Physical Stratigraphy and Trilobite Biostratigraphy of the Carrara Formation (Lower and Middle Cambrian) in the Southern Great Basin By ALLISON R. PALMER and ROBERT B. HALLEY GEOLOGICAL SURVEY PROFESSIONAL PAPER 1047 Nine members are described; a model for Grand Cycle sedimentation is proposed; nine trilobite zonules are defined; and 95 species representing 38 genera are described UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON11979 UNITED STATES DEPARTMENT OF THE INTERIOR CECIL D. ANDRUS, Secretary GEOLOGICAL SURVEY H. William Menard, Director Library of Congress Cataloging in Publication Data Palmer, Allison R. Physical stratigraphy and trilobite biostratigraphy of the Carrara Formation (Lower and Middle Cambrian) in the southern Great Basin. (The Carrara Formation (Lower and Middle Cambrian) in the southern Great Basin) (Geological Survey Professional Paper 1047) Bibliography: p. 121 Includes index Supt. of Docs. no.:119.16:1047. 1. Geology, Stratigraphic—Cambrian. 2. Trilobites. 3. Paleontology—Cambrian. 4. Geology—California. 5. Geology—Neveda. I. Halley, Robert 8., joint author. 11. Title. 111. Series. IV. Series: United States Geological Survey Professional Paper 1047. QE656.P34 565’.393'0979 77—608319 For sale by the Superintendent of Documents, US. Government Printing Office Washington, DC. 20402 Stock Number 024—001—03242—2 CONTENTS Page Abstract ................................................... 1 Introduction ............................................... 1 Acknowledgments .......................................... 4 Stratigraphy of the Carrara Formation ....................... 4 Description of members ................................ 6 Emigrant Pass Member of the Zabriskie Quartzite ..... 7 Members of the Carrara Formation .................. 9 Eagle Mountain Shale Member .................. 9 Faunal characteristics ....................... 9 Thimble Limestone Member .................... 13 Faunal characteristics ....................... 13 Echo Shale Member ............................ 13 Faunal characteristics ....................... 13 Gold Ace Limestone Member ................... 13 Faunal characteristics ....................... 14 Pyramid Shale Member ......................... 14 Faunal characteristics ....................... 16 Red Pass Limestone Member .................... 17 Faunal characteristics ....................... 17 Pahrump Hills Shale Member ................... 18 Faunal characteristics ....................... 18 Jangle Limestone Member ...................... 20 Faunal characteristics ....................... 20 Desert Range Limestone Member ............... 20 Faunal characteristics ....................... 21 Regional lithostratigraphic relations .......................... 21 Lithofacies description and interpretation ................ 21 The lime-mudstone lithofacies ...................... 22 Environment of deposition ...................... 33 The oolite lithofacies ............................... 36 Environment of deposition ...................... 39 The algal-boundstone lithofacies .................... 42 Environment of deposition ...................... 45 Spatial relations of the carbonate lithofacies .......... 49 Depositional model ..................................... 51 Paleontologic analysis ....................................... 55 Biostratigraphy ........................................ 55 Olenellus Zone ..................................... 56 Olenellus arcuatus Zonule ........................ 56 Bristolia Zonule ................................ 57 Olenellus multinodus Zonule ...................... 58 “Plagium-Poliella" Zone ............................. 58 Poliella lamataspis Zonule ........................ 58 Kochaspid Zonule .............................. 59 Albertella Zone ..................................... 59 Ogygopsis Zonule ............................... 59 Zacanthoidid Zonule ........................... 59 Albertella—Mexicella Zonule ....................... 60 Glossopleura Zone and Zonule ......................... 60 Paleoecology ........................................... 60 Systematic paleontology ................................ 63 Order Olenellida ................................... 63 Family Olenellidae ............................. 63 Genus B ristolia ............................. 63 Paleontologic analysis—Continued Page Systematic paleontology—Continued Order Olenellida—Continued Family Olenellidae—Continued Genus Olenellm ............................ 66 Genus Peachella ............................ 74 Order Miomera .................................... 75 Superfamily Agnostoidea ...................... 75 Family Quadragnostidae .................... 75 Genus Peronopiix ....................... 75 Superfamily Eodiscoidea ........................ 76 Family Eodiscidae .......................... 76 Genus M acamlaia ...................... 76 Genus Pagetia .......................... 77 Order Corynexochida .............................. 77 Family Dolichometopidae ....................... 78 Genus Glomopleum ......................... 78 Genus Poliella .............................. 79 Family Dorypygidae ............................ 81 Genus Bonnia .............................. 81 Genus K ootenia ............................. 81 Genus Ogygopsis ............................ 82 Family Oryctocephalidae ........................ 83 Genus Oryctocephalina ....................... 83 Genus Oryctocephalites ....................... 83 Genus Oryctocephalus ........................ 84 Genus Thoracocare .......................... 85 Family Zacanthoididae .......................... 85 Genus Albertella ............................ 86 Genus Albertellina .......................... 89 Genus Albertelloides ......................... 90 Genus F ieldarpis ............................ 92 Genus M exicmpis ........................... 92 Genus Paralbertella ......................... 93 Genus Ptarmiganoidex ....................... 94 Genus Zacanthoides ......................... 96 Order Ptychopariida ............................... 99 Genus Alokistocare .............................. 99 Genus Alokistocarella ............................ 100 Genus Caborcella ............................... 101 Genus Chancia ................................. 102 Genus E lmthina ................................ 103 Genus E optychoparia ............................ 104 Genus Kochaspis .............................. 105 Genus K ochiellina ............................... 106 Genus M exicella ................................ 108 Genus Nyella ................................... 1 10 Genus Pachyarpis ............................... 1 l2 Genus Plagium ................................ l 12 Genus Schistometopus ............................ l 15 Genus Syspacephalus ............................ l 15 Genus Volocephalina ............................ 1 16 References cited ........................................... 121 Index .................................................... l2 7 III 8411 IV CONTENTS ILLUSTRATIONS [Plates 1—16 follow index; plates 17, 18 in pocket] PLATES 1—16. Photographs of trilobites of the Carrara Formation l7. Columnar sections showing occurrence and stratigraphic distribution of all trilobites from the Carrara Formation 18. Composite range chart of all species from the Carrara Formation FIGURE 1. Index map showing localities related to study of the Carrara Formation ........................................... 2. Nomenclatural history of the rocks now included within the Carrara Formation .................................... 3. Members of the Carrara Formation and correlation with adjacent regions .......................................... 4. Outcrop photo and photomicrographs of some lithologic features of the Emigrant Pass Member of the Zabriskie Quartzite .......................................................................................... 5. Isopach maps of the shale members of the Carrara Formation .................................................... 6. Isopach maps of the limestone members of the Carrara Formation ................................................ 7. Photographs of outcrops, vertical-cut surfaces, and thin sections showing some of the features of the Eagle Mountain Shale Member ................................................................................................... 8. Photographs of outcrops, float blocks, and thin sections showing some of the lithologic features of the Pyramid Shale Member or correlative beds .................................................................................. 9. Tracks, trails, and burrows from the upper part of the Pyramid Shale Member, Titanothere Canyon section, California .................................................................................................. 10. Typical Iithologies of the basal part of the Pahrump Hills Shale Member ........................................... l l. Generalized cross section along Nevada-California border showing lithosomal relationships of the members of the Carrara Formation .................................................................................................. 12. Photomicrographs of lime-mudstone textures .................................................................... 13. Photomicrographs and outcrop photo of rocks of the lime-mudstone lithofacies .................................... l4. Photomicrographs and photos of cut surfaces of selected lime-mudstone lithotypes ................................. 15. Photomicrographs of echinoderm debris ........................................................................ 16. Photographs of vertical-cut surfaces or outcrops of rocks from the lime-mudstone lithofacies ,,,,,,,,,,,,,,,,,,,,,,,, 17. Photographs of vertical-cut surfaces or outcrops of rocks from the lime-mudstone lithofacies ........................ 18. Outcrop photos of rocks from the lime-mudstone lithofacies ...................................................... 19. Photomicrographs of rocks from the lime-mudstone lithofacies .................................................... 20. Photographs of a natural exposure and vertical-cut surfaces of rocks of lime-mudstone lithofacies .................... 21. Photomicrographs and photographs of vertical-cut surfaces of rocks from the lime-mudstone lithofacies .............. 22. Photomicrographs of rocks from the oolite lithofacies ............................................................ 23. Photomicrographs of rocks from the oolite lithofacies ............................................................ 24. Photographs of thin sections, vertical-cut surfaces, and outcrops of rocks of the oolite lithofacies ..................... 25. Outcrop photo and photomicrographs of unusual oolite intraclast bed ............................................. 26. Photographs of outcrops and vertical-cut surfaces of rocks of the algal-boundstone lithofacies ........................ 27. Photographs of outcrops, vertical-cut surfaces, and thin sections of rocks from the algal-boundstone lithofacies ........ 28. Photographs of outcrops, float specimens, and thin sections of rocks from the algal-boundstone lithofacies ............ 29. Photographs of vertical-cut surfaces and thin sections of rocks from the algal-boundstone lithofacies ................. 30. Outcrop photo and photomicrographs of rocks from the algal-boundstone lithofacies ............................... 31. Lithofacies distribution maps for the top of each limestone member of the Carrara Formation ....................... 32. Stratigraphic sections of Jangle, Red Pass, Gold Ace, and Thimble Limestone Members of the Carrara Formation ..... 33. Lateral relationships of peritidal and subtidal Iithologies near Pyramid Peak, Funeral Mountains, Calif. ............... 34. Hypothetical model illustrating development of a limestone member of the Carrara Formation ...................... 35. Biostratigraphy of the Carrara Formation and its relation to the lithostratigraphy ............................. ~ ...... 36. Suggested biofacies-lithofacies model for the Albertella Zone faunas of the Carrara Formation ........................ TABLE TABLE 1. Summary of classification of Early and Middle Cambrian trilobites of Carrara Formation ............................ Page 10 11 12 15 16 19 22 24 25 27 28 29 30 31 32 34 35 37 38 40 41 43 45 46 47 48 50 52 53 55 57 61 Page 62 CONTENTS METRIC—ENGLISH EQUIVALENTS [S1, International System of Units, a modernized metric system of measurement] SI unit U.S. customary equivalent SI unit U.S. customary equivalent Length Volume per unit time (includes flow)—-Continued millimeter (mm) = 0.039 37 inch (in) decimeters per second 2 15.85 gallons per minute meter (m) = 3.281 feet (ft) (de/S) (gal/min) = 1.094 yards (yd) = 543.4 barrels per day kilometer (km) : 0.621 4 mile (mi) (bbl/d) (petroleum, = 0.540 0 mile, nautical (nmi) 1 bbl:42 gal) meter" per second (ma/s) = 35.31 feet3 per second (ft3/s) Area = 15 850 gallons per minute (gal/min) centimeter2 (cm?) = 0.155 0 inch2 (in?) meter2 (m2) : 10.76 feet2 (it?) Mass : (1)533 247 1 yardsz (ydz) hectometer’ (hm!) ; 2:471 Eggs gram (3) = 0.035 27 oug‘cyglafoirdupois (oz = 0'003 861 seatirolnz (640 acres or kilogram (kg) 2.205 porings)avoirdupois (lb 3 2 _ . av p kilometer (km ) _ 0.386 1 mile2 (mia) megagram (Mg) = 1102 tons, short (2 000 lb) Volume 2 0.984 2 ton, long (2 240 1b) centimeter-1 (cm3) = 0.0611 02 inch3 (ma) Mass per unit volume (includes density) decimeter“ (dmi‘) : 6;.023 inches3 (i)n3) = . pints (pt i1 14 = .0 24 t a ( 3 = 1.057 quarts (at) k aggfiaper mete 0 6 3 pound per oot _lb/ft) : 0.264 2 gallon (gal) : 0.035 31 foot3 (ft‘i) metera (m3) = 35.31 teeta (its) Pressure : 1.308 yardsa (yda) = 264.2 gallons (gal) kilopascal (kPa) : 0.145 0 pound-force per inch” = 6.290 barrels (bhl) (petro- (lbf/inz) leum, 1 bbl=42 gal) 0.009 869 atmosphere. standard = 0.000 810 7 acre-foot (acre-ft) (atm) hectometer3 (hma) = 810.7 acre-feet (acre-ft) = 0.01 bar kilometer" (km‘) : 0.239 9 mile3 (mi3) : 0.296 1 inch of mercury at _ . . 60°F (in Hg) Volume per unit time (includes flow) “earnest/er: per second = 0.035 31 foot‘1 per second (ft3/s) Temperature m s : 2.119 feet3 per minute (ft’/ min) temp kelvin (K) temp deg Celsius (”C) [temp deg Fahrenheit (°F) +459.67]/1.8 [temp deg Fahrenheit (°F) —32]/1.8 , it?“ Ewewi PHYSICAL STRATIGRAPHY AND TRILOBITE BIOSTRATIGRAPHY OF THE CARRARA FORMATION (LOWER AND MIDDLE CAMBRIAN) IN THE SOUTHERN GREAT BASIN By ALLISON R. PALMER and ROBERT B. HALLEY ABSTRACT The Carrara Formation consists of three complete and one partial clastic—carbonate sedimentary cycles totaling about 400 meters in thick- ness and spanning the time from the upper part of the Olenellw Zone of Early Cambrian age to the lower part of the Glossopleum Zone of Middle Cambrian age. It represents the regional transition from dominantly clastic Early Cambrian miogeoclinal sedimentation to dominantly car- bonate Middle and Late Cambrian miogeoclinal sedimentation and can be recognized over an area of about 36,000 square kilometers in south- ern Nevada and adjacent parts of southeastern California. Nine mem- bers can be distinguished between the underlying Zabriskie Quartzite and the overlying massive carbonate rocks of the Bonanza King Forma— tion. These are, from the oldest to youngest: Eagle Mountain Shale, Thimble Limestone, Echo Shale, Gold Ace Limestone, Pyramid Shale, Red Pass Limestone, Pahrump Hills Shale,jangle Limestone, and Des- ert Range Limestone. The Lower—Middle Cambrian boundary falls within the lower part of the Pyramid Shale Member. The Thimble and Gold Ace Limestone Members are tongues of the Mule Spring Lime- stone of the Inyo Mountains region to the west. The younger parts of the formation are replaced to the west by predominantly thin bedded deeper water carbonate and clastic facies of the Emigrant or Monola Formations. Within the Carrara Formation, the sedimentary cycles are compared with Grand Cycles described from the southern Canadian Rocky Mountains. Each cycle begins with clastics and grades upward to in- creasingly clean carbonates before being terminated by an abrupt re- turn to clastic sedimentation. Carbonate rocks predominate in western and northwestern exposures of the formation and form tongues with diachronous bases and nearly synchronous tops that extend eastward into a region of predominantly clastic sedimentation. The carbonate sediments can be grouped into two subtidal lithofacies, lime mudstone and oolite, and one intertidal and supratidal lithofacies, an algal- boundstone lithofacies. The time and space relationships of these lithofacies, as well as comparisons with Holocene analogs, provide data to support the suggestion that Grand Cycles reflect changes in rates of subsidence within a miogeocline. Although the Carrara Formation is not richly fossiliferous, it contains the most complete representation of stratigraphically documented North American trilobite faunas that span the Lower—Middle Cambrian boundary. These trilobites represent part or all of four assemblage zones. The oldest faunas represent the upper part of the Olmellus Zone, and three locally useful zonules help to identify the lower part of the Eagle Mountain Shale and the Thimble Limestone Members and the lower part of the Pyramid Shale Member. The next younger “Plagium-Poliella” assemblage zone is poorly fossiliferous and is found in the upper part of the Pyramid Shale Member and lower part of the Red Pass Limestone Member. Trilobites from the upper part of the Red Pass Limestone Member to the lower part of the jangle Limestone Member represent the Albenella assemblage zone. These show the exis- tence of three contemporaneous biofacies with very few shared trilo- bites. A deeper water biofacies on the west is characterized by Ogygopsis; a rich shelf-edge biofacies is characterized by abundant representatives of the Zacanthoididae; and an eastern restricted shelf biofacies is characterized by low-diversity faunas including Albertella and Mexicella. The Desert Range Limestone Member includes trilobites from the lower part of the Glossopleura Zone. The biostratigraphic problems created by the spatial distribution of the trilobites are discussed. The trilobite fauna includes more than 95 species representing at least 38 genera. Special attention is given to problems of classification within the Olenellidae, Zacanthoididae, and some Ptychopariida. New taxa areBristolia anteros n. sp.,B.fmgilis n. sp., Olenellus arcuatm n. sp., 0. brachyomma n. sp., 0. cylindricux n. sp., 0. emypan'a n. sp., 0. multinadw n. sp., Peachella brevitpina n. sp., Poliella lomataspis n. sp., Oryctocephalus nymis n. sp., Albertella longwelli n. sp., A. spectrensis n. sp., Albertellina aspinosa n. gen., n. sp., Albertelloides rectimarginatus n. sp., Mexicaspis mdimm n. sp., Paralbertella n. gen., Ptarmiganoidex crassaxis n. sp., P. hexacantha n. sp., Zacanthoides variacantha n. sp., Caborcella pseudaulax n. sp., C. reducta n. sp., Elmthina antiqua n. sp., Eoptychoparia piochensis n. sp., Kochiellina groomensis n. gen., n. sp., K. janglmsis n. sp., Mexicella gmndoculus n. sp.,Nyella immodemta n. gen., n. sp.,Plagium extema n. sp., P. minor n. sp.,P. retracta n. sp., Syspacephalus longus n. sp., S. obscum n. sp., Volocephalina connexa n. gen., n. sp., and V. contracta n. sp. INTRODUCTION The Carrara Formation is a unit of heterogeneous, primarily marine sediments, averaging about 400 m in thickness, that forms the transition between pre— dominantly quartzitic Lower Cambrian rocks and pre- dominantly calcareous Middle and Upper Cambrian rocks in the southern Great Basin in southern Nevada and southeastern California (fig. 1). The formation in- cludes nine members, either of limestone or terrigenous clastic rocks, forming an intertonguing and interlayered complex whose time-space relationships are the subject of the physical stratigraphy part of this report, written by Halley. The formation ranges in age from late Early Cambrian through the early part of the Middle Cambrian Glossopleum Zone. Trilobites are the biostratigraphically important fossils in the formation and their systematics, biostratigraphy, and biofacies analysis are described by Palmer. Structurally uncomplicated sections through the Car- rara Formation are excellently exposed in many moun- 2 CARRARA FORMATION, SOUTHERN GREAT BASIN tain ranges in the southern Great Basin; a list of the places where sections of the Carrara Formation have been studied follows: Location Source Azure Ridge ......... Unpublished measured section by Art Richards, Ben Bowyer, and Robert Cohenour, March 7, 1957. Belted Range ........ This report; Ekren and others, 1971. Bare Mountain ....... Cornwall and Kleinhampl, 1961; measured sections by Bates, 1965. Cucomungo Canyon . . This report; Stewart, 1970. Delamar Mountains. . . Unpublished measured section by Allison R. Palmer, 1970. Dublin Hills .......... Measured section by Bates, 1965. Desert Range ........ This report; Stewart and Barnes, 1966. Echo Canyon This report; Hunt and Mabey, 1966; meas- (Funeral Mountains). ured sections by I. F. McAllister, unpub— lished data, 1963; Bates, 1965; and P. R. Rose, unpublished data, 1969. Eagle Mountain ...... This report; Stewart, 1970; measured sections by Bates, 1965. Frenchman Mountain . Pack and Gale, 1971. Goldfield Hills ....... Stewart, 1970. Groom Range ........ This report; Barnes and Christiansen, 1967. Highland Range ...... Merriam, 1964. Inyo Mountains ...... This report; Nelson, 1962, 1965. jangle Ridge ......... johnson and Hibbard, 1957; Barnes and Palmer, 1961; Barnes, Christiansen, and Byers, 1962. Last Chance Range . . . This report; Stewart, 1965. Las Vegas Range ..... This report; Stewart, 1970. Miller Mountain ...... This report; Nelson and Durham, 1966. Marble Mountains . . .. This report; Stewart, 1970; Hazzard and Mason, 1936. Nopah Range ........ This report. Northern Panamint Bates, 1965. Mountains. Southern Panamint Bates, 1965. Mountains. Paymaster Canyon . . . . This report; Albers and Stewart, 1962; Stewart, 1970. Pahrump Hills ....... This report; Bates, 1965. Pioche District ....... Merriam, 1964. Providence Mountains This report; Stewart, 1970; Hazzard, 1954. Pyramid Peak ........ This report. Northern Resting Bates, 1965. Springs Range. Southern Resting This report; Bates, 1965. Springs Range. Salt Spring Hills ...... Bates, 1965. Spectre Range ....... Burchfiel, 1964. Striped Hills ......... This report. Silurian Hills ......... Kupfer, 1960; Stewart, 1970. Sheep Mountain ...... This report; Hazzard and Mason, 1953. Spring Mountains . . . . This report. Titanothere Canyon .. This report; Reynolds, 1971; Bates, 1965. Ubehebe Crater ...... This report. Winters Pass ......... This report; Stewart, 1970. Study of the stratigraphy and faunas of the formation was begun in 1960 by Palmer in conjunction with prob- lems related to the mapping of Bare Mountain, Nev., by Cornwall and Kleinhampl (1961). At that time, brief re- connaissance visits were also made to the Nevada Test Site and to the Desert Range. Following a more extended series of visits to the Resting Springs Range, Eagle Mountain, Striped Hills, Groom Range, Desert Range, and Bare Mountain in 1961, enough material had been obtained to begin a preliminary study of the systematics of the trilobites. Further fieldwork in 1963 and 1964 included a study of sections in Titanothere Canyon, Echo Canyon, Cucomungo Canyon, the southern Last Chance Range, Dublin Hills, Salt Spring Hills, and Belted Range, in addition to revisiting some previously studied areas. This work established the basic regional stratigraphic framework of the Carrara Formation. Other activities interrupted study of the Carrara stratigraphy and faunas until 1969 when the study was resumed and expanded to include a detailed sedimentologic-environmental analysis. This assignment was undertaken by Halley with support from National Science Foundation Grant A020318 to Palmer. All major sections were remeasured during 1971 and 1972, and extensive samples for petrographic analysis were col- lected. All the stratigraphically controlled trilobite col- lections from earlier work have been placed in the con- text of Halley’s sections and are summarized on plate 17. The results of this joint effort at stratigraphic and paleontologic analysis of rocks and fossils of the Carrara Formation are documented in the remainder of this paper. The Carrara Formation was chosen for detailed sedimentologic—faunal analysis for several reasons. Re- gional paleogeography for the Cambrian of North America shows that, in general, a broad belt of generally shallow marine carbonate sediments occupied the outer part of the Cambrian continental shelf. This belt was flanked on its seaward side by silty clastics and dark siliceous thin-bedded carbonates presumably charac- teristic of deeper waters and on its landward side by predominantly shallow marine noncarbonate clastics. Together, these generalized lithofacies form sedimen- tary belts that have been designated as the Carbonate Belt and Outer and Inner Detrital Belts (Palmer, 1960, 1972; Robison, 1960). Only in the Carrara Formation is it possi- ble to analyze the depositional environments of indi- vidual units of the Carbonate Belt across the facies strike in sufficient detail to relate them to the environments in the adjacent Inner and Outer Detrital Belts and to a dynamic model that might explain their origin. Results of sedimentologic analysis show that the carbo- nate belt included carbonate islands near its oceanward (western) margin at specific times and that the vertical and lateral shifts in carbonate and noncarbonate lithofacies within the Carrara Formation most probably INTRODUCTION 118° 115° 1140 | / ) | I l CHURCHILL I LANDER 1 EUREKA \ 3 i i l //_______ _____ WHITE PINE l __7_,, \\ l I \\ 1 \ I \ \\ \ | \ l l MINERAL >\ I l / \ N Y E I I / \ I I UTAH / \ /AMi|ler MountaiN T°n°Pah J l 38° — / \ I_______.____— _— | ._ Paymaster A ‘ I . . . I Canyon Ploche Dlifl‘lct O | I . \\ E S M E R AL D A ‘ ’ Highland Range I \ GoldfieldA I LINCOLN ' \ Hills I Cucocrrai:ng: \\ i O Delamar I y \ , Mountains I A Inyo A Last\Chan|0e Range Jangle Ridge ~ l - I Mountains AU‘beh beCrater “9 [NYC IAzure 0 Ridge {as Vegaso . Frenchman Mountain) A ,M,\ I \ _ _ / V _ ‘S Re mg Springs Range 1 A No \ . Sheep ) Mountain \ \ ARIZONA \ I .\\ (I, \ C‘ “We: I NEVADA 460’s??? \ CALI- 427\ H FORNIA 0 Providence l Mountains \ ’ Area of recognition 1 Area of i: . figure 1 ARIZONA of Carrara Formation \ -‘— Eastern edge of Mesozoic l overthrusting—teeth on 0 Marble Mountains overthrust block .\ l N U 25 50 KILOMETERS l___L_~_J FIGURE 1.—Index map showing localities related to study of the Carrara Formation. Solid triangles, sections measured for this study; open triangles, sections examined but not measured in detail; solid circles, previously described and published sections, not remeasured: large open circles, unpublished sections by others, examined but not remeasured. 4 CARRARA FORMATION, SOUTHERN GREAT BASIN resulted from variable rates of basin subsidence. Lateral facies changes within members and repetition of similar lithologies among stratigraphically distinct members require that some biostratigraphic control be developed to assist with mapping problems in areas where the Carrara Formation has been faulted or where exposures are discontinuous. In addition to this practical problem, the Carrara Formation is the principal unit within which the biostratigraphic and biofacies relation- ships for the latest Early Cambrian and early Middle Cambrian trilobite faunas of Western United States can be worked out. The paleontological analysis shows that most of the members of the Carrara Formation have distinctive faunas or consistent stratigraphic relations to beds with such faunas so that they can be correctly iden- tified even when isolated by faults or poor exposure from the remainder of the formation. Strong environmental controls on the lateral distribution of some of the trilo- bites are also indicated so that a biostratigraphy com- prised of a single vertical succession of zones and sub- zones is not practicable. The principal environmental controls seem to have been water depth and contrasts in habitat related to the ocean-facing edge of the Carbonate Belt. ACKNOWLEDGMENTS The following US. Geological Survey personnel pro- vided guidance in the field, collections, or unpublished descriptions of the Carrara Formation during the 1960’s; their valuable help in accumulating the basic field data for the faunal collections is gratefully appreciated: Har- ley Barnes, Donald Hibbard, C. B. Hunt, Michael Johnson, C. R. Longwell, j. F. McAllister, M. W. Reynolds, and j. H. Stewart. E. W. Bates of the University of California at Los Angeles supplied a copy of his fine Master’s thesis (1965) on the stratigraphy and faunas of the Carrara Formation which provided supplemental data on faunal ranges for many Carrara sections. Trans- portation for a review of the principal Carrara sections was provided in 1969 by A. J. Rowell of the University of Kansas. All field and laboratory work prior to 1966 was supported by the US. Geological Survey. Work sub- sequent to that date has been supported by the facilities of the State University of New York at Stony Brook and by funds from National Science Foundation Grant A020318. Field assistance for Halley’s sedimentologic study was provided by Barbara Halley in 1971 and 1972 and by K. C. Lohmann in 1973. The many amenities provided to both Palmer and Halley by Mr. and Mrs. Phillip D. Pack of Las Vegas, Nev., are also gratefully acknowledged. STRATIGRAPHY OF THE CARRARA FORMATION The Carrara Formation was defined by Cornwall and Kleinhampl (1961) from the Bare Mountain quadrangle, Nevada. It was named for the ghost‘town of Carrara 13 km east—southeast of Beatty, Nev., from which marble quarries in the upper part of the formation were worked at the turn of the century. At Bare Mountain the typical section of the Carrara Formation is composed of 542 m of interstratified lime— stone and shale with minor amounts of quartzite, dolo- mite, and siltstone. The Carrara Formation lies strati- graphically above the Zabriskie Quartzite (identified as Stirling(?) by Cornwall and Kleinhampl ( 1961) and cor- rected in a footnote on the same map) and below the Bonanza King Formation. Cornwall and Kleinhampl recognized a predominantly clastic lower half of the Car- rara Formation and a carbonate upper half. Within the lower half three subdivisions were described: a lower unit of quartzite, sandstone, siltstone, phyllitic shale, and minor limestone; a middle unit of limestone alternating with shale and capped by a conspicuous cliff-forming “algal” limestone about 46 m thick; and an upper unit of fine-grained clastic rocks. The upper carbonate half of the Carrara Formation was subdivided into two units, the lowest unit being a series of broken cliffs Visible from a distance as a broad band of alternating white, orange, pink, and brown limestone, and the upper unit being a dark-gray limestone. The basal quartzites of the Carrara Formation were described as transitional with the un— derlying Zabriskie Quartzite, and the uppermost lime- stones of the Carrara Formation were described as gra- dational into the overlying Bonanza King Formation. The first published extension of the Carrara Forma- tion beyond its type locality was to the Yucca Flat area of the Atomic Energy Commission Nevada Proving Grounds (Barnes and others, 1962). This extension solved nomenclatural problems on the Nevada Test Site that had arisen from previous attempts to apply existing nomenclature derived from Pioche district, Nevada, (Iohnson and Hibbard, 1957) or from the Providence Mountains of California (Barnes and Palmer, 1961). Barnes, Christiansen, and Byers (1962) subdivided the Carrara Formation into seven units, placing the base of the formation at the base of the lowermost fissile shale above the massive quartzites of the Zabriskie. The top of the Carrara Formation was located above the highest argillaceous limestones that are transitional between the Carrara and the Bonanza King Formations. Quadrangle mapping by the US Geological Survey and various university thesis studies extended recogni- tion of the formation to the southern Nopah Range and the Resting Springs Range (Wilhelms, 1963), the Spectre STRATIGRAPHY OF THE CARRARA FORMATION 5 Barnes and m Humphrey Wheeler Johnson and Barnes and Cornwall and Christiansen This re ort .g (1945) (1948) Hibbard (1957) Palmer (1961) Kleinhampl (1961) (1967) p (g Burrows Chisholm Yucca Flat G Di72232226 Limestone Shale Formation (part) Member Jangle Jan le Jan le Peasley Lyndon Jangle Member Limesgt‘one Limesgone Limestone Limestone Limestone Member Member C C d' .‘2 - - a 'Z P hrum Hills 33 Chisholm Chisholm . a p Formation E Shale Shale E Shale Member 8 2 1: .25. Red Pass 2 Lyndon Lyndon Chambless L' Limestone Limestone Limestone D lmestone Carrara Member Formation Pyramid Tecopa C Shale Member Shale Gold Ace . , B Limestone c Pioche Pioche Latham Member ,9 Shale Shale Shale 2g Echo Shale Mbr 8 Thimble g A Limestone Mbr 3 Eagle Mountain Shale Member FIGURE 2.——Nomenclatural history of the rocks now included within the Carrara Formation. Range (Burchfiel, 1964), and the Pahrump Hills, Salt Spring Hills, Dublin Hills, Eagle Mountain, Funeral Mountains, Grapevine Mountains, and Panamint Mountains (Bates, 1965). Wright and Troxel (1966) rec- ognized the Carrara Formation in the Silurian Hills of California; Hunt and Mabey (1966) used this formation name throughout the Death Valley region; Stewart and Barnes (1966) reported the formation in the Desert Range of Nevada; and Stewart (1965) extended recogni- tion of the formation to the southern Last Chance Range of California. Barnes and Christiansen (1967) described the Carrara Formation in the Groom Range, Nev., super- seding the nomenclature derived from the Pioche district and used there by Humphrey (1945). Stewart (1970), in a regional study of the upper Precambrian and Lower Cambrian clastic rocks of the southern Great Basin, de- scribed the lower part of the Carrara Formation and its stratigraphic relationships to equivalent formations east and west of the Carrara outcrop area. Ekren and others (1971) described intervals in the Belted Range of the northern Nellis Bombing Range, Nye County, Nev., that are equivalent to and in part like the Carrara Formation but seem to be transitional between the Carrara Forma- tion and correlative strata to the west. The study area of this paper and the locations of sections discussed in the text are illustrated in figure 1. The history of the various stratigraphic nomenclatures applied to the Carrara For— mation and their relation to the present nomenclature are shown in figure 2. Surrounding the area in which the Carrara Formation can be identified are four areas that contain correlative strata that have been described and named (fig. 1). To the northeast, in the Highland Range and vicinity, units cor- relative with the Carrara Formation are the Pioche Shale, the Lyndon Limestone, and the Chisholm Shale (Mer- riam, 1964). To the east, in French Mountain and the Grand Canyon, the correlative rocks are the Tapeats Sandstone and the Bright Angel Shale (McKee and Res- CARRARA FORMATION, SOUTHERN GREAT BASIN é Southwest Nevada Marble Mountains, Inyo Mountains, Esmeralda County, Highland Range, Grand Canyon, 8 and adjacent areas California California Nevada Nevada Arizona Desert Range Chisholm Flour Sack Limestone Member Shale Member Meriwitica Tongue Jangle Lyndon Limestone Member Limestone 2 Tinca nebits Tongue 2 c (n .5 .‘5 § Pahrump Hills Emigrant U Shale Member Monola Formation (part) Cadiz Formation 3 2 Formation 2’ 1: A < .‘9 E c .2 E E Red Pass .. .2 Limestone Member f, 65 e a: S 36 5 5 B Pyramid Shale Member _———Susan Duster 7 Limestone Member . I) C 5 .7 .9 Combined 0- Metals Member Gold Ace Chambless g Limestone Member Limestone . Mule Spring 3 MU'B 59""9 Limestone g Limestone Tapeats 0 Echo Shale Sandstone _ Member 3 D 3 . Thimble Lama," Limestone Member Shale Eagle Mountain Saline Valley Saline Valley Shale Member Formation (part) Formation (part) FIGURE 3.—Members of the Carrara Formation and correlation with adjacent regions. ser, 1945); where the Lyndon Limestone is recognized at the top of the Bright Angel Shale (as at Frenchman Mountain), the overlaying shale is the Chisholm Shale, South of the Carrara area, the correlative strata are the Latham Shale, the Chambless Limestone, and the Cadiz Formation in the Providence and Marble Mountains of California (Hazzard and Mason, 1936; Hazzard, 1954; Stewart, 1970). Finally, to the northwest, stratigraphic units correlative with the Carrara Formation include part of the Saline Valley Formation, the Mule Spring Lime— stone, and the Monola Formation (Nelson, 1962, 1965), or the lower part of the Emigrant Formation (Albers and Stewart, 1962; Stewart, 1965). Details of correlation of members of the Carrara Formation with these forma- tions are discussed below and shown in figure 3. DESCRIPTION OF MEMBERS The basic data for this study are stratigraphic mea- surements and descriptions from 36 locations where the Carrara Formation or correlative strata are exposed. Subdivision of the Carrara Formation is based on 23 sections which lie within the area in which the formation is typically developed (fig. 1). Nine members can be recognized within the Carrara Formation over most of the study area. They are, in ascending order: Eagle Mountain Shale Member, Thim- ble Limestone Member, Echo Shale Member, Gold Ace Limestone Member, Pyramid Shale Member, Red Pass Limestone Member, Pahrump Hills Shale Member, jangle Limestone Member, and Desert Range Limestone DESCRIPTION OF MEMBERS 7 Member (fig. 3). In addition to these members, a quartz- itic unit formerly included within the Carrara Formation is here designated as the Emigrant Pass Member of the underlying Zabriskie Quartzite. All contacts between members appear to be conform- able although the tops of some limestone members, where they are represented by supratidal lithologies, must represent hiatuses. Most of the members represent tongues from formations that surround the Carrara Formation. Their regional relationships are shown schematically in figure 11 and will be clarified during the following discussions of individual members. EMIGRANT PASS MEMBER OF THE ZABRISKIE QUARTZITE Cornwall and Kleinhampl (1961) included a transition zone above the Zabriskie Quartzite in the base of the Carrara Formation. This unit is primarily quartzite and sandstone with minor amounts of siltstone and phyllitic shale. Stewart (1970) placed the lower contact of the Carrara Formation at the lowermost occurrences of siltstone, phyllitic siltstone, and shale above massive Vit- reous quartzite of the Zabriskie. He suggested that this contact is sharp and well defined although the quartzites above the contact are very much like the Zabriskie Quartzite. The quartzite and shale transition interval is here named the Emigrant Pass Member for exposures at its type locality in the southern Nopah Range (fig. 1), north of Emigrant Pass, NW1 sec. 25, T. 21 N., R. 8 E., Tecopa quadrangle, California. The Emigrant Pass Member is recognized in 18 of the sections considered in this study; it varies in thickness from 0 to 51 m. In many eastern sections, the Emigrant Pass Member has a distinctive unit of maroon, brown, and yellow mudstone and shale in its lower 2—15 m. This unit is locally sandy or silty, and contains chamosite grains in some sections. In western sections the lowermost shales within the Emigrant Pass Member are pale-green phyl- litic shales interbedded with siltstones and quartzites. Overlying the shaly unit is the orthoquartzitic remainder of the member, a medium-bedded, pink, white, or pale- green quartz arenite. Usually, beds of this unit are com- posed of single sets of laminated or low—angle crossbeds. Most beds are moderately well sorted; maximum grain sizes are medium to coarse sand and vary from bed to bed. Siltstone interbeds occur between quartzite beds. The upper unit of the member varies in thickness from 0—30 In over the study area. In thin section the quartzites are composed of well— rounded monocrystalline quartz grains with few poly- crystalline grains (figs. 4D—F). Smaller, less-rounded grains form supporting matrices of some samples. The quartz wackes of the shaly intervals contain chamosite, mica, and calcite in their matrix (figs. 43, 4C , 4E, 4F). Mudcracks occur in the upper half of the member from the Desert Range to the southern Last Chance Range (fig. 4A). Adjacent sets of crossbeds occasionally dip in opposite directions. At Cucomungo Canyon and in the Last Chance Range, stromatolites and bird’s-eye limestones immediately overlie this member. These lim— ited observations suggest intermittent exposure and perhaps intertidal deposition for parts of this member. An isopach map of this unit would probably not reflect its true geometric shape because of major difficulties in placement of the base of the member. This problem becomes apparent when measurements of the member taken by different workers at the same locality are com- pared. The section at Echo Canyon has been measured on at least four occasions. The thickness of the Emigrant Pass Member has been variously reported as 20 ft by Hunt and Mabey (1966), 70 ft by]. F. McAllister (unpub. data, 1963), 101 ft by Bates (1965), and 106 ft by P. R. Rose (unpub. data, 1969). This last measurement was confirmed by Halley in 1972. Because the highest quartzite bed in the section is an unmistakably prominent bed with more than a hundred meters of shales and limestones overlying it, the discrepancies of measure- ment obviously lie in the choice of a base for the section. Because quartzites of the Emigrant Pass Member are indistinguishable from the main body of the Zabriskie Quartzite, recognition of the Zabriskie—Carrara contact in earlier work has depended on recognition of shales or mudstones at the base of the Emigrant Pass Member. Where the shales or mudstones are not present or ex- posed, or where there is a considerable thickness of inter- bedded shales and quartzites, the assignment of quartzites to either the Carrara or the Zabriskie has been arbitrary. Stewart (1970) found these difficulties in iden- tification of the formational contact in the Groom, Des- ert, and Las Vegas Ranges, and at sections south of Win- ters Pass. Geographic limitations on stratigraphic nomenclature also obscure the regional relationships of the Emigrant Pass Member. For example, at Cucomungo Canyon in the northern Last Chance Range, Calif, the Carrara Formation and Zabriskie Quartzite are not recognized and their partial equivalents are the Saline Valley For- mation, the Mule Spring Limestone, and the Emigrant Formation (Stewart, 1970). The nomenclature from the Inyo Mountains of California was used in this area be- cause the Cambrian section was believed to have more in common with the stratigraphies from that region and Esmeralda County, Nev., t0 the west and north, than with the Carrara Formation to the east. However, several intervals at Cucomungo Canyon have direct counterparts within the Carrara Formation in the southern Last CARRARA FORMATION, SOUTHERN GREAT BASIN FIGURE 4.—Some lithologic features of the Emigrant Pass Member of the Zabriskie Quartzite. A, Outcrop of mudcracks in rippled upper surface of the Emigrant Pass Member, Desert Range section, Nevada. B, Photomicrograph of well-rounded, poorly sorted sandstone containing large dark chamosite grains (pelletSP). Some of the chamosite grains contain a significant portion of quartz silt. Matrix is predominantly clay minerals. Bottom of Emigrant Pass Member, Resting Springs Range section, California. C, Photomicrograph of orthoquartzite (quartz arenite), poorly sorted; larger grains are well rounded; dark minerals and grain rims are iron oxide, which gives rock a pink coloration in outcrop. Bottom of Emigrant Pass Member, Echo Canyon section, California. D, Different view of same thin section as C, here with nicols crossed. E, Photomicrograph of very fine grained sandstone consisting almost entirely of monocrystalline quartz grains in a carbonate and clay matrix. Uppermost part of Emigrant Pass Member, Echo Canyon section, California. F, Photomicro- graph of siltstone composed of predominantly quartz and dolomite with minor amounts of calcite and feldspar. Uppermost part of Emigrant Pass Member, Echo Canyon section, California. DESCRIPTION OF MEMBERS 9 Chance Range 21 km to the southeast. In particular, the upper beds of the Saline Valley Formation have their counterpart in the Emigrant Pass Member in the south- ern Last Chance Range. The Emigrant Pass Member is here removed from the Carrara Formation to become the uppermost member of the Zabriskie Quartzite because the member is lithologi- cally more like the underlying Zabriskie than the overly- ing Carrara. Also, the depositional environment of the member may resemble that of the Zabriskie Quartzite which is also at least in part intertidal in origin (Barnes and Klein, 1975). Finally, the contact between the Zabris- kie Quartzite and the Carrara Formation is more con- sistent when set at the top of the last prominent quartzite bed below the thick shales or limestones of the Carrara Formation. This change precludes the necessity of hav- ing to assign transitional beds arbitrarily to either the Carrara Formation or the Zabriskie Quartzite when the lower shaly unit of the Emigrant Pass Member is either absent or not exposed. l MEMBERS OF THE CARRARA FORMATION Figures 5 and 6 show the areal distribution and re- gional changes in thickness of each of the members of the Carrara Formation. Their individual lithological and faunal characteristics are discussed on the following pages. EAGLE MOUNTAIN SHALE MEMBER The Eagle Mountain Shale Member comprises the first major shale and siltstone accumulations above the mas— sive quartzites of the Zabriskie and is here considered to be the basal member of the Carrara Formation. It is named for its thickest development at its type locality on the west side of Eagle Mountain, Inyo County, Calif. (fig. 5A). The Eagle Mountain Shale Member is typically a green to gray-brown, slope-forming, silty shale. Locally, ma- roon color is related to obvious oxidation zones along fractures. Interbedded with the shale are thin beds (1—10 cm) of terrigenous or carbonate silt- and sand-size mate- rial. The quartz sand interbeds are usually lenses a few meters in length. One 8-cm—thick graded bed occurs at Echo Canyon and has coarse sand and granules at the base. Such terrigenous elastic interbeds are more com- mon at the base of the member. In the upper half of the Eagle Mountain Shale Member carbonate interbeds pre- dominate. These are again lensoidal and thin bedded and consist of echinoderm and trilobite fragment packstones with a muddy carbonate and terrigenous matrix. Occa- sional “floating" quartz sand occurs in these limestone interbeds. Typical lithologies of the Eagle Mountain Shale Member are illustrated in figure 7. The upper contact of the Eagle Mountain Shale Member is placed at the base of the first limestone ledges greater than 0.5 m thick in the Carrara Formation and is readily recognized in most sections of the formation. The Eagle Mountain Shale Member is almost twice as thick at Eagle Mountain as at any other section. It is not recog- nized in the Nopah Range because the overlying Thimble Limestone Member is missing and the Eagle Mountain Shale Member cannot be separated from the Echo Shale Member. Farther to the east and north, beds that corre- late with the Eagle Mountain Shale Member lie in the upper Tapeats Sandstone at Frenchman Mountain, the Latham Shale in the Marble Mountains, and the Pioche Shale at Pioche, Nev. (fig. 3). Westward, in the southern Last Chance Range, the Eagle Mountain Shale Member is replaced by limestone assigned to the lower part of the generally overlying Thimble Limestone Member. The lowermost limestone unit here assigned to the Thimble Limestone Member lies directly upon the Zabriskie Quartzite. These lime- stones consist of stromatolitic bioherms that are well laminated only in their lower parts. The laminated parts of the bioherms are as much as 20 cm high and 30 cm wide, but the bioherms as a whole are 2 m wide and as much as 0.5 m high. Individual bioherms are separated by thin-bedded pelloidal calcarenite. Two other types of limestones occur higher in the part of the Thimble Limestone Member that is correlative with the Eagle Mountain Shale Member at this locality. These are an unusual pisolite bed and a thin-bedded fine—grained pre- sumed pelletal calcarenite with ripple marks, microcross-laminations, and rare trilobite and oncolite grains. The latter limestone lithology is typical of the remainder of the Thimble Limestone Member here and throughout the region. At Cucomungo Canyon in the northern Last Chance Range, the Carrara Formation was not recognized by Stewart (1971), and beds correlative with the Eagle Mountain Shale Member are included in the upper few meters of the Saline Valley Formation (fig. 3). Farther to the northwest, at Paymaster Canyon, this interval is not recognizable and the transition to the stratigraphy of the White-Inyo Mountain region is complete. FAUNAL CHARACTERISTICS This member is generally poorly fossiliferous. In the Titanothere Canyon and Echo Canyon sections, green micaceous siltstones in the basal few meters of the member have yielded two olenellid species, Olenellus ar- cuatus n. sp. and 0. cylindricus n. sp., which characterize the 0. arcuatus Zonule, and 0. nevadensis (Walcott), which 10 118° 116° 1 38° a \ Ifaofi. ”0‘ .u u 0 ' " . . l0 CC". 27 I"? /_-J 0-“ :LC \ l 8 ' JAR M (A 00! 0‘ I I" .792 e / _ I_2 30 l '-Pgn(s) 20‘”) ' 0 SM Sm. ww 36° » A .PM \\ 115° 1 38° W .7‘2-._ \ .. ........ .ul"\\ .GR O \ 30 100 \160'-_\D‘ .. oJR \ E29;— \00 0’1 (9 (TI 0 'l r- n / Member n t recognizable 36° s'u 1‘ A \ K ARIZONA \ \ \ C \\ 1 7 \3/ NEVAoA iumn Member not recognizable l \ \\ K ARIZONA 1 \\ J 1 ’"" \ u s \ 116° T’ 1 I 1 \ NEVADA [UTAH 1 1 CARRARA FORMATION, SOUTHERN GREAT BASIN 114° 118° 115° 1 1 I 1 \ NEVADA \ O l 0 1 l Dfi gang‘s" I2 NR \ Member not recognizable a 36° o l SM 1 \ \\ K ARIZONA \ I .MM \ 1 l \ NEVADA lUTAH I 1 36° 1 'M” \ 1 0 50 100 1 l 1 FIGURE 5.—Isopach maps of the shale members of the Carrara Forma- tion. A, Eagle Mountain Shale Member; B, Echo Shale Member; C, Pyramid Shale Member; D, Pahrump Hills Shale Member. Contour interval, 10 m forA, 20 m for B, C, and D. AR, Azure Ridge; BeR, Belted Range; BM, Bare Mountain; CC, Cucomungo Canyon; DH, Dublin Hills; DR, Desert Range; EC, Echo Canyon; EM, Eagle Mountain; FM, Frenchman Mountain; GR, Groom Range; In, Inyo Mountains; JR,Jangle Ridge; LC, Last Chance Range; LR, Las Vegas Range; MM, Marble Mountains; PaR (S), Southern Panamint Moun- .MM \ 150 200 250 KlLOMETEHS | 1 tains; PC, Paymaster Canyon; PH, Pahrump Hills; PM, Providence Mountains; PP, Pyramid Peak; RS (N), Northern Resting Springs Range; RS (8), Southern Resting Springs Range; SaH, Salt Spring Hills, SH, Striped Hills; SiH, Silurian Hills; SM, Sheep Mountain; SpM, Spring Mountains; TC, Titanothere Canyon; WiP, Winters Pass. Compare area and section localities in figure 1. Dotted line encloses area of recognition of Carrara Formation; sawtooth line, eastern edge of Cretaceous overthrusting (teeth on overthrust block). DESCRIPTION OF MEMBERS 11 118° 116° 114° 118° 115° 114° 1 1 I 1 | 1 I | 38°~— ~ 38°— — 6.4PC I 8.5”: I 6 ' \ / ' NEVADA UTAH / NEVADA UTAH \\ 10%o 50 la \ 39R .0!oou.....--"" . / cc.3- I / I Ioo/cc' -. I //:L'c \\ O 0 6// ° a \/ 'EI§_'L’I‘// '-, EMRs‘m) _\/D.:.Rs.(s) \ 0 °- § NR 0 36 _ -P_aR(S) L 36 — "a...” Said .0 '°.. SiH CALIFORNIA A 1 1 1 113° 115° 118° 115° 114° 1 I I I I | I I 38° — 1 _ 33° _ _ I NEVADA ' \ I \ 67 I UTAH \ NEVADA I UTAH \ _.....a.B.R .._ .----- .. 55,511 | \\\‘E<§R'-. I 107 ' I R I 0"L.C \ OJ 3. 0° — l :,\ 8§\ 5 1100 3 Tc 8 I23 8060 '1 5c \ 5'le '1 PP 83:11:11 '1. M \ '. 55.RS($) 43 ) 1, 5611's \ 36 _ "P113361 '2 — 35 — -. \ 1 CALIFORNIA “”4 \K CALIFORNIA C | \\ D . MM I I \ 1 | 1 1|) 510 190 150 21110 2130 KILOMETERS I FIGURE 6.—Isopach maps of the limestone members of the Carrara Formation. A, Thimble Limestone Member; B, Gold Ace Limestone Member; C, Red Pass Limestone Member; D, Jangle Limestone Member. Contour interval, 10 m for/1, 20 m forB, C, and D. Abnor- mal thinness of the Thimble and Gold Ace at Titanothere Canyon (TC) may indicate obscured faulting near the base of the section. AR, Azure Ridge; BeR, Belted Range; BM, Bare Mountain; CC, Cucomungo Canyon; DH, Dublin Hills, DR, Desert Range; EC, Echo Canyon; EM, Eagle Mountain; FM, Frenchman Mountain; GR, Groom Range; In, Inyo Mountains; JR, Jangle Ridge; LC, Last Chance Range; LR, Las Vegas Range; MM, Marble Mountains, PaR (S), Southern Panamint Mountains; PC, Paymaster Canyon; PH, Pahrump Hills; PM, Providence Mountains; PP, Pyramid Peak; RS (N), Northern Resting Springs Range; RS (8), Southern Resting Springs Range; SaH, Salt Spring Hills; SH, Striped Hills; SiH, Silu- rian Hills; SM, Sheep Mountain; SpM, Spring Mountains, TC, Titanothere Canyon; WiP, Winters Pass. Compare area and section localities in figure 1. Dotted line, area of recognition of Carrara Formation; sawtooth line, eastern edge of Cretaceous overthrusting (teeth on overthrust block). 12 CARRARA FORMATION, SOUTHERN GREAT BASIN FIGURE 7.—Outcrops, vertical-cut surfaces, and thin sections showing some of the features of the Eagle Mountain Shale Member. A, Water-smoothed outcrop surface. The white lenses are fine sand or silt, the medium-gray matrix is argillite, and the dark band under the hammer handle is a carbonate-cemented siltstone. Middle part of the Eagle Mountain Shale Member, southern Last Chance Range section, California.B, vertical-cut surface showing incomplete mudcracks in siltstone. Base of the Eagle Mountain Shale Member, southern Last Chance Range section, California. C, Photomicrograph of carbonate-cemented siltstone composed of quartz, feldspar, and pyrite. Middle part of the Eagle Mountain Shale Member, Echo Canyon section, California. D, Photomicrograph of sandy shale containing very fine grains of quartz and chlorite and trilobite skeletal fragments. The elongate skeletal fragment near the base of the photomicrograph has been partly replaced by quartz and chlorite. Base of the Eagle Mountain Shale Member, Titanothere Canyon section, California. E, Photomicrograph of silty shale with quartz silt scattered throughout a clay mineral matrix. Eagle Mountain Shale Member, Daylight Pass section, California. F, Photomicrograph of quartz wacke, medium-sized quartz sand in a matrix of clay minerals and quartz silt, from a graded sandstone bed. Central part of the Eagle Mountain Shale Member, Echo Canyon section, California. DESCRIPTION OF MEMBERS 13 is also found in the Bristolia Zonule in the overlying Thimble Limestone Member. Locally, thin limestone interbeds in the upper part of the member yield rep- resentatives of the Bristolz'a Zonule, which characterizes the overlying Thimble Limestone Member. THIMBLE LIMESTONE MEMBER This member conformably overlies the Eagle Moun- tain Shale Member. It is overlain by the Echo Shale Member, and is recognized throughout the area indi- cated in Figure 6A. This unit is best exposed at its type locality on the west side of Titanothere Canyon (fig. 1), below Thimble Peak from which its name is derived, in the Grapevine Mountains, Calif. The Thimble Limestone Member is characterized by black, brown, and orange thin-bedded argillaceous dolomitic limestone which varies in argillaceous content throughout the study area. The base of the member is placed at the base of the first limestone ledge in the Carrara Formation thicker than 0.5 m. Typically, lime- stones of the member are bedded on the scale of 1-10 cm. Each bed is a couplet consisting of a lower dark-gray limestone part and an upper orange argillaceous or dolomitic part. The lower part of each couplet contains trilobite debris, quartz silt, and argillaceous orange “rip-up” limestone or dolomite pebbles. In the Striped Hills and Resting Springs Range each couplet is a graded bed, the lower gray part consisting of a fine calcarenite that overlies an erosion surface and grades into the over- lying orange argillaceous upper part. Small-scale current structures are common. In the eastern sections the limestones are relatively barren of fossil debris, but onco— lite, hyolithoid, echinoderm, and trilobite fragments be- come more common northwestward. Oolite grainstones are interbedded in this unit in the southern Last Chance Range and at Titanothere Canyon, and in correlative beds within the Cucomungo Canyon and Paymaster Ca- nyon sections; at Paymaster Canyon this interval also contains pelletoid fenestral limestones. At Echo Canyon in the Funeral Mountains the member contains a bed of low-relief stromatolites. These are subovate—in plain view, 20—30 cm long, 3—5 cm high—and are composed of a well—laminated continuous exterior and a discontinuous “digitate” interior. The Thimble Limestone Member is an extremely widespread, relatively thin unit throughout most of the Carrara Formation. It is absent in the northern Resting Springs Range and sections to the southeast (fig. 6A) and reaches a thickness of more than 50 m in the north and west. At Paymaster Canyon and Cucomungo Canyon, the thickness of apparently correlative beds within the Mule Spring Limestone is estimated conservatively at more than 50 m. The eastward correlatives of the Thimble Limestone Member are clastic sediments which lie in the Tapeats Sandstone at Frenchman Mountain, the Pioche Shale of the Delamar and Highland Ranges, and the Latham Shale of the Marble Mountains. FAUNAL CHARACTERISTICS This member typically has abundant and diverse olenellid trilobites and rare associated ptychopariid trilo- bites which characterize the Bristolz'a Zonule. Locally, as many as nine distinct olenellid species have been recov- ered from a few meters of beds. The total known fauna includes: Bristolia anteros n. sp., B. bristolensis n. sp., B. fragilis n. sp., Olenellus clarki (Resser), 0. emyparia n. sp., O.fremonti? (Walcott), 0. howelli? Meek, O. puertoblancoen- sis (Lochman), Peachella brevispina n. sp., P. iddingsi (Wal- cott), and two undetermined species of ptychopariid trilobites. ECHO SHALE MEMBER This member is a green micaceous platy shale that separates the Thimble and Gold Ace Limestone Mem- bers of the Carrara Formation. It is named for exposures at the “Narrows” of Echo Canyon, its type locality (fig. 1), and is separately recognized only where both overlying and underlying limestone members are present. This unit is similar to the Eagle Mountain Shale Member, although somewhat more calcareous and at some localities consisting of interbedded shale and limestone. The more calcareous intervals are brown or orange. This member becomes more silty in the Desert Range and Jangle Ridge sections. The geometry of the Echo Shale member resembles that of the earlier Eagle Mountain Shale Member in that it thins northwestward from the maximum thickness in the Striped Hills area (fig. 5B). To the northwest this shale thins to zero at Paymaster and Cucomungo Can- yons and is represented by an argillaceous interval of the Mule Spring Limestone. The eastward equivalents of the Echo Shale Member lie in the Tapeats Sandstone at Frenchman Mountain, the Pioche Shale of the Delamar and Highland Ranges, and the Latham Shale of the Mar— ble Mountains (fig. 3). FAUNAL CHARACTERISTICS This member is generally unfossiliferous. A single col- lection from the Titanothere Canyon section in the Grapevine Mountains yielded a few specimens identified as Olenellus clarki (Resser) and Olenellus sp. undet. 1. GOLD ACE LIMESTONE MEMBER This name is applied to the “conspicuous dark—gray cliff-forming algal limestone” (Cornwall and Kleinhampl, 1961) at the top of the second unit from the bottom of the Carrara Formation in the canyon 0.8 km 14 northwest of Carrara Canyon, near the Gold Ace mine, Bare Mountain quadrangle, Nye County, Nev. (the type section of both the Carrara and the Gold Ace). It is primarily a burrowed oncolitic lime mudstone that be- comes increasingly argillaceous toward the east and in- creasingly “clean” toward the west. The lower contact is somewhat gradational with the underlying Echo Shale Member through a series of argillaceous limestones. The contact with the overlying Pyramid Shale Member is very sharp. The bulk of the Gold Ace Limestone Member is a microspar limestone, presumed to have been a lime mudstone or a pelleted lime mudstone when deposited. Although this unit forms massive cliffs where it is thick, it is composed of thin- to medium—bedded limestones de- fined by irregular slightly argillaceous dolomitic bur- rowed horizons. In contrast to the Thimble Limestone Member, most of the upper part of the Gold Ace Lime- stone Member does not separate along the boundaries of these thin beds (because they are not as argillaceous) and does not weather into flaggy or platy pieces. The monotony of the extremely homogeneous lime mudstone is interrupted by a variety of burrows, both open (calcite spar filled) and sediment filled, by recrystal- lized and unrecrystallized oncolites, and by sparse skeletal wackestone and mudstones. The burrow mot- tling and the frequency of skeletal fragments and onco- lites increase northwestward, within the study area, and also southeastward, beyond the study area, in the Chambless Limestone of the Providence and Marble Mountains. Dolomite normally accounts for less than 15 percent of the Gold Ace Limestone Member. It is con- fined largely to some burrows, some oncolites, and some irregular coarsely crystalline patches of calcite. At Paymaster Canyon, the upper 50 m of the Mule Spring Limestone, the westward correlative of the Gold Ace Limestone Member, is dolomite. Although dolomiti- zation has obliterated many of the primary depositional features of this interval, oncolites, skeletal fragments, and some seidmentary structures, such as small crossbeds and fenestral fabrics, can be recognized. This partly dolomitized section is important because it and the sec- tion in the Goldfield Hills area are the only places where peritidal lithologies occur in beds correlative with the Gold Ace Limestone Member. A minor amount of oolite also occurs in the base of the interval at Paymaster Can- yon that is correlative with the Gold Ace Limestone Member. In eastern sections the Gold Ace Limestone Member thins and pinches out. Concomitant with this thinning is an increase in the terrigenous content of the limestone, a change in color from the usual dark gray or black to orange brown, and a change in weathering to a rubbly ledge-forming limestone. CARRARA FORMATION, SOUTHERN GREAT BASIN The Gold Ace Limestone Member is absent in the Pahrump Hills and the Resting Springs Range in the eastern part of the outcrop area of the Carrara Forma- tion and in the Belted Range to the north. It thickens northwestward across the study area (fig. 6B), and cor- relative parts of the Mule Spring Limestone in Paymaster Canyon, Cucomungo Canyon, and the Inyo Mountains are more than 80 m thick. In other areas, beds approxi- mately correlative with the Gold Ace Limestone Member are the Combined Metals Member of the Pioche F orma- tion in the Delamar and Highland Ranges, the Chambless Limestone of the Marble and Providence Mountains, and the uppermost beds of the Tapeats Sandstone at Frenchman Mountain. Fieldwork in 1975, however, proved that trilobites of the Olenellus multinodus Zonule occur in the upper beds of the Combined Metals Member of the Pioche Formation in the Delamar Range and that the top of this member is thus slightly younger than the top of the Gold Ace Limestone Member. FAUNAL CHARACTERISTICS Although this member is moderately fossiliferous, it rarely yields identifiable specimens. Fragments of trilo- bites can be seen on many weathered surfaces, but only two small collections, both from the Titanothere Canyon section of the Grapevine Mountains, were obtained. One included only Olenellus puertoblancoemzls (Lochman) and 0. howelli? (Meek), one of two species pairs recognized within the olenellid assemblages of the Carrara Forma- tion. The other included only fragments of an un- described olenellid with unusual granular surface or- namentation, Olenellus sp. undet. l. PYRAMID SHALE MEMBER This member is named for exposures at its type local— ity, the west base of Pyramid Peak (fig. 1) in the Funeral Mountains, Calif. It overlies the Gold Ace Limestone Member and underlies the Red Pass Limestone Member. Where the Gold Ace Limestone Member is absent, the Pyramid Shale Member is inseparable from the Echo Shale Member. The member is primarily a green shale interbedded with brown and maroon siltstone and shale with minor amounts of quartzite and limestone. It is generally more shaly toward the base and more silty toward the top. Throughout much of the study area the base of the member is a fossiliferous fissile green and brown mica- ceous shale (fig. 8A). The predominant fossils are dis- articulated and rarely complete trilobites scattered on bedding surfaces. Some beds of bioclastic debris occur in this lower part. These are accumulations of transported or winnowed trilobite and echinoderm debris forming DESCRIPTION OF MEMBERS FIGURE 8.—Outcrops, float blocks, and thin sections showing some of the lithologic features of the Pyramid Shale Member or correlative beds. A , Photomicrograph of micaceous shale. Basal part of the Pyramid Shale Member, Titanothere Canyon section, California. B , Float block of well-indurated normally green shale (light gray) which has been oxidized in a pattern of red Liesegang-like rings (dark gray). Lower half of the Pyramid Shale Member, Titanothere Canyon section, California. C, Photomicrograph of micaceous siltstone with mica grains parallel to the horizontal and quartz silt set in a clay matrix. Middle part of the Pyramid Member, Striped Hills section, Nevada. D, Photomicrograph of siltstone composed of quartz and dolomite grains with minor feldspar from the Cadiz Formation, Providence Mountains, Calif.E , Outcrop of thin lensoidal siltstone beds interbedded with micaceous shale. One bed thins to the left beneath the hammer handle. Upper part of the Pyramid Shale Member, Pahrump Hills section, Nevada. F, Flute casts on the base of a siltstone float block. Upper part of the Pyramid Shale Member, Pahrump Hills section, Nevada. 15 16 CARRARA FORMATION, SOUTHERN GREAT BASIN lenses of argillaceous packstones or grainstones. Higher in the member, brown siltstones and maroon shales be- come more abundant. The maroon coloration appears to be secondary and forms Liesegang-like rings of red and green on some of the shales (fig. 83). The siltstone beds are usually lensoidal (fig. 8E), but some occur as more continuous beds. Two such continuous beds, one in the southern Resting Springs Range and one in the southern Nopah Range, display structures believed to be down- slope slump fold indicative of penecontemporaneous de— formation. Two blocks of graded siltstone from this member showing flute casts (fig. 8F) were found as float at Pahrump Hills. The slump folds and flute casts are slight evidence for some depositional slope in this area during deposition of this member. Bioturbation in- creases in the silty upper part of the Pyramid Shale Member but does not become sufficient to homogenize the sediment. Some typical burrows from this member are illustrated in figures QB and 9C. Thickness variations in this member are shown in fig— ure 5C. The member thickens northeastward, largely due to the development of an ochre mudstone at the top of the member at the Groom Range and the Belted Range. The upper silty part of the member becomes finer to the west and is absent in the southern Last Chance Range. The member thins toward the west and northwest as do the underlying Echo and Eagle Mountain Shale Members. The westward correlative of this member is the shale interval at the base of the Monola and Emigrant Forma- tions (fig. 3). At Paymaster Canyon a thin layer of coarse-grained carbonate-cemented quartz sand overlies the Mule Spring Limestone. It occurs nowhere else in the base of the Pyramid Shale Member or its correlatives. To the east, beds correlative with the Pyramid Shale Member probably include maroon and green sandstone and shale intervals within the lower part of the Bright Angel Shale described by Pack and Gayle (1971) from Frenchman Mountain, the C-shale member of the Pioche Shale in the Highland Range, and the lower part of the Cadiz Forma- tion in the Providence and Marble Mountains. FAUNAL CHARACTERISTICS Throughout the area of outcrop of the Carrara For- mation, the lower 10 m of this member, or correlative FIGURE 9.—Tracks, trails, and burrows from the upper part of the } Pyramid Shale Member, Titanothere Canyon section, California. A , Casts of sziana-like arthropod feeding or locomotion trails pre- served on the underside of a siltstone block. B, Cast of hook-shaped horizontal burrow preserved on the underside of a siltstone lens. C, Casts of subhorizontal burrows preserved on the underside of a siltstone bed. DESCRIPTION OF MEMBERS 17 beds in the east where the underlying Gold Ace Lime- stone Member is absent, contain the distinctive associa- tion of olenellids characteristic of the Olenellus multinodus Zonule. This fauna typically includes four species: Olenellus clarki (Resser), 0. fremonti Walcott, O. gilberti (Meek), and 0. multinodus n. sp. Rare ptychopariid trilo- bites and Olenellus brachyomma n. sp. have also been found in the lower part of this member. Olenellus multinodus n. sp. has been found at Frenchman Mountain in the basal part of the Bright Angel Shale in association with the unusual olenellid Bicemtops nevadensis Pack and Gayle (1971). The remainder of this member is generally un- fossiliferous. However, in the western sections, in the Groom and Belted Ranges, a thin limestone unit in the middle of the member has yielded the earliest Middle Cambrian trilobites found within the Carrara Formation. These constitute the Poliella lomataspis Zonule and in- clude Poliella lomataspis n. sp. and undetermined kochas- pid trilobites. Shales immediately overlying this lime- stone in the Belted Range yielded Syspacephalus longus n. sp., Oryctocephalus nyensis n. sp., and Pagetia sp. Aside from those occurrences only a single specimen question- ably identified as Mexicella? stator (Walcott) was found on a float piece from the middle part of this member in the Titanothere Canyon section in the Grapevine Mountains. RED PASS LIMESTONE MEMBER This member overlies the Pyramid Shale Member con- formably and is the only limestone member of the Car- rara Formation that has no limestone correlatives in sur— rounding areas. The member was named by Reynolds (1971) for Red Pass, about 1 km east of the Titanothere Canyon section (fig. 1), the type locality for the member, in the Grapevine Mountains, Calif. The Red Pass Limestone Member generally forms a prominent cliff and consists of burrowed, oncolitic, and skeletal-fragment lime mudstones, oolite, and a variety of laminated lime mudstones and fenestral limestones. The oncolitic or skeletal-fragment lime mudstones are identi— cal to those in the Gold Ace Limestone Member, but much less abundant. Oolite, however, is much more abundant in this member and comprises the bulk of the member in eastern sections. The laminated lime mudstone and fenestral limestones form a relatively thin cap of very light gray or white limestone at the top of this member in western sections. In more easterly sections the lime mudstones and oolites of the Red Pass Limestone Member are interbedded with green and brown calcare- ous Shales, and the member forms a less prominent fea- ture. The base of the Red Pass Limestone Member is placed at the first limestone bed 0.5 m thick or thicker above the Pyramid Shale Member. This somewhat arbitrary contact generally defines the base of the limestone body although some shale beds may lie above it. The upper contact is placed at the abrupt limestone-shale or limestone- siltstone contact with the overlying Pahrump Hills Shale Member in many centrally located sections, such as Pyramid Peak, Titanothere Canyon, Echo Canyon, and the Desert Range. In western sections, such as the south- ern Last Chance Range, the upper boundary is put at the contact between the clean cliff-forming limestones of the Red Pass Limestone Member and overlying argillaceous recessive-weathering limestones of the Pahrump Hills Shale Member. The thickness of the Red Pass Limestone Member shows a general increase toward the northwest (fig. 6C) comparable to the limestone members lower in the sec- tion. The member is present in every section of the Car- rara Formation, but it is absent to the east at Sheep Mountain, Frenchman Mountain, and Azure Ridge, and it is not clearly developed to the northeast in the Delamar and Highland Ranges. Southward, a single 1-m-thick oolite bed in the middle of the Cadiz Formation of the Providence and Marble Mountains may be the last rem- nant of the Red Pass Limestone Member in this area. The westward correlatives of the Red Pass Limestone Member lie in the Emigrant and Monola Formations of Esmeralda County, Nev., and Inyo County, Calif., respectively (fig. 3). FAUNAL CHARACTERISTICS The Red Pass Limestone Member is poorly fossilifer- ous at most localities. However, both its upper and lower beds have yielded trilobites. The lower beds are domi- nated by trilobites of the Kochaspid Zonule of the “Plagium-Poliella” Zone. These include: Fieldaspis? sp., Kochaspis augusta (Walcott), K. liliana (Walcott), Kochiel— lina groomensis n. gen., n. sp., K. janglensis n. gen., n. sp., Plagiura extensa n. sp., P. retracta n. sp., P. cf. P. cercops (Walcott), Schistometopus sp., and two undetermined ptychopariid trilobites. The upper'few meters of the member are locally rich in trilobites of the Zacanthoidid Zonule of the Albertella Zone (p. 59) in the Groom Range and the Nevada Test Site. Three collections yielded a total of 21 species of trilobites as well as several species of molluscs. Although the fauna from these beds is remarkably similar to that of the Naomi Peak Tongue of the Twin Knobs Formation in northern Utah and southeastern Idaho, the units are not correlative (Palmer and Campbell, 1975). Rather, this zonule is the local expression of a distinctive trilobite biofacies that characterizes the ocean-facing margin of the carbonate shelf throughout the time represented by theAlbertella Zone (fig. 36). The trilobites from these beds are: Albertelloides mischi Fritz, Kootenia germana Resser, 18 CARRARA FORMATION, SOUTHERN GREAT BASIN Nyella granosa (Resser), N. clinolimbata (Fritz), N. immod- emta n. sp., Oryctocephalina? maladensis (Resser), Oryc— tocephalites typicalis Resser, Pachyaspis gallagari Fritz, Pagetia ressen' Kobayashi, Paralbertella bosworthi (Walcott), Peronopsis lautus (Resser), Poliella germana (Resser), Ptar- miganoides crassaxis n. sp.,P. hexacantha n. sp., Zacanthoides cf. Z. alums (Resser), Z. variacantha n. sp., and five inde— terminate ptychopariid species. The boundary between the “Plagium-Poliella” and Al— bertella Zones falls somewhere within the Red Pass Limestone member. PAHRUMP HILLS SHALE MEMBER This member is named for exposures above the Red Pass Limestone Member and below the Jangle Limestone Member at its type locality in the Pahrump Hills (fig. 1), northwest of Pahrump, Nye County, Nev. This is the uppermost predominantly terrigenous clastic member beneath hundreds of meters of Middle and Upper Cam- brian limestones and dolomites. The Pahrump Hills Shale Member consists of tan siltstones, red and green mudstones, and shales, with minor amounts of argillace— ous limestone and fine-grained sandstone. Its lower contact with the Red Pass Limestone Member is usually sharp and easily defined. Its upper contact with the Jangle Limestone Member is more gradational and is placed at the base of the first dark oolite or lime mudstone thicker than 2 m. The most common lithology in the lower half of the Pahrump Hills Shale Member is an orange-brown carbonate-cemented siltstone (fig. 10A). This thin- bedded siltstone is usually laminated with thin fine sand laminations along which the bed may part causing the rock to appear as a sandstone on bedding surfaces. Load casts are common along the undersides of these siltstone beds. At several western localities where this lithology overlies the cap of fenestral limestones in the Red Pass Limestone Member, the siltstone is mudcracked and contains rare salt-crystal casts, tracks, and trails (figs. lOB—F). Southeastward in the southern Resting Springs and Nopah Ranges, the basal lithology of the Pahrump Hills Shale Member is a brown silty calcareous shale con- taining echinoderm fragments. In the Groom Range the lowest bed of the Pahrump Hills Shale Member is a black papery fossiliferous shale. An identical black shale occurs above the Red Pass Limestone Member in the Belted Range, although the Pahrump Hills Shale Member is not recognized there because the remainder of the member is replaced by thin-bedded limestones of the Emigrant(?) Formation. The upper half of the member consists of a heterogeneous sequence of red, brown, and green mudstones and shales, chloritic and cryptalgal lime- stones, thin chloritic oolites, and pelloidal limestones. The red mudstones, in particular, form a series of dis- tinctive beds that thicken southeastward from Echo Canyon. The Pahrump Hills Shale Member forms a saddle- shaped three-dimensional unit (fig. 5D) which thickens both to the northeast and the southwest. The member thins to the northwest and somewhat less to the southeast, as do the underlying shale members. A general lithologic change occurs northwestward in the Pahrump Hills Shale Member toward increasing amounts of limestone. At Bare Mountain and in the southern Last Chance Range the Pahrump Hills Shale Member is largely replaced by limestone. This change reflects the intertonguing transition westward of the Pahrump Hills Shale Member with limestones that are assigned to the Jangle Limestone Member. Farther west, beds correlative with the Pahrump Hills Shale Member are included with the Emigrant and Monola Formations. To the east the correlative clastics are believed to be beds of red and maroon sandstones, siltstones, and shales in the Bright Angel Shale below the Lyndon Limestone at Frenchman Mountain and Sheep Mountain, at least part of the A-shale member of the Pioche Shale in the Highland Range, and the upper red siltstones, sandstones, and shales of the Cadiz Formation in the Marble Mountains (fig. 3). FAUNAL CHARACTERISTICS The Pahrump Hills Shale Member is poorly fossilifer- ous, but collections from different areas contain elements of both the Zacanthoidid and Albertella—Mexicella Zonules of theAlbertella Zone. The trilobites identified from west- ern sections of this member in the Groom and Grapevine Ranges and the Nevada Test Site include: Albertelloides rectimarginatus n. sp., Caborcella pseudaulax n. sp., C. re— ducta n. sp., Chanda cf. C. venusta (Resser), Kootem'a ger- mana Resser, Pachyaspis gallagari Fritz, Pagetia resseri Kobayashi, S yspacephalus obscum n. sp., V olocephalz'na con— nexa n. gen., n. sp., Zacanthoides? sp., and one indetermi- nate species each of a ptychopariid and a corynexochid trilobite. These have their strongest affinities with the faunas of the Zacanthoidid Zonule. Collections from sections in the Desert and Spectre Ranges in the central part of the study area include: Albertella longwelli n. sp., A. spectrensis n. sp., Albertellina aspinosa n. gen., n. sp., Mexicella grandoculus n. sp., M. mexicana Lochman, Nyella granosa (Resser), Plagium minor n. sp., and Volocephalina‘connexa n. gen., n. sp. These collections have their greatest affinities with the faunas of the A lbertella—Mexicella Zonule. In the Belted Range, thin-bedded limestones correla- tive with the lower beds of the Pahrump Hills Shale Member yield a rich assemblage of trilobites of the Ogygopsis Zonule of the Albertella Zone. The fauna in- cludes: Chancia? maladensis (Resser), Elrathina antiqua n. DESCRIPTION OF MEMBERS FIGURE 10.—Typical lithologies of the basal part of the Pahrump Hills Shale Member. A, Photomicrograph of carbonate— cemented micaceous siltstone containing iron oxide cement and grains (black). Both dolomite and calcite are present. Note the spherical grains surrounded by iron oxide in the upper central area of the photomicrograph. Pyramid Peak section, Funeral Mountains, Calif. B, C, D, Straight, superimposed, and bigrooved trails preserved on the undersides of siltstone beds. Such trails are characteristic of the base of the Pahrump Hills Shale Member. Pyramid Peak section, Funeral Mountains, Calif. E, Rmophycus-like arthropod resting traces preserved on undersides of siltstone beds. Titanothere Canyon section, Grapevine Mountains, Calif. F, Halite crystal casts in siltstones. Pyramid Peak section, Funeral Mountains, Calif. 19 20 sp., Ogygopsis typicalis (Resser), Pagetia maladensis Resser, P. rugosa Rasetti, Peronopsis lautus (Resser), P. sp., Thoracocare idahoemis (Resser), and an undetermined oryctocephalid trilobite. JANGLE LIMESTONE MEMBER This member, which conformably overlies the Pahrump Hills Shale Member, was named by Johnson and Hibbard (1957. p. 339) from jangle Ridge (fig. 1), in the Halfpint Range, Nev. It is the third and uppermost cliff-forming limestone in the Carrara Formation. Throughout the central part of the study area, the Jangle Limestone Member consists of from one to as many as five limestone units separated by argillaceous recessive- weathering limestone or calcareous shales. The lower boundary of the Jangle Limestone Member is fairly well defined by the first burrowed lime mudstones or oolites more than 2 m thick above the clastics of the Pahrump Hills Shale Member. The upper boundary is less con- sistent and is generally drawn between clean massive limestones of the upper part of the Jangle Limestone Member and argillaceous thin-bedded limestones of the overlying Desert Range Limestone Member. This upper contact is difficult to draw on a lithologic basis in western sections, such as Bare Mountain and the southern Last Chance Range, because the argillaceous content of the limestones of the Desert Range Limestone Member is reduced. The contact is arbitrarily drawn at the topo- graphic break at the top of the cliff-forming Jangle Limestone Member. The lithologies of the Jangle Limestone Member in- clude lime mudstones, trilobite- and echinoderm- fragment wackestones, packstones, and grainstones, ool- ite, fenestral-fabric and laminated limestones. The stratigraphic distribution of lithologies within the Jangle Limestone Member is more varied than in the Red Pass or Gold Ace Limestone Members. The laminated and fenestral-fabric limestones in particular appear to occur in a greater variety of settings in the Jangle Limestone Member than in the underlying lignestone members. Al- though these lithologies still are restricted to the western parts of the member, they occur at several levels throughout the member in different sections. In the Des- ert Range these lithologies are restricted to the upper half of the Jangle Limestone Member, and at Echo Canyon the Jangle Limestone Member consists of two prominent cliffs, each having fenestral-fabric and laminated lime— stone in its upper part. Also, the east-west continuity of these lithologies seems to be less in the Jangle Limestone Member than in the Red Pass Limestone Member. Lat— eral transitions in the Jangle Limestone Member from light-gray or white laminated limestone to black bur— rowed mudstones are evident in the sections at Echo Canyon, Pyramid Peak, and Eagle Mountain. CARRARA FORMATION, SOUTHERN GREAT BASIN Isopachs for the Jangle Limestone Member (fig. 6D) show the member thickening to the northwest and thin- ning to the southeast and southwest. The thickening is accompanied by a decrease in the argillaceous interbeds; the several limestone ledges that make up the Jangle Limestone Member in the southern Resting Springs Range coalesce northwestward to form a single cliff- forming limestone in the Groom Range, at Bare Moun- tain, and in the southern Last Chance Range. To the west, the jangle Limestone Member correlates with undifferentiated intervals in the Emigrant and Monola Formations. Eastward and southeastward the Jangle Limestone Member correlates with the Lyndon Limestone and with oolitic limestones in the upper part of the Cadiz Formation (fig. 3). FAUNAL CHARACTERISTICS The lower part of the Jangle Limestone Member in the southeastern part of the outcrop area of the Carrara Formation has yielded several small low-diversity col— lections of trilobites that are typical of the Albeflella- Mexicella Zonule of the Albertella Zone. The total fauna includes: Albertella longwelli n. sp., A. spectrensis n. sp., Albertelloides sp., Mexicaspis radiatus n. sp., Plagium minor n. sp., and Volocephalina contracta n. gen., n. sp. A slightly more diverse single collection from the mid- dle of the Jangle Limestone Member in the Grapevine Mountains contains a fauna with affinities to both the Zacanthoidid and Albertella-Mexicella Zonules of the Al- bertella Zone. It includes: Mexicella gmndoculm n. sp., Mexicwpis radiatus n. sp., Nyella clinolimbata? (Fritz), Ptar- miganoides hexacantha n. sp., and Volocephalina connexa n. s . Iri)asmuch as the faunas of the overlying Desert Range Limestone Member contain abundant representatives of Glossopleum in many sections, the boundary between the Albertella and Glossopleum zones falls at or near the top of the Jangle Limestone Member. DESERT RANGE LIMESTONE MEMBER This member, the uppermost member of the Carrara Formation, forms a recessive interval between the Jangle Limestone Member and the Bonanza King Formation. It is named for exposures at its type locality, the Desert Range, about 64 km northwest of Las Vegas, Nev. (fig. 1). The Desert Range Limestone Member is typically a thin- bedded black argillaceous limestone with orange dolomitic partings. Occasional trilobite packstones and wackestone characterize this member. In the Striped Hills and Nopah Range thin green or brown shale inter- vals are present but account for only a few meters of the thickness of the member. REGIONAL LITHOSTRATIGRAPHIC RELATIONS 21 The thickness of the Desert Range Limestone Member varies considerably and inconsistently throughout the Carrara study area. It is often involved in faulting be- tween the Bonanza King and the Carrara Formations, which precludes or distorts thickness measurements. Also, even where unfaulted, the Desert Range Limestone Member is gradational into the overlying Bonanza King Formation, and the contact is arbitrarily placed at a point where generally more argillaceous limestones of the Car- rara Formation become indistinguishable from those of the Bonanza King Formation. For these reasons, no isopach map of this interval has been plotted. The base of the Desert Range Limestone Member is easily recognized and is placed at the top of the cliff-forming Jangle Limestone Member. Usually this point corresponds to an abrupt break in slope and a color change from white or light gray to dark gray or brown. The westward correlatives of the Desert Range Limestone Member in Esmeralda County lie within the Emigrant Formation. In the Inyo Mountains it is not known if the correlative rocks lie in the upper part of the Monola Formation or in the lower part of the Bonanza King Formation. To the southeast, correlatives probably lie within the upper part of the Cadiz Formation of Haz- zard and Mason (1936). To the east and north the cor— relative unit is the Chisholm Shale (fig. 3). FAUNAL CHARACTERISTICS This member includes thin beds rich in the dis- articulated remains of species of Glossopleum at many localities. Additional trilobites are rare and the faunal diversity is characteristically low. Decent specimens are difficult to obtain from rocks of this member without heating and rapid chilling to loosen the matrix. The faunas of this member are characteristic for only the lower part of the Glossopleum Zone. The time span for the entire zone includes both the Desert Range Lime- stone Member and at least 150 m of limestones in the lower part of the overlying Bonanza King Formation. The trilobite fauna from the Desert Range Limestone Member includes: Glossopleura walcotti Poulsen, G. lodensis (Clark), Alokistocarella? cf. A. brighamensis (Resser), and at least four other specifically indeterminate ptychopariid trilobites. REGIONAL LITHOSTRATIGRAPHIC RELATIONS Wheeler and Mallory (1956) addressed the problem of lateral and vertical distributions of rock bodies that trans- cend formation and facies boundaries. Their solution was to create the term, “lithosome,” to denote rock masses essentially uniform in lithologic character that have in- tertonguing relationships with adjacent masses of differing lithology. In a regional sense, the members of the Carrara Formation are tongues of lithosomes (fig. 11). One limestone lithosome is formed by the Mule Spring Limestone with tongues extending eastward to form the Thimble and Gold Ace Limestone Members. A younger limestone lithosome is recognized in the southern Last Chance Range where the Pahrump Hills Shale Member is largely replaced by argillaceous limestone joining the Red Pass and Jangle Limestone Members. To the east and intertonguing with the limestone lithosomes lies a terrigenous clastic lithosome, which represents deposits of the Inner Detrital Belt of Palmer (1960); this is com- posed of the Eagle Mountain, Pahrump Hills, and Echo Shale Members of the Carrara Formation, the Latham Shale, the Cadiz Formation, the Bright Angel Shale, the Pioche Shale, and the Chisholm Shale. A model explain- ing these relationships is suggested on p. 51. LITHOFACIES DESCRIPTION AND INTERPRETATION During the past 20 years, descriptions of a number of Holocene carbonate sedimentary environments have provided a framework for interpreting ancient carbonate rocks. The classic areas of carbonate study have become the Florida and Bahama Platforms, the south coast of the Persian Gulf, Shark Bay in Western Australia, the Cam- peche Bank of Mexico, and the Great Barrier Reef of Australia. Several of these areas have aspects in common with the patterns of carbonate sedimentation within the Carrara Formation. Three types of limestones displaying primary deposi- tional textures dominate the carbonates of the Carrara Formation and characterize distinctive lithofacies. These are (following the classification of Dunham, 1962) (l) the lime-mudstone lithofacies—burrowed and current- laminated pelletal lime mudstone, oncolite and skeletal- fragment lime mudstones, and oncolite and skeletal- fragment wackestones, packstones, and minor grainstones; (2) the oolite grainstone facies—oolite grainstone, skeletal-fragment and oncolite grainstones and packstones, intraclast grainstones, and minor amounts of cryptalgal limestone; and (3) the algal bound- stone facies—a variety of cryptalgalaminites, fenestral- fabric limestones, intraclast grainstones, stromatolites, and pelletal mudstones. Subdivision of the algal bound- stones follows the classification of Aitken (1967) for cryptalgal carbonates. Limestones displaying fenestral fabrics (Tebutt and others, 1965) are lime mudstones or pelletal lime mudstones containing unsupported spar- filled voids and are equivalent to dismicrites of Folk (1959) and the bird’s-eye limestone of Shinn (1968). Al— 22 CARRARA FORMATION, SOUTHERN GREAT BASIN NW SE I‘<\ LIMITS OF CARRARA FORMATION NI ME uTHOSO ESTONE \(\NG LIMESTONE Ofipfilp‘ Desert Range Limestone Member 3 / LITHOSOME Jangle Limestone Member OF EMIGRANT BRIGHT Pahrump Hills Shale Member FORMATION ANGEL Red Pass Limestone Member SHALE Pyramid Shale Member LITHOSOME MULE Echo Shale Member SPRING LIMESTONE Thimble Limestone Member LITHOSOME Eagle Mountain Shale Member ZABRISKlE—TAPEATS SANDSTONE LITHOSOM E Middle Cambrian Lower Cambrian FIGURE 11.—Generalized cross section along Nevada-California border from central Esmeralda County, Nev., to eastern Clark County, Nev., showing lithosomal relationships of the members of the Carrara Formation. Horizontal distance about 300 km. No vertical scale. Thicknesses in the middle of the figure are proportional to member thicknesses in the Echo Canyon section, California. though a great variety of fenestral fabrics exists in the Carrara limestones, no attempt has been made to differ- entiate them in the present study. The areal and strati- graphic distribution of the rocks of each lithofacies in each of the limestone members are shown in figures 31—33. Diagenetic changes, rather than metamorphic altera- tions, account for the majority of postdepositional changes of the carbonate rocks of the Carrara Formation. Locally, metasomatic lead and zinc ores and marbles and hornfels occur along faults and near intrusives, but they bear no information concerning the depositional history of the formation. Some diagenetic effects, on the other hand, do bear directly on the depositional history of the Carrara Formation, and their presence and absence will be discussed in some detail. In general, diagenetic fabrics can be recognized and differentiated from primary depositional features. How- ever, the timing and mechanism of formation of many of these diagenetic features is beyond the scope of this work and only the more obvious will be considered here. THE LIME-MUDSTONE LITHOFACIES The lime-mudstone lithofacies of the Carrara Forma- tion is composed predominantly of low-magnesium cal— cite. Other minerals which occur in the lime mudstone include quartz, dolomite, chlorite, micas and clay miner- LITHOFACIES DESCRIPTION AND INTERPRETATION 23 als, albite, microcline, pyrite, hematite, chert, and apatite, approximately in order of decreasing abundance. The basic building blocks of the lime mudstones are equant grains of calcite, 2—30 micrometers (um) in diameter. This size range spans the “micrite curtain,” a gap in the size distributions of small calcite grains de— scribed by Folk (1965, p. 32) to occur between 3 and 4 um. The gap separates micrite (1—3.5 ,um) from microspar (35—30 am) in the study of recrystallization in ancient limestones by Folk (1965). The existence of this gap in grain size distribution within lime mudstones of the Car- rara Formation is problematical. In some samples the complete range of sizes from 2—30 um is evident, whereas in others the grain size may be either micrite or micro- spar. Where micrite and microspar occur together, both porphyrotopic and poikilotopic fabrics are developed (fabric terminology after Friedman, 1965). Folk (1965, p. 32) noted that limestones containing microspar or micrite-microspar associations are charac- teristically interbedded with shales. The microspar- bearing lime mudstones of the Carrara Formation, although not interbedded with shales, usually have a significant insoluble residue content composed pre- dominantly of quartz—silt, mica, and clay minerals (fig. 12E). Even in the relatively clean parts of limestone members this residue rarely falls below 5 percent. Thus, perhaps the terrigenous content of a limestone is the significant factor to be correlated with the appearance of abundant microspar. Many of the limestones of the lime-mudstone facies are pelletal in thin section. The preservation and recognition of pelleted textures seems fortuitous, because pelletal limestones often grade into micrites or microspar lime— stones in which little pelletal texture is recognizable (fig. 12F). Small pockets of pelmicrites and pelsparites are scattered throughout the lime-mudstone facies (fig. 13A ). Pelleted lime mudstones may contain as much as 30 per- cent quartz silt and clay without losing their primary depositional texture (fig. 133), while in relatively clean limestones, pellets may be only barely recognizable. The preservation of pelleted texture is probably a function of early diagenesis (cementation) of the pellets themselves. It is possible that where pelleted textures are preserved, the pellets were cemented at the time of final deposition. Uncemented pellets, on the other hand, could compact very easily and become indistinguishable from micrite mud. Evidence for this comes from some lime mudstones of the Carrara Formation that are seen to be micrite or microspar in thin section but display a variety of current- formed sedimentary structures in outcrop. Features, such as ripples, parallel lamination and crossbedding in- dicate that the sediment was acting as sand or coarse silt when deposited. In these instances, it seems probable that the lime mudstone was pelleted at the time of deposition and that its primary depositional fabric has been obscured postdepositionally, perhaps during later com- paction. Pelletal textures are also obscured during re- crystallization as illustrated in figure 13C. Pelletal tex- tures seem to have been diagenetically obscured in many of the limestones of the Carrara Formation. Much more of the lime-mudstone facies was probably deposited as pelleted lime mud than is now evident. Besides pellets, a variety of other allochems are abun- dant in the lime mudstones of the Carrara Formation. These include oncolites, here considered to be of doubt- ful skeletal origin‘, and trilobite, hyolithoid, brachiopod, and echinodermal skeletal debris. Oncolites are quantitatively the most important al- lochems in the lime-mudstone facies besides pellets. They constitute an average of about 15 percent of the exposed surfaces in the lime-mudstone facies, and locally they may constitute an oncolite packstone (fig. 13D); but the bed-to-bed variation is great. Oncolites vary in size from 10 cm in diameter to an undetermined minimum diameter of less than 1 mm. Typically, diameters range from 1 to 4 cm. The oncolites are sometimes circular, but more often they are ellipsoidal in cross section, and a trilobite or hyolithoid fragment characteristically forms the nucleus (figs. 13E, 13F, 14A). Although oncolites appear concentrically laminated in outcrop, they are dis- continuously laminated on polished surfaces or in thin section (fig. 13E). The laminations, formed by slight color and (or) grain—size differences, suggest periods of growth interrupted by only occasional rotation of the oncolites. In thin section, oncolites are composed of microspar cal— cite finer than the spar replacing skeletal grains (figs. 14A, 14B). Rarely, the oncolitic calcite displays small tubelike molds of Gimanella. As illustrated in figure 14B , the oncolite surface layers differ markedly from the sur- rounding matrix because they do not contain skeletal fragments or silt-sized quartz grains. This suggests that these oncolites are not formed by algal trapping and binding of surrounding sediments, the process which is responsible for oncolite development on the Great Bahama Bank (Buchanan and others, 1972). Rather, on- colites in the Carrara Formation were probably formed from a primary precipitate of calcium carbonate stimu- lated by algae represented by the occasionally preserved tubes of Gimanella. Although all oncolites of the Carrara Formation are tentatively assumed to have essentially the same origin, 'Bathurst (1971a, p. 64) considered Gimanelm oncolites to be probable codiacean remains. 24 CARRARA FORMATION, SOUTHERN GREAT BASIN at“. FIGURE l2.—Phot0micrographs of lime-mudstone textures. A , Micrite (in center of photo) surrounded by micro- spar calcite. Largest grains about 10pm in diameter. Thimble Limestone Member, Echo Canyon section, California. B, Micrite (dark area in center of photo and elsewhere in field of view) surrounded by microspar forming a poikilotopic fabric typical of the Carrara lime mudstones. jangle Limestone Member, southern Last Chance Range section, California. C, Small patches of micrite surrounded by microspar calcite. Large opaque grain in upper right is pyrite. Mule Spring Limestone, Paymaster Canyon section, California. D, Microspar calcite grading into sparry calcite (lower left corner). Jangle Limestone Member, Pyramid Peak section, California. E, Argillaceous microspar limestone containing some platy mica grains, lighter colored quartz silt grains, hematite grains, and hematite-coated dolomite grains in a microspar and clay-mineral matrix. Red Pass Limestone Member, Titanothere Canyon section, California.F, Diagenetic blurring of pelleted texture in micrite and microspar lime mudstone—well preserved only in the left half of the photo. Light grains are quartz silt. Red Pass Limestone Member, Eagle Mountain section, California. LITHOFACIES DESCRIPTION AND INTERPRETATION FIGURE l3.—Photomicrographs and outcrop photo of rocks of the lime-mudstone lithofacies. A, Small pocket of pelsparite surrounded by unpelleted micrite. Red Pass Limestone Member, Eagle Mountain section, Califor- nia. B , Pelleted lime mudstone (pelmicn'te) containing about 30 percent quartz silt. The pelleted texture of the sediment is not lost even though the limestone contains a significant proportion of terrigenous clastic material. Red Pass Limestone Member, Resting Springs Range section, California. C, Dolomitic microspar that contains a remnant pelletal fabric despite recrystallization. Some pellet ghosts are floating in microspar matrix. Titanothere Canyon section, California. D, Outcrop photo of oncolite packstone (oncolitic biomicrudite) in a bedding-plane exposure. Gold Ace Limestone Member, Echo Canyon section, California, E, Large oncolite with hyolithoid fragment as a nucleus. Note the discontinuity of concentric laminations in the structure. jangle Limestone Member, Titanothere Canyon section, California. F, Hyolithoid-, trilobite-, and echinoderm-fragment wackestone with a probable alga] coating around the outer margin of the large hyolithoid fragment in the lower left corner. That specimen may have been an incipient oncolite. Chambless Limestone, Marble Mountains section, California. 25 26 CARRARA FORMATION, SOUTHERN GREAT BASIN this may have not been the case. A peculiar relationship exists between oncolite preservation and the proximity of argillaceous units in the Gold Ace and Thimble Lime- stone Members. Oncolites seem to be ubiquitous in these members, but those that are near shales or in argillaceous limestones appear to be better preserved than those in the Clean limestones. Better preservation is expressed by well-defined laminations, preserved nuclei, large size, and preservation of some Gimanella tubes seen in thin section. In contrast, those oncolites in massive, less argil— laceous limestones are replaced by coarsely crystalline calcite, dolomite, and iron oxide. The two styles of oncolite preservation suggest two possibilities for the origin and diagenetic history of these algal structures. First, the differing modes of preserva- tion may reflect only differing diagenetic histories—the diagenetic history of oncolites in the cleaner limestone being more complex and leading toward total oblitera— tion of the structure. Alternatively, the original deposi- tional environment of the better preserved oncolites may have been sufficiently different, at least more muddy, to allow a different type ofoncolite to develop, perhaps with a different primary porosity or mineralogy which would lead to a different diagenetic history. Evidence support— ing either interpretation must await further detailed study of the oncolites. The matrix around oncolites may be mudstone and free of skeletal grains, but more commonly it contains other allochems common to the lime-mudstone lithofacies. The most abundant of these are trilobite fragments which in thin section appear as circles, hooks, S-shaped fragments, and more irregular grains replaced by a sparry mosaic of calcite (figs. 14C —F ). The fragments may have algal encrustations or oolitic coatings. Articu- lated trilobites are extremely rare in the lime-mudstone lithofacies, the only occurrence being an unusual l-m— thick bed in the Pahrump Hills Shale Member in the Groom Range (USGS colln. 3692—CO, pl. 17). The other abundant biogenic allochems—echinoderm fragments—are also rarely articulated in the lime mudstones of the Carrara Formation. They appear as sand-size calcite grains that are composed essentially of single crystals. In some well-preserved examples (figs. 15A—C), echinoderm plates appear to have serrated edges. These were probably produced by lime-mud fill- ing the pores around the edges of the porous post- mortem fragments. The porous interiors of the grains have been filled with calcite in optical continuity with the rest of the skeletal grain. Excellent descriptions of this porosity and cementation were given by Bathurst (1971a, p. 50—55). Usually, echinoderm fragments do not retain their original shape but are rounded and fractured dur- ing transport. Small pockets and thin beds of well- rounded echinoderm and trilobite debris form thin cal- carenites both within the lime-mudstone facies and in some terrigenous clastic units of the Carrara Formation (fig. 15D). Micrite envelopes (Bathurst, 1966), although noted on some echinoderm fragments (fig. 15E), were never seen on trilobite or hyolithoid debris and are rare. Other fossil fragments are grains and complete, often nested, cones of hyolithoids which are recognized by their subtriangular cross sections (figs. 13E, 17F). These are most common in the Chambless Limestone and the Gold Ace Limestone Member of the Carrara Formation. These fragments are more coarsely crystalline than as- sociated trilobite fragments. Intraclasts are exceedingly rare in the lime-mudstone facies but can be found near the interfaces of the lime- mudstone facies and the algal-boundstone facies. Al- though such occurrences are uncommon, they are qual- itatively important and are discussed in more detail under “Spatial Relations of the Carbonate Lithofacies.” Quartz sand and silt occur in the lime-mudstone facies and silt can account for as much as 40 percent of the rock. Micas, chlorite, and clay make up the very fine terrigen- ous fraction. The most pervasive sedimentary structure of the lime mudstones is thin bedding (figs. 16D, 17‘B, 18A—D), characteristically between 1 and 10 cm in thickness. It is often wavy, nodular, or irregular and is formed by orange-brown dolomitic silty argillaceous limestone that weathers recessively to form partings between thin dark-gray or black lime-mudstone beds. This thin bed- ding reflects the eastward facies change from lime mudstone to shale. Thin-bedded lime mudstones are re- placed to the east by lime mudstone and shale, and then by a shale with thin interbeds of more calcareous mate— rial. Within the thin beds of lime mudstone, a variety Of structures can be seen. Rarely, near the eastern limits of the Thimble and Gold Ace Limestone Members, the thin beds are graded (figs. 16A, 16C); an irregular erosional base which contains trilobite fragments and quartz silt grades upward into a dolomitic argillaceous micrite or microspar. More often the thin beds are simply parallel, current laminated, and burrowed (figs. 16B , 17A ). In thin section, these laminations are formed by concentrations of clay minerals or, where preserved, by slight variation in pellet size or fabric. Small crossbeds and cut-and-fill channels, never more than one bed thick, are the features most often associated with the current—laminated thin- bedded lime mudstones (figs. 16D, 17C , 18A). Although these features are produced in micrite or microspar, they also occur in small lenses or beds of skeletal grainstone, packstone, or intraclast packstone (figs. 173, 17D). The Carrara Formation contains a complete gradation LITHOFACIES DESCRIPTION AND INTERPRETATION FIGURE l4.—Photomicrographs and photos of cut surfaces of selected lime-mudstone lithotypes. A, Detail of algal(?) microspar coating outside of replaced hyolithoid grain. Chambless Limestone, Marble Mountains section, California. B , Oncolite, microspar (left) and skeletal-grain wackestone matrix, which show markedly different compositions in thin section. Many of the small white grains in the matrix of the wackestone are quartz silt, a grain type that is totally absent from the oncolitic microspar. Chambless Limestone, Marble Mountains section, California. C, Cut surface, perpendicular to bedding, 0f trilobite and lithoclast packstone. Thimble Limestone Member, Echo Canyon section, California. D, Characteristics of bioclastic debris from trilobite-fragment packstone. Thimble Limestone Member, Echo Canyon section, California. E, Typical hook-shaped cross section of a trilobite cephalic margin in a lime-mudstone sample. Gold Ace Limestone Member, Echo Canyon section, California. F, Cut surface, perpendicular to bedding, of trilobite-fragment packstone. jangle Limestone Member, Pahrump Hills section, Nevada. 27 28 CARRARA FORMATION, SOUTHERN GREAT BASIN FIGURE 15.—Photomicrographs of echinoderm debris.A , Large, well-preserved echinoderm fragment adjacent to a trilobite spine in a mudstone. Chambless Limestone, Marble Mountains section, California. B , Same asA with crossed polarization. C, Echinoderm plate showing well-preserved marginal serration indicative of post- mortem porosity. Chambless Limestone, Marble Mountains section, California. D, Echinoderm grainstone with syntaxial calcite cement. Pyramid Shale Member, Eagle Mountain section, California. E, Well-rounded echinoderm fragments, pellets, and lithoclasts in grainstone. Central large echinoderm fragment has a micrite envelope. jangle Limestone Member, Eagle Mountain section, California. LITHOFACIES DESCRIPTION AND INTERPRETATION 29 FIGURE 16.—Photographs of vertical-cut surfaces or outcrops of rocks from the lime—mudstone lithofacies.A , Cut surface of thin-bedded crudely graded lime mudstone. The base of each bed is defined by concentrations of quartz sand and echinoderm and trilobite skeletal fragments. The basal layer grades upward into current- laminated pelletal micrite or microspar which in turn is overlain by red argillaceous dolomitic lime mudstone. Thimble Limestone Member, Echo Canyon section, California. B, Cut surface of thin-bedded current- laminated burrowed pelmicrite. Argillaceous limestone interbeds (light gray in photo) are red in outcrop. Thimble Limestone Member, Echo Canyon section, California. C, Cut surface of thin-bedded graded lime mudstone. Each bed consists of an erosion surface which is overlain by a calcarenite or packstone which grades upward into current-laminated pelmicrite and argillaceous red microspar. Thimble Limestone Member, Striped Hills, Nev. D, Outcrop photo of thin-bedded limestone (dark gray) and more argillaceous and resistant weathering interbeds (light gray). Note current laminations and ripple crossbed within the dark lime-mudstone beds. Mule Spring Limestone, Paymaster Canyon section, Nevada. from thin-bedded unburrowed lime mudstones with Both vertical and horizontal burrows occur in the current-dominated depositional textures to homogen- lime-mudstone facies, but by far the most common type eously bioturbated lime mudstone (figs. l7C—E). How- of burrowing is subhorizontal, leading to a mottled ap- ever, the end-member lithologies comprise distinct mi- pearance for many of the lime-mudstone beds. A few crofacies that are discussed under “Environment of Dep- open burrows occur scattered throughout the lime- osition.” mudstone facies and range from about 1 mm to 1 cm in 30 CARRARA FORMATION, SOUTHERN GREAT BASIN Ev!“ FIGURE 17.—Photographs of vertical-cut surfaces or outcrops of rocks from the lime mudstone lithofacies. A , Cut surface of thin-bedded argillaceous limestone. Current-laminated pelmicrite constitutes the dark material of the slab, and argillaceous dolomitic micrite or microspar constitutes the light material. Burrows have displaced the argillaceous limestone. Thimble Limestone Member, Echo Canyon section, California. B, Outcrop photo of crossbedded intraclast grainstone within typically thin-bedded lower Mule Spring Limestone, Paymaster Canyon section, Nevada. C, Outcrop photo of ripple-bedded pelleted dark lime mudstone and thin argillace« ous light-colored limestone interbeds that weather more resistantly. Mule Spring Limestone, Paymaster Canyon section, Nevada. D, Cut surface of trilobite packstone with trilobite fragments crossbedded, suggest— ing current reworking of such fragments. Thimble Limestone Member, Echo Canyon section, California. E, Cut surface of burrowed dolomitic lime mudstone containing oncolites and hyolithoid- and trilobite-skeletal fragments. Chambless Limestone, Marble Mountains, Calif. F, Cut surface of burrow-mottled lime mudstone containing numerous hyolithoid cross sections. Light-colored dolomite bounds the thin bed and is associated with stylolites. Gold Ace Limestone Member, Pyramid Peak section, California. LITHOFACIES DESCRIPTION AND INTERPRETATION 31 diameter. These are filled with clear or white calcite spar (figs. 19A, 19B), and some cement infills show evidence of concentric zonation toward the interior of the burrow. The interbeds or partings of orange, brown, or red argillaceous dolomitic siltstone or silty limestone within the lime-mudstone lithofacies show some evidence of diagenetic alteration. Because they define the thin bed— ding of this facies and because these interbeds are usually horizontal, they appear to be essentially of primary ori- gin. They commonly are more intensely burrowed than the surrounding limestone. Orange argillaceous dolomi- tic limestone often extends from these horizons into overlying and underlying dark-gray or black limestone suggesting selective bioturbation of these more argilla- ceous zones. However, the concentrations of dolomite rhombohedra, the pervasive iron oxide stain, and the FIGURE 18.—Outcrop photos of rocks from the lime-mudstone lithofacies. A, Characteristic thin bedding. Weather—resistant argillaceous interbeds illustrate conformity with primary internal laminations in cleaner lime mudstone. Vertical rills are a weathering phenomenon unrelated to the primary depositional fabric of the limestone. Red Pass Limestone Member, Pyramid Peak section, California. B, Thin beds separated by more irregular and burrowed argillaceous interbeds than those illustrated inA . Gold Ace Limestone Member, Pyramid Peak section, California. C, Argillaceous interbeds of lime mudstone weathered recessively so that the unit usually forms a flaggy or platy slope. In such units the interbeds may be shale. Gold Ace Limestone Member, Pyramid Peak section, California. D, Argillaceous limestone interbeds showing three different degrees of irregularity. The lower third of the photo is very irregular both as a result of burrowing and as a result of subsequent solution along stylolites; the middle third is less so; and the upper third is very evenly interbedded. jangle Limestone Member, Pyramid Peak section, California. 32 CARRARA FORMATION, SOUTHERN GREAT BASIN FIGURE 19.—Photomicrographs of rocks from the lime-mudstone lithofacies. A, A spar-filled burrow, now somewhat flattened and ringed by small dark pyrite grains. Structure is in homogeneous microspar. Thimble Limestone Member, Titanothere Canyon section, California. B, Wall of spar-filled burrow (right) and large calcite crystals expanding toward the center of the burrow (left). Structure is in pelletal micrite and microspar. Jangle Limestone Member, southern Last Chance Range section, California. C, Pelletal micrite and microspar (lower left) being replaced by dolomite (upper right). Jangle Limestone Member, Striped Hills section, Nevada. D, Silty, argillaceous pelletal micrite (upper right) adjacent to even more argillaceous, silty, and dolomitic limestone (lower left). The dolomite here as in most other photomicrographs is coated with iron oxide and appears opaque.]angle Limestone Member, Resting Springs Range section, California.E , Part of a recrystallized ooid (lower left) in argillaceous, micaceous, iron oxide stained dolomite matrix. Eagle Mountain Shale Member, southern Last Chance Range section, California. F, Detail of area marked by arrow in E, showing relationship between recrystallized ooid and dolomitized matrix. LITHOFACIES DESCRIPTION AND INTERPRETATION 33 association of these interbeds with stylolites and relatively insoluble terrigenous clastics suggest diagenetic altera- tion of the interbeds from their original state. Some of the irregularities of these interbeds are undoubtedly caused by solution rather than bioturbation. Such solution takes place along swarms of microstylolites and has been de- scribed from very similar limestones in the Middle Cam- brian of the Grand Canyon (Wanless, 1973). Primary composition and fabric differences of the more argilla- ceous horizons could have provided permeable pathways along which dolomitization, solution, and oxidation pro— duced the interbed features seen today. Dolomitization in the lime-mudstone lithofacies often extends beyond the argillaceous interbeds of the lime mudstone (figs. 19C, 20C, 2lA—D) and selectively alters burrows and grains. Dolomitization of burrows is often associated with a displacement along burrows of argil- laceous material from the orange interbeds (fig. 19C). The selective dolomitization of oolites, intraclasts, and oncolites is difficult to explain. Usually, the dolomitiza— tion appears random. For example, one oncolite may be completely altered to dolomite while another in the same thin section only millimeters away remains calcite, as does the cement between. Always, the replacement is by dolo- mite rhombohedra, 1—50 um across, coated or zoned by iron oxide (figs. 21A, 213). Occasionally, rhombs of iron-stained calcite are noted on exposed surfaces. This calcite is assumed to be a mod- ern dedolomite. (See, for example, Evamy, 1969.) Small irregular spar-filled cracks ramify throughout the lime-mudstone facies of the Carrara Formation. These cracks are filled with calcite that appears black in outcrop and are restricted to the lime-mudstone facies. They were formed before the straighter spar-filled frac- tures that are found in all facies, which are assumed to be associated with the structural deformation of these limestones. These latter fractures appear white in out- crop (figs. 20B—D). Distribution of the lime-mudstone lithofacies of each of the four limestone members of the Carrara Formation is illustrated in figures 31-33. The distribution of lime mudstone in the Thimble and Gold Ace Limestone Members is similar. The northwestern limit of these lime mudstones is far beyond the study area. In the east- central part of the outcrop area of the Carrara Forma- tion, the lime-mudstone lithofacies of the Thimble Limestone Member goes beyond that of the Gold Ace Limestone Member and extends to the Spring Mountains and Pahrump Hills. However, to the southeast, the lime-mudstone lithofacies of the Gold Ace Limestone Member extends beyond that of the Thimble Limestone Member to the Nopah Range and Winters Pass. At Win- ters Pass, Eagle Mountain, and the Desert Range the lime-mudstone lithofacies of the Gold Ace Limestone Member interfingers with shales. To the south, the con- tinuation of this limestone unit in the Providence and Marble Mountains is separately recognized as the Chambless Limestone. The northwestern limit of the lime—mudstone lithofacies of the Red Pass Limestone Member is outside the study area. It is marked by the facies change into thin-bedded deeper water limestones of the Emigrant Formation although the lateral transition is nowhere ex- posed. To the southeast, the lithofacies interfingers with shales. Within the member, it interfingers with the oolite lithofacies and, in the upper part of the member, with the algal boundstone lithofacies. The lime-mudstone lithofacies of thejangle Limestone Member has a northwestern limit that is somewhere be- tween the Belted Range and the Groom Range. The eastern margin of this lithofacies is beyond the study area. At Frenchman Mountain, Sheep Mountain, and Azure Ridge, the correlative Lyndon Limestone contains lime mudstone but the lithofacies disappears eastward toward the Grand Canyon where the laterally equivalent units appear to be the Tincanebits and Meriwitica Tongues of McKee (McKee and Resser, 1945). ENVIRONMENT OF DEPOSITION The lime-mudstone lithofacies of the Carrara Forma- tion is a subtidal marine accumulation. It contains none of the fabrics or sedimentary structures recognized as characteristic of supratidal and intertidal deposition. When Holocene subtidal lime-mud accumulations are compared with the lime-mudstone lithofacies of the Car- rara Formation, two problems arise. The first concerns the origin of the lime mud. In the Holocene, two con- trasting mechanisms have been assumed for the produc— tion of shallow-water (nonpelagic) lime mud: physical precipitation directly from sea water, and accumulation of finely comminuted algal skeletal carbonate. Attempts to analyze the origin of Holocene lime muds have been made at only a few localities and in each case the solution differs (Cloud, 1962; Matthews, 1966; Stockman and others, 1967; Kinsman and Holland, 1969). Without agreement on the source of lime mud in the Holocene it is impossible to suggest any one source for the lime mud of the lime-mudstone lithofacies of the Carrara Formation. The second problem concerns the fact that few inves- tigators of Holocene sediments have studied the fraction of the sediment finer than 62 [LII]. Emphasis has been placed on identification of the grains larger than 62 um, and only the bulk weight of the finer fraction has been recorded. Some workers have considered all carbonate sediment finer than 62 um to be “carbonate mud.” Thus, 34 CARRARA FORMATION, SOUTHERN GREAT BASIN FIGURE 20.—Photographs of a natural exposure and vertical-cut surfaces of rocks of the lime-mudstone lithofacies. A, Outcrop photo of thin-bedded lime mudstone (dark) with argillaceous dolomitic partings and burrows (light). Hammerhead on right margin for scale. Compare this interval with that illustrated in figure 18A . Red Pass Limestone Member, Nopah Range section, California. B, Vertical-cut surface of oncolitic lime mudstone overlain by homogeneous lime mudstone. The oncolites are severely recrystallized and individual crystals can be seen in the photo. The overlying mudstone is also recrystallized in the upper left to a coarse calcite spar. Large tectonic vertical fractures are filled with white calcite. Gold Ace Limestone Member, Echo Canyon section, California. C, Vertical-cut surface of burrowed dolomitized lime mudstone. The dolomite (light) occurs both as a prominent horizontal interbed in the upper third of the sample and as a general mottling associated with the filled burrows. Gold Ace Limestone Member, Echo Canyon section, California. D, Slab photo of oncolitic lime mudstone overlain by burrowed lime mudstone. Oncolites are not severely recrystallized and retain their characteristic concentric lamination although portions are replaced by white crystalline calcite. Compare with B. Gold Ace Limestone Member, Echo Canyon section, California. particle size of Holocene lime muds can range from silt to clay. Despite these difficulties, some generalizations about accumulation of lime mud seem possible. Accumulation occurs generally in a protected setting, although that protection may vary considerably. Examples of such ac- cumulation are (I) Harrington Sound, Bermuda, where most of the muddy sediments accumulate in more than 16 m of water (Neuman, 1965); (2) the interior of the Great Bahama Bank at depths of 0—6 m of water, in the lee of Andros Island and separated from strong tidal currents near the bank edge by oolite shoals (Purdy, LITHOFACIES DESCRIPTION AND INTERPRETATION 35 FIGURE 2l.—Photomicrographs and photographs of vertical-cut surfaces of rocks from the lime-mudstone lithofacies. A, Unusually large rhombs of dolomite with iron oxide coating most crystals. Smaller coated rhombs are typical of replacement dolomite in the Carrara lime mudstones. Chambless Limestone, Marble Mountains, Calif. B, Recrystallized-calcite trilobite fragment in replacement dolomite. Calcite sediment within the fragment has remained unaffected. Chambless Limestone, Marble Mountains, Calif. C, Example of increase in insoluble residue of argillaceous dolomitic interbeds. Normal pelletal lime mudstone (upper left) contains significantly less quartz silt than the interbed (lower right). Note concentration of silt along the contact of the two lithologies. jangle Limestone Member, Eagle Mountain section, California. D, Vertical-cut surface of dark homogeneous lime mudstone illustrating neomorphic recrystallization to coarse-grained spar (right center), irregular dolomitization (light area on left), and fracture filled with dark calcite spar broken by fracture filled with white calcite. Gold Ace Limestone Member, Echo Canyon section, California. 1963); (3) landward side of the Great Barrier Reef, Aus- tralia in about 45 m of water (Swinchatt, 1970); (4) in the Southern Shelf Lagoon of British Honduras in more than 9 m of water (Matthews, 1966; Scholle and Kling, 1972); (5) in the Persian Gulfin more than 15 m ofwater near Qatar (Houbolt, 1957); and (6) in less than 9 m of water in lagoons behind oolite deltas and islands of the Persian Gulf Abu Dhabi complex (Kinsman, 1964). The lime-mudstone lithofacies of the Red Pass and Jangle Limestone Members of the Carrara Formation interfingers with the oolite and algal-boundstone lithofacies to the west and with shales to the east. The oolite grainstone and algal boundstone lithofacies, which formed shoals and islands (p. 41, 49), could have pro- vided a physical barrier to the west. Eastward, depth probably played an increasingly important role in pro- viding a relatively quiet environment for lime-mud ac- cumulation. During the deposition of the Carrara Formation the cratonic shoreline was several hundred kilometers to the 36 CARRARA FORMATION, SOUTHERN GREAT BASIN east, in the vicinity of the eastern Grand Canyon. A broad shelf lagoon dominated by terrigenous clastic deposition lay between the cratonic shoreline and the outer carbonate-producing shoals. The presence of a slight depositional slope at the western edge of the elastic area of the shelf lagoon is indicated by rare graded beds, slump folds, and sole markings present in the Eagle Mountain, Echo, and Pyramid Shale Members of the Carrara Formation. The interfingering of these shales with oncolitic and skeletal lime mudstones indicates that depths were not great. One hundred meters of water is deep enough to permit significant sediment transport and yet still shallow enough so that biological activity could produce abundant skeletal carbonates. The depth of the shelf lagoon may have decreased from perhaps 100 m at the clastic-carbonate interface in the center to sea level westward where the lime mudstones interfinger with intertidal deposits (fig. 37). The lower parts of the limestone members of the Car- rara Formation are characteristically dominated by lime mudstones displaying current features; whereas the upper parts are dominated by burrowed lime mudstones. There is no obvious method of determining whether this change is an upward increase in the activity of burrowing animals or an upward decrease in current activity. How- ever, an upward decrease in current activity may reflect the development of barrier islands or shoals to the west which altered the open shelf to a protected shelf lagoon. The outstanding sedimentary structure of the lime- mudstone lithofacies is thin bedding. Such bedding has no known counterpart in carbonate muds being depos- ited today. Although burrowing has been a significant destructive agent of sedimentary structures within beds, little between-bed burrowing took place in the lime- mudstone lithofacies of the Carrara Formation. Most Holocene lime muds are thoroughly homogenized by burrowers, such as Callianassa (Shinn, 1968). Perhaps the thin bedding of the lime mudstones of the Carrara For- mation and many other lower Paleozoic limestones, indi— cates that burrowers were not as abundant or that they burrowed less deeply in the past than today. THE OOLITE LITHOFACIES The oolites of the Carrara Formation are composed of low-magnesium calcite as are virtually all ancient un- dolomitized, unsilicified oolites. Accessory minerals in the oolite lithofacies are dolomite, hematite, quartz, chlo- rite, and clay minerals, all of which account for less than 5 percent of the rock. Compared to the lime-mudstone lithofacies, the oolite lithofacies is relatively free of ter- rigenous clastic sediment. The oolite lithofacies is constructed almost entirely of oolite grainstone, with minor amounts of intraclastic grainstone, composite grains, grapestonelike grains, and quartz sand. The oolites are typical of many ancient oo- lites and show a wide range of preservation style. Indi- vidual ooids range in diameter from 100 um to about 1 mm. Most ooids possess both a radial and concentric micro- structure characteristic of ancient oolites (fig. 22A). These microstructures are delineated by crystal bound- aries, and by micrite, microspar, and sparry calcite grain-size variations. The concentric microstructure of the oolites is a retention of the primary concentric fabric found in all Holocene aragonite oolites. The radial structure of ancient oolites is thought to be acquired during neomorphism (Shearman and others, 1970). Most ooids show evidence of rim cement which is now preserved as ghosts or as oriented calcite-spar grain boundaries. Much of the cement between ooids is com- posed of silt-sized calcite grains. The matrix between ooids in some eastern localities contains quartz silt (figs. 22B—D). Usually, the ooids themselves are com— posed of micrite and microspar. The preservation of oolites is little affected by struc- tural deformation. Both radial and concentric structure of ooids is still evident despite tectonic deformation (figs. 220, 22E). Other events, not related to tectonism, caused more severe alterations of the oolite texture. Some ooids have been completely altered to micrite (fig. 22C). Others, although texturally not as obscure, have been in part replaced by quartz and chlorite (figs. 23A, 233) or by microspar calcite of only slightly smaller grain size than that of the surrounding matrix (fig. 23C). Solution of oolites takes place along stylolites (fig. 23D) resulting in fabrics similar to those described by Carozzi (1961). Almost all types of grains in the Carrara Formation may serve as nuclei for ooids. Trilobite or echinoderm fragments, or quartz silt grains are the most common nuclei. The shape of the ooid is determined somewhat by the shape of the nucleus (fig. 23E ). Most often, however, the ooids have no obvious nuclei, only a micrite or micro- spar interior. It is possible that these fine-grained centers were pellets. Alternatively, the nuclei may have been minute particles of calcium carbonate which are now impossible to recognize in recrystallized ooid centers. In some ooids, almost the entire grain is micrite (fig. 23F) with only very vague indications of radial and con— centric structure preserved. Where the interior of these micritized ooids is composed of more coarsely crystalline calcite, the center also contains iron oxide stained dolo- mite rhombs (fig. 24A). The oolites of the Carrara Formation display a sur- LITHOFACIES DESCRIPTION AND INTERPRETATION FIGURE 22.—Photomicrographs of rocks from the oolite lithofacies. A, Oolite illustrating radial and concentric microstructure of ooids (top center). Less distinct structure in some ooids is due to the tangential plane of the thin section. Ovoid micrite interiors of some ooids suggest that pellets may have served as nuclei. Alternatively, the interiors may be preferentially micritized. Red Pass Limestone Member, Titanothere Canyon section, California. B, Ooids with vague concentric structure but formed of radially arranged calcite crystals. Quartz silt grains occur both as nuclei and in matrix. Red Pass Limestone Member, Striped Hills section, Nevada. C, Ooids altered almost completely to micrite and microspar. Three ooids are recrystallized to a coarser spar. A few white quartz silt grains are scattered throughout the spar cement. Red Pass Limestone Member, Winters Pass, Calif. D, Tectonically deformed ooids. The radial and concentric microstructure of the grains is clearly visible. The matrix contains a significant amount of quartz silt. Red Pass Limestone Member, Spring Mountains, Nev. E, Well-sorted ooids. Basal part of the Mule Spring Limestone, Paymaster Canyon, Nev. 37 38 CARRARA FORMATION, SOUTHERN GREAT BASIN FIGURE 23.—PhotomicrograpHs of rocks of the oolite lithofacies. A, Ooids containing authigenic silt-sized quartz grains in the outer rims and chlorite crystals arranged radially throughout the ooids. These minerals replace skeletal fragments also in this thin section. Pahrump Hills Shale Member, Pahrump Hills section, Nevada, B, Detail of A, illustrating lath-shaped chlorite crystals in an ooid. C, Ooids replaced by dolomite and microspar calcite, and with iron oxide rims. Matrix is only slightly more coarsely crystalline than ooids. Note that only the concentric microstructure is apparent in these ooids. Cadiz Formation, Marble Mountains, Calif. D, Ooids which are dissolved and compacted in the upper right, presumably as a result of pressure-solution diagenesis, and are separated by a prominent styolite from the uncompacted ooids on the lower left. Red Pass Limestone Member, Eagle Mountain section, California. E, Extremely elongate ooids conforming to the shape of trilobite-fragment nuclei. The skeletal fragments themselves have been replaced by quartz. Thimble Lime- stone Member, Titanothere Canyon section, California. F, Partly micritized ooids with poorly developed rim cement. More coarsely crystalline ooids contain iron oxide stained dolomite rhombs. Note that only the concentric microstructure is visible. Red Pass Limestone Member, Eagle Mountain section, California. LITHOFACIES DESCRIPTION AND INTERPRETATION 39 prisingly small variety of sedimentary structures. As with the lime-mudstone lithofacies, the oolite lithofacies is predominantly thin bedded. The thin beds are burrowed or are composed of single sets of crossbeds (figs. 24B—D). In some western sections, however, internal sedimentary structure is difficult to recognize in the oolite lithofacies. At Titanothere Canyon in the southern Last Chance Range, the oolite in the Red Pass Limestone Member is very well sorted, relatively fine grained, unburrowed, and forms a massively bedded unit. The unit is difficult to recognize as an oolite until thin sections are prepared. Where there is enough variation in grain size and sorting to see sedimentary structures, the oolite is medium bed- ded (10—100 cm) and contains small festoon or trough crossbeds (fig. 24E). The most common nonooid grain types in western sections are skeletal grains. The top of the Red Pass Limestone Member in the Groom Range is an echinoderm-trilobite-fragment calcarenite and is in- cluded in the oolite lithofacies. In contrast, oolites of the Red Pass Limestone Member in the Resting Springs, Nopah, Funeral, and Las Vegas Ranges and in the Striped Hills and Pahrump Hills are thin bedded, burrowed, and interbedded with shales. The few exceptions are several beds about 1 m thick with large-scale high-angle crossbeds. Usually, oolites in this area are composed of somewhat coarser, more poorly sorted ooids than those in northwestern sections. Typi- cally, they are more orange colored and iron stained than the northwestern oolites owing to more replacement by iron-stained dolomite rhombs. The dolomitization tends to mimic low-angle crossbedding resulting in orange and black striping informally called “tiger striping.” Thin sections of eastern oolites contain occasional skeletal fragments and some grapestonelike composite grains (fig. 24F). Ooids occur outside of the oolite lithofacies most com- monly in association with cryptalgal structures. In this setting they are a relatively minor grain constituent, sec- ondary to lithoclasts, skeletal fragments, and quartz grains. An unusual oolite bed occurs in the lower part of the jangle Limestone Member in the Pahrump Hills. This bed consists of plate—shaped oolite clasts, as much as 40 cm long, centered in an oolite matrix (fig. 25A). The clasts are recognizable because the dark pigment in a layer of oolitejust below the surface of the clasts has been removed; thus, the light-colored zone in figure 25A lies just within the clast and is not the outermost surface of the clast. In this section several more characteristics of this unusual oolite intraclast bed may be picked out. Fi- gure 25B is a photomicrograph of the oolite clast bound- ary. The prominent vertical line in the left third of the photo is the clast-matrix contact—clast to the right, mat- rix to the left. Most of the ooids outside the clast are not touching in the plane of the thin section, although they are probably in grain contact. Within the clast most ooids are touching, suggesting some solution along grain con- tacts. The cement within the clast is finer grained than that outside the clast. Also, on the right side of figure 25B and the left side of figure 25C are lighter colored ooids that have been replaced by a more clear calcite spar, in some instances by single crystal grains of calcite. These are the ooids that form the light margins of the clasts seen in the outcrop. Oolite clasts in an oolite matrix indicate early cementa- tion and redeposition of this lithology in the Pahrump Hills area. Similar early cementation was described by Ball (1967) from the Cat Cay sand belt of the Bahama Islands. Ball (1967, p. 563) interpreted this phenomenon as the result of cementation in areas where ooid grains are immobile for some time. Oolites were identified in the Gold Ace Limestone Member and correlative units at Paymaster Canyon and Cucomungo Canyon and in the southern Last Chance Range. This member also contains oolites in the southern Panamint Range (Bates, 1965) where they may represent an eastward advance of the oolite lithofacies beyond its limits in the earlier Thimble Limestone Member (fig. 32). The oolite lithofacies of the Red Pass Limestone Member is found throughout the Carrara Formation and its eastern limit coincides with the approximate eastern limit of thrust faults. Although the present eastern limit of this facies is structurally controlled, it clearly extends much farther to the east than did the equivalent lithofacies of the Thimble or Gold Ace Limestone Mem- bers (fig. 32). Very small accumulations of oolites in the middle of the Cadiz Formation may represent the last vestiges of this lithofacies in the Providence and Marble Mountains. The Jangle Limestone Member has a northwestern oolite lithofacies limit similar to that of the Red Pass Limestone Member. The exception is in the Belted Range where the entire interval correlative with the jangle Limestone Member is replaced by lithologies typi- cal of the Emigrant Formation. The oolite lithofacies is found throughout the jangle Limestone Member. Its distribution to the north in the' Highland Range and Delamar Range is not known. The southeastern limit of the oolite lithofacies is east of Frenchman Mountain where 0.5 m of oolite occurs at the base of the Lyndon Limestone, and west of Azure Ridge where no oolite is found. Oolites in the upper part of the Cadiz Formation probably represent this lithofacies in the Providence and Marble Mountains to the southeast of the study area. ENVIRONMENT OF DEPOSITION The oolite lithofacies of the Carrara Formation shares some features with Holocene oolite accumulations but is identical to none of them. Holocene oolites have been 4O CARRARA FORMATION, SOUTHERN GREAT BASIN FIGURE 24.—Photographs of thin sections, vertical-cut surfaces, and outcrops of rocks of the oolite lithofacies. A, Well-developed dolomite rhombs coated with iron oxide in recrystallized centers of ooids. Red Pass Limestone Member, Eagle Mountain section, California. B, Outcrop photo of thin-bedded oolite. Dolomitic lime-mud- filled burrows occur on the center left and toward the bottom of the photograph. Red Pass Limestone Member, Eagle Mountain section, California. C, Vertical-cut surface of burrowed oolite illustrating the light and dark beds of ooids formed from variations in sorting and dolomitization of the grains. Red Pass Limestone Member, Eagle Mountain section, California. D, Outcrop photo of topsets and foresets in one of the larger crossbed sets in the Red Pass Limestone Member, Nopah Range section, California. E, Outcrop photo of medium-bedded trough crossbedded oolite. Variations in shade are believed to be caused indirectly by sorting variations between crossbed sets. Each dark bar on the left is 10 cm. Red Pass Limestone Member, Titanothere Canyon section, California. F, Photomicrograph illustrating a large composite grain similar to some grape- stone grains described from Holocene deposits. Dark polygonal grains are iron oxide coated dolomite. Red Pass Limestone Member, Eagle Mountain section, California. LITHOFACIES DESCRIPTION AND INTERPRETATION 41 described from a variety of environments including shoreline accumulations (Rusnak, 1960; Logan and others, 1970; Loreau and Purser, 1973), tidal-delta and channel accumulations (Kinsman, 1964;]indrich, 1969; Ball, 1967; Loreau and Purser, 1973), and tidal-bar belts and platform-interior blanket sands (Purdy, 1963; Ball, 1967; Loreau and Purser, 1973). If the oolite lithofacies of the Carrara Formation clearly represented any one of these environments, clues to its environment of deposi- tion should be found in the associated lithologies and the internal sedimentary structures. There are, however, few distinctive sedimentary structures in the oolite lithofacies. One of the most characteristic features of several types of modern oolite sand bodies is the spillover lobe, a series of convex upward cross-sets that may be truncated at their upper surface. The conspicuous ab— sence of this structure from the oolite lithofacies suggests that the oolite is not a tidal-bar belt, bank-edge sand belt or tidal delta—oolite bodies that frequently contain spill- over lobes. The mud content, grapestonelike grains, pre- sence of burrows, and cementation horizons of the oolite lithofacies in sections in the Pahrump Hills, Eagle Mountain, Nopah Range, Winters Pass, and Striped Hills suggest that the best modern analog for this lithofacies is the platform-interior blanket sands of the Bahamian Platform described by Ball (1967, p. 573—576). In more westerly stratigraphic sections, such as in Titanothere Canyon and the southern Last Chance Range, the better sorted mud-free festooned nature of the oolite in the Red Pass Limestone Member indicates more active deposi- tion, perhaps closer to an active sand belt. However, nowhere in the area of distribution of the Carrara For- mation are there large-scale crossbeds that should characterize such a belt. The narrowness of Holocene oolite shoals and sand belts studied by Ball (1967) contrasts with the outcrop pattern of the oolite lithofacies of the Carrara Formation (fig. 31). Few Holocene oolite shoal areas exceed 10 km in width. Given the structure and distribution of strati- FIGURE 25.——Outcrop photo and photomicrographs of unusual oolite } intraclast bed.A, Outcrop photo. The light outline of the clasts is a few millimeters within the clast. Jangle Limestone Member, Pahrump Hills section, Nevada. B, Photomicrograph of an intraclast margin. The intraclast—matrix boundary is the prominent vertical line in the left third of the photo. In the matrix, ooids are separated by blocky calcite cement; in the outermost wall of the clast, the ooids are similar to those in the matrix but are more closely packed; just inside this outermost wall, the ooids are recrystallized and the dark pigment in them is removed. These latter ooids form the light rim seen in the outcrop photo (A). C, Photomicrograph of the interior of an oolite clast illustrating the less recrystallized fabric of ooids in the clasts. The recrystallized ooids on the left form the light rim on the interior of the clast. Note that one ooid is replaced by a single crystal of calcite. 42 CARRARA FORMATION, SOUTHERN GREAT BASIN graphic sections in the western part of the study area, it is possible that a narrow belt of oolite shoals could have existed near the western limit of the areas of shallow- water carbonate sediments. This belt, further suggested by the change in character of the oolite lithofacies in western sections, could have been the source for oolites that spread over the platform interior as a sand blanket. The interpretation of most of the oolite lithofacies as a platform-interior sand blanket is supported by its geo- metry. The Holocene platform-interior sand blankets of the Bahama Platform described by Ball (1967) vary con- siderably in area from a minimum of 18,000 km2 to a maximum of 240,000 kmz. The minimum area of a platform-interior sand blanket is considerably larger than the area covered by other types of sand bodies. The area covered by the oolite lithofacies of the Red Pass Limestone Member, about 40,000 km2, is comparable with the areas covered by platform-interior sand blankets today. Width is also a distinguishing feature of these tabular sand bodies. Platform-interior sand blankets are usually much wider than other sand bodies which rarely exceed 50 km in width. With the exception of the Gold Ace Limestone Member, the oolite lithofacies of all other limestone members of the Carrara Formation exceed 50 km in width in the northwest-southeast direction. Loreau and Purser (1973) stressed the point that the area of active ooid formation in the Persian Gulf is ex- tremely small when compared with the area of ooid dep- osition. They suggest that in time a sheet of oolitic sand may develop whose geometry and magnitude will not reflect that of the ooid—forming environments. Such is believed to be the case for the major part of the oolite lithofacies of the Carrara Formation. THE ALGAL-BOUNDSTONE LITHOFACIES The algal-boundstone lithofacies is the most heterogeneous of the carbonate lithofacies of the Carrara Formation. The primary mineral composing this facies is low-magnesium calcite; however, dolomite is a much more important secondary mineral in this facies than in the mudstone or oolite facies. Other accessory minerals are clays, chlorite, feldspar, pyrite, and quartz. As with the lime-mudstone lithofacies, the dominant grains of the algal-boundstone lithofacies are micrite, microspar calcite, and dolomite; pellets are the most common allochems. Other grain types frequently found in this facies are ooids, skeletal grains, lithoclasts, and oncolites. These larger grains are comparable to those described earlier for the lime-mudstone lithofacies, and there is no need to redescribe them here. Although com- position of the limestone is important in the mudstone and oolite lithofacies, the fabric of the limestone is most important in the algal-boundstone lithofacies. The most characteristic fabric of the algal-boundstone lithofacies is lamination, commonly found in medium and thick beds of limestone or dolomite. Individual laminae are usually horizontal or subhorizontal and vary in thickness from a minimum of 0.1 mm to a maximum of 1 cm but are usually about 1 mm in thickness. Successive laminae are produced by variations in color, grain size, clay content, or, where preserved, pellet size. The laminated units form beds 10 cm—l m thick. The laminations themselves may be relatively flat and even (figs. 26C, top 26D), may be wavy and appear rippled (fig. 26B), or may be uneven and crinkly (figs. 26A, 26C bot- tom). Small cut-and-drape structures are common. Occa- sionally, the drapes are vertical or even overhanging. Rarely, laminations are convex upward forming small stromatolites as much as 10 cm high and 20 cm in diam- eter. Presence of oversteepened laminations suggests that some sedimentary agent other than gravity influ- enced their accumulation. The most probable agent was algae. Some Holocene algae form mats which trap and bind sediment particles in successive layers on the sur- faces with any attitude. Aitken (1967, p. 1164) has applied the term “cryptalgalaminates” to carbonate rocks possibly formed by such algal activity. Dolomite cryptalgalaminates in the algal-boundstone lithofacies are quite different from the replacement dolomites of the lime-mudstone and oolite lithofacies. They are usually composed of micrite-sized grains of dolomite which are not stained with iron oxide. Dolomite rhombs are absent (fig. 26D). The color of these dolo- mites in a fresh surface is black, but they weather orange on exposed surfaces. Staining with potassium fer- rocyanide (Evamy, 1963) shows that these are ferroan dolomites. Cryptalgalaminates are interbedded with the other lithologies of the algal-boundstone lithofacies. Where the cryptalgalaminate is overlain by grainstones, a charac- teristic intraclast bed is formed (fig. 26E). Flat clasts of laminated limestone or dolomite, identical to the cryptal- galaminate lithology, are strewn throughout the over- lying grainstone. The contact between the two lithologies is erosional, and close inspection reveals clasts in all stages of separation from the underlying bed. A variety of epigenetic features disrupts cryptal- galaminates. Mudcracks are common. They are usually seen in vertical section as “stacked plates” whose up- turned edges are the margins of mudcrack polygons (fig. 26F). Some thicker beds of limestone within intervals of mudcracked laminated sediment are probably storm de- posits. Other features of laminated limestones are areas of calcite-spar cement believed to be void fill. These , characterize a class of limestones called dismicrites by Folk (1959), “birdseye limestones” by Ham (1954), lofer- ites by Fischer (1964), and laminoid fenestral fabrics by Tebbutt and others (1965). In outcrop these fenestral fabrics are commonly found in thick, generally light col- LITHOFACIES DESCRIPTION AND INTERPRETATION FIGURE 26.—Photographs of outcrops and vertical-cut surfaces of rocks of the algal-boundstone facies.A, Outcrop showing both wavy and irregular laminations in a cryptalgalaminate. Dark laminations contain more iron oxide and weather darker orange on the surface. Red Pass Limestone Member, southern Last Chance Range section, California. B, Outcrop showing both even and wavy laminations in a cryptalgalaminate. Pahrump Hills Shale Member, Striped Hills section, Nevada. C, Cut vertical surface of cryptalgalaminate illustrating sharp vertical break between crinkly laminations (C) in the lower l of the sample and smooth laminations (S) in the upper é. Note oversteepened laminations in the crinkly laminated portions. jangle Limestone Member, southern Last Chance Range section, California. D, Outcrop of cryptalgalaminate composed of dolomite. Note even lamination and small cut-and-drape structure. Pahrump Hills Shale Member, southern Last Chance Range section, California. E, Outcrop of cryptalgalaminate overlain by grainstone. Erosional contact between them is indicated by the small channel to the left of the hammerhead. Flat pebble intraclasts in the grainstone are identical to the underlying laminated bed. Jangle Limestone Member, Eagle Mountain section, California. F, Outcrop illustrating mudcracks in laminated limestone. jangle Limestone Member, southern Last Chance Range, Calif. 43 44 ored, pink, cream, or white beds where the spar forms equant, irregular, or planar dark areas (fig. 27A). How- ever, some units are black and the spar-filled voids are white (fig. 27F). Fischer (1964) called large planar spar- filled voids sheet cracks. In polished slabs and thin sec- tions, some of these voids have irregularities in their ceilings that match irregularities in the floors, suggesting origin by desiccation shrinkage (figs. 27B, 27C). Some of the more irregular spar-filled voids have rather flat floors covered with silt—sized calcite grains termed “vadose crystal silt” by Dunham (1969) and “M2” sediment by Fischer (1964) (figs. 27B, 27C). The matrix of these fenestral limestones is a pelleted micrite (fig. 270). In some examples, laminae between fenestrae have been disrupted and appear broken and dislodged like clasts (fig. 27E). Such brittle movement, rather than bending, suggests a cemented crustlike layer. In some fenestral limestones it is difficult to demon- strate that the sparry areas ever were voids; however, large sparry areas in an otherwise pelletal micrite, even when unsheltered, almost certainly must be void fill (fig. 28A). In plan view the filled voids also appear as discrete areas of calcite spar (fig. 28C). In many instances of recrystallization, the pelleted texture of the matrix is destroyed, but the sparry areas are still recognizable (fig. 288). Many of the more irregular calcite-void fills are dif— ficult to interpret as desiccation voids. Some have formed in discrete horizons within beds that show no other signs of desiccation (fig. 28D). Others are very large and ir— regular (fig. 28E), and in thin section they are charac- terized by rounded margins with many rounded pro- tuberances projecting into the calcite spar (fig. 28F). Some fenestral limestones are characterized by spar— filled areas that are irregular, elongate, and subhorizon- tal, imparting a wavy spongy fabric to the limestone (figs. 29A—C). These fenestral limestones are most like the loferites of Fischer (1964) and characteristically have areas in which the spar and micrite contain a ramifying network of large tubes, perhaps very large algal filaments (fig. 29D). If these are algal tubes, however, they are an order of magnitude larger than Girvanella tubules. Large stromatolites are rare in the algal—boundstone facies of the Carrara Formation. Their principal occur- rence is in limestones at the base of the formation in the southern Last Chance Range. These stromatolites are poorly laminated and form biostromes, about 1 m in diameter and 0.5 m high, disrupting the surrounding thin-bedded grainstone (fig. 30A). The laminations are formed by alternations of micrite and microspar calcite 0r micrite and quartz silt (figs. 3OB—D). In addition to fenestral carbonates, mudcracked CARRARA FORMATION, SOUTHERN GREAT BASIN FIGURE 27 (facing page).—Photographs of outcrops, vertical-cut sur— faces, and thin sections of rocks from the algal-boundstone lithofaciesA , Outcrop photo of fenestral limestone illustrating two geometries of spar-filled voids. The upper half of the photo is characterized by equant coarse sand and granule-size dark sparry areas, and the lower half, by elongate sheet cracks in a laminated lime mudstone. The white areas are abrasion features in the rock surface. jangle Limestone Member, Eagle Mountain section, California. B, Photomicrograph of fenestral limestone illustrating some former voids (shown by arrows) with matching irregularities in their floors and ceilings although others are more irregular or equant and have flat geopedal floors lined with crystal silt. jangle Limestone Member, Pyramid Peak section, California. C, Photo- micrograph of fenestral limestone illustrating crystal silt partly infilling many of the voids. Note the dense pelletal nature of the matrix. Dark area in center is an imperfection in the thin section. jangle Limestone Member, Pyramid Peak section, California. D, Photomicrograph of spar-filled void with a thin accumulation of crystal silt over its floor. Matrix is a very dense pelleted micrite. jangle Limestone Member, Eagle Mountain section, California. E, Vertical-cut surface of fenestral limestone which is algally lami- nated and contains sheet cracks and more equant voids filled with calcite as well as some vertical burrows or gas-escape structures. The sharp truncation and rotated clast in the top center suggests consolidation, if not cementation, early in the history of this rock. Red Pass Limestone Member, Echo Canyon, Calif. F, Outcrop photo of fenestral fabric developed in a black dolomite. Top of the Mule Spring Limestone, Paymaster Canyon, Nev. limestones, and cryptalgalaminates, the algal-bound- stone lithofacies includes interbeds of grainstones, lime mudstones, oncolitic lime mudstones, and, occasionally, shales. There appears to be no pattern in either the detailed stratigraphic succession of these lithologies or their areal distribution. In the Jangle Limestone Member, their distribution approaches a facies mosaic (Laporte, 1967), perhaps reflecting relative sea level. The distribution of the algal—boundstone lithofacies in each of the limestone members of the Carrara Forma- tion, or correlative beds, is shown in figures 31 and 32. This lithofacies is characteristically light colored and forms distinct white bands in outcrops. Locally, the light coloration extends downward into the oolite lithofacies. In the Lower Cambrian members, this lithofacies is found only in their western correlatives—in the lower part of the Mule Spring Limestone at Cucomungo Can- yon and in the lower and upper parts of the Mule Spring Limestone at Paymaster Canyon and in the Goldfield Hills. The western limit of the lithofacies in the Lower Cambrian is not known. In the Middle Cambrian mem- bers, this lithofacies is restricted to their upper and more oceanward parts. In the Red Pass and Jangle Limestone Members both the northwestern and southeastern mar- gins of the algal-boundstone lithofacies may be roughly delineated. In both members the northwestern margin approximately corresponds to the area of transition be- > 45 tween the Carrara and Emigrant Formations although the actual transition between these formations is not ex- posed. The southeastern boundaries of this lithofacies in the two members differ only at Eagle Mountain where the algal-boundstone facies is present in the Jangle Limestone Member and absent in the Red Pass Lime- stone Member. ENVIRONMENT OF DEPOSITION The algal-boundstone facies is the most, specifically interpretable lithofacies of the Carrara Formation in terms of recent carbonate depositional environments. In all studied major carbonate—mud-producing areas, the intertidal and supratidal zones display a very similar 46 CARRARA FORMATION, SOUTHERN GREAT BASIN FIGURE 28.—Ph0t0graphs of outcrops, float specimens and thin sections of rocks from the algal—boundstone lithofacies.A, Photomicrograph 0f unshadowed sparry area in pelletal lime mudstone, assumed to be primary void. Mule Spring Limestone, Paymaster Canyon section, Nevada. B, Photomicrograph of recrystallized fenestral limestone illustrating vague lamination although the sparry areas are still clearly visible. Mule Spring Limestone, Paymaster Canyon, Nev. C, Weathered surface of fenestral limestone illustrating the discrete nature of voids in plan view. jangle Limestone Member, Echo Canyon section, California. D, Photomicrog- raph of isolated, irregular sparry areas of calcite in a laminated ferroan dolomite. Note the rounded edges of the sparry areas. These features are not clearly desiccation structures. Jangle Limestone Member, southern Last Chance Range section, California.E, Outcrop photo of large irregular sparry areas (light gray) developed in several localities immediately below more normal fenestral limestones. Red Pass Limestone Member, Titanothere Canyon section, California. F, Photomicrograph of a sparry area similar to those pictured in E. Note the well-rounded margins of the sparry area and the rounded protuberances of micritic matrix extending into the calcite spar. Jangle Limestone Member, Pyramid Peak section, California. LITHOFACIES DESCRIPTION AND INTERPRETATION FIGURE 29.—Photographs of vertical-cut surfaces and thin sections of rocks from the algal-boundstone lithofacies. A, Vertical-cut surface of wavy fenestral limestone. Rock is irregularly laminated and contains numerous truncations of subhorizontal laminations. Dark laminations are calcite spar._]angle Limestone Member, Eagle Mountain section, Califor~ nia. B, Photomicrograph of a thin section from specimen of A showing fine laminations in the micrite matrix between areas of massive calcite spar. C, Photomicrograph of a thin section from specimen of A. The laminations in the lower half of the photo are caused by stringers of quartz silt. The spongy appearance of the upper half of the photo is characteristic of this loferitelike lithology. D, Photomicrograph of an area of micrite matrix showing a ramifying network of probable algal- filament molds. These features have been found in many of the fenestral limestones and in some of the clasts of a beachrock-like conglomerate at the interface between the lime-mudstone and algal-boundstone lithofacies. jangle Limes- tone Member, Eagle Mountain section, California. 47 48 CARRARA FORMATION, SOUTHERN GREAT BASIN FIGURE 30.—Outcrop photo and photomicrographs of rocks from the algal-boundstone lithofacies. A, Outcrop photo of an algal biostrome in thin-bedded lime mudstone and grainstone. Eagle Mountain Shale Member, southern Last Chance Range section, California. B, Photomicrograph of algal laminations within a stromatolite illustrating the grain-size variation in successive lamina- tions. Dark laminae are micrite; light laminae are microspar. Eagle Mountain Shale Member, southern Last Chance Range section, California. C, Photomicrograph of algal laminations within a stromatolite. These laminations are formed by successive alternations of micrite and quartz-silt laminae. The irregularity of the laminations leads to a poorly laminated structure. Eagle Mountain Shale Member, southern Last Chance Range section, California. D, Detail of C illustrating quartz-sand and micrite laminae. LITHOFACIES DESCRIPTION AND INTERPRETATION 49 array of sedimentologic criteria that identify these envi— ronments in ancient limestones. Often it is difficult to separate sediments deposited in the intertidal zone from those deposited in the supratidal zone and both are lumped together as peritidal deposits. Algally laminated pelletal mudstones, stromatolites, fenestral limestones, mudcracks, crusts, and flat-pebble conglomerates characterize the intertidal and supratidal zones of south— ern Florida (Ginsburg, 1957; Gebelein, 1971), Andros Island, Bahamas (Shinn and others, 1965, 1969; Gebe- lein, 1973), the Abu Dhabi area of the Persian Gulf (Ken- dall and Skipwith, 1968), and Shark Bay, Western Au- stralia (Logan and others, 1970). In addition, the Persian Gulf and Shark Bay areas are in regions whose annual rainfall is less than 22 cm per year, and the peritidal deposits include well-developed evaporites. The algal-boundstone lithofacies of the Garrara For— mation and the peritidal deposits of south Florida and the Bahamas share all the common features of peritidal car- bonates as well as the special textural features of their fenestral limestones. Molds of very large algal filaments resembling those in figure 290 have been recognized in fresh and brackish water algal marshes (Shinn and others, 1969, p. 1211; Monty, 1967, 1972). These fea- tures are restricted to humid areas of moderate rainfall where brackish and fresh water stand for long periods of time during the year. In contrast, major differences exist between the algal- boundstone lithofacies of the Garrara Formation and the peritidal deposits of the Persian Gulf and Shark Bay. Although evidence for some evaporites (in the form of salt—crystal casts) exists in the Pahrump Hills Shale Member, no evidence was found for massive evaporite deposition. Furthermore, in the highly saline waters of Shark Bay, high-relief stromatolites are well developed (Logan, 1961; Logan and others, 1964). Although high- relief stromatolites are common in many Cambrian limestones, they are conspicuously rare in limestones of the Garrara Formation. Thus, the near absence of evaporites and high-relief stromatolites and the presence of large algal-filament molds associated with the typical features of desiccation and exposure characteristic of Holocene peritidal envi- ronments strongly suggest that algal-boundstone lithofacies of the Garrara Formation accumulated as a peritidal deposit in a rather humid environment perhaps comparable to the Bahamas and south Florida where the annual rainfall is 100—150 cm. The absence of peritidal features in the Emigrant and Monola Formations to the west—and in many of the eastern sections of the Garrara Formation—suggests that the peritidal deposits in the Garrara Formation formed as local low-carbonate islands on the western half of a car- bonate platform. SPATIAL RELATIONS OF THE CARBONATE LITHOFACIES The limestone and shale members of the Garrara For- mation reflect the dynamic interaction between pre- dominantly western limestone lithosomes and pre- dominantly eastern terrigenous clastic lithosomes. The key to understanding this interaction lies in the correct interpretation of the spatial relations of the depositional environments represented by the lime-mudstone, oolite, and algal-boundstone lithofacies. Although faunal con- trol within the Garrara Formation is an adequate aid for identification and correlation of the members, it is insuf- ficient for correlation of lithofacies within members. The consistent presence of trilobites of the Olenellus multinodus Zonule just above the top of the Gold Ace Limestone Member, and trilobites of the Glossopleum Zonule just above the top of the Jangle Limestone Member, together with the sharply defined stratigraphic tops to all the limestone members, suggests that the tops of the mem- bers are approximately synchronous throughout the study region. Thus, the regional distribution of the three carbonate lithofacies in the upper part of each of the limestone members probably reflects the real areal dis— tribution of these lithofacies (fig. 31). The lime-mudstone, oolite, and algal-boundstone lithofacies appear, respectively, to be deposits of a shal- low protected subtidal carbonate platform, a subtidal platform—interior sand blanket (perhaps east of an oolite shoal), and peritidal zones around islands that formed on the western part of the carbonate platform. Although the three environments represented by the carbonate lithofacies did not coexist during all the time represented by the deposition of the Garrara Formation—or even of one limestone member—each of the environments coexisted with one or more of the others for significant periods of time. Rocks of the algal-boundstone lithofacies are restricted both geographically and stratigraphically. They are found primarily in the western exposures of the lime- stone members or their western correlatives, and they are usually found only in the upper beds of these units. The algal-boundstone lithofacies certainly coexisted with the lime-mudstone lithofacies. Most of the sediment in the peritidal zone (algal-boundstone lithofacies) does not originate in this environment. The sediment originates as carbonate mud or pelleted mud in the adjacent subtidal areas and is transported to the peritidal zone catastrophi— cally. Hardie and Ginsburg (1971) have shown that al- gally laminated sediments in the intertidal zone of An- 50 CARRARA FORMATION, SOUTHERN GREAT BASIN 118° 118° 114° 118° 116° 114° 1 1 1 1 38° i 38° —— — '\ o . 1 \\ \ l \ \\ ‘‘‘‘‘‘‘‘ NEVADA l UTAH ’ V . ~ 0 \ - (”"0“0’0‘ 1 i ' " ooo’o’o’o‘o”’” ' ,7 ooooooooooo,o,o, 1 x | , t‘3'3'303'93'3'33333’36 ax«303°3'30339393.?36.39.33}. I ' ”9’9””0099’0’ ’ ’9‘o’o‘o’o‘o’o‘o‘o‘o‘o’o’o’o9096 , o‘o’o’oo’o“’90009 ‘o’oo‘woooooogoooooooo 1 .’.” "‘9‘." ‘o’o’o’feto‘o'o’o’o‘o‘oo’c’o’o’ozozofizo. '. ’o’o’o’o‘029%.o:{9:030:49}:0.9.9.0...9, ‘ _ ' % ”o’o’o‘eto’o.o“9.9.9.9...~.o,o.o.o.o.o " ‘1 ‘o’o‘¢\~%%‘o‘oo 09990900 | ‘ OOO¢99.9.O.O t O...’.0.0.0.Q.§. \ 1 ’o’ozo,¢§§, .o ° o,o,o,o,o.o.¢,¢ 1 ‘ Qx‘O . o .9900. 1 1 ’ 90‘. ~ 0.0.... x 1 l ‘ ‘0» .° ., 0.9.0 1‘ 11 9,9; “90,9 ‘1 :¢:\¢\ ° 0 1 ‘1 1 ’0’. A ° 1 \‘ 1111 —\// 35°” 36°~ y _ It‘ 1 5 \ ARIZONA - 1 \_ ‘ ‘ \ \ CALIFORNIA \ 1 o \\i . . \ Red Pass Limestone Member Jangle Limestone Member . \ 1 I \ 1 1 1 \ 1 118° 116° 114° 118° 118° 114° 1 | 1 1 1 I 1 ‘— 38° W _ 1 \ ' NEVADA 1 UTAH NEVADA i UTAH I ‘ 1 1 ‘1 1‘" 36° — — CALIFORNIA \ CALIFORNIA < Thimble Limestone Member \ Gold Ace Limestone Member 1 \ J 1 \ 1 1 1 1 \ 1 0 50 100 150 200 258 K1LOMETERS g L 1 I 1 1 EXPLANATION .'.V.V.V.V.V.V‘ ' . , . Izzgggggzg Algal—boundstone Lime-mudstone ‘1 Oollte . ' Terrigenous lithofacies lithofacies lithofacies clastic rocks Basinal ' Data points —h-h Eastern limit of Cretaceous overthrusting— lithofacies teeth on overthrust block FIGURE 31.—Lithofacies distribution maps for the top of each limestone member of the Carrara Formation. Dotted line, limit of Carrara Formation. DEPOSITIONAL MODEL 51 dros Island are deposited only following major storms, perhaps as seldom as three times a year. Thus, any peri- tidal carbonate deposit requires a contemporaneous nearby subtidal carbonate-mud-producing area. The subtidal protected mud platform adjacent to Andros Is- land is the source of sediment for the Holocene tidal flats on its west side. By analogy with the Holocene, the sedi- ments of the lime-mudstone facies of the Carrara For- mation were the probable source materials for the peri- tidal algal-boundstone facies. Proof of this relationship is found at Pyramid Peak in the Funeral Mountains, Calif. There, the algal- boundstone cap of the Red Pass Limestone Member con- sists of a fenestral limestone that grades laterally, over a distance of about 40 m, through a medium-bedded crossbedded rounded intraclast conglomerate into a thin-bedded lime mudstone (fig. 33). The intraclast con- glomerate contains lithologies similar to those of the ad— jacent fenestral limestone. The intraclasts are sur— rounded by a well-developed zoned rim cement similar to that of many beach-rock cements (Moore, 1971, 1973; Taylor and Illing, 1971). The stratigraphic distribution of the oolite and lime- mudstone lithofacies in the Red Pass Limestone Member at different localities strongly suggests that sediments of both these lithofacies coexisted at various times and that the oolite lithofacies predominated in the more westerly sections (fig. 32). A similar although less distinct areal relationship for these lithofacies existed for the other limestone members (fig. 32). The oolite and algal—boundstone lithofacies are locally interbedded in the Jangle Limestone Member. The lithofacies probably coexisted locally. Exposures showing a lateral transition, comparable to that between the algal-boundstone and lime-mudstone lithofacies, have not been seen. DEPOSITIONAL MODEL The members of the Carrara Formation constitute four complete, and one partial, generalized asymmetrical sedimentary cycles composed of marine shale—limestone member-pairs. Each cycle begins with terrigenous clas- tics, shows a gradual upward change to increasingly cleaner carbonate sediments, and is terminated by an abrupt return to terrigenous clastic sedimentation. Such asymmetrical cycles on vertical scales of tens to hundreds of meters have been described as Grand Cycles in the Cambrian and Ordovician sequences of the southern Canadian Rocky Mountains (Aitken, 1966). The model proposed here for the genesis of the cycles in the Carrara Formation, which are comparable to the smaller Grand Cycles of Aitken, is probably applicable to other Cam— brian and Ordovician Grand Cycles. The key to the model is the pattern of lithofacies re— lationships that develops in the upper contact areas of each of the limestone members of the Carrara Forma- tion. The abrupt appearance of peritidal deposits in the upper and western parts of the limestone members marks a striking contrast in style of deposition to the tens of meters of subtidal carbonates and terrigenous clastics deposited below. This event seems also to be correlated with a rapid westward spread of terrigenous clastic sedi- ments. Both phenomena could be explained by invoking a marine regression caused by sea—level lowering or basi- nal uplift. However, some facts are inconsistent with this interpretation, and other evidence suggests that it is un- likely. In a region which must have undergone net crustal subsidence to accumulate hundreds of meters of shallow-marine sediments—and at a time when the paleogeographic history of western North America in- volved inundation of the continental interior—sea-level lowering or basinal uplift (both of which represent rever- sals of long-term trends) would be anomalies. Further- more, both basinal uplift and sea-level lowering, unless they ceased as soon as carbonate islands and associated peritidal deposits formed, would have led to dis— conformities and to associated vadose sedimentary fea- tures or solution phenomena. These were searched for and not found within the Carrara Formation. The model proposed below for the production of the Grand Cycles of the Carrara Formation is based on variation in the rate of basin subsidence (or sea-level rise). This model ex- plains more of the observed data than models invoking tectonic emergence or eustatic sea—level fall. It can be best understood if Holocene controls on the appearance, migration, and disappearance of depositional environ- ments similar to those of the Carrara Formation are con- sidered. In all areas of Holocene peritidal carbonate-mud ac- cumulation, the active area of carbonate—mud generation is only a few kilometers wide at most, and it is usually much less. Very wide accumulations of peritidal deposits develop through progradation—the seaward accretion of shorelines by continued sedimentation in the intertidal and supratidal zone. Only through progradation could the peritidal deposits of the Carrara Formation reach the areal extent illustrated by the distribution of the algal- boundstone lithofacies (fig. 31). The widespread de- velopment of a thin stratigraphic interval representing this lithofacies near the top of the Red Pass Limestone Member in the west, and its eastward interfingering with subtidal lime mudstone, suggests that it resulted from a single progradational event away from a carbonate island that developed near the western margin of the subtidal 52 carbonate platform. Numerous interbeds of the algal- boundstone Iithofacies and the lime—mudstone Iithofacies in the more westerly exposures of the Jangle Limestone Member suggest that these peritidal deposits may have originated as a series of islands that appeared, coalesced, and disappeared or remained with subtidal channels and protected mud areas between them. Most of the sediment for the construction of these islands probably came from the broad shallow carbonate-mud-producing platform to the east of the islands, although some sediment may have been supplied initially from their westward side. If a complete barrier was established, all the sediment for eastward progradation must have come from the shallow subtidal carbonate-mud platform to the east. The appearance and progradation of peritidal de- posits over subtidal carbonates and clastics in the Carrara Formation is similar to Holocene sedimentary records resulting from progradation of peritidal sequences in the Top of PC , TC EC EM member ,7 UPPER PART OF THE MULE SPRING LIMESTONE [m III: GOLD ACE LIMESTONE MEMBER Top of PC # TC EC EM member “—u-u LOWER PART 118° 116° 114° OF THE 38,4 PC 1‘; MULE l2 SPRING THIMBLE TC NEVADA E LIMESTONE LIMESTONE MEMBER EC \ : ae°~ EM\ ml— \ I T— CALIFORNIA\\\ .5 | L \% EXPLANATION Algal-boundstone Lime—mudstone 0 Iithofacies Iithofacies E D 20 METERS Oolite Terrigenous Iithofacies clastic rocks CARRARA FORMATION, SOUTHERN GREAT BASIN Persian Gulf and the Bahama Islands. In these areas progradation began after a rapid decrease in the rate of sea-level rise. The change in the rate of sea-level rise was almost an order of magnitude, from about 10 m per 1,000 years to 1—2 m per 1,000 years (Bloom, 1971). At Abu Dhabi in the Persian Gulf the progradation started about 4,000 years B.P. (Evans and others, 1969). On the west side of Andros Island in the Bahamas, the progra- dation may have started as much as 7,000 years B.P. (Gebelein, 1973). The most recent change in rate of sea-level rise is related to melting of the Pleistocene ice cap. However, an apparent decrease in the rate of sea-level rise could also be caused by continuous sedimentation and a decrease in the rate of tectonic subsidence. Whatever the cause, de— crease in the rate of sea-level rise does not drastically increase the absolute rate of sedimentation; it only in- creases the apparent rate of sediment supply by decreas- Top of member NR 0'. ' «:3 00 lg? .. Q23: 0 i' v: .on 118° 118° 114° 38° JANGLE LIMESTONE MEMBER \ LC\ NEVADA EC\\ PP EM\\ (‘V NR \ \ CALIFORNIA ‘ I " UTA—HI— 36° '23 Top of PH member IIIII o I O I. 0. )0. ...e.. RED PASS LIMESTONE MEMBER \ CALIFORNIA hi hi FIGURE 32.—Stratigraphic sections of jangle, Red Pass, Gold Ace, and Thimble Limestone Members of Carrara Formation, showing details of Iithofacies distribution and, for the Gold Ace and Thimble Limestone Members, relations to their western correlative, the Mule Spring Limestone. LC, Last Chance Range; EC, Echo Canyon; PP, Pyramid Peak; EM, Eagle Mountain; NR, Nopah Range; PC, Paymaster Canyon; TC, Titanothere Canyon. DEPOSITIONAL MODEL 53 ing the available space within which sediments can ac- cumulate, thus forcing lateral spread of shoreline envi— ronments into the sea. The absolute decrease in the rate of sea-level rise by about a factor of ten in the Holocene seems to have been sufficient to allow the belt of peritidal sediments to pro- grade seaward. in the Persian Gulf and the Bahamas. A similar decrease in the rate of sea—level rise near the end of the time of deposition of each limestone member of the Carrara Formation could have caused the relative excess of carbonate mud required to initiate the peritidal dep— osition and the eastward progradation that has been ob- served. A decrease in the rate of relative sea-level rise would also explain the westward spread of terrigenous clastics at about the same time as the eastward spread of peritidal carbonate rocks because both phenomena are sedimen- tologic responses to the same stimulus. During the time of deposition of the Gold Ace Limestone Member, clastic sedimentation predominated in the Pahrump Hills and Spring Mountains, and carbonate sedimentation pre- dominated to the west (fig. 31). The abrupt upward change from limestone to shale at the top of the member and its western correlative, the Mule Spring Limestone, reflects a relatively rapid westward expansion of the area of terrigenous clastic deposition. Evidence for westward expansion of terrigenous clastics at this time includes the eastward and upward coarsening of the overlying Pyramid Shale Member. In addition, the upper part of the Mule Spring Limestone to the west is slightly younger than the top of the Gold Ace Limestone Member (Palmer, 1971), and it is composed of peritidal carbonate rocks. Relations between the areas of shallow-shelf sedimen— tation and basinal sedimentation during Grand Cycle development provide important additional clues about the dynamics of Grand Cycle formation.'Although the lateral westward transition from shallow marine carbo- nates to the basinal facies is nowhere exposed in the study area, vertical transitions are included within sections in the Groom Range, Belted Range, Paymaster Canyon, Cucomungo Canyon, and the Inyo Mountains. The first two sections involve the Red Pass Limestone Member of the Carrara Formation and the last three involve the Mule Spring Limestone. In each of the stratigraphic sec- tions the prominent limestone is overlain by a shale or argillite which grades upward into thin and evenly bed— 5 METERS 10 M ETERS FIGURE 33,—Lateral relationships of peritidal and subtidal lithologies near Pyramid Peak, Funeral Mountains, Calif. A, Fenestral limestone. B, Intraformational conglomerate with rim cement suggestive of beach-rock cement. C, Subtidal lime mudstone. 54 CARRARA FORMATION, SOUTHERN GREAT BASIN ded often cherty dark—colored fine-grained limestones that contain no oncolites, few skeletal fragments, and no Stromatolites, mudcracks, or other indications of shallow-water deposition. The thickness of the Mule Spring Limestone and the Red Pass Limestone Member in these sections indicates that establishment Of basinal sedimentation is not corre— lated with a westward thinning of the underlying shallow-water limestones. Such a thinning might be ex- pected if the area of basinal deposition had gradually onlapped the area of shallow-water carbonates to the east. However, eastward migration of the areas of basinal deposition only occurred following termination of shallow-water carbonate deposition marking the end of a Grand Cycle. This observation strongly supports the suggestion that regional sedimentation patterns reflect differential rates of either basinal subsidence or sea-level rise. In either instance, the sea will get deeper in areas where carbonate sedimentation has been terminated, and this should be particularly noticeable on the seaward margins Of former shallow-carbonate areas. Any models explaining cessation of shallow-water carbonate sedimentation by either basinal uplift or by lowering Of sea level cannot simultaneously explain the abrupt ap- pearance of deepwater sediments over shallow subtidal sediments. In the light of evidence given, the sequence of events postulated for the development of an ideal Grand Cycle unit of the Carrara Formation is shown in figure 34, and the sequence is as follows: (1) Shallow subtidal carbonate sedimentation is initiated on the subsiding outer part of the shelf and is rep- resented by either oolite or lime-mudstone lithofacies; (2) these lithofacies spread gradually landward over areas of former terrigenous clastic sedimentation; (3) a decrease in the rate Of subsidence or of sea-level rise triggers two simultaneous sedimentologic responses: supply of ter— rigenous clastics continues and the area of clastic sedimentation begins to spread seaward; at the same time, carbonate sediments build to sea level, low carbo- nate islands develop, and the peritidal areas prograde primarily landward toward the shallow subtidal part of the shelf which is the source Of the carbonate sediment for progradation; (4) landward expansion Of the peritidal facies and seaward expansion of the clastic facies de— creases the area of shallow subtidal carbonate-mud pro— duction so that at some point the area becomes too small tO supply mud for progradation and island growth stops; (5) the area of clastic deposition continues to expand seaward because its source continues to supply sediment, and it overrides part or all the remaining peritidal and subtidal carbonate areas, creating the sharp contact marking the base of a new Grand Cycle. The extent to which the last event reaches completion is variable. For example, the elastic tongue of the Chisholm Shale and correlative clastics within the Desert Range Limestone Member Of the Carrara Formation in- terfinger westward with shallow subtidal carbonate muds and do not completely cover the former carbonate plat- form. The clastic tongue of the Pahrump Hills Shale Member interfingers with shallow-water carbonates in the southern Last Chance Range but appears to have expanded completely across the carbonate platform in the Belted Range and Groom Range areas. The clastic tongue of the Pyramid Shale Member and its westward equivalents are not known to interfinger with shallow— water carbonate at any locality, which suggests that the clastic tongue completely engulfed the former carbonate platform. However, the western margin of this unit is not known, and it is possible that shallow-water carbonate sedimentation persisted farther to the west. Incomplete clastic inundation indicates a waning of clastic deposition either because the distance to the clastic source was increased by sea-level rise, or because the relief of the source area was reduced by erosion, or be- cause subsidence in the area of deposition increased thereby permitting clastic sedimentation nearer the source area. In any of these cases, areas of existing shallow-water carbonate sedimentation simply expand eastward again. However, if all areas Of shallow-water carbonate sedimentation have been destroyed by the spread of terrigenous clastics, then a new initiation of oolite or lime-mudstone deposition becomes necessary. Although little information in the rocks relates to this problem, the bases of limestone units that are thought to be near the western margin Of the area of carbonate sedimentation are commonly oolitic. Examples are the base of the Mule Spring Limestone at Paymaster Canyon and the base of the Red Pass Limestone Member in the Belted Range. This might indicate that at some point on a shelf floored by terrigenous clastics, carbonate deposi— tion is initiated inorganically with the deposition of oolites. Inherent in a model is its usefulness as a predictive tool. In the case of the Carrara Formation, the facies charac- teristics used to establish the mechanism of Grand Cycle sedimentation can be used to predict facies distributions in Other areas. For example, if the Grand Cycles Of the southern Canadian Rockies result from decreases in the rate of subsidence, then the upper parts of the carbonate half-cycles should contain intertidal and supratidal de- posits which herald the oncoming regressive clastics. Aitken (1966) provided enough information to suggest that this prediction is correct. Stromatolites and cryptal- galaminates are commonly found at the top of six of the eight Grand Cycles he described (Aitken, 1966, p. 409, PALEONTOLOGIC ANALYSIS 55 OUTER SH ELF INNER SHELF \ , MW - . FIGURE 34.—Hypothetical model illustrating development of a limestone member of the Carrara Formation. I, Clastic phase of lower member of Grand Cycle; II, Development of subtidal oolite or lime mudstone near shelf margin; III, Subsidence and carbonate sedimentation keep pace, and area of subtidal carbonates expands predominantly across inner shelf; IV, Subsidence slows, carbonate sediments build to sea level and areas of peritidal carbonate prograde primarily towards inner shelf lagoon. Terrigenous clastic influx continues prograding seaward. Landward prograding peritidal carbonate areas and seaward prograding clastic areas eliminate area of subtidal carbonate production, terminating carbonate genesis. Continued seaward progradation of clastics across the slowly subsiding shelf caps former peritidal areas and begins stage V, the basal part of another Grand Cycle. 419). Furthermore, Aitken (1971, pp. 563—564) reported that the peritidal facies of the Eldon and Cathedral For- mations is confined largely to western sections. A second example of support for the model comes from a study of the Meagher Limestone of Montana by Lebauer (1965). The Meagher Limestone lies between two shales and might be the carbonate half of a Grand Cycle. The formation consists of a lower mudstone unit overlain by oolite and grainstone units. The model pre— dicts that peritidal carbonates should occur in the upper and western areas of the Meagher Limestone or its cor- relative formations farther west. Although Lebauer re- ported no intertidal or supratidal lithologies from the Meagher Limestone, southwest and seaward there are mudcracked limestones and laminated dolomites that characterize the upper part of the correlative Blacksmith Limestone in northern Utah (Maxey, 1958, p. 656) and indicate intertidal or supratidal environments. PALEONTOLOGIC ANALYSIS BIOSTRATIGRAPHY Analysis of the biostratigraphy of the Carrara Forma— tion provides a good example of the limitations imposed by the geological record on our attempts to determine the meaning of the spatial distribution of fossilized animal remains. We empirically observe the temporal changes in faunas in one stratigraphic section; we correlate sections by vari- ous means to obtain a composite summary of stratig- raphic ranges of our taxa; and we then describe a succes- sion of synthesized biostratigraphic units characterized by particular elements of our faunas. All too often we become obsessed by our generalizations and assume a sharp focus for our units that is not justified by our data. Furthermore, we often obscure discrete contemporary 56 CARRARA FORMATION, SOUTHERN GREAT BASIN biofacies which are incorporated into our generalized biostratigraphic scheme. The data of plate 17 illustrate some of the opportunities, problems, pitfalls, and limita- tions of the “classical” first-approximation approach to biostratigraphy as it has been applied to North American rocks of late Early Cambrian and early Middle Cambrian age. Plate 18 shows the composite ranges of all the trilo— bite species described from the Carrara Formation. Each of the stratigraphic sections studied has only a few fossiliferous beds. Inasmuch as several of these sections have been examined more than once without detecting significant new fossiliferous beds, the distribution of the fossiliferous beds shown on plate 17 is a reasonably good indication of the available faunal control on the bio- stratigraphy. This density of stratigraphic control is comparable to that reported earlier from Cordilleran sections in southern Canada (Rasetti, 1959), east-central Nevada (Fritz, 1968), and northwestern Mexico (Lochman, in Cooper and others, 1952). Data necessary for detailed evaluation of evolutionary relationships are lacking, and many questions regarding the nature of the boundaries between intervals of contrasting faunas can- not be answered. Nevertheless, biostratigraphic analysis of the faunas of the Carrara Formation has two main values: (1) It provides a guide to stratigraphic position in structurally disturbed areas where stratigraphically dis- tinct but lithologically similar units might be miscorre- lated on physical grounds, and (2) it points up some regional faunal differences between approximately con- temporaneous intervals that may be reflecting the dynamics of animal—environment interactions in Cam- brian time. The published biostratigraphic framework for the part of the Cambrian represented by the Carrara Formation consists of four or five assemblage zones (Rasetti, 1951; Lochman and Wilson, 1958). These zones are generally useful interpretive biostratigraphic units of broad re- gional applicability. However, the data from the Carrara Formation show that the conventional method for graphical presentation which shows these zones in stratigraphic juxtaposition is really misleading for more detailed studies. Not only are contacts lacking between the zones, but also distinct faunules that have few or no common forms may be incorporated within one generalized zone, thus obscuring differences of possible biologic or paleoecologic significance. Figure 35 illustrates the meaning of the bio- stratigraphic nomenclature as applied here. Four inter- vals represent the conventional regional-assemblage zones. They are separated by unfossiliferous sequences so that there is no precise local control on their bound- aries. Furthermore, each of these intervals may contain one or more faunules. These faunules characterize de- scriptive biostratigraphic units designated as zonules which have validity only within the area of study. Within the Carrara Formation, these are the intervals that yield distinctive or widespread trilobite assemblages that can be used for local correlation. The intervals between zonules may or may not be fossiliferous. If they are fos- siliferous, they contain generally inadequate material for precise biostratigraphy. The value of the biostratigraphic scheme presented here is that units of local practical importance can be clearly designated. These are the building blocks for generalizations that can be applied on a regional scale. Thus, each region may have its own scheme of zonules, and at the same time, the local schemes can be integrated into useful conceptual units of regional scope. OLENELLUS ZONE The Lower Cambrian part of the Carrara Formation represents only the upper part of the youngest Early Cambrian Bonniu-Olenellus Zone (in the sense of Fritz, 1972). Older parts of this zone are represented by beds containing Wannen'a (Palmer, 1964) in the Saline Valley Formation of the Inyo—White Mountain region; which together with still older Olenellus—bearing beds of the Harkless Formation are western time—equivalents of the Zabriskie Quartzite. The stratigraphic relations of beds with Wanneria to those with trilobites typical of the Car- rara Formation are shown in the Cucomungo Canyon section of the northern Last Chance Range (pl. 17). The Olenellus Zone in the Carrara Formation contains perhaps the greatest diversity of olenellid species of any part of the Early Cambrian, but very few associated non- olenellid trilobites. The principal fossiliferous intervals are the Eagle Mountain and Pyramid Shale Members and the Thimble Limestone Member. Within these members, three zonules can be distinguished and will be discussed. In addition, olenellid and ptychopariid trilobites, gener- ally as indeterminate fragments, are scattered through- out the Gold Ace Limestone Member; but they are neither common enough nor well enough preserved to justify any subzonal biostratigraphic designation. OLENELLUS ARCUATUS ZONULE Immediately above the Zabriskie Quartzite, the basal few meters of the Eagle Mountain Shale Member have yielded Olenellm arcuatus n. sp. in the Grapevine and Funeral Mountains of California. 0. arcuatus is associated with a less distinctive species, 0. cylindricus n. sp. in the Grapevine Mountains. Although these trilobites are not widespread, they are quite distinct from the fauna of the next younger Bristolia Zonule and warrant separate rec- ognition. 0. arcuatus (pl. 2, fig. 11) has a glabellar struc- ture most similar to that of 0. multinodus n. sp. (pl. 4, fig. BIOSTRATIGRAPHY 57 Regional LITHOSTRATIGRAPHY BIOSTRATIGRAPHY b'°$"°"9'°Ph'° “""5 L . , _ , , . Raset’li ,l95l w.l°°hm°" 5&8 Members Descriptive Units Blochronologlcal Units 150". l9 (3:25:32? G/assop/eura Zonule GLOSSOPLEURA ZONE GLOSSOPLEURA ZONE I ullllllllllllllllIlllllll'llfl'll J o oca conr ““9 e lllllllllllllllllllllllllllllll Limestone A/berle/la- \Mex’cw" ALBERT/ELLA \\Zonu|e Pahrump Hills \\ ALBERTELLA ZONE 2 o ‘\ ZONE : Shale Ogygopsfs Zacanthoidid g Zonule Zonule a: E Red Pass iiiilmiiifliii”HWHWUiH FLAG/URA- Limestone lllllllllllllllllllllllllllllll KOngIfEP/S FLAG/URA- Kochosnid Zonule ”FLAG/URA-POL/ELLA” WENCHEMMA POL/ELM Pyramid ZONE ‘ ZONE POI. lamafaspis Zonule STEP/éégl'lvAé‘P/S Shale llllllNo local controll 0. mu/t/noa’us Zonule Gold Ace < L~ , OLENELLUS g "has °"e OLE/VELLUS ZONE 0: g Echo Shale ZONE 0 Thimble Limestone Bristol/a Zonule Eagle Mountain Shale 0. arcuafus Zonule FIGURE 35.—Biostratigraphy of the Carrara Formation and its relation to the lithostratigraphy and to existing biostratigraphic schemes for the Cordilleran region of North America. 1) from the basal beds of the Pyramid Shale Member. However, the distinctive structure of the posterior part of the cephalon distinguishes 0. arcuatus from all other olenellids in the Carrara Formation. BRISTOLIA ZONULE In almost every section of the Carrara Formation, thin often yellow bioclastic limestones or bedding planes of fine-grained limestones within or below the Thimble Limestone Member yield a diverse assemblage of olenel- lids. The most characteristic forms are species of Bristolia, an olenellid with unusually advanced genal spines, and Peachella, an olenellid with swollen genal spines. The other species are relatively less striking, but most are widespread throughout the area. The richest localities have yielded as many as 9 distinct olenellid species from a few meters of beds, and the total number of olenellid species from this interval is at least 1 1. The specimens in this interval are commonly broken, and often only the distinctive fishhook spines of Bristolz'a and the swollen genal spines of Peachella, which resemble large smooth ostracods, can be recognized. However, some samples from the Titanothere Canyon section in the Grapevine Mountains yielded excellent silicified specimens includ- ing the striking ontogenetic series of Bristolia anteros n. sp. shown on plate 1, figures 1—8. Many elements of the Bristolia Zonule have been col- lected from the Latham Shale in the Marble Mountains southeast of the study area and from the lowest beds of the Pioche Shale in the Pioche and Eureka mining dis— tricts to the north. They are also present in the upper part of a thin-bedded zone within the Mule Spring Limestone, about 60 m above its base, in the Cucomungo Canyon 58 CARRARA FORMATION, SOUTHERN GREAT BASIN section of the northern Last Chance Range (pl. 17) im- mediately to the west of the study area, where they dem- onstrate the dramatic westward increase in thickness of the Lower Cambrian carbonate facies as the Echo and Eagle Mountain Shale Members are replaced by lime— stone. OLENELLUS MULTINODUS ZONULE Clay shales in the lower 10 m of the Pyramid Shale Member throughout the area of study yield a diverse assemblage of olenellids, often partly articulated, and characterized by the distinctive small species, 0. mul- tinodus n. sp. The trilobites are commonly flattened and are frequently distorted slightly by postdiagenetic de- formation of the less competent shales near the contact with the underlying Gold Ace Limestone Member. This is the youngest recognizable Early Cambrian zonule in Western United States. The occurrence of 0. multinodus in the southern Canadian Rocky Mountains (Norford, 1962), in a comparable stratigraphic position, indicates that this species had wide distribution in the Cordilleran region. In two sections in the Delamar Range, at Delamar, Nev., and west of Oak Spring Summit on US. Highway 93, north of the study area in Lincoln County, Nev., the 0. multinodus fauna occurs within the Combined Metals Member of the Pioche Formation. The evidence from this area demonstrates that the top of the Combined Metals Member is distinctly younger than the top of the Gold Ace Member of the Carrara Formation, even though the two units occupy very similar homotaxial positions. In the Delamar Range, the 0. multinodus fauna occurs in shales above a prominent ledge-forming limestone several meters thick that occupies the position of the Gold Ace Limestone Member and immediately below a thin limestone 10—20 cm thick. The thin lime- stone bed is immediately overlain by shales bearing only ptychopariid trilobites. Northward, in the type area of the Pioche Formation, the Combined Metals Member includes considerably more limestone and the ptychopariid-bearing shales immediately overlie several meters of olenellid-bearing limestone at the top of the member. The 0. multinodus fauna, which seems to be confined to shales, has not been identified there, but the change from olenellid to non—olenellid—bearing beds in- dicates that the top of the member must be con- temporaneous with the thin limestone overlying the 0. multinodus fauna to the south and thus younger than the top of the Gold Ace Limestone Member. 0. multinodus has also been collected from a thin lime- stone bed immediately above the Chambless Limestone in its type area in the Marble Mountains of California southeast of the study area. TheBristolia fauna is found in the underlying Latham Shale in the same area, thus dem- onstrating unequivocally the correlation of the Cham— bless Limestone with the Gold Ace Limestone Member (fig. 3). “PLAGIURA-POLIELLA” ZONE The lowermost Middle Cambrian beds of the Carrara Formation, in the upper part of the Pyramid Shale Member and the lower part of the Red Pass Limestone Member, are the most poorly fossiliferous of the fossil- bearing parts of the Carrara Formation. This is also true for equivalent beds in other parts of the Cordilleran region and accounts for the principal contrasts in the biostratigraphic schemes of Rasetti (1951) and Lochman and Wilson (1958). Neither of their zonal schemes is really appropriate for the Carrara Formation although the correlations shown in figure 35 indicate approximate equivalence of the two faunal units within this interval to parts of Rasetti’s zones in southern Canada. Because the existing zonal nomenclature is inappropriate and the fauna preservation is generally poor, this interval in the Carrara Formation is assigned to the “Plagium-Poliella” Zone, which states its stratigraphic position without im- plying any common or characteristic genera. POLIELLA LOMA TASPIS ZONULE A thin limestone unit in the Pyramid Shale Member of the Nevada Test Site, and an equivalent bed in the Belted Range in the northwestern part of the study area have yielded a small fauna characterized by Poliella lomataspis n. sp. and indeterminate kochaspid trilobites. This is the oldest Middle Cambrian faunule in the Carrara Forma- tion, and it is isolated from the younger Kochaspid Zonule above by about 70 m of essentially unfossiliferous shales. It is also separated from the youngest olenellid— bearing beds below by at least 50 m of unfossiliferous shales. Thus, in the Carrara Formation, the nature of the Lower-Middle Cambrian boundary cannot be deter- mined. The limestone containing trilobites of the P. lomataspis Zonule has a stratigraphic position similar to that of the Susan Duster Limestone Member of the Pioche Shale in the Pioche district, Nevada, and may correlate with that member. In the Belted Range, the shales immediately above the P. lomataspis Zonule yield a small contrasting fauna con- sisting of an oryctocephalid, a pagetiid, and a smooth simple ptychopariid—all representatives of long-ranging groups within the early Middle Cambrian. This as— semblage is of no apparent immediate biostratigraphic value. BIOSTRATIGRAPHY 59 KOCHASPID ZONULE The lower part of the Red Pass Limestone Member locally yields small assemblages of trilobites generally characterized by one or more species of kochaspid trilo— bites. (Kochaspid trilobites defined on p. 99.) Such trilo- bites are not restricted to this interval, but they are most common here. In the Echo Canyon section of the Funeral Mountains, Calif, a single specimen of Plagium, very possibly P. cercops (Walcott) (pl. 6, fig. 22), has been col— lected from beds within the Kochaspid Zonule. This strengthens the correlation of these beds with Rasetti’s Plagium-Kochaspis Zone in the southern Canadian Rocky Mountains. In the Groom Range and the Nevada Test Site, small trilobites representing a new species here re- ferred to Plagium are remarkably similar to an un— described species shown to me by N. P. Suvorova of the Paleontological Institute, Academy of Sciences, Moscow, U.S.S.R., in 1968. Her specimens came from the Olek- minskiy horizon of the Lena Stage along the Lena River in Siberia. According to a recent summary of Siberian biostratigraphy (Repina, 1974), the Olekminskiy beds are believed to correlate with the upper part of the Olenellus Zone in North America. Thus, the significance of these trilobites for intercontinental correlation is still to be re- solved. ALBERTELLA ZONE This zone contains the richest and most diverse as— semblages of trilobites in the Carrara Formation. It in- corporates three different zonules (fig. 35) whose con- trasts seem to reflect important biofacies differences. These units are in part spatially distinct but con- temporaneous (Ogygopsis Zonule, Zacanthoidid Zonule) and in part only incompletely overlapping in time and space (Zacanthoidid Zonule, Albertella-Mexicella Zonule). (See also the section, “Paleoecology.”) 0G YGOPSIS ZONULE The most strikingly distinct faunal unit within the Al- bertella Zone is found in the 25 m of beds immediately above the Red Pass Limestone Member in the Belted Range, Nev. (pl. 17). This faunal unit is characterized by abundant specimens of Ogygopsis, some of the earliest agnostids known from western North America—orycto- cephalid, pagetiid, and simple ptychopariid trilobites. One of the ptychopariids is a new species of Elmthina (pl. 15, figs. 1—3), a genus previously thought to characterize beds of the Bathyuriscus—Elmthina Zone, two zones higher in the regional Middle Cambrian biostratigraphy. Also notable in the Ogygopsis beds is the complete absence of any Zacanthoididae, which are common elements of contemporaneous beds to the east and southeast of the Belted Range. The biostratigraphic and physical correct- ness of the stratigraphic position of the Ogygopsis Zonule, however, is undoubted. Several of the agnostid, pagetiid, and oryctocephalid species from the Ogygopsis Zonule are found in Albertella-Zone faunas in eastern Nevada (Fritz, 1968) and the northern Utah—southeastern Idaho area (Resser, 1939b; Robison and Campbell, 1974). Com- parison of the Belted Range section with the nearby sec- tions of the Groom Range and the Nevada Test Site (pl. 17) shows the physical basis for correlation. Every occurrence of Ogygopsis and associated trilobites, however, must be carefully examined before age deter- minations are made. In the spring of 1973, a Visit was made to Cambrian exposures in the Narrows, near Cur- rant, Nye County, Nev., north of the study area at the southern end of the White Pine Range. There, a unit with a rich assemblage of trilobites, including Ogygopsis, is found just above a prominent cliff-forming limestone. However, below this limestone we found shales bearing Paralbertella, a zacanthoidid trilobite typical of the Alber- tella Zone and the lower part of the Pahrump Hills—Jangle Grand Cycle. Thus, the cliff-forming limestone is proba- bly the equivalent of either the Jangle or Lyndon Lime- stones, and the Ogygopsis beds there are probably con- temporaneous with the basal beds of the Glossopleum Zone! Ogygopsis is also common in association with simple ptychopariids, oryctocephalids, and olenellids in beds slightly older than any of the fossiliferous invervals of the Carrara Formation, within the Saline Valley Formation to the west of the study area (Palmer, 1964). In each of these instances, Ogygopsis and associated trilobites are found in black limestone or black limy beds within black shales or siltstones and often as complete individuals. This is also true in the Canadian Rocky Mountains where Ogygopsis characterizes beds within the western exposures of the Stephen Formation (Rasetti, 1951), within the Metaline Limestone in eastern Washington (McLaughlin and Enbysk, 1950), in the Kin— zers Formation in southeastern Pennsylvania (Campbell, 1971), and in the Taconic region of eastern New York (Bird and Rasetti, 1968). Each of these occurrences is near the ocean-facing side of the Carbonate Belt of North America. This suggests that the occurrence of Ogygopsis, typically associated with agnostids, pagetiids, oryctocephalids, and simple ptychopariids, represents a special habitat related to the carbonate platform edge. Assemblages with Ogygopsis can be used for precise correlation within the early half of the Middle Cambrian perhaps only at the species level. ZACANTHOIDID ZON ULE The uppermost beds of the Red Pass Limestone Member, and a few beds in the upper part of the Pah— 60 CARRARA FORMATION, SOUTHERN GREAT BASIN rump Hills Shale Member, particularly in the western and northwestern parts of the study area, have yielded rich associations of trilobites with the greatest species diversity of any collections in the Carrara Formation. Most of these collections contain one or more species of Zacanthoididae, in contrast to their general absence in the contemporaneous and also highly diverse faunas of the Ogygopsis Zonule and in the low diversity faunas of the Albertella-Mexicella Zonule. Whereas the contrast with the Ogygopsis Zonule is reasonably clear cut, that with the Albertella-Mexicella Zonule is more qualitative. The qual- itative difference is stressed here because it reflects a subtle biofacies difference that is of considerable impor- tance for regional biostratigraphy (Palmer and Campbell, 1976). The faunas of the Zacanthoidid Zonule contain a large number of species and genera in common with faunas of the Albertella Zone described from east-central Nevada (Fritz, 1968), northern Utah and southeastern Idaho (Resser, 1939b), and the southern Canadian Rockies (Rasetti, 1951). ALBERTELLA-MEXICELLA ZONULE The upper part of the Pahrump Hills Shale Member and the lower part of the overlying jangle Limestone Member in the central and eastern parts of the study area yield small collections generally characterized by species of either or both Albertella (s.s.) and Mexicella. These faunas are much more comparable to the faunas of the Albertella Zone in the Caborca area of Mexico (Lochman, in Cooper and others, 1952), and the Grand Canyon region of Arizona (McKee and Resser, 1945), than they are to the Albertella Zone faunas containing Zacan— thoididae that are cited just previously. Regional signifi- cance of these contrasts is discussed under “Paleoecol— 77 ogy. GLOSSOPLEURA ZONE AND ZONULE In almost every section of the Carrara Formation, one or more thin beds within the Desert Range Limestone Member will yield a coquina of trilobites dominated by a species of Glossopleum. Because the matrix of these beds is often very tight, few good specimens can be obtained unless the rocks are first heated and then chilled rapidly to loosen the matrix. The diversity of the species assemblages in this interval is consistently low, suggesting, in line with the postulated biofacies relationships of the underlying Albertella Zone faunas (fig. 36), that the Glossopleum fauna of the Desert Range Limestone Member represents the restricted shelf biofacies of this time. Evidence that the Glossopleum—bearing interval in the Carrara Formation is properly designated as the Glossa— pleum Zonule is provided by an important collection with specimens of Glossopleum from a thin-bedded silty unit about 150 m above the base of the Bonanza King Forma- tion, which overlies the Carrara Formation, in the Striped Hills section, Nevada (pl. 17). The trilobites from this collection (7199—CO) are illustrated on plates 15 and 16. They demonstrate that the Glossopleum—bearing part of the Carrara Formation represents only the oldest part of the Glossopleum Zone and that this zone has a consider- able stratigraphic thickness that is not generally apparent because few sections in the Great Basin region have fos- siliferous horizons representing more than one restricted part of the zone. The faunas of the Glossopleum Zone and Zonule in the southern Great Basin share practically no genera or species with the older parts of the Carrara Formation. Thus, the evolutionary significance of the Glossopleum fauna is uncertain. The fact that Glossopleum is a long- eyed corynexochid and that'it is associated elsewhere with Zacanthoides provides a basis for relating the Glossopleum fauna to earlier corynexochid-rich Middle Cambrian faunas rather than later, corynexochid—poor faunas. If a consensus is ever reached about stage subdivision of the North American Middle Cambrian, the interval between the top of the Olenellus Zone and the top of the Glossa— pleura Zone, which characteristically yields collections with one or more long-eyed corynexochids, would be a likely candidate for the earliest Middle Cambrian stage. PALEOECOLOGY Even though the Carrara Formation is not richly fos- siliferous, recognition of the spatial distribution of the principal physical environments permits a few observa- tions of possible paleoecological significance. These con- cern the associations of particular trilobite assemblages with particular depositional environments. The rocks of Early Cambrian age show a subtle contrast between the olenellids recovered from the oncolitic and burrowed lime mudstone of the Gold Ace Limestone Member and those from argillaceous limestones of the Thimble and shales of the Eagle Mountain and Pyramid which represent distinctly muddier and probably very slightly deeper environments. The species pair of Olenellus gilbem' Meek and 0. clarki (Resser) is present and is generally common in the Bristolia Zonule in the Eagle Mountain and Thimble Members and in the 0. multinodus Zonule in the base of the Pyramid Member. However, in the stratigraphically intervening oncolitic and burrowed lime—mudstone environment of the Gold Ace Limestone PALEOECOLOGY 61 Member that spread eastward into the area of more ter— rigenous muds, a slightly different species pair is rep- resented by 0. puertoblancoensis (Lochman) and 0. how- elli(?) Meek. The differences between the two species pairs are most obvious in the relative length of the ocular lobes. The correlation between each species pair and its depositional environment is also apparent in the Pioche region to the north. There, shales within the Combined Metals Member bear the 0. multinodus faunule which includes abundant specimens of 0. gilberti—O. clarki; whereas oncolitic and burrowed lime mudstones within the member yield 0. puertoblancoensis—O. howelli(?). Thus, distribution of at least some species of olenellids seems to be environmentally controlled and their regional bios- tratigraphic value is accordingly reduced. A more dramatic example of environmental control on trilobite distribution is given by the faunules of the Alber— tella Zone. Within the Carrara Formation, there is both a vertical and an areal differentiation of these faunules. The vertical differentiation is reflected in the local se- quence of zonules discussed previously. Areally, the Ogygopsis faunule is found only in the Belted Range, which is the northwesternmost section studied; the Zacanthoidid faunule is best developed in the region of the Nevada Test Site and the Groom Range adjacent to the Belted Range in the east and south; and the Albertella—Mexicella faunule is present predominantly in the central and southeastern sections. The Ogygopsis faunule occurs in dark-gray or black thin-bedded fine- grained limestone that represents sedimentation prob- ably belOw local wave base; the Zacanthoidid faunule occurs in coarse bioclastic limestone in a shallower zone of moderate to high energy; and the Albertella faunule oc— curs in more argillaceous limestones suggestive of lower energy conditions. On the basis of the spatial distribution of these environments, the three faunules are interpre— ted here to represent outer shelf (Ogygopsis faunule), ocean-facing carbonate platform margin (Zacanthoidid Ogygopsis Zacanthoidid | faunule), and inner shelf (Albertella-Mexicella faunule) habitats (fig. 36). Although the Zacanthoidid and Ogygopsz's faunules share many common agnostids, pagetiids, and oryc— tocephalids, there is a complete absence of mixing of Ogygopsis and any members of the Zacanthoididae. Ag- nostids and pagetiids are believed to be pelagic and perhaps planktonic organisms (I ell, 1975), and their presence in both faunules reflects the presence of free access to open oceanic waters. The contrasts between the faunules most probably reflect strong benthic contrasts probably correlated with bathymetry. The presence of assemblages containing elements of both the Albertella— Mexicella and Zacanthoidid faunules in the Grapevine and Funeral Mountains (pl. 17) indicates probable faunal interchange between the inner and outer parts of the carbonate platform and shows that the contrasts between these two faunules are more geographic than bathymet- r1c. Work by Campbell (1974) in northern Utah and south- eastern Idaho has demonstrated the presence in the Al— bertella Zone there of the same three faunules recognized in the Carrara Formation. They are also associated with rocks that represent the same depositional environments as those in the Carrara Formation. However, the strati- graphic sequence of the faunules is markedly different: The oldest faunule is the Albertella—Mexz'cella faunule, and the youngest faunule is the Ogygopsis faunule. This evi— dence demonstrates unequivocally that the time-space distribution of the faunules is environmentally con- trolled, and it emphasizes the extremely important point that the zonules characterized by each faunule are of only local stratigraphic value (Palmer and Campbell, 1976). Regionally, trilobite assemblages within the Albertella Zone may be assigned to particular faunules, but refine- ment of age within the zone will require careful physical stratigraphy as well as information about the location of faunas from the subjacent and superjacent zones. biofacies biofacies I Albertella-Mexicella biofacies —>—l ,4 FIGURE Elev—Suggested biofacies-lithofacies model for the Albertella Zone faunas of the Carrara Formation. 62 CARRARA FORMATION, SOUTHERN GREAT BASIN TABLE l.—Summa7y of classzfiwtion of Early and Middle Cambrian trilobites TABLE l.—Summmy of classification o/‘Early and Middle Cambrian trilobites of Carmm Formation ojCarram F urination—Continued Order Superfamily Family Genus Type Order Superfamily Family Genus Type Albertella A. longwelh' n. sp. 9 g: B. antems n. sp. Walcott A. schenki Resser T; E B. bn'stolemir (Rcsser) A. spectremis n. sp. tn '5 B. fragilis n. sp. Albertellina A. aspmasa n. sp. 3: .8 n. gen. 2 Albertelloides A. misohi Fritz u E 0 Fritz A. rectimarginatus n. sp. % 0' ”mm "‘ Sp‘ ° 4% FieMaspis Fieldaspis? sp. :4 0. braohymmna n. sp. Lr :5 . T) . a '5 Rasetti % E 0. dark: (Resser) I'g _: I . I .... .— . . .z: E Mexwmpu M. radmtm n. sp. = O O. cylmdncm n. sp. 8 a 2 go 0 u m n s g S Lochman 3 E 1" ”I” , ‘ P' ‘5 Paralbertella P. bosworthi (Walcott) O a 0. fremontz Walcott E‘ g n. en. 0. ‘lbefl' M k D g g1 1. ee Ptanniganoides P. crassaxis n. 5]). w 0. howellt? Meek . § 0 multinodus n s Rasetti P. hexacantlm n. sp. 0 0' adensis (Waflott) Zamnthoides Z. vafiuantha n. sp. V my . Walcott Z. cf. Z. alum (Resser) 0. puertoblamomzs (Lochman) Zamnthoides? s Olenellm sp. 1 ' P. . . Corynexochid cranidium undet. l Peachella P. brebuptoa n. SP' Corynexochid pygidium undet. 1 Walcolt P. tddmgst (Walcott) Corynexochid pyg’idium undet. 2 l) “ Al ' to Al Ic' to . 1 58 ‘g Peronopxis P. bonnerensix (Resser) 0““ care a u care sp '3 3 Cor da Peron 51.5; s Lorenz Alolmtocare sp. 2 0 . . g go P P Alokistocarella A? cf. A. b'n'ghamensis Resser 5, ED 5 Resser Alokistocarella? 5p. E < 3? Caborcetta C. pseudaulax n. sp. .9 M . M lode . (R S ) Lochman C. reducta n. sp. , S F . . 2 g; 3.3 “cannula m "m e e Chanaa C.? maladenm (Resser) "" '9 . . l . f. . R g g Pagetia P. ressm Kobayashl Wa F0“ C C C vmmta ( esser) .._ - . Elmthma E. antzqua n. sp. '8 '8 Walcott P. rugosa Rasetti R “l m Pagetia sp. 8 esser I I 2; Eoptychopan'a E. [nochenm n. sp. a. Rasetti w Glossopleura G. tutu Resser o . “1 . -‘= Kochaspts K. augwta (Walcott) 'U U '5- Pwlse" 6' mm". (Clark) 33 Resser K. liliana? (Walcott) 9 G. walcottz C. Poulsen . . I E Kochtellma K. g'roomenm n. sp. ° . n. en. K. 'an [emit n. s . _-§ Poltella P. germana (Resser) g Kojchagspid sp ufidet 1 IS Walcott P' If p” n. sp. Kochaspid sp. under. 2 P. . P. lomat ' . . 5; c Mp” n SP Mexicella M. mexicana Lochman E B ia Bonnia s Lochman M. g'randoculm n. sp. § 0:: I It PP. cf. M.? stator (Walcou) g g a C0 N ella N. clinalimbato (Fritz) t‘ 1: y ' . . . R 8 E Kootem'a K. germana Resser n gen N 5mm ( esser) & Wal tt N. unmodemla n. sp. 3 cr) . . Pochyaspis P. gallagan' Fritz Ogygopm 0. typwalzs (Resser) Resser I It Wa CO Plagiura P. extmsa n. sp. Oryctacephalina 0.? malademis (Resser) Resser 1,: 77:12:713‘1152'}, . C . . g Ljrmohrzloga 0 icalis Ress r P. cf. P. cercops (Walcotl) ' l S . e . g 01:: :64: M, Schistometopus Schutometopus spp. e se .= . R 8- Oryctocephalus 0. nyenszs n. sp. esser 8 Walcott Syspacephalus S. longus n. sp. E‘ Thoracocare T. idahoensis (Resser) Resser . 5' Obscmw n. SP' 0 Robison and V olocephalma V. cannexa n. sp. Campbell n. gen. V. cantmcta n. sp. SYSTEMATIC PALEONTOLOGY 63 TABLE 1.—Summmy of (lassyfi'ration of Early and Middle Cambrian trilobites 0f Carram Formation—Continued Order Superfamily Family Genus Type Ptychopariid sp. undet. Ptychopan'id sp. undet. Ptychopariid sp. undet. Ptychopariid sp. undet. Ptychopariid sp. undet. Ptychopariid sp. undet. Ptychopariid sp. undet. Ptychopariid sp. undet. Ptychopariid sp. undet. Ptychopafiid sp. undet. 10 Ptychopariid sp. undet. ll Ptychopan'id sp. undet. 12 Ptychopariid pygidium undet. l Ptychopariid pygidium undet. 2 (Edam-BURN)!— LO Plychopariida—(Iontinued SYSTEMATIC PALEONTOLOGY The classification of the Early and Middle Cambrian trilobites of the Carrara Formation is summarized in table 1. The taxa are listed in the order that they appear on the following pages. A diagnosis or description is provided for each species and for new genera. Lack of discussion of a supraspecific taxon indicates acceptance of this taxon as it is constituted in “Part 0” of the “Treatise of Invertebrate Paleontology” (Harrington and others, 1959) unless otherwise indicated. Bergstrom (1973) has recently reviewed the suprageneric classifica- tion of trilobites and has made some valuable revisions at the ordinal level. In this paper, the orders are used in the sense of Bergstrom. Most descriptive terms used here were defined or illustrated in Harrington and others (1959, p. 42, 44, 46, 47, 117—126). All illustrated specimens have been given US. National Museum catalog numbers and are deposited in the col- lections of that institution. The collection numbers are recorded in the Cambrian-Ordovician locality catalogs of the US. Geological Survey. All figures on the plates show the exterior of the exo- skeleton unless otherwise specified. All dimensions in the vertical plane that includes the axis of symmetry of the trilobite are sagittal dimensions, those in planes parallel to the sagittal plane are exsagittal dimensions, and those in a vertical plane at right angles to the sagittal plane are transverse dimensions. Particular dimensions on all parts were measured as straight-line distances between fur- rows or from margins to furrows as described earlier (Palmer, 1965, p. 23). Order OLENELLIDA Rosset- Famlly OLENELLIDAE Vogdos Genus BRISTOLIA Harrington Bristalia Harrington, 1956, p. 59; Poulsen, C., in Harrington and others, 1959. p. 192, Poulsen, V., 1964, p. 9. Type species .—M esonacis bristolensis Resser, 1928, p. 7, pl. 2, figs. 5—8. Diagnosis.-——Olenellidae with slender, elongate, hourglass-shaped glabella reaching to inner edge of an- terior border. Anterior glabellar lobe hemispherical, about as wide as occipital ring, remaining lobes moder- ately to well defined by glabellar furrows. Occipital ring has median node at posterior margin. Ocular lobes ele- vated, generally unfurrowed, relatively short; line con- necting posterior tips crosses glabella anterior to occipital ring. Genal spines moderately to very strongly advanced. Discussion—The hourglass-shaped glabella extended to the anterior border, the short ocular lobes and the advanced genal spines distinguish species of this genus from other late Early Cambrian olenellids. Some species of Olenellus may have slightly advanced genal spines, but the glabella generally does not reach the anterior border. If it does, it is neither as slender nor as constricted at its midlength as that ofBristolia species (pl. 1, figs. 13, 19; pl. 2, fig. 14). Bristol“ anteros n. sp. Plate 1, figures l—13 Olmellus gilberti Meek (part). Walcott, 1886, pl. 20, fig. lf; 1891, pl. 86, fig. 1f; 1910, pl. 37, fig. 9; pl. 41, fig. 8. Description—Moderately small olenellids, width of largest observed cephalon about 17 mm exclusive of genal spines. Cephalon, without genal spines, subquad- rate in outline; sagittal length about two-thirds width between intergenal angles at posterior margin; anterior margin gently curved forward in front of glabella. Genal spines of mature specimens slender, tapered, rounded in cross section, project laterally and slightly forward from anterolateral parts of cephalon, then curve strongly backward so that tips are subparallel to axis and posterior to posterior cephalic margin. Lateral margin of cephalon approximately perpendicular to posterior margin. In- tergenal angle strongly rounded; lateral border just an- terior to rounded intergenal angle has slight swelling representing vestige of immature intergenal spine. Cephalic border strongly convex in cross section, well defined around entire margin on mature specimens by deep furrow, interrupted at intergenal angle by in- tergenal ridge on larger immature specimens (pl. 1, figs. 8, ll). Glabella long, extended to inner edge of anterior bor- der, defined at sides by changes in exoskeletal slope. 64 CARRARA FORMATION, SOUTHERN GREAT BASIN Anterior glabellar lobe hemispherical, strongly elevated above extraocular region; width slightly greater than basal glabellar width and about one—third posterior cephalic width; posterior part continuous laterally with ocular lobes. Remainder of glabella indistinctly defined laterally, hourglass-shaped, width at middle glabellar segment (L2) slightly less than three-fourths basal glabellar width. Three glabellar furrows present, exclu— sive of occipital furrow; anterior furrow (S3) represented by dimples or transverse slots on glabella posterior to intersection of ocular lobe with anterior glabellar lobe; middle and preoccipital furrows (S2, S1) slotlike distally, shallow across top of glabella; middle furrow transverse; slots of preoccipital furrow directed posterolaterally from side of glabella. Occipital furrow slotlike at side of glabella, shallow across top. Occipital ring gently convex, with low median node adjacent to posterior margin. Ocular lobe short, arcuate, unfurrowed, strongly ele- vated above cheek, top level with top of anterior glabellar lobe. Line connecting posterior tips of ocular lobes passes over occipital furrow (SI) or posterior part of middle glabellar lobe (L2). Tips separated from glabella by dis- tance approximately equal to transverse width of ocular lobe. Although eye surfaces seem to be perfectly pre- served on some small holaspids (pl. 1, fig. 12) individual facets are not discernible and the entire surface is smooth. Extraocular cheeks gently downsloping; distance from ocular lobe to lateral margin about one-fourth width of cephalon on line through ocular lobes. Thorax, pygidium, and hypostome unknown. Ornamentation minimal, consists of fine bertillon markings (pl. 1, fig. 10) on top of glabella, anterior bor- der, and genal spines, and extremely faint fine granula- tion on infraocular cheeks, observable only on delicately preserved specimens. Ontogeny—A small suite of silicified specimens rep- resenting the five developmental stages described for other olenellids (Palmer, 1957) is available for B. anteros. The first two stages, prior to the appearance of genal spines, are generally similar to those of Olenellw. They differ in having the glabella touching the anterior border and generally more prominent ocular lobes (pl. 1, figs. 1, 2). In the third stage, the genal spines of B. anteros appear slightly in advance of the intergenal spines rather than adjacent to them as in Olenellus (pl. 1, fig. 3). The suc- ceeding stages show a gradual anterior progression of the genal spines to their full holaspid condition (pl. 1, figs. 4—9, 11). A strong intergenal ridge persists into the early holaspid stage separating the posterior and lateral border furrows; but in larger holaspids these furrows are joined at the intergenal angle, and the only vestige of the in- tergenal ridge and spine is a slight swelling of the lateral cephalic border. This series clearly demonstrates that the anterolateral cephalic spines of Bristolia are homologous with the genal spines of Olenellus and not an exaggerated development of the anterior border spines of the imma- ture stages. Discussion—This species differs from all Others in the genus in the mature holaspid position of the genal spines. In B. insolms, these spines are directed strongly forward analogous to antennae. In all other species, the genal spines are directed posterolaterally. The most similar species is B. bristolensis (Resser) which has consistently wider extraocular cheeks in addition to posterolaterally directed genal spines. 0ccm‘rence.—Common (>40 cephala), upper part of Bristolia Zonule. California: 4144—CO, 7183—CO, Titanothere Canyon scction, Grapevine Mountains; 4161—CO, 7180—CO, Cucomungo Canyon section, Last Chance Range. Nevada: 3101-CO, 4152—CO, Echo Can- yon section, Funeral Mountains; 3694—CO, 3786—CO, Nevada Test Site; 6399—CO, Desert Range. Bristolia bristolonsls (Resser) Plate 1, figures 14—19 Olmellus howelli Meek (part). Walcott, 1884, pl. 9, fig. 15; pl. 21, figs. 8, 9. Olemllus gilbem' Meek (part). Walcott, 1886, pl. 20, figs. la, 1k, 11; 1891, pl. 86, figs. la, 1k, 11; 1910, pl. 37, figs. 16, 18, 19. Mesonacis bristolemir Resser, 1928, p. 7, pl. 2, figs. 5—8. Olmellw bristolensis (Resser). Riccio, 1952, p. 30, pl. 7, figs. 1, 2, 5; pl. 8, figs. 1—1 1. Bristolia bristolemis (Resser). Harrington, 1956, p. 59, text fig. 1D. Description—Moderately large olenellids, width of largest observed cephalon about 40 mm exclusive of genal spines. Cephalon, without genal spines, subpenta— gonal in outline; sagittal length equal to or slightly greater than one-half width between intergenal angles at posterior margin; anterior margin gently curved, cur- vature continued onto genal spine with no or only very slight deflection. Genal spine slender, tapered, oval in cross section, directed posterolaterally in broad curve from point about Opposite glabellar midlength; posterior tip subparallel to axis and opposite anterior part of thorax. Lateral margin of cephalon generally perpen- dicular to posterior margin although angle may decrease laterally nearly to 45° on extreme variants (pl. 1, figs. 16, 18). Intergenal angles strongly rounded; short sharp in- tergenal spine may be retained just anterior to corner (pl. 1, fig. 17). Cephalic border extremely narrow in front of glabella, broadens laterally; well defined by broad shallow border furrow around entire cephalic margin. Glabella long, extended to inner edge of anterior bor- der. Anterior glabellar lobe hemispherical, strongly ele- vated above extraocular region; width about equal to basal glabellar width and about one-fourth of cephalic width between intergenal angles; posterior part con- SYSTEMATIC PALEONTOLOGY 65 nected to ocular lobes by slight change in slope. Remain- der of glabella hourglass shaped, defined at sides by shallow axial furrows, narrowest at preoccipital furrow (81). Three glabellar furrows present anterior to occipital furrow: anterior furrow ($3) slightly curved posteriorly, continuous across glabella between junctures with ocular lobes; middle furrow ($2) nearly straight across top of glabella, not connected to axial furrows; preoccipital fur- row (Sl) continuous across glabella in gentle posteriorly directed curve, deepest adjacent to axial furrows. Occip- ital furrow deep adjacent to axial furrows, barely appa- rent across top of glabella. Occipital ring has median node adjacent to posterior margin. Ocular lobe short, arcuate, line connecting posterior tips passes over top of glabella at or just posterior to preoccipital furrow (81). Upper surface rises slightly posteriorly relative to tip of glabella (pl. 1, fig. 15); post- erior tips at same elevation as top of glabella. Very shal- low longitudinal furrow barely apparent near and paral- leling lateral margin of lobe. Posterior tips separated from sides of glabella by distance less than width of ocular lobe. Extraocular cheeks gently downsloping; distance from ocular lobe to lateral margin about one-third width of cephalon at intergenal angles. Faint, narrow intergenal ridge apparent on some specimens. Thorax, pygidium, and hypostome unknown. Ornamentation minimal, consists of faint bertillon markings on tops of glabella and ocular lobes and caecal venation of the extraocular cheeks of some specimens. Discussion .—All the specimens assigned to B. bristolensis from the limestones in the Carrara Formation have a slight deflection of the anterior margin at the base of the genal spine which is absent on specimens illustrated by Resser (1928) and Riccio (1952) from the Latham Shale in the Marble Mountains. The differences between speci- mens from the two lithotopes are considered here to be subspeciflc, possibly reflecting their different habitats. B. bristolensis differs fromB. anteros n. sp. andB. insolens (Resser) by lacking anterolaterally directed genal spines and by having relatively wider extraocular cheeks. The latter character as well as more anteriorly placed ocular lobes distinguish it from B. g‘roenlandicus (Poulsen) and B. kentensis (Poulsen). Differences withB.fmgili§ n. sp. are discussed under that species. Occurrence.——Moderately rare (20 cephala), lower part of Bristolia Zonule. California: 3673—CO, 3674—CO, Re- sting Springs Range; 3677—CO, 3678—CO, Eagle Moun- tain; 4144—CO, Titanothere Canyon section, Grapevine Mountains; 4153—CO, Echo Canyon section, Funeral Mountains; 7179—CO, Cucomungo Canyon section, Last Chance Range. Bristolia fragilis n. sp. Plate 2, figures 1—6 Description.—Moderate-sized olenellids, width of largest observed cephalon about 30 mm exclusive of genal spines. Cephalon, without genal spines, trans- versely subelliptical in outline, with straight posterior margin. Sagittal length about equal to width between intergenal angles at posterior margin; anterior margin broadly and evenly curved; very slightly deflected out- ward at base of genal spine. Genal spine directed post— erolaterally in broad curve from point about opposite occipital furrow (SO) or preoccipital lobe (L1); tip slightly hooked. Lateral cephalic margin behind genal spines forms acute angle with lateral projection of posterior margin, joins posterior margin through broad curve at intergenal angle. Cephalic border narrow in front of glabella, well defined around entire margin by shallow border furrow. Glabella long, extended to inner edge of anterior bor- der. Anterior glabellar lobe hemispherical, strongly ele- vated above extraocular region; width about equal to basal glabellar width and about one-fourth width be— tween intergenal angles; posterolateral part separated from ocular lobes by shallow, anterolaterally directed furrow. Remainder of glabella hourglass shaped, defined at sides by shallow axial furrows, narrowest at pre- occipital furrow (Sl). Three glabellar furrows present anterior to occipital furrow: anterior furrow (S3) rep- resented by pits or short transverse slots adjacent to ocu— lar lobes, connected across top of glabella by very shallow furrow; middle furrow (S2) not connected to axial furrows—on large mature specimens, represented by short transverse distal slots connected by shallow furrow; preoccipital furrow (81) deep adjacent to axial furrows, posterolaterally directed, straight, barely apparent across top of glabella. Occipital furrow deep adjacent to axial furrows, barely apparent across top of glabella. Occipital ring has median node adjacent to posterior margin. Ocular lobe moderately short, arcuate, unfurrowed; line connecting posterior tips passes over preoccipital segment (L1). Upper surface of lobe elevated above top of glabella, rises slightly posteriorly. Posterior tip close to glabella. Interocular cheek present only opposite post- erior part of ocular lobe; anterior part of ocular lobe adjacent to laterally expanded glabellar segment (L3). Extraocular cheeks gently downsloping often with well-developed radial caecal venation. Distance from ocular lobe to lateral border furrow at genal angle slightly more than one-third intergenal width of cephalon. Ornamentation, except for radial caecae on extra- ocular cheeks not apparent. Discussion.—This species differs from all others in the genus by the comparatively slight advance of the genal 66 CARRARA FORMATION, SOUTHERN GREAT BASIN spines. The angularity of the intergenal angle is variable and some specimens are difficult to distinguish from variants of B. bristolensis which have an obtuse intergenal angle. Similar individuals of the two species can generally be separated on two characters: the anterior glabellar furrow (S3) of B. bristolensis is of more uniform depth than that of B. fragilis; and the intergenal angle of B. bristolmsis is less smoothly curved. Generally, also, the interocular cheek of B . fragilis is more restricted than that of B. bristolmsis. Although these differences are qualita- tive, the two species are generally easily distinguished by differences in their genal regions. B. fragilis is a characteristic associate of B. anteros in the upper part of the Bristolia Zone in beds generally younger than those with B. bristolensis. Occurrence.—Moderately common (>25 cephala), upper part of Bristolz'a Zonule. California: 4144—CO, 7183—CO, Titanothere Canyon section, Grapevine Mountains; 4152—CO, Echo Canyon section, Funeral Mountains. Nevada: 3694—CO, 3786—CO, Nevada Test Site; 6399—CO, Desert Range. Genus OLENELLUS Billings olenellus Billings, 1861, p. 11; Walcott, 1910, p. 311 [synonymy to date]; Resser, 1928, p. 3; Bell, 1931, p. 1—22; Poulsen, 1932, p. 35; 1959, p. 192; Resser and Howell, 1938, p. 217; Lake, 1937, p. 236; Stbrmer, 1939, p. 242; Shimer and Shrock, 1944, p. 613; Kindle and Tasch, 1948, p. 135; Riccio, 1952, p. 29, 33; Hupe, 1953, p. 73; Shaw, 1955, p. 790; Raw, 1957, p. 149; Pokrovskaya, 1959, p. 157; Suvorova, N. P., in Chernysheva, 1960, p. 62; Fritz, 1972, p. 11; Robison and Hintze, 1972, p. 5. Fremontia Raw, 1935, p. 243; Harrington, 1956, p. 57; Poulsen, 1959, p. 192. Mesomzcis Walcott, 1885, p. 328; 1910, p. 261 [synonymy to date]; Resser, 1928, p. 5; Bell, 1931, p. 1—22; Kobayashi, 1935, p. 117. Paedeumias Walcott, 1910, p. 304; Raw, 1927, p. 137; 1935, p. 242; Raymond, 1928b, p. 169; Resser, 1928, p. 4; Bell, 1931, p. 1—22; Poulsen, 1932, p. 36; 1959, p. 192; Resser and Howell, 1938, p. 225; Shimer and Shrock, 1944, p. 615; Lermontova, 1951, p. 46; Riccio, 1952, p. 30; Best, 1952, p. 15; Palmer, 1957, p. 124, 126; Suvorova, N. P., in Chernysheva, 1960, p. 62; Opik, 1961, p. 419; Cowie, 1968, p. 13. Type species.—01enm thompsoni Hall, 1859, p. 59, fig. 1. Discussion—Fritz (1972) has recently given a full de- scription of Olenellus and has discussed its scope. He has regrouped into Olenellus, with good justification, species formerly segregated into Paedeumias and F remontia, be- cause the supposedly definitive characteristics of those genera intergrade among the large number of olenellid species now known, and consistent criteria for their rec- ognition are not apparent. Synonymization of Fremontia with Olenellw was also suggested by Robison and Hintze (1972). The diversity of forms now included within Olenellus is well illustrated by the olenellids from the Carrara For- mation where 12 species are assigned to the genus. Species characteristics are based on combinations of cephalic features— particularly those of the glabella, ocular lobes, cephalic border, and genal regions. How- ever, morphologic variability within these species is gen- erally greater than variability within most nonolenellid species. This is most easily noted in details of cephalic outline, ocular lobe length, pattern of glabellar furrows, and form of the genal regions. Variability of the genal regions and in cephalic border width, and some of the variability in ocular lobe length, seem to be biologic, but some of the variability of specimens, particularly in shales, is related to diagenetic flattening or tectonic dis- tortion. Because of these factors, small proportional differences are only considered to be valid discriminatory characteristics if they are consistently observed on a number of associated specimens. In this report, the systematics within olenellus are de- liberately conservative. Although separation of the species described here into several genera might be pos- sible, the present approach has been chosen because bio- logically meaningful or stratigraphically useful subsets of the species within the genus in the Carrara Formation are not apparent. This difficulty in supraspecific discrimina- tion represents an important aspect of evolutionary sys- tematics of trilobites that has perhaps not yet been fully appreciated. Cambrian and Early Ordovician time appears to have been a time of gradual development of distinctness in intermediate-level (genus, family) supraspecific taxa. In the Early Cambrian, species can generally be satisfactor- ily discriminated, but genera and families are much dis- puted. In Middle Cambrian and early Late Cambrian time, genera are more distinct, but families are still dis- puted. Only by the later part of Late Cambrian time are family level taxa generally recognizable with some con- stancy. In post-Cambrian time, and particularly post- Early Ordovician time, taxa assigned the rank of super— families and orders become readily identifiable. This in- crease in effective taxonomic distance at increasingly higher taxonomic levels may reflect the gradual stabiliza- tion of shallow marine environments during Cambrian and Ordovician time. A particularly difficult problem in taxonomy of the olenellids has been caused by differing interpretations of the value to be placed on minor but consistent differences in cephalic border width between generalized olenellids, such as those illustrated on plate 3. The specimens iden- tified here as Olenellus gilberti Meek and 0. clarkz' (Resser) are found together in most collections from shales of the Carrara Formation and their axial cephalic features are essentially identical. However, 0. clarki is characterized SYSTEMATIC PALEONTOLOGY 67 by a narrower cephalic border than 0. gilbem', which results also in a slightly longer preglabellar area. In addi- tion, its genal spines are rarely advanced, and its in- tergenal spines, when observed, point directly posteriorly rather than posterolaterally. Narrow— and broad-bordered olenellids are found as- sociated not only in the Carrara Formation, but also in the Pioche Shale in Nevada (Palmer, 1957), the Parker Slate in Vermont (Walcott, 1910), and the Kinzers Formation in Pennsylvania (Fritz, 1972). Taxonomic placement of these narrow— and broad-bordered forms has ranged from separate genera (Paedeumias and Olenellus) (Resser and Howell, 1938; Lochman, Christina, in Cooper and others, 1952; Palmer, 1957) to variants of a single species (Fritz, 1972). Although in the past I have supported separate recog- nition for Paedeumias, so much is now known about the variety of cephalic features of olenellids that it seems inappropriate to continue to assign so much taxonomic weight to the cephalic border. The more realistic and problematic taxonomic choice now is between interpret- ing narrow- and broad-bordered forms as congeneric species (often but not always as species pairs), or as sub— speciflc, perhaps dimorphic, variants. Dimorphism is favored by the common association of narrow- and broad-bordered forms which have indis- tinguishable axial characteristics as described above. It is strengthened by the fact that pairs of such forms from different stratigraphic levels or different sedimentary environments may have minor but consistent axial differences. For example, the species that I identified as 0. gilbem' and 0. clarki from the Combined Metals Member of the Pioche Shale in Nevada (Palmer, 1957, pl. 19, figs. 19, 20) both have very long ocular lobes that reach nearly to the posterior border furrow. In speci- mens from the Carrara Formation that are assigned to these species, however (pl. 3, figs. 3, 8), posterior tips of the ocular lobes are clearly separated from the posterior border furrow and can usually be connected by a line that passes over the anterior half of the occipital ring. In addition, the shorter eyed forms identified here as 0. gilberti and 0. clarki are found both below and above the Gold Ace Limestone Member of the Carrara Formation, whereas long-eyed forms here identified as 0. puerto- blancoenszls (Lochman) and Olenellus howelli? (Meek) are found in the intervening limestones of the Gold Ace Limestone Member, suggesting a possible environmental control of the associated pairs. Several observations, however, provide counter argu- ments favoring recognition of broad- and narrow— bordered forms as separate species. Although mor- phologic pairs are common, they are not characteristic of all large species suites of Olenellus. For example, O. emyparia n. sp. and 0. multinodus n. sp. have no similar associated species. Also, some distinctive and widespread narrow-bordered species, such as 0. nevadmsis (Walcott), have no broad-bordered associates. Perhaps the most significant evidence against dimorphism is provided by olenellid ontogenies. On the basis of an earlier study of silicified onto- genetic suites of associated narrow- and broad- bordered forms from the Pioche region, Nevada (Palmer, 1957), arguments favoring dimorphism could have been made by interpreting the “Paedeumias”-type immatures (low cephalic relief; slender intergenal spines) and associated Olenellus-type immatures (strong cephalic relief; broad, ventrally open intergenal spines) as di— morphs. However, discovery of a sample with beautifully silicified immature olenellids in the northern Delamar Mountains, Nev., substantially weakens that interpreta- tion. In that sample, forms typical of “Paedeumias” and Olmellus can be easily distinguished and all developmen- tal stages described from the Pioche region can be recog- nized. However, all individuals in developmental stages I-III in the Pioche samples had procranidial spines; whereas a substantial number of specimens from stages I—III of both “Paedeumias” and Olenellus in the sample from the northern Delamar Mountains lack procranidial spines. Thus, the “dimorphs” seem to be dimorphic! The evidence given in the preceding two paragraphs is considered sufficient to raise doubts about interpreting broad- and narrow—bordered species pairs as dimorphs. In this report they are recognized as separate species. Olenellus arcuatus n. sp. Plate 2, figures 11, 12 Description—Small olenellids; width of cephalon of largest observed specimen about 15 mm. Cephalon sub- crescentic in outline, both anterior and posterior margins curved forward. Genal angle acute, located posterior to transverse line through occipital ring, has short sharp posteriorly directed genal spine. Narrow cephalic border defined by shallow lateral and posterior border furrows. Intergenal spine not apparent. Glabella elongate, separated from anterior border by narrow preglabellar area. Frontal lobe prominent, sub- hemispherical, well marked at sides by narrow axial fur- rows; width between one-third and one-half greater than width at occipital ring and slightly less than one—third greatest width of cephalon. Posterior part of glabella slender, slightly constricted at middle glabellar segment (L2). Three glabellar furrows present: anterior (S3) and middle (S2) furrows nearly straight, anterior furrow deepest at distal ends; preoccipital furrow (Sl) directed inward in a gentle posteriorly directed curve from axial 68 CARRARA FORMATION, SOUTHERN GREAT BASIN furrows. Occipital furrow apparent only adjacent to axial furrows. Occipital ring and at least glabellar segments L1 and L2 have low axial nodes. Ocular lobes divergent, crescentic, short, well defined, posteriorly tapered. Ocular furrow not apparent. Line connecting tips of ocular lobes passes over anterior part of preoccipital segment. Intraocular cheek moderately to strongly convex transversely, wider than ocular lobe, forms distinct swollen areas adjacent to glabellar seg- ments L1 and L2. Extraocular cheek gently convex, has very faint vestige of intergenal ridge directed posterolaterally from tip of ocular lobe. Distance between ocular lobe and lateral margin between one-third and one-fourth maximum cephalic width. Ornamentation, except for axial nodes, not apparent. Discussion—This species is distinguished from all other olenellids by the strongly curved posterior cephalic mar- gin and short genal spines. The configuration of the glabella and ocular lobes is most similar to the younger species, 0. multinodus n. sp., and both species have axial nodes on glabellar segments. The morphologic similarities and stratigraphic differences indicate that these species probably form a phyletic subgroup within Olenellus. Occurrence.—Rare, 0. arcuatus Zonule. California: 3148—CO (2 cephala), Echo Canyon section, Funeral Mountains; 4146430 (5 cephala), Grapevine Mountains. Olenellus bmhyomma n. sp. Plate 2, figures 7, 8 Description.—Small olenellids; width of largest ob- served cephalon about 15 mm. Cephalon semicircular in outline with marginal curvature continued into slender posterolaterally directed genal spines that originate at posterolateral cephalic corners. Posterior margin straight, directed slightly posterolaterally from occipital ring. Border narrow, defined by shallow border furrows that are deepest along anterior margin. Intergenal spine short, sharp, posterolaterally directed, close to base of genal spine. Glabella elongate, extended nearly to anterior border furrow; preglabellar area extremely narrow. Frontal lobe subcircular in outline, not noticeably inflated, separated from extraocular cheeks by change in exoskeletal slope; top at same level as remainder of glabella; width about equal to transverse width of occipital ring. Remainder of glabella narrowest at middle glabellar segment (L2), poorly defined at sides by changes in exoskeletal slope. Three glabellar furrows present: anterior furrow (53) shallow, curved slightly posteriorly, continuous between inner ends of ocular lobes; middle furrow (S2) rep- resented only by isolated, slightly transverse pits on glabella; preoccipital furrow (S1) moderately deep at sides of glabella, very shallow across top, very slightly curved posteriorly. Occipital furrow deep at sides of glabella, shallow across top. Occipital ring has prominent median node adjacent to posterior margin. Ocular lobe short, arcuate, unfurrowed, sloped in- ward, and not clearly differentiated from intraocular cheek; line connecting tips of ocular lobes passes over top of glabella at preoccipital furrow (Sl). Intraocular cheeks about as wide as ocular lobe. Extraocular cheeks gently convex, downsloping; dis- tance from ocular lobe to border furrow at genal angle slightly less than one-third width of cephalon between intergenal spines. External surfaces of most parts of cephalon smooth; genal spines thickly covered with granules on well- preserved specimens (pl. 2, fig. 8). Discussion—The combination of a glabella not quite reaching the anterior border furrow, short unfurrowed ocular lobes, granular genal spines at the posterolateral corners of the cephalon, and pattern of glabellar furrows serves to distinguish this species from other olenellids. It is most similar to the larger species, 0. fremonti Walcott, and differs principally by having a narrow preglabellar area and by having a less variable relationship between the genal and intergenal spines and the posterolateral corner of the cephalon. Occurrence.—Locally common, Olenellus Zone, im- mediately above Gold Ace Limestone Member. Nevada: 3696—CO, 7194—CO (10 cephala), Desert Range. Olenellus clarki (Besser) Plate 3, figures 1—5 Paedeumias olarki Resser, 1928, p. 9, pl. 3, figs. 1, 2; Riccio, 1952, p. 33, pl. 9, figs. 1—4. Olenellm gilbem' Meek (Part). Walcott, 1884, pl. 21, fig. 14; 1886, pl. 20, fig. 4; 1891, pl. 85, fig. 1d. Description—Moderately large olenellids; width of largest observed cephalon about 50 mm. Cephalon semi— circular in outline, nearly flat; marginal curvature con— tinuous onto short slender genal spine located at or slightly in advance of posterolateral cephalic corner. Posterior margin nearly straight, slightly deflected for- ward distal to position of intergenal spines on some specimens. Intergenal spine usually not apparent on holaspid cephala. Cephalic border narrow, wirelike, well defined by border furrow around entire cephalic margin. Glabella elongate, separated from frontal border by preglabellar area that is generally two to four times longer sagittally than the border. Frontal lobe subcircular to sagittally subovate in outline, not inflated; width about SYSTEMATIC PALEONTOLOGY 69 equal to width of occipital ring; separated from extra- ocular cheeks by change in exoskeletal slope. Remainder of glabella defined at sides by shallow axial furrows, nar- rowest at preoccipital furrow (81). Three glabellar fur- rows present: anterior and middle furrows ($3 and S2) generally represented by isolated deep transverse slots not connected across top of glabella; preoccipital furrow (SI) and occipital furrow subparallel, deep at sides of glabella, not connected across top. Occipital ring has small axial node adjacent to posterior margin. Ocular lobes slender, arcuate, elongate; line connect- ing tips passes over occipital furrow (SO) or adjacent parts of preoccipital or occipital segments (L1, L0). Shallow ocular furrow present, parallel to outer margin of ocular lobe for entire length of lobe. Intraocular cheek about as wide as ocular lobe opposite preoccipital furrow, narrows to about half this width between tip of ocular lobe and glabella. Extraocular cheek broad, gently convex. Narrow pre- glabellar median ridge present on some specimens. Dis- tance from ocular lobe to border furrow at genal angle about equal to, or slightly greater than, transverse width of occipital ring. Ornamentation consists of faint bertillon markings on the glabella and extraocular cheeks of some specimens (pl. 3, fig. 5). Most specimens appear smooth. Discussion—This species is most similar to O. gilberti Meek with which it is often associated. It differs by having a somewhat greater sagittal length to the preglabellar area, a wirelike cephalic border, and generally less ad- vanced genal spines. However, because of distortion of many specimens in shales, it is sometimes difficult to assign particular individuals to either species with con- fidence. The moderately long ocular lobes, clearly sep- arated from both the axial and posterior border furrows at their tips, distinguish this species from other similar species of Olenellus. Occurrence .—Rare to common throughout most of the Olenellus Zone, >50 cephala. California: 2304—CO, 3097—CO, 4152—CO, Echo Canyon section, Funeral Mountains; 3676—CO, Resting Springs Range; 3681—CO, Eagle Mountain; 3698—CO, 4144£O, 7184a,b—CO, Titanothere Canyon section, Grapevine Mountains; 4168—CO, Salt Spring Hills; 4640—CO, Avwatz Pass. Nevada: 1034—CO, 1995~CO, 3694—CO, 3786—CO, 3787—CO, Nevada Test Site; 7192—CO, Desert Range. Olenellus cylindricus n. sp. Plate 2, figures 9, 10, 13, 14 Description—Moderate to large olenellids; width of largest observed cephalon about 40 mm between in- tergenal angles. Cephalon semicircular in outline with marginal curvature continued into slender, posterolater- ally directed, generally slightly advanced, genal spine. Lateral margin behind genal spine straight, makes an angle of 45° or less with lateral projection of straight posterior margin. Border well defined all around cephalon by shallow narrow border furrow. Intergenal spine short, sharp, laterally directed, poorly preserved on many specimens, located slightly anterior to intergenal angle. Glabella elongate, not quite reaching anterior border, leaving narrow preglabellar area. Frontal lobe expanded, subcircular in outline, defined by shallow anterior axial furrows; width about one-third greater than width at occipital ring. Posterior part of glabella moderately de- fined by shallow axial furrows, sides subparallel or slightly convergent opposite occipital and preoccipital segments and only slightly divergent anterior to pre— occipital segment. Three glabellar furrows present: an- terior furrow (SS) shallow, sinuous, deepest adjacent to inner ends of ocular lobes; middle furrow (52) not con- nected to axial furrows, represented by shallow trans- verse slots connected by shallower transglabellar furrow; preoccipital furrow (81) deep adjacent to axial furrows, shallow across top of glabella. Occipital furrow similar in form and depth to preoccipital furrow. Occipital ring has axial node adjacent to posterior margin. Ocular lobe crescentic, posteriorly tapered, upper sur- face not preserved on specimens studied. Intraocular cheek about as wide as ocular lobe. Line connecting post- erior tips of ocular lobes passes over preoccipital segment (L1). Extraocular cheeks gently convex; distance from ocu- lar lobe to border furrow at base of genal spine about one-fourth width of cephalon between intergenal angles. Ornamentation not preserved on specimens studied. Discussion.—This species is most similar to 0. euryparia, and its relations are discussed under that species. The relatively short ocular lobes well separated from the glabella, generally advanced genal spines, and narrow preglabellar area combine to distinguish this species from other similar olenellids. Occurrence.—Common, O. arcuatus Zonule. California: 4146—CO (12 cephala), Grapevine Mountains. Olenellus euryparia n. sp. Plate 2, figures 15-18 Olenellusfremonti Walcott, 1910, pl. 37, figs. 1, 4, 5 (only). Description—Moderate to large olenellids; width of largest observed cephalon about 50 mm between in- tergenal angles. Cephalon transversely subpentagonal in outline, moderately rounded in front of glabella, gently curved laterally, with curve continuing along slender posteriorly directed genal spine. Lateral margin behind 70 CARRARA FORMATION, SOUTHERN GREAT BASIN genal spine straight, makes angle of 45° or more with lateral projection of straight posterior margin. Border well defined by continuous anterior, lateral, and pos- terior border furrows. Intergenal spine short, sharp, lat- erally directed; present on even largest cephala; located at or slightly anterior to intergenal angle. Glabella elon- gate, anteriorly expanded, extended to inner edge of anterior border. Frontal lobe hemispherical, strongly elevated above adjacent extraocular cheeks, defined at sides by narrow shallow anterior axial furrows; trans— verse width about one-fourth more than transverse width of occipital ring. Remainder of glabella defined at sides by narrow, shallow axial furrows; narrowest at glabellar segment L2. Three glabellar furrows present anterior to occipital furrow: anterior furrow (S3) deep adjacent to inner end of ocular lobe, shallow across top of glabella; middle furrow (S2) nearly straight, deepest at distal ends, curved slightly backward laterally behind distally ex- panded glabellar lobe (L3); preoccipital furrow (S1) deep at sides of glabella, directed inward and backward, shal- low across top. Occipital furrow nearly straight, deep distally, shallow across top of glabella. Occipital ring has moderately large axial node adjacent to posterior mar- gin. Ocular lobe slender, arcuate, separated from glabellar lobe L3 by shallow furrow. Ocular furrow apparent only near glabellar end of ocular lobe, connected to axial fur- row so that only inner part of ocular lobe is connected to frontal glabellar lobe. Line connecting posterior tips of ocular lobes passes over anterior part of preoccipital glabellar segment (L2). Intraocular cheeks slightly nar— rower than ocular lobe, moderately to strongly convex transversely forming a ridge that merges posteriorly with extraocular cheek (pl. 2, fig. 18). Extraocular cheek gently convex, downsloping; dis- tance from ocular lobe to lateral border furrow at base of genal spine between one-third and one-fourth width of cephalon between intergenal spines. Ornamentation consists of strong bertillon markings on glabella and weak bertillon markings on anterior bor- der and genal spines; all other parts lack distinct 0r- namentation; surface of mold smooth. Discussion—This distinctive olenellid is distinguished from all other species by having advanced genal spines, laterally directed intergenal spines on specimens of all sizes, and a hemispherical frontal lobe on the glabella that reaches to the inner edge of the anterior border. The most similar species is 0. altifrontatus Fritz (1972) from the upper part of the Bonnia—Olenellus Zone in the Sekwi Formation of the Mackenzie Mountains in the north- western part of the Northwest Territories, Canada. However, 0. emyparia has narrower and more convex intraocular cheeks, slightly shorter ocular lobes, less slot- like lateral parts to the glabellar furrows, and bertillon markings rather than granules on the external surface of the glabella. In addition, 0. altifrontatus has axial nodes on several glabellar segments; whereas none are apparent on 0. emyparia. Among the Carrara faunas, 0. emypan'a is most similar to 0. cylindricus n. sp., differing principally by having the glabella extended to the anterior border and more con- stricted at the middle segment (L2) and by having the middle glabellar furrow (S2) continuous across the entire glabella. 0. cylindricus is also a slightly older species. Occurrence.—-Locally common, upper part of Bristolia Zonule (P). California: 3680—CO (> 20 cephala), Eagle Mountain. Olenellus fremontl Waleott Plate 3, figures 14—17 Olenellmfremonti Walcott, 1910, p. 320, pl. 37, fig. 2 (only); Riccio, 1952, p. 30, pl. 7, fig. 6. Mesonacisfremonti (Walcott). Resser, 1928, p. 6, pl. 1, figs. 3—9; pl. 2, fig. 9; pl. 3, fig. 8. POIenellm (Fremontia)fremonti Walcott. Lochman, Christina, in Cooper and others, 1952, p. 91, pl. 18, figs 4—5. Description—Large olenellids; width of largest ob- served cephalon about 80 mm. Cephalon semicircular in outline, gently convex; marginal curvature continuous onto moderately long slightly advanced genal spine. Posterior margin nearly straight between rounded in- tergenal angles; deflected forward at varying angles to base of genal spine. Intergenal spine not apparent on holaspid specimens. Cephalic border flattened, well de- fined along lateral and anterior margins by continuous border furrow, less well defined along posterior margin. Glabella elongate, extended to anterior border furrow. Frontal lobe subcircular to sagittally subovate in outline, not inflated; width slightly greater than width of occipital ring; separated from extraocular cheeks by change in exoskeletal slope. Remainder of glabella defined at sides by shallow axial furrows, slightly constricted at pre— occipital furrow (Sl). Three glabellar furrows present: anterior furrow (S3) curved backward, shallow, con— nected across top of glabella; middle furrow (S2) straight or slightly curved backward, shallow, not connected to axial furrows, but connected across top of glabella; pre— occipital furrow (Sl) directed inward and backward from axial furrows, connected across top of glabella. Occipital furrow nearly straight, deepest at sides of glabella, not clearly connected across top. Occipital ring has small axial node adjacent to posterior margin. Ocular lobes short; ocular furrow barely apparent parallel to outer margin of lobe; line connecting tips of lobes passes over preoccipital furrow (SI) or middle glabellar segment (L2). Intraocular cheek about as wide as ocular lobe. SYSTEMATIC PALEONTOLOGY 71 Extraocular cheek broad, gently convex. Distance from ocular lobe to border furrow at genal spine about one- third width of cephalon at intergenal angles. Ornamentation consists of very faint bertillon mark— ings on glabella and extraocular cheeks of some speci- mens. Most specimens appear smooth. Discussion. —When Walcott, in 1910, described this species, he included it in a large number of previously illustrated specimens that had been identified as 0. gil- berti Meek or 0. howelli Meek in earlier publications (Wal— cott, 1884, 1886, 1891). The type locality is given as locality 52, Prospect Mountain, Eureka, Nev. Resser (1928) placedfremonti in Mesonacis and restricted it to the specimen from locality 52 illustrated on plate 37, figure 2 by Walcott (1910) and a specimen from the Resting Springs Range (Walcott, 1910, pl. 37, fig. 1). By so revis- ing the species, he automatically designated the specimen from locality 52 as the holotype, all other specimens from this locality being removed from the species. This speci— men seems to be essentially the same as the much better preserved specimens from the Marble Mountains as— signed by Resser to Mesonacisfremonti. The species is similar to the associated Bristolia bris- tolensis from which it differs by having the glabella barely constricted at the preoccipital furrow and by having the genal spines less strongly advanced. It differs from other species of Olenellus by the following combined charac— teristics: glabella reaching the anterior border furrow, short ocular lobes whose tips are well separated from the glabella, and slightly advanced genal spines. In October 1971 I located all but three of the specimens assigned by Walcott (1910, pl. 37) to 0. fremontz' in the collections of the U.S. National Museum and I reexamined them. In addition, specimens identified by Lochman (1952) as 0. (Fremontia) fremontz' were reexamined. Among Walcott’s specimens, those he showed on plate 37, figures 1, 4, and 5 represent 0. eurypan'a n. sp.; figure 2 is the holotype; figure 3 is a form lacking advanced genal spines and possibly represents Wannefla, although it is in a recrystallized limestone and its surface is not preserved; figures 6, 20, 21, and 22 are indeterminate parts; figure 7 is not well enough pre- served to see critical cephalic characteristics and has genal spines more like those of Bristolz'a fragilis n. sp. than 0. fremonti; figures 8, 10, and 11 represent an undescribed species related to Bristolia anteros n. sp.; figure 9, and figure 8, plate 41, are of a specimen of Bristolia anteros n. sp.; figure 14 represents another undescribed species with a glabellar and ocular lobe structure like that of Bristolia anteros but lacking advanced genal spines; figures 16, 18, and 19 represent Bristolia bristolensis (Resser); and figure 17 represents still a third undescribed species more closely resembling 0. euryparia than 0.fremonti and characterized by narrow extraocular cheeks. The speci- mens in figures 12, 13, and 15 could not be located. Lochman (in Cooper and others, 1952) illustrated two specimens assigned to this species. One (Lochman, in Cooper and others, 1952, pl. 18, fig. 5) is too incomplete for specific identification, although it does have a short eye and the glabella reaches the border furrow. The other (Lochman, in Cooper and others, 1952; pl. 18, fig. 4) has much narrower extraocular cheeks than 0.frem0nti and also has a well-developed intergenal spine close to the genal spine. Of the specim as assigned here to 0. fremonti, the specimen from the Salt Spring Hills (pl. 3, fig. 17) agrees in all respects with the Marble Mountains and Eureka district specimens. The specimens from the Funeral Mountains are tectonically distorted but have no clear-cut features to distinguish them from 0.fremonti. Occurrence.—Rare throughout most of the Olenellus Zone (*10 cephala). California: 2304—CO, Funeral Mountains; 3676—CO, Resting Springs Range; 4168—CO, Salt Spring Hills. Olenellus gilberti Meek Plate 3, figures 6—13 Olenellus gilberti Meek, 1874, in White, 1874, p. 7; White, 1877, p. 44, pl. 2, fig. 38; (part) Walcott, 1886, p. 170, pl. 19, figs. 2, 2a, 2b; pl. 21, figs. 1, la; 1891, pl. 84, figs. 1, 1a; pl. 85, figs. lb, 1c; 1910, p. 324, pl. 36, figs. 1, 2, 3, 6; Shimer and Shrock, 1944, pl. 253, figs. 2, 3. Polmellm gilbem' Meek. Peach, 1894, p. 671, pl. 32, figs. 9, 10; Best, 1952, p. 17, pl. 1, figs. 13—17;Norford, 1962, p. 6, pl. 1, figs. 8, 9; Fritz, 1968, p. 193, pl. 36, figs. 26—28. olenellw truemani Walcott. Lochman, in Cooper and others, 1952, pl. 18, figs. 9, 10 (only). Description—Large olenellids; width of largest ob- served cephalon about 80 mm. Cephalon semicircular in outline, nearly flat; marginal curvature continuous onto short slender genal spine located slightly in advance of posterolateral cephalic corner. Posterior margin nearly straight from occipital ring to intergenal spine, then de- flected slightly forward to base of genal spine. Intergenal spine short, sharp, laterally directed, present on speci- mens of all sizes. Cephalic border well defined around entire cephalic margin by moderately deep border fur- row. Inner margins of anterior and lateral parts of'bor— der rise abruptly and steeply from border furrow; peripheral parts of border flattened. Glabella elongate, separated from frontal border by preglabellar area as wide or wider than anterior border. Frontal lobe subcircular in outline, not inflated; width about equal to width of occipital ring; separated from extraocular cheeks by abrupt change in exoskeletal slope. Remainder of glabella defined at sides by shallow axial 72 CARRARA FORMATION, SOUTHERN GREAT BASIN furrows narrowest at preoccipital furrow (S1). Three glabellar furrows present: anterior furrow (S3) deep, curved, not generally connected across top of glabella; preoccipital furrow (S 1) deep at sides of glabella, directed inward and backward from axial furrow, generally not connected across top of glabella. Occipital furrow deep at sides of glabella, directed nearly straight inward from axial furrow, not connected across top of glabella. Occip— ital ring has small axial node adjacent to posterior mar- gm. Ocular lobes slender, arcuate, elongate; line connect- ing tips passes over occipital furrow (SO) or adjacent parts of preoccipital or occipital segments (L1, L0). Shallow ocular furrow present, parallel to outer margin of ocular lobe for entire length of lobe. Intraocular cheek about as wide as ocular lobe opposite preoccipital furrow, narrows to about half this width between tip of ocular lobe and glabella. Extraocular cheek broad, gently convex. Narrow pre- glabellar median ridge present on some specimens. Dis- tance from ocular lobe to border furrow at genal angle equal to or slightly more than transverse width of occipi- tal ring. Ornamentation consists of extremely faint bertillon markings on the glabella of some specimens. Most speci- mens appear smooth. Discussion—The original group of specimens iden- tified by Meek as 0. gilberti from a collection in the Pioche Hills, Nev., includes an association of 0. gilberti and O. clarki. Specimens of both species were illustrated as 0. gilberti by Walcott, who also included Meek’s species 0. howelli within his concept of O. gilberti. All available specimens assigned to O. gilberti by Walcott and earlier workers were reexamined, and the synonymy reflects my conclusions. 0. howelli has long ocular lobes that reach nearly to the posterior border furrow; and it occurs in a crystalline limestone, which in the Pioche region can only be the Combined Metals Member of the Pioche Shale. This member is partly equivalent to the Gold Ace Limes- tone Member of the Carrara Formation. In both units, the olenellid species are characterized by long ocular lobes, and the constancy of those features suggests that they reflect real population differences, interpreted here to be of specific value. 0. gilberti is restricted to forms sharing the characteris- tics of the broad-bordered specimens of the type lot. It is distinguished from other species of Olenellus by the com— bined features of a narrow preglabellar field, by slightly advanced genal spines, by ocular lobes moderately long, but clearly terminating anterior to the posterior border furrow, and by a slightly flattened moderately broad border. It is most difficult to distinguish from the as- sociated species, 0. clarki (Resser). The difficulties of discrimination between forms assigned to these two species are mentioned in the opening discussion of the genus Olenellm. In addition to the Nevada and California specimens assigned to 0. gilberti, several of the specimens identified by Lochman (1952) as 0. truemam' have the characteristics of O. gilbem' and are included here in its synonymy. Occurrence.—Rare to common throughout most of the Olenellus Zone (>50 cephala). California: 2304—CO, 3097—CO, Funeral Mountains; 3676—CO, Resting Springs Range; 3681—CO, Eagle Mountain; 3698—CO, 4144—CO, 7184—CO, Titanothere Canyon section, Grapevine Mountains; P3148—CO, 4152—CO, Echo Ca- nyon section, Funeral Mountains; 4168—CO, Salt Spring Hills. Nevada: 1034—CO, 1995—CO, 3786—CO, 3787—CO, Nevada Test Site; 4433—CO, Belted Range. Olenellus howelli? Meek Plate 4, figure 16 Olmellus howelli Meek, 1874, in White, 1874, p. 8; White, 1877, p. 47, pl. 2, figs. 4a,b. Olmellus gilbmi Meek (part). Walcott, 1886, pl. 18, figs. 1, la; 1891, pl. 84, figs. 1b,c; 1910, pl. 36, figs. 4, 4a; Palmer, 1957, pl. 114, pl. 19, figs. 1—3, 6,11, 12, 15, 16,19. Discussion—A relatively small broad-bordered olenel- lid is associated with the narrow-bordered species 0. puertoblancoensis (Lochman) and has all other features, including the distinctively long ocular lobes, essentially the same as that species. The basic morphologic charac- ters are shared with the single large olenellid cephalon described as Olenellw howelli by Meek. The reasons for removing 0. howelli from the synonymy of 0. gilbem' where it has been placed since 1886, have already been discussed in the section on 0. gilberti. The differences between the holotype and the two specimens from the Carrara Formation may be due wholly to the size differ- ence of the specimens. The frontal lobe of the glabella enlarges with increasing size in most olenellids, and the lesser gap between the front of the glabella and the bor- der in the large specimen may be explained by this obser— vation. However, without more specimens from either the type region or the Carrara Formation, the species identification of the Carrara specimens must remain tenuous. ' ' Occurrence.—Rare, Olenellus Zone. Californla: 4145—CO (l cephalon), Titanothere Canyon section, Grapevine Mountains. Olenellus multinodus n. sp. Plate 4, figures 1—9 Olenellid trilobite, undescribed, Norford, 1962, p. 6, pl. 1, fig. 3. Description—Small olenellids; width of largest ob- served cephalon about 20 mm. Cephalon semicircular in SYSTEMATIC PALEONTOLOGY 73 outline; anterior margin evenly curved with curvature continuing along short slender posterolaterally directed genal spine; posterior margin nearly straight to in- tergenal angle, then directed slightly anterolaterally to base of slightly advanced genal spine. Narrow border well defined by broad shallow border furrow along entire cephalic margin. Intergenal spine short, posterolaterally directed. Glabella elongate, extended nearly to anterior border; preglabellar area very narrow. Frontal lobe prominent, subhemispherical, strongly elevated above extraocular cheeks, defined at sides by abrupt change in exoskeletal slope; width between one-third and one-half greater than transverse width of occipital ring and about one—third width of cephalon between intergenal spines. Posterior part of glabella slender, slightly constricted opposite middle glabellar furrow (S2), axial furrows present only opposite middle glabellar segment (L2). Three glabellar furrows present: anterior furrow (S3) marked only by pits adjacent to juncture of ocular lobe and frontal glabellar lobe; middle furrow (S2) deep at sides of glabella, very shallow across top; preoccipital furrow (S1) slightly curved posteriorly, deep at sides of glabella, shallow across top. Occipital furrow essentially the same as preoccipital furrow. Preoccipital segment merges lat- erally with intraocular cheek. Occipital ring has short axial spine at posterior margin. Single axial nodes de- creasing in height from back to front are present on glabellar segments L1, L2, and L3. Ocular lobes divergent, crescentic, short, prominent, without ocular furrows. Line connecting tips of ocular lobes passes over anterior part of preoccipital segment (L1) or preoccipital furrow (Sl). Intraocular cheek wider than ocular lobes, on some specimens has two low swell- ings. Extraocular cheeks gently convex; distance from ocu- lar lobe to border furrow at genal angle slightly more than one-fourth width of cephalon between intergenal spines. Low narrow intergenal ridge present on some specimens extending from posterior tip of ocular lobe in sigmoid curve to border adjacent to intergenal spine. Ornamentation consists of bertillon markings on glabella and ocular lobes, in addition to axial nodes on glabella. Discussion—This species is distinguished from all other olenellids by having strong glabellar relief and axial nodes on three glabellar segments; short divergent prominent unfurrowed ocular lobes; and slightly ad- vanced, relatively short genal spines. Most samples col- lected show some evidence for tectonic deformation (pl. 4, figs 2, 3). The most similar species is O. arcuatus n. sp. which differs by having a strongly curved posterior cephalic margin and much shorter genal spines. A fragmentary partial thorax from the northern Del- amar Range (pl. 4, figs. 7, 8) shows this species to have an extremely large macropleural third thoracic segment and a gradual transition from prothoracic to opisthothoracic segments. There is no indication of the axial spine usually found on the 15th thoracic segment, but this could be an artifact of imperfect preservation. The specimen has 17 opisthothoracic segments with no indication that the terminal segment is preserved. If additional specimens show similar thoracic peculiarities, 0. multinodus and probably also 0. arcualus should be removed from Olenellus and placed in a new genus. In addition to its occurrences in the Carrara Formation—always in the shales overlying the Gold Ace Limestone Member—O. multinodus has been collected in shales within the Combined Metals Member of the Pioche Shale in Nevada near Delamar and north of U.S. High- way 93 west of the Oak Spring Summit crossing of the Delamar Range (p. 58), and in a 2.5-cm limestone bed immediately above the Chambless Limestone in the Mar- ble Mountains of southeastern California. A specimen assignable to this species (pl. 4, fig. 6) has been illustrated by Norford (1962) from a locality described by Mountjoy (1962) and 10 m above the top of the predominantly quartzitic Gog Group in Jasper Park, western Alberta, Canada. 0ccurrence.—Common (>40 cephala), 0. multinodus Zonule. California: 2304—CO, 3097—CO, Echo Canyon section, Funeral Mountains; 3676—CO, Resting Springs Range; 3681—CO, Eagle Mountain; 3698—CO, 7184—CO, Titanothere Canyon section, Grapevine Mountains. Nevada: 3696—CO, Desert Range; 7221—CO, 7224—CO, Delamar Range. Olenellus nevadensis (Walcott) Plate 4, figures 10, 13, 17 olenellus gilberti Walcott (part). Walcott, 1884, pl. 9, fig. 16', 1886, pl. 19, fig. 2g; 1891, pl. 85, fig. 1e. Calla-via? nevadensis Walcott, 1910, p. 285, pl. 38, fig. 12. Paedeumias nevademis (Walcott). Resser, 1928, p. 9, pl. 3, figs. 3—7; Riccio, 1952, p. 33, pl. 9, figs. 5, 6. Description.—Moderately large olenellids; width of largest observed cephalon about 65 mm. Cephalon semicircular in outline, nearly flat; marginal curvature continuous onto short slender genal spine at posterolat- eral corner. Posterior margin straight, deflected very slightly forward distal to short sharp intergenal spine that is located near genal spine. Narrow convex cephalic bor- der well defined by narrow border furrow around entire cephalon. Glabella tapered forward, relatively short, separated from anterior border by distance varying between one- 74 sixth and one-half sagittal glabellar length. Frontal lobe subconical, defined by abrupt change in slope. Remain- der of glabella widest at occipital ring, tapers very slightly forward to ocular lobes. Three glabellar furrows present: anterior furrow (S3) represented by moderately deep, elongate slots directed inward and backward from inner ends of ocular lobes, may or may not be connected across top of glabella by shallow furrow; middle furrow (S2) represented consistently by isolated deep transverse slots; preoccipital furrow (81) deep at sides of glabella, directed backward and inward, either connected by shallow furrow or not connected across top of glabella. Occipital furrow deep at sides of glabella, not connected across top. Occipital ring has small median node adjacent to posterior margin. Ocular lobes long, slender, arcuate, not furrowed; di- rected posterolaterally from posterolateral parts of frontal lobe; line connecting tips passes over occipital or preoccipital segment (L0, L1). Intraocular cheek about equal in width to ocular lobe. Extraocular cheek broad, gently convex; distance from ocular lobe to lateral border furrow on line parallel to posterior border between one-third and one-fourth posterior width of cephalon. Very narrow preglabellar median ridge apparent on some specimens. Discussion—This species is distinguished from other species of Olenellus by its anteriorly tapered glabella well separated from the anterior border and by the con- figuration of its glabellar furrows. The statement by Wal- cott (1910) that the species is characterized by short ocu— lar lobes resulted from an erroneous reconstruction of the type cephalon which added extra length. The ocular lobes reach nearly to the occipital furrow on most speci- mens and farther posteriorly on others. Specimens possibly representing this species have been found associated with 0. multinodus n. sp. in the northern Delamar Range, but they have a complete occipital fur- row unlike the forms illustrated from the Death Valley region and in the Marble Mountains to the south. They are also significantly younger than the more characteris- t1c spec1mens. Occurrence.—Rare (25 cephala), Bristolz'a Zonule and underlying beds of the lowermost part of Carrara For- mation. California: 3148—CO, Echo Canyon section, Funeral Mountains; 4144—CO, Titanothere Canyon sec— tion, Grapevine Mountains. Nevada: 7193—CO, Desert Range. Olenellus puertoblanooensis (Lochman) Plate 4, figures 11, 14 Paedeumias puertoblancoemis Lochman, in Cooper and others, 1952, p. 94, pl. 19, figs. 9—16. Paedeumicu clarki Resser. Palmer, 1957, pl. 19, figs. 4, 5, 10, 14, 17, 20. Olenellw puertoblancoensis (Lochman). Fritz, 1972, pl. 17, figs. 1—7. CARRARA FORMATION, SOUTHERN GREAT BASIN Discussion.——Two small collections from the Titanothere Canyon section in the Grapevine Mountains, Calif ., have yielded a few cephala of a species-pair similar to Olenellus gilberti—Olenellus clarkz' except for long ocular lobes that extend to or nearly to the posterior border furrow adjacent to the occipital ring, isolating the in— traocular cheek. The narrow-bordered forms agree in all essential details with specimens from the Buelna Forma- tion near Caborca, Mexico, described by Lochman as Paedeumias puertoblancoensis and are assigned to that species. The broad-bordered forms are assigned to 0. howellz'? Meek discussed in a preceding section. A silicified ontogenetic sequence from the Highland Range (Palmer, 1957) that was assigned to Paedeumias clarkz' Resser rep— resents a long—eyed form differing in this respect from P. (now Olenellus) clarki, and it should be assigned to 0. puertoblancoensis. Both Lochman and Fritz gave full de— scriptions of this species. Occurrence.—Rare, Olenellus Zone. California: 4144—CO, 4145—CO (3 cephala), Titanothere Canyon section, Grapevine Mountains. Olenellus sp. Plate 4, figures 12, 15 Discussion .——A single fragmentary cephalon represents an unusual olenellid characterized by well-developed granular ornamentation on the glabella, ocular lobes, and border. The ocular lobes are long; a line connecting their tips passes over the occipital ring. The anterior margin is broken but the front of the glabella is pre- served, suggesting that a short preglabellar area was present. The nature of the genal spine is not known, but it was located at the posterolateral cephalic corner, and a well—developed laterally directed intergenal spine is adja- cent to it. No other olenellid has the granular ornamentation and long ocular lobes characterizing this species, but the sole specimen is too incomplete for formal naming. Occurrence.—Rare, Olenellus Zone. California: 7184—CO (1 cephalon), Titanothere Canyon section, Grapevine Mountains. Genus PEACHELLA Waloott Peachella Walcott, 1910, p. 342; Shimer and Shrock, 1944, p. 615; Poulsen, C., 1932, p. 35; Poulsen, C., in Harrington and others, 1959, p. 192. Type species.—01mellus iddingsi Walcott, 1884, p. 28, pl. 9, fig. 12. Diagnosis.—Olenellidae with generally effaced cephalic furrows. Cephalon semicircular in outline. Glabella elon- gate, extended to inner edge of anterior border. Ocular lobes short, close to glabella. Gena] spines short, swollen. SYSTEMATIC PALEONTOLOGY 75 Discussion—This is the easiest of all olenellid genera to recognize because of the swollen genal spines and gener- ally featureless cephalon. Good specimens are rare, but the swollen genal spines are moderately common (pl. 5, fig. 5) and permit specific identification of fragments in the absence of whole cephala. Peachella brevisplna n. sp. Plate 5, figures 1—3 Description—Moderately small olenellids, length of largest observed cephalon about 12 mm. Cephalon semicircular in outline with short, swollen, posterolater- ally directed genal spines. Glabella long, extended to inner edge of anterior border, poorly defined by slight changes in exoskeletal slope, breadth nearly constant. Glabellar and occipital furrows not apparent. Ocular lobes short, unfurrowed, close to glabella, poorly dif- ferentiated from frontal lobe and intraocular cheek; line connecting posterior tips passes over glabella at point about two-thirds of glabellar length from anterior end of glabella. Occipital ring seems to lack distinct axial node adjacent to posterior margin. Extraocular cheeks gently downsloping t0 cephalic margin. Anterior and lateral borders poorly defined by shallow, narrow border fur- row; lateral border furrow continues along inner base of genal spine to posterior margin. Posterior border furrow not clearly defined. External surfaces of all parts of cephalon smooth. Discussion .—This species differs from all other olenel- lids by its poor development of cephalic furrows, by short ocular lobes, and by short, swollen, and posterolaterally directed genal spines. The latter character distinguishes it from P. iddingsz' (Walcott). Occurrence.—Moderately rare (”~15 cephala), Bristolia Zonule. California: 3679—CO, Eagle Mountain; 4167—CO, Dublin Hills. Peachella iddlngsi (Walcott) Plate 5, figures 4—9 Olenellus iddingsi Walcott, 1884, p. 28, pl. 9, fig. 12; Walcott, 1886, p. 170, pl. 19, fig. 1. Peachella iddingsi (Walcott). Walcott, 1910, p. 343, pl. 40, figs. 17—19; Shimer and Shrock, 1944, pl. 254, fig. 17. Description—Moderately small olenellids, length of largest observed cephalon about 12 mm. Cephalon semicircular in outline with moderately short posteriorly directed sausage-shaped genal spines at posterolateral corners. Glabella long, extended to inner edge of an- terior border, poorly defined by slight changes in exos- keletal slope, narrowest at about midlength. Glabellar and occipital furrows barely apparent even after whi- tening. Ocular lobes short, unfurrowed, close to glabella, poorly differentiated from frontal lobe of glabella and intraocular cheek; line connecting posterior tips passes over glabella slightly posterior to glabellar midlength and, where apparent, over middle glabellar segment (L2). Occipital ring has median node adjacent to pos- terior margin. Extraocular cheeks gently downsloping to shallow lateral border furrow. Posterior border furrow defined faintly only near genal angle. Anterior border narrow, begins to broaden posteriorly into swollen genal spine opposite anterior glabellar lobe. Posterior border wider than anterior border near genal angle at position of immature intergenal spine. Extremely faint intergenal ridge present on some specimens. External surfaces of all parts of cephalon smooth. Discussion .—This species is easily distinguished from all other olenellids by its short ocular lobes, posteriorly di- rected sausage-shaped genal spines, and poor develop- ment of cephalic furrows. The shape and direction of the genal spines distinguishes P. iddingsi from P. brevispina n. sp. A small suite of silicified specimens from the Titanothere Canyon section includes immature cephala with a more distinctly defined glabella and glabellar fur- rows, and with a short intergenal spine adjacent to the genal spine (pl. 5, fig. 6). Occurrence.—Moderately common (<20 cephala), Bristolia Zonule. California: 3675—CO, Resting Springs Range; 4144—CO, 7183—CO, Titanothere Canyon sec- tion, Grapevine Mountains; 4152—CO, Echo Canyon sec— tion, Funeral Mountains; 4290—CO, Funeral Mountains; 4161—CO, Cucomungo Canyon section, Last Change Range. Nevada: 3694—CO, 3786—CO, 3787—CO, Nevada Test Site; 7193—CO, Desert Range. Order MIOMERA Jaekel Superfamjly AGNOSTOIDEA Salter Family QUADRAGNOSTIDAE Howell This family assignment is used here in the sense of Opik (1961) and has been discussed by me earlier (Palmer, 1968, p. 23). The ordinal and superfamily des- ignations, are those recommended by Jell (1975, p. 14). Genus PERONOPSIS Corda Peronapsiv Corda in Hawle and Corda, 1847, p. 115; Palmer, 1968, p. 31 (for Synonymy to date). Type species .—Battu5 integer Beyrich, 1845, p. 44, pl. 1, fig. 19. Discussion.—Robison (1964) presented a good recent diagnosis of this genus to which the specimens described below conform in all respects. 76 Peronopsis bonnerensis (Resser) Plate 12, figures 11, 15 Agnostus bonneremis Resser 1938b, p. 6, pl. 1, figs. 16, 17; Resser, 1939a, p. 8, pl. 2 figs. 24—26. Agnostus lautus Resser, 1939b, p. 25, pl. 2, figs. 16—18. Description.—Cephalon moderately convex trans— versely and longitudinally. Glabella well defined by nar- row furrows. Anterior lobe bluntly rounded at front, separated from remainder of glabella by straight trans- verse furrow. A second glabellar furrow may be marked by shallow notches at the sides of the glabella. Basal lobes simple. Axial node indistinct. Border narrow, well de- fined, of constant breadth; sagittal length about one- third sagittal length of undivided preglabellar field. Pygidium with axis well defined, bluntly pointed pos- teriorly, reaching nearly to inner part of border; postax- ial furrow absent. First axial segment weakly defined by shallow transaxial furrow. Axial node situated in position of second segment which is only faintly outlined on ex— foliated specimens. Border well defined, with short poorly developed posterolateral border spines. Discussion—Recent work by Campbell (1974) in south- eastern Idaho demonstrated that the differences be- tween P. bonnerensis (Resser) and P. lautus (Resser) are attributable to both preservation and to infraspecific variability; Campbell suggested that P. lautus be suppres- sed as a junior synonym of P. bonnerensis. The specimens from the Carrara Formation conform in all respects to specimens of this species described from southeastern Idaho. P. bonnerensis (Resser) is most similar to P. brighamensis (Resser). It differs by having more weakly developed pygidial spines and a slightly longer pygidial axis, and by lacking a well—developed transverse furrow at the back of the second axial segment. Occurrence.—Moderately rare, Albertella Zone. Zacan- thoidid Zonule: Nevada: 3766—CO (3 cephala, 2 pygidia), Nevada Test Site. Ogygopsis Zonule: Nevada: 4437—CO (1 weathered complete individual, 3 cephala, 7 pygidia), 4438—CO (4 cephala, 4 pygidia), both from Belted Range. Peronopsis‘? sp. Plate 12, figure 7 Discussion—A single agnostid pygidium, associated with P. bonnerenszls (Resser), differs from that species by having an axis that is well defined and crossed by two deep complete transverse furrows. The posterior lobe is pointed posteriorly and is separated from the border by a distance slightly greater than the border width. There is no clear postaxial furrow. A large axial node on the CARRARA FORMATION, SOUTHERN GREAT BASIN second axial segment deflects the furrow outlining the posterior margin slightly backward on the axial line. The border has a slight angulation in the posterolateral area of the pygidium, but no clear border spine is present. The surface of the exoskeleton is smooth. The axial structure of this species is like that of Peronopsis bn'ghamenszls (Resser), but it differs by lacking well-developed border spines. Without more material, a specific identification for this specimen is not possible. It has many characteristics of species of Plychagnostus, and Robison (written commun., 1972) believed that P. brighamensis is a species transitional between the two gen- era. Without knowledge of the associated cephalon, specific and perhaps even generic identification of this pygidium is uncertain. Occurrence..—Rare, Albertella Zone, Ogygopsis Zonule. Nevada: 4437—CO (1 pygidium), Belted Range. Supertmuy Eomscomm Richter Family EODISCIDAE Raymond Genus MACANNAIA J 011 Macannaia jell, 1975, p. 71. Type species.—Pagetia maladensis Resser, 1939b, p. 25, pl. 2, figs. 4, 5. Discussion—This genus was recently proposed by Jell with M. maladensis (Resser) as its type. The material from the Carrara Formation conforms to the type species in all respects and contributes no new information about the genus. The superfamily and family designation are those recommended by Jell (1975, p. 14). Macannaia maladensis (Resser) Plate 12, figures 8, 12 Pagetia malademis Resser, 1939b, part, p. 25, pl. 2, figs. 4 (cranidium in lower center, pygidium in upper center), 5 (cranidium in upper right); Rasetti, 1966a, p. 508, pl. 60, figs. 8—18; Fritz, 1968, p. 190, pl. 43, figs. 14—16. Pagetia (Mexopagetia) malademir Resser, Kobayashi, 1944, p.64, pl.2 fig. 4a (only). Maamnaia maladensis (Resser),]ell, 1975, p. 72 Discussion .—This distinctive species is characterized by a bulbous posterior part of the axial lobe of the pygidium, a subrectangular glabella, and a moderately deep pre- glabellar axial furrow. Only a few specimens have been found in the Carrara Formation, but they agree in all respects with the excellent description given by Rasetti (1966). Occurrence.——Moderately common, Albertella Zone, Ogygopsis Zonule. Nevada: 4436—CO (>10 cranidia, 2 pygidia), 4437—CO (l cranidium), both from the Belted Range. SYSTEMATIC PALEONTOLOGY 77 Genus PAGETIA Waloott Pagetia Walcott, 1916b, p. 407; Cobbold, 1931, p. 462; Lermontova, E. V., in Vologdin, 1940, p. 121; Richter and Richter, 1941, p. 17; Kobayashi, 1943, p. 40; Kobayashi, 1944, p. 63; Shimer and Shrock, 1944, p. 615; Rasetti, 1945, p. 315; Lermontova, 1951, p. 36; Howell, B. F., in Harrington and others, 1959, p. 189; Pok- rovskaya, N. V., in Chernysheva, 1960, p. 55; Yegorova, 1961, p. 215; Yegorova, L. 1., and others, in Khalfin, 1955, p. 104; Poletaeva, O.K., in Khalfin, 1960, p. 154; Repina and others, 1964, p. 253; Lazarenko, N .P., in Demodikov and Lazarenko, 1964, p. 176, Rasetti, 1966a, p. 503; Rasetti, 1967, p. 59; Palmer, 1968, p. 35; jell, 1970, p. 304; Jel], 1975, p. 30. Type species—Pagan bootes Walcott, 1916b, p. 408, pl. 67, figs. 1, 1a—f. Ditcussion.—_]ell (1975) thoroughly described and dis- cussed the characteristics of this well-known genus, and the Carrara specimens conform in all observable features with the description given in his paper. The family and superfamily designations are also those recommended by jell (1975, p. 14). Pagetia ressori Kobayashi Plate 12, figures 16—20, 23-26 Pagetia clytia Resser (not Walcott), 1939b, p. 25, pl. 2, figs. 6—8. Pagctia (Eopagetia) ressen' Kobayashi, 1944, p. 37. Pagetia ressm' Kobayashi, 1943, p. 40; Kobayashi, 1944, p. 64; Rasetti, 1966a, p. 509, pl. 60, figs. 19—25; Fritz, 1968, p. 192, pl. 38, figs. 8, 9. Discussion .—Rasetti (1966) gave a thorough description of this species, with which the Carrara specimens agree in all respects. This species is easily distinguished from other North American species by having deep pleural furrows on the pygidium and by generally having pits rather than slots developed in the cranidial border. One sample of this species has abundant silicified indi- viduals of all growth stages and a rare example of the free cheek. Immature cranidia are characterized by promi— nent elongate swellings on the fixed cheeks, and the glabella is depressed between them. These are essentially comparable to some of the early forms of P. ocellata (I ell, 1970), which is the only other Pagetia for which the early stages have been described. The free cheek is a subrec— tangular plate divided into an outer border and inner ocular platform by a narrow nearly straight border fur- row. Occurrence.—Common, Albertella Zone, Zacanthoidid Zonule. Nevada: 3547—CO (>20 silicified cranidia and pygidia, 1 free cheek), 3766—CO (>20 cranidia and pygidia preserved in limestone), both from Nevada Test Site. Pagetia mgosa Rasetti Plate 12, figures 9, 13 Pagetia malademis Resser (part), 1939b, p. 25, pl. 2, figs. 4 (pygidium upper right corner), 5 (cranidia upper left, upper center, lower right). Pagetia rugosa Rasetti, 1966 p. 509, pl. 60, figs. 1—7. Pagetia armosa Fritz, 1968, p. 189, pl. 43, figs. 10—11. Discussion.—Rasetti recognized that Resser had in- .cluded two species in his concept of P. maladensis. This species was characterized by its pitted and roughened ornamentation and by pygidia lacking a bulbous pos— terior part to the axis. Fritz, who completed his man- uscript before Rasetti’s paper appeared, acknowledged in a footnote that his species arenosa was a synonym for P. rugosa. The specimens from the Carrara Formation have the typical ornamentation and morphology of this species and add nothing to the excellent description given by Rasetti. Occurrence.—Moderately common, Albertella Zone, Ogygopsis Zonule. Nevada: 4436-CO (5 cranidia, 6 pygidia), 4437—CO (4 cranidia, 2 pygidia), 4438—CO (12 cranidia, 7 pygidia), all from Belted Range. Pagetia sp. Plate 12, figures 10, 14 Discussion—Associated with P. resseri Kobayashi is a second species of Pagetia represented by a few pygidia and possible associated cranidia. The pygidia have five distinctly defined axial rings, each with an axial node, and the pleural regions lack any trace of furrows. The cranidia, if properly associated, have the slots in the bor- der typical of many species of Pagetia but have distinctly defined palpebral lobes. The combination of cranidial and pygidial features is unlike that of any other described North American species of Pagetia. However, without more material, the evidence for association of cranidia and pygidia is weak; and no name is proposed at this time. Occurrence.—Rare, Albertella Zone, Zacanthoidid Zonule. Nevada: 3766—CO (3 cranidia, 3 pygidia), Nevada Test Site. Order CORYNEXOCHIDA Kobayashi Although the Orders CoryneXOchida and Ptychopariida are used here is the sense of Bergstrém (1973), they seem to be taxa of lesser rank than the Olenellida and Miomera. Whereas the Olenellida and Miomera each have their own peculiar morphologies and their own distinctive ontogenetic development, the Corynexochida and Ptychopariida have essentially the same kind of ontogenetic development and lack con- sistently clear-cut morphologic differences. For example, 78 CARRARA FORMATION, SOUTHERN GREAT BASIN oryctocephalid trilobites are as different from most corynexochids, such as Albertella or Kootem'a, in cephalic and pygidial structure as they are from ptychopariids, but they are lncluded with the corynexochids in all major classifications. Without a comprehensive review of at least the Cambrian trilobites, which is far beyond the scope of this paper, I do not have a satisfactory alternative suggestion to offer regarding the suprageneric relation— ships of the nonagnostid and nonolenellid trilobites. Bergstrom (1973) has made an important contribution to this problem, but much more work remains to be done before a fully satisfactory classification of Cambrian trilobites above the generic level can be prepared. Family DOLICHOMETOPIDAE Walcott Genus GLOSSOPLEURA Poulsen Glossopleum Poulsen, C., 1927, p. 268; Resser, 1935, p. 29; Kobayashi, 1942, p. 159; Palmer, 1954, p. 67; Poulsen, C., in Harrington and others, 1959, p. 224; Poulsen, V., 1964, p. 25. Sonoraspis Stoyanow, in Cooper and others, 1952, p. 50. Type species.—Dolichomet0pus boccar Walcott, 1916, p. 363, pl. 53, figs. 1, la—f. Discussion—This is a clear-cut genus that has been fully described earlier (Palmer, 1954) except for the hypos- tome. It is characterized by cranidia with long palpebral lobes and a glabella that reaches to the anterior margin and by semicircular to subovate generally broad bor- dered nonspinose relatively large pygidia. Several col- lections from the Carrara Formation that are rich in disarticulated specimens include a number of hypos- tomes that are as distinctive for the genus as the cranidia. The anterior body is anteriorly expanded as in many Corynexochida; but the distinctive and characteristic difference is that there is no differentiation of a separate rostral part, and the anterior margin is strongly deflected dorsally. When the cranidium is reassembled, the sagittal profile forms a continuous curve from the dorsal part of the anterior lobe to the ventral part of the hypostome without interruption by any marginal flange. Glossopleura tutu Resser Plate 16, figures 21—24 Gloxsopleum tutu Resser, in McKee and Resser, 1945, p. 196, pl. 26, figs. 5, 6. Description—A species of Glossopleum with glabella not clearly differentiated from anterior part of fixed cheek; only barely differentiated by broad shallow depression opposite posterior part of cheek. Occipital furrow broad, very shallow, poorly defined. Palpebral lobes well de— fined by abrupt change in slope of exoskeleton, situated below level of interocular area. Free cheek has broad flat border as wide as or wider than the ocular platform. Lateral and posterior border furrows shallow, connected at genal angle. Genal spine flat, tapered; length more than twice length of posterior section of facial suture. Inner spine angle broad, evenly curved. Pygidium semicircular in outline; anterior margin nearly straight. Axis lacks any indication of transverse furrows. Border broad, poorly defined, flat, downslop- ing; width slightly less than twice greatest width of pleural platform. Discussion—This species has been known previously only from a single pygidium from the Grand Canyon. Comparison of the specimens of Glossopleura from the southern Great Basin with those described from elsewhere in North America and housed in the col- lections of the US National Museum showed essential identity between the specimen described by Resser as Glossopleum tum and the specimens described above, which were obtained from the lowest bed of a thin- bedded silty limestone member overlying the basal 120- meter-thick massive limestone member of the Bonanza King Formation. This species is not really a part of the fauna of the Carrara Formation, but is illustrated here because it proves that. the range zone of Glossopleum is represented only by its lower part within the Carrara Formation. Occurrence.—Common, uppermost Glossopleum Zone. Nevada: 7199—CO (>10 pygidia, 1 free cheek, 1 cranidium, many fragments), Striped Hills. Glossopleura. lodensis (Clark) Plate 16, figures 1—5, 9, 10 Buthyuriscus howelli lodensis Clark, 1921, p. 6. Dolichometopus? lodensis (Clark). Resser, 1928, p. 10, pl. 3, fig. 9. Glossopleum lodensis (Clark). Resser, 1935, p. 34. Description—Cranidium elongate, subrectangular in outline. Glabella long, low, slightly expanded anteriorly; sides partly defined by distinct change in slope of exo- skeleton from occipital ring only as far forward as a pair of shallow pits situated slightly anterior to the anterior ends of the palpebral lobes; anterior end not differ- entiated from remainder of cranidium. Occipital furrow broad, shallow; occipital ring simple with low poorly de- fined axial node adjacent to posterior margin. Fixed cheeks narrow, gently convex; width, exclusive of pal— pebral lobes, slightly less than one-half basal glabellar width. Palpebral lobes long, arcuate, situated slightly below surface of cheek; anterior end close to glabella; line connecting posterior tips passes slightly anterior to oc- cipital furrow. Posterior limbs not completely known. Free cheek has broad flat border, slightly wider than SYSTEMATIC PALEONTOLOGY 79 pleural platform at anterior sutural margin. Lateral bor- der furrow shallow, distinct, joined with broader and less distinct posterior border furrow at genal angle. Genal spine flat, broad—based, tapered to a sharp point; length slightly more than length of posterior section of facial suture. Inner spine angle very obtuse, gently curved. Thorax consists of seven thoracic segments lacking axial nodes or spines. Pleural furrows well defined. Pleural tips sharp; spine of fifth segment seems slightly larger than others. Pygidium semicircular in outline. Axis prominent, ele- vated above downsloping pleural regions, defined by change in slope of exoskeleton. Three or four obscure ring furrows observable in oblique lighting. Border poorly defined, downsloping, slightly concave; width slightly greater than greatest width of pleural platform. Pleural furrows obscure or absent; when present, extend onto border. External surfaces of best preserved specimens show an extremely faintly shagreened surface. Most specimens appear smooth. Discussion—This species has never been adequately described. Its cranidium is characterized particularly by having relatively short palpebral lobes. The combined features described for the pygidium serve to distinguish this species from others in Glossopleum. The most similar described species is Glossopleum mckeei Resser, from the Grand Canyon, which has a smooth pygidium and slightly longer palpebral lobes. Occurrence.—Common, Glossopleura Zonule. Califor- nia: 3682—CO (2 pygidia, 3 fragmentary cranidia), Eagle Mountain. Nevada: P3690—CO (1 fragmentary cranidium, 2 free cheeks, 5 fragmentary pygidia, many scraps), Striped Hills. California: 7198—CO (>10 cranidia, pygidia, free cheeks, abundant scraps), Eagle Mountain. Glossopleura waleotti C. Poulsen Plate 16, figures 6—8, 11—19 Glossopleum walcotti Poulsen, C., 1927, p. 268, pl. 16, figs. 20-30; V. Poulsen, 1964, p. 25, pl. 1, figs. 2—4. Glossopleum expansa Poulsen, C., 1927, p. 269, pl. 16, figs. 31, 32. Glossopleum sulcata Poulsen, C., 1927, p. 272, pl. 16, fig. 39. Discussion—This species has been well described by the Poulsens. It is characterized by cranidia with moderately well developed axial furrows and a distinctly expanded anterior end of the glabella. The associated pygidia have a moderately to poorly defined border about as wide as the widest part of the pleural platform, three or four shallow ring furrows and pleural furrows, and faint axial swellings on the anterior three to five axial rings. The pygidial shape varies from semicircular to elliptical. The external surface on well—preserved specimens may be smooth, faintly shagreened, or bear fine scattered pits. One pygidium in the Carrara fauna (pl. 16, fig. 15) has obscure low scattered granules on the pleural regions. Pygidia of this species can be distinguished from those of other Glossopleum species by the combined presence of low axial swellings, shallow ring furrows and shallow pleural furrows, and a border about as wide as the widest part of the pleural platform. Occurrence.——Common, Glossopleum Zonule. Nevada: 3544—CO (1 cranidium, 1 free cheek, l pygidium), Desert Range; 3545—CO (1 cranidium, 3 pygidia, 1 hypostome, numerous scraps), Nevada Test Site; 3767—CO (5 pygidia, 2 free cheeks), Nevada Test Site. California: 3684—CO (2 cranidia, 2 pygidia), Eagle Mountain; 4142—CO (>10 cranidia and pygidia, 6 free cheeks, 2 hypostomes), Titanothere Canyon section, Grapevine Mountains; 4155—CO (3 cranidia, 3 free cheeks, 2 pygidia, 1 hypostome, numerous scraps), Echo Canyon section, Funeral Mountains; 4156—CO (5 cranidia, 5 free cheeks, 19 pygidia, 1 hypostome, numerous scraps), Echo Canyon section, Funeral Mountains. Genus POLIELLA Walcott Bathymiscus (Poliella) Walcott, 1916b, p. 349. Poliella Walcott. Raymond, 1928a, p. 310; Resser, 1935, p. 43; Kobayashi, 1942, p. 153; Poulsen, C., in Harrington and others, 1959, p. 226; Fritz, 1968, p. 206. Type species.—Bathyuriscus (Poliella) anteros Walcott, 1916b, p. 349, pl. 46, fig. 5. Discussion—The concept of Poliella as a long-eyed corynexochid characterized by a small poorly segmented pygidium seems to have been consistently applied by all authors who have assigned species to the genus. How- ever, as pointed out by Fritz (1968), the genus includes, at present, species with, as well as, without axial spines on the occipital ring and thoracic segments. If it should become desirable to split the genus, those species with axial spines should be retained. Poliella germane. (Resser) Plate 11, figures 1—8 Ptarmigania germana Resser, 1939b, pl. 7, figs. 16—20. Poliella germana (Resser), Fritz, 1968, p. 207, pl. 37, figs. 1—9. Dolichometopsis potens Resser, 1939b, p. 36, pl. 6, figs. 17—20 (only). Dolichometopsis gravit Resser, 1939b, p. 36, pl. 7, figs. 6—9 (only). Ptarmigania agrestis Resser, 1939b, p. 39, pl. 7, figs. 1, 2. Ptarmigam'a altilis Resser, 1939b, p. 40, pl. 7, figs. 3, 4 (only). Ptarmigania dig/Lam Resser, 1939b, p. 41, pl. 8, figs. 1, 2, 4—7 (only). Discussion—Fritz (1968) gave a good description of this species and clarified the assignments of many of the specimens described and excessively split by Resser (1939b). In addition to the species placed in synonymy 80 CARRARA FORMATION, SOUTHERN GREAT BASIN with P. germana, Fritz reassigned to P. germana nontype specimens of two other Resser species from the same report: Dolichometopsis comis (Resser, 1939b, pl. 4, left cranidium of fig. 24); and Ptarmigania sobrina (Resser, 1939b, pl. 7, fig. 13, pygidium only; figs. 14, 15). The cranidia described as Dolichometopsis gravis by Resser (1939b) should also be assigned to P. germana. This species is distinguished from all others in the genus by having a nondenticulate pygidial margin and by having two or three shallow pleural furrows continuing onto the inner edge of the pygidial border. It is distinguished, in addition, from the slightly olderP. lomataspis n. sp. in the Carrara Formation by having a less well developed occip- ital spinule, a well-developed border furrow on the free cheek, a narrower pygidial border, and a less distinct pitted ornamentation. Occurrence.-—Common, Albertella Zone, Zacanthoidid Zonule. Nevada: 3695—CO (>10 pygidia), Nevada Test Site; 4440—CO (> 10 cranidia, 1 free cheek, >10 pygidia), Groom Range. Poliella. lomataspis n. sp. Plate 6, figures 1—5, 12 Description—Cranidium, exclusive of posterior limbs, elongate, subrectangular, moderately convex trans- versely and longitudinally; anterior margin gently curved; no anterior arch. Glabella elongate, expanded slightly forward, reaches nearly to anterior margin; sides nearly straight, defined by abrupt change in slope; an- terior end bluntly rounded; anterolateral glabellar cor- ners strongly rounded. Only posterior pair of glabellar furrows apparent, moderately deep, strongly oblique. Occipital furrow deep, straight. Occipital ring broad, nearly flat, with low axial keel terminating in short slen- der spine at posterior margin; sagittal length of occipital ring slightly more than one-fourth sagittal glabellar length. Frontal area consists only of narrow, flat, or slightly concave border about 0.1 length of glabella exclu- sive of occipital ring. Fixed cheeks gently convex, hori- zontal; palpebral lobe elongate, arcuate, well defined by palpebral furrow paralleling margin of lobe; width of palpebral lobe about 0.3 greatest width of palpebral area; width of palpebral area at anterior end of palpebral lobe about one—fourth width of glabella on line connecting anterior ends of palpebral lobes. Posterior limb short, abruptly deflected downward behind palpebral lobe; distal part slightly longer than proximal part. Posterior border furrow broad, shallow; posterior border has slight posterior expansion behind palpebral lobe. External sur- faces of all parts except posterior limb and border cov— ered with shallow coarse pits observable only on best preserved specimens. Course of anterior section of facial suture slightly di- vergent forward from palpebral lobes to border, then curved inward to intersect anterior margin impercepti- bly. Course of posterior section of facial suture gently convex outward from palpebral lobe to posterior margin. Free cheek elongate, nearly flat; border not clearly defined. Lateral margin gently curved; curvature con- tinued onto base of slender flattened genal spine situated at posterolateral cephalic corner. Length of spine at least twice length of posterior section of facial suture. Pygidium broad, subovate in outline; sagittal length about 0.6 greatest width. Axis well defined, convex, ta— pered posteriorly, bluntly rounded, reaches to inner edge of broad concave poorly defined border; two shal- low ring furrows present behind articulating furrow; anterior one or two segments may have low poorly de- fined axial node. Posterior margin straight or slightly indented behind axis. Pleural platforms gently convex, crossed by two widely spaced, gently curved, pos- terolaterally directed shallow pleural furrows. Extremely faint interpleural furrows on one specimen extend straight laterally, nearly forming the diagonal of a rec- tangle bounded by the pleural furrows, the axis, and the border. External surface of axis and pleural fields cov- ered with shallow pitted ornamentation identical to that of the cranidium. Discussion—This species is most like P. germana (Res- ser). It differs by having a stronger pitted ornamentation, wider pygidial border and pleural furrows confined to the pleural platform. The free cheek also lacks a distinct border furrow. Poorly preserved tiny silicified specimens in the type collection are not distinguishable from the tiny individuals of P. cf. P. lomataspis described next. Occurrence.—Common, “Plagium-Poliella” Zone, P. lomataspis Zonule. Nevada: 4434—CO (>10 cranidia, 2 free cheeks, 5 pygidia), Belted Range. Poliella. of. P. lomataspis n. sp. Plate 6, figures 6—10 Discussion—Abundant small silicified specimens of a species of Poliella are present in one collection. The largest cranidium is only 2 mm long, and other parts are comparably small. The cranidium has a narrow border in front of the glabella, a short occipital spine and short distal parts to the posterior limbs, which lack intergenal spines. The free cheek is narrow and lacks a well-defined border. The genal spine is about equal in length to the posterior section of the facial suture. Thoracic segments have deep pleural furrows and short or long axial spines. The pygidium is simple, has one well-defined axial ring, and a semicircular to subquadrate shape. The axis is prominent and wider than the pleural regions; it extends about two-thirds the sagittal length of the pygidium. A fine granular ornamentation is apparent on the axial region of the glabella, thoracic segments, and pygidium. SYSTEMATIC PALEONTOLOGY 81 Despite the fact that this species is represented by many well-preserved parts, it is difficult to assess its charac- teristics relative to other species of Poliella because there are no larger holaspids. It seems to be most similar to P. lomataspis n. sp. from a correlative horizon. However, until larger holaspids can be found, an effective specific identification cannot be made. Occurrence.—Common, “Plagium-Poliella” Zone, P. lomataspis Zonule. Nevada: 3790—CO, (>20 cranidia, 3 free cheeks, 5 pygidia), Jangle Ridge area, Nevada Test Site. Family DORYPYGIDAE Kobayashi Synonym: OGYGOPSIDIDAE Rasetti, 1951, p. 190 In this report Ogygopsis is included in the Dorypygidae rather than separately assigned to its own monotypic family as has been done in the past. When Rasetti (1951) proposed the Ogygopsididae, he was reacting to an ex- tremely unrealistic assignment of Ogygopsis to the Asaphidae by earlier authors. He stressed differences in hypostomal structure and the apparent uniqueness of the cephalic and pygidial combination as reasons for naming a new monotypic family. However, much new knowledge has been obtained about trilobite morphology, and the hypostomal structure among closely related genera seems to be quite variable. (Compare in this report pl. 9, figs. 6, 11 with pl. 10, figs. 5, 13, 20.) Also, species of Ogygopsis from the Lower Cambrian have a small number of pygidial segments, approaching those of typical Dorypygidae; and at least one undescribed species with a full complement of border spines similar to Kootenia is known from the Lower Cambrian of western Nevada. Ogygopsis also shares with other dorypygids a comparable nearly isopygous condition and consequently a thorax that barely diminishes in width backward. Its thorax also has a relatively small number (<10) of thoracic segments. , Thus, the reasons for separately distinguishing Ogygopsis at the family level no longer seem compelling, and it is included here with Bonnia and Kootenia in the Dorypygidae. Genus BONNIA Waleott Corynexochus (Bonnia) Walcott, 1916b, p. 325 Bonnia Walcott. Raymond, 1928a, p. 309; Resser, 1936, p. 6; Resser, 1937b, p. 44; Lermontova, 1940, p. 142; Lochman, 1947, p. 68; Rasetti, 1948a, p. 14; Lermontova, 1951, p. 118; Pokrovskaya, 1959, p. 135; Poulsen, C., in Harrington and others, 1959, p. 217; Suvorova, N. P., in Chernysheva, 1960, p. 80; Yegorova, 1961, p. 225; Demokidov and Lazarenko, 1964, p. 207; Suvorova, 1964, p. 143; Repina, in Repina and others, 1964, p. 300; Palmer, 1964, p. 5; Rasetti, 1966b, p. 43; Palmer, 1968, p. 46 Fritz, 1972, p. 31. Type species.—Bathyurus pamulus Billings, 1861. Discussion—This genus has been described or diag— nosed many times and has elicited little difference of opinion about its characteristics. The specimens from the Carrara Formation contribute no new information about the genus. Bonnia spp. Plate 5, figures 10, 11 Discussion .—Two specimens of Bonnia have been iden— tified in collections from the Carrara Formation, which attests to the rarity of this genus in the southern Great Basin. One of the specimens is an immature form (pl. 5, fig. 11) that is distorted but shows a strongly expanded glabella and moderately distinct posterior glabellar fur- rows. This does not resemble any other Cordilleran rep- resentatives of the genus, but it is too small to adequately compare with other forms. The other specimen (pl. 5, fig. 10) is very similar to Bonnia columbensis Resser in all crani- dial proportions. However, it has extremely faint bertil- lon markings on the glabella and lacks any distinct granules which are said by Fritz (1972, p. 33) to charac- terize this species. In the absence of associated parts, an adequate specific designation cannot be given. Occurrence.—Very rare (2 cranidia), Bristolz'a Zonule and Gold Ace Limestone Member. California: 7181—CO, Cucomungo Canyon section, Last Chance Range. Nevada: 3646—CO, Nevada Test Site. Genu- KOOTENIA Walcott Bathyuriscm (Kootmia) Walcott, 1889, p. 446. Kootenia Walcott, 1925, p. 92; Kobayashi, 1935, p. 156; Lermontova, E. V., in Vologdin, 1940, p. 139, Shimer and Shrock, 1944, p. 613; Rasetti, 1948b, p. 332; Thorslund, 1949, p. 4; Lermontova, 1951, p. 122; Palmer, 1954, p. 64; Hup'e, 1955, p. 91; Ivshin, 1957, p. 37; Poulsen, C., in Harrington and others, 1959, p. 218; Suvorova, N. P., in Chernysheva, 1961, p. 126; Lazarenko, 1962, p. 60; Palmer, 1968, p. 47; Zhuravleva and others, 1970, p. 34; Palmer and Gatehouse, 1972, p. 18; Fritz, 1972, p. 35. Notasaphus Gregory, 1903, p. 155; Whitehouse, 1939, p. 241. Type species.—Bathyuriscus (Kootem'a) dawsom' Walcott, 1889, p. 446. Discussion .—The material from the Carrara Formation does not add any new information to the diagnosis and discussion of this widespread and well-known genus given earlier (Palmer, 1968). Kootenia. germ Bessel- Plate 11, figures 22—24, 27—30 Kootem'a germana Resser, 1939b, p. 49, pl. 9, figs. 19—24 82 CARRARA FORMATION, SOUTHERN GREAT BASIN Description .—Cranidium subquadrate in outline, gently to moderately convex transversely and longitudinally. Glabella prominent, sides subparallel, extended forward onto border. Glabellar furrows not apparent. Occipital furrow deep, straight, and deepest distally. Occipital ring convex, has short slender posteriorly directed axial spine. Frontal area barely apparent on axial line. Fixed cheeks gently convex, downsloping; width of palpebral area slightly less than one-half basal glabellar width. Palpebral lobe small, defined by shallow glabellar furrow, situated about opposite glabellar midlength, connected to an- terolateral corner of glabella by barely discernable ocular ridge. Posterior limb subtriangular; transverse length about equal to basal glabellar width. External surface variably ornamented. Glabella has concentric “finger- print” pattern of ridges either well defined or barely apparent even after whitening. Fixed cheeks may be obscurely pitted, distinctly granular, or roughened. There is no apparent correlation of intensity of or— namentation with size. Thorax composed of seven segments. Each pleuron has deep pleural furrow that terminates near tip. Each segment bears short axial spine and short pleural spine. Pygidium semicircular in outline, moderately convex transversely and longitudinally. Axis prominent, barely tapered posteriorly, extended to inner edge of moder- ately well defined border. Three distinct complete ring furrows and a faint incomplete fourth furrow present behind articulating furrow. No axial nodes or spines present. Pleural fields crossed by four straight shallow pleural furrows that terminate in slightly deeper areas of border furrow. Border nearly flat, bears six pairs of short slender border spines; posterior pair shorter than adja- cent pair. Ornamentation consists of closely spaced fine granules that vary in intensity from moderately distinct to obscure; border spines generally retain distinct granular ornamentation. Discussion—This species is most similar to K. brevispma Resser which differs primarily by having shorter and more sawtoothlike border spines. The short closely spaced posterior pair of border spines seems to be par— ticularly distinctive of K. germana, but a monographic review of the 107 species presently assigned to this genus will be needed to establish the ultimate validity of this observation. This is the only species of Kootenia so far obtained from the Carrara Formation. Occurrence.—Common, Albenella Zone, Zacanthoidid Zonule. Nevada: 3692—CO (>10 cranidia and pygidia, 3 articulated specimens), Groom Range; (> 10 cranidia and pygidia), Nevada Test Site; 4440—CO(> 10 cranidia and pygidia), Groom Range. Rare, 3547—CO (3 pygidia), Nevada Test Site. Genus OGYGOPSIS Waloott Ogygopsis Walcott, 1889, p. 446; Walcott, 1916b, p. 375; Raymond, 1912, p. 116; Shimer and Shrock, 1944, p. 613; Rasetti, 1951, p. 190; Rasetti, F., in Harrington and others, 1959, p. 219; Palmer, 1964, p. 6. Taxioma Resser, 1939b, p. 62; Shimer and Shrock, 1944, p. 617; Romanenko, E. B., in Khalfin, 1960, p. 187. Type species—Ogygia klotzz' Rominger, 1887, p. 12, pl. 1, fig. 1. Discussion—This genus has been described in detail earlier (Palmer, 1964), and the specimens from the Car- rara Formation conform to this description in all re- spects. Ogygopsis typicalis (Resser) Plate 12, figures 1—4 Taxioum typicalis Resser, 1939b, p. 62, pl. 14, figs. 6—14; Shimer and Shrock, 1944, pl. 259, figs. 23, 24. Description.—Cephalon semicircular in outline, gently to moderately convex transversely and longitudinally, bears moderately long slender posterolaterally directed genal spines. Cranidium subtrapezoidal in outline, an- terior margin gently curved. Glabella long, well defined at sides and front by change in slope of exoskeleton; sides slightly bowed outward; anterior end strongly rounded, glabellar furrows not apparent. Occipital furrow straight, deep distally, shallow over axial line. Occipital ring gently convex, withou‘t node or spine. Frontal area consists only of flat border; sagittal length between one-seventh and one-eighth sagittal length of glabella exclusive of occipital ring. Fixed cheeks gently convex, horizontal; width of palpebral area about one-half basal glabellar width. Pal- pebral lobe gently curved, well defined by shallow pal- pebral furrow, situated slightly posterior to glabellar midlength; exsagittal length about one-third sagittal glabellar length exclusive of occipital ring. Ocular ridge narrow, low, extended inward and forward from palpeb- ral lobe to anterolateral part of glabella. Posterior limb long, pointed; transverse length slightly greater than basal glabellar width. Course of anterior section of facial suture slightly divergent forward from palpebral lobe; course of posterior section evenly curved, directed strongly posterolaterally from palpebral lobe to posterior margin. Hypostome moderately to strongly convex; posterior lobe and maculae poorly defined. Lateral and posterior margins have well-developed border that is flared ven- trally opposite junction of anterior and posterior lobes. Anterior wings short, blunt. Free cheek narrow, with border defined by lateral bor- der furrow only anterior to base of slender genal spine; length of spine slightly greater than length of posterior section of facial suture. SYSTEMATIC PALEONTOLOGY 83 Thorax composed of eight segments. Axis tapered backwards, but width of thorax remains nearly constant. Pleurae each bear broad deep pleural furrow and short slender posterolaterally directed pleural spine. Pygidium semicircular in outline, gently convex trans- versely and longitudinally. Axis long, slender, slightly tapered, well defined by changes in slope of exoskeleton, reaches nearly to border and connected to it by short postaxial ridge; width of axis at anterior margin about one-fifth anterior pygidial width. Eight complete shallow ring furrows and a ninth partial ring furrow present behind articulating furrow. Pleural regions crossed by seven or eight deep gently curved pleural furrows that reach to inner edge of narrow well-defined slightly con- vex border. Very shallow poorly defined interpleural furrows present between most pleural furrows. Border bears distinct short slender anterolateral spines analo- gous to those of thoracic segments; nubs of one or two additional pairs of spines apparent on many specimens; posterior margin with slight median indentation. Ornamentation consists of very delicate anastomosing ridges forming an irregular mesh on most surfaces, ap— parent only on well-preserved specimens after whiten- mg. Discussion.—This species is represented by numerous disarticulated specimens and several articulated indi- viduals without free cheeks in several collections from the upper part of the Belted Range section. It agrees in all respects with the abundant material of this species from the upper part of the Naomi Peak Limestone Member of the Langston Formation of Maxey (1958) in northeastern Utah and southeastern Idaho. The presence of only one distinct anterolateral pair of pygidial spines, and seven or more pleural furrows, distinguishes this species from all others in the genus. Occurrence.—Common, Albertella Zone, Ogygopsis Zonule. Nevada: 4436—CO (>10 cranidia and pygidia, 1 free cheek), 4437—CO (3 partly articulated individuals, >10 cranidia and pygidia), 4438-CO (5 partly articulated individuals, >20 cranidia and pygidia), all from Belted Range. Family ORYCTOCEPHALIDAE Beecher Genus ORYCTOCEPHALINA Lermontova Oryctocephalina Lermontova, E. V., in Vologdin, 1940, p. 137; Cher— nysheva, 1960, p. 82; Yegorova, L. 1., and others, in Khalfin, 1960, p. 198; Shergold, 1969, p. 47. Type species.—Oryctocephalina reticulum Lermontova, in Vologdin, 1940, p. 137, pl. 42, figs. 3, 3a,b. Discussion .—Chernysheva (1962) in her monograph of the Oryctocephalidae concluded that the type species of Oryctocephalina, represented only by cranidia, is a proper member of Oryctocephalus. Shergold (1969) revived this genus for oryctocephalids characterized particularly by few pygidial segments and by sinuous axial furrows out- lining the glabella. However, the pygidium is only known for the Australian species, 0. lancastroz'des Shergold. Until a comparable pygidium is found for 0. reticulum, the content and character of this genus must remain un- certain. Oryctocephalina? maladensis (Resser) Plate 12, figures 21, 22, 27 Oryctocephalus maladensis Resser, 1939b, p. 45, pl. 3, figs. 7—9; Fritz, 1968, p. 202, pl. 41, figs. 25—27. Discussion—This species has been adequately de- scribed and figured by both Resser and Fritz. The Car- rara specimens agree in all details with the specimens described earlier. Shergold (1969, p. 47) placed this species un- equivocally in Oryctocephalina because of the sinuous na- ture of the axial furrows on the cranidium. Oryc— tocephalina is characterized by having small poorly differ- entiated pygidia, which might explain why a pygidium has never been found for 0. maladensis, although it is represented by many cranidia. Until the pygidium is identified, any generic assignment for this species within the Oryctocephalidae should be tentative. Occurrence.—Moderately common, Albertelld Zone, Zacanthoidid Zonule. Nevada: 3766—CO (> 10 cranidia), Nevada Test Site. Genus ORYCTOCEPHALITES Resser Oryctocephalites Resser, 1939b, p. 44; Shimer and Shrock, 1944, p. 613; Rasetti, F., in Harrington and others, 1959, p. 220; Chernysheva, 1962, p. 24; Shergold, 1969, p. 28. Type species.—Oryctocephalites typicalis Resser, 1939b, p. 45, pl. 3, figs. 1—6. Discussion .—Resser and Rasetti have given good de- scriptions or diagnoses of this genus. The Carrara speci- mens are identical in all respects with the type species. Shergold (1969, p. 17) made the ad hoc decision that the pygidium of the type species of Oryctocephalus should be in Omctocephalites and that it is not congeneric with the associated cranidium, although he stated that the cranidium of Onctocephalites is of “Oryctocephalus-type.” Inasmuch as this statement could be reversed, he has by implication synonymized Ozyctocephalus and Oryctocepha— lites. However, Oryctocephalus has at least two transglabel- lar furrows while Oryctocephalites has only one. No evi- dence from the type collection of Oryctocephalus exists to support the assumption that the pygidium and cranidium are not congeneric, and until such evidence is presented, their generic separation and the resulting im- plications do not seem justified. 84 CARRARA FORMATION, SOUTHERN GREAT BASIN Oryctooephalites typicalis Resser Plate 13, figures 1—4 Oryctocephalites typicalis Resser, 1939b, p. 45, pl. 3, figs. 1-6; Shimer and Shrock, 1944, pl. 257, figs. l4, l5; Fritz, 1968, p. 202, pl. 41, figs. 9—11; Shergold, 1969, text figs. 93—f. Desaription.—Cranidium subtrapezoidal in outline, gently to moderately convex transversely and longi- tudinally, anterior margin moderately curved. Glabella elongate, subelliptical in outline, well defined by deep axial and preglabellar furrows, anterior end bluntly rounded, extended onto inner edge of flat narrow bor- der. Three pairs of glabellar furrows present; posterior pair consists of pits separated from axial furrow, but connected across glabella; anterior two pairs represented only by pits or short transverse slots isolated from axial furrows. Occipital furrow straight, deep. Occipital ring miderately convex, bears small axial node adjacent to occipital furrow. Frontal area consists of narrow flat bor- der; sagittal length about 0.1 sagittal length of glabella exclusive of occipital ring. Distal part Of border defined by shallow border furrow that curves backward near an— terolateral part of glabella. Fixed cheek moderately con— vex, horizontal; width of palpebral area about two-thirds or slightly more than two-thirds basal glabellar width. Palpebral lobe gently curved, well defined by palpebral furrow; line connecting posterior tips passes over pre- occipital furrow; exsagittal length about 0.4 sagittal length of glabella exclusive of occipital ring. Ocular ridge barely apparent even after whitening. Posterior limb has straight deep posterior border furrow; distal part barely extended beyond palpebral lobe. Course Of anterior sec- tion of facial suture nearly straight forward from palpe— bral lobe; course of posterior section slightly divergent posterolaterally behind palpebral lobe. Pygidium, exclusive of border spines, semicircular in outline, gently convex transversely and longitudinally; sagittal length about one-half anterior width. Axis nar- rower than pleural regions, well defined, gently tapered backward to fourth axial segment and then more strongly tapered nearly to point at posterior margin. Three com- plete ring furrows present posterior to articulating fur- row; an additional ring furrow less well defined. Pleural regions lack a defined border, crossed by four deep straight pleural furrows that extend nearly to margin. Shallow interpleural furrows present outlining posterior edge of macropleural segment. Other interpleural fur- rows very shallow or absent. Border bears five pairs of spines; anterior three pairs of equal length, short; fourth pair long, slender, posteriorly directed; fifth pair short- est, slightly convergent posteriorly. External surfaces of all parts smooth. Discussion .—This species is characterized by the relative sizes, orientation, and number of the pygidial border spines. The three anterior pairs of spines are shorter than those of the Australian species described by Shergold (1969), and the macropleural spines are slightly diver- gent rather than parallel or convergent; the interpleural furrows on the pygidium are not well developed as they are in O. incemu Chernysheva (1962) from Siberia; and 0. lypicalis has five rather than four border spines as in 0. resseri Rasetti (1957). One cranidium (pl. 13, fig. 1) shows much less well developed glabellar furrows than is typical for the species but agrees in all other details, and it is considered to illustrate the range of variability within this species. Occurrence.—Common, Albertella Zone, Zacanthoidid Zonule. Nevada: 3766—CO (>10 cranidia and pygidia), Nevada Test Site. Genus ORYCTOCEPHALUS Waleott Oryctocephalus Walcott, 1886, p. 210; Reed, 1910, p. 10; Kobayashi, 1935, p. 146; Lermontova, E. V., in Vologdin, 1940, p. 136; Shimer and Shrock, 1944, p. 615; Palmer, 1954, p. 68; Rasetti, F., in Harrington and others, 1959, p. 220; Suvorova, N. P., and Cher- nysheva, N. E., in Chernysheva, 1960, p. 82; Yegorova, L. I., and others, in Khalfin, 1960, p. 198; Chernysheva, 1962, p. 11; Shergold, 1969, p. 15; Zhuravleva and others, 1970, p. 37. Type species.—01yctocephalm primus Walcott, 1886, p. 210, pl. 29, figs. 3, 3a. Discussion—Shergold (1969) has presented a good re— cent discussion of this genus and its species content. He restricted the genus to species with six pairs of pygidial spines and arbitrarily concluded that the five-spined pygidium associated with the cranidium of the type species should be assigned to 01yctocephalites. He also recognized two informal subgeneric groups, one with a macropleural fourth pair of pygidial spines and one lacking clear macropleural spine development. 0. nyensis n. sp. belongs to the group lacking macropleural pygidial spmes. Oryctooephalus nyensis n. sp. Plate 6, figures 13—15 Description.—Cranidium, exclusive of distal parts of posterior limbs, transversely subquadrate; anterior mar- gin nearly straight; sagittal length about two-thirds width between palpebral lobes. Glabella well defined by deep narrow axial furrow, very slightly tapered forward, bluntly rounded, reaches to inner edge of narrow convex anterior border that is well defined laterally by deep border furrow; sides nearly straight; sagittal glabellar length slightly more than 1.5 times basal glabellar width. Occipital furrow represented by deep pits connected by shallow furrow. Occipital ring simple. Glabellar furrows represented by three pairs of deep pits isolated from axial SYSTEMATIC PALEONTOLOGY 85 furrows; two posterior pairs connected across glabella by shallow furrow. Additional faint furrows present adja- cent to axial furrows at junction with ocular ridges. Frontal area consists only of narrow border. Fixed cheeks as wide as glabella, crossed by narrow well-defined ocular ridges that diverge only slightly laterally from parallelism with anterior margin. Palpebral lobes long, gently curved, and well defined by narrow palpebral furrow, midlength located slightly posterior to glabellar mid- length; exsagittal length about 0.4 sagittal glabellar length exclusive of occipital ring. Posterior limb has well-developed border furrow; transverse length slightly greater than basal glabellar width. Thorax composed of at least nine segments. Each seg- ment has well-developed diagonal pleural furrow and long slender posterolaterally directed spine. Length of spine relative to transverse length of pleural region in- creases posteriorly. Pygidium moderately large, transversely subovate in outline, has well-defined posteriorly tapered axis with at least four ring furrows posterior to articulating furrow. Pleural regions crossed by four deep pleural furrows reaching to posterior margin between marginal spines. Interpleural furrows present, shallow. Six pairs of slen- der tapered border spines present; anterior four pairs equal in length, fifth pair intermediate in length; sixth pair shortest. Discussion—This species differs most strikingly from all other Oryctocephalus species by having the pygidial spines long and slender and the fourth pair not modified. Evaluation of more subtle distinctions must await more material. Occurrence.—Rare, “Plagium-Poliella” Zone. Nevada: 443'5—CO (l cranidium, 2 pygidia, l thorax), Belted Range. Genus THOMGOCARE Robison and Campbell Thoracomre, Robison and Campbell, 1974, p. 273. Type species .—Vistoia? minuta Resser (Part), 1939a, p. 21, pl. 2, fig. 2 only. Discussion—This remarkable small corynexochid trilobite recently redescribed and clarified by Robison and Campbell is represented in the Carrara Formation only by pygidia. The distinctive small size, pygidial out- line, short and tapered axis, and pleural furrows deepest near the margin easily distinguish this from all other associated trilobites. Thoracocare ldahoensis (Resser) Plate 12, figure 5 Tonkinella idahoemis Resser, 1939b, p. 45, pl. 2, fig. 10. Thoracocare idahoensis (Resser), Robison and Campbell, 1974, p. 279, figs. 3a—g. Description .—Pygidium small, semicircular, gently con- vex transversely and longitudinally. Axis low, defined by shallow axial furrows, tapered backward, extending about two-thirds sagittal length of pygidium, consisting of four or five obscurely defined axial rings; greatest width about one-fourth greatest width of pygidium. Pleural regions have 12 pairs of poorly defined equally spaced radiating furrows best seen along pygidial mar- gins. Posterior pleural furrows parallel to pygidial axis. Border smooth. Discussion .——The tiny pygidia, less than 3 mm wide, that represent this species conform in all respects to a tiny form described by Resser (1939b) from southeastern Idaho as Tonkinella idahoemis. Although the pygidium has superficial resemblances to Tonkinella, it lacks the strong and regular development of pleural furrows and the distinctively scalloped pygidial margin of that genus. Robison and Campbell (1974) assigned this species to a remarkable tiny corynexochid genus Thoracocare. T. idahoensis differs from the only other species presently assigned to the genus, T. minuta (Resser), by having more clearly developed ring furrows on the axis and by having its width and length respectively one-fourth instead of one-third, and two-thirds instead of three—fourths, the width and length of the pygidium. Occurrence.—Rare, Albertella Zone, Ogygopsis Zonule. Nevada: 4437—CO (2 pygidia), 4438—CO (l pygidium), both from Belted Range. Oryctooephalld sp. undet. Plate 12, figure 6 Discussion—A single weathered pygidium from the Belted Range represents an undescribed oryctocephalid species. The axis and pleural fields are too poorly pre- served to see the development of the furrows and character of segmentation, but the outline is well pre- served and shows seven pairs of border spines. The fourth spine is macropleural as in many oryctocephalids, but there are three pairs of spines behind the macro- pleural spines. All described oryctocephalids with the fourth spine macropleural have two or fewer posterior spines behind the macropleural segment. Formal naming of this species is deferred until better material is available. Occurrence.——Rare, Albertella Zone, Ogygopsis Zonule. Nevada: 4438—CO (l pygidium), Belted Range. Family ZACANTHOIDIDAE Swinnerton The Zacanthoididae, as constituted in the “Treatise on Invertebrate Paleontology” (Harrington and others, 1959, p. 227), includes a variety of corynexochid forms characterized by variously spinose pygidia and by a long, 86 CARRARA FORMATION, SOUTHERN GREAT BASIN slender glabella that is slightly expanded anteriorly. The Dolichometopidae (Harrington and others, 1959, p. 220) contain many forms having cranidia similar to the Zacanthoididae but generally lacking spinose pygidia. One exception has been Ptarmiganoides, which has a strongly spinose pygidial margin. Restudy of specimens of Ptarmiganoides in the collections of the US. National Museum and new material from the Carrara Formation shows that Ptarmiganoides cranidia have posterior limbs with distinct intergenal spines (pl. 11, fig. 18) comparable to those of Zacanthoides and Paralbertella n. gen. and un- like any of the typical genera of the Dolichometopidae. On the basis of total morphology, Ptarmiganoides is here assigned to the Zacanthoididae. In the future, perhaps the small—eyed genera, such as Albertella and Vanuxemella, that are now included in the Zacanthoididae should be removed to a separate family or subfamily, leaving the main body of the Zacan- thoididae to be typified then also by long arcuate palpeb- ral lobes. Such modification should be a part of a com— plete reevaluation of the entire Order Corynexochida that is beyond the scope of this report. Genus ALBERTELLA Walcott Albertella Walcott, 1908, p. 18: Resser, 1936, p. 1; Rasetti, 1951, p. 147; Rasetti, F., in Harrington, 1959, p. 227. Type species.—Albertella helena Walcott, 1908, p. 19, pl. 2, figs. 1—4. Description—Small to medium-sized corynexochid trilobites; sagittal length probably not exceeding 50 mm. Cranidium subtrapezoidal in outline, gently convex transversely and longitudinally; anterior margin gently rounded. Glabella elongate, reaches nearly to anterior margin, well defined, sides subparallel or slightly ex- panded anteriorly, straight or concave. Four pairs of shallow glabellar furrows may be present. Occipital fur- row straight, generally shallow. Occipital ring simple, axial node may be present at posterior margin. Frontal area extremely narrow, undivided. Fixed cheeks gently convex, horizontal, or slightly downsloping; width, in- cluding palpebral lobes, generally less than half basal glabellar width. Palpebral lobes generally small, well separated from glabella, situated opposite or slightly an- terior to glabellar midlength. Ocular ridge poorly de- veloped. Posterior limbs broad, triangular. Posterior border furrow shallow, straight. Course of anterior sec- tion of facial suture subparallel, slightly convergent, or slightly divergent anterior to eyes. Course of posterior section of facial suture gently convex. Hypostome and rostral plate fused; rostral area usually not clearly differentiated. Free cheek narrow, with moderately to poorly defined gently convex border and long slender cylindrical genal spine continuing curvature of cheek margin. Thorax composed of seven segments. Third segment macropleural in all known species. Axis prominent, as wide as or wider than pleurae. Pygidium subquadrate, width usually greater than length. Axis prominent, reaches to or nearly to posterior margin, composed of four or five variably defined seg- ments and terminal part. Pleural regions with pleural or interpleural furrows defining three or four segments variably defined. Margin bears pair of long slender spines directed posterolaterally. Spines not clearly re— lated to pleural segments. Posterior margin between spines curved posteriorly. External surfaces of all parts smooth or covered with fine closely spaced granules. Discussion.—Walcott included in Albertella two distinct kinds of trilobites that are now each represented by sev- eral species. One species group, typified by A. helena Walcott, has cranidia with small- to moderate-sized pal- pebral lobes well separated from the glabella, generally broad triangular posterior limbs, a third macropleural segment on the thorax, genal spines not strikingly ad- vanced, the hypostome and rostral plate fused but not clearly differentiated, and pygidial border spines that are widely divergent and not clearly related to particular pleural segments of the pygidium. The second species group, typified by A. boswortki Walcott, has cranidia with long palpebral lobes that have the anterior end close to the glabella, narrow posterior limbs, a fourth macro- pleural segment on the thorax of the one species known with articulated parts, free cheeks indicating advanced genal spines, hypostome and rostral plate fused but strongly differentiated, and a distinctive pygidial struc- ture in which the anterior bands of the first three seg- ments are accentuated as ridges and generally merge laterally with the pygidial border at the base of pygidial spines much less laterally divergent than in the first species group. Most species of the bosworthi group have axial nodes on the pygidial segments that are lacking or weakly developed on species of the helena group. Rasetti (1951, p. 148) noted these differences but chose to retain both groups within Albertella. Fritz (1968) iden— tified a third related group of species with cranidial characters much like the bosworthi group and with similar pygidial pleurae. However, in this group (Albertelloz'des), the pygidial spines are located much more posteriorly, there is consistent development of an occipital spine, and the free cheeks have large genal spines that are not ad- vanced. In order to be consistent in ranking the differences between the three groups of species, either Albertelloides should become a subgenus of A lbertella because it is closer to the bosworthz' group than the bosworthi group is to the SYSTEMATIC PALEONTOLOGY 87 helma group, or the three groups should be recognized as separate but related genera. Use of subgenera creates cumbersome nomenclature, and the range of morphol- ogy that would be included in the genus would be much greater than that of most other corynexochoid genera. Thus, in this report, the three groups are treated as related genera. Albertella must be retained for the group of generally small-eyed forms with normal pygidial pleura that in- cludes the type species. In addition to the species de- scribed in this report, this group includes the following species: A. helena Walcott (synonyms: A. m'tida Resser,A. sampsoni Resser, A. ressensis Resser),A. microps Rasetti,A. proveedom Lochman, and A. schenki Resser. Of these species, only A. helena, which has longer eyes than the others, approaches the bosworthi group, here included in a new genus, Paralbertella, and then only in cranidial structure. The species included in Paralbertella are: P. bosworthi (Walcott) (synonym: Albertella stenorhachis Rasetti), P. declivis (Rasetti), P. limbata (Rasetti), P. rob- sonensis (Resser), P. eiloitys (Fritz), P. lam (Fritz), and P. judithi (Fritz).Albertelloides includesA. mischi Fritz,A. [Jan- dispinata Fritz, A. maladensis (Resser), A. dispar (Resser), and A. rectimargz'natus n. sp. Although the three genera have approximately the same time range, species of Al- bertella s. s. are rarely found in association with either Paralbertella orAlbertelloides and they seem to have a more landward distribution. Albertans: longwelli n. sp. Plate 9, figures 1—3, 6, 7, 9, 10 Description.—Cranidium subtrapezoidal in outline, gently convex transversely and longitudinally, sagittal length about two-thirds width between tips of posterior limbs, anterior margin gently and evenly curved. Glabella low, elongate, expanded forward, reaches nearly to an- terior margin, sides slightly concave; basal glabellar width about seven-eighths width at anterior end. Glabellar fur- rows barely apparent; posterior pair strongly oblique. Posterior end of glabella poorly defined by axial furrows. Occipital furrow shallow, straight. Occipital ring gently convex, without node or spine. Frontal area reduced to wirelike border in front of glabella. Fixed cheeks gently convex, downsloping; width exclusive of palpebral lobe slightly less than one-half basal glabellar width. Palpebral lobe small, situated slightly anterior to glabellar mid- length; exsagittal length about one-fourth sagittal glabellar length exclusive of occipital ring. Palpebral fur- row shallow. Ocular ridge barely apparent, strongly oblique to axial furrow. Posterior limb broad, triangular; transverse length slightly less than basal glabellar width. Course of anterior section of facial suture nearly straight forward in front of palpebral lobe and then curved evenly inward to intersect anterior margin near an- terolateral cranidial corner. Course of posterior section of facial suture directed posterolaterally behind palpe- bral lobe and curved evenly backward to posterior mar— gm. Free cheek narrow; border gently convex, separated from ocular platform by shallow border furrow; width of border uniform, slightly less than length of anterior sutural margin of ocular platform; ocular platform ex— pands posteriorly. Lateral margin gently curved, con— tinuous with very long slender genal spine; length of spine about three times length of posterior sutural mar- gin. Junction of posterior margin of cheek with inner margin of spine nearly a right angle. Rostral plate and hypostome fused, not clearly differ- entiated. Pygidium, exclusive of border spines, short, wide; sagittal length slightly more than one-half anterior width. Axis prominent, transversely convex, crest nearly flat, tapered very slightly posteriorly, rounded at tip, ex— tended nearly to posterior margin. Two shallow straight complete ring furrows present posterior to articulating furrow; a partial third furrow barely apparent. Rings without nodes or spines. Pleural fields narrow, triangu— lar, crossed by three broad shallow pleural furrows. In- terpleural furrow between first and second segments barely apparent near axis. Border differentiated from pleural field by lack of furrows, produced pos- terolaterally into pair of very long slender border spines; length of spines more than three times sagittal length of axis. Posterior margin between spines curved posteriorly. Posterior part of border strongly depressed. External surfaces of all parts covered with very fine, barely apparent, granules. Discussion—This species differs from all others in the genus exceptA. microps Rasetti by having only three ring furrows developed on the axis of the pygidium. It differs from A. microps by lacking any trace of axial nodes. Among the Carrara species, it is most like A. schenkz' Res- ser, but it consistently has fewer ring furrows and pleural furrows on the pygidium, the glabella is less well defined, and a narrow cranidial border is present. 0ccurrence.——Moderately common, Albertella Zone, Albertella-Mexicella Zonule. Nevada: 1616—CO (>20 cranidia, 4 free cheeks, 5 pygidia), Spring Mountains. California: 4154—CO (1 cranidium, 2 free cheeks, 5 hypostome-rostral plates, 1 pygidium, all silicified), Echo Canyon section, Funeral Mountains; 4165—CO (3 cranidia, l hypostome—rostral plate, 2 free cheeks, 6 pygidia, all silicified), Eagle Mountain. 88 CARRARA FORMATION, SOUTHERN GREAT BASIN Albertella. schenki Besser Plate 9, figures 13—15, 17, 18 Albertella schenki Resser, in McKee and Resser, 1945, p. 195, pl. 20, fig. 18. Description.—Cranidium subtrapezoidal in outline, gently convex tranversely and longitudinally, sagittal length about three—fourths width between tips of pos— terior limbs, anterior margin gently and evenly curved. Glabella low, elongate, expanded forward, sides concave, reaches nearly to anterior margin and merges with barely perceptible wirelike anterior border; basal glabellar width about three—fourths width at anterior end. Glabel- lar furrows barely apparent, posterior pair strongly oblique. Glabella well defined at sides by narrow shallow axial furrows. Occipital furrow straight, moderately deep across top of glabella, barely apparent distally. Occipital ring gently convex, without node or spine. Fixed cheeks gently convex, downsloping; width, exclusive of palpe- bral lobe, slightly less than one-half basal glabellar width. Palpebral lobe small, poorly defined, located slightly an- terior to glabellar midlength; exsagittal length about one-fifth sagittal glabellar length exclusive of occipital ring. Ocular ridge barely apparent, strongly oblique to axial furrow. Posterior limb broad, triangular; transverse length about equal to basal glabellar width. Course of anterior section of facial suture nearly straight forward in front of palpebral lobe, curved inward to intersect an— terior margin near anterolateral cranidial corner. Course of posterior section directed posterolaterally behind pal— pebral lobe and curved evenly backward to posterior margin. Free cheek moderately wide, lateral margin and pos— terior sutural margin subparallel. Lateral and posterior borders gently convex, separated from gently convex ocular platform by broad shallow, continuous border furrow; width of border at anterior end about equal to length of anterior sutural margin of ocular platform. Ocular platform expands posteriorly. Lateral margin continuous with long slender genal spine; length of spine more than twice length of posterior section of facial su- ture. Angle between posterior margin of free cheek and inner spine margin slightly less than 90°. Hypostome and rostral plate fused, not clearly differ- entiated. Pygidium, exclusive of border spines, subquadrate; sagittal length about two-thirds anterior width. Axis prominent, transversely convex, crest nearly flat, tapered slightly posteriorly, rounded at tip, extended nearly to posterior margin. Three shallow straight complete ring furrows present posterior to articulating furrow; a partial fourth furrow barely apparent. Rings without nodes or spines. Pleural fields narrow, triangular, crossed by four subparallel broad shallow pleural furrows. Border differentiated from pleural field by lack of furrows, pro- duced posterolaterally into pair of long slender border spines at least twice sagittal length of axis. Posterior mar- gin between spines strongly curved backward, and con- cave in transverse cross section. External surfaces of all parts smooth. Discussion—This species has been known previously only from a pygidium from the Grand Canyon section. The pygidia in the Carrara Formation are indistinguish- able from the Grand Canyon specimen, and the as- sociated cranidia, cheeks, and hypostome-rostral plates provide much additional information about the mor- phology of the species. The most similar species is Alber- tella proveedom Lochman (in Cooper and others, 1952) which differs by having one more axial segment on the pygidium and by having distinctly longer and more pos- teriorly placed palpebral lobes. If the free cheek of A. proveedom is correctly assigned, it has an obtuse rather than slightly acute angle between the inner spine margin and the posterior cheek margin. The most similar species in the Carrara Formation is A. longwelli which has a dis- tinctly differentiated anterior border and one less axial segment on the pygidium. Occurrence.—Common, Albertella Zone, Albertella- Mexicella Zonule. Nevada: 3543—CO (>20 cranidia, 5 hypostome—rostral plates, 5 free cheeks, 8 pygidia), Desert Range. Albertella spectrensis n. sp. Plate 9, figures 4, 5, 8, 11, 12, 16 Description.——Cranidium subtrapezoidal in outline, moderately convex transversely and longitudinally, gently rounded anteriorly. Glabella moderately convex transversely, gently convex longitudinally, straight- sided, well defined by narrow axial and preglabellar fur- rows, slightly expanded forward, reaches to narrow up— turned border. Glabellar furrows barely apparent. Oc- cipital furrow straight, moderately deep. Occipital ring gently convex, has small axial node adjacent to posterior margin. Fixed cheek gently convex, horizontal; width, exclusive of palpebral lobe, slightly more than one-half basal glabellar width. Palpebral lobe moderately small, situated about opposite glabellar midlength; exsagittal length between one-third and one-fourth sagittal glabel- lar length exclusive of occipital ring. Ocular ridge mod- erately distinct, forms acute angle with axial furrow. Deep pit developed in axial furrow anterior to intersec- tion of ocular ridge at anterolateral corner of glabella. Posterior limb triangular; transverse length about equal to basal glabellar width. Posterior border furrow straight, moderately deep. Course of anterior section of facial suture straight forward from palpebral lobe, strongly SYSTEMATIC PALEONTOLOGY 89 curved around anterolateral corner of cranidium. Course of posterior section divergent posterolaterally behind palpebral lobe and curved evenly to posterior margin. Free cheek narrow. Lateral and posterior borders gently convex, well defined by shallow continuous border furrow; width of border at anterior end about equal to width of sutural margin of ocular platform. Ocular plat- form expanded slightly posteriorly. Lateral margin con- tinuous with long slender genal spine. Angle between posterior margin and inner spine greater than 90°. Hypostome and rostral plate fused; rostral part forms distinct angle with hypostomal part on axial line. Pygidium, exclusive of border spines, subquadrate; sagittal length slightly less than anterior width. Axis prominent, transversely convex, nearly flat in profile, tapered slightly posteriorly; tip strongly rounded, reaches nearly to posterior margin. Three shallow straight complete ring furrows posterior to articulating furrow; a fourth incomplete ring furrow also present. Each of the first three or four segments has a low axial node. Pleural fields subtriangular, narrow, crossed by two or three weak pleural furrows. Border distinguished from pleural field by lack of furrows, produced laterally into long slender border spine more than three times sagittal length of axis. Posterior margin between border spines strongly curved posteriorly, slightly depressed. All dorsal surfaces covered with fine granular or- namentation. Discussion .-—This species is not represented by material as well preserved or abundant as the other species from the Carrara Formation. Nevertheless, it differs from both A. longwelli n. sp. and A. schenki Resser by having a well- defined upturned cranidial border, slightly larger more posteriorly placed eyes, an occipital node, an obtuse angle between the posterior margin of the free cheek and the inner spine margin, a distinct differentiation of the junc- tion between the hypostome and rostral plate, and axial nodes on the pygidial segments. The only other species of Albertella s. s. with axial nodes are A. nitida Resser and A. microps Rasetti. A. nitida has much larger palpebral lobes, narrower fixed cheeks and posterior limbs, advanced genal spines, and a more regular spacing of the pleural furrows on the pygidium. A. microps has deeper glabellar furrows and a smaller number of axial segments on the pygidium; the pleural furrows on the pygidium are un— evenly spaced; and only the cranidium has granular or- namentation. Occurrence.—-—Moderately common, fragmentary, Al- bertella Zone, Albertella-Mexicella Zonule. Nevada: 4169—CO (7 cranidia, 2 free cheeks, 3 hypostomes, >10 pygidia, mostly silicified), Spectre Range; 7195—CO (l cranidium), Desert Range. California: 4159—CO (2 cranidia, 2 cheeks, 2 pygidia), Pyramid Peak section, Fu- neral Mountains. Genus ALBERTELLINA n. gen. Type species.——Albertellina aspinosa n. sp. Description .—Moderately small corynexochid trilobites, length of largest known specimens probably about 30 mm. Cephalon subsemicircular in outline, with long flattened genal spines extending backward from pos- terolateral corners. Cranidium, excluding posterior limbs, elongate subrectangular in outline. Glabella long, low, narrow, straight sided, expanded forward, extended onto inner part of flat or slightly concave border; well defined at sides and anterior by changes in slope of exo- skeleton; anterior end bluntly rounded. Four pairs of shallow glabellar furrows variably developed, generally obscure. Occipital furrow shallow, deepest distally. Oc- cipital ring incomplete on all known specimens. Frontal area short, flat, or slightly concave, undivided; sagittal length slightly less than one-eighth sagittal length of glabella exclusive of occipital ring; outer part has zone of low coarse anastomosing ridges generally parallel to an— terior margin. Palpebral area of fixed cheek gently con- vex, horizontal, greatest width more than half basal glabellar width. Palpebral lobe long, slender, curved, well defined by broad shallow palpebral furrow, continuous with low, poorly defined ocular ridge; situated opposite posterior half of glabella; exsagittal length between 0.4 and 0.5 sagittal length of glabella exclusive of occipital ring. Posterior limb moderately slender, spatulate; distal tip strongly rounded; transverse length about equal to basal glabellar width. Posterior border furrow broad, shallow. Anterior section of facial suture slightly diver- gent forward from palpebral lobe; posterior section divergent-sinuous. No intergenal spine. Hypostome and rostral plate fused. Rostral part well defined by abrupt change in slope of exoskeleton. Free cheek moderately narrow, gently convex, with broad flat border about equal to anterior width of ocular platform. Lateral border furrow shallow, not clearly con— tinuous with deeper posterior border furrow which con- tinues onto long flattened genal spine and extends nearly to tip. Genal spine not advanced. Pygidium subtrapezoidal in outline, with sides slightly tapered posteriorly and with both anterolateral and pos- terolateral corners rounded. Posterior margin has slight median inbend. Axis prominent, tapered posteriorly, strongly rounded at rear, well defined by abrupt changes in slope of exoskeleton. Two or three very shallow ring furrows variably developed. Pleural regions crossed by variably developed raised anterior pleural bands of first three pleural segments that continue onto flattened bor-- 90 CARRARA FORMATION, SOUTHERN GREAT BASIN der. No distinct border furrow. Lateral and posterior margins without spines. Ornamentation consists of extremely fine granules on lateral and posterolateral parts of pygidial border. Other parts appear smooth. Discussion .—This genus constitutes the third genus of a group including Albertelloides and Paralbertella. It differs from both of those genera most strikingly in lacking pygidial spines. It differs further fromPamlbertella by the lack of advanced genal spines and from Albertelloides by the lack of a narrow furrow along the outer margin of the free cheek. The development of the anterior bands of the pygidial pleural segments is more variable and less strong than in either Albertelloides or Paralbertella. Albertellina. aspinosa. n. sp. Plate 10, figures 1—6 Discussion—Because this is the only species at present in Albertellina, the generic description and discussion of affinities also suffice for the species. Occurrence.—Moderately common, Albertella Zone, Albertella—Mexicella Zonule. Nevada: 4169—CO (2 pygidia), Spectre Range; 7195—CO (4 cranidia, 1 hypos- tome, 4 free cheeks, 8 pygidia), Desert Range. Genus ALBERTELLOIDES Fritz Albertelloides Fritz, 1968, p. 214. Type species.—Albertelloides mischi Fritz, 1968, p. 215, pl. 38, figs. 1—7. Description.—Moderate-sized corynexochids, length probably not exceeding 60 mm. Cephalon semicircular, with long broad-based flat curved genal spines extending backward from posterolateral corners. Glabella long, low, narrow, moderately well defined at sides and front by abrupt change in slope of exoskeleton; sides slightly concave; anterior end slightly wider than base. Four pairs of short lateral glabellar furrows present, posterior pair deepest and distinctly curved; others straight. Occipital furrow short, deep, slotlike at sides of glabella; shallow across axis. Occipital ring subtriangular, flat, extended into short slender occipital spine. Frontal area short, flat, undivided. Palpebral area of fixed cheek gently convex, horizontal, greatest width more than half basal glabellar width. Palpebral lobe long, slender, curved, well defined by palpebral furrow, situated opposite posterior half of glabella; anterior end connected to moderately distinct ocular ridge. Posterior limb slender, slightly expanded laterally; posterior margin nearly straight. Posterior bor- der furrow well defined. Anterior section of facial suture slightly divergent anteriorly; posterior section strongly divergent, sinuous. Intergenal spine present on some small individuals, absent on cranidia longer than 5 mm. Hypostome and rostral plate fused; rostral part dis- tinctly defined by narrow furrow. ' Free cheek narrow. Ocular platform gently convex, about as wide as flat border that is well defined by narrow lateral border furrow and continues into long flat curved genal spine. Posterior part of lateral margin and inner margin of spine bear narrow raised edges well defined by shallow furrows. Thorax composed of eight segments; width of each pleural region, exclusive of spines, about equal to width of axis. Spines known only for last three segments; spines short, subequal in length, rounded in cross section. Pygidium subquadrate in outline. Axis long, elevated, well defined, reaches nearly to posterior margin; bears two or three distinct ring furrows and one or two addi- tional obscure furrows. Axial rings simple. Pleural re- gions triangular, crossed by three distinct broad pleural furrows and two narrow shallow interpleural furrows. Anterior bands of first three segments prominent, ridgelike. Border nearly flat; bears pair of slender pos- teriorly or posterolaterally directed border spines whose bases are about opposite end of axis. Discussion .—The material representing this genus from the Carrara Formation adds information about the thorax, free cheek, and ventral morphology and proves the correctness of the association of cranidium and pygidium described by Fritz. The intergenal spines men- tioned by Fritz as characteristic of the genus, are limited to small specimens, as in Paralbertella n. gen., and are not found on large specimens. Albertelloides differs from Albertella by having long eyes, slender posterior limbs, eight rather than seven thoracic segments, ridgelike development of the anterior bands of the first three pleural segments on the pygidium, and pygidial border spines that are not strongly advanced. Differences from the more closely related genera Paral- bertella n. gen. and Albertellina n. gen. are given in the discussions of those genera. Albertelloides mlschi Fritz Plate 10, figures 7—13 Albertelloides mischi Fritz, 1968, p. 215, pl. 38, figs. 1—7. Discussion—Fritz has given a good description of the cranidium and pygidium of this species. The free cheek and hypostome-rostral plate are not distinguishable at present from A. rectimarginatus n. sp. and are described with that species. A partly preserved complete specimen that proves the association of cranidium and pygidium of this genus—whereas Resser (1939b) had assigned the pygidia to the ptychopariid genus Kochaspis—is question— ably identified as A. mischi. This species is characterized by having moderately SYSTEMATIC PALEONTOLOGY 91 long and slender pygidial spines directed nearly straight posteriorly, and the posterior margin between the spines is slightly convex posteriorly. The axis of most specimens has only one obscure ring furrow present behind the three distinct anterior ring furrows. The only distinct ornamentation on this species is on the pygidial spines, which are granular on smaller specimens and obscurely marked by anastomosing ridges on some larger speci- mens. The occipital furrow of uniform width and depth described by Fritz is found only on small cranidia. On most cranidia, the axial part of the furrow is quite shal- low. Occurrence.—Moderately common, Albertella Zone, Zacanthoidid Zonule. Nevada: 3766—CO (>10 cranidia, 2 free cheeks, 2 hypostome-rostral plates, >10 pygidia); 3484—CO (1 pygidium, one partially articulated speci- men), both from Nevada Test Site. Albertelloides rectimarginatus n. sp. Plate 10, figures 14—20 Description.—Cranidium low, broad, gently convex transversely and longitudinally; width between palpebral lobes about equal to sagittal length exclusive of occipital spine. Glabella long, low, gently convex transversely and longitudinally, well defined at sides and front by abrupt changes in slope of exoskeleton; sides slightly concave; anterior end expanded; anterior width slightly greater than basal glabellar width. Four pairs of glabellar furrows present; posterior pair deep, short, strongly curved post- eriorly, with shallow short anterior bifurcation; other pairs shallow, narrow, straight. Occipital furrow has deep distal slots and shallow axial part except on small speci- mens where depth is more uniform. Occipital ring has slender spine of unknown length. Frontal area flat, nar- row, undivided; anterior margin has slight raised rim that is continuous with narrow lateral wirelike raised margin of free cheek. Sagittal length of frontal area gen- erally between one—sixth and one-seventh sagittal glabel— lar length exclusive of occipital ring. Fixed cheeks have broad palpebral area and narrow part anterior to distinct ocular ridge. Transverse width of anterior part generally about one-third basal glabellar width. Palpebral area gently convex, nearly horizontal; greatest width, exclu— sive of palpebral lobe,-about three-fourths basal glabellar width. Palpebral lobe long, narrow, arcuate, well defined by palpebral furrow, shaped like an inverted comma, situated opposite posterior half of glabella and at or slightly below level of palpebral area; line between post- erior tips passes over or just anterior to axial part of occipital furrow; anterior end continuous with ocular ridge. Exsagittal length of palpebral lobe slightly more than one-half sagittal length of glabella exclusive of oc- cipital ring. Posterior limb slender, posterior border fur- row broad, deep, straight, approximately equally divided into distal and proximal parts by tip of palpebral lobe. Posterior border of limb widens distally. Course of an- terior section of facial suture slightly divergent forward and then gently curved across frontal area to intersect margin near anterolateral cranidial corners. Posterior section of facial suture strongly divergent behind palpeb- ral lobe, then directed posterolaterally to intersect cephalic margin near base of genal spine. External sur- face smooth. Hypostome and rostral plate fused into single piece. Rostral plate gently convex in sagittal plane, well defined by anteriorly curved furrow at junction with strongly convex anterior body of hypostome. Posterior body small, low, well defined by transverse furrow. Maculae prominent on posterior part of anterior body. Free cheek moderately narrow, with gently curved lat- eral margin continuous with margin of long nearly flat genal spine. Border nearly flat, about equal in width to ocular platform, defined by shallow lateral border fur- row that is continuous with very short section of posterior border furrow at genal angle adjacent to posterior sutural margin. Genal spine has narrow, wirelike inner and outer margins defined by narrow furrows. External surface of spine is weakly ornamented with anastomosing venations and becomes increasingly granular towards tip. Length of spine nearly three times length of posterior sutural margin. Pygidium subquadrate; sagittal length about three- fourths anterior width. Sides subparallel or slightly con- vergent posteriorly. Posterior border spines moderately short, sharp; length about equal to sagittal length of first two axial segments. Posterior margin between spines straight or curved slightly forward. Axis prominent, strongly convex transversely, sides subparallel, posterior end bluntly rounded, high, extended nearly to posterior margin. Axis bears three distinct ring furrows posterior to articulating furrow and generally two additional obscure furrows and a terminal piece. Axial rings without nodes or spines. External surface smooth except for granular ornamentation on surface of spines. Discussion—This species differs from all others as- signed to the genus by having the pygidial spines short and directed nearly straight posteriorly and by having five axial segments. Pygidia are most like A. maladensis (Resser), which is the only other named species with the posterior margin straight or curved forward between the pygidial spines, butA. rectimarginatus consistently has one additional well-defined ring furrow on the axis. The cranidia are distinguished from those of A. mischz' by having a sagittally longer frontal area and a wider an— terior part to the fixed cheek. On A. mischi the sagittal length of the frontal area is about one-ninth the sagittal glabellar length exclusive of the occipital ring, and the 92 CARRARA FORMATION, SOUTHERN GREAT BASIN width of the anterior part of the fixed cheek is only about one-fourth the basal glabellar width. Occurrence.—Moderately common, Albertella Zone, Zacanthoidid Zonule. Nevada: 3547—CO (>10 cranidia, 2 hypostome-rostral plates, 3 free cheeks, >10 pygidia); 3483—CO (1 pygidium, 2 cranidia); both from Nevada Test Site. Genus FIELDASPIS Rasetti Fieldaspis Rasetti, 1951, p. 159; in Harrington and others, 1959, p. 227. Type species .—F ieldaspis furcata Rasetti, 1951, p. 159, pl. 15, figs. 1—8. Discussion .—Rasetti (1951; Rasetti, in Harrington and others, 1959) presented good illustrations and dis- cussions of the characteristics of this genus. Isolated cranidia are not generically separable from those of sev- eral other zacanthoidid genera, and the generic charac— teristic is in the pygidial structure which characteristically has a pair of posterolaterally directed spines or lobes. He also noted (Rasetti, 1957) the difficulty of distinguishing isolated pygidia of F ieldaspis from those of ptychopariids, such as Kochaspis and S chistometopus. Thus, without a large suite of associated parts, or an articulated specimen, a pygidium with paired spines that is not identical with one whose associations are already known cannot be generi- cally identified. Fieldaspis? sp. Plate 6, figure 16 Disoussion.—A single fragment of the left pleural re- gion of a trilobite pygidium, viewed from below, may represent a species of Fieldaspis. The specimen has two pairs of well-developed pleural and interpleural furrows, of which the interpleural furrows are narrower and deeper, and a less well developed third set of pleural and interpleural furrows. The pygidium was subquadrate in outline with a broad nearly straight posterior margin between a pair of long slender posterolaterally directed spines. All these characteristics agree with those of F iel— daspis superba Rasetti from the Plagiura-Kochaspis Zone of the Canadian Rocky Mountains. However, the specimen is too incomplete to do more than suggest the possible presence of Fieldaspis, and perhaps F. superba, in the Plagium-Kochaspis Zone of the southern Great Basin. Occurrence.—Rare (1 specimen), “Plagiura-Poliella” Zone. California: 4139—CO, Titanothere Canyon section, Grapevine Mountains. Genus M'EXICASPIS Lochman Mexicmpit Lochman, 1948, p. 455. Type species.—-Mexicaspzls stenopyge Lochman, 1948, p. 455, pl. 69, figs. 1—11. Diagnosis.—Small to moderate-sized corynexochid trilobites; maximum length probably not exceeding 30 mm. Cranidium gently convex transversely and lon- gitudinally, anterior margin moderately and evenly rounded. Glabella low, poorly furrowed, slightly ex- panded forward, reaches nearly to anterior margin. Oc— cipital ring gently convex, expanded backward, with or without axial spine. Fixed cheeks gently convex, moder- ately broad; width of palpebral area between one-half and three-fourths basal glabellar width. Palpebral lobes moderately long, situated slightly posterior to glabellar midlength. Posterior limbs short, blunt. Free cheek has narrow pleural platform and large broad curved genal spine developed from posterolateral margin; spine at least five times length of posterior sec- tion of facial suture. Pygidium moderately to strongly convex transversely. Axis prominent, sides subparallel; first segment well de— fined by deep ring furrow, usually has axial node. Re— mainder of axis long, obscurely furrowed; tip stands steeply above posterior margin. Pleural regions moder- ately to poorly defined. Border bears two or three pairs of border spines; posterior pair usually largest. Discussion .—Lochman (1948) gave a good description of this genus based on the material of two very similar species from northern Mexico. The Carrara species de— scribed below has a cranidium that conforms fully to Mexicaspis and a pygidium with its axial structure essen— tially like that of the type species, but with a third pair of spines intercalated between the analogs of the spines of M. stenopyge Lochman. Free cheeks can also be associated with the Carrara specimens. The pygidial differences are not considered sufficient to justify generic separation of the species, and the diagnosis given above has been mod- ified to accommodate the morphologic range shown by the pygidia and the new information about the free cheek. Mexicaspis radiatus n. sp. Plate 10, figures 22—25 Description .—Cranidium subquadrate in outline, gently convex transversely and longitudinally, moderately and evenly rounded at front. Glabella low, expanded an- teriorly, reaches nearly to anterior margin, well defined by abrupt changes in slope of exoskeleton. Glabellar fur- rows poorly developed; only posterior oblique pair mod- erately distinct. Occipital ring broad, gently convex; sagittal length about one—third sagittal length of remain- der of glabella. Occipital furrow moderately deep, straight. Fixed cheeks gently convex, slightly downslop— ing; width of palpebral area about 0.6 basal glabellar width. Palpebral lobe moderately long, narrow, curved, well defined by palpebral furrow, situated slightly pos- SYSTEMATIC PALEONTOLOGY 93 terior to glabellar midlength and well separated from glabella; exsagittal length between 0.4 and 0.5 sagittal glabellar length exclusive of occipital ring. Posterior limb short, blunt; transverse length about equal to basal glabellar width; length of distal part less than half length of proximal part. Posterior border furrow broad, shal- low, straight. Free cheek consists of small ocular platform separated by moderately deep border furrow from broader gently convex border that continues backward into large curved genal spine. Length of spine slightly more than five times length of posterior section of facial suture; angle between posterior margin of cheek and inner margin of spine moderately obtuse. Pygidium, exclusive of border spines, subsemicircular in outline; sagittal length slightly less than anterior width. Axis prominent, sides subparallel; end strongly rounded, overhangs posterior margin. First axial segment well de— fined by deep ring furrow, bears small axial node of variable prominence. Two additional very shallow ring furrows present anterior to long terminal part. Pleural fields subtriangular; greatest width less than that of axis. Two shallow pleural furrows present extending to inner edge of moderately well defined border. Border bears three pairs of broad-based border spines; anterior pair laterally directed, relatively small; middle pair pos- terolaterally directed, intermediate in size; posterior pair largest, directed nearly straight posteriorly; spacing of spines nearly uniform around margin. External surfaces of all parts have obscure finely granular ornamentation visible only after whitening of best preserved specimens. Discussion .—This species is easily distinguished from all others in the genus by having three pairs of pygidial border spines. The massive genal spines and axial node on the first axial segment of the pygidium suggest a relationship between this species and species of Ptar- miganoides. However, the pygidial border spines of all species of Ptarmiganoides are slender rather than broad- based, and the genal spine is advanced rather than at the posterolateral cephalic corners. Occurrence.—Common, Albertella Zone, Albertella- Mexicella Zonule(?). California: 4141—CO ( 10 cranidia, 3 free cheeks, 10 pygidia), Titanothere Canyon section, Grapevine Mountains; 7197—CO (>10 cranidia, 1 free cheek, >10 pygidia), Eagle Mountain. Genus PARALBERTELLA n. gen. Type species.—Albertella bosworthi Walcott, 1908, p. 22, pl. 1, figs. 4—6 (only). Description.—Moderate-sized corynexochid trilobites, length probably not exceeding 60 mm. Cephalon trans- versely subpentagonal in outline, anterior margin straight or gently rounded, genal spines distinctly ad- vanced from posterior margin. Cranidium elongate, gently conVCx transversely and longitudinally. Glabella long, well defined at sides and front by axial and pre- glabellar furrows, moderately convex transversely, gently convex longitudinally, sides subparallel, anterior end bluntly rounded. Four pairs of shallow lateral fur- rows present, posterior pair generally deepest and strongly oblique to axial furrow. Occipital furrow straight, occipital ring has small axial node adjacent to posterior margin. Frontal area short, flat. Fixed cheek gently convex, horizontal; width of palpebral area about one-half or slightly more than one-half basal glabellar width. Palpebral lobe long, arcuate, situated opposite posterior half of glabella, well defined by palpebral fur- row that is continuous along ocular ridge to axial furrow. Anterior end of palpebral lobe near glabella; posterior end opposite or posterior to occipital furrow. Posterior limb long, slender, posterior border expands distally; specimens less than 5 mm long show vestiges of in- tergenal spines. Course of anterior section of facial su- ture moderately to strongly divergent forward from pal- pebral lobes; course of posterior section directed nearly straight laterally. Free cheek crescentic in outline with well-defined bor- der furrow and long genal spine projecting pos- terolaterally from posterior margin. Hypostome and rostral plate fused. Thorax composed of seven segments. Axis prominent, usually wider than pleurae. Fourth segment macro- pleural. Pygidium elongate, semielliptical in outline exclusive of pair of advanced lateral border spines. Axis promi- nent, tapered posteriorly, reaches nearly to inner edge of narrow pygidial border, connected to border by narrow postaxial ridge. Five to seven distinct ring furrows present posterior to articulating furrow; most segments have low axial nodes. Pleural regions flat or gently con- vex, characterized by prominent ridgelike development of anterior bands of first three pleural segments. The ridges generally converge laterally to merge with pygidial border at base of border spine. Posterior margin behind lateral spines strongly curved posteriorly, usually down— sloping. Discussion.—This genus includes those species for- merly assigned to Albertella that have long eyes, slender posterior limbs, anteriorly divergent facial sutures, a fourth macropleural segment on the thorax, strongly advanced lateral border spines on the pygidium, a nar- row and well-defined posterior pygidial border, and the anterior bands of the first three pygidial segments de— veloped as ridges and merged laterally with the border at the base of the pygidial spine. The most similar genus is 94 CARRARA FORMATION, SOUTHERN GREAT BASIN Albertelloides, which differs by having a strong occipital spine, broad genal spines that are not advanced, eight instead of seven thoracic segments, fewer axial segments on the pygidium, a less well defined posterior pygidial border, and pygidial spines that are not strongly ad- vanced. Paralbertella bosworthi (Walcott) Plate 9, figures 19—25 Albertella bosworthi Walcott, 1908, p. 22, pl. 1, figs. 4—6 (only); Burling, 1916, p. 470, fig. 2a; Walcott, 1917, p. 38, pl. 7, figs. 3—3c (only); Rasetti, 1951, p. 149, pl. 17, figs. 1—9. Albertella similarit Resser, 1936, p. 2. PAlbertella stenorhachis Rasetti, 1951, p. 155, pl. 18, figs. 18—21. Discussion—This species has been well illustrated and has been discussed by Rasetti. The Carrara material is well preserved in limestone and seems to differ in no important respects from the shale and limestone material from British Columbia. The species differs from others in the genus by having the anterior margin curved and the frontal area slightly upturned on the cranidium, by having commonly five axial segments and pleural fur- rows on the pygidium together with a pleural region only slightly narrower than the axis, and by having long curved pygidial border spines. The examples of fused hypostomes and rostral plates in the sample from the Carrara Formation provide the first information about this structure for P. bosworthi. The rostral area is strongly distinguished from the hypostomal area by a deep curved furrow and by its ornamentation of terrace lines. The anterior lobe is strongly distinguished from the posterior lobe by a deep transverse furrow. Study of the type collections of the U.S. National Museum suggests that A. stenorhachis Rasetti may be no more than an extreme variant of A. bosworthi. I could not find consistent criteria for discrimination of these forms. Occurrence.—Moderately common, Albertella Zone, Zacanthoidid Zonule. Nevada: 3766—CO (>10 cranidia, 2 hypostome-rostral plates, >10 pygidia), Nevada Test Site. Genus PTARMIGANOIDES Rasetti Ptarmiganoides Rasetti, 1951, p. 178; Poulsen, C., in Harrington and others, 1959, p. 226. Type species.——Ptarmiganoides bowenszls Rasetti, 1951, p. 179, pl. 20, figs. 1—8. Description—Moderate- to large-sized corynexochid trilobites; maximum length probably not exceeding 90 mm. Cephalon semicircular in outline with well- developed long genal spines, sometimes advanced in front of genal angle. Cranidium elongate, gently to mod- erately convex transversely and longitudinally; anterior margin gently rounded. Glabella long, low, expanded slightly forward, extended nearly to anterior margin. Glabellar furrows shallow; four pairs usually present. Occipital ring with or without long axial spine. Fixed cheek gently to moderately convex, horizontal; width, exclusive of palpebral lobes, between 0.3 and 0.6 basal- glabellar width. Palpebral lobe long, slender, anterior end near glabella, posterior end about opposite or slightly anterior to occipital furrow. Posterior limb long, slender, bears distinct intergenal spine on posterolateral part of tip. Course of anterior section of facial suture slightly divergent forward in front of palpebral lobe. Course of posterior section strongly divergent behind palpebral lobe. Free cheek always has distinct border furrow, other features variable. Genal spine at or anterior to pos- terolateral corner of cephalon, slender or broad, gener- ally long. Pygidium, exclusive of border spines, semicircular in outline. Axis prominent, as wide as or wider than pleural fields, always has strong vertical axial spine on first seg— ment; other segments may have axial spines or nodes. Pleural regions crossed by one to three shallow pleural furrows that continue onto inner part of border and have a broad pit at inner margin of border. Border bears three to five pairs of long slender border spines. External surfaces of most species show some degree of granular ornamentation. Discussion—Although the description of this genus by Rasetti (1951) is adequate, a new description has been presented because additional information is now availa- ble concerning the posterior limbs, free cheeks, and structure of the pygidial margin. Rasetti (1951) proposed the genus Ptarmiganoides for the species from the Naomi Peak Limestone Member of the Langston Formation that Resser (1939b) assigned to Dolichometopsis, and included a new species from the Canadian Rocky Mountains. Both Rasetti (1951) and Lochman (in Cooper and others, 1952) concluded that Resser had misunderstood the re- lation of the Langston species of “Dolichometopsis” to the specimens described as Dolichometopsis by C. Poulsen (1927) from Lower Cambrian rocks of Greenland, al- though Lochman considered Resser’s species all to be- long to Ptarmigania. Ivshin (1957) reviewed the published material of Resser, Rasetti, and Lochman and concluded that there was insufficient reason to separate Ptar- miganoides from Ptarmigania. However, C. Poulsen (in Harrington and others, 1959) recognized both genera, and Fritz (1968) referred several species toPtarmiganoides without comment about the problem of generic distinc- tion. He did, however, note that some of Resser’s speci- mens of “Dolichometopsis” were referable to Poliella rather than Ptarmiganoides. In this report, Ptarmiganoides is considered as a genus distinct from Ptarmigania primarily because it has three SYSTEMATIC PALEONTOLOGY 95 or more pairs of slender pygidial border spines. Cranidia and free cheeks of both genera are not consistently dis- tinguishable, nor can they be separated from those of Paralbertella n. gen. and some other long-eyed corynexochids without knowledge of associated pygidia. When the whole trilobite is known, pygidia typical for Ptarmigania have one pair of anterolateral border spines and only nubs of one or two additional spines and can be easily distinguished from the multispinose pygidia of Ptarmiganoides. At the present time, grouping of corynexochid species into genera based only on cephalic features, as proposed by Ivshin, would seem to obscure important differences between species groups. Because of the great confusion caused by excessive splitting of species in the Langston Formation by Resser (1939b), and inadequate evaluation of their morphology, the current generic assignment for the holotype of each species of Ptarmigania and Dolichometopsis in that paper is presented here. Present Name Name in Resser (1939b) Dolichometopsis propinqua comis communis gregalis lepida mans teldi media [JouLsem' stella Ptarmigania sobrina aufita Ptarmiganoides propmqua (Resser) Ptamigania exigua Resser Ptarmigania exigua ornata natalis Poliella germana (Resser) Ptarmigania germana altilix ag'restis dignata Dolichometopsis potem grams As noted in the discussion of Poliella germana, not all paratypes of Resser’s “species” were conspecific with their holotypes. Instead of 21 species assigned to 2 gen— era, there are now considered to be 3 species of 3 genera. The three species are: Poliella germana (Resser), already revised by Fritz (1968); Ptarmiganoides propinqua (Resser), chosen from 11 names because its syntype series contains the most representative specimens for the species; and Ptarmigam'a exigua Resser. P. germana has smooth or pit— ted ornamentation, lacks fixigenal spines and has a pygidium that lacks border spines; P. propinqua has a weakly granular ornamentation and four pairs of slender pygidial spines; and P. exigua has a well-developed granular ornamentation and only one pair of short pygi- dial spines and several nubs of additional spines. With this reduction in names, Ptarmiganoides now includes six species: P. bowensz's Rasetti, P. propinqua (Resser), P. bi- spinosa (Lochman), P. amneicauda Fritz, and the two new species from the Carrara Formation described later in this report. Ptarmiganoides crassaxis n. sp. Plate 11, figure512,13, 17,18 Description—Cranidium questionably assigned to this species elongate, moderately convex transversely and longitudinally, gently to moderately rounded at front; width between palpebral lobes equal to or greater than sagittal length exclusive of occipital spine. Glabella long, moderately convex transversely, expanded slightly for- ward, reaches nearly to anterior margin, moderately to strongly rounded at front, well defined by abrupt changes in exoskeletal slope along sides and by narrow preglabellar furrow. Glabellar furrows shallow; posterior two pairs best developed; posterior pair strongly oblique to glabellar margin. Occipital furrow straight, of uniform depth on small forms, shallowest on axial line of large forms. Occipital ring gently convex, produced pos- teriorly into slender occipital spine; length, including spine, about three-fourths sagittal length of glabella. Frontal area very narrow, about one-tenth sagittal length of glabella exclusive of occipital ring. Fixed cheeks gently convex, horizontal; width of palpebral area slightly more than one-half basal glabellar width. Palpebral lobe long, arcuate, well defined by palpebral furrow, situated oppo- site posterior half of glabella, connected to glabella by oblique, moderately well defined ocular ridge; exsagittal length greater than one-half sagittal glabellar length on small specimens, slightly less than one-half sagittal glabellar length on large specimens; width of cheek op- posite anterior end between one-third and one-fourth basal glabellar width. Posterior limb slender, bears well— developed posterolateral fixigenal spine. Course of an- terior section of facial suture nearly straight forward from palpebral lobe. Course of posterior section strongly divergent behind palpebral lobe. Free cheek has broad nearly flat border that expands slightly posteriorly and is separated from the ocular plat- form by a shallow furrow of uniform depth that is curved and continuous with the posterior border furrow. Genal spine long, slender, flattened, slightly advanced so that inner spine angle is slightly acute; length about five times length of short posterior section of facial suture. Surfaces of ocular platform and border covered with moderately 96 coarse granules. Lateral margin also has oblique terrace lines which form anteriorly directed V-shapes in anterior part. Pygidium, exclusive of border spines, subsemicircular in outline; sagittal length slightly greater than one—half anterior width. Axis large, strongly convex transversely, reaches nearly to posterior margin, two ring furrows present. Anterior axial ring well defined by deep first ring furrow, bears large axial spine. Second ring furrow relatively shallow; second axial ring without node or spine. Width of axis almost three times width of narrow triangular pleural field. Pleural field crossed by only one distinct pleural furrow. Inner margin of border has broad shallow depressions between bases of border spines. Four moderately long slender posteriorly di- rected border spines present. External surfaces of cranidium covered with strongly developed granular ornamentation; Granular or- namentation on pygidium obscure. Discussion—This species is represented by only a few specimens, and the correctness of the association of cranidia and pygidia is not certain. For that reason, the pygidium is the designated holotype. The cranidia are very similar to that ofPtarmigam'a exigua Resser, although the largest specimen has a much more strongly rounded anterior margin. The pygidium has all the characteristics of Ptarmiganoides and differs from all other species in the genus by having a very broad axis and poor development of pleural furrows. Occurrence.—Moderately rare, Albertella Zone, Zacan- thoidid Zonule. Nevada: 3766—CO (5 cranidia, 1 free cheek, 2 pygidia), Nevada Test Site. Ptarmiganoides hexacantha. n. sp. Plate 11, figures 9—11, 14—16 Description.—Cranidium elongate, gently convex transversely and longitudinally, anterior margin gently rounded. Glabella long, low, very slightly expanded an- teriorly, bluntly rounded at front, well defined by axial and preglabellar furrows. Only posterior pair of oblique lateral glabellar furrows distinctly developed. Occipital furrow deep distally, shallow across axial line. Occipital ring flat, with position of occipital node marked by four tiny pits; no occipital spine. Frontal area undivided, flat, short; sagittal length between one-seventh and one-tenth sagittal length of glabella exclusive of occipital ring. Fixed cheeks gently convex, horizontal; width of palpebral area about 0.6 basal glabellar width. Palpebral lobe slender, arcuate, well defined by narrow palpebral furrow that continues across cheek to glabellar furrow outlining posterior edge of oblique ocular ridge; width of cheek at anterior end of palpebral lobe about one-third basal glabellar width. Posterior limb slender, transverse length CARRARA FORMATION, SOUTHERN GREAT BASIN about equal to basal glabellar width; border furrow deep, straight; distinct intergenal spine directed pos— terolaterally from tip. Free cheek has narrow crescentic ocular platform of more or less constant breadth separated from broad gently convex border by well-defined evenly curved bor— der furrow. Border produced into broad—based long curved genal spine that originates opposite midlength of eye. Angle between posterior cheek margin and inner spine margin acute. Length of spine more than five times length of posterior section of facial suture. Pygidium, exclusive of border spines, semicircular in outline; sagittal length about one-half greatest width. Axis broad, strongly convex transversely, strongly rounded posteriorly, reaching to inner edge of poorly defined gently convex border. First axial ring well de- fined by first ring furrow and bears large subvertical axial spine; a second shallow ring furrow may be present. Pleural regions downsloping, subtriangular, about as wide as axis at anterior margin, crossed by two shallow pleural furrows that continue onto border and a third pleural furrow represented only by broad pit in position of poorly defined inner margin of border. Border bears three pairs of short pointed spines; posterior pair sepa- rated by gap slightly wider than axis. Ornamentation consists of scattered very faint granules on glabella and palpebral lobes, and either granules or pits on fixed cheeks; genal spine has closely spaced granules; pygidium obscurely ornamented with faint granules on axis and border spines. Discussion—This species is distinguished from all others in the genus by having only three pairs of border spines on the pygidium. It differs, in addition, from P. propinqua (Resser) and P. amneicauda Fritz by lacking an occipital spine on the cranidium. The distinctive free cheek is similar to that of P. amneicauda and also to that of Ptarmigam'a rossensis (Walcott), the type species of Ptar- migam'a, and it emphasizes the close relationship of Ptar- migam'a and Ptarmiganoides. Occurrence.—Moderately common, Albertella Zone, Albertella-Mexicella Zonule(?). California: 414l—CO (6 cranidia, 5 free cheeks, 7 pygidia), Titanothere Canyon section, Grapevine Mountains. Rare, Zacanthoidid Zonule. Nevada: 3695—CO (l pygidium), Nevada Test Site. Genus ZACANTHOIDES Walcott Zacanthoides Walcott, 1888, p. 165; Kobayashi, 1935, p. 123; Shimer and Shrock, 1944, p. 619; Palmer, 1954, p. 69; Rasetti, F., in Har— rington and others, 1959, p. 227. Type species.—-Embolimus spinosa Rominger, 1887, p. 15, pl. 1, fig. 3. Discussion—This genus has already been fully de- SYSTEMATIC PALEONTOLOGY 97 scribed and illustrated by me and by Rasetti. The Cararra species agree with earlier diagnoses and descriptions in all essential features. Zacanthoides variacantha n. sp. Plate 11, figures 19—21 Description.—Cranidium subtrapezoidal in outline, gently convex transversely and longitudinally, anterior margin very slightly curved; width between palpebral lobes slightly greater than sagittal length of cranidium including occipital ring. Glabella low, long, sides sub- parallel, anterior end bluntly rounded, well defined all around by abrupt changes in slope of exoskeleton. Four pairs of glabellar furrows present; all pairs short and deep on larger cranidia, less deep on small cranidia. Occipital furrow of uniform depth on small specimens, shallow in axial region of larger specimens. Occipital ring has small axial node adjacent to posterior margin. Frontal area sagittally long for the genus, strongly expanded forward, bears wide plectrum whose posterolateral mar- gin extends in an irregular curve inward from anterolat- eral corner of cranidium to anterolateral corner of glabella; sagittal length about one-third sagittal length of glabella exclusive of occipital ring. Fixed cheeks flat, horizontal; width of palpebral area three-fourths basal glabellar width on small specimens, slightly less than two-thirds basal glabellar width on large specimens. Pal— pebral lobe very long, crescentic, well defined by deep narrow palpebral furrow, slightly upsloping laterally, anterior end continuous with ocular ridge and near an- terior end of glabella; posterior tip opposite anterior part of occipital ring. Posterior limb very slender, posterior margin curved; distal tip with well-developed fixigenal spine. Course of anterior section of facial suture strongly divergent forward from palpebral lobe; course of pos- terior section almost perpendicular to axis of cranidium. Pygidium, exclusive of border spines, semielliptical in outline; sagittal length about three-fourths anterior width. Axis prominent, tapered posteriorly, bears four distinct ring furrows posterior to articulating furrow; axial rings without nodes or spines. Pleural region gently convex, subtriangular, slightly narrower than axis with only one distinct pleural furrow. Border poorly defined, flat, narrower than pleural field, bears one long pair of anterior marginal spines and three or four pairs of very short more posterior spinules. External surfaces of cranidium and pygidium covered with closely spaced very fine granules barely apparent even after whitening. Discussion—This species has all the typical features of Zacanthoides: anteriorly divergent facial sutures, long palpebral lobes, posterior fixigenal spines, and semi- elliptical multispinose pygidium. Its closest relative, how- ever, is a group of “species” described by Resser (1939b) from the Naomi Peak Limestone Member of Maxey (1958) of the Langston Formation and assigned to Prozacanthoides. Resser’s concept of Prozacanthoides was not based on the type species. Study of a large suite of paratype material of this species, Prozacanthoides stis— singensis, shows this to be a corynexochid with relatively short palpebral lobes, subparallel anterior sections to the facial sutures, subtriangular posterior limbs on the cranidium, and three strong pairs of lateral border spines on the pygidium of which the posterior pair, which is widely separated, is the longest. None of the 14 species assigned to Prozacanthoides, except the genotype, is prop- erly identified, and the particular 5 “species” described by Resser (1939b) from a single collection in the Naomi Peak Limestone all conform fully to the characteristics of Zacanthoides. In addition, their differences are only mat- ters of preservation and the single name Z. alatus (Resser) is recommended here for the specimens named by Resser as Prozacanthoides alatus, decorosus, exilis, optatus, and aequus. This is the only other species of Zacanthoides with a plectrum, and it differs from Z. variacantha n. sp. by having an occipital spinule and only weak development of the glabellar furrows on the cranidium and by having only three ring furrows and poor development of the anterior pair of large border spines on the pygidium. The strong development of only the anterior pair of border spines and the cranidial plectrum distinguish Z. var- iaccmtha n. sp. from all others assigned to Zacanthoides. Occurrence.—Moderately common, Albertella Zone, Zacanthoidid Zonule. Nevada: 3766—CO (8 cranidia, 5 pygidia), Nevada Test Site. Zacanthoides cf. Z. alatus (Resser) Plate 11, figures 25, 26 Prozacanthoidex ulatus Resser, 1939b, p. 26, pl. 3, figs. 10—12. Discussion.—Two cranidia of a species of Zacanthoides with a plectrum differ from Z. variacantha n. sp. by lack- ing strong development of the glabellar furrows on large specimens. The fixed cheeks are less than one—half the basal glabellar width, and the surface is distinctly or- namented by fine granules. The presence of an occipital spinule cannot be determined—the axial margin on the illustrated specimen is broken as if one might have been present. These specimens may be representative of Z. alums (Resser), but a certain identification cannot be made without additional material. The reasons for the change in generic assignment for alatus are discussed under Z. variaczmtha n. sp. A single pygidium (pl. 11, fig. 26) of general zacan— thoidid morphology from the same collection as the cranidia may also belong to this species. The prominent axis is imperfectly preserved but shows at least two ring 98 CARRARA FORMATION, SOUTHERN GREAT BASIN furrows posterior to the articulating furrow. The nearly flat pleural regions are narrower than the axis and show three pleural furrows and two shallow interpleural fur- rows. The pleural furrows are accentuated by the raised anterior bands of the segments. The border bears three pairs of short sharp border spines, with the anterior pair being the largest. This pygidium differs from the pygidium of Z . variacantha n. sp. by having strong pleural furrows, by having only three pairs of border spines, and by having the anterior pair of spines much shorter. With- out more material, it is not even reasonably certain that this pygidium and the cranidia are conspecific. Occurrence.—Rare, Albertella Zone, Zacanthoidid Zonule. Nevada: 3695—CO (2 cranidia, 1 pygidium), Nevada Test Site. Zacanthoides? sp. Plate 6, figure 11 Discussion—A single fragment of the left half of a pygidium showing three slender border spines, narrow pleurae crossed by three pleural furrows, and an axis with two distinct ring furrows has the general shape of pygidia generally assigned to Zacanthoides. It is the only other trilobite found associated with abundant specimens of Syspacephalus obscurm n. sp. in beds assigned to the Plagiura—Kochaspis Zone. Occurrence.——Rare, Albertella Zone. California: 4140—CO (1 fragmentary pygidium), Titanothere Can— yon section, Grapevine Mountains. Corynexochid cranidium undet. 1 Plate 16, figures 20, 25 Discussion .——A peculiar corynexochid, possibly related to Glossopleum, is represented by three specimens in the youngest collection from the Glossopleum Zone. It is characterized by a narrow elongate nearly straight sided glabella whose length, exclusive of the poorly differ- entiated occipital ring, is about twice its width. A narrow flat undivided frontal area is present only directly in front of the glabella; the anterolateral parts reach to the facial sutures. The anterior end of the glabella has a poorly defined median depression. The palpebral lobes are long, narrow, and situated opposite the posterior two—thirds of the glabella; a line connecting the posterior tips passes over the midlength of the occipital ring. The posterior limbs are not known. The external surfaces of all parts appear smooth. Without associated parts, this species is not identifiable. The long slender anterior part of the glabella, anterior glabella depression, flat frontal area, and long arcuate palpebral lobes distinguish this from all known corynexochid species. Occurrence.—Rare, uppermost Glossopleura Zone, Bonanza King Formation. Nevada: 7199—CO (3 cranidia), Striped Hills. Corynexochid pygidium undet. 1 Plate 9, figure 26 Description.——Pygidium subquadrate in outline, gently convex transversely and longitudinally; sagittal length slightly more than one-half anterior width. Axis slender, sides subparallel, reaches nearly to posterior margin. All ring furrows obscure. Pleural regions undifferentiated; only first pleural furrow distinctly developed. Two pairs of marginal spines present; anterior pair small, pos- terolaterally directed, developed from anterolateral cor— ners of pygidium; posterior pair moderately long, di- rected straight posteriorly, continuous with straight pygidial sides; margin between posterior pair of spines nearly straight. External surface smooth. Discussion .—This distinctive species is known only from three specimens in two collections and no other parts can be associated with it. It is somewhat suggestive of Mexi- caspzls diffuntoensis Lochman (in Cooper and others, 1952), but it lacks the good definition of the first axial segment and has a narrower and less prominent axis. Without more knowledge of the whole trilobite, its generic and familial affinities are indeterminate. Occurrence.—Rare, Albertella Zone, Albertella-Mexicella Zonule. Nevada: 1616—CO (2 pygidia), Spring Moun- tains. California: 4166—CO (l pygidium), Resting Springs Range. Corynexochid pygidium undet. 2 Plate 10, figure 21 Discussion.—A single pygidium closely resembles and is probably congeneric with a pygidium identified as Athabaskia sp. by Rasetti (1951, p. 156, pl. 22, fig. 12). The species is characterized by a prominent slender axis bearing three ring furrows and by pleurae crossed by three furrow-pairs composed of a pleural furrow and slightly shallower interpleural furrow that are subparallel to each other and closer to each other than to the furrows of the adjacent pair. A single more posterior pleural furrow is also present. Both pleural and interpleural furrows extend onto the moderately narrow poorly de- fined pygidial border. The fact that the furrows extend across the pleural platform and onto the pygidial border probably influ- enced the generic identification of Rasetti’s specimen. However, I reexamined the type species of Athabaskia, A. astheimeri Raymond, and this has a markedly different structure in the pleural regions of the pygidium. The interpleural furrows are present only near the pygidial axis and are nearly perpendicular to it, while the pleural SYSTEMATIC PALEONTOLOGY 99 furrows extend diagonally posterolaterally across each pleuron so that the anterior band expands distally and the posterior band tapers distally rather than maintain- ing a uniform breadth. These structural differences indi- cate a morphologic difference of at least generic rank. Without sure knowledge of associated parts, this species is not assignable to any described genus. Occurrence.—Rare, Albertella Zone, Zacanthoidid Zonule. Nevada: 3547~CO (1 pygidium), Nevada Test Site. Order PTYCHOPARIIDA Swinnerton This order of trilobites, whether recognized in the restricted sense of Bergstrom (1973) or in the more inclu— sive sense of the trilobite volume of the “Treatise on Invertebrate Paleontology” (Harrington and others, 1959), still provides the greatest problems for su- prageneric classification among all the trilobites. In the early part of the Cambrian this problem is particularly acute because most of the ptychopariid trilobites are rather generalized forms for which there are still no consistently recognized suprageneric taxa. For this rea- son, the ptychopariid genera are presented here in al— phabetical order. However, at least one suprageneric grouping might be recognized among them. The genera Caborcella, Kochaspis, Kochiellina, Nyella, and Schistometopus are all characterized by a prominent tapered glabella with several pairs of moderately to strongly developed glabellar furrows and by a tendency for the glabellar sides to be very slightly concave opposite the second pair of glabellar furrows. (See pl. 8, figs. 3, 8; pl. 13, figs. 6—8; pl. 14, figs. 6, 7.) These trilobites also generally have moderately wide fixed cheeks, distinct narrow ocular ridges, and granular ornamentation. This cranidial morphology seems typical for trilobites only from Glossopleum Zone and older North American Mid— dle Cambrian beds. These trilobites, which share strati- graphic proximity as well as considerable axial similarity, probably represent a genetically related group of forms for which a meaningful family designation could be made. At several places in this report, trilobites of this group are referred to as kochaspid trilobites. Differences in structure of the frontal area and the associated pygidium provide the most useful characters for dis- crimination of kochaspid genera. In the “Treatise on Invertebrate Paleontology” (Har- rington and others, 1959), Kochaspis and Caborcella are in different superfamilies, and Schistometopus was left with- out family assignment. Some other possibly related gen- era, such as Kochz'ella and Kochz'na, are in still a different suprageneric taxon. Nyella and Kochiellina are new gen- era. Until a thorough revision of the Cambrian Ptychopariida is undertaken, I prefer to consider the kochaspids to be an informal grouping to be evaluated in the light of the larger context of all ptychopariid groups. Genus ALOKISTOCARE Lorenz Alokistocare Lorenz, 1906, p. 62; Walcott, 1916a, p. 182; Resser, 1935, p. 4; Rasetti, 1951, p. 202; Palmer, 1954, p. 71, Poulsen, V., 1958, p. 11; Howell, B. F., in Harrington and others, 1959, p. 238; Lazarenko, 1962, p. 65; Kobayashi, 1962, p. 51; Demokidov and Lazarenko, 1964, p. 213; Yegorova and Savitskiy 1969, p. 237; Robison, 1971, p. 802. Amecephalus Walcott, 1924, p. 53; Walcott, 1925, p. 65; Rasetti, 1951, p. 202; Kobayashi, 1962,p. 51; Poulsen, V., 1964, p.41; Fritz, 1968,p. 227. Stratocephalw Resser, 1935, p. 45. Type species .—C0nocephalites subcoronatus Hall and Whit- field, 1877, p. 237, pl. 2, fig. 1. Discussion .—Robison (1971) has given the most recent complete description for this genus. At present, Alokisto- care includes more than 57 named species, and almost every author seems to have a slightly different view of the morphology and morphologic limits of species assignable to it. Since the time of Walcott ( 1924), attempts have been made to discriminate a second genus, Amecephalw, from the group of micropygous Middle Cambrian ptycho— pariids with long frontal areas that are generally poorly differentiated into a flat or concave border and gently convex brim and that often bear a poorly defined low median swelling. Arguments both for (Resser, 1935, p. 4; Palmer, 1954, p. 71) and against (Rasetti, 1951, p. 202; Poulsen, V., 1958, p. 11; Poulsen, V., 1964, p. 41; Fritz, 1968, p. 227) suppression of Amecephalus have been presented. Most recently, Robison (1971) suppressed Amecephalus again, but pointed out the need for a thorough revision of this problematical complex of trilo- bites. The Carrara Formation contains generally frag- mentary remains of several different trilobites belonging to this complex. Because the material is mostly in- adequate for detailed study, the specimens are treated here with open nomenclature, pending a separate inten- sive study of the whole Alokistocare complex. Alokistocare sp. 1 Plate 15, figure 18 Discussion—This species is the most typical rep- resentative of the genus in the Carrara Formation. It is represented only by a few incomplete cranidia which have an obscurely furrowed glabella, a flaring frontal area; a concave poorly defined border slightly longer sagittally than the brim, and a low medium swelling lo— cated at the inner margin of the border and extending slightly backward onto the brim. The shallow border furrow passes over the posterior part of this swelling without deflection. The specimens are exfoliated and 100 have anastomosing veins on the brim and fixed cheeks. No indication of any other ornamentation is present. The median swelling on the frontal area distinguishes this species from others found in the Carrara Formation. Occurrence.—Rare, Glossopleum Zonule. California: 7198—CO (3 cranidia), Eagle Mountain. Alokistocm sp. 2 Plate 15, fig. 22 Discussion .—A single incomplete cranidium represents a species of Alokistocare that is easily distinguishable from the other species in the Carrara Formation by its dis- tinctive ornamentation. The glabella, fixed cheeks be- hind the ocular ridges, and anterior part of the poorly differentiated concave border are covered with low closely spaced intergrown poorly defined granules, so that in some lightings the intergranular spaces are em- phasized and give the area a pitted appearance. The frontal area has scattered large low granules that are also preserved on the internal mold. All other species of Alokistocare so far observed in the Carrara Formation lack granular ornamentation. Occurrence.——Rare, uppermost Glossopleum Zone. Nevada: 7199—CO (1 cranidium), Striped Hills. Genus ALOKISTOCARELLA Resser Alokistocarella Resser, 1938a, p. 57; Howell, B. F., in Harrington and others, 1959, p. 238. Type species.—Alokzlstocarella typicalis Resser, 1938a, p. 57, pl. 7, fig. 43. Discussion—At the time when this genus was first proposed, it was not adequately described and was characterized by Resser (1938) as intermediate “between Alokistocare, Amecephalina, and Ehmaniella.” Subsequently, without further discussion of generic characteristics, eight species from various Middle Cambrian collections have been assigned to it. In the absence of any clearly stated concept for the genus, various authors have stressed different morphologic features when relating their species to A. typicalis. The result of this is an amorphous genus of limited utility. Nevertheless, the species described below share many features of cranidial morphology, particularly those of glabellar shape and structure of the frontal area, withA. typicalis Resser orA. bn'ghamensis Resser, both from the early part of the Mid- dle Cambrian, and are more like these species in cranidial morphology than any other described American early Middle Cambrian simple ptychopariids. Until a better means is found for adequately evaluating generic re- lationships of species such as these, the generic identifi- cation is only tentative. CARRARA FORMATION, SOUTHERN GREAT BASIN Alokistocarella? of. A. brighamensis Resser Plate 15, figures 9—14 Alokistacarella brighamensis Resser, 1939b, p. 53, pl. 13, figs. 17, 18. Description—Small simple ptychopariids with sagittal length of largest known cranidium about 15 mm. Cranidium subquadrate in outline, gently and evenly rounded at anterior margin, gently to moderately convex transversely and longitudinally. Glabella low, tapered forward, bluntly rounded anteriorly, unfurrowed, de- fined at sides and front by shallow lateral and pre- glabellar furrows; anterior end less well defined than sides. Occipital furrow shallow, straight, slightly deeper at sides than across top. Occipital ring simple, with mod— erately distinct median axial node. Frontal area sub- equally divided into gently convex downsloping brim and flat or slightly concave border by slight change in slope of exoskeleton; sagittal length of frontal area about two- thirds sagittal length of glabella exclusive of occipital ring. Fixed cheeks gently convex, horizontal, or slightly upsloping; width of palpebral area about one-half basal glabellar width. Palpebral lobe poorly defined, continu- ous with slope of palpebral area situated about opposite glabellar midlength; exsagittal length slightly less than one-half sagittal length of glabella exclusive of occipital ring. Posterior limb moderately broad exsagittally, bluntly terminated, crossed by moderately deep pos- terior border furrow; transverse length about equal to basal glabellar width. Course of anterior section of facial suture slightly divergent forward from palpebral lobe to sharply curved anterolateral corner of cranidium, merged imperceptibly with anterior margin. Course of posterior section of facial suture divergent-sinuous. Free cheek has lateral margin moderately curved; lat- eral border poorly defined, flat, and slightly narrower than ocular platform; and flat genal spine of unknown length. Pygidium possibly representing this species strongly convex transversely and longitudinally. Axis low, poorly defined, tapered posteriorly, bears one prominent ring furrow and two or three additional obscure furrows. Pleural regions strongly convex, margins depressed, border represented only by poorly defined anterolateral, less strongly depressed marginal area. External surfaces of all parts either smooth or obscurely shagreened. Discussion—This species differs from all species presently assigned toAlokistocarella exceptA. brighamensis Resser by its low cranidial relief. The fixed check of A. brighamensis is slightly wider than that of the Carrara specimens, and the palpebral lobes seem to be situated slightly more posteriorly. Because all samples of these trilobites are small, the differences may not be significant. SYSTEMATIC PALEONTOLOGY 101 Specimens possibly of this species from the Striped I Zonule. Nevada: 3544—CO (1 cranidium), Desert Range; Hills section (USGS colln. 3690—CO) differ from those in the Echo Canyon section (USGS colln. 4155-CO) which were used for the description, by having a slightly better definition of the front of the glabella, a narrower and more distinctly concave border, and slightly longer pos- terior limbs. The associated free cheeks are essentially identical in both samples. Until more material is obtained of both brighamensis and the Carrara forms, the degree of relationship of the samples must remain uncertain. Occurrence.—Moderately rare, Glossopleum Zonule. California: 4155—CO (8 cranidia, 1 free cheek, 3 pygidia), Echo Canyon section, Funeral Mountains. Nevada: 3690—CO (2 cranidia, 1 free cheek), Striped Hills section. Alokistocarella? up. Plate 15, figures 17, 21 Discussion .—A simple ptychopariid represented by sev- eral cranidia and a pygidium, all exfoliated, represents a species unlike any others from the Cordilleran early Middle Cambrian. The cranidia range in size from 3 mm to about 8 mm and are characterized by an anteriorly tapered bluntly rounded glabella bearing four pairs of moderately distinct glabellar furrows and well defined by narrow lateral and preglabellar furrows. The frontal area is subequally divided by a narrow border furrow into a nearly flat and slightly downsloping brim and a slightly convex border. The fixed cheeks are moderately convex and horizontal and bear moderately large palpebral lobes situated opposite the posterior half of the glabella; the width of the palpebral area is about one-half the basal glabellar width, and the exsagittal length of the palpebral lobe' is about one-half the sagittal glabellar length exclu— sive of the occipital ring. The form of the posterior limbs is not known. Internal molds have strongly developed caecal venation on the brim, and some specimens have a granular axial region indicating that this part is probably also granular on the external surface. One fragmentary specimen with part of the external surface preserved has a smooth border, brim, and fixed cheek. This species is like Alokistocarella typicalis Resser in most features except for the frontal area. A. typicalis lacks a distinct separation of brim and border, and the border area is concave rather than slightly convex. An associated incomplete pygidium is essentially the same as Alokis— tocarella? cf. A. Im'ghamenszls Resser. Small cranidia have the glabellar furrows and border furrow accentuated. Without more knowledge of details of ornamentation, structure of the posterior limb, and other associated parts of this generalized form, its identification and relation- ships must remain uncertain. Occurrence.—Moderately common, Glossopleum 3545—CO (2 cranidia), 3767-CO (11 cranidia, 1 pygidium), both from Nevada Test Site. Genus CABORCELLA Lochman Caborcella Lochman, 1948, p. 461; Howell, B. F., in Harrington, 1959, p. 233. Type species. —Caborcella arrojosensz’s, Lochman, 1948, p.461, pl. 70, figs. 19—21. Description.—Moderate-sized kochaspid trilobites with known cranidia] length as much as 15 mm. Cranidium gently to moderately convex transversely and longi- tudinally. Glabella prominent, tapered, strongly to bluntly rounded at front, well defined at sides by deep axial furrow and at front by abrupt change in exoskeletal slope or shallow preglabellar furrow. Three or four pairs of well-defined generally deep glabellar furrows present; posterior pair deepest, curved or straight. Occipital fur- row deep, deepest distally. Occipital ring simple. Frontal area generally concave. Brim very narrow sagitally. Bor- der broad, poorly defined, concave, bearing poorly to well-developed pseudofurrow. Sagittal length of frontal area ranges from slightly less than one-third to about two-thirds sagittal glabellar length exclusive of occipital ring. Fixed cheeks flat or convex, horizontal or upslop- ing; prominent ocular ridge usually present; width of palpebral area between one-half and two-thirds basal glabellar width. Palpebral lobes well defined, situated opposite or slightly posterior to glabellar midlength; ex- sagittal length about one-third sagittal glabellar length exclusive of occipital ring. Posterior limbs about equal in transverse length to basal glabellar width. External sur- face with granular ornamentation. Course of anterior section of facial suture nearly straight forward from palpebral lobe. Course of pos— terior section divergent-sinuous. Associated parts not known. Discussion—Lochman gave a good diagnosis of this genus based principally on the type species although she included in the genus the poorly preserved specimens described by Mason (1935) as Acrocephalz'tes? trifossatus Mason. At that time, the potential value of the structure of the frontal area for recognition of the genus was un- known, and its characteristics were not emphasized. Sub- sequently, Rasetti (1951) and Fritz (1968) added several species to the genus including Poulsenia granosa Resser, which Lochman had specifically excluded. Neither Rasetti nor Fritz discussed the revised generic characters. Among the kochaspid trilobites in the Albertella fauna in the Carrara Formation are two distinct groups of species. One has a poorly defined concave border, and the other has a deep border furrow and a convex border. The forms with the concave border are most like C. 102 arrojosensis Lochman and are retained in Caborcella. Those with convex borders are most like the species as- signed to Caborcella by Rasetti and Fritz. These Carrara species with convex borders and deep border furrows, and most of the Rasetti and Fritz species, are here as- signed to a new genus, Nyella. Caborcella pseudaulax n. sp. Plate 13, figure 6 Description.—Cranidium subtrapezoidal in outline, gently convex transversely and longitudinally, broadly rounded anteriorly; width between palpebral lobes greater than sagittal cranidial length. Glabella promi- nent, tapered forward, bluntly rounded anteriorly, well defined at sides and front by broad deep axial and pre- glabellar furrows. Four pairs of glabellar furrows present; posterior pair very deep, curved; anterior pairs progressively shallower. Occipital furrow deep, broadest on axial line. Occipital ring simple. Presence or position of node not known. Frontal area broad, concave, sagittal length slightly more than one-half sagittal length of glabella exclusive of occipital ring. Brim very narrow. Border concave, with broad shallow pseudofurrow. Inner margin of border slightly elevated above brim lat- erally, poorly defined, best shown by contrast in or- namentation. Exsagittal breadth of border decreases lat- erally. Fixed cheeks wide, gently convex, upsloping; width of palpebral area about two-thirds basal glabellar width. Palpebral lobe small, upsloping from palpebral area, connected to glabella by narrow well-defined gently curved ocular ridge; situated opposite posterior half of glabella. Exsagittal length of palpebral lobe slightly more than one-third sagittal glabellar length exclusive of oc- cipital ring. Posterior limbs broad, strong, transverse length equal to or slightly more than basal glabellar width. Course of anterior section of facial suture nearly straight forward from palpebral lobe to anterior margin. Course of posterior section convex, strongly divergent behind palpebral lobe. Other parts not known. External surfaces of all parts covered with extremely fine closely spaced granules. Strong tubercular or— namentation developed only on cheeks, brim, outer mar- gin of anterior border, convex parts of glabella, and posterior border. Discussion.——This species differs from C. arrojosensis Lochman by having less transversely convex fixed cheeks and a less upturned border; and the pseudofurrow on the border is even in depth rather than noticeably shallow on the axial line. It differs from C. reducta n. sp. by its relatively long (sag.) frontal area and ornamentation of both fine granules and tubercules. Occurrence.—Moderately rare, Albertella Zone, Zacan- CARRARA FORMATION, SOUTHERN GREAT BASIN thoidid Zonule. Nevada: 3547—CO (6 cranidia), 3766—CO (4 cranidia), both from Nevada Test Site. Caborcella reducta. n. sp. Plate 13, figures 7, 8 Description.—Cranidium subtrapezoidal in outline, moderately convex transversely, strongly convex lon- gitudinally, gently rounded anteriorly; width between palpebral lobes greater than sagittal cranidial length. Glabella prominent, tapered forward, bluntly rounded anteriorly, well defined at sides by broad deep axial fur- rows; defined at front by abrupt change in slope of exo- skeleton; reaches to poorly defined inner edge of border. Three pairs of glabellar furrows present, posterior pair deepest, forming distinct angle with axial furrow. Occip- ital furrow deep. Occipital ring simple. Axial node small. Frontal area short, subhorizontal, slightly concave, con- sists only of border in front of glabella. Border tapered laterally, inner margin defined only by change in slope of exoskeleton; sagittal length slightly less than one-third sagittal length of glabella exclusive of occipital ring. Fixed cheek broad, gently convex, horizontal; width of palpe- bral area slightly more than one—half basal glabellar width. Palpebral lobes small, well defined by palpebral furrow, connected to glabella by poorly defined narrow ocular ridge; exsagittal length slightly less than one-third sagittal glabellar length exclusive of occipital ring. Post- erior limb broad; transverse length about equal to basal glabellar width. Course of anterior section of facial suture nearly straight forward from palpebral lobe to anterior margin. Course of posterior section divergent, convex. External surfaces of border, fixed cheeks—including palpebral lobes—convex parts of glabella, and posterior limb covered with closely spaced moderately coarse granules. Axial, glabellar, and occipital furrows lack or- namentation. Discussion.—-This species is related to and associated with Caborcella pseudaulax n. sp. It differs from that species by lacking even a narrow brim in front of the glabella, by having a shorter less concave frontal area, by having well-defined palpebral lobes set below the level of the cheek, and by having a coarse granular ornamenta- tion without scattered tubercules. Occurrence.——Rare, Albertella Zone, Zacanthoidid Zonule. Nevada: 3547—CO (3 cranidia), Nevada Test Site. Genus CHANCIA Waleott Chanda Walcott, 1924, p. 55; Walcott, 1925, p. 80; Shimer and Shrock, 1944, p. 609; Rasetti, 1951, p. 212; Howell, B. F., in Harrington, 1959, p. 238. Type species.—Chcmcia ebdome Walcott, 1924, p. 55, pl. 10, fig. 4. SYSTEMATIC PALEONTOLOGY Discussion .—The characterization of this genus by Wal- cott (1925) gives the principal features of this generalized ptychopariid. The essential cranidial characters are a ta- pered well-defined poorly to moderately furrowed glabella, sagittally long frontal area with flat or slightly concave border, and transversely wide fixed cheeks and posterior limbs. The width of the fixed cheek, exclusive of the palpebral lobe, is greater than one-half the basal glabellar width; and the transverse width of the posterior limbs is greater than the basal glabellar width. The sagit- tal length of the frontal area is greater than one—half the glabellar length exclusive of the occipital ring. Chancia? maladensis (Resser) Plate 15, figure 4 Ehmaniella maladensis Resser, 1939b, p. 60, pl. 12, figs. 17-23. Discussion .—Several cranidia associated with Ogygopsis typicalis (Resser) in the Belted Range, Nev., have all the distinctive characteristics of the species described by Resser in a similar association in southern Idaho. The extremely wide fixed cheeks and transversely long pos- terior limbs, together with small palpebral lobes and finely granular ornamentation (including scattered coarse granules), distinguish this species from all others in the Carrara Formation. The assignment to Ehmaniella by Resser no longer seems appropriate for this species because typical Ehmaniella species lack the strikingly wide fixed cheeks and transversely long posterior limbs of the species dis- cussed here. These features are more typical of Chancia; but the generic assignment is questioned because the type species, C. ebdome Walcott, has a concave cranidial border, whereas the border of C.? maladensis is distinctly convex. More information is needed about the whole trilobite before a confident generic assignment can be made. Occurrence.—Moderately common, Albertella Zone, Ogygopsis Zonule. Nevada: 4436—CO (13 cranidia), 4437—CO (1 cranidium), 4438—CO (4 cranidia), all from Belted Range. Chancia. of. C. venusta. (Resser) Plate 13, figures 11, 12 Kochina venmta Resser, 1939a, p. 53, pl. 6, figs. 9, 10. Chancia venusta (Resser). Fritz, 1968, p. 230, pl. 40, figs. 31—34. Discussion—I agree with Fritz in that the cranidial characters of this species are entirely consistent with a placement in Chancia. The specimens from the Carrara Formation all have a finely granular external surface preserved and do not show the scattered coarse tuber— cules described for the types by Resser. They seem to have the same proportions for all parts. However, be- cause of the differences in ornamentation, the specific 103 identification is qualified. The Carrara forms differ from all other species of Chancia, except C. venusta, by having the border flat or slightly concave, downsloping, and slightly shorter sagittally than the slightly swollen brim. The border furrow is noticeably shallow on the axial line. The surface of the mold of the Carrara specimens is strongly pitted (pl. 13, fig. 11). Occurrence.—Moderately common, Albertella Zone, Zacanthoidid Zonule. Nevada: 3547—CO (>10 cranidia), Nevada Test Site. Genus ELRATHJNA Resser Elmthina Resser, 1937a, p. 11; Deiss, 1939, p. 87; Rasetti, 1951, p. 221; Howell, B. F., in Harrington and others, 1959, p. 240. Type species.—Conocephalites cordilleme Rominger, 1887, p. 17, pl. 1, fig. 7. Discussion .—A reasonable diagnosis of this simple ptychopariid genus was given by Deiss (1939). Its most distinctive features are anteriorly convergent anterior sections to the facial sutures; a glabella that is strongly rounded at the front and has subparallel or only slightly convergent sides; small palpebral lobes situated slightly anterior to the glabellar midlength on gently convex, horizontal, or slightly downsloping fixed cheeks that are generally wider than half the basal glabellar width; free cheeks that lack significant development of genal spines; a thorax of 15—19 segments; and a simple nonspinose pygidium. The species described here are associated with Ogygop— sis typicalzls (Resser) and other species typical of the Alber— tella Zone. This occurrence significantly extends the range of the genus backward in time and emphasizes the long-ranging character of many of the trilobites found in association with Ogygopsis. Elsewhere in North America, Elmthina is considered as a diagnostic element of the Bathyurzlscw-Elrathina faunas. Elrathina. antique. n. sp. Plate 15, figures 1-3 Description .—-Small, micropygous ptychopariid trilo- bites; length of largest observed specimen about 15 mm. Cranidium subtrapezoidal in outline, gently rounded anteriorly, gently to moderately convex transversely and longitudinally. Glabella prominent, well defined by mod- erately deep broad axial furrows and shallower pre- glabellar furrow; moderately to strongly convex trans— versely; very slightly tapered forward, strongly to bluntly rounded at front. Three pairs of glabellar furrows present, all shallow; posterior pair deepest. Occipital fur- row moderately deep, straight; deepest distally. Occipital ring has prominent axial node situated at midlength. Frontal area short, subequally divided into gently convex border and brim by broad shallow nearly straight border 104 furrow; sagittal length about 0.4 sagittal length of glabella exclusive of occipital ring. Fixed cheek gently to moderately convex, downsloping; transverse width about three—fourths basal glabellar width. Palpebral lobe small, defined only by change in slope of surface of cheek, situated slightly anterior to glabellar midlength; exsagit— tal length about 0.3 sagittal glabellar length exclusive of occipital ring. Posterior limb broad exsagittally; trans- verse length slightly greater than basal glabellar width. Posterior border furrow deep, straight. Course of anterior section of facial suture slightly con- vergent forward from palpebral lobes; posterior section ‘ gently curved outward and posterolaterally behind pal- pebral lobes. Free cheek flat, lacks clearly defined border; lateral margin gently curved; posterolateral corner angular, with small genal node. Width opposite eye about one-half length. Thorax composed of 15—16 segments, each with broad deep straight pleural furrow extending nearly to short sharp tip; width of each pleural region slightly greater than width of axis. Pygidium transverse elliptical in outline; sagittal length about 0.3 greatest width. Axis short, subparallel sided, poorly furrowed; pleural region smooth, convex, lacks furrows. Posterior margin smooth. External surfaces of all parts smooth. Discussion—This is the oldest North American species assigned to Elmthina. It differs from others represented by complete specimens by having only 15 or 16 thoracic segments. It is most similar to E. parallela Rasetti from which it differs by having somewhat narrower fixed cheeks and transversely shorter posterior limbs. Occurrence.—Common, Albertella Zone, Ogygopsis Zonule. Nevada: 4436—CO (3 cranidia); 4437—CO (20 cranidia, 5 partially articulated specimens, 2 free cheeks), 4438—CO (20 cranidia, 2 partially articulated specimens, 1 free cheek), all from Belted Range. Genus EOPTYCHOPARIA Rasetti Eoptychoparia Rasetti, 1955, p. 13; Rasetti, in Harrington and others, 1959, p. 236; Shaw, 1962, p. 339; Lazarenko, 1962, p. 64; Repina and others, 1964, p. 323. Type species.—Eoptych0paria normalis Rasetti, 1955, p. 14, pl. 1, fig. 2; pl. 3, figs. 5—11. Discussion .—Rasetti (1955) gave a good diagnosis of this generalized ptychopariid genus and a careful evaluation of its relationships to the similar genera Antagmm, 0n— chocephalus, and Piazella. Later, Shaw (1962) presented an elaborate classification of Early Cambrian simple ptychopariids, stressing the course of the anterior section of the facial sutures as a primary feature for discrimina- CARRARA FORMATION, SOUTHERN GREAT BASIN tion of families. The resulting rearrangement of genera and species placed Antagmus gigas, which Rasetti con- sidered typical of Antagmus, the nominal genus of the Antagmidae, in Cyphambon, a new subgenus of Eop- tychoparia, in a new family Eoptychopariidae. Rasetti compared A. gigas to the type species of Antagmus, A. typicalis Resser, and had considered them possibly synonymous—hesitating to use typicalis primarily because of the poor preservation of the holotype. I have examined the holotype of typicalis and must concur with Rasetti regarding the close relationships of this specimen and A. gigas. The specimen does not have clearly con- vergent facial sutures, which Shaw cited as the charac- teristic discriminating the family Antagmidae from the family Eoptychopariidae, and separate family assign- ments forA. typicalis andA. gigas seem unrealistic. There— fore, the specimens here assigned to Eoptychoparia rep- resent this taxon in the sense of Rasetti (1955). The sub- genus Cyphambon is removed from Eoptychoparia and here is considered as a subjective synonym of Antagmus. Eoptychoparia is perhaps the most central of the generalized Early and Middle Cambrian ptychopariids. The cranidium has a weakly furrowed anteriorly tapered and rounded glabella, an unmodified occipital ring with a median node, a subequally divided frontal area about one-third the sagittal length of the cranidium, a gently curved unmodified border furrow, subparallel or slightly divergent anterior facial sutures, subhorizontal gently convex fixed cheeks about one-half the width of the glabella, unmodified palpebral lobes about opposite the glabellar midlength and connected to it by low ocular ridges, and distally tapered posterior limbs with well- developed posterior border furrows. The free cheek has a broad-based flat pointed genal spine not deflected from the lateral margin of the cheek and about equal in length to the posterior section of the facial suture. The thorax consists of about 15 segments with broad shallow pleural furrows and short pleural tips. The pygidium is small, without any distinguishing characteristics. Among similar genera, Inglefieldia and Luxélla both have wider fixed cheeks and modified posterior limbs; those of Inglefieldz'a are slender, correlated with a longer palpebral lobe; those of Luxella have a short downturned distal part. Piazella has wider fixed cheeks than Eop- tychoparia, and both it and Antagmus have a distinct me- dian inbend to the anterior border furrow. Although the species described here are assigned an earliest Middle Cambrian age, and are thus younger than any others previously included in the genus, no con- sistent criteria exist by which they can be differentiated from the Early Cambrian forms. SYSTEMATIC PALEONTOLOGY 105 Eoptychoparia. piochensis n. sp. Plate 7, figures 1—5 Description—Moderately small, micropygous ptychopariids, probably not exceeding 2 cm in length. Cranidium subtrapezoidal in outline; anterior margin gently curved; width between anterior sections of facial sutures slightly more than one—half width between tips of posterior limbs. Glabella low, well defined by shallow axial and preglabellar furrows, tapered forward, bluntly rounded anteriorly; sagittal length equal to or slightly less than basal glabellar width. Three or four pairs of moder— ately short glabellar furrows present; becoming deeper and more diagonally directed inward from axial furrows posteriorly. Occipital furrow nearly straight, shallowest on axial line. Occipital ring has prominent axial node at sagittal midlength. Frontal area gently downsloping, subequally divided into gently convex brim and border by shallow evenly curved border furrow. Fixed cheeks gently convex, horizontal or slightly upsloping; width of palpebral area between 0.4 and 0.6 basal glabellar width. Palpebral lobe short, arcuate, slightly upsloping from palpebral area, defined by shallow broad palpebral fur- row; length 0.4 or less length of glabella exclusive of occipital ring. Posterior limb tapered distally to sharp point; transverse length about equal to basal glabellar width, distal part slightly longer than proximal part. Posterior border furrow straight, moderately deep. Course of anterior section of facial suture nearly straight forward or slightly divergent anteriorly to bor- der furrow, then curved gently inward across border. Course of posterior section of facial suture gently convex outward from palpebral lobe to posterior margin. Free cheek has gently curved lateral margin continu- ous without deflection along side of flat sharp genal spine; length of spine about two—thirds length of pos- terior section of facial suture. Border defined by shallow continuous lateral and posterior border furrows; width about one-half that of ocular platform at anterior sutural margin. Border furrow not strongly curved at genal angle. Thorax consists of about 15 segments, each with broad straight pleural furrow and short pointed pleural tip. Pygidium small, individual segments not clearly dis- cernable. Neither border nor border spines apparent. External surface smooth or perhaps weakly granulated—no clear ornamentation apparent on speci- mens preserved in fine-grained shale. Discussion—This species is distinguished from others assigned to the genus by its more anteriorly tapered glabella, shallower border furrow, and lack of apparent ornamentation. Occurrence.—Common, earliest Middle Cambrian. Nevada: 7231—CO (3 complete; 20 cranidia; 6 free cheeks), basal “C” Shale Member of Pioche Shale, High- land Range. Genus KOCHASPIS Resser Kochaspis Resser, 1985, p. 36; Rasetti, 1951, p. 225; Palmer, 1954, p. 79; Lochman, C., in Harrington and others, 1959, p. 250. Paleocrepicephalus Kobayashi, 1935, p. 277. Type species.——Crepicephalus liliana Walcott, 1886, p. 207, pl. 28, figs. 3, 3a, b. Discussion—The material from the Carrara Formation and Pioche Shale does not add significant new informa— tion to the generic diagnosis presented earlier (Palmer, 1954). The most distinctive part of this early Middle Cambrian ptychopariid genus is its pygidium, which bears a pair of posterior border spines. Cranidia of this genus are characterized by a broad-based anteriorly ta- pered glabella, bluntly rounded at its front and generally bearing three pairs of distinct glabellar furrows, by a well-developed brim and gently convex border, by gen- erally well developed ocular ridges, by palpebral areas at least one-half the basal glabellar width and by granular ornamentation. This is not an easy genus to identify in small collections because its pygidium can be confused with those of the corynexochid genera Fieldaspis and Albertelloides. Also, undescribed kochaspids with similar cranidia but non- spinose pygidia are present in collections from the Delamar Mountains in Nevada. Nevertheless, the com- bination of all parts characterizes a distinctive group of trilobites. The glabellar structure, which is shared, along with granular ornamentation, by Eiffelaspis, Kochiellina, Schistometopus, and the undescribed genus from the De- lamar Mountains seems to be restricted to early Middle Cambrian North American trilobites; and even though generic identification of isolated cranidia may be in doubt, such specimens do have a stratigraphic utility for identifying beds of this age. Kochaspis augusta (Walcott) Plate 8, figures 15, 16 Crepicephalus augwta Walcott (Part), 1886, p. 208, pl. 28, fig. 2a; Walcott, 1891, p. 653, pl. 96, fig. 9a; Walcott, 1916a, p. 204, pl. 29, fig. 6b. Kochaspis augusta Walcott. Resser, 1935, p. 37; Palmer, 1954, p. 80, pl. 17, fig. 6. Discussion—This species is characterized by short broad-based flat pygidia] spines that have the posterior pygidia] border strongly curved forward between them. Two pygidia from the Groom Range represent this species. The larger of the two specimens is indistinguish— able from the holotype; the smaller specimen has one extra posterior pair of pleural furrows, which is attrib- uted to probable variation of this feature with size. 106 AKochaspis cranidium associated with the pygidia, and three free cheeks, may also represent this species. This cranidium (Kochaspis? sp. undet., pl. 8, fig. 11) has the glabellar structure, broad palpebral areas, gently convex border, and well-defined brim typical of Kochaspis, but it differs from K. liliana—represented in this collection by a pygidium—by having palpebral lobes only about one— fifth as long as the glabella instead of more than one- fourth the glabellar length. The associated free cheek (Kochaspis? sp. undet., pl. 8, fig. 11) has moderately deep and continuous lateral and posterior border furrows, a convex border about one-half the width of the ocular platform, and a slender genal spine about equal in length to the posterior section of the facial suture. Other occur- rences of similar associations of K. augusta pygidia with cranidia and free cheeks of this type will be needed to establish the reliability of the parts as those of a single trilobite. Occurrence. —Rare, “Plagium-Poliella” Zone, Kochaspid Zonule. Nevada: 3691—CO (2 pygidia; Pl cranidium; P3 cheeks), Groom Range. Kochaspis liliana? (Walcott) Plate 8, figures 8, 12, 13 Crepicephalm liliana Walcott (part), 1886, p. 207, pl. 28, figs. 3, 3a; 1891, p. 653, pl. 96, figs. 7, 7a; 1916a, p. 209, pl. 29, figs. 5, 5a. Kochaspis liliana (Walcott). Resser, 1935, p. 36; Palmer, 1954, p. 80, pl. 17, figs. 7, 8, 10, 11. Discussion—The pygidium of this species has slender subcylindrical pygidial spines directed slightly pos— terolaterally and two deep pleural furrows extending onto the base of each spine. The posterior border be- tween the spines is more or less straight. These features easily distinguish it from K. ceccz'na (Walcott) which has four or five deep pleural furrows, and K. augusta (Wal- cott), discussed previously. Pygidia with the characteris- tics of K. liliana have been found in two collections and are associated with Kochasjnls cranidia in one of them. However, the cranidia differ from the type cranidium of K. liliana by having a distinctly greater curvature to the plan View of the border furrow. With such an inadequate sample, the specific identification of the Carrara material must remain uncertain. Pygidia assigned to Kochaspis eifi’elensis by Rasetti (1951; 1957) have essentially the same structure as K. liliana but are significantly shorter. The cranidia that Rasetti tenta- tively associated with those pygidia, and which include the holotype, have long palpebral lobes situated opposite the posterior one-third of the glabella and differ in this respect from cranidia associated with K. liliana. If the associations are correct, and if the cranidial differences are of specific value, then the strong structural differ- ences between pygidia of K. augusta, K. ceccina, and K. CARRARA FORMATION, SOUTHERN GREAT BASIN liliana/K. eijfelensis may represent generic differences. A thorough reevaluation of the systematics of species as- signed to Kochaspis and related genera must await larger collections from the generally poorly fossiliferous early Middle Cambrian beds of the Cordilleran region. Occurrence.—Rare, “Plagium—Poliellu” Zone, Kochaspid Zonule. Nevada: 3546—CO (2 pygidia, 1 cranidium), jangle Ridge area, Nevada Test Site; 3691—CO (1 pygidium), Groom Range. Genus KOCHIELLINA n. gen. Type species.——Kochiellina groomensis n. sp. Diagnosis.—-Moderate-sized ptychopariid trilobites, length of largest individuals between 3 and 4 cm. Cranidium, excluding posterior limbs, subquadrate in outline. Glabella gently convex transversely and longi- tudinally, tapered forward, bluntly rounded anteriorly, well defined by deep axial and shallower preglabellar furrows. Three pairs of distinct glabellar furrows usually present. Occipital ring simple, well defined by occipital furrow that is deep at sides and shallow across axial re- gion. Frontal area subequally divided into gently convex brim and flat or weakly concave border. Palpebral areas gently convex; width equal to or slightly greater than basal glabellar width. Palpebral lobes upsloping, well de- fined, connected to glabella by distinct narrow straight or slightly curved oblique ocular ridge, situated opposite middle third of glabella. Posterior limb moderately slen— der, about as long as basal glabellar width; posterior border furrow broad, deep. Anterior section of facial suture slightly convex outward, directed nearly straight forward from palpebral lobe to border furrow and then curved inward to intersect anterior margin near an- terolateral cranidial corners. Posterior section of facial suture divergent, convex. Free cheek has broad flat border, wider than ocular platform. Lateral margin evenly curved. Genal spine short, broad based, flat. Lateral and posterior border furrows continuous. Pygidium semicircular in outline, gently convex trans- versely and longitudinally. Axis narrower than pleural regions, well defined, not reaching to posterior margin. Pleural regions have broad concave poorly defined bor- der. Three or four narrow pleural furrows extend later- ally onto but not across border. One or two shallow in- terpleural furrows may be present adjacent to second and third pleural furrows. External surfaces of all parts granular. Discussion—This is one of several genera with a dis- tinctive tapered and furrowed glabella, moderately wide palpebral areas, distinct ocular ridges, and well- developed brim and border that seem to be characteristic of lower Middle Cambrian beds in North America. Cranidia can be distinguished from Kochaspis primarily SYSTEMATIC PALEONTOLOGY by having a flat or weakly concave border; the free cheek has a flat border and a broad-based short genal spine; and the pygidium lacks spines and has a broad concave border and several narrow shallow pleural furrows. Kochiella and Ezflelaspis both have considerably wider palpebral areas and consequently longer (tr.) posterior limbs. In addition to the two species described below, On~ chocephalus maior (Rasetti, 1951, p. 234, pl. 14, figs. 19—23), from the Plagium-Kochaspis Zone of the southern Canadian Rockies seems to represent this genus. It is a much larger and more robust form than the typical Early Cambrian trilobites assigned to Onchocephalus, but con- firmation of the generic change would have to come from finding the associated free cheeks and pygidia. Kochiellina groomensls n. sp. Plate 8, figures 3, 4, 7 Description.—Cranidium, excluding posterior limbs, subquadrate in outline, gently convex transversely and longitudinally; anterior margin gently rounded. Glabella low, broad, tapered forward, bluntly rounded anteriorly, well defined at sides by deep, straight, or slightly concave axial furrows; anterior end well defined by slightly shal- lower preglabellar furrow. Three pairs of distinct glabellar furrows; anterior pair weakest; posterior two pairs moderately deep, subparallel, directed obliquely inward and backward from axial furrows. Occipital fur- row nearly straight, deepest distally. Occipital ring sim- ple, with median node on axial line. Frontal area down- sloping, divided into gently convex brim and flat or slightly concave border. Sagittal length of brim slightly more than two-thirds that of border. Fixed cheek gently convex, horizontal; width of palpebral area about one- half basal glabellar width. Palpebral lobe upsloping from surface of cheek, defined only by change in slope; located opposite middle third of glabella; exsagittal length about one-third sagittal glabellar length exclusive of occipital ring. Narrow ocular ridge connects palpebral lobe to anterior end of glabella along gentle curve. Posterior limb about equal in length to basal glabellar width; pos- terior border furrow deep, broad. Course of anterior section of facial suture directed nearly straight forward in slightly convex outward curve between palpebral lobe and border furrow, then turned inward to intersect anterior margin near anterolateral cranidial corners. Posterior section directed strongly posterolaterally behind palpebral lobe; inner part forms gentle convex curve; course changes abruptly and is di- rected nearly straight backward between border furrow and posterior margin. Free cheek gently convex; border broad, flat, slightly wider than ocular platform along anterior sutural mar- gin; well defined by shallow narrow border furrow. Lat- 107 eral and posterior border furrows meet at sharp curve at genal angle. Genal spine broad based, flat, sharply pointed; length about equal to length of posterior sutural margin. Pygidium semicircular, posterior margin with slight median inbend; sagittal length slightly more than one— half greatest width. Axis narrow, obscurely furrowed; sagittal length about 0.6 sagittal length of pygidium; width slightly less than one-fourth greatest pygidia] width. Pleural regions divided into gently convex pleural field and gently concave but not distinctly demarcated border. Three or four narrow pleural furrows continue onto inner part of border. Interpleural furrows are barely apparent adjacent to second and third pleural furrows on downsloping distal part of pleural field. External surfaces of all parts covered with closely spaced fine granules. In addition, the cranidium has widely scattered coarse granules. Discussion—This species differs from K. janglemis n. sp. by having a longer brim and lacking a distinct low swelling on the posterior axial part of the border on the cranidium and by having a semicircular rather than sub— quadrate pygidium with one more clearly defined seg- ment. The association of the pygidium and the cheek with the cranidium seems reasonably reliable. The pygidia and cranidia occur in about equal abundance in the type collection and seem to represent the only large ptychopariid in the sample aside from Kochaspis. The presence of granular ornamentation on all parts supports the association. The lack of scattered large granules on the free cheek makes its assignment to K. groomensis less certain, but its ornamentation is the same as that of the pygidium. The association of similar, but specifically dis- tinct, cranidia and pygidia in another sample further strengthens the probability that they are parts of the same trilobite. Occurrence.——Moderately common, “Plagium-Poliella” Zone, Kochaspid Zonule. Nevada: 3691—CO (8 cranidia; 1 cheek, 7 pygidia), Groom Range. Kochiellina janglensis n. sp. Plate 8, figures 20, 24 Description.—Cranidia are essentially like those of K. groomensis, differing only in features of the frontal area, width of the palpebral area, and length of the palpebral lobe. The sagittal length of the brim is about one-half that of the border, and the border has a broad low median swelling on its posterior part that noticeably reduces the depth of the border furrow on the axial line. The palpe- bral areas are slightly greater than one-half the basal glabellar width, and the exsagittal length of the palpebral lobe is about one-half the sagittal glabellar length exclu- sive of the occipital ring. 108 Free cheek not known. Pygidium subquadrate in outline, gently convex trans- versely and longitudinally; sagittal length slightly more than one-half greatest width; posterior margin with slight median inbend. Axis obscurely furrowed, moderately broad, short; width slightly less than one-third greatest pygidial width; sagittal length about 0.6 length of pygidium. Pleural regions have gently convex pleural field, and concave border not clearly demarcated. Three or four narrow pleural furrows continue across pleural field onto inner part of border. Shallow interpleural fur- rows apparent adjacent to second and third pleural fur- rows. External surfaces of all parts covered with closely spaced granules. Cranidium has scattered coarse granules in addition. Discussion—The differences between this species and K. groomensis n. sp. are discussed in the preceding species description. The slight median swelling on the inner part of the cranidial border and the subquadrate nonspinose pygidium distinguish this species from other trilobites with Kochaspis-like cranidia. Occurrence.—Moderately rare, “Plagium~Poliella” Zone, Kochaspid Zonule. Nevadaz3546—CO (4 cranidia, 3 pygidia), jangle Ridge area, Nevada Test Site. Kochaspid, sp. undet. 1 Plate 8, figures 9, 14, 17, 18 Description—Cranidium has well-defined anteriorly tapered glabella bearing three pairs of shallow glabellar furrows. Occipital ring well defined by straight occipital furrow and has prominent axial node adjacent to pos- terior margin. Frontal area gently downsloping, nearly flat, and lacks noticeable anterior arch. Narrow, shallow, straight, or slightly curved border furrow parallels an- terior margin. Sagittal length of nearly flat border equal to or slightly greater than that of brim. Fixed cheeks strongly upsloping to prominent arcuate palpebral lobes, and crossed by a well-defined strongly oblique ocular ridge. Palpebral lobes situated posterior to glabellar midlength. Width of palpebral area about two-thirds basal glabellar width. Length of palpebral lobe about two—thirds sagittal glabellar length exclusive of occipital ring. Posterior limb slender; length slightly greater than basal glabellar width. Posterior border furrow broad, shallow. Course of anterior section of facial suture nearly straight forward from palpebral lobe to border furrow, then curved broadly inward across border. Course of posterior section strongly divergent behind palpebral lobe and evenly curved nearly to posterior margin; just before margin, course is deflected slightly outward. CARRARA FORMATION, SOUTHERN GREAT BASIN Surfaces of all parts covered with closely spaced fine granules and interspersed coarse granules. Associated free cheek has a broad flat genal spine with length at least twice length of posterior section of facial suture and a few scattered coarse granules on border. Lateral border furrow defines nearly flat border and dies out posteriorly. Width of border about half length of anterior section of facial suture. Discussion—This distinctive kochaspid cannot be as- signed with confidence to any kochaspid genus because of lack of knowledge of the associated pygidium. It is most similar to Kochz'na macrops (Rasetti, 1951, pl. 19, figs. 17—19), but it differs in having a nearly flat frontal area and a border that does not taper noticeably laterally. The position and size of the palpebral lobes of the Carrara species do not conform at all to the characterization of Kochma given by Resser (1935, p. 39), which cites an- teriorly placed palpebral lobes and anteriorly convergent facial sutures as generic features. Rasetti did not explain why he included K. macrops in the genus. Neither species seems capable of generic assignment with present knowl- edge. 0€currence.—Moderately common, “Plagiura-Poliella” Zone, P. lomataspis Zonule. Nevada: 4434—CO (7 cranidia, 2 free cheeks), Belted Range. Kochaspid, sp. undet. 2 Plate 8, figures 21, 22 Discussion—A small sample of silicified trilobites in- cludes a few tiny cranidia and a pygidium of a kochaspid trilobite lacking pygidial spines. The cranidia have a strongly developed granular ornamentation, a well— defined poorly furrowed glabella, a narrow brim and convex border, and fixed cheeks wider than half of the basal glabellar width. The associated coarsely granular pygidium has a transversely subovate shape, poorly de— fined axis about one third of the pygidial width, and a narrow poorly defined border. The posterior margin is unevenly curved, and spines are absent. No described kochaspid has these characteristics, but the specimens are too small and fragmentary to use for formal taxonomic designation. They are associated with equally small specimens of a species of Poliella. Occurrence.—Moderately common, “Plagium—Poliella” Z0ne,P. lomataspis Zonule. Nevada: 3790—CO (8 cranidia, l pygidium), Nevada Test Site. Genus MEXICELLA Lochman Mexicella Lochman, 1948, p. 456; Howell, B. F., in Harrington and others, 1959, p. 240. Type species.—Mexicella mexiama Lochman, 1948, p. 457, pl. 69, figs. 12—22. Discussion—Lochman (1948) has given a thorough SYSTEMATIC PALEONTOLOGY analysis of the characteristics of this genus. Slight modifi- cation of the generic diagnosis is required to include a new species M. grandoculus, with palpebral lobes whose exsagittal length is nearly equal to half of the sagittal glabellar length exclusive of the occipital ring. All species of Mexicella are characterized by a sagittally long swollen frontal area with a poorly defined border that is narrower than the brim and by wide gently convex slightly down- sloping fixed cheeks. No other genus in the Albertella faunas of the Cordilleran region closely resembles Mexicella. Mexicella mexicana Lochman Plate 13, figures 13—21 Mexioella mexicana Lochman, 1948, p. 457, pl. 69, figs. 12-22; Lochman, C., in Cooper and others, 1952, p. 150, pl. 24, figs. 1—25. Discussion—This species has been well described and illustrated from the Albertella fauna of northern Mexico by Lochman. A distinctive feature not noted by Lochman but present on some specimens from both Mexico and the Carrara Formation is the presence of low scattered coarse granules on the border of the cranidium and free cheek (pl. 13, figs. 17, 19; also Cooper and others, 1952, pl. 24, fig. 24). This ornamentation has not been ob- served on either very small specimens or any of the larger specimens that may represent this species. Large cranidia, comparable in size to those of Mexicella stator (Walcott), are rare associates of the abundant smaller cranidia of this species. They are variably effaced (pl. 13, figs. 16, 18) and may have a distinct pitted ornamenta- tion. An associated larger free cheek is slightly wider than the cheek associated with the small cranidia, but it has the characteristic presence of only a slight node for the genal spirie. It has the same pitted ornamentation as the cranidium and has a very poorly defined border. This is quite unlike the large cheek assigned to the species by Lochman (1948, pl. 69, fig. 18; in Cooper and others, 1952, pl. 24, fig. 22) and casts some doubt on the correct- ness of the assignment to this species of the large cheek from Mexico. Occurrence.—Common, Albertella Zone, Albertella- Mexicella Zonule (>20 cranidia and free cheeks, Pl pygidium, including some silicified). Nevada: 1616—CO, Spring Mountains; 3543—CO, P7195—CO, 7196—CO, De- sert Range. California: 4165—CO, 7197—CO, Eagle Mountain; 4159—CO, Pyramid Peak section, Funeral Mountains; 4166—CO, Resting Springs Range. Mexicans. grandoculul n. sp. Plate 13, figures 5, 9, 10 Description—Small ptychopariid trilobites, sagittal length of largest observed cranidium 8 mm. Cranidium 109 subquadrate in outline, gently to moderately curved an- teriorly, gently to moderately convex transversely and longitudinally. Glabella prominent, sides slightly convex and convergent forward, anterior end bluntly rounded, defined at sides by moderately abrupt change in slope of exoskeleton, anterior end well defined by shallow pre- glabellar furrow; sagittal length, exclusive of occipital ring, slightly less than basal glabellar width. Three pairs of shallow short glabellar furrows apparent. Occipital furrow deepest distally. Occipital ring has well-developed axial node. Frontal area moderately convex in sagittal profile, slightly upsloping from front of glabella; sagittal length about three—fourths sagittal length of glabella exclusive of occipital ring. Border narrow, continuing outer downsloping surface of frontal area, very poorly differentiated from brim; sagittal length between one- third and one-half that of frontal area. Fixed cheek wide, flat, nearly horizontal, with moderately long, un- differentiated palpebral lobe; width, including palpebral lobe, between two-thirds and three-fourths basal glabel- lar width. Ocular ridge poorly defined, directed slightly posterolaterally from anterior end of glabella. Palpebral lobe situated about opposite glabellar midlength; ex- sagittal length between 0.4 and 0.5 sagittal glabellar length exclusive of occipital ring. Posterior limbs de- pressed distal to palpebral lobes; transverse length about equal to basal glabellar width. Posterior border furrow well defined, straight. Course of anterior section of facial suture very slightly divergent forward, strongly curved at anterolateral cranidial corners. Course of posterior sec- tion of facial suture convex. External surface without obvious ornamentation. Other parts not known. Discussion—This species is comparable in size to M. mexicana and can be distinguished by its larger palpebral lobes and slightly sunken anterior end of the glabella. The anterior sections of the facial sutures are also slightly divergent rather than slightly convergent forward. The species is included in Mexicella because of its large gently convex poorly differentiated frontal area. Occurrence.——Moderately common, Albertella Zone, Albertella—Mexicella Zonule(?). California: 4141—CO (> 10 cranidia), Titanothere Canyon section, Grapevine Mountains. Moderately common, Albertella—Mexicella Zonule. California: 4149—CO (4 cranidia), Echo Canyon section, Funeral Mountains; 4158—CO (7 cranidia), Pyramid Peak section, Funeral Mountains. Nevada: P4169—CO (>10 cranidia), Spectre Range. cf. Mexicella? stator (Waleott) Plate 8, figure 23 Agraulos stator Walcott, 1916a, p. 173, pl. 36, fig. 6; Walcott, 1917, p. 28, pl. 6, fig. 6. Mexicella stator (Walcott). Rasetti, 1951, p. 231, pl. 20, fig. 14—19. 110 Discussion—A single cranidium, preserved in siltstone and somewhat compressed from front to back by com- paction, has the extremely poorly defined narrow bor- der, sagittally long frontal area, broad fixed cheeks, small palpebral lobes, broad posterior limbs, and low poorly defined anteriorly tapered and truncate glabella charac- teristic of M exicella? stator (Walcott). The lack of other less compressed specimens for comparison, a straight rather than sinuous proximal part to the posterior section of the facial suture, and a position in slightly older beds than the types are the reasons for uncertainty of the specific iden- tification. Occurrence.—Rare, “Plagium-Poliella” Zone. California: 7234—CO (1 cranidium), Titanothere Canyon section, Grapevine Mountains. Genus NYELLA n. gen. Type species.—Poulsmia granosa Resser, 1939b, p. 59, pl.l3, figs. 19, 22—30. Description—Moderately small kochaspid trilobites, sagittal length of largest known cranidium about 10 mm. Cranidium subquadrate in outline, gently to moderately convex transversely and longitudinally, gently to moder— ately rounded at front; width between palpebral lobes slightly greater than sagittal length. Glabella prominent, tapered forward, strongly to bluntly rounded at front; sides straight or slightly concave, well defined by deep axial furrows; front defined by shallow preglabellar fur- row or abrupt change in slope. Three or four pairs of moderately deep glabellar furrows usually present. Oc- cipital furrow deep, shallowest and curved slightly for- ward across axis. Frontal area clearly divided by well- defined border furrow into flat brim and convex border. Fixed cheeks flat or gently c0nvex,' horizontal; width of palpebral area between 0.4 and 0.5 basal glabellar width. Ocular ridges moderately developed. Palpebral lobe well defined, situated about opposite glabellar midlength; ex- sagittal length varies from about one-third to about one- half sagittal glabellar length exclusive of occipital ring. Posterior limbs about equal in transverse length to basal glabellar width. Posterior border furrow broad, deep. Course of anterior section of facial suture straight for— ward from palpebral lobe. Course of posterior section divergent-sinuous. Free cheek has broadly rounded lateral margin form- ing continuous curve with genal spine. Border convex, well defined anteriorly by border furrow that fades to- wards base of genal spine. Genal spine convex in cross section, sharply pointed, about as long as posterior sec- tion of facial suture. Hypostome and thoracic segments not known. Pygidium transversely subovate in outline with broad poorly defined slightly tapered axis. Axial furrows CARRARA FORMATION, SOUTHERN GREAT BASIN obscure. Only first pleural furrow distinct. Border not separately defined. External surfaces of all parts covered with one or two sizes of granules. Discussion—This genus is proposed for species for- merly included in Caborcella by Rasetti (1951) and Fritz (1968) and an additional species from the Carrara For- mation, all of which differ from Caborcella as redefined previously (p. 701), by having a narrow well-defined bor- der furrow separating a convex border from a generally narrow flat slightly downsloping brim. The species differ among themselves in proportions of the brim, border, and frontal area, and in ornamentation. As constituted here, Nyella is found in both the Plagium—Kochmpis Zone and the Albertella Zone and con- tains the following species: Poulsenia granosa Resser (syn. P. bearensis Resser), Ptychoparia skapta Walcott, Caborcella mm Rasetti, Caborcella clinolimbata Fritz, Poulsenia col- umbiana Rasetti, and Nyella immodemta n. sp. Rasetti (1957) changed the assignment of P. skapta from Cabar- cella t0 Onchocephalus, but this seems to require too broad a characterization for Onchocephalm. The grouping of the coarsely granular early Middle Cambrian ptychopariids with a well-defined convex border into a separate genus as proposed here seems to reflect more reasonable mor- phologic relationships. Fritz (1968, p. 233) implied that Poulsem'a columbiana (Rasetti, 1957) belonged to Cabar- cella. In accord with the reorganization of these simple ptychopariids proposed here, this species would also be- long to Nyella. The most similar genus to Nyella is Parapoulsenia (Rasetti, 1957), which differs principally by having much broader fixed cheeks, a less anteriorly tapered glabella, generally smaller palpebral lobes, and shorter (tr.) and broader (sag) distal parts to the posterior limbs. Nyella clinolimbata (Fritz) Plate 14, figures 1—4 Caborcella clinolimbata Fritz, 1968, p. 221, pl. 41, figs. 33—35. Discussion—This species has been adequately de- scribed and figured by Fritz although his statement that the preglabellar field is absent medially is not exactly correct. A distinct flattened or depressed brim (or pre- glabellar area) lies between the glabella and the border. The border is the most distinctive feature of this species. In longitudinal profile, it rises up from the border furrow and then turns downward to have a flattened or slightly concave downsloping marginal area. In anterior View, the anterior cranidial margin is nearly straight, but the bor- der furrow rises to a high point on the axial line. In addition to the structure of the border, the palpebral lobes are larger and more medially located than those of SYSTEMATIC PALEONTOLOGY N. granosa, which is the other moderately common species of this genus in the Carrara Formation, and the ornamentation is more uniformly granular. The depth of the glabellar furrows is somewhat variable in the Carrara sample of this species. A single free cheek may also belong to this species. It has a gently convex border separated from a slightly wider ocular platform by a shallow border furrow that disappears towards the genal angle. The genal spine is slender, oval in cross section, and slightly longer than the posterior section of the facial suture. The surface is cov- ered with low obscure granules of uniform size. A single small cranidium from the Funeral Mountains may also represent this species. It has the typical de— velopment of the border and the same cranidial dimen- sions and ornamentation as the cranidia from the Nevada Test Site, but the fixed cheeks are distinctly less convex transversely. Occurrence.—Moderately rare, Albertella Zone, Zacan- thoidid Zonule. Nevada: 3766—CO (4 cranidiaP, 1 free cheek, P1 pygidium), Nevada Test Site. California: P4141—CO (1 cranidium), Echo Canyon section, Funeral Mountains. Nyella granosa (Bessel) Plate 14, figures 5—10 Poulsenia granosa Resser, 1939b, p. 59, pl. 13, figs. 19, 22—30 [not figs. 20, 21, assigned to Amecephalus laticaudatum (Resser) by Fritz (1968)]; Shimer and Shrock, 1944, pl. 259, figs. 6, 7. Caborcella granosa (Resser). Fritz, 1968, p. 221, pl. 39, figs. 9—15. Poulsenia bearemis Resser, 1939b, p. 60, pl. 13, figs. 5—8. Description—Cranidium gently to moderately convex transversely and longitudinally, moderately rounded anteriorly, width between palpebral lobes distinctly greater than sagittal length. Glabella well defined, ta- pered forward, strongly to bluntly rounded anteriorly, well defined by axial and preglabellar furrows; sides very slightly concave. Three or four pairs of moderately to strongly developed glabellar furrows present; posterior pair curved slightly backward. Occipital furrow deep distally, shallower across axial line. Occipital ring simple, with poorly defined axial node. Frontal area has deep gently curved border furrow separating convex border from nearly flat slightly downsloping brim; sagittal length of border slightly greater than that of brim. Sagit- tal length of frontal area about one-half sagittal length of glabella exclusive of occipital ring. Border on some specimens has slight median inbend. Brim varies in sagittal length and ornamentation from relatively short and nearly smooth, to nearly as long as sagittal length of border and bearing scattered tubercules. Fixed cheeks gently convex, horizontal; width of palpebral area vari— able between 0.4 and 0.5 basal glabellar width. Palpebral lobes upsloping, defined by abrupt change in slope of 111 exoskeleton, connected to glabella by distinct narrow backswept ocular ridges; exsagittal length slightly more than one—third sagittal glabellar length exclusive of oc- cipital ring. Posterior limbs have deep broad border fur- row; transverse length about equal to basal glabellar width. Course of anterior section of facial suture slightly bowed outward, but directed nearly straight forward from palpebral lobe. Course of posterior section divergent-sinuous, outlining broad rounded tip of pos- terior limb. Free cheek triangular in outline exclusive of genal spine. Lateral margin moderately and evenly curved. Border convex, defined anteriorly by deep border fur- row that nearly fades out towards genal angle before intersecting posterior section of facial suture; slightly narrower than ocular platform at anterior section of fa- cial suture. Genal spine convex, sharply pointed; length about equal to length of posterior section of facial suture. Pygidium transversely subelliptical in outline; sagittal length about one—half width, greatest width about oppo— site midlength. Axis low, broad, poorly defined by changes in slope of exoskeleton. Two or three poorly defined ring furrows present. Pleural regions un- differentiated, gently convex, strongly downsloping posterolaterally. Anterior pleural furrow deep, extended nearly to margin. Shallower first interpleural furrow and second pleural furrow apparent on some specimens. All parts of exoskeleton covered by fine closely spaced granular ornamentation. Cranidium and free cheek also thickly covered with scattered tubercules. Pygidium has tubercular ornamentation less well developed. Discussion—Specimens assigned to this species have now been described from southeastern Idaho and east- central and southern Nevada. The Carrara sample pro- vides the first information about the free cheek and also shows the range of variability in the structure of the frontal area that was suspected by Fritz (1968) when he tentatively and correctly synonymized Poulsenia bearensis Resser with N. granosa. This species differs from N. clinolimbata Fritz by having the cranidial border evenly convex in lateral profile rather than slightly recurved and downsloping; and by having a much stronger tubercular ornamentation. The broad border furrow and con— sequently narrower border distinguish N. ram (Rasetti) from N. gmnosa. N. skapta (Walcott) is distinguished from N. granosa by having a uniform granular ornamentation, more convex and slightly downsloping fixed cheeks, a more prominent medially thickened anterior cranidial border, and shorter palpebral lobes. N. columbiana (Rasetti) has a more convex cranidium with a more an- terolaterally depressed frontal area, less well developed glabellar furrows, and a coarser granular ornamentation with fewer scattered tubercules than N. granosa. Occurrence.—Moderately common, Albertella Zone, 112 Zacanthoidid Zonule. Nevada: 3695—CO (> 10 cranidia, 2 free cheeks, 1 pygidium), Nevada Test Site; 4440—CO (16 cranidia), Groom Range. Rare, Albertella Zone, Zacanthoidid Zonule. Nevada: 3766—CO (1 cranidium), Nevada Test Site; 7195—CO (1 cranidium), Desert Range. Nyella immoderata n. sp. Plate 14, figures 11, 12 Diagnosis—Small members of Nyella (largest known cranidium about 4 mm long) with three pairs of deeply incised glabellar furrows and with border furrow and furrows outlining the glabella also deep. Anterior border has distinct median inbend. Exsagittal length of palpe- bral lobes about one-half sagittal glabellar length exclu- sive of occipital ring. External surface covered with closely spaced moderately coarse granules that often grow together, producing a roughened appearance. Discussion—This distinctive species conforms in all re- spects to the description of the genus, and the diagnostic features cited above serve to distinguish it from other species in the genus. No other species so far described from the Albertella faunas of western North America has distinctive slotlike glabellar furrows comparable to those of N. immodemta. Occurrence.—Moderately common, Albertella Zone, Zacanthoidid Zonule. Nevada: 3766—CO (>15 cranidia), Nevada Test Site. Genus PACHYASPIS Resser Pachyaspis Resser, 1939b, p. 60; Shimer and Shrock, 1944, p. 615; Howell, B. F., in Harrington and others, 1959, p. 241; Balashova, E. A., in Chernysheva, 1960, p. 106; Yegorova, L. 1., and others, in Khalfin, 1960, p. 223. Type species—Pachyaspzis typicalis Resser, 1939b, p. 61, pl. 11,f1gs. 15—20; pl. 12, figs. 1—3. Discussion—Resser (1939b) gave a reasonably good diagnosis of the characteristics of this genus based only on its type species. The addition of several species from the Albertella and Glossopleum Zones by Resser (in McKee and Resser, 1945), Lochman (in Cooper and others, 1952), Rasetti (1951), and Fritz (1968) required very little modification of that original diagnosis. The species differ in subtleties of glabellar shape and development of glabellar furrows, in the structure and proportions of the frontal area on the cranidium, and in ornamentation. One of the more characteristic features of most species seems to be a well-defined narrow furrow continuously outlining the glabella. Complete specimens of P. gallagari Fritz from the Groom Range show a trilobite with 16 thoracic segments and a small poorly furrowed pygidium, demonstrating that at least one species of Pachyaspis is a micropygous form with a moderate number of thoracic segments. CARRARA FORMATION, SOUTHERN GREAT BASIN Pachyaspis gallagari Fritz Plate 15, figure 8 Pachyaspia gallagari Fritz, 1968, p. 231, pl. 40, figs. 11—13. Discussion—Specimens from two collections in the Carrara Formation seem to conform to the characteristics of this species well described by Fritz. The slight differ— ences in glabellar shape between specimens from the two collections are not considered to be sufficient justification for specific separation. The species is characterized by having a well-defined border only slightly narrower than the brim, moderately developed glabellar furrows, a slight axial shallowing of the anterior border furrow, and a variable, but generally finely granular ornamentation. The complete specimens from the Groom Range have 16 thoracic segments with short pleural spines and a deep narrow subcentrally located pleural furrow. The pygidium is small and transversely subovate, and seem- ingly lacks either axial or pleural furrows, although the axis is moderately prominent. Occurrence.——Common, Albertella Zone, Zacanthoidid Zonule(?). Nevada: 3692—CO (>10 cranidia, 7 partially or completely articulated individuals), Groom‘ Range. Rare and questionably identified, Albertella Zone, Zacanthoidid Zonule(?). Nevada: 3547—CO (3 cranidia), Nevada Test Site. Genus PLAGIURA Resser Plagiura Resser, 1935, p. 42; Lochman, 1947, p. 66; Rasetti, F., in Harrington and others, 1959, p. 516. Plagiurella Resser, 1937a, p. 22. Type species.—Ptychoparia? cercops Walcott, 1917, p. 81, pl. l2,f1gs. 1, la—d. Diagnosis.——Cranidium subtrapezoidal, glabella sub- triangular, weakly furrowed. Frontal area divided into brim and border; sagittal length less than half that of glabella. Fixed cheeks narrow. Palpebral lobes small, lo- cated opposite anterior end of glabella. Posterior limbs broad, with convex sutural margins. Free cheek with curved lateral margin subparallel to posterior section of facial suture. Genal spine‘present or absent. Discussion—Lochman (1947) and Rasetti (in Har- rington and others, 1959) presented diagnoses of this genus based on analysis of the type species, which was the only one known at that time. Both have pointed out that Plagiurella is based on small holaspids of Plagiura. The two species described here provide a better basis for evaluating generic characteristics and have led to the revised diagnosis of the cephalic features given. There is no other early Middle Cambrian trilobite with anteriorly located palpebral lobes and large posterior limbs with which this can be confused. SYSTEMATIC PALEONTOLOGY The cranidia of P. extensa n. sp., P. retracta n. sp., and small holaspid cranidia of P. cercops, out of context, could easily be associated with the Late Cambrian genus Aphelotoxon (Palmer, 1965); and perhaps a suprageneric relationship between Plagiura and Aphelotoxon should be considered. However, the pygidium of P. cercops is gently convex transversely, wide and short, with an axis nar- rower than the pleural fields, which contrasts with the strongly convex pygidium oprhelotoxon, which is nearly as long as it is wide and which has an axis wider than the pleural fields. The contrasting pygidial structure sug- gests a contrasting thoracic structure, and the complete trilobites were probably not as siniilar as their cranidia suggest. Although the large specimens of P. cercops and the small species described below seem too dissimilar to be congeneric, the small specimens of P. cercops are suffi- ciently similar to the new species in all cephalic features so that a consistent discrimination at the generic level can- not be satisfactorily made. The fact that all the species occur in the same approximate stratigraphic interval further supports a close relationship. Plagiura. extensa n. sp. Plate 6, figures 17—20, 23 Description—Small ptychopariid trilobites, cranidial length generally less than 5 mm. Cranidium subtrape- zoidal in outline, moderately convex transversely and longitudinally, anterior margin slightly curved, width between anterior sections of facial sutures about one- third of width between tips of posterior limbs. Glabella subtriangular in outline, well defined by shallow axial and preglabellar furrows, strongly rounded anteriorly; sagittal length, exclusive of occipital ring, slightly less than basal glabellar width; three pairs of short evenly spaced moderately deep and broad glabellar furrows ap- parent near axial furrows. Occipital furrow deep, nearly straight. Occipital ring has short axial spine on posterior margin, continuous with upward slope of surface of ring. Frontal area broad, concave; sagittal length slightly greater than one-half sagittal glabellar length exclusive of occipital ring. Border upturned, strongly convex, not clearly separated from flat or slightly convex brim; sagit- tal length slightly less than that of brim. Fixed cheeks narrow, slightly upsloping; width between axial furrow and facial suture at palpebral lobe slightly less than one- half basal glabellar width. Palpebral lobe small, slightly upsloping, differentiated from surface of fixed cheek by change in slope, situated opposite anterior end of glabella; length slightly less than one-third sagittal glabellar length exclusive of occipital ring. Short ocular ridges barely apparent. Posterior limbs broad, moder- 113 ately convex, downsloping; exsagittal and transverse di- mensions nearly equal; transverse length slightly less than basal glabellar width. Posterior border furrow broad, deep, expanded slightly distally. Course of anterior section of facial suture moderately convex anterolaterally in a more or less even curve from anterior end of palpebral lobe to anterior margin. Rostral suture nearly as long transversely as anterior cranidial width. Course of posterior section of facial suture strongly convex, directed posterolaterally behind pal- pebral lobe and curving uniformly backward to intersect posterior margin nearly at right angles; curvature re- verses slightly after crossing posterior border furrow. Free cheek moderately narrow, gently convex, has strongly curved lateral margin that is nearly parallel to posterior section of facial suture and continues without deflection along outer edge of genal spine. Border nar- row, gently convex, poorly defined by shallow continuous lateral and posterior border furrows; width about one- third of distance between lateral and posterior sutural margins. Genal spine slender, shorter than posterior sec- tion of facial suture. External surfaces of all parts covered by very fine closely spaced granules apparent only after lightly whitening best preserved specimens. Surface of mold has scattered fine pits. Discussion—This species differs from P. cercops (Wal- cott) by having a strongly upturned cranidial border, an occipital spine, and granular ornamentation. P. cercops also reaches significantly greater size, but the com- parisons here are with comparable-sized specimens of P. cercops. Free cheeks for small specimens of P. cercops have short laterally directed genal spines, which also serve to distinguish these species. P. extema differs from P. retracta n. sp. by having a longer brim, shallower border furrow, slightly larger palpebral lobes, more convex posterior course to the facial suture, a genal spine whose lateral margin con- tinues the curvature of the border of the free cheek, and a narrower free cheek border. Two small cranidia assign- able to P. extensa are associated with P. retracta in USGS collection 3546—CO (pl. 6, figs. 19, 20). Although these were first thought to indicate that the differences be- tween the species were only well developed in larger cranidia, the discovery of still smaller cranidia in the same sample with the typical characters of P. retracta (pl. 6, fig. 21) indicates that the characters hold true throughout the observed size range and that both species are present. Occurrence.—Moderately common, “Plagium—Poliella” Zone, Kochaspid Zonule. Nevada: 3691—CO (>10 cranidia, 6 free cheeks), Groom Range. Rare, “Plagiura- Poliella” Zone, Kochaspid Zonule. Nevada: 3546—CO (2 cranidia), Nevada Test Site. 114 Plagiura minor n. sp. Plate 13, figures 22—25 Description—Small ptychopariid trilobites, cranidial length generally less than 3 mm. Cranidium subtrape— zoidal in outline, gently convex longitudinally, moder- ately convex transversely. Anterior margin nearly straight, width between anterior sections of facial sutures about one-half width between tips of posterior limbs. Glabella subtriangular in outline, defined all around by change in slope of exoskeleton; sagittal length, exclusive of occipital ring, about equal to basal glabellar width. Glabellar furrows not apparent. Occipital furrow deepest distally, shallow or absent across axial line. No occipital node or spine. Frontal area very short, subequally di- vided into concave brim and moderately convex border; sagittal length varies from one-fourth to slightly more than one-third sagittal length of glabella exclusive of occipital ring—shortest on smaller individuals. Fixed cheeks downsloping, narrow; width, including small poorly defined palpebral lobe, one-half or slightly less than one—half basal glabellar width. Palpebral lobe situated opposite anterior end of glabella; exsagittal length about one-fourth sagittal glabellar length exclu- sive of occipital ring. Posterior limb broad, downsloping; transverse width about equal to basal glabellar length. Course of anterior section of facial suture directed nearly straight forward or convergent from palpebral lobe to anterolateral cranidial corners and then turned more sharply inward before intersecting border. Course of posterior section convex outward behind palpebral lobe and curved inward before reaching posterior margin. Free cheek subtriangular in outline, gently convex, with moderately curved lateral and posterior margins. No genal spine. Discussion—This species is easily distinguished from P. extensa n. sp. and P. retracta n. sp. by its subdued cranidial relief, downsloping fixed cheeks, and absence of glabel- lar furrows. The short frontal area with a moderately convex border and a straight anterior margin that is bowed upward in anterior view distinguishes this species from comparably sized specimens of P. cercops (Walcott). Occurrence.—Moderately rare, Albertella Zone, Albertella—Mexicella Zonule. California: 4154—CO (7 silicified cranidia), Echo Canyon section, Funeral Mountains; 4165—CO (10 silicified cranidia, 2 free cheeks), Eagle Mountain. Nevada: 7196—CO (>10 cranidia, 1 free cheek), Desert Range. Plagiura retracta n. sp. Plate 6, figures 21, 24—27 Description—Small ptychopariid trilobites, cranidial length generally less than 5 mm. Cranidium subtrape- CARRARA FORMATION, SOUTHERN GREAT BASIN zoidal in outline, moderately to strongly convex trans- versely and longitudinally. Anterior margin nearly straight; width between anterior sections of facial sutures slightly more than one-third width between tips of pos- terior limbs. Glabella subtriangular in outline, well de- fined at sides by shallow axial furrows, poorly defined at strongly rounded front; sagittal length, exclusive of oc- cipital ring, about equal to basal glabellar width, three pairs of short, evenly spaced, moderately deep glabellar furrows present adjacent to axial furrows. Occipital fur- row deepest distally, shallow and slightly curved forward across axial line, posterior margin not known; internal molds suggest presence of either node or short spine. Frontal area short, strongly concave; sagittal length slightly less than one-half sagittal glabellar length exclu- sive of occipital ring. Border upturned, strongly convex, outer margin nearly vertical, separated from very short brim by broad deep nearly straight border furrow; sagit- tal length to middle of border furrow nearly twice sagittal length of brim. Fixed cheeks narrow, slightly upsloping; width between axial furrow and facial suture at palpebral lobe one-half or slightly less than one-half basal glabellar width. Palpebral lobe small, poorly defined, located op- posite anterior end of glabella; exsagittal length about one-fifth sagittal length of glabella exclusive of occipital ring. Short ocular ridges barely apparent. Posterior limbs broad, subtriangular, moderately convex, downsloping; transverse length about equal to basal glabellar width. Posterior border furrow broad, deep, expanded slightly distally. Course of anterior section of facial suture directed nearly straight forward from palpebral lobe to border furrow and then curved sharply inward and across bor- der. Course of posterior section gently convex pos- terolaterally from palpebral lobe to posterior margin. Free cheek moderately narrow, gently convex, lateral margin strongly curved, more or less parallel to posterior section of facial suture. Border narrow, convex, moder- ately well defined by continuous lateral and posterior border furrows; width about one-half width of ocular platform between lateral border furrow and posterior section of facial suture. Genal spine slender, directed posterolaterally at strong angle to lateral margin of check; length slightly less than length of posterior section of facial suture. External surfaces of all parts faintly roughened but not distinctly granular; vertical part of anterior cranidial border and anterior part of border of free cheek have well-developed terrace lines parallel to margin. Discussion—The differences between this species and P. extensa n. sp. have been discussed.P. retracta also differs from P. cercops by its smaller size, strongly upturned and convex cranidial border, and deep anterior border fur- row. SYSTEMATIC PALEONTOLOGY Occurrence.—Moderately rare, “Plagium-Poliella” Zone, Kochaspid Zonule. Nevada: 3546—CO (8 cranidia, 1 free cheek), Nevada Test Site. Plagiura cf. P. col-oops (Walcott) Plate 6, figure 22 Plagium cercops (Walcott), Rasetti, 1951, p. 237, pl. 13, figs. 10—16. Discussion.—A single weathered cephalon from yellow—weathering silty limestone at the base of the Red Pass Member of the Carrara Formation in the Echo Can- yon section in the Funeral Mountains is referable to Plagium. The specimen preserves the cranidial outline, showing a tapered glabella reaching to the inner edge of a broad border, anteriorly placed palpebral lobes, and large triangular posterior limbs. The partly displaced free cheeks seem to lack genal spines. There is in- adequate information about the external surface and about details of the cranidial and cheek margins to make comparisons at the specific level, but the specimen seems to agree in all observable characteristics with P. cercops (Walcott). Occurrence .——Rare, “Plagium-Poliella” Zone. California: 7189—CO (1 incomplete cephalon), Echo Canyon section, Funeral Mountains. Genus SCHISTOMETOPUS Resser Schistometopus Resser, 1938b, p. 10; Rasetti, F., in Harrington and others, 1959, p. 516. Type specie5.—Schistometopw typicalzls Resser, 1938b, p. 10, pl. 1,f1g. 12. Discussion .—The present concept of this genus is based on the work of Rasetti (1951, 1957), who added three species to the monotypic genus of Resser, all based on cranidia, and who established the probable nature of the pygidium for one of these. Cranidia are characterized by a glabella that has three distinct pairs of lateral furrows, tapers forward, and reaches to the inner edge of a convex well-defined border. The fixed cheeks are relatively broad, with palpebral lobes situated opposite or slightly posterior to the glabellar midlength. The external or- namentation consists of granules of one or more sizes. The pygidium is characterized by convergence of the pleurae into a pair. of broad-based flat spines and by having a short axis that does not reach to the posterior margin. Schistometopus spp. Plate 8, figures 1, 2, 5, 6 Discussion .—Several cranidia from one collection and a distorted cranidium and nearly complete pygidium from another seem to represent one or more species of Schis— tometopus. The pygidium and cranidium from USGS col- 115 lection 4139—CO (pl. 8, figs. 1, 5) are most like S. convexus Rasetti, which is a common and diagnostic fossil for the Plagium-Kochaspis Zone (Rasetti, 1957, p. 965). The cranidia from USGS collection 3546-CO include a small form (pl. 8, fig. 6), two larger fragments with nearly straight anterior border furrows, most similar to S. con— vexus Rasetti, and a larger form (pl. 8, fig. 2) with a broken anterior border and a suggestion of a slight posterior median inbend to the border furrow that is more like S. collaris Rasetti. None of the specimens are well enough preserved or provide sufficient material to make adequate judgments about identifications at the species level. Occurrence .—-Rare, “Plagium-Poliella” Zone, Kochaspid Zonule. Nevada: 3546—CO (3 cranidia), Nevada Test Site. California 4139—CO (1 cranidium, 1 pygidium), Titanothere Canyon section, Grapevine Mountains. Genus SYSPACEPHALUS Resser Syspacephalus Resser, 1936, p. 28; Lochman, 1947, p. 64; Rasetti, 1951, p. 241; Rasetti, F., in Harrington and others, 1959, p. 237; Shaw, 1962, p. 337. Type species.—Agraulos champs Walcott, 1917, p. 72, pl. 13, figs. 2, 2a. Discussion .—This genus has been well characterized by Lochman (1947) and Rasetti (1951; in Harrington and others, 1959). It includes small, micropygous simple ptychopariids with small palpebral lobes situated slightly anterior to the glabellar midlength and with slightly con- vergent anterior sections of the facial sutures. The new species described hereafter have the cranidial charac- teristics typical for the genus and provide new informa- tion about the free cheek, rostral plate, thorax, and pygidium. Syspacephalus longus n. sp. Plate 7, figures 14, 16—18 Description—Small simple ptychopariids, total length probably not exceeding 2 cm. Cranidium subtrapezoidal in outline, anterior margin moderately rounded. Glabella low, obscurely furrowed, tapered slightly for- ward, bluntly rounded at front, defined by shallow lateral and preglabellar furrows. Occipital furrow deepest at sides, shallow across axial line. Occipital ring has median axial node. Frontal area subequally divided by shallow border furrow into gently convex brim and border. Bor- der tapered towards anterolateral cranidial corners. Fixed cheeks gently convex, horizontal or downsloping; width about one-half basal glabellar width. Palpebral lobe small, poorly defined, situated slightly anterior to glabellar midlength; exsagittal length about one-fourth sagittal glabellar length exclusive of occipital ring. Pos- 116 terior limb moderately broad exsagittally; transverse length about equal to basal glabellar width. Posterior border furrow about as deep as occipital furrow. Course of anterior section of facial suture subparallel to axis or slightly convergent forward. Course of posterior section moderately convex. Free cheek small, with poorly defined lateral border. Genal spine short, deflected laterally from margin of cheek; length slightly less than length of posterior section of facial suture; base adjacent to junction of suture with posterior margin. Thorax consists of 15 or 16 segments. Pleural regions of each segment traversed by broad, deep, straight pleural furrow; pleural tips geniculated downward; short posterolaterally directed spines present. Pygidium simple, transversely subovate in outline. Axis low, broad, bluntly terminated, reaches nearly to pos- terior margin; one ring furrow present posterior to ar- ticulating furrow. Pleural regions crossed by pleural fur- row of first segment and faint first interpleural furrow. Border narrow, poorly defined. Discussion .—This species has a cranidium most like that ofS. perola (Walcott) (Rasetti, 1951, pl. 9, figs. 17—22), but it has a free cheek with a well-developed genal spine, at least two more thoracic segments, and less strongly con- vergent anterior sections of the facial sutures. Isolated cranidia of S . longus n. sp. would be difficult to distinguish from S. perola, but the total trilobite morphology indicates that the Nevada and Canadian specimens are otherwise quite distinct. Occurrence.—Common, “Plagiura-Poliella” Zone. Nevada: 4435—CO (5 partial individuals, 20 cranidia, 4 free cheeks, 1 pygidium), Belted Range. Syspaeephalus obscurus n. sp. Plate 7, figures 6—13, 15 Description—Small, micropygous ptychopariid trilo- bites probably not exceeding 1 cm in total length. Cranidium subtrapezoidal in outline, gently to moder- ately rounded at front. All parts barely outlined by extremely shallow furrows on most specimens; some in- dividuals may have better definition of the glabella or border. Glabella low, tapered forward, bluntly rounded anteriorly. Glabellar furrows obscure. Occipital furrow moderately deep distally, shallow across axis; broad poorly defined median axial node may be observable. Frontal area downsloping, barely differentiated into border and brim by gently curved or straight shallow furrow or slight change in slope. Sagittal length of border variable, most commonly subequal to length of brim; may be as little as one-half length of brim. Fixed cheeks down- sloping, palpebral lobes only differentiated by slight upward deflection of cheek surface; width of cheek in- cluding palpebral lobe about 0.6 basal glabellar width. CARRARA FORMATION, SOUTHERN GREAT BASIN Palpebral lobe situated just anterior to middle third of glabella; length about one-third sagittal length of glabella. Posterior limbs subtriangular; exsagittal length behind palpebral lobe about twice length of palpebral lobe; posterior border furrow shallow, well defined. Course of anterior section of facial suture subparallel or slightly convergent forward from palpebral lobes to border furrow, then curved gently inward to intersect anterior margin near anterolateral cranidial corners. Course of posterior section of facial suture forms gentle outwardly convex curve from palpebral lobe to posterior margin. Rostral plate broad transversely, narrow; sagittal length about one-fifth breadth; slightly narrower distally. Free cheek narrow, border not differentiated; width opposite ocular notch about 0.3 total length. Genal angle acute, projected backward into short broad-based genal spine. Pygidium simple, subovate in outline; sagittal length slightly more than one-half greatest width. Axis low, broad, weakly to moderately defined at sides, poorly de- fined posteriorly; one to three ring furrows barely appa- rent; width about 0.4 greatest pygidial width; length about 0.9 sagittal pygidial length. Pleural regions down- sloping, triangular. Border not differentiated; two shal- low pleural furrows and intervening interpleural furrow may be present, not reaching to margin. Ornamentation consists of extremely densely packed uniform granules that merge at their contacts so that many specimens appear pitted. Discussion—The small anteriorly placed palpebral lobes and consequently broad posterior limbs of this sim- ple ptychopariid are the basis for including it in Sys— pacephalus. It differs from all other species in the genus by the poor development of furrows outlining the glabella and border. In addition to its generally poor relief, it is characterized by its distinctive granular ornamentation. Occurrence.—-Common, Albertella Zone. California: 4140—CO, (>20 cranidia, 3 free cheeks; >10 pygidia), Titanothere Canyon section, Grapevine Mountains. Rare and questionably identified, Albertella Zone. California: 719l—CO (5 distorted cranidia), Echo Canyon section, Funeral Mountains. Genus VOLOCEPHALINA n. gen. Type species.—Volocephalina connexa n. sp. Description .—Small ptychopariid trilobites, largest cranidia about 4 mm in sagittal length. Cranidium sub- trapezoidal in outline, gently to moderately convex transversely and longitudinally, all parts well defined, anterior margin nearly straight. Glabella prominent, well defined at sides by broad axial furrows; defined at front by abrupt change in slope of exoskeleton; tapered slightly SYSTEMATIC PALEONTOLOGY forward, bluntly rounded anteriorly. Three or four moderately deep glabellar furrows present; anterior pair or pairs short, not connected to axial furrows. Occipital furrow very shallow across axis, deep distally. Occipital ring moderately broad, bears prominent median node. Frontal area subequally divided into depressed, concave brim and strongly upturned convex border; sagittal length between one-third and two—thirds sagittal length of glabella exclusive of occipital ring. Fixed cheeks broad, flat, slightly to moderately upsloping; width, including palpebral lobes, between two-thirds and equal to basal glabellar width. Palpebral lobes small, upsloping from surface of cheek, situated opposite anterior third of glabella, connected to glabella by moderately to strongly developed anteriorly curved ocular ridge. Exoskeleton in front of ocular ridge sharply depressed. Posterior limb large, broad; transverse length equal to or greater than basal glabellar width. Posterior border furrow deep, well defined. Course of anterior section of facial suture slightly convergent forward from palpebral lobes and then curved inward more sharply at cranidial corners to intersect cephalic margin about midway to axial line. Posterior section convex. Free cheek elongate, subtriangular, with poorly de- fined border and short flat broad-based genal spine. Hypostome, rostral plate, and pygidium unknown. External surface of cranidium bears scattered coarse tubercules. Discussion—This distinctive small genus is unlike any other described early Middle Cambrian genus. It is most similar to the Early Cambrian genus Periommella from which it is most easily distinguished by having large broad posterior limbs and small upsloping palpebral lobes. Vol- ocephalina may represent an early form in the lineage of small ptychopariids leading to Bolaspidella and the Menomoniidae in the upper Middle and lower Upper Cambrian. Volocephalina connexa n. sp. Plate 14, figures 17, 18, 21, 22 Description .—Members of Volocephalina with sagittal length of frontal area about two-thirds sagittal length of glabella exclusive of occipital ring; width of fixed cheeks about equal to basal glabellar width; and transverse width of posterior limbs about 1% times basal glabellar width. Palpebral lobes and anterior end of glabella connected by nearly continuous ocular ridge only slightly or not at all interrupted by axial furrow. External surface between scattered tubercules smooth or obscurely pitted. Discussion .—This species differs from V. contracta n. sp. by having broader fixed cheeks, a longer frontal area, and larger posterior limbs and by having the ocular ridge nearly imperceptibly merged with both the palpebral lobe and glabella. The ornamentation between the tuber- 117 cules is also smooth or pitted rather than finely granular. Occurrence .——Rare, Albertella Zone, Zacanthoidid Zonule(?). Nevada: 3483—CO (2 cranidia) and 3547—CO (5 cranidia), both from Nevada Test Site; 3543—CO (1 silicified cranidium), Desert Range. California: 4141—CO (8 cranidia), Titanothere Canyon section, Grapevine Mountains. Volocephalina contracts. :1. sp. Plate 14, figures 13—16, 20 Description—Members of Volocephalina with sagittal length of frontal area about one-half sagittal length of glabella exclusive of occipital ring, width of fixed cheeks about two-thirds basal glabellar width, and transverse width of posterior limbs about equal to basal glabellar width. Exoskeleton between scattered tubercules is finely granular. Ocular ridge clearly interrupted by axial fur- rows at junction with glabella. Free cheek gently convex, elongate, triangular. Border poorly defined by shallow border furrow; width about one-half width of anterior part of ocular platform. Genal spine moderately short, broad based, flat. Length of posterior sutural margin about twice length of anterior sutural margin. Discussion—This species differs from V. connexa n. sp. by having less prominent ocular ridges reaching to, but not interrupting, the axial furrow, a shorter frontal area, narrower fixed cheeks, and shorter posterior limbs; and it has a granular ornamentation between the scattered tubercules. Occurrence.—Moderately rare, Albertella Zone, Albertella-Mexicella Zonule. California: 4149—CO (12 cranidia, 1 free cheek), Echo Canyon section, Funeral Mountains; 4158—CO (8 silicified cranidia, 1 limestone cranidium) and 4159—CO (2 silicified cranidia), both from Pyramid Peak section, Funeral Mountains. Ptychopariid sp. undet. 1 Plate 5, figures 12, 13 Discussion—This species has the relatively wide fixed cheeks, anteriorly downsloping and truncate glabella, subparallel anterior sections of facial sutures, and me- dially expanded border indicated by Rasetti (1955) to be generally characteristic of Onchocephalus. It is dis- tinguished from other Early Cambrian ptychopariids in the Carrara Formation by having the glabella only slightly tapered forward, deep axial furrows, and a sagi- tally long occipital ring. The external surface lacks any distinct ornamentation. The most similar described species are Antagmus trun- catus Fritz and Onchocephalus solitarius (Lochman) (Fritz, 1972; Lochman, in Cooper and others, 1952), from which this differs by lacking granular ornamentation and a prominent occipital node. 118 Occurrence.——Rare, lower part of Bristolia Zonule. California: 7179—CO, Cucomungo Canyon section, Last Chance Range. Nevada: 7192—CO, Desert Range. Ptychopariid sp. undet. 2 Plate 5, figure 14 Discussion—This species is represented by two frag- mentary cranidia and one moderately well preserved cranidium in one collection. It is the largest of the Early Cambrian ptychopariids found in the Cararra Formation and is characterized by a low anteriorly tapered glabella (rounded at the front), very weak glabellar furrows, deep axial furrows, a moderately deep nearly straight border furrow, a sagitally narrow occipital ring, moderately wide fixed cheeks, and moderately small palpebral lobes lo— cated about opposite glabellar midlength. The external ornamentation is not known. The form of the occipital ring and glabellar outline distinguish this form from other Early Cambrian ptychopariids in the Cararra For- mation. This generalized species is not closely similar to any of the Early Cambrian Cordilleran ptychopariids although it shares many cranidial proportions with species as- signed to Antagmus and Onchocephalus. Occurrence.—Rare, Bristolia Zonule. California: 4153—CO, Echo Canyon section, Funeral Mountains. Ptychopariid sp. undet. 3 Plate 5, figure 15 Discussion—This species is represented by several im- perfectly preserved internal molds of cranidia from one collection. It is characterized by having a low bluntly rounded glabella defined by shallow narrow axial and by preglabellar furrows of nearly uniform depth. The bor- der is not expanded mesially and is separated from the brim by a narrow shallow gently curved border furrow. The fixed cheeks are only about one-half as wide as the basal part of the glabella, and they are gently convex and slightly downsloping. The occipital furrow is broad and deep, and the occipital ring has an axial node. The sur- face of the mold is strongly pitted on all parts except the glabella. The species is most similar to a species described by Fritz (1972) as Piazella? mm from which it differs principally by lacking the slight posterior median deflec— tion of the anterior border furrow. The low cranidial relief and uniform nature of the furrows outlining the glabella distinguish this species from other Early Cam- brian ptychopariids in the Carrara Formation. 0ccurrence.—Rare, upper part of Early Cambrian, thin limestone just above Gold Ace Limestone Member of Carrara Formation. Nevada: 7194—CO, Desert Range. CARRARA FORMATION, SOUTHERN GREAT BASIN Ptychopariid sp. undet. 4 Plate 5, figure 16 Discussion—This species is represented by the only cranidium that has been found in the Early Cambrian shales of the Carrara Formation. It is characterized by a glabella tapered gently forward and strongly rounded anteriorly, by three moderately distinct pairs of glabellar furrows, by a shallow border furrow deflected posteriorly by a median expansion of the anterior border, and by palpebral lobes that are situated about opposite the glabellar midlength. The general cranidial proportions are most like those suggested for Onchocephalus by Rasetti (1955), but the moderately distinct glabellar furrows are unusual and distinguish this form from other Early Cambrian ptychopariids in the Carrara Formation and elsewhere in the Cordilleran region. Occurrence.—Rare, upper part of Lower Cambrian, in shales immediately above the Gold Ace Limestone Member of Carrara Formation. California: 7188-CO, Echo Canyon section, Funeral Mountains. Ptychopariid sp. undet. 5 Plate 15, figure 5 Discussion .—The diverse A lbertella Zone assemblage in USGS collection 3547—CO contains two small cranidia of a simple ptychopariid species of uncertain affinities. It is characterized by a well-defined slightly tapered an- teriorly truncate glabella bearing weak glabellar furrows. The occipital furrow is deep distally, and the occipital ring is simple. The frontal area has a gently convex down— sloping brim slightly wider than the gently convex down- sloping border. The border furrow is shallowest on the axial line. The fixed cheeks are gently convex, horizontal; and the transverse width of the palpebral areas is about 0.6 as much as the basal glabellar width. Nearly straight poorly defined ocular ridges are almost perpendicular to the axis. The palpebral lobe is poorly defined, situated opposite the glabellar midlength and about 0.4 the length of the glabella exclusive of the occipital ring. The poste- rior limbs are broad, and their transverse length is slightly greater than the basal glabellar width. The an- terior facial sutures are slightly divergent forward, and the posterior sutures are divergent and convex. The ex— ternal surface is covered with very fine obscure granular ornamentation. No other parts can be certainly associated with the cranidia of this species. Because it is such a nondescript form, its generic assignment must await more knowledge of the whole trilobite. It differs from the associated sim- ple form assigned to Pachyaspis gallagari Fritz by having the glabella truncated at the front, by lacking a well— defined preglabellar furrow, and by having the palpebral lobes more centrally placed. SYSTEMATIC PALEONTOLOGY Occurrence.-—Rare, Albertella Zone, Zacanthoidid Zonule(?). Nevada: 3547—CO (2 cranidia), Nevada Test Site. Ptychoparlid sp. undet. 6 Plate 15, figure 6 Discussion—Two small cranidia in the large collection from 3766—CO, Nevada Test Site, represent an unknown additional species to the Albertella fauna. It is charac- terized by a glabella only slightly tapered forward and bluntly rounded anteriorly, by a subequally divided frontal area with the shallow border furrow interrupted by a slight swelling on the axial line, by small palpebral lobes, about 0.4 sagittal length of the glabella, situated opposite the anterior third of the glabella, and by an exsagittally broad posterior limbs with a well-developed broad posterior border furrow. Three pairs of shallow glabellar furrows are Visible, and the occipital furrow is very deep and straight. The occipital ring seems to have had an occipital spine, because there is a large subcircular broken area at the back of the occipital ring. This species seems closest to Syspacephalus champs (Wal- cott). The principal differences are the deep occipital furrow of the form described here and its less anteriorly convergent facial sutures. Without more material, a meaningful identification cannot be applied to this specimen. Occurrence.—Rare, Albertella Zone, Zacanthoidid Zonule. Nevada: 3766—CO (2 cranidia), Nevada Test Site. Ptychopariid sp. undot. 7 Plate 15, figure 7 Discussion .—This small simple ptychopariid represents a species perhaps related to Nyella n. gen. It is charac- terized by an anteriorly tapered glabella with the sides well defined by deep axial furrows and slightly concave. Glabellar furrows are barely apparent. The frontal area is divided into a narrow brim and convex slightly down- sloping border. The distinct border furrow seems to be shallowest across the axial line. The fixed cheeks are gently convex and slightly downsloping, and the palpe- bral lobes are situated about opposite the glabellar mid- length. A part of the exoskeleton is preserved and has an apparently coarsely pitted ornamentation that could re— flect the interstices between intergrown coarse granules. The species lacks the well—developed glabellar furrows of species of Nyella and has an ornamentation unlike that of any of the other species in the Albertella Zone of the Cararra Formation. More material is needed to evaluate its generic affinities and to justify a formal identification. Occurrence.—Rare, Albertella Zone, Zacanthoidid Zonule. Nevada: 3695—CO (1 cranidium), Nevada Test Site. 119 Ptychopariid sp. undet. 8 Plate 8, figure 19 Discussion—A unit of orange—weathering silty lime- stones at the base of the Red Pass Member of the Cararra Formation in the Echo Canyon section of the Funeral Mountains, Calif, has yielded rare poorly preserved trilobites representing at least two genera. One is an indeterminate species of Plagium, and the other is a form with a broad cranidium of low relief that has a broad concave border about equal in sagittal length to the brim. The fixed cheeks are considerably wider than one-half of the basal glabellar width, and the palpebral lobes are of moderate length and are situated slightly anterior to the glabellar midlength. The anterior sections of the facial sutures are directed slightly anterolaterally from the pal- pebral lobes. A partial articulated specimen shows the species to have had at least 14 thoracic segments and a long genal spine. The forms seem to be closest to species assigned by Rasetti (1951) and Fritz (1968) to Amecephalus; but the position of the palpebral lobe is more anterior than in other species of Amecephalus, and more material of better quality is needed before a meaningful identification of this species can be made. Occurrence .-Rare, “Plagium-Poliella” Zone. California: 4148—CO (1 cranidium; 1 partially articulated specimen) and 7189—CO (2 poor cranidia), Echo Canyon section, Funeral Mountains. Ptychopanid sp. undet. 9 Plate 14, figure 19 Discussion—Several simple ptychopariid cranidia in one collection are characterized by a prominent poorly furrowed anteriorly tapered and truncate glabella, a sub- equally divided frontal area with the border furrow nearly effaced on the axial line, and medially placed poorly defined palpebral lobes. The width of the fixed cheeks is slightly more than one—half the basal glabellar width and the exsagittal length of the palpebral lobe is about one-half the sagittal glabellar length exclusive of the occipital ring. The external surface is covered with closely spaced moderately coarse granules that grow to— gether in the frontal area to give it a superficial pitted appearance. No other trilobites in the Carrara Formation have the cranidial morphology and distinctive ornamentation of this species. Until more and better material can be found, it is left unnamed. Some poorly preserved cranidia in a second collection, at least one with a pitted ornamentation on the fixed cheeks, may also represent this species. Occurrence.—Moderately rare, Albertella Zone, Zacan- thoidid Zonule. Nevada: 4440—CO (6 cranidia), Groom Range; P7195—CO (6 cranidia), Desert Range. 120 CARRARA FORMATION, SOUTHERN GREAT BASIN Ptychopariid sp. undet. 10 Plate 15, figure 15 Discussion—Several small cranidia, the largest only 5 mm in sagittal length, represent a species unlike any other simple ptychopariid in the lower Middle Cambrian beds of the Cordilleran region. The glabella is large, moderately convex transversely, tapered forward, strongly rounded at front, and distinctly defined by abrupt changes in slope of the exoskeleton. Glabellar furrows are marked by smooth areas in an otherwise strongly granular glabellar ornamentation. The occipital furrow is deep and narrow distally, is broad and shallow across the axis, and bears granular ornamentation in its axial part. The occipital ring is simple, with a low axial swelling near its posterior margin. The frontal area con- sists of a smooth flat or concave brim and a convex granular border; the sagittal length of the frontal area varies from 0.4 to 0.5 the sagittal length of the glabella exclusive of the occipital ring. The fixed cheeks are gently convex and granular, with low ocular ridges and prominent, slightly upturned palpebral lobes. Trans- verse width of the palpebral area is slightly less than one-half the basal glabellar width. The posterior limbs are short and blunt; transverse width varies from about 0.7 to 0.8 of the basal glabellar width. The anterior sec- tions of the facial sutures are directed nearly straight forward from the palpebral lobes and the posterior sec- tions are moderately to strongly convex. This species is one of three associated ptychopariids in USGS collection 4155—CO. It is easily distinguishable from the others, Alokistocarella? cf. A. brighamensis Resser and ptychopariid sp. undet. 11, by its strongly granular ornamentation and strongly convex border. Occurrence.—Rare, Glossopleura Zonule. California: 4155—CO (3 cranidia), Echo Canyon section, Funeral Mountains. Ptychopariid sp. undet. 11 Plate 15, figure 16 Discussion—Several small cranidia, length of largest specimen about 3 mm, represent a simple ptychopariid unlike any other from the early Middle Cambrian of the Cordilleran region. The glabella is tapered forward, sharply rounded anteriorly, well defined at sides and front by shallow axial and preglabellar furrows, and bears four pairs of narrow moderately distinct glabellar furrows of which the anterior pair is most deeply im- pressed. The occipital ring is simple, without a distinct node or spine. The frontal area is subequally divided into a flat brim and slightly convex border by a narrow border furrow. The sagittal length of the frontal area is slightly less than one-half of the sagittal length of glabella exclu- sive of the occipital ring. The fixed checks are gently convex, horizontal, crossed by low and straight ocular ridges, and have moderately large palpebral lobes situated about opposite the glabellar midlength. The width of the palpebral area is about one-half the basal glabellar width, and the exsagittal length of the palpebral lobe is about one—half the glabellar length exclusive of the occipital ring. The posterior limb is bluntly terminated and bears a deep posterior border furrow; its transverse width is about 0.8 of the basal glabellar width. The course of the anterior section Of the facial suture is nearly straight forward from the palpebral lobe and the course Of the posterior section is divergent and convex. The external surfaces of all convex parts are very faintly granular. This species differs from the two associated simple ptychopariids, Alokistocarella? cf. A. brighamensis Resser and ptychopariid sp. undet. 10, by having moderately distinct glabellar furrows, a short frontal area, and mod- erately wide fixed cheeks. 0ccurrence.—Moderately rare, Glossopleum Zonule. California: 4155—CO (5 cranidia), Echo Canyon section, Funeral Mountains. Ptychopariid sp. undet. 12 Plate 15, figures 19, 20 Discussion—Two small very distinctive cranidia rep- resent a species unlike any other early Middle Cambrian ptychopariid so far described from the Cordilleran re- gion. It is characterized by a prominent convex glabella, slightly tapered forward, strongly rounded at front, reaching to a broad deep border furrow, and well de- fined by deep axial furrows. Four pairs of glabellar fur- rows are present; the posterior pair is deepest and is deflected strongly posteriorly. The occipital furrow is deep and narrow, and the occipital ring is simple. The frontal area consists only of a convex border with a sagit— tal length about one-seventh of the sagittal length of the glabella exclusive of the occipital ring. The fixed cheeks are moderately to strongly convex and slightly down- sloping, with a well defined moderately small palpebral lobe situated opposite the second pair of glabellar fur- rows and below the level of the cheek. The transverse width of the palpebral area is about one-third the basal glabellar width, and the exsagittal length of the palpebral lobe is about one-third the sagittal glabellar length exclu- sive of the occipital ring. The posterior limbs are down- sloping, have a deep posterior border furrow, and are bluntly terminated; the transverse length is about two- thirds of the basal glabellar width. The external surfaces of all convex parts are thickly covered with granules. This species is associated with Glossopleura in the youngest collection from the Glossopleum Zone in the southern Great Basin. There are no comparable forms known from the Glossopleum Zone elsewhere, but the general morphology, particularly the glabellar shape and REFERENCES CITED deep glabellar furrows, suggests a possible relationship to trilobites of the younger Middle and Late Cambrian family Lonchocephalidae. Occurrence.-—Rare, uppermost Glossopleum Zone. Nevada, Bonanza King Formation: 7199—CO (2 cranidia), Striped Hills. Ptychopariid pygidium undet. 1 Plate 14, figure 23 Discussion .——Several small simple transversely subellip- tical pygidia are characterized by a prominent slightly tapered axis bearing two ring furrows posterior to the articulating furrow. The pleural regions are crossed by three broad shallow pleural furrows that reach to the inner edge of a slightly raised posteriorly tapered border. These appear to be ptychopariid pygidia and may belong to a species of Nyella, which is the commonest ptychopariid in the collection with these pygidia. The specimens lack obvious ornamentation, however, so the affiliation with the granular Nyella cranidia is uncertain. Occurrence.—Moderately rare, Albertella Zone, Zacan- thoidid Zonule. Nevada: 3766—CO (5 pygidia), Nevada Test Site. Ptychopariid pygidium undet. 2 Plate 14, figure 24 Discussion—A single pygidium has the general morph- ology of a pygidium assigned to Nyella granosa (Resser) by Fritz (1968, pl. 39, figs. 12, 13). It is characterized by a transversely elliptical shape, a poorly defined axis, one deep narrow pleural furrow, and an unusual fold of the exoskeleton producing a narrow furrow wrapping around the posterior end of the axis. The surface is covered with closely spaced granules. This pygidium differs from the one illustrated by Fritz by having an ornamentation of only one size of granules. Without more specimens, the affinities of this pygidium are un- certain. 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A Page A-shale member of Pioche Shale .............. 18 Abstract ................................... 1 Abu Dhabi complex, Persian Gulf, limemud accumulation ................... 35 progradation, per-itidal sequences ........ 52 Acrocephalites trifossatus ........... 101 aequus, szacantlwides ........ 97 Agnostus bonnerensis ........... . . . 76 lautus ................................. 76 Agmulos champs ........................... 115 stator ...................... . 109 agrestis, Ptarmigania ....................... 79, 95 alums, Prozacanthoides ..................... 97 Zacanthoides .................... 18, 62, 97; pl. 11 Albertella . ... 86, 93,101,109, 112,119 baswartht . ................. 86, 93, 94 dispar ................................. 87 helena ................................. 86 Iangwelli . . ........ 18, 20, 62, 87, 89: pl. 9 maladensis ............................. 87, 91 micmps ................................ 87 mischi ..................... 87, 91 nitida ...................... 87 pandispinata ............... . . . 87 pmueedara ............................. 87 recfimarginatus ........................ 87, 90 ressensis ................... 87 sampsoni .................. . . . 87 schenki ........... 62, 88; pl. 9 similaris ............................... 94 spectrensis .................... 18, 20. 62. 88; pl. 9 stenorhachis . 87, 94 Albertella Zone ..... 17. 59, 76, 77, 80, 82, 83, 84, 85, 87, 88, 89, 90, 91, 92, 93, 94, 96, 97. 98. 99. 102. 103, 104, 109, 111. 112, 114, 116, 117, 119, 121; pie. 7, 9, 10, ll, 12, 13, 14, 15 Albertella-Mexicella Zonule .......... 18, 60, 61. 87, 88, 89, 90, 93, 96, 98, 109, 114, 117 Jangle Limestone Member ........... 60 Albertellina ............................. 89 aspinosa . . . . . . . 18, 62. 89, pl. 10 Albertelloides , . . ......... 86, 90, 94, 105 mischi .......... . . . 17, 62, 90; pl. 10 rectimarginatus ..... . 18. 62, 91; pl. 10 sp ......................... 20 Albite ..................................... 23 Algal-boundstone lithofacies ................. 22, 42 Algal limestones, cliff-forming . . . . . 4 Gold Ace Limestone Member . . ..... 13 Allochems .......................... 23, 42 Alokistacare . . . 99 species 1.... .............. 99; pl. 15 species 2.... .. 100; pl. 15 sp ...................................... 62 Alokistocarella ............................. 100, 120 brighamensis .............. 21, 22, 100. 120; pl. 15 typicalis ............................... 100, 104 sp ...................... altifmntatus, Olenellus ...... altilis, Ptarmigania ......... Amecephalina .............. Amecephalus ............................... 99, 119 INDEX [Italic page numbers indicate major references] Page Analysis, paleontological .............. , ..... 4 petrographic .................. 2 sedimentologic ................... 2 sedimentologic-environmental ........... 2 sedimentologic-faunal ................... 2 Andros Island, Bahamas, lime-mud accumula- tion ............................ 36 progradation, peritidal sequences ........ 52 Antagmidae ................................ 104 Antagmus ...................... 104, 118 ........... 104 anteros, Bathyun'scus (Poliella) .............. 79 Bristolia ................... 13, 57, 62, 63, 71; pl. 1 sp ............................ 63, 65, 71; pl. 1 antiqua, Elrathinu ...... 20, 62, 103; pl. 15 23 Aphelotaxon ............................... 113 amneicauda, Ptarmiganoides ................ 95 arcuatus, Olenellus . . . . . . 9, 56, 62, 67, 73; pl. 2 arenosa. Pagetia . . . . ............... 77 Arenosus .................................. 77 arrojosensis, Caborcella ..................... 101 aspinosa, Albertellina . . . . . 18, 62, 89; pl. 10 Athabaskia ostheimeri . ......... 98 sp ............................. 98 augusta, Crepicephalus ...................... 105 Kochaspis ....................... 17, 62, 105; pl. 8 write, Ptarmigania . . . 95 Avwatz Pass, fossil localities ................ 69 Azure Ridge ................................ 2, 33 B Bahama Islands, progradation. peritidal se— quences ........................ 52 Bahama Platform, carbonate study .......... 21 platform-interior blanket sands .......... 41 Bare Mountain ............................. 2. 20 Bare Mountain quadrangle .................. 4, 14 Bathyun'scus-Elrathina Zone ................ 59, 103 Balhyun'scus howelli lodensis ............... 78 (Kootenia) .............................. 81 dawsoni ............................ 81 (Poliella) .. . 79 anteros . 79 Bathyurus parvulus ........................ 81 Battus integer ......................... . 75 bearensis, Paulsenia ........................ 110 Belted Range ........ . . 2, 16, 33. 39, 54, 58, 59. 61 fossil localities .................. 72, 76, 77, 80. 83. 85, 103, 104, 108, 116 Ogygopsis Zonule ....................... 59 vertical transitions ....................... 53 Biceratops nevadensis ................. 17 Bioherms, stromatolitic ............ 9 Bird’s-eye limestone ............. 7 bispinosa, Ptarmiganoides ....... . . 95 boccar, Doliclwmetopus ..................... 78 Bolaspidella ................................ 1 17 Bonanza King Formation . . . 4, 21, 60, 98, 121 Glossopleura .......... 60, 78 bonnerensis, Agnostus . . . . . . . 76 Peronopsis ............................. 76; pl. 12 Page Bonnie ............................. 81 columbensis . .............. 81 app .................................. 62, 81; pl. 5 Bonnie-Olenellus Zone ...................... 56, 70 bones, Pagetia ...... 77 bosworthi, Albertella . 86, 93 Paralbertella .................. 18, 62, 87, 94; pl. 9 bowensis, Ptanniganoides ................... 94 brachyamma, Olenellus ................ 17, 62, 68; pl. 2 brevispina, Kootenia . . . 82 Peachella .......................... 13, 62, 75,- pl. 5 brighamensis, Alokistocarella . . . 21, 22, 100, 120; pl. 15 Perorwpsis ............................. 76 Bright Angel Shale .......... . .. 5, 14, 18. 21 bristolensis, Bristolia 13, 62, 64, 71; pl. 1 Mesomzcis ............................. 63 Olenellus ............................... 64 Bristolia , . . . .................... 63 anteros . . . ......... 13. 57. 62, 63, 71; pl. 1 bristolensis ......... 13. 62. 64, 71; pl. 1 fragilis ........................ 13, 62, 65. 71; pl. 2 groenlandicus ........ . . 65 insolens ....... 64 kentensis .............................. 65 Zone ................................... 66, 81 Zonule ......................... 13,57, 60. 64, 65. 66, 70, 74, 75, 81, 118 sp ...................................... 56 Burrowers. Callinassa ....................... 36 Gold Ace Limestone Member ............ 14 limemudstone lithofacies ........... 21. 29, 33, 36 oolite litbofacies ........................ 39 Red Pass Limestone Member ............ 17 C C-shale member of Pioche Shale .............. 16, 105 Caborca, Mexico, Albertella Zone ............ 60 Caborcella ........................ 99, 101, 110 arrojosensis . . . 101 climolimbata . . 110 gmnosa ................................ 111 pseudaulax ..................... 18, 62, 102,- pl. 13 mm . . . .................... 110 reducta ........................ 18. 62. 102; pl. 13 Cadiz Formation ..................... 6, 16, 20, 21. 39 oolites .......................... 17. 39 Calcarenite. pelloidal . .................... 9 Calcite ....................... 7, 14. 23, 36. 42 Callavia nevadensis ......................... 73 Cauianassa ................................ 36 Cambrian continental shelf .................. 2 Campeche Bank, Mexico, carbonate study . . .. 21 Canadian Rocky Mountains, Grand Cycle ..... 51, 54 Ogygopsis ......................... . 59 Plagiura-Kochaspis Zone ............ 69 Carbonate Belt ......................... . . 2 Carbonate interbeds ........................ 9 Cat Cay sand belt, Bahama Islands, cements- tion ....................... 39 ceccina, Kochaspis .......................... 106 car-cops, Plagiura ............. 17. 59. 62, 113, 115; pl. 6 Ptyclwparis ............................ 112 127 128 Page Chambless Limestone .................... 6, 14, 33, 58 Olenellus multinadus .................... 73 Chamosite ............................. 7 Chancia . . . .................. . 102 ebdome . . . .............. 102 maladensis . . 20, 62, 103; pl. 15 uenusta ............. . . 18, 62, 103; pl. 13 champs, Syspacephalus . .......... 119 Chert ...................................... 23 Chisholm Shale ............................. 5, 21, 54 Chlorite ........................ 23, 36, 42 clarki, Olenellus ............. 13, 17, 60, 62, 66, 68; pl. 3 Paedeumias . . . .................... 68 Clay minerals ............................. 23, 36, 42 clinolimbata, Caborcella ..................... 110 Nyella ..................... 18,62,110, 121; pl. 14 clytia, Pagetia . 77 collar-is, Schistometopus ..................... 115 columbensis, Bonnia .................... 81 columbiana, Nyella . 111 Poulseru'a .......................... . 110 Combined Metals Member, Pioche Formation . . 14, 58, 61 Olenellus ............................... 67, 72 comis, Dolichometopsis ............... 80, 95 cammunis, Dolichometopsis ........... 95 connexa, Volocep'halina ...... . . 18, 62, 116,- pl. 14 Conacephalites cordillerae ................... 103 subcomnatus ........................... 99 contra-ta, Volocephalina . . . . . 20, 62, 116‘; pl. 14 convexus, Schistometapus ................... 115 cordillerae, Conocephulites ................. 103 Corynexochid, cranidium undetermined 1 . 62, %; pl. 16 pygidium undetermined 1 ............. 62, 98; pl. 9 pygidium undetermined 2 ...... 62, 98,- pl. 10 Carynexochida ............................. 77 Corynexochus (Bonnia) ...................... 81 cranidium undetermined 1, Corynexochid . . .. 98; pl. 16 cmsaxis, Ptarmiganoides ............ 18, 62, 95; pl. 11 Crepicephalus augusta . . . .......... 105 liliana ........................... 105 Cucomungo Canyon section . . . 2, 7, 13, 39, 56, 57 fossil localities ................. 64, 65, 75, 81, 118 oolites ................................. 39 stromatolites . . . . .............. 7 vertical transitions . .............. 53 cylindricus, Olenellus . . . . 9. 56. 62. 69, 70; pl. 2 Cyphambon ................................ 104 D dawsoni, Bathyuriscus (Kootenia) ............ 81 declivis, Paralbertella ....................... 87 decarosus, Prozacanthoides .................. 97 Deformation. penecontemporaneous .......... 16 Delamar Mountains ......................... 2, 13, 58 fossil localities . . . ....... 67, 73, 105 Depositional model .. ............ 51 Desert Range ...................... 2, 7, 13, 18, 20, 33 fossil localities ........ 64. 65. 68, 69, 73, 74, 75, 79, 88, 89. 90, 101.109, 112, 114, 117, 118, 119 Desert Range Limestone Member . . . . 6, 2a 54, 60 Glossopleum ............ . . . . 60 Detrital Belt ............................... 2, 21 dignata, Ptarmigania ....................... 79, 95 dispar, Albertella ...... 87 Dolichometopidae .......................... 78 Dolichametopsis ............................ 94 camis ............... commurus ........... grauis .............. gregalis ................................ lepida .................................. mansfieldi . media ............... potens .............. poulseni ................................ propinqua .............................. 95 Stella .................................. 95 INDEX Page Dalichometopus boccar ..................... 78 lodensis ....................... 78 Dolomite ......... . . 4, 14, 18, 23, 36, 42 Dorypygidae .................... 81 Duan Hills ..................... 2 fossil localities .......................... 75 E Eagle Mountain .......................... 2, 9, 20, 33 fossil localities .................. 65. 69. 70, 72, 73 75. 79, 87. 93, 100, 109, 114 Eagle Mountain Shale Member. .. 6. 9, 21, 36, 56, 58, 60 ebdome, Chancia ............................ 102 Echo Canyon section .................. 2, 9, 13, 20, 59 fossil localities ........... 65, 66, 68, 69, 72, 73, 74, 75. 79, 87, 101, 109, 111. 114, 115,116, 117, 118, 119, 120 stromatolites ........................... 13 Echo Shale Member ................ 6, 9, 13, 21, 36, 58 Ehmaniella ................... 100, 102 maladensis ............................. 103 Eiffelaspis ................................. 105, 107 eiffelensis, Kochaspis . 106 eiloitys, Paralbertella . 87 Elmthina ............ 103 antiqua ........................ 20, 62, 103; pl. 15 parallela ............................... 104 sp ........................... 59 Embolimus spinosa . . . ........... 96 Emigrant Formation ............ 6, 14, 18, 20, 33 Emigrant Pass Member. Zabriskie Quartzite .. 7, 8 Eodiscidae ........... 76 Eoptychoparia ....... 104 normalis ............................... 104 piochensis .......................... 62, 105; pl. 7 Eureka mining district 57 eurpyaria, Olenellus . . . . 13, 62, 67, 69; pl. 2 exigua, Ptarmigam‘a . . 95 exilis, Prozacanthoides . . . . 97 expansa, Glossopleura ...................... 79 extensu, Plagimu .................... 17, 62, 113; pl. 6 superba ............ 92 sp ................................ 17. 62, 92' pl. 6 Florida Platform, carbonate study . . . z ....... 21 Formations, Bonanza King .................. 4, 60 Cadiz ........................ 6, 16. 20, 21, 39 Emigrant .......... 6, 14, 18, 20, 33 Stephen ................................ 59 ............. 5. 9, 13 Tapeats Sandstone . fi'agilis, Bristolia . . . fremonti, Mesonacts Olenellus ............... 13, 17, 62, 68, 69, 70; pl. 3 (Fremontial ......................... 70 Fremontia ................... . . . 66 (Fremontial fremonti, Olenellus .............. 70 French Mountain ........................... 5 Frenchman Mountain . . . . 2, 6, 13, 18, 33 Funeral Mountains . . . . ...... 2, 13, 39, 51, 56, 61 Echo Canyon section, fossil localities . . . . 65, 66, 68. 69, 72, 73, 74, 75, 79, 87, 101, 109, 111, 114, 115, 116, 117, 118, 119, 120 fossil localities ....................... 7 1, 72, 75 1 1 l ..... l 1 5 Ptychopariid ...................... 1 19 Pyramid Peak section, fossil localities . 89, 109, 117 furcuta, Fiekiaspis .......................... 92 G Page gallagari, Pachyaspis ........... 18, 62, 112, 118; pl. 15 gennana, Kootenia ..................... 17, 62, 81, 82 Poliella ............................ 18, 62, 80, 95 Ptarmigania ......... 95 gigas, Antagmus .............. . . 104 gilberti, Olenellus ........... 17, 60, 62, 63, 66, 71; pl. 3 Gimanella ................................. 23 Glossopleura, Bonanza King Formation . 60, 78 Desert Range Limestone Member . . . 60 Grand Canyon .......................... 78 Glossopleum .......................... 21, 78, 98, 120 expanse . . ................. 79 lodensis . . ................ 21, 62, 78; pl. 16 mckeei . ....................... 79 sulcata ................................. 79 tuta ................................ 62. 78,- pl. 16 walcott‘i ......................... 21, 62, 79; pl. 16 Zone . 1, 20, 60, 78, 98, 100, 101, 112, 121; pls. 15,16 Zonule ................... 49, 60, 79, 100, 101, 120 Gold Ace Limestone Member ............. 6, 13, 21, 33, 39, 49, 56, 58, 60 algal limestone .................... . 13 burrowers .............................. 14 deposition .............................. 53 fossil localities ........... . 67, 81. 118 Olenellus ............................... 67, 72 oolites ................................. 39 Gold Ace Mine . ................ . 14 Goldfield Hills . . .............. . . 2, 14, 44 Grand Canyon ....................... . 5, 35 Albertella schenki ....................... 88 Glossopleura ........................... 78 Grand Cycle ..................... 1, 51, 54, 59 stromatolites . ................ . 54 formation ......................... . . 63 gmndoculus, Mexicella .............. 18, 62, 109; pl. 13 gmnosa, Caborcella ................... 111 Nyella ............... 18, 62, 111, 121; pl. 14 Poulsenia .............................. 101, 110 Grapevine Mountains ............. 5, 13, 18, 56, 57, 61 fossil localities ..................... 64, 65. 66, 68 Titanothere Canyon section ..... . . 57 fossil localities ....... 64, 65, 66, 69, 72, 73, 74, 75, 79, 92, 93, 96, 98, 109, 110, 115, 116, 117 gmuis, Dolichometopsis .............. 79, 95 Great Bahama Bank ................. . 23, 35 lime-mud accumulation .................. 35 oncolite development .................... 23 Great Barrier Reef, Australia ......... 35 carbonate study ................. 21 gregalis, Dolichometopsis ............ . 95 gmenlandicus, Bristolia ..................... 65 Groom Range ........... 2, 16. 18, 20, 33, 39, 54, 59, 61 fossil localities ...... 80. 82, 106, 107, 112, 113. 119 vertical transitions ...................... 53 Zacanthaides sp ......................... 61 groomensis, Kochiellina ......... 17, 62, 106, 107; pL 8 H Halfpint Range ............................. 20 Harkless Formation ................... . 56 Harrington Sound, Bermuda ................ 35 helena, Albertella ........................... 86 Hematite .................................. 23, 36 hexacantha, Ptarmiganoides . . ...... 18, 62, 96; pl. 11 Highland Range ........................ 2, 5, 13, 18 fossil localities .......................... ' 105 Hornfels ................................... 21 howelli, Olanellus ........... 13, 60, 62, 64, 67, 72; pl. 4 lodensis, Bathyuriseus .................. 78 I idahoensis, Thomocare .............. 20, 62, 85; pl. 12 Tonkinella ............................. 85 iddingsi, Olenellus .......................... 74 Peachella ......................... 13, 62, 75; pl. 5 Page immaderata. Nyella 5p ............... 18 62 110; pl. 14 incertus, Oryctocephalites .......... . . 84 Inglefieldia ..................... . . 104 Inner Detrital Bell: .......................... 2. 21 insolens, Bristolia .......................... 64 Introduction ...... Inyo Mountains ................. vertical transitions ...................... J Jangle Limestone Member ...... 6, 20. 33. 39. 49. 59. 60 oolites ................................. 20. 39 Jangle Ridge area. Nevada Test Site ...... 2. 13, 20 fossil localities ................ 81. 106. 108 janglensis, Kochiellina . . . . . 17 . 62. 107; pl. 8 judithi, Paralbertella ........................ 87 K hentensis, Bristalia ......................... 65 Kinzers Formation... ........ 59. 67 klotzi, Ogygia ..................... 82 Kochaspid trilobites . .................. 17 Kochaspid Zonule ....... 17. 59. 106, 107. 108. 113, 115 Kochaspid. species undetermined 1 ....... 62. 108,- pl. 8 species undetermined 2 .............. 62. 108,- pl. 8 Kochaspis . . . ............. 90. 92. 99. 105, 107 augusta . . . ..... 17. 62, 105; pl. 8 ceccina ........................... 106 eiffelensis .............................. 106 liliana ................ 17. 62. 106; pl. 8 sp ..................................... 106,- pl. 8 Kochiella .. . ........................... 99. 107 Kochiellina . . . . ............ 99. 105. 106 groomensis . . . . 17 62 106. 107; pl. 8 janglensis . . . ....... 17 62. 107; pl 8 Kochina ................................... 99 macrops ............................... 108 uenusta . . . .................... 103 Kootenia .......................... 81 brevispina. .................... germane .............. (Kootenial, Bathyunscus .................... dawsoni, Bathyunscus .................. L lancestraides, Oryctocephalus ............... 83 Las Vegas Range ........................... 2. 39 Last Chance Range .......... 2, 7. 13.20.39. 54, 56. 58 Cuoomungo Canyon section. fossil localities . 64, 65. 75. 81, 118 stromatolites ........................... 44 law. Paralbertella . . . 87 Latham Shale ......... . . 6, 9. 13.21.57. 58 lautus. Agnostus . . . ............ 76 Pemapsis ...................... . 18, 20, 76 lead ore ............................. 22 Lena Stage. Siberia. Plagiura tribolites. 59 lepida. Dalichometapsis ..................... 95 liliana. Crepicephalus ....................... 105 Kochaspis .................. 17. 62, 106; pl. 8 limbota. Paralbertella . . . ........ 87 Lime-mudstone lithofacies ............ 2 burrowers .................. 21. 29. 33. 86 Limestone, Chambless .......... . .. 6. 14.33.58 Lithofacies, algal-boundstone ..... 42 carbonate .............................. 49 description ............................. 21 interpretation ............. 21 oolite ....................... 36 Localities ......................... 2 lodensis, Bathyuriseus hawelli . ....... 78 Dolichometopus ............... 78 Glassopleuru ....... . . . 21. 62. 78; pl. 16 lomataspis, Poliella ...... . .......... 17. 58, 62. 80; pl. 6 longus, Syspacephalus ............... 17. 62. 115; pl. 7 INDEX Page longwelli, Albertella ............. 8. 20. 62, 87, 89; pl. 9 Luyella .................................... 104 Lyndon Limestone ................... 5. 18, 33. 39. 59 M Mecannaia ................................. 76‘ maladensis . . . . .......... 62. 76; pl. 12 macmps. Kochina . . . .............. 108 maior, Onchocephalus ....................... 107 maladensis. Albertella ...................... 87. 91 Chancia ...................... 20. 62.103; pl. 15 Ehmaniella .. .................. 103 Macanmu'a . . . . ........... 76; pl. 12 Oryctocephalina ................. 18. 62. 83; pl. 12 Pagetia ........................ . 20. 76, 77 (Mesopagetial ........... . 76 mansfieldi, Dolichometopsis ................. 95 Map. isopach ............................... 10, 11 localities ................. ... 3 Marble .......................... 22 Marble Mountains ........... 2. 6. 13, 18. 33.39. 57 58 mckeei, Glossopleura ....................... 79 media. Dolichometopsis ..................... 95 propinqua .............. 95 Meriwitica Tongue .......................... 33 Mesonacis ................................. 66 bristolensis .................. 63 fremonti ...................... 70 Metaline Limestone. Ogygopsis . . ......... 59 mexicana, Mezicella ................ 18. 62, 108; pl. 13 Mexicaspis ................................. 92 radiatus . . 20, 62, 92; pl. 10 stenopyge .............................. 92 Mexicella ............................ 108 grandee-ulna .................... 18. 62. 109; pl. 13 meacicuna ............... . 18. 62, 108. 109; pl. 13 stator ................ . . 17. 62. 109; pl. 8 microps, Albertella ......................... 87 Miller Mountain ............................ 2 minor, Plagium ......... . 18, 20. 62. 114; pl. 13 minute. Thomocare ............ 85 Vistoia .................... 85 mischi, Albertella ........................... 87. 91 Albertelloides . .................. 17. 62. 90; pl. 10 Model, depositional ......................... 51 Molluscs. Red Pass Limestone Member ....... 17 Monola Formation ....................... 6. 14. 18. 20 Mule Spring Limestone... . 6. 13.21.44. 53. 57 deposition ........................... 53 mulnnodus, Olenellus ....... 17 56 58 62 67 72, pl 4 N “Narrows . Echo Canyon ................... 13, 59 Mtalis, Ptarmigania . . . . ............... 95 Nevada Test Site ..... 2. 18, 58, 59. 61 fossil localities ................. 66. 69, 72. 75. 76. 77. 79. 80. 81. 82. 83. 84. 91. 92. 94. 96. 97, 98. 99. 101. 102, 103. 108. 111. 112. 113. 115. 117, 119. 121 Zacanthoides sp ......................... 61 neuadensis, Bicemtops . ................. 17 Callavia ......................... 73 Olenellus .................. 9. 62, 67, 73,- pl. 4 Puedeumias ....................... 73 nitida. Albert‘ella . ................. 87 NopahRange... .............. 2.7.9.16. 20. 33. 39 normalis, Eoptychoparia .................... 104 Northern Panamint Mountair 5. See Panamint Mountains. Northern Resting Springs Range. See Resting Springs Range. Nomaphus ......................... 81 Nyella, Funeral Mountains . 111 Nyeua .............................. 99.102 110, 119 clinolimbata . . columbiana .. gmuosa .................... 18. 62, 111. 121; pl. 14 129 Page .. 18.62. 110; pl. 14 ........... 1 l l skapta ................................. 111 nyensis, Oryctocephalus .................. 17. 84; pl. 6 0 Oak Spring Summit ......................... 58 obscurus. Syspacephalus ........ . 18. 62. 116; pl. 7 ocellata, Pagetia ................. 77 Ogygia hlotzi ............................... 82 Ogygopsididae ............................. 81 Ogygapsis, Belted Range ......... . . 61. 83. 103 Ogygopsis . . . ..................... 61. 81. 82. 103 typicalis .. ............... 20, 62, 82, 103; pl. 12 Zonule ........... 18, 59, 61. 76.77.83.85. 103.104 Belted Range ....................... 59 Olekminsky horizon. Siberia ................. 59 Olenellidae . . . 63 Olenellids ................................. 17 Olenellus. Combined Metals Member. Pioche Shale ...................... . 67. 72 Gold Ace Limestone Member ..... 67. 72 Olenellus .................................. 63, 66 ' ......................... 70 9. 56. 62. 67, 73; pl. 2 ..... 9. 56, 68. 69 brachyomma . . . 17. 62, 68,- pl. 2 bristolensis ............................. 64 clarki ................... 13. 17, 60. 62. 66. 68; pl. 3 cylindricus ......... . . 9. 56. 62. 69. 70; pl. 2 euryparia ............... 13. 62. 67. 69; pl. 2 fremonti. .............. 13. 17. 62. 68. 69; pl. 3 gilberti ................. 17. 60. 62. 63, 66. 71; pl. 3 hawelli ............... 13. 60. 62. 64. 67. 72; pl. 4 iddingsi . . ..................... 74 multinodus ............. 17. 56. 58. 62. 67. 72; pl. 4 Zonule ................... 14. 17. 49. 58, 60, 73 nevadensis .............. 9, 62, 67. 73; pl. 4 puertoblanooensis .......... 13. 60, 62. 67. 74; pl. 4 truemani ............................... 71 Zone ....................... 56‘, 60; pls. 1, 2. 3. 4. 5 fossil localities .............. 68. 69, 71. 72. 74 (Fremontial fremonn' . 70 sp ................................ 13. 62. 74; pl. 4 Olenus thompsom' .......................... 66 Onchocephalus ................ . . 104. 117 maior ..................... 107 solitarius .................. . 1 l7 Ooids ...................................... 36 Oolites. Cadiz Formation .................... 17. 39 Cucomungo Canyon ...... 39 deposition ............... 41 Gold Ace Limestone Member . 39 grainstone ................ . . . . 36 J angle Limestone Member . . ...... 20. 39 lime-mudstone lithofacies . . . ...... 88 lithofacies .............................. 36 borrowers .......................... 39 Pahrump Hills Shale Member . ...... 18 Panamint Range ................ 39 Paymaster Canyon ............... 14. 39 Red Pass Limestone Member . ...... 17. 39 southern Last Chance Range . . ........ 39 optatus. Prozacanthoides ............. 97 amata. Ptarmigania ......... 95 Oryctocephalid species undetermined ........ 85; pl. 12 Oryctocephalidae ........................... 83 Oryctocephalimz ............. 83 lancastroides ................ 83 maladensis ...................... 18. 62, 8.9; pl. 12 reticulum .............................. 83 Oryctocephalites ...... 83, 84 incenus ................................ 84 reason“ . . ........................... 84 typiculis . . . . . 18, 62. 83; pl. 13 Oryctocephalus . . .......... 88, 84 nyensis.... ....... 17.84;pl.6 pn'mus ................................. 84 130 Page ostheimeri, Athabaskia ..................... 98 Outer Detrital Belt 2 P Pachyaspis ................................ 112 gwagari ................... 18,62,112, 118; pl. 15 typicalis ........................... 1 12 Paralbertella bosworthi 18, 62. 87 , 94; pl. 9 Paedeumias ..................... 66 clarki ....................... 68 nevadensis ............................. 73 puertoblancaensis ....................... 74 Pagetia .................... 77 arenosa .................. boates ................... clytia . . . . maladensis ocellata . . . resseri .......................... 18. 62, 77; pl. 12 rugosa .......................... 20, 62, 77; pl. 12 (Eopagetia/ resseri ...................... 77 (Mesopagetia/ maladensis ............... 76 sp .......................... . 17. 62, 77,-pl. 12 Pahrump Hills .......................... 2. 18. 33. 39 Pahrump Hills Shale Member ...... 6, 18, 21. 54, 59, 60 evaporites .............................. 49 oolites . . . . Panamint Mountains . . . . . pandispinata, Albertella ..................... Pumlbertella .............................. 59. 86. 93 bosworthi ..... 18, 62. 94; pl. 9 declivis ................................ 87 eiloitys ................................ 87 judithi .................... 37 lam ......................... 87 Iimbam ..................... 87 mbsanensis ............................ 87 pamllela, Elrathina ......................... 104 Pampaulsenia ......... 110 Parker Slate ................................ 67 paruulus. Bathyurus ................ 81 Paymaster Canyon .... 2. 13, 39 Dumas ........................ 14, 39 vertical transitions . . . ........ 53 Peachella .................................. 74 brevispina ........................ 13. 62, 75; pl. 5 iddingsi ............. . . 13, 62. 75; pl. 5 sp ...................................... 57 Pelmicrites ................................. 23 Pelsparites ...................... 23 Periommella ...................... l 1 7 perola. Syspacephalus ........ . 1 16 Peronopsis ................................. 75 bonnerensis ............................ 76‘; pl. 12 brighamensis . . . . 76 ........ 18.20.76 sp ....................... 20, 62. 76,- pl. 12 Persian Gulf. carbonate study ............... 21 lime-mud accumulation .................. 35 acid formation ................. . . 42 progradation. peritidal sequences ........ 52 Piazella .................................... 104 118 Pioche Formation. . . 14, 58 . 2, 57, 61 5 9 13, 21. 57 67 62 105,- pl. 7 9 Plagiura, Funeral Mountains ................ 115 Plagiura ................................... 112, 119 cercops . ......... 17. 59. 62. 113, 115; pl. 6 extensa . . . . . . ......... 17, 62, 113; pl. 6 minor ....................... 18. 20, 62. 114; pl. 13 retracta ......................... 17, 62. 113; pl. 6 Plagiura-Kachaspis Zone .............. 59, 92. 98, 107 “Plagium-Poliella" Zone ..... 17. 58, 80. 81.85.92, 106. 107, 108. 110. 113, 115. 116, 119; pls. 6. 7, 8 INDEX Page Plagiurella ................................. 1 12 Poikilotopic fabric ............... . 23 Poliella ................... 79, 94, 108 germana ....... .18. 62, 79, 95; pl. 11 lomataspis ..... . . 17. 58, 62, 80; pl. 6 Zonule ..................... 17,58, 80. 81. 108 (Paliella) anteros, Bathyuriscus ....... 79 Bathyun'scus ................ 79 Porphyrotopic fabric . . . 23 potens, Doliclwmetopsis ........... . 79, 95 poulseni,Dolichometopsis................... 95 Poulsenia bearensis ......................... 110 columbiana . . . 110 gmnosa ................................ 101. 110 primus, Oryctocephalus ..................... 84 pmpinqua, Dolichometopsis ................. 95 Ptarmiganoides ......................... 95 proveedora, Albertella . . . . 87 Providence Mountains ................. 2, 6. 14, 33, 39 Prozacantlwides aequus ..................... 97 alatus .......... 97 decomsus .............................. 97 exilis .................................. 97 optatus ................................ 97 stissingensis ........................... 97 pseudaulax, Caborcella . . ....... 18. 62, 102; pl. 13 Ptarmigania ........................ 95 agrestis . . . . ................. 79. 95 ultilis .................................. 79. 95 aurita .................................. 95 dignatu . . . . ................. 79, 95 exigua ............................ 95 germana .......................... 95 natalis ........................ 95 ornate .......................... 95 rossensis .................... 96 sobrina ................................ 80. 95 Ptarmiganoides ........................... 86, 93, 94 amneicauda . . . . . . . 95 bispinosa ........ 95 bowensis ......... 94 crassuxis ........................ 18. 62, 95; pl. 11 hextwantha ...................... 18. 62, 96; pl. 11 propinqua ............ 95 Ptychugnostus ............................. 76 Ptychoparia cercops ........................ 1 1 2 skapta .......................... 1 10 Ptychopariid, Funeral Mountains . . ....... 119 pygidium undetermined 1 . . . . . 63, 121; pl. 14 pygidium undetermined 2 ........... 63, 121; pl. 14 species undetermined l .............. 63. 117; pl. 5 species undetermined 2 . . . . 63. 118; pl. 5 species undetermined 3 .............. 63, 118; pl. 5 species undetermined 4 .............. 63. 118; pl. 5 species undetermined 5 ...... . 63, 118; ,pl. 15 species undetermined 6 ...... . 63, 119; pl. 15 species undetermined 7 ...... . 63. 119; pl. 15 species undetermined 8 .............. 63, 119; pl. 8 species undetermined 9 ............. 63, 119; pl. 14 species undetermined 10 ..... . 63, 120; pl. 15 species undetermined 11 ..... . 63, 120; pl. 15 species undetermined 12 ..... . 63. 120; pl. 15 Ptychopariid trilobites .................. 13. 17. 21, 58 Ptychopariida .............................. 99 puertoblancoensis, Olenellus . . . . 13, 60. 62, 67, 74; pl. 4 Paedeumias ............................ 74 Pyramid Peak section, Funeral Mountains . . . 2. 14, 20, 51 fossil localities ...................... 89. 109. 117 Pyramid Shale Member ..... 6. 14. 36, 53. 56, 57, 58, 60 deposition .............................. 53 Pyrite ..................................... 23. 42 Q. R Quadmgnostidae ........................... 75 Quartz ................................... 23, 36, 42 Quartz arenite .............................. 7 Quartzite .................................. 4, 7 Page radiatus, Mexicaspis ................. 20, 62. 92; pl. 10 rura, Caborcella . . . . 110 N yella ................................. 1 1 1 Piazella ................................ 118 rectimarginatus, Albertella .................. 87, 90 Albertelloides ................... 18, 62. .91.- pl. 1'0 reducta, Caborcella ................. 18, 62, 102; pl. 13 Red Pass Limestone Member ............. 6, 17, 21. 33, 39, 51, 58. 59 bur-rowers .............................. 17 oolites ............ I7, 39 Plagium .......... 115 Ptychopariid sp ......................... 1 19 ressensis. Albertella ........................ 87 ressen, Oryctocephahtes .......... 84 Pagetia ................... 18 62, 77; pl 12 (Eapagetia) ..................... 77 Resting Springs Range ............ 2, 13. 16, 18. 20. 39 fossil localities ....... 65, 69. 71, 72, 73, 75, 98. 109 reticulum, Oryctocephalina .................. 83 retracta, Plagiura .................... 17, 62. 113; pl. 6 mbsonensis, Parulbertella 87 rossensis, Ptarmigania ............... 96 mgosa, Puget-in ...................... 20.62.77, pl. 12 S Saline Valley Formation ................... 6. 9, 56. 59 Salt Spring Hills ............................ 2 fossil localities ......................... 69. 71, 72 sampsoni. Albertella . ................... 87 schenki. Albertella . . ........ .62. 87; pl. 9 Schistometopus . . ........ .92, 99, 105.115 collan‘s ................................. 115 conuexus ............................... 1 15 spp .............................. 17,62,115, pl 8 Sediments, marine carbonate ................ Shale ....................................... 4, 7, 18 Shark Bay. Western Australia. carbonate study .. Sheep Mountain . . . . Silurian Hills ............................... similar-is, Albertella ......................... 94 simpta, Nyella ..................... 1 11 Ptychapan'u , . ............... 110 sobrina, Ptarmigania . . . . ............... 80, 95 solitarius, Onchocephalus . ............... 117 Sonoraspis ................................ 78 Southern Panamint Mountains. See Panamint Mountains. Southern Resting Springs Range. See Resting Springs Range. Southern Shelf Lagoon, British Honduras, lime- mud accumulation ............... 35 spectrensis, Albertella ........ . . 18. 20, 62, 88; pl. 9 spinosa. Embolimus ................. 96 Spring Mountains . . . . ....... 2, 33 fossil localities ....................... 87. 98. 109 Spectre Range .............................. 2. 18 fossil localities . . . . 89, 90. 109 stator. Agmulos . . . . . . ....... 109 Mexicella ......... . . . 17. 62. 109, pl. 8 Stella, Dolichometopsis ...................... 95 stenopyge, Mexicaspis ...................... 92 stenorhachis, Albertella ............ 87, 94 Stephen Formation, Ogygopsis ..... 59 stissingensis, Prozacanthoides . . . . . 97 Stotacephalus ..................... 99 Striped Hills .................. 2, 13, 21. 39. 60 fossil localities . . . . 78. 79. 98. 100, 101, 121 Stromatolites .............................. 7, 13 algal‘boundstone lithofacies ............. 42 Cucomungo Canyon ......... 7 Echo Canyon ............... 13 Grand Cycle ................ . . . 54 southern Last Chance Range ............. 44 Thimble Limestone Member ............. 9 subcoronazus, Conacephalites ...... 99 sulcata, Glossopleum ....................... ' 79 Page superba. Fieldaspis ......................... 92 Susan Duster Limestone Member. Pioche Shale ........................... 58 Syspacephalus . . . . 115 champs ....... . . 119 longus .......................... 17, 62. 115; pl. 7 obscurus ........................ 18. 62. 116; pl. 7 pemla .................................. 116 T Taconic region. New York ................... 59 Tapeats Sandstone ....................... 5. 9. 13 Taxioura ................................... 82 Tecopa quadrangle ......................... 7 Thimble Limestone Member . . 6. 9, 13, 21. 33. 56. 57, 60 stromatolibes ........................... 9 Thimble Peak ....................... 13 thompsoni, Olenus . .................... 66 Thomacare ......................... 85 idahoensis ....................... 20. 62. 85; pl. 12 minute ................................. 85 Tincanebits Tongue ........... Titanothere Canyon section . . . . fossil localities ........ 64. 65. 66. 69, 72, 73, 74, 75 79. 92. 93, 96. 98. 109, 110. 115. 116. 117 Tankinella ........ 85 idahaznsis ......................... . . 85 trifossatus, Acrocephalites .................. 101 tmemani, Olenellus ......................... 71 INDEX Page tutu. Glassopleura ...................... 62. 78; pl. 16 . . . . . . . . 104 Ogygopsis .......... . 20. 62. 82, 103; pl. 12 Oryctocephalites ................. 18, 62. 83; pl. 13 Pachyaspis ............................. 112 U. V Ubehebe Crater ............................. 2 Vanuyemella ............................... 86 vun'acantha, Zacanthaides ..... . 18. 62. 97; pl. 11 venusm, Chancia ................... 18. 62, 103; pl. 13 Kochina ................................ 103 Vistoia minute .................. 85 Valocephalina ...................... 116 connexa .................. 18, 62; 116; pl. 14 contracta ....................... 20. 62. 116; pl. 14 W walcotti. Glossopleura . . . . . . 21, 62. 79,- pl. 16 Warmen'a ..................... 56 White Mountains ........................... 56 White Pine Range .......................... 59 Winters Pass ............................... 2. 33 Y, Z Yucca Flat ................................. 4 131 Page Zabriskie Quartzite ......................... 4. 56 Zacanthoides ............................... 86. 96 alatus ........................... 18, 62. 97,- pl. 11 variacantha ........... 18. 62. 97; pl. 11 sp .......................... 18. 60, 62. 98; pl. 6 Groom Range . ............. 61 Zacanthoidid Zonule ................ 17,59, 61. 76, 77, 80, 82. 83. 84, 91, 92. 94. 96. 97. 98. 99. 102. 103. 111, 112. 117. 121 Zacanthoididae . . . . ...................... 85 Zinc ore ........................... 22 Zone. Albertella ................. 17. 59, 76. 109: pls. 7. 9. 10, 11, 12. 13.14,15 Bathyuriscus—Elrathina ................. 59 Bonnia-Olenellus ....................... 56. 70 Bistolia ................................ 66. 81 Glossopleura .................... 1. 20, 60, 78. 98, 101. 112, 121; pl. 16 Olenellus ............... 56, 60, 68; p15. 1, 2, 3. 4. 5 Plagiura-Kochaspis ................ 59, 92. 98. 107 “Plagiura-Poliella" ............ 17. 58. 80, 92. 106. 107, 108. 110, 113; pls. 6. 7. 8 Zonule, Albertella-Mexicella ....... 18. 60. 87, 109. 114 Bristolia ............... 13. 57, 60, 64. 70. 118 Glossopleura ........... . . 49. 60, 79. 100. 120 Kochaspid ................. .. 17, 59, 106. 113 Ogygopsis ......... 18.59, 76,83,103 Olenellus urcuatus ...................... 9. 56, 68 multinodus ............... 14. 17. 49. 58, 60. 73 Poliella lomamwis . . .......... 17, 58, 80, 108 Zacanthoidid .............. 17. 59, 77, 91. 111. 117 PLATES 1— 16 Contact photographs of the plates in this report are available, at cost, from the US. Geological Survey Photographic Library, Federal Center, Denver, Colorado 80225. PLATE 1 OLENELLUS ZONE FIGURES 1—13. Bristolia anteros n. sp. (p. 63). 1. 2. 3—6. 7,8. 9,12. 10. ll. 13. Cephalon, stage I, X15, USNM l77l79a. Cephalon, stage II, X12, USNM 177l79b. Cephala, stage III, X12, USNM 177179c—f. Cephala, stage IV, X12, USNM 177179g, h. Cephalon, top View and anterior oblique view showing eye sur- face, stage V, X6, USNM 177180. Closeup of glabella of holotype showing ornamentation, X6, USNM 177181. Latex cast of holotype cephalon, X2.5, USNM 177181. Cephalon, stage V, X3, USNM 177182. All except figures 9 and 12 from USGS colln. 4144—CO, Grape- vine Mountains, Calif. Specimen in figures 9 and 12 from USGS colln. 3694—CO, Nevada Test Site. 14—19. Bristolia bristolem's (Resser) (p. 64). 14, 15. 16. 17. 18. 19. Top and right side views of latex mold of cephalon, X1.5, USNM 177183. USGS colln. 4144—CO, Grapevine Moun- tains, Calif. Cephalon, Xl.5, USNM 177184, USGS colln. 4153—CO, Fu— neral Mountains, Calif. Cephalon, X 1.5, USNM 177185, USGS colln. 3673—CO, Resting Springs Range, Calif. Cephalon, Xl.5, USNM 177186, USGS colln. 4168—CO, Salt Spring Hills, Calif. Cephalon, X2, USNM 177187, USGS colln. 4144—CO, Grapevine Mountains, Calif. GEOLOGICAL SURVEY PROFESSIONAL PAPER 104'] PLATE! $8 ‘mx } e CLEVELLUS ZONE PLATE 2 OLENELLUS ZONE FIGURES 1—6. Bristoliafrag'ilix n. sp. (p. 65). l. Cephalon, X2, USNM 177188, USGS colln. 3694—CO, Nevada Test Site. 2. Immature silicified cephalon, stage III, X 10, USNM177189a. 3. Immature silicified cephalon, stage IV, X5, USNM l77189b. 4. Holotype cephalon, X 1.5, USNM 177190. All from USGS colln. 4144—CO, Grapevine Mountains, Calif. 5. Latex cast of cephalon, X1.5, USNM 177191, USGS colln. 6399—CO, Desert Range, Nev. 6. Cephalon, X2, USNM 177192, USGS colln. 3786—CO, Nevada Test Site. 7, 8. Olenellus brachyomma n. sp. (p. 68). 7. Holotype cephalon, X3, USNM 177193. 8. Closeup of genal spine, X6, USNM 177194. Both from USGS colln. 3696—CO, Desert Range, Nev. 9, 10, 13, 14. Olenellus cylindricw n. sp. (p. 69). 9. Latex cast of small cephalon, X2, USNM 177195. 10. Latex cast of larger cephalon, X 1.5, USNM 177196. 13. Holotype cephalon, X 1.5, USNM 177197. 14. Questionably assigned cephalon lacking advanced genal spines, X1, USNM 177198. All from USGS colln. 4146—CO, Grapevine Mountains, Calif. 11, 12. Olenellus arcuatm n. sp. (p. 67). 11. Latex cast of cephalon, X3, USNM 177199, USGS colln. 4146—CO, Grapevine Mountains, Calif. 12. Holotype cephalon, X3, USNM 177200, USGS colln. 3148—CO, Funeral Mountains, Calif. 15—18. Olenellm emyparia n. sp. (p. 69). 15. Left part of large cephalon showing intergenal spine, X1, USNM 177201. 16. Cephalon, X2, USNM 177202. 17. Cephalon, showing ornamentation, X2, USNM 177203. 18. Holotype cephalon, X1.5, USNM 177204. All from USGS colln. 3680—CO, Eagle Mountain, Calif. PROFESSIONAL PAPER 1047 PLATE 2 GEOLOGICAL SURVEY OLENELLUS 20 N E PLATE 3 OLENELL US ZONE FIGURES 1—5. Olenellw clarki (Resser) (p. 68). 1, 2. Cephala showing differences due to deformation, X 1.5, USNM 177205, 177206, USGS colln. 2304—CO, Funeral Mountains, Calif. 3. Latex cast of cephalon, X1, USNM 177207, USGS colln. 4168—CO, Salt Spring Hills, Calif. 4. Latex cast of cephalon, X1, USNM 177208, USGS colln. 6399—CO, Desert Range, Nev. 5. Latex cast of cephalon showing ornamentation, X3, USNM 177209, USGS colln. 2304—CO, Funeral Mountains, Calif. 6—13. Olenellus gilberti Meek (p. 71). 6—8. Latex casts ofcephala showing variation in outline due to distor- tion, X 1, USNM 177210, 177211, 177212, USGS colln. 2304—CO, Funeral Mountains, Calif. 9. Latex cast of cephalon, X0.7, USNM 177213, USGS colln. 4153—CO, Funeral Mountains, Calif. 10. Latex cast of large cephalon, X0.5, USNM 177214. 11. Latex cast of cephalon, X 1.5, USNM 177215. Both from USGS colln. 4168—CO, Salt Spring Hills, Calif. 12. Small cephalon, X2, USNM 177216, USGS colln. 4153—CO, Funeral Mountains, Calif. 13. Cephalon, X1, USNM 177217, USGS colln. 3681—CO, Eagle Mountain, Calif. 14-17. Olenellusfremonti (Walcott) (p. 70). 14. Cephalon, X1, USNM 177218. 15. Cephalon, Xl.5, USNM 177219. 16. Latex cast of cephalon, X 1.5, USNM 177220. All from USGS colln. 2304—CO, Funeral Mountains, Calif, showing variability of advancement of genal spine. 17. Cephalon, X1, USNM 177221, USGS colln. 4168—CO, Salt Spring Hills, Calif. PROFESSIONAL PAPER 1047 PLATE 3 OLENELLUS 20 N E PLATE 4 OLENELL US ZONE FIGURES 1—9. Olenellw multinodm n. sp. (p. 72). 1. Latex cast of small cephalon, X45, USNM 177222. 2, 3. Latex casts of cephala showing effects of deformation, X3, USNM 177223, 177224. All from USGS colln. 2304—CO, Funeral Mountains, Calif. 4. Latex cast of holotype cephalon, X4, USNM 177225, USGS colln. 3097—CO, Funeral Mountains, Calif. 5. Latex cast showing profile of left side of cephalon and axial nodes, X4, USNM 177226, USGS colln. 3676—CO, Resting Springs Range, Calif. 6. Plaster replica of cephalon, X2, GSC 16858, GSC loc.42591, Jasper Park, Alberta, Canada. 7. Closeup of opisthothorax of specimen shown in figure 8, X6, USNM 177227. 8. Only known specimen showing thorax, X3, USNM 177227, USGS colln. 7224—CO, northern Delamar Mountains, Nev. 9. Cephalon, X3, USNM 177228, USGS colln. 3095—CO, Pana- mint Range, Calif. 10, 13, 17. Olenellus nevademis (Walcott) (p. 73). 10. Latex cast of cephalon, X1, USNM 177229, USGS colln. 4144—CO, Grapevine Mountains, Calif. 13. Latex cast of cephalon, X2, USNM 177230, USGS colln. 3148—CO, Funeral Mountains, Calif. 17. Cephalon, X2, USNM 177231, USGS colln. 4144—CO, Grapevine Mountains, Calif. 11, 14. Olenellm puertoblancoensis (Lochman) (p. 74). 11. Latex cast of cephalon, X3, USNM 177232. 14. Latex cast of cephalon, X2, USNM 177233. Both from USGS colln. 4145—CO, Grapevine Mountains, Calif. 12, 15. Olenellus sp. 1 (p. 74). 12. Closeup of glabella and ocular lobe of specimen in figure 15 showing ornamentation, X4, USNM 177234. 15. Cephalon, X2, USNM 177234, USGS colln. 7184—CO, Grapevine Mountains, Calif. 16. Olenellus howelli? (Meek) (p. 72). Cephalon X2, USNM 177235, USGS colln. 4145—CO, Grapevine Mountains, Calif. GEOLOGICAL SURVEY (> PROFESSIONAL PAPER [047 PLATE 4 OLENELLUS ZONE PLATE 5 OLENELL US ZONE FIGURES 1—3. Peachella brevispina n. sp. (p. 75). 1. Holotype cephalon, X2, USNM 177236. 2. Cephalon, X3, USNM 177237. Both from USGS colln. 4167—CO, Dublin Hills, Calif. 3. Cephalon, X2, USNM 177238, USGS colln. 3679—CO, Eagle Mountain, Calif. 4—9. Peachella iddingsi (Walcott) (p. 75). 4. Holotype cephalon, X2, USNM 15407a, USNM 10c. 52, Eureka, Nev. 5. Typical surface showing only tumid spines of P. iddmgsi, X 1, USNM 177239, USNM loc. 22s. 6. Small silicified cephalon, X5, USNM 177240, USGS colln. 4144—CO, Grapevine Mountains, Calif. 7, 8. Latex casts of cephala, X2, USNM 177241, 177242. 9. Cephalon, X2, USNM 177243. All from USGS colln. 3786—CO, Nevada Test Site. 10, 11. Bannia spp. (p. 81). 10. Cranidium, X4, USNM 177244, USGS colln. 3646—CO, Nevada Test Site. 11. Small cranidium, X9, USNM 177245, USGS colln. 7181—CO, Last Chance Range, Calif. 12, 13. Ptychopariid sp. undet. 1 (p. 117). 12. Latex cast of cranidium, X8, USNM 177246, USGS colln. 7179—CO, Last Chance Range, Calif. 13. Cranidium, X6, USNM 177247, USGS colln. 7192—CO, Desert Range, Nev. 14. Ptychopariid sp. undet. 2 (p. 118). Cranidium, X3, USNM 177248, USGS colln. 4153—CO, Funeral Moun- tains, Calif. 15. Ptychopariid sp. undet. 3 (p. 118). Latex cast of cranidium, X8, USNM 177249, USGS colln. 7194—CO, Desert Range, Nev. 16. Ptychopariid sp. undet. 4 (p. 118). Latex cast of cranidium, X8, USNM 177250, USGS colln. 7188—CO, Funeral Mountains, Calif. GEOLOGICAL SURVEY OLENELLUS 20 N E FIGURES 1—5, 12. 6—10. 11. 13—15. 16. 17—20, 23. 21, 24—27. 22. PLATE 6 “PLAGIURA-POLIELLA” ZONE Poliella lomatzupis n. sp. (p. 80). 1. Free cheek, X10, USNM 177251. 2, 3. Top and oblique views of holotype cranidium, X6, USNM 177252. 4. Pygidium, X5, USNM 177253. 5. Latex cast of pygidium, X12, USNM 177254. All from USGS colln. 4434—CO, Belted Range, Nev. Poliella cf. P. lomataxpis n. sp. (p. 80). 6. Cranidium, X10, USNM, l77255a. 7. Free cheek, X10, USNM 177255d. 8. Thoracic segment, X10, USNM 177255c. 9. Hypostome, X10, USNM 177255b. 10. Pygidium, X10, USNM 1772556. All from USGS colln. 3790—CO, Nevada Test Site. Zatanthoidex? sp. (p. 98). Pygidium, X4, USNM 177256, USGS colln. 4140—CO, Grapevine Mountains, Calif. Oryctocephalus nyensis n. sp. (p. 84). 13. Latex cast of holotype cranidium, X5, USNM 177257. 14. Latex cast of pygidium, X5, USNM 208042. 15. Latex cast of thorax and pyg‘idium, X5, USNM 208043. All from USGS colln. 4435—CO, Belted Range, Nev. Fieldaspis? sp. (p. 92). Pygidium, USNM 208044, USGS colln. 4139—CO, Grapevine Moun- tains, Calif. Plagium extema n. sp. (p. 113). 17. Holotype cranidium, X 10, USNM 208045. 18. Exfoliated cranidium, X5, USNM 208046. 19, 20. Top and oblique views, small cranidium, X 10, USNM 208047. 23. Free cheek, X 10, USNM 208048. Figures 17, 18, and 23 from USGS colln. 3691—CO, Groom Range, Nev. Figures 19 and 20 from USGS colln. 3546—CO, Nevada Test Site. Plagium retrmta n. sp. (p. 114). 21. Small cranidium, X 10, USNM 208049. 24. Free cheek, X8, USNM 208050. 25. Cranidium, X10, USNM 208051. 26, 27. Top and oblique views, holotype cranidium, X6, USNM 208052. All specimens from USGS colln. 3546—CO, Nevada Test Site. Plagiura cf. P. cercops (Walcott) (p. 115). Incomplete cephalon, X5, USNM 208053, USGS colln. 7189—CO, Fu- neral Mountains, Calif. PLATE 6 PROFESSIONAL PAPER 1047 GEOLOGICAL SURVEY “PIAGIURA-POLIELLA” 20 N E PLATE 7 “PLAGIURA-POLIELLA” AND ALBERTELLA ZONES FIGURES 1—5. Eoptychoparia piochemis n. sp. (p. 105). 1. Free cheek, X4, USNM 208054. 2. Latex cast ofcranidium and partial thorax, X5, USNM 208055. 3. Latex cast of surface of shale showing abundance of specimens and effects of tectonic distortion, X5, USNM 208056. 4. Holotype cranidium,><6, USNM 208057. 5. Left lateral view of partially preserved complete specimen, X6, USNM 208058. All from USGS colln. 7231—CO, “Plagium—Poliella” Zone, Highland Range, Nev. 6—13, 15. Syspacephalm obscurus n. sp. (p. 116). 6. Typical cranidium, X 10, USNM 208059. 7. Free cheek, X8, USNM 208060. 8, 12. Top and right side views of holotype cranidium, X 10, USNM 208061. 9. Small cranidium showing dorsal furrows moderately well de- veloped, X20, USNM 208062. 10. Cranidium—variant with unusually well developed glabellar furrows, X15, USNM 208063. 11. Rostral plate, silicified, X 10, USNM 208064. 13. Pygidium, X10, USNM 208065. 15. Pygidium, X 10, USNM 208066. All from USGS colln. 4140-CO, Albertella Zone, Grapevine Moun- tains, Calif. 14, 16—18. Syxpacephalus longus n. sp. (p. 115). 14. Latex cast of free cheek, X5, USNM 208067. 16. Latex cast of pygidium, X8, USNM 208068. 17. Latex cast of cranidium and attached thorax, X5, USNM 208069. Note—small bumps on cranidium are artifacts of preparation. Surface is smooth. 18. Latex cast of holotype specimen, X5, USNM 208070. All from USGS colln. 4435—CO, “Plagiura-Poliella” Zone, Belted Range, Nev. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1047 PLATE 7 “PLAGIURA-POUELLA” AND ALBERTELIA ZONES FIGURES 1, 2, 5, 6. 3, 4, 7. 8, 12, 13. 9, 14, 17, 18. 10,11. 15,16. 19. 20, 24. 21, 22. 23. PLATE 8 “PLAGIURA—POLIELLA” ZONE Schistometopm spp. (p. 115). l. Cranidium, X3, USNM 208071, USGS colln. 4139—CO Grapevine Mountains, Calif. 2. Cranidium, X6, USNM 208072, USGS colln. 3546—CO, Nevada Test Site. 5. Pygidium, X3, USNM 208073, USGS colln. 4139—CO, Grapevine Mountains, Calif. 6. Cranidium, X 10, USNM 208074, USGS colln. 3546—CO, Nevada Test Site. Kochiellz'na groomemis n. gen., n. sp. (p. 107). 3. Holotype cranidium, X4, USNM 208075. 4. Free cheek, X6, USNM 208076. 7. Pygidium, X5, USNM 20807621. All from USGS colln. 3691—CO, Groom Range, Nev. Kochaspis liliana? (Walcott) (p. 106). 8. Latex cast of cranidium, X4, USNM 208077. 12. Pygidium, x5, USNM 208078. 13. Pygidium, X8, USNM 208079. All from USGS colln. 3546—CO, Nevada Test Site. Kochaspid sp. undet. 1 (p. 108). 9, l4. Oblique and top views of cranidium, X6, USNM 208080. 17. Free cheek, X8, USNM 208081. 18. Cranidium, X6, USNM 208082. All from USGS colln. 4434—CO, Belted Range, Nev. Kochaspis? sp. undet. (p. 106). 10. Cranidium, X2, USNM 208083. 11. Free Cheek, X2, USNM 208084. Both from USGS colln. 3691—CO, Groom Range, Nev. Kochaspis auguxta (Walcott) (p. 105). 15. Pygidium, X6, USNM 208085. 16. Pygidium, X4, USNM 208086. Both from USGS colln. 3691—CO, Groom Range, Nev. Ptychopariid sp. undet. 8 (p. 119). Cranidium, X2, USNM 208087, USGS colln. 4148—CO, Funeral Moun- tains, Calif. Kochiellina janglensis n. gen., n. sp. (p. 107). 20. Holotype cranidium, X2, USNM 208088. 24. Pygidium, X4, USNM 208089. Both from USGS colln. 3546—CO, Nevada Test Site. Kochaspid sp. undet. 2 (p. 108). 21. Cranidium, X10, USNM 208090. 22. Pygidium, X 10, USNM 208091. Both from USGS colln. 3790—CO,Nevada Test Site. cf. Mexicella? stator (Walcott) (p. 109). Cranidium, X3, USNM 208092, USGS colln. 7234—CO, Grapevine Mountains, Calif. ; PLATE 8 PROFESSIONAL PAPER 1 0 4 7 1 23 “PLAGIURA-POLIELIA” 20 N E PLATE9 ALBERTELLA ZONE FIGURES 1—3, 6, 7, 9, 10. Albertella longwelli n. sp. (p. 87). 1. Free cheek, X3, USNM 208093. Cranidium, X3, USNM 208094. Cranidium, X4, USNM 208095. Hypostome, X4, USNM 208096. Free cheek, X4, USNM 208097. Holotype pygidium, X3, USNM 208098. 1 Pygidium, X6, USNM 208099. Figuresl, 2, 9from USGScolln. 1616—CO, Spring Mountains, Nev.; figures 3, 6, 7, 10 from USGS colln. 4165—CO, Eagle Mountain, Calif. 4, 5, 8, 11, 12, 16. Albertella spectrensis n. sp. (p. 88). 4. Cranidium, X4, USNM 208100. 5. Free cheek, X4, USNM 208101. 8. Cranidium, X6, USNM 208102. 11. Hypostome, X5, USNM 208103. 12. Holotype pygidium, X4, USNM 208104. 16. Pygidium, X8, USNM 208105. All from USGS colln. 4169—CO, Spectre Range, Nev. 13—15, 17, 18. Albertella schenki (Resser) (p. 88). 13. Latex cast of cranidium, X3, USNM 208106. 14. Free cheek,x4, USNM 208107. 15. Pygidium, X2, USNM 208108. 17. Latex cast of cranidium, X5, USNM 208109. 18. Latex cast of hypostome, X3, USNM 208110. All from USGS colln. 3543—CO, Desert Range, Nev. 19-25. Paralbertella bosworthi (Walcott) (p. 94). 19. Cranidium, X2, USNM 208111. 20. Cranidium, X3, USNM 208112. 21. Cranidium, X4, USNM 208113. 22. Hypostome, X3, USNM 208114. 23. Pygidium, X2, USNM 208115. 24. Pygidium, X4, USNM 208116. 25. Pygidium, X4, USNM 208117. All from USGS colln. 3766—CO, Nevada Test Site. 26. Corynexochid pygidium undet. 1 (p. 98). Pygidium, x4, USNM 208118, USGS colln. 1616—CO, Spring Mountains, Nev. owswww GEOLOGICAL SURVEY PROFESSIONAL PAPER 1047 PLATE 9 w“ ALBERTELLA ZONE PLATE 10 ALBERTELLA ZONE FIGURES 1—6. Albertella (mimosa n. gen., n. sp. (p. 90). 1. Qweww Latex cast of free cheek, x4, USNM 208119. Cranidium, X3, USNM 208120. Holotype pygidium, X3, USNM 208121‘. Pygidium, X3, USNM 208122. Hypostome, x4, USNM 208123. Pygidium, x4, USNM 208124. Figures 1— 3, 5, 6 from USGS colln. 7195—CO, Desert Range, Nev.; figure 4 from USGS colln. 4169—CO, Spectre Range, Nev 7—13. Albertelloidex mischi (Fritz) (p. 90). 7. 8. 9. 10. 11. 12. 13. Free cheek, X2, USNM 208125. Cranidium, x2, USNM 208126. Articulated specimen, x2, USNM 208127. Free cheek, xl.5, USNM 208128. Pygidium, x3, USNM 208129. Pygidium, x3, USNM 208130. Hypostome and cranidium, x3, USNM 208131. Figure 9 from USGS colln. 3484—CO; all other specimens from USGS colln. 3766—C0; both collections from Nevada Test Site. 14—20. Albertelloides rectimarginatus n. sp. (p. 91). 14. 15. 16. 17. 18. 19. 20. All Free cheek, xl.5, USNM 208132. Latex cast of cranidium, X2, USNM 208133. Cranidium, x2, USNM 208134. Cranidium, X3, USNM 208135. Holotype pygidium, X3, USNM 208136. Pygidium, X3, USNM 2081037. Hypostome, X2, USNM 208138. from USGS colln. 3547—CO, Nevada Test Site. 21. Corynexochid pygidium undet. 2 (p. 98). Pygidium, X4, USNM 208139, USGS colln. 3547—CO, Nevada Test Site. 22—25. Mexicaxpiy radiatus n. sp. (p. 92). 22. 23. 24. 25. All Pygidium, X3, USNM 208140. Holotype pygidium, X3, USNM 208141. Cranidium, X3, USNM 208142. Free cheek, X2, USNM 208143. from USGS colln. 4141—CO, Titanothere Canyon section, Grapevine Mountains, Calif. PROFESSIONAL PAPER 1047 PLATE 10 GEOLOGICAL SURVEY ALBERTELLA 20 N E FIGURES 1—8. Poliella ge 1 . >195"ng 8. All 9—11, 14—16. Ptarmigan 9. 10. 11. 14. 15, 16. All PLATE 1 1 ALBERTELLA ZONE mana (Resser) (p. 79). Latex cast of free cheek, X2, USNM 208144. Cranidium, X2, USNM 208145. Cranidium, X2, USNM 208146. Small cranidium, X5, USNM 208147. Pygidium, X2, USNM 208148. Pygidium, X2, USNM 208149. Hypostome, X3, USNM 208150. Pygidium, X3, USNM 208151. from USGS colln. 3695—CO, Nevada Test Site. oidex hexacantha n. sp. (p. 96). Cranidium, X2, USNM 208152. Cranidium, X3, USNM 208153. Free cheek, X2, USNM 208154. Cranidium, X3, USNM 208155. Top and profile views of holotype pygidium, X3, USNM 208156. from USGS colln. 4141—CO, Titanothere Canyon section, Grapevine Mountains, Calif. 12, 13, 17, 18. Ptarmiganoides crassaxis n. sp. (p. 95). 12. 13. 17. 18. All Cranidium, X2, USNM 208157. Free cheek, X2, USNM 208158. Holotype pygidium, composite photo, X4, USNM 208159. Small cranidium, X6, USNM 208160. from USGS colln. 3766—CO, Nevada Test Site. 19—21. Zacantlwides variacantha n. sp. (p. 97). 19. 20. 21. All Cranidium, x4, USNM 208161. Holotype pygidium, X4, USNM 208162. Latex cast of pygidium, X3, USNM 208163. from USGS colln. 3766—CO, Nevada Test Site. 22—24, 27—30. Kootem'a gen/Lana (Resser) (p. 81). 22. 23. 24. 27. 28. 29. 30. Cranidium, X 1.5, USNM 208164. Cranidium, X3, USNM 208165. Cranidium, X3, USNM 208166. Pygidium, X2, USNM 208167. Pygidium,X 1.5, USNM 208168. Pygidium, X2, USNM 208169. Latex cast of articulated specimen, X 1.5, USNM 208170. Figures 22—28 from USGS colln. 3695—CO, Nevada Test Site; figure 29 from USGS colln. 3547—CO, Nevada Test Site; figure 30 from USGS colln. 3692—CO, Groom Range, Nev. 25, 26. Zamntlwides cf. Z. alatus (Resser) (p. 97). 25. 26. Cranidium, X3, USNM 208171. Pygidium, X4, USNM 208172. Both from USGS colln. 3695—CO, Nevada Test Site. GEOLOGICAL SURVEY ‘ e, M As» 2 ALBERTELLA ZONE «xv PLATE 12 ALBERTELLA ZONE FIGURES 1—4. Ogygopsis typicalis (Resser) (p. 82). 1. Complete individual, X2, USNM 208173. 2. Pygidium, x 1.5, USNM 208174. 3. Latex cast of pygidium, X2, USNM 208175. 4. Hypostome, X3, USNM 208176. All from USGS colln. 4438—CO, Belted Range, Nev. 5. Thoracocare idahoemis (Resser) (p. 85). Pygidium, X 15, USNM 208177, USGS colln. 4438—CO, Belted Range, Nev. 6. Oryctocephalid sp. undet. (p. 85). Pygidium, X3, USNM 208178, USGS colln. 443&CO, Belted Range, Nev. 7. Peronopsis? sp. (p. 76). Pygidium, X 10, USNM 208179, USGS colln. 4437—CO, Belted Range, Nev. 8, l2. Macmmaia malademis (Resser) (p. 76). 8. Cranidium, X20, USNM 208180. 12. Pygidium, X20, USNM 208181. Both from USGS colln. 4436-CO, Belted Range, Nev. 9, l3. Pagetia rugom (Rasetti) (p. 77). 9. Cranidium, X20, USNM 208182. 13. Pygidium, x20. USNM 208183. Both from USGS colln. 4438-CO, Belted Range, Nev. 10, 14. Pagetia sp. (p. 77). 10. Cranidium, X20, USNM 208184. 14. Pygidium, x20, USNM 208185. Both from USGS colln. 3766—CO, Nevada Test Site. 11, 15. Peronopsis bonneremis (Resser) (p. 76). ll. Cephalon, X 10, USNM 208186, USGS colln. 4437-CO. l5. Latex cast of pygidium, X10, USNM 208187, USGS colln. 4438—CO. Both from Belted Range, Nev. 16—20, 23—26. Pagetia resseri (Kobayashi) (p. 77). 16, 17. Immature cranidia, X30, USNM 208188g, f. 18. Immature pygidium, X30, USNM 208188j. 19. Small cranidium, X 15, USNM 208188e. 20. Cranidium, X 15, USNM 208188b. 23. Free cheek, X30, USNM 2081883. 24. Pygidium, x15, USNM 208188h. 25. Cranidium, X20, USNM 208189. 26. Pygidium, X20, USNM 208190. Figures 18—20, 23, 24 from USGS colln. 3547—CO; figures 25, 26, from USGS colln. 3766—CO; both from Nevada Test Site. 21, 22, 27. Oryctocephalina malademis (Resser) (p. 83). 21. Cranidium, X4, USNM 208191. 22. Cranidium, X5, USNM 208192. 27. Cranidium, X5, USNM 208193. All from USGS colln. 3766—CO, Nevada Test Site. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1047 PLATE 12 25 ALBERTELLA ZONE PLATE 13 ALBERTELLA ZONE FIGURES 1—4. Omctocephalites typicalis (Resser) (p. 84). 1. Cranidium with weak furrows, X8, USNM 208194. 2. Typical cranidium, X8, USNM 208195. 3. Small cranidium, X8, USNM 208196. 4. Pygidium, X8, USNM 208197. All from USGS colln. 3766—CO, Nevada Test Site. 5, 9, 10. Mexicella grandoculus n. sp. (p. 109). 5, 9. Top and oblique views, holotype cranidium, X6, USNM 208198. 10. Small cranidium, X 12, USNM 208199. All from USGS colln. 4141—CO, Titanothere Canyon section, Grapevine Mountains, Calif. 6. Caborcellu pseudaulax n. sp. (p. 102). Holotype cranidium, composite photo, X 3, USNM 208200, USGS colln. 3547—CO, Nevada Test Site. 7, 8. Caborcella reducta n. sp. (p. 102). 7. Holotype cranidium, X3, USNM 208201. 8. Cranidium, X3, USNM 208202. Both from USGS colln. 3547—CO, Nevada Test Site. ll, 12. Chancia cf. C. venusta (Resser) (p. 103). ll. Latex cast of cranidium, X3, USNM 208203. 12. Small cranidium, X6, USNM 208204. Both from USGS colln. 3547-CO, Nevada Test Site. 13—21. Mexicella mexicana (Lochman) (p. 109). 13. Free cheek, X4, USNM 208205. 14, 15. Top and oblique views of cranidium, X8, USNM 208206. 16. Large cranidium, X3, USNM 208207. 17. Free cheek, X 10, USNM 208208. 18. Large cranidium, X2, USNM 208209. 19. Cranidium, X6, USNM 208210. 20. Cranidium, X 10, USNM 208211. 21. Free cheek, X 10, USNM 208212. Figures 13-17 from USGS colln. 7196—CO, Desert Range, Nev.; figures 18, 19, from USGS colln. 3543—CO, Desert Range, Nev.; figures 20, 21, from USGS colln. 4165—CO, Eagle Mountain, Calif. 22—25. Plagium minor n. sp. (p. 114). 22. Cranidium, X10, USNM 208213. 23. Free cheek, X 10, USNM 208214. 24. Holotype cranidium, X 10, USNM 208215. 25. Free cheek, X 10, USNM 208216. Figures 22, 23 from USGS colln. 4165—CO, Eagle Mountain, Calif.; figures 24, 25 from USGS colln. 7196—CO, Desert Range, Nev. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1047 PLATE l3 ALBERTELLA 20 N E PLATE 14 ALBERTELLA ZONE FIGURES 1—4. Nyella clinolimbata (Fritz) (p. 110). 1,2. Top and oblique views of cranidium, X6, USNM 208217. 3. Cranidium, X5, USNM 208218. 4. Free cheek, X4, USNM 208219. All from USGS colln. 3766—CO, Nevada Test Site. 5—10. Nyella granosa (Resser) (p. 111). 5. Free cheek, X5, USNM 208274. 6. Cranidium, X4, USNM 208275. 7. Cranidium, X8, USNM 208276. 8. Pygidium, X8, USNM 208277. 9. Cranidium, X4, USNM 208278. 10. Cranidium, X8, USNM 208279. Figures 5—8 from USGS colln. 3695—CO, Nevada Test Site; figure 9 from USGS colln. 4440—CO, Groom Range, Nev.; figure 10, from USGS colln. 3766—CO, Nevada Test Site. 11, 12. Nyella immoderata n. gen., n. sp. (p. 112). 11. Holotype cranidium, X6, USNM 208280. 12. Cranidium, X10, USNM 208281. Both from USGS colln. 3766—00, Nevada Test Site. 13-16, 20. Volocephalina amtracta n. gen., n. sp. (p. 117). 13, 14. Top and oblique views, holotype cranidium; X12, USNM 208282. 15. Cranidium, X 10, USNM 208283. 16. Cranidium, X 10, USNM 208220. 20. Free cheek, X 10, USNM 208221. Figure 13-15 from USGS colln. 4158—CO, Pyramid Peak section; figures 16, 20 from USGS colln. 4149—CO, Echo Canyon sec- tion; both in the Funeral Mountains, Calif. 17, 18, 21, 22. Volocephalina connexa n. gen., n. sp. (p. 117). 17, 18. Top and oblique views of holotype cranidium, X8, USNM 208222. 21. Latex cast of cranidium, X 10, USNM 208223. 22. Cranidium, X10, USNM 208224. Figures 17, 18, 21, from USGS colln. 3547-CO, Nevada Test Site; figure 22 from USGS colln. 4141—CO, Titanothere Canyon section, Grapevine Mountains, Calif. 19. Ptychopariid sp. undet. 9, (p. 119). Cranidium, X5, USNM 208225, USGS colln. 4440—CO, Groom Range, Nev. 23. Ptychopariid pygidium undet. 1, (p. 121). Pygidium, X 8, USNM 208226, USGS colln. 3766—CO, Nevada Test Site. 24. Ptychopariid pygidium undet. 2, (p. 121). Pygidium, X 8, USNM 208227, USGS colln. 3766—CO, Nevada Test Site. PROFESSIONAL PAPER 1047 PLATE 14 GEOLOGICAL SURVEY V v ‘ , { ALBERTELLA 20 N E FIGURES 1—8. 9—14. 15. 16. 17, 21. 18. 19, 20. 22. PLATE 15 ALBERTELLA ZONE Elrathma antiqua n. sp. (p. 103). 1. Holotype, nearly complete individual, X4, USNM 208228. 2. Cranidium, X6, USNM 208229. 3. Free cheek, X6, USNM 208230. Figure 1 from USGS colln. 4437—00; figures 2, 3 from USGS colln. 4438—CO; both from Belted Range, Nev. . Chanda? malademix (Resser) (p. 103). Cranidium, X4, USNM 208231, USGS colln. 4438—CO, Belted Range, Nev. . Ptychopariid sp. undet. 5 (p. 118). Cranidium,><10, USNM 208232, USGS colln. 3547—CO, Nevada Test Site. . Ptychopariid sp. undet. 6 (p. 119). Cranidium,X l2, USNM 208233, USGS colln. 3766—CO, Nevada Test Site. . Ptychopariid sp. undet. 7 (p. 119). Cranidium,X 6, USNM 208234, USGS colln. 3695—CO, Nevada Test Site. . Pachyaspix gallagan' (Fritz) (p. 112). Complete individual, X 4, USNM 208235, USGS colln. 3692—CO, Groom Range, Nev. GLOSSOPLEURA ZONE Alokistowrella? cf. A. bn'ghamensis (Resser) (p. 100). 9. Free cheek, X4, USNM 208236. 10. Cranidium, X3, USNM 208237. 11. Cranidium, X5, USNM 208238. 12. Pygidium, X4, USNM 208239. 13. Cranidium, X3, USNM 208240. 14. Free cheek, X3, USNM 208241. Figures 9—12 from USGS colln. 4155—CO, Echo Canyon section, Funeral Mountains, Calif.; figures 13, 14 from USGS colln. 3590—CO, Striped Hills, Nev. Ptychopariid sp. undet. 10 (p. 120). Cranidium, X5, USNM 208242, USGS colln. 4155—CO, Echo Canyon section, Funeral Mountains, Calif. Ptychopariid sp. undet. 11 (p. 120). Cranidium, X8, USNM 208243, USGS colln. 4155—CO, Echo Canyon section, Funeral Mountains, Calif. Alokistocarella? sp. (p. 101). 17. Latex cast of cranidium, X5, USNM 208244, USGS colln. 3545—CO, Nevada Test Site. 21. Cranidium, X6, USNM 208245 USGS colln. 3767, Nevada Test Site. Alokistomre sp. 1 (p. 99). Latex cast of cranidium, X4, USNM 208246, USGS colln. 7198—CO, Eagle Mountain, Calif. Ptychopariid sp. undet. 12 (p. 120). 19, 20. Top and oblique views, cranidium, X8, USNM 208247, USGS colln. 7199—CO, Striped Hills, Nev. Alokistowre sp. 2 (p. 100). Latex cast of cranidium, X4, USNM 208248, USGS colln. 7199—CO, Striped Hills, Nev. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1047 PLATE l5 ALBERTELLA AND GLOSSOPLEURA ZONES PLATE16 GLOSSOPLE URA ZONE FIGURES l—5, 9, 10. Glossopleura lodemis (Clark) (p. 78). 1. Free cheek, X2, USNM 208249. Cranidium, X2, USNM 208250. Cranidium, X4, USNM 208251. Pygidium, X4, USNM 208252. Pygidia,X3,USNM 208253. Pygidium, X3, USNM 208254. 1 . Pygidium, X4, USNM 208255. Al from USGS colln. 7198—CO, Eagle Mountain, Calif. 6—8, 11—19. Glossopleum walcom' C. Poulsen (p. 79). 6. Cranidium, X3, USNM 208256. 7. Free cheek, X5, USNM 208257. 8. Small cranidium, X6, USNM 208258. 11. Hypostome, X6, USNM 208259. 12. Hypostome, X5, USNM 208260. 13. Pygidium, X1.5, USNM 208261. 14. Pygidium, X4, USNM 208262. 15. Small pygidium, X6, USNM 208263. 16. Free cheek, X5, USNM 208264. 17. Cranidium, X2, USNM 208265. 18. Pygidium, X2, USNM 208266. 19. Pygidium, X4, USNM 208267. Figures 6-8, 12—15 from USGS colln.4l56-CO, Echo Canyon sec- tion, Funeral Mountains, Calif,; figures 11, 16—19 from USGS colln. 4142-CO, Titanothere Canyon section, Grapevine Moun- tains, Calif. 20, 25. Corynexochid cranidium undet. l (p. 98). 20. Latex cast of cranidium, X5, USNM 208268. 25. Small cranidium, X6, USNM 208269. Both from USGS colln. 7199—CO, Striped Hills, Nev. 21—24. Glosxopleum tutu (Resser) (p. 78). 21. Latex cast of fragmentary cranidium, X4, USNM 208270. 22. Free cheek, X2, USNM 208271. 23. Pygidium, X 1.5, USNM 208272. 24. Pygidium, X3, USNM 208273. All from USGS colln. 7199—CO, Striped Hills, Nev. Opweww GEOLOGICAL SURVEY GLOSSOPLEURA ZONE aU.S, GOVERNMENT PRINTING OFFICE: 1979—677-129/9 .00 .2 030020522 03:0205 9020;: 02022020: 0::0205 x005. 20:3 0::0205 100005 .2220 03:0205 3020:: 209202 0:0:000nw III .00 00:0:05 III Eoo_m>>v 0.0200000: 00:0:05 III 1.00005 0020:0002: 0:0:01m: PLATE 17 .00 n.0:0:000:0._:0:< 200500 000003 05030005 .00 .2 0002200 02:0:Q000:0> 100000 2:020:00 0:020::< .00 .2 .6222 05.2005 20E:00._ 0200.002: 0:00:02 .00 .2 0002.300 02:00:02.0: .00 .2 002020000 0:020:20. 100005 000205 0:022 . .00 .2 00002052 05:0205 7. III 2022 20:20 0302020 IIIII m .0005 .00 0:500:05 III .00 .2 0222023002: 0::0205 I 100005 220:0 03:0:05 III Eco—0:5: 0.0200000: 0::0205 TI] .00 .: 0:502: 0:80.20 III 3020;: 200202 0:0:000Q III .00 .: 0020020 0:0:0._2N .II .00 0:825 III F .0005 .00 21000550 (IUS. GOVERNMENT PRINTING OFFICE: l979—677—I29/9 PROFESSIONAL PAPER 1047 3674—CO O range; open box indicates second area of occurrence EXPLANATION Cbk—Bonanza King Formation indicates second area of occurrence Carrara Formation species listed Fossils noted, not collected Species occurrence and EARLY CAMBRIAN PART ONLY Ccem—Eagle Mountain Shale Member Ccdr—Desert Range Limestone Member ch—Jangle Limestone Member cha—Gold Ace Limestone Member Cz—Zabriskie Ouartzite Cce—Echo Shale Member Cot—Thimble Limestone Member Ccrp—Red Pass Limestone Member €cph—Pahrump Hills Shale Member Cop—Pyramid Shale Member I Sp. Species identification uncertain X cf. Specimen comparable to RESTING SPRINGS RANGE, CALIF. Cms—Mule Spring Limestone Csv—Saline Valley Formation 36775—(30 O 7 3675—CO 4432—CO. Collecting location; open circle Ccem 3673—CO Cct F .00 020000020000 . 1 200300 0:00:03 050100005 0105: 0.02000: 050300005 .00 .2 2022 05.505 .00 .: £030.20: 0:020::< :0E:oo._ 0200.002: 0:00.002 .00 .2 03200.. 00000002 .00 .2 00002052: 0::0205 zoo_0>> 2:202:02: 5:005 0.00:: 2202.0. 00:0205 100005 .0120 03:0:05 .00 .2 0:520: 0:80.:m .00 .2 02.50.50: 0:0:000Q .00 .2 0.200050 00:0205 10.0005 0:020:05: 0:025 DESERT RANGE, NEV. 3544—CO O 3543—CO O 7196—CO O 7195—CO O 3696a-CO O 7193—CO 0 7192—CO O 739210—90, 7194-co 0 III- EAGLE MOUNTAIN, CALI F. 5000c 05: 050300005 NP .0005 .00 0:500:020 r .2005 2:22:05 0200082300 N .00 02003::o:< 100000 2020202022: .< .20 5:058:50? 0028 0.02000: 050300005 .00 .2 :20m .2 0002.300 02502020. .00 .c ~0:::000202m 0:00.002 .00 .2 0:020:00“? 0:020:00: .0005 .00 02:00:03. .00 0.05.305 .00 0::0205 100005 2020:0001: 0:0:0tm— mas—co 3682—CO o 3681—CO o 3686—co o 3679—CO o 3678—CO . ,, 3677—CO 0 4165—CO O L : 7197—CO O Ccdr cha . :~ Cbk 73684—CO» €ce Cct 200300 28:03 050100005 3 .2005 .00 0:500:05 or .0002: .00 0:500:030 100005 002025292: .0. .20 ~0:0500:0._:0:< .00 .0 202.22 05505 .00 00202092200“: .00 .2 503020: 0:020:70. .00 0020:0233 .00 .2 0202020000 2020:? :0E:oo._ 0200.002: 0:00.002 .00 .0 0002200 02:0:0000:0> .00 .2 0200002020 0:00.002 .00 .2 005030 05:0:0000Q0mw w .0005 .00 0:500:0>E 9020;: 02:00:00 .n: .00 05.50E w .0002: .00 21009530 .00 .2 00002052 00:0:05 :00_m>> 0202202.: 00:0:05 1.00005 .2220 00:0:05 .00 .2 0:50;: 0:80.20 3020;: 2002.202 0:0:000n: .00 .2 0020020 0:80.20 N .0005 .00 0:500:03: 100005 0:020:03: 0:0:0tm 0.8.2 2020 30:00 3020;: 0.0200000: 03:0205 .00 .2 050305 0::0205 STRIPED HILLS, NEV. SPECTRE RANGE, NEV. o & CI 7199—CO O 3690—CO O 4169—CO 0 3689—CO O Ccdr PYRAMID PEAK SECTION 0 & E] .00 0.0:0200020203 200500 20003 0500000005 N .0002: E:_2m>0 0200082100 m .2005 .00 210002030 .00 .2 00:00: 0:005:00 100005 0:03:00 .0 .5 0.00:0:0 .00 .2 00202200 02.:0:Q000:0> .00 .2 05028202000: 0020:0233 .00 .2 08500000: 0:005:00 NE“: £00.22 0020:0233 _:mm>0:ov_ .200002 02009: N .0005 £2290 0:500:030 F .0005 E22030 200002030 0 .0005 .00 0:500:030 10E_00 000000222: 0:032 :51”: 80:22:02.:0 0:032 n: 0.0200202: ~02:0:Q0080:20 wawwm 0:00.53 002:0:00000030 100005 20200220: 2302023: .00 .2 002000.20: 0020:2005 .00 .2 0.0800020 002020922205 12020;: E20300: 0:020:55 5:0 0000:00 0:003:03: m .0005 0:500:030 100005 000205 0:032 100000 0202200 020203: 100005 0202200 0:0:0n: 100005 050:0 .N .00 0020:2000N n .0005 .00 0:500:03“. .00 .2 20200000: 00202092205 .00 .2 002000 05.605 9020;: 300mg 03:00:03: 200300 0:00:03 050300005 .00 .2 02020220020 0:52:00: 25:”: ~0:0:E:02:0 0:002 3020;: 020:: 0:00:08: . .00 .2 0002200 02:0:00020> .00 .2 :20m .2 0.020020: 0:52:00: .00 .2 052002 05000202 .00 03520200003004 .00 .2 05200000: 00202002220E .00 .2 00020: 05.505 . .00 .2 020000205 0:00.002 N 0005 .00 2000:03. .00 N00020::2000N .00 .2 0.5005220: .n: .00 0:0:0n: .00 .2 005030 02300000030 .00 .2 03002202: 03:0:05 .. .00 ~0..Q0020E 0.00.2 .2025 00:0:05 .00 0225022000200 100005 .250 0::0205 .0002 .00 2000:03. ECU—0;: ._0m2._02 0:0:000l I 120203: 2050 00:00.00: .20 .00 .2 0020220 0:90.2m . I .00 .2 00002202 00:0205 000_m>> 0202202: .0 :0 0::0205 : .0002: .00 5:02.05 210305 08:20.2: 200.20 0.022 20:0 30:00 .00 .2 02:00:: 0:80.20 10000E 2.20:0 0::0205 F .2005 .00 0:500:030 0.005. ©5030: 00:0205 [II 1:22:00: 2020002030200“: 0::0205 II. 22020;: 0202000002 03:0205 300203: 002.002 0:0:000n: .00 .2 0:59: 0:00.20 .00 .2 0020020 0:30.:m .00 .2 0300020 0::0205 .00 .2 08:02:00 03:0205 FUNERAL MOUNTAINS, CALIF. ECHO CANYON SECTION 0 & I 4156—CO 4155—CO 3148—C9 0 2304—CO, CO, 7188—CO O. 4159—CO, 4154—CO O. 3101-—CO, 4152—CO O 0 "3.047: : 24148—CO, 7189—CO O 'Ennnnuonuunu[u I See Cct CI 59-? [JUDGE rill DEJD J EQUIVALENTS IN SOUTHWEST NEVADA AND ADJACENT AREAS IN CALIFORNIA O O 3693—CO 3547—CO O 0:3545—CO, 3767-CO 0 CC] 3483—00 0 covered 3692—CO o 3691—CO o 354eco o 3790co o :7 "74440430 . 3766—CO GROOM RANGE, NEV. NEVADA TEST SITE— 0 & CI 0 3695—CO GRAPEVINE MOUNTAINS, CALIF. 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GL OSSOPLEURA 20 N E .Qm .: 02%05802 020.29% Eco_m>>v 005% A. .2 .20 0200.0me v .0005 dm 0:500:55 m .0005 .am 025005030 .Qm .: 90503005 5202020 ALBERTELLA 20 N E .00 .: 500523,: 5205020 _II dw .: 0:05.50 5202020 I dw .: 0030505 020:000l too_m>> 0:02:02 .0 vs 5202020 F 30:: dm 5202020 N .605 dm 025005030 “PLAGIURA-POLIELLA” 20 N E 20 N E OLENELLUS 20505 02520 5202020 F .505 .3 0__._ «00:05; v.022 «220302 5202020 305.505 £5000203005Q 5202020 JI _II_II _.le jJI 3020;. 25503 0202000n~ :12le :I_I_II JIJI :: _ .9. .: £052 233$ dw .: 00.650 020000m 00505 02502025 0200th _ _ _ _ v02>. 0552535520 _I_I._JI7 2:00_m>>v 02500000: 5200020 .I dw .: 55:05 5202020 _| dm .: 5000530 5202020 UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY wZONEOI ZO_._.Um._._OU 5.500.200 aU.S. GOVERNMENT PRINTING OFFICE: I979—677-I29/9 COMPOSITE RANGES FOR IDENTIFIED TRILOBITES IN THE CARRARA FORMATION Ptepfiréd on'ééehalf 0f- Natwnal/IemnauticsW'- ‘ min tratian: ‘ I; GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS C colors). Cross-polarized light. Lo darker high-relief pyroxene. Geology of the Apollo 16 Area, Central Lunar Highlands Edited by GEORGE E. ULRICH, CARROLL ANN HODGES, and WILLIAM R. MUEHLBERGER GEOLOGICAL SURVEY PROFESSIONAL PAPER 1048 Prepared on behalf of the National Aeronautics and Space Administration UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON 1981 UNITED STATES DEPARTMENT OF THE INTERIOR JAMES C. WATT, Secretary GEOLOGICAL SURVEY Doyle G. Frederick, Acting Director Library of Congress Cataloging in Publication Data Geology of the Apollo l6 area, central lunar highlands Contributions to astrogeology. Geological Survey Professional Paper l048 Bibliography; p. 534—539. Supt. of Docs. No.: I l9.l6:l048 l. Lunar geology. 2. Project Apollo. I. Ulrich, George E. II. Hodges, Carroll Ann. 111. Muehlberger, William R. IV. United States. National Aeronautics and Space Administration. V. Series. VI. Series: United States. Geological Survey. Professional Paper l048. QB592.G47 559.9'l 80-607170 For sale by the Superintendent of Documents, US. Government Printing Office Washington, DC. 20402 T Af’ f4; "There you are, our mysterious and unknown Descartes highland plains, Apollo 16 is going to change your image.” John Young could hardly have known the truth of his prediction when he first set foot on the lunar surface at the Apollo 16 landing site. His mission was the most surprising geologically and has generated the most controversy of all six Apollo landings. The Descartes region of the central lunar highlands, since its first serious consideration as a site for manned exploration 4 years earlier, had been strongly supported as a place to sample volcanic rocks much different from those of the maria and the basin margins. Three days of field exploration ranging 4 to 5 km from the lunar module failed to turn up a single recognizable volcanic rock. Instead, a variety of breccias, complicated beyond belief, were collected from every location. Crystalline rocks were found whose tex- tures were clearly igneous (see frontispiece), but they were not volcanic. And therein lies the heart of the geologic mystery of Descartes. “Well it’s back to the drawing boards, or wherever geologists go” (T. K. Mattingly, Apollo 16 Command Module Pilot from lunar orbit). PREFACE This volume contains the final results compiled by the Apollo Field Geology Investigations Team for the Apollo 16 mission. Some of the data presented here were reported in preliminary form shortly after the mission (ALGIT, 1972a, 1972b; AFGIT, 1973; Batson and others, 1972; Muehlberger and others, 1972), but most of the discussion and interpretations that follow are products of individual efforts which have incorporated much of the large body of data available from postmission studies of the rocks, the geophysical and geochemical data, and the extensive collection of photographs taken by the Apollo 16 astronaut crew on the lunar surface and from orbit. The chapter format was chosen to permit individual authors to develop their ideas independently, and we trust this approach will serve to stimulate rather than confuse the reader. Our purpose in this volume is to summarize the field observations at the Apollo 16 site and to bring together the various interpretations placed upon these observations by the astronauts and the Field Geol- ogy Team. Much of the extensive geochemical and geophysical data published since 1974 on the Apollo 16 site has not been incorporated or referred to here. The intent is not to provide a grand synthesis but rather to document the local and regional geologic relations and to summarize what inferences can be made from them. Our expectation is that the volume will be used as a reference for researchers desiring more complete information on the geologic context of the Apollo 16 samples and on the interpretations of those intimately involved with the planning, execution, and analysis of the geologic exploration. john Young, Charles Duke, and Kenneth Mattingly deserve special credit for the quality of their performance while exploring this com- plex area on the surface, from lunar orbit, and later in discourse with the lunar science community. Their continuing interest in the develop- ing story of Descartes began with an unwavering enthusiasm for geologic training exercises in the field. With the able help of Anthony England, mission scientist and communicator during the EVA’s, and Friedrich Horz, their geologic trainer in Houston, their competence as scientific investigators reached the high level shown by their ready adaptation to the unexpected conditions encountered on the mission. A significant stimulus to the exceptional performance on the Moon was provided by the outstanding backup crew, Fred Haise, Edgar Mitchell, and Stuart Roosa, whose high scientific standards the prime crew was continuously challenged to surpass. We hope that the monthly mission-oriented field exercises planned and executed by members of the Field Geology Team prior to the Apollo 16 flight provided the variety of experience in field situations that enabled the crew to make the appropriate observations and geologic judgments required during the mission. We received valuable assistance before, during, and after the mis- sion from the following associates of the US. Geological Survey who are not credited elsewhere but who nonetheless made significant con— tributions directly or indirectly to the preparation of this volume: N. G. Bailey, F. E. Beeson, B. M. Bradley, V. ]. Fisher, M. H. Hait, E. D. jackson, R. H. Jahns, D. E. johnson, ]. S. Loman, R. S. Madden, R. Carroll, W. E. Miller, R. A. Mills,]. C. Nuttall, D. L. Peck, R. E. Sabala, L. T. Silver, R. B. Skinner, L. B. Sowers, G. A. Swann, H. F. Thomas]. W. VanDivier, and D. E. Wilhelms. Immensely helpful editing by ‘james Pinkerton in preparing the manuscripts for publication was a monumental task and is greatly appreciated. M. B. Duke, Curator, and R. B. Laughon, Assistant Curator, Lunar Receiving Laboratory, Johnson Space Center, Houston, very kindly made arrangements for members of the Field Geology Team to study the Apollo 16 and 17 thin-section collections and to use their photo- graphic equipment for illustrating some of the discussions in the field geology chapters of this report. CONTENTS Page Preface _________________________________________________________________________________________________________________________ V A. Summary of geologic results from Apollo 16, by William R. Muehlberger and George E. Ulrich ________________________________ 1 B. Apollo 16 regional geologic setting, by Carroll Ann Hodges __________________________________________________________________ 6 C. Apollo 16 traverse planning and field procedures, by William R. Muehlberger ________________________________________________ 10 D1. Field geology of Apollo 16 central region, by Gerald G. Schaber ______________________________________________________________ 21 D2. Field geology of North Ray crater, by George E. Ulrich ______________________________________________________________________ 45 D3. Field geology of areas near South Ray and Baby Ray craters, by V. Stephen Reed ____________________________________________ 82 D4. Field geology of Stone mountain, by Anthony G. Sanchez __________________________________________________________________ 106 E. Petrology and distribution of returned samples, Apollo 16, by Howard G. Wilshire, Desiree E. Stuart-Alexander, and Elizabeth C. Schwarzman ___________________________________________________________________________________________ 127 F. Regolith of the Apollo 16 site, by Val L. Freeman __________________________________________________________________________ 147 G. Ejecta distribution model, South Ray crater, by George E. Ulrich, Henry J. Moore, V. Stephen Reed, Edward W. Wolfe, and Kathleen B. Larson ________________________________________________________________________________________________ 160 H. Optical properties at the Apollo 16 landing site, by Henry E. Holt __________________________________________________________ 174 I. Morphology and origin of the landscape of the Descartes region, by John P. Schafer __________________________________________ 185 J. Stratigraphic interpretations at the Apollo 16 site, by George E. Ulrich and V. Stephen Reed ________________________________ 197 K. Summary and critique of geologic hypotheses, by Carroll Ann Hodges and William R. Muehlberger __________________________ 215 L1. Documentation of Apollo 16 samples, by Robert L. Sutton __________________________________________________________________ 231 L2. Apollo 16 lunar surface photography, by Raymond M. Batson, Kathleen B. Larson, V. Stephen Reed, Robert L. Sutton, and Richard L. Tyner __________________________________________________________________________________________________ 526 M. Impact geology of the Imbrium Basin, by Richard E. Eggleton ______________________________________________________________ 533 References cited ______________________________________________________________________________________________________________ 543 ILLUSTRATIONS [Plates are in separate case] FRONTISPIECE. Crystalline rock 68415. PLATE 1. Geologic map of the Apollo 16 landing site and vicinity, by Carroll Ann Hodges. 2. Apollo 16, Descartes landing site. 3—11. Photographic panoramas taken on the lunar surface: From within and near the lunar module. . The ALSEP area and partial panoramas of House and Outhouse rocks. . Stations 1 and 2 and a partial panorama of Buster crater. . Stations 4, 5, and 6 on Stone mountain. . Stations 8, 9, and 13, and partial panoramas of Shadow rock. . Station 11, North Ray crater, including sketch map. . Station 11, including telephoto mosaics. . Telephoto mosaics of Stone mountain taken from the lunar module and station 2 and of Smoky mountain taken from station 11. 11. Telephoto mosaics of South Ray crater, Baby Ray crater, Stubby crater, and the central and northern parts of the traverse area, taken from station 4. 12. Map of the impact geology of the Imbrium basin of the Moon, by Richard E. Eggleton. ozone-p»: H OCDCDQ VII VIII AET AFGIT, ALGIT ALSEP ANT AP/C ASE CC CDR C/S CSM CSVC CSSD CTR DC DMB DPS DS DSB DT END CTR EVA EXP FIIR HFE IR KREEP LAC LM LMB LMP LOC CONTENTS ABBREVIATIONS AND ACRONYMS Apollo Elapsed Time, time after launch of" mission from Kennedy Space Center Apollo Field (Lunar) Geology Investigation Team Apollo Lunar Surface Experiment Package Anorthosite-norite-troctolite rock suite Analytical plotter, model C Active Seismic Experiment Capsule communicator at Mission Control in Houston, A. W. England Commander, John W. Young Central Station controlling the ALSEP Command Service Module, spacecraft that or- bited Moon during EVA’s. Core Sample Vacuum Container Contact Soil Sampling Device (Surface Sam- pler) Crater Dark-haloed crater Dark-matrix breccia Descent Propulsion System on LM Down-sun sampling, photograph Down-sun before sampling, photograph Drive tube, also core tube End crater Extravehicular activity; astronaut activity outside the LM Experiment Fine-grained intersertal igneous rock Heat-Flow Experiment Interagency Report, US. Geological Survey Lunar rock or soil with high concentrations of potassium, rare-earth elements, and phos- phorus Lunar Aeronautical Chart Lunar Module Light-matrix breccia Lunar Module Pilot, Charles M. Duke, Jr. Photograph of sample showing location with respect to LRV or LM LPM LRL LRV LSM LSPET META-ANT MISC MPA N RAY CTR PAN PEN-2 PPAN POIK PSE REE ROVER RTG SCB SEQ SPL S RAY CTR SRC STA STEREO STEREOPAIR SURF SPLR SWC USA USB USD UV CAMERA xs, XSUN XSA XSB XSD +,—Y FOOTPAD +,—z FOOTPAD Lunar Portable Magnetometer Lunar Receiving Laboratory Lunar Roving Vehicle Lunar Surface Magnetometer Lunar Sample Preliminary Examination Team ‘ Metamorphosed anorthosite-norite-troctolite Miscellaneous Mortar Package Assembly North Ray crater Photographic panorama, normally 360° Location of second penetrometer reading Partial panorama Poikiloblastic or poikilitic Passive Seismic Experiment Rare-earth elements Lunar Roving Vehicle Radioisotopic Thermoelectric Generator Sample collection bag Scientific equipment bay, in LM Sample South Ray crater Sample return container Station, sampling location on traverse Stereoscopic sequence or offset in photographs Overlapping pair of photographs that give a three-dimensional view Surface sampler (also CSSD) Solar Wind Composition device Up-sun, after sampling, photograph Up-sun, before sampling, photograph Up-sun, during sampling, photograph Far-ultraviolet camera, positioned in shade of the LM Cross—sun, sampling photograph Cross-sun, after sampling, photograph Cross-sun, before sampling, photograph Cross-sun, during sampling, photograph Front and rear footpads, respectively, of LM Left and right footpads, respectively, of LM A. SUMMARY OF GEOLOGIC RESULTS FROM APOLLO 16 By WILLIAM R. MUEHLBERGER and GEORGE E. ULRICH INTRODUCTION The Apollo 16 mission to the central lunar highlands has provoked a variety of stimulating debates concern- ing the nature of the original lunar crust, the effects of impact processes on this crust, and the interpretation of lunar landforms from photographic evidence. Con- siderable disagreement remains about ultimate sources of the samples returned from the Cayley plains and the Descartes mountains. Although the major problems of origin and lunar processes may not be re- solved in this volume, it is hoped that subsequent re- search will take into account the facts of field relations as recorded by the cameras and first-hand observations of the astronauts. The arrangement of topics in this volume is partly chronologic in that discussions of geologic setting and mission planning are followed by sections on the field geology of four geographic areas sampled by the as- tronauts: central Cayley plains, North Ray crater, vicinity of South Ray and Baby Ray craters, and Stone mountain. These observation sections are followed by topical discussions on the petrology, regolith, South Ray ejecta distribution, optical properties, morphology, and stratigraphy of the landing site. A summary dis- cussion of the source materials for the Cayley plains and Descartes mountains in the light of available data concludes the interpretive part of the volume. Supple- mentary sections on the surface photography and the documentation of samples collected by Apollo 16 are updated revisions of US. Geological Survey Inter- agency Reports, Astrogeology 48, 50, 51, 54, prepared immediately after the mission. Twelve folded plates in the separate case include nine plates of lunar surface panoramas mosaicked from 70-mm photographs and annotated with respect to geographic features and geologic data, a premission photomosaic map of the landing site (scale 125,000), a postmission geologic map of the landing-site region (1:200,000), and a post- mission map of Imbrium-basin-related geology (125 million) for the near side of the Moon. Some geographic names not yet approved by the In- ternational Astronomical Union are used informally in the text and figures where identification or reference to their location is considered essential to the discussion for purposes of context or clarification. A glossary of abbreviations and acronyms used in the texts, illuStrations, photographic and sample catalogs, and the photographic panoramas is appended to the volume. The paragraphs that follow in this chapter are essen— tially abstracts of each of the succeeding separately authored chapters. Thus this section serves as an over- view or extended abstract of the volume that incorpo- rates the major conclusions reached in the independent chapters in the order in which they occur, beginning with the regional geologic setting and ending with the summary of geologic hypotheses. Chapter A.—The Apollo 16 landing site permitted investigation of two geologic units that are widespread in the lunar highlands: light plains and mountainous “hilly and furrowed” terra, both superposed on old cra- tered terrain. Outside the landing area, they are em- bayed by, and are therefore older than, the maria. A volcanic origin for these units, generally accepted prior to the mission, was not supported by the mission re- sults. Various hypotheses of impact-related origins have been proposed to explain the crudely stratified, impact-generated breccias found at the site. Chapter B.——Apollo 16 was the only site within the central lunar highlands to be explored by astronauts on the surface. It is on the Cayley plains, which are relatively level as compared with the adjacent rugged Descartes mountains. The site is about 70 km west of the Kant plateau, which marks part of the third ring of the Nectaris basin, and about 600 km west of the cen- ter of that basin. Other multiringed basins that prob- ably infiuenced the geology of the landing site are Im- brium, centered about 1,600 km to the northwest, and Orientale, centered 3,500 km to the west—southwest. A geologic map of the landing site and vicinity (pl. 1) prepared after the mission illustrates a current in- terpretation of the distribution of geologic materials. 1 2 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS The geologic aspects of the Cayley plains and Descartes mountains can be summarized as follows: (1) The sur- face units are Imbrian in age; the plains surface has a cratering age that is similar to, if not identical with, that of Orientale basin ejecta; cratering ages of the Descartes materials are not so well defined because of their rugged topography, but they are at least as old as Imbrian. (2) The site is within the “sphere of influence” of the Imbrium basin, as evidenced by the radial sculpturing of highlands northwest of the site and by the ridgy morphologic aspect of the Descartes mountains that appears nearly continuous with the Imbrium sculpture. Thus Imbrium ejecta and local material disrupted by the ejecta produced both the mountains and the plains. (3) Because of proximity to the Nectaris basin, the Apollo 16 stratigraphic column probably includes Nectaris basin ejecta at depth, but the basin is so old that these materials are no longer exposed, except perhaps in the lowest walls of the largest craters. Chapter C .—The three lunar-surface traverses of the Apollo 16 mission were designed to insure maximum return of useful data for a community of scientists and engineers with widely varying objectives. Because the time available for geologic investigations and other experiments was limited, an intricate system of priorities was established for both station locations on each traverse and tasks to be performed at each sta- tion. The astronaut crew, John Young and Charles Duke, kept abreast of the planning and the constantly changing priorities, in addition to learning how to travel to and from the Moon. Their terrestrial field training for 18 months before the mission was designed to simulate the lunar traverses and to develop their skills in identifying and describing significant geologic features while photographically documenting and sampling the rocks and soils representing these fea- tures. As a result, all primary geologic objectives were es- sentially achieved. Well-documented samples were re- turned from Cayley plains, North and South Ray crater ejecta, and Stone mountain materials that may be rep- resentative of the Descartes mountains in this part of the lunar highlands. Photographic coverage of all sam- pling areas and the entire traverse route and telephoto views of all important points remote from the traverse area were obtained. Chapter D1—D4 .—The central region of the Apollo 16 landing site was investigated at three locations, LM/ ALSEP, station 1, and station 2. The samples documented probably represent materials of the under- lying Cayley plains down to depths of 70 m or more and ejecta from more distant regions (specifically North and South Ray craters). The percentage of rock types collected from each station was clearly affected by time constraints and may therefore not be representative of the stratigraphic sequence. The most intensively sam- pled area, LM/ALSEP, probably yielded the most rep- resentative collection of the Cayley plains materials. The rock types are similar in all respects to those col- lected at other stations during the mission. They in- clude fine- to medium-grained, moderately homogene— ous crystalline rocks; rocks composed primarily of glass; and breccias, by far the dominant type. The vari- ety of rock types collected indicates that the Cayley plains breccias are heterogeneous and suggests that they are composed of isolated pockets of both light and dark breccias deposited by a turbulent process. Extensive sampling and photography on the rim (station 11) and near the outer edge of the continuous ejecta blanket (station 13) of North Ray crater provide a basis for stratigraphic interpretations in the north- ern part of Apollo 16 traverse area. Breccias on the rim and walls are of two main types, light matrix and dark matrix. The areal distribution and petrographic rela- tions of the boulders sampled or photographed suggest a generalized stratigraphic sequence within the crater and, by extrapolation, in the northern part of the land- ing site. The light-matrix boulders are friable, rounded, and heavily filleted. Their abundance on the rim and upper-crater wall suggests that they were de- rived from the upper part of the section. The dark- matrix boulders are coherent and appear to be the latest ejecta to fall on the crater rim. One of these, Outhouse rock, was the source of several igneous and metaclastic fragments. Most of the dark-matrix brec- cias may be derived from a deeper horizon near the present crater floor. Several types of evidence other than the fresh-rayed appearance argue for the youthfulness of North Ray crater. Spallation exposure ages of 27 to 51 my have been reported for five North Ray rocks. Within that time interval, a very thin regolith (approximately a centimeter thick) formed locally; it thickens to 15 cm or more where it forms fillets around the friable light- matrix boulders. South Ray and Baby Ray craters are fresh blocky craters in the southwestern part of the Apollo 16 land- ing site. Rays from South Ray can be traced as far as 10 km from the crater to the vicinity of North Ray crater. Although South Ray crater itself was not actually visited by the astronauts, Cayley plains materials ejec- ted from it probably are present at most stations. Sta- tion 8 was purposely located on a bright ray from the crater to insure collection of South Ray materials; SUMMARY OF GEOLOGIC RESULTS 3 dark-matrix breccias and light-gray igneous rocks were the two main rock types sampled. They appear to represent two lithologic units in South Ray crater, dark-matrix breccias being the upper unit. The South Ray event, if correctly dated by the 1- to 4-m.y. exposure ages in the boulders, apparently depos- ited ejecta recognizable only in the coarse debris at station 8, about five crater diameters away. Associated soils are reported to give much older ages. No ejecta from the younger Baby Ray crater were recognized in the sample suite, although such materials may be present in small amounts. Three sampling localities were established on Stone mountain at the south limit of the traverse area with the objective of collecting materials representative of the Descartes mountains. The two highest stations (4 and 5) appeared on premission photographs to be out- side ray patterns related to South Ray crater, but con- tamination by South Ray ejecta appears likely at Sta— tion 4. The location of station 4a on the edge of ejecta from Cinco a crater suggests that samples collected might contain local material from a depth of 15 m on Stone mountain. Sampling at station 5, on the wall of a small crater shadowed from South Ray and void of visible blocky ray material, would be expected to in- clude rocks of the Descartes mountains. Station 6, on a bench at the base of Stone mountain very near a ray, may be a mixture of fragments from the Cayley plains and materials of the Descartes mountains. Chapter E.—Apollo 16 rocks are classified by a de- scriptive scheme into three groups: crystalline rocks, subdivided as igneous (Cl) or metamorphic (C2); glass (G); and breccias (BI—B5), subdivided on the basis of clast and matrix colors and proportions. These rock- type symbols are used throughout this volume. The crystalline igneous rocks consist of 1 certain and 1 possible anorthosite, 11 fine-grained ophitic to inter— sertal rocks of troctolitic to anorthositic composition, and 1 troctolite enclosed in fine-grained meltrock of the same composition. Derivation of the fine-grained igne- ous rocks by impact melting of feldspathic plutonic source rocks is indicated by the common occurrence of unmelted relics derived from coarse-grained plutonic rocks and a bulk compositional range like that of the plutonic rocks with essentially the same compositions. Metamorphic crystalline rocks studied consist of 1 medium-grained granoblastic rock considered to be a product of metamorphism in a plutonic environment prior to excavation and 10 poikiloblastic rocks. Grada- tion from poikiloblastic to unequivocally igneous tex- tures in these rocks is taken as evidence of metamor- phic origin with minor melting. Five breccia types have been derived by comminu- tion of a first-cycle breccia that consisted of anorthosi- tic clasts in a fine-grained matrix ranging from melt texture to metamorphic texture. The first-cycle breccia is considered to be multiring-basin ejecta because it contains clasts of plutonic rock whose origin appears to be deep in the lunar crust. These breccias have been modified to varying degrees by subsequent smaller im- pacts. Rocks representative of first—cycle breccias are suffi- ciently abundant in the Apollo 16 collection that least-metamorphosed samples may be identified. From some such samples displaying minimum modification, it should be possible to date the crystallization of the original crustal rocks, the preexcavation metamorph— ism of these rocks, and the time of excavation. A review of age data shows that most samples selected for isotopic measurement are so severely modified by sub- sequent impact that the ages are ambiguous. The sam- ples petrologically most favorable for dating significant and identifiable events in the histories of the rocks are tabulated with the hope that they will help in obtain- ing unambiguous ages, because such data from Apollo 16 rocks are now so scarce that basin chronologies are only speculation. The distribution of the various sample types shows no significant differences between Cayley and De- scartes materials. Statistical and compositional data on soils support the view that the Cayley Formation and materials of the Descartes mountains are facies of the same ejecta deposit. The Cayley Formation may contain a somewhat higher proportion of matrix con- sisting of melt and powdered rock. Chapter F .—-The appearance of the regolith is gen- erally that of a rocky gray soil. Rays from young cra- ters in hard substrata are distinguishable mainly as local concentrations of blocky fragments. The bright- ness of a ray appears to result from a combination of the density and the angularity of fragments, both of which are higher for South Ray than for North Ray crater. The regolith thickness on the plains has a median value of between 6 and 10 m based on photogrammetric measurements of concentric craters. The thickness of regolith on Stone mountain ranges from a minimum of 5 to 10 m to more than 20 m and may vary greatly owing to the accumulation of mass-wasted debris on a softer, weaker bedrock that may underlie much of the Descartes mountains. Regolith compositions for most of the site are chemi- cally similar except for North Ray soils, which are significantly enriched in alumina and depleted in iron, 4 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS titania, and nickel by comparison with the remaining stations. Soils from station 4 tend to be intermediate in titania and nickel content with respect to soils from the plains and North Ray crater. As a group, the soil sam— ples are a homogenized mixture of the bulk rock analyses from the entire site. Chapter G.—South Ray crater ejecta totaling 5 to 10 million m3 are scattered over the Apollo 16 landing site in an irregular pattern that reflects a nonuniform mantle of debris. The ejecta thin rapidly from about 10— 15 m at the crater rim to an estimated 1 cm or less of equivalent uniform thickness at the southern sam- ple localities (stations 4, 5, 6, 8, and 9) and to less than 1 mm at the northern localities (stations 11 and 13). The power function best describing this thinning has a slope of approximately —3.0. The fragment population on the lunar surface (for sizes larger than 2 cm) can account for most of the total volume of ejecta, although an equal amount of finer grained material can be ac- commodated by the model. Ray material from South Ray Crater can be deter- mined best by the combined evidence of computer- enhanced orbital photographs and the density of fresh rock fragments observed on the lunar surface. Station 8 has the highest potential for materials from South Ray; next most likely are stations 9, 6, 4, and 5. The probability of identifying South Ray ejecta from field data for areas farther away than these stations (3.5—4 km from the crater) is remote. Possible exceptions are station 2 samples taken within a bright ray patch in the central part of the landing site. Chapter H.—An investigation of the photometric properties of the Apollo 16 landing site indicates that albedo values of several areas, including the rim of South Ray crater, are 50 to 55 percent, the highest measured at any Apollo site. Measurements for the sampled areas range from 15 percent at the central area, 20 percent in the Stone mountain and station 8 areas, to 24 percent at North Ray crater. The polarimetric properties of the north and east wall of North Ray crater reveal that very little, if any, crystalline material is present in that area and that most of the rocks are more highly shocked than the Fra Mauro breccias at Cone crater. Chapter I .—Four highland terrain types have been morphologically defined in the Descartes mountains in and adjacent to the Apollo 16 landing site. Lineated patterns of crater chains, ridges and scarps, and crosslineations represent three of these. These features exhibit both erosional and depositional characteristics whose orientations show that they were formed by the Imbrium impact event. The main highlands mass probably is a tongue of Imbrium basin ejecta. The fourth highland terrain type is represented by isolated mountains inferred to be older Nectarian massifs pro- jecting through the mantle of Imbrium ejecta. The mountain terrain can be traced beneath the Cayley plains. The plains materials are thin enough along some margins to reveal a subdued reflection of the buried mountain terrain but thick enough in cen- tral parts to conceal the mountainous unit. The grada- tional character of the morphologic contact between plains and mountains does not indicate intergradation between the units but rather the overlapping of Cayley fill on the edge of slightly older mountain terrain. The smooth to gently undulating surface of the Cayley plains indicates high mobility of the plains- forming materials at the time of their deposition. Of the hypotheses currently offered, the concept that the plains represent fluidized ejecta from one or more multiring basins is most consistent with the morphologic evidence. Chapter J.—The ejecta deposits from craters that penetrated materials beneath the Apollo 16 landing site, together with the morphologic characteristics of the craters themselves, provide the best clues for a stratigraphic interpretation of the region. The Cayley plains, whatever their source, consist of three textural rock units: light-matrix breccias, dark-matrix breccias, and nearly holocrystalline rocks. These materials are locally mixed but form a gradational assemblage com- patible with a crudely layered sequence of rocks whose chemical composition is grossly homogeneous. V At the north end of the traverse area, samples from the ejecta of North Ray crater reveal a population dom— inated by friable light-matrix breccias. These rocks, easily eroded, account for the convex upper slopes of the crater wall and the rounded and deeply filleted boulders on the rim and ejecta blanket. The lowermost ‘materials of the crater’s floor mound are most likely represented by coherent glass-rich dark-matrix rocks found as sparse unfilleted blocks on the rim. The third main lithologic type is coherent light-gray igneous- textured rock that occurs interstitially in light-matrix breccias and as inclusions within dark-matrix breccias. This type, the holocrystalline rocks, reaches sizes of 50 cm at station 8 and occurs as smaller angular rocks in the central part of the landing site. The relative abundances of the holocrystalline rock and the dark-matrix breccias at stations 8 and 9.and the photographic evidence for layering within South Ray and Baby Ray craters suggest that the crystalline rocks occur as large lenslike masses underlying and grading upward into melt-rich to melt-poor breccias SUMMARY OF GEOLOGIC RESULTS 5 within the upper 150 In over much of the site. A discon- tinuous resistant layer at about this depth, becoming shallower in the South Ray area, may be reflected as benches in some crater walls (such as South Ray) and by floor mounds in other kilometer-size craters within the Cayley plains. In the south-central and eastern parts of the landing site plains and everywhere in the nearby mountains, evidence for this layer is lacking. The materials of the Descartes mountains in and ad- jacent to the traverse area show little evidence of layer- ing. The dominant rock type below the regolith at the highest point sampled on Stone mountain is most likely light-matrix breccia. The upper 100 m or so of the North Ray crater wall appears to have the same lithology, possibly representing similar materials of Smoky mountain. The lack of coherent blocks in the ejecta of a fresh Copernican crater (Dollond E), about 1 km in depth, 35 km south of the landing site, and the high reflectance of the Descartes mountains indicate that they are made up mainly of friable light-matrix breccias. Chapter K .—Several hypotheses have been proposed to explain the origin of the terra plains and the hilly and furrowed terra, both of which are nonvolcanic ac- cording to evidence from the Apollo 16 mission. Orbital and surface results of the mission, together with post- mission photogeologic investigations, suggest that ejecta from the Imbrium basin constitutes a major part of both plains and mountains at this site. The younger Orientale basin provides a model for investigating basin deposits. Both erosional and depo- sitional landforms occur in the ejecta blanket around the basin, and conspicuous lineations, together with lobate escarpments, strongly indicate lateral flow of materials. Fitting and grooving by secondary impact occurred contemporaneously with deposition of pri- mary hummocky ejecta. Smooth plains deposits appear , to be a late-stage fluid facies that ponded in topo- graphic lows. Extrapolation from this young well- preserved basin to the older and larger Imbrium basin implies similar origins for similar morphologic fea- tures. Hummocky ejecta, plains, and secondary craters are recognizable around Imbrium. The close spatial as- sociation of Cayley-type plains with the Fra Mauro formation is strong evidence for a genetic relation to Imbrium. Furthermore, ridged Fra Mauro-type mate- rials shown on Apollo orbital photographs appear to extend as far as the Kant plateau, forming a depo- sitional unit that partly filled the crater Descartes. The hypothesis considered most defensible is that primary ejecta from the Imbrium basin, which itself must have included a mixture of preexisting crustal materials, and probably debris incorporated en route, formed rugged deposits as far away as “the Kant plateau. The resulting Descartes mountains were sculptured penecontemporaneously by secondary pro- jectiles, also from Imbrium. Fluid, perhaps partly molten, ejecta entrained in these debris flows pooled in topographic lows. The morphology of plains within the belt circumferential to Imbrium is produced by a pla- nar facies of ejecta from Imbrium. Because the ages of the Cayley—type planar surfaces, as determined by crater-erosion models and crater-frequency distri- butions, are equivalent to those of Orientale ejecta, "crater-clocks” appear to have been reset in some way by the Orientale event. The Cayley Formation may have been somewhat analogous to a gigantic ignimbrite—incorporating lenses or pods of molten material in a matrix of cooler debris that flowed into topographic lows and produced subplanar deposits. The molten blobs must have re- tained heat long enough and been of sufficient mag- nitude to mobilize and thermally metamorphose the debris around them. Since igneous textures developed, cooling must have been relatively slow locally, possibly allowing this partly molten material to acquire the anomalous remanent magnetism recorded at the sur- face. The Cayley Formation and the materials of the De- scartes mountains, both largely derived from the Im- brium basin, may be veneered by debris from the Orientale basin or smoothed by the seismic effects of that basin impact. Nectaris ejecta (J anssen Formation) is undoubtedly present at depth. Conclusive identifica- tion of these various basin deposits in the samples re- turned from the Apollo 16 site awaits further investi- gation. B. APOLLO 16 REGIONAL GEOLOGIC SETTING By CARROLL ANN HODGES CONTENTS Page Geography _____________________________________________________________________________ 6 Geologic description of Cayley plains and Descartes mountains ___________________________ 6 Relation in time and space to basins and craters _________________________________________ 8 ILLUSTRATIONS Page FIGURE 1. Composite photograph of the lunar near side showing geographic features and multiring basins _______________________ 7 2. Photographic mosaic of Apollo 16 landing site and vicinity ___________________________________________________________ 8 GEOGRAPHY Soderblom and Boyce, 1972). The type area of the Apollo 16 landed at approximately 15°30’ E., 9° S. on the relatively level Cayley plains, adjacent to the rug- ged Descartes mountains (Milton, 1972; Hodges, 1972a). Approximately 70 km east is the west-facing escarpment of the Kant plateau, part of the uplifted third ring of the Nectaris basin and topographically the highest area on the lunar near side. With respect to the centers of the three best-developed multiringed basins, the site is about 600 km west of Nectaris, 1,600 km southeast of Imbrium, and 3,500 km east-northeast of Orientale. The nearest mare materials are in Tranquillitatis, about 300 km north (fig.1). GEOLOGIC DESCRIPTION OF CAYLEY PLAINS AND DESCARTES MOUNTAINS The principal geologic objective of the mission was investigation of two major physiographic units, the Cayley plains and the Descartes mountains (fig. 2). Materials of both local units had been interpreted as volcanic before the mission (Milton, 1968; Wilhelms and McCauley, 1971; Milton, 1972; Hodges, 1972a; Elston and others, 1972a,b,c; Trask and McCauley, 1972; Head and Goetz, 1972), mainly on the basis of their topographic expression. Much of the surrounding central highlands was assumed to be largely primitive crustal material, bombarded repeatedly by impact. The Cayley plains are of Imbrian age according to stratigraphic relations, crater size-frequency distri- butions, and crater degradation models (Wilhelms and McCauley, 1971; Trask and McCauley, 1972; 6 Cayley Formation is east of the crater Cayley, north of the landing site (Morris and Wilhelms, 1967); the name was extended to the apparently similar plains material at the Apollo 16 site (Milton, 1972; Hodges, 1972a). These materials were presumed to be represen- tative of the widespread photogeologic unit, Imbrian light plains, which covers about 5 percent of the lunar highlands surface (Wilhelms and McCauley, 1971; Howard and others, 1974). Characteristics include rel- atively level surfaces, intermediate albedo, and nearly identical crater size-frequency distributions. The plains were first interpreted as smooth facies of Imbrium basin ejecta (Eggleton and Marshall, 1962), but as the characteristics and apparent age of the ma- terials were better defined, a volcanic origin became the favored hypothesis (Milton, 1964; Milton, 1968; Wilhelms and McCauley, 1971; Milton, 1972; Hodges, 1972a; Elston and others, 1972a,b,c; Trask and McCauley, 1972). Frequency distributions of super- posed craters are lower on the plains than on the Fra Mauro Formation (Imbrium ejecta), and plains mate- rials are superposed on Imbrium sculpture, indicating that the plains postdate the Imbrium basin. This age relation is further supported by the crater-erosion model (Boyce and others, 1974). In morphology and mode of occurrence, the plains resemble mare mate- rials; surfaces are relatively level, and the plains are confined to craters and broad depressions, suggesting local derivation and fluid emplacement. In the landing site area and elsewhere, craters 0.5 to 1.0 km in diame- ter commonly have conspicuous central mounds on their floors. Throughout the central highlands (Wil- REGIONAL GEOLOGIC SETTING 7 helms and McCauley, 1971), Cayley-type plains are es- pecially prominent in large old craters—Ptolemaeus, Albategnius, and Hipparchus. Where adjacent to the maria, as at the type area of the Cayley Formation, the plains are embayed or overlapped by mare lavas. Orbi- tal geochemical data obtained during the Apollo missions indicate that the higher albedo of the plains N S FIGURE 1.—Lunar near side. A, Location of major features men- tioned in the text; Apollo landing sites indicated by numbers. B, Major rings of near-side multiring basins in relation to Apollo 16 landing site. From Wilhelms and McCauley (1971). materials is produced by an aluminum-to-silicon ratio higher than in rocks of the maria (Adler and others, 1973). In several places, large subdued craters appear to be mantled by Cayley-type materials, suggesting that a relatively thin deposit was emplaced on an older sur- face. To account for the apparent differential compac- tion in the upper layer, ash falls or flows, or possibly mass-wasted debris, were proposed as the depositional materials (Howard and Masursky, 1968; Cummings, 1972). In the large crater Alphonsus, dark conelike structures interpreted as volcanic vents occur along graben in the plains material, an association that sup- ported the volcanic interpretation of the plains (McCauley, 1969). The Descartes mountains topography is virtually unique on the Moon. No other deposits of identical morphology have been recognized, although similar hilly and furrowed materials of Imbrian age have been mapped in several places (Wilhelms and McCauley, 1971). Sixty kilometers south of the landing site, the materials overlap and nearly fill the degraded 50-km crater Descartes; they are clearly depositional and perhaps 1 km or more thick (Milton, 1972). No genetic relation to a local impact crater is apparent, and the morphology of the hills and furrows suggested an ori- gin analogous to terrestrial volcanic extrusions or fis- sure cones to Trask and McCauley (1972). A partly gradational relation with the Cayley Formation was proposed prior to the mission (Milton, 1972; Hodges, 1972a; Elston and others, 1972a,b,c). Although super- posed crater populations indicate an Imbrian age for most of the Descartes mountains (Trask and McCauley, 1972), a patch of unusually high albedo near the north rim of the crater Descartes was inter- preted as a Copernican pyroclastic deposit (Head and Goetz, 1972). As a result of the wide acceptance of these volcanic interpretations, developed independently by several authors, premission models of lunar history generally incorporated: (1) a Moonwide, postbasin, premare episode of fluid or pyroclastic volcanism producing Cayley-type plains and (2) a later and more localized phase of relatively viscous extrusive activity, best exemplified by the Descartes mountains. The Apollo 16 mission was designed to test these hypotheses. The impact origin of the rocks returned from the landing site forced reinterpretations of the geologic units (pl. 1), Textures of the highly feldspathic samples are nearly all indicative of shock metamorphism of various degrees. The rocks are mainly breccias, but even the relatively few crystalline rocks contain “ghost clasts” indicating thermal metamorphism and recrys- tallization. New interpretations of the landing-site geology must 8 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS now explain not only the brecciated nature of the rock samples but also all of the characteristics previously ascribed to volcanism. Extrapolation of the data from the Apollo 16 site to similar photogeologic units elsewhere imposes new constraints on the framework of lunar geologic history. RELATION IN TIME AND SPACE TO BASINS AND CRATERS Impact sources and emplacement mechanisms for the geologic units at the landing site and for similar materials elsewhere are not readily apparent. Al- though local derivation of the rocks has been suggested (Oberbeck and others, 1974a, b; Head, 1974), large multiringed basins now appear to have had pervasive influence throughout the Moon’s geologic history (Howard and others, 1974) and probably contributed material to the landing site. Youngest and best pre- served of these basins is Orientale, whose outer and most conspicuous ring is the Cordillera, 930 km in di- ameter. Next youngest—and largest on the near side—is the Imbrium basin, whose outer ring, the Apennine, is 1,340 km across; this basin and its ejecta (Fra Mauro Formation) form the stratigraphic and structural base of the Imbrian System (Wilhelms, 1970). The sequence of basin formation becomes pro- gressively ambiguous with increasing age, but Nectaris, nearest the Apollo 16 site, is one of the best preserved of I; M ,4 . 4 .. the pre-Imbrian basins on the near side. Its most promi- nent ring, the Altai, is 840 km in diameter. Its ejecta blanket, the Janssen Formation (Stuart- Alexander, 1971), denotes the base of the Nectarian System, immediately preceding the Imbrian System in the time-stratigraphic nomenclature established on the east limb and farside areas of the Moon (Stuart- Alexander and Wilhelms, 1975). Because of age and proximity, each of these enormous impact events al- most certainly influenced the latest stratigraphic and structural development of the entire central highlands including the landing site area. Inasmuch as multiringed basins formed throughout the Moon’s early history, unraveling the stratigraphic column at any given place requires an estimate of the thickness of ejecta contributed by these basins as well as by locally derived material. Nectaris basin—The Apollo 16 area, only 600 km from the center of Nectaris, is well within range of the continuous ejecta from the Nectaris basin, but the Im- brian age of the Cayley and Descartes units sampled precludes their derivation from that basin. Further, no deposits as fresh in appearance as the Descartes mountains occur elsewhere around the Nectaris basin. The Nectaris ejecta that should be present at the site must be buried by these younger materials. Imbrium basin.—The Apollo 16 site is about 1,600 km southeast of the center of the Imbrium basin and FIGURE 2.—Apollo 16 landing site and vicinity. Andel M, 130 km west of the site, may be filled with as much as 1 km of mixed Imbrium ejecta and debris from its destroyed north rim. Prominent ridges and furrows trending predominantly southeast reflect Imbrium sculpture (secondary cratering) and possible flow lineations in primary ejecta. (Apollo 16 mapping-camera frames 439, 440, 441, 442.) REGIONAL GEOLOGIC SETTING 9 within a well-defined belt of plains peripheral to that basin in both the central highlands (Eggleton and Schaber, 1972) and on the north (Lucchitta, 1978). Al— though the site is beyond the range of Imbrium ejecta previously mapped (Wilhelms and McCauley, 1971), this spatial association of plains and basin suggests a genetic relation (Eggleton and Marshall, 1962; Eggle- ton and Schaber, 1972). Size-frequency distribution of superposed craters, crater degradation models, and stratigraphic relations indicate that the central plains are younger than the Fra Mauro Formation (Wilhelms and McCauley, 1971; Greeley and Gault, 1970; Soderblom and Boyce, 1972), whereas two patches of northern plains are equivalent in age to Fra Mauro Formation (Boyce and others, 1974). The Descartes mountains may be composed of Im- brium ejecta banked against the Kant plateau, analo- gous to the deceleration ridges (Trask and McCauley, 1972) of the Hevelius Formation trapped by preexist- ing crater walls around Orientale (Hodges, 1972b; Hodges and others, 1973). Smaller scale analogs have been described within the ejecta blanket of a crater only 3.5 km in diameter (Head, 1972). Discontinuous Fra Mauro materials occur west of the site where the crater Andel M (fig. 2) appears to have been partly filled by Imbrium ejecta that destroyed its north rim (Moore and others, 1974). Orientale basin.—The Apollo 16 site is about 3,500 km from the center of Orientale—well beyond any pre- viously recognized extent of that basin’s ejecta. The Cayley-type plains, however, appear to be contem- poraneous with the Hevelius Formation (McCauley, 1967), which is the continuous ejecta from Orientale and which includes a conspicuous planar facies of broad extent, mainly at the distal margin of the tex- tured ejecta (Soderblom and Boyce, 1972; Hodges and others, 1973). In order to account for the age of the plains surfaces, as deduced from cratering models, Orientale was proposed as the source of the uppermost deposits of both mountains and plains at the Apollo 16 site (Chao and others, 1973; Hodges and others, 1973). Theoretical analyses of ejecta volume argue that ejecta from Orientale may be dispersed over the entire Moon (Moore and others, 1974); broad distribution of crater ejecta is demonstrated photogeologically by young craters such as Tycho, whose rays extend more than 3,000 km (Baldwin, 1963). Local craters.—Because of stratigraphic constraints, local craters are an unsatisfactory source for the mate- rials at the Apollo 16 site. The Cayley plains are younger than any large adjacent craters, all of which have clearly been sculptured by Imbrium ejecta. A pre-Imbrian crater 150 km in diameter centered on the landing site has been conjectured (Milton, 1972; Head, 1974), but materials formed by such a crater would be several kilometers deep at the landing site and are not likely to have been included in the sample collection. Head (1974) proposed that the plains were essentially floor materials of a 60-km crater whose rim crest in- cludes Stone and Smoky mountains. This seems impos- sible, however, for such a crater would have to be younger than the Descartes mountains of Imbrian age, yet older than the pre-Imbrian crater Dollond B (fig. 2), an obvious incongruity; even allowing the Descartes mountains and the plains to be pre-Imbrian would re- quire the plains to be sculptured, and they are not. Furthermore, this mechanism, requiring local origin within craters, cannot be extrapolated, inasmuch as craters containing Cayley-type plains are generally considerably older than the enclosed plains, and some plains (for example, at the Cayley Formation’s type locality) are not within craters. A possible derivation of plains materials by local secondary cratering was advocated by Oberbeck and others (1975), who demonstrated that the mass of ejecta from a secondary crater far exceeds the mass of the primary projectile at increasing distances from the continuous ejecta blanket. The pervasiveness of Im- brium sculpture caused by secondary projectiles around the Apollo 16 site indicates that such cratering, together with mass wasting and extensive lateral transport, could have concentrated material in topo- graphic lows, although the crater size-frequency dis- tributions of the surficial plains suggest a younger age for the deposits than is accountable by this postulate. The potential sources for rocks returned from the Apollo 16 mission are reexamined in Hodges and Muehlberger (this volume) after presentation of field data and pertinent orbital information. To summarize the position of the Cayley plains and Descartes mountains in space and time: (1) The units are Imbrian in age, and the uppermost plains deposits are essentially contemporaneous with the formation of the Orientale basin; cratering ages of the Descartes materials are not so well defined because of their rug- ged topography, but they are at least as old as Imbrian. (2) Because of proximity to the Nectaris basin, stratig- raphy at the Apollo 16 site must surely include Nec- taris ejecta at depth, but the basin is too old to have produced the materials now at the surface. (3) The site is within the “sphere of influence” of the Imbrium basin, as indicated by the sculpturing produced by gouging of secondary projectiles, and Imbrium deposits may well be present. (4) The hypothesis that Orientale ejecta reached the site is based largely on the apparent contemporaneity of that basin with the surficial plains deposits. Deposition of Orientale ejecta on the order of several tens of meters (a speculation not represented on the accompanying geologic map, pl. 1) seems re- quired to “reset” the Imbrium “crater clocks.” C. APOLLO 16 TRAVERSE PLANNING AND FIELD PROCEDURES By WILLIAM R. MUEHLBERGER CONTENTS Page Geologic objectives ____________________________________________________________________ 10 Preparation for field geology at Descartes ________________________________________________ 12 Traverse design ________________________________________________________________________ 14 The mission ____________________________________________________________________________ 18 Hindsight ______________________________________________________________________________ 20 ILLUSTRATIONS Page FIGURE 1. Composite photograph of near side of the Moon showing the Apollo landing sites _____________________________________ 10 2. Photograph showing Apollo 16 landing site and regional lunar features _____________________________________________ 11 3. Photographs illustrating sampling equipment and techniques used on Apollo 16 _____________________________________ 13 4. Diagram showing premission traverses and geologic objectives ______________________________________________________ 17 5. Photograph showing locations of actual Apollo 16 traverses _________________________________________________________ 19 GEOLOGIC OBJECTIVES The geologic objectives of the Apollo 16 mission were to understand better the nature and development of the highland area north of the crater Descartes, includ- ing an area of Cayley plains and the adjacent Descartes mountains, and to study processes that have modified highland surfaces. The objectives were to be met through the study of the geologic features both on the surface and from orbit and through analyses of the samples returned. The plans for the mission finally evolved from back- room discussions and formal review between interested personnel: scientists, engineers, and, foremost, the as- tronauts themselves. The premission plan as finalized shortly before launch underwent modification during the mission as the science support team evaluated re- vised times available for traverses, problems that arose during the mission, and changing geologic concepts of the area being investigated. Highlands materials had been collected at the Apollo 14 and 15 landing sites (fig. 1): from the continuous ejecta blanket of the Imbrium basin at Apollo 14; from the base of the Apennine front, the outer ring of mountains bounding the Imbrium basin, at Apollo 15. Each of these sites yielded highlands materials of dif- ferent types that could be related to Imbrium basin formation. At the Apollo 16 site, materials of both a widespread highlands plains unit and the rugged Descartes mountains were of interest; neither geologic unit had 10 yet been sampled in the Apollo reconnaissance of the Moon. Ray materials from two small but conspicuous Copernican craters, North Ray and South Ray, both on the Cayley plains, mantle a considerable part of the traverse area, on both plains and adjacent mountains FIGURE 1.—Near side of the Moon showing the Apollo landing sites. TRAVERSE PLANNING AND FIELD PROCEDURES 11 (Hodges, 1972a; Elston and others, 1972a, b). Impact rimmed, irregular depressions were mapped as craters craters of Imbrian to late Copernican age are promi- of either secondary impact from Theophilus, 300 km to nent throughout the region (fig. 2). Rimless to low- the east, or volcanic origin. ‘E .. . > . ~ ‘ "’ >= .‘ s’ ‘x > , FIGURE 2.—-Apollo 16 landing site, traverses, and regional lunar features. From AFGIT (1973) and Hodges and others (1973). Reprinted with permission of the American Association for the Advancement of Science and Pergamon Press. l2 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS Lithologic layering in the Cayley plains was sug- gested by albedo bands and ledges in the walls of sev- eral craters and by mounds in the floors of craters about 1 km in diameter. Lithologic layering in the ma- terials of the Descartes mountains was suggested by topographic benches and bands of slightly varied al- bedo on the flanks of Stone mountain. Materials at depth beneath the Cayley plains were interpreted as including both the Fra Mauro Formation derived from the Imbrium basin and ejecta from the nearer but older Nectaris basin (Hodges, 1972a). Elston and others (1972b) projected the flank of a highly cratered pre- Imbrian hill beneath the traverse region. The depth to these units was unknown, but all were believed to be well below the depth of local cratering and therefore unlikely to be sampled in the traverse area. PREPARATION FOR FIELD GEOLOGY AT DESCARTES The name of the game in traverse planning is maximum science return. Most surface experiments and the central station of the Apollo Lunar Surface Experiments Package (ALSEP) that telemetered data to Earth required deployment by the astronauts, or required astronaut voice data transmission as in the procedure for the Lunar Portable Magnetometer. Each of these types of operations required rapid deployment (using minimum time), and a definite period of time was allocated to each experiment. The geologic experiment was more difficult to struc- ture, and the observations, sampling, and photography necessary to satisfy the collective geologic community required time and equipment beyond that available. For example, a fourth traverse 0r Extravehicular Ac- tivity (EVA) was requested by the Field Geology Ex- periment Team (with the concurrence of the as- tronauts) in order to study South Ray crater and its ejecta blanket. This request was denied because it would have gone beyond the time limits deemed safe for the LM systems. As time was extremely limited, an intricate system of priorities was established for both station locations and tasks performed at each station. The development of priorities involved many individ- uals and advocate groups for the various aspects of the traverse activities. The final system of priorities and contingency plans appeared in the “Lunar Surface Procedures” and “Science Contingency Plan” docu- ments for the mission. The field training of the astronauts developed their abilities to identify and describe the significant geologic features in View, to sample and document pho- tographically the geologic units at a sampling site, to document the significant relations of areas remote from the traverse line by use of telephoto cameras and description, and to integrate previous observations into a general geologic picture of the landing site. Both sampling procedures and photographic tech— niques evolved with experience during training and throughout the actual missions. Sampling procedures focused on obtaining a truly representative collection of materials at the site While staying within severe weight restrictions. In addition to standard sampling procedures (illustrated in fig. 3), several special tech- niques were used to: (1) support studies of the surface character of the regolith, the optical properties of the FIGURE 3.—Sampling equipment and techniques used on Apollo 16. A, Sample 61295 broken from large rock under gnomon. Regolith samples were taken from fillet surrounding rock. Photograph taken to include LRV to assist in locating sample areas. Station 1, Plum crater. AS16—109—17804. B, Gnomon in standard position with color chart leg toward sun and near sample to be collected. Gray scale and color chart on leg and wand gives true color; bands are 2 cm wide, for photographic scale; wand is mounted in gimbels to give local vertical. Station 5, cross-sun View. ASl6— 110— 18024. C, Same as B but with sample 65035 removed. Station 5, cross-sun view. ASl6—110— 18025. D, Sampling area of B and C after collec- tion of rake sample. Gnomon leg at right edge. Station 5, cross-sun View. ASlG—110—18026. E, Sample 60018 being chipped from large rock by Astronaut Charles Duke. Rake being used for scale. Wires in rake are spaced 1 cm apart. Cuff checklist of notes strap- ped to astronaut’s wrist, above hammer. Camera lens sun-shade and sample bags hanging from a clip below the camera are visible. Station 10. ASlS—116— 18689. F, Astronaut John Young breaking chips from spall zone, Outhouse rock, North Ray crater. Sample bags being carried by hand because clip under camera fell off. Each ' bag is numbered and called out by astronaut when sample is placed in it. Camera and mounting bracket on astronaut’s chest, and cuff checklist clearly visible. ASl6— 116— 18647. G, Tongs being used as scale for sample site. Astronaut John Young pulling rake. Rim of North Ray crater; LRV in background; white breccia boulder sampling area on skyline. ASl6— 106— 17340. H, Tongs holding rock 60115, just removed from small depression (arrow) in which rock had lain on lunar surface. Station 10. ASl6—114— 18446. I , Closeup stereo view of boulder 1 at station 8 showing textural details of breccia not visible in small samples returned. AS16—108—17693/17694. J, Scoop being used as locator. Dark stripe on handle used as guide by the astronaut to give proper distance for closeup photography. Sample 60275 marked by arrow. Sampling station at LM. A816—117—18833. K, Area of J after re- . moval of sample 60275 with scoop. ASlG—117—18835. L, Scoop, gnomon, and sample collection bag (SCB). The unlatched and open top shows two single core tubes (drive tubes) stowed within the bag. This bag can be carried by hand or attached to the astronaut’s life support system. Individual samples in their numbered bags are stored in the SCB. Station 4, down-sun, before sampling. AS16— 107—17464. M, Double core attached to extension handle. Lower tube about half driven, Upper tube (number 29) visible. Station 8, AS16— 108— 17682. N, Double core hammered to total depth. Sta- tion 8, location changed from that shown in M. ASIB— 108— 17686. 0, Hinged rack (in open position) on rear of LRV, showing (right- to-left) rake, both tongs, and penetrometer drum in stowed position for travel. Lunar portable magnetometer deployed at end of 15-m cable. Other equipment under seats. A816—114— 18433. TRAVERSE PLANNING AND FIELD PROCEDURES 13 lunar surface, the unabraded surfaces of lunar rocks, boulder erosion and filleting, the adsorption of mobile elements in shaded areas, cosmic ray tracks in large and small boulders, and chemical homogeneity throughout single units and (2) support future studies on uncontaminated lunar soil. Horz and others (1972) described these procedures and special samples re- turned, including an X-ray description of the cores col- lected. Photographic requirements included two panoramas at each station, one taken immediately upon arrival at the station, the other just prior to leaving the station, so that the undisturbed surface could be studied, sam- ple locations more easily identified, and a stereobase established for detailed study. Telephoto surveys were made from two stations to obtain a stereobase of Stone and Smoky mountains for analysis of lineaments like those first recognized on Mount Hadley during Apollo 14 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS 15. In addition, two polarimetric surveys were made at station 11: one to establish calibration control in the near-field of a sampled area and one of the inaccessible interior of North Ray crater taken from the rim. Finally, the photographs required included a stand- ard set for sample documentation, closeup stereopairs for analysis of rock textures, and “flight-line” stereo, that is, a series of photographs perpendicular to a boul- der that would provide a stereo base for study. TRAVERSE DESIGN The three traverses (one per EVA) were designed to optimize investigations of the Cayley plains and the Descartes mountains (fig. 4). For that purpose, a pre- liminary photomosaic and topographic base map, plate 2, was prepared from existing Apollo 14 Hasselblad photographic coverage 9 months before the mission. This allowed detailed traverse planning to start de— TRAVERSE PLANNING AND FIELD PROCEDURES l5 spite the low resolution of the photography and long before more accurate maps became available. The Cayley Formation was to be sampled during each traverse in order to determine lateral variations of the stratigraphic section between North Ray and South Ray craters, the petrology of the formation throughout the area, and the characteristics of the upland plains regolith. The prime sampling areas were located at Flag and Spook craters and in the vicinity of the LM and ALSEP, where crater dimensions suggested that the unit might be sampled to depths of approximately 60 m. Avoiding ray material so as to obtain locally derived samples of Cayley Formation was a major con- sideration in the LM-Spook-Flag sampling areas. Prime sampling sites for deeper parts of the Cayley were in the ejecta of North Ray and South Ray craters. The short distance between Flag and Spook craters, about 1 km, made it possible early in the lunar surface activities (EVA— 1) to test the lateral continuity of bed- rock layers. Good stratigraphic correlations in these craters could provide a solid base for extending the stratigraphy into the LM-ALSEP area and a geologic basis for the interpretation of the Active Seismic Ex- periment profile. It was hoped that the stratigraphy could then be carried northward through Palmetto to North Ray crater and southward to South Ray crater. Both Flag and Spook craters are degraded and have a veneer of South Ray ejecta across or near them. Station 16 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS 1 was located on Plum crater, a small fresh crater on the rim of Flag crater, thought large enough to have penetrated the entire Flag crater ejecta blanket, and station 2 was on Buster crater, thought to have pene- trated the upper layer of the underlying Cayley For- mation even though it lies on the outer part of the ejecta blanket of Spook crater. A third station, for sam- pling, coring, and experiments in soil mechanics in the ALSEP area, was moved late in the planning stages to the end of EVA~2 so that maximum sampling time could be spent at Flag and Spook craters. Deeper parts of the Cayley Formation were assumed to have been excavated by the larger North Ray and South Ray impacts and exposed near the rim of North Ray crater (stations 11, 12, and 13, fig. 4) and in the ray deposits of South Ray crater (station 8). On the second traverse, stations 4, 5, and 6 on the flank of Stone mountain were the principal sampling TRAVERSE PLANNING AND FIELD PROCEDURES 17 sites for Descartes mountains materials (fig. 4). These stations were on benches delineated on the premission topographic map (US Army Topographic Command, 1972). The station farthest upslope (station 4) was lo- cated between Cinco d and e, a pair of craters that must penetrate the regolith, excavating blocks of Stone mountain material. It was hoped that ray material from South Ray crater, anticipated at these stations, could be recognized and avoided. In addition to employ- ing a wide variety of sampling techniques, penetrome— ter tests of soil were to be performed; the elevation of the station would permit good telephoto viewing of the rim and interior of South Ray and Baby Ray craters on the plains. Locations of the lower stations on Stone mountain (5 and 6) were spaced at equal intervals down the slope but subject to change if the astronauts observed outcrops, blocky-rimmed craters, or other fea— tures of particular interest on their outbound traverse. Station 14, on the lower slopes of Smoky mountain, was planned for the third traverse in order to compare the two mountain units. The rim of North Ray crater, nearly 1 km in diame- ter and more than 200 m deep, was the prime site for obtaining the deepest samples of Cayley plains. The W \, 39“ Cayley Formation ."I" \_l‘; sampling site Lateral variations /_\ /NF?d\;h ): Visible stratigraphy (7 layers) Deepest area of Cayley Formation (160 m) Central mound [/ Kiva> ' ' \._/ ’Station 11 Station 16 - Flag and Spook craters Prime Cayley Formation .!.f' sampling site Palmetto .- Vertical sequence to 60 m ":5" Lateral continuity between craters Station 10 South Flay rays across site Station 2 l Flagfiz'tm' . Station 1/- ...... ' \ Cove/ Nature of surface layers - Comparison with subsurface tation 9 layers ' ( Trap / _ \--"-Wrecl<),- -' ., Baby Flay—c: _/'\}.-,.\ y / . ‘- ' Station 17 - ‘s: bb‘ :1; —"-.-Station 5 {- W \ u \// I. . ' , “Station 4 younger South Ray crater was believed inaccessible because of the blockiness of the ejecta blanket and the large deep craters (Trap-Wreck-Stubby) that obstructed the direct route from the LM. Although many large blocks were observed in the ejecta of North Ray crater, there appeared to be relatively smooth ap- proaches along which the astronauts could drive to the crater rim or at least to within walking distance of it. Seven stratigraphic layers within the crater were in- terpreted on the basis of albedo differences (Elston and others, 1972a, b, c) visible on premission photographs having a resolution no better than 5 m. Lateral varia- tions in these bands across the crater, a large dark central mound on the crater floor, and a 25-m-long dark boulder on the crater rim were identified as fea- tures of interest. Stations 11 and 12, approximately 200 m apart on the crater rim, were located as end points of a sampling strip that would provide materials representative of all layers penetrated, except possibly the top one. Station 12 was at the huge dark block named "House rock” by the astronauts, assumed, in premission planning, to be Visible from a distance and therefore useful as a navigation aid. To guarantee samples from the uppermost layers of the Cayley Station 12 Station 13 _ Smoky mountaln Ravine .-.’-’.‘\. It 2/ / / isxf. / Station 14 Compare Descartes mountains with Stone mountain Investigate irregular crater Station 15 ‘ /-—— Palmetto crater Old large crater Central mound /"- Magnetic survey ' Gator) / Regolith studies . 1 ., / Vertical sequence Lateral continuity Soil mechanics properties South Ray crater Large fresh crater Cayley stratigraphy through ray block samples ‘,-/ / Station 6 Stone mountain Main Descartes sampling site I l f, i . Map units extend 100 by 60 km K.’./ ' \ 1 Station 7 south and east \-‘_/' \ Cause of benches /'\ \' South Ray FIGURE 4.—Planned traverses and geologic objectives. 18 plains, station 13 was established far out on the ejecta blanket. A wide variety of photographic techniques was planned to document the compositional, textural, and stratigraphic relations of the returned samples: panoramas from several locations for stereoviewing, 500-mm telephotography of far crater wall, near- and far-field polarimetric surveys, close-up stereo for tex- tural details of individual boulders, “flight-line” stereo of large boulders, as well as conventional photographic documentation during sampling. Palmetto crater, about the same diameter as North Ray crater, is older and very subdued; a few large fresh craters occur near its rim. Stations 16 and 17 (fig. 4) were selected as the best places for sampling Palmetto ejecta. In addition, the outbound traverse was specifically planned along the Palmetto rim so that the astronauts could observe features within the crater and on its ejecta blanket not visible on the premission photographs and thereby recommend changes in the plan for the end of the traverse. Station 15 was planned at a small fresh crater for sampling the local top layer of the Cayley Formation to establish lateral continuity. Stations 15, 16, and 17 were also planned as mag- netometer stations designed to determine whether magnetic anomalies occur around a large crater (Pal- metto). Rays from South Ray crater were visible across much of the landing site area on premission photographs, but the nature of the ejecta in rays was unknown. Either a blanket of debris of various sizes or a string of blocks and associated fines that produced secondary craters, or perhaps a combination of both, was thought to ac- count for the apparent characteristics. Ascertaining the composition of rays was essential in order to assign samples collected to their proper source craters. Ideally the procedure for sampling these rays would have included intensive study of several widely sepa- rated patches, as each patch represents only a small volume of the crater ejecta. The more patches studied, the better the stratigraphic sampling of the crater, de- spite the fact that most ray material in the vicinity of the LM was likely derived from only the upper quarter or less of the crater. South Ray material was expected in cores from the LM/ALSEP and station 8 areas and in some of the surficial samples returned. Station 8, near the rim of Stubby crater in the brightest ray patch accessible, was planned specifically to obtain materials from South Ray crater. Sampling by all techniques available was designed to obtain a variety of rock types representative of stratigraphic units. Trenching and coring was expected to indicate the thickness of near— surface units; special samples from the top and bottom of large boulders and from the soil beneath such boul- ders might provide an exact date of the South Ray im- pact. Photographs of secondary craters and the boul- GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS ders that formed them would indicate azimuths toward the source. The objectives of station 9 required a mature regolith surface, free of recent contamination by ejecta from fresh young craters. The station location had to be selected by the crew as they traveled, although the general area was delimited prior to the mission. The primary purpose of this station was to study the sur- face of the regolith visible in photographs and tele- scopes and analyzed by nonpenetrating geochemical and geophysical devices. The station had to be in a patch of Cayley Formation of “typical” or “average” albedo such that the data could be extrapolated re- gionally. A series of successively deeper samples were to be collected to determine the nature of the regolith. Samplers were designed to collect uppermost layers of surface grains, and a surface skim sample was to be collected, as well as a deeper scoop sample directly under the skim. A special vacuum-sealed short core was designed to protect the most pristine sample yet returned from the Moon, and several padded bags were included to preserve fragment surfaces (see Horz and others, 1972, for details). A very readable booklet on details of premission planning for various surface and orbital experiments and hardware aboard the Apollo 16 mission was writ- ten by Simmons (1972). THE MISSION Several mechanical and operational problems arose during the mission that prevented exact execution of the premission plans. Because a mechanical problem developed in the CSM engine, the lunar landing was delayed for three revolutions, or nearly 5 hours. This delay changed the mission plans. To keep the as- tronauts’ work day within acceptable medical limi- tations, a sleep period was assigned first upon landing instead of an immediate EVA. This change precluded observing the flanks of Stone mountain for lineaments like those seen on Mount Hadley at the Apollo 15 land- ing site. The second of two planned telephoto panoramas to be taken during EVA—1 for stereo study of Stone mountain was cancelled because of lack of time and was taken instead at the start of EVA—3. This panorama, taken at high sun angle, shows no shadow lineaments. During EVA—2 (fig. 5), problems with the LRV navi- gation system, a lack of landmarks, and difficult trafficability combined to stop the astronauts short of the prime goal near Cinco e. In order to preserve the schedule at station 8 and 9 and to keep enough time at station 10 to do the preplanned tasks and, if required, to remove the broken cable on the Heat Flow Experi- ment, station 7 was cancelled. This station, planned for 15-minutes duration, was intended for sampling of a TRAVERSE PLANNING AND FIELD PROCEDURES FIGURE 5.—Actua1 traverses. Apollo 16 panoramic-camera frame 4618. 20 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS fresh crater near the mapped Descartes-Cayley contact and a telephoto survey of Smoky mountain and the interior of Stubby crater. EVA—3 was shortened from 7 to 5 hours when it was decided to lift off from the lunar surface at the pre- planned time rather than extend the lunar surface stay and risk problems with nearly depleted LM systems. All activities other than those scheduled for North Ray crater were cancelled. The astronauts drove the LRV to the rim of the crater without difficulty, allowing time for nearly all of the preplanned tasks for stations 11 and 12 to be accomplished. The near-field polarimetric survey was cancelled and a second abbreviated tele- photo panorama into North Ray crater was taken from near House rock. The operational aspects of the mis- sion are described in the Apollo 16 preliminary science report (Baldwin, 1972). Despite exigencies that devel- oped through the mission, all of the primary geologic tasks were carried out: sampling of the Cayley plains, of ejecta from North Ray and South Ray craters, and of materials from Stone mountain, representative of the Descartes mountains; photographic coverage of all sampling areas, the entire traverse route, and tele- photo views of all important points remote from the traverse route. HINDSIGHT Photogeologic interpretations for this mission were hampered by the low resolution of the best available premission photographs. As it turned out, nearly all the large blocks (5 In or larger) had been located. (Boudette and others, 1972), but because the an- nounced resolution of the photographs was 5 m or poorer, it was not certain whether features at or near the limit of resolution were real or simply artifacts of photoprocessing. The number of boulders identified and the blockiness predicted from radar studies of the site convinced us that travel through the rays from both South Ray and North Ray craters would be dif- ficult if not impossible. The Virtual absence of rocks on North Ray, except for those identified before the mis- sion, was startling. Had the spacing of blocks on South Ray rays been known, the mission might have been designed differently: an alternative considered was a dash to Stone mountain along with deployment of the ALSEP on EVA—1, followed by EVA’s to South Ray and Baby Ray craters, and then to North Ray crater. Better geologic data from the youngest crater rims could have helped immeasurably to determine the na- ture of the Cayley Formation, its composition, and stratigraphic makeup. Data from afresher or larger crater on Stone mountain, remote from South Ray cra- ter ejecta, could have better defined the character of the materials composing the Descartes mountains. Certainly if we had better understood, before the mission, the enormity of the events forming the Im- brium and Orientale basins and the potential extent of their ejecta, we would have considered geologic alter- natives to the volcanic interpretation of the units at the Apollo 16 site. The geologic field training might thus have been different, many of the special sampling experiments might never have been scheduled for this mission, and as a result, the time available for geologic traverses would have been allocated differently. é . D1. FIELD GEOLOGY OF APOLLO 16 CENTRAL REGION By GERALD G. SCHABER CONTENTS Page The LM/ALSEP station ________________________________________________________________ 21 Station 1 ______________________________________________________________________________ 33 Station 2 ______________________________________________________________________________ 37 Summary ______________________________________________________________________________ 44 ILLUSTRATIONS Page FIGURE 1. Planimetric map of the LM/ALSEP area _______________________________________________________________________ 22 2. Photograph showing distribution of ejecta near the Apollo 16 landing site _________________________________________ 23 3. Photographic-topographic map and stereopairs of the central part of the landing site _______________________________ 24 4. Diagram showing size and distribution of fragments photographed along traverses _________________________________ 26 5. Map showing block distribution within 10 m of panorama site north of the LM ___________________________________ 27 6. Sketch map of landing site and central region ___________________________________________________________________ 28 7— 10. Photographs: 7. Sample 60016 _________________________________________________________________________________________ 29 8. Sample 60018 _________________________________________________________________________________________ 30 9. Sample 60025 _________________________________________________________________________________________ 31 10. Sample 60315 _________________________________________________________________________________________ 32 11. Planimetric map of station 1 ___________________________________________________________________________________ 34 12. Map showing block distribution within 10 m of northeast station 1 panorama _____________________________________ 34 13—18. Photographs: 13. Sample 61016 _________________________________________________________________________________________ 35 14. Samples 61135 and 61195 _____________________________________________________________________________ 35 15. Sample 61295 (including stereopair) ______________________________________ i _____________________________ 36 16. Sample 61015 _________________________________________________________________________________________ 37 17. Sample 61175 (including stereopair) ___________________________________________________________________ 38 18. Large filleted boulder at Flag crater ___________________________________________________________________ 39 19. Planimetric map of station 2 ___________________________________________________________________________________ 40 20. Map showing block distribution within 10 m of station 2 panorama _______________________________________________ 40 21—24. Photographs: 21. Sample 62235 (including stereopair) ___________________________________________________________________ 40 22. Sample 62255 _________________________________________________________________________________________ 42 23. Sample 62275 (including stereopair) ___________________________________________________________________ 43 24. Sample 62295 (including stereopair) ___________________________________________________________________ 44 TABLES Page TABLE 1. Number and percentages of rocks (>2 g) documented at the LM/ALSEP station ___________________________________ 27 2. Number and percentages of rocks (>2 g) documented at station 1 _________________________________________________ 33 3. Number and percentages of rocks (>2 g) documented at station 2 _________________________________________________ 42 THE LM/ALSEP STATION . . . . parklng Site—ranglng from approx1mately 70 In east The central region of the Apollo 16 landing site includes three major areas—LM/ALSEP, station 1, and station 2—all underlain by materials of the Cayley plains. The LM/ALSEP station comprises five general areas—Lunar Module or LM, Apollo Lunar Surface Experiments Package or ALSEP, station 10, station 10’, and the Lunar Roving Vehicle or LRV final to 140 m southwest of the LM (pls. 3 and 8; fig. 1). All five sites lie within but at the east edge of distinct ray material ejected from South Ray crater 5.7 km to the southwest (fig. 2). The Cayley plains in the LM/ALSEP region are broadly undulating and slope to the southwest; the maximum relief within a radius of 400 m from the LM 21 22 site is 25 In (fig. 3). The amount of surface covered by 2- to 20-cm fragments ranges from 1.3 to 6 percent and averages about 2 percent (figl 4). Blocks as large as 0.5 m are relatively common (fig. 5). The largest boulder GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS (33 m north of ALSEP) is several meters across. The rocks are uniformly distributed, not deeply buried, and are poorly filleted, some are perched, unburied, and lack fillets entirely. The rocks with little or no fillet are 60600 60610—79 (rake) . DT 60014/60013 Pan :7AD \‘ Boulder . 60115 X en A/P 7 60135 X )gx60018 / x swc /' ,\ Flag X Pan 2 ‘_\‘ 60335 X / , i/ Area of\\ \ X LPM and 60335 \ 60015 i \ \\ / . \_/ . . ' P pan 1 \ LRV final location \ , approximately 100m—-. Pan 17 A / from LM ' 60025X \ . 60016 X ( \ \ >1. ./ ' -— “\ \ . ./ \ Area of Area of 60255 . 60235 (rVery subdued 180—m—diameter crater / Pa" 16 X\60500, 60510-35 (rake) \ / or 60010/60009 xx\ Pen 1 . /. XPen3Pen2 \-\ /- . _ _ __,. . Geophone line X MPA X Pen 4 ' ’/'- . , C/S ‘ - - . / PSE FlTG x g/ X Pen 5 ALSEP area LSM -< Pan 3 N El HFE X Deep core 60001 to 60007 60095 60050-59 (fl 1'0 210 3'0 410 5'0 METERS 60075 60035 X EXPLANATION x: Crater rim PSE Passive seismic experiment X 50335 Sample locality and number LSM Lunar surface magnetometer DT Drive tube HFE Heatflow experiment P pan Partial panorama RTG Radioisotopic thermoelectric APan 2 Panorama location and number generator LRV; dot on front MPA Mortar package assembly X Pen 5 Penetrometer reading, location LPM Lunar portable magnetometer and number SWC Solar wind composition C/S Central station FIGURE 1.—Planimetric map of the LM/ALSEP area. FIELD GEOLOGY OF CENTRAL REGION 23 EXPLANATION Outermost visible extent of discontinuous ray materials; hachures within rays Boundary of conspicuous ray within eiecta. Mapped only near traverses Boundary of continuous high-albedo ejecta near South Ray and Baby Ray craters ........... Inferred boundary 0 1 2 KILOMETE ' s . N North Ray ejecta S South Bay ejecta B Baby Ray ejecta FIGURE 2.—Distribution of ejecta near the Apollo 16 landing site. Derived from second-generation film positives of Apollo 14 orbital photographs ASl4—69—9520 and 9522 (500 mm), using stereoanalytic plotter (from Muehlberger and others, 1972). 24 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS 1K|LOMETER I FIGURE 3,—Map and stereopairs of the central part of the landing site. A, Contour map of Apollo 16 central landing site region superimposed on Apollo 16 panoramic photograph, frame 4618. LM sites and EVA—1 traverse indicated. Contour interval, 5 m; arbitrary datum. Geographic names on figure 6. Topography compiled on AP/C plotter by G. M. Nakata from panoramic-camera photographs ASl6—4618 and 4623. B, Stereopair showing the hummocky nature of the Apollo 16 landing site and central traverse region. Area of coverage identical to 3A. C, Stereopair showing the Lunar Module (arrow) on the lunar surface in the Descartes highlands. Note the relatively fresh 30-m-diameter crater 10 m east of the LM. Same photographs as in 3A and B, greatly enlarged. FIELD GEOLOGY OF CENTRAL REGION FIGURE 3.—Continued. 25 26 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS Station 11 N Station 13 (17403) 18164 0 5 1 2 KILOMETERS L l | l [(9 N \ 15¢ 10 t0 5 to 2 to . . 49/ >15 cm 15cm 10 cm 5cm Particle Size I? WA N Ida/j l ......... [—4 ...... |____[ / v @‘375 I / \f’?» area covered 4 Percentage of surface I | | S South Ray ejecta : I N North Ray ejecta i lnterray area +—4 7fi_____1 _l_._.._1 -|——l A—Ai—i i 5’ I 7 4-41 : l I’ 4% @% . , , .W H +31 1 it a, i a: a 91111 iias 4» ii/ ('1 .41, \o\$ a 0% «so JO; 38% 3?}, m 4903 Rt: 73:. " L: a: < ¢ EH'SH (1 ) \ ‘LM 49% Stafion 1 ~ (17816) (18317L ... Station [/18550 V4??? ......... If <—15 S Station 9 (17723) {6% Station 8 I -J——<"' S) 6 If) . 7 ’(\ (17679) (17614) X1“ ~ Station 4 1179691/ FIGURE 4.—Size distribution of fragments larger than 2 cm as determined from lunar surface photographs. Each line represents a size-distribution determination from a single photograph. Length is proportional to surface area covered by fragments as shown by bar scale. Five-digit numbers identify photographs; leaders tie them to their approximate positions along the traverse path (from Muehlberger and others, 1972). FIELD GEOLOGY OF CENTRAL REGION 27 thought torepresent ejecta from South Ray crater. The largest boulder near ALSEP has a well-developed fillet and may have been ejected from the older North Ray crater. The LM landed on the western wall of a very sub- dued crater, approximately 180 m in diameter, 10 m west of a moderaely subdued crater about 30 m in di- ameter. There are eight very subdued craters 125 m to 360 In in diameter within a radius of 400 m from the LM (fig. 6). Ejecta from these craters with excavation depths of 25 m to 70 m may be included in the material sampled at this station. The ALSEP was deployed in an intercrater area AS16710? 17425 17426 Near limit field of view 17435 17434 17433 012345METERS l__Ll_l_J—1 EXPLANATION Fragment symbols 10 to 20 cm 20 to 50 cm Round . \. Subangular I \. Angular A \‘ Hachures on outer circle show direction of individual photographs that constitute the panorama FIGURE 5.—Rock distribution within 10 m of the panorama site north of the LM (see pl. 3, pan 8). about 3.5 In higher than the elevation of the LM. Sta- tions 10 and 10’ were on the western rim crest of the crater in which the LM landed (fig. 6). Smaller, younger craters are common in the LM/ALSEP area, ranging from numerous 0.5 m to 2 m secondaries (prob- ably produced by ejecta from South Ray crater) to less common primary craters as large as 40 m in diameter. Samples collected in the LM/ALSEP area include all eight categories of rocks described in the petrology sec- tion'of this report (Wilshire and others, this volume; Wilshire and others, 1973): crystalline rocks (igneous, metaclastic), glass, and five types of breccias (table 1). The only other station where all rock types were col- lected was station 11. LM/ALSEP and 11 were the most thoroughly sampled of mission 16 stations. The source areas and depths of the LM/ALSEP sam- ples are not known with certainty, but some assump- tions can be made. As the LM site is on the eastern edge of a distinct ray from South Ray crater (fig. 2), a large proportion of the samples collected may be from that source. The 30-m crater just east of the LM site (figs. 1, 3A), however, may have ejected material from as deep as 6 m in the floor debris of the LM crater. A possible secondary source of sampled material is the reworked ejecta from the eight very subdued craters mapped within a 400-m radius of the LM (fig. 6). Many of the rocks collected in the LM/ALSEP area are at least partly glass coated and range from highly an- gular to subround (figs. 7—10). In general, the fine- TABLE 1.—N umber and percenta es of rocks ( >2 g) documented at the LM/AL EP station Category Number of rocks collected Percentage Igneous Cl ______________________ 3 5.4 Metaclastic: C2 ______________________ 11 19.6 Brecc1a Bl (light matrix, light clast) __________ 14 25.0 B2 (light matrix, dark clast) __________ 4 7.1 B3 (light and dark clast) ______________ 6 10.7 B.I (dark matrix, light clast __________ 8 14.3 B5 (dark matrix, dark clast) __________ 1 1.8 Glass: ______________________ 9 16.1 Total ________________ 56 100.0 28 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS ///// /////////////// /////////////// ///// ///// / / // // / ////////// ////////// /// / /////////// // / / / / / / / //////// / //// / // / / / / / / x= - 1 4 // / / -t —/ 63> C9 / // /// /// _ /// - /// - 1 /// - /// - / Ir ‘II/// .- //-' ‘-///, .- //- --//// - / //////////I -M - ///////////////////,I - ////_ - /////////////////// I -//////u /////////////////////‘ ‘///// — //////////////////////_///// v 2 /////////////////////// /////// N .5 1 KILOMETER _ EXPLANATION — — — — Lineament _Y_ _. L Base of subdued scarp; barbs point downslope Q) Crater rim crest 5 Freshest crater rim 1 Most subdued crater rim 3 Ridge near Buster crater FIGURE 6.—Sketch map of landing site and central region showing distribution of fresh to greatly subdued craters of significant siZe and their relation to EVA—1 traverse stations. 29 FIELD GEOLOGY OF CENTRAL REGION FIGURE 7 .—Sample 60016. NASA photograph 8—72—43829. 30 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS FIGURE 8.—Sample 60018. A, NASA photograph S—72—41499B. B, Approximate lunar orientation reconstructed in Lunar Receiv- ing Laboratory compared with enlarged part of EVA photograph ASl6—116— 18689, taken cross-sun, looking north (inset photo- graph, S—72—41840). Reconstruction by R. L. Sutton. FIELD GEOLOGY OF CENTRAL REGION 31 FIGURE 9,—Samp1e 60025. A, NASA photograph S—72—42593b. B, Approximate lunar orientation reconstructed in LRL, compared with enlarged part of EVA photograph A816—110— 17886, taken cross-sun, looking north (inset photograph, 8—72—44019). Re- construction by R‘ L. Sutton. 32 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS FIGURE 10.—Sample 60315. A, NASA photograph 8—72—41572. B, Approximate lunar orientation reconstructed in the LRL com- pared with an enlarged part of EVA photograph ASl6—117— 18836, taken oblique to sun, looking southwest (inset photo- graph, S—72—41842). Reconstruction by R. L. Sutton. FIELD GEOLOGY OF CENTRAL REGION 33 grained chalky and crystalline rocks, approximately 5 percent of the rocks observed by the crew, are smaller (6- to 12-cm range) than most breccia fragments. Documentation photographs of the samples collected at the LM/ALSEP station show that most of the rocks were either perched or only slightly buried, indicating that many samples from this station may be South Ray material. The soil in the LM/ALSEP area is in general medium gray, but patches of high-albedo soil are present near the ALSEP. White soils are more abundant to the west (toward stations 1 and 2), where they underlie a thin, darker surface layer. The soil in the LM/ALSEP area generally is firm except in the intercrater area of the ALSEP, Where it was found to be exceptionally loose and powdery. Soil of the intercrater regions associated with very subdued 200- to 300-m diameter craters typi- cally is less compact than the walls and rim crests of such craters (Schaber and Swann, 1971). Special samples collected at LM/ALSEP include a deep drill core at the ALSEP, double-core tubes at 10 and 10’, rake samples at 10, and the Lunar Portable Magnetometer (LPM) sample at the LRV final park position (fig. 1). The deep-core, rake, and double core- tube samples may contain North Ray crater ejecta but should contain material representative of the Cayley plains beneath the LM/ALSEP station. The deep drill core (223 cm) may have penetrated the ejecta from the “LM” crater and the subdued crater, 270—m diameter, immediately west of the station (see fig. 6). Two Lunar Portable Magnetometer readings were taken in the LM/ALSEP vicinity, the first the ALSEP site, the second at the LRV final park position (approximately 80 m east of the LM). The ALSEP site remanent field strength was very high, 231 gammas, the LRV park reading considerably lower, 121 gammas. This differ- ence represents a field magnitude gradient of 370 gamma/km, the maximum recorded during the mis- sion. The minimum gradient measured was 1.2 gammas/km between station 5 and the LRV final park position (Dyal and others, 1972, p. 12—5). Near the LRV final park location (fig. 1), two LPM measurements were made to calculate the magnetic field of a surface rock sample (60335) in order to deter- mine the total magnetization. The magnetic field was found to be below the resolution of the LPM (Dyal and others, 1972, p. 12—6). The passive seismometer (PSE) deployed at the ALSEP station was the most sensitive of the four lunar seismograph stations in operation at that time. On the basis of the initial 45-day record of operation, seismic events occurred at a rate of 10,000 per year; the rate at the Apollo 14 site was 2,000 per year, and at the 12 and 15 sites, 700 per year (Latham and others, 1972, p. 9—1). The higher sensitivity of the Apollo 16 seismome- ter has been attributed by Latham and others to the depth and elastic properties of the regolith, the infer- ence being that the Apollo 16 regolith is deeper or weaker, or both. The results of both the active and passive seismic experiments at Apollo 16 indicate that the regolith is not underlain by competent lava flows. Rather, the seismic velocities recorded suggest that a brecciated or impact-derived debris unit of undetermined depth underlies a 12.2-m-deep regolith. Petrographic analysis of the returned samples (almost entirely brec- cias) supports this hypothesis. STATION 1 Station 1 was located near the rim of Plum crater approximately 1,400 m west of the LM and 45 m lower. Plum crater, 30 m across and 5 m deep, is on the rim of Flag crater, 290 m in diameter (pl. 5, pans 4 and 5; fig. 11) and 40 m deep. When formed, Flag crater probably penetrated 60 In into the underlying Cayley plains material, but it has been partly filled by talus. The crater is subdued, having only a slightly raised rim, and no rocky exposures are visible in its walls or floor. Small subdued craters as large as 10 In in diameter are common in the area. The east part of station 1 appears to be crossed by a very faint ray from South Ray crater, but rock frag- ments >2 cm are less abundant (0.6 to 1.8 percent) than at station 2 or at the LM/ALSEP area (figs. 2, 4, 12). Rocks larger than 10 cm cover only 0.2 percent of the surface at this station, whereas at station LM/ALSEP rocks of similar size cover 0.3 to 0.9 percent (fig. 4). The crew mentioned that South Ray crater ray material was visible about 50 In east of the station 1 area. Samples (>2 g) collected at station 1, in table 2, are predominantly breccias of types B2, B3, and B4. The complete absence of B1 breccias, at least in the 'samples collected, may be significant with respect to the low TABLE 2.—Number and percentages of rocks ( >2 g) documented at station 1 Category Number of rocks collected Percentage Igneous C1 ______________________ 1 3.3 Metaclastic: C2 ______________________ 2 6.7 Breccia B1 ______________________ 0 0 B2 ______________________ 3 (1 in rake) 10.0 B3 ______________________ 10 (7 in rake) 33.3 B, ______________________ 4 (3 in rake) 13.3 Glass: ______________________ 10 (7 in rake) 33.3 Total ________________ 30 99.9 34 proportion of South Ray material in this station area relative to station LM/ALSEP, where 25 percent of the samples are Bl breccias. Four large samples, 61016 (B4; 11,745 g), 61135 (B3; 245 g), 61195 (G; 586 g), 61295 (B3; 172 g), were col- lected from the rim crest of Plum crater (pl. 5, pan 5), and are probably ejecta from that crater (figs. 13—15). Large samples 61015 (B2; 1,803 g) and 61175 (B3; 543 g) were collected away from the Plum rim crest and in an arc concentric to and about 30 m from the rim crest of Flag crater (pl. 5, pans 5 and 6; figs. 16, 17). These samples may represent original ejecta from Flag cra- ter, or possibly Flag rim materials reejected by Plum crater, which undoubtedly penetrated the upturned bedrock beneath Flag crater. A distinct, but smooth and somewhat subdued bench occurs in Plum approxi- mately 3 m below the surface. No outcrop is visible, but the benched topography suggests a change in cohesion of the materials in the walls of the crater. This change may reflect the contact beween Flag ejecta and raised bedrock in the eroded rim of Flag crater and may be the source area of the large, filleted, partly buried boulder from which sample 61295 (B;,) was collected (fig. 15B; pl. 5, pan 5). The largest of the Plum crater samples are B3 and B4 type breccias, whereas samples related to Flag crater are in the B2 and B3 categories. The B2 breccias at this station may represent the deepest excavation level (60 In) of Flag crater, a stratigraphic horizon not tapped by the smaller Plum crater (5 m). Sampling of all rock I 61510 (rake) I X61500 (soil) / 61155-58 X61140-44 Flag crater / L Apan4 x61175.61160-64 // \ / 61135,61195 \ h 6124049 61180 Trenc 2 - / \X / 61255,61220-26 / \ DLRV / Plum crater ‘ 361016 /\ 61295, 61280-84 / / .< / /LRV tracks / A \\ __'/ N Pan 5 1 ° 10 20 30 METERS g1____l__l .61015 FIGURE 11.—Planimetric map of station 1. GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS types present at this station may not have been statis- tically sufficient because of time constraints. At two places on the rim of Plum crater, the as- tronauts noted white regolith beneath a top layer of gray soil 1 to 2 cm thick. At one of these places, the light material lay beneath the gray on the fillet of a large boulder (fig. 18). This suggests that the fillet was formed by one of two mechanisms: (1) shedding of light material from the rock followed by postfillet deposition of a thin dark layer or (2) deposition of light material followed by darkening of the surface. White soil was observed at the trench site on the northeast rim west of Plum crater, where the top centimeter of gray soil was underlain by several tens of centimeters of white soil. Other samples collected at station 1 included those from the trench (61240, 61245 to 61249, 61255 and 61220), a fillet soil (61280 at 61295-boulder), and two surface soil samples (61160 and 61180). The crew observed that the large rocks were clearly more abundant on the rim crests of both Flag and Plum craters than in the intercrater areas, indicating that AS16—109 17782 17781 17780 17783 Hidden from view .—,r"‘ by crater slope V. 17779 17784 17785 Near limit field of view Astronaut shadow ___— 17775 ‘ 0 17793 «(\K\\\ O V O 0 [Hidden from\’ '- 17787 ._ &\\view by\ ‘ 17792 crater slope 17788 17789 N 17790 01 234 SMETERS L_.l_1__L_Ll EXPLANATION Fragment symbols 10 to 20 cm 20 to 50 cm Round . 7. Subangular I \- Angular A ‘A Hachures on outer circle show direction of individyal photographs that constitute the panorama FIGURE 12.—Rock distribution within 10 m of site of panorama 4 station 1. FIELD GEOLOGY OF CENTRAL REGION 35 Lr 1 ‘FIGURE 14.—Samples 61135 and 61195 showing approximate lunar orientations reconstructed in the LRL compared with an enlarged part of EVA photograph ASlG—114— 18405, taken cross-sun, look- ing south (inset photographs, 8-72—41609 and 43315, re- spectively). Reconstruction by R L. Sutton. ‘34- .( 36 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS FIGURE 15.—Sample 61295. A, Stereopair composed of NASA photographs 8—72—409468 and 40946. B, Approximate lunar orientation reconstructed in the LRL compared with an enlarged part of EVA photograph ASl6—114— 18412, taken cross-sun, looking north (inset photograph, 8—72—40967). Reconstruction by R. L. Sutton. FIELD GEOLOGY OF CENTRAL REGION 37 these craters are the most recent source of the deposits. Two very large craters 180 m south of station 1 (450-m diameter and 630-m diameter, “Eden valley”) may have contributed ejecta to the area from depths of 90 to 130 m before the impact at Flag crater (fig. 6). The significance of these materials in the collected samples has not been ascertained. The surface rocks at station 1 are considerably less abundant, more eroded, less angular, and distinctly more buried than at station LM/ALSEP, demonstrat- ing (pls. 3, 4, and 5) the scarcity of fresh South Ray ejecta at station 1. STATION 2 Station 2, located approximately 850 m west of the LM, is just north of Spook crater (370 m diameter) and on the blocky south rim of Buster crater (90 m diame- ter) (pl. 5, pan 6; fig. 19). The area is crossed by a faint ray of high-albedo material thought to be derived from South Ray crater, 5.7 km to the southwest (fig. 2). Sub- dued, grooved lineaments radial to South Ray crater cross the area. FIGURE 16,—Sample 61015 showing approximate lunar orientation reconstructed in the LRL compared with an enlarged part of EVA photograph ASl6— 109— 17808, taken cross sun, looking north (in- set- photograph, S—72—41058). Reconstruction by R. L. Sutton. Fragments as large as 0.5 m, but mostly 5 to 10 cm, are scattered over the station area; they cover 1.6 to 2.6 percent of the surface, averaging 2.0 percent (figs. 4, 20). Rocks larger than 5 cm cover 0.4 to 1.5 percent of the surface, averaging less than 0.8 percent. Most fragments are angular to subangular and are perched or only slightly buried. Fillets are rare. Station 2 lies within the continuous ejecta blanket of both Spook and Buster craters. Samples collected should include some material from both craters, al- though Buster is more clearly associated with surface rock fragments. Spook crater is symmetrical with a subdued but slightly raised rim; no rock exposures are discernible on the walls. Buster crater is about 100 m north of Spook crater and is superimposed on its outer rim. The rim of Buster is fairly sharp, the inner walls fairly steep. Ninety percent of the floor and a large part of the walls and rim of Buster crater are covered by blocky debris that trends northeast across the crater floor (pl. 5, pan 6). The rocks in the crater floor, as large as 5 In, are angular. The crew discerned northeast- trending planar structures dipping northward within the blocks and a parallel organization of the blocks. Buster crater penetrates about 18 m into the south end of a subtle ridge, 15—18 m high (maximum) and 700 m long, that trends northwest from the station area (“B” in fig. 6). The conspicuous blocks on the floor of Buster crater may have been derived from this ridge. Halfway crater, 155 m west of Buster and off the ridge, is slightly more subdued and has very few associated blocks. The nature and distribution of the blocks in the floor and walls of Buster (pl. 5, pan 7) suggest that it penetrated a more coherent substrate than most craters of similar size and age in this region. A bench recognized in the blocky part of the wall of Buster cra- ter may represent the change in coherence between the regolith and the inferred bedrock. Spook crater penetrated 75 m into the Cayley plains; its location on the northeast edge of the “Eden valley” crater complex (penetration to 120 m) suggests that some of the material ejected may be from the earlier “Eden valley” impact (fig. 6). A total of eight rocks larger than 2 g were collected from the station 2 vicinity; they represent both crystal- line and breccia types, as shown in table 3. The percentage of the B1 breccias collected from sta- tions LM/ALSEP (25 percent), station 1 (0 percent), and station 2 (37 percent) appears to show a relation to the presence of continuous-ejecta deposits from South 38 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS B FIGURE 17.—Sample 61 175. A, Stereopair, NASA photographs 8— 72—41197 and 41 197B. B, Approx- imate lunar orientation reconstructed in the LRL compared with EVA photograph ASIB— 109— 17798, taken down sun, looking west (inset photograph, S—72—40966). Reconstruction by R. L. Sutton. FIELD GEOLOGY OF CENTRAL REGION 39 FIGURE 18‘—Large filleted boulder showing high-albedo material kicked by astronauts (ASl6— 109— 17802). 4O GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS I Buster crater / / AS16-109 / _ -——-” X 62235 to 62237, P pan 7 62240, 62255 17815 17816 N A U 1 /\ 17813 \/ X 62275 17819 ’\ ‘ J \ X 62295, 62280 17812 17820 X LPM 17811 17821 a LRV 17827 17822 A Pan 6 17824 012 3 4 5METERS Spook crater I l | | I 0 10 20 30 METERS L l L 1 1 J /’ EXPLANATION / Fragment symbols / 10to20cm 20t050cm Round 0 7. FIGURE 19.——Planimetric map of station 2. For explanation of SUbanQU'ar I \- Angular A ‘A symbols see figure 1. Hachures on outer circle show direction of individual photographs that Constitute the panorama. FIGURE 20.—Rock distribution within 10 m of site of station 2 panorama. FIGURE 21,—Sample 62235. A, Stereopair (NASA photographs 8—72—41280 and 41280B). B , Samples 62235, 62236, and 62237 showing ap- proximate lunar orientation recon- structed in the LRL compared with an enlarged part of EVA photograph AS16—109—17838, taken cross-sun, looking south (inset photographs, 8—72—41424, 41837, and 41838, re- spectively. Reconstruction by R. L. Sutton. FIELD GEOLOGY OF CENTRAL REGION FIGURE 21.—Continued. 41 42 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS TABLE 3.—N umber and percentages of rocks ( >2 g) documented at station 2 Category Number of rocks collected Percentage Igneous 1 ______________________ 1 12.5 Metaclastic: 2 ______________________ 1 12.5 Breccia: 1 ______________________ 3 37.5 B2 ______________________ 2 25.0 B3 ______________________ 1 12.5 B., ______________________ 0 0 Total ________________ 8 100.0 Ray crater. South Ray ejecta crosses stations LM/ ALSEP and 2 but is extremely sparse at station 1. This relation does not appear to hold, however, when the sample types collected at stations 6 and 8 are exam- ined. Although these stations are much closer to South Ray crater, no B1 breccias were collected from either site. If indeed the B1 rocks at the stations LM/ALSEP, 1, and 2 sites are related to South Ray ejecta, they would have to represent a very shallow horizon within that crater, deposited primarily downrange. The asso- ciation is tenuous at best. Breccia type B4 was not sam- FIGURE 22.—Sample 62255. A, Stereopair (NASA photographs S—72—41823B and 41823). B, Approximate lunar orientation re- constructed in the LRL compared with an enlarged part of the EVA photograph A816—109— 17844, taken cross-sun, looking south (inset photograph, 8—72—41834). Reconstruction by R. L. Sutton. FIELD GEOLOGY OF CENTRAL REGION pled at station 2 but made up 14 percent of the rocks collected at LM/ALSEP and 13 percent of those re- turned from station 1. The planimetric map of station 2 (fig. 19) clearly shows that most sampling was done closer to Buster crater rim than to Spook crater. The samples collected nearest Spook were 62295 (Cl) and 62280 (soil) at a distance of about 70 m. Photographs and orientation diagrams for the station 2 large rocks are shown as figures 21 to 24. 43 Astronaut Duke commented regarding Buster cra- ter, “The blocks are angular, but they are definitely coming out of Buster.” The most recent source of col- lected samples therefore may have been Buster crater, which probably reexcavated much Spook crater mate- rial. The surface soil at station 2 is medium gray with a higher albedo soil below the upper centimeter or so, similar to light soil at the ALSEP and at station 1. The compaction and granularity of the soils are typical of FIGURE 23.—Sample 62275. A, Stereopair (NASA photographs S—72—40922B and 40922). B, Approximate lunar orientation re- constructed in the LRL compared with an enlarged part of EVA photograph AS16— 109— 17846, taken cross-sun, looking south. The sample is fragile and minor breakage has occurred; shadow details were impossible to duplicate accurately in the laboratory (inset photograph, 8—72—41426). Reconstruction by R. L. Sutton. 44 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS the area. Small craters as much as 2 m in diameter are distributed fairly uniformly; they are generally sub— dued but a few small fresh craters, possibly South Ray secondaries, have sharp rims on which cloddy ejecta is discernible. SUMMARY The samples collected from stations LM/ALSEP, 1, and 2 most probably represent materials of the Cayley plains to depths of 70 m or more and materials from the upper layers within South Ray crater. The proportions of rock types collected from each station were constrained by time available and may not be clearly indicative of the rocks present at depth. The variety of rock types collected at stations LM/ ALSEP, 1, and 2 indicates that the Cayley plains brec- cias are heterogeneous and suggests that they are composed of pockets of both light and dark breccias deposited by a turbulent process characteristic of large-basin ejecta emplacement. The great amount of South Ray ejecta within the central plains of the landing site, suggested by the dis- tribution of high-albedo materials radial to that crater (fig. 2), appears to be a heterogeneous collection of light and dark breccias including all types collected throughout the region traversed during the mission. FIGURE 24.—Sample 62295. A, Stereopair (NASA photographs S—72—44492 and 44492B). B, Approximate lunar orientation re- constructed in the LRL compared with an enlarged part of EVA photograph ASl6—109—17848, taken cross-sun, looking south (in- set photograph, S—72—42563). Reconstruction by R. L. Sutton. FIGURE 12. 13. 14. 15—21. 22. 23. 24—27. 28. 29. 30. 31. 32. 33. 34. ‘- ~r ~17" mud-‘9; (,8; D2. GEOLOGY OF NORTH RAYCRATER By GEORGE E. ULRICH CONTENTS Page Introduction _________________________________________________________________________ 46 Physiographic setting _________________________________________________________________ 46 Block distribution and rock types _______________________________________________________ 46 Sample localities _____________________________________________________________________ 52 House rock area ___________________________________________________________________ 53 White breccia boulders ___________________________________________________________ 61 Interboulder area _________________________________________________________________ 69 Shadow rock area _________________________________________________________________ 69 North Ray soils _______________________________________________________________________ 78 Geophysics ___________________________________________________________________________ 79 Summary _____________________________________________________________________________ 79 ILLUSTRATIONS Page Hypsographic map of the Apollo 16 site __________________________________________________________________________ 47 Photograph of northern part of Apollo 16 landing site ____________________________________________________________ 48 Topographic map of North Ray crater and vicinity ________________________________________________________________ 49 Stereopair showing northeast wall of North Ray crater from east panorama station ________________________________ 50 Map of boulders, craters, and ejecta grooves in North Ray crater area ______________________________________________ 50 Maps showing block distribution within 10 m of station 11 and 13 panoramas ______________________________________ 51 Photographs: 7. Dark-matrix breccia boulder in White breccia boulder area ________________________________________________ 54 8. Partial panorama of House rock and Outhouse rock at station 11 __________________________________________ 55 9. Partial panorama and sketch of Shadow rock at station 13 ________________________________________________ 56 10. Fillets and sample locations, White breccia boulders ______________________________________________________ 56 11. Stereopair and sketch map showing surface texture and clast distribution, White breccia boulder ____________ 57 Map and histogram showing proportions of light and dark fragments counted in surface panoramas at North Ray crater ____________________________________________________________________________________________________ 58 Maps showing location of rocks and soils collected at stations 11 and 13 ____________________________________________ 59 Histogram of abundance of rock types collected from four localities at North Ray crater ____________________________ 60 Photographs: 15. Stereopair of sample 67915 ______________________________________________________________________________ 60 16. Sample 67955 __________________________________________________________________________________________ 62 17. Impact-spalled area on east face of Outhouse rock ________________________________________________________ 63 18. Sample 67935 __________________________________________________________________________________________ 64 19. Sample 67937 __________________________________________________________________________________________ 64 20. Sample 67956 __________________________________________________________________________________________ 65 21. Three dark-matrix breccias ____________________________________________________________________________ 65 Photomicrographs of ophitic texture in fragment 67948 ___________________________________________________________ 66 Telephotograph of large light-matrix breccia blocks on northeast wall of North Ray crater __________________________ 66 Photographs: ___________________ 24. Broken fragments and fines of sample 67455 ____________________________________________________________ 67 25. Stereopair and photomicrograph of sample 67455 ________________________________________________________ 68 26. Sample 67475 __________________________________________________________________________________________ 70 27. Samples 67016, 67035, 67415, and stereopair of 67435 ____________________________________________________ 70 Photomicrographs of metamorphic clasts within light-matrix breccias ______________________________________________ 72 Photographs of samples 67015, 67075, 67115, and stereopairs of 67055 and 67095 __________________________________ 73 Photomicrographs of a typical light-matrix breccia, 67075 ________________________________________________________ 75 Photographs of Shadow rock and closeup of surface texture _______________________________________________________ 76 Photograph of sample 60017 ____________________________________________________________________________________ 77 Photomicrograph of sample 60017 _____________________________________________________________________________ 78 Photograph showing estimated exposure to sunlight beneath overhang of Shadow rock during one lunation __________ 80 45 46 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS TABLES Page TABLE 1. Distribution of blocks at North Ray crater by size and shape __________________________________________________ 46 2. Rock samples greater than 2 g from the House rock area ______________________________________________________ 52 3. Rock samples greater than '2 g from the White breccia boulders area __________________________________________ 52 4. Rock samples greater than 2 g from the Interboulder area ____________________________________________________ 53 5. Rock samples greater than 2 g from the Shadow rock area, station 13, on outer North Ray ejecta ________________ 53 6. North Ray crater soil samples greater than 26 g ______________________________________________________________ 53 INTRODUCTION North Ray crater was the primary sampling target of 7the last of three traverses made during the Apollo 16 mission. Its apparent youth minimizes the chance of contamination by ejecta from younger craters; its deep exposures, 230 m into the subsurface, reveal strati- graphic differences to approximately that depth. Orbi- tal and surface photographs illustrating the vertical sequence of units exposed in the wall of North Ray crater, together with the rocks and soils collected on its rim and ejecta blanket and the crew’s first-hand obser- vations, provide the controlling data for interpreting a stratigraphic model in this area of the landing site. This model is extended to the larger region explored by Apollo 16 in Ulrich and Reed (this volume). PHYSIOGRAPHIC SETTING North Ray crater lies at the foot of Smoky mountain and is one of the highest sampling sites in the landing area. Its setting is well illustrated from a surface per- spective on plate 11 (pan 34). Station 4, on Stone mountain, is at approximately the same elevation; the rim of South Ray crater, 10 km to the south, is about 170 m lower (fig. 1). About 1 km across, North Ray crater straddles a ridge approximately 50 m high and a little narrower than the crater rim. The crest of this ridge, informally named North Ray ridge, is nearly parallel to the base of Smoky mountain. Its similarity in morphology to Smoky mountain and to the De- scartes highlands in general was not recognized until after the mission when orbital photography with low- sun-angle illumination became available (fig. 2). The top of the ridge is 400 m below the top of Smoky mountain, which suggests that the ridge may be a downfaulted segment of the mountain and therefore that North Ray crater may expose material from part of the Descartes mountains in its walls. That part of the crater interior visible from the rim is shown by the postmission topographic map (fig. 3). The crest is rounded but falls off rapidly to the steep crater wall, whose upper slopes are generally convex, ranging from 27° at the top to 34° in the lower half. Precipitous drops in the foreground slopes below the rim crest made photographing the lowest parts of the crater wall impossible. Only the upper ‘60 percent of the crater wall is observable from the .v-antage point at station 11 (figs. 3, 4). The rounded form of the crater rim, the smooth walls with few blocky areas, and the predomi- nance of breccias in the observable rocks on the surface are evidence that the target materials impacted by North Ray crater were breccias of relatively low strength. BLOCK DISTRIBUTION AND ROCK TYPES The concentration of blocks on the trim of North Ray crater was considerably lower than anticipated. The low frequency of fragments was observed on the ap- proach to the crater rim. Fragments range from 25 m to less than 1 m in maximum diameter. Most of the large boulders observable on postmission orbital photo- graphs, mapped here on figure 5, had been identified on premission photographs. Within 10 m of the site of panorama 18 (pl. 8), fragments 10 cm and larger cover 4.3 percent of the surface (figs. 4, 6A); at station 13, 0.75 km away, they cover only 0.5 percent with about one-fourth as many fragments (fig. 6B and panorama 23, pl. 7). Nearly 70 percent of the fragments counted at these stations are rounded (fig. 6; table 1). At station 11, more than 20 percent are larger than 20 cm in diameter, at station 13, only 10 percent. All the blocks with discernible textures are clastic in appearance. Their matrices range from dark to light gray, as seen in the black-and-white photographs. The TABLE 1.—Distribution of blocks at North Ray crater by size and sha e [Number of blocks counted and percentage Idf total within 10 m of center of station 2 panoramas. Data from figure 6] Shape Shape 10—20 20—50 >50 Total percent Cm cm cm Station ll—rim crest Rounded __________________________________ 145 35 0 180 69.0 Subangular ________________________________ 44 1 1 0 55 2 1.0 Angular __________________________________ 13 3 10 26 10.0 Total ________________________________ 202 49 10 261 Size percent ______________________________ 77.4 18.8 3.8 100.0 Station lfi—outer ejecta blanket Rounded __________________________________ 41 6 0 47 68.1 Subangular ________________________________ 13 1 0 14 20.3 Angular _____ i e i i 8 0 0 8 1 1.6 Total ________________________________ 62 7 0 69 Size percent ______________________________ 89.9 10.1 0 100.0 NORTH RAY CRATER 47 e°4a'215:20l'8"E I5°37'32"E ° 5 8°48'20"S SMOKY MOUNTAIN EXPLANATION' . ' . ' . ELEVATION, IN METERS ' . ' . E >aooo [:2] 7950—8000 . 7900— 7950 7850 — 7900 7800- 7850 7750 - 7800 7700— 7750 7650 7700 - < 7650 — — -Line of traverse, dashed where approximate '2 Station 9°II‘I5"s 9°|I'l5"S '5°2° '8 E I .5 o IKILOMETER |5°37'32"E FIGURE 1.—Hypsographic map of the Apollo 16 site showing topographic zones in 50-m increments. Modified from Muehlberger and others (1972) and AFGIT (1973). Copyright 1973 by the American Association for the Advancement of Science. 48 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS FIGURE 2.—Northern part of Apollo 16 landing site, showing princi- pal named features. Dashed line, possible fault; U, upthrown side; D, downthrown side. Apollo 16 panoramic camera frame 4558, sun elevation 16°. From Ulrich (1973) Reprinted with permission of Pergamon Press. NORTH RAY CRATER 49 8°47‘40”S , x Y 6 A y ’ 2 $/ 7875J ( L Vs E /\Comour interval 5 meters, from topography by G.Nakata \/‘using Apollo l4 Hosselblad and Apollo I6 Panoramic camera photography on AP/C planer / / A l \1 \ will 4 _ p , A I ‘ ~ , nan: “W W \\\\ MM , b $§§§§§\ , ‘ ] fl\ . §§§§§§i rfl 9 ‘ «j J! r (\\ e k K) 79 7X K ) roc / M f/& ; 8°52'37"S 15°27'12"E FXGURE 3.—Topographic map of North Ray crater showing station localities and area visible from rim. Contour interval 5 m. Topography by G. M. Nakata from Apollo 16 panoramic camera frames 4618 and 4623. From Ulrich (1973). Reprinted with permission of Pergamon Press. 50 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS FIGURE 4.——Stereopair showing northeast wall of North Ray crater from east panorama station. Foreground shows typical slopes inside rim crest. ASl6—106— 17301, 17302. 8°45'52" \o‘i J °/ 0 o o / I I o 0 °\\ \ | O H \\ \ \\ <° \ I ° ° \ \ ° 0 \o\\\°\\.\)/ o o (_)\\ °. r\ Stone \ 0 'O \O \o5 t \.J mountain w» 0 . ‘ -- o ° C, k) C \\ . - . o . o o o o .. - .- _ , 9 . o On 0 .' o 1',- An - o o ., -.-..I (3 o ' "f A"; ~ 0 O (W o . ' \- O . m ., . .0 North Ray / 0 ° . 0 (f) 'o -. . o \ . .. ll . ° ' fa) () '- _ ‘House rock k . 0 a Q ‘ o ‘ o . 0 -_ o O . \ ' l o a. I \ \ o N ' \\\\ '\00 0 | \ (J . "-Sthow . ' o 500 IOOO METERS ,\ \_ \ , JOCK I__;_l OO ( \ \ °/\ \ EXPLANATION \\/O k )0 ° o r\\ ‘\ - Boulder 0 V \ 0 Fresh crater C) Subdued crater \ f Ejecta grooves / 8°54'55"s , .. l5°2528 I5°34‘07"E NORTH RAY CRATER 51 AS16406 18599 18600 18592 012 3 4 5METERS l__|._Ll_1_l EXPLANATION Fragment symbols 1010 20 cm 20 to 50 cm Round . ‘0 Subangular I \- Angular ‘ \‘ Hachures on outer circle show direction of individual photographs that constitute the panorama A AS16-106 Near limit field of View 17404 17403 012 3 4 5METERS LLJ__1_1_1 EXPLANATION Fragment symbols 10 to 20 cm 20 to 50 cm Round . \. Subangular I \- Angular ‘ \‘ Hachures on outer circle show direction of individual photographs that constitute the panorama B FIGURE 6.—Block distribution within 10 m of sites of station 11 and station 13 panoramas. A, Station 11. B, Station 13. From Muehlberger and others, 1972. {FIGURE 5.~—Map of boulders, craters, and ejecta grooves in North Ray crater area. Data from Apollo 16 panoramic camera frames 4563 and 52 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS dark-matrix rocks consistently exhibit angular edges and pronounced jointing, and few have soil fillets .de- veloped at their bases (figs. 7—9). Light-matrix boulders are distinctly more rounded, more crudely jointed, and more deeply filleted by soil inferred to be their own residual debris (figs. 10 and 11). The rock sample characteristics, discussed below and by Wilshire and others (this volume), reflect simi- lar differences in coherence or friability. Megascopi- cally and microscopically, textures indicate that varia- tions in rock colors and coherence are produced by differences in amounts of impact melt incorporated in the rocks and in rates of cooling. Of more than 800 rocks in the near field of four pho- tographic panoramas taken on the rim and ejecta blanket of North Ray crater, 70 to 90 percent are rela- tively light colored (fig. 12). These include the light- and medium-gray-matrix breccias (B., B2, and B3 of Wil- shire and others, this volume) and probably some igneous and metaclastic rocks (C1 and C2) that are in- distinguishable from the light-matrix breccias in sur- face photographs. Rocks consisting largely of glass (class G of Wilshire and others, this volume) may be counted as dark rocks (dark-matrix breccias, B4 and B5) except where large amounts of light-colored soil adhered to their surfaces. The percentage of dark rocks increases from about 10 in the western part of the southeast rim (panorama 19 and sketch, pl. 8) to nearly 30 at a location midway between the White breccia boulders and House rock. About 20 percent of the fragments at Shadow rock are dark. SAMPLE LOCALITIES In order to reconstruct the stratigraphic sequence in North Ray crater, the distribution and concentration of the several rock types with respect to their location on the crater wall and floor were studied. The sampled area is subdivided into four localities, the White brec- cia boulders, the Interboulder area, the House rock TABLE 2.—Rock samples greater than 2 g from the House rock area Weight group (g) Classification ___ (Wilshire and Sample 2—25 25— 100 100+ others, this Geologic significance 0. volume, table 1) 67915 WW WW X B4 Representative of House and Outhouse rocks. 67935 __W _W_ X I(CZ) Metaclastic matrix from Out» house rock. 67936 _W_ X __W C. Same as 67935, in impact-spell zone. 67937 WW x WW B. Dark-matrix breccia from im» pact spall zone. 67945 X _W_ WW B. Rock from "east-west split.” 67946 X W__ __W (B.) Do. 67947 X _W_ WW (B.) 0. 67955 __W WW X B. Light-matrix clast from Out- house rock. 67956 X WW WW C. Igneous fragment from Out- house rock. 67975 WW WW X B2 Fragmelzit in soil near Outhouse roe . ‘( ) Provisional classification by Wilshire and others, this volume, table 1. area and the Shadow rock area (fig. 13), whose names were derived from descriptive terms used by the crew. All but Shadow rock are on the crater rim crest. Shadow rock is approximately 0.75 km southeast of the TABLE 3.—Rock samples greater than 2 g from the White breccia boulders area Classification (Wilshire and Weight group (g) Sample 2—25 25—100 100+ others, this Geologic significance No. volume, table 1) 67016 ___. __W X ‘B.(B2) Large loose rock on crater rim crest. 67025 X WW WW B2(B.) Coherent fragment, possibly from 67016. 67035 _W_ ____ X B2 "Three-rock" breccia 20 m inside rim crest. 67215 _W_ WW X Unclass Unopened rock in padded bag. 67415 ___. WW X B. Friable rock at base of light- matrix breccia boulder. 67435 WW WW X 2(B4) Glass-coated; may be dark- and light-matrix breccia. 67455 __W WW X B2 Fragments off top of 6 m light- matrix breccia boulder. 67475 WW ___. X B. Clast from the same boulder as 67485 X ____ WW (0.) Fra ent in soil near 67455 ight-matrix boulder. 67486 X WW ___. (B.) 0. 67487 X WW __ W (Cg) Do 67488 X ____ W __ (0.) Do. 67489 X _ ___ __ __ (0,) Do. 67515 WW X W__ B2 Breccia in rake sample near 67455 light-matrix boulder. 67516 X WW WW B2(B.) D0. 67517 X ____ __W B2(B.) Do 67518 X WW __W B2(B.) Do 67519 X ____ __W B2(B.) Do 67525 X W W __W B203.) Do 67526 X WW __W B2(B.) Do 67527 X W__ WW B2(B.) Do 67539 X W W __ W B2(B.) Do. 67549 WW X __W B. Do. 67555 W W W W B. Do. 67556 _ W_ X W W B. Do. 67557 X W W Unclass Do. 67558 X WW Unclass Do. 67559 WW X WW (C2) Olivine basalt“ in rake sample near 67455 boulder.3 67565 X WW WW C2 Basalt“ in rake sample near 67455 boulder. 67566 X WW WW C2 D0. 67567 X WW W__ G Breccia in rake sample near 67455 boulder. 67568 X ____ __W G Do. 67569 X W__ ____ G Do. 67575 X ____ ____ G Do. 67576 X __W ____ G Do. 67605 WW X WW B2 Fragment from soil sample in rake area. 67615 X ____ WW C2 Basalt" in rake sample 10 m in- side rim crest. 67616 X W__ WW C2 0. 67617 X WW ___. C2 Basaltic breccia“ in rake sample ' 10 m inside rim crest. 67618 X WW WW C2 Do. 67619 X __W WW C2 D0. 67625 X W__ WW C2 Metaclastic rock in rake sample 10 m inside rim crest. 67626 X _W_ WW G Breccia in rake sample 10 m in- side rim crest. 67627 _W_ X __W G D0. 67628 WW X G Do. 67629 WW X G Basalt“ clast from light-matrix breccia. 67635 X WW W__ B. Breccia in rake sample 10 m in- side rim crest. 67636 X WW WW B. Do. 67637 X ____ __W B. Do. 67638 X _ __ _ WW B2 Do. 67639 X W _ _ W _ _ B. Do. 67646 X WW WW 2 Do. 67647 WW X WW Unclass Do. 67648 X WW WW B2 Do. 67655 X W W 13. Do. 67665 X __ W (13;) Do. 67666 X W W 2 Do. 67667 X ___- Cg Ultramafic?“ in rake sample 10 to inside rim crest 67668 X WW WW C2 Basaltic breccia* in rake sample 10 to inside rim crest 67669 X WW WW (3..) Breccia in rake sample 10 m in- side rim crest 67676 X WW WW C2 Basalt." in rake sample 10 m in- side rim crest ‘BZ(B3) Alternative classification by Wilshire and others (this volume). 2( ) Provisional classification b Wilshire and others (this volume). 3*Interpretation from Smith an Steele (1972). NORTH RAY CRATER 53 crest, but still on continuous North Ray ejecta. For each of the four areas, the rock samples weighing more than 2 g are tabulated and their geologic significance indicated in tables 2 to 5. Their occurrence by rock type is graphically compared in figure 14. The larger soil samples and their location and geologic significance are given in table 6. HOUSE ROCK AREA The largest boulder visited and one established as a sampling target before the mission is House rock. It is an angular, predominantly dark-matrix boulder, ap- proximately 25 m long and 12 m high, at the north- eastern limit of the crater-rim-crest traverse area (figs. 8, 13; pl. 8, pan 28). It was so named when Astronaut Duke, on first observing it at station 11, compared its size to that of a house. Less than 1 m away on the south end of House rock is a 3-m boulder of similar texture, anonymously named Outhouse rock, the source of most of the rock samples collected at this locality. TABLE 4.—Rock samples greater than 2 g from the I nterboulder area Sample 2—25g 25— 100 100+ No. Classification (Wilshire and others, this Geologic significance volume) 67015 __-_ ____ X 133(32) Large loose rock inside rim crest. 67055 __-. _-_- X 82033) Collected for abundant black clasts (more than 67035). 67075 ___. ____ X Bl Found as two broken pieces of white shocked rock. 67095 __-_ ____ x G Collected for ap arance as "really blac lass.” 67115 _-__ ____ X 2(33) Same location as 7095; more rounded. 67235 ____ _-.- X Unclass Unopened rock in padded bag. 67705 X _-__ _-__ (G) Fragment in rake soil on rim crest. 67706 X _-__ _-__ Unclass Do. 67715 X ____ -_-- 4 Basalt“ probably clast from light-matrix breocia.’ 677 16 X __ _ _ _ - _ _ B, Breccia, probable clast from light-matrix breccia. 67717 X -_-- -._- B. Do. 67718 -_-_ X __-_ (13;) Do. 67719 X ---_ __._ B, . 67725 X ____ -_-_ B. Breccia in rake sample on rim crest. 67726 X - __ _ B. . 67728 X _ __ _ G Fragment in rake sample on rim crest. 67729 ____ X ____ G Do. 67735 X --__ ___- 3,033) Do. 67736 X -_-. .--- C2 Olivine basalt with ultramafic inclusion; zapped on all _ sides.‘ 67737 X __-- ____ B, Basalt“ probable clast from light-matrix breccia. 67738 X ___- ____ B. Do. 67739 X ___- ___- B4 Fragment in rake sample on rim crest. 67745 X --_- ___- B4 Basalt“ in rake sample on rim crest. 67746 X ___. ___. C, Norite?‘ in rake sample on rim crest. 67747 X _--_ ---_ C, Troctoliw?‘ in rake sample on rim crest. 67748 X _--_ __-_ C, Fragment in rake sample on rim crest. 67749 X ____ -.-_ B, Breccia in rake sample on rim crest. 67755 X B, Do. 67756 X B2 Do. 67757 X B, Do. 67758 X B, Do. 37759 X B, Do. 67766 X -. .- _ -__ B, Do. 67769 X ____ ___- B, Do. 67775 X __._ ___- B, Do. 67776 X -___ ____ 8, Do. lBg(Ba) Alternative classification by Wilshire and others (this volume). 2( ) Provisional classification by Wilshire and others (this volume). ”Interpretation from Smith and Steele (1972) TABLE 5.—Rock samples greater than 2 g from the Shadow rock area, station 13, an outer North Ray ejecta Classification (Wilshire and others, this Sample 2—25g 25—100 100+ Geologic significance No. volume) 60017 ___- --__ X lB‘(B5) Large rock broken off from 2 in area on southwest side of Shadow rock. 63335 ____ X ____ z(B5) Chip rock broken 011” from 2 in area on southwest side of Shadow rock. 63355 --__ X ___- B. Do. 63505 X ____ ___- (B4) Fragment in rake soil 5—10 m west of Shadow rock 63506 X ___- __-_ Cl Do. 63507 X ___- ___- B, Do. 63508 X _-_- __-_ B, Do. 63509 X -_-_ -___ B2 Do. 63525 X ____ -___ (3.) Do. 63526 X --_- ____ (B1) Do. 63527 X -__- ___- (3.) Do. 63528 X -_-- ____ (3.) D0. 63529 X __._ -_._ (3.) Do. 63535 X __._ ___- (13.) Do. 63537 X ____ -_-_ (Cg) D0. 63538 ._-- X ___- (01) Do., 63545 X (C1) D0. 63546 X (13;) Do. 63547 X (C1) D0. 63549 ___. (C2) D0. 63555 X (34) Do. 63556 X __ __ -_-_ (C2) D0. 63557 X __ __ .--. (3.) Do. 63558 X __._ -_-. (Ca) Do. 63559 X __._ ___. (G) Do. 63566 X __._ -_-. (G) Do. 63567 X ____ -_-- (G) Do. 63568 X __._ ___. (G) Do. 63575 X _ ___ -_-- (G) Do. 63577 X ____ __._ (B.(Cz)) Do. 63578 X _-__ ____ (3;) Do. 63579 X __._ ___. (33) Do. 63585 __-- X ____ (Cg) Do. 63587 X ____ ___- (3;) Do. 63588 X ---_ ___- (3,) Do. 63589 X _ ___ ---- (33(32» Do. 63595 X _ ___ __-_ (33) Do 63596 X _-_- ____ (Bx) Do. 63597 X _-__ ____ (3;) Do. 63598 X ___- ___- (B3) Do. IB‘(B ) Alternative classification b Wilshire and others (this volume) 2( ) f’rovisional classification by ilshire and others (this volume). TABLE 6.—North Ray crater soil samples greater than 26 g Sample White breccia Interboulder House Shadow Geologic No.* boulder area area rock rock significance area area 63320—4 ___- -__- -___ X "Shadowed" soil on surface under northwest overhang of Shadow rock. 63340—4 _--- ___- __-_ X Soil beneath 63320 under northwest overhang of Shadow rock. 63500—4 .-.- ____ ---- X Rakelsoil5'r10mwestofShadow roc . 67010 _ _ _ _ X _ _ _ _ _ _ _ _ ReIindu'Ie in sample collection bag 0. 67020 X ___. ___. ___- Residue in Buddy Secondary Life Support System bag with rock 67016. 67030—4 X ____ -___ ____Residue in sample bag with rock 67035. 67410 X -_-_ ___. __._ Residue in sample bag with rock 674 15. 67450 X --_- ____ ___-Res’i7r1151e in sample bag with rock 5. 67460-4 X _-_- ___- ____ Fillet at boulder from which 67455 and 67475 were col- . 67480—4 X -- - - _ _ _ _ _ _ _ _ Reference soil for comparison with 67460; same location as sample 67510. 67510—4 X ____ ---- --_-Soil in rake sample near large, light-matrix breccia boulder. 67600—4 X __._ __._ _.--Rake soil collected about 25 m east of 67510; inside rim crest. 67610 X _--- -_-_ -___Soil in rake sample from same location as 67600. 67700—4 _-__ X -_-- -___Ra.ke soil from halfway between White breccia boulders and House rock. 67710—4 __-_ X _-__ ____Soil in rake sample from same location as 67700. 67910 - _ - _ _ _ _ _ X _- __ Rerslidu: in sample collection bag 0. . 67940—4 ____ _-__ X ___-Soil from‘"east-west split” be- ' tween House and Outhouse rocks. *-4 indicates sample was sieved in LRL into newly numbered fractions, 1 through 4, for less than 1 mm, 1—2 mm, 2—4 mm, and 4—10 mm, respectively. 54 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS FIGURE-7.—Dark-matrix breccia boulder in White breccia boulder area. For location see panorama 19, pl. 8. 55 .vmmmH 8 mvmi leg was 3w: mmwwfi $3|me< .83..“ @353 .3393 98 $3 umafla mo :93 302 .9823: 3895 xEquEEU he oofi amao mEBoLm ,: ccSSm an aEEccma :2: $3550 “in Jack omzomlw 55lo NORTH RAY CRATER hp 3ch we m2< «:3 Saafinm wmmmmg hm‘mnmhw ¥UOI meOI ¥UOI meOIPDO 56 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS \Smoky m‘CDLlntaill\ ll //l \\\\\y;\ x / \I/ /] Large dark clast\ / - ///\ Light-matrix / stringer\ — \—— \ \ \ \ \ [’1 Moat between fillet and rock] A B FIGURE 9.—Shadow rock panorama at station 13. A, South face of 5-m-wide boulder of dark-matrix breccia. A516—106—17413 to 17415. B, Sketch map of fractures and clasts. Samples 67455 and 67 75 Taken from distant boulder \ Edge of fillet/ ”'5 FIGURE 10.—White breccia boulders showing rounded outlines and deeply filleted margins. AS16—106—17325 and 17326. NORTH RAY CRATER B FIGURE 11,—Surface texture and distribution of dark clasts, White breccia boulder. A, Stereopair showing surface texture. A816— 106— 17327 to 17328. B, Sketch map showing distinction of dark clasts and top of fillet. 57 58 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS North Ray crater rim crest - ~~~ / \ \ \ / . . House rock 85 / / . Outhouse rock’ 227 N ._ / / l V A / EXPLANATION fl . Dark rocks \ I Approximate _ / I / / V " / East partial pan ,r'll / E Light rocks 411 Number of rocks counted Nfl \ . A ' , ““““ STATION 11 / 360O pan ' West partial pan I ' / / C ,/' b-———..——— ' / LFlV -\ ’750 m to station 13 ::: White breccia boulders B X a‘ r '.. ,, 100 rocks 0 50 METERS STATION 13 360° pan FIGURE 12.—Proportions of light and dark fragments counted in surface panoramas. Data from plate 7, pan 23, plate 8, pans 18 and 19, and plate 9, pan 20. Boulder map from Sutton (this volume). NORTH RAY CRATER 59 Ncnh Ray mm rim crest . Novlh Ray mm vim crest l. a 610I5 a 67055 067035 . . STATION II 961II5 / 5TATI0N II / mun-mum House mk - Invmoumu HMS, mu - f) / I: 61605 \t- Oumouse ruck 0mm”. you 0 67621 ' '\. - 619I5 67940 0 67528 ' ' ~\/ Xx 67935 ' \/ 679m 0 61629 \ . , V . . \ + 67936 @7600 V A u 67647 _ 67937 676 \ . - \ a 61035 \ I0 97 A \ A7075\ 6 61955 (clash) f 67030 I \\ 670l0\\ wmv: eveccia ‘ ' \‘ a 57975 9 A \. haumm (57435/ ‘\u67235 “‘77‘3‘C'W’ ”LEE?“ /\ \67700 ,1 n ‘ 067729 I \ - \ I“ U 67T|0 ’ / 3 / \ \ \- 0 \ \ \_) 67450\ \ \ \H._—/ I 6612I5 '\. ./‘ 67020 9 610I6 —‘ 674K, I: 67455 a 6746 67460 ' EV“? D 6755 61460 Cias! a 61549 675m 6 61556 x 61559 6 Unclassified 6 LIqm-munix nreccm (16,92) 1 Davk~mamx bucc‘m (64.5) e luv-Immune launch: (63) 0 Guns (G) N + Igneous-'ex'uved lock (CI) 5 Mafitl‘lacloshc rockKCZJ N u I! r! I“ ’1 Eauldu ‘_\ \J °'°'°' K/ U Crave: ‘2 sum A sum)" '3 5“"9 STATION 13 I Lun‘" Row" veh'm \ j C) (.\ fl Lunuv Raving Vehicle K 2' f‘) . v . . 63335 . 63340 0 I00 200 300 400 METERS x 5353a p. snags». 0 I00 200 300 6006167563 \ Shadow x 63549 5 0° /l! ”ck x 63565 A 63500 A N97"! Ray mm rlm c165! . STATION II / = ' + I 1 l - 61635 NONE NONE ”MM” Noun mck 67636 f) 51637 a x \N omen: rock 61636 67665 616I5 \j \ - 57945 61639 67669 676I6 ‘ - 61946 67646 New ' \ 'A . O - 67941 61646 0 516m \ + 61956 61655 61626 676I9 J7 . . \\ A \ 61666 61625 _ ‘ _6 61667 mm. mm: \ 7 69 boulders . / \ u - + 5 5 f-i I \ 61149 611I5 NONE NONE \ 97675 \J . \ 61155 617I6 . . / 67156 671I1 o x \ _ . / 61151 677I9 67105 61136 61759 67725 61726 61146 _ O + 67159 67126 61141 67025 67567 NONE 67’“ 57735 571“ 67466 a 67566 57759 67757 615I6 E 57569 X 61715 61733 67106 575', "0" 67575 61465 61116 61139 G75|B 61576 574‘" 577“ 675I9 5"” 61525 67469 . . a + 61565 63509 63505 63501 63506 67526 61566 63525 63506 57527 0 63526 63516 x 57539 “ Unclmm“ 63559 63527 63579 63531 “"55 . 65...“..7. MucmaIzI 63566 6:53; 2323: 2353: - Duvk-malnx ammo (94,5) “2:; 53:35 3569 6:47 6 Imam-aim music (93) 63 s s 0 6m: (5) 63575 63546 63595 63555 + Igneous- mm: 706! (CI) 63555 232:: 53553 N x Munclasli: rock (:2) 5355 M 63517 63596 a Bou u soon \J Cram (‘1 " 5WD STAYION I3 I! Lunar Roving vo ell . AnuranmuI. A "Mo oanvwmo .J 0 I00 200 300 400 METERS . snaaw ng—l—l—g fl 7666 A - . , FIGURE 13.—Location of rocks and sods collected at statlons 11 and B 13. A, Rocks weighing more than 25 g. B, Rocks weighing 2 to 25 g. C, Soil samples weighing more than 26 g. GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS STATION ll STATION I3 Rock type Whlte Breccia lnterboulder House rock Shadow boulders area area urea rock area Light-matrix j] l J] O breccios 3| i 32 _—-"-I Intermediate _ breccios 3: |_..l Dork-matrix O I breccias -. . 34.35 E o Metoclastic _ ‘1 0 m :__J :I . . o 3 C2 3 Igneous o o 3 rocks ;. Ci 0 o :3 o o ' ———l Glass 0 - - - J G O I I I I I I I I I 1’ O 5 IO 15 20 5 IO 5 IO 5 IO NUMBER OF ROCKS EXPLANATION Rocks provisionally assigned by Wilshire and others (this volume) H L_| Rocks weighing 2-25 q Rocks heavier than 25 q °§U No rocks assigned FIGURE 14,—Abundance of rock types collected from four localities at North Ray crater. FIGURE 15,—Sample 67915, a dark-matrix breccia, the largest fragment collected from Outhouse rock. Scale in centimeters. NASA S—72—43917 and 43917B. NORTH RAY CRATER 61 Six samples larger than 25 g were collected from the east face of Outhouse rock (table 2). The largest, 67915, is probably most representative of both large boulders (fig. 15), and its exact position on Outhouse rock is known (Sutton, this volume). It is a dark-matrix brec- cia containing a wide variety of clasts (Roeder and Weiblen, 1974a). Two plateau ages for 67915 deter- mined by the 40Ar-39Ar method, 3.91:0.05 and 3.99:0.05 b.y. (Kirsten and others, 1973, p. 1760 and 1762), are considered to have selenochronologic significance. The lower age was determined on an anorthosite clast, the higher age from the matrix. The precision indicates that an age of about 3.95 by for both samples is likely. Other fragments collected from the face of Outhouse rock are mainly dark-matrix breccias and coherent metaclastic and igneous rocks (B4, B5, CZ, and C1 of Wilshire and others, this volume), a common lithologic association. One exception was a clast of light-matrix breccia, 67955 (fig. 16), selected for its unshocked ap- pearance from the edge of an impact-spalled area (fig. 17), where the face of Outhouse rock had been struck by a high-velocity projectile. Other types of clasts within the boulder are represented by 67935 (fig. 18) and 67937 (fig. 19), metaclastic (C2) rocks. A third type of clast, 67956 (fig. 20), is an igneous (Cl) rock having a subophitic texture much like that of 68415 (see Reed, fig. 9B, this volume) and 65055 (see Sanchez, fig. 20, this volume). Parts of Outhouse rock are highly frac- tured, presumably as a result of the North Ray impact. The spalled area outlined on figure 17 apparently re- sulted from a much younger impact within the past few hundred thousand years based on 26Al measurements on 67937 (Eldridge and others, 1973, p. 2119). Other rocks likely to show effects of this event are 67935 and 67936. Local melting during the North Ray event is indicated by the dark glass splashes on the face of Out- house rock (fig. 17) and the glass coating on fragments elsewhere on the rim crest. Loose undocumented fragments and soil were col— lected in the east-west split between House and Out- house rocks. Three of the four small rocks collected are dark-matrix breccias (67945—47, fig. 21). The fourth and smallest, 67948, may be a relict inclusion of mare basalt; it contains 40 to 50 percent mafic minerals with an ophitic texture (fig. 22). These rocks are most likely all fragments spalled from the large boulders. Several lines of evidence suggest that these dark- matrix boulders came from a lower horizon near or at the bottom of North Ray crater. They are perched on the crater rim within the shallow depressions formed by their impact and are not overlain by subsequent debris; they are clearly late arrivals in the sequence of crater ejecta. This perched position is typical of the deepest material in terrestrial impact and explosion craters. In size and color, the rocks resemble the coarse rubble on the crater floor and, by comparison with the central mounds in nearby craters, may represent a more resistant stratum near the floor of the craters (Hodges, 1972a; Ulrich and Reed, this volume). Dark rocks are sparse on the crater rim crest (10—30 percent, fig. 12). The more abundantlight-matrix breccias here and radially away from the rim probably represent shallower materials overlying the dark-matrix rocks in the crater wall. The large 10-m blocks in the northeast wall of the crater appear in telephotographs to be light-matrix breccias (fig. 23, and pl. 9, pan 36) with some degree of lateral continuity, suggesting at least a crude stratigraphic relation to the materials above and below. The slightly convex shape of the crater wall as seen from the southeast rim (fig. 4) indicates that rela- tively softer, less coherent materials in the upper wall overlie more resistant material at depth. WHITE BRECCIA BOULDERS A group of rounded light-colored boulders was another major sampling target at the rim of North Ray, about 50 m west of the LRV parking spot. The sam- pling done in the vicinity of the LRV was within this area, and the largest number of samples from station 11 was collected at this westernmost location, as shown in figure 13. The classification and geologic significance of all the rocks weighing more than 2 g (figs. 13A, B) are given in table 3. The most distinctive characteristics of the rocks here are the well-rounded profiles, deeply filleted margins, and light-gray to white color (fig. 10). The lengths of the largest boulders are about four times their height. The returned samples typically are light-matrix brec- cias, which are generally very friable and contain coherent clasts of dark-matrix breccia (fig. 11). The rock probably most representative of these boulders is sample 67455 (fig. 24), collected from several loose fragments on top of a boulder approximately 6 m long and 1.5 m high (figs. 10 and 25A). A light-colored clast from this sample has a plateau age of 3.91:0.12 b.y. determined by the 40Ar-39Ar method (Kirsten and others, 1973, p. 1762), essentially the same as the age of 67915 from Outhouse rock. This rock, like many of the rocks of this group, crumbles so badly that it is impossible to reconstruct its lunar orientation. The fri- able texture is expressed microscopically by extensive irregular fracturing through the matrix and around the more coherent clasts (fig. 25B), referred to as glass selvages by Wilshire and others (this volume, fig. 4A). 62 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS FIGURE Iii—Sample 67955, a clast of light-matrix breccia from Outhouse rock. Cube is 1 cm. NASA S—72—45681. NORTH RAY CRATER FIGURE 17.—Impact-spalled area on east face of Outhouse rock. ASIG— 106— 17345. 63 64 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS FIGURE 19,—Sample 67937, a metaclastic rock from Outhouse rock. NASA S—72—37771. NORTH RAY CRATER 65 1 CENTIMETER I I FIGURE 20,—Sample 67956, a rock with igneous texture from Out- house rock. NASA S—72—37547. FIGURE 21.———Three dark-matrix breccias collected from the east-west split between House and Outhouse rocks; left to right, 67945, 67946, 67947. Scale in centimeters. NASA S—72—38977. 66 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS 0 1MlLL|METER 1M|LL|METER l I F0 FIGURE 22.—Ophitic fragment 67948 (1.59 g) collected from the east-west split between House and Outhouse rocks. A, Photomicrograph of 67948, 15 showing pyroxene (high relief) and plagioclase laths. Plane-polarized light. B, Same samples as A, cross-polarized light. FIGURE 23.—Telephotograph of large light-matrix breccia blocks on northeast wall of North Ray crater. Intentionally underexposed to enhance textures in shadows. From AFGIT (1973). Reprinted with permission of the American Association for the Advancement of Science. NORTH RAY CRATER FIGURE 24.—Broken fragments and fines of sample 67455, a light- matrix breccia collected from the top of a White breccia boulder illustrated in figures 10 and 25A. Note few small dark clasts. NASA 8—72-38194. Cube is 1 cm. 67 68 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS 2O 3OCENTIMETERS Approximate FIGURE 25.—Sample 67455. A, Stereopair of the top of a White brec- cia boulder and the fragments of sample 67455 before sampling. ASl6—106—17331, 17332, B, Photomicrograph of 67455, 57 illus- trating irregular fractures that penetrate the matrix of shocked feldspar grains but avoid dark-matrix clasts. Plane-polarized light. NORTH RAY CRATER 69 The rapid mechanical breakdown of these rocks rela- tive to the dark—matrix boulders may be explained by a combination of thermal cycling, which doubtless causes unequal expansion of the dark clasts and light matrix, and micrometeorite bombardment of the sur- face whereby the rock disintegrates along the irregular fractures and the more coherent fragments collected in the rake samples are preferentially preserved. These processes do not appear to be as effective in the dark- matrix boulders. A dark-matrix breccia clast (67475) collected from the same boulder as 67455 illustrates very well the criteria by which some clasts can be identified, even when separated from their host. Three views of 67475 (fig. 26) show the weathered surface, a fresh dark- matrix surface, and a surface coated with the feldspathic host material. Fragment 67718 from a rake sample in the Interboulder area is another specimen whose surfaces reveal its relation to the host (see Smith and Steele, 1972, p. 81). Other samples in the White breccia boulder area that exceed 100 g in weight and probably represent the majority of rocks there are shown in figure 27. The only crystalline rocks recognized by Wilshire and others (this volume) are 16 rake samples classified as meta- clastic (C2); all but one of these weigh less than 25 g. Their occurrence as smaller rocks suggests only that they are residual coherent clasts “weathered” out of the local boulders. Two examples of such clasts within light-matrix breccias are 67415 and 67455 (fig. 28). One rock, 67215 (also weighing more than 100 g), was collected because of its unabraded rock surface. It is described by Horz and others (1972, p. 7—25) as a moderately tough breccia. This rock has not been studied (as of this writing). INTERBOULDER AREA Approximately midway between the White breccia boulders and House rock is a sampling area chosen because it was relatively free of large rocks (fig. 13). From this location, a third photographic survey (east panorama, pl. 9, pan 20; and fig. 4) was taken of the far crater wall. (Table 4 and figs. 13A, B, and 29A—E show the types of breccias collected in this area.) Light- matrix breccias, typified by 67055 and 67075 (fig. 293, C), are abundant but not as predominant as in the White breccia boulder area. The appearance of sample 67075 in this section is typical of a crushed anorthosite (B.) breccia (fig. 30). Samples 67015 and 67115 (fig. 30A, E), assigned to the intermediateBg class by Wil- shire and others (this volume) are considered here to be light-matrix breccias because of their matrix color and friable textures. The one dark-matrix fragment col- lected (67718, 49 g) is covered with white material (Smith and Steele, 1972, p. 82—1) indicative of its former location within a light-matrix host. Rock 67095 (fig. 29D), glass-coated and cemented, is agood exam- ple of the glass of class G of Wilshire and others (this volume). Astronaut Young associated it with a l-m secondary crater on the North Ray rim; it may be an exotic arrival postdating the North Ray event or, al- ternatively, a fragment of late-stage melt from North Ray. Fragments weighing less than 25 g and collected in the Interboulder area (see figs. 13B, 14) reflect a con— centration of intermediate-gray-matrix breccias (B3) collected mainly in the rake sample (67715—67776). This breccia class appears to be transitional between the light- and dark-matrix breccias and is most com- monly listed with light-matrix breccias as an alterna- tive designation by Wilshire and others (this volume). Its origin may be considered similar to that of the light-matrix breccias, with some enrichment in the dark glass components. Consequently, a selective con- centration of more resistant clasts of B3 material occurs as residuum from an inferred light—matrix (BI and B2) host rock. Rock 67235, like 67215 from the White brec- cia boulder area, has not been studied as of this writing but is described by Horz and others (1972, p. 7—25) as a hard recrystallized breccia in appearance. SHADOW ROCK AREA Station 13 was planned for the outer edge of the con- tinuous ejecta blanket of North Ray crater. The objec- tive was to collect a radial sample in the region where the shallowest stratigraphic material'would be pres- ent. As the outer edge of the ejecta blanket was not identifiable, the astronauts selected a location in the vicinity of several large boulders described while en- route to the crater rim crest. The primary source of rock samples greater than 25 g was the single large boulder named Shadow rock, about 5 m long and about 4 m high. It has a distinct moat around its base (fig. 9), presumably part of a shal- low secondary crater created by impact of the boulder when ejected from North Ray crater. No fillet of mate- rial was shed from its surface. Its shape and apparent resistance to erosion suggest that it is similar to the dark-matrix breccias in the House rock area. And its color and texture are typical of dark-matrix rocks (il- lustrated close-up in figure 31). Of the rock samples collected at station 13, (table 5) only one, 60017, weighs more than 100 g (fig. 32). It is very dark, fine grained, and vesicular and apparently has a high percentage of glass in its matrix. Prominent elongate vugs or vesicle pipes were noted by Astronaut 70 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS FIGURE 26.—Sample 67475, a dark-matrix clast from the White breccia boulder of 67455. A, Weathered surface with glass-lined zap pits (NASA 8—72—43359). B, Fresh broken surface showing white feldspathic clasts (NASA S—72—43363). C, Broken surface showing coating of light feldspathic matrix of host material (NASA 8—72—37958). NORTH RAY CRATER 71 O 5 CENTIMETERS I__.___l C FIGURE 27.——Several rocks heavier than 100 g collected in the White breccia boulder area. A, Part of 67016, intermediate-gray matrix (B;; of Wilshire and others, this volume). 8—72—39230. B, 67035, light-matrix (B2) broken in transit, 8—72—37542. C, 67415, light- matrix (B) broken in transit, 8—72—39038. D, 67435, half light, half dark. (B4 of Wilshire and others, this volume). S—72~43897 stereopair. 72 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS 1M|LL|METER L______l L l FIGURE 28,—Photomicrographs of metamorphic clasts within light-matrix breccias. A, Granoblastic plagioclase clasts in matrix consisting predominantly of crushed feldspar; 67415, 14; cross-polarized light. B, Poikiloblastic plagioclase enclosing mafic minerals; 67455, 57; plane-polarized light. FIGURE 29,—Caption on facing page. NORTH RAY CRATER FIGURE 29.—Rocks heavier than 100 g collected from the Interboulder area. A, 67015, light-matrix (B3 of Wilshire and others), S—72—37216.B, 67055, light-matrix (B2), S— 72—43880 stereopair. C, 67075, light-matrix (B,), 8—72—37539. D, 67095, glass coated (G), 8—72—43076 stereopair. E, 67115, light-matrix (B3 of Wilshire and others), S—72—37718. 73 74 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS E FIGURE 29.—Caption on preceding page. NORTH RAY CRATER FIGURE '30.—Photomicrographs of a typical light-matrix breccia from the»Interboulder area. A, Plane-polarized light. B, Cross- polarized light. Glass occurs as veinlets within larger plagioclase clasts and in fine-grained matrix. 75 76 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS Smoky mountain Shadow rock + L _ ‘_ o 10 20 CENTIMETERS Phptograph-" . i _ . Approximate taken here ‘ ‘ FIGURE 31.—Surface texture of Shadow rock. Closeup of overhanging southwest corner (arrow). ASIG— 106— 17410; inset photograph ASIB— 106— 17393; view is northeast. NORTH RAY CRATER 77 FIGURE 32,—Dark-matrix breccia, 60017, (B4) from near Shadow rock. Scale in centimeters. NASA 8—72—36943. 78 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS Duke. Microscopically, it can be seen that plagioclase microlites crystallized out of the glassy matrix and vesiculation probably occurred during the quenching of the glass; some late-stage vesiculation is indicated by abruptly terminated laths at some vesicle boundaries (fig. 33). The remaining samples weighing more than 25 g are dark—matrix (B4, B5) and metaclastic (C2) rocks. Of the samples less than 25 g, a large number (nine) are tentatively classified as intermediate- gray-matrix breccias (B3) (Wilshire and others, this volume); 11 are dark-matrix breccias (fig. 14). Meta- clastic and glassy rocks collected in the rake sample, 5 to 10 m west of Shadow rock, probably represent rocks high in the North Ray walls. Removal from these as- signments of samples of uncertain classification (fig. 14) leaves few samples that can be interpreted with confidence. The most significant rocks,’ then, are the largest samples derived from a known local source, Shadow rock. Like House rock and Outhouse rock, Shadow rock must have been derived from North Ray crater and deposited late in the ejecta sequence; otherwise later deposits would have banked against its northwestern side. Whereas most of the local blocks are light colored (fig. 12), Shadow rock belongs to a small group of dark rocks that are larger and more angular than most of the fragments (about 20 percent of all the blocks in View). It is probably part of a discontinuous ray of dark resistant breccias from a deep unit that is overlain by light-matrix rocks in North Ray crater. NORTH RAY SOILS The soils on the rim of North Ray crater are distinct from those at other sampling stations within the traverse area in that they are generally very thin and light in color. They are similar to one another in modal and chemical composition (Heiken and others, 1973, p. 261—263). Light-matrix breccias are especially abun- dant in these soils (approximately 40 percent, G. J. Taylor and others, 1973, fig. 8). The soils at each of the sampling localities (table 6) were described by the astronauts. At the White breccia boulders, where large fillets occur around the very fri- able rocks, Duke commented, “The regolith here * * * on this crater rim is really soft. We’re sink- ing in on the slopes about six inches or so” (see fig. 10). Elsewhere it was a centimeter or less as indicated by the bootprints in the station 11 panorama (pl. 8, pan 18). At the Interboulder area, illustrated in the fore- » ground of figure 4, descriptions were, “Right under the upper dull-gray soil there’s a layer of whitish material, much like it was at South Ray” and “It’s hard under there * * * there must be a big rock under here. I can’t 0 1 MILLIMETER l__—_J FIGURE 33.—Photomicrograph of 60017, 112, showing vesicles (V) that both conform to and crosscut plagioclase quench crystals in glassy dark-matrix breccia. Plane-polarized light. get the rake in* * * It’s all white under here. Down about a centimeter or less, it’s all white” (Duke). This color difference, gray on the surface and white below, was also described near Shadow rock (station 13) and everywhere else at the site except stations LM, 8, and 9. It is probably caused by the accumulation of aggluti- nates at the surface (Adams and McCord, 1973, p. 171), a process that may also account for the dark tongues of surface debris seen draping the upper wall of North Ray in figure 3. The lighter areas between these tongues may represent more active soil movement downslope, where darker soils have slid away. Low scarps commonly border the more stable gray slopes, and a few boulder tracks are present where larger fragments have rolled or slid downward. The agglutinate contents of the darker soils, much lower than elsewhere in the traverse area, indicate a lack of maturity and thus the low relative age of North Ray soils (McKay and Heiken, 1973, p. 42). Exposure ages have been reported as 30 to 60 my. (Schaeffer and Husain, 1973, p. 1858; Kirsten and others, 1973, p. 1775; Turner and others, 1973, p. 1903; Marti and others, 1973, p. 2039). At House rock, Duke, while attempting to sample the east-west split (fig. 8), reported, “This soil here is very hard and the rake really won’t go into it. It’s bend- ing tines* * *.” The purpose of sampling in the east- west-trending opening was to obtain materials (soil 67940) shielded from the solar wind and to identify, by NORTH RAY CRATER 79 comparison with a nearby reference soil sample (67960), the components concentrated or redistributed by the solar wind. No chemical or modal differences are found in these soils (Heiken and others, 1973, p. 262); only minor contributions of soil-size particles spalled from the adjacent boulders are recognized. Adams and McCord (1973, fig. 4 and p. 170), however, found a lower reflectance for 679411 when compared with 67461 from the White breccia boulder area, even though the agglutinate contents are the same (20 per- cent). They attribute the lower reflectance of the House rock soils to enrichment in dark-matrix breccia frag- ments. At Shadow rock the astronauts collected a soil sam- ple from beneath the overhang on the west end of the rock in the deepest recess (fig. 31). It was hoped that the sample had been permanently in shadow since the rock was emplaced, and the investigators intended to determine whether volatile elements had been concen- trated in such a cold trap. The shadow at the time of sampling is shown in figure 34; the sun elevation angle was 46° above horizontal, its azimuth was 12° north of east. At sunrise and sunset, the maximum prvgression of the sun’s azimuth is 1° to 2° north of an east-west line. This and the estimated movement of sunlight into the shadowed area (shown on fig. 34) during a single lunation make it unlikely that any exposed soil re- mains permanently shadowed, despite Astronaut Duke’s observation that the shadowed area was downslope (beneath the rock). A second soil sample (63340) was collected from beneath the first and there- fore was a buried soil rather than an exposed shadowed soil. The North Ray soils have not been found to differ significantly in lithophile trace-element abundances; strontium contents are slightly higher in these soils than elsewhere, probably reflecting higher plagioclase contents in North Ray target materials (Philpott and others, 1973, p. 1433). North Ray rim soils (including 67941) exhibit no apparent differences in carbon con- tent but as a group are significantly lower in carbon than all other Apollo 16 soils measured by Moore and others (1973, p. 1616). If carbon content is mainly a product of solar wind effects, the contribution on the rim of North Ray crater is relatively small and is the same for the east-west split as in unshielded areas. The apparent meteoritic component in the North Ray soils is lower than elsewhere; this too is indicative of relative immaturity (see Freeman, this volume). ‘The fifth digit "1" in sample numbers denotes the sieve fraction of soil that is less than 1 mm. GEOPHYSICS Geophysical data in the North Ray area consist of a single three-vector reading on the Lunar Portable Magnetometer at station 13. The resultant magnetic anomaly reported was about 300 gammas, down and to the southwest, the largest recorded at this site and larger than any recorded at Apollo 14 or 15 sites (Dyal and others, 1972, p. 12—7). This and the readings from station 2 and in the LM area are interpreted by Strangway and others (1973, p. 113—114) as indicative of a breccia blanket of the order of 1 km thick under the Cayley plains. This blanket, by their hypothesis, was emplaced within a field of a few thousand gammas cooled from a temperature higher than 700°C, forming a moderately welded rock mass with a high remanent magnetization. The only lunar rocks known at this time (1974) to have stable magnetization sufficient to fit this model are a moderately welded, dark-matrix soil breccia (15498) from Dune crater at the Hadley-Apennine (Apollo 15) site and an Apollo 11 chip from soil 10085 (Strangway and others, 1973, p. 113). As unwelded ma- terials and (surprisingly) highly welded and igneous rocks do not carry strong remanent magnetizations, it is possible that the large magnetic fields required are produced by local or regional impact events (such as 10-km or larger craters) wherein only the melted and rapidly cooled breccias retain the transient fields. The igneous-textured rocks cooled slowly enough that the short-lived impact-induced fields had disappeared by the time they passed through the Curie point. The melt-poor light-matrix breccias, never hot enough to pass through the Curie point, therefore were not mag- netized. SUMMARY North Ray crater proved to be an excellent source for a large variety of samples and photographs represent— ing the best available documentation for stratigraphic interpretations anywhere in the Apollo 16 traverse area. The rounded form of the crater rim and the con- vex shape of its generally smooth walls indicate a target material of relatively low strength. Rocks on the rim and wall of North Ray crater are mainly of two types: light-matrix and dark-matrix feldspathic breccias with clasts and inclusions of glassy to crystalline texture. The large boulders (0.2 m and larger) are mainly light-matrix breccias (B1, B2 of Wil- shire and others, this volume); many have well- rounded profiles and have accumulated deep fillets of soil by erosion of their friable surfaces. Similar rocks occur as possible outcrops in the upper half of the cra- ter wall. Dark-matrix rocks (B4, B5) make up 10 to 30 percent of the boulders present and appear to be very 80 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS resistant to erosion. Generally perched or sitting within shallow depressions, they are interpreted as the deepest material exposed in the crater wall and therefore the latest to be deposited on the crater rim. The small fragments (2 to 25 g) collected in soils and rake samples reflect in part the more resistant compo- nents contained interstitially and as clasts within the larger boulders. These include the coherent dark- and intermediate-gray (B3) breccias, metaclastic (C2) rocks, and holocrystalline fragments with igneous textures (CI of Wilshire and others). The metaclastic and holo- crystalline rocks were documented from the matrix of only one boulder, the dark-matrix breccia called Out— ,Sun azimuth 07480 '4’ ’~ 45 in. house rock. Light-matrix breccias and glass-coated fragments (G) are common locally in the smaller sam- ples and as clasts from the dark—matrix breccias. The sample suite is divided into four subgroups based on their locations. Three are on the rim crest of North Ray, the fourth is near the edge of the continu- ous ejecta blanket. Of 148 rock samples, only a fourth weigh more than 25 g, but these probably represent the abundance and distribution of rock types more accu- rately than do the smaller fragments. Light—matrix breccias characterize two of the three rim crest areas; dark-matrix breccias with associated metaclastic and igneous inclusions are typical of the large dark boul- Sun elevation angle, day 4 (this photo) Smoky mountain * , m +5 X M- m, t... Soils 63320 - ”"" Soil'possibly permanently w 4 ~ . ‘ 17.. . ” in?“ ’ . . and 631240 - . shadowed . ‘ ‘ 7‘. p . , p _ - p ‘ ,, / .. . .. ; «. ”hive ~ ‘ , A“ a «“y . . s * . , ’ ' N " 9 *T Z . 2.5.,” - ' 4;... .. «f _.. . . i; FIGURE 34,—Estimated exposure to sunlight beneath overhang of Shadow rock during one lunation. Predicted sun-elevation angles (dashed lines) for earth days 10 and 12.3 correspond to inclined surface on Shadow rock above soil sample 63320. Angle error due to changing sun azimuth is 2° to 3°. ASlG— 106— 17393. NORTH RAY CRATER 81 ders at one rim crest site and at station 13, 0.75 km away. Shadow rock, at station 13, appears atypical of the normally light-colored block population on the outer rim. It is therefore interpreted as part of a discon- tinuous ray extending southeast from the crater rim. The light-matrix materials that constitute the main fragment population are derived from at least the upper half of North Ray (possibly deeper) and overlie a zone of dark material indicated by a small mound on the crater floor. The stratigraphic implications for other parts of the landing site are discussed by Ulrich and Reed (this volume). The generally thin regolith (about 1 cm) thickens to 15 cm or more where it forms fillets around the friable light-matrix boulders. The soils on this fresh crater rim are generally very light gray but not as light as those immediately beneath the surface. Their mineral com- positions, while distinct from other areas, are reported to be very similar within the North Ray ejecta blanket. Mass movement on the steep crater wall and rim has transported soil and a few blocks toward lower areas. Magnetic readings from the Lunar Portable Mag- netometer were high where measured at station 13. They are believed (Strangway and others, 1973) to re- flect moderately welded breccias that were emplaced and cooled from temperatures higher than 700°C in a field of a few thousand gammas. In view of the appar- ent lack of remanent magnetization in more crystalline rocks, it is suggested here that the magnetic field was very short lived and was induced by a large local or regional impact event affecting only melt-rich breccias that cooled rapidly, thereby retaining the transient field. FIGURE TABLE 82 10—1 18. NSDQOF‘Q‘P‘H‘WNH D3. GEOLOGY OF AREAS NEAR SOUTH RAY AND BABY RAY CRATERS By V. STEPHEN REED CONTENTS Page Introduction __________________________________________________________________________ 83 Description of South Ray and Baby Ray craters ________________________________________ 83 South Ray crater ________________________________________________________________ 83 Baby Ray crater __________________________________________________________________ 83 Geology of the station areas __________________________________________________________ 83 General description ______________________________________________________________ 83 Sampling ________________________________________________________________________ 87 Station 8 ________________________________________________________________________ 87 Description __________________________________________________________________ 87 Sampling ____________________________________________________________________ 87 Station 9 ________________________________________________________________________ 91 Description __________________________________________________________________ 91 Sampling ____________________________________________________________________ 91 Age of South Ray crater ______________________________________________________________ 91 ILLUSTRATIONS Geologic and topographic maps and photograph of South Ray crater and surrounding area ,,,,,,,,,,,,,,,,,,,,,, 84 Photograph showing prominent features of South Ray crater __________________________________________________ 87 Telephoto mosaics of South Ray crater and Baby Ray crater __________________________________________________ 88 Map of ejecta from South Ray crater ________________________________________________________________________ 89 Photograph showing features of Baby Ray crater ____________________________________________________________ 90 Planimetric map of station 8 ________________________________________________________________________________ 90 Planimetric map of station 9 ________________________________________________________________________________ 91 Stereopairs of 68115 (and closeup), 68415, 68416, 68815, and 69955 ____________________________________________ 92 Photomicrographs of rocks shown in figure 8 ________________________________________________________________ 94 Photograph and sketch map: 10. 15-m crater at station 8 ____________________________________________________________________________ 96 11. Boulder 1, station 8 ________________________________________________________________________________ 97 12. Boulder 1, station 8 (closeup) ________________________________________________________________________ 98 13. Boulder 2, station 8, showing location of samples 68415 and 68416 __________________________________ 100 14. Boulder 3, station 8 showing location of sample 68815 ______________________________________________ 100 15. Station 9 boulder showing location of sample 69935 __________________________________________________ 101 16. Station 9 boulder showing texture on shadowed side ________________________________________________ 102 17. Bottom of overturned boulder at station 9 showing location of sample 69955 __________________________ 103 Schematic cross section through South Ray crater __________________________________________________________ 105 TABLES Samples collected at stations 8 and 9 ________________________________________________________________________ 87 Reported crystallization ages for samples 68415 and 68416 ____________________________________________________ 91 Chemical compositions of samples 68415, 68115, and 68815, station 8 ________________________________________ 104 Reported exposure ages of rocks collected at stations 8 and 9 ________________________________________________ 104 Page Page SOUTH RAY AND BABY RAY CRATERS 83 INTRODUCTION The surface of the southern part of the Apollo 16 landing site is dominated by fragmental debris derived from South Ray crater (fig. 1). Although the crater was not actually visited, several samples collected can be directly attributed to that impact event. Premission maps by Hodges (1972a) and Milton (1972) from Apollo 14 orbital photographs show a distinct ray pattern around the crater. Traverse station 8 was planned as a sampling site for ray material excavated from South Ray crater, station 9 as an interray sampling site. South Ray Crater, 680 m in diameter and 135 m deep, is near the western flank of the Descartes mountains on a plains surface underlain by the Cayley Formation. Mapped as a young Copernican crater by Hodges (1972a), it appears extremely fresh, with a sharp, raised rim and abundant blocky ejecta (fig. 2). A smaller, 130-m diameter crater, Baby Ray, lies about 1.8 km northeast of South Ray crater, also in smooth plains. Younger than South Ray crater (mapped as the youngest Copernican crater material by Hodges, 1972a), its rays overlie the South Ray debris. The two major rock types collected in the station 8 and 9 areas are dark-matrix breccias and light-colored igneous rocks. This paper presents evidence that the rock samples collected are impact ejecta from South Ray crater and that they represent some of the mate- rials visible in the walls of the crater. DESCRIPTION OF SOUTH RAY AND BABY RAY CRATERS SOUTH RAY CRATER South Ray crater is a fresh-appearing blocky crater with a sharp, raised rim (figs. 2, 3). About 50 m below the rim crest, a discontinuous terrace is visible on the low-sun photographs. The interior of the crater is ex- tremely blocky; a large mound of blocky debris occu- pies the central part of the floor. A few dark patches are visible in the upper third of the crater wall. On the high-sun Apollo 16 photographs, bright rays extend at least 15 km northeast, overlying North Ray crater ejecta, 10 km to the north (fig. 4) (ALGIT, 1972a and AFGIT, 1973). Blocks were deposited in abundance as far as Survey ridge, 4.5 km to the northeast, where the highest concentration of b10cks found during the traverse occurred (Muehlberger and others, 1972). It is unlikely that the 10-m relief on Survey ridge is con- structional, made up of ejecta from South Ray, as ridges withamplitudes of 10 to 30 m are common on the plains. The ridge probably formed by the intersec- tion of two large old subduedcrater rims that inter- cepted a mass of South Ray impact debris traveling on a low trajectory. The ejecta are distributed asymmetrically around South Ray crater, being practically absent southwest of the crater. Boulders appear concentrated mainly in three directions (fig. 1) that correspond roughly to the three principal trends of high-albedo material. One of these blocky rays trends directly toward stations 8 and 9. Several linear grooves on the surface are radial to South Ray crater. At the ends or along the margins of many of the grooves are large boulders. The continuous ejecta thins rapidly outward from the crater, as several dark-haloed craters have excavated dark material from beneath the light South Ray ejecta. BABY RAY CRATER Baby Ray crater (figs. 3, 5) is a fresh blocky crater, 130 m in diameter, about 1.8 km northeast of South Ray crater on the rim of an old, subdued 1.1-km crater. Debris ejected from Baby Ray~ overlies South Ray ejecta. High albedo of the underlying South Ray mate— rial makes it difficult to trace the rays much farther than the limit of the continuous ejecta. Scattered blocks are Visible in the orbital photographs and abun- dant in the telephotographs. In general, the blocks on Baby. Ray are smaller and more numerous than on South Ray. The interior of Baby Ray crater is unusual in the following respects. About one-third of the way down the western crater wall is a .faint discontinuous concen- tric terrace (fig. 5). In the eastern wall are two distinct terraces, one in the upper wall, discontinuous across the crater, another that extends almost across the en- tire width of the crater. These may be slump features rather than terraces reflecting different lithologies. A small dark-haloed crater nested in the center of Baby Ray is similar to other nested craters of the same size range within the landing area. Some subsurface . stratum, perhaps more consolidated than the overlying material, may have influenced this morphology (Quaide and Oberbeck, 1968). GEOLOGY OF THE STATION AREAS GENERAL DESCRIPTION Of all Apollo16 traverse stations, station 8, on the north edge of a high-albedo ray, had the highest proba- bility of location in predominantly South Ray material. Station 8 was planned as a prime sampling station of ejecta from South Ray crater, 3.3 km (about 5, crater diameters) to the southwest. Station 9, between two visible rays near the rim of a 110-m subdued crater about 400 m northeast of station 8, was planned for collection of surface samples in Cayley plains in an area free of South Ray debris. Although stations 4, 5, and 6 were designed for collection of Descartes mate- 84 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS ( l / J /) _/\ “A“, ' C_/-. , K \ _/ / / <\\ \ \ V/>i\ J /' ‘ \ \ \' ll/ TRAP / l —\ St r 9 r") \ .> \ / i \ /:.// \ “19LF/ \ /-/ \ f" - \ —/\\. /' ”\Station/ /,// '\/'V' J l / \ / av/ ' 8 / '// \ . l WRECK / x ,/’3 l ' /, l } -/' '\ . i l / />/°/\\/ ./ l » / ' \ ~ _/ \ K \ STUBBY//I\ V (ky A") / g \\ % // n d \‘ '/ dC-o I ' 2/ ' ~ _/ \\ \.\ Q... . .~ //:\\ ( dc ,\ ‘ . ’l) /Dark debris “ ' \ / / _/ 59° \BANCROFT //’ mun ' - ' . (/\\ \29/ h \—/' . » ' Terrace ) / "dC r‘\ Shadow A l ' \ - / \ L \ ‘\l Terrace l / ’\ d3; Active slopes .. o._dc / j - a . dC /' . \i sm°°m dean; ’ ' SOUTH 'RAY J ‘ (f erroce- \7 ' .. ”:r’") EXPLANATION .- - C2 Boulder track —— Continuous ejecta " C. —-— Discontinuous ejecia . \ ————— Thin discontinuous ejec’ra ( /‘\ } N do Dork haloed crater F“ ) \\ i Q Grooves O 500 1000 METERS/ / fl / .A- .2 - Blocks Ll__L_l_Ll__l \Ng/ \, J LA) Crater rim Q—dc C: l A FIGURE 1.—South Ray crater and surrounding area. A, Geologic map. E, Apollo 16 panoramic camera frame 4623 on which the geologic map was compiled. C, Topographic map of the southern part of the Apollo 16 landing site. Prepared by G. M. Nakata from Apollo 16 panoramic camera frames 4618 and 4623. SOUTH RAY AND BABY RAY CRATERS B O 500 lOOO-METERS l_l_l_1_L_|_—l ' FIGURE 1,—Continued. 85 86 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS \\\\\* N ,2, 2, 7“, fl 277.2212. ,, i 3/ . // iIVW/xfij////7’ / / 22/2 ///,2/’/ /, ,2 no /‘ // / / / (ll/(”W w W ,/ woo MET! as N CONTOUR INTERVAL O METEM I FIGURE 1.—Continued. rials on Stone mountain, there is evidence (Sanchez, this volume; Muehlberger and others, 1972) of con- tamination by South Ray debris. At station 8, fragments larger than 2 cm occupy about 3 percent of the surface, between stations 8 and 9, as much as 6 percent (Muehlberger and others, 1972). In the area of station 9, the fragment population drops to 2 percent, and in the LM/ALSEP area, frag- ments range from less thanl percent to as much as 3 percent of the surface, the percentage of . larger rock fragments (greater than 15 cm) decreasing northward. The stratigraphy at stations 8 and 9 was complex prior to the deposition of South Ray ejecta. As station 8 is within the ejecta blankets or continuous rim deposits of four craters having a diameter of about 1 km, the regolith in the vicinity of these stations is probably made up of a series of several overlapping ejecta blan- kets. Superposed'on this surface is debris excavated from South Ray crater that apparently consists mainly of blocks with very minor distinguishable‘fines. Evi- dence against South Ray’s being the source of fine material in the soilscolleeted around these stations is the considerably older exposure age of the soils relative to the age of rocks more convincingly”representative of South Ray crater (McKay and Heiken, 1973; Schaeffer and Husain, 1973; Adams and McCord, 1973; D. A. Morrison and others, 1973; Behrmann and others, 1973; Huneke and others 1973b; Kirsten and others, 1973; Drozd and others, 1974). Counts of light and dark fragments in the down-sun photographs in the panoramas, where the reflectance most nearly approaches the albedo of the surface, in- dicate that at least 75 percent are dark breccias. This estimate is probably somewhat low, as it is difficult to distinguish a dark-colored rock having a flat surface directed toward the sun from a light-colored rock. SOUTH RAY AND BABY RAY CRATERS 87 Terrace South Ray Active rim crest slopes Terrace Crater o 100 11209 sue on. SOOMETERS L"—"“‘l—‘_ _ i I " _' i FIGURE 2,—Prominent features of South Ray crater. Photograph en- larged from Apollo 16 panoramic camera frame 4623 (fig. 18). SAMPLING Three 05- to 1.5-m boulders were sampled at station 8, one 0.5-m boulder at station 9 (figs. 6 and 7). Several soil samples and small fragments were collected from the surface. These samples are shown by rock type in table 1. The larger samples are pictured in figure 8 and photomicrographs of parts of the samples in figure 9. STATION 8 DESCRIPTION Station 8 is located on an undulating surface near two subdued 15- to 20-m craters. Regionally the sur- face slopes gently up to the northeast. Several scat- tered rock fragments, most of which are in the size range of 5—20 cm, are visible on the surface. The largest block in the area, one from which sample 68815 was collected, is about 1.5 m across. A small (15—20 m) subdued crater provides direct evidence for the presence of South Ray ejecta in the station 8 area (fig. 10). Boulder 1, from which sample 68115 was collected (fig. 11), is perched on its rim. On the northeast wall, small fragments are abundant and small, fresh craters numerous. The opposite wall is nearly devoid of rocks and fresh craters. The downrange side of this old crater (the side facing South Ray crater) appears to have collected South Ray debris, whereas the uprange side was ballistically shadowed. SAMPLING Boulder 1. Boulder 1, approximately 1.5 m across, perched on the northeast rim of its own secondary cra- ter, is rounded in appearance and friable (fig. 11). A large fragment chipped from the boulder (sample 68115) is a dark—matrix dark-clast breccia (B5) that separated from the boulder along fracture planes in- truded by glass. The boulder itself has a predominantly dark matrix with an abundance of light clasts (B4?, fig. 12). Sample 68115 may represent only the matrix. The presence of a few small vesicles (fig. 12) suggests that the boulder was at one time partly molten. One area where some of the light clasts have been smeared out appears to have been heated sufficiently to allow mobilization of the matrix. The many fractures in the rock probably account for its friable nature. Dark glass was injected along some of these fractures. Boulder 2. Boulder 2, a light-gray rock about one- half m across, was reported by Astronaut Duke to be representative of several he could see on the surround- ing surface. Two samples were collected, 68415 from the side and 68416 from the top (fig. 13). The boulder appears homogeneous in photographs of its surface, but minor differences in phenocryst content are seen in the TABLE 1.—Samples collected at stations 8 and 9 A. Boulder samples Rock type' Location B, Small fragment near raked area. B, Boulder 1, station 8. C. Boulder 2, station 8. C| Boulder 2, station 8. 3,, Boulder 3, station 8. B, From top of boulder, station 9. .. rC. 7 7 ‘lromibottom of boulder, sitionié). . B. Other samples iDescription 7 Location 10 m west of 15-m crater. 68002/68001 ,,,,,,,, Double drive tube ,,,,,, , ‘ Near boulder 1, station 8. 1 68500 , do ___________ _ From within rake area. 68505 _ C2 ,,,,,,,,,,,,, , Collected with the soil 68500. 68510 Rake fragments2 _ From 1 m2 area near 15-m crater. 68820 .__ _ 01 ________________ _ At base of boulder 3, station 8. 5 m from boulder 3, station 8. 10 in NW. of station 9. Near station 9 boulder. Beside station 9 boulder. 69001 ,,,,,,,, eSingle drive tube. _ -Surface samples Do. _ Collected with soil 69940. Beneath station 9 boulder. ' Rock tyges from Wilshire and others (1973, and this volume): C.— rystalline igneous Cg—Metaclastic Bg—Light-matrix, dark—clast breccia B4—Dark-matrix, light-clast breccia Bs—Dark-matrix, dark—clast breccia 2 Twelve rake sample fra ents were collected from a 1-m-square area on the north rim of a 15—m subdued crater. 0ft e 12, 6 were igneous and metamorphic rocks, 6 partially melted breccias (ISPET, 1972). Of the rake fragments examined by Wilshire and others (this vogxgiaegéi‘lfre Bz breccias (68515, 68517, and 68519), 3 C2 metaclastic rocks (68526, 68527, an 5 . 88 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS B FIGURE 3.—Telephotographs of South Bay crater (top) and Baby Ray crater (bottom) taken from station 4 on Stone mountain (A816— 112— 18246, 18247, and 18256, South Ray, and AS16—112— 18253 and 18254, Baby Ray). South Ray is about 680 m in diameter. SOUTH RAY AND BABY RAY CRATERS 15° 11'24"E 15° 36' 56" E 8° 48'12"S p ,f‘. 89 K ) NORTH RAY -~..O11 fl ,I’f 1 3 (approximate) N 0 5 KILOMETERS 4) 9° 22's EXPLANATION — - — Boundary of computer enhanced photograph D No South Ray ejecta visible Continuous 9180153 0 Traverse station D iscontinuous ejecta E33] Thin discontinuous ejecta FIGURE 4.—Map of debris ejected from South Ray crater. Compiled on computer-enhanced Apollo 16 panoramic camera frame 5328. 90 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS FIGURE 5,—Features of Baby Ray crater. Photograph enlarged from Apollo 16 panoramic camera frame 4623 (fig. 13). samples. Both samples are fine-grained, highly feldspathic rock (Wilshire and others, 1973). Sample 68415, an igneous-textured rock, is composed of 79.3 percent plagioclase, 4.8 percent olivine, 4.4 percent au- gite, and 10.3 percent pigeonite (Helz and Appleman, 1973). Plagioclase An98_56 makes up 75 volume percent (Hodges and Kushiro, 1973). Both samples are textur- ally homogeneous but have a few shocked plagioclase inclusions in a fine-grained matrix (fig. 9B ). It has been suggested that these rocks were produced not by par- tial melting of the deep lunar interior but rather by shock melting of an anorthositic rock (Wilshire and others, 1973; Helz and Appleman, 1973; Hodges and Kushiro, 1973; Walker, Longhi, Grove, and others, 1973; L. A. Taylor and others, 1973; and Warner and others, 1974) and rapid crystallization (Hodges and Kushiro, 1973; Nord and others, 1973) and that the N '-\ / \ I\ / x 68840 \\_// 68815,68820\. LRV x 68500, 68505, 68510(rake), 68035 Pan -\ \ If ULRV x 68002/68001 \ DT \~"68120,68115 0 68415, 68416 0 1O 20 30 40 50 METERS l_ I l l l l EXPLANATION /~\ l I Crater rim \ .1 . Boulder X 67012 Sample number DT Drive tube A Panorama D Lunar Roving Vehicle FIGURE 6.—Planimetric map of station 8 showing locations of samples. inclusions represent unmelted anorthosite (Helz and Appleman, 1973, Wilshire and others, 1973). Boulder 3. The third boulder sampled (fig. 14) at sta- tion 8, a 1.5-m dark boulder about 40 m northeast of boulders 1 and 2, is very coherent and angular and has only a few small fractures. Scattered large vesicles are visible. A “fillet” soil sample collected on the north side of the rock appears to be old regolith pushed up when the boulder landed rather than a fillet formed by rock degradation. Sample 68815, termed a “fluidized lithic breccia,” (Brown and others, 1973) contains a variety of basaltic and anorthositic clasts. Swirls of basaltic and feldspathic glasses or pockets of glass are common. Most of the material that has flowed is of plagioclase composition, whereas the basalt clasts have sharp un- melted boundaries (Brown and others 1973). Large, wormlike tubular vesicles are present (LSPET, 1972). Sample 68815, similar to 68115, is a dark-matrix dark-clast (B5) breccia. The dark clasts in both differ only slightly from the matrix, and gas cavities are well developed in the matrices (Wilshire and others, 1973). The bulk chemical compositions of rocks from station SOUTH RAY AND BABY RAY CRATERS 91 LRV LRV tracks PanA - ‘1 DT 69001 X l‘ \I . (fi) 69003, 69004, x\ - 69920, 69940, 69935, 69955, 69960, 69945 69965 / ’ _ ‘ \ / \ / \ N / \ / \ I / \ / \ \ / \ / \ / \ / \ \ // \ \ \ __ / 0 10 20 30 4O 50 METERS I I I l I I EXPLANATION ’“\ l / Crater rim \- . Boulder X 67012 Sample number DT Drive tube A Panorama I] Lunar Roving Vehicle FIGURE 7.—Planimetric map of station 9 showing locations of samples. Symbols same as in figure 6. 8 boulders, shown in table 3, reveal a close similarity in their chemistry that reflects a common source mate- TABLE 2.—Chemical compositions of samples 68415, 68115, and 68815, station 8 Rock type ____________ C. B,—, B5 Sample No _____________ 68415.79 68115 68815120 Boulder 2 Boulder 1 Boulder 3 Source ,,,,,,,,,,,,,,,, (Nava, 1974) (S. R, Taylor and others, 1974) (Scoon, 1974) 45.9 44.8 45.33 28.19 27.6 27.59 4.01 5.10 5.17 4,41 5.79 5.38 16.39 15.4 15.56 .47 .47 .48 060 .06 .17 _ -__ .05 28 .34 .48 072 _,, .21 048 .05 07 , .08 rial despite the varied histories recorded in their tex- tures. STATION 9 DESCRIPTION Station 9, about 400 m northeast of station 8, is in an area of lower albedo. The surface is considerably smoother than at station 8, where there are many small, sharp-rimmed fresh craters. The small craters at station 9 are rimless and subdued. The fragment popu- lation varies in both size and abundance; fragments are fewer and mean size is smaller than at station 8. SAMPLING At station 9, the sampling was confined to the im- mediate vicinity of one boulder, about one-half m across, perched on the north rim of a small crater that may be a secondary crater formed by the boulder. Two rock chips were taken from the boulder, 69935 from the top and 69955 from the bottom. The photographs show that the rock consists predominantly of dark material but has a large component of light material (fig. 15), visible as discrete clasts as well as "streamed” through the boulder (fig. 16). Sample 69935 came from a pre- dominantly dark part of the boulder. The boulder ap- pears coherent, mostly angular, and is fractured throughout. Although most of the bottom was soil- caked, some of the rock is visible. One part of the bot- tom face is covered with dark glass. No glass was re- ported by the crew on the top, but apparently some glass has been injected into fractures. Sample 69935 is a dark-matrix light-clast breccia (B4). The sample from the bottom, 69955 (fig. 17), is an igneous (C1) clast form within the dark matrix. Most of the other clasts in this boulder appear to be breccias. Several soil samples designed to collect successively deeper regolith material were taken in the vicinity of the boulder: first, two surface samples (69003, 69004) collected the uppermost layer of regolith; then a skim sample (69920, penetration 5mm), a scoop sample (69940, penetration 3 cm), and a drive-tube sample (69001, penetration 27 cm) were taken. For comparison, a soil sample was collected from beneath the boulder. AGE OF SOUTH RAY CRATER The presence of distinct light-colored rays in the vicinity of stations 8 and 9 in orbital and surface pho- tographs suggests a substantial thickness of South Ray-derived material in this region. The exposure ages of rocks and soils collected at stations 8 and 9, however, have generated some uncertainty (McKay and Heiken, 1973) as to the amount of South Ray debris actually 92 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS FIGURE 8.-——Larger samples collected at stations 8 (A—E) and 9 (F). A, Sample 681 15 (stereopair), from boulder 1. B, Closeup of 681 15 showing boulder 3. F, Sample 69955 (stereopair), from SOUTH RAY AND BABY RAY CRATERS 93 Vugs. C, Sample 68415 (stereopair), from boulder 2. D, Sample 68416 (stereopair), from boulder 2. E, Sample 68815'(stereopair), from bottom side of the boulder. Scales in centimeters. 94 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS FIGURE 9.—-Photomicrographs of rocks shown in figure 8. A, 68115, 95, plane-polarized light; glass and crushed plagioclase groundmass with relict plagioclast clasts. B, 68415, 142, cross-polarized light; subophitic plagioclase (twinned laths) and pyroxene with clast of shocked SOUTH RAY AND BABY RAY CRATERS 95 plagioclase in center. C, 68416, '78, cross-polarized light; seriate twinned plagioclase with pyroxene. D, 68815, 148, plane-polarized light; brown glass invading polymict breccia indicating several shock events. E, 69955, 30, cross-polarized light; shocked, partly melted coarse- grained anorthosite. 96 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS Stone mountain . . C o . ——-""'- ‘ __ -u-— ___._ a _———-k— "-_‘ ’ . p-_-—- A r_—_—_:_"‘___.,__ ____,——"' ' 2/ \ _..——__’__—g—-—.-— . 0" . ’ . —- . _ ’\ G (,1 o . o - . “2" «“3 ~ ‘ ° A l t . (I ‘ ~ \b‘ (’1' \ ’ ' f‘s ' ,-__——'-~<'\._ \ . O I \r ' _‘ , ' I. _o . v. ' . ~.-— ' ' .. g,“ o ..,.5_} 5., .. \(__", . . .‘*‘v) . ’3 ,-___—. . ;_/ o . o ' ' ',. . ’ O ' n .» ' . ... . C O . SOUTH RAY AND BABY RAY CRATERS 97 Field of view White rock beyond of figure I?) 684l5, 68416) A Secondary crater ’ Lighi clost _|_ Fractures B FIGURE 11,—Boulder 1, station 8. A, Photograph, view is southwest, ASIS— 108— 17689. B, Sketch map. ‘FIGURE 10.—Crater at station 8 that predates South Ray crater. A, Southeast view of 15-m crater. South Ray material is preferentially deposited on the downrange (left) side of the crater (ASl6— 108— 17676). B, Sketch map of fragments (solid), fillets (whiskers), and craters (dashed) drawn from A. 98 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS FIGURE 12,—Boulder 1, station 8. A, Closeup view, SOUTH RAY AND BABY RAY CRATERS 99 EXPLANATION . Light clast O Vesicle' —. / [ Fractu res \\ Light rock beyond (68415, 68416) b“ w» ’ Smeared clasts Predominant dark glass? \ O;"". Shadow of tongs Apollo 16 photograph, ASl6—108—17694. B, Sketch map. B 100 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS FIGURE 13—Boulder 2, station 8, showing location of samples col- lected; View is south (AS16—107—17549). 688|5 Shadow EXPLANATION -- Fracture <> Ve§c|e FIGURE 14.—Boulder 3, station 8. A, Photograph before sampling, view is south (A316—108—17700). B, Sketch map. SOUTH RAY AND BABY RAY CRATERS Predominantly ‘ligh1(c|osts?) /// Shadow Secondary //// \czer Darknmotrixll ‘\ / Finely vesicular? \ / EXPLANATION \ / x \ / 4Fractures — — ” FIGURE 15—Station 9 boulder. A, Photograph, View is north, A816— 107—17558. Boulder is about 50 cm wide. B, Sketch .map. 101 102 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS Predominantly light (clasts?) Predominantly dark 'matrix'I Predominantly Iigh1(c|asts ?) ,// Shadow / / EXPLANATION ‘/ Light clast /l Fractures SOUTH RAY AND BABY RAY CRATERS 103 %955 Dust-free area \ Dust—coated area I<—— ~35cm —>-I B FIGURE 17.—-Bottom of overturned boulder at station 9. A, Photo- graph before sampling, view is west, ASl6—107—17576. B, Sketch map. {FIGURE 16.—Station 9 boulder. A, Photograph, view is northeast (ASl6—107—17558). B, Sketch map. 104 present. Exposure ages have been calculated for sev— eral station 8 and 9 rocks by several investigators (ta- ble 4). The samples collected in the station areas appear to represent two lithologic units penetrated by the South Ray crater. Both light and dark fragments were col- lected, and light and dark blocks are visible on the rim of South Ray. The upper, dark unit (fig. 18) is about 50 m thick, the lower, light unit at least 70 m thick. (See Ulrich and Reed, this volume, for more detail.) Most of the exposure ages for the station 8 and 9 boulders are about 2 to 3 m.y., which probably dates the South Ray impact. Older ages, however, indicate that exposure history may be complex or that the dif- ferent dating techniques used have not'yet been recon- ciled. Neukum and others (1973) noted that the surface of 68415 is not saturated with microcraters, indicating it is freshly exposed rock. High exposure ages of 87—105 m.y. contradict this evidence but may represent an ear- lier exposure history for this boulder, preserved some- how in the material analyzed. Behrmann and others (1973) calculated an exposure age of 2 my for 68815 and suggest that, prior to its ejection, it was buried at a depth greater than 7 m, which could place the boulder within the upper part of the dark unit prior to its exca- vation. Drozd and others (1973) calculated a 4.1—m.y.- exposure age for 69955, 2 my. for 69935. They sug- gested that the boulder was in the upper few centime- ters of the regolith in the South Ray target area, in- verted from its present position for 2.1 m.y., then ejected from South Ray 2 my. ago. It seems unlikely, however, that a half-meter boulder near the surface of the South Ray impact point could have survived the event as well as the flight to station 9. More reason- ably, the boulder was part of the upper dark layer and was ejected by the South Ray impact 2 my ago. The boulders from which samples 68815, 68115, and 69955 were collected probably all represent the dark unit in TABLE 3.—Reported exposure ages of rocks collected at stations 8 and 9 Age Age Rock No. (my) Method source 68415 2—3 Microcraters D. A. Morrison and others, 1973. 22:03 “Kr-“Kr and Behrmann and others, 1973. NIKr_7XKr 95—105 Cosmic ray Huneke and others, 1973a. 87:5 “'Ar-“Ar Kirsten and others, 1973. 92.51133 “Kr-Kr Drozd and others, 1974. 68815 20:02 mKr-"Kr and Behrmann and others, 1973. MKr_x:iKr 1 7:0.4 22Na-“Na Do. 2 04:0.20 “Kr-Kr Drozd and others, 1974. 68115 2.08:0.32 “Kr-Kr Do. 68416 23 Microcraters D. A. Morrison and others, 1973. 89:4 ”Ar-““Ar Kirsten and others, 1973. 69935 2-3 Microcraters D. A. Morrison and others, 1973. 19:02 “‘Kr-"Kr Behrmann and others, 1973. 33:03 “Kr-”Kr Do. 22:03 22Na-“Na Do. 1.99:0.37 “Kr-Kr Drozd and others, 1974. 69955 4.25: .41 “Kr-Kr Do. GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS South Ray crater, as all three are dark matrix (B.. and B5) breccias. The presence of light-gray rocks and fines on South Ray and Baby Ray craters and in the station areas suggests that igneous rocks 68415 and 68416 from boulder 2 are representative of the underlying light layer (impact melt). Crystallization ages reported for these rocks (table 4) are 3.68 to 4.09 by and 3.87 to 4.00 by, respectively. These are inferred to represent the approximate age of emplacement of the fluidized material within the Cayley Formation as proposed by Hodges and Muehlberger (this volume). It seems fairly conclusive that the impact that formed South Ray cra- ter occurred 2 to 3 my ago and that the dark breccias and light igneous rocks sampled at stations 8 and 9 are representative of two discrete layers penetrated by South Ray. The problem of assigning the samples collected at stations 8 and 9 to South Ray crater arises from the exposure ages of the fines (McKay and Heiken, 1973). Walton and others (1973) and Kirsten and others (1973) reported exposure ages of 180 m.y., 170 m.y., and 240 my for 68841, 69941, and 69921, respectively. Schaeffer and Husain (1973) analyzed eight 2- to 4-mm fragments, obtaining exposure ages of 122 to 168 my Adams and McCord (1973) stated that station 8 soils are mature, according to their high agglutinate con- tent. It appears that little fine debris was sampled that can be attributed directly to South Ray. Two expla- nations have been proposed: (1) the fines collected rep- resent older regolith ejected by the South Ray impact (McKay and Heiken, 1973) or (2) there is little or no fine South Ray debris in these areas. If the soils do represent older ejected regolith, it would probably be indistinguishable from the preexisting regolith in the station areas. Size analysis of the soils (Butler and others, 1973), however, indicates that there may be recognizable mixing of South Ray and underlying fines and that the coarser fractions are likelier to represent the latest depositional material. McKay and Heiken (1973) calculated that approxi- mately 20 percent of the material ejected from South Ray was preexisting regolith, based on a regolith thickness of 10— 15 m. As the regolith may not be more TABLE 4.—Reported crystallization ages for samples 68415 and 68416, station 8 68415 Age (b.y.) Method Source 3847:0071 L f, ,1: fibis} f, f, l: :Pflapanaistasisiour {mi vivéséeibfir’g,’ 1M2; 7 7 ' 3.68:0.08," H Total Ar ,,,,,,,,,, Kirsten and others, 1973. 3.85:0.06". ,, "’Ar-“Ar ,,,,,,,,,, o. 3.96: 0.18 , , , , , 207Pb-me ,,,,,,,,,, Anderson and Hinthorne, 1973. 4.09 :0.04 , , , , , “’Ar-““Ar __________ Huneke and others, 19733. 3.85: 0.04 '“Ar-79Ar ,,,,,,,,,, Do. 3.85:0.01 ,,,,,,,,,, Rb-Sr ______________ Tera and others, 1973. 6 841 6 3.87:0.08 ,,,,,,,,,, Total Ar .......... Kirsten and others, 1973. ,,,,,,,,,, Do. 4.00:0.05 ,,,,,,,,,, ”Ar-”Ar SOUTH RAY AND BABY RAY CRATERS NORTHWEST SOUTH RAY CRATER / \I II \ — ‘/ /\’| \ \ ’/\‘/\ I I\'/\,:‘/\ ’ I_, (\ \ \‘7 I- 105 l l l l l SOUTHEAST EXPLANATION 7800 Ejecta blanket 7700 . Regollth 7600 A Dark breccia Light unit 7500 (impact melt?) METERS 500 METERS 1 FIGURE 18.—Schematic cross-section through South Ray crater. than 6—7 m thick (Freeman, this volume), older reg- olith in the ejecta may be considerably less than calcu- lated. McKay and Heiken suggested that the amount of freshly produced fine material may be very small. It is possible, then, that little fine material in this area can be attributed directly to South Ray, either as older, preexisting regolith or as freshly produced fines. If there is little or no soil produced by South Ray in the area, there must be another explanation for the high-albedo rayed surface at station 8. In several other station areas, the crew reported light-colored soil un- derlying a thin dark surface layer. At station 8, the soil appears to be a uniform gray. This uniformity may have been produced by churning of the upper few cen- timeters of the regolith as fragments from South Ray impacted. Such a process, in the absence of much fine debris, could generate a surface of higher albedo. The surface at station 8 (located on a prominent ray) has a rough appearance suggestive of such churning of the upper regolith, whereas the surface at station 9 has a lower albedo and is much smoother, compatible with a less prominently rayed terrain. The apparent absence of primary South Ray fines is not surprising considering the intense mixing of the upper regolith as the rays were deposited. It is appar- ent that there was not a “blanket” of material depos- ited but rather that the high albedo was produced by a turbulent, churning disturbance of the older, darker regolith surface by South Ray ejecta, which deposited only sparse new material as blocks and fragments in the ray-covered area. This is consistent with the con- clusion of Oberbeck and others (1974a, b, 1975) that beyond the continuous ejecta blanket, the proportion of primary material present is small relative to the local material excavated by secondaries from the crater. These conclusions are also in agreement with a South Ray ejecta model proposed by Hodges and others (1973) (see also Ulrich and others, this volume) that presents an average thickness of ejecta based on fragment popu- lation, evenly distributed over 360° of arc. According to their preferred model, “an indeterminate, but small amount of South Ray ejecta should be expected in the interray areas, and the materials of the rays should be dominantly coarse debris.” FIGURE TABLE 106 12. 13. 14. 15. 16—22. 23. 24. 25. 26-30. 1. D4. GEOLOGY OF STONE MOUNTAIN By ANTHONY G. SANCHEZ CONTENTS Page Introduction __________________________________________________________________________ 107 Geology of the station areas __________________________________________________________ 108 Station 4 ____________________________________________________________________________ 108 Station 5 ____________________________________________________________________________ 111 Station 6 ____________________________________________________________________________ 115 Discussion and summary ______________________________________________________________ 122 ILLUSTRATIONS Page . Photograph showing location of traverses 1 and 2 and Stone mountain area ______________________________________ 107 . Telephotographic mosaic of Stone mountain taken from station 2 ________________________________________________ 108 . Photograph of station 4 and vicinity ____________________________________________________________________________ 109 . Planimetric map of station 4 __________________________________________________________________________________ 109 . Photographs: 5. Sample 64425 _________________________________________________________________________________________ 110 6. Sample 64435 with photomicrographs __________________________________________________________________ 111 7. Stereopair, sample 64475 ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 113 8. Stereopair, sample 64476 ______________________________________________________________________________ 113 9. Sample 64535 ________________________________________________________________________________________ 113 10. Sample 64455 with photomicrographs __________________________________________________________________ 114 11. Sample 64815 ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 114 Map showing block distribution within 10 m of station 4a panorama ______________________________________________ 114 Photograph of station 5 and vicinity ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 115 Planimetric map of station 5 __________________________________________________________________________________ 115 Map showing block distribution within 10 m of station 5 panorama ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 116 Photographs: 16. Stereopair of sample 65035 _________________________________________________________________________ ""116 17. Sample 65075 ____________________________________________________________________________________ ""117 18. Stereopair of sample 65095 ________________________________________________________________________ “"117 19. Stereopair and photomicrographs of sample 65315 ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, "“118 20. Stereopair and photomicrographs of sample 65055 ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 119 21. Stereopair of sample 65015 ____________________________________________________________________________ 120 22. Station 6 and vicinity ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 120 Topographic map of the Stone mountain area ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 121 Planimetric map of station 6 ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, “7,122 Map showing block distribution with 10 m of station 6 panorama ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, “-7122 Photographs: 26. Sample 66075 ____________________________________________________________________________________ ,1,,123 27. Stereopair and photomicrograph of sample 66035 ________________________________________________________ 124 28. Stereopair of sample 66055 ____________________________________________________________________________ 124 29. Stereo and photomicrographs of sample 66095 ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, ,__- 125 30. Stone mountain traverse showing location of boulder fields identified on 16 mm photographs ______________ 126 TABLES Page Block shape and size distribution at stations 4, 5, and 6 __________________________________________________________ 109 STONE MOUNTAIN INTRODUCTION Stone mountain is a westward projection of the Des- cartes mountains extending into the southeastern part of the Apollo 16 traverse area. It is approximately 550 m above the Cayley plains and has a domical morphology. The largest craters on Stone mountain include 107 Crown, 100 m in diameter, and two nearby unnamed craters, 80 m and 140 m in diameter; most range from 50 m down to the limit of resolution. The crater density on Stone mountain is qualitatively the same as that on the adjacent Cayley plains, but craters larger than 100 m are more abundant on the plains (fig. 1; see also Freeman, this volume). None of the resolvable primary craters on Stone mountain appear to be younger than FIGURE 1.-—Location of traverses 1 and 2, features discussed in text, and areas covered by figures 3, 13, and 22. Apollo 16 panoramic camera frame 4618. 108 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS the prominent South Ray and Baby Ray craters on the plains. The average thickness of the regolith on Stone mountain based on radar data and concentric craters (Freeman, this volume) is estimated to be about 7 m. The surface is relatively smooth and undulating. The upper part of the regolith on Stone mountain probably includes ejecta from South Ray crater over much of the surface. GEOLOGY OF THE STATION AREAS The main objective of the sampling at stations 4, 5, and 6 was to collect materials characteristic of the Des- cartes mountains. This task was constrained by lack of outcrops, difficulty of recognizing craters that pene- trated bedrock, contamination by South Ray ejecta, and the lack of obvious characteristics by which to dis- tinguish Descartes material from Cayley. The contact between Cayley and Descartes material was not recog- nized on the ground; the crew noted the gradual in— crease in slope but observed no apparent difference in color or texture of regolith. Station 4, the highest point reached, was about 150 m above the plain on Stone mountain (fig. 2) on a steep slope that was more blocky than expected owing to blocky ray material from South Ray crater. Station 5, lower on the slope and approximately 550 m north of station 4, was on a gently sloping bench near a 15-m crater in an area sparsely covered with blocks. Station 6 was on the edge of the Cayley plains at the base of Stone mountain. A subdued 10-m crater and several small craters are present in the station 6 area, and small blocks are fairly common. The traverse route on Stone mountain is sprinkled with blocks in the 10- to 100-cm size range interspersed with smaller rocks down to the limit of resolution (2 cm). The crew observed that blocks less than 30 cm in size are the most abundant. Their observations were confirmed by block counts made from the station panorama (pl. 6, pans 9—12; table 1). STATION 4 As a result of this study the location of station 4 has been redetermined at about 100 m east of the location reported earlier in Muehlberger and others (1972); the new location places the LRV on the outer part of the ejecta blanket of Cinco a crater. Two localities were occupied at station 4: station 4a (the LRV parking spot and principal sampling area, inside the northeast rim of a subdued doublet crater approximately 15 m across), approximately 40 m west of the rim of Cinco a crater, and 4b, about 50 m south of the LRV (figs. 3 and 4). The regional slope averages 10—15° down toward the northwest. EXPLANATION _._._.-Traverse route estimated from I6- mm photo- graphy FIGURE 2.—Stone mountain showing location of stations 4, 5, and 6 and traverse line. Mosaic of 500-mm photographs from station 2. AS16—112—18200,02,17,19,27-32, STONE MOUNTAIN A block field, radial to and possibly derived from South Ray crater, covers part of the sample area at 4b (pl. 6, pan 10). Alternatively this block field and that at (pl. 6, pan 9) both may be ejecta from Cinco a crater, 65 m in diameter and about 15 m deep. However, larger blocks are present away from the rim of Cinco a rather than being concentrated on it; thus the evidence for Cinco a as a source is not overwhelming. Indurated regolith samples (64800, 64810) from the block-free rim of the crater at 4b may be from underly- ing Descartes material partly derived from Cinco a TABLE 1,—Block shape and size distribution at stations 4, 5, and 6 Station 4 7 7 7 777 7 771372072; 7207457m7755 5177717617 77 7 7s7ha7p7e7 7 7 percent fiaEfid7ed7L7_7_:7_'__::77417777 277 707 77 7743 727.7 Subangular __ 55 25 0 80 51.6 Angular ______ 23 8 1 32 20.7 Total , __ 119 35 1 155 Size percent ____________ 76.8 22.6 0 6 100.0 Station 5 7 63 4777 7707777 6777 7 7371.77 7 101 9 1 1 11 52.6 26 7 O 33 15.7 t 190 20 l 211 Size percent ____________ 90.1 9.5 0.4 100.0 Station 6 fiEKdgd:Z7_7_7:.7__7_7 2787 77 727 7 777 7 77307 26 5 t , . 4 O 100 l l 200 METERS I FIGURE 3.——Station 4 and Vicinity. Numbers in parentheses in- dicate features correlated with plate 6, pans 9 and 10. Apollo 16 panoramic camera frame 4618. 109 ejecta and reworked by local impact. The regolith sur- face is light gray. Near the rim of the subdued doublet crater at 4a, white material similar to that at station 1 occurs at a depth of about a centimeter; yet a trench in the floor of the crater exposed no white soil or evidence of layering. The crew collected samples in the Vicinity of the LRV at 4a but attempted to avoid sampling the large boul- der field believed to be ejecta from South Ray crater. One rock, a 14-g light-matrix breccia (fig. 5; B2 of Wil- shire and others, this volume) and 0.3 kg of soil were collected from the bottom of the trench; a double-core drive-tube sample was also taken; all three of these samples should have come from below South Ray ejecta if it were present on the surface. I 4a West rim i , of Cinco a \ x x4 North pan soo mml\ 3LRV\ x or 64002/64001 \ A x1 ) x 2 “K \\ 64420-25(trench),l X ”4,455 \ 6447s \6443: /x 64510(rake). \ 4 00 \ \ _. / 6 5 N 4b r\’ —\ A; \ AX 64810(rake), 64800 So th 1 u pan ‘ 0 1o 20 30 4o METERS \ I \ / \ / \ _ , / EXPLANATION ,- i \/ Crater rim \ a X 64455 Sample number DT Drive tube A Panorama U LRV; dot shows heading X3 Penetrometer reading FIGURE 4.-—Planimetric map of station 4 modified from Muehlberger and others (1972). 110 GEOLOGY OF‘ THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS FIGURE 5.—Sample 64425; light-matrix dark-clast breccia from bottom of trench at station 4a (NASA photograph S—72—41584). At station 4b, the blocks are mainly light colored although glass and dust coatings obscure many rock surfaces. Breccia is the predominant rock type in the area, and light clasts are visible in some of the blocks photographed (pl. 6, pan 10). Soil and rake samples consisting mainly of friable, poorly consolidated clods were collected from the northwest rim. No white soil or evidence of layering was found beneath the surface. The blocks on the northeast wall of the crater appar— ently are breccias containing mainly light but some dark matrices. The most abundant rocks sampled at station 4, ac- cording to Wilshire and others (this volume), were light-matrix dark-clast breccias (B2) and dark-matrix light-clast breccias (B4). Their data, however, are heav- ily weighted by rake samples, and as they point out, many of the small fragments are probably clasts from larger rocks. Eight samples weighing 25 g or more were collected at station 4a, none at 4b. Seven of the samples from 4a are light-matrix dark-clast breccias; one is a metaclastic crystalline rock. From the location of 4a, well within the ejecta blanket of Cinco a, these larger fragments may be taken as characteristic of un- derlying rocks in the area. Sample 64435 (fig. 6A), the largest light-matrix (B2) breccia collected at this sta- tion, is described as a cataclastic two-pyroxene, olivine-bearing anorthosite, partly coated with a glass rind (Wilshire and others, this volume). In thin section it appears to consist mainly of crushed feldspar in- vaded by dark matrix material (fig. GB, C). Samples 64475, 64476, and 64535 (figs. 7—9) are additional examples of B2 breccias collected at station 4. Probably most of these samples were deposited as ejecta from South Ray, although the crew attempted to avoid the block field. Other samples collected at this station in- clude a glass-coated anorthosite (64455, fig. 10) and a crushed, annealed mafic rock (64815, fig. 11), both classified as metaclastic (02) by Wilshire and others (this volume). A K-Ar crystallization age of 39:02 by. is reported for 64421 (Kirsten and others, 1973) and an exposure age of 210 my. for soil samples 64421 and 64501. These soils probably are not part of South Ray ejecta, as reliable exposure ages of 2 to 4 my. have been reported for rocks believed to be South Ray mate- rial collected at stations 8 and 9 (see Reed, this volume). Within the doublet crater at station 4a, blocks are much less numerous on the southwest wall, a distribu- tion suggesting that this side was probably shielded from South Ray ejecta. Approximately 2 percent of the surface at station 4a is covered by rocks more than 10 cm across; blocks as large as 0.8 m are scattered over the area (Muehlberger and others, 1972). Rocks less than about 5 cm across are abundant. Most of the blocks are angular, a characteristic of the ejecta be- lieved to be from South Ray crater, but some of the smaller blocks are subround to round (table 1, fig. 12). The angular, perched appearance of the blocks near the LRV suggests derivation from South Ray crater. At station 4b, angular blocks are concentrated on the northeast wall and rim of the crater, the rest of the rim being relatively block free. At station 4b (pl. 6, pan 10), the east wall of a 20-m crater appears to be plastered with blocks that have destroyed the raised rim of the STONE MOUNTAIN crater. As these blocks appear to be ejecta from South Ray, samples were collected only from the northwest interior wall of the crater, shielded from the South Ray ejecta by being on the uprange side. The strongly asymmetric distribution of these blocks, the lack of recognizable ejecta elsewhere around the crater, the partly buried rim under the block-covered area, and the relatively large size of the crater suggest that it is 111 not of secondary origin but was formed prior to South Ray and was subsequently mantled by South Ray ejecta. STATION 5 At station 5, the LRV was parked near the north rim of a 20-m crater (figs. 13, 14; pl. 6, pan 11). Blocks are asymmetrically distributed within the crater; their A FIGURE 6,—Sample 64435, B; breccia from station 4. A, NASA photograph 8—72—39674. B, Photomicrograph of 64435,73 showing glass rind (dark material, right) and moderately fractured plagioclase feldspar (left). Plane-polarized light. C, Same asB, cross-polarized light. 112 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS O 1M|LLIMETER L______J 0 1 MILLIMETER I__—__._J C FIGURE 6.—Continued. STONE MOUNTAIN 1 13 0 1 2 3CENT|METERS ;L_I_J FIGURE 7—Stereopair of sample 64475, a coherent B2 breccia from station 4 (NASA photographs 8—72—43089— 4308913). O 1 ZCENTIMETERS ;J_l FIGURE 8,—Stereopair of sample 64476, a coherent B2 breccia from station 4 (NASA photographs S—72—43114—43114B). FIGURE 9.——Sample 64535, a highly fractured B2 breccia from station 4 (NASA photograph 8—72—43420). 0 1MILLIMETER FIGURE 10.—Sample 64455, a metaclastic (CZ) glass-coated rock. A, NASA photograph S—72—40130. B, Photomicrograph showing metaclastic texture. Plane-polarized light. C, Same as B, cross- polarized light. GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS 3 CENTIMETERS FIGURE 11.——Sample 64815, an unusually mafic fragment from sta- tion 4. NASA photograph 3—72—42074. AS16410 LRV shadow 8.7 m2 17959 /’ ,I 17960 17961 0.8 m2‘ in shadow,‘ § ...17962 I ~O“: — 64420(trench) Penetrometer 2___.. ',’. Near limit field of view 22 m2 012 3 4 5METERS L_1_1_J_I_J E XP LANATION Fragment symbols 10 to 20 cm 20 to 50 cm Measured size Round 0 ‘0 O— 0.7 m Subangular I ‘I C}- O.7 m Angular A ‘A A’ 0.7 m Hachures on outer circle show direction of individual photographs that constitute the panorama FIGURE 12,—Rock distribution within 10 m of station 4a. STONE MOUNTAIN scarcity on the southwest wall indicates that the blocks are South Ray ejecta. Large angular blocks are sparsely scattered around the crater; 10 to 20 cm and smaller fragments are abundant (fig. 15); as observed by the crew and shown on photographs (table 1), sta- tion 5 has the highest percentage of rounded boulders on Stone mountain. Fillets occur around some rounded cobbles; some rocks are partly buried, others perched. Soil samples are characteristically gray, although lighter soils were present beneath a gray surface at one locality. Of the samples collected at station 5, medium- gray-matrix breccias (B3) are the most common mainly in rake samples; glasses are also abundant. The largest samples collected are light-matrix dark-clast breccias (B2). Of these, 65035, 65075, 65095, and 65315 (figs. 16 to 19A) are classified as cataclastic anorthosites (Wil- shire and others, this volume). Typical matrix in B2 breccias is shown in figure 198, C. Two crystalline igneous-textured (Cl) rocks were collected; the largest is 65055 (fig. 20A). The subophitic texture typical of igneous rocks is shown in figure 20B, C. One very large (1.8 kg) metaclastic (C2) rock, 65015 (fig. 21), is de- scribed as an anorthosite (LRL, 1972): It was collected from a small depression, possibly a secondary crater. A 0 50 100 METE RS l__J____l FIGURE 13,—Enlargement of orbital photograph showing statiOn 5‘ and vicinity. Apollo 16 panoramic camera frame 4618'. 115 Rb-Sr crystallization age of 3.92 by. reported for this rock (Tera and others, 1973) as-well as a 40Ar-39Ar crys- tallization age of 3.92:0.4 by. and an exposure age of 365: 20 fl have been reported (Kirsten and others). STATION 6 Station 6 is at the foot of the lowest observable bench on Stone mountain. The LRV was parked near the northeast rim of a subdued 10-m crater (fig. 22). The northwest regional slope is somewhat less steep than at station 4 and 5 (fig. 23). Station 6 was selected before the mission for the purpose of sampling and photo— graphing the base of Stone mountain, its mass—wasted materials, and, if observable, the contact with the Cayley plains. The primary objective was to identify compositional or textural changes between the geomorphic units. The sampling at station 6 was on the rim and along PanA LRV /— \ / x 6550 \ 65510(rake) I x 65600 6509"5\" 65°55 \ 65610(rake) ) \ x 65075 / 65700‘\ / 65710(rake) x X 65310(rake) \ ’65035 (65015 and 65016 not located) 0 10 20 30 |_ l I I 40 METERS 4| EXPLANATION / ~\ 1 , Crater rim \ , X 64455 Sample number DT Drive tube A Panorama B LRV; dot shows heading FIGURE 14.——Planimetric map of station 5; 116 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS AS16-1 10 18018 17992 Near limit field of view 012 3 4 5METERS L_l_l_LJ__J EXPLANATION Fragment symbols 10 to 20 cm 20 to 50 cm Measured size Round 0 ‘O O- 0.7 m Subangular I ‘I D- O.7 m Angular A ‘A A’ 0.7 m Hachures on outer circle show direction of individual photographs that constitute the panorama FIGURE 15,—Rock distribution within 10 m of site of sta- tion 5 panorama. See figure 12 for explanation of sym- bols. 0 1 2 '3 4CENTIMETERS .L__l_l__l_l FIGURE 16.—Stereopair of sample 65035 a light-matrix dark-clast (B2) breccia (NASA photo- graphs S—72—42057—42057B). STONE 'MOUN'I‘AIN 1 1 7 FIGURE 17.—Sample 65075, a highly fractured light-matrix dark- clast (B2) breccia (NASA photograph S—72—39412). FIGURE 18.—Stereopair of sample 65095, a glass-coated light-matrix dark—clast (132) breccia. NASA photographs S— 72—40975—40975B. 118 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS 0 1 2 SCENTIMETERS L_|_L_l 1.,» 4::- 1M|LLIMETER 1MILL|M L.—._—J ETER FIGURE 19.—Sample 65315, a light-matrix dark-clast (B2) breccia displaying a partly glass-coated surface. A, Stereopair. NASA photographs S—72— 42103—421033 B, Photomicrograph of a crushed feldspar matrix in 65315, typical of cataclastic anorthosites. Plane-polarized light. C, Same as B, cross-polarized light. STONE MOUNTAIN 1 19 0 1 2 SCENTIMETERS 0 1M|LL|METER FIGURE 20.—Sample 65055, an angular igneous crystalline rock (Cl). A, Stereopair. NASA photo- graphs S—72—43867B. B, Photomicrograph showing subophitic texture. Plane-polarized light. C, Same as B, cross-polarized light. 120 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS 0 2 4CENTIMETERS |__L_.J._|_l FIGURE 21.—Stereopair of sample 65015, a metaclastic rock (CZ). NASA photographs S— 72—39209—39209B. ' FIGURE 22.—Station 6 and vicinity. Apollo 16 panoramic camera frame 4618. 122 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS ———.2 ,66030, 66055, 66040 x/lAPan /\ULRV 66080 and 66085 x / \ 66075 x \ / \’ 66095" LRV tracks 10 20 30 4O METERS I F0 EXPLANATION /"\ l I Crater rim \ a X 64455 Sample number DT Drive tube A Panorama E] LRV; dot shows heading FIGURE 24,—Planimetric map of station 6. AS16-108 Near limit ,field of view 17612 15.6m2 17618 x66080 and 66085 17619 17623 0 1 2 3 4 5METERS L_L.J_.LJ__J EXPLANATION F ragment symbols 10 to 20 cm 20 to 50 cm Round . ‘. Subangular I \- Angular A ‘A Hachures on outer circle show direction of individual photographs that constitute the panorama, the west wall of the crater where the LRV was parked (pl. 6, pan 12; fig. 24). The surface is covered by numer- ous small shallow craters; only a few are as large as 10 m. Angular blocks to 0.5 m are scattered throughout the area; 10- to 20-cm fragments are most common, covering about 1 percent of the surface, (fig. 25, table 1). As shown on plate 6, pan 12, the rock distribution within the subdued 10-m crater at the LRV appears asymmetric; rocks are sparse on the southwest wall, which was probably shielded from South Ray crater ejecta. The rocks described and photographed exhibit a wide variety of shapes and sizes. Angular glass-coated blocks are scattered over much of the surface. Small white clasts common in many of these rocks indicate that breccias predominate. Fillets are moderately de- veloped around some rocks. Several rocks appear to be partly buried; others appear perched, suggesting that they were transported to their present location as ejecta from South Ray crater. One white “splotch” of indurated soil, 66080, was collected from the southwest wall of the crater; the reg- olith elsewhere was apparently gray throughout. Only four large rock samples were collected at sta- tion 6; all have been classified as breccias by Wilshire and others (this volume). Samples 66075 and 66035 (figs. 26 and 27A) are classified as intermediate-gray- matrix breccias (B3), with approximately equal amounts of dark and light clasts. As shown in figure 273, 66035 has cataclastic texture. Sample 66055 (fig. 28) is a light-matrix dark-clast breccia (B2), described as a cataclastic anorthosite by Wilshire and others (this volume). Sample 66095 (fig. 29A) is a dark-matrix light-clast breccia (B,). It weighs more than a kilogram and is highly fractured. The rock has been called "rusty rock” and was the first discovered to contain a significant amount of hydrated iron oxide believed to be of lunar origin (Nunes and Tatsumoto, 1973; Fried- man and others, 1974). It can be described as an anor- thositic breccia (LRL, 1972) with a locally recrystal- lized matrix (fig. 293, C). ”Ar-”Ar data suggest that this rock was partly recrystallized by an impact event around 3.6 by. ago (Turner and others, 1973, p. 1899). DISCUSSION AND SUMMARY Stations 4 and 5 on the north slope of Stone mountain were selected as the prime localities for Des- cartes mountains materials. Chemical analyses and petrographic characteristics of the samples collected on Stone mountain do not differ significantly from those of {FIGURE 25.-—Rock distribution within 10 m of site of station 6 panorama. See figure 12 for explanation of symbols. STONE MOUNTAIN leeo75g7.” 123 FIGURE 26.—Sample 66075, a well-indurated B3 breccia. NASA photograph 8—72-37203. samples from the Cayley plains. As ray materials from South Ray crater occupy much of the landing site, it is possible that underlying Descartes bedrock may not have been sampled. Alternatively, both plains and highlands at this site may be accumulations of similar breccias. Detailed comparisons of soils and rocks from stations 5 and 6, which lie on opposite sides of the ap- parent Cayley-Descartes contact, indicate no major chemical differences between the two sample suites'If the materials that formed the Descartes mountains were indeed sampled, then whatever differences exist between the two formations must be expressed by properties other than chemical composition and pe- trography. The greater abundance of angular blocks of the 20- to 5-cm size fraction at station 4 can be attrib- uted to a relatively heavy concentration of large blocks of ray material there. From a review of surface evidence (station panorama photographs, Hasselblad .70-mm, and 16-mm photo- graphs), it appears that station 4 may be located on the edge of a minor ray from South Ray crater. From orbit, however, no rays are visible near the station 4 location. Additional evidence for South Ray ejecta is the large asymmetric boulder field of fresh angular blocks ob- served at station 4. Of the three stations, station 5 has the greatest percentage of rounded boulders on the sur- face and appears to be contaminated by few angular blocks of South Ray ejecta. Station 6 appears to be lo- cated on the edge of a ray from South Ray crater (Freeman, this volume, fig. 1), although no large block fields are visible. As station 6is at the base of Stone mountain, Descartes materials may have accumulated by mass wasting from the mountain and may be quite thick (see Freeman, this volume). Boulder fields possi- bly representing South Ray ejecta were identified on 16-mm photographs along the traverse route (fig. 30). Both stations 4 and 6 fall within boulder fields; station 5 does not, although it is near, one. Whether the materials making up the Descartes mountains were actually sampled remains undeter- mined. Stations 4 and 6 appear to be contaminated by Cayley materials ejected from South Ray crater, al- though the larger (25+ g) samples collected at station 4a are possibly Cinco a ejecta from beneath the reg- olith. Station 5, which appears to be free of South Ray ejecta, may be the most promising locality from which Stone mountain material may eventually be identified inthe sample collection. 124 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS FIGURE 27.—Sample 66035, a coherent B3 breccia. A, Stereopair. NASA photographs S—72—41300—41300B. B, Photomicrograph B showing cataclastic texture. Plane-polarized light. 1 2 acENTIMETERE gl—I_J FIGURE 28.—Sample 66055 (stereopair), a light-matrix dark-clast (B2) breccia. NASA photographs S—72—42722—42722b. STONE MOUNTAIN 125 0 1 2 3CENTIMETER 0 0.25 MILLIMETER FIGURE 29.—Sample 66095, “rusty rock,” a highly fractured dark-matrix light-clast B4 breccia. A, Stereopair. NASA photographs S—72—41436—41436B. B, Photomicrograph showing ophitic mat- rix and interstitial opaque minerals that are partly oxidized. C , Same as B, cross-polarized light. 126 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS tOO - FIGURE 30,—Boulder fields, possibly South Ray ejecta, identified on 16-min traverse photographs. E. PETROLOGY AND DISTRIBUTION OF RETURNED SAMPLES, APOLLO 16 By H. G. WILSIIIRE, l). E. S'I‘LYAR'l‘-AI.EXANI)ER, and E. C. S(1HWAR’/.MAN CONTENTS Page Introduction __________________________________________________________________________ 127 Megascopic structures ________________________________________________________________ 128 Hand-specimen petrology ____________________________________________________________ 128 Megascopic rock types ________________________________________________________________ 130 Crystalline rocks ________________________________________________________________ 130 Glass ____________________________________________________________________________ 130 Breccias ________________________________________________________________________ 130 Thin-section petrology ________________________________________________________________ 131 Crystalline rocks ________________________________________________________________ 131 Igneous groups (C.) __________________________________________________________ 131 Metaclastic groups (C2) ______________________________________________________ 131 Breccias ________________________________________________________________________ 133 Group Bl (light matrix, light clasts) ____________________________________________ 133 Group B; (light matrix, dark clasts) ____________________________________________ 134 Group B3 (intermediate matrix color, light and dark clasts) ______________________ 134 Group B4 (dark matrix, light clasts) ____________________________________________ 134 Group 13,, (dark matrix, dark clasts) ____________________________________________ 134 Interpretation of the breccias __________________________________________________ 134 Chronology of Apollo 16 rocks ________________________________________________________ 140 Areal distribution of classified samples ________________________________________________ 143 Summary and conclusions ____________________________________________________________ 146 Acknowledgments ____________________________________________________________________ 146 ILLUSTRATIONS Page FIGURE 1. Diagram showing scheme used for classification of Apollo 16 rocks ______________________________________________ 130 2. Photomicrographs of Apollo 16 rocks and one Apollo 17 rock ____________________________________________________ 132 3. Photomicrographs of Apollo 16 metaclastic rock and breccias and photograph of breccia 61015 ____________________ 135 4. Photomicrographs of Apollo 16 breccias; photograph and phobomicrographs of pseudotachylites of Vredefort structure, South Africa ____________________________________________________________________________________________ 139 5. Histograms showing distribution of rock types at each sampling station __________________________________________ 144 6. Composite histograms of the two groups of stations ____________________________________________________________ 145 7. Histograms showing distribution of microscopic textures at each of the two groups of stations ____________________ 145 TABLES Page TABLE 1. Megascopic classification of Apollo 16 rock samples heavier than 2 g ____________________________________________ 129 2. Microscopic textures of the crystalline rocks and of the matrices of the least-modified breccias ____________________ 132 3. Degree of modification of selected Apollo 16 rocks ______________________________________________________________ 136 4. Isotope data on Apollo 16 samples ___________________________________________________________________________ 140 INTRODUCTION cm. The station locations are known for all rocks; 47 rocks heavier than 20 g (excluding rake samples) have Apollo 16 returned about 96 kg of samples, collected been identified and oriented using lunar surface photo- by astronauts Young and Duke over a distance of about graphs (Sutton, this volume). 20 km during the three traverses. About 75 percent of Apollo 16 rocks, like the samples returned by Apollo the total by weight are rock fragments larger than 1 14 and nonmare samples returned by Apollos 15 and 127 128 17, are predominantly fragmental: they consist of clasts (larger than 1 mm) and microclasts (0.1—1 mm) of glass, minerals, and lithic fragments in generally fine-grained matrices. Homogeneous crystalline rocks constitute a small proportion of the samples and have their counterparts as clasts in or matrix components of the breccias; a number of such rocks were collected directly from breccias or were dislodged from breccia samples in transit. It is therefore likely that all the crystalline rocks are either breccia clasts or pieces of breccia matrix. MEGASCOPIC STRUCTURES Reports by the Field Geology Team (Muelhberger and others, 1972) briefly describe fractures and discon— tinuous color bands in some large breccia boulders pho- tographed by the astronauts. The fractures are multi- ple sets of irregular to planar joints. Irregular discon- tinuous light-colored lenses occur in Shadow rock at station 13 (Ulrich, this volume, fig. 9); study of samples suggests that this type of layering results from cata- clastic flow of relict feldspathic clasts as a consequence of multiple brecciation. In addition to planar fractures, hand specimens re— veal two structures not visible in most surface photo- graphs: glass coatings and thin light-colored veins. The glass in breccias occurs in three ways in addition to clasts: (1) exterior veneers that have sharp contacts with the coated rock; (2) selvages that have grada- tional boundaries with the coated rock; (3) veins that commonly form complex anastomosing networks. Thin glass was injected as impact melt into fractures or formed by fusion along fractures beneath a transient impact crater (Wilshire and Moore, 1974). As the cra- ter grew, the glass was excavated by disaggregation along the same fracture systems. The light-colored veins appear to be largely unannealed mineral debris derived from feldspathic clasts and injected into cracks in the breccia matrices. These cracks and the mobiliza- tion of crushed feldspathic material apparently result from multiple impact events (Wilshire and others, 1973). HAND-SPECIMEN PETROLOGY The hand-specimen petrology of Apollo 16 rocks was described by Wilshire and others (1973) and will not be repeated in detail. Subsequent examination of thin sec- tions, however, has led to revision of sample classifica- tion (table 1) and pointed up the gradational character of the class boundaries. All sources of information available to us were used to compile table 1: our own GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS extensive examination of the samples as members of the Preliminary Examination Team, the Apollo 16 sample information catalog (LRL, 1972), rake sample catalogs (Keil and others, 1972; Phinney and Lofgren, 1973), and other published sources cited in table 2. The 468 samples heavier than 2 gare placed in three major groups, crystalline rocks, glasses, and breccias, and these are further subdivided into nine categories (table 1, fig. 1): two (Cl and C2) are subdivisions of the crystalline rocks; one (G) consists of glass; five (Bl—B5) are subdivisions of the breccias; and one (U) consists of unclassified samples. The class boundaries are not rigid, and ambiguities arise in classifying certain rocks. In hand specimen, the finest grained crystalline rocks can be subdivided as "igneous” (0,) or “metaclas- tic” (C2) only on the basis of crystallinity and occur- rence of angular mineral debris; some thin sections show that even rocks containing comparatively large amounts of mineral debris may have a predominantly igneous texture or a texture that is not easily classified as either igneous or metamorphic. The distinction be- tween fine-grained crystalline rocks and dark-matrix breccias is somewhat arbitrary. The crystalline rocks are generally lighter in color because of coarser grain size and the absence of conspicuous lithic clasts. The matrices of dark-matrix breccias, however, have finer grained igneous or metamorphic textures of the same types as the crystalline rocks. Breccias may be as- signed to the B2 class (light matrix, dark clasts) rather than B1 (light matrix, light clasts) on the basis of a few dark clasts seen in hand specimens that may not have been thin sectioned. The B3 group is intermediate in color mainly because of the development of matrix glass. Many of these rocks are the so—called soil brec- cias, but they may have originated in the same way as some multiply brecciated but little-melted rocks classed as B2 breccias or some multiply brecciated and extensively melted rocks classed as B, or By, breccias. As certain samples (designated (F) in table 1) are known to be nonrepresentative parts of larger rocks, the classification should be used in conjunction with the sample documentation report (ALGIT, 1972b, and Sutton, this volume). And a number of rocks classified as B, breccias have light-colored fragmental material adhering to one or more surfaces, suggesting that they are clasts from breccias. Despite these practical and conceptual difficulties, classification on the basis of megascopic properties, with subdivision based on available data from microscopy, has the advantage of describing the sample as a whole, whereas many thin sections are known to be quite unrepresentative of the sample. Representative sampling by thin section is generally difficult because of the great complexity im- PETROLOGY AND DISTRIBUTION OF RETURNED SAMPLES 129 TABLE 1.—Megascopic classification of Apollo 16 rock samples greater than 2 grams [Sample number in parentheses, tentative identification based on cursory laboratory description. (F), sample nonrepresentative piece from a larger rock. Letter and class number in parentheses, possible alternative classification (B), possible exotic mare basalt sample] Crystalline Glass Unclassified Breccia ,Light "18955,, L .1 Mgdmimymtriz ,, , , W m, ,Qarlcflarix , ,, , fl , , , , Igneous Metaclastic Light Dark Light and Light Dark clasts clasts dark clasts clasts # J l clags’ # _ W, { 7777 1 fl ,, W A 1 r 7 7 c. 02 G U B. B2 8.1 B4 B5 60335 60235 60095 60617 60015 60016 (83) 60535 60017 (B5) 60019 60615 60315 60528 60025 60075 (8.) 60637 60018 (63335) 60635 60525 (8.) 60646 61017 60035 60115 (B4) 60639 60255 67735 (B3) (61576) 60526 60665 61245 60055 60659 (8.) (60648) 60275 63115 62295 (60527) 60666 61246 60056 61015 60655 60645 63315 (63506) 60616 60668 61247 60057 61155 (8.) 60656 (60657) 65055 60619 60669 62285 60058 (61516) 61135 (60658) 235385 60625 60677 62286 60135 62255 61175 60667 63932 (F) 60626 60679 62287 60215 62275 61295 60676 67956 (F) 60627 61157 64505 60515 63509 (61525) 61016 63415 60636 61153 64506 60516 (63533) (84) (61526) 61568 68416 61156 (61195) 64507 60618 (64425) (61536) 61569 69955 F 61225 61546 64508 60628 64435 (61537) (61575) < ) 62235 61547 64509 60629 64475 (61538) 63355 (62245) 61543 64515 62236 64476 (61539) (63505) (63537) 61549 64516 62237 64477 (3,) (61545) (63525) (63533) 61555 65908 62246 64535 (62247) (63526) (63545) 61556 65909 64589 64536 63507 (63527) (63547) 61553 65915 64319 64537 63508 (63528) (63549) (63559) 66035 (65588) 64538 (63578) (63529) (63556) (63566) 66036 (65759) (64539) (63579) (63535) (63558) (63567) 67215 65739 (64545) (63537) (63546) (63535) (63568) 67235 67075 (64546) (63539) (B2) (63555) 64455 (63575) 67557 67415 (64547) (63595) (63557) 64576 65016 67558 (67436) (64543) (63596) (63577) (C2) 64815 (B) 65056 67647 67635 (64549) (63597) 64478 (8).) 64817 65343 67706 67636 (64555) (63598) (64565) 65015 65349 63825 67637 (64556) (64559) (64566) 65357 (65355) 68345 67955 (64557) (64538) (64567) 65358 (65356) 68846 (64558) 64325 (64568) 65365 65366 68347 (64537) 64326 (64569) 65777 65585 65035 64327 (64575) 65773 65536 65075 (8.) 64829 (64577) 65779 65587 65095 (8.) 64335 (64578) (65905) (65767) 65315 64837 (64579) (65906) (65768) 65325 (3,) (65337) (64585) (67435) (65769) 65326 (65338) (64586) (67487) (65775) 65327 (8.) (65515) 64316 (C2) (67488) (65776) (65359) (65516) 64313 (0,) (67489) 67095 (65719) (65517) 66095 (67559) 67567 65757 (65513) (67435) 67565 67568 (65758) (65519) 67475 (F) 67566 67569 65907 (Bu) (65525) 67715 67615 67575 66055 (65526) 67716 67616 67576 67025 (Bx) (65527) 67717 67617 67626 67035 (65528) 67719 67618 67627 67055 (13),) (65529) 67725 67619 67623 67455 (65535) 67726 67625 67629 67515 (65537) 67737 67667 (B) (67705) 67516 (8.) (65538) 67738 67668 67723 67517 (8.) (65539) 67739 67676 67729 67518 (13,) (65548) 67745 67736 (63529) 67519 (8.) (65549) 67915 67746 67525 (3,) (65555) 67937 (F) 67747 67526 (BI) (65715) 67945 67748 67527 (3,) (65716) (67946) (67935) (F) 67539 (B.) (65717) (67947) (68525) 67549 (65718) (8)) (63516) (68526) 67555 (65725) (Bi) (68518) (68527) 67556 (65726) 69935 (63535) 67605 (65727) 69945 67638 (65728) 67639 (65729) 67646 (65735) 67648 (65736) 67655 (65745) 67666 (65746) 67749 65736 67755 (65787) (C2) 67756 (65788) (Ci) 67757 (65925) 67753 (65926) 67759 66035 67766 66036 67769 66037 67775 66075 (B2) 67776 67015 (B) 67975 67016 (B!) 68035 (67115) 63515 (67665) (68517) (67669) (68519) (67718) 130 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS TABLE 2.—Microscopic textures of the crystalline rocks and of the Igneous 60016 (LM-ALSEP) 60018 (LM-ALSEP) 60019 (LM-ALSEP) [Parentheses enclose station numbers] ioililiibiésiic’ ’ 60255 (LM-AISEP) 60275 (LM—AISEP) 60315 (LM-ASLEP) ' ’ Granoblasticw W 60115 (LM~AISEP) 61155 (LM—ALSEP) 65338 (5) matrices of the least—modified breccias Olassy or 7 7 fragmental 60017 (13? 7 7 7 7 60535 (LM»ALSEP) 60655 (LM-ALSEP) 60656 (LM-AISEP) 60335 (LM-ALSEP) 60526 (LM-ALSEP) 67946 (11) 61135 (1) 60615 (LM-ALSEP) 60616 (LM-ALSEP) 67955 (11) 61175 (1) 60618 (LM-ALSEP) 60625 (LM-ALSEP) 67975 (11) 61295 (1) 60635 (LM-ALSEP) 60645 (LM-AISEP) 63507 (13) 60667 (LM-ALSEP) 61156 (1) 6333503) 61015 (1) 63505 (13) 66036 (6) 61016 (1) 64435 (4) 67015 (11) 62295 (2) 64478 (4) 67016 (11) 63506 (13) 65015 (5) 67035 (11) 64476 (4) 65055 (5) 67075 (11) 64477 (4) 65356 (5) 67445 (11) 65035 (5) 65357 (5) 67475 (11) 65075 (5) 65778 (5) 67735 (11) 65095 (5) 67435 (11) 67915 (11) 65359 (5) 67945 (11) 68815 (8) 65719 (5) 68035 (8) 69935 (9) 65785 (5) 65795 (5) 66055 (6) 66095 (6) 67025 (11) 67936 (11) 67937 (11) 67956 (11) 68415 (8) 68416 (8) posed by small-scale changes in degree of granulation and lithologic mixing, degree of melting and thermal metamorphism, and degree of admixture from the pro- jectiles that caused brecciation. Moreover, fewer than 25 percent of the samples have been thin-sectioned at this time (1974). MEGASCOPIC ROCK TYPES The three rock groups and the number to which samples are assigned are defined by their principal characteristics. CRYSTALLINE ROCKS Of the 76 samples classified as crystalline (table 1), 14 (group C1) appear to be fine- to coarse-grained igne— ous rocks. They are highly feldspathic, containing ir- regular plagioclase inclusions up to 10 mm across and irregularly scattered crystal-lined vugs. Sixty-two crystalline rocks (group C2) appear to be metaclastic rocks containing variable amounts of fine angular mineral and lithic debris. The matrix of some is so fine grained that igneous and metamorphic textures cannot be distinguished in hand specimen. The few rocks that have been thin sectioned are classified in table 2. Two samples of this group, 64815 and 67667, appear in hand specimen to be crushed and annealed mare basalts with ilmenite in about the same proportion given for Apollo 12 and 15 mare basalts. GLASS Of the 53 glass samples, two are spheres, the rest irregular glass fragments and coarse agglutinates con- taining small amounts of mineral and lithic debris. Igneous Cl Crystalline rocks < Metaclastic C2 Glass 6 f O ‘5 o _o E Breccias o 3 B x E 3 E m o E 2 _ E e B .9 l J 2 Light Intermediate Dark Clast color FIGURE 1.—Scheme used for classification of Apollo 16 rocks. From Wilshire and others (1973). Many of these samples may have spalled from melt- veneered ejecta while the veneer was still molten. BRECCIAS The fragmental rocks are divided into five groups according to proportions of light- and dark-gray clasts and matrix color (fig. 1). Although there are clasts of all shades of gray and of varying crystallinity, two types are clearly dominant: (1) dark-gray aphanitic to finely crystalline hard lithic fragments and (2) white to light-gray partly crushed to powdered feldspathic fragments. Matrices are of mainly three types: light- and medium-gray matrices, generally friable and not visibly altered by thermal events; dark matrices that are made coherent by fusion and thermal metamorph- ism. On the basis of clasts and matrices, the 263 samples of breccia are classified into five types, in order of abundance: (1) light matrix breccias with dark clasts (B2—85 samples); (2) breccias with medium-gray mat- rices and roughly equal proportions of light and dark clasts (B3—83 samples); (3) dark-matrix breccias with light clasts (B4—60 samples); (4) light-matrix breccias with light clasts (B.—30 samples); and (5) dark-matrix breccias with dark clasts (B5—5 samples). Because PETROLOGY AND DISTRIBUTION OF RETURNED SAMPLES clasts of the same color as the matrix are harder to identify, the B1 and B5 breccias may be more abundant than indicated. Thirty samples (table 1) remain un- classified for lack of adequate catalog descriptions and photographs. All are small,‘ and none appear in any» way unusual. THIN-SECTION PETROLOGY Thin sections have been studied of 77 samples exam- ined in hand specimen. Although statistics on the clasts in breccias have not yet been compiled, textural characteristics and qualitative data on rock-type dis- tribution allow preliminary subdivision of the mega- scopic classification. CRYSTALLINE ROCKS IGNEOLTS GROUPS ((1,) Of the 14 samples of igneous group C], only two (61576 and 69955) appear to be coarse-grained plutonic rocks; one (65785) is composite coarse- and fine-grained rock. Sample 61576, a 6-g rock, may be a single large grain of plagioclase with a glass coating (Phinney and Lofgren, 1973); 69955, coarse-grained polycrystalline rock, probably is more than 95 percent plagioclase (see Rose and others, 1973), making it one of the few true lunar anorthosites (Wilshire and Jackson, 1972b; Jackson and others, 1975). Sample 65785 (Dowty and others, 1974a) consists of a small fragment of spinel troctolite in a fine-grained feldspathic igneous matrix having essentially the same minerals and bulk compo- sition as the troctolite. The remaining 11 samples in group C1 are fine- grained rocks, consisting of approximately 60 percent or more very calcic plagioclase, magnesian olivine and pyroxenes, and metallic Fe-Ni with or without magne- sian spinel and a variety of minor phases (Dowty and others 1974a; LSPET, 1973; Agrell and others, 1973; Hodges and Kushiro, 1973; Gancarz and others, 1972; Helz and Appleman, 1973; Brown and others, 1973). Textures of these rocks range from intersertal, sub- spherulitic (“radiate”) through fine-grained ophitic to intergranular. All are characterized by abrupt varia- tions in crystallinity and texture (fig. 2A), due partly to incomplete melting of inclusions (60335, 60615, 60635, 65796, 68415, 68416) and partly to proximity to vugs, where the grain size is typically coarser (especially 68415, 65055). In some rocks (65055, 68415, 68416) a few large plagioclase grains appear to be euhedral phenocrysts (fig. 2B), but similar grains in sample 60618 (Dowty, and others, 1974a) are almost certainly derived by disaggregation and incomplete melting of a coarse-grained spinel-olivine anorthosite into which the fine-grained igneous-textured rock grades. The proportion of unmelted mineral debris is extremely 131 variable, ranging from negligible in 60635 to probably more than 25 percent in samples 60335 and 65795. Textural similarity of these fine-grained feldspathic igneous rocks to terrestrial impact melts (Grieve and others, 1974) suggests that they are products of whole- rock impact melting. This interpretation, supported by a number of workers (among them, Agrell and others, 1973; Wilshire and others, 1973; Dowty and others, 1974a; Walker and others, 1973; Helz and Appleman, 1973), is substantiated by common occurrence of un- melted relics derived from coarse—grained rocks. This class of rocks has a bulk composition spread like that of cataclastic plutonic clasts in breccias (essentially troc- tolitic, 62295 and 60335, to anorthositic, 65795); gra- dations from melt texture through disaggregated fragments of plutonic rock with interstitial melt tex- ture to plutonic rock of essentially the same bulk com- position further support an origin of the fine-grained igneous rocks by impact melting of plutonic rocks. Tex- tures of breccia matrices formed by melting of plutonic feldspathic rocks differ from those of group C1 melt rock only by being finer grained and more variable. Departures in bulk composition of the melt rocks from single plutonic rock types are to be expected and may result from melting of soils or mixed breccias (Dowty and others, 1974a), homogenization of litholog- ically layered rocks (see Grieve and others, 1974), and contributions from the projectile that caused melting (see Moore, 1969). Partial melting (Warner and others, 1974) has been postulated as a cause of variation in melt rocks but does not seem likely to be a critical consequence of impact melting (Grieve and others, 1974). M ETACLASTIC GROUPS (C2). The 11 metaclastic rocks examined in thin section, all have poikiloblastic texture except 60619, which has a medium-grained granoblastic texture that resembles the textures formed by local recrystallization within plutonic igneous rocks (Wilshire, 1974). The remaining 10 samples consist of variable pro- portions of angular mineral and lithic debris and small euhedral plagioclase crystals partly to wholly enclosed in larger anhedral mafic mineral grains (oikocrysts) and interstitial “diabasic” material. This constitutes what is termed a poikilitictexture by those favoring an igneous origin of the texture (Simonds and others, 1973; Warner and others, 1973; Crawford, 1974), a poikiloblastic texture by those favoring a metamorphic origin (Wilshire and others, 1973; Bence and others, 1973; Albee and others, 1973b; Hodges and Kushiro, 197 3). Angular mineral debris, which occurs either as inclusions in, or interstitial to, mafic oikocrysts, is pre- dominantly plagioclase and olivine, both commonly 132 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS FIGURE 2.—Photomicrographs of Apollo 16 crystalline rocks and one Apollo 17 rock. A. Sample 68415 (group C,), showing textural variations within an impact melt that cooled moderately slowly. Cross-polarized light. B, Sample 65055 (group C1), showing inequigranular texture within an impact melt that cooled moderately slowly. Cross-polarized light. C, Sample 60616 (group Cg), showing fine-grained poikilo- blastic texture. Mafic minerals do not interlock; areas between them have granoblastic texture. Cross-polarized light. D, Sample 60625 (group C), medium-grained poikilobastic texture. Mafic minerals interlock; enclosed minerals dominantly very fine grained, anhedral. Cross-polarized light. E, Sample 65778 (group Cg),,showing coarse-grained poikiloblastic texture. Mafic minerals interlock; note unusual amount of mineral debris (light color). Cross-polarized light. F ; Sample 60315 (group Cg), showing interstitial igneous texture between large poikiloblastic orthopyroxene grains. Plane-polarized light. G, Sample 60315 (group C2), showing spherical droplets with intersertal b0 intergranular igneous texture in coarse-grained poikiloblastic rocks. Plane-polarized light. H , Apollo 17 sample 76215, showing transition from. poikiloblastic texture (left) in which orthopyroxene oikocrysts enclose abundant mineral debris to ophitic texture with poikilitic clinopyroxene and less mineral debris. Vesicles occur only in the ophitic area. Cross-polarized light. PETROLOGY AND DISTRIBUTION OF RETURNED SAMPLES zoned. Lithic debris is predominantly medium-grained hornfels derived from troctolitic or gabbroic rocks. Var- ious proportions of euhedral plagioclases, occuring both as inclusions in mafic Oikocrysts and interstitially between them, range from equant to lath shaped and appear optically to be zoned. Oikocrysts are most com- monly slightly zoned pigeonite or orthopyroxene, but in some rocks are olivine (Simonds and others, 1973). The degree of development of the poikiloblastic tex- ture varies from incipient, spotty, very fine grained Oikocrysts (moderately common in matrices of B4 and B5 breccias and dark clasts in B2 and B3 breccias) to coarse grains easily visible in hand specimen (fig. 2C—E). In the much better examples of this lithologic type returned by Apollo 17 (for example, 76215), a sys- tematic increase in grain size with proximity to cavities can be observed, but thin-section study of Apollo 16 and 17 samples reveals rapid lateral varia- tions from the fine-grained poikiloblastic texture to granoblastic texture and from coarser poikiloblastic textures to those with unequivocal igneous textures (fig. 2H). Interstitial material with igneous texture (fig. 2F) has been noted by a number of authors (Delano and others, 1973; Bence and others, 1973; Walker and others, 1973; Hodges and Kushiro, 1973), and spherical blebs with igneous texture (fig. 2G) are widespread. The origin of the poikiloblastic texture is still uncer- tain; some workers favoring crystallization from a melt, others recrystallization in the solid state. Most workers agree that interstitial material with interser- tal to intergranular texture (“diabasic” material) in— dicates the presence of some melt, and the common occurrence of cavities indicates the presence of a vapor phase. There is little doubt that most of these rocks contained at least a small proportion of melt. Moreover, as one attempts to classify these rocks and the fine-grained breccias, the rather subtle and grada- tional character of the differences between poikiloblas- tic texture and ophitic texture are often apparent (for example, the rock classified by Simonds and others (1973) as poikilitic in their figure 9, we would probably classify as ophitic and place in group C1). We believe, however, that the distinctive textural differences in the coarser grained poikiloblastic rocks between those parts that most workers consider igneous (interstitial “diabasic” material) and the main body of the rock suggest a metamorphic origin of the coarse pyroxene Oikocrysts (see Bence and others, 1973). This appears to be substantiated in rock 76215 (fig. 2H) by the .gra- dation from a coarse—grained poikiloblastic texture in which orthopyroxenes enclose abundant undigested mineral debris to a well-developed ophitic texture with Oikocrysts of clinopyroxene and much less, mineral de— bris. It is highly unlikely that both partsof the rock crystallized from a liquid. 133 The suggestion by Simonds and others (1973) and Warner and others (1973) that gas cavities and flow structures are evidence of igneous origin is equivocal, as cataclastic flow structures in solids are well known and vesiculation of powdered material lacking a liquid phase seems at least possible. In many lunar rocks, gas cavities commonly are locally surrounded by un- equivocal melt textures; a good example is the well known Apollo 15 rock 15418; another is Apollo 17 rock 76215 (fig. 2H), in which spherical cavities are concen- trated in the ophitic part of the rock. Lowering of melt- ing temperature by the presence of a gas phase may locally induce melting. The suggestion of Albee and others (1973b) and of Bence and others (1973) that the cavities were present in a glassy precursor of the poikiloblastic rocks seems implausible, especially in view of the shapes and distribution of cavities de- scribed by Simonds and others ( 1973) and concentra- tion of cavities in more extensively melted parts of poikiloblastic rocks. The nature of the precursor of poikiloblastic rocks remains a critical problem (see Duncan and others, 1973). The statement of Bence and others (1973) that there is little disagreement that the precursor to these rocks was either a polymict highlands breccia or a clast-laden glass is not supported by any facts known to us. While statistical information on relics may aid in solution of this problem, a subjective View of the domi- nant types of mineral and lithic debris suggests that partly metamorphosed troctolitic rocks were important contributors. Several Apollo 17 poikiloblastic rocks, however, contain scattered mineral debris (plagio— clases spongy with inclusions; brown clinopyroxenes) derived from distinctive vug and vein fillings in the blue-gray breccias with which the poikiloblastic rocks are associated. Some mixing of lithologic types is evi- dent. BRECCIAS (}R()L'l’ B, (LIGHT \lA'l‘RlX, LIGHT (LIAS'I‘S) The 30 samples in group Bl range from cataclastic plutonic feldspathic rocks to cataclastic hornfels to polymict breccias. Study in hand specimen indicates that many of the coarse-grained feldspathic compo- nents of B1 breccias were partly metamorphosed to medium-grained hornfels before cataclasis; the hornfelsed parts appear to survive crushing better than the coarse igneous rocks from which they were derived and may be represented disproportionately in thin section. Of the 10 rocks thin sectioned so far (1974), all are cataclastic plutonic feldspathic rocks ex- cept 67075, which may be a polymict breccia, and 67955, a cataclastic coarsely hornfelsed olivine gabbro. In the, eight anorthositic rocks, the matrix is unan- nealed or weakly annealed crushed anorthosite and the 134 clasts are relics that survived the crushing. Sample 67075 contains medium-grained hornfels fragments that apparently were derived from different kinds of anorthositic rocks, as their mineral assemblages are highly varied; mineral debris shows major variations in constituent proportions from thin section to thin sec- tion. This rock, as well as some others not yet thin sectioned, may therefore represent mixed lithologies rather than a single rock that has been crushed. The cataclastic plutonic rocks range from norite through noritic anorthosite to anorthosite. Some nori- tic anorthosites are olivine bearing (for example, 60025), and some anorthosites contain both olivine and spinel (for example, 60618, Dowty and others, 1974a, b). Most of the cataclasites have not undergone severe cataclastic mixing (fig. 3A, B); the original coarse to very coarse grain size is evident from the size of relict mineral debris (table 3). Because of this, individual thin sections may be misleading with respect to the modal composition of the original rock and the textural relations between plagioclase and mafic minerals. In a few of these rocks and similar ones occurring as clasts in other breccia types, textural relations suggest that mafic minerals in the most feldspar-rich rocks are in- terstitial postcumulus phases (fig. 3C) but form cumulus phases with or without cumulus plagioclase in the more mafic rocks (fig. 3D). (iROI'I’ B2 (LIGHT MATRIX, DARK (ILASTS) The B2 breccias are extremely variable, ranging from breccias that have been little modified since the first impact event (for example 64435, 61015) to multicycle breccias, some of which are ploymict (for example, 60016, 67075) (Wilshire and others, 1973). In the 19 thin sections examined, even the simplest, least- modified breccias show mild rebrecciation of a first- cycle breccia that consisted of highly feldspathic clasts in a fine-grained dark matrix (some relics of which are visible in the lower left part of the rock in fig. 3E). Rebrecciation resulted in a large-scale fracturing and dilation of the brittle, fine-grained original matrix and injection of the friable feldspathic clast material into the fractures. The injected plagioclase debris-remained unannealed (fig. 3F). The texture of the dark fine- grained clasts generally remains unchanged in this brecciation. In these clasts, very fine grained interser- tal textures predominate but grade to fine—grained poikiloblastic and granoblastic textures on the one hand and to fine-grained ophitic textures on the other (table 2). Somewhat more severe second-generation brecciation resulted in local fusion of the original dark matrix along fractures (fig. 30) (Wilshire and Moore, 1974). Small droplets of melt, many with unmelted cores, spalled from the glass selvages during emplace- ment of the unmelted feldspathic debris (fig. 3H). Se- GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS vere brecciation accompanied by local fusion adds to the complexity of a second—cycle breccias but involves the same number of impacts. Later impacts tend to break down the friable feldspathic material to small- size particles and concentrate the tough dark clasts in the coarser size fractions. It is clear from the extraor- dinary variety of lithologic types (fig. 4A) in some of these breccias (for example, 67455, 60115) that mixing of fragments of diverse origin has occurred as well as disaggregation of originally simple breccias. (IROL'I’ B5; (INTERMEDIATE MATRIX COLOR, LIGHT AND DARK (ILASTS) Of the 83 samples in group B3, only 7 have been examined in thin section. These are polymict breccias with a wide range of mostly fine grained lithic clasts, glass, and mineral debris in a friable, glassy to very weakly annealed matrix (fig. 4B). The thin-sectioned rocks are loosely aggregated regolith.ma.terial that clearly corresponds to the “soil breccias’.’ returned from other missions. Although their origin has not been de- termined, they appear to differ little from some polymict breccias of group B2 except for the presence of glass. (}R()I'I’ B. (DARK MATRIX, LIGHT (ILASTS) A wide variety of lithologic types is represented in the 14 rocks of group B4 studied in thin section. The clasts vary from metaclastic fragments with poikilo- blastic textures to annealed cataclastic feldspar-rich fragments to rare fine-grained feldspathic igneous fragments (fig. 4C). The matrices are tough and fine grained with igneous or granoblastic textures. Some of the B4 breccias (table 3) are little-modified fragments of first-cycle breccias, but the polymict character of many shows repeated impact events, each severe enough to anneal the pulverized rock. (lROL'I’ B;(D1\RI\' MA'I‘RIX, DARK (ILAS'I‘S) The four samples in group B, that have been thin sectioned are lithologically very complex, consisting of a variety of dark fine-grained metaclastic rock frag; ments and mineral debris in a tough, annealed elastic matrix. There is some evidence of derivation by multi— ple impact of simpler types of breccia. In thin section (fig. 4D), characteristics of B2 breccias can be discerned; net veins of broken feldspathic debris in dark fine- grained igneous-textured rock have survived multiple impacts. IN'I'ERI’RE'I‘.\'1‘I()X ()15'1‘111“. BR1€(I(ZI:\S Wilshire and others (1973) attempted to reconstruct the sequence of brecciation leading to diversification of the breccias. Even though no unbrecciated outcrops were found at the Apollo 16 site, the sequence can be established by comparison with products of single im- PETROLOGY AND DISTRIBUTION OF RETURNED SAMPLES 135 FIGURE 3.—Photomicrograph of Apollo 16 metaclastic rock and breccias and photograph of breccia 61015. A, Sample 60619 (group Cg), showing coarse hornfels texture in metaanorthosite. Cross—polarized light. B, Sample 62237 (Bl breccia), showing coarse mineral relics and cataclastic flow structure in troctolite. Cross-polarized light. C, Sample 65785 (group C3), a lithic relic in cataclasite, having postcumulus olivine (high relief) separating cumulus plagioclase grains twinned. Cross—polarized light. D, Sample F6? 35 (B4 breccia), showing lithic clast in breccia with postcumulus plagioclase (low relief, white) separating cumulus olivine (high relief) and spinel (in extinction) grains. Cross-polarized light. E, Sample 61015 (NASA photograph $72—40585B), showing net-veining of original dark matrix by elastic material derived from the white clasts. F, Sample 61015 (B2 breccia), showing weakly annealed, coarse mineral debris in fractures in original matrix (dark). Cross-polarized light. G, Sample 66055 (B2 breccia), showing glass selvage (dark gray) on lighter gray fragment of original matrix. Note surrounding fragments of spalled selvage in feldspathic debris derived from original clasts. Plane- polarized light. H, Sample 66055 (B2 breccia), showing incompletely spalled ellipsoid of glass selvage. Plane-polarized light. 136 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS TABLE 3.—Degree of modification of selected Apollo 16 rocks Sample Classification Glass‘ Lithic relics2 Mineral relics2 Major events Notes (maximum size in mm; preserveda pc, plagioclase; px, pyroxene; . 01’ olivme) a: .2: g (Numbers give references to 5;, % m :2. 8 E additional petrologic, chem- : E .g a f, g ical, and age data. Standard 0 '3 g 1:, 3’0 5 : catalog and classification > 3 R g E .2 references not given) 2:: a}; g 5'} ° 3 g- a t‘. ‘1 a: o g 5 ‘3 5 E La 60015 B. X X Medium-grained PC 12. POSSIHY 15 Major modification by multiple hornfels‘. impacts. (1,2,3,4,5,6) 60016 B2033)" Medium-grained pc 1 Major modification by multiple hornfels. impact and mixing’. (7,8) 60017 BAR.) X Major modification by multiple impact. (2,9,10) 60018 B. X X X Medium-grained pc 7 X 10 Major modification by multiple hornfels, cata- impact. Some clasts robably clastic anortho— represent first-cycle Ereccia site, troctolite. matrix. 60019 Bs X ? Major modification by multiple impact, 60025 B. X Noritic anortho- pc 15 x Cataclastic noritic annrthosite. site. No first-cycle matrix present. (2,4,10,11,12,13) 60215 B. X pc 6 X Mafic minerals severely modi- fied. Cataclastic noritic anorthosite. No first-cycle matrix present. 60235 C2 pc 10 ? ? Insufficient data“. 60255 B. X pc 4 Major modification by multiple impact. (14) 60275 B. X X Major modification by multiple impact. 60315 C; pc 4 ? ? Poikiloblastic texture". (10,11,13,15,16,17) 60335 C2 pc 5, px, ol 3 ? 7 Ophitic-poikiloblastic texture. (10,13,18) 60516 B. pc 4, possibly 5 X Cataclastic anorthosite. No first-cycle matrix present. (19 60526 C2 pc 01 ? 7 Poikiloblastic texture. Very scarce mineral debris. 60615 C. [)0 0.75 ? 7 Medium-grained ophitic texture. (2,20) 60616 C2 Medium-grained pc 07, 01 0.1 7 ? Poikiloblastic texture. hornfels. 60618 B. pc greater than 5 x? X Cataclastic spinel, olivine- bearing anorthosite. First- cycle matrix subspherulitic. (19,20) 60619 C, x Medium~grained hornfels, No first-cycle matrix present. 60625 C2 X 7 Poikiloblastic texture. 60629 B. X pc 3.5 X Cataclastic anorthosite, No first-cycle matrix present. (19) 60635 C. pc 2.5 ? ? Medium-grained ophitic texture. (20) 60645 B. pc 11, px 0.3 ? ? Cataclastic anorthosite. First- cycle matrix weakly poikilo- b astic. 60658 B. X pc 1.0 Insufficient data. 60659 B..(B4) pc 0.75 Major modification by multiple impact. (19) 60667 B4 Medium-grained pc 0.6 '? F irst-cycle matrix? Interser- hornfels. tal texture. 60676 B. pc 1.6 61015 B; X pc 3 ? 61016 B4 X X pc 15 Major modification by multiple impact. (1,2,10,12,24,25,26,27,28) 62235 C, pc 2 ? ? Poikiloblastic-ophitic tex~ ture. (25,29) 62236 B. PC 4 X Cataclastic norite or noritic anorthosite. No first-cycle matrix resent. 62237 B. 1 Norite pc 3 X Cataclastic olivine-bearing norite or noritic anorthosite, No first-cycle matrix present. 62246 B. X Insufficient data. 62255 B. X x Gabbro(?) pc 1, px 5 X Cataclastic clinopyroxene- bearing anorthosite. (8) 62295 C. PC 2 Subspherulitic quench texture, (10,11,13,18,30,31,32,33) 63335 (B5) pc 1 Major modification by multiple impact. (9,34) 63505 B. pc 1 7 First-cycle (7) matrix, poi- kiloblastic texture, 63506 (02) ? First-cycle(?) matrix, poi- kiloblastic to intergranular texture. 64435 B2 X X pc 15 X X Cataclastic two~pyroxene, oli- vine-bearing anorthosite. First-cycle matrix weakly poi- . kilitic. (8,8,34) 64455 C2 X X Medium-grained pc 1 Insufficient data. (35) hornfels(?) PETROLOGY AND DISTRIBUTION OF RETURNED SAMPLES 137 TABLE 3.—Degree of modification of selected Apollo 16 rocks ——Continued. Sample Classification Glass‘ Lithic relics2 Mineral relics? giggigggfns Notes (maximum size in mm; pc, plagioclase; . ‘ Pf» pyroxefie; , .1 4?, (Numbers give references to 53 3'0 0 , 0 ivme g g E additional petrologic, chem- : S E = Z : ical, and age data. Standard a, 7’ ‘3 33 o .9. catalog and classification > w > at“ ‘5 5 r t ' ) a > E ._ re erences no given 5 a a .E ‘a‘ 73‘s :5 g E 5 $5 :3 .5 '5 ca E ca 6 4 476 B2 x pc 1.5 x x x Partly metamorphosed (medium- gramed hornfels) cataclastic two- pyroxene anorthosite in in- tersertal to weakly poikilitic matrix. 64477 B2(B4) ? x Cataclastic gabbro; first-cycle matrix very fine-grained in: tersertal to subspherulitic. , 64478 B4033) ? ? Poikiloblastic texture, grading to feldspathic material with recrystallized mafic minerals. 64535 B2 x '? ? ? Insufficient data. 65015 C2 pc 2 ? Medium-grained poikiloblastic texture. (17,27,36,37) 65035 B; X Medium-grained x X Cataclastic nor-itic anortho— homfels. site clasts in intersertal matrix. 65055 C, Medium-grained ophitic textures. 65075 B203.) X X Anorthosite(?); pc 10 x X X Partly metamorphosed gabbroic gabbroid; medium- anorthosite; first-cycle ma- grained hornfels. trix ophitic. (35) 65095 32(3.) ? pc 6.5 ? '? Cataclastic olivine-bearing noritic anorthosite and other clasts in intersertal matrix grading to ophitic. 65315 B, X pc 6 X ? Cataclastic anorthosite; first- :ficle matrix component not in in section. (38) 65326 B, pc 2+ X ? Cataclastic anorthosite; first- cycle matrix forms very small proportion of sample. (19) 65357 C: pc 0.45, 01 0,15 Medium-grained poikiloblastic texture. 65359 B: X x X Cataclastic troctolite, anortho- site; first-cycle matrix inter- sertal grading to ophitic. 65365 C; pc 075 ? Medium-grained poikiloblastic- ophitic texture. 65719 (B2) pc 1 7 ? Feldspathic mineral debris; first-c cle matrix interser- tal-op itic. 65757 82 x pc 13 X ? Cataclastic anorthosite. No first-cycle matrix. (19) 65778 C2 pc 0.45, 01 0.3 7 Medium-grained poikiloblastic texture. 65785 C2 01 5+, pc 2.5, X X Spinel troctolite. No first» spine] 15 cgcle matrix in thin section. ( 0) 65789 B. x pc 0.5 X Cataclastic anorthosite. No first-cycle matrix present, 65795 C. pc 125 ? Medium-grained ophitic texture. (20) 66055 B2 pc 3; mafics 3 X X X Cataclastic anorthosite and coarsely hornfelsed troctolite; first-cycle matrix intersertal to weakly poikilitic. (39) 66095 B. x pc 35, pass. 5 ? First-cycle matrix ophitic. Very few clasts in rocks. (12,24,25,27,37,40) 67015 33(32) pc 6, px 1 Major modification by multiple impact. ( 1) 67016 B3(B,) pc 4 Major modification by multiple impact. (8,27) 67025 32(31) x x Major modification by multiple impact. 67035 B? pc 1 Major modification by multiple impact. (2) 67055 BABA) Mediumvgrained pc 3 Major modification by multiple hornfels. impact. 67075 B. ? Medium-graind pc 6, px 2 7 Possible major modification by hornfels. multiple impact and mixing. (14,18,28,37,41) 67415 Bl Medium-grained pc 2 7 Possible major modification by hornfels. multiple impact and mixing. 67435 B; x Spinel troctolite. pc 1, ol 2 7 ? Possible major modification by {Egltiple impact and mixing. ) 67455 82 X Major modification by multiple impact and mixing. (10,37) 67605 B2 pc 3 Insufficient data. 67915 B. x Marie 2, pc 2 Major modification by multiple impact. (12,27,33,43) 67936 (C2) X pc 1 ? First»cycle(?) matrix with granoblastic texture grading to intersertal and ophitic. No clasts. 67937 B4 Moderate modification of first— cycle(?) matrix with interser- tal to ophitic texture. Clasts of metaclastic rock. 138 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS Sample Classification Glass‘ Lithic relics2 Mineral relics2 Major events preserved3 Notes (maximum size in mm; pc, plagioclase; px, pyroxene; ,_ e 01, olivine) a t” m . l: _> .E _ g I: (91’ 50 g g 0’ (Numbers give references to 5 I- E additional petrologic, chem- S ‘5 g ical, and a e data. Standard a E” a g catalog an classification ‘6 S > E '5 references not given) _ w 3 ._ w 8 ° >< i is =‘ E 8 s a E ‘5 a: g La 67945 B, X pc 5 ? First cycle matrix, poikilo- blastic texture. 67946 (3,) 7 Major modification by multiple impact, 67947 (8,) ? pc 2 0. 67955 B, X Medium-grained ? Cataclastic olivine gabbro hornfels. hornfels. No first—cycle matrix present. (44) 67975 B2 pc 4 Major modification by multiple im act. 68035 B; X pc 3 Insu cient data 68115 B, pc 2 Major modification by multiple impact, (8,21) 68415 C, W 3 Medium-grained ophitic texture. Few clasts, (10,15,18,22,23,24) 68416 CI pc 8 Medium-grained o hitic texture Clasts moderate y abundant. (10,11,182?) 68515 B? X X X Insufficient data. 69955 CI pc 7 7 Cataclastic anorthosite. Sample from boulder. (2,10) ‘Glass occurs in three modes (Wilshire and Moore, 1974) other than as clasts: (l) veneer—sha coated rock, (3) veins, commonly occurring in complex, anastomosing patterns; Theglass is tho rply bounded exterior coatings; (2) selvages—coatings with gradational boundaries with the ught to have formed during comparatively small impact events followin initial excavation. 2Lithic and mineral relics are considered to be impact target materials that escaped major damage resulting from impact; the matrices of breccias containing these re ics were derived by comminution, melting, and thermal meta-morphism of the same types of rock represented by the relics. "This column represents a qualitative attempt to give petrologic guidance in interpreting major events in Apollo 16 rocks. Most Apollo 16 rocks have been multiply brecciated so that their ages are not specifically meaningful. However, some have undergone little reworking since their initial excavation (see Wilshire and others, 1973); the clasts (relics) in these breccias represent original target material, which consists of plutonic igneous and metamorphic rocks (Wilshire, 1974), and thoroughly metamorphosed or melted material forming their matrix. From such rocks it may be possible to date the three types of events listed in this column, as well as specify the petrologic conse uences of those events. ‘Medium-grained hornfels (Wilshire, 1974) may represent preexcavation metamorphism in a plutonic environment. These parts 0 plutonic rocks survive crushing more consistently than the coarsevgrained igneous rocks from which they are derived. "Parentheses following letter and class number indicate alternative classification. Parentheses unaccompanied enclose tentative classification. “Textures formed at time ofinitial excavation of the rock have undergone major modification by subsequent impact(s); age not meaningful with respect to primary excavating event or crystallization age of source rock. 7Multiple impacts have resulted in mixing diverse lithologies that may or may not have been significantly modified by postexcavation impacts. Difficult or impossible to determine the significance of ages with respect to primary excavating event or crgstallization age of source rock(s). "Metaclastic rocks have relict lithic and mineral debris in thoroug ly recrystallized (granoblastic to poikiloblastic textures) to partly or wholly (intersertal, intergranular, subspherulitic, ophitic textures) melted matrices. Isotopic data (table 4) indicate that relict material may yield minimum ages of target material, whereas wholerock data yield age of metamorphism. The significance of these data with respect to initial excavating event or crystallization age of the source rock(s) is not known. References: ( 1) Juan and others, 1974 ( 2) Lual and Schmitt, 1973 ( 3) Nunes and others, 1974 ( 4) Schaeffer and Husain, 1974 ( 5) Sclar and others, 1973 ( ( ( (l2) Nakamura and others, 1973 (13) Walker and others, 1973 (14) Scoon, 1974 (15) Bence and others, 1973 (16) Delano and others, 1973 (17) Simonds and others, 1973 (18) Brown and others, 1973 (19) Dowty and others, 1974b (20) Dowty and others, 1974a (21) Grieve and others, 1974 (22) Gancarz and others, 1972 6) Solar and Bauer, 1974 7) Johan and Christophe, 1974 8) S. R, Taylor and others, 1974 ( 9) Kridelbaugh and others, 1973 (10) Rose and others, 1973 (11) Hodges and Kushiro, 1973 pacts on terrestrial crystalline targets—the Vredefort‘ Ring, South Africa (fig. 4E) and Sudbury Crater, Canada—impacts that produced a breccia consisting of relics of the target material encased in a dark fine— grained annealed (fig 4F) to partly melted (fig. 4G) matrix of the same composition. Several Apollo 16 samples approach this simplicity (table 3, footnote 2 and notes on 60018, 60616, 67936), but none has sur- vived untouched. At least slight rebrecciation has af— fected all, resulting in fracturing of the original matrix and injection of broken feldspathic debris derived from original clasts (forming Bz-type breccias from a Bi-type parent). Continued brecciation gradually destroyed the remnants of the original target material, although pieces of the tough first-cycle matrix apparently sur- (23) Helz and Appleman, 1973 (24) Nava, 1974 (25) Brunfelt and others, 1973a (26) Drake, 1974 (27) Duncan and others, 1973 (28) Steele and Smith, 1973 (29) Crawford, 1974 (30) Agrell and others, 1973 (31) Mark and others, 1974 (32) Roedder and Weiblen, 1974b (33) Weiblen and Roedder, 1973 (34) Laul and others, 1974 (35) Grieve and Plant, 1973 (36) Albee and others, 1973a, b (37) El Gorsey and others, 1973 (38) Stettler and others, 1974 (39) Fruchter and others, 1974 (40) Friedman and others, 1974 (41) Peckett and Brown, 1973 (42) Prinz and others, 1973a (43) Roedder and Weiblen, 1974a (44) Hollister, 1973 vived. Beyond a certain stage, however, it is not possi- ble to determine whether the different parts of a brec- cia were originally related or were derived from differ- ent sources. The source rocks from which the Apollo 16 breccias were derived are represented at least in part by the clasts in the simplest, least-reworked breccias. These clasts are consistently of two lithologic types: (1) cataclastic plutonic feldspathic rocks of a troctolite-norite- anorthosite suite; relics show coarse to very coarse grain sizes and pyroxenes with coarse exsolution lamellae (fig. 4H); (2) cataclastic feldspathic hornfelses with medium-grained granoblastic textures, commonly modifications ofthe plutonic rocks (Wilshire and others, 1972). The hornfelses are far coarser grained PETROLOGY AND DISTRIBUTION OF RETURNED SAMPLES 139 FIGURE 4.—Photomicrographs of Apollo 16 breccias; photograph and photomicrographs of pseudotachylites of Vredefort structure, South Africa, E—G. A, Sample 67035 (B2 breccia), showing clasts with selvages embedded in a friable light-gray matrix containing a variety of lithic and mineral microclasts. Plane-polarized light. B, Sample 61295 (BC breccia), showing a variety of clasts, including glass, in a fine—grained glassy matrix. Plane-polarized light. C, Sample 60018 (B. breccia), showing a cataclastic anorthositic clast at one edge grading into an impact melt zone with ophitic texture, and this into intersertal texture. Plane-polarized light. D, Sample 68815 (B; breccia), showing a small area in a rock dominated by dark clasts in a dark matrix. This area shows a remnant of B2 breccia with feldspathic debris in fractures in the fine-grained dark original matrix. Plane-polarized light. E, Pseudotachylite, Vredefort structure, South Africa, showing breccia composed of clasts of crystalline rock in finely comminuted and locally fused material of the same chemical composition as the clasts. Photograph by Warren Hamilton. F, Pseudotachylite in alkali granite, Vredefort structure, South Africa, showing cataclastic flow structures in comminuted alkali granite, metamorphosed to Very fine grained granoblastic texture. Cross- polarized light. G, Pseudotachylite in Old Granite, Vredefort structure, South Africa; local fused zone showing newly crystallized feldspar laths and flow structure. Cross-polarized light. H, Sample 62236 (Bl breccia), showing coarse irregular and finer regular clinopyroxene exsolution lamellae (white) in orthopyroxene (dark). Cross—polarized light. 140 than those forming the matrices of intensely deformed impact breccias. The hornfelsic breccia clasts have the same textures and compositions as B. group breccias and therefore could have a common origin. The most common type of crystalline igneous rock, ophitic feldspathic rock, is not present as clasts in the simplest, least-reworked breccias, nor is the coarsely poikiloblastic lithology. Both of these rock types ap- pear in the Apollo 16 samples only as clasts in complex breccias. The balance of evidence indicates that these rocks result from solidification of impact melts. It seems apparent, then, that the target material for the first major impact event shown in Apollo 16 rocks was a plutonic suite composed of troctolite, norite, and anorthosite that had undergone partial thermal metamorphism prior to impact. These rocks constitute the “ANT” suite of Prinz and others (1973b), whose existence they inferred largely from the chemical com- positions of fine-grained, impact-generated hornfelses. CHRONOLOGY 0F APOLLO 16 ROCKS Relics of the coarse-grained target materials and of the finely pulverized, partly to wholly melted rock pro- duced in the first major excavation are sufficient to allow us to specify the nature of the products and perhaps to date three significant events: crystallization and differentiation; metamorphism that produced the coarse hornfels; and primary excavation and breccia- tion. Table 3 presents a qualitative guide to the sam- ples that might yield this information. Isotope data gathered on Apollo 16 rocks have not generally been systematically directed by the petrol- ogy of the collection as a whole. A number of ages (ta- ble 4) have been determined on complex rocks with no indication of what part or parts of the rock were meas- ured. Other ages date unknown events that took place after initial excavation and deposition of the Apollo 16 breccias. The problem of terminology (see Wilshire and Jackson, 1972b; Jackson and others, 1975) adds con— siderably to confusion about the meaning of the ages. TABLE 4.—Isotope data on Apollo 16 samples Sample Rock type Part of rock Age (10”) Method and Notes dated (b.y.) source 60015 B. Whole rock 3. 55:0. 05 Ar“’- Ar 9 (1) Age probably time of shock deforma- tion. 60015 ,-,,do .._,3.6—3,8 U-Pb (2) 60025 B. . _ _ .do . . , ,418 t 0.06 Arm-Ar“ (1) Age of excavation or minimum age of crystallization. 60315 C, Ludo ,,,,,, 3.94:0.05 Ar“’-Ar39 (3) Maximum a e of metamorp ism? 60315 "ado ______ 4.03:0.03 Arm-A1"m (4) 60315 ”ado ______ About 3.99 U-Pb (2) Age of metamorph- ism. 61016 B. 7 (3.651004) Arm-Ar19 (5) Poorly defined plateau. Rock very in- homogeneous. 62242,3 Anonhosite Whole rock 4.5:03 Arm-Ar“ (4) Total Ar age. May have excess Ar. GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS TABLE 4.——Isotope data on Apollo 16 samples—Continued Sample Rock Part of rock Age Method and Notes type dated (by) source 62295 C. , , "do ______ 4.00 :0.06 Rb-Sr (6) Age of crystalliza- tion of melt rock. 62295 ”,‘dO LLLLLL 3. 89:0. 05 Arm-Ar” (7) 63502,l7a B.? 3. 89:0. 01 Ar“‘-Ar"” (4) "Monomict anor- thositic breccia.” 63502,17b ? Whole rock? (3.8103) Arm-AI"m (4) "A hanitic dark ragrnent.” No well defined plateau. 63502,17c2 Anorthosite Whole rock (4.1:0.1) Arm-Ar” (4) "Unshacked anor- thositic particle.” 63502.17d Plagioclase ,,,,,,,,,,,, (3.9:03) Arm-Ar” (4) "Clear plagioclase crystals.“ No well-defined plateau. 63503,13,2 Anorthosite Whole rock? 3.98:0.07 Arm-Ar” (8) 63503,13,7 G Whole rock 4.00:0.06 Arm-Ar” (8) 63503,15,3 C. _s__do ,,,,,, 3.95:0.06 Ar“'—Ar“" (8) Possible excavation age. 63503,17 ? ? 4.19:0.06 Arm-Ar“ (9) No description 63503,17 7 7 3.981004 Arm-Ar” (9) Do 63503,17 ? 7 3. 99:0 03 Arm-Ar” (9) Do. 63503,17 7 7 3. 99:0 02 Arm-Ar” (9) Do. 65015 C2 Whole rock? 3. 98; 3 93 Arm-Ar"m and Whole rock, age of Plagioclase About 4. 5; Rb-Sr (10,11) metamorphism; 4.42 plagioclase, minimum age of precursor. 65015 Whole rock 4 0 U-Pb (2) 65015 "fldo ,,,,,, 3 92:0. 04 Arm-A13” (4) 65315 B2 7 4. 30:0. 26 Ar"‘~Ar'“‘ (9) Interpreted as 3— 4 two—stage evolu- tion, old age = time of crystalli- zation of parent, young = time of excavation. 66043,1,9 G Whole rock >16 Arm-Ar“ (8) 66043,2,4 C. , , "do ,,,,,, 4.13 :005 Arm-Ar” (8) Possible excavation age. 66403,2,5 C. _0d ______ 4. 01 :0. 05 Arm-Ar” (8) D0. 66095 B, Whole rock? About 3.6 Arm-Ar” (7) Complex release pattern. 66095 Whole rock About 4.0 U-Pb (12) 67015 B;.(B-_)) Black clast ~4.42 U—Pb (2) Clast = original Matrix ,, , 399 matrix? Model age. 67075 B. 7 4. 04:0. 05 Arm-A13” (7) 67455,Sa B._, Dark clast "(4 15:0 1) Arm-Arm (4) No well-defined plateau. 67455,Sb B... Light clast,,3,91 10.12 Ar“’-Ar"” (4) 67483,]3,6 B.,Bg? 7 24.2 Arm-Ar” (8) Matrix partly melted. 67483,13,8 BUB-1? ‘7 4.26:0.05 Arm-AI“9 (8) 67483,14,2 B.,B.. 7 4.24:0.05 Ar“‘-Ar'19 (8) D0. 67483,14,6 13.337? 4 05:0. 08 Ar“‘»Ar"‘ (8) Do. 67483,]4,7 B.,B._ ? ? _ Ar“'-AIJ9 (8) 67483,]5,2 7 7 3. 93: 04 Ar‘“ 2.3 Arm-Ari” (8) Sources: 1. Schaeffer and Husain, 1974 10. Jessberger and others, 1974 2. Nunes and others, 1973 11. Papanastassiou and Wasserburg, 1972b 3. Husain and Schaef’fer, 1973 12. Nunes and Tatsumoto, 1973 4. Kirsten and others, 1973 13. Albee and others, 1973b 5. Stettler and others, 1973 14. Hueneke and others, 1973a 6. Mark and others, 1974 15. Hueneke and others, 1973b 7. Turner and others, 1973 16. Tera and others, 1973 8. Schaef‘fer and Husain, 1974 17. Papanastassiou and Wasserburg, 19723 9. Stettler and others, 1974 PETROLOGY AND DISTRIBUTION OF RETURNED SAMPLES An effort is made here to point out some of these prob- lems with respect to specific samples and to interpret the data where possible. The discussion is based, as is table 3, on the assumption that the plutonic rocks, whether clasts in breccias or isolated fragments, were excavated from the deep lunar interior by basin- forming impacts (Wilshire, 1974). The significance of their ages, as well as those of rocks that were melted or metamorphosed as a consequence of this excavation, depends on their subsequent history. The petrology of the samples shows that impact events following the initial excavation of Apollo 16 rocks produced effects ranging from minor to effects so profound as to have completely reset radiogenic clocks. Moreover, extreme effects can be registered in small areas of rocks that have not otherwise been much changed since excava— tion. Breccias that have been little modified since excava— tion can be recognized by large areas of unmixed cata- clastic feldspathic rock with coarse mineral and lithic relics and large areas of the dark fine grained original matrix; the first—cycle matrix is generally broken, but the pieces commonly are not much rotated. A significant number of Apollo 16 rocks have these characteristics (table 3), but few of them have been dated, and none has had all of its components (matrix and plutonic igneous and metamorphic clasts) dated separately. The ages of samples such as soils and the C. and C2 crystalline rocks are ambiguous because their history since excavation has not been determined. Age data (table 4) have been determined on eight samples called “anorthosite.” Three of these are documented rocks (60015, 60025, 67075); five are sam- ples from 2 to 4 mm coarse fines (62242, 3; 63503, 13, 2; 63502, 17, 02; 67483, 14, 18; 68503, 13, 7). Ages range from 3.55 by. to 4.5i0.3 b.y. Sample 60015, dated at 3.55 by. by “’Ar-“i‘Ar, is considered to be the “youngest anorthosite” yet found on the Moon (Schaeffer and Husain, 1974). The hand specimen, however, clearly reveals heavy shock damage that resulted in extensive pulverization, melting, and maskelynitization of the anorthosite. Moreover, some areas have a coarsely sugary texture typical of preexcavation (‘?) metamor- phic textures (Wilshire, 1974). Where information is insufficient to determine the exact nature of the part of the sample dated, the age may be interpreted to repre— sent the age of crystallization of the anorthosite as im- plied by Schaffer and Husain (1974), the age of preex- cavation (?) thermal metamorphism, age(s) of shock deformation, or some averaged combination of these. If the age represents shock deformation, as seems likely from the extensive shock damage and from its primi- tive initial ““Sr (Nunes and others, 1974), it has no significance with respect to basin chronology. Sample 141 61016, which is texturally similar to 60015, is a breccia that has undergone extreme shock damage following its excavation and following crystallization of the melt rock matrix that encloses the anorthositic clasts (see references, table 3). These events may have no relation at all to the initial excavation of rocks and conceivably are the more extreme results of minor impacts. Moreover, Nunes and others (1974) documented loss of lead from 60015 glass less than 1.3 by. ago, indicating further modification by a still more recent event. Sam- ple 60025, dated by 40Ar-39Ar at 4.18 by, is intensely pulverized and locally partly melted. It is not as badly damaged as 60015, and the age may represent a minimum crystallization age, although no description of the piece analyzed is given. The presence of substan— tial amounts of olivine and orthopyroxene in the cata- clastic parts of the rock as well as unpulverized relics of the original rock suggest that more meaningful ages could be obtained by dating these relics (table 3). Sam- ple 67075, dated by "’Ar-“”Ar at 4.04 by, is a complex Bl breccia in which a variety of coarse hornfels clasts (preexcavation metamorphism?) are the dominant lithic relic. As the grain size of much of the mineral debris is too coarse grained to have been derived from the hornfelses, the breccia as a whole may be derived from one or more partly metamorphosed plutonic rocks. The whole—rock age of the rock could represent an average of several metamorphic and crystallization ages. “Anorthosite” samples from the 2- to 4-mm fines dated are accompanied by meager descriptions. As material called “anorthosite” in the literature is com- monly hornfels, sometimes glass, and rarely anortho- site, one does not know whether the ages represent time of crystallization of the parent rock, time(s) of thermal metamorphism, or time(s) of melting in a reg- olith environment. Two samples called “troctolite,” one (62295) a documented rock, and one (68503,16,12) from 2 to 4 mm coarse fines, have been dated (table 4). Sample 62295 is probably an impact melt (see references, table 3), and its age that of crystallization of the melt. The rock does contain a small amount of unmelted relics that could affect the age, producing the spread of ages determined by Rb-Sr (4.00:0.06 by.) and 40Ar-i’s‘Ar (3.89:0.05 by.) methods. Whether 68503,16,12 is an impact melt, a plutonic igneous rock, or a hornfels is not known from the description given, and the significance of the age is therefore unknown. Other dated samples of apparent impact melt rocks other than glass include documented rocks 68415 and 68416 and 2—4 mm coarse fines samples 63503,15,3; 66043,2,4; 66043,2,5; 68503,16,31; and 68503,16,33. Many dates are available for the ophitic rock 68415 142 (table 4); they show a range from 3.80i0.04 to 4.47 b.y., with a Rb-Sr internal isochron registering 3.84:0.01 by. A plagioclase separate from 68415 analyzed by Huneke and others (1973a) has a dis- tinctly higher (4.09 by.) 4UAr—"‘9Ar plateau age than the whole rock and a high—temperature release age of about 4.5 by The plagioclase separate may include unmelted relics of the precursor of the rock. Sample 68416, taken from the same boulder as 68415 (ALGIT, 1972b) and having an essentially identical bulk com- position (Rose and others, 1973), yielded a 40Ar-39Ar whole-rock age of 4.00:0.05 by. Our descriptions of this sample in hand specimen indicate a higher abun- dance of relict plagioclase than in 68415, which may account for the older apparent age of the whole rock. Rocks like 68415 and 62295 are not abundant in the Apollo 16 collection, but the evidence seems good (see Dowty and others, 1974a) that they represent impact melts derived from older, highly feldspathic rocks. Their relatively coarse grain sizes compared with other Apollo 16 impact melt rocks indicate slower cooling, but they did not cool so slowly that isotopic equilibrium was achieved. The ages of these rocks, exclusive of un- melted residual material, may be significant in basic chronology, but are nevertheless ambiguous, as direct ties to plutonic source rocks have not been made. The 2—4-mm samples that are probable impact melt rocks are identified as <<fine-grained intersertal igneous rocks” (Schaffer and Husain, 1973) in the terminology of Delano and others (1973). Such rocks form significant amounts of the matrices of many simple breccias (table 2), but also survive as clasts through multiple impacts. The histories of such materials in 2—4-mm coarse fines are therefore impossible to de— cipher, and their ""Ar-39Ar ages cannot be meaning- fully interpreted. Two documented samples (60315, 65015) of C2 metaclastic rocks have been dated. Sample 60315 yielded 40Ar-3-L’Ar ages of 3.94:0.5 by. and 4.03:0.03 by. and a U-Pb whole-rock age of 3.99 by; 65015 yielded a Rb-Sr whole-rock age of 3.93:0.02 b.y., “'Ar- 39Ar whole-rock ages of 3.92:0.04 by. and 3.98 b.y., and a U-Pb whole-rock age of 3.99 by. These rocks have moderately coarse grained poikiloblastic textures with variable amounts of unrecrystallized mineral and lithic debris. Both dating methods indicate that unre— crystallized plagioclase in 65015 is not in isotopic equi- librium and is much older (4.40—45 b.y.) than whole- rock ages. Angular plagioclase relics in 60315 are zoned; this chemical disequilibrium suggests that isotopic equilibrium may not have been achieved in this rock either. Differences in whole-rock ages may reflect differences in amount of unrecrystallized debris GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS in the particular parts of the rock analyzed. The whole-rock 4"Ar-”Ar ages are of course older, by an ; unknown amount, than the age of metamorphism be- cause plagioclase that yields a greater age was present in the rock measured. As lithologic mixing may have occurred during formation of these rocks (see Bence and others, 1973; Albee and others, 1973b), the whole— rock Rb-Sr and unrecrystallized plagioclase ages may also average rock materials of different ages. The lack of direct ties between these rocks and plutonic rocks makes their times of metamorphism ambiguous with respect to basin chronology. Of 17 breccias dated (table 4), 10 are parts of six documented rocks (61016, 65315, 66095, 67015, 67455, and 67915); the rest are samples taken from coarse fines (63502,17a; 67483,13,6; 67483,13,8; 67483,14,2; 67483,14,6; 67483,14,7; 68503,13,5). Our criteria (table 3) indicate that of the analyzed group, only documented samples 65315 and 66095 are likely to yield unambiguous information on basin chronology. Sample 65315 yielded an 4UAr-39Ar age of 4.30:0.26 b.y., interpreted (Stettler and others, 1974) as possibly reflecting the crystallization age of the anorthositic component, with indications of excavation between 3 and 4 b.y., and rebrecciation (converting the rock to a B2 breccia) at about 2 by. We believe that the excava- tion age could be determined precisely from the origi- nal matrix component of this breccia, but we do not know what component of the rock was dated by Stettler and others (1973). Sample 66095 is dated by U-Pb at about 4.0 by. (Nunes and Tatsumoto, 1973); this may represent an excavation age, but its relation to excava- tion ages of little-modified breccias remains unknown. Sample 61016 is a complex breccia consisting of ex- tensively shattered, partly maskelynitized, and partly coarsely metamorphosed anorthositic clasts in a fine- grained intersertal matrix. Maskelynitization of the plagioclase laths in the matrix indicates that the entire rock was severely shocked after consolidation of the intersertal matrix. The poorly defined 40Ar-“i’Ar age of about 3.65 by. (table 4) has no significance with re- spect to basin chronology or crustal formation. Sample 67015, which may be a complex soil breccia, and 67455 are so thoroughly reworked by multiple impacts that the postexcavation histories of their components are extremely difficult to decipher. Sample 67915 is another very complex rock of which three components have been analyzed. Our classification of the rock as a B, breccia disregards the extensive glass net-veining; as the event that produced the glass may have altered significant portions of the rock, we regard the ages as ambiguous. Furthermore, the component dated at 3.99:0.05 by. (67015, 41d) is called "friable matrix” of PETROLOGY AND DISTRIBUTION OF RETURNED SAMPLES the breccia by Kirsten and others (1973). The rock as a whole, viewed either as including or excluding the glass veins, does not have a friable matrix; we do not know what was actually dated nor its relation to the rest of the rock. The seven breccia samples taken from coarse fines (table 4) could have been derived from virtually any source among the breccias; therefore, their significance in basin chronology and crustal formation is unknown. Five samples of glass (63503,13,7; 66043,1,9; 68503,13,6; 68503,16,1; 68503,16,34) and one of plagioclase (63503,17d) from coarse fines were analyzed (table 4). In many of the documented samples, it is clear that glass formation is among the youngest events in the history of the rocks and presumably is the consequence of comparatively small impacts that do not produce thick ejecta deposits in which the melt could crystallize. The glass ages have no obvious significance with respect to basic chronology or crustal formation. Five analyzed samples (63503,17, four samples from 2 to 4 mm coarse fines and 67483,15,2) were not well enough described for us to interpret their ages. Of the 47 samples of Apollo 16 rocks dated, only one appears to have a reasonably unambiguous age: the age of 60025, 4.18 by, may represent the minimum crystallization age of this rock, or, if Turner and others (1973) are correct in assuming that degassing in the lunar interior occurs continuously to the time of exca- vation, the age may represent the minimum age of ex- cavation. However, the "“Ar—"9Ar ages obtained on plagioclase separates from 65015, which are older than those obtained from the whole rock, and the results obtained by Stettler and others (1974) on 65315 sug- gest that crustal anorthositic rocks were not degassed prior to excavation. Hence, the ages of the least- damaged anorthositic components of breccias more likly represent minimum ages of crystallization than time of excavation (Stettler and others, 1974), but both ages could probably be made more reliable by more selective sampling of the hand specimen (see table 3). Four other samples that ambiguously date basin- forming events are 62295, 4.00 by, 3.89 by; 68415, 3.80—3.85 by; 60315, 3.94 by, 4.03 by; and 65015, 3.93 by, 3.98 by. The only criterion by which these rocks are identified as possible derivatives of very large impact events is their comparatively coarse grain size. Two of these samples (68415, 4.09—4.53 by; 65015, 4.40—4.5 b.y.) yield possible ages of their precursors that may be significant with respect to crustal forma- tion. These results do not appear to us to provide a sound basis for speculating on the chronology of basin- forming events or crustal formation. It seems clear 143 however, that useful information can be obtained from the least-damaged breccias, as detailed in table 3, if they are selected and dated systematically with regard to their petrology. AREAL DISTRIBUTION OF CLASSIFIED SAMPLES The field distribution of all samples classified in table 1 is plotted in histogram (fig. 5). Samples from stations 4, 5, and 13 are heavily weighted by rake sam- ples collected from a small area. The LM-ALSEP and station 11 areas are much better represented by documented samples than the other stations. Samples of all eight rock groups described were found at these two stations, suggesting that more extensive sampling at other stations would have expanded the range of rock types at each station. The stations can be divided into two groups (1) Cayley plains stations are LM-ALSEP, 1, 2, 6, 8, and 9; LM-ALSEP and station 6 may be mantled by a thin discontinuous veneer of material from the Descartes mountains. (2) Descartes mountains stations are 4 and 5, located on Stone mountain but possibly partly man- tled by ejecta from South Ray crater; and 11 and 13, on the North Ray crater ejecta blanket, which may sample the Descartes mountains. Although proportions of rock types vary from station to station, depending on thoroughness of documented sampling, there are no distinctive differences in rock populations between the two groups of stations (fig. 5). When all data within the two station groups are com— bined (fig. 6), some differences appear: Cayley stations have higher proportions of 01 and C2 crystalline rocks and a lower proportion of B2 breccia. According to our view of the breccias, both B1 and B2 breccias are deriva- tives of B4 types, the Bl’s differing from Bz’s only by having none of the first matrix component attached. If these close relations are considered, there do not ap- pear to be significant differences in rock populations between sample sites on the Descartes mountains and those on the Cayley plains. The comparatively small number of samples thin sectioned to date does not allow final conclusions on possible petrographic differences between rocks from the Descartes mountains and the Cayley plains, but the data available (table 2) indicate that differences are not significant. In figure 7, the textures of crystal- line rocks and unmodified breccia matrices are placed in the two station groups. The histograms are virtually identical. Studies of soils from the Apollo 16 site (Delano and others, 1973; G. J. Taylor and others, 1973) suggest that, in general, materials derived from the Cayley plains are comparatively rich in fine-grained igneous 144 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS STATION | STATION 2 STATION 8 IO — O (3, c2 G 3, 82838485 Icllczls IBIEBZEB3IB4IBS' lcllczl GIBIIBJB3IB4|85| LM'ALSEP, 6 9 STATION 9 LM—ALSEP STATION 6 l0 — U) x U E! 0 — farm—mm % LL CI C2 G BI 32 333435 CI C2 G 8| 32 338435 C26 8| 32 338485 0 m LIJ “2° 40 — 3 STATION 4 STATION 5 STATION || STATION l3 7 _ 3o — / _ <:> / / % 20 — / é 7/ 10 ~— 21% O CI'CZ'BG'BIIBZI 31TB4'85 ICIICZIG'BIIBZIBB 34%;} lc,Ic2JG|B,IBZI131331 Ic ICZIGIBIIBZIBgB4IB5' FIGURE 5.—Histograms showing distribution of rock types at each sampling station. Rocks in group 1 are from Cayley plains, those in group 2 from Descartes mountains and the ejecta blanket of North Ray crater, and poikiloblastic lithic fragments whereas materials ite, troctolite) lithic fragments. Heiken and others derived from the Descartes mountains are compara— (1973), who studied a wider size range of particles, tively rich in what is termed “ANT” (anorthosite, nor- found the reverse situation at station 4 on the Des- PETROLOGY AND DISTRIBUTION OF RETURNED SAMPLES STATIONS 4, 5. H, l3 7°” 7 _ é / 3 3° ‘ / g .0 _ / % / ROC K T YPE FIGURE 6.—Composite histograms of the two groups of stations. cartes highlands, where samples had a higher propor- tion of “medium- and high-grade” metamorphic frag- ments (poikiloblastic and sheaf-textured rocks) than soils from the Cayley plains or North Ray crater sta- tions. Such differences in the soil components may re- flect differences in proportions of clasts and matrix of parent breccias; Cayley soils might be taken as derived from breccias with a larger matrix component than Descartes soils. This type of information is not included with the distribution of the larger rock samples shown by the histograms (figs. 5 and 6). While the bulk chemical composition of soils (LSPET, 1973; Rose and others, 1973) shows little var- iation, Duncan and others (1973) noted subtle differ- ences between Descartes and Cayley materials that 145 STATIONS STATIONS LM-ALSEP, 4,5,ll, I3 I, 2, 6, 8, 9 20 -1 co 2 o o (r o 0: Lu m 2 3 z o _ I 2 3 4 | 2 3 4 l=lgneous 2=Poikiloblastic 3=Granoblastic 4=Glassy or fragmental FIGURE 7.—Histograms showing distribution of micro- scopic textures at each of the two groups of stations. could be accounted for by Descartes materials enriched in “anorthosite” and depleted in “KREEP,” “granite,” “high-Mg basalt,” and the meteoritic component rela- tive to Cayley materials. These differences may reflect compositional differences between matrix and clast components of the first-cycle breccias, perhaps in part a consequence of partial melting (Warner and others, 1974); the statistics on coarse fines and compositional variations indicate a larger proportion of first-cycle breccia matrix in soils of the Cayley Formation. These results are consistent with the concept of Hodges and Muehlberger (this volume) that the Cayley Formation and Descartes mountains units are lateral facies of the same ejecta deposit. In this view, the Des- cartes material is the comparatively “dry,” clast-rich part of the ejecta, the Cayley Formation the compara- tively “wet,” matrix-rich part. Ulrich (1973) suggested that at the Apollo 16 site, dark “melt-rich” breccias are relatively abundant at lower elevations, “dry,” light- matrix breccias at higher elevations, concluding that the stratigraphic section consists of light-matrix brec- cias overlying dark-matrix melt-rich breccias. The soils data are less in accord with this View, unless South Ray crater distributed a considerable amount of debris from the hypothetical dark breccia layer over the southern and central Cayley stations. Delano and others (197 3) utilized the same hypothet- 146 ical stratigraphic section but identified the dark layer as either a brecciated volcanic flow or a regolith con- taining abundant volcanic material (“FIIR”:fine- grained intersertal igneous rock). The enrichment of Cayley soils in poikiloblastic and fine-grained interser- tal rocks raises the same problem with their hypothesis as with Ulrich’s. Moreover, the fine-grained intersertal texture is well developed as impact melt matrix in many breccias, much likelier sources of the "FIIR” than a volcanic flow. The significance of the FIIR ages (Schaffer and Husain, 1973)is unknown, but the range of values from 3.86:0.07 by. to 4.13:0.05 by is much too great for one lava flow. There seems to be little basis for the supposition (G. J. Taylor and others, 1973) that soil components from the Cayley indicate stratigraphic layering in which the Cayley Formation is composed predominantly of poikiloblastic rocks underlain by a regolith of light- matrix breccias. The documented rock collection clearly shows that all components of those soils could have been derived from a section composed of a single breccia parent with no vertical lithologic variations. There is even less basis for the postulated bedrock of anorthosite-norite-troctolite (ANT) on which the light-matrix-breccia regolith is thought to have formed (Taylor and others, 1973). The sample data seem rather to support derivation of the soils from ejecta deposits in which an original matrix component (pow- dered and partly melted rock) was present in somewhat higher proportion than anorthositic clasts in the areas underlain by Cayley Formation than in areas under- lain by Descartes materials. Whether these ejecta de— posits overlie still older ejecta is not known but seems likely. SUMMARY AND CONCLUSIONS Apollo 16 samples heavier than 2 g are classified by a descriptive scheme of three groups: (1) crystalline rocks, subdivided as igneous or metamorphic; (2) glass; and (3) breccias, subdivided 0n the basis of color of clast and matrix and proportions of these components. The crystalline igneous rocks consist of one certain and one possible anorthosite, 11 fine-grained ophitic— to-intersertal rocks of troctolitic to anorthositic compo- sition, and one troctolite enclosed in fine-grained melt rock of the same composition. Derivation of the fine- grained igneous rocks by impact melting of feldspathic plutonic source rocks is indicated by common occur- rence in the fine-grained rocks of unmelted relics de- GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS rived from coarse-grained plutonic rocks, a bulk com— positional spread like that of the plutonic clasts in breccias, and gradations from fine-grained melt tex- tures to plutonic rocks of essentially the same composi— tion. Metamorphic crystalline rocks studied consist of one medium-grained granoblastic rock, considered to be a product of metamorphism in a plutonic environment prior to excavation, and ten poikiloblastic rocks. We conclude that gradation from poikiloblastic to un— equivocal igneous textures in these rocks is evidence of metamorphic origin with minor melting. The five breccia types have been derived by rebrecci- ation of a first-cycle breccia that consisted of anortho- sitic clasts in a fine-grained matrix that varied from melt texture to metamorphic texture. The first-cycle breccia is considered to be multiring basic ejecta, as it contains clasts of plutonic rock derived from deep in the lunar crust. These breccias have been modified in varying degrees by subsequent smaller impacts. Rocks reflecting modification of first-cycle breccias are sufficiently well represented in the Apollo 16 col- lection that least-damaged samples can be identified. From such samples, it may be possible to date the crys- tallization of the original crustal rocks, the preexcava- tion local metamorphism of those rocks, and the time of excavation. A review of age data shows that most sam- ples selected for isotopic measurement are so severely modified by subsequent impacts that the ages are am- biguous. The samples petrologically most favorable for dating significant and identifiable events in the his- tories of the rocks are tabulated with the hope that they will help in obtaining unambiguous dates, now so scarce that speculation on basin chronology is at pres- ent unwarranted. The distribution of classified samples shows no significant differences among Cayley and Descartes sample sites. Statistical and compositional data on soils support the view that the Cayley plains and mate- rials of the Descartes mountains are facies of the same ejecta deposit and that a somewhat higher proportion of matrix, melt and powdered rock, was segregated to form the Cayley Formation. ACKNOWLEDGMENTS We are indebted to M. Prinz, University of New Mexico; W. R. Muehlberger, University of Texas; P.D. Nunes, R. L. Sutton, and G. E. Ulrich, US. Geological Survey, for review and assistance with this report. F. REGOLITH OF THE APOLLO 16 SITE By VAL L. FREEMAN CONTENTS Page Introduction __________________________________________________________________________ 147 Appearance of the regolith ____________________________________________________________ 147 Thickness of regolith ________________________________________________________________ 148 Composition of regolith ______________________________________________________________ 149 Summary ____________________________________________________________________________ 156 ILLUSTRATIONS Page FIGURE 1-4. Photographs: 1. Apollo 16 traverse area in high-sun illumination ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 148 2. Comparison of lunar surface within and between rays from South Ray crater ______________________________ 150 3. Comparison of old and young ray-covered areas ___________________________________________________________ 152 4. Location of concentric craters used to estimate depths of regolith __________________________________________ 154 5. Map of kilometer-size craters in Apollo 16 region ________________________________________________________________ 155 6-9. Variation diagrams, soil samples and rock and soil samples: 6. FeO, TiOZ, A120. and Ni ________________________________________________________________________________ 156 7. T102 relative to A1203 1111111111111111111111111111111111111111111111111111111111111111111111111111111111 157 8. A1203 relative to FeO __________________________________________________________________________________ 158 9. Ni relative to FeO ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 159 TABLES Page TABLE 1. Apollo 16 soil analyses for A1203, TiOg, FeO, and Ni ____________________________________________________________ 155 2. Apollo 16 rock analyses for A120“, TiOZ, FeO, and Ni ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 155 INTRODUCTION The lunar regolith is generally defined as the rela— tively unconsolidated fragmental material that forms the surface layer of the Moon. The term is used for all loose surficial debris and for subunits that can be rec- ognized, such as regolith above, beneath, and mixed with the ejecta of North Ray crater. It is commonly assumed that regolith is solely the product of repeated meteorite bombardment, that is, the accumulation and mixing of impact crater ejecta on the lunar surface. Accordingly, the median thickness of regolith above some stratum is related to the time elapsed since for- mation of that stratum (Shoemaker, 1971). In this re- port, the term regolith is used in the several senses defined. "Soil” is used as a synonym for the regolith. This report describes the regolith at the Apollo 16 site, provides new measurements of its thickness, and examines the composition of the soils in comparison with the rocks within the site. APPEARANCE OF THE REGOLITH Premission investigations of the Apollo 16 site sug- gested that differences in regolith would be found. Rays of high albedo extending across the surface from South Ray, North Ray, and Baby Ray craters were seen in orbital photographs (pl. 2). The Cayley plains (LM landing area) and the Descartes mountains (Stone mountain) were considered to be underlain by different bedrock types that would be reflected by differences in composition of regolith. The astronauts on the surface were able to recognize the rays by changes in abun- dance of rock fragments and secondary craters but otherwise found the surface appearance of the regolith the same throughout the area traversed. No difference between regolith on the Cayley plains and on Stone mountain was observed. An unexpected finding was the presence of a white layer just below the surface at most of the stations (Muehlberger and others, 1972). The regolith appeared to the astronauts as a gray, 147 148 rocky soil unit with a heavily cratered surface that seemed to lack truly flat areas. The LM touched down in one of the smoothest areas available; local relief amounted to only a few meters except for a fresh 30-m crater immediately east of the LM. The crew observed that this area might be the floor of a very subdued 180-m crater. The surface along the traverses was crossed by long rays of two ages shown by premission mapping (Elston and others, 1972c), an older set radiating from North Ray crater and a younger set from South Ray crater. The crew’s description of the surface gives a picture of the composition and form of a young ray and valuable data on the aging of rays as discussed below. During the three traverses, they crossed many ray segments (fig. 1) on different azimuths, at various distances from their source craters, and under different lighting con- ditions. The fresh rays were distinguished by the crew on the basis of concentrations of rock fragments on the sur- face, the presence of large blocks, the high angularity SOUTH RAY , CRATER FIGURE 1.—Apollo 16 traverse area. Apollo 16 panoramic camera frame 5328, computer enhanced to show ray patterns from North and South Ray craters; sun elevation 60°. GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS of the rocks, the absence of dust on the rocks, the pres- ence of secondary craters, and, under favorable light— ing conditions, higher albedo of the ray area. No topo- graphic form was associated with rays, and no color or other property of the fine-grained (granules or finer) surface materials was described that would distinguish ray areas from interray areas. The greatest concentra- tion of blocks was seen on Survey ridge within a ray from South Ray crater (fig. 2A), whereas interray areas were generally devoid of blocks (fig. 23). The discon- tinuous patterns of rays viewed from orbit (fig. 1) within traverse areas apparently do indicate ir- regularities of the original distribution of ejected rocks. Near Survey ridge, the crew observed that the cobble concentration was clearly the greatest near the center of the ray, decreasing gradually toward the edges. Elsewhere, they were moderately certain of the edge of a ray. Probably both sharply delineated edges and gra- dational edges of rayed ejecta are common, as indicated by the types of variation in albedo seen on photographs (fig. 1). On the surface, the astronauts thought they could recognize several rays from North Ray crater. From a distance, they could see very large blocks forming a North Ray ray on the slopes of Smoky mountain. Near Palmetto crater, they noted a concentration of 20— to 30-cm blocks that also appeared to be a ray from North Ray crater. Photographic measurement of visible blocks (Schaber, this volume, fig. 4; Muehlberger and others, 1972) clearly show the blocks on these older rays and ejecta blanket of North Ray crater to be less abundant than those on rays from South Ray crater (fig. 3). Many blocks in the older rays were reported by the crew as rounded and dust covered. THICKNESS OF REGOLITH Premission work by Oberbeck (1971b) on regolith thicknesses predicted less than 6.7 m (range of 3.1 to 6.7 m) at the Apollo 16 site. Oberbeck obtained a calculated thickness of 22 In using the total crater population and assuming that all of these craters are of impact origin and that a greater density of craters cor- relates with a greater thickness of regolith. To explain this difference, Oberbeck (1971b, p. 9) suggested that because most of the craters are subdued and probably of impact origin “a deep regolith has been produced. However, it is further suggested that the regolith and impact craters have been mantled by a deposit that was indurated after deposition. This would produce the subdued appearance of the large craters and provide an indurated formation that could subsequently be modified by recent impact craters to produce a thinner regolith deposit.” The preliminary geologic report after the mission REGOLITH (Muehlberger and others, 1972) suggested a regolith thickness of 10 to 15 m based on the position of a bench in Buster crater. A new attempt is made here to determine regolith thickness using the relation of crater shape to thick- ness (Quaide and Oberbeck, 1968) and measurements from a stereo model of Apollo 16 panoramic camera photographs. Ten craters with terraced or concentric internal shapes, indicating an underlying harder layer were examined (fig. 4). The depth from the average ground surface beyond the rim deposit to the top of the hard layer was measured by R. Jordan (US. Geological Survey) for each crater. The regolith thickness thus obtained ranged from 3.5 to 8.7 m; reproducibility of measurements was within about 2 in Half of the cra- ters gave thicknesses of 6.0 to 6.8 m. The only crater other than Buster that permits an estimate of regolith thickness substantiated by lunar-surface photographs is WC crater, 700 m south of the LM. It is about 40 m in diameter, and the photographs of WC ejecta taken from the LRV indicate that bedrock was reached. The WC ejecta contains abundant blocks; a regolith thickness of 6.7 m above bedrock was measured photogrammetri- cally for WC crater. Other craters in the landing area are larger than the craters cited but are “V” shaped indicating local areas of thicker regolith. These new measurements of regolith thickness at points of concentric craters are in very close agreement with the results obtained by Oberbeck (1971b) using diameters of the craters. His postulated older, thicker (22 m) regolith and its covering deposit upon which the presently active regolith has formed were not found on careful examination of the Apollo 16 panoramic cam- era photographs. Other methods of obtaining the thickness of regolith have yielded different results, summarized here. The thickness of the regolith in the area of the active seismic experiment was determined as 12.2 m by Kovach and others (1972, p. 10—1). Although the pas— sive seismic experiment did not measure the regolith thickness directly, Latham and others (1972, p. 9—1) stated: “The signal character and background noise at each station have distinctive characteristics appar- ently related to the depth and elastic properties of the regolith at each site. To explain these differences, the Apollo 16 station, compared to Apollo 12, 14, and 15, must overlie the deepest or weakest regolith, or both, according to criteria now applied. This condition also would explain the much higher sensitivity of the Apollo 16 station.” Zisk and others (1972) concluded from 3.8—cm radar data that there is little distinction between Cayley plains and Descartes mountain areas. "The 70-cm radar shows that the Cayley regolith is freer of meter- 149 sized boulders to depths as great as *** 10 to 15 m at the landing site *** than is the Descartes regolith.” Muehlberger and others (1972, p. 6—26) stated that “the thickness of the regolith on Stone Mountain, based on crater shapes, is similar to that on the Cayley plains.” Only one crater on Stone mountain, about 100 m in diameter 4 km east of Crown crater, has a terrace indicating the top of a hard layer. Using Oberbeck’s (1971b) relation of depth to diameter, the thickness there above a hard layer is less than 12.5 m. An average thickness of regolith at the Apollo 16 site is difficult to determine from direct observations. The thicknesses found on the Cayley plains range from 3.1 to 15 m. The 12.2-m thickness at the active seismic site is probably greater than the median because the seis- mic line lay across the ejecta deposits of a very large subdued crater. A subjective evaluation of the data presented above is that on the Cayley plains the me- dian regolith thickness above some bench-forming layer is between 6 and 10 m, generally about 7 m. Stone mountain has a smaller number of visible craters than the Cayley plain. This is true for the rela- tively flat top as well as for its steeper slopes. Espe- cially striking is the distribution of 1—1.5-km craters, common on the plain and absent from Stone mountain (fig. 5). As they are of several ages on the plain, not members of a single cluster, it is highly unlikely that original distribution could account for their absence from Stone mountain unless Stone mountain is much younger, and the returned samples do not support a younger age. It is therefore concluded that craters of l-km diameter have existed on Stone mountain but have been destroyed there at a more rapid rate than on the plain, possibly because of a very weak bedrock, as well as mass movements of debris under the influence of gravity, and shaking of seismic or impact origin. The 5- to 10-m thickness of regolith indicated on the Descartes mountains by radar and concentric cra- ters represents areas of average thickness on the upper surface, not the lower slopes. Regolith of this thickness might have formed since mass movements stripped the area of an older regolith or since formation of some hard layer on the older regolith. It is probably not the total thickness formed in place since emplacement of the underlying bedrock. The zone of thick accumulation of mass-wasted de- bris extends up Stone mountain to an abrupt change in slope about 300 m southeast of Crown crater, a sharp- rimmed 100-m crater with no visible boulders in its ejecta. A regolith thickness of at least 20 m is sug- gested in this part of the Descartes mountains. COMPOSITION OF REGOLITH The samples from the Apollo 16 site have a high 150 degree of chemical consistency indicating that they were derived from a local suite of rocks. Only a few small rock fragments found in the rake samples are. exotic and probably not representative of the Descartes area (Warner and others, 1973; Steele and Smith, 1973; Delano and others, 1973). The local suite of rocks is distinct from the rocks found at other Apollo sites (Rose and others, 1973), including the Apollo 14 site that sampled the Fra Mauro Formation. As can be seen from results of orbital chemistry (Adler and others, 1973; Metzger and others, 1973), the Descartes area is typical of the lunar highlands in general. Materials of the Descartes mountains and the Cayley plains are not separable chemically (Delano and others, 1973), al- though Ulrich and Reed, and Hodges and Muehlberger (this volume) argue that rocks with the highest degree of impact nielt may occur within the plains. Regolith samples were taken from all stations within GEOLOGY OF THE APOLLO '16 AREA, CENTRAL LUNAR HIGHLANDS the Apollo 16 site. They represent both Cayley plains and Descartes mountains, and rays from North and South Ray craters, as well as thin younger regolith on the rim of North Ray crater, and older regolith remote from fresh craters. In evaluating the chemistry of these samples and the related rocks, only four elements, Fe, Ti, and Al as oxides, and Ni, are considered (tables 1 and 2), but the results of analyses for these are in general agreement with conclusions of other workers using other ele- ments. ln average A1203 and TiOz content, the regolith from all stations does not differ greatly except for sta— tions 11 and 13. Station 11 soils, on the rim of North Ray crater, contain less titanium and more aluminum than regolith elsewhere. Soil at station 13, on the ejecta blanket of North Ray crater, contains a slightly greater amount of titanium and about the same amount of aluminum as station 11 regolith. The differ- FIGURE 2.—Comparison of lunar surface within and between rays from South Ray crater. A, Area within blocky ray on Survey ridge, 5 km from South Ray crater. View is southeast. Photograph A816—110— 17891. B, Area between rays near station 8, 3.3 km from South Ray crater. View is northeast. Photograph ASl6—108-17703. REGOLITH ence in titanium may reflect a contribution from Shadow rock at station 13, which has a relatively high ratio of titanium to aluminum. In absolute amounts of iron, titanium, and aluminum (fig. 6), the regolith samples fall into two groups: (1) stations 11 and 13, dominated by North Ray ejecta with high aluminum content and (2) the remaining stations, with only small differences. Station 4 soils on Stone mountain tend to be intermediate chemically between values at North Ray crater and those from the plains. The variation of TiO2 relative to A1203 (fig. 7) shows analyses of both rock samples and regolith samples. The regolith samples are grouped near the center of the scatter of rock samples except for a tail of regolith samples collected from North Ray rim (station 11). Similar variations are shown in the Aleg‘FeO dia- gram (fig. 8). The plots indicate that the regolith was formed by a mixing of the compositions of the rock NORTH RAY CRATER B 151 samples. There is no significant difference in the reg- olith composition of stations 4, 5, and 6 (on Stone mountain) and stations on the Cayley plain in these plots, although station 4 soils approach North Ray compositions in Ti and Ni. The regolith samples from the plain and the mountain, though similar to each other, are different from regolith samples collected at other Apollo landing sites, including highland stations at Apollos‘ 14, 15, and 17. Regolith samples that show a unique composition at— tributable to North Ray crater ejecta are those taken on the rim or continuous ejecta blanket of the crater. N0 composition identifiable as South Ray crater ejecta added to the soil can be distinguished in the analyses. Ray materials, even as young as those from South Ray crater, apparently are not identifiable by major- element content of the regolith. This supports the sug- gestion that fine-grained materials are lacking in the SMOKY MOUN AIN FIGURE 2.—Contin Jed. 152 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS FIGURE 3.—Comparison of old and young ray—covered areas. A, Area of old ray deposit 1.5 km from rim of North Ray crater. A816—111— 18143, View is northeast. B, Area of young ray deposit 4.5 km from rim of South Ray crater. A816—110— 17898, View is south. REGOLITH 1 53 STONE MOUNTA N FIGURE 3.—C0ntinued. 154 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS Crater . ’ Depth to diameter (m) hard layer (m), . 55 t 6.0 p 45 6.5 3‘mmqmmpwunv FIGURE 4.—L0cations of concentric craters used to estimate depth of regolith. Apollo 16 panoramic camera frame 4623. REGOLITH 1 55 rays of South Ray crater (McKay and’Heiken, 1973). The variation of nickel relative toiron in the rocks and soils from the Apollo 16 site is shown infigure 9. The trend line that results from addition of nickel and iron in proportions equal to the average composition of meteoritic matter (Mason, 1962, p. 164—5) has been added to the diagram. Several pairs of data points are joined for comparison: (1) sample 67455 from a light- U '0 smoxv (a MOUNTAIN Cum cluster :0 matrix breccia boulder at station 11 with sample C O S 67481, a soil probably derived from light-matrix brec- 0 O .6 MOUNTA'N ; cia (ALGIT, 1972b, p. 161 and 167); (2) an average for D O O \ ‘5‘ ; allt‘station 11; rocks with the average of all soils from O ‘0 N the same station; (3) sample‘61221;-from the white o , 2 K,LOMETER:”"'°“"‘"° {FIGURE 5.-—Apollo 16 region showing Cayley plains, Descartes '—‘—-‘ mountains, and outline of craters of about 1 km in dlameter. After 0 Hodges (1972a). TABLE .1.—Apollo 16 soil analyses for A1203, Ti02, and Ni [Averages of values from numbered references, in weight percent; Ni in parts per million] Sample No. Anon TiO, FeO Ni Refeiieengeis num r in . ’ ‘ ' accompanying “st TABLE 2. Apollo 16 rock analysts for A1203, T102, and Ni 0.44 4.50 270 18 Averages of values from numbered references, in weight percent; Ni in parts per million 0.60 5.49 415 2,9, 16, 17 0.66 5.55 403 1,5,7. 0.15 Sample No. Ale;. TiOz FeO Ni References 0.58 5.12 355 3,10 * numbered in 0.58 5.25 400 10 accompanying list 0.66 5.47 340 5 0.68 4.96 135 1,3,7 1”. 0.26 ___- 5 0.67 5.30 230 1,3,7 0.15 ’ 2.76 207 3,5 0.54 5.07 440 3 0.62 4.76 210 5 0.52 5.23 372 1,5,10 0.08 0.54 16 3,6,7,8 0.57 5.12 414 3,1 1.29 9.35 703 1.2.3.4,5 0.57 5.5 380 15 0.61 4.65 256 1.3.6.7 0.35 4.67 311 '19 0.68 4.42 335 1,3,83,10,11 0.60 4.54 345 19 0.64 7.68 184 1.4 0.50 4.67 322 4.19 0.56 4.52 114 1 0.55 4194 323 1,4,10,17 1.11 9.650639 1.4.11 . 0.55 4.20 320 2.7 0.04 2.20 ____ 12 _ 0.56 5.18 300 4,5.17 0.71 6.13 313 3,4,6 . 0,49 5.59 290 18 0.42 3.23 26 1 , 0.70 5.96 390 9,16 0.65 5.47 540 7 _ 0.66 5.69 414 1,5.7,10,17 0.72 7.08 __., 20 _ 0.61 5.8 500 15 1.7 9.5 ___ 20 _ 0.60 5.46 4 17 19 1.20 8.45 349 4,579.13 _ 0.65 5.90 428 1,3,15, 16 0.73 6.59 482 1,8,9,1 _ 0.67 6.12 446 1,3,15,16,17 .03 3.7 65 11 _ 0.35 4.14 120 10, 7 0.07 2.24 1 1,7 . 0.41 4.42 147 1,9 ‘ 0.24 2.60 62 3 . 0.46 4.05 145 1,7 0.05 . 5.8 ____ 12 - 0.38 4.08 145 5,17 0.25 3.88 22 3,10 _ 0.26 2.96 90 18 0.85 5.29 350 7 , 0.58 5.67 422 17 0.5 2.95 -11. 8 . 0.57 5.40 420 4,5 0.27 3.84 108 1 _ 0.50 ' 5.40 550 18 0.32 4.02 1 16 1,3,6 . 0.58 5.65 296 1,17 0.31 4.30 176 3,4,14 , 0.61 5.61 422 3,15 0.49 4.75 206 l _ 0.65 5.62 492 3,7,15 0.22 2.34 302 3 0.60 5.73 530 3 1 0.01 0.36 43 3 References for analysis used: 1. Lunar Receiving Laboratory, 1972. 2. Morrison; G. H., Nadkarni, R. A., Jaworski, J., Botto. R. B., Roth, J. R., 1973. 3. Rose, H. J., Jr., Cuttitta, F., Berman, S., Carron, M. K., Christian, R. P., Dwornik, E. J., Greenland, L. P., and Ligon, D. T., Jr., 1973. 4. Bansal, B. M., Gast, P. W., Hubbard, N. J., Nyquist, L. E., Rhodes, J." M., Shih. C. Y., and Wiesmann. H., 1973. 5. Taylor, S. 11., Carbon, M. P.. Muir, P.. Nance. W. B., Rudowski, R., and ‘Ware, N., 1973. 6. Walker, D., Lon hi, J., and Ht: 5, J. F., 1973. 7. Haskin, L. A., elmke, P. A., lanchard, D. R, Jacobs, J. W., and Telander, K., 1973. 8. Nakamura. -N., Masuda, A., Tanaka, T., and Kurasawa, H., 1973. 9. Duncan, A. R., Ahrens, L. H., Erlank, A. J., Willis, J. P., and Gurney.‘J J., 1973. 10. Wanke, 3H,, Baddenhausen, H., Dreibus, G, Jaqoutz, B., Kruse, H., Palme, H., Spettel, B., and Teschke, F., 1973. 11. Brunfelt, A. 0.. Heier, K. S.. Nilssen, B., and Sundvoll, B.,-1973a. 12. Prinz, M., Dowty, E., Keil. K.. Bunch. T. F1, 1973. 13. Albee, A. L., Gancarz, A. J..'and Chodos, A. A., 1973. 14. Juan, V. C., Chen, J. C., Huang, C. K., Chen; P. Y., and Wang Lee, C. M., 1973. 15. Laul, J. C., and Schmitt, R. A., 1973. 16. Baedecker, P. A., Chou, C. L., Sundberg, L. L., and Wasson, J. T., 1972. 17. Compston, W., Vernon, M. J., Chappell, B. W., and Freeman. R 1973. 18. Mason, Brian, Simkin, T., Noonan, A. F., Switzer, G. S., Nelen, J. A., Thom son, G., and Melson, W. G., 1973. 19. anfelt, A. 0., Heier, K. S., Nilssen, B., Steinnes, E., and Sundvoll, B , 1973b. 20. Hubbard, N. J., Rhodes, J. M., Gast, P. W., Bansal, B. M., Shih. C. Y., Wiesmann, H., and Nyquist. L. E., 1973. 156 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS layer in the trench at station 1 is joined with sample 61241, the overlying gray layer possibly derived from the white layer (ALGIT, 1972b, p. 75); (4) an average of all rocks at the Apollo 16 landing site with the average of all soils at the site. The nearly parallel trend of the lines connecting rocks and soils indicates an addition of nickel and iron in similar proportions during the process of soil forma- tion. The divergence of this trend from that of Mason’s indicates that the composition of added meteoritic material at the Apollo 16 site is more Fe-rich (or Ni- poor) than that on Earth. SUMMARY The appearance of the regolith is generally that of a rocky gray soil. Rays from young craters in hard sub- strata are distinguishable mainly as local concen- trations of blocky fragments. The brightness of a ray appears to result from a combination of the density and the angularity of fragments, both higher for South Ray than for North .Ray crater. The regolith thickness on the plains has amedian value between 6 and 10 m based on photogrammetric measurements of depth to the first bench in 10 concen- tric craters. The thickness of regolith on Stone mountain ranges from a minimum of 5 to 10 m to more than 20 m and may vary greatly owing to accumula- tion of mass-wasted debris on a softer, weaker bedrock that may underlie much of the Descartes mountains. Regolith compositions for most of the Apollo 16 site are chemically similar except for North Ray soils, sta- tions 11 and 13, which are significantly enriched in alumina and depleted in iron, titania, and nickel by comparison with soils from other stations. Soils from station 4 tend to be intermediate in titania and nickel content with respect to soils from the plains and North Ray crater. As a group, the soil samples cluster near the middle of the compositional ranges representing the rocks from all stations. Iron and nickel show a marked increase from a par- ent rock to the soil produced by its disintegration. A similar change is seen between the average compo- sitions of rocks and soils and between two soils in superposition. Analyses indicate a component of meteoritic material richer in iron (or poorer in nickel) than the average meteoritic material on Earth. FIGURE 6.—Plots of analyses for FeO, TiOZ, A1203, and Ni for soil’ samples taken at traverse stations. STATIONS 11 13 1 2 LM 9' 8 5 4 l l l I I l 0 l T 6.0 L— l . o o o — T _. o . 0 '° L. 0 o o u . e .— 2 o . —- o 5.0 — z _ .I. ’ o o . o 40 ' EXPLANATION ' — . Analysis or average of analyses on a single sample —- Mean value for samples '2 ._‘ z 8 3‘0— 0 F50 L” II E l“ s ' 8 t . I . . «I. I Lu 0 0.5— O 7 O T .. O . 9 m - — .I_ ;,_ x g o 0 g 0.5r— o ' o . o o _ o 0.4 L 0 O 0.3 — Ti02 o o o _ .1. 29 . :— o 28— ° ' 0 ° 0 3. ' _ . _ __ 27 L , . _ . : O . . . L 26— L . . . o A|203 o o E z 500— L ' . o . I h — T — z -' ._ L 3 ° T ° u: :1 400 z . . E E o . — n: _ 8 u, 300— T . o f- _| n. 9 < 200— Z n. “.7 . T 100'— . l l I l l I l l l l 11 13 1 2 LM 9 8 6 5 4 Tl02 CONTENT, IN WEIGHT PERCENT REGOLITH 1.6 l °4 l l l l l l l l l 1.4 _ _( EXPLANATION °L 0 Rock Sample - Soil-sample 1.2 —— 05 — Station number; L, LMAALSEP area; 3, Station 13; 7, Station 11; others 02 same as station number 1.0 — —~ 07 0.8 — _. 06 02 04 .5 01 1 .1 04 01 .9 2 613-2 '«1 0.6 —- °L °L '..°5 '6 .3 _ L 2 9/”7‘ :32 ’4-4 °1 18 8.1'1 ’8 '1|°8 .3 07 '7 -L 0.4 _ -7 °3 _ .7 03 '7 0°8 07 .7 O7 07 0.2 ._ °9 _ 0L 7 07 L0 ° . 02 o | L I l l l | 27 l ale 15 17 19 21 23. 25 27 29 31v 33 35 A|203 CONTENT, IN WEIGHT PERCENT ' 157 FIGURE 7.——Plot of TiO2 relative to A1203 for rock and soil samples. Points are averages of all available analyses of each sample. 158 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS 45 l l I l l l I l l EXPLANATION a Rock Sample . Soil sample 40 — Station number; L, LM-ALSEP area; 3, Station 13,- 7, Station 1 1; others L same as station number i 9 / L E 35’— ° 0/ 2 LU g 1/7 :1 ° /9 [7 'E ° ° °L o3 °707 g 73/ 0 30 ~— g’ [/Q 80:7;7'." / 7 22/112 [z/A 8 6 E 07 7.4 3'1 08.44/ 4/4.” 5/ 5 5.‘ u n/ . a // ”'97-“ 5 F 25 — ° BL 06 z 07 8 l 4 ol 0 6, 04 N . 2 20 — o 2 05 l 02 o 04 07 L/ 15 —- — ,0 l | l l l I I l O 2 3 4 5 6 7 8 9 FIGURE 8,—Plot of A1303 relative to FeO of rock and soil samples. Multiple analyses of same samples are averaged. FeO CONTENT, IN WEIGHT PERCENT 1O REGOLITH 159 700 600 — 400 '— 300 — 200 — NICKEL CONTENT, IN PARTS PER MILLION 100— 500 —- 09 CL I I l I I EXPLANATION 0 Rock sample 0 Soil sample Stations numbers: L, LM-ALSEP area; '084 9 3, Station 13; 7, Station 11; others 0 same as station number 91.5 o 06 1' '6 8 _ .2 8.0 .21) 1. oL 05 a .2 \ Meteoritic trend line 1. o7 03 .1 Average soil, Apollo 16 site 410 . V/ O o 02 09 '4 4.08 I Average soil, station 11 Average rock, station 11 m7 Average rock, Apollo 16 site 1 61241 0L 88 ‘\\,K 1 61221 67955 ° 07 05 1 2 6 7 F60 CONTENT, IN WEIGHT PERCENT 10 FIGURE 9.—Plot of nickel relative to FeO of rock and soil samples. Multiple analyses of same samples are averaged. The meteoritic trend line is calculated from average meteorite composition (Mason, 1962) and assumes Fe/Ni remains constant at 17 for material added in soil formation. G. EJECTA DISTRIBUTION MODEL, SOUTH RAY CRATER By GEORGE E. ULRICH, HENRY g]. MOORE, V. STEPHEN REED, EDWARD W. WOLFE, and KATHLEEN B. LARSON CONTENTS Page Introduction ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 160 Definition of South Ray ejecta ________________________________________________________ 160 Mapping techniques ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 161 Measurement of ejecta- and ray-covered areas ___________________________________ 161 Measurement of rim height and crater volume __________________________________ 161 Surface observations ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 163 Distribution models __________________________________________________________________ 166 Summary ____________________________________________________________________________ 173 Acknowledgments ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 173 ILLUSTRATIONS Page FIGURE 1. Premission photomosaic map of Apollo 16 landing site ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 162 2. Photograph of Apollo 16 landing site and traverse locations in high-sun illumination ________________________________ 163 3. Digitally enhanced regenerations of photograph in figure 2 ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 164 4. Topographic map of South Ray crater and approximation of pre-South Ray surface ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 165 5. Outline of hummocky ejecta around South Ray crater rim and rim heights above outer rim margin ____________________ 166 6. Map of concentric rings centered on South Ray crater ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 167 7. Histogram of area covered by mappable ejecta and rays within each annulus shown in figure 6 ,,,,,,,,,,,,,,,,,,,,,,,, 168 8. Histogram of percentage of area covered by ejecta and rays in annuli of figure 6 ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 169 9. Illustration of terms used for crater measurements discussed in text ________________________________________________ 169 10. Ray-covered areas photographed from the Lunar Roving Vehicle ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 170 11. Semilogarithmic plot showing model thicknesses of South Ray ejecta relative to distance from the crater rim __________ 172 TABLES Page TABLE 1. Ejecta distribution models for South Ray crater ____________________________________________________________________ 171 INTRODUCTION localities sampled lie within rays of ejecta from South Ray crater and to what extent or depth these localities may have been covered by ejecta is to estimate the apparent volume of the crater and then to distribute this volume as ejecta using several models. In one set of models, ejecta are confined within observable ray pat- terns; in a second set, ejecta are not confined. The pur- pose of this chapter is to determine a reasonable model for the areal distribution and variation in thickness of ejecta material within rays as a function of distance from South Ray crater. A stratigraphic interpretation of materials ejected from South Ray is treated elsewhere (AFGIT, 1973; Ulrich and Reed, this vol- ume). South Ray is a fresh, blocky crater, 680 m across and 135 m deep, in the southern part of the Apollo 16 land- ing site. Its bright rays extend northward radially across the traverse area. Sampling of ejecta from South Ray was a prime objective of the mission because of its location on the Cayley plains, 6.2 km south of the Lunar Module (LM). Direct sampling and photograph- ing of its rim and flanks, where less equivocal prove- nances could have been established, were prohibited by the distance from the LM, the limited time available for traversing, and the anticipated roughness of the terrain. Therefore additional evidence and interpreta- tion are required to relate certain samples collected to South Ray. The approach taken here in determining which of the 160 DEFINITION OF SOUTH RAY EJECTA Part of the problem in defining South Ray ejecta is to EJECTA DISTRIBUTION MODEL, SOUTH RAY CRATER establish those properties that characterize the ejecta on the lunar surface and correlate them with reflected brightness and topography using the best available or- bital photography. Block concentrations, surfaces dis— turbed by the impact of ballistic debris, lineations pro- duced by deposition of ejecta, and individual secondary craters were observed on a local scale by the astronauts and can be seen in photographs taken by them. For a crater the size of South Ray, these features are not resolvable on orbital photographs except at a few places. The properties of crater ejecta seen on orbital photography are reflected brightness and irregularities in topographic expression. Bright areas around young lunar craters photographed under high sun-elevation angles are produced by a combination of effects: (1) concentrations of blocks and rock fragments, (2) steep surface slopes, and (3) composition of material. Bright- ness contrasts in surface materials of a crater and its ejecta decrease with the age of the crater. Topographic expression of ejecta is most evident near the crater, and its definition is a function of photographic resolution. For South Ray, contrasts in reflected brightness were used to delineate the ejecta on orbital photography, because the high sun-elevation angle of available pho- tographs proved to be a sensitive indicator of ejecta distribution (figs. 1 and 2). The distribution of bright regions, including South Ray, its flanks, and rays or filaments extending radially from it, attest to the cra- ter’s youth. Bright areas beyond the rim are inferred to be covered partly to completely by ejecta from the cra- ter. MAPPING TECHNIQUES Previous mapping of ejecta distribution around South Ray consisted of compilation by Visual inspec— tion of Apollo 14 photographs (Hodges, 1972a; Elston and others, 1972b; Muehlberger and others, 1972; fig. 1, pl. 2 this volume). Here, digital processing of Apollo 16 panoramic camera photographs taken when the sun-elevation angle was 60° was used to delineate the distribution of ejecta from South Ray beyond the crater flanks. An unaltered photograph of the landing site, figure 2, was digitized and, by means of computer filter- ing techniques, regenerated to enhance reflected brightness variations at three different levels (fig. 3). These images, together with figure 1 and selected pre- mission photographs, were the basis for compilation of a ray map of South Ray ejecta (see Reed, fig. 4, this volume). The procedure required a minimum of arbi- trary judgment in drawing the boundaries of ray- covered areas. The units mapped were designated as continuous, thin to discontinuous, and discontinuous ejecta. A topographic map of South Ray crater (fig. 4) ena- bles us to estimate the amount of material ejected from 161 South Ray, the height of the rim (fig. 5), and the thick- ness of ejecta at the rim. MEASUREMENT OF EJECTA— AND RAY-COVERED AREAS The area covered by mappable rays was measured (at a scale of 150,000) with a planimeter, in concentric annuli (or bands) one crater diameter (680 m) wide, expanding outward from the crater rim, as illustrated by figure 6. A plot of the area of ejecta measured within each annulus, figure 7, shows the ejecta-covered areas to be clearly asymmetric in their distribution around South Ray. In each of the third through seventh an— nuli, however, they remain nearly constant at 7—9 km2 while the total annulus area increases by 2.0 km2 per ring. Beyond the seventh annulus, the ray-covered areas decrease at a nearly constant rate of 0.9 to 1.0 km2 per annulus. Another means of viewing these data is to plot the percentage of total area within each an- nulus covered by ray material as a function of distance from South Ray rim (fig. 8). The histogram shows that only the six inner annuli are more than 50 percent covered and that all of the Apollo 16 samples come from annuli where less than 57 percent of the area is covered by mappable rays. MEASUREMENT OF RIM HEIGHT AND CRATER VOLUME Using the topographic map of South Ray (fig. 4), a precrater surface was estimated by extrapolating con- tours from outside the hummocky rim across the exist- ing crater. Intersections of this surface with the crater wall determine the elevation of the original ground surface. Differences in elevation of points on the rim crest and the projected original ground surface beneath the points represent the rim height. Values obtained in this way range between 19 and 26 m; the average is 22 In. Another method of calculating these values is to determine the average difference in elevation between the rim crest and the outer margin of hummocky ejecta, shown in the sketch map (fig. 5) along with ele- vation differences between the rim crest and this edge. The range in values for rim height by this method is 13 to 28 m, the average about 20 m. From this, we con- sider the average rim height to be near 20—22 In. The rim height includes two components, the amount that the original ground surface was uplifted and the thickness of the ejecta deposited on the uplifted surface (fig. 9). For terrestrial explosive craters, the percentage of the total rim height resulting from upwarping of ground surface ranges from 17 to 71 per- cent (Carlson and Jones, 1965, table 1); for six craters in alluvium 31 to 366 m across, an average of 45 per- cent of the rim height is the result of upwarp of the original ground surface. Recent drilling at Meteor Cra- ter, Ariz., reveals that 35 to 60 percent of the present GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS 162 ..NE< magmas; dsew \Emgmofimo 33285 mUwD .momwim .2 .nm NE “35958? 533;? :25me 8mm .23 mfifimsofi 58.3 E 223 .2 .0 N3 :oSmoaSuE MEN mcflofimoz .mowm «Em 99:10:35”; » ommm .mmmm » V 86 “FREE 3 o:om< we mac: oEmoESosm :onmESLIA meoE 1|] mmm—FWEOIZM N EJECTA DISTRIBUTION MODEL, SOUTH RAY CRATER 2 l°“"'.°‘-~,o LM 0 1 2 3 4 5 KILOMETERS FIGURE 2.—Apollo 16 landing site and traverse locations, taken from orbit after surface activity was completed. Sun—elevation angle is 60° (Apollo 16 panoramic photograph 5328). rim height is the result of uplift of the original ground surface (D. J. Roddy, oral commun., 1974). It is there- fore reasonable to assume that 45 to 50 percent or ap- proximately 10 m of the rim height of South Ray can be attributed to uplift; then that part of the rim height attributable to ejecta is 50 to 55 percent or 10 to 12 m. Total crater volume was established by dividing the topographic depression into 25-m-thick disks and add- ing their volumes to those of the irregular increments at the top and at the bottom (shown in fig. 9). The areas of the upper and lower surfaces of each disk were measured by planimeter, then averaged. This value, multiplied by the disk thickness, provides an estimate of the volume for that increment. The sum of all incre- ments is the volume of the existing crater below the rim crest (15.6 million m“). The total volume is greater 163 than the apparent crater volume by an amount equal to that part of the crater volume above the precrater surface. When this amount is subtracted, the resulting apparent crater volume is 10.0 million m“. Apparent crater volume is taken here to represent a reasonable estimate of the volume of ejecta of South Ray. Because data on explosive craters in alluvium (Carlson and Jones, 1965, table 4) indicate that appar— ent crater mass may be as much as twice the ejecta mass, our ejecta volume could be too large. On the other hand, bulking of material beneath the crater walls and floor can have an opposite effect, making our estimate of ejecta volume a reasonable value in the light of data available. We assume target and ejecta density to be equal, as for craters in alluvium (Carlson and Jones, 1965, p. 1899). SURFACE OBSERVATIONS The astronauts observed secondary craters at several localities during the lunar mission and described rays formed by large concentrations of blocks alined in linear patterns generally radial to South Ray crater. Such areas are discussed and illustrated elsewhere in this volume. (See chapters by Freeman, Holt, Sanchez, Schaber, and Reed.) Ray-covered surfaces were documented by Has- selblad photography while the LRV was enroute dur- ing all three EVA’s. On 324 of the 544 frames taken (Batson and others, this volume), the populations of fragments 2 cm and larger were measured with the aid of a perspective grid within the interval 5 to 10 m from the camera. The results are illustrated by Muehlberger and others (1972) and reproduced by Schaber (fig. 3, this volume). Several conclusions can be drawn from these data: (1) The abundance of fragments larger than 2 cm in diameter increases progressively, but some- what irregularly, toward South Ray crater over the entire traverse area. (2) Ejecta from South Ray crater is characterized along the traverses by a relative abundance (generally 2 to 7 percent surface cover) of angular fragments, commonly perched on the surface (fig. 10A ). The surfaces with higher fragment densities also are covered by numerous small craters approxi- mately 2 m or less in diameter (Reed, fig. 10, this vol- ume). (3) Most of these areas occur in bright-ray patches. A notable example, as shown in figure 103, is Survey ridge, between the LM and station 6, where approximately 7 percent of the surface area is covered by fragments larger than 2 cm. Station 6 lies on the northeast edge of a fragment-covered surface that coin- cides with the discontinuous ejecta as mapped from or- bital photography (see pl. 6, pan 12). The fragments 2 cm and larger within 10 m of station 6, however, oc- cupy only 1 to 2 percent of the surface (Muehlberger CENTRAL LUNAR HIGHLANDS 7 GEOLOGY OF THE APOLLO 16 AREA 164 .NC< ragga—m Sfizumh mEmmmoEm mums: mUmD in: kaofcxw 3 “5.233% $3383me "$885 mmmaimiv :mwnuawhm: x>mwc v5» 6::me Jam: 3w 0 wcm ,m J\ .N mpzmc E LQmeSOLQ go 90:95:33» Ramsay 3_mfim5|.m 55on I 165 EJECTA DISTRIBUTION MODEL, SOUTH RAY CRATER 1.0 KILOMETER l 0.5 l CONTOUR INTERVAL S METERS . 5 mm... mam rla umfi sa a YUM mxm ea hec mm.m e &vm em Na 3 mm mm nr 0 C d w a l O P a Y. t X ations (in meters) of the elev ale 1:10,000; photographic model from Apollo 16 panor t; numbers are shows crater rim cres al ground surface. Compilation so 4618 and 4623. Topography compiled by G. M. Nakata. Dashed line FIGURE 4.—-Topographic map of South Ray crater. Dotted lines are e origin 166 South Roy crater rim crest + 0 500 METERS Approximate l_l_l_l_l_l FIGURE 5.—Outline of hummocky ejecta around South Ray crater rim (from J. P. Schafer, un-pub. data, 1973.) Values for height of rim were measured from figure 4 as the difference in elevation between edge of hummocky ejecta and rim crest. Rim-crest diame- ter averages 680 m. and others, 1972, fig. 6—6 and table 6—1). (4) By com- parison with South Ray, the fragment population of the continuous ejecta of North Ray crater generally oc- cupies less than one percent of the area except on the rim crest, because erosional history is longer and the majority of North Ray rocks are more friable. Some large concentrations of blocks are unrelated to North or South Ray. The highest block density found anywhere at the site was in an area about 700 m south of the LM (fig. 100), where blocks occupy nearly 16 percent of the surface and probably represent the rim of a fresh young crater 40 m in diameter. This area lies near a small bright ray radial to South Ray crater, where the block density is much higher than expected for South Ray material at this range (5.6 km). Farther from South Ray, mappable rays becomethin and are difficult to recognize (fig. 10D). DISTRIBUTION MODELS With the quantitative estimates derived herein, we now combine the orbital and surface information to construct models of ejecta distribution for South Ray crater. Having measured the volume of the apparent crater, 10 million m3, its rim height, 20—22 m, the area within which most of this ejecta was deposited, and the thickness of ejecta at the crater rim, 10— 12 In, we can GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS derive expressions that describe the distribution and thickness of ejecta as a function of distance from the crater rim. The additional data of fragment counts per unit area made from photographs on the lunar surface permits a comparison of the volume of fragments larger than 2 cm in diameter with the ejecta thicknes- ses predicted by various curves]. Carlson and Roberts (1963) have shown that the thickness of ejecta (t) as a function of distance from the center of the crater (r) can be approximately described by t = K (1‘)", (1) where K is a constant and s is an exponent having values commonly near —2.0 to -3.5 The volume, V, of ejecta deposited from the crater rim to infinity is given by Rs+2 V = 27TKS+2 where R is the radius of the crater and s is less than minus 2. R for South Ray is 340 m. When 3 is exactly —2, another formula applies. For our purposes, we will consider two general models: (1) All ejecta is'confined to the mappable rays (Reed, fig. 4, this volume) and deposited within 16 cra- ter diameters (r=11,220 m). (2) Ejecta is uniformly de- posited from the rim outward to infinity with thickness decreasing according to equation (1). To test these models, we chose several values ofs: —2.0, —2.5, —3.0, and —3.5. Corresponding values of K were calculated using equation (2). Thicknesses of ejecta (T) at the cra- ter rim were then calculated using equation (1) with 340 m. Experimental data from explosion craters show that s varies from — 1.97 to —3.65 (Roberts and Carlson, 1963) and can steepen to values of —6.5 near the crater rim (Carlson and Jones, 1965). Laboratory experiments with hypervelocity impact craters in sand (Stoffler and others, 1975, p. 4074) follow equation (1) with an average value of s of —3.3. McGetchin and others (1973) estimated that lunar craters probably obey equation (1) with 3 near —3.0. The selected values of s, which cover the range of experimental data cited above, are given in table 1 with corresponding values 'szlallculation of the thickness of material represented by fragment counts was performed as 0 0W5: The fragments were assumed to have a spherical geometry, producing minimum volume estimates. (Cubic geometry would rovide a maximum value, nearly double that calculated here.) Fragment volumes were ca culated using median diameters for each fragment-size range: 3.5 cm (2—5 cm), 7.5 cm (5— 10 cm), 12.5 cm (10— 15 cm), and 20 cm (greater than 15 elm).rPercelnt areas covered by each size range were converted to an equivalent thickness by t e ormu a: (fraction of area covered) (volume of fragments, m") Thickness (m) : (area covered by fragments, m2) Thicknesses derived from median diameters of fragment-size ranges are smaller than. thicknesses calculated from median volumes of the same fragment-size end members (ap- proximately 10 to 25 percent lower). The method used tends to compensate for the bias of fragment-Size distributions toward the smaller size ranges. EJECTA DISTRIBUTION MODEL, SOUTH RAY CRATER IS 15‘ /4\ ’II 13\ f:\ Survey ridge 0 5 KILOMETERS I l I l l J 3 \B\oby Ray 2 / FIGURE 6.—Concentric rings centered on South Ray crater. The radius of each successive annulus is increased by one crater diameter. Area covered by ray material within each annulus was measured by planimeter at 1250,000 scale. Station locations are shown by dots. 167 168 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS 9 5 EXPLANATION , S 4 8 fizzy 8 Sampling station at radial dis- '| I tance from South Ray rim T T I W\ WK§ m \\ \W X \\§\§ RX AREA COVERED BY EJECTA AND RAYS, IN SQUARE METERS X 106 T \KW 1— V % 13 _ / I n 7 Z % % a g / ’ o % a m. 0 1 2 3 4 5 6 7 8 9 10 11 KILOMETERS L I I I | | I I I I I I | I I | | | I I I I I I I I | I I 0 1 2 3 4 5 6 7 8 9 1O 11 12 13 14 15 16 Crater diameters DISTANCE FROM RIM OF SOUTH RAY CRATER FIGURE 7.—Area covered by mappable ejecta and rays within each annulus shown in figure 6. Measurements are from superposed data of figures 3 and 6. EJECTA DISTRIBUTION MODEL, SOUTH RAY CRATER 169 100 j W EXPLANATION _ 3 9° 8 Sampling station at radial distance Z 4' 8 from South Ray rim 2 V < I _ Z 80"" E \ 5, 6 ’5 | 3 9, 70“ § _ :2 a U 9 3 < 60— I _ Lu CC V >, w m E V Survey 0 E 50- ridge — u: a; 5 I 1 uJ D 40 > - _ CE 0 I- <2 LU _. _ II 0 30 < Lu u. 2 O O 20— _ DJ (3 < 13 ,_ _ 11 _ Z 10 I 2: § I E 0 N m m ‘L 1 2 3 4 5 8 9 10KILOMETERS I I I I I I I l I I | I | I I I I I I I I I 0 1 2 3 4 5 6 7 10 11 12 13 14 15 Crater diameters DISTANCE FROM RIM OF SOUTH RAY CRATER FIGURE 8.—Percentage of area covered by ejecta and rays in annuli of figure 6 relative to distance from South Ray crater rim. |¢—— Crater diameter ——..I Ejecta thickness at rim Rim height Original ground surface Apparent crater volume v1+V2+V3 +...+vn Vejecta FIGURE 9.—Illustration of terms used for crater measurements discussed in text. 170 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS FIGURE 10.—Ray-covered areas photographed from the Lunar Roving Vehicle. Television camera obscures part of foreground. A, Block field west of the LM taken on return leg of EVA 1, looking east (ASl6—109— 17860). Percentage of area covered by fragments larger than 2 cm: 5.3; equivalent to uniform surface mantle 2.1 mm thick. B, Survey ridge, a bright ray area about 5 km northeast of South Ray crater (ASlFrllO— 17894). Percentage of area covered by fragments larger than 2 cm: 7.0; equivalent to uniform surface mantle 4.3 mm thick. C, Block field 700 m south of the LM, near a fresh 40~m~diameter crater (A816—115—18533). Percentage of area covered is 15.9; equivalent to uniform surface mantle 1.5 cm thick. D, Approach to North Ray crater area. Shadow rock on right is location of station 13 (A816—111~18155). Percentage of area covered is 0.15 equivalent to uniform surface mantle 0.05 mm thick. EJECTA DISTRIBUTION MODEL, SOUTH RAY CRATER TABLE 1.—Ejecta distribution models for South Ray crater [Volumez 10x 10‘ m3; crater radius: 340 m; rim height: 22 m] Factors Slope of ejecta thickness decay —2 4.5 —3.0 —3.5 7 7 7 7 Ejecm confined to gapsfiant. K : ,,,,,,,,, 0.068x 10 2.15x 10 60.8x 10 1561x10 mappable rays. to ness at rim, T (meters) __________ 5.9 10.1 15.5 21.5 Tm‘ “1““ d“ T/ ‘ h i ht 27 46 70 95 posited within 16 “m, e g ---------- ‘ . - . diameters. Fraction of volume beyond 16 .J.‘ L a , .0 .0 .0 .0 Constant,K __________ ‘.056X10’ 1.47x107 54.0x107 1497x107 . . Thickness at rim, E190”. “mfmmlly T (meters) __________ 25.0 6.9 13.7 20.6 dlfimbuted 8! 8‘ T/rim height __________ .23 .31 .52 .94 azxmuths to infin- Fraction of volume ":3" ejected beyond 16 diameters ,,,,,,,,,, "0 .17 .03 .0053 ‘Calculated from equation using‘S= —2 and T=5 m. ’Assumed for calcu ation. “No ejecta deposited beyond 16 diameters; volume of ejecta accounted for at 5,000 m from crater rim. of K and T calculated from equations (2) and (1), re- spectively. The resulting thickness decay curves (fig. 11) can be compared with the calculated thicknesses of a uniform ejecta deposit represented by fragments (larger than 2 cm) (shown in fig. 11 by vertical bars) representing the ranges of thickness determined from individual photographs. These data supersede those il- lustrated in an earlier paper by Hodges and others (fig. 10, 1973), whose model assumed an ejecta thickness of 10 m at the rim and predicted greater maximum thicknesses in the Apollo 16 traverse area than the present model by a factor of three to five from station 8 to station 13. If the actual volume of ejecta is 5 million In3 rather than the 10 million m3 measured above, model thicknesses plotted in figure 11 and given in table 1 would be half the values indicated and the constant (K) would be half as large. We can now evaluate the data and select a preferred ejecta thickness distribution model for South Ray cra- ter. The factors to be considered are slope (3), thickness at the rim (T), and T/rim height given in table 1: the resulting decay curves are plotted in figure 11, to- gether with the ranges of thickness derived from frag- ment counts. If the fragments greater than 2 cm show an obvious relation to distance from South Ray crater, as they certainly do at Survey ridge (fig. 108) and by their decrease away from South Ray (fig. 11), then there may be a contribution from fragments smaller than 2 cm. McKay and Heiken (1973, p. 45) argue from soil agglutinate contents, exposure ages, and size dis- tribution of experimental crater ejecta that relatively little fine-grained South Ray ejecta (possibly 1 or 2 mm) would be expected in ray areaanolt (this vol- ume), however, maintains that the optical properties of the visible rays are likelier to be a product of fine- grained (comminuted) ejecta than of coarse fragmental debris. It is possible that the dilution of fresh fines from South Ray due to mixing with old soils at the site may 171 be so great that dating techniques cannot yet distin- guish the younger materials. The volume of fine mate- rial is probably not much greater than the volume of all fragments measured. Assuming an extreme case, that the fine-grained volume is twice the fragmental volume, the total thickness of ejecta shown in figure 11 would increase approximately to the tops of the range bars shown for the fragments. The fragments counted may include a pre-South Ray population that in effect reduces the mean values attributable to the South Ray event. The models forincreasing values of s can be reviewed relative to the data of table 1 and the plot of figure 11. For 3: —2, the value of T is 5.9 and 5.0 (assumed) for the confined and uniform models, respectively. These values result in thickness-to-rim-height ratios of 0.23 and 0.27; that is, 73 to 77 percent of the rim height is attributed to uplift, too high a percentage when com- pared with experimental data, though not an impossi- ble value. In addition, both models result in an exces- sive thickness (several millimeters) at the distance where the total volume is used up. For s== —2.5, the decay curves for the confined model produce a reasonable T/rim-height ratio (0.46) because of the required thickness of ejecta (10 m) at the rim. T is smaller (6.9 m) for the uniform model, wherein 17 percent of the total volume is still unused at 16 crater diameters. If the volume of fine-grained ejecta (less than 2 cm) were more than twice that of the fragments counted and if the fragments are assumed to have a cubic rather than spherical geometry, the decay curves for s=—-2.5 produce a reasonable model. But because the total volume of 10 million m3 used in our calcula— tions may be high by a factor of two, we believe that the preferred decay curve (fig. 11) must lie below that for s = — 2.5. For 3 = —3.0, the thickness-decay curves appear to be in fair agreement with the computed fragment vol- umes provided an additional volume of fines approxi- mately equal to the fragment volume is allowed. This amounts to the equivalent of a few millimeters at sta- tion 8 and a few tenths of a millimeter at North Ray crater. The model gives T/rim-height ratios of 0.62 and 0.70, or 30-38 percent uplift, in reasonably good agreement with experimental data. Finally, for 5': —3.5, the values ofT (20.6 and 21.5 m) and T/rim-height ratio (0.94 and 0.98) are too high rel- ative to experimental data, and the corresponding thicknesses from figure 11 are too low relative to frag- ment counts. This model is therefore eliminated in favor of the model based on our measurements and calculations wherein s: —3.0. It must be pointed out that the preferred model is only a best estimate at this time. The equations used 172 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS | I l I I I I I I I I I I | l l I I I l I I I I I I | Rim of South Ray crater 10.0 _ EXPLANATION — — Ejecta confined to mappable rays —— Ejecta distributed uniformly over 360° of arc to infinity 8 Power of thickness-decay function _ Range and mean values of thickness based on >20m I.O-— fragment population _ _ _._ Thickness from fragment population given by Hodges — __ and others (I973) __ 8 Location of sampling station with respect to South — Ray rim _ £2 Lu O,I — -—- ,_ _ ~ LLJ E _ _ E <[ _ __ ,_ 0 Lu 1 Lu — I3 || '— * l < I (z I Fresh crater ,_ 0.0I —— south of LM ——- D _ o (I) u. _ o (I) .— (I) LLJ Z x S I _ ,_ 0.00I — O.OOO|F— _ KILOMETERS _ I 2 3 4 5 6 7 8 9 IO II I | l l l l l l l I I l l l l l l l I I I l l l l I I O I 2 3 4 5 6 7 8 9 10' || |2 I?) I4 15 IS CRATER DIAMETERS DISTANCE FROM RIM OF SOUTH RAY CRATER FIGURE 11.—Semilogarithmic plot showing thickness of ejecta relative to distance from rim of South Ray crater. Curves are based on data from table 1 and calculations using equations 1 and 2 (see text) for total ejecta volume of 10 million m“. EJECTA DISTRIBUTION MODEL, SOUTH RAY CRATER here may not be an exact representation of the ejecta decay function. Other, more explicit functions may be required to describe in detail the thickness of ejecta as a function of distance from the crater; such refined data are not available at this time. SUMMARY South Ray crater ejecta totaling about 10 million In3 covers the Apollo 16 landing site in an irregular ra- dial pattern that reflects a nonuniform mantle of scat- tered debris. The ejecta thins rapidly from perhaps 10—15 m at the crater rim to 1 cm or less at the south- ern station localities (4, 5, 6, 8, and 9) and less than 1 mm at the northernmost stations (11 and 13). Using the general equation where thickness is a function of the crater radius to describe the thinning of ejecta with increasing distance from the crater, the preferred ex— ponent for the radius is — 3.0. The fragment population on the lunar surface (for sizes larger than 2 cm) accounts for a significant part of the total volume of ejecta. An equal amount of material finer than 2 cm can reason— ably be accommodated by the preferred model. Review of the photographic data, enhancement of the 173 various levels of reflectance directly related to South Ray crater, and observations of evidence for ray mate- rials on the surface provide a basis for assigning a South Ray origin to selected sample localities. With the information available at this time, we believe that sta— tion 8 has the highest potential for collection of South Ray fragments and fines; next highest are stations 9, 6, 4, and 5 in that order. The probability of collecting or identifying South Ray ejecta at stations farther away (>5 km from the crater) is considered very remote with the possible exception of station 2 samples, which may have been from the bright area at that locality. Deter- mination of the provenance of individual samples will rely on additional evidence of other parameters— angularity, perchment, abundance of microcraters, particle-track ages, and rare-gas ages. ACKNOWLEDGMENTS This paper benefitted significantly from comments and suggestions of D. J. Roddy and W. R. Muehlberger. The work was done under NASA Contract T— 5874A, except for that of H. J. Moore, done as part of NASA Experiment 8—222. H. OPTICAL PROPERTIES AT THE APOLLO 16 LANDING SITE By HENRY E. HOLT CONTENTS Page Introduction __________________________________________________________________________ 174 Photometric studies __________________________________________________________________ 174 Procedures ______________________________________________________________________ 174 Observations ____________________________________________________________________ 175 Interpretations __________________________________________________________________ 181 Polarimetric studies __________________________________________________________________ 182 Procedures ______________________________________________________________________ 182 Observations and interpretations __________________________________________________ 183 Conclusions __________________________________________________________________________ 183 ILLUSTRATIONS Page FIGURE 1. Graph showing comparison of telescopically measured photometric function with measured luminances at stations 8 and 13 ___________________________________________________________________________________________________________ 175 2. Map showing albedo variations within the Apollo 16 site _____________________________________________________________ 176 3. Photograph of the Apollo 16 landing site, sun elevation angle 60° _____________________________________________________ 177 \ 4. Computer-generated enlargements of northern, central, and southern areas outlined in figure 2 _______________________ 178 5. Photograph of north wall and southeast rim of North Ray crater and digitized image showing degree of polarization for the same scene ___________________________________________________________________________________________________ 183 INTRODUCTION The optical properties at the Apollo 16 landing site in the central highlands can be characterized by meas- urements from surface and orbital photographs. The purpose of this study is to interpret the optical varia- tions over the landing area in relation to the local geol- ogy as deduced from the soil and rock samples photo- graphed and collected at the traverse stations. The data provide an opportunity to observe, in some detail, bright rays and older regolith surfaces in the landing site and to compare the optical nature of the Cayley Formation with the adjacent Descartes mountains. Fi- nally, polarimetric studies were conducted with photo- graphs taken through a polarizing filter at two loca- tions on the rim of North Ray crater to determine the degree and orientation of reflected. polarized light. PHOTOMETRIC STUDIES The brightness reflectances or albedos of materials on the Moon’s surface, measured under prescribed lighting conditions, constitute the photometric prop- erties of those materials. Determination of these prop- erties provides an independent method of estimating 174 the age and composition of texture of lunar surface materials. PROCEDURES The Apollo 16 mission provided the first opportunity to test the photometric function of the fine-grained highland regolith for small-scale variations. Photo- graphs taken down-sun, which include the astronaut’s shadow, allow the measurement of surface reflectance from approximately 50° to near 0° phase angle. Micro- densitometer scans were made across photographs taken at stations 6, 8, and 13. The film-density lumi- nances (or percent reflectances) were calculated and plotted relative to phase angle (fig. 1). Down-sun photographs of the lunar surface at each traverse station were utilized in determining the photometric properties of the undisturbed soil and rock materials. These materials normally appear darker when disturbed. At the Apollo 16 landing site, how- ever, patches of lighter materials were exposed below a thin surface layer at stations 1, 2, 4a, 5, 11, and 13. Surface areas within a few degrees of zero phase angle were scanned by densitometer and the film-density OPTICAL PROPERTIES AT LANDING SITE EXPLANATION —— Photometric function - — Measured at station 8 --- Measured at station I3 5 o CO 0 70 60 50 4o -30 -IO 0 IO 20 -20 PHASE ANGLE, lN DEGREES NORMALIZED LUNAR REFLECTANCE, IN PERCENT FIGURE 1.—Comparison of telescopically measured photomet- ric function with measured luminances from photographs ASlfi~ 106— 17386 (station 13) and ASlG— 108— 17702 (station 8). luminances calculated. The Hasselblad cameras with 60-mm and 500-mm focal length lenses used on the lunar surface were calibrated for variation in film den- sity as a function of absolute light intensities of photo- graphed objects. Photometric control before and after the mission was obtained from film measurements of the photometric chart and gnomon photographed on the lunar surface and from film sensitometry data. The camera orientation with respect to lunar azimuth, lunar vertical, and position of the sun was established for each measurement, and the measured luminances were then converted to 0° phase-angle reflectance for albedo determination. The resultant albedo value of the regolith is the down-sun reflectance expressed as a percentage of the solar irradiance; for instance, 14 per- cent albedo indicates that 14 percent of the solar light is reflected. Albedo distributions over the Descartes landing area were mapped from orbital panoramic camera frame 5328, taken under high sun angle (60° elevation) and 10° forward tilt, producing a 19° phase-angle View of the lunar surface. Relative film densities were digi- tized on a Joyce—Loebel microdensitometer at a scan— ning aperture of 50 ,u‘z, approximately equivalent to an integrated area of 9 m2 on the lunar surface. The film densities are proportional to the normal albedos of the lunar surface materials, and the density variations were calibrated to the albedos determined in the down—sun surface photographs at the traverse stations. A photomap showing the distribution of albedo levels was produced by relating appropriate range of digital numbers to quantified albedo levels. Areas of slope 175 were determined from a topographic map of Descartes landing area (US. Army Topographic Command, 1972); slope direction and steepness were computed, and the albedo deviation from a level surface was cal- culated using the average lunar photometric function. In areas beyond the topographic map coverage, the slopes were compared with known slopes by stereo- scopic study to determine slope direction and steep- ness. The topographic corrections were applied to the albedo levels to neutralize the effects of topographic slopes. OBSERVATIONS Slight differences in the slopes of the photometric function curves occur at phase angles near zero, indi- cating that variations in the backscattering nature of lunar fine-grained materials are minor. The lunar photometric function for mare surface (Holt and Ren— nilson, 1970) is very similar to that of the curves for stations 8 and 13, which is remarkable considering the differences in composition of bedrock. Apparently, the soil textures resulting from the comminution of lunar material by cratering produces the unique backscatter and lunar photometric function while composition con- trols the albedo. The albedo map of a 500-km2 area (fig. 2) can be compared with an orbital photograph at similar scale (fig. 3). The mapped area is dominated by the two bright areas of North Ray and South Ray craters and their radiating ejecta patterns. Map units 6 and 7, rep- resenting albedo levels of 11 through 15 percent, cover more than 58 percent of the mapped area. Where map unit 5 occurs, representing 15 to 17 percent albedo, there is nearly always clear evidence of relatively re— cent, bright small craters or diffuse ray patterns. The more clearly radial, diffuse to discontinuous bright ray material from North Ray and South Ray craters makes up unit 4, which ranges from 17 to 20 percent normal albedo. Map unit 3, ranging from 20 to 25 percent al- bedo, represents continuous to discontinuous streaks of ejecta from South Ray crater, both raylike patterns and continuous ejecta from North Ray crater, and rim de- posits on many smaller craters. The rim deposits of North Ray crater and the outer parts of the continuous ejecta from South Ray crater make up map units 1 and 2, varying from 25 to 40 percent albedo. The unit with the highest reflectance, about 40 to 60 percent normal albedo, makes up most of the crater wall of North Ray crater, the wall, rim, and some continuous ejecta of South Ray crater, and the rim and wall of Baby Ray crater. The albedos of the fine-grained regolith at the traverse stations in the Descartes landing area range from 14 to 32 percent. The albedos of the regolith at the 176 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS Albedo Albedo Albedo Albedo Albedo Albedo Albedo ll-l3 percent l3-l5 percent l5-l7 percenl I7—20 percent 20-25 percent 25-40 percent 40-60 percent N O I 2 3 4 5 KlLOMETERS t I—L—I—gL—1 Approximale FIGURE 2,—Albed0 of the Apollo 16 site based on Apollo 16 panoramic camera frame 5328. Normal albedos, divided into seven percentage ranges, are shown by the gray scale Enlargements of areas A, B, and C are shown in figure 4. Numbered localities are stations on EVA traverses. Albedo corrections were made for topographic slope elements measured on the premission topographic map (US. Army Topographic Command, 1972). OPTICAL PROPERTIES AT LANDING SITE 177 FIGURE 3.—The Descartes landing area as viewed on Apollo 16 panoramic camera frame 5328. Scale of photograph is same as albedo map of figure 2. Sun elevation 60°, camera tilt 10° from Vertical toward the west, producing a phase angle of 19°. 178 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS Noam RAY 9 RATE? 7 6 , 5 = l Albedo Albedo Albedo Albedo Albedo Albedo Albedo ll-l3 percent l3-l5 percent l5—l7 percent l7-20 percent 20-25 percent 25-40 percent 40—60 percent N O | KlLOMETER L l A Approximate FIGURE 4.—Computer-generated enlargements of areas A, B, and C outlined in figure 2. Station locations identified by number inside scribed areas. Gray shades represent same ranges as given in figure 2. A, Area A. B, Area B. C, Area C. 7 Albedo ll-l3 percenl OPTICAL PROPERTIES AT LANDING SITE 179 2 Albedo , Albedo Albedo Albedo Albedo Albedo l3-I5 percent l5-l7 percenl |7-'-20 percent 20—25 percent 25—40 percent 40-60 percent N 0 l KILOMETER L J Approximate» B FIGURE 4.—-Continued. 180 T Albedo ll-l 3 percent GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS 5 4 ~ 2 Albedo Albedo Albedo Albedo Albedo Albedo l3-l5 percent l5-l7 percent l7-20 percent 20-25 percent 25-40 percent 40-60 percent N 0 | KILOMETER L l C Approximate FIGURE 4.—Continued. OPTICAL PROPERTIES AT LANDING SITE traverse stations fall into three groups (fig. 2) that ap- pear to be controlled by proximity to North Ray and South Ray craters. Stations 11 and 13 (fig. 4A) are situated on the bright North Ray crater ejecta and ex- hibit albedos of 21 to 32 percent. The albedos of sta- tions 1, 2, 6, 8, 9, and LM vary from 16 to 19 percent over the discontinuous ray area between North Ray and South Ray craters. Stations 4 and 5 on Stone mountain show 14 to 15 percent albedo. Rock meas- urements vary from 18 to 51 percent; the brightest rocks are the light-matrix breccias on the rim of North Ray crater. The bright raylike materials on the rim of South Ray crater reach a maximum albedo of 60 per- cent, the brightest materials on the walls of North Ray crater 52 percent. These high albedos are more than twice the highest telescopically measured lunar albedo of 24 percent on the crater walls of Aristarchus (Pohn and Wildey, 1970). The extremely wide range of al— bedos, 14 to 60 percent, is the greatest of any lunar landing area. The high values stem from the high reso- lution possible with lunar surface photography relative to that from a telescope. INTERPRETATIONS Units 1, 2, 3, and 4 on the albedo map can be clearly related to ejecta from identifiable craters. Unit 5 is traceable around isolated craters, forming a pattern radiating from South Ray and North Ray craters, and occurs as small diffuse irregular patches of probable ejecta. Albedo units 6 and 7 represent the more mature regolith surface where lighter subsurface materials have not been excavated or recycled to the surface for a long period of time. The albedo map does not indicate any measurable differences between the optical properties of the reg- olith overlying the Cayley Formation and the regolith on Descartes materials of Stone and Smoky mountains. The range of albedo values over both areas is similar, suggesting that there is no significant difference in gross chemical composition of the regolith materials. Soil samples collected from both the Cayley Formation and Stone mountain are reportedly similar in chemical composition (LSPET, 1972) although their percentages of agglutinates, glasses, mineral, and lithic fragments vary. The regolith over the Apollo 16 area may be het— erogeneous on a local scale; it becomes more homogeneous on a regional scale, presumably through the maturing action of the repetitive small cratering events. The chemical and optical properties of the more mature soil areas suggest that the regolith over the Cayley plains and Descartes mountains was derived from a similar suite of rocks. Soil samples obtained from traverse stations consist of various mixtures of agglutinates, glassy fragments, 181 light-colored lithic fragments, and dark lithic frag- ments (Heiken and others, 1973). As a soil “ages” or matures on the surface, it becomes darker, the aggluti- nate content increases, and the soil becomes finer grained (Adams and McCord, 1973). The soils from sta- tions 4 and 5 are the darkest, having the highest agglutinate content and the smallest average grain size of the traverse stations. Lighter soils (stations 11 and subsurface 1) are coarsest, have a higher percent- age of light-colored lithic fragments and the lowest percentage of agglutinates. Soils at the other stations are intermediate between the lighter and darker soils and could be considered mixtures of the two types. The lighter soils at station 11 are immature soils of North Ray crater ejecta; sam- ples of soils collected in areas of high-albedo ray patches (station 8, map unit 4) are not clearly derived from South Ray crater. The coarser fractions, lighter color, and lower proportion of agglutinates in the soils from stations 1, 2, and 6 suggest the contamination, probably by South Ray fine-grained ejecta, of a more mature preexisting soil at these locations. The combination of surface photographs, crew obser- vations, soil samples, and albedo mapping from orbital pictures permits a detailed study of the character of recent ray ejecta and provides insights into the aging process of rays. The crew recognized discontinuous ray patches as concentrations of rock fragments on the sur- face along linear trends. Changes in albedo were not noticed near the edge of a ray patch, and no charac- teristic of the fine-grained regolith was described that could identify ray areas. The rock fragments in ray areas were mainly less than 5 cm across; they covered from less than 1 to as much as 7 percent of the surface area, with the most frequent size range comprising 2- to 5-cm cobbles (Muehlberger and others, 1972). The interray and ray areas delineated on orbital photog- raphy generally appear to have similar fragment fre- quency in the high-resolution surface photograph al- though local ray segments identified on the surface are not necessarily visible on orbital photographs. The lighter colored ray materials gradually darken, by an aging process that must be similar to regolith darkening, until their surfaces become indistinguish- able from adjacent interray areas. The upper surface of ray material will darken with increase in agglutinate and reduction of the average grain size as well as by mixing with darker preray regolith, both laterally and from below. Gardening by numerous small impact cratering events has been estimated to take 10 my to turn over the uppermost centimeter at least once (Gault and others, 1974). The occurrence of 2~3 cm of darker soil overlying lighter material at stations 1, 2, 6, 11, and 13 is reasonably consistent with a North Ray crater source 50 to 60 million years ago. South Ray 182 crater fine-grained ejecta would be expected to show little aging in 2 to 4 m.y. POLARIMETRIC STUDIES The polarimetric properties of rocks and soils at North Ray crater were investigated to determine the degree and orientation of polarized light reflected from those materials in the north and northeast crater wall. Measurements of these properties help to establish the abundance of brecciated rocks and the lack of crystal- line material at that location. On the high-sun (19° phase angle) Apollo 16 orbital pictures, individual rays from South Ray crater can be observed to extend at least 10 km northward, overlap- ping North Ray ejecta west and southeast of North Ray crater. Rays become slightly discontinuous about 3 km from South Ray crater. Rays extend eastward over Stone mountain as far as 7 km from South Ray crater. Continuous ejecta and rays from North Ray crater ap- pear to extend only 3 km and 5 km, respectively. This more restricted distribution may result from the greater age of North Ray crater (50 m.y., Walton and others, 1973) compared with South Ray crater (2—4 m.y., McKay and Heiken, 1973) and consequently greater mixing and aging of the ray materials. North Ray crater excavated more than three times as much material as South Ray crater, and its ejecta must have been scattered over a significantly larger area than covered by the present distribution of visible South Ray crater ejecta. Most of the traverse area should have been nearly continuously covered by North Ray ejecta and ray materials. Lighter materials were ob- served 2 to 3 cm below a darker gray surface layer at many stations and may represent North Ray crater ejecta. The rays are features that become more visible as the phase angle approaches zero (also referred to as the opposition effect), a property of fine-grained materials. Those rays that become most visible at opposition con- tain a higher proportion of light soil. Rock fragments show a Lambertian type reflectance, greatest relative to the fine-grained regolith at 30° to 50° phase angle. Surface fragments tend to reduce the overall opposition effect except where the fragments are covered by a dust layer. As described by Muehlberger and others (1972), rock-fragment concentrations are commonly similar in ray and interray areas; hence the light soils must be the controlling factor. Several areas of rock concentra— tion were considered rays by the crew, but those areas do not exhibit consistently high albedo at low phase angles, indicating that light soil is- not present (station 4 and 5 are examples). In one of the brightest areas crossed, Survey ridge, albedo 24 percent, as muchas 7 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS percent of the surface is covered by fragments larger than 2 cm (Muehlberger and others, 1972; Schaber, this volume, fig. 2). A, similar concentration of frag- ments occurred near station 5, where the soil albedo was 14 percent compared with 24 percent-at Survey ridge. The ray patterns are Visible at low phase angles only because lighter colored fine-grained material oc- curs as ray material, with or without any concentra- tion of rock fragments. PROCEDURES A polarizing filter attached to the lunar surface Has- selblad camera permitted measurement of the degree of polarization and the orientation of the plane of maximum polarization of light reflected from the lunar surface. Three photographs were needed, one each with the polarizing filter at the 0, 45, and 90° positions. To obtain the data needed, overlapping photographs were taken at one filter position through a 120° sector across North Ray crater from station 11. The filter was then rotated to the second position and the sector rephoto- graphed. This was repeated a third time in the final filter position. Differences in image intensity of the same image element or object in the three photographs are a function of the amount and orientation of the linear component of polarized reflected light from that object. Three sets of polarization frames were selected for computer processing from the returned photographs: frames ASl6— 106— 17239, 17241, 17257, 17259, 17266, and 17268 from the southwestern panoramic position at station 11, and frames ASl6— 106— 17283, 17296, and 17310 from the northeastern panoramic position at station 11. The data for computer reduction were taken from second-generation master positives. The sets of photographs were digitized and the frames filtered using a 3- by 3-pixel matrix to smooth the data. The first frame (horizontal polarization) became the prime photograph against which the remaining two were reg- istered. Camera displacements between frames were sufficiently large to yield stereopairs from frames within a given set. Registration of stereopairs to pixel resolution is extremely difficult and requires lengthy computer processing. To reduce expensive computer time, a special set of positive transparency enlarge- ments of the digitized photographs was made. The frames were then registered visually and displacement coordinates were determined for 70 to 80 points in each frame. These point displacements were used to com- pute linear interpolation of the displacement coordi- nates. This interpolation factor was applied to each photograph element. The registrations, .while still im- perfect, were within 5 pixels in the far field. The three registered frames were used to compute OPTICAL PROPERTIES AT LANDING SITE the degree of polarization and the angle of its maximum. Following this calculation, a nine-gray-step conversion table was generated to illustrate areas of equivalent polarization in the three sets, one taken at high phase angle (shown in fig. 5). Polarization values on overlapping areas of the photograph sets are in rela- tively good agreement. OBSERVATIONS AND INTERPRETATIONS A comparison of the polarimetric functions of re- turned samples with those of rocks in accessible or re- mote areas permits some correlation and classification of materials at a distance. In the area of North Ray crater, for instance, such a study shows three polarimetrically distinct materials: (1) a region of reg- olith that covers Smoky mountain (area A, fig. 5A) and dark smooth material on the crater wall (area B, fig. 5A), (2) blocky material on the crater wall (area C, fig. 5A), and (3) a region on the west wall of the crater (left side of pl. 8, pan 19) characterized by high albedo and by relatively high degree of polarization for that phase angle. It was found that individual rock fragments ranging in width from 25 cm in the foreground to 10 m on the northwest rim have low degrees of polarization. All rock fragments around North Ray crater show less than half the polarization measured on the Apollo 11 183 and 12 crystalline rocks and one-half to two—thirds the polarization measured on Apollo 14 breccia samples 14305, 14311, and 14321 from the Fra Mauro region (Swann and others, 1978). The rock surfaces around North Ray crater apparently contain little crystalline material that can polarize reflected light. CONCLUSIONS A rather uniform upper-soil layer evolved over the Descartes landing area during its geologic history prior to the formation of North Ray crater. The soil matured (darkened) to a nearly uniform albedo of 12 to 14 per- cent over both the Cayley plains and the Descartes mountains. Because a similar-looking soil developed over both terrains, it seems probable that the subsur- face material is of similar bulk composition. The North Ray cratering event scattered predomi- nantly light subsurface material (mostly as coarse- grained fragmental soil) over a large area, including most, if not all, of the traverse areas. Surficial pro- cesses aged the upper 2—3 cm of the widely dispersed 1—5 6—10 11—15 16—20 21—25 26-30 31—40 41—50 >50 POLARIZATION, lN PERCENT B FIGURE 5.—Polarimetry of north wall and southeast rim (near field) of North Ray crater. A, One frame (A816—106— 17239) from the left polarization panorama. Filter oriented horizontally. This frame was the basis for registering the two additional filter positions. B, Computer printout of polarization data from the scene inA. Degree of polarization, divided into nine percentage ranges, is shown by gray scale. Apparent mean of polarization in this scene is 10 to 11 percent; maximum polarization approximately 30 percent on a few rocks. 184 light fragmental soil, destroying the typical ray struc- ture. Most of the continuous to discontinuous ray ma- terials merged into a diffuse halo around North Ray crater having albedos of 25 to 30 percent on the rim deposits, decreasing outward to 16 to 18 percent as far as 8 km away. The South Ray crater event, 2 to 4 million years ago, scattered light subsurface material over much of the traverse area. The light discontinuous patches of ray materials are visible, in the author’s opinion, because of the light fine-grained component of the ejecta rather than the fragment population (2—7 percent of area) over the surface of a ray. The Baby Ray impact event scattered more light-colored subsurface material over distances of a few kilometers. The surficial gardening processes should have had little effect in altering or darkening ray materials from South Ray and Baby Ray craters. The surface albedo patterns over the Descartes area are produced by a combination of the older North Ray and the younger South Ray and Baby Ray ejecta deposits and the preexisting nearly uniform regolith GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS surface. Bright, continuous-to-discontinuous ejecta (albedo units 1, 2, 3, and 4) cover 23 percent of the mapped area. More diffuse lightened regolith (unit 5) in patterns radial to North Ray and South Ray craters occupies more than 18 percent of the area and probably represents a mixture of light ejecta with preexisting regolith. The rocky surfaces around North Ray crater rim and within the crater wall contain little crystalline mate- rial that can polarize reflected light. The polarimetric properties of these rocks suggest that they are much more highly shocked than the Fra Mauro breccias from Cone crater at the Apollo 14 site. No areas, layers, or blocks of intermediate to strong polarization such as would be expected for relatively unshocked basaltic crystalline rock were observed. On the basis of unpub- lished laboratory measurements on crushed anortho- site, all measurements at North Ray crater are consis— tent with the polarimetric properties of highly brec- ciated and shocked material of predominantly anor- thositic composition. I. MORPHOLOGY AND ORIGIN OF THE LANDSCAPE OF THE DESCARTES REGION By JOHN P. SCHAFER CONTENTS Page Introduction __________________________________________________________________________ 185 Descartes mountains __________________________________________________________________ 186 Terrain lineated by crater chains __________________________________________________ 187 Terrain lineated by ridges and scarps ______________________________________________ 187 Crosslineated terrain ____________________________________________________________ 187 Isolated mountains ______________________________________________________________ 188 Origin of Descartes mountains ____________________________________________________ 190 Origin of isolated mountains ______________________________________________________ 190 Cayley plains ________________________________________________________________________ 192 Morphology ______________________________________________________________________ 192 Relation between Cayley plains and Descartes mountains __________________________ 192 Origin of Cayley plains as ejecta from multiring basins ____________________________ 194 Possible ejecta drainage features __________________________________________________ 194 Other hypotheses of origin of Cayley plains ________________________________________ 195 Conclusions __________________________________________________________________________ 195 ILLUSTRATIONS Page FIGURE 1. Orbital photograph of the Descartes region _________________________________________________________________________ 186 2. Photograph of Apollo 16 landing site and vicinity ___________________________________________________________________ 188 3. Sketch map of morphologic features of Descartes region shown on figure 2 ___________________________________________ 189 4. Oblique photograph of Descartes region showing Imbrium sculpture _________________________________________________ 191 5. Generalized topographic map of Cayley plain at and west of the Apollo 16 landing site _________________________________ 193 INTRODUCTION The origin of the landscape and materials of the cen- tral lunar highlands has been a subject of discussion and disagreement since before the Apollo 16 mission. The dominant premission hypotheses of volcanic origin were contradicted by examination of the returned samples, mostly impact breccias. The materials have been reinterpreted as ejecta of local craters or of dis— tant multiringed basins. The various hypotheses for origin of the geologic units are summarized by Hodges (this volume). A credible hypothesis must explain not only the character of the materials but also the morphology of the landscape. This study of the surface morphology of the Descartes region (fig. 1) includes the mapping of certain features within an area of about 2,900 km2 (figs. 2 and 3) in order to determine constraints that the morphology may place upon genetic hypotheses for the region. Photogeologic interpretation of landforms pro- duces inferences rather than certainties, and such in- terpretation has more bearing on some problems than on others. For example, interpretation of landforms may well reveal whether they are intrinsic to the ejecta believed to constitute the highlands or were imposed on those materials after their deposition. Such in— terpretation has little to say about how much of the ejecta was derived from primary impact craters or basins and how much was derived from mixing of local subjacent materials by secondary impacts. This study has been made within the framework of the geologic map of the region (pl.1), which includes topographic contours (interval 50 m) for part of the area. Premis- sion maps of the region (Milton, 1972; Hodges, 1972a; Elston and others, 1972b) show some of the morphologic features. Topographic unconformities—breaks between land- forms or groups of landforms—are critical in a morphologic study. They separate surfaces of different ages or of the same age but produced by different proc- esses. The principal topographic unconformity in the Descartes region is that between the Descartes 185 186 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS DQLLONDC‘Z . p 9; M ‘ . N ' ., V ‘1”. M D < LU l- <1 Ll > O. .— Z < M § FIGURE 1.—Orbital photograph (Apollo 16 mapping camera frame 0440) of the Descartes region. Rectangles outline areas of figures 2, 3, and 5. Letters indicate localities referred to in text. mountains and Cayley plains. The main problem is to figures 2 and 3 contain terrains mainly of three aspects determine how the landscape was differentiated into that are interrelated and intergradational: lineated by these rugged highlands and smooth plains. crater chains, lineated by ridges and scarps, and crosslineated. Small patches of knobby terrain occur DESCARTES MOUNTAINS within areas of other terrain types. Several isolated mountains of distinctive form and relief are mapped as The highlands within and adjacent to the area of a separate unit, probably Nectaris ejecta. LANDSCAPE OF THE DESCARTES REGION 187 TERRAIN LINEATED BY CRATER CHAINS The terrain in the east-central part of the area, east of Stone and Smoky mountains and extending north- west beyond the mapped area, is characterized by chains and irregular groups of craters. Most of these craters are 0.7 to 2.0 km in diameter. All show greater degradation than do the younger, sharper craters shown on the geologic map (pl. 1) by Hodges as Im- Jbrian, Eratosthenian, or Copernican in age. All such younger craters, except North Ray and South Ray, are omitted from the sketch map (fig. 3). The crater chains have an average trend of north- northwest. Some, such as the chain at A on the sketch map (fig. 3), 14 km long and made up of at least 13 craters, are notably sinuous. The longest crater line- ament in this area, and the most conspicuous on the photographs, is that extending from B to C (fig. 3), a distance of 27 km. This lineament, however, is a com- posite feature, consisting of three separate crater chains, connected fortuitously at D by a pair of younger craters (mapped on pl. 1 by Hodges, as Copernican sec- ondary craters, perhaps satellitic to Theophilus) and at E by a broad depression of uncertain origin. The rela- tively deep, steep-walled, sharp-rimmed trough at F (fig. 3) has a slightly beaded shape in plan View, and an identifiable crater at each end, is parallel to nearby chains, and is very similar to the more closely spaced sections of other chains (as at A). Such troughs are inferred to result from very closely spaced craters. Sharp narrow creases at the junction of opposing slopes occur in a few places, generally in deep crater chains or troughs. The upland surface between mapped craters is un- dulating to hilly and ridged. One of the largest rem- nants of this surface is the undulating plateau on the southwest side of the trough at F (fig. 3). The highland salient at B (fig. 3) is the north end of a broad ridge, considerably obscured by craters, that appears to ex- tend south-southeast to Smoky mountain. Such ridges are roughly parallel to the crater chains. The Cayley plains embayment in which Apollo 16 landed is continuous eastward with a conspicuous to— pographic sag in the highlands. Within that sag, somewhat degraded craters such as those that form the crater chains in the adjacent areas to the north and south are notably absent. TERRAIN LINEATED BY RIDGES AND SCARPS Ridges and scarps are conspicuous in a belt that ex— tends from about 20 km north of Smoky mountain to at least 25 km south of Stone mountain and includes those mountains; terrain of this type is extensive to the southwest and west outside the area of figure 3. The belt forms the high west margin of the Descartes mountains that overlooks the adjacent Cayley plains and the Apollo 16 site. It includes west-facing scarps, apparently somewhat degraded by colluviation, such as the high west slope of Smoky mountain (G, fig. 3) and the smaller scarp that crosses the top of Stone mountain (H, fig. 3). Low sinuous ridges lie at the foot of the highland slope at J and K (fig. 3). The Cayley plains embayment in which Apollo 16 landed separates the belt into north and south segments. The mountain tops‘stand about 500—600 In above the Cayley plains; relief within the mountains generally does not exceed 200—300 111. Although some craters are present, chains of them do not constitute the dominant landform as in the terrain to the east and north. The most conspicuous landforms here are the somewhat sinuous ridges (fig. 1) that trend north to north- northwest. The furrows between them are mostly shaped by intersection of the side slopes of the ridges and lack the series of bowl-shaped concavities of the crater chains. The walls of the furrows, unlike the walls of craters, do not meet remnants of upland sur- face with topographic unconformity; rather, the slopes are continuously convex over the crests of ridges. Patches of knobby terrain showing few or no linea- tions are dominated by subcircular, smoothly convex knobs, 1.0 to 2.5 km in diameter and about 50 to 200 m high. A group of three knobs occurs at L (fig. 3), just southeast of Stone mountain; others in and just beyond the southwest corner of the area of figure 3; outside the area, similar knobs occur in the terrain lineated by ridges and scarps and in other terrain units. CROSSLINEATED TERRAIN A large area southeast of the Apollo 16 site, of which only a small part appears in the southeast corner of figures 2 and 3, shows two sets of directional features: one of crater chains, ridges, and noncratered furrows that trend northwest to north as in other parts of the highlands; one of features that trend northeast to north-northeast. The intersection of these transverse sets produces a crosshatched, blocky landscape. The conspicuous northwest boundary of this crosslineated terrain is a northeast-trending, southeast-facing scarp. The well-preserved straight segments of the scarp at M and N (fig. 3) are sharp at both crest and base; between these segments, the scarp is obscured by a cluster of craters younger than the scarp. The sharpness with which the scarp cuts across ridges, furrows, and craters shows that it postdates many of these morphologic features. The scarp seg- ment at N curves into, and appears to be continuous with, the west wall of the north-south trough at P (fig. 3), whose beaded shape indicates that it is a chain of closely spaced craters. This apparent continuity may be only fortuitous, as the boundary of the crosslineated 188 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS terrain appears to continue southwest as a low, the line). Southwest of the ridge at Q, the position of straight ridge at Q (fig. 3; not easily Visible on fig. 2). the terrain boundary is not clearly shown. This ridge, at most a few tens of meters high, is directly on line with the crest of the scarp and is connected with ISOLATED MOUNTAINS it by an albedo boundary (lighter material southeast of Certain isolated mountains standing above their o 5 10KILOMETERS L_L_.l FIGURE 2.—Orbital photograph of Apollo 16 landing site and vicinity. Apollo 16 mapping camera frame 0440; photographic base for figure 3. LANDSCAPE OF THE DESCARTES REGION surroundings have been identified as terrain probably different from the rest of the Descartes mountains (Hodges, this volume, pl. 1; Elston and others, 1972b). They commonly have a distinctive, roughly trapezoidal 189 form produced by relatively straight scarps on one or more sides; some of the mountains are cut across by straight troughs. Some of these blocky mountains ap- pear to be tilted. Only two occur within the area of 7°2o’s o 5 10KILOMETERS QC? JG Q) ”9@@§ \\-"\ (3G Q N f \0 (g r > NOT 0 Q / MAPPED (g ( 0g 0 ‘00 o‘ D O J L 303 x"""?\.9 q t {IV\\\>\ ({)/\ /—Q\(/ \\‘\’/} # 0‘ ,JI \\ uyq K /] (\(d F_/W\ R\K \ G Apollo 16 v Stone /’ mountain, 0 Southo 03 Ray Q’ N O x f/ Itr f” f < ’ K0: 2 F‘ Q % I/ O )9) l \\\ /\ K\ O Itr E3/L)\‘J () j EXPLANATION Ica Cayley Formation ltr Rugged terra material; probably ejecta from Imbrium basin Terra material; probably electa from Nectaris basin Contact between geologic units (princi- pally as on plate 1) Q 00 Rims of ore-Copernican impact craters, believed to be Imbrium secondaries \O A Rim of crater believed to predate part or all of Imbrium event A \\il\ll1 llllm ##2— Scarp; triangles indicate foot of SCarp ——H—£—-—E—— \0 Narrow crease Narrow low ridge C) Subcircular k nob Section of line obscured by Younger impact crater A > E Locality referred to in text / 16°12’E FIGURE 3,—Sketch map of morphologic features of Apollo 16 landing site Vicinity. Derived principally from study of three stereopairs: Apollo 16 mapping camera frames 0439 and 0441, 1265 and 1266, 2179 and 2180. Area and scale same as figure 2. 190 figure 3 (shown as map unit Nt), others lie just outside that area. The isolated mountain in the southwest part of the area of figure 3 stands about 500 m above the sur- rounding Cayley plain; its west side is a steep, straight scarp. A larger massif of this terrain lies 7 km to the west (a, fig. 1). Two shallow, saucer-shaped depressions on this mountain are tentatively interpreted as de- graded craters older than other craters shown on the map (fig. 3). The isolated mountain (map unit Nt) in the north- central part of the area of figure 3 stands well above the surrounding Descartes mountains and has a gen- erally smooth surface, without the rough texture and numerous craters of the highlands. A larger massif of this terrain lies 20 km to the east (b, fig. 1) and appears to be an outlier of the Kant plateau. ORIGIN OF DESCARTES MOUNTAINS The most conspicuous feature of the landscape of the Descartes mountains is the north to northwest lineation that pervades the terrains lineated by crater chains and by ridges and scarps and continues south- ward as one of the two sets of features of the crosslineated terrain. Extensive areas of such lineation, radial to the Imbrium basin, occur to the west and northwest, and are designated Imbrium sculpture (pl. 12). This similarity has led to general agreement among the authors in this volume that the lineation is Imbrium sculpture related to the impact event that formed the Imbrium basin. Within the terrain lineated by Imbrium sculpture, the chains of craters are most likely erosional effects of secondary impacts. The craters mapped on figure 3 show only a moderate range of degradation, likely ex- plained as the result of different degrees of mantling of secondary craters by ejecta from other secondary cra- ters or by primary ejecta. The origin of the terrain lineated by ridges and scarps is not so obvious. The furrows between the ridges show no indication of being crater chains. Some furrows in Imbrium sculpture have been suggested to be endogenetic in origin: fractures, perhaps with some accompanying volcanic activity, produced by the shock of the Imbrium impact (for instance, Scott, 1972; other references in Howard and others, 1974, p. 323). The fur- furrows in this area, however, do not match Scott’s criteria for volcano-tectonic origin; they are sinuous and lack the linearity expected of fractures and are mostly shaped by the intersection of the convex slopes of the ridges. I therefore infer a depositional origin for the ridges and that the furrows are the concavities be- tween adjacent ridges. Such depositional ridge-and- furrow terrain may be compared to the radially GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS lineated and braided part of the Hevelius Formation, the ejecta blanket of the Orientale basin (Moore and others, 1974, p. 75; Howard and others, 1974, p. 312), or to similar terrain in the Fra Mauro Formation, the ejecta blanket of the Imbrium basin (Hodges and others, 1973, p. 21). Some sharp creases and scarp crests that occur in the Imbrium sculpture appear much fresher than other features of the Imbrium landscape, yet ’their orienta- tions show that they are part of that landscape. Most of these sharp features are at the tops or bottoms of steep high slopes and probably owe their apparent freshness to the still rapid colluviation of the slopes. The crests are still being undercut, and the creases are being maintained by continued intergrowth of colluvium from facing slopes. The less rapid colluviation on lower, gentler slopes has permitted the rounding of scarp crests and creases. The position of the Descartes mountains just outside the third (main) ring of the Nectaris basin has led to the suggestion that the mountains are dominantly a blanket of N ectaris ejecta and that Imbrium sculpture was superposed on it, mainly by erosion by primary projectiles from Imbrium, with little actual addition of Imbrium ejecta deposits (Wilhelms, 1972a; Head, 1974, p. 83). I believe, however, that the morphologic fea- tures of the area support the interpretation that the Imbrium sculpture of the Descartes mountains is in- trinsic to the materials of which the mountains are formed and that they are therefore part of the ejecta blanket deposited during the Imbrium event. The evi- dence is: (1) The ridge-and-furrow morphology of at least part of the mountains, as discussed here, indi- cates a depositional rather than erosional origin. (2) On a larger scale, there are broad ridges within the mountains, such as that which extends from B (fig. 3) south-southeast to Smoky mountain. The Imbrium sculpture of such ridges is parallel to them, indicating that both features were formed at the same time. (3) The main part of the mountains as a whole forms a belt parallel to the Imbrium sculpture, between the west foot of the Kant plateau and the scarp along the west side of the Smoky mountain—Stone mountain belt (fig. 4). (4) The southward extension of the furrowed high- lands into Descartes crater, through the northeast wall of the crater, has the form of a compound tongue ex- tending south—southeast, with internal lineaments in the same direction (figs. 1 and 4; Hodges and .Muehlberger, this volume, fig. 6). This is parallel to the Imbrium sculpture but more than 100° from a radial to the center of the Nectaris basin. Thus the large forms and the detailed features of the highlands are con- gruent, indicating that they were formed in a single event. This corroborates similar conclusions reached LANDSCAPE OF THE DESCARTES REGION 191 4’: PLATiEAU .. w FIGURE 4.—Westward-looking oblique view of Descartes region from orbit, showing Descartes mountains with furrowed patterns parallel to Imbrium sculpture. Apollo 16 mapping camera frame 0556. by Moore and others (1974, p. 94) and Hodges and Muehlberger (this volume). The crosslineated topography, with its two sets of intersecting lineaments, poses a more complicated problem. The data within the study area are compati— ble with the conclusions of Hodges and Muehlberger (this volume, fig. 6) that the doubly lineated terrain "may have been caused by a surge of ejecta up the flanks of the Kant plateau and subsequent deflection southwestward.” Within the area of figure 3, the southwest-trending scarp at M to N appears to cut across some southeast features and is interrupted be— tween M and N by a south—southeast-trending crater chain. This overlap of features presumably all devel- oped in a very brief period of time during the Imbrium event. If these two sets of lineations are the erosional and depositional results of movement of ejecta in two directions, then this is adequate to explain the morphology, making comparisons with deceleration dunes (Moore and others, 1974, p. 79; Hodges and Muehlberger, this volume) unnecessary. The west-facing scarps along the Smoky mountain— Stone mountain belt are possibly fault scarps. Their concentration along the generally steep west face of the highlands indicates that they may be near-surface gravity-controlled features. One possible fault block includes the ridge in which North Ray crater was exca- vated (Ulrich, 1973, fig. 5). All are considerably de- graded and may well have formed during or im- mediately following the Imbrium impact. The sinuous narrow ridges along the foot of the highland slope (J and K, fig. 3) might also have resulted from gravity collapse. ORIGIN OF ISOLATED MOUNTAINS The two isolated mountains within the area of figure 3 are identified mainly by comparison with better examples just outside that area. The massifs west- southwest of the Apollo 16 site (a, fig. 1; southwest part 192 of fig. 3) are very similar in form to part of the rim of Dollond B, which is interpreted as a Nectarian crater that has been sculptured and partly buried by Imbrium ejecta (pl. 1). The massifs northeast (and north) of the site (b, fig. 1; north-central part of fig. 3) are, in both position and morphology, outliers of the Kant plateau, a part of the third ring of the Nectaris basin. The iso- lated mountains are therefore tentatively inferred to be Nectarian materials projecting through the mantle of Imbrium ejecta, themselves bearing at most a thin mantle of such ejecta (pl. 1). The blocky forms may result from faulting caused by the Imbrium impact. CAYLEY PLAINS MORPHOLOGY The Cayley plains in the central lunar highlands, as elsewhere, are most strikingly characterized by their “ponded” appearance and by the sparsity or absence of lineaments except for chains of impact craters of Copernican age. The following description of Cayley refers almost entirely to the plain on which Apollo 16 landed; other plains nearby have similar characteris- tics. A map of the east half of the landing-site plain (fig. 5) shows smoothed contours produced by eliminating, as far as possible, younger impact craters. The surface thus delineated is very smooth, having, in most parts, only gentle undulations. The total relief in this area of about 25 by 38 km is about 400 m. The principal fea- ture of the surface is the slope eastward and south- eastward to an enclosed depression north of South Ray crater. The slopes between the 8,000-m contour near the west edge of the map and the 7,750-m contour in the depression are about 15m/km west from the depres- sion and 10 m/km northwest from the depression (17 m/km is 1°). These slopes are comparable to those of mare basalts at the margin of Mare Serenitatis (Muehlberger, 1974, p. 104), interpreted as the results of initial flow gradients and gentle tectonic tilting. If this general slope results partly from tilt of the stereo- scopic model (compare Eggleton and Schaber, 1972, p. 29—8), the actual slope is even less. RELATION BETWEEN CAYLEY PLAINS AND DESCARTES MOUNTAINS Parts of the contact between plains and mountains are not sharp and are difficult to map, particularly at large scale. The gradational zone between the two types of landscape commonly shows the numerous small craters and even texture characteristic of the Cayley, together with the more irregular relief and variable texture of low parts of the highlands. Where the highland surface descends abruptly to the GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS plain, as along many parts of the Smoky mountain— Stone mountain belt, the zone of uncertainty of the contact is narrow, commonly less than 0.3 km. This minimal width of the zone probably represents col- luvium at the angle between plain and highland. No features as much as 1 km wide on the map are iden— tified as colluvial deposits. Where the highland surface descends more gently to the plain, the zone of uncertainty of the contact is wide, more than 2 km at S (fig. 5). The uncertainty is mainly the result of the slight difference between gentle slope and plain; such an originally gentle slope is unlikely to have accumulated great amounts of colluvium. Several broad low hills in the adjacent northeast part of the Cayley plain are shown by the contours of figure 5. Only one of these hills was mapped as a projecting hill of highland material (pl. 1; T, figs. 3 and 5); others are almost as conspicuous. This somewhat subdued hilly topography evidently represents a continuation of highland materials form the north, probably thinly and discontinuously covered by Cayley. Certain features along the west side of the Smoky mountain—Stone mountain belt that may have re- sulted from slumping, probably during or immediately following the Imbrium event, appear to be overlapped by Cayley. The scarps on the west side of Stone mountain decline northward and disappear at the con- tact. The scarp 10 km north of North Ray crater lies in part directly along the contact, as if the possibly down-dropped block on the west side of the scarp were tilted southward and partly covered by Cayley. Some low hills below the contact (as at U, fig. 5) may be either depositional hills of highland materials or col- lapse blocks mantled by Cayley. The narrow ridges at J and K (fig. 3), whether depositional or collapse fea- tures, are recognizable not only on the lower slopes of the highlands but also within the edge of the Cayley, where they are shown by the contours (J and K, fig. 5) to have a relief of a few tens of meters at most. The features described here show that highlands landforms appear on the adjacent plain in several dif- ferent settings; that farther out on the plain the forms are more subdued because of filling of the swales be- tween them by Cayley material; and that post- Imbrium colluvium is recognizable only as a minor fea- ture at the scale of figure 3. These observations support the conclusions that (1) the Descartes mountains terrain extends beneath the Cayley plains; (2) the Cayley plains are formed by a basin fill that is thick enough in some places to conceal completely the rugged topography of the mountain ma- terials but thin enough in at least some marginalareas to reveal a subdued and mantled mountain terrain; and (3) the gradational character of the contact be- LANDSCAPE OF THE DESCARTES REGION 8°O5'S . \ I o \ (Q \ / , ‘. _ \ \ \SOD/ M KILOMETERS If \\ I I/\J.\? \\ /, \i/ ) / 9\o / l / \ , 1’ 06° “\\ ’ o \J o m 9°00 e°°° 2 'P I) 4 \ 9°37‘ I l4°48' E I5°52' topographic map of plate 1; smoothed in an attempt to eliminate effects of later impact cratering and to restore FIGURE 5.—Generalized topographic map of Cayley plain near the Apollo 16 landing site. Contours derived from approximately the original depositional surface. Contour interval, 50 m. Dashed line, boundary of Cayley plains; dotted where obscured. See figure 3 for explanation of other symbols. 193 194 tween plains and mountains is mostly the result of the overlapping of Cayley fill on the edge of the mountains rather than concealment of the contact with colluvium. None of the gradational character of the morphologic contact is attributed to actual intergradation of the two deposits. The features on the Cayley plains mapped as subcir- cular knobs are small domical or conical hills, 0.7 to 1.5 km in diameter, which occur in groups (north part of fig. 3) or singly. In as much as most of those within the area of the 50-m contours are shown by only one con— tour, their exact heights are not known. However, the knob at R (fig. 5) is more than 100 m high. Only those knobs that are clearly distinct from crater rim seg- ments are sketched on figures 3 and 5. The knobs are much sharper in form than the summits of almost all hills in the uplands except for some knobs scattered among larger hills. They occur both near the margin and in the middle of plains, where the Cayley fill may be inferred to be much thicker. Partial submergence of mountain terrain by Cayley fill would seem unlikely to produce such small, sharp knobs scattered across a plain, and I infer that the knobs are not the summits of partly buried hills rising from beneath Cayley. It is possible that such knobs “may be constructional land- forms intrinsic to the Cayley Formation,” formed by emission of fragmental or fluid material from the Cayley itself (Eggleton and Schaber, 1972, p. 29-8, 29— 15). ORIGIN OF CAYLEY PLAINS AS EJECTA FROM MULTIRING BASINS The discovery that the Cayley plains samples at the Apollo 16 site were mostly breccias led to a reevalua- tion of the possibility that the plains materials were ejecta from one or more multiring basins (Eggleton and Schaber, 1972) and specifically to the concept that the Cayley Formation was transported as fluidized Im- brium ejecta and deposited in lowlands. The ponded character of the Cayley fill certainly demonstrates that at the time of deposition it was much more mobile than the material that became the mountains, perhaps be- cause of higher proportions of impact melt and finely crushed material. The marginal relations between these terrains and the complete absence of Imbrium- lineated morphology on the Cayley surface demon- strate that at least the upper part of the fill is younger (if only by minutes) than the mountain materials (or than the Imbrium sculpture of those materials). The most critical observation to explain is the con- centration of the Cayley in large depressions. Deposi- tion of relatively mobile ejecta in thicknesses sufficient to conceal completely the morphology of the buried GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS mountains under present Cayley plains must have been accompanied by at least fleeting emplacement of substantial amounts of such ejecta over the rest of the mountains. If a proposed Orientale contribution alone were “several hundred meters” thick (Boyce and others, 1974, p. 21), this would require the draining of much of the material off the mountains to avoid the widespread concealing of the Imbrium morphology. Most of that morphology has a local relief of only a few hundred meters, and many of the Imbrium secondary craters are only 100—300 m deep. Even if much of the mobile ejecta drained off open slopes and out of swales onto a Cayley plain, many craters and troughs would have been subdued or actually filled. A lesser thickness of this superposed ejecta layer, say the “local thicknesses of 50 to 100 m or more” of Hodges, Muehlberger, and Ulrich (1973, p. 19), veneering an existing plain of Imbrium origin, would pose a lesser morphologic problem. Despite this unresolved diffi- culty, the general hypothesis of origin of the Cayley from large-basin impact processes faces fewer morphologic problems than any of the others discussed below and appears to be the most likely one at present. A plains facies of Orientale basin ejecta has been clearly identified around Orientale (Chao and others, 1975, p. 384), and such a facies most likely accom- panied Imbrium basin ejecta too. POSSIBLE EJECTA DRAINAGE FEATURES Several features in the area are consistent with a hypothesis of drainage of mobile ejecta from higher to lower ground. Mantling of a crater 5.5—7 km in diame- ter at V (figs. 3 and 5) by the highlands material indi- cates that the crater predates part or all of the Im- brium ejecta. The crater is mapped as containing a “puddle” of Cayley 3.5 km in diameter whose saucer- shaped surface has a relief of about 100 m and is at about the same elevation as the Cayley plain 4 km to the south. Unlike the many craters less than 3 km in diameter, this crater was large enough to accumulate its own pool of mappable Cayley. The topographic sag in the highlands east of the Apollo 16 site contains many relatively young craters, including some Copernican secondaries; the surface be- tween them has a smooth Cayley-like texture, particu- larly in the west part of the sag, and an undulating topography. Various maps of the area (for example, fig. 3; Milton, 1972; Hodges, 1972a; Elston and others, 1972b) have put the contact between Cayley plains and Descartes mountains at approximately the same place, where undulations not characteristic of Cayley become conspicuous. Chains of Imbrium secondary craters occur immediately to the north and south and must LANDSCAPE OF THE DESCARTES REGION have continued across the sag but are now absent from an area 4—5 km wide. The drainage of mobile ejecta into the sag from slopes no more than a few kilometers long may have obscured any Imbrium secondary cra- ters once present but did not sufficiently conceal the rest of the surface to make it mappable as Cayley. The general absence of Imbrium secondary craters on the lower slopes of the mountains, along the contact with Cayley, may also be the result of ejecta drainage from mountains toward plains. The small plateau on the west side of the trough at F (fig. 3) has very low relief, comparable to much of the Cayley, but a less regular texture, and is clearly part of the mountains rather than the Cayley plains. The slopes draining to this plateau were evidently of too small extent for a recognizable amount of Cayley—type material to accumulate on the plateau. OTHER HYPOTHESES OF ORIGIN OF CAYLEY PLAINS ' Another hypothesis of origin of the Cayley Forma— tion suggests that the plains materials gradually “were emplaced as ejecta of secondary craters made by impact of fragments ejected from many distant craters and basins and as a result. of deposition and secondary cra- tering by material ejected from nearby highland pri- mary craters” (Oberbeck and others, 1974a, p. 112; see also Oberbeck and others, 1975). Like the multiring— basin ejecta hypothesis, this hypothesis is constrained by the difficulty that ejecta fall on highlands and low- lands alike. Secondary ejecta, furthermore, is likelier to contain smaller proportions of impact melt and finely crushed material than is the ejecta of multiring basins and therefore to be less mobile and less capable of draining off highlands onto plains. The primary and secondary craters in the region that are younger than the Imbrium secondary craters of the Descartes mountains seem too few and too small‘to produce the plains by this process, but that aspect deserves quan— titative study. For the concentration of material in low- lands, this hypothesis appears to rely mainly on the gravity descent of material loosened by impact on cra- ter rims and on landslides. These processes are not likely to be adequate for deposition of plains material in an extensive lowland such as that at the Apollo 16 site, where: much of the highland margin is rather gently sloping; there is little evidence of landsliding, as discussed above; and some of the higher parts of the plains surface (as at the leftedge of fig. 5') occur around isolated peaks that could not supply enough material to build up those parts. It seems likely that colluviation from the side walls of depressions smaller than that at V (figs. 3 and5) may actually encroach on and eventu- 195 ally conceal tiny puddles of Cayley fill, thereby produc- ing a lower limit of area of mappable Cayley. Cratering (both primary and secondary) on the Cayley itself probably maintains some relief rather than act as an agent of smoothing. Crater fallback material as a source of Cayley was emphasized by Head (1974, p. 91), who stated that “Cayley plains in the Apollo 16 landing site area prob- ably owe much of their original smoothness to the rela- tively smooth fallback deposits formed during the un- named crater B events.” Distinctive Descartes mountains materials, however, drape the rim of this crater and descend into it, disappearing beneath the Cayley fill. Thus the crater is older than the Descartes mountains mass, which therefore covers any fallback material of the crater. A “liquefaction” hypothesis for the origin of both Cayley plains and maria has been proposed by Bastin (1974), who suggested that at times of high near- surface temperatures, low areas on the Moon’s surface, though not liquid, had a sufficiently low viscosity for the surfaces to relax more or less completely, becoming level. The relations in this area where the Cayley ma- terials bury and lap up onto the margins of the mountains clearly do not fit that hypothesis. CONCLUSIONS From study of the morphologic features of the Des- cartes region, the following conclusions can be drawn: 1. The lineated terrain types of the Descartes mountains include both erosional (secondary crater- ing) and probably depositional features (ridges). 2. The trends of these forms show that they origi- nated in the direction of the Imbrium basin. 3. The congruence between the terrain features and the overall shape of the Descartes mountains supports the hypothesis that the mass as a whole is a tongue of Imbrium basin ejecta. 4. The morphology of the crosslineated part of the mountains is in agreement with the hypothesis that some of the ejecta that crossed this area had been de- flected southwestward from the west side of the Kant plateau. 5. A few isolated mountains are interpreted as pro- jecting blocks of older materials, probably including Nectaris basin ejecta. 6. The generally very smooth surface of the Cayley plains indicates high mobility of the plains-forming materials at the time of their deposition. 7. The Descartes mountains materials and morphology descend beneath and are buried by Cayley plains materials, which, at the Apollo 16 site, occupy a 196 GEOLOGY OF THE APOLLO 16 AREA, CENTRAL LUNAR HIGHLANDS depression that may be a pre-Imbrium crater mantled The principal question faced by this hypothesis is by Imbrium ejecta. whether such ejecta could drain freely from highlands 8. The hypothesis of deposition of the Cayley fill as to plains and whether that process would have relatively mobile ejecta from one or more multiring obscured the Imbrium terrain features to a greater de- basins seems more consistent with the morphology of gree than is apparent. There is some evidence of such the area than does any other hypothesis. drainage producing local crater filling. J. STRATIGRAPHIC INTERPRETATIONS AT THE APOLLO 16 SITE By GEORGE E. ULRICH and V. STEPHEN REED CONTENTS Page Introduction __________________________________________________________________________ 197 Stratigraphic framework ______________________________________________________________ 198 Regolith ____________________________________________________________________________ 199 Classification of materials ____________________________________________________________ 199 Local evidence for stratigraphic sequence ______________________________________________ 200 North Ray crater ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 203 South and Baby Ray craters ______________________________________________________ 204 Regional evidence for stratigraphic sequence ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 205 Stratigraphy of the mountains ________________________________________________________ 207 Summary of previous stratigraphic interpretations ______________________________________ 209 Conclusions ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 213 Acknowledgments ____________________________________________________________________ 214 ILLUSTRATIONS Page FIGURE 1. Photographs of light-matrix breccia on rim crest of North Ray crater ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 199 2. Photographs of dark-matrix breccia boulder at station 8 _________________________________________________________ 201 3. Photographs of white angular boulder at station 8 and sample 68415 and photomicrograph of 68415 _________________ 202 4. Schematic cross section showing the southeastern wall and floor of North Ray crater _______________________________ 203 5. Cross sections of terrestrial and lunar impact craters ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 204 6. Schematic cross section through South Ray crater _______________________________________________________________ 205 7. Partial panoramas and sketch maps showing block populations and ejecta patterns of South Ray and Baby Ray craters ___________________________________________________________________________________________________ 206 8. Photomap of the Apollo 16 region showing kilometer-size craters with and without floor mounds _____________________ 208 9. Photographs of the Descartes highlands and crater Dollond E _____________________________________________________ 209 10— 16. Cross sections: 10. North and South craters from AFGIT ( 1973) ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 210 11. North Ray crater from Hodges and others (1973) ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 211 12. North Ray crater from Ulrich (1973) ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 211 13. North Ray and South Ray craters from Delano and others (1973) ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 212 14. Schematic stratigraphy of the landing site from Taylor and others (1973) _________________________________ 212 15. Cross section of the landing site modified from Head (1974) _______________________________________________ 213 16. Geologic cross section proposed in this paper for the Apollo 16 traverse area _______________________________ 214 TABLE Page TABLE 1. Physical parameters (in meters) of craters with floor mounds within the Apollo 16 area ,,,,,,,,,,,,,,,, , ____________ 207 . INTRODUCTION “The geologist *** has been forced to rely almost ex- clusively upon the accidental exposure of underlying formations by uplift and erosion. Hardly a geologic . map exists which does not depend upon assumptions about) invisible rocks, many of which might be verified :or disproved by drilling. <