Sinusimn. Al Imagine: ‘ IE. ii Potassium-Argon Geochronology of the Eastern Transverse Ranges and Southern Mojave Desert, Southern California By FRED K. MILLER and DOUGLAS M. MORTON GEOLOGICAL SURVEY PROFESSIONAL PAPER 1152 UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1980 UNITED STATES DEPARTMENT OF THE INTERIOR CECIL D. ANDRUS, Secretary GEOLOGICAL SURVEY H. William Menard, Director Library of Congress Cataloging in Publication Data Miller, Fred K Potassium-argon geochronology of the eastern Transverse Ranges and southern Mojave Desert, southern California. Bflfliqaaflm: p.2u Supt. of Docs. no.: I l9.l6:ll52 l. Potassium-argon dating. 2. Geology-~California ——Transverse Ranges. 3. Geology--California--Mohave Desert. I. Morton, Douglas M., joint author. II. Title. III. Series: United States. Geological Survey; Professional paper ; 1152. GE 08 -M5 55 l. 7 ' 097% 80-60709? For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, DC. 20402 CONTENTS Page Page Abstract __________________________________________________ 1 Discussion and interpretation of apparent ages ______________ 9 Introduction ______________________________________________ 1 General characteristics and distribution of apparent ages 9 Acknowledgments ____________________________________ 3 The zone of discordant ages ____________________________ 13 Geologic setting ___________________________________________ 4 Area of anomalous cooling ages ________________________ 15 San Bernardino Mountains ____________________________ 4 Emplacement or near-emplacement ages ________________ 16 San Gabriel Mountains ________________________________ 4 Other anomalous features of the apparent ages __________ 17 Mojave Desert ________________________________________ 5 Interpretation of apparent potassium—argon ages ________ 18 Rock types dated __________________________________________ 6 Fault offsets of contours ________________________________ 21 San Bernardino Mountains _____________________________ 6 Histograms __________________________________________ 22 San Gabriel Mountains ________________________________ 6 References cited __________________________________________ 24 Southern Mojave Desert ______________________________ 7 Sample localities and descriptions __________________________ 25 Sampling and analytical procedures ________________________ 8 ILLUSTRATIONS - Page PLATE 1. Maps showing generalized geology, sample localities, apparent ages of Mesozoic granitic rocks, and contours of biotite apparent ages, eastern Transverse Ranges and southern Mojave Desert, California __________________________ In pocket FIGURE 1. Map showing selected geographic features of the eastern Transverse Ranges and southern Mojave Desert ______________ 2 2. Map showing relation of age subdivisions to large faults in southern California ______________________________________ 4 3. Diagram showing apparent ages of coexisting hornblende-biotite pairs from pre-Cretaceous rocks ____________________ 15 4. Histograms showing relative abundance of apparent ages in the eastern Transverse Ranges and southern Mojave Desert and in selected structural subdivisions ________________________________________________________________________ 23 TABLE Page TABLE 1. Analytical data and calculated potassium-argon ages of plutonic and metamorphic rocks from the San Bernardino and San Gabriel Mountains and the eastern Mojave Desert ____________________________________________________________ 10 POTASSIUM-ARGON GEOCHRONOLOGY OF THE EASTERN TRANSVERSE RANGES AND SOUTHERN MOJAVE DESERT, SOUTHERN CALIFORNIA By FRED K. MILLER and DOUGLAS M. MORTON ABSTRACT More than 200 potassium-argon apparent ages on minerals from crystalline rocks, chiefly from the San Bernardino and eastern San Gabriel Mountains and the southern Mojave Desert, define an area greater than 10,000 ka in which the potassium-argon isotopic sys- tematics have been highly disturbed. The disturbance or disturb- ances appear to have culminated at different times in different parts of the region, ranging from 57 m.y. ago in the eastern San Gabriel Mountains to about 70 m.y. ago in the southern Mojave Desert. The region can be subdivided into three parts on the basis of potassium-argon dating: (1) An inner area of anomalous ages in which the rocks yield apparent potassium-argon ages that indicate complete or nearly complete resetting of the isotopic system. (2) An outer area in which the rocks yield apparent ages that are, or ap- proach, emplacement ages. (3) A zone separating these two areas from which rocks yield discordant apparent ages on coexisting min- eral pairs. This discordant zone varies in width from about 6 to 12 km and grades inward to rocks reset to the degree that they yield concor- dant potassium-argon apparent ages on coexisting mineral pairs and outward toward rocks that yield near-concordant apparent ages. Rocks from the center and the inner parts of the discordant zone yield the most discordant apparent ages. Contouring of the apparent ages defines the extent of the reset region that occurs on both sides of the San Andreas fault. The appar- ent ages can be contoured across the fault, although the position of the fault is well defined by abrupt deflection of the contours parallel to the fault. The reverse fault bounding the north side of the San Bernardino Mountains may or may not be reflected by offset con- tours; correlation of possible offset features across the fault is uncer— tain. Several northwest—trending faults on the Mojave Desert strongly disrupt the contours but do not show the right-lateral dis- placements that have been attributed to them on the basis of appar- ent offsets ofgeologic features. These faults may have a component of vertical movement, and it is not known what effect this might have on the contours; even a small amount could be profound. The cause of the isotopic disturbance is not well understood, as the area of most complete resetting does not appear to be coincident with any single batholithic mass. The apparent-age contours cross the boundaries of individual plutons, and the configuration of the con- tours shows no apparent relation to the shapes of plutons or groups of plutons. Even though there does appear to be a lack of correlation» between individual plutons or batholith-size collections of plutons, this lack of correlation may be more apparent than real. It is possible that some of the plutons within the area of anomalous ages are part of an extensive batholithic mass of which only the uppermost part is exposed. . An alternative interpretation of the anomalous ages is that a con- tinuing postemplacement heat source generated by continued under- thrusting of the Pacific plate beneath North America caused the region to remain at elevated temperatures such that argon retention by minerals datable by potassium-argon methods was not possible for some time after pluton emplacement. As suggested by Coney and Reynolds (1977), possibly the angle of underthrusting was shallower than when the Transverse Range plutons were emplaced. Locally, the youngest ages show a spatial relation to the Vincent thrust fault and its correlatives. If this fault is the cause of the region-wide resetting, it has to have extended under most of the western part of southern California. The configuration of the anomalous-age zone is roughly coincident with the position of the Transverse Ranges, the recently discovered southern California uplift, a relatively shallow high-velocity zone in southern California, and the projection of the Murray fracture zone. The eastward extent coincides roughly with the eastern limit of high seismicity in southern California. INTRODUCTION Potassium-argon apparent ages were determined on mineral separates from 158 granitic and gneissic rocks from an area of about 14,000 km2 of the eastern Transverse Ranges and southwestern Mojave Desert (fig. 1). Most potassium-argon-datable granitic rock bodies from the San Bernardino, San Gabriel, and Santa Monica Mountains were sampled and “dated.” Biotite was analyzed from most samples, and coexist- ing hornblende and biotite were analyzed from about 30 percent of the samples. The granitic rocks range in composition from alkali quartz monzonite to mafic quartz diorite; gneissic rocks include amphibolite and Precambrian quartzofeldspathic gneiss. All rocks yield Meso’zoic or early Tertiary po- tassium-argon apparent ages,“ even the known Pre- cambrian gneiss. The apparent ages range from 57 m.y. to 199 m.y.; they vary in a regular and systematic way such that it is possible to contour them throughout most of the region. .Contouring the apparent or anomalous ages was done both for the entire region sampled (p1. IC) and within individual fault-bounded blocks (pl. 1D). 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Only a few of the potassium-argon ages obtained may approach emplacement ages; most reflect a com— plex postintrusive thermal history that affected the en- tire region sampled. The area yielding apparent and (or) reset ages is surrounded by a zone of discordant ages, outside which granitic rocks yield concordant1 or near-concordant ages from‘ coexisting mineral pairs and are considered to approach closely the age of 'The age of a rock is considered concordant if a mineral pair (hornblende and biotite or muscovibe and biotite) from a single sample of that rock yields dates that differ by no more than 6 percent (2 3 percent for each mineral), emplacement of the sampled plutons (fig. 2). All the rocks in the thoroughly reset area surrounded by the zone of discordant ages yield anomalous potassium- argon cooling ages, even though most mineral pairs from this anomalous area are concordant or nearly concordant. Although the style of the contours on either side of the San Andreas fault is somewhat different, the dif- ference in the range of apparent ages is small and there are no striking contrasts across the fault. This lack of isotopic contrast across the fault is not significant in itself because granitic rocks yielding potassium-argon apparent ages in this age range are common through- out the Western United States and Baja California (Evernden and Kistler, 1970; Armstrong and Suppe, 1973; and Krummenacher and others, 1975). 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'4 "/44 .. \ 1.1, 4, (0/1/le “'19 P), y..y0\l7 7/; ,§ 5 4:; /; wentynlne . / 3M g g i : Séf "—A Wk ”mi/mullnnr 1011111“ Palm .\\ “NW ”’1" “H11 111 1 . 9* 111111111111/1/«4, 3‘ I 1444: 14 4,, M111 Creek . San Gorgonlo Mountain WWW11m111111i§ 4111‘“ 57 L .- u , C Badlands (W 441,,” {4” 668 ”ms “\‘111111111111111179 SKI,“ “ e“: ...Pkrfi 4,,,,,,4, , . Crafton HIHS g”?- L ”Wang: -' i. L l I I 34°00, T0 RIVERSIDE T0 IND/O FIGURE 1.—Continued. potassium-argon ages that fall almost exclusively in about the same age span and lie in a continuous zone that straddles a fault that may have more than 240 km of right-lateral slip along it (Crowell, 1962; Ehlert and Ehlig, 1977). To refer to this area of reset ages as a zone may be misleading, because the anomalous ages occur over an extremely large area, the bounds of which are known incompletely. West of the San Andreas fault, there ap- pears to be a marked change in the configuration of apparent age patterns across the frontal fault system of the Transverse Ranges, which separates this province from the Peninsular Ranges province to the south. East of the San Andreas fault, the area of reset ages grades into only partially reset and possibly emplacement ages. The boundar between these two isotopically dif— ferent areas east of the San Andreas has a sinuous, though roughly east—west, trend that passes just north of lat 34°30’N, turning to a south—southeast trend about 20 km northeast of the San Bernardino Mountains (see fig. 2 and pl. 10). The west and south- east extension of this boundary is unknown but under investigation. On the west side of the San Andreas, no such potassium-argon isotopic boundaries have yet been recognized; it is not known if plutonic rocks west of the San Andreas and north of the San Gabriel Mountains yield potassium-argon ages that approach emplacement ages. The apparent ages and the interpretations reported here constitute a progress report on a continuing potassium-argon isotopic study that will eventually cover most of southern California north of lat 33°N. Interpretations presented here may be modified or changed as more information becomes available. ACKNOWLEDGMENTS We are indebted to E. A. Rodriguez and P. N. Castle for their help in collecting the samples; to D. H. Sorg, 4 GEOCHRONOLOGY OF THE TRANSVERSE RANGES AND MOjAVE DESERT. SOUTHERN CALIFORNIA 119° 118° 117° 116° 36° I I I I two Areas shown in figure a 1 and plate 1 35 .- Are of near emplacement 34° — 33° — o 40 80 KILOMETERS San Diego 0 40 MILES I I FIGURE 2.—Sketch map showing the relation of the three apparent- age subdivisions to large faults in southern California. The discor- dant zone is shown dark stippled. for performing all mineral separations, and to Brent Fabbi and Joe Christy for the K20 analyses. C. C. Smith did the argon extractions and mass spectrometry on many of the samples, for which we thank him. We are particularly indebted to R. O. Cas- tle for many discussions on all aspects of southern California geology relating to this study. GEOLOGIC SETTING With the exception of the Uinta Mountains, the Transverse Ranges of southern California are the only major east-trending mountain ranges in the western conterminous United States. They constitute a major physiographic province that disrupts the northwest- oriented Cordilleran trends of the Peninsular Ranges to the south and the Coast Ranges to the north (fig. 1 and pi. 1A). The San Andreas fault passes through the province but appears to displace the overall eastward trend of the mountains only slightly if at all. From east to west, the major ranges of the province are the San Bernardino Mountains, San Gabriel Mountains, Santa Monica Mountains, and Santa Ynez Mountains. Gra- nitic rocks of Mesozoic age occur mainly in the San Bernardino and San Gabriel Mountains and the east end of the Santa Monica Mountains; in the western ranges, except in the Ridge Basin and Frazier Mountain areas, the crystalline rocks are covered by thick sections of Tertiary sedimentary rocks. SAN BERNARDINO MOUNTAINS The San Bernardino Mountains are 95 km long and average about 2,000 m in height except for the mass centered on San Gorgonio Mountain in the southern part of the range, which rises to about 3,350 In. Most of the range is underlain by intermediate composition granitic rock of Mesozoic age. Precambrian schist and gneiss make up about 20 percent of the basement rock; they occur chiefly in the southern part of the range and to a lesser extent, in the central and north parts. Un- conformably overlying the gneiss is relatively un- metamorphosed younger Precambrian quartzite, phyl- lite, and dolomite that is overlain by Paleozoic lime- stone and dolomite, part of which is Mississippian in age (Richmond, 1960; Stewart and Poole, 1975). Other than the granitic plutons, no rocks of Mesozoic or early Tertiary age are present. The other rocks in the range consist of several patches of Pliocene basalt, and, in structural depressions, Pliocene and (or) Pleistocene rocks ranging from conglomerate to shale. Discontinu- ous Quaternary gravels and alluvial deposits are wide- spread, particularly around the flanks of the range, The San Bernardino Mountains are bounded on the north by a relatively narrow, irregularly trending zone of south-dipping reverse faults that dip under the range. This zone of faults appears to die out eastward as the mountains gradually decrease in elevation al— most to the desert floor near Yucca Valley. No historic earthquakes have occurred along this fault zone, but youthful-appearing scarps as high as 30 m occur in all but the youngest alluvial gravels. The various branches of the San Andreas fault bound and occur within the southwest part of the San Bernardino Mountains. The north-dipping Banning reverse fault zone forms the south boundary, and the Pinto Mountain fault roughly coincides with the ill-defined southeast margin of the range, Just southeast of San Gorgonio Mountain, the Pinto Mountain fault, which has components of left-lateral and possibly reverse slip along it, trends northeastward, then eastward from its intersection with the north branch of the San Andreas fault. SAN GABRIEL MOUNTAINS The San Gabriel Mountains are one of the most rug- ged mountain ranges in southern California with steep-sloped peaks rising to more than 2,700 In, and one to 3,050 m. Petrologically, the range is more di- verse than the San Bernardino Mountains. A large Precambrian (Silver and others, 1963) anorthosite GEOLOGIC SETTING 5 complex intrudes Precambrian gneiss and schist at the west end of the range. These rocks are in turn intruded by the Late Permian to Early Triassic Mount Lowe Granodiorite of Miller (1926), which underlies a large part of the west half of the range. Cretaceous granitic rocks (Silver, 1971) ranging in composition from quartz diorite to granodiorite intrude the older rocks. In the eastern part of the mountains, several zones of mixed metamorphic and cataclastic rocks occur along the south front, including an unusually thick zone of north-dipping mylonite and ultramylonite. The mylo- nite and less cataclastically deformed rocks along the mountain front were derived from a variety of high- grade metamorphic rocks. North of these cataclasites is a second zone of cataclasites that appear to have been derived chiefly from mafic granitic rocks that range in composition from granodiorite to quartz diorite. Many of these granitic rocks are still preserved and are un- cataclasized in the interior of the range, especially in the southeastern part. They intrude gneiss and schist of probable Precambrian age and schist, quartzite, and carbonate rock that may be Paleozoic and (or) Mesozoic. In the northeastern part of the range, gneissic rocks and plutonic rocks are thrust over the Cretaceous or older Pelona Schist, a low-grade but pervasively metamorphosed assemblage of schist, greenstone, quartzite, and carbonate rock. The Pelona Schist and the structurally overlying gneiss are everywhere sepa- rated from one another by a thick zone of mylonite and cataclastic rock developed along the Vincent thrust fault. The rocks in this zone differ from the mylonite and cataclastic rock near the front of the range. Intrud- ing the schist and the Vincent thrust is a medium- grained relatively leucocratic granodiorite that yields an early or mid-Miocene potassium-argon age (19 my or 14 my, see Miller and Morton, 1977) and estab- lishes an isotopically determined upper limit on the age of thrusting (Hsii and others, 1963, Miller and Morton, 1977). No pre-Tertiary plutonic rocks are known to intrude the Pelona Schist in the Transverse Ranges. ' The San Gabriel Mountains are bounded on the south by a zone of north-dipping reverse faults that separate the Transverse Ranges province from the Peninsular Ranges province. From east to west, this zone is composed of the Cucamonga fault and Sierra Madre fault. The east end of the Santa Susana thrust fault bounds the southwest edge of the San Gabriel Mountains but is completely within the Transverse Ranges province. The Raymond Hill, Hollywood, Santa Monica, and Malibu Coast faults branch southwest- ward off of the Sierra Madre fault in a continuation of the boundary between the two provinces, forming the southern boundary of the Verdugo Mountains and the Santa Monica Mountains (see fig. 1 and p1. 1A). His- toric earthquakes on the Malibu Coast fault and a branch of the Santa Susana fault indicate that the west end of this reverse fault system is active. Large (6 1m) scarps in the youngest alluvial fans at the east end of the fault system (Cucamonga fault) suggest that this part of the zone is active, although no historic seismic- ity of significant magnitude has been recorded. The north edge of the range is bounded by the San Andreas fault and probably includes the southeast end of the zone of surface rupture that occurred during the 1857 Fort Tejon earthquake. Within the range there are several large faults, but the magnitude, sense, and recency of latest movement are‘not well understood for any of them. The San Ga- briel fault forms an arcuate trace that cuts through the western and southern parts of the range. Continuity at either end of the fault is not well understood; at the east end, the fault is covered by alluvium and either dies out, merges with faults in upper San Antonio Canyon, or is terminated by these faults. At the west end, the fault either dies out or is concealed beneath the late Tertiary rocks or the thrust complex near Frazier Mountain. MOJAVE DESERT The area from which samples were collected in the southern Mojave Desert is largely underlain by Mesozoic plutons and lesser amounts of Paleozoic and Mesozoic metamorphic rock. These rocks are exposed in low mountain ranges separated by large areas of Quaternary alluvium; bedrock is exposed over only about 40 percent of the area. Most of the granitic rocks in the southern Mojave Desert fall within the same general compositional range as those in the San Bernardino Mountains, from alkalic quartz monzonite to mafic quartz diorite. The Paleozoic rocks, marble, quartzite, and schist, are slightly to highly metamorphosed and strongly de- formed. The Mesozoic metamorphic rocks are part of the Sidewinder Volcanic Series of Bowen (1954); they consist of metamorphosed flows and breccia of inter- mediate composition (Bowen, 1954). Small areas underlain by gneiss that have been mapped as Pre- cambrian are found at various places throughout the region; the largest is in the west half of the 0rd Mountains (Dibblee, 1964a). The San Andreas fault bounds the Mojave on the southwest, the reverse fault system at the base of the San Bernardino Mountains on the south. On the south- east side, the boundary between the Mojave and Col- orado Deserts is ill defined but it is usually considered to be the eastward projection of the San Bernardino 6 GEOCHRONOLOGY OF THE TRANSVERSE RANGES AND MOIAVE DESERT, SOUTHERN CALIFORNIA Mountains. The most prominent structures within the southern Mojave block are a series of northwest— striking right-lateral strike-slip faults. Total offset across individual faults is poorly established on the basis of displaced lithologic units but it is thought to range from a few kilometers to about 40 km (Gar— funkle, 1974). All of these northwest-trending strike— slip faults have youthful-appearing primary fault fea— tures along them developed in young alluvium, and several have had historic seismic activity (Hill and Beeby,1977). ROCK TYPES DATED SAN BERNARDINO MOUNTAINS Within the San Bernardino Mountains, the rocks dated fall into five general groups: 1. The oldest rock is the Baldwin Gneiss and several unnamed gneiss bodies that are probably related to or directly correlative with the Baldwin Gneiss of Guillou (1953). Two samples taken from exposures of known Baldwin Gneiss are fairly well layered biotite- and muscovite-rich quartzofeldspathic gneiss. The highly porphyroblastic part of the gneiss that is thought to be metaplutonic in origin (Guillou, 1953) was not sam- pled. Silver (1971) obtained a zircon uranium-lead age of 1750 my. for the gneiss that locally is overlain by younger Precambrian and fossiliferous Paleozoic rock. 2. Mafic plutonic rock, which ranges in composition from monzonite to quartz monzonite and is chemically and petrologically distinct from most other granitic rocks in the San Bernardino Mountains, crops out on the north flank of the range, north of Big Bear Lake. Hornblende is the primary characterizing mineral and makes up more than 15 percent of the rock in most of the body. Much of the hornblende has partly altered cores of clinopyroxene. Biotite, present locally is completely absent at most places. The rock, medium to fine grained and commonly lineated and (or) foliated, contrasts with most of the relatively structureless younger Mesozoic rocks that intrude, it. Miller (oral commun., 1977) obtained an age of 220 my. for this rock on the basis of uranium-lead data. 3. A wide east-trending zone of porphyritic foliated hornblende-biotite quartz monzonite occurs in the south half of the range and extends nearly from one end of the mountains to the other. The rock is ubiqui- tously foliated and (or) lineated and contains pheno— crysts of pink microcline as long as 8 cm (average length 3—4 cm). On the basis of its internal structure, we consider this rock to be older than most of the grani- tic rocks in the range even though the potassium-argon apparent ages have been completely reset. 4. Several large plutons, at least one larger than 125 ' kmz, make up the bulk of the plutonic rocks in the range. Rocks of these plutons range in composition from granodiorite to quartz monzonite; the quartz monzonite is much more common. Several plutons con— tain both hornblende and biotite; a few plutons have muscovite and biotite and two of the largest bodies have biotite only. Most of these rocks are massive; the only exception is foliated rock found locally along the margins of some bodies. Several of the plutons are made up of porphyritic rock or are at least porphyritic in part. Because of petrologic similarities, all plutons of this group may be approximately the same age or close to the same age, but it was not possible to determine this with potassium-argon methods. 5. Diverse plutonic rock types form small bodies at several places in the range. These rocks make up a miscellaneous group that ranges in composition from alaskite to hornblende quartz diorite. Most of these rock bodies are less than 3 or 4 km2 in areal extent. Many are internally inhomogeneous and may be hy- brids. All dated samples from these small bodies reflect the same cooling history in the potassium-argon ap- parent ages as the plutonic rocks that surround them. ‘ SAN GABRIEL MOUNTAINS Sampling in the San Gabriel Mountains was res— tricted to rocks of known or presumed Mesozoic age. None of the known Precambrian gneiss and (or) anor- thosite complex in the western part of the range were sampled. Most dated rocks of the San Gabriel Mountains do not fall into relatively well defined pet- rogenetic groups, as do rocks in the San Bernardino Mountains. In addition, the mafic nonporphyritic dio- ritic to granodioritic Cretaceous plutonic rocks of the San Gabriel Mountains markedly contrast with the relatively leucocratic, porphyritic granodioritic to quartz monzonitic rocks typical of the San Bernardino Mountains. In the descriptions that follow, the rocks are grouped in order of decreasing suspected age. The Mount Lowe Granodiorite of Miller (1926) is a porphyritic highly lineated and (or) foliated rock, one of the few porphyritic rocks in the San Gabriel Mountains. It is leucocratic, with streaked-out hornblende crystals accounting for less than 10 percent of most samples collected. Biotite and minor amounts of muscovite are present in a highly porphyritic specimen taken from near the top of Pacifico Mountain (sample 13, pl. 13). In general, the groundmass of this rock is highly cataclastic, and the phenocrysts com- monly have a milled appearance. Silver (1971) ob- tained an age on zircons from the Mount Lowe Granodiorite of 220:10 m.y. using uranium-lead methods. ROCK TYPES DATED 7 Mafic hornblende-biotite granodiorite, quartz dio- rite, and diorite plutons make up a large part of the plutonic rocks in the range; proportionately the largest number of samples from the San Gabriel Mountains were taken from these bodies. Many of these rocks have a pronounced secondary cataclastic fabric devel- oped in them. Most have a relatively high color index, and in these, hornblende is more abundant than bio- tite. Small irregularly shaped bodies of amphibolite or hornblendite near the front of the range may be related to these mafic plutons. Potassium-argon dating does not yield emplacement ages for any of these rocks, but Hsii, Edwards, and McLaughlin (1963) report a rubidium-strontium age of 105: 10 my. for a sample collected at the east end of the range. Silver (1968), on the basis of uranium-lead ages, indicates emplacement of batholithic rocks in the San Gabriel Mountains be- tween 100 my. and 160 my, and in a later paper (1971) he notes conspicuous episodes at 160—170 my and .75—90 m.y. Cataclastically deformed plutonic rocks are common throughout the eastern part and near the south front of the range and in the crystalline complex just above the Vincent thrust fault. They range from sheared plutonic rocks in which the granitic texture is still relatively well preserved to ultramylonite in which any vestige of the primary rock is lacking. Potassium-argon determi- nations on hornblende and on whole rocks from the ultramylonite yield ages that fall into the general con- tour pattern of the other plutonic rocks (Miller and Morton, unpub. data 1979); their range implies that the cataclastic rocks underwent the same final cooling history as the other rocks. SOUTHERN MOJAVE DESERT The variety in plutonic rocks of the southern Mojave Desert is greater than in either the San Bernardino or San Gabriel Mountains. Many of the same general rock types found in the San Bernardino Mountains are present in the Mojave, but no plutons were mapped that crossed the boundary between the two provinces. There may be exceptions to this generalization at. the east end of the San Bernardino Mountains, however, where the fault system on the north side of the range appears to die out. No detailed mapping of the plutonic rocks has been done in this area. Most of the crystalline rocks dated can be roughly grouped into six categories. 1. Probably the oldest rock unit sampled in the Mojave Desert is hornblende gneiss shown as Precam- brian on the San Bernardino sheet of the State geologic map series (Rogers, 1969). A sample from this unit (No. 79 on pl. 13) yielded an apparent Mesozoic potassium— argon age (96 my.) on hornblende but was collected within the area of anomalous cooling ages. The gneiss ranges from well-layered quartzofeldspathic gneiss to highly contorted hornblende-rich quartzofeldspathic gneiss. Small smeared-out pods of highly recrystallized carbonate rock and calcsilicate rock are locally present. 2. Lineated and foliated hornblende monzonite makes up most of the Granite Mountains west of Lucerne Valley (Ross, 1972). This body was studied by C. F. Miller (1976), who established the emplacement age of these rocks at 220 my. using the uranium-lead method on zircons. Miller suggested that the monzonite is probably related to the mafic monzonite to quartz monzonite in the San Bernardino Mountains on the basis of chemical, petrological, and age similarities. The Granite Mountains plutonic rock is medium to coarse grained and contains about 10 per- cent hornblende that commonly forms highly lineate crystal aggregates streaked out in the plane of folia- tion. Many hornblende crystals have cores of clinopyroxene. At several places, the foliation is clearly cut by younger, massive granodiorite (sample 68) and quartz monzonite plutons. 3. A few plutons of nonporphyritic medium-grained hornblende-biotite granodiorite have yielded discor- dant Jurassic potassium-argon ages and may be as old as Triassic. These rocks lack any secondary fabric, such as that developed in the monzonite in the Granite Mountains, and have relatively high color indexes that generally range from 20 to 30. A pluton exposed along the south flank of Bell Mountain, northeast of Victorville (sample 72), is a good example of this group. With the possible exception of two characteristics, we detected no consistent differences in appearance be- tween these rocks and. those of any other group that would allow us to reliably give an age assignment in the field. These two characteristics, neither of which is totally reliable, are high color index and a hornblende-biotite ratio equal to, or greater than, one. Most plutons of known or suspected Cretaceous age have a lower color index and a hornblende-biotite ratio considerably less than one. The mafic granodiorite plu- tons are grouped here only on the basis of their older potassium-argon apparent ages, consistently high color index, and high hornblende-biotite ratio. Some of the mafic granodiorite and quartz monzonite plutons within the area of anomalous cooling ages in the San Bernardino Mountains that yield relatively young ap- parent potassium-argon ages may or may not belong to this group. 4. A distinctive porphyritic hornblendetbiotite granodiorite makes up an estimated 20—30 percent of all exposed plutonic rocks from east of the Lenwood fault to the limits of the area sampled-The granodi- 8 GEOCHRONOLOGY OF THE TRANSVERSE RANGES AND MOjAVE DESERT, SOUTHERN CALIFORNIA orite contains 2- to 4-cm phenocrysts of gray to purple-gray orthoclase. The phenocryst content is highly variable, ranging from almost none to about 40 percent. The groundmass is medium to coarse grained; the color index ranges from 15 to 20; and the ratio of hornblende to biotite is in most cases less than one. Sphene is abundant in all samples collected. The rock is massive at all sample localities and only locally has poorly developed foliation. Outside the area of anomal- ous cooling ages, this rock yielded an apparently con- cordant potassium-argon hornblende-biotite age slightly greater than 160 my, although there is some question as to the reproducibility of the hornblende age. Another sample (79A) gave a hornblende apparent age. of 185 my; this age may be close to the emplace- ment age of the rock. 5. Both porphyritic and nonporphyritic plutons of quartz monzonite to granodiorite yielding concordant Cretaceous potassium-argon apparent ages are found throughout the southern Mojave Desert both within and outside the area of anomalous cooling ages. Some of these plutons may be completely reset older bodies, ' but none show clear signs of recrystallization with re- spect to either mineralogy or texture. Most of these bodies are made up of rock with a relatively low color index, generally less than 15. The rock ranges from fine to coarse grained, but it is typically homogeneous with regard to grain size within any individual pluton. Almost none display any distinct fabric. 6. A collection of small bodies is considered here as a miscellaneous group. These rock types are found at places throughout the Mojave Desert, but they cannot be demonstrated to be consistently associated with one or another of the more voluminous plutoni'c rock types. Many are probably equivalent to similar rocks in cate- gory (5) or to rocks described from the San Bernardino Mountains. _ The most common rock type in this group is hornblende-biotite quartz-diorite or diorite. Most sam- ples have a color index between 35 and 40 and are medium to fine grained. Locally, the rock approaches a hornblendite in composition. Quartz content is vari- able from body to body and is near'zero in some. A slight but noticeable foliation and (or) lineation is common. In many occurrences, this rock forms small pods or dissociated bodies, each up to several hundred meters in length, around a larger pluton. Three sam- ples of this rock type (Nos. 133, 73D, and 780) yielded- strongly discordant apparent ages ranging from Late Triassic to Late Cretaceous (199 my on hornblende to 77 my. on biotite) suggesting that all of the highly mafic bodies may be relatively old. Mafic inhomogeneous rock, probably a hybrid of Jurassic and Cretaceous plutonic rocks and older metamorphic and plutonic rocks, is common through- out the southern Mojave, but it does not make up a significant proportion of exposed rocks. These bodies are generally made up of finely mixed metamorphic and plutonic rocks and are rarely more than 1 km2 in outcrop area. Most are foliated or lineated in whole or in part. They are highly variable in texture and compo- sition within a given body. Samples 107 and 120 both are from within the area of anomalous ages. SAMPLING AND ANALYTICAL PROCEDURES Early in the dating of the plutonic crystalline rocks of southern California, it became evident that most concordant potassium-argon ages did not represent emplacement ages and that the area yielding the con— cordant ages was bounded on the north and east by areas yielding discordant potassium-argon ages. It also became evident that these apparent ages varied in a systematic way that could be contoured, presumably to reflect the cooling history of the area. We assumed that within the area of concordant but anomalously young ages, any crystalline rock, regardless of its age based on other dating methods, would yield a potassium- argon age that would fit the contouring. This assump- tion appears to be justified, as known Precambrian and Permian to Triassic rocks yielded Cretaceous potassium-argon apparent ages that fall exactly on the contours of granitic rocks of probable Cretaceous age. Since this thorough resetting was documented fairly early in our dating program, subsequent sampling, with few exceptions, was done to obtain an even distri- bution of samples for contour control. In addition to the distribution criteria for sampling, samples were collected from as many individual plu- ~ tons as possible, and more than one sample was col- lected from the larger plutons. Most plutons in the San Bernardino Mountains north of Santa Ana Canyon, more than half of the plutons in the San Gabriel Mountains, and probably between 50 and 75 percent of those in the Mojave Desert were sampled. Because many of the individual plutons in the Mojave are com- bined into larger plutonic units on published maps, it is not known for certain how many plutons are present. Gneissic or schistose metamorphic rocks known or sus- pected of being older than the Mesozoic plutonic rocks were sampled at various places in the area to test the degree to which the ages of the rocks have been reset. About 10 kg of rock was taken at each sample site. At all sites, the most representative, least altered, and least weathered rock present was collected. In some areas, all exposed rock was too altered or weathered in a place where a sample was needed for contouring con- trol. At those places, no sample was taken. Most of the DISCUSSION AND, INTERPRETATION OF APPARENT AGES 9 areas where altered rock was a problem were in the Mojave Desert. Weathering or alteration did not pre- vent sampling at relatively regular intervals in the Transverse Ranges except in the Santa Monica Mountains and the northwestern San Gabriel Mountains. The most serious impediment to a regular sampling interval was absence of datable rock over large al— luviated areas in some parts of the region, particularly in the southwestern part of the Mojave Desert. In the western San Gabriel Mountains, the Precambrian anorthosite complex occupies a large area where no samples were taken, as does the Pelona Schist in the eastern San Gabriel Mountains. Relatively un- metamorphosed Precambrian and Paleozoic sedimen- tary rocks that underlie two large areas in the central San Bernardino Mountains were not sampled. All mineral separates were checked for impurities in oil with a petrographic microscope. With few excep- tions, mica separates were more than 99 percent pure, and most hornblende separates were nearly 100 per- cent free of foreign material, especially mica. Hornblende from sample 85 contained pyroxene cores that could not be completely separated from the hornblende. That separate, which has an anomalous age, is discussed in the section on anomalous features of the apparent ages. Argon analyses were made using standard isotope- dilution techniques in a 6-in. 60° Nier-type mass spectrometer, except for sample 126, which was analyzed on a 9-in. 90° multicollector mass spectrometer. Constants used to calculate the ages are AB = 4.962 X 10"0 yr"; A6 = 0.581 X 1010 yr‘1 (Beckinsale and Gale, 1969); and 40K/K = 1.167 X 10’4 (Garner and others, 1975). Since these constants were recently adopted by the IUGS Subcommittee on Geochronology (Steiger and J ager, 1977), previously determined dates using the old constants must be recalculated before they are compared with our data. At least two potassium analyses were made on each sample using a flame photometer with a lithium inter- nal standard. If a pair of analyses differed by more than 2 percent, replicate analyses were made. The values used in the age calculations are averages. Errors (: values for the ages) have been assigned 0n the basis of experience with duplicate analyses; they represent the additive effects of uncertainties in the argon and potassium analyses, in the isotopic composi- tion of the 3"Ar tracers, and in the concentration of the flame-photometer standards. Replicate argoneanalyses were made for many of the samples as‘ a check on re- producibility; none differed from the initial analysis by more than 1.5 percent. DISCUSSION AND- INTERPRETATION OF APPARENT AGES GENERAL CHARACTERISTICS AND DISTRIBUTION OF APPARENT AGES Potassium-argon age determinations were made on 216 mineral separates of plutonic and metamorphic rocks from the Transverse Ranges and Mojave Desert—155 on biotite, 56 on hornblende, and 5 on muscovite (table 1). From 45 of the samples, separate ages on coexisting hornblende and biotite were ob- tained, and from 5 samples apparent ages on coexisting muscovite-biotite pairs. The apparent ages, which range from 57 my. to 199 m.y., represent discordant, concordant, and possible emplacement ages. The latter two are not necessarily synonymous in this region. The potassium-argon apparent ages fall into three well-defined groups that in the following discussion will be referred to as (1) areas of anomalous cooling ages, (2) discordant zone, and (3) emplacement or near-emplacement ages. The majority of these appar- ent ages fall within and define the zoneof anomalous cooling ages, a region that appears to have undergone a long and perhaps complex thermal history. The area most completely affected by this complex thermal his- tory covers the eastern San Gabriel Mountains, the entire San Bernardino Mountains, and .the south- ernmost Mojave Desert. This area is surrounded by a zone of discordant ages constituting the discordant zone; outside of this zone, the third group occurs (fig. 2 and pl. 1C). In this outer group, coexisting mineral pairs give concordant or near concordant potassium- argon ages that are probably close to the emplacement age of the individual plutons. All the following comments on the contoured appar- ent ages refer to the contours using all biotite ages, plate 10, and only when specifically noted, to contours for individual blocks, plate 1D. Before discussing what we interpret the contour map to show, however, a few comments should be made regarding the control for the contours, the contour interval, and the relative significance of trends defined by the contours. Control for the contours is good throughout the area shown on plate 1C and 1D except for the large al- luviated area between C‘ajon Pass and Victorville, and an area in the northeastern‘San Gabriel Mountains that is underlain by the Pelona Schist. Granitic rock samples from the western two-thirds of the Santa Monica Mountains and the San Fernando Valley would be desirable in order to extend contouring in that direc- tion, but owing to the Tertiary and Quaternary sedi- mentary cover, none are exposed. For this reason, the few dates from the eastern Santa Monica Mountains are not contoured. 10 GEOCHRONOLOGY OF THE 'I‘RANSVERSE RANGES AND MOJAVE DESERT, SOUTHERN CALIFORNIA TABLE 1.——Analytical data and calculated potassium-argon ages of plutonic and metamorphic rocks from the San Bernardino and San Gabriel Mountains and the eastern Mojave Desert [Constants (Steiger and Jager, 1977): AB=4.962 x 10"“ yr"; Ae:0.581 >< 10"’yr"; "’K/K:1.167 x 10". BIO:biotite, HBL=homb1ende, MUS:muscovite] Sample Calculated localities K20 “’Arrad “’Arrad age Field (pl. 18) Mineral (in percent) (10"‘" mol/gm) (in percent) (m.y.) No. 1 BIO 8.69 12.68 92 98613.0 T2—5 HBL .893 1.385 73 10513.2 HBLl .893 1.364 62 10313.1 1A BIO 9.63 12.48 89 87.8126 WT—2 HBL .947 1.309 78 93.5127 2 B10 9.05 9.452 75 71.1 12.1 T1-5 3 BIO 8.92 9.303 91 71.0121 T76—4 4 BIO 9.16 9.145 93 68.0120 T77—4 5 B10 8.69 8.966 92 70.3121 T50—4 6 BIO 8.76 9.180 93 71.4121 T49—4 HBL .695 .7191 53 70.5121 7 HBL 1.284 1.223 87 65.0126 T33—4 8 B10 9.03 8.793 90 66.4120 T80—4 HBL 1.052 1.158 70 74.8122 9 B10 9.09 8.672 93 65.1 12.0 T34—4 10 B10 6.82 6.453 89 64.61 1.9 T79—4 11 BIO 9.13 8.654 92 64711.9 T78—4 12 B10 8.66 7.707 90 60811.8 T48—4 13 B10 9.37 10.91 93 79.1124 T38—4 MUS 10.31 12.99 92 85.5126 14 B10 9.17 8.950 84 66.6120 T82—4 15 B10 8.99 8.507 83 64.61 1.9 T83—4 16 B10 9.36 8.966 82 65.3120 T36—4 17 HBL 1.392 2.299 84 11313.4 T35—4 18 BIO 7.76 6.426 77 56.61 1.7 T67-4 BIO2 8.93 7.550 86 57.81 1.7 T2—6 19 B10 8.68 9.144 93 71.7129 T47—4 HBL 1.259 1.356 65 73.3122 20 BIO 8.78 9.122 95 70.8128 T46—4 21 B10 8.33 7.835 88 64.21 1.9 T68—4 22 BIO 7.63 8.049 91 71.8122 T105—4 HBL .288 .5059 43 11813.5 22A B10 823 7.828 93 64.91 1.9 T1—6 BIO3 8.23 7.841 79 65.0120 HBL .357 .7851 79 14714.4 23 B10 9.10 7.967 89 59811.8 T41—4 HBL 1.655 1.531 86 63111.9 24 B10 8.95 7.655 92 58.51 1.8 T37—4 25 BIO 9.11 9.808 94 73.3122 T102—4 HBL 1.276 1.324 70 70.6121 26 BIO 8.42 9.246 92 74.7122 M26—4 27 B10 9.53 10.41 85 74.3122 M27—4 28 BIO 9.35 10.30 92 74.9122 M30—4 29 B10 9.27 9.142 85 67.2120 M31—4 30 BIO 9.43 10.75 93 77.5123 M32—4 31 B10 9.50 10.94 79 78.3123 M33—4 HBL .579 .6402 58 75.2123 31A BIO 8.79 9.986 86 77.2123 M52—7' 32 B10 9.25 10.44 88 76.2123 M34—4 33 BIO 9.56 11.57 81 82.2125 M28—4 HBL .635 .7890 70 84.3125 34 B10 8.55 9.313 72 74.1 12.2 M35—4 35 BIO 8.70 10.67 91 83. 12.5 M29—4 36 BIO 9.06 9.223 80 69.4121 T100-4 37 B10 8.97 9.454 92 71.8122 T101—4 38 BIO 9.22 8.509 88 63.01 1.9 T84—4 39 BIO 9.14 9.498 90 70.8121 T99—4 40 BIO 8.90 9.098 92 69.6121 T98—4 , HBL 1.542 1.718 73 75.8123 41 HBL 1.490 1.457 80 66.7120 T106—4 HBL3 1.490 1.450 75 66.3120 42 BIO 8.29 7.560 87 62.31 1.9 T70—4 HBL 1.250 1.202 79 65.6120 43 BIO 9.18 8.067 87 60.0118 T71—4 44 BIO 9.26 9.907 93 72.8122 T72—4 45 B10 9.07 9.727 89 73.0122 T103—4 46 BIO 9.22 10.20 92 75.3123 T104—4 HBL 1.267 1.383 68 74.2122 47 BIO 8.21 8.228 88 68.3120 T73—4 48 BIO 9.21 9.530 87 70. 12.1 T74—4 49 BIO 9.32 10.21 93 74.5122 T75—4 50 BIO 9.43 9.891 94 71.4121 T19—3 HBL 1.810 1.782 77 67.1134 51 BIO 9.06 9.295 85 69.9121 T86—4 DISCUSSION AND INTERPRETATION OF APPARENT AGES 11 TABLE 1.—A nalytical data and calculated potassium-argon ages of platonic and metamorphie rocks from the San Bernardino and San Gabriel Mountains and the eastern Mojave Desert—Contlnued Sample Calculated ‘ localities K30 “’Arwd “’Armd age F leld (pl. IB) Mineral (in percent) (101" mol/g’m) (in percent) (m.y.) N0. 52 B10 9.16 9.544 93 71.0121 T4—3 HBL 1.07 1.083 81 69.0131 53 BIO 9.08 9.485 91 71.1121 T85—4 54 BIO 9.20 9.453 85 70.0121 T1—4 HBL .880 .8577 73 66.5120 HBL3 .880 .8432 74 65.4120 55 BIO 8.05 8.337 94 70.5_2.8 T2—4 B10" .805 8.361 93 70.7128 56 BIO 8.41 8.558 92 69.3128 T3—4 57 BIO 9.25 9.526 94 70.1121 T53—4 57A HBL 1.312 1.257 70 65.3120 416 58 BIO 9.50 9.284 88 66.6120 T18—4 59 BIO 9.16 9.030 90 67.2120 T66—4 HBL 1.222 1.328 78 73.9122 59A BIO 8.31 8.093 87 66.4120 M17—7 60 BIO 8.62 8.352 87 66.1120 T12-4 61 BIO 9.25 9.005 88 69.4120 T15—4 BIO" 9.25 9.453 94 69.6121 HBL .984 1.062 87 73.4129 62 BIO 8.88 9.057 90 69.5121 T16—4 63 B10 9.24 9.408 86 69.4121 T65—4 64 BIO 9.33 11.17 90 81.3124 T21—3 65 BIO 9.25 10.88 93 79.9124 T43—4 66 BIO 9.40 10.00 92 72412.9 T44—-4 67 HBL 1.436 3.003 81 14015.6 M1—3 68 BIO 9.51 10.31 92 73.8122 M2—4 69 BIO 8.85 9.384 80 72.2122 M14—4 70 BIO 9.50 9.970 92 71513.6 M1—4 71 BIO 8.95 9.516 94 72.4122 M9—4 72 B10 8.71 10.71 90 83.4125 M8—4 HBL .521 1.328 68 1691118 73 BIO 8.92 11.31 91 86.0126 M7—4 73A BIO 9.19 10.28 88 76.1 1 .3 M3—6 73B BIO 8.86 9.742 88 74.8122 M1—7 HBL .632 .6434 49 69.41 .1 HBL .632 .6597 10 71.81 .2 73C BIO 8.88 13.31 82 99.21 .0 M2—7 73D BIO 9.22 15.88 55 11613.5 M3—7 HBL .459 1.391 71 19916.0 74 B10 8.74 9.472 92 73.7122 M6—4 75 B10 9.25 11.91 92 87.3126 T90—4 76 BIO 9.35 14.68 92 10613.2 T91—4 HBL .704 1.985 77 18615.6 76A BIO 9.04 9.660 74 74.9123 M20—7 77 BIO 8.89 9.803 79 75.0123 T92—4 78 BIO 9.25 10.58 78 77.7123 T93—4 78A BIO 9.34 20.26 94 14514.3 M5—7 HBL .430 1.105 47 17015.1 78B BIO 9.11 18.18 95 13414.0 M6—7 78C BIO 9.00 13.27 39 99614.0 M7—7 HBL .855 2.152 87 16715.0 79 HBL 1.200 1.705 79 96.1 14.8 T94—4 79A BIO 9.21 10.57 85 78.0123 M10—7 HBL .898 2.524 87 18515.6 79B BIO 9.19 9.605 57 71.2121 M11—7 80 BIO 9.21 9.468 89 70.0121 M13—4 81 BIO 9.04 9.825 86 74.0122 T95—4 82 BIO 9.51 9.800 91 70.2121 T97—4 HBL 1.089 1.155 64 72.2122 83 B10 9.26 9.660 92 71.0121 T89—4 84 BIO 8.70 9.040 89 70.8121 T96—4 85 B10 9.16 11.07 90 82.0125 T3lA—4 HBL‘ .644 1.21 1 82 12613.8 HBL5 .550 1.651 55 1971 5.8 86 BIO 9.08 9.484 88 71.1 12.1 T544 87 B10 8.73 9.037 96 70.5121 T13—4 88 BIO 9.24 10.03 90 73.9122 T14—4 MUS 10.64 11.37 89 72712.2 89 BIO 9.16 9.369 95 69.7121 T11—4 HBL 1.209 1.332 85 74.9122 90 BIO 9.16 9.708 96 72212.2 T10—4 HBL .960 1.003 76 71.1136 91 B10 9.35 9.603 94 70.0121 T55—4 92 BIO 9.42 9.890 89 71.5121 T32—4 HBL .763 .7901 64 70.5135 93 BIO 9.30 9.333 87 68.4121 T64—4 12 GEOCHRONOLOGY Ol: THE TRANSVERSE RANGES AND MOJAVE DESERT, SOUTHERN CALIFORNIA TABLE 1.—Analytical data and calculated potassium-argon ages of platonic and metamorphic rocks from the San Bernardino and San Gabriel Mountains and the eastern Mojave Desert—Continued Sample Calculated localities K20 “’Arrau “'Armd age Field (p1. LB) Mineral (in percent) (10’10 mol/gm) (in percent) (m.y ) No. 94 B10 983 10.20 92 70.7121 T30—4 MUS 10.75 10.97 93 69.5121 95 HBL 1.156 1.250 73 73.6132 T87—4 96 BIO 9.48 9.534 92 68.5121 T5—4 97 B10 9.27 9.301 89 68.4121 M3—4 98 BIO 8.75 8.768 90 68.3121 M10—4 99 BIO 9.52 10.39 88 74.3130 M36—4 100 BIO 9.44 21.10 97 14914.5 M38—4 100A BIO 8.95 9.389 79 71.4121 M44—7 101 BIO 8.87 9.969 93 76.4123 M39—4 HBL .568 .6146 59 73615.9 102 BIO 9.31 10.97 93 80.0124 M40—4 102A BIO 9.48 11.28 90 80.4124 M22—7 HBL 1.061 2.608 60 16314.9 103 BIO 9.17 9.994 87 74.2122 M41—4 104 BIO 9.34 10.30 91 75.0123 M19—4 105 BIO 8.91 9.143 94 69.9121 M15-4 HBL .725 .7707 20 72412.9 106 BIO 9.22 9.327 91 68.9121 M11—4 107 BIO 8.87 8.792 89 67.6120 M12—4 HBL 1.061 1.007 69 69.2121 108 BIO 8.96 9.215 92 70.1121 T45—4 HBL .926 .9916 48 72.9129 109 BIO 9.26 8.817 85 65.0120 T61—4 110 BIO 9.64 9.354 90 66.2120 T63—4 111 BIO 9.01 9.187 94 69.5128 T62—4 MUS 10.69 11.14 89 71.0121 112 BIO 9.07 9.601 93 72112.2 T9—4 HBL 1.059 1.145 85 73.6122 112A BIO 8.92 7.716 94 59.11 1.8 TA—6 113 B10 948 9.451 54 68.0120 T60—4 114 BIO 9.62 10.12 96 71.6121 T8—4 115 BIO 9.12 9.264 84 69.2121 T52—4 116 BIO 9.29 9.550 94 70.0121 T51—4 116A BIO 9.15 9.412 91 70.1121 M15—7 117 BIO 9.15 9.358 90 69.7121 T59—4 118 BIO 9.11 9.381 93 70.1121 T58—4 119 BIO 8.95 9.546 93 72.6122 T56—4 120 BIO 9.18 9.499 94 70.5121 T57—4 121 BIO 9.06 9.003 86 67.7120 M16—4 122 BIO 9.52 9.996 91 71.5121 M18—4 123 BIO 9.13 10.85 90 80713.2 M17—4 123A BIO 9.08 15.65 85 11613.5 M13—7 HBL .564 15.15 63 17815. 1238 BIO 9.37 21.66 86 15414.6 M14—7 HBL .517 1.312 38 16815.0 124 BIO 9.72 10.21 87 71.512 1 M4—4 125 BIO 9.26 9.264 82 68.2120 M5—4 HBL .916 .9844 77 73113.7 126 BIO 9.28 9.862 93 72.3122 M43—4 127 BIO 9.60 10.01 94 71.012 1 M25-4 HBL .727 .7633 60 71.512 1 128 BIO 9.22 10.08 77 74.4122 M42—4 HBL .769 1.502 72 13113.9 129 BIO 9.10 9.094 90 68.1 12 0 T19—4 MUS 10.75 11.24 95 71.212 1 130 BIO 9.37 13.10 96 94.6128 M22—4 131 BIO 9.56 10.40 94 74.0122 M24—4 132 BIO 8.99 14.60 85 10913.3 M44—4 133 BIO 9.31 10.75 94 78.5124 M20—4 HBL .996 1.608 74 10916.5 133A BIO 9.26 17.35 95 12613.8 M12—7 HBL .649 1.628 63 16615.0 134 BIO 8.86 16.05 96 12215.4 M21—4 135 BIO 9.36 21.62 95 15414.6 M47—4 136 BIO 8.70 21.31 97 16314.9 M45—4 HBL .635 1.551 69 16214.9 136A BIO 8.79 19.59 83 14814 4 M96—7 HBL 0.472 1.312 56 18315 5 ‘With yrex flux. 2Recollgm‘ed. “Replicate. '11 percent pyroxene. 515 percent pyroxene. DISCUSSION AND INTERPRETATION OF APPARENT AGES 13 The experimental precision of the dating method for most samples is 2—3 m.y. This precision justifies a con- tour interval no smaller than 5 m.y. In places such as the southern Mojave Desert and most of the San Ber.- nardino Mountains, the apparent age gradient is so low that the detailed configuration of features generated by contouring the apparent ages may or may not be real. This area was first contoured using a 5-m.y. interval. The overall trends and positions of apparent-age highs and lows. were basically the same as shown on plate 1C, but visually these features did not show up well. We therefore used the 2-m.y. interval on plates 10 and 1D simply to graphically accentuate the location and basic trends of apparent-age highs and lows in areas with low apparent-age gradients. Little value should be placed on the detailed configurations of individual fea— tures in these areas. Except for the apparent-age high between Big Bear Lake and Lake Arrowhead, the total apparent-age range in this area is only about 7 m.y. All the apparent ages were computer contoured to test the objectivity of the hand contouring. Even though basic forms and trends of the contours gen- erated by the two methods did not differ significantly, the hand contouring is preferred because the available computer program was not able to create a grid suffi- ciently detailed so that a contour of some particular value consistently passed exactly through and not just near a sample locality yielding that age. In addition, around the margins of the area, where the concentra— tion of data points decreased, the computer-generated contour maps showed unjustifiable creativity. Within the area of anomalous cooling ages bounded by the discordant age zone, the apparent potassium- argon age of any particular rock seems to be a function of location and is independent of the composition, rock type, and age of emplacement. The apparent ages within this area can be contoured so that they show a regular and orderly change from place to place. These changes are both within and across the boundaries of individual plutons so that the configuration of the con- tours shows little or no relation to the shape of the individual plutons. The systematic relation between apparent age and geographic locality is true only for the completely reset apparent ages, not for the entire area covered by the. contours on plates 1C and 1D. The justification for con- touring the apparent ages lies in the assumption that the entire contoured region at some point in geologic time underwent a thermal event that affected all exist- ing rocks, and that the event caused all radiogenic argon existing at the time to be outgassed. This as- sumption, though partly justified for some of the re- . gion, is obviously not entirely justified for the region as a whole. Outside the zone of discordance, for example, the rocks are only slightly or not at all affected by the thermal event, and from the zone of discordance, the rocks were only partly outgassed. With a few possible exceptions discussed in a later section, the rocks within the area enclosed by the discordant zone were probably outgassed fairly completely at the time of the thermal disturbance, because coexisting mineral pairs com- monly give concordant or near-concordant numbers, and because known Precambrian and Permian to Triassic rocks give the same Cretaceous apparent ages as the surrounding younger plutonic rocks. The contours may reflect not just a simple cooling pattern for a uniform thermal disturbance but the ac- tual or relative chronology of the disturbance from place to place, the completeness of outgassing from place to place, or some combination of these. Probably the contours within the area of anomalous cooling ages are a reflection of all the factors mentioned. Within the discordant zone, the contours must be interpreted dif- ferently than those within the zone of anomalous cool- ing history, and outside the discordant zone, where the ages may approach emplacement ages, they cannot be contoured. Using only the potassium-argon method, it is not possible to determine whether the thermal dis- turbance began and developed uniformly over the en- tire region at the same time, although the method can furnish information on how the disturbance ended and in approximately what span of time. THE ZONE OF DISCORDANT AGES The zone of discordant ages is one of the more obvi- ous features defined by the contours. It ranges in width from about 6 km to at least 12 km. On the contour maps, plates 1C and 1D, most of the zone is shown with a stippled overprint. The inner margin is poorly de- fined because it is gradational. Therefore, the shaded overprint is shown only from the 80-m.y. contour where .the contour interval jumps from 2 m.y. to 10 m.y. We chose the 80-m.y. contour as marking the beginning of the discordant zone, because beyond that contour, the apparent ages of the reset rocks rise rapidly, and the discordance between coexisting hornblende and biotite increases markedly. Where best defined, the zone shows an extremely steep gradient in the center two-thirds that declines rapidly to less steep gradients both toward the "emplacement ages” on the outside and the more com- pletely reset apparent ages on the inside. The zone is well developed north of the Pinto Mountain fault be- tween Yucca Valley and Twentynine Palms for a dis- tance of about 40 km north of the fault where it inter- sects the Camprock fault. Along this 40-km segment, the zone trends north-northwest except at the south- 14 GEOCHRONOLOGY OF THE TRANSVERSE RANGES AND MOJAVE DESERT, SOUTHERN CALIFORNIA east end, where it appears to swing sharply eastward. As the eastward swing is controlled by only one appar- ent age (sample 136A), the validity of this change in strike of the contours is not well established. At present, only six apparent ages have been deter- mined east of the Camprock fault, enough to locate the zone but not enough to establish the trend on the east side of the fault (see pl. 1D). About 25 km north of where the zone intersects the west side of the Camprock fault, it is again seen on the west side of the fault, but in this segment, the overall trend, though sinuous, is more easterly oriented. The zone is fairly well defined westward for about 50 km but appears to be offset by the Johnson Valley- Lenwood and Helendale faults (pl. 1D). West of the Mojave River, alluvium cover over a large area pre— cludes sampling, so it is not known if the zone con- tinues westward. If it does, the contours must bend sharply northward or southward to carry the zone around the collection of 67-m.y. to 83-m.y. apparent ages between Lancaster and Victorville. It is not known if those apparent ages fall inside or outside the discordant zone, although if the manner in which the contours are drawn in this area on the maps is approx- imately correct, then these apparent ages should be south of the discordant zone. The location of the east- trending part of the zone beyond where it is shown on plates 10 and 1D is not precisely known. Reconnais- sance dating of granitic rocks to the north suggests that the zone may turn sharply back on itself, forming a roughly west-pointing prong of relatively "older” ap- parent ages that has an axis just north of where the zone is shown on plate 10. The apparent-age high of relatively low gradient defined by the cluster of ages between Victorville and Lancaster could reflect the westward projection of this axis. Dating in the north- ern Mojave is not complete enough as yet, however, to preclude the possibility of the zone turning again and intersecting either the Garlock or the San Andreas fault. It is also not known where the zone continues south of the Pinto Mountain fault at the opposite end although some samples have been taken from that area. Control for the east-trending segment of the discor- dant zone is not so good as for the north-northwest— trending segment because the apparent ages used for the contouring are on rocks that may have a consider- able range in age of emplacement. Samples 79B (71 m.y.), 101 (76 m.y.), and 103 (74 my) in particular may have considerably younger emplacement ages than most of the samples contoured to define the dis- cordant zone. If the apparent ages that define the dis- cordant zone are measured on rocks from plutons that have a range in emplacement ages, the contours gen- erated by these apparent ages may be misleading. This is particularly true where the rocks were only partially reset as they are in the discordant zone, and where the range in emplacement ages is considerable. Since the rocks within the zone were not completely outgassed at the time of the thermal disturbance, they were not reset to a common starting point, and since they are of different emplacement ages, there was no common ini- tial starting point. Contouring the apparent ages is essentially a graphic method of comparing one appar- ent age to another, but for samples from within the discordant zone that were not completely reset and that did not have the same emplacement age, it may be a case of comparing apples and oranges; Some control on this problem, however, is provided by an easily recognized porphyritic hornblende-biotite granodiorite and a group of highly mafic bodies that are widely distributed in the eastern and northeastern part of the area shown on plates 1C and 1D. These rocks were emplaced during at least two, and possibly several, periods of plutonism that appear to be sepa- rated by a relatively short period of geologic time. They therefore provide at least a somewhat common starting point to compare degrees of resetting. The maximum time span between the beginning of emplacement and the end could be as much as 50 m.y., but it is probably closer to 30 my Even though these rocks are not reset from a single emplacement age, the difference in emplacement ages is small compared to the time inter- val represented by the difference between emplace- ment age and reset apparent ages. The porphyritic granodiorite yielded apparently con— cordant hornblende and biotite ages of 162 and 163 m.y., respectively, from a sample (No. 136) outside the discordant zone. There is some question, however, as to . whether the 162-m.y. hornblende age is valid, because sample 136A, from the same pluton, yielded a hornblende age of 183 my and a biotite age of 148 my It was discovered after sample 136 was analyzed that many hornblendes from this region are highly refrac- tory and do not release all radiogenic argon at standard laboratory fusion temperatures. Because the amount of hornblende remaining from sample 136 was insuffi- cient for a reanalysis, sample 136A was collected from freshly blasted outcrops close to the original locality. This sample and sample 123B from the same pluton, which yielded apparent ages of 154 my on biotite and 168 my on hornblende, were analyzed after the refrac- tory nature of the hornblende was discovered. The argon was extracted at higher than normal tempera- tures. Because these later samples yielded lower bio- tite and higher hornblende apparent ages than the cor- responding minerals from sample 136, it is thought that the hornblende from sample 136, if reextracted, would yield an apparent age exceeding 168 m.y., and probably greater than 183 my. DISCUSSION AND INTERPRETATION OF APPARENT AGES 15 Samples 123B, 136, and 136A are the only represen- tatives of the porphyritic hornblende-biotite granodio- rite from which coexisting hornblende-biotite pairs have been analyzed. Samples 100, 104, and 123 are from this plutonic rock type, but only biotite was analyzed from them. Only biotite was analyzed from samples 75 and 135, which have strong lithologic similarities to the porphyritic hornblende-biotite granodiorite but may or may not be the same genetic unit. The highly mafic bodies, which have wide distribu— tion in the eastern and northeastern parts of the area, yield biotite apparent ages that range from 74 to 145 m.y., and hornblende apparent ages that range from 109 to 199 my years. Figure 3 illustrates the degree to which hornblende is more retentive of argon than bio- tite in these samples. The cluster or hornblende appar- ent ages between 163 and 199 my represents rocks that have been reset varying degrees, as indicated by the much wider scatter of coexisting biotite apparent ages. Of 24 apparent ages on biotite from samples unques- tionably within the discordant zone, 5 (samples 100, 104, 123, 123B, and 136 A) were from the porphyritic hornblende-biotite granodiorite, and 14 (samples 72, 73, 73D, 75, 76, 78, 78A, 78B, 78C, 79, 81, 122, 133, and 134) were from mafic plutonic types that are probably from 160 my to more than 200 my old on the basis of their apparent potassium-argon ages. Six samples either in or on the periphery of the zone were from plutons of unknown age; none of the apparent ages within the zone that were used in the contouring were on rocks known to be post-Jurassic in age. Samples 73A and 73B purposely were not used in the contouring because they are both from a pluton that is probably about 75 my. old. The outer limits of the discordant zone are not well defined because the apparent age gradient becomes progressively less steep away from the center of the zone. The discordant ages in the outermost part of this zone probably grade very gradually into concordant near-emplacement ages over a distance of as much as 10 km. Samples 134, 135, 136, and 136A and their contours appear to be representative of this gradation. The gradient between samples 134 and 135 is very steep but changes sharply somewhere near sample 135, then rises very gradually for 20 km eastward to the apparently near emplacement age at 136. AREA OF ANOMALOUS COOLING AGES Apparent ages on biotite from samples collected within the area enclosed by the discordant zone range from a low of 57 my in the San Gabriel Mountains to a high of 82 my in the San Bernardino Mountains. The - Lu [I d E E E 50 _ W Z _ /Biotite Homblende\ 7o — — 81 133 79A 80 — 102A ~ 72 73 so A _ 100 — 78C . — g 76 _ 109 _ > 110 u. 730 a 123A> 120 — — 2 Q 134 2' 133A 5 130 - ~ §_ 78B 5 < 140— - '2 a: 1222 \ E 150 ‘ \\ ' a. \ < 1233 -\ \ . \\§ 160 — ‘\‘\\ _ — 136 —-————5'<- \ \ ‘ \\ \ \ \ 17o — \ _ \\ \\ , 180 — - 190 .1 _ 200 — - FIGURE 3,—Apparent ages of coexisting hornblende-biotite pairs from pre-Cretaceous rocks. Line from labeled bio- tite sample conn acts coexisting hornblende. No line in- dicates only biotite dated; dashed lines connect samples from the porphyritic hornblende-biotite granodiorite. 99-m.y. and 88-m.y. biotite ages on samples 1 and 1A, respectively, are not included in this discussion be- cause there may be a large fault separating the base- ment rocks of the Santa Monica Mountains, where the two samples were collected, from the basement rocks of the San Gabriel Mountains to the east. The spacing between samples in most of the San Gabriel Mountains is close enough that the contours accurately portray the arcuate trough in the center of the range. The small apparent-age high located just east of the trough is probably real, but the northern prong defined by the 72-m.y. contour may not be. 16 GEOCHRONOLOGY OF THE TRANSVERSE RANGES AND MOjAVE DESERT, SOUTHERN CALIFORNIA Except for the northwest-trending apparent—age high in the western San Bernardino Mountains, the detailed configuration of features defined by the con— tours east of the San Andreas fault may or may not be real. The gradient of the contours is so low that the experimental error of the dating method is great enough to change the details of these features in many places. Even though the detailed configuration may be different than shown, the existence, location, and gen- eral trends defined by the apparent-age highs and lows probably are real. In the eastern half of the San Ber- nardino Mountains, for example, the 66-m.y. and 68- m.y. troughs and the 72-m.y. high that separates them are probably real, although the actual shape of these features and their exact magnitude may be slightly different than shown. The east-west structural trends characteristic of the Transverse Ranges are prominently reflected by the apparent-age contours in the southern part of the San Gabriel Mountains and show up well on both contour maps. The northwest trends in the northeasternmost part of the range (pl. 1C) may or may not be real be- cause they were generated by including apparent ages from samples on the northeast side of the San Andreas fault. If the displacements proposed for the San An- dreas fault are accurate (Hill and Dibblee, 1953; Crowell, 1962; Ehlig, 1968; and Ehlert and Ehlig, 1977), the trends within the San Gabriel Mountains generated by using apparent ages on the northeast side of the fault are probably not real. Contours using only ages within individual blocks (pl. 1D) showonly east- ward trends in the eastern San Gabriel Mountains and may more accurately portray the real trend of the con- tours than the map using all biotite ages. This may obtain in the southern San Bernardino Mountains south of the Santa Ana Canyon fault where the con— tours show a fairly pronounced east trend on line with the east trends along the front of the San Gabriel Mountains. The gradient of the contours south of the fault in Santa Ana Canyon, as shown on plate 1D, however, is so shallow that these trends may or may not be real. Most of the control for the trough of low ages near the intersection of the Pinto Mountain and north branch of the San Andreas fault (pl. 1C) is from a single date on a sample (112A) collected south of the San Andreas fault. The contours were drawn to connect this relatively young apparent age with the area of young apparent ages northeast of the San Andreas fault. The contour pattern generated by connecting these two areas may be misleading, however, as the geologic setting in the area of sample 112A is the same as that in the eastern San Gabriel Mountains and not the same as that on the northeast side of the San An— dreas fault. The entire block bounded by the San An- dreas, San J acinto, and Banning faults appears to have been displaced southeastward along the San Jacinto fault. EMPLACEMENT OR N EAR-EMPLACEMENT AGES Only six samples, 136, 136A, 123B, 78A, 73B, and 1, have yielded dates that approach concordance and may be close to emplacement ages; three others, 135, 100, 73A, on the basis of their position relative to the dis- cordant zone, might yield near-concordant potassium- argon ages if coexisting minerals were dated or were available to be dated. The paucity of concordant num- bers outside the discordant zone is in part misleading owing to the fact that the zone of discordance lies near the limit of our sampling. It is not known how far east or northeastward the rocks will yield emplacement or near-emplacement potassium-argon ages, although Lanphere (1964) reports a 1,190-m.y. potassium—argon apparent age on biotite from a sample taken in the Marble Mountains, about 60 km northeast of the 10- cality of our sample 136. The same rock yielded a 206Pb/WU zircon age of 1,450 my. (Silver and McKin- ney, 1963). The 18-percent difference between the lead-uranium age and the potassium-argon apparent age is probably produced by contact effects of nearby mesozoic plutonic rocks on the biotite; if it is, then the plutonic rocks in the Marble Mountains do not reflect the regional resetting found west of the discordant zone. The ambiguity of sample 136 yielding an apparently concordant age, 163 my. on biotite and 162 my. on hornblende, is discussed in the section on the discor- dant zone. The emplacement age of this rock is prob- ably greater than 183 m.y. as indicated by the appar- ent hornblende age from sample 136A. The 170-m.y. apparent age of hornblende from sam- ple 78A may be approaching the emplacement age of that rock, because the coexisting biotite yielded an ap- parent age only 25 m.y. younger. The pluton from which this sample was taken is a medium-grained hornblende-biotite granodiorite. It is texturally and modally different from the porphyritic hornblende- biotite granodiorite of sample 136, but because of their close apparent ages, the two plutonic types may have been emplaced at about the same time. Sample 73B (75 m.y., biotite;) 72 my. hornblende is a leucocratic hornblende-biotite quartz monzonite that yielded a concordant age that probably is close to the emplacement age of the rock. Sample 73A, 76 m.y., biotite, is from the same pluton, but only biotite was dated from this sample. Note that not all granitic rock outside the zone of discordance is necessarily old—in the 150-m.y. to 200-m.y. range. Samples 73A and 73B are cases in point; both were collected from a relatively DISCUSSION AND INTERPRETATION OF APPARENT AGES 17 young pluton that is near the limits of the thermal disturbance. Because they are younger than the rocks whose apparent ages are used in the contouring, and because contouring of apparent ages outside the dis- cordant zone has essentially no meaning, these younger apparent ages have not been used in any of the contouring. OTHER ANOMALOUS FEATURES OF THE APPARENT AGES The relative ability of hornblende and biotite to re- tain radiogenic argon at elevated temperatures is well documented both experimentally (Mussett, 1969) and empirically (Hart, 1964; Hanson and Gast, 1967; Mil- ler and Engels, 1975). In almost all cases, if coexisting hornblende and biotite give discordant apparent ages, the hornblende will give the older age of the two. Hart (1964) and Mussett (1969) in particular showed that over a fairly wide range of temperatures, hornblende is much better able to retain radiogenic argon at any given temperature within that range. The refractory character of hornblende is particu- larly well demonstrated in samples from the report area. After most of the hornblendebiotite pairs had been dated, it became apparent that an unusually large number of them (about 35 percent) gave results in which the hornblende was younger than the biotite by 3 my. or more. When checks on analytical proce- dures were made, we discovered that many of the hornblendes dated were extremely refractory and were not completely melting during the argon-extraction process. As a result, all hornblendes for which a suffi- cient amount of sample remained were reextracted at much higher than normal melting temperatures for much longer than normal melting times, and for one sample, sample 1, a flux of pyrex glass was used to insure that melting was absolutely complete. Samples were recollected at a few localities and new mineral separates prepared. Most of the new determinations on hornblende gave apparent ages that were as old or older than coexisting biotite. Three of the 45 hornblende-biotite pairs still gave apparent hornblende ages younger than the coexisting biotite. Even though the amount by which the hornblende was "younger” than the biotite is less than the analytical error of the method, we considered it significant that 7 percent of the pairs showed a bias in the direction opposite that which is normal for this mineral pair. Although only three of the redetermined samples, 31, 54, 73B, gave apparent hornblende ages that showed the reversal, the amount of sample remaining was insufficient to redetermine ages on five other sam- ples, 25, 50, 52, 101, and 136. Recollection and rede- termination of these five samples may or may not re- move the unexpected hornblende-biotite apparent age reversal; nonetheless, the three results obtained ap- pear to have well-established reversals that are real. In southern California, this reversal phenomenon appears to be limited to rocks from the San Gabriel Mountains and from east of the San Andreas fault. Of about 30 discordant ages on coexisting hornblende- biotite pairs reported by Krummenacher, Gastil, Bushee, and Douport (1975) from the Peninsular Ranges province, southern California, hornblende is in all cases older than the coexisting biotite. Even more detailed dating by F. Miller, D. Morton, and C. Smith (unpubl. data, 1979) and by V. Todd and W. Hoggatt (oral commun., 1977) in the northern part of the Penin- sular Ranges bear out the apparent absence of hornblende-biotite apparent-age reversals in that province. Possible exceptions to this generalization are near-concordant ages reported by Dalrymple (1976) from two samples of the San Marcos Gabbro on the west'side of the Peninsular Ranges that show the ap- parent hornblende-biotite reversal. The complete ab- sence of reversals in all other potassium-argon dating done in the Peninsular Ranges suggests that the argon extractions on these two hornblendes may not have been at high enough temperatures for long enough periods to obtain all radiogenic “"Ar. Reversals in southern California have been reported on 20-m.y.-old plutonic rocks from the Chocolate Mountains southeast of the Salton Sea on the east side of the San Andreas fault (Miller and Morton, 1977). In all samples dated, hornblende was younger than coexisting biotite, but the difference was small enough that all dates were concordant. It is not known if the age reversal in these rocks is produced by refractory hornblende, however, because the refractory nature of hornblendes from southern California rocks was not known when the paper was published. The most refractory hornblendes appear to come from two groups of rocks: (1) hornblende-biotite rocks in which the hornblende-biotite ratio is near one or greater than one and (2) rocks that show cataclasis. The rocks having near one or greater than one hornblende:biotite ratio generally have a higher color index than rocks that contain relatively nonrefractory hornblende. Only one of the relatively leucocratic quartz monzonite plutons with a low hornblende:bio- rtite ratio, sample 73B, may contain anomalously re- fractory hornblende. Since this is one of the samples that was not rerun, it is not known if the hornblende is unusually refractory or if it indeed is yielding an ap- parent age lower than the coexisting biotite. Rocks that show signs of cataclasis, particularly in the San Gabriel Mountains, contained refractory hornblende; samples 19 and 46 are examples. 18 GEOCHRONOLOGY OF THE TRANSVERSE RANGES AND MOJAVE DESERT, SOUTHERN CALIFORNIA In addition to the samples showing hornblende- biotite reversals, a few other samples yielded unex- pected apparent ages that warrant explanation or at least mention. Sample 13 is a highly porphyritic biotite-bearing phase of the Mount Lowe Granodiorite of Miller (1926). It contains no hornblende, but it does contain small amounts of muscovite, which is probably a late-stage primary mineral or could be secondary. Because the 6-m.y. difference in the biotite—muscovite apparent ages, regardless of the origin of the musco- vite, is outside the error of our measurements, the pair should be considered discordant. Samples 22 and 22A were collected within 100 m of one another; not only did both give discordant ages, but the difference in hornblende ages—29 my (22, 118 m.y.; 22A, 147 m.y.)—is greater than might have been expected from samples collected so close together. Al- though both rocks are hornblende-biotite diorite, sam- ple 22A is almost a hornblendite; it has a color index of about 80, whereas sample 22 has an index of 50. Sam— ple 22A is also slightly coarser grained than 22 and in places exhibits pegmatitic textures. The difference in the apparent ages yielded by the hornblendes could be a function of differences in emplacement ages although both samples appear to be no more than different phases from a single contiguous body. Most likely, the difference in apparent ages is a result of differences in the structure of the hornblende crystals of each sample and their relative ability to retain argon under condi- tions conducive to partial outgassing of the argon. Samples 8 and 40 also yielded discordant hornblende-biotite pairs, although sample 40 is barely discordant by our definition. Both of these samples are relatively mafic hornblende-biotite granodiorites, and both contained hornblende that was highly refractory. Samples 59 and 89 from the San Bernardino Mountains are both discordant, but they are sur- rounded on all sides except the south by concordant reset ages. The samples from localities 8, 13, 22, 59, and 89 yield discordant apparent ages; they may indicate a transi- tion from a zone of concordant anomalous ages to a discordant zone similar to that found north and east of the San Bernardino Mountains. However, the lack of datable material northwest of localities 8 and 13 and the fault boundary and local structural complications south of localities 22, 59, and 89 make it impossible to test this hypothesis. It is not known why sample 40 is discordant, as it appears to be in a part of the area of anomalous ages where the resetting is fairly complete. Sample 37, only 16 km to the northwest, is a gneiss of probable Precambrian age, but it gives an apparent biotite age of 72 my ‘ Sample 85, taken northwest of Big Bear Lake in the San Bernardino Mountains, is from a mafic hornblende-biotite monzonite that appears to differ chemically and petrologically from all other plutonic rocks in the San Bernardino Mountains. The rock con- tains 18 modal percent less quartz than the average for all plutonic rocks in the range, and plots well off the apparent differentiation curve for all other plutonic rocks in the range. Much of the hornblende in this rock has a core of partly altered pyroxene that could not be separated completely from the hornblende. Two splits of different purity (determined by grain counts of sepa- rates in immersion oils) were analyzed for argon; one with 11 percent pyroxene gave an apparent age of 126 m.y.; and the other, with 15 percent pyroxene, gave an apparent age of 197 my Because of these results and past experience where pyroxene yielded anomalously old potassium-argon ages (see Engels, 1975; and Dal— rymple and Lanphere, 1969, p. 125), the hornblende apparent ages obtained for this sample are not consid- ered indicative of emplacement age or degree of reset- ting by a younger thermal event, even though the rock is probably older than the biotite apparent age indi- cates (see Miller, 1976). INTERPRETATION OF APPARENT POTASSIUM-ARGON AGES With the possible exception of samples from a few restricted areas, the potassium-argon apparent ages of rocks surrounded by the zone of discordance appear to be the result of almost complete resetting by a thermal disturbance that culminated in Late Cretaceous to early Tertiary time. Three independent lines of evi- dence point up the degree to which the completeness of the resetting has occurred. 1. Rocks known to be much older than their potassium-argon ages indicate resetting similar to that of the Mesozoic plutonic rocks. Samples 94 and 110 from the Precambrian Baldwin Gneiss of Guillou (1953) yield Cretaceous potassium-argon apparent ages that fit exactly the contoured apparent ages for the surrounding Mesozoic granitic rocks. Sample 94, in fact, yielded concordant potassium-argon apparent ages on coexisting muscovite and biotite. The Precam- brian age of the Baldwin Gneiss is well established on the basis of a lead-uranium date on zircon (1750 my, Silver, 1971) and because it is unconformably overlain by late Precambrian and Paleozoic sedimentary rocks (Stewart and Poole, 1975). Sample 37 from the San Gabriel Mountains and samples 59A and 116A from the San Bernardino Mountains are from unnamed gneisses of probable Precambrian age. All of these samples give Cretaceous apparent ages that fit the contouring of the Mesozoic granitic rocks. Sample 79 is from a hornblende-gneiss of probable Precambrian age DISCUSSION AND INTERPRETATION OF APPARENT AGES 19 in the Mojave Desert. Although it gives an age about 20 m.y. older than what a biotite would be predicted to yield at that locality, it is located only about 3 km from the steep gradient of the discordant zone, and therefore it is probably strongly reset. 2. Coexisting mineral pairs within the area enclosed by the discordant zone in general yield concordant or near-concordant ages. Many of these concordant ages are on rocks known to be much older than the meas- ured potassium—argon age on the basis of lithologic cor-, relation with rocks outside the reset area. 3. The apparent ages yielded by different samples from the same pluton are dependent on where in the pluton the samples were collected. The form of the con- tours generated by these apparent ages shows no rela- tion to the configuration of the pluton, nor does the form of the contours of all the apparent ages in the region show any relation to the configuration of any single pluton. A large quartz monzonite pluton that occupies most of the area between Lake Arrowhead and Big Bear Lake is an excellent example to illustrate the range of apparent ages yielded by a single plutonic body. Samples 60 (66 m.y.), 87 (70 m.y.), 86 (71 m.y.), 88 (74 m.y.), and 91 (70 m.y.) were all collected within this pluton, and sample 93 (68 m.y.) was collected from a slightly more mafic marginal phase. The 8-m.y. range in apparent ages is beyond the experimental error of our measurements, and the configuration of the contours generated by these apparent ages is inde- pendent of the shape of the pluton. The thermal disturbance that caused such complete resetting may or may not have been associated with the emplacement of the major part of the plutonic rocks in the region. Study and limited geologic mapping of the plutons to date does not support or disprove the association. A reconnaissance examination of the plutonic rocks in the Transverse Ranges and southern Mojave Desert was made during the potassium-argon sampling. Even though the petrology, extent, and internal and contact relations of these bodies could not be studied in detail, a qualitative estimate of the rock types, their gross distribution, and their relative abun- dance was gained. On the basis of petrologic associ- ations and geologic relations with dated rocks outside the discordant zone, it is felt that many of the plutons in the area enclosed by the discordant zone east of the San Andreas were emplaced 70—80 m.y. ago. These plutons, voluminous in the San Bernardino Mountains and smaller and more widely scattered in the Mojave Desert, consist of biotite quartz monzonite to granodiorite. They are clearly younger than most, if not all, other plutonic rocks in that region. Where in- trusive relations with other granitic rocks are exposed, these plutons clearly intrude the other rocks. They have almost no internal structures such as foliation or lineation and commonly crosscut these structures in older plutonic rocks. These younger bodies, in most cases, are considerably more leucocratic than the plutonic rocks they intrude. The chief line of evidence supporting the association between the resetting and the relatively young plutonic rocks just described (Cretaceous) is the coinci- dence of the large area of “young” apparent ages in the San Bernardino Mountains, and three probable Cre- taceous plutons of almost batholithic size that form the core of the range. Even though these "younger” plutons are more widely separated in the southern Mojave Desert, they could be more voluminous at a relatively shallow depth. If they have more volume at depth, then the large reset area of anomalous ages and the enclos- ing discordant zone could have been produced by emplacement of this large volume of relatively young plutonic rock. The complex potassium—argon appar- ent-age patterns that exist at present, then, pre- sumably result from emplacement of the relatively young plutons and resetting of older rocks by the younger bodies, compounded by a nonuniform cooling history for the region. Two other lines of evidence, though not completely negating the presumed younger plutons in the region as being the cause of the anomalous ages, suggest that they may have a minor role, if any at all. (1) Recon- naissance potassium-argon dating by the authors and by Janet Morton of the U. S. Geological Survey sug- gests that the anomalous-age zone may be more exten- sive than is now known, extending much farther northwest, at least to the Garlock fault. In much of this area of reconnaissance dating, none of the presumed younger plutons occur. A large number of contrasting plutonic types yield approximately the same potassium-argon apparent ages, suggesting complete resetting. (2 The large area of relatively young potassium-argon apparent ages in the San Gabriel Mountains is not associated with any plutons that even approach being as young as the apparent ages. In fact, most of these rocks are probably in the 100—220-m.y. range. The relatively young apparent ages in the San Ga- briel Mountains may be a special case, however, as there appears to be a general relation between the Vincent thrust fault and other thrust faults correlated with it and areas of unusually low apparent ages in southern California. In the San Gabriel Mountains, the youngest apparent ages lie above the projection of the Vincent thrust (pl. 10), and the area ofyoung apparent ages in the Whitewater River area is above the projec- tion ofa probable correlative of the Vincent. Two alas- kite‘ masses from the upper plate of the Chocolate 20 GEOCHRONOLOCY OF THE TRANSVERSE RANGES AND MOJAVE DESERT, SOUTHERN CALIFORNIA Mountains thrust, 3 Vincent correlative, yielded 49.2 m.y. and 53.0 m.y. apparent ages on muscovite. Ehlig, Davis, and Conrad (1975) consider the minimum age of the Vincent thrust to be 52.7 m.y. on the basis of a rubidium-strontium isochron. If the relatively young rubidium-strontium and potassium-argon apparent ages are related to the thrust fault, it suggests that the potassium-argon resetting in the vicinity of the thrust may extend some distance into the upper plate; and that the thrust underlies a large part of southern California. Although there is a coincidence between exposures of the Vincent thrust and the areas of un- usually low apparent ages, there is no evidence to either support or refute a relation between the reset- ting of the entire region and the thrust faulting. Since the anomalous cooling ages apparently extend over such a large region, the geologic process that caused the resetting presumably operated over as great or greater an area. The anomalous cooling ages may in fact be related to continued plate motion beneath the region of resetting for an extended period after magma generation and pluton emplacement in this region had - ceased (R. 0. Castle, oral commun., 1978). After emplacement of plutons in the Cretaceous, continuing motion of the Pacific plate being thrust beneath the North American plate may have furnished sufficient heat to the region so that the temperature of the plutonic rocks did not fall beneath the closing tempera- tures of biotite, hornblende, and muscovite until latest Cretaceous or early Tertiary. Coney and Reynolds (1977) have suggested that the regional distribution in the ages of plutonic rocks in western North America is a function of the angle at which the subducting plate plunged under the conti— nent; that is, the shallower the plate angle, the farther inland plutons were generated and emplaced. They conclude from the distribution of ages that the angle of the plunging plate was relatively steep in the Early Cretaceous, and plutons were intruded near the edge of North America. As the angle became progressively shallower, younger plutons were intruded farther in- land. Finally, about 40 m.y. ago, the angle began to steepen, and plutons were again emplaced closer to the edge of the continent. During this process, the combi- nation of regional heating by emplacement of Creta- ceous plutons and continued heat generation by the downgoing Pacific plate at progressively shallower levels may have kept the crystalline rocks of our sam- ple area at a temperature too high to permit the min- erals used for potassium-argon dating to retain argon. There appears to be no relation between topography and apparent age. Even though the main part of the area of anomalous ages coincides with the San Gabriel and San Bernardino Mountains, it extends into the topographically lower Mojave Desert. Although the significance of the association is not understood, several geologic features that occur in the Transverse Ranges may possibly be related; the zone of anomalous ages is one. 1. The mountain ranges themselves, the inter— nal features within the ranges, and the bounding structures all aline in an eastward trend. These features have long been recognized and are well summarized by Baird, Morton, Baird, and Wood- ford (1974), who discuss the interdependent rela- tions between the various east-trending features“ 2. The western part of the 1959—74 southern California uplift identified by Castle, Church, and Elliott (1976) and another uplift that occurred be- tween 1897 and 1906 (R. 0. Castle, oral commun., 1978) coincide closely in form, trend, and location to the western Transverse Ranges. 3. The east—trending alinement of the mountain / ranges with the Murray fracture zone has long been recognized, but the two features are consid- ered to be only indirectly related by von Huene (1969), who has investigated the association. 4. A prominent high-velocity zone (8.3 km/sec), identified by Hadley and Kanamori (1977) utiliz- ing P-wave delay times from natural and artificial seismic events occurring in southern California, is roughly east-trending and coincides closely with the location of the Transverse Ranges. This zone, .which they interpret to be at a depth of about 40 ‘ km beneath the Transverse Ranges, crosses the San Andreas fault and is neither offset by the fault nor shows any reflection of the fault. The high- velocity zone, which appears to be an extremely fundamental feature, may represent the link be- tween the Transverse Ranges and Murray fracture zone, suggested by von Huene (1969, p. 475), "Pos- sibly a fundamental lineament in the crust, an ex- tension of the Murray, inactive since at least the mid-Tertiary, provided a convenient trend for de- velopment of the Transverse Ranges in response to deformation along the San Andreas fault system.” Since the Tranverse Ranges and the Transverse Ranges structures cross the San Andreas fault, and because the Transverse Ranges structures and the San Andreas fault are contemporaneously act- ive and have been for some time, it would appear that whatever controls development of the Transverse Ranges structures is of a nature fun- damental enough to persist at depth on both sides of the San Andreas fault despite continued move- ment on the fault. The high-velocity zone identified by Hadley and Kanamori crosses the San, Andreas, and in a similar way, so does the zone of anomalous cooling ages as shown on plate 1C. The configuration and extent of DISCUSSION AND INTERPRETATION OF APPARENT AGES 21 both the P-wave delay-time contours and the zone of anomalous cooling ages show a remarkable similarity on the east side of the San Andreas. Even some of the specific areas of minimum P-delay times correspond fairly well to areas of minimum apparent potassium- argon ages. Although Hadley and Kanamori are able to interpret the anomalous P—delay times as indicating the rela- tively shallow occurrence of a high-velocity zone be- neath the Transverse Ranges, the significance of the zone of anomalous ages is not clear to us beyond the speculations made in preceding paragraphs. If the similarity in configuration of the two unlike phenomena is indicative of a relation between the two, particularly a cause and effect relation, then the rela- tion must date back to at least 60 my. to 70 my. ago because of the completeness of resetting to this general age range in the zone of anomalous ages. FAULT OFF SETS OF CONTOURS In contouring the apparent ages within individual fault blocks (pl. ID), only those blocks bounded by major faults with a relatively long trace length were considered. These include the westernmost three of the major northwest-trending faults in the southern Mojave Desert, that fault system that bounds the north side of the San Bernardino Mountains, the fault in Santa Ana Canyon, the San Andreas fault, the San Gabriel fault, the Sierra Madre fault, and the frontal fault system for the San Gabriel Mountains. Only the apparent ages within an individual fault-bounded block were used for contouring that particular block; no apparent ages outside a particular block were al- , lowed to affect the form or position of the contours within that block. Where data were particularly sparse or an interpretation particularly subjective, the con- tours were not extended to the boundary of the particu- lar block. It should be kept in mind that since the apparent-age contours are poorly understood features, all apparent offsets are at best only estimates. The contours repre- sent the smoothed surface trace of planes of equal ap- parent age and the attitude of these planes is essen- tially unknown. If in places the planes have a low dip, then any component of vertical movement would cause a large apparent offset. By far the best feature to indicate offsets across faults is the zone of discordance north and east of the San Bernardino Mountains. Control on the zone is rel- atively good, and the apparent age gradient is steep. It is not known, however, if the attitude of the contours (planes of equal age) is steep even though the gradient is steep. The only faults intersected by the discordant zone are three in the Mojave Desert—the Helendale, the Lenwood, and the Camprock faults. At present, age control east of the Camprock fault is insufficient for contouring; therefore only the Helendale and Lenwood faults are discussed here. The contours appear to be offset by both of these faults, but the amount and sense of offset do not agree with estimates from other geologic evidence (Garfunkle, 1974). Apparent left-lateral displacement of about 8 and 10 km is suggested by offset of the projections of the 80- m.y. and 100- my contours, respectively, to the Len- wood fault. The 80-m.y. interval is well controlled by sample 79A on the east side of the fault, but samples 783 and 99 on the west side are 16 km apart. On the west side, the 80-m.y. contour is projected approxi— mately straight, but it could curve as much as _2 km in either direction without causing a contour concentra- tion different from that found on, other parts of the map. The 100-m.y. contour has about the same degree of control as the 90— m.y. contour on the west side of the fault, but it is well controlled by sample 78C on the east side. If the contour spacing near the Camprock fault were about constant to the Lenwood fault, the projection of the 120-m.y. contour, for which there is good control on the west side of the Lenwood fault, would show about the same offset as the 100-m.y. con- tour. At the Helendale fault, there appears to be a disrup- tion of the discordant zone, but the nature and amount of offset are ambiguous. Because of the lack of control, the drawing of the contours is even more subjective here than on most of the map. As drawn, however, the 804m.y. contour shows a left-lateral displacement of 4 km, the 80-m.y. contour 3 km, and the 100-m.y. con- tour 2 km. As drawn on plate ID, a small embayment of 80+ m.y. apparent ages on the east side of the Helendale fault is required by sample 75. This embay- ment of relatively higher apparent ages is not consid- ered to be the right laterally offset equivalent of higher apparent ages on the west side of the fault. The prong of low apparent ages north of the embayment and the rapidly increasing apparent ages north of the prong are considered more likely to be the offset equivalent of the relatively old ages on the west side of the fault. Little quantitative value is placed on any of these conflicting estimates, although the sharp bend of the contours as drawn on plates 10 and 1D suggest some sort of dis- ruption at the fault. S. M. Miller (oral commun., 1977) has pointed out several geologic features showing about 4 km of right- lateral offset across the Camprock fault. These features are shown on the geologic map of the Rodman Mountain quadrangle (Dibblee, 1964b) and include the contact between a tactite and quartzite unit, the west edge of a quartz monzonite pluton, and an offset body of granite and quartz monzonite. Examination of the 22 geologic map of the Apple Valley quadrangle (Dibblee, 1960) shows about 6 km of apparent right-lateral offset of a quartz monzonite body west of Sidewinder Mountain. The quartz monzonite was checked in the field and found to be the same rock type on both sides of the fault, although this particular granitic type is fairly common at many places in the southern Mojave Desert and may or may not be the offset parts of a once-continuous body. A petrologically distinct pluton occurs in the area where Interstate Highway 15 intersects the Helendale fault. Samples 73A and 73B were collected from this body on opposite sides of the fault. Although the pluton and its outer contacts have not been mapped in detail, inferred extent of the body precludes a right-lateral offset of more than 1 or 2 km. These estimated offsets are considerably less than those suggested by Garfunkle (1974) and are consid- ered to be more soundly based on the geologic evidence available. The apparent offsets of the 80- and 100-m.y. contours by the Helendale fault do not agree with es— timates made from the offset plutons in either sense or amount. The apparent offset of the contours along the Lenwood fault is in the sense opposite that predicted from geologic evidence, and the amount twice as great. The most plausible explanation for the lack of agree- ‘ ment of both faults is that there is a component of vertical displacement on them. If it is assumed that the apparent ages are progressively more reset at depth, and that the contours dip outward from the source of the isotopic disturbance, then the block between the Helendale and Lenwood faults has been uplifted rela- tive to the adjacent blocks. It is not possible, however, to predict the quantitative effects of vertical movement on the contours because of the lack of information on the configuration of the planes of equal age at depth. Presumably, any distortion of these planes would be most apparent in and near the discordant zone where the apparent-age gradient is greatest. In the western San Bernardino Mountains, the prominent northwest-trending high in apparent ages could be the offset equivalent of the “nose” of high ap- parent ages immediately north of it on the Mojave Des- ert. If these two highs were once alined, the compo- nent of apparent right—lateral slip across the reverse fault system separating them would be about 15 or 20 km. If this offset is real and the apparent age lows on both sides of the east end of the same fault are real, then the amount of apparent slip across this zone de- creases eastward. There is no geologic evidence to sug- gest a component of strike-slip movement on this fault. The contour gradient in the vicinity of the Santa Ana Canyon fault immediately to the south is too low to define distinctive features for evaluation of possible GEOCHRONOLOGY OF THE TRANSVERSE RANGES AND MOJAVE DESERT, SOUTHERN CALIFORNIA offsets. This, however, is true for almost all of the anomalous age zone, and any of the relations suggest- ing offset should be considered little better than speculation, not only because the gradient of the ap— parent age contours is very low, but because of the unassessable effect on the contours by vertical movements across the numerous reverse faults in this part of the region. As contoured on plate 10, there is a clear break in both the contours and the style of the contours at the San Andreas fault. West of the fault, the pattern of the contours is relatively simple, an area of low apparent ages in the central part of the range flanked by a single high to the east. East of the fault, the pattern is consid— erably more complex and irregular, although the over— all east trends occur along the southern part of the San Bernardino Mountains, just as they do along the San Gabriel Mountains west of the fault. As mentioned in an earlier section, however, the gradient of the con- tours in the southern San Bernardino Mountains is so low that details defined by the contours may or may not be real. If the two areas of low apparent ages just south of the San Gabriel fault, one defined by a 60-m.y. contour and the other by a 58-m.y. contour, are separate lows, then the low defined by the 58—m.y. contour north of the fault might be the offset part of one of them (pl. ID). If the San Gabriel is considered a right-lateral strike-slip fault and one of the southern lows is the offset segment of the northern one, then presumably it is the more westerly of the two, which would entail a right—lateral separation of roughly 10+ km. The density of control points on the north side of the fault is so low, however, that the suggested correlation of the lows is speculative at best. HISTOGRA MS The histograms shown in figure 4 are probably a fair representation of the relative abundance of potassium-argon apparent ages for the plutonic rocks in the region because the region was sampled in a fairly uniform manner. No particular type or emplacement-age group was preferentially sampled, but, inescapably, most of the plutonic rocks are of Mesozoic emplacement age. The data show a prominent cluster of apparent ages between 65 my. and 75 m.y., with a prominent peak at about 70 my. Almost all of the apparent ages that make up this cluster are from the zone of anomalous ages, and most of those trailing off from 90 my. to 199 my. are from within, or just outside, the discordant zone. If more samples were available from outside the discordant zone, and if the uniform sample distribution were maintained, probably another peak would appear DISCUSSION AND INTERPRETATION OF APPARENT AGES 23 25- 20a 15- 10— 15" 10- NUMBER OF SAMPLES O 01 8 I .I I A. All samples B. west of San Andreas fault C. East of San Andreas fault In I nun. I'll-I rflm‘m nnm [I I I I I I I I EXPLANATION I Biotite D Hornblende N Muscovite _ | 70m.y. reference line Il'II I'III_El'_J I[‘HI'ITI'I'II I'I'l'll'I'II III'I 10- l D. San Bernardino Mountains E. Mojave Desert 50 60 70 80 90 1 00 1 1 0 i 0- lI:I_!IuI lll'll IQLMMW- 130 140 150 160 170 180 190 200 I APPARENT AGE, IN MILLIONS OF YEARS FIGURE 4,—Relative abundance of potassium-argon apparent ages of plutonic rocks in the eastern Transverse Ranges and southern Mojave Desert (A) and in selected structural subdivisions (B—E). between 160 m.y. and 200 m.y., the number of ages around 75 m.y. would increase, and possibly a cluster of ages between 200 m.y. and 220 m.y. would appear. The form of figure 4C points out the gradation from the zone of anomalous ages through the discordant zone to essentially emplacement ages on the east 24 GEOCHRONOLOGY OF THE TRANSVERSE RANGES AND MOJAVE DESERT, SOUTHERN, CALIFORNIA side of the San Andreas fault; no such transition exists on the west side (fig. 4B). The difference is more strik- ing when it is remembered that the two oldest appar- ent ages on 43 are from essentially the same locality. Almost all the apparent ages older than the main clus— ter on the east side of the San Andreas fault are from the Mojave Desert (compare figs. 40, D, and E). The main cluster of ages west of the San Andreas (fig. 4B) shows a distinct bimodal distribution and a slight shift of the mass as a whole toward the young direction. This shift clearly reflects the generally lower ages in the San Gabriel Mountains, and the relative paucity of apparent ages in the mid-sixties may be a function of the relatively steep gradient of the contours in this age interval. The lower age node of the bimodal distribution, however, could reflect resetting that is due primarily to the influence of the Vincent thrust fault. The higher age node and the separating trough could result from a different source of disturbance or could represent the rapid falling off of the effects of the thrust fault. In general, the histograms point up the same basic distribution of apparent ages in each of the major structural subdivisions except for those within and outside the discordant zone. REFERENCES CITED Armstrong, R. L., and Suppe, J., 1973, Potassium-argon geo- chronometry of Mesozoic igneous rocks in Nevada, Utah and southern California: Geological Society of America Bulletin, v. 84, p. 1375—1392. Baird, A. K., Morton, D. M., Baird, K. W., and Woodford, A. 0., 1974, Transverse Ranges province-A unique structural-petrochemical belt across the San Andreas fault system: Geological Society of America Bulletin, v. 85, p. 163—174. Beckinsale, R. D., and Gale, N. H., 1969, A reappraisal of the decay constants and branching ratio of “’K: Earth and Planetary Sci- ence Letters, v. 6, p. 289—294. Bowen, 0. E., Jr., 1954, Geology and mineral deposits ofthe Barstow quadrangle, San Bernardino County, California: California Di- vision of Mines and Geology Bulletin 165, p. 1-185. Castle, R. 0., Church, J. P., Elliott, M. R., 1976, Aseismic uplift in southern California: Science, v. 192, p. 251—253. Coney, P. J., and Reynolds, S. J., 1977, Cordilleran Benioff zones: Nature, v. 270, p. 403—406. Crowell, J. C., 1962, Displacement along the San Andreas fault, California: Geological Society of America Special Paper 71, 61 p. Dalrymple, G. B., 1976, K—Ar age of the San Marcos and related gabbroic rocks of the southern California batholith: Isochron West, no. 15, n.p. Dalrymple, G. B., and Lanphere, M. A., 1969, Potassium-argon dating—Principles, techniques, and applications to geochronol~ ogy: San Francisco, W. H. Freeman, 258 p. Dibblee, T. W., 1960, Preliminary geologic map of the Apple Valley quadrangle, California: US. Geological Survey Miscellaneous Field Studies Map MF—232, scale 1262,500. 1964a, Geologicmap of the 0rd Mountains quadrangle, San Bernardino County, California: US. Geological Survey Miscel- laneous Geologic Investigations Map I—427, scale 1:62,500. 1964b, Geologic map of the Rodman Mountains quadrangle, San Bernardino County, California: US. Geological Survey Map I—430, scale 1:62,500. Ehlert, K. W., and Ehlig, P. L., 1977, The “polka dot" granite and the rate of displacement on the San Andreas fault in southern California: Geological Society of America Abstracts with Pro- grams, v. 9, no. 4, p. 415-416. Ehlig, P. L., 1968, Cause of distribution of Pelona, Rand, and Orocopia Schists along the San Andreas and Garlock faults, in Proceedings of Conference on geologic problems of San Andreas fault systems: Stanford University Publications in Geological Sciences, v. 11, p. 294—306. Ehlig, P. L., Davis, T. E., and Conrad, R. L., 1975, Tectonic implica- tions of the cooling age of the Pelona Schist: Geological Society of America Abstracts with Programs, v. 7, no. 3, p. 314—315. Engels, J. C., 1975, Potassium-argon ages of the plutonic rocks, sec- tion in Miller, F. K., and Clark, L. C., Geology of the Chewelah- Loon Lake area, Stevens and Spokane Counties, Washington: US. Geological Survey Professional Paper 806, p. 52—58. Evernden, J. F., and Kistler, R. W., 1970, Chronology of emplace- ment of Mesozoic batholithic complexes in California and west- ern Nevada: US. Geological Survey Professional Paper 623, 42 p. Garfunkle, Zvi, 1974, Model for late Cenozoic tectonic history of the Mojave Desert, California, and for its relation to adjacent re- gions: Geological Society of America Bulletin, v. 85, p. 1931— 1944. Garner, E. L., Murphy, T. J., Gramlich, J. W., Paulsen, P. J., and Barnes, 1. L., 1975, Absolute isotopic abundance ratios and the atomic weight of a reference sample of potassium: Journal of Research, National Bureau of Standards-A, Physics and Chemistry, v. 79A, p. 713—725. Guillou, R. B., 1953, Geology of the Johnston Grade area, San Ber- nardino County, California: California Division of Mines and Geology Special Report 31, 18 p. Hadley, D., and Kanamori, H., 1977, Seismic structure of the Transverse Ranges, California: Geological Society of America Bulletin, v. 88, p. 1469—1478. Hanson, G. H., and Gast, P. W., 1967, Kinetic studies in contact metamorphism zones: Geochim. et Cosmochim. Acta, v. 31, p. 1119—1153. Hart, S. R., 1964, The petrology and isotopic mineral age relations of a contact zone in the Front Range, Colorado: Journal of Geology, v. 72, no. 5, p. 493—525. Hill, M. L., and Dibblee, T. W., Jr., 1953, San Andreas, Garlock, and Big Pine faults, California: Geological Society of America Bulle- tin, v. 64, p. 443—458. Hill, R. L., and Beeby, D. J., 1977, Surface faulting associated with the 5.2 magnitude Galway Lake earthquake of May 31, 1975: Mojave Desert, San Bernardino County, California: Geological Society of America Bulletin, v. 88, p. 1378— 1384. Hsii, K. J., Edwards, G., and McLaughlin, W. A., 1963, Age of the intrusive rocks of the southeastern San Gabriel Mountains, California: Geological Society ofAmerica Bulletin, v. 74, no. 4, p. 507—512. . ‘ Jennings, C. W., and Strand, R. G., compilers, 1969, Geologic map of California, Olaf P. Jenkins edition, Los Angeles sheet: Califor- nia Division of Mines and Geology, scale 1:250,000. Krummenacher, D., Gastil, R. G., Bushee, J., Douport, J., 1975, K-Ar apparent ages, Peninsular Ranges batholith, southern Califor- nia and Baja California: Geological Society of America Bulletin, v. 86, p. 760—768. Lanphere, M. A., 1964, Geochronologic studies in the eastern Mojave Desert, California: Journal of Geology, v. 72, p. 381—399. Miller, C. F., 1976, Alkali-rich monzonites, southern and central California—a unique magmatic episode?: Geological Society of America Abstracts with Programs, v. 8, no. 3, p. 395. SAMPLE LOCALITIES AND DESCRIPTIONS 25 Miller, F. K., and Engels, J. C., 1975, Distribution and trends of discordant ages of the plutonic rocks of northeastern Washing- ton and northern Idaho: Geological Society of America Bulletin, v. 86, p. 517—528. Miller, F. K., and Morton, D. M., 1977, Comparison of granitic intru- 'sions in the Pelona and Orocopia Schists, southern California: US Geological Survey Journal Research, v. 5, no. 5, p. 643—649. Miller, W. J., 1926, Crystalline rocks of the middle-southern San Gabriel Mountains, California (abstract): Geological Society of America Bulletin, v. 37, no. 1, p. 149. Mussett, A. E., 1969, Diffusion measurements and the potassium- argon method of dating: Royal Society of London Geophysical Journal, v. 18, p. 257—303. Richmond, J. F., 1960, Geology of the San Bernardino Mountains north of Big Bear Lake, California: California Division of Mines Special Report 65, 68 p. Rogers, T. H., compiler, 1969, Geologic map of California, Olaf P. Jenkins edition, San Bernardino sheet: California Division of Mines and Geology, scale 1:250,000. Ross, D. C., 1972, Petrographic and chemical reconnaissance study of some granitic and gneissic rocks near the San Andreas fault from Bodega Head to Cajon Pass, California: US. Geological Survey Professional Paper 698, 92 p. Silver, L. T., 1968, Preliminary history for the crystalline complex of the central Transverse Ranges, Los Angeles County, California: Geological Society of America Special Paper 101, p. 201-202. 1971, Problems of crystalline rocks of the Transverse Ranges: Geological Society of America Abstracts with Programs, v. 3, no. 2, p. 193—194. Silver, L. T., and McKinney, C. R., 1963, U/Pb isotopic studies of a Precambrian granite, Marble Mountains: Geological Society of America Special Paper 73, p. 65. Silver, L. T., McKinney, C. R., Deutsch, S., Bolinger, J., 1963, Pre- cambrian age determinations in the western San Gabriel Mountains, California: Journal of Geology, v. 71, no. 2, p. 196— 214. Steiger, R. H., and Jager, E., 1977, Subcommission on geochronology: Convention on the use of decay constants in geo- and cosmo- chronology: Earth and Planetary Science Letters, v. 36, p. 359— 362. - Stewart, J . H., and Poole, F. G., 1975, Extension of the Cordilleran miogeosynclinal belt to the San Andreas fault, southern Califor- nia: Geological Society of America Bulletin, v. 86, p. 205—212. von Huene, R. E., 1969, Geologic structure between the Murray Fracture Zone and the Transverse Ranges: Marine Geology, v. 7, p. 47 5—499. SAMPLE LOCALITIES AND DESCRIPTIONS [All measurements from southwest corner of section indicated in feet] Map Field No. No. Locality Rock type 1 T2—5 150 E, 1,160 N, sec. 4, T. Hornblende-biotite quartz diorite or granodiorite, medium- to coarse-grained. 1 S., R. 14 W. Cataclastic foliation. Sphene-bearing. C.I. ~25 1A WT—2 4,320 W, 8,960 S, sec. 8, Hornblende-biotite granodiorite, medium-grained, sphene-bearing. C.I. ~15 T. 1 N., R. 13 W. , 2 T1—5 7,6501500 E, 5,150:’500 Hornblende-biotite quartz diorite, medium- to fine-grained. Slight cataclastic S, sec. 9, T 1 N., foliation. C.I. ~60 R. 13 W. 3 T76—4 1,310 E, 3,690 N, sec. 6, Biotite quartz diorite, medium- to fine-grained. Probably metamorphosed. T. 2 N., R. 14 W. C.l. ~18 4 T77—4 3,900 E, 980 N, sec. 2, T. Hornblende-biotite granodiorite, medium-grained, equigranular, C.I. ~18 2 N ., R. 13 W. 5 T50—4 630 E, 7,400 N, sec. 31, T. Hornblende-biotite granodiorite, coarse-grained, equigranular. C.I. ~20 2 N., R. 12 W. 6 T49—4 2,800 E, 8,350 S, sec. 31, Hornblende-biotite granodiorite, slightly gneissic. Probably metamorphosed. T. 2 N., R. 12 W. Medium-grained. C.I. ~25 7 T33—4 12,500 E, 500 N (approx), Mount Lowe Granodiorite of Miller (1926), foliate and lineate. Bimodal grain size. sec. 12,T.2N.,_R. 13 W. Cataclastic, recrystallized. C.I. ~6 8 , T80—4 18,680 E, 10,410 N, sec. Hornblende-biotite granodiorite, medium-to fine-grained, equigranular. 01. ~20 1, T. 2 N., R. 13 W. 9 T34—4 22,000t500 E, 150:200 Biotite quartz diorite, medium-grained, slightly foliate. Probably metamor- S, sec. 12, T. 2 N., phased. C.l. ~20 R. 13 W. 10 T79—4 2,470 E, 2,650 N, Sec. 24, Hornblende-biotite diorite, medium-to fine-grained. Faint foliation. T. 2 N., R. 12 W. 01. ~25 to 30 11 T78—4 3,150 E, 670 N, sec. 29, T. Hornblende-biotite granodiorite, medium-grained, equigranular. C.I. ~20 2 N., R. 11 W. 12 T48—4 2,950 E, 5,060 N, sec. 10, Hornblende-biotite granodiorite, medium-grained, equigranular. C.I. ~22 T. 1 N., R. 11 W. 13 T38—4 3,825 E, 4,075 N, sec. 4, Muscovite-biotite granodiorite, medium-grained, with phenocrysts to 6 cm in T. 3 N., R. 11 W. length. Foliate, C.I. ~10. Mount Lowe Granodiorite of Miller (1926). 14 T82—4 460 E, 2,810 N, sec. 19, T. Biotite quartz monzonite, coarse-grained, foliate. Slightly cataclasized, but re 4 N., R. 10 W. crystallized. C.I. ~12 26 GEOCHRONOLOGY OF THE TRANSVERSE RANGES AND MOJAVE DESERT, SOUTHERN CALIFORNIA Map Field No. No. Locality Rock type 15 T83—4 430 W, 2,220 N, sec. 31, Biotite quartz monzonite, coarse-grained. Slightly porphyritic. C.I. ~5 T.4N.,R. 10 W. . 16 T36—4 2,450 E, 1,350 N, sec. 13, Biotite quartz monzonite, coarse—grained, equigranular. C.I. ~7 T. 3 N., R. 11 W. 17 T35—4 4,300t500 E, 100:200 N, Mount Lowe Granodiorite of Miller (1926), foliate and lineate. Bimodal grain size. sec. 2,T. 2N.,R. 11 W. Cataclastic, recrystallized. C.I. ~10 18 T67—4 5,500 E, 3,080 N, sec. 25, Biotite quartz monzonite, leucocratic, medium-grained, slightly foliated. C.I. ~4 T. 2 N., R. 11 W. 19 T47—4 860 E, 2,660 N, sec. 13, T. Hornblende-biotite granodiorite, mildly cataclasized, coarse-grained. C.I. ~30 1 N., R. 11 W. 20 T46—4 50 E, 3,200 N, sec. 23, T. Cataclastic hornblende-biotite granodiorite, coarse-grained foliate. Slightly 1 N., R. 10 W. banded. C.I. ~25 21 T68—4 50 E, 18,350 N, sec. 2, T. Hornblende-biotite-bearing granitic gneiss, medium-grained. Incipient segrega- 1 N., R. 10 W. tion bands. C.I. ~25 22 T105—4 1,500 E,-640 N, sec. 15, T. Hornblende-biotite diorite or amphibolite, fine-grained. Slightly foliate. C.I. ~50 1 N., R. 9 W. 22A T1—6 1,500 E, 640 N, sec. 15, T. Hornblendite. Biotite-bearing, medium-grained. Massive. C.I. ~80 1 N., R. 9 W. 23 T41—4 1,350 E, 19,100 S, sec. 9, Hornblende-biotite granodiorite, fine-grained, equigranular. Large maflc segre- T. 3 N., R. 9 W. gation in more leucocratic plutonic rocks. C.I. ~25 24 T37—4 4,050 W, 2,030 S, sec. 9, Gneissic biotite quartz diorite. Collected from a zone of mixed metamorphic and T. 3 N., R. 9 W. granitic rocks. Slightly foliate, medium-grained abundant inclusions. C.I. ~18 25 T102—4 1,680 E, 3,090 N, sec. 6, Hornblende—biotite granodiorite. Slight cataclasis. Slight foliation. C.I. ~12 T. 4 N., R. 9 W. 26 M26~4 950 E, 1,950 N, sec. 10, T. Hornblende-biotite granodiorite, medium-grained. C.I. ~30. Hornblende: 5 N., R. 8 W. biotite ~10:1 27 M27—4 3,850 E, 420 N, sec. 15, T. Biotite quartz monzonite: Porphyritic. Large quartz crystals. Medium-grained. 6 N., R. 9 W. C.I. =12 28 M30—4 4,300 E, 00 N, sec. 7, T. 6 Hornblende-biotite quartz monzonite. Slightly porphyritic. Medium-grained. N., R. 8 W. C.I. ~15 29 M31-4 5,110 E, 3,770 N, sec. 6, Muscovite-biotite quartz monzonite, medium-grained. Weathered rock, but micas T. 6 N., R. 9 W. fresh. 30 M32—4 1,550 E, 3,200 N, sec. 15, Hornblende-biotite quartz monzonite, medium- to coarse-grained, equigranular. . T. 7N.,R. 9w. C.I. ~15 31 M33—4 60 E, 5,480 N, sec. 1, T. 7 Hornblende-biotite quartz monzonite. Probably from same pluton as sample 30. N., R. 9 W. 31A M52—7 200 E, 100 S, sec. 17, T. 8 Hornblende-biotite granodiorite, coarse-grained. Massive. Large books of biotite. N., R. 9 W. Hornblende: biotite ~ 1:2. Sphene-bearing. C.I. ~15 32 M34—4 60 E, 650 N, sec. 12, T. 7 Biotite quartz monzonite, medium- to fine-grained. Biotite very fine grained. N., R. 8 W. C.I. ~5 33 M28—4 1,030 E, 1,820 N, sec. 9, Hornblende-biotite quartz monzonite, medium—grained, equigranular, C.I. ~12 T. 6 N., R. 7 W. 34 M35—4 300 E, 3,490 N, sec. 11, T. Alaskite. Garnet bearing. Contains about 1 percent biotite. Fine-grained, equi- 7 N., R. 7 W. granular. , 35 M29—4 1,180 E, 5,040 N, sec. 27, Biotite quartz monzonite, medium- to fine—grained. Equigranular. C.I. ~7 T. 7 N ., R. 6 W. 36 T100—4 4,170 E, 3,340 N, sec. 18, Biotite quartz monzonite. Leucocratic,banded. Fine-grained, nonporphyritic. C.I. ~4 T. 4 N., R. 8 W. 37 T101—4 4,870 E, 5250 N, sec. 24’ Banded gneiss. Biotite is only mafic mineral, no muscovite. Average layer about T. 4 N., R. 9 W. 5 mm thick. 38 T84—4 2,300:500E,2,500:500 Hornblende-biotite diorite. Fine-grained, equigranular, C.I. ~60 N,sec. 11,T. 3 N., R. 9W. 39 T99—4 800 E, 3,150 N, sec. 25, Hornblende-biotite quartz diorite. Medium- and fine-grained, bimodal grain size. T. 4 N., R. 8 W. Nonfoliate. C.I. ~45 40 T98—4 5,150 E, 2,000 N, sec. 4, Hornblende-biotite granodiori-te. Coarse grained, slightly foliate, C.I. ~25 T. 3 N., R. 7 W. 41 T106—4 4,640 E, 3,060 N, sec. 6, Hornblende-biotite quartz diorite. Medium-grained. Foliate, Biotite all T. 2 N., R. 7 W. chloritized. C.I. ~25 42 T7044 2,930 E, 12,100 N, sec. 1, Hornblende-biotite diorite. Fine-grained, equigranular, but slightly lineate. T. 1 N., R. 9 W. C.I. ~35 43 T71—4 1,640 E, 10,550 N, sec. 4, Hornblende-biotite quartz diorite. Medium- to fine-grained, slightly foliate. T. 1N.,R.8W. C.I. ~30 SAMPLE LOCALITIES AND DESCRIPTIONS 27 Map Field No. No Locality ROCk WW 44 T72—4 660 E, 2,150 N, sec. 20, T. Hornblende-biotite quartz diorite. Slightly cataclasized. Coarse-grained, equi- 2 N., R. 7 W. granular. C.I. ~30 45 T103—4 1,260 E, 390 N, sec. 6, T. Biotite quartz monzonite. 1 N., R. 7 W. 46 T104—4 960 E, 2,120 N,sec. 6, T. 1 Cataclastic hornblende-biotite quartz diorite. Faintly banded. Coarse-grained. N., R. 7 W 01. ~25 47 T73—4 1,680 E, 220 N, sec. 12, T. Cataclastic hornblende-biotite diorite. Almost a mylonite. Foliate and lineate. 1 N., R. 7 W. C.I. ~40 48 T74-4 5,025 E, 1,060 N, sec. 8, Cataclastic hornblende-biotite diorite. Coarser than sample 47. Foliate and ‘ T. 1 N., R. 7 W. lineate. C.I. ~30 49 T75—4 3,380 E, 3,190 N, sec. 1, Hornblende-biotite diorite. Cataclasized. Medium-grained, slightly foliate. T. 1 N., R. 7 W. C.I. ~25 50 T19—3 2,700 E, 2,020 N, sec. 11, Cataclastic quartz diorite. Medium-grained. Foliate and lineate. C.I. ~25 T. 2 N., R. 7 W. , 51 T86—4 950 W, 320 S, sec. 17, T. 2 Same as sample 53, except finer grained, and distinctly lineate. N., R. 6 W. 52 T4—3 2,960 E, 3,450 N, sec. 3, Hornblende-biotite quartz diorite. Coarse-grained, foliate. Cataclastic. C.I. ~20 ’ T. 1 N., R. 6 W. 53 T85—4 4,600 E, 4,480 N, sec. 27, Cataclasite. Coarse grained. Slightly foliate. Contains hornblende and biotite. T. 2 N., R. 6 W. 54 T1—4 4,270 E, 1,200 N, sec. 36, Hornblende-biotite-granodiorite. Porphyritic, slightly foliate. T. 3 N., R. 6 W. 55 'T2—4 650 E, 4,000 N, sec. 31, T. Hornblende-biotite granodiorite. Porphyritic. Same pluton as sample 54. 3 N., R. 4 W. 56 T3—4 200 E, 5,110 N, sec. 35, T. Biotite quartz monzonite. Equigranular. Slightly weathered. 3 N ., R. 4 W. 57 T53—4 1,890 E, 840 N, sec. 10, T. Hornblende-biotite granodiorite. Porphyritic. Probably same pluton as 2 N., R. 4 W. sample 54. 57A 416 4,760 E, 3,660 N, sec. 19, Medium-grained hornblende-biotite quartz-bearing monzonite. Abundant T. 2 N., R. 4 W. sphene. C.I. ~20 58 T18—4 1,180 E, 670 N, sec. 30, T. Hornblende-biotite quartz diorite, fine-grained. Possibly a hybrid rock. 2 N., R. 3 W. 59 T66—4 4,320 E, 1,220 N, sec. 13, Hornblende-biotite granodiorite. Slightly foliate. Medium-grained. C.I. ~20 T. 1 N., R. 3 W. 59A M17—7 2,000 E, 3,400 N, sec. 22, Amphibolite, biotite-bearing. Fine-grained. Lineate. Faintly banded. Rock at T. l N., R. 3 W. sample site is heterogeneous banded gneiss. C.I. ~60 60 T12—4 2,970 E, 2,150 N, sec. 12, Biotite quartz monzonite, nonporphyritic, slightly weathered. T. 1 N., R. 3 W. 61 T15—4 2,550 E, 3,660 N, sec. 31, Hornblende-biotite granodiorite. Coarse-grained, sparsely porphyritic. T. 2 N., R. 2 W. 62 T16—4 340 E, 2,830 N. sec. 13, T. Hornblende-biotite granodiorite. Same pluton as sample 61. 2 N., R. 3 W. i 63 T65—4 2,230 E. 5,020 N, sec. 28, Biotite quartz monzonite. Fine-grained, equigranular. C.I. ~8 T. 3 N ., R. 3 W. 64 T21—3 2,625 E, 2,150 N, sec. 31, ‘ Biotite quartz monzonite. Porphyritic. Part of the Rattlesnake pluton. T. 4 N ., R. 2 W. 65 T43—4 3,390 E, 3,990 N, sec. 9, Biotite quartz monzonite, porphyritic. Part of the Rattlesnake pluton. T. 3 N., R. 2 W. 66 T44—4 3,940 E, 3,180 N, sec. 35, Porphyritic biotite quartz monzonite. Nonfoliate. Probably part of Rattlesnake T. 3 N., R. 2 W. pluton. 67 M1—3 160 E, 4,030 N, sec. 11, T. Lineate hornblende-pyroxene monzonite. 4 N ., R. 2 W. 68 M2—4 1,300 E, 2,880 N, sec. 31, Hornblende-biotite granodiorite. Medium-grained, nonporphyritic, sphene- T. 5 N., R. 2 W. bearing. 69 M14—4 2,050 E, 2,480 N, sec. 17, Biotite quartz monzonite. Fine-grained. Slightly foliate. May be a hybrid. T. 5 N ., R. 3 W. 70 M1—4 3,840 E, 2,400 N, sec. 10, Leucocratic biotite quartz monzonite. Fine-grained, nonporphyritic. T. 5 N ., R. 4 W. 71 M9—4 2,360 E, 525 N, sec. 29, T. Hornblende-biotite granodior'ite, medium-grained, nonfoliate, nonporphyritic. 6 N., R. 4 W. C.I. ~10. 72 M8—4 4,480 E, 3,550 N, sec. 6, Hornblende-biotite granodiorite, medium-grained, nonfoliate, nonporphyritic. T.5N.,R.4W. C.I. ~15. 28 GEOCHRONOLOGY OF THE TRANSVERSE RANGES AND MOJAVE DESERT, SOUTHERN CALIFORNIA Map Field No. No. Locality Rock type 73 M7-4 2,025 E, 3,600 N, sec. 22, Hornblende-biotite quartz monzonite. Medium-grained, slightly porphyritic. T. 6 N., R. 3 W. - 73A M3—6 250 E, 3,640 N, sec. 16, T. Hornblende-biotite granodiorite. Medium—grained. Massive. Hornblende: biotite 7 N., R. 3 W. 21:5. Euhedral biotite. CI. :10 73B M1—7 2,550 E, 2,300 N, sec. 18, Same lithology as 73A; these samples from the same pluton. T. 7 N., R. 3 W. 73C M247 1,370 E, 500 N, sec. 2, T. Biotite quartz monzonite. Coarse-grained. Deeply weathered. Very slight folia- 6 N., R. 3 W. tion. C.I. ~10 73D M3—7 4,240 E, 2,460 N, sec. 12, Gabbro. Medium- to coarse-grained with pegmatitic segregations. Mixed with T. 6 N., R. 3 W. other granitic rocks at sample site. C.I. ~40. 74 M6—4 4,650 E, 150 N, sec. 4, T. Biotite quartz monzonite. Leucocratic. Fine grained with 7 mm phenocryst of 5 N., R. 2 W. microcline. 75 T90—4 940 E, 1,830 N, sec. 26, T. Biotite quartz monzonite. Coarse-grained, equigranular. Abundant sphene. 6 N., R. 2 W. C.I. ~6 76 T91—4 340 E, 3,150 N, sec. 22, T. Hornblende-biotite granodiorite. Medium-grained, equigranular. 7 N., R. 2 W. C.I. ~15 76A M20—7 260 E, 4,370 N, sec. 17, T. Biotite quartz monzonite. Medium-grained. Biotite partly chloritized, but 6 N., R. 2 W. analyzed mineral separate was clean biotite. Nonporphyritic, slight foliation. , C.I. ~15 77 T92—4 2,200 E, 3,300 N, sec. 35, Biotite quartz monzonite. Medium-grained, equigranular. Mixed with other rock T. 7 N., R. 2 W. types at sample locality. Probably hybridized. 78 T93—4 [700 E, 4,850 N, sec. 26, T. Biotite quartz monzonite, coarse-grained, equigranular. Slightly altered. 7 N., R. 1 W. 01. ~5 78A M5—7 1,500 E, 3,900 N, sec. 12, Hornblende-biotite granodiorite. Medium-grained slightly porphyritic. Massive. T. 7 N., R. 1 W. Hornblende: biotite 21:1 Sphene-bearing. CI. :15 78B M6—7 4,570 E, 3,370 N, sec. 19, Hornblende—biotite granodiorite. Same lithology and same pluton as 78A, except T. 7 N., R. 1 E. hornblende: biotite 21:2. 78C M7—7 950 E, 50 N, sec. 16, T. 7 Hornblende-biotite diorite. Quartz-bearing. Medium-grained. Equigranular. C.I. N., R. 1 E. ~50. Intruded by alaskite 100 m from sample site. 79 T94—4 1,160 E, 2,440 N, sec. 1, Banded gneiss. Layers from 1 to 30 mm thick. Hornblende is only mafic mineral. T. 6 N., R. 1 W. 79A M10—7 1,400 E, 4,100 N, sec. 1, Hornblende-biotite granodiorite. Porphyritic. Potassium feldspar is purple-gray. T. 6 N., R. 1 E. May be same plutonic type as sample 136. CI. ~20 793 M11—7 1,700 E, 1,700 N, sec. 7, Biotite quartz monzonite. Leucocratic. Potassium feldspar is pink. Weathered. T. 6 N., R. 2 E. 01. ~8 80 M13—4 1,600 E, 3,900 N, sec. 5, Biotite quartz monzonite. Probably a hybrid rock, contaminated by T. 5 N., R. 1 E. metamorphic rocks. 81 T95—4 790 E, 920 N, sec. 11, T5 Hornblende-biotite granodiorite. Fine-grained. Slightly foliate. Hornblende has N., R. 1 W. pyroxene cores. 01. ~20 82 T97—4 3,080 E, 1,640 N, sec. 4, Hornblende-biotite quartz diorite. Medium-grained, lineate. C.I. ~12 T. 4 N., R. 1 E. 83 T89—4 2,120 E, 5,090 N, sec. 5, Muscovite-biotite quartz monzonite. Medium-to coarse-grained, but micas fine- T. 3 N., R 1 E. grained. C.I. ~8 ' 84 T96—4 4,940 E, 2,300 N, sec. 12, Hornblende-biotite granodiorite. Medium-grained, equigranular. Abundant T. 3 N., R. 1 W. Sphene. C.I. ~20 85 T31A—4 2,520 E, 3,640 N, sec. 33, Hornblende-biotite monzonite. Hornblende contains altered pyroxene cores that T. 3 N., R. 1 W. cannot be completely separated from the hornblende. 86 T5L4 3,200 E, 200 N, sec. 10, T. Biotite quartz monzonite. Medium-grained, slightly porphyritic. C. I. = 6 2 N., R. 2 W. 87 T13—4 2,940 E, 2,830 N, sec. 34, Biotite quartz monzonite. Sparsely porphyritic. Same pluton as sample 86. T. 2 N., R. 2 w. ' 88 T14—4 3,620 E, 4,560 N, sec. 19, Biotite quartz monzonite. Locally contains muscovite. Fine-grained. T. 2 N., R. 1 W. 89 T11—4 1,320 E, 4,720 N, sec. 3, Hornblende-biotite quartz monzonite. Very porphyritic, slightly foliate. T. 1 S., R. 1 W. 90 T10—4 1,050 E, 3,350 N, sec. 24, Hornblende-biotite granodiorite. Medium-grained, nonporphyritic. - T. 1 N., R. 1 W. 91 T55—4 4,060 E, 2,750 N, sec. 2, Biotite quartz monzonite. Equigranular. Same pluton as sample 86. T. 2 N., R. 1 W. - 92 T32—4 3,470 E, 2,970 N, sec. 11, Hornblende-biotite granodiorite. Coarse-grained. Slightly porphyritic. T. 2 N ., R. 1 W. 93 T64—4 1,800 E, 3,040 N, sec. 15, Biotite quartz monzonite. Fine-grained, equigranular. T. 2N.,R. 1 E. SAMPLE LOCALITIES AND DESCRIPTIONS 29 Map Field No. No Locality Rock type 94 T30—4 5,040 E, 30 N, sec. 23, T. Baldwin Gneiss of Guillou (1953). Coarse-grained orthogneiss, porphyroblastic. 3 N ., R. 1 E. 95 T87—4 2,780 E, 3,780 N, sec. 24, Hornblende-biotite quartz diorite. Medium-grained, equigranular. C.I. ~30 T. 3 N., R. 1 E. 96 T5—4 3,170 E, 2,960 N, sec. 24, Biotite quartz monzonite. Foliate. Part 'of Cactus Quartz Monzonite of Guillou T. 3 N., R. 1 E. (1953). 97 M3—4 1,650 E, 1,300 N, sec. 5, Leucocratic biotite quartz monzonite. Medium- to fine-grained, trace of mus- T. 4 N., R. 2 E. covite. 98 M10—4 4,500 E, 2,920 N, sec. 25, Biotite quartz monzonite. Leucocratic, nonfoliate, nonporphyritic. T. 5 N., R. 1 E. 99 M36—4 1,020 E, 3,780 N, sec. 36, Hornblende-biotite granodiorite. Porphyritic, medium-grained. C.I.~20 T. 6 N., R. 1 E. 100 M38—4 5,100 E, 1,720 N, sec. 30, Hornblende-biotite quartz monozonite, fine-grained, porphyritic. Dark feldspar. T. 7 N., R. 3 E. C.I. ~12 ' 100A M44—7 1,400 E, 4,030 N., sec. 19, Biotite quartz monzonite. May be same plutonic type as sample 73C. Medium- to T. 8 N ., R. 2 E. coarse-grained. Massive. Pink potassium feldspar. C.I. ~8 101 M39—4 870 E, 1,120 N, sec. 23, T. Hornblende biotite quartz monzonite. Medium-grained, sparsely porphyritic. 6 N., R. 3 E. C.I. ~15 102 M40—4 4,690 E, 1,220 N, sec. 6, Hornblende-biotite quartz monzonite. Porphyritic. Slightly foliate. Medium- T. 5 N., R. 3 E. grained. C.I. ~14 102A M22—7 1,650 E, 5,220 N, sec. 2, Hornblende-biotite granodiorite. Same plutonic type as 79A. Porphyritic. T. 5 N., R. 2 E. C.I. ~15 103 M41—4 2,330 E, 1,680 N, sec. 21, Hornblende-biotite quartz monzonite. Small, sparse phenocrysts, Medium- T, 6 N., R. 4 E. grained. C.I. ~10 104 M19—4 4,520 E, 1,830 N, sec. 5, Same pluton as sample 123. Mixed with numerous other plutonic types at sam- T. 5 N., R. 4 E. ple locality. 105 M15—4 290 E, 2,100 N, sec. 1, T. Hornblende-biotite quartz monzonite. Medium-grained, slightly porphyritic. 4 N., R. 3 E. C.I. ~12 106 M11—4 4,900 E, 4,800 N, sec. 14, Same pluton as sample 98. T. 4 N., R. 2 E. 107 M12—4 1,020 E, 710 N, sec. 30, T. Hornblende biotite quartz monzonite. Slightly foliate, medium-grained. C.I. ~12 4 N., R. 3 E. 108 T45—4 2,980 E, 1,840 S, sec. 17, Hornblende-biotite granodiorite. Slightly foliate. C.I.~25 T. 3 N ., R. 3 E. 109 T61—4 2,460 E, 2,800 N, sec. 3, Muscovite-biotite quartz monzonite. Highly lineate. Medium-grained. C.I. ~12 T. 2 N., R. 2 E. 110 T63—4 5,100 E, 1,730 N, sec. 14, Baldwin gneiss of Guillou (1953). Foliate and highly lineate. Contains muscovite T. 2 N., R. 2 E. and biotite. Medi’um- to fine-grained. 111 T62—4 4,800 E, 3,590 N, sec. 18, Muscovite-biotite quartz monzonite. Medium- to coarse-grained. Garnet-bearing. T. 2 N., R. 3 E. C.I. ~7 112 T9-4 5,130 E, 2,110 N, sec. 16, Hornblende-biotite quartz diorite. Medium- to fine-grained, nonporphyritic. T. 1 N ., R. 2 E. 112A TA—6 1,875 E, 400 N, sec. 33, T. Hornblende-biotite granodiorite or quartz diorite. Massive. Medium-grained. 1 S, R. 2 E. 113 T60—4 3,540 E, 0 N, sec. 24, T. 1 Biotite quartz monzonite. Fine-grained, equigranular. Contains segregations of N., R. 2 E. dark minerals from partially resorbed inclusions. 114 T8—4 4,110 E, 2,320 N, sec. 1, Biotite quartz monzonite. Sparsely porphyritic. T. 1 N ., R. 2E. 115 T52—4 3,125 E, 350 N, sec. 10, T. Muscov'rte-biotite quartz monzonite. Medium- to fine-grained. Nonfoliate, non- 1 N., R. 3 E. porphyritic. 116 T51—4 680 E, 820 N, sec. 16, T. 1 Biotite quartz monzonite. Medium- to fine-grained, nonporphyritic. N., R. 4 E. 116A M15—-7 2,150 E, 200 N, sec. 32, T. Banded quartzofeldspathic gneiss. Biotite in lenses to 0.5 cm thick is only mafic 1 S., R. 4 E. mineral. Medium-grained. 117 T59—4 940 E, 570 N, sec. 32, T. 2 Hornblende-biotite granodiorite. Slightly foliate. Medium-grained. C.I. ~15 N ., R. 4 E. 118 T58—4 1,920 E, 2,130 N, sec. 10, Biotite quartz monzonite. Fine-grained, equigranular. Pale-brown color. C.I. ~15 119 T56—4 4,360 E, 4,830 N, sec. 30, Biotite quartz monzonite. Medium-grained, sparsely porphyritic. C. I. ~10 T.3N.,R.4E. ’ 120 157—4 400 E, 1,590 N, sec. 7, T. Biotite granodiorite. Probably metamorphosed. Medium-grained, equig'ranular. 3N., R. 4 E. C. I. ~15 30 GEOCHRONOLOGY OF THE TRANSVERSE RANGES AND M()JAVE DESERT, SOUTHERN CALIFORNIA Map Field No. 0. Locality Rock type 121 M16—4 2,080 E, 5,020 N, sec. 10, Biotite quartz monzonite. Traces of muscovite. Fine-grained. Leucocratic. T. 4 N., R. 4 E. 122 M18—4 3,620 E, 4,360 N, sec. 19, Biotite quartz monzonite, pale-gray. Abundant myrmikitic intergrowths. C.I. ~5 T. 5 N., R. 5 E. 123 M17—4 1,050 E, 800 N, sec. 32, T. Hornblende-biotite quartz monzonite. Highly porphyritic. C.I. ~15 5 N., R. 5 E. 123A M13—7 925 W, 125 N, sec. 18, T. Hornblende-biotite granodlorite. Medium-grained. Nonporphyritic, but probably 4 N., R. 6 E. part of same plutonic type as 133A. C.I. ~25 123B M14—7 1,180 E, 1,590 N, sec. 5, Hornblende-biotite granodiorite. Medium- to coarse-grained. Same plutonic type T. 4 N., R. 6 E. as 136. Dark gray, large potassium feldspar phenocrysts. C.I. ~15 124 M4—4 5,120 E, 4,840 N, sec. 11, Porphyritic biotite quartz monzonite. Biotite is in clusters of fine-grained T. 3 N., R. 4 E. crystals. 125 M5—4 4,640 W, 7,300 N, sec. 16, Hornblende-biotite granodiorite. Medium-grained, faintly foliate, nonporphy- T. 2 N., R. 5 E. ritic. 126 M43—4 570 E, 4,350 N, sec. 33, T. Biotite quartz monzonite. Medium-grained, porphyritic. Phenocrysts to 2.5 cm in 2 N., R. 5 E. length. C.I. ~12 127 M25—4 3,460 E, 2,110 N, sec. 34, Hornblende-biotite granodiorite. Medium- to coarse-grained. Nonfoliate. T.2N., R. 5E. C.I. ~15 - 128 M42—4 1,940 E, 1,730 N, sec. 2, Hornblende-biotite granodiorite. Medium-to coarse-grained. Equigranular. C.I. T. 1 N., R. 5 E. ~18 129 T1974 3,780 E, 4,470 N, sec. 29, Muscovite-biotite quartz monzonite. Medium-grained, nonfoliate. T. 1 N., R. 5 E. ‘ 130 M22~4 2,110 E, 1,850 N, sec. 24, Biotite quartz monzonite. Nonfoliate. Slightly cataclasized. C.I. ~10 T. 1 N., R. 6 E. 131 M24—4 580 E., 5,160 N, sec. 27, Gneissic biotite monzonite. Slightly porphyroblastic. C.I. ~20 T. 2 N., R. 6 E. 132 M44—4 3,650 E, 4,350 N, sec. 4, Hornblende-biotite granodiorite. Medium-grained, equigranular. C.I. ~25. Much T. 2 N., R. 6 E. variation in composition on small scale at sample site. 133 M20—4 2,200 E, 2,140 N, sec. 30, Hornblende-biotite quartz diorite. C.I. ~25. Small mafic-rich body associated T. 3 N., R. 6 E. with large quartz monzonite pluton. 133A M12—7 1,110 E, 360 S, sec. 27, T. Hornblende-biotite granodiorite. Porphyritic, but with very inhomogeneous 3 N., R. 6 E. phenocryst distribution. Hornblende: biotite ~ 1:1. Dark potassium feldspar. C.I. ~25. 134 M21—4 4,020 E, 3,110 N, sec. 31, Biotite quartz monzonite. Foliate. Slightly porphyritic. Contains abundant alla- T. 2 N., R. 7 E. nite. C.I. ~20 135 M47—4 1,550 E, 920 N, sec. 34, T. Hornblende-biotite quartz monzonite. Porphyritic. Same plutonic type as 2 N., R. 7 E. sample 123. 136 M45—4 2,130 E, 1,520 N, sec. 34, Hornblende-biotite quartz monzonite. Porphyritic. Same plutonic type as T. 2 N., R. 9 E. sample 123B. 136A M96—7 3,750 E, 4,800 N; sec. 10 Hornblende-biotite quartz monzonite. Porphyritic. Same pluton as 136. T. 1 N., R. 9 E. , GPO 689-143 Geological Mapping by Use of Computer-Enhanced Imagery in Western Saudi Arabia By H. w. BLODGET and G. F. BROWN GEOLOGICAL SURVEY PROFESSIONAL PAPER 1153 Prepared in cooperation with the Directorate General of Mineral Resources, Ministry of Petroleum and Mineral Resources, Kingdom of Saudi Arabia An attempt to separate geologic units on the basis of land smface reflectance as shown on satellite imagery UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1982 UNITED STATES DEPARTMENT OF THE INTERIOR JAMES C. WATT, Secretary GEOLOGICAL SURVEY Dallas L. Peck, Director Library of Congress Cataloging in Publication Data Blodget, H. W. Geological mapping by use of computer-enhanced imagery in western Saudi Arabia. (Geological Survey professional paper; 1153) Bibliography: p. Supt. of Docs. no.: I 1916:1153 1. Geological mapping. 2. Geology—Saudi Arabia—Maps. 3. Landsat satellites. I. Brown, Glen Francis, 1911—joint author. II. Title. III. Series: United States. Geological Survey. Professional paper; 1153. QE36.B53 526.9’823 80—607149 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 47 an ‘Tfi CONTENTS '6 n: N :0 Abstract Introduction Methods Landsat imagery Computer manipulation of digital Landsat data and Landsat image enhancement _______ Geologic background Stratigraphy, igneous activity, and relative ages Precambrian geology Phanerozoic deposits and volcanism Geomorphology Rock units defined on enhanced imagery Metamorphic rocks Plutonic rocks Gossan and laterite Tertiary volcanic rocks Conclusions References cited OQDQDCDQQK‘IU‘CfldkanBNNMh-‘H H ILLUSTRATIONS [Plates are in pocket] Plate 1.—Imagery and geology of the Al Wajh area (test area 1), northwestern Saudi Arabia. 2.—Imagery and geology of the Zahrin area (test area 2), southwestern Saudi Arabia. Ill 7"" ‘r r?“ GEOLOGICAL MAPPING BY USE OF COMPUTER-ENHANCED IMAGERY IN WESTERN SAUDI ARABIA By H. W. BLODGET‘ and G. F. BROWN ABSTRACT Several computer-based classifications and image-enhancement techniques that use Landsat multispectral scanner (MSS) data are compared to determine their value as aids for geologic mapping in the low-latitude desert of western Saudi Arabia. Discrimination among various surface materials can be improved with Landsat data manipu- lated by a variety of computer algorithms. The most effective method described is the simultaneous use of two differently computer- enhanced Landsat MSS color-composite images. These were con- structed using the ramp-cumulative distribution function contrast stretch and the ratio-contrast stretch algorithms, the latter using MSS bands as, «56, and 56 projected through blue, green, and red filters, respectively. The contrast-stretched imagery increases the separation of low-spectral values of picture elements in the display at the expense of the brighter values and has proven especially useful for identifying geological structures. The ratio-contrast stretch im- agery, on the other hand, provides the greatest capability for rock discrimination. Computer processing of MSS data obtained at high sun angle (sum- mer) provided significantly better rock-class separability than was attained using low sun angle (winter) data. The winter data, however, provided more detailed structural information. The spectral response of individual rock classes is also influenced by a wide variety of fac- tors, such as weathering, soil development, desert varnish, eolian sand blasting, and abundance of vegetative cover—all these factors must be considered when making geologic interpretations. This study demonstrates that digital Landsat data manipulated by various computer techniques can produce imagery that greatly in- creases the geologic interpretability and can be used successfully to aid geological mapping at regional scales. INTRODUCTION Geologic mapping of the crystalline rocks in the Ara- bian segment of the Arabian-Nubian Shield (pl. 1) was begun on a systematic basis in 1950 by the US. Geolog- ical Survey at the request of the late King Abdul Aziz ibn Saud. The prime concern of the Government of Saudi Arabia was finding potable water supplies for populated and agricultural areas. A secondary objective was to locate and evaluate economic raw materials and (or) ore deposits. Out of necessity, the early work was of a recon- naissance nature and consisted mainly of the prep- aration of base maps that showed roads, trails, and watering points. Those maps were published at a scale of 1:500,000. After an initial demonstration photographic project conducted by the US Geological Survey, the late King Faisal ibn Saud, then Viceroy of the Hejaz, agreed to finance complete aerial photographic cover- age. The precise location of these aerial photographs had to be largely determined by using shoran geodetic control, for the inhospitable terrain made surface sur- veying extremely difficult. The photographs were then ‘ National Aeronautics and Space Administration. made into mosaics which served as a base for the first accurate maps on which the reconnaissance geology was drawn (examples are pls. 1A and 2A, the two test areas discussed in this report). Mapping on a scale of 1:100,000 was begun in 1961. However, only during the last 14 years, with the availability of fixed-wing and helicopter transportation and full-laboratory, -geophysical, -geochemical, and -diamond-drilling support, has it been possible to map in the desired detail for specific economic targets. At present, about one-half of the shield has been mapped at this scale and rather intensively prospected. This work has been accomplished by several national teams under contract to the Directorate General of Mineral Re- sources, as well as by the U.S. Geological Survey, in cooperation with the Directorate staff. Currently, the Government of Saudi Arabia is preparing a new series of geologic maps at a scale of 1:250,000. For this purpose, computer—enhanced satellite imagery provides a valua- ble new aid for geologic interpretation and the contin- uing search for water and raw materials. In 1972, satellite imagery became available for the entire Arabian Peninsula and now provides synoptic views of many aspects of the terrain. These images are now used routinely to supplement the aircraft photog- raphy in regional mapping efforts. Standard Landsat color-composite images show relief, drainage, and the major differences in reflectivity of different rock types. With sufficient geological mapping on the land surface for local controls, the standard Landsat imagery can be used as a suitable orthographic base that has greater accuracy than most photographic mosaics have. This is especially true in areas where there is much relief in the terrain. This study is an outgrowth of a. doctoral thesis pre- pared by the senior author for presentation at George Washington University. The test areas discussed herein are adjacent, with some overlap in the Zahran area, to two that Blodget (1977) described in his thesis (pl. 1). The test areas were selected with the intent to supple- ment and extend over a wider area containing a greater variety of diverse rock types the concepts formulated by Blodget. Acknowledgments. ——The interpretation of the computer-enhanced Landsat imagery would not have been possible without access to the unpublished geologic maps by S. Okumi, K. Komura, and T. Hatanaka of the Japan Geological Survey; John Kemp and C. Pellaton of the Bureau de Recherches Geologiques et Minieres of 1 2 GEOLOGICAL MAPPING BY USE OF COMPUTER-ENHANCED IMAGERY, WESTERN SAUDI ARABIA France; and R. E. Anderson, W. R. Greenwood, and D. B. Stoeser, US. Geological Survey. The authors are grate- ful to these men and their organizations. The staff of the Directorate General of Mineral Re- sources, Kingdom of Saudi Arabia, made the field work possible and cooperated in the formulation of the con- cepts. Field support in the southern test area by Abdul- aziz Bagdady is gratefully acknowledged. Salman Bloch, US. Geological Survey, did much of the geological com- pilation and reviewed the report. The color-composite maps of the A1 Wajh area were prepared by Seiscom Delta, Inc.; the index mosaics and color composite of the Zahran area were made by the General Electric Co.2 The report was prepared at the suggestion of John Reinemund, US. Geological Survey, who reviewed the manuscript and suggested its present form. Raymond Fary, Wenonah Bergquist, Alfred Chidester, and David Davidson also reviewed the manuscript. Wenonah Berg- quist helped with the preparation of the illustrations and suggested methods of presentation. J. G. Moik of the National Aeronautics and Space Administration (NASA), Goddard Space Flight Center, created the computer-enhanced imagery. Paul Lowman, NASA, gave constructive advice regarding geological applica- tions of satellite imagery and reviewed the paper. METHODS LANDSAT IMAGERY Remote-sensing techniques have been used to com- plement geologic field mapping for more than a half century. The techniques, however, have been largely limited to the interpretation of standard black and white aerial photography. The traditionally successful photointerpretation techniques have more recently been extended for use with Landsat imagery that became available on a routine basis in the latter half of 1972. Most of the currently available Landsat imagery has been provided by the multispectral scanners (MSS) carried on the Landsat 2 and 3 satellites. These scanners record reflected visible and near-infrared radiation from terrestrial surfaces in each of four spectral bands which have been designated as follows: MSS band 4 for the 0.5—0.6 micrometer (um) (green) wavelength inter- val, MSS band 5 for the 0.6—0.7 pm (red) interval, and MSS bands 6 and 7 for the 0.7—0.8 um and 0.8—1.1 um (near-infrared) intervals. The radiation is sensed by an array of detectors on the spacecraft and then encoded into a digital format that furnishes a continuous data stream for radio transmittal to ground receiving sta- tions. These data are recorded on tape at the receiving station and then shipped to the NASA Data Processing Facility.3 There the uncorrected data tapes are re- We names and trademarks in this publication is for descriptive purposes only and does not constitute endorsement by the US. Geological Survey. 3 These procedures were changed February 1, 1979. (See Us. Geological Survey, Landsat Data Users Notes, Issue 8, p. 4-5.) formatted and translated to gray-scale values prior to being converted to imagery for each of the four bands. The original data can also be translated to digital computer—compatible tapes. The standard Landsat image products that are available for general distribu- tion consist of several black and white photographic formats made from each of the MSS bands from master 70-millimeter (mm) film. In addition, color-composite imagery that simulates the familiar near-infrared false-color photography can be constructed photo- graphically by using the appropriate black and white film and color-filter combinations. Photogeologists readily accepted these Landsat photo- graphic products, for the data are intelligible and useful. The immediate advantage of this small-scale, high-resolution imagery, of course, is for construction or revision of small-scale regional maps. An area 185 km2 is covered in each scene, and enlargements from the 70-mm master film can be made up to a scale of 1:250,000 without introduction of serious graininess. COMPUTER MANIPULATION OF DIGITAL LANDSAT DATA AND LANDSAT IMAGE ENHANCEMENT Experience indicates that only a small part of the spectral information contained in the multispectral Landsat data is shown in the standard film products. During the past several years, an increasing amount of Landsat-based research has involved computer manipu- lation techniques designed to enhance and (or) classify specific discipline-defined parameters (Siegal and Gil- lespie, 1979). Interactive multispectral classification systems using both parallelepiped and Bayesian maximum-likelihood algorithms have been formulated and are commercially available from several manu- facturers. These systems have been designed to accept several classes of multispectral data but have been par- ticularly successful in using Landsat digital MSS input for small-scale thematic mapping. In California, for ex- ample, regional agricultural activities can be inven- toried and monitored to accuracies adequate for many planning activities (Colwell, 1973). The ability to iden- tify temporal changes further provides the capability to rapidly update cultural maps, to monitor strip mining and restoration activities, to quickly assess damage caused by major floods, and a host of similar tasks. Attempts to use these classification systems to dis- tinguish differences among rock types were much less successful than mapping of vegetation had been else- where. Computer-training sites were established for a wide variety of rock classes in the Sahl al Matran area in the northwest part of the country (Blodget and oth- ers, 1975). The only rock types that could be classified with any consistency were those exposed in nearly hor- izontal surfaces. These included such lithologic units as fissure basalt flows and alluvium. In addition, in some areas under the proper conditions, it appeared possible f I 1 fi‘jfi METHODS 3 to relate specific alluvial classes to the lithology of their provenance. Igneous and metamorphic assemblages in very highly dissected terrane make up most of the Ara- bian Shield. Obtaining representative training areas re- quired for computer classification of specific rock units within these areas ranged from very difficult to impos- sible. The principal reason for this is that spectral reflec- tances from specific lithologies are strongly influenced by differences in surface slope and attitude and by shad- ows inherent in the rugged land surfaces. Multispectral classification thus appears to have only limited applica- tion for rock identification in the shield areas of Saudi Arabia. Landsat image enhancement. —Several digital proce- dures have also been devised to enhance specific param- eters contained in Landsat imagery. These techniques range from the relatively simple single-band contrast » enhancement to two-dimensional filtering in spatial or Fourier domain and complex cluster analyses, some- times coupled with ratioing of spectral bands (Rowan and others, 1974). The two computer-enhanced products that proved most useful for geologic mapping in the Sahl al Matran test area were (1) color composites of individually contrast-enhanced MSS bands and (2) contrast-enhanced band ratios. The Landsat MSS system is designed to accommodate the entire dynamic range in scene brightness that may be encountered during the whole of the near-global cov- erage of the satellite, and this can be equated to 256 shades of gray on film. Consequently, the brightness range of any specific scene can be stretched to fill the entire dynamic range of the medium. Several types of stretches have been devised to increase the contrasts among specific parameters; these can be either linear or nonlinear. The stretch considered optimum for in- creasing contrast among the rock units of northwestern Saudi Arabia uses the ramp-cumulative distribution function (CDF), which is formed by defining the sum of succeeding values of groups of pixels (picture elements) in the brightness distribution, to approximate a linear ramp function (Goetz and others, 1975, p. 112). The stretched data for the individual MSS bands can further be combined to form color-composite imagery having a Wide range of color. This type of stretch increases the separation among pixel values in the low-radiance areas of a display at the expense of separation in the brighter areas and is ideal in the crystalline Arabian Shield com- plex, where igneous and metamorphic rocks all tend to have low reflectance. To further increase contrast among surface features, MSS band-paired data can be ratioed prior to applica— tion of the stretch algorithms; this reduces the environ- mental effects on the surface reflectance. Ratio-stretch data sets composited into color imagery provided the single best enhancement products for rock discrimi— nation in northwestern Saudi Arabia. This enhance- ment procedure consists of three fundamental steps: (1) paired data from selected MSS bands are ratioed pixel by pixel, (2) the resultant values from each pair are then stretched using the ramp-CDF stretch algorithm, and (3) the values are combined into color—composite im- agery using various combinations of filters and light- exposure intensities. In this procedure, alternative ratio and filter combinations can be used to optically enhance specific rock classes. In a northwestern Arabian test site, a combination of MSS bands 46, §6, and 9? stretched- ratio values projected through blue, green, and red filters, respectively, provided the best combination for lithologic discrimination (Blodget and others, 1975). The use of ratio values allows for a substantial increase in contrast by reducing brightness variations due to topography, shadowing, and reflectance-angle vari- ation. The ratio values for any single scene, however, generally have a narrow range and must be contrast stretched to further enhance the visibility of the spec- tral differences. Ratio-stretched color-composite images of the same scene vary with differences in sun angle. On one such enhanced image made from low winter-sun angle Land- sat data of the Sahl al Matran test site, it was possible to recognize two rock types in addition to the ones that could be discriminated by the earlier use of digital classification systems. These included a broad class of granites and a hornblende-biotite-quartz monzonite, both of which had been defined in the field by Hadley (1973a). The remaining igneous units, as well as all the metamorphic rocks that had been mapped by Hadley, were still not readily separable. Subsequent enhancement of MSS data for the same test site but obtained during a July satellite pass, using the identical digital techniques (Blodget, 1977), pro- duced a considerably greater correspondence between the spectral units and the rock units described in the field by Hadley (1973a, 1974, 1975). The increased dis- crimination capability was obviously due to the higher sun angle and resultant shadow reduction in the sum- mer scene. Although the contrast enhancement of ratios com- monly provides an excellent image for discriminating among rock types, the products suffer resolution reduc- tion of a factor of about 3 below that of a color-composite image constructed using contrast stretch. In addition, the alluvium was commonly found to show the spectral characteristics of its parent rock, and this makes identi- fication of outcrop margins difficult. These margins, as well as fault lines and other structural features depend- ent on relief (see pl. 10 and D and pl. 20), are generally considerably better defined 'on the MSS color composites of stretched images. Because of these factors, images made by using both of these enhancement techniques should be used in complementary roles for optimum use of data in geologic interpretation. 4 GEOLOGICAL MAPPING BY USE OF COMPUTER-ENHANCED IMAGERY, WESTERN SAUDI ARABIA Because of the success of enhanced Landsat imagery for rock discrimination in the Sahl a1 Matran test site (Blodget, 1977), similar enhanced imagery was made for two other areas of the Arabian Shield to complement an active geologic mapping program. These are the A1 Wajh area (test area 1, pl. 1) immediately west of the Sahl al Matran test site and the extremely mountainous south- western area of Saudi Arabia near the town of Zahran (test area 2) in the Asir. In this report, we correlate computer-enhanced imagery derived from the Landsat multispectral scanner system with 1:100,000-scale geol- ogy mapped on the ground in the two geologically di- verse areas. We have also attempted extrapolation of meager geologic ground-reconnaissance data through the use of the characteristics of rock reflectances as seen in the enhanced imagery. Plate 1 illustrates the geology of test area 1 in the northern part of Saudi Arabia, and plate 2 illustrates test area 2, which is in the southern part. Plates IB and 23 show standard Landsat color- composite imagery of test areas 1 and 2, respectively, along with overlays compiled using the best available geological data. When more than one Landsat image is required to obtain complete coverage of a study area, two frames can be combined to maintain spectral continuity by directly processing several computer- compatible satellite tapes into Landsat mosaics. Plate 13 provides an example of such a multiscene area. GEOLOGIC BACKGROUND STRATIGRAPHY, IGNEOUS ACTIVITY, AND RELATIVE AGES The test areas for computer-enhanced imagery were chosen so as to include nearly all the major rock units of the Arabian Precambrian shield and some Phanerozoic outcrops (see explanations for pls. 1B and 23). The Pre- cambrian and Cambrian assemblages range in age from about 1 billion to 510 million years, according to radio- metric isotope measurements, and span at least three orogenic events. The oldest of these events produced lineations that were formed by a combination of schis- tosity, fold axes, and faults. These trend northeast and may possibly be an interrupted extension of the Kib- aran or Irumidian belt in East Africa. The next younger event produced the major Hejaz orogenic-cycle trend which in general produced north-trending lineations. The youngest orogenic event was the Najd movement, and this consisted primarily of sinistral faulting that trended to the northwest. Metamorphism of the rocks within both test areas is diverse, ranging from essen- tially unmetamorphosed sedimentary and igneous rocks through polymetamorphosed zones, which range from greenschist facies generally imposed on amphibolite facies to gneissic and granitoid cores of possible ana- tectic origin. The tectonic events were accompanied or followed by outpourings of basaltic, andesitic, dacitic, and rhyolitic lavas, as well as invasions of hypabyssal and plutonic rocks that ranged from narrow dikes to batholiths. Intrusive igneous rocks range from gener- ally serpentinized ultramafic, through gabbro, to per- alkaline granite composition. Although most of these plutonic rocks are calc-alkaline, the oldest are in gen- eral calcic, Whereas the youngest are generally alkaline and peralkaline. The excellent exposures and diverse rock types present an opportunity to analyze the various types of satellite imagery and to extend geologic interpretation from areas studied in considerable detail on the ground into areas where only reconnaissance studies have been made. The reference sources of geologic data for the southern area have not been published, and thus the geologic sketch map based on enhanced images (pl. ZB, C, and D) and accompanying explanation give only the rock-type symbols used by the three field geologists, R. F. Anderson, W. R. Greenwood, and D. B. Stoeser (pl. 2, Explanation). The same graphic approach has been used to designate outcrops in test area 1 where field work was done independently by several geologists, including S. Okumi, K. Komura, and T. Hatanaka of the Japan Geological Survey; C. Pellaton, John Kemp, and M. Bigot of the Bureau de Recherches Geologiques et Minieres, France (pl. 13); and one of us (G. F. B.). PRECAMBRIAN GEOLOGY The oldest dated rocks in the Arabian Shield consist of basaltic and andesitic flows, agglomerate, and tuf‘f. Several gneissic belts, however, that are of questionable (probably mixed) ages may be older. Where shearing has not been too intense, the more massive flows have pillow structures indicative of marine eruptions. Where shearing has been severe, the flows have been altered to chloritic, sericitic, and graphitic or carbonaceous schists, many of which are talcose or serpentinized. The less abundant conglomeratic, graphitic, or carbona- ceous shale, limestone, graywacke, and sandstone that were interbedded in the flows are now mostly schists in greenschist and amphibolite facies. Retrograde green- schist metamorphism is, in general, superposed on amphibolite-grade schists. The older “bedded” rocks are several thousand meters thick, are heavily volcano- genic, and are cut by calcic intrusive rocks. In several places, these are tonalite gneiss having batholithic dimensions. An assemblage of somewhat younger bedded rocks, largely alkaline-calcalkaline andesite and dacite flows and tufl’s, is also present but includes lesser amounts of metagraywacke, marble (generally dolomitic), chert, quartzite, and graphitic or carbonaceous schist. These are now mostly in the greenschist facies. This assem- blage also includes quartz, sericite, and chlorite schists of uncertain origin and is intruded by calc-alkaline GEOLOGIC BACKGROUND 5 igneous stocks and batholiths composed of granodiorite gneiss and related rock types. The Precambrian units, next younger than the mostly synkinematic plutonites that cut the above-mentioned beds, contain a wider variety of sedimentary units. These include graywacke, sandstone, siltstone, polygenic conglomerate, and related elastic rocks, with minor amounts of limestone and argillite. Most of the sedi- ments contain grains of feldspar, angular quartz, and rock fragments derived from volcanic terranes. This suggests a single erosion and deposition cycle. Graded bedding and crossbedding are widespread, but ripple marks are less common; desiccation cracks and rain splatter marks are rare. Although this assemblage is largely of sedimentary origin, volcanism did not cease during this cycle. Andesite, rhyolite, and tufls are pres- ent throughout the section but are most common in the younger sequences. These beds, both sedimentary and volcanic, are several thousand meters thick and are folded and faulted along northwest-trending shear zones several kilometers wide. Metamorphic grade ranges from essentially unmetamorphosed to amphibolite fa- cies. Much slaty cleavage is developed where the rocks were derived from shale or tuff and metamorphosed to slate. Other beds are altered to sericitic and chloritic schists that now enclose amphibolite-grade infrastruc- tures having gneiss and granite cores. Folding of these beds was accompanied and followed by intrusion of ealc-alkaline stocks and batholiths, most of which were composed of quartz monzonite and gran- ite; these have been radiometrically dated by Rb/Sr whole-rock isochrons and range from about 680 to 620 million years before present (my. B.P.). (Brown, 1972; Fleck, 1976). Still younger, essentially unmetamorphosed flows, tufi's, and sediments that are composed of rhyolite, ig- nimbrite, water-laid tufl’s, agglomerate, conglomerate, and wacke are confined to the northeastern part of the shield. Related siliceous dikes, however, are more widespread. Intrusive rocks associated with these younger sequences are largely alkaline-peralkaline granitic rocks characterized by sodic amphiboles. Iso- topic ages (Kw—Ar) range in age from 600 to 550 my. with a culmination at about 570 my. for the coarse- grained intrusive rocks. The latter generally form circu- lar stocks or batholiths throughout the shield (Brown, 1972; Greenwood and others, 1975; Fleck and others, 1976). Gneisses in test area 1 were most likely formed during this time. The youngest rocks are most likely of Cambrian age. They are also unmetamorphosed and are confined to the northwest-trending shear zones of the Najd transverse fault system. These rocks are composed of conglom- erate, sandstone, cherty limestone, minor andesite, basalt, and rhyolite and are uneonformable above all the older shield rocks; they are openly folded as a result of late movement along the underlying faults (Delfour, 1970; Baubron and others, 1976; Hadley, 1973b). PHANEROZOIC DEPOSITS AND VOLCANISM The lower Paleozoic strata consisting mostly of Or- dovician sandstone encircle the crystalline shield and are essentially undisturbed. Although the sandstone is devoid of fossils in the lower several meters, it contains arthropod and gastropod trails in siltstone layers about 50 m stratigraphically above the crystalline basement. These siltstone layers are considered to be of Ordovician or youngest Cambrian age (Adolph Seilacher, written commun., 1973). The only Mesozoic rocks in the test sites are in a small outlier of Jurassic sandstone and limestone that remains as an erosional remnant 500 m above Ordovician sandstone on the high plateau near the Yemen border (pl. ZB, Jc, J a; Anderson, 1978a). The oldest Tertiary material within the two test areas is made up of saprolitie and lateritic weathering products. These are mostly limited to areas covered with later Tertiary and Holocene flood-basalt flows. In the Sarat Plateau, 20 to 30 m of saprolite capped by laterite under- lies 300 to 580 m of flood basalt. The latter ranges in age from 29 my. B.P. for the base to 25 my. B.P. on the crest (Brown, 1970; Overstreet and others, 1977). The volcanic rocks that form the crests of several ridges within the test sites range in age from middle Oligocene to late Miocene. They are part of the most extensive volcanism of the Arabian Shield and are ge- netically related to the origin of the Red Sea. Although spreading probably began at the end of the Mesozoic, the most important rifting and widening seems to have been concentrated in middle and late Oligocene time, possibly somewhat earlier. This period of tectonic activ- ity was followed by a quiescent, relatively static period that lasted until about 5 my. B.P. At that time, sepa- ration of the Arabian Shield from the Nubian Shield began again; it continued until the present (Girdler and Styles, 1974). During the quiescent period, a thick series of sediments that included as much as 2,800 m of evap- orite deposits accumulated in the Red Sea depression that developed as a result of late Tertiary ramping of the flanks. These beds range from Miocene to Pliocene age and crop out along the coast (pl. 13). The less solu- ble components together with Miocene coral coquina form terraces behind (east of) the elevated Pleistocene coral reefs (pl. 13). GEOMORPHOLOGY Basement rocks in the low-latitude deserts of North Africa and the Middle East are commonly well exposed. Especially good exposures are found along the flanks of the Red Sea where ramping in connection with rifting has removed much of the surficial debris. The nearly level surfaces away from the scarps have been formed by classical desert pedimentation. 6 GEOLOGICAL MAPPING BY USE OF COMPUTER—ENHANCED IMAGERY, WESTERN SAUDI ARABIA Local sandstone outliers of probable Ordovician age that cap J abal Tin (lat 22° N ., long 41°36’ E.) and J aba] Tamiyah (lat 25°35’ N., long 42° E.) attest to an Early Paleozoic period of shield burial. Additional evidence for burial is provided by the presence of Cambrian (?), and Ordovician sandstone in the grabens of the southeast-trending Najd fault system along the north- ern edge of the shield. The Precambrian surface was later exhumed and further eroded by pediment exten- sion throughout the rest of Phanerozoic time. Postcratonization beveling is far advanced but not complete. Bornhardts, small inselbergs, and koppies are widely spaced on the grus plains of the older granitoid rocks, and younger posttectonic granites commonly form inselbergs or mountains. The latter are found mostly along the scarps of the rift where their relief is attributed to Cenozoic epeirogeny. Sedimentary beds older than about 450 my. RP. were at least partly stripped from the shield by Late Or- dovician glaciation centered in North Africa (Beuf and others, 1971), especially in the northern reaches of the crystalline plains where deep-weathering profiles are absent. In addition, Carboniferous and Permian glacia- tion has been identified as far north as lat 14°30’ N. in Tigre Province, Ethiopia (Dow and others, 1971), and may have extended into western Arabia. The 950—m thickness of the Wajid Cambrian (I) and Ordovician sandstone at lat 19° N. suggests, however, that Gond- wanian (Carboniferous and Permian) glaciation scour was minimal, if it did indeed extend that far north. Epeirogeny initiating increased fluvial action and aided by wind scour has been a far more potent ero- sional mechanism. The doming prior to, during, and following rifting caused orographic convection, es- pecially in the monsoon belt in southern Arabia. The consequent fluvial erosion deposited 2,000 m of elastic rocks, mostly of continental origin, above the Miocene evaporite beds in the southern Red Sea trough (Gill- mann, 1968). The beveled surfaces that represent more than half the area of the shield are of three principal periods: the extensive older exhumed peneplains and pediplains and two younger pediments worn into the flanks of the Red Sea rift ramps. The opening of the Red Sea that began early in the Tertiary, or possibly during the Latest Cre- taceous (Maestrichtian), furnished a new base level for pedimentation, which accompanied the widening of the rift from the Oligocene onward. This produced the bev- eled, somewhat dissected surface that rises from be- neath the eastern edge of the coastal plain at about 50 m altitude, attaining an altitude of about 500 m above the Red Sea. The youngest pediment along the coast lies along the eastern edge of the alluvial plain and represents pedimentation since the second stage of opening of the Red Sea. This surface is largely undissected even though several major wadis have cut channels now filled with gravel across it. It merges with coral reefs and alluvial fans. In most places it is less than 10 km wide and often is difficult to define because of the presence of superposed alluvial scree that extends down from the scarp mountains and discontinuously across the older pediment. In the southern part of the shield, continued epeiro- genie movement in connection with the rifting has tilted the pediplain and peneplain surfaces to the northeast. Along the northern beaches of the eastern Red Sea shore, it appears that the terraces are elevated from the 3-m surface at J iddah to 520 m on Tiran Island near the mouth of the Gulf of Aqaba. The elevated surfaces are stepped benches from Jiddah northward, reflecting the intermittent character of the uplift, and are especially well developed between A1 Wajh and the Gulf of Aqaba (pl. 10 and D). The middle Tertiary pediment also rises to the northeast in this region (pl. 18 ). Whereas fluvial processes are dominant in the south- ern part of the shield, the effect of eolian erosion is more noticeable farther north. Rainfall is much less through- out the northern desert (probably less than 5 em per year in most places), and mountain ranges are nearly barren of vegetation. The limited rain comes during the winter season and is associated with the southern part of the belt of prevailing westerly winds. Wind scour in an easterly direction is apparent on all aerial photo- graphs and satellite imagery. The effect is most marked downwind from sources of sand and silt such as the Paleozoic sandstone that rims the northern edge of the shield and east of the grus plains on the shield where the older granitoids are exposed and weathered. Many surfaces are stripped of weathered material by wind- borne sandblast, and joints, faults, and sedimentary contacts are opened and widened. Because the initial openings are along zones where the meager rain or dew accumulates in depressions, frost action and the wide diurnal temperature range induce mineral separation by means of differential expansion and contraction upon heating and cooling. Thus, grains are loosened to a sufficiently small size to be windborne. One direct result is an emphasis of lineation patterns in the direc- tions of the prevailing winds. Where airborne sand and silt are insufficient to serve as a scouring tool, the dark iridescent desert varnish may markedly change the spectral reflectance of the underlying rocks, especially if considerable iron and manganese are involved in the weathering process. Diorite or basalt, for example, com- ‘monly show desert varnish, and, if there is adequate abrasion to remove the varnish, shiny surfaces of desert polish are formed. Accumulation of desert varnish, and other results of weathering processes on pediments, pediplains, and peneplains, has a direct bearing on the nature of the surface materials and may dramatically influence the spectral reflectance of specific rock types. r ROCK UNITS DEFINED ON ENHANCED IMAGERY 7 In some areas this has made interpretation of both air- craft and satellite imagery difficult. ROCK UNITS DEFINED ON ENHANCED IMAGERY METAMORPHIC ROCKS The two areas selected to test the applicability of computer-enhanced Landsat imagery in active regional mapping programs are shown on plate 10, D, and plate 20, D. These images illustrate the geological informa- tion that can be obtained by using differently enhanced Landsat data. Images made using the ramp-stretch and ratio-stretch methods are particularly complementary to each other. The ramp-CDF stretch images (pls. IC, 20) clearly define topographic relief and drainage lines. In addition, some fundamental differences of terrane reflectance among rock types can be determined on the basis of both color and surface texture. Topographic features are shown even better on images obtained dur- ing winter months than on the spring images shown here, as the lower sun angle increases the shadows that define the surface texture. Because of increased color contrast, the CDF contrast-stretch images also show tectonic features more clearly than does the standard Landsat imagery (pl. 13 and pl. 23). For example, lin- eaments that are commonly indicators of faults, or bed- ding where the strata are folded and differentially erod- ed, are more clearly visible on plate ZC than on 23. In general, rocks that are dark in outcrop are also dark on the contrast-stretched Landsat images. For example, metabasalt and amphibolite schist (pl. 13) appear near- ly black on plate 10 in the northern test site. The meta- morphosed dark igneous rocks in the southern test site, however, are somewhat lighter in tone (except in cliff shadows), whereas the Oligocene flood basalts (pl. 23) show a lighter brown hue on pl. 20. The plutonic rocks, and especially the granitoids in both test areas, are generally light tan or brown, except that, in the north- ern area, some have a light greenish cast. The calc- alkaline plutonic rocks in the southern test area near the Yemen border are generally lighter tan in color than similar rocks in the north. This difference in tone be- tween apparently similar rocks is possibly caused by a thin loessal and alluvial cover that is present where the outcrops tend to form plains. Some quartz diorite is pale blue (qd in pl. 20), whereas other batholiths and stocks on pl. 2D are yellow green to olive green. Alluvium derived from dark rocks appears blue in both test areas; coral reefs and loess are nearly white. In general, the rock types not readily separated on the ramp CDF stretch image can be separated more readily on the ratio-contrast-stretched imagery. This discrimi- nation capability is especially effective when geo- logic interpretations are made by using both types of imagery in concert (pl. 10, D and pl. 20, D). In the northern test site, the darker rocks, notably the green- stones, can be separated in the ratio-stretch enhance- ment because specific classes are grouped into shades of blue, green, red, and orange. The relief, drainage, struc- tural features, and resolution are deemphasized in this product. However, the presence of even sparse vegeta- tion can create a blue-to-purple cast on the ratio-stretch image, as the color and density of the cast are deter- mined by the vegetation density. These dominant hues tend to mask the reflectance signatures of the under- lying rock surfaces, and care must be taken not to con- fuse the two. The distribution of the vegetation can frequently be distinguished by comparison with the characteristic red vegetation signature shown on the standard color-composite Landsat imagery. Examples of vegetative masking can be seen in the northeastern corner of plate 1D in the northern test area and along the west side of the Sarat Plateau at the western edge of plate 2D in the southern test area. The significance of vegetation on rock and soil spectral reflectance has re- cently been field tested by Siegal and Goetz (1977) by use of a portable field-reflectance spectrometer. Their tests show that the effect of 10 percent cover of manzanita brush in southwestern United States, which is similar to the vegetative cover in western Saudi Arabia, would probably not interfere significantly with rock (andesite) reflectances, whereas in areas of 30 percent or greater vegetation cover, the plant reflectance dominates the scene. In western Arabia, a native brush covering of more than 10 percent is limited, in general, to the crest and uppermost western flank of the scarp mountains where the ‘Asir Mountains intercept the southwesterly mon- soon moisture-bearing winds (pl. 2D). PLUTONIC ROCKS In the shield areas of western Arabia, the plutonic rocks generally become darker as the pyribole-biotite content increases. This seems to be a factor influencing the rock discrimination capability in the false-color im- agery; for example, compare the biotite hornblende granodiorite (grbh) with the granite (gr) and quartz monzonite (qm) on the ramp CDF stretch image (pl. 10). The granite (gr) at J abal Liban is petrographically similar to the granite southeast of Bi’r Aba al Qazaz; both are predominantly cataclastic and contain two generations of feldspar. J abal Liban, however, shows a reddish cast on the ratio-stretch image, whereas the granite in the fault zone is nearly black. This difference in color may be due to granulation and weathering in the fault zone or, alternatively, to an increase of meta- morphic hornblende in the sheared granite. Indeed, the fault-zone granite has a reflectance similar to that of the granite gneiss west of Wild? Thari, yet the rocks are of different origin and history (p1. 1D). The expla- nation for this apparent spectral incongruity is not 8 GEOLOGICAL MAPPING BY USE OF COMPUTER-ENHANCED IMAGERY, WESTERN SAUDI ARABIA immediately obvious. The quartz monzonite of Jabal Ra‘al and nearby intrusive rocks are petrographically similar to the quartz monzonite of J abal Lahiya at the east edge of plate 1D, but the J abal Lehiya batholith appears darker on the contrast-stretch image and has a lighter, greenish cast when compared with Jabal Ra‘al on the ratio-stretch image (pl. 1D). Here the crest of J abal Lahiya is an old pediment, probably dating from Oligocene opening of the Red Sea, and weathering has darkened the monzonite. J abal Ra‘al, on the other hand, is a faulted young bornhardt on the Holocene pediment exposed during the last 5 my. B.P. and is thus a much fresher surface under active erosion. Why the granite or quartz monzonite (qm) in the top center of plate 1D differs so much from J abal Lahiya on the eastern edge of plate 1D is not clear. Both batholiths are beveled at 1,200 m above the Red Sea and both are biotite- hornblende quartz monzonite with local granodiorite facies. A single K40-Ar age for Jabal Lahiya is 605118 m.y., whereas for the northern batholith a single K40-Ar age is 591 i 18 m.y., so both are obviously postkinematic in age. In spite of the obvious field similarity, the north- ern batholith is light tan on the contrast-stretch image compared with a dark olive green for Jabal Lahiya. Moreover, the northern batholith is black on the ratio- stretch image, whereas Jabal Lahiya is a bluish green. The only apparent difference in the two rocks is the presence of large (1 cm) potassic-feldspar phenocrysts in the northern batholith. In the southern test area, similar postkinematic cir- cular stocks of biotite-hornblende granodiorite ranging to quartz monzonite (gqm, pl. 23) mapped by Green- wood (1979a,b) are dark blue, bluish black, and bright blue on the ratio-contrast stretch image (pl. 2D). Like- wise, trondhjemite (tj) has two reflectance colors, olive brown and greenish-gray brown on plate 2D. Metamor- phosed gabbro (gb) and related rocks are blue green (pl. 2D), and somewhat more turquoise blue on the image of the northern test area east of Al Wajh (pl. 13, D). From these findings and information from W. R. Greenwood, it appears that many of the igneous units mapped at a 1:100,000—scale can be subdivided when mapped at a larger scale. The older metamorphosed bedded rocks in the Ara- bian Shield are mostly mafic volcanic or associated sed- imentary rocks now of the amphibolite facies. In the Al Wajh area they are characterized by bright and vari- colored hues on the ratio-stretch image, as might be expected from the variety of source rocks (gdss, sedimentary; gdsv, colluvium, pl. 1D). The meta- sedimentary rocks appear orange tinted compared with a more mauve blue for the metavolcanic rocks. A bluish tone forming a crescent east of Jabal Liban in the Al Wajh region (west center of pl. 1D) appears to represent the older metamorphosed sedimentary rocks and flows that have been further metamorphosed in a contact aureole around a small granodiorite intrusion (gds), rather than the reflectance characteristic of vegetation. Most of the andesitic greenstones and associated metasedimentary rocks on the northeast side of the Najd fault are in the greenschist metamorphic facies (ha, pl. 1D). Their color is similar to that of the metafiows in the vicinity of Al Wajd (gdsv and gdss, p1. 1D) except for a greenish cast not seen in the Al Wajd metafiows. They underlie a thick series of pelitic meta- sedimentary rocks (mu), so their identification here is partly based on our knowledge of the stratigraphic pos- ition. Some ophiolitic or ultramafic metamorphosed rocks (ub, pl. 1D) shown by Pellaton (1979) lie within the outcrops of the greenstone; however, the sparse veg- etation especially at the mountain crest west of Wadi Thari makes the distinction of these rocks difficult. A yellow-orange color correlates with known out- crops of what has been designated either graphitic or carbonaceous schist in the field. Most likely these rocks are graphitic if the metamorphism is in the amphibolite facies. However, carbonaceous material in similar rocks has been identified as being derived from blue-green algae on the Sinai Peninsula and has been dated at 934180 m.y. B.P. (Shimron and Brookins, 1974; Shim- ron and Horowitz, 1972) (carb, marked carbonaceous on pl. 1D). A similar yellow-orange color on the ratio- stretch image of the southern area (pl. 2D) demarcates a belt of similar graphitic or carbonaceous meta- sedimentary rocks near Al Yemen. On the basis of this spectral unit and later field confirmation, it has been possible to correlate this carbonaceous schist unit over an area of 1 degree in latitude (carb, pl. 2D) (Green- wood, 1979a; Anderson, 1978b) and to define its exten- sion southward across the border into Yemen. The Najd fault zone extends diagonally across plate 1D. The areas of sheared rocks within the zone range in width from 5 to 20 km, depending on the bifurcation and coalescence of the various shear zones, and are greenschist-facies schists grading into the lenses of garnet-amphibolite schist and finally into gneisses and granitic rocks. The ability to separate chlorite-sericite schist (sc, scs) from biotitic and amphibolitic schists (am) is not apparent on the ratio-stretch image, but the contrast-stretched image generally shows the higher grades of metamorphic rocks in dark bluish-brown tones and somewhat darker than the greenschist facies (pl. 10). On the other hand, the amphibolitic schists (am) are easily separated within the fault zones on the ratio-stretched enhanced imagery, even though difier~ ences between these units are not apparent even on aerial photographs or from visual inspection from air- craft. The amphibolite schist is also generally darker than the greenschists on the standard simulated false- color Landsat imagery (pl. 13). The enhanced-image pair shown on plate 10 also provides an excellent exam- ple for the visualization of the process of granitization. CONCLUSIONS 9 Note how the eastern elongated gneiss dome (amg) north of Jabal Ra‘al and the north-trending gneiss dome (gn) southwest of Jabal Galab both grade from greenschist into amphibolite and granite or quartz monzonite, the latter being late or postkinematic. Al- though their lithology is similar, the domes are labeled differently because field investigations show that the north-trending dome is associated with at least two periods of tectonism, whereas the east-elongated dome north of Jabal Ra‘al is associated with the Najd fault tectonism—the latest diastrophism of consequence within the shield. GOSSAN AND LATERITE The graphitic or carbonaceous sedimentary rocks and associated andesite and dacite that extend southward along the eastern edge of the Zahran area include lenses of gossan formed from the weathering of sulfide miner- als. A distinctive spectral signature for gossan was identified on the ratio-stretch image where the alter- ation is exposed over areas large enough to register at the scale of the imagery (g, pl. 20). This gossan overlies massive sulfide deposits or lenses within the meta- volcanic and metasedimentary rocks. The sulfide miner- alization consists mostly of pyrrhotite and pyrite. The gossan itself is composed of hydrated iron oxides and silica, is locally calcareous, and is brown, buff, and ma- roon in outcrop. On the ratio-stretch imagery, it is identified by a distinct reddish-orange color, but it is not distinctive on either the standard color-composite Landsat imagery or the contrast-stretch enhancement or even on aerial photographs (pl. 2A and B). However, a very similar hue marks the outcrop of a deeply weath- ered, partly lateritized saprolite, which underlies the Sarat volcanic rocks, where reddish-orange color forms a rim around the volcanic rocks located about 100 km west of the gossans described above (Tl, pl. 2D). The deeply weathered laterite-saprolite zone is red, yellow, and white in outcrop and composed mostly of kaolinite and quartz but also includes local concentrations of goe- thite and alunite (Overstreet and others, 1977). The orange-red color is most intense where goethite crops out, as might be expected, but, surprisingly, all the lat- eritic outcrops show a similar hue. TERTIARY VOLCANIC ROCKS Flood-basalt fields of different ages have previously been found to reflect striking differences in color on the ratio-stretch imagery (Blodget and others, 1975). The only basalt fields within the two test areas studied with- in this report are the Sarat (Ts on plate 20 and D), the tips of an outlying prong of Harrat ‘Uwayrid east of Al Wajh, and two small outliers of Harrat ‘Uwayrid (Tb, p1. 1D). The Sarat lavas are hypersthene-normative basalt, alkali picrite, and alkali olivine basalt. About 20 flows range in age from 29.4 to 24.7 my. RP. (Coleman and others, 1977). On the basis of two samples collected near the test site, the northern Harrat ‘Uwayrid is inter- preted to be alkalic olivine basalt. A late Miocene age of 7.4 my. RP. has been determined by Richard Marvin of the US. Geological Survey. On the ratio-stretch image, the Harrat ‘Uwayrid-type basalt is bright blue, whereas the older Sarat lavas are a distinctively different light green-blue hue on the same image. The Sarat lava reflec- tance is partly obscured by vegetation that imparts a violet cast to much of the upland surface of the flows. CONCLUSIONS Certain types of computer-enhancement techniques significantly increase the geologic interpretability of Landsat satellite data for regional mapping. The two computer-enhanced products that proved most useful in this experiment were color-composite images made from individually contrast-stretched MSS bands and contrast-stretched ratio images. The former provided greater contrast among terrestrial features than could be attained using standard Landsat color-composite imagery and at the same time retained the optimum 79-m resolution. Color-composite images made using stretched-ratio data, on the other hand, generally in- creased separability of surface materials, but resolution was inherently degraded during the enhancement proc- ess. Optimum geologic interpretations can be made if these two image classes are used in concert. A wide variety of rock types could be distinguished using a combination of both types of data in two Ara- bian test areas used in this report. Although a complete separation of all the different surface materials could not be accomplished, many spectral units could be re- lated to field-mapped rock units and, thus, could be used to supplement regional geological mapping provided sufficient field work is done on the land surface. The most important applications of enhanced im- agery used in lithologic identification for this region are as follows: 1. Gossan and laterite can be identified readily if ex- posed in large enough outcrops. 2. Lava sheets, mostly basalt, ranging in age from Oli- gocene to Holocene can be separated by color for each period of extrusion. 3. Graphitic or carbonaceous schists for which bound- aries are difficult to identify on the ground have a distinct color on enhanced imagery. 4. Granitoid exposures can be separated with difficulty by rock type. Some quartz monzonite or granite stocks appear identical from petrographic study but have different colors on the enhanced imagery. Con- versely, some granitic rocks showing similar en- hanced color have different mineral compositions. 10 GEOLOGICAL MAPPING BY USE OF COMPUTER-ENHANCED IMAGERY, WESTERN SAUDI ARABIA 5. Amphibolite can be separated from greenschist eas- ily, and gneissic granitic infrastructures stand out in the imagery, whereas on the ground or in low- altitude aerial viewing, they are often indistinguish- able from the amphibolite flanks. REFERENCES CITED Alabouvette, B., and Pellaton, C., 1973, Geology and mineral ex- ploration of the Widi Kamal quadrangle: France, Bureau de Re- cherches Geologiques et Miniéres, Saudi Arabian Mission, 45 p., maps and appendixes. Anderson, R. E., 1978a, Geology of the Widi Atf quadrangle, sheet 17/43A, Kingdom of Saudi Arabia: Saudi Arabia Directorate General of Mineral Resources Geologic Map GM—30, scale 1:100,000. 1978b, Geology of the Mayza quadrangle, sheet 17/43B, King- dom of Saudi Arabia: Saudi Arabia Directorate General of Min- eral Resources Geologic Map GM~31, scale 1:100,000. Baubron, J. C., Delfour, J., and Vialette, Y., 1976, Geochronological measurements (Rb/Sr/K/Ar) on rocks of the Arabian Shield, Kingdom of Saudi Arabia: France, Bureau de Recherches Geolog— iques et Minieres, Open-File Report 76—JEd—22, 168 p. Beuf, Serge, Biju-Duval, Bernard, Charpal, Oliver de, Rognon and others, 1971, Les gres du Paleozo'lque inférieur au Sahara: Paris, Editions Techni, 464 p. (Institut francais du Petrole, Collection Sciences et Technique du Petrole, no. 18). Blodget, H. W., 1977, Lithologic mapping of crystalline shield test sites in western Saudi Arabia using computer manipulated multi- spectral satellite data: Washington, DC, George Washington Univ., Ph. D. thesis, 191 p. Blodget, H. W., Brown, G. F., and Moik, J. C., 1975, Geological mapping in northwestern Saudi Arabia using Landsat multispectral tech- niques: US. National Aeronautics and Space Administration Technical Memorandum no. X—58168(v. I—B, Geology information systems and services), p. 971—989. Brown, G. F., 1970, Eastern margin of the Red Sea and the coastal structures in Saudi Arabia, in A discussion on the structure and evolution of the Red Sea and the nature of the Red Sea, Gulf of Aden and Ethiopia rift function: Royal Society of London, Philo- sophical Transactions, ser. A, v. 267, no. 1181, p. 75—87. 1972, Tectonic map of the Arabian Peninsula: Saudi Arabia Di— rectorate General of Mineral Resources Peninsula Map Series Map Ap—2. Coleman, R. G., Fleck, R. J., Hedge, C. E., and Ghent, E. D., 1977, The volcanic rocks of southeast Saudi Arabia and the opening of the Red Sea: Saudi Arabia Directorate General of Mineral Resources, Bull. 22, p. D1-D30. Colwell, R. N., ed., 1973, Integrated study of earth resources in the State of California: Berkeley, California University, Space Sci- ence Laboratory, 419 p. (Progress report to NASA for studies conducted under contract NAS-5—21827.) Delfour, Jacques, 1970, Le groupe de J’Balah, une nouvelle unite du bouclier arabe: France, Bureau de Recherches Geologiques et Minieres Bulletin, 2d ser., sec. 4, no. 4, p. 19—32. Dow, D. B., Beyth, M., and Hailu, Tsegaye, 1971, Paleozoic glacial rocks recently discovered in northern Ethiopia: Geological Magazine, v. 108, no. 1, p. 53-59. [Fleck, R. J .], 1976, International cooperation in the earth sciences, in US. Geological Survey, Geological Survey research 1976: US. Geological Survey Professional Paper 1000, p. 302. Fleck,_R. J ., Coleman, R. G., Cornwall, H. R., Greenwood, W. R., Had- ley, D. G., Schmidt, D. L., Prinz, W. C., and Ratte, J. C., 1976, Geochronology of the Arabian Shield, western Saudi Arabia: K-Ar results: Geological Society of America Bulletin, v. 87, no. 1, p. 9-21. Gillmann, Michael, 1968, Primary results of a geological and geo- physical reconnaissance of the J izan coastal plain in Saudi Ara- bia: American Institute of Mining and Metallurgical Engineers, Society of Petroleum Engineers, Saudi Arabia Section, Regional Technical Symposium, 1968, 2d, Dhahran, Saudi Arabia, Pro- ceedings, p. 189—212. Girdler, R. W., and Styles, P., 1974, Two stage Red Sea floor spreading: Nature, v. 247, no. 5435, p. 7—11. Goetz, A. F. H., Billingsley, F. C., Gillespie, A. R., Abrams, M. J., Squires, R. L., Lucchitta, I., and Elston, D. P., 1975, Application of ERTS images and image processing to regional geologic problems and geologic mapping in northern Arizona: California Institute of Technology, Jet Propulsion Laboratory, Technical Report 32— 1597, 188 p. Greenwood, W. R., 1979a, Geology of the Wind? Malahah quadrangle, sheet 18/43D, Kingdom of Saudi Arabia: Saudi Arabia Direc- torate General of Mineral Resources, Geologic Map GM—39, scale 1:100,000. —-——1979b, Geologic map of the Widi Wassat area, Geologic Map Series, sheet 18/440: Saudi Arabia Directorate General of Min- eral Resources, scale 1:100,000. [Greenwood, W. R., Hadley, D. G., Anderson, R. E., Fleck, R. J., and Schmidt, D. L.], 1975, Cratonization in the Arabian Shield, in US Geological Survey, Geological Survey research 1975: US. Geolog- ical Survey Professional Paper 975, p. 271. Hadley, D. G., 1973a, Geology of the Sahl al Matran quadrangle, northwestern Hijaz, Kingdom of Saudi Arabia: Saudi Arabia Di- rectorate General of Mineral Resources, Geologic Map GM—6, text, 14 p. 1973b, The taphrogeosynclinal J’Balah Group in the Precam- brian shield, northwest Saudi Arabia [abs]: Geological Society of America Abstracts with Programs, v. 5, no. 7, p. 646—647. 1974, Geologic map of the Wayban quadrangle, Kingdom of Saudi Arabia: Saudi Arabia Directorate General of Mineral Re- sources, Geologic Map GM—7, text, 10 p. 1975, Geology of the Qalat as Sawrah quadrangle, sheet 26/ 38D, Kingdom of Saudi Arabia: Saudi Arabia Directorate General of Mineral Resources, Geologic Map GM—24, text, 28 p. Overstreet, W. C., Stoeser, D. B., Overstreet, E. F., and Goudarzi, G. H., 1977, Tertiary laterite of the As Sarat Mountains, Asir Province, Kingdom of Saudi Arabia: Saudi Arabia Directorate General of Mineral Resources, Bull. 21, 30 p. Pellaton, C. P., 1979, Geologic map and section of the Widi Daghalah quadrangle: France, Bureau de Recherches Geologiques et Mini- eres, Saudi Arabia Mission, scale 1:100,000. ' Rowan, L. C., Wetlaufer, P. H., Goetz, A. F. H., Billingsley, F. C., and Stewart, J. H., 1974, Discrimination of rock types and detection of hydrothermally altered areas in south-central Nevada by the use of computer-enhanced ERTS images: US. Geological Survey Pro- fessional Paper 883, 35 p. Shimron, A. E., and Hornwitz, Ahron, 1972, Precambrian organic microfossils from Sinai: Pollen and Spores, v. 14, no. 3, p. 338—342. Shimron, A. E., and Brookins, D. G., 1974, RB—Sr radiometric age of late Precambrian fossil-bearing and associated rocks from Sinai: Earth and Planetary Science Letters, v. 24, no. 1, p. 136-140. Siegal, B. S., and Gillespie, A. R., 1979, Remote sensing in geology: New York, John Wiley and Sons, Inc. Siegal, B. S., and Goetz, A. F., 11, 1977, Effect of vegetation on rock and soil type discrimination: Photogrammetric Engineering and Re- mote Sensing, v. 43, no. 2, p. 191—196. fl U.S. GOVERNMENI’ PRINTING OFFICE: I982— 361-614/“9 it. Cr UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY 35°00' 37°00 37°30 27°00 J y . 27°00 ’0'" 26°30 20°30 25°00 26°00' 36°00 37°00 37°30 A. SEMICONTROLLED AERIAL PHOTOMOSAIC :gJ Ling}: “3E§EL Edae~4e QF‘PLIED SKEU= 189‘ sum E DEGREES C. ENHANCED, RAMP—STRETCHED SIMULATED-COLOR LANDSAT IMAGE IMAGERY AND GEOLOGY 30°00 15’ 30 45/ 37°00 15/ 37°30 27°00, .. . , . - - - 27°00 45' 45' 30 30, 15' i0 25°00' ‘ ‘ CTR r “ ' 25°00 45’ 37°00 15’ 37°30 30’ 36°00’ 15’ Base prepared by Seiscom Delta Inc. See Index for mapping responsibility B. GEOLOGIC MAP ON COLOR COMPOSITE LANDSAT IMAGE ”” Dfithne— ~e HUG 13 41E86~- -“e “BHQE—DFxE036~39 Nee—D. INPUT 1; - _ r x 4 INF- APPLIED arr; STRETCH - nfitnn HDG 1:9 SUN E c INPUT 2) z '6‘ D. ENHANCED, RAMP—STRETCHED, AND RATIOED SIMULATED-COLOR LANDSAT IMAGE OF THE AREA NORTHEAST OF AL WAJH (TEST AREA 1), NORTHWESTERN SCALE APPROXIMATELY 1:500 000 10 O 10 2O 3O 4O 50 MILES I—I I—I I-—I I—I I—-I 10 O 10 20 3O 4O 50 60 7O KILOMETERS I-I I-—I H H H I—*l i—-———i I————i Pg ‘75 P0 v. II53 I012 NOV 31982 (‘ e , PROFESSIONAL PAPER 1153 PLATE 1 ESTIMATED ISOTOPIC EXPLANATION OF MAP UNITS AGESlmV-B-R) PLUTONKIROCKS—JGNEOUS AND METAMORPHKI LAYERED Rooks—SEDmnnns AND VOLCANN2FLoum Gal—Quaternary alluvium Qu—tiiégdifferentiated alluvium, includes some Tertiary clas— QUATERNARY Ot—terraces and Pleistocene elevated coral reefs Tr—R h F t' M‘ ag ama ormalon( iocene) TERTIARY Tb—basalt remnants on hilltops Cs—Cambrian sandstone, Nubian type } CAMBRIAN 580—570 ill—polymict conglomerate, andesite, alkalic basalt, and rhyolite flows; limestone, unmetamorphosed pelitic sed— iments z INFRACAMBRIAN 635—570 gp—alkaline to peralkaline granite, syenite, some intrusive sr—rhyolite, tuffs, volcanogenic sediments rhyolite J 680—620 gbm—gabbro, grbh—granite qm—quartz ‘ alkaline and monzonite and ‘ calcalkaline granodiorite mu—~clastic sc—sericite, chlorite, quartz scs—schistose sediments feldspar, schist, mostly in the sediments greenschist metamorphic facies; some biotite and hornblende 700~620 gr—calcalkaline biotite-hornblende granite and quartz mon~ zor.ite, some granodiorite 665—650 hau—rhyolite, ignimbrite and tuff 780—660 gb—gabbro dL—diorite qdi—quartz gm—granodiorite ha—andesite, mostly in greenschist metamorphic facies PRECAMBRIAN diorite and granodiorite gneiss ub——ultramafic igneous rocks 780 B—calcic metagabbro, metadiorite, anorthosite, migmatite complex 1100—1000 gdsa—metabasalt, metaandesite; gdsvametarhyolite; gdss—some metasediment; gds—undifferentiated gn—gneiss, mostly paraamphibolite; schistose am—amphibolite schist and gneiss; amg—amphibolite gneiss in Nejd fault zone, includes rocks as young as mu, possibly younger J ‘7‘ Geologic contact—dashed where approximately located Fault—dashed where approximately located Thrust fault—teeth on upper plate, queried where doubtful *“i—> Gneiss dome "W Escarpme nit '3‘ 36° 39° 42° 45“ 48° \ \K 1 '\ JORDAN \ % \\ an > i. ’/ T‘I /-- l IRAQ \\ l GULF ‘\ /\ 4 or \ \ AQABA 4 >__ KUWAIT m \\ ’a \ a Test area I (Plate 1) \/ \ 28 Q (AI Wajh study areal __ Trran b Bi’r Aba ales; JABAL SHAMMAR Qazaz AI ._ JABAL/ 5‘ / RA’AL 24° \ 619/6 <0 3 E’ JABAL TIN cf 5 Jiddaho '5 \ MAKKAH S (Mecca) ' 20° Area of satellite image prepared by -neral Electric Co. and aerial 0 100 MILES LLJ_I_I_I_i_LJ_i_i 16“ ADEN —l INTERIOFPGEULOGICAL SURVEY, HESTON, VA 49827679493 Boundary representation is ”0T necessarily authoritative. a. Area north of dotted line (26°30’) reconnaissance mapped by John Kemp b. Area east of Al Wajh (dashed line) mapped by S. Okuma, K. Komura, and T. Hatanaka, Japan Geologi— cal Survey c. Area east of 37°30’ E and north of 26° N mapped by C. PeIIaton, Bureau de Rechereches Geologiques et Minieres (BRGM), France . Mapped by M. Bigot, BFIGM . Geology by D. B. Stoeser . Geology by W. R. Greenwood . Geology by R. E. Anderson . Geology from satellite imagery D'LQ—NCDD. INDEX MAP SAUDI ARABIA UNITED STATES DEPARTMENT OF THE INTERIOR . PROFESSIONAL PAPER 1152 GEOLOGICAL SURVEY PLATE 1 3501018; ' “8'00 . 117:00' “WW 3986,8030 118:00’ 117:00' “5°00, EXPLANATION EXPLANATION QUATERNARY ROCKS AND ALLUVIAL . 76 Potassium—argon sample locality (upper number) and measured apparent age (lower MATERIAL 17R number)—All ages rounded to nearest million years. Exact calculated age and 186H analytical data given in table 1. B, biotite; H, hornblende; M, muscovite. Exact .., , TERTIARY ROCKS location and brief description of each sample given in section on ”Sample Localities El Barstow I“: MESOZOIC GRANITIC ROCKS El Barstow and Descriptions” at end of report ALL OTHER CRYSTALLINE ROCKS—Includes : .A. _. Major fault—Dashed where inferred. Sawteeth on upper plate of thrust or reverse Mesozoic schist and metavolcanic rocks, fault. Arrows show relative motion on strike-slip faults Paleozoic metasedimentary rocks, and Precambrian gneiss, schist, and intrusive rocks Contact —\ .L._ Major fault—Dashed where inferred. fl Sawteeth on upper plate of thrust or .773 reverse fault. Arrows show relative motiOn 7371 \ tr'k — l' f It 788 on s 1 eslp au s .75H 34 \6’6 32 _- \ fl , 743 El Lancaster _ - 30 73B 7 . iv 83 3'5 ea 29 838 . €73 72H .2 . 28 . .fi . "w QELENDALE 33 K) FAULT . E. 34213 71 . T El Palmdale .2. 3‘ 84 Cl Palmdale 748 fi 72 # w m : ' _— 7GB .‘ Q Q 4/ 838 __.‘ 44/0,? 26 169H Victorville El .‘5' Q 54S ,fié D .70 p Victorville «— 4W 723 34°30’ 34°30, _ 7 25 ~— m 71H . a 3L . 593 i 728 . . 678 g 13 .713 §_ 8013 69B. . . . - . - l . 25$ T ’ O 56 _. . ._.. . “3"“ m 57 69B 32 5 SI? .- " ' ~ ' GABRIEL 718 fig ”M703, fl ‘71H ‘ '7' ' . SAN FAULT . fl.” - - '111 131 '. I' _ 2:11. . ‘”"' 18 '21 57A. LakeArrawhead .331 . 793* m m 1.2.7. m. 134 . . ’1 . -, . -. . .. . _ . , - . ' * 74B BlgBearLake 683 653 71M 713 1.58 .. . ' " 65H 58‘ $53!; . 61 . 73M 91 114 % 126' .72H . ' .; '- , .5_:~’-: ‘:.:'-' fig 60 7 87 .7073 _ 7 . 7 _ . . Q .‘ ' a 7““ fl. $33 708 728- 723 L22 4.5 "" .. .. ' . W \ 7 H '7 115' 173% 130 ' . Pasadena \j 1-. ' 2' Twentynine Palms Cl Pasadena 6 fl EB: V .% - 90 ~13 fi 116 ‘ ,§5—B Twentynine Palms III VP“) - El VP“) 118H 147H g $23 ° W 129' M D “M _ D “M 0 703 fig % We PINTO OUNTAIN FAULT RAYMON A ' I:I Yucca RAYMON SIERRA N‘" 300, ”TH 3,74 75”- 71M 13‘ Yucca Valley Valley ’7’ ,5, ’VCH OF 0 Pomona 4/1/07 El 0 AN F 548 F (844/ 4 AULT 4/0 — T 116A & \AN/V/NG R543 p 1.112;“ .W 34°00 T 34°00' \ \ FAULT I 400 593 Geology generalized and modified from Los Angeles (Jennings and Strand, 1969) and San Bernardino ‘ . A.—GENERALIZED GEOLOGIC MAP SHOWING DISTRIBUTION OF MESOZOIC GRANITIC ROCKS (Rogersr 1959’ Sheets 0‘ the GGO'OG'C map 0‘ Gamma B.—SAMPLE LOCALITIES AND MEASURED APPARENT AGES 0 / o I 0 / 118030, 0 I 0 ' 35001018 30 “3'00 Him, 116 00 35,00, 118,00 “7:00, 116 00 EXPLANATION EXPLANATION soil—L‘L— Contours of biotite apparent ages—Dashed where control is poor. Hachured contours surround minimum apparent ages. Contour interval 2 my. for apparent ages less than 80 my, 10 my. for ages greater than 80 my. Barstow (area of 10—m.y. interval is shaded). No D hornblende or muscovite apparent ages are included or allowed to influence the contouring. All biotite ages are used except those from a few plutons outside the discordant zone that are considered to have Cretaceous emplacement ages 44; _ Contours of biotite apparent ages—Contour interval, symbols, and other data same as in plate 1C. Apparent ages outside any particular fault block do not influence position or configuration of contours within that block [I] Barstow ; .A. __ Major fault—Dashed where inferred. Sawteeth on upper plate of thrust or reverse fault. Arrows show relative motion on strike—slip faults Major fault~Shown for reference only: possible influence of faults on contours is disregarded Sample locality used for control in contouring III [ancaster III Lancaster 844/. Palmdale El Palmdale 44, U 0,9548 ‘4 OZ 7. S 44/ 34°30' 34°30! _ ’l’o ( 2 ._ e / 7‘ \ \‘V: Lucerne Valley K‘ )9 )6‘ ‘90 0 SAN GA/BRIEL FAULT / 7 \j o Q) a 0- o ‘8» 0‘ . 74 0 A /~/ 7 /~/ I o 6‘ o 8007 \74/ '4/ 8,9 Twentynine Palms Pasadena \j , 2/e\ ONGA FAULT Twentynine Pal \) AM 0 ms Pasadena D IF 5 v7 (:1 44/0 653x INTO MO D (’P‘ ,CUC fl [:1 an} Isms C} . 6' Ivo P UNTAIN FAULT we 66 / MOUNTAIN FAULT RAYMOND 4 MADRE-CUCAMQNGA w)» ’65 San Bernardmo OF Sir/v BRA/(7 , DYucca Valley “An/10W SIERRA w ,/ D INN“3 ’97 4/ All/D CH 0/: S // Yucca Valley I] Pomona Q) 5548 AN NDRE / El Pomona AS \ /F4Ulr FAULT/ s / ANN/N ’60 / G FAULr 0 34°00' l I 34°00' a INTERIOR—GEOLOGICAL SURVEY, RESTON, VA ~19804679466 C.—CONTOURS OF BIOTITE APPARENT AGES FOR ENTIRE REGION D.—CONTOURS OF BIOTITE APPARENT AGES WITHIN INDIVIDUAL FAULT BLOCKS U 10 20 30 40 50 KILUMETERS | l l | I l | I l l I I I I I I I I 0 10 20 30 MILES MAPS SHOWING GENERALIZED GEOLOGY, SAMPLE LOCALITIES, APPARENT AGES OF MESOZOIC GRANITIC ROCKS, AND CONTOURS OF BIOTITE APPARENT AGES, EASTERN TRANSVERSE RANGES AND SOUTHERN MOJAVE DESERT, CALIFORNIA UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY 43°00’ 17°30’ 44°IOO' 43°30’ 18°00’ 7°45’ 17°30’ 44°00’ H ash- A 43°30’ 43°OD’ A. SEMICONTROLLED AERIAL PHOTOMOSAIC Base prepared by General Electric CD. See Index (Plate l) for mapping responsibility DQHRMH . ‘ . 43.: ' H331“ w APPLIEB C. ENHANCED, RAMP-STRETCHED SIMULATED-COLOR LANDSAT IMAGE IMAGERY AND GEOLOGY OF THE ZAHRAN AREA (TEST AREA 2), SOUTHERN SAUDI ARABIA imam 1‘1 «m t if), H J a ”H?! {Lei $5131 {new it t- » iii. (.3 . we 1': WW K \ ' 9d1‘9t Q Tb gbz TI" ' a, ( 8' k l i i a l i, l lNTEHIOHiGEOLUGICAL SURVEY, RESTON, VA.-—1982*G79493 D. ENHANCED, RAMP-STRETCHED, AND RATIOED SIMULATED-COLOR LANDSAT IMAGE SCALE APPROXIMATELY l1500 000 10 O 10 2O 3O 4O 50 MILES I—l l—l l—-4 l—l i—i . l 10 O 10 20 3O 4O 50 60 7O KILOMETERS H H H H H l———( l—-——l l————l h—A I \ NOV 31982 \ “X Qt DESCRIPTION OF MAP UNITS PROFESSIONAL PAPER 1153 PLATE 2 Abbreviations in parentheses show interpretation based on ramp CDF contrast stretch (CS) 2C or ratio, ramp CDF stretch (RS) 2D computer—enhanced Landsat images of frame 1226—07013 from geology by R. E. Anderson, W. R. Greenwood, and D. B. Stoeser. The following formations are explained in the text: 9, gql, jdql, and q. * Asterisk indicates that color altered by vegetation reflectance. Compiled by G. F. Brown and Salman Bloch R. E. Anderson (1978) Mayza‘ and Wadi Atf quadrangles 17/433, 17/43A Qa—Alluvium: light tone (CS) Tl—Laterite: bright red (RS) Jc—Sandy limestone and calcareous: grayish green (RS) Ja—Sandstonezmoderate brown (CS) OCw*——Wajid Sandstone OC w1—Salmon tone (RS) 06 wz—grayish olive tone (RS) Ts* —Sirat volcanics: bluish purple (RS) gp—Granophyre: moderate brown (RS) grp—Leucocratic granite: bluish green with arfvedsonite qm*—Quartz monzonite: olive gray (RS) glg—Granodiorite and quartz diorite: glg1—Moderate yellowish green (RS) glgz—Olive gray (RS); dark yellowish brown (CS) dal*—diorite and andesinite: dark gray 2-pyroxene diorite and hornblende metadiorite—light gray andesinite daI1—Bluish green with purple tint (RS) dalz—Dark yellowish green (RS) gs*—Granitic rocks, zoisite-biotite—quartz diorite, granodiorite, and quartz mon— zonite gs1—Medium olive green with bluish tint (RS) gsz—Olive green (RS) qd*—Siliceous to intermediate rocks: light grayish olive green (RS) di*—Mafic to intermediate rocks di1—Light grayish olive green (RS) (same spectral signature as that of qd on both RS and CS) dig—Moderate bluish yellow green (RS) mr*—-Metasedimentary schist: light yel— lowish green (RS) j‘t—Quartzo—feldspathic meta-tuff and as- sociated metasedimentary rocks, mostly graphitic and pyritiferous: dark yellow (RS) id—Metadacite and associated meta— sedimentary rocks: jd1——-M0derate yellow (carbona— ceous )(RS) jdz—Light olive, brownish hue (RS); brownish gray (CS) jd3—Moderate brown (RS) im—Metavolcanic and metasedimentary rocks, undivided: light olive, brownish hue (same as idz) *(RS); olive black (CS) jmv—Metavolcanic rocks—andesite and basalt lava: grayish green (RS) ims—Metasedimentary rock, pyritiferous slate, graphite schist, metaconglomer— ate, and biotite schist Geologic contact W. R. Greenwood (1980) Malahah and Wadi Wassat quadrangles 18/43D, 18/44C SEDIMENTARY ROCKS QaI—Alluvium: very light tan, in places bluish cast (CS) OCw—Wajid Sandstone: salmon tone (RS) IGNEOUS ROCKS Extrusive Plutonic and hypabyssal qmm—Muscovite quartz monzonite: dark blue green (RS) qmba—Biotite—arfvedsonite quartz mon— zonite: reddish green (RS) qmbc—Biotite quartz monzonite: mod— erate blue (RS) gqm—Biotite hornblende granodiorite to quartz monzonite: dark blue (RS) gqm1—bluish black (RS) gqmz—bright blue (RS) tj—Trondhjemite: olive brown (RS) tj1-—Greenish gray brown (RS) qd—Quartz diorite: dusky yellow green (RS) qd1—Yellow green with light brown hue (RS) qdz—Grayish brown (CS) di—Biotite hornblende diorite: greenish yellow (RS) gb—Gabbro: blue green (RS) dgb—Gabbro, diorite, and quartz diorite: light greenish gray brown (RS) dgbz—Moderate bluish yellow green (RS) (same spectral signature as diz on Mayza‘ map) qp—-Quartz porphyry: orange green (RS) qdn—Quartz diorite gneiss: greenish tan (CS); dusky yellow green (RS) dgn—Diorite to quartz diorite gneiss: greenish tan (CS): dusky yellow green (RS) METAMORPHIC ROCKS jdqg—Graphitic metasedimentary con— glomerate, phyllite, and marble: orange yellow (RS) same reflectance jdw—Metabasaltic to dacitic flows and breccia: grayish green (RS) D. B. Stoeser (Unpub. data) Wadi Tarib quadrangle 18/43C Tl—Laterite and saprolite: bright orange red (CS) Tt—Feldspathoidal trachyte: blue-gray (CS) Tb—Flood basalt: dark brown (CS); light tone slightly green *(RS) grz—Granite or quartz monzonite: light olive green (CS); dark reddish olive green *(RS) grk—Biotite quartz monzonite: moderate olive brown (RS); grayish yellow (CS) gm—Biotite quartz monzonite: very light gray (CS). The quartz monzonite can be distinguished on contrast stretch KQ—Mixture of grk and qd (diorite gneiss): moderate olive brown (RS) KT—Mixture of grk and th (quartz dio- rite): moderate brown (RS) KF—Mixture of grk and qdz (grano— diorite): moderate olive green (RS); dark grayish yellow (CS) gt—Trondhjemite: greenish gray brown (RS) gdz—Biotite and hornblende quartz dio— rite: moderate olive brown (RS) iden- tical reflectance signature qdi—Hornblende biotite quartz diorite: moderate olive brown (RS); pale blue (CS)—identical reflectance signature gb1——Metamorphosed gabbroic rocks, pre- or early tectonic: light blue (RS) gbz—Metamorphosed mafic gabbro and ultramafic rocks: light blue (RS) gd—Metagranodiorite and quartz diorite, pre— or early syntectonic: very light gray, lighter than gm (CS) ms—Metasedimentary graywacke, gra- phitic schist: orange yellow (same as it on Mayza‘ map) (RS) mv—Metavolcanics: light bluish green, some orange tone (RS) mu—Undifferentiated metamorphics Fault ———‘ Boundary representation is not necessarily authoritative. GE ’ Pl/ v. ”53 up Stratigraphy and Structure of the Strawberry Mine Roof Pendant Central Sierra Nevada, California By WARREN J. NOKLEBERG GEOLOGICAL SURVEY PROFESSIONAL PAPER 1154 Miogeosynclinal sedimentation, contemporaneous volcanism and plutonism, and multiple deformation in metasedimentary and metaigneous rocks of the central Sierra Nevada UNITED STATED GOVERNMENT PRINTING OFFICE, WASHINGTON : 1981 UNITED STATES DEPARTMENT OF THE INTERIOR CECIL D. ANDRUS, Secretary GEOLOGICAL SURVEY H. William Menard, Director Library of Congress Cataloging in Publication Data NokLeberg, Warren J. Stratigraphy and structure of the Strawberry mine roof pendant, centraL Sierra Nevada, CaLifornia GeoLogicaL Survey ProfessionaL Paper 1154 BibLiography: p. Supt. of Docs. No.: I 19.16:1154 1. GeoLogy, stratigraphic--Mesozoic. 2. Roof pendants (GeoLogy). 3. GeoLogy--Sierra Nevada Mountains. I. TitLe. II. Series: United States. GeoLogicaL Survey. Professionat Paper 1154. QE675.N64 551.7'6'097944 80-607173 For sale by the Superintendent of Documents, US. Government Printing Office Washington, DC. 20402 CONTENTS Page Page Abstract __________________________________________________________________________ 1 Structure .................................................................................................. 10 Introduction... __________________ 1 First-generation structures ______________________________ 10 Stratigraphy ______ 2 Second-generation structures 11 Metasedimentary rocks _____________________________________________________________ 2 Third-generation structures _____________________________________ 12 Fossil, age, and regional correlations ____________________________ 4 Fourth-generation structures .................................................... 13 Metaigneous rocks ........................................................................ 5 Relation of major to minor structures ____________________________________ 14 Age and regional correlations. 8 Timing and cause of structures ................................................ 14 Granitic rocks _______________________________________________________ 8 Jurassic and Cretaceous regional deformations ................ 15 Contemporaneous plutonism and volcanism 9 Summary and conclusions 16 Metamorphism ______________________________________________________________________________________ 9 References cited ______________________ 17 ILLUSTRATIONS Page PLATE 1. Geologic map of the Strawberry mine roof pendant, Merced Peak quadrangle, central Sierra Nevada, Calif. ...................................................................................................................................................................................................... In pocket 2. Structural diagrams for the Strawberry mine roof pendant, Merced Peak quadrangle, central Sierra Nevada, Calif. ...................................................................................................................................................................................................... In pocket FIGURE 1. Generalized geologic map of central Sierra Nevada, Calif, showing location of various roof pendants and areas in western metamorphic belt .............................................................................................................................................................. 2 2—4. Photographs of: 2. Graded beds in lower biotite hornfels unit ........................................................................................................................................ 4 3. Plaster cast showing imprint of Mesozoic bivalve, possibly Inoceramus pseudomytiloides of Early Jurassic age, from metasedimentary rocks of the Strawberry mine roof pendant ................................................. 4 4. Metarhyolite dike crosscutting folded metasedimentary rocks .................................................................................................. 5 5. Photomicrograph of metadacite, showing porphyroclast of plagioclase derived from a microphenocryst in recrystal- lized matrix of quartz, feldspar, and biotite ........................................................................................................................................ 5 6. Plot of variation in silica content of metaigneous rocks of Strawberry mine roof pendant ........................................................ 7 7. Plot of rubidium-strontium isochron-age determination and analytical data on five specimens of metaigneous rocks of Strawberry mine roof pendant ................................................................................................................................................ 7 8. Schematic diagram showing sequential development of major folds ................................................................................................ 10 9—12. Photographs of: 9. First-generation fold in middle quartz-plagioclase hornfels unit ............. 11 10. Second-generation fold in lower biotite hornfels unit .................................................................................................................. 12 11. Third-generation fold crosscutting second-generation fold in lower biotite hornfels unit ______________________________________________ 13 12. Fourth-generation fold in lower biotite hornfels unit .................................................................................................................. 13 13. Diagram showing relation of minor folds of all generations to a major second-generation fold .............................................. 14 TABLE S Page TABLE 1. Metasedimentary rock units of the Strawberry mine roof pendant, listed in order of increasing age ...................................... 3 2. Metaigneous rock units of the Strawberry mine roof pendant, listed in order of increasing age ................................................ 6 3. Chemical analyses of and normative minerals in metaigneous rocks of the Strawberry mine roof pendant ........................ 7 III + i, 2 H {EefiEuSEWH‘Dv {. I; STRATIGRAPHY AND STRUCTURE OF THE STRAWBERRY MINE ROOF PENDANT ‘ CENTRAL SIERRA NEVADA, CALIFORNIA By WARREN J. NOKLEBERG ABSTRACT The Strawberry mine roof pendant, 90 km northeast of Fresno, Calif., is composed of a sequence of metasedimentary rocks of probable Early Jurassic age and a sequence of metaigneous rocks of middle Cretaceous age. The metasedimentary rocks are a former miogeosynclinal sequence of marl and limestone now metamorphosed to calc-silicate hornfels and marble. A pelecypod found in the calc-silicate homfels has been tentatively identified as a Mesozoic bivalve, possibly Inoceramus pseudomytiloides of Early Jurassic age. These metasedimentary rocks are similar in lithology, structure, and gross age to the metasedimentary rocks of the Boyden Cave roof pendant and are assigned to the Lower Jurassic Kings sequence. The younger metaigneous rocks are metamorphosed shallow-intrusive rocks that range in composition from granodiorite to rhyolite. These rocks are similar in com- position and age to the metavolcanic rocks of the surrounding Merced Peak quadrangle and nearby Ritter Range, and probably represent necks or dikes that were one source for the metavolcanic rocks. The roof pendant is intruded by several plutons, ranging in composition from dioritic to highly felsic, that constitute part of the granodiorite of Jackass Lakes, also bf middle Cretaceous age. The contemporaneous suites of metaigneous, metavolcanic, and plutonic rocks in the region represent a middle Cretaceous period of calc-alkalic volcanism and plutonism in the central Sierra Nevada and are interpreted as part of an Andean-type volcanic- plutonic arc. Three deformations are documented in the roof pendant. The first deformation is reflected only in the metasedimentary rocks and consists of northeast- to east-west-trending folds. Similar structures occur in the Boyden Cave roof pendant and in the Calaveras Formation and represent a Middle Jurassic regional deformation. Evidence of the second deformation occurs in the metasedimentary and metaigneous rocks and consists of folds, faults, minor structures, and regional metamorphism along N. 25° W. trends. Crosscutting of these structures by the contemporane- ous granodiorite ofJackass Lakes indicates that this deformation occurred simultaneously with volcanism and plutonism during the middle Cretaceous. The third deformation involved both the roof pendant and adjacent plutonic rocks and consists of folds, faults, schistosities, and regional metamorphism along N. 65° —90° W. trends. Crosscutting of similar structures in other middle Cretaceous plutonic rocks of the Merced Peak quadrangle by undeformed late Cretaceous plutonic rocks indicates a regional deformation ofmiddle to late Cretaceous age. Structures ofsimilar style, orientation, and age occur elsewhere in metavolcanic and plutonic rocks throughout the central Sierra Nevada. INTRODUCTION The Strawberry mine roof pendant in the central Sierra Nevada, Calif., is part of a discontinuous belt of metamorphic rocks of the Sierra Nevada batholith between the Ritter Range roof pendant and the western metamorphic belt (fig. 1). In this discon- tinuous belt, the roof pendants generally contain miogeosynclinal assemblages of contact-metamor- phosed shale, marble, marl, and siltstone of Paleozoic and Mesozoic age, and (or) eugeosynclinal assem- blages of metamorphosed andesitic to rhyolitic flows, tuff, breccia, shallow-intrusive bodies, and occasional interlayers of graywacke and shale, all of Mesozoic age. The Strawberry mine roof pendant, however, contains metasedimentary rocks of probable Jurassic age as well as metaigneous rocks of middle Creta- ceous age. In this report I present a detailed description of the stratigraphy and structure of the Strawberry mine roof pendant and compare the geologic features of the roof pendant with those of other roof pendants in the central Sierra Nevada and the western meta- morphic belt to obtain a better understanding of the regional geology of wallrocks of the Sierra Nevada batholith. Finally, this report partly tests the regional—deformation hypothesis of Kistler and Bateman (1966) and Kistler (1966a) that was extended by Brook (1974, 1977), Russell and Nokleberg (1974, 1977), and Nokleberg and Kistler (1977). This hypoth- esis proposes that several superposed regional defor- mations are recorded in the wallrocks of the central Sierra Nevada batholith and that these deformations can be correlated between widely separated roof pendants. The Strawberry mine roof pendant is 90 km north- east of Fresno, Calif., in the southeast corner of the Merced Peak 15-minute quadrangle, at an elevation of about 2,300 m (fig. 1). For this study, a 5-km2 area 1 2 STRAWBERRY MINE ROOF PENDANT, CENTRAL SIERRA NEVADA, CALIFORNIA \ //x/XX§\ ‘ xxxx XXXX X EXPLANATION Granific rocks WESTERN SIERRA NEVADA \\ Slate, greenschist, and serpenfinite :|> MESOZOIC m Calaveras and Shoo FM?)— Formations l' PALEOZOIC EASTERN SIERRA NEVADA X XXXXX X X X Eugeosynclinal metavolcanic and metasedimentary rocks (KS)-Kings sequence (Lower Jurassic) Miogeosynclinal metasedimentary rocks Miogeosynclinal metasedimentary rocks ‘ Metamorphic rocks of unknown age — MESOZOIC / // — UPPER PALEOZOIC — LOWER PALEOZOIC SADDLEBAG LAKE ‘ , XPENDANT x x ‘3“ XMOUNT DANA ‘ 6s PENDANT V9 \ x x€0xxxx Xx‘qxxx ERCED PEAK ‘1 ‘ x STRAWBERRY MINE ‘ arposa ‘ x x X 4X X PENDANT (KS); x x x04 x X x x OAKHURST x xgfi/ x x x XPL'E‘IIJCEEIEK x PENDeNIxfixxxxxxxXxx XXé‘é‘XXXXXXXXX x x 039x DINKEY CREEK 5 X. X x gENDANTX x - x ’< §§> "MOUNT x LOWER KINGS RI ER x $833.33? x PEANDAANIX%XXXXXX X X X X X X X X X V _x x x x x x x x mi} x x §S< "BOYDEN CAVE X X X x xPENDANT (KS) x x x x » JUNE LAKE PENDANT PENDANT x x 0 4 8 12 16 20 I I I I 2.4 KILOMETERS Contact Fault FIGURE 1.—Generalized geologic map of central Sierra Nevada, Calif., showing location of various roof pendants and areas in western metamorphic belt. Cenozoic rocks and faults are omitted. was mapped by planetable survey at a scale of 1:3,600 (pl. 1). Most of the area lies on a series of unpatented mining claims owned by J. A. McDougald and J. E. Cobb of O’Neals , Calif., and is currently leased to the Teledyne Tungsten Corp. Contact-metasomatic tung- sten deposits on the margins of the roof pendant were studied by Krauskopf (1953) and Nokleberg (1970a, b; 1980), and the surrounding Merced Peak quadrangle was mapped by Peck (1964). Earlier versons of this study have been presented by N okleberg (1970a, b; 1971). Acknowledgrhents.--The study of the Strawberry mine area was suggested by D. L. Peck and P. C. Bateman. The company operating the tungsten mine at the time of this study, the New Idria Mining and Chemical Co., gave me complete access to their files, maps, and workings. I benefited considerably from discussions with mine managers M. C. Richardson and D. J. Beauregard and geologists R. Lynn, M. ,, Ward, and K. Rank. I also enjoyed discussions with D. L. Peck, P. C. Bateman, W. S. Wise, C. A. Hopson, A. G. Sylvester, R. W. Kistler, and O. T. Tobisch. STRATIGRAPHY METASEDIMENTARY ROCKS The metasedimentary rocks of probable Early Jurassic age, the oldest exposed rocks of the Straw- berry mine roof pendant, are a sequence of calc- silicate hornfels, marble, and biotite hornfels derived from marl, limestone, and calcareous shale, respec- tively. These metasedimentary rocks are divided into STRATIGRAPHY 3 six stratigraphic units, from youngest to oldest: upper biotite hornfels, upper quartz-plagioclase hornfels, lower biotite hornfels, middle quartz-plagio- clase hornfels, diopside-plagioclase hornfels and marble, and lower quartz-plagioclase hornfels. Except for the quartz-pl’agioclase hornfels units, the units are lithologically distinct, and contacts between units are sharp. Table 1 summarizes the field and petrologic characteristics of each unit; thicknesses are approximate and were estimated in areas where bedding is more or less continuous and has not been transposed to foliation. Top directions are indicated by relict graded beds in the lower biotite hornfels unit. These graded beds are defined by light-colored quartz-rich bases grading upward into dark-colored biotite-rich tops (fig. 2); thicknesses of the graded beds range from a few millimeters to a few centimeters. The graded bedding consists of former quartz-rich silt grading upward into iron-rich clay that contains only sparse amounts of quartz silt. Top directions in the sedimentary sequence are plotted on the geologic map (pl. 1). In determining these top directions, several graded beds in each outcrop were checked; local reversals in top directions, although they exist, are uncommon. Generally, the quartz-plagioclase, diopside-plagio- clase, and biotite hornfels units are thin-bedded fine- grained aggregates containing varying proportions TABLE 1.—Metasedimentary rock units of the Strawberry mine roof pendant, listed in order of increasing age Unit and approximate thickness (meters) Upper biotite hornfels; min 50 (upper contact unex- posed). Upper quartz-plagioclase horn- fels; 235. Lower biotite hornfels; gray- green; 140. Middle—quartz plagioclase hornfels; 235. Diopside-plagioclase hornfels and marble; 27- Lower quartz—plagioclase horn— fels; min 200 (lower contact unexposed). Minerals--major :_minor Quartz, biotite, muscovite, plagioclase; :_magnetite, zircon. Quartz, diopside, plagioclase, K-feldspar; :_pyrite, sphene. Quartz, biotite, plagioclase, diopside, hornblende; : opaque materials, zircon, rutile. Quartz, plagioclase, diopside, biotite; :_pyrite, zircon. Hornfels: plagioclase, diopside, orthoclase; : zircon, opaque materials. Marble: calcite; : wollastonite. diopside. Quartz, plagioclase, diopside; : pyrite, scapolite, zircon. Average grain size, texture, and structure Comments 0.1 mm; relict subangular quartz Interbeds of diopside- grains; thin bedded. plagioclase hornfels; intruded by metadacite dikes 0.05 mm; thin bedded Very uniform lithology; intruded by metarhyolite dikes 0.05 mm; thin bedded; relict graded Thin to thick interbeds of bedding. diopside—plagioclase horn— fels; abundant minor folds; intruded by metarhyolite dikes. 0.07 mm; thin to thick bedded Two 3— to 8-m-thick interbeds of diopside—plagioclase hornfels and marble near top of unit; some biotite hornfels near base; intruded by metarhyolite dikes Hornfels: 0.2 mm; thin bedded Marble beds metasomatized near Marble: 0.5 mm; thin to thick granodiorite; four thick bedded- marble beds, 1 to 3 m thick, equally spaced through unit. 0.7 mm; thin to thick bedded; A few 25- to 50—cm-thick beds relict graded bedding. of biotite hornfels; one 2- to 5—m—thick marble bed near top of unit. 4 STRAWBERRY MINE ROOF PENDANT, CENTRAL SIERRA NEVADA, CALIFORNIA FIGURE 2.—Graded beds in lower biotite hornfels unit. Quartz-rich bases grade upward into biotite-rich tops. of quartz, diopside, plagioclase, and biotite; wollas— tonite and muscovite are much less common (table 1). The average grain size is 0.1 mm. The various hornfels units are mostly distinguished by their varying proportions of quartz, biotite, and such calc— silicate minerals as plagioclase, diopside, and wollastonite. Differences in the relative proportions of these major minerals cause striking contrasts in color, a feature that was the chief field characteristic used in mapping the metasedimentary rocks. Acces- sory pyrite in the quartz-plagioclase hornfels units imparts a red-brown, weathered appearance to them. The biotite hornfels units are marked by prominent graded bedding, generally 1 or 2 mm thick. The diopside-plagioclase hornfels and marble unit consists of equal proportions of green-gray hornfels and light-gray marble; commonly, bedding is a few centimeters thick. Within this map unit are five or six thicker beds of marble 1 to 3 m thick. The marble is generally coarse grained, massive, and contains accessory wollastonite and diopside. Locally, thin and thick marble beds pinch out owing to severe deformation. Along strike in such areas, sparse boudins of marble occur. Adjacent to the grano- diorite in the areas of the No. 1 and No. 4 mines, the marble layers are extensively metasomatized to varieties of hornblende, pyroxene, garnet, and wollastonite skarns, some of which contain signifi- cant amounts of scheelite. Skarn replaces marble layers as far as 100 m from the intrusive contact. Within a few meters of the contact, the diopside- plagioclase hornfels is locally metasomatized to a hedenbergite-quartz skarn; none of the other meta- sedimentary units show any significant metasoma- tism. Genesis of the skarn has been studied by Nokleberg (1971, 1980). The quartz-plagioclase, diopside-plagioclase, and biotite hornfels units were derived from marl that varied in the relative proportions of quartz, calcite, dolomite, and clay. The marble was derived from a fairly pure calcite limestone containing accessory quartz, dolomite, and clay. Because of the absence of interbedded volcanic rocks and the presence of a thin-bedded calcareous section in which individual beds are persistent, the metasedimentary rocks are interpreted as a miogeosynclinal sequence of marl and limestone. FOSSIL. AGE, AND REGIONAL CORRELATIONS In 1975, a poorly preserved pelecypod was found by Frank J. Maglio in float from the quartz—plagioclase hornfels unit on the side of a hill at about 7,600 feet elevation in an area about 310 m north-northwest of the No. 1 mine (pl. 1; fig. 3). R. W. Imlay (oral commun., 1978) identified the fossil as a Mesozoic bivalve, possibly Inoceramus pseudomytiloides of Early Jurassic age. The metasedimentary rocks of the Strawberry mine roof pendant resemble those of other roof pendants included in the Upper Triassic and Lower Jurassic Kings sequence of Bateman and Clark (1974); this sequence includes the Boyden Cave, Dinkey Creek, and Mineral King roof pendants. In each roof pendant, miogeosynclinal calc-silicate hornfels, pelitic hornfels, and marble occur (Christensen, 1963; Moore and Marks, 1972; Girty, 1977). The metasedimentary rocks of each pendant contain fossils of Late Triassic and (or) Early Jurassic age, except for the Dinkey Creek roof pen- dant (Bateman and Clark, 1974). Considerable debate FIGURE 3.—Plaster cast showing imprint of Mesozoic bivalve, possibly Inoceramuspseudomytiloides of Early Jurassic age, from metasedimentary rocks of Strawberry mine roof pendant. Cast is 7.62 cm long. STRATIGRAPHY 5 persists concerning the age of the unfossiliferous Dinkey Creek roof pendant, which Kistler and Bateman (1966) and Russell and Nokleberg (1977) considered probably Paleozoic on the basis of its lithologic and structural similarities to the Mount Morrison roof pendant (Rinehart and Ross, 1964); Bateman and Clark (1974), however, determined an Early Jurassic age on the basis of its lithologic similarity to the Boyden Cave roof pendant. Although the Dinkey Creek and Boyden Cave roof pendants both contain thick quartzite units (Kistler and Bateman, 1966; Moore and Marks, 1972; Girty, 1977), the quartzite of the Dinkey Creek roof pendant is a relatively pure orthoquartzite, whereas the quartzite of the Boyden Cave roof pendant contains abundant potassium feldspar (Moore and Marks, 1972; Girty, 1977). In any case, the metasedimentary rocks of the Strawberry mine and Boyden Cave roof pendants have similar lithologies and ages, and the meta- sedimentary rocks of the Strawberry mine roof pendant should be considered part of the Lower Jurassic Kings sequence of Bateman and Clark (1974). The Kings sequence was tentatively identified as the upper, younger part of rocks designated the Calaveras Complex by Schweickert, Saleeby, Tobisch, and Wright (1977). This broader use of the name “Calaveras” to include the Calaveras Formation, the Kings sequence, and other similar metasedimentary rocks of the Sierra Nevada foothills is inappropriate because (1) each named formation, sequence, and (or) complex should be defined to include rocks of a unique type and narrow age range rather than be so broad as to inclu e lithologically dissimilar rocks of greatly diverse‘ages; and (2) the Kings sequence, which includes the metasedimentary rocks of the Strawberry mine roof pendant, differs greatly in age, geographic position, and lithology from the Cala- veras Formation. For these reasons, I consider the assignment of the Kings sequence to the Calaveras Complex by Schweickert, Saleeby, Tobisch, and Wright (1977) to be invalid. METAIGNEOUS ROCKS The metaigneous rocks of the Strawberry mine roof pendant are a sequence of fine-grained blasto- porphyritic quartz-biotite hornfels units derived from shallow-intrusive rocks. These metaigneous rocks are divided into six intrusive units, from youngest to oldest: metagranodiorite, metarhyolite, metarhyolite breccia, metadacite, and metadacite breccia and metabreccia. Because of the similar mineralogies of the various metaigneous rocks, genetic instead of metamorphic names are used; all units are litho- logically distinct and have sharp contacts. Table 2 summarizes the field and petrographic character- istics of each unit; this age sequence was determined from contact relations. Locally, postintrusive shearing and faulting along contacts tend to resemble stoping relations; therefore, correct observation of field relations was required. The suite of metaigneous rocks is younger than the suite of metasedimentary rocks. The metabreccia and metadacite breccia units contain inclusions of metasedimentary rocks, as do the younger metaig- neous units. In addition, the metarhyolite and meta- granodiorite units also intrude the metasedimentary rocks (fig. 4). Generally, the metaigneous rocks are fine- to medium-grained aggregates of metamorphic quartz, FIGURE 5.—Photomicrograph of metadacite, showing porphyro- clast of plagioclase derived from a microphenocryst in recrystal- lized matrix of quartz, feldspar, and biotite. Crossed nicols. STRAWBERRY MINE ROOF PENDANT, CENTRAL SIERRA NEVADA, CALIFORNIA TABLE 2.—Metaigneous rock units of the Strawberry mine roof pendant, listed in order of increasing age Name Minerals-—major; : minor ,Texture Comments Metagranodiorite Metarhyolite Metarhyolite breccia Metadacite Metadacite breccia Metabreccia Plagioclase (An15_30), quartz, biotite, orthoclase, horn- blende; :_apatite, zircon, epidote, opaque materials. Orthoclase, quartz, albite (An0_10), biotite; :_musco— vite, zircon, opaque materials. Orthoclase, quartz, albite (Ans), biotite; : muscovite, epidote, zircon, opaque materials. Plagioclase (An30_60), biotite, quartz; j_hornblende, musco- vite, epidote, chlorite, opaque materials. Plagioclase (An25_t0), quartz, orthoclase, biotite, horn— blende; : sphene, opaque materials, chlorite, zir— con, apatite. Quartz, biotite, plagioclase, orthoclase; : hornblende, rutile, sphene, opaque materials. Plagioclase porphyryoclasts (Ange); a few orthoclase por- phyroclasts; matrix of quartz, plagioclase (Anls), biotite, orthoclase, and hornblende. Albite porphyroclasts (Ano-S) and orthoclase porphyroclasts; matrix of quartz, orthoclase, albite (Ans), and biotite; some albite porphyroclasts zone out- ward to antiperthite or per- thite; a few glomeroporphyro— clastic feldspar clots. Sparse to locally abundant ortho— clase porphyroclasts; matrix of quartz, orthoclase, albite (Ans), and biotite; abundant biotite streaks. Plagioclase porphyroclasts (Anu0_60); matrix of biotite, plagioclase (Ange), and quartz. Plagioclase (An25-ao) porphyro- clasts; a few hornblende por— phyroclasts; matrix of quartz, orthoclase, biotite, and plagio— clase (Anzst Sparse porphyroclasts of ortho- clase, quartz, and plagioclase (Anao); matrix grades from one similar to lower biotite hornfels unit to one similar to matrix in metadacite breccia unit; plagio- clase porphyroclasts probably relict phenocrysts; subangular quartz porphyroclasts probably relict detrital grains Contains inclusions of meta- rhyolite intrusive rocks and metasedimentary rocks mostly bounded by faults. Contains inclusions of meta- rhyolite breccia and meta- sedimentary rocks; dikes of metadacite, metarhyolite breccia, and metasedimentary rocks. Contains inclusions of meta- dacite intrusive rocks and metadacite breccia; dikes of metadacite breccia. Contains inclusions of meta— breccia, metadacite breccia, and metasedimentary rocks; dikes of metadacite breccia and metarhyolite dikes in metadacite breccia; relict flow banding. Grades from massive to brecci- ated; breccia consists of mas- sive metadacite intrusive rocks in very fine grained meta- dacite matrix; age relative to metabreccia unit unknown Contains abundant inclusions of metasedimentary rocks and meta- rhyolite; age relative to meta- dacite breccia unit unknown; mostly bounded by faults STRATIGRAPHY 7 feldspar, biotite, and hornblende containing sparse to abundant relict microphenocrysts of plagioclase and (or) orthoclase (fig. 5). The relative proportions of relict microphenocrysts and groundmass minerals were used to determine the genetic names. The more mafic metaigneous rocks, such as the meta- granodiorite unit, contain abundant hornblende and relict plagioclase microphenocrysts and less quartz, whereas the more siliceous metaigneous rocks, such as the metarhyolite unit, contain abundant biotite, quartz, and orthoclase microphenocrysts. Table 3 shows the results of chemical analyses of five specimens of the metaigneous rocks. Samples with a wide compositional variation were chosen to yield a rubidium-strontium isochron with the longest possible slope. Chemical analyses of the metaigneous rocks fall along smooth trends on a silica-variation diagram (fig. 6). These regular variations suggest a common source for the metaigneous rocks, and the Peacock index of 60—61 indicates a calc-alkalic suite. Chemical analyses of metavolcanic rocks from TABLE 3.—Chemical analyses of and normative minerals in metaigneous rocks of the Strawberry mine roof pendant [Rapid rock analyses in weight percent. Analyst: Lowell Artis] Sample‘ ........ GC-50 6010 6041 GC-204 GC-62 Chemical analyses 62.40 64.60 64.00 73.20 73.20 16.60 17.20 16.80 14.70 14.30 1.20 1.00 1.60 .40 .71 4.60 4.30 3.10 1.60 .90 2.60 1.70 1.50 .38 .28 4.80 4.80 4.10 .92 ..74 3.30 2.80 3.50 4.10 4.70 2.40 1.40 2.40 3.90 4.50 .96 1.10 1.30 .71 .54 .81 .98 .71 .26 .23 .21 .26 .18 .05 .05 .11 .1 1 .14 .07 .07 .02 .02 .04 .02 .02 Total--- 100.01 100.27 99.37 100.31 100.24 CIPW norms 28.28 22.62 30.93 26.39 3.01 1.52 2.22 .51 8.25 14.27 22.97 26.52 23.62 29.80 34.58 39.67 21.92 19.03 4.09 3.21 4.22 3.75 .94 .69 5.64 3.48 2.30 .81 1.44 2.33 .57 1.02 1.85 1.35 .49 .43 .61 .42 .11 .11 .04 .09 .04 .04 Total---- 99.05 98.91 98.70 99.29 99.46 Differen- tiation index ----- 59.72 60.15 66.69 88.49 92.60 lSamples: GC-50, meta ranodiorite; GC-lO, metadacite; GC-41, metadacite breccia; C-204, metarhyolite breccia; GC-62, metarhyolite. nearby roof pendants in the Merced Peak quarangle, reported by Peck, Stern, and Kistler (1977), also fall on the same calc-alkalic trend. 10 l r l I ._~ ( a ,- / E 8 * /// A O // U l— Anficline—Showing trace of axial plane and bearing and plunge of axis — + -> Syncline—Showing trace of axial plane and bearing and plunge of axis FIGURE 13.—Relation of minor folds of all generations to a major second-generation fold. STRUCTURE 15 tures formed during a middle Cretaceous defor- mation, which I designate the “second deformation.” This deformation consisted of moderately appressed to isoclinal folding, faulting, and regional meta- morphism under conditions approximating the upper greenschist to amphibolite facies; folding and faulting had average trends of N. 25° W. Because the metaigneous rocks and the granodiorite of Jackass Lakes have nearly identical radiometric ages, the second deformation was contemporaneous with volcanism, shallow intrusion, and batholithic intrusion. Third-generation structures occur in both the roof pendant and the granodiorite of Jackass Lakes and also in other middle Cretaceous plutonic rocks of the Merced Peak quadrangle, but not in the Late Cre- taceous plutonic rocks (D. L. Peck, oral commun., 1977). These relations indicate that these third- generation structures formed during a middle to Late Cretaceous deformation between two periods of batholithic intrusion. This deformation, which I designate the “third deformation,” consisted of folding, faulting, and regional-grade metamorphism under conditions approximating the amphibolite facies; folding and faulting had average trends of N. 65°—90° W. This deformation cannot be related to forceful emplacement of younger plutonic rocks because the structures crosscut large older plutonic rocks many kilometers from younger rocks. Fourth-generation structures are rare and occur only on the east margin of the roof pendant, in an area of abundant third-generation folds. The fourth- generation folds have average strikes of N. 60°—65° E. that cross the average strikes of third-generation folds at a high angle. Thus, these fourth-generation structures may be a conjugate set of folds and faults that formed simultaneously with or just after the third-generation structures. Tobisch and Fiske (1976) described conjugate folds with similar trends and styles in the central Sierra Nevada and pointed out the possibility of conjugate folding in the Strawberry mine roof pendant. Accordingly, the fourth-genera- tion structures are here assigned to the third deformation. In summary, the four generations of structures in wallrocks and adjacent granitic plutonic rocks of the Strawberry mine roof pendant probably formed from three deformations during Middle Jurassic to Early Cretaceous, middle Cretaceous, and middle to Late Cretaceous time. No evidence that any generation of structures formed from forceful emplacement of plutons was observed. The second deformation occurred during the middle Cretaceous, contempo- raneously with volcanism, shallow intrusion, and batholitic intrusion, and denotes simultaneous orogeny and magmatism. The first and third defor~ mations appear to be related to widespread regional deformations recorded elsewhere in the central Sierra Nevada. JURASSIC AND CRETACEOUS REGIONAL DEFORMATIONS The first, Middle Jurassic through Early Cretaeous deformation in the Strawberry mine roof pendant is recognized in other roof pendants and in parts of the western metamorphic belt in the central Sierra Nevada. An Early or Middle Jurassic regional defor- mation was identified in the upper Paleozoic Calaveras Formation and in the Boyden Cave roof pendant (Girty, 1977; Nokleberg and Kistler, 1977). The Calaveras Formation (fig. 1) is intensely deformed along N. 30°—50° E. trends in a large area from the Stanislaus to Merced Rivers (fig. 1), with the development of melange, broken formation, cata- clasites, and isoclinal to open folds. This generation of structures, with fold axes that commonly plunge steeply northeast, is superposed on older northwest- trending structures that formed during the Triassic and was redeformed by the Late Jurassic Nevadan orogeny. The Boyden Cave roof pendant along the Kings River (fig. 1) contains an older generation of structures nearly identical in style, geometry, and orientation to those in the Calaveras Formation and the Strawberry mine roof pendant. Cale—silicate hornfels is intensely deformed along N. 60° E. trends with the development of open to isoclinal folds, schistosities, and melange (Girty, 1977). The fold axial planes strike N. 60° E., and the fold axes plunge gently toward azimuth 060° (Girty, 1977). The age of this deformation in the Boyden Cave roof pendant is bracketed by the Early Jurassic age of the calc- silicate hornfels and slate (Jones and Moore, 1973; Girty, 1977) and by the redeformation of this genera- tion of structures by structures formed during the Late Jurassic Nevadan orogeny (Girty, 1977). The overall similar style of folds, orientations of fold axial planes, and timing of deformations in the Calaveras Formation, in the metasedimentary rocks of the Strawberry mine roof pendant, and in the calc- silicate hornfels ofthe Boyden Cave roofpendant are strong evidence of a regional deformation of wall- rocks of the central Sierra Nevada batholith during Middle Jurassic time. Similarities in lithology, age, structure, and age of deformation between the Strawberry mine and Boyden Cave roof pendants strongly suggest that these two pendants were part of a once—continuous sequence. As previously mentioned, Bateman and 16 STRAWBERRY MINE ROOF PENDANT, CENTRAL SIERRA NEVADA, CALIFORNIA Clark (1974) grouped the Boyden Cave, Mineral King, and Dinkey Creek roof pendants into the Kings sequence of Late Triassic and Early Jurassic age. The Strawberry mine and Boyden Cave roof pen- dants have similar lithologies, ages, and structural histories, and so the metasedimentary rocks of the Strawberry mine roof pendant should be considered part of the Kings sequence of Bateman and Clark (1974). Although these two roof pendants share a common Middle Jurassic deformation with the Calaveras Formation, the lithologies, ages, and geo- graphic positions of the Kings sequence and the Calaveras Formation strongly differ. Because of these differences, the Kings sequence should not be included with the Calaveras Complex of Schweic- kert, Saleeby, Tobisch, and Wright (1977). The Kings sequence and the Calaveras Formation have in common only a Middle Jurassic regional defor— mation, which may have resulted from tectonic juxtaposition of the two belts of rocks. The second, middle Cretaceous deformation in the Strawberry mine roof pendant has not yet been recognized in other areas of the central Sierra Nevada; second-generation structures, however, are nearly identical in style, orientation, and regional metamorphism to structures formed during the Late Jurassic Nevadan orogeny in several roof pendants and in the western metamorphic belt. Structures formed during this orogeny in the Ritter Range roof pendant, the Mineral King roof pendant, and the western metamorphic belt generally consist of N. 20°—40° W.-trending folds and faults associated with greenschist- to amphibolite-facies metamorphism (Christensen, 1963; Huber and Rinehart, 1965; Wetzel and Nokleberg, 1976; Nokleberg and Kistler, 1977). Both major and minor folds commonly-plunge moder- ately southeast toward azimuth 155°. The similarity between structures of the Strawberry mine roof pen- dant and those of other wallrocks of the central Sierra Nevada suggests, but does not prove, that in the Strawberry mine roof pendant the Nevadan orogeny continued into the middle Cretaceous. On the other hand, the second, middle Cretaceous defor- mation in the Strawberry mine roof pendant may have resulted from a local pulse of contemporaneous orogeny, volcanism, and plutonism. The third, middle to Late Cretaceous deformation in the Strawberry mine roof pendant is also recog- nized in other roof pendants and in parts of the western metamorphic belt. A period of intense folding, cataclasis, and regional metamorphism along N. 500—80O W. trends can be identified in the Ritter Range, Mount Morrison, Mount Dana, Saddle- bag Lake, and lower Kings River roof pendants (fig. 1) (Nokleberg, 1975; O. T. Tobisch, oral commun., 1976; Nokleberg and Kistler, 1977). The similarity in style, age, and orientation of structures in these areas is evidence of a regional deformation in the central Sierra Nevada during middle to Late Cretaceous time. Tobisch and Fiske (1976) concluded that the east-west- and north-south-trending conjugate folding in the western metamorphic belt and Ritter Range roof pendant occurred during the Late Jurassic in response to a relaxation of stress after the Nevadan orogeny. On the other hand, data from the Strawberry mine roof pendant, the Ritter Range roof pendant (Nokleberg and Kistler, 1977), and the lower Kings River roof pendant (Nokleberg, 1975) indicate that this generation of conjugate folds and associated structures formed during the middle to Late Cretaceous. SUMMARY AND CONCLUSIONS The oldest rocks of the Strawberry mine roof pendant are a miogeosynclinal sequence ofmarl and limestone, now metamorphosed to calc-silicate hornfels and marble. A pelecypod found in float from calc—silicate hornfels has been tentatively identified as a Mesozoic bivalve, possibly Inoceramus pseu- domytiloides of Early Jurassic age. These meta- sedimentary rocks of the Strawberry mine roof pen— dant are probably Early Jurassic because of their lithologic, structural, and gross age similarities to the metasedimentary rocks of the Boyden Cave roof pendant, and they are here accordingly assigned to the Kings sequence of Bateman and Clark (1974). I consider the assignment ofthe Kings sequence to the Calaveras Complex by Schweickert, Saleeby, Tobisch, and Wright (1977) to be invalid. A middle Cretaceous sequence of metaigneous rocks derived from shallow-intrusive rocks, ranging in composition from granodiorite to rhyolite, is the next younger suite. The metaigneous rocks, which are similar in composition and age to the meta- volcanic rocks ofthe surrounding Merced Peak quad- rangle, probably represent necks or dikes that were a source of the metavolcanic rocks. The suites of metaigneous and metavolcanic rocks represent a middle Cretaceous calc-alkalic period ofvolcanism in the central Sierra Nevada. Similar metaigneous and metavolcanic rocks occur to the north and east in the central Sierra Nevada and represent part ofa middle Cretaceous Andean-type volcanic arc. The Strawberry mine roof pendant is intruded by several plutons that range in composition from dio- rite to felsic dikes and masses. These plutonic rocks constitute part of the granodiorite of Jackass Lakes REFERENCES CITED 17 and the leucogranite of Timber Knob (Peck, 1964), which have the same general radiometric ages as the metaigneous and metavolcanic rocks of the sur- rounding area. According to Peck, Stern, and Kistler (1977), these metavolcanic, metaigneous, and plu- tonic rocks represent a major volcanic-plutonic center of middle Cretaceous age. Three superposed deformations affected the Straw- berry mine roof pendant and adjacent plutonic rocks. Structures of the first deformation occur only in the metasedimentary rocks and consist of northeast- to east-west-trending folds. Folds of similar style and orientation as well as other structures, which occur in both the Boyden Cave roof pendant and the Calaveras Formation, represent a regional deformation of Middle Jurassic age. Structures of the second defor- mation occur in both the metasedimentary and metaigneous rocks and consist of folds, faults, and minor structures that trend about N. 25° W.; regional metamorphism was coeval with this deformation. Crosscutting of these structures by the granodiorite of Jackass Lakes, which has the same radiometric age as the metaigneous rocks, indicates that the second deformation occurred simultaneously with volcanism and plutonism during the middle Cre- taceous. This second deformation may be a distinct event that followed the same trends as the earlier Nevadan orogeny. Structures of the third deforma- tion occur in wallrocks and granitic rocks adjacent to the roof pendant and consist of folds, faults, and schistosities trending from N. 65° to 90°W.; regional metamorphism was coeval with this deformation. Although similarly oriented shear zones crosscut the middle Cretaceous plutonic rocks of the Merced Peak quadrangle, these shear zones are in turn crosscut by undeformed Late Cretaceous plutonic rocks (D. L. Peck, oral commun., 1977). Similar structures also occur in other areas of the central Sierra Nevada and represent a regional deformation along N. 65° —90° W. trends during the middle to Late Cretaceous. REFERENCES CITED Bateman, P. C., and Clark, L. D., 1974, Stratigraphic and structural setting of the Sierra Nevada batholith, California: Pacific Geology, v. 8, p. 79-89. Bateman, P. C., Clark, L. D., Huber, N. K., Moore, J. G., and Rinehart, C. D., 1963, The Sierra Nevada batholith—a syn- thesis of recent work across the central part: US. Geological Survey Professional Paper 414—D, p. D1—D46. ‘Brook, C. A., 1974, Nature and significance of superposed folds in the Saddlebag Lake roof pendant, Sierra Nevada, California [abs.]: Geological Society of America Abstracts with Pro- grams, v. 6, no. 3, p. 147-148. 1977, Stratigraphy and structure of the Saddlebag Lake roof pendant, Sierra Nevada, California: Geological Society of America Bulletin, v. 88, no. 3, p. 321-334. Christensen, M. N., 1963, Structure of metamorphic rocks at Mineral King, California: University of California Publi- cations in Geological Sciences, v. 42, no. 4, p. 159-198. Donath, F. A., and Parker, R. B., 1964, Folds and folding: Geolog- ical Society of America Bulletin, v. 75, no. 1, p. 45-62. Ernst, W. G., 1970, Tectonic contact between the Franciscan melange and the Great Valley sequence—crustal expression of a late Mesozoic Benioff zone: Journal of Geophysical Research, v. 75, no. 5, p. 886-901. Evernden, J. F., and Kistler, R. W., 1970, Chronology of emplace- ment of Mesozoic batholithic complexes in California and western Nevada: US. Geological Survey Professional Paper 623, 42 p. Fiske, R. S., and Tobisch, O. T., 1978, Paleogeographic significance of volcanic rocks of the Ritter Range pendant, central Sierra Nevada, California, in Howell, D. G., and McDougall, K. A., eds., Mesozoic paleogeography of the western United States: Pacific Coast Paleogeography Symposium 2: Los Angeles, Calif, Society of Economic Paleontologists and Mineralogists, Pacific Section, p. 209-222. Girty, G. H., 197 7, Multiple regional deformation and metamorphism of the Boyden Cave roof pendant, central Sierra Nevada, California: Fresno, California State University, MS. thesis, 82 p. Hamilton, Warren, 1969, Mesozoic California and underflow of Pacific mantle: Geological Society of America Bulletin, v. 80, no. 12, p. 2409—2430. Huber, N. K., and Rinehart, C. D., 1965, Geologic map of the Devils Postpile quadrangle, Sierra Nevada, California: US. Geo- logical Survey Geologic Quadrangle Map GQ-437, scale 1:62,500. Jones, D. L., and Moore, J. G., 1973, Lower Jurassic ammonite from the south-central Sierra Nevada, California: US. Geo- logical Survey Journal of Research, v. 1, no. 4, p. 453-458. Kistler, R. W., 1966a, Structure and metamorphism in the Mono Craters quadrangle, Sierra Nevada, California: US. Geolog- ical Survey Bulletin 1221-E, p. E1-E53. 1966b, Geologic map of the Mono Craters quadrangle, Mono and Tuolumne Counties, California: US Geological Survey Geologic Quadrangle Map GQ-462, scale 1:62,500. Kistler, R. W., and Bateman, P. C., 1966, Stratigraphy and structure of the Dinkey Creek roof pendant in the central Sierra Nevada, California: US. Geological Survey Professional Paper 524-B, p. B1-B14. Krauskopf, K. B., 1953, Tungsten deposits of Madera, Fresno, and Tulare Counties, California: California Division of Mines Special Report 35, 83 p. Loney, R. A., 1965, Structural analysis of the Pybus-Gambier area, Admiralty Island, Alaska: University of California Publi- cations in Geological Sciences, v. 46, no. 2, p. 33—80. Moore, J. G., and Marks, L. Y., 1972, Mineral resources of the High Sierra primitive area, California, with a section on Aeromag- netic interpretation, by H. W. Oliver: US. Geological Survey Bulletin 1371-A, p. A1-A40. Nokleberg, W. J ., 1970a, Multiple folding in the Strawberry mine roof pendant, central Sierra Nevada, California [abs.]: Geo- logical Society of America Abstracts with Programs, v. 2, no. 2, p. 125-126. 1970b, Geology of the Strawberry mine roof pendant, central Sierra Nevada, California: Santa Barbara, University of California, Ph. D. thesis, 156 p. 1971, Zoned skarns of the Strawberry tungsten mine roof pendant, central Sierra Nevada, California: An end member example of the contact metasomatic process [abs.]: Geological Society of America Abstracts with Programs, v. 3, no. 2, p. 171-172. 18 STRAWBERRY MINE ROOF PENDANT, CENTRAL SIERRA NEVADA, CALIFORNIA 1975, Structural analysis of a collision between an oceanic plate and a continental plate preserved along the lower Kings River in the Sierra Nevada [abs]: Geological Society of America Abstracts with Programs, v. 7, no. 3, p. 357-358. 1980, Geologic setting, petrology, and geochemistry of tungsten-bearing skarns at the Strawberry mine, central Sierra Nevada, California: Economic Geology [in press]. Nokleberg, W. J., and Kistler, R.W., 1977, Mesozoic deformations in the central Sierra Nevada, California [abs.]: Geological Society ofAmerica Abstracts with Programs, v. 9, no. 4, p. 475. Peck, D. L., 1964, Preliminary geologic map of the Merced Peak quadrangle, California: U.S. Geological Survey Mineral Investigations Field Studies Map MF—281, scale 1:48,000. Peck, D. L., Stern, T., and Kistler, R. W., 1977, Penecontempo- raneous volcanism and intrusion in the Sierra Nevada batho- lith, California [abs.]: International Associations of Seis- mology and Physics and Volcanology and Chemistry of the Earth’s Interior, Joint General Assemblies, Durham, NC, 1977, abstracts. Rinehart, C. D., and Ross, D. C., 1964, Geology and mineral deposits of the Mount Morrison quadrangle, Sierra Nevada, California, with a section on A gravity study of Long Valley, by L. C. Pakiser: U.S. Geological Survey Professional Paper 385, 106 p. Russell, S. J., 1976, Geology of the Mount Dana roof pendant, central Sierra Nevada, California: Fresno, California State University, M.A. thesis, 86 p. Russell, S. J., and Nokleberg, W. J., 1974, The relation of super- posed deformations in the Mt. Morrison roof pendant to the regional tectonics of the Sierra Nevada [abs]: Geological Society ofAmerica Abstracts with Programs, v. 6, no. 3, p. 245. 1977, Superimposition and timing of deformations in the Mount Morrison roof pendant in the central Sierra Nevada, California: Geological Society ofAmerica Bulletin, v. 88, no. 3, p. 335—345. Schweickert, R. A., Saleeby, J. B., Tobisch, O. T., and Wright, W. H., III, 1977, Paleotectonic and paleogeographic significance of the Calaveras Complex, western Sierra Nevada, California, in Stewart, J. H., Stevens, C. H., and Fritsche, A. E., eds., Paleozoic paleogeography of the western United States: Pacific Coast Paleogeography Symposium 1: Los Angeles, Calif, Society of Economic Paleontologists and Mineralogists, Pacific Section, p. 381—394. Tobisch, O. T., and Fiske, R. S., 1976, Significance of conjugate folds and crenulations in the central Sierra Nevada, Cali- fornia: Geological Society of America Bulletin, v. 87, no. 10, p. 1411-1420. Turner, F. J ., 1968, Metamorphic petrology: New York, McGraw- Hill, 403 p. Weiss, L. E., 1959a, Geometry of superposed folding: Geological Society of America Bulletin, v. 70, no. 1, p. 91—106. 1959b, Structural analysis of the basement system at Turoka, Kenya: Overseas Geology and Mineral Resources (London), v. 7, no. 1, p. 3-35 [pt. 1], no. 2, p. 123-153 [pt. 2]. Weiss, L. E., and McIntyre, D. B., 1957, Structural geometry of Dalradian rocks at Loch Leven, Scottish Highlands: Journal of Geology, v. 65, no. 6, p. 575—602. Wetzel, Nicholas, and Nokleberg, W. J ., 1976, Plate tectonic and structural relations for the origin and deformation of the western metamorphic belt along the margin of the central Sierra Nevada batholith [abs]: Geological Society of America Abstracts with Programs, v. 8, no. 3, p. 420. UNITED STATES DEPARTMENT OF THE INTERIOR PROFESSIONAL PAPER 1154 GEOLOGICAL SURVEY PLATE 1 CORRELATION OF MAP UNITS DESCRIPTION OF MAP UNITS SURFICIAL DEPOSITS SURFICIAL DEPOSITS Qal 0t Os }Holocene _ 0a: ALLUVIUM Unconformity QUATERNARY Qt TALUS 09 }Pleistocene Os STREAM GRAVEL Unconionmty 09 GLACIAL DEPOSITS IC ROCKS GRANIT GRANITIC ROCKS Kal Various units forming part of granodiorite of Jackass Lakes which has U/ Pb zircon age of 98 my. (Peck, Stern, and Kistler, 1977) Kai ALASKITE AND FELSIC DIKES AND MASSES qu BIOTITE QUARTZ MONZONITE Kgd HORNBLENDE GRANODIORITE Intrusive contact I QUARTZ DIORITE METAIGNEOUS ROCKS _ Lower — CRETACEOUS ” ' ‘ Cretaceous METAIGNEOUS ROCKS Rb/Sr isochron age of 98 my. Metamorphosed shallow intrusive bodies and intrusive breccias j METAGRANODIORITE METARHYOLITE METARHYOLITE BRECCIA , METADACITE METADACITE BRECCIA METABRECCIA METASEDIMENTARY ROCKS Mesozoic bivalve, possibly Inoceramus pseudomytiloides (Early Jurassic) found in float from middle quartz-plagioclase hornfels unit UPPER BIOTITE HORNFELS qu Kgd Intrusive contact METASEDIMENTARY ROCKS . Lower Km 5 se uence ‘ 9 OS: Batgman Jurassic(?) JURASSICL ) and Clark (1974) UPPER QUARTZ-PLAGIOCLASE HORNFELS LOWER BIOTITE HORNFELS MIDDLE QUARTZ—PLAGIOCLASE HORNFELS —— Contains a few beds of diopside—plagioclase homfels and marble (Jm) I DIOPSIDE— PLAGIOCLASE HORNFELS AND MARBLE LOWER QUARTZ-PLAGIOCLASE HORNFELS —— Contains a marble bed near top . « ' z ‘ t . A I x / 1 ,1" ' / / . 119°I7’ 37°33 ’20” 1/: ‘\ 1’ '. .x . . ‘ ‘ / /fiUr&J . \\ if? INTERIOMGEULOGICAL SURVEY, RESTON VA~1980~G79494 Geology mapped by INJJL Nokleberg, 1966— 67 y __ o """"" Contact — Dashed where approximately located; dotted where concealed; y, intrusion or metaintrusion; o, wallrock . '— """"""""" Trace of marker bed —--—o.-a0 I Fault— Dashed where approximately located; dotted where con— ) cealed \x I _\ \ , ‘—I— — — ' ’ ‘ ' ' ' Anticline — Showing trace of axial surface and bearing and plunge r \ y ‘3) \/ of axis; dashed where approximately located; dotted where con— 70\ ) Kg’ cealed ‘\ thl \Jqpu\\ +—— ‘ ' ' ' ' ' Syncline — Showing trace of axial surface and bearing and plunge \ \ \ of axis; dashed where approximately located; dotted where con— \ \\ \ cealed I \\\ \\‘\ I” \ 55 <— Bearing and plunge of fold axes — Includes fold axes, boudins, and Base from planetable survey by New Idria Mining """" biotite-streak lineations and Chemical Company, 1955—60 . . and by Helen Nokleberg, 1955_ 57 \_\ 70 Strike and dlp of beds — Top direction unknown "‘ —J~ Inclined —I— Vertical 119°l7’ Strike and dip of beds — Top direction known Inclined —¥— Vertical ' —£1— Overturned CALIF (7 Foliation and schistosity — Flowage foliation in plutonic rocks; penetrative schistosity in plutonic and metamorphic rocks AREA OF MAP 1 Inclined 4— Vertical 0 None observed Strike and dip of joints SCALE 1:3 600 —6-0~ Inclined 1000 2000 FEET + Vertical 0 100 200 300 400 METERS Trace of felsic dike H H H I—' H ' ' ‘ ' Inclined / < I CONTOUR INTERVAL 20 FEET (41/; /: I K to; DATUM IS 125 FEET ABOVE MEAN SEA LEVEL Vertical 6/ / \\ M , / - 5 NATIONAL GEODETIC VERTICAL DATUM OF 1929 /{/x\\ X 7 r N g Abundant mafic inclusions in plutonic rocks / g L ,,/r T 1’ APPROXIMATE MEAN I , ‘fi DECLINATION, 1980 \-,.,/ / GEOLOGIC MAP OF THE STRAWBERRY MINE ROOF PENDANT, MERCED PEAK QUADRANGLE, CENTRAL SIERRA NEVADA, CALIFORNIA PROFESSIONAL PAPER 1154 PLATE 2 UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY FIRST GENERATION SECOND GENERATION THIRD GENERATION FOURTH GENERATION POLES TO BEDDING: Insufficient data 342 1,2,4,6,8 1b ‘ 2b 3b ‘ 4b / POLES TO AXIAL PLANES: 75 1,2,4,6 93 1,5,10,20 103 1,5,10,20 66 1,5,10,15 3c 40 FOLD AXES: ‘ a 75 1,2,4,6,8,10 113 1,5,10,20,30 42 1,5,10,15,20 40 1,5,10,15 2d / 4d .r . POLES TO SLIP CLEAVAGES: '“Sumdent data Insufficient data V "‘ 46 1,5,10,15 7° 1,5,10 28 3e POLES TO FOLIATION IN METAIGNEOUS ROCKS: None Observed Insufficient data 92 1,5,10,15 73 1,5,10 EXPLANATION 2e Diagram number --------- Great circle drawn through maxima of poles to bedding, axial planes, cleavages, or foliation 32 Major fold axis defined by pole to great circle—Number + refers to generation of fold Contours showing percent points per L3 Center of concentration of 1 percent area minor fold axis—Number refers to generation of fold 92 1,5,10,15 Points Contours DIAGRAM EXPLANATION ' filNTEHIDH—GEOLOGICALSURVEV,FIESTDN,VAiIBBD—G79494 STRUCTURAL DIAGRAMS FOR THE STRAWBERRY MINE ROOF PENDANT, MERCED PEAK QUADRANGLE, CENTRAL SIERRA NEVADA, CALIFORNIA .,.,7.:,.. .. . .H, , 77 .., ...:.,.:A,4,74.,AHH.., A.,.,.,...4.7.,47.7H,..A... .....4:.4A,H4. H.4. ,. .7....7 .. ,.,7,,.. 417,4, 4.544 4444.7744A 747.44 .A. 7444747 47777 .AA, : . 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HH. , , ..4.4...,., .:AA.7774A,.,:,.7.,.. .,A:,H4AH4H.:A,,.,..H7H...,.,., 4.4747,,.7..H.:..HmmmA7,A,4A..HH, .,.A,..,.H,.,.,,7.H.HH7.,.44H,.,47..H,7A,4,H.H...HH.HH:.A.7,H.A7:H.,.4:.,..,., . 4744 . . . , 4,.4.74.,: . . 7 :.,7 A,,H:A7.,.,.,., 4 .H,7A,.H.A,, A,.,H4A4..H.:.H4.A.,7,.H4A,,..,,,.,.4.,A.,7,A,.,4..7.H4A7,H...,,774 A747444. , .,,H,:.H:,,4,.,.,4A., ,,A,:A,.,7A7. ,.7 7 : . :..,4., .44 . ,.H:.,77H.,.,4.7HHA,.,.,A,.....,4.H.:.4H.:.,3,H.,, ..,.HA.,A,.H4,,,H44.,.:7.,A4,.HH..7..A,.HA,..:H.4.,mmA74H47.77,H.AAH, ..,:,.A7,4.7HH:.,,,H. .AH,AA7HH4A.,4, ., .,.H7H:, , H..H. ., 7,:A ,,:.,HH, . ,,:7.,..,41 .H4 47,,.. .,, .,A..74.:, .A 44 ,A,7H,:77 ,7H,:. 7:A7.H,:.:.,, ,..,.4. ., , 4.7,7. ,: ,4,.4,,,.4... , .:,7 ..:.HH:.4 . 444.4. w m yum-M,- ” , USGS Rock Standards, III: Manganese-Nodule Reference Samples USGS— Nod—A—l and USGS— Nod— P— 1 By F. J. FLANAGAN and DAVID GOTTFRIED GEOLOGICAL SURVEY PROFESSIONAL PAPER 1155 Analytical data by various techniques and best estimates for some elements in two manganese—nodule reference samples UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1980 UNITED STATES DEPARTMENT OF THE INTERIOR CECIL D. ANDRUS, Secretary GEOLOGICAL SURVEY H. William Menard, Director Library of Congress Cataloging in Publication Data Flanagan, Francis James, 1915— USGS rock standards, III. (Geological Survey professional paper ; 1155) Bibliography: p. Supt. of Docs. no.: I 19.1621155 1. Manganese nodules———Composition. I. Gottfried, David, joint author. II. Title. III. Series: United States. Geo- logical Survey. Professional paper ; 1155. QE390.2.M35F43 552'.5 79-607084 For sale by the Superintendent of Documents, US. Government Printing Office Washington, DC. 20402 TABLE 7,8. 9, 10. 11. 12—21. CONTENTS Page Abstract _________________________________________________________________ 1 Introduction _____________________________________________________________ 1 Preparation of samples ___________________________________________________ 2 Experimental design for the determinations ________________________________ 2 Semiquantitative spectrochemical analysis and homogeneity __________________ 2 Tests for homogeneity ____________________________________________________ 4 Estimation of best values _________________________________________________ 5 Selection process and lack of clear choices __________________________________ 7 Summary estimates and discussion _________________________________________ 8 Comparisons with data from Marsden Squares 049 and 116 ___________________ 10 Availability of samples ___________________________________________________ 10 References cited __________________________________________________________ 12 TABLES Estimates from the analysis of variance of computerized semiquantitative spectrochemical determina- tions of trace-elements data for USGS—Nod—A—l and USGS—Nod—P—l ________________________ Number of calculated F ratios smaller or larger than the fractile of the F distribution indicated __ Summary of best estimates and confidence limits for averages of several elements in: 3. USGS—Nod—A—l _____________________________________________________________________ 4. USGS—Nod—P—l ______________________________________________________________________ Comparison of best estimates for several elements in USGS—Nod—A—l with estimates of the distribu- tion of the elements for data in samples from Marsden Square 116 __________________________ Comparison of best estimates for several elements in USGS—Nod—P—l with estimates of the distribu- tion of the elements for data in samples from Marsden Square 049 ___________________________ Determinations of several elements, by instrumental neutron—activation analysis, by P. A. Baedecker, US. Geological Survey, in: 7. USGS—Nod—A—l _____________________________________________________________________ 8. USGS—Nod—P—l ______________________________________________________________________ Determinations of several elements and oxides by John Marinenko, US. Geological Survey, in: 9. USGS—Nod—A—l ______________________________________________________________________ 10. USGS—Nod—P—l ______________________________________________________________________ Determinations of U and Th in USGS—Nod—A—l and USGS—Nod—P—l, by delayed neutron-activation analysis, by H. T. Millard, Jr., and C. M. Ellis, U.S. GeOIogical Survey _______________________ Determinations of several elements in USGS—Nod—A—l and USGS—Nod—P—l: 12, 13. By the National Physical Research Laboratory, South Africa: 12. USGS—Nod—A—l __________________________________________________ __ ______ 13. USGS—Nod—P—l _________________________________________________________ 14, 15. By S. E. Calvert, Institute of Oceanographic Sciences, England: 14. USGS—Nod—A—l _________________________________________________________ 15. USGS—Nod—P—l __________________________________________________________ 16,17. By R. T. T. Rantala, Bedford Institute of Oceanography, Canada: 16. USGS—Nod—A-l _________________________________________________________ 17. USGS—Nod—P-l _________________________________________________________ 18, 19. By the National Institute for Metallurgy, South Africa: 18. USGS—Nod—A—l _________________________________________________________ 19. USGS—Nod—P—l _________________________-_____- __________________________ Page 3 5 8 9 11 11 14 15 16 17 18 18 19 20 21 22 23 24 25 IV TABLES 12—21. 22, 23. 24, 25. 26, 27. 28, 29. 30, 31. 32, 33. CONTENTS Page Determinations of several elements in USGS—Nod—A—l and USGS-Nod—P—l—Continued 20, 21. By the Institute of Geological Sciences, England: 20. USGS— Nod—A— 1 _________________________________________________________ 26 21. USGS—Nod— P— 1 __________________________________________________________ 27 Determinations of several elements in USGS—Nod—A—l and USGS— Nod— P—1, by atomic— absorption spectrometry . 22. By David Piper, U.S. Geological Survey _______________________________________________ 27 23. By Lockheed Ocean Laboratory, California _____________________________________________ 28 Complete analyses by M. Saunders, Grant Institute of Geology, Scotland, of : 24. USGS—Nod—A—l ____________________________________________________________________ 28 25. USGS—Nod—P—l _____________________________________________________________________ 29 Determinations of several elements by David Felix, Ocean Mining Laboratory, California, in: 26. USGS—Nod—A—l ____________________________________________________________________ 30 27. USGS-Nod—P—l ____________________________________________________________________ 31 Determinations of several elements, by atomic-absorption spectrometry, by Wayne Mountjoy, James G. Crock, and George Riddle, U.S. Geological Survey, in: 28. USGS—Nod—A—l ____________________________________________________________________ 32 29. USGS—Nod—P—l _____________________________________________________________________ 33 Chemical determinations of several constituents by Sarah T. Neil, U.S. Geological Survey, in: 30. USGS—Nod—A—l ____________________________________________________________________ 34 31. USGS—Nod—P—l _____________________________________________________________________ 35 Averages of determinations of elements by all contributing analysts, in: 32. USGS—Nod—A—~1 ____________________________________________________________________ 36 33. USGS—Nod—P—l _____________________________________________________________________ 38 CONVERSION FACTORS Metric unit Inch»Pound equivalent Metric unit Inch-Pound equivalent Length Specific combinations—(bntinued millimeter (mm) = 0 03937 inch (in) liter per second (L/s) = .0353 cubic foot per second meter (m) = 3. 28 feet (ft) cubic meter per second : 91.47 cubic feet per second er kilometer (km) = .62 mile (mi) per square kilometer square mile [(ftfl/s /mi2] [(ms/Sflkm’l Area meter per day (m/d) : 3.28 feet per day (hydraulic conductivity) (ft/d) square meter (m2) : 10.76 square feet (ftz) meter per kilometer : 5.28 feet per mile (ft/mi) square kilometer (km?) : .386 square mile (mi?) (m/km) hectare (ha) : 2-47 acres kilometer per hour .9113 foot per Iecond (ft/s) km/h) Volume meter per second (m/s) : 3.28 feet per second cubic centimeter (cm-1) : 0.061 cubic inch (in?) meter squared per day = 10.764 feet squared per day (ftfi/d) Htiii (L)t ( ) = (3%. gig cugic inchesft) (mz/d) (transmissivity) cu cmeer m3 : cu ic ee ( 3 2 - - cubic meter : .00081 acre3,200 ________________________________ Neg. .99 .29 NS 1 3.3 ________________________________ Neg. 14.7 .54 NS 107 8 10 2.21 NS Neg. 23,100 .50 NS 252,000 20,200 21,200 2.81 NS 13 19 1.95 NS 718 74 41 7.55 NS 1.4 21 1.01 NS 1 82.6 ________________________________ 264 122 10.3 NS(0.975) 14,170 1,000 1,470 1.92 NS Neg. 115 .36 NS 470 Neg. 35 28.38 NS (0.99) Neg. 1.7 .39 NS 7.6 1.9 .78 12.35 NS (0.975) Neg. 110 .07 NS 332 76 44 6.93 NS Neg. 27 .82 NS 265 23 12 8.33 NS Neg. 27 .56 NS 265 17 13 4.36 US Neg. 18 .21 NS 55 16 5.0 20.86 NS(0.99) Neg. 2.6 .22 NS 8.6 3.0 .79 29.01 NS(0.99) 33 15 10.53 NS (0.975) 1,530 119 58 9.50 NS 2.9 64 1.00 NS 260 100 24 36.79 S (0.99) ' 1 Average of 5 determinations. there are two compilations of data (Flanagan, 1969, 1976) are now used to supplement the original spec- trographic standards made to approximate the com- position of the “average” silicate (Myers and others, 1961). Neither set of standards even remotely ap— proximates the composition of manganese nodules, and because of the effects of the different matrices, spectrographic estimates for the nodules could be ex- pected to deviate from any best values subsequently calculated. Nevertheless, the data in table I serve a useful purpose. Because the size of the sample taken for the spectrographic technique is small, these data may serve as an initial indication of the homogeneity of the material. If the samples are homogeneous for this techniuqe, then as a first approximation they should be homogeneous for those methods for which a larger portion of sample is taken for analysis. The homogeneity of the material does not depend on the closeness of the data to any “true” value but on the variation between and Within bottles of a sample. Thus, if for a given element the F ratio— the variation attributable to bottle means divided by the variation Within these bottles—is not larger than the value listed in the table for the 95-percent fractile of the F distribution with the appropriate degrees of freedom, one may infer that the element is homogeneously distributed among the bottles. The conclusions resulting from the analysis of variance of the semiquantitative spectrographic de- terminations that have the form of quantitative data are of some interest. Of the 22 elements for which complete sets of data are available for USGS—Nod— A—l, the calculated F ratios for 20 sets of data are not significantly larger than the allowable value of FM, (d.f. 2,3) =9.55, and the two remaining F ratios are not significant when tested against F0.,,,,—,(d.f. 2,3) = 16.0. We may conclude on the basis of these spectrographic data that the elements determined are homogeneously distributed among the bottles. Complete sets of data for 19 elements are avail- able for USGS—Nod—P—l. As the six determinations for cobalt are identical, no F test could be made, and cobalt is distributed homogeneously. The calculated F ratio is not significant at FM, for 11 elements and at FM”, for 2 others, and these elements may be inferred to be homogeneously distributed. Of the remaining five elements for which sets of data are complete, the F ratios for three elements do not equal or exceed the allowable value for F0.90 (d.f. 2,3), and ratios for two elements exceed this value. Because the allowable ratio, 30.8, is rather 4 USGS ROCK STANDARDS: MANGANESE—NODULE SAMPLES USGS—NOD—A—l, USGS—NOD—P—l large, the five elements appear to be heterogeneously distributed. Perhaps because of the semiquantitative nature of the technique, we should not be unduly worried by- the five conclusions of heterogeneity, but some brief discussion is justified. Samples to be analyzed routinely by the technique are never dried, and the powdered nodule samples were also not dried. Fur- thermore, the nodules from the Pacific were partly covered with a thin coating of gray pelagic clay. This clay was not removed from the nodules, and the small amount of clay was incorporated in the ground sample. The tendency of both the nodule material and the clay to absorb atmosphere moisture and the tendency of clays to absorb cations may be partly responsible for some of the demonstrated heterogeneity. TESTS FOR HOMOGENEITY The elements silicon through manganese were re- ported as percentage of either the oxide or the ele- ment, probably because no method of reporting had been specified. The elements reported as the oxides were reduced by the appropriate gravimetric factor to percentages of the elements before the analysis of variance. Such transformations from oxide to element also reduce the variation among the deter- minations of an element. Cobalt, copper, and nickel are considered as minor elements in the nodules, and data are listed therefore as percentages because their contents in the samples equal or exceed 0.1 percent. Elements usually considered as trace ele- ments in rocks but reported as percentages were converted to parts per million by multiplying by 104 and adding nonsignificant zeros Where necessary; these data were used in the calculations for the analysis of variance and for the best values. The data in tables 7 through 21 presented no spe- cial problems, and the calculations of the analysis of variance were made on a laboratory calculator for which a program was available. The data in tables 22 and 23 also presented no special problems, as one analyst reported averages of two determinations and the other made determinations on a single por- tion from each bottle of sample; these data cannot be used in the calculations. The data in tables 24 and 25 are rather complete comprehensive analyses of each sample, and these single determinations also cannot be used. However, the data in tables 26 to 29 were presented in a form that required a change in the analysis of variance. The analyst who contributed the data shown in tables 26 and 27 apparently planned to make a single determination on a portion from each bottle of both samples on a single day and then repeat the procedure on two other days. However, the solu- tion for the single determinations for bottle 2 of USGS—Nod—P—l was contaminated on the first day, and data were therefore not reported. An extra set of determinations on a portion from bottle 2 was reported for the third day. The analyst, by his deci- sion to make determinations on three days, added another variable of classification (days) to the original design with a single variable of classifica- tion (the bottles). As the extra determinations for bottle 2 were made on day 3, these determinations could not be legitimately substituted for the missing determinations for day 1. We therefore decided to omit the two determinations on day 1 and the extra determination on day 3 and to treat the remain- ing data as a two-way analysis of variance, with the bottles and the days as the two variables of classification. The results of the analysis of variance reflect the significance of these variables of classi- fication. Although the determinations for USGS— Nod-A—l were completed according to the plan of the analyst, we decided to treat both samples sim- ilarly, and the determinations for Nod—A—l on days 2 and 3 were also used in the two-way analysis of variance and in the calculations for best estimates. The data in tables 28 and 29 presented a similar problem. The analysts for these determinations had intended to make the determinations in two “runs,” but some determinations were delayed for about two months. To simplify matters, we ignored the delay and treated the data as a two-way design with bot- tles of sample and “runs” as the two variables of classification. In other tables of data, one or both determinations for a bottle of sample were missing in a few places. Such missing data reduced the number of bottles to two, and the changes in degrees of freedom for both bottles and for error are given in footnotes. Where data are missing, the laboratory means and vari- ances were not used in the calculations of best val- ues. Data reported as less than some lower limit were treated the same as missing data. Data in the form <90 belong to the ordinal scale of measurement (Stevens, 1946) and cannot be treated by the same mathematical or statistical procedures as the ordi- nary quantitative data that are classified as the ratio scale of measurement. The conclusions resulting from the F tests in the analysis of variance for the quantitative data con- ESEIMATION 0F BEST VALUES 5 firm the conclusions from similar tests with the semiquantitative spectrochemical data. Table 2 shows the frequencies, by element and by the fractile of the F distribution, for the significance or non- significance of the F ratios for those quantitative data for which the analysis of variance could be made. The proportion of F ratios not significant at Em5 (118/124=0.952 for USGS—Nod—A—l, and 115/119=0.966 for USGS—Nod—P—l) furnish con- vincing evidence for both samples that most ele- ments are indeed homogeneously distributed among the bottles. ESTIMATION OF BEST VALUES “Best” values for elements or oxides in rock ref- erence samples have been derived by many (Abbey, 1977; Christie and Alfsen, 1977; Ellis and others, 1977; Flanagan, 1969, 1976; Govindaraju and de la Roche, 1977 ; and Sutarno and Faye, 1975), but ob- jections can be made to some methods. Deriving best values from large compilations of data is tedi- ous; calculating them where the data are reported in equivalent form is much easier. We decided to derive best values for the data for the nodules by a procedure involving three steps: 1. Determine which of the It sets of data have a common variance. 2. From this common variance, calculate the stand- ard deviation of the means of the n determi- nations. 3. Use this standard deviation to obtain the Stu— dentized range to determine which of the TABLE 2.—Number of calculated F ratios smaller or larger than the fractile of the F distribution indicated Element USGS—Nod-A—l USGS—Nod—P—l Fo.m| (Fans Fo,oo 5 _ _ _ 5 _ _ .. 6 _ _ _ 6 _ _ _ 8 - _ _ 7 1 _ _ 4 _ 1 _ 5 _ ._ .. 5 _ _ _ 4 1 _ _ 2 _ _ _ 2 _ _ - 5 _ 1 _ 6 _ _ _ 4 _ _ _, 3 _ _ _ 4 _ .. _ 4 _ _ .. 6 _ 1 .. 6 1 .. .. 9 _ _ _ 8 _ _ _ 7 _ _ _ 6 _ - .. 6 _ _ _ 5 _ _ _ 1 _ _ _ - 1 _ _ 5 _ _ _ 5 ._ - .. .. 1 _ _. 1 _ _ _ 1 .. _. _ 1 - _ _ 2 _ .. _ 1 _ - _ 1 _ _. _ 1 _ _ _ _ _ _ 1 1 .. _ _ 1 _ _ _ 1 - _ _ 1 _ _ _ 1 _ _ _ 1 _. _ _ 1 _ _ _ 1 .. _ _ 1 _ _ _ 5 _ _ - 5 _ _ .. 1 .. .. _ 1 _ .. .. 4 _ _ _ 5 _ ._ _ _ _ _ .. 1 _ _ _ 1 _ _ _ 1 _ .. _ 1 _ _ _ 1 _ _ _ 1 _ _ _ 1 _ _ .. 3 - _ _ 3 _ _ _ 1 _ _ - 1 _ - - 1 _ 1 _ 2 - _ _ 1 .. .. ._ 1 _ _. _ 2 _ .. _ 2 .. .. .. 3 - _ - 2 - _ .. 1 _ _ _ 1 - ._ _ 1 _ _ _ 1 _ .. _ 6 .. _ _ 5 _ _ _ 1 _ .. _ 1 _ _ _ 1 1 8 1 4 1 1 1 5 4 0 0 6 USGS ROCK STANDARDS: MANGANESE-NODULE SAMPLES USGS—NOD—A—l, USGS—NOD—P—l several means can be considered to have been derived from the same population mean. We then consider the average of the several means so selected as the best estimate. The question of which of the It sets of data, each with n determinations, have a common variance was resolved with Cochran’s test for the homogene- ity of variances (a brief discussion and tables are available in Dixon and Massey, 1951). Sample vari- ances, with n—1=5 degrees of freedom, were cal- culated for all sets of data that included six deter- minations of an element by each of the several laboratories. The variances of the In groups of data, omitting the factor of the technique used, were listed in a column from the least to the greatest variance. Starting with the third least variance (the two lowest variances may be tested, where neces- sary, by the F ratio), the sums to the 3rd, 4th . . . kth variances (82) are listed in an adjacent column; Cochran’s test, (Largest s?) / (Sum 33) , is then made with the largest variance. Because analysts did not use methods of equal precision for the same ele- ment, the kth (the greatest) variance can be a very significant part of the sum of the lc—l smaller variances, as shown in the tabulation for the calcu- lations for cobalt in USGS—Nod—A—l. Many texts contain tables at probabilities p=0.05 and p=0.01 for Cochran’s test, where the allowable values are for k variances, each with v degrees of freedom. We used the test iteratively until a homogeneous set of variances was reached. For several elements in the samples, we accepted a test that was not sig- nificant at the greater ratios for p=0.01 so that a set of three or more homogeneous variances might be available. Cumulative N. Varianges 5“!“ of WW Nfzgs'fimznf’rs (X 10 ) V3333? Sum s” p :305 I) = 0101 > 9 1,160 1,309 0.8862 S S 8 97 149 .6510 S S 7 17 52 .3269 NS 6 15 35 5 8 20 4 7 12 3 3 5 2 1 ____. 1 1 In the tabulation of the variances for cobalt the ratio of the seventh variance over the sum of the first seven (17X10—6/52X10—6) does not exceed the allowable ratio for Cochran’s test at p=0.05. The calculated ratio is not significant, and the lowest seven variances are accepted as a homogeneous set. From this homogeneous set of variances, we then calculate the standard deviation of the means of the n (=6) determinations. In calculations where the numbers of determinations are unequal, usually the individual variances multiplied by their respec- tive degrees of freedom are summed, and the sum thus obtained is divided by the sum of the degrees of freedom. The procedure is less complicated where variances are calculated from equal numbers of determinations. In the tabulation for the cobalt variances, the sum of the seven smaller variances, 52X10—“', is divided by the number of variances, 7, to obtain the average of the set of homogeneous variances. When this result, 7.4X10—6, is divided by 6, the number of determinations for each variance, and the square root is taken, we obtain 1.11><10*3 as the standard deviation of the mean of six determinations. As each variance has 5 degrees of freedom, we have 35 de- grees of freedom associated with this standard deviation of the mean. Standard deviations for the other elements are calculated similarly. The averages of the data are then tested by the Studentized range to determine if all or some of the means form a homogeneous group. The means of the several sets of data are ordered, the means being taken for the purpose of discrimination to more decimal places than are generally warranted. The order for the cobalt averages, each calculated to four digits, is 0.3900, 0.3363, 0.3265, 0.3215, 0.3128, 0.3127, 0.3080, 0.2813, and 0.2527. We may see that this ordered set of means shows appreciable varia- tion and that we may need to use the procedure itera- tively. The range of these nine averages is then divided by the standard deviation of the mean to yield an estimate of the Studentized range. Tables for the allowable values for percentage points of the Studentized range are given in Bennett and Franklin (1954, p. 188—189), and elsewhere, for samples of size n, each with v degrees of freedom, where these degrees of freedom are the sums of the degrees of freedom for the several laboratory vari- ancs included in the homogeneous variance. The range for the 9 cobalt means is 0.14, which yields, when divided by the standard deviation of the mean, 1.11X10—3, an estimate of 126 for the Studentized range. This is far larger than the allow- able values of 4.68 for the 5-percent point or 5.58 for the 1-percent point of the Studentized range for the set of 9 means with 35 degrees of freedom. The average, 0.39, is the extreme mean of the group, and it is omitted from further consideration. The range, 0.08, of the remaining eight means is also highly significant for values for 8 means and 35 O ESTIMATION OF BEST VALUES 7 degrees of freedom, and the extreme mean, 0.2527, is then dropped. After further iteration, we deter- mined that the values in the order 0.3128, 0.3127, and 0.3080 form a homogeneous group, and their average, 0.311 percent cobalt, is taken as the best estimate. The average of the original 9 means is 0.319, a value not too far from the best estimate. The agreement between the two estimates is prob- ably due to the almost symmetrical differences be- tween the best estimate and the two extreme means, an event that happens infrequently for the groups of means of the remaining elements for the two samples. Best estimates for the remaining elements were calculated similarly. SELECTION PROCESS AND LACK OF CLEAR CHOICES During the selection process, we frequently ar- rived at some step where we had to make a decision, but criteria for these decisions may be absent or perhaps conflicting because of their subjectivity. Tables 3 and 4 contain a number of best estimates listed as means without upper and lower confidence limits, and some discussion of difficulties encoun- tered in the selections seems warranted. The labora- tory averages for determinations for Nod—A—1 that are discussed for several elements below may be found in table 32 and those for N od—P—l in table 33. Silicon—The highest laboratory average for N od—A was obtained by atomic-absorption spectro- scopy, and the two lowest averages by X-ray fluor- escence. After the two extreme means were elimi- nated, averages of 1.82, 1.73, and' 1.63 remained. If the middle value is paired with either extreme of these three, the Studentized range is not signifi- cant at p=0.01 for either pair. However, because the lowest average, 1.63, was obtained by X-ray fluorescence and the two higher means by gravime- try, the average of 1.82 and 1.73 was accepted as the best value. The highest average for silicon in Nod—P, 6.97, was obtained by atomic-absorption spectroscopy, but this is the extreme mean that was eliminated first. The range for the four remaining means, 6.65, 6.64, 6.38, and 6.36, is unacceptably large as is the range when the two extreme averages are discarded. The two higher and the two lower means, when paired, do not differ within themselves. We cannot resort to the analytical method as a criterion for our choice because both gravimetry and X-ray fluorescence were the methods for each pair. The average of the four means is therefore accepted as a provisional estimate without confidence limits. Aluminum—0f the six available averages for the aluminum content of Nod—A, only two means, 2.06 and 2.04, survived the selection process, and the average of 2.05 percent aluminum is accepted as the best value. The Studentized range for three means for Nod—P, 2.59, 2.56, and 2.41, did not exceed the tabled value for p=0.01, and their average is ac- cepted as the best value. The acceptance of a wider range for means for Nod—P is due to the larger standard error of the mean (0.05 as against 0.03) and to the higher acceptable values for the range for three rather than two means. Magnesium—All differences between adjacent pairs of means for magnesium in Nod—A proved significant at p=0.01 because of the small standard error of 0.01, and the average of the four means, 2.93, 2.89, 2.85, and 2.80, was accepted as a provi- sional estimate without limits. We had no problem in the selection for N od—P. S0d2'um.—The two lower of the three means for N od—A were accepted, but there was no choice for the three means for Nod—P, and their average is taken without limits. Titanium.—The small standard error, 0.004, for titanium in Nod—A results in the choice of two identical means, 0.32, and in the rejection of 0.28 and 0.29. The still smaller standard error, 0.002, for Nod—P leaves no choice, and the average of the four means is taken as a provisional estimate. Cobalt—The small standard error, 0.0011, for the means for cobalt in N od—A resulted in the rejec- tion of all but three of the nine means available. The rounded average of the three means, 0.311 per- cent cobalt, is accepted as the best value. The selec- tion process, again with a small standard error of 0.0011, resulted in two pairs of means for Nod—P, 0.2287 and 0.2280, and 0.2203 and 0.2200, that dif- fered between but not within themselves. As there is no criterion for a choice, the average of the four means is listed as a provisional estimate. Nickel.~—The selection of a best estimate for nickel in Nod—A presented no difficulties, and the average of 0.636 percent nickel, calculated from laboratory means, 0.6400, 0.6372, and 0.6300, whose Studentized range was acceptable, is taken as the best value. However, the selection for Nod—P pro- duced surprises. The two lowest means, 1.243 and 1.276, were rejected first because they were far removed from the center of gravity of the distribu- tion of the eight means. Further tests showed that the Studentized range for the three largest means, 1.40, 1.395 and 1.382 (average, 1.392) is not sig- nificant at p=0.01 but that the range for the next 8 USGS ROCK STANDARDS: MANGANESE-NODULE SAMPLES USGS—NOD-A—l, USGS—NOD—P—l three lower means, 1.350, 1.328, and 1.32 (average, 1.333), is significant. Without the benefit of the several tests with the Studentized range, one might normally accept the grand average, 1.337, of the eight means as the best estimate of central tendency. As the average, 1.392, of the three means deemed acceptable by the test is far removed from the grand average of the eight means, this grand average is accepted as the con- ditional best estimate without confidence limits. Future data from other analysts will undoubtedly resolve this dilemma. SUMMARY ESTIMATES AND DISCUSSION The best estimates obtained by the Studentized range and the provisional estimates obtained when the dispersion among the means was too large are given in tables 3 and 4. Because the elements to be determined were not specified, the number of means for either type of estimate is variable. The number of variances used for the standard error of the mean may be obtained by dividing the degrees of freedom shown in tables 3 and 4 by the number of degrees of freedom (five) for each laboratory variance. The number of laboratory means that were used for best estimates will differ because of the selection process; the numbers of means that survived this process are given in tables 3 and 4. The numbers of averages from which the provisional estimates without con- fidence limits were calculated are given in paren- theses. Laboratory averages for all elements in both samples are listed in tables 32 and 33 to facilitate comparisons of the estimates by different analysts. The column headings indicate the table number from which the averages were taken. The number of de- terminations included in these averages is noted in each column heading as “n=x,” where x is the number. This provision is necessary because not all data reported by two analysts were used in the analysis of variance for reasons of symmetry, and two other analysts had insufficient time to complete the requested work. Nonsignificant zeros added where percentage of an element or oxide reported by analysts was converted to parts per million are indicated by the lowercase letter “0.” In either table the spread of the data for the major or minor elements produced no surprises, ex— cept perhaps for one or two elements. The hypothe- sis associated with the analysis of variance—that the content of an element differed among bottles of the sample—was not accepted for the determina- tions of cobalt, copper, and nickel by any analyst whose data were amenable to the analysis of vari- ance; eight analysts or laboratories have therefore effectively inferred that these elements are homo- geneously distributed among the bottles of samples. TABLE 3.—Summary of best estimates and confidence limits for averages of several elements in USGS—Nod—A—I [Estimates in percent or in parts per million, as indicated. Estimates in brackets are averages, without limits, of the number of laboratory means shown in parentheses. Student’s loss was used for confidence limits] Standard error Number of Degrees of Best values and confidence limits laboratory Element 0f mean freedom Lower limit < Mean < Upper limit mggrigssted values Percent Si __________ 0.022 20 1.737 1.775 1.813 2 A1 __________ 032 25 1.995 2.05 2.105 2 Fe __________ 042 30 10.861 10.932 11.003 6 Mg _________ 0099 25 _________ [2.87] _________ (4) Ca __________ 039 30 10.964 11.03 11.096 4 Na _________ 0056 15 .765 .775 .785 2 K '_ __________ 0086 30 .485 .50 .515 4 Ti __________ 004 20 .315 .32 .325 2 P ___________ 007 15 .588 .60 .612 2 Mn _________ .050 25 18.459 18.545 18.631 4 C0 __________ .0011 35 .309 .311 .313 3 Cu __________ .0010 35 .1082 .1099 .1116 7 Ni __________ 0024 35 .632 .636 .640 3 Parts per million Ba __________ 30.8 15 1,616 1,670 1,724 3 M0 __________ 8.7 30 433 448 463 3 Pb __________ 8.2 25 831 846 861 2 Sr __________ 13.7 20 1,724 1,748 1,772 3 V ___________ 6.2 10 _________ [770] _________ (3) Zn __________ 4.6 30 579 587 595 4 SUMMARY ESTIMATES AND DISCUSSION 9 TABLE 4.——Summary of best estimates and confidence limits for averages of several elements in USGS—Nod—P—I [Estimates in percent or in parts per million, as indicated. Estimates in brackets are averages, without limits, of the number of laboratory means shown in parentheses. Student’s toms was used for confidence limits] ygmbg of S d d - D f Best values and confidence limits a are ry Element “Effiefim 5523:5113 Lower limit < Mean < Upper limit migi'ié'ssfd values Percent Si __________ 0.016 15 _________ [6.508] _________ (4) A1 __________ .049 25 2.466 2.55 2.634 3 Fe __________ 031 30 5.727 5.78 5.833 4 Mg _________ 0085 20 1.975 1.990 2.005 4 Ca __________ 012 30 2.167 2.187 2.207 6 Na _________ 0043 10 _________ 1.64 _________ (3) K ___________ 012 35 1.030 1.05 1.070 3 Ti __________ 002 10 _________ [.30] _________ (4) P ___________ 002 15 .199 .203 .207 3 Mn _________ .080 20 29.002 29.14 29.278 3 CO __________ .0011 35 _________ [.224] _________ (4) Cu __________ .0049 30 1.143 1.151 1.159 4 Ni __________ .0064 30 _________ [1.337] _________ (8) Parts per million Ba __________ 27.7 10 _________ [3,350] _________ (3) M0 __________ 4.1 20 _________ [762] _________ (5) Pb __________ 5.8 25 _________ [555] _________ (6) Sr __________ 3.3 10 _________ [682] _________ (3) V ___________ 10.3 15 _________ [567] _________ (3) Zn __________ 5.9 25 1,585 1,595 1,605 2 In View of these inferences, one might have expected the laboratory averages for these elements of poten- tial economic interest to be more closely grouped than the data in tables 32 and 33 indicate. _ Data for several trace elements are sparsely dis- tributed in tables 32 and 33. An average by a single laboratory is reported for 19 of the 32 trace ele- ments listed, and 13 of these 19 were included in the suite of elements determined by instrumental neutron-activation analysis. The trace elements molybdenum, vanadium, and zinc may be of economic interest, depending on the commercial process used for treatment. Although most laboratories that determined these elements by completing the requested work found the ele- ments to be homogeneously distributed in the sam- ples, the dispersion among laboratory means is too large. Further analytical work will be necessary to obtain better estimates for these elements, espe- cially if the samples are to be used as reference materials for future determinations that may form the basis for an economic decision. Conspicuous by their absence in tables 32 and 33 are estimates for gold and the platinum metals. Harriss and others (1968, table 2) have determined palladium, iridium, and gold in nodules taken from near the sites for Nod—A—l and Nod—P—l. After this paper had been completed, P. J. Arus- cavage (written commun., 1979) determined plati- num, palladium, and ruthenium in the two nodule samples. The three precious metals were determined by a method involving fire assay and flameless atomic-absorption spectroscopy with the same ex- perimental design used while obtaining other data for these samples. His averages of six determina- tions, by samples and by elements, are given as follows: Platinum-metal contents [In parts per billion] Sample Pt Pd Ru USGS—Nod—A—l _____ 453 2.5 18 USGS—Nod—P—l _____ 123 5.6 4.7 The possible recovery of the platinum metals and gold as byproducts of a commercial extraction proc- ess designed for an anticipated production of 1—3 million tons 'of nodules per year (Pearson, 1975) might lower the unit cost of the mining and extrac- tion operations and thereby make more attractive the economic decision to proceed. Chemical determinations of several constituents in both nodule samples were furnished by Sarah T. Neil of the US. Geological Survey, Menlo Park, Calif., after the manuscript had been completed. We corrected these determinations, which were on sample portions not dried, to a dry basis (105° C) 10 USGS ROCK STANDARDS: MANGANESE-NODULE SAMPLES USGS-NOD—A—l, USGS—NOD—P—l using the determinations of H20- for each portion of sample. Gravimetric factors were used to convert data reported as oxides to elements. The data by Neil are shown in tables 30 and 31, and her averages are listed with all other averages in tables 32 and 33. The analysis of variance, under the usual assumptions for the design with a single variable of classification, results in F ratios that are not significant at F”, for 34 of the possible 35 tests; the remaining ratio is not significant at Fm”. Al- though data for two elements (titanium and sodium) in Nod—A and for three (titanium, sodium, and calcium) in Nod—P are outside the range of data provided by other analysts, we feel that these addi- tional data would not significantly affect calculated best values. These data, plus others published later, will be used in calculations to revise or establish best values. Anne E. Childress of the US. Geological Survey determined niobium in the two samples with the same experimental design used by the other ana- lysts. Analyses of variance of the data showed that niobium was distributed homogeneously in the bot- tles of both samples. Childress obtained averages of 43.2 parts per million niobium for six determina- tins for Nod—A—l and 21.2 parts per million for Nod—P—l. These estimates were confirmed by Esma Y. Campbell, who found averages for two determi- nations of 43.8 parts per million niobium for Nod—A—1 and of 21.4 parts per million for Nod—P—l. The contents of some lithophilic elements such as the rare earths, zirconium, hafnium, niobium, thorium, and uranium, shown in tables 32 and 33, are similar to the contents of these elements in frac- tionated crustal rocks. The relatively high abund- ances of these elements in the nodules, which con- tain high amounts of chalcophilic elements, pose an interesting problem for future geochemical research because of the low abundance of lithophilic elements in sea water and in basaltic rocks typical of the ocean floor. COMPARISONS WITH DATA FROM MARSDEN SQUARES 049 AND 116 Because of the differences among data published for elements determined in manganese nodules, we have shown estimates for our nodule samples and those of the distribution of data on samples from the Marsden Squares that include the collection areas for our samples. Monget and others (1976), in their compilation, have listed the pubished data by the number of the Marsden Square, the rectangles enclosed by each 10° of longitude and latitude. Our estimates for Nod—A—l are listed in table 5 with estimates of the distribution of data from Marsden Square 116, and our estimates for Nod— P—1, together with estimates for Marsden Square 049, are given in table 6. We feel that our data and those from the squares should not be formally com- pared, because of the extremely low sampling den- sity in the two squares—one sample per 100,000 km2 in square 049 and one sample per 20,000 km”: in Square 116. The USGS samples were probably taken from test sites with areas of less than 35 kmz, whereas Marsden Square 049 covers about 1,550,000 km2 and square 116 in the Atlantic Ocean, about 500,000 km2 after the land area included in the square is subtracted. The ranges shown in the data for the samples from each Marsden square are very wide. Although some dispersion may be partly due to analytical methods and error, the major part may be due to compositional differences among single nodules that were analyzed. In addition to the average for man- ganese, the averages for copper and nickel, the two elements of considerable economic interest in the two USGS samples, agree well with, or exceed, the averages of data for the respective squares, but our cobalt averages are one-quarter to one-third lower. The manganese contents of the USGS samples are both about 6 percent (absolute) higher than the averages of similar data for samples from the cor— responding squares. AVAILABILITY OF SAMPLES Because of the limited amounts of the two sam- ples, we must have restrictions on their distribution until commercial exploitation begins and more mate- rial is available for future reference samples. Re- quests are anticipated from those who wish to use the samples as standards and from those who, in addition, wish to confirm or improve the estimates given here. Information on the availability of the samples may be obtained from either author. The powder density of the processed material is less than that of powdered igneous rocks, and a full bottle is estimated to contain not more than 30 grams. The units of issue will be packaged routinely from the randomized stock of the samples, and some bottles may be only half filled as a result of our normal sampling procedure. Neither the authors nor this laboratory has hand specimens of the nod- ules from which the two samples were made. ESTIMATES FOR MARSDEN-SQUARE AND USGS SAMPLES 11 TABLE 5.—Comparison of best estimates for several elements in USGS—Nod—A—I with estimates of the distribution of the [Data for Marsden Square elements for data in samples from Marsden Square 116' from Monget and others (1976). Estimates in percent or in parts per million, as indicated. 11, number of determinations; 5, average; s.d., standard deviation] Estimates of data from Marsden Square 116 Element USGS — Range N°d_A—l n x 5"“ Lower < Upper Percent Si __________ 1.78 20 1.76 1.48 0.3 5.9 A1 __________ 2.05 20 1.6 .88 .1 2.8 Fe __________ 10.93 24 11.38 4.4 1.6 20.0 Mg _________ 2.87 16 1.97 .67 1.09 3.70 Ca __________ 11.03 23 14.30 7.12 1.9 28.7 Na __________ .77 __ ________________________________ K ___________ .50 17 .30 .10 .14 .54 Ti __________ .32 21 .27 .15 .06 .68 P ___________ .60 17 2.08 2.35 .05 7.0 Mn _________ 18.54 23 12.64 3.75 6.9 21.5 C0 __________ .311 9 .44 .05 .38 .55 Cu __________ .110 23 .116 .062 .03 .26 Ni __________ .636 24 .412 .156 .13 .77 Parts per million Ba __________ 1,670 __ ________________________________ M0 __________ 448 6 1,107 1,570 350 4,300 Pb __________ 846 8 1,658 295 1,200 2,100 Sr __________ 1,748 20 1,660 684 676 3,380 V ___________ 770 __ ________________________________ Zn __________ 587 8 508 94 390 670 TABLE 6.—Comparison of best estimates for several elements in USGS—Nod—P—I with estimates of the distribution of the elements for data in samples from Marsden Square 049 [Data for Marsden Square from Monget and others (1976). 5, average; s.d., standard deviation] Estimates in percent or in parts per million, as indicated. n, number of determinations; USGS Estimates of data from Marsden Square 049 Element _ Range NDd P 1 n ac 3"" Lower < Upper Percent 6.51 12 7.62 1.59 5.4 11.2 2.55 10 3.43 .57 2.8 4.6 5.78 18 7.69 2.24 2.4 10.4 1.99 4 1.90 .11 1.7 2.0 2.19 14 1.4 .24 .9 1.8 1.64 __ ________________________________ 1.05 9 .93 .22 .69 1.40 .30 11 .46 .15 .29 .74 .20 2 .12 (average) ________________ 29.14 18 23.8 4.10 18.5 32.9 .224 17 .307 .091 .10 .44 1.15 17 1.00 .22 .47 1.4 1.33 18 1.18 .32 .47 1.9 Parts per million 2,350 _. ________________________________ 762 9 520 152 380 900 555 9 911 482 280 1,700 682 8 795 182 510 990 567 3 587 121 460 700 1,505 8 856 337 400 1,400 12 USGS ROCK STANDARDS: MANGANESE NODULE’ SAMPLES USGS—NOD—A—l, USGS—NOD—P—l REFERENCES CITED Abbey, Sydney, 1977, Studies in “standard samples” for use in the general analysis of silicate rocks and minerals, pt. 5, 1977 edition of “usable” values: Canada Geological Survey Paper 77—34, 31 p. Andermann, George, and Kemp, J .W., 1958, Scattered X-rays as internal standards in X-ray emission spectroscopy: Analytical Chemistry, v._30, no. 8, p. 1306—1309. Baedecker, P. A., Rowe, J. J., and Steinnes, E., 1977, Applica- tion of epithermal neutron activation in multielement analysis of silicate rocks employing both coaxial Ge(Li) and low energy photon detector systems: Journal of Radioanalytical Chemistry, v. 40, nos. 1 and 2_. p. 115—146. Bennett, C. A., and Franklin, N. L., 1954, Statistical analysis in chemistry and the chemical industry: New York, John Wiley and Sons, 724 p. Christie, 0. H. J., and Alfsen, K. H., 1977, Data transforma— tion as a means to obtain reliable consensus values for reference materials: Geostandards Newsletter, v. 1, no. 1, p. 47—49. Dixon, W. J., and Massey, F. J., Jr., 1951, Introduction to statistical analysis: New York, McGraw-Hill, 370 p. Ellis, P. J., Copelwitz, I., and Steele, T. W., 1977, Estimation of the mode by the dominant cluster method: Geostand- ards Newsletter, v. 1, no. 2, p. 123—130. Flanagan, F. J., 1967, U.S. Geological Survey silicate rock standards: Geochemica et Cosmochimica Acta, v. 31, no. 3, p. 289—308. 1969, U.S. Geological Survey standards—II. First compilation of data for the new USGS rocks: Geochimica et Cosmochimica Acta, v. 33, no. 1, p. 81—120. 1974, Reference samples for the earth sciences: Geo- chimica et Cosmochimica Acta, v. 38, no. 12, p. 1731— 1744. 1976, Descriptions and analyses of eight new USGS rock standards: U. S. Geological Survey Professional Paper 840, 192 p. 1979, Have trace element data on rocks by spetro— scopic methods improved? Part , Geoanalysis ’78, A symposium on the analysis of geological materials: Canada Geological Survey Paper 79— , [In press]. Glasby, G. P., ed., 1977. Marine manganese deposits: New York, Elsevier, 523 p. Govindaraju, K., and de la Roche, H., 1977, Rapport (1966—- 1976) sur leg elements en traces dans trois roches stand- ards géochimiques du CRPG; Basalte BR et Granites, GA et GH: Geostandards Newsletter, v. 1, no. 1, p. 67—100. Harriss, Robert C., Crocket, J. H., and Stainton, M., 1968, Palladium, iridium, and gold in deep-sea manganese nodules: Geochimica et Cosmochimica Acta, v. 32, no. 10, p. 1049—1056. Mero, J. L., 1965, The mineral resources of the sea: New York, Elsevier, 312 p. Millard, H. T. Jr., 1976, Determination of uranium and thorium in USGS standard rocks by the delayed neutron technique: U.S. Geological Survey Professional Paper 840, p. 61—65. Monget, J. M., Murray, J. W., and Mascle, J., 1976, A world- wide compilation of published multicomponent analyses of ferro-manganese concretions: NSF—IDOE Manganese Nodule Project Technical Report No. 12, August, 1976, 127 p. Myers, A. T., Havens, R. G., and Dunton, P. J., 1961, A spectrochemical method for the semiquantitative analysis of rocks, minerals, and ores: U.S. Geological Survey Bul- letin 1084—1, p. 207—229. Norrish, K., and Hutton, J. T., 1969, An accurate X—ray spec— trographic method for the analysis of a wide range of geological samples: Geochimica et Cosmochimica Acta, v. 33, no. 4, p. 431—453. Pearson, John S., 1975, Ocean floor mining: Park Ridge, N. J., Noyes Data Corp., 201 p. Rantala, R. T. T., and Loring, D. H., 1973, New low-cost Teflon decomposition vessel: Atomic Absorption News- letter, v 12, no. 4, p. 97—99. 1975, Multielement analysis of silicate rocks and marine sediments by atomic absorption spectropho- tometry: Atomic Absorption Newsletter, v. 14, no. 5, p. 117—120. Stevens, S. S., 1946, On the theory of scales of measurement: Science, v. 103, no. 2684, p. 677—680. Sutarno, R., and Faye, G. H., 1975, A measure for assessing certified reference ores and related materials: Talanta, v. 22, no. 8, p. 675—681. TABLES 7—33 14 TABLE 7.—Dete1~minations of several elements in USGS—Nod—A—I by instrumental neutron-activation analysis by P. A. [Determinations in parts per million or in percent, as indicated. d. Baedecker, U.S. Geological Survey 1 USGS ROCK STANDARDS: MANGANESE—NODULE SAMPLES USGS-NOD—A—l, USGS—NOD—P—l f., degrees of freedom; S, significant; NS, not significant; Neg., negative bottle variance obtained, F ratios tested at F0115 or the fractile in parentheses. Analytical method: Baedecker, Rowe and Steinnes (1977)] Bottle Standard deviation Element 30/25 52/1 53/18 Mean (£322) ((511.1122) F ratio Percent Fe __________ 10.75 10.86 11.05 10.88 Neg. 0.15 0.05 NS 10.98 10.89 10.77 Parts per million Ba __________ 1,458 1,451 1,457 1,518 Neg. 120 .72 NS 1,738 1,551 1,454 Ce __________ 676 672 667 668 6.2 7.0 2.58 NS 670 673 651 Co __________ 2,522 2,506 2,550 2,527 Neg. 22.2 .04 NS 2,530 2,544 2,512 Cr __________ 26.4 30.7 19.1 ________________________________ 27.3 <67.7 <65.1 . Eu __________ 4.49 4.54 4.48 4.48 .04 .04 2.74 NS 4.45 4.52 5.39 Gd __________ 28.1 33.2 20.8 26.5 6.3 1.4 43.4 S (0.99) 25.1 32.6 19.4 Hf __________ 6.4 6.6 6.9 6.2 Neg. .75 .14 NS 6.4 5.4 5.5 La __________ 134 133 139 132.5 Neg. 4.6 .16 NS 129 131 129 Lu __________ 2.10 2.10 2.25 2.16 .03 .06 1.42 NS 2.12 2.22 2.17 Nd _________ 86 82 93 85.3 Neg. 4.4 .57 NS 83 85 83 Sb __________ 33.0 33.6 33.0 33.5 Neg. .95 .35 NS 34.6 32.5 34.3 Sc __________ 11.09 11.10 11.32 11.23 Neg. .12 .55 NS 11.36 11.23 11.27 Sm _________ 18.5 21.4 20.8 20.9 Neg. 1.3 .74 NS 21.6 21.8 21.4 Tb __________ 4.54 4.36 5.76 Neg. 1.03 .24 NS 6.00 4.81 3.74 4.87 Th __________ 25.4 25.6 26.4 .56 .19 18.3 NS (0.99) 25.7 25.3 26.6 25.8 Tm _________ .78 1.62 2.29 2 .77 3 .37 9.57 NS 1.52 <1.88 2.30 1.72 U ___________ 5.8 6.7 6.5 Neg. .60 .37 NS 5.5 5.5 5.7 5.95 Yb __________ 16.0 15.9 15.6 Neg. .76 .38 NS 17.1 15.9 17.1 16.3 1 Reston, VA 22092. - d.f.:1 3 d.f = TABLES OF DATA BY ANALYSTS 15 TABLE 8.—Determination of several elements in USGS—Nod—P—I by instrumental neutron-activation analysis by P. A. Baedecker, U.S. Geological Survey1 [Determinations in parts per million or in percent, as indicated. d.f., degrees of freedom; NS, not significant; Neg., negative bottle variance ob- tained. F ratios tested at Fem. Analytical method: Baedecker, Rowe, and Steinnes (1977)] Bottle Standard deviation Element Mean Bottle Error . ' 7/1 ”/19 48/“ (31.22) (d.f.=3) F “no Percent Fe __________ 5.80 5.94 6.03 5.76 Neg. 0.33 0.72 NS 5.76 5.15 5.85 _______ Parts per million Ba __________ 2,512 2,617 2,519 2,498 Neg. 2290 .95 NS 2,766 2,069 ____ 2,498 Ce __________ 278 288 287 289 6.5 9.9 1.85 NS 282 287 311 C0 __________ 1,789 1,813 1,806 1,808 11.4 29.1 1.30 NS 1,802 1,775 1,865 Cr __________ 21.0 <57.5 <56.0 ____ __________________________ 11.3 <57 .9 <84 8 Eu __________ 6.16 6.67 6.59 6.57 .32 .19 6.44 NS 6.18 6.75 7.06 Gd __________ 26.4 24.4 36.1 29.4 1.5 4.5 1.21 NS 25.9 33.6 30.1 Hf __________ 4.3 4.2 4.2 4.3 Neg. .10 .50 NS 4.4 4.4 4.3 La __________ 126 130 127 120 Neg. 213.7 .26 NS 121 103 _. - __ Lu __________ 1.89 1.95 1.86 1.85 Neg. 2.16 .55 NS 1.93 1.63 ____ Nd __________ 106 113 111 112.8 5.4 6.4 2.40 NS 104 117 126 Sb __________ 49.5 51.5 50.1 50.1 Neg. 2.4 .58 NS 50.2 46.4 52.9 Sc __________ 9.54 9.65 9.61 9.47 Neg. .41 .98 NS 9 53 8.67 9 84 Sm _________ 28.3 29.6 31.1 30.4 .64 1.2 1.61 NS 30.9 30.3 32.0 Tb __________ 5.18 5.71 5.23 5.31 Neg. .35 .34 NS 5.65 5.02 5.06 Th __________ 17.3 16.3 16.8 17.0 Neg. .61 .35 NS 16.5 17.2 17.7 Tm _________ 1.75 1.70 1.54 1.77 Neg. .17 .19 NS 1.91 1.82 1.91 U ___________ 2.7 3.4 3.3 3.5 .30 .53 1.64 NS 3.2 4.3 4.1 Yb __________ 14.2 14.8 15.0 13.8 Neg. 2 1.4 .34 NS 14.2 11.9 ____ ’ Reston, VA 22092. 2 d.f.=2. 16 USGS ROCK STANDARDS: MANGANESE-NODULE SAMPLES USGS-NOD—A—l, USGS—NOD-P—l TABLE 9,—Dete7‘minations of several elements and oxides in USGS—Nod—A—I by John Marinenko, U.S. Geological Survey‘ [Determinations in percent. T, total; d.f., degrees of freedom; NS, not significant: Neg., negative bottle variance obtained. F ratios tested at Fo.9a or the fractile indicated in parentheses] Element 01‘ Bottle n Standard deviation F oxide 1 2 3 Mean Mean - ((1135215) ((515.1213) ratio SiOg _________ 3.98 3.92 3.90 3.90 1.82 Neg. 0.06 0.21 NS 3.83 3.91 3.85 A1203 ________ 3.32 2.99 3.43 3.30 1.75 Neg. .17 .62 NS 3.35 3.40 3.33 F6203(T) __-_ 15.57 15.40 15.49 15.53 10.86 .03 .11 1.12 NS 15.49 15.49 15.74 Mg __________ 2.80 2.88 2.85 2.85 2.85 .01 .03 1.49 NS 2.85 2.85 2.88 Ca __________ 11.10 11.38 11.10 11.17 11.17 .10 .11 2.71 NS 11.25 11.20 10.98 - Na __________ .79 .82 .79 .80 .80 .006 .011 1.50 NS .79 .80 .81 K ___________ .50 .51 .58 .50 .50 .02 .04 1.27 NS .46 .46 .50 T10: ________ .54 .53 .53 .53 5 .32 .004 .004 3.00 NS .54 .53 .54 P20; _________ .96 .99 .76 .97 .42 Neg. .15 .20 NS .93 1.06 1.12 Mn _________ 18.35 18.36 18.49 18.40 18.40 .08 .02 20.2 NS (0.99) 18.31 18.41 18.50 Co __________ .328 .334 .323 .326 .326 .002 .003 2.01 NS .325 .326 .323 Cu __________ .112 .112 .112 .112 .112 .0006 .0011 1.50 NS .110 .114 .112 Ni __________ .649 .653 .650 .648 .648 Neg. .0057 .98 NS .639 .644 .654 1 Reston, VA 22092. ‘-‘As percent element. Analytical methodsz—Si02, gravimetry; A1203, fluorimetric analysis; Total Fe and Mn, volumetric analysis: Mg, Ca, Na, K, Co, Cu, and Ni, atomic- absorption spectrometry; and TiO: and P205, spectrophotometry. TABLES OF DATA BY ANALYSTS 17 TABLE 10.——Determinations of several elements and oxides in USGS—Nod—P—I by John Marinenko, US. Geological Survey‘ [Determinations in percent T total‘ d.f., degrees of freedom; NS, not significant; Neg., negative bottle variance obtained. F ratios tested at F605. Esti- mates of the mean. standard deviation, and F ratio Calcuated for the symmetrical data for bottles 2 and 3] Bottle Standard deviation F E13393: °r 1 2 3 Mean Mean 2 ( (13:21:) ( 33g) ratio 810. _________ 14.48 14.45 14.17 14.08 6.64 Neg. 0.34 0.08 Ns 13.82 13.90 14.46 A1203 ________ 3.90 3.30 3.44 3.62 1.97 Neg. .36 .0008 NS 3.94 3.78 4.02 Feeosvr) ____ 8.23 8.36 8.15 8.20 5.73 Neg. .11 .83 NS 8.14 8.15 . 8.10 Mg __________ 2.00 1.98 1.96 1.99 1.98 Neg. .03 .03 NS 1.99 2.02 1.95 Ga __________ 2.20 2.25 2.22 2.20 2.20 .02 .04 1.25 NS 2.21 2.14 2.21 Na __________ 1.62 1.82 1.74 1.70 1.68 Neg. .11 .24 NS 1.64 1.61 1.63 K ___________ .96 1.04 1.03 1.00 .99. Neg. .04 0.0 NS .97 .98 .98 Tio. ________ .51 .52 .52 .51 .31 Neg. .01 0.0 NS .50 .50 .52 P205 _________ .41 .43 .41 .42 .17 Neg. .011 .20 NS .42 .43 .22 Mn _________ 29.49 28.66 29.10 29.06 29.19 Neg. .38 .006 NS 29.42 29.04 29.42 Co __________ .219 .226 .223 .221 .220 Neg. .005 .01 NS , .217 .219 .218 Cu __________ 1.20 1.19 1.18 1.19 1.20 .005 .007 2.00 NS 1.20 1.19 1.21 Ni __________ 1.37 1.41 1.41 1.41 1.40 .007 .011 1.80 NS 1.39 1.42 .37 ‘ Reston, VA 22092. 2 Average of six determinations, as the element, used for best values. Analytical methodsz—Si02, gravimetry; A1209, fluorimetric analysis; Total Fe and Mn, volumetric analysis; Mg, Ca, Na, K. Co, Cu, and Ni, atomic- absorption spectrometry; sndTi02 and P205, spectrophotometry. 18 USGS ROCK STANDARDS: MANGANESE-NODULE SAMPLES USGS—NOD—A—l, USGS—NOD—P—l TABLE 11.—Determinations of U and Th in USGS—Nod—A—I and USGS—Nod—P—I by delayed neutron activation analysis by H. T. Millard, Jr., and C. M. Ellis, U.S. Geological Survey1 [Determinations in parts per million. d.f., degrees of freedom: NS, not significant; Neg., negative bottle variance obtained. F' ratio tested at 170.95. Analytical method described by H. T. Millard, Jr., 1976] Standard deviation F Element Bottle Mean ( Egg?) Max:212 ) ratio USGS—Nod—A—l 17/13 18/01 24/32 Th __________ 24.84 27.30 25.79 27.35 2.71 3.55 2.17 NS 25.37 35.93 24.88 U ___________ 6.84 6.84 6.85 6.86 .02 .08 1.14 NS 6.91 6.97 6.74 USGS—Nod—P—l 13/12 22/29 55/04 Th __________ 17.80 15.65 19.11 17.65 Neg. 1.96 .12 NS 16.47 19.80 17.08 U ___________ 4.18 4.36 4.09 ' 4.28 Neg. .14 .30 NS 4.36 4.31 4.37 ‘ Stop 424, Box 25046 DFC, Lakewood, CO 80225. TABLE 12.—Determinations of several elements in USGS—Nocl—A—I by the National Physical Research Laboratory ‘ [Determinations in percent. d.f., degrees of freedom; NS, not significant; Neg., negative bottle variance obtained. F ratio tested at Fans] Bottle Standard deviation F Element 22/1 51 /12 63/24 Mean ( fgtgg, ( 1&2?) ratio Al __________ 1.8 2.0 1.9 1.66 Neg. 0.33 0.20 NS 1.3 1.5 1.5 Fe .......... 10 0 10.3 10.3 9.7 Neg. .74 .17 NS 9.1 8.9 9.6 K ___________ .13 .18 .19 .17 Neg. .03 .38 NS .18 .18 .14 Mn __________ 13.3 14.6 14.0 13.7 Neg. .70 .57 NS 13.4 12.9 14 2 Ba __________ .32 .36 .23 .27 Neg. .08 .09 NS .21 .22 .29 CO __________ .30 .32 .32 .31 Neg. .01 .11 NS 31 .30 30 Cu __________ .11 .11 .11 .11 .000 .004 1.0 NS .12 .11 .11 Mo __________ .034 .038 .039 .036 Neg. .003 .02 NS .039 .034 .034 N1 __________ .64 .64 .64 .64 .007 .004 7.0 NS .64 .63 .65 Pb __________ .10 .094 .094 .095 Neg. .004 .08 NS .091 .094 .095 Sr __________ .19 .20 .21 .18 Neg. .03 .54 NS .14 .16 .18 Zn __________ .057 .061 .059 .059 Neg. .0009 3.8 NS .058 .059 .059 1 CSIR, P.O. Box 395, Pretoria 0001, South Africa. Analytical method:—A mixture of 20 mL HF and 10 mL concentrated HCl was added to l-g portions of the samples and the mixtures taken to dry- ness on a. hotplate. This procedure was repeated. Twenty mL of 50 percent 1101 was added to the residue and evaporated to a volume of 5 mL. These were transferred to a 25-mL volumetric flask and made to volume with distilled water. Aliquots of these solutions were diluted to suitable concentra- tions for the determinations of the elements. These determinations were made using a Techtron AA51 atomic-absorption instrument with the recom- mended analytical conditions. 1 Any trade names in this publication are used for descriptive purposes only and do not constitute endorsement by the U.S. Geological Survey. TABLES OF DATA BY ANALYSTS 19 TABLE 13,—Determinations of several elements in USGS—Nod—P—I by the National Physical Research laboratory 1 [Determinations in percent. d.f., degrees of freedom; NS, not significant; Neg., negative bottle variance obtained. F ratio tested at F035] Bottle Standard deviation F Element 38/28 37/2 44/5 me“ ( £3213) ( £121; ) ratio A] __________ 1.5 1.9 1.9 1.8 Neg‘. 0.21 0.27 NS 2.0 1.8 1.9 Fe __________ 5.2 5.2 5.4 5.2 Neg . .32 .64 NS 5.7 5.2 4.8 K ___________ .29 .29 .26 .28 Neg. .04 .52 NS .23 .28 .35 Mn __________ 25.9 25.4 26.3 25.5 Neg. .94 .12 NS 25.2 26.0 24 2 Ba __________ .67 .58 .70 .67 .04 .03 4.98 NS .69 .65 .73 C0 __________ .22 .21 .24 .22 .004 .009 1.40 NS .22 .22 .22 Cu __________ 1.2 1.2 1.3 1.2 .000 .04 1.00 NS 1.2 1.2 1.2 M0 __________ .068 .063 .063 .063 .004 .003 4.50 NS .068 .058 .058 Ni __________ 1.4 1.4 1.4 1.4 .000 .04 1.00 NS 1.5 1.4 1.4 Pb __________ .052 .051 .054 .052 Neg . .002 .71 NS .053 .053 .051 Sr __________ .099 .11 .11 .108 .000 .004 1.00 NS .11 .11 .11 Zn __________ .17 .17 .15 .16 .000 .01 (N0 test) .15 .15 17 1 CSIR, P.O. Box 395, Pretoris 0001, South Africa. Analytical method:—A mixture of 20 mL HF and 10 mL concentrated HCl was added to l-g portions of the samples and the mixtures taken to dry- ness on a hotplate. This procedure was repeated. Twenty mL of 50 percent H01 was added to the residue and evaporated to a volume of 5 mL. These were transferred to a 25-mL volumetric flask and made to volume with distilled water. Aliquots of these solutions were diluted to suitable concentra- tions for the determinations of the elements. These determinations were made using a Techtron AA5 atomic-absorption instrument with the recom- mended snalytical conditions. 20 USGS ROCK STANDARDS: MANGANESE-NODULE SAMPLES USGS—NOD—A—l, USGS—NOD—P—l TABLE 14.—Determinations of several elements in USGS—Nod—A—I by S. E. Calvert, Institute of Oceanographic Sciences1 [Determinations in percent or parts per million, as indicated. d.f., degreea 0;. fre]edom; NS, not significant; Neg., negative variance obtained. F ratio tested at 0.95 Element Bottle Standard deviation F or oxide 1 2 3 Mean ($323) ( E; 1:2) ratio Percent Si ___________ 1.45 1.20 1.35 1.42 Neg. 0.16 0.16 NS 1.44 1.54 1.56 Al __________ 2.32 2.18 2.11 2.27 .04 .10 1.28 NS 2.41 2.25 2.34 Fe __________ 11.24 10.78 10.86 10.98 Neg. .19 .45 NS 10.90 10.99 11.12 Ca __________ 11.40 11.35 11.32 11.42 .07 .13 1.64 NS 11.70 11.32 11.41 Mg _________ 3.27 3.11 3.18 3.20 .10 .05 9.12 NS 3.36 3.14 3.11 K ___________ .46 .44 .51 .48 .02 .02 2.17 NS . 51 .47 .50 Ti __________ .29 .29 .29 .29 Neg. .006 .5 NS .30 .30 .29 P ___________ .57 .58 .60 .59 Neg. .02 .1 NS .62 .59 .58 Mn _________ 18.89 18.71 18.56 18.64 .12 .12 3.04 NS 18.65 18.65 18.39 CO: _________ 11.66 11.80 11.44 11.64 Neg. .15 .35 NS 11.70 11.55 11.70 Co __________ .44 .37 .41 .39 .02 .02 3.08 NS .39 .34 .39 Cu __________ .18 .19 .18 .18 Neg. .006 .5 NS .18 .18 .19 Ni __________ l .60 .57 .57 .57 .01 .02 1.44 NS .57 .52 57 Parts per million As __________ 315 280 285 298 Neg. 14.4 .74 NS 300 300 310 Ba __________ 1,695 1,625 1,665 1,671 26 23 3.70 NS 1,680 1,645 1,715 M0 __________ 460 460 465 460 2.5 5.0 . 1.5 NS 450 465 460 Pb __________ 1,310 1,315 1,325 1,323 13 14 2.66 NS 1,315 1,315 1,360 Rb __________ 10 10 10 10 ____________ (N0 test) 10' 10 10 Sr __________ 1,760 1,715 1,775 1,728 Neg. 41 .09 NS 1,695 1,725 1,700 Y ___________ 115 110 115 115 1.4 2.9 1.5 NS 115 115 120 Zn __________ 880 865 865 870 2.9 5.8 1.5 NS 870 875 885 Zr __________ 320 310 320 317 Neg. 5.8 .5 NS 310 320 320 1 Brook Rd., Wormley, Godalming, Surrey, GU8 5UB, England. Analytical methods:—(1) Major elements Si to Mn, plus Co, Cu, and Ni. were determined by X-ray fluorescence on samples fused with Li28401 and LagOn; the method follows that of Norrish and Hutton (1969); (2) trace elements As to Z1- were determined by X-ray fluorescence on powders pressed into discs at 15 tons; the method follows that of Anderman and Kemp (1958); (3) C02 was determined gravimetrically after treating the sample with hot 10 percent HCl. TABLES OF DATA BY ANALYSTS 21 TABLE 15.—Determinations of several elements in USGS—Nod—P—I by S. E. Calvert, Institute of Oceanographic Sciences‘ [Determinations in percent or parts per million, as indicated. d.f., degrees of freedom: NS, not significant; Neg., negative variance obtained. F ratio tested at F035 or the fractile indicated in parentheses] Element Bottle Standard deviation F or oxide 1 2 3 M63“ ( flit—:13) ( £123 ratio Percent Si __________ 6.67 6.62 6.74 6.65 0.04 0.06 2.20 NS 6.54 6.62 6.69 A1 __________ 2.51 2.51 2.58 2.59 Neg. .11 .65 NS 2.53 2.78 2.65 Fe __________ 4.80 4.63 4.83 4.76 .11 .05 11.0 NS (0.975) 4.90 4.62 4.76 Ca- __________ 2,18 2.15 2.20 2.16 Neg. .04 .04 NS 2.12 2.17 2.12 Mg _________ 2.00 2.01 2.17 2.08 Neg. .11 .06 NS 2.12 2.19 2.00 K ___________ 1.13 1.15 1.10 1.14 .01 .02 1.48 NS 1 14 1.18 1 15 Ti __________ .30 .30 .30 .30 ____________ (No test) .30 .30 .30 P ___________ .22 .21 .21 .21 Neg. .006 .5 NS .21 .22 .21 Mn _________ 29.66 29.15 29.65 29.06 Neg. .61 .16 NS 28.75 28.59 28 59 CO, _________ 1.21 1.91 1.14 1.39 .46 .06 2 102 1.06 1.94 1.10 Co __________ .30 .28 .28 .28 .008 .004 9.0 NS .29 .28 .28 Cu __________ 1.02 1.11 1.12 1.04 Neg. .10 .01 NS 1.07 .95 .95 Ni __________ 1.26 ‘ 1.40 1.34 1.28 Neg. .14 .13 NS 1.38 1.11 1.17 Parts per million As __________ 40 50 25 39 9.6 4.6 9.8 NS (0.975) 35 50 35 Ba __________ 3,405 3,500 3,460 3,453 Neg. 37 .60 NS 3,455 3,425 3,475 Mo __________ 820 825 835 823 Neg. 7.6 .50 NS 825 815 820 Pb __________ 700 700 690 715 Neg. 27 .14 NS 740 740 725 Rb __________ 20 20 20 21 .000 2.0 1.0 NS 20 25 20 Sr __________ 755 765 760 751 Neg. 12.2 .11 NS 745 745 740 Y ___________ 90 90 85 89 .000 2.0 1.0 NS 90 90 90 Zr. __________ 1,975 1,985 1,990 1,998 Neg. 20 .12 NS 2,010 2,010 2,015 Zr __________ 280 285 280 280 Neg. 4.1 .0 NS 280 275 280 1 Brook Rd., Wormley, Godalming, Surrey, GU8 BUB, England. 2 F' ratio is extremely significant. Analytical methoda:-—(1) Major elements Si to Mn, plus Co. Cu, and Ni, were determined by X-ray fluorescence on samples fused with Li2B401 and La203; the method follows that of Norrish and Hutton (1969): (2) trace elements As to Zr were determined by X-ray fluorescence on powders pressed into discs at 15Ht81ns; the method follows that of Anderman and Kemp (1958): (3) CO: was determined gravimetrically after treating the sample with at 10 percent . 22 USGS ROCK STANDARDS: MANGANESE-NODULE SAMPLES USGS—NOD—A—l, USGS—NOD—P—l TABLE 16.—Determinations of several elements in USGS—Nod—A—I by R. T. T. Rantala, Bedford Institute of Oceanography ‘ [Determinations in percent or in parts per million, as indicated. d.f., degrees of freedom; NS, not significant; Neg., negative bottle variance obtained. F ratio tested at Foes or the fractile indicated in parentheses] Bottle Standard deviation F Element 5/29 18/15 28/11 Me“ ( £31313) (dfifgg) ratio ' Percent Si __________ 1.98 1.95 1.98 2.005 Neg. 0.09 0.6 NS 2.05 2.15 1.92 Al __________ 2.04 2.11 2.09 2.060 Neg. .04 .43 NS 2.04 2.02 2.06 . Fe __________ 11.20 10.80 11.00 11.08 .13 .26 1.49 NS 11.00 10.90 11.60 Mg _________ 2.80 2.84 2.79 2.803 .01 .02 1.75 NS 2.80 2.80 2.79 Ca __________ 11.00 11.00 11.00 10.97 Neg. .06 .5 NS 10.90 10.90 11 00 Na __________ .76 .80 .75 .767 .01 .01 3.1 NS .7 6 .77 .7 6 / K ___________ .51 .52 .53 .518 .012 .004 19 NS (0.99) .50 .52 .53 Ti __________ .27 .27 .26 .275 Neg. .012 .33 NS .28 .29 .28 Mn _________ 17.60 18.10 17.90 17.80 Neg. .24 .26 NS 17 90 17.70 17 60 Parts per million Ba __________ 1,700 1,580 1,640 1,668 Neg. 55.5 0.91 NS 1,680 1,670 1,740 ' Be __________ 5.5 5.8 5.3 5.57 .20 .08 13.0 NS (0.975) 5.5 5.8 5.5 Go __________ 3,100 3,090 3,100 3,128 Neg. 48 .12 NS 3,170 3,180 3,130 Cr __________ 25 25 2O 23 Neg. 2.9 .5 NS 20 25 25 Cu __________ 1,050 1,060 1,040 1,052 Neg. 9.1 .2 NS 1,050 1,050 1,060 Li __________ 77 76 77 76.3 Neg. .58 .5 NS 76 76 76 Mo __________ 460 443 465 457.3 Neg. 13.1 .82 NS 440 468 468 Ni __________ 6,300 6,300 6,200 6,300 29 58 .5 NS 6,400 6,300 6,300 Pb __________ 798 778 778 792.8 3.9 17.4 1.10 NS 805 820 778 Sr __________ 1,680 1,650 1,660 1,660 Neg. 28.9 .78 NS 1,650 1,700 1,620 V ___________ 578 580 590 586.3 Neg. 12.9 .35 NS 590 605 575 Zn __________ 561 565 553 558.7 3.6 6.0 1.71 NS 548 565 560 1 Dartmouth, N.S., Canada, BZY 4A2. Analytical method.—Samples were decomposed by acid in teflon bombs as described by Rantala and Loring (1973); the elements were determined by flame atomic-absorption spectrometry as described by Rantala and Loring (1975), with slight variations due to dilutions used. TABLES OF DATA BY ANALYSTS 23 TABLE 17.—Dete’rminations of several elements in USGS-Nod—P—I by R. T. T. Rantala, Bedford Institute of Oceanography 1 [Determinations in percent or in parts per million, as indicated. d.f., degrees of freedom; NS, not significant; Neg., negative bottle variance obtained. F ratio tested at F035 or the fractile indicated in parentheses] Bottle Jew—Lillie“— F Element 29/23 52/24 57/10 me“ (fit—292) (5472?» "t“ Percent Si __________ 6.85 6.90 6.85 6.968 Neg. 0.22 0_72 NS 6.88 6.95 7.38 Al __________ 2.42 2.37 2.44 2.407 Neg. .04 .03 NS 2.38 2.45 2.38 Fe __________ 5.76 5.76 5.94 5.813 .03 .08 1.27 NS 5.74 5.88 5.80 Mg _________ 1.96 1.97 1.97 1.975 Neg. .01 .33 NS 1.98 1.99 1.98 Ca __________ 2.16 2.16 2.18 2.157 .008 .018 1.4 NS 2.16 2.12 2.16 Na __________ 1.63 1.62 1.62 1.630 Neg. .013 .90 NS 1.64 1.65 1.62 K ___________ 1.04 1.05 1.04 1.040 .005 .010 1.5 NS 1.05 1.04 1.02 T1 __________ .28 .26 .28 .277 .010 .006 6.5 NS .29 .27 .28 Mn _________ 28.90 29.20 29.30 29.17 .22 .08 16.0 NS (0.975) 28.90 29.40 29.30 Parts per million Ba __________ 2,710 2,940 2,800 2,862 Neg. 103 0.38 NS 2,930 2,880 2,910 Be __________ 2.8 2.8 2.8 2.8 .06 .11 1.5 NS 2.6 3.0 2.8 Co __________ 2,240 2,270 2,290 2,280 18 30 1.72 NS 2,260 2,340 2,280 Cr __________ 20 20 20 20 __________________________ 20 20 20 Cu __________ 11,300 11,400 11,500 11,370 64 58 3.50 NS 11,300 11,300 11,400 Li __________ 142 143 141 141.8 Neg. 1.5 .08 NS 142 140 143 Mo __________ 795 803 785 801.7 Neg. 12.9 .32 NS 800 812 815 Ni __________ 13,000 13,200 13,400 13,280 Neg. 220 .24 NS 13,400 13,500 13,200 Pb __________ 428 430 442 436.2 12 10 4.10 NS 415 442 460 Sr __________ 618 628 665 638.2 10.4 15.8 1.86 NS 625 655 638 V ___________ 483 478 470 479.8 8.6 5.7 5.46 NS 490 490 468 Zn __________ 1,460 1,490 1,470 1,467 Neg. 12.9 .70 NS 1,460 1,460 1,460 1 Dartmouth, N.S., Canada, B2Y 4A2. Analytical method:—Samples were decomposed by acid in teflon bombs as described by Rentals and Loring (1973): the elements were determined by flame atomic-absorption spectrometry, described by Rantala and Loring (1975), with slight variations due to dilutions used. 24 USGS ROCK STANDARDS: MANGANESE-NODULE SAMPLES USGS—NOD—A—l, USGS—NOD—P—l TABLE 18.——Determ7‘nations of several elements in USGS—Nod—A—Z by the National Institute for M etallu'rgy1 [Determinations in percent, or in parts per million, as indicated. d.f., degrees of freedom; NS, not significant; Neg., negative bottle variance ob- tained. F ratio tested at F095 or the fractile indicated in parentheses. Si through P reported as the oxide but converted to the element] Bottle Standard deviation F Element 9/30 12/3 36/17 Me” ( £3262) ( (11:33?” ratio Percent Si __________ 1.64 1.56 1.71 1.63 0.04 0.04 2.7 NS 1.68 1.58 1.61 Al __________ 1.85 1.87 1.86 1.86 .02 .08 1.13 NS 1.95 1.72 1.94 Fe __________ 10.37 10.25 10.32 10.29 .04 .03 3.39 NS 10.31 10.25 10.26 Mg _________ 2.77 2.73 2.72 2.74 .025 .009 16.2 NS (0.99) 2.76 2.71 2.72 Ca __________ 11.33 11.28 11.30 11.30 .008 .062 1.03 NS 11.31 11.40 11.21 K ___________ .35 .38 .40 .40 Neg. .03 .62 NS .42 .40 .44 T1 __________ .32 .32 .32 .32 .008 .015 1.50 NS .35 .30 .31 Mn _________ 18.72 18.62 18.61 18.63 Neg. .04 .91 NS 18.61 18.61 18.61 P ___________ .64 .58 .62 .60 .02 .02 2.28 NS .59 .58 .62 CO __________ .278 .285 .278 .281 .002 .002 1.77 NS .282 .283 282 Cu __________ .108 .107 .108 .107 Neg. .0009 .20 NS .106 .107 .107 Ni __________ .624 .639 .623 .625 Neg. .008 .78 NS .616 .621 .625 Parts per million Mo _________ 561 535 562 567 19 30 1.80 NS 561 549 635 Zn __________ 496 579 619 574 28 34 2.32 NS 578 569 603 ‘Private Bag X3015, Randburg, 2125, South Africa. Analytical methods:— 1. MnO, 0.75 g of Nod—P and 1 g of Nod—A were dissolved in HCl and HNOx and taken to fumes with H2S04. After cooling, water was added and the solutions diluted in a volumetric flask. Mn was determined on an aliquot by potentiometric titration with KMn04. 2. SiO:, Al20::, Fe:0::, M20, CaO, K20, TiOz, MnO, and P205 were determined by X-ray fluorescence on a disc made by fusing 0.5—0.6-g sampla with 7.5 g of a flux of 10 percent Li23107, 51 percent N82340:, and 39 percent Na:CO::. 3. For Go, Cu, Mo, Ni. and Zn, 0.4-g samples were dissolved with 10 mL HNOn, 20 mL HF, and 3 mL H0101 in platinum dishes. Solutions were fumed to incipient dryness and 3 mL HCl added. Solutions were warmed and 3—4 drops of H202 added to oxidize Mn. The resulting clear solu- tions were transferred to volumetric flasks and diluted to the mark. Appropriate dilutions of these solutions were measured by atomic-absorption spectrometry. 4. The Canadian sample, CSRMisU—l, was used as a control sample; results are listed as follows: National Institute for Certified Metallurgy Value Co _______ ppm__ 568, 553, 581, 569 630 Cu _____ percent-. 0.845, 0.845, 0.846, 0.838 0.87 Mo _______ ppm__ <40, <40, <40, <40 ..... Ni _____ percent“ 1.46, 1.46, 1.45, 1.46 1.51 Zn _______ ppm__ 319, 311, 304. 312 294 TABLES OF DATA BY ANALYSTS 25 TABLE 19.—Determinations of several elements in USGS—Nod—P—l by the National Institute for Metallurgy 1 [Determinations in percent, or in parts per million, as indicated. d.f., degrees of freedom; NS, not significant; Neg., negative bottle variance ob- tained. F ratios tested at 170.95 or the fractile indicated in parentheses. Si through P reported as the oxide but converted to the element] Bottle Standard deviation F Element 18/6 24/30 58/11 M9“ ( (11.332192) (55:15) ratio Percent Si ___________ 6.30 6.37 6.61 6.36 0.06 0.14 1.34 NS 6.17 6.41 6.30 Al __________ 2.55 2.61 2.66 2.56 Neg. .08 .83 NS 2.44 2.57 2.50 Fe __________ 5.60 5.60 5.49 5.52 .075 .06 4.09 NS 5.56 5.54 5.36 Mg _________ 1.88 1.77 1.82 1.80 Neg. .06 .14 NS 1.75 1.82 1.74 Ca __________ 2.21 2.20 2.18 2.20 .019 .009 9.8 NS (0.975) 2.21 2.22 2.17 K ___________ .96 .90 .95 .93 Neg. .04 .50 NS .94 .95 .88 Ti __________ .31 .31 .29 .29 .006 .024 1.15 NS .26 .31 .26 Mn _________ 29.96 29.96 29.91 29.93 .02 .02 2.10 NS 29.91 29.94 29 90 P ___________ .22 .21 .20 .20 .003 .010 1.16 NS .20 .20 .19 Co __________ .200 .203 .201 .201 Neg. .0019 .48 NS .202 .199 .200 Cu __________ 1.16 1.16 1.17 1.16 .003 .006 1.5 NS 1.16 1.15 1.16 Ni __________ 1.31 1.33 1.32 1.32 .003 .006 1.50 NS 1.32 1.32 1.32 Zn __________ .148 .149 .148 .151 Neg. .0052 .73 NS .147 .157 .158 Parts per million Mo __________ 990 980 970 982 10.4 7.1 5.33 NS 1,000 970 980 1 Private Bag X3015, Randburg, 2125, South Africa. Analytical methods:— 1. For MnO, 0.75 g of Nod—P and 1 g of Nod—A were dissolved in H0] and HNOn and taken to fumes with H2804. After cooling, water was added and the solutions diluted in a volumetric flask. Mn was determined on an aliquot by potentiometric titration with KMnOi. 2. SiO-g, A1203, Fe20::, MgO, CaO, K20, Ti02, MnO, and P205 were determined by X-ray fluorescence on a disc made by fusing 0.5—0.6-g samples with 7.5 g of a flux of 10 percent LizBiO-r, 51 percent Na2B40-1, and 39 percent Na2C03. 3. For Co, Cu, Mo, Ni, and Zn. 0.4 g samples were dissolved With 10 mL HNOa 20 mL HF, and 3 mL H0104 in platinum dishes. Solutions were fumed to incipient dryness and 3 mL HCl added. Solutions were warmed and 3-4 drops of H202 added to oxidize Mn. The resulting clear solutions were transferred to volumetric flasks and diluted to the mark. Appropriate dilutions of these solutions were measured by atomic-absorption spectro- metry. 4. The Canadian sample, CSRM-SU—l, was used as a control sample; results are listed as follows: National Institute for Certified Metallurgy Value Co _______ ppm__ 568, 553, 581, 569 630 Cu _____ percent-_ 0.845, 0.845, 0.846, 0.838 0.87 Mo ....... ppm-- <40, <40, <40, <40 _____ Ni _____ percent.. 1.46, 1.46, 1.45, 1.46 1.51 Zn _______ ppm" 319, 311, 304, 312 294 26 USGS ROCK STANDARDS: MANGANESE-NODULE SAMPLES USGS—NOD—A—l, USGS—NOD—P—l TABLE 20.—Determinations of several elements in USGS—Nod—A—I by the Institute of Geological Sciences 1 [Determinations in percent. '1‘, total; d.f., degrees of freedom; NS, not significant; Neg, negative bottle variance obtained. F ratio tested at F035. Analysts: N. Cogger, chemical analysis, and Linda Ault, spectrographic analysis] Standard deviation El t M th d2 Rome M F W“ . ° we 13/24 49/29 (32:12. (Egg. Si _________ GR _________ 1.72 1.71 1.72 1.73 Neg. 0.03 0.72 NS 1.70 1.76 1.77 Fe (T) _____ SA __________ 10.92 10.88 10.91 10.91 Neg. .03 .57 NS 10.90 10.93 10.96 Mg ________ AA _________ 2.90 2.92 2.95 2.93 .02 .02 1.97 NS 2.90 2.97 2.92 Ca _________ GR _________ 11.02 11.03 11.05 11.00 Neg. .062 .31 NS 11.02 11.00 10.90 Ca _________ AA _________ 11.08 11.06 11.15 11.07 Neg. .079 .46 NS 10.98 11.15 11.01 K __________ FE _________ .46 .45 .46 .46 .003 .006 1.5 NS 47 .46 .46 Mn(T) _____ PT __________ 18.50 18.51 18.54 18.51 .009 .018 1.47 NS 18.51 18.48 18.51 P __________ SA __________ .52 .53 .52 .53 Neg. .006 .50 NS .53 .53 .53 Ba _________ ES _________ .256 .260 .204 .232 .022 .014 5.86 NS .230 .237 204 Co _________ AA _________ .312 .315 312 .313 Neg. .0013 .70 NS .312 .312 313 Co _________ SA __________ .322 .321 .322 .322 .0008 .0004 9.00 NS .322 .320 .322 Cu _________ AA _________ 107 .108 .108 .109 Neg. .003 .17 NS 112 .109 .112 Mo ________ ES __________ .0527 .0546 .0487 .0514 .0015 .0020 2.04 NS .0534 .0497 .0495 Ni _________ SA __________ .635 .635 .633 .637 Neg. .004 .15 NS .642 .638 .640 Pb _________ AA _________ .085 .082 .083 .084 .002 .001 3.77 NS .087 .082 .086 Sr _________ AA _________ .18 .18 .17 .177 Neg. .0058 .50 NS .17 .18 .18 T1 _________ ES __________ .0045 .0073 .0073 .00608 Neg. .0020 .09 NS .0077 .0040 .0057 V __________ ES __________ .0964 .1013 .0848 .0916 .0047 .0055 2.46 NS .0951 .0878 .0843 Zn _________ AA _________ .061 .061 061 .062 Neg. .0015 .54 NS .063 .061 .064 1 64/78 Gray’s Inn Rd., London, WClX 8NG. England. 21‘1nalya‘ieall methods:—AA, atomic-absorption spectrometry: ES, emission spectrography; FE, flame- potentiometrie titrimeti‘y; and SA, solution absorptiomeh'y. emission spectrophotometry: GR, gravimetry: PT, TABLES OF DATA BY ANALYSTS 27 TABLE 21.—Determinations of several elements in USGS—NodPP-I by the Institute of Geological Sciences ' [Determinations in percent. T, total: d.f., degrees of freedom: NS, not significant: Neg., negative bottle variance obtained; F ratio tested at Fins. Analysts: N. Cogger, chemical analysis, and Linda Ault, spectrographic analysis] Botle Standard deviation F Element Method 2 25/31 57/3 58/27 Menu (3312; ) ($151215) ratio Si _________ GR _________ 6.36 6.36 6.44 6.38 0.02 0.02 2.40 NS 6.37 6.39 6.39 Fe (T) _____ SA _________ 6.06 6.05 6.03 6.05 .02 .02 2.40 NS 6.04 6.09 6.03 Mg ________ AA _________ 2.01 2.01 1.99 2.00 Neg. .03 .45 NS 1.97 2.00 2.04 Ca _________ AA _________ 2.20 2.26 2.21 2.20 .02 .04 1.62 NS 2.14 2.21 2.16 K __________ FE _________ 1.00 1.10 1.04 1.05 Neg. .039 .63 NS 1.08 1.05 1.03 Mn(T) _____ PT _________ 29.80 29.95 29.87 29.86 Neg. .065 .46 NS 29.91 29.85 29 81 P __________ SA __________ .20 .21 .20 .202 ~ 0 .004 1.00 NS .20 .20 .20 Ba. _________ ES __________ .397 .377 .383 .374 Neg. .025 .15 NS .336 .373 .377 Co _________ AA _________ .229 .229 .226 .227 .0009 .0013 1.90 NS .228 .226 .226 C0 _________ SA _________ .231 .231 .231 .231 .001 .002 1.48 NS .236 .229 .229 Cu _________ AA _________ 1.15 1.17 1.13 1.15 .006 .011 1.50 NS 1.15 1.15 1.15 Mo ________ ES _________ .0706 .0678 .0631 .0678 .0026 .0015 7.41 NS .0700 .0691 .0664 Ni _________ SA __________ 1.34 1.36 1.34 1.35 .01 .00 Indet. 1.34 1.36 1.34 ' Pb _________ AA _________ .046 .048 .048 .047 .0004 .0009 1.40 NS 046 .047 046 Sr _________ AA ___________________________ .09 ______________________ Tl _________ E S _________ .0177 .0161 .0183 .0154 Neg. .0033 .08 NS .0140 .0155 .0111 ‘ V __________ ES _________ .0588 .0556 .0557 .0548 Neg. .0027 .48 NS .0539 .0529 .0520 Zn _________ AA _________ .164 .167 .164 .166 .0009 .0013 1.90 NS .165 167 167 1 64/78 Gray's Inn Rd., London, WClX SNG, England. ”Analytical methods:—AA, atomic-absorption spectrometry: ES, emission spectrography; FE, flame-emission spectrophotometry; GR, gravimetry, PT, potentiometric titrimetry: and SA. solution absorptiometry. TABLE 22.—Det.erminations of several elements by atomic-absorption spectrometry in USGS—Nod—A—I and USGS—Nod—P—I by David Piper, U.S. Geological Survey 1 [Determinations in percent. Data are averages of two determinations] USGS—Nod—A—l USG S—Nod—P—l Element Bottle Bottle Average Average 35/11 45/21 45/24 2/15 33/11 44/10 F‘e __________ 10.6 10.5 10.7 10.6 6.49 6.31 6.54 6.45 Mn _________ 17.1 16.9 16.8 16.9 27.6 27.1 27.3 27.3 C0 __________ .30 .30 - .31 .30 .22 .22 .22 .22 Cu __________ .088 .087 .088 .088 1.11 1.11 1.11 1.11 Ni __________ .61 .61 .61 .61 1.28 1.25 1.25 1.26 Zn __________ .047 .044 .047 .046 .14 .14 .14 .14 ‘ Stop 97, 345 Middlefield Rd., Menlo Park, CA 94025. 28 USGS ROCK STANDARDS: MANGANESE—NODULE SAMPLES USGS—NOD—A—l, USGS—NOD—P—l TABLE 23.—Determinations of several elements by flame atomic-absorption spectrometry in USGS—Nod—A—I and USGS—Nod— P—1 by Loekhead Ocean Laboratory ‘ [Determinations in percent] USGS—Nod—A-l USGS—Nod—P—l Element Bottle Bottle Average Average 4/27 28/21 32/6 26/19 50/25 51/26 Fe __________ 10.4 10.3 10.0 10.2 5.13 5.26 4.74 5.04 Mn _________ 17.6 17.0 17.3 17.3 27.2 26.9 29.4 27.8 Co __________ .28 .28 .29 .28 .20 .20 .20 .20 Cu __________ .11 .11 .11 .11 1 12 1.14 1.12 1.13 Ni __________ .58 .59 .59 .59 1:24 1.26 1.21 1.24 1 3380 North Harbor Dr., San Diego, CA 92101. TABLE 24,—Complete analyses of USGS—Nod—A—I by M. Saunders, Grant Institute of Geology 1 [Determinations in percent] Oxide or Bottle Average as 2 element 21/21 28/13 54/28 Oxide Element Methoa 8102 ____________ 3.91 3.96 3.90 3.92 1.83 C A1203 ____________ 4.34 4.36 4.35 4.35 3.26 A F6203 ___________ 15.82 15.75 15.72 15.76 11.02 C MgO ____________ 4.76 4.75 4.71 4.74 2.86 A CaO ____________ 15.70 15.68 15.69 15.69 11.22 G NagO ____________ 1.09 1.12 1.12 1.11 .82 F K20 _____________ .55 .55 .56 .55 .46 F T103 ____________ .47 .46 .47 .47 .28 C P205 ____________ 1.23 1.22 1.21 1.22 .53 C MnO ____________ 23.81 23.97 23.97 23.92 18.51 T C02 _____________ 11.59 11.56 11.59 11.61 _____ G C00 _____________ .43 .44 .45 .44 .34 A CuO ____________ .139 .138 .140 .139 .111 A N10 _____________ .90 .91 .88 .90 .71 A Excess 0 ________ 5.31 5.30 5.29 _____ 5.30 T H20+ ________________ ____ ____ ~7.9 _____ G BaO ____________ .19 .20 .20 .20 .18 A Cl ______________ .54 .54 .54 _____ .54 G M003 ____________ .062 .061 .060 .061 .041 A PhD ____________ .100 .104 .107 .104 .096 A SI‘O _____________ .203 .208 .197 .203 .172 A V205 ____________ .108 .110 .110 .109 .061 A Z110 ____________ .082 .080 .080 .081 .065 A Subtotal -_- 99.23 99.47 99.24 ________________ Less O=CI _______ .12 .12 .12 _________________ Total ______ 99.11 99.35 99.12 ‘University of Edinburgh, West Mains Rd., Edinburgh EH9 3JW, Scotland. 2Analytical methods:—-A, atomic-absorption spectrometry; C, colorimetry; F, flame photometry; G, gravimetry; and T, titrimetry. Notes:—Both dried nodule samples rapidly absorbed moisture during weighing. When exposed to the atmosphere overnight. NodiA—l absorbed between 1] and 13 percent H20 and Nod—P—l, between 8 and 10 percent H20. Incon- sistent data were obtained for H20+ by two methods, andthe results are reported as an approximate value. TABLES OF DATA BY ANALYSTS TABLE 25.—Complete analyses of USGS—Nod-P—I by M. Saunders, Grant Institute of Geology 1 [Determinations in percent] . Bottle Average as 0x1de or Method 2 element 31/2 1/5 47/15 Oxide Element 14.61 14.60 14.63 14.61 6.82 G 5.12 5.19 5.12 5.14 3.85 A 8.50 8.48 8.41 8.46 5.91 C 3.29 3.32 3.27 3.29 1.98 A 2.91 2.87 2.91 2.90 2.07 A 2.21 2.26 2.23 2.23 1.65 F 1.23 1.21 1.21 1.22 1.01 F .48 .47 .46 .47 .28 C .48 .48 , .48 .48 .21 C 38.64 38.67 38.65 38.65 29.92 T .69 .77 .82 .76 _____ G .32 .34 .34 .33 .26 A 1.71 1.70 1.66 1.69 1.35 A 1.98 2.01 1.99 1.99 1.56 A 8.42 8.40 8.42 _____ 8.41 T ____ ____ ___- ~8.2 ___- G .33 .32 .32 .32 .29 A .15 .14 .14 _____ .14 C .113 .113 .108 .111 .074 A .058 .060 .057 .058 .054 A .091 .086 .090 .089 .075 A .092 .094 .095 .094 .053 A .208 .210 .213 .210 .169 A Subtotal ___ 99.83 99.99 99.82 ________________ Less 0=C1 ______ .03 .03 .03 ________________ Total ______ 99.80 99.96 99.79 ‘University of Edinburgh, West Mains Rd., Edinburgh EH9 3JW, Scotland. ZAnalytical methods:-—A, atomic-absorption spectrometry; C, colorimetry; F, flame photometry: G, gravimetry; and T, titrimetry. Nolan—Both dried nodule samples rapidly absorbed moisture during weighing. When exposed to the atmosphere overnight, Nod-A—l, absorbed between 11 and 13 percent H20 and Nod—P—l, between 8 and 10 percent H20. In- consistent data were obtained for 1120+ by two methods, and the results are reported as an approximate value. 30 USGS ROCK STANDARDS: MANGANESE-NODULE SAMPLES USGS—NOD—A—l, USGS-NOD—P—l TABLE 26.—-Determinatlons of several elements in USGS—Nod—A—J by David Felix, Ocean Mining Laboratory 1 [Determinations in percent or in parts per million, as indicated. Data for day 1 for all elements are not included in the analysis of variance. S, significant; NS, not significant; VS, very significant (calculated F>Fo.995). Means and F ratios from the analysis of variance for the complete sets of three data on days 2 and 3. Degrees of freedom for mean sums of squares: bottles, 2; days, 1: and residual (error), 2. F' ratios tested at Foss or the fractile indicated in parentheses. For any element except Pb, the upper mean is for all data and the lower is for the six data used in the analysis of variance and for best values] Bottle F'ratio Element Day Mean 1 2 3 Bottles Days Percent AI __________ 1 ______ 1.78 1.84 1.81 1.96 2 ______ 2.14 2.00 2.00 2.04 <1 NS 16.54 NS (0.99) 3 ______ 2.03 2.04 2.01 Fe __________ 1 ______ 11.2 11.3 11.2 11.38 2 ______ 11.1 11.2 11.2 11.43 2.0 NS 16.0 NS (0.99) 3 ______ 11.6 12.0 11.6 Mn _________ 1 ______ 18.2 18.5 18.5 17.84 2 ______ 18.0 19.0 18.2 17.57 1.82 NS 32.65 S (0.995) 3 ______ 16.8 16.8 16.6 C0 __________ 1 ______ .330 .329 .329 .3340 2 ______ .337 .340 .338 .3363 <1 NS 30.5 S (0.995) 3 ______ .336 .334 .333 Cu __________ 1 ______ .10 .11 .11 .110 2 ______ .11 .12 .11 .112 (No test) (No test) 3 ______ .11 .11 .11 Ni __________ 1 ______ .67 .68 .67 .662 2 ______ .66 .65 .65 .657 <1 NS 11.45 NS (0.99) 3 ______ .66 .66 .66 Parts per million Cr _______‘___ 1 ______ 13 14 13 20.8 - 2 ______ 21 22 22 24.5 <1 NS 160.9 VS 3 ______ 28 26 28 Mo 2 _________ 1 ______ 420 420 420 425.6 2 ______ 430 430 440 428.3 4.19 NS 13.44 NS (0.99) 3 ______ 420 420 430 Pb 2 ________________ 1,260 1,280 1,260 1,267 (No test) (No test) V 2 __________ 1 ______ 850 870 850 830.0 2 ______ 800 800 800 816.6 3.08 NS 73.19 VS 3 ______ 830 840 830 Zn " _________ 1 ______ 630 620 600 600.0 2 ______ 600 620 590 591.7 2.71 NS 11.29 NS (0.99) 3 ______ 580 580 580 ‘ Kennecott Exploration, Inc., 3377 Carmel Mt. Rd., San Diego, CA 92121. 2Data for element converted from percent, and nonsignificant zero added. Analytical method:—1-g portions of the dried samples were digested in teflon beakers with hot HCI, HClOI, and HF to form dense perchloric fumes. After making to volume, appropriate dilutions were made to bring concentrations of each metal to its optimum range for atomic absorption. Deter- minations were made without background corrections on a Perkin-Elmer model 306 atomioabsorption unit. In-house standards and analyzed samples, plus standards prepared from spectrographic-quality metals, were used to bracket the unknowns. Calibration curves were not used. TABLES OF DATA BY ANALYSTS 31 TABLE 27.—Determinations of several elements in USGS—Nod—P—I by David Felix, Ocean Mining Laboratory 1 [Determinations in percent, or in parts per million, as indicated. Data for day 1 and the second listed determination for day 3 for all elements are not included in the analysis of variance. S, significant; NS, not significant; VS, very significant (calculated F' >Fo.995). Means and F ratios from the analysis of variance for the complete sets of three data on days 2 and 3. Degrees of freedom for mean sums of squares: bottles, 2; days, 1- and residual (error), 2. F ratios tested at F0115 or the fractile indicated in parentheses. For any element except Pb, the upper mean is for all data and the lower is for the six data used in the analysis of variance and for best values] Bottle Fratio Element Day Mean 1 2 8 Bottles Days Percent Al __________ 1 ______ 2.45 _________ 2.42 2.819 2 ______ 2.40 2.39 2.40 2.893 1.13 NS 158 NS(0.995) 3 ______ 3.54 3.26 3.37 3 _______________ 3 14 _________ Fe __________ 1 ______ 6.2 _________ 6.1 6.33 2 ______ 6.8 6.8 7.2 6.47 <1 NS 49 NS(0.99) 3 ______ 6.0 6.0 6.0 3 _______________ 5.9 _________ Mn _________ 1 ______ 30.4 _________ 30.2 29.34 2 ______ 27.4 27.6 27.5 28.87 <1 NS 320 VS (0.995) 3 ______ 30.4 30.3 30.0 3 _______________ 30.3 _________ Co __________ 1 ______ .236 _________ .240 .2401 2 ______ .242 .238 .240 .2410 <1 NS 1.75 NS 3 ______ 241 243 242 3 _______________ .239 _________ Cu __________ 1 ______ 1.17 _________ 1.17 1.163 2 ______ 1.14 1.14 1.14 1.158 <1 NS 100.5 NS(0.995) 3 ______ 1 18 1.18 1 17 3 _______________ 1.18 _________ N1 __________ 1 ______ 1.41 _________ 1.40 1.388 2 ______ 1.37 1.37 1.38 1.382 1.3 NS 3.42 NS 3 ______ 1.39 1.40 1 38 3 _______________ 1.40 _________ Parts per million Cr __________ 1 ______ 30 _________ 18 18.9 2 ______ 19 19 19 17.5 3 (N0 test) 3 (No test) 3 ______ 16 16 16 3 _______________ 17 _________ Mo 2 _________ 1 ______ 700 _________ 720 672.2 2 ______ 650 650 650 658.3 <1 NS 24.47 NS(0.975) 3 ______ 670 670 660 3 _______________ 680 _________ Pb2 _________ 2 ______ 650 640 640 698.3 <1 NS 30.25 NS(0.975) 3 ______ 740 790 730 3 _______________ 730 _________ V 9 __________ 1 ______ 590 _________ 590 663.3 2 ______ 650 650 630 673.3 <1 NS 27.0 NS(0.975) 3 ______ 700 690 720 3 _______________ 750 _________ Zn 2 _________ 1 ______ 1,670 _________ 1,660 1,638 2 ______ 1,620 1,620 1,600 1,625 <1 NS 6.97 NS 3 ______ 1,640 1,630 1,640 3 _______________ 1,660 _________ ‘ Kennecott Exploration, Inc., 3377 Carmel Mt. Rd., San Diego, CA 92121. 3 Data for element converted from percent, and nonsignificant zero added. 3 All variation in the analysis of variance due to days. Analytical method:-—l—g portions of the dried samples were digested in teflon beakers with hot HCl, H0101, and HF to form dense perchloric fumes. After making to volume, appropriate dilutions were made to bring concentrations of each metal to its optimum range for atomic absorption. Deter- minations were made without background corrections on a Perkin-Elmer model 305 atomic-absorption unit. In-house standards and analyzed samples, plus standards prepared from spectrographic-quality metals, were used to bracket the unknowns. Calibration curves were not used. 32 USGS ROCK STANDARDS: MANGANESE-NODULE SAMPLES USGS—NOD-A—l, USGS—NOD—P—l TABLE 28,—Determinations of several elements in USGS—Nod—A—I by atomic-absorption spectrometry by Wayne Mountjoy, James G. Crack, and George Riddle, US. Geological Survey 1 [Determinations in percent or in parts per million, as indicated. Alkalies, alkaline earths, and iron were determined by Mountjoy, and other ele- ments by Crock and Riddle. d.f., degrees of freedom; NS, not significant. F ratios tested at Foes or the fractile indicated in parentheses] Bottle F ratio Element Run Mean Bottle Run 1 2 3 (2 d.f.) (1 .11.) Percent Fe __________ 1 ______ 10.8 109 10.8 10.88 2.00 NS 4.00 NS 2 ______ 11.0 11.0 10.8 Mg _________ 1 ______ 2.90 2.90 2.87 2.893 16.0 NS (No test) 2 ______ 2.91 2.91 2.87 Ca __________ 1 ______ 11.2 111 11.0 11.08 <1 NS <1 NS 2 ______ 11.0 11.1 11.1 Na __________ 1 ______ .77 .79 .79 .783 <1 NS (No test) 2 ______ .79 .79 .77 K ___________ 1 ______ .518 .508 .511 .510 <1 NS <1 NS 2 ______ .507 .513 .503 Cu __________ 1 ______ .1070 .1060 .1070 .1072 1.78 NS 1.21 NS 2 ______ .1070 .1090 .1070 Ni __________ 1 ______ .5690 .5800 .5600 .5718 1.05 NS <1 NS 2 ______ .5720 .5750 .5750 Parts per million Ag ____________________________________________ <5 __________________ Cd __________ 1 ______ 6 7 7 6.5 <1 NS <1 NS 2 ______ 6 7 6 Li __________ 1 ______ 72 72 72 72 1 0 NS No test 2 ______ 71 72 '73 Pb __________ 1 ______ 845 855 845 850.8 2 32 NS 3.04 NS 2 ______ 850 855 855 Rb2 _________ 1 ______ 9 9 10 11 2.94 NS 98 NS(0.99) 2 ______ 12 13 13 Sr __________ 1 ______ 1,510 1,500 1.500 1,500 (No test) <1 NS 2 ______ 1,490 1,500 1,500 Zn __________ 1 ______ 590 608 593 594.3 <1 NS <1 NS 2 ______ 588 590 597 1 Stop 928, Box 25046 DFC, Lakewood, CO 80225. 9 Determinations near the limit of estimation of the method. TABLES OF DATA BY ANALYSTS 33 TABLE 29.——Determinations of several elements in USGS—Nod—P—I by atomic-absorption spectrometry by Wayne Mountjoy, James G. Crack, and George Riddle, U.S. Geological Survey 1 [Determinations in percent or in parts per million, as indicated. Alkalies, alkaline earths, and iron were determined by Mountjoy, and other ele- ments by Crock and Riddle. d.f., degrees of freedom; NS, not significant. F ratios tested at Foes or the fractile indicated in parentheses] Bottle F ratio Element Run Mean Bottle Run 1 2 3 (2 u.) (1 am.) Percent Fe __________ 1 ______ 5.82 5.80 5.81 5.845 1.2 NS 7.3 NS 2 ______ 5.87 5.84 5.93 Mg _________ 1 ______ 2.01 2.01 2.01 2.005 1.0 NS 3.0 NS 2 ______ 1.99 2.01 2.00 Ca __________ 1 ______ 2.17 2.20 2.20 2.195 1.0 NS <1 NS 2 ______ 2.20 2.19 2.21 Na __________ 1 ______ 1.62 1.62 1.60 1.613 2.0 NS (No test) 2 ______ 1.61 1.62 1.61 K ___________ 1 ______ 1.08 1.08 1.07 1.058 <1 NS 100.5 NS(0.995) 2 ______ 1.04 1.04 1.04 Cu __________ 1 ______ 1.08 1.08 1.06 1.077 2.0 NS 2.0 NS 2 ______ 1.08 1.08 1.08 Ni __________ 1 ______ 1.25 1.21 1.26 1.243 7.13 NS <1 NS 2 ______ 1.25 1.23 1.26 Parts per million Ag ____________________________________________ <5 Cd __________ 1 ______ 22 22 23 22.3 (No test) (No test) 2 ______ 22 23 22 Li __________ 1 ______ 139 139 139 137.5 1.0 NS 6.75 NS 2 ______ 138 136 134 Pb __________ 1 ______ 485 480 490 488.3 <1 NS 2.24 NS 2 ______ 490 495 490 Rb __________ 1 ______ 22 24 21 23.0 3.08 NS 4.15 NS 2 ______ 24 24 23 Sr __________ 1 ______ 655 655 645 655.8 <1 NS 6.23 NS 2 ______ 660 660 660 Zn __________ 1 ______ 1,580 1,570 1,600 1,590 1.29 NS 2.29 NS 2 ______ 1,590 1,600 1,600 ‘Stop 928, Box 25046 DFC, Lakewood, CO 80225. 34 USGS ROCK STANDARDS: MANGANESE-NODULE SAMPLES USGS-NOD-A—l, USGS—NOD—P—l TABLE 30.—Chemical determinations of several constituents in USGS—Nod—A—I by Sarah T. N eil, U .S. Geological Survey 1 [Determinations in percent. Data, except those for F, Cl, S, Ni, Co, and Cu, were reported as oxides on sample portions not dried. All data were calculated to the dry basis by the individual determinations of H20— (at 105°C), given in parentheses as the last entries in the table. Oxides were then converted to elements by gravimetric factors. d.f., degrees of freedom: NS, not significant; Neg., negative bottle variance obtained. F ratios tested at 170.95] Element Bottle Mean Standard devmtioh I". or oxide “/32 33/15 38/10 (fgtélez) “Err—315) ratio Si __________ 1.66 1.66 1.71 1.69 Neg. 0.03 0.64 NS 1.72 1.68 1.69 A1 __________ 1.94 1.90 1.90 1.93 0.02 .03 2.02 NS 1.97 1.90 1.96 Fe __________ 10.99 11.09 10.99 11.01 Neg. .04 .90 NS 10.99 10.99 11.00 Mg _________ 2.86 2.92 2.91 2.91 Neg. .03 .97 NS 2.92 2.93 2.90 Ca __________ 11.28 11.27 11.31 11.28 Neg. .02 .70 NS 11.30 11.26 11.26 Na __________ .88 .88 .87 .88 Neg. .02 .50 NS .88 .87 .92 K ___________ .51 .49 .49 .50 Neg. .02 .76 NS .50 .49 .53 H20+ _______ 8.26 8.29 8.38 8.35 Neg. .06 .78 NS 8.37 8.40 8.41 Ti __________ .37 .38 .38 .38 .00 .00 1.00 NS .38 .38 .38 P ___________ .53 .54 .54 .54 .00 .00 3.00 NS .53 .53 .54 CO. _________ 11.80 12.12 12.18 12.07 .07 .12 1.62 NS 12.09 12.06 12.14 F ___________ .10 .10 .10 .10 ____________ (No test) .10 .10 10 Cl __________ .42 .41 .42 .43 Neg. .02 .20 NS .44 .45 .42 S ___________ .40 .45 .39 .40 .03 .02 7.19 NS .39 .43 .35 Mn _________ 18.03 18.17 18.21 18.13 .17 .11 5.50 NS 17 80 18.31 18.24 Ni __________ .65 .65 .65 .65 Neg. .01 .50 NS .66 .65 .66 Co __________ .35 .34 .34 .34 Neg. .01 .20 NS .33 .34 .35 Cu __________ .12 .10 .12 .11 Neg. .01 .50 NS .12 .12 .10 (H20—) _____ (13.45) (14.12) (13.82) ___________________________ (13.35) (14.02) (13.79) 1 Menlo Park, CA 94025. Analytical methods:— Gravimetry: Total H20 (Penfield); H2O—: SiOe; A1203 (weighed as A1P04); CaO (weighed as CaCOx): MgO (weighed as Mg2P207); and total S (weighed as BaSOa). Other methods: Na-zO and K20, by flame photometry; Ti02, by spectrophotometry with Tiron; P205 by spectrophotometry with molybdovanadate method; Ni, Co, and Cu, by atomic-absorption spectrometry; total Fe, by spectrophotometry with orthophenanthroline; F, by F- electrode; Cl, by spectro- photometry using Fe(CNS)::: C02, as total C, by combustion with Leco WR—12; and total Mn, volumetrically with sodium bismuthate. TABLES OF DATA BY ANALYSTS 35 TABLE 31.—Chemical determinations of several constituents in USGS—Nod—P—I by Sarah T. N ell, US. Geological Survey ‘ [Determinations in percent. Data, except those for F, Cl, S, Ni, Co. and Cu, were reported as oxides on sample portions not dried. All data were calculated to the dry basis by the individual determinations of H20— (at 105°C), given in parentheses as the last entries in the table. Oxides were then converted to elements by gravimetric factors. d.f., degrees of freedom; NS, not significant: Neg” negative bottle variance obtained. F ratios tested at F035 or the fractile indicated in parentheses] Element Bottle mean Standard devmtion F or ox1de 21/10 23/3 36/8 (dégtgeé) ((11.3?ng ratio Si __________ 6.60 6.57 6.56 6.57 0.00 0.02 1.00 NS 6.56 6.55 6.55 Al __________ 2.47 2.47 2.48 2.47 .01 .02 2.17 NS 2.48 2.43 2.49 ' Fe __________ 5.95 5.95 5.97 5.95 Neg. .02 .72 NS 5.95 5.92 5.94 Mg _________ 2.04 2.03 2.06 2.08 .01 .05 1.12 NS 2.08 2.06 2.18 Ca. __________ 2.26 2.26 2.37 ' 2.31 .06 .03 10.46 NS(0.975) 2.27 2.32 2.40 Na __________ 1.74 1.73 1.72 1.73 Neg. .01 .00 NS 1.72 1.73 1.74 K ___________ 1.06 1.05 1.04 1.05 Neg. .01 .17 NS 1.04 1.04 1.05 , H204. _______ 8.47 8.59 8.62 8.57 .09 .05 8.85 NS 8.47 8.53 8.72 Ti __________ .36 .38 .37 .37 .00 .01 1.00 NS .36 .36 .37 P ___________ .20 .21 .21 .21 .01 .00 7.00 NS .20 .22 .21 C0. _________ .81 .83 .80 .82 Neg. .02 .73 NS .81 .84 .85 F ___________ .04 .03 .03 .04 Neg. .01 .00 NS .03 .04 04 C1 __________ .17 .10 .12 .12 Neg. .03 .76 NS .11 .12 .11 S ___________ .20 .20 .20 .20 .01 .01 1.46 NS .20 .17 .22 Mn _________ 29.78 29.79 29.74 29.74 .06 .09 2.05 NS 29 67 29.88 29.58 Ni __________ 1.35 1.40 1.37 1.37 .01 .02 1.36 NS 1.37 1.37 1.38 Co __________ .25 .25 .24 .25 .01 .00 7.00 NS .25 .26 .24 Cu __________ 1.18 1.15 1.19 1.18 Neg. .03 .07 NS 1.18 1.20 1.15 (11.0-) _____ (6.70) (7.19) (6.39) ____________________________ , (6.70) (7.25) (6.29) _______ ‘Menlo Park, CA 94025. Analytical methods:— Gravimetry: Total H2O (Penfield): 1120—: Si02; A1203 (weighed as AlP04): CaO (weighed as Ca003); MgO (weighed as MgszO-I); and total S (weighed as BaSOi). Other methods: NazO and K20, by flame photometry; Ti02, by spectrophotometry with Tiron; P205 by spectrophotometry with molybdovanadate method: Ni, Co, and Cu, by atomic-absorption spectrometry; total Fe, by spectrophotometry with orthophenanthroline; F, by F- electrode; Cl, by spectro- photometry using Fe(CNS):1; C02, as total C, by combustion with Leco WR—12; and total Mn, volumetrically with sodium bismuthate. 36 USGS ROCK STANDARDS: MANGANESE NODULE SAMPLES USGS—NOD—A—l, USGS—NOD—P—l TABLE {Ra—Averages of determinations of elements [Averages in percent or in parts per million as indicated. Averages are indicated by the table number and the number of determinations (n) for surviving the selection process Table No. ....... 7 9 22 11 12 14 Element n=6 n=6 n26 n23 11:6 n=6 n=6 Percent Si ____________________________ 1.82 _____ __-_ _______ 1.42 A1 ____________________________ 1.75 _____ ____ 1.7 2.27 Fe __________ 10.88 10.88 10.86 10.6 ____ 9.7 10.98 Mg __________________ 2.89 2.85 _____ -___ _______ 3.20 Ca ___________________ 11.08 11.17 _____ _-__ _______ 11.42 Ca ______________________________________ ———_ ______________ Na ___________________ .78 .80 _____ ____ ______________ K ____________________ .510 .50 _____ _-__ .17 .48 Ti ____________________________ .32 _____ -_-- _______ .29 Mn ___________________________ 18.40 16 9 ____ 13.7 18.64 P _____________________________ .42 _____ ____ _______ .59 Co __________ .2527 _________ .326 30 _-__ .31 .39 Co ______________________________________ ____ ______________ Cu ___________________ .1072 112 .088 ____ .11 .18 Ni ___________________ .5718 648 .61 ____ .64 .57 C02 _____________________________________ ____ _______ 11.64 H20+ ___________________________________ -___ ______________ Excess O _1__ ____________________________ ____ ______________ Parts per million Ag ___________________ <5 —————————— ———~ ______________ As ______________________________________ ———_ _______ 298 Ba __________ 1,518 ___________________ __-_ 2,700 1,671 Be ______________________________________ ____ ______________ Cd ___________________ 6.5 __________ ____ ______________ Ce __________ 668 ___________________ ____ ______________ C1 ______________________________________ ——__ ______________ Cr __________ ‘ 25.9 ___________________ ___- ______________ Eu __________ 4.48 ___________________ ____ ______________ Gd __________ 26.5 ___________________ --__ ______________ Hf __________ 6.2 ___________________ _-__ ______________ La __________ 132.5 ___________________ ____ ______________ Li ___________________ 72 __________ _-__ ______________ Lu __________ 2.16 ___________________ ____ ______________ Mo ______________________________________ ____ 360 460 Nd __________ 85 3 ___________________ -_-_ ______________ Pb ___________________ 851 __________ __-_ 950 1,323 Rb ___________________ 11 __________ ———- _______ 10 Sb __________ 33.5 ___________________ ____ ______________ Sc __________ 11.23 ___________________ _-__ ______________ Sm _________ 20.9 ___________________ ____ ______________ Sr ___________________ 1,500 __________ ____ 1,800 1,728 Tb __________ 4.87 ___________________ ____ ______________ Th __________ 25.8 ___________________ 27.35 ______________ T1 ______________________________________ -___ ______________ Tm _________ ‘ 1.72 ___________________ .._-_ ______________ U ___________ 5.95 ___________________ 6.86 ______________ V _______________________________________ _-__ ______________ Y _______________________________________ —___ _______ 115 Yb __________ 16.3 ___________________ -___ ______________ Zn ___________________ 594 _____ 460 ____ 590 870 Zr ______________________________________ ___- ....... 317 ‘ Average of four. '-' Average of three. AVERAGES FOR USGS—NOD—A—l BY ALL ANALYSTS in USGS—Nod—A—I by all contributing analysts each average. Lower case letter A; u 0 indicates nonsignificant zeros added to values and estimates calculated from them] for tracecelement averages. Bold-faced 37 numbers indicate averages 16 18 20 24 26 23 30 “Best" 11:6 11.26 11.26 11:3 11:6 n=3 11:6 value Percent Si ________ 2.00 1.63 1.73 1.83 ________ __-_ 1.69 1.78 A1 _______ 2.06 1.86 ________ 3.26 2.04 ____ 1.93 2.05 Fe _______ 11.08 10.29 10.91 11.02 11.4 10.2 11.01 10.93 Mg _______ 2.80 2.74 2.93 2.86 ________ ____ 2.91 2.87 Ca _______ 10.97 11.30 11.00 11.22 ________ __-_ 11.28 11.03 Ca ______________________ 11.07 ________________ ____ _______________ Na _______ .77 ______________ .82 ________ __-_ .88 .775 K ________ .52 .40 .46 .46 ________ ____ .50 .50 Ti ________ .28 .32 ________ .28 ________ ____ .38 .32 Mn _______ 17.80 18.63 18.51 18.51 17.6 17.3 18.13 18.54 P _________________ .60 .53 .53 ________ ____ .54 .60 Co _______ 3128 .281 .313 .34 .336 28 .34 .311 C0 ______________________ .322 ________________ -_-_ _______________ Cu _______ 1052 .107 .109 .111 112 11 .11 .11 Ni _______ 6300 .625 .637 .71 .657 59 .65 .636 CO2 _____________________________ 11.61 ________ ____ 12.07 ________ H20+ ____ _______________________ ~7.9 ________ ___- 8.35 ________ Excess 0 __ _______________________ 5.30 ________ __-_ _______________ Parts per million Ag ______________________________________________ __.._ _______ As ______________________________________________ ____ _______ Ba _______ 1,668 ______ 2,320 1,800 ________ ____ _______ Be _____________________________________ -___ _______ Cd ______________________________________________ _--_ _______ Ce ______________________________________________ _-__ _______ Cl _______________________________ 5,400 ________ ____ 4,300 ________ Cr _______ 23 ______________________ 24 ____ _______________ Eu ______________________________________________ __-_ _______________ Gd _______________________________________________ __-_ _______________ Hf ______________________________________________ ____ _______________ La ______________________________________________ _-__ _______________ Li _______ 76.3 ______________________________ ____ _______________ Lu ______________________________________________ -___ _______________ 1130 _______ 457 567 514 410 428 ____ _______ 448 d ______________________________________________ _--_ _______________ Pb _______ 793 ______ 840 960 2 1,267 ____ _______ 846 Rb ______________________________________________ ____ _______________ Sb ______________________________________________ _--_ _______________ Sc ______________________________________________ _--- _______________ Sm ______________________________________________ ___- _______________ Sr _______ 1,660 ______ 1,770 1,720 ________ -_-_ _______ 1,748 Tb ______________________________________________ __-_ _______________ Th ______________________________________________ __-_ _______________ Tl ______________________ 61 ________________ ____ _______________ Tm ______________________________________________ -___ _______________ U _______________________________________________ ____ _______________ ¥ ________ 586 ______ 916 610 817 ____ _______ 770 YbIIII :IIII III IIII IIII IIII II III: IIII En _______ 559 574 620 650 592 __-_ _______ 587 r 38 USGS ROCK STANDARDS: MANGANESE-NODULE SAMPLES USGS—NOD—A—l, USGS—NOD—P—l TABLE 33.—Averages of determinations of elements in [Averages in percent or in parts per million as indicated. Averages are indicated by the table number and the number of determinations (n) for surviving the selection process Table No. ....... 8 29 10 22 11 13 15 Element n26 n26 n26 n23 n26 n26 n=6 Percent Si ____________________________ 6.64 _____ ___- _______ 6.65 A4 ___________________________ 1.97 _____ ____ 1.8 2.59 Fe __________ 5.76 5.84 5.73 6.45 ____ 5.2 4.76 Mg __________________ 2.00 1.98 _____ ____ _______ 2.08 Ca ___________________ 2.20 2.20 _____ ____ _______ 2.16 Na ___________________ 1.61 1.68 _____ -___ ______________ K ____________________ 1.06 .99 _____ ____ .28 1.14 Ti ____________________________ .31 _____ ____ _______ .30 Mn ____________________________ 29.19 27.3 _.._- 25.5 29.06 P _____________________________ .17 _____ -___ _______ .21 Co __________ .1808 _________ .220 .22 ____ .22 .28 Co _______________________________________ -___ ______________ Cu ___________________ 1.08 1.20 1.11 _.___ 1.2 1.04 Ni ___________________ 1.24 1.40 1.26 ____ 1.4 1.28 002 _____________________________________ _-__ _______ 1.39 H20+ ___________________________________ ____ ______________ Excess O ____ ____________________________ —-—— ______________ Parts per million _________ <5 _____ _____ -___ __-____ _______ ____________________________ ____ _-_____ 39 ‘ 2,498 ___________________ ____ 6,700 3,453 ZZZ—.2: ____ 2— 23'" II: :2: I: III: III: 289 ___________________ ___- ______________ 2.1.5"--- 1:21: I: 2:: I: III: III: 6.57 ___________________ ___- ______________ 29.4 ___________________ -_-_ ______________ 4.3 ___________________ ____ ______________ ‘ 120 ___________________ __-_ ______________ _________ 137.5 _____ -____ ____ _______ _______ 1 1.85 ___________________ ___- ______________ ____________________________ ____ 630 823 112.8 ___________________ ____ ______________ _________ 488 _____ --___ _-__ 520 715 _________ 23 __-__ _____ ____ -______ 21 50.1 ___________________ ____ ______________ 9.47 ___________________ --__ ______________ 30.4 ___________________ ____ ______________ _________ 656 _-__- ___-_ _-__ 1,080 751 5.31 ___________________ ____ ______________ 17.0 ___________________ 17.65 ______________ T1 ______________________________________ __-- ______________ Tm _________ 1.77 ___________________ ____ ______________ U ___________ 3.5 ___________________ 4.28 ______________ V _______________________________________ ____ ______________ Y _______________________________________ --_.. _______ 89 Yb __________ 1 13.8 ___________________ ____ ______________ Zn ___________________ 1,590 __________ _-__ 1,600 1,998 Zr ______________________________________ _~__ _______ 280 1 Average of four. AVERAGES FOR USGS—NOD-P—l BY ALL ANALYSTS 39 USGS—Nodr-P—I by all contributing analysts u n each average. Lower case letter 0 indicates nonsignificant zeros added to values for trace-element averages. Bold-faced numbers indicate averages and estimates calculated from them] 17 19 21 25 27 23 31 “Best" 11:6 n:6 n26 11:3 n26 n23 11:6 value Percent Si ________ 6.97 6.36 6.38 6.82 ________ ____ 6 57 6.51 A1 _______ 2.41 2.56 ________ 3.85 2.89 __-_ 2.47 2.55 Fe _______ 5.81 5.52 6.05 5.91 6.47 5.04 5.95 5.78 Mg _______ 1.98 1.80 2.00 1.98 ________ ____ 2.08 1.99 Ca _______ 2.16 2.20 2.20 2.07 ________ ____ 2.31 2.19 Na _______ 1.63 ______________ 1.65 ________ __-_ 1.73 1 64 K ________ 1.04 .93 1 05 1.01 ________ ____ 1.05 1 05 T1 ________ .28 .29 ________ .28 ________ ____ .37 30 Mn _______ 29 17 29.93 29 86 29.92 28 87 27.8 29.74 29 14 P _________________ .20 2 .21 ________ ____ .21 20 Co _______ 2280 .201 227 .26 241 20 25 224 Co ______________________ .231 ________________ ___- _______________ Cu _______ 1.137 1.16 1.15 1.35 1.16 1 13 1.18 1.15 Ni _______ 1.328 1.32 1.35 1.56 1.38 1.24 1.37 1.34 002 _____________________________ .76 ________ ____ .82 ________ H20+ ____ _______________________ ~8.2 ________ In 8.57 ________ ExcessO __ _______________________ 841 ________ __.._ _______________ Parts per million Ag ______________________________________________ _--_ _______________ As ______________________________________________ ____ _______________ Ba _______ 2,862 ______ 3,740 2,900 ________ -___ _______ 3,350 Be _____________________________________ _--- _______________ Cd ______________________________________________ ____ _______________ Ce ______________________________________________ -___ _______________ Cl _______________________________ 1,400 ________ ____ 1,200 ________ Cr _______ 20 ______________________ 17 5 ____ _______________ Eu ______________________________________________ __-_ _______________ Gd ______________________________________________ -___ _______________ Hf ______________________________________________ --__ _______________ La ______________________________________________ _--- _______________ Li _______ 142 ______________________________ ____ _______________ Lu ______________________________________________ ____ _______________ 11:11:11 _______ 802 982 678 740 658 ____ _______ 762 Pb III: "43:60" III "47—0 ______ 5 ‘4?) ''''' 6 68"" II III: "5‘55"" Rb _______________________________________________ ____ _______________ Sb ______________________________________________ _--_ _______________ Sc ______________________________________________ _-_- _______________ Sm ______________________________________________ __-_ _______________ Sr _______ 638 ______ ~900 75o ________ ____ _______ 680 Tb ______________________________________________ ____ _______________ Th ______________________________________________ _-__ _______________ Tl ______________________ 154 ________________ _-__ _______________ Tm ______________________________________________ __-- _______________ U _______________________________________________ _--_ _______________ ¥ ________ 480 ______ 548 530 673 __-_ _______ 570 YbIIII IIIII III IIII IIII IIII II III: IIII Zn _______ 1,467 1,510 1,660 1,690 1,625 ____ _______ 1,595 Zr ______________________________________________ ____ _______ *U.S. GOVERNMENT PRINTING OFFICE: I980 0—311-344/81 Patterns and Trends of Land Use and Land Cover on Atlantic and Gulf Coast Barrier Islands By Harry F. Lins, Jr. ‘GEOLOGICAL SURVEY PROFESSIONAL PAPER 1156 UNITED STATES GOVERNMENT PRINTING OFFICE: 1980 UNITED STATES DEPARTMENT OF THE INTERIOR CECIL D. ANDRUS, Secretary GEOLOGICAL SURVEY H. William Menard, Director Library of Congress Cataloging in Publication Data Lins, Harry F. . Patterns and trends of land use and land cover on Atlantic and Gulf Coast barrier islands. (US. Geological Survey professional paper ; 1156) Bibliography: p. Supt. of Docs. no.: I 19.16zll56 1. Coastal zone management—United States. 2. Land use—United States. I. Title. II. Series: United States. Geological Survey. Professional paper; 1156. HT392.L55 333.78’4 80—607 144 For sale by Superintendent of Documents, US. Government Printing Ofiice Washington, D.C. 20402 CONTENTS Page Page Preface VII References 12 Abstract 1 Appendices 13 Introduction 1 I Tables (9-27) summarize area values of land use and land Methodology cover on Atlantic and Gulf coast barrier islands, Data description and regional analysis ____________________ 2 1945—55 and 1972—75, with changes. Statistical significance 10 II Land use and land cover maps (figs. 2-125) of Atlantic Conclusions 11 and Gulf coast barrier islands, 1972—75. TABLE S Page Page TABLE 1. Land use and land cover classification system for Area values of Level I land use and land cover on Atlantic and use with remotely sensed data _________________ 2 Gulf Coast barrier islands in 1945—55 and 1972—75, with changes: 9. For 9 barrier islands off the Maine coast _________ 15 2' Area ”Flues 0f Level I land use and land cover on 10. For 2 barrier islands off the New Hampshire coast _ 15 barrier lslands for 1945—55’ by State ““““““ 3 11. For 27 barrier islands off the Massachusetts coast _ 16 3. Area values of Level I land use and land cover on 12. For 6 barrier islands off the Rhode Island coast ____ 18 barrier islands for 1972—75, by State ____________ 4 13. For 2 barrier islands off the Connecticut coast _____ 18 _ 14. For 15 barrier islands ofi' the New York coast _____ 19 4' Changes m area “13165 0f Level I land use and land 15. For 10 barrier islands off the New Jersey coast ____ 20 cover on barrier islands between 1945—55 and 16. For2barrier islands off the Delaware coast _______ 21 1972—75’ by State """""""""""""""""" 5 17. For 2 barrier islands of!" the Maryland coast _______ 21 5. Area values of Level I land use and land cover on 18. For 11 barrier islands off the Virginia coast _______ 22 barrier islands for 1945—55, by regional group -___ 7 19. For 23 barrier islands off the North Carolina coast _ 23 20. For 34 barrier islands off the South Carolina coast _ 25 6' Area values 0f Level I land use and land cover on 21. For 15 barrier islands off the Georgia coast _______ 27 barrier 1s1ands for 1972-75. by regional group —-—— 7 22. For 80 barrier islands off the Florida coast _______ 28 7. Changes in area values of Level I land use and land 23' For 5 barrier islands Off the Alabama coast ------- 33 cover on barrier islands between 1945_55 and 24. For 5 barrier Islands ofl" the Miss1ss1pp1 coast _____ 33 197245, by regional group ____________________ 8 25. For 18 barrier'lslands off the LouISIana coast _____ 34 26. For 16 barrier Islands off the Texas coast _________ 36 8. Statistical significance of land use and land cover 27. Summary of changes for all barrier islands in the 8 area changes by regional group ________________ 11 regional groups 37 ILLUSTRATIONS Page Page FIGURE 1. Map of regional groupings of Atlantic and Gulf Land use and land cover maps of the New England and New coast barrier islands ________________________ 6 York Bight barrier islands (figs. 8—27): Indexes to land use and land cover maps (figs. 2—7): 8. Of the coastal area near Bath, Me., with 2. Of the New England and New York Bight barrier associated barrier islands ___________________ 43 islands (ffgS‘ 8‘27.) ----f--_- ----------------- 41 9. Of the coastal area near Portland, Me., with 3. 0f the Mid-Atlanticbamer islands (figs. 28—48).- 42 associated barrier islands ___________________ 44 4. Of the M1d-Atlant1c, Sea Islands, and Florida , Atlantic barrier islands (figs. 49—70) ___________ 43 10' 0f the coastal area near Gloucester, Mass, “nth 5, Of the Florida Atlantic and Eastern Gulf barrier assoc1ated barrier Islands ““““““““““ 45 islands (figs, 71-95) ________________________ 44 11. Of the coastal area near Boston, Mass, with 6. 0f the Eastern Gulf and Louisiana barrier islands associated barrier islands ___________________ 46 (figs. 96—112) 45 12. Of the coastal area near Plymouth, Mass, with 7, 0f the Texas barrier islands (figs. 113—125) _____ 46 associated barrier islands ___________________ 47 III IV FIGURE 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. Of the coastal area near Cape Cod, Mass., with associated barrier islands ___________________ Of the coastal area near Provincetown, Mass., with associated barrier islands _______________ Of the coastal area near Nantucket, Mass., with associated barrier islands ___________________ Of the coastal area near Martha's Vineyard, Mass., with associated barrier islands __________ 0f the coastal area near New Bedford, Mass., with associated barrier islands ___________________ 0f the coastal area near Newport, R. 1., with associated barrier islands ___________________ Of the coastal area near Mystic, Conn., with associated barrier islands ___________________ Of the coastal area near New Haven, Conn., with associated barrier islands ___________________ Of the coastal area near Bridgeport, Conn. with associated barrier islands ___________________ Of the coastal area near New London, Conn., with associated barrier islands ____________________ Of the coastal area near Southampton, N.Y., with associated barrier islands ___________________ Of the coastal area near Brookhaven, N.Y., with associated barrier islands ___________________ 0f the coastal area near Fire Island, N.Y., with associated barrier islands ___________________ 0f the coastal area near Lindenhurst, N.Y., with associated barrier islands ___________________ Of the coastal area near New York, N.Y., with associated barrier islands ___________________ Land use and land cover maps of the Mid-Atlantic barrier islands (figs. 28—48): 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. Of the coastal area near Sandy Hook, N.J., with associated barrier islands ___________________ 0f the coastal area near Toms River, N.J., with associated barrier islands ___________________ Of the coastal area near Atlantic City, N.J., with associated barrier islands ___________________ Of the coastal area near Ocean City, N.J., with associated barrier islands ___________________ Of the coastal area near Rehoboth Beach, Del., with associated barrier islands _______________ Of the coastal area near Ocean City, Md., with associated barrier islands ___________________ Of the coastal area near Assateague Island, Md., with associated barrier islands _______________ 0f the coastal area near Chincoteague, Va., with associated barrier islands ___________________ Of the coastal area near Cape Charles, Va., with associated barrier islands ___________________ 0f the coastal area near Virginia Beach, Va., with associated barrier islands ___________________ 0f the coastal area near Kitty Hawk, N.C., with associated barrier islands ___________________ Of the coastal area near Nags Head, N.C., with associated barrier islands ___________________ Of the coastal area near Waves, N.C., with associated barrier islands ___________________ 0f the coastal area near Cape Hatteras, N.C., with associated barrier islands ___________________ CONTENTS Page FIGURE 42. 48 43. 49 44. 50 45. 51 46. 52 47. 53 48. 54 55 56 49. 57 50. 58 51. 59 52. 60 53. 61 54. 62 55. 56. 57. 63 58. 64 59. 65 60. 66 61. 67 62. 68 63. 69 64. 70 65. 71 66. 72 67. 73 68. 74 69. 75 70. 76 Of the coastal area near Ocracoke, N.C., with associated barrier islands ___________________ Of the coastal area near Atlantic, N.C., with associated barrier islands ___________________ Of the coastal area near Cape Lookout, N.C., with associated barrier islands ___________________ Of the coastal area near Morehead City, N.C. with associated barrier islands ___________________ Of the coastal area near Jacksonville, N.C., with associated barrier islands ___________________ 0f the coastal area near Hampstead, N.C., with associated barrier islands ___________________ 0f the coastal area near Wrightsville Beach, N. C., with associated barrier islands _______________ Land use and land cover maps of the Mid-Atlantic, Sea Islands, and Florida Atlantic barrier islands (figs. 49—70): Of the coastal area near Cape Fear, N.C., with associated barrier islands ___________________ Of the coastal area near Seaside, N.C., with associated barrier islands ___________________ Of the coastal area near Georgetown, S.C., with associated barrier islands ___________________ Of the coastal area near Cape Romain, S.C., with associated barrier islands ___________________ Of the coastal area near Isle of Palms, S.C., with associated barrier islands ___________________ Of the coastal area near Charleston, S.C., with associated barrier islands ___________________ Of the coastal area near Edisto Island, S.C., with associated barrier islands ___________________ 0f the coastal area near Beaufort, S.C., with associated barrier islands ___________________ 0f the coastal area near Hilton Head, S.C., with associated barrier islands ___________________ Of the coastal area near Savannah Beach, Ga., with associated barrier islands _______________ Of the coastal area near St. Catherines Island, Ga., with associated barrier islands ___________ Of the coastal area near Sapelo Island, Ga., with associated barrier islands ___________________ 0f the coastal area near Brunswick, Ga., with associated barrier islands ___________________ 0f the coastal area near Cumberland Island, Ga., with associated barrier islands _______________ Of the coastal area near Fernandina Beach, Fla, with associated barrier islands _______________ Of the coastal area near Jacksonville, Fla., with associated barrier islands ___________________ Of the coastal area near St. Augustine, Fla., with associated barrier islands ___________________ Of the coastal area near Marineland, Fla., with associated barrier islands ___________________ Of the coastal area near Daytona Beach, Fla., with associated barrier islands ___________________ Of the coastal area near Titusville, Fla., with associated barrier islands ___________________ Of the coastal area near Merritt Island, Fla., with associated barrier islands __________________ Of the coastal area near Cocoa Beach, Fla., with associated barrier islands ___________________ Page 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 Land use and land cover maps of the Florida and Eastern Gulf barrier islands (figs. 71—95): FIGURE 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. Land use and land cover maps of the Eastern Gulf and Louisiana Of the coastal area near Vero Beach, Fla., with associated barrier islands ___________________ 0f the coastal area near Fort Pierce, Fla., with associated barrier islands ___________________ Of the coastal area near Jupiter, Fla., with associated barrier islands ___________________ Of the coastal area near West Palm Beach, Fla., with associated barrier islands _______________ Of the coastal area near Boca Raton, Fla, with associated barrier islands ___________________ Of the coastal area near Fort Lauderdale, Fla., with associated barrier islands _______________ Of the coastal area near Miami, Fla., with associated barrier islands ___________________ 0f the coastal area near Cape Sable, Fla., with associated barrier islands ___________________ Of the coastal area near Alligator Cove, Fla., with associated barrier islands ___________________ 0f the coastal area near Everglades, Fla., with associated barrier islands ___________________ 0f the coastal area near Marco, Fla., with associated barrier islands ___________________ Of the coastal area near Naples, Fla., with associated barrier islands ___________________ 0f the coastal area near Fort Meyers, Fla., with associated barrier islands ___________________ Of the coastal area near Venice, Fla., with associated barrier islands ___________________ 0f the coastal area near Sarasota, Fla., with associated barrier islands ___________________ Of the coastal area near St. Petersburg, Fla., with associated barrier islands ___________________ Of the coastal area near Tarpon Springs, Fla.. with associated barrier islands _______________ Of the coastal area near Chassahowitzka, Fla., with associated barrier islands _______________ Of the coastal area near Cedar Key, Fla, with associated barrier islands ___________________ Of the coastal area near Panacea, Fla, with associated barrier islands ___________________ Of the coastal area near Saint Teresa, Fla., with associated barrier islands ___________________ Of the coastal area near Carrabelle, Fla., with associated barrier islands ___________________ 0f the coastal area near Apalachicola, Fla., with associated barrier islands ___________________ Of the coastal area near Port St. Joe, Fla., with associated barrier islands ___________________ 0f the coastal area near Panama City, Fla, with associated barrier islands ___________________ barrier islands (figs. 96—112): 96. 97. Of the coastal area near Fort Walton Beach, Fla, with associated barrier islands _______________ Of the coastal area near Mary Esther, Fla, with associated barrier islands _. _________________ CONTENTS Page FIGURE 98. 99. 106 100. 107 101. 108 102. 109 103. 110 104. 111 105. 112 106. 113 107. 114 108. 115 109. 116 110. 117 111. 118 112. 119 120 121 (figs. 113—125): 122 113. 123 114. 124 115. 125 116. 126 117. 127 118. 128 119. 129 120. 130 121. 122. 123. 124. 131 125. 132 Of the coastal area near Pensacola, Fla., with associated barrier islands ___________________ Of the coastal area near Warrington, Fla., with associated barrier islands ___________________ Of the coastal area near Gulf Shores, Ala., with associated barrier islands ___________________ Of the coastal area near Dauphin Island, Ala. with associated barrier islands ___________________ Of the coastal area near Pascagoula, Miss., with associated barrier islands ___________________ Of the coastal area near Biloxi, Miss., with associated barrier islands ___________________ Of the coastal area near Gulfport, Miss., with associated barrier islands ___________________ Of the coastal area near Chandeleur Islands, La., with associated barrier islands _______________ Of the coastal area near Breton Island, La., associated barrier islands ___________________ 0f the coastal area near Venice, La., with associated barrier islands ___________________ 0f the coastal area near Pilottown, La., with associated barrier islands ___________________ Of the coastal area near Grand Isle, La., with associated barrier islands ___________________ Of the coastal area near Caminada Pass, La., with associated barrier islands ___________________ Of the coastal area near Leeville, La., with associated barrier islands ___________________ Of the coastal area near Isles Dernieres, La., with associated barrier islands ___________________ Land use and land cover maps of the Texas barrier islands Of the coastal area near Galveston Island, Tex., with associated barrier islands _______________ Of the coastal area near Jamaica Beach, Tex., with associated barrier islands _______________ Of the coastal area near Freeport, Tex., with associated barrier islands ___________________ Of the coastal area near Matagorda, Tex., with associated barrier islands ___________________ Of the coastal area near Palacios, Tex., with associated barrier islands ___________________ Of the coastal area near Port O’Connor, Tex., with associated barrier islands ___________________ 0f the coastal area near Austwell, Tex., with associated barrier islands ___________________ Of the coastal area near Corpus Christi, Tex., with associated barrier islands ___________________ Of the coastal area near Laguna Vista, Tex., with associated barrier islands ___________________ Of the coastal area near Griffins Point, Tex., with associated barrier islands ___________________ Of the coastal area near Lopena, Tex., with associated barrier islands ___________________ Of the coastal area near Padre Island South, Tex., with associated barrier islands _______________ Of the coastal area near Port Isabel, Tex., with associated barrier islands ___________________ V Page 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 Group 1 New England: (Sheepscot, Me., to Long Beach, Mass.) Group 2 New York Bight: (Sandy Neck, Mass, to Rockaway, N. Y.) Group 3 Mid-Atlantic: (Sandy Hook, N. J., to North Is., S. C.) Group 4 Sea Islands: (South Is., S. C. to Cumberland Is., Ga.) Group 5 Florida Atlantic: (Amelia Is., Fla., to Key Biscayne, Fla.) 1 Group 6 Eastern Gulf Coast: New England (Cape Sable, Fla., to Cat Is., Miss.) \ Group 7 Louisiana: “ (Chandeleur Is., La., to Isles Dernieres, La.) Group 8 Texas: ’ 2 (Bolivar Peninsula, Tex., to Brazos Is., Tex.) ' , New York Bight \ A 4 Sci lslé'ndE " u} 3 Mid-Atlantic 6 Eastern Gulf Coast 5 Florida Atlantic: 200 400 MILES o—ro I 600 KILOMETERS REGIONAL GROUPINGS OF ATLANTIC AND GULF COAST BARRIER ISLANDS PREFACE Reconciling the conflicts arising from alternative uses of natural resources is one of the preeminent problems facing the United States now. It is only through cooperation between Federal, regional, State and local agencies, that this problem can be addressed effectively. In the 1960’s and early 1970’s the Federal government took numerous legislative steps toward promoting such cooperation. The Coastal Zone Management Act is a prime example. In his May 1977 Environmental Message to Congress, President Carter stated “In- telligent stewardship of the environment on behalf of all Americans is a prime responsibility of government. Con- gress has in the past carried out its share of this duty well—so well, in fact, that the primary need today is not for new comprehensive statutes but for sensitive ad- ministration and energetic enforcement of the ones we have. Environmental protection is no longer just a legislative job, but one that requires—and will now receive—firm and unsparing support from the Executive Branch.” The scope of this commitment is vast and covers the preservation of wilderness, wildlife, natural and historical .resources, and concerns the effects of pollution, toxic chemicals, and potential damage caused by energy resource extraction. One of the specific problems considered by the Carter administration is the uncontrolled, and often hazardous, development on coastal barrier islands. Within the Department of the Interior a work group was establish- ed in 1977 to develop an effective plan for protecting the barrier island resource. This group was composed of specialists from various disciplines, agencies, and in- stitutional levels. With only one year alloted to prepare its plan, the work group utilized existing data bases from the operational programs of participating agen- cies. The data in this report, which are from the U.S. Geological Survey’s nationwide land use and land cover mapping program, represent the USGS contribution to the barrier island study. Thus, this report indicates the commitment of the U.S. Geological Survey to applying earth science information to environmental manage- ment and problem-solving. Since data are primarily being presented for analysis, rather than as being analyzed in this report, the text has been kept brief by summarizing why and how the data were prepared, what statistical significance these data have, and finally, by a general discussion of regional pat- terns. The basic land use and land cover data are compil- ed in two appendices: the one tabular—of area statistics by individual barrier island; and the other one graphic—of sections of the 1972-75, 1:250,000-scale USGS open-file land use and land cover maps showing the barrier islands and adjacent coastal land. Using this format, a complete, although generalized, data set on barrier island land use and land cover conditions and trends is presented herein for use in resource and en- vironmental analysis. Care should be exercised in the interpretation and use of the land use and land cover area values. Any limita- tion in the utility of these data results from several fac- tors characteristic of the photointerpretation and area measurement techniques used. For example, the 1945—55 data were derived from unrectified aerial photographs. Without planimetric control, measure- ments made from these photographs contain inherent geometric inaccuracies. Similarly, the planimeter technique used in measuring the area of each land use and land cover category may contain a degree of inac- curacy. Also, there are “selectivity” errors intrinsic to mapping limitations necessarily specified for any land use and land cover classification system. A prime exam- ple is minimum mapping sizes. Using the criteria applied to Geological Survey maps, a beach 10 miles long and 500 feet wide will not appear on the maps because the USGS rule is that linear features must be at least 660 feet wide in order to be mapped. Similarly, some small residential or commercial areas will go unmapped since the minimum mapping unit for all urban or built-up areas is 10 acres. Thus, a small housing development (15 to 20 houses on 7 or 8 acres) built along the primary dune line would be mapped as beach, and appear in the area summary as part of the barren land acreage. Several other problems complicated the compilation of the land use and land cover data. The boundary of each barrier island, for example, was not precisely delineated by the Department of the Interior work group. In some . cases the barrier islands were actually barrier beaches, with no distinct landward boundary. In such instances arbitrary delineations had to be made by the land use data compilers. Since the photographs used for the 1945—55 data were of lesser optical quality than the 1972-75 data, consistent boundary determinations be- tween the two time periods, for each barrier island, were often not possible. This frequently resulted in differences in the total area of barrier islands between the two time periods. In many cases these differences were insignificant, but in others they might be quite VII VIII significant. It should be recognized, therefore, that a difference in the total area of a barrier island between these two time periods is not necessarily attributable en- tirely to actual land area change. Similarly, area differences could result from varia- tions in tidal conditions between the two periods. It is possible that the 1945—55 photographs were obtained during high tide and the 1972—75 photographs during low tide, or vice versa. Although this may have a small effect on the measured area for most islands, in some cases (where there is a high tidal range or a low beach profile) it may be significant. Clearly, problems and differences like those stated PREFACE above make difficult the precise measurement of land? use and land cover acreage at two points in time. With all such factors operating simultaneously, the area measurement task is a complex one, and the acreage values obtained are inexact. Nevertheless, the author believes that the percentage values of land in each category reflect the true surface condition. Several members of the U.S. Geological Survey made substantial contributions to this report. Karen Letke, Robert DeAngelis, Thomas Johnson, and David Wolf compiled and planimetered the 1945—55 land use and land cover maps. George Rosenfield provided the statistical method by which the data were analyzed. PATTERNS AND TRENDS OF LAND USE AND LAND COVER ON ATLANTIC AND GULF COAST BARRIER ISLANDS By Harry F. Lins, Jr. ABSTRACT Data prepared as part of the US. Geological Survey’s nationwide landuse and land cover mapping program have been applied to a Federal study designed to provide recommendations to the President on methods for protecting undeveloped coastal barrier islands. These land use and land cover data covered two time periods, 1945—55 and 1972—75, and included information on intervening changes. They were used by the Federal study group in an inventory and assessment of developed and undeveloped barrier islands. In addition, state and regional summaries were prepared to facilitate area analysis. Based on the 1972-75 data, several general patterns of land use and land cover were discerned along the Atlantic and Gulf coast barrier islands. Wetlands were found to cover nearly one-half of the total area of all barrier islands. Urban and built—up land, and barren land each occupied almost 14 percent of the total area, while forest land covered about 10 percent. In combination, these four categories accounted for nearly 90 percent of the total 1972—75 barrier island land area. Changes in land use and land cover between 1945—55 and 1972—75 were significant along the entire coastline from Maine to Texas. With the exception of urban or built—up land, all categories of land use and land cover decreased between the two time periods. Urban or built-up land in- creased by nearly 140,000 acres, while wetlands, the category most af- fected by this urban growth, declined by almost 80,000 acres. INTRODUCTION On May 23, 1977 President Carter presented a broad and comprehensive environmental message to the Con- gress (Carter, 197 7). The President proposed actions to control pollution and protect health, assure environmen- tally sound energy development, improve the urban en- vironment, protect natural resources, preserve national heritage, protect wildlife, affirm our concern for the global environment, and improve the implementation of environmental laws. As part of his plan for protecting natural resources the President specifically included coastal barrier islands when he said: Coastal barrier islands are a fragile buffer between the wetlands and the sea. The 189 barrier islands on the Atlantic and Gulf Coasts are an integral part of an ecosystem which helps protect inland areas from flood waves and hurricanes. Many of them are unstable and not suited for development, yet in the past the federal government has subsidized and insured new construction on them. Eventually, we can expect heavy economic losses from this shortsighted policy. About 68 coastal barrier islands are still unspoiled. Because I believe these remaining natural islands should be protected from unwise development, I am directing the Secretary of the Interior, in consulta- tion with the Secretary of Commerce, the Council on Environmental Quality, state and local oflicials of coastal areas, to develop an efl’ective plan for protecting the islands. His report should include recommendations for action to achieve this purpose. 1 In following the President’s directive, the Secretary of the Interior established the Barrier Island Work Group consisting of representatives from the Heritage Conser- vation and Recreation Service (HCRS, formerly the Bureau of Outdoor Recreation), the Fish and Wildlife Service (FWS), the National Park Service (NPS), the Office of Coastal Zone Management (OCZM), the Council on Environmental Quality (CEQ), and the Barrier Island Coalition (a consortium of private conservation organizations), with the Heritage Conservation and Recreation Service functioning as lead agency. The Geological Survey was subsequently invited to par- ticipate by the HCRS through the Secretary of the In- terior and the Assistant Secretary for Energy and Minerals. The work group’s mandate included the development of protection methods, and recommendations for their implementation. This requred detailed scientific and resource information on each barrier island, in addition to an evaluation of the numerous possible legal forms of protection. The group’s first step was to separate those islands which were developed from those undeveloped or unspoiled. The undeveloped islands then had to be separated into protected and unprotected classes. A bar- rier island classification system was established with Category I, developed; Category II, undeveloped and unprotected; and Category III, protected. This classification system formed the basis for protection planning. Island categorization (developed versus undeveloped) could most easily be determined by using recent infor- mation on land use and land cover. The US. Geological Survey was asked to provide these data, which were be- ing compiled as part of its nationwide land use and land cover mapping program. Since the Geological Survey ‘ Although the President’s message specified 189 barrier islands, the total number of islands included in the resulting study was 282, reflecting broader definitional guidelines established by the work group. 1 2 PATTERNS AND TRENDS OF LAND USE AND LAND COVER ON BARRIER ISLANDS had given priority to the mapping of coastal areas in the preceding three years, nearly all of the Atlantic and Gulf coastal barrier islands had been mapped before the HCRS request. In addition to providing land use and land cover statistics for the 1972—7 5 period for use in determining the developed state of barrier islands, an assessment of land use and land cover changes on the barrier islands was also made. The purpose of this assessment was to provide data on the location, types, and magnitude of land use and land cover changes on barrier islands which could be used as a guide for estimating future trends in land use change. METHODOLOGY The barrier island land use and land cover area statistics depict land conditions for both 1945—55 and 197 2—75, and the attendant changes between these two time periods. These data are presented as Appendix 1. Sections of the maps, from which the 197 2—75 data were compiled, are presented as Appendix II. The area values of land use and land cover were determined from two series of maps that had been compiled from remotely sensed data. This study was initiated with land use and land cover information being interpreted from, and mapped direct- ly on, a series of 1945—55 aerial photographic indices. 2 This interpretation was based on the Level I categories of the USGS classification system designed specifically for use with remotely sensed data (Anderson and others, 1976) (table 1). Area measurements of land use and land cover on each barrier island were then compiled using an electronic digitizer as a planimeter. A similar technique was then used to compile the statistical data for the 1972—75 period. Maps were not compiled, however, since mapped data were already available for this time period from the Geological Survey’s nationwide land use and land cover mapping program. These maps, compiled from remotely sensed data using the Level II categories of the USGS classification system, were similar to the maps of the 1945—55 period. To facilitate comparisons between the two time periods, however, all data were recorded at Level 1. Because of the dissimilarities in the aerial photographs for the two time periods, and the medium to small mapping scales used (approximately 1:63,360 for 1945—55, and 1:250,000 for 1972—75), the accuracy of the Appendix I data varies. This problem is complicated by the 10-acre minimum mapping unit used in compiling both sets of maps. Some land features, such as pocket beaches, wooded parcels, and residential areas are often 2 These data included USGS photo indices (scale 1262,500 to 1:68.500) and high-altitude black and white photographs (1:30,000 and 1:60,000), Agricultural Stabilization and Conservation Service (ASCS) photo indices (1:63,360) and black and white photographs (120,000), Soil Con- servation Service (SCS) photo indices (1:63,360), and National Ocean Survey (NOS) black and white photographs (1:10,000 and 120,000). TABLE 1.—Land use and lomd cover classification system for use with remotely sensed data [Single-digit classes (boldface type) represent Level I categories; twodigit classes (lightface) represent Level II categories] 1 . Urban or Built-up Land 11. Residential 12. Commercial and Services 13. Industrial 14. Transportation, Communications and Utilities 15. Industrial and Commercial Complexes 16. Mixed Urban or Built-up Land 17. Other Urban or Built-up Land 2. Agricultural Land 21. Cropland and Pasture 22. Orchards, Groves, Vineyards, Nurseries, and Ornamental Horticultural Areas 23. Confined Feeding Operations 24. Other Agricultural Land 3. Rangeland 31. Herbaceous Rangeland 32. Shrub and Brush Rangeland 33. Mixed Rangeland 4. Forest Land 41. Deciduous Forest Land 42. Evergreen Forest Land 43. Mixed Forest Land 5. Water 51. Streams and Canals 52. Lakes 53. Reservoirs 54. Bays and Estuaries 6. Wetland 61. Forested Wetland 62. Nonforested Wetland 7. Barren Land 71. Dry Salt Flats 72. Beaches 73. Sandy Areas other than Beaches 74. Bare Exposed Rock 75. Strip Mines, Quarries, and Gravel Pits 76. Transitional Areas 77. Mixed Barren Land 8. Tundra 81. Shrub and Brush Tundra 82. Herbaceous Tundra 83. Bare Ground Tundra 84. Wet Tundra 85. Mixed Tundra 9. Perennial Snow or Ice 91. Perennial Snowfields 92. Glaciers smaller than 10 acres and thus are not mapped, resulting in inaccurate area values. DATA DESCRIPTION AND REGIONAL ANALYSIS In addition to the compilation of area statistics of land use and land cover by individual barrier island, state summaries of these data were also prepared for the Bar- rier Island Work Group (tables 2—4). The State sum- maries were useful to the work group in two ways. First, DATA DESCRIPTION AND REGIONAL ANALYSIS 3 TABLE 2.—Area values of Level I land use and land cover on barrier islands, 1945—1955, by State [Acres in thousands (boldface type); percents below (lightface); dashes ( _____ ) indicate negligible or no mapping data available; NA indicates category not applicable] Island location by State U143]; lizéiuilt- Agrlxsczlltural Rangeland Forest land. Water bodies Wetland Barren land Total acres Maine ____________ 593 NA 105 206 _____ 531 213 1,648 36.0 NA 6.4 12.5 _____ 32.2 12.9 New Hampshire ..__ 467 NA NA NA NA 546 NA 1,013 46.1 NA NA NA NA 53.9 NA Massachusetts ..___ 4,519 11 4,793 1,310 528 9,608 13,511 34,280 13.2 0.1 14.0 3.8 1.5 28.0 39.4 Rhode Island ______ 773 184 153 74 243 1,334 566 3,327 23.3 5.5 4.6 2.2 7.3 40.1 17.0 Connecticut _______ 264 NA NA NA NA 778 185 1,227 21.5 NA NA NA NA 63.4 15.1 New York ________ 8,140 358 1,524 2,228 357 7,455 9,813 29,875 27.2 1.2 5.1 7.5 1.2 25.0 32.8 New Jersey _______ 17,746 88 NA 1,323 1,603 15,701 10,881 47,342 37.4 0.2 NA 2.8 3.4 33.2 23.0 Delaware _________ 1,507 101 NA 696 114 5,711 1,957 10,086 15.0 1.0 NA 6.9 1.1 56.6 19.4 Maryland _________ 820 NA NA 484 100 6,413 4,208 12,025 6.8 NA NA 4.0 0.9 53.3 35.0 Virginia _____________________ NA 3,360 2,554 51,703 9,398 67,015 __________ NA 5.0 3.8 76 8 14.0 North Carolina ___— 5,862 NA NA 14,148 1,118 88,925 40,812 151,195 3.9 NA NA 9.4 0.9 58.8 27.0 South Carolina ____ 1,654 9,766 NA 26,133 1,731 107,802 7,792 154,878 1.1 6.3 NA 16.9 1.1 69.6 5.0 Georgia __________ 5,161 1,116 4,724 43,577 3,297 106,786 6,774 171,435 3.0 0.7 2.8 25.4 1.9 62.3 3.9 Florida ___________ 32,007 3,057 593 69,505 75,722 281,186 52,835 514,905 6.2 0.6 0.1 13.5 14.7 54.6 10.3 Alabama ______________ NA _____ 4,301 3,398 13,288 5,494 26,481 _____ NA _____ 16.2 12.8 50.2 20.8 Mississippi _______ NA NA NA —0— NA 5,946 3,732 9,678 NA NA NA 0.0 NA 61.4 38.6 Louisiana _________ 1,651 NA NA NA 1,419 26,447 7,611 37,128 4.5 NA NA NA 3.8 71.2 20.5 Texas ____________ 9,246 65 89,127 816 9,508 187,855 80,545 377,162 2.5 0.02 23.6 0 2 2.5 49.8 21.4 Totals: All States _ 90,410 14,746 101,019 168,161 101,992 918,015 256,357 1,650,700 5.5 0.9 6.1 10.2 6.2 55.6 15.5 many State-level agencies provided information in the form of State summaries. Similarly, cooperating Federal agencies supplied data which were aggregated by State. The State summaries of land use and land cover information were, therefore, more easily cor- related with these other data sets. Second, a major part of the work group’s investigation focused on barrier island protection. Since the legal protection of land in- volves a consideration of ownership that, in turn, often involves State law, it was expedient to have the land use and' land cover data summarized by State. Several distinct patterns of land use and land cover can be quickly discerned from table 3. For example, Florida had the largest barrier island area in 1972—75, with more than one-half million acres. Barrier islands in Florida also had the largest area in urban or built-up land with nearly 102,000 acres. This value represents nearly 20 percent of the total barrier island area within the state and about 6 percent of the total or built-up area on all barrier islands of the Atlantic and Gulf coasts. New Hampshire, in contrast with Florida, has the smallest barrier island area, just under 1,100 acres, with a little less than 800 acres or 72 percent urbanized. Ur— ban or built-up land is found on the barrier islands of every state along the Atlantic and Gulf coasts except Mississippi. Its five islands, all located offshore, are only accessible from the mainland by boat. Moreover, The Mississippi islands are in a natural, undeveloped condi— tion with about 61 percent of their area in wetland, 37 percent in barren land (beaches and dunes), and nearly 2 percent in forest land. Wetland is the only land use and land cover category consistently found on the barrier islands of every State (table 3). Composing about half of the total barrier island land area, wetland varies from less than 15 percent in Maine to more than 67 percent in Virginia. Barren land, another ubiquitous category, occupies slightly more area than urban or built-up land (approx- f. PATTERNS AND TRENDS OF LAND USE AND LAND COVER 0N BARRIER ISLANDS TABLE 3.—A’rea values of Level I land use and land cover on barrier islands, 1972—1975, by State [Acres in thousands (boldface type); percents below (lightface); dashes ( _____ ) indicate negligible or no mapping data available; NA indicates category not applicable] Urban or built- Agricultural Island location by State up land la n d Rangeland Forest land Water bodies Wetland Barren land Total acres Maine ____________ 1,165 NA _____ 84 _____ 239 134 1,622 71.8 NA _____ 5.2 _____ 14.7 8.3 New Hampshire ___ 780 NA NA NA NA 301 NA 1,081 72.1 NA NA NA NA 27.9 NA Massachusetts ____ 8,128 70 4,454 1,220 582 8,900 14,407 37,761 21.5 0.2 11.8 3.2 1.5 23.6 38.2 Rhode Island ______ 1,226 246 153 162 213 1,430 94 3,524 34.8 7.0 4.3 4.6 6.0 40.6 2.7 Connecticut _______ 576 NA NA NA NA 563 218 1,357 42.4 NA NA NA NA 41.5 16.1 New York ________ 11,578 273 1,580 1,508 550 7,368 10,171 33,028 35.0 0.8 4.8 4.5 1.7 22.4 30.7 New Jersey _______ 22,719 358 NA 627 1,824 13,255 9,172 47,955 47.4 0.8 NA 1.3 3.8 27.6 19.1 Delaware _________ 2,956 26 NA 64 262 4,115 2,688 10,111 29.2 0.2 NA 0.6 2.6 40.7 26.7 Maryland _________ 1,848 NA NA 651 160 5,975 4,850 13,484 13.7 NA NA 4.8 1.2 44.3 36.0 Virginia __________ 1,144 51 NA 4,487 2,327 46,404 14,505 68,918 1.6 0.1 NA 6.5 3.3 67.5 21.0 North Carolina ____ 21,625 NA NA 11,769 1,224 78,202 42,057 154,877 14.0 NA NA 7.6 0.8 50.5 27.6 South Carolina ____ 13,081 5,152 NA 24,994 2,178 100,949 8,234 154,588 8.5 3.3 NA 16.2 1.4 65.3 5.3 Georgia __________ 8,436 1,459 3,930 42,375 3,903 103,551 7,944 171,598 4.9 0.9 2.3 24.7 2.3 60.3 4.6 Florida ___________ 101,988 2,437 1,260 56,001 73,769 244,791 38,687 518,933 19.7 0.5 0.2 10.8 14.2 47.1 7.5 Alabama _________ 5,273 NA 2,130 6,951 3,123 6,687 4,049 28,213 18.7 NA 7.5 24.8 11.0 23.7 14.3 Mississippi _______ NA NA NA 179 NA 5,964 3,584 9,727 NA NA NA 1.8 NA 61.4 36.8 Louisiana _________ 6,746 NA NA NA 1,504 24,030 6,238 38,518 17.5 NA NA NA 3.9 62.4 16.2 Texas ____________ 19,410 88 85,305 1,152 9,631 186,158 82,209 383,953 5.3 0.02 23.5 0.3 2.7 51.2 21.0 Totals: All States _ 228,679 10,160 98,812 152,224 101,250 838,882 249,241 1,679,248 13.6 0.6 5.9 9.1 6.0 50.0 14.8 imately 249,000 acres). Almost all barren land occurs naturally as beaches or dunes. There are, however, some cases where barren land appears as transitional or “fill” areas, and these are characteristically found along the back-bay margins of barrier islands, marking sites of planned urban or built—up development. Such areas are observable in New Jersey, Delaware, Maryland, Virginia, North and South Carolina, and Florida- especially on the Gulf coast side. Land use and land cover changes between 1945—55 and 1972—75 on the barrier islands of Atlantic and Gulf coast states have been diverse, reflecting varying social, economic, and. political influences. Certain trends, have been uniform (table 4). Urban or built-up land, for example, has increased on barrier islands in every state except Mississippi, which has no urban land, and usually by dramatic proportions. Florida’s urbanized land in- creased by nearly 70,000 acres, North Carolina’s by more than 15,000 acres, and South Carolina’s by more than 11,000 acres; however, Connecticut and New Hampshire’s urbanized area increased by only 300 acres each. Most of this increase has been oriented toward recreation and second home development, although in Louisiana a part of the urban trend was commercial and industrial, in support of the development of offshore energy resources. With the exception of small increases in Rhode Island and Mississippi, wetland area decreased considerably in all states between 1945—55 and 1972—75, for a total loss of 80,000 acres. Barren also decreased, by more than 7,100 but this was not in a uniform pattern. In some states—Massachusetts, Connecticut, New York, Delaware, Maryland, Virginia, North Carolina, South Carolina,Georgia, and Texas—barren land actually in- creased—primarily as a result of increased transitional land area. Most of these gains, however, were each less than 1,200 acres, although Texas was nearly 1,700, and were readily offset by the sizeable losses in the other DATA DESCRIPTION AND REGIONAL ANALYSIS 5 TABLE 4.—Chomges in area values of Level I land use and land cover on barrier islands between 1945—55 and 1972—75, by State [Acres in thousands (boldface type); percents below (lightface); dashes ( _____ ) indicate negligible or no mapping data available; NA indicates category not applicable] Changes mapped Island location by State Urban or built- Agricultural Rangeland Forest land Water bodies Wetland Barren land between up land land 1945—55 and 1972—75 Maine ____________ +572 NA —105 ——122 _____ —292 —79 —26 +96.0 NA —100.0 —59.0 _____ —55.0 —37.0 —2.0 New Hampshire ___ +313 NA NA NA NA —245 _____ + 68 +67.0 NA NA NA NA —45.0 _____ +7.0 Massachusetts ___- + 3,609 + 59 ~ 339 — 90 + 54 — 708 + 896 + 3,481 +80.0 +5360 —7.0 —7.0 +10 —7.0 +7.0 +10.0 Rhode Island ______ +453 +62 _____ +88 —30 +96 —472 197 +59.0 +340 _____ +119.0 —12.0 +7.0 —83.0 +6-0 Connecticut _______ + 312 NA NA NA NA — 215 + 33 + 130 +118.0 NA NA NA NA ~28.0 +18.0 +11.0 New York ________ +3,438 —85 +56 —720 +193 —87 +358 +3,153 +42.0 —24.0 +4.0 -32.0 +54.0 —1.0 +4.0 +11.0 New Jersey _______ + 4,973 + 270 NA ~ 696 + 221 — 2,447 —1,709 + 613 +280 +307.0 NA —53.0 +14.0 —16.0 —16.0 +10 Delaware _________ + 1,449 — 75 NA — 632 + 148 — 1,596 + 731 + 25 +96.0 —74.0 NA —91.0 +56.0 —28.0 +37.0 +0-2 Maryland _________ + 1,028 NA NA + 167 + 60 — 438 + 642 + 1,459 +125.0 NA NA +35.0 +60.0 —7.0 +15.0 +12-0 Virginia __________ +1,144 +51 NA +1,127 —227 —5,299 +5,107 +1,903 + + NA +34.0 —9.0 —10.0 +54.0 +3-0 North Carolina - ___ + 15,763 NA NA — 2,379 — 194 —- 10,723 + 1,215 + 3,682 +269.0 NA NA ~17.0 —14.0 —12.0 +3.0 +2-0 South Carolina ___- +11,427 —4,614 NA —1,139 +447 —6,853 +442 —290 +691.0 +47.0 NA —4.0 +26.0 -6.0 +6.0 -0-2 Georgia __________ +3,275 +343 —794 —1,202 +606 —3,235 +1,170 +163 +63.0 +31.0 ~17.0 —3.0 +18.0 —3.0 +17.0 +0.09 Florida ___________ + 67,981 — 620 + 667 — 13,504 —- 1,953 — 36,395 —14,148 + 4,028 +219.0 —-20.0 +1120 —19.0 —3.0 —13.0 —27.0 +1.0 Alabama __________ + 5,273 NA + 2,130 + 2,650 — 275 — 6,601 . — 1,445 + 1,732 + NA + +62.0 —8.0 —-50.0 —26.0 +7.0 Mississippi ________ NA NA NA + 179 NA + 18 — 148 + 49 NA NA NA + NA + 0.3 — 4.0 + 0.5 Louisiana _________ + 5,095 NA NA NA + 85 —- 2,417 —1,373 + 1,390 +309.0 NA NA NA +6.0 —9.0 —18.0 +4.0 Texas ____________ + 10,164 + 23 -— 3,822 + 336 + 123 — 1,697 + 1,664 + 6,791 +110.0 +35.0 —4.0 +41.0 +1.0 —1.0 +2.0 +2.0 TOTALS _____ + 138,269 — 4,586 — 2,207 — 15,937 — 742 — 79,133 —-7,116 + 28,548 +153.0 —31.0 —2.0 —10.0 —0.7 —9.0 —3.0 +2.0 states. Florida, for example, lost more than 14,000 acres of barren land, New Jersey over 1,700, and Alabama more than 1,400 acres. For regional and environmental analysis of barrier island land use and land cover data, a systematic mor- phological grouping based primarily on barrier island geological and geomorphological characteristics, and following in part the coastal classification work of Dolan and others (1975) was prepared. Eight regional groups were delineated along the Atlantic and Gulf coasts (fig. 1). Each has a different set of shoreline configurations, composition, and dynamic properties. The land use and land cover data, summarized according to this regionalization, appear in tables 5 to 7. A description of each regional group follows. Group 1, consisting of 21 New England barrier islands, is located between Sheepscot, Me., and Long Beach, Mass. (App. II, figs. 8—12). The shoreline characteristics of this coastal region vary from rocky in Maine, to sandy pocket beaches in Massachusetts. The coastline throughout is essentially low-cliffed and com- posed primarily of older resistant rocks (Putnam and others, 1960). The 1972—75 data show 18 islands of this group with some level of urban development, 13 of them being more than 50 percent urbanized, and 4 of them,-Pine Point, Goose Creek, Wells Beach, and Nan- tasket Beach—totally, or 100 percent, urbanized. This high degree of urbanization is influenced by several conditions. First, barrier islands are aethestical- ly desirable for recreation and residence. Although these two societal factors exert considerable develop- ment pressure on all barrier islands, that pressure is strongly felt in the New England group where all 21 islands total a relatively small 14,769 acres. The size PATTERNS AND TRENDS OF LAND USE AND LAND COVER ON BARRIER ISLANDS Group 1 New England: (Sheepscot, Me., to Long Beach, Mass.) Group 2 New York Bight: (Sandy Neck, Mass, to Rockaway, N. Y.) Group 3 Mid-Atlantic: (Sandy Hook, N. J., to North ls., S. C.) Group 4 Sea Islands: (South ls., S. C. to Cumberland ls., Ga.) Group 5 Florida Atlantic: (Amelia ls., Fla., to Key Biscayne, Fla.) Group 6 Eastern Gulf Coast: (Cape Sable, Fla., to Cat ls., Miss.) Group 7 Louisiana: (Chandeleur ls., La., to Isles Dernieres, La.) Group 8 Texas: (Bolivar Peninsula, Tex., to Brazos ls., Tex.) lfi—LflJ—‘r—‘W—‘WA 0 200 400 REGIONAL GROUPINGS OF ATLANTIC AND GULF COAST BARRIER ISLANDS 400 MILES 600 KILOMETERS FIGURE 1.—Regional groupings of Atlantic and Gulf coast barrier islands. becomes even more critical when the area is further influenced by proximity to large coastal cities. Most of these Group 1 barrier islands are located near Bath, Portland, Portsmouth, and Boston, and are linked to these cities by a good transportation network. Finally, the relatively stable geomorphological nature of these islands enhances their suitability for development, thereby attracting people who might otherwise choose to build in safer areas. Approximately 43 percent, or nearly 6,300 acres, of the total New England group area is urban or built-up land (table 6). Wetland accounts for 30 percent or nearly DATA DESCRIPTION AND REGIONAL ANALYSIS 7 TABLE 5.——Area values of Level I land use and land cover on barrier islands for 1945—55, by regional group [Acres in thousand (boldface type); percents below (lightface): dashes ( _____ ) indicate negligible or no mapping data available; NA indicates category not applicable] Urban or built- Agricultural Island location by group up land land Rangeland Forest land Water bodies Wetland Barren land Total acres New England _____ 4,279 _____ 105 726 _____ 5,627 2,935 13,672 31.3 _____ 0.8 5.3 _____ 41.2 21.4 New York Bight ___ 10,477 553 6,470 3,092 1,128 14,625 21,353 57,698 18.2 1.0 1.2 5.4 1.9 25 3 37.0 Mid-Atlantic ______ 26,234 189 NA 20,599 6,421 179,341 69,723 302,507 8.7 0.1 NA 6.8 2.1 59.3 23.0 Sea Islands _______ 6,516 10,882 4,724 69,122 4,396 203,700 12,129 311,469 2.1 3.5 1.5 22.2 1.4 65.4 3.9 Florida Atlantic ___ 22,646 3,057 _____ 45,071 749 54,088 21,130 146,741 15.4 2.2 _____ 30.7 0.5 36.8 14.4 Eastern Gulf Coast- 9,361 NA 593 28,735 78,371 246,332 40,931 404,323 2.3 NA 0.1 7.2 19.4 60.9 10.1 Louisiana _________ 1,651 NA NA NA 1,419 26,447 7,611 37,128 4 5 NA NA NA 3.8 71.2 20.5 Texas ____________ 9,246 65 89,127 816 9,508 187,855 80,545 377,162 2.5 0.02 23.6 0.2 2.5 49.8 21.4 TOTALS _______ 90,410 14,746 101,019 168,161 101,992 918,015 256,357 1,650,700 5.5 0.9 6.1 10.2 6.2 55.6 15.5 4,500 acres of the group area, barren land 22 percent or a little more than 3,200 acres (primarily beaches), and forest land 5 percent or nearly 800 acres. Between 1945—55 and 197 2—75 the predominant land use and land cover trend on the New England barrier islands was toward an increase in urban land of 47 percent, or a little over 2,000 acres. This urbanization was primarily at the expense of wetland, which diminished by 21 percent or nearly 1,200 acres. Group 2, the New York Bight barrier islands, is a quite different island group morphologically. Stretching from Sandy Neck, Mass, to Rockaway, N.Y. (App. II, figs. 12-27), this group is a remnant of Pleistocene glacia- tion, composed of glacial and fluvioglacial deposits (King and Beikman, 1974). The coastal zone adjacent to the New York Bight is hilly, with moderate local relief and gentle slopes. The barrier island shorelines are primarily of sandy beach form, although some are characterized by pocket beaches (Putnam and others, 1960). With a total area of nearly 64,000 acres in the 40 islands, 24 evidence some urban development, 9 are more than 50 percent urbanized, and 2—Madaket and North Haven—are totally urbanized. Although the Group 2 islands had over 17,000 acres of urban or built-up land in 1972—75 (nearly three times that in Group 1; see table 6), this acreage corresponded to 27 percent of the total group area, much less than the 43 percent value in Group 1. One reason for this is that several of the Group 2 islands are physically isolated so access is limited. Muskeget, Nashawena, Cuttyhunk, and Block Islands, as well as parts of Martha’s Vineyard and Nantucket, are good examples. Another reason is TABLE 6.—Area values of Level I land use and land cover on barrier islands for 1972—75, by regional group [Acres in thousands (boldface type); percents below (lightface); dashes ( _____ ) indicate negligible or no mapping data available: NA indicates category not applicable] Island location by group U113; lgzguilt- Agrlifiztlltural Rangeland Forest land Water bodies Wetland Barren land Total acres New England _____ 6,291 __________ 779 _____ 4,461 3,238 14,769 42.6 __________ 5.3 _____ 30.2 21.9 New York Bight __ 17,162 589 6,187 2,195 1,345 14,340 21,786 63,604 27.0 0.9 9.7 3.5 2.1 22.5 34.3 Mid-Atlantic ______ 52,173 435 _____ 18,469 6,380 158,441 73,681 309,579 16.8 0.1 _____ 6.0 2.1 51.2 23.8 Sea Islands _______ 19,636 6,611 3,930 66,498 5,498 194,010 15,769 311,952 6.3 2.1 1.3 21.3 1.8 62.2 5.0 Florida Atlantic ___ 69,659 2,281 214 26,618 1,171 39,754 10,745 150,442 46.3 1.5 0.1 17.7 0.8 26.4 7.2 Eastern Gulf Coast- 37,602 156 3,176 36,513 75,721 217,688 35,575 406,431 9.2 0.04 0.8 9.0 18.6 53.6 8.8 Louisiana _________ 6,746 NA NA NA 1,504 24,030 6,238 38,518 17.5 NA NA NA 3.9 62.4 16.2 Texas ____________ 19,410 88 85,305 1,152 9,631 186,158 82,209 383,953 5.1 0.02 22.2 0.3 2.5 48.5 21.4 TOTALS _______ 228,679 10,160 98,812 152,224 101,250 838,882 249,241 1,679,248 13.6 0.6 5.9 9.1 6.0 50.0 14.8 8 PATTERNS AND TRENDS OF LAND USE AND LAND COVER ON BARRIER ISLANDS TABLE 7 .——Changes in area values of Level I land use and land cover on barrier islands between 1945—55 and 1972-75, by regional group [Acres in thousands (boldface type) : percents below (lightface) ; dashes ( _____ ) indicate negligible or no mapping data available; + sign only indicates increase not compared: NA indicates category not applicable] Changes Island location by group Urban or built- Agricultural Rangeland Forest land Water bodies Wetland Barren land 1:232:31 up land land 1945_55 and 1972—75 New England _____ +2,012 _____ —105 +53 _____ —l,166 +303 +1,097 +47.0 _____ —100.0 +7.0 _____ ~21.0 +10.0 +8.0 New York Bight ___ +6,685 +36 —283 —897 +217 +285 +433 +5,906 +39.0 +7.0 —4.0 —29.0 +19.0 ~2.0 +2.0 +10.0 Mid-Atlantic ______ + 25,939 + 246 _____ —- 2,130 — 41 — 20,900 + 3,640 + 7,072 +99.0 +130.0 _____ —10.0 —0.6 —12.0 +6.0 +2.0 Sea Islands _______ +13,120 —4,271 —794 —2,624 +1,102 —9,690 +3,617 +483 +201.0 —39.0 —17.0 —4.0 +25.0 —5.0 +30.0 +0.2 Florida Atlantic -__ +47,013 —776 +214 —18,453 +422 —14,331 —10,385 +3,701 +208.0 —25.0 + —41.0 +56.0 —27.0 —49.0 +3.0 Eastern Gulf Coast_ +28,241 +156 +2,583 +7,778 ~-2,650 —28,644 —5,356 +2,108 +302.0 + +436.0 +27.0 —3.0 —12.0 ~13.0 +1.0 Louisiana _________ + 5,095 NA NA NA + 85 — 2,417 -— 1,373 + 1,390 +309.0 NA NA NA +6.0 -9.0 —18.0 +4.0 Texas ____________ +10,164 +23 —3,822 +336 +123 —1,697 +1,664 +6,791 +110.0 +35.0 —4.0 +41.0 +1.0 —.0 +2.0 +2.0 TOTALS _______ +138,269 —4,586 —2,207 —15,937 —742 —79,l33 —7,116 +28,548 +1530 ~31.0 —-2.0 —10.0 —0.7 —9.0 —3.0 +2.0 that several islands, including Eastham, Nauset, and Monomoy, are protected as national seashores, national wildlife refuges, or state parks. In 1972—75, besides the 17,000 acres in urban or built-up land, the New York Bight islands had approximately 22,000 acres in barren land (primarily beaches), 14,000 acres in wetland, 6,000 acres in rangeland (vegetated dunes), and 2,200 acres in forest land. Land use and land cover change on these islands was minimal between 1945—55 and 1972—75, except in the ur- ban or built-up category where there was a 39 percent or 6,700-acre increase. Contributing to this were cor- responding decreases in forest land (900 acres), rangeland (300 acres), and wetland (300 acres). In- terestingly, the total Group 2 area increased by nearly 6,000 acres. Such a large increase in total area is difficult to explain with certainty since it is unlikely that filling operations accounted for so much additional land area. It is more probable that part of this measured change is erroneous, and is the cumulative effect of smaller inaccuracies in interpretation and measure- ment. Of the changes in total group area, between 1945—55 and 1972—75, Group 2 with 10 percent had the largest percentage area change for all eight groups. Most of the other changes fell within four percent, a range almost entirely attributable to error in interpreta- tion and to mensuration technique. The statistical significance of measured changes is discussed later in the report. Continuing south along the coast, from Sandy Hook, NJ. to North Island, 8.0., are the Group 3 or Mid- Atlantic barrier islands (App. 11, figs. 28—52). This entire group forms a part of the seaward edge of the continent’s eastern coastal plain. These islands are characterized by broad sandy beaches, and are primarily composed of Pleistocene marine sediments (Dolan, 1970; King and Beikman,‘ 1974). There are 53 barrier islands in the Mid-Atlantic group, with a total area of over 300,000 acres. Of the 53 islands, 35 contain some urban development. Only 6 however, Sandy Hook, Barnegat, Long Beach, Atlantic City, Ocean City, and Fenwick South, are more than 50 percent urbanized, and none are totally urbanized. Wetland vegetation is the predominant land cover type throughout this group with nearly 159,000 acres, or just over half the total group area. Wetlands form a nearly continuous strip along the back-bay side of these barrier islands. The next major area, with over 73,000 acres or 24 percent in barren land, is primarily ocean- front beach and dunes. Urban or built-up land is third in extent with 52,000 acres or 17 percent. Most of this con- sists of resort cities, such as Wildwood, Rehoboth, Bethany, and Ocean City. These areas are characterized by extensive commercial sectors (hotels, motels, and restaurants) and large seasonal population fluctuations. There are, however, some permanent urbanized com- munities in Group 3 that maintain a more stable popula- tion and economy throughout the year. The New Jersey coastline between Atlantic City and Ocean City is the best example. Urban development on these Mid-Atlantic barrier islands has typically located along the primary dune line, and extended back through the adjacent DATA DESCRIPTION AND REGIONAL ANALYSIS 9 grassland zone. In highly developed areas, building has continued even farther back-island, into the marshlands bordering the back-bays. Between 1945—55 and 1972—75 the most significant changes occurring on the Mid-Atlantic islands were in the urban or built-up and wetland categories. As with Group 2, the largest change occurred in the area of ur- ban land, which doubled, increasing by nearly 26,000 acres. Most of this urban expansion was into wetlands, which decreased by nearly 21,000 acres or 12 percent. Group 4, the Sea Islands, extends from South Island, SC. to Cumberland Island, Ga. (App. II, figs. 53—62). These 44 islands are also a part of the eastern coastal plain but, unlike their Mid-Atlantic counterparts, are primarily composed of Holocene, not Pleistocene, sediments (King and Beikman, 1974). They are further differentiated from the Group 3 islands by their physical structure. While the Mid-Atlantic islands are primarily a system of elongated sandy beaches, the Sea Islands ex— hibit no such elongated, interconnecting beach characteristic. These islands stand more as individual outliers of a broad wetland—estuarine system. Group 4 has a total area of 312,000 acres: of its 44 islands, only 15 have any urban development, and only one, Sullivans, is more than 50 percent urbanized. The Sea Islands are largely dominated by wetland vegeta- tion which totals over 194,000 acres, or more than 60 percent of their total area. Forest land also occupies a relatively large area with over 66,000 acres. Urban or built-up land, on the other hand, constitutes less than 7 percent of the total area with just under 20,000 acres. Even so, there has been a threefold or 13,000 acre in— crease in urban land use between 1945—55 and 197 2—75. Accompanying this urban area increase were corre— sponding decreases in the area of agricultural land by over 4,000 acres (—39 percent), and in wetland by over 9,000 acres (—5 percent). Group 5, the Florida Atlantic barrier islands, begins at Amelia Island and continues to Key Biscayne (App. II, figs. 63—77). The first 12 of its 22 islands, including Hut- chinson Island,are composed of Holocene materials,and the remaining 10, from Jupiter Island south, of Pleistocene materials (King and Beikman, 1974). All these islands are more like those in Group 3, and less like those in Group 4, in that they form an elongated beach continuum rather than a series of dissected islands. Based on the 1972—75 data, 21 of these 22 islands show some urban development. Of these, 11 are more than 50 percent urbanized, and 1 (Hillsboro Beach) is totally urbanized. Out of a total area of about 150,000 acres, almost 70,000 acres are in urban or built-up land. The second largest category is wetland, comprising nearly 40,000 acres or 26 percent of the total area. Forest land occupies about 27,000 acres, or roughly 18 percent of the Group 5 area, while barren land covers nearly 11,000 acres or just over 7 percent of the total. Between 1945—55 and 197 2—75 changes on the Florida Atlantic barrier islands were extensive. As in the Group 4 islands, urban or built-up land, for example, sustained a threefold increase, corresponding in this case to over 47,000 acres. Balancing this urban increase were marked decreases in several other land use and land cover categories. Forest land was most affected, losing over 18,000 acres (— 41 percent). Wetland area decreas- ed by more than 14,000 acres (—27 percent), and barren land lost over 10,000 acres (—49 percent). Immediately adjacent to the Florida Atlantic barrier islands, on the south side, are the Florida Keys. Geologically, the Keys form a break in the chain of Atlantic and Gulf coast barrier islands. Whereas Florida’s barrier islands are formed of sand, the Florida Keys are formed of limestone. As a result of this mor- phological distinction, and since the Florida Keys are a relatively small proportion of all barrier islands, the Bar- rier Island work group elected not to include these in its study. The Group 6 or Eastern Gulf Coast barrier islands, form a chain northwestward from the Keys along the Gulf of Mexico, beginning at Cape Sable, Fla., and con- tinuing to Cat'Island, Miss., (App. II, figs. 78—104). This group includes 68 islands of varying geological composi- tion. Most of the Florida barrier islands are composed of either Eocene, Miocene, or Pleistocene sediments. However, all the Alabama and Mississippi islands are composed of Holocene materials (King and Beikman, 1974), and many are backed by extensive marshlands. As a group, the Eastern Gulf Coast barrier islands are much less developed than the Florida Atlantic islands. Of the 68, only 39 or 57 percent have some urban development, and of these only 12 islands (18 percent) are more than 50 percent urbanized. None are totally ur- banized. Based on the 1972—7 5 data, the Group 6 islands have a total area of over 406,000 acres. Wetland, the largest area, amounts to more than 217,000 acres or 54 percent of the total. Water bodies, primarily as em— bayments, form the next largest area with nearly 76,000 acres (19 percent), while barren land, forest land, and urban or built—up land all total approximately 36,000 acres or roughly 9 percent each. Between 1945—55 and 1972—75, the greatest change on the Group 6 islands occurred in urban or built-up land, which increased by slightly more than 28,000 acres. This considerable gain (302 percent) coincided with losses of 12 percent in wetland (29,000 acres), of 3 percent in water bodies (—2,600 acres), and 13 percent in barren lands (— 5,400 acres). There were also gains of 436 percent in rangeland (+ 2,600 acres), and of 27 per- cent in forest land (+ 7,800 acres). Farther to the west in the Gulf of Mexico, stretching from the Chandeleur Islands to Isle Dernieres, are the Louisiana, or Group 7, barrier islands (App. II, figs. 105—112). Totaling nearly 39,000 acres, this entire 10 PATTERNS AND TRENDS OF LAND USE AND LAND COVER 0N BARRIER ISLANDS group is composed of fine-grained deltaic deposits of Holocene age from the Mississippi River (Dolan, 1970; King and Beikman, 1974). Of these 18 islands, only Grand Isle is linked to the mainland by road. Most of the others form the leading edge of an isolated and segmented wetland-estuarine system. Only 8 of the Louisiana islands contain any urban development and all of those are less than half urban- ized. Grand Isle is the most extensively developed, with 48 percent of its area or 1,900 acres in urban or built-up land. The major portion of the group’s land area consists of 24,000 acres in wetlands, or 62 percent of the total area. Urban or built-up land is next in extent with just over 6,700 acres or 18 percent. A large part of this usage is related to the offshore oil and natural gas industry, with a comparatively small part devoted to residential or recreational land. Barren land occupies roughly the same area as urban or built-up land, just over 6,200 acres. The basic pattern of land use and land cover change on the Louisiana barrier islands is typical of most other groups between 1945—55 and 197 2—75. Urban or built-up land area has increased, while wetland area has de- creased. The magnitude of change was, however, greater in Louisiana than in most other island groups. For example, in the Louisiana group with less than 39,000 total acres, the urban or built-up land area in- creased by more than 5,000 acres. Whereas in 1945—55 urban or built-up land accounted for 4.5 percent of the total Group 7 area, by 197 2—75 this figure had soared to 17.5 percent, an increase of 13 percentage points. Within most other barrier island groups, the percentage of urban or built-up land increased by only 3 to 9 points during the same period. The development of Louisiana’s offshore petroleum industry is the primary reason for this difference. The Texas barrier island group, the eighth and final in this regional stratification, ranges from Bolivar Penin- sula to Brazos Island, Texas (App. II, figs. 113—125). Much of the backing coastal zone is composed of Pleistocene materials, although the islands themselves are almost entirely composed of Holocene deposits (King and Beikman, 1974). Their physical appearance is similar to the Mid-Atlantic barrier islands, with an inter- connecting system of elongated sandy beaches backed by an extensive wetland-estuarine system. Of the eight island groups, Texas has the second largest total area with nearly 384,000 acres. Also, with 16 it has the fewest number of islands, making them some of the largest along the Atlantic and Gulf coasts. Of these 16 islands, 11 contain some urban or built-up land. None, however, are more than 50 percent urbaniz- ed. Galveston Island is the most extensively developed, with 33 percent of its land area in an urban condition. To put this value in perspective, however, although only one-third of the area, it corresponds to nearly 10,000 acres, giving Galveston one of the largest proportions in urban or built-up land of all 282 barrier islands. In Group 8, as with most other groups, the largest individual land use and land cover category is wetland, with about 186,000 acres or 49 percent of the total area. This is followed by more than 85,000 acres in rangeland (22 per- cent), 82,000 acres in barren land (21 percent), and slightly less than 20,000 acres in urban or built—up land (5 percent). Despite the diversity of land use and land cover types in Group 8, land use and land cover changes between 1945—55 and 1972—75 were dominated by 2 categories, urban or built-up land and rangeland. Urban or built-up land more than doubled during this period, increasing by over 10,000 acres. Rangeland, on the other hand, decreased in area by nearly 4,000 acres. STATISTICAL SIGNIFICANCE At the beginning of the data compilation process it was recognized that inherent error factors exist in pho- tointerpretation, area measurement, and change men— suration procedures. Although some assumptions can be made in assessing the accuracy of a given data set based on consistency factors of interpreters and equipment, these assumptions cannot be applied to all compilation variables. Thus, to validate assessments of land use and land cover changes for the barrier islands, this in- vestigator needed to know if the values of change, as measured by a planimeter, were real, or part of the in- herent error involved in the mapping and measuring technique. A particular concern was with the statistical significance of the change values that resulted from mapping work done at two different times, with different types of photography, and at several different scales. To determine the amount of change which could be at- tributable to procedural “noise” versus real change, a statistical technique was designed and applied to the land use and land cover change data. Based on the stan- dard error factor for mapping at various scales, and the areas of measured categories, the expected value of area change—that is, the change resulting from inherent technique errors—was calculated. A test of the null hypothesis, which assumes the change in area to be due to measurement error, was then employed to determine whether or not the indicated change was caused by error in measurement alone. If the null hypothesis was re- jected (indicating that the change in area was probably real) then an alternative hypothesis, which assumes the change in area to be real, was tested. The alternative hypothesis was evaluated at the 95 percent level of confidence using the Student’s t-statistic. Acceptance of the alternative hypothesis indicates that the change in land use area was real. The results of this evaluation are presented in table 8. As table 8 shows, it is possible to discern several significant statistical characteristics in the study’s land STATISTICAL SIGNIFICANCE / CONCLUSIONS TABLE 8.—Statistical significance of land use and land cover area changes by regional group [The “N” signifies acceptance of null hypothesis meaning that the change measured was probably due to measurement error. The “A” signifies ac- ceptance of the alternative hypothesis meaning that the change measured was probably real, at the 95 percent confidence level] Urban or Agricul- Island built-up tural Range- Forest Water Wet- Barren group . land land land land bodies land land New England A A A N New York Bight A N N A N N N Mid-Atlantic A N N N A A Sea Islands A A A A A A A Florida Atlantic A A N A A A A East Gulf Coast A A A A A A A Louisiana A N A A Texas A N A N N N N use and land cover change data. For example, in all 8 of the barrier island regional groups, the measured change in urban or built-up land area was determined to be statistically significant at the 95 percent level of confidence. This determination indicates that most of the area change measured was real, that is, not at- tributable to inherent measurement error. The relative- ly large increases in each region’s urban or built—up area, which ranged from about 2,000 acres in the New England grOup to about 47,000 acres in the Florida Atlantic group, accounted for the statistical determina- tion that the changes were real rather than inherently erroneous. In contrast to this condition, area changes in agricultural land were not as statistically significant. Of the 8 island groups, only 5 contained any agricultural land—New York Bight, Mid-Atlantic, Sea Islands, Florida Atlantic, and Texas. Of these, the Sea Islands and the Florida groups were the only 2 with statistically significant area changes between 1945—55 and 1972—75. In both cases, moreover, the area of change was sizeable. The Sea Islands agricultural area dropped from about 10,900 acres to 6,600 acres, for a 4,300-acre loss during the 25-year period. In the same period, the same land use in the Florida Atlantic islands dropped from 3,100 acres to 2,300 acres, for an 800-acre loss. Com- paratively, agricultural land area changes in the other 3 island groups were small, amounting to about 20 acres, 40 acres, and 250 acres respectively for the islands of Texas, New York Bight, and Mid-Atlantic, which ac- counted for the acceptance of the null hypothesis for these groups. CONCLUSIONS Land use and land cover patterns on barrier islands vary widely in response to geographically diverse natural, cultural, and economic conditions. There are, however, several general patterns which prevail over most of the Atlantic and Gulf coast islands. For exam- ple, wetland and barren land (primarily beaches and 11 dunes) are naturally dominant cover conditions and are often accompanied by sizeable areas of forest land. Of the nearly 1.7 million acres making up the 282 barrier islands, wetland covers roughly half or 840,000 acres. Barren land occupies another 15 percent or 250,000 acres, while forest land covers slightly less than 10 per- cent or over 150,000 acres. The area of urban or built-up land is slightly less than the area of barren land, which means that four categories—wetland, urban or built-up land, barren land, and forest land— account for nearly 90 percent of the total 2,600-square mile area of Atlantic and Gulf Coast barrier islands. From a regional perspective, the most developed bar- rier islands are those in the Florida Atlantic group. Not only do these Group 5 islands have the largest total ur- banized acreage, nearly 70,000 acres, but they also have, with more than 46 percent, the largest proportion of ur- ban or built-up area of any group. Identification of the least developed group among the barrier islands depends on the criteria used to determine extent or degree of development. For example, with about 6,300 acres, the New England group has the smallest urban or built-up area. Accounting for nearly 43 percent of the Group 1 land area, however, this value represents the second largest urban area percentage among all the groups. New England also has the smallest total area among the 8 groups. The Texas group, on the other hand, has over 19,000 urbanized acres (more than three times that in New England), yet maintains the smallest urbanized percent of total area at just over 5 percent. Texas has the second largest total group area with over 380,000 acres. The most significant aspect of barrier island land use and land cover patterns relates to recent changes. Dur- ing the intervening period from 1945—55 to 1972—75, all categories of land use and land cover decreased except urban or built-up land, which increased by 138,000 acres. Wetlands were most affected by this urban development, losing nearly 80,000 acres. Forest land lost about 16,000 acres, while barren land decreased by 7,000. The most significant regional changes occurred on the Group 5 Florida Atlantic barrier islands where ur- ban or built-up land increased by over 47,000 acres, while forest land, wetland, barren land, and agricultural land all decreased by about 20,000, 15,000 10,000, and 1,000 acres respectively. The Group 6 Eastern Gulf Coast barrier islands also sustained significant changes during the 1945—55 to 1972—75 period. Urbanized land increased by more than 28,000 acres and forest land in- creased by nearly 8,000 acres, while wetlands were reduced by 30,000 acres and barren land lost over 5,000 acres. Although the two Florida groups appear to have undergone some of the largest changes recently, the land use and land cover data presented in this report in- dicate that barrier islands from Maine to Texas have ex- perienced substantial increases in urban land use since World War II. 12 PATTERNS AND TRENDS OF LAND USE AND LAND COVER ON BARRIER ISLANDS REFERENCES CITED Anderson, J. R., Hardy, E. E., Roach, J. R., and Witmer, R. E., 1976, Dolan, Robert, Hayden, Bruce, and Vincent, Mary, 1975, Classification A land use and land cover classification system for use with remote of the coastal landforms of the Americas: Zeitschrift fur Geomor- sensor data: U.S. Geological Survey Professional Paper 964, 28 p. phologie, Supplementband, v. 22, p. 72—88. Carter, J. E., 1977, Presidential message to the Congress on the envi- King, P. B., and Beikman, H. M., 1974, Geologic map of the United ronment, Office of White House Press Secretary, May 23, 23 p. States: U.S. Geological Survey, scale 12,500,000, 3 sheets. Dolan, Robert, 1970, Coastal landforms: National Atlas of the United Putnam, W. C., Axelrod, D. I., Bailey, H. P., and McGill, J. T., 1960, States of America, Washington, D.C.,Government Printing Office, Natural coastal environments of the world: Washington, DC, p. 78—79. Government Printing Office, 140 p. with maps. APPENDIX I Area values of land use and land cover on Atlantic and Gulf Coast barrier islands, 1945—55 and 1972—75 with changes (tables 9—27). Throughout the following broad measure tables, acres are in boldface type, percents in lightface; dashes (————) indicate negligible mapping data or none available; NA ind1cates category not applicable; + sign alone indicates increase not compared. 15 LAND USE AND LAND COVER ON ATLANTIC AND GULF COAST BARRIER ISLANDS FOR 1942—55 AND 1972—75 3+ ogl Sal 95+ ”5+ < ...... £38 wands . . . muINgH IIIIIIIIIIIII an“ :3 2 <2 <2 m N Sn <2 <2 <2 <2 <2 <2 <2 <2 2 Nr emu III: «5.2 <2 <2 afim 3m <2 <2 <2 <2 <2 <2 <2 <2 2.3. 5v 3%va £53 flouwado cdl gal ~21. 93+ «22+ < . . rINrmH 3m <2 <2 v m« can <2 <2 <2 <2 <2 <2 <2 <2 w.wm 3” m uuuuuuuuuuuuuuuu gm <2 <2 mdc N5... <2 <2 <2 <2 <2 <2 <2 <2 w on «E mmxmwaa ash—«um . l l 9.3+ 22+ q 92+ o 2. ”Nu . . I BLINK: <2 <2 2 3 G <2 <2 <2 <2 <2 <2 <2 <2 flaw Ev uuuuuuuuuuuuuuuu WWW <2 <2 wdw :— <2 <2 <2 <2 <2 <2 <2 <2 N am nmN mmxmvafi £35.32 a mwau< Q: mmho< g mwuo< a» mw2u< g mwho< m.» mwuo< 0% mwuo< £33 xuuflfl :2th c5233 3:53 2335 as“. umwhch andnwmcnfi ES: ":5— a=-u:=p «5.52500 find—mm mo 0:32 .282 ~25332N< .5 5322 mug? 363 mtigssm Q32 2: fie $3233: EELS N sex $98 NEE 32:9 am: $83 N Egg <8 353:. 3:8 3 mwugufioldfi mamflw .ucuflmm muofi how 53. 32:05 «0: on £53 “mmwmwau how «haunts». ozawumgosn 02H oNI. 9.6m! anl cumml NaNI odml N2! 922' m3... 93+ Nun + < uuuuuu £33 wwcuso Nu¢.n m.w «52 b.42 wa 2N an 26N NNH <2 <2 <2 <2 «.5 man SUNS: uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu <2 <2 <2 <2 Ill .1: 3+3? ulxxllnn 2 £262 Ewanem < can <2 <2 « rm «NN <2 <2 va 3: <2 <2 <2 <2 <2 <2 anNEH lllll <2 <2 III- III <2 <2 ll- 1... <2 <2 <2 <2 <2 <2 3|me ullllullll q «833.5 9% mw.8< ax» mwao< ox,» mwko< ex“ mm.~o< 9x» mwav< ex» mwao< g mwho< m—ES v33 :vundm cum—$3 mwmvnfi 2335 2.53 ammaoh uflflwwcafi HEN— 15: 25-225 vwhwnfioo van—mm mo 0:52 .352 12:253..me .5 EdnuD @2de 368 23:93 2: “m8 wwxgmw sfiig % sex $93 3:3 3:3 mm: 3:: ~ Ngmfl Kc 3339 623 § wumzefibld mafia. APPENDIX 1: TABLES OF AREA VALUES OF LAND USE AND LAND COVER 16 92 + 93+ 33+ 98:] 8&1 3+ 3: + 92.! 29:! 93: + «3+ < 3:3 9s 33 3. 1T 23 2:. <2 <2 3: 3a.: <2 <2 S: 33.: 3&2: 39:. &.3 $3 2m 22. 9:. 3” <2 <2 9:” e33 <2 <2 :3 n3 3&2: ............ 2:58:22..— 9w+ 9.2.1 3| 93+ 3+ < 3:. <2 <2 3: 3 <2 <2 93 32.. <2 <2 <2 <2 <2 <2 3&2: 5% <2 <2 me 9: <2 <2 v.3. 5..” <2 <2 <2 <2 <2 <2 mmxmvmfi uuuuuuuuuuu via—mm «3.19 93+ 93+ 3+ 9:&+ 3+ 98:I ”2| 9:w+ 3&+ < 39: :3: «a: 93 :3 <2 <2 99 no- <2 <2 <2 <2 93 :3 3&2: cum 9»: 3: 93 2:. <2 <2 93 3: <2 <2 <2 <2 9:. 24.. 3&1: ......... 2.2:: 33532 9:: + 3+ 3+ 93+ 22+ 9m:l «VI < 2.3 93 $9: v.3 23.: <2 <2 <2 <2 2: :2 <2 <2 <2 <2 3&2: 3&& 93. 28.: 3:. 2a.: <2 <2 <2 <2 :3: an» <2 <2 <2 <2 3&2: ............. 282 3:5 93:. 93 I 3| < E 98: 2 <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 3&2: 3: 98: 3: <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 3: 3:: ............. 53m «:9: 9: I 93 + ”3+ 98:1 gal 9o I..- < n::.: 93 25 9o I? <2 <2 <2 <2 <2 <2 <2 <2 9»: S: 3&2: 3:: 93 2e 93 can <2 <2 <2 <2 <2 <2 <2 <2 :3: S: 3&3: ................. 2.355 9&+ 931 «3| 93+ «3+ < 2:: <2 <2 3.: 2; <2 <2 <2 <2 <2 <2 <2 <2 93 31: 3&2: 39: <2 <2 93 :2. <2 <2 <2 <2 <2 <2 <2 <2 98 39: 3&2: ............... 48.25: 93+ 93+ «3+ «4 3:. <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 98: N3 3&2: w: <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 ode—H mg mmxmvmfi lllllllll Jason noxmuufia2 9:.1 <2 <2 93+ :&+ 9SI 31 < 2:. <2 <2 9.3. 3” <2 <2 <2 <2 <2 <2 <2 <2 23 3». 3&2: m3 <2 <2 9% 3” <2 <2 <2 <2 <2 <2 <2 <2 23 3:. 3&2: ............ 582 9352 92+ 93+ 3+ 93+ 3+ < 3& 93 3: <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 1:. S: 3&2: 2E 93 :2: <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 23 3 3&2: .................. 2212 93+ 95| 3| 3+ 2+ 9::l ::| 93+ 3+ 2. 3*. 9m: 5 :.:< 3& <2 <2 93 2 <2 <2 <2 <2 93 EN 3&2: 2:. 9m: 3: «.2. SN <2 <2 93: :5: <2 <2 <2 <2 93 3: 3&2: ................... €38. 9w+ 9&&| 3:| 9&:+ 3+ 93+ 22+ + 2+ < 39: :3 333 &.w& :3 <2 <2 93 2; <2 <2 <2 <2 9.. n: 3&2: «3.: <3 2:. 93 2:. <2 <2 95 2.: <2 <2 <2 <2 9.. 1? 3&3: ............. “:82 2:25 93+ 92+ :3+ 931 «2| 93+ 3:+ < 23.» 93 3:: :.:& 2:: <2 <2 <2 <2 <2 <2 <2 <2 :3: :3 3&2: 39a. 2:” n2 «.3 39: <2 <2 <2 <2 <2 <2 <2 <2 :.&: 3n 3&2: ............. 23:: 52.: 9:: + 93&+ 3+ 931 2.:I 93+ ”2+ < 39: 9:. 8 :3 .3 <2 <2 <2 <2 <2 <2 <2 <2 9S. :3 3&2: 3N: 9: e: 9&3 2; <2 <2 <2 <2 <2 <2 <2 <2 :3 an 3&3: ................ 253:6 exv mwho< axe mw2u< e\c mwno< 9% moxu< axe mwuo< ax» mw2u< ax» mmhu< £53 253 :wuaam wad—$3 3:5: 2335 v5: «mach wad—wwsam v52 ASA—2:5 25.5258 @233 «o wan 2 .532 fiduzfinofiwaw .5 5323 9:82 «meow 3233208333 23 «we £3233 2.3.2.82 hm .Sx 2.239 3:3 223 an: 223 N Ean x0 @9239 3.29 2.2 wquEKDIAH 22:52. 17 ON ATLANTIC AND GULF COAST BARRIER ISLANDS FOR 1942-55 AND 1972—75 93+ 93+ 22+ 93| mfil 92+ 3+ 92.1 cal 931 23.1 936+ 3+ 93+ 23+ < ...... 238 325.5 :2; 8% 22.: 93 223 5 22 &.m :3: m2: :3 &.o 3 EN 32 3&2: ES 3&4” «.3 :23 93 2: 5 3m 9» Sn: 9: $5. 3 2 an: :3. 3&2: y--- 258 2335 93+ 922I 3| 9%! «3| 9o Iel 9mm| 3! 922+ 3+ 93m+ N3+ < a3; 92. AT ”.5 :3 <2 <2 «3 3: «1w :2 3. 3 2.3 x; 3&2: 2;: 9w 2. 9s 2; <2 <2 5 3: 93 :3 m5 2 9m «2 3-32: ........ :23: “.8593: El 92:1 3| 9:1 e1 9.. I? < 5. <2 <2 <2 <2 <2 <2 9o no: 98 2:. <2 <2 9” 2 3&2: :2. <2 <2 <2 <2 <2 <2 2m 3 28 :2. <2 <2 m.& .: 3&2: ........ ESE 2.5.235 9m&l 982I SI 93+ 22+ < 32 99 tel <2 <2 <2 <2 <2 <2 92: 3: <2 <2 <2 <2 3&2: $2 fiwu 5. <2 <2 <2 <2 <2 <2 9:. 32 <2 <2 <2 <2 3,32: .............. SEES—=2 93+ 92:I 2:1 923+ 22+ + w+ < 3» 9c I... <2 <2 <2 <2 <2 <2 52.. 2; <2 <2 22 e 3&2: 22 9mm 2: <2 <2 <2 <2 <2 <2 E: 3 <2 <2 9: no: 2332: ..... 2.5.2 :95 2.3.2.3 9EI 92:! ENI 93+ 3+ < 3» 9c I? <2 <2 <2 <2 <2 <2 92: 8” <2 <2 <2 <2 3&2: 3;. «=3 :2. <2 <2 <2 <2 <2 <2 93 can <2 <2 <2 <2 3-32 -- 2:52 235 5.3252 93+ 93+ 3+ < 3: 92: 3: <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 3&2: 22 92: 2: <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 3,32: ............. mum «E352 93+ 9ml SI 95 + &:+ < 32. mg :3 <2 <2 <2 <2 <2 <2 68 E. <2 <2 <2 <2 3&2: «an «.3 «nu <2 <2 <2 <2 <2 <2 93 2; <2 <2 <2 <2 3&2: .............. swam 2:6 9.2+ 93+ 3+ 9oSI on! < a: 92: 2,” <2 <2 <2 <2 <2 <2 3. AT <2 <2 <2 <2 3&2: 3m 35 £2 <2 <2 <2 <2 <2 <2 3 3.. <2 <2 <2 <2 3&2: ......... ESE 83.152 93! 92:1 «ml 92:| 2:! 9.2+ 3+ < 2. 9: no- 9: I? <2 <2 <2 <2 <2 <2 <2 <2 92: 3 3&2: 3m :29.” 2 2:: 2: <2 <2 <2 <2 <2 <2 <2 <2 93 3 3,32: ................. “SEE: 9m+ 9&vl 3&1 93+ 32+ 3. no: 95+ 22+ < n3: 9% 3m &.&& 22.. &.& 3 <2 <2 93 2; <2 <2 <2 <2 3&2: 2:: 93. 22 m3 :3 &.u 3. <2 <2 93 :5 <2 <2 <2 <2 3‘32: .................. 0526 3| 93+ 22+ 9&wl «El 927 Edl 92:I «SI < :3 w; 83 3 2: &.& mm 92. I? <2 <2 <2 <2 <2 <2 3&2: 33 2.2. m2: 2: 2; 2w 2: Q 2: <2 <2 <2 <2 <2 <2 3:32 ................ 2:55.: 93+ 9w! 3| 95+ 32+ 923+ 322+ < 2:.” 9.3 3:: 9: 2”: <2 <2 <2 <2 <2 <2 <2 <2 5N N2. 3&2: 2&.& NE SN: 22“ :2 <2 <2 <2 <2 <2 <2 <2 <2 9m .2: 3&2: .................. «33.2 93+ 92:I NSI 9w+ 3+ + 22+ < 22 9o Io: Em :3 <2 <2 <2 <2 <2 <2 <2 <2 3.: 2: 3&2: Sm E: a: 2% <5 <2 <2 <2 <2 <2 <2 <2 <2 9.. I? 3. 32: ................ £2.32 Q; mwno< ex» swho< av mw.5< Vb ww20< 9% mw.8< «\s ww..u< 95 83¢ 3&an ©25— flwhhmm "HEN—avg mwmvcfi kwafla GENH Hwy—Ohm fir—NENSMMH @Efim mar—N— Dian—mau— UwthEOU Ufldumm MO vauz hawww ~a.~5:30m2u< he ENQHD whgw 25:25:80'338 mfimmsfigmsg vi “we £9233 23.233 52 Lox ($28 223 ~82: mm: 22.3 N 25nd kg 3323 3:. 3.2 3228201.: mqm<fi APPENDIX 1: TABLES 0F AREA VALUES OF LAND USE AND LAND COVER 18 92+ 93+ 3+ 9mN| maul 932+ nil. < llllll £53 $530 $9— 2.3 man 9:. men <2 <2 <2 <2 <2 <2 <2 <2 «.mv chm muleaH uuuuuuuuuuu and ham; 92 m2 1mm w: <2 <2 <2 <2 <2 <2 <2 <2 méu 3N mmtmvmfi vuua £53 towwudo 9wm+ 93+ 3+ 9mu+ 3+ < wmv 9mm 2: <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 2.5 an 2733 emn mdm w: <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 93 won $133 uuuuuuuuuuuu x32 mun—m 9w+ 9SI :I 9wml mal + 63+ 4 :m 5.9 mm 9% new <2 <2 <2 <2 <2 <2 <2 <2 Emu 9mm mplmbmfi 3w fiw 3 98 w: <2 <2 <2 <2 <2 <2 <2 <2 9o lei nmlmvafi lllll nick «guano—Hie: g mwho< NR» mono< ex» mwau< ex» mwxu< ax. mw~o< “Nu mw~o< axe mmao< £33 ":3— :whumm ecu—$3 3:5; Sung vnfi $982 «Emfiwwnmm v53 6:2 57:15 vwnmnfioo and—mm mo wfla2 haw? Exsfiavimlw .8 £513 macaw “mace 38.339980 S: «8 «8:33 sewing m sex $98 N353 ES» 3: 8:»: N NSSQ VS 3539 39$ § mmuzuNKOldH ”33.9 .mfiEd—mm «mg—u you 33. 3.33.: ”.0: cc £33 ”mmlmwmfi How emaam>oo 3:95.530an 02“ 9w+ 9me El 3+ 3+ 9S| owl 9mS+ 3+ 9.. lei 93H+ 3+ 93+ 34+ < ...... 283 85:5 «$5 9N we .93. e2.“ 9w 2m 9... Nu: 9v «2 9b wvu 9:“ was; 3.132 uuuuuuuuuuuuu 9; sum.» 9: can flow «an; ms mvu Na 3 9w 3— 9m «2 9mm at. mmxmvmfi III: 233 hquwqu 9o 90 lcl 9o lo: 9: Iol 9o Iol < awn 95 3 <2 <2 9m 2 <2 <2 9% mm" 9w mu <2 <2 mplmumfi awn 9% «a <2 <2 9m N.— <2 <2 9Nm “Hm— rd mu <2 <2 mmxmvafi uuuuuuuuuuu use—mm Jag—m a. uuuuuuuuuuuuu <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 mrlmgfi me 922 we <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 mm ‘33 uuuuuuuuuuuuu — :cuufifiouw < lllll lulu: .iuna <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 mblmgfi ms 922 a: <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 mmlmwafi uuuuuuuuuuuuuuu H 095232 3| 3| 2| 95+ .+ < :w <2 <2 93 awn <2 <2 <2 <2 <2 <2 <2 <2 Rom mun mplmbmfi 5v <2 <2 2.: as <2 <2 <2 <2 <2 <2 <2 <2 9mm a: mmlmwmfl uuuuuuuuuuuuuuuuu oflflafi< 9m| 9om| Nwl 93+ 3+ < m3 <2 <2 93 3: <2 <2 <2 <2 <2 <2 <2 <2 93. e: mplmhmfi «an <2 <2 93 SN <2 <2 <2 <2 <2 <2 <2 <2 9mm 5: mmxmvmfi |||||||||||||| Muss—.333 9m+ 9ooH| “5| 9NN+ S“ + 92.1 owl 922+ wm+ 9mm+ 3+ 98+ ~wm+ < gmfi 9o Iol 93 33 ms 22 m6 New <2 <2 9w HNN firm mum £133 mafia mdN «3 9mm m; 9m was ”m up <2 <2 9w m2 9mm 5m $133 IIIIIIIIIIII 53331.30 9% mmao< ox» mwxo< 0% mw.$< ax» mmgu< n8 mw.8< we mwS< ex. mw.8< 233 2:52 :3wa $5383 3:53 LESS MES €982 cum—wwcam «ES 323 Effiii 3.39:3 can—mm .«o wfia2 haww flu.~3_=o2w< .3 SEED 2.3% “was 3:23 385* 3: m8 332:3 Swiss m it .393 ~33: mass 3: 3:3 N Kama \o mugs; 3.29 E wwuxmébldfi mam—<8 19 ON ATLANTIC AND GULF COAST BARRIER ISLANDS FOR 1942—55 AND 1972—75 9::+ 3+ 3:. 9:I 27 93+ «2+ 9&ml ofil 3+ 3+ 9§l 3| 92+ 2222+ < ...... 233 $525 39$ 23“ :26: «.N& we: 2: :3 m4 mom: M3 22.: m6 3& 9mm 39:: 3&2: ............. :25 32.2 93 «:3: 93 3: &.: 5» ms 33 :.m «S: a: $3: &.3& 3.; 3:32: 1.. 238 383:0 9::+ 9m| 3| 93+ 22+ < 3m.” 93 :2 <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 9% 39m 3&2: m5.“ QNN Sb <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 2.: mad mmwmvafi uuuuuuuuuuuuuuu .335.qu 93+ 3| El 931 El 93+ 23+ < 2:3 2:: 3:. 9v 2: <2 <2 <2 <2 <2 <2 <2 <2 2% 323 3&2: SN.” :.m: an” 3: e3 <2 <2 <2 <2 <2 <2 <2 <2 9% 5&2 3&2: ............. 2262 9.3 92+ 9m| ail 9m&+ 23+ 922+ m::+ 95+ «3+ 4 2:: &.&m 3:.” 9mm 23 9: 3: <2 <2 <2 <2 <2 <2 m.&: 2:: 3&2: amud 93: was.” ”Am unuJ. m6 3 <2 <2 <2 <2 <2 <2 Nd amp 5752 lllllll “Ea—m— 2932 3:3. 93+ 93+ 32+ 93| e3! 93| «3| 9:o:+ 35+ < :23 9S 2;.” a.:& fin: <2 <2 9: 2 <2 <2 <2 <2 <5 :3: 3&2: 83 WE $3" 32 23.: <2 <2 2 can <2 <2 <2 <2 2: 3a 3.3;: .............. E3: E2 9m: + 93+ 32+ 9:] :mnl 9% + 22+ < 33 «.3 «3.: S: 2:; <2 <2 <2 <2 <2 <2 <2 <2 v.3 £9: 3&2: 3?: &.&m 3:. N3. 2: <2 <2 <2 <2 <2 <2 <2 <2 9% 23 3'32: ................ 535.2 9:: + 9m + :: + 9% + 3+ < :3 9E Ev <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 93 3: 3&2: uum w.mw 3% <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 «.22 mp mwimwmw IIIIIIIIIIIII EeunEnsuunw 9:| 931 en] 9m&+ 1+ < 22 93: 3.. <2 <2 <2 <2 gm 2: <2 <2 <2 <2 <2 <2 3&2: «an m.mm 3. <2 <2 <2 <2 mew 3: <2 <2 <2 <2 <2 <2 £13m: IIIIIIIIIIIIIIIIII 55.82 9:| 98:| :o:| 9m:&+ 22+ < 5.: <2 <2 <2 <2 <2 <2 9:. I? <2 <2 <2 <2 98: S: 3&2: 3: <2 <2 <2 <2 <2 <2 2% 3: <2 <2 <2 <2 m.:m S. 3&2: ............ 5.32 5.32 9m. + 9m + a: + < 3» 98: :3 <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 3&2: m...» 92: man <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 mmxmva: IIIIIIIIIIII .2232 2.2.5 9m+ 9:.:| ml 9&ml m: I 9:&: + 22+ < :3 &.a :m <2 <2 <2 <2 <.:& E: <2 <2 <2 <2 «.8 3n 3&2: 3m 2:: 3 <2 <2 <2 <2 93 SN <2 <2 <2 <2 «.2: 2.: 33:: ........... :52”: 23:25 o5 o.o 1e: < 2: 98: 2 <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 3&2: ea 92: em <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 mmlmwg ....... 22.32 2335.32 92:! 9:&| :&| 98:| 3| + 3+ < m: 23 .3 9o no: <2 <2 <2 <2 <2 <2 <2 <2 «:5 an 3&2: 3: «.3 8: 93 3 <2 <2 <2 <2 <2 <2 <2 <2 9: AT 3.32: .......... inn: 9:33.32 9::l 93I $1 92:+ 2+ < mm- 0.5 m: <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 9mm an 3&2: 3 2mm 3 <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 mdm or. mmxmva: uuuuuuuuuuuuuuuu ova—mourn 9:+ 9mml 3| <2 <2 9&&+ 23+ 9:+ :+ 92+ &&:+ 9<&| 3| < :2: 3 en: <2 <2 2:: a; :5 «a .33 $9: 9m: 3& <2 <2 3&2: 25.: 22 $2 <2 <2 8&2 cum fim ma «.3 Sm Wm: wmn <2 <2 3‘33 lllllllll 33:3 29:33“... 9:1 + .+ + 2+ 9m&+ 3+ 92ml Nvul 92! 3| 93+ 3&+ q 33 m5 2: 2o 3: 9m 2: 2% 39: m.:& :G <2 <2 93 m: 3&2: “:3 9:. AT 9:. I? 2...” 2 3m 22.: 9m& Em <2 <2 5: 3:. 313a: ............ ESE 3.32 ex» mw2v< axe mwno< R. m0.:o< gxo mmuu< ox» mw:o< eke $20< ob mw2u< £33 1:3 222nm 62533,? $253 2335 was: ”.3202 22339232 via. 37:25 2522228 and?“ Ho 2252 .23.», E25332M< no 5322 382 383 9292 $92 23 he mwfisfi swisso 3 sex $98 23:3 339 33 2:3 N 333 xo «2:3; 89% 2.3 maQ§§OIol.m2 mumflb 25 ON ATLANTIC AND GULF COAST BARRIER ISLANDS FOR 1942—55 AND 1972—75 9m+ 9««+ «2+ 9:m| «2| 32+ 23+ 4 2:2 92 com 9«« 2; <2 <2 <2 <2 <2 <2 <2 <2 :.&n «2 2&3: ::9& m2: «2 92 =««.: <2 <2 <2 <2 <2 <2 <2 <2 90: SN 2.2.x: ............. ESE .58: 93+ + 5+ 9m+ 22+ a :2." 9: :m «.2 2:3. <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 2&2: «Sin :6 Iol 0.22 Sad <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 mmévm— ............ “Ea—mm 22.52 9m+ 98:1 m&:| 9m| 5| + 2+ 92+ m:&+ < :9: 9o é: w.:« 2:. 9« 2 <2 <2 <2 <2 <2 <2 92 can 2&8: 22.: 2 2: 95 m2 9:. non <2 <2 <2 <2 <2 <2 92 2:. 22:: .......... ESE ”53:15 9w| 9w«l «2| 9m| «2| 9:1 2:1 9«::+ e«e+ < 2.2." «.3 3” w.:« 2.9: <2 <2 SN 8:: <2 <2 <2 <2 :3 2a 2| 2:: «$5 3: 2e 2.&« «2.: <2 <2 92 «N9: <2 <2 <2 <2 9a ”2 212.: ............ 255: E oE osl 9:&| 2| 9%! «m«| + 3+ 9E:+ «2+ < 22.: :.:: :a: 92 «3 9“ «a. 92 :2 <2 <2 <2 <2 <2 <2 2&3: 2;.— N.m2 an a.mr «3".— cd Ion 9.2 me <2 <2 <2 <2 <2 <2 mmlmvaa uuuuuuuuuuuu 15:: $9302 9m] 92| «2| 9:1 :NI 9m+ «w+ < 2m.“ 9: 2 :2 $3 <2 <2 «.2 .29: <2 <2 <2 <2 <2 <2 2&2: 29» «.w :2 «.5. 23 <2 <2 83 2; <2 <2 <2 <2 <2 <2 22:: ............ ESE 22:6 9:+ 9w+ 2+ 92| 29:| 9mm| 2| 92+ 29:+ < 2“.“ m.& «N: «.2 2: 9c 2 9«« 23 <2 <2 <2 <2 <2 <2 2&2: «26 N.& 2: «.2 29m x: E :2 ”2.: <2 <2 <2 <2 <2 <2 2'22 .............. ESE :3: 3| 92| 2| 9«| :NI + &::+ < 23 9: 2 «:5 :3 <2 <2 o & 2: <2 <2 <2 <2 <2 <2 2&5: 2% Wu 2: 98 «:3 <2 <2 9:. no: <2 <2 <2 <2 <2 <2 2:23 ............ .32 5585: 92+ 9: J? 92+ 2:+ 9.2+ 2+ < :21: k :« :2. «1,5 22:: <2 <2 w.& 2 <2 <2 <2 <2 <2 <2 2&2: St: 92 a2 93 ”2 <2 <2 9& 2 <2 <2 <2 <2 <2 <2 2&2: .............. ESE 2:5 9¢+ 92+ 2:+ 9:+ «:71 92] 2| 9:m+ e2+ < 9.3 5. «2. 92 292. m. e S 2. :2 <2 <2 <2 <2 <2 <2 2&2: 2:2 9& : :N 92.. «2:. 9c 2 9m :5 <2 <2 <2 <2 <2 <2 22:: ........... EEE 33:2 9«+ 92+ 2+ 9«+ 22+ < 2% :.& .5 a E 23 <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 2&2: h : 3. 9: 2 :2: 2.22. <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 2222 ............ ESE =30 9w+ 93+ 22+ o m+ 92+ 9m+ 2+ 3| 2| < 55. 92 :3 92 2:.” 9&: as «.a «2. <2 <2 <2 <2 <2 <2 2&5: :33 «.m « S. :95 when 9N: can 0.: 9: <2 <2 <2 <2 <2 <2 mmfimii lllllllllllll Eng—n— 550w &.¢+ 92| mEI 9a+ «2+ 9::| 2| < & $6 9& 2: 22 $3 :.: 2 <2 <2 <2 <2 <2 <2 <2 <2 2| 2:: 235 mg: :3 Www m —w.m m2 hm <2 <2 <2 <2 <2 <2 <2 <2 mmlmvmm llllllllllll aid—mu 5.32 9m:| 9&wl 2d] 951 ail 98:| 2| 92+ 2u+ + 2+ < $2.: Na :m m2 22 9o 1:7 «.2 «3 <2 <2 <2 <2 9« 2 2&2: «E..— S: enm mém 3 1— ad em «.2 wan <2 <2 <2 <2 od Icl $222 lllllllll .1qu 25399 9&:+ 92| :mnl 92+ «2+ 3.2+ «2+ < 22:: N : a: 9:. 2a <2 <2 <2 <2 <2 <2 <2 <2 2” 2m 2 &:: & S: w.«& e2 9 5 :2 <2 <2 <2 <2 <2 <2 <2 <2 &.«: :2 2&3: .......... ESE 223:: 9&I 9$I :2I 921 gal 9:.I 2| 922+ &2+ < 29.... :4. 2: :. E 2%: « 2 3.“ <2 <2 <2 <2 <2 <2 «.2 2m 2&3: S” in 2.2 mew mew mmod .1: aum <2 <2 <2 <2 <2 <2 :.m we mmsmi: lllllllllll ”3—:— 2.2.52 9w&| 92| nil 9m&| m:&| 9m+ 2+ + 29+ < 2.9: E 2 92 .2 <2 <2 &.:: :2 <2 <2 <2 <2 «.«& 2n 2&2: cue; mém 2:. 26m 53 <2 <2 «v.2 «an <2 <.2 <2 <2 :6 lo: mmfmvam lllllllllll tau—rd 3335 ex» wu.:o< 3 mwau< ax. mw.:o< wk ww~u< ax: mwho< m0 moho< <8 mwao< 2qu ~53 22:32 MESH—35 3:25 2355 1:5.— ummaoh wad—wuflwm 22:: 22:: 22:72:22 69:22:25 “Ed—mm we war—N2 haw? 2<.:::.:zu.:.:u< .5 2:222 mama? 2250 333ch £232 2: “we 3232 38.2.33 Sm .Sx swag ~23 EEG was 283 ~ Nwamg xo 2.58; 82$ 2.: moniafibldm 2238 APPENDIX 1: TABLES OF AREA VALUES OF LAND USE AND LAND COVER 26 $1. 92+ &:.:.+ 951 final 93+ 54+ 9:.1 SEI 95| «Sal 9:$+ 512+ < ..... WES SEED mam «mu m.m 2.2+ 922+ 222+ o.S.| 222.2! + 22+ c.2wl 2222.21 2.221 Sal 922+ 222.°2+ < 222.22 2.2. 222 22.2.2 2222.2 2.22 22 2.22 222.2 <2 <2 2.2 222 2.22 222.22 222222 22.2.2.2 2.2 222 2.22 222.2 22.22 lei 2.22 222.22 <2 <2 22 222 2.22 222.2 2222.2 ...... 2.52222 222622 285 2.2+ c.2ml 222! c.22l 222.21 2222+ 22.2.I wal 22.22! + 222+ 2.2.22.2+ 82.2.2+ 4 222.22 2.2 222. 2.2 222.2 2.2 2.22 2.2 222.2 2.2 2.22 <2 <2 2.22 2.22.2.2 222222 222.22 2.2. 222 2.22 222.2 2.2. 222 2.2.2 2.22.22 22.2 :22: <2 <2 2.2 23 2222.22 .......... 222.2520 225 o.2| 2.2+ 222+ c.22l 22.2.2I + 22+ o.22l 222| 222+ 222+ < 2.22.22 2.22 2.22.2 2.22 222.2 2.2 22 2.2 222.2 <2 <2 <2 <2 2.22 222.2 22- 2222 222.22 22.22 222.2 2.2.2 22.2.22 3. I? 2.2 222.2 <2 <2 <2 <2 22 222. 22-22.22 ................ 822.3322 2.2+ c.22l 222.2I odml 23+ + 22+ 2.22I 222.2! 9222+ 2222+ < 222.22 2.2 222.2 2.2 22.22 2.2. 22 2.22 222.2 <2 <2 <2 <2 2.22 222.2 22,222 28.22 2.22 222.2 2.22 2.2.2.2 2.22 12' 2.22 222.2 <2 <2 <2 <2 2.22 222.2 22-22.22 .................. 52222.2 2.22! 2.21 221 2.221 225.2I 982+ 2222+ 2.2.21 22I 9222+ 222+ 22 222.2. 2.22 222 2.2 22.2 <2 <2 2.22 2222.2 <2 <2 2.2 22 2.2 22.2 22- 22222 222.2. 2.22 222 2.2.2 222.2 <2 <2 2.22 222.2 <2 <2 2.2 2.22 2.2 22 2222.22 ............... 32.25.2222 2.2+ 2.221 222.| 2.221 222.2I + 2222+ 9222+ 2222+ < 222.222 2.22 2222.2 2.22. 222.2. <2 <2 2.22 222.2 <2 <2 <2 <2 2.22 222.2 22- 2222 222.2 2.22 222.2 2.22 222.2 <2 <2 9o :27 <2 <2 <2 <2 2.2 222 2222.22 ............... «2252:; o.2| 2.22! 222| 3.2+ 222+ 2.2+ 222+ 322+ 222+ 22 222.2 2.2 2.22. 2.22. 2.2.2 <2 <2 2.22 222.2 <2 <2 <2 <2 2.22 222 2222.2 222.2 2.22 22.2.2 2.22 222.2 <2 <2 2.2.2 2.22.2 <2 <2 <2 <2 2.2 222 2222222 .................. 25:6 c.22l 2.22] 222| c.22l 222] 922+ 222+ + 222+ 22 , 222.2 2.22 222. 2.2 222 <2 <2 2.2.2 2.22.2 <2 <2 <2 <2 2.2 22.2 222222 222.2 2.22 222 22.22 222 <2 <2 2.22. 222.2 <2 <2 <2 <2 32 :2: 2222.22 ............ 2:22.222 22:22.2. 2.22I c.22l 221 < 22 2.82 22 <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 222222 22 0.2222 22 <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 222222 ............. 2:32.22 2:222 o.2| 22.22] 222| c.22l 222.21 9222+ 2292+ c.82l 2222! 3222+ 2222+ 4 2222.22 2.2 222 2.22 222.2 <2 <2 2.22. 2.22.2 <2 <2 2.2 :2. 2.2.2 222.2 222222 222.22 2.2 222.2 2.22. 222.2 <2 <2 2.2.2 222.2 <2 <2 2.2 222 2.2.2 22.2.2 2222.22 ........... 2.5222 a22uE< 2x2 mw.2o< .3 83¢ 2% mw2o< 2R» 3.294 2&2 mw2o< 2% mw2u< 2% 55¢ 233 2223 2292.232 2222223025 wwmwon 23223 @2222— umm2om 2222239222 22222 2:222 222.2225 25222222228 cud—mm .«o 92.52 222.2% 2N2~222=om2w< .20 22222222 9222222 2283 2.8.2.282 3: $8 222223.22 22.2.2st 3. SK .2253 2323 232.22 2.2.: 2:23 ~ 2.2pr x0 2652222 28.23 :2 mwmfiafiblfim 22.2229 29 ON ATLANTIC AND GULF COAST BARRIER ISLANDS FOR 1942—55 AND 1972—75 92+ 927 gel 92+ 22+ + 2+ + 3+ + 2+ + 3+ < 223 9c on 93 :3 m.& 3 mam £4. <.& E. <2 <2 9o 3. 2&2: vmwfi Namu as M62. mnefi o6 Iol c6 Ia: o6 tel <2 <2 o6 Io! mmwmvafi IIIIII 2:26 0932 23: 3| + 223+ 9$| £2”! + “3+ 98| all + :2 + + 35.2 + < 39m 2.: N32 93 in m< mvu m.& a: 3“ 2: <2 <2 2.2” 392 3&2: 33 3. lo. 2:. 33. 9o 1? 93 33 3. AT <2 <2 9.. AT 312.: ............ v.52 8:: 9&+ 9&+ 2+ < :2; <2 <2 92: :2; <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 3&2: 22.2 <2 <2 92: $1— <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 mmlmvmfi uuuuuuuuuuuuuu .222 SE 9&+ 9S| $21 + 22+ 4 2:: <2 <2 m,ww EN; 92 mg <2 <2 <2 <2 <2 <2 <2 <2 3&2: 2} <2 <2 92: 2:} 9o lei <2 <2 <2 <2 <2 <2 <2 <2 $-32 ............ 2:25.: 2:5 9m+ 92+ 32+ 9?. 2.3! 93+ “22+ < 22% <2 <2 23 29% 9% 23.3 <2 <2 We 2:, <2 <2 <2 <2 3&2: 39E <2 <2 «.mm «<22 of“ 23.3.. <2 <2 9o Em <2 <2 <2 <2 mnxmvmm II 3:33 v5.3.5.2. 5% 9m | 9a| Emil 93| 22; | < $13 <2 <2 93 32.: 2mm 2...: <2 <2 <2 <2 <2 <2 <2 <2 3&32 $3» <2 <2 93 39: 95 25.2 <2 <2 <2 <2 <2 <2 <2 <2 3‘32 .............. :82 :25 92| 92| SwJI 9&I &:l < 3a.: <2 <2 92. $92 2% :3 <2 <2 <2 <2 <2 <2 <2 <2 m2 2: :22: <2 <2 2.3 2232 93 3:3 <2 <2 <2 <2 <2 <2 <2 <2 3&2: ........... 950 Siam—2 2.6+ 293+ «3.2+ o.m| m2! < 2:22 <2 <2 «.2 2.5.: 5. 2:2 <2 <2 <2 <2 <2 <2 <2 <2 5&2: $2: <2 <2 ada :3: 26 «$2 <2 <2 <2 <2 <2 <2 <2 <2 3&me ............. £2»:qu 9m! 9m| wmmgl 97» “I < $95 <2 <2 3m 32% A; :1.“ <2 <2 <2 <2 <2 <2 <2 <2 3&2: 25.3 <2 <2 NS 32% w.m 3&2 <2 <2 <2 <2 <2 <2 <2 <2 3&2: ............. «Eon {saw 92 I 92 l 2. | < 39m <2 <2 922 2.3 <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 3&2: 221w <2 <2 92: 2:; <2 <2 <2 <2 <2 <2 <2 <2 <2 <2 mmwmvmfi ................ .32 .32 92+ 9m| 2_| + ”2+ < 2.: <2 <2 22” 223.. 3 «2 <2 <2 <2 <2 <2 <2 <2 <2 3&22 omeJ. <2 <2 99.2 omo.< o6 Ie| <2 <2 <2 <2 <2 <2 <2 <2 mmrwvafl llllllllllllll 03am onaO 9m] 92:1 “fill 9$I SNI + N5+ 9&m&+ 29+ < gnfi ed Io! 2cm m3 <2 <2 o.? 3:25 .333 "ES ummaoh ccflmwimm HEN— wnfl fins-£25 wwawnfioo @332 HO wgaz 23> Haaafisuiwzw no 5323 musk» “mace 3.33%»ng 22 he £3232 33-23 mm 38. .398 3:3 ~83» $3 $32 N ESQ US 33:99 3.39 3 mum-ssfiblfim mqmfih 35 ON ATLANTIC AND GULF COAST BARRIER ISLANDS FOR 1942—55 AND 1972—75 o6} hikul 3+ 3+ o4+ .2le «Sn—l odom+ 236+ < ...... £33 3:30 as? «.2 £3 «.Nw $3“ 3 gm; 0 0 825m. EEEE ‘ r O \o Hm u .2 ,. H II :2 II II I: / II2 ” 4, ' )@ ,Z@ .. a ., Q9 \Wells Beach ., r2 ‘ u u " II 72 u 1 n2 . .0 ,, g I: “‘1’ I. II 1; v! II, u" A75 \ - u :' Ogunqurt '! u I“. I2 .— I, I: ,, .1 Ls" .. i. u I .. u ’ ® . .. o 5 10 MILES I I I I I I o 5 In KILOMETERS This map is a portion of the US. Geological Survey 1:250,000-scale Land Use and Land Cover map, Portland IL—83) I I FIGURE 9.—Land use and land cover map of the coastal area near Portland, Maine, with associated barrier islands. 43°00’ 42°45 ' OF THE NEW ENGLAND BARRIER ISLANDS 49 70°45' 70°30’ \ re “’ J"? I ~ " 5:" é} A; ’ w. a? ‘3) ‘9 0 5 10 MILES L i i i i i [J 5 10 KILOMETERS ll, _ 2 (5..“ 3 ‘°.\Hampton ea w ’2 7 I 2, I u M 5o 1 u ‘Seabrook \Pium Island This map is a portion of the US. Geological Survey 1 :250,000-scale Land Use and Land Cover map, Boston (L—69) FIGURE 10. —Land use and land cover map of the coastal area near Gloucester, Mass, with associated barrier islands. APPENDIX 11: GROUP 1 AND GROUP 2 70°45’ 71 n \2’ W [2" .1 “v %am“/2cfl ‘3 «7 I Q} ,, 5v ‘ Nahant 0 5 1'0 MiLES *l ['14 5'+ (~72 5* l[ I l J .A l. V M 0 5 10 KiLOMETERS w ‘ n . ”a ”I This map is a portion of the US. Geological Survey 1 :ZSOmO-scale Land Use and Land Cover map, Boston (L—69) 2 42°15’ 42°00' ’ FIGURE 11. —Land use and land cover map of the coastal area near Boston, Mass, with associated barrier islands. LAND USE AND LAND COVER MAPS 51 70°30, 42°00 .' ‘5‘} . my I o 5 10 MILES I J I I I o 5 IO KILOMETERS This map is a portion of the US. Geological Survey 1 1250,000-scale Land Use and Land Cover map, Providence (L434) —-—-A Sandy Neck 3}». 41°45’ FIGURE 12. —Land use and land cover map of the coastal area near Plymouth, Mass, with associated barrier islands. 52 42°00’ 41°45' APPENDIX 11: GROUP 2 LAND USE AND LAND COVER MAPS 70°15, 69°53] I i Nobscusset Point\ /Sandy Neck 5 10 MILES I J zMonomoy Da—O l 5 10 KILOMETERS é This map is a portion of the US. Geological Survey 1 :250,000-sca|e Land Use and Land Cover map, Providence (L—84) I l FIGURE 13. — Land use and land cover map of the coastal area near Cape Cod, Mass., with associated barrier islands. OF THE NEW YORK BIGHT BARRIER ISLANDS 53 70°15' 70000: i 0 5 10 MILES l I J i i i 0 5 10 KiLOMETERS This map is a portion of the US. Geological Survey 1 2250,000-scale Land Use and Land Cover map, Boston (L—GQ) 42°15’ -— -— 42°00’ FIGURE 14.—Land use and land cover map of the coastal area near Provincetown, Mass, with associated barrier islands. 54 APPENDIX II: GROUP 2 LAND USE AND LAND COVER MAPS 70°15’ 69°53’ /Muskeget Island 41 °1 5’ -— 0 5 10 MILES I l J F l I 0 5 10 KILOMETERS This map is a portion of the US. Geological Survey 12250.000-scale Land Use and Land Cover map, Providence (L-84) 41 °00' I FIGURE 15. —Land use and land cover map of the coastal area near Nantucket, Mass, with associated barrier islands. 41°30' 41°15' OF THE NEW YORK BIGHT BARRIER ISLANDS 55 70°45’ 70°30’ | 5% Nashawena r so ea \Tisbury Great Ponds \ Katama Bay Edgartown Great Ponds 5 10 MILES o i i J l 7 i o 5 10 KILOMETERS This map is a portion of the US. Geological Survey 1 2250,000-scale Land Use and Land Cover map, Providence (L—84) FIGURE 16. —Land use and land cover map of the coastal area near Martha’s Vineyard, Mass., with associated barrier islands. 56 41 °30’ 41°15’ APPENDIX 11: GROUP 2 LAND USE AND LAND COVER MAPS \% 71°00' .4 ,5ng Beach Q Nashawena\ 32 32 0, Cuttyhunk Island/ 10 MILES l A l 10 KILOMETERS o l l l o 5 This map is a portion of the US. Geological Survey 1 2250,000-scale Land Use and Land Cover map, Providence (L-84) 70°44’30” $3. II- 32 0-H 5‘4 l 7% FIGURE 17. — Land use and land cover map of the coastal area near New Bedford, Mass, with associated barrier islands. OF THE NEW YORK BIGHT BARRIER ISLANDS 71°30’ 71°15’ 41°30’ 41°15' '— 0 10 MILES L i l i i i 0 5 10 KILOMETERS This map is a portion of the US. Geological Survey 1 :250,000-scale Land Use and Land Cover map, Providence (L—84i 57 FIGURE 18. —Land use and land cover map of the coastal area near Newport, R.I., with associated barrier islands 58 41°15’ 41 °00’ APPENDIX 11: GROUP 2 LAND USE AND LAND COVER MAPS Stonin ton ‘2 \Weeka au "'2 g \ \Atlantic p g 0 5 10 MILES l I 1 I l I 0 5 10 KILOMETERS This map is a portion of the US. Geological Survey 1 2250,000-scale Land Use and Land Cover map, Providence (L—84) FIGURE 19. —Land use and land cover map of the coastal area near Mystic, Conn., with associated barrier islands. 41°15’ 41 °00’ OF THE NEW YORK BIGHT BARRIER ISLANDS 59 \( ,s - K . r, ‘ 'I_ -k l is ‘- I , ' ® - 2 1W. 9 , 0A ‘Hég ' . ifrg Er‘ 1‘ H g 2 '\,2 ‘ 11“} ' Earl—113's; v 12:. 520’“ ‘- z ‘ _ x_,.,——/”“\ v ' 9'" w WW; " ‘ "r ‘ 0/ ‘ as (J it ( TI 0 5 10 MIlES L | l i I I o 5 10 KILOMETERS This map is a portion of the US. Geological Survey 1 :250,000-scale Land Use and Land Cover map, Hartford (L—79) Hammonasset Point “ FIGURE 20. —Land use and land cover map of the coastal area near New Haven, Conn., with associated barrier islands. 60 APPENDIX II: GROUP 2 LAND USE AND LAND COVER MAPS 73°15' 73°00' “L“ ,13/ D; a wQuQ mu 41°15' ' 0 5 10 MILES I I I I l I 0 5 10 KILOMETERS This map is a portion of the US. Geological Survey 1 :250,0m-scale Land Use and Land Cover map, Hartford (L—79) 41 °00’ I I FIGURE 21. —Land use and land cover map of the coastal area near Bridgeport, Conn., with associated barrier islands. 41°15’ 41 °00’ OF THE NEW YORK BIGHT BARRIER ISLANDS 72°15’ ,. ,. WW 7, ‘\/‘H :3 1r 1]. :2 ”D “ QH‘ ',’ (25%; 42 a '2 . I ‘I2 1 l 10 MILES J 5 10 KILOMHERS This map is a portion of the U.S.‘Geologioa| Survey 1 2250,0w-scale Land Use and Land Cover map, Hartford (L—79) ,Gardiners Island Northwest Harbor Maidstone Park FIGURE 22. - Land use and land cover map of the coastal area near New London, Conn., with associated barrier islands. 62 APPENDIX 11: GROUP 2 LAND USE AND LAND COVER MAPS 4 00 72°15’ 72°00’ 1° ’ / U 72/ o W V34 /yz H 2 N t was? ”we a 40°45’ — U 5 10 MILES l I J [ I y o 5 10 KILOMETEHS This map is a portion of the US. Geological Survey 1 :250,000-sca|e Land Use and Land Cover map, New York (L—BZ) FIGURE 23. — Land use and land cover map of the coastal area near Southampton, N.Y., with associated barrier islands. 40°45’ 40°30 ' OF THE NEW YORK BIGHT BARRIER ISLANDS 63 72°30’ ii\ i W U l) \3 Q \0 1 M2 52?}? flwvi’j \/ v i4 52/ ‘ r "2 r V Qfii 4’, [L 7"“ I “(A H 5L4“ fl? E s; v ‘r // 5270 i1 Q’s-fl @ ~ q ’ \ Southampton 5 10 MILES i i I i 5 10 KILOMETERS o—i—c: This map is a portion of the US. Geological Survey 12250.000-scale Land Use and Land Cover map, New York (L—82i FIGURE 24. — Land use and land cover map of the coastal area near Brookhaven, N.Y., with associated barrier islands. 64 40°45 ’ 40°30’ APPENDIX 11: GROUP 2 LAND USE AND LAND COVER MAPS UV? "QB '2 D7 /u H V ’ r ’ i2 /‘ we NE%\‘ ‘9” Eve n , 7‘ \ 7‘ 4‘ (\ M "A1 fl \Cl ”“6 / 4 I I ” D/d 0 0 ',r2\ * qg— I. ’ 7‘ g ‘7 42/ l} '/ i7.‘ /2 will ~i2 3‘74. (’2 // ‘—/2 6 >5 0 1 i} H v *wfek Fire Island 0 5 10 MILES I l J l l l 0 5 10 KILOMETERS This map is a portion of the US. Geological Survey 12250.000-scale Land Use and Land Cover map, New York (L-«82) FIGURE 25. —Land use and land cover map of the coastal area near Fire Island, N.Y., with associated barrier islands. 40°45 ’ 40°30 ’ OF THE NEW YORK BIGHT BARRIER ISLANDS 65 73°30’ 73°15' l/P * l ll l2 '1 ,2 l? r, 332,16 ll‘ 22 HQ ,3 ,2 0,51 l2 41 [’2 7% ll u l2 g’ H H AA '1 IL /7 5, 4% £2 Wm 12 I! [2 .1 G x , l 7? l1 l2 Q3” // 17 Jones Beach Island Fire Island 0 5 10 MILES l l J l l l 0 5 10 KILOMETERS This map is a portion of the US. Geological Survey 1:250,000-scale Land Use and Land Cover map, New York (L—82) FIGURE 26. — Land use and land cover map of the coastal area near Lindenhurst, N.Y., with associated barrier islands. 66 74°00’ APPENDIX 11: GROUP 2 AND GROUP 3 73°45 ’ 40°30’ — 40°15’ Jones Beach Island Sandy Hook 0 5 10 MILES l 1 V I l 0 5 1o KILOMETERS This map is a portion of the US. Geological Survey 1:250,000-sca|e Land Use and Land Cover map, New York (L—82) FIGURE 27. —Land use and land cover map of the coastal area near New York, N.Y., with associated barrier islands. 40°30' 40°15' LAND USE AND LAND COVER MAPS 67 °‘°" 5' 4. ea 0 5 10 MILES I l l 1 I l 0 5 10 KILOMETERS This map is a portion of the US. Geological Survey 1 :250,000-scale Land Use and Land Cover map, Newark (L—33) FIGURE 28. —Land use and land cover map of the coastal area near Sandy Hook, N .J ., with associated barrier islands. 68 APPENDIX II: GROUP 3 LAND USE AND LAND COVER MAPS 74°1 5’ 74°00' 40°00’ 39°45' \Long Beach Island 5 10 MILES l l l l 5 1o KILOMETEHS D——v—C This map is a portion of the US. Geological Survey 1 :250m0-scale Land Use and Land Cover map. Wilmington (L—38) FIGURE 29. -Land use and land cover map of the coastal area near Toms River, N.J., with associated barrier islands. 39°30' I 39°15’ OF THE MID-ATLANTIC BARRIER ISLANDS 69 74°15’ 0 5 10 MILES I I I I I I 0 5 10 KlLOMEIERS This map is a portion of the us. Geological Survey 1 :250m0-scale Land Use and Land Cover map, Wilmington (L—38) FIGURE 30. —Land use and land cover map of the coastal area near Atlantic City, N.J., with associated barrier islands. 70 APPENDIX II: GROUP 3 LAND USE AND LAND COVER MAPS 39°15’ N. " 39°oo' ‘ 5 10 MILES I J I l 5 10 KILOMETERS This map is a portion of the US. Geological Survey 1 :250m0-scale Land Use and Land Cover map, Wilmington (L—38) FIGURE 31. —Land use and land cover map of the coastal area near Ocean City, N.J., with associated barrier islands. 39°00’ 38°45’ OF THE MID-ATLANTIC BARRIER ISLANDS 71 75°00' 74°45' w iiy/ ‘ \ 2i 53:“ OH“ 5‘42 \i‘) ll T qtflfis% a? PMQ/ i3 ’¥ 4§VIZ r: G»! <5 i ii ‘ W Q A i- Q ' 6’2 5/ "flag f2 k»; L ’ ED Wildwood 5i W9 0 5 10 MILES l l l l I D 5 10 KILOMEI'ERS 1% U “Inn ll zFenwick Island North This map is a portion of the US. Geological Survey 1 2250,000-scale Land Use and Land Cover map, Salisbury (L—65) FIGURE 32.—Land use and land cover map of the coastal area near Rehoboth Beach, Del., with associated barrier islands. 72 APPENDIX 11: GROUP 3 LAND USE AND LAND COVER MAPS 75°00' I Q‘u‘ 3".“ m 1 I b ro 2/ “‘70 4 aw), .1 , ax \ In I ‘F’ «Wu II 1' 21 a ‘3 \~2t 1w 2| u 2 r3 (7— 2‘ W 38°30' “ 272‘ 43‘\ III at @23’.;- BI c? .ZI N.) 231 Q 2 ' ’43 AFB ' 2I 2’ 0 2I ¢ 2, \W 54 w 45’ 245." x a ' - 3 43‘ a" an” a» 9‘ ” Vs Fenwick Island South 0 5 10 MILES I I I I I I o 5 10 KILOMETERS This map is a portion of the us. Geological Survey 1 :250,000-scale Land Use and Land Cover map, Salisbury IL—65I FIGURE 33. —Land use and land cover map of the coastal area near Ocean City, Md., with associated barrier islands. OF THE MID-ATLANTIC BARRIER ISLANDS 73 75°15' 38°15' —Fenwick Island South 7i Q V12‘.U "F’ _ 23’ ‘r i —Assateague Island North 1 10 MILES J W I l o 5 10 KILOMETERS This map is a portion of the US. Geological Survey 1 :250,(m-scale Land Use and Land Cover map. Salisbury (L—65) —Assateague Island South «In 38°00’ FIGURE 34.-Land use and land cover map of the coastal area near Assabeague Island, Md., with associated barrier islands. 74 38°00’ 37°45’ APPENDIX II: GROUP 3 LAND USE AND LAND COVER MAPS 75°30’ 75°15' \Assateag ue Island South 23PM ' /‘?5 2_ 75‘: QM EL, 2 w 4 h 2‘ .5: is :33 f Metomkin Island 10 MILES ea I l J b , r l l 7; e 0 5 10 KlLOMETERS / Parramore Island This map is a portion of the US. Geological Survey 11250.000-scale Land Use and Land Cover map, Eastville (L-58) X“ s. o 01 4,: 4i )1 FIGURE 35. — Land use and land cover map of the coastal area near Chincotueague, Va., with associated barrier islands. 76°00’ 75°45’ 37°30' 37°15’ ,, OF THE MID-ATLANTIC BARRIER ISLANDS 75 7) \Parramore Island 10 MILES I l J V I I o 5 1o KILOMETERS This map is a portion of the us. Geological Suwey 1 2250,000—scale Land Use and Land Covet map, Eastville (L-58) FIGURE 36. -Land use and land cover map of the coastal area near Cape Charles, Va., with associated barrier islands. 76 APPENDIX II: GROUP 3 LAND USE AND LAND COVER MAPS 76°00' 36°45' 36°30’ ‘ ~ , ‘ zBodielsland South —— 75°45’ / :4 4/ a“ 5 a) ‘ N .1 M /Bodie Island North on» Q \g H [19¢ '4 .s 0 5 lDMlLES E 1 L l l 0 5 1o KILOMETERS This map is a portion of the US. Geological Survey 1 1250,000-scale Land Use and Land Cover map, Eastville lL—58) FIGURE 37. — Land use and land cover map of the coastal area near Virginia Beach, Va., with associated barrier islands. OF THE MID-ATLANTIC BARRIER ISLANDS 76°00’ 75°45’ 77 36°15’ -— 36°00’ \ ‘ Q 9‘9 0 5 10 MILES I l 4 f \ i7 i i 0 5 10 KILOMETEHS 54 Q62 ”I?" ‘ This map is a portion of the US. Geological Survey 1 :250,000-scale 3” ”3‘ . 41 Ex Land Use and Land Cover map, EastviHe (L—58) 2 l6 l fl'AVIQG \ H» 41 t 75 H FIGURE 38. — Land use and land cover map of the coastal area near Kitty Hawk, N.C., with associated barrier islands. 78 APPENDIX II: GROUP 3 LAND USE AND LAND COVER MAPS 75°45' 75°30’ 36°00’ 35°45 ’ / Hatteras Island 0 5 10 MILES l l J l l 0 5 10 KILOMETERS This map is a portion of the US. Geological Survey 1 :250,000-sca|e Land Use and Land Cover map, Manteo (L—61) FIGURE 39. —Land use and land cover map of the coastal area near Nags Head, NC, with associated barrier islands. 79 OF THE MID-ATLANTIC BARRIER ISLANDS .mwcfifl gwwiwn wmafioaww firs r0. Z £263 Em: «9% 13280 9: mo E2: 850 ES was $5 «5wa .3 550E 9.2m. metmI\ :wh: 8232 due .98 9.2 new mm: 22 m_8m-o8.ommu — $25 595088 .0: m5 B 5an m a a9: 25 mummies. o— a _ $132 9 CD——C) +m M6 .omomh ‘omnvmm 80 35°30’ 35°15’ A «1' APPENDIX 11: GROUP 3 LAND USE AND LAND COVER MAPS '75°30' 75°15' % \Hatteras Island 4M 0 5 10 MILES l l J V i i 0 5 io KILOMETERS This map is a portion of the US. Geological Survey 1 :250,000-scaie Land Use and Land Cover map, Manteo (L—61) FIGURE 41.—Land use and land cover map of the coastal area near Cape Hatteras, NC, with associated barrier islands. 81 OF THE MID-ATLANTIC BARRIER ISLANDS .mwcflmm 3:23 wBNBOmmm 5:5 :02 A363200 Laws No.3 Ramada 23 we 92: .526 95 Ex om: wcwdl .Nw 550E .37.: 8:82 .92: .98 ES 95 3: ES BEWSQBNH _ >m>sm _S_mo_8o .m.: 05 B 8an m 2 as: 2: mEEESQ 9 m fl _ _ _ _ $52 9 m cy——o 6:22 9.8200 95.2 mmhmzml/ boomm .Il .mFomm \ omomh _ mvomh booms 34°45’ 82 APPENDIX 11: GROUP 3 LAND USE AND LAND COVER MAPS 76°15’ 35°00’ \Portsmouth Island M " \Core Banks North U1 0 10 MILES l . i J D 5 10 KILUMETEHS This map is a portion of the US. Geological Survey 1:250,000-sca|e Land Use and Land Cover map, Beaufort (L—67) 76°00’ FIGURE 43. —Land use and land cover map of the coastal area near Atlantic, N.C., with associated barrier islands. 34°45’ 34°30’ OF THE MID-ATLANTIC BARRIER ISLANDS 83 éZ 62 (in flwfizz 4 42 Bogue Banks \Core Banks South Shackleford Banks/ 0 5 I F l I o 5 10 KILOMETERS Land Use and Land Cover map, Beaufort (L—67) l 10 MILES I This map is a portion of the US. Geological Survey 12250.000-scale FIGURE 44. — Land use and land cover map of the coastal area near Cape Lookout, N.C., with associated barrier islands. 84 APPENDIX II: GROUP 3 LAND USE AND LAND COVER MAPS 77°00' 34°45' ms? Bogue Banks 34°3o' — ”a o 5 10 MILES i J l i o 5 10 KILOMETEHS This map is a portion of the U3. Geological Survey 12250.000-scale Land Use and Land Cover map. Beaufort (L—67). FIGURE 45.—Land use and land cover map of the coastal area near Morehead City, N .C., with associated barrier islands. 34°30' — 34°15’ OF THE MID-ATLANTIC BARRIER ISLANDS 85 Bogue Banks Hammock Island " ,3 In: $fi 43 «is ' ‘ fl . - \ F» 43 m “5‘ \ Onslow Beach > fig ”m w J .1 Ashe Island 0 5 10 MILES I I I I I I o 5 10 KILOMETERS This map is a portion of the US. Geological Survey 12250.000-scale Land Use and Land Cover map, Beaufort (L—67) FIGURE 46. —Land use and land cover map of the coastal area near Jacksonville, NC, with associated barrier islands. 86 34°30’ ' 34°15' APPENDIX II: GROUP 3 LAND USE AND LAND COVER MAPS 77°45’ 77°30' v \ Ashe Island Rich Inlet Z \Figure Eight Island L Wrightsville Beach 0 5 10 MILES I l l l ‘ l l 0 5 1o KILOMETEHS This map is a portion of the US. Geological Survey 12250.000-scale Land Use and Land Cover map, Beaufort (L—67) FIGURE 47. —Land use and land cover map of the coastal area near Hampstead, N.C., with associated barrier islands. 34°15' ' 34°00' OF THE MID-ATLANTIC BARRIER ISLANDS / \Lee Island \Rich Inlet 7W“) WI/ H ,, V 3339’? :Figure Eight Island "0 ” 43” 6'Q/Wrightsville Beach \h o I I o 5“ g u‘ All-JG In“ ' @q-‘ 2‘; I 5 5 I l 10 KILOMETEHS 10 MILES J This map is a portion of the US. Geological Survey 1:250.000-scale Land Use and Land Cover map, Beaufort (L—67) FIGURE 48. —Land use and land cover map of the coastal area near Wrightsville Beach, NC, with associated barrier islands. 87 88 34°00' 6 33°45’ APPENDIX II: GROUP 3 LAND USE AND LAND COVER MAPS 78°15’ 78°00’ W _,L\ sz 5‘ 1. 2 g 1 .r ,2 2/ 3b mg a £3 bl . ,2- if 4 go [7 a a s2 “1% w 4;» l E Q 2 fig - \ ' ’4 2/ ‘1 H-” “L 4’ fi , ‘62 a: “(lay r jg ‘4’ fl ‘2 ‘ ’ ’2’ {I Carolina V l '2‘ 42 ‘2‘ Q 'H" l 42 5: Hr“ -. Beach ‘ Z V ' V ' w 7‘ Island H _ - m 54 MM it: .~ g H \Holden Beach Island Oak Island/ .fl ' 7 fl “N Smith Island (Cape Fear)/ l— _ 5 10 MILES l J o I l l l o 5 1o KILOMETEHS This map is a portion of the U3. Geological Survey 12250.000-scale Land Use and Land Cover map, Georgetown (L—76) FIGURE 49. -Land use and land cover map of the coastal area near Cape Fear, N.C., with associated barrier islands. 34°00’ 33°45’ OF THE MID-ATLANTIC BARRIER ISLANDS 89 78°30' of” “map 81",“ Holden Beéch Island ”0 \Q 62/) \Hales Beach Island % ‘v’sr 5" r a , Q1? é" of @ W’wt Beach Island I" k) . N V = Il'd Island 2' «9% 'Xites Island 0 5 10 MILES l l l l I I o 5 10 KILOMETERS This map is a portion of the US. Geological Survey I 2250,000-scale Land Use and Land Cover map, Georgetown (L—76) FIGURE 50. —Land use and land cover map of the coastal area near Seaside, N.C., with associated barrier islands. 90 APPENDIX 11: GROUP 3 LAND USE AND LAND COVER MAPS 33°30’ 33°15’ \North Island 5 10 MILES l J l l 5 10 KILOMETERS o—fi—o 54 This map is a portion of the US. Geological Survey 12250.000-scale Land Use and Land Cover map, Georgetown (L-76) FIGURE 51. —Land use and land cover map of the coastal area near Georgetown, S.C., with associated barrier islands. OF THE MID-ATLANTIC BARRIER ISLANDS 91 33°15' 79°30’ 79°15, \—x '9' “ml w 2’ \5 U3 2/ L U 62 5 IV 51 Z l :1 m 5 2 O 9' a? / #12 @ 93 fl 2 El ’ 62 ' l 1 3' II ‘ 4A .9 // ‘I3 u e, 52! 2| 6,2 ’ /) W H 2/ , (p 6 6/ 9/ 62 72\ 42 5‘ ‘f 51 "l l 5 0 / 52\o2 l 6- \7_ (2 l 62 52 .3 'r z , (,2 H ,4 62 sl/ ‘2 ” 1,: 43 ‘3 71,, 43 W I 43 ‘ , Q] L7 ” e 2/ .75 a z 71: I 4} ‘4 n 52 ,2. 2/ % 62 K 33°00' :4 62 —North Island 54 62 4’1 52» U 2/ 43> 62 ‘ II 2/ \ 62 g 54 / 52 62 2 / 72 . 52 5’ 54 52 ' 43 7; c2 2 5 \South Island 62 43x '52 L41 *3- 052 Cedar Island 42 72 \Murphy Island Cape Island 0 5 10 MILES I l l l T l 0 5 10 KILOMETERS This map is a portion of the US. Geological Survey 1 :250,000-scale Land Use and Land Cover map, Georgetown (L—76I u 7/ 45 45 W 62 >/\ 62 43 _ oz e/ l 2l fl 2/ 45 4l -5/ @ %9 a? “a u /52 2/ > 21/9 4’ 45 2l~ so 62 elf 2/. 2/ 45 5? ll 52 J4! ‘2 62 5‘ ’71 42 .57 62 ‘2 ‘, 4| 72~ FIGURE 52. — Land use and land cover map of the coastal area near Cape Romain, 8.0., with associated barrier islands. 92 APPENDIX 11: GROUP 4 LAND USE AND LAND COVER MAPS 79°45 I 79030 I 32°45' WM. \‘éD 011, W ‘l . 4 L 21» Q‘“ (D an 67. 61 5 %% age s?“ #620? / 3 » 5 +5 62\ y {1/ 6L g) Q ‘ Capers Island 5' ’le 1 Jewees Island 62 \Morris Island 135 o 5 10 MILES l T l 0 5 1o KILUMETERS This map is a portion of the US. Geological Survey 1 :250,000-scale Land Use and Land Cover map, James Island (L—59) FIGURE 53. — Land use and land cover map of the coastal area near Isle of Palms, 8.0., with associated barrier islands. OF THE SEA ISLANDS BARRIER ISLANDS 93 80°00’ 79°45’ 21 5/ 54 ”’72, H II ‘ 62 n Q l 'w, __ 32°45' & a, a I ”12"] ' a 5/ . ‘ ‘3 ’\ _ M Morris Island 6/ 62 Folly Island 62 ‘72 32°30’ — — u 10 MILES g l l T l o 5 10 KILUMETEHS This map is a portion of the US. Geological Survey 12250.000—scale Land Use and Land Cover map, James Island (L—59l FIGURE 54. —Land use and land cover map of the coastal area near Charleston, 8.0., with associated barrier islands. 94 32°30 ’ 32°15' 4 L... \Otter Island APPENDIX 11: GROUP 4 LAND USE AND LAND COVER MAPS 80°15’ \Kiawah Island @ Lf Q ’DSeabrooklsland \ Q 12’ K ) \ @zDevaux Banks Botany Bay Island \Edisto Island Pine Island 80°00’ 5 10 MILES 0 .e 0 l 5 l I 10 KILOMETEHS This map is a portion of the US. Geological Survey 11250.000-scale Land Use and Land Cover map, Savannah (L—56) FIGURE 55. — Land use and land cover map of the coastal area near Edisto Island, 8.0., with associated barrier islands. 32°30’ 32°15' OF THE SEA ISLANDS BARRIER ISLANDS 95 _/ \Pritchards Island \ Little Capers Island \St. Phillips Island Bay Point Island ‘Q Q 3‘ <9“ 1" % I3 “0‘ I~ Hilton Head Island 5 1'0 MILES 0 l I I l o 5 10 KILOMETERS This map is a portion of the US. Geological Survey 1 :250,000-scale Land Use and Land Cover map, Savannah (L—56l FIGURE 56. —Land use and land cover map of the coastal area near Beaufort, 8.0., with associated barrier islands. 96 APPENDIX 11: GROUP 4 LAND USE AND LAND COVER MAPS 32°15’ 9! :fl : : \ o 5 10 MILES " H l I A Q Turtle Island fi l 1 “I o ; 5: ' n i/ L J 5 10 KILOMETERS .. ' t:- ones ‘ ‘ Island _ V a 6 u "‘ . This map is a portion of the US. Geological Survey 1 2250,000-scale V J/\ . \Tybee island Land Use and Land Cover map, Eastville (L—56) n t 3/" , _ 5" I", n‘ ‘ FIGURE 57. —Land use and land cover map of the coastal area near Hilton Head, 8.0., with associated barrier islands. 32°00’ 31°45' 81°00’ SI 7 Ossabaw Island OF THE SEA ISLANDS BARRIER ISLANDS 97 80°45' £23 5‘ n \Tybee Island éZ \Little Tybee Island ’fWilliamson Island \Wassaw Island 0 5 10 MILES I I l I I I 0 5 ID KILOMETEFIS This map is a portion of the US. Geological Survey 1 2250,000-scale Land Use and Land Cover map, Brunswick (L—71I FIGURE 58.—Land use and land cover map of the coastal area near Savannah Beach, Ga., with associated barrier islands. 98 APPENDIX 11: GROUP 4 LAND USE AND LAND COVER MAPS o 8,1015, 81°00, 32 00 ‘ i4 oz 9 *Si , 'Z 47. ‘2 n 43 '«3 "4 gym" 5" 6W 5‘_ “’7‘ ‘7“ / 31’ 43 2' (’2 fj§ 53 ' 9 1| '1 Ilia 5/ 31°45' — i 7? ‘ A }—-St. Catherines Island c. if (m 0 5 10 MILES i l l V i i 0 5 10 KItOMETEHS This map is a portion of the US. Geological Survey 1 :250,000-scale Land Use and Land Cover map, Brunswick (L-71) I ”(2 l FIGURE 59. —Land use and land cover map of the coastal area near St. Catherines Island, Ga., with associated barrier islands. 31°3o' ‘ OF THE SEA ISLANDS BARRIER ISLANDS 81°15’ 31°00' 99 o 10 MILES 1 1 I l 0 i l 5 10 KILOMETERS This map is a portion of the US. Geological Survey 12250.000-scale Land Use and Land Cover map, Brunswick (L—71) FIGURE 60. — Land use and land cover map of the coastal area near Sapelo Island, Ga., with associated barrier islands. 100 APPENDIX II: GROUP 4 LAND USE AND LAND COVER MAPS 81°15’ < 4’ 243/ \Sapelo Island 31°15' _ ’— 0 5 10 MILES | i J i l l 0 5 10 KILOMETEHS This map is a portion of the US. Geological Survey 1 :250,000-scale Land Use and Land Cover map, Brunswick (L—71) 31°oo' (*2 ”r“ 5+ FIGURE 61. —Land use and land cover map of the coastal area near Brunswick, Ga., with associated barrier islands. OF THE SEA ISLANDS BARRIER ISLANDS 101 81°30’ 81°15' Little Cumberland Island —-Cumber|and Island 30°45' o 5 10 MILES l l J l T l 0 5 1o KILOMETERS This map is a portion of the US. Geological Survey 12250.000-scale Land Use and Land Cover map, Jacksonville (L—Q) FIGURE 62.—Land use and land cover map of the coastal area near Cumberland Island, Ga., with associated barrier islands. 102 APPENDIX 11: GROUP 5 LAND USE AND LAND COVER MAPS 81°30’ 81°15' 30°45’ ' 30°30' 0 5 10 MILES l l J l l l o 5 10 KILOMETERS This map is a portion of the US. Geological Survey 1 Imam-scale Land Use and Land Cover map, Jacksonville (L—9) - :2 “My q) ,, I "17— FIGURE 63. —Land use and land cover map of the coastal area near Fernandina Beach, Fla., with associated barrier islands. OF THE FLORIDA ATLANTIC BARRIER ISLANDS 103 81°30' 81°15, 30°15' 30°00 ’ 0 5 10 MILES l l l ' l l 0 5 10 KILOMETERS This map is a portion ofthe US. Geological Survey 12250.000-scale Land Use and Land Cover map, Jacksonville (L—Qi FIGURE 64. -Land use and land cover map of the coastal area near Jacksonville, Fla., with associated barrier islands. 104 30°00’ 29°45' APPENDIX II: GROUP 5 LAND USE AND LAND COVER MAPS 81°15’ 81°00’ 0 5 10 MILES I l J I l l 0 5 10 KILOMETERS This map is a portion of the US Geological Survey 1:250,000-scale Land Use and Land Cover map, Daytona Beach (L-6) Matanzas FIGURE 65. — Land use and land cover map of the coastal area near St. Augustine, Fla., with associated barrier islands. OF THE FLORIDA ATLANTIC BARRIER ISLANDS 81°00' 105 O—'—O 29°30’ ill q n t bl \Flagler & ““6; V“ 10 MILES l J l l 5 10 KILOMETERS This map is a portion of the US. Geological Survey 1 :250,000-sca|e Land Use and Land Cover map, Daytona Beach (L—6) FIGURE 66. —Land use and land cover map of the coastal area near Marineland, Fla., with associated barrier islands. 106 APPENDIX II: GROUP 5 LAND USE AND LAND COVER MAPS 81 °00 ’ 80°45 ’ o 5 10 MILES I; I I f I 0 5 10 KILOMETEHS This map is a portion of the US. Geological Survey 1:250,000-scale n Land Use and Land Cover map, Daytona Beach (L—6) 29°15’ ‘ 29°00' FIGURE 67. — Land use and land cover map of the coastal area near Daytona Beach, Fla., with associated barrier islands. 29°00' 28°45’ OF THE FLORIDA ATLANTIC BARRIER ISLANDS 107 80°45' i 0 10 MILES l l J V i | 0 5 10 KILOMETERS This map is a portion of the US. Geological Survey 12250.000-scale Land Use and Land Cover map, Orlando (L—12) ‘i\ ‘Q o ‘ \3\\ Wm . q 69 s /1”\ ”g kw \ ‘4‘ A" ,.| y. , "\ FIGURE 68. —Land use and land cover map of the coastal area near Titusville, Fla., with associated barrier islands. 108 APPENDIX II: GROUP 5 LAND USE AND LAND COVER MAPS 80°45’ 80°30’ 5 10 MILES l c) fire I 5 10 KILOMETERS This map is a portion of the US. Geological Survey 1 :250,000-scale Land Use and Land Cover map, Orlando (L-12) 28°30’ 28°15’ FIGURE 69. — Land use and land cover map of the coastal area near Merritt Island, Fla., with associated barrier islands. 28°15' 28°00’ OF THE FLORIDA ATLANTIC BARRIER ISLANDS 80°30’ 109 l 5 Ofi—O I 10 KILOMETERS This map is a portion of the US. Geological Survey 1 2250,000-scale Land Use and Land Cover map, Orlando (L—12) 10 MILES i FIGURE 70. —Land use and land cover map of the coastal area near Cocoa Beach, Fla., with associated barrier islands. 110 APPENDIX 11: GROUP 5 LAND USE AND LAND COVER MAPS 80°35’ 28°00’ U 5 10 MILES IL I I I ' 5 10 KILOMETERS This map is a portion of the US. GeologicaLSurvey 1 :250,000-scale Land Use and Land Cover map, Fort Pierce (L—7) 27°45’ FIGURE 71. ——Land use and land cover map of the coastal area near Vero Beach, Fla., with associated barrier islands. OF THE FLORIDA ATLANTIC BARRIER ISLANDS 11]. 80°15’ 10 MILES F‘U' 0 l I I l o 5 1o KILOMETERS This map is a portion of the US. Geological Survey 1 :250,000-scale Land Use and Land Cover map, Fort Pierce (L—7) 27°30 ' FIGURE 72. — Land use and land cover map of the coastal area near Fort Pierce, Fla., with associated barrier islands. 112 27°15' APPENDIX 11: GROUP 5 LAND USE AND LAND COVER MAPS 80°15’ 80° 00’ 5 10 MILES l J l l 5 10 KlLUMETERS O—v—D This map is a portion of the US. Geological Survey 1 :250,000-scale Land Use and Land Cover map, Fort Pierce (L—7) Hutchinson Island FIGURE 73. —Land use and land cover map of the coastal area near Jupiter, Fla., with associated barrier islands. OF THE FLORIDA ATLANTIC BARRIER ISLANDS 113 80°00' /Lake Worth 26°45’ £3 ants ‘ E-n-BD—l-IJ-I < a /Palm Beach 0" ,. 0 10 MILES ’4 L l I ) ' I i i D 5 10 KILOMETEHS This map is a portion of the US. Geological Survey 1:250,000-sca|e Land Use and Land Cover map, West Palm Beach (L—18) FIGURE 74.—Land use and land cover map of the coastal area near West Palm Beach, Fla., with associated barrier islands. APPENDIX 11: GROUP 5 LAND USE AND LAND COVER MAPS 114 80°00’ I ' 4— Palm Beach 26°30’ . =1 in?” —Boca Raton "i E by! P-” M g I g 0 5 10 MILES l l I l I l 0 5 10 KILOMETERS Hillsboro Beach This map is a portion of the US. Geological Survey 1 2250,000-scale ‘ Land Use and Land Cover map. West Palm Beach (L—18) In ‘ o I 7‘ L ‘ q 1’ n" _- 2615 @- Evmau g FIGURE 75. —Land use and land cover map of the coastal area near Boca Raton, Fla., with associated barrier islands. OF THE FLORIDA ATLANTIC BARRIER ISLANDS 115 80°00’ /’ \Hillsboro Beach 26°1 5’ __ 0 5 10 MILES l I l l | I 0 5 10 KILOMETERS This map is a portion of the US. Geological Survey 1:250,000-scale Land Use and Land Cover map, West Palm Beach (L—18l 26°00’ FIGURE 76. — Land use and land cover map of the coastal area near Ft. Lauderdale, Fla., with associated barrier islands. 116 APPENDIX 11: GROUP 5 AND GROUP 6 80°15’ 80°00’ 26°00’ ., 25°45' b” _ V “A; ,l—Virginia Key 1/ iKey Biscayne fl 0 5 . 10 MILES / i i i i J 0 5 10 KlLOMETERS This map is a portion of the US. Geological Survey 1 :250,000—scale Land Use and Land Cover map, Miami (L—11) FIGURE 77. —Land use and land cover map of the coastal area near Miami, Fla., with associated barrier islands. LAND USE AND LAND COVER MAPS 117 81°15’ @913 g“ i l < 5» d ®’ z? a £7 1 Shark Point/ 5* (9| 5. 0/ 5 I.51 iai Mud Ba a Y\ 3? I m a s” um oi 5‘ 25°15' —— 00’ — Q “M fl'" Cape Sable/ U 5 10 MILES i i I ' 0 5 10 KILOMETERS This map is a portion of the US. Geological Survey 11250.000-scaie Land Use and Land Cover map, Miami (L—ii) FIGURE 78. —Land use and land cover map of the coastal area near Cape Sable, Fla., with associated barrier islands. 118 APPENDIX 11: GROUP 6 LAND USE AND LAND COVER MAPS 81°30’ um‘ W 81‘115’ \ O O \u \0 0% \m 5| Duck Rock/ Alligator Cov 25°30’ rm 0 10 MILES i I I i i 0 s m KILOMETERS This map is a portion of the US. Geological Survey 12250.000-scale Land Use and Land Cover map, Miami (L—11) McLaughlin/ u FIGURE 79. — Land use and land cover map of the coastal area near Alligator Cove, Fla., with associated barrier islands. OF THE EASTERN GULF COAST BARRIER ISLANDS 81°30’ WV? wigs“ “Q13 “Bragg? 5'! /(.| 3 4o /Cape Romano 9,. 25°45’ ‘— Duck Rock 25°30’ —— 0 5 10 MILES —— l I l 1 J 0 5 io KILOMETERS This map is a ponion of the US. Geological Survey 1 2250,000-scale Land Use and Land Cover map, Miami (L—1 1) FIGURE 80. — Land use and land cover map of the coastal area near Everglades, Fla., with associated barrier islands. 120 APPENDIX II: GROUP 6 LAND USE AND LAND COVER MAPS 81°45’ 25°45’ — Little Marco Group/“1, Cape Romano/ o 5 10 MILES I I I I I I o 5 10 KILOMETEHS This map is a portion of the US. Geological Survey 1:250.000-scale Land Use and Land Cover map, Miami IL—III FIGURE 81. -Land use and land cover map of the coastal area near Marco, Fla., with associated barrier islands. 82°00’ OF THE EASTERN GULF COAST BARRIER ISLANDS 121 81°45’ 26°15' b ”aha (Emu E» _m I 5m i..\ @ Bonita Beach—'1’ O—i—D 26°00’ 5 10 MILES l l "4* l l 5 10 KILOMETERS ‘ b E This map is a portion of the US. Geological Survey 1:250,000-scale Land Use and Land Cover map, West Palm Beach (L—18) Little Marc- Group ..\ \‘ .':' D? FIGURE 82. —Land use and land cover map of the coastal area near Naples, Fla., with associated barrier islands. 122 30°30 ' APPENDIX 11: GROUP 6 LAND USE AND LAND COVER MAPS 82°15, 82°00, Cayo Costa Sanibel Island/ 5 10 MILES l J 0 l V I l 0 5 10 KILOMETERS This map is a portion of the US. Geological Survey 1 :250.000—scale Land Use and Land Cover map, Tampa (L—16) FIGURE 83. — Land use and land cover map of the coastal area near Fort Meyers, Fla., with associated barrier islands. 27°00 ’ 26°45’ 123 OF THE EASTERN GULF COAST BARRIER ISLANDS 82°30' 82°15' w Gaspariiia/ ‘\ i7 54 0 5 10 MILES [L i i i J 5 10 KILOMETERS This map is a portion of the US. Geological Survey 1 :250,000—scale Land Use and Land Cover map, Tampa (L-iB) FIGURE 84. —Land use and land cover map of the coastal area near Venice, Fla., with associated barrier islands. 124 APPENDIX 11: GROUP 6 LAND USE AND LAND COVER MAPS [5 ,_., 27°30’ —— 27°15' — o 10 MILES l l | I l l o 5 10 KILOMETERS This map is a portion of the us. Geological Survey 1 :250,000-sca|e Land Use and Land Cover map, Tampa (L—16) FIGURE 85. —Land use and land cover map of the coastal area near Sarasota, Fla., with associated barrier islands. OF THE EASTERN GULF COAST BARRIER ISLANDS 125 'l-sz-I z...- 28°00’ 27°45’ Irma, [2,, I-l. am ,, i {fly-i ' 3”,” i 9:5 a ' Y ,. 5. Long Key’ “’ ‘5' W6? 7 Q Cabbage Key Group M ‘ ? as 0 5 10 MILES i I l V i i l /\ 0 5 10 KILOMETERS '” V‘Mullett Key Group This map is a portion of the US. Geological Survey 1:250,000—scale Land Use and Land Cover map, Tampa (L—i 6) ((Egmont Key \“T 54 i @‘I D‘igassage Key /:/ J" I ,7: /Anna Maria Key ”3% J12 Z 12 ..... FIGURE 86. - Land use and land cover map of the coastal area near St. Pebersburg, Fla., with associated barrier islands. 126 APPENDIX II: GROUP 6 LAND USE AND LAND COVER MAPS 82°45’ 0 5 10 MILES I l I I I t 0 5 10 KILOMETERS This map is a portion of the US. Geological Survey 12250.000-scale Land Use and Land Cover map, Plant City (L—M) 28°15’ -—— Anclote Keys\ 71’ Clearwater . Bea'ch Island\ FIGURE 87.—Land use and land cover map of the coastal area near Tarpon Springs, Fla., with associated barrier islands. 28°45 ’ 28°30’ OF THE EASTERN GULF COAST BARRIER ISLANDS 127 82°45’ M Z ( 7b Q1” 5 l '2 H 4/ l _ _ 5, Chassahownzka/ 19’ / L, / 6, @— Li 4L d 21 . a a :4 9%" 4E9 04/ 62 ,l ” 4:7 8 ‘72 4L QM” /g _ ‘7' n u 7; L! 34» 7»; H D/ @ 7L ‘3‘? z x 5‘ L £5 M u :4 éZ 7' 62 ‘1 £1 E m H a 2’ 54 V i’ a 4 Pine Island/ ‘3; 5 L/ 62 l H 63 57. a 62 3 5| :4 L, H " ‘7 i-z Bay Port/ 4 u ’6 A 20v 5 5-1 “5/ H D"1 w n 11 L' I n. 7‘ 0) 0 5 10 MILES A 2 ” u .p n 42 ‘2 . i I ‘ u ' ,. 5" V 6, 5% l [1. o 5 1o KILOMETERS LL 4 / 63 _ w E7 _ This map isaportion ofthe US. Geological Survey1:250,000-scale " 7e 42 Land Use and Land Cover map, Plant City (L—14) 76 n 3, 7b ‘ F’ ) ~ ea FIGURE 88.—Land use and land cover map of the coastal area near Chassahowitzka, Fla., with associated barrier islands 128 APPENDIX 11: GROUP 6 LAND 83°15’ USE AND LAND COVER MAPS 29°15' — 29°00’ 71 " " “m U{ H ”42 b2 ‘ 5&3 as Z\ fij ” (a? £1} 0 l I 0 This map is a portion of the US. Geological Survey 1 :250,000-scale Land Use and Land Cover map, Gainesville (L—B) l 10 KILOMETERS 10 MILES J l FIGURE 89. —Land use and land cover map of the coastal area near Cedar Key, Fla., with associated barrier islands. OF THE EASTERN GULF COAST BARRIER ISLANDS ,. - .1, .. J: B” 15’ n 5, n. l“ u ' I lagé @196 g, u 129 84°15’ | “v .l M "an a“ W n u: ,. 5;, 5‘, n“ J/ 0-" u /Piney Island 5: 30°00’ 0 5 10 MILES l I -4 l l 0 5 10 KILOMETERS This map is a portion of the US. Geological Survey 11250.000-smle Land Use and Land Cover map, Tallahassee (L—15) FIGURE 90. —Land use and land cover map of the coastal area near Panacea, Fla., with associated barrier islands. 130 29°45 ’ APPENDIX II: GROUP 6 LAND USE AND LAND COVER MAPS 34°30' 84°15’ " 5;; 656:2, 9 (:9 6L) u “may fig 0 5 10 MILES l l l l I l O 5 10 KILOMETERS This map is a portion of the US. Geological Survey 1 :250,000—scale Land Use and Land Cover map, Apalachicola (L—S) FIGURE 91. - Land use and land cover map of the coastal area near Saint Teresa, Fla., with associated barrier islands. 29°45 ' OF THE EASTERN GULF COAST BARRIER ISLANDS 84°45’ 131 Dog Island // 62 \ / 0 5 10 MILES [P l ‘ 5 10 KILOMETERS This map is a portion of the US. Geological Survey 1 :250,000-scale Land Use and Land Cover map, Apalachicola (L—5l FIGURE 92,—Land use and land cover map of the coastal area near Carrabelle, Fla., with associated barrier islands. 132 APPENDIX 11: GROUP 6 LAND USE AND LAND COVER MAPS 85°00' 29°45’ 29°30’ 0 5 10 MILES l I I I | l _ 0 5 1D KILOMETERS This map is a portion of the US. Geological Survey 1 :250,000-sca|e Land Use and Land Cover map, Apalachicola (L—5) FIGURE 93. — Land use and land cover map of the coastal area near Apalachicola, Fla., with associated barrier islands 29°45’ OF THE EASTERN GULF COAST BARRIER ISLANDS St. Vincent Island/ 5 10 MILES o l l l l l o m KILOMETEHS This map is a portion of the US. Geological Survey 1 1250,000-scale Land Use and Land Cover map, Apalachicola (L—5) FIGURE 94. —Land use and land cover map of the coastal area near Port St. Joe, Fla., with associated barrier islands. 134 APPENDIX 11: GROUP 6 LAND USE AND LAND COVER MAPS 85°30’ 30°00’ “Wow W ‘I @ 43.; u g { fie ', Shell Island/ 5 10 MILES l J l 5 1o KILOMETERS o | l l 0 This map is a portion of the US. Geological Survey 1 :250,000-sule Land Use and Land Cover map, Tallahassee (L—15) FIGURE 95. —- Land use and land cover map of the coastal area near Panama City, Fla., with associated barrier islands. OF THE EASTERN GULF COAST BARRIER ISLANDS 135 86°15’ 30°15’ 10 MILES I I l I 5 10 KILOMETERS This map is a portion of the US. Geological Survey 1 :250,000—scale Land Use and Land Cover map, Pensacola (L—13) o—r—o (J1 FIGURE 96. —Land use and land cover map of the coastal area near Fort Walton Beach, Fla., with associated barrier islands. APPENDIX 11: GROUP 6 LAND USE AND LAND COVER MAPS 136 86°45’ 30°15' —“ 10 MILES J o | F I 0 5 10 KILOMETERS This map is a portion of the us. Geological Survey 11250.000-scale Land Use and Land Cover map, Pensacola (L—13) 30°00’ FIGURE 97. — Land use and land cover map of the coastal area near Mary Esther, Fla, with associated barrier islands 30°15’ OF THE EASTERN GULF COAST BARRIER ISLANDS 87°15,” 87000! 137 033” \Santa Rosa Island 0 5 10 MILES L I J l l l o 5 10 KILOMETERS This map is a portion of the US. Geological Survey 12250.000-soale Land Use and Land Cover map, Pensacola (L—13) 30°00’ FIGURE 98. —Land use and land cover map of the coastal area near Pensacola, Fla., with associated barrier islands. APPENDIX 11: GROUP 6 LAND USE AND LAND COVER MAPS 138 87°30’ t S a E V. e K 0 w d r e D- (fl flf/f \ if an” Romar Beach 10 MILES l 10 KILOMETERS This map is a portion of the US. Geological Survey 11250.000—scale Land Use and Land Cover map, Pensacola (L43) 30°15' ‘—— 30°00’ FIGURE 99. —Land use and land cover map of the coastal area near Warrington, Fla., with associated barrier islands. 88°00’ 30°15’ OF THE EASTERN GULF COAST BARRIER ISLANDS 139 5‘1 M‘— ‘u o ’ @ L‘s-J / u‘ bl‘ IR 5! ” «w 4—“ b,” R°mar Beach 7: Mobile Point 0 5 10 MILES k i l i 5 1o KILOMETERS This map is a portion of the US. Geological Survey 1 1250,000-scale Land Use and Land Cover map, Pensacola (L—13) 30°00’ FIGURE 100. —Land use and land cover map of the coastal area near Gulf Shores, Ala., with associated barrier islands. 140 APPENDIX II: GROUP 6 LAND USE AND LAND COVER MAPS 8801 5 I 88000 I 30°15' 30°00’ \ H )l 5* a (53‘? Q—ea 62 54 54 54— \Dauphin Island Mobile Point/ 7; Sand Islandx \Petit Bois Island 5 10 MILES J o | V l l o 5 10 KILOMETEHS This map is a portion of the US. Geological Survey 1 :250,000-smle Land Use and Land Cover map, Mobile (L—53) FIGURE 101.—Land use and land cover map of the coastal area near Dauphin Island, Ala., with associated barrier islands. 30°15’ 30°00’ OF THE EASTERN GULF COAST BARRIER ISLANDS 141 88°30’ :A' All: W; W _ n ufi‘ "4‘41 2 54 qA": E": :3 Eu“ 5‘ £6, ‘52. i; 54 B43 54 Horn lsland/ \Petit Bois lsland l—U'l 0 10 MILES L I l l l o 5 10 KILOMETEHS This map is a portion of the US. Geological Survey 1:250,000-sca|e Land Use and Land Cover map, Mobile (L—53) l FIGURE 102. —Land use and land cover map of the coastal area near Pascagoula, Miss, with associated barrier islands. APPENDIX 11; GROUP 6 LAND USE AND LAND COVER MAPS 142 89°00' 88°45' {Q ,3 l‘ -“ U Uzi 4 75% 7, 69 2/14: U I u uyl _. 7Q; SQZEFDW ?//IE_'§ I “WED/:5, in 53 510 fl /;E2\ 63 J—a\ B ‘2 //,,;, xxxaL/IVHHQOM ’ .5 [Ll/Tram "" 1 1:72 5" “Mg ‘7" a? , 1 we .1 a” 54 \72 Deer Island/ 1 54 jéL 30°15' \Ship Island 10 MILES l l_“" I 5 This map is a portion of the us. Geological Survey 1 :250.000-scale Land Use and Land Cover map, Mobile (L—53) o—T—o l 10 KILOMETERS 12 ill 1 30°00’ FIGURE 103. —Land use and land cover map of the coastal area near Biloxi, Miss., with associated barrier islands. 30°15’ 30°00’ — OF THE EASTERN GULF COAST BARRIER ISLANDS 143 89°15’ 89°00, a .7 paw ‘T .4 ” m " 4. —22 .. .2 9'2 :1 m 62 u 71/ E E, QL” 5.. I; digger/pl 3.. a}. fi2 Q - p” . flag: ‘ F \n 47. (32922?”6C‘gk / pflhfl “ 015“” Q 0-H” l ”V \ Cat lsland Ship Island/ 5 10 MILES- l I I 5 1o KILOMETERS D—q—O .— This map is a portion of the US. Geological Survey 12250.000-scale Land Use and Land Cover map, Mobile (L—53) l l FIGURE 104. —Land use and land cover map of the coastal area near Gulfport, Miss., with associated barrier islands. 144 APPENDIX II: GROUP 7 LAND USE AND LAND COVER MAPS 89°00’ o , 55 bl 55 A% 55 Chandeleur Island 29°45' — 55 J 5‘5 9;, o 5 1o MlLES l l #l V l l o 5 1o KILOMETERS This map is a portion of the US. Geological Survey 1 :250,000—scale fl Land Use and Land Cove: map, Breton Sound (Open file 75—246). 5 5 FIGURE 105. —Land use and land cover map of the coastal area near Chandeleur Islands, La., with associated barrier islands. OF THE LOUISIANA BARRIER ISLANDS 145 89°15’ 89°00’ 2 22/ J “(a 5 5 5 5 l Chandeleur Island Group/ / 3; g! 5 S Grand Gosier lsland/ 29°30’ — m fl * JBreton Islands 5 5 0 5 10 MILES l l ./ l l l l 5 5 0 5 10 KILOMETERS This map is a portion ofthe US. Geological Survey 1:250,000-scale Land Use and Land Cover map, Breton Sound (Open file 75—246). FIGURE 106. —Land use and land cover map of the coastal area near Breton Island, La., with associated barrier islands. 146 APPENDIX II: GROUP 7 LAND USE AND LAND COVER MAPS 29°30’ 89°30’ 89°15’ ‘ Qt! l 55 0 5 10 MILES I I J I 0 5 10 KILOMETERS This map is a portion of the US. Geological Survey 1:250,000—scale Land Use and Land Cover map, Breton Sound (Open file 75—246). 3 55 % 55 ’ _ a ,ct u fi _ flu Breton Islands C3” ‘ \ 9 4? ”'4 5 +— c 9‘ w Sable Island oquille Point /Raccoon Point 55 a 7 ?\Bird Island gem" ES ‘ {67. 54— aw L®w ‘\ E a. I w I I u. LL 5' l 5‘ 52 61 We G‘% i é: ,fl (VIII; FIGURE 107. —Land use and land cover map of the coastal area near Venice, La., with associated barrier islands. 29°15’ 29°00’ OF THE LOUISIANA BARRIER ISLANDS 147 L6W (7/96“ w L» 6 '“ .x 51 62 9‘ 5;’@ , f \0 e s LW ,1 ‘A’jLAD kwv y > M 53 u I 1" 1 / 01?;5‘ Bastian i3 Island ’ m 5-1 h 61 r— .fi/ 17 Pelican Island/ “U62 l Ln 0 10 MILES \ IL | J l J 6 0 5 10 KllOMETEHS .{I‘ This map is a portion of the us. Geological Survey 12250.000-scale Land Use and Land Cover map, Breton Sound (Open file 75—246). J, FIGURE 108. —Land use and land cover map of the coastal area near Pilottown, La., with associated barrier islands. 148 90°00 ’ 29°15’ 29°00 ’ APPENDIX II: GROUP 7 LAND USE AND LAND COVER MAPS 9 A 4, , it. Ronqunlle lsland “ l9 Bay LaMer W Q & , o 5 a \ / \Grande Terre . .l r y)“ ‘1 EL Island Group Bay Joe Wise \7‘1 I! '5 Bastian lsland/ , 5 s 5 Pelican Island/ \Grand Isle 0 5 10 MllES l J I l l l o 5 10 KILOMETERS This map is a portion of the US. Geological Survey 11250.000-scale Land Use and Land Cover map, Breton Sound (Open file 75—246). FIGURE 109. —Land use and land cover map of the coastal area near Grand Isle, La., with associated barrier islands. OF THE LOUISIANA BARRIER ISLANDS 90°08’ 90°00’ 29°15’ 29°00 ’ 89°45’ 149 0 I 0 I 5 10 MILES l h | l 5 10 KILOMETERS This map is a portion of the US. Geological Survey 1 :250,000-scale Land Use and Land Cover map, New Orleans (Open file 75—245). L FIGURE 110. — Land use and land cover map of the coastal area near Caminada Pass, La., with associated barrier islands. 150 APPENDIX 11: GROUP 7 LAND USE AND LAND COVER MAPS 90°30, 90°15: Timbalier lsland/ 29°00’ '- 0 5 10 MILES } x I I 28°45' __ o 5 10 KILOMETERS _ This map is a portion of the US. Geological Survey 1:250,000-scale Land Use and Land Cover map, New Orleans (Open file 75—245). FIGURE 111. -Land use and land cover map of the coastal area near Leeville, La., with associated barrier islands. OF THE LOUISIANA BARRIER ISLANDS 151 91°00’ 90°45' 5v \ i d 42 2% Q5: $3 9% <2 , ,l . I 9 ‘ V ‘ as A: ‘ W X 51 ( a) d? ' < 5‘! d“ ) n 927/ 11 ~ V / k* 1 «Ag/ ( 72 \lsles Dernieres 29°00’ — — 0 5 10 MILES l l 1 , ‘ 28°45' — o 5 10 KILOMETERS This map is a portion of the US. Geological Survey 1 :250,000-sca|e Land Use and Land Cover map, New Orleans (Open file 75—245). FIGURE 112. — Land use and land cover map of the coastal area near Isles Dernieres, La., with associated barrier islands. 152 APPENDIX II: GROUP 8 LAND USE AND LAND COVER MAPS 94°45' 94°30' l <39 I 29°30' 29°15’ o 5 10 MILES i 1 l l I I 0 5 1o KILOMETERS This map is a portion of the US. Geological Survey 1 :250,000-scale Land Use and Land Cover map, Houston (L—51) l I FIGURE 113.—Land use and land cover map of the coastal area near Galveston Island, Tex., with associated barrier islands. OF THE TEXAS BARRIER ISLANDS 153 95°00’ 29°00’ 19 5% e \_ W" 29°15r_%@ %j' W» “ 01 41 M (02 W0 a ® \ Galveston Island a. @3‘ ~ 57‘ Rattlesnake Point 0 5 10 MILES l I J V l l 0 5 10 KILOMETERS This map is a portion of the US. Geological Survey 1 2250,000-scale Land Use and Land Cover map, Houston (L—Sl) l FIGURE 114.—Land use and land cover map of the coastal area near Jamaica Beach, Tex., with associated barrier islands. 154 APPENDIX 11: GROUP 8 LAND USE AND LAND COVER MAPS o , 95°30’ 29 00 W 42 fl ac.--” & .\ , 1» fl" ., w a ~ 7., ,~_ we». 63 ¥ ,0 ,2 I Iw‘ '2‘ 53%”, \\\ \ /z ZIII Q ‘ 95°15’ 28°45’ >—-— 10 MILES I I I 5 1o KILOMETERS 0 IL 0 This map is a portion of the US. Geological Survey 12250.000—scale Land Use and Land Cover map, Bay City (L—50) FIGURE 115. — Land use and land cover map of the coastal area near Freeport, Tex., with associated barrier islands. OF THE TEXAS BARRIER ISLANDS 155 96°00’ 29°00’ 28°45’ \Brown Cedar \Matagorda Peninsula East 5 10 MILES | i i l 5 10 KILOMETERS D—-—D This map is a portion of the US. Geological Survey 12250.000-scale Land Use and Land Cover map, Bay City (L—50) 1 FIGURE 116. -Land use and land cover map of the coastal area near Matagorda, Tex., with associated barrier islands. 28°30’ — 28°15’ 156 APPENDIX 11: GROUP 8 LAND USE AND LAND COVER MAPS 96°15' is“ Matagorda Peninsula West 0 5 10 MILES [L I 0 I 5 10 KllOMETEHS This map is a portion of the US. Geological Survey 1 2250.000-scale Land Use and Land Cover map, Beevilie (L—68) FIGURE 117. —Land use and land cover map of the co‘ tal area near Palacios, Tex., with associated barrier islands OF THE TEXAS BARRIER ISLANDS 157 96°30’ DZ 12. /7 [—342 W J 7“”.1," / \ LD—zlr m 5y “/2124 @~ la 12 \72 u 6 El 22 /2 R,» . Joseph Island 3 This map is a portion of. the US. Geological Survey 1 :250,000-scale / a 13 Land Use and Land Cover map, Beeville (L—68) FIGURE 119. —Land use and land cover map of the coastal area near Austwell, Tex., with associated barrier islands. OF THE TEXAS BARRIER ISLANDS 159 0 97°15' 97°00' 28 00 ' T [/52 577 (/7 3/ 55‘ J 72‘ 2/! / 3/ 19 St. Joseph Island 27°45 ’ 5 10 MILES i l l l 5 '10 KILUMETEHS w \. b3 oj~—o 73" This map is a portion of the us. GeoIogical Survey 1 :250,ooo-scale Land Use and Land Cover map, Corpus Christi (L—73) I FIGURE 120. - Land use and land cover map of the coastal area near Corpus Christi, Tex., with associated barrier islands. 160 27°30’ APPENDIX II: GROUP 8 LAND USE AND LAND COVER MAPS 97°15’ /5 4 K1 Padre Island North W 62 l é \—7s a, A? 3/ \Mustang Island 10 MILES I I 10 KILOMETEHS This map is a portion of the US. Geological Survey I:250,000-scale Land Use and Land Cover map, Corpus Christi (L—73I FIGURE 121. — Land use and land cover map of the coastal area near Laguna Vista, Tex., with associated barrier islands. OF THE TEXAS BARRIER ISLANDS 161 /Padre Island North 27°15' 52 —-—Padre Island Central 0/ 3/ 0 5 10 MILES | I J F l l 0 5 10 KlLOMETERS This map is a portion of the US. Geological Survey 1:250,000-sca|e Land Use and Land Cover map, Corpus Christi (L-73) 27°00’ FIGURE 122. - Land use and land cover map of the coastal area near Griffins Point, Tex., with associated barrier islands. 162 APPENDIX 11: GROUP 8 LAND USE AND LAND COVER MAPS 97°30’ 97°15’ 27°00’ 54 a) V 313 ‘2 75 52 o 5 10 MILES- l l I l l l o 5 10 KILOMETERS This map is a portion of the US. Geological Survey 1 2250,000-scale Q) Land Use and Land Cover map, Brownsville (L—70) 26°45’ ‘— Padre Island South FIGURE 123. —Land use and land cover map of the coastal area near Lopena, Tex., with associated barrier islands. OF THE TEXAS BARRIER ISLANDS 163 97°15' 97°00’ ED 0 5 10 MILES l l l l l l 0 5 10 KILOMETERS This map is a portion of the US. Geological Survey 1 :250,000-scale Land Use and Land Cover map, Brownsville (L—70) ——l 26°30’ Padre Island South 26°15’ FIGURE 124. —Land use and land cover map of the coastal area near Padre Island South, Tex., with associated barrier islands.. 164 26°00’ 25°45’ APPENDIX II: GROUP 8 LAND USE AND LAND COVER MAPS 97°15’ 97°00’ )5 I (.2 I g ,C? 2 32 I‘ 76-“ ' /Padre Island South o 5 10 MILES L l l V l l 0 5 1o KILOMETERS This map is a portion of the US. Geological Survey 1:250,000-scale Land Use and Land Cover map, Brownsville (L—70) l FIGURE 125. —Land use and land cover map of the coastal area near Port Isabel. Tex.. with associated barrier islands. fir U.S. GOVERNMENT PRINTING OFFICE: I980 0— 3I I-344/I88 Geology of the Eastern Part of the Marathon Basin, Texas by PHILIP B. KING GEOLOGICAL SURVEY PROFESSIONAL PAPER 1157 UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1980 UNITED STATES DEPARTMENT OF THE INTERIOR CECIL D. ANDRUS, Secretary GEOLOGICAL SURVEY H. William Menard, Director Library of Congress Cataloging in Publication Data King, Philip Burke, 1903- Geology of the eastern part of the Marathon Basin, Texas. (Geological Survey professional paper ; 1157) Includes bibliographical references. Supt. of Docs. no.: I 19.1611157 1. Geology--Texas--Harathon Basin. I. Title. II. Series: United States. Geological Survey. Pro- fessional paper ; 1157. QE168.M36K49 551.7'09764 80-607171 For sale by the Superintendent of Documents, US. Government Printing Office Washington, DC. 20402 CONTENTS Page Page Abstract __________________________________________________ 1 Stratigraphy—Continued Introduction ______________________________________________ 1 Lower Cretaceous (Comanchean) Series ________________ 20 Stratigraphy ______________________________________________ 3 Trinity Group ____________________________________ 20 Pre-Mississippian rocks ________________________________ 4 Glen Rose Limestone __________________________ 20 Carboniferous rocks __________________________________ 4 Maxon Sandstone ______________________________ 21 Tesnus Formation ________________________________ 4 Basement Sands ______________________________ 22 Dimple Limestone ________________________________ 7 Fredericksburg Group ____________________________ 22 Haymond Formation ______________________________ 9 Washita Group ____________________________________ 22 Boulder-beds __________________________________ 12 Conditions of deposition of Lower Cretaceous rocks __ 23 Fossils and age ________________________________ 12 Tertiary igneous rocks ________________________________ 23 Origin ________________________________________ 14 Quaternary deposits __________________________________ 23 Gaptank Formation ________________________________ 15 Tectonics ________________________________________________ 24 Area near Gap Tank __________________________ 15 Surface structure of the pre-Permian rocks ______________ 24 Exposures east of Gap Tank ____________________ 18 Subsurface structure of the pre-Permian rocks __________ 27 Origin ________________________________________ 18 Structure of the Permian rocks ________________________ 28 Permian rocks ________________________________________ 18 Structure of the Cretaceous rocks ______________________ 28 Neal Ranch Formation ____________________________ 18 Tectonic history of Marathon region ________________________ 33 Hess Limestone __________________________________ 19 Well data ________________________________________________ 35 Permian rocks above the Hess Limestone __________ 20 References cited __________________________________________ 39 ILLUSTRATIONS PLATE 1. Geologic map of eastern part of Marathon Basin and adjacent areas, Texas ____________________________________ In pocket Page FIGURE 1. Photograph showing angular unconformity between Paleozoic rocks of Marathon Basin and Cretaceous cover rocks. Southwest face of Housetop Mountains 18 miles east of Marathon at eastern rim of Marathon Basin ____________ 2 2. Map of the Marathon Basin, western Texas, showing area covered by this report __________________________________ 3 3. Map of the Marathon Region, showing topographic quadrangle maps referred to in text ____________________________ 4 4. Columnar section showing geological formations that occur in the report area ______________________________________ 4 5. Photographs showing thick-bedded sandstones of upper part of Tesnus Formation, with interbedded shale ____________ 6 6. Photograph showing Dimple Limestone east of Haymond Station 15 miles east-southeast of Marathon ______________ 8 7. Photograph showing structures in Dimple Limestone similar to those in figure 6 __________________________________ 9 8. Photograph showing lower part of Haymond Formation in cut on US. Highway 90 east of Lemons Gap 18 miles east of Marathon ________________________________________________________________________________________________ 10 9. Field sketch made in 1930 of outcrop area of Haymond Formation 3 miles south of Dimple Hills, showing outcrops and structure of fusulinid-bearing limestone layers ______________________________________________________________ 11 10. Photographs showing boulder-beds of Haymond Formaton at an area of greatest concentration of large boulders, at west foot of Housetop Mountains 19 miles east-southeast of Marathon ______________________________________________ 13 11. Photograph of medium-sized slablike boulder of Pennsylvanian limestone at a locality not far to the north, projecting from mudstone matrix ______________________________________________________________________________________ 14 12. Photograph of large rounded boulder of brecciated Caballos Novaculite in boulder-bed at a locality near figures 10 and 1 1 14 13. Geologic map of the Gap Tank area, showing details of subdivisions of the Gaptank Formation ______________________ 16 14. Photographs showing roundstone cobbles in lowest conglomerate member of the Gaptank Formation south of Gap Tank and 20 miles northeast of Marathon ________________________________________________________________________ 17 15. Profile of Gaptank Formation and associated beds 7 miles east of Gap Tank ________________________________________ 19 16. Map of report area showing structural pattern of the Paleozoic rocks ______________________________________________ 26 17. Map of the Marathon Region, showing locatons of deep drill holes in the Marathon Basin and Glass Mountains and the depth of penetration to the great thrust fault (Dugout Creek overthrust) ______________________________________ 29 18. Graphic representation of records of deep drill holes in the Marathon Region ______________________________________ 3O 19. Map of report area showing outcrops of the Cretaceous rocks and structure contours on two horizons in the Cretaceous 32 20. Map of part of south-central United States. showing the location of the Marathon Region and the Ouachita Mountains 34 III GEOLOGY OF THE EASTERN PART OF THE MARATHON BASIN, TEXAS ByIanLn)B.K1NG ABSTRACT This report covers the Paleozoic rocks in the eastern part of the Marathon Basin, west Texas, and in the eastern end of the Glass Mountains to the north, as well as the Cretaceous rocks which lie unconformably on them to the northeast, east, and southeast. The geologic map accompanying the text amplifies ground surveys made between 1927 and 1931, and is based on recent topographic maps, and on photogeology derived from the later air photographs. The accom- panying text summarizes the results of the earlier ground surveys, and subsequent observations made by other geologists. The Marathon Basin exposes pre—Permian Paleozoic rocks. Within the report area these are largely of Carboniferous (Mississippian and Pennsylvanian) age; older Paleozoic rocks are exposed mainly west of the report area. The Carboniferous consists of the Tesnus Formation, the Dimple Limestone, the Haymond Formation, and the Gaptank Formation. The first three are thick, sparsely fossiliferous Hysch depo- sits, of Chesterian, Morrowan, and Atokan ages. The fourth is an abundantly fossiliferous shallowvwater marine deposit of Des Moinesian, Missourian, and Virgilian ages. The Tesnus and Haymond Formations are largely sandstone and shale; the Dimple is largely limestone, but contains flysch features similar to the other two. Striking features of the Haymond Formation are boulder-beds, or wildflysch, which contain heterogeneous cobbles and boulders, including great slabs of carbonate rocks as long as 130 feet across. The overlying Gaptank Formation is mainly sandstone and shale, but contains interbedded conglomerate layers in the lower part, and thick limestone layers in the upper part. The conglomerates indi- cate that important deformation was taking place in the older rocks not far to the south. The succeeding Permian rocks of the eastern Glass Mountains are largely of Wolfcampian age, and consist of the thin Neal Ranch For- mation and the thick overlying Hess Limestone. The Hess lies with conspicuous angular unconformity on the Neal Ranch and Gaptank Formations. The Lower Cretaceous Comanchean Series is divided on the map into the Trinity, Fredericksburg, and Washita Groups. It is mostly limestone and interbedded tnarly limestone, but the Maxon Sandstone forms a persistent layer at the top of the Trinity Group. A few small bodies of intrusive igneous rocks of Tertiary age occur in the Cain boniferous rocks in the southwest part of the report area. Extensive areas of lower ground within the area are covered by thin deposits of gravel of Quaternary age. The deposits are ofseveral l’leis- tocene and Holocene ages, the older of which are unrelated to modern topography. The most extensive deposits form broad gravel plains, which toward the south are dissected so that younger alluvial deposits lie below them along the present drainage. The structures of the area are of several ages, the oldest being more cotnplex than the younger. The oldest are in the pre-Permian rocks. which are strongly folded and faulted. These deformed pre-Permian surface rocks are shown by deep drilling to lie with marked discon— tinuity along a great thrust fault (Dugout Creek overthrust) on another sequence of pre-l’ermian rocks like those in the cratonic area north of the Marathon (()uachita) orogenic belt. The Permian rocks in the Glass Mountains to the north are younger than the deformation of the older rocks, and are at most gently tilted to the north, but they are nevertheless unconformable below the Cre— taceous. The Cretaceous rocks slope at low angles northeast, east, and southeast away from the Marathon dome, but structure contours in— dicate that they are warped into broad, east-plunging arches and troughs. INTRODUCTION The Marathon Basin is a topographic feature in western Texas, formed by the removal of the Creta- ceous strata that originally covered the Marathon dome, and subsequent excavation of the relatively weaker, strongly deformed pre-Permian rocks beneath. The Glass Mountains to the north are formed of stronger Permian rocks, mainly carbonate, from which the Cretaceous rocks have also been largely stripped. The Cretaceous strata along the edges of the Marathon dome stand above the deformed pre-Permian rocks of the Marathon Basin in prominent escarpments, many of which show clearly the angular unconformity be- tween the pre-Permian rocks and the Cretaceous (fig. 1). The Cretaceous rocks extend outward toward the east, north, and south into the plateaus and mesas that are characteristic of this part of Texas. This report covers the eastern part of the Marathon Basin, east of the 103°5’ meridian (pl. 1; fig. 2), as well as the eastern end of the Glass Mountains and part of the surrounding Cretaceous plateaus. The northern part lies in Pecos County, the southern part in Brew- ster County. It is traversed across the center by the Sunset Route of the Southern Pacific Railroad and by US. Highway 90. US. Highway 385, from Marathon to Fort Stockton, extends across the north part of the area. All the area of this report was mapped geologically between 1927 and 1931, as a part of a comprehensive survey of the Marathon Region (King, 1930, 1937). Surveys west of the 103° meridian were made in detail on topographic maps, but no topographic maps were available at the time for the area to the east, which covers about a quarter of the Marathon Basin, so that mapping was by reconnaissance surveys of greater or less accuracy. Since 1968, topographic maps of the eastern part of 2 GEOLOGY OF THE EASTERN PART OF THE MARATHON BASIN, TEXAS FIGURE 1.—Angular- unconformity between Paleozoic rocks of Marathon Basin and Cretaceous cover rocks. Southwest face of Housetop Mountalns 18 miles east of Marathon at eastern rim of Marathon Basin. Tilted Tesnus Formation (Carboniferous) overlain by flatvlying Glen Rose Limestone (Lower Cretaceous). the basin, east of the 103° meridian, have been pub- lished on the 1:24,000 scale, and two sets of air photo— graphs on different scales have also become available. The topographic maps form the Marathon Gap, Rei- ninger Draw, Dimple Hills, Caprock Butte, Housetop Mountains, Tesnus NE, Tesnus, and Tesnus SE 71/2- minute quadrangles (fig. 3). The writer has had these eight quadrangles reduced photographically to make two 15-minute quadrangles on the 1:62,500 scale, in order to match the already available 15-minute quad- rangles to the west. The present report includes the results from a photo— geologic survey of the area of the eight 71/2-minute quadrangles, based on examination of air photographs, the 124,000 topographic maps, and available ground surveys made in 1927 to 1931 (pl. 1). The resulting mapping in the north is mainly a refinement of the original surveys, with more precision as to form and location. The mapping in the south, especially south of the line of the Southern Pacific Railroad, is in an area that was covered only cursorily before and adds many geological details; however, because these details have not been verified by additional ground surveys, consid— erable uncertainty of interpretation exists. For orien- tation purposes, a 5—minute strip of the area west of the 103° meridian is also included. The northern part of the strip is taken Without modification from the previously published maps. Farther south, greater or lesser modifications have been made on the basis of the photogeologic survey. The ensuing text describes the bedrock and surficial formations of the area, based in part on the original S'I‘RA'I‘IG RAPHY 103°30' 30030,”... .. .. .. EXPLANATION Cretaceous and younger rocks E Permian rocks Upper Pennsylvanian rocks Lower Pennsylvanian rocks E Mississippian rocks Lower Paleozoic rocks Post-Cretaceous thrust fault .A_A_A. Pennsylvanian thrust fault Structure contours on Cretaceous In feet \ 0 5 10 15 20 ._ 0 5 10 Geosynclinal sequence 25 KILOMETERS 15 MILES FIGURE 2.——Map of the Marathon Basin, western Texas, showing area covered by this report. Report area outlined by dashed line. work of 1927 to 1931, but with many additions result- ing from subsequent developments, including the re— sults of investigations by others. STRATIGRAPHY The bedrock of the area reported on is of Ordovician, Devonian, Mississippian, Pennsylvanian, Permian, and Cretaceous ages (fig. 4). The older, pre-Missis- sippian rocks emerge in the Marathon Basin farther west, and only a few outcrops extend into the western edge of the report area. A few intrusive igneous rocks of Tertiary age occur in the southwestern part of the area. Extensive areas are covered by deposits of Quaternary gravels, of which several ages can be dif- ferentiated. 4 GEOLOGY OF THE EASTERN PART OF THE MARATHON BASIN, TEXAS 103°30’ i03° I SIERRA MADERA I _. -:-__ REININGER DRAW 3030 .. .. .4 ALTUDA HESS CANYON " MARATHON GAP DIMPLE HILLS MARATHON I MARATHON BIASI MONUMENT I ' TESNUS NE SPRING TESNUS SE I TESNUS ' . HOOD SPRING . _ DOVE MOUNTAIN-f- 0 5 10 15 20 25 KILOMETERS 0 5 i0 15 MILES FIGURE 3.—Map of the Marathon Region showing topographic quad- rangle maps referred to in text. Area of report outlined by dashed line. PRE-MISSISSIPPIAN ROCKS Fre-Mississippian rocks are exposed in the Warwick Hills at the western edge of the report area, and in the Lighting Hills and Horse Mountain a few miles west of the area farther south. They are the eastern edge of a large area of pre-Carboniferous rocks, principally in the large Dagger Flat anticlinorium. These rocks have been strongly folded, and in part are repeated in a series of thrust slices, and they plunge eastward be- neath the Mississippian and overlying Carboniferous. The nearest outcrops consist of the Caballos Novacu- lite (Dc), of Devonian and early Mississippian age, and the Marvillas Chert (Om) of Late Ordovician age. These siliceous formations are resistant to erosion, and in the Warwick and Lightning Hills stand in low strike ridges, but they rise farther south into Horse Moun- tain, altitude 5,010 feet, the highest point in the Mara- thon Basin. CARBONIFEROUS ROCKS This thick sequence of strata between the Devonian below and the Permian above is partly of Mississippian and partly of Pennsylvanian age, with a rather uncer- tain boundary between them. Hence, they will be re- U) —_ _J._ A- . 3 “j _ WashIta Group 5% [ l l l l d . k b G 53— .'....'. .7, Fre erIcs urg roup ‘8 MINI '__.i_ Trinity Group _ ‘I I J a I I I | l | l I I I I E Ij T] T I I - .‘E I I I I Hess LImestone E _ l l l | | TI 1 5 _,1.'.. '..'. OQED I O I 0.3 :— :‘:—‘:‘ Neal Ranch Formation — — I I I _l¥—l¥—l —|_ I: II: fi.—.—”-.—.—. Gaptank FormatIon - 3000 METERS 15,000 FEET - 5.3 Haymond Formation ‘3 5 1‘. :::.‘ "2000 o ‘E . . . . . . ‘- to 1 I I 10,000 - ~§_ _;_ [H'H Dimple o w ‘ I ' I ' Limestone e E ' .1. . 8 £ — 1000 5000 - iiiiiii _ Tesnus ~ 1 Formation C .9 g 0 -- 0 .6 _ .9 g 2 'a .52 _ — 'g-(EuCE—i Caballos Novaculite '50) _l]lllJ_llll g Q 1"“”1111"|I|I”“II Maravillas Chert Ordovician FIGURE 4.—Columnar section showing geological formations that occur in the report area. ferred to herein as Carboniferous. TESNUS FORMATION The lowest Carboniferous strata in the report area belong to the Tesnus Formation (Ct), named for Tesnus STRAiiGRAPHY 5 Station‘ on the Southern Pacific Railroad within the report area (Baker and Bowman, 1917, p. 101—102). The Tesnus consists of flysch composed of sandstone and shale, interbedded,in units a few feet to several hundred feet thick. It is less resistant to erosion than the underlying Caballos Novaculite or the overlying Dimple Limestone, and hence forms low ground within the Marathon Basin. To the north, it is extensively masked by Quaternary gravel deposits, but in the southeast part of the basin (as in the south part of the report area), it projects in a confusion of low, rough ridges, which are known by such titles as Hells Half Acre and Devils Backbone. The Tesnus has a variable thickness that increases southeastward, In the northwestern part of the Marathon Basin it is no more than 300 feet thick. In the area south of the town of Marathon, a section 1,619 feet thick was measured. Farther east, in the west part. of the report area, a section between the Haymond Mountains and Perla Blanca Spring to the west totaled 6,520 feet. No surface sections of the Tesnus Formation are available farther east and southeast, but in the south part of the report area the thickness must be greater than any of these figures, as the formation crops out over wide areas and dips at high angles, al- though with unknown duplications by folding and thrusting. Deep drilling in the northern part of the report area has provided some additional data on the thickness of the Tesnus Formation. In the Continental-Allison well east of Gap Tank, the Tesnus is reported to be 4,210 feet thick. The Mobil-Cox well 6 miles to the south apparently passed through three sequences of Tesnus, repeated by thrusting, which were 3,690 feet, 2,490 feet, and 1,960 feet thick, respectively. Farther south- west, immediately west of the report area, the Exxon- Law well passed through 5,070 feet of Tesnus. These thicknesses are not definitive, because no data are av- ailable as to the steepness of dip of the strata in these wells, or details of the structure. The lower part of the Tesnus Formation is domi- nantly shale, but sandstone beds dominate in the upper part. The lower shaly part was originally termed the Rough Creek Shale Member (Baker and Bowman, 1917, p. 101) after an anticlinal area on Rough Creek immediately south of the report area, but this name is preoccupied by another stratigraphic unit in central Texas. Moreover, there is no assurance that these lower shaly beds are at the same stratigraphic level in all parts of the Marathon Basin; nevertheless, the gen- eral shaliness of the lower part of the formation is ‘Tesnus is on the line of the Sunset Route of the Southern Pacific Railroad, and the name is simply the word “Sunset" spelled backwards. genuine. Shales dominate the lower 2,000 feet of the 6,510-foot section between the Haymond Mountains and Pena Blanca Spring, and the lower 1,189 feet of the 1,620-foot section south of Marathon. Most of the 300- foot section in the northwestern part of the Marathon Basin is shale. In the eastern part of the Marathon Basin, the upper 300 to 400 feet of the Tesnus is again black shale, which contains thin limestone beds in the upper part that are gradational into the Dimple Lime- stone. The general stratigraphy and lithology of the Tesnus Formation were described in the earlier reports (King, 1930, p. 31~36; 1937, p. 55—62). Within the last few decades its petrography and sedimentary structures have been investigated by various geologists (Johnson, 1962; McBride and Thomson, 1965; Cotera, 1969; Thomson, 1969; Flores, 1977; McBride, 1978, p. 131~ 136). The lower shales are dominantly illite; higher up they are chlorite and illite, with some montmorillonite. Many of the lower shales are black or blue-black, but there are some interbedded greener layers, and these dominate in the higher strata. The sandstones form layers a few inches to several feet thick, which frequently occur in groups or bundles (fig. 5), separated by shaly units of somewhat lesser thickness. This characteristic distinguishes the Tesnus from the otherwise very similar Haymond Formation, in which the layering is much thinner: and more regu- lar. Some thick, massive sandstone beds occur; such ledge-making sandstones are particularly prominent in the eastern part of the Marathon Basin, just above the lower shales, and are well shown on the air photo- graphs. The sandstones are commonly fine grained and weather rusty brown; on fresh surfaces they have a greenish tinge, due to chlorite in the matrix. Quartz grains form somewhat over half of the sandstones; the remainder are grains of other minerals and of rock fragments. The sandstones may be classed as quartz wackes, or immature subgraywackes. Ac- cording to Cotera (1969) the middle part of the upper sandstones in the eastern part of the Marathon Basin contains more feldspar than the parts above or below, which contain more metamorphic rock fragments. Ac- cessory heavy mineral grains include abundant garnet in the lower part, and also significant amounts of apa- tite. Other accessory minerals include zircon, magne- tite, tourmaline, and hornblende. In the southeastern part of the Marathon Basin, in the southern part of the report area, are layers of mas- sive white quartzite (q), enclosed in the more usual sandstones and shales. These are probably only two or three in number, but they are much repeated by fold- ing and thrusting. They form especially prominent, GEOLOGY OF THE EASTERN PART OF THE MARATHON BASIN, TEXAS STRATIGRAPHY 7 light-colored, sharp-edged ridges that stand out on the air photographs. Thin layers of chert-pebble conglomerate occur in places near the base, and are also reported at a few places in the upper part‘in the southeastern part of the Marathon Basin. The fragments are black, green, brown, and white chert, mostly derived from the under- lying Caballos Novaculite. The pebbles are commonly cemented by chalcedony. Sedimentary structures in the Tesnus sandstones have been described by various geologists (Johnson, 1962; McBride and Thomson, 1965; Thomson, 1969). Graded bedding is not prominent, owing to the general fine grain of the sandstones, but bases of each bed are generally sharply marked, whereas their upper con- tacts are less prominent. The basal contacts are frequently marked by flute casts and groove casts. In some beds these are crossed at right angles by soft- sediment faults with displacements of less than an inch or two. In some layers there are well-marked slump structures that produce warped, folded, and disrupted sandstone beds. Commonly these are associated with sandstone dikes. Paleocurrent measurements from beds of sandstone in the Tesnus Formation in all parts of the Marathon Basin show an invariable movement from southeast to northwest (Johnson, 1962, p. 790—791). Opinions have varied through the years as to the conditions of origin of the Tesnus Formation, but it is now generally believed that it was deposited in a trough of consider- able depth, into which the sandstones, at least, were transported by turbidity currents. They have the characteristics of submarine fan deposits (McBride, 1978, p. 135; T. H. Nilsen, written commun., 1978). Fossils are not abundant in the Tesnus Formation. The most common are plant fragments, mostly worn and comminuted. Larger plant fragments, including sizeable logs, occur at a few places, especially in the upper part, as at a locality south of Marathon. Accord- ing to David White (King, 1937, p. 61) these are of Early Pennsylvanian (Pottsville) age. From shale samples near the top of the formation, Bruce Harlton has obtained Foraminifera said to be of Early Pennsyl- vanian age (King, 1930, p. 36). However, conodonts from shales near the base of the Tesnus are Mississippian (Ellison, 1962). Radiolarians (Baker, 1963) and a crustacean (Brooks, 1955) are also re- ported. { FIGURE 5,—Thick-bedded sandstones of upper part of Tesnus Forma- tion, with interbedded shale. A, On San Francisco Creek 16 miles southeast of Marathon. B, Cut on U.S. Highway 90 east of Lemons Gap 19 miles east of Marathon; stratigraphic top to the right. The Tesnus Formation therefore includes strata of Mississippian and Early Pennsylvanian age. It is prob- ably equivalent to the similar but thicker Stanley and Jackfork Formations of the Ouachita Mountains, which are of Meramecian, Chesterian, and Morrowan age. DIMPLE LIMESTONE The Dimple Limestone (Cd) is named for the Dimple Hills (Baker and Bowman, 1917, p. 105), a synclinal mass in the north part of the present report area, which rises 750 feet above W B Flats. The hills are so-named for the dimpled appearance of their dissected slopes. The Dimple projects from the low ground of the Mara- thOn Basin in prominent ridges, only a little lower than those of the Caballos Novaculite. Within the report area, the Dimple is repeated in many ridges, from the Dimple Hills and W B Flats southward nearly to Shely Peaks (Tres Hermanas).2 In the south part of the area, the ridges curve about in synclinal hooks, each enclos- ing Haymond Formation in their centers. In the north part of the area, the outcrops are much more inter- rupted by the cover of Quaternary gravels, but the fragments of outcrop clearly show the same orderly pattern (fig. 16). In the Dimple Hills the writer (King, 1930, p. 36—38) measured a thickness of 1,160 feet of the formation, which, however, includes 66 feet of transition beds below and over 200 feet of transition beds above, which are dominantly shaly, with only a few thin interbedded limestone layers. Thomson and Thomasson (1964) re- port 905 feet on the ridge west of Frog Creek about 6 miles southwest of the Dimple Hills. These are appar- ently maximum thicknesses of the formation. Meas- urements by the writer and Thomson and Thomasson along the north and northwestern edges of the Marathon Basin yield thicknesses of 380 to 400 feet. In the buttes 7 miles east-southeast of Gap Tank, Thom- son and Thomasson report a thickness of 435 feet. The formation also thins southeastward from the maxi- mum. Measurements by the writer (1937, p. 62—63) and Thomson and Thomasson indicate a thickness of about 500 feet in the Haymond area, and in the southeastern part of the Marathon Basin near Panther Peaks, Thomson and Thomasson report 250 to 400 feet. The sedimentology of the Dimple Limestone has been studied by Thomson and Thomasson (1964; 1969a, b), who distinguish three facies. Along the north edge of the Marathon Basin is a shelf facies, presumably formed in fairly shallow water, composed 2On the older maps, the group of peaks on the promontory of Cretaceous rocks in the southeast part of the report area were designated as 'I‘res Hermanas. On the recently published Tesnus 1:24.000 topographic sheet they are designated as Shely Peaks, but the earlier name is perpetuated by the name of the triangulation point on the western peak. In the present text, both names are indicated. 8 GEOLOGY OF THE EASTERN PART OF THE MARATHON BASIN, TEXAS of grainstones in beds several feet thick, crossbedded in part, but not graded; they are interbedded with lenticu- lar layers of chert-pebble and chert-cobble conglomer- ate. Southeast of this, in a belt about 4 miles wide, is a slope facies, transitional from the shelf facies into a basin facies; it includes the exposures in the Dimple Hills. The remainder of the Dimple farther southeast, including the part in the report area, is a basin facies. Beds are mostly thinner than in the shelf facies, and more regular. The rock is fine-grained, and all beds are graded, their lower parts being lime packstones, their upper parts spicular lime mudstones, passing into shales and spicular cherts. Upper parts of some of the layers are prominently convoluted, the convolutions being emphasised by silicification of the laminae (figs. 6 and 7). The basin facies is a calcareous flysch. The distinguishing features of the shelf and basin facies are very evident in the field. They were apparent to the writer during his earlier field work in the area, al- though without realization of their meaning. Directional structures, such as groove casts, cross- bedding, overturning of convolute laminae, and aligned sponge spicules, all show paleocurrents di- rected southeastward, except in the southeasternmost belt near Panther Peaks, where a few determinations show northwestward-directed paleocurrents. Fossils are fairly common in the Dimple Limestone, but most of them are fragmented shells, so that it is difficult to obtain identifiable material. From various localities in the Marathon Basin, the writer has col- FIGURE 6.—Dimple Limestone east of Haymond Station 15 miles east-southeast of Marathon. Inverted beds of resedimented carbonate, with convolute layers outlined by silicified bands. STRA'I‘IGRA PH Y 9 FIGURE 7,—Structures in Dimple Limestone similar to those in figure 6, originally described (King, 1930, pl. II) as “dome-like structures outlined by chert bands.” On ridge west of Frog Creek, 15 miles east of Marathon. lected corals, brachiopods, and a few poorly preserved ammonoids (probably Gastrioceras). These were con- sidered by G. H. Girty to be of Pottsville (Early Pennsylvanian) age (King, 1937, p. 64). Bruce Harlton has collected Foraminifera from shales interbedded in the Dimple which are believed to be of Marble Falls or Wapanucka age (King, 1930, p. 39). Ellison and Graves (1941) identified species of conodonts considered to be of Morrowan age. Sanderson and W. E. King (1964) have obtained fusulinids from the Dimple Limestone at many 10— calities in the Marathon Basin, and recognize three zones—the oldest containing Millerella, the next high- est Pr'ofusulinella and Eoschubertella, and the highest Fusulinella. They consider the oldest to be of Morrowan age and the two higher ones Atokan. The Millerellas occur at localities all over the Marathon Basin, the two higher zones being more restricted, the last occurring only at a few localities in the northwest- ern part of the basin. In summary, all the fossils in the Dimple Limestone indicate an early Pennsylvanian age (Pottsville of Girty). Most of them indicate a Morrowan (Marble Falls or Wapanucka) age, but some of the fusulinids are evidently Atokan. HAYMON D FORMATION The Haymond Formation (Ch) is named for Haymond Station on the Southern Pacific Railroad in the eastern part of the Marathon Basin, in the report area (Baker and Bowman, 1917, p. 107), Where it is exposed in two synclines east and west of the station. The formation is a elastic, sandy and shaly flysch deposit somewhat like the Tesnus Formation, and like it forms low ground in the Marathon Basin. Its extent is more restricted than the Tesnus, however, as it is confined to synclinal rem- nants, and it is further masked by Quaternary depos- its. The most extensive areas of the Haymond Forma- tion in the Marathon Basin are in the report area, those elsewhere in the basin being smaller and preserving a smaller thickness of beds. In the north part of the Marathon Basin, the cover of Quaternary deposits is especially extensive, the largest areas of exposure being along the bases of Cretaceous mesas southeast of Gap Tank. Outcrops are more con- tinuous farther south, especially in the two synclinal 10 GEOLOGY OF THE EASTERN PART ()F THE MARATHON BASIN. TEXAS areas east and west of Haymond Station. A little- known area of Haymond Formation occurs in the southeastern part of the Marathon Basin south of Tes- nus Staton, south of an outcrop band of Dimple Lime- stone that extends eastward from Panther Peaks. No complete sections of the Haymond Formation from base to top are exposed. In most of the synclinal remnants the top is not preserved, and only the upper part, in downward sequence below the Gaptank For- mation, is preserved southeast of Gap Tank. In the syncline east of Haymond Station, the writer estimated a thickness of 3,600 feet of strata above the Dimple Limestone; McBride (1966, pl. 1) gives 4,200 feet in the same area. Southeast of Gap Tank, both the writer and McBride found about 2,000 feet of strata below the Gaptank Formation. A possible tie between the two sequences is the occurrence in both of boulder- beds. The Haymond Formation is at least 5,000 feet thick, and might be thicker. The Haymond Formation was described at length by the writer (1937), p. 64—73) and by others during the 1930’s. Within the last few decades it has been given extensive sedimentological study (McBride, 1964a, 1966, 1969, 1970, 1978, p. 141—146; Dean and Ander— son, 1966; Flores and Ferm, 1970; Flores, 1972, 1974, 1975; among others). Most of these recent studies have been made on outcrops within the report area. The most abundant rock type in the Haymond is thin-bedded sandstone and shale, in alternating layers a few inches thick (fig. 8). This particular facies seldom occurs in the Tesnus Formation and is a good field guide for distinguishing these otherwise similar sandy FIGURE 8.—Lower part of Haymond Formation in cut on US. Highway 90 east of Lemons Gap 18 miles east of Marathon. Height of cut about 10 feet. Thin-bedded flysch composed of interbedded sandstone and shale; bending of strata at top of cut results from soil creep. Compare with sandstone beds of Tesnus Formation in figure 53, Which is faulted against the Haymond to the east. STRA'I‘IG RA PH Y and shaly flysch formations. The facies forms all the lower part of the sequence in the synclines near Haymond Station, but only a small part of the section southeast of Gap Tank. The sandstone layers are com- monly a few inches thick, and are mainly fine grained, verging on coarse siltstone; a few coarser sandstone beds are a foot or more thick. The shale beds have the same general thickness as the sandstone beds. McBride estimates that there may be more than 15,000 alter- nating sandstone and shale layers in the synclines near Haymond. By statistical analysis, Dean and An- derson (1966) propose a correlation of layers of the sandstone and shale between exposures on US. High- way 90 and on the Southern Pacific Railroad 7 miles to the south, thus implying a great persistence of individ- ual layers. McBride (1966, p. 18—22) records various small-scale sedimentary structures in the sandstone and shale beds. Graded bedding occurs in many layers, but is obscure. Many of the layers are finely laminated, and the upper parts are crossbedded or even convolute-laminated. Many of the lower bedding sur- faces are marked by groove casts or flute casts. Some of 11 the bedding surfaces contain plant fragments. Coarse sandstone beds are minor constituents in the sequences to the south, but are much thicker and more prominent in the sequence southeast of Gap Tank to the north. They were termed “arkose” by the writer (1930, p. 42; 1937, p. 66), but McBride (1966, p. 23) states that they contain no more feldspar than the other sandstones of the Haymond, although they con- tain less fine-grained matrix. Nevertheless, the coarse sandstones differ from these in their lighter colors, greater friability, and thicker, structureless layers. In- dividual beds may be as thick as 5 feet, but southeast of Gap Tank bundles of the sandstone beds exceed 50 feet in thickness. Limestone layers are uncommon in the Haymond Formation. The only exceptions are two thin layers of brown sandy and pebbly limestone in the synclinal area 3 miles south of the Dimple Hills that contain fusulininds (Skinner and Wilde, 1954) (fig. 9). They are interbedded in the prevailing thin-bedded sandstones and shales, and McBride (1966, p. 15) believes that they are turbidites like the enclosing strata. ii 09 Brewster—Pecos County line (approximate)/'\ l EXPLANATION Quaternary gravel Cretaceous rocks 09 Haymond Formation Is, limestone Dotted lines, other traceable beds + 30°17’30” CJ—DO I 102°55’ 1| KILOMETEH | 1/2 MILE FIGURE 9.——Field sketch made in 1930 of outcrop area of Haymond Formation 3 miles (5 km) south of Dimple Hills, showing outcrops and structure of fusulinid-bearing limestone layers. 12 GEOLOGY ()F 'l‘HE EASTERN PART OF 'l‘HE MARATHON BASIN, TEXAS BOULDER-BEDS The most spectacular rocks in the Haymond Forma- tion are the boulder-beds (Chb), which have aroused much interest and study since their discovery by the writer in 1930. They occur in two areas—in the syncline east of Haymond Station below Housetop Mountains3 where they crop out for a distance of about 8 miles, and in the area of Haymond Formation southeast of Gap Tank where they crop out for a dis- tance of about 4 miles. The boulder-beds in the two areas are of somewhat different character, although they probably occur at nearly the same stratigraphic level. The boulder-beds below Housetop Mountains are about 1,800 feet above the base of the formation, and form a lenticular complex a few hundred feet to more than 900 feet thick. The assemblage includes boulder- bearing mudstone, interbedded coarse sandstone, con— torted thin-bedded flysch, and chert conglomerate. The boulder-bearing mudstones attain their greatest thickness and greatest concentration of boulders in an area west of the summit of Housetop Mountains, and lens out and interfinger with other clastic rocks north- east and southwest along the strike. The most impressive feature of the boulder-beds in this area is the large size of some of the individual blocks (figs. 10 and 11). The largest blocks are of lime- stone, mainly a fossiliferous Pennsylvanian limestone, but including one block of Dimple Limestone 130 feet across at a locality south of the Southern Pacific Rail- road. The fossiliferous limestone is unlike any forma— tion in the Marathon Basin, or in any nearby regions, but its fauna is of Early Pennsylvanian age, hence ap- proximately the age of the Dimple Limestone. Somewhat smaller fragments are from older forma- tions of the Marathon Basin sequence, especially of the Caballos Novaculite (fig. 12), but there are a few others from the Tesnus Formation and the Maravillas Chert. Besides these, are numerous well-rounded cobbles of crystalline rocks—rhyolite, schist, aplite, syenite, vein quartz, and the like; they have yielded radiometric ages by Rb/Sr methods of 370 to 410 my. (Silurian and Devonian) (Denison and others, 1969, p. 249). Many, perhaps most of the boulders of Caballos Novaculite are brecciated. The writer (1937, p. 91) compared the brecciation of the novaculite in the boul- ders to that seen at the bases of thrust sheets elsewhere a0n older maps, small groups of mountain peaks have been indicated by the singular word "Mountain,” and this has been used on older maps for the peaks of Cretaceous rocks at this place. Within the last few decades the US. Geological Survey has used the plural form for these features, hence "Housetop Mountain" of older usage becomes "Housetop Mountains” on the Housetop Mountains 1:24,000 topographic map. in the Marathon Basin, and interpreted the brecciation as having been produced tectonically, before emplace- ment in the boulder-bed. However, Folk (1973, p. 718) has observed novaculite breccias in outcrops of the Caballos which he believes formed penecontemporane— ously with the sedimentation. The tectonic origin of the brecciation of the novaculite in the boulders is there- fore questionable. The following data on the larger boulders from the Housetop Mountains area have been compiled from the author’s detailed map of the area (King, 1937, plate 10): Number and diameter of boulders Formation Total 3—10 ft 10—50 ft 50+ ft Fossfliferous . . 24 24 7 55 Pennsylvanian limestone Dimple Limestone 1 1 1 3 Tesnus Formation 5 6 7d- 11 Caballos Novaculite 73 15 —— #7 88 Maravillas Chert 1 — — , 7 A , 1 _ 1 The boulder-beds southeast of Gap Tank are about 400 feet below the base of the Gaptank Formation and lie in a sequence of prevailingly coarse, thick—bedded sandstone. The boulder-beds are each no more than 10 to 25 feet thick. McBridge (1966, p. 28) and Flores (1972) record two or more layers, separated by as much as 150 feet of other strata. The exotic fragments are cobbles and boulders as much as 3 feet in diameter, with one block 7 feet long. Most of the fragments are of Caballos Novaculite, but there are also many of Maravillas chert and limestone; a very few are sandstone from the Tesnus, fossiliferous Pennsylva- nian limestone, and rhyolite. The composition of the fragments thus differs from those in the Housetop Mountains area to the south, and it contrasts notably with fragments in the conglomerates of the Gaptank Formation nearby and higher in the section. FOSSILS AN D AGE Indigenous fossils are rather rare in the Haymond formation. Plant fragments are fairly common, but most of them are small and clearly reworked. Larger identifiable material has been found at a few places. In a layer southeast of Gap Tank, about 1,200 feet below STRA'HGRAPHY FIGURE 10.—B‘oulder-beds of Haymond Formation at an area of greatest concentration of large boulders, at west foot of Housetop Mountains 19 miles east—southeast of MarathonA, General view, looking northwest. The small knobs are mainly giant blocks or slabs of fossiliferous Pennsylvanian shelf limestone. Lower half of Haymond Forma— tion and Dimple Limestone in middle distance; scarps of Lower Cretaceous on skyline. B, Nearer view of one of the exotic limestone blocks at same locality, with mudstone matrix of boulder-bed in foreground. 13 14 GEOLOGY OF THE EASTERN PART OF THE MARATHON BASIN, TEXAS FIGURE 11.-—Medium-sized slablike boulder of Pennsylvanian lime- stone at a locality not far to the north, projecting from mudstone matrix. FIGURE 12.—Large rounded boulder of brecciated Caballos Novacu- lite in boulder-bed at a locality near figures 10 and 11. the boulder-bed, David White and the writer collected plant remains considered by White to be of Pottsville age. The thin limestone beds in the middle of the Haymond south of the Dimple Hills contain fusulinids identified by Skinner and Wilde (1954, p. 803) as Fusulinella haymondensis n. sp., considered to be of Atokan age. The Haymond Formation seems to be ap- proximately equivalent to the Atoka Formation of Ok— lahoma and Arkansas. The blocks of fossiliferous Pennsylvanian limestone in the Haymond Formation of the Housetop Mountains area contain a large fauna of invertebrates, which were thoroughly collected by J. Brookes Knight in 1931 (King, 1937, p. 72-73). G. H. Girty states that these are of Early Pennsylvanian age and mentions their resemblance to various Morrowan faunas. This sug- gests that the limestones in the blocks are of nearly the same age as the Dimple Limestone, although they are of a very different facies. ORIGIN The Haymond Formation, like the Tesnus, is a flysch deposit, composed largely of interbedded sandstone and shale; however, the details of its character, and thus the conditions of its formation, are considerably differ- ent. Most of it was deposited in water of much depth, and the thin-bedded sandstones and shales, at least, are clearly turbidite deposits, but they are basin—plain deposits rather than submarine fan deposits as in the Tesnus (McBride, 1978, p. 143— 144; T. H. Nilsen, writ- ten commun., 1978). Paleocurrent observations by McBride (1966, p. 54-55) show a dominant sediment transport toward the northwest, but with a minor turn- ing of the currents westward down the axis of the trough. More uncertainty attends the origin of the coarse sandstone beds, especially those of the upper part of the formation southeast of Gap Tank. McBride (1966, p. 53) proposes that they were probably deep-water depos- its like the thin-bedded sandstones and shales, al- though with some doubt, whereas Flores (1972, p. 3424) interprets them as delta-front and delta-plain deposits, thus implying a shallow water origin. They also have many characters of deeper water submarine fan deposits (E. T. McBride, written commun., 1978). Many ideas have been expressed through the years as to the origin of the boulder-beds. Notions that they were glacial deposits (Baker, 1932; Carney, 1935), beach deposits (Flores and Ferm, 1970), a tectonic moraine (Van der Gracht, 1931), or the crests of broken folds (Hall, 1957) have little merit. The writer has always believed, from the time of their first discovery, that the boulder-beds were some- how intimately related to the tectonic evolution of the region. Later, in line with developing concepts of sedimentology, he (1958, p. 1734) proposed that the boulder-beds “were subaqueous deposits, laid down in a deep, rapidly subsiding trough, with tectonically un- stable, probably faulted margins. Into the trough, probably from both sides, the blocks, boulders, well- rounded cobbles, and muds were carried from the un- STRATIGRAPHY 15 stable shelves, in subaqueous landslips which devel- oped proximally into turbid flows.” The boulder-beds are thus an exaggeration of the more usual sedimenta- tion, or a wildflysch. McBride (1966, p. 49—52) has elaborated on the same scheme. McBride, however, on the basis of paleocurrent data from the enclosing more usual flysch strata, c0ncludes that the boulders were all carried into the sedimentary trough from the southeast. A southeastern source is plausible for many of the fragments—those 0f the older Paleozoic Tesnus, Caballos, and Maravillas Forma- tions, as well as the rounded cobbles of crystalline rocks. The Paleozoic radiometric ages obtained from the latter and incompatible with those of the basement of the craton to the north, and they must have come from a backland that was being orogenically deformed during early Paleozoic time. The well-rounded charac- ter of the crystalline cobbles indicates that they had been first laid down on beaches before they slumped and slid into their present positions. Nevertheless, the great limestone blocks and slabs could not have had a southeastern source, and the writer believes that they were derived from an unsta- ble shelf to the northwest. The slab of Dimple Lime- stone is of shelf, or northwestern facies, and the more numerous slabs of fossiliferous Pennsylvanian lime- stone probably had a similar source, from the craton to the northwest. The rocks of the boulder-bed thus ap- pear to have had a composite source, from unstable margins on both the southeastern and the northwest- ern sides of the depositional trough. GAP’I‘ANK FORMATION The Gaptank Formation (Cg) is named for Gap Tank (Udden, 1917, p. 38) at the edge of the Glass‘Mountains in the north part of the report area. The Gaptank For- mation forms the top of the Pennsylvanian in the Marathon Basin sequence and is exposed along the north edge of the basin, at the bases of the Glass Mountains escarpments. The main area of exposure is in the foothills south of Gap Tank in the northwestern part of the report area. Smaller exposures of the Gap- tank occur farther east in the north part of the report area. From the Gap Tank area, the upper part of the formation is exposed along the base of the Glass Mountains escarpment westward from the report area for 3 miles to the Wolf camp Hills. Still farther west are other outcrops south of the Glass Mountains of rocks of Late Pennsylvanian, or Gaptank age, but they are of another facies, lie in a different structural setting, and will not be considered further here. AREA NEAR GAP TANK In the area south of Gap Tank, the Gaptank Forma- tion is folded into an east-plunging anticline, steepest on the south flank, but dipping more gently on the north flank beneath the Permian rocks of the Glass Mountains (fig. 13). In this area, the writer estimated a thickness of the formation of about 1,800 feet between the underlying Haymond Formation and the overlying Wolfcampian strata. On the geologic map, the forma- tion in this area is divided into a lower (Cgl) and an upper (Cgu) part. At its base, resting on shales and sandstones of the Haymond Formation, is the Chaetetes limestone, about 50 feet thick. This is followed by 150 feet of shale and sandstone. In the next 750 feet of section the sandstone and shale contains five conglomerate layers 15 to 40 feet thick, which are thickest to the south, and thin rapidly on the north flank of the anticline. The upper 750 feet of the formation (Cgu) containes five limestone layers 50 to 75 feet thick, separated by sandstone and shale, the thickest limestone layers being at the top. The conglomerate beds of the lower part of the for- mation contain well-rounded limestone cobbles as much as a foot in diameter, mostly from the Dimple Limestone, but including a significant number from the Chaetetes limestone at the base of the formation (fig. 14); minor fragments of chert from the lower for- mations of the Marathon Basin have also been re- ported. The rapid northward thinning of the conglom- erate beds indicates that their cobbles were derived from an area undergoing deformation not far to the south (King, 1930, p. 110—112). However, the succes- sion of the lower beds in the Gap Tank area itself is to all appearances conformable. Nevertheless, Ross (1967, p. 372) places a major un- conformity beneath the lowest conglomerate bed, and reassigns the beds beneath, including the Chaetetes limestone, to the upper part of the Haymond Forma- tion. This interpretation is very questionable; uncon- formities (and pseudo-unconformities) are a “dime-a- dozen” in this part of the sequence, and assigning a major role to any of them is highly subjective. Ross’s supposed time gap between the Chaetetes limestone and the conglomerates is not convincing, as the faunas below and above are of Desmoinesian and Missourian age, respectively, with a considerable thickness of un- fossiliferous beds between. The greatest change in sedimentation in the sequence is between the silici- clastic Haymond beds and the succeeding Chaetetes limestone, hence I continue to place the base of the Gaptank Formation where it was originally described. To the north, at Gap Tank, the Gaptank Formation is overlain by about 100 feet of the Neal Ranch Forma- tion of early Wolfcampian age (Ross, 1965, p. 81, sec- tion 41), but this unit pinches out a short distance to the west. Both the Gaptank and the Neal Ranch are overlain with moderate angular unconformity by the 16 GEOLOGY OF THE EASTERN PART OF THE MARATHON BASIN, TEXAS 3/ 30°25' 2 . ) Lower Gaptank ‘ k055i) bed Yank A 104°57/30" _ J; / 0/ "1| so V k/ I .rfiap ran) o/‘K . —-— 9 ._3 ‘ EXPLANATION Quatemary deposits Comanchea n Series (Cretaceous) Hess Limestone c, conglomerate h 9 Neal Ranch Formation ' ‘ ' ' ‘ ‘ f1 (Permian) i/ —- ti /', .. / x L3 ./ -osm- .. 2r.— ........ M‘fiifi W ...... — "“915" Jié‘féyli/ Upper part 70 / / L, limestone bed Gaptank Fonnafion (Carboniferous) Lower part c, conglomerate bed In, Chaetetes limestone Haymond Formation (Carboniferous) Chb, boulder-bed in upper part 4 KILOMETERS J I 2 MILES FIGURE 13— ~Geologic map of the Gap Tank area showing details of sub-divisions of the Gaptank Formation, based on surveys made in 1927 (King, 1930, fig. 15), which are difficult to reconcile in detail with the modern topographic data. basal conglomerate of the Hess Limestone of upper Wolfcampian age. The strata below the unconformity are considerably truncated by it. Ross (1967, p. 373) suggests that as much as 400 to 500 feet of upper Gap- tank beds, mainly limestone, may wedge in below the unconformity between Gap Tank and the Wolfcamp Hills. Fossils occur at many levels in the Gaptank Forma- tion in its type area, and indicate that the formation embraces all of the late Pennsylvanian (Des Moinesian, Missourian, and Virgilian), in contrast to the rather limited age range of the vastly thicker and Late Mississippian and Pennsylvanian flysch deposits (Chesterian, Morrowan, and Atokan). The Chaetetes limestone at the base contains Chae— tetes millepomceus, cup corals, brachiopods, and the fusulinids Fusulina attenuate, F. haworthi, and Wedekindelina euthisepta, which are of Des Moinesian age. Fossils next appear between the second and third conglomerate beds, but the most prolific lower Gaptank fossils are in shales between the fourth and fifth conglomerate beds, at a locality originally discovered by J. A. Udden (1917, p. 38—39) and Emil Elise (1917, p. 17—18), at the south foot of the Cretaceous mesas, 2 miles southeast of Gap Tank. The bed contains corals, bryozoans, pelecypods, gastropods, a cephalopod (Schistoceras smithi), a large assemblage of brachiopods, and a large number of small Triticites re- FIGURE 14.—Roundst0ne cobbles in lowest conglomerate member of the Gaptank Formation south of Gap Tank and 20 miles northeast of Marathon. The clasts are mainly from the Dimple Limestone, but include a few from the Chaetetes limestone at the base of the Gaptank, one of which (C) appears below the hammer in B. S'I‘RA'I‘IGRAPHY 17 18 lated to T. irregularis. This fauna is of Missourian age. Fossils are less abundant in the higher limestones and associated beds of the Gap Tank section, but a few brachiopods and other forms occur at different levels. From the lower part of the interval Ross (1965, p. 11) has identified Triticites ohioensis, T. burgessae, and T. joensis of Missourian age, and from the upper part of the interval T. compactus, T. beedei, T. primarus, and T. cullomensis of Virgilian age. Conodonts have been recovered at a few places in the Gap Tank section (Ellison, 1964). Many conodonts have been obtained from the Chaetetes limestone at the base which are of Des Moinesian age, and a collection from the lower part of the upper limestone sequence has yielded conodonts of Missourian age. EXPOSURES EAST OF GAP TANK East of Gap Tank, the Gaptank Formation is exposed at only a few places. The first exposure is 31/2 miles south of the Allison Ranch.4 Here, Ross (1965, p. 82, section 42) records 155 feet of the formation, mainly limestone and shale, overlain by conglomerate of the Hess Limestone, with the Neal Ranch Formation miss- ing. The base of the formation was not observed, but the Haymond Formation is exposed nearby to the south. A much larger exposure occurs 7 miles east of Gap Tank, which is the easternmost occurrence of the Gap— tank Formation in the Marathon Basin. It was visited by the writer in 1930, and has not since been reported on; it much deserves further study. At the time the following section was recorded (fig. 15). Stratigraphic section of Gaptank Formation and associated beds 7 miles east of Gap Tank Cretaceous limestone (Trinity Group) at top, unconformable on beds beneath. Paleozoic rocks: Feet (15) Slabby and crossbedded sandstone ,,,,,,,,,,,,,,,,,, 100 (14) Brown limestone, with some conglomerate ____________ 10 (13) Lower and upper part of interval not exposed; beds of gray sandstone near middle, locally quartzitic ,,,,,,, 120 (12) Brown limestone ______________________________________ 5 (11) Covered ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 100 (10) Massive gray limestone, with marls at base containing various brachiopods, and Triticites irregularis ,,,,,, 25 (9) Brown sandstone, with interbedded shale that is mostly covered ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 250 (8) Conglomeratic limestone, containing large blocks of Dimple Limestone ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 10 (7) Sandstone and shale ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 20 (6) Brown massive sandstone ,,,,,,,,,,,,,,,,,,,,,,,,,, 10 (5) Sandstone and shale ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 30 (4) Brown limestone ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 4 ‘The name is omitted from the Marathon Gap 1:24,000 topographic sheet, although the group of buildings at the ranch is shown. GEOLOGY ()F THE EAS’I‘ERN PART ()F 'I‘HE lVIARA’I‘HON BASIN. 'I‘EXAS (3) Ferruginous brown and red sandstone ________________ 4O (2) Brown limestone _____________________________________ 5 (1) Ferruginous brown and red sandstone at base; base not exposed, but Haymond Formation is exposed nearby Without more critical study, many features of this sequence are enigmatic. The lower beds of the section dip 30° or more to the north, but the dip gradually flattens northward to 10° or 15°, yet there are no evi- dent breaks or unconformities in the sequence. The only certain indication of age is the identified Triticites in bed 10, which is of Missourian age. Beds 14 and 15 at the top may represent the base of the Hess Limestone, as they seem to be continuous with the Hess to the north, but there is no indication of the intervening Neal Ranch Formation. The strata below bed 10 some- what resemble the lower part of the Gaptank Forma— tion of the Gap Tank area, but conglomerate beds are subordinate here. ORIGIN As a whole, it is evident that the Gaptank Formation was deposited in much shallower water than the flysch that preceded it, although McBride (1964b, p. 43—44) has recorded some turbidite structures and soft-sedi- ment deformation in the shales and sandstones of the lower part. Ross (1967, p. 373-379) interprets the upper limestone units as having been deposited on shallow banks, passing into somewhat deeper water nearby. The conglomerate beds in the lower part of the Gaptank Formation afford clear evidence of important deformation in the older rocks of the Marathon Basin to the south, and may indicate a major orogeny of Des Moinesian age in that area, to which most of the Gap- tank Formation is postorogenic. The Gaptank Forma- tion was probably laid down only along the northern fringes of the deformed belt, and not farther south. The formation has sometimes been compared with molasse, although this is not entirely apt, as the original Molasse of Switzerland is mainly a continental and fresh-water deposit, whereas this formation is entirely marine. PERMIAN ROCKS NEAL RANCH FORMA'I‘ION The Neal Ranch Formation (Pnr) corresponds to the original Wolfcamp Formation of Udden (1917) and Bose (1917), whose type area is the 400- to 500-foot sequence in the Wolfcamp Hills 3 to 5 miles west of the report area. The formation was given its present name by Ross (1959, p. 299—301; 1965, p. 20), as a lower subdivision of the expanded Wolfcampian Series. After the original work by Udden and Bose, the Neal Ranch Formation of present usage was restudied in more de- tail by the writer (1930), p. 52—57), and later by Ross S'l‘RA'l‘IGRAPHY 19 SOUTH NORTH - A «a ~\~.\e~;\ \\\1\=\\\,\\§ \\~\ \\~\\ F‘ \ 13 1 \- . \4 6 8 9 \ \Fusulinids 2 10 0 100 200 METERS 31 1310 2310 3310 4310 5310 FEET Approximate scale FIGURE 15,—Profile of Gaptank Formation and associated beds 7 miles east of Gap Tank. From a field sketch made in 1930. Numbers refer to units described in text. (1965) and by Cooper and Grant (1972, p. 30~44). The writer mapped the formation as a continuous band of outcrop from the Wolfcamp Hills eastward as far as Gap Tank, mainly because of the inclusion at the base of the Uddenites-bearing shales which were later excluded. Later observers have concluded that for much of this distance it has been cut out by pre-Hess erosion, so that the basal Hess conglomerates lie di- rectly on various limestone layers in the upper part of the Gaptank Formation. A small remnant of the Neal Ranch Formation reap- pears, however, immediately south and southeast of Gap Tank within the report area, where Ross (1965, p. 81—82, section 4) records about 100 feet of shale and calcarenite, with a little limestone-pebble conglomer- ate at the base, lying on the upper limestone bed of the Gaptank Formation. The Neal Ranch here contains the fusulinids Pseudoschwagerina uddefli, P. beedei, Schwagerina compacta, S. gracilitatis, Paraschwa- gerina acuminata, Triticites koschmani, and other species; Cooper and Grant (1972, p. 37) found very few other fossils. The Neal Ranch Formation records the same type of shallow-water, irregular deposition as the upper part of the Gaptank Formation, and is essentially an upward continuation of Gaptank sedimentation. In fact, the precise position of the Gaptank-Neal Ranch boundary has fluctuated through the years, and from observer to observer. This problem mainly concerns the beds in the more complete sections west of the report area, and will not be dealt with here. HESS LIMESTONE The Hess Limestone (Ph) forms much of the bulk of the pre-Cretaceous rocks of the Glass Mountains from the report area westward for about 12 miles, and crowns the southern escarpment of the mountains, that overlooks this part of the Marathon Basin. The formation has undergone various changes in classification since it was named by Udden (1917, p. 43). Originally, it was conceived of as a separate forma- tion, or time-stratigraphic entity, between the Wolfcamp and Leonard Formations (Udden, 1917; King, 1930). Later (King, 1932) it was interpreted as a lateral facies of the lower part of the Leonard Forma- tion of the western part of the Glass Mountains, from which it was separated by a reef barrier. Still later, when the concept of an expanded Wolfcampian Series was adopted, it was found that many characteristic Wolfcampian fusulinids occurred in the lower part of the Hess. Ross (1965) therefore transferred this lower part, comprising 200 to 400 feet of beds to his Lenox Hills Formation, named in the western part of the Glass Mountains, and he supposed that it was sepa- rated from the overlying Hess by an unconformity. Cooper and Grant (1972, p. 60) failed to find evidence for this supposed unconformity and retained the whole unit in the Hess Formation. However, they consider that the whole of the Hess, including its upper or Taylor Ranch Member, to be of Wolfcampian age. The basal unit of the Hess is a conglomerate of lime— stone and chert pebbles and cobbles. Ross (1965, p. 30) notes considerable variation in the thickness of the conglomerate—from more than 200 feet to 50 feet or less, and even disappearing in places—suggesting de— position over an eroded topography of mild relief. It lies with angular unconformity on the Neal Ranch and Gaptank beds beneath. This unconformity is, in fact, 20 GEOLOGY OF THE EASIERX I’AR'I' OI" TH E MARATHON BASIN, TEXAS the only well-marked structural break between the rocks of the Marathon Basin and the Permian rocks of the Glass Mountains to the north; structural breaks lower in the sequence have been claimed, but are either less well-marked, or dubious. In the eastern Glass Mountains the unconformity is only moderate, although well-marked everywhere. In the northwest- ern part of the Marathon Basin, farwest of the report area, the beds above lie with right-angled unconform- ity on orogenically deformed beds beneath. The un- conformity was long supposed to be at the top of the Wolfcamp Formation, but according to modern con- cepts of the Wolfcampian Series, it lies between its lower and upper parts. Within the report area, the Hess Limestone forms most of the exposures of Permian rocks of the eastern end of the Glass Mountains, but its outcrops are much interrupted by Cretaceous outliers, and it finally passes beneath the Cretaceous about 6 miles east of Gap Tank, and is not exposed again in the northeast- ern part of the report area. In the report area (as elsewhere) the Hess is separated from the Cretaceous by an angular unconformity, but the divergence is slight, as the formation dips low to the north, generally at an angle of 5° or less. No sections of the Hess have been measured within the report area. Above the Wolfcamp Hills, 4 to 6 miles to the west, the writer measured 1,839 feet (1930, p. 61, section 24), but above the Montgomery Ranch at the west edge of the report area, he obtained 2,128 feet (1930, p. 145-146, section 27); a similar considerable thickness must exist farther east, judging from the very wide outcrop belt of the formation. The overlying main body of the Hess, in its typical development from the Wolfcamp Hills eastward, is a thick, monotonous mass of thin-bedded limestones, mostly containing few fossils other than poorly pre- served fusulinids. In the lower part, especially in the equivalent of the Lenox Hills Formation, is much in- terbedded red and green shale with thin beds of sandstone, which become more prominent eastward. Marker beds are few. The most persistent is a layer of silicified fossils 200 to 400 feet below the top, which Cooper and Grant (1972, p. 56) have termed the Taylor Ranch Member (tr). It contains numerous branchiopods, rare ammonoids (Perrinites), and nota- ble numbers of sponges (Heterocoelia). From the lower part of the Hess Limestone (Lenox Hills equivalent) Ross (1965, p. 32) records various species of Pseudo- schwagerina, Schwagerina, and other fusulinids characteristic of the Wolfcampian. Near the middle, below the Taylor Ranch Member, is a zone of Schwagerina crassitectoria and S. gumblei, Thevupper part, above the Taylor Ranch Member, contains var- ious species of Parafusulina, which are similar to those of the Leonardian. The Hess Limestone is clearly a backreef deposit, like the other backreef deposits higher in the Permian sequences in the Glass Mountains, Guadalupe Mountains, and elsewhere in west Texas. The writer’s (1932) interpretation that the Hess Limestone in the eastern Glass Mountains is equivalent to ledge— making limestones and interbedded shales in the west- ern Glass Mountains has been verified in modified form by Cooper and Grant (1972, p. 44—52), who interpret the Hess above the Lenox Hills equivalent as correla- tive with their Skinner Ranch Formation in the west- ern part of the mountains, which they divide on the basis of thick limestone units and interbedded shale units into the Decie Ranch, Poplar Tank, and Sullivan Peak Members. I’ERXIIAN ROCKS ABOVE ’I‘IIE IIESS LIMESTONE The northwestern corner of the report area contains a small segment of the bands of outcrop of the higher Permian rocks of the Glass Mountains sequence—the originally mapped as Leonard Formation (Pl) (now the Cathedral Mountain Formation of the Leonardian Series), the Word Formation (Pw), and the Vidrio and Gilliam Limestones (Pv, Pg). The latter three units form the Guadalupian Series. The outcrops of these formations within the report area are small and not distinctive, and they Will 1101 be considered further here. LOWER CRETACEOUS (COMANCHEAN) SERIES A large part of the report area, especially in the northeastern and southeastern parts, is occupied by the Comanchean Series, which lies with prominent an- gular unconformity on the Paleozoic rocks. On the map, the Comanchean Series is divided into the Trin- ity, Fredericksburg, and Washita Groups; more detailed subdivision is not feasible without further field examination. ’I‘RINI'I'Y GROUP The Trinity Group (Kt) crops out mainly south of the latitude of Gap Tank, and consists largely of the Glen Rose Limestone. It also includes the persistent Maxon Sandstone at the top, which serves to divide the Glen Rose from the overlying limestones of the Fredericks- burg Group. GI.EN ROSE LIMESTONE The Glen Rose makes it appearance in the mesas southeast of Gap Tank, where it is about 50 feet thick. It wedges out by overlap to the north, and is missing at the base of the Cretaceous west of the tank. It thickens progressively to the south. A thickness of 312 feet was measured on the west face of Housetop Mountains (see S'l‘RATIGRAPHY 21 section below), and the topographic map suggests that it is 800 feet or so thick on Shely Peaks (Tres Her- manas) at the south edge of the report area. However, Graves (1954, p. 16—19) measured 475 feet in the Hood Spring Quadrangle to the southwest, on the south rim of the Marathon Basin. In the Gap Tank area the Glen Rose consists of buff marls, in part sandy, with inter- bedded ledges of white marly limestone. Farther south, the limestone beds increase in prominence, but inter- bedded marls and sandy marls continue south of the latitude of Housetop Mountains. On Shely Peaks in the south part of the area, air photographs indicate that the Glen Rose is largely limestone, with four or five ledges more prominent than the rest, and in places with an exceptionally prominent cliff-making unit at the base. The following section of the Glen Rose Limestone and overlying Cretaceous beds was measured in 1931 on the west face of Housetop Mountains. Section of Glen Rose Limestone and overlying Cretaceous strata on the west face ofHousetop Mountains. By P. B. King, 1931 Edwards Limestone: (22) Limestone, light gray, massive, in part somewhat cherty, forming a sheer cliff on the face of the mountain ________________________________________ 122 Comanche Peak and Walnut equivalent: (21) Marl, passing into white marly limestone toward the top 50 Maxon Sandstone: (20) Sandstone, medium-grained and sugary, pale brown or buff on fresh surfaces, dark brown on weathered sur- faces. Forms thin to thick beds, many of which are crossbedded at low to steep angles. Some layers are honeycombed. In places forms a sheet cliff, but rock is more or less loosened along joints, and thus breaks out Feet into great angular blocks __________________________ 102 Glen Rose Limestone: (19) Marl, sandy, with some nodular limestone layers ______ 16 (18) Sandstone, calcareous, forming a ledge ______________ 5 (17) Marl, buff and sandy, with thin nodular limestone ___, 8 (16) Sandstone, crossbedded and sugary __________________ 4 (15) Marl, brown and sandy _______________________________ 16 (14) Limestone, massive, gray-brown ____________________ 19 (13) Marl, not well exposed ______________________________ 21 (12) Limestone, gray, in 3-foot to 8-foot ledges ,,,,,,,,,,,, 38 (11) Marl, white and buff, and white thin-bedded nodular limestone ________________________________________ 32 (10) Limestone, massive, forming a single ledge, with thin— ner bedded limestones below and above. Top part is full of oyster shells. Forms second massive ledge in the Glen Rose ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 16 (9) Marl, brown and buff, and marly limestone __________ 37 (8) Limestone, gray and massive, in 3-foot to 4-foot ledges. Forms first main ledge of the Glen Rose ,,,,,,,,,,,, 32 (7) Limestone, white, with some interbedded marl ________ 24 (6) Limestone, white to pale buff, in thick ledges ,,,,,,,, 13 (5) Marl, white and buff ________________________________ 4 (4) Limestone, massive, white ,,,,,,,,,,,,,,,,,,,,,,,,,, 2 (3) Limestone, white, soft, and platy ____________________ 5 (2) Limestone, buff, mottled, nodular, with oyster fragments 7 (1) Marl, nodular, sandy, containing numerous fragments of oysters and some whole shells, probably Exogyra quitmanensis ____________________________________ 13 U nconformity; bed lies on upturned and truncated strata beneath. Tesnus Formation at base of section. The Glen Rose Limestone contains many oysters and rudistids. Near Housetop Mountains an oyster, prob- ably Exogyra quitmanensis, is abundant in the basal layers. Higher up, the foraminifer Orbitolina texana is common at some levels; near Housetop Mountains and Tesnus it forms a zone about 100 feet below the top. MAXON SAN DS'I'ONE The Glen Rose Limestone is separated from the over- lying Fredericksburg Group by the Maxon Sandstone, named for Maxon, a former station on the Southern Pacific Railroad where it leaves the Marathon Basin in the southeastern part of the report area (King, 1930, p. 92); its ledges are prominent on the escarpment east of the railroad at this locality. The Maxon has the same stratigraphic position and habit as the Paluxy Sand of north-central Texas, but a separate name is used be- cause of the wide geographic separation of the two areas. The Maxon is a brown, well-indurated, coarse- to medium-grained, crossbedded sandstone, which forms one or more conspicuous ledges that are cut by vertical joints that cause it to break out into great cubical blocks. In the mesas immediately southeast of Gap Tank it is 90 feet thick, but like the underlying Glen Rose it thins abruptly northwestward, so that it is ab— sent at the base of the Cretaceous west of Gap Tank. Several miles to the east, however, it is traceable northward, past the point of disappearance of the Glen Rose, to merge with the Basement Sands of King (1930, p. 93) of the north part of the report area. South of Gap Tank the Maxon thickens somewhat; 102 feet was measured on Housetop Mountains (see section above), and it may be somewhat thicker farther south. Graves (1954, p. 18) reports 115 to 157 feet of the Maxon on the south rim of the Marathon Basin in the Hood Spring Quadrangle, but here the formation is losing its character and is grading into sandy shale and marl. The Maxon Sandstone was studied for master’s theses at the University of Texas at Austin by Donald A. Butterworth (1970) and Marvin G. Thompson (1977), who have added details of its petrography and sedimentology. They found that the sandstone is well- sorted, rounded, fine- to medium-grained, made up mainly of quartz with very minor amounts of feldspar and heavy minerals, and with a clacite-hematite-clay matrix, the dominant clay being kaolinite. Sediment transport was to the south, and it was deposited in a fluvial-deltaic environment. 22 GEOLOGY 01‘ Till“. l-lx'\S'l‘ERI\" PART ()1: THE MARATHON BASIN. TEXAS The Maxon Sandstone is generally recognizable on air photographs as a prominent dark ledge, which is most evident along the escarpments at the edge of the Marathon Basin, but is less conspicuous on the lower mesa slopes farther east. The top was used as the Trinity-Fredericksburg boundary in constructing the geologic map of the area. The writer has observed no fossils in the Maxon Sandstone, but Graves (1954, p. 21) lists a small as- semblage of pelecypods and gastropods (including Ac- taeonella) in the Hood Spring Quadrangle. Whether the Maxon should be assigned to the Trinity or the Fredericksburg Group is somewhat uncertain, but the general preference has been to place it in the Trinity. BASEMEN'I' SAN US In the north part of the report area a thin basal sand lies on the Permian rocks, and has been termed the “Basement Sands” (King, 1930, p. 93). It corresponds to the "Basal Cretaceous Sandstone” of Adkins (1927, p. 31) in the Fort Stockton area to the north; the same unit was termed the Antlers Sand on the Pecos Sheet of the Geologic Atlas of Texas (Bureau of Economic Geol- ogy, 1976), this name being derived from localities much farther northeast in southern Oklahoma. In the north part of the report area the formation varies from a featheredge to as much as 75 feet. It consists of coarse, brown, crossbedded sandstone much like the Maxon Sandstone, with which it is laterally continuous east of Gap Tank. On the geologic map, it is included with the Trinity Group for convenience, although Ad- kins (1927, p. 33) found Exogyra weatherfordensis near the top in the Fort Stockton area, which is a charac— teristic fossil of the Fredericksburg Group. The Base- ment Sands are probably a transgressive deposit, mainly of Trinity age in the south, but becoming younger farther north. FREDERICKSBL'RG CROL'I’ Within the report area the Fredericksburg Group (Kf) is mainly thick-bedded limestone that was termed Edwards Limestone in the earlier reports (King, 1930, p. 95). At the base, however, is about 50 feet of more shaly or marly beds that may be equivalent to the Walnut Clay and Comanche Peak Limestone of central Texas, and at the top in the north part of the area is a persistent layer of marly clay that is equivalent to the Kiamichi Formation of farther east in Texas. Within the last few decades a different terminology for the Fredericksburg Group has been used for areas south of the Marathon Region, notably in the Big Bend area (Maxwell and others, 1967, p. 35, 36, 40; St. John, 1966). The softer beds below are termed the Telephone Canyon Formation, the thick-bedded medial lime- stones the Del Carmen Limestone, and the softer beds above the Sue Peaks Formation. The applicability of these terms to the present report area is dubious, as the sequence in the south is a thicker, more dominantly carbonate facies. Within the report area the group is 190 to 220 feet thick in the Glass Mountains to the north, and of about the same thickness in the Fort Stockton area still farther north (Adkins, 1927, p. 37), but it thickens southward. Graves (1954, p. 21—26) records about 400 feet on the south rim of the Marathon Basin in the Hood Spring Quadrangle, and the group is apparently of about the same thickness in the southeastern part of the report area. In the Glass Mountains to the north the group includes prominent ledges as thick as 10 feet of light- gray, dense or finely crystalline limestone, containing rudistids and much concretionary brown chert. Be- tween the limestone ledges are softer, more marly strata. The limestones fade out farther north, and in the Fort Stockton area the group consists of marly limestones below, a medial fossiliferous calcareous clay, and a few thin limestone ledges at the top, just below the Kiamichi horizon (Adkins, 1927, p. 37—41). The Kiamichi equivalent at the top of the Freder- icksburg Group is prominent only in the north part of the report area, where it forms a white or yellowish slope between limestone ledges below and above. In this area, it forms a conspicuous light band that can be traced on the air photographs for long distances. The Kiamichi equivalent is not as evident farther south on the photographs, but Graves (1954, p. 25—26) recog- nized it in the Hood Spring Quadrangle as a poorly resistant layer about 50 feet thick, separating lime- stone ledges below and above. The Kiamichi equiva- lent is generally quite fossiliferous, and contains among other forms the characteristic oyster Gryphea navza. WASH l'l‘A (LROL'I’ The Washita Group (Kw) is scantily represented in most of the report area, except in the extreme south- eastern corner, where it covers most of the surface; elsewhere it is preserved only as remnants on the tops of the ridges of the older Cretaceous strata. The part of the group preserved in the report area was termed the Georgetown Limestone in previous reports (King, 1930, p. 96—97). In the Big Bend region its equivalent is the Santa Elena Limestone (Maxwell and others, 1967, p. 47), but this is a much thicker more massive phase, and the applicability of this name to the report area is questionable. Higher parts of the Washita Group, the Del Rio Clay and Buda Limestone, are not preserved in the report area. A rather complete section of the Georgetown about 200 feet thick occurs in the north part of the report S'I‘RA’I‘IGRAI’HY area, east of the Marathon-Fort Stockton highway. Here, it consists mainly of marly limestone, but it con- tains two prominent ledges of rudistid limestone near the middle and top, which correspond to the Middle and Upper Caprocks of the Fort Stockton district, that Ad- kins (1927, p. 46—48) correlated with the Denton and Main Street Formations of north-central Texas. Farther south, the marly intervals in the limestone disappear. In this region the position of the Washita beds was located in places during the field surveys, and seems to correspond on the air photographs with prom- inent light-colored beds on the tops of the ridges. These light-colored beds were assumed to be Washita, in the absense of additional ground inspection, and were used in marking the Washita Group on the geologic map. Graves (1954, p. 27—28) reports 380 feet of Washita beds on the south rim of the Marathon Basin in the Hood Spring Quadrangle, again with the top eroded and the Del Rio and Buda missing at the top. They are probably as thick or thicker in the southeastern part of the report area. In this area, various ledge-making units are evident on the photographs that are higher than the layer selected as the base of the Washita in mapping, but no data are available as to their charac- ter; much yet remains to be learned about the Creta- ceous stratigraphy in this part of the area that would only be possible from additional ground surveys. CONDITIONS OI“ DEPOSITION OI“ LOWER (IRE'I‘ACEOL'S ROCKS A long pause in deposition intervened between the formation of the Permian rocks and those of the Lower Cretaceous. During this interval, the report area and all the surrounding region was subjected to erosion, and was reduced to a nearly level plain, which has been called the Wichita paleoplain. The Cretaceous deposits overlapped this paleoplain from south to north, and formed in a shallow-water marine environment rich in lime. As a result of this northward overlap, the Trinity deposits only extend into the northern part of the report area, where they wedged out against a low scarp on the paleoplain produced by the Permian carbonate rocks on the site of the present Glass Mountains; farther north, Freder- icksburg beds form the basal deposits. The basal depos- its in the north are the Basement Sands, formed of sands eroded from regions farther north, which prob— ably became slightly younger northward. Farther south, beyond the edge of the wedge of Trinity deposits, a sheet of sands of about the same age, the Maxon Sandstone, extends across the reprt area over the older Cretaceous deposits. The northward overlap is also reflected by a change 23 in facies—from thick, massive limestones in the south, as in the Big Bend area, through a mixed assemblage in the report area of interbedded limestones and more marly and shaly strata, into a thinner sequence in the north, as in the Fort Stockton area, of dominant marl and clay, with only rare, persistent limestone inter- beds. This change in facias is reflected in the faunas. Among the pelecypods, for example, the rudistids, a sessile, reef-building group, are common in the domi- nant limestones in the south, whereas oysters such as Gryphea abound in the dominant marls and clays in the north. Even in the north, however, rudistids made occasional incursions, and built the prominent "cap- rocks” of the Washita Group in that area. TERTIARY IGNEOUS ROCKS A few bodies of intrusive igneous rocks (Ti) occur in the southwest part of the report area, and were mapped by the writer during his survey of the Marathon Quad- rangle in 1930 (King, 1937, p. 117—118). The largest bodies are on Twin Peaks, where two thick dikes a mile in length cut the Tesnus Formation. The dikes dip 70° southeast, whereas the enclosing strata dip at a lower angle. According to C. S. Ross (King, 1937), the rock is a porphyritic quartz diorite, with very alkalic feldspar and ferromagnesian minerals. A mile south of Twin Peaks, a series of narrower dikes follows the trace of the Hells Half Acre fault for nearly 2 miles. Megascop- ically, these rocks resemble those on Twin Peaks. The intrusive rocks in this area are probably of Tertiary age, like the others in surrounding parts of the Marathon Region. QUATERNARY DEPOSITS More than a quarter of the report area is covered by a thin blanket of gravel deposits of Quaternary age; this cover is most extensive in the north part of the area. It is also more extensive in the eastern part of the area than had been indicated on previously published maps, as all the valleys draining eastward and northeast- ward from the Marathon Basin through the Cretaceous mesas are floored by gravel deposits a mile or so wide. The Quaternary gravel deposits are of Pleistocene and Holocene ages, the younger being the most extensive. Possibly the oldest Quaternary deposit forms a belt about 3 miles long at an altitude of 3,400 feet on top of the divide south of Alamo Creek in the southeast part of the report area (QgO), in an outcrop area of the Washita Group. Air photographs indicate that its gravels break off in dissected scarps along its edges, and that they have no evident relation to modern drainage or topography. The gravels must have been deposited when drainage and topography were very different from those of today. It is probably equivalent to the upland gravel deposits described previously 24 (King, 1937, p. 10) from localities east of the Marathon Region. The deposit has not been examined on the ground, and it would probably repay examination. Another, more extensive gravel deposit (also mapped as ng), perhaps nearly as old, forms a plain several square miles in extent, which slopes northwestward from an altitude of more than 3,900 feet to 3,800 feet near Copeland Trap, where it meets the younger Quaternary deposits along the Southern Pacific Rail- road west of Tesnus. Its broad, smooth surface conceals the steeply dipping Carboniferous rocks and like the first deposit mentioned, its surface breaks off in erosion scarps along its edges. The other Quaternary deposits are considerably younger. In the west-central part of the area, and farther west in the Marathon Basin, in areas drained southward by San Francisco Creek and its tributaries, two levels are represented—older deposits (Qg) that stand 100 feet or more above modern drainage and are preserved in large and small remnants on the low hilltops of tilted Carboniferous rocks, and alluvial de- posits (Qa) along the present streams. These distinc— tions fade out in the north part of the report area, in which drainage flows eastward and northeastward, and has not been subjected to renewed dissection. Here, broad alluvial plains (mapped as Qg) extend over many square miles, from W B Flats between Gap Tank and the Dimple Hills, eastward to the edge of the report area. These plains conceal large parts of the deformed Carboniferous, although ridges of Tesnus, Dimple, and Haymond Formations project here and there, and fur— nish clues as to the general bedrock pattern. Interesting features of the east-central part of the report area are the eastward-draining “dry valleys,” such as those followed by US. Highway 90 and the Southern Pacific Railroad in their courses eastward from the Marathon Basin. These appear to have been beheaded by drainage of San Francisco and Maxon Creeks rather late in Quaternary time. This appear- ance is particularly striking in the southern valley fol- lowed by the Southern Pacific Railroad. Where this valley leaves the Marathon Basin it is drained by Maxon Creek, but about 3 miles to the east, Maxon Creek abruptly leaves the valley, and drains south- eastward through a canyon cut in the Cretaceous lime- stones, although a broad valley continues east- northeastward. For about 4 miles east of the Maxon Creek turnoff, the valley is drained by westward- flowing Cox Creek with east-directed barbed trib- utaries, but beyond this the valley slopes eastward with no evident drainage lines, past Rosenfeld siding. The flow of Cox Creek has clearly been reversed from east to west into Maxon Creek. Along the Cretaceous escarpments facing southward GEOLOGY OF THE EAS’I‘ERN PART OF THE MARATHON BASIN, TEXAS toward W B Flats in the north part of the report area are many patches of landslide debris (Q1) that partly obscure the Carboniferous rocks along the bases of the escarpments. Some of the masses consist of large cohe- rent blocks of Cretaceous rocks which at first sight appear to be in place. The landslides were formed by undermining of the Cretaceous strata by the weaker Carboniferous rocks beneath. The time of undercutting and landsliding was probably considerably before the present. Similar landslide masses are rather common farther west, along the south-facing escarpment of the Glass Mountains. TECTONICS The rocks of the report area are partitioned into sev- eral groups, each separated by angular unconformities and structural discontinuities, and each having its own distinctive set of structures. The oldest group of rocks is that of the pre—Permian Paleozoic age exposed in the Marathon Basin, and their structures exhibit the most complex deformation. Moreover, deep drilling in the basin discloses that these rocks lie on a major discon- tinuity, or great overthrust fault, beneath which are a different set of pre—Permian rocks and structures. The next group of rocks is that of Permian age in the Glass Mountains to the north, which are tilted northward at low angles, rather than folded. Finally, above both groups of Paleozoic rocks, are those of Cretaceous age, which are much less deformed, but which slope gently eastward and northeastward off the flanks of the Marathon dome. SURFACE STRUCTURE OF THE PRE-PERMIAN ROCKS The pre-Permian rocks of the report area are a small part of the Marathon segment of the Ouachita orogenic belt that is exposed in the Marathon Basin, which con— sists of strongly deformed rocks of Cambrian to Pennsylvanian age. Exposed parts of the orogenic belt extend for about 30 miles west of the report area, but their extensions eastward and westward from the basin are concealed by the Cretaceous cover. Clearly, the belt must extend for long distances beyond beneath this cover, and this is confirmed by well penetrations, especially toward the east (Flawn and others, 1961). Within the report area, the surface rocks of the deformed belt are mostly of Carboniferous age; the pre—Carboniferous components emerge only up the plunge of the folds farther west (fig. 2). Except in the southern part, the Carboniferous rocks are deformed into broad folds, broken on their flanks by thrust faults, that trend northeastward to eastward. In the extreme south part of the area, folding and thrust faulting are more complex. The structural pattern of the pre-Permian rocks can be reconstructed from their outcrops, even where they are partly concealed by the 'I‘EUI‘ONICS 25 cover of Cretaceous strata and Quaternary deposits (fig. 16). South of W B Flats the next conspicuous feature in the Carboniferous rocks is the Dimple Hills, which are a compact, semicircular mass of Dimple Limestone of synclinal structure. The limestones dip rather regu- larly at angles of 10° to 45° toward the center of the hills from all sides, and they are apparently sur- rounded on all sides by outcrops of Tesnus Formation. The syncline of Dimple in the hills is, however, a wrinkle on the crest of an anticlinorium, whose extent is well exposed southwestward, where it is bordered on both the northwestern and southeastern sides by belts of Dimple Limestone, but whose extension eastward is mostly concealed by the Quaternary deposits of W B Flats. Southwest of the Dimple Hills, the northwestern flank of the anticlinorium is broken by a fault, termed the Frog Creek thrust, which dips 20° east at a locality where it is well exposed. It carries Dimple Limestone on the border of the anticlinorium over Haymond For- mation to the west. West of the area of Haymond For- mation, and west of Frog Creek, is a prominent hook- shaped ridge of Dimple Limestone, which is folded with a northeastward plunge. Air photographs show that the ledges of the Tesnus Formation enclosed within the hook have a much more complex pattern than the sim- ple hook in the overlying Dimple, suggesting consider- able disharmonic folding. The southward extension of the structures of this area is concealed by the broad expanse of Quaternary deposits of W B Flats, beyond which only older Car- boniferous rocks come to the surface. The Gaptank and Haymond Formations are not preserved here, yet in the last exposures on the north the strata dip toward the south, so that there must be a reversal of the struc- ture beneath the flat. An eastward extension of the structures south of the flat occurs on its north side in an area 7 miles southeast of Gap Tank, where the Dimple Limestone dips steeply northward beneath the Haymond Formation. Between these north-facing strata and the south-facing strata near Clark Butte is a gap of about a mile concealed by Quaternary deposits. It does not seem possible to reconcile the structures on the two sides of the gap by any system of folding, so there must be faulting between of undetermined character. The reconstruction proposed by Flores (1972, p. 3417) is much too simple. The northernmost structures of the system are those near and south of Gap Tank, where the Gaptank For- mation and the underlying Haymond Formation are folded into a broad, east-plunging anticline, steeper on the south flank than the north, where the upper Gap- tank strata pass beneath the Permian rocks of the Glass Mountains with dips of 15° or less (fig. 13). Another fold is exposed along the edges of the Cretaceous mesas 3 to 6 miles southeast of Gap Tank, as far as Clark Butte. Here, the rocks are all Haymond Formation, whose boulder-bed layer in the upper part is exposed discontinuously along the edge of W B Flats for a distance of 4 miles and dips 15° to 80° to the south. The dip reverses in the underlying sandstones of the formation to the north, defining an anticline whose north flank dips gently toward the north; within the limits of exposure, the boulder-bed layer does not reap- pear on this flank. At the western end of the outcrop of the boulder-bed, its dip also reverses to the northeast, indicating that the anticline plunges westward be- neath the nearest exposures of Gaptank Formation. The western extension of this anticline must lie be- neath the Quaternary deposits of W B Flats, south of the anticline of the Gap Tank area. Southeast of this anticlinorium, between Gap Tank and the Dimple Hills and a long westward extension of the Cretaceous mesas 4 miles to the south, Carbonifer- ous rocks emerge from the Quaternary deposits only in small discontinuous areas, but enough are exposed to define broadly the structural pattern (fig. 16). The Dimple Limestone projects here and there in occasional ridges, which outline a synclinal area of Haymond Formation south of the hills (including the area shown in fig. 9) and an anticlinal area of Tesnus beyond it. The Dimple Limestone is exposed in a few places south of this anticlinal area of Tesnus, the easternmost being on a ridge just northeast of the Skevington (formerly Puring‘ton) Ranch at the eastern edge of the report area—the easternmost outcrop of Paleozoic rocks in the Marathon Basin. The structures in the Carboniferous rocks are better revealed in exposures south of the long westward ex- tension of Cretaceous mesas that ends in Spencer Mountain? The poorly exposed structures north of the mesas can be correlated across the Cretaceous cover with the structures to the south (fig. 16). To the south, the most conspicuous features are the two synclinal, northeast-plunging belts east and west of Haymond Station, bordered by long ridges of Dimple Limestone that end southwestward up the plunge in synclinal hooks, and which preserve Haymond Forma- tion along their axes. The southeastern syncline is the larger and deeper, and preserves nearly 4,000 feet of Haymond Formation west of Housetop Mountains, including the boulder-beds in the upper part. Between each syncline, and to the northwest, are narrower and ‘Termed Cedar Mountain on older maps. The present term is indicated on the Housetop Mountains 1:24.000 topographic sheet. 26 GEOLOGY OF THE EASTERN PART OF THE MARATHON BASIN, TEXAS 30°30" 105.. ., 30°19} Mounlains / Housetop Continentaerllison 0 TD 11,870 D—"— O FIGURE 16. 30 4|0 5|0 KlLOMETERS l 20 30 MILES EXPLANATION Cretaceous rocks Permian rocks Gaptank Formation (Carboniferous) Outcrop areas shown by stipple Haymond Formation (Carboniferous) Dimple Limestone (Carboniferous) Outcrop areas shown by ruling Tesnus Formation Do—a' Devonian and Ordovician rocks Contact Dotted where concealed Normal fault H— ......... Thrust fault Includes both high- and low—angle thrusts; dotted where concealed Sawteeth on upper plate ++ Anticlinal and synclinal axes Approximately located 0 Deep drill holes With name and total depth, in feet Map of report area showing inferred structural pattern of the Paleozoic rocks. 'i‘Ec'rONIcs 27 steeper anticlines of Tesnus Formation, with the lower shale unit in their cores. Each syncline is faulted on its southeastern flank, so that the Dimple of each syncli- nal hook is terminated northeastward, beyond which Tesnus is in fault contact with Haymond. The two faults have been termed the Haymond and Arden Draw6 thrust faults (King, 1930, p. 106). A few poor exposures of the faults show dips of 60° to 80° southeast. They evidently formed by simple breaking of the flanks of the folds. Southeast of the two synclines just described, toward Tesnus Station, is a broad area of Tesnus Formation. The trends of the Tesnus ledges, as indicated on the air photographs, show that the same broad folding con- tinues in this direction. The ledges outline two ad- ditional northeast—plunging synclines that are struc- turally higher than those just described, so that only Tesnus is preserved with its lower shale unit on the flanks. Down the plunge to the northeast in each of these two synclines, small areas of Dimple Limestone are preserved, northwest and southwest of Tesnus Sta- tion, before the whole deformed complex disappears beneath the Cretaceous. South of this area of open folds, in the southeast part of the report area, a change in structure of the Car- boniferous rocks is clearly revealed on the air photo- graphs. The trends of the ledges change from open bends around the folds into a much more consistent east-northeast trend. During the writer’s mapping of the southeastern corner of the Marathon Quadrangle, west of the 103° meridian, in 1930, he recognized at this change in structure a major, probably low-angle, thrust fault termed the Hells Half Acre overthrust (King, 1937, p. 130). West of San Francisco Creek, the trace of this fault is followed by narrow slivers of Caballos Novaculite and Maravillas Chert, and by dikes of Tertiary porphyry. East of San Francisco Creek are slivers and broader wedges of Dimple Lime- stone. Lack of time and of adequate base maps prevented the tracing of this fault east of the 103° meridian. The air photographs indicate that the wedges of Dimple Limestone coalesce in this direction into a continuous east-northeast-striking belt that ex- tends eastward until it passes beneath the Cretaceous south of Tesnus Station. Where the Hells Half Acre overthrust extends east of the 103° meridian is conjectural. There must be a fault north of the belt of Dimple Limestone, because it is quite discordant with the openly folded Tesnus to the north, but this may be a subsidiary feature. Toward the east end of the belt of Dimple, Haymond Formation is “Named for the valley draining southwestward into San Francisco Creek southeast of the Haymond Mountains. This was marked as "Arden Draw" on earlier editions of the Marathon 1:62,500 topographic sheet, but on later editions the name is changed to "China Draw.” preserved south of it; Haymond was sketched here dur- ing the writer’s brief reconnaissance in 1930, and McBride (1964a, fig. 7, p. 39) has recorded sedimen- tological observations on it. Complications are intro- duced, however, because the air photographs reveal another belt of Dimple Limestone 2 miles south of the first one. Does this second belt dip to the south also, in another thrust slice, or does it form the southeastern flank of the area of Haymond, which would have a synclinal structure? Very tentatively, the second al— ternative is accepted on the geologic map, and the Hells Half Acre fault is projected south of it. It is as- sumed that the Hells Half Acre fault is such a funda- mental feature that it would hardly preserve on its upper plate any areas of Haymond Formation, or any extensive areas of Dimple Limestone. The area south of the Hells Half Acre fault, in the south part of the report area, is primarily a domain of the Tesnus Formation, which is strongly deformed, and probably thicker than elsewhere in the Marathon Basin. The formation contains two or more layers of white quartzite, that project in sharp ridges, such as Devils Backbone, and are plainly visible on the air photographs. Sharp folds, broken by thrust faults, were mapped on Devils Backbone; one of these, termed the Devils Backbone thrust, preserves small wedges of Dimple Limestone on its downthrown side, but its ex- tent farther east and west has not been traced. Some folds in the white quartzite layers are also visible farther east on the air photographs, but on the whole the ledges strike nearly east and west. The general structure is enigmatic, and could only be worked out by additional ground surveys. During the writer’s fieldwork in 1930 (1937, p. 130) he was impressed with the effects of much greater deformation of the rocks in this area than farther north. There are numerous shear zones and veinlets of quartz and calcite in the massive sandstone beds, and the shaly layers show the effects of incipient metamorphism and the develop- ment of secondary mica. SUBSURFACE STRUCTURE OF THE PRE-PERMIAN ROCKS The structures just described only extend to depths of 2 miles or so, at least in the north half of the report area, as indicated by deep drilling by oil companies which has been done in the last few decades; at greater depths are quite different structures and formations. Most wells drilled earlier in the Marathon Basin were only carried to depths of 3,000 feet or less, and pene- trated the usual Marathon Basin formations and struc— tures (King, 1930, p. 129). The later wells, by contrast, have been extended to depths as great as 20,000 feet. All are Wildcat tests, put down in hopes of obtaining new petroleum deposits. The early wells were drilled to test the Marathon Basin formations; the later wells 28 were drilled to test the possibilities of the deeper-lying formations. Small showings of oil or gas have been re— ported in some of the wells, but none have encountered any commercial production. The locations of the deep drill holes are shown in the accompanying figure 17, and the drill records are illus- trated graphically in figure 18. They are also sum- marized verbally in the section “Wall Data.” The deep drilling discloses that the familiar surface formations of the Marathon Basin lie on a major sur- face of discontinuity, below which are formations characteristic of the cratonic area north of the orogenic belt—Pennsylvanian above, with older Paleozoic beneath, including the Middle Ordovician Simpson Group and the Lower Ordovocian Ellenburger Lime- stone. This discontinuity emerges in a small area in the northwestern part of the Marathon Basin, where it is a nearly fiat-lying thrust fault that the writer named the Dugout Creek overthrust (King, 1930, p. 108—110). Along its outcrop in the northwestern part of the Marathon Basin, the Dugout Creek thrust is seen to truncate the bases of all the folds in the Marathon Basin rocks, so that it is a shear that has cut through structures that had previously been deformed. In this area, it is also seen to be truncated above by the uncon- formity at the base of the upper Wolfcampian Lenox Hills Formation, yet Wolfcampian fusulinids have been reported at several localities in the folded complex beneath it (which is mainly Upper Pennsyl- vanian Gaptank equivalent). These lower Wolfcam- pian fusulinids indicate that the Neal Ranch equiva- lent was involved in the thrusting; hence, the time of thrusting was in the middle of the Wolfcampian Epoch. Extending these data eastward, the Gaptank and Neal Ranch Formations of the eastern Glass Mountains must be allochthonous to the thrusting, even though they are synorogenic to postorogenic to the Des Moinesian and Missourian orogeny in that area. The angular unconformity at the base of the Hess Lime- stone, although seemingly modest in this area, must mark the time of emplacement of the thrust sheet. The eastward extension of the leading edge of the Dugout Creek thrust is concealed by the unconforma- bly overlying Permian rocks of the Glass Mountains, but its existence farther east (as in the north part of the report area) is proved by the subsurface penetration of the thrust in drill holes in the northeastern part of the Marathon Basin. Here, the buried trace of its leading edge must lie beneath the Permian rocks of the eastern Glass Mountains north of Gap Tank. For the most part, the drill records indicate that the thrust surface slopes fairly regularly southeastward from its leading edge, but there are some exceptions in the western part of the Marathon Basin. Two wells GEOLOGY OF THE EASTERN PART OF THE MARATHON BASIN, TEXAS drilled near Marathon, the Mobil-Adams and the Gulf-Combs, although located only 3 miles apart, show a difference in depth of the thrust of more than 4,000 feet. Also the record of the Turner, Combs well 16 miles south of Marathon, if correctly interpreted, indicates the thrust at a depth of only 1,600 feet, whereas it lies much deeper farther north. The reasons for these dis— crepancies are at present unknown, due to incomplete- ness of data. Either the surface of the thrust was origi— nally irregular in these areas, or it has been warped or even folded. The southeastward extent of the thrust beneath the Marathon Basin rocks is unknown. It is reported that seismic profiles extend it far southeastward from the last well penetrations, so it may underlie all the deformed surface formations in the Marathon Basin. STRUCTURE OF THE PERMIAN ROCKS The Permian rocks (Hess Limestone and younger) all occur in the Glass Mountains, whose eastern end ex- tends into the northwestern part of the report area. Unlike the older Paleozoic rocks, the Permian rocks are little deformed, and dip northwestward or north- ward at angles of 15° or less. Their inclination is, however, steeper than that of the Cretaceous rocks which overlie them unconformably. In the western and central Glass Mountains the Permian rocks and the overlying Cretaceous are broken by a system of nearly vertical northwest-trending normal faults, with ' displacements as great as several hundred feet, and variable directions of downthrow, which were imposed on the rocks after the other structures in the Glass Mountains were created. These faults decrease in numbers eastward, and very few of them appear in the eastern part of the Glass Mountains, including the re— port area. Within the report area the Permian strata, mainly the Hess Limestone, have the same gentle northwest- ward dip as the Permian rocks farther west in the Glass Mountains, and have a moderate discordance with the overlying Cretaceous. Dips recorded in the Hess are all less than 12°, and most are 5° or less. In the easternmost exposures of the Hess, about 5 miles east of Gap Tank, the recorded observations include some dips to the northeast, -and a few to the south, which indicate a minor warping of the Permian rocks, whose extent cannot be traced. STRUCTURE OF THE CRETACEOUS ROCKS Within the map area, the Cretaceous rocks slope northeast, east, and southeast off the eastern side of the Marathon dome. In the north part of the area, the slope is less than 100 feet to the mile and is barely 'i‘EC'roxics 29 new .1030 EXPLANATION Pre-Permian Paleozoic Dotted lines outline geologic units shown on figure 2 Permian Cretaceous Trace of Dugout Creek thrust fault _, g9 _, , : : ‘ ‘ Dotted where can- ' .' t :5 ' 5' ; cealed by younger 680 .5 -' -« deposits (1369);:- . 4 o 680 O |:IMarathon . (+369) " Deep wells Depth to Dugout Creek fault shown in feet. Approximate elevation shown within parentheses in feet 0 5 10 15 20 25 30 35 KILUMETEHS IL I L I | I | | 0 | l l 5 10 15 20 MILES FIGURE 17.—Map of the Marathon Region showing locations of deep drill holes in the Marathon Basin and Glass Mountains and the depth of penetration t0 the great thrust fault (Dugout Creek overthrust). Report area outlined by dashed line Wells are as follows: 1, Gulf-Lippit; 2, Mobil-Sibley; 3, Slick-Urschell-Decie; 4, Mobil-Adams; 5, Gulf-Combs; 6, Turner-Combs; 7, Forrest-Moore; 8, Continental-Allison; 9, Exxon-Law; 10, Mobil-Cox. perceptible to the eye. In parts of the extreme southern tained from their positions on the contours of the part of the area the slope steepens to more than 800 topographic maps. Structure contours on two horizons feet to the mile. are shown: on the top of the Trinity Group, and on the The structure of the Cretaceous rocks is illustrated base of the Washita Group; as the intervening Freder- by the accompanying map (fig. 19). Elevations of con- icksburg Group thickens southward, it was not feasible tacts from which the contours were made were ob- to reduce all the contours toacommon datum. Because 30 GEOLOGY OF THE EASTERN PART OF THE MARATHON BASIN, TEXAS Mobil No. 1 Sibley METERS FEET 2 8 0——0 Vidrio and Gilliam Word Leonardian 2000 — Wolfcam pian 3000110,000 Woodford and Silurian Montoya — 15,000 Simpson 5000— Ellenburger TD 19,500 6000 — —20,000 Gulf No. 1 Lippit 1 3 Permian dolomite Syenite intrusive No record Mississippian . Devonian and Silurian Montoya Simpson Ellenburger TD 9360 TD 9471 Continental No. 1 Allison Cretaceous Hess Gaptank Haymond Dimple Tesnus Caballos ‘ MINOR THRUST Tesnus and Caballos Haymond Dimple Tesnus and Caballos DUGOUT CREEK THRUST Wolfcampian Slick—Urschell No. 1-47 Decie _ Caballos 4 DUGOUT CREEK THRUST MINOR THRUST Wolfcampian and Pennsylvanian (7) Strawn Woodford Devonian and Silurian Montoya Simpson Ellenburger Forrest No. 1 Moore 7 . . Haymond Dimple Tesnus ‘ MINOR THRUST Dimple Tesnus TD 9865 Barnett to Montoya Simpson TD 11,870 Mobil No. 1 Adams Marathon DUGOUT CREEK THRUST Wolfcampian and Pennsylvanian (7) Woodford Devonian and Silurian Montoya Simpson . Ellenburger TD 10,604 FIGURE 18.~—Graphic representation of records of deep drill holes in the Marathon Region. Upper sections in the eastern part of the region; lower section in the western part. of the gross nature of the source data, it was not possi— ble to reproduce minor wrinkles in the structure; hence, the contours are generalized to show only the regional structure. The contours show a broad, easterly-plunging arch in the north part of the area, with northeastward dips in the north in the Glass Mountains, and southeast- ward dips in the south toward US. Highway 90. This arch is accentuated in an anomalously high area 6 miles southeast of the Dimple Hills, where the Maxon Sandstone at the top of the Trinity Group stands higher on the escarpment than to the east or west; it is Mobil No. 1 Cox No. 1 Law 'I‘ECI‘ONICS 31 Exxon 10 Quaternary 9 Haymond V Dimple Tesnus MINOR THRUST Dimple Tesnus '5 Tesn us :2: Caballos Caballos and Maravillas MINOR THRUST Tesnus Caballos and Maravillas DUGOUT CREEK THRUST Maravillas Woods Hollow Fort Pefia Wolfcampian Woodford to Montoya Alsate Marathon EXPLANATION Simpson H Ellenburger ‘ DUGOUT CREEK THRUST TD 13,941 ’ Wolfcamplan Older Paleozoic of Gaptank geosynclinal sequence ‘ Atokan : Woodford ‘ Fusselman ~ - ‘ Montoya Older Paleozoic of . . cratonic sequence ' Simpson TD 9865 Total depth in feet . ‘ Ellenburger TD 20, 688 Gulf T rner N0. 1 Combs No. 1uCombs 5 .‘ ' ' Woods Hollow ' : Fort Pena . Dagger Flat (Cambrian) DUGOUT CREEK THRUST Wolfcampian and Pennsylvanian TD 9500 DUGOUT CREEK THRUST l?) Shale and Iimstone Wolfcampian (7) and Pennsylvanian (7) Shale and sandstone TD15,480 FIGURE 18.—Continued. provided for on the contour map by a closed 4,600-foot In the southeast corner of the report area, south of contour. the Southern Pacific Railroad, is a southeast-plunging GEOLOGY OF THE EASTERN PART OF THE MARATHON BASIN, TEXAS 104°45' 30°30 EXPLANATION Cretaceous rocks (areas of outcrop) -—4300—-— Contours on base of Washita Group —-4900—- Contours on top of Trinity Group Contour interval 1 00 feet m o 6‘ o v" a 00 Housetop 0‘70 Mountains 5,00 Tres Hermanas 30° | 0 5 10 KILOMETERS U 5 MILES FIGURE 19.-—Map of report area showing outcrops of the Cretaceous rocks and structure contours on two horizons in the Cretaceous. Tl‘ICI‘ON [(1 HISTORY Ol trough, expressed on the geologic map by a nearly un- broken expanse of Washita Group. West of this, in the direction of Shely Peaks (Tres Hermanas), is a northeast-dipping homocline, with the steepest tilting of the Cretaceous rocks in the map area (more than 800 feet per mile); it is a small segment of the northeastern flank of a southeast-plunging anticline which is prom- inent near the Jones Ranch, in the Dove Mountain Quadrangle to the south. In the southeastern corner of the report area the Washita beds and the underlying Cretaceous rocks are traversed by prominent, closely spaced, northwest- trending linear features. Some, perhaps many of these are faults of moderate displacement, and offsets of the formation contacts have been detected on some of them on the air photographs. These linears are at the nor— thwestern end of a system of fractures and faults that are more prominent southeast of the report area. Two or three of them cross the Rio Grande in this direction, with west-northwest trend and scarps that face southwest. What is the relation of the Cretaceous structure to the salients and recesses on the eastern side of the Marathon Basin—to the broad flats exposing Car- boniferous rocks, partly covered by Quaternary gravels that project eastward, and the intervening areas of westward-projecting Cretaceous mesas? The most striking salient is that in the north, along W B Flats and eastward into Big Canyon, which extends entirely across the map area. A lesser salient occurs near Tes- nus, between the west-projecting Cretaceous mesas of Housetop Mountains and Shely Peaks, which is drained in part by Maxon Creek; this extend about halfway across the map area. It can be assumed that the original consequent drainage off the eastern side of the Marathon dome consisted of streams that followed the Cretaceous structure; these streams would have taken their courses in the eastward-plunging downwarps, leaving the upwarps on the interfluves. The relation of drain- age to structure cannot be verified in detail, because most of the Cretaceous rocks in the salients have been eroded, so that contour control is lacking. It is clear, however, that the drainage pattern is not related to the Cretaceous structure in the manner outlined. The great salient in the north part of the report area, east- ward from W B Flats, broadly follows the crest of the eastward-plunging arch. The salient to the south, near Tesnus, has no clear relation to the Cretaceous struc- ture, so far as data are available. Clearly, therefore, much erosional adjustment has occurred since the time when the consequent drainage was first established on the Cretaceous surface. : THE MARATHON REGION 33 TECTONIC HISTORY OF THE MARATHON REGION The rocks and structures within the report area have been described. It is now worthwhile to summarize the tectonic history of these rocks and structures. The writer’s interpretations of this history have been set forth at length in various previous publications (King, in Flawn and others, 1961, p. 176—190; King, 1977, 1978) and will be summarized here, based partly on data from within the report area, but also including that from a larger region. The pre-Permian rocks of the Marathon Region ac- cumulated in a segment of the Ouachita geosyncline, which lay on the southern border of the North Ameri- can continent, extending from east of the present Ouachita Mountains of Oklahoma and Arkansas, southwestward to western Texas (including the Marathon Region), and possibly beyond into Mexico. The rocks of the geosyncline and the orogenic belt which formed from it are only exposed for 280 miles of this distance, in the large segment in the Ouachita Mountains, and in smaller segments in the Marathon Region and elsewhere in west Texas (fig. 20). Many data on the intervening segments are afforded by drill records. In all these areas, however, only the marginal parts of the geosynclinal rocks and their structures are revealed; the inner parts are beyond the reach of the drill and are deeply covered by younger sediments. In all the segments, the rocks of the Ouachita geo- syncline are remarkably alike, and contrast strongly with those of the cratonic area to the north; they also differ in many particulars with the character and tec- tonic history of those in the Appalachian orogenic belt to the east and northeast. In the Marathon Region and the Ouachita Mountains, the Ouachita rocks are characterized by a relatively thin sequence of lower Paleozoic leptogeosynclinal or starved basin deposits (Cambrian through Devonian into Early Mississippian), followed by a vastly thicker flysch se- quence of Carboniferous age (Late Mississippian, Morrowan, and Atokan). During early Paleozoic time, the shelf break at the margin of the continental carbonate platform lay along the northwestern edge of the Ouachita geosyncline and orogenic belt, rather than within it, as in the Appala- chian orogenic belt. Hence, the lower Paleozoic rocks were mainly shales and other fine-grained clastic depo- sits, with significant units of siliceous sediments (such as the Maravillas Chert and Caballos Novaculite of the report area and westward). Within the Ordovician of the Marathon Region (exposed west of the report area) there are many layers of bouldery debris of carbonate 34 GEOLOGY OF THE EASTERN PART OF THE MARATHON BASIN, TEXAS OZQF'SPPIWR Gulf of Mexico ('1 film 2(|]0 3(110 4E|JO 51130 KILOMETERS | l | l 0 100 200 300 MILES EXPLANATION Lower Paleozoic rocks Upper Paleozoic rocks Paleozoic rocks of Mesozmc rocks Cenozouc rocks Includes small areas Ouachita orogenic belt of Precambrian rocks FIGURE 20.—Map of part of south—central United States, showing location of the Marathon Region and Ouachita Mountains. Report area is outlined rocks derived from the adjacent shelf, which slumped stone and shale, laid down in a deeply subsiding area or slid into the deeper waters of the geosyncline. by turbid flows from adjacent lands, mainly southeast The succeeding Carboniferous sequence (exposed in of the present outcrops. They accumulated on sub- the report area and farther west in the Marathon marine deep-sea fans (as in parts of the Tesnus), or on Basin, is a vastly thicker flysch deposit, mainly sand- basin plains beyond (as in parts of the Haymond). The WELL'DATA 35 northwestern border of the flysch trough lay not far northwest of the present exposures, as shown by the abrupt thinning of the Tesnus Formation in this direc- tion (as in the northwestern part of the Marathon Basin), and by the shelf facies of the Dimple Limestone (along the northern edge of the basin). Late in the flysch cycle, deposition of the mainly fine-grained flysch sediments was punctuated by the deposition of boulder-beds, or wildflysch, in the Haymond Formation and comparable somewhat older deposits in the Ouachita Mountains. Their large clasts were derived in part from older geosynclinal rocks and other rocks farther southeast, and in part from the shelf to the northwest. The geosynclinal rocks were deformed during an orogeny in Des Moinesian and Missourian time, when roundstone conglomerates derived from the deformed rocks of the fold complex were spread along its north- western margin to form layers in the lower part of the Gaptank Formation. In contrast to the deep-water flysch deposits of the earlier Carboniferous, the Gap- tank is a much thinner, shallower-water deposit. The Gaptank and the succeeding early Wolfcampian Neal Ranch Formation are synorogenic or postorogenic to the Des Moinesian and Missourian orogeny, and were probably deposited only along the northern mar- gin of the foldbelt. They are succeeded with angular unconformity by the later Wolfcampian Hess Lime- stone and by later Permian marine deposits that ac- cumulated along the southern margin of the West Texas Permian basin. Before late Wolfcampian time, however, the Gaptank and Neal Ranch, as well as the earlier Paleozoic formations, were subjected to a new orogenic pulse, in Virgilian and early Wolfcampian time. During this pulse, the already deformed geosyn- clinal rocks were transported for many miles north- westward over their foreland along a frontal or Dugout Creek thrust, so that all the rocks exposed in the Marathon Basin are allochthonous, and so far as known lie with discontinuity at rather shallow depth on the cratonic rocks of their foreland. As a result of this orogeny, a new flysch trough, the Val Verde basin, developed along the northwestern front of the orogenic belt, which was thickly filled with Late Pennsylvanian and early Wolfcampian deposits. These are exposed beneath the Dugout Creek thrust in a small area in the northwestern part of the Marathon Basin, and have been penetrated beneath the thrust in deep wells farther east in the basin, where they lie on the older cratonic Paleozoic foreland rocks. The deformed pre-Permian complex exposed in the Marathon Basin, and known elsewhere in the Ouchita orogenic belt, is merely the marginal part of the orogenic belt. The inner parts of the belt are little known, and are deeply covered by Mesozoic, mainly Cretaceous, deposits. A small area of schist, represent- ing this inner belt, is exposed south of the Marathon Region on the Mexican side of the Rio Grande east of the village of Boquillas, and similar schists have been penetrated by drilling in places farther east. The rela- tion of these schists to the marginal belt in! the Marathon Basin and elsewhere is undetermined. It is also unknown how the marginal structures are related to probable plate convergence in the inner parts of the system. The upper Wolfcampian and younger rocks of the Glass Mountains are postorogenic to the Paleozoic orogenies, and are tilted gently northward away from the orogenic belt toward the West Texas Permian basin. In their lower parts, however, (as in the basal ,Hess Limestone) they contain much debris eroded from the orogenic belt; they are otherwise fine grained and are mainly carbonate deposits. After Permian time all the Paleozoic rocks—the oro- genically deformed pre-Permian and the tilted Per- mian alike—were subjected to prolonged erosion, which leveled them into a nearly featureless surface, the Wichita paleoplain, before the Lower Cretaceous deposits were laid over them. The Cretaceous rocks overlapped northward from a basin farther south, as shown by the thickening of all the Lower Cretaceous formations from north to south, and by a regional change from solid massive limestones to the south (as in the Big Bend area) into clays and marls to the north (as in the Fort Stockton area). Within the report area, the northward overlap is manifested by the abrupt wedging out of the Trinity Group (Glen Rose Lime- stone and Maxon Sandstone) toward a low scarp in the paleoplain on the site of the front of the present Glass Mountains. After Cretaceous time, early in the Tertiary, the west Texas region was subjected to various episodes of the Cordilleran deformation. This was more intense to the west, but along the orogenic front the Marathon dome was raised. Along its eastern side (as in the re- port area) the effects of the doming were only moder- ate, and resulted merely in a gentle slope of the Cretaceous rocks eastward, northeastward, and south- eastward. These events were, however, associated with the intrusion of igneous rocks, a few small bodies of which occur in the southwestern part of the report area. WELL DATA Below are summaries of the records of ten deep drill holes that have been put down in the Marathon Basin and Glass Mountains since 1956. Their locations are 36 GEOLOGY OF THE EASTERN PART OF THE MARATHON BASIN, TEXAS shown on figure 17, and their records are illustrated graphically on figure 18. Other wells drilled earlier were only a few thousand feet deep, hence they are not of interest; some of them were listed in 1930 (King, 1930, p. 129). The records of later wells drilled in sur- rounding regions are given by Flawn, Goldstein, King, and Weaver (1961, p. 233—238). Logs of the wells are summarized below; they have been made by several commercial services in Midland, Tex. Where records are available that were made by several services they differ somewhat in detail; in the summaries given be— low, I have reconciled the differences to give the most probable version. Depths recorded in the wells were given in feet. Abbreviations.—The following abbreviations are used in the records: G. C. & S. F. R.R., Gulf, Colorado and Santa Fe Railroad; G. H. & S. A. R.R., Galveston, Harrisburg, and San Antonio Railroad; T. C. R. R., Texas Central Railroad. FNL, FWL, FEL, and FSL, from north line, from west line, from east line, and from south line, respectively. (1) Gulf Oil Corporation, No. 1 Dora Lippit County: Brewster. Location: Block 306, G.C. & S.F. R.R., 1,290 ft FNL, 600 ft FWL. Near Bisset Mountain, about 6 miles northeast of Altuda. Elevation: 4,750 ft. Total depth: 9,360 ft. Completed: 1967. Surface formation: Upper Permian dolomite. Drill record: Permian dolomite ________ 550—4,46O ft Syenite intrusive ______ 4,600—5,560 ft No record ______________ 5,560—6,680 ft Mississippian __________ 6,680—6,940 ft Woodford ______________ 6,940— 7,130 ft Devonian ______________ 7,130—7,440 ft Fusselman ____________ 7,440— 7,460 ft Montoya ______________ 7,460— 7,770 ft Simpson Group ________ 7,770—9,200 ft Ellenburger ____________ 9,200—9,360 ft TD Comments.—Below the Permian rocks this well penetrated a normal middle and lower Paleozoic cratonic sequence. The syenite intru- sive is related to the doming of Bissett Mountain. (2) Mobil Oil Company, No. 1 D. J. Sibley County: Pecos. Location: Block 331, section 82, 4,330 ft FNL, 2,304 ft FWL. In northern part of Glass Mountains, about a mile east of the Pecos- Brewster County line. Elevation: 4,700 ft from topographic map; origi- nal record gives 2,596 ft. Total depth: 19,500 ft. Completed: 1969. Surface formation: Gilliam Limestone (Upper Permian). Drill record: Permian limestone ______ 1,490—2,900 ft Word Formation, with Parafusulina __-_ 2,900—4,620 ft Leonardian, with Parafusulina, Boultonia, Staffella, and Schubertella __________ 4,620—6,410 ft Wolfcampian, with Schwagerina, Pseudo- fusulina, and Triticites 6,410—15,170 ft Middle Paleozoic (Barnett, Kinderhookian, Woodford, and Devonian cherty dolomite) __________ 15,170— 15,820 ft Fusselman Limestone 15,829—15,990 ft Montoya Limestone __ 16,825— 16,285 ft Simpson Group ______ 16,825—18,350 ft Ellenburger Limestone 18,350—19,500 ft TD Comments.—The 8,760 feet assigned to the Wolfcampian is part of the Val Verde basin se- quence. The middle and lower Paleozoic rocks beneath are a normal cratonic sequence. (3) Slick-Urschell Oil Company (Woods Oil & Gas Company), No. 1—47 Mary Decie and others. County: Brewster. Location: Block 4, G.C. & S.F. R.R., section 47, 660 ft FEL, 330 ft FWL of NE 1A; of section. Six miles northwest of Marathon, at foot of Glass Mountains escarpment, in northwest- ern part of Marathon Basin. Elevation: 4,661 ft. Total depth: 9,471 ft. Completed: 1956. Surface formation: Caballos Novaculite, in klippe of overthrust. ' Drill record: Caballos Novaculite __________ 0—160 ft Dugout Creek thrust plane ______ 160 ft Wolfcampian and Pennsylvanian (?), with Triticites and Schwagerina; thrust fault at 1,600 ft -_ 160—6,820 ft Strawn Group, with F usulina and Fusulinella ______ 6,820—6,980 ft Woodford ______________ 6,980—7,270 ft Silurian and Devonian ____________ 7,270—8,070 ft Montoya Limestone ___, 8,070—8,250 ft Simpson Group ________ 8,250—9,637 ft Ellenburger Limestone ____________ 9,637—9,471 ft TD Comments.—This well drilled through a klippe of Caballos Novaculite into 6,660 of upper Paleozoic rocks, generally called Wolfcampian (but prob- ably including Upper Pennsylvanian Gaptank WELL DATA 37 Formation, which is exposed in surrounding areas). Below is a normal cratonic sequence, pro— ving that the Dugout Creek thrust carries Marathon Basin rocks over equivalent rocks of their foreland. (4) Mobil Oil Company, No. 1 Adams County: Brewster. Location: Block 4, G.C. & S.F. R.R., section 25, 1,320 ft FSL, 1,320 ft FWL. About 1 mile west of Marathon. Elevation: 4,049 ft. Total depth: 10,604 ft. Drilled: in 1960’s. Surface formation: Marathon Limestone. Drill record: Marathon Limestone __________ 0—680 ft Dugout Creek thrust ____________ 680 ft Wolfcampian and Pennsylvanian? clastic rocks __________________ 680—7,720 ft Woodford ______________ 7,720—8,106 ft Silurian and Devonian __8,106—8,436 ft Fusselman Limestone __ 8,436—8,52O ft Montoya Limestone ____ 8,529—8,730 ft Simpson Group ________ 8,730—10,000 ft Ellenburger Limestone __________ 10,020— 10,604 ft TD Comments:—See well 5, below. (5) Gulf Oil Corporation, No. 1 D. S. C. Combs County: Brewster. Location: Block 4, G.C. & S.F. R.R., section 16,660 ft FSL, 1,980 ft FEL. About 11/2 miles southeast of Marathon. Elevation: 4,114 ft. Total depth: 9,500 ft. Completed: 1956. Surface formation: Woods Hollow Shale. Drill record: Lower Paleozoic formations of Marathon se- quence, from surface down to 4,850 ft, or to 5,860—6,100 ft. Different records make dif- ferent formation assignments; cherts from 320 to below 700 ft are variously assigned to the Fort Pena Formation, or Caballos Novaculite and Maravillas Chert. The rocks below 700 ft are partitioned accord- ingly, but all agree that the lower part is Marathon Limestone. Andesitic intrusions recorded between 3,870 and 3,990 ft Dugout Creek thrust, variously placed at 4,850 ft and 5,980—6,100 ft. Beneath to total depth at 9,500 ft is light gray, fine-grained sandstone of Wolfcam- pian or Late Pennsylvanian age, with a few fusulinids. Comments:—This well, and the Mobile, Adams well about 3 miles to the northwest, drilled through the Dugout Creek thrust into a foreland sequence. Note, however, that the Adams well passed through the thrust at a depth more than 4,000 ft shallower than the Combs well, and reached formations older than those penetrated in the Combs well. (6) Fred Turner, Jr., N0. 1 D. S. C. Combs County: Brewster. Location: Block 21, (G.H.S.A. R.R.), section 37, 433 ft FSL, 2,406 ft FWL. About 16 miles south of Marathon, near middle of Dagger Flat anticlinorium. Elevation: 3,469 ft. Total depth: 13,980 ft. Completed: 1957. Surface formation: Dagger Flat Sandstone. Drill record: Interbedded shale and sandstone, probably Dagger Flat ______________ 0—1,600 ft Change in formation, possibly Dugout Creek thrust ______________________ 1,600 ft Interbedded shale, limestone, and sandstone. In the upper part shale and limestone dominate, below 8,400 ft, mostly shale and sandstone. Chert occurs from 2,180—3,300 ft; fragments of spines and shells, 2,730—2,740 ft; no other fossils re- corded ______________ 1,600— 13,980 ft TD Comments:——The whole sequence penetrated in this well consists of deformed shaly and sandy rocks, but in the absence of determinable fossils, interpretaton is engimatic. The change in forma- tion at 1,600 ft may indicate that the well passed from Cambrian clastics into Pennsylvanian clas- tics, with the Dugout Creek thrust between, but this would place the thrust at a higher level than most of the other penetrations in the Marathon Basin. (7) Forrest Oil Company (Lone Star Producing Com- pany), No. 1 Jo Ann Moore. County: Pecos. Location: Block 1, G.C. & S.F. R.R., section 7, 660 ft FSL and 1,320 ft FEL. About 11/2 miles southwest of Gap Tank in the flat south of the Glass Mountains escarpment. Elevation: 4,416 ft. Total depth: 9,865 ft. Completed: 1961. Surface formation: Haymond Formation. Drill record: Haymond Formation, with Triticites at 150—180 ft __ 60—6,360 ft Dimple Limestone, with M illerella, Paramillerella, and Pseudostaffella at 6,500—7,730 ft__ 6,360— 7,000 ft 38 GEOLOGY OF THE EASTERN PART OF THE MARATHON BASIN, TEXAS Tesnus Formation ______ 7,000—8,480 ft Dimple Limestone (repeated), with Paramillerella, Millerella, and Endothyra at 8,456—8,960 ft ______ 8,480— 8,800 ft Tesnus Formation ______ 8,800—9,865 ft TD Comments.—This well failed to reach the Dug- out Creek thrust at total depth. The recorded repetition of Dimple Limestone, probably by thrust slicing, indicates greater structural complexity at depth than the rather open fold- ing in the surface formations. (8) Continental Oil Company, No. 1 J. E. Allison et al County: Pecos. Location: Block 2, TC. R.R., section 10, 2,180 ft FSL, 1,320 ft FEL. In valley between Cre- taceous mesas, 8 miles east of Gap Tank. Elevation: 4,300 ft (approximately, from topo- graphic map), Total depth: 11,870 ft. Completed: 1974. Surface formation: Lower Cretaceous. Drill record: Cretaceous ____________ 0— 663 ft Hess Limestone __________ 663—1,242 ft Gaptank Formation _ _ _ _ 1 ,242— 1,612 ft Haymond Formation _,__ 1,612—2,342 ft Dimple Limestone ______ 2,342—2,500 ft Tesnus Formation ______ 2,500—6,7 10 ft Caballos Novaculite ____ 6,710—6,870 ft Fault ________________________ 6,870 ft Tesnus Formation ______ 6,870-7,070 ft Caballos Novaculite w-__ 7,070—7,500 ft Fault __________________________ 7,500 ft Haymond Formation ____ 7,500—8,742 ft Dimple Limestone ______ 8,742—8,900 ft Tesnus Formation ______ 8,900— 9,158 ft Caballos Novaculite ___v 9,158—9,510 ft Sole fault (Dugout Creek thrust) ______ 9,510 ft Wolfcampian and Pennsylvanian ______ 9,510— 10,730 ft Barnett Shale ________ 10,730—11,022 ft Woodford and Devonian __________ 11,022— 1 1,182 ft Fusselman Limestone 11,182—11,220 ft Montoya Limestone __ 11,220—11,812 ft Simpson Group ______ 11,812— 11,870 ft TD Commentsc—This well lies several miles south of the projected subsurface trace of the leading edge of the Dugout Creek thrust, or sole fault of the Marathon orogenic belt. The repetition of the Carboniferous formations above it indicates much thrust slicing of the rocks of the upper plate. Beneath the sole fault is a normal se- quence of the Paleozoic cratonic formations, ending in the Simpson Group at total depth. (9) Exxon Company (Humble Oil & Refining Com- pany), No. 1 Virginia Law County: Brewster. Location: Block 2 GO. & S.F. R.R., section 91, 1,980 ft FNL and FEL. At south end of a syn— clinal trough of Dimple and Haymond For- mations west of Frog Creek, and 10 miles east of Marathon. Elevation 4,832 ft. Total depth: 20,688 ft. Completed: 1972. Surface formation: Haymond Formation. Drill record: Haymond Formation ________ 70—400 ft Dimple Limestone ________ 400—1,000 ft Tesnus Formation ______ 1,000—6,070 ft Caballos Novaculite ____ 6,070—6,500 ft Maravillas Chert ______ 6,500—6,830 ft Woods Hollow Shale _1_- 6,830—9,850 ft Fort Pena Formation __ 9,850— 10,230 ft Alsate Shale ________ 10,230—11,506 ft Marathon Limestone 1. 11,506— 13,280 ft Sole fault (Dugout Creek over- thrust) ____________________ 13,280 ft Wolfcampian and Gaptank; limestone in upper part, clastics below _-__ 13,280— 16,7 60 ft Atokan ______________ 16,760—16,870 ft Woodford and Devonian __________ 16,870— 17,470 ft Fusselman Limestone and other Silurian ____________ 17,470—17,620 ft Montoya Limestone __ 17,620—18,020 ft Simpson Group ______ 18,020—19,550 ft Ellenburger Limestone __________ 19,550—20,688 ft TD Comments.—-This is currently the deepest well that has been drilled‘ in the Marathon Basin, and has the deepest penetration of the sole fault. The formations beneath are of the normal cratonic se- quence. (10) Mobil Oil Company, No. 1 Cox County: Pecos. Location: Thomas J. Hall survey, section 100, 1,980 ft FNL and FEL. In the middle of W B Flats, about 6 miles east of the Dimple Hills. Elevation: 4,006 ft. Total depth: 13,941 ft. Completed in 1960’s. Drill record: Valley fill ____________________ 0—292 ft Tesnus Formation ________ 292—4,205 ft Fault ________________________ 4,205 ft REFERENCES CITED 39 Dimple Limestone ______ 4,205—4,385 ft Tesnus Formation ______ 4,385—6,875 ft Caballos Novaculite ____ 6,875-7,167 ft Maravillas Chert ______ 7,167—7,5 16 ft Fault ________________________ 7,516 ft Tesnus Formation ______ 7,526—9,477 ft Caballos Novaculite ____ 9,477—9,568 ft Maravillas Chert ______ 9,568—9,7 10 ft Sole fault (Dugout Creek over- thrust) ____________________ 9,710 ft Wolfcampian (and upper Pennsylvanian?) ____ 9,710— 11,350 ft Woodford ____________ 11,350— 11,368 ft Fusselman Limestone and other Silurian ____________ 11,368— 11,510 ft Montoya Limestone -- 11,510—11,870 ft Simpson Group ______ 11,870— 13,053 ft Ellenburger Limestone __________ 13,053—13,941 ft TD Comments. —The sole fault was penetrated in this well at an elevation only a little deeper than in the Continental-Allison well 6 miles to the north. Of interest is the considerable duplication by thrust slicing of the Marathon Basin rocks above it. The formations beneath the thrust are part of the normal cratonic sequence. REFERENCES CITED Adkins, W. S., 1927, The geology and mineral resources of the Fort Stockton quadrangle: Texas Univ. (Bur. Econ. Geology) Bull. 2738, 166p. Baker, C. L., 1932, Erratics and arkoses in the middle Pennsylva- nian Haymond Formation of the Marathon area, Trans-Pecos Texas: Jour. Geology, v. 40, p. 577—603. 1963, Radiolaria in the Tesnus Formation, Marathon Basin, Trans-Pecos Texas: Jour. Paleontology, v. 37, p. 502. Baker, C. L., and Bowman, W. F., 1917, Geologic exploration of the southeastern Front Range of trans-Pecos Texas: Texas Univ. (Bur. Econ. Geology) Bull. 1753, p. 67~172. Bose, Emil, 1917, The Permo-Carboniferous ammonoids of the Glass Mountains, west Texas, and their stratigraphical significance: Texas Univ. (Bur. Econ. Geology) Bull. 1762, 241 p. Brooks, H. K., 1955, A crustacean from the Tesnus Formation (Pennsylvanian) of Texas: Jour. Paleontology, v. 29, p. 852—856. Bureau of Economic Geology, 1976, Pecos Sheet, Geologic Atlas of Texas. Carney, Frank, 1935, Glacial beds of Pennsylvanian age in Texas (abs): Geol. Soc. America Proc. 1934, p. 70. Cooper, G. A., and Grant, R. E., 1972, Permian brachiopods of west Texas, v. 1: Smithsonian Contributions to Paleobiology, no. 14, 230 p. Cotera, A. 8., Jr., 1961, Petrology and petrography of the Tesnus Formation, in McBride, E. F., ed., A guidebook to the stratig- raphy, sedimentary structures, and origin of the flysch and pre- flysch rocks of the Marathon Basin, Texas: Dallas Geol. 800., p. 66—71. Dean, W. E., and Anderson, R. Y., 1966, Correlation of turbidite strata in the Pennsylvanian Haymond Formation, Marathon Region, Texas: Jour. Geology, v. 74, p. 59—75. Denison, R. E., Kenney, G. S., Burke, W. H., Jr., and Hetherington, E. A., Jr., 1969, Isotopic ages of igneous and metamorphic boul- ders from the Haymond Formation, Marathon Basin, Texas, and their significance: Geol. Soc. America Bull., v. 80, no. 2, p. 2457 256. Ellison, S. P., Jr., 1962, Conodonts from trans-Pecos Texas (abs): Am. Assoc. Petroleum Geologists Bull., v. 46, no. 2, p. 266. 1964, Conodonts of the Gaptank Formation, in The filling of the Marathon geosyncline: Permian Basin Section, Soc. Econ. Paleontologists and Mineralogists Publ. 64—9, p. 45—46. Ellison, S. P., Jr., and Graves, R. W., Jr., 1941, Lower Pennsylvanian (Dimple Limestone) conodonts of the Marathon Region, Texas: Univ. Missouri School of Mines and Metallurgy, Tech. Ser. Bull., v. 14, no. 3, p. 1—21. Flawn, P. T., Goldstein, August, Jr., King, P. B., and Weaver, C. E., 1961, The Ouachita system: Texas Univ. (Bur. Econ. Geology) Publ. 6120, 401 p. Flores, R. M., 1972, Delta-front delta-plain facies of the Pennsylva- nian Haymond Formation, northeastern Marathon Basin, Texas: Geol. Soc. America Bull., v. 83, no. 11, p. 3415—3424. 1974, Characteristics of the lower- middle Haymond Forma- tion delta-front sandstones, Marathon Basin, west Texas: Geol. Soc. America Bull., v. 85, no. 5, p. 706—716. 1975, Short-headed stream delta model for Pennsylvanian Haymond Formation, west Texas: Am. Assoc. Petroleum Geologists Bull., v. 59, no. 12, p. 2288—2301. 1977, Marginal marine deposits of the upper Tesnus Forma— tion (Carboniferous), Marathon Basin, Texas: J our. Sedimentary Petrology, v. 40, p. 621—628. Flores, R. M., and Ferm, J. C., 1970, A recent model for Pennsylva- nian deposition in the Marathon Basin, west Texas: Jour. Sedimentary Petrology, v. 40, no. 2, p. 621—628. Folk, R. L., 1973, Evidence for peritidal deposition of Devonian Caballos N ovaculite, Marathon Basin, Texas: Am. Assoc. Petro- leum Geologists Bull., v. 57, no. 4, p. 702—725. Graves, R. W., Jr., 1954, Geology of the Hood Spring Quadrangle, Brewster County, Teas: Texas Univ. (Bur. Econ. Geology) Rept. Inves. 21, 51 p. Hall, W. E., 1957, Genesis of Haymond boulder beds, Marathon Basin, west Texas: Am. Assoc. Petroleum Geologists Bull., v. 41, no. 8, p. 1633— 1637. Johnson, K. E., 1962, Paleocurrent study of the Tesnus Formation, Marathon Basin, Texas: Jour. Sedimentary Petrology, v. 32, no. 4, p. 781—792. King, P. B., 1930, The geology of the Glass Mountains; part 1, De- scriptive geology: Texas Univ. (Bur. Econ. Geology) Bull. 3038, 167 p. 1932, Limestone reefs in the Leonard and Hess Formations of trans-Pecos Texas: Am. Jour. Sci., 5th ser., v. 24, no. 142, p: 337—354. 1937, Geology of the Marathon Region, Texas: US. Geol. Sur- vey Prof. Paper 187, 148 p. 1958, Problems of boulder beds of Haymond Formation, Marathon Basin, Texas: Am. Assoc. Petroleum Geologists Bull., v. 42, no. 7, p. 1731—1735. 1977, Marathon revisited, in Stone, C. G., ed., Symposium on the geology of the Ouachita Mountains, v. 1: Arkansas Geol. Comm., p. 41—69. 1978, Tectonics and sedimentation of the Paleozoic rocks in the Marathon Region, west Texas, in Mazzullo, S. J., ed., Tec- tonics and Paleozoic facies of the Marathon geosyncline, west Texas: Permian Basin Sec., Soc. Econ. Paleontologists and Mineralogists Publ. 78—17, p. 5—37. McBride, E. F., 1964a, Sedimentology and stratigraphy of the Haymond Formation, Marathon Basin, Texas, in The filling of 40 GEOLOGY OF THE EAS'I‘ERN PART OF THE MARATHON BASIN, TEXAS the Marathon geosyncline: Permian Basin Sec., Soc. Econ. Paleontologists and Mineralogists Publ. 64—9, p. 35—40. 1964b, Stratigraphy and sedimentology of the Gaptank For- mation, Marathon Basin, Texas, in The filling of the Marathon geosyncline: Permian Basin Sec., Soc. Econ. Paleontologists and Mineralogists Publ. 64—9, p. 41—44. 1966, Sedimentary petrography and history of the Haymond Formation (Pensylvanian), Marathon Basin, Texas: Texas Bur. Econ. Geology Rept. Inves. 57, 101 p. 1969, Stratigraphy and sedimentology of the Haymond For- mation, in McBride, E. F., ed., A guidebook to the stratigraphy, sedimentary structures, and origin of the fiysch and pre-fiysch rocks, Marathon Basin, Texas: Dallas Geol. Soc., p. 86—92. 1970, Flysch sedimentation in the Marathon Region, Texas, in Lajoie, J ., ed., Flysch sedimentology in North America: Geol. Assoc. Canada Spec. Paper 7, p. 67—93. 1978, Tesnus and Haymond Formations, siliciclastic flysch, in Mazzullo, S. J ., ed., Tectonics and Paleozoic facies of the Marathon geosyncline, west Texas: Permian Basin Sec., Soc. Econ. Paleontologists and Mineralogists Publ. 78—17, p. 131— 147. McBride, E. 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Econ. Paleontologists and Mineralogists Publ. 64—9, p. 31—34. Skinner, J. W., and Wilde, G. L., 1954, New early Pennsylvanian fusulinids from Texas: Jour. Paleontology, v. 28, no. 6, p. 796— 803. St. John, B. E., 1966, Geology of Black Gap area, Brewster County, Texas: Texas Univ. (Bur. Econ. Geology) Quadrangle Map 30, scale 1:62,500. Thomson, A. F., 1969, Soft-sediment faults in the Tesnus Formation and their relation to paleoslope, in McBride, E. F., ed., A guidebook to the stratigraphy, sedimentary structures, and ori- gin of the flysch and pre-flysch rocks of the Marathon Basin, Texas: Dallas Geol. Soc., p. 66—71. Thomson, A. F., and Thomasson, M. R., 1964, Sedimentology and stratigraphy of the Dimple Limestone, Marathon Region, Texas, in The filling of the Marathon geosyncline: Permian Basin Sec., Soc. Econ. Paleontologists and Mineralogists Publ. 64-9, p. 22—30. 1969a, Shallow to deep water facies in the Dimple Limestone (lower Pennsylvanian), Marathon Region, Texas: Soc. Econ. Paleontologists and Mineralogists Spec. Publ. 14, p. 57-78. 1969b, Sedimentology of the Dimple Limestone, Marathon Region, Texas, in McBride, E. F., ed., A guidebook to the stratig- raphy, sedimentary structures, and origin of the flysch and pre- flysch rocks, Marathon Basin, Texas: Dallas Geol. Soc., p. 78—85. Udden, J. A., 1917, Notes on the geology of the Glass Mountains: Texas Univ. (Bur. Econ. Geology) Bull. 1753, p. 4—59. Van der Gracht, W. A. J. M. van Waterschoot, 1931, Pre-Car- boniferous exotic boulders in the so-called "Caney shale” in the northwestern front of the Ouachita Mountains of Oklahoma: Jour. Geology, v. 39, no. 8, p. 697—714. 30°00' 103°05' UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY 1 03°05’ 102°45’ 3030' w. _ - A“ 44/ 5“»1‘1’3”? :4’ / #‘flt' t 5133,33 . 38:11:11.0 \ \ “56v .—_—.-----\‘ (.285)! .-\-c at 5,54 § ’\_/ ==x=::='9 ;= $5" _—5 -95 m £221. ,gs-=..== , ’, . *t:= g t , u , “ n a ”dB-“gr” [07 [V “‘;.7€fiypfi; 30°30’ Duw . 30°15’ masa‘m pop’eland \\ “wk , “b {w ~ _1 , s my», g MW? ' V‘ ‘ Mr '1 103° 102°45' Base from US Geological Sun/ey SCALE 1'62 500 f‘IINTEHIORifiEOLOGlCAL SURVEY, RESTUN, VA—1980-G79527 Hess Canyon 1262,500, 1921; , I Geology mapped by Philip B. King, 1978 Marathon 1:52,500, 1920; ‘ L. H .1.“ H ._4 ° 1 2 3 1‘ f. ”"455 Marathon Gap, Reininger Draw, Dimple Hills; Caprock Butte, 1H H '3 0 1 2 3 4 5 6 7 KILOMETERS E CONTOUR INTERVALS 20 AND 50 FEET NATIONAL GEDDETIL‘ VERTICAL DATUM OF 1929 Housetop Mts, Tesnus NE, Tesnus, Tesnus SE 124,000, 1968 GEOLOGIC MAP OF THE EASTERN PART OF THE MARATHON BASIN AND ADJACENT AREAS, TEXAS o I PROFESSIONAL PAPER 1157 PLATE 1 EXPLANATION Oa Alluvium and younger gravel deposits 09 Gravel deposits — 009 QUATERNARY Older gravel deposits l l l Landshde deposits - L Intrusive igneous rocks TERTIARY Kw, Washita Group Kf Fredericksburg Group Kt | CRETACEOUS Trinity Group (In the south,GIen Rose Limestone with Maxon Sandstone at top; in the north, Basement sands) Gilliam and Vidrio Limestones Word Formation Pl Cathedral Mountain Formation (Of Leonardian age) 13h”; Hess Limestone (Of late Wolfcampian and Leonardian? age. Taylor Ranch Member, tr, near middle) PERMIAN Neal Ranch Formation (Of early Wolfcampian age) Gaptank Formation (Upper and lower divisions, Cgu, and C91, separated locally) Haymond Formation (With boulder-bed units,Chb. Coarse sandstone or arkose beds shown by heavy dashed lines) I PENNSYLVAN IAN | CARBONIFEROUS Dimple Limestone Ct cl mam Tesnus Formation (Lower shaly beds, Cts. White quartzite beds, a, in south part of area) MISSISSIP- PIAN ORDO- DEVON- VICIAN IAN Caballos Novaculite J Maravillas Chert Traces of ledges in Carboniferous and other formations as indicated on aerial photographs T Thrust fault Dashed where approximately located; dotted where concealed; T on upthrown side D Normal fault D on downthrown side /5 _l_ Strike and clip of beds —9— 60 Strike and dip of overturned beds + Strike of vertical beds a Deep drill hole With name and total depth shown in feet