent the degree of
correlation relative piezometer water levels and relative
cumulative precipitation surplus values. Complete cor-
relation is 100 percent; random distribution is 50 per-
cent; and complete inverse correlation is 0 percent.
The curves show a relatively short—term relation be-
tween precipitation surplus and ground—water levels
in the shallower piezometers (fig. 32, A, B), but effects
are random in the deepest ones (fig. 32, C). Percentage
values of the shallowest piezometers, except A—30, are
above for the 2-, 3-, and 4-month periods of cumulative
precipitation surplus. For the 55— to 59—foot piezo-

REFERENCES 63

meters there is a similar but smaller rise in the 2— to
5—month values. The inference is that short-term (a
few months) precipitation surplus conditions have an
appreciable effect on ground-water conditions down to
depths of at least 30 feet. These effects decrease with
depth; they become minor at about 60 feet and: in-
effective ‘at greater depths.

The correlation between near-surface ground-water
conditions and the short-term cumulative precipitation
surplus values strengthens the assumption that ground
water triggers landslides. The annual winter and
spring precipitation-surpluses (fig. 31) give maximum
values for 2- to 4-month cumulative precipitation sur—
pluses in the spring, when landslide activity is greatest.
The long-term cumulative precipitation surplus values
(fig. 32)—i.n particular, the 12-month surpluses—show
no correlation with piezometer water levels. Two fac-
tors may contribute to this apparent lack of correla—
tion. The first is that the 12—month cumulative precipi-
tation values were considered an indication of ground-
water conditions in the Pierre Shale as a whole, where-
as the piezometers used for ground water-precipitation
surplus correlation probably reflect special conditions
in the shale. Data only from piezometers in which
water levels had reached equilibrium rapidly were used
for the correlation because they gave the longest-
periods for comparison. The correlation data, as a
result, probably are based on ground-water conditions
in shale fractures, which would differ from conditions
in massive shale. The second factor is the short period
for which comparisons were made, inasmuch as the
ground-water data used were only from February 1954
through November 1956. Although a correlation was
found between landslide activity and a 12-month cum-
ulative precipitation surplus after only one period of
excess precipitation surplus might not be confirmed
until at least two periods of abnormally high rainfall
were observed.

CONCLUSION

The available data strongly suggest correlation be
tween (1) surplus precipitation available to augment
ground-water supplies, (2) landslide activity, and (3)
ground-water levels. Both the short-term ground-water
effects believed to trigger landslides and the long-term
ground-water changes that have general effects on over-
all slope stability seem to indicate a correlation.

The best correlation seems between winter and spring
precipitation surpluses and spring landslide activity
triggered by ground water. The 2- to 4-month cumula-
tive precipitation surpluses are highest in the spring
after several months of surplus precipitation during
the winter and early spring. Near-surface (less than
about 60 ft deep) ground-water levels roughly reflect

the cumulative precipitation surplus values, and they
also tend to be above average in the spring, when most
landslide activity occurs. It seems reasonable, there-
fore, to postulate that after 2 to 4 months of surplus
precipitation, the surplus water that infiltrates the
ground, along with ground water already present, can
create sufficiently unstable conditions to promote land-
sliding.

The relation between available surplus precipita-
tion, landslide activity, and long-range ground-water
changes is less certain. There is an interesting coinci-
dence between an extensive period of positive 12-month
cumulative precipitation surplus values and abnorm-
ally active landsliding in the spring of 1952. Ground-
water data are unavailable for that year; however,
without positive evidence that ground-water conditions
were unfavorable to earth movements, a logical conclu-
sion is that a direct correlation exists between 12-month
cumulative precipitation surplus values, ground-water
conditions, and general slope stability conditions.

REFERENCES

American Society for Testing Materials, 1950. Standard method
of mechanical analysis of soils, in A.S.T.M. procedures

for testing soils: Am. Soc. Testing Materials, p. 44—55.
Baldwin, Brewster, and Baker, C. L., 1952, Areal geology of
the Iona quadrangle: South Dakota Geol. Survey (map).
Casagrande, Arthur, 1949, A non-metallic piezometer for
measuring pore pressures in clay, in Soil mechanics in the
design and construction of the Logan Airport: J our. Boston
Soc. Civil Engineers, app., v. 36, no. 2, p. 214—221.
Crandell, D. R., 1950, Revision of Pierre shale of central South
Dakota: Am. Assoc. Petroleum Geologists Bull., v. 34, no.
12, p. 2337—2346.
1952, Origin of Crow Creek member of Pierre shale in
central South Dakota: Am. Assoc. Petroleum Geologists
Bull., v. 36, no. 9, p. 1754—1765.
1958, Geology of the Pierre area, South Dakota: US
Geol. Survey Prof. Paper 307, 83 p.
Croxton, F. E., and Cowden, D. J ., 1955, Applied general statis-
tics [2d ed.]: New York, Prentice-Hall, Inc., 843 p.
Curtiss, R. E., 1950, Cement materials near Mobridge, South
Dakota, in Report of the South Dakota State Cement
Commission to the 32d session of the Legislative Assembly
of the State of South Dakota: p. 63—81.

Dixon, W. J ., and Massey, F. J., 1951, Introduction to statisti-
cal analysis: New York, McGraw-Hill Book Co., Inc, 370 p.

Flint, R. F., 1955, Pleistocene geology of eastern South Dakota:
US Geol. Survey Prof. Paper 262, 173 p.

Goddard, E. N., chm., and others, 1948, Rock-color chart: Natl.
Research Council, 6 p. (repr., 1951, by Geol. Soc. America).

Granton, L. 0., and Fraser, H. J ., 1935, Systematic packing of
spheres, with particular relation to porosity and permeabil-
ity: Am. Assoc. Petroleum Geologists Bull., v. 43, no. 8, pt.
1, p. 785—909.

Gries, J. P., 1942 Economic possibilities of the Pierre shale:
South Dakota Geol. Survey Rept. Inv. 43, 79 p.

Grim, R. E., 1953 Clay mineralogy: New York, McGraw-Hill
Book 00.. Inc., 384 p.

 

 

64 LANDSLIDES NEAR FORT RANDALL RESERVOIR, SOUTH DAKOTA

Holtz, W. G., and Gibbs, H. J ., 1951, Consolidation and related
properties of loessial soils, in Symposium on consolidation
testing of soils: Am. Soc. Testing Materials Spec. Tech.
Pub. 126, p. 9—33.

Meek, F. B., and Hayden, F. V., 1861, Descriptions of new
Lower Silurian (Primordial) Jurassic, Cretaceous, and
Tertiary fossils, collected in Nebraska Territory * * *,
with some remarks on the rocks from which they were
obtained: Acad. Nat. Sci. Philadelphia Proc., p. 415—447.

Olds, E. G., 1949, The 5 percent significance levels for sums of
squares of rank dilferences and a correction: Annals Math.
Statistics, v. 20, p. 117—118.

Petsch, B. 0., 1946, Geology of the Missouri Valley in South
Dakota: South Dakota Geol. Survey Rept. Inv. 53, 78 p.

Petsch, B. C., and Fairbanks, Donald, 1952, Areal geology of
the Chamberlain quadrangle: South Dakota Geol. Survey
(map).

Schultz, L. G., 1965, Mineralogy and stratigraphy of the lower
part of the Pierre Shale, South Dakota and Nebraska:
U.S. Geol. Survey Prof. Paper 392—B, p. B1—B19.

Searight, W. V., 1937, Lithologic stratigraphy of the Pierre
formation of the Missouri Valley in South Dakota: South
Dakota Geol. Survey Rept. Inv. 27, 63 p.

Searight, W. V., and Meleen, E. E., 1940, Rural water supplies
in South Dakota: 4 volumes, prepared by the Work Proj.
Admin. as a report on the well survey conducted as Work
Proj. Admin. Ofl‘icial Proj. 665—74—3—126; sponsored by
the Ext. Service and the Expt. Sta, South Dakota State
0011., in coop. with the State Geol. Survey.

Simpson, H. E., 1954, Geology of an area about Yankton,
South Dakota: U.S. Geol. Survey open-file report, 317 p.

1960, Geology of the Yankton area, South Dakota and
Nebraska: U.S. Geol. Survey Prof. Paper 328, 124 p. [1961].

Stevenson, R. E., and Carlson, L. A., 1950, Areal geology of the
Bonesteel quadrangle: South Dakota Geol. Survey (map).

Stokes, W. L., and Varnes, D. J., 1955, Glossary of selected
geologic terms with special reference to their use in engi-
neering: Colorado Sci. Soc. Proc., v. 16, 165 p.

 

Terzaghi, K. 0., 1950, Mechanism of landslides, m Paige, Sid-
ney, chm., Application of geology to engineering practice:
Geol. Soc. America, Berkey volume, p. 83-123.

Terzaghi, K. 0., and Peck, R. B., 1948, Soil mechanics in engi-
neering practice: New York, John Wiley & Sons, Inc.,
566 p.

Thornthwaite, C. W., 1948, An approach toward a rational
classification of climate: Geog. Rev., v. 38, p. 5—94.
Truesdell, P. E., and Varnes, D. J ., 1950, Chart correlating
various grain—size definitions of sedimentary materials:

U.S. Geol. Survey.

U.S. Army Corps of Engineers, 1947, Missouri River survey,
Gavins Point near Yankton, S. Dak., to Stanton, N. Dak.:
U.S. Army Corps of Engineers, Omaha district, sheets 23,
26, 30, 37, 39, 42 of topographic map series.

U.S. Bureau of Reclamation, 1951, Mechanical analyses of
earth materials, in Earth manual: U.S. Bur, Reclamation,
tentative ed. (repr. with revisions Feb. 1952), p. 135—145.

U.S. Department of Agriculture, 1941, Climate of South Dakota,
in Climate and man—1941 Yearbook of agriculture: U.S.
Dept. Agriculture p. 1109—1118.

U.S. Weather Bureau, 1948—56, Climatological data, South
Dakota section, in Climatological data for the United
States by sections: U.S. Weather Bur. [volumes for the
years 1947—55].

Varnes, D. J., 1958, Landslide types and processes, Chap. 3 of
Eckel, E. B., ed., Landslides and engineering practice:
Natl. Research Council, Highway Research Board Spec.
Rept. 29, p. 20—47.

Visher, S. S., 1954, Climatic atlas of the United States: Har-
vard Univ. Press, 403 p.

Warren, 0. R., 1952, Probable Illinoian age of part of the Mis-
souri River, South Dakota: Geol. Soc. America Bu11., v.
63, No. 11, p. 1143—1155.

Warren, 0. R., and Crandell, D. R., 1952, Preliminary report
on geology of part of the Chamberlain quadrangle, South
Dakota: U.S. Geol. Survey open-file report. 45 p.

U.S. GOVERNMENT PRINTING OFFICElel 0—472—783

INDEX

[Italic page numbers indicate major references]

 
 
  

 

 
 
 
 
 
 
 

 
 
 
  
 
 
  
   
 

Page

Acknowledgments ............................................................ 2
Alluvium ................................................ 9
terrace, slow-draining.- ......................................... 35
Analyses, Pierre Shale... ......................................... 20
landside data. . . . .............................................. 44
Bedrock slumps and block glides ............................................. 11
Brannock, W. W., mineral studies ............................................ 24, 28
Cable School earthflows ....... . .............................................. 53
Cable School slump-earthflow. ............................................... 53
Carroll, Dorothy, mineral studies ............................................ 24, 28
Chamberlain ................................................................. 47
Climate ______________________________________________________________________ 4
Colluvium ................................................................... 9
Conclusion, landslide study areas ............................................ 45
Coteau du Missouri .......................................................... 3
Cretaceous, Upper, sedimentary rocks ....................................... 4
Crow Creek Member, Pierre Shale ........................................... 6
Culture .............................................. . ....................... 3
DeGrey Member, Pierre Shale ............................................... 6
Earthflows, Cable School._ 53
slow ...................................................................... 14
Elk Butte Member, Pierre Shale ............................................. 8
Erosion, cause of landslides ................................................... 16
Evapotranspiration and precipitation, Pickstown. . ......-...._ ............... 59
Fieldwork .................................................................... 2
Fort Randall Reservoir, environment ........................................ 2
Geographic setting ........................................................... 3
Geologic mapping, representative study areas ................................ 34
Geologic materials, correlation with landslides, slope angles ................... 43
Geologic setting and stability conditions ..................................... 35
Geology ...................................................................... 4
Gregory Member, Pierre Shale ........................................ . 6
Ground water, behavior ............................................. _ 48
cause of landsliding .......................................... . 16
cyclic processes .......................................... . 48
investigations ..................................... _ 46'
weight. .................................................................. 16
Hathaway, J. C., mineral studies ...................... . 24, 28
Highway 16 slump .................................. _ 52
Hydrostatic pressure, ground water. ......................................... 17
Introduction ................................................................. 2
Landing Creek siump—earthflow .............................................. 54
Landslides, active ............................. _ 32
causes, Fort Randall Reservoir area ....... . 16
classification ........................ . 10
correlation with slope angles... _ 43
description. ........................ . 52
movements ........................ _ 61
reactivated .............. . 32
recently active._.._.._............... ............... . 32
stabilized ............................................ . . 30
study areas .............. £8, 35, 43
summary and conclusion .................................. .. 45

 

 
 

 
  

 
   
  
  
  
 
 
 
  
 
 
 

 
 

 

 

 

 

 

Page

Location, Fort Randall Reservoir ............................................ 2
Lcess ...................... 10
Lubrication by groundwater ................................................ 16
Missouri River trench ........................................................ 3, 10
Mobridge Member, Pierre Shale. 7
Montmorillonite, Pierre Shale- _ . 25
Mudflows .................................................................... 15
Niobrara Formation .......................................................... 5
Ogallala Formation ........................................................... 9
Parker, 0. J ., mineral studies- ............................................... 24, 28
Paulson slump . . . 56
Physiography. 3
Pickstown... 47
Pierre hills. _ 3
Pierre Shale ........... 5
mechanical analyses. 21
mineral composition. 24
montmorillonite ....... 25
thicknesses of map units. 34
Piezometer, described . 46
installation ...... 47
measurements. . . 51
Piping, ground water ______ . 20
Precipitation, slope stablity. . 58
surplus .......................................... _ 59
Precipitation and evapotranspiration, Pickstown...._. ......................... 58
Quaternary deposits .......................................................... 8
References. - 6'3
Rockfalls ..................................................................... 11
Sharon Springs Member, Pierre Shale ........................................ 5
Shear failure, defined ......................................................... 11
Slope angle, average, formula .................. 43
correlation with landslides, geologic materials ............................. 43
Slope stability, appraisal. . .................................................. 29, 32
prereservoir. .......... . 41
Soil slumps ................................................................... l2
Soilfalls- ..................................................................... 11
Spearman’s rank correlation coeflicient, defined.. . 44
Stability conditions, geologic setting .......................................... 35
Stable ground ................................................................ 29
Structure, Upper Cretacqu sedimentary rocks. _. 8
Summary, ground-water investigations ....................................... 50
landslide study areas ..................................................... 45
Tertiary deposits ............................................................. 8
Till .......................................................................... 9
Varnes, D. J., quoted ......................................................... 10
Varnes, Helen, acknowledgment of aid ....................................... 2
Vegetation ............................ 4
Verendrye Member, Pierre Shale ............................................. 7
Virgin Creek Member, Pierre Shale ........................................... 7
Water level, reservoir and ground-water relation. ............................. 4

65

 

PROFESSIONAL PAPER 675
PLATE 1

3°22? 2 5‘9 000 FY 98“.? ,7’

UNITED STATES DEPARTMENT OF THE INTERIOR
GEOLOGICAL SURVEY

   
  

  
 
 

    
  
  

m

        
   
 
 
 
  
 
  

98°33’ ' '" 98°32’ 24850GO FT

98°31' :2 490 coo FT 98°30’ 98°29 l: I.

99°28 ‘ 2‘10 cm H

 

 

    
        

43°49 EXPLANATION 4m:
' Landslide classification Showing percentage of landslide area

I

36 ,»

 

 

 

 

 

Active Recently active
Area 1, 1.1 percent Area 1, 0.6 percent —
Area 3, 1.3 percent Area 3, 0.8 percent
Area 4, 0.8 percent Area 4, 0.2 percent . , \ .
Area 5, 5.0 percent Area 5, 0.5 percent ' 1 ‘ ' , / ' ~- : . ~ ., ,_ l . ' ‘ . ' . . . , I \A ' . .......

 

  

 

 

 

 

 

Reactivated Stabilized .
Area 1, 0.4 percent Area 1, 97.9 percent I
Area 3, 0.6 percent Area 3, 97.3 percent '
Area 1,, 0.1 percent Area 4, 98.9 percent I
Area 5, 0.0 percent Area 5, 94.5 percent

 

 

Contact of landslide
Dashed where approximately located; 43,02.

 

 

 

 

43°43
I’
5 . I
g}; 1" l)‘ w... ........
I: I.
PG }' 30
g‘ 1’ Area 1

 

 

 

 

 

Representative area selected for
study of geology and slope stability

Numbers in upper right refer to topo— - ‘ . ' . ‘ , ' . L ' fascia?“
graphic map series prepared by US. ' ‘ , 2 ' :

I i Army, Corps of Engineers for the Mis-

souri River valley from Gavins Point
near Yankton, S. Dale, to Stanton, N.
Dale.

 

2:17 use”

 

 

 

 

 

 

 

Geologic and slope stability map

 

 

 

 

 

 

 

 

/ :
.._‘.,_...-,.‘__,......_,x .

 

Slope stability map

 

43 44 © 4 3°01' l i ‘ I
" ’ . . . , 98°35” 247 0 FT 98°34' 2475000 FT
Landslldes studled 1n detall

4 I l A
Piezometer installations

 

e)
(a

\

WA: e-.,._.x
I.
v-
v-
Q

 

4.3“414’

 

 

 

 

 

._..,,.. x“,

 

 

 

 

 

 

 

 

 

 

   
   
   
 
 
 
 

 

  
 
  
  
  
 

 

 

 

   
 

 

 

 

 

 

 
 
  

 

 

:211.7%} .I y ‘ , , . . . . _ ’ - ,. ‘ , ' -_ , T 100°oo' 99°oo'
‘ . . , I . EB I I l I EB
..... , " . ' ._ .. ll 1 ‘y . I, t . , " ,_ Pierre i |
HUGHES l HYDE ' HAND BEADLE EB /
l
STANLEY l l G
__, , -___L____ _. - _ __-_- - '2
i 1— 2504300 FT I
ah- I
l \ i
I . BUFFALO my, 5
. Cowl! I
I Fort Thompson . ' .- ., . I J '
I I JERAULD ' 2 ,
° , w 442% _|_
44 00 63° 0 I7
l o | I
——————__-;—.;d___— _— .1\I
2 L 43°00? __ - _ 43.00,
45 43 JONES, i
, K
at: 505 000 FT I

 

 

 

 

 

 

 

 

 

MELLETTE

 

 

 

   

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I
I i I __ ,,.,L._._I*....._is_...—~.—_.._nu
” I
I I
! —. LANDING CREEK DOUGLAS
; SLUMP-EARTHFLOW PAULSON l\
f i @ SLUMP \
. l -- \\
I I \
i I I CHARLES MIX \
' GREGORY
. TODD l Area 3 L k 53 \
, a e An es
soc pro :7 O 10 20 MILES I -
J ' Former site of
500000 FT Ll I Wheeler Bridge FDR
. , . I I ‘ ‘ - -.. I I Area 2 Sir/DAL 42°59 I i ' ' ' “. , , I 42°39
43° 2' " ‘ ‘ I ' ' ' I 'l ' ' I 43042' i Pickstown 98°33’ 2480000 H 98°32 98°31' 94950::- 98“29’ 9,;7
‘ g o, .1 ; 225, I 7 our . . _ .~: ' = 7' 2 .oor, Fl' v I ,3 I: or ' o— , :2 more IT I .
39 29 ()0 I )9 28 99 2 as )0 99 26 2 00 ) F1 99 .25 4 If 93 (33 43,00, _—_“_l'T——-- —_ —_ I SOUTH DAKOTA ‘ . ,
. _ , y . , _‘ _" _ N-ETER—ASIEA— —"'—‘— D — Base from U-S- ArmyI Corps 0f Engineers (1947, sheet 23) A R EA 1 Slope stability appraIsaI by C. F. ErskIne, assisted by

Base "0m U~5- A’mYI Corps 0* Engmefs’ ”947- Sheet 42’ and A R E A 5 SIooe stabIIIty appralsal by C. F. Erskme. asswted by CHERRY ' KEYA PAHA Area 1 5,000-foot grid based on South Dakota Lambert (south) system Herman Ponder and D. s. Kroenlein, 1953—55

extended to sheet edges by U.S. GeologIcaI Survey Herman Ponder, 1953-55 I BOYD _

5,000-foot grid based on South Dakota Lambert (south) system I | 1 1

99°24’ 2250000 275 9973’ 22KB 000 FI 99°22 99°21‘ 99"20' 9 “1.9“ i 21/ I 99°18 I :2/:~IIIIII i'T 99°13” I

 

 

      
 

 

 

  

98"?)0’ l2.300000 H 98°49 43°? 7' (.1 t/ a v
I? r 4.3“14’ O .

 

 

 

 

53;) 000 I7
________ -I.

 

 

Eiu-zu’l

465 000 FT

 

 

 

43°36

43‘ ; ‘ . . . _ ' : .. , . . 43°13’

32‘)

    
   

“nxhu L_L~:;,A—La_

 

 

 

460 000 FT

 

 

 

310 000 I‘" I

320 000 FT

,,...

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43°3

43° 12’ 43°17

 

  

as

 

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~ .

  

455 0‘00 I‘I’

    

36-4

 

  

    

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315000 Fl

 

 

43°11, 43°34' M

450 000 I' i

 

 

 

 

 

 

 

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coo F'I ' 99°23' 1.2:)”000 F'I‘ 99°21?

  
 

 

   

 

 

 

s 43.3»...
99"15’

 

43°10’
98°49'

- Slope stability appraisal by C. F. Erskine, assisted by Base from U.S. Army, Corps of Engineers, (1947, sheet 39) and AR EA 4 Slope stability appraisal by C. F. Erskine, assisted by
Herman Ponder and D. S. Kroenlein, 1953—55 extended to sheet edges by U.S. Geological Survey Herman Ponder, 1953—55

5,000-foot grid based on South Dakota Lambert (south) system

 

’ '2 325 000 F ' . . “ . 98'54' 2385000 PT

I
I

v

 

 

)5) coo Fl 99°20

99°21’ Z

 

 

000 T- T

 

 

‘
(.

   

98°5/”

Base from U.S. Army, Corps of Engineers, (1947, sheet 30) and
extended to sheet edges by U.S. Geological Survey
5,000—foot grid based on South Dakota Lambert (south) system

SCALE 1 :24 000

1 12% 0 MILE

L I J a I—--i |-——I I 1 l

1 .5 0 1 KILOMETER
l—l I—l I——I l-—l l--l

CONTOUR INTERVAL 10 FEET, ABOVE 1400—20 FEET
DATUM IS MEAN SEA LEVEL

.4..-

 

 

MAPS SHOWNG SLOPE STABILITY APPRAISALS OF AREAS 1, 3, 4, AND 5,
FORT RANDALL RESERVOIR, SOUTH DAKOTA

472»7B3 O . 73 (In pocket) No. 1

UNITED STATES DEPARTMENT OF THE INTERIOR

 

 

PROFESSIONAL PAPER 675

 

 

 

  
 
 
 

   

 

GEOLOGICAL SURVEY PLATE 2
TYPE OF MOVEMENT (BEFORE MOVEMENT)‘
SOILS
BEDROCK (CLASTIC MATERIAL, INCLUDING ROC FRAGMENTS, SHEARED BEDROCK, ORGANIC MATTER, ETC.)
I. FALLS \\ Niooraro Formation
thrgiigiis ti’ilergiiiuigcflzilfs'sfrrggsiaiif mgvgrfigggg; :0 ROCKFALP’ clayey Till, slow-draining alluvium, alluvium,
leaps and bounds, and rolling of rock and debris A extremely mp‘d gravel B colluvium, and loess unit, and loess
fragments without much interaction of one frag- a: clean_
ment with another. 50“ SOILFLL
very rld

II. SLIDES

Movement caused by finite shear failure along ROTATIONAL PLANAR 'Pierre Shale PLANAR ROTATIONAL
one or several surfaces which are visible or whose Pierre Shale Pierre Shale D ..

    

presence may reasonably be Inferred.

A. Material in motion not greatly deformed.

Movrng mass consists of one or a few units.
Maximum dimension of units is greater than 9
displacement between units. Movement may be “
controlled by surfaces of weakness such as
faults, bedding planes or joints.

I) SLUMP= Movement only.along internal slip
surfaces, which are usually concave upward.
Backward tilting of units is common. 2) BLOCK
GLIDE: Movement of a single unit out and down
along a more or less planar surface of weakness,

sandstone

Diversion ditch
(water seeped down
and softened weak

agglomerate)

  
 

  
  

  
  
   

$4.37!“: \-_ \ flefififfif‘

\\
. \‘

strong andesne AN
\

brecma \_§.

 
   
 

BLOCK GLIDE

 
 
  
 

LCI Pita Slide

 

generally a bedding plane. Block may glide far
out on original ground surface.

 

B. Material in motion is greatly deformed or con-

sists of many semi-independent units.
Movement frequently is structurally controlled

by surfaces of weakness such as faults, joints,
bedding planes variations in shear strength be-
tween layers of, bedded deposits, or by the con-
tactbetween firm bedrock and overlying detritus.
Maxrmum dimension of units is comparable to or
less than displacement between units, and gen-
erally much smaller than displacement of center
of gravity of the whole mass. Movement may pro-
gress beyond original slip surface so that parts
of mass slide over the ground surface.

srump firearm“ BLOCK GLIDE ”WW
moderate
ROCKSLIDE
control by

jaints

very slow to extremely rapid

 

 
  
     
  
  
  

\ extremely slow

   
 
 
     

  
 

to slow?

        
 
 

firm clay‘
soft clay with water-
bearing silt and sand layers-
firm clayey gravel‘ 3.2,,

 

 

    

DEBRIS sup?“

very slow to rapid

 

Alluvium, colluvium and loess

unit, loess, and till(?)

    
  

 

ALL UNCONSOLI DATED

 

MOSTLY PLASTIC

 

DRY

.\

ROCK FRAGMENT FLOW

than I30 ft per sec at Elm.)

111. FLOWS

Movement within displaced mass such that
the form taken by moving material or the ap-
parent distribution of velocities and displace
ments resemble those of viscous fluids. Slip
surfaces within moving material are usually
not visible or are short-lived. Boundary be-
tween moving mass and material in place may
be sharp or a zone of distributed shear.

GRAD/I T/0/VAL WATER CONTENT

WET

 

 

     

   
  

dry sandx I
rapid to very

firm Siiix mp'd

sands;

LOESS FLOW

after Heim 0932)
Elm, Switzerland
l88l

(Variety: ROCKFALI AVALANCHE)

This type of movement occurs only when large rocktalls and
rockslides attain unusual velocity. Extremely rapid (more

 

after Sharpe o

RAPID EARTHFLOW

  

SAND OR SILT FLOW

rapid to very rapid

  
  

(caused by earthquake)
extremely rapid

NONPLASTIC OR SENSITIVE _
MOSTLY LARGE ROCK FRAGMENTS SORTED SAND OR SILT MIXED ROCKS, SOIL, CLAY, ETC.
l
SAND RUN

N

gradational

Kansu Province China ‘
20 , series

(dry)

 

 
 
  

c
Weathered ‘)
bedrock,
soil, etc.

very rapid to
extremely rapid

glacial clay
and silt

Riviére Blondie,
Quebec

Iooo‘

very rapid

MUDFLOW

very rapid

 

DEBRIS FLOW

 

slow to rapid

Weathered Pierre Shale, till, and colluvium

EARTH FLOW

MUDFLOW

 

 

N. COMPLEX LANDSLI DES

Movement is by a combination of one or more of
the three principal types of movement described
above. Many landslides are complex, although, as
illustrated in Pls. I-k and H, one type of movement
generally dominates over the others at certain areas
within a slide or at a particular time in the evolution
of a slide.

 

 

Nomenclature of the parts of a landslide
(see drawing at right)

MAIN SCARP- A steep surface on the undisturbed
ground around the periphery of the slide, caused by
movement of slide material away from the undisturb-
ed ground. The projection of the scarp surface under
the disturbed material becomes the surface of
rupture.

MINOR SCARP— A steep surface on the disturb-
ed material produced by differential movements within
the sliding mass.

HEAD- The upper parts of the slide material
along the contact between the disturbed material and
the main scarp.

TOP— The highest point of contact between the dis-
turbe?’ material and the main scarp.

FOOT— The line of intersection (sometimes buried)
between the lower Jaart of the surface of rupture and
the original groun surface.

TOE — The margin of disturbed material mast dis-
tant—fan the main scarp.

 

 

 
    
     
  
   
   

ORIGINAL
GROUND SURFACE

TRANSVERSE

TRANSVERSE CRACKS
RIDGES

  
  

  

/» 9 i
\ 4”(I.u;"’//\’o’l<“v€

“4/ /// _

lif— The point on the toe most distant from the top of the slide.
FLANK— The side of the landslide. ,

CROWN — The material that is still in place, practically undisturbed,

 

and adjacent to the highest parts of the main scarp.

ORIGINAL GROUND SURFACE- The slope that existed before the
movement which is Being con3idered took place. If this is the surface of
an older landslide that fact should be stated.

LEFT AND IGHT— Compass directions are preferable in describ-
ing a slide, but if right and left are used they refer to the slide as viewed
from the crown.

 

*The type of material involved is classified according to
its state prior to initial movement or, if the type of move—
ment changes, according to its state at the time of the
change in movement. Thus, the Elm slide ( Pl.1-l) began
as a rock slide and rock fall in bedrock, but at the time a
flowing type of movement started the material ‘was an
"unconsolidated" mass of extremely rapidly movmg rock
fragments.

The following definition of a landslide has been adopted for use in
this book:

LandsMe—The term "landslide" denotes downward and outward move-
ment of slope—forming materials composed of natural rock, soils, artefrcral
fills, or combinations thereof.

Landslides move along surfaces of separation by falling, sliding, and
by flowing. Parts of a landslide may move upward while other parts
move downward. The lower limit of‘the rate of movement of landslide
material is restricted in this book by the economic aspect to that actual

or potential rate of movement which provokes correction or maintenance. *TBY debris is meant natural 50" and rock detritus.

CHART SHOWING CLASSIFICATION OF LANDSLIDES

Reprinted from Varnes (1958, pl. 1) with certain
additions for this report

Approximate ranges of rates of movement
are according to the scale below

ff/se<:

extremely
rapid

 

very

rapid

 

la"-

rapid

IO'/sec

I'/min

 

i0'5-

moderate

='lday

 

:0"—

slow

Elma nth

 

10‘"-

very
slow

S‘lyear

 

extremely

 

lo"-

 

slaw

l'lSyears

472-783 0 - 73 (In pocket) No. 2

‘UNITED STATES DEPARTMENT OF THE INTERIOR
GEOLOGICAL SURVEY

98°46

98°47
43%} 7’

; 931' 0013‘ “I ‘ “420080 l-T

 
     
  

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Base from U.S. Army, Corps of Engineers, (1947, sheet 26) and
extended to sheet edges by US. Geological Survey

5,000~foot grid based on South Dakota Lambert (south) system

 

 
 
   

 

SCALE 1:24 000

98°42

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1 V2 0 1 MILE
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1800’
1700’
1600'
1 500’
1400’

1300’ %W/WWWWWW¢WW%/W//m

2000’
1900'
1800’
1700’
1600’ i i .

Stabilized landslide
1500'
1400’

1300: . :, , ,. , ‘ . , / Ill/1111?”?

 

1900’
1800’
1 700’

l 600' vac ‘
/WWWMW%

1 500’
1400’
1300’

 

 

1 KILOMETER

 

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PROFESSIONAL PAPER ~ 675

'.

§ 9

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t '0

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are

PLATE 3

“ .14: cm r'rf 98°40

it?

Q ' ' '1
“‘3'42

9

'0 O I’

‘ . ’3?!”
o ‘3’,"
e , r

f

 

 

43°06

 

 

 

{Mi 1 '4T

43°04'

 

 

Geology and slope stability appraisal by C. F. Erskine, assisted by
Herman Ponder, J. H. Smith, and D. S. Kroenleln, 1953—55

 

 

 

 

 
   

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

EX P LA N AT! 0 N
Alluvium, colluvium, and loess
E E
D ‘3 Alluvium, slow dralmng
2 o
it t
>_
Stabilized landslide . SE
Terrace alluvium, slow draining Z
t E
//////////(4 W/I/I/I/I/I/mmmfl/[l/IM/I/fl/(I/{M/(g/lz/MMuW/I/I,”gII; (”lamp/(mu l—
O
’ >-
a» D: ,
t § s
§ 8 l—
0: i: E
'§
3 , l—
8
g
/////////////
U)
§ 2)
’ 8
U , -: O
S .' ‘ Lu
g < Pierre Shale > O
O er, Elk Butte Member if
E. Kpm, Mobridge Member LLI
-- - a, vac, Virgin Creek Member EC
Stabilized landslide b vad, Verendrye and DeGrey Members 0
Recently active landslide 3‘) 250 500 FEET Kpg, Gregory Member
3 Kps, Sharon Springs Member
5
l////////////////////////////////////(////_//////////////////IIII/(11111111501011, ”0”,”... E
t Niobrara Formation

 

GEOLOGIC AND SLOPE STABILITY MAP AND SECTIONS OF AREA 2,
FORT RANDALL RESERVOIR, SOUTH DAKOTA

___7 _______
Contact
Dashed where approximately

located; dotted where concealed;
queried on cross sections
where thickness of landslide
deposits unknown

Active, 2.6 percent
Landslide classification showing
percentage of landslide area

Recently active, 2.3 percent

 

Reactivated, 2.8 percent

Stabilized, 92.3 percent

Note: Sections D—D ’ to J -J ’
not illustrated

472—783 0 - 73 (In pocket) No. 3

 

UNITED STATES DEPARTMENT OF THE INTERIOR
GEOLOGICAL SURVEY

 

 

vi

PROFESSIONAL PAPER 675

 

 

 

 

 

 
  

 

 

 

     

 

 

  
  
 

 

  
  

 

 

   
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

    

 

 

 

 

 

 

 

 

 

 

 

  

 

 

 

 

 

 
 
  
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  

 

  

    

  

      

       

 

     

 

   
 

 

 

 

 

 

 

 

 

 

 

 

 

 

  

 

  

 

  
 

  

  

    

  
 

  

    
  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

PLATE 4
PIEZOMETER P'EZOMETER
SITE 5 NUMBER *
NUMBER ': AND 1954 1955 1956 DRILL LOG DESCRIPTION
AND E ELEVATION DEPTH, lN FEET
0F BOTTOM
LOCATION -‘
”4 OF POROUS
JIFIMIAIMIJIJIAISIOINID JIFIMIAIMIJIJIAISIOINID 11114141111011” oI~
| | | I I | | I | I | | | | I | I I I I I I | | I |
1345.4 1344.3
_, 1343.2 1343.0 1343.2
1.1.1 1341.5
> _
E E 1340’ —
n: 5
#3 E
é “5° 1330.3
,2 < 1326.9
5 :5 1325.0 1326.6
>
E 2 1325.8
3
a: 1320’ — ‘
1324.1
1380’ _ Top of piezometer at elev. 1,381 feet — '— _
Loose brown sandy clay
Lu
0
<
c:
1::
1.1.1
I—
E 1 _ _
5 1360 dry 1352 3 dry dry dry 1353.5 1353.5 Loose brown clayey sand
5 dry dry dry dry 13522 dry dry 1'353 7 1353-7 1352.3 dry 1352.2 dry 1352.2 1353.8 J 1353.6 1 1353.3 1353.5 13533
CD 1—29 13519 1352.1 1352.2 1352.2 1352.2 1352.1 ' 1352.7 1352.2 1352.2 . - . w - g
E o-_____ _‘ - t A w - - . ‘
‘1‘ 1352.1
0
LI.
0 1341 1
1.. 1337.6 .
2 1339.0 Stiff brown lean cla
8 1340’ r— . 1338.5 1338.5 1337-4 1337.4 1338.6 1339.0'fi 1!
LI.
1—2
”294 Plastic brown fat clay
1328.4 1328.9 1329.4
Stiff brown lean clay
/
.// Stiff black fat clay
1—60.’/
1 _ Niobrara Formation
1320 — 1321.4
Lu
o
E
5 Top of piezometer at elev. 1,390 feet -— ——
I—
2 Friable brown lean clay
E
—' 1
E 1380’ —- —
g Friable brown sandy clay
3‘:
0 dry '1367-4 1367.4 1367.4 dry dry 1368 o 78 1367 9 1368 7 1369.6 1370.5
LL dry 1365.7 1367. 13 . 1367.6 1367.9 1 1367.4 13674 J 1367.0 1367.9 ' 1367.4 136 . ‘ ‘ _
0 2—24 ___...1367'3 1365.7 J (:74 k ‘ ‘ 4 1365.8 1365.8 Stiff brown fat clay
5 """‘
g 1365.7 Loose brown clayey sand
N 1360’ — — Niobrara Formation
Top of piezometer at elev. 1,414 feet — ——
2 Loose black silt
<7:
—I
1:
Lu
m
E 1400' — —
I
o
g Stiff brown lean clay
o
co
<
(/3
Lu
:‘
E
0' _ _
:- 138 Stiff brown sandy clay
z
:1: 1369.5 1369.5 1369 5 dry Loose brown clayey gravel
“3 1369.5 13696 I J 11 1369.9 1369.5 ' dry dry dry 1370.2 1369.9 1369.9 1369.8 1369.9 . .. .
E 3—46 _____‘ 136.95 - 4. 1 ”695 1367.8 ”695 1369's 1369's 1367.8 1368'11368.1 1368.2 # = - 1359] - Loose brown gravelly sand
:5 13677 E Niobrara Formation
1360’ — “
Top of piezometer at elev. 1,450 feet —-————— ~ _ _ ___..___.____
Hard brown silt
r _ _.
1440 1433.9 1433.7 1433.8
1434.0 1433.9 J 14340 I 1433.9 1433.9 1433.8 1434.3 1433.8 1433.3 1433.614333 1433.7 1434.1 1433.8 1432,13
/ - - - - Afi —% - a N
/
/
/
/
//
E 1420’ ~ 4-32 /‘ __
5 6/
E 1417.7
m
2
<
I
o
3
o . .
_1 Firm blackish-gray
L“ I — dry dry — Pierre Shale
(11: 1400 1394 7 13948 13914334181 1394 6 dry 13941;“8 13947 dry 13932 “W 13932 13949 13949 1394 8
§ 4—57 ”V; _ _ ’ 1393.1 139.” 1394.5 -' 1393.2 1393.2 ' 1' -
2 ._,..;———
00 1393.1
:6
z
<
m
E
1.1.1 1380’ -‘ —-
_l
<:
.. 1359.3 1359.4
1359.2 359.3 1361.8 1359.2
13 1359. 1359.3 1359.3 1359-1 13539-4 1359.3 1359.4 1359.4 1359.4 1359.4 1359-4
1360' 1359.2 59.2 1 / _ L ‘ - _ - _
4‘93 ,’/" = 4: ' - fi ' ' ' Niobrara Formation
0‘"
1357.0
I | | I l I I I l I l |

 

 

 

 

 

 

 

 

 

 

 

 

 
   
 

  
 
 

 

 

 

 

 

 

 

 

 

    

  
 
  

 

 

 

 

 

PIEZOMETER
PIEZOMETER
NUMBER *
SITE (2,
_ AND 1955 1956
NUMBER 1— 1954 DR'LL L0G ESCRIPTION
AND § SEQ/gag?“ DEPTH, IN FEET D
1.11
LOCAT'ON d 0F POROUS
(PL.1)
TUBE JIFIMIAIMIJIJIAISIOINID JIFIMIAIMIJIJIAISIOINID JIFIMIAIMIJIJIAISIOIN
| I l I | | I | | | | | I | T I | | | I I I I | I
1360’ ————-——-—-— Top of piezometer at elev. 1,360 feet ———-————————————-~——-———_——————~——__—.________._-____——____.____________
dry o dry
1347.7 1350.2 1348.0
13459 13459 13 80
1347.6 1347.2 1347.7 1348.1 1347.8 1347.5 1347.8 1347.9 4%
E A-14 .——-—-~"’"
at 1345.8 Stiff brown lean clay
_, 1340'— /13 _
40.9 1340.4 1340.2
.1 / 1339.9
< 1339.1 1338.5 1338.4 1338. .
g ,/ 1334.3 1340.8 1340-1 1339.3 13392 13339 9 13381 1337.0
/
< _ /
c: A 30 o’
'1; 1330.3
O
L].
5
d 1320'~ —
ca
3
:‘
2 Stiff gray lean clay
_\N
H
:5
E
m 1300’ -- _
'5‘:
‘2
1 Loose gray fine sand
<'
1284.4 1286.8 1283.3 1284.7 1284.8 1284.7 1284.9 1284.9 .
- 1284.2 PIaStIC gray clayey sand
1284.1 1284.2 1284.1 I ӣ1 1284.6 IZWJ 1284.4 Llws I 1284.7 1284.8 1284.5 1 12831 1 1284.5 1284.5 1284.8 L f d
_ _ - i - 1 w - v ' - v ' oose gray ine san
A—81 —’// N' b F '
1280’ __ r/ _ 30 _ Io rara ormatron
1279.4
2 1342.9 1342.7 1344") 1340.2
5 13414 1340.0 1340.5 1340.0
_1 1340’ - —
2' 1339.1
D
Z
<
C:
1—
m
O
U.
’2
_.1 1320’—— —
Lu
>
Lu
_J
K
Lu
2
3
E
O
E r
1.1 1300 — —
m .
LIJ
M
————-— ——- Top of piezometer at elev. 1,444 feet —————-———-—————-—-————————————————~———-————-————-————————-——-———-——
Stiff brown lean clay
1440' — my —
1431.6 1433.2 1433.3 dry dry 1433.5 . .
dry dry 14329 dry 1433.4 dry dry 1433.3 1433.3 1433.3 dry1431.6 dry 1431.6 1433.5 1433.2 14334 14334 14335 ”327 St'f‘g'ay :Ierre Sha'e
8—12 143115 143117 - 1431.6 1431.6 1431.6 1431.6 1431.6 4 A j -‘ fi. fi- (Weat Bred)
o--—q———
1431.6
2 Subfirm gray Pierre
3 dry dry d, Shale (weathered)
:1‘ 14201 __ dry dry dry 1414.3 dry 1414.2 dry 14114
< dry dry dry 1414.2 dry 1414.2 dry dry 1414.3 dry 1414.2 dry 1414.2 dry dry dry dry ' dry dry dry
2 1414.2 1414.2 1414.2 L 1414.2 1414.2 1414.6 1 1414.3 1 1414.2 1 1414.2 1414214141 1414.3 1414.1 1414.2 1414.2
< 3‘30. _—;7 ‘ fl. .7 - 3 v v v — w 3 ‘ v ‘ fl -
‘3‘ 1414.2
'—
a:
0
LI.
Lu
>
8
1400’ -- -
<
‘0 139433”3 13943494-4 13941 139411;“4 13944 13944 139‘” 1393'6 13945 13943 13939
‘11 1394.2 1394.2 ‘- _~ ~ 1393.3 ' ' ‘ 1393.8 I 1393813938 4 - ' 139412 I 1393-6 1393-7 1393.6
E //~ ‘v - i - ~ ' - - 6
N
N. // 1386.2 1386.3 1386.5 1386.4 1386.5 13865 1386.4
1385.4 - - -
x 3'59 / 13826 13839 13843 v - v -
<2: ( ‘ ' ' Firm gray Pierre Shale
at: 13846
':E 1380 — —
9
D:
m'
1360’ —— __
B— 2 ’
9 r/
1352.1
I—g
—-——————-— Top of piezometer at elev. 1,463 feet ———————-—-————-—-————-—-————————-—--—-——-—————~—-———————-——-——————————— 0
1460’— —‘
Stiff brown lean clay
10
E 20
D
1_ dr dry dry __ . .
:1' 1440 dry 1 1434.6 1435.4 14356 dry 1434.3 dry 1434.3 1435.4 Subfirm gray Pierre
a: 0-29 1435.3 1435.4 1434.7 1434.2 1435.4 1435.4 1435.4 1434.3 1435.3 _1435.3 1435.4 14115.4 1435.3 1435.3 Shale (weathered)
z '_______ - - - w a
< 1434.2 30
9: 1427.5 1428.1 1427.6 1427-6
1427.1 ”27-2 275 l
E 14262 1425] 1427212 1427101 14272 I 142114273 1427.5 1427.7 1428.1 14$; 14-. 1427.6;‘1427‘6 1427;142:713 1427.9 ”27.2: 1427.8
0 ._ - fi fi - j -
1,. ’f 1426.8 ‘ ‘r 4' ‘ — + 4
111 / 14249 1425.9 14251 14254 14251 1426-” ”251-;263 14253 1426.0 1425.3 1425.2 1425.3 1425.7 1425.6 1425.4 1425.1 1425.6 40
5 , / / 1425.9 ‘ 1425.4 14253
on 1420 — / / ._
“ /
3 / 50
_l
E c 55 / /
g _ J /
<4 1408.4 /
x“
5 / 60
m 1400— / —
E / Firm gray Pierre Shale
1.1.1
.1 / 70
o'
/ so
1380’ —— / _
C—88‘
1374.5 90
1500’ —- ‘ —*
—————-— —-—— Top of piezometer at elev. 1,498 feet —————————————————————-——-————————-———————————————————————— SW brown lean clay
Subfirm gray Pierre
Shale (weathered)
1480’— 14746 14756 1475 14755 ”75‘5 —
1475.1 - 1475.3 ' ~51 ' 1476.1 1476.4 1476.5 1476.6 1476.3
‘2: 14743 1474.5 1474.7 1475.24 11475314753 1475-0 1475.1 1475-7 ”755 E3 ”75-3 $ f A 5 = 4
1:1 'fi: 4' 4 A 1 1 - , - ‘ 5 14 51 5 14754 '14758 14759 14758 1475.9 1476.2 1475.8
1 . . . 4 . . - ~ - -
j / /?73.6 1473.9 1474.0 147415474314743147414T 474414741 14745 14748 17511475214750 1474.9 4 ‘ - g _
< / - ' 1470.5 1470.6 1470.6 1471.2 1471.3
3 D—32 / / 14684 1469.1 1469114691 ”700 14702
< ./ 1467.7 1468.0 ' 1468.0
'3‘ 1465.9 / 1465.6 1467.4
’—
4: 1460' — / _
° /
LL.
5, /
a /
m /
3 /
E / Firm gray Pierre Shale
..\“‘ 1440’ — / —-
Ln
:— D—62./
<2: 14352 1435.4
m /
E /
5 /
o‘ /
1420' — // —
//
D-921
1406.2
1400’ — ——
l | | I I I I l I I l I I I | 1 I

 

 

*Second part of piezometer number indicates depth in feet

GRAPH SHOWING PIEZOMETER READINGS

AND RESERVOIR WATER LEVELS

472-783 0 — 73 (In pocket) N0. 4

44°00’

43°00’

UNITED STATES DEPARTMENT OF THE INTERIOR
GEOLOGICAL SURVEY

 

 

 

EXPLANATION

56 55
23 ./54
- 53

Control point
Showing successive positions of control
stakes and dates of measurement

53 August 28—29, 1953
54 September 23, 1954
55 August 9, 1955

56 September 4, 1956

9*7'

500

15/0

[52

 

I53

I 540

I55

[56

 

 

Assumed stable

 
 

Assumed stable .1 ‘580

97'

0 Y
Assu med stable

\

069 '

 
   

    

 

444444

54

54

  
 
 
  
  
 
  
 
 
  
  
  
 
 
 
   
  
 
  
 
 
 
    

490 .1

C)

U
o

“0599*
~34

WW?

I

\\\\\\\\\\

s\\\\\\\

 

 

Former site of

 

\

I NEBRASKA
PAHA

l L I

 

BOYD

 

Wheeler Bridge " "
‘ Area 2 'r

BEADLE

AURORA

   

 

EXPLANATION

 

30

 

 

Area 1

 

Dak.

Representative area selected for
study of geology and slope stability
Numbers in upper right refer to topo-
graphic map series prepared by US.
Army, Corps of Engineers for the Mis-
souri River valley from Gaoins Point
near Yankton, S. Dak., to Stanton, N.

 

 

 

 

Geologic and slope st

 

ability map

 

 

 

©

Landslides studied in detail

4- IA

Piezometer installations

O 10

LiJ

 

 

 

Slope stability map

20 MILES

\

55

o
051) /

56

Pierre Shale
A

 

\

 

 

 

 

EXPLANATION

Y-3
55
55 1:. 54
Control point

ShOwing successive positions of control
stakes and dates of measurement

53 August 8. 1953

54 October 2, 1954

55 August 27, 1955
56 September 1,1956

53
6 O 54
55
56

Control point and locus of movement
Vectors too closely spaced to be Matted

 

 

Topography planetabled bv C. F. Erskine,

D. S. Kroenlein, and W. Smyth, 1952—53

 

Q

 

Alluvium

 

. 9".1'.'
. ."Qaf‘°_
-. “’AL‘“

 

Fast-draining alluvium (gravel)

 

a'-'o"_o , 4'0
c.» . Qt 9.],
“a a .' - '...

a -" a

o
a

 

Till

 

 

 

 

 

Mobridge Member

7/
/'/e

Virgin Creek Member

 

va, Verendrye Member
Kpd, DeGrey Member

 

 

 

 

Crow Creek Member

V
/%

Gregory Member

 

Sharon SprIngs Member

%
/e

Niobrara Formation

O 1 2 FEET

l |
MOVEMENT~VECTOR SCALE

CONTOUR lNTERVAL 5 FEET
CABLE SCHOOL EARTHFLOWS

NW1/4NW‘/4NW‘/4 SEC. 30, T. 103 N., R. 71 W.
BRULE COUNTY,SOUTH DAKOTA

EXPLANATION

—\

Verendrye and DeGrey Members

Y
QUATERNARY

Y
CR ETACEOUS

 

Contact
Long dashed where approximately located;
short dashed where inferred

 

Edge of landslide or major crack in
landslide
Dashed where approximate

(HIDE)

Major scarp
Dashed where approximate

W

Top of minor scarp

Approximate contact between slump and flow

9

Spring

 

 
   
      
 
      
   
  
 

’

 

               

 

 

 
      
  

 
  
     
  
   
   
   
   
   
   
     
       
   
   

    
    
      
      
     

Geology by C. F. Erskine, 1956

PROFESSIONAL PAPER 675
PLATE 5

 

EXPLANATION

55 56
5.3/24 3

Control point
Showing successive positions of control
stakes and dates of measurement

53 August 4—5, 1953
54 October 2, 1954
55 August 27, 1955
56 September 2, 1956

 

2:
55
56‘54
z, 54
'55 6 53
55 54':

55

 

 

 

Topography planetabled by C. F. Erskine Geology by C. F. Erskine, 1956

and D. S. Kroenlein, 1953

O 1 2 3
l_ I I .1

MOVEMENT-VECTOR SCALE
CONTOUR lNTERVAL 5 FEET

HIGHWAY 16 SLUMP
NE1/4NE1/4 SEC. 22, T. 104 N., R. 71 W.
BRULE COUNTY, SOUTH DAKOTA

4 FEET
J

 

0‘ 56
X—2

55

 

 
 
  
 

EXPLANATION

55

Control point
Showing successive positions of control
stakes and dates of measurement
53 August 23, 1953
54 October 4, 1954
55 July 23, 1955
56 September 2, 1956

 
 

was;

7 I '4 ”I/ /
‘ '9,

  
   

         
     
   
  

 
  
    

/////

”4%

   

A—l
54
56"

 

 

 

 

 

Topography planetabled by C. F. Erskine

Geology by C. F. Erskine and J. A. Sharps, 1956

and J. A. Sharps, 1956

O 1 2 3

l 41 I
MOVEM ENT»VECTOR SCALE

CONTOUR INTERVAL 10 FEET

PAULSON SLUMP
NE1/4SE1/4SWI/4 SEC. 6, T. 98 N., R. 69 W.
CHARLES MIX COUNTY, SOUTH DAKOTA

4 FEET
l

 

 

 

 

 

Topography planetabled by C. F. Erskine
and D. S. Kroenlein, 1953

O 5 10 15
l l I

MOVEMENT-VECTOR SCALE
CONTOUR INTERVAL 10 FEET

20 FEET

LANDING CREEK SLUMP-EARTHFLOW
SE1/4NEI/4 SEC. 25, T. 100 N., R. 72 W.
GREGORY COUNTY, SOUTH DAKOTA

DETAILED GEOLOGIC MAPS OF SELECTED SLUMPS AND EARTHFLOWS IN THE
FORT RANDALL RESERVOIR AREA, SOUTH DAKOTA

Geology by C. F. Erskine and J. A. Sharps, 1956

EXPLANATION

53b 53::
53a

4

Control point
Showing successive positions of control
stakes and dates of measurement

53a August 12, 1953
53b September 2, 1953
53c September 27, 1953
53d November 7, 1953

54a June 22, 1954
54b July 21, 1954

54c August 21, 1954
54d September 18, 1954

553. June 17, 1955
55b July 27, 1955

55c August 25,1955
55d September 27, 1955
533-d

54a-d
SSa—d

56

Control point and locus of movement
Vectors too closely spaced to be plotted.
Arrow indicates general trend of move-
ment, if any

   
 
 
   
  
 
 
 
  
 
 
 
   
       
   
  

55d
55c
55b

553

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55b

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Topography planetabled by C. F. Erskine
and D. S. Kroenlein, 1953

Geology by C. F. Erskine, 1956

O 1 2 3 4 5 6 7
l_ l I | I I I l

MOVEMENT-VECTOR SCALE
CONTOUR INTERVAL 5 FEET

CABLE SCHOOL SLUMP—EARTHFLOW
SEI/4NE1/4NE1/4 SEC. 25, T. 103 N., R. 72 W_
BRULE COUNTY, SOUTH DAKOTA

8 FEET
|

472-783 0 — 73 (In pocket) No. 5

U (:76 " (o 7‘1
$75" ,7 DAY
'L K/“f”

971a Geology and Fuel Resources

“of the Fruitland Formation
and Kirtland Shale of the
San Juan Basin, New Mexico

and Colorado

GEOLOGICAL SURVEY PROFESSIONAL PAPER 676 '

 

Geology and Fuel Resources
of the Fruitland Formation
and Kirtland Shale of the
San Juan Basin, New Mexico
and Colorado

By JAMES E. FASSETT and JIM S. HINDS

 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 676

A snosnrface ana’ surface staa’y of Me coal-oear—
z'ng Fraz't/ana’ Formation, Me Kiri/anal Sna/e, ana’

aysocz'atea’ rocks, wz'M empnayz's on Me re/az‘z'on

 

oez‘ween regional stratzgrapny and Me a’z'sz‘rz'oaz‘z'on,
Mz'céness, ana’ qua/2'4); of coal

 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1971

UNITED STATES DEPARTMENT OF THE INTERIOR
ROGERS C. B. MORTON, Secretary

GEOLOGICAL SURVEY
W. A. Radlinski, Acting Director

Library of Congress catalog-card No. 75-611172

 

For sale by the Superintendent of Documents, US. Government Printing Oflice
Washington. DC. 20402

CONTENTS

 

 

Page
Abstract ___________________________________________ 1 Geology of the San Juan Basin—Continued
Introduction _______________________________________ 1 Stratigraphy—Continued
Purpose and scope ______________________________ 1 Upper Cretaceous rocks—Continued Page
Location and extent of area ______________________ 2 Kirtland Shale _________________________ 23
Earlier investigations ____________________________ 2 Definition _________________________ 23
Surface geology _____________________________ 2 Lithology __________________________ 24
Subsurface geology __________________________ 3 Contacts __________________________ 24
Present study __________________________________ 3 Mode of deposition _________________ 25
Geography _____________________________________ 3 Fossils and age _____________________ 25
Drainage __________________________________ 3 Extent and thickness ________________ 26
Landforms _________________________________ 3 Paleocene rocks ____________________________ 28
Access ____________________________________ 4 Ojo Alamo Sandstone ___________________ 28
Geology of the San Juan Basin _______________________ 4 Definition _________________________ 28
Geologic setting ________________________________ 4 General features ____________________ 28
Electric—log interpretation _______________________ 4 Contacts __________________________ 29
Stratigraphy ___________________________________ 6 Fossils and age _____________________ 31
Upper Cretaceous rocks _____________________ 6 Upper Cretaceous, Paleocene, and younger
Lewis Shale ____________________________ 6 rocks ________________________________ 33
Huerfanito Bentonite Bed ___________ 6 Animas Formation and younger rocks _____ 33
Pictured Cliffs Sandstone ________________ 8 Structure ______________________________________ 34
Definition _________________________ 8 Geologic history ________________________________ 37
Lithology __________________________ 8 Fuel resources ____________________________________ 39
Contacts __________________________ 8 Oil and gas ____________________________________ 39
Mode of deposition _________________ 9 Uranium ______________________________________ 44
Fossils and age___-___________s _____ 15 Coal __________________________________________ 44
Extent and thickness ________________ 16 Origin and distribution ______________________ 44
Fruitland Formation ____________________ 17 Correlation ________________________________ 54
Definition _________________________ 17 Character and quality _______________________ 57
Lithology __________________________ 17 Over-burden ________________________________ 63
Contacts __________________________ 19 Resources _________________________________ 67
Mode of deposition _________________ 19 Development _______________________________ 70
Fossils and age _____________________ 19 References cited __________________________________ 71
Extent and thickness ________________ 22 Index ___________________________________________ 75
ILLUSTRATIONS
Page
PLATE 1. Geologic map of the San Juan Basin, northwestern New Mexico and southwestern Colorado __________ In pocket
2. List of wells, and stratigraphic cross sections showing the interval from the Huerfanito Bentonite Bed of the
Lewis Shale to the base of the Ojo Alamo Sandstone, the Animas Formation, or the Nacimiento
Formation, San Juan Basin, Colorado and New Mexico _____________________________________ In P001“?t
3. Sections of coal beds in the Fruitland Formation in the San Juan Basin, northwestern New Mexico and
southwestern Colorado ____________________________________________________________________ In pocket
FIGURE 1- Index map showing the location of the San Juan Basin ______________________________________________ 2
2. Induction-electric log and lithologic column of the type well of the Huerfanito Bentonite Bed of the Lewis
Shale showing the interval from below the Huerfanito through the lower part of the Ojo
Alamo Sandstone ___________________________________________________________________________ 5
3- LOSS 0f tWO wells showing the response of the curves to the Huerfanito Bentonite Bed ____________________ 7
4- Map showing the North American epeiric seaway ___________________________________________________ 10
5. Diagrammatic cross sections showing regressive, stable, transgressive, and regressive phases of the Pictured
Clifl's shoreline ______________________________________________________________________________ 11

111

FIGURE

TABLE

6.
7.

8.
9
1 O.

11.
12.
13.

14.
15.
16.

17.
18.
19.
20.
21.
22.
23—26.

27.

CONTENTS

Photographs of outcrop of Fruitland Formation on Lewis Shale _______________________________________
Isopach map of the interval between the Huerfanito Bentonite Bed of the Lewis Shale and the top of the
Pictured Cliffs Sandstone ____________________________________________________________________
Electric log and lithologic column of the cored portion of borehole GB—l, Project Gasbuggy ______________
Map showing subsurface extent of the Fruitland Formation, the Kirtland Shale, and the Ojo Alamo Sand-
stone ______________________________________________________________________________________
Generalized section showing relative stratigraphic positions of samples collected for pollen and spore analysis
on Mesa Portales ___________________________________________________________________________
Isopach map of the Fruitland Formation and Kirtland Shale _________________________________________
Photographs of pinchout of basal bed of Ojo Alamo Sandstone on the south edge of Mesa Portales ________
Isopach map of the interval between the Huerfanito Bentonite Bed of the Lewis Shale and the base of the
Ojo Alamo Sandstone _______________________________________________________________________
Structure map of the San Juan Basin ______________________________________________________________
Contour map of the Huerfanito Bentonite Bed _____________________________________________________
Diagrammatic paleogeographic map showing the environments of deposition of the Fruitland Formation and
the Kirtland Shale __________________________________________________________________________
North-south cross sections showing the evolution of the San Juan Basin area ____________________________
East-west cross sections showing the evolution of the San Juan Basin area _____________________________
Map of oil and gas fields and coal mines in the Fruitland Formation and the Kirtland Shale ______________
Logs through the lower part of the Fruitland Formation _____________________________________________
Isopach map showing total coal thickness in the Fruitland Formation _________________________________
Isopach map showing the thickest coal beds in the Fruitland Formation ______________________________
Maps showing:
23. Locations and as-received Btu values of coal samples ________________________________________
24. Distribution of ash in coal samples from the Fruitland Formation _____________________________
25. Distribution of moisture- and ash-free Btu values of coal samples from the Fruitland Formation__
26. Distribution of fixed-carbon percentage of coal samples from the Fruitland Formation ____________
Isopach map showing average thickness of overburden on Fruitland Formation coal deposits ____________

 

TABLES

 

Selected palynomorphs from samples from the San Juan Basin _______________________________________
Statistical summary of oil and gas pools of the Kirtland Shale and the Fruitland Formation ______________
Wells and measured sections used for plotting coal resources _________________________________________
Analyses of coal samples from the Fruitland Formation ______________________________________________
Average percent of total coal in beds of indicated thickness in areas with given total coal thickness ________
Fruitland Formation coal resources in millions of short tons under indicated overburden, arranged by States

according to bed thickness and total coal thickness_-____ _________________________________________
Coal resources of the Fruitland Formation _________________________________________________________
Production and dates of operation of coal mines in the Fruitland Formation ____________________________

Page
13

14
18

20

22
27
30

32
35
36

37
4O
41
43
51
53
55

61
62
64
65
66

Page
23

45
58

68
71
71

GEOLOGY AND FUEL RESOURCES OF THE FRUITLAND FORMATION
AND KIRTLAND SHALE OF THE SAN JUAN BASIN, NEW MEXICO
AND COLORADO

By JAMES E. FASSETT and JIM S. HINDs

ABSTRACT

The San Juan Basin is an asymmetric structural basin in
northwestern New Mexico and southwestern Colorado con-
taining sedimentary rocks that range from Cambrian to Holocene
in age and are as much as 15,000 feet thick. Upper Cretaceous
rocks, which are more than 6,000 feet thick, are composed of
intertonguing marine and nonmarine sedimentary rocks de-
posited during three basin—wide cycles of transgression and
regression of an epicontinental sea. The final regression of the
sea is represented by the marine Pictured Cliffs Sandstone.
Subsurface studies of this unit, based primarily on well-log
interpretation, and surface evidence indicate that the Pictured
Cliffs regression was interrupted frequently by relatively minor
transgressive episodes that resulted in vertical buildups and
intertonguing of the Pictured Cliffs Sandstone with the over—
lying Fruitland Formation. The strand lines of the Pictured
Clifl‘s Sea had northwest alinements, and the Pictured Cliffs
Sandstone and the overlying Fruitland Formation and Kirtland
Shale are younger in the northeastern part of the basin than in
the southwestern part. Concomitant with the Pictured Cliffs
regression, an area southeast of the basin was uplifted, resulting
in either lack of deposition or possible erosion of the Pictured
Cliffs; there the Fruitland Formation now rests on the Lewis
Shale.

After deposition of the Fruitland and Kirtland, the Upper
Cretaceous McDermott Member of the Animas Formation was
deposited in the northwestern part of the basin area. Next, the
basin area was tilted toward the northwest, and as much as
2,100 feet of rocks was eroded in the east. Following this erosion
cycle, the fluvial Ojo Alamo Sandstone of Paleocene age was
deposited. The source of the Ojo Alamo was primarily from the
west, as indicated by a decrease in pebble size in the Ojo Alamo
conglomerates toward the east, although renewed uplift to the
east may have furnished some Ojo Alamo sediment. In the
northeastern part of the basin, the Ojo Alamo rests on Lewis
Shale. After deposition of the Ojo Alamo, the Paleocene Nacimi—
ento Formation and upper shale member of the Animas Forma-
tion were deposited, followed by deposition of the Eocene San
Jose Formation. These units seemingly rest unconformably on
older rocks near the edge of the basin and rest conformably on
older rocks in the central part of the basin.

Fuel resources of the Fruitland Formation and the Kirtland
Shale include uranium, oil, gas, and coal. The uranium occurs
in channel sandstone in the Fruitland Formation. Oil and gas
occur mostly in small scattered stratigraphic traps. The thickest
coal beds occur in the lower part of the Fruitland Formation.
Deposition of the coal was controlled by the position and the
relative stability of the strand lines of the Pictured Cliffs Sea.

 

The thickest coal occurs adjacent to and southwest of major
stratigraphic rises of the Pictured Cliffs Sandstone. The coal
occurs in elongate tabular bodies whose long axes trend north-
west parallel to the strand lines. The coal beds intertongue with
and pinch out into marine rocks to the northeast and grade
southwestward into flood-plain deposits.

The wells selected for detailed study of coal beds are generally
about 6 miles apart. Because of stratigraphic complexities, this
spacing did not permit reliable correlation of individual coal
beds, although many of the beds are continuous for more than
10 miles and a coal zone generally overlies the Pictured Cliffs
Sandstone.

Analyses of Fruitland coal samples from rotary-drill cuttings
show that the highest quality coal on an as-received basis
underlies the northwestern part of the San Juan Basin. As-
received Btu values in this area range from about 12,000 to more
than 13,000 compared with values elsewhere of about 9,000—
12,000. The coal from the washed drill cuttings is low in moisture
content, ranging generally between 2—6 percent. The ash content
of the coal is unusually high and erratic, ranging from 10 to more
than 30 percent. The lowest ash contents are in the west-central
part of the basin; the highest ash contents are in the middle and
eastern parts of the basin. The moisture and ash-free Btu values
and fixed—carbon ratios of the samples show a well-defined
zonation across the basin paralleling the trends of deposition
and the basin axis.

The statistical method of analysis used in this report indicates
that the Fruitland Formation in the San Juan Basin contains
approximately 200 billion tons of coal in beds more than 2 feet
thick at depths of as much as 4,500 feet.

INTRODUCTION
PURPOSE AND SCOPE

The purpose of this report is to illustrate and describe
the occurrence and extent of the Fruitland Formation
and Kirtland Shale in the San Juan Basin, N. Mex.
and 0010., and to present in detail the distribution of
the fuel resources, principally coal, of these units.
Analyses of coal samples collected from cuttings during
drilling of oil and gas test wells provided coal Btu
values at selected locations throughout the basin.
Reconnaissance surface geological mapping was con-
ducted as needed, particularly on the east side of the
basin, to clarify the relationship between the subsurface
and outcrop occurrence of Fruitland and Kirtland

1

2 GEOLOGY AND FUEL RESOURCES, FRUITLAND FORMATION AND KIRTLAND SHALE, SAN JUAN BASIN

rocks. The reconnaissance mapping resulted in some
revision of formation boundaries shown on previously
published geologic maps.

LOCATION AND EXTENT OF AREA

The San Juan Basin is in northwestern New Mexico
and southwestern Colorado (fig. 1). The part of the
basin discussed in this report is shown on plate 1 and
is the area inside the outcrop of the Pictured Cliffs
Sandstone. This area includes parts of San Juan, Rio
Arriba, Sandoval, and McKinley Counties in New
Mexico and La Plata and Archuleta Counties in
Colorado. It also includes parts of the Navajo, Southern
Ute, and Jicarilla Apache Indian Reservations. The
basin is elliptical; it is about 100 miles long (north-
south) and 90 miles wide (east-west) and extends over
an area of about 7,500 square miles.

 

EARLIER INVESTIGATIONS
SURFACE GEOLOGY

The Kirtland Shale and the Fruitland Formation
were defined and named by Bauer (1916) in a paper
on the stratigraphy of the western San Juan Basin;
Bauer divided the Kirtland Shale into an upper and a
lower shale member separated by the Farmington Sand-
stone Member. The Ojo Alamo Sandstone was named
by Brown (1910), was redefined by Sinclair and Granger
(1914), and was redefined again by Bauer (1916) and
by Baltz, Ash, and Anderson (1966). The Pictured
Cliffs Sandstone was named by Holmes (1877) and
was redefined by Reeside (1924).

Other early workers in the San Juan Basin area
included Gardner (1909a, b; 1910) who mapped the
“Laramie formation” in parts of the northern and

 

 

  
 
  
 

 

 

 

 

  
  

 

  
    
 

 

 

  

109 ° 108 ° 107 °
l |
Cor-tea !8
I Pagosa Springs
<fl
E1 E1
:l 9.. it:
s-l ' m
rt ka
37° _ COLORAD_O_ i443 —
NEW MEXICO 1’
a” Dulce
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“in
Z
O
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2 mRJwLBAgg _ _ _ __
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<
m
36., _ _SAN JqAN co _ |__
MCKINLEY C0
0 10 20 30 MILES
;L____.J__—l

 

 

 
 

 

 

FIGURE 1.—Index map showing the location of the San Juan Basin. ka. Fruitland Formation and Kirtland Shale; outcrop is shaded.

INTRODUCTION « 3

southern San Juan Basin; Bauer and Reeside (1921)
who described the occurrence of coal in the Fruitland
Formation in the western and southwestern parts of
the basin; Reeside (1924) whose paper on the western
part of the San Juan Basin summarized earlier data
and offered new conclusions as to the stratigraphic
relations between the Kirtland Shale and the Fruitland
Formation; and Dane (1936) who mapped the south-
eastern part of the basin and noted that Kirtland,
Fruitland, and Pictured Cliffs rocks were not present
on the east side of the basin.

In more recent years. the following geologists mapped
the outcropping Kirtland Shale and Fruitland Forma-
tion in other parts of the San Juan Basin: Dane (1946,
1948). Wood, Kelley, and MacAlpin (1948), Zapp
(1949), Barnes (1953), Barnes, Baltz, and Hayes (1954),
Hayes and Zapp (1955), Beaumont and O’Sullivan
(1955), O’Sullivan and Beaumont (1957), Baltz, Ash,
and Anderson (1966), Fassett (1966), Hinds (1966), and
Baltz (1967).

SUBSURFACE GEOLOGY

Many of the early subsurface geologic studies of the
Kirtland Shale and the Fruitland Formation were done
by oil-company geologists and consulting geologists,
most of whose work has never been published. Nearly
all the material on the subsurface occurrence of the
Kirtland and Fruitland rocks that has been published
is in Guidebooks of the New Mexico Geological Society
and the Four Corners Geological Society.

Silver (1950, 1951) illustrated and described the
subsurface attitude of the Kirtland and Fruitland rocks
of the basin and speculated on their source. Bozanic
(1955) and Kilgore (1955) briefly discussed the Fruitland
and Kirtland rocks and illustrated their subsurface
occurrence in cross sections. Dilworth (1960) discussed
the subsurface occurrence of the Farmington Sandstone
Member of the Kirtland Shale. Baltz (1962, 1967)
described the Fruitland and Kirtland rocks in the
southeastern part of the basin. Fassett (1964) illus-
trated with electric-log sections the subsurface relation
of the Kirtland and Fruitland rocks throughout the
basin and discussed their source, mode of deposition,
and tectonic history. Hinds (1964) discussed the
sampling of Fruitland coals from wells in the San
Juan Basin and illustrated the distribution of heating
values based on analyses of these samples.

PRESENT STUDY

This report resulted from a study of the coal deposits
of the Fruitland Formation throughout the San Juan
Basin. The study was started by the US. Geological
Survey in 1961 to provide a basis for classification of
public lands in outstanding coal-land withdrawals. The

 

Fruitland Formation and the Kirtland Shale were
studied in the subsurface by using well logs, sample
descriptions, cores, and drilling time records, and by
the authors “sitting on wells” being drilled through the
Fruitland and Kirtland rocks. During the study more
than 2,000 electric logs were examined to determine the
thickness and distribution of coal beds in the Fruitland
Formation. Coal samples were collected from well
cuttings at 64 selected sites throughout the basin and
at a few localities from outcropping Fruitland coal
beds. These coal samples were analyzed by the US.
Bureau of Mines to determine the heating value and
the moisture, volatile matter, fixed-carbon, ash, and
sulfur content. The surface geology of a stratigraphi-
cally complex area in the southeastern part of the San
Juan Basin was mapped in detail by the authors
(Fassett, 1966; Hinds, 1966). In addition, reconnais-
sance geological mapping was done in several other
areas around the margin of the basin. The results of
this and previous mapping are synthesized on plate 1.

GEOGRAPHY
DRAINAGE

The north-trending Continental Divide lies along the
east side of the San Juan Basin. The streams west of
the divide are in the San Juan River drainage area,
whereas the streams east of the divide are in the Rio
Grande drainage area. The major stream in the basin
is the San Juan River, which flows southwestward
through the Colorado part of the basin and into northern
New Mexico to the town of Blanco; from Blanco it
flows westward across the basin and joins the Colorado
River in Utah. The Animas River flows south through
Durango, 0010., into New Mexico and joins the San
Juan River at Farmington, N. Mex. The La Plata
River flows south near the west rim of the basin and
joins the San Juan River in Farmington, about 2 miles
below the Animas—San Juan junction. In addition to
these three perennial streams, many intermittent
streams, of which the largest are the Chaco River and
Canyon Largo, drain the area. The Chaco River drains
the southern and western parts of the basin and enters
the San Juan from the south near the town of Shiprock.
Canyon Largo drains the south-central part of the basin
and joins the San Juan at the town of Blanco.

LANDFORMS

The San Juan Basin lies in the Navajo physiographic
section of the Colorado Plateaus province (U.S. Geol.
Survey, 1946). The topographic relief in the basin is
nearly 3,000 feet. Altitudes range from slightly more
than 8,000 feet in the northern part of the basin to
about 5,100 feet on the west side where the San Juan
River crosses the basin rim. The most prominent

4 GEOLOGY AND FUEL RESOURCES, FRUITLAND FORMATION AND KIRTLAND SHALE, SAN JUAN BASIN

physiographic feature in the area is Hogback monocline
(fig. 14), which rims the basin on the northwest, north,
and east sides and rises as much as 700 feet above the
adjoining country on the west side of the basin. The
central part of the basin is a dissected plateau, the
surface of which slopes gently to the west. The principal
streams have cut into the plateau to form deep steep-
walled canyons. On the upland plains between the
canyons, stabilized sand dunes are numerous. Along the
San Juan and Animas Rivers several stream-terrace
levels can be distinguished.

The climate throughout most of the San Juan Basin
is arid to semiarid. The rainfall in the basin ranges from
as low as 3 or 4 inches a year at lower altitudes to nearly
20 inches a year at higher altitudes, and the annual
average is less than 15 inches. Precipitation is gener-
ally rare in early and middle summer and is more fre—
quent in late summer and spring. The temperature
ranges from below O°F in the winter to above 100°F
in the summer. The mean annual temperature at
Farmington, N. Mex., is 526°, and the annual range is
about 115°. The daily variation in temperature often
exceeds 30°.

At lower altitudes short grass, sagebrush, and many
varieties of cactus are common. The mesas of the basin
generally support a growth of pinyon and juniper,
scattered sagebrush, and sparse scrub oak. Ponderosa
pine grows on the higher areas, mostly around the
north and east rims of the basin. Cottonwood trees grow
in the valleys of many of the streams.

ACCESS

The three main roads in the San Juan Basin are New
Mexico State Highways 44 and 17 and US. Highway
550. Other State highways and a myriad of oil and gas
well access roads furnish entry to almost every part of
the basin. The Denver and Rio Grande Western Rail-
road narrow-gage line crosses the northern part of the
basin from Durango eastward through Dulce and
southward from Durango through Aztec to Farmington.

GEOLOGY OF THE SAN JUAN BASIN
GEOLOGIC SETTING

The San Juan Basin is an asymmetric structural de—
pression which contains Cambrian, Devonian, Missis-
sippian, Pennsylvanian, Permian, Triassic, Jurassic,
Upper Cretaceous, Tertiary, and Quaternary rocks.
The maximum known thickness of sedimentary rocks
in the basin was penetrated by the El Paso Natural
Gas Co. San Juan 29—5 Unit 50 in the SEM sec. 7, T.
29 N ., R. 5 W., New Mexico principal meridian. This
well was drilled to a total depth of 14,423 feet and
penetrated Precambrian rocks at 14,030 feet. The
Upper Cretaceous rocks of the basin are 6,000 or more

 

feet thick and consist of intertonguing marine and non-
marine units that represent three basin-wide trans-
gressive-regressive cycles of deposition. The final
regression of the sea resulted in deposition of the marine
Pictured Cliffs Sandstone.

The Pictured Cliffs is overlain by three Cretaceous
units of continental origin: the Fruitland Formation,
the Kirtland Shale, and the McDermott Member of
the Animas Formation. These units are composed of
interbedded sandstone, siltstone, shale, and coal and
attain an aggregate thickness exceeding 2,100 feet in
the northwestern part of the basin. The Tertiary rocks
of the basin consist of part (locally) of the Kirtland
Shale, the Ojo Alamo Sandstone, part of the Animas
Formation, and the Nacimiento Formation of Paleocene
age, the San Jose Formation of Eocene age, and intru-
sive rocks of possible Miocene age. Quaternary deposits
consist of Pleistocene and Holocene terrace gravels and
alluvium. The Tertiary and Quaternary rocks attain a
maximum total thickness of more than 3,900 feet.

ELECTRIC-LOG INTERPRETATION

Several different kinds of geophysical devices are
lowered and raised through drill holes to determine
various properties of the rocks penetrated. Each of
these devices measures a different physical character—
istic or group of characteristics. The log of a well or
borehole is the graphic record of the characteristics of
the rocks penetrated as determined by a given borehole
device. Three major classes of devices used to measure
rock characteristics in a borehole are: electric, radio-
activity, and sonic.

The electric 10g shows the conductivity, resistivity,
and spontaneous potential of the formations pene-
trated. The radioactivity log shows both the natural
and the induced radioactivity of the material pene-
trated. The sonic log shows the rate at which sound
travels through the rocks adjacent to the borehole. Other
devices are used to measure the size of the borehole,
temperature in the hole, and inclination of the hole.

Approximately 9,500 wells have been drilled in the
San Juan Basin, and the majority of these have had
some sort of logging device run in them. In preparing
this report the authors examined more than 2,000 logs,
most of which were electric logs. Radioactivity and
sonic logs were used wherever possible to supplement
and confirm electric—log interpretation. Electric and
induction-electric logs were used primarily because they
form the bulk of the log file for the San Juan Basin.

Figure 2 shows a typical induction-electric log
through the Lewis Shale, Pictured Cliffs Sandstone,
Fruitland Formation, Kirtland Shale, and Ojo Alamo
Sandstone. The contacts between the various units
composing this sequence and a graphic representation

SPONTANEOUS
POTENTIAL
(Millivolts)

10

—H+

ELECTRIC-LOG INTERPRETATION

CON DUCTIVITY
(Millimhos/m)

400 200 0
0.00 Z[00
0 50 1
0 00
RESISTIVITY 0J0 ALAMO
(Ohms m 2/m) SANDSTONE

 

1 400

1 500

1 600

1800

1900

DEPTH, IN FEET

 

2.000

2100

FARMINGTON SANDSTONE
MEMBER
AND
UPPER SHALE MEMBER
OF
KIRTLAND SHALE

LOWER SHALE MEMBER
OF
KIRTLAND SHALE

FRUITLAND
FORMATION

 

2200

PICTU RED CLIFFS
SANDSTONE

 

2300'

2400

2500

LEWIS
SHALE

 

 

2600

 

 

LEWIS
SHALE

 

H>U ERFANITO BENTONITE BED

EXPLANATION

 

 

 

 

 

Sandstone

Shale

E

CoaI

 

 

 

 

 

SiItstone, sandy shale

 

Sandy limestone

FIGURE 2.———Induction-electric log and lithologic column of the type well of the Huerfanito Bentonite Bed of the Lewis Shale showing.
the interval from below the Huerfanito through the lower part of the Ojo Alamo Sandstone. Lithologies are based on an inter-
pretation of the three curves shown. The curves were traced from an induction-electric log of well 5 in cross section B—B’ (pl. 2).
The induction curve was deleted to avoid masking the resistivity curve.

416-332 0 - 71- 2

6 GEOLOGY AND FUEL RESOURCES, FRUITLAND FORMATION AND KIRTLAND SHALE, SAN JUAN BASIN

of the lithology based on interpretation of the log
curves are also shown. Imaginary reference lines called
shale lines are useful in interpreting rock types from
' electric logs. These are imaginary vertical lines con-
necting the points furthest to the right on the spon-
taneous-potential (S.P.) curve and the points furthest
to the left on the resistivity curve. In areas where
both curves move outward, away from the shale lines,
sandstone or siltstone is indicated; in areas where the
resistivity curve moves to the right and the spon-
taneous-potential curve stays on or close to the shale
line, coal or limestone is indicated. This is an over—
simplification, but it will serve for a general interpreta-
tion of the log in figure 2.

Figure 2 shows that the Lewis Shale is predomi-
nantly shale that contains some thin limestone and
sandstone stringers. The Huerfanito Bentonite Bed is
conspicuous on the conductivity curve. The lithology
and response of the Huerfanito on various types of logs
is discussed at length in the section “Stratigraphy.”
The Pictured Cliffs Sandstone, Which directly overlies
the Lewis Shale, has a distinct contact with both the
underlying Lewis and the overlying Fruitland. The
contact of the Fruitland Formation with the lower
shale member of the Kirtland Shale is picked at the
highest coal or carbonaceous shale bed (1,800-ft depth,
fig. 2) above the base of the Fruitland. The contact of
the lower shale member of the Kirtland Shale with the
overlying Farmington Sandstone Member of the Kirt-
land is picked at the base of the first relatively thick
sandstone above the lower shale member. The contact
of the upper shale member of the Kirtland with the
base of the Ojo Alamo Sandstone is picked at the base
of the first thick massive sandstone above the upper
shale member. The base of the Ojo Alamo is character-
ized throughout much of the San Juan Basin by
high resistivity on the electric log.

STRATIGRAPHY
UPPER CRETACEOUS ROCKS

LEWIS SHALE

A detailed discussion of the Lewis Shale is beyond the
scope of this report; however, the Lewis is briefly
described because the Huerfanito Bentonite Bed, a new
name in this report and used as a datum in several
illustrations, is in the upper part of the Lewis.

The Lewis Shale is the stratigraphically highest unit
of marine shale in the San Juan Basin. It is a light- to
dark-gray and black shale that contains interbeds of
light-brown sandstone, sandy to silty limestone, cal-
careous concretions, and bentonite. The Lewis ranges
in thickness from 0 feet in the southwestern part of the
basin to about 2,400 feet in the northeastern part. It

 

was named by Cross, Spencer, and Purington (1899)
for exposures near the former Fort Lewis army post,
about 15 miles southwest of Durango, Colo.

HUERFANITO BENTONITE BED

Oil-company geologists who have studied the sub-
surface Upper Cretaceous rocks of the San Juan Basin
have long been aware of the existence of several marker
beds in the Lewis Shale that show as distinctive
responses on electric logs. One of these markers was
used as a datum by Hollenshead and Pritchard (1961)
and was given the name “Green Marker Horizon.”
The “Green Marker Horizon” is near the base of the
Lewis Shale and is characterized by low resistivity on
electric logs.

Another marker bed, here named the Huerfanito
Bentonite Bed, is in the upper part of the Lewis Shale.
The Huerfanito Bentonite Bed is named for the type
well, Huerfanito Unit 60, drilled by Turner and Webb,
and completed in November 1960. The well is
in the SWMSWX sec. 4, T. 26 N., R. 9 W. (pl. 2).
The surface altitude of the well is 6,396 feet; the kelly-
bushing altitude from which the log depths were
measured is 6,403 feet; total depth of the well is 6,760
feet. This well is in the Huerfanito Unit operated by
El Paso Natural Gas Co. The unit name is derived
from Huerfanito Peak, about 2 miles northeast of the
well.

The induction-electric log of the type well, the
Huerfanito Unit 60, is shown in figure 2. On this log
the Huerfanito Bentonite Bed exhibits typical high
conductivity at the drilled depths of 2,550—2,562 feet.
This bed, which is 12 feet thick in this well, exhibits a
characteristic response on several types of well logs.
Figure 3 shows the response to the Huerfanito Bentonite
Bed on induction-electric and sonic—gamma ray logs
run in two wells 78 miles apart in the San Juan Basin.

In the left-hand log of figure 3A, spontaneous-poten-
tial, resistivity, and conductivity curves are shown. It
is apparent that the conductivity curve responds mark-
edly to the Huerfanito Bed. The Huerfanito has a
conductivity value of about 550 millimhos/m (millimhos
per meter) on this log. The resistivity curve and the
spontaneous-potential curve respond only slightly to the
marker bed on this log. In the right-hand log, the gamma
ray and the interval-transit-time curves are shown. The
response of the interval-transit-time curve to the
Huerfanito in this well is pronounced, giving a reading
of about 140 microseconds per foot. The gamma ray
curve also responds to the Huerfanito, but this curve
alone would not serve to identify the marker bed.

The logs shown in figure SB exhibit similar but more
subdued responses to the Huerfanito Bed; nevertheless,
the bed is the most conductive unit shown on the con-

 

 

  

 

 

    

 

 

 

 

 

 

 

  
  
 

  
 

STRATIGRAPHY 7
A
INDUCTION-ELECTRIC
LOG CONDUCTIVITY SONIC-GAMMA RAY LOG
(Millimhos/m)
SPONTANEOUS 400 200 0 INTERVAL TRANSIT TIME
1 . . (Microseconds/foot)
POTENT'A" E lS V. 600 4 0 GAMMA RAY 130 90 50
(Millivolts) (Shim-[:12 LI) .___9 (A. P. l. units) ; I J
10+ 50 100 24 144 29 16155 1?5
_ II Backup interval—transit-
time curve; refer to
lower interval-transit-
time scale above
1400_ _ _ _ Huerfanito Bent_o_nite Bed 1400
E Backup conductivity
u. curve; refer to lower
2 conductivity scale
—. above
E 1500 — 1500
o.
u:
D
1600 1600
B
INDUCTION-ELECTRIC LOG SONIC-GAMMA RAY LOG
SPONTANEOUS CONDUCTIVITY GAMMA RAY
POTENTIAL Willimhos/m) (A. P. l. units) INTERVAL TRANSIT TIME
(MilliVOItS) 4 90 290 9 24 144 (Microseconds/foot)
10 O 8 60
_|_.| + 0 50 100 1‘14 . 2§4 19 -° .
l—_L__J
"2
229.0_ _ __ _______ _ ELEEQQiIQEeJ‘E'LV‘e Bel2@Q_
'—
fl Backup gamma ray
"" curve; refer to lower
E gamma ray scale
~ above
E 2300 \— 2300
0.
Lu
0
2400 2400

 

 

 

 

FIGURE 3.—Induction-electric and sonic—gamma ray logs from two wells 78 miles apart, showing the response of the curves to the
Huerfanito Bentonite Bed. A, Logs from a well on the west side of the San Juan Basin (NEM sec. 4, T. 27 N., R. 14 W.; well 2
in section F—F’ on pl. 2). B, Logs from a. well on the east side of the basin (NE% sec. 36, T. 31 N., R. 2 W.).

8 GEOLOGY AND FUEL RESOURCES, FRUITLAND FORMATION AND KIRTLAND SHALE, SAN JUAN BASIN

ductivity curve. The conductivity is much less, about
190 millimhos/m in contrast with 550 millimhos/m
in figure 3A. As in figure 3A, the response of the resis-
tivity and the spontaneous-potential curves to the
marker bed is slight. On the sonic—gamma ray log, the
the gamma ray curve shows the Huerfanito to be rela-
tively more radioactive than it is in figure 3A. The in-
terval transit time, however, is much less in figure 33
than in 3A.

To summarize: (1) The marker bed is more conduc-
tive than the rocks above and below it, particularly on
the west side of the San Juan Basin. (2) The marker bed
is more radioactive than the rocks above and below
it, especially on the east side of the basin. (3) The
marker bed transmits sound waves more slowly than the
beds above and below it, particularly on the west side
of the basin. The Huerfanito Bentonitc Bed has been
traced by the authors throughout the subsurface of the
San Juan Basin on electric logs.

The bentonite composing the Huerfanito Bed repre—
sents an ancient volcanic ash fall into the Lewis Sea.
The source of the ash was probably to the west because
the relative response of both the conductivity curve and
the interval-transit-time curve decreases from west to
east across the basin, indicating a thicker bed of ash to
the west. Unfortunately, the Huerfanito has never been
cored in the San Juan Basin, so it has never been seen.
Also, it has not been possible to correlate a specific
Lewis bentonite bed on the outcrop with the Huerfanito.
Hollenshead and Pritchard (1961, p. 106) stated:
“The examination of cuttings demonstrated that the
‘Green Marker Horizon’ lies within a somewhat ben—
tonitic zone, but did not conclusively prove that the
marker is actually representative of a bentonite bed.”
Until the portion of the Lewis Shale containing the
bentonite bed is cored and the cores are compared with
electric logs, the precise composition of the bed will not
be known; nevertheless, the Huerfanito Bed is an
excellent time surface to which the stratigraphy of the
Pictured Cliffs Sandstone, Fruitland Formation, Kirt-
land Shale, and Ojo Alamo Sandstone may be related.

PICTURED CLIFFS SAND STONE

DEFINITION

The Pictured Cliffs Sandstone was named by Holmes
(1877, p. 248) for outcrops along the north side of the
San Juan River west of Fruitland, N. Mex., where
Indian petroglyphs are numerous. Holmes described the
Pictured Cliffs as consisting of 140 feet: “Forty feet
of white sandstone; 60 to 80 feet yellowish-gray sand-
stone. Beneath these 30 to 40 feet of brownish laminated
sandstones.” Reeside (1924, p. 18) revised the original
definition to include interbedded sandstones and shales
beneath the massive sandstones referred to by Holmes.

 

LITHOLOGY

Throughout most of the San Juan Basin the Pictured
Cliffs Sandstone can be divided into two parts: an
upper part consisting of one or more massive sandstone
beds interbedded with a few thin beds of shale; and
a lower part, sometimes called the transition zone,
composed of relatively thin interbeds of shale like the
underlying shale of the Lewis, and sandstone like the
overlying sandstone in the upper part of the Pictured
Cliffs. The sandstone beds are medium to fine grained
and well sorted and have an average composition of 86
percent quartz, 7 percent potassium feldspar, 6 percent
plagioclase feldspar, and 4 percent coal (fragments),
according to Burgener (1953, p. 19). Cementing
material averages 60 percent calcite, 30 percent clay,
and 10 percent silica. Iron oxide makes up less than 1
percent of the cementing materials. The shale beds are
concentrated in the transition zone.

In some parts of the basin the Pictured Cliffs
Sandstone is characteristically capped by a hard
red-brown iron-cemented sandstone layer, which ranges
in thickness from a few inches to approximately 1 foot
This hard zone is noticeable when penetrated by
drilling because it causes the drill string to bounce and
vibrate. The presence of the hard zone has aided in
surface mapping of the Pictured Cliffs, particularly in
the southeastern part of the basin where the Pictured
Cliffs becomes thin and argillaceous and somewhat
difficult to trace.

CONTACTS

The Pictured Cliffs Sandstone is conformable with
both the underlying Lewis Shale and the overlying
Fruitland Formation throughout most of the basin.
The lower contact is gradational in most places;
shale beds of the Lewis intertongue with sandstone
beds of the Pictured Cliffs. The contact is arbitrarily
placed to include predominantly sandstone in the
Pictured Cliffs and predominantly shale in the Lewis.

The contact of the Pictured Cliffs and the overlying
Fruitland is usually much more definite than the lower
contact with the Lewis. On electric logs the Pictured
Cliffs—Fruitland contact is placed at the top of the
massive sandstone below the lowermost coal of the
Fruitland except in those areas where the Fruitland
and the Pictured Cliffs intertongue. On the surface, the
contact is placed at the top of the highest Ophiomorpha
major—bearing sandstone. This fossil is here used as a
distinctive lithologic characteristic of the Pictured
Cliffs in the sense referred to in Article 6(b) of the code
of stratigraphic nomenclature (American Commission
on Stratigraphic Nomenclature, 1961). Intertonguing
of the Pictured Cliffs and the overlying Fruitland is
common throughout the basin, and the tongues of
Pictured Cliffs in the Fruitland are generally distinct

STRATIGRAPHY 9

enough in the subsurface and on the outcrop to be
mapped or delineated as discrete units.

MODE 0F DEPOSITION

The Upper Cretaceous rocks of the Western Interior
of the United States were deposited in and near an
epeiric sea that extended from the Gulf of Mexico to
the Arctic Ocean. This seaway, which was 1,000 miles
Wide and 3,000 miles long, divided the North American
continent into two landmasses as shown in figure 4. The
San Juan Basin area lies on the west margin of the
Cretaceous epeiric sea and was intermittently above
and below sea level as the sea advanced and retreated
during Late Cretaceous time. The final retreat of the
sea from the San Juan Basin area is represented by
the shallow-water and beach-sand deposits of the
Pictured Cliffs Sandstone.

The approximate westernmost advance of the sea
just prior to the Pictured Cliffs regression is indicated
by the westernmost extent of the Lewis Shale. The
Lewis resulted from deeper water deposition of the finer
grained fraction of the sediment that was carried to
the sea in Pictured Cliffs and Lewis time. The Lewis
is wedge shaped with the wedge pointing southwest.
The maximum extent of the Pictured Cliffs Sea would
parallel and be southwest of the Lewis wedge edge.
Erosion has removed this edge in most of the basin
area; however, about 8 miles east of NeWcomb Trading
Post in T. 24 N., R. 16 W. (projected), the Pictured
Cliffs and the underlying Cliff House Sandstone merge,
and the intervening Lewis Shale wedges out (Beaumont
and others, 1956, p. 2159). The westernmost position
of the Pictured Cliffs shoreline was, thus, probably only
a few miles to a few tens of miles west of the Pictured
Cliffs—Cliff House coalescence.

The problem of how and Why the sea transgressed and
regressed during Late Cretaceous time was thoroughly
discussed by Sears, Hunt, and Hendricks (1941, p. 103—
105). The salient point of their discussion regarding
regressive deposition was that there are two probable
explanations for regressing shorelines: (1) regression
caused by rising of the trough containing the sea, and
(2) regression caused by trough filling and the outward
growth of the land by nearshore deposition. Sears, Hunt,
and Hendricks were unequivocal in stating that “the
regressive deposits of the Upper Cretaceous described
in this paper resulted from a process of trough filling.”
Pike (1947, p. 15, 19) also discussed theories of trans-
gressive and regressive deposition and concluded that
“regression of the sea was brought about by silting-in
along the margins of the trough.” Both papers dealt
with the Mesaverde Group and did not discuss the
Pictured Cliffs Sandstone.

 

The authors’ studies of the Pictured Cliffs Sandstone
throughout the San Juan Basin indicate that the regres—
sion of the Pictured Cliffs Sea from the San Juan Basin
area was primarily the result of trough filling along the
west margin of the sea; however, locally, particularly
on the east side of the present basin, uplift of the shore-
line may have been a secondary factor in causing the
sea to retreat.

Trough filling, the predominant cause for regression
of the Pictured Cliffs Sea from the basin area, is shown
in figure 5, which illustrates in cross section the relation
among the various rock units involved in a shifting
shoreline situation. The units here shown are general-
ized but could be labeled as follows: Marine shale, Lewis
Shale; marine sandstone, Pictured Cliffs Sandstone;
continental deposits and coal beds, Fruitland Forma-
tion and Kirtland Shale; and continental deposits and
fluvial sandstone, Farmington Sandstone Member of the
Kirtland. Time lines in these sections are obviously
parallel to the subaerial-subaqueous paleoslope; thus,
each of the rock units shown is younger in the northeast
than in the southwest. It is assumed that throughout
the time represented by these illustrations the area was
continuously subsiding.

Figure 5A shows a section through a hypothetical
strand-line environment. Sediment was transported to
the sea by rivers that probably were eroding a high-
land somewhere to the southwest of the present San
Juan Basin area. When these rivers reached the sea, they
dropped their coarser sediment fraction close to the
shoreline to be distributed along the coast by littoral
drift; thus, at and close to the sea—land contact, beach
and shallow—water marine sands were laid down. The
finer fraction of the sediment brought to the sea was
carried farther from shore and deposited below wave
base as marine mud. As the shoreline continued to build
outward, the sea was pushed back. However, if the
sediment supply decreased slightly or the rate of
subsidence of the sea trough increased slightly to the
extent that sediment supply exactly balanced subsi-
dence, the shoreline position would become geographi—
cally stable.

Figure 5B shows a section through a hypothetical
strand line after a period of stability. The subsiding
seaway, which itself would have caused the sea to
transgress, was exactly balanced by the influx of
sediments that were continuously being dumped into
the sea by rivers. The word stable as used here refers
to the relative geographic position of the shoreline. In
all probability a stable or fixed shoreline seldom, if
ever, existed. In figure 5B the shoreline was relatively
stable in that, even though it was moving back and
forth constantly through time, it crossed and recrossed
the same geographic area, resulting in a vertical

10 GEOLOGY AND FUEL RESOURCES, FRUITLAND FORMATION AND KIRTLAND SHALE, SAN JUAN BASIN

 

   
  

Prince Patrick

Islandw
r-T T5 -

   
 

   
      
     

5 v' Aléské .1 '
: ._1USA;

. , Nugssuag
‘ «' -' Peninsula

1000 MILES
|_.L_1_.L_1_l___—J

 

 

 

FIGURE 4.—-Probable configuration of the North American epeiric seaway at the time that the
Upper Cretaceous rocks of the San Juan Basin were being deposited. After Gill and Cobban (1966, fig. 15).

STRATIGRAPHY 11

SOUTHWEST

   
  

, Swamp Sea level NORTHEAST

 

 

 

 

SOUTHWEST

NORTHEAST

 

Sea level

 
  

 

 

 

 

 

SOUTHWEST

Sea level NORTHEAST

  
   
 

 

 

 

 

 

 

Sea level NORTH EAST

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

__ m

_ _ _ _ m

Marine Marine ' Continental Coal Fluvial
shale sandstone deposits sandstone

FIGURE 5.——Diagrammatic cross sections showing the relations of the continental, beach, and marine deposits of Pictured
Clifl's time after (A) shoreline regression, (B) shoreline stability, (0') shoreline transgression, and (D) shoreline regression.

12 GEOLOGY AND FUEL RESOURCES, FRUITLAND FORMATION AND KIRTLAND SHALE, SAN JUAN BASIN

buildup of sand. The stable shoreline situation also
allowed for the maximum amount of vegetal-matter
buildup in coastal swamps (discussed in detail in the
section “Fuel Resources”).

Figure 50 illustrates a shoreline that has trans-
gressed, which resulted either when the sediment
supply decreased while the rate of subsidence remained
constant, or when the rate of subsidence of the sea
floor increased and the sediment supply remained
constant. The sea moved overland, depositing beach
and shallow-water marine sand deposits on top of
continental deposits. As shown in panel 0, the new
deposits formed on top of vegetal matter that had
been accumulating in a coastal swamp. Figure 5])
shows a shoreline that has regressed, where again the
sediment supply exceeded the rate of subsidence of the
sea floor, resulting in a shift of the shoreline to the
northeast. As shown in panel D, the past history of
the regression (and associated minor transgressions) of
the sea from the basin area is faithfully recorded in
the sediments deposited during that time.

The Pictured Cliffs Sandstone is absent in two areas
on the east side of the San Juan Basin (pl. 1). In the
northeastern area the Lewis Shale is overlain by the
Ojo Alamo Sandstone; in the southeastern area the
Lewis is overlain by the Fruitland Formation. The
absence of the Pictured Cliffs in the northeastern area
is explained by post—Lewis and pre-Ojo Alamo erosion.
The absence of the Pictured Cliffs in the southeastern
area is not so easily explained. Here, the carbonaceous
silicified-wood—bearing rocks of the Fruitland overlie
the marine rocks of the Lewis. Figure 6 shows a roadcut
in the SWXNWX sec. 23, T. 21 N., R. 1 W., about 3
miles northeast of Cuba, N. Mex., where the contact of
the Fruitland and the Lewis is well exposed. The
contact seems to be disconformable, but the irregularity
may be the result of slumping of the overlying Fruitland
rocks. The Lewis here contains thin sandstone stringers
that might be of Pictured Cliffs lithology. However, the
Lewis is known to be sandy throughout most of its
thickness in this area (Dane, 1936, p. 109; Fassett,
1966), and the authors believe that there is no sub-
stantial reason to call these sand stringers Pictured
Cliffs Sandstone. Furthermore, at this locality there is
more shale than sandstone in the rocks underlying the
Fruitland; thus, the majority of the geologists working
in the San Juan Basin would probably assign these
rocks to the Lewis Shale 'rather than to the Pictured
Cliffs Sandstone.

Possible explanations for the absence of Pictured
Cliffs Sandstone in the southeastern San Juan Basin
are: (1) .No sand was available to be deposited in this
area, (2) a relatively sudden increase in sediment influx
caused the sea to regress rapidly and allowed insufficient

 

time for the beach and shallow marine sands to be
developed, (3) uplift in the area resulted in the rapid
retreat of the sea which prevented development of
strand-line sands, and (4) uplift resulted in erosion of
the sand prior to Fruitland deposition. The authors
believe the last two explanations best explain the
absence of Pictured Cliffs Sandstone in this area. Up-
lift. in addition to causing the sea to regress rapidly,
probably resulted in subaerial erosion of some marine
sediments prior to deposition of the Fruitland rocks. A
local disconformity between the Fruitland and the
Pictured Cliffs is indicated by channels at the base of
the Fruitland, which have cut as much as 50 feet into
the underlying Pictured Cliffs in T. 19 N ., R. 2 W., near
Mesa Portales (Fassett, 1966). The exposures in the
roadcut shown in figure 6 indicate a hiatus between the
Fruitland and the Lewis. The absence or scarcity of
coal deposits in a narrow band along the east edge of
the San Juan Basin (fig. 21) also indicates that there
was uplift in this area either contemporaneous with or
slightly later than the retreat of the Pictured Cliffs Sea.
Uplift may have been centered southeast of the present
basin area in the Nacimiento Mountains, which may
have been an island or a peninsula in the Pictured
Cliffs Sea.

If the Huerfanito Bentonite Bed is an ancient vol-
canic ash fall laid down in the Lewis Sea, then the bed
is a. time surface which reflects the configuration of the
sea floor at the time it was laid down. What the con—
figuration or gradient of the sea floor was at the time
the Huerfanito was deposited in the basin area is not
known; however, it is highly probable that the sea floor
was relatively smooth and even and the gradient was
extremely low. For the purpose of discussing past
orientations of the Pictured Cliffs shoreline, it is as-
sumed that the Huerfanito was a horizontal surface.
Presuming that there was no basin-area tilting between
the time the Huerfanito was deposited and the time the
Pictured Cliffs Sandstone was deposited, lines drawn
on top of the Pictured Cliffs Sandstone which parallel
the Huerfanito should represent both time lines and the
configuration of the Pictured Cliffs Sea shoreline.
Figure 7 is an isopach map of the interval between the
Huerfanito and the top of the Pictured Cliffs Sandstone,
and the isopachs, in efiect, should approximately repre-
sent past shoreline orientations of the Pictured Cliffs
Sea.

The minimum thickness of the interval between the
top of the Pictured Cliffs Sandstone and the Huerfanito
Bentonite Bed is 150 feet in the southwestern part of
the basin. Note that the 150-foot isopach nearly paral-
lels the present outcrop of the top of the Pictured Cliffs
Sandstone. The 200- and 250-foot isopachs parallel the
ISO-foot line and are roughly an equal distance apart.

 

STRATIGRAPHY

 

B

FIGURE 6.—Outcrop of Fruitland Formation on Lewis Shale. A, In roadcut in the SW}£NW% sec. 23, T. 21 N., R. 1.W.,
about 3 miles northeast of Cuba, N. Mex. B, Closeup of contact, at left of road shown in A; contact appears to be
disconformable. Note reverse fault.

416*332 O - 71 — 3

13

14: GEOLOGY AND FUEL RESOURCES, FRUITLAND FORMATION AND KIRTLAND SI-IALE, SAN JUAN BASIN

108" 107“
H 10 9 8 R1W R 1 E

    
   

LA PLATA mm

0
ONTEZUMA ARCHULETA

37., _c9L0RAgo_ [V __

NEW MEXICO

Outcrop of Fruitland
Formation and
Kirtland

RIGW

EX P LA N AT] 0 N
36 " ._
0
Control points represent oil or gas
wells MCKINLEY

Thickness of isopached interval (Huer-

fanito Bed to top of Pictured Cliffs
Sandstone) was determined from electric
logs. Contour interval is 50feet

0 5 10 15 20 MILES
L|_|_.L_]_L__L.—l———l

FIGURE 7.—Isopach map of the interval between the Huerfanito Bentonite Bed of the Lewis Shale and the top of the Pictured Clifl‘s
Sandstone.

STRATIGRAPHY 15

Thus, when the Pictured Cliffs was being deposited in
this part of the basin, the shoreline trended northwest
and the sea regressed northeast.

A change in configuration of the Pictured Cliffs
shoreline is indicated in the basin area between the 300-
foot and the 500- to 550-foot isopachs, particularly in
the southeastern part of the basin. The shoreline ap-
parently shifted from a northwest trend at the 300-foot
isopach to nearly an east trend at the 500-foot isopach.
This shift in shoreline orientation may have resulted
from a more rapid regression of the sea in the southeast
than in the west. The rapidity of the regression could
have been caused by (1) a greater influx of sediments
into the southeastern part of the basin while the sedi-
ment supply being brought in to the west remained
constant or perhaps even decreased; (2) local uplift in
the southeastern part of the basin area; or (3) the fact
that the slope of the sea floor in the southeast was
gentler than the slope of the sea floor to the northwest
with the result that, given equal sediment influx, the
shoreline would regress faster in this area.

During the time that the Pictured Cliffs Sandstone
was being deposited in the area between the 500- and
650-foot isopachs, the shoreline was again relatively
straight, trending nearly east, and the sea was regressing
to the north. However, between the 650- and 750—foot
isopachs, the alinement again swung around to a north-
west trend, probably in response to an increased sedi-
ment supply from the west or northwest and decreased
sediment influx in the east, local uplift in the north-
west, or a more gently sloping sea floor in the northwest.

The 700-foot depression isopach in the northwestern
part of the basin and the two 750-foot isopachs south-
west of this line are anomalous and may represent
irregularities of the sea floor present at the time of
deposition of the Huerfanito Bentonite Bed rather than
highs and lows in the top of the Pictured Cliffs. The
shoreline of the Pictured Cliffs Sea continued to main-
tain the northwest trend as the sea retreated out of the
present basin area. The total rise of the top of the
Pictured Clifis Sandstone across the basin is 1,100 feet,
ranging from 150 feet above the Huerfanito in the
southwest to 1,250 feet above the marker bed in the
northeast.

This stratigraphic rise is best shown in the six cross
sections which were constructed across the basin area
(pl. 2). The sections are based on data obtained from
electric logs of wells drilled for oil or gas in the San Juan
Basin, and the datum is the Huerfanito Bentonite Bed.
The three northeast sections, A—A’, 3—H, and 0—0’,
best show the stratigraphic rise of the Pictured Cliffs
because these sections are in general normal to the
ancient Pictured Cliffs shoreline. There are a large
number of steplike rises in the stratigraphic position of

 

the Pictured Cliffs Sandstone. Many of the rises are
inferred between control wells, but some are shown at
the control wells. Each step represents either a regres-
sion or a temporary stabilization or minor transgression
of the Pictured Cliffs shoreline. In particular, two
prominent areas of abruptly rising Pictured Cliffs can
be seen in the sections, one on the southwest edge of
the basin and one in the northeastern part. The south-
west rise is between wells 1 and 5 in section A~A’,
between wells 1 and 4 in section 3—H, and between
wells 1 and 3 in section 0—0’. The same rise was mapped
by the authors on the outcrop in T. 19 N., Rs. 3 and
4 W. The northeast rise is between wells 8 and 9 in
section A—A’, wells 9 and 11 in section B—B’, and
between well 8 and the outcrop in section 0—6". The
northeast rise is much more apparent and continuous
than the one to the southwest and is clearly shown in
figure 7, the isopach map of the interval between the
Huerfanito Bed and the top of the Pictured Cliffs.
The northeast rise was noted by the authors on the
outcrop in sec. 7, T. 27 N., R. 1 E. It is probably the
same stratigraphic rise mapped by Zapp (1949) in the
Durango, Colo., area.

The west-east section, F—F’ (pl. 2), also illustrates
the two major stratigraphic rises of the Pictured Cliffs.
The southwest rise occurs between the outcrop and well
3, and the northeast rise occurs between wells 12 and
15. The south-north section, D—D', shows the two major
rises but not as distinctly as does the west-east section.
In the south-north section, the southwest rise occurs be-
tween wells 1 and 4, and the northeast rise occurs
between wells 13 and 15. The northwest-southeast
section, E—E’, does not show either of the two major
rises because it is about parallel to and between them.

The large stratigraphic rise in the northeastern part of
the basin is not time-equivalent along its extent but,
rather, is older in the southeast than in the northwest.
As shown in figure 7, this rise or vertical upbuilding of
the Pictured Cliffs is between the 550-foot and the 800-
foot isopachs in the southeast and between the 800-foot
and 950-foot isopachs in the northwest. Thus, at the
same time that the Pictured Cliffs shoreline was rela-
tively stable in the southeast, the sea was regressing
relatively more rapidly in the northwest.

FossrLs AND AGE

The most abundant and widespread fossil in the
Pictured Cliffs Sandstone consists of molds and casts
of Ophiomorpha major (crustacean burrows; compare
Weimer and Hoyt, 1964). This fossil is of little use as
an age indicator; however, its presence indicates a
shallow marine environment and can be used in most
instances to differentiate nonmarine sandstone beds of
the Fruitland from lithologically similar marine sand-

16 GEOLOGY AND FUEL RESOURCES, FRUITLAND FORMATION AND KIRTLAND SHALE, SAN JUAN BASIN

stone beds of the Pictured Cliffs, especially where the
two formations intertongue. Reeside (1924, p. 19) listed
fossils collected from the Pictured Clifis at four localities
in the north-central and northwestern parts of the San
Juan Basin. He concluded that these fossils indicate a
littoral marine environment of deposition and are of
Montana age. In the southern part of the basin, Dane
(1936, p. 112) collected Pictured Cliffs fossils. to which
Reeside assigned a Montana age.

The authors collected fossils from a thin limestone
bed in the Pictured Cliffs in the SWMSWM sec. 10,
T. 19 N., R. 2 W., on the southeast end of Mesa Por—
tales about 10 miles southwest of Cuba, N. Mex.
(Fassett, 1966, fossil loc. 29200). The fossils were
identified by D. H. Dunkle of the US. National
Museum (written commun., January 8, 1965) as follows:

Sharks:

Lamna appendiculata (Agassiz)—Cosmopoli~
tan, Cenomanian to Maestrichtian and
?Danian.

Omyrhina angustidens Reuss—Cosmopolitan,
range combined with that 'of Odontaspis
cuspidata, with which it is often identified,
Campanian to Sarmatian.

Scapanorhynchus raph’iodon (Agassiz)—-Cos-
mopolitan, Cenomanian to top of Maes-
trichtian.

Squalicorax pristodontus (Agassiz)—Cosmo—
politan, Campanian to Ludian.

Ischyrhiza mira Leidy—North and South
America, Campanian to top of Maestrich-
tian.

Teleost:
Enchodus sp.——Cosmopolitan, upper Albian to
top of Maestrichtian.
Reptiles:
Indeterminate turtle and ?dinosaur scrap.
Dunkle stated that the widest Cretaceous age range of
the above fossils is Campanian to Maestrichti'an. This
age range is compatible with the Montana age deter-
mined by Reeside for fossils found in the Pictured
Cliffs at other localities in the basin.

The Pictured Cliffs Sandstone rises stratigraphically
northeastward across the basin (pl. 2); thus, it must be
younger in the northeastern part than in the south—
western part. The exact difference in age has not yet
been determined, but preliminary fossil evidence
affords an indication of what the age difference may
be. The authors collected fossils from the upper part
of the Lewis Shale at USGS Mesozoic locality D4834
in the SWMSWM sec. 29, T. 25 N., R. 1 E. Unfor-
tunately, the exposures at this locality were not good
enough to establish the thickness of the interval be-
tween the fossil horizon and the base of the Fruitland

 

Formation; the Pictured Cliffs is apparently not present
in this area. The collection included Didymoceras
nebrascense (Meek and Hayden), according to W. A.

'Cobban of the US. Geological Survey (written com-

mun., 1965). If the isopachs in figure 7 are equivalent
to time lines, as hypothesized on page 12, then they
should also be equivalent to faunal zones. Theoreti-
cally, the 500—foot isopach, which would intersect the
Lewis Shale outcrop at the point where Didymocems
nebrascense was collected, represents the Didymoceras
nebmscense faunal zone across the basin. By the same
reasoning, because Didymoceras cheyennense was in—
ferred to occur in the Pictured Cliffs in the Durango,
Colo., area (Gill and Cobban, 1966, pl. 4), this faunal
zone is probably equivalent to the 950-foot isopach,
which would intersect the Pictured Cliffs outcrop near
Durango,

Gill and Cobban (1966, table 2) showed the Dialy-
moceras nebrascense zone to be about 1.5 million years
older than the Didymoceras cheyennense zone. Applying
this figure to the corresponding isopachs gives a value of
300,000 years for each 100 feet of rise of the Pictured
Cliffs Sandstone. Extrapolating across the basin from
the 150—foot isopach to the 1,250-foot isopach yields an
age difference of about 3 million years for the Pictured
Cliffs between the southwestern and the northeastern
parts of the basin. ,

EXTENT AND THICKNESS

The Pictured Cliffs Sandstone crops out around the
north, west, and south sides of the San Juan Basin but
is absent along parts of the east side (pl. 1). It is present
throughout the subsurface of the basin except in a
narrow band along the east side. In the areas in the
southeastern part of the basin, where the Pictured
Cliffs is not present, the Lewis Shale is overlain by the
undivided Fruitland Formation and Kirtland Shale.
In a small area in the northeastern part of the basin, the
Pictured Cliffs, the Fruitland, and the Kirtland are
absent, and the Lewis Shale is overlain directly by the
Ojo Alamo Sandstone. In this area scattered thin
stringers of sandstone occur in the uppermost Lewis.
The Pictured Clifls is present in a small area near the
center of the east side of the San Juan Basin in .T. 27
N., R. 1 E., and T. 28 N., R. 1 W. In the southern part
of this exposure, the Pictured Cliffs apparently inter-
tongues with the Fruitland. In another area to the
south, in T. 25 N., R. 1 E., there is an outcrop that
is believed to be Pictured Cliffs.

Baltz (1967, p. 19) stated that the Pictured Cliffs is
not present along the east-central margin of the San
Juan Basin. Baltz wrote:

In this area the stratigraphic interval of the Pictured Cliffs is

occupied by silty, sandy upper beds of the Lewis Shale. Subsur-
face data from other parts of the basin indicate that the silty,

STRATIGRAPHY 17

sandy upper part of the Lewis Shale that is equivalent to the
Pictured Cliffs persists northwestward across the structurally
deepest part of the Central basin nearly to the northwestern edge
in Colorado. This body of shale divides the Pictured Cliffs into
southwest and northeast lobes which merge in the northwestern
part of the Central basin near the outcrops on the Hogback
monocline southwest of Durango, Colo. Thus, the Pictured
Cliffs is a horseshoe-shaped body of sand that is open to the
southeast (fig. 7).
In his figure 7, which is a paleogeographic map, Baltz
showed an interpretation of the subsurface distribution
of the Pictured Cliffs. The figure shows the Pictured
Cliffs absent in a northwest-trending area in the
northern part of the basin.

The authors believe that the Pictured Cliffs Sand-
stone is present throughout nearly all the area where
Baltz showed it missing in the northern part of the basin.

Sections A—A’ through D—D’ and F—F' (pl. 2) all inter- '

sect the area, and the Pictured Cliffs was found to be
present in all the wells in these cross sections. Indeed,
the zone of thickest Pictured Cliffs in the San Juan Basin
trends northwestward directly through the area in
which Baltz showed the Pictured Cliffs to be absent.
A core log (Fassett, 1968a, b) from a well in sec. 36, T.
29 N., R. 4 W., near the center of that area, described
the Pictured Cliffs between the drilled depths of 3,913
and 4,200 feet, a total thickness of 287 feet. The lithology
of this interval is predominantly fairly well sorted
fine-grained glauconitic sandstone that contains abun-
dant Ophiomorpha. Figure 8 shows the electric log and
lithologic column of the cored portion of this well. The
core was from one of the test holes, GB—l, for Project
Gasbuggy (Holzer, 1967, 1968), an experimental project
to evaluate stimulation of natural gas production from
the Pictured Cliffs Sandstone by the use of nuclear
explosives.

The Pictured Cliffs Sandstone ranges in thickness
from 0 feet on the east side of the basin to about 400
feet in the north-central part. Sections A—A’ to E—E’
(pl. 2) illustrate the variability of thickness of the
Pictured Cliffs and show that there are two belts of
relatively thick sandstone in the basin. Both belts trend
northwest and coincide with the two areas of prominent
stratigraphic rise of the Pictured Cliffs discussed on
page 15. The Pictured Cliffs was not recognized
outside the San Juan Basin until Dickinson (1965)
mapped a white to yellow fine-grained sandstone,
200—250 feet thick, that cropped out in a small area in
the southeastern part of the Cerro Summit quadrangle
in Montrose County, Colo. He called this unit the
Pictured Cliffs Sandstone on the basis of lithic evidence.

FRUITLAND FORMATION

DEFINITION
The Fruitland Formation was first defined by Bauer
(1916). The name was derived from the town of Fruit-

 

land, N. Mex., on the San Juan River where outcrops
of the formation are well exposed. Earlier, the rocks
comprising the Fruitland had been included by Holmes ' ‘
(1877) in the Laramie Formation, which was equivalent
to the sequence from the base of the Pictured Clifis
Sandstone to the top of the Ojo Alamo Sandstone (pl. 1).
Bauer (1916, p. 274) gave the thickness of the Fruitland
as ranging from 194 to 292 feet. He wrote that both its
upper and lower contacts were conformable, with
“interfingering” with the Pictured Cliffs at the base and
a “gradational” contact with the Kirtland at the top.
Bauer suggested that the top of the Fruitland was
marked by “a gradational zone containing in many
places sandstone lenses that are apparently of fluviatile
origin.”
LITHOLOGY

The Fruitland is composed of interbedded sandstone,
siltstone, shale, carbonaceous shale, carbonaceous sand-
stone and siltstone, coal, and, at places in the lower
part, thin limestone beds composed almost entirely of
shells of brackish-water pelecypods. Nearly all the rock
units composing the Fruitland are discontinuous. Most
individual beds pinch out laterally, usually within a few
hundreds of feet. The coal beds are the most continuous
rock units in the Fruitland and, in places, are traceable
for several miles. The average composition of Fruitland
sandstone beds in the northern part of the San Juan
Basin, as determined by Burgener (1953), is 85 percent
quartz, 6.5 percent orthoclase feldspar, 5.5 percent
plagioclase feldspar, and 2.7 percent coal. Burgener
stated that calcite is the most common cement, es-
pecially toward the top of the formation, and clay
cement is somewhat less abundant. Locally, thin iron-
cemented sandstone beds and sporadic thin barite
concretion zones and calcite concretion zones are con-
spicuous markers in the Fruitland. The lithology of the
Fruitland changes vertically in a generally consistent
way: the thicker coal beds are invariably confined
to the lower one-third or even to the lower one-fifth of
the formation, the limestone beds are found only in the
lowermost part of the formation, sandstone is usually
more abundant in the lower part than in the upper
part, and predominantly siltstone and shale is found
in the upper part.

In the southeastern part of the basin, the Fruitland
contains sandstone beds that seem to be lithologically
different from sandstone beds in the Fruitland through-
out the rest of the basin. These beds are conspicuous
in surface exposures and on electric logs. In surface ex-
posures they consist of scattered lenses of white fine-
to coarse-grained sandstone which contain numerous
silicified wood fragments and flattened clay balls as
much as 1 foot across. The clay balls readily weather

18 GEOLOGY AND FUEL RESOURCES, FRUITLAND FORMATION AND KIRTLAND SHALE, SAN JUAN BASIN

3"" - H - - {/ NACIMIENTo FORMATION

       
        
   
   

   

 

 

 

   

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I = ” LONG NORMAL
(64 in. snacmg)
d.)
c
o
0
8
'16 ,. 0J0 ALAMO
o. ”2- - -\-\-'" SANDSTONE
LATERAL
(18 ft 8 In. spacing)
EXPLANATION
Sandstone Siltstone Shale
Not cored\
Core .05! .> SHORT NORMAL § 212°: T'TT:
“j; (16 in. spacung) b.0993). - - ~
|_ 3800 " Coal Conglomerate Sandstone and
m . ,_: shale
L1. _~ .4'” ...... . +00
Z . .‘ :- .
_. - ’ Abundant ()phmmm’plm
I
l:
15' 3900 - { FRUITLAND FORMATION
Core lost ‘ a >
(I)
3 -
o
8
g PICTURED CLIFFS
5 SANDSTONE
5 (upper part)
a.
o.
D
C FRUITLAND FORMATION (lower tongue)
PICTURED CLIFFS
SANDSTONE
(lower part)
SPONTANEOUS
”TENT” LEWIS SHALE

 

 

 

FIGURE 8.——-Electric log and lithologic column of the cored portion of borehole GB—l, Project Gasbuggy (after Fassett,
1968b, fig. 2).

STRATIGRAPHY

out, giving the sandstone a vuggy appearance on the
outcrop. The beds represent channel sands that may
have had a source southeast of the present basin area.
The age of the sandstone beds is not definitely known.
Some beds were obviously deposited contemporaneously
with other sedimentary rocks composing the Fruitland
Formation and Kirtland Shale because they are en-
closed by typical Fruitland and Kirtland rocks. Other
beds, however, seem to represent post-Fruitland dep-
osition and may have been laid down in channels
formed during the last phases of basin-wide erosion
that preceded deposition of the Ojo Alamo Sandstone.
Good exposures of these sandstone beds can be ob-
served on the southwest and east-central edges of Mesa
Portales in the 8% sec. 7, T. 19 N., R. 2 W., and the
NW% sec. 25, T. 20 N., R. 2 W.

CONTACTS

The lower contact of the Fruitland has been dis-
cussed in the section on the Pictured Cliffs Sandstone.
Early geologists used several criteria to separate the
Kirtland and the Fruitland. Reeside (1924, p. 20)
stated that “the highest of the sandstones has been
taken as the top of the Fruitland formation and the
overlying softer rocks have been assigned to the Kirt-
land shale.” Dane (1936, p. 113) stated that the upper
boundary of the Fruitland should be drawn “at the top
of the stratigraphically highest brown sandstone.”
Barnes (1953) suggested that the top be picked to
“include within the Fruitland formation all thick
persistent coal beds and all prominent sandstone beds.”
Nearly all oil-company geologists and geologic con-
sultants in the Four Corners area now place the top of
the Fruitland at the top of the highest coal bed or
carbonaceous shale bed, and the authors use this
criterion.

On the east side of the San Juan Basin, the Fruitland
is overlain by the Ojo Alamo Sandstone, and the Kirt-
land Shale is absent (fig. 9). Sections C—C’, F—F’, and
E-E’ of plate 2 show areas where the base of the Ojo
Alamo lies directly on top of the Fruitland. The nature
of the basal Ojo Alamo contact is discussed in the section
on the Ojo Alamo Sandstone.

Mom: or DEPOSITION

The Pictured Cliffs Sandstone was laid down during
the final retreat of the Upper Cretaceous sea from the
San Juan Basin area. As the sea regressed, coastal-
swamp, river, flood-plain, and lake deposits were laid
down shoreward on top of the Pictured Cliffs. These
deposits compose the Fruitland Formation. Figure 5
shows the environment of deposition of the Fruitland.
As the Pictured Cliffs Sea retreated, coastal swamps
formed, and vegetal matter accumulated in the swamps.

 

19

While the shoreline was regressing at a relatively
steady rate, the vertical thickness of vegetal material
that could accumulate was relatively small; also,
swamps were probably unconnected and of rather small
size along the shoreline. However, when the shoreline
became geographically stable (fig. 5B), vegetal matter
built up vertically to greater thicknesses, and swamps
probably became more widespread behind and parallel
to the shoreline. As the sea continued to regress, swamps
continued to form close to the shoreline, and older
swamps were covered by silt and sand laid down as river
and flood-plain deposits. Some smaller swamps formed
some distance landward of the retreating shoreline,
but these swamps were usually ephemeral and ac-
cumulation of vegetal material in them was small.

FOSSILS AND AGE

Fossils are numerous in the Fruitland, and they have
been described by Gilmore (1916), Knowlton (1916),
Stanton (1916), and Osborn (1923). Since 1961, Dr. W.
A. Clemens of the University of Kansas Museum of
Natural History has collected mammalian fossils from
the upperpart of the Fruitland and the lower part of
the Kirtland at about a dozen localities in the San
Juan Basin. The best collections were made from the
Fruitland in Hunters Wash in the southwestern part
of the basin. Clemens (written commun., 1967)
reported:

Preliminary analysis suggests the collections made at these
different sites are samples of one faunal unit, and all have been
considered in preparing the following provisional lists:

Multituberculata
Mesodma, possibly M. formosa.
C’imolodon, two species, one resembling C. m'tidus, the
other including animals of smaller individual size.
A new species with a low, eucosmodontidlike P4.
A new species with high, trenchant P2.
Marsupialia
Alphadon marshi or a closely related species and at
least one other, as yet undescribed species.
Pediomys sp.
Eutheria
Gypsonictops sp.
Cimolestes sp.
A therian mammal that cannot be referred to the
Marsupialia or Eutheria on the available evidence.

* * * * *

Comparison of this faunal unit with the Lance local fauna
from the Late Cretaceous of eastern Wyoming points out some
interesting differences. For example, M eniscoessus (a multi-
tuberculate) and Pediomys (a marsupial) have high relative
abundances in the Lance local fauna. The former is unknown
and the latter very rare in New Mexico. Our collections are new
large enough to warrant suggesting that their absence or low
frequency of occurrence are not a product of bias in collecting
technique or small sample size. Whether these faunal differences
reflect differences in age, ecology, or combinations of these and
other factors, remains to be determined.

20 GEOLOGY AND FUEL RESOURCES, FRUITLAND FORMATION AND KIRTLAND SHALE, SLAN JUAN BASIN

108° 107°
H 10 9 8 RIW 'R1E

LA PLATA T36N

O
ONTEZUMA ARCHULETA

   

37., _ch0RAp_g ( __

NEW MEXICO

Outcrop of Fruitland
Formation and
Kirtland

R16W

36“

MCKINLEY

O 5 10 15 20 MILES
L|_|_1_J_1___l—_l—l

STRATIGRAPI-IY 21

EXPLANATION

 

 

Ojo Alamo Sandstone absent

////

Upper shale member and Farming-
ton Sandstone Member of Kirt—
land Shale absent

\\

Lower shale member of Kirtland
Shale absent

 

 

 

 

 

 

 

 

 

 

 

 

Kirtland Shale absent

 

Kirtland Shale and Fruitland
Formation absent

/—L-—~L
/)’ \NL

Ojo Alamo Sandstone

__L_

y,/ \TK
Upper shale member and Farming-
ton Sandstone Member of Kirt—

land Shale

A

Lower shale member of Kirtland Shale

.,§.. .4.. ,g. '

.\- .1,

Fruitland Formation

Arrows point to areas where each of the
above rock units is absent in the sub -
surface

Oil or gas well

FIGURE 9.—Subsurface extent of the rock units composing the Fruitland Formation,
the Kirtland Shale, and the Ojo Alamo Sandstone,rand locations of all wells used
for stratigraphic subsurface control in this report.

R. H. Tschudy of the US. Geological Survey exam-
ined rock samples collected by the authors from USGS
paleobotany localities D4017—A, —B, and —C and
D3738—C in the SE}£SE%SW}£ sec. 9, T. 19 N., R. 2 W.,
on the south edge of Mesa Portales, Sandoval County,
N. Mex., and D4149 near the center of sec. 32, T. 33 N.,
R. 2 W., New Mexico principal meridian, Archuleta
County, Colo. The sample from locality D4149 was
from a coal bed resting directly on top of the Pictured
Cliffs Sandstone. The samples from localities D4017—A,
—B, and —C were from a coal bed 100 feet above the
top of the Pictured Cliffs, a green-gray shale 14 feet
above the top of the coal bed, and a dark-gray shale
103 feet above the top of the coal bed, respectively;
sample D3738—C was from a dark-green shale bed 165
feet above the top of the coal bed and about 40 feet
below the base of the Ojo Alamo Sandstone (fig. 10).
Locality D4149 is about 750 feet stratigraphically
higher than locality D4017—A.

Table 1 shows the palynomorphs identified by
Tschudy (written commun., 1968) from these localities.

416-332 0 - 71 - 4

 

Of the samples from the Mesa Portales area, Tschudy
reported:

All the productive samples yielded specimens of the genus
Proteacidites. The presence of this genus indicates a Cretaceous
age. Sample D4017-A was from a coal and yielded an assemblage
different from the assemblages from the shale samples. This is
common, as the coals are deposited under different ecological
conditions than are most shales.

In his report on the sample from the northeastern part
of the basin, D4149, Tschudy stated:

Sample D4149 I believe to be Cretaceous. The coal yielded a
poor corroded assemblage. I was able to find only two specimens
of the marker genus Proteacidites. This assemblage appears to
have a closer resemblance to the Trinidad and Vermejo of the
Raton Basin than to the assemblage reported by Anderson from
the southern San Juan Basin.

The most abundant fossil of the Fruitland is Ostrea,
which in parts of the basin locally forms coquina beds
several feet thick. Fossil wood is abundant throughout
the Fruitland, and some silicified logs are 4—5 feet in
diameter. Fossil evidence indicates that the Fruitland
is of Montana age. Most fossils are of fresh-water
origin, but a few, notably Ostrea, are of brackish-water

origin.

22 GEOLOGY AND FUEL RESOURCES, FRUITLAND FORMATION AND KIRTLAND SHALE, SAN JUAN BASIN

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Ojo
Alamo D3738—A
Sa nd ston e
>.
0:
S
E D3738-B
IJJ
[—
._ ____. __?____ _
U)
3 D3738-C
0
Lu
0
If .
m Kirtland
n:
0
04017-0
Shale
and
D4017—B
Fruitl a n d
D4017—A
Formation
Shale and
. Sandstone
Pictured
Cliffs
Sandstone

 

 

FIGURE 10,—Generalized geologic section showing the relative
stratigraphic positions of samples collected for pollen and
spore analysis on Mesa Portales. Vertical scale, 1 inch=50 feet.

 

EXTENT AND Ti-ucxmzss

The Fruitland Formation crops out around the north,
west, and south sides of the San Juan Basin but is
missing in two areas on the east side (fig. 9). It is also
present throughout the subsurface of the basin except
in the two areas on the east side. In both areas where the
Fruitland is absent, the Pictured Cliffs Sandstone is
also absent, and the Lewis Shale is overlain by the
Ojo Alamo Sandstone. The Fruitland was not recog-
nized outside the San Juan Basin area until Dickinson
(1965) mapped a poorly exposed 50-foot-thick rock
sequence consisting of white to yellow sandstone inter-
bedded with coal, carbonaceous shale, and green shale
in Montrose County, Colo. Dickinson assigned this
rock unit to the Fruitland on the basis of lithic evidence.

In the southwestern part of the San Juan Basin,
the Fruitland Formation and Kirtland Shale were
mapped undivided by Zieglar (1955) near Newcomb,
N. Mex. (pl. 1), outside the Pictured Cliffs Sandstone
outcrop. Zieglar showed the undivided Kirtland and
Fruitland resting on the Menefee Formation. This area
is west of the coalescence of the Pictured Cliffs Sand-
stone and the underlying Clifl' House Sandstone. Allen
and Balk (1954, p, 96, 97) discussed these outcrops
and applied the name Tohatchi Formation (spelled as
Tohachi by some authors) to rocks correlative with
tongues of the Cliff House and Pictured Cliffs, and to
the Fruitland and possibly part of the Kirtland in this
area. They stated:

The stratigraphic position, lithology, thickness, and distribu-
tion of carbonaceous material suggest a tentative correlation of
the lower member of the Tohatchi formation with the combined
tongues of the Clifl House and Pictured Cliffs Sandstone * * *.
The upper bentonitic unit may prove to be the equivalent of the

Fruitland formation, and possibly part of the Kirtland formation,
since similar vertebrates also occur in these units.

O’Sullivan, Beaumont, and Knapp (1957, p. 189) stated
that this rock sequence is

shown on map OM 190 (O’Sullivan and Beaumont, 1957) to be
a part of the Menefee formation, although it is recognized to
contain equivalents of the Tohatchi formation as used by Allen
and Balk and the Kirtland-Fruitland formations undivided as
used by Zieglar (1955) in the Toadlena quadrangle.

They further stated:

In the Chuska Mountains the absence of the Pictured Clifl's—
Cliff House tongue and the lack of suitable stratigraphic horizons
in the associated nonmarine strata, virtually eliminates placing
the position of the change from transgressive to regressive
deposition which would correspond to the change from Menefee
to Fruitland-Kirtland.

Whatever they are called, it is clear that rocks equiva-
lent to the Fruitland and possibly to the Kirtland are
present southwest of the Pictured Cliffs Sandstone
outcrop in the Newcomb area.

STRATIGRAPHY

23

TABLE 1.—Selected palynomorphs from samples from the San Juan Basin

[Identifications by R. H. Tschudy, US. Geological Survey. Age: P, recorded from the Paleocene only; K, recorded from the Cretaceous only; P, K, knOWn from both the
Paleocene and the Cretaceous; no prefix indicates a longer ranging species. Names in parentheses are those used by Anderson (1960)]

U.S. Geological Survey paleobotany locality number

 

 

 

 

   

 

  

 

 

 
 
  
 
 
 

 

 
   
 
  
  
  
     
   
    
  
 
 
  
 
 
 
 
 
 
  
  
 
  
  
 
 
 
 
  
   
 
  
 
 

   

  

Age Palynomorph Paleocene Cretaceous
D3738—A D3738—B D3803 D3738—C D4017—A D4017—B D4017—C D4149
P Momipites sp. (Momipites inuqualis And.) X ....... X
P Monosulcitee sp. (Rectosulcites lotus And ) X . X
P Triatriopollenitea sp. A . _ _ _ _ . X ...........
P Triatriopollenites 58. B . . _ _ X
P, K? Cupaneidites sp. ( paneidites afl. C. major And). ..... X
Laevigatosporites sp. (Polypodiidites sp. And.) .............. X
P Tricolporitea sp. (Tricol arms anguloluminosus And.)._ _____ X
P, K Tricolpopollenim sp. ( uercua ezplanala And.) ............... X
Abietimaepollenites sp. (Podocarpue sellowi/ormia And.) ..... X X _
Classapoll‘ (51p ......................................................... X _
Abidineaep enitea sp. (Podocarpux northropi And). ...... X .
P, K Zliviaporia sp ____________ 7 ............................. ._ . _ X .
P, K Ulmipollenitea sp. (Ulm ozdepitea tricostatus And.) ...... .. ...... X _
P, K Liliacidites sp__.__ ______________________________________ .. . _ X _
P Polyporopollenitce sp .......................... . X ..........
P Tricolporites sp. (Tricolporites rhomboidea And).
P Tricolporites sp ................
Tricolporitea sp. (?Elcagnaceu]
Osmundacidites sp
P Tricolporites sp.. . .....
K Proteacidites (Prote a thalmamu' And). ................. X
K Pratcaciditea (Proteaciditea retuaua And.)_.._ X
K Monoporopollmites sp ...... _ .............. .. . . X
K Araucuriacites sp ____________ . . . _ . . X
Erdtmannipollis sp- _ . _ . _ __ _ . X
K Grunabiveaiculitea sp ................... .. . . X
P. K Liliaciditee sp. (Liliacidues leei And.) __________ _ X
P, K Liliaciditea sp. (Liliaci‘dites h uulacinatus And.)_ _ X
Liauidamharpollmim sp .................... . . . X
K Tricolpites interanaulus Newman
Tricolpopollenim sp .............
Eucammiiditee sp .......................
Foremporitea sp. cf. F. canalis Balme._ .
Ina erturopollenites cf. I. hiatus (R Pot
K Ep edra sp. of. E. voluta Stanley
K Zmalapollenites sp. .
K Neoraiatrickia sp. _ _ i
K Tricolpopollenitea sp. A. . x
K Monoaulcites sp ........ _ X
K Tricolporites sp ...... . _ . _ X
K Tricolpo ollenitea sp. B ..................... x
K Tiliaepo lenites sp. ( ilia wodchmtsei And)... X
P, K Tricolpopouenms sp. 0 .................................................................................................................................. X

 

 

The thickness of the Fruitland ranges from 0 to
about 500 feet and is variable locally owing to the
rather indefinite upper contact. Intertonguing of the
Fruitland and the underlying Pictured Cliffs also
results in abrupt local variation in the Fruitland
thickness. The average thickness is about 300—350 feet
with a very general depositional thickening from the
southeast to the northwest of about 100—150 feet.
Sections A—A’ through F—F’ (pl. 2) show the variations
in thickness of the Fruitland in the basin. In the
eastern part of the basin where the Kirtland Shale is
absent, the Fruitland is overlain by the Ojo Alamo
Sandstone. There the Fruitland thins to the east from
about 300 feet to 0 feet. This thinning is partly the
result of erosion or beveling of the Fruitland prior to
deposition of the overlying Ojo Alamo and partly the
result of the stratigraphic rise of the Pictured Cliffs
Sandstone in this area. Sections 0—0’, F—F’, and E—E’
(pl. 2) show the thinning of the Fruitland on the east
side of the basin.

 

KIRTLAND SHALE

DEFINITION

The Kirtland Shale was defined by Bauer (1916,
p. 274) and was named for the town of Kirtland,
N. Mex., on the San Juan River. Bauer stated that the
Kirtland could be divided into three parts, “a lower
shale 271 feet thick, a sandy part, here named the Farm-
ington sandstone member * * *, and an upper shale
110 feet thick.” Bauer further stated that the Farming-
ton Sandstone Member was 455 feet thick along the
San Juan River and that it there consisted of a series
of discontinuous crossbedded overlapping sandstone
lenses separated by shale interbeds.

In this report a twofold division of the Kirtland
Shale is used: the lower shale member of Bauer and
the undivided Farmington Sandstone Member and
upper shale member of Bauer. The reasons for combin—
ing the Farmington and the upper shale are: (1) Well
logs throughout most of the basin indicate that sand-
stone beds are present throughout the interval between
the top of the lower shale member of the Kirtland Shale
and the base of the Ojo Alamo Sandstone. Thus, on

24

the basis of subsurface evidence, no upper shale member
of the Kirtland can be differentiated. (2) A reconnais-
sance examination of the outcropping Kirtland rocks
indicates that in some places a shale zone does exist
between the stratigraphically highest sandstone lens
of the Farmington and the base of the overlying Ojo
Alamo Sandstone, but in other places, notably in the
bluffs just south of Farmington, N. Mex., Farmington
lenses crop out directly under the Ojo Alamo. Thus,
even though an upper shale member is in some places
locally differentiable, it can not be traced continuously
any great distance on the outcrop. Hayes and Zapp
(1955), in their discussion of the Kirtland in the area
between the San Juan River and the Colorado border,
stated: “The upper boundary of the Farmington mem-
ber is even less distinct, for the overlying upper member
of the Kirtland shale contains a large proportion of
sandstone * * *.”

It is the authors’ opinion that the upper shale member
as used by Bauer and as subsequently mapped by other
geologists is not a continuous unit throughout most of
the basin, but, rather, consists of the random shale
interbeds that exist at any given outcrop immediately
beneath the Ojo Alamo Sandstone. It will be shown in
the discussion of the basal Ojo Alamo contact that
these shale interbeds, which have been collectively
called the upper shale member, are actually a series of
shale lenses Which are progressively older and strati-
graphically lower toward the southeastern part of the
basin.

LITHOLOGY

The lower shale member of the Kirtland Shale is com-
posed predominantly of gray shale that contains a few
thin interbeds of siltstone and sandstone. The Farming-
ton Sandstone Member and upper shale member of the
Kirtland are composed of a series of interbedded sand-
stone lenses and shale. The shale interbeds in the lower
part of the Farmington are lithologically similar to the
lower shale member of the Kirtland. The shale interbeds
at the top of the Kirtland, however, are much more
colorful than in the lower shale member and are purple,
green, white, and gray. In the northwestern part of the
basin, north of Pinyon Mesa near the La Plata River,
channel deposits of quartz and jasper pebble conglomer-
ate in a matrix of very fine grained to silt—size red to
reddish—brown and yellow limonite and hematite occur
in the upper part of the Farmington Sandstone Member
and upper shale member. In the western and south-
western parts of the basin, local conglomeratic beds and
purple shale beds occur in the Farmington and upper
shale. In the Pinyon Mesa area, beds of tufl’ ranging in
thickness from thin laminae to beds several feet thick
and thicker sandstone beds which contain abundant

 

GEOLOGY AND FUEL RESOURCES, FRUITLAND FORMATION AND KIRTLAND SHALE, SAN JUAN BASIN

andesitic debris occur in the uppermost Kirtland; these
beds are in what Reeside (1924) originally called the
McDermott Formation.

The Farmington Sandstone Member and the upper
shale member of the Kirtland Shale contain a higher
percentage of sandstone in the northern part of the
basin than in the southern part. Electric logs indicate
that the individual sandstone lenses composing the
Farmington Sandstone Member become thinner and
fewer in the southern part of the basin. The sandstone
is fine to medium grained, the largest fraction being
fine grained. According to Dilworth (1960), the average
mineralogic composition of the Farmington based on
petrographic examination of 11 thin sections from
samples collected near the San Juan River is: 21 per-
cent quartz, a trace to 5 percent chert, 12 percent
potash feldspar, 33 percent plagioclase feldspar, 9 per—
cent biotite, and 20 percent clay cement. Minor amounts
of muscovite, chlorite, heavy minerals, limonite, and
hematite are present. Mineral grains are angular and
poorly sorted.

CONTACTS

The lower contact of the Kirtland Shale has been
described on page 19. The contact between the lower
shale member and the Farmington Sandstone Member
of the Kirtland is transitional and is placed at the
base of the lowest sandstone lens of the Farmington.
In figure 2, the base of the Farmington is just above
1,700 feet. Because of lateral discontinuity of sandstone
lenses in the Farmington, the base of the Farmington
is erratically variable; the contact must be moved up
or down to other sandstone lenses where a particular
basal sand lens wedges out laterally.

In general, the contact at the base of the Farmington
becomes stratigraphically higher toward the northeast.
In section D—D’ (p12), it is clear that from south to
north, except at well 5, the base of the Farmington
rises regularly. This stratigraphic rise is also shown in
the southwest-northeast sections A—A’, B—B', and
0—0’ (pl. 2), although the rise is irregular in these
sections.

The Kirtland is overlain by the Ojo Alamo Sandstone
throughout most of the San Juan Basin; however, in
the northern part of the basin it is possibly overlain
by the N acimiento Formation, by the Animas Forma-
tion, and in at least one area by the San Jose Formation.
Figure 9 shows the subsurface extent of the Ojo Alamo.
North of the Ojo Alamo limit line in figure 9, the Ojo
Alamo ceases to be a distinguishable unit, and in this
area it is practically impossible to differentiate the
Kirtland from the overlying Nacimiento and Animas
Formations on electric logs. The subsurface contact
between the Animas and the underlying Kirtland is

STRATIGRAPHY 25

inferred in sections A—A’ and D—D' (pl. 2). The position
of this contact between well 7 and the outcrop in
section A—A’ and between well 13 and the outcrop in
section D—D’ is based on interpolation.

On the surface, north of the Ojo Alamo Sandstone
termination, between Pinyon Mesa in the southwestern
part of T. 31 N., R. 13 W., and the New Mexico—
Colorado border, it is extremely difficult to distinguish
the contact between the Kirtland and the overlying
Animas Formation or the Nacimiento Formation. At
Pinyon Mesa, a quartz and jasper pebble conglomerate
zone at the base of the Ojo Alamo rests on the Kirtland ;
north of the New Mexico—Colorado border, a purple
shale and andesite pebble conglomerate zone at the
base of the McDermott Member of the Animas rests
on the Kirtland. Hayes and Zapp (1955) mapped the
geology in the Pinyon Mesa area and stated:
Considerable efiort was expended during this investigation in an
attempt to establish and trace a precise upper contact of the
Kirtland shale, to be drawn at the lowest occurrence of pebbles,
or megascopically identifiable andesitic detritus. Careful tracing
of beds in areas of continuous exposures revealed that the
stratigraphic horizon at which these materials appear is not
constant, that the beds are lenticular, and that lithologies
common in the Kirtland shale recur above the lowest coarse
clastics. The upper contact of the Kirtland shale is therefore
transitional and arbitrary.

The contact between the Kirtland and the Ojo Alamo
Sandstone seems to be disconformable on the basis of
subsurface evidence; however, evidence for a discon-
formity based on surface exposures is inconclusive. The
nature of the basal Ojo Alamo Sandstone contact is
discussed at length in the section on the Ojo Alamo
Sandstone.

MODE or DEPOSITION

The lower shale member of the Kirtland Shale was
deposited in an environment similar but not identical to
the depositional environment of the upper part of the
Fruitland Formation. As stated earlier, the best
criterion for differentiating the Kirtland from the
Fruitland is the presence or absence of carbonaceous
shale or coal beds. Because the lower shale member of
the Kirtland contains little coal or carbonaceous shale,
it must have been deposited in an environment that was
not conducive to the accumulation and preservation of
organic material. This change in depositional environ-
ment was probably gradual because nearly everywhere
in the San Juan Basin the coal and carbonaceous shale
become progressively less abundant stratigraphically
upward in the Fruitland. Figure 2 clearly shows this
gradual upward decrease in coal content of the Fruit-
land. The most obvious explanation for the scarcity of
coal in the lower shale member of the Kirtland is the
lack of sites for accumulation of organic material at

 

the time of its deposition. Because organic material can
be preserved in quantity only in a reducing environ-
ment, usually under swamp waters, it is probable that
swamps were practically nonexistent at the places where
the lower shale member was being deposited. The
absence of swamps suggests relatively good drainage,
which, in turn, might indicate greater stream gradients
in these areas.

In all probability, the sandstone beds of the Farm-
ington Sandstone Member were laid down in aggrading
stream channels. Between the channels, silt and mud
were laid down as flood-plain deposits during periods
of rapid runoff when the rivers spilled over their banks.
As the streams overflowed, natural levees were built up,
causing the streams to build their channels above the
surrounding flood plain in unstable positions. Ulti-
mately, the streams broke through the levees and sought
lower and more stable channels. Old channels were
ultimately covered by flood-plain deposits as other
streams continued to aggrade the area.

Figure 5 is a diagrammatic reconstruction of the dep—
ositional relation of the Kirtland Shale and the Fruit-
land Formation. Figure 5A shows sand lenses being
deposited at the extreme left, shale being deposited
toward the shoreline, coal and shale being deposited
even further toward the shoreline, and marine sand
being deposited at and somewhat seaward of the shore-
line. The rock units here represented are the Farming-
ton Sandstone Member and the lower shale member of
the Kirtland Shale, the Fruitland Formation, and the
Pictured Cliffs Sandstone. Figures 53, 0, and D show
the same general relations between the rock units com-
prising the Kirtland and the Fruitland at later times;
each unit transgresses to the right following the regres-
sive Pictured Cliffs shoreline. The paleoslope looks rela-
tively steep in these cross sections, but the vertical
exaggeration is about 60:1.

FossrLs AND AGE

Fossils collected from the Kirtland Shale are listed
by Reeside (1924, p. 23). They include vertebrates de-
scribed by Gilmore (1919, p. 8), invertebrates described
by Stanton (1916, p. 310), and plant remains described
by Knowlton (1916, p. 330). Reeside stated that all
these fossils indicate a fluviatile origin and a late Mon-
tana age for the Kirtland.

Dilworth (1960, p. 25) and Baltz (1967) indicated
that marine fossils had been collected from the Kirtland
and Fruitland sequence. Dilworth listed the following
Foraminifera from the Farmington Sandstone Member
southwest of the town of Farmington: Bathysiphon sp.,
Haplophromoides sp., and Ostracoda (fragments). In
describing these fossils, Dilworth stated: “All of these
fossils have been replaced by iron compounds and are

26 GEOLOGY AND FUEL RESOURCES, FRUITLAND FORMATION AND KIRTLAND SHALE, SAN JUAN BASIN

of too poor quality to photograph. It cannot be said
with certainty that these foraminifera do not represent
a reworked fauna * * *.” Dilworth concluded, how-
ever, that these fossils were in place and that they were
indicative of a marine origin for the Farmington Sand-
stone Member. It is the authors’ opinion that the fos—
sils described by Dilworth were reworked because (1)
the total physical character of the Farmington clearly
indicates a fluviatile origin, and (2) all the earlier fossil
collections indicate a fluviatile origin for the Farmington.

Baltz (1962, p. 88) stated that he found Halymenrites
(now Ophiomorpha) and Inoceramus sp. in the undivided
Fruitland and Kirtland in the eastern part of the San
Juan Basin. In a later report, Baltz (1967, p. 18, ff.)
reaffirmed the presence of marine fossils in “unit A”
of the undivided Kirtland and Fruitland on the east
side of the basin. Because the Fruitland and the
Kirtland were defined as nonmarine units, it seems
more logical to conclude that the presence of these
marine fossils indicates that the rocks are not Kirtland
and Fruitland. The authors’ reconnaissance mapping
on the east side of the San Juan Basin indicates that
the rocks in which Baltz found Halymenites and
Inoceramus are probably tongues of the underlying
Pictured Cliffs Sandstone and Lewis Shale rather than
a marine f acies of the undivided Kirtland and Fruitland.

Pollen and spore identification by R. H. Tschudy
from samples collected by the authors from the un-
divided Kirtland Shale and Fruitland Formation on
Mesa Portales indicates that there the uppermost part
of the Kirtland is Paleocene in age (table 1; fig. 10).
The details of the fossils and age of the Ojo Alamo
Sandstone are given on pages 31—33.

EXTENT AND THICKNESS

The Kirtland Shale crops out around the north,
west, and south sides of the San Juan Basin. The
subsurface extent of the Kirtland is indicated in figure
9, which shows the Kirtland missing in the subsurface
in the eastern part of the basin. Figure 9 also shows
the subsurface limit of the lower shale member and
the undivided Farmington Sandstone Member and
upper shale member of the Kirtland. The crisscrossing
of the lower shale member limit line and the undivided
Farmington and upper shale limit line indicates that
in some areas the lower shale is absent and the Farm-
ington and upper shale is present, whereas in other
areas the lower shale is present and the Farmington
and upper shale is absent. This rather complicated
pattern is believed to be the result of the interaction
of two factors: (1) The Farmington Sandstone Member
and upper shale member of the Kirtland Shale are
missing on the east side of the San Juan Basin because
they were removed by erosion prior to deposition of

 

overlying rocks; nowhere are these rocks missing
because of depositional thinning or wedging out. (2)
The lower shale member is missing on the east side of
the basin in some places owing to lack of deposition
and in other places owing to erosion prior to deposition
of overlying rocks.

All the cross sections of plate 2, except sections
A—A’ and D—D’, show the way in which the Kirtland
thins and pinches out on the east side of the San Juan
Basin. In section B—B’ the lower shale member pinches
out between wells 9 and 10; east of this pinchout, the
Fruitland Formation is overlain by the Farmington
Sandstone Member of the Kirtland. In section 0—0’
the F armington and upper shale are absent in a narrow
interval between wells 4 and 5, in a wider interval
between wells 6 and 8, and between well 8 and the
outcrop; the lower shale member pinches out between
wells 4 and 5. Section E—E’ shows the truncation of
both the lower shale member and the Farmington and
upper shale member prior to deposition of the Ojo
Alamo Sandstone. The Farmington and upper shale
are cut out between wells 10 and 11, and the lower
shale is cut out between wells 13 and 14. In section
F~F’ the lower shale member pinches out between
wells 11 and 12, and the Farmington Member and
upper shale member of the Kirtland are cut out be-
tween wells 12 and 13.

The thickness of the lower shale member of the
Kirtland is variable because of the arbitrary and en atic
contacts at its base and top. The thickness ranges
from 0 feet along the subsurface limit line (fig. 9) on
the east side of the basin to 450 feet in the subsurface
in the vicinity of the town of Farmington in the western
part. In general, the lower shale thins to the east as a
result of lenses of the Farmington Sandstone Member
occurring at successively lower stratigraphic positions
to the east. The lower shale has an average thickness
of about 200—250 feet.

The thickness of the undivided Farmington and
upper shale member of the Kirtland ranges from 0
feet on the east side of the basin (fig. 9) to about 1,500
feet in the northwestern part. In figure 11 the area of
thickest Kirtland and Fruitland, shown by the 2,000-
foot isopach line, more or less coincides with the area
of greatest thickness of the undivided Farmington
and upper shale. The Farmington and upper shale
thin regularly southeastward (pl. 2, section E—E’).
This thinning is primarily the result of the consistently
lower stratigraphic position of the Ojo Alamo Sand-
stone from northwest to southeast across the basin.

In the northern part of the basin in the area where
the Ojo Alamo Sandstone is absent (fig. 9), the Farm-
ington Member and upper shale member thin northward
and northeastward, as illustrated in sections A—A’ and

27

 

 

 

 

 

 

 

 

  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

   

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
 

 

 

 

 

 

 

 

 

 

 

 

 

STRATIGRAPHY
mew is 14 4 3 2 [10‘1ng RlE
T36N
IVIIONTEIZUMAJ ARCI—lULET‘A 35
L L L.
34
1/ \ y w 33
37°___C_QI:_Q§_§QQ_ ______ . _ -5... r 3 \\ §§T _ -\ _ M4 32
NEW MEXICO 13 *0 u 1* / ‘7 5 '4 . 2 — = ._ R15
Outcrop of Fruitland 2>€9\/;/j//;9%(\/( {4/ . / 3 D2113:
Formation and ,l800///_\J'( ° y? o W
Kurtland Shal 179%50‘;V>/ . . I . _|’ 8 X f I 3‘ 31
R16w jiggi/ . . o / . . _/.‘ . . . I V
........ ' 1;)01/ 6 “00 / . . <( j /> 30
.___-/.-\i°/ /_/. - -/- PX.
, //’ /'/bo / A ‘l/ . A. K v M
/ / -/ 2/9 . / rm new . -.{ as
' oxlotepo l' / 1 . . .
/°\ // ° 100e90/«90 ' OJ 'Kx \ 2527
f /'J-/ ”‘3 We
P - ' ' \- l’ g - 72
'g °—_./ .\ \ 0/. '55

36°

 

 

 

 

 

 

/\.\.

 

 

 

 

 

 

EXPLANATION

 

 

 

 

 

 

 

 
    

 

 

 

0
Control points represent oil or gas
wells
Thickness of isopaehed interval (base of
__ Fruitland Formation to top of Fruit-

 

 

 

 

land Formation or Kirtland Shale) was
determined from electric logs of these
wells A

Triangles represent measured sur-
face sections of the Kirtland
Shale and Fruitland Formation

 

Contour interval is 100 feet

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

5, 10

20 MILES

FIGURE 11.——Isopach map of the Fruitland Formation and Kirtland Shale,

28 GEOLOGY AND FUEL RESOURCES, FRUITLAND FORMATION AND KIRTLAND SHALE, SAN JUAN BASIN

D—D’ (pl. 2). These sections show the rather abrupt
change in the nature of the upper contact of the Farm-
ington and upper shale in the northern part of the basin.
Between well 13 and the outcrop to the north in section
D—D’, the contact of the Animas and the upper shale
and the contacts of the underlying rock units converge.
South of well 13 the contact of the Ojo Alamo and the
upper shale and the contacts of the underlying rock
units converge in the opposite direction. Section A—A'
also crosses this area and illustrates the same relations——
the convergence of the base of the Animas and the
underlying contacts northeast of well 7, and the conver-
gence of the base of the Ojo Alamo and the underlying
contacts southwest of well 8.

PALEOCENE ROCKS
0J0 ALAMO SANDSTONE

DEFINITION

The “Ojo Alamo Beds” were named by Brown (1910,
p. 268) for exposures south of the store at Ojo Alamo
Arroyo. Brown said that the Ojo Alamo was a dinosaur-
bearing shale unit overlain unconformably by a con—
glomerate bed. Brown put no lower boundary on the
Ojo Alamo. Sinclair and Granger (1914, p. 301—304)
raised the upper contact of the Ojo Alamo to include the
overlying conglomerate because they found “the cen—
trum of a dinosaurian caudal vertebra * * * loose on the
surface * * *” of the “conglomeratic sandstone with
much fossil wood.” They also located a lower conglom-
erate, 6—8 feet thick, 58 feet below the upper conglom-
erate. Sinclair and Granger, also, did not place a lower
boundary on the Ojo Alamo.

Bauer (1916, p. 275—276) redefined the Ojo Alamo as
“a sandstone including lenses of shale and conglomer-
ate.” He agreed with Sinclair and Granger that the top
of the OjoA lamo was the top of the conglomeratic sand-
stone, but he placed the base of the Ojo Alamo at the
base of the lower conglomerate of Sinclair and Granger.
Reeside (1924, p. 28) accepted Bauer’s redefinition and
mapped the Ojo Alamo as a conglomeratic sandstone
throughout the western San Juan Basin. Reeside, how-
ever, designated the Ojo Alamo as Tertiary(?). Dane
(1936, p. 116—121) discussed the Ojo Alamo, also agreed
with Bauer’s definition of it, but suggested that it
“should be classified as Cretaceous.” Dane mapped the
Ojo Alamo throughout the southeastern San Juan Basin
as a coarse-grained, in places conglomeratic, sandstone.

Baltz, Ash, and Anderson (1966, p. D13) suggested
that “the name Ojo Alamo Sandstone be restricted to
apply only to the upper conglomerate of Bauer’s
(1916, p. 276) type Ojo Alamo Sandstone on Ojo Alamo
Arroyo.” This redefinition of the Ojo Alamo eliminated
the last remnant of Brown’s original “Ojo Alamo Beds”

 

on Ojo Alamo Arroyo from the “restricted Ojo Alamo
Sandstone” of Baltz, Ash, and Anderson.

During the time that the definition of the Ojo Alamo
was evolving, as briefly outlined above, the vertebrate
remains collected by Barnum Brown, C. W. Gilmore,
and others in the Ojo Alamo Arroyo area were being
referred to in paleontological papers in publications
throughout the world. Nearly all these publications
referred to the Ojo Alamo as a dinosaur-bearing shale
unit in much the same sense as the original definition of
Brown. Thus, today the name Ojo Alamo has two dis-
tinct meanings: to rock stratigraphers, it is a conglomer-
atic sandstone of Paleocene age; to biostratigraphers,
it is a shale unit containing a distinctive dinosaur fauna
of Late Cretaceous age. The first meaning is the one used
by the authors in this report.

GENERAL FEATURES

The Ojo Alamo Sandstone overlies the Kirtland Shale
and the Fruitland Formation throughout a large part of
the San Juan Basin. It is composed of interbedded
sandstone, conglomeratic sandstone, and shale. The
sandstone is arkosic, ranges from light brown to rusty
brown, and contains abundant silicified wood and a
few large sandstone blocks and clay balls as much as a
a few feet in diameter. The conglomerate is typically
near the base of the Ojo Alamo. Conglomerate pebbles
range widely in composition; siliceous pebbles of quartz-
ite, jasper, and chalcedony are most common; pebbles
of granite, andesite, and clay are less common. The peb-
bles generally decrease in size from west to east across
the basin. Ojo Alamo conglomerates on the west side
of the basin contain pebbles several inches in diameter,
whereas on the east side in the vicinity of Cuba, pebbles
are scarce and small.

The Ojo Alamo throughout most of the basin consists
of overlapping massive sandstone beds interbedded
with shale. The sandstone beds are sheetlike and
discontinuous. Sheets terminate by merging with
underlying or overlying sandstone sheets or by wedging
out into overlying or underlying shale beds. Sandstone
sheets are, for the most part, parallel; intervening
shale beds maintain a relatively constant thickness.
Large-scale channeling at the base of the sandstone beds
is common. Channels of 50 or more feet cut into the
underlying Kirtland or the Fruitland have been
measured by Fassett (1966) and Hinds (1966). In some
areas, channels at the base of an upper sandstone
sheet have cut through the intervening shale bed and
into an underlying sandstone sheet.

The thickness of the Ojo Alamo varies according to
the number of sandstone beds that constitute it at any
given locality. Thicknesses range from less than 20
feet to more than 400 feet throughout the basin;

STRATIGRAPHY 29

thicknesses of about 50—150 feet are the most common.
The Ojo Alamo crops out around the west, south, and
east sides of the basin. It does not crop out in the
northern part, and in the subsurface it cannot be
distinguished on electric logs north of the limit of the
Ojo Alamo shown in figure 9. In an area along the east
rim of the basin from slightly north of Llaves in T. 25
N., R. 1 E., to the northern part of T. 23 N., R. 1 E.,
the Ojo Alamo is not exposed. Whether this is due to
thinning or nonexistence of the Ojo Alamo or to
relatively recent erosion and cover by alluvium is not
known.
CONTACTS

The upper contact of the Ojo Alamo Sandstone and
the‘overlying Nacimiento Formation is conformable
throughout most of the basin, and intertonguing of Ojo
Alamo sandstone beds and Nacimiento shale beds is
common and widespread. This intertonguing has been
mapped by Fassett (1966). The nature of the basal con-
tact of the Ojo Alamo, however, is not clear cut. Sub-
surface evidence very strongly indicates that an angular
unconformity is present everywhere in the basin at the
base of t? e Ojo Alamo. Surface information, however,
dors not everywhcre support this conclusion. On Mesa
Portales, for example, which is 11 miles southwest of
Cuba, basal sandstone beds of the Ojo Alamo thin and
pinch out into shales. Figure 12 shows one of these basal
sandstone pinchouts. On the left (west) side of figure
12A, the Ojo Alamo consists of two sandstone sheets
separated by a shale bed. In the middle of the figure,
the lowermost sandstone sheet abruptly thins, pinches
out, and is replaced laterally by shales to the east. A
careful examination by the authors of the shales east of
the termination of the lower sandstone failed to indicate
any sign of a shale-on—shale unconformity at the level of
the lower sandstone pinchout. In other words, the basal
contact of the Ojo Alamo seems to be gradational with
the underlying undivided Kirtland Shale and Fruitland
Formation on Mesa Portales and not unconformable as
subsurface evidence seems to indicate. Figure 123 is a
closer view of the lower sandstone pinchout.

The subsurface evidence of an unconformity at the
base of the Ojo Alamo is clearly indicated in strati-
graphic cross sections F—F’, D—D’, and E— ’ (pl. 2).
Section F—F" crosses the San Juan Basin from west to
east. The uppermost correlation line in this section
represents the base of the Ojo Alamo. Notice that this
line does not parallel the underlying formation bound-
ary lines but, rather, it and the underlying formation
contacts converge on the east side of the basin. From
west to east the Fruitland and the Kirtland thin from a
maximum thickness of 1,325 feet at well 3 to a minimum
thickness of less than 20 feet on the outcrop just east
of well 16. This thinning is the result of two separate

416-332 0 - 71 - 5

 

and independent causes: (1) The Pictured Cliffs Sand-
stone rises 850 feet stratigraphically from the west to
the east side of' the basin; from well 3 to the east edge
of the basin the stratigraphic rise is 500 feet. (2) The
base of the Ojo Alamo becomes stratigraphically lower
from west to east across the basin; this lowering ac-
counts for a decrease in thickness of the underlying
Fruitland and Kirtland of slightly more than 800 feet
between well 3 and the east edge of the basin. The loss
of uppermost Fruitland and Kirtland rocks that places
progressively older rocks in contact with the base of
the Ojo Alamo from west to east indicates that the
Fruitland and Kirtland were beveled by erosion prior
to deposition of the Ojo Alamo.

In section D—D’ (pl. 2) the Fruitland and the Kirt-
land thin from 1,730 feet at well 13 in the northern
part of the basin to 530 feet near well 2 in theesouthern
part. As in section F—F’, the basal contact of the Ojo
Alamo does not parallel underlying formation boundary
lines but is at a distinct angle to them. As a result,
progressively older rocks underlie the Ojo Alamo from
north to south across the San Juan Basin, which
indicates beveling of the Kirtland prior to deposition
of the Ojo Alamo.

Section E—E’ (pl. 2) trends northwest. At the outcrop
northwest of well 1, the thickness of the Fruitland
and the Kirtland is 1,900 feet. At the outcrop southeast
of well 16, the thickness of the Fruitland and Kirtland
rocks is 180 feet; thus, the Fruitland and the Kirtland
are more than 1,700 feet thinner in the southeastern
part of the basin than in the northwestern part. This
thinning, with progressively older rocks in contact with
the Ojo Alamo southeastward, again indicates beveling
by erosion of the Fruitland and Kirtland rocks prior
to Ojo Alamo deposition.

Sections A—A’, B—B’, and 0—0’ (pl. 2) do not in-
dividually indicate the presence of an unconformity at
the base of the Ojo Alamo because their alinement is
approximately parallel to the isopachs in figure 13.
The thinning of the Fruitland and the Kirtland to the
northeast in these sections is almost exclusively the
result of the stratigraphic rise in the position of the
Pictured Cliffs Sandstone. However, these three sec-
tions collectively illustrate the thinning of the Fruit-
land and the Kirtland toward the southeastern part of
the San Juan Basin. In section A—A’ the thickness of
the Fruitland and the Kirtland between the base of the
Ojo Alamo and the top of the Pictured Cliffs ranges
from 1,600 to 1,900 feet. In section B—B’ the Kirtland
and Fruitland thickness ranges from 350 to 900 feet.
In section 0—0’ the thickness of this interval is from
less than 10 feet to slightly more than 550 feet. This
thinning, with the Ojo Alamo in contact with progres-
sively older rocks in sections B—B’ and 0—0’ . strikingly

30 GEOLOGY AND FUEL RESOURCES, FRUITLAND FORMATION AND KIRTLAND SHALE, SAN JUAN BASIN

 

Ojo Alamo Sandstone (upper bed)

Ojo Alamo Sandstone
.Uwerbed

    

FIGURE 12.-—0jo Alamo Sandstone. A, Pinchout of a lower sandstone sheet of the Ojo Alamo Sandstone in the SEMSEM
SW54 sec. 9, T. 19 N., R. 2 W., on the south edge of Mesa Portales, 11 miles southwest of Cuba, N. Mex. B, Closeup
view; locations of US GS paleobotany localities D3738—A, —B, and —C are shown.

STRATIGRAPHY 31

illustrates the beveling of the Fruitland and the
Kirtland throughout the San Juan Basin area prior to
deposition of the Ojo Alamo. Figure 13 also shows the
thinning of the Fruitland and the Kirtland in the basin
prior to deposition of the Ojo Alamo. The maximum
amount of thinning indicated by this isopach map is
2,100 feet.

To restate the problem of the basal contact of the
Ojo Alamo Sandstone, subsurface evidence indicates
that throughout the San Juan Basin the basal contact
of the Ojo Alamo is unconformable with underlying
rocks, whereas in places on the outcrop, for example
on Mesa Portales, the contact apparently is conforma-
ble and transitional because basal sandstone beds of
the Ojo Alamo intertongue with underlying shale beds
of the Kirtland. In the past, the following explanations
have been offered to resolve this problem: (1) There is
no unconformity at the base of the Ojo Alamo. The
thinning of the Fruitland and Kirtland rocks toward
the southeast in the San Juan Basin is the result of less
original deposition of these rocks in the southeast.
(2) The sandstone beds, which intertongue with under-
lying shales, are not Ojo Alamo sandstone beds but,
rather, are Fruitland or Kirtland sandstone beds. This
interpretation assumes that a basal Ojo Alamo uncon-
formity is present at the base of a sandstone bed
stratigraphically above the intertonguing sandstones
and shales.

The first explanation was proposed by Dane (1936,
p. 118—119). Dane mapped the Fruitland and Kirtland
rocks throughout a large area in the southeastern
San Juan Basin and found intertonguing of basal
sandstone beds of the Ojo Alamo and underlying shales.
He believed that this intertonguing indicated “a
transitional change in sedimentation,” and he con-
cluded that no unconformity was present at the base of
the Ojo Alamo and that the thinning of the Kirtland
and Fruitland interval from west to east was deposi—
tional. Thinning of the Fruitland and Kirtland rocks
toward the southeastern part of the basin due to less
deposition, however, does not agree with subsurface
data which indicate that sediment was being derived
from the southwest and was filling in and pushing back
the Pictured Cliffs Sea toward the northeast.

The second explanation was proposed by Baltz
(1967, fig. 8) to explain the sandstone pinchouts on the
east side of Mesa Portales. The authors carefully
examined the basal Ojo Alamo contact on the east and
south sides of Mesa Portales and found that in several
places a sandstone bed which pinched out into under-
lying shale in one direction merged with an overlying
sandstone bed in another direction. Also, no single
sandstone with an unconformable base could be traced
throughout the Mesa Portales area.

 

A third explanation is here offered to resolve the
apparently conflicting data regarding the basal Ojo
Alamo contact. The authors believe that an obscure
unconformity is present in some areas in the shale and
siltstone sequence beneath, but near, the base of the
Ojo Alamo. The unconformity, which represents the
erosion surface from which as much as 2,100 feet of rock
was stripped away, may coincide with the Cretaceous-
Tertiary time boundary. The sequence of rocks lying
between the unconformity and the Ojo Alamo is
probably relatively thin, so that on electric-log cross
sections A~A’ through F—F’ (pl. 2) the unconformity
seems to be at the base of the Ojo Alamo; the un—
conformity itself is not apparent on logs. This rock
sequence above the unconformity is transitional with
the Ojo Alamo in parts of the basin as Dane (1936)
suggested. However, in many areas the Ojo Alamo
probably was deposited directly on the erosion surface.

FOSSILS AND AGE

The Ojo Alamo Sandstone has not yielded macro-
fossils diagnostic of age. In the past, paleontologists
assigned dinosaur remains to the Ojo Alamo, particu-
larly in the vicinity of Ojo Alamo Arroyo, the type
locality of the Ojo Alamo Sandstone. Baltz, Ash, and
Anderson (1966) discussed these early assignments
and concluded that the rocks in which the dinosaur
remains were found are not part of the rock-
stratigraphic Ojo Alamo but rather are part of the
Kirtland Shale. Plant remains are relatively numerous
in the Ojo Alamo, but they are principally in the form
of silicified wood, which has little age significance.
F. H. Knowlton, however, identified fossil leaves
collected from the Ojo Alamo at three localities on the
west side of the San Juan Basin and stated (in Reeside,
1924) that two of the collections suggested a Tertiary
age but that the leaves in the third collection were too
broken to identify with any certainty.

Anderson (1960) made pollen and spore collections
from the Ojo Alamo at two localities in the south-
eastern part of the San Juan Basin. He concluded that
the collections suggested a Tertiary age for the Ojo
Alamo. Anderson later identified pollen and spores
collected from the Ojo Alamo near Barrel Springs
Arroyo, and he stated (Baltz and others, 1966, p. D17)
that this Ojo Alamo florule “does not directly fix the
age of the restricted Ojo Alamo Sandstone * * *.” He
further stated, however, that this florule contains
“forms that are known to occur also in the Fort Union
Formation and other formations generally considered
to be of Paleocene age * * *.”

R. H. Tschudy examined rock samples collected by
the authors at USGS Paleobotany localities D3738—A
and —B (figs. 10, 12) on the south edge of Mesa Portales

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

32 GEOLOGY AND FUEL RESOURCES, FRUITLAN D FORMATION AND KIRTLAND SHALE, SAN JUAN BASIN
108° 107°
R16 15 14 13 12 / 11 10 l 9 8 7 6 5 4 3 2 1 mm RIE
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EXPLANATION l ' O
-— — ——.—- ”K - as- L , -—
Control points represent oil or gas \ \rx/ 3 ' /o ' 20
Th. 1 wells. MCKINLEY W
wkness of tsopached 'mterval (marker I
bed to base of Ojo Alamo Sandstone) was \
determined from electric logs. Contour " H V 19
interval is 100feet I
I 1 1

 

 

 

 

 

 

 

 

 

 

10

15'

20 MILES

FIGURE 13.—Isopach map of the interval between the Huerfanito Bentonite Bed of the Lewis Shale and the base of the Ojo Alamo

Sandstone.

STRATIGRAPHY 33

in the SE1/4SEMSWM sec. 9, T. 19 N., R. 2 W. The
sample from locality D3738—A was from a black silty
shale bed 10 feet beneath the base of the massive
sandstone bed capping Mesa Portales; the sample
from locality D3738—B was from a thin black shale
bed in a sequence of interbedded buff sandstone and
silty shale 5.5 feet beneath the base of the lower
sandstone bed of the Ojo Alamo (fig. 123). The palyno-
morphs identified by Tschudy (written commun.,
1968) from these localities are listed in table 1. Tschudy
reported on the palynomorphs from locality D3738—A
as follows: “This assemblage is clearly of Paleocene
age and is equivalent to the assemblages found by
Anderson in the Ojo Alamo Sandstone.” He further
stated that “Sample D3738—B is from the Tertiary.”

It is clear from table 1 and figures 10 and 12 that
the palynological Tertiary-Cretaceous boundary is in
the 36-foot interval between localities D3738—B and
D3738—C, below the lower sandstone bed shown
pinching out on the south edge of Mesa Portales in
figure 12. This finding is significant for two reasons:
(1) It conflicts with the interpretation by Baltz (1962,
1967) and Baltz, Ash, and Anderson (1966) that an
unconformity which represents the Cretaceous-Tertiary
boundary is present at the base of thc uppermost sand-
stone bed of the Ojo Alamo capping Mesa Portales;
since the palynological boundary is below the lowermost
Ojo Alamo sandstone bed. (2) It indicates that the
uppermost part of the Kirtland (mapped undivided
with the Fruitland in the Mesa Portales quadrangle) is
Paleocene in age, at least in places in the southeastern
part of the basin.

Palynological evidence suggests a possible uncon-
formity beneath the Ojo Alamo Sandstone on Mesa
Portales. R. H. Tschudy (written commun., 1967)
reported:

It is possible to postulate a hiatus between the Cretaceous and
Paleocene at this locality. The genus Araucariacites [table 1] has
not been found in rocks younger than Campanian in the Rocky
Mountain Region. Moreover, the Cretaceous assemblages found
in your samples are different from those found in the latest
Cretaceous of the Raton Formation. However, it must be em-
phasized that we do not have enough control data from your area
to do more than guess at a possible hiatus. For example, the
closest area from which we have control on the occurrence of
Araucariacites in the Upper Cretaceous is northern Colorado.
Furthermore, we know that several floral provinces existed
during Late Cretaceous time.

An effort was made to determine if the Tertiary-
Cretaceous boundary coincides with a lithologic change.
In some places on Mesa Portales, and elsewhere in the
basin, a bed of rusty-brown friable coarse-grained, in
some places conglomeratic, sandstone as much as sev-
eral inches thick is present below and near the base of
the lowermost sandstone bed of the Ojo Alamo. This

 

conglomeratic sandstone may be a lag deposit and
could mark the Tertiary-Cretaceous boundary in some
areas. Unfortunately, this sandstone bed is usually not
well exposed, and it is difficult to trace. Exposures can
be seen below the base of the Ojo Alamo above the
roadcut shown in figure 6 and on the south edge of
Mesa Portales below and west of the lower part of the
Ojo Alamo Sandstone pinchout in the west-central part
of sec. 10, T. 19 N ., R. 2 W. However, in some localities,
for example in the blufls south of Farmington, a rusty-
brown conglomeratic sandstone is the basal part of the
lowermost Ojo Alamo sandstone bed. In such areas the
base of the Ojo Alamo, the unconformity, and the
Tertiary-Cretaceous boundary are probably coincident.

UPPER CRETACEOUS, PALEOCENE, AND YOUNGER ROCKS
ANIMAS FORMATION AND YOUNGER ROCKS

The Fruitland Formation and the Kirtland Shale
are overlain by the Upper Cretaceous and Paleocene
Animas Formation throughout most of the San Juan
Basin north of the limit of the Ojo Alamo Sandstone
(fig. 9). At the outcrop the Animas is distinct from the
units underlying it in that it contains an abundance of
rock material of volcanic origin. It is conglomeratic
and characteristically contains boulders and pebbles
of andesite in a tufl’aceous matrix; the conglomerate
beds are interbedded with variegated shale and sand-
stone. Less commonly, conglomerate beds contain
pebbles of quartz, quartzite, and chert. The Animas
Formation was divided (Barnes and others, 1954) into
the basal Upper Cretaceous McDermott Member and
an unnamed Upper Cretaceous and Paleocene upper
member in the northwestern part of the San Juan Basin;
however, the McDermott Member has not been differ-
entiated in the northeastern part of the basin, and
there the Animas Formation is considered to be of
Paleocene age.

The Animas is limited to the northern part of the
basin. It attains a thickness of 2,670 feet on the outcrop
near the La Plata—Archuleta County boundary line in
Colorado (Reeside, 1924, pl. 2). On the east and west
sides of the basin, the Animas loses its identity because
it interfingers to the south with the Nacimiento
Formation. On the west side of the basin, the Animas
cannot be traced southward much beyond the New
Mexico—Colorado border; on the east side, the southern-
most limit of the Animas is probably near Dulce,
N. Mex. In the subsurface, the southern limit of the
Animas has not been located because of the difficulty
in differentiating the Animas from the Nacimiento on
electric logs.

The nature of the upper and lower contacts of the
Animas is problematical. Some geologists believe that
both contacts are conformable, whereas others believe

34

that both contacts are unconformable. In the authors’
opinion, the thinning of the Fruitland and the Kirtland
beneath the Animas from 1,200 feet at the outcrop
northeast of well 9 in section A—A’ (pl. 2) to less than
300 feet at the outcrop north of well 13 in section B—B’
indicates that more than 900 feet of Fruitland and
Kirtland rocks may have been removed by erosion in
the northeastern part of the basin prior to deposition
of the Animas. The isopach map of the Fruitland and
the Kirtland (fig. 11) shows the thinning of these
rocks toward the east side of the basin. The convergence
of the basal Animas contact and underlying formation
boundaries in the northeast in section A—A’ (pl. 2)
and in the north in section D—D’ (pl. 2) also indicates
beveling of the Fruitland and Kirtland rocks and
possible truncation of the Ojo Alamo Sandstone before
deposition of the Animas.

The Nacimiento Formation may overlie the Kirtland
Shale in the northwestern part of the basin in the area
west of the La Plata River and north of Pinyon Mesa.
The Tertiary rocks in this area have never been mapped
in detail, so the exact relationship of the Animas and
the Nacimiento in this part of the basin is not known.
In all probability, however, the Animas grades laterally
into the Nacimiento with a gradual compositional
change from abundant andesitic material in the north
to no andesitic material in the south.

R. H. Tschudy examined a coal sample collected by

the authors from a 0.6-foot-thick coal bed located
about 130 feet stratigraphically above the base of the
N acimiento Formation in the NEXSWMSWX sec. 12,
T. 20 N., R. 2 W., on a spur extending southward
from Cuba Mesa. The palynomorphs identified by
Tschudy from this locality (USGS paleobotany loc.
D3803) are listed in table 1. Tschudy (written commun.,
1966) reported:
This assemblage is of definite early Paleocene age. Some of the
species identified have been reported previously by Anderson
(1960) from the Nacimiento and Ojo Alamo Formations. Some
of the species recovered from this sample were not mentioned
by Anderson. This may suggest that this sample was from a
stratigraphically higher position than any of the samples studied
by Anderson.

The Eocene San Jose Formation overlies the Kirtland
on Bridge Timber Mountain in a small area north of
the New Mexico—Colorado border in the northwestern
part of the basin (Barnes and others, 1954), and
according to Baltz (1967, p. 42), the San Jose rests
unconformably on rocks as old as Lewis Shale in sec.
23, T. 22 N., R. 1 W., a few miles northeast of Cuba, in
the southeastern part of the basin.

In the northeastern part of the basin, a large number
of north-trending dikes and sills occur (pl. 1). The
dikes are vertical for the most part and range in

 

GEOLOGY AND FUEL RESOURCES, FRUITLAND FORMATION AND KIRTLAND SHALE, SAN JUAN BASIN

thickness from 1 to 30 feet. The intrusives, which are
biotite-hornblende lamprophyres, cut rocks as young
as the San Jose Formation and, thus, are younger than
this unit. The dikes contain free oil in vesicles in some
places (Dane, 1948). Faulting occurred both before
and after the intrusion of the igneous rocks; however,
the intrusions apparently were subsequent to the major
folding in the area.

STRUCTURE

The structural setting of the San Juan Basin and
the structural elements of the basin and the area
surrounding it are shown in figure 14. The Central
Basin area shown in this map coincides roughly with
the San Juan Basin of this report. The Central Basin
is structurally bounded by the Hogback monocline on
the northwest, north, and east sides. In the southern
and southwestern parts of the basin there is no sharp
structural boundary; the rocks dip gently in toward
the basin axis across the entire Chaco Slope.

The internal basin structure is shown in the contour
map of the Huerfanito Bentonite Bed (fig. 15). This
map shows the steep dip of the beds into the basin in
the northwestern, northern, and eastern parts and the
relatively gentle and even dip in the southwestern and
southern parts. The basin is distinctly asymmetric,
characterized by an irregular northwest-trending axis
that is about one-third of the distance across the basin
from the north side. The Central Basin area is modified
very little by faulting or folding. In a report on the
structural geology of the Colorado Plateau, Kelley and
Clinton (1960, p. 22) stated that “the fracture systems
of the San Juan Basin bear little regular relationship
to the over-all form of the basin; rather they are more
a part of the irregular structures that reflect irregular
deformation of the basin from place to place.”

The exact time of formation of the structural San
Juan Basin is difficult to determine. The isopach map
(fig. 13) of the interval between the Huerfanito Ben—
tonite Bed and the base of the Ojo Alamo gives no
indication of truncation around the west, south, or east
sides of the basin, so the basin probably had not yet
started to form, at least in these areas, at the time that
the Ojo Alamo was deposited. The first definite evidence
of uplift around the basin rim is the overstepping nature
of the basal San Jose Formation contact in the Bridge
Timber Mountain area in the northwest, and northeast
of Cuba in the southeast. Thus, the present basin con-
figuration must have started to develop after deposition
of the Ojo Alamo and prior to deposition of the San
Jose. Lakebed deposits of the Nacimiento Formation
indicate the presence of a closed basin prior to deposi-
tion of the San Jose.

37°

 

 

 

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yment / {o k
O .5/
/ 0° (2‘ Q
/ v Q L/ 0:

ARIZONA

Carrizo

 

  

 
 

 

STRUCTURE
109° 108° 107°
I (
l
Paradox S
Basin 5
La Plata o ’7 was)?
La Plata

_flA_H_ __ __
COLORADO

+

  

tral Basin

__COLORA:DO __
NEW MEXICO

  
  

      
  
      
 

 
 

   

Pagosa

Jemez Mts

 

 

 

 

   
  

   

     
 

 

 

 

 

 

FIGURE l4.—Structure map of the San Juan Basin. After Kelley (1951, p. 125).

35

36 GEOLOGY AND FUEL RESOURCES, FRUITLAND FORMATION AND KIRTLAND SHALE, SAN JUAN BASIN

ONTEZUMA

37° __c_gLORA_go_ [ __

NEW MEXICO
Outcrop of Fruitland

Formation and
Kirtland

RIGW

EXPLANATION

36° _.
0

Control points represent oil or gas
wells
Depth to contoured marker bed was de-
termined from electric logs. Datum is
mean sea level. Contour interval is 400

feet

107”
8 RIW FHE

LA PLATA T36N

ARCHULETA

   

o 9400'

RIO ARRIoBA.

MCKINLEY

5 10 15 20 MILES

FIGURE 15.—-Contour map of the Huerfanito Bentonite Bed.

GE OLOGIC HISTORY

GEOLOGIC HISTORY

The final retreat of the Late Cretaceous sea. from the
San Juan Basin area was accompanied by deposition of
the nearshore and beach deposits that now compose the
Pictured Cliffs Sandstone. The orientations of the Pic—
tured Cliffs shoreline as the sea regressed to the north-
east across the basin area are indicated in figure 7. The
shoreline trends were northwest most of the time, but
a shift to nearly an east trend is indicated in the cen-
tral part of the basin. The Pictured Cliffs shoreline was
rising stratigraphically as the sea was filled in and
pushed out of the basin area. During regression of the
Pictured Cliffs Sea, minor transgressive-regressive cycles
occurred frequently and resulted in both local thicken-
ing of the Pictured Cliffs and intertonguing of the Pie-
tured Clifis with the overlying Fruitland Formation.

On the landward side of the Pictured Cliffs shoreline,
three environments of deposition paralleled the shore-
line and migrated to the northeast as the sea regressed
(fig. 5). The sediments of a given environment thus
continuously overlapped the sediments of the next sea-
ward environment, except during minor transgressions
of the sea. Figure 16 is a diagrammatic paleogeographic
map of these three environments, showing a swamp
environment closest to the shoreline, a flood-plain en-
vironment farther away from the shore, and a river and
flood-plain environment even farther inland. In all
probability, these environments were, at least in part,
a function of the change of gradient of the paleoslope.
The steepest gradient was in the river and flood-plain
environment, and the swamp environment was nearly
flat. The observed sedimentary relations indicate that
there was a rising highland southwest of the present
San Juan Basin area. Sediment-laden streams flowed
northeast from this highland and ultimately emptied
into the Pictured Cliffs Sea. These streams were aggrad—
ing throughout much of the present San Juan Basin
area.

Eventually, the Pictured Cliffs Sea regressed out of
the San Juan Basin area, and an unknown thickness of
Fruitland and Kirtland rocks was laid down on top of
the Pictured Cliffs Sandstone. In northeastern New
Mexico, the Trinidad Sandstone is the highest regressive
marine sandstone, so it is probable that both the Trini—
dad and the Pictured Cliffs represent sandstone
deposited at and near the shoreline of the retreating sea
(here called the Pictured Cliffs Sea). The Trinidad is
overlain by the coal—bearing Vermejo Formation, which
is undoubtedly analogous to (although probably
younger than) the Fruitland Formation. Earlier writers
suggested that a landmass existed between the north-
eastern and northwestern parts of New Mexico during
Pictured Cliffs time and that the Pictured Cliffs Sea
was receiving sediment from both the east and west

 

37

 

 

 

 

 

 

FIGURE 16.——Diagrammatic paleogeographic map showing en—
vironments of deposition of the rocks that now compose the
Fruitland Formation and the Kirtland Shale.

sides of this landmass at that time. If this land area did
exist as Baltz (1967, fig. 7) showed, then the Pictured
Cliffs Sandstone should be equivalent in age in parts of
the northern and southern San Juan Basin and also it
should be equivalent in age to part of the Trinidad
Sandstone in the Raton Basin. Unfortunately, the age
of the Trinidad in the Raton Basin relative to the
Pictured Cliffs is not known. The evidence relating to
the age of the Pictured Cliffs of the San Juan Basin,
however, indicates that the Pictured Cliffs becomes
progressively younger from southwest to northeast.
Thus, it seems probable that the Pictured Cliffs shore-
line was regressing to the northeast as the sea left the
present basin area, which indicates that there was no
landmass immediately northeast of the area at that
time.

Silver (1950, p. 119) suggested that “a late Cretaceous
basin of deposition” existed in the northwestern part of
the present San Juan Basin area. He based this hypothe-
sis on an isopach map (his fig. 3) of “the combined
Fruitland and Kirtland formations” which showed, as

38 GEOLOGY AND FUEL RESOURCES, FRUITLAND FORMATION AND KIRTLAND SHALE, SAN JUAN BASIN

does figure 11 of this report, a thickening of the Kirtland
and Fruitland in the northwestern part of the basin. In
later reports (1951, 1957), Silver referred to this basin as
the Kirtland basin. The data developed in this report
indicate that there was no Kirtland basin of deposition
in the northwestern or western part of the San Juan
Basin. The greater thickness of the Fruitland and Kirt-
land in the northwestern part of the basin appears to be
the result of the combined effects of the stratigraphic
rise of the Pictured Cliffs Sandstone to the northeast
(fig. 7), the progressively lower stratigraphic position
of the Ojo Alamo Sandstone to the southeast (fig. 13),
and the progressively lower stratigraphic position of the
Animas Formation to the north and northeast (pl. 2).
In other words, the thicker Fruitland and Kirtland
rocks in the northwestern part of the San Juan Basin
reflect erosional episodes after the Kirtland and Fruit-
land rocks were laid down, rather than greater original
sediment accumulation in a basin existing during
Kirtland and Fruitland time.

Evidence of volcanism that occurred during deposi-
tion of the Fruitland Formation and the Kirtland Shale
can be found in several parts of the San Juan Basin.
In the southeast, near Cuba, bentonitic shales are
present in the lower part of the Fruitland. In the Ojo
Alamo Arroyo area, purple shales containing andesite
debris (Reeside, 1924) occur in the Kirtland. 1n the
Pinyon Mesa area in the northwestern part of the
basin, bentonitic shales are present in the Fruitland,
and volcanic tuff beds occur in the Kirtland. The loca-
tion of the volcanic vents is unknown; they may have
been located north, west, and southeast of the basin
area at different times. The final Upper Cretaceous
episode of volcanism is represented by the coarse ande-
site conglomerate and tuff beds of the McDermott
Member of the Animas Formation in the northwestern
part of the basin.

During the time of Fruitland and Kirtland deposi-
tion, there was probably uplift east or southeast of
the present basin area in the vicinity of the Nacimiento
uplift of figure 14. This highland probably served for a
time as a source area for the Fruitland, Kirtland, and
Pictured Cliffs and speeded the retreat of the Pictured
Cliffs Sea from the eastern basin area to such an extent
that swamps did not form, and today there is little coal
in this area.

After deposition of the Kirtland and McDermott
rocks, the basin area was tilted toward the northwest
and a basin-wide cycle of erosion followed. This cycle
resulted in the removal of as much as 2,100 feet of
sediment in the southeastern part of the basin. The
areas in Tps. 29 and 30 N., R. 1 W., and T. 26 N.,
R. 1 E., where the Pictured Cliffs Sandstone, Fruitland
Formation, and Kirtland Shale are absent and the Lewis

 

Shale is overlain by the Ojo Alamo Sandstone (pl. 1),
probably represent areas which were relatively slightly
uplifted at the time of erosion. The area in Tps. 27
and 28 N., R. 1 W., where a remnant of Pictured Cliffs
Sandstone and Fruitland Formation crops out prob-
ably represents an area of local downwarping during
the erosion cycle.

Figure 13. an isopach map of the interval from the
Huerfanito Bentonite Bed to the base of the Ojo Alamo
Sandstone, indicates the amount of rock removed by
erosion in the basin area and also shows the trend of the
thinning, which is primarily from northwest to south-
east. The pre-Ojo Alamo surface was probably a rela-
tively flat peneplain. Thus, if the isopachs in figure 13
are thought of as structure—contour lines and the values
as below-sea—level values, then this isopach map is
probably a fair representation of the basin area structure
contoured on the Huerfanito just prior to Ojo Alamo
deposition. Cross sections through the basin at that
time are shown in B of figures 17 and 18. Figure 13 also
indicates that the basin structure as we know it today
had not yet started to form before the Ojo Alamo
Sandstone was deposited, at least not in the part of the
basin covered by the isopachs. If there had been some
tectonism around the area of the present basin rim, the
isopachs would tend to curve where they approach the
rim, but they do not. The few irregularities that do occur
in the isopachs could represent either pre-Ojo Alamo
paleotopography or localized post-Huerfanito tectonism.

The source of the Ojo Alamo was, for the most part,
west of the present basin area, as evidenced by the east-
ward decrease in the size of the pebbles contained in the
Ojo Alamo conglomerates. This decrease in pebble size
was observed in surface outcrops in the southern part
of the basin and is indicated in the subsurface by the
absence of pebbles in a core from a well in sec. 36, T. 29
N., R. 4 W., described by Fassett (1968a, b). Apparently
the gradients of the streams carrying Ojo Alamo sedi-
ment into the basm decreased from west to east, so that
coarser gravels were deposited on the west side of the
basin and progressively finer grained material was de-
posited eastward. Baltz (1967, p. 33) wrote that the
strikes of channel edges and crossbedding measurements
near Farmington “indicate that in this part of the basin
the Ojo Alamo was deposited by streams flowing from
the west-northwest and the northwest * * *.” Other
sources of sediment to the south or east may have
existed (Baltz, 1967, p. 33). The depositional conditions
in the northern part of the basin area at the time the
Ojo Alamo was being deposited to the south are not
known. At the present time, no Ojo Alamo Sandstone is
present in the northern part of the basin. Whether it is
absent because of lack of deposition or removal by ero-
sion after it was deposited is not known.

GEOLOGIC

The Nacimiento Formation was deposited on top of
the Ojo Alamo. The Nacimiento and the Ojo Alamo
intertongue throughout most of the basin area, and the
contact of these units is probably conformable, at least
in the southern two-thirds of the basin. The Nacimien to
may overlap the Ojo Alamo in the northwestern part of
the basin. It apparently directly overlies the Kirtland
Shale in the area north of Pinyon Mesa and west of the
La Plata River just south of the Colorado—New
Mexico border. The nature of the lower Nacimiento
contact north of Pinyon Mesa has not been determined.
If the contact is unconformable, it would indicate that
the northwest rim of the basin had been uplifted and
beveled after deposition of the Ojo Alamo Sandstone
and prior to deposition of the Nacimiento Formation.

The next phase of basin development was probably
uplift along the Hogback monocline (fig. 14), principally
in the Colorado part of the basin and in the northeastern
New Mexico part. This episode of uplift resulted in and
was accompanied by erosion and beveling of the
Fruitland and Kirtland and possibly the Nacimiento
and the Ojo Alamo around the north rim of the basin.

It is not possible to determine if the thinning of the
Fruitland and Kirtland rocks southeastward in the
northeastern part of the basin is the result of the pre-
Ojo Alamo erosion cycle, the pre-Animas erosion cycle,
or a combination of both. The convergence of the basal
Animas contact and underlying contacts illustrated in
sections A—A’ and D—D’ (pl. 2) indicates that there
were at least two cycles of erosion in the northern part
of the basin that resulted in beveling of the Fruitland
and Kirtland.

The pre—Animas erosion cycle was followed by an
outbreak of volcanic activity north of the basin,
possibly in the area of the La Plata Mountains (fig. 14),
that resulted in deposition of the upper member of the
Animas in the northwestern part of the basin and the
Animas in the northeastern part. After deposition of
the Animas, renewed uplift along the Hogback mono-
cline in the northern and eastern parts of the basin
resulted in erosion, at least in the Bridge Timber
Mountain area in the northwestern part and in an
area about 8 miles northeast of Cuba in the south-
eastern part (Baltz, 1967, p. 53). In both these areas,
the San Jose Formation was deposited unconformably
and at a sharp angle to the underlying rocks. The full
extent of the pre-San Jose erosion in the basin area has
not yet been determined. As the San Jose was being
deposited, the basin probably continued to form and
ultimately achieved its present configuration. Some time
after the San Jose was deposited, a large number of
dikes and sills were intruded in the northeastern part
of the basin. The dikes have a north-south alinement,

 

and according to Dane (1948), they are probably

HISTORY

39

Miocene in age and were “intruded subsequent to the
major period of folding of the rocks.”

The sequence of major geologic events discussed
above that affect the uppermost Cretaceous rocks of the
San Juan Basin is shown diagrammatically on the north-
south and east-west cross sections in figures 17 and 18.
Both figures represent three points in time in the
geologic history of the basin: (1) after deposition of the
Kirtland rocks and before deformation, (2) after uplift
and basin-Wide beveling but before deposition of the
Ojo Alamo, and (3) the present time.

In summary, it seems that the only erosional cycle
that affected the entire basin area, after the deposition
of the Pictured Cliffs Sandstone, was that preceding
deposition of the Ojo Alamo Sandstone. This stage in
the basin development is represented by B in figures
17 and 18. The erosional cycle was probably the result
of northwestward tilting of the entire basin area. The
authors believe that other erosional cycles occurred
along the north and east sides of the basin as the
Hogback monocline was being formed, but that during
these cycles deposition was relatively continuous in the
interior of the basin. Thus, the unconformities at the
base of the Animas and San Jose Formations that reflect
past uplift and attendant erosion along the basin rim
probably fade out and disappear toward the center of
the basin.

FUEL RESOURCES
OIL AND GAS

Commercial gas was discovered in the Farmington
Sandstone Member of the Kirtland Shale in 1921 when
the Aztec Oil Syndicate completed its State No. 1 well
in sec. 16, T. 30 N., R. 11 W., 1 mile south of Aztec,
N. Mex. This well had an initial potential of 250,000
cubic feet of gas and 4 barrels of oil per day. Gas from
the well was piped into Aztec and was used domestically
throughout most of the 1920’s, thereby establishing the
first commercial use of natural gas in New Mexico
(Barnes, 1950). The Aztec well became part of the Aztec
Farmington gas field from which five wells ultimately
produced. The field was abandoned in 1933. Since the
first discovery, 74 wells have produced oil and gas
from the Fruitland Formation and the Farmington
Sandstone Member of the Kirtland Shale in the New
Mexico part of the San Juan Basin. Thirty-five wells
have produced gas from the Fruitland Formation at
Ignacio dome in the Colorado part of the basin. The
statistical summary of the pools is given in table 2;
distribution of the pools is shown in figure 19.

Except for the Ignacio Blanco—Fruitland pool in La
Plata County, 0010., the Kirtland and Fruitland reser-
voirs consist of small scattered stratigraphic traps. The
extreme lenticularity of the sandstone beds in these

40

GEOLOGY AND FUEL RESOURCES, FRUITLAND FORMATION AND KIRTLAND SHALE, SAN JUAN BASIN

SOUTH

Paleosurface
NORTH

Fruitland Formation and Kirtland Shale

Pictured Cliffs Sandstg‘f/I/I
Lewis Huerfanito Bentonite.Bed

 

 

 

 

 

Shale
A
SOUTH
Paleosurface NORTH
Pictured Cliffs Sandstone Fruitland Formation and Kirtland Shale

 

 

 

 

B
N 0 RT H
//
S O U T H ‘
g\' 39"” 006 //
,- 109° 0 $9/
32, r t 6'90 00/
a Prese“ 6° 09/

  

5000 ft above sea level

FEET
2000

1500
1000

500

 

5 10 15 MILES
O

VERTICAL EXAGGERATION ABOUT X 34

 

 

C

FIGURE 17.—North—south diagrammatic cross sections showing the probable sequence of geologic events that affected uppermost

Cretaceous rocks. A, Depositional attitude of the upper part of the Lewis Shale, the Pictured Cliffs Sandstone, and the Fruitland
Formation and Kirtland Shale before deformation of the rocks occurred; reference datum, Huerfanito Bentonite Bed. B, The
same rock sequence after the southeastern part of the basin area was tilted and the Kirtland and Fruitland rocks were beveled by
erasion; reference datum, paleosurface line. 0, Present structure and topography of the basin; reference datum, mean sea level.
These sections are along the line of cross section D—D’ (pl. 2).

OIL AND GAS 41

WEST

”MST

Fruitland Formation and Kirtland Shale

I i
Pictured CllffS Sandstone Lewis Huerfanito Bentonite Bed

Shale

 

 

 

 

 

 

EA T
WEST Paleosurface S

   
 
    

Fruitland Formation and Kirtland Shale

Huerfanito Bentonite Bed

 

 

 

EAST

WEST

FEET
2000

1500

1000

 

500

 

5 10 15 MILES

 

O
VERTICAL EXAGGERATION ABOUT X 34 C

FIGURE 18.—East-west diagrammatic cross sections showing the probable sequence of geologic events that affected uppermost
Cretaceous rocks. A, Depositional attitude of the upper part of the Lewis Shale, the Pictured Cliffs Sandstone, and the Fruit-
land Formation and Kirtland Shale before deformation of the rocks occurred; reference datum, Huerfanito Bentonite Bed.
B, The same rock sequence after the southeastern part of the basin area was tilted and the Kirtland and Fruitland rocks were
beveled by erosion; reference datum, paleosurface line. C, Present structure and topography of the basin; reference datum,
mean sea level. These sections are along the line of cross section F—F’ (pl. 2).

42

GEOLOGY AND FUEL RESOURCES, FRUITLAND FORMATION AND KIRTLAND SHALE, SAN JUAN BASIN

TABLE 2.——Statz'stical summary of oil and gas pools of the Kirtland Shale and the Fruitland Formation
[MC F, thousand cubic feet of gas; MC FPD, thousand cubic feet of gas per day; B0. barrels of oil; BOPD, barrels of oil per day. Number at left Is 011 or gas field number in fig. 19]

 

 

 

 

 

 

 

 

 

Location Total Number
No. Pool name Discovery Discovery well Initial wells that of wells Accumulated
date See. T. N. R. W. production produced producing production
NEW MEXICO
Jan. 1, 1966'
1 Aztec Farmington..._. _ 1921 Agree]. 011 Syndicate State 16 30 11 250 MC FPD, 4 BOPD 5 0 Unknown
2 Aztec Fruitland ........ June 19,1952 F L. Harvey Hare No 1.. 14 29 11 470 MCFPD ............ 32 6,834,146 McF, 2,114 B0
3 No. Aztec'Fruitland. Apr. 24,1954 El Paso Gage No.1 ....... 20 30 10 206MCFPD 1 0 15,138 MCF
6 Bloomfield Farm- July 1924 Blgopiigldl Oil 6: Gas 14 29 11 3 BOPD 29 4 40,010 B0
lngton. a z o
5 Cottonwood Fmitland- Nov. 11,1953 Pan fixm S. J. U 32—5 No.35 32 5 396 MCFPD 0 ____________
6 Flora Vista Fruitiand-. Dec. 28,1956 NNW. fired. Blanca 30—12 10 30 12 10,651 MC FPD 5 5 701,087 MCF
7 Gallegos Fruitland ..... Mar. 16, 1952 Wfitern Eev. Douthlt 27 27 11 1,300 MC FPD 1 1 663,938 MCF, 13 B0
8 Kutz Farmington ...... Nov. 1,1955 1%de Drlg.Co.No.11 K. 28 28 11 2,000 MCFPD 3 3 211,428 MCF
9 Kutz Fruitland ........ Aug. 30,1956 RgG D5rlg Co. Schlosser 27 28 11 5,000 MCFPD 4 4 2,132,245 MCF, 912 B0
0.2 J.
10 West Kutz Fruitland..- Oct. 22,1952 Locke Taylor Tycksen 23 29 13 370 MC FPD 2 2 302,170 MCF
11 La Jara Fruitland ...... June 25, 1952 Elng'so Abraham No. 13 30 6 2,530 MC FPD 1 0 54,008 MCF
12 Np. Iaos Pinos Fruit- July 31,1953 Pgillips S.J.U. 32—7 No. 18 32 7 1,370 MCFPD 1 0 220,364 MCF
an . .
13 So. Los Plnos Fmit- Aug. 24, 1953 ”(131.12” S.J.U. 32-7 No. 17 31 7 1, 790 MC FPD 1 1 377,956 MCF
an . .
14 Oswell Farmington---. Jan. 1.1932 Anna Oil Oswell No. 2—D- 34 30 11 25 B010 2 44,000 BO
15 Wyper Farmlngton ..... Aug. 2,1946 BrioqwnldzOStei-ns Wyper 29 30 12 750 MCFPD, 12 BOPD 2 0 6,852 B0
0. — .
Undesignated wells, Jan. 1, 1964
16 Undesignated _______________ El Paso Omler Fed. No. 1.. 36 28 10 673 MC FPD l 1 82,543 MCF
Farmington.
17 ._._.do .................. 1955 Mtfinanla Gas Sullivan 25 29 11 6,084 MC FPD l 1 223,220 MCF
o. .
Pal? Ainer. Trujillo Unit 21 29 10 5,011 MC FPD 1 0 8,191 MCF
o. .
Rgldteran Redfern Fed. 28 28 ll 69 BOPD 1 0 1,933 BC
Robert Elvis Bergin Fed. 21 29 11 559 MC FPD 1 1 11,880 MCF
Soi‘Udnlonl Prod. Arm'enta- 27 29 10 2,120 MC FPD 1 1 170,043 MCF
ed
22 Undesignated ............... Devonian Gas & 011 Fed. 4 29 12 1,322 MC FPD 1 1 53,649 MCF
Fruitland. No.
23 ..... do ................................. Elgasp Bolack Fed. 1 30 12 4,922 MC FPD 1 1 212,582 MCF
24 _ _._do .................. 1963 SoNUnlipn Angels Peak 13 28 11 4,900 MC FPD 1 216,816 MCF
o. .
COLORADO
June 1, 1965
25 Ignacio Blanco— 1950 Stanolind Ute No. B—l._.. 18 33 7 3,240 MC FPD 35 12 26,152,176 MCF
Fruit t.land
Total ............................................................................................................. 109 73 38,643,580 MCF,
95,834 B0

 

formations and the gentle dip of the rocks result in
many updip porosity pinchouts. The lenticularity re-
sponsible for the oil and gas accumulations also limits
their size. The sandstone beds in places contain gas
under relatively high initial pressure, but completions
in these beds have shown that the pressure usually
declines rapidly. Reserves are generally small, and only
a few of the wells have proved economical to complete
and operate. Gas shows in the Kirtland and the Fruit-
land are ignored during most drilling in the San Juan
Basin. In parts of the basin, however, it has become
customary for drilling companies to take precautions
against gas blowouts before penetrating the Kirtland

 

and Fruitland, since at least five drilling rigs have been
lost by fires owing to gas blowouts from these strati-
graphic units.

The gas field at Ignacio is on a northwest-trending
dome. Almost pure methane is produced from the coal
zone in the Fruitland, which is highly fractured over the
dome. The field has produced gas since 1950. The con-
tinuing production is attributed to the structural
closure of the field, a highly developed fracture system,
and a water drive which maintains the pressure of the
reservoir. This field has produced more than two-thirds
of all the gas that has been recovered from the Fruitland
Formation and the Kirtland Shale (table 2).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

OIL AND GAS 43
108° 107°
mew 15 14 13 12 j 11 1o 9 l 8 7 5 l 4 3 2 l R1w1 R112
F/ LAl PLATA , ' T36N
' ' 1210
f Duranlg?) 15 ' ’ ’1 13 6
MONTEIZUMA / 16 v “ 7 1 ARCHULETA 35
I l l ._._. ‘ '
L. L \/ -” 17 __
l' 25
, |
37° __C_91:933}20. _. _. _. ._
NEW MEXICO 11 10 F 9

Outcrop of F ruitland

 

 

 

 

 

Formation and

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Kirtland Shale
“3., . {14- -

R 16 w 63% 6 0 @3 >

. "1,7: 4 \

, l
1 29

! \

I 0 AR R I BA i 28
Ll 27

 

 

 

 

 

 

 

EXPLANATION

 

 

 

 

 

 

 

_-—__ —_—__.__—.4.——__.4——_‘_ __

 

 

 

 

 

 

@
Gas field

Fmitland Formation

 

 

 

 

 

 

 

SANDOVAL

 

 

 

®
Gas field
Farmi'ngum Sandstone Member
qf Kirtland Shale

dIIJIID
Oil field
Farmington Sandstone Member
Qf Kirtland Shale
92‘
Coal mine
Fmithmd Formation

 

 

 

 

 

 

of this
report

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

10

15

20 MILES
Lu_|_L.l___l___J__l

FIGURE 19.—Oil and gas fields and coal mines in the Fruitland Formation and the Farmington Sandstone Member of the Kirtland
Shale. The numbered oil and gas fields are listed in table 2; the coal mines are listed in table 8.

44

Small isolated oil pools in the Farmington Sandstone
Member of the Kirtland Shale are the only known oil
accumulations in the San Juan Basin that probably
originated in nonmarine rocks. The sandstone lenses
that contain the oil are enclosed in fresh-water shale and
are separated from the nearest marine deposits of the
area, the Pictured Clifi's Sandstone, by several hundred
feet of swamp and flood-plain sediment comprising the
Fruitland Formation and the lower part of the Kirtland
Shale. The oil is of high gravity, 56°—59° API, but the
production rate is low, and the wells produce much
connate water. As of January 1966, four fields had
produced a cumulative total of 95,834 barrels or oil from
the Farmington Sandstone Member. The total includes
small amounts of distillate from some Fruitland gas

fields.
URANIUM

Only one published report of uranium mineralization

in the Fruitland Formation, the Boyd deposit, is known.
This deposit is described by Clinton and Carithers
(1956, p. 449:) as follows:
The Boyd deposit is in a tuflaceous sandstone of the Fruitland
formation on a mesa 12 miles northwest of Farmington, N. Mex.
About 40 tons of ore containing 0.15 to 0.20 percent U308 have
been mined from a sharply defined light-pink zone at the base of
the tufiaceous sandstone. Just above the ore zone is 1 foot of gray
sandstone that grades upward into barren buff—colored, tufiaceous
sandstone. Beneath the ore there is a thin zone of gray sandstone;
this in turn is separated from a 1-foot bed of mudstone and sand-
stone containing carbonaceous fragments and marine (or brackish
water?) gastropods by a sharp, scoured contact. Bentonitic and
tufiaceous beds underlie the fossiliferous unit. The uranium
mineral is too fine to be readily identified.

The ore, exposed in an area of about 25 by 50 feet in an open
pit, is from 3 inches to 36 inches thick. The ore body occupies a
shallow depression scoured into the subjacent, tuflaceous sedi-
ments. It is on the flank of the Hogback monocline in beds dipping
12° SE. The pink color of the ore unit is due to iron oxide.

The authors visited the Boyd location in July 1968.
It appears that little, if any, development work has
been done at the deposit in recent years. A few shallow
bulldozer trenches were seen in the area near the old
workings, but none appeared to be recent cuts.

COAL
ORIGIN AND DISTRIBUTION

Coal in the Fruitland Formation occurs chiefly in
northwest-trending elongate lenticular bodies whose
long axes parallel the strand lines of the Pictured Cliffs
Sea. The organic material that formed the coal beds
accumulated, for the most part, in a belt of long, rela—
tively narrow coastal swamps which formed behind the
barrier beaches of the sea. The general character and
the physical dimensions of the coal beds indicate that
the belt of swamps generally ranged in width from 6 to
20 miles. Individual swamps ranged in size from small

 

GEOLOGY AND FUEL RESOURCES, FRUITLAND FORMATION AND KIRTLAND SHALE, SAN JUAN BASIN

bogs to inundated areas of more than 100 square miles.
Some swamps existed for only a brief time; they are
recorded by thin usually silty and discontinuous streaks
of coal and carbonaceous shales. Other swamps per-
sisted for long periods, during which sufficient organic
debris accumulated to compact into coal beds more
than 30 feet thick. Between these extremes were all
degrees of size and duration.

The belt of swamps was dissected in places by the
winding distributaries of sluggish streams. A few larger
rivers crossed it from the south and the west, carrying
sand to the beaches and fine silt and clay to the open sea.
Encroaching over the landward side of the swamps,
through a wide transition zone, were broad, low flood
plains. At some points the environment of the flood
plain protruded deep into the swamp belt. In other
areas, far inland, the vegetal matter, which today forms
scattered lenses of coal in the upper part of the Fruitland
Formation, was accumulating in small isolated bogs.
A diagrammatic illustration of Fruitland environmental
zones is shown in figure 16.

The general regression of the Late Cretaceous sea
was interrupted repeatedly by minor transgressions
and oscillations of the shoreline. The brief transgres-
sions temporarily displaced the barrier beaches and
coastal swamps landward (southwestward) geographi-
cally and upward stratigraphically so that today the
Fruitland coals in places intertongue with the marine
Pictured Cliffs Sandstone. In some areas, coal zones,
separated by thick intertongues of sandstone, siltstone,
and shale, occur one above another over a stratigraphic
interval of 300 or more feet. At most places the upper
coal zones of these areas are the landward extensions
of thick coal deposits which built up behind barrier
beaches to the northeast. As each minor transgression
began, the coastal swamps were pushed inland and
covered previously deposited flood—plain sediment. The
magnitude of the transgression or the duration of a
period of oscillation determined the distance of the
inland migration of the swamps and controlled the
thickness of the resulting coal deposits. Typically, the
thickest Fruitland coal beds occur immediately south-
west of the pronounced stratigraphic rises of the
Pictured Cliffs Sandstone. In a northeast direction the
coal beds wedge out abruptly against intertonguing
sandstones of the Pictured Cliffs. Toward the southwest
they are first split by and then grade into flood-plain
deposits. In a northwest trend the coal zones maintain
a relatively consistent overall thickness for many miles,
although individual beds may split, thin, pinch out,
merge, or terminate abruptly against channel deposits.

The depositional relations described above resulted,
in most areas, in the concentration of the thickest and

COAL

most extensive of the Fruitland coals in the lowest part
of the formation. In places, however, the lowest ap-
proximately 100 feet of the Fruitland is barren of coal
beds. Such barren areas may be explained as follows:
(1) The areas may represent large stream channels in
which deposits of silt, sand, and mud were the first
Fruitland sediments; (2) the areas may have resulted
from postswamp erosion—streams cut channels through
the peat deposits and the channels subsequently filled
with clastics, resulting in a gap or “want” in the coal
beds; or (3) some relatively deep lagoons and lakes did
not support plant growth or preserve the organic
remains necessary for coal formation but instead filled

 

45

with fine clastics and mud that locally formed the
lowermost Fruitland beds.

The subsurface thickness and distribution of Fruit-
land coal beds in the San Juan Basin, shown on plate
3, were determined by interpretation of the electronic—
log records and drilling-rate charts of holes drilled by
petroleum companies. The locations of the drill holes
and surface sections are shown on plate 3. Most of the
measured sections were taken from published reports,
but those near the east margin and the southeast corner
of the basin were measured by the authors. The control
points and the source of information are listed in
table 3.

TABLE 3.-—Wells and measured sections used for plotting coal resources

 

 

 

 

 

tI)~Ium— Location
Sign Published reference or company Measured section or well name Sec. T. N. R.
Colorado
1 Zapp (1949) ________________________ 75 ___________________________ 27 35 9 W.
2 _____ do _____________________________ Composite of 82 and 83 ________ 17 35 8 W.
3 Barnes (1953) ______________________ Coomposite of 2 and 3 __________ 12 35 8 W.
4 _____ o ........................................................ 9 35 7 W.
5 _____ do _____________________________ 13, Schutz mine _______________ 14 35 7 W,
6 _____ d0 ........................................................ 18 35 6 W.
7 _____ do _____________________________ 24, Shamrock mine No. 1, 2, 3__ 13 35 6 W.
8 _____ do _____________________________ 30 ___________________________ 33 35 5 W.
9 Northwest Production Corp __________ Bondad 34— 10 No.1—32 ________ 32 34 10 W.
10 Barnes, Baltz, and Hayes (1954) ______ 56 ___________________________ 9 34 10 W.
11 Zappd (1949) ________________________ 66 ___________________________ 5 34 9 W.
12 __________________________________ 69 (Carbon Junction) __________ 5 34 9 W.
13 Consolidated Oil and Gas, Inc ________ Spring Creek No 2—29 _________ 29 34 6 W.
14 Wood, Kelley, and MacAlpin (1948)-__ 1 ____________________________ 4 34 5 W.
15 _____ do _____________________________ 2 ____________________________ 24 34 5 W.
16 Barnes, Baltz, and Hayes (1954) ______ 39 ___________________________ 30 33 11 W.
17 _____ do _____________________________ Composite of 49 and 50 ________ 3 33 11 W.
18 Val R. Reese and Associates, Inc ------ Ute No. 2—34 _________________ 34 33 11 W.
19 Pacific NW Pipeline Corp ____________ Bondad 33— 10 No. 4— 3 --------- 3 33 10 W.
20 U S. Smelting, Refining and Mining 00- So. Ute 33-10 No. 2—35 ________ 35 33 10 W.
21 Northwest Production Corp __________ Bondad 33—9 No. 20— 5 _________ 5 33 9 W.
22 Pacific NW Pipeline Corp ____________ Bondad 33— 9 No. 30— 21 ________ 21 33 9 W.
23 _____ do _____________________________ Bondad 33—9 No. 12— 1 _________ 1 33 9 W.
24 Compass Exploration, Inc ____________ Black Mesa No.1—33 __________ 33 33 8 W.
25 Pacific NW Pipeline Corp ------------ Ignacio 33— 8 No. 10— 2 _________ 2 33 8 W.
26 _____ do _____________________________ Ignacio 33— 7 No. 8— 32 _________ 23 33 7 W.
27 Consolidated Oil and Gas, Inc -------- Superior Ute No.1— 6 __________ 6 33 6 W.
28 Wood, Kelley, and MacAlpin c(1948)_-_3 ____________________________ 16 33 3 W.
29 ----- do _________________________________________________________ 32 33 2 W.
30 _____ do _____________________________ 5, Klutter Mountain ___________ 20 33 1 W.
31 Barnes, Baltz, and Hayes (1954) ______ 34, Fort Lewis mine ___________ 1 32 12 W.
32 Feldt and Maytag ___________________ Ute Govt. No. 1 ______________ 4 32 6 W.
33 Pacific NW Pipeline Corp ____________ NW Cedar Hill 32— 10 No 10—8- 8 32 10 W.
34 El Paso Natural Gas Co _____________ Carter Ute No.2 ______________ 23 32 10 W.
35 Skelly Oil Co _______________________ Sam Burch No.2 ______________ 4 32 9 W.
36 Compass Exploration, Inc ------------ Southern Ute No.1— 10 _________ 10 32 11 W.
37 Stanolind Oil and Gas Co ____________ Southern Ute No. 1 ____________ 22 32 3 W.
New Mexico

38 Hayes and Zapp (1955) ______________ 44 ___________________________ 21 32 13 W.
39 _---do ________________________________________________________ 18 32 12 W.
40 Pan American Petroleum Corp ________ Fed. Gas Unit No.1 ___________ 20 32 12 W.
41 El Paso Natural Gas Co _____________ Moore No. __________________ 25 32 12 W.
42 Great Western Drilling Co ___________ Decker No. 3 _________________ 17 32 11 W.
43 El Paso Natural Gas Co _____________ S. J. U. 32—9 No.48 ____________ 14 32 10 W.
44 Pacific NW Pipeline Corp ____________ S. J. U. 32—9 ___________________ 9 32 9 W.
45 El Paso Natural Gas Co _____________ S. J. U. 32—9 No.63 ____________ 36 32 9 W.
45 Pacific NW Pipeline Corp ____________ S. J. U. 32—8 Mesa 9—20 _________ 20 32 8 W.

4:6 GEOLOGY AND FUEL RESOURCES, FRUITLAND FORMATION AND KIRTLAND SHALE, SAN JUAN BASIN

TABLE 3.—Wells and measured sections used for plotting coal resources—Continued

 

INum- Location
er on —___________
pl. 3 Published reference or company Measured section or well name Sec. T. N. R.

 

New Mexico— Continued

 

 

47 El Paso Natural Gas Co _____________ Allison No. 16 (MD) ___________ 15 32 7 W.
48 ____do _____________________________ Allison No.13 ________________ 12 32 7 W.
49 ____do _____________________________ Allison No 17 ________________ 24 32 7 W.
50 Pacific NW Pipeline Corp ____________ S J. U. 32— 5 No. 6— 10 __________ 10 32 6 W.
51 El Paso Natural Gas Co _____________ S. J. U. 32- 5 No.14 ____________ 26 32 6 W,
52 LaPlata Gathen'ng System, Inc _______ S.J.U. 32—5 No. 1—31 __________ 31 32 5 W.
53 Belco Petroleum Corp _______________ Carracas Mesa Unit No. 1—26___ 26 32 5 W.
54 Phillips Petroleum Co ________________ Mesa Unit No. 32—4 No. 1—29__ 29 32 4 W.
55 ____do _____________________________ Mesa Unit No. 32—4 No. 2—16__ 16 32 4 W,
56 Pan American Petroleum Corp ________ Pagosa Jicarilla No.1 __________ 23 32 3 W.
57 Hayes and Zapp (1955) ______________ 22 ___________________________ 26, 35 31 15 W.
58 _-__d0 _____________________________ 26 ___________________________ 29 31 14 W.
59 ---_d0 _____________________________ 34 ___________________________ 23 31 1 14 W.
60 ..... do .............................. 37 ........................... 7, 18 31 13 W.
61 Southern Union Production Co _______ Fed. Lea No. 1 ________________ 34 31 13 W.
62 Ohio Oil Co _________________________ Ohio Govt. No. 1—20 ___________ 20 31 12 W.
63 El Paso Natural Gas Co _____________ Case No 7 ___________________ 19 31 11 W.
64 __________________________________ Heaton No.9 _________________ 32 31 11 W.
65 Delhi-Taylor Oil Corp _______________ Mudge No 1 _________________ 10 31 11 W.
66 Wood River Oil and Refining Co, Inc- Lamb No.3 __________________ 21 31 10 W.
67 El Paso Natural Gas Co _____________ S. J. U 32—9 No.64 ____________ 2 31 9 W.
68 Pacific NW Pipeline Corp ____________ S.J.U. 32—8 Mesa 8—22 _________ 22 31 8 W.
69 _____ do _____________________________ S.J.U. 31—6 No. 5—31 __________ 31 31 6 W.
70 _____ do _____________________________ Rosa Unit No 10— 13 __________ 13 31 6 W.
71 _____ do _____________________________ Rosa Unit No.15— 29 __________ 29 31 5 W.
72 Shar- Alan Oil Co ____________________ Carson No.1 _________________ 10 31 5 W.
73 Humble Oil and Refining Co __________ Jic Tr 29—1 __________________ 32 31 2 W.
74 J. S. Hinds and J. E. Fassett _________ Unpub. outcrop data __________________ 31 1 W.
75 Hayes and Zapp (1955) __________________________________________ 28 30 15 W.
76 A. C. Bruce, Jr _____________________ Fed. Pipkin No 1 _____________ 5 30 14 W.
77 Stone Drilling, Inc __________________ Kirtland No. 1— 20 _____________ 20 30 14 W.
78 Compass Exploration, Inc ____________ Aztec No 2-35 ________________ 35 30 14 W.
79 Texas National Petroleum Co _________ Govt. No. 1 __________________ 29 30 13 W.
80 Southern Union Production Co _______ Fed No. 2—25 _________________ 25 30 13 W.
81 Northwest Production Corp __________ Blanco 30—12 No. 1—4____ 4 30 12 W.
82 Pubco Petroleum Corp _______________ State No. 30 __________________ 36 30 12 W.
83 Tennessee Gas Transmission Co _______ Blanco State No. 1 ____________ 2 30 11 W.
84 International Oil Co _________________ E. E. Fogelson No. 1—25 _______ 25 30 11 W.
85 El Paso Natural Gas Co _____________ Sunray No. l—J (PM) __________ 7 30 10 W.
86 LaPlata Gathering System, Inc _______ Riddle No.2 __________________ 23 30 10 W.
87 Delhi Oil Corp ______________________ Florence-Fed 2—10 _____________ 30 30 9 W.
88 El Paso Natural Gas Co _____________ Howell No. 4—0 _______________ 18 30 8 W.
89 _____ do _____________________________ Gartner No.8 ________________ 26 30 8 W.
90 _____ do _____________________________ Manning No. 1— A _____________ 20 30 6 W.
91 _____ do _____________________________ S. J. U. 30—5 No. 29—14 _________ 14 30 5 W.
92 _____ do _____________________________ S.J.U. 30—5 No. 32—26 _________ 26 30 5 W.
93 _____ do _____________________________ S. J. U. 30—4 No.31 ____________ 14 30 4 W.
94 _____ do _____________________________ S. J. U. 30—4 No.32 ____________ 33 30 4 W.
95 Sunray DX Oil Co __________________ Jicarilla Tr No.1 _____________ 34 30 3 W.
96 Hayes and Zapp (1955) ______________ Composite of 4 and 6 __________ 3 29 15 W.
97 El Paso Natural Gas Co _____________ Foutz No 1 __________________ 12 29 15 W.
98 Sunray Mid-Continent Petroleum 00.. N. M. Fed No. 1— 6 ____________ 15 29 14 W.
99 Humble Oil and Refining Co __________ Navajo L No 3 _______________ 26 29 14 W.
100 Tennessee Gas Transmission Co _______ USA Glenn Callow ____________ 33 29 13 W.
101 Pan American Petroleum Corp ________ Gallegos Can. No. 144 Unit 16 29 12 W.
o. 1.
102 El Paso Natural Gas Co _____________ Bloomfield No. 1 ______________ 17 29 11 W.
103 Redfern and Herd, Inc _______________ Nye No. 1 ____________________ 32 29 11 W.
104 International Oil Co _________________ Fogelson No. 1-11 _____________ 11 29 11 W.
105 Congress Oil Co _____________________ Congress No. 4 ________________ 35 29 11 W.
106 LaPlata Gathering System, Inc ________ Houck No. 2—12 _______________ 12 29 10 W.
107 H.D.H. Drilling Co __________________ San Juan N0. 2 _______________ 33 29 9 W.
108 El Paso Natural Gas Co _____________ MV Strat test No.3 ___________ 21 29 8 W.
109 _____ do _____________________________ S..J U. 29—7 No.65 ____________ 22 29 7 W.
110 Pacific NW Pipeline Corp ____________ S. J. U. 29—6 Mesa 20—8 _________ 8 29 6 W.
111 El Paso Natural Gas Co _____________ S. J. U. 29—5 No.13—30 _________ 3O 29 5 W.
112 _____ do _____________________________ S. J. U. 29—5 No. 32—29 (MD)-___ 29 29 5 W.
113 _____ do _____________________________ S.J.U. 29—5 No. 48—15 _________ 15 29 5 W.
114 _____ do _____________________________ S..J U. 29—4 No.14—31 _________ 31 29 4 W.
115’ _____ do _____________________________ S. J. U. 29—4 No.16—36 _________ 36 29 4 W.
116 Pacific NW Pipeline Corp ____________ Jic Ind. A—2 __________________ 30 29 3 W.

See footnote at end of table.

COAL

TABLE 3.—-—Wells and measured sections used for plotting coal resources—Continued

 

 

 

Num- Location
broil? Published reference or company Measured section or well name Sec. T. N. R.
New Mexico—Continued
117 Phillips Petroleum Co ________________ Indian D No. 1 _______________ 21 29 3 W.
118 Smith Drilling Co ___________________ Jic. S—l ______________________ 19 29 2 W.
119 Aztec Oil and Gas Co ________________ Stinking Lake No. 1 ___________ 35 29 1 W.
120 Bauer and Reeside (1921) ____________ Composite of 161—163 (Ojo 30 28 1 15 W.
Alamo Arroyo).
121 Floyd J. Ray _______________________ Cole No. 1 ____________________ 22 28 15 W.
122 Sunray DX Oil Co __________________ Gulf-Navajo No. l ____________ 21 28 14 W.
123 British-American Oil Producing Co____ Scott D No. 1 _________________ 20 28 13 W.
124 Pan American Petroleum Corp ________ Gallegos Cany. No. 116 ________ 24 28 13 W.
125 Sunray DX Oil Co __________________ Gallegos Cany. No. 127 ________ 21 28 12 W.
126 Pan American Petroleum Corp ________ Gallegos Cany. No. 125 ________ 24 28 12 W.
127 Redfern and Herd, Inc _______________ Lucerne “C” No. 1_ ___________ 21 28 11 W.
128 Angel Peak Oil Co ___________________ Angel Peak No. 20-B __________ 24 28 11 W.
129 Pan American Petroleum Corp ________ J. C. Davidson No. G—l ________ 21 28 10 W.
130 El Paso Natural Gas Co _____________ Michener No. 4—A (PM) _______ 28 28 9 W.
131 _____ do _____________________________ Bolack No. 3—B (PM) _________ 33 28 8 W.
132 _____ do _____________________________ S.J.U. 28—7 No. 73 (PM) _______ 28 28 7 W.
133 _____ do _____________________________ S.J.U. 28—6 No. 76 ____________ 23 28 6 W.
134 _____ do _____________________________ S.J.U. 28—5 No. 32 ____________ 20 28 5 W.
135 _____ do _____________________________ S.J.U. 28—5 No. 13 ____________ 9 28 5 W.
136 _____ do _____________________________ S.J.U. 28-5 No. 25 ____________ 13 28 5 W.
137 _____ do _____________________________ S.J.U. 28—4 No. 111—29.. ________ 29 28 4 W.
138 Pacific NW Pipeline Corp ____________ Jicarilla L No. 2 _______________ 16 28 3 W.
139 Skelly Oil Co _______________________ Jicarilla No. 1—A ______________ 3 28 2 W.
140 Gulf Oil Corp _______________________ Jicarilla 298 No. 1 _____________ 10 28 1 W.
141 J. S. Hinds and J. E. Fassett _________ Unpub. outcrop data __________________ 28 1 W.
142 Bauer and Reeside (1921) ____________ Composite of 183—186 __________ 2 27 1 16 W.
143 _____ do _____________________________ Composite of 201—205 __________ 22 27 1 16 W.
144 Davis Oil Co _______________________ Budd-Navajo No. 1__-_________ 17 27 15 W.
145 William Callaway ___________________ Navajo No. 1 _________________ 14 27 15 W.
146 Miami Oil Producers, Inc _____________ Ojo Alamo No. 1 ______________ 14 27 14 W.
147 Royal Development Co ______________ Ojo Amarilla No. 2 ____________ 6 27 13 W.
148 Sunray DX Oil Co __________________ Hoska-ne-nos-wot No. 1 ________ 22 27 13 W.
149 Stanolind Oil and Gas Co ____________ USA E. H. Newman No. 1 _____ 31 27 13 W.
150 Sunray Mid Continent Co ____________ Fed. J. No. 1 _________________ 35 27 13 W.
151 Southwest Production Co ____________ Thompson Fed No. 2 __________ 10 27 12 W.
152 Tenneco Oil Co _____________________ Watson Unit No. 1 “A” ________ 21 27 12 W.
153 Texaco Inc _________________________ Navajo “AA” No. 1 ___________ 19 27 11 W.
154 British-American Oil Producing Co____ Scott No. 8 ___________________ 22 27 11 W.
155 Tennessee Gas Transmission Co _______ Bolack Gas Unit A No. 1 _______ 2 27 11 W.
156 Stanolind Oil and Gas Co ____________ Huerfano No. 6 _______________ 31 27 10 W.
157 Pan American Petroleum Corp ________ J. G. Gordon No. 2 ____________ 22 27 10 W.
158 El Paso Natural Gas Co _____________ Lodewick No. 8 _______________ 19 27 9 W.
159 J. Glenn Turner (for Turner-Webb)_-_ Huerfanito No. 43-22 __________ 22 27 9 W.
160 Southern Union Gas Co ______________ Navajo No. 3—B _______________ 19 27 8 W.
161 El Paso Natural Gas Co _____________ Bolack No. 9 (PM) ____________ 31 27 8 W.
162 _____ do _____________________________ S.J.U. 28—7 No. 98 (MD) ______ 29 27 7 W.
163 _____ do _____________________________ S.J.U. 28—7 No. 93 (PM) _______ 9 27 7 W.
164 _____ do _____________________________ S.J.U. 28—7 No. 64 ____________ 22 27 7 W.
165 _____ do _____________________________ Rincon No. 97 (PM) ___________ 18 27 6 W.
166 _____ do _____________________________ S.J.U. 28—6 No. 23 ____________ 9 27 6 W.
167 _____ do _____________________________ S.J.U. 27—5 No. 19 ____________ 20 27 5 W.
168 _____ do _____________________________ S.J.U. 27—5 No. 21 ____________ 3 27 5 W.
169 ..... do _____________________________ S.J.U. 27—5 No.'33 ____________ 26 27 5 W.
170 _____ do _____________________________ S.J.U. 27—4 No. 16 (MD) ______ 17 27 4 W.
171 _____ do _____________________________ S.J.U. 27—4 No. 17 (PM) _______ 29 27 4 W.
172 Phillips Petroleum Co ________________ Indian ”C” No. 1 _____________ 20 27 3 W.
173 Magnolia Petroleum Co ______________ Jicarilla “G” No. 2 ____________ 25 27 3 W.
174 Northwest Production Corp __________ NE No. 1—16 _________________ 16 27 2 W.
175 Magnolia Petroleum Co ______________ Jicarilla No. 1 _________________ 20 27 2 W.
176 J. S. Hinds and J. E. Fassett _________ Unpub. outcrop data __________________ 27 1 W.
177 Bauer and Reeside (1921) ____________ Composite of 239—242 and 250 ________ 26 1 16 W.
. (Pina Veta China Arroyo).
178 _____ do _____________________________ Composite of 277, 279, 281, 282, ________ 26 16 W.
289, 301 (Klaychin Arroyo).
179 Shell Oil Co ________________________ Burnham No. 1 _______________ 14 26 15 W.
180 British-American Oil Producing Co____ Navajo No. 1 _________________ 15 28 14 W.
181 Skelly Oil Co _______________________ A. L. Duff No. 13 _____________ 18 26 13 W.
182 Benson-Montin-Greer Drilling Corp_ _ _ Foster No. 4 __________________ 15 26 13. W.
183 El Paso Natural Gas Co _____________ Sullivan No. 1—C ______________ 17 26 12 W-
184 _____ do _____________________________ Nelson No. 1—A _______________ 9 26 12 W.

See footnote at end of table.

47

48 GEOLOGY AND FUEL RESOURCES, FRUITLAND FORMATION AND KIRTLAND SHALE, SAN JUAN BASIN

TABLE 3.—Wells and measured sections used for plotting coal resources—Continued

 

 

 

lNum- Location
er on —— ———~
pl. 3 Published reference or company Measured section or well name Sec. T. N. R.

 

New Mexico—Continued

 

185 Skelly Oil Co _______________________ Navajo D No.1 _______________ 13 26 12 W.
186 Pan American Petroleum Corp ________ O. H Randel No. 4 ____________ 15 26 11 W,
187 El Paso Natural Gas Co _____________ Huerfano No. 104 _____________ 17 26 10 W.
188 _____ do _____________________________ Huerfano No. 92 ______________ 7 26 9 W,
189 Turner-Webb _______________________ Ballard 11-15 _________________ 15 26 9 W.
190 Southern Union Gas Co ______________ Newsome No. l-A _____________ 15 26 8 W.
191 El Paso Natural Gas Co _____________ Hamilton State No. 7 __________ 32 26 7 W.
192 Caulkins Oil Co _____________________ Breech No. 307 (MD) __________ 13 26 7 W.
193 El Paso Natural Gas Co _____________ Johnson State No. 1 ___________ 32 26 6 W.
194 Northwest Production Corp __________ West No. 1— 7 _________________ 7 26 5 W.
195 _____ do _____________________________ Indian W No. 2—5 _____________ 5 26 5 W.
196 Tenneco Oil Co _____________________ Jicarilla B No.5 ______________ 21 26 5 W.
197 Southern Union Gas Co ______________ Jicarilla No. 2—H ______________ 17 26 4 W.
198 _____ do _____________________________ Jicarilla No. 2—A ______________ 14 26 4 W,
199 Magnolia Petroleum Co ______________ Jicarilla D No.2 ______________ 14 26 3 W.
200 Northwest Production Corp __________ Jicarilla E No. 3-34 ___________ 34 26 3 W.
201 Cabot Carbon Co ___________________ Humble Fed. B No. 1 __________ 16 26 2 W.
202 Bolack, Greer, et a1 __________________ Bolack No. l _________________ 9 26 1 W.
203 J S. Hinds and J. E. Fassett _________ Unpub. outcrop data __________________ 26 1 E.
204 Bauer and Reeside (1921) ____________ Composite of 338—340, 349 ________ 25 16 W.
350 (Brimhall Wash)
205 Amerada Petroleum Corp ____________ Navajo T R No. 19—1 ________ 21 25 14 W.
206 Gulf Oil Corp _______________________ Pinabete Navajo No.1 _________ 3 25 14 W.
207 F. R. Anderson _____________________ Federal No. 11—18 _____________ 18 25 13 W.
208 BritiSh-American Oil Producing 00.... Ross No. 2 ___________________ 24 25 13 W.
209 Shell Oil Co ________________________ Govt. No. 41—21 ______________ 21 25 12 W.
210 _____ do _____________________________ Bisti Wtr. Well W No. 1 _______ 24 25 12 W.
211 _____ do _____________________________ Carson No. 3 _________________ 7 25 11 W.
212 _____ do _____________________________ Govt. A No. 21—22 ____________ 22 25 11 W.
213 El Paso Natural Gas Co _____________ McKee No. 1 _________________ 1 25 11 W.
214 Wellshire Development Co ___________ Ma-Ga-El No. 2 ______________ 19 25 10 W.
215 El Paso Natural Gas Co _____________ Brookhaven No. 3—A __________ 29 25 10 W.
216 Consolidated Oil and Gas, Inc ________ Sunshine No.1— 13 _____________ 13 25 10 W.
217 M. B. Rudman _____________________ Federal No. 21— 1 ______________ 21 25 9 W.
218 Texas National Petroleum Co _________ Govt No. 1— 25-9 _____________ 1 25 9 W.
219 Davis Oil Co _______________________ Govt-Mead No. 1 _____________ 24 25 9 W.
220 El Paso Natural Gas Co _____________ Quitzau No.13 ________________ 15 25 8 W.
221 _____ do _____________________________ Harvey State No.2 ____________ 16 25 7 W.
222 Superior Oil Co _____________________ Hightower-Govt. No.1— 24 _____ 24 25 7 W.
223 El Paso Natural Gas Co _____________ Harvey State No.11 ___________ 16 25 6 W.
224 Kay Kimbell _______________________ Salazar-Federal No. 1— 22 _______ 22 25 6 W.
225 Humble Oil and Refining Co __________ Jicarilla J—4 __________________ 6 25 5 W.
226 Amerada Petroleum Corp ____________ Jicarilla Apache No. F—10 ______ 16 25 5 W.
227 El Paso Natural Gas Co _____________ Jicarilla No.6 ______________ 29 25 5 W.
228 Amerada Petroleum Corp_ ____________ Jic- Apache A6 N05. 5 ____________ 25 25 5 W.
229 El Paso Natural Gas Co _____________ Jicarilla No. 2—C ______________ 15 25 4 W.
230 Skelly Oil Co, ______________________ C. W. Roberts No. 3_____-__-__ 18 25 3 W.
231 Southern Union Gas Co ______________ Lebow No. 1 __________________ 14 25 3 W.
232 El Paso Natural Gas Co _____________ Federal No.15 ________________ 3 25 2 W.
233 San Juan Gas Corp __________________ Federal 27—IC- _ _ _ _ _ - _ _ _ _ _ _ _ __' 27 25 2 W.
234 Skelly Oil Co _______________________ N M. Fed. ”E” No.1 _________ 18 25 1 W.
235 Bolack- Greer, Inc ___________________ Canada Ojitos No. 1— 16 ________ 16 25 1 W.
236 Mtn. States Petroleum Corp __________ Gavilan No. 31—1—C ___________ 31 25 1 W.
237 Bolack— Greer, et a1 __________________ Bolack No. 1— 14 ______________ 14 25 1 W.
238 Bolack-Greer Inc ____________________ Canada Ojitos No.1— 23 ________ 23 25 1 W.
239 J. S. Hinds and J. E. Fassett _________ Unpub. outcrop data __________________ 25 1 E.
240 Bauer and Reeside (1921) ___________ Composite of 360—363, 370, 375 ________ 24 16 W.
(Medio Arroyo).
241 Davis Oil Co _______________________ Perry Navajo No.1 ___________ 6 24 14 W.
242 Monsanto Chemical Co ______________ Chaco No. 1 __________________ 20 24 13 W.
243 Humble Oil and Refining Co __________ Tanner Unit No.1 ____________ 21 24 12 W.
244 H. I. Fanning _______________________ Vanderslice No.1 ______________ 13 24 12 W.
245 Magnolia Petroleum Co ______________ Beamon- Fed. No. 1 ____________ 29 24 11 W.
246 Phillips Petroleum Co ________________ Gallegos No.1 ________________ 14 24 11 W.
247 Forest Oil Corp _____________________ Huerfano Fed. No. 1 ___________ 13 24 10 W.
248 Gulf Oil Corp _______________________ S. Huerfano Fed. No. 1— X ______ 15 24 9 W.
249 Exeter Drilling Co ___________________ Escrito Fed. No. 1 _____________ 20 24 8 W.
250 Lemm and Maitatico ________________ Govt. No. 1 __________________ 34 24 8 W.
251 Ray Smith, Trustee _________________ Federal No. 2 _________________ 13 24 8 W.
252 Standard Oil Co. of Texas ____________ Federal No. 1 _________________ 27 24 7 W.
253 Pan American Petroleum Corp ________ John S. Dashko No. l __________ 15 24 7 W.

See footnote at end of table.

COAL

TABLE 3.—Wells and measured sections used for plotting coal resources—Continued

 

Num- Location
her on ———— ———————
pl. 3 Published reference or company Measured section or well name Sec. T. N. R.

 

New Mexico—Continued

 

254 Val R. Reese and Associates, Inc ______ Lybrook No. 1—19 _____________ 19 24 6 W.
255 El Paso Natural Gas Co ............. Bolack No. 1E ________________ 35 24 6 W.
256 _____ do ............................. Bolack No 1— D _______________ 13 24 6 W.
257 _____ do _____________________________ Jicarilla No 4—A ______________ 15 24 5 W,
258 Amerada Petroleum Corp ____________ Jicarilla Apache No. El ________ 3O 24 4 W.
259 Magnolia Petroleum Co ______________ Jillson- Fed. No. 1 _____________ 7 24 3 W.
260 E1 Pasoo Natural Gas Co _____________ Lindrith No.35 _______________ 15 24 3 W.
261 __________________________________ Lindrith No.30 _______________ 18 24 2 W,
262 San Juan Gas Corp __________________ Federal A No.13 ______________ 13 24 2 W.
263 Shar-Alan Oil Co ____________________ E A Down-Fed.No.1 ________ 16 24 1 W.
264 Magnolia Petroleum Co ______________ Duff- Fed No 1 _______________ 27 24 1 W.
265 Reading and Bates, Inc .............. Duff No.1 ___________________ 24 24 1 W.
266 J. S. Hinds and J.E E.Fassett _________ Unpub. outcrop data __________ ____ 24 1 E.
267 Bauer and Reeside (1921) ____________ COWpofiite of 388—390 (Hunters 1 23 15 W.
as .
268 _____ do _____________________________ Composite of 419, 420, 443, 432, 23 13 14 W.
434, 433, 430.
269 Humble Oil and Refining Co __________ Tanner Unit No.3 ____________ 5 23 12 W.
270 Bauer and Reeside (1921) ____________ Cogggosite of 520, 521, 524, 526, ______ 23 12 W.
271 Shell Oil Co ........................ Meyer Govt No. 3 ____________ 20 23 11 W.
272 _____ do _____________________________ Meyer Govt. No. 1 ____________ 14 23 11 W.
273 E. B LaRue, Jr _____________________ Kinebeto No.2 _______________ 17 23 10 W.
274 Great Western Drilling Co ___________ Lucy English No.1 ___________ 25 23 10 W.
275 _____ do _____________________________ Chaco Unit No. 1 _____________ 14 23 9 W.
276 _____ do _____________________________ Chaco Unit No. 3 _____________ 21 23 8 W.
277 El Paso Natural Gas Co _____________ Sapp No. 1— A _________________ 18 23 7 W.
278 Rhodes Drilling Co __________________ Elkins Fed. No. 1 _____________ 13 23 7 W.
279 S. D. Johnson ______________________ Chapman No. 1 _______________ 20 23 6 W.
280 Sinclair Oil and Gas Co ______________ Tex. Nat’l Fed. No. 1 __________ 25 23 6 W.
281 Sunray DX Oil Co __________________ N. M Apache No.1 ___________ 21 23 5 W.
282 Pubco Petroleum Corp _______________ Jic. 23—5 No. 23— 11 ___________ 23 23 5 W.
283 San Juan Drilling Co ________________ Vanderslice No.1 _____________ 21 23 4 W.
284 Caswell Silver ______________________ Jicarilla No. 2—S ______________ 19 23 3 W.
285 U.(S).0 Smelting, Refining and Mining Jicarilla No.1 ________________ 7 23 3 W.
286 El Paso Natural Gas Co _____________ Jicarilla 183—2 ________________ 27 23 3 W.
287 Wagenseller and August _____________ Mobile- Apache No. 9—P ________ 12 23 3 W.
288 Shar-Alan Oil Co ____________________ Jicarilla “L” No.3 ____________ 15 23 2 W.
289 Magnolia Petroleum Co ______________ Evans Fed. No. 1 _____________ 18 23 1 W.
290 Shar-Alan Oil Co ____________________ Northcut No 1 _______________ 2 23 1 W.
291 Bauer and Reeside (1921) ____________ Composite of 537, 538, 546, 541- 10, 11 22 11 W.
292 E. B. LaRue, Jr _____________________ Kinebeto No. 4 _______________ 9 22 10 W.
293 Bauer and Reeside (1921) ____________ Composite of 560, 559 25, 26 22 10 W.
(Escavada Wash).
294 Great Western Drilling Co ___________ So. Chaco No. 1 _______________ 9 22 9 W.
295 Humble Oil and Refining Co __________ So. Chaco No. 3 _______________ 23 22 9 W.
296 _____ do _____________________________ So. Chaco No.4 _______________ 10 23 8 W.
297 Northwest Production Corp __________ 22— 7 No.1— 23 ________________ 23 22 7 W.
298 Plymouth Oil Co ____________________ Tomas No.1 __________________ 22 22 6 W.
299 Humble Oil and Refining Co __________ Jic “B” No.1 ________________ 1 22 5 W.
300 Skelly Oil Co _______________________ Jic. “E” No.1 ________________ 8 22 4 W.
301 Exeter Drilling Co ___________________ Jicarilla Apache No.1 _________ 28 22 4 W.
302 Bonanza Oil Co _____________________ Jicarilla No.1 _________________ 2 22 3 W.
303 Lloyd H. Smith _____________________ Jicarilla No. 32—1 ______________ 32 22 2 W.
304 Shar-Alan Oil Co ____________________ Humble Dakota No.1 _________ 21 22 2 W.
305 J. S Hinds and J. E. Fassett _________ Unpub. outcrop data __________________ 22 1 W.
306 Ray McGlothlin ____________________ Federal No.1 _________________ 22 21 8 W.
307 Davis Oil Co _______________________ Govt. Co—op No.1 ____________ 20 21 7 W.
308 Kingsley-Locke Oil Co _______________ Miles KL No.1 _______________ 21 21 6 W.
309 Shell Oil Co ________________________ Pool Four No.1 _______________ 22 21 5 W.
310 Roy Furr __________________________ Sun—Fed. No. 1 ________________ 14 21 4 W.
311 Sun Oil Co _________________________ McElvain Govt. No. 1 _________ 23 21 2 W.
312 J S. Hinds and J. E. Fassett _________ Unpub. outcrop data __________________ 21 1 W.
313 Dane (1936) ________________________ Measured coal sec _____________ 8 20 7 W.
314 ______________________________________ do _______________________ 23 20 7 W.
315 Davis 0Oil Co _______________________ McCollum Govt. No. 1 ________ 12 20 6 W.
316 Austral Oil Co., Inc _________________ Salvador Toledo Heirs No.1____ 23 20 5 W.
317 Atlantic Refining Co _________________ Torreon No. 3 ________________ 15 20 3 W.
318 A. N. Brown ________________________ Magnolia Fed. No. 1 ___________ 8 20 2 W
319 J. S. Hinds and J. E. Fassett _________ Unpub. outcrop data __________________ 20 1 W'

See footnote at end of table.

50

GEOLOGY AND FUEL RESOURCES, FRUITLAND FORMATION AND KIRTLAND SHALE,

SAN JUAN BASIN

TABLE 3.—Wells and measured sections used for plotting coal resources—Continued

 

 

 

 

 

Num- Location

bar on Published reference or company Measured section or well name ________
pl. 3 Sec. T. N. R.

New Mexico—Continued

320 Dane (1936) ________________________ Measured coal sec _____________ 12 19 6 W.
321 _____ do _____________________________ Composite of 2, 7, 9 ___________________ 19 5 W.
322 J. S Hinds and J. E. Fassett _________ Unpub. outcrop data __________ 11 19 4 W.
323 _____ do _________________________________ do _______________________ 7 19 3 W.
324 _____ do _________________________________ do _______________________ 8 19 2 W.

 

1 Projected.

The most commonly available logs for wells in the
San Juan Basin are electric, induction-electric, and
gamma ray—neutron (radioactivity) logs. Also available
for this study were several dozen drilling—rate logs which
the authors collected from various oil companies.
Figure 20 illustrates the character of the response to
Fruitland coal beds on an induction-electric log, a drill-
ing-rate log, and a gamma ray—neutron log. The logs
illustrated in this figure are of the lower part of the
Fruitland interval at well control location 52 (pl. 3).
Characteristic of the coal are high resistivity, sometimes
with but usually without a spontaneous potential, a
very rapid drilling rate, and low radiation intensity for
both gamma ray and neutron responses.

The rapid drilling penetration rate is very distinctive
of coal in the Fruitland Formation at depths of more
than 1,500 feet. The drilling speeds for all rock types in
the formation are rapid at shallower depths, and dis-
tinctions on the drilling-rate log are not pronounced.

The gamma ray—neutron log curves reliably identify
Fruitland coal beds at any depth. Both curves are
deflected far to the left on the log scale, which indicates
very low radiation intensity. The gamma ray instru-
ment measures the intensity of natural radioactivity.
Natural gamma rays originate chiefly from three
radioactive elements: uranium, thorium, and potassium.
The combined activity of these elements in each lithol-
ogy is recorded on the gamma ray log. These elements
are present in very low proportions in Fruitland coal
beds, and consequently, the coal beds have a very low
gamma radiation intensity. The neutron log records
gamma radiation which is induced by bombardment
of the formations with neutrons from a radioactive
source in the logging tool. The neutrons emitted by the
source are captured by atoms in the formation. The
capturing atom emits a powerful gamma ray which is
registered by a counter in the tool. Before capture is
possible, however, the fast neutrons must be slowed
to thermal speed. This speed loss is caused by collision
of the neutrons with atoms in the formation. Carbon
and hydrogen atoms are among the most effective in
slowing and capturing the neutrons. The high concen-

 

tration of carbon and hydrogen atoms in coal results in
the capture of most of the neutrons within inches of the
source. The counter in most logging tools is 12 or more
inches above the source and is shielded from the source
by a tungsten shield. As a result, the gamma rays
emitted by capture of neutrons near the source never
reach the counter and are not registered. High carbon
and hydrogen content in the rock near the source
results in a very low intensity of neutrons penetrating
deeper into the formation and so results in a low
neutron-gamma counting rate. Because coal consists
primarily of carbon and hydrogen, it is readily identi-
fiable on neutron logs of the Fruitland Formation by
characteristically very low radiation intensity readings.

The electric and induction-electric logging instru-
ments measure the electrical resistivity of the rocks
and the differences in their spontaneous potentials.
Coal is normally highly resistive to electrical currents
and is characterized by a marked deflection of the
resistivity curves to the right on the electric logs. In
the northern half of the San Juan Basin, the Fruitland
Formation contains numerous highly resistive beds,
probably compact calcite-cemented sandstone or silt-
stone, that have electrical properties similar to those
of the coal beds (for example, the bed between 3,290
and 3,300 ft in fig. 20). Determination of coal from
electric logs in this part of the basin, therefore, must be
supported by drilling-rate logs or radioactivity logs,
either of which can be used to differentiate other high
resistivity beds from coal beds. In the southern and
western parts of the basin, coal is normally the only
highly resistive rock in the formation, and the coal
beds may be identified directly from the electric logs
with a high degree of accuracy (fig. 2).

Normally, the Fruitland coal beds do not cause a
marked deflection of the spontaneous-potential curves.
Such deflections may occur, however, where the coal is
fractured and contains water or gas or where partings
of other rock types are present within the coal beds.
Thus, spontaneous-potential variations are of limited
value for coal-bed identification.

51

COAL

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00:. ZOmFDMZ-><m (ES—<0 604 m.._.<m_-OZ_:_4_mD 604 U.mk0m..w-ZO_._.ODn-Z_

52 GEOLOGY AND FUEL RESOURCES, FRUITLAND FORMATION AND KIRTLAND SHALE, SAN JUAN BASIN

Other types of well logs, particularly acoustic (sonic)
logs and focused varieties of electric logs (microlog
and microlaterolog of Schlumberger, FoRxo log and
guard log of Welex), are useful in delineating coal
beds. By the use of these logs, the boundaries of the
coal beds can be established within 6 or less inches,
and partings of 6 or less inches in the coal beds can be
detected. Logs of these types through the Fruitland
Formation, however, are available for only a small
number of wells in the San Juan Basin.

Conventional electric logs are run with sondes in
which the shortest electrode spacing is normally 16
inches. Coal beds thinner than the 16—inch spacing
are not recorded definitively on the logs, and for this
reason such thin beds were ignored in this study
except in areas where they are. the only coal present
or where they constitute a significant part of the total
coal. Partings as thin as 12 inches are usually detectable
in the coal beds by use of conventional logs. Thinner
partings in a predominantly coal sequence generally
can not be identified without the aid of one of the more
detailed logs mentioned above. Therefore, some of the
coal beds illustrated undoubtedly contain partings as
much as 12 inches thick which are not shown. Where
thin partings are numerous, however, they tend to
reduce the resistivity readings recorded through a
coal section. In a section of thinly interbedded coal
and partings, only those coal beds thicker than the
spacing of the electrodes on the logging sonde are
clearly recorded, and only such clearly recorded beds
were used. The authors believe, therefore, that only a
few of the coal sections shown (pl. 3) contain as much
as 10 percent of interbedded thin partings included in
the coal measurements. The surface sections from the
literature were generalized to conform with the format
of the log interpretations. Most thin partings less than
12 inches thick were omitted from the surface sections.

Figure 21 is an isopach map that shows the total
thickness of coal in the Fruitland Formation. The map
shows that, in spite of the extreme lenticularity of
individual beds and the random occurrence of most of
the higher coal beds, clearly defined patterns of distri-
bution of the total coal in the formation are visible. In
the southwest corner of the basin, where the oldest
preserved Fruitland coals are exposed in outcrop, an
area centered around T. 23 N., R. 12 W., shows the
total coal thickness exceeding 30 feet, and an irregular
area around this shows total coal thicknesses of 20—30
feet. The area of relatively thick coal is adjacent to the
southwesternmost of the two major stratigraphic rises
in the position of the Pictured Cliffs Sandstone pre—
viously discussed. Stratigraphic cross sections A—A’,
B—B’, 0—0’, and F—F’ of plate 2 illustrate these strati-
graphic rises.

 

Southeastward along the outcrop from the area of
thick coal, a narrow band (fig. 21) contains total
measured coal thicknesses of less than 10 feet. This
area is anomalous in that it occurs along the same
trend as the thicker beds to the northwest. The delinea-
tion of the narrow band is based on scattered measured
sections of coal zones taken from Dane (1936). The coal
beds along this stretch of outcrop are commonly burned
or covered, and good exposures are rare. The apparent
lack of thick coal in this area is probably due to this
surface burning and poor exposure. Future exploration
by drilling may show the presence of considerably more
coal than is currently shown in this area.

Northeastward from the areas just discussed, a belt
10—20 miles wide contains total coal thicknesses of less
than 20 feet and in many places of less than 10 feet.
This belt extends across the southwest third of the basin
and represents a time of relatively uninterrupted re-
gression of the coastline, although many minor oscilla-
tions occurred. In general, the width of the belt is
greater in the southeastern part of the basin, and the
cumulative thickness of coal in the southeastern part
of the belt is much less than in the northwest. This
indicates that withdrawal of the sea was somewhat
more rapid in the southeast than in the northwest at
that time, affording less time in the southeast for the
accumulation of organic material in the coastal swamps.
(See p. 15.) The total thickness of the coals in the
northwestern part of this belt is about double that of
the southeastern part, and the width of the belt is
about half as great in the northwest. Isolated areas
within the northwestern part, however, have total coal
thicknesses of less than 10 feet and more than 20 feet.
These anomalies probably reflect local paleotopographic
features of the coastal area. The areas of thin total coal
may have been areas of a few feet of local relief, and the
thicker coal patches may represent local depressions.

Northeastward from the belt of thin total coal, the
coal thickness increases steadily across the basin for
the next 20 miles. The cumulative coal thickness reaches
a maximum of more than 70 feet in a northwest—trending
band near the central part of the basin (fig. 21). The
northeast limits of this thick buildup are defined by the
trend of the northeasternmost and largest of the two
principal stratigraphic rises of the Pictured Cliffs Sand-
stone. This rise extends generally along a line from T.
25 N., R. 1 W., in New Mexico through T. 34 N., Rs. 9
and 10 W., in Colorado. In the southeast, the extensive
swamps of this zone appear to have ended near the base
of a well-drained highland. The uplift which caused the
highland was probably centered near the area of the
present Nacimiento Mountains, but some uplift at the
time may have occurred along the monocline which
forms the east rim of the San Juan Basin. Slight uplift

53

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

COAL
107°
mew m 14 6 5 4 3 2 [ Raw; R1E
I T36N
19 11+
/25‘
MONTEKZUMAI -20 ffim AchULErA 35
l l '
L L, / e . _~ <23“ :2 . L L.
50% I\ 27 34
5. \ M
54 16
33
/J \J \ ’3‘, 4%
I O
49 | \ W” 32
37o__62w2<>_f.__ .14 __

 

NEW MEXICO ’

 

 

 

 

 

Outcrop of Fruitland \ 0 .

Formation and 32 . \ 31 .38 %\ .65 33. m

Kurtland Shale 17 20 . . \ .65 \ 330 x 31
W \ .. 7

RIGW

 

 

 

 

30

 

 

 

 

 

29

 

 

 

 

 

 

 

 

 

 

   
   

 

 

n 8““ .
11': '24-:524E-H
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13-

 

 

 

 

 

 

 

 

 

 

 

 

EXPLANATION

 

 

 

 

 

)(
39‘ ‘12 .
Measured surface sectlons

 

 

 

 

4
0
Well control location
Numbers represent aggregate coal thick-
ness, in feet, at each location

 

 

 

 

 

 

 

 

 

 

 

 

Isopachous interval: 1 0 feet

/

 

 

0 5 10 15 20 MILES
L|_|_u_l—l_l—I

FIGURE 21.-—Isopach map of total thickness of coal in the Fruitland Formation.

54: GEOLOGY AND FUEL RESOURCES, FRUITLAND FORMATION AND KIRTLAND SHALE, SAN JUAN BASIN

along the monocline during Fruitland deposition explains
the abrupt southeastward termination of the thick coal
deposits and the absence of significant Fruitland coal
beds in a narrow strip along the east side of the basin
(fig. 21).

After the prolonged oscillation of the strand line,
which caused the buildup of the Fruitland Formation’s
most extensive thick coal beds, the sea again receded
northeastward. Withdrawal was intermittent, and a
second area 'of coal totaling more than 50 feet in cumula-
tive thickness developed in the Colorado part of the
basin while thicknesses of less than 50 feet were ac-
cumulating in the New Mexico part. As the receding
shoreline approached the northeast limits of the present
basin, its rate of withdrawal accelerated. The total coal
thicknesses decrease abruptly in the extreme north-
eastern part of the basin, as exemplified by the cumula—
tive 4 feet of coal in the Klutter Mountain outlier in
T. 33 N., R. 1 W., in Colorado.

In summary, the coal in the Fruitland Formation is
distributed in a series of northwest-trending belts
across the San Juan Basin. The thicker coal zones are
adjacent to and southwest of stratigraphic rises in the
position of the Pictured Cliffs Sandstone. Along the
east edge of the basin, uplift prevented the accumula-
tion and preservation of the organic debris necessary
for coal formation, and a band from 2 to 10 miles wide
is barren of significant coal beds. To the north and
northwest, the coals are truncated by the present
erosion surface along the monocline that bounds the
San Juan structural basin. To the south and southwest,
thinning of the Lewis Shale indicates that within a
few miles of the present outcrop the beds of the Fruit-
land Formation formerly merged with the coal measures
of the Menefee Formation of the Mesaverde Group.
The intervening Lewis Shale wedged out, and the
Pictured Cliffs Sandstone merged with the Cliff House
Sandstone of the Mesaverde Group before in turn
wedging out into combined Menefee and Fruitland
rocks.

Figure 22 is an isopach map that records at each
control location the thickest individual coal beds that
contain no partings in excess of 3 feet thick. This map,
in general, reflects the pattern of the total coal thickness
map (fig. 21). The areas of thickest total coal deposition
generally contain the thickest individual beds. It must
be emphasized that the measurements recorded on this
map are not necessarily of the same or correlative coal
beds; they represent the particular bed that reaches
the maximum thickness at the point of measurement.
Although the thickest beds may be continuous between
two or three control points, they ultimately split, thin,
or pinch out, and other beds thicken or merge and
become dominant. Many of the local variations on this

 

map are due to the separation of beds beyond the
arbitrary 3-foot limit on partings. This is unavoidable
because any other choice of limit on included parting
thickness would give similar results.

Areas of thick total coal generally contain several
thick beds in two or more major zones and a few thin,
scattered beds. The thickest beds are usually in the
lowest zone near the bottom of the formation, but in
some places beds in higher zones are dominant. In most
areas of thin total coal, only a single major bed or zone
is present, and it is nearly always in the lowest part of
the formation and in most places lies directly above the
Pictured Cliffs Sandstone. In such areas the regression
of the sea was relatively rapid, and the encroachment
of the flood-plain environment followed swiftly. The
details of the vertical distribution of the coal beds are
described in the next section.

CORRELATION

Because of environmental variations which controlled
deposition and preservation, individual Fruitland coal
beds are extremely lenticular, and reliable correlations
can be made only by direct tracing along the outcrop
or by evaluation of data from closely spaced drill holes.
Efforts at surface tracing have been generally unsatis-
factory in most areas owing to cover, burning of the
beds, or complex stratigraphic intertonguing. Along
the northwest edge of the basin, Barnes, Baltz, and
Hayes (1954) found that

Individual beds of coal are lenticular and cannot be followed in
the Red Mesa area for more than 2 or 3 miles, but the basal coal
sequence as a whole is fairly continuous, except where it pinches
out against intertonguing beds of the Pictured Cliffs sandstone.

In the Durango area, Zapp (1949) reported,

It was found, however, that the thick growth of vegetation over
most of the area makes visual tracing of coal beds or associated
nonmarine strata impossible, and natural and artificial exposures
are too few to permit interpolation. * * * It appears probable
that core drilling with spacing of not more than half a mile will be
necessary to establish the position of all the coal beds of com-
mercial importance.

Zapp further stated:

The Fruitland formation at most places contains at least three
coal zones, with the thickest zone in the lower 100 feet of the
formation and usually at or near the base. The ”Carbonero” bed
near Carbon Junction south of Durango consists of about 80 feet
of thin coal beds separated by numerous thin partings and is the
thickest coal deposit thus far reported in the San Juan Basin.
Beginning about a quarter of a mile northeast of Carbon J unc-
tion, this bed is split into two widely separated thinner beds by a
tongue of the Pictured Cliffs sandstone. To the southwest it thins
as various portions of the bed are replaced by nonmarine sand-
stone and shale of the Fruitland formation.

In his graphic section of the coal at Carbon Junction,
Zapp showed a 1-foot-thick bed of bony coal on top of
the Pictured Cliffs Sandstone, overlain by about 3 feet
of sandy shale and 33 feet of coal containing many thin

COAL 55

 

 

 

 

 

 

 

 

 

 

 

 

 

 
 

 

 

 

 

 

 

 

 

 

    
  
 
 
 
  
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
 

 

 

 

 

 

 

 

 

 

 

     
 

 

 

 

  

 

 

108° 107°
R16 15 14 13 12 /11 10 g 9 I 8 7 6 5 4 3 2 J RIWl‘RlE
/
1/ L A ‘ P L AT A 1 T 36 N
i 5 16 11 13 11 12
/ Dnremg‘oO 18
MONTEIZUMA / Lfiif 1\18 ARCHULETA 35
1 1 , \ . 1 .
L. / _ m K
x 27 '
g /' .....
i, 15
/ 28 I o
I I 09 ‘ V
25» . \ 29 4 '33
37o__09¥23§29. ..__._.._.27 -10 25.16.. 30
NEW MEXICO 13 , v 12 F- 11 10- 139
32 25 . ‘2

Outcrop of Fruitland 25:

Formation and 17 \ / g 16 6

Kirtland Shale 11 11 o o .1

.. V' .- A7 7 l o 21
R 16w 15- _8'14' 1 , /'12 ‘ ' .11
EXPLANATION _
‘9‘ .8 1)‘ Lgba 0 21
36° —~ Measured surface sections — __._
.18
Well control location 0 20
Numbers represent the thickness, in feet, ‘of '

the thickest single coal unit at each lo- of this

cation (no parting more than 3ft thick); ”9°" ’9

Thickness does not include partings

1 1

 

 

 

 

 

 

 

 

 

 

 

 

O 5 10 15 20 MILES
L1_|_|_|_|_J___..__L____l

FIGURE 22.—Isopach map of the thickest individual coal units (no parting in excess of 3 ft thick) in the Fruitland Formation.

56 GEOLOGY AND FUEL RESOURCES, FRUITLAND FORMATION AND KIRTLAND SHALE, SAN JUAN BASIN

partings. About 5 feet of siltstone and sandstone overlie
the 33-foot bed and separate it from an overlying coal
bed about 40 feet thick. The number and thickness of
partings in the 40-foot bed were not shown. Zapp
showed an additional 5 feet of coal that contained two
6—inch partings approximately 150 feet above the 40-
foot bed. The total coal thickness at Carbon Junction
is, thus, about 78 feet if the basal 1-foot bed of bony
coal and the thin partings are disregarded. This is the
thickest total coal section reported in the basin (N 0. 12
on pl. 3). The next thickest sections were recorded at
coal control locations No. 18, T. 33 N., R. 11 W., 0010.,
and No. 109, T. 29 N., R. 7 W., N. Mex. (pl. 3). At
location 18, 76 feet of coal is present in two major zones
and in three other separate beds. At location 109, 76
feet of coal is distributed among several beds in three
major zones. At the Carbon Junction location, 73 feet
of coal that contains a 5—foot parting near the middle
is in one major unit. No occurrence comparable to this
coal unit was found in any other part of the basin. The
abrupt lateral facies change of the basin’s thickest coal
bed as described by Zapp illustrates the diflciculties
encountered in attempted correlations of individual
beds in the Fruitland Formation.

Barnes (1953), reporting on the Fruitland coals of
the Ignacio area of Colorado, stated: “Few individual
coal beds have been correlated between measured
sections because of the uncertainties caused by the
lenticularity of the strata of the Fruitland formation
and the scarcity of expOsures.” He did, however,
correlate one 13-foot coal bed for 2% miles. In their
study of southern Archuleta County, 0010., in the
extreme northeastern part of the basin, Wood, Kelley,
and MacAlpin (1948) did not map or correlate coal beds.

In the Barker Dome—Fruitland area of New Mexico
on the northwest edge of the basin, Hayes and Zapp
(1955) indicated that one coal bed is correlative for
more than 15 miles, although midway in its course it
crosses one of four significant stratigraphic rises of the
Pictured Cliffs Sandstone that they mapped in this
area. This particular rise on their coal sections dis-
places the Pictured Cliffs Sandstone approximately
100 feet upward in the section. They found that in the
area covered by their map, “The Fruitland formation
contains at least 16 coal beds with thicknesses of 30
inches or more, though not more than 4 beds are
present at any one locality.” Bauer and Reeside (1921)
had apparently traced the main bed of Hayes and
Zapp in their study of the coal in San Juan County,
N. Mex. Although they were able to trace this and
other beds for some miles in the northern part of San
Juan County, they recognized that “extensive correla—
tions are doubtful south of the San Juan [River]. In
the extreme southern part of the field the coal beds

 

decrease in number, thickness, and extent * * *.” This
statement qualifies their maps, which show numerous
isolated coal outcrops connected by dashed lines,
whereas many others extend for only a short distance.
It is noted, however, that the beds studied by Bauer
and Reeside crop out over a large area nearly parallel
to the northwest depositional trend of the coal zones,
and thus correlation should be more reliable than in
areas where the present outcrop crosses the depositional
trend, as is the case in the northern part of the basin in
Colorado.

Dane (1936) commented on the excessive lenticularity
of the coal in the southern and southeastern parts of
the basin. In the extreme southeast corner of the basin,
Fassett (1966) traced a 4-foot-thick coal bed for more
than 4 miles around Mesa Portales. The bed pinches
out in sec. 35, T. 20 N., R. 2 W., and, except for a 1.5-
foot—thick coal bed which crops out near the center of
sec. 20, T. 24 N., R. 1 E., is the last known occurrence
of outcropping coal in the Fruitland Formation along
the east side of the basin between this point and T. 31
N., R. 1 W.

The present study of F ruitland coal beds was done
mainly through the use of logs from drill holes spaced
from 2 to more than 6 miles apart throughout the area
of the San Juan Basin. The same stratigraphic condi—
tions found on the outcrop by previous writers were
found throughout the basin in the subsurface. Correla—
tion of coal beds at angles to the generally northwest
trend of deposition is complicated because the beds
wedge out abruptly northeastward against intertonguing
sandstones of the Pictured Clifl's Sandstone; correlation
to the southwest is difficult because the beds are first
split by and then grade into nonmarine sandstone and
shale, which was deposited behind and along the trailing
edge of the Fruitland swamps. These transitions gen-
erally take place within a distance of only a few miles.
Correlation of the coal beds in a northwest direction is
more reliable because this is the trend of the elongate
axis of the coal bodies and the beds retain their identity
farther in this direction. Between widely spaced control
points, however, correlation along the northwest
trend has proved only slightly more feasible than corre-
lation at angles to it. Some of the variables that disrupt
the continuity of the coal beds along their depositional
trend are: (1) Channel sandstone deposits and associ—
ated stream deposits filled the channels of the streams
which flowed across the coal swamps to the coast.
Some streams were contemporaneous with adjacent
swamps, and the coal beds thin toward the channels by
lateral facies change. The horizontal separation of time-
equivalent coal beds adjacent to such channels may be
several thousand feet. Other streams eroded previously
deposited material, and the channel filling causes a

COAL 57

disruption of only a few hundred feet in the lateral
continuity of the coal. (2) Scattered areas among the
swamps that had a few feet of topographic relief were
apparently above the swamp water level and were too
well drained to allow preservation of organic material.
These may have been localities of buried beach dunes
or bars or the preserved levees and bars of abandoned
stream channels. The coal beds thin and split over these
areas or terminate on their flanks. (3) At other places
among the coastal swamps, fine clastics filled lakes and
lagoons. Such areas may be reflected in the present
sediments where coal beds disappear laterally into a
sequence of carbonaceous mudstone and shale. (4) The
environment of the flood plain extended irregularly far
into the swamplands, causing wide gaps in the continu-
ity of some of the coal beds, particularly those above
the basal part of the formation. (5) Irregularities of the
shoreline probably caused indentations along the
seaward edge of the swamp zone. (6) Differential
compaction of sediments during diagenesis has probably
caused some contemporaneous coal beds to occupy
different stratigraphic positions, whereas beds of differ-
ent ages may lie in the same stratigraphic plane.

Correlation of Fruitland coal beds by comparing their
stratigraphic position is subject to considerable error.
This is shown by comparison of coal sections 109—118
(pl. 3). Sections 109 and 118 are 26 miles apart in an
east-west direction. The graphic columns show that
sections 109—118 each contain a thick coal unit that
rests directly on the Pictured Cliffs Sandstone. By
comparison of stratigraphic position, these coals would
seem correlative. However, examination of figure 7
shows that the stratigraphic position of the coal at
section 118 is at least 300 feet higher than the coal at
section 109 owing to upward stratigraphic migration of
the Pictured Cliffs. Thus, some or none of the basal
coals shown in the graphic illustrations between sec-
tions 109 and 118 may be correlative between adjacent
locations, but such correlation is not certain and if
attempted over distances of more than a few miles is
impossible.

In summary, the band of coastal swamps was gen—
erally continuous along the Late Cretaceous shoreline,
but individual swamps were limited in area and sep—
arated from one another by the paleogeographic features
described above. These features shifted laterally through
time, causing the coal swamps to migrate over all parts
of the coastal area. The result was an averaging of the
total amount of coal deposited in belts or zones parallel-
ing the shore so that the total coal thickness was due
to the oscillations of the shoreline rather than to the
transitory environments of the swampland. The Fruit-
land coal deposits as a whole form a decipherable pat-
tern, but few individual coal beds are traceable at the

 

surface or in the subsurface for more than a few miles.
Dependable correlation of the coal beds requires control
spacing of not more than 1 or 2 miles and even less
spacing in areas of very abrupt facies change. Because
of the spacing of control points used in this study,
individual coal beds have not been correlated. The
reader may make tentative correlations from the graphic
columns on plate 3, but he is cautioned that such corre-
lations can be only suggestive. If he chooses to correlate
zones, rather than beds, he is reminded that, although
a thick coal zone generally lies above the Pictured Cliffs
Sandstone, the age and stratigraphic position of the
Pictured Cliffs change progressively across the basin.

CHARACTER AND QUALITY

The physical properties of Fruitland coal have been
described in numerous reports. In summary, the coal is
hard, brittle, and black; it decomposes, or slacks, on
exposure to weather and cannot be stored for long pe-
riods. It contains, in places, many woody charcoal frag—
ments and small lumps of fossil resin. Iron sulfide, in the
form of small grains and veinlets of pyrite and marcasite
(F682), has been observed by the authors in many well
cuttings and cores.

Table 4 shows analyses of 67 samples of Fruitland
coal taken from 65 locations in the San Juan Basin. The
locations are shown and numbered in figure 23. Loca—
tions 19, 59, and 61 are coal core holes; locations 62
through 65 are surface outcrops; the remainder are well
locations. An attempt was made to sample the lowest
coal bed or zone at each location. Two separate zones
were sampled at locations 14 and 23. At outcrop loca-
tions (62-65) only one bed more than 1 foot thick is
present.

The samples from the well locations were obtained
by collecting rotary—drill cuttings from shale shakers
as the cuttings from coal zones were discharged from
the borehole. After collection, the cuttings were
thoroughly mixed to insure representative sampling
and then were washed at the well site to remove drill-
ing mud. The samples were dried by a cool forced-air
current and floated in carbon tetrachloride (specific
gravity 1.59) to remove rock cuttings and cavings
picked up by the sample in the mud column during
circulation (the specific gravity of coal ranges generally
from 1.2 to 1.5). Any shale or sand partings and car—
bonaceous material with a specific gravity greater than
1.59 were removed through flotation. The lighter
fraction from the floating process was sent to the US.
Bureau of Mines laboratory at Pittsburgh, Pa., for
analysis. The resultant Btu values are maximum
figures for the heating values of the coals sampled.
With the exception of the sample from location 59,
the samples from the coal core holes and outcrops were

58

GEOLOGY AND FUEL RESOURCES, FRUITLAND FORMATION AND KIRTLAND SHALE, SAN JUAN BASIN

TABLE 4.——Analyses of coal samples from the Fruitland Formation

[Form 0! analysis: A, as received; B, moisture tree; C, moisture and ash free]

 

 

 

 

 

 

 

 

 

Sampled U.S. Location Approximate Form Proximate Heating
location Bureau Well or other source ———.———— depth interval oi anal- value Remarks
in fig. 23 Mines Section T.N. R.W. of sample (it.) ysis Mois- Volatile Fixed (Btu)
lab. No. ture matter carbon Ash Sulfur
Colorado
1 H—38041... El Paso Nat. Gas ......... 36 ......... 34 10 2,406—2,438..... A 20. 8 51. 7 26. 6 0 8 11, 230
Bondad 34-10 No. 3X. B 21. 0 52.2 26. 8 8 11, 330
C 28. 7 71. 3 ________ l 1 15, 480
2 H—55350... Mobil Oil ................. NE% 5. .. 32 7 2,656—2,669 _____ A 21.5 56. 4 21.3 7 12, 140
Schofield Auto 31X—5. B . . 21. 6 56. 9 21. 5 7 12, 240
C ........ 27. 6 72. 4 ........ 8 ,
3 H—46452. .. Atlantic Rein ............. NE% 15.. . 32 10 2,825—2,890 ..... A 2. 3 23. 6 54. 6 19. 5 7 12, 070
Southern Ute 32-10 B ________ 24. 2 55. 9 19. 9 7 12, 360
No. 15—1. C ........ 30. 2 69. 8 ........ 9 15, 440
New Mexico
4 H—33642. ._ La Plate. Gathering ....... SE% 27. . . 32 6 2,811—2,830..._ . A 1. 1 20. 6 50. 6 27. 7 0. 6 11, 020
San Juan Unit 32-50 B ........ 20. 8 51. 2 28. 0 . 6 11, 130
No. 2—27 C ........ 28. 9 71. 1 ________ . 9 15, 470
5 H—55381... Delhi-Taylor .............. NE% 24..- 32 10 3.3703400 _____ A 1. 5 24. 4 44. 9 29. 2 . 7 10, 690
Wickens N o. 1. B ........ 24. 8 45. 5 29. 7 . 7 10, 860
C ........ 35. 3 64. 7 ________ l. 0 15, 440
6 H—16696... El Paso Nat. Gas ......... SW% 5. _ . . 31 5 3,124—3,l36 _____ A 1. 6 23. 5 50.0 24. 9 .7 11, 550
Rosa Unit No. 41. B ________ 23. 8 50. 9 25. 3 . 7 11, 740
C ........ 31. 9 68.1 ........ l. 0 15, 720
7 H—50012. . . Delhi-Taylor .............. SW% 20. . . 31 9 3, 230-3, 255. . . . A 1.3 33. 7 49. 2 15.8 . 7 12, 830
Barrett No. 1. B ........ 34.1 49. 9 16.0 .7 13, 000
C ........ 40. 6 59. 4 ________ . 9 15, 470
8 H—15777. . . El Paso Nat. Gas ......... SW% 8. . _ . 31 11 2, 710—2, 740... _ A 1. 7 40. 3 47. 0 ll. 0 .7 3, 350
Case No. 9. B ........ 41. 0 47. 9 11.1 . 7 13, 580
C ........ 46. 1 53. 9 ________ . 8 15, 280
9 131—19884. .. Consolidated Oil dz Gas. . . SW% 5. . . . 31 12 2, 215—3, 000. ._ . A 2. 4 39. 4 47. 3 10 9 . 5 13, 090
Mitchell No. 1-5. B ________ 40. 4 48. 5 11. 1 . 5 13, 410
C ________ 45. 5 54. 5 ........ .6 15, 100
10 H—1514l... Consolidated 0116: Gas... NE% 11... 31 13 1,776-l,782__.. A 2.3 37.9 43. 6 16. 2 1. 3 12,040
Freeman No. 1—11. B ........ 38. 8 44. 7 16. 5 1. 3 12, 320
C ........ 46. 5 53. 5 ........ L6 14, 760
11 H—15142.._ El Paso Nat. Gas ......... NE% 10... 30 6 3,100—3,105-... A 1.5 24.1 49.4 25.0 .7 11,310
S.J.U. 30-6 No.37. B ........ 24. 5 50.1 25. 4 . 7 11, 480
‘ C ........ 32. 8 67. 2 ........ . 9 15, 380
12 H-50079 Delhi-Taylor .............. NE% 5.... 30 8 2, 800-3, 028... . A 1. 7 32. 6 41. 4 24. 3 1. 8 11, 250
Moore No. 6. B ........ 33. 2 42. 1 24.7 1. 8 11, 440
C ........ 44. 0 56. 0 ........ 2. 4 15, 190
13 H—35925.. . El Paso Nat. Gas ......... SE34 28. . _ 30 9 2, 385—2, 390... . A 1. 5 39. 9 45. 5 13.1 2. 2 12, 960
Turner No. 3. B ........ 40. 5 46. 2 13. 3 2. 2 13, 150
C ........ 46. 7 53. 3 ........ 2. 5 15, 170
14(a) H-19882. . . El Paso Nat. Gas ......... SW14 29. . _ 30 10 2, 340-2, 360.. .. A 2. 3 33. 1 39. 9 24. 7 . 7 0, 800 Uppermost of two
Ludwick No. 20. B ........ 33. 9 40. 9 25. 2 . 7 11,060 samples from
C ........ 45. 3 54. 7 ........ . 9 14, 790 this location.
14(b) 211-19883 ........ do .................... SW% 29... 30 10 2, 505—2, 515.... A 2. 6 41. 7 44. 5 11. 2 .6 13, 080 Lowermost 01 two
B ........ 42. 9 45. 6 11. 5 . 6 13, 420 samples from
C ........ 48. 4 51. 6 ........ . 7 15, 160 this location.
15 H—13062. _ . Aztec Oil 6: Gas .......... NE% 7.... 30 11 2, 020-2, 030... . A 1. 4 37. 2 44.1 17 3 . 6 12, 010
Ruby Jones No. 1. B ........ 37.7 44. 8 17 5 .6 12, 180
C ........ 45. 7 54. 3 ........ . 7 14, 770
16 211-15140. . . Southwest Production ..... NE% 22.. . 30 12 1, 713—1, 742. . . _ A 2. 2 38. 8 45. 3 13. 7 . 6 12,370
Sullivan No. 1. B ........ 39. 7 48. 3 14. 0 . 6 12. 640
C ........ 46. 1 53. 9 ........ . 7 14, 700
17 H—16308. . . R&G Drilling ............. NWM 18... 30 13 1, 425—1, 440. . . . A 2. 8 40. 4 44. 7 12.1 .6 12,390
Lunt No. 62. B ........ 41. 6 45. 9 12. 5 . 6 12, 750
C ........ 47. 5 52. 5 ........ . 7 14, 570
18 H-19399. . . Com ass Exploration ..... NE% 31.. . 30 13 1, 070—1, 080. _. . A 5. 7 38. 8 43.0 12. 5 .6 11,840
Fe eral No. 1—31A. B ........ 41. 2 45. 5 l3. 3 . 6 12, 540
C ........ 47. 4 52. 6 ........ . 7 14, 460
19 H—78945. _ . N.M.P.S.C.C ............. 21 ......... 30 15 69-70 .......... A 5. 6 39.7 43.3 11. 4 .7 11,850 Sample from 0081
Core Hole No. 7. B ________ 42.0 46. 0 12.0 .7 12,540 core—not floated
C ........ 47.8 52. 2 ........ .8 14,260 in 0014. A is air-
dried analysis.
20 H—18102. .. El Paso Nat. Gas .......... NE% 5.. . . 29 5 3, 175—3, 200. . _ _ A 2. 2 29. 3 44.8 23.7 .8 11, 460
SJ. U. 29—5 No.17. B ........ 30.0 45.8 24. 2 .8 11,720
0 ........ 39. 5 60. 5 ........ 1. 1 15, 470
21 H—7560. . . . El Paso Nat. Gas __________ SW% 9. _ _ . 29 6 3, 575-3, 580. . . . A 1. 2 27. 7 42. 6 28. 5 . 6 10, 780
S.J.U. 29-6 N0. 66. B ........ 28. 0 43. 1 28. 9 . 6 10, 910
C ........ 39. 4 60. 6 ........ . 8 15, 330
22 H—16310_ . _ Aztec Oil& Gas ........... SW‘A 30. . . 29 9 1, 985—2, 005. . _ . A 1.6 41.1 46. 6 10 7 .7 13, 310
Cain No. 16—D. B ........ 41. 7 47. 5 10 8 . 7 13, 520
C ........ 46. 8 53. 2 ........ . 7 15, 160
23(a) H—27541. .. Aztec Oi] & Gas ........... SW34 5. . . . 29 10 2, 065—2, 080. . . _ A 2. 3 39. 1 42. 1 16. 5 1. 9 12, 020 Uppermost 0f two
Grenier “B” No. 3. B ........ 40. 0 43. 1 16. 9 2. 0 12. 300 sam les from
C 48.1 51. 9 ........ 2. 4 14,800 this ocation.
23(b) H-27540 ........ do _____________________ SW% 5. . . . 29 10 2, 150-2, 160. . . . A 40. 6 . . . 5 13, 300 Lowermost of tWO
B 41.4 . 5 13, 560 sam les from
C 46. 0 . 6 15, 070 this ocation.
24 H-l3060. _ . Tidewater ................. SE% 12.... 29 11 2, 065-2, 070. . . . A 38. 7 . 6 12,830
N.M.-Fed.No.12—E. B 39. 5 .6 13, 100
C 44. 7 . 7 14, 820
25 H—3028... _ International Oil .......... NW% 9. . . 29 11 1,905—1,910_ _ _ . A 39. 9 . 7 12, 360
Fogelson No. 1—9. B 40. 6 . 7 12, 590
C 47. 6 . 8 14, 750
26 H—3030.... Tennessee 011 & Gas ...... NW% 10. . 29 12 1,740—1,750. _ _. A 40.0 . 5 12,340
Cornell Gas Unit A B 40. 9 . 5 12, 600
No. 1. C 47.2 .6 14, 560

   

COAL

TABLE 4.—Analyses of coal samples from the Fruitland Formation—Continued

[Form of analysis: A, as received; B, moisture free; 0, moisture and ash tree]

59

 

 

 

 

 

 
   

 

Sampled U.S. Location Approximate Form Proximate Heating
location Bureau Well or other source —————— depth interval of anal— value Remarks
in fig. 23 Mines Section T.N. R.W. of sample (it.) ysls Mois- Volatile Fixed (Btu)
lab. No. ture matter carbon Ash Sulfur
New Mexico—Continued
27 H-8360.... Aztec 011 & Gas .......... SW% 20... 29 13 1,125—1,140. . _. A 5 6 39.0 41. 3 14 l 0.6 11, 580
Hagood No. 21-0. B ________ 41. 3 43.8 14 9 . 6 12, 260
C ________ 48. 5 51. 5 ________ . 7 14, 420
28 H-4052.... Aztec Oil & Gas .......... SE54 34... 29 13 1,635-1,640. . .. A 3 5 39. 6 43.2 13 7 . 5 11, 910
Hagood No. 13—G. B ........ 41.0 44.8 14 2 . 6 12, 330
C ________ 47. 8 52. 2 ........ . 6 14,370
29 H-4051.... Humble 0116: Gas ........ SE% 36... 29 14 1,490—1,495. . .. A 4 1 40. 0 40. 6 15. 3 .7 11,600
Humble No. L—9. B ________ 41. 7 42.3 16. 0 . 7 12, 100
C ........ 49 7 50. 3 ........ . 9 14,400
30 H-3855.... El Paso Nat. Gas ......... NE% 19. . 28 4 4,115—4,120. . .. A 1 6 31 1 43.7 23. 6 . 7 11, 580
S.J.U. 28—4 No.28. B ________ 31 6 44.4 24.0 . 7 11, 770
C ........ 41 6 58.4 ........ . 9 15,480
31 H—7224.... El Paso Nat. Gas ......... SW% 28... 28 5 3,323—3,345. . .. A 2 6 31. 6 39.0 26 8 .6 10, 640
S.J.U. 28-5' No. 50. B ........ 32. 5 40.0 27 5 . 6 10, 920
C ........ 44. 8 55. 2 ........ . 9 15, 070
32 H-13779. . . El Paso Nat. Gas ......... NE% 30. _ 28 8 2,185—2,195_ _ . . A 1. 9 33. 7 35.1 29.3 . 6 10, 270
Florence No. 10-C. B ........ 34. 3 35.8 29.9 . 7 10,460
C ........ 48. 9 51.1 ........ . 9 14, 920
33 H—1306l. .. Aztec Oil & Gas .......... SW% 17. .. 28 9 1, 985—1, 990. .. . A 1. 4 36.1 42.1 20. 4 . 8 11, 670
Reid N0. 23-D. B ________ 36. 6 42. 7 20. 7 . 8 11, 830
C ........ 46. 2 53. 8 ........ 1. 0 14, 920
34 H-5472. . . . Aztec Oil dz Gas .......... NW% 16. . 28 10 1, 842—1, 853. .. . A 1. 6 38. 4 40. 7 19. 3 . 6 11,760
Caine No. 13. B ........ 39.0 41. 4 19. 6 . 6 11,950
C ........ 48. 5 51.5 ........ .8 14, S70
35 H-12704. .. Rediern & Herd .......... SW% 10. . 28 11 1, 490—1, 500. _ .. A 2. l 39. 8 43. 4 14. 7 . 6 12,190
Redern dz Herd No. 5. B ........ 40. 7 44. 3 15.0 .6 12,460
C ........ 47. 9 52. 1 ........ . 7 14,670
36 H-24567. . . Sunray Mid-Continent. . _ . NW% 18. . 28 12 1, 305—1, 315. _ . . A 3. 0 38. 9 44.4 13. 7 . 6 12, 010
Gallegos No. 122. B ........ 40. 1 45. 8 14. 1 .6 12, 390
c ........ 46.8 53.2 ........ . 7 14, 430
37 H—7225.... Pan AmeriCan ............ NW% 16.. 28 13 1, 705—1, 715 ._. A 4. l 39. 4 42. 8 13. 7 .6 11,740
Holder N0. 7. B ........ 41. 1 44.6 14. 3 . 6 12, 240
C ........ 47. 9 52. 1 ........ . 7 14, 290
38 H-18101... El Paso Nat. Gas ......... SW% 32. . 27 4 3, 935-3, 945.... A 2. 2 33. 9 37. 9 26. 0 . 7 10, 780
S.J.U. 27—4 No. 30. B ........ 34. 6 38. 8 26.6 .7 11,010
0 47. 2 . .9 15,020
39 H—33317... E Paso Nat. Gas ......... SE% 23.. . 27 5 3, 250-3, 260 . .. A 34. 4 . 8 11, 080
S.J.U. 27—5 No.74. B 35. 6 . 9 11, 440
C 46. 6 1. 1 15, 010
40 H—33643... El Paso Nat. Gas .......... SW% 21... 27 6 3,165—3,180._.. A 39. 3 .9 , 690
Rlnmn Unit No. 171. B 39.8 .9 12,870
0 46. 9 1.1 15, 150
41 H—35788. .. El Paso Nat. Gas ......... SE34 13. .. 27 7 3,130—3, 140.. .. A 32. 9 .8 9, 900
Rincon Unit No. 177. B 33. 7 .8 10,130
C 48. 9 1. 2 14, 720
42 H—21490. . . El Paso Nat. Gas ......... NE% 8. . . 27 8 2, 800—2, 820. ... A 29. 5 .6 9,170
Schwerdtieger No. 20—14. B 30. 0 .6 9, 350
C 47. 2 1. 0 14,700
43 H—12705. . . Aztec Oil dz Gas .......... SW34 8. _ . _ 27 9 2, 215-2, 230. . . . A 36. 7 .8 11, 440
Whitley No. 6—D. B 37.5 . 8 11,700
0 ........ 47. 1 1. 1 14,700
44 H—13063... Aztec Oil & Gas. ......... NW% 29. . 27 9 2,135—2, 145.... A 2. 7 38.3 .8 11, 650
Hudson No. 5—D. B ........ 39. 3 .8 11,970
C ........ 48. 6 1.0 14,800
45 H~15776. ._ Aztec Oil & Gas .......... SW% 12. .. 27 10 1, 900—1, 905. . _ _ A 2. 2 40. 4 .6 12,520
Hanks No. 14—D. B ........ 41.3 . 6 12,790
C ........ 47. 9 .7 14,820
46 H-5021.... British-American Oil. . N E54 14. . 27 11 1, 920-1, 930.... A 3. 3 40. 8 .6 12,370
Fullerton No. 8 B ........ 42.2 .6 12,790
C 48. 1 .7 14,600
47 H—3031.... Southwest Production. . .. NE% 26... 27 12 1, 900-l,910.... A 41.2 .6 11,810
Cambell No.2. B 42.3 .6 12,120
C 50. 4 .7 14,440
48 H—36175. . . Royal Development ...... SW54 6. . . _ 27 13 1, 214—1, 245. . .. A 39. 7 .7 11, 970
030 Amarillo No. 2. B 41.4 .7 ,
C 47.0 .8 14,190
49 H—32698. . . Caulkins Oil .............. NE% 2. . . 26 6 3,184—3,200... . . A 38.9 . 7 12, 130
State “A” MD No. 62. B 39. 4 . 7 12,290
C 48. 4 . 9 15, 120
50 H—5020.... Kay Kimbell ............. SW% 19... 26 7 2,105—2,150...._ A 38. 1 . 6 11,760
Leiberman No. 5. B 39. 1 . 6 2, 060
C 48. 1 . 8 14, 830
51 H—12706. . . Southwest Production. . . . NE% 5. . . 26 11 1,700—1,705 ..... A 40. 6 . 7 11, 540
Ted Henderson No. 1. B 42. 1 . 7 11, 970
C 50. 8 . 8 14, 430
52 H—37832... Mcrrion & Associates ...... SW34 35... 25 6 2,455—2,465 ..... A 36. 3 . 8 10, 440
Federal No. 3—35. B 37.7 .8 10, 830 .
C 50. 5 1. 1 14, 510
53 H-16695... Century Exploration ...... SW% 21... 25 9 1,620—1,625 ..... A 31.5 .9 9, 280
Mobil-Rudman No. 2. B 32. 8 .9 9, 680
C 48. 6 1. 4 14, 310
54 1140806... Standard of Texas ......... SW% 16... 25 13 1,156—1,208 ..... A 30. 9 1.8 10,270 Abnormal mois-
State No. 1. B 34. 1 2.0 11, 340 ture content
C 41. 6 2. 5 13, 820 may be due to
inadequate
drying of sample
during prepare-
tlon process.
55 H—32405... El Paso Nat. Gas ......... NE% 22. . 24 3 3,194—3,205 ..... A 38.7 36.7 22 5 7 10,990
Lindrith No. 42. B 39. 5 37. 5 23 0 7 11,230
’ C 51 3 48. 7 ........ 1.0 14, 580

 

6O GEOLOGY AND FUEL RESOURCES, FRUITLAND FORMATION AND KIRTLAND S}IALE, SAN JUAN BASIN

TABLE 4.—Analyses of coal samples from the Fruitland Formation—Continued

[Form of analysis: A, as received; B, moisture free; 0, moisture and ash free]

 

 

 

 

 

 

 

Sampled U.S. Location Approximate Form Proximate Heating
location Bureau Well or other source ————————— depth interval of anal— value Remarks
in fig. 23 Mines Section ’1‘.N. R.W. of sample (It.) ysis Mois- Volatile Fixed (Btu)
lab. No. ture matter carbon Ash Sulfur
New Mexico—Continued
56 H—22075. . . Val Reese dl Assoc ........ NE% 31. - 24 6 2,070—2,090 ..... A 3. 6 41. 1 40. 6 14.7 0. 7 11, 840
Bobby “B” No. 2-31. B ........ 42. 6 42. 2 15.2 .7 12, 280
C ........ 50. 2 49. 8 ........ . 9 14, 480
57 11—31101-.. Val Reese dz Assoc ________ NE% 27. _ 24 7 2,140—2,150 ..... A 4. 4 40. 9 41. 2 13. 5 . 6 11,790
Lybrook No. 7-27. B ........ 42. 8 43. 1 14. l . 6 12, 340
C 49. 9 50. l ________ . 7 14, 370
58 H—5022..._ Doriman Production ______ SE% 12-.. 24 8 2,526—2,535 _____ A 35.4 33. 7 27. 0 1. 1 , 960
Nancy Fed. No. 1. B 36. 8 35.1 28.1 1.1 10,370
0 51.2 48. 8 ........ 1. 5 14,410
59 H—19885__. N.M.P.S.C.C_ ......._.... NW% 32- _ 24 13 100-112 ........ A 32.5 39.3 16. 2 .5 9, 670 Coal core crushed
DH-32-1. B 36. 9 44. 7 18. 4 . 6 10, 990 and floated in
C ________ 45. 2 54. 8 ........ .7 13,460 0014.
60 11—16309. _. Val Reese & Assoc ________ NW% 15. - 23 7 2,180—2,195 ..... A 5. 7 39. 3 40.8 14.2 . 6 11,410
Betty “B” No. 1—15. B ........ 41. 7 43. 3 15. 0 . 7 12,100
0 ........ 49. 1 50. 9 ________ . 8 14, 240
61 H—22722... N.M.P.S.C.C_.........._. SW% 3.... 23 13 42-44 .......... A 6. 7 35. 9 46. 9 10. 5 . 6 11,320 Coal core not
D —3—2. B ________ 38. 5 50. 3 11. 2 . 6 12, 140 floated in 0014.
C ........ 43. 4 56. 6 ........ . 7 13, 680
62 1—2723 ..... Fruitland outcrop ......... SW% 3... _ 19 2 Surface ....... A 5. 9 33. 6 29. 8 30. 7 . 6 7, 370 Weathered coal
B ........ 35. 7 31. 7 32. 6 . 7 7, 830 from surface
C ________ 53.0 47.0 ________ 1.0 11,620 exposure. Not
floated in 0014.
63 I—2722 .......... do .................... SE% 7. . .. 19 2 ..... do ________ A 6. 5 37.0 35.0 21. 5 . 7 8, 350 D0.
B 39. 6 37. 4 23. 0 . 7 8, 930
C 51. 4 48. 6 ........ .9 11,590
64 11—99246 ________ do .................... NE% 11. . 19 4 _____ do ________ A 36. 2 37. 1 20. 5 . 5 8, 610 Do.
B ........ 38. 6 39. 6 21.8 . 5 9, 170
C ........ 49. 3 50. 7 ________ . 6 11,730
65 I—53220. .. . Pit sample ................ SE% 9. . _ _ 19 5 ................ A 5. 8 35.8 31.0 27.4 . 6 9, 450 Sample from
B ________ 38. 1 32. 8 29. 1 . 6 10, 040 small prospect
C ________ 53. 7 46. 3 ........ . 9 14, 160 pit in Fruitland

outcrop .

 

not treated by flotation. They were prepared in the
usual prescribed manner.

The analyses show that the coal of the Fruitland
Formation is low in moisture and sulfur content. The
low moisture values recorded for these samples may be
due in part to the unavoidable drying of the samples
during the flotation process. The coal core and outcrop
samples, which were not floated in carbon tetra—
chloride, had moisture contents of about 5 or 6 percent,
whereas the floated samples normally contained about
2—4 percent moisture. The core and outcrop samples,
however, were from surficial or very shallow beds
that undoubtedly were affected to some degree by
weathering, and it is likely that their moisture contents
are abnormally high. The low range of moisture in the
well samples, taken from deeply buried and unweath-
ered beds, is probably more representative of the coal.
The question is whether surficial weathering or a
brief bath in carbon tetrachloride has the greater
effect on inherent moisture. The truly representative
moisture content of unaltered Fruitland coals probably
ranges between about 2 and 5 percent.

Analyses from mine samples in Colorado (George and
others, 1937, p. 88—91) show a moisture range in the
Fruitland coal of 25—116 percent. Of seven Fruitland
coal analyses reported, however, only two had moisture
of as much as 5 percent, and these were from samples
which were taken within a few tens of feet of the entry
of the mines (the location in the mine of one of the sam-

 

ples is given as “25 feet from outcrop” and of the other
simply as “Back of entry”). Published analyses of
Fruitland coal from mines in New Mexico show a some-
what higher range of moisture content—from about 6
percent to more than 16 percent. The coal beds in New
Mexico, however, crop out over a wider area and have
a much lower angle of dip than those in Colorado.
Consequently, they have been subjected to a greater
degree of weathering, and the moisture content of
analyzed mine samples shows the influence of perco-
lating ground water. Our data indicate that fresh, un-
weathered coal from the Fruitland Formation has a
moisture content generally between 2 and 5 percent.
The sulfur content of the coals is consistently somewhat
less than 1 percent.

The ash content of Fruitland coal is variable but
generally high in comparison with other western coals.
The ash values in table 4 and several in published
analyses of mine samples from the north and northwest
edges of the basin are plotted in figure 24. As shown in
this illustration, there are three general zones of ash
distribution in the Fruitland coals across the San Juan
Basin. An irregular area in the west-central part of the
basin contains coal that has an ash content of 8-15
percent. An intermediate zone has ash content between
15 and 20 percent except for a few localities in which it
is slightly less than 15 percent. The coal in the east half
of the basin contains ash in amounts exceeding 20 per—
cent, and four samples (three well samples and one

COAL 61

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  
    
  
 
 
   
  
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  
   
 
 
 
  
   
    
  
 
  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

   
   
  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

108" 107"
mew 15 14 13 12 j 11 1o 9 l 8 7 6 5 4 3 2 lel‘RlE
/
F L A! PLATA 1 T 36 N
I ,
// Durangoo fl , ~
MONTEQZUMA ,1 f 1\ ARCHULE’IZA 35
1 1 , 1 .
L. L / 2 _ . 12/ _ _ _ 2K L L,
‘ Y
1 I § 34
l 11,230 0 M
., ,. .
{ _, | k
/l ”*9 w 33
, <3) 2 .9.
0
121070 12140 ' M4 32
37o...02m___13§2‘l ._.. _._. - _ _...___._ r... -.. ' _. l .. _. ___. _ .., ._
NEW MEXICO 13 ,. - 11 10 g 9 8 7 @102ng 5 4 3 2' R 1 W RTE
. 4
Outcrop of Fruitland 09 8 10590 I 05 Dulce
Formation and O ) \
Kirtland Shale 131090 13 350 o7 / 11,550 K 3‘
, . ' 12,830 —' \
15 012 ’/ 11 \
R ‘6 W 16 92 010 13980 11250 f O '2
o ’ (10,800) 12,960 r. 11,310 X 30
121370 12 830 814 13° . 20 ‘
25 24 23 1 21 o
3 0 13.300 0 11,460 \
12,360 (12,020) 22 10,780 I 29
35 013,310 1 \
174012 010 12'190 10137460 <1313270 32 I 11,58 030
' ' O10,270 10,640Em31 AR R I BA 28
46 45 43 42 l
O O o 41
0 11.440 9 170 0 11 080 L
11.8100 12,370 12,520 044 1 9,900 040 , O ’27
47 51 11.650 , 12,690 39 n 38
° ' 049
11,540 50 12,130 10,780 \{6
1 11,760 ,
I
9.280 I
0 10.440 ’é5
53 1 520 l
58
o
9’960 '11 790 O55 4
, 11,840
| 57 055 10,990 I
m - _.._.._. ._ ._ 23
l
22
SANDOVAL
1
EXPLANATION 21
., 23 13,300
36 " °(12,020) - - __
Sampled location and as-received 20
Btu value of coal m
Smaller number is location number keyed '§_ Area
to analyses charts. Number in paren— Ziggy:
theses refers to uppermost of two samples 19
from locations 14 and 23
l

 

 

 

O 5 10 15 20 MILES
LJ_1_.1_L.L_____J___|___I

FIGURE 23.—-Locations of drill holes and surface sections sampled for coal analyses and as-received Btu values of the samples.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
 

 

 

 

 
  

 

 

 

 

 

 

 

    

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

62 GEOLOGY AND FUEL RESOURCES, FRUITLAN D FORMATION AND KIRTLAND SHALE, SAN JUAN BASIN
108° 107°
mew 15 14 13 12 j 11 10 9 I s 7 6 l 5 4 3 2 mw; RIE
J
F L A f P LAT A 1 T 36 N
/ Duran‘go 14'7
- 11.4
MONTE'ZUMA / 6% |\ ARCHULETA 35
I x l , l I 1 l
L L. L / - L ./ _- — L—
\ .
l1 1 " / 3“
U V. o 26.6
I 1 .5 ~ I 1 1 “\fl
[1 2 / ‘3 Q25 33
I 12.6 0‘ a-
‘1 19.5 021.3 l W« 32
37°__C91:9_13520_ “'r"-- 1.? -._. _ ._ __ .. I .. _.. __. - .. ._
NEW MEXICO 1,163.. K H l or 9 8 7 T 6 5 4 3 Z R 1 W R1 E
- . -- 13.1 29.2 . {If
Outcrop of Fruitland ' . \\ 27 7‘0 Dulce
Formation and O\ 010.9 o \ U
Kirtland Shal . ‘ . <5 0 ) 24'9 31
15.8 .1 / \
l6 w 0 {I \
R
8 3 24'3 f 25.0 ,2 30
.. 11.2 13.1 {-1 v1
0 _ 1
I o
o \
J I 28.5 23‘7 I 29
3 I \
293 R 216'8 A I? 1213168A
I30\ 6 28
35.7
o 30.5 L
\ 9 fl 23.0
o i 27
L 18.40 \ 6
18.2 f
l j l
I
I 5::
I 24.50 t
27.0 .
o 22.5 4
”75h O
O O ' 1
( 14.2 23
22
SANDOVAL
1
EXPLANATION 21
36°— 11.2 2. — — __....
(24_7)o .1 7
Sampled Mine m 20
Localities ,1...—
Number is percentage of ash content of % oAfrtehTs
coal; number in parentheses refers to report
uppermost of two samples taken at ‘9
locations 11, and 23
l A

 

 

 

 

 

 

 

 

 

 

 

 

 

 

10

15

20 MILES

FIGURE 24.—Distribution of ash in coal samples from the Fruitland Formation. Contour values in percent; interval varies.

COAL 63

outcrop sample) yielded ash in excess of 30 percent.
The zones do not follow depositional trends and are
seemingly unrelated to bed thickness, fixed-carbon to
volatile ratios, absolute (moisture and ash free) Btu
values, or relative age of the coal beds. The distribution
shows only that the east half of the basin area received
a greater amount of extraneous matter in the swamp
belt than did other areas. Analyses of the ash might
offer clues to its origin and depositional history, but
such analyses were not made for the present study.

The as-received Btu values (form of analysis A,
table 4) of the coal beds sampled are plotted in figure 23.
They range generally between 9,000 and 13,000.
Anomalously low values of 7,370 and 8,350 were deter-
mined for the weathered outcrop samples from locations
62 and 63 in the extreme southeast corner of the basin.
A few samples in the northwestern part of the basin
had as—received Btu values exceeding 13,000, the highest
being 13,350 at location 8. The distribution of the as-
received values does not reveal a specific pattern. In
general, the values are highest in the northwestern
part of the basin and lowest in the south and southeast.
The absolute heating values of Fruitland coals, which
form the definite patterns described in the following
paragraph, are obscured in the as-received analyses by
the ash content.

The Btu values from the moisture- and ash-free
analyses (form of analysis 0, table 4) are plotted in
figure 25. In contrast to the as-received values (fig. 23),
these values show a definite pattern of distribution.
Again, the outcrop samples in the southeast had low
values. Whether this is due entirely to the weathered
state of the coal or is inherent in the quality of the coal
in this area is unknown. The latter would seem probable,
because the outcrop sample from location 65 in T. 19 N.,
R. 5 W., had a near normal Btu value for Fruitland
coal for both as—received and moisture- and ash—free
analyses. Otherwise, the absolute Btu values increase
regularly across the basin from 13,460 in the southwest
to 15,720 in T. 31 N., R. 5 W. Zones characterized by
about the same values trend northwest across the basin.
They parallel almost exactly the zones of deposition
that have been discussed and are shown in figure 21.
These trends also reflect generally the present basin
structural axis and may be related in part to depth of
burial.

Two mine sample analyses (George and others,
1937, p. 88—91) indicate a reversal of the northeast
trend of increasing absolute heat values in the extreme
northeastern part of the basin and suggest a zone of
lesser values across this area.

At locations 14 and 23 in Tps. 29 and 30 N., R. 10 W.,
analyses were made of coal from two zones. At both
locations the lower coal had the highest Btu values. The

 

short—dashed line around these locations in figure 25
shows where the 15,000 moisture- and ash-free Btu line
would fall if the values from the upper coal zone were
used.

Figure 26 shows the distribution of the fixed-c’arbon
percentage of the coal from the moisture- and ash-free
analyses. This map, like the map of moisture- and ash—
free Btu values, reflects the depositional zones shown
in figure 21. In the first area of coal buildup in the south-
western part of the basin, the analyses yielded absolute
(moisture and ash free) fixed-carbon contents in excess
of 55 percent. Across the zone of thin total coal, the
fixed-carbon values range between 50 and 55 percent,
except in the area of very thin coals in the southeast
where the values are usually slightly less than 50 percent.
Northeastward, across the zones of thickest coal ac-
cumulation, the fixed-carbon percentage increases to a
maximum recorded 72.4 percent at location 2 in T. 32
N ., R. 7 W., Colorado. Two mine sample analyses
(George and others, 1937, p. 88—91) from the north
edge of the basin indicate that the fixed-carbon per-
centage, like the Btu values, declines across the north-
eastern part of the basin to slightly less than 60 percent.

Fruitland coal has generally been considered sub-
bituminous in rank in the New Mexico part of the San
Juan Basin and low-grade bituminous in Colorado. Clas-
sification of the coal in these ranks has been based largely
on the weathering tendency of the coal, bituminous
coals being relatively unaffected by exposure. In a
classification based solely on percentage of fixed carbon
and heating value on a mineral-matter-free basis, most
of the coal in the north half of the basin would range
from high-volatile to medium-volatile bituminous in
rank. Because of the known slacking tendency of the
coal in the western part of the basin and the very high
ash content of the coal in the east half of the basin, all
the F ruitland coal is considered subbituminous for the
purposes of this report. Resource calculations in a fol-
lowing section were made on the basis of the weight per
ton of subbituminous coal.

OVERBURDEN

Figure 27 shows the thickness of rock overlying the
Fruitland coal deposits. The thicknesses shown are
from the land surface to the base of the Fruitland
Formation, as measured on well logs. Owing to the
mesa-canyon topography prevalent over much of the
San Juan Basin, the depth to this datum may vary
several hundred feet within short horizontal distances.
Therefore, the isopachs on this map are average values.

The range of overburden thickness is from 0 to more
than 4,000 feet. The thickest overburden noted occurs
in sec. 13, T. 28 N., R. 5 W., New Mexico principal
meridian, New Mexico, where it is 4,478 feet thick.

64

o

37

36°

GEOLOGY AND FUEL RESOURCES, FRUITLAND FORMATION AND KIRTLAND SHALE, SAN JUAN BASIN

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

   
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

108“ 107°
mew 15 14 13 12 /n 10 i 9 E 8 7 6 i 5 4 3 2 J RIWl R1E
/
/ LA‘ PLATA 9 ,3“
i i
Durangoo flrk‘gmliwot
!
MONTEIZUMA / l 96840 |\ ARCHULETA 35
1 1 , ;r-- 1 1
L L 1/“ _ 2 W: _- ~ _. L M —~——
\ l 7 _ F’éjo K
g 7 ~ 00 l , 34
., l 15,4800\ \_2\ M
I \-?\ k
[1 \9“ *2 w 33
, l \ o ‘ 1 a.
. 15,440 \ 15,600 ' t ‘5‘ 32
“EQWQQ. . _.__ ...._..____ __ “x I _ __ .. ..._. ..
NEW MEXICO 11 10 OT 9 8 7 * 5 4 2 a R 1w R15
1 .470
Outcrop of Fruitland 15'440 l (O l 15,720 \ Dulce
Formation and O O \
Kirtland Shale 15'4") 4 31
.J/ \
O S. r/ O ‘> \
15,190 a
60‘ 15,170 [a 15,380 ‘60 2 30
‘ O O\ \‘
7'0(14,800) ' o O \ \
15,330 15470 I 29
15,160
0 l 5 O} \\ \
' 1 48
O O ,
14 920 70 A \
' 8
014320: R 556 A R R I B \ 2
o
14'700 14170 14,728 3150 o L) 27
14,800 _ 15,010 m
. .
015120 15920 \ 6
\ ‘ \ \ 1’
14$ *5 \\ \ 55
o' 00 14,510 (
14 410 ‘ O
0' \ 14,580 4
14,370 \
' 0 014,480 I
\/§ 14,240 \—. -_’
'00 n _. ,_,_ _ _ _ ._ _ 23
o\ I
.. Jfi‘ \ 1
L»,
EXPLANATION 5'
14,820 " '-
“' C)(144300) '14’510 ‘ “—77 fi\\
Sampled Mine
Localities
Number is moisture- and ash—free Btu MCKINLEY
value of coal. Number in parentheses
refers to uppermost oftwo samples
taken at locations 14 and 23
l

 

 

 

 

 

 

 

 

 

 

 

 

 

 

10 15

20 MILES

FIGURE 25.—Moisture- and ash-free Btu values of coal samples from the Fruitland Formation.

COAL I 65

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

   

 

 

 

 

  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

108° 107°
mew 15 14 13 12 j n 10 i 9 [ 8 7 6 I 5 a 3 2 I mw; FHE
l 1
/
r L A ‘ PLATA I T 36 N
// Duranlgg- flm 59 4 .
MONTEIZUMA I Fizz /r>\ ARCHULETA 35
1 . - g *
L L :7’1__/ __ __ L. L...
' \\ 3 34
I k
*3 w 33
v Q 0 ’ fl.
| New
"CQaLMQQL" _- " . - -5. 7“- I _ 1/ ___ _ ._ ._ 32
NEW MEXICO 7 s 5 4 3 2 "m“ R 1 w RT?
. \7 W711} / 4f D 1
Outcrop of Frultland 0‘ (O Q 11 ce
Formafionand .. U .
Kirtland Shale><\/ . 3-5 54-5 53.9 \R\Q / 68'1 // W. 3‘
’ 59.4 6
16 w ’ " ‘ ’ \\o\\ 5&2; 2 1/ \\
R 2. g I. ' V 5 O . O
. 54 3 51-6 53 3 56.0 \QQQ \_/ ,2 30
0647) O ‘ o\ 7 '1
524 O \ 60.6 o /" ’ ' ‘
3 o 54.0 x K 605/ \
55.3 (51.9) 9
053.2 0 / \ 29
.1 \ \
053-8 ‘ 52 | 058.4
51-5 o511 l \316' ARRIBA 28
521 529 523} 511 ‘w‘?
. o o . . . .
o O I 0 053.1 53.42D L, 27
:.j ;; 5,25 ‘_:’~ , 1‘: 51.4 i 0 052.8
.SAN'JU?N \ L 51.6 \ 5
: H. E , 51.9 \i
-\ . 2
\ ' \ 514 l ”7 _‘?_— 45
\
\

 

 

 

 

 

f
/
e

 

 

SANDOVAL

  5166 "L? 50.9 .
aw». Q «'5 go; _ - um - — ..
l

 

EXPLANATION

59.4
(51.9)0 ° 52-2

Sampled Mine

 

 

 

 

 

 

 

 

Localities
Numberis fixed-carbon percentage of coal
from moisture- and ash-free analyses.
Number in parentheses refers to upper-
most of two samples taken at locations
1.4 and 23

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

O 5 10 15 20 MILES
LL_|_1_I_I___L__|__I

FIGURE 26.——Fixed-carbon percentage of coal samples from the Fruitland Formation. Contour values in percent; interval varies.

66 GEOLOGY AND FUEL RESOURCES, FRUITLAND FORMATION AND KIRTLAND SHALE, SAN JUAN BASIN

108° 107°
11 10 9 8 RlW 'R l E

LA PLATA

     

T36N

O “\
ONTEZUMA 2000 ”000: ARCHULETA

8500

/

37. .ngagfin

NEW MEXICO
Outcrop of Fruitland

Formation and
Kirtland

RlGW

EXPLANATION

36° /‘ .

Measuret‘l/sugface sections
0 GOLD
MCKINLEY

Control points represent oil or gas fi— Are.
wells w

Contour interval is 500 feet

0 5 10 15 20 MILES
LI_I_1_J_L—I_I__J

FIGURE 27.—Isopach map showing average thickness of overburden on Fruitland Formation coal deposits.

COAL

It includes sandstone and shale of the Fruitland For-
mation, Kirtland Shale, Ojo Alamo Sandstone, Naci-
miento Formation, and San Jose Formation. In the
northern part of the basin, the Kirtland Shale and the
Animas Formation constitute the bulk of the
overburden.

The existing pattern of overburden is primarily due
to the structure of the basin combined with the present-
day topographic surface. The structural relief in the
basin is about 4,000 feet (fig. 15); the topographic
relief ranges from about 5,100 feet to slightly more
than 8,000 feet, a span of 2,900 feet. The thickest
overburden occurs where areas of higher altitude
overlie the lower parts of the structural basin.

Gently dipping beds and rolling topography along
the south and west flanks of the basin result in a band
4—6 miles wide that is underlain by Fruitland coal
beds at depths of less than 500 feet. Another band of
approximately equal width lies to the northeast where
the coal is less than 1,000 feet below the surface. Along
the north and east sides of the basin, the Fruitland
beds dip steeply basinward in monoclinal hogbacks
and are generally more than 1,000 feet below the sur-
face within 1 or 2 miles of their outcrops. For the most
part, coal is absent from the Fruitland outcrop along
the east side of the basin and lies at depths exceeding
2,000 feet where identified on well logs near the east
rim of the basin. The thickest coal zones of the Fruit-
land crop out only along the northwest flank of the
basin, where they dip abruptly to depths in excess of
2,000 feet.

RESOURCES

About 200 billion tons of coal is contained in the
Fruitland Formation between its outcrop and its
greatest depth of somewhat more than 4,000 feet. The
following estimates of these coal resources were cal-
culated with the assumption that all the coal in the
formation is of subbituminous rank and as such has an
average weight of 1,132,560 tons per square mile-foot
(1,770 tons per acre-foot). This figure is the value as-
signed as the weight of subbituminous coal in the ground
in all recent US. Geological Survey estimates of coal
reserves (Averitt, 1961).

The coal is reported in three categories of bed
thickness and six categories of overburden. The bed-
thickness categories are the standard categories used by
the Geological Survey in estimating subbituminous
resources, exceptthat the lower limit of thickness is 2
feet in this report instead of the 2% feet of the stand—
ard. This difference was made because it is usually easy
to interpret the response to Fruitland coal beds on well
logs to the nearest foot, but it is difficult and unreliable

 

67

on most logs to be specific to a 05—foot interval. Such
determinations can be made accurately with some
focused logs such as the microlog, microlaterlog, or
sonic log (Schlumberger designations), but these logs
are available for only a few wells in the San Juan Basin.
The 2-foot—thickness limit was the lower limit of most
of the beds recorded and illustrated in this study, and
only these beds are included in the resource estimates.

The six categories of overburden used in reporting
the resources are: 0—500 feet, 500—1,000 feet, 1,000—
2,000 feet, 2,000—3,000 feet, 3,000—4,000 feet, and
4,000+ feet. Standard Geological Survey resource
estimates are made to a depth of only 3,000 feet, owing
in part to the fact that information is seldom available
for greater depths. Even estimates for lesser depths are
usually based largely on projected outcrop data. The
coal is reported to 4,000+ feet in this report because
the information gained during the investigation permits
estimates to this depth as reliable as to any other. More
than 85 billion tons of coal in the Fruitland Formation
lies below 3,000 or more feet of overburden (tables
6, 7).

The resource tables are arranged according to zones
of total coal thickness, because the percentage of coal in
the different bed-thickness categories varies with the
total amount of coal present. In areas of thin total
coal, most of the resources are in comparatively thin
beds. In the thicker coal zones, a large part of the coal
is in beds more than 10 feet thick. The average per-
centage of coal within the respective bed-thickness
categories was computed for each zone of total thick-
ness. The results are shown in table 5.

TABLE 5.—-Average percent of total coal in beds of indicated thickness
in areas with given total coal thickness

 

Average percent of total coal

 

Total thickness of coal in area
(ft)

 

Beds 2—5 Beds 5—10 Beds >10

feet thick feet thick feet thick
0-10 ______________________ 67 33 __________
10—20 _____________________ 33 38 29
20—30 _____________________ 24 38 38
3040 _____________________ 16 27 57
40—50 _____________________ 20 20 60
50—60 _____________________ 15 17 68
60—70 _____________________ 15 13 72
> 70 ______________________ 1 1 16 73

 

The amount of coal in the formation was determined
from the average total thicknesses shown in figure 21.
This map was combined with the overburden map
(fig. 27), and the area of each zone of total thickness
was measured by planimeter in each of the depth
categories. The resulting areas in square miles were
multiplied by the average total thickness in feet of coal
in each area. The figures thus obtained were the square

68 GEOLOGY AND FUEL RESOURCES, FRUITLAND FORMATION AND KIRTLAND SHALE, SAN JUAN BASIN

mile-feet of coal in each area. These figures were
multiplied by the weight per square mile-foot of
subbituminous coal (1,132,560 tons) to obtain the total
tonnage of coal within the respective areas. The totals
were then multiplied by the percentage figures given in
table 5. The final products are the tons of coal present
in beds of indicated thickness within zones of given
total thickness under each category of overburden. The
above computations were made separately for areas in
Colorado and New Mexico to facilitate the possible
use of these results in future State estimates of resources.
In these computations no allowance was made for the
dip of the beds. Especially along the northern margin
of the basin where the coals dip steeply to depths greater

than 3,000 feet, the dip would have the effect of in-
creasing the area of the coal bed and so its total tonnage.

The results of the computations just described are
given in table 6. Table 7 summarizes the data in more
compact form. As a result of this study, it was deter—
mined that approximately 6,250 square miles within
the area of the San Juan Basin is underlain by coal beds
of the Fruitland Formation and that the beds contain
an aggregate of about 200 billion tons of coal. Owing
to the regional nature of this study and the methods
used in estimating the coal resources, the results are
considered to be “inferred by zone” rather than
“measured” or “indicated” as defined by Averitt
(1961).

TABLE 6.—Fruitland Formation coal resources in millions of short tons under indicated overburden, arranged by States according to bed
thickness and total coal thickness

 

Area underlain

Coal thickness (it) (square miles)

Coal resources by bed thickness, in millions of short tons

 

 

 

 

 

 

 

 

Range Average Colorado New Mexico Thickness of beds (ft) Colorado Mew Mexico Total Combined tota.
Overburden: 0-500 feet

- 2—5 ________________ 121. 4 698. 1 819. 5

0 10 ————————————————— 0 32- 0 184' 0 {5_10 _______________ 59. 8 343' 8 403. 6} 1; 223' 1
2—5 ________________ 64. 5 1, 289. 4 1, 353. 9

10—20________- ________ 15 11.5 230. 0 5—10 _______________ 74. 2 1, 484. 8 1, 559. 0 4, 102. 7
>10 _______________ 56. 7 1, 133. 1 1, 189. 8
2—5 ________________ 88. 3 988. 7 1, 077. 0

20—30 ________________ 25 13. 0 145. 5 5—10 _______________ 139. 9 1, 565. 5 1, 705. 4 4, 487. 8
>10 _______________ 139. 9 1,565. 5 1, 705. 4
2—5 ________________ 50. 7 586. 7 637. 4

30—40 ________________ 35 8 0 92 5 5—10 _______________ 85. 6 990. 0 1, 075. 6] 3, 983. 7
> 10 _______________ 180. 7 2, 090. 0 2, 270. 7
2—5 ________________ 35. 7 30. 6 66. 3

40—50 ________________ 45 3 5 3 0 5—10 _______________ 35. 7 30. 6 66. 3 331. 3
>10 _______________ 107.0 91. 7 198. 7
2—5 ________________ 18. 7 ____________ 18. 7

50—60 ________________ 55 2 0 __________ 5—10 _______________ 21. 2 ____________ 21. 2 124. 6
> 10 _______________ 84. 7 ____________ 84. 7
2—5 ________________ 22. 1 ____________ 22. 1

60—70 ________________ 65 2 0 __________ 5—10 _______________ 19. 1 ____________ 19. 1 147. 2
> 10 _______________ 106. 0 ____________ 106. 0
2—5 ________________ 26. 2 ____________ 26. 2

70+ _________________ 70+ 3. 0 __________ 5—10 _______________ 38. 1 ____________ 38. 1 237. 9
> 10 _______________ 173. 6 ____________ 173. 6

Totals __________________ 75. 0 655. 0 All beds ____________ 1, 749. 8 12, 888. 5 14, 638. 3 14, 638. 3

Overburden: 500-1,000 feet

2—5 ________________ 19. 0 290. 2 309. 2

0‘10 ----------------- 5 5 0 76- 5 {5—10 _______________ 9, 3 143. 0 152. 3} 461- 5
2-5 ________________ 148. 6 1, 098. 8 1, 247. 4

10—20 ________________ 15 26. 5 196. 0 5—10 _______________ 171. 1 1, 265. 3 1, 436. 4] 3, 780. O
> 10 _______________ 130. 6 965. 6 1, 096. 2
2—5 ________________ 91. 7 1, 365. 9 1, 457. 6

20—30 ________________ 25 13. 5 201. 0 {5—10 _______________ 145. 3 2, 162. 6 2, 307. 9} 6, 073. 4
>10 _______________ 145. 3 2, 162. 6 2, 307. 9
2—5 ________________ 76. 1 364. 7 440. 8

30-40 ________________ 35 12. 0 57 5 {5—10 _______________ 128. 4 615. 4 743. 8} 2, 754. 9
>10 _______________ 271. 1 1, 299. 2 1, 570. 3
2—5 ________________ 45. 9 25. 5 71. 4

40—50 ________________ 45 4 .5 2 5 {5—10 _______________ 45. 9 25. 5 71. 4 356. 8
> 10 _______________ 137.6 76.4 214.0
2—5 ________________ 14. 0 ____________ 14. 0

50—60 ________________ 55 1 5 __________ {540 _______________ 15. 9 ____________ 15. 9 93. 4
> 10 _______________ 63. 5 ____________ 63. 5

COAL 69

TABLE 6.—Fruitland Formation coal resources in millions of short tons under indicated overburden, arranged by States according to bed
thickness and total coal thickness—Continued

 

Area underlain
Coal thickness (It) (square miles) Coal resources by bed thickness, in millions of short tons

 

Range Average Colorado New Mexico Thickness of beds (it) Colorado Mew Mexico Total Combined total

 

Overburden: 500-1,000——Continued

 

 

 

 

 

 

 

 

 

2—5 ________________ 16. 6 ____________ 16 6

60—70 ________________ 65 1 5 __________ [5—10 _______________ 14. 3 ____________ 14 3} 110. 4
>10 _______________ 79. 5 ____________ 79 5
2—5 ________________ 26. 2 ____________ 26 2

70+ _________________ 70+ 3 0 __________ {5-10 _______________ 38. 0 ____________ 38 0 237. 8
> 10 _______________ 173. 6 ____________ 173 6

Totals __________________ 67. 5 533. 5 All beds ____________ 2, 007. 5 11, 860. 7 13, 868. 2 13, 868. 2

Over-burden: LOW—2,000 feet

2—5 ____________________________ 1, 817. 4 1, 817. 4

0—10 ................. 5 ........ 479 0 {5—10 ___________________________ 895, 1 895. 1} 2, 712. 5
2—5 ________________ 84. 1 3, 324. 5 3, 408. 6

10—20 ________________ 15 15. O 593 0 {5-10 _______________ 96. 8 3, 828. 2 3, 925. 0} 10, 329. 0
>10 _______________ 73. 9 2, 921. 5 2, 995. 4
2—5 ________________ 214. 1 2, 303. 6 2, 517. 7

20—30 ________________ 25 31. 5 339 0 {5—10 _______________ 338. 9 3, 647. 4 3, 986. 3] 10, 490. 3
>10 _______________ 338. 9 3, 647. 4 3, 986. 3
2—5 ________________ 120. 5 247. 3 367. 8

30—40 ________________ 35 19. 0 39. 0 {5—10 ............... 203. 4 417. 4 620. 8} 2, 299. 1
>10 _______________ 429. 3 881. 2 1, 310. 5
2—5 ________________ 132. 5 107. 0 239. 5.

40—50 ________________ 45 13. 0 10. 5 {5-10 _______________ 132. 5 107. 0 239. 5} 1, 197. 6
>10 _______________ 397. 5 321. 1 718. 6
2-5 ________________ 37. 4 ____________ 37. 4

50—60 ________________ 55 4 0 __________ {5—10 _______________ 42. 4 ____________ 42. 4] 249. 2
> 10 _______________ 169. 4 ____________ 169. 4
2-5 ________________ 27. 6 ____________ 27. 6

60—70 ________________ 65 2. 5 __________ {5-10 _______________ 23. 9 ____________ 23. 9} 184. 0
> 10 _______________ 132.5 ____________ 132. 5
2-5 ________________ 52. 3 ____________ 52. 3

70+ _________________ 70+ 6. 0 __________ [5—10 _______________ 76. 1 ____________ 76. 1} 475. 7
>10 _______________ 347. 3 ____________ 347. 3

Totals __________________ 91. 0 1, 460. 5 All beds ____________ 3, 471. 3 24, 466. 1 27, 937. 4 27, 937. 4

Overburden: 2,000—3,000 feet

2—5 ____________________________ 349. 1 349. 1

0'10 ----------------- 5 -------- 92- 0 5—10 ___________________________ 171. 9 171. 9} 521- 0
2—5 ____________________________ 1, 934. 1 1, 934. 1

10—20 ________________ 15 ________ 345. 0 {5—10 ___________________________ 2, 227. 2 2, 227. 2} 5, 861. 0
>10 ___________________________ 1, 699. 7 1, 699. 7
2—5 ________________ 163. 1 1, 827. 9 1, 991. 0

20—30 ________________ 25 24. 0 269. 0 5-10 _______________ 258. 2 2, 894. 3 3, 152. 5 8, 296. 0
>10 _______________ 258. 2 2, 894. 3 3, 152. 5
2-5 ________________ 773. 8 1, 484. 1 2, 257. 9

30—40 ________________ 35 122. 0 234. 0 5—10 _______________ 1, 305. 7 2, 504. 4 3, 810. 1 14, 111. 7
> 10 _______________ 2, 756. 6 5, 287. 1 8, C43. 7
2—5 ________________ 1, 590. 1 1, 457. 6 3, L47. 7

40—50 ________________ 45 156. o 143. 0 5—10 _______________ 1, 590. 1 1, 457. 6 3, 047. 7 15, 238. 6
> 10 _______________ 4, 770. 4 4, 372. 8 9, 143. 2
2-5 ________________ 878. 3 560. 6 1, 438. 9

50-60 ________________ 55 94. 0 60. 0 5-10 _______________ 995. 4 635. 4 1, 630. 8 9, 592. 8
> 10 _______________ 3, 981. 6 2, 541. 5 6, 523. 1
2—5 ________________ 325. 8 226. 3 552. 1

60—70 ________________ 65 29. 5 20. 5 {5—10 _______________ 282. 3 - 196. 2 478. 5 3, 680. 8
>10 _______________ 1, 563. 6 1, 086. 6 2, 650. 2
2-5 ________________ 143. 9 21. 8 165. 7

70+ ................. 70+ 16. 5 2. 5 5-10 _______________ 209. 3 31. 7 241. 0 1, 506. 3
>10 _______________ 954. 9 144. 7 1, 099. 6

Totals __________________ 442. 0 1, 166. 0 All beds ____________ 22, 801. 3 36, 006. 9 58, 808. 2 58, 808. 2

 

70 GEOLOGY AND FUEL RESOURCES, FRUITLAND FORMATION AND KIRTLAND SHALE, SAN JUAN BASIN

TABLE 6.——Fruitland Formation coal resources in millions of short tons under indicated overburden, arranged by states according to bed
thickness and total coal thickness—Continued

 

Area underlain

Coal thickness (ft) (square miles)

Coal resources by bed thickness, in millions of short tons

 

 

 

 

 

 

 

 

Range Average Colorado New Mexico Thickness of beds (ft) Colorado Mew Mexico Total Combined total
Oven-burden: 3,000—4.000 feet
2—5 ____________________________ 127. 1 127. 1
0‘10 ----------------- 5 -------- 33- 5 {5—10 ___________________________ 62. 6 62. 6} 189- 7
2—5 ____________________________ 577. 4 577. 4
10—20 ________________ 15 ________ 103. 0 5-10 ___________________________ 664. 9 664. 9} 1, 749. 8
> 10 ___________________________ 507. 5 507. 5
2—5 ____________________________ l, 590. 1 1, 590. 1
20—30 ________________ 25 ________ 234. 0 5—10 ___________________________ 2, 517. 7 2, 517. 7} 6, 625. 5
> 10 ___________________________ 2, 517.7 2, 517.7
25 ________________ 215. 6 2, 524. 3 2, 739. 9
30—40 ________________ 35 34. 0 398. 0 5—10 _______________ 363. 9 4, 259. 7 4, 623. 6} 17, 124. 3
> 10 _______________ 768. 2 8, 992. 6 9, 760. 8
2—5 ________________ 494. 4 2, 813. 3 3, 307. 7
40—50 ________________ 45 48. 5 276. 0 5—10 _______________ 494. 3 2, 813. 3 3, 307. 6} 16, 538. 2
> 10 _______________ 1, 483. 1 8, 439. 8 9, 922. 9
2—5 ________________ 513. 9 1, 504. 3 2, 018. 2
50—60 ________________ 55 55. 0 161. 0 5—10 _______________ 582. 4 1, 704. 9 2, 287. 3} 13, 454. 8
>10 _______________ 2, 329. 7 6, 819. 6 9, 149. 3
2—5 ________________ 220. 9 2, 352. 0 2, 572. 9
60-70 ________________ 65 20. 0 213. 0 5—10 _______________ 191. 4 2, 038. 4 2, 229. 8} 17, 152. 6
> 10 _______________ 1, 060. 1 11, 289. 8 12, 349. 9
2—5 ________________ 348. 8 750. 0 1, 098. 8
70+ _________________ 70+ 40. 0 86. 0 5—10 _______________ 507. 4 1, 090. 9 1, 598. 3] 9, 989. 2
> 10 _______________ 2, 314. 9 4, 977. 2 7, 292. 1
Totals __________________ 197. 5 1, 504. 5 All beds ____________ 11, 889. 0 70, 935. 1 82, 824. 1 82, 824. 1
Overburden: 4,000+ feet
2—5 ___________________________________________________
0-10 _________________ 5 .................. { _10 __________________________________________________ } ............
2—5 ___________________________________________________
10—20 ________________ 15 __________________ {5—10 __________________________________________________ } ____________
> 10 __________________________________________________
2—5 ____________________________ 40. 7 40. 7
20-30 ________________ 25 ________ 6. 0 {5—10 ___________________________ 64. 6 64. 6} 169. 9
>10 ___________________________ 64. 6 64. 6
2—5 ____________________________ 107. 8 107. 8
30—40 ________________ 35 ________ 17. 0 5—10 ___________________________ 182. 0 182. 0} 673. 9
>10 ___________________________ 384. 1 384. 1
2—5 ____________________________ 81. 5 81. 5
40—50 ________________ 45 ________ 8. 0 5—10 ___________________________ 81. 5 81. 5} 407. 7
>10 ___________________________ 244. 7 244. 7
2—5 ____________________________ 116. 8 116. 8
50—60 ________________ 55 ________ 12. 5 [5—10 ___________________________ 132. 4 132. 4} 778. 7
>10 ___________________________ 529. 5 529. 5
2—5 ____________________________ 154. 6 154. 6
60—70 ________________ 65 ________ 14. 0 5-10 ___________________________ 134. 0 134. 0} 1, 030. 6
2>330 ___________________________ 742. 0 742. 0
70+ _________________ 70+ __________________ :5—10 __________________________________________________ } ____________
> 10 __________________________________________________
Totals __________________________ 57. 5 All beds ________________________ 3,060. 8 3, 060. s 3, 060. 8
DEVELOPMENT

Approximately 30 known mines and prospect drifts
have been excavated in Fruitland coal beds; the ma-
jority of these were small truck mines, which were
operated briefly for local markets. The coal from them
could not compete successfully for broader markets
with the higher quality coal produced from the Menefee
Formation of the Mesaverde Group in the same areas.
As of 1968, the very large Navajo strip mine of the

Utah Construction and Mining Co. on the Navajo
Indian Reservation in New Mexico is the only mine
known by the authors to be currently producing coal
from the Fruitland Formation. The output from this
mine is used to fuel the steam-operated power plant of
the Arizona Public Service Co. near Kirtland, N. Mex.

The locations of most known Fruitland mines are
shown in figure 19; some of the data about these
mines is tabulated in table 8.

REFERENCES CITED 71

TABLE 7.——Coal resources of the Fruitland Formation

[In millions at short tons]

 

Total coal in beds of indicated thickness

 

 

 

Overburden (ft) Total
2-5 feet 15-10 feet >10 feet

0—500 _________ 4, 021. 1 4, 888. 3 5, 728. 9 14, 638. 3
500—1,000 ______ 3, 583. 2 4, 780. 0 5, 505. 0 13, 868. 2
LOGO—2,000- _ _ _ 8, 468. 3 9, 809. 1 9, 660. 0 27, 937. 4
2,000—3,000- s _ _ 11, 736. 5 14, 759. 7 32, 312. 0 58, 808. 2
3,000—4,000- _ __ 14, 032. 1 17, 291. 8 51, 500. 2 82, 824. 1
4,000+ ________ 501. 4 594. 5 1, 964. 9 3, 060. 8

Total____ 42, 342. 6 52, 123. 4 106, 671. 0 201, 137. 0

 

TABLE 8.——Production and dates of operation of coal mines in the
Fruitland Formation

[N.D.A., no data available]

 

 

Number Total
in figure Name of mine Period of operation production
19 (tons)
1 Archuleta _______________ N.D.A _______ N.D.A.
2 Talian __________________ 1913—15 ______ 7, 637
3 Columbine ______________ 1938—56 ______ 10, 596
4 Cooper _________________ N D. A _______ N.D.A.
5 Triple S ________________ 1941—51 ______ 5, 348
Shamrock No. 1 _________ 1928—36 ______ 3, 916
Shamrock No. 2 _________ 1937—41 ______ 2, 398
6 Morning Glory __________ 1930—36 ______ 4, 207
7 Palmer _________________ N.D.A _______ N.D.A.
8 Blue Jay ________________ 1935-44 ______ 3, 135
9 Love ___________________ N.D _______ .D.A.
10 Excelsior (3 shafts) ______ 1927—38 ______ 3, 914
11 Schutz (2 shafts) ________ N D. A _______ N.D.A.
12 Prospect pit _____________ N.D.A _______ N.D.A.
13 Unknown _______________ N.D.A _______ N.D.A.
14 _____ do _________________ N.D.A _______ N.D.A.
15 _____ do _________________ N. D. A _______ N.D.A.
16 La Plata ________________ 1893- 1902---- 5, 447
17 Unknown _______________ N. D. A _______ N.D.A.
18 Mormon ________________ N. D. A _______ N.D.A.
19 Fort Lewis ______________ 1943—49 ______ 1, 395
Henderson ______________ N.D.A _______ N. .A.
20 Soda Spring _____________ 1928—47 ______ 5, 218
21 Cinder Butte (Pruitt?)_ __ N.D.A _______ N. .A.
22 New Mexico (Kempton)__ 1928—45 ______ 10, 361
23 Bill Thomas (Morgan)____ 1931—47 ______ 7, 521
24 Jones ___________________ ?—1918? ______ N.D.A.
25 Prospect drift ___________ N.D.A _______ N.D.A.
26 Marcelius (Caudell?) _____ 1924—38 ______ 10, 318
27 Blanchard ______________ N. D. A _______ N.D.A.
28 Black Diamond 1918— 33(?)____ N.D.A.
(Christenson), (3
mines?).
29 L. W. Hendrickson_______ 1929—30(?)____ N.D.A.
30 Utah Construction and 1963— ________ 1 19, 490, 600
Mining Co. Navajo
(strip).
31 Prospect drift ___________ N.D.A _______ N.D.A.

 

1 To August 2, 1970.

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72 GEOLOGY AND FUEL RESOURCES, FRUITLAND FORMATION AND KIRTLAND SHALE, SAN JUAN BASIN

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the San Juan Basin, New Mexico and Arizona, 2d Field
Conf., 1951: p. 124—131.

Kelley, V. C., and Clinton, N. J., 1960, Fracture systems and
tectonic elements of the Colorado Plateau: New Mexico
Univ. Pubs. Geology, no. 6, 104 p.

Kilgore, L.W., 1955, Geology of the Durango area, La Plata
County, Colorado, in Four Corners Geol. Soc. Guidebook
of parts of the Paradox, Black Mesa, and San Juan Basins,
1st Field Conf., 1955: p. 118—124.

Knowlton, F. H., 1917, Flora of the Fruitland and Kirtland
formations: U.S. Geol. Survey Prof. Paper 98—S, p. 327—353.

Osborn, H. F., 1923, A new genus and species of Ceratopsia
from New Mexico, Pentaceratops sternbergii: Am. Mus.
Novitates, no. 93, 3 p.

O’Sullivan, R. B., and Beaumont, E. C., 1957, Preliminary
geologic map of western San Juan Basin, San Juan and
McKinley Counties, New Mexico: U.S. Geol. Survey Oil
and Gas Inv. Map 0M—190.

O’Sullivan, R. B., Beaumont, E. C., and Knapp, L. M.,1957,
Road log for second day, in Four Corners Geol. Soc. Guide-
book of southwestern San Juan Basin, 2d Field Conf., 1957:
p. 187—198.

O’Sullivan, R. B., and Beikman, H. M., 1963, Geology, structure,
and uranium deposits of the Shiprock quadrangle, New
Mexico and Arizona: U.S. Geol. Survey Misc. Geol. Inv.
Map I—345.

Pike, W. 8., Jr., 1947, Intertonguing marine and nonmarine
Upper Cretaceous deposits of New Mexico, Arizona, and
southwestern Colorado: Geol. Soc. America Mem. 24, 103 p.

Reeside, J. B., Jr., 1924, Upper Cretaceous and Tertiary forma-
tions of the western part of the San Juan Basin of Colorado
and New Mexico: U.S. Geol. Survey Prof. Paper 134, p.
1—70.

Sears, J. D., Hunt, C. B., and Hendricks, T. A., 1941, Trans-
gressive and regressive Cretaceous deposits in southern
San Juan Basin, New Mexico: U.S. Geol. Survey Prof.
Paper 193—F, p. 101—121.

Silver, Caswell, 1950, The occurrence of gas in the Cretaceous
rocks of the San Juan Basin, New Mexico and Colorado, in
New Mexico Geol. Soc. Guidebook of the San Juan Basin,
New Mexico and Colorado, 1st Field Conf., 1950: p. 109—123.

 

 

REFERENCES CITED 73

1951, Cretaceous stratigraphy of the San Juan Basin, in

New Mexico Geol. Soc. Guidebook of the south and west

sides of the San Juan Basin, New Mexico and Arizona, 2d

Field Conf., 1951: p. 104—118.

1957, Relation of coastal and submarine topography to
Cretaceous stratigraphy [N. Mex.], in Four Corners Geol.
Soc. Guidebook of the geology of southwestern San Juan
Basin, 2d Field Conf., 1957: p. 128—137.

Sinclair, W. J., and Granger, Walter, 1914, Paleocene deposits
of the San Juan Basin, New Mexico: Am. Mus. Nat.
History Bull., V. 33, p. 297—316.

Stanton, T. W., 1917, Nonmarine Cretaceous invertebrates of
the San Juan Basin: U.S. Geol. Survey Prof. Paper 98—R,
p. 309—326.

 

 

 

U.S. Geological Survey, 1946, Physical Divisions of the United
States (prepared by N. M. Fenneman): U.S. Geol. Survey,
map.

Wcimer, R. J., and Hoyt, J. H., 1964, Burrows of Callianassa
major Say, geologic indicators of littoral and shallow neritic
environments: Jour. Paleontology, v. 38, no. 4, p. 761—767.

Wood, G. H., Kelley, V. C., and MacAlpin, A. J., 1948, Geology
of the southern part of Archuleta County, Colorado: U.S.
Geol. Survey Oil and Gas Invs. Prelim. Map 81.

Zapp, A. D., 1949, Geology and coal resources of the Durango
area, La Plata and Montezuma Counties, Colorado: U.S.
Geol. Survey Oil and Gas Invs. Prelim. Map 109.

Zieglar, D. L., 1955, Preliminary geologic map of the Toadlena
quadrangle, San Juan County, New Mexico: U.S. Geol.
Survey Coal Inv. Map 0-30.

 

 
 
 
 
  
  
  
   
  
 

A, B
Page
Abstract ...................................... 1
Access to area . _ 4
Acoustic logs .......... . 4, 52
Allan, J. E., quoted- . . . 22
Analyses, coal ..... 58, 60

Animas Formation. .. 33, 38, 39
Aztec, N. Mex., oil and gas. .. 39
Balk, Robert, quoted... ....... 22

 

   
  
 
 

 

Baltz, E. H., quoted ............. 16,54
Barker Dome-Fruitland area . 56
Barnes, Harley, quoted...__ ___________ 54
Barrel Springs Arroyo. .......... 31
Beaumont, E. C., quoted 22
Boyd deposit, uranium... .............. 44
Bridge Timber Mountain ..................... 34, 39
C
Carbon Junction, thickest coal reported ...... 54, 56
Carithers, L. W., quoted ______________________ 44
Central Basin area. ............ 34
Chaco Slope ............ 34
Clemens, W. D., quoted ...................... 19

Clinton, N. 1., quoted ........................
Coal, analyses..

 

barren areas ..............................
bed-thickness categories _________________ 67
Btu values _______________ _ . 63
classification .............................. 63
coastal swamps ........................... 44
continuity of beds, variables.. 56
correlation ................................ 54, 56
depositional environments _____________ 37, 44, 52
distribution patterns _____________________ 52
fixed carbon .............................. 63, 65
iron sulfide content ....................... 57
lenticularity of beds ______________________ 52
Menefee Formation _______________________ 70
mining ................................... 70
moisture content _________________________ 60
origin .................................... 44
overburden pattern _______________________ 67
overburden thickness ..................... 63
physical properties ______________________ 57
production ............................... 70
resources _________________________________ 67
resources control points ................... 45
response to drilling and logging ___________ 50, 52
sample preparation ....................... 57
sampling from wells ...................... 3, 57
sulfur content ____________________________ 60
thickness ........................... 44, 50, 54, 56
volatile matter ___________________________ 63
Goal mines ................................... 70
Cobban, W. A., quoted ....................... 16
Contact relations, Animas Formation ________ 33, 39
Fruitland Formation .............. 6, 8, 12, 19, 23
Kirtland Shale ......................... 6, 19, 24
010 Alamo Sandstone. - . 6, 16, 19, 23, 24, 29, 31, 39
Pictured Clifi's Sandstone ............ 6, 8, 16, 23
Cuba Mesa ................................... 34

 

INDEX

 

[Italic page numbers indicate major references]

 

   
  
  

D, E

Page

Depositional environments, coal ........... 37, 44, 52
Fmitland Formation ..................... 19, 37
Huerfanito Bentonite Bed ................ 8,12
Kirtland Shale .......... . 25,37
Ojo Alamo Sandstone ____________________ 38
Pictured Ciifi's Sandstone ............ 4, 9, 12, 37
Dikes ..................... 34, 39
Dinosaur remains ................. . 28, 31
Drainage of area ................... . 3
Drilling-rate logs. _ _ _ _ 50

 

 
 
   

    

 

 

 

Dunkle, D. H., quoted._ 16
Electric logs ................................... 4. 50
F

Farmington Sandstone Member, Kirtland
Shale ............................. 23, 89
Faulting....... 34
Folding ____________________ 34
Fossils, Fruitland Formation _________________ 19
Kirtland Shale ................... 25
N acimiento Formation. 34
Ojo Alamo Sandstone ____________________ 28, 31
palynomorphs ____________________________ 23
Pictured Cliffs Sandstone ........ . . 8, 15
undivided Kirtland and Fruitland ....... 26
Four Corners area, Fruitland contact ......... 19
Fruitland. N. Mex ___________________________ 17
Fmitland Formation, age ____________________ 21, 23
coal. See Coal.
contact relations ................... 6, 8, 12, 19, 23
correlation- .............................. 23
depositional environments.
earlier work .......................... 2, 3, 17, 19
fossils ..................................... 19
gas production. 42
lithology ................................. I7
methane from coal zone .................. 42
named .................................... 2, 17
oil and gas wells .......................... 39, 42
outcrop thickness ......................... 22
regional extent ............................ 22
thickness ................................. 23
uranium __________________________________ 44
G, H, I
Gamma ray—neutron logs ...................... 50
Gas, discovery well history ................... 39
Ignacio field .............................. 42
location of fields .......................... 43
precautions in drilling .................... 42
production ............................... 39, 42
stratigraphic traps ........................ 39
tabulation of pools ........................ 42
Geologic history .............................. 87
Green Marker Horizon ....................... 6, 8
Hayes. P. T., quoted ......................... 25, 54
History of present study ...................... 3
Hogback monocline ........................ 4, 34, 39

 

 

   

 

   

  
   
  
  
  
   
  
 
  

 

 

 

Page
Huerfanito Bentonite Bed, correlation ........ 8
depositional environments ..... . 8, 12
logging ................................... 6
named .................................... 6
surface correlation diificulties _ 8
time surface .............................. 8, 12
Ignacio Blanco—Fruitland pool ................ 39
Ignacio dome ................................. 39, 42
Induction—electric logs ........................ 50
Intrusive rocks, age.. 34
Iron sulfide, in coal ........................... 57
K
Kirtland, N. Mex ............................. 23
Kirtland basin _____ 38
Kirtland Shale, age .......................... 25
contact relations _____ 1 .................. 6, 19, 24
depositional environments.. _. 25, 37
distribution .................. . 26, 29. 38
earlier work ...................... _ . 2
Farmington Sandstone Member 2, 23, 39
fossils ......................... 25
lithology ............. 24
named......_. 2, 23
oil accumulations ............ 44
011 and gas wells in New Mexcio . . 39, 42
present usage ................. 23
subsurface correlation ............. . 26
surface distinction of upper contact. 25
thickness in subsurface ................... 26
tufl ................. . 24
Klutter Mountain outlier- ...... 54
Knapp, L. M., quoted ........................ 22
L, M, N
La Plata Mountains .......................... 39
Laramie Formation __________________________ 2, 17
Late Cretaceous basin of deposition..... . . . . . . 37
Lewis Sea .................................... 12
Lewis Shale ................................ 6,16, 54
Huerfanito Bentonite Bed. See Huerfanito
Bentonite Bed.
Location of area ______________________________ 2
McDermott Formation _______________________ 24
McDermott Member, Animas Formation. . 25, 33, 38
Menefee Formation ........................ 22, 54, 70
Mesa Portales ................. 16, 21, 26, 29, 3], 33, 56
Methane. . . ,a.’ . 42
Mining, coal .................................. 70
Nacimiento Formation ....................... 34, 39
Natural gas ___________________________________ 39, 42
Navajo physiographic section ................. 3
Navajo strip mine ____________________________ 70
0
Oil ........................................ 39, 42, 44
Vesicular, in dikes ........................ 34
Ojo Alamo Arroyo ............................ 28, 31
Ojo Alamo Beds .............................. 28

75

76

 

 

 

 

 

Page

Ojo Alamo Sandstone, age assignments _______ 28, 31
bedding geometry ........................ 28
contact relations ......... 6,16,19, 23, 24, 29, 31, 39
depositional environments. _ _ A 38
fossils ..................................... 28, 31
intertonguing ............................. 29
lithology ................................. 28, 33
named .................................... 2, 28
predepositional surface. 38
redefinitions .............................. 28
regional extent ____________________________ 29
source of sediments _______________________ 38
thickness _______________________ 28
O'Sullivan, R. B., quoted ...... _ 22
Overburden on coal ________________________ 63, 67

P

Paleocene and younger rocks ................. 33
Paleocene rocks _______________________________ 28
Paleogeographic map ......................... 37
Petroleum ____________________________________ 42, 44
Polynomorphs. list ........................... 23
Peneplain. pre-Ojo Alamo ........ _ 38
Pictured Clifis Sandstone, age ................ 16, 37
age equivalents ___________________________ 37
contact relations ______________________ 6, 8, 16, 23
depositional environments ______________ 9, 12, 37

 

 
 

 

   
 
 

INDEX
Page
Pictured Clifis Sandstone—Continued
drilling characteristics ____________________ 8
fossils _____________________________________ 8,15
geologic history ___________________________ 37
interval between top and Huerfanito _____ 14
lithology ________________________ 8, 17
named..__.___._ _____________ 2,8
outcrop thickness _________________________ 17
regional extent ____________________________ 12,16
relation to Huerfanito deposition _____ _ 12
significance of isopach maps _________ _ 15
source of sediments _______________________ 9, 37
stratigraphic rises_.
relation to coal ................. 44, 52, 54, 56
subsurface correlation _____________________ 16
thickness in subsurface ................... 17
Pictured Clifis Sea ............ 9,12, 15, 37, 44
Pinyon Mesa .......
Previous investigations _______________________
Radioactivity logs..
Rainfall ____________
Raton Basin __________________________________ 37
References cited ______________________________ 71
Relief in area ________________ 3, 67
Resources, coal _____________________________ 67

O

 

   

 

 

  

Page
San Jose Formation __________________________ 34, 39
Scope of study ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 1
Sills ....................... __ 34,39
Sonic logs ................. . . 4, 52
streams. . , . , . 3
Structure .................................. 34, 35, 3S
Thickness of sedimentary rocks. maximum_ 1 . 4
Tohatchi (or Tohachi) Formation ____________ 22
Transportation ________________ 4
Trinidad Sandstone __________________________ 37
Tschudy, R. H., quoted ___________________ 21,33, 34
Tufi .......................................... 24, 38
U, V, W, Z
Unconiormity, Cretaceous-Tertiary __________ 33
Upper Cretaceous rocks ........... 9, 19, 25
sequence of deposition ____________________ 4, 37
thickness _________________________________ 4
Uranium ...... , _______________________________ 4 4‘
Vegetation ___________________________ 4
Vermejo Formation" ________ 37
Volcanism .................................... 38, 39
Well logging, scope ____________________________ 4
Zapp, A. D., quoted......____..____..___‘.».__ 25,54

36°

UNITED STATES DEPARTMENT OF THE INTERIOR PROFESSIONAL PAPER 676
GEOLOGICAL SURVEY

PLATE 1
108°

l d/ L__ ' I
13 16 13 1.1 1 13,_ 13 /11/ 10 31 11 i i3 6 3, 311.33%}? __ MINEIRAL 3 r

.5
r / Hermosa 1,, i
. LaPIata S” l . ,J ' i I I. 2 W
J Trimhle g l L ' 21 "' ‘
1 x». ._J . 1
ayday

 

 

EXPLANATION

 

 

 

 

 

 

 

 

 

 

 

 

Intrusive igneous rocks
Dikes and sills of basalt, diabase, and andesite; augite
andesite sill caps Archuleta Mesa, 300 feet thick.
Vertical biotite hornblende lamprophyre dikes in
northeastern part of basin, 1—30 feet thick

Miocene (? )
A

f

 

LA .PLATAI

. . . —..ir‘ ‘ p c ' [I . .—...._.
Klo
[' .
Hesperus J ,
Kam .
~\.—.p/~\-’~ O u 0 1 ‘
. , agos
. . JF— Springs

« 150 . ‘
Ft Lewyfl J8: Pie dra 3 \
' ' ' 'Faifa ' ‘ ' -
Tau

 

 

 

 

 

Tsj

 

 

 

 

 

San Jose Formation

Fine- to coarse-grained arkosic locally conglomeratic
sandstone and interbedded shale; 0-2,500feet thick.
In northern part of basin, abundant volcanic debris
including andesite pebbles; proportion of volcanic

. debris and sandstone decreases southward; conglom-
erate pebbles include quartzite, jasper, granite,

\ andesite, and shale; silicified wood common

h..-

L_.

 

 

 

Eocene
A

 

 

 

 

 

 

 

NATVJNAL

A L \ v fE
M sa Verde

NatiTal Park '

 

 

 

 

 

 

 

«LT

 

 

 

 

 

 

 

 

 

—
o

Bre

 

 

 

E?

V
TERTIARY

‘ «E’- 2

Kli 5"
//J Kpc

41*

MESA . LET I 5011:5571: '5 . 34 T”

Ti Nacimiento Formation

 

 

\191
G

 

 

‘\

 

     

 

Light-gray to black fluvial and lacustrine shale and
some scattered sandstone beds; sandstone more abun-
it I ka dant in upper part. 0—1,300 feet thick

//

Ojo Alamo Sandstone

o Kbé
K / / -’
Overlapping massive sheets of fluvial light- to dark-
brown medium- to coarse—grained arkosic conglom-
eratic sandstone. Conglomerate pebbles smaller to

\f/‘\ N“ ~ Q I r ' 32

r o ‘3 W ‘ ‘
COLORADO nonexistent toward eastern part of basin. 0—400 feet
1. I. .—

W
.- — .1- ._ I dL — ... , 1 ' _ _ _J a 7:6
NEW MEXICO » - I '1‘ 33- --l 37 , ‘h k .3 I , , .<
i l . I V 32 N ‘ Animas Formtion
I C A R s o N . P

I ~ AAmargO Tau, upper member; fine- to coarse-grained fluvial

\\/ Ti l / l Lu b rt , Kirtland Shale and Fruitland Formation‘ conglomeratic andesitic sandstone beds and scattered
' I Toin Moner Kk, Kirtland Shale. Upper unit consists of the upper thin shale interbeds and thm coal beds; 0-216 70 feet
l pc shale member and Farmington Sandstone Member; thwk

M - . —— 31 Qrgo interbedded tabular fine- to medium-grained arkosic Kam, McDermott Member; more andesitic and coarsely

ka - sandstone and shale, infrequently conglomeratic; conglomeratic facies 0f the Animas; teT'MWLat’LO’fl Of

{\K - lower shale member, light- to dark-gray and brown the McDermott south of the Colorado border near the

(F W3 shale and silty shale and rare sandstone interbeds. La Plata River marks the southernmost extent of
r

' 0—1,500 feet thick the andesite pebble conglomerate
(fl ‘1 Tsj // I
—Tl ' .
I

Ignacio . I
O

Marv I Ti Klo]

Jpan

Red mesa

/
s o u T H’IE R N u T E

 

Tsj

oal
RESERVA ION , ' /T-.',’ >930

ka
u

 

 

 

 

 

 

 

 

Paleocene
A

 

-I

 

 

 

NORTHERN PART

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

   

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Kf, Fruitland Formation; interbedded fluvial and
We Resemoir paludal shale, carbonaceous shale, sandstone, silt-
(5650) C , NORMAL. Poor ELEV 6085

stone, coal, and thin scarce coquina beds; coquina
MAXIMUM POCL ELEV 6/0;

and coal concentrated in lower part. 0—500 feet thick
_ Navajo City 7 "’ /

 

NATIONAL
17

 

 

 

 

 

 

ogback
C/ Klo

a,
k.
G.)
I)

6

7 5 4 3 2
FOREST

Upper Cretaceous
A
W
C R ETAC E0 U S

Pictured Cliffs Sandstone

Fine-grained sandstone; contains Ophiomorpha major
and scattered grains of carbonaceous shale, coal,
glauconite, and mica which give rock a salt—and-
pepper appearance. 0—400 feet thick

- Klo

Lewis Shale
Dark marine shale and scattered interbeds of marine
sandstone, sandy to silty limestone, calcareous
o concretions, and bentonite. 0—9400 feet thick J

 

 

 

 

 

 

 

 

 

 

 

 

16

N i

 

 

05st

 

3/.
.9
'\.
8.

to}
4“ \

cc
<._

 

 

 

 

 

 

Lewis Shale and older rocks

 

 

 

 

 

 

 

 

 

1 Tertiary pollen and Spores identified by R. H. Tschudy (see text) were
collected from the upper part of the Kirtland Shale and Fruitland
Formation undivided at Mesa Portales in the southeastern part of the
-- San Juan Basin.

0 Huerfanito
Peak

D

* ' ] RIO—"ARRIB.

 

 

 

 

 

 

l. . Contact I
Dashed where inferred

U
D

Fault
U, upthrown side; D, downthrown side

 

 

Tapicitoes
Hueriiano
M 1
iii?

Si

 

 

 

 

 

 

 

 

 

 

Ojito

 

NAVAJO l ' *7 1

x" 51
t /

 

l Gavilan

 

 

 

 

 

 

 

 

 

 

 

A

 

Lindrith
Newcomb \l.

A»

 

 

\

 

Nageezi,

 

 

 

 

   
   

f _
,/

 

 

 

 

 

 

 

Tsi \

../

 

{
, Outcrop of [4
.q .._1\/' ’ _ " , ' // y// / Counselor'

Fruitland
Formation

8 and
Kirtland Shale

 

 

 

 

 

 

 

 

 

 

I
I .
I
I
I

 

 

 

 

 

 

 

Naschitti

 

  

M...
Juans Lake \

 

 

 

, .\ ‘ ., ,, ‘va . LaJara I
21 I

 

 

 

 

21

 

, acgimienio Peak I
.97. I
SOURCES OF GEOLOGIC DATA
. Barnes (1953).
. Barnes, Baltz, and Hayes (1954).
. Bauer and Reeside (1921).
. Dane and Bachman (1957; covers entire New Mexico part of San
Juan Basin).
. Fassett (1966).
6. Fassett, J. E., and Hinds, J. 8., 1961—68, US. Geological Survey

 

/\. .

 

 

NMONAL FORtb I

 

 

 

 

 

"WM—TN)?“ 0/7 .
Klo U c, «» I Tn

Pueblo Pintado . TI 1 20
I
I

 

— 36°

(i
I
\
~1/\
i
l;
£4 SANTA FE

20

“BOUND-I

 

 

 

 

UT

 

 

 

4/

 

 

. Hinds (1966).

. O’Sullivan and Beikman (1963).

. Wood, Kelley, and MacAIpin (1948).
. Zapp (1949).

 

 

 

 

 

 

 

 

 

 

 

M /\ 1/

J.

 

 

 

 

 

reconnaissance mapping. These areas were not completely re-
mapped; only selected contacts in parts of the areas shown
l9 MC KINLEY I; were examined and in some cases altered.
J SANJ-BOVAL
n

 

I
Klo I
1
1

 

La Vei is

107°
. INTERIOR—GEOLOGICAL SURVEY, WASHINGTON. D.C. —1971—C69352 NOTE

Base from U.S. Geological Survey SCALE 12380160 San Jose—Nacimiento contact in northwestern part of
1:500,000: New Mexico, 1959 and . basin from Reeside (1924). Fruitland-Kirtland
Colorado, 1967 Ad L $0 1,5 2:0 j2‘5 MILES contact on west and south sides of basin in New
Mexico from Bauer and Reeside (1921), Dane
5 0 5 10 15 20 25 KILOMETERS (1936), Hayes and Zapp (1955), and O'Sullivan and

5—H H '7 ' Beaumont (1957).

 

 

OWOOQ

 

 

GEOLOGIC MAP OF THE SAN JUAN BASIN, NORTHWESTERN NEW MEXICO, AND SOUTHWESTERN COLORADO

UNITED STATES DEPARTMENT OF THE INTERIOR

GEOLOGICAL SURVEY

 

 

 

 

 

 

WELLS
W 11 [Kind of log used: IE, induction electric; E, electric]
e
No. Company Well name Location Kind of
Sec, T. N. R.W. log used
Section A—A’ (SW—NE)
New Mexico
1 Continental Oil Co _________________ Cottonwood Navajo IX _________ 29 27 15 IE
2 Walter Duncan ___________________ Gulf Navajo 1 _______________ 31 28 14 IE
3 El Paso Natural Gas Products Co _______ Ojo Amarillo 1 _______________ 27 29 14 'IE
4 Compass Exploration, Inc ____________ City of Farmington 1—4 _________ 4 29 13 IE
5 Pan American Petroleum Corp _________ -L. C. Kelly 2 ________________ 5 30 12 IE
6 Aztec Oil and Gas Co _______________ East 6_ _ _ ‘_ ________________ 23 31 12 IE
7 El Paso Natural Gas Co ______________ Barnes 7 ___________________ 23 32 11 E
Colorado
8 Compass Exploration, Inc., and
Mountain States Development Co‘ _____ Ute 1—22 ___________________ 22 33 9 IE
9 Pan American Petroleum Corp _________ J. M. Keyes 1 ________________ 2 34 8 E
Section B-B’ (SW—NE)
New Mexico
1 Magnolia Petroleum Co _____________ Beamon Federal 1 ____________ 29 24 11 E
2 Davis Oil Corp ___________ ' ________ Fannin Govt. 1 _______________ 3 24 11 IE
3 Sun Oil Co ______________________ Heirs of Ith-Hal-E-Wood 1 ______ 19 25 10 IE
4 El Paso Natural Gas Co _____________ Huerfano 120 ________________ 25 26 10 IE
5 Turner and Webb_ _ _ '_ _____________ Huerfanito 60—4 ______________ 4 26 9 IE
6 El Paso Natural Gas Co _____________ Schwerdtfeger 13—A- _ _‘ ________ 8 27 8 E
7 _ _ _do _________________________ San Juan 28—7 30 _____________ 18 28 7 E
8 _ _ _do _________________________ San Juan 29—7 65 _____________ 22 29 7 E
9 _ _ _do _________________________ Barron Kidd 7 ________ ‘ _______ 21 30 6 E
10 '_ _ _do _________________________ Rosa Unit 24 ________________ 32 31 5 E
11 Stanolind Oil and Gas Co- ___________ San Juan 32—5 2 ______________ 35 32 5 E
12 Phillips Petroleum Co _______________ Mesa 32—4 2—16- _ _ _ _ _' _________ 16 32 4 E
Colorado
13 Stanolind Oil and Gas Co ____________ Southern Ute 1 ______________ 22 32 3 E
Section C—C’ (SW—NE)
New Mexico
' 1 Davis Oil Corp _________________ '__ Govt. Co-op 1 _______________ 20 21 7 IE
2 Northwest Production Corp ___________ Sandoval 22-7 2—35 ____________ 35 22 7 IE
3 Texas National Petroleum Co _________ Maddox FA 1 _______________ 34 23 6 E
4 Humble Oil and Refining Co __________ Jicarilla C 1 ________________ 4 23 5 E
5 Amerada Petroleum Corp ____________ Jicarilla Apache G—1 __________ 16 24 4 IE
6 Skelly Oil Co ____________________ L. L. McConnell 1 _____________ 30 25 3 E
7 Honolulu Oil Corp _________________ J icarilla A 1 ________________ 26 26 3 IE
8 Bolack-Greer, et al ________________ Bolack 1 ___________________ 9 26 1 IE
Section D—D’ (S—N)
New Mexico
1 Ray McGlothlin ___________________ Federal 1 __________________ 22 21 8 IE
2 Humble Oil and Refining Co __________ South Chaco 4 _______________ 10 22 8 IE
3 Great Western Drilling Co ___________ Chaco Canyon 3 ______________ 21 23 8 E
4 Century Drilling Co ________________ ..Century Royal Federal 1-3 _______ 3 24 8 IE
5 Western Natural Gas Co _____________ Keeling Federal 1 _____________ 20 25 8 IE
6 Southern Union Gas Co, _____________ Hodges 7 __________________ 22 26 8 E
7 El Paso Natural Gas Co _____________ Florence 14—D _______________ 21 27 8 E
8 _ _ _do _________________________ Jones l—A __________________ 10 28 8 E
9 Southern Union Gas Co ______________ Hill 2 _____________________ 4 29 8 E
10 Delhi Oil Corp ___________________ C. J. Moore 1 ________________ 8 30 8 E
11 El Paso Natural Gas Co _____________ San Juan 32-8 13—9 ____________ 9 31 8 E
12 Phillips Petroleum Co ______________ Mesa 32—8 4-15 ______________ 15 32 8 E
Colorado
13 Compass Exploration, Inc ____________ Trail Canyon 1—3 _____________ 3 32 8 E
14 Stanolind Oil and Gas Co ____________ Worford B 1 ________________ 10 33 8 E
15 Pan American Petroleum Corp ________ J. M. Keyes 1 _______________ 2 34 8 E
16 Aspen Drilling Co _________________ Govt. 1 ____________________ 22 35 8 IE
Section E—E’ (NW—SE)
New Mexico
1 Adobe Oil Co ____________________ Cuccia 1 ___________________ 14 31 13 IE
2 Pan American Petroleum Corp _________ State BD 1 _________________ 32 31 12 IE
3 _ _ .do _________________________ Lilywhite 1 _________________ 13 30 12 ' IE
4 Beta Development Co ______________ Bloomfield Canyon-Federal 1 _____ 35 30 11 IE
5 Southern Union Production Co _________ Albright 6 _________________ 22 29 10 IE
6 El Paso Natural Gas Co _____________ Reid 1 _____________________ 8 28 9 E
7 _ _ _do _________________________ Story 10—C _________________ 35 28 9 E
8 - _ _do _________________________ Florance 10—D _______________ 17 27 8 E
9 International Oil and Gas Corp ________ Federal Miles D—1—5 ___________ 5 26 7 IE
10 El Paso Natural Gas Co _____________ Vaughn 4 __________________ 29 26 6 E
11 Kay Kimbell ____________________ Jicarilla 1—20 ________________ 20 25 5 IE
12 Continental Oil Co _________________ Northeast Haynes 8 ___________ 15 24 5 IE
13 Skelly Oil Co ____________________ Jicarilla D 2 ________________ 5 23 4 IE
14 Reynolds Mining Corp ______________ J icarilla 1 __________________ 29 23 3 E
15 Shar-Alan Oil Co __________________ Humble Dakota 1 _____________ 21 22 2 IE
16 Sun Oil Co ______________________ McElvain Govt. 1 _____________ 23 21 2 E
Section F—F' (W—E)
New Mexico
1 Standard Oil Co. of Texas ____________ Navajo Tribal 9—1 ____________ 9 27. 15 IE
2 Gulf Oil Corp ____________________ Gulf-Raven-Ojo-Navajo 1 ________ 4 27 14 IE
3 Benson-Montin-Greer Drilling Corp ______ ' Douthit 1 __________________ 5 27 13 IE
4 Pan American Petroleum Corp _________ Gallegos Canyon 147- .. _________ 4 27 12 IE
5 El Paso Natural Gas Products Co _______ Frontier 3—B ________________ 4 27 11 IE
6 Sunset International Petroleum Corp- v , _ Sipco Kutz Federal 2—F _________ 4 27 10 IE
7 El Paso Natural Gas Co _____________ Blanco 27—9 5 ________________ 2 27 9 IE
8 _ _ _do ___________ V ______________ S chwerdtfeger 12—A ___________ 6 27 8 E
9 ___do____L_______; ____________ SanJuan28—785 _____________ 6 27 7 IE
10 _ _ _do _________________________ San Juan 28—6 40 _____________ 4 27 6 E
11 LL_do_____-L __________________ San Juan 27—5 89 _____________ 4 27 5 IE
12 _ _ _do _________________________ San Juan 27—4 2 ______________ 5 27 4 E
13 L _ _do _________________________ Jicarilla 84—2 ________________ 21 28 3 IE
14 Sunray DX Oil Co _________________ Jicarilla Tribal l—A ___________ 27 28 2 IE
15 Foutz and Bursum _________________ Foutz and Bursum Val 1 ________ 17 28 1 IE
16 Mobil Oil Co _____________________ Boulder 23—23 _______________ 23 28 1 IE

 

108°

MONTEZUMA

I

__._C£)1_4913.I§_DQ_
NEW MEXICO

37°

Outcrop of Fruitland
Formation and
Kirtland

R16

Area of '
report a
EXPLANATION
36 °
. 12
Numbered points indicate locations
of oil or gas wells
Electric logs of these wells were used for
control in constructing the stratigraphic

cross sections the traces of which are
shown here

0 5

1 RIO

ARRIB

SANDOVAL

10 15 20 MILES

MAP SHOWING LINES OF SECTIONS

 

107°

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

NORTH
15
Anima
r
n "1 - 6
13 dyolln er atIOn
uL‘ ‘14 rock-
12 _ F o
C
-l
11 g
V5 Upper shale,member and Farminglton . O
ear ‘00 M/ Sandstone Member of Kirtland Shale "3
you“ 9/ ______ _ _ _
a _ _
“35‘0“ 8/ ._-—__:———— ——‘
S 7 _—__‘__‘; Shale—~_r___________._—-r——I——L-L—
,‘_—— —— -i‘- of Kirtland ‘I.
_____; member F'TTT-__ \
shalg____r--.— g 1
__ ’7' Formation ____:— . Sandstone —
FruItIand Pictured S CIIffs
3
Lewis Shale
Huerfanito Bentonite Bed D ,
Datum
NORTHWEST
Nacimiento 2
Formation
and FEET
younger I 1500
rocks .
\ Surface casmg
0. ~-
0 \\ 1000
a: 3
('3 \
D 4
0 Upper shale member’\5 j 500
° 4/
and Farmington Sandstone Member\6\7 3070 Sand F
Sto
-- ~--- ~ — — — ——7of Kirtland Shale \8 ne an O 5' 10 15 MILES
L°Wer Shale L' — — TL — — — — \9 yOUnger VERTICAL EXAGGERATION ABOUT x 53
__ _r *— — 7member of KIRIaerL r°Cks SOUTHEAST
F:I_5_Z—_:”_7SLaI—_T" 06
ml an . I
F — -- — -L _ _ A
11—37:”: g
# i S . L 16 O
Pictured Cliffs SandstoneE 1
Lewis
E Huerfanito Bentonite Bed

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Datum

El

 

PROFESSIONAL PAPER 676
PLATE 2

   

NORTH EAST

O o
89
5 1o 15 MILES 0

EXAGGERATION ABOUT X 53

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Formation boundaries were determined from electric logs of oil or gas wells located
at numbered points. The datum is the Huerfanito.

LIST OF WELLS, AND STRATIGRAPHIC CROSS SECTIONS SHOWING THE INTERVAL FROM THE HUERFANITO BENTONITE BED OF THE LEWIS SHALE TO THE
BASE OF THE OJO ALAMO SANDSTONE, THE ANIMAS FORMATION, OR THE NACIMIENTO FORMATION, SAN JUAN BASIN, COLORADO AND NEW MEXICO

A12 990 n

n 1 Ir- _LLLAA

FEET
1500
1000
500‘
3 '4 15 MILES
5 10
<§Surface casing Ojo Ala 0
‘~ 5 6 mo Sandstone and VERTICAL EXAGGERATION ABOUT X 53
' 8\9 younger rock EAST
Upper sha e member and' FarmIngton 10 s O
Sandstone Member of Kirt_lafld_Shale 11 12 13 14 a
"‘—' _l_-_—:- "—-— ——‘ ___.’____r":;_7.-_—..—————= 15 160
shlgleT-fiwember of Kirtlgng Shg|§__ _.—— — — — —\ rzg—r—x ’5
___‘———-—-__ _s'": :3 §—. rt)
Fruitland FormatIon E J:
If: :2 J
E: \Pictured Cliffs
Sandstone Lewis Shale
l i Huerfanito Bentonite Bed F,
Datum
NOTE

 

UNITED STATES DEPARTMENT OF THE INTERIOR ‘ PROFESSIONAL PAPER 676
GEOLOGICAL SURVEY

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

   

 

 

 

 

 

 

 

. ‘ PLATE 5
1 . ' 21 22 2 . 26 9 30 34 35 36 37 38 39 T 40 41 42 43 44 45 46 47 48
2 3 4 5 3% __7_ 8 9 52953 3% 1 1 12 13 14 , 15 1 3 167T1_2 . 17 18 52890 19 4 2369 20 2587 82822 2847 3 62565 24 25 82707 . _2695 28 2 r— 4 3093 —-— 8 2 3 1972 2605 3 43034 5 3100 7 3518 5 3108
T 25 5 3 2735 64.1259 ' 1-7 4 4 19 13 F 7 _3 T ANIMAS FORMATION 12 3 19 25 5 g 17 15
T 7 3 4 5 — 3 8 . 24 '3 ' . 7 7
Anlmas 47 27 —3 5 9 97
9 11 Frn 4 53M 10 43 T
2 49 44 37 10 1 4 + 2 8 93 8
9o: 12 22 32 6 5° 1 3 1 4 100‘ 1 1 3 3430
4.5 99 1 3 102 w v ‘5 5 4 6 4
200: % 5 3 4 5 81 3 4 75 13 5 5 3 9 22
37 102 . 29 5 _4 ' 45 8
63 9 I 4. 3 8 1 10 44 7 1 5 1.5 9 39 4_‘3 36 5 33562 7
1 T 1.4 1 2. 200: 1 1.6 T 3 3 83 I : 240 75 71 42614 2 ' 2 2 18 4
3 1 1 2.7 9 1 2 4.1 7 14 11 40 1 T 4 1.5 2.= 2 4 2 1 14
115 65 ‘ 0-8 1.5 3.1 1 4 . , 6 3477 65 8 1 2.5 21 3 3 8 3 g
20 250+ 4 4 6 12 1 8 5 1 4
35: T“ 12 1:3 27 2 15 2 1 5 5 33 61 13 82m 2 5 1 2 7 3
I 65: T 651“ 48 51 42 45 3 75M _13 40 7 278 1 g 2 I 5 7 20 5 7
2-9 8 50: . 3 49 5 3 3 6 5
140: m 5 3.7 T 5 5 12-3 ' 4 115 2 1 g 59 “mg“ 4 1° 12 —5 11 _4 43 16 3104
6 0.8 ; 6:4 9 5 8 3.6 52 4 3 2 ' 5 11:2? 2 15° 6 95+ 92% 9 2 9 2 3 2 13 16
6 3 1 4 32 1.2 5.8 . 7 7 3 4 3 14 44 1 11 61 80 44 2 3 3 5
6 13.3 50+ 2.7 1- . 7 2 5 36 4 2 170 15 2 2 10 10 3
15 3.1 5.2 11.5 , 2 ~ 5 43 6 5 120 2 2 3 40 7 30 6
10 1 57 17.6 1 4' 4 35 4 10 10 14 8
12 2.5 40 2 3 5 40 36 7 , 5
“We 75: s 2 T 10 15 3-5 2 2 4 a - 1 7 _5 92 2 4
°' 2 6. 47 1 ° 2‘7 1 6 10 3 9 1 4'9 g 7 5 78 2 2 38 02%“ 1 7 2 7 2 4 1 5 7O 2 3 24 34
6.7 J
200: 05125 2 52 T 2.1 32 11-4 11 1.6 5— 3 4.8 1'4 23.5 11 17 _14 .1136; 3 5 6 58 2 19 2 9 1,5 2-5 2 3 1 8 4 5 4 3
- 1 7 15 7 5 , 5 15 118 1 5 2 12
49 32+ 11.1 10 56+ 10.2 . 1.5 14 2 1 17 1 33 4 4 41 1 81455 17 1 6 12 50
— 10 1.6 2— 3 8.6 10 33 2 10 10.8 8.1 26 2 3 6 30 4 10 4 30 81 4 7 46 6 15
3 7 0 4 17 8 15 _— 1 3 25 6.2 0 8 5.3 70 7 3 4 6 7 4 22 1 2 13 1 5.5 14 4
16 11 15 15+ 1 3 11 7 7 19 5 5 20 1.5 . 2.2 6 6 5 1 4 4 T 19 6 3 2 6 2 1.5 7 4 3 11 10 6 14 9
4» 4 6 3249 184 2 9 3 _1 72960 9'9 ”'3 8 3182 2707 6 . 2835 1 2 3057' 3127 ——2915 6 3610 3065 42832 5 7 I ’ 3375 3265 2763 1482 3 10 2222 B 3014 3363 3455 3772 3431 3718 3612 3200
MS MS MS MS MS MS MS Ms ' M MS Ms 4 MS MS MS Ms Mb MS MS
I ‘ 1
49 50 51 52 53 54 55 56 . 57 55 59 60 61 62 6 64 65 66 67 68 3157 69 2860 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96
__ 22..

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

   

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

3
. _ _3—2148 F4235“) @2981 5 171? 1 "1 ill—1732
OJO
104 _ 112 2 4 2472
41 N 11 ALA 1
1 3 _3 , 18
1706 2653 3 ‘ '
1 ‘3 3 _3T 5 6 :13 ' S \N DSTONE .1—02196 11
T - 19 5 2432 33 2 5 48 AND 106 ‘ 5 3
T 1 2 2'5 4 112 . , 18 12
6 1.2 140 2 2172 79 69 2946 OUNGER fizz“; "-3 3
6 9 1—3 2129 23 2
43 12 ROCKS 2:7
70 -- 4 17 83 5 9 937 3 1 1 4 3034
3344 T 33 118W 7 3 1 4 F 31019 2 - o 5 14 53297
63 6 8 4 839 1: 1164 1=2 15 2677 23 ' ' 10
24 3602 75+ 4 3 9 8 2 6 3—3 » 7 6
5 1 8 3 44 3303 —3 3 3 5
13 39+ 1 _ 25 3 4 42 7 . 7 75 108 9 3 19 14
3126 112716 4 11.2 1.1 3 -_61-1 17 1° 3 2992 Tongue 49 1 4 j . 5 T
1 10 2 .3017 24 -1 O. 1 2373 4 45 7 9 ' 5 f 137 6 34 3 6 524
7 2 2 6-5 1 1-4 79 47 6 4 1 3 3205 45 T 07 D 57 9 21 W3 46
2 2 1 6 2 7 ' 57 4020 9.1 16-5 ‘1 g 1 4 4.7 1 Km? 97 82 27 40 4 4046
3 5 II 2 2 23 / LTongue 46 33 5 108 2 3 2 6 11 49 12 4 4 10 29
2 24 46+ 5 28 102 9 2 3 7 8 9
20 10 2 4 v 75+ 76 0f .42 10 53 28. 12 1 2 3 5 5 3758 2 50
4 3765 Tongue Tongue Kim 21 5 . 1819 10 1 6 7 - 7 6 12 8
1 4 “12 2 9 60+ of 60 of 3 3 2 4 6 5 L 50+ 2 42 ~ I 7 22 45 42 13 3 3 5 3 1 2 _5
10 36 29 9 34 6.1 Knc Kpc 2:4 19 1 4 94 3 4 4 23 4 1 7 10 3 14 9 10 22 3
~ 31 1 4 . 44 1030 28 12 92 3 3 g 7 6 35¢ 2 8 1 5 36 40 7 6 5 30 15 24 . 6 4 3_6
22 9 3 9 5:2 H10 25+ 4 9 26 =2 9 4 6 4 1 3 15 i 5 12 4 8 940 1.1 11.12 14 5 8 7 12 g 3 8 4 11: 6 7 4 1E3. 5 2 17 8—3 1 11.5
.3215 8 2808 7 3095 3468 8 3807 3.4090 3714 10 1050 MS 5+ M5 ‘ -6-2 “4‘56 1900 2 3 2458 4 2580 “2396 3 2650 6 2905 9 3369 6 3465 43138 5 3093 3277 63408 7947 M 8 MS 955 3 1070 5 1140 5 1278 5 1859 2273 .1962 2436 2382 2683 6 2800 2757 3080 2900 3162 3420 3804 4115 3600 Ms
. 9 ,
97 98 99 100 101 102 103 104 105 1C5 ' 107 108 109 111 ‘ 112 113 114 115 116 117 118 119 120 121 122 123 124 125 ‘9 126 _ 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144
1575 6 1336 —— 2858 . ——n —‘
5 11 3443
2 2338312-4 OJO ALAMO SANDST NE
7
- 7 5 9 AND YOUNGER ROCKS _51985 3290 OJO ALAMO SANDSTONE
1739 5 — '
2% 4 9 3476 .Ffi3245 E5169] 7 AND YOUNGER ROCKS
101 7 1 2
1—3 ‘ 7 121
148
X “62391 25 2 74 53 77
2050 6 3 ‘ _35153 3253
4 _3 90 2 144 . .
1629 2 6 3 2 5 61 4 795 . 4.51949 21
6 772 11 2 4 124 3478 L5 1514 3 5.5 2553 3252 4185
1080 196 24 5 4 4 10 3 6 , 9
5 17 20 50 18 41429 2924 20 2 6 22 —3
—’§T337 ‘_ _4 10 119 78 395 2 5 8 5 3 6
157 3 2— 3 4 6 4 s 4046 44 9 3 3 7 37 6 4 4_'3 460
38 2 4 10 16 16 151 5 7 2 5 3 5 _63704 2.5 6
_74-1096 _8 2 —3 13 97 1295 3 2 16 21 2 9 6.5
54 4 4 2 8 4 3565 58 2.5 _3 2 2-5 4 5
104 ‘3 —9 12 5 12 14 8 5 i ' 5 3 3 ‘3 6 4 48 g 18 4o 85 5 20
50 T 4 8 .
. 4O 67 3 2 17 10 14 3454 T“ 0" 1-5 2'5 4 28 62 32 3.5
195 35 11 . 14 32 9 3666 4 Lewis 15+ 40 47 2 4 5 Tea
4 54 4 87 9 2 9 50 6 8 22 Shale 1.1 8 328 —5 68.5 51 18 4 27 10 °"7 , T 3.5 T 21 5
34 154 1545 3_3 4 2 15 5 _ 32 6 11 25 29 3 7 4 3449 :11 2'5 ‘ 4'5 _11 47 5 12 14 19 28 3 K7154). 3‘5 4‘5 8
5 % g 1 g ' 3—3 3 5 2 9 3 7 9 Km: 40+ 44 1409 22 2 3 2 7 2 13 9 6 1 g 1 5 3574 L T 16: - 1
2 2 8:: =: 31 u —4 H5 1 5 17 2 22 23 3 — 7 g 2: 27 29 4 13 6 4 9 11 ”7' ""' 37 28 11 11 2 10 20 41 22 2 7 18 3 2 2 10 3 5 1 7'7 16+ 4 29
6 20 3 4 5 7 16 7 1 17 1 ' 16 5 i 20: >12 i
10 8 13 13 6 1 1 1 4 3 4 10 12 11 7
-445 7 903 8 1200 1186 1579 1800 1585 1925 1765 2195 5 2547 4 3084 4 3 3595. 3658 3557 3429 3606 4150 3727 103646 5 3516 5 3493 ‘|' MS 7'5 380 935 —i1544 6 1433 1382 8 1682 ‘7_‘-3—1645 4 1870 2087 8 3035 . 2175 4 2678 3375 3400 3466 3 4310 3797 , 3602 ' 735 MS MS 4 MS 1-5 557
145 146 971 147 . 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 ' 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 #1392 187 188 189 190 191 192
0J0 ALATMO SANDSTONE . 5 1795
15.919823 ‘51891 AND YOUNGER ROC KS T 2 5 2113
8 3394 —4 5
43 4
8 1751 5 2957 10 4 3742 4— 215m 86 31
216 1268 1 21 3 2 7 2151 6 2728 13 9 3 70: _4
W 2 1% 5.5 2=T1885 1 2 2 3505
H1218 124 2 31.5 7 1911 .13 1 2 -—2863 3054 143130 27 ‘ g 30
48 3 6 2173 13 7 12 4 6 6 9 3
72 ‘3 4 , 10 —
723 39 5 43 11 12 5 6 3 2.5 T 2 4 1205
=5 1635 7 4 5'5 49 67 4 ~3032 3350 4 4 9 19 6 3'3 4
2 2 1698 4 5 20 3 7 ' 2.8
5 4 3.5 10 113 7 3 50 64 9 4 5 5 3270 13 30: 3.3 _6_621 2° 13 49 114
2 5 2.5 4 8 6 5.5 . 25 17 5 3 _2 5 2_5 -_ 1167 3 592225
50 _51177 T 9 ' 4 31 12 3 5 38 5 3 12 7 10 80 15+ ' 15: 32 7 2 3
54 of 10 6~25 10 5 3:3 5 17 16 2 5 34 93. 2 3 7‘— 7 4.8 5.1 32 7 2661
87 41 K —6 159 9 13 g 4 5 11 5 - 17:15 4 7 61624 . 52 72 1928 2 6
21300 9° \\ 48 10 22 22 2 3 5 12 39 T 19 1.2 3 1245 3:175 5 47
14 1220 4— 3 —1491 57 7 13 11 10 . 42 54 , + 2 4 16 17(many - 5-5
8 7 5 9 48 33.5 2 2 9 3697 . + 35, 4 12 . 50 2878
21 ' I 2 2 4 2 34.5 28 21 3 6 13 4 4 16 6 4 5 1 3 30 35‘ 12 1° 8 mm”) 4 4 1078 1216 4 28 33 18
17 22 24 1 5 3 14 14 7
3 6 14 2 ° ‘25 7 .1. 2‘5 7'5 2:3 2 8 17 4 5 7 1% 29 13 4 3‘5 8 9 6 15 18 -L1 3 7 4 13 4 3 5 1 1 8 3 6 7 6 14 8 5 4 l4 :1 7 4 17 5 -§' —3 8 1:3
820 1227 1252 1407 , 1336 1244 1524 21338 —1784 -7.2012 1826 4 2077 1905 "2289 -2302 3 2017 1 2029 2869 3112 3 2978 . . 3174 - 3 3135 3357 3450 3357 3565 3638 3395 3875 2 3722 3630 M s - M s l - MS 2 704 1238 1670 1283 1100 2 1236 1308 1695 1995 229 1977 ~—2710 2904 2297
193 194 195 196 197 198 200 201 202 203 204 205 206 207 208 209 210 211 891 212 213 _1337 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240
' 7 2 3 —' ’— '7"
0J0 ALflMO SANDSTONE
AN 3 YOUNGER ROCKS OJO ALAMO SAN DSTONE
16
3542 85 AND YOUNGER ROCKS
72$ 10 L17
4
2 2704 1 2 2975 9—y3255 2 3
26 £2906 3 3 25 2 2178 F75 2419
42 —’373767 —.3 5 41086 2 2 2525 2 _5 2741
18 4 48 _‘3 2913 17 13 4 7 16_ 3 4—4 ’3—3595
11 1 ~ _
5 — 3 4 3554 6—4 \ A5 1349 - 1724 1694 2512 _3 56 —3 2512 4
2 4 9 98 60 6684 6 3 _51494 6:3' 14 ‘92717 40
8 2 5 4—7 51150 65 3 2° 17 —3 97 46 3047 1 ‘ 1 T 0-5
1° 10 5 56 12 - 3:8 1 I 5 3 h 4 2 3 9 3335 6 2 46 ‘6 3.5
6 . Ir T 2184 4 40 1 5 _ 3 3276 Tea on Toa on 1.3 17-9
6 ’ 11 10 ongue l 3 6% 6 3 30 2 18 5 4 4 29 lower Lewis 8.5
- 23 . 13 .
1.05 . 8 3495 10 103 °f 1o 6 2 5 1253 3 146K 84 82 87 18 52 84 2 3 1 7 15 3 11 43690 83 24 Km. Share 20$
9 3 4 K00 Tea 3 \\’\\ ,3— 1878 - 5 8 3 16 3 3 2 1 2 4 KM Kk
55 59 12 11 _L. on 5.3 57 1 4 6 2 3 1295 1059 82 _ —‘ 80 70 _4 13 2‘ ‘4 19 5 4 5 12 3 3 10 and and 2
9 1° 10 37 “”17" 20+ 5 15 1° 2 5 4° ”—2100 , 12 3 4 2 2 35 4 1 5 ””4“" “DC 15:
2 g 10 2 m — 4 18 10 H6186 — 3 37 4o 2 32 2 g 2 3 3 f0 5 g 15 3 2 g 5 2 10% 12 3 KW 2mm 53
3 43 1,7 31 5 4 2 2 Ah pm 1 10
2 9 3 2.5 3'5 3 23 10 2 7 4 3 3 7 2 4 63218 5 1 14
6m w 1 4 17 15 2 3 I L 18 12 4 5 6 a 4 17 7 2‘ 1 4E 14 4: 4 1:41 e 7 13 13 4 nfi =3: 3 a s 6 5 3 9 3 15 15 2 3 ”I 2 12 I ”141248 I “8 0-7
~ 2861 3054. 3134 2 3038 3420 3555 3666 3905 _13727 3595 MS MS 2 . 788 1234 4 1310 6 1342 1100 2 1265 1180 61223 1608 1460 61596 _92132 2!— 1829 1 3 1928 7 1804 2256 2622 2669 2317 4 2566 2820 2875 2 2628 3133 3418 —3715 3350 3750 3236 3582 2410 2 2492 M73 MS 5-7
241 242 243 244 245 246 247 248 249 250 251 252 253 - 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 \ 280 281 282 283 284 285 286 287 288
' 0J0 7‘ OJO ALAMO SANDSTONE
OJO ALAMO SANDSTONE ALAMO T 46 208% ¥
AN 3 YOUNGER ROCKS 18 259
2205 2003 SAN DSTON E .10: x 1748 180
5 is 1.5 —§138 2 220 V\’\.\
16 193R AND - 25+ 1877 \\ 110:
165 \ OUNGER 7 2 5 no: 120
570 4 W 1821 41
2 5 2255 1876 4.5 _g 2 1747
25 74 17 "-3 ROCKS 15 27 1 _2 142
,— 50 4 2304
—3 515 7 —7900 3 5'3 1F2 1985 1:7— 121
25 12389 2 3 1991 2255 30+ 15 26 8 2854 2927
1928 4 1 4 _—2339 3037 T 134 24 23 3 1 3f
4 29 . 5 3 51 4 2 5 3 11 86 85 2 26 r—3072 9 5
10 14 22 27 4 7 3122 10.5 1 1-5 165 32 4 5 Z 1 g 2 Z
2 g 6 67 30 —3 —3 1 1 4 63 72 0-5 2 2 4 3 11
143 ’ 14.5 145
17 798 148K 3 .. 48 1 31 12 . _ 21 15 21 7 .
20 PM 4 33 30 1 3 7 1“ °" 1 3 33 2 6 2981
53 3 5 2 5 17 66 5 83192 2 2 3320 Lewis 494 9 4 5 9 3 5
4 6 103 57 . 2 5_3 3 . 1 9 g 2 5 6 2 9 3426 3009 saute. 30 2 :0 1074 95 —.3 6—72767 15 2 —13 69 20
460 ‘5 5 5 r 4 5 2 7 1
4 17 2 2 10 . and to 8 5 64
45 2 13 54 28 61 . _5 29 24 55 9 3 10 4 2 6 . 2 2 KM T 59 3 5 12 859 9 . lag 1 $1262 45 58 4 3 50 3 3
3 74 4 3 1775 121694 ' 8—3 42 1 4 4 6 7 3 2 25 L T E 72 4 2 2 2 6 1 2 5 8 17 37 9
15 6 3 6 14526 .33 19 £1624 16 7 6 Z 11 3 37 2 10 3 ‘ 10 9 g E 15 1 20+ 478 13 18 2 9 2:675 25 17 i162“) A 6 13 3
1 17 14 i — 1.4 ' 12.7 10 1 ‘2
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289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 7 313 314 315 316 317 318 319 320 321 322 323 324 108° 107°
0J0 ALAMO SAN DSTON
0J0 ALAMO LL 939 ALAMO, SANDSTONE OJO ALAMO SAN DSTONE
AND YOUNGER ROCKS OJO AL MO SANDST N
SAN DSTDNE ANE YOUN 3ER ROCKS
206kM 2 747 AND Y UNGER R0 KS
AN D 217 N
.. 133 ,
YOUNGER N 201i. W 160
W 200: \2 89 N
ROCKS 31000 41785 \x -133
3:;
2r5435
1.5 - 272
3.5 2 91793 49 4 2598 52 m
4 2 3 184 170 1 5 T T 2.3
T 2 4 1 7% 411 10 4 ' 3_5 4 0.4
- 584
122 1i” 56 5 2 _271623 ‘5 ' 143 /
29 35 175 w 2 ——3 2398 50: 37° €099.11..qu _1___ _ _
54 43 NEW MEXICO
2.2 155 105
2.5
15 _5 8 481 1076 x 5 66 1.5 112 fi_8 5 98
fin 322 .Ts ‘ 78 61 6 244 _5 5 453 T '
20 r 5 T 10 T 1
10 2967 50 40 55 43 36 28 “f 7 60: T 6 3 40 T
20 £13 (39 T 2.6 32 2 7 Kpc 30: 3—3 38 2 g 1461 30+ 113.5 T {4 3 474 40: T T .1 5 . 0.7
1.8 ‘ 3 12 —‘3 2690 17 1 3 T 5 2 5 5 '
0-6 8 2‘2 —A —R L ‘ m 8 8 8 10 1.5 1 5 - ‘1 6-2 4 5
2997 1.4 4-3 1124 1184 _ 1 1935 17 67 1-5 3 . 5 490 482 475
2636 M3 0.5 366 MS 513 536 1598 1910 08 2712 2473 2698 MS 290 6 95? 1480 1730 1502 Ms MS 0 5 Ms , 949 Ms MS Ms MS . MS MS
92'. .94
l .110
.108 109. “3
07 4}}2 114 11
EXPLANATION '
65 . 7 60 ' .132 . ‘ 1 .137
\ Location numbers keyed to location/ I 134
map and table 3 .163 1
.170 .175
| .1 .167 171 .172 .174
152 169 . 17 27
2432/Drilled :eOth tofirst measured T//T°p of measured interval 1 - 192. 94 .197. 199. .201 '202 35203
5 ru1t|and coal bed 2_5

'196 198

ThickneSS,in feet,of/79 Brokefi section of noncoal strata

'225
noncoal intervals / C 21421 217 '226 .2331' - ‘ 235‘ '
\ 7O / overed or poorly - ° . ~ 21 . 233. / 25
7 47Thickness, in feet, of coal intervals exposed interval 215 227 '236
3

247 ' 257. 261 .263

SECTIONS OF COAL BEDS IN THE FRUITLAND FORMATION IN THE SAN JUAN BASIN, 42 :1: ' »

Unmeasured Interval 1

 

 

 

 

. 7
6 (not shown to scale; 1:58 andtenths of feet . .7285 28 288 289
generally less than ' — .—— .-— m———._. .._
NORTHWESTERN NEW MEXICO AND SOUT- HWESTERN COLORADO l
42 ongue .300 .302
O
60 Kpc
1 4 12 .303
6 12 Drilled depth to base of
3 4 265 ' Fruitland Formation (top (if 6 AT 311.
' ' t
0 Pictured Cliffs Sands one MS—Measured section 360 EXPLAN ION

NOTES

The coal sections are numbered from
west to east. beginning in the northwest- .
em part Of the basm" Measured surface sectlons

Rock symbols: Kpc, Pictured Cliffs Sand- . 78
stone; Toa, Oio Alamo Sand:to:'1e;dKéh | . 2
Fruitland Formation; ka, irt an a e 1 .
and Fruitland Formation. Well 0011th p01nt

.317 .318

0' 9‘ 10 15. 20 MILES ' 324
I 6 RIW

LOCATION OF MEASURED.SECTIONS AND WELL CONTROL POINTS

416—332 0 - 71 (In pocket)

7 Uéfiii/

POSTGLACIAL LAHARS FROM

aw

MOUNT RAINIER VOLCANO,

 

WASHINGTON

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Postglacial Lahars From
Mount Rainier Volcano,

Washington

By DWIGHT R. CRANDELL

 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 677

14 stzmjl 0f tfle age, extent, and origin of more
tfian 55 pong/acid] muq’flows and deérz's flows
from Mount Raz'm'er

 

 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1971

UNITED STATES DEPARTMENT OF THE INTERIOR
ROGERS C. B. MORTON, Secretary

GEOLOGICAL SURVEY
W. A. Radlinski, Acting Director

Library of Congress catalog-card No. 79—611942

 

For sale by the Superintendent of Documents, US Government Printing Oflice
Washington, D.C. 20402

CONTENTS

 

III

Page Page
Abstract ........................................... 1 Description of lahars—Continued
Introduction ....................................... 1 Lahars in the Nisqually River valley—Continued
Geographic setting of the volcano and the lahars. . . . 2 Origin of lahar assemblages in the Nisqually and
Climate ....................................... 3 White River valleys ....................... 41
Terminology and distinctive features of lahars ..... 3 Lahar assemblage D ........................ 43
Ways in which lahars originate ................... 8 Lahars in the Nisqually River valley downstream
Age and lithology of Mount Rainier volcano ....... 10 from the park ............................ 44
Dating of lahars ................................ 11 Kautz Creek valley lahar assemblage .............. 45
Origin of the clay in some lahars .................. 12 Lahars in the valleys of Tahoma Creek and the North
Description of lahars ................................ 17 and South Puyallup Rivers .................... 49
Lahars in the White River drainage basin. . . . . . . . . . 17 Round Pass Mudflow ....................... 49
Greenwater lahar ........................... 18 1,000—year-old lahar ......................... 56
Pre-Osceola lahar assemblage ................. 23 Electron Mudflow .......................... 56
Osceola Mudflow ........................... 24 Lahar assemblage in the Tahoma Creek valley. . 57
Distribution and volume ................. 24 Lahar assemblage in the South Puyallup River
Texture and mineralogy ................. 26 valley ................................... 62
Origin ................................. 29 Block-and—ash flow in the South Puyallup River
Post-Osceola lahar assemblage ................ 30 valley ................................... 64
Post-Osceola lahar assemblage in the West Fork Lahars in the North Puyallup River valley ...... 66
valley ................................... 32 Lahars in the Mowich River valley ............... 67
Lahars in the Nisqually River valley .............. 32 Lahar in the Carbon River valley ................. 67
Paradise lahar .............................. 33 Lahars in the Muddy Fork of the Cowlitz River and
Older lahar at Paradise Park ................. 36 Ohanapecosh River valleys .................... 68
Lahars at Van Trump Park .................. 37 The association of lahars with volcanism ............... 68
Lahar assemblage A ......................... 38 Hazards from future lahars .......................... 69
Lahar assemblage B ......................... 39 References cited ................................... 71
Lahar assemblage C ......................... 40 Index ............................................. 75
ILLUSTRATIONS
Page
PLATE 1. Topographic map of Mount Rainier National Park ______________________________________________ In pocket
2. Profiles and cross sections of the valley floors of the White River, the Nisqually River, and Kautz Creek_ In pocket
3. Topographic map of the Mount Rainier area. showing the Osceola and Electron Mudflows and the
Paradise lahar __________________________________________________________________________ In pocket
FIGURE 1. Map showing location of Mount Rainier ___________________________________________________________ 2
2- Graph showing average annual precipitation at Longmire and Paradise Ranger Station __________________ 3
3. Graph showing cumulative curves and sorting coefficients of three samples of Evans Creek till ___________ 6
4. Graph showing cumulative curves of samples from avalanche deposits on floor of White River valley-___ __ . 7
5- Photograph showing avalanche deposit at and on the terminus of Tahoma Glacier ______________________ 18
6- Map showing distribution of Greenwater lahar _____________________________________________________ 19
7—10. Photographs of: ‘
7. Mounds on the Greenwater lahar _____________________________________________________________ 20
8. Mound on the Greenwater lahar ______________________________________________________________ 21
9. Large breadcrusted block in a lahar __________________________________________________________ 23
10. Osceola Mudflow southeast of Greenwater ____________________________________________________ 25
11- Graph showing cumulative curves of size distribution of samples from the Osceola Mudflow _______________ 28
12- PhotOgl‘aph of lahar exposed near the mouth of Fryingpan Creek ______________________________________ 31
13. Photograph of Paradise lahar above pyroclastic layer 0 east of Ricksecker Point _________________________ 34

IV

FIGURE

TABLE

14.

15.
16.
17.
18—21.

22.

23.
24.
25.
26.
27.

28.
29.

30.
31—35.

36.
37.

b—I

accoxxcap‘mpato

10.
11.
12.

CONTENTS

 

Page
Graph showing cumulative curves of grain-size distribution of Paradise lahar at three localities and older lahar
at Paradise Park ____________________________________________________________________________ 35
Photograph of outcrop of Paradise lahar and older lahar at Paradise Park _______________________________ 37
Photograph of lahar in streambank on west side of Nisqually River flood plain __________________________ 39
Graph showing cumulative curves of size distribution of lahars near Longmire ___________________________ 41
Photographs of:
18. Fluvial gravel in lahar assemblage C in west bank of Nisqually River ___________________________ 42
19. Deposits in west bank of Kautz Creek ______________________________________________________ 47
20. Bouldery surface of a pre—W lahar assemblage that underlies the floor of Kautz Creek valley _______ 48
21. Lahars and fluvial sand and gravel deposited near mouth of Kautz Creek in October 1947 _________ 48
Graph showing cumulative curves of size distribution of deposits formed by floods and lahars in the Kautz
Creek valley in October 1947 _________________________________________________________________ 49
Photograph of flood in Kautz Creek channel on August 23, 1961 ______________________________________ 50
Photograph of banks of Kautz Creek shortly after flood of August 23, 1961 ____________________________ 51
Map showing inferred original extent of Round Pass Mudflow ________________________________________ 52
Photograph showing south edge of Round Pass Mudflow at Indian Henrys Hunting Ground _____________ 53
Photograph showing Round Pass Mudflow on top of pyroclastic layer Y above floor of North Puyallup
River valley _______________________________________________________________________________ 54
Graph showing cumulative curves of size distribution of Electron Mudflow, lahar in the Tahoma Creek valley,
1,000-year—old lahar in South Puyallup River valley, and Round Pass Mudflow ______________________ 55
Photograph of lahar on top of fluvial cobble-and—boulder gravel in the Tahoma Creek valley ________________ 59
Photograph showing bouldery deposit left in Tahoma Creek picnic area on August 31, 1967 ________________ 60
Photographs showing:
31. Aerial View of South Tahoma Glacier _______________________________________________________ 61
32. Rockfall debris above head of South Tahoma Glacier _________________________________________ 63
33. Bomb-bearing block-and-ash flow deposit along West Side Road near South Puyallup River _______ 64
34. Outcrop of relatively fine grained facies of block-and-ash flow along West Side Road near South Puyallup
River _______________________________________________________________________________ 65
35. Breadcrust bombs from the block-and-ash flow in South Puyallup River valley __________________ 65
Graph showing cumulative curves of size distribution of the block-and-ash flow ________________________ 66
Point diagram of azimuth and dip of north-seeking poles in dense rock fragments and bombs from block-and-
ash flow in South Puyallup River valley _______________________________________________________ 67
T A B L E S
Page.
Average monthly and average annual precipitation at Longmire for the 51-year period preceding 1966 and
at Longmire and Paradise Ranger Station for the period 1956 through 1965 ________________________ 3
. Size-distribution data on eight lahars, each sampled from two different horizons ________________________ 8
Subdivisions of Quaternary time in western Washington _____________________________________________ 10
. Radiocarbon dates pertaining to surficial deposits less than 6,000 years old _____________________________ 11
Source, age, and description of some postglacial pyroclastic deposits ___________________________________ 12
. Postglacial eruptions, lahars, avalanches, and block-and—ash flows _____________________________________ 14
. Mineralogy of clay fractions of Evans Creek till ________ '_ ___________________________________________ 16
. Mineralogy of clay fractions of hydrothermally altered andesite _______________________________________ 17
. Sequence of lahar assemblages and their stratigraphic relation to pyroclastic deposits in the White River and
West Fork valleys __________________________________________________________________________ 19
Size-distribution data from samples of postglacial lahars and a block-and-ash flow _______________________ 27
Mineralogy of clay-sized fraction of lahars _________________________________________________________ 29
Grain-size distribution data on deposits formed by floods and lahars in the Kautz Creek valley ___________ 48

POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO,
WASHINGTON

By DWIGHT R. CRANDELL

ABSTRACT

More than 55 lahars (mudflows and debris flows from a
volcano) originated at Mount Rainier during Holocene time.
These ranged in length from a few miles to 70 miles and in
volume from a few million cubic yards to more than half a
cubic mile. Some lahars were created by landslides of altered
volcanic rock; they contain significant amounts of clay, which
consists of montmorillonite and kaolinite and lesser amounts of
other clay minerals, which were formed by hydrothermal altera-
tion of rock within the volcano. Some of these lahars have been
deep enough, when flowing, to fill valleys to depths of hundreds
of feet; the fluidity of the lahar permitted most of it to progress
downvalley and to leave in passing only a thin deposit on valley
sides and terraces. Smaller lahars of the same kind seem to have
progressed downvalley in a single massive wave hundreds of
feet high. Clay-rich lahars originated in massive slides of clayey
rock that had a high moisture content. The slides may have been
triggered either by strong earthquakes or by volcanic explosions,
or possibly by swelling that accompanied the ascent of molten
rock into the volcano. Other lahars were created by the eruption
of hot volcanic bombs, dense rock fragments, and ash onto ice
and snow at the summit of the volcano. Rapid melting of snow
created floods down the volcano’s flanks which carried down
rock debris and also picked up loose detritus on valley floors
to form lahars. Still other lahars resulted from precipitation of
cloudburst proportions and by glacier outburst floods. Some
outburst floods may have been caused by excessive melting of ice
around subglacial steam vents.

There have been repeated episodes of volcanism at Mount
Rainier within about the last 10,000 years. The last major erup-
tive period, between about 2,000 and 2,500 years ago, witnessed
the eruption of pumice and lava flows and the formation of
many lahars. During this period, erosion alternated with ag-
gradation of lahars and fluvial gravels on the valley floors of
the White and Nisqually Rivers, and possibly on those of
some other rivers as well. The last pumice eruption, which
occurred in the mid-1800’s, apparently was on a very small
scale, and there is no known record of floods or lahars at that
time.

If future eruptions of Mount Rainier were to be similar
in scale and type to those of the last 10,000 years, the greatest
hazard would be that of lahars. Because of the restriction of
lahars to the lower parts of valleys away from the immedi-
ate flanks of the volcano, valley floors would be especially haz-
ardous. In view of the increased probability of lahar formation
during an eruption, valley floors should be evacuated immedi-
ately within a radius of at least 25 miles from the volcano if
an eruption should begin. It is proposed that permanent resi-
dences should not be constructed on certain valley floors near

 

Mount Rainier, that consideration be given to the relocation
of campgrounds that are now in potentially hazardous areas,
and that future highways and bridges be designed and located
to minimize destruction by future lahars. Likewise, the plan-
ning of all other residential, economic, and recreational devel-
opments within valleys that head on the volcano should be
concerned with lahars as potential geologic hazards.
Artificial traps that might prevent large lahars from enter-
ing densely populated areas now exist in the form of hydro-
electric power dams and flood-control dams in some valleys.
To control a lahar, reservoirs behind these dams would have
to be empty. N0 reservoir, however, would be of any avail
in controlling or diverting a lahar comparable in size with the
largest that originated at Mount Rainier in postglacial time.

INTRODUCTION

Within postglacial (Holocene) time, which consti-
tutes about the last 10,000 years, various events of a
catastrophic nature have occurred at Mount Rainier.
These have included repeated eruptions of pumice,
lava flows, and hot volcanic bombs, and most devastat-
ing of all, recurring avalanches of rock debris from
the summit and slopes of the volcano which created
lahars (mudflows and debris flows from a volcano)
hundreds of feet deep and many miles long. Within
the last 10,000 years Mount Rainier has lost a much
greater volume through these avalanches and other
erosional processes than it has gained from the eruption
of new lava.

Some postglacial lahars from Mount Rainier have
had sufficient volume and mobility to extend into the
Puget Sound lowland northwest of the volcano (fig. 1)
and to spread over areas there that are now densely
populated. Lahars of comparable size today would
doubtlessly be disastrous. My purpose of studying the
postglacial lahars was to determine their stratigraphy,
physical characteristics, distribution, and especially
their manner and place of origin so as to assess the po-
tential hazards presented by future lahars from the
volcano.

The study was begun in 1960 as the principal part
of a broader investigation of surficial deposits in
Mount Rainier National Park and in selected areas in

1

2 POSTGLA‘CIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON

122°

 

   
  
 
   
   
   
   
 

Enumclawj
White .

47° —

'Packwood

 

 

 

 

 

0
WASHINGTON
Gilmore Corners ,Seattle
M' um Rainier
A
Mount St Helens Area of larger map
0 10 20 30 MILES

L___lr—_l___l

FIGURE 1.—Location of Mount Rainier with respect to the Gas-
cade Range and the Puget Sound lowland of western Wash-
ington. The dotted line marks the approximate boundary
between lowland and mountains. Patterned area around
Mount Rainier indicates glaciers.

the adjacent mountains. I shared the fieldwork of the
first two summers with Robert D. Miller, who assumed
primary responsibility in 1961 for working out the
glacial history of the upper Nisqually River valley.
Donal R. Mullineaux joined the project in 1962 and
undertook a study of the lithology, distribution, strati—
graphy, age, and source of the postglacial pyroclastic
deposits in Mount Rainier National Park. I was ably
assisted in the field by my son Thomas D. Crandell (de-
ceased) in 1960, by Jon Koloski in 1962, by Michael P.
Lane in 1963, and by Jack H. Hyde in 1966.

Fieldwork in the park was greatly facilitated by the
cooperation of the Superintendent and staff of the Na-
tional Park Service, and grateful acknowledgement is
made of the enthusiastic encouragement and help given
by Vernon R. Bender, Charles J. Gebler, and Norman
A. Bishop, successive Chief Park Naturalists. Apprecia-

 

tion is also expressed to the St. Regis Paper Co. for
permission to conduct field investigations on private
land west of Mount Rainier National Park.

I profited immeasurably from numerousdiscussions
in the field with Richard S. Fiske, Clifford A. Hopson,
and Aaron C. Waters, who were completing their study
of the bedrock geology of the park when my investiga-
tion was just getting under way. My interest in studying
the surficial geology of the park was encouraged by
Professor Waters, who foresaw the desirability of hav-
ing such a study to supplement their studies of the
rock formations.

Unless otherwise specified, all the analyses reported ,
here were made in the laboratories of the US. Geo-
logical Survey. The radiocarbon age determinations
were supervised by Meyer Rubin, and grain-size an-
alyses were supervised by Thomas C. Nichols and
Edward E. McGregor. X-ray determinations of the
mineralogy of silt and clay fractions of lahars and
other surficial deposits were conducted by Paul D.
Blackmon, Dorothy Carroll, John C. Hathaway, Ed-
ward E. McGregor, and Harry C. Starkey.

GEOGRAPHIC SETTING OF THE VOLCANO AND LAHARS

Mount Rainier volcano dominates the landscape of a
large part of western Washington. It stands nearly 3
miles higher than the lowlands to the west and 11/;
miles higher than the surrounding mountains. The base
of the volcano spreads over an area of about 100 square
miles, and lava flows that radiate from the base of the
cone extend to distances of as much as 9 miles. The
flanks of Mount Rainier are drained by five major rivers
and their tributaries. Clockwise from the northwest the
major rivers are the Carbon, White, Cowl‘itz, Nisqually,
and Puyallup (fig. 1; pl. 1). Each river flows westerly
through the Cascade Range and, with the exception of
the Cowlitz, empties into Puget Sound near Tacoma,
Wash. The Cowlitz joins the Columbia River in the
southwestern part of the State to flow to the Pacific
Ocean.

Each major river in Mount Rainier National Park
occupies a deep canyon whose floor is LOGO—3,000 feet
below the adjacent divides. Valley-floor gradients are
100—400 feet per mile near the park boundaries and in-
crease markedly upstream. The valley floors of Tahoma
Creek, the North and South Puyallup Rivers, and
the Mowich River have gradients of 700—800 feet per
mile in their upper reaches and are among the steepest
in the park. The volcano’s summit towers 9,000—11,000
feet above valley floors only 3—6 miles away. The flanks
of the volcano itself have slopes mostly between 25°
and 30°, although those of Willis Wall on the north
side are between 40° and 45°. ‘

INTRODUCTION 3

Partly because of its position astride a high, dis-
sected part of the Cascade Range, Mount Rainier does
not have broad peripheral aprons of laharic and
fluvial deposits like those fringing the base of Mount
Shasta in northern California and some large strato-
volcanoes elsewhere. Instead, large lahars originating
on the volcano in Quaternary time repeatedly flowed
far down the canyons of the Cascade Range, and some
came to rest beyond the mountain front in parts of
the adjoining Puget Sound lowland (Crandell, 1963b).

Within the mountains, lahars typically are found on
valley floors, although the deposits of some of the larg-
est lahars also veneer valley walls to heights of hun-
dreds of feet. Some even mantle divides that are a
thousand feet or more above valley floors near the
volcano. Lahars that formed within the last thousand
years commonly form low terraces or veneer other un-
consolidated deposits that form the terraces. Older
lahars are often found interbedded with fluvial terrace
deposits, duff horizons and stumps that represent old
forest floors, and thin layers of pyroclastlic material.

CLIMATE

The climate of Mount Rainier National Park is cool
and moist during fall, winter, and spring, but the sum-
mers are relatively warm and dry. Monthly precipita-
tion at Paradise Park, at an altitude of about 5,400
feet, generally is greater than 10 inches from October
through March and decreases to an inch or two during
July (table 1). Within the period from 1956 through
1965 the highest yearly precipitation at Paradise
Ranger Station was 146.31 inches in 1959, and the lowest
was 94.56 inches in 1965. As much as 48 feet of snow
has fallen at Paradise Park in a single winter, and
snowbanks frequently linger there until late July or
August. The average January and July temperatures,
respectively, at Paradise Park are 26.4° and 53.0°F.
Minimum daily temperatures below freezing can be
expected there any month of the year, whereas at Long-
mire, at an altitude of 2,672 feet, daily minimum tem-
peratures generally are above 32°F. during June, July,
and August. Because of its lower altitude Longmire re—
ceives considerably less precipitation than does Paradise
Park (table 1), and the January and July average tem-
peratures there are 302° and 60.6°F., respectively. The
long-term average annual precipitation at Longmire is
about 82 inches, but within the last 40 years the annual
precipitation has ranged from a low of 43.22 inches in
1952 to a high of 113.60 inches in 1933 (fig. 2).

Winds throughout the year are generally from the
west. From May through August, average monthly
winds are mostly from the west and southwest, and dur-
ing November through January, they are from the west

 

TABLE 1.—-Average monthly and average annual precipitation
(inches) at Longmire (1) for the 51-year period preceding 1966‘
and at Longmire (2) and Paradise Ranger Station (3) for the
period from 1956' through 1965

[Compiled from Climatology Data published by the U.S. Weather Bureau]

 

 

       

1 2 3

January _________________________ 10. 92 11. 87 17. 21
February- __ ___- 8. 98 9. 47 13. 82
March ______ ___- 8. 32 8. 21 11. 89
April _________________ ___ 5. 11 6. 41 8. 87
May ____________________________ 4. 12 4. 07 4. 60
June ____________________________ 3. 63 4. 29 3. 95
July _____________________________ 1. 35 1. 19 1. 71
August __________________________ 1. 75 2. 79 4. 09
September _______________________ 3. 92 4. 49 6. 33
October- _ _ _. _____________________ 8. 63 8. 14 11. 26
November _______________________ 11. 91 12. 69 18. 20
December ________________________ 13. 79 11. 75 17. 94

Annual average _____________ 82. 43 85 37 119 87

 

and northwest. The directions from which average
monthly winds come during the other months range
from northwesterly to southwesterly. One geologic ef~
fect of these prevailing winds was the determination of
the fallout pattern of postglacial pyroclastic deposits,
each of which lies mostly east of the volcano.

TERMINOLOGY AND DISTINCTIVE FEATURES OF
LAHARS

The term “lahar” is an Indonesian word that is used

. in this report as a general designation for deposits that

have resulted from rapid mass flowage of rock debris
mobilized by water and that have originated on the
slopes of a volcano. The term is also used to refer to the
flowing mixture of rock debris and water. This defini-
tion follows the usage of van Bemmelen (1949, p. 191)
and is adopted because of the need for a general term
that is independent of reference to the texture of the de-

 

15OIIIIIIIIIIIIIIII|IIIIIIIIIIIIIIIIII
..
.

140 v .3 . —
.' ; .".

PRECIPITATION, IN INCHES

 

 

 

IllIllllIlilIII|l|I|l|1I|I|lllll—

 

I I I
o
m
m
._.

1926
1935
1940
1950
1955
1960
1965

Ln
V
G)
H

FIGURE 2,—Average annual precipitation at Longmire from 1926
through 1965 (solid line) and average annual precipitation
at Paradise Ranger Station from 1956 through 1965 (dotted
line).

4 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO,‘ WASHINGTON

posit and the sediment to water ratio during movement.
Thus, use of the term “lahar” avoids the necessity of
adoping such textural designations as debris flow and
mudflow, even though these terms are conveniently ap-
plied here to certain appropriate lahars. Even though
all the deposits to be described originated on a volcano,
it is well to emphasize at the outset that not all of them
originated as the direct and immediate result of volcanic
activity.

Most of the lahars described in this report conform to
the definition of either mudflow or debris flow as used
by many workers. Sharp and Nobles (1953) used the
term “debris flow” as a general designation for all types
of rapid flowage involving rock debris of various kinds.
They suggested that mudflows are a variety of debris
flow in which the mud gives the mass a mode of behavior
which distinguishes it from a flow of wet rock debris
devoid of mud. Varnes (1958, p. 37) subsequently clari-
fied this usage by restricting the term “mudflow” to
deposits that have at least 50 percent material of sand
size and smaller.

The sand fraction of a lahar may not be as important
as the silt and clay fraction in imparting certain flowage
characteristics to a sediment-water mixture. It has been
experimentally shown that the fall velocity of sand-
sized material in such a mixture decreases as the clay-
fraction increases (Simons and others, 1963), and under
some conditions this has the effect of allowing the coarse
fraction to be suspended by less turbulence.

Bull (1964) adopted a threefold classification to de-
scribe the deposits of alluvial fans in Fresno County,
Calif. His classification, shown below, was based on
sorting coefficient (So), phi standard deviation (cup),
and phi quartile deviation (QD¢) .1

SO 04> QD¢
Waterlaid sediments (upper limit)_-_ 3 2. 3 1. 6
Intermediate sediments (limits) _____ 3—5 2. 9—4. 1 1. 6—2. 3
Mudflows (lower limit) ____________ 5 4. 1 2. 3

Few grain-size analyses of “waterlaid sediments”
were made during the present investigation; deposits
thought to be of this origin are generally referred to in
this report as fluvial deposits or fluvial sediments, but
some of them may also belong in Bull’s category of
“intermediate sediments.” Although nearly all the de-
posits called lahars in this report are mudflows accord-
ing to B'ull’s classification, a few samples fall within
the limits of his “intermediate sediments” category. For
example, a sample from the fine, graded top of the Elec-

1 A “sorting coefficient” is the square root of the ratio of the third (larger) quartile
(the 75 percent value) to the first (smaller) quartile (the 25 percent value). The two
percentiles refer to the percentage of material that is finer than the grain diameter for
the percentile on the cumulative curve. As the degree of sorting increases, the two
quartiles become more nearly equal, and the sorting coefficient approaches 1.0.

The designation “phi” is equal to the ~10g2 of the grain diameter in millimeters.
The formula for the phi standard deviation (w) is (¢16—¢84)/2 and the formula
for phi quartile deviation (QD¢) is (¢25 —¢75)/2.

 

tron Mudflow has a sorting coefficient, phi standard de-
viation, and phi quartile deviation that fall in the
“intermediate” category; a sample from the base of
the Electron at the same locality, however, has pa—
rameters characteristic of Bull’s mudflows.

Some of the lahars described in this report may have
been formed by “hyperconcentrated flows” (Beverage
and Culbertson, 1964), which are water—sediment mix-
tures that have between 40 and 80 percent sediment by
weight. These flows are intermediate between normal
steamflow, in which there is no more than 40 percent
sediment by weight, and mudflow, which has more than
80 percent sediment by weight, according to Beverage
and Culbertson. Richardson (1968) suggested that some
of the outburst floods that have originated in Nisqually
and South Tahoma Glaciers Within the last 40 years
(p. 44, 58), have been “hyperconcentrated flows.”

Lahars have some features in common with deposits
of other origins, such as till, fluvial deposits, colluvium,
and landslides. I know of no single common feature that
serves to distinguish all lahars from all other kinds of
deposits. Instead, many different characteristics none of
which may be individually definitive, often indicate a
laharic origin when considered collectively. For exam—
ple, the principal features that led to the recognition of
the so-called Osceola till of Willis (1898) as a mudflow
were its flat topography and highly digitate pattern of
distribution in the Puget Sound lowland (Crandell and
Waldron, 1956). These features were considered in con-
junction with the deposit’s provenance, lack of sorting,
coarse texture, and vertical distribution on valley walls
in the Cascade Range and at Mount Rainier. We con—
cluded that the Osceola in the Puget Sound lowland
had been transported and deposited by a medium of
which no part could have been appreciably higher than
the present surface of the deposit, a requirement that is
satisfied only by assuming that the material flowed into
its present position.

The distribution of a deposit is very helpful in de-
termining its origin, although the presence of lahars on
some ridgetops close to the volcano caused much initial
uncertainty concerning their mode of origin. More
commonly, lahars occur on valley floors, especially at
some distance away from their source. Their distribu-
tion and provenance generally are adequate to distin-
guish them from local colluvium.

The texture of some lahars resembles that of coarse
fluvial sand and gravel deposits, with which lahars are
typically interbedded. Probably the most diagnostic
feature of a lahar in such a comparison is its lack of
internal stratification, even though some successions of
lahars form an assemblage of deposits that is bedded in
gross aspect. However, each individual lahar lacks in-

INTRODUCTION 5

ternal bedding because it moved and came to rest as a
single mass-flowage unit. A fine line cannot be drawn
between some fluvial deposits that are very crudely
bedded and some lahars; in fact, the processes of trans-
portation apparently are gradational. The transport
ability of a lahar is tremendous because of its relatively
high viscosity and high specific gravity; thus, large
blocks of rock are common in the deposits. However,
large boulders also are present in some crudely stratified
fluvial deposits (fig. 18) .

Many lahars closely resemble till, and the distinction
between the two sometimes is not possible in the field.
The striated, soled, and snubbed stones that are gen-
erally regarded as being typical of till are not very help-
ful in distinguishing tills from lahars. Stones with
these features were not observed in any of the lahars,
but neither are they abundant enough in the till to be
useful criteria at Mount Rainier. Some deposits that I
initially regarded as till were soon found to be of post-
glacial age, and their distance from the present glaciers
indicates that they cannot have been formed by glacial
advances of Holocene age. These deposits are inter-
bedded with alluvium in some terraces and form ve-
neers on others, but a laharic origin is inferred because
all have a distribution that can be explained only by
mass flowage.

The size distribution and sorting characteristics of
some tills (fig. 3) are similar to those of many lahars.
The sorting coefficients of seven samples of Evans Creek
till range from 3.16 to 9.5 (avg. 6.41), and those of the
lahars discussed in this report range from 3.41 to 17.
It is nearly impossible to obtain a truly representative
sample of these coarse deposits, and the true maximum
sorting coeflicient of both kinds of deposits probably is
greater than 17.

Some lahars are lithologically similar to the deposits
of hot dry block-and-ash flows. The high mobility of
some block-and-ash flows, provided by gas contained in
the flow, by entrapment, heating, and expansion of cold
air (McTaggart, 1960), and by the conversion to steam
of water, snow, and ice incorporated by the flow, would
permit the flows to move down a valley floor in a man-
ner similar to that of a lahar. One manner of distin-
guishing between the deposits of these two processes
is by determining the temperature of the deposits when
they were emplaced; this can 'be approximated from a
study of the orientation of remanent magnetism and
Curie temperature of the included rock fragments
(Aramaki and Akimoto, 1957) . The orientation is deter-
mined by the ferromagnetic mineral or minerals in the
rock, which is magnetite in the andesites from Mount
Rainier. As the magnetite in originally molten rock
cools through its Curie point, it takes on a magnetic

420—479 0 - 71 — 2

 

Orientation that is parallel to the earth’s magnetic field
at that moment. This is known as thermoremanent mag-
netism (TRM). If a deposit came to rest while rock
fragments in it were still above the Curie temperature
of the magnetite, then the TRM orientations of the
fragments should be uniform and parallel. But if the
fragments cooled sufficiently before incorporation in a
moving mass, or while the mass was still moving, their
present TRM orientations would be random.

It seems possible that a block-and-ash flow could
grade downvalley into a lahar if the following sequence
of events occurred (Mullineaux and Crandell, 1962).
A mass of hot rock fragments, bombs, and ash might ac-
cumulate at the summit of the volcano during an erup-
tion and then might avalanche to form a block-and-ash
flow. Snow incorporated by the flow as it crossed snow-
fields and glaciers could become water and steam in
transit; the steam would increase turbulence, and both
the steam and water would dissipate heat and increase
mobility by decreasing internal friction. If the matrix
cooled below the boiling point of water as the flow moved
beyond the base of the volcano the mass might become
a lahar as conversion of water to steam diminished.
When the lahar came to rest, possibly as a result of the
water and steam evaporating in such quantity that they
were no longer effective lubricants, many bombs and
dense rock fragments might still be hot enough to car-
bonize wood. In this regard, Kemmerling (1921) re—
ported a temperature of 92°C at a depth of about 1 foot
in a lahar a few days after it had been formed during
the 1919 eruption of Kelut in Java. About 2 weeks after
the eruption, the temperature had dropped to 50° C, and
2 weeks later the temperature had dropped to 30°C.
Kemmerling also mentioned a temperature of more than
360°C in ‘a gas vent in the same lahar, and a temperature
of 100°C at the same spot a year later. He attributed
the source of the heat to blocks of pumice which had
been ejected by the volcano and incorporated in the
lahar. Kemmerling mentioned that a person had been
caught and transported some distance in another lahar
from Kelut without having been burned. On the other
hand, many corpses found later in the same lahar were
severely burned.

The texture of some lahars resembles that of some
avalanche deposits. This similarity is not surprising,
for many lahars originated in avalanches, and became
lahars only because substantial amounts of water were
present in the rock that formed the avalanches or be-
cause water was incorporated during movement. Size
data were obtained on two samples of the avalanche de—
posits that resulted from rockfalls at Little Tahoma
Peak in 1963 (fig. 4) (Crandell and Fahnestock, 1965).
The samples had sorting coefficients of 6.38 and 6.63.

POSTGLA‘CIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

E E
E E E E E E
8 H E E o 9
Lu 0. 0 ~. Q o' 8
E 1000 o o .—u H H
m
O z” // l.
E //F /
(‘5 90 / l
a //
E 80 V / //
< / /*’
I 1 // /
*— 7o , 9 ,
r— 1 /// 4
I 90/ / //
m 60 9”
g / ’\'// /
E / 90/ <5 /
S.
E 50 3/// 60%)”
E 96/ //
._._ 40 a“ o / / //
m /
Ci // ‘ x //
E 30 / 9?/ 'L
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t 20 f / 1/ ij‘9
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g 10 / / ,z / /
*— #//’ //
Z // fl, —
8 O / g
5 1L L ’W‘ ’
0' CLAY SILT SAND GRANULES PEBBLES COBBLES

FIGURE 3.—Cnmu1ative curves and sorting coefficients (So) of three samples of Evans Greek till. Sample 1 is from a cutbank
of the Nisqually River in the NW14 sec. 35, T. 16 N., R. 6 E., 1 mile southeast of Ashford, Wash. Sample 2 is from a
Roadcut at Round Pass, and sample 3 is from a roadcut 1 mile southeast of Box Canyon.

Neither sorting index, however, truly represents the de-
gree of sorting in the deposits because of my inability
to include in the samples a proportionate amount of the
abundant large rock fragments.

Two common features of lahars, which may help in
recognition, are the presence of innumerable air spaces
within the matrix and a vertical size gradation from
coarse material at the base to fine material at the top. Air
spaces seem to be most common in lahars that have a
fine-grained matrix. Most of the air spaces are of ir-
regular shape and range in size from a fraction of a
millimeter to several millimeters, but air bubbles of
spherical shape were noted in the fine-grained, graded
top of a young lahar from Mount St. Helens. Bull
(1964, p. A31) described bubble cavities in both water-
laid deposits and mudflows in alluvial fans in Cali-
fornia. He noted that they are more common in the
mudflows and that they are larger and more spherical
if the mudflow has a considerable content of clay or
silty clay. Air spaces in lahars seem to have been
formed by air bubbles trapped within the matrix rather
than by the draining away of free water or part of the
matrix after the lahar came to rest.

The vertical gradation in texture of lahars is illus-
trated by data in table 2. This gradation is most con-

 

spicuous where the entire thickness of the lahar is
exposed and commonly it is best shown by the upper
few feet of a lahar; some lahars grade imperceptibly
upward from coarse, unsorted material into a silty sand
that is quite well sorted. An outcrop of the middle third
of a lahar, in contrast, might show no such gradation
to the eye, and the gradation possibly might not even be
detected from grain—size analysis. I have seen this verti-
cal gradation in dozens of lahars at many localities in
the Western United States. These lahars range in age
from Tertiary to historic and in thickness from a few
inches to many tens of feet. Unfortunately, however,
the vertical gradation in texture is not present in all
lahars, nor even in each lahar of a vertical succession
of several in the same outcrop.

Size-distribution analyses of several lahars indicate
that the proportion of silt and clay to the whole — 2-mm
(millimeter) fraction is remarkably similar for any
given lahar, regardless of the horizon from which the
sample came. This relation seems to be true even though
the total amounts of the several size fractions change
considerably from top to bottom of a given deposit. A
tabulation of data from eight lahars sampled at two
horizons (table 2) indicates a range in the proportion
of silt and clay to the -2-mm fraction of only 0.4—3.4

INTRODUCTION I 7

0.001 mm
0.01 mm
0.1 mm

‘ 100.0 mm

1.0 mm
10.0 mm

 

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60

 

50

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PERCENTAGE OF PARTICLES FINER BY WEIGHT THAN INDICATED SIZE

CLAY SILT

SAND GRANULES PEBBLES COBBLES

FIGURE 4.——Ci1mulative curves of samples from the avalanche deposits on the floor of the White River valley. (See Crandell
and Fahnestock, 1965, fig. 3.) Samples 1 and 3 are from units 1 and 3 of the avalanche deposits from Little ’l‘ahoma Peak.

So, sorting coeflicient.

percent. The similarity in proportions of material
within the +2-mm fraction suggests that the matrix is
nearly uniform in texture and that the textural change
in the lahar vertically is principally one of an upward
decrease in the percentage of material larger than 2 mm.

Schmincke (1967) also called attention to the graded
nature of lahars and, in addition, noted (p. 440) a basal
zone less than a foot thick of vaguely stratified, fine to
coarse sand in the lahars he studied. Basal zones of sand
like those described by Schmincke were not noted in the
lahars at Mount Rainier. I have seen beds of sand
beneath many lahars of Cenozoic age in western
Washington, but these beds seem to be genetically
related to the underlying sequence of fluvial deposits
rather than to the lahar.

One interesting and significant relation that was
found in this study is the propensity of lahars to flow
down a valley and to leave only a thin deposit on the
valley sides and floor to mark their passage. Thick fills
commonly are formed by lahars only at some distance
from the volcano, mostly at places where the valleys
widen and become less steep and in areas of the lowland
beyond the mountain front. During the passage of some
lahars of great volume, such as the Osceola Mudflow,
valleys probably were filled with flowing mud to depths

 

of hundreds of feet for many minutes. The Paradise
lahar, however, probably progressed downvalley as a
single rapidly moving wave of fluid material hundreds
of feet high, and, except momentarily, it did not fill
valleys to the maximum height recorded by its
remnants.

Because of the ephemeral character of a deep flowing
current of mud in a steep and narrow valley and its
characteristic manner of leaving only a veneer to record
its passage, some conventional inferences that can be
made with regard to the aggradation and downcutting
of fluvial fills are not pertinent to lahars. For example,
each terrace of a flight of several in a valley may be
veneered with a lahar. According to a conventional
interpretation, the lahar on each terrace would represent
a separate event—the lahar on the highest terrace would
be the oldest, and the formation of each lahar would
be followed by fluvial downcutting. However, this study
has demonstrated that each terrace may be veneered
with the same lahar, which was deep enough to cover
them all temporarily before the fluid material drained
downvalley. A corollary is that the same lahar that caps
a high terrace in a flight of several terraces may lie
beneath younger lahars and fluvial deposits in a lower
terrace. It is important to recognize, further, that the

8 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON

TABLE 2.—Si2e-dtstribution data on eight lahars, each sampled
from two difierent horizons

[In each lahar the proportion of silt and clay to the whole —2-mm fraction is closely
similar in both horizons]

 

 

 

—0.0625 mm
—0.0625 mm —2 mm —2 mm
Lahar (percentage (percentage (percentage
Lahar thickness Horizon of sample of silt and of silt, sand, of silt and
(it) clay) and clay) clay to
whole
—-2 mm
fraction)
13 Top 1 ft ........... 13 59 22
Bottom 1 ft _______ 8 37 21. 6
>9 Top 1 it ........... 15 68 22. 1
5—7 it below top. _ . 12 50 24
8. 5 Top 1 ft ........... 19 83 22. 9
Basal 4 it .......... 7 28 25
6 5 Top 1 It ........... 36 93 38. 7
Bottom 1 it _______ 20 57 35. 1
18 Top 1 it ........... 25 70 35. 7
Bottom 1 ft _______ 24 66 36. 4
25 57 it below top__ . 18 54 33. 3
3—4 it above 20 63 31. 7
bottom.
7 _________ 9 Top 1 it ........... 8 37 21. 6
Bottom 1 it _______ 11 52 21.2
8 _________ 8 Top 1 ft ........... 6 34 17. 6
Bottom 1 it ....... 6 31 19. 4

 

1. Uppermost lahar of three exposed in the walls of a gravel pit at Gilmore Corners,
Wash. (See Mullineaux and Crandell, 1962, p. 859—860, unit 5 in measured sec-
gion.) Lahar originated at Mount St. Helens volcano probably within the last

,000 years.

. Lowermost lahar of three at Gilmore Corners (unit 1 in measured section.)

. Upper lahar of two in the Alderton Formation oi early(?) and middle(?) Pleisto-
cexii‘t fie near Sumner, Wash. (See Crandell, 1963b, p. A78, measured section 6,
u .

WM

4. Electron Mudflow. Samples from outcrop at confluence of Carbon and Puyallup
Rivers near McMillin, Wash. (See Crandell, 1963b, p. A51.) The mudflow origi-
nated at Mount Rainier about 500 years ago.

5. Lahar in the Puyallup Formation of mid le(?) Pleistocene age exposed in the
north wall of the Fennel Creek valley, in the NW% sec. 8, T. 19 N ., R. 5 E.,
about 3.5 miles southeast of Sumner, Wash.

6. Lahar from Mount Hood volcano(?) in the Gresham Formation of middle(?)
Pleistocene age. (See Trimble, 1963, p. 55.) Samples taken from roadcut out-
crop in the NE% see. 14, T. l S., R. 4 E., in the valley of the Big Sandy River
east of Portland, Oreg.

7. Uppermost lahar oi three in sedimentary deposits oi Miocene age near Buckley,
Wash. (See Mullineaux and others, 1959, p. 689, unit 6 in measured section.)

8. Middle lahar of three in sedimentary deposits of Miocene age. (See above; unit 2

in measured section.)

lahar remnants on even the highest terrace do not neces-
sarily mark the maximum height attained by the lahar
at that point while it was moving.

Despite the remarkable thickness or depth some la-
hars attained during movement, they evidently did not
erode deeply even on fairly steep gradients. For ex-
ample, lahars in some valleys are commonly found on
top of relatively thin layers of sand and volcanic ash
that presumably would be easy to erode. These valleys
have gradients of as much as 700 feet per mile today,
and they probably had comparable slopes when the la-
hars occurred. The inability of many mudflows to erode
at their base was recognized by Blackwelder (1928).
This characteristic is particularly well illustrated in
western Washington by the presence of leaves between
the base of a poorly consolidated lahar of Miocene age
and an underlying layer of fine volcanic ash only a few
inches thick (Mullineaux and others, 1959), and I have
observed a similar relation in the Rocky Mountain foot-
hills near Denver, 0010., where a semiconsolidated lahar
of the Upper Cretaceous and Paleocene Denver Forma-
tion is separated by a thin layer of leaves from an un-

 

derlying bed of volcanic ash. Schmincke (1967) de-
scribed thin tubes that extend upward into the basal
part of a Miocene or Pliocene lahar in central Washing—
ton; these tubes seem to be the molds of plants that were
engulfed by the moving lahar. However, Schmincke re-
garded these features as low—gradient, low-velocity phe-
nomena, because he inferred (p. 447) that on steeper
gradients, closer to the source volcano, similar lahars
had “picked up stream gravels and alluvium and up-
rooted bushes along their way” and (p. 440) that else—
where one of the lahars was thought to have “possibly
carved a creek channel in the underlying gravels.”

There can be little question that lahars can and do
pick up some loose materials from the surfaces over
which they flow, and this erosive ability may be related
not so much to degree of slope as to local turbulence
caused by channel and valley configuration. Although
some lahars of Pleistocene age in the southern part of
the Puget Sound lowland seem to have traveled 40—50
miles from their source without appreciable contamina-
tion (Crandell, 1963b, p. A10), more than half of the
pebbles in samples of the Osceola and Electron Mud-
flows, at comparable distances from their source, are of
rocks not derived from Mount Rainier (Crandell, 1963b,
p. A14).

The apparent inability of many lahars to erode, espe-
cially when spreading out on a surface of low slope,
suggests that the lower part of a lahar is character-
ized by laminar flow rather than turbulent flow, and
also that once the front of a lahar has passed a given
point, the material immediately above the base at that
point becomes motionless or nearly so, even though
movement is continuing in the main mass at higher
horizons. It is as if the lahar moved forward as a rug
is unrolled; the immobilized layer (the rug) then acts
as a buffer zone immediately above the underlying sur-
face to protect it from erosion.

WAYS IN WHICH LAHARS ORIGINATE

Lahars can be grouped by origin into several cate-
gories for the purpose of discussion: (1) those that are
the direct and immediate results of eruptions, (2) those
that are indirectly related to an eruption or that occur
shortly after an eruption, and (3) those that are not
related in any way to contemporaneous volcanic activity.

Lahars that are the direct and immediate results of
volcanism can be formed in many ways: some of these
are discussed and a few are illustrated by examples that
have occurred within historic time.

Floods and lahars are sometimes formed when a
crater lake is forcefully expelled during an eruption.
The Indonesian volcano Kelut on the island of Java is
notorious for causing lahars in this manner. In 1919, an

INTRODUCTION 9

eruption through Kelut’s crater lake spilled 39 million
cubic yards of water down the south and southwest
slopes of the volcano. The water picked up great quanti-
ties of loose rock debris and the resulting lahars totally
or partly destroyed 104 villages and killed 5,500 people.
Some lahars reached a distance of 12 miles from the
volcano (Kemmerling, 1921). A crater lake can also be
released by the failure of its enclosing walls. During
eruptions of Seméru (Smeru) volcano, also on Java,
magma rising in the cone has repeatedly pushed aside
parts of the crater walls, and this material has ava-
lanched down the sides of the volcano to produce lahars
(Baak, 1949, p. 5—6).

Repeated floods of hot water and hot lahars were one
of the dominant features of the 1902 eruption of Mount
Pelée on Martinique, and some of them were caused by
emptying of the crater lake (Anderson and Flett, 1903,
p. 489). Two of the largest hot lahars preceded, by 4
hours, the nuéc ardente that destroyed the town of St.
Pierre at the foot of the volcano (Hovey, 1902, p. 346).
The contemporaneous eruptions of La Soufriere on the
island of St. Vincent also caused a crater lake to empty
and to form a “torrent of ‘boiling hot’ water and mud”
(Hovey, 1902, p. 342). The front of this lahar was at
least 50 feet high as it rushed down a valley that heads
on the volcano.

Mud has been extruded directly by some volcanoes.
According to Cinouye (1971), mud consisting of finely
divided plagioclase, hypersthene, augite, magnetite,
glass, and hematite was erupted in 1910 from five craters
in the summit of Usu volcano in Japan. During an
eruption of Yaké Daké in Japan in 1962, hot mont-
morillonite-bearing mud ejected from a vent on the
volcano formed a small mudflow (Morimoto and Ossaka,
1964). From a study of andesitic breccias of Tertiary
age in the Cascade Range of northern California, Dur—
rell (1944) concluded that mudflows can be extruded
directly from volcanic fissures. He suggested that the
solid fraction of the breccias he studied represented a
highly mobile mass of andesite fragments in a matrix
of comminuted andesite and alteration products and
that the water was derived directly from the associated
magma.

Avalanches of rock debris can cause lahars by tem-
porarily damming rivers. The water may spill over the
dam, erode it, and the entire deposit may sweep down-
stream as a lahar. An event of this kind occurred during
an eruption of Asama volcano in Japan in 17 83 when a
hot avalanche dammed a nearby river. Within an hour
the river overtopped the dam, eroded it, and caused it to
collapse. The debris rushed downstream as a hot mud-
flow that traveled more than 50 miles and killed more

 

than 1,300 people (Aramaki, 1956). During the 1929
eruption of Santa Maria volcano in Guatemala, glowing
avalanches moved down into the valleys of the Rio
Tamblor and Rio Concepcion and produced boiling-hot
lahars. The top of the lahar in the Rio Tamblor was
covered with incandescent rock debris, and the lahar
overflowed a channel more than 300 feet deep and 250
feet wide (Sapper and Termer, 1930, reviewed by J ag-
gar, 1931).

Avalanches of hot rock debris have also caused lahars
by melting snow and ice on a large scale. During an
eruption in 1955 of Bezymianny volcano in Kamchatka,
block-and—ash avalanches spread over a broad area at
the east base of the cone. Snow which was melted by the
hot debris caused lahars that fl0wed downvalley more
than 45 miles (Gorshkov, 1959). During the 1938
eruption of Avacha volcano, also in Kamchatka, lahars
were caused in part by the deposition of hot pyroclastic
material on snow and ice (Meniailov, 1939). Solid ma-
terial in the lahars consisted of breadcrusted and scoria-
ceous bombs in a black sand matrix.

Volcanic explosions commonly cause landslides in
rocks that have been weakened by hydrothermal altera-
tion. An explosive eruption of Tokachi‘dake volcano in
Japan caused a large part of the cone to collapse in 1926.
An immense avalanche of hot rock fragments accom—
panied by steam and possibly by hot water from the
crater descended the west flank of the volcano and
melted an accumulation of snow. The resulting lahar
poured down the mountain and reached a distance of
nearly 15 miles (Tada and Tsuya, 1927). An explosion
of the same volcano in 1962 caused a slide of about 4
million cubic meters of rock on one side of the cone,
which became a hot lahar as it moved downslope. The
slide occurred in rocks that had been extensively de-
composed by fumarolic activity (Murai, 1963).

An unusually large avalanche that moved like a lahar
was caused by a phreatic explosion at Bandai-san v01-
cano in Japan in 1888. The horizontally directed force
of the explosion caused the failure of a large segment
of the cone. In all, 1,487 million cubic yards of rock
debris flowed downslope and covered an area of 27
square miles at the base of the volcano. The mass was
thought to have been in a relatively dry state during
movement (Sekiyo and Kikuchi, 1889). A similar, but
prehistoric, event occurred at Asama volcano when a
phreatic explosion destroyed the eastern part of the
cone and caused a lahar that spread over an area of

about 35 square miles. The rocks involved had previously

been extensively altered to clay by solfataric activity
(Aramaki, 1963). An even older lahar originated from
a catastrophic phreatic explosion of a pre-Asama

' volcano at the same site (Aramaki, 1963, p. 267).

10 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON

At Lassen Peak in northern California, lahars moved
down two valleys north of the volcano for a distance
of more than 20 miles in May 1915. Day and Allen
(1925) attributed the lahars to the rapid melting of
snow on the volcano by hot rain, hot volcanic ash, and
a steam blast. It seems more likely, however, that rapid
melting of snow was caused by a lava flow near the sum-
mit of the volcano (Finch, 1930).

Lahars can also result indirectly from eruptions in
many different ways. A crater lake may be released
suddenly by failure of part of its restraining embank-
ment for some reason not associated with simultaneous
volcanism. In 1953, failure of part of the natural dam
that impounded Crater Lake on Mount Ruapehu in New
Zealand permitted a large volume of water to rush down
the side of the volcano, where great quantities of loose
ash and boulders were picked up to form a lahar. The
lahar swept away a railroad bridge a few minutes
before the arrival of an express passenger train, and
151 lives were lost (O’Shea, 1954).

Pyroclastic deposits that are formed during an erup-
tion are especially susceptible to saturation during pe-
riods of heavy precipitation, and sliding and flowage
of these masses commonly cause lahars. These “rain
lahars” are an almost daily occurrence during the mon-
soon season following an eruption of the Javanese vol-
cano Kelut (Kemmerling, 1921). A few weeks after the
eruptions of La Soufriere, in 1902, heavy rains caused
boiling-hot lahars to flow repeatedly down valleys that
headed on the flanks of the volcano (Anderson and
Flett, 1903, p. 422—424, 428—434). The sediment in the
lahars was principally derived from thick deposits of
hot sand-sized ash that had been formed during the
eruption. Between episodes of volcanic activity at
Vesuvius in 1906, rain and melting snow saturated
loose rock debris on the flanks of the volcano and
caused repeated lahars (P‘errett, 1924, p. 102). During
the 1963—1964 eruptions of Irazu in Costa Rica, flash
floods resulted from runoff whose volume was greatly
increased by a thin compact layer of newly erupted
ash. The floods became debris flows as they scoured
valley sides which were formed by poorly consolidated
deposits. One debris flow caused great damage and some
loss of life in the city of Cartago at the south base of
the volcano (Waldron, 1967).

The last general category of lahars consists of those
that are unrelated to volcanism. Mudflows and debris
flows can result from saturation of loose rock debris by
rain and melting snow in an alpine region wherever cer-
tain conditions are metfia source of rock debris, ade-
quate moisture, and a steep slope. They may occur
at volcanoes more often than elsewhere because of the
combination there of all these conditions. Lahars are

also frequently caused by the sudden release of a body
of water impounded by a glacier. Although the water
released may be wholly the product of glacier melting
related to atmospheric conditions, a flood from a glacier
on a volcano may also result from rapid, large-scale
melting caused by a steam vent or by some other source
of volcanic heat.

AGE AND LITHOLOGY OF MOUNT RAINIER VOLCANO

The earliest evidence of Mount Rainier volcano is
present in unconsolidated deposits in the Puget Sound
lowland to the northwest. These deposits include lahars
derived from an active volcano at the site of Mount
Rainier (Crandell, 1963b, p. A10—A11). They are in-
terbedded with glacial drift deposited by a lobe of the
Cordilleran ice sheet which moved southward down the
Puget Sound lowland. The oldest known lahars were
formed during the Alderton Interglaciation, of mid-
dle Pleistocene age (table 3). Stones in these lahars
are chiefly hornblende- and hypersthene-bearing ande-
sites. A hornblende—hypersthene andesite lava flow is
known to occur at only one locality in Mount Rainier
National Park, and its age is unknown (Fiske and
others, 1963, p. 64). However, lahars that contain
fragments of a hornblende-hypersthene andesite crop
out in Glacier Basin on the northeast side of Mount
Rainier (pl. 1), where they underlie glacial drift and
lava flows of pyroxene andesite.

The oldest hypersthene-andesite lavas from Mount
Rainier form thick flows that filled canyons in the
Cascade Range to depths of as much as 2,000 feet (Fiske
and others, 1963, p. 66—69). These old resistant flows
now underlie divides that radiate outward from the

TABLE 3.—Subdivisions of Quaternary time in western Washington

[The Burroughs Mountain Stade occurred between about 3,000 and 2,500 years ago;
the Garda Stade probably began about 800 years ago and extends to the present
(Crandell and Miller, 1964; Porter and Denton, 1967, p. 198—201)]

 

 

 

 

 

 

Age Geologic—climate unit
Winthrop Creek Garda Stade
Glaciation Burroughs Moun-
Holocene tain Stade
“Hypsithermal interval”
Sumas Stade
Everson Inter-
stade
Fraser Glaciation Vashon Stade
Evans Creek
Stade
Pleistocene Olympia Interglaciation
Salmon Springs Glaciation
Puyallup Interglaciation
Stuck Glaciation
Alderton Interglaciation
Orting Glaciation

 

 

 

INTRODUCTION 11

base of the volcano, and the sites of some of the former
canyon walls or divides are now valleys. At a later stage,
Mount Rainier erupted hundreds of thin lava flows and
built up its present cone. Fragmental deposits inter-
layered with lava flows on the flanks of the volcano
include well-indurated flow breccias as well as loose
rubbles that may have originated as block-and-ash
avalanches; pyroclastic deposits interbedded with these
breccias and rubbles are few (F iske and others, 1963,
p. 75).

The early canyon-filling lavas, as well as the rocks of
the modern cone, are chiefly pyroxene andesites; hy-
persthene is ubiquitous and is the dominant mafic min-
eral in most flow rocks. According to Fiske, Hopson,
and Waters (1963), augite is generally abundant but
slightly subordinate to hypersthene, which it encloses
in some flow rocks. Brown hornblende is a sparse con-
stituent of some flows. Flows of olivine andesite were
erupted at two small satellite vents at Echo and Obser-
vation Rocks relatively late in the history of the vol-
cano, but before the Fraser Glaciation. The most recent
flows, which make up the present summit cone and
which probably are no more than 2,000 years old (table
6), are of an augite-hypersthene andesite (Fiske, Hop-
son, and Waters, 1963). Some Holocene pyroclastic
deposits erupted by Mount Rainier show somewhat
greater diversity in mafic minerals than some of the
flows (D. R. Mullineaux, oral commun., 1969). For ex-
ample, layer D (table 5) contains variable amounts of
hypersthene, augite, hornblende, and oxyhornblende.

Mount Rainier volcano seems to have been intermit-
tently active during about the last 10,000 years, although
it has apparently been much more active during some
extended episodes than during others. During this time
interval the volcano has erupted lava flows at least once;
bombs, blocks, and ash, which caused hot avalanches, at
least three times; and pyroclastic material at least 11
times. In addition, thin layers of fine-grained rock
debris, which may be lithic ash, are found at many
horizons in the sequence of pyroclastic deposits and
may record a dozen or more eruptions that are not
known to be represented by other deposits (D. R. Mul—
lineaux, oral commun., 1969).

DATING OF LAHARS

All the lahars described in this report are of Holocene
age, except for one that probably was formed during
a late part of the Fraser Glaciation (table 3). The post-
glacial age of most lahars can be readily determined
because they overlie glacial deposits formed during the
Fraser Glaciation.

Many of the lahars either contain wood from which
radiocarbon age determinations could be made or are

 

closely associated with other deposits that are wood
bearing. Age determinations cited here (table 4) of less
than 6,000 years have been corrected by Meyer Rubin
(written commun., 1969) from data provided by H. E.
Suess. These corrections are based on a C“ half life of
5,730 years and also take into account past variations
in atmospheric C“. Ages of less than 6,000 years that
are given in the following text will be the corrected
ages in 1970 unless specified to be uncorrected ages.

Some lithologically similar lahars have been distin-
guished, traced, and correlated by their stratigraphic
relation to pyroclastic deposits. In some places the py-
roclastic deposits are interbedded with the lahars; else-
where, the age of a given lahar can be bracketed by the
presence or absence of certain pyroclastic layers on top
of it. The ages of most of the pyroclastic deposits in
Mount Rainier National Park are known to within a
few hundred years from radiocarbon age determina-
tions of associated organic matter or from age determi-
nations of such matter from horizons immediately
above and below each layer of pumice (table 5). All the
postglacial lahars recognized in the valleys heading at
Mount Rainier are shown in chronological order in table
6, together with the pyroclastic deposits which help to
date them.

TABLE 4.—Radiocarbon dates pertaining to surficial deposits
less than 6,000 years old near Mount Rainier

[The radiocarbon dates shown in the first column are based on a 014 half life of 5,568
years. The “true” dates shown in the next column are based on a half life of 5,730
years and are corrected for CM variations in the atmosphere. (Based on a written
commun. from H. E. Suess to Meyer Rubin, 1968.)]

 

 

 

Radio- “True” Years
Sample carbon date ago in Stratigraphic position of sample
date (yr) 1970 1
7
W—1120 _____ 2905:200 1525 AD. 450 Wood from dufi above pyroclastic layer
W from Mount St. Helens.
1119 _____ 3205:200 1500 A.D. 450 Wpod frvéim dufi below pyroclastic
ayer .
565 ______ 530:1:200 1380 AD. 600 Wood from Electron Mudflow.
2113 _____ 1, 0505:350 950 A.D. 1,000 Woorli1 from mudflow in Puyailup River
va ey.
1971 ..... 1, 100:1:250 900 A.D. l, 050 Wood from mudflow in South Puyailup
River valley.
1393 ..... 2, 040:1:200 160 B.C. 2,150 Wood from above pyroclastic layer 0
from Mount Rainier.
566 ...... 2, 170:1:200 220 B.C. 2,200 Wood from mudflow at month of Mo-
wich River.
1396 _____ 2,3401200 520 B.C. 2,500 Wood from below pyroclastic layer C.
1587 ..... 2, 3503:250 530 B.C. 2,500 Charcoal from block-and—ash flow in
South Puyallup River valley.
930 ...... 2, 550:1:200 750 B.C. 2, 700 ngd from clay above pyroclastic layer
2114 ..... 2, 6105:3150 850 B.C. 2,800 Wood from Round Pass Mudflow in
Tahoma Creek valley.
1972 _____ 2,710;l:250 950 B.C. 2,900 Wood from Round Pass Mudflow in
Puyallup River valley. _
1118 _____ 2. 980:1:250 1300 B.C. 3. 250 Carbon from duff above pyroclastic
layer Y from Mount St. Helens.
1115 _____ 3, 5005:250 2010 B.C. 4, 000 Wlood frgfm peat below pyroclastic
ayer .
564 _____ 4, 700:1:250 3600 B.C. 5,550 Wood from Osceola Mudflow.
L-223A2_._ _ 4, 8003:300 3640 B.C. 5, 600 Do.
L-223B2__. . 4, 950d:300 3730 B.C. 5, 700

Do.
Peat from above pyroclastic layer N,
below layer F, both from Mount

aimer.
Wood from Osceola Mudflow.

W-2053 _____ 5, 020i300 3810 B.C.

UW-—623 ..... 5,040:i:150 3820 B.C. 5,800

 

1 Rounded of! to the nearest 50 years.
2 Lamont Geological Observatory.
3 University of Washington.

12

TABLE 5.—Source, age, and description of some postglacial pyro-

clastic deposits in Mount Rainier N ational Park
[D. R. Mullineaux, Written commun., 1970]

 

 

Pyroclastic Source Approximate Description
layer volcano age (yrs)

X ____________ Rainier ....... > 110-<150 Scattered pumice lapilli.

W ____________ St. Helens _ _ _ _ 450 Pumice ash.

C ____________ ainier _______ >2, l50—<2, 500 Plbllmce lapilli and scattered

oc s.

Y ____________ St. Helens. . . _ >3, 250—<4, 000 Pumice ash.

B ____________ Rainier ....... >4, GOO-<5, 800 Plllmiile ash and scattered
ap .

 

>4, 000-<5, 800
5, 700

>5, 700—<6, 600

Scattered pumice lapilli.
Montmorlllonite-rich ilthic

ash.
Sand- to block-sized lithic

 

 

 

rubble.
>5, BOO-<6, 600 Lithic ash.
>5, SOD—<6, 600 Pumice lapilli.
>5, BOO—<6, 600 Do.
>5, SOD—<6, 600 Pumice ash and scattered
lapilli.
O _ ........... Mazama ______ 6, 600 Pumice ash.
R ............ Rainier _______ >8, 750—<1l, 000? Punlllice and lithic lapilli and
as .

 

The most distinctive and widespread pyroclastic de-
posits at Mount Rainier are from two other volcanoes.
Layer 0 (table 5) has mineralogic characteristics that
correspond to those of the pumice and ash that were
erupted by Mount Mazama volcano at the site of Crater
Lake, Oreg., about 6,600 years ago (Crandell and
others, 1962; Powers and Wilcox, 1964). This pumice
layer is especially useful in stratigraphic studies be-
cause it blankets the entire park and the adjoining
region to a depth of 1—2 inches and is a distinctive
yellowish orange.

The other two exotic pumice deposits are layers Y
and W, both of which were erupted by Mount St. Hel-
ens, a volcano about 50 miles south-southwest of Mount
Rainier. Layer Y is a light-yellowish-brown pumice of
medium to very coarse sand size. It thickens westward
from about 1 inch near the east edge of the park to
about 12 inches near the southwest corner. Layer Y is
between 3,250 and 4,000 years old, and for convenience
it will be arbitrarily assumed to have an age of about
3,600 years.

Pyroclastic layer W is a white pumice of fine to me-
dium sand size. It thickens from about a quarter of an
inch on the west side of the park to about 3 inches near
the southeast corner. A radiocarbon date of 3201200
years (W—1119) was determined for charcoal in a hori-
zon of dufl’ beneath layer W, and age of 290i200 years
(W—1120) for charcoal in a layer above the pyroclastic
deposit (Crandell and others, 1962). Radiocarbon ages
of about 300 years have a “true” age of about 450 years
(table 4). An age of about 450 years for pyroclastic
layer W is consistent with tree-ring data, because there
are trees at least 435 years old growing on the surface
of deposits at Mount Rainier that are younger than the
pumice.

 

POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON

Although most of the recognizable pyroclastic de-
posits in the park originated at Mount Rainier, few are
widespread, distinctive, or preserved well enough to be
of use in dating other deposits except in limited areas.
The most useful pumice from Mount Rainier is layer C,
which is mostly of lapilli size and which is widely dis-
tributed over most of the park east of the volcano. It is
generally one to several inches thick and is between
2,150 and 2,500 years old. For convenience of reference,
it will be assumed to have an age of about 2,300 years.

The following description of lahars and some other
unconsolidated deposits at Mount Rainier contains
many references to the stratigraphic relations of these
deposits to certain pumice layers. The reader is urged
to take special note of the following pyroclastic deposits
and to remember their approximate age: layer W, about
450 years old; layer C, about 2,300 years old; layer Y,
about 3,600 years old; and layer 0, about 6,600 years
old.

The reader may wonder why the pyroclastic deposits
were not given letter designations in alphabetical order
by age. Letters were arbitrarily assigned to the deposits
at an early stage of the study, when only five layers
were recognized (Crandell and others, 1962), to allow
for the possible later addition of other layers. More
than 15 pyroclastic deposits have now been distin-
guished and given letter designations.

ORIGIN OF THE CLAY IN SOME LAHARS

Many lahars at Mount Rainier contain substantial
amounts of montmorillonite or kaolinite, or both, as
well as lesser amounts of some other clay minerals. The
source of these clays is a critical problem because most
other unconsolidated deposits at Mount Rainier are
typically poor in clay minerals. The magnitude of the
problem can be illustrated by some very crude estimates
of the volume of clay in the Electron and Osceola Mud-
flows, which, respectively, are about 600 and 5,700
years old and which originated on the west and east
sides of the volcano. The Electron Mudflow has a vol-
ume of at least 200 million cubic yards in the Puget
Sound lowland alone, where it has a clay-size fraction
of about 9 percent; the clay-mineral content of this
fraction is about 60 percent. The total clay-mineral con-
tent of the mudflow, therefore, probably is at least 10
million cubic yards. The estimated volume of the
Osceola Mudflow is at least 2.6 billion cubic yards. The
clay-sized fraction of nine analyzed samples averages
about 9 percent, of which clay minerals make up an
average of 75 percent. The mudflow, therefore, may
contain as much as 150 million cubic yards of clay
minerals.

INTRODUCTION 13

The large amount of clay in some lahars seems to have
a direct bearing on their manner and place of origin.
The two most obvious possible origins of the clay min-
erals are through weathering processes and by hydro-
thermal alteration of rock in the volcano.2

Montmorillonite and kaolinite are known to be prod-
ucts of weathering processes and are commonly found
together, although in different proportions, in many
soils (Grim, 1953, p. 340—341). At Mount Rainier, I
found no extensive area of rock or surficial deposits al-
tered to clay by surface weathering processes on the
lower slopes of the volcano. This lack of weathered
material is readily explained by the predominance of
mechanical weathering processes near and above timber-
line. Furthermore, in the unlikely event that clayey pro-
files of weathering ever existed on the flanks of the vol-
cano, they surely would have been stripped away during
the Fraser Glaciation. No such profiles have been formed
in Holocene time at Mount Rainier.

Nevertheless, Fiske, Hopson, and Waters (1963, p.
85) suggested that weathered material provided the
primary source of the largest Holocene lahar from
Mount Rainier—the Osceola Mudflow. Crandell and
Waldron (1956, p. 353) reported abundant montmoril-
lonite in the matrix of the mudflow, which was accom—
panied by a kaolin mineral. They thought both of these
minerals were derived from hydrothermally altered
rocks of the volcano. Fiske and his colleagues, however,
concluded that the primary source of the montmoril-
lonite was in “altered water-laid pumiceous sediments
and pumice-slurry flood deposits interstratified in the
valley fills along the headwaters of White River.” Such
a deposit on the south side of Inter Fork valley, which
was first identified as the Osceola Mudflow by Crandell
and Waldron (1956), was described by F iske and his
coworkers as consisting of two parts—a lower part of
chiefly “well—stratified sands and gravels” and an upper
part of “water-laid pumiceous sediments and pumiceous
mudflows now partly altered to a sticky clay.” When I
reexamined this outcrop during the present investiga-
tion, I found a lower unit of glaciolacustrine sand and
silt interbedded with thin layers of till, all part of the
Evans Creek Drift, which was deposited during the
Fraser Glaciation. Size-distribution analysis of a sam-
ple of the till indicated 8 percent clay-sized material. An
X-ray examination of the clay fraction revealed feld—
spar, cristobalite, and quartz; no clay minerals were
identified. A sample of the fine-grained glaciolacustrine
sediment also contained 8 percent clay—sized material,
most of which consisted of feldspar and cristobalite but

2I am indebted to Professor Howard A. Coombs of the University of
Washington for first suggesting to me, in 1953, that the abundant clay
in the Osceola Mudflow might have been derived from hydrothermally
altered rock at Mount Rainier.

420—479 0 - 71— 3

 

included a small amount of an unidentified clay min—
eral. The overlying unit, which was described by F iske,
Hopson, and Waters (1963, p. 86) as pumiceous sedi-
ments and pumiceous mudflows, is the Osceola Mudflow
itself, which is as much as 100 feet thick here. I found
no pumice within the mudflow, although several feet
of young, unweathered pumice overlies it. This remnant
of the Osceola is indistinguishable from the mudflow
farther upvalley, where it veneers the floor and sides of
Glacier Basin, as well as the ridgetops bordering the
basin.

Remnants of sedimentary fills, such as those described
by Fiske and his coworkers, are present in some of the
valleys that head at Mount Rainier; some of the fill
remnants include clayey lahars, and some include layers
of fresh, unaltered pumice a few inches thick. The clay
in such lahars was thought by Fiske and his associates
to have been partly formed in place by weathering of
pumice, and some of the clay was thought to have been
transported by slopewash and derived from a blanket
of weathered volcanic ash on the adjacent valley walls.
As evidence of a widespread blanket of weathered ash,
Fiske, Hopson, and Waters (1963, p. 80) described a
layer “mostly altered to a greasy yellow clay contain-
ing abundant montmorill‘onite” at Mist Park and in the
headwaters of Marmot Creek, both northwest of the
volcano. The layer they noted at these two localities is
pyroclastic layer 0, the Mazama ash (table 5). Mechani-
cal analyses of four samples of this ash, collected from
outcrops at various places within Mount Rainier Na-
tional Park, show that the ash contains only from 1 to
7 percent of clay—sized material (D. R. Mullineaux, oral
commun., 1969). In one sample, montmorillonite and
a mixed-layered montmorillonite-mica mineral each
made up one part in 10 and were accompanied by a
trace of kaolinite. In the other three samples, clay min-
erals either were absent or were present in only trace
amounts. According to D. R. Mullineaux (oral com-
mun., 1969), microscopic examination shows that deli—
cate shard points and filaments of glass from layer 0
are intact, and the glass appears to be virtually un-
weathered. Thus, I do not believe that layer 0 could
have provided an adequate source for the large volume
of clay in the Osceola Mudflow.

Hopson, Waters, Bender, and Rubin (1962, p. 640)
and Fiske, Hopson, and Waters (1963, p. 81) evidently
considered the ash layer at Mist Park to be correlative
with a layer of yellow clay (pyroclastic layer F) on the
uplands northeast of the volcano (Crandell and Wal—
dron, 1956, p. 355). That latter clay is, however, strati-
graphically above layer 0, as is demonstrated in count-
less natural exposures and roadcuts. In contrast to the
meager clay content of layer 0, the yellow clay in-

14

POSTGLACIAL LAHAR‘S FROM MOUNT RAINIER VOLCANO, WASHINGTON

TABLE 6.—Postglacial eruptions, lahars, avalan

{Dates based on the approximate ages of bracketing pyroclastlc layer

 

Years
380

Eruptions that produced summit
cone of Mount Rainier and main
pyroclastic deposits in Mount
Rainier National Park

West Fork of the
White River valley

Inter Fork and White
River valleys

Ohanapecosh River valley

Muddy Fork of the
Cowlitz River valley

Nisqually River valley

 

2,000

3.000

4,000

5,000

6,000

7,000

8,000

9,000

 

 

Layer G erupted by Mount Rainier
between 110 and 150 yr ago

Layer W erupted by Mount St‘
Helens about 450 yr ago

present summit cone of
Mount Rainier

a,
i
\

Lava flows erupted to form

t
Layer C erupted by Mount Rainier
about 2,300 yr ago

Layer Y erupted by Mount St.
Helens about 3,600 yr ago

Layers B and H erupted by Mount
Rainier between 3,600 (Y) and
5,800 (N) yr ago

Layer F erupted by Mount Rainier
about 5,700 yr ago

Layer S erupted by Mount Rainier
between 5,700 (F') and 6,600 (0)
yr ago

Layers N, D, L, and A erupted by
Mount Rainier between 5,800 and
6,600 yr ago

Layer 0 erupted by Mount Mazama
at Crater Lake, Oreg" about
6,600 yr ago

Layer R erupted by Mount Rainier ,
more than 8,750 yr ago

 

Lahar extended at least
18 miles beyond Win-
throp Glacier between
275 and 400 yr ago

Lahar extended atleast
18 miles beyond Win-
throp Glacier between
2,300 (C)
(Y) yr ago

Two lahars extendedllto
18 miles beyond Win-
throp Glacier between
3,600 (Y) and 5,700
(F) yr ago

Osceola Mudflow ex-
tended at least 70
miles downvalley
from volcano about
5,700 yr ago

and 3,600 --

it

 

Avalanches of rock
debris from Little
Tahoma Peak in 1963
extended as far as
4.3 miles downvalley

At least 4 lahars extended
between 4 and 13 miles
beyond Emmons Gla-
cier between 1,000 and
2,300 (C) yr ago

Labar extended atleast
15 miles beyond Em-
mons Glacier between
2,300 (C) and 3,600
(Y) yr ago

Osceola Mudflow

At least 5 lahars extended
215 to 9 miles beyond
Emmons Glacier be-
tween 5,700 and 6,600
(0) yr ago

Green water lahar ex-
tended at least 28 miles
downvalley from vol-
cano between 5,700
and 6,600 (0) yr ago

 

Lahar extended at least
6 miles beyond Ohan-
apecosh Glacier be-
tween 450 (W) and
3,600 (Y) yr ago

Lahar extended at least
6 miles beyond Ohan-
apecosh Glacier be-
tween 3,600 (Y) and
6,600 (0) yr ago

Lahar extended at least
as far downvalley as
Indian Bar more than
6,600 (0) yr ago

 

Lahar extended at least
3.5 miles beyond Cow-
litz Glacier between
450 (W) and 3,600 (Y)
yr ago

Lahar extended down-
valley at least as far
as Longmire in the
1860’s

Lahar extended at least
1 mile beyond Long-
mire about 400 yr ago

At least 7 lahars ex-
tended 45 to 9 miles
beyond Nisqually Gla-
cier between 800 and
3,600 (Y) yr ago

Lahar extended at least
25 miles beyond Nis-

< qually Glacier some-

time after 3,600 (Y)
yr ago

At least 3 lahars ex-
tended more than 15
miles beyond Nis-
qually Glacier be-
tween 3,600 (Y) and
6,600 (0) yr ago

Paradise lahar extended
at least 18 miles down-
valley from volcano
between 5,800 and
6,600 (0) yr ago

Avalanches of clayey
rock debris covered
Paradise Park more
than 5,800 (N) yr ago,
and Van Trump Park
more than 6,600 (0)
yr ago

 

 

 

ch98, and block-amd-ash flows at Mount Rainier

INTRODUCTION

s are followed by the letter designation of that layer in parentheses]

15

 

Kautz Creek valley

Tahoma Creek valley

South Puyallup River
x’alley

North Puyallup River
vaHey

South Mowich River
valley

Carbon River valley

Years ago

 

 

Lahars extended down-
valley to Nisqually
River in 1947

At least 2 lahars ex-
tended more than 4
miles beyond Kautz
Glacier within last
450 yr

At least 3 lahars ex—
tended more than 3
miles beyond Kautz
Glacier between 450
(W) and 3,600 (Y) yr
ago

Lahar extended more
than 4 miles beyond
Kautz Glacier before
3,600 (Y) yr ago

Lahar extended 3.5
miles from South
Tahoma Glacier in

1967
Lahar extended at least
4.5 miles beyond

South Tahoma Gla-
cier about 440 yr ago

Two lahars extended
more than 2 miles
beyond South Tahoma
Glacier between 450
(W) and 2,800 yr ago

Round Pass Mudflow
extended at least 7

Tahoma Glacier about
2,800 yr ago

 

-— miles beyond South _

 

At least 4 lahars of un-
known extent have
occurred within last
450 (W) yr

Electron Mudflow ex—
tended about 30 miles
downvalley from volA
cano about 600 yr ago

‘ Lahar extended at least

14 miles beyond
’I‘ahoma Glacier about
1,000 yr ago

Block-and-ash flow exA
tended at least 3 miles
beyond Tahoma Gla-
cier about 2,500 yr
ago

Lahar extended at least
3 miles beyond Ta-
homa Glacier between
2,500 and 2,800 yr ago

Round Pass Mudflow
extended at least 15
miles beyond Tahoma
Glacier about 2,800 yr
ago

Lahar of unknown ex-
tent occurred more
than 3,600 (Y) yr ago

At least 2 lahars of un-
known extent oc-
curred more than 400
yr ago

Round Pass Mudflow

 

 

Lahar extended at least
2.5 miles beyond
South Mowich Gla~
cier within last 450
(W) yr

Lahar extended at least
3 miles beyond South
Mowich Glacier be—
tween 450 (W) and
3,600 (Y) yr ago

At least 1 lahar ex—
tended more than 7
miles beyond South
Mowich Glacier be-
fore 3.600 (Y) yr ago

 

Lahar extended at least
5 miles beyond Car-
bon Glacier between
3,600 (Y) and 6,600
(0) yr ago

2,000

3,000

4,000

— 5,000

- — 6,000

_ 7,000

— 9,000

 

 

 

16

cludes from 50 to 90 percent clay-sized material, in
which clay minerals make up as much as eight parts
in 10. Montmorillonite is the most common mineral;
it is accompanied by illite or kaolinite, or by both min-
erals in some samples. The stratigraphic relations and
lithology of this layer of yellow clay suggest that the
clay was formed at the same time as the Osceola
Mudflow.

A possible source of clayey material is the masses of
glacial drift that lie on the lower slopes of the volcano
and in the adjacent valleys. This drift is not regarded,
however, as a potential source of clayey lahars chiefly
because it is typically poor both in clay-sized material
and in clay minerals. The Evans Creek Drift, which is
the most widespread glacial deposit in the park, is char-
acterized by an immature soil profile with little or no
clay in the thin B horizon. X-ray analyses of clay frac-
tions of unweathered till from five localities in the park
revealed clay minerals in only trace amounts in three
samples and none in the other two (table 7). These data
suggest that the drift is not an adequate source for
clayey lahars.

From these data I conclude that neither the pyroclas-
tic deposits nor the glacial drift at Mount Rainier could
have provided an adequate source for the clayey lahars
of Holocene age.

Clay minerals are well-known products of hydro-
thermal alteration of rock, as has been amply demon-
strated by studies of hot-springs areas and of mining
districts, where the clays are associated with metallif-
erous veins. Hydrothermal wallrock alteration at
Butte, Mont, for example, has resulted in a zoned clay-
mineral distribution in which montmorillonite and
chlorite are farthest from the source of the hydro-
thermal solutions, and kaolinite lies in a zone closer
to that source (Sales and Meyer, 1948) . Similarly, zones
of hydrothermal alteration in wallrock in the Cochiti
mining district of New Mexico are represented by a
kaolinite-group clay mineral (dickite), illite-kaolinite,
vermiculite-halloysite, and chlorite-montmorillonite,

 

POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON

successively, from the vein outward into the host rock
of rhyolite and andesite flows (Bundy and Murray,
1959, p. 365). In some mineralized districts, similar
zones of alteration seem to be superimposed (Bateman,
1950, p. 104).

Studies of hydrothermal alteration in andesite and
granodiorite at Steamboat Springs, Nev., show that
the principal hydrothermal clay minerals are illite,
montmorillonite, and mixed-layered illite-montmoril-
lonite (Sigvaldason and White, 1962, p. D115). Where
these minerals have been leached by strongly acid solu—
tions percolating downward from the ground surface,
kaolinite is found (Sigvaldason and White, 1961, p.
D117; 1962, p. D115). Similarly, alteration of basalt
in Iceland by nearly neutral hot-spring waters has pro-
duced kaolinite, which is associated with montmoril-
lonite in some areas (Barth, 1950, p. 53).

Montmorillonite and kaolinite are also closely associ-
ated in the hydrothermally altered rocks of some vol-
canoes (table 8). Altered andesite that is part of the
solfatarized vent rocks of Brokeoff Volcano in Lassen
Volcanic National Park has been described by Williams
(1932) and Anderson (1935). I collected three samples
of this rock from a roadcut in the NElANW14 sec. 15,
T. 30 N., R. 4 E., within a lateral distance of 200 feet,
which were analyzed for clay mineralogy. The samples
contained 10, 21, and 70 percent of clay-sized material,
80—90 percent of which consisted of clay minerals. Kao-
linite, illite, and chlorite, listed in order of abundance,
occurred in one sample; kaolinite and montmorillonite
were identified in a second sample; and montmorillonite
alone occurred in the third (table 8, samples 15—7). The
clay mineralogy of these three samples clearly indicates
that the presence or absence of a specific clay mineral
in a single sample may have little significance with
respect to the overall clay mineralogy of rocks that have
been hydrothermally altered.

Active fumaroles were recognized at the summit of
Mount Rainier at the time of the first authenticated
climb to the top of the volcano in 1870, and the lavas

TABLE 7.—Mineralogy of clay fractions determined from X-ray analysis of five samples of Evans Creek till in Mount Rainier National Park

[Values are estimated parts in ten]

 

 

Montmorlllonite- Amor hous silica
Till sample Montmorlllonite Chlorlte Mica chlorite mixed- Feldspar Quartz and or) opaline Cristobalite
layer mineral silica
1 ___________________________________________ Trace ______________ 5 Trace 1 3
2 ___________________ Trace < 1 __________ Trace 4 + 1 + < 1 1 +
3 ___________________________________________________________________ 6 1 ______________ 3
4 _________________________________ Trace ________________________ 6 1 + ______________ 2
5 ___________________________________________________________________ 6 + < 1 ______________ 3

 

 

 

 

 

 

 

 

 

1. Fromkan outcrop a few hundred feet northwest of the visitor center at Paradise
ar .

2. From a roadcut opposite the Marine Memorial at Round Pass.
3. From a. roadcut 1 mile southeast of Box Canyon.

4. From a roadcut in Stevens Canyon 0.3 mile west oi a highway tunnel.
5. From an outcrop on the south side of the valley oi Inter Fork about 1% miles
west of Whlte River campground.

DESCRIPTION OF LAHARS 1 7

of the summit cone have locally been hydrothermally
altered to a loose, sandy, clay-bearing material. A
sample Obtained by Jack H. Hyde from the ground sur-
face at the north rim of the eastern crater near Co-
lumbia Crest contained an estimated seven parts in 10 of
montmorillonite in the silt and clay fraction, and the
remainder of the fraction consisted of feldspar and
cristobalite (table 8, sample 4).

An even larger area of altered clayey rock at Mount
Rainier is now exposed in the east wall of Sunset Am-
phitheater (fig. 5), where a mass of yellow altered rock
forms the western part of a solfatarized plug in the
eroded central conduit of the volcano (Fiske, Hopson,
and Waters, 1963, p. 72, 75). A sample of this rock was
reported by Fiske and his coworkers (p. 75) to be opal-
ized and to contain “some kaolinite, tridymite, cristo—
halite, and also a little pyrite mostly altered to limon—
ite.” They pointed out that the sample “strikingly re-
sembles the solfatarized vent rocks of the Brokeofi vol-
cano, near Mount Lassen” in northern California. They
(p. 85) also emphasized the absence of montomorillonite
from their sample and concluded from this that hydro-
thermally montmorillonitized rock was not available in
the volcano which would provide montmorillonite for
the Osceola Mudflow.

An avalanche of debris from the altered plug in Sun-
set Amphitheater, which occurred some time between
1910 and 1930, formed a deposit that now lies on and
just beyond the end of Tahoma Glacier (fig. 5). In three
samples collected from the avalanche deposit, clay-sized
material made up from 17 to 31 percent of the plastic
yellow matrix. Montmorillonite was identified in two
of the samples and was accompanied by kaolinite in
the third (table 8).

The clay mineralogy of the three samples of the
avalanche deposit, as well as that of the altered rock
from the summit cone, clearly indicates that hydro-
thermal alteration of the rocks of Mount Rainier typi-
cally produces montmorillonite or kaolinite, or both clay
minerals. Altered rocks like these obviously could have
been available in the past to provide the clay component

 

of mudflows. The single sample reported by Fiske,
Hopson, and Waters (1963, p. 85), in which montmoril-
loni'te was not identified, may have come from a part
of the plug that had been strongly leached by acid
solutions, so that montmorillonite was altered to kao-
linite. Or, clay minerals in the plug may be zonally
distributed like those adjacent to some hydrothermal
ore veins. If the clay minerals are zonally distributed,
debris derived from a specific zone could contain only
one clay mineral.

In summary, montmorillonite and kaolinite, as well
as some other clay minerals, are normal and expectable
products of hydrothermal alteration within a volcano.
Because of the inherent structural weakness of hydro-
thermally altered rock, the rock should be especially
susceptible to large—scale failure and sliding. Moreover,
if slides of altered rock were to occur in an active hydro-
thermal area, the slide material most likely would
already be wet because of condensed steam and thus
would readily become a lahar as the slide moved down-
slope. The evidence now available clearly indicates that
all the large clayey lahars at Mount Rainier were de-
rived from areas of hydrothermally altered rock on the
volcano.

DESCRIPTION OF LAHARS

LAHARS IN THE WHITE RIVER DRAINAGE BASIN

A sequence of lahars and fluvial deposits extends
down the White River and West Fork valleys for many
miles beyond the base of Mount Rainier. The most
voluminous units in this sequence are the Osceola Mud-
flow, which extended far into the Puget Sound lowland,
and the older Greenwater lahar, which moved down—
valley at least as far as a point 2 miles beyond the com-
munity of Greenwater.

The stratigraphic relation of these lahars to one an-
other and to pyroclastic deposits is summarized in
table 9. The term “lahar assemblage,” used in this table
and in the following discussion, refers to a succession
of two or more lahars which may be interbedded with

TABLE 8.——Mineralogy of clay fractions determined by X—ray analysis of hydrothermally altered andesite

[Values are estimated parts in ten]

 

Montmorillonite

Kaolinite

Chlorite Iilite Feldspar Quartz Cristobaiite

 

 

 

1-3. From various parts of a clayey avalanche deposit at the terminus of Tahoma

Giac er.

4. From the ground surface on the rim of Mount Bainier's summit cone near
Columbia Crest.
6-7. From roadcuts in Lassen Volcanic National Park, Calif. (See text.)

18 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON

 

FIGURE 5.—Avalanche deposit at and on the terminus of Tahoma Glacier. Parts of the avalanche debris are a sticky yellow
clay, which is the product of hydrothermal alteration of rock within the volcano. The alteration evidently occurred
in an old conduit of the volcano which is now exposed in cross section in the cliffs immediately left of the area where
Tahoma Glacier spills down from the summit snowfields. The ice face in the center foreground is about 150 feet high.

alluvium. Thus, in the White River valley, the pre-
Osceola lahar assemblage is a group of deposits which
includes at least four lahars interbedded with fluvial
gravels, all of which are younger than the Greenwater
lahar and older than the Osceola Mudflow.

GREENWATER LAHAR

A lahar whose surface is dotted with scores of mounds
forms terraces at several places in the White River
valley as far downstream as a point about 2 miles west
of the community of Greenwater (fig. 6). The largest
remnants of the deposit lie on the west side of the White
River valley between the mouth of Silver Creek and
Buck Creek, at the mouth of the Huckleberry Creek
valley, and in an area near Greenwater.

The lahar consists of gray to yellowish-brown sand
to angular and subangular blocks several tens of feet
in diameter. In some places abundant large rock frag-

 

ments are embedded in a loose sandy matrix; elsewhere
the lahar consists largely of sand- and pebble—sized
material. Pebbles were picked at random from the
matrix of the lahar in a shallow pit 0n the west side
of the White River valley about 0.8 mile south—
southeast of Greenwater and examined for rock types.
Pebbles derived from rocks of Mount Rainier made
up 73 percent of the sample, those of granodiorite made
up 7 percent, and those of volcanic rocks derived from
other formations of Tertiary age made up the remain-
der. These pebbles were mostly subrounded and
subangular.

The mounds on the lahar are its unique feature. They
range in height from 4 to about 35 feet and are a few
tens of feet to about 200 feet in diameter. Most have a
roughly circular ground plan, but some are elongate in
seemingly random directions. Although most mounds
have a single peak, some have two or more crests. The
mounds are separated by flattish areas that generally

DESCRIPTION OF LAHARs 19

TABLE 9.—Sequence of lahar assemblages and their stratigraphic relation to pyroclastic deposits (layers W, C, Y, and 0) in the White
River and West Fork valleys

 

White River valley

West Fork valley

 

Layer W

Several lahars interbedded with fluvial gravels.

Layer 0
Lahar
Layer Y

Osceola Mudflow about 5,700 years old.

Several lahars interbedded with fluvial gravels.

Lahar
Two bomb-bearing lahars

l

Post-Osceola lahar
assemblage.

Pre-Osceola lahar
assemblage.

Lahar and fluvial gravel
Layer W

Layer C

Lahar

Layer Y

Lahar

Lahar

Osceola Mudflow

Post-Osceola lahar
assemblage.

Greenwater lahar
Layer 0

Layer 0

 

 

 

47°OO’

     
   

3’ . 4/
, x , P“_,v
exxi/MOUNT ’1‘ §teamboat Prow
\l RAINIER/’ ' \\
A /’-\ _)
C R», V,
pg \ \ \ “\
“(a \ ‘ \ \r\
\\ \\__\I‘\
\\ \\ ‘ 0

2 4 MILES

‘ L_q_q

1 Little

|// Tahoma
Peak

1 l

 

 

 

FIGURE 6.—Distribution of remnants of Greenwater lahar north-
east of Mount Rainier is shown by the heavy pattern; its
inferred original extent is shown in a light pattern. The lahar
probably originated in massive rockslides from the northeast
flank of Mount Rainier between Steamboat Prow and Little
Tahoma Peak.

slope both toward the center of the valley and down-
valley.

Some mounds have been partly excavated, and their
internal composition can be seen. They are mostly

 

made up of very large blocks of rock, or clusters of

blocks, incorporated in an unsorted matrix of sand and
smaller rock fragments. The blocks consist mostly of
breccias from Mount Rainier. Two mounds were noted,
however, that consist entirely of fragments of granodi-
orite. One of these, near the mouth of Buck Creek, con-
sists of angular and subangular fragments, which range
in maximum dimension from less than an inch to at
least 6 feet (fig. 7). A search of adjacent mounds within
a radius of a hundred yards located only one small
boulder of granodiorite; the adjacent mounds are made
up almost exclusively of rock fragments from Mount
Rainier volcano, a few are made up of breccia from the
Tertiary bedrock.

The core of one mound, which is about 20 feet high
and 100 feet in diameter, in the area near Greenwater
is made up of a large mass of flow breccia from Mount
Rainier (fig. 8). The breccia is extensively altered to
a plastic yellow clay, and some parts of it closely
resemble the matrix of the Osceola Mudflow. This core
of altered rock is veneered with a mixture of sand and
rock fragments as large as a foot in diameter. The
veneer is as much as 4 feet thick, and faint bedding in
it that dips about 25° parallels the slope of the mound.

The core of a nearby mound, which is about 10 feet
high and 50 feet in diameter, is also a block of flow
breccia from the volcano, but it is not altered to clay.

The core of a mound in the same general area, but a
little farther downvalley, consists of a block of reddish-
brown and gray breccia which was derived from Mount
Rainier. Some zones in this breccia are entirely altered
to clay. A nearby mound that is about 12 feet high
and 60 feet in diameter has been cut through by a road
on the west side of sec. 9, T. 19 N., R. 9 E., 1 mile west
of Greenwater. The interior of this mound is a jumble
of angular and subangular rock fragments, and there
is little or no matrix of finer material. Most of the frag-
ments are from Mount Rainier, but a few are granodi-
orite and breccia derived from the Tertiary bedrock.

20 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON

 

FIGURE 7.—Mounds on the Greenwater lahar in the Buck Creek area. The mound at the right center consists wholly of
angular blocks of granodiorite; it is about 25 feet high and 100 feet in diameter. Adjacent mounds consist mostly of

material derived from Mount Rainier

The distribution of mounds within remnants of the
lahar seems to be random; however, two of the mound
groups are elongate in a downvalley direction, and in
each of them the area of mounds is separated from the
adjacent valley wall by a broad shallow depression that
also is underlain by the lahar.

The remnant of the lahar at the mouth of Huckle-
berry Creek extends back into the creek valley for more
than half a mile. The surface of the lahar at the up—
valley end of this backfill is about 200‘ feet higher than
the present floor of the White River valley. Likewise,
the highest remnant of the lahar in the Vicinity of Buck
Creek is about 200 feet higher than the White River,
Although a thickness of more than 10 feet is rarely ex—
posed, the vertical height of the lahar above the present
valley floor suggests that the White River valley was
filled to a depth of at least 200 feet during movement.
The present surface of the lahar therefore, in most
places, does not represent its original upper surface

 

while it was moving. At the mouth of Huckleberry
Creek, mounds dot the surface of the lahar in places
100 feet lower than its inferred top during movement
(pl. 2).

The blocks that form the mounds probably were
brought downvalley by an initial rush of the lahar, came
to rest, and remained in place while much of the fine-
grained fluid matrix of the lahar drained away from
them and moved more slowly down the valley. The flat
areas between the mounds, and between groups of
mounds and the valley wall, probably were produced
during this downvalley flowage of the fine-grained
material.

The Greenwater lahar was not recognized within
Mount Rainier National Park for certain, although
three large mounds in the valley of Fryingpan Creek,
about 1 mile upstream from the mouth of the valley
may be part of it. Comparable mounds were not ob-
served anywhere in the White River valley within the

DESCRIPTION OF LAHARS 21

 

FIGURE 8.—Mound on the Greenwater lahar consists of an andesite breccia which was derived from Mount Rainier and which
has been extensively altered to a plastic yellow clay.

park, but their absence there may be due to burial be-
neath the Osceola Mudflow.

The area thought to have originally been covered by
the Greenwater lahar north of the park boundary is
about 8 square miles. If it is assumed that the lahar had
a thickness of 100 feet throughout this area after com-
ing to rest, its original volume would have been a little
more than 800 million cubic yards.

Near the upper limit of the lahar in the Huckleberry
Creek valley a roadcut exposes the deposit on top of py-
roclastic layer 0, which is about 6,600 years old. Al-
though the Osceola Mudflow, which is about 5,700 years
old, was not seen on top of the lahar, the topographic
relations of the two deposits indicate that the Osceola
is younger; thus, the Greenwater lahar is between 5,700
and 6,600 years old.

Mounds are known on the surfaces of lahars in the
vicinity of other volcanoes, but they are by no means
common. Aramaki (1963, p. 290—292) described a pre—
historic mounded lahar on the south side of Asama

420-479 0 - 71 - 4

 

volcano in Japan. This lahar resulted from a phreatic
eruption that destroyed the eastern part of Kurofu-
yama, the oldest of three major volcanoes that make up
Asama. The material shattered by the explosion formed
lahars that spread northward and southwestward be—
yond the volcano. The surface of the lahar southwest
of the volcano is dotted with mounds arranged in groups
that trend toward the southwest, the inferred direction
of flowage; individual mounds are elongate in the same
direction. The mounds have basal diameters of as much
as 330 feet and heights up to 50 feet. The cores of most
consist of very large blocks of pyroxene andesite from
the volcano, some of which are 100 feet in maximum
dimension.

Hills that rise above the surface of a large Pleisto-
cene lahar at the south base of Yatsuga-dake volcano
in Japan have been studied by Mason and Foster (1956).
Many of these hills are substantially larger than those
reported on other lahars; some have heights of as much
as 700 feet and basal diameters of nearly half a mile.

22 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON

These large hills do not seem to have rock cores, and
Mason and Foster concluded that the material of the
hills was extruded above the top of the mudflow by hy-
drostatic pressure While still fluid, through cracks in a
dried, hardened crust.

The length of the lahar described by Mason and
Foster is a little less than 15 miles, but its inferred orig—
inal volume is at least 9.5 billion cubic meters, or
roughly 2.3 cubic miles The largest lahar from Mount
Rainier, the Osceola Mudflow, has an inferred volume
of a little more than half a cubic mile (p. 26), and the
Greenwater lahar only about a third of that. Mason
and Foster suggested that the lahar originated in an
avalanche of loose ejecta on the side of Yatsuga-dake
that possibly was triggered by an earthquake or a vol-
canic explosion.

A lahar whose surface is characterized by many
mounds originated during an eruption of Komaga-take
volcano in Japan that caused a large avalanche (Ishi-
kawa and Yokoyama, 1962). The mounds are about 30
feet high, and their cores are formed by blocks of lava
from the volcano.

Grange (1931) described the conical hills, which num-
ber in the thousands, on the slopes of Mount Egmont
and Mount Ruapehu volcanoes in New Zealaud. The
mounds range in height from a few feet to 100 feet, but
most are 25—30 feet high. The cores of most mounds
that Grange examined consist of large blocks of agglom-
erate. He suggested that the blocks and the deposits
that enclose them are of laharic origin.

A plain studded with several thousand mounds lies at
the southeast foot of Galunggung (Galounggoung)
volcano on Java. The mounds are as high as 230 feet,
and large andesite blocks form their cores. The blocks
are enclosed in a matrix of finer rock debris similar to
that between the mounds. The entire deposit is as much
as 70 feet thick and has an estimated volume of nearly
190 million cubic yards. The deposit heads at the mouth
of a very large alcove in the southeast flank of the
volcano. Escher (1925) concluded that the mounded
deposit is an exceptionally large prehistoric landslide
or mudflow from Galunggung. He suggested that when
the side of the volcano slid outward and flowed down?
slope to the southeast, large blocks included in it came
to rest first; continued downslope flowage of fine mate-
rial lowered the overall surface of the mudflow and
caused the blocks to protrude.

It is noteworthy that in several of the lahars just
described, mound dimensions are similar to those of the
White River valley, and cores of large blocks from the
volcanoes are found in all of them. However, the Green-
water lahar may be unique in having some mound com
that consist of rock not derived from the volcano.

 

The Greenwater lahar is also unique among the lahars
from Mount Rainier in that it contains abundant large
blocks. Although the surfaces of some others have a few
scattered blocks of andesite derived from the volcano,
these blocks number only one or two dozen on any in-
dividual deposit. In contrast, scores of mounds thought
to have block cores can be seen on nearly every remnant
of the Greenwater lahar, and these seemingly deserve
some special explanation. Glacial drift like that in
Holocene moraines in the White River valley probably
would not have been a suitable source, because blocks of
rock comparable with those in mound cores are sparse.
In contrast, large blocks are abundant in the 1963 rock—
fall and avalanche deposits from Little Tahoma Peak.
(See Crandell and Fahnestock, 1965, p. A5—A8.)

The abundant blocks in the Greenwater lahar there—
fore probably originated in rockfalls and rockslides
from the slopes of the volcano and from the walls of the
White River valley. The blocks of ‘granodiorite could
have fallen from outcrops at the head of the Fryingp-an
Creek valley, or from the walls of the White River
valley between Emmons Glacier and the mouth of Sun-
rise Creek.

The rockslides or rockfalls on the volcano may have
been triggered by a steam explosion or by an earthquake
which also shook down masses of granodiorite from the
sides of the White River valley or at the head of Frying-
pan Creek valley.

Evidence of a volcanic explosion some time between
5,700 and 6,600 years ago is present in the form of pyro-
clastic layer S in the Yakima Park area and on top of
Goat Island Mountain (Crandell and Mullineaux, 1967,
p. 7). The layer consists of an unsorted mixture of sand,
silt, and angular rock fragments as large as 1.5 feet
across and is entirely derived from Mount Rainier. The
lack of new pumice or scoria suggests that the rubble
was formed by a steam explosion that blew out pre-
viously solidified rock in the northeast flank of the
volcano. Although there is' no known way to make a firm
correlation between layer S and the Greenwater lahar,
the explosion that created the pyroclastic deposit could
also have triggered the rockslides that caused the lahar.

The absence of clay from the matrix of the lahar
points to relatively fresh rock as the chief source; how-
ever, the presence of blocks of clayey, altered rock sug—
gests that some of the material came from areas of
hydrothermal alteration. The main source area of the
lahar probably lay between Little Tahoma Peak and
Steamboat Prow. In fact, these two features may be the
only surviving remnants of the northeast side of the
volcano that was largely destroyed when the lahar was
formed.

DESCRIPTION OF LAHARS 23

The great rockslides that created the Greenwater
lahar may have stripped a mass of mostly unaltered
rock from the northeast flank of the volcano, thereby
not only exposing the underlying rocks that had been
extensively altered by hydrothermal solutions but also
removing the support from these altered rocks. Thus,
the events that created the Greenwater lahar may have
set the stage for the subsequent rockslides that produced
the Osceola Mudflow.

PRE-OSCEOLA LAHAR ASSEMBLAGE

A sequence of lahars and fluvial deposits, hereafter
referred to as the pre-Osceola lahar assemblage, is ex-
posed at many places along the White River valley
within the park. Farthest upvalley, this assemblage
consists of two lahars that contain volcanic bombs and
one that does not contain bombs. These three lahars are
exposed in the south bank of the White River about
half a mile upstream from the highway bridge over the
river. Were it not for a few inches of stratified sand
between them, the two bomb-bearing lahars probably
could not be differentiated from one another. Both are
gray, have a matrix consisting mostly of coarse friable
sand, and contain abundant angular and subangular
fragments of dense flow rock from Mount Rainier as
large as 10 feet in diameter. Bombs, which are sparsely
scattered throughout the lahars, range in maximum
dimension from 6 inches to several feet; all are strongly
breadcrusted, and none have been modified by erosion.
Some masses of dense flow rock are also breadcrusted
(fig. 9). The lower lahar is more than 20 feet thick and
probably extends below the level of the White River.
The upper lahar is about 12 feet thick and is successively
overlain by a lahar about 20 feet thick in which bombs
were not seen and by the Osceola Mudflow. The mud-
flow forms the top unit and caps a broad terrace about
100 feet above the river; owing to an erosional uncon-
formity, the Osceola locally also lies below river level.

The three lahars in the assemblage contain very little
silt or clay. The two bomb-bearing lahars were seen
nowhere else in the valley, and their original extent is
not known.

Remanent magnetism determinations made on ori-
ented samples from three bombs in the upper lahar
and from five in the lower show a random orientation
of the direction of remanent magnetism; thus, the tem—
perature of the bombs apparently was below the Curie
point of the included ferromagnetic minerals when the
lahar came to rest (p. 5). Although the material in
the lahars could have had a temperature above the
boiling point of water, it seems more likely that the
masses were cooler and were moving as lahars when
they came to rest, rather than as hot dry avalanches.

 

 

FIGURE 9,—Large breadcrusted block of dense flow rock in a
lahar exposed in south bank of the White River about half
a mile downstream from White River campground.

However, the lahars may have originated in such ava-
lanches that descended Emmons Glacier and melted
large amounts of snow and ice.

A roadcut on the south side of the valley near the
south end of the highway bridge over the White River
exposes a lahar that has a sandy matrix and is about
40 feet thick. The lahar rests on granodiorite and is over-
lain by the Osceola Mudflow. One or more pre-Osoeola
lahars also are exposed on the north side of the valley
a few hundred feet northeast of the bridge.

Farther downstream, the pre-Osceola lahar assem-
blage is exposed on the south side of the White River
about half a mile below the highway bridge across the
river. In this area the assemblage is at least 80 feet thick
and consists of several lahars 3—30 feet thick that are
interbedded with fluvial deposits. The assemblage crops
out half a mile farther downstream in a high bank near
the mouth of Fryingpan Creek, Where the material is
mostly stratified and consists largely, if not wholly, of
fluvial deposits. The assemblage also is seen in cuts along
the highway between F‘ryingpan Creek and the White
River Ranger Station and in the face of a terrace on the
west side of White River 1 mile downstream from the
mouth of Crystal Creek. At this northernmost exposure,
more than 50 feet of coarse bouldery lahars and pebble—
to-boulder gravel of fluvial origin forms a terrace that
is capped with a few feet of Osceola Mudflow. The base
of the lahar assemblage also apparently lies below the
level of White River here.

24 POSTGLACIAL LAI-IARS FROM MOUNT RAINIER VOLCANO, WASHINGTON

Although it is possible that some of the deposits just
described are those of the Greenwater lahar, the ab—
sence of very large blocks suggests that they are not cor-
relative. Furthermore, the Greenwater lahar forms a
fill in the White River valley north of the park that is
as much as 200 feet above the valley floor. The deposi-
tional top of the pre-Osceola lahar assemblage is no—
where known to extend to a height greater than about
80 feet above the White River. Topographic relations
imply that the lahar assemblage is younger than the
Greenwater lahar and thus less than 6,600 years old,
because the Greenwater lahar post-dates pyroclastic
layer 0 of that age.

The lahar assemblage forms a valley fill that was dis-
sected to a depth of 200—250 feet by the White River
before the Osceola Mudflow occurred. The base of the
lahar assemblage is below the White River at nearly
every outcrop; at many of these outcrops the Osceola
unconformably overlies the lahar assemblage, and its
base is also below river level. The deposition of the
assemblage, which was followed by downcutting, was
probably not climatically controlled, as is valley ag-
gradation in some regions. Instead, the presence of
breadcrust bombs in two of the lahars strongly suggests
that the aggradation was the result of volcanism.

The pre-Osceola lahar assemblage probably orig-
inated as a direct consequence of hot rock debris ava-
lanching down Emmons Glacier during or shortly after
eruptions at the summit of the volcano. The assemblage
was probably formed by floods and lahars caused by the
rapid melting of snow. The building up of the lahar
assemblage in the valley thus is thought to have been
caused by large quantities of rock debris added to the
White River as a result of volcanic activity. With the
cessation of eruptions and of lahar deposition in the
White River valley, the river cut down into the valley
fill. No significant unconformities were noted within
the lahar assemblage, and all the deposits within it
probably were formed within a relatively short time,
perhaps not more than a few years.

OSCEOLA MUDFLOW

The Osceola Mudflow is by far the largest mudflow
of postglacial age from Mount Rainier and is one of the
largest known volcanic mudflows in the world. Many of
the facts concerned with the distribution, age, and ori-
gin of the mudflow have been discussed previously
(Crandell and Waldron, 1956; Crandell, 1963a, b).

The Osceola was first described by Willis (1898, p.
143) as “a sheet of till that covers the plateau between
the Green and White Rivers and extends southwest be-
yond White River about the head of Fennel Creek”
(pl. 3). He correctly recognized the Mount Rainier

 

provenance of the deposit, but thought that the Osceola
had been formed by a piedmont glacier that issued into
the lowland from the Cascade Range. Willis noted that
knobs of Vashon till deposited during the last major
glaciation are topographically higher than the surface
of the adjacent Osceola deposit, and he thought that this
indicated that the Osceola was somewhat older than the
Vashon till.

Investigation of the Osceola (Crandell and Waldron,
1956; Crandell, 1963b; Mullineaux, 1961, 1965a, b) has
shown that the mudflow overlies the Vashon Drift and
that the upper part of the drift contains a soil profile.
This soil was formed after the Puget glacier lobe with—
drew from the southeastern part of the Puget Sound
lowland, about 14,000 years ago, and before the mud-
flow occurred. Four radiocarbon dates obtained from
wood incorporated in the mudflow range from
43001-250 (W—564) to 5,040il50 (University of
Washington radiocarbon date No. 62; this report, table
4). When corrected for variations in atmospheric C“
and for a C“ half life of 5,730 years, these ages range
from 5,550 to 5,800 years; a “true” age of about 5,700
years is here arbitrarily assumed for the Osceola
Mudflow.

DISTRIBUTION AND VOLUME

Within Mount Rainier National Park the Osceola
Mudflow underlies terraces in the White River and West
Fork valleys and veneers valley sides above the ter-
races. The mudflow is, however, not well preserved in
these valleys near the volcano because of erosion by
younger valley glaciers. The largest outcrops of the
Osceola close to the volcano are in the valley of Inter
Fork. Near the mouth of the valley the mudflow is
banked against a lateral moraine of Evans Creek Drift,
which constricted the valley and caused the mudflow
to accumulate behind it to a thickness of as much as 100
feet. Farther upvalley, the mudflow veneers bedrock
and glacial drift on the floor of Glacier Basin and on
the floor of a high cirque directly north of the basin.
During the Winthrop Creek Glaciation, Inter Glacier
reworked part of the mudflow deposit and formed a
series of lateral moraines in the upper part of Glacier
Basin.

The mudflow is preserved at many places on the
ridgetops at the head of Inter Fork valley; the high-
est outcrop is at the top of Steamboat Prow at an alti-
tude of 9,700 feet. On the ridgetop between Glacier
Basin and the unnamed cirque directly to the north,
several feet of the mudflow veneers a lava flow. Iron
oxide, apparently derived from the mudflow, has im—
pregnated the flow rock, forming a resistant iron-rich
crust at its surface. This crust was recognized by Fiske,
Hopson, and Waters (1963, p. 85), but they thought

DESCRIPTION OF LAHARS 25

that it had formed beneath deeply weathered volcanic
ash, whereas the crust in fact lies beneath a remnant of
the mudflow.

Downstream from Inter Fork, above White River
campground, the Osceola blankets a lateral moraine on
the north valley wall to a height about 500 feet above
the present valley floor. Pits dug on the crest of the next
higher lateral moraine, which is about 1,000 feet above
the valley floor, revealed a clayey deposit in the strati-
graphic position of the Osceola Mudflow. The deposit is
pale yellow and contains small rock fragments; it may
be part of pyroclastic layer F (table 5; p. 12). The
mudflow evidently did not reach this height on the val‘
ley wall.

According to information provided by H. W. Ander-
son of the US. Geological Survey (written commun,
December 1964), the Osceola Mudflow was penetrated
at a depth of about 50 feet during drilling for a water
well at the Silver Creek Ranger Station, on the White
River valley floor near the north boundary of the park.
The well was still in the mudflow when drilling was
stopped at a depth of about 200 feet. The mudflow
veneers the sides of the valley to a height of about 125
feet a few miles downstream from the Silver Creek
Ranger Station. At Federation Forest State Park, about
14 miles downstream from Silver Creek, a well was re-
ported by Mr. Anderson to have entered the Osceola
Mudflow at a depth of about 200 feet beneath the val—
ley floor. In this area the top of the mudflow forms a
terrace that is about 35 feet higher than the White
River (fig. 10).

This information from drilling on the valley floor
indicates that the valley was at least 200 feet deeper
when the mudflow occurred than it is today. The mud-
flow must have temporarily filled the valley near Silver
Creek Ranger Station to a depth of more than 300 feet
during movement.

The Osceola Mudflow also coats valley sides and
forms terraces in the West Fork valley. The highest
outcrop of the mudflow in the West Fork drainage
basin, other than the one on Steamboat Prow, is at an
altitude of about 6,800 feet just west of Winthrop Gla-
cier. The mudflow crops out in streambanks along the
West Fork and Winthrop Creek at many places. On
the east bank of the river at the mouth of Winthrop
Creek, the base of the mudflow is below river level, and
its eroded top is 25 feet above the river. Successively
above the mudflow are a layer of organic matter that
contains logs, a coarse gravel deposit, and another lahar.

At a point about 2.5 miles upstream from the mouth
of West Fork valley the Osceola veneers the northwest
valley wall to a height of about 320 feet above the val-
ley floor, and at the mouth of the valley the mudflow ex-

 

 

FIGURE 10.—Osceola Mudflow exposed in the face of a terrace 2
miles southeast of Greenwater. Drilling for a well a few
miles downstream from this point revealed that the mudflow
extends to a depth of about 200 feet beneath the valley floor.
The largest boulder in the center of the photograph is about
6 feet in diameter. The fluvial sand and gravel that underlies
the mudflow in the foreground probably is an old terrace de-
posit that was mantled by the Osceola.

tends below river level. If the pre-Osceola valley of
West Fork was as deep as that of the White River (see
above), the Osceola may have temporarily reached a
depth of at least 500 feet in the lower part of the West
Fork valley.

Forty miles downvalley from Mount Rainier, just
inside the Cascade mountain front, the White River
passes through a bedrock gorge that is now blocked by
Mud Mountain Dam. The gorge lies at the south edge
of the White River valley, which is about 3 miles wide
in this vicinity. A long, narrow, flat-topped ridge (Mud
Mountain) several hundred feet high, which extends
southward across the broad White River valley, is made
up largely of unconsolidated deposits that range in age
from early or middle Pleistocene to late Pleistocene.
The Osceola Mudflow was temporarily at least 450 feet
deep in this part of the valley and cascaded in a sheet
nearly a hundred feet deep down the west slope of
Mud Mountain to the floor of a glacial melt-water chan-
nel. The mudflow poured from the Mud Mountain area
into the Puget Sound lowland along several different
routes (pl. 3).

West of the mountain front the Osceola spread widely
on a plain of Vashon till and melt-water deposits. The
mudflow is only a few feet thick on some topographic
scarps and till drumlins; elsewhere it is as much as
75 feet thick. A high degree of fluidity permitted the
mudflow to flow long distances down narrow topo—
graphic depressions on the drift plain. As a result the

26 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON

Osceola finally came to rest in the lowland as a lobe as
much as 8 miles wide and 20 miles long with very un—
even, or digitate, margins (pl. 3).

The mudflow profoundly changed the lower course
of the White River. Before the mudflow, the river
turned southward where it debouched from the moun-
tain front and followed the valley of South Prairie
Creek to join the Puyallup River near Orting. When
the mudflow rushed out onto the drift plain, one lobe
of it extended down the Old White River valley, but
the greatest share flowed northwesterly across the plain,
inundating all but the highest relief features. As the
mudflow became more dilute and approached the con-
sistency Of a muddy stream, it became the White River;
this river began to cut a new valley along the axis of
the broad lobe, trending northwestward toward Auburn
( Crandell, 1963b) .

The mudfiow crops out in banks of the Puyallup
River and has been penetrated in wells drilled into the
flood plain south of Sumner (Crandell, 1963b). The
Osceola also has been identified at a depth of about 265
feet below sea level, beneath the floor of the Puyallup-
Duwamish valley, 4 miles northwest of Auburn (Luzier,
1969, p. 14). At the time of the mudflow the Puyallup-
Duwamish valley was an arm of Puget Sound between
Orting and Renton. This arm was filled first by the mud-
flow and later by deposits of the White River (Mulli-
neaux, 1961, p. 185; Crandell, 1963b, p. A68).

At least 30 blocks of reddish-brown breccia derived
from Mount Rainier are scattered on the surface Of the
mudflow. The largest measures 30 by 40 feet and stands
20 feet above the mudflow surface; it is located about 4
miles west of Enumclaw. Nearly all these blocks are
situated along topographic breaks in the mudflow sur-
face that coincide with scarps in the buried drift plain.
More than half the blocks in the Buckley-Enumclaw
area lie along a northwest-facing scarp 1 mile west of
Enumclaw that represents a side of a buried melt-water
channel; the opposite side was formed by the glacier
itself (Crandell, 1963b, p. A66, pl. 2). Blocks are prob-
ably concentrated along this scarp because the mudflow
thinned considerably while flowing over it, and the large
blocks became grounded on the underlying surface much
as icebergs become grounded in shallow water. The
presence of lower ground immediately northwest Of the
scarp permitted the fine matrix of the mudflow to drain
away and leave blocks standing above the surrounding
surface. The concentration along this scarp, as well as a
lack of blocks to the southeast, suggests that this was the
first place in the lowland where the mudflow thinned
sufficiently for the blocks to become grounded.

The volume of the Osceola Mudflow can be estimated
on the basis of the known area of distribution of the

 

flow, if several assumptions are made concerning its
total inferred area and thickness: The mudflow origi—
nally covered a total land area of at least 100 square
miles, in addition to a submerged area in the Puyallup
River valley where the mudflow extended into a former
arm of Puget Sound (pl. 3). The mudflow probably
extended as far south in the Puyallup River valley as
the confluence of the Puyallup and Carbon Rivers, as
far west as the town of Puyallup, and northward in the
Green River valley to the outskints of Kent and covered
a submerged area of at least 27 square miles. The mud-
flow has subsequently been removed from a consider-
able part of its former total area by stream erosion or
has been buried by younger alluvium. The mudflow
ranges in thickness from a few feet to at least 200 feet.
It is a reasonable assumption that the Osceola had an
original average thickness of 20 feet over the land areas
it covered; if it did, the mudflow would have had a
volume of about 2 billion cubic yards. If the Osceola
had had a comparable average thickness in the sub-
merged areas, there would have been an additional
volume of about 660 million cubic yards, making a
probable total volume of a little more than half a cubic
mile.
TEXTURE AND MINERALOGY

Grain-size distribution studies were made of samples
of the Osceola Mudflow taken from outcrops at nine
localities in the Cascade Range (samples 29—37, table
10), from a point near Auburn to Glacier Basin (pl.
3). Most of the samples were collected from a 3-foot-
wide vertical trench at a depth of 4—7 feet below the
mudflow surface. Because boulders are sparse at this
depth, the samples represent the average texture of
the mudfiow in this zone. At greater depths, the cobble
and boulder content increases and coarse material makes
up a large proportion of the lower third of the deposit.

The texture of the samples at each locality is shown
in table 10; the clay-sized fraction of the samples ranges
from 6 to 12 percent, the silt-sized fraction from 11 to
16 percent, and the sand-sized fraction from 28 to 41
percent. The sortng coefficients of these samples range
from 9 to 16.34 and average 11.53. The cumulative
curves prepared from the size-distribution data are
presented in figure 11.

The overall texture of the mudflow does not seem to
change with increasing distance from its source. The
sample having the highest proportion of material
smaller than 2 mm, as well as the lowest sorting index
(sample 35), came from the crest of Mud Mountain.
The material sampled there is a veneer left after the
main body of the mudflow spilled across the top of a
ridge (p. 25).

DESCRIPTION OF LAI-IARS

27

TABLE 10.—Size-disiributz'on data from samples of postglacz'al lahars and a block-and-ash flow from Mount Rainier

[Arranged by age from youngest at top to oldest at bottom]

 

 

 

 

 

Size distribution (percentage) M d1 Sorting
e an
Sample Clay Silt Sand diameter Sorting co« Phi standard Phi quartile
((0.004 mm) (0004—60625 (0.0625—2 mm) (mm) efficient (So) deviation deviation
mm) (at) (Oqu)

1 ____________________________________________ 4 10 49 0. 8 8. 10 4. 35 3. 03
2 ____________________________________________ 4 11 60 . 6 3. 41 2. 78 1. 78
3 ____________________________________________ 2 10 35 2. 8 13. 40 4 4. 10
4 ____________________________________________ 7 7 32 2. 9 5. 48 3. 95 2. 48
5 ____________________________________________ 3 11 31 4 7. 75 3. 85 2. 98
6 ____________________________________________ 11 25 58 . 1 3. 94 3. 15 1. 70
7 ____________________________________________ 7 13 37 1 8. 83 4. 36 3. 15
8 ____________________________________________ 9 18 45 . 3 7. 42 4. 74 2. 90
9 ____________________________________________ 3 11 29 4. 2 8. 72 4. 2 3. 13
10 ___________________________________________ 6 __________ 40 3. 6 8. 88 3. 94 3. 20
11 ___________________________________________ 12 17 40 . 4 9. 75 4. 95 3. 29
12 ___________________________________________ 5 13 33 1. 9 10. 60 4. 58 3. 42
13 ___________________________________________ 8 16 21 1. 1 14. 18 5. 13 3. 83
14 ___________________________________________ 5 17 36 . 8 11. 20 4. 76 3. 50
15 ___________________________________________ 7 13 33 I. 6 9 56 4. 54 3. 28
16 ___________________________________________ 9 13 45 . 5 6. 70 4. 16 2. 75
17 ___________________________________________ 7 __________ 43 2 5. 48 3. 43 2. 72
18 ___________________________________________ 5 __________ 38 3. 2 10. 82 3. 56 3. 44
19 ___________________________________________ 1 5 46 1. 5 6. 63 3. 99 2. 74
20 ___________________________________________ l 5 51 1. 1 4. 64 3.11 2. 21
21 ___________________________________________ 1 15 37 1. 5 9. 84 4. 80 3. 30
22 ___________________________________________ 2 10 27 12. 5 13. 20 __________ 3. 73
23 ___________________________________________ 1 13 31 4. 2 13. 60 4. 66 3. 77
24 ___________________________________________ 5 28 44 2 7. 75 4. 35 2. 90
25 ___________________________________________ 1 7 16 13 9. 04 2. 90 1. 53
26 ___________________________________________ 2 16 32 2 14. 56 4. 97 3. 88
27 ___________________________________________ 4 15 33 1. 4 15. 75 4. 91 3. 99
28 ___________________________________________ 3 14 27 4. 3 16. 25 4. 94 4. 03
29 ___________________________________________ 9 13 28 2 11. 53 5. 23 3. 54
30 ___________________________________________ 12 16 31 7 16. 34 5. 79 4. 10
31 ___________________________________________ 8 15 35 . 8 11. 27 4. 82 3. 50
32 ___________________________________________ 9 12 31 1. 6 12. 85 5. 25 3. 70
33 ___________________________________________ 7 11 33 1. 8 14. 63 5. 12 3. 88
34 ___________________________________________ 8 15 35 . 9 11. 62 4. 90 3. 58
35 ___________________________________________ 8 15 41 . 6 9 4. 58 3. 18
36 ___________________________________________ 7 13 35 1. 3 10. 02 4. 61 3. 18
37 ___________________________________________ 6 14 36 1 11. 79 4. 95 3. 20
38 ___________________________________________ 2 12 36 2 10. 86 4. 38 2. 34
39 ___________________________________________ 9 __________ 51 1 6. 25 3. 53 2. 70
40 ___________________________________________ 7 35 33 . 1 10. 20 5. 22 3. 76
41 ___________________________________________ 3 18 32 l. 3 17 5. 03 4. 10

1. Kau‘tz Creek lahars of 1947.. North bank of Nisqually River 1A) mile 15. Round Pass Mudflow (fig. 25). North bank of Mowich River at its
ilphstream from mouth of Kautz Creek. Sample of a fairly coarse inculth. Sample of mudflow at a horizon about 20 feet above river
a ar. eve .

2. Kautz Creek lahars of 1947. Same location as sample 1. Sample of 16. Lahar in Puyallup River valley. Same location as sample 8. Sample
a relatively fine-grained lahar. of 1,000-year-old lahar that is unit 2 in measured section 7.

3. Post-Osceola lahar in West Fork valley. Roadcut at the west side 17. Lahar in Muddy Fork valley. Terrace on east side of Muddy Fork,
of sec. 26, T. 19 N., R. 9 E. Sample of unoxidized lahar that over- and 65 feet higher than river level, about 15 mile upstream from
lies pyroclastic layer Y. highway bridge at Box Canyon. Sample of a pre-W, post-Y lahar

4. Lahar in South Puyallup River valley. Exposure adjacent to Won- that underlies the terrace.
deriand Trail near south abutment of footbridge over South 18. Lahar in Nisqually River valley. Roadcut in terrace on east side of
Pupallup River (fig. 25). Sample of unit 3 in measured section 10. the Nisqually River near the mouth of the Paradise River. Sample

5. Lahar in South Puyallup River valley. Same location as sample 4 of a post-Y. pre-W lahar that directly underlies the terrace.
Sample of unit 1 in measured section 10. 19. Block-and—ash flow deposit in South Puyallup River valley. Roadcut

6. Electron Mudflow. Streambank at confluence of Carbon and 0.2 mile northwest of bridge over river (fig. 25). Sample of coarse
Puyallup Rivers near McMillin in the Puget Sound lowland. facies of deposit that contains breadcrust bombs and is about
Sample taken from top foot of mudflow. 2,500 years old.

7. Electron Mudflow. Same location as sample 6. Sample taken from 20. Block-and-ash flow deposit in South Puyallup River valley. Roadcut
basal foot of mudflow. 0.4 mile northwest of bridge over river. Sample of fine facies of

8. Electron Mudflow. North bank of Puyaliup River about 1 mile deposit represented by sample 19.
downstream from the mouth of the Mowich River, in the SW14 21. Lahar in Nisqually River valley. Roadcut 0.2 mile southwest of
sec. 34, T. 17 N., R. 6 E. (fig. 25). Sample of unit 4 in measured Longmire. Sample of unit 6 in measured section 4.
section 7. 22. Post-Osceola lahar in West Fork valley. Same location as sample 3.

9. Lahar in ”Dahoma Creek valley. North bank of Tahoma Creek 1.25 Sample of oxidized lahar that underlies pyroclastic layer Y.
miles upstream from Tahoma Creek campground (fig. 25). Sample 23. Paradise lahar. Bank adjacent to parking lot 200 feet northwest of
of lahar that is unit 9 in measured section 9. visitor center at Paradise Park.

10. Lahar in Tahoma Creek valley. Same location as sample 9. Sample 24. Paradise lahar. Cut adjacent to trail to Paradise ice caves, near west
of lahar that is unit 6 in measured section 9. base of Mazama Ridge.

11- L811” in SOUth Puyallup River valley. NOI'th bank 013 50111511 25. Paradise lahar. Bank along Paradise River about V2 mile northeast
Puyallwp River at Wonderland Trail footbridge (fig. 25). Sample of Narada Falls.
of 1,000-year-old lahar. 26. Paradise lahar. Roadcut about 1/2 mile east of Ricksecker Point.

12. Round Pass Mudflow. Same location as sample 9- Sample 0‘1 unit 3 27. Paradise lahar. Same location as sample 21. Sample of unit 4 in
in measured section 9. measured section 4.

13. Round Pass Mudflow. Roadcut at Round Pass (fig. 25). Sample of 28. Paradise lahar. Roadcut near the center of sec. 5, '1‘. 14 N., R. 8 E., in
brown facies 01‘- mudflow. the Nisqually River valley near the south edge of Mount Rainier

14. Round Pass Mudflow. Roadcut at Round Pass. Sample of purplish- National Park.

gray facies of mudflow.

Footnotes continued on following page.

28

Footnotes continued from previous page.

29. Osceola Mudflow. Bank of Inter Fork near old Storbo Camp in

POSTGLACIAL LAI-IARS FROM MOUNT RAINIER VOLCANO, WASHINGTON

36. Osceola Mudflow. Exposure along the north wall of the White River
valley near the center of the SE14 sec. 29, T. 20 N.. R. 6 131., about

2.5 miles northwest of Buckley in the Puget Sound lowland.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

    

 

 

 

 

 

 

 

 

 

 

  

 

 

 

 

 

 

 

 

 
 
 

 

   

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Glacier Basin. 37. Osceola Mudflow. Exposure at top of bluir overlooking the Green
30. Osceola Mudflow. Roadcut about 1/2 mile north of highway bridge River valley, at the east edge of sec. 28. T. 21 N... R. 5 En about
over Fryingpan Creek. 12 nine: southeast of the town of Auburn in the Puget Sound
. 1 . d h ' F k lle mil 0‘” an .
31 0333231 fififigfloui‘fiffiffigréfi West or va y about 1%} e 38. Lahfar in liliisqually Rigger viailley‘.1 Same location as sample 21. Sample
32. Osceola Mudflow. Roadcut in the White River valley along U.S. High- 0 “n.“ n measur sec 0“ '
way 410 about 0.1 mile north of the mouth of Ranger Creek. 39- L311)”; m “7%;th Rig.“ valley. South] banét 3; {liver alboigt midway
33. Osceola Mudflow. Bank on east side of the White River in the NWIA rfvgi‘ecérhm leldlr' 1033:st gfitingreggih liliar g way r ge across
sec. 14, T. 19 N.,.R. 9 E., 2 miles southeast of Greenwater. ‘ p g '
l M dfl R l U S H h 4 0 h th 40. Lahar at Van Trump Park. Bank of shallow ravine about 800 feet
34- 08335:“ :11 d west awgtcgegfig ' - lg way 1 near t e mou S nlortthealst of t6ail fihetlhtet' Sample fromllailhatr tphat prfigateslpfig
. 0 I
35. Osceola Mudflow. Roadcut near the center of the south edge of sec. 8, §e§islig379r an a may ave or g na e m re all
T- 19 N., R. 7 15- (approach road to spillway at Mud Mountain 41. Lahar at Paradise Park. Same location as sample 23. Sample of lahar
Dam). that underlies the Paradise labar.
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m (sa n le 37
a: 50 I pl l
142'] Twin Creeks
_ (sample 34)
“- 40 '
m
m
_l
2
,_ 30
g yi gpan C eek
g_ (sample 30)\
u. 20 I | | -
0
Lu
3 10
l—
Z
8
o: 0
iii k A A_. #
CLAY SILT SAND GRANULES PEBBLES COBBLES

FIGURE 11.—Oumuiative curves of the size distribution of samples of the Osceola Mudflow. The shaded zone represents the
area covered by the curves of samples from eight localities; three of these samples are represented by individual curves

as labeled; sample number refers to table 10.

The samples obtained from two different localities in
the Puget Sound lowland (localities near Auburn and
Buckley, samples 37 and 36) show about the same degree
of sorting. Furthermore, the sorting coefficient of the
sample obtained at the outcrop near Auburn (sample 37)
is nearly the same as that of the sample from Glacier
Basin (sample 29), even though the two localities are
nearly 70 miles apart. The only downvalley change in
texture noted in the lowland is an apparent decrease in
the maximum size of stones in the basal zone of the mud-
flow, but this observation was not quantitatively
verified.

The highest sorting coefficient, 16.34, was determined
on a sample from the locality near Fryingpan Creek

(sample 30). Although the sample came from near the
top of the outcrop there, the actual top of the mudflow
during flowage probably was 100—200 feet higher than
the sample horizon. The deposit from which the sample
was obtained is a veneer left after most of the mudflow
passed downvalley.

The Osceola Mudflow is unique among the lahars in
the White River drainage basin because of its relatively
high clay content. Clay minerals make up from 60 to 80
percent of the clay-sized fraction of each sample. Mont-
morillonite and kaolinite predominate in various pro-
portions in every sample of the deposit (table 11,
samples 29 through 37), and other clay minerals are

 

present in some samples. The remainder of the clay-sized

DESCRIPTION OF LAHARS

29

TABLE 11.—Mineralogy determined by X-ray analysis of clay-sized fraction of lahars

[Values are estimated parts in 10. Localities and ages of the samples are given in table 10. Leaders (. ..) , not present; Tn, trace; n.d., not determined]

 

 

3
2 <5
"4 e
se 2e Be as a
Sample 3 Eng Egg a: gag E‘ g
E 55 E5 a? 25 a .. .
a 1: E; e as a; 5;; IE “é s g e s
‘3 ’e‘ 75 a 2 8 = a 8 >4 8. 3 E “ u r:
s a as s s as as 55 a .2 3 i 5 s
______ 9 ___-_- n.d. 1 n.d.
1 1+ ______ Tr. 1+ - 1
5 2 ______ n.d. 3 n.d.
5 2+ ______ n.d. 2+ n.d.
6 2 ______ n.d. 1 n.d.
3 3 — 1 n.d. 2+ n.d.
3+ 2 ______ Tr. 2+ 1+
4 4 ______ n.d. 2 n.d.
Tr. 2+ ______ — 1 1+ Tr.
3 3 Tr. — 1 2 — 1
4 3 ______ n.d. 3 n.d.
3 4 ______ n.d. 3 n.d.
______ 3 _ _ _ _ _ _ 1 6 n.d.
Tr. 5 ______ —1 3 1
3+ 1+ Tr — 1 1+ 1
Tr. 2 ______ —— 1 2 —- 1
5 1 1 n.d. l n.d.
6 Tr. 3 n.d. 1+ n.d.
3 1 1 n.d. — 1 n.d.
6 1 1 n.d. 1 n.d.
5 3 Tr. n.d. 1+ n.d.
2 1 1 n.d. — 1 n.d.
1 1 2 n.d. ~l n.d.
3 1 1 n.d. 1 n.d.
3 1 1 n.d. 1+ n.d.
2 4+ Tr. — 1 —2 Tr.
______ 1 + - _ _ _ _ _ 8 1 n.d.
3+ 1+ ______ Tr. 2 1+

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

fraction in all samples consisted chiefly of plagioclase,
quartz, and cristobalite. In the sand-sized fractions, the
‘heavy mineral suite is dominated by hypersthene, which
makes up as much as 95 percent of the sample. The light
fraction consists mostly of rock fragments, glass, and
feldspar.

Atterberg limits were determined on the —0.420-mm
fraction of eight samples (samples 29—37) of the Os-
ceola Mudflow from outcrops in the Cascade Range
and Puget Sound lowland and are as follows:

Plasticity
Plastic limit Liquid limit index
Range _____________________ 19-28 28—42 2-15
Average ___________________ 24. 6 33 8. 4

A plasticity index of 2 was determined on mudflow
samples 34 and 36. These, and other low plasticity in—
dices, indicate a need to control moisture content care-
fully when the mudflow is used to construct a fill. The
Osceola was used extensively in the impermeable core
of Mud Mountain Dam, and some unusual construc-
tion problems were encountered because of its proper-

420-479 0 - 71— 5

 

ties. Before emplacement in the fill, it was necessary to
pass the material through heated rotating drums to
remove excess moisture and to erect a huge canvas
tent over the core to shield it from precipitation.

ORIGIN

The Osceola Mudflow apparently originated in
avalanches of hydrothermally altered rock from the
summit of Mount Rainier. The presence of the mud-
flow high on the flank of the volcano at Steamboat
Prow indicates that the flow came from above that
point, and its distribution in Glacier Basin and the
cirque north of the basin suggests that debris that de-
scended the volcano surmounted Steamboat Prow and
cascaded into Glacier Basin in a sheet or sheets many
hundreds of feet thick. The clay mineralogy of the
mudflow is most readily explained if the avalanches
originated in an extensive mass of rock that had pre-
viously been hydro‘thermally altered in large part to
clay.

30 POSTGLA‘CIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON

The water component of the mudfiow may have been
as much as 800 million cubic yards during movement
if it is assumed that the material required a water
content of 33 percent in order to flow. The rock de-
bris probably was derived from an active hydrother-
mal area on the volcano; if so, the clayey material
could have had a high moisture content from conden-
sation of steam. Moreover, if the avalanches contained
steam as well as hot rock debris, snow could have been
melted to provide added moisture as the masses moved
down ‘the flank of the volcano.

An adequate source of material was not known when
the Osceola was first recognized as a mudflow. Crandell
and Waldron (1956, p. 360) suggested that the mudflow
was initiated by a volcanic explosion that expelled
masses of hydrothermally altered rock from the north-
east flank of the volcano, but I (Crandell, 1963a) later
suggested that the mudflow originated at the summit
of the cone. The source area I postulated also accounted
for a “missing summit” of the volcano that was first
noted by Russell (1898). The present summit of Mount
Rainier is at the top of a young lava cone constructed
within a large depression about 114 miles across; high
points on the rim of this depression are at Point Suc-
cess, Gibraltar Rock, and along the ridge between
Liberty Cap and Russell Clifl’. These high points indi-
cate that the summit of the volcano was removed above
an altitude of about 14,000 feet. Both Russell (1898)
and Matthes (1914) suggested that the top of the vol-
cano had been blown off by a mighty volcanic explosion,
but Coombs (1936) proposed that the former summit
was removed piecemeal during a series of eruptions.
Fiske, Hopson, and Waters (1963) concluded that the
summit was lowered by subsidence into magma, by out»
ward slumping and flowage of solfatarized rock in the
central part of the volcano, or by headward glacial ero-
sion into the weak core rock. I (Crandell, 1963a) pro-
posed that the summit of the volcano slid off and formed
very large rockslides and avalanches that descended
the northeast side of the cone to form the Osceola Mud-
flow.

The discovery by D. R. Mullineaux (oral commun..
1969) of newly erupted material in an airlaid deposit
formed at .the same time as the Osceola Mudflow sug—
gests that the rockslides and avalanches were caused
by volcanism. The airlaid deposit is layer F (table 5),
and its correlation with the mudflow is based on strati-
graphic relations, on its resemblance to the matrix of
the mudflow, and on the similar radiocarbon ages of
the two deposits. Layer F does not occur on top of the
Osceola Mudflow and thus cannot be younger, and or-
ganic material beneath layer F at Cowlitz Park has
an age of 5,800 years (table 4, sample W—2053).

 

According to Mullineaux, layer F is made up of three
units in the Yakima Park—Berkeley Park area. The
basal unit, 1—3 inches thick, consists mostly of clay and
fragments of dense rock, about half of which have been
strongly altered. The clay is mostly montmorillonite.
The middle unit, 14—1 inch thick, consists mostly of
glass-encrusted mineral euhedra and pumice, and the
top unit is 1—3 inches of clay that contains abundant
altered and unaltered dense rock fragments as well as
mineral euhedra and pumice. Mullineaux believes layer
F to be primarily of pyroclastic origin. He concludes
that the pumiceous ash and lapilli in layer F demon—
strate an eruption of magma and Visualizes that the fol-
lowing sequence of events occurred. A phreatic explo-
sion threw dense rock fragments and clay onto areas
northeast of the volcano; this explosion was closely fol-
lowed by an explosive eruption of magma that formed
the thin layer of pumiceous ash and lapilli. Still later,
pumiceous material was erupted along with dense rock
fragments and clay. The initial explosion probably
caused the slides of altered rock that formed the Os-
ceola Mudflow, but perhaps less likely, the rockslides
could have been triggered by earthquakes accompany-
ing the eruption.

There is little evidence concerning the behavior in
detail of the Osceola Mudflow, and one can only specu-
late about its characteristics during flowage. The mud-
flow probably moved downvalley in a series of large
surges, each initiated by an avalanche of moist, clayey
rock debris. The mudflow’s tremendous volume resulted
in hydraulic damming and pending at valley constric—
tions in the Cascade Range and caused inundation of a
broad area of the lowland. In the absence of any topo-
graphic or stratigraphic evidence to the contrary, it is
assumed that the Osceola’s entire fluid mass came to rest
before any part of it dried enough to solidify. The time
involved in the formation, movement, and emplacement
of the mudflow may have been several days, or as little
as a few hours.

POST-OSCEOLA LAHAR ASSEMBLAGE

Deposits in the White River valley that are younger
than the Osceola Mudflow include at least four lahars
and as many or more fluvial deposits; these are referred
to collectively as the post-Osceola lahar assemblage. The
assemblage is typically exposed in the face of a terrace
near the mouth of Fryingpuan Creek (measured section
1). The basal five units in this section evidently were
deposited in a swamp adjacent to the White River; they
seem to record a stable flood plain following the Osceola
Mudflow, when the valley floor was at a level similar to
that of the present. Some time after 2,700 years ago (see
unit 5, measured section 1), alluvium and a thin lahar

DESCRIPTION or LAHARS 31

Measured section 1

[South bank of White River near mouth of Fryingpan Creek, Mount Rainier

National Park]
Thickneu
(IL) on.)
19. Sand, very fine __________________________________ $4
18. Pyroclastic layer W (about 450 years old) __________ 2
17. Sand, very fine, pinkish-gray _____________________ V2
16. Sand, very fine, yellowish-brown __________________ ‘ 1
15. Sand and coarse bouldery gravel of fluvial origin,
light-yellowish-brown ______________________ 19 0

14. Lahar: rock fragments as large as 8 in. in yellow-

ish-brown sand matrix; rock fragments are

mostly angular and subangular Mount Rainier

rock types, a few of granodiorite and breccia

from Ohanapecosh Formation. Material in

uppermost 2% ft. grades up from granule

gravel, which contains scattered pebbles and

cobbles, to medium sand ___________________ 3 0
Minor erosional unconformity.
13. Lahar: rock fragments as large as 12 in. in

matrix of purplish-gray coarse sand; grades into

uniform medium sand at top ________________ 6 0
12. Sand, fine, horizontally stratified, purplish-gray__ 2 0
11. Lahar: grades from pebble-sized material in a

purplish-gray sand matrix at base to coarse

sand at top _______________________________ 2 0
10. Sand and pebble to boulder gravel of fluvial ori-

gin, iron-strained; contains lenses of openwork

gravel ___________________________________ 3 0
9. Sand, very fine, purplish-gray to light-yellowish-

brown ___________________________________ 1 6
8. Peat _______________________________________ 1 6

7. Lahar: grades from angular rock fragments of

pebble size in a purplish-gray sand matrix at

base to very coarse purplish-gray sand at top- 2 0
6. Pebble-and—cobble gravel of fluvial origin,

purplish-gray, lenticular; as thick as _________ 1 3
5. Sand and silt, purplish-gray; contain scattered

rock fragments and logs; lenticular; sample of

wood from this unit is 2,700 years old (table 4,

sample W—930); as thick as _________________ 2 0
4. Pyroclastic layer Y (about 3,600 years old):

includes contorted layer of peat above fairly

pure basal layer of pumice 8 in. thick ________ 1 6
3. Clay, peaty, gray to light-yellowish—brown ...... 2
2. Volcanic ash(?), sand-sized, micaceous, light-

brownish-gray ____________________________ 3
1. Clay, woody and peaty; contains logs __________ >5 0

were deposited, but a continued-stable flood plain is
indicated by the overlying peat (unit 8). Flood plain
stability ended when lahars and fluvial deposits ag—
graded the valley by at least 35 feet.

The lahars exposed in the section near the mouth of
Fryingpan Creek consist mainly of sand and fine gravel
(fig. 12), but lahars of considerably coarser texture oc-
cur in the same assemblage both upstream and down-
stream.

A series of terraces is cut into, or formed by, the lahar
assemblage along the valley wall at several places be-
tween the mouth of Inter Fork and Fryingpan Creek.

 

 

FIGURE 12.——Lahar exposed near the mouth of Fryingpan Creek
grading from sand- and pebble-sized material in the lower
two thirds to a well-sorted medium sand at the top. The
lahar is unit 13 of measured section 1. The pick head is at the
contact of the lahar with an underlying fluvial sand deposit.

White River campground is situated on one of these
terraces. The terrace is about 3,600 feet long and is about
30 feet above White River at its upper end and about
45 feet at the downstream end. Its gradient is about 280
feet per mile, whereas that of the river is about 300 feet
per mile in this segment of the valley. A cut in the face
of the terrace at the campground exposes crudely strati-
fied fluvial gravel overlain by a lahar that contains
boulders as large as 4 feet in diameter. Pyroclastic layer
W veneers the terrace, but layer C is absent, even though
present on the adjacent valley wall.

On the south side of the valley, opposite from and just
downstream from White River campground, a 40-foot
terrace is formed by a lahar 15—30 feet thick that over-
lies the Osceola Mudflow. A higher terrace here lies
about 80 feet above the river, but the material that
forms it is not exposed.

On the north side of the valley, just downstream from
the highway bridge over the White River, post-Osceola
terraces are found at heights of about 10, 15, and 30 feet.
A quarter of a mile farther downstream, on the south
side of the river, a lahar older than pyroclastic layer W
forms a terrace about 30 feet above the flood plain. The
lahar consists of angular rock fragments in a matrix of
purplish-gray sand. A still-higher terrace in the same
vicinity, which is formed by one or more lahars younger
than pyroclastic layer C but older than layer W, is about
45 feet above the river.

32 POSTGLA'CIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON

Near the north boundary of the park, at Silver Creek
Ranger Station, U.S. Highway 410 is situated on a post-
C, pre-W terrace that is only a few feet above the sur—
face of the flood plain and is probably underlain by a
lahar. This terrace is littered with boulders as large as
10 feet in diameter. A little farther downstream, in the
vicinity of Silver Creek Lodge, a terrace that is about 60
feet above the river is underlain by pre-W alluvium and
a lahar. On the west side of the valley and still farther
downstream, a terrace at a comparable height above the
flood plain is underlain by a pre-C sandy lahar about 4
feet thick, beneath which are pyroclastic layer Y and
the Osceola Mudflow. A diagrammatic cross section of
the valley floor in this area is shown on plate 2.

POST-OSCEOLA LAHAR ASSEMBLAGE IN THE WEST
FORK VALLEY

At least four post-Osceola lahars have been recog-
nized in the West Fork valley north of Mount Rainier
National Park; two are older than pyroclastic layer Y,
one is younger than Y and older than layer C, and one
is younger than layer W. Only one post-Osceola lahar
was recognized within the park.

One pre-Y lahar crops out in a roadcut near the mouth
of the valley on the west side of sec. 26, T. 19 N., R. 9 E.
(Greenwater quadrangle). It is at least 4 feet thick and
consists of subangular to subrounded stones in a matrix
of oxidized dark-yellowish-brown sand. The lahar over—
lies the Osceola Mudflow and underlies, in the same
outcrop, pyroclastic layer Y, another lahar, and pyro-
clastic layers C and W. Its top is about 50 feet higher
than the West Fork of the White River. Grain-size an-
alysis of a sample of the lahar indicated a median dia-
meter of 12.5 mm and a sorting coefficient of 13.2 (table
10, sample 22) . An oxidized lahar 3—4 feet thick, which
probably is correlative with the one just described, crops
out in a roadcut 1.5 miles farther upvalley in the NEML
sec. 33.

A second pre-Y lahar is exposed 3.5 miles farther
upvalley in a small borrow pit near the mouth of Jim
Creek. It is more than 10 feet thick and contains bould—
ers as much as 8 feet in diameter. The matrix of the
upper part of the lahar grades upward from sand-and-
cobble gravel to medium and coarse gray sand. Some of
the large boulders are of granodiorite, but all the smaller
fragments and the matrix seem to have been derived
from Mount Rainier.

A post-Y, pre-C lahar that is about 6 feet thick is
exposed near the mouth of West Fork valley at the
roadcut in sec. 26 just mentioned. Size analysis of a
sample from a zone 4—5 feet below the top of the lahar
indicated a median diameter of 2.8 mm and a sorting
coefficient of 13.40 (table 10, sample 3).

 

A deposit that probably is part of the same lahar oc-
curs in a streambank exposure on the north side of the
valley about 1 mile away, near the center of sec. 23.
There, the lahar is 20 feet thick and consists almost
wholly of rock fragments derived from Mount Rainier.
It overlies a succession of deposits that includes, from
top to bottom, 3 feet of fluvial sand derived from Mount
Rainier, a layer of humic material a few inches thick,
pyroclastic layer Y, and the Osceola Mudflow, the base
of which is below river level.

A broad area of the floor of the West Fork valley near
its mouth is underlain by the youngest post-Osceola
lahar. The lahar and fluvial deposits associated with it
form a terrace 25—30 feet higher than West Fork. The
lahar is a lenticular, bouldery deposit as much as 8 feet
thick where it is exposed in a gravel pit south of West
Fork, near the center of sec. 33. Granodiorite boulders
as large as 12 feet in diameter are scattered over the
surface, and boulders as large as 7 feet in diameter can
be seen in the walls of the gravel pit. The lahar’s matrix
is purplish-gray sand and granule gravel. The lahar
overlies as much as 15 feet of stratified purplish-gray
sand and fine gravel that rests on top of the Osceola
Mudflow. The absence of pyroclastic layer W from the
top of the lahar indicates that it is less than 450 years
old, and ring counts of tree stumps on the lahar’s surface
indicate an age of more than 275 years.

Within Mount Rainier National Park, a post-Y lahar
is exposed at the mouth of Winthrop Creek in the West
Fork valley. It consists of 16 feet of angular and sub—
angular rock fragments, which range in size from gran-
ules to boulders, in a purplish-gray sand matrix. The
lahar overlies a bed of silt, clay, and sand 1 foot thick
that contains pumice derived from layer Y. This fine
deposit overlies about 20 feet of poorly sorted pebble to
boulder gravel, which rests on top of the Osceola Mud-
flow.

LAHARS IN THE NISQUALLY RIVER VALLEY

Postglacial deposits in the Nisqually River valley
within Mount Rainier National Park include at least 12
lahars, more than eight fluvial deposits, and three lay—
ers of volcanic ash. Their sequence is as follows:

Several lahars and associated fluvial Lahar assemblage D.
deposits.

Pyroclastic layer W (about 450 years
old)

At least seven lahars and at least eight Lahar assemblage C.
fluvial deposits.

Peat

Pyroclastic layer Y (about 3,600 years
old)

Peat and peaty silt

DESCRIPTION or LAHARS 33

Lahar assemblage B.
Do.

Paradise lahar

Fluvial sand and gravel

Pyroclastic layer 0 (about 6,600 years
old)

Two lahars interbedded with fluvial
deposits.

Lahar assemblage A.

Although many of the lahars are intermittently exposed
in the valley from the vicinity of Christine Falls down-
stream beyond the park boundaries, their general simi-
larity makes correlation diflicult or impossible. This
large group of lahars and alluvium is divided for con-
venience of discussion into four lahar assemblages, each
consisting of two or more lahars or alluvial deposits,
which are separated by pyroclastic deposits. The most
widespread deposit that is recognized within these as-
semblages is the Paradise lahar, which also mantles the
Paradise Park area. This lahar, and a similar one at
Van Trump Park, will be discussed first; this discus-
sion will be followed by a description of the assemblages
along the floor of the Nisqually River valley.

PARADISE LAHAR

Ridges and valleys between Panorama Point and
Ricksecker Point are veneered with a yellowish-orange
deposit of angular to subrounded rock fragments in a
plastic matrix consisting of a mixture of sand, silt, and
clay. Although originally the deposit was informally
designated as the Paradise debris flow (Crandell,
1963a), its name is changed here to Paradise lahar be-
cause of the textural variability within it. The lahar is
younger than pyroclastic layer 0 and predates layer
D; it was formed some time between about 5,800 and
6,600 years ago (table 5).

Blocks as large as 8 feet in diameter are embedded in
the lahar, and even larger masses are scattered on its
surface. Iron oxide occurs within the deposit as thin
layers and lenses, and as thin coatings on most rock frag-
ments. The lahar is 1—5 feet thick in most outcrops, al-
though thicknessss of as much as 15 feet are not uncom-
mon. Owing to its general thinness, the lahar does not
have a constructional topography of its own in most
places, but mantles ridges, knobs, and depressions
formed of bedrock and glacial drift. At Reflection
Lakes, however, the surface of the lahar is hummocky,
and the lakes occupy shallow basins in the deposit. In
outcrops along the floor of the Nisqually River valley
the lahar is 2—81/2 feet thick, but it veneers the valley
sides to a height of more than 100 feet near the mouth
of the Kautz Creek valley.

Nearly everywhere that the base of the Paradise lahar
is exposed along the Nisqually River valley it rests di-
rectly on pyroclastic layer 0, and there is little or no

 

evidence of erosion along the contact. A layer of forest
dufl' several inches thick lies on top of the lahar at
several places and underlies pyroclastic layer Y and
a younger lahar.

In the Paradise Park area the lahar underlies the
surface south of Panorama Point and from Mazama
Ridge westward to the young lateral moraines of Nis-
qually Glacier (pl. 3). According to D. R. Mullineaux
(oral commun., 1969), the lahar is represented on Ma-
zama Ridge by a deposit a few inches thick that under-
lies pyroclastic layer D and other layers just south of
Sluiskin Falls. The maximum height of the lahar de—
posit in that area is about 600 feet above the floor of
Paradise Valley. Farther south, a large lobe of the lahar
underlies the Reflection Lakes area.

Evidently the Paradise lahar entered the Reflection
Lakes area through a saddle on Mazama Ridge that is
about 200 feet higher than the floor of Paradise Valley.
A thin remnant of the lahar that crops out along the
highway at Reflection Lakes (measured section 2) indi-
cates that the lahar initially filled that area to a level
at least 20 feet higher than the present lake level. How-
ever, the surface of the lahar was subsequently lowered
as the still-fluid material drained away to the west and
rejoined the main mass of the lahar in the Paradise
River valley (pls. 1, 3). The west end of the largest
lake may be dammed by laharic material that flowed
off Mazama Ridge.

High remnants of the Paradise lahar both upstream
and downstream from Narada Falls indicate that a very
large mass of material moved down the Paradise River
valley. The most conspicuous remnant is exposed in a
roadcut near Ricksecker Point (fig. 13). The lahar there
is a few feet thick and directly overlies pyroclastic layer
0 at a height of about 800 feet above the floor of the
Paradise River valley. Because of the position of the
lahar on a south-facing slope overlooking the valley,
there seems to be no other way to explain its presence
except by the temporary filling of the valley with the
lahar to a height of at least 800 feet.

Measured section 2

[Roadcut south of the center of the largest lake at Reflection Lakes]

Thickness
(It) (in)

. Colluvium: reworked volcanic ash and forest duff __ 1—2 0
. Pyroclastic layer Y ___________________________ 4-6
. Colluvium: reworked pumice and forest duff _____ 2. 5
. Paradise lahar: unsorted mixture of angular to
subrounded pebbles and cobbles in matrix of
sand, silt, and clay _________________________ 2—4
. Sand, gray __________________________________
. Pyroclastic layer 0 ___________________________ 1
Sand, gray __________________________________ 0—
Evans Creek till: gray, lenticular _______________ 0
. Granodiorite (bedrock) _______________________

@‘lmw
O

HEQQDHBCJ‘

34 POSTGLACIAL LAHAR‘S FROM MOUNT RAINIER VOLCANO, WASHINGTON

 

FIGURE 13.—Paradise lahar above pyroclastic layer 0 in roadcut half a mile east of Ricksecker Point. Beneath layer 0
are Evans Greek till and a lava flow from Mount Rainier. This outcrop is about 800 feet higher than the floor of the
adjacent Paradise River valley and indicates that the lahar was at least 800 feet deep here

Farther down the valley the Paradise lahar forms
part of assemblage B. Its vertical extent indicates that
the valley was at least as deep when the lahar was mov-
ing as it is today and that the lahar was temporarily
several hundred feed deep at Longmire. The lahar was
identified as far downvalley as a point near the mouth
of Tahoma Creek, and it may be one of several lahars
that crop out in the valley near National, 12 miles west
of Longmire.

Stones in the lahar are principally of Mount Rainier
provenance. Identification of 100 pebbles in the deposit
at Reflection Lakes and at Longmire showed 75 and 80
percent, respectively, to be of Mount Rainier origin. At
Reflection Lakes the deposit contains only 5 percent
granodiorite in the pebble—sized fraction, but this rock
type makes up 20 percent of the pebbles at Longmire.
The greater proportion of granodiorite at Longmjre
may be due to incorporation of loose gravel from the
Nisqually flood plain.

 

Three samples of the lahars from the Paradise Park
area contained 1—5 percent clay, 7—28 percent silt, and
16—44 percent sand (table 10, samples 23, 24, 25) . X-ray
examination of a sample from an outcrop near the vis-
itor center at Paradise Park indicated that montmoril-
lonite and kaolinite are the predominant clay—sized
minerals (table 11, sample 23). They are accompanied
by small amounts of cristobalite, feldspar, iron oxide,
and quartz. Amorphous silica constituted 6.4 percent of
the clay-sized fraction. It is of interest to note that a
sample of Evans Creek till (table 7, sample 1) from the
same outcrop had mostly feldspar and cristobalite in the
clay-sized fraction, and only a trace amount of clay min-
eral was found. Some samples of the lahar are among
the most poorly sorted of those examined in this study
(fig. 14). It is especially interesting to note the poor
sorting of the lahar at Ricksecker Point (sample 26).
The deposit there must represent a zone in the upper

DESCRIPTION OF LAHARS

0.001 mm
001 mm
0.1 mm

100

90

80
Sorting

coefficient

70

13.60
60 14.56

15.75
50

17.00

40

3O

20

10

PERCENTAGE OF PARTICLES FINER BY WEIGHT THAN INDICATED SIZE

CLAY SILT

v
SAND

00

5

1.0 mm
10.0 mm
100.0 mm

 

AT

HA
GRANULES PEBBLES COBBLES

FIGURE 14.—Gu.mu1ative curves of size distribution of the Paradise lahar (solid lines) at three localities and of an older lahar
(dashed line) at Paradise Park. Sample 23 is from an outcrop near the visitor center at Paradise Park, 26 is from an
outcrop near Ricksecker Point, and 27 is from measured section 4 at Longmire. Sample 41 is from the older lahar, at
the same locality as sample 23. The samples are those described in table 10.

10—20 feet of a lahar that was momentarily at least 800
feet deep in the Paradise River valley during flowage.

Silt and clay made up about 19 percent: of a sample
(27) of the Paradise lahar that was taken from an out-
crop near Longmire. (See measured section 4.) X-ray
diffraction analysis of the clay-sized fraction of this
sample showed a kaolinite—halloysite mixed-layer min-
eral, and cristobalite, feldspar and a small amount of
iron oxide (table 11, sample 23). Amorphous silica made
up 8.3 percent of the clay fraction.

The distribution of the Paradise lahar in the area be—
tween Panorama Point and Ricksecker Point suggests
that the lahar originated in one or more huge avalanches
of moist rock debris that swept down the south flank
of the volcano. The clay mineralogy of the deposit indi-
cates that it was derived in part from hydrothermally
altered rocks, perhaps at the summit of Mount Rainier.
Although I once thought that the deposit at Paradise
Park was of the same age as the Osceola Mudflow
(Crandell, 1963a, p. B139), I now know that the Para-
dise lahar is somewhat older because it is stratigraphi-
cally below pyroclastic layer D, which is older than the
Osceola (D. R. Mullineaux, oral commun., 1969). It
seems likely that counterparts of the slides that resulted

 

in the Greenwater lahar in the White River valley
caused the Paradise lahar and were triggered in the
same way (p. 22).

Although the distribution of the lahar in the Paradise
Park area indicates that the lahar originated in an
avalanche down the south side of Mount Rainier, the
area of transition from an avalanche to a lahar is not
known. At Paradise Park, where the transition may
have occurred, grain-size distribution in samples of the
deposit indicate a rather wide variability in texture
and a range in sorting coefficients of 7 .7 5—136 (samples
23—28, table 10). Median diameters range from 0.2 to 13
mm in these samples. Samples obtained from two loca-
tions farther downvalley (samples 27, 28), where there
is little doubt that movement was that of a lahar, have
sorting coefficients of 15.7 5 and 16.25 and median diam-
eters of 1.4 and 4.3 mm, respectively. One might ex-
pect that the deposit would be most poorly sorted where
it was moving as a rapid avalanche and that it would
show somewhat better sorting where it was moving as a.
lahar. However, the opposite seems to be true, if the
samples described here are representative.

The original volume of the Paradise lahar is diflicult
to determine because the deposit is highly variable in

36 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON

thickness, and nowhere does it form a broad thick fill in
the Nisqually River valley. Beyond the community of
National, 6 miles west of the park, Evans Creek Drift
directly underlies surfaces on both sides of the river;
if the lahar reached this far downvalley, it must
have been confined to a narrow channel, and its top
could not have been appreciably higher than the present
flood plain. The depth of the channel of the Nisqually
River at that time is not known.

The volume of the lahar was originally estimated to be
400—500 million cubic yards on the basis of the heights
to which it reached on valley sides, the assumption that
the Paradise and Nisqually River valleys were simul-
taneously filled with the lahar upstream from Rick-
secker Point, and the probability that the lahJar was
draining from one area while its crest was passing
points farther downvalley (Crandell, 1963a). Subse-
quent geologic mapping has shown that the total area
covered by the lahar probably is no more than about 13
square miles, and its original average thickness in this
area after it came to rest and lost much of its water con-
tent probably was between 5 and 10 feet. The estimated
volume is either 67 million or 134 million cubic yards,
according to whether the smaller or larger average thick“
ness value is used in the computation.

The great depth of the Paradise lahar at some places,
notably in the lower Paradise River valley, seems en-
tirely out of proportion to such a relatively small vol-
ume, even if it is assumed that the lahar probably
contained an additional volume of water of as much as
one-third of the estimated volume of the deposit. The
anamolous relations involved can be illustrated by con-
sidering the capacity of the lower Paradise River valley.
Near Ricksecker Point, the valley has a cross-sectional
area of about 130,000 square yards up to a height of
about 800 feet above the valley floor. The 1-mile seg-
ment of the valley immediately east of Ricksecker Point
has an estimated volume of at least 230 million cubic
yards up to a similar height. Thus, it is apparent that
even the total estimated volume of the lahar could
not entirely fill this short valley segment at one time.
The problem becomes even more acute when it is re-
membered that a considerable part of the estimated vol-
ume of the lahar remained in the area above the lower
Paradise River valley and in the Nisqually River valley
above Ricksecker Point. Moreover, to explain the great
depth of the lahar in the Paradise River valley by any
conventional means, it is necessary not only to have this
valley segment full of mud, but simultaneously to have
mud of comparable thickness in the Nisqually River
valley at the mouth of the Paradise River.

On the basis of the assumption that the estimated vol-
ume of the lahar is not grossly in error, the most prob-

 

able explanation of the contradictory relations just
described is that the lahar moved across Paradise Park
and down the Paradise River valley in a single massive
transient wave with a height of as much as 800 feet.
Such a wave must have been generated by a large ava-
lanche of wet, clayey, rock debris from an area high
on the south flank of the volcano, or perhaps at its sum-
mit. Because of momentum the avalanche-generated
wave swept across Paradise Park, rather than moving
directly down the Nisqually River valley. The valley
swings from a southward course to a southwestward
course just west of Panorama Point. Here the great
momentum of the wave, created by a vertical drop of
perhaps as much as 8,000 feet, carried it up over the
east valley wall. The wave surmounted the ridge be-
tween Panorama Point and Alta Vista, surged across
Paradise Park, and slopped up 'onto Mazama Ridge just
south of Sluiskin Falls. The bulk of the material, how-
ever, was deflected by Mazama Ridge to the southwest
and down the Paradise River valley.

The transient wave probably lost much of its height
when it debauched from the Paradise River valley at
Ricksecker Point. Its momentum must have carried it
high on the flank of Rampart Ridge along the west
side of the Nisqually River valley. At Longmire, a lit-
tle more than 1 mile downvalley, the lahar was at least
80 feet and probably several hundred feet deep. As the
lahar wave progressed farther down the Nisqually
River valley, it gradually lost height as the valley
widened and as more and more volume was lost by
material being left behind as a coating on the lower
valley walls and valley floor.

OLDER LAHAR AT PARADISE PARK

An older lahar that underlies the Paradise lahar
is exposed at several places in the Paradise Park area.
The contact between the two deposits is marked by
a humic zone several inches thick that formed in and
on the lower lahar (fig. 15; measured section 3).

A grain-size distribution analysis of a sample of the
lower lahar from the measured section indicates 21 per—

Measured section 3

[Trench exposure temporarily open during construction of sidewalk and retaining
l?“ at)]the northwest edge of the Paradise Visitor Center in September 1966
g. 15

Thickness

(It) (in)

5. Pyroclastic layer W ______________________________ 1
4. Pyroclastic layer Y ___________________________ 1 3

3. Paradise lahar: light-yellowish—brown (2.5Y 6/4)

to brownish-yellow (IOYR 6/6) mixture of

rock fragments, sand, silt, and clay; humified

in upper 4—6 in ____________________________ 1 8
2. Older lahar: light-yellowish-brown (2.5Y 6/4)

mixture of rock fragments, sand, silt, and clay;

humified in upper 1—3 in ____________________ 2-3 0
1. Evans Creek till: gray (2.5Y 4/0) _______________ >5 0

DESCRIPTION OF LAHARS 37

 

dxse iahar

' 3:3 . '13 ’
’ a&——-HUmified

EVans Creek ~
tilt.

FIGURE 15.—Outcrop of the Paradise lahar and an older lahar in a trench excavated for a retaining wall at the north edge of
the visitor center at Paradise Park (measured section 3).

cent clay and silt and 32 percent sand (table 10, sample
41; fig. 14). The sample had a median diameter of 1.25
mm and a sorting coeflicient of 17.

The clay minerals in a sample of the older lahar
were chiefly montmorillonite and a small amount of
kaolinite. The remainder of the clay-sized fraction
was cristobalite, feldspar, and iron oxide (table 11,
sample 41) .

The older lahar at Paradise Park probably originated
in a slide of hydrothermally altered rock from the sum-
mit or south flank of the volcano. It may be correlative
with the lahar that is older than layer 0 at Van Trump
Park. (See below.)

LAHARS AT VAN TRUMP PARK

At Van Trump Park, the ridge between Van Trump
and Comet Creeks is veneered with a yellowish-orange
lahar, which is older than pyroclastic layer 0 and which
consists of stones up to 11/2 feet in diameter in an un-
sorted matrix of sand, silt, and clay. On the ridgetop
the deposit ranges in thickness from a few inches to as

 

much as 4: feet, but the lahar is as much as 6 feet thick
on the east slope of the ridge, where it overlies Evans
Creek till and a lava flow from Mount Rainier. It ex-
tends down the east side of the ridge to the floor of Van
Trump Creek, but it was not seen on Cushman Crest or
the ridge at the west edge of Van Trump Park.

The lahar’s distribution suggests that it was formed
by an avalanche of rock debris on the south flank of the
volcano. Although the lahar was not identified in the
Van Trump Creek valley below Van Trump Park, it
may be represented in the Nisqually River valley by one
of the lahars of assemblage A.

The lahar is not present on top of a lateral moraine of
Van Trump Glacier. The lateral moraine probably is of
Sumas age (table 3). However, the lahar does overlie
Evans Creek Drift in areas just beyond the moraine.
This relation suggests that the mudflow occurred dur-
ing the Everson Interstade.

A sample of the lahar from an outcrop about 800
feet northeast of the Van Trump trail shelter con-
tained 42 percent clay and silt and 33 percent sand

38 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON

(table 10, sample 40). The sample had a median diam-
eter of 0.1 mm and a sorting coefficient of 10.2. X—ray
analysis of the clay-sized fraction of the lahar resulted
in the identification of glass (probably amorphous sili-
ca), feldspar, and cristobalite.

A series of younger lahars is exposed in the valleys
of Van Trump and Comet Creeks. The basal lahar of
this series in the Van Trump Creek valley is a purplish-
gray bouldery deposit 1—2 feet thick that underlies
pyroclastic layer 0 and unconformably overlies a gray
fluvial gravel as much as 10 feet thick. Above layer
0 is a bouldery reddish—brown lahar at least 3 feet thick.
It is overlain by pyroclastic layer Y, above which is
another reddish-brown lahar, only about 1 foot thick,
in which the coarsest material is of pebble size. This
deposit is overlain by pyroclastic layer W and a post—W
gray lahar 1.5—6 feet thick that is oxidized to a depth
of about 1 foot. The gray lahar is overlain by scattered
boulders and coarse, unsorted, lenticular deposits that
were formed by a still younger lahar or flood. These
deposits form low bouldery ridges that trend down-
valley.

At least two bouldery lahars form low terraces in the
Comet Creek valley upstream from Comet Falls. The
lower terrace is about 5 feet above Comet Creek and is
underlain by a lahar and fluvial gravel; the upper
terrace is about 12 feet higher and is underlain by a
lahar.

The lahars in the Van Trump drainage basin occur in
the same stratigraphic position with respect to pyro-
clastic deposits as some of those in the Nisqually River
valley. Lahars having a reddish-brown matrix, similar
to that of some deposits in the Van Trump Creek valley,
were not recognized along the Nisqually River.

LAHAR ASSEMBLAGE A

Lahar assemblage A contains the oldest postglacial
deposits recognized in the Nisqually River valley. These
deposits consist of two lahars and interbedded fluvial
sand that overlie Evans Creek Drift and predate pyro-
clastic layer 0. The assemblage is intermittently ex—
posed in streamka outcrops between Longmire and
a point about 1% miles downstream, where the Nis-
qually River turns westward. Sporadic exposures as
far west as the mouth of the Tahoma Creek valley sug—
gest that the deposits originally extended downstream
beyond the park boundary.

In exposures 17/2—11/2 miles downstream from Long-
mire, the lahars in assemblage A are composed of an-
gular to subrounded pebbles, cobbles, and boulders as
large as 12 feet in diameter in a friable, purplish-gray,
silty sand matrix (fig. 16). The matrix contains voids,
and some small lenses of pebbles within the lahars have

 

openwork texture. The top 2—3 feet of the upper lahar
is oxidized to a light yellowish brown, and films of iron
oxides coat the surfaces of most stones. At one locality,
a layer of humus occurs at the top of the upper lahar
immediately beneath pyroclastic layer 0, but no wood
was seen in either lahar. In most outcrops, the two
lahars rest directly on one another, but at one locality
they are separated by 1—2 feet of stratified sand and
pebble gravel.

The maximum thicknesses of these lahars are difficult
to determine because their base and top are rarely seen
in the same outcrop. At an exposure adjacent to the
Nisqually flood plain in the NW1/4 sec. 5, the lower lahar
is 8 feet thick, but its base is not exposed. The greatest
exposed thickness of the upper lahar is only 4—5 feet,
but the vertical distance between its base and top is 37
feet at a locality 11/2 miles downstream from Longmire.
Although the lahar must thus have been at least 37 feet
deep during movement, nowhere are the veneers that
were left on valley sides after its passage known to
reach a comparable thickness.

A sample of the oldest lahar of assemblage A at
Longmire (unit 1, measured section 4) was analyzed
for size distribution and clay mineralogy (tables 10,
11, sample 38; fig. 17). The sample was taken from a
zone about 4% feet below the top of the deposit in the
outcrop. X—ray analysis of the fine fraction ‘of the
sample resulted in the identification of montmorillonite

Measured section 4

[Riverbank outcrop on the west side of the Nisqually River in center of the NE%
sec. 32, T. 15 N., R. 8 E., at Longmire]

Thicknesa
(It) (in)

8. Dufi; thickness variable, as thick as ________________ 6
7. Pyroclastic layer W ______________________________ 1—2
6. Lahar: subangular to subrounded pebbles,

cobbles, and boulders in matrix of sand and

silt, unsorted and unstratified, mottled light

yellowish brown and purplish gray __________
5. Pyroclastic layer Y: contains scattered frag-

ments of charcoal in upper 2 in ____________ 1 1
4. Paradise lahar: subangular to subrounded

pebbles, cobbles, and boulders in matrix of

silt and sand, slightly plastic, unsorted and

unstratified; matrix purplish gray, but stones

coated with yellowish-brown iron oxides _____ 8 6
3. Sand, coarse to fine, lenticular; contains

scattered pebbles; as thick as ______________ 4 0
2. Pyroclastic layer 0 _______________________________ 1—3

1. Lahar: angular to subrounded pebbles, cobbles,

and boulders in matrix of silt and sand; has

some zones that show faint planar structures

that suggest bedding; has some layers of

openwork gravel a few inches thick; purplish

gray, oxidized to light yellowish brown in

upper 2—3 feet ___________________________ > 10 0
The base of unit 1 is below the level of the adjacent flood plain.

DE SCRIPTION

39

 

FIGURE 16.—Lahar in srtreambank on west side of Nisqually River flood plain at measured section 4, about a quarter of a mile
southwest of Longmire. The lahar shown here, which is older than pyroclastic layer 0, is unit 1 in the measured section.

(2 parts in 10). The rest of the clay-sized fraction con-
sisted chiefly of feldspar and cristobalite.

The lahars in assemblage A could be the downvalley
correlatives of the older lahar at Paradise Park or of
the lahar at Van Trump Park that is older than pyro-
clastic layer 0.

LAHAR ASSEMBLAGE B

Lahar assemblage B is overlain by more recent de-
posits at most places along the valley floor and is best
exposed in the faces of terraces along the Nisqually
River. The most extensive lahar in assemblage B is the
Paradise lahar, which has already been described. The
basal part of the assemblage is a deposit of sand and
gravel that was noted at three localities. One is in a
roadcut at a switchka near the mouth of Van Trump
Creek, where pebble to boulder gravel underlies pyro~

 

elastic layer Y. The Paradise lahar was not seen here,
and units beneath the gravel are not exposed. The top
of the gravel deposit is about 70 feet higher than the
Nisqually River.

Fluvial gravel and the Paradise lahar are also exposed
in a series of outcrops about 1,000 feet upstream from
the bridge to Longmire campground (measured section
5). The gravel is a crudely stratified deposit of cobbles
and boulders more than 15 feet thick. Its base locally
lies below river level. In one streambank outcrop the
gravel overlies 4 feet of fine sand, which is underlain
by talus. In another outcrop the Paradise lahar is 3
feet thick and overlies the fluvial gravel at a height of
about 15 feet above the flood plain. A short distance up-
stream, however, the base of the lahar is below the level
of the flood plain; there, the lahar is overlain by fluvial
gravel younger than pyroclastic layer Y.

4O POSTGLA‘CIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON

Measured section 5

[East bank of Nisqually River about 1,000 It upstream from bridge at Longmire]

Thickness
) (in)
12. Pyroclastic layer W: white pumiceous ash __________ 2
11. Lahar: angular to subrounded pebbles, cobbles,
and boulders in matrix of purplish-gray sand- 10 0
10. Sand and pebble to boulder gravel; boulders as
large as 5 ft across; dark yellowish brown- _ _ _ 12 0

Erosional uneonformity.

9. Lahar: angular to subrounded pebbles, cobbles,

and boulders, as much as 4 ft across, in matrix

of purplish-gray sand ______________________ 6 0
8. Pebble to boulder gravel; both crossbedding and

horizontal bedding locally present; purplish

gray, but iron stained along some bedding

surfaces __________________________________ 3 0
7. Lahar: angular to subrounded boulders, as much

as 4 ft across, in matrix of purplish-gray sand;

as thick as _______________________________ 13 0
6. Sand and pebble to boulder gravel, dark-yellow-

ish-brown; boulders are as large as 3 ft in diam-

eter _____________________________________ 6 0
5. Peat interbedded with medium to coarse sand;

individual beds of each are lenticular; as thick

as _______________________________________ 2 O
4. Pyroclastic layer Y: yellow pumiceous ash,

lenticular; as much as ______________________ 1 3
3. Peat and peaty silt; contains fragments of wood;

as thick as ___________________________________ 6

2. Paradise lahar: angular to subrounded boulders
in plastic clay and sand matrix; purplish gray
Where unoxidized, light yellowish brown where
locally oxidized; as thick as _________________ 15 0
Erosional unconformity.
1. Pebble to boulder gravel, crudely stratified,
purplish-gray; extends beneath level of ad-
jacent flood plain; more than _______________ 15 0

A third exposure in which fluvial deposits underlie
the Paradise lahar is at measured section 4, a short dis—
tance downstream from Longmire. Here the top of the
fluvial deposit is about 15 feet above flood—plain level.

After the formation of lahar assemblage A, and for
some time after deposition of pyroclastic layer 0 about
6,600 years ago, the Nisqually River evidently was flow-
ing on a surface lower than the present flood plain.
Later, but before the Paradise lahar was formed, the
river aggraded to a profile that was at least 15 feet
higher than it is now in the vicinity of Longmire, only
to cut down again to a lower profile before the Paradise
lahar occurred. The causes of this aggradation and
downcutting are not known. The Nisqually River flood
plain seems to have been nearly stable between the time
the Paradise lahar occurred and deposition of pyroclas—
tic layer Y about 3,600 years ago.

LAHAR ASSEMBLAGE C

Lahar assemblage C consists of fluvial gravels and
lahars which are stratigraphically between pyroclastic

 

layers Y and W (p. 32). The fluvial deposits are best
exposed in banks along the west side of the Nisqually
River between Van Trump Creek and Longmire. Just
south of Van Trump Creek the lahar assemblage is rep-
resented by poorly sorted fluvial gravel (fig. 18) about
25 feet thick, locally capped by two lahars that are 3
and 5 feet thick. In this area and farther downvalley
the lahar assemblage forms terraces that are from 20 to
80 feet above the adjacent Nisqually River flood plain.
The terrace on which the entrance road is situated has
a gradient of about 250 feet per mile.

At the mouth of the Paradise River valley a terrace
underlain by the assemblage extends a few hundred
yards back into the valley, and the river flows along
the south edge of the terrace’s southward-sloping sur—
face. An outcrop in the face of the terrace a quarter of
a mile north of the Paradise River reveals a series of
four lahars separated by beds of fluvial sand and gran-
ule gravel 1—2 feet thick. The lowest lahar exposed is
more than 15 feet thick and consists of an unsorted rub-
ble that contains angular and subangular blocks as
large as 7 feet in maximum dimension in a matrix of
purplish-gray sand. Blocks in the rubble consist of an-
desite that was derived from the volcano and granodi-
orite. The three overlying lahars are texturally similar
and are from 1 to 4 feet thick. The clay-sized frac-
tion of the uppermost lahar consists of cristobalite,
feldspar, and glass (probably amorphous or opaline sil-
ica, or both) ; no clay minerals were identified by X—ray
examination (table 11, sample 18). This lahar probably
is correlative with the one that caps the terrace at
Cougar Rock campground on the opposite side of the
valley. The lahar at the campground is at least 5 feet
thick, and blocks on its surface are as large as 14 feet
in maximum dimension.

The stratigraphic complexity of lahar assemblage C
is well illustrated by outcrops on both sides of the Nis—
qually River about a quarter of a mile north of Long-
mire (measured section 5). There are six terraces with-
in the valley in this area, at heights ranging from 20
to about 80 feet above the river. The stratigraphic suc-
cession of the deposits and the relation of the deposits
to the terraces are shown diagrammatically on plate
2. The sequence of events that can be inferred from
this cross section follows. The sequence depends on an
uncertain correlation of individual gravel deposits and
lahars. If the correlations are incorrect, the sequence
would be different in detail but not in overall complex
character.

18. Downcutting to level of present flood plain.
17. Aggradation of fluvial deposit J.
16. Downcutting probably of at least 20 feet.

DESCRIPTION OF LAHARS

.4;
H

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

E E
E E E E E E
E E 0
Lu 0 o -1 O o' o
’2‘ O O O H r—c v—1
<0 100
/
Lu
2 ///
I
§ 90 / ,
o / /
E 80 I /
z Sorting /
E Sample coefficient 1
l- a
70 L.
I— 3 z
I 9,«% ray/i
9 ,/«\9 a}
"” 60 21 9.84 I a?
3 ///
E 38 10.86 //
50 /.
g ////
_ 5/
L 40
U) z
m /
§ 30 /A/
E /
e. /
u. 20 z /
O // r’
/ /'

LLJ ¢/’
‘5 10
< /
I2 ”f/
LIJ ’ g1=r’
0 g
E 0 4x A v
0' CLAY SILT SAND GRANULES PEBBLES COBBLES

FIGURE 17.—Oumulative curves of grain-size distribution of lahars near Long-mire. Sample 38 is unit 1 of measured section 4,
and sample 21 is unit 6.

15. Deposition of pyroclastic layer W about 450 years
ago.
14. Deposition of lahar I.
13. Downcutting of about 20 feet.
12. Aggradation of about 30 feet by fluvial deposit H.
11. Downcutt'ing of about 35 feet.
10. Deposition of lahar G.
9. Aggradation of at least 20 feet by fluvial deposit F.
8. Downcutting of at least 20 feet.
7. Aggradation of about 40 feet by fluvial deposit E.
6. Downcutting of unknown amount.
5. Deposition of lahar D.
4. Deposition of fluvial gravel C.
3. Deposition of lahar B.
2. Channel of Nisqually River represented by fluvial
deposit A.
1. Deposition of peat and pyroclastic layer Y on top
of Paradise lahar.
In reconstructing these events, I assumed that the
presence of a lahar at a certain height does not neces-
sarily imply that the valley was filled by solidified lahar
to that height. This is because lahars typically attain a
“high-water mark” formed by a transient crest and may
only leave veneers on preexisting terraces of various
heights as the bulk of the flow drains on down the
valley.

 

ORIGIN OF LAHAR ASSEMBLAGES IN THE NISQUALLY
AND WHITE RIVER VALLEYS

The histories of the White and Nisqually River val-
leys are strikingly similar during the period between
deposition of pyroclastic layers Y and W. When layer
Y was formed about 3,600 years ago, both valley floors
were at or near their present altitudes, and peat was be—
ing deposited in both valleys, probably in back swamps
adjacent to the flood plains or on low swampy terraces.
At this time flood plains in both valleys probably were
relatively stable and Mount Rainier volcano had long
been dormant, or nearly so. A radiocarbon date on wood
from a bed of clay in the White River valley indicates
that the White River flood plain was still relatively
stable until some time after 2,700 years ago (p. 30).
Some time later, however, both valley floors changed
drastically as the rivers began alternately to aggrade
and erode.

Possible explanations for the drastic change in the
habit of the White and Nisqually Rivers, as well as that
of some other rivers that head on the volcano, include
the following three factors: tectonic movement of the
land, climatic change, or most likely, an episode of
volcanism. The relatively short time during which the
valley floors were repeatedly aggraded and eroded sug-
gests that recurring vertical movements of the land were

42 POSTGLA’CIAL LAHAR‘S FROM MOUNT RAINIER VOLCANO, WASHINGTON

 

FIGURE 18.—Orudely stratified poorly sorted fluvial gravel in lahar assemblage O, exposed in west bank of Nisqually River
near the mouth of Van Trump Creek The large granodiorite boulder at the upper right is about 11 feet long; handle of
pick beneath boulder is about 17 inches long.

not the cause. Nor is it likely that the climate could have
changed sufficiently and often enough in this interval to
account for the recurring cutting and filling. Climate
changes generally alter the discharge-load ratio of
streams and cause them to erode or aggrade. Aggrada-
tion of a valley floor in a basin occupied by valley
glaciers typically occurs during a glacial episode, and
downcutting follows during late glacial and early inter-
glacial time; in such an environment most of the re-
mainder of the interglacial interval is normally char-
acterized by relative stability of the flood plain
(Schumm, 1965, and references therein). At Mount
Rainier the valleys in question contain glaciers today
at their heads, and there is little question that these
glaciers have been present, though variable in size,
throughout Holocene time.

 

The lahar assemblages must predate trees growing on
them. In the White River valley a tree more than 700
years old was found on a terrace underlain by the lahar
assemblage just downvalley from the terminal moraine
of Emmons Glacier. Sigafoos and Hendricks (1961, p.
A16) thought that the forested surface of this terrace
is at least 1,000 years old. In the Nisqually River valley
I found a living tree at least 790 years old on the surface
of lahar assemblage C near Cougar Rock campground.
The lahar assemblages in both valleys probably were
formed prior to 1,000 years ago.

The interval during which the White and Nisqually
Rivers repeatedly aggraded and eroded coincides gen-
erally with the Winthrop Creek Glaciation (table 3).
During the Burroughs Mountain Stade of that glacia-
tion, which probably occurred between 3,000 and 2,500

DE SCRIPTION

years ago, most glaciers in the park were no larger than
they were at the beginning of the present century, and
Emmons and Nisqually Glaciers were somewhat smaller
(Crandell and Miller, 1964). Most of the lahar assem-
blage in the White River postdates pyroclastic layer C,
which was erupted about 2,300 years ago, and thus its
origin seemingly cannot be related to climatic or gla-
cial events of Burroughs Mountain time. The strati-
graphic relation of lahar assemblage C in the Nisqually
River valley to pyroclastic layer C cannot be directly
determined.

The oldest known moraines of the Garda Stade of the
Winthrop Creek Glaciation were formed about”! 50 years
ago (Crandell and Miller, 1964). Inasmuch as the lahar
assemblages in the Nisqually and White River valleys
evidently are more than 1,000 years old, both predate the
oldest known glacial advance of the Garda Stade. The
assemblages in both valleys probably were formed dur-
ing the interval between the two glacial stades of the
Winthrop Creek Glaciation and thus have no genetic
relation to glaciation. It is pertinent to note that in, no
valley heading on Mount Rainier is there a depositional
record of large—scale aggradation and downcutting dur-
ing the Garda Stade comparable to that represented by
lahar assemblage C in the White and Nisqually River
valleys.

Aggradation of the complex lahar assemblages in
the two valleys and the periods of downcutting re-
corded within the assemblages probably were caused
by intermittent eruptive activity of the volcano at the
time the present summit cone was formed. Eruptions
of the lava flows that form the cone could have caused
a succession of floods down the flanks of the volcano
by melting extensive fields of snow and ice at the sum-
mit. Some floods may have been transformed into la-
hars as they picked up loose material from taluses, gla-
cial drift, and alluvium on the valley floors. Tempor—
ary aggradation farther downvalley, resulting from
a series of lahars and debris-laden floods, probably was
quickly followed by downcutting between eruptions,
When the discharge of rivers approached or returned to
normal. Subsequent floods and lahars, separated by pe-
riods of downcutting, formed the deposits that under—
lie the terraces.

The lahars of these assemblages in valleys on the
east and south sides of the volcano seem to be nearly
or wholly lacking in clay minerals. This lack is at-
tributed to the derivation of the rock debris in the
lahars chiefly from talus, glacial drift, alluvium, and
newly erupted detritus, rather than from hydrother-
mally altered rocks of the volcano.

The proposed cause-and-efl'ect relation between

 

building of the summit cone and the formation of the

43

0F LAIIARS

lahar assemblages cannot be proved, but it is consistent
with all the known facts. The cone-building eruptions
are not dated, but they are thought to have occurred
during a late part of an extended episode of volcanism,
early parts of which are represented by the formation
of a bomb-bearing block-and—ash flow deposit in the
South Puyallup River valley that is about 2,500 years
old and by the eruption of pyroclastic layer C.

If this cause-and-effect relation is valid, the relative
abundance of lahars and fluvial deposits in the White
River valley may be due to the fact that the summit
cone was built on the east side of the depression formed
at the top of the volcano by the landslides that led to
the Osceola Mudflow. Floods caused by melting snow
and ice at the summit descended Emmons, Winthrop,
Nisqually, and Kautz Glaciers. Lahars of post-Y, pre-
W age in each of the valleys below these glaciers prob—
ably originated during the building of the smmnit cone.
Comparable lahar assemblages of the same age are
lacking in the O'hanapecosh, Mowich, and Carbon Riv—
er valleys, probably because none of these valleys drain
the summit cone of the volcano.

LAHAR ASSEMBLAGE D

Assemblage D in the Nisqually River valley consists
of alluvium and lahars, younger than the 450-year-old
pyroclastic layer W, that form low, tree-covered ter—
races adjacent to the modern flood plain. The park head-
quarters building, museum building, many of the resi-
dences, and maintenance buildings at Longmire are con-
structed on a coarse bouldery lahar that is part of this
unit. The oldest tree I found on this deposit started to
grow in the 1860’s. The lahar evidently topped the west
riverbank immediately downstream from the site of the
bridge over the river at Longmire and formed a lobe
that spread westward into the Longmire meadow. The
presence of old trees around the lobe’s south margin in-
dicates that it did not rejoin the lahar along the center
of the valley. A similar but older lahar forms the ter-
race on the opposite side of the valley at Longmire
campground. The terrace is 5-10 feet higher than the
surface of the adjacent channeled and unvegetated flood
plain of the Nisqually River. The oldest tree I found on
the lahar at the campground started to grow about 400
years ago, and the absence of pyroclastic layer W indi-
cates that the lahar cannot be older than about 450 years.
The surface of the lahar is crossed by south-trending
gullies 1—5 feet deep and is strewn with boulders as
large as 4 feet in diameter.

Small lahars have occurred in the upper reaches of
the Nisqually River valley several times within the last
few decades. Descriptions of some of these lahars are in

4:4 POSTGLA‘CIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON

the files of the National Park Service, and they have
recently been discussed by Richardson (1968).

On October 14, 1932, a lahar destroyed a highway
bridge across the Nisqually River just below Nisqually
Glacier. Eyewitnesses told of a mixture of rock debris,
mud, and water which had a front 25 feet high and 150
feet wide and which advanced rapidly downvalley to—
ward the bridge. The impact of the flowing mass car-
ried away the center span of the reinforced concrete
bridge, which was 27 feet wide, 55 feet long, and
weighed an estimated 40 tons. The bridge was carried
more than half a mile downstream. The observers re-
ported that the moving mass resembled wet concrete
except for being darker in color, and they stated that
large boulders in it were thrown 10—30 feet into the air
as the mass moved forward. The lahar evidently termi-
nated on the flood plain between the highway bridge
and Longmire.

Two years later, on October 24 and 25, 1934, a series
of four floods or lahars again carried masses of debris
down the Nisqually River valley. This time rock debris
was dumped to a depth of 15 feet on top of a new high-
way bridge. Richardson (1968) described other “glacier
outburst floods” that occurred in October 1947 and Oc-
tober 1955. At the same time as the 1947 flood, lahars
moved down the Kautz ICreek valley (p. 46).

LAHARS IN THE NISQUALLY RIVER VALLEY DOWN-
STREAM FROM THE PARK

Lahars of Holocene age are present in the Nisqually
River valley at least as far downstream as Elbe. Al-
though they have not been seen in the valley below
Alder Dam, it seems likely that remnants also underlie
the part of the valley inundated by Alder Reservoir.
Upstream from the reservoir, the deposits are divided
into two groups by their stratigraphic relation to pyro-
clastic layer Y; thus, the pre-Y lahar assemblages A
and B of the upper part of the valley are grouped here,
as are the post-Y assemblages C and D.

The deposits older than layer Y [include at least two
lahars as well as fluvial gravel. These deposits crop out
in streambank exposures on both sides of the Nisqually
River downstream from the Kernahan Road, which is
a north-south road that crosses the river 3 miles west
of the park. On the south side they form a terrace about
40 feet above the flood plain, which abuts a hill of drift-
veneered bedrock. An exposure in the face of this ter-
race 0.6 mile downstream from the Kernahan Road
reveals 15—20 feet of fluvial gravel, overlain by a pre-Y
lahar about 20 feet thick. The sand and gravel may be
outwash of Evans Creek age. A similar sequence occurs
on the north side of the valley only a few hundred yards
downstream, where two lenticular lahars, with a total

 

thickness of about 12 feet, overlie 30 feet of fluvial
gravel.

Another lahar older than layer Y was noted near
stream level in the face of a 20-foot terrace in the same
area. An outcrop at the upstream end of the terrace
exposes a compact lahar, whose base is below river level;
this lahar is overlain by lenticular fluvial gravel and
sand. The fluvial deposit is unconformably overlain
by layer Y, above which is another fluvial gravel.

Near the mouth of Big Creek, 21/2 miles downstream
from Kernahan Road, outcrops in the face of a terrace
that is older than pyroclastic layer Y show in descend-
ing order a lahar 18 inches thick, lenticular sand 20
inches thick, and a lenticular lahar as much as 10 feet
thick. The lower lahar lies in a channel cut into fluvial
boulder gravel 12—20 feet thick. The terrace is about 25
feet above the Nisqually flood plain.

Fluvial gravels and lahars along the Nisqually River
valley that are younger than layer Y form low terraces
adjacent to the flood plain. The most extensive deposit
floors a channel south of the flood plain for a distance of
5 miles between the park and Ashford. The channel,
which marks a former course of the Nisqually River,
is separated from the modern flood plain by ridges and
knobs of drift-veneered bedrock. The gradient of the
channel is less steep than that of the flood plain, so the
relative height of the channel increases downstream. At
its upstream end, the channel’s floor is only about 5 feet
above the present Nisqually flood plain, but at its west
end it is 35 feet above the flood plain. Exposures of the
deposits beneath the channel are poor and for the most
part reveal only a few feet of poorly sorted sand and
gravel. In some shallow exposures the texture of this
material resembles that of coarse lahars with a sand
matrix.

Near the east end of the channel there is a gap in the
bedrock ridge that separates the channel from the Nis-
qually River flood plain. In a shallow cut in the floor
of the gap can be seen a compact sandy lahar 3 feet
thick which overlies a 20-inch layer of Y pumice. A
shallow excavation in the floor of the channel near a mill
pond (SW14 sec. 36, T. 15 N., R. 6 E.) 0.4 mile west
of Kernahan Road shows 6 feet of boulder gravel. Most
of the boulders are less than 11/2 feet in diameter, but a
few are as large as 8 feet. Farther west, downcutting
by Catt Creek into the channel deposit has exposed
lahars interbedded with fluvial sand.

From the mouth of Mineral Creek to Elbe, deposits
younger than layer Y consist principally of fluvial sand
and fine gravel. However, a lenticular lahar crops out
in the north bank of the Nisqually River (SW14 sec.
26, T. 15 N., R. 5 E.) 0.2 mile downstream from the
railroad bridge south of Park Junction. The deposit

DESCRIPTION

is as much as 12 feet thick and lies in a channel about
125 feet wide which is floored by pebble to boulder
gravel and sand. Farther downstream, most exposures
on the valley floor are of deposits of medium to very
coarse gray sand and granule gravel. Such a deposit
was exposed in 1962 in the sides of a trench used as a
trash dump by the residents of Elbe, in the NElfll sec.
29, T. 15 N., R. 5 E. There the sand and gravel deposit
is about 5 feet thick and contains granule-sized pumice
derived from layer Y; it overlies a sandy lahar more
than 2 feet thick in which there are a few scattered
cobbles.

The generalized sequence of postglacial events in the
valley downstream from the park, reconstructed from
the deposits preserved in terraces, is as follows (event
1 is the oldest) :

1. Aggradation by fluvial gravel from a surface below
the present flood plain to one at least 20 feet
higher.

2. Deposition of lahar, locally as much as 20 feet thick,
to form a surface 40 feet higher than the present
flood plain.

3. Downcutting of valley floor to a level below present
flood plain.

4. Deposition of lahar on valley floor.

5. Deposition of thin fluvial gravel on valley floor.

6. Deposition of pyroclastic layer Y.

7. Aggradation of valley floor by fluvial gravel to sur-
face 10—15 feet higher than present.

8. Deposition of lahar as much as 12 feet thick on val-
ley floor.

9. Downcutting of at least 20 feet to level of present
valley floor.

The complex sequence of aggradation and down-
cutting that is recorded by the deposits, terraces, and
unconformities within lahar assemblage C upvalley
from Longmire is only poorly represented in the valley
west of the park. However, both the channel south of
the flood plain and that followed by the Nisqually River
today were aggraded during the deposition of that as—
semblage. It seems likely that the effects of the recur-
ring episodes of aggradation and downcutting dimi—
nished progressively downvalley and that they may not
have extended as far as the Puget Sound lowland.

KAUTZ CREEK VALLEY LAHAR ASSEMBLAGE

The floor of Kautz Creek valley is underlain by an as-
semblage of lahars and fluvial deposits into which the
creek has cut a trench about 31/2 miles long, 100—200
feet wide, and as much as 75 feet deep; the south end
of the trench is about 11/2 miles upstream from the mouth
of the creek. Exposures in the sides of the trench reveal
a succession of unweathered gray fluvial deposits and

 

or LAHARS 45

lahars interbedded with horizons of forest duff and
tree stumps (fig. 19) and pyroclastic layers Y and W.
Beyond the edges of the trench the surface of the as:
semblage is interrupted by old channels of Kautz Creek

that are separated by ridges and terraces. Parts of the

surface are forested (fig. 20) and some of these for-
ested areas are older than pyroclastic layer W. Because
of the convex surface of the assemblage (pl. 2), Pyramid
Creek flows along its west margin for about 31/2 miles
before joining Kautz Creek.

Pyroclastic layer Y and deposits beneath it were seen
at only three places along the valley floor, although the
pumice mantles the valley walls above the surface of
the lahar assemblage. A buried pumice deposit was first
noted by Hopson, Waters, Bender, and Rubin (1962)
in the east wall of the trench about three-fourths mile
upstream from the Wonderland Trail bridge across
Kautz Creek, and my associates and I (Crandell and
others, 1962) subsequently also examined the sequence
of deposits exposed there. In that outcrop, pyroclastic
layer Y overlies cobble—and-boulder gravel and is over-
lain by interbedded fluvial gravels and lahars (meas-
ured section 6). Layer Y'also crops out in the east bank
of the creek about 11/2 miles upstream from its
mouth. At a third outcrop the pumice overlies a lahar
more than 12 feet thick. This locality is about 100 yards
downstream from the south end of the “box canyon” of
the Kautz, which is a bedrock-walled constriction in
the valley southeast of Pearl Falls and 5 miles north-
east of the Entrance Road. The “box canyon” is about
a quarter of a mile long and 250—300 feet wide.

The lower pyroclastic deposit at measured section 6
was referred to by Hopson, Waters, Bender, and Rubin
(1962, p. 641) as “the main ash fall of sand- to granule-
sized pumice, which constitutes the major part of the
youngest ash blanket from Mount Rainier.” They found
stumps of two trees in the bed of Kautz Creek 25 feet
from the wall of the trench, which they thought were
rooted in the deposit beneath the pumice. Radiocarbon
age determination of their sample of wood from one
of these stumps indicated an uncorrected age of 3501'
250 years (W—925). However, microscopic examination
of pumice taken from the outcrop led D. R. Mullineaux
(in Crandell and others, 1962) to conclude that it is
pyroclastic layer Y. Layer Y has been bracketed by
uncorrected radiocarbon dates of 3,500i250 (W—1115)
and 29801-250 years (W—1118) (table 4; Crandell and
others, 1962). The marked increase in grain size and
thickness of the pumice layer toward Mount St. Helens
indicates that this volcano was its source.

The relations at the Kautz Creek locality and the
addition of a “correction factor” to the radiocarbon date
led Hopson and his associates to conclude that the

46 POSTGLACIAL LAHAR-S FROM MOUNT RAINIER VOLCANO, WASHINGTON

Measured section 6

[East bank of Kautz Creek about 3,000 ft upstream from Wonderland Trail
footbridge across creek]
Thickneu

(It) (in)

21. Lahar: boulders and cobbles in medium- to

fine-sand matrix. Deposited in October

1947 _________________________________ 2—8 0
20. Dufl", silty, dark-grayish—brown; contains

roots and wood fragments ____________________ 6
19. Boulders; 1—4 ft in diameter, in matrix of

stratified coarse sand __________________ 3 0
18. Sand, fine to medium, gray; horizontally

stratified and interbedded with layers of

yellowish-gray silt _____________________ 2 0
17. Dufi'; contains fragments of carbonized

wood ______________________________________ 2

16. Silt and fine sand, yellowish-gray, horizon-

tally bedded; contains pebbles and gran-

ules near top _________________________ 1 0
15. Dufl’ and roots (radiocarbon sample W—

1120, uncorrected age: 2903: 200 years,

see table 4) _________________________________ %—}/2
14. Sand, fine, gray _______________________________ %-}/2
13. Pyroclastic layer W: white pumiceous ash ______ %—2

12. Sand, fine, gray _______________________________ %
11. Duff, wood, and carbonized wood fragments
(radiocarbon sample W—1119, uncorrected

age: 320:1: 200 years) _________________________ }é—1 $6

10. Sand, fine to medium, gray; contains scat-
tered cobbles _______________________________ 6

9. Lahar: pebbles and cobbles in compact sand
and granule matrix; gray _______________ 2 0

8. Sand, medium; mostly horizontally strati-
fied but has some faint crossbedding;
contains reworked pumice of layer Y
and wood fragments ___________________ 5 0

7. Lahar: boulders and cobbles in fine- to
medium-sand and granule matrix _______ 2 6

6. Duff mixed with gray fine sand; contains
fragments of charcoal ________________________ }é—2

5. Sand, fine, gray; contains reworked pumice
of layer Y and wood fragments _________ %-2 0

4. Lahar: boulders as large as 4 ft in diameter
in gray sand and granule matrix ________ 15

3. Sand, fine to medium, stratified, lenticular-_ 1—3

2. Pyroclastic layer Y: yellow pumiceous ash ________

1. Pebble-to-boulder gravel and sand _________ 1+

OMOO

latest eruptions of Mount Rainier occurred about 500
years ago. However, the pumice deposit on which they
based this conclusion is not an eruptive product of
Mount Rainier. A probable explanation for the rela-
tively young radiocarbon date they cited is that the
stump from which they took their sample was at a
horizon stratigraphically above the pumice deposit, in-
stead of below it, as they thought.

Most of the lahars and fluvial deposits exposed in
the walls of the Kautz Creek trench are younger than
layer Y, but some are older and some younger than
layer W. The lahars range from layers less than 1 foot
thick to unstratified, unsorted beds 20 feet thick that

 

contain boulders as much as 10 feet across. Despite their
unconsolidated nature, the alluvium and lahars stand
in very steep and locally vertical banks along the trench.
Although the lahars are not cemented, the fine mate-
rial in them makes them somewhat more coherent than
fluvial gravels in which the fine component is less
abundant. The layers of fluvial gravel are distinguished
chiefly by the presence of bedding and by somewhat
better sorting. However, the overall range in texture in
a thick lahar and some comparably thick fluvial de-
posits does not appear to be appreciably different.

Layers of forest litter in the lahar assemblage range
from beds of dufi' less than an inch thick to accumula-
tions of logs and organic trash that may represent log
jams in stream channels that were subsequently buried
by lahars or alluvium. The only horizon of duff that is
easily traceable along the trench walls is that associated
with layer W. Stumps are commonly rooted in material
just beneath layer W (fig. 19) .

The youngest deposits of the lahar assemblage in the
Kautz Creek valley were formed during the night of
October 2—3, 1947, and during the early morning hours
of October 3. Details of the events that preceded and
accompanied the lahars are largely taken from reports
by R. K. Grater (1948; unpub. data, Oct. 28, 1947, in
files of the National Park Service) and from an unpub-
lished, undated report by C. E. Erdmann and Arthur
Johnson of the U.S. Geological Survey, also in the files
of the National Park Service.

According to Erdmann and Johnson, rain started to
fall a few hours after midnight on October 1 and
reached its greatest intensity between 5 and 9 a.m. on
October ‘2. A total of 5.85 inches fell at the Ranger Sta-
tion at Paradise Park between 4: 30 pm. October 1 and
the same time the next day, but very little fell during the
early hours of October 3. During the downpour, a cloud-
burst evidently occurred in the upper part of the Kautz
Creek drainage basin, and an additional amount of
water may have been contributed by a “glacier outburst
flood” from Kautz Glacier (Richardson, 1968, p. D83).
The discharge of Kautz Creek increased greatly during
the daylight hours of October 2, and between 7 and 8
p.m., high water washed out the entrance road bridge
over the creek. The first lahar occurred between 10 and
11 pm. and was heralded by a dull roar and vibration
of the ground as it advanced down the valley. A succes-
sion of lahars flowed downvalley during the night, and
the last occurred at 8 a.m. the next morning. The lahars
were described by eyewitnesses as having the consis-
tency of wet concrete, carrying along vegetation and
boulders as large as 13 feet in diameter.

After the lahars Ceased, Kautz Creek was flowing in
a trench 30—75 feet deep and 100—200 feet wide south

DESCRIPTION OF LAHARS 47

 

FIGURE 19.—Deposits in west bank of Kautz Creek, about 0.35 mile downstream from the Wonderland Trail. The cobble
and<bouilder gravel (A) at the base is probably a fluvial deposit. It is overlain by a layer of duff and roots (B), above
which is a lenticular lahar (C) a few feet thick. Above the lahar, at the right side of the photograph, is a layer of
roots and duff (D) which includes pyroclastic layer W. Above this are other lahars and fluvial deposits.

of the “box canyon.” How much of this trench existed
before the lahars occurred is not clear; Grater (1948,
p. 279) stated that “an entirely new stream channel was
out, with the old bed of Kautz Creek left high on the
side of the canyon.” The topography of the valley floor
suggests, however, that the present trench could have
been localized along a preexisting channel (pl. 2.) Rem-
nants of the 1947 lahars form discontinuous narrow
strips along the edges of the trench, and although they
locally extend beyond the trench in lobes, they do not
veneer wide areas in the upper part of the valley. Their
distribution suggests that the lahars were largely con-
fined to the trench and that the trench either predates
them or was formed contemporaneously. The narrow
strips of laharic deposits are generally less than 10 feet
thick, but near the south end of the trench they are as
much as 18 feet thick.

Even though the present trench may have been local-
ized along a former course of Kautz Creek, that stream
course undoubtedly was cut down and widened at some
time on October 2 or 3. Evidence from the lahar assem-
blages exposed in the Kautz Creek valley and in other
valleys at Mount Rainier indicates that lahars them—
selves are not efl’ective erosional processes at the gradi-

 

ents found on most valley floors below the glaciers. If
this is true, downcutting of the trench probably was
accomplished not by the lahars themselves, but by flood-
waters.

During the morning of October 3, according to the
report of Erdmann and Johnson, the valley floor down-
stream from the trench aggraded about 28 feet where
it is crossed by the entrance road. The area of aggrada—
tion forms a fan whose base, along the Nisqually River,
has a breadth of about 2,500 feet. The area narrows
northward to 500 feet or less and apexes at the mouth
of the trench. Although the fan in the lower part of the
valley probably contains most of the coarse debris trans-
ported on October 2 and 3, much of the fine material
was carried downstream by the Nisqually River and
was deposited on the floor of Alder Reservoir. Grater
(1948) estimated the total volume of the lahars and flood
deposits to be at least 50 million cubic yards.

During a subsequent investigation of the upper Kautz
Creek valley, R. K. Grater (unpub. data, 1947; 1948)
found that the lower 1—mile segment of Kautz Glacier
had largely disappeared, and a gorge 300 feet deep and
as much as 900 feet wide had been cut into the ice. Grater
inferred that the gorge had been cut by excessively high

48 POSTGLA‘CIAL LAHARS FROM MOUNT

 

FIGURE 20.—Bouldery surface of a pre-W lahar assemblage that
underlies the floor of the Kautz Creek valley about 1 mile
north of the Wonderland Trail crossing of Kautz Creek.

runoff, aided by toppling of ice masses as the glacier was
undercut. Blocks of ice, accompanied by masses of gla-
cial drift that slid from the precipitous canyon walls,
created temporary dams in the “box canyon,” the failure
of which caused floods of water and masses of saturated
debris to flow down the valley. Repetition of sliding and
damming caused successive lahars and floods to surge
down the valley. The trench of Kautz Creek probably
was cut by the floods, and this erosion itself may have
created lahars as the undercut sides of the trench top-
pled into the floodwaters.

Samples of some of the fluvial gravels and lahars de—
posited on October 3, 1947, were obtained from an out-
crop in the bank of the Nisqually River along the south
edge of the fan (fig. 21). The size distribution of four
samples, and other data, are shown in table 12 and fig-
ure 22. X-ray analysis of a sample of one of the lahars
(sample 2, table 11) indicated that the silt and clay

fractions consist almost wholly of plagioclase feldspar. ,

TABLE l2.—Gratn-size distribution data on deposits formed by
floods and lahars in October 1947 in the Kautz Creek valley

 

 

 

Unit Thick- Clay Silt Sand Median Sorting
(fig. Description ness (per- (per- (per— diameter coefli-
21) (ft) cent) cent) cent) (mm) clent
4 Sand and pebble
3-4 1 5 53 l. 6 2. 32
3. 5 4 11 48 . 8 8. 10
2 ..... do ........... l. 5 3 11 51 . 63 3. 41
1 Sand and
granule gravel. >2 1 3 40 2. 75 3. 38

 

 

RAINIER VOLCANO, WASHINGTON

 

FIGURE 21.—Lahars and fluvial sand and gravel deposited near
the mouth of Kautz Creek in October 1947. Units 2 and 3
are fine and coarse lahars, respectively; units 1 and 4 are
probably both fluvial deposits.

On August 23, 1961, a short-lived flood was observed
in Kautz Creek at the entrance road bridge by Park
Service personnel (fig. 23). This flood occurred during
a dry spell and thus apparently originated from the re—
lease of unusual amounts of melt water by Kautz Gla—
cier. Photographs of the flood and eyewitness accounts
suggest that the flood was heavily laden with both fine
and coarse rock debris, but not so extensively as to form
a viscous mudflow. In its proportion of water to rock
debris, the flood may have been a “hyperconcentrated
flow” (Beverage and Culbertson, 1964; p. 4, this re-
port).

Photographs taken of various parts of the Kautz
Creek trench in the vicinity of Wonderland Trail be-
fore and after the flood indicate that the increased dis-
charge caused aggradation in some parts of the trench,
removed loose debris along the sides, and in some places
resulted in sideways erosion into the lower parts of the
trench walls (fig. 24). If the increased discharge had
been appreciably greater and of longer duration, whole-
sale sloughing of the trench walls probably would have

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DESCRIPTION OF LAHARS 49
E E
E E E E E E
E E

8 H E E o g
El 2 3 S 3 ‘3 B
<0 100 .
O I
E /’ ,/ /
< /, ,
9 9° /// / /
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- 80 / /
E Sorting / / V
I Sample coefficient / l ’1’
t- 70 WW // /
l— \ r
I 1 8.10 «9 \// /
g 6’? o\e/ /
L; 50 2 3.41 r a“ q,
> / 3 \w/ /
m A 3.38 / x [5 bx

50 ro \3
E B 2.32 // ‘0 63/
/
Z / 6°}
‘ / / /
‘L 40 /,
(I)
Lu I
d / / /
I: 30 / / ,1
E / / /
/ /
3 20 I], /
/’ / /

a / //
< 10 i,
I'- _/ ’ .—;//
Z — fl” ’ ’ : :w “’
DJ —_——-=-—— —'
o — -‘"‘
5 ° 4 A A A
m CLAY SILT SAND GRANULES PEBBLES COBBLES

FIGURE 22,—Cumulative curves of size distribution of deposits

formed by floods and lahars in the Kautz Creek valley in

October 1947. Samples 1 and 2 are both from lahars; samples A and B are probably both fluvial deposits and are

from units 1 and 4, respectively, in figure 21.

resulted from undercutting, and lahars might have been
formed.

I traversed the Kautz Creek valley from Wonder—
land Trial to the entrance road on September 13, 1.961,
and found that the flood had been at least 6 feet deep and
perhaps as much as 12 feet deep in places because it had
overflowed the stream channel where the banks are that
high. Part of this channel depth, however, may have
been caused by stream downcutting following the flood’s
passage. At the entrance road, the flood was confined
to the channel of Kautz Creek (fig. 23).

This flood formed bouldery ridges in some places on
the flood plain. Boulders and trees in its path were
coated up to a height of 4 feet with a cementlike slurry
of coarse sand in places Where the flow was not con-
fined to a well-defined channel. The slurry had been
subsequently washed off the lower 11/2 feet of these
boulders and trees; thus, the pasage of the flood evi-
dently was followed by high discharge of relatively
clear water before Kautz Creek returned to normal.

LAHARS IN THE VALLEYS OF TAHOMA CREEK AND THE
NORTH AND SOUTH PUYALLUP RIVERS

Nine lahars were recognized in the valleys of Tahoma

 

Creek and the two branches of the Puyallup River;

their age and stratigraphic relation to some other Holo-
cene deposits present on the west side of the volcano are
as follows:

Two or more lahars of unknown age.

Lahvar about 440 years old.

Pyroclastic layer W (about 450 years old).

Electron Mudflow about 600 years old.

Lahar about 1,000 years old.

One or more lahars of unknown age.

Bomb-bearing block-and-ash flow about 2,500 years old.

One or more lahars of unknown age.

Round Pass Mudflow about 2,800 years old.

Pyroclastic layer Y (about 3,600 years old).

Lahar of. unknown age.

The Round Pass Mudflow, the 1,000-year-old lahar,
and the Electron Mudflow occur in more than one val-
lay and are described first; others, which are not lmown
in more than one valley, are discussed subsequently,
according to the valley in which they are found.

ROUND PASS MUDFLOW

Roadcuts at Round Pass (fig. 25) expose a mudflow
as much as 25 feet thick, Which overlies pyroclastic
layer Y and underlies layer W. The color of the mud-
flow is purplish to pinkish gray where seen in the road-
cuts. The deposit is here named the Round Pass Mud-

50 POSTGLA‘CIAL LAHAR-S FROM MOUNT RAINIER VOLCANO, WASHINGTON

 

FIGURE 23.—F‘lood in Kautz Greek channel at entrance road on August 23, 1961. The character of the water surface
and the mudditness of the water suggest that the flood was a “hypereoncentrated flow.” The dead trees in the back-
ground were killed by the 1947 labels and floods in the Kautz Creek valley. National Park Service photograph.

flow; its type locality is at Round Pass. Roadcuts on
the north side of the Tahoma Creek valley between the
valley floor and Round Pass show a veneer of mudfl'ow
a few inches to as much as 6 feet thick on top of layer
Y and Evans Creek Drift. In one exposure, reworked
pumice from layer Y forms irregular masses within
the mudflow. The Round Pass Mudflow crops out along
the trail to Lake George (fig. 25) up to an altitude of
about 4,350 feet, which is about 350 feet higher than
the pass and a little more than 1,000 feet above the floor
of the Tahoma Creek valley.

The Round Pass Mudflow also underlies parts of
Indian Henrys Hunting Ground, which is on the divide
between Tahoma Creek and Kautz Creek. The south-
west margin of the mudflow ends there in an abrupt
front about 17 feet high (fig. 26) where it is crossed by

 

the Wonderland Trail about 300 yards south of a patrol
cabin (pl. 1). The boundary between the mudflow and
the adjacent Evans Creek Drift is conspicously marked
by the absence or presence of pyroclastic layer Y. At
Indian Henrys Hunting Ground the mudflow extends
to a maximum altitude of about 5,350 feet, which is
nearly 1,000 feet higher than the floor of the Tahoma
Creek valley directly to the north.

The Round Pass Mudflow crops out at several places
along the Tahoma Creek valley. One of these outcrops
is a streambank exposure about 1 mile upvalley from
Tahoma Creek campground (measured section 9).
There the mudflow unconformably overlies coarse flu-
vial gravel, from which it is separated by pyroclastic
layer Y, and is as much as 20 feet thick. The mudflow
contains boulders as large as 6 feet in maximum dimen-

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DE SCRIPTION OF LAHARS

 

52 POSTGLA'CIAL LAI-IARS FROM MOUNT

122°

RAINIER VOLCANO, WASHINGTON

 

47" I

Rushiwwa ter

. Ashford

\J 'N’ational K/\

 

    
    
  

Mywich Lake

 
 
    

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Nisqwlly

 

 

3 4 MILES

lull | | l l

FIGURE 25,—Inferred original extent of Round Pass Mudfiow. The west edge of the Cascade Range lies about 4 miles
beyond the northwest corner of the map. Numbers show localities of samples (table 10) of the Round Pass Mudflow

and other lahars west of the volcano.

sion and logs as large as 4 feet in diameter. The mudflow
was identified downvalley to a point about 1 mile north
of the Nisqually River. At that point it caps a terrace
which is about 60 feet higher than the Tahoma Creek
flood plain.

In the North and South Puyallup River valleys I
recognized the mudflow as far downstream as a point 10
miles beyond the park boundary, and it may have ex-
tended even farther. Remnants of the mudflow veneer
the valley walls of the North Puyallup River up to a

DESCRIPTION

or LAI-IARS 53

 

FIGURE 26.——South edge of Round Pass Mudflow along the Wonderland Trail at Indian Henrys Hunting Ground. The front
of the mudflow is about 17 feet high; surface to the right is underlain by thin Evans Greek Drift and bedrock and veneered
with pyroclastic layer Y. The pumice is absent from the mudflow.

maximum height of about 350 feet above the valley floor
directly north of Klapatche Park. Farther downstream,
a quarter of a mile west of Mount Rainier National
Park, the mudflow coats the valley walls to a maximum
height of about 240 feet. The mudfiow, exposed there in
cuts along logging roads, lies on top of layer Y (fig.
27) and talus. In these exposures, the base of the pumice
layer contains many small pieces of charcoal, but none
were noted either at the top of the layer or in the over-
lying mudflow. About three-quarters of a mile farther
downvalley, near the mouth of the North Puyallup
River, cuts along another logging road expose the
Round Pass Mudflow up to a height of a little more than
200 feet above the river.

In the South Puyallup River valley, remnants of the
mudflow coat the valley walls to a height of about 1,000
feet above the river at a point 1.7 miles north of Round
Pass, about 350 feet at the mouth of St. Andrews Creek

 

just west of the park, and about 250 feet at the north-
west end of Klvapatche Ridge (fig. 25). Near the mouth
of the Mowich River, 51/; miles farther downstream, the
highest remnants are 160 feet higher than the Puyallup
River, and the base of the mudflow is below river level.
An imaginary line connecting these high remnants of
the mudflow has a downvalley slope of about 550 feet
per mile between Round Pass and the mouth of St.
Andrews Creek, whereas the valley floor now has a
gradient of about 300 feet per mile between these points.
However, this line might not represent the sloping up-
per surface of a continuous, deep, flowing stream of
mud, but instead could record the maximum height
reached by one or more transient waves of the mudflow.
Below St. Andrews Creek, where the valley widens
appreciably, the slope, as reconstructed from high
mudflow remnants, decreases and becomes more nearly
parallel to the present slope of the valley floor.

54 POSTGLA‘CIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON

 

FIGURE 21—120qu Pass Mudflow on top of pyvoclastic Layer Y at a point 240 feet above the floor of North Puynalllup River
valley 9. quarter of a mile west of the park.

The Round Pass Mudflow underlies a broad area in
the Puyallup River valley from the mouth of Deer
Creek downstream to the mouth of LeDoux Creek. The
Puyallup River has cut a trench as much as 100 feet
deep into this mudflow fill. Although the Round Pass
Mudflow may underlie the floor of the Puyallup River
valley beyond the mountain front, I did not recognize
it in outcrops while mapping the valley nor did I iden-
tify it in logs of wells beneath the valley floor.

Two samples of the mudflow at Round Pass were ex-
amined for grain-size distribution, and one was ex-
amined for clay mineralogy. The samples contained 24
and 22 percent silt- and clay-sized material, respectively,
and had sorting coeflicients of 14.18 and 11.2 (table 10,
samples 13 and 14) . Montmorillonite is the predominant
clay mineral; it is accompanied by feldspar and cristo‘
balite in the clay—sized fraction (table 11, sample 14) .

A sample of the Round Pass Mudflow from an outcrop
near the mouth of the Mowich River contained 20 per-
cent silt and clay; montmorillonite made up about four
parts in 10 of the clay (tables 10 and 11, sample 16).

 

Cumulative curves of grain-size distribution of samples
of the mudflow from two localities are shown in figure
28.

A sample taken from 1—2 feet below the top of the
mudflow at measured section 9 in the Tahoma Creek
valley contained 18 percent clay and silt and had a
sorting coeflicient of 10.6 (table 10, sample 12). The
clay—sized fraction of the sample consisted mostly of
feldspar and cristobalite and contained small amounts
of several clay minerals (table 11, sample 12).

Atterberg limits were determined for one sample of
the Round Pass Mudflow from the outcrops at Round
Pass. The plastic limit of the sample was 20, and the
liquid limit 25; thus, it had a plasticity index of 5.

Because remnants of the Round Pass Mudflow can
be found on the slopes of the volcano at least as far
as the east end of Emerald Ridge and to an altitude
of nearly 7,000 feet on the ridge that extends from St.
Andrews Park to Puyallup Cleaver, I presume that
the mudflow originated somewhere on the flank of the
volcano upslope from those points. The mudflow’s clay

DESCRIPTION OF LAHARS

55

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

E E
E E E E E E
H E E O.
o ._. O. 0
Lu 0 0 "f O. o o
g o' o o .—. .4 a
m 100 , _ . ————— ;- ,,~ 7'
o / x 47
E z” / [I .’
5 90 x ’/ [I 4‘;
a \Q I; ’/ ’l {I
E ”80 r / l/ ,'
80 *7 ' // 7"
E Sorting /’ // ll ,'
I Sample coefficient / x / .'
0-— 70 / \ox / 4 ‘ '
1— 6 3.94 / page}, 1 «a \3 ”L 9/
g /l // 993$,va oz \21."
m 60 8.83 , 7’ 90‘“ / edge '59,
s 9 7.42 ,’ // / / 112'
>- 7 I / z” / '
m 50 ll 9. 5 l/ // // '.
E 12 10.60 ,’ ’/' , I
z 13 14.18 4’ / A“ z
_ 4' r // z
“- 40 // / // A
I
m I’ / 4/ / ,
—| I 1’ / / , '
9 30 I, ' r’/ ’
+— / ' ’ .v'
E .r’ ////’ //’ _'.v"
D. 0 ,4/ / r "
2 , ,
LL
0 ’:¢.?/é,/I;/ .-‘
, a z .—
3 1o .4 r" r' ,4’7
-,, / fl, ________
E (-E—“f::==25"¢”7 """
L|J Errxf" ..... " "
O O
E J J
0' CLAY SILT SAND GRANULES PEBBLES COBBLES

FIGURE 28.—O'umulative curves of size distribution of samples of the Electron Mudflow (samples 6 and 7), lahar that is unit 9
in measured section 9 in the Tahoma Greek valley (sample 9‘), 1,000-year-old lahar in the South Puyallup River valley
(sample 11), and the Round Pass Mudflow (samples 12 and 13).

mineralogy suggests derivation from masses of altered
and partly altered rock similar to those now present
in the east wall of Sunset Amphitheater (p. 17). The
mudflow probably originated as a massive avalanche
or series of avalanches of this kind of rock. The dis-
tribution of the mudflow as a veneer on older deposits
in the valleys close to Mount Rainier indicates that the
mud was very fluid and that almost all of it drained
away after the crest of the mudflow passed downvalley.

The heights reached by the mudflow suggest that the
flow had enough volume to fill temporarily the upper
South Puyallup and Tahoma Creek valleys to a depth
of at least 1,000 feet, either as a flowing stream of mud or
as one or more large waves. The mass of the mudflow
needed to form a deep flowing stream of mud prob—
ably is adequately represented in the Puyallup River
drainage by extensive deposits which probably have a
volume of at least 200 million cubic yards in the area
west of the park. Because of its water content, the lahar
must have had a substantially greater volume while
moving. Deposits of comparable volume have not been
found in the Tahoma Creek valley, and the mudflow ap-
parently had a depth of only a few tens of feet at a point
just 4 miles downvalley from Round Pass. These rela-

tions may have resulted from movement of the mudflow
down Tahoma Creek valley as a single huge transient
wave, which progressively decreased in height, similar
to that inferred for the Paradise lahar (p. 36). Sub-
stantial amounts of the mudflow were left only in areas
where a low slope did not permit it to drain away;
elsewhere veneers only a few thick were left on the
sides and floor of the valley. Different volumes of the
mudflow in the three valleys may have resulted from
slightly different directions of initial downslope move-
ment of successive avalanches from Sunset Amphi-
theater, which caused unequal amounts of debris to move
into the respective valleys. Or, the different volumes
could have been caused by unequal lateral distribution of
rock debris within a single enormous avalanche.
Three radiocarbon dates have been determined on
wood from logs contained in the Round Pass Mudflow.
One of these was from a streambank exposure in the
Tahoma Creek Valley (measured section 9) ; it had a
radiocarbon age of 2,6101-350 years (W—2114). Two
other samples were from streambank outcrops near the
mouth of the Mowich River. One sample, from the north
bank 500 feet upstream from the river’s mouth, had a

 

radiocarbon age of 2,170:200 years (W—566). The

56 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON

other, from the south bank 500 feet further upstream,
had an age of 2,710i250 years (W—1972). When cor-
rected, these three dates are about 2,800, 2,200, and
2,900 years, respectively (table 4). The reason for the
substantial age difference is not known because there is
no stratigraphic evidence in the outcrops near the mouth
of the Mowich River of two mudflows. I assume that the
Round Pass Mudflow is about 2,800 years old.

1,000-YEAR-OLD LAHAR

A clayey lahar initially recognized at a streambank
outcrop in the South Puyallup River valley near the
Wonderland Trail bridge was first thought to be the
Round Pass Mudflow, but a radiocarbon date of 1,1001.-
250 years (W—1971) on a log from the outcrop showed
it to be younger. The lahar also was subsequently identi-
fied 10 miles farther downstream by a radiocarbon date
of 1,050:350 years (W—2113) on a log from a pre-
Electron lahar at measured section 7. When corrected,
these two dates are about 1,050 and 1,000 years, respec-
tively (table 4).

At the Wonderland Trail outcrop in the South Puy-
allup River valley, the lahar is more than 10 feet thick;
its base is below the river, but bedrock probably is not
far below river level there. On top of the lahar is a
bouldery lahar about 6 feet thick that may be only a
few decades old. The 1,000-year-old lahar is compact,
clayey, and yellowish brown. It contains about 29 per-
cent silt and clay (table 10, sample 11) in which the
clay-sized fraction consists of montmorillonite, cristo-
balite, and feldspar (table 11, sample 11) .

Atterberg limits determined on a single sample of the
mudflow obtained from the Wonderland Trail outcrop
are as follows: plastic limit 21, liquid limit 25, and
plasticity index 4.

The 1,000-year—old lahar may have a correlative in the
Tahoma Creek valley, where, at measured section 9,
there are two lahars younger than the Round Pass Mud-
flow but older than pyroclastic layer W.

ELECTRON MUDFLOW

The Electron Mudflow was named from Electron,
a small community beside the Puyallup River at the
west margin of the Cascade Range (Crandell, 1963b,
p. A50). Remnants of the mudflow underlie much of
the valley floor from Electron northward to the out-
skirts of Sumner (pl. 3). The mudflow is an unsorted
mixture of subangular to subrounded rock fragments
in a purplish-gray matrix of sand, silt, and clay. It
generally exhibits a size gradation upward from coarse
material at the base to fine material at the top. Samples
of the bottom foot and top foot of the mudflow from
a section 61/2 feet thick near McMillin were examined

 

for grain-size distribution. The bottom and top samples
had median diameters of about 1 and 0.1 mm and a silt
and clay content of 20 and 36 percent, respectively (table
10, samples 7 and 6). The cumulative curves of these
samples are shown in figure 28. In the clay—sized frac-
tion of sample 6, montmorillonite made up an estimated
six part in 10, plagioclase feldspar two parts, and cristo-
balite one part.

A sample of the Electron Mudflow from the outcrop
at measured section 6 contained about 27 percent silt
and clay, in which montmorillonite and chlorite together
made up about four parts in 10, with the former clay
mineral predominating (tables 10 and 11, sample 8).
The remainder of the silt and clay fraction consisted
of feldspars and quartz.

Rocks from Mount Rainier volcano made up an aver-
age of 41 percent and older rocks of the Cascade Range
59 percent of samples of pebbles collected from the mud-
flow at five different localities in the lowland (Crandell,
1963b). The most distinctive rock in the mudflow in the
lowland is a scoriaceous, black, hypersthene andesite,
which occurs as boulders as large as 5 feet in diameter.
These are mostly found lying on the surface of the mud-
flow. The largest boulders, however, are of a reddish-
brown breccia derived from the volcano, some of which
are at least 35 feet in maximum observable dimension.
These large boulders were seen mostly in an area extend-
ing from Orting southward for a distance of about 2
miles. This distribution probably is a result of a more
gentle gradient in this area than along the valley farther
upstream. The gradient of the mudflow is about 68 feet
per mile just downstream from the mountain front at
Electron; however, at a point 2 miles south of Citing
the valley widens, and the gradient decreases to about
34 feet per mile. The very large masses of breccia prob-
ably lodged on the old valley floor in this area as the
mudflow spread laterally, thinned, and decreased in
velocity.

Hand augering and power angering, in addition to
natural exposures, show the mudflow to overlie fluvial
sand and gravel deposited by the Puyallup and Carbon
Rivers; the mudflow itself is overlain by fluvial sand
and silt deposited by overbank floods. A wood fragment
obtained from the mudflow near Electron had a radio-
carbon age of 5301-200 years (W—565; 'Crandell, 1963b,
p. A51). When corrected, this age is about 600 years
(table 4).

The Electron Mudflow has been tentatively identified
at many places along the Puyallup River valley between
Electron and the lower slopes of Mount Rainier. The
following units crop out in a streambank on the north
side of the river about 1 mile downstream from the
mouth of the Mowich River (measured section 7).

DESCRIPTION

Measured section 7

[streambank on north side Puyallup River in the SW% sec. 34, T. 17 N., R. 6 E.]

Thickness
(ft)

4. Electron Mudflow: subrounded to subangular pebbles,
cobbles, and boulders as large as 7 ft across in
plastic matrix of purplish-gray clayey sand ________ 9

Erosional unconformity. '

3. Sand and pebble to boulder gravel, lenticular; contains
some layers of openwork pebble gravel, oxidized to
yellowish brown; as thick as _____________________ 3

2. Lahar: subrounded to subangular pebbles, cobbles, and
boulders as large as 3 ft across in plastic matrix of
purplish-gray clayey sand, mottled with yellowish-
brown iron oxide; lenticular; contains logs and wood
fragments, one of which was dated as about 1,000

years old (table 4, sample W—2113); as thick as- -__ 5
1. Sand and pebble to boulder gravel __________________ > 1
Covered, to river level _______________________________ 4

Unit 2 in measured section 7 is the 1,000-year-old
lahar described previously; this lahar and the Electron
Mudflow lie Within a valley eroded into the Round Pass
Mudflow by the Puyallup River. The top of the lahars
and alluvium within this valley is only a little more than
20 feet above river level, whereas the top of the Round
Pass Mudflow in this area is about 100 feet above the
river.

Near the mouth of St. Andrews Creek, just west of
the park boundary, the Electron Mudflow is about 6 feet
thick and overlies a sandy lahar more than 15 feet thick.
The two deposits form a terrace in the South Puyallup
River valley whose top is about 50 feet above river
level. Ring counts of recently cut stumps indicate that
some trees on the terrace were at least 435 years old.
Inside the park two clayey lahars, one of which may be
the Electron, overlie the bomb-bearing block-and-ash
flow; the three deposits are superposed in a cut (meas-
ured section 7) along the West Side Road near the South
Puyallup River bridge.

Measured section 8

[Cut along the West Side Road about Mmlle northwest of the South Puyallup River
bridge] Thickness
(It) (in)
4. Lahar: subangular to subrounded pebbles, cobbles,
and boulders as large as 2 ft across in a plastic
clayey yellowish—brown sand matrix __________ 4 6
3. Lahar: angular to subangular rock fragments as
large as 4 in. across in a purplish-gray sand
matrix; lenticular. Locally, only fine sand occurs
at this horizon, which contains scattered grains
of pumice W and bits of carbonized wood _____ 6
2. Electron(?) Mudflow: subangular to subrounded
pebbles, cobbles, and boulders as large as 2 ft in
diameter in a plastic clayey yellowish—brown
sand matrix _______________________________ 7 0
1. Bomb-bearing block-and-ash flow ______________ >10 0

The Electron Mudflow underlies about 14 square

 

miles of the Puyallup River valley in the Puget Sound

57

OF LAHARS

lowland. In this area its thickness ranges from a few
inches to more than 26 feet; it is generally about 15
feet thick from McMillin southward to a point 2 miles
south of Orting. If an average thickness of 15 feet is
assumed for the area beyond the mountain front, the
deposit has a volume of a little more than 200 million
cubic yards. An additional amount of unknown area
and volume lies between the lowland and its source,
22 miles away, on the west flank of Mount Rainier.

The clay-mineral content of the Electron Mudflow
suggests an origin like that proposed for the other
clayey mudflows from Mount Rainier; thus, the Elec-
tron probably was caused by massive slides of moist,
hydrothermally altered rock. These slides may have
been triggered by an earthquake or by a volcanic
explosion.

The Electron Mudflow may have occurred at a time
when the volcano was dormant, for we have found no
deposits that indicate an eruption about 600 years ago.

LAHAR ASSEMBLAGE IN THE TAHOMA CREEK VALLEY

Four lahars have been recognized in the valley of
Tahoma Creek; three are older than pyroclastic layer
W, and one is younger. All are younger than layer Y.
The sequence is as follows:

Several small lahars and floods in 1967, 1968, and 1970.
Lahar about 440 years old.

Pyroclastic Isayer W (about 450 years old).

Two or more lahars of unknown age.

Round Pass Mudflow about 2,800 years old.
Pyroclastic layer Y (about 3,600 years old).

Coarse fluvial gravel.

Seldom can more than one post-Round Pass lahar
be recognized in a single outcrop, but streambank ex-
posures about 1 mile upvalley from the Tahoma Cneek
picnic area reveal an unusually complete section (meas-
ured section 9). In these outcrops, lithologically similar
lahars in the assemblage can readily be differentiated
because of the presence of interbeds of alluvium, vol-
canic ash, and forest duff. Especially striking in the
measured section is the reddish~brown zone at the top
of one lahar (unit 5). The association of this zone with
abundant carbonized wood indicates that its color is the
result of a forest fire. One can speculate that the forest
fire was caused by the hot, bomb-carrying block-and—
ash flow in the South Tahoma Creek valley abOut 2,500
years ago (p. 64). When some of the lahars are traced
along the outcrop beyond the limit of a lenticular inter-
bed, the contact between them disappears, and they are
so similar that they cannot be differentiated.

The youngest lahar in measured section 9 also under—
lies low terraces at Tahoma Creek picnic area and
veneers terraces between the picnic area and recent mo-

58 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON

Measured section 9

[North bank of Tahoma Creek 1% miles upstream from Tahoma Creek picnic area]

Thickness
(fl) (in)
9. Lahar: subangular to subrounded cobbles and boul-

ders as large as 2 ft in diameter in matrix of silt
and sand; no apparent sorting or stratification;
oxidized throughout to brownish yellow (IOYR
6/8) ; contains wood fragments and logs as large as
3 ft in diameter ______________________________ 6

8. Pyroclastic layer W: lenticular; as thick as ________

7. Duff ; contains bits of carbonized wood; stumps
rooted in unit 6 extend up through 7 and 8 and are
truncated by unit 9. Horizontally bedded, medium
to coarse fluvial sand 2—3 in. thick locally under-

$0

lies the dufl _________________________________ l—-6
6. Lahar: lithologically similar to unit 9; lenticular; as
thick as _____________________________________ 3 0

5. Lahar: lithologically similar to unit 9; uppermost
1—4 in. is reddish brown (5YR 5/4); at top is a
lenticular layer of carbonized wood 1—4 in. thick.

Lahar is lenticular; as thick as _________________ 3 0
4. Sand, fine to medium, and granule gravel, horizon-
tally bedded, lenticular; as thick as _____________ 1 0

3. Round Pass Mudflow: subangular to subrounded

cobbles and boulders in a purplish-gray matrix

of sand, silt, and clay; contains scattered wood

fragments throughout and in a concentration

near the base; sample of wood from log had an

age of 2,800 years (sample W—2114, table 4);

lenticular; as thick as _________________________ 20 0
2. Pyroclastic layer Y: lenticular; as thick as ____________ 8
1. Fluvial gravel: cobbles and boulders as large as

5 ft across in purplish-gray coarse sand matrix;

crudely stratified; thickness more than __________ 20 0

raines of South Tahoma Glacier. The lahar is exposed
south of the creek in the banks of a small tributary that
is crossed by the Wonderland Trail; the highest rem-
nants 0f the deposit in this vicinity are a little more than
200 feet higher than the valley floor of Tahoma Creek.
The oldest trees growing on the lahar are at least 435
years old. Inasmuch as the lahar is younger than pyro-
clastic layer W (fig. 29), it probably is about 440 years
old.

Grain-size analysis of a sample taken from the lower
2 feet of the lahar at measured section 9 showed a me-
dian diameter of 4.2 mm and a sorting coefficient of 8.72
(table 10, sample 9) ; the cumulative curve of its size
distribution is shown in figure 28. The sample contained
14 percent clay- and silt-sized material. The clay frac-
tion consisted of about three parts in 10 of clay minerals,
almost wholly montmorillonite, although traces of kao-
linite and a montmorillonite-chlorite mixed-layered clay
were also identified. The remainder of the clay fraction
consisted mostly of cristobalite, feldspar, and iron oxide
(table 11, sample 9).

Each of the lahars in the Tahoma Creek valley ori-
ginated in avalanches of clay and partly altered rock on

 

the west flank of Mount Rainier. These avalanches prob—
ably were caused by rockfalls in Sunset Amphitheater,
which moved southward across Tahoma Glacier and
into the head of the Tahoma Creek valley.

Lahars and floods occurred in the Tahoma Creek
valley in late August and September of 1967. Their
formation was heralded on August 29 by a short-lived
flood on Tahoma Creek. On the afternoon of the 29th,
probably between 1 and 1:30 pm, the Wonderland
Trail footbridge across the creek was washed out, and
shortly thereafter the stream rose between 1 and 2 feet
at Tahoma Creek picnic area (then a campground). At
the footbridge, the creek flows through a channel con-
stricted by a low bedrock cliff on the south and a ridge
of very large boulders on the north, and the channel is
only about 30 feet wide. The flood had a crest in this
channel about 15 feet above the normal stream level. On
the morning of August 30, the creek was still unusually
high and muddy.

The flood occurred on a clear day after a long spell
of warm dry weather and probably was caused by the
sudden release of a considerable volume of water that
had been impounded within South Tahoma Glacier.
According to David L. Fluharty (oral commun., Sep-
tember 1967), Fire Control Aid at the Gobblers Knob
Fire Lookout, the water that caused the flood seemed
to emerge at an ioefall on South Tahoma Glacier at an
altitude of about 7,500 feet. Gobblers Knob is about
11/; miles west of Tahoma Creek picnic area and is
2,500 feet higher in elevation (pl. 1.)

Two days after the flood, at about 8 :40 pm. on Au-
gust 31, Mr. Fluharty reported hearing a loud roar
coming from the Tahoma Creek valley. Park Ranger
James D. Erskine (oral commun., September 1967),
who arrived at the Tahoma Creek campground be-
tween 9 and 9 :30 pm, found that the part of the camp-
ground that is only 5 feet above the river was being
buried by a slurry of mud and boulders that resembled
wet concrete.3 By means of a powerful flashlight he
was able to see large boulders being moved by the
slurry along the main channel of Tahoma Creek, and
he also noted that many small stones were being
thrown, with a forward projection, above the surface
of the moving mass. Erskine reported that there was
a deafening roar, and the ground was vibrating very
strongly under his feet at the west edge of the camp-
ground. He left the area because of concern for his
safety; when he returned about an hour later, relatively
clear water was flowing in the main channel, and
shallow water was also flowing across the low part of
the campground. Richardson (1968) inferred that the

3The camtpground had been closed by the National Park Service
on August 3 because of an extremely high danger from forest fires.

DESCRIPTION

LAHARs 59

OF

 

FIGURE 29.——Lahar resting on top of fluvial cobble-and-boulder gravel at measured section 9 in the Tahoma Creek valley.
Separating the two deposits is %—% inch of duff and py‘roclastic layer W. Three more lahars occur in the stratigraphic
interval between layer W and the fluvial gravel in outcrops out of View to the right.

rapidly moving mass seen by Erskine was a “hyper—
concentrated flow” (p. 4), but because of a lack of data
on the sediment-to-water ratio, it will be referred to
here as a lahar.

The deposit in the campground area now is no more
than about 3 feet thick and consists of boulders as large
as 2 by 3 by 4 feet in a matrix of medium to coarse sand
(fig. 30). The lahar evidently terminated a short dis-
tance from the campground, for I could not identify
deposits formed by it on the valley floor at a point about
1 mile downstream.

At the Wonderland Trail footbridge over Tahoma
Creek, the lahar banked up on the south channel wall
to a maximum height of about 25 feet. Two hundred
yards downstream, on the outside of a bend, the lahar

 

banked up to a maximum height of 35 feet, whereas on

the inside of the bend on the opposite bank, 150 feet
away, it only reached a height of 15 feet. The lahar
left a coating of sand and granule—sized material on the
tops and sides of boulders and tree trunks, but this
material had been washed off by the creek up to a height
of 6 feet after the lahar passed downvalley.

The lahar of August 31 was caused by a flood similar
to, but evidently of greater volume than, the one of
August 29. The second flood issued from the glacier at
the icefall and carved a deep channel down the glacier’s
surface (fig. 31). Upon reaching the valley floor, the
floodwaters picked up large amounts of loose glacial
drift and alluvium and were transformed into a lahar.

The peak discharge of Tahoma Creek at the camp-
ground was estimated by Richardson (1968) to be about
24,000 cfs, of which perhaps half consisted of sediment.

60 POSTGLACIAL LAI-IAR-S FROM MOUNT RAINIER VOLCANO, WASHINGTON

 

FIGURE 30.——Bouldery deposit left in Tahoma Greek picnic area (then a campground) on evening of August 31, 1967. The
photograph was taken on the following day. The unvegetated part of the Tahoma Greek flood plain is faintly visible in the

background.

A flood crest was reached about 10: 30 p.m. at the high-
way bridge across Tahoma Creek, 4.3 miles below the
campground. From high—water marks left by the flood
crest, Richardson estimated a peak discharge there of
only about 100 cfs and inferred that the higher dis-
charge farther upstream had been dissipated by channel
storage and infiltration downstream from the camp-
ground.

Evidently the conditions that led to the lahar and
floods continued for some time, because a small lahar
moved downvalley as far as the campground on Sep-
tember 15, 1967 (N. A. Bishop, Chief Park Naturalist,
oral commun., 1968). Floods not associated with rain-
fall also moved down the valley from time to time dur-
ing the summer of 1968, and one again inundated Ta-
homa Creek picnic area on August 21, 1970.

 

The cause for large volumes of water to be released
suddenly and repeatedly by South Tahoma Glacier is
not known, but there is a possibility that the floods were
related to thermal activity of volcanic origin. On the
afternoon of September 23, 1967, Miss Marilyn Siehl
(oral commun., September 1967) of Tacoma, Wash,
was in the vicinity of the Wonderland Trail footbridge
across Tahoma Creek with a companion when she heard
what she described as a loud explosion from the direc—
tion of Mount Rainier. The explosion was followed
by a rumbling noise and a vibration of the ground un-
derfoot. She quickly moved to a vantage point from
which she could see the volcano and observed clouds of
what she believed to be brown dust and white water
vapor (“steam”) billowing from a west-facing clifl' at
the head of South Tahoma Glacier. Miss Siehl observed

DESCRIPTION OF LAHARS 61

 

FIGURE 31.—Aerial View of the debris-covered surface 0d! South Tahoma Glacier (at right). The channel down the middle of
the glacier was carved by floods in late August and early September 1967 that iseued from the icefall at the right center.
Gimle indicates the area in which a rock fall occurred in February 1969. The glacier is about 500 feet Wide near its
terminus. Photograph taken September 18, 1967, by Austin S. Post, US. Geological Survey.

62 POSTGLACIAL LAHAR‘S FROM MOUNT RAINIER VOLCANO, WASHINGTON

the clouds the rest of the afternoon and evening from
the point where the Wonderland Trail crosses Emerald
Ridge and noted that clouds were still being formed the
next morning when she left the area. She described
the weather both days as hot, dry, and clear.

Hikers and climbers reported seeing an unusual num-
ber of dust clouds rising from the area near the head of
South Tahoma Glacier earlier in the summer, and some
days these could also be seeen from Longmire. It seems
likely that the clouds were caused by recurring rock-
falls. Small rockfalls continued at the same general
locality at least until mid-October (N. A. Bishop, oral
commun., 1968) (fig. 32).

While at Longmire one evening in August 1968, D. C.
Thompson and Duane Nelson of the National Park
Service observed four or five clouds of what seemed to
be water vapor which rose at intervals above the cliffs
at the head of South Tahoma Glacier. They noted that
each of these white clouds was followed by a cloud which
was brown and apparently consisted of rock dust. An-
other observer witnessed a similar succession of clouds
at the same place a few days later (D. C. Thompson, oral
commun., 1969). The recurrence of clouds of what
seemed to be water vapor and of dust could have re-
sulted from a succession of small steam explosions which
caused repeated rockfalls.

On February 16, 1969, still another event occurred on
the west side of Mount Rainier which may bear on the
origin of the recent floods and lahars in the South
Tahoma Creek valley. Local newspapers in western
Washington reported that on the afternoon of that day
Mr. and Mrs. Oliver Edmonds of Seattle had seen
“steam and smoke” rising from the west side of the vol-
cano for about 45 minutes. Their viewpoint was in the
vicinity of Buckley, which is about 25 miles northwest of
Mount Rainier. On February 20, Jack H. Hyde of
Tacoma Community College, and Stewart Lowther of
the University of Puget Sound, flew over the west flank
of the volcano in an attempt to find the cause of the re-
ported “steam and smoke.” They found an area of newly
deposited rock debris lying on the snow-covered surface
of South Tahoma Glacier at an altitude of between 6,500
and 7,000 feet near the point in the icefall at which
floods emerged in late August 1967 (fig. 31).

The clouds observed on the west side of Mount Rainier
on February 16 may have been caused by water vapor
rising from a short-lived steam vent and by dust orig-
inating in a small rockfall that resulted from a steam
explosion. Thus, there has been a repetition of events in
the area of South Tahoma Glacier which may have been
caused by some kind of thermal phenomena. It seems
likely that the repeated floods in Tahoma Creek were

 

caused by abnormal melting of South Tahoma Glacier
around steam vents.

LAHAR ASSEMBLAGE IN THE SOUTH ’PUYALLUP RIVER
VALLEY

At least eight lahars are present in the valley of the
South Puyallup River, only one of which is older than
pyroclastic layer Y. The sequence is as follows:

Four lahars younger than layer W.

Pyroclasfic layer W (about 450 years old).

Lahar about 1,010 years old.

Bomb-bearing block-and-ash flow about 2,500 years old.
Lahar and fluvial deposits.

Round Pass Mudflow about 2,800 years old.

Pyroclastic layer Y (about 3,600 years old) .

The pre-Y lahar is dark brown and has a clayey plastic
matrix. It is a foot or less thick and was observed in a
roadcut at Round Pass. It occurs between layer Y and
the underlying Evans Creek till in an outcrop 100 feet
southwest of the Marine Memorial there, and the lahar
is texturally similar to the Round Pass Mudflow which
is above layer Y in the same exposure. Layer Y and the
lahar are separated by a mixed layer about 10 inches
thick, which probably is colluvium derived from both
units. Perhaps downslope movement of the pumice and
the lahar occurred after part of the pumice had been
deposited, but before the upper, clean pumice was laid
down. The pre—Y lahar was not recognized elsewhere,
and the significance of this single outcrop is not known.
However, it may record a lahar that was temporarily
at least 600 feet deep in the South Puyallup River
valley.

An inexplicable section that may be due partly to
local downslope creep or flowage is exposed in a out
along the West Side Road on the valley wall about 500
feet directly north of Round Pass. Here a very compact,
greenish-gray deposit 14 feet thick which texturally re-
sembles a mudflow is overlain by a purplish-gray mud-
flow 2 feet thick. The contact between the two units is
indistinct, and the units may be facies of the same de-
posit. Above them is a layer a few inches thick of dufl"
and carbonized wood mixed with gray sand. The dufl'
and sand layer is conformably overlain by a third mud-
flow which is lenticular and as much as 32 inches thick
and which has a layer of dufl' and wood fragments. The
upper dufl' layer contains a few pumice grains of layer
W. Conformably above the duflz‘ is a fourth mudflow, as
much as 5 feet thick, which is unconformably overlain
by still another layer of (1qu and carbonized wood
mixed with gray sand, and by a fifth mudflow, also 5
feet thick. Some of these deposits probably are of col-
luvial origin and were derived from other mudflows on
the side of the South Puyallup River valley, but it is not

DESCRIPTION OF LAI-IARS

 

FIGURE 32.—Straight slanting area of dirty snow, formed by rockfall debris below Point Success, heads at a clifi where a
steam vent was witnessed on September 23—24, 1967. The rockfall debris reaches down to the head of South Tahoma
Glacier. Photograph taken with a telephoto lens at Round Pass October 8, 1967, by N. A. Bishop, National Park Service.

known which deposits represent the original mudflows
in the valley and which ones might be colluvium.

Several lahars are exposed in a trail cut in the front
of a terrace at the Wonderland Trail footbridge across
the South Puyallup River (measured section 10). The
terrace is about 42 feet above river level. The basal lahar
of this section contains about 14 percent silt and clay.
Montmorillonite makes up about half of this size frac-
tion, and feldspar and cristobalite the other half (table
11, sample 5). The lahar that is designated as unit 3 in
the measured section contains about 14 percent silt and
clay (table 10, sample 4) about half of which consists of
montmorillonite; the remainder is mostly feldspar and
cristobalite (table 11, sample 4).

A lahar is exposed in a cutbank on the north side of
the river to a height of about 10 feet directly opposite

 

Measured section 10

[In south bank of the South Pnyallup River at Wonderland Trail bridge]
Thickneas
(fl) 0'71.)

5. Lahar: boulders as large as 6 ft in diameter in a
purplish-gray matrix of silt and sand ___________ 4—8 0
4. Fluvial deposit: sand and pebble-to-cobble gravel,

poorly sorted ________________________________ 5 0
3. Lahar: cobbles and boulders in a ye110wish—brown

sand, silt, and clay matrix _____________________ 7 6
2. Lahar: cobbles and boulders in a purplish-gray ma

trix of medium to coarse sand __________________ 6 0
1. Lahar: boulders and cobbles in a yellowish-brown

matrix of sand, silt, and clay __________________ >6 0

Covered interval of 10 feet to river level.

the measured section. It is very compact, yellowish
brown, and does not resemble any of the lahars in the
measured section nearby, all of Which probably are

64 POSTGLA‘CIAL LAHARS FROM MOUNT

younger. A log taken from the lahar in the north bank
was reported to have a radiocarbon age of 1,]101-250
years (W—1971). The lahar is overlain by a bouldery
lahar about 6 feet thick that is younger than any of the
deposits in the measured section. Bedrock crops out in
the riverbed a few hundred feet upstream from the meas-
ured section.

Size analysis of a sample of the 1,100-year-old lahar
indicated that it contains about 37 percent silt and clay
(table 10, sample 11). X-ray examination of this size
fraction indicated the presence of montmorillonite, cris—
tobalite, and feldspar (table 11, sample 11).

BLOCK-AND-ASH FLOW IN THE SOUTH PUYALLUP
RIVER VALLEY

One of the most interesting deposits on the west side
of Mount Rainier contains innumerable light-olive-
gray breadcrust bombs. The deposit resembles some
lahars in its coarse, unsorted texture and distribution,
but the presence of charcoal suggests that the deposit
was formed by a hot dry flow of rock debris. The re-
sults of a remanent magnetism study of rock fragments
in the deposit indicated emplacement of the debris at
a high temperature.

The block-and-ash flow deposit is well exposed in
cuts along the West Side Road in the South Puyallup
River valley (figs. 33, 34). From a distance it resembles
glacial drift, and a succession of sharp-crested ridges
cut through by the road could easily be mistaken for
lateral moraines. However, when each ridge is fol—
lowed a short distance upvalley, it is found to merge
with a terrace that represents the flattish top of the
deposit. The ridges are simply narrow interfluves be-
tween adjacent small valleys cut into the deposit. The
top of the block—and-ash flow is about 135 feet above
the river near the highway bridge and about 200 feet a
mile further upvalley.

Bombs in the deposit have black glassy interiors,
range in diameter from 6 inches to 4 feet, and have
breadcrusted exteriors (fig. 35). Most are highly vesicu-
lar, and many have large voids in their interiors, adja-
cent to which the rock is locally iridescent. Some bombs
are nearly spherical, but most are flat on one or more
sides. The bombs are very abundant and are randomly
distributed throughout a loose matrix of purplish-gray
sand and small angular to subangular fragments of
dark-gray to black glassy rock. Only a few bombs are
present in the northwestemmost outcrop of the block-
and-ash flow along West Side Road, and the deposit
there consists mostly of material smaller than 4 inches
in diameter.

Where the base of the block-and-ash flow is exposed.
it is flat and lies on a lenticular fluvial gravel a few feet

 

RAINIER VOLCANO, WASHINGTON

 

FIGURE 33,—Bomb—bearing block-and-ash flow deposit in out-
crop along the West Side Road near the South Puyallup
River overlies a coarse lahar that does not contain any
bombs. The contact is marked by a thin horizontal layer
of lighit’gray sand.

thick or on a very coarse lahar that lacks bombs and is
more than 15 feet thick.

The bomb-bearing deposit was not identified in the
South Puyallup River valley outside of the park, al-
though a lahar that forms a terrace 50 feet higher than
the river west of the park contains much scoriaceous
black andesite. This lahar, which was seen in cuts along
a logging road near the mouth of St. Andrews Creek,
may have been derived from the block-and-ash flow.

Grain-size distribution was determined on samples
of the coarse-grained and the fine-grained facies of
the block-and-ash flow; no bombs were included in
either sample. The sample of the coarse-grained facies
contained 6 percent silt and clay and had a median diam-
eter of 1.5 mm (table 10, sample 19) ; its sorting coef-
ficient was 6.63, and the cumulative curve of the size
distribution is polymodal (fig. 36). The sample of the
relatively fine-grained facies is texturally similar. It
contained 6 percent silt and clay and had a median diam-
eter of 1.1 mm (table 10, sample 20) ; its sorting index
was 4.64, and its cumulative curve also was polymodal.

A log completely converted to charcoal, about 6
inches in diameter and 4 feet long, was found 1 foot
above the base of the bomb-bearing deposit, resting on
and against bombs. The log had no bark and was sur-
rounded by a layer of White sand, silt, and clay a frac—
tion of an inch thick. The charcoal was relatively fragile,

DESCRIPTION

or LAHARS 65

 

FIGURE 3'4.—Outcrop of a relatively fine grained facies of the bomb-bearing block-and-ash flow along the West Side Road
near the South Puyallup River. A large breadcrust bomb is just left of the pick, but most other rock fragments are of

dense rock.

and probably could not have been transported without
being broken into small fragments. The wood probably
was fresh when incorporated by the block-and-ash flow
and was converted to charcoal by heat retained in the
adjacent bombs and rock fragments after the flow came
to rest. The radiocarbon age of a sample of the log was
2,350i250 years (W—1587), and the corrected age is
about 2,500 years (table 4) .

Samples oriented with respect to magnetic north
and the horizontal were taken from eight bombs and
five dense rock fragments in the deposit exposed along
the West Side Road. Examination of cores taken from
these samples indicated that the north-seeking poles in
all but four have northward dips of 50°—72° and that
their azimuths lie within 20° of magnetic north (fig.
37). This strong preferred orientation of thermorem-
anent magnetism suggests that most of the bombs and
many of the dense rock fragments were above the Curie

 

 

FIGURE 35.—Breadcrust bombs from the block-and-ash flow in
the South Puyallup River valley. The bomb on the right has
been broken open to show the highly vesicular interior.

66

POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

E E
E E E E E E
v—4 E E O O
O H . O
L” O. O "‘. O o o
g o o o v—1 .—. H
100
o /
w /
f, 90 ’
a /
Z /
so /
Z
<
E
,_ 7o /
I /
9 /
s 60 /
>- /
m /
o: 50 5
0
Lu /0)
z 50/
‘L 40
U)
L, z
9 /
i— 30 q /
E a”
n. (09
u. 20 (on
0
Lu
0
10
E- ///’
E ’z/
3 o
la-J A A A— _A
CLAY SILT SAND GRANULES PEBBLES COBBLES

FIGURE 36.—Oumu1ative curve of the size distribution of the relatively coarse facies of the bomb-bearing block—and-ash flow
in the South Puyallup River valley. So, sorting coeflicient.

point of the magnetite in the rock when the block-and-
ash flow came to rest. The few samples that do not have
this orientation presumably had cooled below the Curie
point during movement of the flow.

The Curie temperature of a sample of dense rock
from the block-and-ash flow was experimentally deter-
mined to be 517°C during both heating and cooling of
the sample (Richard R. Doell, unpub. commun., 1968).
The Curie temperature of a sample of a bre‘adcrust bomb
was found to be 485°C during heating and 332°C dur—
ing cooling. Both samples were taken from rocks in the
deposit whose remanent magnetism was oriented to-
ward magnetic north (fig. 37).

These Curie—point determinations indicate that rock
fragments were still several hundred degrees centigrade
above the boiling point of water after movement of the
rock debris had stopped. In View of these high tem-
peratures, it seems unlikely that any incorporated water
could have remained in the liquid state long enough to
have provided mobility to the debris. Thus, I conclude
that the debris was moving not as a lahar but as a block-
and-ash flow which owed its mobility to entrained hot
air, steam, and perhaps other gases.

The close similarity in age of the bomb—bearing block-
and-ash flow (about 2,500 years) and pyroclastic layer

 

C (between 2,150 and 2,500 years) suggests that both
originated during the same episode of volcanism.

LAHARS IN THE NORTH PUYALLUP RIVER VALLEY

Three lahars were recognized in the North Puyallup
River valley, the oldest of which is probably correlative
with the Round Pass Mudflow. In exposures near the
north end of the West Side Road this lahar consists
of a mixture of angular and subangular rock frag-
ments as large as 8 feet in maximum dimension in a
plastic matrix of yellowish-brown silty and clayey sand
Along the Wonderland Trail on the south side of the
North Puyallup River valley, the Round Pass Mudflow
is present up to an altitude of about 3,920 feet—a height
of about 400 feet above river level.

Younger lahars form two terraces on the north side
of the valley downstream from the end of the West Side
Road, 55 and 90 feet higher than the North Puyallup
River. A boulder about 20 feet in diameter was seen
near river level in the lahar that makes up the lower
terrace, and living trees 3—4 feet in diameter and as
much as 400 years old are growing on the terrace. Bould-
ers as large as 8 feet across lie on the upper terrace, and
although no trees were cored, the largest are of com—
parable diameter with, or a little larger than, the largest

DESCRIPTION or LAHARS 67

 

S

FIGURE 37.—Point diagram of azimuth and dip of north—seek—
ing poles in dense rock fragments (squares) and bombs
(circles) from block-and-ash flow in the South Puyallup
River valley. A 1-inch core from each sample was split into
two pieces for determination of the direction of rem-anent
magnetism; open circles or squares tied together represent
the results of determination on the two pieces, and the solid
circles and squares represent determinations on two pieces
that coincided or nearly coincided in azimuth and dip. The
two samples on which Curie temperatures were determined
are indicated by arrows.

trees on the lower terrace. An exposure of the material
making up the upper terrace was not seen, but the size
of boulders on the terrace suggests that it is underlain
by a lahar. Pyroclastic deposits were seen on neither
terrace.

LAHARS IN THE MOWICH RIVER VALLEY

Inside Mount Rainier National Park the South
Mowich River valley contains at least one lahar that
is older than pyroclastic layer Y, one younger than
layer Y but older than layer W, and one that is younger
than layer W. The pre-Y lahar crops out in the stream-
bank on the north side of the river about a mile up-
stream from its mouth. There it forms a terrace whose
top is about 30 feet above the adjacent flood plain.
Farther upstream, two post-Y lahars can be seen in scat-
tered outcrops in the face of a terrace whose height
above the flood plain ranges from a few feet to as much
as 25 feet. This difference in height seems to be due to

 

variations in slope of the flood-plain surface. The
post-W lahar at the surface of the terrace is yellow to
yellowish brown and contains abundant angular to sub-
angular fragments of altered rock. It ranges in thick-
ness from 3 to at least 15 feet and closely resembles some
post-Y lahars in the Puyallup River and South Tahoma
Creek valleys.

The post-W lahar was seen as far downstream as a
point about 1.5 miles above the mouth of the South
Mowich River. In some outcrops the lahar is on top
of fluvial sand and gravel, and in others it overlies a
coarse gray lahar which contains pumice reworked from
layer Y and which includes angular and subangular
boulders as large as 4 feet in diameter. The maximum
thickness of the gray lahar is at least 20 feet.

One or more lahars that are older than pyroclastic
layer Y are present in the Mowich River valley down-
stream from the park. In the SW14 sec. 30, T. 17 N., R.
7 E., a lahar that contains boulders as large as 5 feet
forms a terrace that is about 25 feet above the Mowich
River flood plain. Farther upstream, in the Sl/z sec. 29,
outcrops reveal a lahar that consists of angular and sub-
angular rock fragments as large as 3 feet in a matrix
of purplish-gray silt and sand. This deposit extends to a
height of at least 40 feet above the flood plain. At one
place, in the SW1/2 sec. 29, a compact lahar that con-
tains boulders as large as 7 feet may be a facies of the
lahars previously described or it may be an entirely dif-
ferent deposit. The stratigraphic relation of these lahars
to those of the Puyallup River valley is not known.

LAHAR IN THE CARBON RIVER VALLEY

The only lahar observed in the Carbon River valley
is on the south side of the valley opposite Chenuis Falls.
It is as much as 10 feet thick and consists of angular
and subangular rock fragments as large as 6 feet across
in a matrix of purplish-gray medium to coarse sand.
The lahar lies on top of bedrock and is overlain by
pyroclastic layer Y.

The scarcity of lahars in this valley may be due in
part to the configuration of the volcano above the head
of Carbon Glacier. At the top of Willis Wall a ridge
extends eastward from Liberty Cap to Russell Clifi. I
believe this ridge to be the north rim of a depression in
the volcano that was left when massive slides to the
northeast created the Osceola Mudflow. Because of the
ridge, a flood originating at or near the summit of the
volcano would be diverted away from the head of Car-
bon Glacier. This ridge is the largest remnant of the old
crater rim, and its preservation may be due to a lack of
hydrothermal alteration or to less intense alteration in
these rocks than in those elsewhere on the volcano.

68 POSTGLA‘CIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON

LAHARS IN THE MUDDY FORK OF THE COWLITZ RIVER
AND OHANAPECOSH RIVER VALLEYS

A single lahar was found in the Muddy Fork valley
above Canyon Bridge (pl. 1), but none downstream
from it. About half a mile north of the highway bridge
over the Muddy Fork, terraces on both sides of the val-
ley are 50 or 60 feet higher than the flood plain. The
terrace on the west side is formed by a coarse fluvial
deposit of sand and pebble-to-boulder gravel in which
there are boulders as large as 5 feet in diameter. The
terrace deposit on the east side of the valley is capped
by a lahar 13 feet thick. It is made up of angular to
subrounded rock fragments as much as 5 feet in di—
ameter in a dark-yellowish-brown matrix of silt and
sand. X—ray analysis of the clay-sized fraction of the
lahar indicated the presence of feldspar, cristobalite,
and glass, and a lack of clay minerals. The only pyro-
clastic deposit on top of it is layer W, and it seems
likely that the lahar as well as the underlying fluvial
deposits are the same age as lahar assemblage C in the
Nisqually River valley and that they originated in the
same manner (p. 43).

Lahars were noted in the Ohanapecosh River valley
at Indian Bar and near the mouth of Chinook Creek.
The part of the valley that lies between these two places
was not examined because accessibility is relatively diffi-
cult. Streambank outcrops in the meadow at Indian Bar
reveal a lahar that consists of subangular to subrounded
rock fragments in a purplish-gray matrix of silty sand.
The lahar is more than 5 feet thick and extends beneath
the base of the outcrops. It is overlain by a fluvial sand
and pebble-to-boulder gravel deposit 2—3 feet thick and
by layer 0 and younger pyroclastic deposits. A short
distance upstream from the mouth of Chinook Creek a
compact lahar is exposed where the East Side Trail
crosses the Ohanapecosh River. The lahar is between 5
and 10 feet thick, and it overlies sand and pebble—to-
boulder gravel about 5 feet thick that is mantled with
pyroclastic layers Y and W.

THE ASSOCIATION OF LAHARS WITH
VOLCANISM

The possible relation of lahars at Mount Rainier to
volcanism was of paramount concern in this study. The
possibility of lahar formation would undoubtedly be in-
creased by the phenomena that are typically associated
with eruptions. There are a number of indications, or
lines of indirect evidence, that link the formation of
some lahars to contemporary volcanism. The presence of
fresh volcanic bombs in a lahar suggests that the lahar
was caused in some way by an eruption. The eruption
of pyroclastic material at the same time a lahar is
formed carries a strong implication that the lahar was

 

caused by volcanism. The occurrence of lahars within a
general period during which pyroclastic deposits were
erupted is another, but less satisfactory, basis for infer-
ring a causal relation. Still another line of reasoning
to support the association of lahar formation with vol-
canism is the presence of complex assemblages of fluvial
deposits and lahars whose aggradation is best explained
by repeated floods from the volcano. These floods, in
turn, are most readily explained by repeated eruptions
of hot pyroclastic debris or lava onto snow and ice.
Finally, because of their size and composition, some
lahars could only have been caused by tremendous slides
from the volcano. The most probable causes of these
slides are volcanic explosions, earthquakes associated
with volcanism, and possibly lateral spreading or tilting
of parts of the volcano caused by the rise of magma;
however, nonvolcanic earthquakes cannot be ruled out
as possible triggering mechanisms.

The lahars discussed below seem to have been trig-
gered by eruptions or to have occurred during known
periods of eruptive activity; lahars for which there is
no independent evidence of contemporaneous volcanism
are not mentioned here.

Evidence of the age of lahars and eruptions before
6,600 years ago is too fragmentary to relate them with
confidence. The oldest eruptions recorded by pyroclastic
deposits are those that produced layer R more than 8,750
years ago (tables 5, 6). Lahars older than layer 0 have
been found in the valleys of Van Trump Creek and
the Nisqually River, but their age with respect to layer
R is not known.

The Paradise lahar is between 5,800 and 6,600 years
old and thus was formed sometime during an interval
of repeated pumice eruptions (table 6). Pyroclastic
layer N, formed during this interval, is younger than
the Paradise lahar, but any one of the eruptions that
produced layers A, L, D, or S could have triggered the
avalanche that caused the lahar. The Greenwater lahar,
also formed by avalanches of rock debris, may have been
caused by the same volanic explosion that produced
pyroclastic layer S. (p. 22). Most of the pre-Osceola
lahar assemblage in the White River valley probably
was formed after the Greenwater lahar occurred. The
two bomb-bearing lahars in the assemblage evidently
were caused by eruptions of hot rock debris and bombs.

A detailed study of airlaid deposits contemporaneous
with the Osceola Mudflow indicates that an eruption led
to the formation of the Osceola (p. 30).

The last major episode of volcanic activity began with
the formation of the block—and-ash flow in the South
Puyallup River valley about 2,500 years ago. The evi-
dence that it was hot clearly shows that the flow was
associated with an eruption. A lahar older than pyro-

HAZARDS FROM FUTURE LAHARS ‘ 69

elastic layer C in the White River valley may have been
formed at about the same time. Pyroclastic layer C was
erupted next in sequence, after which the summit lava
cone of the volcano was built and accompanied by ag-
gradation of lahar assemblages in the valleys of the
White River, Nisqually River, and Kautz Creek. Lahars
probably also moved down the Muddy Fork, West
Fork, and Van Trump Creek valleys at the same time.

This attempt to assign individual lahars or lahar
assemblages to certain eruptive episodes leads to the
speculation that there is a genetic relation between kinds
of volcanic activity and certain types of lahars. Lahars
at Mount Rainier that lack a considerable content of
clay and clay minerals probably resulted from eruptions
that produced large quantities of blocks and lithic ash
or from eruptions during which much ice and snow
was melted by hot pyroclastic debris or lava flows.
Lahars that contain a significant amount of clay (per
haps 5 percent or more) seem to be derived from old,
hydrothermally altered parts of the volcano, and some
may have been started by‘ phreatic explosions. Such ex-
plosions may not necessarily have been accompanied by
the eruption of new magma.

HAZARDS FROM FUTURE LAHARS

A recent evaluation of volcanic hazards at Mount
Rainier (Crandell and Mullineaux, 1967) was based on
an examination of the events that have occurred there
during the last 10,000 years, as inferred from a study
of the surficial deposits of the park. We concluded that
if future phenomena of the same type and magnitude
occur with the same frequency as in the past, the direct
danger from lahars greatly exceeds that from lava flows
and pumice eruptions. Lahars are especially dangerous
because of their possible very large size and ability to
move long distances, and also the speed with which they
can move. In areas downstream from the lower slopes
of the volcano, their effects would be mostly confined to
valley floors and the lower parts of valley walls.

The scale of the hazard presented by larhars might be
illustrated by a brief review of their number and fre-
quency in Holocene time. The deposits of at least 55 dif-
ferent lahars, representing a vast range “in size, have
been recognized in the various valleys that head on
Mount Rainier (table 6), and many more probably oc-
curred whose deposits were not seen or recognized dur-
ing this study, or had been removed by erosion. Some
areas have been affected by lahars more often than
others; the valleys of the White and N isqually Rivers
and Tahoma Creek have been devastated frequently
during certain intervals of postglacial time. Large
lahars have moved down the White River valley at least
10 times within the last 6,600 years; thus, the average

 

frequency of large lahars in that valley has been at least
one per 660 years. In the Nisqually River valley the
average frequency indicated by 12 lahars in the last 10,-
000 years is at least one per 830 years, and in the Ta-
homa Creek valley, four lahars in about the last 3,300
years indicate an average frequency of at least one per
825 years. Even though they are roughly similar, these
indicated minimium average frequencies do not signify
repetition of lahars at regularly spaced intervals. Dur-
ing a long interval when the volcano is dormant, few,
if any, large lahars might occur. However, conditions
that lead to lahar formation are substantially increased
during relatively brief intervals of volcanic activity.
It has been noted elsewhere in this report that at least
seven lahars occurred in the Nisqually River valley dur-
ing a relatively brief interval. In fact, lahars caused in
various ways could occur again and again in more than
one valley within a space of only a few weeks, as they
did during the eruption of Mount Pelée in May and
June of 1902 (Hovey, 1902, p. 346—347) and during the
eruption of Irazu Volcano (Waldron, 1967, p. I l—I 17).

In regard to the speed of lahars, Kemmerling (1921)
noted that during the 1919 eruption of Kelut in Java,
the passage of lahars down valleys lasted only 45 min-
utes, and some lahars had an average speed of 45 miles
per hour. A velocity of about 56 miles per hour was
reported by Iida (1938, p. 681) for a mudflow at Mount
Bandai in Japan in 1938. Waldron (1967, p. I 24) found
Velocities of as much as about 22 miles per hour in debris
flows that resulted indirectly from eruptions of Irazu
Volcano in Costa Rica. He reported that the flows hav—
ing the highest velocities had sediment concentrations
between 60 and 74 percent. These were “hyperconcen-
trated flows,” according to the terminology of Beverage
and Culbertson (1964; this report, p. 4) .

One conclusion reached from the present study is that
the largest lahars of postglacial time originated in mas-
sive slides and avalanches of hydrothermally altered
rock. Presumably, therefore, future slides and lahars
may originate in those parts of the volcano that have
been affected by hydrothermal alteration. The only large
outcrops of altered rock known today are at the head of
Sunset Amphitheater, but smaller areas are also present
high on the west side of the volcano at the heads of
North and South Mowich Glaciers.

Although the visible outcrop area of altered rock is
small today, there may be large masses of such rock
tens or hundreds of feet below the surface at many
places within the volcano. Because of the possibility
that such zones exist at depth, we cannot be certain that
a massive rock slide comparable to those that produced
the Greenwater and Paradise lahars, or the Osceola,
Round Pass, and Electron Mudflows, will not occur

70 POSTGLACIAL LAHARS FROM MOUNT RAINIER VOLCANO, WASHINGTON

again, triggered perhaps by a severe earthquake or by
a volcanic explosion.

The chance that a destructive lahar will affect a given
segment of a valley decreases with distance from the
volcano. Thus, on the basis of the events of the last 10,-
000 years, a devastating lahar might cover the floor of
the Nisqually River valley within or close to the park on
an average of at least once in 800 years, and in the White
River valley at least once in 600 years. In contrast, be-
yond the Cascade mountain front, the White River val-
ley has been afl’ected by only one lahar within the last
10,000 years, and the Nisqually River valley apparently
by none.

Ways of reducing the hazard of future lahars include
the evacuation of valley floors and zoning the valley
floors to prevent construction of permanent residences
and other installations within areas that are relatively
hazardous. In addition, existing dams could be utilized
to trap all or part of a lahar and prevent it from reach-
ing populous areas.

One of the greatest difficulties to overcome in the
evacuation of critical areas probably will be the in-
ability of people to comprehend the nature of the threat
facing them in the event of a future eruption. For this
reason, extensive publicity should be given, at the first
sign of renewed volcanism, of the possible consequences
of an eruption. In this way the residents of areas that
might be affected by lahars and floods could be fore-
warned that rapid evacuation might become necessary.

To be most effective, evacuation of people from
valley floors would require foreknowledge of which
valley or valleys might be affected. This information
might be available if an eruptive vent appeared low on
a flank of the volcano, because lahars would then most
likely be restricted to the drainage basin heading on
that slope of the cone. However, an eruption at the pres-
ent summit crater could affect valleys on almost any side
of the volcano. Furthermore, inasmuch as the subsur—
face distribution of possible large masses of hydro-
thermally altered rock is not known, it should be as-
sumed that a large clayey lahar also could originate on
any side of the volcano.

The valley floors adjacent to the park that have been
inundated most frequently by lahars are not yet densely
populated. From the standpoint of the lahar hazard
alone it seems appropriate to recommend that permanent
residences should not be constructed on the floor of the
Nisqually River valley, downstream from the park, on
surfaces that are less than 20 feet above river level.
Construction is also inadvisable on the floors of the
White River and West Fork valleys between the park
and Greenwater (pl. 3). In addition, new campgrounds
and other recreational facilities within and adjacent to

 

the park could be constructed, and existing facilities re-
located, in areas of low or nonexistent hazards. A re-
lated consideration should be the design and location of
new bridges and highways to accommodate or avoid
floods and lahars of small to moderate dimensions, so
that routes will remain usable for safe evacuation if an
eruption should result in these phenomena.

Within the mountains, the topographic setting is es-
pecially significant in areas that are on or closely ad-
jacent to valley floors, for the degree of hazard decreases
with greater height. Sites less than 10 feet above present
rivers are susceptible to inundation by floods and lahars
of modest size, whatever their origin. Sites 30 feet or
higher above the rivers probably would be affected only
by major floods or lahars resulting from volcanism of
some kind. In the Nisqually River valley west of the
park, for example, the terrace along the north side of
the river for about 4 miles west of Ashford is less haz-
ardous with respect to lahars and floods because of its
height than is the valley floor farther west. The cross-
section area and configuration of the valley below and
adjacent to a terrace also is important because it will
affect the capacity of that part of the valley to accommo—
date a flood or lahar without inundating the terrace.

Large dams in valleys downstream from Mount
Rainier could trap all or part of a lahar if reservoirs
behind the dams were empty. Such a trap now exists in
the White River valley in the form of Mud Mountain
Dam, which would substantially reduce the hazard of a
lahar no larger than the Electron Mudflow. The flood-
control reservoir created by the dam is designed to store
106,000 acre-feet of water, which is the equivalent of
about 170 million cubic yards and roughly comparable
to the inferred volume of the Electron Mudflow in the
Puget Sound lowland. The dam is an earthfill structure
that has an impervious core made up chiefly of material
derived from the Osceola Mudflow. If the reservoir
could not accommodate the entire volume of a lahar,
mud would initially discharge through the concrete
spillway and then might overtop the dam itself. Spill-
over would proceed down the White River valley, but
probably would not be a threat unless it were deep
enough to overtop the valley wall near Buckley or of
sufficient volume to reach the Auburn urban area.

Similarly, Alder Dam could trap a lahar in the Nis-
qually River valley, but only if the reservoir had previ-
ously been drained. Otherwise a lahar would displace
the lake very rapidly and would cause it to spill over the
concrete-arch dam and flood the valley below. The ca-
pacity of the reservoir is 232,000 acre feet, or about 375
million cubic yards. The only areas of relatively dense
population along the Nisqually River between Alder
Dam and Puget Sound are at the small communities of

REFERENCES

Yelm and McKenna. Yelm is situated 50—7 5 feet higher
than the river, but parts of McKenna are close to the
flood plain.

Lahars were not recognized in the Cowlitz River val—
ley outside the park during this study, although the
valley has been inundated by floods within historic time.
A future lahar that would have the volume of the Elec-
tron Mudflow would bury the valley floor at Packwood
and perhaps also at Randle. A lahar no larger than the
Electron might not extend much beyond Randle be-
cause of the loss of volume and velocity as it spread
across the broad, gently sloping floor of the valley west
of Packwood.

I recommend that responsible authorities establish
procedures to be followed if MOunt Rainier should
again become active. These procedures should include
the following:

1. The development and installation of a detection sys-
tem in certain critical valleys, whereby a large flood
or lahar could be detected at an early stage.

2. The development of a warning system, whereby res-
idents of valley floors could be warned, either
night or day, of a need for immediate evacuation.

3. The establishment of an evacuation plan for areas
likely to be threatened by floods or lahars.

4. A plan for lowering the level of Alder Reservoir in
the event of a major eruption.

5. Plans for restricting travel in hazardous areas.

There is a strong likelihood that a lahar could travel
with such speed that a warning system for individual
lahars would provide little benefit except for areas many
miles from the volcano. For the purpose of planning,
it should be assumed that a lahar might travel at a speed
of as much as 50 miles per hour. For this reason, espe-
cially, valley floors within a radius of at least 25 miles
from the center of the volcano should be evacuated as
soon as possible after an eruption actually began.

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Meniailov, A. A., 1939, The eruption of Avacha in 1938: Kam-
chatka Volcanol. Sta. Bull. 6, p. 21—27.

Morimoto, Ryohei, and Ossaka, Joyo, 1964, Low temperature
mud-explosion of Mt. Yaké, Prefs. Nagano—Gifu, central
Japan, on 17th June 1962 as an example of endogenous
katamorphism of volcanic rock at the destructive stage of
the volcano [abs] : Bull. Volcanol., v. 27, p. 49—50.

Mullineaux, D. R., 1961, Geology of the Benton, Auburn, and
Black Diamond quadrangles, Washington: U.S. Geol. Sur-
vey open-file report, 202 p.

1965a, Geologic map of the Auburn quadrangle, King

and Pierce Counties, Washington: U.S. Geol. Survey Geol.

Quad. Map GQ—406.

1965b, Geologic map of the Black Diamond quadrangle,
King County, Washington: U.S. Geol. Survey Geol. Quad.
Map GQ—407.

Mullineaux, D. R., and Crandell, D. R., 1962, Recent lahars from
Mount St. Helens, Washington: Geol. Soc. America Bull.,
v. 73, no. 7, p. 855—869.

Mullineaux, D. R., Gard, L. M., Jr., and Crandell, D. R., 1959,
Continental sediments of Miocene age in Puget Sound low-
land, Washington: Am. Assoc. Petroleum Geologists Bull.,
v. 43, no. 3, p. 688—696.

 

 

 

Murai, Isamu, 1963, A brief note on the eruption of the Tok-
achi-dake volcano of June 29 and 30, 1962: Tokyo Univ.
Earthquake Research Inst. Bull., v. 41, pt. 1, p. 185—208.

Cinouye, Y., 1917, A few interesting phenomena on the eruption
of Usu: J our. Geology, v. 25, no. 3, p. 258-288.

O’Shea, B. E, 1954, Ruaphu and the Tangiwai disaster: New
Zealand Jour. Sci. and Technology, sec. B, v. 36, no. 2, p.
174—189.

Perrett, F. A., 1924, The Vesuvius eruption of 1906: Carnegie
Inst. Washington Pub. 399, 151 p.

Porter, S. C., and Denton, G. H., 1967, Chronology of Neoglacia-
tion in the North American Cordillera: Am. Jour. Sci, v.
265, no. 3, p. 177—210.

Powers, H. A., and Wilcox, R. E., 1964, Volcanic ash from
Mount Mazama (Crater Lake) and from Glacier Peak: Sci-
ence, v. 144, no. 3624, p. 1334—1336.

Richardson, Donald, 1968, Glacier outburst floods in the Pa-
cific Northwest in Geological Survey research 1968: U.S.
Geol. Survey Prof. Paper 600—D, p. D79—D86.

Russell, I. C., 1898, Glaciers of Mount Rainier, with a paper on
the rocks of Mount Rainier, by G. 0. Smith: U.S. Geol.
Survey 18th Ann. Rept., pt. 2, p. 349-423.

Sales, R. H., and Meyer, Charles, 1948, Wall rock alteration at
Butte, Montana: Am. Inst. Mining Metall. Engineers Trans,
v. 178, p. 9—35.

Sapper, Karl, and Termer, Franz, 1930, Der Ausbruch des
Vulkans Santa Maria in Guatemala vom 24 November
1929 : Zeitschr. Vulkanologie, v. 13, no. 2, p. 73—101.

Schmincke, H. U., 1967, Graded lahars in the type sections of the
Ellensburg Formation, south-central Washington: J our. Sed.
Petrology, v. 37, no. 2, p. 438—448.

Schumm, S. A., 1965, Quaternary paleohydrology, m Wright,
H. E., Jr., and Frey, D. G., eds., The Quaternary of the
United States: Princeton, Princeton Univ. Press, p. 783—794.

Sekiya, S., and Kikuchi, Y., 1889, The eruption of Bandai-san:
Imp. Univ. Japan Coll. Sci. Jour., v. 3, pt. 2, p. 91—172.

Sharp, R. P., and Nobles, L. H., 1953, Mudflow of 1941 at Wright-
wood, Southern California: Geol. Soc. America Bull., v. 64,
no. 5, p. 547—560.

Sigafoos, R. S., and Hendricks, E. L., 1961, Botanical evidence
of the modern history of Nisqually Glacier, Washington:
U.S. Geol. Survey Prof. Paper 387—A, 20 p.

Sigvaldason, G. E., and White, D. E, 1961, Hydrothermal altera-
tion of rocks in two drill holes at Steamboat Springs,
Washoe County, Nevada in Short papers in the geologic and
hydrologic sciences: U.S. Geol. Survey Prof. Paper 424—D,
p. D116—D122‘.

1962, Hydrothermal alteration in drill holes GS—5 and
GS—7, Steamboat Springs, Nevada, in Short papers in the
geologic and hydrologic sciences: U.S. Geol. Survey Prof.
Paper 450—D, p. D113—D117.

Simons, D. B., Richardson, E. V., and Haushild, W. L., 1963, Some
effects of fine sediment on flow phenomena: U.S.. Geol. Sur-
vey Water-Supply Paper 1498—G, p. G1—G47.

Tada, Fumio, and Tsuya, Hiromichi, 1927, The eruption of the
Tokachidake Volcano, Hokkaido, on May 24, 1926: Tokyo
Univ. Earthquake Research Inst. Bull., v. 2, p. 49—84
(English summ, p. 49—50).

Trimble, D. E., 1963, Geology of Portland, Oregon, and adjacent
areas: U.S. Geol. Survey Bull. 1119, 119 p.

Varnes, D. J ., 1958, Landslide types and processes, Chapt. 3 of
Eckel, E. B., ed., Landslides and engineering practice: Natl.
Research Council, Highway Research Board Spec. Rept. 29,
p. 20—47.

 

REFERENCES CITED 73

Waldron, H. H., 1967, Debris flow and erosion control problems Park, California: California Univ. Dept. Geo]. Sci. Brull.,
caused by the ash eruptions of Irazfi Volcanic, Costa Rica: v. 21, no. 8, p. 195—385.
U.S. Geol. Survey Bull. 1241—1, p. I 1—1 37. Willis, Bailey, 1898, Drift phenomena of Puget Sound: Geol. Soc.

Williams, Howe], 1932, Geology of the Lassen Volcanic National America Bull., v. 9, p. 111—162.

 

  
 
 

Page
Age of lahars ................................. 11
Age of Mount Rainier Volcano .............. 10
Alder Dam ____________________
Alder Reservoir.
Alderton Interglaciation ...................... 10
Alta Vista .............

Avalanche deposits_.

Block-and—ash flows __________________ 5, 11, 4a, 57, 64
Bombs ______ - 5, 11, 23, 43, 57, 64,68

  
 

  
 
  
   
 
 
 
 
  
 
 

Buck Creek ________________ . ... 18, 19
Burroughs Mountain Stade ................... 10, 42
Carbon Glacier ............................... 67
Carbon River ........... 2,26, 43, 56
Carbon River valley, lahars. . . 67
Catt Creek .............. _ 44
Chinook Creek.. _ 68
Christine Falls .......... . 33
Clay, origin in some lahars. _ 12
Climate ................... . 3

Columbia Crest.
Comet Creek-.

  

 

Cowlitz River ........... _ 2, 71
Cowlitz River valley, lahars. _ 68
Crystal Creek ........... _ 23
Cushman Crest .............................. 37
Dating of lahars .............................. 11
Description of lahars ......................... 17
Echo Rock ................................... 11
Electron Mudflow .................. 4, 8, 12, 66, 70, 71
Emerald Ridge ............................... 54, 62
Emmons Glacier... __ 22, 23, 24, 42, 43
Evans Creek Drift ............... 13,16,24, 36, 38, 50
Evans Creek till ........................... 34, 37, 62
Everson Interstade ........................... 10, 37
Features of lahars ............................ 3
Fluvial deposits. .. . 4, 5, 23, 32, 39, 40, 44, 45, 48, 68
Fraser Glaciation _____________________________ 11, 13
Fryingpan Creek ................. 20,22, 23, 28, 30, 31
Fumaroles .................................... 16
Garda Stade .................................. 10, 43
Geographic setting, volcano and lahars ....... 2
Gibraltar Rock ............................... 30
Glacier Basin ........................... 10, 13, 24, 29
Goat Island Mountain ........................ 22
Gobblers Knob ............................... 58
Green River Valley .......................... 26
Greenwater lahar .................... 17, 18, 24, 68, 69
Hazards from lahars .......................... 69
Huckleberry Creek ________________________ 18, 20, 21
Hydrothermal alteration ______ 16, 22, 29, 37, 43, 57, 69
Indian Bar ................................... 68
Inter Fork .............................. 13, 24, 25, 31
Introduction .................................

 

INDEX

[Italic page numbers indicate major references]

Page
Kautz Creek .............................. 33,44, 50
Kautz Creek valley, lahar assemblage. _.. 45

  

Kautz Glacier ..................... 43, 46, 48
Klapatche Ridge ............................. 53
Lake George ................................. 50
LeDoux Creek .................. . 54

 
 
 
 

 
 
 
  

 

 

 

Liberty Cap ......................... . 30,67
Lithology 01 Mount Rainier Volcano. . 10
Little Tahoma Peak .......................... 5, 22
Marmot Creek ................................ 13
Mazama Ridge ............................... 33, 36
Mineral Creek ................................ 44
Mist Park .................................... 13
Mounds on lahars ............................. 18, 19
Mowich River ....................... 43, 53, 54, 55,56
Mowich River valley, lahars .................. 67
Mud Mountain ............................... 25, 26
Mud Mountain Dam ...................... 25, 29, 70
Muddy Fork ................................. 69
Narada Falls ................................. 33
Nisqually Glacier ....................... 4, 33, 43, 44
Nisqually River .......... 2, 36, 37, 38, 39, 47, 52, 69, 70

Nisqually River valley, lahar assemblage,
origin ............................. 41
lahars .................................... 44
North Mowich Glacier ........................ 69
North Puyallup River ....................... 2, 52
North Puyallup River valley, lahars ......... 49, 66'
Observation Rock ............................ 11
Ohanapecosh River .......................... 43
Ohanapeoosh River valley, lahars ............ 68
1,000-year—old lahar ........................... 66
Origin of lahars ............................... 8
Osceola Mudflow ............................. 7,
8,12, 13, 17, 19, 21, 22, 23, 24, 30,32, 35, 43,

67, 68, 70

Panorama Point ........................... 33, 35, 36
Paradise lahar ..................... 7, .33, 39 40, 55, 69
Paradise Park .............................. 3, 33, 34

older lahar ...............................
Paradise River ............................... 36, 40
Pearl Falls ................................... 45
Phi quartile deviation ________________________ 4
Phi standard deviation. . _ . 4
Point Success ............... 30
Post-Osceola lahar assemblage ....... 30
Pre~0sceoia lahar assemblage ................. 2:
Puget Sound lowland _______ 1, 4, 8, 10, 17, 25,43, 70
Pumice deposits ..................... 12, 22,45, 46, 62
Puyallup River ...................... 2, 26, 54, 56, 67
Pyroclastic deposits. 3, 11, 12, 22, 45, 68
Pyroclastic layer A ___________________________ 40, 68
C ......................... 12, 31, 32, 40, 43, 66, 68
._ 33. 35, 68
F ...................................... 13, 25,30

L _________________________________________

 

Page
Pyroclastic layer N ........................... 68
0 ................ 12, 13,21, 24,33, 37, 38, 39, 40, 68
R ________________________________________ 68
S ......................................... 22, 68
W _ _ 12, 31, 32, 38, 40, 41, 43, 45, 46, 49, 57, 58, 62, 67, 68
Y ........................................ 12,

31, 32. 33,38, 39, 40, 41, 44, 45, 46, 49 ,50,
52, 53, 57, 62, 67, 68

  

   

 

 

 

 

 
  

 
 

 
 

 
 
 
  

Rampart Ridge ______________________________ 36
Reflection Lakes ............................. 33, 34
Remanent magnetism ................... 5, 23, 64, 66
Ricksecker Point ........ _._. 33, 35, 36
Round Pass Mudfiow ............ 49, 55, 57, 62, 66, 69
Russell Cliff __________________________________ 30, 67
St. Andrews Creek ........................... 53,57
St. Andrews Park ............................ 54
Silver Creek _____________ 18
Size-distribution analyses__.. 6, 26,32, 35, 37, 54, 58, 64
Sluiskin Falls ................................ 33,36
Sorting coefficient. . _ 4, 26, 28, 32, 35, 37, 54, 58, 64
South Mowich Glacier ........................ 69
South Prarie Creek ........................... 26
South Puyallup River___.... ..... 2, 43, 53, 56, 68
South Puyallup River valley, block-and-ash
flow ............. 6'4
lahar assemblage 6:
lahars .................................... 49
South Tahoma Glacier .................. 4, 58, 60, 62
Steamboat Prow ...... 22, 24, 25, 29
Sunrise Creek... 22
Sunset Amphitheater ................... 17, 55, 58. 69
Tahoma Creek ........... 2, 34, 38, 50, 54, 55, 58, 62, 69
Tahoma Creek valley, lahar assemblage. _ _ . 5 7
lahars ............................. 4.9
Tahoma Glacier .............................. 17,58
Terminology of lahars ........................ 3
Thermoremanent magnetism. . 5, 65
Till ......................................... 5, 13, 16
Van Trump Creek ............................ 37, 38
Van Trump Park. ...................... 33
lahars ........................... 87
Vashon Drift. . 24
Vashon till. - .................... 24, 25
Volcanic ash .................................. 11, 32
Volcanism, associated with lahars ............. 68
West Fork ................................. 17, 25, 70
West Fork valley, Post-Osceola lahar assem-
blage ............................. 32
White River ................. 2, 20, 22, 23,24, 26, 69, 70
White River drainage basin, lahars ........... 17
Willis Wall ____________________________________ 2, 67
Winthrop Creek .............................. 32
Winthrop Creek Glaciation ................ 24, 42, 43
Winthrop Glacier ............................. 25,43
Yakima Park ................................ 22

75

11.3. GOVERHIEIT PRINTING OFFICE: |97l

GEOLOGICAL SURVEY

 

 

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8* .9 Control by USGS and USC&GS

Topography by planetable surveys 1910, 1911,
and 1913

Culture revised by National Park Service 1928,
1938, and 1955

Polyconic projection. North American datum.
10,000<foot grid based on Washington coordinate
system, south zone. To place on 1927 North
American datum move projection lines 115 feet
north and 85 feet west

Culture revised in part and topography in south-
west corner of map revised in part by U.S.
Geological Survey, 1967

Glacier margins shown were compiled trom aerial
photographs by M. F. Meier and A. S. Post, and
represent extent of ice during the period 1966—67;
perennial snowfields and areas of stagnant glacier
ice are shown, as well as active glaciers
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75 Ml. TO U.S. 99

TOPOGRAPHIC MAP OF MOUNT RAINIER NATIONAL PARK, WASHINGTON

 

 

|NTER|OR—GEOLOG|CAL SURVEY, WASHINGTON. D.C.#197l —G70184

 

  
  
  
 
  
    
  
 
    
  
  
 
   
  

 

DEPARTMENT OF THE INTERIOR PROFESSIONAL PAPER 677
UNITED STATES GEOLOGICAL SURVEY PLATE 2

 
    
   

 
   
   
    
        
  

 

 

 

 

 

 

 

 

 

  
     
   

 
  
  
 
 
 

 

 

 

 

 

 

 

    
    
   
 
      
  
  
 
 

 

   

 

 

    

 
 
  
  
 

 

    

   
  

 

 

 

 
 
 
    
 

 

 

 

 

 

 

 

   

 

     
  
 

   

 

 

 

 

A A’
FEET Layer 0 FEET
250 "7 — 250
Layer Y
Layer C
//Layer W
./
Emergency
landing strip
200 L Greenwater Iahar L 200
l 0 V2 1 MILE
I J’ I I I I l . I I
MAP SHOWING LOCATION OF CROSS SECTION A—A’
150 7‘ — 150
700 feet of lateral
distance omitted
I IGreenwater Iahar
100 — i 100
Lahar Osceola 2:233: . WIhite
Note: Although the Osceola Mudflow is shown resting on bed- MUdflOW I Fluwal RM)”
rock above the level of the White River, a well drilled at a Igravel I
point 1.5 miles upstream showed that the Osceola extends ‘
to a depth of more than 200 feet beneath the valley floor. ””0””? C’SDWWWOOOOOW“ " °°"° .. ..
This deep buried valley which has been filled with the mud- , . I . _, . - _ ~ " » Zéqoado'a'n‘
50 _ flow is not shown in the cross section, but it probably lies -‘ .- 5‘ .. .‘ . .. . ... . . .. -". ,. .' j .. -I . I, -. . . __ _. .. .. . Op _ 50
‘ between the White River and the west valley wall ‘ “ " ‘ ' “ - ' "' "'- ‘ ~ " i -‘ ’ ' "' -' '- ‘ ‘ '
O 100 200 300 FEET Bedrock
I I I
O ’ ‘ O
/
PROFILE AND IN FERRED CROSS SECTION OF VALLEY FLOOR IN TH E WHITE RIVER VALLEY NEAR BUCK CREEK
SHOWING THE STRATIGRAPHIC RELATION OF THE GREENWATER LAHAR TO TH E OSCEOLA MU DFLOW, TO A
YOUNGER LAHAR, AND TO PYROCLASTIC DEPOSITS
FEET FEET
100 i 100
7
West valley .
wa” [ragga/Em Lahar 0(7)
Pyroclastic layer Y
Fluvial deposit EI?)
80 h u. .-..,..,L.,.,.--~v-..t...,.,. '17 80
.. 009000-?
9992-050 0 .0 .00? 0.0 O Q 00.92903:
O o ... I . _.. I. ' Lahar G(?)
g ~ ’ ~ °°:' ..‘?,.'.:..°?°= ~-' I _ ENTRANCE ROAD Fluvial deposit E , East valley
v “ - . I‘ Pyroclastlc layer W wall
60 i ‘ . . - Pyroclastic layer Y Lahar D‘ /i 60
“Paradise Iaha' Lahar G Fluvial deposit F Pyroclastic layer w Lahar G Fluv'a' depos't C. \
Fluvial deposit F
, Pyroclastic layer Y
Note: The line of section trends east-west; on the west side of Pyroclastic
4O 7* the valley it is located 0.8 mile north-northeast of Longmire, Fluvial deposit H layer W 7 40
and on the east side of the valley 0.6 mile northeast of Long- I
mire. The texture of the deposits represented is diagram-
matic and is not intended to be true to scale. The vertical
exaggeration is X 5 Laharl
Fluvial deposit H(.7) ”(2,0ch ppaasbéao ' I“; _ 00‘"; fife.
, .-.?-;O.00 2‘ EN‘ . h ‘ >06 9:,
Paradise Iahar _ 921.09.7- Fluvial deposit A
20! I IO'IOOQO' *20
A! '- 'O'Ooob-‘S'
Fluvial deposit J 000'on DO (-3.0 H" Paradise Iahar
Nisqually River Q 5.0. 0'5""
0 100 200 300 FEET ”0°" 9'3””
I I I I 400 feet of flood Fluvial deposit
plain omitted
0 f‘ o
DIAGRAMMATIC GEOLOGIC CROSS SECTION OF FLOOR OF NISOUALLY RIVER VALLEY
V253: Lateral extent of Iahars in 1947 Egg:
100 H'" r "A“ -. 100
- Valley wall L
e
W ' D V || H
* Pyroclastic O Pyroclastic layer W Pyroclastic layer W Pyroclastic layer W 3 . a ey wa T
_ layer W 3 g Lahars of 1947 Pyroclastic i
S l' . {:4 layer W
50 S g \___4 / . so
0..
— I .
_ T I Pyroclastic
* Pyroclastic layer Y 7 layer Y T
_ O 100 200 300 FEET //\lnterbedded Iahars and '"
_ l ‘ I I fluvial deposits
VERTICAL EXAGGERATION X 2 /
O C...- O

 

Profile surveyed by Robert D. Miller
PROFILE ACROSS FLOOR OF KAUTZ CREEK VALLEY AT MEASURED SECTION 6

PROFILES AND CROSS SECTIONS OF THE VALLEY FLOORS OF THE WHITE RIVER, THE NISQUALLY RIVER,
AND KAUTZ CREEK, MOUNT RAINIER AREA, WASHINGTON

420—479 0 - 71 (In pocket)

UNITED STATES DEPARTMENT OF THE INTERIOR PROFESSIONAL PAPER 677
GEOLOGICAL SURVEY , PLATE :5

v 'x' stallolxnlll lK I

land
Summli

EXPLANATION

Electron Mudflow
Inferred original extent

Osceola Mudflow

Inferred original extent

Paradise lahar
Inferred original extent

Contact
Dashed where approximately located;
dotted where mudflow margins
have been eroded or buried by
younger deposits, or are under
water

0 23
Sample locality

 

122°

Base from U.S. Geological Survey: Hoquiam, 1958; Seattle, Geology compiled by D. R. Crandell, 1968
1958—65; Wenatchee, 1957—63; Yakima, 1958—63 SCALE 1:250 000
5 O 5 10 MILES

 

 

5 O 5 10 KILOMETERS
l—-l l-—l l——-l -
CONTOUR INTERVAL 200 FEET
SUPPLEMENTARY CONTOURS AT 100 FOOT INTERVALS

 

TOPOGRAPHIC MAP OF THE MOUNT RAINIER AREA, WASHINGTON, SHOWING
INFERRED ORIGINAL DISTRIBUTION OF THE OSCEOLA AND ELECTRON
MUDF LOWS AND THE PARADISE LAHAR Semen")

47°

 

\ 7 DAY

. W
V '

{£75 Permafrost and

N .(07 . . ‘
Dripmilelated Engmeermg Problems

in Alaska

 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 678

 

 

fl? @.S.D¢

 

Pegmafrost and
Related Engineering Problems

in Alaska

By OSCAR J. FERRIANS, JR., REUBEN KACHADOORIAN, and
GORDON W. GREENE

 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 678

 

 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1969

UNITED STATES DEPARTMENT OF THE INTERIOR

WALTER J. HICKEL, Secretary

GEOLOGICAL SURVEY

William T. Pecora, Director

 

For sale by the Superintendent of Documents, US. Government Printing Office
Washington, D.C. 20402 - Price 55 cents (paper cover)

CONTENTS

Abstract ________________________________
Introduction _____________________________
Permafrost ______________________________
Definitions ___________________________
Origin and thermal regime _________________
Areal distribution and thickness ______________
Related geomorphic features ___________________
Polygonal ground _______________________
Stone nets ____________________________
Solifluction ___________________________
Thaw or thermokarst pits __________________
Thaw lakes ___________________________
Beaded drainage ________________________
Pingos ______________________________
Muck deposits _________________________
Summary of geomorphic features _____________
Engineering geology ________________________

Page
1
1
4
4
5
6
8
8
8
9

12

12

12

12

12

14

14

Engineering geology—Continued
Engineering problems ____________________
Thawing of permafrost ________________
Frost heaving _______________________
Frost heaving of piles __________________
Specific structure _______________________
Railroads __________________________
Highways and roads ___________________
Airfields __________________________
Buildings __________________________
Dams ____________________________
Telephone and power transmission lines ______
Pipelines __________________________
Utilidors __________________________
Icings _______________________________
Conclusions _____________________________
References cited _________________________

ILLUSTRATIONS

FIGURE 1.

Map showing extent of permafrost zones in Northern Hemisphere ____________________________

2. Map showing distribution of permafrost in Alaska ______________________________________
3. Block diagram showing where taliks can occur in relation to the active layer, suprapermafrost zone,
permafrost table, and permafrost _______________________________________________
4. Diagrammatic sketch showing the effect of surface features on the distribution of permafrost in the con-
tinuous permafrost zone _____________________________________________________
5. Diagram showing relation of amplitude of ground-surface temperature fluctuations to amount of thawing_ ‘ _
6. Diagrammatic sketch showing the distribution of permafrost in the discontinuous permafrost zone,
Fairbanks area ____________________________________________________________
7. Aerial photograph of coastal plain near Barrow, showing polygonal markings on ground surface caused
by underlying ice-wedge polygons ______________________________________________
8. Aerial photograph showing polygonal markings on ground surface (caused by ice-wedge polygons) in the
vicinity of Meade River ______________________________________________________
9. Photograph of ice wedge (ground ice) in permafrost exposed by placer mining near Livengood _________
10. Aerial photograph of thermokarst mounds near Fairbanks __________________________________

1 1— 15. Photographs of —

11. Thermokarst mounds near Fairbanks ________________________________________ '_ _
12. Sorted stone circles caused by frost action in Alaska Range ___________________________
13. Large mass of ground ice in silt bluff near Fairbanks _______________________________
14. Thaw or thermokarst pit near Fairbanks ________________________________________
15. Shoreline of a thaw lake about 40 miles northwest of Glennallen ________________________
16. Aerial photograph of pingo in Yukon-Tanana Upland ____________________________________
17. Diagram showing effect of gravel fill upon thermal regime _________________________________
18. Map showing location of transportation routes in Alaska __________________________________
19. Photograph of differential subsidence of roadbed along the Murphy Dome Spur of The Alaska Railroad
caused by thawing permafrost ________________________________________________

Page

15
15
17
17
17
18
21
28
29
32
3 3
33

34
34
36
37

Page
2
3

4

6
6

7

8

9
10
11

11
11
12
13
13
13
16
19

20

IV

FIGURE 20

21

22—27

32-36.

TABLE

28.
29.
30.

31.

DD

CONTENTS

. Photograph of differential subsidence of roadbed of Copper River and Northwestern Railway __________

. Map of the Moody area on The Alaska Railroad showing landslides and slumps caused by thawing of
permafrost and remedial measures taken to combat them _______________________________

. Photographs of—

22. Landslide area at mile 353.5, The Alaska Railroad __________________________________
23. Polygonal ground in permafrost exposed by removal of vegetation by a highway crew __________
24. ThaWed lake sediments flowing around blade of bulldozer ____________________________

25. Gravel road near Umiat showing severe differential subsidence caused by thawing of ice-wedge
polygons in permafrost ________________________________________________
26. Slump block of fine-grained highway fill material near mile 113 on the Richardson Highway 111111
27. Gully along edge of road caused by surface drainage thawing the permafrost in loess deposits _____
Oblique aerial photograph of Chariot Site, northwestern Alaska _____________________________
Oblique photograph of tractor trail near Canning River, North Slope ___________________________
Photograph of frost—heaved piling of bridge ___________________________________________
Geologic sketch of foundation conditions of frost—heaved bridge _______________________________

Photographs of—

32. Frost-heaved steel-pile bridge _______________________________________________
33. Roadhouse, mile 278.5, Richardson Highway ______________________________________
34. The schoolhouse at Glennallen ______________________________________________
35. Fracture due to frost heaving of 4—inch concrete foundation of apartment house, Fairbanks ______
36. Utilidor under construction at Fort Wainwright __________________________________

TABLES

Mean annual temperature and precipitation data from representative stations in Alaska _____________

. Common topographic features that indicate ground conditiOns in arctic and near arctic regions _________
. Hypothetical example of seasonal frost penetration into silt in central Alaska and possible upward push

on 40-inch-perimeter pile (ground temperature constant) _______________________________

. Comparison of construction costs between permafrost and permafrost-free areas of the highway between

Rex and Lignite, Alaska _____________________________________________________

Page
21 '

22

23
24
25

26
27
28
29
30
31
31

32
33
34

,35

35

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7

14

17

22

PERMAFROST AND RELATED ENGINEERING PROBLEMS IN ALASKA

By OSCAR J. FERRIANS, JR., REUBEN KACHADOORIAN,
and GORDON W. GREENE

ABSTRACT

Permafrost, or perennially frozen ground, is a wide-
spread natural phenomenon. It underlies approxi-
mately 20 percent of the land area of the world. The
permafrost region of Alaska, which includes 85 percent
of the State, is characterized by a variety of perma-
frost-related geomorphic features including patterned
ground, pingos, thaw lakes, beaded drainage, thaw or
thermokarst pits, and muck deposits. Known perma-
frost thickness ranges from about 1,300 feet near
Barrow in northern Alaska to less than a foot at the
southern margin of the permafrost region. The dis-
tribution of permafrost is controlled by climatic,
geologic, hydrologic, topographic, and botanic factors.

The extensive permafrost region of Alaska poses
special engineering problems for the design, construc-
tion, and maintenance of all types of structures. Lack
of knowledge about permafrost has resulted in tre—
mendous maintenance costs and even in relocation or
abandonment of highways, railroads, and other struc-
tures. Because of the unique geologic-environmental
conditions that exist in permafrost areas, special
engineering procedures should be used, not only to
minimize disruption of the natural environment, but
also to provide the most economical and sound methods
‘ for developing the natural resources of the perma—
frost region of Alaska.

INTRODUCTION

The recent discovery of potentially vast reserves of
oil at Prudhoe Bay in northeastern Alaska (estimates
range from 2 to 40 billion barrels) has focused atten-
tion on the geologic-environmental factors unique to
the Arctic which pose special engineering problems
for the design, construction, and maintenance of roads,
railroads, airfields, pipelines, buildings, and other
structures. Permafrost, or perennially frozen ground,
is the most significant of these environmental factors.

A road and railroad from Fairbanks in interior
Alaska to the Arctic North Slope have been proposed
to aid in the development of the mineral wealth of

this remote and presently inaccessible region. Pre-
paratory work is under way for the construction of an
800-mile—long pipeline extending from the oil fields
to Valdez, a year-round seaport. A winter road
connecting Fairbanks with Sagwon on the Arctic
North Slope has been completed. These major engi-
neering activities are just a part of the overall con-
struction effort that will take place in northern Alaska
because of the recent oil discovery and because of
potential future discoveries of other natural resources.

All this activity requires an understanding of the
arctic environment, to establish sound cost-saving
engineering procedures and to preserve the natural
environment insofar as possible. In most areas
where roads or buildings are constructed on perma-
frost, the procedures that cost the least in the long
run are those that disturb the natural environment
the least, and therefore, are conservation oriented.
Generally, the initial capital investment is greater
when correct procedures are used; however, mainte-
nance cost is considerably less. If improper procedures
are used, expensive maintenance cost far exceeds the
additional expense of the initial investment, and in
some cases, structures are damaged to the extent that
they become unusable after just a few months or
years. The financial losses caused by such problems
as impassable roads, unusable airstrips, or damaged
machinery in buildings which have settled differen-
tially can be extremely high.

Very few people realize the geographic extent of
permafrost or the magnitude of the problems it causes.
Approximately 20 percent of the land area of the

world is underlain by permafrost. Figure 1 shows the
extent of the permafrost zones in the northern hemi-

sphere where most of it occurs. In the southern
hemisphere, the main land area underlain by perma-
frost is Antarctica. About 50 percent of both Canada
and the USSR. and 85 percent of Alaska are Within
the permafrost zones (figs. 1 and 2).

To date most permafrost research has been carried
on in the USSR; major industrial cities have been

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in Northern Hemisphere.

1 —Extent of permafrost zones

FIGURE

   

  

AREAS WITHIN PERMAFROST
REGION

Mountainous areas, generally underlain
by bedrock at or near the surface

 

MI

 

Underlain by continuous permafrost

 

 

 

 

 

Underlain by isolated masses of permafrost

INTRODUCTION

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EXPLANATION

Lowland areas, generally underlain by
thick unconsolidated deposits

 

 

 

 

 

Underlain by thick permafrost in areas
of either fine-grained or coarse-
grained deposits

 

 

 

 

 

Underlain by moderately thick to thin
permafrost in areas of fine -grained
deposits, and by discontinuous or iso-
lated masses of permafrost in areas
of coarse—grained deposits

FIGURE 2.—Distributi0n of permafrost in Alaska.

after Ferrians (1965).

 

 

 

 

 

Underlain by isolated masses of perma-
frost in areas of fine-grained deposits,
and generally free of permafrost in
areas of coarse-grained deposits

AREAS OUTSIDE OF PERMAFROST
REGION

 

 

 

 

Generally free of permafrost, but a few
small isolated masses of permafrost
occur at high altitudes, and in lowland
areas where ground insulation is high
and ground insolation is low, espe—
cially near the border of the perma-
frost region

Modified

4 PERMAFROST AND RELATED ENGINEERING PROBLEMS IN ALASKA

built in the permafrost region. This construction
demonstrates that the deleterious effects of perma-
frost can be overcome, and that major development
can take place in the arctic regions. In regard to
the success of the Soviets, the following statement
(Muller, 1943, p. 2) is pertinent: “It is worth noting
that in Soviet Russia since about 1938 all government
organizations, municipalities, and cooperative societies
are required to make a thorough survey of permafrost
conditions according to a prescribed plan before any
structure may be erected in the permafrost region.”

The purpose of this report is to present a survey of
some of the more important aspects of permafrost
and to create an awareness of the tremendous prob-
lems that can be caused by constructing on, or other-
wise disturbing, permafrost if proper procedures are
not used. It is hoped that the information presented
will facilitate the development of the natural resources
of northern Alaska and at the same time minimize
disruption of the natural environment.

PERMAFROST
DEFINITIONS

Permafrost is defined exclusively on the basis of
temperature. It is rock or soil material, with or with-
out included moisture or organic matter, that has
remained below 0° C (32° F) continuously for two or
more years. In most areas it has remained frozen for
many thousands of years; however, permafrost can
be quite young in areas where very recent sediments

have been laid down, where very recent changes in
the location of water bodies have taken place, and
where man has disturbed the terrain.

Permafrost may be ice free at 0° C when the water
it contains is saline or when it contains no water at
all. The latter is commonly referred to as dry perma-
frost. When permafrost contains clay, substantial
amounts of unfrozen moisture can persist at temper:
atures several degrees below 0° C because of the
depression of the freezing point by capillary forces.
Ice in permafrost can occur as coatings, grains, vein-
lets, or masses, and in unconsolidated materials it
commonly acts as a cementing agent making the mass
of unconsolidated materials hard as a rock.

The permafrost table is the upper surface of the
permafrost, and the ground above the permafrost
table is called the suprapermafrost layer. The active
layer is that part of the suprapermafrost zone that
freezes in the Winter and thaws in the summer, or
simply, seasonally frozen ground. Because water in '
the soil tends to reduce temperature fluctuations from
summer to winter, the summer thawing—and hence
the active layer—is deeper in drier materials. Seasonal
frost penetrates down to the permafrost table in most
places; however, if it does not, an unfrozen zone called
a talik remains between the bottom of the seasonal
frost and the permafrost table. Unfrozen zones
within and below the permafrost also are called taliks
(fig. 3). If the thickness of permafrost is increasing,
permafrost is said to be aggradtng, and if decreasing,
permafrost is said to be degrading.

Active layer (seasonally frozen
ground) '

 

  

Surface of ground

31/,

Talik (unfrozen ground be
tween base of active layer
and permafrost table)

 

Suprapermafrost layer (ground\
above permafrost table in-
cluding taliks, if present)

Permafrost table (upper sur-
face of permafrost)

Permafrost (perennially frozen\
ground)

 

 

Talik (unfrozen ground within
permafrost)

Talik (unfrozen ground below
permafrost)

 

 

 

FIGURE 3.—Occurrence of taliks in relation to the active layer, suprapermafrost zone, permafrost table, and permafrost.

ENGINEERING GEOLOGY 5

ORIGIN AND THERMAL REGIME

Permafrost forms when the mean annual air tem-
perature is low enough to maintain a mean annual
ground—surface temperature below 0° C (32° F). If
climatic conditions in an area change in such a way
as to reduce the mean surface temperature below
0° C, the depth of winter freezing will exceed the
depth of summer thawing and if the mean surface
temperature remains below 0° C, a layer of frozen
ground will be added each year to the base of the
permafrost until the downward penetration (aggrada—
tion) of the frozen ground is balanced by the heat
flowing upward from the earth’s interior. Thus, the
thickness to which permafrost can grow depends
upon the mean surface temperature and the geo-
thermal gradient. The lower the temperature and
gradient, the greater the thickness of the permafrost.
In this manner, permafrost, hundreds of feet thick,
can form over a period of several thousand years.

Because the formation of permafrost depends upon
temperature at the ground surface, the thickness and
areal distribution of permafrost are directly affected
by the kind and size of natural surface features
(bodies of water, topography, drainage, and vegeta-
tion) that act as a heat source or heat sink or as
insulation. Changes in the surface environment—such
as would be produced by a transgressing (or regressing)
sea, or building of roads and other surface structures,
draining of lakes, and clearing of vegetation—produce
profound changes in the permafrost (Lachenbruch,
1957a, 1957b; Greene and others, 1960).

Although the surface of the permafrost may be
quick to respond to surface changes, it requires
centuries, or tens of centuries, for surface changes to
affect the bottom of the permafrost. Therefore, the
present thickness and distribution reflect former
thermal environments (Lachenbruch and others, 1966).

A few examples demonstrate how these consider-
ations can be applied to make a qualitative appraisal
of permafrost conditions beneath various surface
features. (For quantitative calculations see Lachen—
bruch and others, 1962, and references cited therein.)
Example 1. Shallow lakes freeze completely in the
winter; thus, they behave like the active layer of the
nearby terrain. However, the spring warming is
accomplished efficiently by water circulating around
and beneath the deteriorating ice, whereas the fall
cooling is achieved inefficiently by conduction through
the ice. The result is that mean annual temperatures
on shallow lake bottOms are higher than those of the
surroundings and permafrost is thinned beneath them
(fig. 4). Example 2. Deeper lakes (greater than 6 ft
deep) that do not freeze completely during the winter

356-549 0 - 69 - 2

have mean annual bottom temperatures above freezing
and thus are underlain by a thawed basin. The
permafrost beneath a thawed basin is also thinned by
upward indentation (fig. 4). If the lake is drained,
the thawed basin refreezes and expansion of the ice
within it creates a pingo (see p. 12). If the minimum
horizontal dimension of a deep lake is greater than
approximately twice the local undisturbed permafrost
thickness, the upward indentation coalesces with the
thawed basin to form an unfrozen “chimney” through
the permafrost beneath the lake (fig. 4). Such
features provide a potential year-round source of
ground water in regions of continuous permafrost.

A river behaves like a long thin lake, and the ocean
can be viewed as a large deep lake (fig. 4). Example
3. Well-drained areas will generally have summer
surface temperatures several degrees higher than
nearby poorly drained bogs because of the thermal
effects of the water. Inasmuch as the best drained
areas are generally underlain by gravels and have a
temperature anomaly, aerial infrared mapping might
show the best locations for constructing roads and
buildings and indicate likely sources of gravel for
construction purposes.

In the absence of various modifying conditions
such as those described above, the top and bottom of
the permafrost layer tend to parallel the ground
surface, rising under hills and lowering beneath
valleys (fig. 4).

A gradual climatic warming during the last century
has caused a warming of the permafrost to depths of
several hundred feet (Lachenbruch and Brewer, 1959;
Lachenbruch , and others, 1962, 1966). Hence near
Barrow, Alaska, the temperatures at a depth of 150
feet (about —9.7° C) are lower than those at 50 feet
(about —‘9.4° C). Below 300 feet, however, the
temperatures increase in accordance with the antici-
pated geothermal gradient (Lachenbruch and others,
1962). Near the southern limit of permafrost the
effect 'of the climatic warming is to keep the perma-
frost very close to 0° C throughout its entire depth.
The permafrost is, therefore, very vulnerable to deep
thawing and often will not regenerate when active
construction procedures are used.

It should be pointed out that in a given area the
mean ground-surface temperature is usually higher
than the mean air temperature, largely because the
ground is insulated by snow during the cold winter
but is bare during the summer.

It is important also that the fluctuations of air
temperature from summer to winter are normally
substantially greater than corresponding fluctuations
at the ground surface. Typically, ground-surface

 

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FIGURE 4.—The effect of surface features on the distribution of permafrost in the continuous permafrost zone.
After Lachenbruch (1968, p. 837).

temperatures fluctuate 20° C to 50° C seasonally, the
smaller values occurring in wetter terrains. The
fluctuations diminish rapidly with depth, normally by
a factor of 10 for approximately every 20 feet. Thus
the seasonal variation of temperature at 20 feet is a
few degrees, at 40 feet it is a few tenths of a degree,
and at 60 feet it is barely detectable. Seasonal
fluctuations normally propagate into the earth at the
rate of about 5 feet per month. Because of this lag
the minimum temperature at 30 feet occurs in mid—
summer. This explains the summer freezing of some
water wells in the subarctic.

'Curve A in figure 5 shows how the change in annual
ground-surface temperature, assumed here to be
sinusoidal, produces thawing of the permafrost even
though the mean annual ground—surface temperature
is well below 0° C. The stippled area indicates the
amount of thawing that takes place. Note that if
either the mean annual temperature or the amplitude
of the temperature fluctuations is increased there will
be a greater amount of thawing. If the permafrost
is dry, that is, without interstitial ice or water, the
temperatures will follow curve A. However, if water
is present the latent heat released when water freezes
will cause the temperature to remain at the freezing
point while this heat is dissipated as shown by curve
B. The latent heat absorbed in the spring and lib-

 

 

 

 

. CurveA

T ———V ———_———r— 0°C

3 LCurve B

.3 \ Amp itude

3

Q.

E \ Mean annual temperature

fl
Ground- surface
temperature

0 Time —>

 

FIGURE 5.—Relations of amplitude of ground-surface
temperature fluctuations to amount of thawing.

erated in the fall by moisture in the arctic layer tends
to reduce the temperature fluctuations at the perma-
frost table.

AREAL DISTRIBUTION AND THICKNESS

‘ijo broad zones of permafrost can be differentiated

in the northern hemisphere (fig. 1)—the continuous
zone which is underlain by permafrost nearly every—
where, and the discontinuous zone which includes
numerous permafrost-free areas. Within the dis-
continuous zone the extent of the permafrost-free
areas increases progressively from north to south.
South of the discontinuous permafrost zone, perma—
frost generally is absent except for a‘few isolated

occurrences, usually at high altitudes. The distribution
of permafrost is largely controlled by temperature
variations related to differences in latitude, altitude,
and major climatic patterns.

In Alaska (fig. 2), the two broad permafrost zones
can be subdivided into: (1) mountainous areas where
bedrock generally is at or near the surface, and (2)
lowland areas commonly underlain by thick unconsol-
idated deposits. The thickness, distribution, and
temperature of permafrost are extremely variable in
the mountainous areas; in the lowland areas these
characteristics are more uniform.

From north to south, the mountainous areas can be
further subdivided into areas underlain by continuous
permafrost, areas underlain by discontinuous perma-
frost, and areas underlain by isolated masses of per-
mafrost.

The lowland portion can also be subdivided into (a)
a northern area (largely north of the Brooks Range)
which is underlain by thick permafrost; (b) a central
area (between the Brooks and Alaska Ranges but
including the Copper River basin), which is underlain
by moderately thick to thin permafrost in areas of
fine-grained deposits and by discontinuous or isolated
masses of permafrost in areas of coarse-grained de—
posits; and (c) a southern area (including the Bristol
Bay area and the eastern and western margin of the
Susitna Lowland north of Anchorage), which is under-
lain by numerous isolated masses of permafrost in
areas of fine—grained deposits, and which generally is
free of permafrost in areas of coarse-grained deposits.

Because climate is the major factor that controls the
regional (and global) distribution of permafrost, the
permafrost regions in Alaska can be characterized by
the mean annual air temperature and precipitation

HILLS

FEET
1500

1000
/
s \/

50° \< '1'»? I

\Mme masses

SEA LEVEL
Unfrozen schist bedrock

    
 

91

7

data for representative stations (table 1). Within the
continuous permafrost zone, Barrow has the lowest
mean annual air temperature, 10° F, Whereas Anchor-
age, just outside of the permafrost region, has a
mean annual air temperature of 35° F.

TABLE 1.—Mean annual temperature and precipitation data
from representative stations in Alaska

[Data from US. Weather Bureau records]

Station Mean annual temperature Mean annual precipitation
(°F) (inches)
Continuous permafrost zone
Barrow-________,____10 4
Umiat____________-_10 6
Discontinuous permafrost zone
Bettles,‘____,-______22 —
Nome ________________ 26 19
Fairbanks_-__________26 12
Glennallen (Gulkana) __ 7_ 27 12
Bethel______________30 18
N0 permafrost
Anchorage ____________ 35 15
Valdez____-_________36 62
Seward ______________ 40 69
Juneau______-__-____41 56

The climatic control is also reflected by the thick-
ness of permafrost which ranges from more than 1,300
feet near Barrow to lenses less than a foot thick in the
southernmost part of the permafrost zone. ’

Even though the annual precipitation is low at the
stations within the permafrost region, ground condi-
tions'generally are wet, especially in areas underlain
by fine-grained sediments. This poor drainage is
caused by the impervious permafrost layer, generally
within a few feet of the surface, and by the low

ALLUVIAL APRON FLOOD PLAIN S

l
l
l
l
l
l
l
l
l

Fairbanks\

”i" v“: a
Permafrost

 

Unfrozen sediment

 

500

 

\ ,
\ \ K .p"
O 4000 8000 FELT EXPLANATION
HORIZONTAL SCALE ''''''' I —7# i
Inferred boundary Doubtful boundary

FIGURE 6.—Distribution of permafrost in the discontinuous permafrost zone, Fairbanks area.

Slightly modified after

Péwé (1954, p. 326).

8 PERMAFROST AND RELATED ENGINEERING PROBLEMS IN ALASKA

evaporation rate at the prevailing low temperatures.
Also, the low annual precipitation indicates that the
snow cover is not thick.

In any area where the mean annual air temperature
is around 0° C (32° F), the microclimate, which is
governed largely by local features, can be critical in
determining whether or not permafrost is present.
For example, the mean annual air temperature
recorded at a site underlain by unvegetated dry soils
can be 1° or 2° warmer than a nearby site underlain
by vegetated wet soils. Slope exposure also controls
microclimate in mountainous or hilly areas where
south-facing slopes may receive considerably more
solar heat than the north-facing slopes. This is
important in the southern margin of the permafrost
region where south-facing slopes often are completely
free of permafrost, whereas nearby north-facing slopes
are underlain by thick permafrost.

Permafrost thickness also varies depending upon
the amount of heat flowing outward from the earth’s
interior. Generally, the temperature of the earth
increases 1° C (18° F) for each 100 to 200 feet of depth;
however, locally, the near-surface temperatures can
be relatively high. '

In the discontinuous zone where the permafrost
layer is thinner, surface features affect the distribu-
tion of permafrost in much the same way as in the
continuous zone (fig. 4); thus lakes and rivers cause
smaller anomalies because their temperature does not
contrast as much with the surroundings. The distri-
bution of permafrost in the Fairbanks area, as shown
in figure 6, is typical of much of interior Alaska.
Permafrost is absent under the south-facing hillslope,
continuous under the flood plain, and absent under
the Chena River.

RELATED GEOMORPHIC FEATURES

Permafrost and frost action produce several types
of geomorphic features (Washburn, 1956; National
Academy of Sciences, National Research Council,
1966). Among these features are polygonal ground
(ice wedges), stone nets, garlands and stripes, soli-
fluction sheets and lobes, thaw lakes and thaw pits,
beaded drainage, and pingos. Because these features
are closely related to the permafrost problems a brief
description of each is warranted.

POLYGONAL GROUND

Polygonal ground (figs. 7 and 8), which covers many
thousands of square miles of northern Alaska is caused
by shallow troughs which overlie a honeycomblike
network of vertical wedge-shaped ice masses (ice
wedges) that have joined to form polygons in the

 

FIGURE 7.—Aerial View of coastal plain near Barrow, in north-
ern Alaska showing polygonal markings on ground surface

caused by underlying ice-wedge polygons. The bank along
Elson Lagoon in foreground is being undercut by thawing of
permafrost and by wave action. Photograph taken in August
1958.

permafrost. Individual polygons range from 30 to a
few hundred feet in diameter. Figure 9 shows a
typical ice wedge. Where the surface of the ground
is disturbed and the thermal regime upset, the ice
wedges can melt, causing severe differential settle-
ment of the ground surface. For example, clearing
of the ground near Fairbanks caused ice wedges to
melt, and large mounds were left (figs. 10 and 11.)

Polygonal ground indicates relatively fine grained
unconsolidated sediments with the permafrost table
near the ground surface. It also occurs in coarser
sediments and gravels where the formation of ice
wedges is less extensive than in the fine-grained
sediments.

Many different hypotheses for the origin of ice-
wedge polygons have been proposed; however, the
thermal contraction theory first clearly described by
Leffingwell (1915, 1919) has been generally accepted
by most workers. A quantitative appraisal of the
mechanics of the thermal contraction theory was
made by Lachenbruch (1962), and he concluded that
the theory is compatible with the thermal and me-
chanical properties and thermal regime of the perma-
frost in which the ice-wedge polygons occur.

STONE NETS

Stone nets, garlands, and stripes are extensive in
the arctic. Frost heaving in granular soils produces
netlike concentrations of the coarser rocks (fig. 12).
If the area is gently sloped, the net is distorted into
garlands by downslope movement. If the slope is

RELATED GEOMORPHIC FEATURES

 

FIGURE 8.—Polygonal markings on ground surface (caused by ice—wedge polygons) in the vicinity of Meade River, about 35
Photograph by U.S. Navy, July 1949.

miles southeast of Barrow, in northern Alaska.

steep, the coarse rocks lie in stripes that point down-
hill. Generally, in garlands and stone stripes the
downslope flow pattern is readily apparent. Stone
nets, garlands, and stripes indicate strong frost action
in moderately well drained granular sediments that
vary from silty fine gravel to boulders. These sur-
ficial materials are commonly susceptible to flowage.

SOLIFLUCTION

Solifluction sheets and lobes are masses of uncon-
solidated sediment that range from less than a foot
to hundreds of feet in width. These features are
extensive in the arctic and may cover entire valley

walls. They occur on slopes as low as 3°. Solifluction
plays a major role in the formation of patterned
ground. This type of patterned ground is formed by
the gradual downslope (gravity) movement of water—
saturated sediments. The surficial materials are
especially mobile in the permafrost region because the
active layer commonly is supersaturated with moisture.
This condition is caused by the impermeability of the
underlying permafrost and by the low evaporation
rate. Downslope movements of solifluction features
are so rapid that a structure resting upon one will
either be subjected to large earth pressures or will
move passively downslope.

10 PERMAFROST AND RELATED ENGINEERING PROBLEMS IN ALASKA

 

FIGURE 9.—Ice wedge (ground ice) in permafrost exposed by placer mining near Livengood about 50 miles northwest of
Fairbanks. Photograph by T. L. Péwé, September 1949.

RELATED GEOMORPHIC FEATURES 11

 

FIGURE 10.—Thermokarst mounds near Fairbanks. Mounds
range from 10 to 30 feet in diameter. See figure 11 for ground
View of mounds and explanation. Photograph by R. F. Black
and T. L. Péwé, September 1948.

 

 

FIGURE 11.—Thermokarst mounds near Fairbanks caused by
melting of ice wedges. The resulting ground settlement

formed deep trenches in polygonal patterns and left mounds .
in the intervening areas. The thawing was started after the FIGURE 12.—Sorted stone circles caused by frost action, in Alaska

area was cleared for agricultural purposes. Figure 10 is an Range, south—central Alaska. Photograph by T. L. Péwé,
aerial View of similar mounds. Photograph taken in June 1955. June 1968.

 

12 PERMAFROST AND RELATED ENGINEERING PROBLEMS IN ALASKA

THAW 0R THERMOKARST PITS

Thaw or thermokarst pits occur in areas underlain
by permafrost containing large masses of ground ice
(fig. 13). If the ground surface is disturbed above a
large ice mass, such as the one shown in figure 13, the
resultant change in the thermal regime can cause the
ice mass to thaw; this thawing causes a thaw pit to
form (fig. 14).

The occurrence of these pits indicates poorly drained,
fine-grained sediments with the permafrost table near
the surface.

THAW LAKES

Hopkins (1949, p. 119) defines a thaw lake as one
which occupies a thaw depression; however, the
definition includes lakes that originated in other ways
but that have been enlarged considerably by the
thawing and caving of their margins. The term
“cave-in-lake,” (Muller, 1943, p. 214) is used somewhat
synonymously with “thaw lake,” but the original
definition limits its usage to lakes formed in caved-in
depressions caused by thawing of ground ice.

Thaw lakes are common throughout the permafrost
region and usually indicate poorly drained, fine-
grained, unconsolidated sediments with the perma-
frost table near the surface. These lakes are
characterized by undercutting and caving along their
margins, caused by the thawing permafrost (fig. 15).
Trees along the shorelines that lean toward the lake
because their root systems are being undercut are
conspicuous indicators of thaw lakes.

Oriented lakes, a very common type of thaw lake
in northern Alaska, cover more than 25,000 square
miles of the arctic coastal plain (Black and Barksdale,
1949, p. 105). They range in size from small ponds to
more than 9 miles long and 3 miles wide. The long
axis of these lakes is oriented in a northwesterly
direction (ranging from 10° to 15° west of true north).
This preferred orientation is strikingly shown on the
topographic maps of northern Alaska.

BEADED DRAINAGE

Beaded drainage occurs in areas underlain by
systems of ice wedges. The heat in the flowing sur-
face water thaws the underlying ice masses (usually
at ice-wedge intersections) forming depressions
occupied by pools of water connected by the normally
flowing stream. The overall appearance, when viewed
from the air, is like a string of beads,'hence the name
“beaded drainage.” Beaded drainage is a surface
indicator of the presence of permafrost.

PINGOS

Small ice-cored conical hills called pingos are common
in the continuous permafrost zone along the coastal

plain of northern Alaska and northwestern Canada

_ (Mackay, 1966, p. 71) and in the discontinuous perma-

frost zone in central Alaska (Holmes and others,
1968). Figure 16 shows a pingo of the type found in
the forested central part of Alaska. Pingos range
from 50 to several thousand feet in diameter, and
from 10 to several hundred feet in height. Commonly,
they have craters on their summits, which are occupied
by ponds.

Pingos indicate silty sediments and the presence of
ground water (with some hydraulic head) that is con-
fined between the seasonal frost and permafrost
table or is flowing in a thawed zone within the perma-
frost. Those in former lakebeds indicate saturated
fine-grained sediments.

MUCK DEPOSITS

Although not actually a geomorphic feature, peren-
nially frozen “muck” or organic-rich silt deposits are
widespread throughout interior Alaska (figs. 7 and 16)
and are important in permafrost areas. In the Fair-
banks area, the muck deposits are composed of
organic-rich windblown silt (loess) that has been re-
deposited (Péwé, 1966, p. 14). The tremendous amount
of organic material in the deposits presumably was
incorporated when the windblown silt was being
transported from the hillsides to the valley bottoms
by solifluction, sheet wash, and other gravity-type
processes. Muck deposits can be thawed in a few
months or years when the insulating quality of the
surface is modified. This material liquifies when
thawed and can create severe engineering problems.

 

FIGURE 13.-Large mass of ground ice exposed by gold placer

mining in silt bluff near Fairbanks. Thawing of a large ice
mass causes severe differential settlement of the surface of
the ground, as is shown in figure 14. Photograph taken in June
1955.

RELATED GEOMORPHIC FEATURES 13

FIGURE 14.—Thaw or thermokarst pit near Fairbanks formed
by the thawing of a large ice mass that caused severe differ—
ential settlement of the surface of the ground. ' Photograph
by T. L. Péwé, June 1948.

 

FIGURE 15.——Shoreline of a thaw lake about 40 miles northwest
of Glennallen in south—central Alaska. Shoreline undercut
because of thawing of permafrost. Vegetation mat of peat
is draped over surface of steep bank (8—12 ft high) and is
caving into lake. Trees in foreground are leaning toward
lake, and they too will cave into the lake as the undercutting
progresses landward. Photograph taken in June 1960.

 

FIGURE 16.~—Pingo in Yukon-Tanana Upland, east-central
Alaska. Light birch trees on pingo contrast with dark spruce
trees surrounding it. Pingo is about 300 feet in diameter and
50 feet high; water-filled crater on its summit makes it
“donut shaped.” Photograph by H. L, Foster, August 1960.

 

356-549 0 - 69 < 3

14

SUMMARY OF GEOMORPHIC FEATURES

Table 2 has been prepared as a quick reference to
the descriptions and ground conditions associated
with these common topographic features in permafrost
areas.

ENGINEERING GEOLOGY

Construction and maintenance of structures in the
arctic and subarctic regions underlain by permafrost
are characterized by a wide range of problems in
addition to those experienced elsewhere. Engineers,
designers, and construction and maintenance personnel
are continuously plagued by extremely severe frost
heaving, subsidence caused by thawing permafrost,
soil creep or solifluction, landslides, and icings. These
processes not only present construction and mainte-
nance problems but in the more severe cases may be
a hazard to the users of the structures.

There are two basic methods of constructing on
permafrost: (1) the active method and (2) the passive
method.

The active method is used in areas where permafrost
is thin and generally discontinuous or where it contains

PERMAFROST AND RELATED ENGINEERING PROBLEMS IN ALASKA

a relatively small amount of ice. The object of this
method is to thaw the permafrost, and if the thawed
material has a satisfactory bearing strength, then
construct in a normal manner. Sometimes the struc—
ture itself can be used to thaw the permafrost, and
the surface brought back to grade at intervals while
the thawing process takes place. Generally, the
thawing of the permafrost is accomplished simply by
clearing the vegetation, which normally insulates the
permafrost from the heat in the air and from solar
radiation. Heat from steam and warm water piped
into the ground has also been used to thaw perma-
frost. Naturally, the active method of construction
has limited application, because of the great thick-
ness of permafrost throughout most of the region,
and because of the time required for thawing the
ground.

The passive method, which has broad application
throughout most of the permafrost region, is used in
areas such as the North Slope, where it is impractical
to thaw the permafrost. The object of this method
is to minimize disturbance of the permafrost and of
the thermal regime. The thermal regime in an area

TABLE 2.— Common topographic features that indicate ground conditions in arctic and near arctic regions

Feature and description

Polygonal ground (ice wedges) ——Usually indicates the presence
of a network of ice wedges—vertical wedge-shaped ice masses
that form by the accumulation of snow, hoarfrost, and melt-
water in ground cracks that form owing to contraction
during the winter. Wedge networks are also common in wet
tundra where no surface expression occurs. (Subject to ex-
treme differential settlement when surface disturbed)

Stone nets, garlands, and stripes—Frost heaving in granular
soils produces netlike concentrations of the coarser rocks
present. If the area is gently sloped, the net is distorted
into garlands by downslope movement. If the slope is steep,
the coarse rocks lie in stripes that point down hill.

Solifluction sheets and lobes—Sheets or lobe-shaped masses of
unconsolidated sediment that range from less than a foot to
hundreds of feet in width that may cover entire valley walls;
found on slopes that vary from steep to less than 3°.

Thaw lakes and thaw pits—Surface depressions form when local
melting of permafrost decreases the volume of ice-rich sedi-
ments. Water accumulates in the depressions and may
accelerate melting of the permafrost. Often form impassible
bogs.

Beaded drainage—Short, often straight minor streams that
join pools or small lakes. Streams follow the tops of melted
ice wedges, and pools develop where melting of permafrost
has been more extensive.

Pingos—Small ice-cored circular or elliptical hills that occur in
tundra and forested parts of the continuous and discontinuous
permafrost areas. They often lie at the juncture of south-
and southeast—facing slopes and valley floors, and in former
lakebeds.

Associated ground conditions

Typically indicates relatively fine grained unconsolidated sedi-
ments with permafrost table near the ground surface; also
known from coarser sediments and gravels where wedge ice
is less extensive.

Indicate strong frost action in moderate well-drained granular
sediments that vary from silty fine gravel to boulders. Sur-
ficial material commonly susceptible to flowage.

Indicate an unstable mantle of poorly drained, often saturated
sediment that is moving downslope largely by seasonal frost
heaving. On steeper slopes they often indicate bedrock near
the surface, and on gentle slopes, a shallow permafrost table.

Usually indicate poorly drained, fine-grained unconsolidated
sediments (fine sand to clay) with permafrost table near the
surface.

Indicate a permafrost area with silt-rich sediments or peat
overlying buried ice wedges.

Indicate silty sediments derived from the slope or valley, and
ground water with some hydraulic head that is confined be-
tween the seasonal frost and permafrost table or is flowing
in a thawed zone Within the permafrost. Those in former
lakebeds indicate saturated fine-grained sediments.

ENGINEERING GEOLOGY 15

in a natural undisturbed state is normally in quasi-
equilibrium with all the environmental factors, but
in many areas this state of equilibrium is very sensi-
tive. The simple passage of a tracked vehicle that
destroys the vegetation mat is enough to upset the
delicate balance and to cause the top of the perma-
frost layer to thaw. This thawing can cause differ-
ential settlement of the surface of the ground, drainage
problems, and severe frost action. Once the equilibrium
is upset, the whole process can feed on itself and be
practically impossible to reverse. However, if a
structure is founded on permafrost that remains
frozen, the frozen ground provides rocklike bearing
strength. In special cases it may be practical to keep
the permafrost intact by using a refrigeration system.

Engineering problems in permafrost nearly always
are associated with the active layer (the layer that
freezes and thaws annually) and the active layer-
permafrost interface (permafrost table). Changes in
the surface environment, either natural or man made,
produce thermal changes in this zone that can have
serious effects upon engineering works and structures.

ENGINEERING PROBLEMS

The engineering problems associated with perma-
frost are not similar in every type of rock or sediment.
For example, bedrock that contains ice in its fractures
will present few, if any, construction or maintenance
problems. Well-drained coarse-grained sediments
such as glacial outwash gravel, although below 0° C,
may not contain any ice. Here again few, if any,
construction problems will arise. If water is saline,
it will remain in the liquid state even if its temper-
ature is below 0° C. The problems associated with
this condition are different from those asSociated
with permafrost containing moisture in the frozen
state. '

Major engineering problems arise where permafrost
occurs in poorly drained fine-grained sediments. In
such sediments there are generally large amounts of
ice, and when the thermal regime is disrupted the
ice begins to melt. The thawing produces excessive
wetting and undesired plasticity of the fine-grained
sediments and renders them unstable. This instability
can result in settling, caving, and subsidence of the
ground surface, and in many cases, in flowage of the
sediments either laterally or downslope.

During the winter months the active layer freezes

' downward from the ground surface to the perma-
frost table. In the fine-grained material, formation
of this ice results in frost heaving.

Thawing of permafrost and the heaving and sub-
sidence caused by frost action are responsible for the

major engineering problems in the subarctic and
arctic regions. The following discussion on the thaw-
ing of permafrost, the freezing of the active layer,
and frost action on ground surface and on piles is
presented to prevent repetition of engineering prob-
lems. Many of the problems are common to most, if
not all, of the structures discussed.

Thawing of Permafrost

In the past it was engineering practice to remove
the protective vegetation cover during construction;
thus some of the insulating effect was lost. As soon
as the delicate thermal equilibrium is disrupted,
permafrost starts to thaw. The result of this thaw-
ing is to lower the permafrost table underneath the
fill and to make the active layer thicker. The thicker
active layer collects larger quantities of moisture,
and consequently during the winter greater heaving
of the ground surface occurs when the moisture
freezes. On the other hand, during the summer, the
active layer thaws and the sediments lose their
strength causing subsidence, flowage of sediments,
and landslides if the structure is on a slope.

With few exceptions, structures in the arctic require
some sort of pad or fill. The nature and thickness of
the fill—particularly the thickness— are the controlling
factors. Figure 17 shows the effects of the pad or fill
upon the temperature fluctuations, depth to the
permafrost table, and thickness of the active layer.
The result of too little fill is shown in figure 17A. In
this example the insulating effects of the fill plus the
compacted active layer is less than the insulating
effect before construction. The result is thawing
permafrost and an increase in the thickness of the
active layer.

Figure 173 shows what will happen if the insu-
lating effects of the fill and the compacted layer is
greater than the original active layer. In this case,
the permafrost table is raised because the amplitude
of the seasonal temperature variation is smaller.

The procedures for calculating the appropriate
thickness of gravel fill for various climates and
materials are explained in detail by Lachenbruch
(1959). When the calculated thickness of fill becomes
so great as to be impractical, alternative procedures
are necessary, such as using insulating materials
under the fill.

Although the ice in the sediments is responsible for
the heaving, it does give the sediments strength
during the winter. However, when the ice melts
during the summer, this strength no longer exists and
the results may be damaging. If a structure is con-
structed during the winter, the ice-rich sediments will

TEMPERATURE

PERMAFROST AND RELATED ENGINEERING PROBLEMS IN ALASKA

 

 

 
   

 

 

 

 

 

0000:0350‘luoo o °°ee°§°°0 no 06°00

90° as :QNO‘H‘O" Gravelfill ° op “00003000 0

Originalgroundsurface“o°‘§°” c700 "oi.°°"°‘2 0 9°°Oo° °
50 00° 0 go o cage 0 00., o 0 0° 0 o A

c ° ° 5 s ; ‘5 ‘ 5 °

°°n°°° aOooao moo/\OO n°a°oo°o 0° o /#
Active? . // i
\ Compacted active layer —flfir /’

 

      
  
 

 

layer

 

 
  

' permafrost
- table '

 

permafrost
. table

 
 
  

 

A. Effect on permafrost table if insulating of fill plus compacted active layer is less than the insulating effects of
original active layer.

 

 

  

0
Q Q a o o _o 0- C° 0 O
C Dc 0 u ” a 0 O 0 00
o C o 0 o Gravelfill ° 0 o
a Q o a
3 A o o c °
0 " C a g 2 ° :7 °

° 0 ° QPost fill permafrost table

          
     
   
 

 

  
 

Active

layer Compacted active layer

- Original perrnafrost table ,-

 

 

 
    

 

 
      

 

 

   

 

B. Eflect on permafrost table if insulating effect of fill and active layer is greater than the insulating effect of the
original active layer.

 

/ —\ finance temperature

/ //___\CafleA \

l

l

I

/// \\\\ I
// \ \ i
l

l

 

. . \
/ //0rrgrna| temperature at \
/ permafrost tablL \\ \

0°C
Mean
annual
temper-
ature

 

 

 

 

Summer" TIME Winter
C. Effects of cases A and B on amplitude of seasonal temperature variation at original permafrost table.

FIGURE 17.—Diagram showing effect of gravel fill upon thermal regime.

ENGINEERING GEOLOGY ‘17

not fail, but when the ice thaws, the structure will be
damaged by subsidence or by flowage of sediments
from beneath the structure. Highways become im-
passable during the summer, whereas during the
Winter they are considered to be relatively high-
speed roads.

Frost Heaving

Frost heaving has long been known as a major
destructive factor to structures. Although the frost-
heaving mechanism is complex, the major factors
controlling it are ground-surface temperatures, sur—
face condition of the soil, and characteristics of the
soil. Soil properties include structure, permeability,
thermal properties, physical and chemical properties,
and moisture content. Of these factors, the most
important are the moisture content and texture of
the sediments.

The nature of the ice in the active layer, as well
as the thickness of the layer, has an important effect
on the amount of frost heaving. In relatively coarse
grained sediment with a low water content the ice
acts as a binder and does not produce much heaving.
If coarse sand is interbedded with silt and the water
content is not high, ice forms as layers in the silt and
as a binder in the coarse sand. In this case, thin ice
lenses are formed and moderate heaving results. If
the sediments are silt and fine sand and the water
content is high, large masses of segregated ice will
form and maximum frost heaving will occur.

Frost heaving is a major problem in the arctic and
subarctic primarily because most of the low-lying
areas are covered by fine-grained surface materials
which are poorly drained.

Frost Heaving of Piles

The use of piles for support of structures is as com-
mon in the arctic region as it is in the lower latitudes.
The problems, however, are quite different. In the
warmer climates, the chief problem with the use of
piles is to obtain sufficient bearing strength. In arctic
regions, the chief problem is to keep the piles in the
ground. Frost action heaves them up, and any struc-
ture placed upon the piles is also displaced upward,
usually differentially.

The force that tends to displace the piles upward is
generated in the freezing active layer and is a func-
tion of the adfreezing strength between the pile and
the active layer, the depth to which the pile has been
driven in the active layer, and the perimeter of the
pile. The forces acting downward are the load upon
the pile, the weight of the pile, and the forces pro-
duced in the unfrozen active layer and in the perma-
frost. The force in the unfrozen active zone is the

skin-friction bond between the pile and unfrozen
ground over the lateral surface of the pile. The force
in permafrost is equal to the tangential adfreezing
strength between the pile and the frozen ground
distributed over the pile length and the lateral sur-
face of the pile.

The upward-acting forces become greater as the
active layer freezes, therefore the thicker the active
layer the greater the upward forces. The downward-
acting forces in permafrost depend on how deeply the
piles penetrate it. If the thermal regime is disrupted
and the permafrost starts to thaw, the downward
force of the permafrost becomes less and the upward
force of the active layer becomes greater. Conversely
if the permafrost table rises from its original position,
the downward force of permafrost becomes greater
after an initial upthrusting.

Péwé and Paige (1963, p. 364) give a hypothetical
example of seasonal frost penetration (freezing of
active layer) into silt and show the possible upward
forces on a 40-inch-perimeter pile. Their data are re-
produced in this report as table 3. Note that the up-
ward force becomes greater as the frozen layer
becomes thicker at a rate of about 21,600 pounds per
foot. It should be stated that Péwé and Paige had
to make the assumption that the texture of the silt
and the water content was the same throughout the
41/2-f00t zone. These two factors definitely influence
the bond between the frozen active layer and the
pile, and therefore the tangential adfreezing strength.
The general discussion of thawing permafrost, the
freezing active layers, and frost heaving of piles given
above applies to all the descriptions of individual
structures that follow. The problems are common to
all structures in the arctic.

TABLE 3,—Hypothett’cal example of seasonalfrost penetration into
silt in central Alaska and possible upward push on 40-t'mh-
perimeter pile (ground temperature constant)

[After Péwé and Paige, 1963, p. 364]

Depth of frost
penetration
(feet)

Maximum force
pushing upward
(pounds)

Date

November 1____,_~~______ 1 21,600
December 1____‘________- 11/2 32,400
January1_____—v__——————— 2 43,200
February 1 ________________ 3 64800
Marchl —————————————————— 4 86,400
Apr111—————————~——————-— 41/2 97,200

SPECIFIC STRUCTURES

The problems associated with permafrost and frost
action affect structures in numerous ways. There-
fore, a brief description of the engineering problems
associated with these effects is presented in the fol—
lowing pages.

18 PERMAFROST AND RELATED ENGINEERING PROBLEMS IN ALASKA

Railroads

Railroad engineers prefer to keep grades under2
percent (2 ft of vertical for every 100 ft of horizontal
distance). Unfortunately this requires that the road—
bed be placed in low-lying terrain which is usually
underlain by poorly drained fine-grained sediments
containing permafrost. Therefore, construction
problems arise, and expensive maintenance problems
develop.

The Alaska Railroad, which runs from Seward (mile
0) to Fairbanks at mile 470.3 (fig. 18), was started
about 1910 by a private company, The Alaska Central,
and was completed in 1923 by The Engineering Com—
mission.

Railroad personnel encountered many construction
problems because of thawing permafrost. A minimum
of fill and ballast was placed on the right-of-way,
causing areas underlain by ice-rich permafrost to
thaw. When the thawing occurred the fine-grained
sediments lost their strength and the sediments either
subsided or flowed from underneath the roadway.

The roadway of The Alaska Railroad is underlain
locally by ice-rich permafrost where sediments are
fine grained and poorly drained between Broad Pass
(mile 304.5) and Dunbar (mile 431.6) and almost con—
tinuously from Dunbar to Fairbanks, where the rail-
road follows the valley of Goldstream. The mainte-
nance from Dunbar to Happy (mile 463.0) amounts to
about $200,000 per year (T. C. Fugelstad, The Alaska
Railroad, personal commun.) because of the need to
install shims beneath the rails and replace ties dama-
ged by frost heaving during the winter. Locally,
slower than usual train speeds (slow-orders) are in
effect during the winter with a consequent loss to
The Alaska Railroad.

When winter has passed and summer arrives, The
Alaska Railroad has other permafrost problems. In
summer the active layer and eventually the under-
lying permafrost starts to thaw. When this happens
the track subsides, usually differentially (fig. 19).

If the subsidence is not corrected yearly and the
track not brought to grade, the track would look like
the roadbed shown in figure 20. The railroad which
ran from McCarthy to Cordova (fig. 18) was con-
structed in 1911 to carry copper ore to the port of
Cordova. The railroad was abandonedin 1938, and
much of its roadbed is now being incorporated into
the Copper River Highway.‘

During the summer The Alaska Railroad places
great quantities of gravel in the sink holes caused by
thawing permafrost in order to maintain grade. Line

changes and ditching are also required in order to
control permafrost problems. About $177,500 is spent
annually to correct the effect of the thawing.

At Moody. a point on The Alaska Railroad where it
follows the Nenana Canyon through the Alaska
Range toward McKinley Park. the roadbed is under-
lain by fine silt and clay that was deposited in an
ancient glacial lake. The temperature of permafrost
here is close to ()7 C. and when the railroad was con-
structed the thermal equilibrium was disrupted and
the permafrost started to thaw. Over the years this
thawing has required numerous line changes and
remedial measures. Figure 21 shows some of the land-
slides that have occurred. Figure 22 is a photograph
of the landslide area near mile 353.5. Piles were
driven immediately downslope from the rails in order
to prevent the tracks from sliding into the canyon. The
pebbles, cobbles, and boulders shown in the photo-
graph are from the gravel which overlies the lake
silts and clays. Vertical displacements at the Moody
slide have been as much as 4 feet in one day. During
the period when landsliding is expected, the track is
patrolled in advance of all trains. Remedial measures
to combat the landsliding vary from year to year.
During the summer of 1967, over $400,000 was spent
to realine the track and bring it to grade.

Many bridges on The Alaska Railroad are also
affected annually by frost heaving and require
maintenance. Time does not permit a discussion of
all the structures, and therefore only two bridges are
described—one supported by piles and the other by a
concrete pier.

The bridge at mile 458.4, in Goldstream valley, is 71
feet long and supported by six bents of wooden piles.
Péwé and Paige (1963, p. 380—383) present a detailed
description of this structure. A summary of their
description of the bridge and its history follows.

The bridge, which was constructed in 1917, is under-
lain by perennially frozen silt. The permafrost table
on September 20, 1954, was 11 or 12 feet below the
ground surface at the ends of the bridge and 13 feet
deep under the creek.

This wooden-pile bridge has had a continual history
of frost heaving and was affected more than any
other wood-pile bridge on The Alaska Railroad. The
earliest record of pile history was in 1923 at which
time all the piles were replaced. The new piles were
sunk to depths ranging from 12 to 23 feet, the great-
est penetration being at the end bents. During the
winter of 1952—53, Péwé and Paige report that the
center of the bridge was heaved 14 inches—a dis-

ENGINEERING GEOLOGY

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EXPLANATION

- ——.*.*r~._‘_

Abandoned railroad

 

Winter road

Highway

Abandoned highway

Clear

Existing route of The Alaska Railroad,
showing station house

._.-—._..—.-o«.»~...

Proposed route of The Alaska Railroad,

showing mile posts. Alternate routes
are indicated by numbers

FIGURE 18.—Location of transportation routes in Alaska.

20 PERMAFROST AND RELATED ENGINEERING PROBLEMS IN ALASKA

 

FIGURE 19.—Differential subsidence caused by thawing permafrost along the Murphy Dome Spur of the Alaska Railroad.

Roadbed is in Goldstream valley and is underlain by silt.

placement great enough to decouple railroad cars.
The Alaska Railroad cut off the top of the piles and
brought the rails back to grade—a common practice
in this area.

Frost heaving continued in the winter of 1953—54,
and by February 1954 the bridge had heaved 9 inches.
In the latter part of February the piles were again
replaced, most of the piles being sunk deeply in
permafrost. Frost heaving was not evident during
the winter of 1954-55. However, during the Winter
of 1955—56, frost heaving again occurred and by
February 8, 1956, the bridge had been heaved 3 inches
at bent III, and by the end of the winter it had risen
to 5 inches. Péwé and Paige’s record stops in 1956.
However, Bruce E. Cannon of The Alaska Railroad
stated that heaving of the bridge is of only minor
consequence at this time (personal commun., 1969).

The explanation for this sequence of events is as
follows: The piles were driven into steam-thawed
holes and emplaced deep in the thawed permafrost.
The permafrost then started to refreeze and must
have completely refrozen during the winter of 1955—

Photograph by T. L. Péwé, June 1954.

56. The first winter after the piles were placed
(1954—55) the only forces heaving the piles upward
were those of the active zone. Apparently these
forces were not very strong. The second winter
(1955—56), when as much as 5 inches of heaving oc-
curred, the permafrost must have contained more
moisture than when the piles were placed. When this
additional moisture froze, it expanded and added to
the upward force of the active layer. This upward
force acted only in the winter of 1955—56, because by
the end of that winter the permafrost had refrozen to
its original position.

The railroad bridge spanning Riley Creek at mile
347.4 near McKinley Park is a 570-foot steel-viaduct
structure supported by concrete piers and concrete
abutments. At the request of The Alaska Railroad
the bridge site was examined by Reuben Kachadoorian
in 1957 to determine the cause of differential heaving
of the bridge. In some places the heaving was as
much as 5 inches. The piers rest upon sandy stream
gravels, which generally are not susceptible to very
severe frost action. However, the permafrost table

ENGINEERING GEOLOGY 21

beneath the bridge was irregular and varied from a
position lower than the pier bottoms beneath the piers
to positions higher than the pier bottoms between the
.piers. This position varied because the concrete in
the piers had a much higher thermal conductivity
than the snow or water which surrounded the pier
during the winter. Therefore, heat was drawn off
from the ground by the piers and ice formed beneath
the piers. As the ice grew, additional water was
drawn from the unfrozen area around and beneath
the piers until a sufficient amount of ice formed to
heave the piers. After this explanation was given,
The Alaska Railroad took remedial measures, and the
effect of frost action upon the Riley Creek bridge was
minimized.

Highways and Roads

There are over 2,000 miles of primary and secondary
roads in Alaska; the majority are subjected to frost
action and are underlain by permafrost. The recent

discovery of petroleum north of the Brooks Range at
Prudhoe Bay will no doubt stimulate a great deal of
highway construction in the area, and all highways

 

will be underlain by permafrost and subject to
heaving from frost action. If constructed improperly,
the roads will require costly maintenance or even
abandonment.

A highway constructed during the winter months
may lead the builder into false security. If, for ex-
ample, the vegetation cover were removed and the
roadbed smoothed with heavy equipment, winter use of
the highway would not generate any problems of thaw-
ing, and any frost heaving of the roadway would be
minor.

Bogs, swamps, or other such areas are perfectly
capable of supporting traffic during the winter
months when they are frozen to a depth of 2 feet or
more. Since they are level, they actually invite
construction.

In order not to disrupt the thermal equilibrium in
permafrost areas, more fill is necessary in the road-
bed. The amount of this extra fill is variable under
different geological conditions, but it is always a
major cost factor. For example, highway contsruc-
tion costs in areas underlain by permafrost are sub-
stantially higher than in areas free of permafrost.

FIGURE 20.—Differentia1 subsidence of roadbed of Copper River and Northwestern Railway near Strelna, 75 miles northeast

of Valdez.

The thermal equilibrium of the fine-grained sediments underlying the roadbed was disrupted during construc-

tion and the permafrost started to thaw. Maintenance and use of the railroad was discontinued in 1938. Subsidence as
well as lateral displacement, however, has continued. Photograph by L. A. Yehle, September 1960.

\

22 PERMAFROST AND RELATED ENGINEERING PROBLEMS IN ALASKA

 

EXPLANATION

T_T_I_T_|_l_1_

Landslide scarp
at head of slide

Old drainage structure

 

 

New drainage structure

CMP = Corrugated metal pipe

Milepost

 

 
  
   
 
 
 
  
 
 
  
 
  
  
 

—————>N

French drain

Wood pilings

xisting alignment

  

200

 

400

 

600 FEET

 

APPROXIMATE SCALE

 

FIGURE 21.—Map of the Moody area on The Alaska Railroad showing landslides and slumps caused by thawing of permafrost
and remedial measures taken to combat them. Map prepared by The Alaska Railroad, 1967.

Mr. R. D. Shumway, Alaska Department of Highways,
supplied the authors with an analysis of costs of the
highway between Rex and Lignite in central Alaska
north of the Alaska Range. His results are shown
in table 4. One can see that the cost of borrow
material in permafrost areas was about 11/2 times as
much as in permafrost-free areas; the costs of gen-
eral excavation and of pit stripping were about twice
as much.

TABLE 4.—Compariso'n of construction costs, per cubic yard, be—
tween permafrost and permafrost-free areas of the highway
between Rex and Lignite, Alaska

Nonpermafrost area Permafrost area

Borrow material- _ _ _ _ _ _ _ _ A _ $0.509 $0.749
General excavation _ _ _ _ _ _ _ _ _ .464 .967
Pit stripping__ __ __ __ __ ___ .164 .370

Many of the highways in Alaska were originally
pioneer or “tote” roads constructed chiefly by re-

moving the vegetation and adding fill. Figure 23
shows the character of the ground surface in July
immediately after the removal of the insulating
vegetation. The permafrost was exposed in the hope
that the sun would thaw it sufficiently by late
summer so that fill could be placed upon the thawed
sediments. By September the ice in and around the
polygons had thawed to a depth of at least 4 feet;
this thawing resulted in differential subsidence of the
ground surface. In addition, the silt had lost all its
bearing strength and was nothing more than a
quagmire; consequently, the site was abandoned and
the location of the road was moved.

The thermal disturbances created by a roadway
have been studied in detail along the Richardson,
Glenn, and Tok Highways near Glennallen, Alaska
(Greene and others, 1960). Here the permafrost is
relatively thin (50—150 ft thick) and mean annual
temperatures below the undisturbed ground surface
are rarely lower than —2° C. Thus conditions favor
extensive thawing when the surface is disturbed. It

ENGINEERING GEOLOGY 23

was found that beneath the roadway the amplitude
of seasonal temperature fluctuations was two to three
times that found in the nearby undisturbed ground.
Furthermore, the ground beneath the roadway was
more sensitive to random climatic variations from
year to year. A change of only 4° C in the mean
annual air temperature over a 2-year period caused a
25° C change in the mean annual temperature at
depths of 5 to 10 feet beneath the roadway and a
change of less than 1° C at similar depths in undis-
turbed ground nearby. The increased amplitude of
seasonal temperature variations together with the
greater sensitivity to an increase in the mean surface
temperature caused a trough of thawed ground to
form beneath the roadway. Water from thawed
permafrost drained along the trough until it was
trapped in a basin or escaped by exterior drainage.
Settling of the roadway followed. Heaving resulted
where the melt water was trapped and later refrozen.
In subsequent years freezing and thawing of the
active layer was accelerated where the melt water

had drained away because of the absence of latent
heat. Therefore, thawing in colder years reached
depths previously attained only in warm years.

During the summer of 1954,the Alaska Road Com-
mission (now Alaska Department of Highways) ex-
posed permafrost in lake silts 2 miles north of Paxson.
The ice-rich lake sediments started to thaw and
actually flowed (fig. 24).

In many places the thickness of the fill used by the
road crews is insufficient to prevent the thawing of
the permafrost under the roadbed. An excellent ex-
ample of one such place is shown in figure 25. The
photograph shows the remains of a road from the
Umiat Airstrip to several drilling sites in the area; it
was constructed about 1950 and abandoned around
1953. The road is underlain by fine-grained sediments
containing ice—wedge polygons. The breaks across
the roadway are due to the melting of the ice wedges.
Such conditions will occur again if the potential
effectsof thawing permafrost are not considered
during highway planning and construction.

 

FIGURE 22.-—Landslide area at mile 353.5, The Alaska Railroad. Note the tops of piles immediately downslope from the rails
to prevent displacement of the tracks.

24 PERMAFROST AND RELATED ENGINEERING PROBLEMS IN ALASKA

 

FIGURE 23.—Initial location of part of the Denali Highway near the Susitna River, interior Alaska.
moving the insulating vegetation to expose polygonal ground in permafrost.
overlying silty glacial till.
graph taken in July 1953.

The location of a highway on a slope underlain by
unconsolidated materials always presents problems.
One must bear in mind that the highway is in a deli-
state of equilibrium, and that any change, not neces-
sarily to the highway itself, may generate a slump or
landslide in the structure.

Nichols and Yehle (1961, p. 25) describe such a slump
and slide in the Richardson Highway roadbed at
Simpson Hill near mile 113. This particular section
of the highway crosses a small gully in a long sidehill
cut. A thick fill was used to cross the gully. In the
spring of 1954, a new telephone line upslope from, and
parallel to, the road was constructed. During the
construction, a wide swath of the insulating vegeta-
tion cover was stripped off. Rapid thawing of the
permafrost during the summer resulted, releasing
moisture to saturate the fill downslope. This increased
moisture caused some small slumps in the fill. Early

The dark areas outlining the polygons overlie ice wedges as much as 12 inches wide.

Construction crew is re-
Sediments are windblown sand and silt
Photo—

in September 1954, in order to bring the road back to
grade, fill material was obtained from upslope and
downslope of the roadway. Overnight, a 15-foot-wide
section of the road slid downslope 10 feet (fig. 26).
The slide was repaired with large amounts of silt
excavated along the cut. Almost a year later, the
same part of the road again slid 10 feet after attempts
had been made to level minor slumps by the addition
of a small amount of fill. Black layers above the
culvert in the scarp of the landslide (fig. 26) are
asphalt, representing layers of paving laid during the
settlement or subsidence of the fill.

In nonpermafrost areas any fill or pad, Whether it
be for a railroad, highway, airstrip, or any other
structure, requires adequate drainage along its mar-
gins. Improper drainage may saturate the fill and
cause slumping or water may flow along the margins
of the fill and cause ersion. In permafrost areas

ENGINEERING GEOLOGY 25

improper drainage causes additional problems. If
the fill is allowed to saturate, it is much more sus-
ceptible to frost heaving and solifluction. In addition,
water flowing alongside the fill may melt the perma-
frost and cause thawing and subsequent collapse. The
results of inadequate drainage along the Sheep Creek
road northwest of Fairbanks are shown in figure 27.
Rainwater runoff, which should have been channeled
away from the highway, was allowed to flow along
the side. The water thawed the permafrost and the
edge of the roadway collapsed as much as 8 feet.
Thawing by flowing water does not occur only at the
edge of the road but may also develop on the road-
way itself.

Roads in permafrost areas that are built on the
vegetation, without fill, quickly become useless. In

addition they may do irreparable damage to the envi-
ronment. For example, at a camp in northwestern
Alaska (fig. 28) trails over the tundra were made by a
tracked vehicle called a “weasel." The trail from the
camp to the upper right of figure 28 climbs to the top
of a ridge. The constant use of weasels on this trail
compacted and destroyed the protective vegetation,
causing the underlying permafrost (about 1 ft below
the surface) to thaw. This thawing was accelerated
by runoff from rainfall, and by 1962 the gullies in the
road were as much as 15 feet deep. In the area ad-
j acent to the campsite the vegetation cover was com-
pletely destroyed, the underlying permafrost thawed,
and quagmire areas formed.

The removal of the vegetation cover during winter
highway construction will eventually create problems.

 

FIGURE 24.—Thawed lake sediments flowing around blade of bulldozer.
cut during the construction of the Richardson Highway 2 miles north of Paxson.

Ice-rich permafrost in the lake silts was exposed in a
Photograph by T. L. Péwé, June 1954.

26 PERMAFROST AND RELATED ENGINEERING PROBLEMS IN ALASKA

 

FIGURE 25.——Gravel road near the Umiat showing severe differential subsidence caused by thawing of ice-wedge polygons in

permafrost.

The winter road from Livengood on the Yukon River
to Sagwon on the Arctic North Slope was constructed
in the winter of 1968—69. By the end of the summer,
it is almost certain that thawing will have advanced
to the extent that the once high-speed road will be
impassable in places. It will either require fill to
bring the road up to grade or rerouting for use
during the coming winter.

Figure 29 is a photograph of a tractor trail con-
structed on the north slope near Canning River during

Photograph taken in August 1958.

the winter of 1967—68. The trail was built by bull-
dozing off the vegetation cover. The small ponds in
the abandoned trail formed during the summer of
1968. These ponds will continue to grow deeper and
wider as the permafrost thaws.

Frost heaving of highway bridges is as severe as

' that of bridges on The Alaska Railroad. The same

mechanism applies to both, Whether the piles are of
wood or of steel. Two examples of frost action on
bridges—one with wood piles whose ends were heaved

ENGINEERING GEOLOGY 27

 

FIGURE 26.—Slump block of fine-grained highway fill material at Simpson Hill, near mile 113 on the Richardson Highway.
Centerline of road formerly lay over exposed part of sheared culvert. Note bulldozer tracks on slump block surface, which
are a continuation of those at road level on right side of photograph. Photograph by D. R. Nichols, September 1955.

28 PERMAFROST AND RELATED ENGINEERING PROBLEMS IN ALASKA

and the other with steel piles whose center was
heaved—are shown in figures 30 and 31. The pattern
of heaving damage depends largely upon the amount
and distribution of water in the foundation material.
PéWé and Paige (1963) present an explanation for
the heaving of the ends of the bridge shown in
figure 31.

Figure 32 is a photograph of a steel-pile bridge on
the Kougarok Highway in the Seward Peninsula.
This highway extended from Nome to the mining
camp of Taylor, but is now maintained only to about
mile 84. The steel piles driven into fine-grained sat-
urated sediment heaved because of frost action.
Yearly frost heaving of the piles has completely de-
stroyed the structure. Center heaving of this bridge,

in contrast to the end heaving of the bridges shown
in figures 30 and 31, was caused by the complete
freezing of the flowing water and the underlying
sediments during the winter. The underlying sedi-
ments at the point of maximum heaving of the piles
contain a much higher moisture content than those
elsewhere underneath the structure. The bridge at
the outlet of Clearwater Lake (fig. 30) did not heave
near the center of the structure because the flowing
water and underlying sediments did not freeze.

Airfields
The gravel pad on an airstrip has the same effect
on permafrost as the gravels fills on railroad and
highway beds. Frost action or heaving also occurs on

 

FIGI'RIC 27.701d Sheep Creek Road northwest of Fairbanks.
thawed the permafrost in the underlying loess deposits. Photograph by T. L. Péwé, summer 1955.

Gully along edge of road was caused when the surface drainage

ENGINEERING GEOLOGY 29

 

FIGURE 28.—Oblique aerial photograph of Chariot Site, northwestern Alaska.
heavy equipment that moved over the terrain while the barges were being unloaded. Trails were caused by tracked vehi-

cles. Photograph by R. H. Campbell, summer 1960.

airstrips, but generally does not present a major en-
gineering problem. However, this does not neces-
sarily mean that frost heaving should be ignored; it
should be taken into consideration in determining the
«location of the airstrip and the design of the drainage
system around the airfield.

For years the paved runways at Northway, Alaska,
have been affected by thawing permafrost. The run-
ways are underlain by fine silts and sand with local
areas of ice-rich permafrost. At Gulkana, Alaska,
Where the airstrip also is paved, the runways are
underlain by ice-rich clayey lacustrine silts. Because
of differential subsidence the east-west runway at
Gulkana has been condemned. At Umiat, the air-
strip was constructed by placing a small gravel pad
upon fine-grained sediments containing ice-rich per-
mafrost. The runway was not paved. By 1952 the
runway had subsided differentially to the extent that
it had to be resurfaced with additional gravel (J. C.
Reed, personal commun, 1969).

Dark area to the left of camp was caused by the

Buildings

A building has a different effect on the thermal
regime of the underlying permafrost than does a road,
a runway, or an open storage area. There have been
many studies made of the influence of a building on
the thermal regime of permafrost, including one by
Lachenbruch (1957a). Lachenbruch’s paper presents
a basic formula for determining the thermal dis-
turbance caused by a heated building as well as other
important thermal problems caused by permafrost.
For example, the geothermal disturbance caused by
bodies of water and by highway and railroad fills can
be analyzed by his theory. Brewer (1958) collected
data beneath a heated building 40 feet by 100 feet at
Barrow, Alaska, which showed that the temperature
rose about 51/2" C at a depth of 20 feet. Based on
Lachenbruch’s formula, the temperature would rise
about 6° C.

Some of the heated buildings at Barrow settled
differentially as much as 20 inches in 3 to 4 years

30 PERMAFROST AND RELATED ENGINEERING PROBLEMS IN ALASKA

 

FIGURE 29.—0blique photograph of tractor trail near Canning River, North Slope. Note small ponds due to thawing permafrost
in roadway. Photograph by Averill Thayer, Bureau of Sport Fisheries and Wildlife, August 1968.

(Brewer, 1958). When the buildings were no longer
heated the thawed ground beneath the structures re-
froze, and in some instances as much as 1 foot of frost
heaving occurred within a year.

Figure 33 is a view of a roadhouse on the Richardson
Highway. The building, constructed in 1951, sub-
sided’the most near the front of the center section
where the furnace was located. The porch did not
subside as much as the center of the building because
it was unheated. The building had to be razed in 1965.

The problem of averting settlement of heated
buildings in permafrost areas has received a great
deal of attention. The most promising method of

solving the problem is to build the structure above
ground with large air holes in the foundation. This
allows the cold winter air to circulate beneath the
floor of the building, counteracting the effects of the
heat. Figure 34 is a photograph of a schoolhouse on
a concrete foundation at Glennallen, Alaska. The
air vents through the foundation are opened during
the winter and closed during the summer. The jacks
are used to keep the structure level because of dif-
ferential subsidence in the ice-rich sediments that
underlie the building.

Frost heaving of buildings is a common occurrence
in arctic and subarctic environments. If piles are

ENGINEERING GEOLOGY 3 1

 

FIGURE 30.——Frost—heaved piling of bridge spanning outlet of Clearwater Lake, 8 miles southeast of Big Delta. Files are of
wood. Photograph by M. F. Meiser, August 1951.

     
     
     

 

 

 
 

Bridge floor
1'9: m
Wat

 

 

 

 

 

 

 

 

 

 

/

AfterT L Péwé, 1951

 

10 O 10 20 FEET

HORIZONTAL AND VERTICAL SCALE

FIGURE 31.—Geologic sketch of foundation conditions of frost-
heaved bridge, 8 miles southeast of Big Delta. Compare
with figure 30. After Péwé and Paige (1963, p. 349).

32 PERMAFROST AND RELATED ENGINEERING PROBLEMS IN ALASKA

 

FIGURE 32.——Frost-heaved steel-pile bridge spanning North Fork at about mile 120 on the Kougarok Highway, Seward Peninsula.
Photograph by G. D. Eberlein, summer 1955.

improperly emplaced, frost heaving is as damaging to
buildings as it is to highway and railroad bridges.
Buildings resting upon concrete foundations may be
heaved beyond the yielding point of the concrete.
Figure 35 shows the results of frost action upon the
foundation for an apartment house in Fairbanks. The
foundation was laid during the late summer of 1953
and left exposed during the winter of 1953—54. The
underlying flood-plain silts were saturated and during
the winter sufficient ice formed to heave and rupture
the structure.

Power and heating plants produce large amounts
of heat which, if improperly insulated, may thaw the
underlying permafrost. Therefore, these structures
require special attention in location, design, and con-
struction.

Aircraft hangers usually cover a large ground area
and require heating. Because the underlying sedi-

ments vary, permafrost will thaw differentially,
causing an uneven settlement of the floor.

Dams

Dams constructed on bedrock present no major
permafrost or frost-heaving problems. However, if
the structure is placed on sediments containing ice-
rich permafrost, the impounded water will initiate
thawing of the underlying permafrost. The dam will
then settle differentially and will crack. Also, water
may seep or be piped beneath the dam, eventually
eroding the support for the structure; thus, a careful
study of the nature of the reservoir section of the
damsite should be made to determine whether the
dam is founded in bedrock or sediments. Any frozen
sediments under the impounded body of water will
thaw, and will result in slumping and landsliding.

ENGINEERING GEOLOGY 33

Telephone and Power Transmission Lines

Telephone lines and powerlines carried on wood
poles present major problems, because of frost
heaving. Telephone and power poles are much more
severely heaved than the bridge piles because the
poles have a much less load and usually are not deeply
emplaced in permafrost. Service and construction
roads along the telephone lines and powerlines cause
additional problems by melting the underlying perma-
frost. Eventually the roads become impassable and
rerouting is necessary.

Large steel transmission lines requiring more than
one foundation may heave differentially during the
winter and settle differentially during the summer.
These massive, usually high, structures are sensitive
to differential displacement and may require continued
maintenance in permafrost regions.

Pipelines
The construction of pipelines in an arctic environ-
ment is, at best, a major undertaking. If the pipeline
is placed underground, the vegetation cover overlying
the permafrost is destroyed, disrupting the thermal
regime. This disruption can cause differential settle—

ment of the pipeline, and, since it is underground, the
settlement may not be noticed until the pipeline has
been ruptured. If the line carries a warm fluid, it
will thaw the permafrost and cause differential
subsidence which could cause the structure to lose
support.

Pipelines on the surface or on a supporting structure
are subjected to frost heaving during the winter and
subsidence during the summer. This action will be
especially strong if the line passes over fine-grained
sediment or over a bog or swamp. Other areas to be
avoided are solifluction lobes where slow gravitational
flowage of masses of surficial material occurs. These
masses move downslope during the summer months
after the active layer is thawed. If a pipeline were
placed in or on these solifluction lobes, it probably
would be damaged by the downslope movement.
Therefore, such areas should be recognized and
avoided. Another place to be avoided is the bottom
of a stream channel, where winter ice on the stream
might damage the pipeline.

In areas where the permafrost contains ice wedges,
severe damage to an above-ground pipeline will occur
if the ice wedges are allowed to thaw. The effects of

 

FIGURE 33,—Roadhouse, mile 278.5, Richardson Highway. The structure is distorted because of thawing of the underlying
ice-rich permafrost in fine-grained silts and sands. Photograph by T. L. Péwé, May 29, 1962.

34 PERMAFROST AND RELATED ENGINEERING PROBLEMS IN ALASKA

 

FIGURE 34.—View of the schoolhouse at Glennallen.
counteract heat from building.
settlement. Photograph by T. L. Péwé, May 1954.

thawing ice wedges has already been described in the
the discussion of highways.

Construction and service roads for pipelines present
the same problems as those built along powerlines
and telephone lines.

Utilidors

Utilidors are used extensively in arctic and sub-
arctic regions to carry utilities such as water, steam,
gas, sewerlines, powerlines, and telephone lines.
Figure 36 is a picture of a utilidor under construction
near Fairbanks. An ideal location for an underground
utilidor is an area underlain by well-drained ice-free
materials that extend to depths of at least 15 feet.
However, ideal locations are not always available, and,

Air vents, which are open, allow cold air to enter crawlway in winter to
The vents are closed during the summer.

Jacks are used to counteract any differential

therefore, many utilidors are damaged by subsidence
and frost heaving.

Above-ground utilidors are constructed in areas
Where the active layer normally freezes down to the
permafrost table. These above-ground structures
will be subjected to the same engineering problems
as above-ground pipelines.

ICIN GS

In arctic and subarctic regions, water which reaches
the surface in the winter from a river or spring may
freeze in successive sheets, until the ice covers a large
area. These sheetlike masses are termed “icings.”
Icings are usually small—seldom larger than a few
acres. However, some as large as 48,000 to 54,000

ENGINEERING GEOLOGY 35

 

FIGURE 35.—Fracture due to frost heaving of 4-inch concrete foundation of an apartment house in Fairbanks. Photograph by
T. L. Péwé, June 1954.

 

FIGURE 36.—Utilidor under construction at Fort Wainwright near Fairbanks, Alaska. Photograph by T. L. Péwé, J uly‘1947.

36 PERMAFROST AND RELATED ENGINEERING PROBLEMS IN ALASKA

acres are found on the Mony River valley in Siberia.
Icings as much as 30 feet deep, 1/2 mile wide, and 1
mile long were noted in the John River valley south
of Anaktuvuk Pass by T. C. Fugelstad of The Alaska
Railroad during early 1969.

A study of icings on the Glenn, Richardson, and
Alaska Highways of the Alaska Highway system
indicated that they were quite extensive and usually
occurred at road cuts (Williams, 1953). The maximum
icings were about 5 feet thick and originated at seeps
or springs. The Alaska Railroad is also plagued with
winter icings. These are more damaging and require
more maintenance than those on highways; the ice on
the railroads has to be removed to expose the rails,
whereas on highways icings need only to be leveled.
Winter icing increases the maintenance costs,for it
necessitates extra labor, special equipment, and
special techniques to combat the growing ice mass.
Countermeasures to reduce icing, such as the con-
struction of larger culverts to divert the source of the
icings, also increase construction costs.

Icings cause extensive damage to bridges through
diversion of streamflow and burial of the structure.
For example, river icings engulfed the bridge spanning
the Chistochina River 26 miles west of Slana, Alaska.
On February 15, 1950, the ice was 6 feet below the
bridge deck but had overflowed the west approach; it
was necessary to reroute the traffic across the river
ice (Williams, 1953).

Structures built on slopes may be filled with ice
during the winter if icing conditions are suitable.
Poorly insulated, heated buildings keep the under-
lying ground from freezing. If water with a hydrau-
lic head is trapped between the frozen ground and the
permafrost table, it may flow upward into the house.
In some places, houses have been filled very rapidly
by water that froze and filled the house with ice.

CONCLUSIONS

Construction and maintenance of structures under-
lain by permafrost pose a wide range of problems.
Engineers, designers, and construction and mainte-
nance personnel are continuously plagued by severe
frost heaving of structures, subsidence due to melting
ground ice, soil creep or solifluction, landslides, and
icings related to the presence of permafrost.

Some guidelines that can be followed to minimize
the adverse effects of permafrost and frost action
upon structures are summarized below.

1. Wherever possible, locate structures on coarse-
grained materials. Avoid fine-grained, poorly drained,
ice-rich sediments, since they are subject to much

greater frost-heaving and, if the permafrost is thawed,
to greater differential settlement.

2. Insofar as possible, make any gravel pad—
whether it be for a roadway, railroad grade, building
site, airstrip, or drilling site—sufficiently thick to
prevent permafrost from thawing.

3. Provide ample and proper drainage around
any structure to prevent the thawing of permafrost
and to minimize frost action and icings.

4. For heated buildings, whenever possible pro-
vide space for circulating air between the surface of
the ground and the floor to minimize the transfer of
heat into the ground.

5. Avoid the disruption or destruction of the
vegetation overlying permafrost by using such tech-
niques as end-dumping. Restrict tracked vehicles,
trucks, and other heavy equipment to roads and do
not permit them on the tundra or vegetation where
they will destroy its insulating quality and cause the
permafrost to thaw.

6. Minimize frost heaving of supporting piles by
providing the best possible drainage or by anchoring
them securely in permafrost if feasible.

7. Avoid borrow sits upslope or downslope
from structures. Thawing of the sites may cause
drainage problems or damaging slumps and land
slides.

8. Where parallel linear structures—such as pipe-
lines, roads, or telephone lines—follow the contours
of the slope, minimize disruption of the vegetation so
that slumping along one structure will not damage
the other.

9. Consider the following problems when pipe-
lines are laid across creeks or rivers: a) If the pipeline
crosses the creek or river underground, it may be
damaged by the slumping of huge blocks of perma-
frost undercut at the banks, or it may be exposed by
erosion and damaged by boulders, ice, or other debris
during flood stage. b) Pipelines placed on the surface
of a flood plain may be subject to inundation and pos-
sible damage by ice and floating debris.

10. Avoid construction in areas with natural icings
whenever possible, or if such areas must be utilized,
provide diversionary drainage.

The guidelines given above cannot be successfully
applied without a thorough understanding of the
thermal and mechanical problems unique to perma-
frost regions. Engineering procedures based on such
an understanding should permit optimum utilization
of the resources in the far north at a minimum over-
all cost and with a minimum disruption of the natural
environment.

PERMAFROST AND RELATED ENGINEERING PROBLEMS IN ALASKA 37

REFERENCES CITED

Black, R. F., and Barksdale, W. L., 1949, Oriented lakes of north-
ern Alaska: Jour. Geology, v. 57, no. 2, p. 105—118.

Brewer, M. C., 1958, Some results of geothermal investigations
of permafrost in northern Alaska: Am. Geophys. Union
Trans., v. 39, no. 1, p. 19—26.

Ferrians, O. J., Jr., 1965, Permafrost map of Alaska: U.S. Geol.
Survey Misc. Geol. Inv. Map I—445, scale 122,500,000.

'Greene, G. W., Lachenbruch, A. H., and Brewer, M. C., 1960,
Some thermal effects of a roadway on permafrost, in Short
papers in the geological sciences: U.S. Geol. Survey Prof.
Paper 400—B, p. B141—B144.

Holmes, G. W., Hopkins, D. M., and Foster, H. L., 1968, Pingos

in central Alaska: U.S. Geol. Survey Bull. 1241-H, 40 p.

Hopkins, D. M., 1949, Thaw lakes and thaw sinks in the Imuruk
Lake area, Seward Peninsula, Alaska: Jour. Geology, v. 57,
no. 2, p. 119—131.

Lachenbruch, A. H., 1957a, Three—dimensional heat conduction
in permafrost beneath heated buildings: U.S. Geol. Survey
Bull. 1052—B, p. 51—69.

1957b, Thermal effects of the ocean on permafrost:
Geol. Soc. America Bull., v. 68, no. 11, p. 1515—1529.

1959, Periodic heat flow in a stratified medium with
application to permafrost problems: U.S. Geol. Survey Bull.
1083—A, p. 1—36.

1962, Mechanics of thermal contraction cracks and ice-
wedge polygons in permafrost: Geol. Soc. America Spec.
Paper 70, 69 p.

1968, Permafrost, in Fairbridge, R. W., ed., The ency-
clopedia of geomorphology: New York, Reinhold Publishing
Corp., p. 833—839.

Lachenbruch, A. H., and Brewer, M. C., 1959, Dissipation of the
temperature effect of drilling a well in Arctic Alaska: U.S.
Geol. Survey Bull. 1083—0, p. 73-109.

Lachenbruch, A. H., Brewer, M. C., Greene, G. W., and Marshall,
B. V., 1962, Temperature in permafrost, in Temperature——
Its measurement and control in science and industry: New
York, Reinhold Publishing Corp., V. 3, pt. 1, p. 791—803.

Lachenbruch, A. H., Greene, G. W., and Marshall, B. V., 1966,
Permafrost and the geothermal regimes, Chap. 10, Wilimov-
sky, N. J., and Wolfe, J. N., eds., in Environment of the Cape
Thompson region, Alaska: U.S. Atomic Energy Comm. Rept.
PNE—481, p. 149—163.

Leffingwell, E. de K., 1915, Ground-ice wedges—The dominant
form of ground ice on the north coast of Alaska: Jour.
Geology, v. 23, p. 635—654.

1919, The Canning River region, northern Alaska: U.S.
Geol. Survey Prof. Paper 109, 251 p.

Mackay, J. R., 1966, Pingos in Canada, in Permafrost Interna-
tional Conference, Lafayette, Ind., 1963, Proceedings: Natl.
Research Council Pub. 1287, p. 71—76.

Muller, S. W., 1943, Permafrost or permanently frozen ground
and related engineering problems: U.S. Army, Office Chief
of Engineers, Military Intelligence Div. Strategic Eng.
Study 62, 231 p. Also 1947, Ann Arbor, Mich., Edwards
Bros.

National Academy of Sciences—National Research Council, 1966,
International Conference on Permafrost, Lafayette, Ind.,
1963, Proceedings: Natl. Research Council Pub. 1287, 536 p.
(Includes over 100 papers covering many aspects of perma-
frost research, as well as engineering and construction
solutions for problems of building in permafrost areas.)

Nichols, D. R., and Yehle, L. A., 1961, Highway construction
and maintenance problems in permafrost regions, in
Symposium on geology as applied to highway engineering,
12th Ann., 1961: Tennessee Univ. Eng. Expt. Sta. Bull. 24,
p. 19—29.

Péwé, T. L., 1954, Effect of permafrost on cultivated fields, Fair-
banks area, Alaska: U.S. Geol. Survey Bull. 989-F, p. 315—351.

1966, Ice wedges in Alaska—Classification, distribu-
tion, and climatic significance, in Permafrost International
Conference, Lafayette, Ind., 1963, Proceedings: Natl. Re-
search Council Pub. 1287, p. 76—81.

Péwé, T. L., and Paige, R. A., 1963, Frost heaving of piles with
an example from the Fairbanks area, Alaska: U.S. Geol.
Survey Bull. 1111—I, p. 333—407. \

U.S. Weather Bureau, 1943, Climatic atlas for Alaska: U.S. Air
Force Weather Div. Rept. 444, 229 p.; suppl., 72 p.

1958, Climatic summary of Alaska—Supplement for
1922 through 1952, no. 11—43: 39 p.

1950—68, Climatological data, Alaska: U.S. Weather
Bur., v. 36—54.

Washburn, A. L., 1956, Classification of patterned ground and
review of suggested origins: Geol. Soc. America Bull., v.
67, no. '7, p. 823—865.

Williams, J. R., 1953, Icings in Alaska, 1949—50: U.S. Geol. Survey
in cooperation with Engineer Intelligence Div., Office
Chief Engineers, U.S. Army, Eng. Notes 32, 23 p.

U. 5. GOVERNMENT PRINTING OFFICE : 1969 0 - 356-549

 

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3/ QETES 7 DAY
av ‘PCo
No. 6:79

Geology, Petroleum Development,
and Seismicity of the Santa Barbara

Channel Region, California
A. Geologic Framework of the Santa Barbara Channel Region
B. Petroleum Development in the Region of the Santa Barbara Channel

C. Geologic Characteristics of the Dos Cuadras Offshore Oil Field

D. Seismicity and Associated Effects, Santa Barbara Region

r

GEOLOGICAL SURVEY PROFESSIONAL PAPER 679

 

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5‘ (”W .\
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Geology, Petroleum Development,
and Seismicity of the Santa Barbara

Channel Region, California

A. Geologic Framework of the Santa Barbara Channel Region
By J. G. VEDDER, H. C. WAGNER, and J. E. SCHOELLHAMER

B. Petroleum Development in the Region of the Santa Barbara Channel
By R. F. YERKES, H. C. WAGNER, and K. A. YENNE

C. Geologic Characteristics of the Dos Cuadras Offshore Oil Field
By T. H. MCCULLOH

D. Seismicity and Associated Effects, Santa Barbara Region

By R. M. HAMILTON, R. F. YERKES, R. D. BROWN, JR., R. o. BURFORD,
and J. M. DENOYER

 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 679

 

 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1969

UNITED STATES DEPARTMENT OF THE INTERIOR
WALTER J. HICKEL, Secretary

GEOLOGICAL SURVEY

William T. Pecora, Director

Library of Congress catalog-ch No. 70—603491

 

For sale by the Superintendent of Documents, U.S. Government Printing Office
Washington, DC. 20402

FOREWORD

Southern California is rich in petroleum and natural gas accumulations
both on land and offshore. Over the past century, California has produced
more than 8 billion barrels of oil and more than 23 trillion cubic feet of gas.
The petroleum industry is one of the major economic factors of the State and
involves a capital investment in excess of $7 billion and employs more than
100,000 people. Daily production. of petroleum measures in excess of 1 million
barrels of oil, which is about 65 percent of the requirements for the region.
The situation is one of current shortage of production and projected increase
in need. As a natural extension of development of State tidelands, which
began in earnest in 1958, a public sale of Federal wildcat leases in 1968 drew
a surprisingly large total of $603 million.

During normal development of a prospective petroleum-bearing oil pool
on the Rincon structural trend, about 6% miles southeast of Santa Barbara,
a gas blowout occurred on January 28, 1969, during completion of the fifth
well being drilled from Platform A on Federal Tract OCS P-0241. Until
February 7, when the well was killed by cementing, uncontrolled flow led
to local oil pollution on the sea surface. Reservoir, damage during this
period caused a subsequent moderate and steady oil seepage from the
sea floor that has since caused a continual slick on the surface. This seepage,
estimated to be at a daily average rate of 30 barrels in the 4-month period
March through June 1969, was substantially reduced by early September to
less than 10 barrels per day as a result of a drilling and grouting program-
authorized by the Secretary of the Interior following recommendations of a
special Presidential Advisory Panel.

The Santa Barbara incident was the first significant oil-pollution experi-
ence resulting from drilling or working 7,860 wells under Federal jurisdiction
on the Outer Continental Shelf since 1953. In consequence of this event, by
direction of the Secretary of the Interior, Federal operating and leasing
regulations have been strengthened, and additional safeguards have been
added in all Federally supervised operations.

The purpose of this report is to present specific information that will
help provide a better understanding of the geologic framework of the Channel
region and of the circumstances relating to the oil seepage in the vicinity of
Platform A. The four chapters of this report and accompanying appendixes
have been compiled by staff members of the US. Geological Survey. Several
petroleum companies have permitted use of their proprietary technical data
in order to prepare a balanced and complete report. Opportunity to include
these data is gratefully acknowledged.

This report incorporates information upon which the recommendations
of the Presidential Advisory Panel were based as well as information that
subsequently has become available.

w?.....

W. T. Pecora
Director, US. Geological Survey

 

CONTENTS

Page
Foreword ___________________________________________________ III
(A) Geologic framework of the Santa Barbara Channel region, by J. G. Vedder, H. C.

Wagner, and J. E. Schoellhamer ________________________________ 1
(B) Petroleum development in the region of the Santa Barbara Channel, by R. F.

Yerkes, H. C. Wagner, and K. A. Yenne ___________________________ 13
(C) Geologic characteristics of the Dos Cuadras Offshore oil field, by T. H. McCulloh _ _ _ 29
(D) Seismicity and associated effects, Santa Barbara region, by R. M. Hamilton, R. F.

Yerkes, R. D. Brown, J r., R. 0. Burford, and J. M.DeNoyer ______________ 47
References cited _________________________________________________ 69
Appendix A ___________________________________________________ 71
Appendix B ___________________________________________________ 73
Appendix C ___________________________________________________ 73
Appendix D ___________________________________________________ 75
Appendix E ___________________________________________________ 76

PLATES

[In pocket]

PLATE 1. Generalized geologic map of the Santa Barbara Channel region.
2. Map showing oil and gas fields, leased areas, and seeps in the Santa Barbara
Channel region.
3. Structure of the Dos Cuadras oil field and contiguous parts of the Rincon trend.

 

 

 

Geologic Framework
of the Santa Barbara
Channel Region

By J. G. VEDDER, H. C. WAGNER, and J. E. SCHOELLHAMER

GEOLOGY, PETROLEUM DEVELOPMENT, AND SEISMICITY OF THE
SANTA BARBARA CHANNEL REGION, CALIFORNIA

 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 679—A

 

 

CONTENTS

Page

Regional setting ____________________________________________
Stratigraphic summary ________________________________________
Cretaceous marine rocks _____________________________________
Paleocene and Eocene marine rocks _____________________________
Oligocene marine and nonmarine rocks ___________________________
Miocene marine rocks ______________________________________
Lower part __________________________________________

Middle part __________________________________________

Upper part __________________________________________
Miocene volcanic rocks ______________________________________
Lower and upper Pliocene marine rocks ___________________________
Lower and upper Pleistocene deposits ____________________________
Holocene deposits ________________________________________
Generalized structure of the Santa Barbara Channel region ________________

Geologic history ____________________________________________

memehhwwwwmmHH

H

ILLUSTRATIONS

Page
2
6
8
9

10

FIGURE 1. Index map showing major geomorphic provinces of southern California _____________
2. Selected stratigraphic sections of the Santa Barbara Channel region _______________
3. Onshore structure section, Santa Barbara to Santa Ynez fault ___________________
4. Interpretive drawing of acoustic subbottom profile, Santa Barbara to Anacapa Passage- _ _

5. Schematic structure contour map of the Rincon trend _________________________
IX

365-228 0 - 69 - 2

 

GEOLOGY, PETROLEUM DEVELOPMENT, AND SEISMICITY OF THE
SANTA BARBARA CHANNEL REGION, CALIFORNIA

GEOLOGIC FRAMEWORK OF THE SANTA BARBARA CHANNEL REGION

By J. G. VEDDER, H. C. WAGNER, and J. E. SCHOELLHAMER

REGIONAL SETTING

The Santa Barbara Channel region forms the
westernmost part of the Transverse Range province,
which is one of several large geomorphic and struc-
tural provinces of southern California (fig. 1). As
here defined, the channel region includes the Santa
Ynez Mountains to the north and the Channel Islands
to the south; Point Conception and San Miguel Island
lie near the west margin; the town of Ojai and
Hueneme Canyon are situated near the east edge
(pl. 1).

The west-trending topographic features of the
elongate Transverse Range province transect the
dominant regional northwest structural grain of
California. The high terrain in the eastern part of
the province is composed primarily of crystalline rocks
that are older than most of the exposed rocks in the
Santa Barbara Channel region. The channel region
forms the western part of the province; it is the
partly submerged extension of the Ventura basin, a
topographic and structural depression that contains
more than 50,000 feet of Cretaceous and Tertiary
strata. The bordering mountain ranges and islands
consist of complexly folded and faulted sedimentary
and igneous rocks that are underlain by a basement
complex, part of which is equivalent in age and lithol-
ogy to that exposed in the high ranges to the east.

The characteristic west-trending structural grain
of the Transverse Range province is clearly reflected
in the channel region by the Santa Ynez Mountains,
which rise to heights of more than 4,000 feet to form
the picturesque backdrop for Santa Barbara, and by
the Channel Islands, which culminate in the 2,450—foot
Devils Peak on Santa Cruz Island. The channel itself

has a length of nearly 80 miles, a width of about 25
miles, and an area of about 1,750 square miles. The
deepest part, about 2,050 feet below sea level, lies
about midway between El Capitan Beach on the main-
land and Carrington Point, the northernmost prom-
ontory on Santa Rosa Island. The configuration of
this sea-floor topographic basin is illustrated by the
bathymetric contours on plate 1.

STRATIGRAPHIC SUMMARY 1

Strata in the western Ventura basin and Santa
Ynez Mountains range in age from Early Cretaceous
to Holocene and unconformably overlie, or are faulted
against, basement rocks that are pre-Cretaceous(?) in
age (pl. 1). The basement rocks consist of three
distinct assemblages, one of which occurs in fault
slivers along the Santa Ynez fault and the other two
as belts of outcrops on the south half of Santa Cruz
Island. In the Santa Ynez Range, the so-called base-
ment rock consists of discontinuous pods and lenses
of sheared graywacke, shale, and chert that commonly
are assigned to the Franciscan Formation. These
severely deformed strata are intruded by greenstone
and serpentine. On Santa Cruz Island, metamorphic
rocks, in part schistose, are intruded by hornblende
diorite and may be related to similar rocks that form
the basement complex in the eastern Santa Monica
Mountains. The location of the subsurface boundary
between Franciscan-type basement rocks of the Santa
Ynez Range and the crystalline rocks that underlie
the Channel Islands is not known.

 

l‘flka stratigraphic nomenclature used in this report is from many sources and may
not entirely conform to Geological Survey usage.

1

2 GEOLOGY, PETROLEUM DEVELOPMENT, SEISMICITY, SANTA BARBARA CHANNEL, CALIF.

121 120‘ 119‘

 
 
 
 
 
   

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CRETACEOUS MARINE ROCKS

An enormous thickness of Lower and Upper Cre-
taceous marine sedimentary rocks lies in the San
Rafael Mountains to the north of the Santa Ynez
Mountains, and it is possible that similar thick suc-
cessions may also be widely distributed deep in the
subsurface beneath much of the Santa Barbara
Channel region. South of the Santa Ynez fault (pl. 1),
Lower Cretaceous strata crop out in the western
Santa Ynez Mountains, and fragmentary sections of
Upper Cretaceous strata are scattered along the fault
throughout its length. Middle Cretaceous rocks have
not been found in the channel region. Much of the
western part of San Miguel Island is formed by Upper
Cretaceous sedimentary rocks, and equivalent strata
have been penetrated by wells on Santa Cruz Island
and farther east on the mainland. An exploratory
well near the middle of the channel between More’s
Landing on the mainland and Diablo Point on Santa

Santa
/ C, Catalina
Island

0

San Clemente
Island

FIGURE 1.—Index map showing major geomorphic provinces of southern California.

~‘
~94 ~

’—
I

4~~\\\ ““““
0,, \-_, E‘\
9 \
Mountains 4s #IRANSVERSE RANGES \
b‘r San \
‘\ Bernardino \
\‘\\ Mountains \

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00

B San Diego

15
“NITED STAT? ’—

I .— — ——’ fifiuco

Modified from Yerkes and others (1965).

Cruz Island is reported to have bottomed in Creta-
ceous rocks. In general, the Upper Cretaceous se-
quences are composed of interlayered sandstone, silty
claystone, and small amounts of pebble and cobble
conglomerate that contain fossil faunas that range
from the Campanian Stage to the Lower Maestrichtian
Stage (Popenoe and others, 1960). On San Miguel
Island the Upper Cretaceous succession is about
10,000 feet thick (Kennett, in Redwine and others,
1952); north of the Santa Ynez fault the combined
Lower and Upper Cretaceous formations are more
than 20,000 feet thick. J alama is the formation name
commonly applied to the Upper Cretaceous rocks and
Espada to the Lower Cretaceous rocks (Dibblee, 1950).

PALEOCENE AND EOCENE MARINE ROCKS

Paleocene rocks are very limited in extent within
the Santa Barbara Channel region. They are known
from a narrow belt of sea-cliff exposures on San
Miguel Island, where they consist of about 1,600 feet

GEOLOGIC FRAMEWORK OF THE SANTA BARBARA CHANNEL REGION 3

of interlayered sandstone, claystone, and conglomerate
(Kennett, in Redwine and others, 1952), and from a
single small area in the southwestern part of Santa
Cruz Island (Bremner, 1932 [as Martinez Formation]).
At San Miguel Island the base is faulted against
Upper Cretaceous rocks and on Santa Cruz Island it
is not exposed.

Many of the resistant strata that form the crest
and south face of the Santa Ynez Mountains are
marine sandstone beds of Eocene age. Similar Eocene
rocks are exposed on San Miguel and Santa Rosa
Islands and south of the Santa Cruz Island fault.
They have been penetrated at depth beneath the
central part of the channel and in the subsurface
section in many of the oil fields along the north and
east margins. Several relatively persistent forma-
tional units have been differentiated in the Santa
Ynez Mountains. These units consist primarily of
clayey siltstone or sandstone and small amounts of
conglomerate; locally, a distinctive algal limestone,
which is unconformable on Cretaceous rocks, occurs
at the base. North of Santa Barbara these forma-
tions have a composite maximum thickness of nearly
15,000 feet. The entire succession ranges in age from
early to late Eocene and includes fossil faunas that
are assigned to Mallory’s (1959) Bulitian, Penutian,
Ulatisian, and Narizian Stages. Commonly used for-
mation names (Dibblee, 1966) in ascending order are
Sierra Blanca Limestone, J uncal Formation (or Anita
Shale), Matilija Sandstone, Cozy Dell Shale, and Cold-
water Sandstone (or Sacate Formation).

OLIGOCENE MARINE AND NONMARINE ROCKS

Variegated strata, including red beds, that discon-
formably overlie the Eocene succession from the
vicinity of Goleta eastward are composed chiefly of
nonmarine conglomerate, sandstone, and claystone.
These nonmarine strata are as much as 5,000 feet
thick in the Carpinteria district, but westward they
thin, tongue into, and are underlain by marine sand-
stone and siltstone beds that have an aggregate thick-
ness of about 3,500 feet. The western limit of the
red-bed section is in the vicinity of Gaviota Pass.
Nonmarine beds also crop out on Santa Rosa Island
and are present in the subsurface sections in deeper
parts of onshore and offshore oil fields. East of the
area of plate 1, the nonmarine section thickens to as
much as 8,000 feet and incorporates both older and
younger rocks, so that both late Eocene and early
Miocene strata are included at the base and top. The
marine beds, which extend westward at least to the
vicinity of Point Conception, contain mollusks and
foraminifers that are assigned to the Refugian Stage
(Schenck and Kleinpell, 1936). Nonmarine beds east
of the channel region have yielded vertebrate remains

that range in age from Uintan to Arikareean (Wood,
H. E., 2d, and others, 1941). The names “Gaviota
Formation” and “Alegria Sandstone” are commonly
used for the marine units, and “Sespe Formation” is
used for the nonmarine sequence (Dibblee, 1950, 1966).

MIOCENE MARINE ROCKS

The diverse Miocene stratigraphic succession can
be divided conveniently into lower, middle, and upper
parts, which, in turn, can be subdivided into relatively
persistent map units along the coastal side of the
Santa Ynez Mountains and on parts of the Channel
Islands. Similar units are recognized in the subsur-
face sections in onshore and offshore oil fields.

Lower Part

Thick-bedded shallow marine sandstone lenses, in
part conglomeratic, form the bulk of the basal for-
mation of the Miocene succession along the south
flank of the Santa Ynez Mountains from the vicinity
of Point Conception to Santa Barbara. This unit is
disconformable on the underlying red-bed section, and
it forms a persistent narrow belt of outcrop. At
places in the western Santa Ynez Mountains these
coarse-grained strata are as much as 600 feet thick,
but elsewhere, they average about 300 feet in thick-
ness. A few hundred feet of stratigraphically equiv-
alent beds crop out on the southern part of Santa
Rosa Island. Fossil mollusks from both the island
and the mainland suggest an early Miocene age, and
the unit is assigned to the Vaqueros Formation
(Vaqueros Sandstone; Dibblee, 1950, 1966).

Conformably overlying the basal sandstone unit is
a sequence of concretionary claystone, mudstone, and
siltstone beds that have a total thickness of as much
as 1,800 feet along the coast west of Santa Barbara
and 2,500 feet in the Ventura area. Somewhat similar
strata crop out on San Miguel and Santa Rosa Islands,
but generally they are coarser grained and are more
than 2,000 feet thick. Zones of bentonitic clay occur
in the upper and lower parts of the section along the
mainland coast. Foraminifers diagnostic of Kleinpell’s
(1938) Zemorrian and Saucesian Stages are present in
this fine-grained unit which is called the Rincon Shale
(Dibblee, 1950, 1966).

Middle Part

Sedimentary breccia beds and associated sandstone
and siltstone interbeds that are genetically unrelated
to any of the adjacent mainland Miocene rocks attain
a thickness of about 2,000 feet on the southern part
of Santa Cruz Island. These distinctive strata include
lenses of glaucophane schist breccia that are similar
to the San Onofre Breccia of the northern Peninsular
Range province. A unit having similar lithology and

4 GEOLOGY, PETROLEUM DEVELOPMENT, SEISMICITY, SANTA BARBARA CHANNEL, CALIF.

stratigraphic position is interbedded in the volcanic
sequence on Anacapa Island.

The bulk of the middle part of the Miocene succes-
sion along the mainland coast is a remarkably uniform
siliceous shale that includes diatomaceous and phos-
phatic beds as well as chert and limestone. Rhyolitic
tuff and bentonite are present at the base westward
from the vicinity of Gaviota Canyon. Exposures of
this formation extend along much of the shoreline in
the sea cliffs between Point Conception and Santa
Barbara and between Carpinteria and Rincon Point.
At most places this formation gradationally overlies
the Rincon Shale and is as much as 2,300 feet thick
just west of Santa Barbara; its foraminiferal assem-
blages span most of the Relizian, Luisian, and Mohnian
Stages (Kleinpell, 1938). Laminated units of the same
age and lithology are present on San Miguel Island
and north of the main faults on Santa Rosa and
Santa Cruz Islands. Assignment of these stratigraphic
sequences to the Monterey Shale is widely accepted.

Upper Part

Along parts of the mainland coast an indistinctly
bedded unit composed predominantly of diatomaceous
mudstone, claystone, and siltstone gradationally or
disconformably overlies the hard laminated shales of
the middle part of the Miocene succession. At some
places these beds contain dolomitic concretions and
lenses. The sand content of the unit increases east-
ward. This fine-grained formation varies in thick-
ness, but is more than 2,000 feet thick east of Car-
pinteria; in the vicinity of Santa Barbara it has been
eroded completely. Diagnostic fossils are sparse, but
microfaunal assemblages are assigned to the upper
Mohnian and Delmontian Stages of Kleinpell (1938).
On the mainland the names “Santa Margarita Shale”
and “Sisquoc Formation” are used interchangeably
for this formation. Lenticular sandy siltstone and
tuffaceous sandstone beds more than 3,000 feet thick
are associated with volcanic agglomerates north of
the Santa Rosa Island fault. The island beds discon-
formably overlie the Monterey Shale and are assigned
to the “Santa Margarita Formation” by Kennett (in
Redwine and others, 1952).

MIOCENE VOLCANIC ROCKS

Extrusive and intrusive sequences of basaltic,
andesitic, and rhyolitic composition form a significant
part of the rock sequence on the Channel Islands, in
the western Santa Monica Mountains, and in the
westernmost Santa Ynez Mountains (chiefly outside
the map). On Santa Cruz and Santa Rosa Islands, the
Monterey Shale separates the volcanic sequence into
lower and upper units. In the western Santa Monica
Mountains east of the Channel Islands, these volcanic

rocks are more than 15,000 feet thick; on Santa Cruz
Island the lower volcanic unit alone aggregates more
than 6,000 feet in thickness. The name “Conejo Vol-
canics” has been applied to the basaltic and andesitic
rocks in the middle part of the Miocene succession on
the mainland southeast of the Montalvo oil field and
in the western Santa Monica Mountains. On the
islands the name “Conejo” has been used informally
for the lower volcanic unit, and andesitic and rhyolitic
rocks higher in the Miocene section have been assigned
to the “Santa Margarita Formation” (Kennett, in
Redwine and others, 1952). Both units of volcanic
rocks seem to thin rapidly northward; they are not
present in the coastal section near Santa Barbara.
The rhyolitic extrusives at the west end of the Santa
Ynez Mountains are as much as 1,200 feet thick and
are named “Tranquillon Volcanics” (Dibblee, 1950).

LOWER AND UPPER PLIOCENE MARINE ROCKS

Outcrops of interbedded siltstone, sandstone, and
thin lenticular conglomerate form the lower part of
the Pliocene succession and conformably overlie the
marine Miocene rocks in the coastal area near Rincon
Point and just offshore. Within the onshore part of
the map area, exposures are restricted to the Rincon
Beach—Ventura area and to the sea cliff near Goleta,
where only the upper part crops out. Pliocene strata
are not present in the Santa Ynez Mountains or on
the Channel Islands; if they ever were deposited on
those margins of the Pliocene basin», they have been
eroded completely. However, great thicknesses of
Pliocene rocks are present along the basin axis on-
shore and presumably are widespread beneath the
channel floor. In the vicinity of Ventura, the upper
part of the Pliocene stratigraphic sequence is composed
of interlayered and intertongued mudstone, siltstone,
sandstone, and conglomerate. Eastward, these strata
become increasingly coarse and lenticular. A thin
bed of vitric tuff occurs in the uppermost part; the
source probably was far distant, for there is no other
evidence for a center of Pliocene volcanism in or near
the Santa Barbara Channel region.

A few miles northeast of Ventura, the Pliocene
sequence has an aggregate thickness of more than
12,000 feet, thus forming one of the thickest marine
Pliocene successions in the world. This remarkable
section thins westward beneath the channel; it is not
represented on the Channel Islands. Fossil forami-
nifers and mollusks indicate that most of Pliocene
time is represented in this extraordinarily complete
section.

Throughout much of the Ventura district the lower
part of the Pliocene section contains a deep-water
foraminiferal facies and is designated “Repetto For-
mation.” In the basin the name “Pico Formation”

GEOLOGIC FRAMEWORK OF THE SANTA BARBARA CHANNEL REGION 5

has two connotations; in the eastern part it is applied
to most of the marine Pliocene sequence, but in the
western part (area of pl. 1) it is commonly restricted
to the upper portion. The names “Repetto” and
“Pico” are here used in the latter sense to correspond
with common usage.

Thin belts of marine conglomeratic sandstone beds
that have been assigned a Pliocene age (Dibblee,
1966) also are exposed along Santa Ynez Valley north
of the Santa Ynez Mountains.

LOWER AND UPPER PLEISTOCENE DEPOSITS

Limited exposures of marine sandstone, siltstone,
and small amounts of conglomerate unconformably
overlie Pliocene and older strata in the Santa Barbara
area. However, at places between Santa Barbara and
Rincon Point these isolated remnants of poorly con-
solidated marine deposits grade upward and laterally
into nonmarine clayey sandstone and conglomerate
beds that are lenticular and indistinctly stratified.
Near Ventura these deposits appear to be gradational
with upper Pliocene strata.

In the vicinity of Santa Barbara both the marine
and nonmarine lower Pleistocene deposits vary greatly
in thickness. They total more than 3,000 feet near
Carpinteria, and east of the Ventura River they
thicken to 6,000 feet and contain lenticular marine
and nonmarine beds in the upper part. Fossil mollusks
indicate that the bulk of the marine section near
Santa Barbara is early Pleistocene in age, but the
lowermost part may be late Pliocene. Mammal re-
mains, including diagnostic horse teeth of Blancan
age (Wood, H. E., 2d, and others, 1941), occur in non-
marine equivalents near Ventura. In the vicinity of
Santa Barbara the name “Santa Barbara Formation”
has been applied to the marine beds and “Casitas For-
mation” to the nonmarine beds (fig. 2, col. 2). Near
and east of Ventura the informal names “marine
Saugus,” “San Pedro,” and “Las Posas” have been
used for strata that correlate in part with those
farther west (fig. 2, col. 3).

Poorly consolidated nonmarine gravels that contain
a large amount of siliceous shale fragments border the
Santa Ynez River Valley (pl. 1). The lower part of
these deformed alluvial deposits may be as old as late
Pliocene, but the bulk of the unit is inferred to be
Pleistocene in age. The name “Paso Robles Forma—
tion” is commonly applied to these beds.

Upper Pleistocene marine deposits occur mainly as
a discontinuous thin veneer on elevated wave-cut
platforms that are as high as 700 feet above sea level
along the south side of Rincon Mountain (Putnam,
1942). Similar platforms are evident at 1,200 feet
above sea level, but have no identifiable marine cover.
At most places the marine remnants are covered by

slope-wash detritus or stream deposits. Both the
marine and nonmarine sediments truncate older
Pleistocene formations and are composed primarily of
poorly consolidated silt, sand, and gravel. Mollusks
from the marine layers generally are assigned a late
Pleistocene age, as are vertebrate assemblages and
floras from the nonmarine terrace cover. Fossil
floras and dwarf elephant remains from nonmarine
terrace deposits on the islands corroborate these age
interpretations. Except for the tar-saturated and
diversely fossiliferous deposits southeast of Car-
pinteria, informally designated “Carpinteria Forma-
tion,” these deposits are unnamed in the Santa
Barbara coastal area. Informal names also have been
applied to terrace deposits and wave-cut platforms
near Ventura (Putnam, 1942) and on Santa Rosa
Island (Orr, 1960).

HOLOCENE DEPOSITS

Alluvial deposits composed of clay, silt, sand, and
gravel fill most of the coastal valleys and flood plains.
Beach sand and gravel cover segments of both the
mainland and island coasts; eolian sand, both active
and inactive, blankets the windward parts of the
larger islands and the coastal area near Point Con-
ception. Alluvial deposits in Goleta Valley are as
much as 225 feet thick and extend below present sea
level off major drainage systems (Upson, 1949; Thomas
and others, 1954). Sand, silt, and mud mask much of
the shelf along the mainland coast, except in very
nearshore areas and on crestal parts'of some offshore
anticlines where older rocks are present. Generally,
these unconsolidated sediments are progressively finer
grained seaward, except for an unusual concentration
of highly organic clayey silt between Santa Barbara
and Pitas Point. It may be significant that bottom
sediments near natural oil and gas seeps are stiff and
dark colored. This condition is especially evident west
of Pitas Point where a notably dense population of
Listm’olobus, an echiuroid worm, thrives in the silt-
covered tract, in contrast to its sporadic distribution
elsewhere on the shelf (Stevenson and others, 1959).
An isolated patch of coarse-grained sand within the
tract has also been noted and interpreted as a possible
relict beach ridge formed at a lower stand of sea
level. Holocene sediments are sparse on the near-
shore parts of the island shelves, and large areas of
bare rock are common, particularly in the passages
and on the windward shelf west of San Miguel Island.

GENERALIZED STRUCTURE OF THE SANTA
BARBARA CHANNEL REGION

The Santa Barbara Channel is a tectonic depression
that forms the westward extension of the Ventura
basin and a submerged part of the Transverse Range

GEOLOGY, PETROLEUM. DEVELOPMENT, SEISMICITY, SANTA BARBARA CHANNEL, CALIF.

 

   
  
 
 

 

 

 

    

 

       
    
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

WESTERN SANIA YNEZ MOUNIAINS AND VICINITV CENTRAL SANIA YNEZ MOUNTAINS VENTURA RIVER AREA
Modified lroni Dibblee (1950) Modified lrom Dibblee (1966) Modified lrom Bailey (in Redwine, 1952)
Series Description Series Formation Lithology Feet Description Series Formation Lithology Feet Description
Holo» Silts and ravels Holo- Alluvium N g Gravel, sand. and silt ll Coarse sand and sandy
O
cene A cyaveis ‘ cene/ WWW c', Sand, silt, and gravel “g gravel; sdty clay:
Pleisto~ . _ deposits (N o pebbly silt in middle
Diatomaceous siltstone u) . 8 Boulder, cobble,
cene / z Casrtas (N) m . 3 - _
Cla stone and 5 c; and pebble gravel, andy silt, sand, con
“2" y. 53 sand, 5m, and clay glomerate, and clay;
3 diatomaceous r4: , l nonmarine
W H ‘ ‘
E Sisquoc mudstone : .4 P53“ H § _
o e to m
— ?— Thin~bedded ‘ . U Santa g g . _
and laminated g 5 Barbara @- Sand and silt 3 Sand, silt, and gravel;
diatomite “- ° 3 marine
:
Porcelaneous and _ _
8 cherty siliceous _Siliceous shale
9’ shale °
Monterey cl Monterey S _ _
g _ . N Organic shale;
u ._. Organic shale and thin-limestone Santa =1 Massive mudstone:
é thin limestone i; lentils Barbara § thick conglomerate
‘2 g Rhyolite and basalt, é _ 7 N lenses
2 Tranquillon .V S: agglomerate, tuft, E ' —'
o bentnnite Rincon E Claystone
o
S
Rincon ._. Cla stone
5 y Vaqueros 300 Sandstone
_ _7 _
8
Vaqueros { °,‘ Sandstone and conglomerate
n o . Variegated arkosic ’
Sespe (N) o Variegated sandstone u, “83 sandstone and Alternating thick
8 and siltstone é Sespe (N) T siltstone; basal conglomerate
N ,
Lu 5 a E sandstone and and siltstone
5 Alegria Marine sandstone 5' N conglomerate
8
‘3
..
O l
Gawota § Sandstone and siltstone
8 L; I Pico § -
‘2 § Sandstone 8 (ower part E,
Sacate c3 Sandstone and claystone Coldwater ",3 9 commonly g
8 § I called a, Siltstone With
"' N Repetto) H locally thick
3 S d l sandstone and
e an stone and si tstone
Cozy Dell ‘7' Claystone conglomerate
w 8 interbeds
Z N
a s
w o Cozy Dell 2 Clasyrsgiline and _
o In e
Matiliia S Arkosm sandstone 2
o
0 Very thick to thin
Anita 5 § Shale and claystone E g 5 d conglomerate and
Matiliia ' an stone sandstone units
Ierra 0~ o A ‘“ °
Blanca 5 lgal limestone § § interbedded With
‘3 Claystone and 5"“ shale
E S + siltslone: line-
5: 32 g . .
2 E Ja|ama N grained sand-
5 N stone at top Shale andthin
and middle platy ‘
' H § Massive diatomaceous
8 Sandstone 83"“ T mudstone: thin limy
B Margarita" 3 b d d n t' ns
U, Juncal ol Claystone and 2 e s an co cre i0
8 § shale
8 Carbonaceous
E g h I "d min Sandstone Siliceous shale,
5 E Lhasa)“ w E laminatedorganic
x Es ada I -
E p + Claystone and g Monterey g'
3 8 shale 2 '2. Alternating laminated
o 2 .
v shale; hard limestone
m .
l— 7- 5 L33 Conglodn'ierate, Massive mudstone; dolo-
Basal pebbly g: g Jalama san stone, , mite concretions
x P; sandstone 3 g and shale Rincon
t... m
g 3 Hard :anhdsltone - - ‘SFeafaiglliaTeand— - — Fine~grained sandstone
2 Franmscan A. an S a e 5 2‘ h sandstone intruded locally "93' base
. l 52 F ' b l and
Ser entine intrusions '3— “ ”"05“” H .
p =2 m ”NJ—"M Continued to right

 

 

 

 

 

 

 

 

 

FIGURE 2.—Selected stratigraphic sections

GEOLOGIC FRAMEWORK OF THE SANTA BARBARA CHANNEL REGION

Continued lrom section to lelt

SANTA CRUZ ISLAND (COMPOSITE)
Moqilied trorn Kennett(in Redwine, 1952)

.SAN MIGUEL ISLAND (COMPOSITE)
Modified trom Kennett (in Redwine, 1952)

 

 

 

 

0LlGOCENE

.—7_

      
 

Sespe (N)

3500 - 6000

Series Formation Lithology [Feet DescriptiOn

a. 9
o‘ E Vaqueros 300 Sandstone and conglomerate
E 8 ' L—

Variegated mudstone,
sandstone.
grit, and conglom~
erate; massive to
very thick bedded

 

EOCENE

Coldwater

  

2500

Hard, line to coarse-
grained sandstone
and srlty claystone
interbedded

 

Cozy Dell

  

3000 — 3300

Massrve silty shale
and micaceous
mudslone

 

Matilua

2500 ~ 3000

Thin-bedded hard sand-
stone: siltstone beds
in upper and lower
parts: middle part
massive hard
sandstone

 

 

 

 

 

 

 

 

 

 

  

     

 

  

 

 

 

 

luncal

 

 

5000 - 6500

Thin-bedded shale and
mudstone: thin mica-
ceous sandstone
interbeds

Thin-bedded hard sand-
stone and shale:
orbitoidal Irmestone
locally at base

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

UPPER
CRETACEOUS

 

 

 

2300

Hard silty shale: mas
sive 500-toot con-
glomerate about 800
leet below top

Shale. locally crushed
in upper part. limy
in lower part

 

 

 

of the Santa Barbara Channel region.

365-228 0 - 69 - 3

Series Formation I Lithology Feet Description Series Formation I Lfiholoy Description
Rhyohte. andesite. and " ”WM" Dune sand
basalt bleml 8820"“- Monterey \ Oiatomaceous shale
erate. and scoriaceous
_ flows _ Basaltic tutt, siltstone,
Rhyolrte and andeSIte "Cone'o sandstone, and breccia;
J _ agglomerate Volcanlics" andesitetlows and
"Santa o‘ ‘ agglomerate locally at
Margarita" «3 Rhyolite tulf and tuft .5. top
breccia: some rhyolite g
C
agglomerate E
Rhyolite and andesite . . ,
. Foraminileral srlty
conglomerate Rincon shale; tossililerous
______ I sandstone interbeds
l
I Tuttaceous siliceous _ _ ' _ _ _ _ —
i dratomaceous shale: Unnamed — _- FAULT- _ _ .
Monterey c
I a3 thin beds 0' dense ————— Thick-bedded sandstone
: limestone near base y_ _ _ FAULT _ __ _ _
I E Alternating thicllrbedded
I g sandstone, thin-bedded
' " “J Unnamed sandstone and loraminil-
. eral shale; concretionary:
“‘ l
E cobble conglomerate at
8 l . . base
g | Alternating olivme basalt.
- amygdaloidal and
“Conejo I scorraceous basalt, w
I ‘9 basalt and andesite z ,
Volcanics" 8 8 Alternating thin~bedded
l 8 breccra. grading upward 8 Unnamed h l dth lib dd (1
‘I to basalt and andesite :2 s a: tan '6 ‘ e e
I agglomerate. tutti °' 53" 3 one
I and sandstone ». _ _ _ .. _ _
I ———FAULT--—-
l
l
l
I_
‘— Massive, poorly sorted
' breccia and conglom-
l erale ot mainly glauco-
53" I § phane schist, green-
Onotre ' N stone schist,and diorite;
' shale unit in middle part
I (n
8
Cozy l c . w
-n Sand and Silt shale ° Unnamed
99” ' ‘° y y E, Massive sandstone and
Unnamed I E Sandstone and conglomerate U thrn‘bedded 5"“
c:
c... I E
z _ > n.
g I Alternating silty shale =’
8 I o and thin-bedded
| E sandstone
' —
: Thick-bedded sandstone
“" + S dstone c n | merate
z I an . 0 go .
5 5 hUnnamed I E and siltstone
—‘8 ----- a
5’. Diorite % Hornblende diorite
E
E; —--—-FAULT———_.
E Greenstone . .
U Chlorite schist
O
EXPLANATION ‘000
(N)
Nonmarine unit
All others are marine 2000
3000 FEET

8 GEOLOGY, PETROLEUM DEVELOPMENT, SEISMICITY, SANTA BARBARA CHANNEL, CALIF.

v4—> N 20C E

4000' "
3000' —
2000' ‘
1000' —
SEA LEVEL ‘
'OOO' _ Susquoc
2000' “Formation
3000' w
4000' —
5000'

Oldevailuvtum
(nonmaune)

Older alluvmm
kmanne and

   

   

 

Formation 7/.l ':
1/~ .
‘ Rincon

 
  

 
 

 

" Goldwaterc “

q 05
Shale FormationA,_.
l /'\,/'\~

Santa Ynez Mountains

‘ __ Juncal

Cozy MatIIIJa Fovmation
Dell Sandstone -
Shale " '

SANTA YNEZ FAULT

 
 
  
 
 
 

 

Goldwater
Sandstone _ .

  

Monteiey Sespe

Formation

  
        
    
 
    
 

  

FIGURE 3.—0nshore structure section, Santa Barbara to Santa Ynez fault. T on fault indicates movement toward observer;
' A, movement away from observer.

province of southern California (fig. 1). The Santa
Barbara Channel is bounded on the north by the
homoclinal Santa Ynez Mountains and the Santa Ynez
fault zone; on the south it is bounded by the Channel
Islands, which, in turn, may be bounded on the south
by the westward extension of the Santa Monica fault
zone. The western limit is not definitely known, but
a shallowing of the ocean and a northwestward bend
of the structures in the area south of Point Conception
may indicate a change of structural pattern.

Although basement rocks have not been reached by
the deepest wells drilled within the area, presumably
they form the floor of the entire basin area. A total
structural relief on the order of 60,000 feet exists
between the deep central part of the basin and its
elevated north and south margins. Imposed on this
regional structural basin and its north and south
margins are numerous normal and reverse faults and
steep-limbed folds indicative of intense deformation.
On shore these features can be observed and studied
directly; but in the areas covered by the ocean, only
such indirect methods as geophysical techniques,
shallow coring, and deep stratigraphic drilling are
available to decipher the geology. Land areas sur-
rounding the channel have been studied in considerable
detail; and, although some offshore areas such as the
Montalvo and Rincon trends are fairly well known,
little is known about others because information does
not exist or is unavailable. Many such offshore areas
undoubtedly have structures that are as complicated
as those on the adjoining mainland. Known major
structural features are shown on plate 1.

The dominant structural feature north of the Santa
Barbara area is the Santa Ynez fault. It extends
from east of the map area to the vicinity of Point
Conception where its northern branch seems to die
out and where its southern branch extends seaward
in a southwesterly direction. In general, the fault
dips steeply to the south, and the south side appar-

ently has been raised 5,000—10,000 feet relative to the
north side. The net slip on the fault has not been
determined because of complex stratigraphic and
structural relations, but some geologists suggest that
it is a major active fault zone along which there has
been left-lateral oblique slip (Page and others, 1951;
Dibblee. 1966). I

The structure of the Santa Ynez Mountains between
the Santa Ynez fault and the channel is, in general,
a steeply south-dipping homocline (fig. 3), which in-
corporates Cretaceous to Miocene rocks west of Santa
Barbara and includes strata as young as Pleistocene
east of Santa Barbara. In the area north of Car-
pinteria, an overturned syncline and a faulted anticline
disrupt the homoclinal nature of the structure (Lian,
1954), and a faulted syncline complicates the pattern
at Santa Barbara. On the north side of the mountains
northwest of Santa Barbara, a reversal in dip forms
an anticline against the Santa Ynez fault.

Along the mainland coast of the channel the younger
and less competent late Cenozoic rocks are cut by
many faults that generally trend parallel to the range
front. The strata have been folded into complex
anticlines and synclines that vary in size from a few
inches to prominent folds, such as the Ventura anti-
cline which is nearly 17 miles long and about 4 miles
wide. Other, less prominent anticlines are present in
the areas of Summerland, Montecito, the Mesa of
Santa Barbara, Goleta, Capitan, and Elwood. Nu-
merous small folds are evident along the sea cliffs
and on wave-cut platforms when the tide is low.

The Channel Islands form the southern margin of
the Santa Barbara basin. Faults with a west or
northwest trend are the dominating structural fea-
tures, and the fault-bounded anticlines and synclines
on Santa Rosa and Santa Cruz Islands have similar
trends. Santa Rosa and Santa Cruz are each cut by
a large median fault that divides the island into dis-
similar geologic parts; both faults are believed to

GEOLOGIC FRAMEWORK OF THE SANTA BARBARA CHANNEL REGION

Santa Barbara shelf

A—SEA LEVEL

 

    
          
 
  

 
   
  
  
       

 
 

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INDEX

VERTICAL EXAGGERATION
APPROXIMATELY X 6

Interpretation of seismic data by S C Wolf, 1969 ‘

FIGURE 4.—Interpretive acoustic subbottom profile, Santa Barbara to Anacapa Passage.

have a component of left-lateral displacement. In
general, the Channel Islands form a complexly folded
and faulted anticlinal uplift that is a seaward struc-
tural extension of the Santa Monica Mountains (fig.
1).

The west-trending Santa Monica fault zone, which
bounds the Santa Monica Mountains on the south and
which may extend westward beneath the sea south
of Santa Cruz Island, is a north-dipping reverse fault
that juxtaposes completely dissimilar basement and
younger rocks. Only north-over—south reverse fault
movement can be demonstrated from outcrop relations
in the Santa Monica Mountains, but left-lateral dis-
placement may have occurred before late Miocene
time.

The eastern part of the channel floor is divided into
subparallel segments by large west-trending faults
(pl. 1). Each segment includes numerous small faults
and folds that generally are alined with the regional

structural grain. The western part of the channel is
not known well enough to project or correlate indi-
vidual structural features.

A zone of faults closely follows the ZOO-meter bathy—
metric contour along the south margin of the deep
trough of the channel. Most of the faults within this
zone have steep north dips, but some are nearly verti-
cal or dip steeply to the south. The type and amount
of displacement is not known. Another zone of faults
extends along the ZOO-meter contour along the north
side of the central trough; individual faults in this
zone dip to the south. In combination With the bottom
topography, these two zones suggest that an elongate,
grabenlike feature forms the deeper part of the
channel (fig. 4).

The east-central part of the shelf includes the off-
shore extension of the Montalvo trend, which is
bordered on the north by north-dipping normal faults.
The northern of these faults appears to die out to the

GEOLOGY, PETROLEUM DEVELOPMENT, SEISMICITY, SANTA BARBARA CHANNEL, CALIF.

 

|
119°30’

DSanta Barbara DSummerland

   
   
  
 
 
 
    
 
 
 

 

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_34 22 30 Dos Cuadras Offshore Carpinteria Offshore
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EXPLANATION

— - 5000 ——
Structure contour
Dashed where approximately located.
Contour interval 500feet

Drilling platform

Rincon oil field
Contours approx. 3700 it

above top ”Repetto Formation"
4 Ventura oil field

  
   

Contours approx. 400 ft
above top “Repetto Formation"

an Miguelito oil field
Contours approx. 400 ft
above top “Repetto Formation"

|jVentura

   

 

 

FIGURE 5,—Schematic structure

west as it approaches the deeper part of the channel.
West of the longitude of Santa Barbara, the Montalvo
trend and related structures adjacent to it on the
north and south seem to merge westward.

The offShore part of the Rincon trend lies within
the nearshore shelf area where its eastern end is
bounded on the south by a fault that extends west
from the vicinity of Pitas Point. Similarly, the north
boundary of this part of the trend is the offshore
extension of the Red Mountain fault. Several faults
parallel the Rincon trend and displace the axial part
upward; others trend northeasterly and may offset
the axis toward the southwest. The northernmost
structural unit in the eastern part of the channel lies
north of the western extension of the Red Mountain
fault. The fault-bounded anticline that forms the
Summerland Offshore field is located in this structural
block.

Geologic information on the shelf area between Coal
Oil Point and Point Conception is sparse, but the
configuration of the offshore oil fields in the area
suggests that the structures follow the regional
westerly trend. The exact location of the offshore
extension of the south branch of the Santa Ynez fault
is not known; presumably, it continues southwest for
a considerable distance.

It should be emphasized that the exact nature of
fault movement in the offshore region is not definitely
known, for lateral components of offset that are
difficult to detect may have developed on many of

contour map of the Rincon trend.

the faults that are shown as normal faults on plate 1.

The Rincon anticlinal trend is one of the most
prominent in the Santa Barbara Channel (fig. 5; pl. 2).
It extends westward from the Rincon oil field through
the Carpinteria Offshore and Dos Cuadras Offshore
fields into the Federal Ecological Preserve, where it
may merge with the structures of the Coal Oil Point
Offshore and South Elwood Offshore fields. West of
the South Elwood field, a similar structure may merge
with the structure of the Molino Offshore field or
that of a recently discovered unnamed field to the
south. Thus, there seem to be two parallel trends
west of the South Elwood Offshore field. One lies
within the 3-mile boundary and includes several fields;
another parallel trend is roughly 3 miles to the south
and includes the new oil field.

Another prominent anticlinal trend in the channel
lies just south of the Montalvo trend and may extend
west and northwest for more than 20 miles. This
structure is recorded on subbottom acoustical profiles
and is plainly discernible from the configuration of
the bathymetric contours.

Seismic information indicates that the young sedi-
ments in the central deep of the Santa Barbara
Channel are not greatly faulted, but they may be looally
deformed by small discontinuous folds beneath the
deepest part. In contrast, the region between the
Channel Islands and the ZOO-meter bathymetric
contour appears to be extensively faulted, resembling
the structure of the islands (fig. 4).

GEOLOGIC FRAMEWORK OF THE SANTA BARBARA CHANNEL REGION 11

GEOLOGIC HISTORY

The geologic record of the Santa Barbara Channel
region is traceable for more than 100 million years
and indicates recurrent tectonic activity followed by
periods of relative quiescence. Because of the short
duration of the historic record, however, it is difficult
to determine which part of this cycle is now operative.

The Franciscan assemblage in the Santa Ynez and
San Rafael Mountains may have originated on and
beneath the deep sea floor far west of the present
shoreline. During Early Cretaceous time the marine
strata (Espada Formation) that now occupy parts of
the same area may have been deposited on ancestral
outer continental shelves and slopes. Great lateral
dislocations, perhaps resulting from underthrusting
at the continental margin, or from great strike-slip
faulting, may have brought these contrasting rocks
into their present juxtaposition during middle Cre-
taceous or later time. The middle Cretaceous record
is obscure, for strata of this age are missing through-
out the region. Much of the pre-Late Cretaceous
geologic history is thus conjectural.

Throughout most of Late Cretaceous time, regional
subsidence of an older erosional surface permitted the
sea to transgress the area, and a thick succession of
argillaceous sediments, sands, and gravels was de-
posited. This deposition was followed by uplift and
erosion over much of the area during latest Cretaceous
and earliest Tertiary time, but deposition continued
locally as indicated by isolated remnants of Paleocene
strata that are preserved only in the southern part of
the area. Regional subsidence early in Eocene time
permitted the sea to reenter the area, and simulta-
neous uplift of the margins and accelerating depres-
sions of the sea floor resulted in the deposition of
thick accumulations of argillaceous and arenaceous
sediments on what may have been the outer shelf and
slope. Near the close of Eocene time, the sea once
again shallowed, resulting in Widespread deposition of
sands typical of an episode of regression.

Major tectonic activity occurred during Oligocene
time. Uplift north of the present site of the Santa
Ynez Mountains caused the sea to withdraw westward
and southward with concurrent deposition of shallow-

water marine sediments that, in turn, were buried by
a thick sequence of terrestrial gravel, sand, and clay.
During early Miocene time a new episode of sub-
sidence, widespread transgression, and sediment de-
position began. As the sea advanced northward
across a broad sinking land surface, the shallow-water
marine sands were successively covered and over-
lapped by argillaceous sediments as the area continued
to subside and the water deepened. Deposition of
calcareous, phosphatic, and siliceous sediments in
widespread seas containing abundant micro-organisms
continued during much of middle and late Miocene
time. During this time thick sea-floor extrusions and
explosive emanations of volcanic material interrupted
normal sedimentation along the south, east, and
northwest margins of the region, and coarse blue-
schist detritus derived from an unknown source was
distributed locally along the south edge.

Restriction of the basin began during early Pliocene
time as the margins to the north and south were
elevated above sea level. At the same time axial parts
of the basin subsided so rapidly that some sediments
were deposited in water as deep as 4,000 feet. Struc-
tural deformation continued throughout the region
during the latter part of the epoch and intensified at
places, resulting in localized deposits of extremely
varied nature and origin. The same general pattern
of restriction of the basin and sedimentation continued
uninterrupted into early Pleistocene time. About mid-
way through the Pleistocene epoch, major tectonism
began to produce most of the structural and geo-
morphic features that are evident in the Santa Barbara
Channel region today. Prominent anticlines, such
as the Rincon trend, started to form, and many faults
originated throughout the area. During the same
time several thousand feet of Pliocene and early
Pleistocene strata were eroded from the crest of the
growing anticline that now forms the Dos Cuadras
Offshore oil field (pl. 2). Following this episode of
intense deformation, local differential movements
coupled with warping and minor faulting continued
into the Holocene epoch. Sea-level changes and the
development of marine terraces both above and below
present sea level also modified the landscape.

 

Petroleum Development
in the Region of the
Santa Barbara Channel

By R. F. YERKES, H. C. WAGNER, and K. A. YENNE

GEOLOGY, PETROLEUM DEVELOPMENT, AND SEISMICITY OF THE
SANTA BARBARA CHANNEL REGION, CALIFORNIA

 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 679—B

 

CONTENTS

Page Page
Production _______________________________ 13 Oil and gas fields—Continued
Natural seeps near Santa Barbara ______________ 13 Goleta area—Continued
Onshore asphalt deposits _ _' ________________ Elwood oil field ______________________ 19
Onshore oil and gas seeps __________________ 14 South Elwood Offshore oil field ___________ 19
Offshore oil seeps and asphalt deposits _________ 14 Las Varas oil field (abandoned) ___________ 19
Oil and gas fields __________________________ 15 Glen Annie gas field (abandoned) __________ 19
Rincon trend area _______________________ 15 Point Conception area ____________________ 19
Ventura oil field _____________________ 15 Naples Offshore gas field _______________ 19
San Miguelito oil field _________________ 16 Capitan oil field _____________________ 19
Rincon oil field ______________________ 16 Refugio Cove gas field (abandoned) ________ 19
Carpinteria Offshore oil field _____________ 17 Molino Offshore gas field _______________ 20
Dos Cuadras Offshore oil field ____________ 17 Gaviota Offshore gas field _______________ 20
Ojai area _____________________________ 17 Caliente Offshore gas field ______________ 20
Tip Top oil field ______________________ 17 Alegria oil field _____________________ 20
Lion Mountain oil field _________________ 17 Alegria Offshore area __________________ 20
Weldon Canyon oil field ________________ 17 Cuarta Offshore oil field ________________ 20
Oakview oil field (abandoned) ____________ 17 Conception Offshore oil field _____________ 20
Canada Larga oil field _________________ 17 Point Conception Offshore oil field _________ 20
Goleta area ___________________________ 18 OCS P—0197 unnamed offshore oil field _______ 20
Summerland oil field (abandoned) __________ 18 OCS P—0188 and P—0190 unnamed offshore oil
Summerland Offshore oil field ____________ 18 field ___________________________ 20
Mesa oil field _______________________ 18 Montalvo area _________________________ 21
Goleta oil field (abandoned) ______________ 18 West Montalvo oil field ________________ 21
La Goleta gas field (abandoned) __________ 18 OCS P—0202 unnamed offshore oil field ______ 21
Coal Oil Point Offshore oil field ___________ 18 Summary _______________________________ 21
TABLE
Page
TABLE 1. Production and geologic data on oil and gas fields of the Santa Barbara Channel region ______________ 22

365-228 0 - 69 - 4

III

 

 

 

 

 

 

GEOLOGY, PETROLEUM DEVELOPMENT, AND SEISMICITY OF THE
SANTA BARBARA CHANNEL REGION, CALIFORNIA

PETROLEUM DEVELOPMENT IN THE SANTA BARBARA CHANNEL REGION

By R. F. YERKEs, H. C. WAGNER,and K. A. YENNE

PRODUCTION

Petroleum has been associated with human culture
in the region of the Santa Barbara Channel for many
hundreds of years. Active natural seeps of tar, oil,
and gas are present in and along the margins of the
channel, and in prehistoric times asphalt from them
was used in tool- and weapon-making. At the present
time, there are about 20 producing oil and gas fields
in the immediate channel area, and products from
these dominate the local economy. A recent survey
estimates that of the $310 million income annually de-
veloped in Santa Barbara County alone, about one-
third (32 percent) comes from oil and gas production
(Bickmore, 1967). Lesser percentages are from agri-
culture (21 percent), manufacturing (20 percent),
tourism (13 percent), and others (14 percent).

California is the dominant crude -oil producer in the
US. Bureau of Mines District V, which also includes
Arizona, Nevada, Oregon, and Washington. In 1968
District V had a total supply of 1,877,800 bpd (barrels
per day) of crude oil, of which California oil fields
produced about 65 percent, or 1,216,500 bpd, and of
which 661,300 bpd were imported, chiefly from foreign
sources (Conservation Committee of California Oil
Producers, 1969).

California’s 1968 crude oil production of 375 million
barrels was valued at nearly $1 billion; of this total,
the fields of the Santa Barbara Channel region pro-
duced 22.9 million barrels (table 1) or 6.1 percent. For
comparison, oil fields of the Los Angeles basin pro-
duced 160.9 million barrels, or 43 percent of California’s
total. At the end of 1968 the Santa Barbara Channel
region had produced 1.1 billion barrels of crude oil or

about 7.5 percent of California’s cumulative production,
compared with the Los Angeles basin’s 5.87 billion
barrels or 40 percent.

The development of the petroleum resources of the
area can be traced from early descriptions of natural
seeps, on which the first wells were located, through
extensions to offshore and onshore fields, to discovery
of fields by sophisticated geologic and geophysical
methods in areas covered by hundreds of feet of
water.

NATURAL SEEPS NEAR SANTA BARBARA

Many active natural seeps of asphalt or tar, and oil
and gas, occur onshore along the inland margins of
the channel as well as offshore in the tidal zone and
on the deeper sea floor (pl. 2).

ONSHORE ASPHALT DEPOSITS

Although many of the onshore asphalt deposits have
been obliterated, the existence of an extensive litera-
ture makes it possible to describe some of the more
important ones. The largest ones were at Carpin-
teria and at More’s Landing; numerous others occur
along the sea cliffs between Point Conception and
Punta Gorda near the Rincon oil field (pl. 2).

The asphalt deposit at Carpinteria was located near
the sea cliff, about half a mile southeast of town. The
archeologic record reveals that aborigines used asphalt
for holding points on weapons (Abbott, 1879); and
Spanish explorers, dating back to at least 1775, ob-
served that Indians near the present site of Carpin-
teria used tar from those deposits to calk their boats
and to seal their water pitchers (Heizer, 1943). As
early as 1857 the Carpinteria deposit supplied material

13

14 GEOLOGY, PETROLEUM DEVELOPMENT, SEISMICITY, SANTA BARBARA CHANNEL, CALIF.

from which illuminating oil was distilled; the quarry
pits were as deep as 25 feet and covered several acres
(Eldridge, 1901). The asphalt impregnates the basal
12—15 feet of flat-lying older alluvium where it rests
on steeply dipping Monterey Shale that forms the sea
cliff. Eldridge also reported several active tar seeps,
and one of these, a “tar volcano,” is illustrated by
Arnold (1907, p1. 1118).

The asphalt deposit near More’s Landing consists of
asphalt-impregnated sandstone at the base of the
Pliocene strata, which unconformably overlie steeply
dipping Monterey Shale. The asphalt accumulated
to a thickness of about 20 feet near the trough of a
gentle syncline in the Pliocene sandstone where the
asphalt issues from large seeps at the unconformable
contact. This deposit was once mined as a source of
roofing and paving material (Whitney, 1865). A sim-
ilar deposit near the coast at Elwood (the La Patera
mine of Eldridge, 1901) consisted of veins so thick,
extensive and pure that they were mined to depths of
about 100 feet. Eldridge also notes that a point on
the coast half a mile east of the mine was heavily
coated by petroleum washed ashore from offshore
seeps.

Veinlike deposits of asphalt in the Monterey Shale
were also mined at Punta Gorda, 2% miles southeast
of Rincon Point. Nearby, on the seaward slope of
Rincon Mountain, a 4-foot—thick bed of bituminous
sandstone of Pliocene age rests unconformably on shale
(Eldridge, 1901). Other asphalt or tar sands are
known, especially near the inland edge of the terrace
near and west of Gaviota and near Point Conception.

ONSHORE OIL AND GAS SEEPS

Petroliferous seeps are also very common along
the northern coast of the channel; they occur along
the sea cliffs southeast of Carpinteria and at the base
of nonmarine gravels at and near Summerland. Other
seeps are widely distributed along the sea cliffs west-
ward to Point Conception, especially at the Mesa near
Santa Barbara and westward to Goleta and Elwood.
The approximate positions of these and other seeps
are shown on plate 2.

Most of the onshore seeps have been desiccated to
asphaltic tar or heavy asphalt-base oil. The seeps
are believed to be indigenous to the Monterey Shale, as
most of them issue from or near exposures of frac-
tured shale that affords routes for migration from
depth (Dibblee, 1966).

OFFSHORE OIL SEEPS AND ASPHALT DEPOSITS

Written records, dating from as early as 1792, de-
scribe effects of offshore seeps in the Santa Barbara
Channel. Oil and tar “slicks” have long been a trade-

mark of the channel. In 1792, Captain Cook’s navi-
gator, Vancouver, recorded on passing through the
Channel (Imray, 1868):

The surface of the sea, which was perfectly smooth and
tranquil, was covered with a thick, slimy substance, which
when separated or disturbed by a little agitation, became very
luminous, whilst the light breeze, which came principally from
the shore, brought with it a strong smell of tar, or some such
resinous substance. The next morning the sea had the appear-
ance of dissolved tar floating on its surface, which covered
the sea in all directions within the limits of our view. . . .

In 1889, another trained observer, A. B. Alexander,
of the US Commission of Fish and Fisheries, also
reported extensive “slicks” caused by petroleum bub-
bling up through the water about 4 miles south of
Santa Barbara Light (Alexander, 1892). During this
same year J. W. Fewkes, returning from a biological
collecting trip to Santa Cruz Island, reported as
follows: ’

. . . sailed through a most extraordinary region of the channel
in which there is a submarine petroleum well. The surface for

a considerable distance is covered with oil, which oozes up from
sources below the water, and its odor is very marked.

(Fewkes, 1889). Evidence of submarine seeps re-
corded by the U.S. Coast and Geodetic Survey during
channel crossings prior to 1900 is also reported in sev-
eral annual reports, such as for 1855 and 1859.

Sea-floor deposits of tar in the Point Conception,
Goleta, and Carpinteria areas have been studied by
Vernon and Slater (1963), who photographed tar
mounds 1% miles offshore and east of Point Concep-
tion, in 90 feet of water. There, a sheet of tar covers
an area of at least one-fourth of a square mile and
has a 10- to 12-foot scarp at its seaward edge. Else-
where, near Point Conception, tar. mounds are as much
as 100 feet in diameter and 8 feet in height. They
appear to be distributed along east-trending anticlines
in Monterey Shale. At Coal Oil Point and off Carpin-
teria, the mounds are only a few inches high, and some
are elongated along fractures in the Monterey. Pro-
lific gas and oil seeps also issue from the sea floor
about a mile off Coal Oil Point.

Tar mounds are formed where tar is slowly ex-
truded from sea-floor vents forming mounds like
shield “volcanos.” In some places, pencillike strands
or “whips” of tar, through which the more fluid tar
flows, were observed issuing from the centers of the
mounds. If seepage through the whips is slow enough,
they become more dense than sea water and sink to
form part of the mound; if seepage is faster, the whip
is torn away by agitation of the water and it floats to
the surface to become part of the drifting tar so com-
mon to beaches of the area.

Drill cores from a group of mounds show that the
tar fills all fractures and interstices in the host rock

PETROLEUM DEVELOPMENT IN THE REGION OF THE SANTA BARBARA CHANNEL 15

to a depth of 10 feet; below 10 feet the fractures are
free of tar at this locality. Oil and gas also issue from
some of the mounds, but more commonly from frac-
tures or sand nearby. It is inferred, on the basis of
sea-level changes, that the mounds formed during the
last 9,000 years (Vernon and Slater, 1963).

OIL AND GAS FIELDS

The first oil well in the Ventura basin, and probably
the first commercially successful well drilled in Cali-
fornia, was completed in 1866 by the California Petro-
leum Company about 8 miles east of Ojai. Oil had
previously been produced here from shafts and tunnels.
Within the map area (pl. 2), the first field well was
completed near Summerland in 1894.

Offshore oil exploitation in the Santa Barbara
Channel region began in 1896 With the extension sea-
ward of the Summerland oil field. Since then more
than 1,100 holes have been drilled offshore, and about
250 of these have been completed as producers. In
1921 the State of California introduced regulations
governing offshore development, and many exploration
permits and leases were granted. The development
resulted in the discovery of the offshore parts of the
Rincon field in 1927 and the Capitan and Elwood fields
in 1929 (Frame, 1960). The first production in Cali-
fornia from an offshore platform was in 1958 from
platform Hazel in the Summerland Offshore oil field.

Shortly after World War II several major oil com-
panies began extensive geological and geophysical
exploration of the offshore area by means of piston
and jet coring of surficial deposits, as well as shallow
and deep test drilling programs and seismic surveying.
A peak in the exploration program was reached in
1956—59; new methods and improved equipment made
it feasible to drill to depths of 7,500 feet and to oper-
ate in water as much as 400 feet deep. In 1958, new
and accelerated development of the tideland part of
the Rincon field followed the completion of Rincon
Island 2,800 feet offshore, near which the first ocean-
floor completions were made in 1961 in about 55 feet
of water. Later the same year, the first important
new offshore discovery in the channel was made about
2 miles off the coast in the Summerland Offshore oil
field.

In July 1958, five tideland parcels were awarded
by the State in one area between Goleta Point and
Point Conception, and new discoveries in that area
began early the following year—Gaviota Offshore gas
field in 1958, Cuarta Offshore in April 1959, Concep-
tion Offshore in November 1959, and Naples Offshore
gas field in September 1960.

Following discovery of the Coal Oil Point Offshore
field in 1961 and the Alegria, Caliente, and Molino
Offshore fields in 1962, no new discoveries were made
in the tidelands until the South Elwood and Carpin-
teria Offshore fields were discovered in 1966; the latter
discovery led to the first sale of Federal leases in the
Santa Barbara Channel—a drainage sale of lease OCS
P-0166. Since 1966, offshore developments have been
on Federal leases, chiefly on the westward extension
of the Rincon trend, OCS leases P—0166, P-0240, and
P—0241 (Carpinteria Offshore field and the Dos
Cuadras Offshore field).

The channel region contains 24 producing oil and
gas fields. The reservoir rocks are varied but consist
chiefly of sandstone and interbedded siltstone and
sandstone: the age of the reservoir rocks ranges from
Eocene to Pleistocene, but strata of Pliocene age have
yielded the greatest amount of oil. Most of the oil
and gas accumulated in faulted anticlines that were
formed chiefly during the Pleistocene deformation.
Production statistics and basic geologic data for the
fields are presented in table 1. The fields are divided
into five groups on geologic-geographic grounds: the
Rincon trend area, the Ojai area, the Goleta area, the
Point Conception area, and the Montalvo area.

RINCON TREND AREA

The Rincon trend area includes the Ventura, San
Miguelito, Rincon, Carpinteria Offshore, and the Dos
Cuadras Offshore oil fields. All these fields are on
the intensely folded and faulted Rincon anticlinal trend
(pls. 1, 2). The general eastward plunge of this struc-
tural feature is indicated by the fact that at the Dos
Cuadras field, at the west, the top of the “Repetto
Formation” is exposed at the sea floor; in the eastern
part of Carpinteria Offshore, it is at a depth of about
2,000 feet; and at the point where the Rincon field
crosses the shoreline, it is at a depth of about 6,700
feet. The flanks of this trend are cut by intersecting
en echelon reverse faults, and the result is repetition
of the stratigraphic section and formation of a thick
producing sequence, which at Ventura is about 7 ,500
feet in thickness.

Ventura oil field

Gas and oil were first found at Ventura in 1885 in
a 200- to 300—foot-deep water well near the axis of
the field, just east of the Ventura River. The Ventura
anticline was mapped in 1898 and recommended for
exploration, but exploration was not attempted until
1903, when nine commercial gas wells were drilled to
depths of 400—800 feet in the Ventura River bed.
However, the gas wells were difficult to drill in the

16 GEOLOGY, PETROLEUM DEVELOPMENT, SEISMICITY, SANTA BARBARA CHANNEL, CALIF.

river bed with the cable-tool rigs, the water could not
be controlled, and the wells were abandoned. For many
years the Ventura oil field had the reputation of
being one of the most difficult in California in which
to complete deep wells (Hertel, 1929).

Exploratory drilling for oil was begun in 1914, but
the first well was suspended after 2 years of work,
because formation water could not be controlled. The
second discovery well was begun in May 1916; in
September the well blew out at 2,253 feet. The blow-
out destroyed the rotary rig and formed a crater
around the well from which gas, oil, and water were
sprayed, confirming the presence of petroleum under
high pressure. Subsequent efforts to develop oil
production from this level, known as the upper “light
oil” zone, were relatively unsuccessful. Water shut-

off was difficult to attain, the zone was flooded, and '

the excessive gas pressures caused several more severe
blowouts. One well, after being shut in, broke out at
the surface 400 to 500 feet from the well, where a gey-
ser of water, oil, and gas shot 8 or 10 feet into the air
until the well bore was reopened (Hertel, 1929). Fin-
ally, in April 1919, hard-won experience and improved
methods resulted in successful completion of a com-
mercial well at about 3,500 feet in what is called the
upper “heavy oil” zone. After this success, additional
and better wells were completed in successively deeper
zones: 3,700 feet in 1921; 3,855 feet in 1922; and also in
1922, a well for 1,900 bpd from 5,050 feet. In 1925, a
real “gusher” was completed for more than 4,600 bpd
from 5,150 feet. By 1928, more than 100 wells, some
flowing at rates of 5,700 bpd, had been completed at
depths to 7,100 feet. At the same time, the field was
being expanded areally; it is now about 7 rniles along
the east-west axis and about 1 mile wide: ‘

In addition to the difficulties of controlling forma-
tion water, the Ventura field is almost unique in
California for its abnormal reservoir pressures below
depths of about minus 6,000 feet. Although these
conditions had long required the use of heavy-mineral
drilling muds, considerably higher pressures were en-
countered in the early 1940’s in the “D—7” zone at
depths below about minus 9,000 feet. Initial reservoir
pressures in the “D—7” zone near the crest of the anti-
cline range from about 85 percent of inferred litho-
static pressure at minus 6,000 feet to about 92 percent
of that at minus 9,000 feet (Watts, 1948). 'Ihese
pressures produce very high gradients in the well
bore and well-head pressures as great as 5,300 psi
(pounds per square inch).. In addition to drilling
hazards resulting from these high fluid pressures, wells
commonly failed by collapse and shearing of pipe
(Watts, 1948).

San Miguelito oil field

San Miguelito field adjoins the Rincon field on the
northwest. It was discovered by surface geologic
mapping. The discovery well flowed 600 bpd from
6,750 feet on completion in November 1931. Later
development extended the productive section to
depths of about 11,000 feet, for a total of about 3,940
feet in vertical dimension, and by 1961 the section had
been tested to a depth of 14,155 feet in the Miocene.
However, production comes only from Pliocene strata.
As at the adjoining Ventura oil field, reservoir pres-
sures exceed “normal” hydrostatic pressure at depths
5,500 feet below sea level and greater (fig. 11). Res-
ervoir pressures exceeding 10,000 psi in the interval
11,300—15,600 feet below sea level were reported by
McClellan and Haines (1951). Reservoir pressure of
10,000 psi would be about 90 percent of inferred litho-
static pressure at a depth of 11,000 feet below sea
level.

The field lies in an east-trending asymmetrical
closed anticlinal structure. It is separated from the
Rincon field to the northwest by a south-dipping re-
verse fault: its eastern boundary is an arbitrary line
near the west edge of R. 23 W. The reverse fault
marks the upper boundary of a very thick zone of
crushed beds; it apparently formed in the south limb
of a tightly compressed, overturned anticline.

Rincon oil field

Although the Rincon area was explored after the
success at Ventura in the 1920’s, it was not until
December 1927 that sustained commercial production
was obtained from the present limits of the field by
a well drilled onshore and extended seaward. The
second well of the field was completed in 1931 at 7,825
feet after having been plugged back from 10,030 feet.
Although contemporary accounts of drilling history
do not mention abnormal reservoir pressures, all the
early completions were flowing wells.

As in the Ventura field, production is from Pliocene
strata; the structure, also similar to that of Ventura,
is an elongate anticline with limbs sheared by reverse
faults. The producing section is about 6,000 feet in
vertical dimension.

The State tideland part of the Rincon field was
developed very slowly by wells drilled from piers until
completion in 1958 of the manmade Rincon Island
about 2,800 feet from shore in 45 feet of water. The
first well was completed in October of that year, and
46 wells had been completed by August 1960. All
the wells were directionally drilled, and hole angles
were as great as 68° from vertical. The deepest

PETROLEUM DEVELOPMENT IN THE REGION OF THE SANTA BARBARA CHANNEL

drilled depth was 7,725 feet, but all production comes
from Pliocene strata above about 3,000 feet subsea
(Frame, 1960). In March 1961, California’s first ocean-
bottom completion was made at Rincon. The well
was drilled from an anchored barge in 55 feet of
water to a depth of 2,290 feet; the well was completed
flowing 64 bpd clean 28°-gravity oil and 18 Mcf
(thousand cubic feet) gas through a 3,000-foot ocean-
floor pipeline to shore (Frame, 1960).

Carpinteria Offshore oil field

The Carpinteria Offshore field extends about 4 miles
from State tideland tract PRC 3150 westward into
Federal OCS P—0166 and P—0240. The inferred pro-
ducing area is about half in State tidelands and half
in Federal OCS tracts. Production was obtained in
February 1966 by a well drilled from platform “Hope,”
the second platform west of the Rincon Island; the
well had an initial production of more than 250 bpd
flowing. Since then, 89 wells have been drilled from
four platforms, and 88 of them produced in 1968 (see
table 1). The peak production year was 1967, when
the average was 9,894 bpd.

Dos Cuadras Offshore oil field

The Dos Cuadras Offshore field, in Federal OCS

P-0241, is a western development on the Rincon trend.
An early test from 2,000 to 2,700 feet flowed at the
rate of 1,800 bpd of 27 .8°-gravity oil; a test from 725 to
1,205 feet flowed at 346 bpd of 23.4°-gravity oil. All
production is from the “Repetto Formation” of early
Pliocene age. The first platform, “A,” was set in
September 1968, and the first well drilled from the
platform, No. A-20, bottomed at 3,673 feet and was
completed between 2,137 and 3,427 feet, flowing at
1,080 bpd (data from Californa Oil World, 1969).
‘0 Federal OCS P-0240 adjoins P—0241 on the east.
The second well drilled on P—0240 was tested in July
1968; it flowed at an average rate of 1,042 bpd of 342°-
gravity oil from 3,437 to 3,535 feet.

OJAI AREA

The Ojai area includes the Tip Top, Lion Mountain,
Weldon Canyon, Oakview, and Canada Larga oil fields.

The first successful oil well in California was com-
pleted in 1866 about 20 miles east-northeast of Rincon
Point in the east part of what is now the Ojai oil field
area; oil had previously been recovered from tunnels
in the same area. Several small fields were later dis-
covered in the same area, including Lion Mountain,
Tip Top, Weldon Canyon, and Oakview. These fields
are located in the northeast part of the present map
and are included as part of the Ojai group (pl. 2,
table 1).

17

Tip Top oil field

The Tip Top field, located about 5 miles south-
southwest of Ojai, was discovered in 1918. The dis-
covery well had an initial production of 15 bpd from
a depth of about 430 feet in fractured Miocene shale
that is exposed at the surface. Only small production
was obtained from a total of eight wells. The peak
production year was 1935, when the daily average

was 18 barrels of oil. The area did not produce in
1968.

Lion Mountain oil field

The Lion Mountain field, located about 1 mile south
of Ojai, was discovered in 1893 by a well that produced
about 20 bpd from a depth of about 1,200 feet in
the Sespe Formation. Production was discovered
in Eocene strata in 1949 by a well that produced about
26 bpd from a depth of about 3,500 feet. Peak pro-
duction of about 55 bpd was attained in 1950. The
structure of the field is a faulted asymmetrical anti-
cline, bounded on the north by a south-dipping, east-
northeast-trending reverse fault.

Weldon Canyon oil field

The Weldon Canyon field adjoins the Tip Top
field on the south. The discovery well was completed
in 1951 with an initial production of 133 bpd from
about 3,050 feet in Pliocene strata. The peak pro-
duction year was 1954, when the daily average was
118 barrels. In 1968 the area produced 22,000 barrels
from two wells. The structure is a pinchout on the
steep south flank of an anticline.

Oakview oil field (abandoned)

The Oakview field is located about 6 miles south-
west of Ojai. The discovery well was completed in
April 1955 and pumped 15 bpd of 35°-gravity oil from
about 1,545 feet in the Vaqueros Formation. Only
one well was completed; the field was abandoned in
September 1955 after producing 726 barrels of oil.

Production came from the crestal part of a broad
east-plunging anticline, which has been drilled to 4,709
feet, or about 3,100 feet into the Sespe Formation.

Canada Larga oil field

The Canada Larga field is located about 5 miles
south of Ojai. The discovery well was completed in
August 1955 for 128 bpd of 26°-gravity oil, 48 percent
cut. Recompletion the following month resulted in
production of 75 bpd of clean oil. By 1960, only three
wells had been completed. Production comes from a
depth of about 2,500 feet in the “Repetto Formation.”
The structure consists of a stratigraphic trap on the
south flank of a faulted anticline, which at Canada
Larga has been drilled to 5,770 feet, or about 970 feet
into upper Miocene strata below the “Repetto.”

18 GEOLOGY, PETROLEUM DEVELOPMENT, SEISMICITY, SANTA BARBARA CHANNEL, CALIF.

GOLETA AREA

The Goleta area includes the following fields: Sum-
merland (abandoned), Summerland Offshore, Mesa,
Goleta (abandoned), La Goleta gas (abandoned), Coal
Oil Point Offshore, Elwood, South Elwood Offshore,
Las Varas (abandoned), and Glen Annie gas (aban-
doned).

Summerland oil field (abandoned)

Oil production in the channel area dates from about
1894, when the Summerland oil field was discovered
from oil seeps. Early development of the field was
along the inland margin of the marine terrace; begin-
ning in 1896, development was extended seaward and
then out over the ocean by means of wells drilled from
wooden piers as much as 700 feet offshore. More
than 400 wells were drilled from the piers to depths
of 100—600 feet. This field brought in the first known
offshore production in the United States. Peak pro-
duction of the field was attained in 1899, when the

daily average was 571 barrels of oil, chiefly from shal--

low Pliocene strata. Later exploration led to the
development of small pools in the Vaqueros(?) Forma-
tion of early Miocene age, and a second, lower pro-
duction peak was attained in 1929. The field has been
virtually abandoned for many years.

Summerland Offshore oil field

In 1957, during the peak of offshore exploration, sev-
eral test holes were drilled from a barge in State
tideland tract 1824, offshore from the old Summerland
field. As a result, a permanent drilling platform
(“Hazel”) was constructed in 100 feet of water. The
first well to be drilled from Hazel was completed in
November 1958; it was reported to have flowed at a
rate of 865 bpd. The well was drilled to a total depth
of 7,531 feet (Frame, 1960). By the end of 1960, a
total of 16 wells had been drilled, of which 14 were
producers. A second platform (“Hilda”) was con-
structed about 2 miles west of Hazel in August 1960.
By the end of 1968, 46 wells had been drilled, of which
31 were producing; the average drilled depth is 7,937
feet. Production is from unnamed sands in the
Vaqueros Formation. The peak production year
was 1964, when the daily average was 10,362 barrels.
Details of the structure are not available.

Mesa oil field

The Mesa field was discovered in 1929, a small
production of oil being obtained from the Vaqueros
Formation at about 2,200 feet. One well was drilled
to 10,047 feet in the Sespe Formation, but no oil was
found. Initial production of some wells was 200 bpd,
but by 1950 oil had given way to water; at the end of
1968 there were only three active wells, which pro-

duced chiefly water. The structure is a gently arched
dome transected on the northeast by a northwest-
trending, south-dipping reverse fault, about half .a mile
inland from the coast (California Division of Oil and
Gas, 1961).

Goleta oil field (abandoned)

Surface mapping led to identification of an anticline
in Tecolote Canyon, and in 1926 a well was drilled to
test the Eocene strata. The test was unsuccessful,
but two oil zones were found in the Sespe Formation
at depths of 613 and 1,527 feet. A second well was
completed in 1927 for 450 bpd, and a third well was
completed for 1,040 bpd. Only eight of 27 wells drilled
were completed, and these were soon depleted as edge
water encroached; the field was abandoned 13 months
after its discovery.

La Goleta gas field (abandoned)

Gas seeps had been known for many years along the
east edge of Goleta Slough. The La Goleta gas field
was discovered in the same area in 1929 by a well that
blew out at 4,533 feet and later was completed, flowing
58 Mch (million cubic feet) gas per day from the
Vaqueros Formation. One well was drilled through
the Sespe Formation to bottom in Eocene at 6,912 feet;
although several oil shows were reported from the
Sespe, none yielded commercial production. The six
wells that were completed from the Vaqueros included
one well that produced at the rate of 145 Mch per day.
At one time this field contained some of the largest
gas-producing wells in California. The field was credited
with a cumulative production of 15,363 Mch on De-
cember 31, 1968. It is now used for gas storage.

The structure of the field is a small asymmetric anti-
clinal dome, bounded on the north by a south—dipping
reverse fault that trends parallel to the coast about
2,000 feet inland (Swayze, 1943). The structure is
offset in plan about 800 feet by a northeast-trending
normal fault (California Division of Oil and Gas, 1961).

Coal Oil Point Offshore oil field

The Coal Oil Point Offshore field is located in State
tideland tract PRC 308. The field was discovered in
1948 by a nearshore well that had an initial production
of 89 bpd from the Vaqueros Formation. Peak an-
nual production of 1,279 barrels was attained in 1948.
Two wells were drilled to an average depth of 10,047
feet, but only one was completed. This area of the
field is now abandoned.

In 1961, additional production was obtained about
2 miles offshore in Sespe-equivalent strata from a
well drilled from a barge to a depth of about 5,598 feet.
Peak production averaging 637 bpd was attained in
1966.

PETROLEUM DEVELOPMENT IN THE REGION OF THE SANTA BARBARA CHANNEL 19

Elwood oil field

The discovery well at Elwood was completed in
1928. The well flowed 1,775 bpd of 38°-gravity clean
oil from 3,208 feet in the Vaqueros Formation. The
field was extended westward offshore by wells drilled
from piers and was also extended eastward onshore.
By the end of 1930 there were six producing tideland
wells. Peak production was attained in 1930 when
33 wells averaged 40,069 bpd, accounting for 6 percent
of California’s production for that year. In 1931, 22
more tideland wells were completed, and beginning in
1944, slant drilling from shore extended the field a
mile or more westward. The reserves of the field
were thus increased, but the production peak of 1930
was not surpassed. Although several wells produce
from the Sespe Formation at depths between 3,700
and 5,700 feet, the bulk of the production comes from
the Vaqueros Formation at shallower depths.

The field includes two elongate east-trending en
echelon anticlines, the western of which is entirely
offshore. Closure of the eastern anticline is provided
by a south-dipping reverse fault that trends subparal-
lel to the coast (California Division of Oil and Gas,
1961)

South Elwood Offshore oil field

The South Elwood Offshore field is located in State
tideland tract PRC 3120 and 3242, about 2% miles
offshore from the Elwood field. The discovery well
was drilled in November 1966 to a depth of 6,287 feet.
Production is from sands in the Vaqueros and Sespe
Formations. The average drilled depth of 11 wells
completed from platform “Holly” is 6,290 feet. The
peak production year was 1967, when the average
was 4,167 bpd.

Las Varas oil field (abandoned)

The Las Varas field was discovered in 1958; all pro-
ducing zones were in the Sespe Formation at depths
of about 2,400—3,000 eet. The deepest test was to
3,404 feet in Eocene geds. Only two of seven wells
drilled were completed. The peak production year
was 1958, and the field was abandoned in 1960. The
structure consists of a small northeast—trending anti-
cline that is bounded on the south by an east-trending
south-dipping reverse fault (California Division of
Oil and Gas, 1961).

Glen Annie gas field (abandoned)

The Glen Annie field was discovered in 1959; the
initial production of the discovery well was 855 Mcf
per day. Production was from an 80—foot sand in the
Vaqueros Formation at an average depth of 3,350 feet.
Only two wells were drilled and one completed; the
field was abandoned in 1961 after producing 491,000
Mcf of gas.

365-228 0 — 69 - 5

POINT CONCEPTION AREA

The Point Conception area includes the following
fields: Naples Offshore, Capitan, Refugio Cove (aban-
doned), Molino Offshore, Gaviota Offshore, Caliente
Offshore, Alegria, Alegria Offshore, Cuarta Offshore,
Conception Offshore, Point Conception Offshore, and
two unnamed offshore oil fields in Federal OCS
P—0188—90 and P—0197.

Naples Offshore gas field

The Naples Offshore gas field is located in State
tideland tract PRC 2205. It was discovered by a well
drilled from onshore to a depth of 8,871 feet and com-
pleted in September 1960. The initial production was
estimated at 70,000 Mcf per day. The production ap-
parently comes from Vaqueros-equivalent sands. The
cumulative production on December 31, 1968, was
20,815 M’cf; no wells produced in 1968 (Conservation
Committee of California Oil Producers, 1969).

Capitan oil field

The Capitan oil field was discovered in 1929, after
discovery of the Elwood oil field. The discovery well
was completed for 180 bpd from 1,446 feet in the
Vaqueros Formation. Several wells produce from the
Sespe Formation at depths as great as 3,400 feet, but
the Vaqueros is the most important producer. The
deepest test by 1960 was 10,216 feet in Eocene.

Commercial production was not obtained from the
tideland part of the field until 1932. In that year the
discovery well blew out during plugging operations
after being deepened to 2,821 feet in the Sespe For-
mation. Only seven tideland wells were drilled, all
from wooden piers; tideland production was suspended
in 1958.

The field is developed in a broad, gently arched,
north-trending dome that is transected on the north
by a folded west-northwest-trending, north-dipping
normal fault (California Division of Oil and Gas, 1961).

Refugio Cove gas field (abandoned)

The Refugio Cove field consists of two separate ac-
cumulations, one on either side of Refugio Canyon.
The initial discovery in 1946 was east of the canyon.
The discovery well produced 5,000 Mcf gas per day
from a depth of 2,500 feet in the Vaqueros Formation.
Minor production was discovered in 1958 west of the
canyon. This production came from about 3,550 feet
in the Sespe Formation. The deepest test, 6,148 feet,
bottomed in the Eocene. Of the 18 wells drilled, only
three were completed. The fields were abandoned in
1961 after producing 990,000 Mcf of gas and 3,000
barrels of oil.

20

Molino Offshore gas field

The Molino Offshore field, the largest natural gas
field in southern California, was discovered in Decem-
ber 1962. It is located in State tideland tracts 2920
and 2933 and reportedly produces from the Vaqueros
Formation. Production for 1968 was 28.5 M2cf gas
from nine wells; the cumulative production on De-
cember 31, 1968, was 139 ch.

Gaviota Offshore gas field

Located in State tideland tract PRC 2199, the
Gaviota Offshore gas field was discovered in 1958, but
the first well was not completed until August 1960.
The first three wells were drilled from a barge, but
the first three to be completed were slant-drilled from
shore. In 1960, the three completed wells produced
1,113 Mch of gas; the cumulative production on Decem-
ber 31, 1968, was 57,093 M2cf from three producing
wells. Production is apparently from Vaqueros-equiv-
alent sands.

Caliente Offshore gas field

The Caliente Offshore gas field was discovered in
October 1962. Production, reported from the Vaqueros
Formation, was 3,804 M20f from two wells in 1968; the
cumulative production on December 31, 1968, was
19,625 M2cf.

Alegria oil field

The Alegria onshore field was discovered in 1959;
its minor oil and gas production comes from about
4, 350 feet in the Rincon Formation. Only eight. wells
were drilled, none of which were producing in 1968.

Alegria Offshore area

The Alegria Offshore field was discovered in Feb-
ruary 1962. Production in this one-well field is from
a depth of 4,033 feet in Sespe-equivalent sands. The
peak production year was 1964, when the average was
748 bpd. Production for 1968 was 23,000 barrels of
oil and 439 M2cf gas.

Cuarta Offshore oil field

Located in State tideland tracts PRC 2206 and
2793, the discovery well of the Cuarta Offshore oil
field had an estimated initial production of 1,393 bpd
of 35°-gravity oil and a large amount of gas; total
depth was 6,751 feet. The well was suspended in April
1959 pending completion of facilities. A platform
(“Helen”) was constructed in PRC 2206 about 2,200
feet southeast of the discovery well in 94 feet of water,
and production started in January 1961. On Decem-
ber 31, 1968, eight wells had been drilled; their aver-
age depth was 6,910 feet, and six wells were producers.

GEOLOGY, PETROLEUM DEVELOPMENT, SEISMICITY, SANTA BARBARA CHANNEL, CALIF.

Production is from Vaqueros and Sespe equivalents.
The peak production year was 1962, when the daily
average was 518 barrels of oil. Production for 1968
was 20,000 barrels of oil and 815,588 Mcf gas.

Conception Offshore oil field

The Conception Offshore field was discovered in
November 1959. It is located in State tideland tracts
PRC 2207 and 2725 between 3 and 7 miles east of Point
Conception. The discovery well was drilled from a
barge to a depth of 6,854 feet, and the well was sus-
pended. A platform (“Harry”) was later erected
over the site, and the well was recompleted. By the
end of 1960, a total of 11 wells had been drilled, and
by the end of 1968, 45 wells had been drilled, of which
32 were producers. Production is from Sespe For-
mation, and the average drilled depth is 6,845 feet.
The peak production year was 1964, when the average
production was 13,539 bpd. A new pool discovery in
February 1969, made at about 4,050 feet in the Alegria
Formation, produced 384 bpd of 35°-gravity oil.

Point Conception Offshore oil field

The Point Conception Offshore field, located about
1 mile southeast of the point on State tideland tract
2879, was discovered in 1965. The discovery well had
an initial production estimated at 214 bpd from Eocene-,
Sespe-, and Vaqueros—equivalent sands. In the first
year of production, 1968, about 5,000 barrels of oil and
2 Mcf gas were produced from three wells. By Feb-
ruary 1969, the three wells had a combined production
of 406 bpd of oil.

OCS P-0197 unnamed offshore oil field

An unnamed offshore oil field is located 4 miles
south of Point Conception in OCS P—0197. The dis-
covery of commercial oil in “substantial quantities”
was announced in September 1968. Two holes have
been drilled in more than 600 feet of water, but no
completions have been made (California Oil World,
1969, v. 62, no. 4).

OCS P-0188 and P-0190 unnamed offshore oil field

On July 9, 1969, the discovery of a new offshore oil
field in Federal OCS P—0188 and P—0190 was announced.
0f the four wells now drilled, three have been tested
at rates ranging from 900 to 6,000 bpd for each well.
The oil was 17° to more than 40° gravity and came
from five separate producing horizons which were
found between the depths of 6,945 feet and more than
12,000 feet. The first well in OCS P-0190 was drilled
in a record 1,300 feet of water (Rintoul, 1969).

PETROLEUM DEVELOPMENT IN THE REGION OF THE SANTA BARBARA CHANNEL 21

MONTALVO AREA

This area includes two fields—the West Montalvo
oil field and an unnamed offshore oil field in Federal
OCS P—0202.

West Montalvo oil field

This field includes three areas that were discovered
separately: the McGrath in 1947, the Colonia in 1951,
and the tideland in 1953.

The discovery well of the McGrath area was com-
pleted for 154 bpd from a depth of about 9,000 feet
in the “Repetto” Formation; Pico gas sands above this
oil zone produce the only dry gas in Ventura County.
A structural—stratigraphic trap is developed in an arch;
the axial area includes a buried east-northeast—trend-
ing branch of the Oakridge fault—a reverse fault dip-
ping steeply to the south (California Division of Oil
and Gas, 1961).

The discovery well of the Colonia area was com-
pleted in 1951 for 191 bpd of 13°- to 27°-gravity oil.
Production comes from about 11,500 feet in a series
of discontinuous sand bodies in a complexly faulted
north—dipping homocline in the Sespe Formation.

The discovery well of the tideland area was com-
pleted for 390 bpd of clean oil from a depth of 12,3184
12,529 feet (Frame, 1960) in the Sespe Formation. By
the end of 1960, 13 wells had been slant—drilled from
onshore. One of these, the deepest offshore well
known at the time, bottomed at a drilled depth of
14,850 feet, a vertical depth of 13,622 feet, and a hori—
zontal distance of 5,632 feet from the surface location.

OCS P-0202 unnamed offshore oil field

An unnamed field is located 3% miles off Point
Hueneme in Federal OCS P—0202. The field was dis-
covered in July(?) 1969 by a well drilled to a total
depth of 8,452 feet. It flowed 15.8°-gravity oil at a
rate of about 1,000 bpd from a depth of about 5,000
feet (Californa Oil World, 1969, v. 62, no. 7 [13]).

SUMMARY

Oil, tar, and gas have been features of the natural
environment of the Santa Barbara Channel region for
thousands of years; petroleum has been the chief min-
eral resource of the region for decades.

In 1968, the oil fields of the channel area produced
22.9 million barrels of oil, about 6 percent of California’s
production. Cumulative oil production at the end of
1968 for these fields was about 1.1 billion barrels, or
about 71/2 percent of California’s cumulative produc-
tion. Dry gas production for the offshore gas fields
in 1968 was about 12 percent of the State production,
and their cumulative production was about 5 percent
of the State total.

The first commercial oil well in California was com-
pleted in 1866 just east of the channel region; it was
located on the basis of oil seeps. Since that time, the
channel region has participated directly in the suc-
cessful development of every phase of southern Cali-
fornia’s oil industry, from prospecting on land because
of the presence of oil seeps, to prospecting offshore
by geophysical methods.

The oil fields along the Rincon anticlinal trend, in—
cluding the offshore Carpinteria field, have completely
dominated the production statistics of all the other
channel-region fields combined:

Production (1,000 bb_lL

Cumulative

 

. Field 1963 on 1-1—69
Rincon, San Miguelito, Ventura __________ 11,814 884,853
Carpinteria Offshore _______________ 5,564 9 884
Subtotal _ _ _ _ _ _ _ _ _ _ _~ _________ 17,378 894,737
All others- _ _ _ _ _ - _ 1 -_ 1 ____________ 5,516 203,576
Total ______________________ 22,894 1,098,313

Note that the 1968 production from Carpinteria Off-
shore alone exceeds that from all the other non-Rin-
con trendfields combined. The large production of
the Rincon-trend fields is attributable to thick, oil-
saturated sections and relatively high porosities and
permeabilities.

22 GEOLOGY, PETROLEUM DEVELOPMENT, SEISMICITY, SANTA BARBARA CHANNEL, CALIF.

TABLE 1.———P'roduct0'on and geologic data on oil

[Except as noted, data are from Conservation

 

Average depth

 

to Average Number of wells,
Date of shallowest API December 1958
FIELD, area, and pool discovery production1 gravity Producing Total2
(feet) (degrees)
ALEGRIA ———————————————————— July 1959 9,300+ 22 ______ 8
ALEGRIA OFFSHORE ——————————— Feb. 1962 9,000: 38 l 1
CALIENTE OFFSHORE (gas)——-— Oct. 1962 —————— _ ————————— 2 3
CANADA LARGA ——————————————— Aug. 1955 2,558 26 3 u
CAPITAN ———————————————————————————————————————————— 05 75
Vaqueros ————————————————— 001:. 1929 1,300 22 33 ’41
Sespe ____________________ { Jan. 1931 } 2,000 no 12 33
Feb. 1995
Coldwater ———————————————— Aug. 1995 2,850 39 —————— 1
CARPINTERIA OFFSHORE ——————— Feb. 1966 2,600+ 26 88 89
COAL OIL POINT OFFSHORE———— ——————————————— - ————————— 3 3
Nearshore area ——————————— Aug. 1998 ——————————————— Abandoned
Offshore area ———————————— Aug. 1961 —————— 30 3 3
CONCEPTION OFFSHORE ———————— Mar. 1961 —————— ”0 32 95
CUARTA OFFSHORE ———————————— Jan. 1961 —————— SH 6 8
DOS CUADRAS OFFSHORE3 —————— Mar. 1968 2,137 ——————————————— ————
ELWOOD ————————————————————————————————————————————— 22 56
Vaqueros ————————————————— July 1928 3,900 35 21 #8
Sespe ———————————————————— Oct. 1931 3,700 37 1 8
GAVIOTA OFFSHORE (Gas) ————— July 1960 ——————————————— 3 ————
GLEN ANNIE (Gas) ——————————— Nov. 1958 3,350 ————————— Abandoned 1961
GOLETA ————————————————————— Feb. 1927 400 92 Abandoned 1928
LA GOLETA (Gas storage)———— July 1932 3,800 ——————————————— 15
LAS VARAS —————————————————— Mar. 1958 2,900 38 Abandoned 1960
MESA ——————————————————————— May 1929 2,200 17 1 5
MOLINO OFFSHORE (Gas) —————— Dec. 1962 ——————————————— 9 10
NAPLES OFFSHORE (Gas) —————— Sept. 1960 ——————————————— Abandoned 1966
LION MOUNTAIN ————————————————————————————————————— 2 10
Sespe ———————————————————— May 1935 1,200 21 ------ 8
Eocene ——————————————————— June 1999 3,550 29 2 2
OAKVIEW ———————————————————— Apr. 1955 1,595 30 Abandoned 1955
TIP TOP ———————————————————— 1918 H30 29 —————— 8
WELDON CANYON —————————————— June 1951 3,050 29 2 2
POINT CONCEPTION 0FFSHORE—— Mar. 1965 —————— 31 3 3
REFUGIO COVE ——————————————— 1996 2,900 63 Abandoned 1961
RINCON ————————————————————————————————————————————— 327 921
Main area ———————————————— Dec. 1927 2,900 30 218 291
Oak Grove area ——————————— Dec. 1937 6,800 31 34 H7
Padre Canyon area ———————— Oct. 1953 ”,150 26 _75 83
SAN MIGUELITO —————————————— NOV. 1931 7,000 31 82 118
SOUTH ELWOOD OFFSHORE —————— Nov. 1966 6,200: 31 11 11
SUMMERLAND ————————————————— 1899 140 19 ------ 8
SUMMERLAND OFFSHORE ———————— NOV. 1958 —————— 3H 31 96
VENTURA ———————————————————— June 1917 3,000 30 986 1,295
WEST MONTALVO —————————————————————————————————————— 57 86
McGrath —————————————————— Apr. 1997 9,000 29 9 18
Colonia —————————————————— Feb. 1951 11,500 16 H7 67
Fleischer ———————————————— Aug. 1957 —————— 15 1 1
Laubacher ———————————————— July 1955 —————— 28 Abandoned

Totals ———————————————————————————————————————————————— ____

 

PETROLEUM DEVELOPMENT IN THE REGION OF THE SANTA BARBARA CHANNEL

and gas fields of the Santa Barbara, Channel region

Committee of California Oil Producers (1969)]

 

Oil production

Net withdrawal
formation gas

Water production

(thousands of barrels)

(millions of cu ft)

(thousands of barrels)

 

1968 nguijiigg 1968 Cumulative 1968 cgguiifig:

to 1—1—69
——————— 7 -——————_ 13 1 39
23 80 939 2,206 1 16
————————————— 3,805 19,625 —-—-- ——————
3 78 ________ 77 ————— 98
102 18,993 109 19,819 9,138 ——————
79 12,067 39 3,958 3,526 ——————
28 6,599 75 10,976 612 13,629
——————— 377 ————-——- 385 ————-— 1,289
5,569 9,889 3,893 6,951 1,938 3,156
116 986 227 2,999 107 ——————
——————— 1 -——————— 18 -————- ——_———
116 985 227 2,976 107 933
692 19,226 983 12,926 9,999 16,669
20 581 0.816 11,178 933 9,580
265 102,792 918 89,996 2,963 ------
260 99,131 906 29,967 2,888 ——————
5 3,520 12 59,973 75 ——————
————————————— 6,816 57,093 —————— —-————
————————————————————— 990,983 —---—— ——--——
——————— 191 ———--——— 56 ——-——— ———-——
————————————————————— 15,363 -————— —--———
_______ 1 _-_--___ _________ __....__ ______
3 3,733 ———————— 8 —————— 20
————————————— 28.5 139,007 ——-——— ——————
————————————————————— 20,815 ————_- ——————
12 363 1 207 6 ——————
6 181 ———————— 130 5 ——————
6 182 1 77 1 ——————
_______ 1 _-_____- __-_____- ______ ______
——————— 106 -—————-— 67 —————- ——-——-
22 512 19 302 3 22
5 5 2 2 ————————————
——————— 3 —-——-——— 80.990 —————— ——————
2,568 99,993 9,527 152,978 9,953 ——————
1,612 65,212 2,323 83,139 3,287 ——————
259 13,568 630 37,729 258 3,856
697 20,713 1,579 32,115 908 12,392
831 53,262 972 155,059 628 10,963
1,929 3,999 2,812 9,999 299 369
——————— 3,210 ——————— *1,709 -——-—— ————--
1,285 20,783 8,537 69,602 1,021 6,793
8,915 732,098 18,566 1,919,819 8,567 ——————
1,089 29,107 561.578 *10,312 1,105 19,203
102 3,257 “23 7,613 33 520
980 25,598 0.578 810,291 1,072 13,681
7 161 -------- 9 —————— 2
_______ 91 ————-——— 39 —-—-—— ———-——
22,899 1,098,899 80,685 2,927,386 ————————————

 

GEOLOGY, PETROLEUM DEVELOPMENT, SEISMICITY, SANTA BARBARA CHANNEL, CALIF.

TABLE 1.—Product1l¢m and geologic data on oil and gas

 

 

 

 

Peak
Production Geologic data
Year B d Producing

FIELD, area, and P001 p formation and age

ALEGRIA ———————————————————————— 196”} Rincon, early Miocene ————————
748
ALEGRIA OFFSHORE ——————————————— 196” Sespe equivalent, Oligocene——
CALIENTE OFFSHORE (Gas) ———————— -——- ————— Vaqueros, early Miocene ------
CANADA LARGA ——————————————————— 1956 55 "Repetto," early Pliocene————
CAPITAN ———————————————————————— —-—— ——————————————————————————————————
Vaqueros ————————————————————— 1993 3,105 Vaqueros, early Miocene ------
________________________ 1935 1,261 Sespe Oligocene-————------——
SESPe 1996 1,728 5

Coldwater ———————————————————— 1997 160 Coldwater, Eocene ————————————
CARPINTERIA OFFSHORE ——————————— 1967 9,899 "Repetto," early Pliocene--——
COAL OIL POINT OFFSHORE ———————— ———— ——————————————————————————————————
Nearshore area ——————————————— 1998 2 Vaqueros, early Miocene ------
Sespe, Oligocene —————————————
Offshore area ———————————————— 1966 637 Sespe equivalent -------------

CONCEPTION OFFSHORE ____________
CUARTA OFFSHORE ________________

DOS CUADRAS OFFSHORE3 __________
ELWOOD _________________________
Vaqueros _____________________

Sespe ------------------------
GAVIOTA OFFSHORE (Gas) —————————

GLEN ANNIE (Gas) _______________
GOLETA _________________________

LA GOLETA (Gas storage) ————————
LAS VARAS ______________________
MESA ———————————————————————————
MOLINO OFFSHORE (Gas) ——————————
NAPLES OFFSHORE (Gas) ——————————

LION MOUNTAIN __________________
Sespe ————————————————————————
Eocene- ______________________

OAKVIEW ________________________

TIP TOP ________________________

WELDON CANYON __________________

POINT CONCEPTION OFFSHORE ——————

REFUGIO COVE————-——______-___;_
RINCON _________________________
Main area ____________________

Oak Grove area _______________
Padre Canyon area ————————————

SAN MIGUELITO __________________
SOUTH ELWOOD OFFSHORE __________

SUMMERLAND _____________________

SUMMERLAND OFFSHORE ____________

See footnotes at end of tables.

196H 13,539

1962 515
1930 90,069
1936 2,698
1958 2
1935 3,027
1938 us
1950 55
1955 2
1935 18
ISBN 118
1959 n
1961 6,735
1950 3,515
Vl95u 2,918
1951 6,758
1967 H,16u
1899 571
196u 10,362

Vaqueros, early Miocene ——————
Sespe equivalent _____________

Vaqueros, early Miocene ——————
Sespe equivalent _____________

"Repetto," early Pliocene—--—

Vaqueros, early Miocene ——————

Sespe, Oligocene _____________
Vaqueros, early Miocene ——————

Vaqueros, early Miocene ——————
Sespe, Oligocene —————————————

Vaqueros, early Miocene ------
Sespe, Oligocene _____________
Vaqueros, early Miocene ——————
Vaqueros equivalent ——————————
Vaqueros, early Miocene ——————

Sespe, Oligocene _____________ }
Eocene _______________________
Vaqueros, early Miocene ______
Mid-late Miocene _____________
Pico, late Pliocene ——————————
Vaqueros, early Miocene ——————
Sespe, Oligocene _____________

Sespe, Oligocene _____________
Pico and "Repetto," late

and early Pliocene.
Pico, late Pliocene ——————————
Pico, late Pliocene ——————————

Pico, late Pliocene ----------
Vaqueros, early Miocene ------ }

Sespe, Oligocene _____________
Pliocene, Miocene ____________

Vaqueros, early Miocene ——————

PETROLEUM DEVELOPMENT IN THE REGION OF THE SANTA BARBARA CHANNEL 25

fields qf‘ the Santa Barbara Channel region—Continued

 

Geologic datae-Continued

 

Nature of trap1

Method of discovery3

Remarks 1 3

 

Offshore tract No. and
completion data

 

Faulted
anticlinal

nose.
Faulted anticline
on Rincon trend.

Faulted anticline
on Rincon trend.
{Faulted anticline———

Stratigraphic trap
in fold.
Asymmetrical
anticline.
Anticlinal dome -----
Faulted anticline---
Faulted dome ————————

Faulted asymmetric
anticline.
Faulted anticline---

Faulted anticline
on Rincon trend.

Faulted anticline
on Rincon trend.

Faulted anticline-——

Anticline ___________

GeOlogic mapping ____________

Geophysical and geological--

Geophysical and geological-

Geologic mapping ___________

Geologic mapping ___________
Geologic mapping ___________

Geologic mapping ———————————
Geologic mapping ———————————

Geologic mapping ___________

Geologic mapping -----------

State 2199.

Seven tideland wells drilled from
piers.

State 3150; Federal OCS 166. Wells
completed from platforms "Hope,"
"Heidi," "Hogan," and "Houchin."

State 308; wells completed on ocean
floor.

State 2207 and 2725; wells completed
from platforms "Harry" and "Herman."

State 2206; wells completed from
platform "Helen."

Federal OCS #02, platforms "A" and
"B" '

Gas injected for pressure mainte-
nance.

State 2199; completed wells drilled
from shore.

Produced for only 18 months.
Gas storage since 19Hl.

Inactive.

State 2920 and 2933.

State 2205; wells drilled and com-
pleted from onshore.

State 2879; wells completed on
ocean floor.

State 1H66; wells completed from
manmade Rincon Island; first
ocean-bottom well completed in
tideland (1961).

Excessively high reservoir pres-
sures at 11,300 ft subsea.

State 3120 and 32H2; wells com—
pleted from platform "Holly."

More than U00 shallow wells drilled
in tideland from piers beginning
1896.

State 182M; wells completed from
platforms "Hazel" and "Hilda."

26 GEOLOGY, PETROLEUM DEVELOPMENT, SEISMICITY, SANTA BARBARA CHANNEL, CALIF.

TABLE 1.—Production and geologic data on oil and gas

 

 

 

Peak
Production Geologic data
Year de Producing

FIELD, area, and pool formation and age

VENTURA ———————————————————————— 1930 ”5,323 Pico and "Repetto," late and

and early Pliocene.

WEST MONTALVO —————————————————— ———— ___________________________________
McGrath —————————————————————— 1952 815 "Repetto,"early Pliocene —————
Colonia —————————————————————— 1962 7,501 Sespe, Oligocene —————————————
Fleischer ____________________ 1958 106 Sespe, Oligocene —————————————
Laubacher ———————————————————— 1956 107 Sespe, Oligocene —————————————

Totals —————————————————————— ———— ——————————————————————————————————

 

l‘Injected gas deducted.

1Data from California Division of Oil and Gas (1961).
*Chiefly dry gas.

2Total includes storage, idle, and active service wells.
3Data from various sources.

SEISMICITY AND ASSOCIATED EFFECTS, SANTA BARBARA REGION 27

fields of the Santa Barbara Channel region—Continued

 

 

 

Geologic data——Continued Remarks! 2
Offshore tract No. and
Nature of trap1 Method of discovery3 completion area
Faulted anticline Geologic mapping and gas seeps. Excessively high reservoir pressures
on Rincon trend. below 6,000 ft subsea.
Stratigraphic trap Includes a tideland lease, developed
in faulted arch. —————————————————————————————— by wells drilled from shore.

 

365-228 0 - 69 - 6

 

Geologic Characteristics

of the Dos Cuadras
Offshore Oil Field

By T. H. MCCULLOH

GEOLOGY, PETROLEUM DEVELOPMENT, AND SEISMICITY OF THE
SANTA BARBARA CHANNEL REGION, CALIFORNIA

 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 679—C

 

 

CONTENTS

 

Page
Introduction ____________________________________________________________ :3
Acknowledgments _______________________________________________________ 30
Structure ____________________________________________________________ 32
Lithology and stratigraphy _________________________________________________
Petrophysical characteristics ________________________________________________ g:
Fluid properties ______________________________________________________
Reservoir and reservoir characteristics __________________________________________ 41
Seepage and subsurface fluid communication ______________________________________ 42
Subsidence potential ______________________________________________________ 45
ILLUSTRATIONS
_ ___— Page
FIGURE 6. Composite type log of the Dos Cuadras oil field ______________________________ 31
7-9. Graphs showing:
7. Porosity versus depth for analyzed core samples, Dos Cuadras oil field __________ 34
8. Permeability versus porosity of analyzed sandstone cores, Dos Cuadras oil field- _ _ _ 35
9. Oil gravity versus depth, Dos Cuadras oil field __________________________ 37
10. Schematic relations between producing “zones,” stratigraphic subdivisions, and structural
divisions in the Dos Cuadras oil field __________________________________ 37
11. Graph showing fluid pressures and fluid-pressure gradients versus depth for the Rincon
trend including the Dos Cuadras oil field _______________________________ 38
12. Graph showing fluid pressures, fluid-pressure gradients, and uncased and perforated in-
tervals of Dos Cuadras oil-field wells that were shut in or drilling on January 28,
1969 ________________________________________________________ 40
13. Map showing Dos Cuadras oil-field oil and gas seepage area ______________________ 44
TABLE
Page

TABLE 2. Comparison of certain geologic and engineering characteristics of the Dos Cuadras oil
field with the Wilmington, Calif, oil field _______________________________ 46

III

 

GEOLOGY, PETROLEUM DEVELOPMENT, AND SEISMICITY OF THE
SANTA BARBARA CHANNEL REGION, CALIFORNIA

GEOLOGIC CHARACTERISTICS OF THE DOS CUADRAS OFFSHORE OIL FIELD

By T. H. MCCULLOH

INTRODUCTION

The Dos Cuadras Offshore oil field is a large multi-
zone anticlinal accumulation of oil of intermediate
gravity in a sandstone and siltstone sequence of early
Pliocene age (“Repetto Formation”). The accumula-
tion occurs in an elongate, doubly plunging, faulted
culmination of the Rincon anticlinal trend beneath
OCS leases P—0241 and P-0240, about 5% miles south
of Santa Barbara. Figure 5 shows the generalized
structure along that part of the Rincon trend from
the eastern part of the Ventura oil field to the area
south of Santa Barbara. An area of roughly 1,000
acres is estimated to be potentially productive from
multiple sandstone reservoirs at subsea depths of 4,000
feet and less, but revisions to the estimate will prob-
ably be required as more detailed geologic informa-
tion becomes available from drilling.

When compared with any other known anticlinal
oil field of “giant” dimensions1 and comparable area
in the Santa Barbara Channel region, in the eastern
Ventura basin, or in California, the Dos Cuadras
petroleum accumulation is unique in one special way.
The shallowest commercial reservoirs of the other
small-area “giant” anticlinal fields are covered and
confined by a thousand to many thousands of feet of
relatively impermeable strata incapable of yielding
commercial amounts of fluid hydrocarbons to a well
bore. By contrast, at the structurally highest point
beneath OCS P—0241, the top of the shallowest major
reservoir of the Dos Cuadras field is overlain by a
section of less than 300 feet of interbedded siltstone,
claystone, and minor sandstone. Even these upper-
most 300 feet of strata are porous and permeable

enough to contain mobile hydrocarbons that locally
are producible.

Development of the Dos Cuadras field began late
in 1968 when the first of 54 wells planned for drilling
and completion from Platform A on OCS lease P—0241
was spudded. The normal development of the field
was stopped when the fifth well on Platform A(A-21)
blew out on January 28, 1969, prior to logging.

ACKNOWLEDGMENTS

The engineering, exploration, and exploitation data
on which this report is based were made available to
the author between February 14 and August 20, 1969.
Data regarding OCS P—0241 were provided chiefly by
the Union Oil Co., and came either directly to the
author from company representatives, from the files
of the U.S. Geological Survey, and through documents
provided to the Presidential Advisory Panel. Data
regarding leases to the east of OCS P-0241 came from
several operators. The very valuable assistance of
R. L. Brennan, K. S. Fox, and G. W. Lester of Union
Oil Co., and of K. A. Yenne, R. J. Lantz, and V. C.
Kennedy of the Geological Survey is gratefully ac-
knowledged. Many other persons and organizations
contributed in numerous important ways; among
them H. C. Wagner, J. E. Schoellhamer, and R. E.
von Huene deserve special thanks, together with the
staffs of the Los Angeles and New Orleans offices
of the U.S. Geological Survey Conservation Division.

 

1 An oil field is termed “giant” if it contains producible reserves of 100 million
barrels or more.

30 GEOLOGY, PETROLEUM DEVELOPMENT, SEISMICITY, SANTA BARBARA CHANNEL, CALIF.

STRUCTURE

The writer’s present knowledge of the structure of
the Dos Cuadras field is based upon his examination
of data from 17 of 27 wells coupled with interpreta-
tions of reflection seismic surveys and supplemented
by sea-floor geologic mapping and extrapolation
based on better known parts of the structurally lower
part of the Rincon trend east of 008 lease P-0241
and P—0240.

Of primary importance in the structural interpre-
tations are the data derived from logging and sampling
of holes drilled to explore for, or to produce oil and
gas. In August 1969, data were available from one
deep well, one well of intermediate depth, and six
shallow exploratory wells; from 15 development or
evaluation wells of shallow to very shallow vertical
depths (including the unlogged blown-out well A—21
and its very shallow redrill); from an abandoned
shallow hole begun as a relief well to the A—21 (well
008 P—0241 No. 4); and from three extremely shallow
abandoned cement grouting holes. On January 28,
1969, the date of the blowout, only the exploratory
wells and five of the development wells had been
drilled. However, the data acquired from subsequent
drilling has served only to refine local details of the
earlier geological interpretations.

Correlations from well to well by electric logs permit
determination of local structural elevations of many
distinctive subsurface stratigraphic horizons. Simi-
larly, stratigraphic repetition (or deletion) by faulting
in a well can be detected by electric log interpretation
once the local normal stratigraphic section has been
determined. Dip-meter data provide reliable indica-
tions of local bedding-plane attitudes of the strata
penetrated by a well. Micropaleontological analyses
of samples of drill cuttings and of conventional cores
permit faunal zonation and faunal correlations of the
rocks penetrated relative to rocks encountered in
other wells and outcrops in the Santa Barbara Channel
region. Each of these well-established techniques
has been used in arriving at the present interpretation
of the structure of the Dos Cuadras part of the Rincon
anticlinal trend, particularly in the axial region, and
especially within the area of present and potential oil
production.

Also of primary importance in the structural inter-
pretations are reflection seismic data. Somewhat
curiously, seismic data quality is poor along and over
the structurally highest parts of the Rincon trend,
particularly the productive area of the Dos Cuadras
field. In that important region, strong parabolic
reflections from point or line reflectors at or just
below the sea floor are so numerous and predominant

as to partly or wholly obscure seismic ‘signals that
might be generated by velocity contrasts associated
with flat or gently dipping strata below. Therefore,
the near-surface seismic data are virtually useless for
crestal structural interpretations. On the other hand,
seismic data quality along the outer flanks of the Dos
Cuadras part of the Rincon trend is excellent, and,
after correction for change of velocity with depth,
permits fairly accurate general delineation of the
anticlinal flanks.

Geologic mapping on shore led to early recognition
of the conspicuously large and very productive Ventura
Avenue anticline, the complexly faulted, doubly plung-
ing eastern culmination of the Rincon trend. Similarly,
discovery of the Rincon field in 1927 and of the San
Miguelito field in 1931 resulted from drilling of
prospects selected on the basis of surface geologic
mapping of the deeply eroded, though geologically
young, strata astride the Rincon anticlinal axis.

Geologic mapping of selected parts of the Santa
Barbara Channel floor was conducted by various
‘companies, including the Union Oil Co. of California,
for years prior to leasing of Federal offshore lands
for oil and gas exploration. Lithologic and paleon-
tologic analyses of spot samples of sea-floor outcrops
and some diver observations of strata] attitudes were
used to compile geologic maps of variable quality.
The offshore Rincon trend was one such area mapped,
and it was recognized that the area now known as the
Dos Cuadras field is one of the structurally highest
culminations along the trend. Although sea-floor
geologic information is a helpful supplement to the
well data and the reflection seismic data now available
for 008 lease P—0241 and P-0240, it provides only
sufficient detail for supporting or confirmatory use
in present structural interpretations.

The current interpretation of the shallow structure
of the major part of the Dos Cuadras field is shown
on plate 3 by structure contours drawn principally on
the basis of electric log correlations that are supple-
mented locally by dip-meter measurements and ex-
trapolated down the flanks using reflection seismic
interpretations. The stratigraphic horizon used to
contour the structure is the top of the sandstone unit
that forms the shallowest major commercial oil zone
in the Dos Cuadras field. This horizon, the C electric
log marker (fig. 6), lies within a conformable sequence
of elastic marine strata of early Pliocene age and
about 900 feet stratigraphically below the faunally
determined boundary between rocks of the upper
Pliocene “Pico Formation” and the lower Pliocene
sequence called “Repetto Formation” (pl. 3). At the
C horizon, the anticline is elongate, faulted, and
doubly plunging, with nearly symmetrical flanks

GEOLOGIC CHARACTERISTICS OF THE DOS CUADRAS OFFSHORE OIL FIELD 31

 

that dip as much as 33° north and south from the
nearly east-trending fold axis.

Just north of the area contoured on plate 3, the C
horizon is presumably broken by a south-dipping
Mud Ilne thrust fault of area-wide extent that has been pene-

§ gamma trated in the majority of wells drilled in the Dos
- 8—15 ' —

E-Iog marker
Approximate
subsea depth
(feet)

Age

 

 

Cuadras field and down the plunge to the east. This
500 thrust fault divides the rocks into an upper and lower
' fault block (pl. 3). Just south of the area contoured,
the south dip of the C horizon increases progressively.
This dip indicates a strongly asymmetrical, locally
overturned, and probably faulted south limb.

Too few wells have been drilled through the thrust
fault to clearly define structural detail in the lower
fault block. Enough is known to state confidently
that the major structure in the lower fault block is
anticlinal (pl. 3). The fold axis immediately below
the fault is displaced about 500 feet from the axis
above the fault at the C horizon. Moreover, dip-
meter data in the directionally drilled deep redrill of
the 008 P—0241 No. 1 indicate that the axial surface
of the anticline dips north at greater depth. Other
structural complications in the lower fault block will
almost certainly emerge as more information is
acquired from drilling. These are suggested by the
mismatching oil-water contacts below the F and above
the H horizons between wells of Platform A and the
No. 2 exploratory hole shown on the longitudinal
structure section (pl. 3).

Two important faults that break the C horizon in
the block above the thrust are well defined and dis-
place the contours on the structure contour map (pl.
3). Toward the west end of the field is an east-north-
east-trending oblique slip fault that dips steeply
northwest and has reverse displacements over most of
its length. This fault presumably cuts the thrust
fault, but may be a genetically related tear fault. Like
many other faults along the Rincon trend, this fault
is a permeability barrier to unimpeded movement of
fluid hydrocarbons, as shown by the different dis-
tributions of oil and water in the permeable strata of
the two structural blocks that it separates (pl. 3). A
south-dipping normal fault located about 500 feet
south of the anticlinal axis extends parallel to the axis
at the C horizon for much of the length of the field.
This fault has a throw ranging from 30 to 60 feet
in the western part and 120 feet at the south-
eastern end. A difference of 160 feet in the level of
the oil-water contacts in the C sand reservoirs on
opposite sides of this fault indicates that it also is a
FIGURE 6.—-Composite type log of the Dos Cuadras oil field. barrier to movement of Oil. It is not known With
certainty if the east— to southeast-trending normal
fault stops at the deeper thrust fault, cuts it, or is cut
by it. Also uncertain is the relationship between the

 

IIM IIIII ”Inn“ IAIIIM {Ii
| I I | |§I I I I

N
O
O
0

Lower Pliocene (”Repetto Formation")
I
I
I
I 1
”Will“ I "IIIIII‘IAI "WWII
N
|§I I I | I

 

I I I

r—X

I J

ll 1
W
I§II|II§IIIII§

 

 

Upper
Miocene

 

 

 

 

 

 

365-228 0 - 69 - 7

32 GEOLOGY, PETROLEUM DEVELOPMENT, SEISMICITY, SANTA BARBARA CHANNEL, CALIF.

normal fault and the east-northeast-trending tear
fault.

Near the eastern limits of the Dos Cuadras field,
understanding of the structure of the east-plunging
Rincon trend beneath OCS P-0240 is very incomplete.
Not only are fewer data available here, but also less
time and attention have been directed by the writer
to interpretation of the structural data. The sea-
floor geology and the data from exploratory wells
indicate that the general structure is a steeply plung-
ing anticlinal fold (pl. 3). The generalized seismic
interpretation is consistent with this view. The ir-
regular distribution of hydrocarbons suggests the
presence of permeability barriers produced by faults
across the fold axis; similar conditions exist farther
east along the Rincon trend in the productive strata
beneath OCS P—0166.

The deformation responsible for the structure along
the Rincon trend cannot be precisely dated at the
Dos Cuadras field; the strongly folded and extensively
faulted conformable sequence ranges in age from late
Miocene through late Pliocene and is unconformably
overlain by a nearly flat lying and slightly faulted
thin veneer of stiff fossiliferous silt and sand. The
fossil shells have yielded radiocarbon dates ranging
from 8,750:300 to 13,920i350 years.

Onshore, on the south limb of the Ventura Avenue
anticline, early Pleistocene strata dip steeply and are
conformable with folded Pliocene beds. This dip
indicates a mid-Pleistocene date for the greatest part
of the deformation. Evidence of continuing deforma-
tion and uplift along structural elements that are
associated with the Ventura Avenue anticline is
described by Putnam (1942).

LITHOLOGY AND STRATIGRAPHY

Sandstone, siltstone, claystone, and shale are the
predominant rock types (in order of decreasing abun-
dance) comprising the lower Pliocene and uppermost
Miocene strata penetrated by drilling in the Dos
Cuadras field. A limited number of rubber-sleeve and
conventional cores and some sidewall cores permit
direct observation of some of the rocks and lithologic
description by conventional petrographic means.
However, for most of the section, less direct methods
of determining lithology have been used. Logs of
spontaneous potential and electrical resistivity (IES
logs), gamma radiation, and gamma-gamma radiation
(“formation density”) were recorded in most of the
wells drilled. These logs have been interpreted in
the light of core samples recovered from these wells
and with knowledge and experience gained in equiv-
alent or similar rocks elsewhere. The results have

been used for continuous, accurate, and fairly detailed
lithologic determinations in nearly all the wells
drilled.

The stratal sequence beneath Platform A on OCS
P-0241 is best discussed by reference to the type log,
figure 6. Three parts of the logs of two wells (Nos.
1 and 5), drilled 500—700 feet east of Platform A, have
been joined to form one idealized log showing standard
borehole electrical (or induction-gamma ray) properties
of the complete 4,200-foot-thick stratigraphic column
penetrated between 200 feet and about 4,850 feet
below sea level. This composite log is uncomplicated
by the repetitions or deletions of some strata in actual
logs of most of the wells. The type log shows three
major lithologic divisions in the section. The upper-
most 287 feet (from the top down to the C horizon)
displays electrical properties like those of a section in
which siltstone and claystone or shale predominate
and sandstone lenses and beds are subordinate. Be-
neath this cap of fine-grained and thinly bedded
strata is a 2,250-foot section (between the C and the
H—2 horizons) in which the predominant lithology is
sandstone interbedded with subordinate siltstone,
mudstone, or shale. Below the base of the predomi-
nantly sandstone section (below the H-2 horizon and
about 3,400 feet drilled depth in the No. 1 hole), the
section is composed almost entirely of siltstone, clay-
stone, and shale, interrupted by a few scattered thin
beds of sandstone. The rocks of these three major
subdivisions are considered in some detail below.

At the time of the drilling of well A—21 the upper-
most 200 feet of strata beneath Platform A had been
cored only in small part and had been subjected to
borehole geophysical logging in only one well on OCS
P-0241. Knowledge of these strata was restricted to
the following: log measurements in stratigraphically
equivalent beds in wells about half a mile east, south-
east, and north of Platform A; percussion core samples
taken at 5- to 15-foot intervals in three shallow
(greatest depth, 150 feet) holes drilled at and near
the Platform A site for engineering investigations
prior to platform construction; and information
gleaned from responses to problems encountered
during construction of the platform supports and
during drilling of the shallowest parts of the first
four exploitation wells. Taken together, these diverse
and fragmentary sources indicate the following char-
acteristics for the strata between the sea floor and
the C horizon at the location of the platform. Siltstone
and claystone predominate in the section and are
interbedded with subordinate lenses and thin (as much
as a few feet) beds of fine-grained sandstone, in part
calcareous and weakly cemented. Oil saturation was

GEOLOGIC CHARACTERISTICS OF THE DOS CUADRAS OFFSHORE OIL FIELD 33

reported by Dames and Moore, Inc. (under contract
to the operator) in samples of some of the sandstones
(the shallowest noted at a depth of 30 feet below the
mudline), and volatile hydrocarbon odors were detected
in some of the fine-grained rocks. These beds are
exceptionally tough or resistant (under penetrative
compression) when compared with younger strata at
other platform sites along the Rincon trend. This
conclusion was reached mainly from empirical rela-
tionships between the number of standard blows
required to drive a rock-coring device a certain incre-
ment of depth in foundation-site investigation holes.
It was further corroborated by data on the depths of
penetration into the ocean floor at different locations
along the trend of the jack-up legs of the floating
drilling vessel used in preliminary exploration, and
by data obtained in driving the pilings for the founda-
tion of the platform. Oil and gas were found in these
rocks at the time the pilings were being driven, and
gas was bubbling from the ocean while the platform
was being emplaced.

In each of the four development wells drilled to
total depth from Platform A prior to the blowout, lost
circulation of drilling fluid caused difficulties while
penetrating the rocks below the shoe of the drive pipe
and above the point selected for cementing the first
conductor casing string. This point was between 50
and 100 feet (drilled) above the C horizon and was
from 155 to 242 feet vertically below the sea floor.
This repeated loss of circulation indicated qualitatively
that some part or parts of the capping strata above
the shallowest major reservoir of the Dos Cuadras
field were permeable to drilling fluid and cement (or
had a very low hydraulic fracturing threshold) prior
to the blowout, in spite of being mainly fine-grained
argillaceous rock exceptionally resistant to driving
penetration.

Subsequent to the blowout, and particularly since
May 1969, much detailed information about the rocks
above the C horizon was acquired. Part of the inter-
val was logged in the relief well (008 P—0241 No. 4).
Evaluation holes on Platform A (well A—24) and
Platform B (well B-18) were extensively cored and
logged through the interval. This information was
supplemented by the drilling or coring, logging, and
cementing operations conducted in three of the six
shallow grout holes about 600 feet east of Platform A.
Eighty-nine percent was recovered of the 246 feet of
rubber-sleeve cores attempted in well A—24 between
23 and 269 feet below the sea floor (the latter depth
is 18 feet above the C horizon). Of the recovered
core, predominantly fine-grained light-colored slightly
calcareous silty oil sand constitutes nearly 7 percent;
whereas claystone, some of it also oil-bearing in pores

and cracks, constitutes 88 percent. Some calcareous
claystone and some of the more indurated sandstone
are brittle and hard enough to fracture, but most of
the core is so porous and soft that it can be crumbled
or mashed in the fingers. Lithologies in the A—24
cores correlate well with lithologic interpretations of
the induction-gamma ray log of that hole, thus pro-
viding corroboration of the earlier lithologic interpre-
tations based on the fragmentary data available at
the time of the blowout.

Beginning a few feet above the C horizon, there is
a rapid downward transition from the sequence of
capping rocks, in which claystones without hydro-
carbon saturation predominate, into a sequence of
predominantly permeable sandy rocks in which most
of the pore space is saturated by oil containing some
dissolved gas. Such strata predominate from the C
horizon to the base of the sandstone unit about 40 feet
above the H—2 marker (fig. 6). Beneath Platform A
nearly all the beds that are permeable enough to
permit entry of hydrocarbons under moderate pressure
differentials are saturated with petroleum. Enough
logging and conventional and sidewall coring had been
done before the blowout to permit a fairly satisfactory
understanding of the lithology of this part of the
section. Sandstone beds range in grain size from very
fine grained and silty to coarse grained and pebbly.
Almost all are quartz rich and fairly well sorted.
Most are composed of grains that are well rounded to
subrounded. Beds are well defined and range in
thickness from laminations to massive beds several
feet thick. Most of the sandstone is firm but friable
and uncemented. Cemented beds are calcareous and
tend to occur close to contacts of oil and water, except
for some thin hard gray “shells” that separate un-
cemented rich oil sand from siltstone or mudstone
layers of relatively low permeability. Interbedded
fine-grained argillaceous and silty strata are sub-
ordinate, thin, and numerous but sporadic. More than
60 percent of the interval is estimated to be sand-
stone (as judged by the S.P. curve), and fewer than
20 discrete siltstone or “shale” interbeds of major
significance (thickness greater than 10 feet) occur.
The two thickest are above the G marker (55 feet) and
at the F marker (45 feet).

From 40 feet above the H—2 marker to below the
M marker (the approximate base of the “Repetto For-
mation”) the strata beneath Platform A are almost
entirely siltstone and shale. Thin interbeds of per-
meable fine-grained sandstone as much as 15 feet
thick are oil saturated in appropriate structural
positions but are so few and so widely separated that
they are of minor commercial importance.

34 GEOLOGY, PETROLEUM DEVELOPMENT, SEISMICITY, SANTA BARBARA CHANNEL, CALIF.

Assignment of the strata portrayed on the type log
for 008 P—0241 to the lower Pliocene and uppermost
Miocene series is based upon paleontological analyses
of microfossils, primarily Foraminifera, from drill
cuttings and cores. These analyses have been con-
ducted entirely by the paleontological staffs of the
Union Oil Co. of California and its partners, and their
determinations and conclusions are accepted. The
interpretations are in close agreement With deter-
minations based on electric-log correlations with wells
to the east in which faunal interpretations by other
workers are available.

Within the Dos Cuadras field, stratigraphic varia-
tions are minor but significant. Most of the thicker
lithologic units may be readily traced by electric-log
correlations throughout the field and for considerable
distances along the trend and to the north and south.
In general, the “Repetto Formation” thins from east
to west, and the relative abundance of sandstone
decreases as individual sandstone units thin and grade
into siltstone and shale. These relationships are
depicted on the longitudinal section (pl. 3). The extent
to which such stratigraphic changes affect the distri-
bution of hydrocarbons in the Dos Cuadras field is
difficult to evaluate now, but it is likely that some of
the reservoirs will be far more productive in the
eastern than in the western end of the field because
some of the sandstone units there are thicker, more
permeable, and probably coarser.

PETROPHYSICAL CHARACTERISTICS

The ease and rapidity with which a fluid, including
hydrocarbon fluids such as oil (or gas), moves through
a sequence of granular rocks depends upon the per-
centage of the total rock volume that is intergranular
pore space (porosity) and upon the number and
absolute size of the pore openings and the capillary
connections between them. Other factors, such as
the number of fluid phases in the pores, the viscosity
of the mobile phase or phases, and the driving pressure
differentials are influential, but total porosity and
average capillary size (or, conversely, grain size)
fundamentally control the permeability. In general,
fine-grained rocks, especially those composed chiefly
of platy grains such as clay crystals or mica flakes,
have smaller pores and pore connections than coarser
grained rocks composed of more nearly equidimensional
grains. In addition, moderately to well compacted
fine-grained rocks tend to be less porous than inter-
bedded coarser grained rocks. Thus, most sandstone
is both more porous and more permeable than inter-
bedded shale, claystone, mudstone, or siltstone.

Knowledge of the distribution of porosity and
permeability in the rocks of the Dos Cuadras field

stems from laboratory measurements of core samples
and from interpretation of well logs, particularly
gamma-gamma (density) logs. A plot of porosity in per-
centage versus depth for all samples of punch cores,
rubber-sleeve cores, and conventional cores that were
available from the vicinity of Platform A immediately
following the blowout of well A-21 is shown in figure
7. Measurements of 238 samples are plotted, 199 of
them from sandstone beds below the C marker, the
remaining 39 being mostly from claystone beds above
the B—15 marker and Within 150 feet of the sea floor.
Nearly all the plotted porosities exceed 15 percent,
and most of them exceed 20 percent. All but two of
the samples within 1,500 feet of the sea floor exceed
25 percent porosity, and the samples within 150 feet
of the sea floor cluster around median values that
range from 34 to nearly 40 percent. Interpretations
of gamma-gamma (Schlumberger FDC) logs from the
No. 1 exploratory hole and the A—20 well are in sub-
stantial agreement with core analyses in the parts of

POROSITY, IN PERCENT

0 10 20 30 40 50 60 70 80
l l I l l

 

KB=0

1
Sea icvci

 

No. of
samples

Sea lloor

A 21 casmg

 

0
X X X . Punch 39
cores
239M below sea floor v. 514 ltdrilled — 500
o I 0' o o depth 7
. .. 3
500 ..
v9.4" 18
g — 1000
a a...“ g 11
E
Norecovery : x
1000 — g;

L: ° 602.33% “‘ 29
E i:
E u'r-I'.‘ 13 — 1500 a:
=6 E
o .
o a
.1 m, 5
El 1500 —' ' ' 20 E
m o
g I
O i—
d a
m — 2000 c.

I
E
3 °' “A" 12

2000 EXPLANATION
X

Foundation core holes - 2500

A1, A2, A3; Dames 23

and Moore, 1968 4

o .W'“

2500 — .
Well A—21, Union Oil Co.
lease 005 P0241;
Core Labs. Inc.,
1/30/69
. 0
Well A-20, Union Oil Co. 41
lease 008 P0241;
Core Labs. Inc.,
12/11/68and 1/11/69

- 3000

Conventional cores

6
gm“; 7
3000 — 1’

Ranae

.e— *° 20

 

 

 

FIGURE 7.—Porosity versus depth for analyzed core samples,
Dos Cuadras oil field.

GEOLOGIC CHARACTERISTICS OF THE DOS CUADRAS OFFSHORE OIL FIELD 35

the wells where hole caliper data indicate a hole that
is not seriously washed out. From the core data and
the logs available prior to or at the time of the blow-
out it can be concluded that extremely high porosities
characterize both the sandstone beds and the fine-
grained rocks within 1,500 feet of the sea floor be-
neath the vicinity of Platform A. However, neither
cores (and core measurements) nor gamma-gamma
logs provide any measure of widely spaced fracture
porosity if present. Cores and gamma—gamma logs
yield measurements that are least representative of
the most porous materials.

Extensive coring and logging since the blowout have
provided (mainly in June 1969) a large additional
amount of data of high quality to corroborate the
conclusions reached on earlier scanty evidence. For
example, the average porosity measured by Core Labs,
Inc., from 20 samples of'sandstone and claystone select-
ed from nearly continuous rubber-sleeve cores between
40 and 284 feet below the sea floor in well A-24 is 38.7
percent. This value is slightly higher than, but in
general agreement with, the results (fig. 7) obtained
in 1968 by Dames and Moore on punch cores taken
for engineering site investigations. This slightly
higher value may reflect the relatively greater
abundance of measurements on sandstone samples
and particularly on interbedded oil sands.

The relationship between porosity and permeability
of sandstone from the shallower part of the section
in the vicinity of Platform A was also established from
core samples available at the time of the blowout.
Figure 8 is a plot of porosity versus permeability for
39 samples of sandstone selected from rubber-sleeve
cores from well A—21 between about 300 and 800 feet
below the sea floor. Permeabilities of these soft
highly porous sandstone samples range from approxi-
mately 50 millidarcys to nearly 5 darcys, and there
seems to be a slight tendency for permeability to in—
crease as the porosity increases. Additional measure-

PERMEABI LITY, IN DARCYS

0 l 2 3 4 5
0 I l 1 l

 

20— «

30—. . ' _

:.:"...£-,-. . .
0':

.
4o- ’

POROSITY, IN PERCENT

50 l | | |

 

 

 

FIGURE 8.——Permeability versus porosity of analyzed sandstone
cores, Dos Cuadras oil field.

ments from newly available samples from well A-24
between 40 and 284 feet below the sea floor average
773 millidarcys at an average porosity of 38.7 percent
and include some claystone and some very fine grained
silty sandstone, together with oil sands. The lowest
permeability measured is 4.1 millidarcys at 33.2 per-
cent porosity and the highest is more than 8 darcys at
43.4 percent porosity. These additional measure-
ments indicate that the capping rocks above the C
marker at Platform A are not unlike the silty oil
sands at greater depths in their range of porosities
and permeabilities. Lower and higher permeabilities
occur in the cap samples. In addition, the average
permeability of capping rock probably is much lower
because of the greater abundance there of fine—
grained claystone. However, if widely spaced frac-
tures are present, core samples provide no means of
measuring overall rock permeability. The fact that
the capping layer at the Dos Cuadras field confines
and preserves large reserves of mobile hydrocarbons
in the shallowest major reservoirs, in spite of the very
high porosities and low to extremely high perme-
abilities measured on core samples, attests to the rela-
tively low effective permeabilities of the capping
strata as a whole. If an important fracture system
had existed in the capping layer prior to the blowout,
more complete dissipation of the mobile hydrocarbons
in the shallower reservoirs should have resulted.
Nonetheless, it is known that natural seepage was
occurring on this tract prior to drilling.

The previously mentioned problems of loss of cir-
culation of drilling fluid while drilling in rocks of the
capping layer prior to the blowout attest to high per-
meabilities of the capping beds or their low resistance
to hydraulic fracturing. However, quantitative
evaluation of these matters is not possible without
detailed records of mud pressures and thorough un-
derstanding of the possibly damaging effects on the
surficial‘ rocks of driving the platform foundation
pilings and (or) the drive casings of the wells (both
pilings and casing were cemented after driving)._

Another qualitative measure of the high perme-
ability of the capping formation was obtained after
the blowout when cement was emplaced by gravitative
flow into six shallow grouting holes drilled into the
sea floor about 600 to 900 feet east of Platform A and
into two others west of the platform. It was in these
areas that large parts of the uncontrolled sea-floor
seepage of oil occurred. Each of the holes was cased
from the sea floor to about 150 feet and then drilled
to a total depth of about 250 feet below the mud line.
In successive gravity grouting operations, a total of
24,855 sacks of cement were emplaced through the
uncased parts of these holes. Much of this massive

36 GEOLOGY, PETROLEUM DEVELOPMENT,SEISMICITY, SANTA BARBARA CHANNEL, CALIF.

volume may have gone into open fractures, fissures,
or partings. An attempt to identify grossly mega-
scopic fractures in the first of these shallow holes
(OCS P-0241 N o. 5) by use of a novel Borehole Tele-
viewer yielded completely negative results and there
is no other direct evidence of fracture channels. How
much may have entered the more permeable beds
Within the mid-part of the section (the sandstone units
close to the B—15 marker) is unknown.

This section should be concluded with a summary
comparison of petrophysical characteristics of the
capping rocks at Platform A and at Platform B about
2,600 feet to the west. The C marker in well A—24
(directly beneath Platform A) is at a subsea elevation
of minus 475 feet. The same stratigraphic horizon
in well B-18 (directly beneath Platform B) is at a
subsea elevation of minus 556 feet, some 81 feet lower.
Rocks cored above the C marker at Platform B (both
those cored for engineering site investigations prior
to the blowout of A and those cored for control and
information following the blowout at A) contain no
fluid hydrocarbons identifiable by sight, smell, or
fluorescence. Hydrocarbon traces were detected in
a few samples during laboratory core analysis. The
average porosity and permeability of the 17 samples
of rubber-sleeve cores from the B—18 well selected for
analysis by Core Labs, Inc., are 35.4 percent and 882
millidarcys (in a range from 16 to 2,900) versus the 38.7
percent and 773—millidarcy averages measured
from the samples from well A—24. No surface seepage
oil has been detected in the vicinity of Platform B.

FLUID PROPERTIES

Petroleum and natural gas are complex fluid hydro-
carbons of Widely ranging composition and physical
properties. They are uncommon, mobile, and highly
fugacious constituents of certain especially favored
parts of the discontinuous veneer of sedimentary
rocks that rests on essentially non-oil-bearing rocks
in the deeper parts of the earth’s crust. Petroleum
has a tendency to escape from underground natural
reservoirs and seep to the surface. It is well known
that seepages served as guides to early prospectors
and still form the basis for some petroleum explora-
tion. This escaping tendency is also used in the con-
trolled production of crude oil and accounts in large
part for the expulsion of oil from reservoir rocks
through flowing wells. Unfortunately the tendency
also accounts for the uncontrolled flow of oil from
“gushers,” “wild wells,” and blowouts and has neces-
sitated the use of numerous precautionary procedures
and special mechanical devices.

The motive force behind the tendency for oil and
gas to escape from the pore spaces of rocks and move
to the surface is the force of gravity. Crude oil is

generally lighter than the water that saturates the
pores of most underground rocks, and it tends to be
buoyant and to float to the highest possible level.
Natural gas dissolved in the oil increases its buoyancy
and decreases its viscosity, thus increasing its mobility.
A solution of crude oil and “gases” is a relatively
compressible fluid. It has a strong tendency to expand
and to become less dense and more buoyant as the
pressure confining it in an underground reservoir
rock is reduced. Additionally, as a natural solution
of “gases” in crude oil is decompressed, it boils at its
saturation pressure. As the solution is decompressed
below this saturation pressure, gaseous hydrocarbons
of extremely low density (compared with pore water)
may be released in large volumes. The explosive
violence of many well blowouts is attributable to un-
controlled expansion of solution gas resulting from
sudden accidental lowering of the pressure in a well
bore.

In order to understand the manner in which fluid
hydrocarbons tend to flow (or not flow) through
porous and permeable rocks, it is necessary to know
the fluid compositions (density and dissolved gas con-
tent), compressibilities, saturation pressures, natural
fluid pressures, and pressure gradients. To understand
the possible damaging effects on rocks by the uncon-
trolled flow of large volumes of fluids from regions
of higher pressure to shallow regions of lower pres-
sure, it is necessary to know the natural lithostatic
pressure gradients and the hydraulic fracturing
gradients of the rocks. These topics are considered
below.

Data available regarding oil gravities and producing
gas-oil ratios in the “Repetto Formation” of the Dos
Cuadras field at the time well A—21 blew out include
the following: (1) fluids recovered during one drill-
stem test and one clean-up production test of per-
forated intervals in the deeper zone exploitation well
A—25, (2) the gravity of oil produced during a clean-
up test in the shallow- to intermediate-depth exploita-
tion well A—41, and (3) complete analytical data, in-
cluding saturation pressures and oil and gas composi-
tions, for recombined separator samples obtained
during two tests at an intermediate depth and a shallow
depth in exploratory hole No. 2. Gravities of oil ex-
tractable from conventional cores recovered during
drilling of well A-21 were potentially available. These
compositional data are shown in figure 9. They indi-
cate that the densities of the mobile fluid hydrocar-
bons decrease systematically and markedly With in-
creasing depth from API gravity values of about 21°
above minus 1,000 feet to 33° and possibly greater in
the range from minus 3,000 to minus 4,000 feet.
Also plotted in figure 9 are equivalent data measured

GEOLOGIC CHARACTERISTICS OF THE DOS CUADRAS OFFSHORE OIL FIELD

A. P. I. GRAVITY, IN DEGREES

 

 

 

 

 

18 20 22 24 26 28 30 32 34 36
0 I I | | I | I
Sea floor
I:
N o
E = O
z :
d a O I?
E 1000 — J: 0 a _
<
Q N O
3 s
S 5
Lu a. In
°° s ‘7
E 2000 — E “ g
E fi' 3
:1: < O E
D.
E s g
Q)
E < N «.3
E 3000 _ EXPLANATION . m _
5 O < '5'. O
A-21 conventional <
core exlractions Z

 

 

 

‘000 I I I I I I I I l I I I I I I I I
0.94 0.93 0.92 0.91 0.90 0.89 0.88 0.87 0,36 0.85
SPECIFIC GRAVITY AT 60 DEGREES FAHRENHEIT

 

FIGURE 9.—Oil gravity versus depth, Dos Cuadras oil field.

on samples of fluid obtained from selected exploita-
tion wells that had achieved settled rates of production
following the blowout. These latter data are consistent
with the 'pre-blowout data and indicate that the tend-
ency for the oil to be more dense in reservoirs nearer
the surface extends upward into the so-called “Red
zone” (fig. 10), the name applied to the thin producible
sands within the capping layer close to the B—15

marker. _ -. .
Analogies between the crude-oil gravities of the

Dos Cuadras field and those of other fields in Cali-
fornia lead to the conclusion that the denser crudes
in the shallower reservoirs at Dos Cuadras contain
limited quantities of potentially gaseous constituents
in solution and probably are undersaturated. By the
same reasoning, the less dense crudes from the deeper
reservoirs in the “Repetto Formation” might be ex-
pected to contain appreciable quantities of dissolved
low-molecular-weight fractions and to be saturated
or nearly saturated with gas. This expectation is
supported by the limited data available at the time
of completion of well A—20, and by the somewhat
more extensive data made available to the Presidential
Advisory Panel in May 1969 by the operator (lessee).
Analyses of the recombined separator samples from
tests of exploratory hole No. 2 give the following data:
(1) Lower zone sample (minus 2,677 to minus 2,028 feet)
at average reservoir pressure and temperature of
1,095 psig (pounds per square inch gage) and 105° F
at minus 2,350 feet had a field-tested gravity of 27.1°

37

and a producing GOR (gas-oil ratio) of 165 cubic feet
per barrel. Laboratory determinations indicate a
saturation pressure of 983 psig, a reservoir fluid GOR
of 183 and FVF (formation volume factor) of 1,090
(barrels of fluid in the reservoir per barrel of stock
tank oil), and a gas specific gravity of 0.820 (relative
to air). (2) Upper zone sample (minus 698 to minus
1,178 feet) at an average reservoir pressure and tem-
perature of 470 psig and 85°F at minus 938 feet had
a field-tested gravity of 23.4° and producing GOR of
50 cubic feet per barrel. Laboratory analyses show
a saturation pressure of 351 psig, a reservoir GOR of
52, and a FVF of 1.031.

During a flowing drill-stem test on January 9—10,
1969, well A-25 produced from the interval minus 3,962
to minus 3,300 feet (interval below the base of the
predominantly sandstone section above the I marker)
328° oil at a producing GOR of 595 cubic feet per
barrel. From mud weights required to control the
well during drilling of this interval, a formation fluid
pressure of 2,140 psi is indicated for the base of the
tested interval. Assuming a temperature of 138.6°F
(by extrapolation), and a gas gravity of 0.85, calcu-
lations using the table of Standing (1947) indicate that
the formation fluid is saturated with respect to gas
with a reservoir GOR of 510 and FVF of 1.252.

In summary, it is evident from the data existing at
the end of January 1969 that the Dos Cuadras field
is a many-zoned composite oil accumulation in which

—-—> North

WELL WELL

WELL /
/

 

Sea floor

Red zone { Red zone /

 

    
  
   

 

 

 

   

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

U C E L
I: Brown zone :0 av
E E Red zone I: E
R 4922 /—_ R
(up) upge 99.97. D(“Q”)
B E B
L 402 { L
u or zone
0 on F 0
C C
K ‘ K
H 4 G
402 402
I lower zone lower zone
3 / H
E Ihrustfault
50/ l
Lu
/ 0 500 1000 FEET

l__l_l
APPROXIMATE VERTICAL SCALE
Note: F-G markers are included in 402 upper zone above thrust fault
and in 402 lower zone below thrust fault

FIGURE 10.—Schematic relations between producing “zones,”
stratigraphic subdivisions, and structural divisions in the Dos
Cuadras oil field.

38 GEOLOGY, PETROLEUM DEVELOPMENT, SEISMICITY, SANTA BARBARA CHANNEL, CALIF.

the mobile (producible) hydrocarbons decrease in den-
sity (increase in API gravity) with increasing depths,
from 21° or less at depths less than minus 1,000 feet
to 33° or more at depths greater than minus 3,500 feet.
Also evident is the fact that the reservoir fluids range
from strongly undersaturated (with respect to gas)
at shallow depths to saturated and at bubble-point
pressures for the deepest interval tested (minus 3,962
to 3,300 feet).

California oil fields generally are characterized by
so—called “normal” fluid pressures, that is, fluid pres-
sures equal to the hydrostatic pressure exerted by a
column of nearly fresh water extending from the sub-
surface point of measurement to the surface (or to
the natural ground- water level in the aquifer). In con-
trast to this are the fluid pressures in the deeper zones
of the onshore fields along the Rincon trend, particu-
larly the Ventura field, where fluid pressures range
upward from “hydrostatic” to values approaching the
“lithostatic” pressure, or pressure due to the weight
of a column of rock extending from the subsurface
point of measurement to the surface vertically above
that point. The “lithostatic” pressure gradient is
commonly assumed to be 1 psi per foot of depth, and
most calculated gradients depart very little from this
assumption. Figure 11 summarizes the published
pressure data from onshore Rincon trend fields (Watts,
1948; Glenn, 1950; Duggan, 1964) and from the Dos
Cuadras field. Pressures in onshore wells between

 

0 I l
I EXPLANATION

\
005 P0166, gradient of
0.454 psi per fool
2000 G)

008 P0241, well 1, mud
weights

I

Union A-Zl,
total depth *
008 P0241, well A-25. mud _

4000 . .
weights and production test

6,3 _)

. , 0%,, OCSP-0241,wellA-20,

0 San VMIngelllO ’9 pressure buildup 4/3/69
First Grubb “.0

5000 (Glenn, 1950) 39x,

Z“
91
9;
o}.
/
f’

DEPTH BELOW SEA LEVEL, IN FEET

  
  

Ventura ‘
“D-7" top

, (Duggan,
1964)
a a . . .5,
10,000 i '
0

2000 4000 6000 8000
STATIC PRESSURE, IN POUNDS PER SQUARE INCH

8000

l
(3

x

:5,”

 

 

 

10,000

FIGURE 11.——Fluid pressures and fluid-pressure gradients versus
depth for the Rincon trend including the Dos Cuadras oil
field.

depths of minus 4,000 and about minus 9,000 feet
range above “normal” along gradients of 0.6-0.9 psi
per foot of depth. These well-known abnormalities
raise questions concerning fluid pressure gradients at
the Dos Cuadras field, since it is located along the
same structural trend.

Data regarding fluid pressures in reservoirs of the
Dos Cuadras field come from measurements made
during drill-stem tests, production tests, and pressure-
buildup tests, and from determinations based on the
weights of drilling fluids required to maintain pres-
sure control in drilling wells. Prior to the leasing of
OCS P—0241, a gradient of 0.454 psi per foot was well
established on lease OCS P—0166 in the “Repetto For-
mation” reservoirs (fig. 11) from many determinations.
Before Platform A was constructed, exploratory hole
No. 1 had demonstrated that 71 and 72 pounds per
cubic foot drilling mud (0.493 psi per foot and 0.500
psi per foot gradients, respectively) could be safely
used in drilling near the Platform A site to depths of
minus 3,356 feet (1,680 psi). At greater depths
“kicking” of the mud column necessitated higher mud
weights (at minus 3,821 feet, 80-pound mud was re-
quired, indicating a fluid pressure of 2,120 psi on a
gradient of 0.555 psi per foot). Trial production tests in
exploratory well No. 2 about 1 mile west of the Plat-
form A site yielded pressure measurements consistent
with a pressure gradient of 0.44 psi per foot down to
minus 2,677 feet. Before the, blowout of well A—21,
exploitation well A—25 was drilled to a total vertical
depth of 4,051 (minus 3,963 feet); gas “kicking” oc-
curred at minus 3,448 feet (after drilling below 9%—inch
casing cemented at minus 3,318 feet) requiring 73
pounds per cubic foot mud (0.505 psi per foot gradient).
At total drilled depth of 4,051 feet the hole began to
“unload” 77-pound mud, but use of 78-pound mud led
to loss of circulation, indicating a fluid pressure of
2,146 psi on a gradient of about 0.538 psi per foot.
These data are shown in figure 11, and have been cor-
roborated by more detailed information gathered
since the blowout. Evidently, the “Repetto” reservoir
rocks of the Dos Cuadras field, down to the base of the
dominantly sandy section, contain fluids that are at
or only slightly above “normal” hydrostatic pressures
on a gradient of 0.44 psi per foot. Below the base of
the dominantly sandy section, and especially below the
I marker at about minus 3,440 feet, the minor thin
sandstone beds are charged with fluids at notably
greater pressures. These same sandstones are also
the sources of the gas-saturated oils of lower density
(higher API gravity).

Taken together, the compositions and pressures of
the fluids in the reservoir rocks of the Dos Cuadras
field tell much about the nature of the reservoirs and

GEOLOGIC CHARACTERISTICS OF THE DOS CUADRAS OFFSHORE OIL FIELD

of the accumulation. The gradual decrease in oil
density and increase in solution gas content with in-
creasing sample depth would be unstable and impos-
sible or unlikely in one or several thick reservoirs,
each containing oil columns having vertical dimensions
totaling several thousands of feet (Sage and Lacey,
1939; Roof, 1959). In addition, the adherence of the
fluid pressures to near the gradient of low-salinity
water throughout most of this thick oil-bearing section
is also indicative of many reservoirs in the Dos Cuadras
field. Lastly, multiple oil-water contacts have been
recorded by electrical logging of the wells drilled (pl.
3). Each of these reservoirs has a fairly short vertical
oil column, and they are stacked one upon another in
a sequence that is continuous (or nearly so) in the
structurally highest locations, but separated in flank
locations by water-saturated sands. The fluids in
such a large composite accumulation must have been
in a delicate, metastable equilibrium, and any drastic
uncontrolled disturbance of this balance could result
in far-reaching consequences. The blowout of well
A-21 triggered such a disturbance.

In modern, soundly engineered deep drilling, “Well
planning . . . includes accurate prediction of formation
pressures and fracture gradients in the formations to
be drilled” (Records, 1968, p. 66). This statement is
equally applicable to shallow drilling in areas such as
the offshore Rincon trend where thick permeable
sections charged in some places with oil containing
solution gas may be present at shallow depths. Fluid
pressures in the rocks along the Rincon trend have
been examined; the question of lithostatic pressures
and hydraulic fracturing pressure gradients in relation
to casing practice must also be considered.

The range of densities of fluid-saturated sedimen-
tary rocks is such that the static pressure exerted
at the base of a rock column departs very little from
a gradient of 1 psi per foot of depth. To verify this
assumption, the porosity data summarized in figure 7
were used, together with those data considered reli-
able from the gamma-gamma (formation density) log
of the A—20 well, to construct a profile of rock density
versus depth for the Dos Cuadras field. This profile
was used to calculate a local “lithostatic pressure”
gradient for comparison with the theoretical gradient.
Because sea water instead of rock makes up the top-
most 188 feet of the column, calculated lithostatic
pressures from the sea floor down to about minus 750
feet are notably lower than pressures based on an as-
sumed gradient of 1 psi per foot. However, at depths
greater than minus 750 feet the local lithostatic pres-
sure ranges from values equal to the theoretical gra-
dient to values substantially in excess of it at depths

39

of more than minus 2,000 feet. Such close agreement
is general and expectable.

The significance of lithostatic pressure gradient in
the Dos Cuadras field may be best explained by imag-
ining the effect of connecting a pump to the pore fluids
at depth in a sequence of strata. At the outset the
indigenous fluid pressure in the rock pores may be
roughly one-half the lithostatic pressure at that depth
due to the weight of the overlying rock column. By
pumping fluid at high rates into the pores at that
depth, the fluid pressure will be raised locally and
theoretically could be raised to pressure equal to the
lithostatic pressure. If this were accomplished, the
weight of the overlying rock column would be lifted
by the hydraulic action of the pumped fluid; the rocks
surrounding the confined high-pressure pore fluid
would be deformed, either by plastic yielding or by
brittle fracturing or both, depending upon the nature
of the material (Whalen, 1968).

This process is known as hydraulic fracturing and
is a well-established technique used in many oil-pro-
ducing regions for increasing well productivity. High-
pressure fluids are pumped down cased wells and into
the rock pore spaces through open intervals or perfor-
ations in casing until fractures form and open up
around the well bore. Hydraulic fracturing (or, in
soft rocks, its equivalent, plastic parting or rupturing)
occurs whenever the pore fluid pressure exceeds the
lithostatic pressure. In most regions rock fracturing
occurs if pore fluid pressure exceeds a threshold value
somewhat lower than the lithostatic pressure, giving
rise to the concept and term “hydraulic fracturing
gradient.” These gradients range between 1 psi per
foot and perhaps 0.6 psi per foot. In most California
oil fields hydraulic fracturing has proved ineffective
as a means for increasing well productivity, so that
local data are sparse; from these sparse data it appears
that “hydraulic fracturing gradients” in California
fields range from 0.7 psi per foot to the lithostatic
gradient. In the deeper Pliocene zones of the Ventura
field “hydraulic fracturing” pressures must nearly
equal the lithostatic pressures, because natural fluid
pressures have gradients up to 0.9 psi per foot (fig. 11).

Knowledge about hydraulic fracturing has been
gained by experiments in artificial well stimulation.
The principals involved are generally applicable and
help to understand damage that may be done inadvert-
ently to rocks during oil field operations. The con-
sequences of the blowout of well A—21 are clarified in
the light of such considerations.

The fluid pressures and the fluid and lithostatic
pressure gradients encountered in the Dos Cuadras
field are shown in figure 12, together with a vertical

40

 

0 I
Sea floor

:A-Zl

3,
<

1000

l
l

N
“\VASBW
: A-25

IA-20

2000 -

DEPTH BELOW SEA LEVEL, IN FEET
00am“

3000 E— —

Fluid pressure gradient,
4000 ' \ L
0

Dos Cuadras oil field
1000 2000 3000
STATIC PRESSURE, IN POUNDS PER SQUARE INCH

 

 

 

 

4000

FIGURE 12.—Fluid pressures, fluid-pressure gradients, and un-
cased and perforated intervals of the Dos Cuadras oil-field
wells that were shut in or drilling on January 28, 1969.

line indicating the vertical depth interval in well A—21,
which was not protected by casing at the time control
of the drilling fluid was lost and the well blew out.
A single string of conductor casing was cemented at
a drilled depth of 514 feet (238 feet vertically below
the sea floor) in fine-grained rocks of the capping
layer (fig. 6) between the B—15 and C markers. The
bottom of the hole was at a total vertical subsea
depth of minus 3,313 feet, presumably characterized
by fluid pressures only slightly above “normal” on a
pressure gradient of 0.5 psi per foot, and presumably
stratigraphically above the base of the predominantly
sandstone section. When the hole began to “unload”
through the drill string, the drilling mud was followed
by what the drilling crew described as a “heavy con-
densate mist,” rather than black oil, thus indicating
that the source of the hydrocarbons was either gas-
saturated oil or a gas cap (no other evidence of any
gas cap is known) and that the fluid column in the
well bore had a very low density. For 13 minutes the
well blew blinding gaseous mist in large volumes with
a deafening roar. After an attempt to stab with the
kelley failed, the crew dropped the drill string and
closed the blowout preventer, thereby abruptly con-
fining the low-density condensate fluid to the largely
uncased well bore (see Appendix A). Within minutes
myriads of small gas bubbles unaccompanied by oil

GEOLOGY, PETROLEUM DEVELOPMENT, SEISMICITY, SANTA BARBARA CHANNEL, CALIF.

rose to the water surface in a large area adjacent to
Platform A. No other signs of impending trouble
were visible. From 1% to 2 hours after shutting the
rams, the crew observed a large and turbulent boiling
of the water about 800 feet east of the platform (fig.
13), the first emergence to the surface of large vol-
umes of seeping gas accompanied by abundant black
oil. As this initial boil intensified and expanded,
another similar boil began at the northeast corner of
the platform and partly beneath it. Within 24 hours
oil and gas were seeping vigorously from numerous
ocean-floor sources along an east-west zone extending
from a point about 250 feet west of the platform to a
point about 1,050 feet east of the platform. In time,
the area of seepage expanded and changed in char-
acter.

Figure 12 offers an explanation for the sequence
of events just described, especially when compared
with figures 7 and 8 relating rock porosity and per-
meability to the shallow depth to which the bore of
well A—21 was protected by casing. As control of the
drilling mud was lost during pulling of the drill pipe
from the hole, low-density hydrocarbon fluid entered
the well bore, presumably at or near the bottom, at'
a pressure probably not exceeding about 1,660 psi
(0.5 psi/ftx3,313 ft depth). When the rams of the
blowout preventer were shut and the column of low-4
density fluid was prevented from escaping freely from
the wellhead, the fluid pressure built up in the well
bore below the cemented shoe of the casing. The
pressure, potentially capable of reaching a theoretical
limiting value somewhere between 1,150 and 1,660 psi,
built up until the pore fluid pressure in the strata be-
low the casing shoe was exceeded (normal pore fluid
pressure at the casing shoe—minus 514 feet—is esti-
mated to be 226 psi—514 ftX0.44 psi/ft). At that
time, higher pressure gas and oil began flowing into
the shallow permeable beds from the deeper sands.

When the pressure of the newly energized pore fluids
in the shallow sands below the C marker had built up
to equal the “hydraulic fracturing” pressure of the
cover (estimated to be less than 360 psi at the depth
of the casing shoe and certainly not greater than the
lithostatic pressure of 514 psi for that depth), capping
rock rupturing occurred and the “boiling” seeps began.

The first outbreak occurred east of Platform A at what
is probably the structurally highest point (the B—15
marker is at minus 313 feet easterly from the A—21
surface location as compared with minus 332 feet in
well A—24). The localization of the other major “boil”
at the northeast corner of the platform may have re-
sulted from slightly greater penetrations close to that
corner of two of the foundation pilings.

GEOLOGIC CHARACTERISTICS OF THE DOS CUADRAS OFFSHORE OIL FIELD 41

Prior to the blowout three production wells (A—20,
A-25, A—41) had been drilled without incident, cased,
completed, tested, and shut in pending completion of
pipeline facilities. The perforated vertical intervals
of each of these wells is indicated in figure 12 by a
vertical line for comparison with the uncased interval
of the well that blew out. Each of these wells was
“killed” with heavy-weight mud following the blow-
out; however, a casing pressure of 1,000 psi was meas-
ured at the head of A—20 some days later. This
pressure can be interpreted as indicating that the
responsible hydrocarbon fluid in the “killed” well had
a density of between 0.75 and 0.65 grams per cubic
centimeter, indicative of a hole full of oil rather than
of gas. Inasmuch as wells A—20 and A-21 both bottom
at close to the same subsea vertical depth (minus
3,334 feet and minus 3,313 feet respectively) in struc-
turally similar locations and presumably with nearly
the same stratigraphic penetrations, the heavy gaseous
mist emitted at the time of the blowout remains puz—
zling in view of this shut-in casing pressure of well
A-20. The most obvious explanation, that well A—21
penetrated a small high-pressure gas reservoir in
which pressure dropped rapidly and equalized with
other reservoirs by flow to the borehole, is the simplest
of several alternative hypotheses consistent with all
available facts.

RESERVOIRS AND RESERVOIR CHARACTERISTICS

A natural petroleum reservoir is easily defined in
many oil fields where pressure communication through-
out a unit is indicated by a single oil-water contact
and a hydrocarbon fluid of fixed or consistently depth-
variable composition. The problem of defining a single
natural reservoir and of determining the total number
of such reservoirs is much more difficult in a large,
composite, multizone accumulation such as Dos
Cuadras field. There an obviously large number of
separate oil-water levels and fluid compositions (in-
consistently depth-variable) indicate the presence of
many reservoirs that could not have been in unimpeded
pressure communication prior to drilling of the first
exploitation well.

An attempt has been made on plate 3 to portray as
accurately as the well data permit the many strati-
graphic and structurally controlled subdivisions of the
oil-bearing strata of Dos Cuadras field. From the
transverse section it is evident that the thicker and
more continuous interbeds of siltstone and shale sub-
divide the Pliocene section in the vicinity of Platform
A into not less than six natural strata] reservoir units.
Moreover, the section-repeating thrust fault and the
high-angle normal fault in the upper block (both of

which appear to have constituted barriers to free fluid
communication) further divide the section in such a
manner that no fewer than eight or nine separate
reservoirs may occur in the fault blocks above the
thrust and no fewer than four or five below the thrust.
Each of these was hypothetically capable of being
separately produced, before they were placed in partial
communication through pre-blowout exploitation—well
completions and the blowout.

To combine so many natural units into “zones”
during production in such a manner as to exploit the
entire accumulation efficiently and economically re-
quires knowledge not only of the productive charac-
teristics of the major reservoirs and the values of
their fluid contents but also of the many and complex
economic variables affecting such a large and costly
exploitation effort.

Figure 10 shows schematically the zonal subdivisions
proposed (and thus far followed) for development
of the Dos Cuadras field by the Union Oil Co. of
Califoma as operator for itself and its partners. The
diagram is self-explanatory except for two matters.
First, the so-called “Red zone” was introduced after
the blowout when it was first recognized that some of
the strata in the capping interval above the C marker
are producible. Production from this “zone” is prob-
ably not commercial because of low well productivity,
low-gravity oil, high water cuts, and limited zonal
area and thickness. Most likely it will be produced
only so long as required to aid in abatement of the
surface seepage. Secondly, well Al—20 (shown on both
structure sections) was completed in the “402 lower
zone” and has been producing continuously since
March 29, 1969. This well is perforated selectively
from just below the F marker in the subthrust (or Q)
block down to the base of the dominantly sandstone
section between the H and I markers. Since May 25,
1969, it has been flowing commingled 28° oil through
a choke at a rate in excess of 2,200 barrels net oil per
day and a gas-oil ratio of about 440 cubic feet per
barrel from these three major productive intervals
(possibly as many as five separate reservoirs). No
gage of short—term open-flow potential has been ob-
tained, but crude calculations suggest a figure possibly
in excess of 10,000 barrels per day. In contrast, a shal-
lower well (A—41) producing continuously sinCe early
March 1969 has yielded much less from selectively
perforated intervals between a point midway between
the C and D markers down to the F marker in the
upper (“P”) block. This. “Brown zone” to upper “402
upper zone” completion has had a sustained production
(pumping) of about 950 barrels net oil per day of about
24.5° oil with a gas-oil ratio averaging about 220 cubic

42 GEOLOGY, PETROLEUM DEVELOPMENT, SEISMICITY, SANTA BARBARA CHANNEL, CALIF.

feet per barrel. Well A—21 was scheduled for a com-
pletion similar to that of A—20, but when it blew out,
communication was opened, at least temporarily, from
the highly productive “402 lower zone” sands to all
the lower-pressure sands up to the C marker. The
documented high rate of controlled production of well
A—20 though a choke of less than 1 inch diameter
leads one to speculate about the possible rate of flow
of well A—21 through a partly blocked bore hole of
unknown diameter against only moderate back pres-
sure through the ruptured capping rocks to the sea
floor.

All reservoirs in the Dos Cuadras field are sand-
stone with porosities ranging from nearly 40 percent
at the top of the “Brown zone” in the upper (P) block
to 25 to 30 percent for sands in the “402 lower zone.”
Average reservoir permeability ranges between nearly
1 darcy at the top of the “Brown zone” to a low of 50
millidarcys for the interval between the G and H
markers in the upper (P) block. Oil gravity ranges
between 185° API in the “Red zone” to 35° in some
of the thin sands below the I marker. Reservoir gas-
oil ratios range from negligible in the shallower sands
to 185 cubic feet per barrel for the “402 lower zone.”
The crude oil in the shallower sands is strongly under-
saturated, but that in the lower sands of the “402
lower zone” appears to be saturated. Interstitial
water content appears to be low to moderate through-
out, but data are insufficient to permit setting figures
on these quantities. Solution gas analyses are so few
that conclusions may have to be revised, but available
data show compositions that are normal for such crude
oils except for a surprisingly high C02 content, sug-
gestive of an unusually oxidized (and perhaps stag-
nant) accumulation.

Production from the field has been so limited that
reservoir performance cannot be evaluated. From
analogies between the reservoirs of Dos Cuadras field
and those of some other shallow California fields, it
might be expected that the reservoir drive mechanism
is a combination of solution gas expansion, accom-
panied and followed by gravity drainage, with natural
water drive being of minor importance. Present de-
velopment plans call for injection of water to help
maintain reservoir pressure after sufficient production
data are available for sound planning.

On July 28, 1969, 14 wells were producing 10,000
barrels of oil per day from the lower Pliocene zones
(one “Red zone,” 10 “Brown zone,” one lower “Brown
zone” to upper “402 upper zone,” and two “402 lower
zone” wells). A total of 635,000 barrels have been
withdrawn since controlled production for pressure
drawdown was authorized following the blowout. The
amount of seepage estimated by the US. Geological

Survey for the period March 22 to August 31, 1969, is
given in Appendix B.

SEEPAGE AND SUBSURFACE FLUID
COMMUNICATION

Although natural seepages of oil and gas have long
been a matter of record at several places (both off-
shore and onshore) along the Rincon trend, no docu-
mented observation identified the Dos Cuadras sector
as a seepage source until work was undertaken on
OCS P—0241 following the lease sale.

In a letter dated February 29, 1968, 11 months prior
to the blowout of well A—21, Mr. F. J. Simmons, Dis-
trict Drilling Superintendent for Union Oil Co. of
California, notified Mr. D. W. Solanas, Regional Oil
and Gas Supervisor for the Conservation Division of
the Geological Survey, of observations made on Feb-
ruary 23, and confirmed on February 28, 1968, “a fairly
large oil slick with some gas bubbles” at a location
within OCS P—0241 approximately 2,300 feet west and
3,500 feet south of the northeast corner of the lease.
Mr. Simmons further stated, “From all indications and
records available to us, this is apparently a natural
seep.” This opinion is consistent with the tendency
toward intermittent activity of some known seeps
along the trend. The stated location is almost exactly
on a line connecting Platforms A and B (along the C
horizon axis of the Dos Cuadras culmination) and
about 960 feet westerly along that line from the
center of Platform A.

Somewhat later in 1968, after tentative selections
had been made for sites for three projected drilling
platforms on OCS P—0241, eight shallow coreholes
were drilled to obtain on-site information to aid in
planning foundations for these large structures. Three
coreholes were drilled in the vicinity of what was to
become the site of Platform A, three more at Plat-
form B site, and two at the site of proposed Platform
C, about 2,600 feet westerly from B. Technicians of
Dames and Moore, Inc., who planned and supervised
these operations under contract to the operator, ob-
served live oil shows while drilling and coring all
three holes at site A, and subsequently reported these
findings along with descriptions of oil-saturated core
samples and measurements of bulk densities indicative
of very high porosities for these oily shallow beds. No
fluid hydrocarbons were reported from any of the
cores from the coreholes at the B or C sites.

Even though there are no earlier documented ob-
servations of natural seepage from the Dos Cuadras
field, there is abundant suggestive evidence that the
accumulation may have been seeping over a long
period of time. Apart from the very general and
widespread evidence that most large or highly pro-
ductive petroleum accumulations seep at least some
low-molecular-weight hydrocarbon fractions (McCul-

GEOLOGIC CHARACTERISTICS OF THE DOS CUADRAS OFFSHORE OIL FIELD

loh, 1969) are the facts that the shallower reservoirs
of the field are strongly undersaturated with respect
to gas and contain high— to intermediate-density crude
oils. Both of these characteristics suggest long-con-
tinued loss of the potentially gaseous and more mobile
liquid fractions from these reservoirs. Consistent with
these facts is the gradational decrease in oil density
and increase in dissolved gas content from the shallow
to the deep reservoirs (fig. 9). Finally, the excep-
tionally high 002 content of the analyzed solution gas
samples is suggestive of an unusually oxidized stag-
nant accumulation, another interpretation consistent
with long-continued seepage.

Whatever the duration and rate of natural seepage
from the shallow reservoirs of the Dos Cuadras field
may have been, the blowout of well A—21 on January
28, 1969, drastically changed that rate and triggered
other changes more difficult to evaluate. The sequence
of events that occurred at the time of the blowout
and during the hours following already has been
described. To complete that history it is necessary
to add that the blown-out well continued to feed high-
pressure fluid to the low-pressure near-surface rocks
and thence through many openings of varied dimen-
sions to the sea floor until emergency measures to kill
the well and to cement the borehole succeeded on
February 8, 1969. Even after cementing, however,
there was evidence that suggested continuing move-
ment of fluid from deeper to shallower reservoirs
through channels outside the well bore that were
opened during the lengthy period of unimpeded flow.
The well was reentered, the cement was drilled out of
the surface casing, and extensive additional cement
grouting was done before sidetracking the original
hole and redrilling the well (A—21 RD) for completion
and production from the upper part of the “Brown
zone.” Net oil pumped from this well since early
March 1969 has declined from an early high of about
860 barrels per day of 25° crude to a current (August
1969) rate of about 600 barrels per day.

On February 25, While remedial work was being
done in well A—41 to help abate the decreased but con-
tinuing seepage, a high though intermittent rate of
oil flow resumed. It was thought by many at that time
that well A-41 was permitting deep-zone oil to enter
into the formation at about 900 feet below the ocean
floor and subsequently through some type of fissure
onto the channel floor. Further remedial work on well
A—41, plus the recementing of well A—21, corrected
this condition, and there have been no more such in-
cidents. The cause of this second episode of uncon-
trolled flow is not known, but it is one bit of evidence
of the ease with which fluids from some of the major
reservoirs at depth are able to find egress to the
surface.

43

The natural seepage reported in February 1968,
before Platform A was emplaced, was located about
960 feet westerly from what is now the platform
center. The first conspicuous boil of oil and gas fol-
lowing the blowout issued with great energy from a
source or group of sources located 800—900 feet easterly
from the center of the platform along the anticlinal
crest of C horizon. A third boil erupted near the
northeast corner leg of the platform and around the
point at which the driven slant conductor pipe of well
A—41 enters the ocean floor, and smaller boils occurred
within a few hundreds of feet west of the platform.
Much gas issued with the oil during the days immedi—
ately after the blowout, posing continuous danger of
fire and forcing repeated suspensions of work and
evacuation of personnel from the platform. Although
the shallow reservoirs of the field were known to be
(and still are) strongly undersaturated with respect
to gas, large volumes of gas had evidently found a
path or paths into and through these shallow reservoirs
over an extensive area.

After the well had been controlled and the energetic
flow abated, much gas accompanied by some oil con-
tinued to seep from many sources and the area of see-
page gradually expanded. Figure 13 is a map showing
the limits of the maximum area within which seepage
is known or inferred to have occurred. This map has
been compiled from aerial photographs; from personal
observations made from the air, from surface boat,
and from a submersible on the ocean floor; and from
submersible diver observations of other US. Geological
Survey personnel, from visual sighting observations
of US. Geological Survey personnel on the platform,
and from side—scanning sonar data supplied by the
operator. At its greatest extent in late February
1969, the zone or belt of seepage, as much as 500 feet
wide, extended for about 3,900 feet from a point 1,300
feet westerly of the center of Platform A to a point
on OCS P-0240 approximately 2,600 feet easterly of
the platform. The total area of seepage was about
50 acres. Gas and some oil were observed rising to
the sea surface at the easterly point in late March
1969, from a small fresh-appearing sea-floor crater
observed by US. Geological Survey personnel from a
submersible.

The area of seepage east of Platform A was per-
sonally observed in late April 1969 on a calm day.
The otherwise smooth water surface was ruffled over
a broad area by myriads of small breaking bubbles of
gas accompanied by rising globules of light oil that
quickly spread as they surfaced to form iridescent
films streaked with brown. On the sea floor the oil
issued as streamers from pinpoint and larger openings
in siltstone outcrops and soft sediment alike. Pits
and elongate craters on the sea floor ranged from a

44

few feet to many feet in length and up to several feet
in depth. In this vicinity the sea floor was littered
with angular rock debris, some of it identifiable as
Pleistocene in age from included fossil shell fragments,
presumably ejected forcefully from the sea-floor
depressions at the time of the blowout eruptions.
Whether some of the largest crater— and fissure-like
depressions existed prior to the blowout cannot be
proved or disproved. However, the abundance of
angular soft porous rock fragments, some of them a
foot or more across, and their restricted distribution
close to and generally north of the sea floor depres-
sions where the most energetic gas and oil flows
erupted indicate a genetic relationship. No sea-
floor deposit of tar or tar residues indicative of ancient
seeps has been seen or reported in this area. How—
ever, inactive craters were identified about 200 feet
southeast of the active seeps by a sonar survey (fig.
13) under charter to the operator.

Estimates of the varying rate of seepage during or
following the blowout range widely and are difficult
to evaluate. On-site estimates that 300—500 barrels
of oil per day were leaking through the sea floor dur-
ing the early period of uncontrolled flow of the blown-
out well were widely quoted in the press. On the
other hand, Allen (1969a) has stated that “During the
first ten days of the leak many thousands of barrels
of oil were released daily onto surface waters. . . .”
Allen’s estimates were based primarily on his attempt
to interpret discharge from evaluation of areal limits
of the slick reported by the US. Coast Guard. As
noted earlier, the known production rate of well A—20,
together with the similarities between it and the blown-

GEOLOGY, PETROLEUM DEVELOPMENT, SEISMICITY, SANTA BARBARA CHANNEL, CALIF.

out well, is permissive of an independent guess by the
author that the rate of uncontrolled flow might have
been any place in the range between 500 and 5,000
barrels per day.

J. M. DeNoyer of the Geological Survey has made
a special study of data regarding the oil slick and has
supplied the following comments (written commun.,
Sept. 4, 1969).

Allen’s first estimates were based on aerial reconnaissance
mapping of the extent of the oil slick during the first few days
of leakage. Difficulties in accurately determining the distri-
bution of oil-covered water and open water and thickness of
oil slick are recognized by Allen (1969b). Between March 1
and March 22, 1969, the Geological Survey conducted a number
of high- and low-altitude detailed aerial photographic missions
to determine the extent of oil distribution and dynamic charac-
teristics of oil movement. The method used for mapping the
distribution of oil within the slick was to take photographs at
frequent intervals and mosaic the sun glint pattern that shows
the presence of oil in great detail. Maps prepared from these
photographs indicate that an overestimate of the volume of
oil is obtained from the extent of the slick. The degree of
overestimation ranges between a factor of four and 10, de-
pending on wind and current conditions and the rate of leaking.
Reducing Allen’s estimates of about 5,000 bpd by a factor of
four would give an estimate of 1,250 bpd and a reduction by a
factor of 10 would suggest 500 bpd. The latter figure is in
agreement with visual estimates made by Union Oil Company
and independently by engineers and inspectors of the Geological
Survey’s Conservation Division but they may be too conserva-
tive. A leak rate of slightly over 1,000 bpd during the most
severe periods of the spill is consistent with Allen’s mapping
of the maximum extent when the degree of oil coverage is
taken into consideration.

Emergency measures for collecting the oil seeping
from the ocean floor were put into effect soon after
the blowout but were largely ineffective until late in

 

 

N UNION OlL CO. AND OTHERS SUN OIL CO.

003 P0241 AND OTHERS

003 P0240
Approximate maximum limits of
the seepage area from 1/28/69

Approximate location of natural to 5/12/69\
, _ seepage first sighted 2/23/68 / \)\\ OCS P-024l
: /\\
M and officially reported 2/29/68>\x v ‘13 F— No. l
/ /x/ \\ _ 87V \ \
_ .2 \
Dames and Moore VVL; %\‘\\
foundation core “0'95 Locations 0‘ ma or boilf \7§ / F‘\ Gas seeps located by submersible
l chartered by Sun on Co. 4/3/69
Craters without seeps located ,___.
by Union Oil Co. sonar §uj

surve 3/16/69

0 500 1000 FEET y Oil and gas seeps located by su -

008 P0241 mersible chartered by U.S.G.S.

No. 4 3/15/69

 

 

 

FIGURE 13.—Dos Cuadras oil-field oil and gas seepage area.

GEOLOGIC CHARACTERISTICS OF THE DOS CUADRAS OFFSHORE OIL FIELD 45

March. The Geological Survey Conservation Division
visual estimates of total seepage (collected and escap-
ing) were ranging about 24 barrels net oil per day be-
tween March 14 and 27.

From late March 1969 to the end of July, methods
of collection improved, and methods of measuring
seepage rates also improved. A well-verified nearly
constant average daily rate of 30 barrels net oil char-
acterize the period from March 22 through July 13,
in contrast to Allen’s estimate of 200 barrels per day,
which he has since revised to a lower figure (oral
commun., September 1969). This rate was abruptly
reduced from 30 to 20 and then to 15 barrels .daily
between July 13 and July 31, and it has been still
further reduced since then. (See Appendix B.) These
reductions have been a result either of shallow cement
grouting of the capping rocks in the vicinity of Plat-
form A or of controlled fluid withdrawals from the
shallowest reservoirs or both, as consequences of the
recommendations of the Presidential Advisory Panel
Meeting of May 12—13, 1969. During this same period,
the percentage of seepage oil trapped and collected
by various means has risen from an estimated 10 per-
cent during the final week of March to more than 50
percent for the last 2 weeks of July. As of early
September 1969, the daily seepage rate was reduced
to less than 10 barrels.

The composition of the seeping oil is important in
trying to determine its source. Colorless gas, low-
density greenish-brown crude oil of low viscosity, and
high-density brownish-black oil are the seeping ma-
terials. These three constituents have been emitted
separately or together, and all three seem to have
seeped at one time or another from all known major
seepage sources. Of the seepage oil collected from
sources beneath and close to Platform A, most ranges
in API gravity between 18° and 20°, although some
measurements range as high as 24". These high den-
sities (low gravities) suggest a source in the shallow-
est sands of the “Red zone” (figs. 9, 10), but the lower
densities (higher gravities) are more consistent with
possible sources in the “Brown zone.” Oils from about
900 feet east of Platform A, collected on several dates,
range in API gravity between 19° and 28°, and lumps
of even heavier black tarry oil have floated to the sur-
face. Analyses of trace metals, molecular structure,
acidity, and minor element composition have been
made of these surface samples, samples from Platform
A seeps, and samples of oils produced from some of the
wells. Comparisons of these analyses, like the range
of oil gravities, suggest that the seepage oils may
come from sources ranging in depth from the shallow-
est reservoirs of the “Red zone” to at least as deep as
the upper part of the “402 lower zone.”

SUBSIDENCE POTENTIAL

The possibility must be considered that withdrawal
of fluids from the reservoirs of the Dos Cuadras oil
field may be accompanied and followed by shallow
subsurface readjustments and localized subsidence of
the sea floor. The exceptionally shallow depth of
much of the reservoir volume, the very high porosities
and permeabilities of the reservoir rocks, the imperfect
caprock seal above the shallowest major reservoir,
and the intentional reduction of reservoir pressures,
particularly in the shallowest reservoirs, all suggest
that fluid withdrawals may be accompanied by reduc-
tion of pore pressure and gradual compaction of the
petroliferous rocks. If compaction occurs, readjust-
ments of the demonstrably weak capping stratum
would follow, and highly localized differential subsi-
dence of the crestal region of the anticline would
occur. It is possible that subsidence would be accom-
panied by localized peripheral tensional fracturing
of the capping layers. It is very difficult to judge
Whether or not such fracturing, if it did take place,
would permit further sea—floor seepage of oil and gas.

Peripheral water injection may be feasible and
prove effective in maintaining reservoir pressures in
the producing intervals below the F electric-log
marker. Water injection into reservoirs above the F
horizon in the upper fault block must be pursued with
great care and forethought to avoid upsetting the del-
icate pressure balance. The risks unavoidably entailed
in shallow injection may prove to be so undesirable
that the risks of differential deformation of the cap-
ping layer and the sea floor will be regarded as
preferable.

The numerous complexly interrelated variables that
determine whether or not subsidence occurs when pore
fluids are withdrawn from a reservoir are understood
so poorly that accurate prediction beforehand of the
amount of subsidence is difficult, if not impossible.
Some perspective may be gained for a view of the
possibility that Dos Cuadras offshore field may un—
dergo subsidence during exploitation by comparing it
with other fields in the same region in regard to those
geologic and reservoir parameters that enter into the
mechanisms of compaction. The Wilmington, Calif,
oil field is well known as a place where oil-field oper-
ations have led to extreme surface subsidence (Gilluly
and Grant, 1949). Located in the same region, and
an offshore field in part, the Wilmington field is the
one most closely resembling Dos Cuadras for which
the pertinent data are published.

Similarities between the Dos Cuadras and Wilming-
ton fields are numerous and close, and the differences,
small (table 2). Nevertheless, opinions of those with

46 GEOLOGY, PETROLEUM DEVELOPMENT, SEISMICITY, SANTA BARBARA CHANNEL, CALIF.

TABLE 2.—- Comparison of certain geologic and engineering characteristics of the D03 Cuadras oil field with the Wilmington,

Depth of top of shallowest
zone, in feet.

Mean depth of principal
zones contributing to
subsidence, in feet.

Age of reservoir rock _____________

Average porosity, percent __________

Oil gravity range API ____________

Maximum total net oil
sand, in feet.

Fluid pressures _________________

Well productivity,in
barrels of oil
per day.
Maximum flank dip
angle.
Maximum width of field
(productive limits),
in miles.
Productive area, in acres ___________

Maximum surface subsidence,
in feet.

1Halbouty (1968).

Cali/I, oil field

Wilmington, Calif.
(extracted from Gilluly
and Grant, 1949)

About 2,200
(“Tar”)

About 2,500
(“Tar” and “Ranger”)

Early Pliocene
(“Repetto Formation”)

30
12° —25 °
340

Near normal hydrostatic

Max 2,700
Min 50

20° (?)
About 3

17,800
29 (to 1966)

Dos Cuadras
(compiled by T. H. McCulloh)

About 483 (subsea)
About 296 (below mudline)
(“Brown”)

1,800
(All zones)

Early Pliocene
(“Repetto Formation”)

28
21 ° —33°
299

Near normal hydrostatic

Max 2,200+
Min 50(?)

330

About 1

1,000
(?)

Whom the author has had opportunity to discuss the
matter range from the extreme that no subsidence
would occur at Dos Cuadras in any case to the oppo-
site extreme (one held by the author) that some sub-
sidence will occur no matter what preventive measures
are employed. The consensus of expert opinion since

the May 12—13, 1969, meeting of the Presidential
Advisory Panel appears to be that subsidence would
accompany production of hydrocarbons, but that main-
tainance of “optimum” pressures through water injec-
tion will limit and control the amount of subsidence.

Seismicity and
Associated Effects

Santa Barbara Region

By R. M. HAMILTON, R. F. YERKES, R. D. BROWN, JR., R. 0. BURFORD,
and J. M. DENOYER

GEOLOGY, PETROLEUM DEVELOPMENT, AND SEISMICITY OF THE
SANTA BARBARA CHANNEL REGION, CALIFORNIA

 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 679—D

 

 

CONTENTS

Page
Seismicity ________________________________________________ 47
Recent (instrumental) evidence ________________________________ 47
Historic record ___________________________________________ 49
Geologic record __________________________________________ 50
Future earthquakes ________________________________________ 63
Associated effects __________________________________________ 63
Ground motion and failure ____________________________________ 63
Tsunamis ______________________________________________ 64
Seismic effects on oil field installations ___________________________ 64
Oil-field operations ________________________________________ 65
Summary _________________________________________________ 66
ILLUSTRATIONS

Page

FIGURE 14. Map showing earthquakes of magnitude 6 and greater in southern
California since 1912 _______________________________ 48

15. Map showing epicenters of earthquakes in the Santa Barbara Chan-
nel region from 1934-67 _____________________________ 49

16. Map showing epicenters of 1968 earthquake sequence in the Santa
Barbara Channel __________________________________ 49

17. Map showing bathymetric contours and structural features of the
central part of the Rincon trend _______________________ 51

TABLE

Page

TABLE 3. Partial list of earthquakes felt in the vicinity of Santa Barbara Chan-
nel, 1800 to 1952 ____________________________________ 52

III

 

GEOLOGY, PETROLEUM DEVELOPMENT, AND SEISMICITY OF THE
SANTA BARBARA CHANNEL REGION, CALIFORNIA

SEISMICITY AND ASSOCIATED EFFECTS, SANTA BARBARA REGION

By R. M. HAMILTON, R. F. YERKES, R. D. BROWN, J 11.,
R. O. BURFORD, and J. M. DeNOYER

SEISMICITY

The Santa Barbara Channel region is located with-
in the circum-Pacific seismic and volcanic belt and
has been tectonically active throughout much of
Cenozoic time. This tectonism seems to have been
accelerated during the latter part of this era, maxi—
mum activity having occurred in Quaternary time.
One way of depicting the seismic setting of the Santa
Barbara Channel region in relation to the rest of
southern California is to show the distribution of
recent large earthquakes (fig. 14). Since 1912, more
than 20 earthquakes of magnitude 6.0 or larger have
occurred in southern California. The San J acinto
fault zone, which trends southeast from San Bemardino
and is part of the San Andreas fault system, was the
site of eight of these shocks; four others occurred
near Bakersfield during the Kern County earthquake
sequence of 1952; and two were located in the Santa
Barbara Channel. The 1927 earthquake of magnitude
7.5, west of Point Arguello, should perhaps be grouped
with the other two events in the channel region be-
cause all three may have occurred on faults in the
Transverse Range province.

RECENT (INSTRUMENTAL) EVIDENCE

In California, the installation of instruments for
recording earthquakes began in the 1920’s. Since
1934, southern California earthquake locations have
been reported by the Seismological Laboratory of the
California Institute of Technology in its quarterly
bulletin. Records of earthquakes for the period 1934
through 1967 within about 85 km (53 miles) of Santa
Barbara were recently selected from the Seismological
Laboratory data by A. G. Sylvester of the University

of California, Santa Barbara, and were kindly made
available for use in this report.

Epicenters of the 1934—67 earthquakes in and near
the channel are plotted in figure 15, which shows
most of the events greater than magnitude 3 and a
few smaller ones. Each symbol represents at least
one earthquake; the dots represent shocks of mag-
nitude 4 or larger. The epicenterseprior to June 1961
are given to the nearest minute (about 2 km), where-
as more recent ones are given to 0.01 minute; the
precision of the earlier data introduces several short,
artificial lineations in the epicenter pattern.

The largest shock (magnitude 6.0) during the period
occurred on June 30, 1941, approximately 15 km (9
miles) southeast of Santa Barbara. The symbol for
this earthquake also represents 72 aftershocks. Al-
though epicenters are scattered throughout the Santa
Barbara Channel region, they tend to be more heavily
concentrated in its eastern part. In contrast, the
western part of the channel has been relatively quiet
seismically since 1934. No conspicuous trends are
evident in the epicenter pattern. .

The reliability of an earthquake location depends
on the number of seismograph stations recording the
event and on the geometry of the station distribution;
maximum precision is obtained where stations are
numerous and uniformly distributed around the earth-
quake source. The difficulty in locating an earth-
quake with a poorly distributed station net is analogous
to determining position by triangulation where either
the base line is much shorter than the distance to the
point, or the point is near the trend of the base line.

Most of the locations in figure 15 were plotted
using readings from seismograph stations that cover

47

48 GEOLOGY, PETROLEUM DEVELOPMENT, SEISMICITY, SANTA BARBARA CHANNEL, CALIF.

 

 

 

 

 

 

 

     

   

  
 
 

 

        
 
 
   
 
 

 

 
 
 
 

DSanta Maria
ff” . 1916(6)
19270.5) BIG—5mg FA“/\’ Gorman “Iva
SANTA YNEZ mm- “‘14, ”4‘45
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1941(60) “We \40
1925(63) ”U”
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1940 7.1
1915(625, 6.25) (317,1
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Modified from Allen and others, 1965

FIGURE 14,—Earthquakes of magnitude 6 and greater in southern California since 1912. Modified from Allen and others (1965).

an azimuthal range of about 135° around the channel.
From 1957 to 1968, a seismograph was operated on
San Nicolas Island, about 72 miles south of Santa
Barbara, but its data were of limited value for locating
earthquakes in the channel region. Because of the
inadequacy of the network and because of the lack of
knowledge of crustal structure in the channel region,
individual epicenters cannot be located within 5 or 10
km (3 or 6 miles), and errors at some places exceed 25
km (16 miles). Consequently, the epicenter locations
are inadequate to identify or delineate specific active
faults in the region.

The principal seismic activity in the Santa Barbara
Channel region after 1967 was the earthquake sequence
in June, July, and August of 1968. Nineteen of these
earthquakes were felt in the Santa Barbara-Goleta
Valley area (A. G. Sylvester, written commun.). The

largest shock (magnitude 5.2) occurred on July 4
(Pacific time) and in Goleta caused minor damage to
merchandise, windows, light fixtures, and acoustic
tile; cost of the damage amounted to $12,000. Minor
damage also occurred at Carpinteria, but no structural
damage is known to have resulted from this earth-
quake.

Epicentral locations for 63 earthquakes (magnitude
22.8) in this sequence are shown in figure 16. The
epicenters cluster in the channel approximately mid-
way between Santa Cruz Island and the mainland.
When the sequence began, only two seismograph
stations were operating in the channel area; one at
Santa Barbara and the other at Santa Ynez Peak.
This coverage was improved on July 7, 1968, by the
installation of portable stations on Santa Cruz and
Santa Rosa Islands and at several other mainland

SEISMICITY AND ASSOCIATED EFFECTS, SANTA BARBARA REGION 0 49

sites. These stations recorded through July 31, 1968,
and substantially increased the precision of locating
the epicenters for that period. Overall distribution
of the epicenters for earthquakes during the period
of operation of the island stations is not significantly
different from the distribution of the earlier ones, but
10 of the 22 shocks recorded in this period were
grouped in the northeastern part of the area.

The earthquake sequence was centered about 16
miles southeast of Santa Barbara and 10 miles south-
west of the Carpinteria Offshore oil field. Pertinent
information concerning the relationship between the
earthquakes and the drilling operations was also pro-
vided by A. G. Sylvester:

According to company officials, production was in no way
affected by the earthquakes. A temporary oil well drilling
platform, WODECO VI, drilled two exploratory holes in the
main fault-bounded anticline and was in the process of drilling
a third when the swarm commenced. The drilling was not
interrupted, the hole was dry, and it was capped. At least two
more dry holes were drilled on the anticline and were capped
after the swarm. Platform A, which blew out on 28 January
1969 and resulted in a massive oil spill. . . was not constructed
until 14 September 1968, and drilling did not commence until
November 1968.

HISTORIC RECORD

The seismic history prior to the installation of
seismographs is given, though in a more qualitative
and nonuniform manner, by numerous written de-
scriptions of earthquake effects. Reliable accounts
of California earthquakes date from about 1800. The
earliest reports are found in notes of Spanishexplorers
and early settlers, and in the records of the Franciscan
Missions. Earthquakes that affected the Santa
Barbara Channel region prior to 1953 are listed in
table 3.

Four of these earthquakes were especially destruc-
tive. The earliest, in 1812, destroyed Missions Santa
Barbara and Purisima Concepcion (about 10 miles
northeast of Point Arguello) and caused a tsunami
along the north coast of the channel. Reported esti-
mates of the high-water mark of this tsunami were
as much as 50 feet near Gavita. A recent detailed
studylof historic records, however, concludes that such
accounts are unsubstantiated and cannot be accepted
at face value. Several asphalt (crude oil) springs
reportedly began to flow at places inland from the
coast, and a burning oil spring near Rincon Point was
enlarged. In the area of Santa Barbara the destruc-
tion had a Rossi-Forel intensity of IX to X. The re-
ported damage and other effects resemble those

1 “Examination of Tsunamis Potential at San Onofre Nuclear Generating Station,”
unpublished report submitted to Southern California Edison Co. by Marine Advisers,
Inc., in 1965.

 

  
 
 
 

120‘ 00’
o a O] o o 0
° . o o 0 a O 0 o 0 Q
o 0 ° 0 0 o
I 0
o o. 0 Santa Ynez Mountains 00 :0 o o : .
o 0 Sarge: Ynez 03 ° 0 °
4" eak o

30' __ o A . o 0 9° on: a o o (9. _.

  

' Pt oConceptcon San: Barlggrao
0
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° Santa O o o o 0

° Santa Rosa

 

 

 

Island
San Miguel ' iggaca’pa Is 8 co 0°88'
Island 0 ' Santa Cruz . 0 ° on
0 Island 0 0° °o
. a I a sec 0 on
O 30 MILES

O 30 KILOMETERS
l_|__|__‘

FIGURE 15.—Epicenters of earthquakes in the Santa Barbara
Channel region from 1934—67. 0 , magnitude less than 4;
o, magnitude greater than or equal to 4.

accompanying other California earthquakes of mag-
nitude 7.

An earthquake on June 29, 1925, caused widespread
damage in coastal communities from Pismo Beach on
the northwest, through Santa Barbara, to Ventura on
the east. Twenty people were killed. Almost the
entire business section of Santa Barbara was destroyed
or rendered unsafe. The damage was estimated at
$6 million and this figure does not include damage to
residences. Mission Santa Barbara again was heavily
damaged with partial destruction of two bell towers,

120° 00'
I

Santa Ynez Mountains

 

    

34. . Santa Ynez Peak
30 c'Santa Barbara

 
  
  
 

 

P1 Conception

   
 

8°
DVentura
Santa
Barbara . H Pm
' . ueneme
San Miguel Santa Cruz , ‘ 059727291 D
Island Island , '
4: h @ Anacapa Is
\—
Santa 11$ MILES
Island 0 30

 

 

l—L—J—.—l
l O 30 KILOMETERS

 

FIGURE 16.—Earthquake sequence in 1968 in the Santa Bar-
bara Channel (Sylvester and others, unpub. data). a ,
epicenters of earthquakes that occurred during the period
J une—August 1968;O, epicenters of earthquakes that occur-
red during the period July 1967 to June 1968.

50 GEOLOGY, PETROLEUM DEVELOPMENT, SEISMICITY, SANTA BARBARA CHANNEL, CALIF.

collapse of the front facade, and failure of some older
interior adobe walls. Nunn (1925) reports that crude
oil was extruded through beach sand at several points
along the Santa Barbara coast about 3 hours before
the main earthquake and at approximately the same
time as a series of slight foreshocks began. An oil
spout also was observed at the shoreline near the west
end of the present Summerland oil field one night
after an earthquake in 1883 (Goodyear, 1888). The
epicenter of this magnitude 6.3 earthquake was prob-
ably less than 10 miles southwest of Santa Barbara.

The third major earthquake occurred on November
11, 1927, northwest of the channel off Point Arguello
(Byerly, 1930). This shock, with a magnitude of 7.5,
ranks as the second largest California earthquake
since the San Francisco earthquake of 1906. Effects
were most pronounced at Surf and Honda, just north
of Point Arguello, where people were thrown from
their beds, the concrete highway was cracked, a rail-
road bridge was damaged, and several hundred
thousand cubic feet of sand were shaken down from
a beach cliff. Buildings were damaged along the
coast from Cambria, about 80 miles northwest of Point
Arguello, to Gaviota, 28 miles to the east. A seismic
sea wave was generated by the main event, and seis-
mic disturbances from the main shock and some of its
stronger aftershocks were felt in ships at sea. The
seismic sea wave, or tsunami, was observed at Surf
and Pismo Beach, 10 and 40 miles, respectively, north
of Point Arguello. The wave was at least 6 feet high
and resembled a large storm wave. At Port San Luis
(Avila) near Pismo Beach, a 5-foot wave was followed
by 1 hour of water agitation. Tide gage records at
San Francisco and San Diego confirm this tsunami.

The last of the four important earthquakes occurred
on June 30, 1941. Its magnitude was 5.9—6.0, and its
epicenter was located in the channel about 5 miles
south of the coastline between Santa Barbara and
Carpinteria. Several communities along the Santa
Barbara coast were damaged.

The historic records of the channel region document
numerous periods characterized by sequences of fre-
quent or nearly continuous low-magnitude seismic
activity Without exceptionally large shocks (table 3).
Such sequences are called “earthquake swarms” and
are commonly associated with volcanic activity; how-
ever, there is no evidence of a volcanic origin for the
earthquake sequences in the Santa Barbara Channel
region.

A more distant earthquake, but one that strongly
shook the northern part of the Santa Barbara Channel
(Wood, 1955) occurred January 9, 1857. Its epicenter
was on the San Andreas fault near Fort Tejon, about
50 miles northeast of Santa Barbara. The surface
faulting that accompanied this earthquake was not

mapped at the time, but contemporary accounts and
recent geologic studies (Wallace, 1968; Vedder and
Wallace, 1968) demonstrate substantial right-lateral
displacement On a fault break at least 150 miles long.
The effects of this earthquake are comparable to those
of more recent earthquakes of about 8.0 magnitude.
Early deseriptions indicate that all the houses in
Santa Barbara were damaged (Wood, 1955) and that
shaking in the Santa Clara River Valley east of
Ventura was severe. Differential subsidence occurred
in the river bed, and long cracks formed from which
water was ejected to heights of 6 feet.
GEOLOGIC RECORD

An indication of long-term seismic activity is pro-
vided by data on the amount, rate, and nature of
crustal deformation at the earth’s surface. Accurate
dating of the deformation of such features as young
rock units, terraces, drainages, or other geologic
markers yields a useful and reliable extension of
historic and instrumental records.

The Santa Barbara Channel region is a part of the
Transverse Range province, in which west-trending
structures and topographic features contrast with the
predominantly northwest structural and topographic
trends found elsewhere in California, especially those
of the adjoining Coast Range, Sierra Nevada, and
Peninsular Range provinces (fig. 1). Many of the
latest fault movements in the Santa Barbara Channel
region seem to involve vertical slip, although many
of the larger fault zones, such as the Santa Ynez,
Big Pine, and Santa Monica, may have had major left-
lateral components of movement in the geologic past,

The Santa Ynez fault zone, which trends westward
for about 82 miles along the northern margin of the
Transverse Ranges (fig. 1), exhibits some physiog—
raphic evidence that suggests recent movements, and
it has been considered an active tectonic feature by
some geologists (Page and others, 1951). The mag-
nitude 7.5 earthquake off Point Arguello in 1927 may
have occurred on the westward extension of the Santa
Ynez fault zone.

The Big Pine fault, a major left-lateral fault with
oblique slip near its western end, may have had
measurable movement during historic time. The
southern California earthquakes of November 1852
(table 3) were accompanied by about 30 miles of sur-
face faulting in Lockwood Valley (Townley and
Allen, 1939) about 40 miles northeast of Santa Barbara.
The exact trend and location of the surface faulting
is unknown, but geologic evidence and contemporary
reports indicate that it may have been along the Big
Pine fault. Independent evidence of very young
movement along the fault includes scarplets that cut
Quaternary terrace deposits and apparent left-lateral

SEISMICITY AND ASSOCIATED EFFECTS, SANTA BARBARA REGION 51

offset of stream channels (Vedder and Brown, 1968).

The Malibu Coast fault, a segment of the Santa
Monica fault zone southeast of the Santa Barbara
Channel, is not known to have had recent movement.
However, faulting and local warping associated with
the fault have deformed upper Pleistocene marine-
terrace platforms and their deposits at seven known
localities along a 20-mile segment of the fault border-
ing the south side of the Santa Monica Mountains
(Yerkes and Wentworth, 1965).

That recent topographic surfaces and very young
rock units have been deformed in the eastern part of
the channel region has long been recognized. In the
Ventura anticline, lower Pleistocene strata form the
upper part of a sedimentary sequence that is more
than 40,000 feet thick. These lower Pleistocene beds
dip 35°—60° on the south flank of the anticline, and,

because they conformably overlie older rocks, they
provide clear evidence that the structure has been
formed since early Pleistocene time. At Loon Point,
6 miles east of Santa Barbara, upper Pleistocene
alluvial fan deposits are tilted and cut by a northeast- '
trending thrust fault that offsets the base of the
oldest fan by at least 400 feet (Lian, 1954). This
faulting may have continued into Holocene time.
Faulted terrace deposits are well exposed about 2
miles southeast of Carpinteria, where highway cuts
reveal a southwest-dipping (40°) reverse fault that
juxtaposes upper Pleistocene marine terrace deposits
and highly deformed Tertiary sandstone and siltstone.
This fault may also cut the present topographic sur-
face; presumably it has moved during Holocene time.

Several west-trending faults have been mapped in
the northeast part of the channel (fig. 17), and sub-

119° 35'

 

Santa
Barbara El

   

O l 2 3 MILES

;l____L__.__J
BATHYMETRIC CONTOUR INTERVAL 3 FEET

 

Rlncon Point

 

EXPLANATION

.L .83 - 2
Fault Location of gravity core
Bar and ball on dmnthrown side I
Platform

+

Anticlinal axis

 

 

Bathymetry by R. G. Martin, Jr., 1969.
from US, Geological Survey
precusnon fathometer records

FIGURE 17 .—Bathymetric contours and structural features of the central part of the Rincon trend.

GEOLOGY, PETROLEUM DEVELOPMENT, SEISMICITY, SANTA BARBARA CHANNEL, CALIF.

52

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GEOLOGY, PETROLEUM DEVELOPMENT, SEISMICITY, SANTA BARBARA CHANNEL, CALIF.

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59

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SEISMICITY AND ASSOCIATED EFFECTS, SANTA BARBARA REGION

bottom profiles show that they extend at least several
hundred feet beneath the sea floor. Some of the pro-
files, and especially the two that bound the offshore
extension of the Rincon anticline, form scarps in very
young bottom sediments (fig. 17). These bordering
scarps are evident on precision depth records; one lies
about 1% miles south of Platform A, the other about
2 miles north.

Three short gravity cores collected in unconsolidated
sediments across the axis of the anticline in the
vicinity of Union Platform A (fig. 17) penetrated a
shell-rich zone. The shells occurred from 0—4.7 inches
in core SB—2, 5.3—6.6 inches in SB-5, and 98—160
inches in SB—6. Meyer Rubin of the US. Geological
Survey dated these shells by using the radiocarbon
method. The following ages were obtained: SB—2,
8,750: 300 years(W-2297); SB—5, 13,140:350 years
(W-2298); SB-6, 13,920:350 years (W-2299). The
locality Of core SB-6 is just north of the south boundary
fault of the Rincon trend. Because this fault has
produced a scarp in the bottom sediments, it probably
has moved since the shells were deposited. Core SB—2
is 3,300 feet south of the north boundary fault of the
Rincon trend. Again, the presence of a scarp indicates
that faulting may have occurred less than 83501-300
years ago. The facts that the scarps are preserved
in relatively soft bottom sediments, and that move-
ment presumably occurred after the shell layer was
buried at core SB—6, suggest that the last movement
on these faults may have been more recent than the
radiocarbon dates.

The fault scarps indicate Holocene tectonic activity,
some of which may have been accompanied by felt
historic earthquakes in the Santa Barbara Channel.
At least two earthquakes of magnitude 6.0 or larger
have occurred in the channel; both were large enough
to have resulted in surface faulting.

FUTURE EARTHQUAKES

Although the Santa Barbara Channel region is not
known to have been the site of a great (magnitude>
8.0) earthquake, the historic record shows that it has"
experienced several severe shocks. In addition, the
geologic record shows that a high level of tectonic
activity has continued at least through late Tertiary
and Quaternary time.

The history Of destructive earthquakes provides an
indication of what might happen in the future, but
due to the small number of such events the record
does not provide a statistically reliable basis for pre—
diction. In many areas, however, the number of large
earthquakes that occur in a region is simply related
to the number of small earthquakes. More specifically,
the numbers of shocks Of different magnitudes are

related by the equation

log10N= a — bM
where M is the Richter magnitude, N is the number
of events greater than magnitude M, and a and b are
constants that vary with the seismic region being
considered (Richter, 1958).

Allen and others (1965) found that for the southern
California region (Bishop to Ensenada) the smaller
earthquakes provide a fairly good estimate of the rate
of occurrence of the larger events. They calculated
that on the average a magnitude 6.1 earthquake
should occur each year in this entire region, and a
magnitude 8.0 earthquake should occur once in 52
years. Such a great earthquake anywhere in southern
California probably would have destructive effects in
the Santa Barbara Channel region. Its aftershocks,
many of which also would be destructive, might be
expected to occur over an area the size of southern
California.

The record of small shocks could also be used to
estimate the frequency of occurrence of large earth-
quakes in the Santa Barbara Channel region. How-
ever, Allen and others (1965) found that for other
areas of southern California such an analysis was
unreliable and in some places misleading. The best
indicator of future activity in the channel region,
then, is the historic record.

Since 1900, two earthquakes of magnitude 6 have
occurred in the area (in 1925 and 1941). No magnitude
7.5 earthquakes are definitely known, although the
1812 event could have been of that size. The mag-
nitude 7.5 earthquake that occurred in 1927 was
located outside the channel area, but it could have
relieved stored seismic energy in the region, because
it may have been associated with an extension of the
Santa Ynez fault. The magnitude 7.7 Kern County
earthquake of 1952 along the White Wolf fault, which
is also alined transverse to the general structural
trend of California, may have had a similar effect.

ASSOCIATED EFFECTS
GROUND MOTION AND FAILURE

The intensity of ground shaking during an earth-
quake depends largely on local geologic factors; chief
of these are the thickness and physical properties Of
the materials composing the uppermost few hundred
meters beneath the site. In general, the greatest am-
plitudes and longest durations Of ground motion
have been observed on thick, water-saturated, uncon—
solidated materials.

Although field experimental data that bear on
ground amplification are sparse, research has been
been done on seismic waves generated by under-
ground nuclear explosions in Nevada and recorded

64 GEOLOGY, PETROLEUM DEVELOPMENT, SEISMICITY, SANTA BARBARA CHANNEL, CALIF.

in the San Francisco Bay region (Borcherdt, 1969).
Ground-motion amplitudes recorded on soils and sedi-
ments near the margins of the bay were compared
with those recorded on nearby bedrock outcrops.
Maximum amplifications (in the horizontal component
of ground motion) were observed on thick sections
of “younger Bay mud” near the margins of the bay.
At such sites, the peak ground-motion velocities were
as much as 10 times larger than on nearby bedrock
sites; and corresponding peak values in the ratio of
the Fourier spectra (which reflect the duration and
amplitude of shaking) were as much as 30 times larger
than those observed on bedrock. This means that
the amount of power or energy that is dissipated at
a given frequency can be as much as 30 times greater
on unconsolidated sediments than on bedrock.

It is probable that soft sediments in the Santa
Barbara Channel region would also suffer such
amplified shaking. The resulting failure could take
one or more of several forms, such as liquefying,
cracking, lurching, slumping and sliding, and gener-
ating of turbidity currents, with associated effects on
bottom installations in the channel. Failures of this
nature on the sea floor would be most likely to occur
on the steeper offshore slopes. Maximum persistent
sea-floor gradients within the channel are 121/é°—15°
along a short segment of the shelf break about 4 miles
southwest of Coal Oil Point. About 12 miles south
of Ventura, the steepest gradients on this same fea-
ture are as much as 7°. Similar slopes occur about 3
miles north of Santa Cruz Island. For comparison,
the steeper persistent slopes on the south flank of the
Santa Ynez Mountains are about 25° and shorter
slopes are as much as 38° (fig. 3).

TSUNAMIS

The two largest tsunamis known to have been
generated on the western coast of the United States
formed in the Santa Barbara Channel region. The
earthquake of 1812 near Santa Barbara caused waves
that reportedly flooded the lower part of the town,
and the 1927 shock off Point Arguello caused waves
at least 6 feet high. The channel region is not known
to have experienced high waves from externally
generated tsunamis.

Sudden vertical movement of the sea floor is the
most effective means of generating a tsunami, but
alternate methods include horizontal movement on a
sea floor of high relief and submarine landsliding.
Energy radiation by tsunamis is greatest in the direc-
tion perpendicular to the axis of sea-floor deforma-
tion. Because faults in the channel generally are
subparallel to the shoreline, the largest wave ampli-
tudes from a locally generated tsunami probably

would be directed toward the Santa Barbara coast or
the north sides of the islands. In view of the possi-
bility that tsunamis could be produced in the channel
region, their effects on oil installations in Alaska
after the 1964 earthquake will be reviewed.

SEISMIC EFFECTS ON OIL-FIELD INSTALLATIONS

Some of the effects that might accompany earth-
quakes in the channel region have been demonstrated
by several moderate earthquakes in the Los Angeles
area, the Kern County earthquake of 1952, and the
Alaska earthquake of 1964.

In October 1941, a moderate earthquake (magnitude
4.9) affected the southwest part of the Los Angeles
basin. The epicenter (as located instrumentally) was
about 3 miles southeast of the Dominguez oil field on
the Newport-Inglewood zone of faults and folds. 0n
the same date, 15 flowing wells in the western part
of the Dominguez field were damaged by subsurface
movement on and near a previously recognized south-
dipping reverse fault that trends west, subparallel
to the Dominguez anticline. Bravinder (1942) con-
cluded (1) that the faulting was due to relief of pre-
existing stresses near the crest of the anticline., and
(2) that the relieved stresses were chiefly tectonic in
origin.

In November of the same year (1941) a second
earthquake, with a magnitude of 5.4, occurred with
an instrumental epicenter about 4 miles south of that
of the October earthquake. No subsurface damage
was reported, although the Long Beach oilfield is
less than 2 miles from the epicenter; however, surface
installations in the Torrance-Gardena area northwest
of the epicenter were damaged. Two storage tanks
on unconsolidated alluvium were “destroyed” and two
more were badly buckled, a 6—inch oil pipeline (broken
in one place during the October earthquake) was rup-
tured in four additional places, and an 8-inch natural-
gas pipeline was broken. Ground cracks formed near
the broken oil line (Wood and Heck, 1941).

Two and a half years later, on June 18, 1944, two
moderate earthquakes (magnitude 4.4 and 4.5) oc-
curred, with instrumental epicenters between that of
the October 1941 shock and the Dominguez oil field.
Later the same day, 16 oil wells in the Rosecrans
field, 4% miles northwest of the epicenters and 2%
miles northwest of the Dominguez field, were found
to be damaged by subsurface movement on a south-
dipping reverse fault that trends west at a small
angle from the axis of the Rosecrans structure
(Martner, 1948). The faulting of October 1941 and
June 1944 is attributed by Richter (1958) to direct
seismic shaking or readjustment of the local strain
pattern.

SEISMICITY AND ASSOCIATED EFFECTS, SANTA BARBARA REGION 65

Three oil wells in the Inglewood field, also located
along the Newport-Inglewood zone, were damaged
during two small earthquakes (magnitudes 3.4 and
3.0) in February and March, 1963 (Hudson and Scott,
1965). The damage occurred at depth along pre-
viously recognized faults, but the instrumentally
located epicenters were about 6 and 17 miles away.
Hudson and Scott (1965) imply that the subsurface
displacements at Inglewood were triggered by the
earthquakes.

Oil pipelines, storage tanks, and subsurface instal-
lations were slightly affected by the Kern County
earthquake of July 21, 1952. The magnitude of the
shock was 7.7; damage occurred chiefly on uncon-
solidated alluvium, although pipelines were severed
elsewhere by landslide movements and by repeated
flexing. Other damage included settling of the ground
around wells, which affected the pumping equipment,
and collapsing of casing or kinking of tubing in shallow
wells. The shock also caused collapse of the supports
of two large spherical butane tanks at a gas-cycling
plant and rupture of connecting pipelines and release
of their contents, which led to an explosion and a
costly fire (Johnston, 1955; Steinbrugge and Moran,
1954).

Oil-storage tanks sustained great damage as a
result of the 1964 Alaska earthquake, chiefly from
seismic shaking; in a few places, tanks were also
affected by earthquake-associated subsidence or by
landsliding, and some were affected by seismic sea
waves. Storage tanks were damaged in Anchorage,
Kodiak, Nikiski, Seward, Whittier, and Valdez. At
Seward, ground motion caused almost immediate rup-
ture of the storage tanks on the waterfront, and spills
and widespread fire resulted; a submarine landslide in
the alluvial deposits then carried a large part of the
waterfront, including many of the tanks, into Resur—
rection Bay. The landsliding was followed by seismic
sea waves, which inundated the entire waterfront
area and severely damaged the remaining fuel tanks.
Damage to the tanks was chiefly by seismic vibration,
which caused rupture or buckling; some were totally
destroyed by fire or waves.

Reports indicate that well equipment was not
damaged in the Swanson River oil field and Kenai
gas field. A 12-inch gas pipeline extended 93 miles
from the Kenai field to Anchorage; an 8-mile, 2-pipe
segment embedded in bottom silt of the Turnagain
Arm of Cook Inlet was not seriously damaged, and
only one small break occurred in the entire line. Ex-
tensive rupturing of the gas-distribution system in
Anchorage resulted chiefly from landslides (Eckel,
1967).

The Kodiak—Valdez region was a natural laboratory
for full-scale testing of a number of standard-design
oil-storage tanks, some of which were fully loaded
and others of which were partly loaded. Rinne (1967),
who investigated the damage to tanks in Seward,
Nikiski, and Anchorage, classified the effects as
follows: (1) buckling of the shell (tank wall) near its
base, (2) buckling of conical roofs and top covers,
(3) damage to floating roofs and accessories, and (4)
damage to connecting piping. The buckling response
of the tank shells near the base received the most
study and is attributed to lateral forces that prob-
ably acquired substantial amplification during several
minutes vibration. Rinne (1967) found that standard-
design tanks in the 20- to 70-foot diameter range were
considerably less resistant to buckling than other
sizes; tanks of about 30 feet diameter were found to
be most susceptible. All the damaged tanks were
founded on unconsolidated alluvial deposits. Fisher
and Merkle (1965) suggest that the buckling may
have been due to vertical displacement of the concrete
base. The displacement accelerated the liquid and
increased the fluid pressure acting on the lower part
of the tank.

Seismic sea waves caused much of the damage
after the Alaska earthquake, especially at Valdez
and Seward. High-water marks of about 30 feet
above “normal tide level” were recorded at several
places, including Cordova, Kodiak, Seward, and
Whittier. In addition, a mark of 170 feet was recorded
at Valdez (Grantz and others, 1964, fig. 7). The
effects of the waves were devastating in most of these
areas, but many of the tanks vulnerable to them had
already failed.

OIL-FIELD OPERATIONS

The removal of large volumes of fluid from Ceno-
zoic elastic strata, such as those that contain California
oil reservoirs, has led to complex readjustments with-
in and above the reservoirs. Such readjustments
commonly result in differential subsidence of the
ground surface over and around the reservoir, and,
in some places, in earthquakes and fault displace-
ments. Although these effects may be prevented or
minimized by maintaining original reservoir fluid
pressures through fluid injection during extraction of
the petroleum, fluid injection itself has recently been
recognized as the probable cause of earthquakes in
two places.

More than 40 examples of differential subsidence,
horizonal displacement, or surface faulting have been
associated with the operation of 28 California and
Texas oil fields (Yerkes and Castle, 1969). Maximum

66 GEOLOGY, PETROLEUM DEVELOPMENT, SEISMICITY, SANTA BARBARA CHANNEL, CALIF.

recorded movements are: more than 29 feet of differ-
ential subsidence and 11 feet of horizontal displace-
ment in the Wilmington oil field and 2.4 feet of fault
displacement in the Buena Vista oil field, California.

Differential subsidence is the most common and
widespread of the effects, but it is easily detected
only in shoreline areas where it may result in local
flooding. Where level surveys have determined the
size and shape of the subsidence bowl, the subsided
areas are centered over and extend well beyond the
producing area. Subsidence was first reported in 1926
over the Goose Creek oil field near Houston, on the
Texas Gulf Coast (Pratt and Johnson, 1926). The
most spectacular and costly example of differential
subsidence in the United States is that of the Wil-
mington oil field, where an elliptical area of more than
29 square miles has been affected. Large subsidence
bowls also have been delineated over California oil
fields at Huntington Beach, Long Beach, and Ingle-
wood.

Centripetally directed horizontal displacement of
the ground surface accompanies differential subsi-
dence, but can be precisely documented only by tri-
angulation surveys, and hence has been determined
in only three United States oil fields: Buena Vista,
Inglwood, and Wilmington, all in California. Surface
installations such as foundations, piers, and piles are
most seriously affected by such displacements.

Surface faulting, in addition to being the most con-
spicuous and easily documented effect, may also occur
suddenly, and it is therefore potentially more dam-
aging to oil wells and surface structures. Subsidence-
associated surface faulting is most commonly high
angle and normal, peripheral to the subsidence bowl,
and downthrown on the oil field side; it commonly
trends subparallel to the isobase contours. Examples
of this type have developed over the Goose Creek and
Mykawa fields in Texas and over the Inglewood and
Kern Front fields in California. The surface fault at
Kern Front developed over a preexisting subsurface
fault; the surface break extends for 3 miles and is the
longest known example of this type. Displacement
has been virtually continuous for at least 20 years
and totaled more than 1 foot in 1968.

A thrust fault has formed in response to intense
horizontal compression induced by measured subsi-
dence in a unique example at the Buena Vista oil field
in California. The fault sheared about 20 wells at
depths no greater than 794 feet below the surface and
no further than 1,800 feet from the fault trace, but
the fault has not been detected in numerous other
wells it should intersect if it were a tectonic feature.
Cumulative displacement during 38 years of nearly
continuous movement totals more than 2.4 feet.

Subsurface effects associated with oil-field opera-
tions also have been observed at the Wilmington oil
field. In the central part of the field, sharply defined,
nearly horizontal shear movements occurred at aver-
age depths of 1,550 and 1,770 feet in December 1947
and November 1949 (Frame, 1952). The movements
were recorded at Pasadena, 28 miles away, as seis-
mograms that were characterized by unusually large
developments of long-period motion, suggestive of
a shallow focus and lack of sharpness at the beginning
of the motion (Hudson and Scott, 1965). Oil wells
intersected by the slippage surfaces were damaged
during each event; the maximum horizontal displace-
ment in each event was about 9 inches (Frame, 1952),
but the sense of displacement was not recorded. The
November 1949 event was a major economic disaster,
involving 302 wells, chiefly in the central part of the
subsidence bowl; damages exceeded $9 million. Sim-
ilar, less costly events also occurred in August 1951
and January 1955.

Fluid injection seems to have caused earthquakes
in at least two places. The injection of water into a
12,000-foot deep well at the Rocky Mountain Arsenal
northeast of Denver, 0010., is generally considered
to have initiated the earthquake sequence that began
there in 1962 (Healy and others, 1968). Three of
these earthquakes had magnitudes greater than 5 and
resulted in minor damage. The probable cause of the
earthquakes was weakening of rock through increased
pore pressure, which allowed natural rock stresses to
be released. Another situation that possibly is similar
to that in Denver was subsequently recognized in the
oil field near Rangely, Colo. (Healy and others, 1968).
The earthquakes there occurred in areas of high-
pressure gradients generated by injection of water
for purposes of secondary recovery.

SUMMARY

The Santa Barbara Channel region is seismically
active: since 1900 it has experienced two earthquakes
of magnitude 6, and in 1812 it was the site of a shock
that may have attained magnitude 7. Several earth-
quakes greater than magnitude 7 are known to have
occurred in nearby regions of California. Tsunamis
have been generated in the channel region; however,
none was associated with the magnitude 6 earthquakes
of 1925 and 1941, which were located under the chan-
nel. Earthquakes of magnitude 6 and larger can be
expected to occur in the future in the vicinity of the
channel, and it would be consistent with past behavior
if several such events occurred in the next century.
At present it is not known which of the several chan-
nel faults are seismically active, because the quality

SEISMICITY AND ASSOCIATED EFFECTS, SANTA BARBARA REGION 67

of the existing seismograph network does not allow
accurate epicenter location. The possibility must be
recognized that natural earthquakes or tectonic de-
formation could occur in the channel region and mis-
takenly be associated with oil-field operations. In
the past, onshore southern California oil wells have
been damaged by subsurface faulting during natural
distant earthquakes, as well as by locally induced sub-
surface and near-surface faulting. No surface spills
have resulted from any of these events. Surface in-
stallations, chiefly storage tanks and pipelines, have
been damaged by the effects of seismic shaking during
both moderate- and large-magnitude earthquakes.

A large earthquake (magnitude 7 or greater) in the
Santa Barbara Channel region would cause intense
shaking with associated ground deformation and fail-
ure, particularly in artificially-filled areas, alluviated
valleys, and unstable hillside slopes. The resulting dam-
age to manmade structures would no doubt be great,
especially during the wet season when water satu-
rated ground would slide more easily. Oil installations
would probably also suffer damage, but not out of
proportion with other damage. Effects from such
damage can be reduced by certain reasonable precau-
tions, many of which are standard practice. The
hazards to oil installations, in order of what is con-
sidered to be decreasing importance, are tabulated
below.

Hazard Remarks
Rupture of storage tanks re- This hazard can be minimized
sulting in leakage and fires. by: (1) Selecting firm

ground for necessary stor-
age areas, (2) designing
storage tanks to withstand
earthquake forces, (3) using
only the minimum number
of tanks necessary, (4) con-
structing well-engineered
containment dikes for ade-
quate volumes, and (5) pro-
viding fire equipment
adequate to cope with nu-
merous, simultaneous fires.

Fracture of ground resulting This hazard exists irrespective

Hazard—Continued

Damage to oil wells, such as

sheared casings, resulting
in oil leakage into the ocean.

oil from the platforms to
shore resulting in oil leak-
age into the ocean.

Partial or complete destruc-

tion of a drilling platform
by an earthquake or tsunami.

Remarks—Continued

Many wells have been sheared

by movement in California
without causing serious
leaks. In many places the
effect of the movement is
to pinch off the well casing,
which would actually inhibit
leakage. The possibility of
leakage caused by fault
movements in the Santa
Barbara Channel region,
however, cannot be ignored.
If high subsurface pressures
were released to the sur-
rounding rocks in shallow
reservoirs and fractures
formed to the sea floor, a
leak could result. Proce-
dures for coping with an
event such as this are simi-
lar to those described for
the preceding hazard.

Rupture of pipelines carrying This type of accident would

release only a limited vol-
ume of oil. A break in the
deeper parts of the pipeline
would release less oil than
a break near shore, but
would probably be more
difficult to repair. Present
regulations require cutoff
valves in the pipelines to
prevent further oil pumping
if a leak occurs. The volume
of oil carried in an existing
6-mile-long pipeline owned
by Phillips Oil Co. is 515
barrels per mile; a Union
Oil Co. pipeline 101/; miles
long contains 731 barrels
per mile.

The major loss in platform

destruction would be a fi-
nancial loss to the producer
with minor danger to the
environment unless wells
are at critical stages of

in oil migration from depth
to the surface and into the
ocean.

of the oil operations and
would normally be consid-
ered “ an act of God;” how-
ever, the possibility exists
that an earthquake could
reopen cracks or reactivate
leaks that originated from
oil field exploitation.
Equipment for collecting
oil both from the ocean sur-
face and from the leak at
the sea floor, techniques for
plugging leaks, and oil-slick
dispersants can reduce ef-
fects from this hazard.

drilling or development.
Completed wells have chokes
and automatic cutoff valves
at the sea floor. Their
control does not depend on
the integrity of the plat-
form. Uncompleted wells
present special problems
and must be dealt with as
special problems. It is
noteworthy that platforms
have been destroyed by gulf
coast hurricanes and have
not resulted in significant
oil spills.

68 GEOLOGY, PETROLEUM DEVELOPMENT, SEISMICITY, SANTA BARBARA CHANNEL, CALIF.

Operators have provided the information that plat-
forms on offshore Federal leases have been designed
by engineering consultants in conformance with
regional construction code standards. For example,
the platforms on Dos Cuadras field have a freeboard

that exceeds the height of any predicted storm wave
or tsunami at that location and are designed for a
seismic load factor of 0.15 g (maximum ground
acceleration).

GEOLOGY, PETROLEUM DEVELOPMENT, SEISMICITY, SANTA BARBARA CHANNEL, CALIF.

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APPENDIX A

History of Well No. A-21, [ease OCS P—024l, as Compiled by M. V. Adams,
Petroleum Engineer, U.S. Geological Survey, June 1969

The notice to drill this well was approved by the
U.S.G.S District Engineer on January 9, 1969. The
coordinates of the rotary table were X 2984,848 and
Y: 804,198 with the proposed bottom hole coordinates
of X =984,715 and Y=803,750 at a measured total
depth of 3,455’ KB(3,179’ BOF), or 3,400’ KB(3,124’
BOF) true vertical depth.

There is 20”, 104.13 lb conductor driven to 291’
KB(15’ BOF). The well was spudded with drilling
mud at 4:00 pm. on January 14, 1969, using the Peter
Bawden vertical rig. A 12%” directional hole was
drilled to 520’ KB(244’ BOF) with full returns. The
hole was opened to 17%” and a string of 13%”, 61 lb,
J -55, surface casing was run to 514’ KB(238’ BOF).
The casing was cemented with 300 sacks of class “G”
cement with 25 lb of Gilsonite per sack added followed
by 100 sacks of class “G” neat cement. Cement returns
to the surface were obtained.

While standing cemented a 13%”, 3,000 psi working
pressure, Shaffer unitized well head was installed.
Blowout prevention equipment consisting of a 12”
series 900 double Shaffer gate with blind and 4%"
pipe rams and a 12” series 900 GK Hydril was installed
and tested prior to drilling out the 13%” shoe.

Between January 17 and January 28, a 12%” direc-
tional hole was drilled to a total depth of 3,479’
KB(3,203’ BOF) measured depth. A directional survey
(apparently the last taken) at 3,222’ KB(2,946’ BOF)
showed a true vertical depth of 3,143.67’ KB(2,867.67’
BOF), a deviation of 2°30’ and a direction of N. 19° W.
The coordinates of the hole at this point were 417.72’
south and 134.59’ west of the surface location.

On the morning of January 28, the drilling crew
started out of the hole to run logs. It was reported
that the first five stands of drill pipe pulled tight but

the next three pulled free. However, while breaking
out the eighth stand (at 10:45 am.) the well started
blowing through the drill pipe. An attempt was
made to stab the inside blowout preventer but the
well was blowing too hard to do it. They then set
out to pick up the kelly to stab it into the drill pipe
but in picking it up the rotary hose caught on a bull
plug in the standpipe and broke it off. With the
standpipe open it was considered too great a fire
hazard to pursue stabbing the kelly. Accordingly,
they picked up the drill pipe with the elevators until
a tool joint was above the pipe rams, closed the rams
to hold the pipe while they unlatched the elevators,
then opened the rams and dropped the drill pipe down
the hole. They then closed the blind rams (at 11:00
am.) to shut the well in.

Shortly after closing the well in the surface pressure
was 400 psi and boils of gas began to appear on the
surface of the water. An attempt was made to kill
the well by pumping 90-lb mud down the casing
through the kill line and bleeding off the gas through
the choke line. This operation was not successful so
stripping drill pipe into the hole, under pressure,
through a pair of GK Hydril blowout preventers was
commenced.

By late January 29 adequate drill pipe had been
stripped into the hole and was successfully screwed
into the fish. It was attempted to circulate through
the drill pipe but the bit was plugged and even at
5,000 psi circulation could not be established. An
attempt was then made to pull the drill pipe but al-
though it did move some 7’, it would not pull free.

Several attempts were made to back off the drill
pipe deep enough to kill the well with mud but in
each instance the pipe backed off above the top of
the original fish. During this operation the pressure
on the casing was on the order of 180 psi which
would drop to 40 to 80 psi by flowing through the
casing. Also, sea water was pumped into the casing
at rates as high as 15 barrels per minute which would
drop the pressure to 60 psi but it would quickly build
back up to 180 psi.

When the drill pipe was originally snubbed into the
hole to screw into the fish it was, of course, necessary
to blank off the inside of the drill pipe at the bottom
of the first joint. This was done with a Gray inside
blowout preventer. Then, since the drill pipe could
not be backed off deep enough to kill the well it was
decided to mill out the Gray float. The milling was
done using a 2%” mill run on 2%” tubing driven by a
power swivel. Milling began at 4:30 am. on February
3, at a depth of 731’ KB(455’ BOF).

The milling was completed later in the day and a
Schlumberger 1%5’ scallop gun was successfully run

72 GEOLOGY, PETROLEUM DEVELOPMENT, SEISMICITY, SANTA BARBARA CHANNEL, CALIF.

to a depth of 2,942’ KB(2,666’ BOF). Since there was
heavy weight drill pipe up to 2,913’ KB(2,637’ BOF),
‘it was decided to perforate in the lighter pipe above
this point. Accordingly, the pipe was perforated with
97 holes, 0.34" in diameter, in the interval from 2,860’—
2,883’ KB(2,584’—2,607’ BOF). Before perforating,
the drill pipe was pressured to 500 psi which bled to
zero after perforating, indicating that the perforating
job had succeeded.

While rigging up to kill the well, sea water was
pumped down the drill pipe at a rate of 23 barrels per
minute and a pressure of 2,100 psi with no indication
that it was killing the well. On February 5, 100
cubic feet of water with green dye was pumped into
the drill pipe and displaced with 685 barrels of water
at a rate of 14 barrels per minute and a pressure of
1,000 psi. An additional 100 cubic feet of dye water
was pumped down the casing and displaced with 565
barrels of water at a rate of 14 barrels per minute
and a pressure of 1,050 psi. None of this dye appeared
on the surface of the ocean. The dye water was fol-
lowed with 250 barrels of 100-lb mud pumped at a
rate of 8 barrels per minute and a pressure of 275
psi. After pumping the mud the casing pressure was
180 psi. Pumping sea water down the drill pipe was
continued during the night of February 5, and part
of the day of February 6, while assembling and hook-
ing up additional HOWCO pumping units on the plat-
form and waiting on a mud barge with an additional
supply of mud. While pumping down the drill pipe
the annulus was blown down from 190 psi to zero in
10 minutes but when it was closed in, it built back up
to 190 psi in 2 hours.

After checking out and testing the HOWCO pump-
ing units 1,000 barrels of sea water was pumped down
the drill pipe at a rate of 27 barrels per minute and
a pressure of 2,500 psi. The water was followed with
210 barrels of 116-lb mud pumped at a rate of 27
barrels per minute and a pressure of 2,650 psi. At
this point a line blew off the fracing head and it was
necessary to shut down the HOWCO pumps to repair
it. After effecting repairs the mud in the drill pipe
was displaced with 230 cubic feet of sea water and
the well was shut in. During the entire operation
the casing pressure on the well had remained at 190
psi. However, after pumping the mud the bubble at
the east end of the platform was noticeably smaller
but after 10 minutes it had returned to its original
Size.

In the meantime a massive effort had been made
on the part of essentially all of the operating and
service companies in the area to assemble mud, equip-
ment and cement for a maximum effort to kill the
well. This effort commenced at 11:05 am. on February
7, by pumping sea water with dye, calcium chloride
water and mud down the drill pipe while repairing
leaks in lines and organizing the pumping operation.
Steady pumping down the drill pipe began at 4:00
pm. and by 5:00 pm. all nine HOWCO units were in
operation pumping mud down the drill pipe at a rate
of 30 barrels per minute and a pressure of 3,750 psi.
At this time the rig pumps started pumping mud
down the annulus. By 5:30 pm. the bubble began to
decrease and the well was eventually killed with 13,000
barrels of 90-1b to 110-lb mud.

GEOLOGY, PETROLEUM DEVELOPMENT, SEISMICITY, SANTA BARBARA CHANNEL, CALIF.

APPENDIX B

Seepage at Lease OCS P—0241 estimated by the U.S. Geological Survey for the

73

 

 

 

 

period March 22 to August 31, 1969

Time eriod Days Barrels recoveredI 2 Barrels lost (estimated)2 Seepage (estimated)2

From To elapsed Total Daily rate Total Dally rate Total Daily rate
Mar. 223 Apr. 2 12 38 3.0 3211 27 360 30
Apr. 3 May 2 30 220 7.3 681 22.7 901 30
May 3 May 22 20 351; 17.7 2H6 12.3 600 30
May 23" June 15 23 599 25.8 101 u.1+ 691 30
June 155 June 18 1+ 37 9.2 83 20.8 120 30
June 19 June 28 8 182 22.8 57 7.2 239 30
June 275 June 28 2 12 6 48 zu 60 30
June 29 July 1 3 51 17 39 13 90 30
July 25 --— 1 l 1 29 29 30 30
July 3 July 13 11 253 23 77 7 330 30
July 155 July 15 2 u 2 36 18 1+0 20
July 186 July 31 16 128 8 112 7 2u0 15
Aug. 16 7 Aug. 31 31 86 2.8 221+ 7.2 310 10
Totals ------ 153 1,950 --- 2,057 —-- 0,011 ——-

 

1Measured oil recovery (net barrels) from
hoods, funnels, and tents, plus oil recovered on
surface by skimming boats. Oil slicks, monitored
by photographs and daily observations.

One barrel equals H2 gallons.

3First installation of collecting devices.

”Large tents added east of Platform A.
Hose line damaged.
6Remedial shallow drilling and grouting pro—
gram in progress.
7Large tent, 800 feet east of Platform A,
damaged.

APPENDIX C

Drilling Programs Authorized for Lean OCS P-0241 Following Recommendations of the Presidential Advisory Panel Transmitted June 2, 1969

 

 

 

Programs authorized June 9, 1969
Drilling Producing Perfs. Casing depth—~vertical penetration, in feet, for in—
Well Rig distance, zones (RT) dicated casing diameter, in inches
1n feet 20 16 13 3/8 10 3/” 9 5/0 7
. (cement
(drive) (cement) conductor) (cement) (cement) (cement)

A-3--- Vertical 1,260 Brown-- 608-1,1H0 19 10” 276 801 --- ---

PIUg

back

1,159
A—22-— Vertical U75 Red-——- 3Hu-U7l 18 107 -—- 195 --— —-—
A—2'+——Vertical 1,092 Brown-- 578-l,082 101 -—- 255 797 --- ——-
A—HU-— Slant 1,971 Brown-- 713—1,677 10 101 261 832 --- —--

P1u€

back

1,705
B—l3--Vertica1 1,28” Brown-- 738—l,279 15 92 310 886 -—— ---
B—18——Vertica1 1,150 Brown 6U8—53 15 98 299 --— 867 -——

core test 772—97

hole and 1,089-8u

shut-in

B—30—-Vertical 1,275 Brown—- 670-1,264 1% 101 315 861 —-— -—-
B—H0--Slant 1,610 Brown—- 813—1,601 90 --- 332 900 —-— ---
B-U7—- Slant 1,588 Brown-- 826—J,395 10 108 28“ 811 -—- ---

PIUE

back

1,H00

 

74 GEOLOGY, PETROLEUM DEVELOPMENT, SEISMICITY, SANTA BARBARA CHANNEL, CALIF.

Programs authorized August 1, 1969

 

 

Drilling Casing depth-—vertica1 pentration, in feet,
Well Rig distance, Producing zones Perfs. for indicated casing diameter, in inches
in feet (RT) 20 16 13 3/8 10 SH; 7
(cement

(drive)(cement) conductor) (cement) (cement)

 

Upper zones

 

A-37-— Slant —————— 2,300 Yellow 1,385—2,210 10: 101 23% 857 1,7uu
Purple E

A-u3-— Slant ------ 2,500 Yellow l,350—2,385 10 100 235 855 1,975
Purple B
Yellow

B-H1-- Slant ------ 2,475 Yellow 1,u70—2,uoo 10: 98 395 879 1,831
Purple E
Yellow

B—u3-- Slant ------ 2,750 Yellow 1,565—2,662 12 100 237 827 1,912
Purple E
Yellow

 

Lower zones

 

A—30-- Vertical—-— 3,500 Purple 2,180—3,u38 10: 100 255 1,052 3,107
Orange B—2
Green

A-36—— Vertical-—- ”,250 Purple 2,810-M,160 11 100 255 1,015 3,HH5
Orange E—l
Green

B—29-- Vertical—-- 3,900 Purple 2,060.3,818 10: 100 360 1,139 3,330
Orange E—l
Green

B-2-—— Vertica1——- 9,150 Orange 2,960-4,090 10: 101 306 1,151 3,231

Green E-l

 

GEOLOGY, PETROLEUM DEVELOPMENT, SEISMICITY, SANTA BARBARA CHANNEL, CALIF. 75
APPENDIX D

Status of wells drilled from Platform A on Lease OCS P—0241, May 10, 1969, showing selective pressure

 

 

drawdown zones authorized
Drilling Producing Perforations Production
Well Rig distance, zones (drilled depth, in feet) (bbl oil per day)
in feet
A—20-—-- Vertical ------- 3,673 Purple 2,131—3,427 2,110
plug Orange
back Green
3,uu2
A-Q1---- Vertical ------- 1,081 Brown 591-1,070 56H
(redrill)
A-25---— Vertical ------- ”,550 Orange 2,433-3,876 1,056
plug Purple
back Orange
3,900 Green
A-38---— Slant ---------- 3,030 Brown BBS—1,010 Shut-in
Plug
back
1,086
A-ul-h-- Slant ---------- 3,010 Brown 9H6¢1,916 982
plug Yellow
back
1975

 

76

GEOLOGY, PETROLEUM DEVELOPMENT, SEISMICITY, SANTA BARBARA CHANNEL, CALIF.

APPENDIX E

Blowouts from outer Continental Shelf drilling and workovers since enactment of OCS Lands Act of 1953

Wells drilled for oil and gas on OCS—1953 to Aug. 1, 1969 (excludes 25” wells drilled prior to 1953 and

102 salt and sulfur wells):
Drilling wells —————————————————————————————————————————————————————————————————— 133
Wells completed for production or service (732% zone

 

 

 

completions: 5507, oil; 1717, gas) -------------------------------------------- H028
Dry or abandoned holes ---------------------------------------------------------- 3299
Total wells drilled --— ———-r ----------------------------------------- 7860
Area and block, Type blowout, depth, How Volume
lease and well No., and and out—of—control controlled oil spill Extent of damage
No. operator period
Gulf coast region

1———— Vermilion Block 26 Gas; 11,H35'; Drilled ————————— Lost platform,
OCS 029, well A—l 6—8—56 to relief rig, and two
Union Oil of Cali— 11-7—56. well. wells by crater.

fornia

2———— Eugene Island Block 175 Gas; 11,290'; Bridged—-— --------- Caught fire but
OCS 0H38, well A-6 Sin- 10—19—57 continued with

Clair Oil 8 Gas Co. (11 hours). same rig.

3———— South Pass Block 27 Gas; 1,869'; Bridged-—— ————————— Caught fire but

OCS 0353, well 25 6—1H-58 (2 little damage.
Shell Oil Company hours).

u-——— West Delta Block #5 Oil; (swabbing); By last of (None re— Explosion, then

OCS 0138, well E—7 10-15—58 to three ported.) fire. Two other
CATC 11—21—58. relief wells also. Lost
wells. platform. Seven

casualties.

5-——— S. Timbalier Block 13” Gas; 4,880'; Bridged-—- ————————— Caught fire but
OCS 0061, well D—l 7-27—59 (4 hours). little damage.
Gulf Oil Corpora-

tion

6—-—- Vermilion Block 115 Gas; 13,001', Bridged——— ————————— None reported.

OCS 0770, well 1 11—18—60 (M
Phillips Petroleum hours).
Co.

7-—-— Grand Isle Block 9 Gas; (shallow); Ceased---- ————————— Fire. Lost plat—
OCS 035—8, well l—3H-B 3—18—62 (36 form and rig.
Freeport Sulphur Co. hours).

8—--- West Delta Block 28 Gas; 10,871', Mud ———————————————— No damage.

OCS 038”, well 3 l—lS-Gu (12
Chevron Oil Company hours).

9-——— West Delta Block 117 Gas and oil; (com— Bridged——— (None re— Caught fire. Plat—

OCS-G—llUl, well A-5 pleted); 1-20—6H ported.) form damaged ex-
Gulf Oil Corporation to 1—27—6”. tensively.

10--- Eugene Island Block 273 Gas; BBN'; 6—30—6u Ceased---— ————————— Explosion, fire.
OCS-G—0987, well u (2 days) Drilling-vessel
Pan American Petroleum sank. Casuala

Corp. ties 22.

11-—— Eugene Island Block 158 Gas; 15,867'; Bridged--- ————————— (None reported.)

OCS-G-1220, well B-3 3—15—65 (5
Shell Oil Company days).

12——— S. Marsh Island Block Gas; (shallow); Ceased-—-- --------- (None reported.)

”8 OCS 0786, well B—u 9—16—65 (Several
Gulf Oil Corporation days).

13——— S. Timbalier Block 21 Gas; 11,716'; Ceased-—-— ————————— Removed rig before

OCS 0263, well 70 9-25-65 to we11.cratered.
Gulf Oil Corporation 10-8—65.

1H—-- Ship Shoal Block 208 Oil; (workover); Installed (None re— (None reported.)
OCS 6-1294 2—5—66 (15 min.). valve. ported.)

Union Oil of Cali—
fornia

15——- Eugene Island Block Oil and gas; Ceased———— (None re— Little damage.

275 OCS 6—0988, well A—9 10,551'; ported.)
Texaco Inc. 2-13—66 (2 days).
16-—— S. Timbalier Block 57 Gas; 1,477'; Bridged-—- —————————— One corner plat—

OCS 020, well C-l2
Humble Oil 8 Refining
Co.

4—17-57 (8 hours).

form settled.

 

GEOLOGY, PETROLEUM DEVELOPMENT, SEISMICITY, SANTA BARBARA CHANNEL, CALIF. 77

 

 

 

 

 

Area and block, Type blowout, depth, How Volume
lease and well No., and and out—of—control controlled oil spill Extent of damage
operator period
Gulf coast region-—Continued
l7--— S. Timbalier Block Oil; (workover); Closed (None re- Caught fire, rig
OCS 0463, well J-15 2-21—68 (1 hour). valve. ported.) destroyed.
Gulf Oil Corporation
18--— South Pass Block 62 Gas; 8,u26; H—68. Cemented ————————— (None reported.)
OCS 6—129” drill —————————
Shell Oil Company pipe.
19—-— Grand Isle Block H3 Gas; 1H,18H'; 9—68 Bridged--- ————————— (None reported.)
OCS 0175 (several days).
Continental Oil Co.
20—-- S. Timbalier Block 67 Gas; 910'; 9-28-68 Bridged——- ————————— Caught fire.
OCS 020, well C-lB (9 hours). Later removed
Humble Oil 8 Refining rig, platform
Co. settled.
21——- S. Marsh Island Block Gas; 387'; 10—30-68 Bridged——— ————————— (None reported.)
38 OCS 078M (1 day).
Pan American Petroleum
Corp.
22--- Vermilion Block 119 Gas; 9,5uu'; Bridged——— --------- (None reported.)
OCS OM87, well D—ll\ 11—24—68
Continental Oil Co. (12 hours).
23--— Vermilion Block H6 Gas; 8,158' 3—lH—69 Mud ———————————————— No. damage.
OCS 0709, well A—3 to 5—16—69.
Mobil Oil Corporation
2H——- Ship Shoal Block 72 Oil; 9,03H', Capped-——— 900 bbl No damage.
OCS 060, well 3 Mobil 3-16—69 to per day;
Oil Corporation 3—19—69. 2,500 bbl
total.
Pacific region
l--—— Santa Barbara Channel Oil and gas; 3,H79'; Cemented—- 300—500 bbl (None reported
OCS P-02Hl, well A—21 1—28—69 to per day on platform.)

Union Oil Co. of Cali-
fornia

2—7-69.

 

U. S. GOVERNMENT PRINTING OFFICE : 1869 O - 365-228

UNITED STATES DEPARTMENT OF THE INTERIOR
GEOLOGICAL SURVEY

120° 30’

        
  

120°00’ 119°30’

’1 my ‘ l” u. ,

34°3o'k M , / I

‘h-In-n.

Carrington
;‘ Paint '

 

34°00’

 

 

Shoreline from US. Geological Survey Maps

NI 10—6,9 (Santa Maria) and NI 11—4 (Los Angeles)
Bathymetry from U 8 Coast and Geodetic

Survey Maps 1206N—15, 1306N—19, 1306N—20

GENERALIZED GEOLOGIC MAP OF THE SANTA BARBARA CHANNEL REGION

TRUE NORTH

 

SCALE 1:250 000

APPROXIMATE MEAN
DECLINATION, I969

 

 

 

 

5 0 5 IO 15 NAUTICAL MILES
: . E J g I
5 0 5 IO 15 STATUTE MILES
‘ l
5 O 5 10 15 KILOMETERS

 

F—I l—l r——i L . ,
BATHYMETRIC CONTOUR INTERVAL 50 METERS

120030, 120000! 119030,

34°OO'

 

INTERIOR—GEOLOGICAL SURVEY. WASHINGTON, D.C.—1969—G70137

Onshore geology from Santa Maria Sheet (Jennings 1959)
and Los Angeles Sheet (Jennings, in press) of the

Geologic Map of California; modified in places.

Offshore geology from unpublished reconnaissance
acoustical surveys by the US. Geological Survey

and other sources

PROFESSIONAL PAPER 679

PLATE 1

EXPLANATION

    

“ALI

Holocene deposits

 

Upper and lower Pleistocene
marine and nonmarine deposits

 

marine rocks

Upper, middle, and lower
Miocene marine rocks

 

AL 1‘
7va:7
"7 L

Miocene volcanic rocks

Oligocene marlne
and nonmarine rocks

Paleocene and Eocene
marine rocks

Cretaceous marine rocks

 

 

 

 

 

 

Pre—Cretaceous (?)
basement rocks

 

Contact

Fault
Dashed ofi‘shore and where inferred on-
. shore; dotted where concealed onshore;
queried where doubtful. Arrows show
lateral movement. Bar and ball on
downthrown side

___l___

Axis of anticline
Solid onshore; dashed ofishore

 

UNITED STATES DEPARTMENT OF THE INTERIOR .
GEOLOGICAL SURVEY .

PROFESSIONAL PAPER 679

 

     

 

120°30’ 120°oo' I I 119°3o' .
| I
3mg ' M __
30' V ' O U i '
REFUGIO COVE . ' N T A
Gaviota ' b d d . ' I
CUARTA AESR'A V . (a an one ) CAPITAN N S

   

OFFSHORE
POINT CONCEPTION .

Capitan
OFFSHORE D . V

\LAS VARAS. Keenan
. (abandoned) (abandoned)
GLEN ANNIE Goleta
r<aband°n°3d> ‘3 LA GOLETA

(abandoned) SANTA . .
BARBARA Monteclton . (abandoned) . . .
n

Summerland SUMMERLAND

’ E-PRC-3242

_ - . N MESA .« . Ca interia
‘% . V . . a; » . I:I rp

IIIWMM .

 

SAN MIGUEL Devils Peak
ISLAND A
337 SANTA CRUZ ISLAND
SANTA ROSA ISLAND
120

120°oo' ‘ 7 7 H i 7 7 ”119°30'
Shoreline from US. Geological Survey Maps
NI 10—6,9 (Santa Maria) and NI 11—4 (Los Angeles)

Bathymetry from US. Coast and Geodetic
Survey Maps 1206N—15, l306N—19. 1308N—20

MAPSHOWING OIL AND GAS FIELDS,LEASED AREAS, AND SEEPS
IN THE SANTA BARBARA CHANNEL REGION

TRUE NORTH

 

APPROXIMATE MEAN
DECLINATION,1959 ~

SCALE 1:250 000

 

 

 

 

5 o 5 lo 15 NAUTICAL MILES
I; [.__ _| ——| *I i
5 o 5 Io 15 STATUTE MILES
gfi. 1—. I
I .
5 o 5 10 15 KILOMETERS
l: ’_| H ———-1 I

 

 

BATHYMETHIC CONTOUR INTERVAL 50 METERS

 
 
  
 

Ojai
a

. LION ,
MOUNTAIN

JOAKVIEW CANADA

, TIP TOP
. g LARGA\.
‘WELDON

CANYON

Rincon
Mountain
A

R | NCON
SAN

MIGUELITO

VENTURA
u

WEST
MONTALVO

 

 

34°
30’

PLATE 2

EXPLANATION

4.

Oil field

0
Gas field
I HOLLY
Drilling platform
0
Oil and (or) gas seep
x
Brea and (or) oil sand deposit

Three—mile limit

 

 

 

Leased Federal parcels

 

 

 

 

 

Leased State parcels
P—0215
Federal lease number
PRC-3403
State lease number

LEASE HOLDER

A . Ashland Oil and Refining Co.
Colorado Oil and Gas Corp.
J. M. Huber Corp.

Husky Oil Co.
Kewanee Oil Co.
Midwest Oil Corp.
Pauley Petroleum Inc.

B . Atlantic-Richfield Co.

C . Atlantic-Richfield Co.
Humble Oil and Refining Co.
Standard Oil Co. of Calif.

D . Atlantic-Richfield Co.
Marathon Oil Co.

Getty Oil Co.

E . Atlantic-Richfield Co.
Mobil Oil Corp. .

F . Atlantic-Richfield Co.
Mobil Oil Corp.

Signal Oil and Gas Co.

G. Atlantic-Richfield Co.

Pan Petroleum Co., Inc.
Standard Oil Co. of Calif.

H . Atlantic-Richfield Co.
Signal Oil and Gas Co.

| . Atlantic-Richfield Co.
Standard Oil Co. of Calif.

J . Cities Service Oil Co.
Continental Oil Co.

Phillips Petroleum Co.

K . Continental Oil Co.

L .- Gulf Oil Corp.

Mobil Oil Corp.

M. Gulf Oil Corp.

Mobil Oil Corp.
Texaco, Inc.
Union Oil Co. of Calif.

N. Gulf Oil Corp.

Mobil Oil Corp.
Union Oil Co. of Calif.

0. Gulf Oil Corp.

Union Oil Co. of Calif.

P . Humble Oil and Refining Co.

Q. Humble Oil and Refining Co.
Phillips Petroleum Co.

R. Humble Oil and Refining Co.
Standard Oil Co. of Calif.

S . Humble Oil and Refining Co.
Texaco, Inc.

T . Humble Oil and Refining Co.
Union Oil Co. of Calif.

U. Marathon Oil Co.

Sun Oil Co.
Sunray DX Oil Co.
The Superior Oil Co.

V . Mobil Oil Corp.
Union Oil Co. of Calif.

W‘. Pan Petroleum Co., Inc.
Phillips Petroleum Co.

X. Pauley Petroleum, Inc.
Phillips Petroleum Co.

Y . Shell Oil Co.

Z . Shell Oil Co.

Standard Oil Co. of Calif.
AA . Signal Oil and Gas Co.
BB . Standard Oil Co. of Calif.
CC . Texaco, Inc.
DD . Union Oil Co; of Calif.

UNITED STATES DEPARTMENT OF THE INTERIOR
GEOLOGICAL SURVEY

 

 

UNION OIL CO. AND OTHERS
OCS P-0241

 

 

 

 

Union Oil Co.
No. 3
o

 

WEST

Union Oil Co.
No. 3
SEA LEVEL

1000'

2000’

3000’

TD 3565

4000’

Continental Oil Co.

 

 

// No. 4
7" —————————— e ‘
— 7000 Q
/
\
._ 600 w/
Continental Oil Co. /
No. 8 / //

O ,.,,:::1—--—--‘600

/ Union Oil Co.
// o NO- 2 Platform

   
   
  
   
   
   

‘~_
‘~
_‘
“

Union Oil Co.
No. 2

Sea floor

TD 3775

 

. ,
\600 /

Union Oil Co.
Platform Union Oil Co. No. 1
I . No. A-20

Union Oil Co.

 

  
   
       
      
   
 

“Repetto
Formation”

Sun Oil Co.
No. 2

 

    

Union Oil Co.
0 No. 15

Sun Oil Co.

' No.3
’————\ O __\
~800 __\

 

\\

 

 

Modified slightly from map compiled by
the Union Oil Company of California

 

\
\ t
/
W _~~_§

\\

\
\
- Q
Sea floor contact between “Plco” and / §<§ / /
“Repetto” Formations — — \ \ \ \

\

 

 

MAP SHOWING STRUCTURE CONTOURS BASED ON WELL LOGS AND SEISMIC-REFLECTION DATA

l
l
Platform A I
l
l

Union Oil Co. Union Oil Co.
No. A-2O No. 1

Thrust fault

F

Union No. A-21 TD 3479
Bottom projected 450 ft due
north to line of section TD 3671

Bottom projected 50 it due TD 6451
south to line of section

LONGITUDINAL STRUCTURE SECTION OF THE RINCON TREND

5000’

6000’

STRUCTURE OF THE DOS CUADRAS OIL FIELD AND CONTIGUOUS PARTS OF THE RINCON TREND

Sun Oil Co.
No. 2

 

TD 4312

   

__ :Pllo Formation n SQQ IIOOI’
u ‘~—~
Repetto Formation .,

TD 4612

SCALE 1:12 000

2000 3000 4000 FEET
I

500 750 1000 M ETERS
' l

 

__ flmer Pliocene

     
   
 
 
    
 

 

" Pico Formation ” I

“Repetto Formation”|

Lower Pliocene

\ _ 4
~ —~—~

  

PROFESSIONAL PAPER 679

 

 

PLATE 5
\ \ _
/ \
/ \\\
/ »~\ \\\\
,v’ ‘ /// \\ \ EXPLANATION
/ / \
SUN OIL CO. AND OTHERS // / \\\\ ________ _
ocs P-024o / / /__\ \~_ Fault
I // // // \\‘\ _________
\_.../ / / \\
\\ // // \\\ Structure contour
‘__._..’/ // \\____._ Solid where drawn on Cmarkerlw/m'zon;
__ / / dashed where drawn on seismic phan-
————“ -2000—-——""/ /’—\\ tom horizon. Contour interval 100
// \\\ feet for solid lines, 200 feet for dashed
_____ /————-‘——~-“/ \\~\\ lines. Based on well logs and seismic-
, 1800 / ————— \\\\\ reflection data.
\ //// . \\
.2 \\‘\\\ ///// ,._—— ————————————————— \ Phillips Pet. Co.
\\\\\ \‘__/ / /// \\ No.4
\\\\\ , -1600 ’ \\ /o/
\\ /” / ______ .
\\\\\\ \‘fl/ ’,//"“*’ T Sun Oil Co.\ 011 sand
' T ———— \\ /____’-—"’" \\ No.15 __________________
\\ \\ ~__. / Oil-water contact
\\\\\ “PICO Sun Oil Co. I C
\\\\ Formation" I \ E-log marker
\\\ \\\ \
\ \\ l
Sun OilCo. \ \\ an Oil Co. “ _____ \ /
\ \ NO. 4 \ \ /
\ \ \\ j / /,» __________
\ \ \ / / //
/
/ \ j / / / // ~\\
/ I / // // // / ,—-\ \
/
// / / / / / // / \\
/ / / / / / / / //~
/ // /// / /// // //// Note: T on thrust fault indicates
/ , // / // // // // / movement toward observer; A,
/ / / / / movement away from observer
/ / /
/
/ // // // / / PET. co.
// // // /// AND
//’/ / / /
/ / / /
// // // // OCS P-OIGS
/// // // //
\__./ /
\ ,,,,, 1400 ~~~~~ \\__.// //
I
l EAST SOUTH platform NORTH
A
Sun Oil Co. Sun Oil Co. Sun Oil Co. I Phillips Pet. Co. Union Oil Co. Union Oil Co. Continental Oil Co.
No. 4 No. 5 | No. 4 No. 4 No. A-20 = No. 4

   

 

 

 

   
    
 
 
 
  

 

 

 

 

 

 

    

 

 

SEA LEVEL
Sea floo-
1000' —
ill’
0 \V
2000' - ‘h.k\_‘
Shallowest oil ’I—‘iw
II\
“I“ 5n:
/7 A
, / a;
3000 — Union No. A-21 I —
TD 3479 '
Bottom projected 50 ft due I "g
east to line of section II? \
|
TD 3671 Bottom projected 150 ft due
Letter symbols are west to line of section
4000 I _ E-log markers _
5000’ — -
TRANSVERSE STRUCTURE SECTION
THROUGH PLATFORM A
TD 13,508
6000 ’ " —

INTERIOR—GEOLOGICAL SURVEY. WASHINGTON, D.C.—1969—G70137