University of Southern California Dissertations and Theses

Stratigraphy, sedimentology and vertebrate ichnology of the Copper Canyon Formation (Neogene), Death Valley National Monument

(USC Thesis Other)

Stratigraphy, sedimentology and vertebrate ichnology of the Copper Canyon Formation (Neogene), Death Valley National Monument

PDF

Download

Open document

Flip pages

Download a page range

Download transcript

Copy asset link

Request this asset

Transcript (if available)

Content STRATIGRAPHY, SEDIMENTQLQGY A N D VERTEBRATE ICHNOLOGY O F THE CO PPER C A N YO N FORMATION (NEOGENE), DEATH VALLEY NATIONAL M O NUM ENT by Paul Joseph Scrivner A Thesis Presented to the FACULTY O F THE G RADUATE SCH O O L UNIVERSITY O F SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree M ASTER O F SCIENCE (Geological Sciences) May 1984 UMI Number: EP58739 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. Dissertation Pbbnshmg UMI EP58739 Published by ProQuest LLC (2014). Copyright in the Dissertation held by the Author. Microform Edition © ProQuest LLC. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106- 1346 UNIVERSITY OF SOUTHERN CALIFORNIA THE GRADUATE SCHOOL UNIVERSITY PARK LOS ANGELES. CALIFORNIA 90 0 0 7 This thesis, written by .............. P A U L..JO S .^ H ..S C R 3X N E R ............................................... under the direction of hkP.....Thesis Committee, and approved by a ll its members, has been pre sented to and accepted by the Dean of The Graduate School, in partial fulfillm ent of the requirements fo r the degree of MASTER OF S C IE N C E Dean Date-.L^PT.^.y... A Z. i . -1 . . 9 . . §f i ..... TH COMMITTEE itrmi ABSTRACT The sedimentology, stratigraphy and vertebrate ichnology of the Copper Canyon Formation (Neogene) in Death Valley National Monument has been studied with the object of reconstructing its depositional environments and relating these to the preservation of its rich fauna of vertebrate tracks. The formation was deposited when block faulting and synclinal folding in the late Tertiary created a small basin in which over 3,000 meters of alluvial fan and lacustrine sediments were accumulated. The formation is divided into two members -a dominant conglomerate member and a subordinate carbonate one. Their respective environments of deposition were large alluvial fans which surrounded and graded laterally into fine-grained sediments which accumulated in a lake in the center of the basin. Debris-flow deposits dominated the proximal fan facies, while braided stream deposition characterized the medial and upper distal fan facies. The finest grained clastic sediments were deposited in the distal fan facies by sheet floods. Two distinct lithofacies are recognized within the lacustrine carbonate member. Fine-grained dolomitic carbonate and gypsum strata make up most of the carbonate member and are called the evaporite facies. The environment of deposition is interpreted to be a shallow playa-lake in which large carbonate m ud flats surrounded a small, central salt pan containing mostly gypsum. Numerous cycles of basin flooding, lake evaporation and evaporite i i mineral precipitation gave rise to the thick section of evaporite lithologies. The uppermost carbonate member, termed the bioclastic carbonate facies, consists of ca lcitic bioclastic carbonate strata which were deposited in a freshwater lake environment. The change between playa-lake and freshwater-1ake environments of deposition probably resulted from a combination of increased annual precipitation, lower annual temperatures, and possibly the development of an outlet in the basin. The carbonate mudflats of the evaporite facies served to record the footprints of a large variety and number of mammals and birds. An analysis of track abundance shows that artiodactyls most commonly frequented the playa-lake environment; birds, horses, carnivores and proboscideans were less abundant. Using the vertebrate footprint classification scheme of Vialov (1966), four different mammalian ichno-orders containing four ichnogenera and ten ichnospecies are recognized. Six ichnospecies of avian tracks are also recognized. The identification of the footprints is fa c ilita te d through comparison of the Copper Canyon tracks with those described from other Cenozoic deposits and from a study of both recent and ancient vertebrate hoof and foot structures. A survey of the available literature on Cenozoic vertebrate tracks indicates that a lacustrine shoreline environment provides one of the best environments for preservation of footprints. The association of the Copper Canyon vertebrate ichnofauna with mudcracks, raindrop impressions and in-place fossil reeds suggests that most of the preserved tracks were emplaced in playa-lake shoreline environments. The morphological distinctness of the tracks is best preserved in fine-grained dolomitic carbonate and siltstone strata. Distinctness of preserved tracks also increases with apparent decrease, within a certain range, of sediment water content at the time of impression. The combined effects of grain size and sediment water content act to produce a wide range of track morphologies for each individual trackmaker. The sedimentological and environmental factors of the ancient Copper Canyon playa-lake which contributed to good footprint preservation include the fine grain size of the sediments which accumulated in the playa, the relationship of the shoreline to the sediment surfaces involved in track formation, the opportunities for sub-aerial exposure and subsequent drying of the track-impressed surfaces, and the presence of sediment accumulation rates sufficiently high to insure quick burial of the tracks. The existence of the temporary lake attracted animals seeking water and food to wander across the mudflats. The tracks in the Copper Canyon Formation reflect part of the wide diversity of vertebrates present in southern California during the HemphiIlian. ACKNOW LEDGMENTS I am deeply appreciative of the people who had the time and patience to assist m e in this study. M y advisor, Dr. David Bottjer, encouraged further work on the vertebrate tracks after n \y in itia l contact with them and provided intellectual and mpral support when needed most. M y other committee members, Drs. David Whistler and Donn Gorsline, also provided guidance and c ritic a lly reviewed the final thesis manuscript. Drs. Lawford Anderson and Warren Thomas and Mr. Tom Hoisch helped in thin-section mineral identification and in the use of the X-ray diffractometer. Dr. Raymond Alf of the W ebb School for Boys provided m e with a thin section of the dolomitic carbonate stratum containing the Proboscidean trackway. Special thanks are due to the people who provided translations of som e of the foreign track literature: to Joceline Boucher for French, Victor Santos for Spanish, Sonya Saruba for Russian and Dr. Warren Thomas for German. M y office colleagues Jim Browning, Steve Buck and Gene Enzweiler, provided humor when needed most and also indulged m e in fru itfu l conversations on geology and allied subjects. Pam Tartaglio provided consultation on sedimentological subjects. The rangers and naturalists of the National Park Service in Death Valley National Monument provided m e the utmost assistance in obtaining permission to do fieldwork in Copper Canyon and in allowing m e to use their track collection and library. Pete Sanchez expedited obtaining entrance and collection permits by wholeheartedly supporting m y research. Appreciation is also extended to Larry Norris, Ranger-Naturalist, and his wife Nancy, who fir s t introduced m e to Copper Canyon, and showed m e extraordinary hospitality and kindness during n jy visits to the valley. Funding for this thesis was provided by grants from the Death Valley Natural History Association, the U.S.C. Department of Geological Sciences Graduate Research Fund and the Society of the Sigma Xi. M y thanks also go to Susan Turnbow for patiently typing this thesis. vi TABLE O F CONTENTS Page ABSTRACT...................................................................................................... 11 ACKNOW LEDGMENTS............................................. v LIST O F FIGURES........................................................................................ x LIST O F TABLES............................ f LIST O F PLATES Xyi i PURPOSE................................. 1 M ETHO DS O F INVESTIGATION..................................................................... 1 I. STRATIGRAPHY A N D SEDIMENTOLOGY O F THE CO PPER C A N YO N FORMATION....................................... 4 INTRODUCTION.................................................................................... 5 EVAPORITES............................... 16 Dolomitic Carbonates......................................................... 16 Interpretation................................................................ 38 Gypsum....................................... 46 Interpretation..................................................................... 49 BIOGENIC CARBONATES..................................................................... 51 Bioclastic Carbonates....................................................... 52 Interpretation..................................................................... 74 CLASTICS............................................................................................ 78 Pebble-Cobble Conglomerate............................................ 78 Interpretation..................................................................... 81 Granule-Pebble Conglomerate....................................... 84 Interpretation..................................................................... 87 Sandstone........................................... 89 Interpretation..................................................................... 94 v ii Page Siltstone.................................................................................. 96 Interpretation....................................................................... 102 Cl ay stone.................................................................................. 104 In te rp reta tio n .,................................................................... 105 IGNEOUS ROCKS.................................................................................... 107 V itric Tu ff.......................................................... 107 Interpretation....................................................................... 108 Basalt................ 110 Interpretation....................................................................... I l l PROVENANCE ............................................................................. 115 GEOLOGIC A N D DEPOSITIONAL HISTORY.......................................... 118 AGE........................ 133 I I . VERTEBRATE ICHNOLOGY O F THE CO PPER C ANYO N FORMATION... 137 INTRODUCTION........................................... 138 SYSTEMATIC ICHNOLOGY - M A M M A L IPEDIA......................................... 152 Artiodactipedida................................................................... 152 Discussion...................... 170 Perissodactipedida............................................................... 173 Discussion................................................................................ 180 Carni voripedida..................................................................... 181 Discussion................................................................................ 186 Proboscipedida....................................................................... 187 Discussion.................................................................... 187 SYSTEMATIC ICHNOLOGY - AVIPEDIA................................................. 191 vi i i Page Discussion.............................................................................. 207 STRATIGRAPHIC A N D LITHOLOGIC SETTING O F TRACKS... 208 ENVIRONMENTAL FACTORS AFFECTING TRACK PRESERVATION... 214 RATE O F TRAMPLING A N D RATE O F BURIAL.................................. 278 ENVIRONMENTS O F TRACK PRESERVATION...................................... 283 PALEOECOLOGY.................................................................................... 292 SU M M A R Y A N D CONCLUSIONS............................................................ 295 REFERENCES........................................................................... ....................... 297 APPENDIX A: Summary of thin-section data from major lithologies in the Carbonate Member..................... 307 APPENDIX B: Geologic and section location map, detailed strati graphic sections................................... 313 PLATES (in m ap packet) ix LIST O F FIGURES Figure Page 1. Map showing location of the Copper Canyon Formation.... 6 2. Photograph showing the southern edge of the formation.. 10 3. Photograph showing the lower and middle evaporite facies of the carbonate member of the formation............... 12 4. Photograph of the upper part of the carbonate member at the top of the formation...................... 14 5. Outcrop photo of dolomitic carbonate strata typical of the evaporite facies.......................................................... 17 6. Photograph showing in-place fossil reeds in dolomitic carbonate......................................................................... 20 7. Photograph of disturbed bedding typical of the dolomitic carbonates in the evaporite f a c i e s . . . . . . 22 8. Photograph of large burrows on the bottom of a dolomitic carbonate bed in the evaporite facies............... 25 9. Photograph of small, tube-shaped burrows in a dolomitic carbonate laminae......................................................... 27 10. Photograph showing groove marks on a dolomitic carbonate surface.............................................................................. 29 11. Photomicrograph of a dolomitic mudstone showing planar micro-laminations.............................................................................. 31 x LIST O F FIGURES (Continued) Figure Page 12. Photomicrograph of a dolomitic wackestone showing presence of the unidentifiable allochem present in many of the carbonates in the evaporite facies............................... 34 13. Photomicrograph of dolomitic packstone..................................... 36 14. Photograph of disturbed gypsum strata in the lower evaporite facies............................................................ 47 15. Outcrop photograph looking out across the upper evaporite facies and the bioclastic carbonate fa c ie s ... 52 16. Photograph showing close-up of bioclastic carbonate strata................................................................................ 54 17. Photograph of a bioclastic carbonate surface with polygonal cracks..................................................................... 57 18. Photograph of a bioclastic carbonate covered wi th bowl-shaped mounds................................................................. 59 19. Close-up photograph of two bioclastic carbonate mounds.................. 61 20. Close-up photograph of bedding surface beneath one of the carbonate mounds......................................................... 64 21. Photomicrograph of bioclastic packstone showing peloids cemented together by chalcedony................................ 67 22. Photomicrograph of bioclastic packstone showing thin-walled, articulated ostracod shell in fille d with chalcedony................................................ ................................. 69 xi LIST O F FIGURES (Continued) Figure Page 23. Photomicrograph of bioclastic wackestone............................... 72 24. Photomicrograph of a typical sandstone from the formation.......................................................... 91 25. Photomicrograph of dolomitic siltstone................................... 97 26. Photomicrograph of jarosite-rich s ilts to n e ......................... 100 27. Photomicrograph of basalt showing z e o lite -fille d amygdule and plagioclase laths.................................................. 112 28. Photograph showing isolated playa-lake deposit within the conglomerate member.................. 123 29. Schematic block diagram of a playa-lake complex, modified from Eugster and Hardie (1975).......... 130 30. Photograph showing impressions of Pecoripeda (Ovipeda) sp. A.................................................................................. 153 31. Photograph showing casts of Pecoripeda (Ovipeda) sp. A...................................................................................................... 155 32. Photograph showing impressions of Pecoripeda (Ovipeda) sp. B.................................................................................. 157 33. Photograph showing cast of Pecoripeda (Ovipeda) sp. B....................................................................................................... 159 34. Photograph showing casts of Pecoripeda sp. C and Pecoripeda (Ovipeda) sp. B.................................................. 161 35. Photograph showing impression of Pecoripeda sp. C 164 x ii LIST O F FIGURES (Continued) Figure Page 36. Photograph showing cast of Pecoripeda sp. D......................... 166 37. Photograph showing cast of Pecoripeda sp. D......................... 168 38. Photograph showing impressions of Hippipeda sp. A 174 39. Photograph showing impressions of Hippipeda sp. B . 176 40. Photograph showing impressions of Hippipeda sp. C 178 41. Photograph showing cast of Bestiopeda (Felipeda) sp. A....................................................................................................... 182 42. Photograph showing cast of Bestiopeda (Felipeda) S£. B................... .................. ...................... .. ...................................... 184 43. Photograph showing proboscidean trackway............................... 188 44. Photograph showing cast of Avipeda sp. A............................... 192 45. Photograph showing impressions of Avipeda sp. B................ 194 46. Photograph showing casts of Avipeda sp. C . . . . . .................. 196 47. Photograph showing impressions of Avipeda sp. D................ 199 48. Photograph showing casts of Avipeda sp. E............................. 201 49. Photograph showing impression of Avipeda sp. F................... 203 50. Photograph showing impressions of Avipeda sp. F................ 205 51. Photograph showing artiodactyl hoofprint p a rtially fille d by granule-pebble conglomerate.................................... 210 52. Photograph of gypsum cast of artiodactyl hoofprint.............................................................................................. 212 53. Photograph showing trackways, probably of invertebrate origin, in dolomitic carbonate mudstone......................................................................... ...................... 216 x ii i LIST O F FIGURES (Continued) Figure Page 54. Schematic diagram showing the relationship of grain size and sediment water content to vertebrate track preservation, from Laporte and Behrensmeyer (1980).............................................. . ................... 219 55. Photograph of deep (greater than 2 cm), well-preserved, artiodactyl hoof impression............................ 225 56. Photograph showing two deep (around 2 cm in depth) artiodactyl tracks formed in recent m ud around Crater Lake in the Maroon Wilderness, Colorado................................................................................................... 227 57. Photograph of surface of dolomitic carbonate bed showing an artiodactyl track with a continuous raised rim, cat tracks and raindrop impressions............................................................ 230 58. Photograph of two artiodactyl hoof impressions surrounded by bedding surface which has been arched slightly upward...................................................................... 232 59. Photograph of an artiodactyl hoof impression surrounded by bedding surface which has been arched strongly upward...................................................................... 234 60. Photograph showng close-up of squeelch mark.......................... 237 61. Photograph of track-congested dolomitic carbonate surface consisting mostly of squeelch marks.......................... 240 xi v LIST O F FIGURES (Continued) Figure Page 62. Photograph of dolomitic carbonate surface containing artiodactyl impressions formed i n st 1 cky and moi st mud................... . ...................................... 242 63. Photograph showing artiodactyl hoof impression formed somewhere between gooey and sticky sediment conditions......................................................................... 244 64. Photograph showing presence of subtle interdigital ridge in artiodactyl hoof im pression................................... 246 65. Photograph showing presence of interdigital ridge in shallow artiodactyl hoof impressions................................ 248 66. Photograph showing artiodactyl hoof impression formed in sediment with a water content between gooey and sticky conditions........................................ 251 67. Photograph showing an artiodactyl track impression formed in sticky mud....................................................................... 253 68. Photograph of dolomitic carbonate surface showing artiodactyl impressions formed in sticky, moist, and hardening sediment................................................................. 256 69. Photograph of artiodactyl impression formed in hardening sediment......................................................................... 258 70. Photograph of artiodactyl impression formed in hardening sediment with crinkled edges on one side.......................................................................................... 260 xv LIST O F FIGURES (Continued) Figure Page 71. Photograph of bird tracks formed in gooey mud.................. 264 72. Photograph of bird tracks formed in sticky mud.................. 267 73. Photograph of dolomitic carbonate surface containing artiodactyl and carnivore impressions formed in gooey mud.......................................................................... 269 74. Photograph showing horse tracks formed under sticky and moist sediment conditions..................................................... 272 75. Photograph showing horse tracks formed under moist and hardening sediment conditions............................................ 274 76. Schematic diagram showing relationship between rate of trampling and rate of burial and their effects on vertebrate track preservation, from Laporte and Behrensmeyer (1980)................................................ 279 xvi TABLE Page 1. Annotated references from Cenozoic vertebrate track lite ra tu re .................................................................. 139 LIST O F PLATES (in back pocket) 1. Generalized sections for bottom half of the Copper Canyon Formation. 2. Generalized sections for top half of the Copper Canyon Formation. xvi i PURPO SE Although a large number of papers on vertebrate footprints have accumulated since the mid-1800's, m uch of this literatu re has been concerned only with the morphological description of tracks. Generally absent are detailed analyses of the environmental settings of the lithologies containing track impressions and the sedimentologic variables controlling their preservation. The purpose of this study is twofold. The fir s t is to provide an environmental analysis of the lithologies in the Copper Canyon Formation. The second part of this study is concerned with the analysis of the mammalian and avian tracks preserved in the fine-grained lithologies of the formation. This includes the sedimentological and environmental factors affecting th eir preservation and influencing th eir morphology. Lastly, the paleoecology of the vertebrates leaving track impressions is interpreted based on a combined analysis of their tracks and the lithofacies they are preserved in. M ETHODS O F INVESTIGATION Field work for this study was completed during February-May, 1981 and during the month of March 1982. This consisted of measuring stratigraphic sections, obtaining rock samples and measuring and photographing vertebrate footprints. Four generalized sectons were measured from the bottom to the top of the Copper Canyon Formation (Plates 1 and 2) as well as nine detailed 1 sections in the major lithofacies above the last basalt lens (Appendix B). For the generalized sections, thicknesses were determined from a geologic m ap of the area (Drewes, 1963) when actual fie ld measurements were impossible due to rough terrain . Samples of the different lithologies in this formation were obtained while detailed sections were being measured. Samples of lithologies preserving vertebrate track impressions were also collected. Petrographic analysis of rock samples was performed by visually estimating the types and percentage abundances of grains and matrix components in each thin section. X-ray diffraction analysis was used primarily to identify mineral constituents too fine-grained for optical identification alone. The data were tabulated (Appendix A) and used to classify these rocks using the Dunham (1962) and Folk (1962) classifications for carbonate rocks and the Folk (1974) classification for clastic lithologies. A potassium-argon age determination was obtained for a basalt sample taken from the youngest basalt lens in the format/ion, from Drewes1 location number 19 (Drewes, 1963, see geologic map, Appendix B). A block of basalt was hammered from outcrop and sawed ! to obtain a fresh, unweathered sample from its center. The Geochron Laboratories Division of Krueger Enterprises, Inc. in Cambridge, Massachusetts, performed the age analysis on the sample (Geochron Laboratories sample no. R-5967) in November, 1981. Measurements of the maximum width and length of well-preserved | vertebrate tracks were made. Other measurements included depth of 2 impression and the thickness of the stratum of impression. Photographs were taken of the different varieties and preservational types of tracks. In order to relate this study to other published accounts of footprints, a survey of the available lite ra tu re on Cenozoic mammalian and avian tracks was also undertaken. I.- STRATIGRAPHY A N D SEDIMENTOLOGY O F THE COPPER C A N YO N FORMATION 4 INTRODUCTION The Copper Canyon Formation is located in Copper Canyon in the Black Mountains, Death Valley National Monument (Fig. 1). The formation was fir s t informally referred to as the Copper Canyon beds by Curry (1941). These beds were later given the formal nam e Copper Canyon Formation by Drewes (1963). The best exposures of the formation occur in Copper Canyon, the type location suggested by Drewes, with the total lateral extent of the outcrops underlying a rectangular area of about five square miles. The formation occurs in an embayment which extends about three miles into the Black Mountain range front and forms a topographic low along that front. The embayment is bounded on the southeast by a low-angle northwesterly dipping fa u lt, on the east by high-angle normal faults and on the north and northwest by other faults and a southeast-tilted depositional contact (Otton, 1977). The formation is folded into a series of northwest trending anticlines and synclines, with the thickest deposits of fine-grained rocks occurring along the axis of the largest syncline in the northern part of the formation (see geologic map, Appendix B). The Copper Canyon Formation unconformably overlies Drewes' "older volcanics," consisting of shallow intrusive and extrusive volcanic rocks. The older volcanics, in turn, unconformably overlie lower Tertiary monzonitic rocks and limestones, dolomites Fig. 1. Map showing location of the Copper Canyon Formation (modified from Drewes» 1963). 6 : i : . ‘V ■ < • < /■ V, • ■ » ^ ■ : " • < r ■ ■ ■ }> -}-'*■ • - '• ; ■ > « ^ ^ • i? ! \ ' " V > « 50 M l" s l.n n r I’im s? 0 '. * £ % ; y<y > S \ - / L a s V i'p a s ^ -%<§>• a rh s !.• NKVADA Vr Av'nw^tj X^V'J 3 ■ H i i k i T , d'l • ’ i tj /, f i ' t ' i.SWd lj S L ’S » X 5 *->. .s Arra of ilinvrm n ."v V - Rnrslnu INDEX MAP and quartzites of the Paleozoic Pogonip and Noonday Formations. The top of the Copper Canyon Formation is in unconformable contact with the conglomerates of the lower member of the Plio-Pleistocene Mormon Point Formation, as defined by Otton (1977). The thickness of the formation is highly variable (Drewes, 1963). Along the axis of the largest syncline, i t is approximately 7,000 feet thick, thinning appreciably towards the northern and southern ends of the basin. I t is at least 10,000 feet thick toward the southwest where the basal part is incompletely exposed, probably occurring in the downdropped block of the Death Valley graben. Drewes (1963) divided the Copper Canyon Formation into two members: a dominant conglomerate member and a subordinate siltstone and evaporite member. The conglomerate member forms most of the lower part and some of the middle and upper parts of the formation, representing about 70% of the formation as a whole. The conglomerate member intertongues la te ra lly with Drewes' siltstone and evaporite member that forms the remainder of the middle and upper parts of the formation. Based on petrographic and X-ray diffraction analysis of the lithologies in Drewes' siltstone and evaporite member, the member m ay be renamed and broken down into two distinctive lithofacies. The lower and middle parts of Drewes' member consist predominantly of dolomitic carbonates and gypsum formed as precipitation products in the ancient Copper Canyon lake. This thick section of rocks is 8 called the evaporite facies (see Plates 1 and 2). Conformably overlying this facies are mostly c a lc itic bioclastic carbonates, which are defined as forming the bioclastic carbonate facies (see Plates 1 and 2). Since Drewes' siltstone and evaporite member consists mostly of carbonate rock, it is called the carbonate member of the Copper Canyon Formation. The dominant conglomerate member (Fig. 2). consists primarily of red pebble to cobble conglomerate. The carbonate member (Figs. 3, 4) consists, in order of greatest to least occurrence, of dolomitic carbonate, bioclastic carbonate, sandstone, siltstone, v itric tu ff, granule-pebble conglomerate, pebble-cobble conglomerate, gypsum and claystone. Lenses of basalt occur within the lower parts of the evaporite facies. The sedimentology and environments of deposition of the lithologies occurring in the Copper Canyon Formation are discussed in the sections that follow. 9 Fig. 2. Photograph showing the southern edge of the formation. The dolomitic carbonate strata of the evaporite facies in the foreground are enclosed by and interfinger la te ra lly with the red conglomerate member in the background. The gray to green rock in the right side of the photograph is the last basalt lens in the evaporite facies. Death valley and the Panamint Mountains are in the far background. 10 M 11 Fig. 3. Photograph showing the lower and middle evaporite facies of the carbonate member of the formation. Note the presence of the basalt lens (the dark gray to green rock) which extends into the con glomerate member from the left side of the photograph. 12 13 Fig. 4. Photograph of the upper part of the carbonate member at the top of the formation. The pinkish-gray rock overlying the light-colored limestones of the carbonate member of the Copper Canyon Formation is part of the conglomerate unit of the Mormon Point Formation. 14 EVAPORITES Do!omitic Carbonates The dolomitic carbonates occur almost entirely in the evaporite facies of the formation where they account for approximately 80% of the lithologies present (Plates 1 and 2). The evaporite facies (Fig. 5) makes up most of the carbonate member and consists primarily of dolomitic carbonate rocks devoid of biologically produced allochems. A few thin beds also occur within the bioclastic carbonate facies. The dolomitic carbonates exist as laminae only a few millimeters thick to beds up to 23 centimeters in thickness. The rock almost always occurs in bedded form with occasional intervening strata of siltstone, sandstone and rarely granule-pebble conglomerate. The dolomitic carbonate strata are laterally continuous across the carbonate member except in the lower and central sections of the evaporite facies where they enclose and grade laterally into gypsum strata. The dolomitic carbonate also grades laterally into terrigenous clastic strata near the contact between the evaporite facies and the conglomerate member of the formation. The rock is typically pale greenish-yellow (10Y 8/2), pale yellowish brown (10YR 6/2), and yellowish gray (5Y 7/2) fresh and light brown (5YR 6/4) to moderately yellowish brown (10YR 5/4) weathered, moderately to well-indurated and cliff-forming. Less commonly, and only near the top of the evaporite facies, the dolomitic carbonate appears pale red (5R 6/2) to pale reddish 16 Fig. 5. Outcrop photo of dolomitic carbonate strata typical of the evaporite facies. This is locally known as carnivore ridge because of the cat tracks and large number of artio- dactyl tracks found there. The green bush in the foreground is approximately one-half meter high. 17 18 brown (10R 5/4) fresh and weathered. The only fossil material found in the dolomitic carbonate is in-place reeds (Fig, 6). Preservation is poor, making further identification impossible. Bedding in the dolomitic carbonates is generally even and parallel, but some strata are slightly contorted into small folds (Fig. 7) and rarely convoluted. The disturbed beds sometime occur immediately above undeformed carbonate strata with some of the folds in the disturbed beds showing truncation at their contact with the undeformed beds below. Planar and very low angle cross-stratification is sometimes evident within both the disturbed and undisturbed beds in outcrop. The sedimentary structures within the dolomitic carbonate beds are best seen in thin section. Mica flakes and heavy mineral grains define planar micro-laminations and low-angle cross-bedding. Convoluted micro-laminae and erosional surfaces are highlighted by limonite and hematite staining. Grading is often evident in those carbonates with a significant percentage of clastic material, with fine sand and silt-sized clasts fining upward into pure carbonate mudstone. Even though most of the dolomitic carbonate bedding surfaces are smooth, a wide variety of surface markings exist. Vertebrate tracks are the most com m on surface feature. The tracks include, in order of greatest to least abundance, those of artiodactyls, birds, equids, felids and a proboscidean. Horizontal branching burrows 19 Fig. 6. Photograph of in-place fossil reeds in dolomitic carbonate from Carnivore Ridge Sample approximately 8 cm high. 20 21 Fig. 7. Photograph of disturbed bedding typical of the dolomitic carbonates in the evaporite facies. Planar laminations are faintly visible in some of the strata. The ruler is 15 cm long. 22 23 up to several centimeters wide and a meter long also occur (Fig. 8). Tube-like burrows, 6 m m or less in diameter and up to several centimeters long, occur both parallel to bedding and sometimes show abrupt vertical penetration into the dolomitic carbonate strata (Fig. 9). The tube-like burrows are fille d with fine, calcareous siltstone typically light gray in color. Both types of burrows are rare in the dolomitic carbonate. The most com m on non-biogenic surface features are raindrop impressions, m ud cracks and ripple marks. Runzel marks, consisting of small ridges less that 1 m m thick and several centimeters long, also texture some of the dolomitic carbonate surfaces. Groove, prod and flute marks also exist. Groove marks are the most commonly occurring of these, consisting of three closely spaced parallel ridges ranging in length from 1 to 10 cm (Fig. 10). The dolomitic carbonates occur as mudstones, wackestones and packstones. The dolomitic carbonate mudstones have a dolomitic micrite matrix abundance ranging approximately from 73% to 95% (Fig. 11). Minor amounts of clay occur dispersed in the matrix. Sparry calcite is sometime present in small patches within the micrite matrix but never exceeds approximately 2% of the matrix material. The matrix is lightly to heavily stained by limonite or hematite, and sometimes a combination of both. Allochems within the mudstone are rare and are mostly an unidentifiable variety to be described below. Total allochem abundance in the mudstones ranges from approximately 0% to 2%. Terrigenous clastic material, 24 Fig. 8. Photograph of large burrows on the bottom of a dolomitic carbonate bed in the evaporite facies. The knife is 9 cm long. 25 26 Fig. 9. Photograph of a small, tube-shaped burrow in a dolomitic carbonate laminae. The burrow has been in fille d with fine, calcareous siltstone. Note the abrupt vertical penetration of the burrow into the laminae. The quarter is 2.2 cm across. 27 28 Fig. 10. Photograph of groove mark in a dolomitic carbonate lamina overlying a granule conglomerate. The groove mark consists of three closely spaced parallel ridges. In this example, the grooves between the ridges extend into the conglomerate beneath the dolomitic carbonate laminae. The quarter is 2.2 cm across. 29 30 Fig. 11. Photomicrograph of a dolomitic mudstone showing planar micro-laminations. 31 mostly angular to sub-rounded, elongate quartz and feldspar grains, ranges in visual estimates from less than 1% to 21%. The clasts are s ilt to fine-sand in size, with their long axes sometimes parallel to stratificatio n. Approximate accessory mineral composition includes less than 1% to 4% heavy minerals such as magnetite or hornblende, less than 1% to 3% biotite, chlorite and muscovite flakes and less than 1% microcrystal1ine epidote. The mica flakes are up to 1m m in length and are almost always oriented parallel to stratificatio n. The wackestones and packstones contain approximately 15% to 85% dolomitic micrite matrix (Figs. 12 and 13). The matrix is moderately to heavily stained by limonite and sometimes hematite. Allochems range in abundance from approximately 3% to 37% and consist almost exclusively of an unidentifiable type. The unidentifiable allochems are square to rectangular in shape and range in size from approximately 88 to 177 microns across their longest axis. They are made of crystalline carbonate and sometimes show polysynthetic twinning. Many show signs of abrasion due to transport. Intraclasts similar in size and composition to those in the mudstones never exceed approximately 2% total rock composition. The highest abundance of intraclasts occurs in the sample with the largest percentage of terrigenous clastic material. Terrigenous elastics, similar to those described for the mudstones, account for approximately 3% to 37% total rock composition. Accessory minerals, also similar to those described for the mudstones, make up less than 1% of the wackestones and packstones. 33 Fig. 12. Photomicrograph of a dolomitic wackestone showing presence of the unidentifiable allochem present in many of the carbonates in the evaporite facies. Note that most of the allochems appear abraded due to transport. One exception to this is the rhombohedral allochem in the lower le ft corner of the photograph. 34 35 Fig. 13. Photomicrograph of a dolomitic packstone containing large numbers of the unidentified allochems. Note the presence of polysynthetic twinning, comm on to sparry calcite and dolomite, in the allochem in the upper right hand of the photomicrograph. 36 Interpretat1 on The thick sequence of dolomitic carbonate is interpreted as having been deposited in a playa-lake mudflat environment. This is suggested by the relationship of the carbonate strata with other lithologies occurring in the evaporite facies, sedimentary structures, and the grain size and mode of formation of the carbonate. The occurrence of the dolomitic carbonate near the center of the formation enclosing and interfingering laterally with gypsum strata within the evaporite facies is strong evidence for origin of the dolomitic carbonate in a playa-lake environment. Many modern analogs similar to this relationship exist, of which one of the best studied is Deep Springs Lake, California (Eugster and Hardie, 1978). Deep Springs Lake contains a central salt pan, equivalent to the gypsum strata in the evaporite facies, surrounded by calcium-magnesium carbonate m ud fla ts . Saline Lake, another recent playa-lake in California, has a gypsum salt pan surrounded by muddy sediment flats (Hardie, et a l . , 1978). The relationship of the alluvial fan deposits with the evaporite facies is further indication of formation of the dolomitic carbonate in a lake in the center of a basin. Modern-day playa lakes are characterized by the accumulation of fine-grained sediments in the hydrologic, or lowest areas, of an enclosed basin usually surrounded by alluvial fans (Cooke and Warren, 1973). The evaporite facies interfingers with the pebble to cobble 38 conglomerate of the alluvial fans that fringed the ancient Copper Canyon Lake. The interfingering relationship between fine-grained playa sediments and coarser fan material is common to almost all modern day and ancient playa-lake systems as well (Motts, 1970; Picard and High, 1972). Sedimentary structures indicative of the playa-lake origin of the dolomitic carbonate also exist. The occurrence of invertebrate and vertebrate tracks and tra ils , raindrop imprints (Fig. 57) and mudcracks (Fig. 34) indicate that the flats were, at times, subaerially exposed. Modern day playa-lakes commonly have mudflats that are subaerially exposed due to shrinking shorelines caused by evaporating lake water, for at least part of the year (Hardie, et a l . , 1978). Invertebrate and vertebrate tracks and tra ils , raindrop imprints and mudcracks are often found in ancient shoreline lake deposits, as in part of the Green River Formation (Moussa, 1968; Curry, 1957). Mudcracks are also com mon features on recent playa-lake surfaces (Cooke and Warren, 1973). The runzel marks observed on some dolomitic carbonate surfaces were formed by wind activity on the playa m ud fla ts. Runzel marks are known to form on sediment surfaces that are partly cohesive and covered by only a very thin film of water (up to 1 cm in depth). Their origin is attributed to the action of strong winds which blow over the sediment surface developing wrinkles (Reineck, 1969). Wrinkle marks can be considered a good indicator of intermittent emergence of a sediment surface (Reineck, 1969). The ripple marks 39 on some of the dolomitic carbonate surfaces also record periods of wind activity over the shallow temporary lake. The groove marks were probably made by tools carried either directly by the wind or flood currents, dragging tools along a soft bottom. Playa scrapers, such as rocks and sticks, have been observed to form drag marks on the surfaces of recent playa lakes {Motts, 1970). Strict conditions for the preservation of drag marks on playa surfaces exist (Motts, 1970). Saturated, fine-grained sediments and high wind conditions must be present. Water depth must also be 2.5 cm or less before movement can be recorded. The drag marks, then, were probably formed on the carbonate m ud surfaces during an evaporative phase of the lake, when water depth was sufficiently low to allow tool movemement to be recorded. The prod marks, however, were probably formed during periods of playa flooding. Floodwaters coming from the alluvial fans could have carried rock fragments or other tools which impinged onto s t ill plastic playa muds to form the prod marks. Although this wide variety of surface markings exists, they are not ubiquitous in the dolomitic carbonates. Most of the bedding surfaces are completely smooth. Playas commonly develop a smooth, hard surface where the capillary rate is low or lacking and where a relatively large number of floodings occur (Motts, 1970). The low capillary rate is considered to be a result of clay and 40 silt-sized sediments (Cooke and Warren, 1973). The fine grain size of the dolomitic carbonates may have resulted in low capillary rates which contributed to the development of their smooth surfaces. The ancient Copper Canyon playa also probably experienced a large number of annual floodings. Set in a structural basin with tectonically active margins (Drewes, 1963) and with annual precipitation in Mio-Pliocene time being between 15 and 20 inches (Axelrod, 1957), depositional rates m ay have been very high. Rapid deposition of sediment would have precluded the development of features related to subaerial exposure on many of the carbonate surfaces. Most of the ra in fa ll, however, occurred during the warm season (Axelrod, 1957) in an arid to subtropical climate. It was probably during the dry season that less frequent floodings of the playa occurred allowing development of structures formed through sub-aerial exposure of the carbonate surfaces. It was also this combination of warm temperatures and seasonal rainfall that allowed for the development of the playa-lake. All playas exist in areas where annual evaporation is considerably greater than annual precipitation (Cooke and Warren, 1973). The warm temperatures in the Mio-Pliocene, then, must have allowed for high evaporative rates of the 15 to 20 inches of annual ra in fa ll. During wet periods, sheets of run-off water from the alluvial fans would have flooded the wide carbonate m ud fla ts . The flute marks were probably formed during one of these events, originating from scouring of the s t ill plastic m ud from sheet floods coming off 41 the alluvial fans. The micro-planar and cross stratification observable in thin section probably resulted from floodwater reworking of the s t ill water-saturated carbonate muds precipitated from a previous evaporative phase of the lake. The planar micro-stratification was formed by running water either in the lower or upper flow regime (Reineck and Singh, 1980). Low angle cross bedding most likely formed in the low flow regime (Reineck and Singh, 1980). The micro-stratification may reflect high energy conditions where floodwater fir s t impinges on the playa surface from the alluvial fans to lower energy conditions as the water spreads out over the horizontal playa surface. Micro-convolutions and erosional surfaces probably developed due to current activity after the m ud became more cohesive due to sediment water loss. The convolutions may have resulted from shearing action of flood currents over the sediment acting as a cohesive layer (Sanders, 1965). The occurrence of grading in those carbonates with a significant percentage of terrigenous clasts most likely originated from selective clast size deposition due to waning flow of the floodwaters. Flooding of a previously dry, mud-cracked playa surface or erosion of s t ill plastic carbonate sediment would account for the presence of micrite intraclasts. The disturbed and sometimes convoluted beds are a penecontemporaneous slump feature possibly resulting from deposition on a slight slope. Movement and displacement of the 42 soft sediment was most likely accomplished under the influence of gravity aided by loading of sediments on a slight slope. Movement may have been triggered by seismic events related to faulting along the margins of the basin. The occurrence of deformed beds overlying even and parallel beds indicates that the disturbed beds were formed as a result of detachment and movement along a more stable, probably better consolidated surface. Slump structures are generally associated with rapid sedimentation (Reineck and Singh, 1980). The fine grain size of the dolomitic carbonate and its mode of origin is also indicative of playa-lake deposition. As a result of their central location within a basin, playa-lakes receive mostly fine-grained clastic sediments washed down from alluvial fans and also act as a storage area for carbonate production (Eugster and Hardie, 1975). Some clastic material occurs in the dolomitic carbonate but the rock is almost pure carbonate. The absence of biologically produced allochems, the fine-grain size of the carbonate, and the lateral association of the carbonate strata with gypsum strata are strong evidence for the origin of the carbonate by direct and inorganic precipitation from evaporating playa-lake water. Low and high-magnesium calcite is known to precipitate directly from evaporating water in playa-lakes (Eugster and Hardie, 1975). The dolomite present in the carbonate rocks of the evaporite facies is probably not primary since primary dolomite is s tric tly a secondary carbonate in lacustrine deposits except those 43 deposited in hypersaline lakes (Muller, et_ ^1_., 1972). There is no evidence that the ancient Copper Canyon Lake was ever hypersaline since the only minerals found are calcite, dolomite and gypsum. Calcite was thus probably precipitated as a result of evaporative concentration of lake water and then later dolomitized during di agensi s. After storm flooding of a playa ceases, evaporation begins to concentrate solute load. The firs t minerals to be precipitated are low or high magnesium calcite. Upon further evaporation, many waters next become saturated with respect to gypsum (Hardie, et a l . , 1978). The order with which carbonate minerals and gypsum precipitate explains the occurrence of the dolomitic carbonate strata surrounding and grading laterally into gypsum strata. As water evaporated in the ancient Copper Canyon playa-lake, calcite was precipitated forming m ud fla ts . With further evaporation, gypsum saturation was reached so that this mineral was precipitated in the central salt pan of the playa. The exact source of the carbonate is unknown, but several good possibilities exist. The limestone and dolomite clasts contributed to the alluvial fans by the Noonday Formation m ay have charged water running off the fans with carbonate through dissolution. Another strong possibility is weathering of the abundant plagioclase-rich volcanic clasts in the alluvial fans contributed by Drewes' "older volcanics" (1963). Carbonic acid (atmospheric CO 2 44 dissolved in rainwater) weathering of plagioclase-rich igneous rocks can contribute as much calcium and carbonate ions to inflow water as dissolution of limestone (Hardie, et a l . , 1978). The clay in the dolomitic carbonates also probably resulted from carbonic acid weathering of alluvial fan clasts. Carbonic acid weathering of rock accounts for the presence of clay minerals in the fine sediments washed into desert basins (Hardie, et a l . , 1978). The origin of the unusual allochem in the dolomitic carbonate is enigmatic. The absence of any certain biologically produced allochems m ay be related to the playa-lake environment. The lack of a permanent standing body of water and the increasing salt content of the lake as i t evaporated would prevent a fresh-water fauna from becoming established. The only indications of invertebrate activity are tra ils and burrows; their rarity also possibly suggesting, at best, only marginally suitable conditions for aquatic lif e in the ancient Copper Canyon playa-lake. 45 Gypsum The gypsum strata in the Copper Canyon Formation occur primarily in the lower part of the evaporite facies as small outcrops in Copper Canyon wash (Plates 1 and 2). The outcrops occur several hundred meters above the thickest section of the last basalt unit in the formation, so that they are enclosed both vertically and laterally in dolomitic carbonate. The surfaces of the dolomitic carbonate units grading laterally into the gypsum strata are generally smooth, with no signs of subaerial exposure as mudcracks or raindrop impressions occurring. Bedded gypsum is most common, with individual strata ranging from laminae only a few millimeters thick to beds up to 12 centimeters in thickness. Mud and fine siltstone laminae are sometimes found separating the strata. Single units of gypsum, several millimeters to 30 centimeters in thickness, also occur interbedded with dolomitic carbonate, shaley siltstone and fine sandstone beds. Thin gypsum veins typically cut through the clastic beds associated with the gypsum strata. Bedding structure in the gypsum units is wavy and parallel (Fig. 14). The gypsum is light gray (N7) and light olive gray (5Y 6/2) fresh and medium light gray (N6) weathered, moderately to well indurated and slope forming. The rock is composed of almost entirely pure, fibrous gypsum with approximately 1% dispersed silt-sized quartz and feldspar grains and m ud forming micro-laminae 46 Fig. 14. Photograph of disturbed gypsum strata in the lower evaporite facies. Width of outcrop pictured is approximately 2 meters 47 within the gypsum strata. A chalky mineral, possibly anhydrite, forms pods in some of the gypsum beds (Drewes, 1963). Interpretation Gypsum precipitation probably occurred in a playa-lake environment. This interpretation is suggested by the vertical and lateral association of the gypsum beds with the dolomitic carbonate strata, which also formed by precipitation from evaporating playa-lake water. Carbonate minerals are generally the fir s t to precipitate from evaporating lake water. The next mineral to reach saturation and to precipitate is gypsum (Hardie, et a l . , 1978). The dolomitic carbonate strata grading laterally into and surrounding the gypsum strata reflect this order of precipitation brought about by evaporation of playa-lake water. The gypsum strata and their central location within the enclosing dolomitic carbonate is analogous to recent playa lakes where a central salt pan is surrounded by m ud flats (Cooke and Warren, 1973). The gypsum salt pan in the ancient Copper Canyon playa-lake was near the center of the basin, as suggested by its position above the thickest section of the basalt flow, which m ay indicate the deepest or central part of the basin. The absence of halite and other highly soluble salts indicates that they were either precipitated and then redissolved or that the playa-lake never evaporated to the point of their precipitation. The next minerals to form after gypsum in an evaporating lake basin are quite soluble and not precipitated until the solute load is 49 increased manyfold (Hardie, et a l . , 1978). The absence of any sign of subaerial exposure in the dolomitic carbonate strata that grade laterally into the gypsum units may indicate that the lake never completly dried up, or evaporated to the point of precipitation of the more highly soluble salts. The micro-laminae of m ud in the gypsum strata probably record flooding of the playa from gentle ra in fa ll, since storms would probably carry larger amounts of coarser material into the central salt pan. Once flooding occurred and the small quantities of m ud settled out of suspension, the playa-lake evaporated with carbonate precipitation dominating the early phases of evaporation until gypsum saturation was reached and then precipitated in the center of the playa-lake. The siltstone and sandstone beds in the gypsum facies probably resulted from more severe flooding of the basin with the distal facies, or toes of the fringing alluvial fans, prograding out onto the salt pan as sheet wash material. The dolomitic carbonate interbeds probably reflect changing position of the central salt pan in response to migration of the center of the basin brought about by tectonic activity or changing configuration of the shoreline of the playa lake by alluvial fan deposits. The wavy bedding is most likely a post-depositional structure related to slight flowage of the gypsum strata. 50 BIOGENIC CARBONATES Bioclastic Carbonate The bioclastic carbonate facies occurs in the uppermost part of the carbonate member (Plate 2) (Fig. 15), consisting predominantly of ostracod and peloid-rich calcitic carbonate rocks. Thick sections of bedded bioclastic carbonate form laterally continuous ridges which thin appreciably towards the southwest and northwest edges of the of the formation. Thinner sections of bioclastic carbonate also form laterally continuous ridges in the upper part of the evaporite facies, separated by thick sections of dolomitic carbonate. The bioclastic carbonate occurs as laminae less than 1 cm thick to beds as thick as 65 cm (Fig. 16). Most beds are between 5 and 10 cm thick. Interbedding with v itric tu ff and other clastic beds is common. Bedding in the bioclastic carbonates is even and parallel with contacts showing only minor signs of erosion where interbedding with terrigenous clastic strata occurs. No internal stratification or crossbedding is evident. The bioclastic carbonate is wel1-indurated and cliff-forming. The rock occurs in a wide range of colors, both in fresh and weathered samples. Fresh colors include shades of yellow and orange (grayish yellow 5Y 8/4, grayish orange 10YR 7/4, very pale orange 10YR 8/2), brown (light brown 5YR 5/6, moderate brown 5YR 3/4, grayish brown 5YR 3/2) and gray (medium gray N5, yellowish gray 5Y 7/2, 5Y 8/1, light olive gray 5Y 6/1). Weathered colors include shades of orange (dark yellowish orange 10YR 6/6, grayish 51 Fig. 15. Outcrop photograph looking out across the upper evaporite facies and the bioclastic carbonate facies. The brown strata are mostly bioclastic carbonates and, to a lesser extent, v itric tu ffs . One large bioclastic carbonate bedding surface in the upper evaporite facies is pointed out by the arrow. The white strata are mostly dolomitic carbonates and fine-grained siltstones and sandstones. The photograph shows approximately the upper 150 m of the Copper Canyon Formation. 52 53 Fig. 16. Photograph showing close-up of bioclastic carbonate strata. Note the color banding typical of the bioclastic carbonates. The Knife is 9 cm long. 54 orange 10YR 8/2, 10YR 7/4), brown (moderate brown 5YR 4/4, 5YR 3/4, dusky yellowish brown 10YR 2/2, dark yellowish brown 10YR 4/2, grayish brown 5YR 3/2) and gray (medium dark gray N4, olive gray 5Y 4/1), The lighter colored carbonates often have a salt and pepper appearance due to black dendrite growth. The dark brown and gray carbonates exhibit profuse dendrite growth. Most of the bioclastic carbonates, however, have a banded appearance with the colors listed above appearing in discrete bands less than 1 cm to 2 cm wide. The only fossils identifiable by visual examination of the bioclastic carbonate are narrow, medium and high-spired gastropods approximately 1 cm long. These gastropods occur on the surfaces and imbedded within the bioclastic carbonate strata. The gastropods occurring on the surfaces are flattened parallel to bedding. They have been identified as belonging to the family Hydrobidae (Drewes, 1963). Most of the exposed bioclastic carbonate bedding surfaces are smooth and featureless. One surface that occurs in the upper evaporite facies, however, has large, well-developed polygonal cracks (Fig. 17). Unusual structures found on another bioclastic carbonate surface, also within the upper evaporite facies, are bowl-shaped carbonate mounds ranging from approximately 5 cm to 30 cm in diameter and height (Fig. 18). The mounds are usually flattened or depressed at the top (Fig. 19). In some places, the mounds have slipped or been eroded off the bedding plane to reveal the structure underneath. The bedding surface is arched up slightly under the mounds, sometimes having three or four radial 56 Fig. 17. Photograph of a bioclastic carbonate surface with polygonal cracks in the upper evaporite facies. The width of the cracked surface is approximately 5 meters. 57 Fig. 18. Photograph of a bioclastic carbonate surface covered with bowl-shaped mounds. Most of the mounds are about 25 cm in diameter. 59 Fig. 19. Close-up photograph of two bioclastic carbonate mounds. The knife is 9 cm long. 61 62 joints leading from a central carbonate-filled core, or pipe (Fig. 20). Unfortunately, the carbonate unit with the mounds was not visible in cross section to see how far below the mounds bedding was disturbed or where the disturbance originated from. The mounds stand out of a bedded bioclastic carbonate unit 40 cm thick composed of beds 3 cm to 18 cm thick, overlying siltstone and granule-pebble conglomerate strata totalling 239 m in thickness. The beds lying above the carbonate mounds are mostly bioclastic carbonate strata interbedded with thin siltstone and fine-grained sandstone strata. Thin section analysis of one of the mounds shows the lithology to be similar to the undeformed bioclastic carbonate surrounding the mounds. The only difference between the two carbonates is in the percentages of chalcedony occurring as matrix material. In the mounds, chalcedony forms approximately 21% of the matrix, while the undeformed carbonate has approximately 2% chalcedony matrix (thin sections B' and C‘ , respectively, Appendix A). No structures indicative of stromatolitic origin of the carbonate mounds were present either in slabbed samples or in thin section. The bioclastic carbonates are composed chiefly of ostracod shells and peloids. Intraclasts, gastropod and algal fragments and terrigenous elastics are either low in abundance or absent. Most of the bioclastic carbonate occurs as packstone with a matrix abundance ranging from approximately 4% to 40% and averaging approximately 25% in overall abundance in the thin sections studied 63 Fig. 20. Close-up photograph of bedding surface beneath one of the carbonate mounds. Note the presence of a central pipe in the arched-upward bedding surface with four radial joints coming from the edge of the central pipe. The knife is 9 cm long. 64 qmmm m "tjfc, y ' . ;•« f - v wmim 65 (Figs. 21 and 22). The matrix is almost entirely calcitic micrite. Sparry calcite occurs in a few of the samples, ranging from approximately 1% to 12% of the cement-matrix component. Chalcedony occurs in patches within the micrite matrix in some of the samples and sometimes is the sole cementing agent. In those samples where chalcedony is present, it accounts for approximately 2% to 100% of the cement-matrix material. Allochem abundance ranges from approximately 60% to 96% total thin section composition. The allochems in the bioclastic carbonates range from approximately 1 to 91% ostracods, 5 to 99% peloids 0 to 2% intraclasts, 0 to 1% gastropod fragments and 0 to 5% algal fragments. Ooids occur in one sample only and make up less than 1% of the allochem component. The ostracods are 250 to 710 microns in length, usually articulated (Fig. 22) and thin-shelled with some showing several molting stages. Some ostracod shells are in fille d with chalcedony and rarely with sparry calcite. The peloids are 88 to 350 microns in diameter, composed of calcitic micrite and round to ellipsoid in shape. They are devoid of internal structure. The peloids are almost always stained with limonite and sometimes hematite similar to the surrounding matrix material, but often show deeper staining. Intraclasts, approximately 250 to 1000 microns in diameter, are also composed of micrite. Terrigenous clastic material, ranging from fine s ilt to medium sand-sized grains, accounts for approximately less than 1% to a maximum of 3% of the total grains in thin section. The majority of the terrigenous clastic grains 66 Fig. 21. Photomicrograph of a bioclastic packstone (chalcedony-cemented packed peloidal carbonate rock) showing micrite peloids cemented together by chalcedony. 67 Fig. 22. Photomicrograph of a bioclastic packstone showing a thin-wailed, articulated ostracod shell in fille d with chalcedony. 69 are angular quartz and plagioclase feldspar. Volcanic rock fragments, spherulites, and accessory minerals such as muscovite, biotite, epidote and possibly rutile account for less than 1% grain abundance. One packstone sample differed markedly from the majority of bioclastic carbonates. It contained approximately 65% allochems and terrigenous clastic grains (approximately 25% peloids, 15% intraclasts, 5% ostracods and 20% terrigenous elastics) and approximately 35% matrix material consisting of dolomitic carbonate (approximately 57% sparry calcite and dolomite, 43% micrite). The rock lacked the typical color banding or the salt and pepper color of the other bioclastic carbonates, being closer to the colors exhibited by the dolomitic carbonate rocks. I t is yellowish gray (5Y 7/2) and pale greenish yellow (10Y 8/2) as fresh and grayish orange (10YR 7/4) and light brown (5YR 6/4) weathered. The rock is bedded with calcitic bioclastic carbonates and fine-grained clastic strata. Some of the bioclastic carbonates are wackestones. Approximate allochem abundance ranges from 30 to 33% (Fig. 23). Ostracods, ranging from approximately 20 to 91% of total allochem abundance, and peloids, ranging from approximately 5 to 80% total allochem abundance, are most common. Gastropods and algal fragments make up no more than approximately 5% of the allochems. Matrix material, composed chiefly of calcitic micrite, makes up between approximately 67 and 70% of the thin sections examined. 71 Fig. 23. Photomicrograph of a bioclastic wackestone containing peloids (center) and ostracod shell fragments. 72 ' ’%< Sparry calcite and chalcedony occur in patches surrounded by micrite matrix in some of the samples. Interpretation The bioclastic carbonate formed in a quiet, freshwater lake environment. This is suggested principally by the high abundance of biologically produced allochems and the lack of planar or cross-stratification within the bioclastic carbonate beds. The absence of internal stratification may be due to intense bioturbation of the carbonate sediment as is suggested by the abundance of peloids, or fecal pellets, in the carbonate rock. The habitat of the only gastropod discovered in the bioclastic carbonates, Hydrobidae indet., was probably a freshwater lake without much current action (Drewes, 1963). The thin-walled carapaces of the ostracods are also indicative of fresh-water conditions (Scholle, 1978) and their articulated shells suggest a quiet environment. The environment of deposition of these bioclastic carbonates is probably similar to the depositional environment interpreted for similar carbonates found in the Green River Formation. Here, the laterally continuous carbonate beds composed principally of calcitic micrite with no apparent laminae or cross-stratification, the lack of terrigenous clastic grains and the presence of gastropods, ostracods and algal allochems were interpreted as being formed in a quiet, shallow lagoon connected to a large freshwater 74 lake (Williamson and Picard, 1974). The small size of the ancient Copper Canyon lake, as interpreted from the lateral extent of the bioclastic carbonate beds, and its probable location within the deep, central parts of the ancient basin formed an environment protected from winds and allowed for lagoon-like carbonate deposition to occur. The type of carbonate in the rock also suggests freshwater conditions. The carbonate is, in all but one case, pure calcite. Calcite is preferentially precipitated at low salinities in lake environments (Kelts and Hsu, 1978). The calcitic micrite matrix in the bioclastic carbonate probably formed as a precipitation product in the ancient Copper Canyon freshwater lake. The source of the calcite is the same as that described for the dolomitic carbonates. The allochems, however, form the greatest percentage of the rock. Ostracods, gastropods and algae commonly represent the major source of carbonate in softwater lakes (Kelts and Hsu, 1978). The unusual dolomitic bioclastic carbonate strata probably reflect an intermediate or transitional environment between to tally freshwater, more permanent lake conditions evident in the calcitic bioclastic carbonates and the dolomitic carbonates typical of the playa-lake environment. The basin m ay have had a standing body of water for a sufficiently long period of time to allow a freshwater population to become established, but underwent evaporation typical of playa-lakes. This would have allowed low or high magnesium calcite to form and precipitate as salinity increased. The 75 high abundance of intraclasts and terrigenous elastics, and the similarity in color to the dolomitic carbonates together with the faunal elements typical of the bioclastic carbonates supports the interpretation of a transitional environment. Mud-cracks on one exposed carbonate surface indicate drying of the lake and subaerial exposure of the carbonate. This may reflect seasonal changes in rainfall or drought conditons. The carbonate mounds present on one surface are probably features caused by loading of the bioclastic carbonate strata over sandstone and conglomerate beds. Loading may have caused water to move up from the terrigenous clastic beds, forming pipes in the carbonate where water pressure disturbed and moved the s t ill plastic carbonate upward and onto the bedding surface to form mounds. This interpretation is suggested by the arched-up bedding surfaces underneath the mounds and the presence of radial joints which spread from central pipes. The pipes underneath the mounds and the radial joints are similar to those observed in sandstone beds (Hawley and Hart, 1934). Their formation is attributed to the action of water currents rising vertically through the strata. The permeable nature of the sandstones, however, allowed for the emergence of springs on the bedding surface rather than mound formation. The development of mounds in the carbonate surfaces m ay be due to the less permeable nature of the bioclastic carbonate because of its m ud content. Water pressure in the terrigenous 76 clastic beds that developed from overburden would tend to displace the carbonate rather than flow through i t . Hydroplastic disruptions in lacustrine rocks have been used as evidence for deposition in quiet, standing water (Picard and High, 1972). That the mounds and the surfaces of the underlying pipes are both bioclastic carbonate indicates that overburden pressure was not sufficient to bring any terrigenous clastic material up onto the surface to become part of the mounds. Evidence that the disturbance originated from the terrigenous clastic beds underlying the bioclastic carbonate strata comes from thin sections taken from both the carbonate mounds and the surrounding, undeformed surfaces. The higher percentage of chalcedony in the mound carbonate may be explained by the incorporation of silica-rich fluids from the terrigenous clastic beds into the carbonate as mound development occurred. 77 CLASTICS Pebble-Cobble Conglomerates The dominant type of conglomerate in the formation is a red, pebble to cobble conglomerate that surrounds and interfingers laterally with the carbonate member of the formation (Plates 1 and 2). Pebble-cobble conglomerate also occurs interbedded within the carbonate member as well, but differs in color and occurs in long lenticular or laterally continuous beds across the member. The pebble-cobble conglomerate exists in beds or groups of beds from less than 0.3 m to over 1.0 m in thickness. Two distinct types of this conglomerate exist, based on differences in rock fabric and strati fication. Both types of pebble to cobble conglomerate are usually pale reddish brown (10R 5/4) fresh and moderate red (5R 4/6) weathered, wel1-indurated and c l i f f forming. The matrix is composed of m ud to sand sized grains and is calcareous. The matrix accounts for the deep red color of the rock, while the clasts are mostly lighter shades of red, pink, purple, orange and gray. The clasts are composed chiefly of extrusive and shallow intrusive volcanic rocks of acidic composition. These include layered friable and welded tuffs sometimes with igneous rock fragments, tuff-breccia and felsophyres. Intrusive igneous clasts, principally porphyritic quartz la tite and quartz monzonite also occur but are more common in the upper parts of the formation (Otton, 1977). Sedimentary 78 clasts, principally limestones, dolomites and quartzites occur infrequently and also have a greater abundance in the upper part of the formation. Basalt clasts are rare and occur only in the conglomerate beds immediately overlying the basalt units in the lower part of the evaporite facies. The firs t type of pebble-cobble conglomerate consists of an unordered fabric that is poorly sorted, largely ungraded and clast supported. Stratification within the beds is generally absent, although the beds themselves are well-defined. Crude planar stratification is sometimes evident and occurs in beds where clast packing is less dense, with a higher proportion of matrix material present than in the unstratified beds. The contacts between the clast-supported conglomerate and other strata show l i t t l e or no erosion. The clasts in this conglomerate are very angular to subrounded. Boulder-sized material is commonly present. The pebble to cobble conglomerate that occurs in laterally continuous or long lenticular beds in the upper sections of the evaporite facies and the bioclastic carbonate facies is similar to the conglomerate described above, differing in only a few details. First it differs in color from the majority of the coarse conglomerate in the formation. Fresh colors are mostly shades of gray and purple (yellowish gray, 5Y 7/2, light brownish gray 5YR 6/1, light gray N/7, pinkish gray SYR 8/1 and pale purple 5R 6/2). Weathered colors are typically shades of orange, brown and darker 79 gray (light moderate reddish orange 10R 6/6, dark yellowish orange 10 Y R 6/6, grayish orange pink 5 Y R 7/2, light brown 5YR 6/4, and medium gray N5). Crude grading of the clasts is sometimes evident with cobbles and rarely boulders more common at the base of the beds. Planar or cross-stratification is absent. The second type of pebble to cobble conglomerate consists of horizontally stratified sets of cobble conglomerate fining and grading upwards into pebbly sandstone or pebbly conglomerate. The rock is grain-supported and is generally finer-grained than the fir s t type of conglomerate, containing a larger proportion of sand to granule sized clasts and boulder sized material is mostly absent. The horizontally stratified sets are on the order of 15 to 30 cm thick, but bedding planes are poorly defined and usually erosional. The clasts are usually subrounded. Most of the pebble to cobble conglomerate surrounds and interfingers laterally with the carbonate member of the formation. The deepest interfingering of the red pebble to cobble conglomerate occurs in the upper part of the evaporite facies and bioclastic carbonate facies. Where interfingering occurs, the conglomerate beds generally become progressively finer-grained, better sorted and thinner towards the center of the carbonate member. The fingers of the pebble to cobble conglomerate grade laterally into granule-pebble conglomerates and finer grained clastic strata interbedded in the carbonate member. 80 Interpretati on The red pebble to cobble conglomerate was deposited in the proximal to medial facies of alluvial fans fringing the ancient Copper Canyon basin. This interpretation is supported by the enclosing and interfingering relationship of the red conglomerate with the finer grained carbonate member near the center of the formation and the coarse grained nature of the conglomerate. Different modes of deposition are interpreted for the two types of red pebble to cobble conglomerate. The grain-supported conglomerate with the unordered fabric and lack of good stratification is interpreted as resulting from debris-flows on the upper fan. This is suggested by the large grain size, poor sorting, poor or absent stratificatio n , the presence of well-defined beds with erosionless contacts and the clast-supported and unordered fabric (Gloppen and Steel, 1981). The grain-supported matrix in these debris-flow deposits is also an indication of deposition in a subarid or arid environment (McGowen and Groat, 1971). The gray and purple conglomerate that forms laterally continuous or long lenticular beds within the carbonate member is also interpreted as resulting from debris-flow deposition. The crude grading evident in some units m ay have resulted from a more fluid debris-flow (Bull, 1972) or subaqeous deposition in a lake in the center of the basin. The presence of these conglomerates 81 interbedded within the carbonate member suggests that debris-flow deposition sometimes extended beyond the fans and into the central basi n. The second type of pebble to cobble conglomerate, containing horizontally stratified sets of fining upward sequences, is interpreted as resulting from braided stream deposits on the medial to upper distal fan environments. This is indicated by the s tra tific atio n, the better rounding and sorting of clasts than in the debris flow deposits and the lack of well-defined bedding planes (Gloppen and Steel, 1981). Braided stream deposition is characteristic of the medial and upper distal facies of both modern and ancient alluvial fan deposits (McGowen and Groat, 1971). A nearby, uplifted source terrain is indicated by the angularity and size of the clasts derived from the pre-existing formations uplifted along normal faults at the basin's margins. Intense cloudbursts in the mountains surrounding the basin may have generated floods that triggered debris flows on the steep areas of the alluvial fans and braided stream deposits as the water spread out in channels on the medial fan. Debris flow deposition usually predominates on the upper parts of alluvial fans while water laid deposits predominate on the lower parts of fans because of the ab ility of floods to transport debris further downslope (Hooke, 1967; Bull, 1972). The existence of deep interfingering of fan material into the carbonate member suggests occasional progradation of the medial and 82 upper distal fan facies towards the center of the basin. Alluvial fans commonly show intertonguing relationships with the deposits of other depositional environments (Bull, 1972). The occurrence of deepest interfingering of conglomerate and interbedded debris flow deposits within the upper evaporite and bioclastic carbonate facies may indicate more frequent flooding of the basin later in its history and possibly increased tectonic activity along the basin*s margi ns. The intense red color of most of the pebble to cobble conglomerate is characteristic of ancient alluvial fan deposits (Bull, 1972). The color probably results from oxidation of iron-rich minerals, or the diagenetic alteration of silicate minerals in the volcanic and plutonic clasts, releasing iron oxides to diffuse within the sediment (Walker, 1967; Van Houten, 1973). The gray and purple fresh colors of the pebble to cobble conglomerate interbedded within the carbonate member result mostly from the color of the component volcanic clasts rather than deep staining of the matrix. The lack of red color of this conglomerate may be due to lack of subaerial exposure resulting from quicker burial by the finer-grained deposits in the center of the ancient Copper Canyon basin. 83 Granule-Pebble Conglomerate Most of the granule to pebble conglomerate units occur in the upper part of the evaporite facies and the bioclastic carbonate facies (Plate 2). This conglomerate sometimes occurs as lenticular beds tens of meters long, but many beds are laterally continuous across the carbonate member. Bedding thickness ranges from 0.1 to 4.0 m thick. Like the pebble to cobble conglomerate, two basic types of granule-pebble conglomerate exist. The firs t type consists of a grain-supported fabric displaying poor to moderate sorting of sub-angular to sub-rounded clasts. Cobbles, and very rarely boulders, are also sometimes present. Planar or cross-stratification is absent. Grading of the clasts sometimes occurs, with granule-pebble conglomerate fining upwards into granular sandstone. When present, cobbles and boulders typically occur at the base of the granule-pebble conglomerate beds. The rock is moderately to well indurated and usually cli ff-formi ng. Thin section and X-ray diffraction analysis of one sample of the firs t type of granule-pebble conglomerate was performed. The conglomerate contains approximately 80% grains and 20% matrix material. The matrix consists mostly of dolomitic micrite and, to a minor extent, of clay. A variety of different clast types exists. Approximate clast composition includes 60% volcanic rock fragments and glass of acidic composition, 20% carbonate allochems, 12% feldspar, 5% quartz, 2% plutonic rock fragments and 1% 84 accessory minerals. The volcanic rock fragments consist of felted masses of plagioclase feldspar microlites, larger euhedral plagioclase crystals, and embayed quartz crystals set in a dark, glassy matrix. Much of the glass showed signs of devitrification and spherulites were common, although not abundant. Staining of a sandstone sample similar in composition to the granule-pebble conglomerate revealed that much of the glass is postassium feldspar. Carbonate allochems present include disarticulated ostracod shells, micrite peloids and micrite rip-up clasts. The feldspar grains were principally twinned plagioclase and sanidine, of which both are sometimes highly seritized and corroded. Quartz grains are typically water-clear, show straight extinction and often have straight edges and sometimes embayments. Silica overgrowths are present around some of the quartz grains. Plutonic rock fragments are generally smaller than the volcanic rock fragments and are formed of equant grains of quartz and feldspar. Accessory minerals include biotite, chlorite, rutile and epidote grains and also chalcedony occurring in patches within the micrite matri x. The conglomerate discussed above lies on top of a bioclastic carbonate bed. This conglomerate bed was the only one in the formation to yield any large fossil material. A s ilic ifie d tree trunk, probably representing some variety of palm, was found flattened parallel to the bedding plane. 85 The fresh and weathered colors of the fir s t type of conglomerate vary greatly. Fresh colors are most commonly grays (light brownish gray 5YR 6/1, light gray N7, pinkish gray 5YR 81, yellowish gray 5Y 8/1), shades of purple and pink (very pale purple 5P 6/2, grayish pink 5B 8/2) and shades of brown and yellow (pale yellowish brown 10YR 6/2 moderate greenish yellow 10Y 7/4, pale greenish yellow 10Y 8/2). Weathered colors are mostly darker shades of gray (medium gray N4, N5 and dark gray N3, light brownish gray 5YR 6/1) and browns, dark oranges and light red (moderate yellowish brown 10YR 5/4, light brown 5YR 6/4, 5YR 5/6, dark yellowish orange 10YR 6/6 and light red 5YR 6/6). The second type of granule-pebble conglomerate is matrix- supported and contains subrounded to rounded volcanic clasts. The matrix consists of silty and sandy calcareous mudstone. Bedding is, for the most part, even and parallel and contacts with other lithologies show no signs of erosion. The matrix-supported conglomerate occurs only rarely in the formation, with the grain-supported variety being much more common. Color in the matrix-supported conglomerate is also varied. Fresh colors include shades of gray and yellow (grayish yellow 5Y 7/2, pinkish gray 5YR 8/1, light brownish gray 5YR 6/1) and red and olive (pale red 10YR 6/2, pale olive 10Y 6/2). Weathered colors are mostly dark yellowish orange (10YR 6/6) and light brown (5YR 6/4). 86 Interpretati on The granule to pebble conglomerate represents a continuum of sedimentation from the coarser pebble-cobble conglomerate in the proximal and upper medial alluvial fan facies to the lower medial and upper distal facies. This interpretation is supported by the smaller grain size and the better rounding and sorting of the clasts than in the pebble-cobble conglomerates. The lateral grading of the pebble-cobble conglomerate into the granule-pebble conglomerates towards the center of the carbonate member also substantiates this interpretation. The firs t type of granule-pebble conglomerate is interpreted as having been deposited as sheet-flood material. This is suggested by the laterally continuous and sometimes lenticular nature of the beds, the lack of stratificatio n, the grain-supported matrix, and the better sorting of grains than in the coarser conglomerate (Bull, 1972). The rare occurrence of larger clasts, as cobbles and boulders, in some of these beds probably resulted from the abrupt drop in competence associated with the increased flow width as flood waters expanded outward from main channels on the upper fan (Gloppen and Steel, 1981). The grading of clasts m ay have resulted from waning flow associated with this expansion of flood water. Sheet floods have been interpreted as having originated from a network of very shallow, braided channels and low, longitudinal bars, such as commonly form and spread out from the end of the main stream channels on fans (Bull, 1972; Gloppen and Steel, 1981). The incorporation of carbonate allochems into the granule-pebble conglomerate occurs where the fans prograded onto the bioclastic carbonate facies of the formation. This interpretation is substantiated by the presence of disarticulated ostracod shells and micrite rip-up clasts. The s ilic ifie d palm trunk probably originally grew on higher areas of the fan and was carried down and deposited by flood waters in the lower fan facies. Although not a useful indicator of age, the presence of the palm does indicate mild winters and summer rainfall (Axelrod, 1973). It may also indicate that a savanna-type vegetation existed while the formation was undergoing deposition (Axelrod, 1973). The second type of granule-pebble conglomerate probably originated from debris flows coming off the medial fan. This interpretation is suggested by the matrix-supported rounded clasts and the lack of eroded contacts and internal stratification (McGloppen and Steel, 1981). The better rounding and sorting of the clasts in these beds than in the pebble-cobble debris flow deposits indicates that the clasts were reworked by fluvial processes prior to becoming incorporated into a debris flow. The medial or distal fan facies seems the most appropriate place of origin for these flows since these facies are typically dominated by fluvial processes. Even though slope angles are often low in the lower medial and distal areas of alluvial fans, debris flows have been known to occur on slopes as low as 1° although they most commonly occur on slopes around 5° (Blatt, et a l . , 1980). 88 Sandstones The sandstones in the Copper Canyon Formation are most abundant in the upper evaporite and bioclastic carbonate facies (Plate 2). They occur as laterally continuous or long lenticular beds 1 to 60 cm thick with most beds being around 10 crn in thickness. Crude planar stratification is present in some of the beds, but most are massive. Bedding is even and parallel. Grading sometimes occurs with coarse sand grains near the base of the bed fining upwards to silty fine-grained sandstone. Granule and pebble sized clasts sometime are present in the sandstone and generally occur at the base of the beds. No large fossil material was found in any of the sandstone units. The sandstones are poorly to well indurated and are both slope and cliff-forming. The rock occurs in a wide variety of colors in both fresh and weathered forms. Fresh rock colors include shades of yellow (grayish yellow, 5Y 8/1, yellowish gray, 5Y 7/2, pale greenish yellow), orange (dark yellowish orange 10YR 6/6, grayish orange, 10YR 7/4), green (very pale green 10G 8/2) and brown (light brown 5YR 6/4). Weathered colors are mostly shades of brown (moderate brown, 5YR 3/4, 5YR 4/4, light brown, 5YR 5/6, pale brown 5YR 5/2, moderate yellowish brown (10YR 6/6), gray (brownish gray 5YR 4/1), and sometimes green (grayish yellow green, 5GY 7/2, light olive, 10Y 5/4). The sandstones may be compositionally classified as calcareous feldspathic volcanic arenites, calcareous volcanic arenites and 89 calcareous volcanic arkoses. Some of the compositional elements typically found in these sandstones are shown in Figure 24. They are fine to very coarse grained, sometimes slightly granular and usually s ilty . The rock is poorly sorted and immature with micrite and rarely sparry calcite as the matrix-cementing agents. The matrix accounts for approximately 10 to 40% of the sandstones and is usually dolomitic. Clay constitutes a minor percentage of the m ud matrix. Mineral grains and rock fragments in the sandstones are most often angular to sub-angular and sometimes sub-rounded. Quartz grains have an approximate abundance of between less than 1% to a maximum of 28%. The grains are mostly monocrystalline, show straight extinction and are usually water-clear. Straight edges, rounded corners and embayments typical of volcanic quartz are sometimes evident. Rarely the quartz clasts are polycrystal 1ine, show undulose extinction and contain vacuoles and inclusions. The most abundant mineral grain in the sandstones is feldspar, ranging approximately from 3 to 91% of total thin section content. The most com m on feldspar is plagioclase and typically shows well-developed Carlsbad and albite twinning. Sanidine commonly occurs, but rarely exceeds approximately 10% total feldspar content. Most of the feldspar clasts are water-clear and only slightly altered by seritization. Some of the sandstone samples, however, have highly seritized and corroded feldspar grains. Some of the larger feldspar grains exhibit vermicular patterns of alteration typical in feldspars undergoing alteration to kaolinite 90 Fig. 24. Photomicrograph of a typical sandstone from the formation. Volcanic rock fragments, feldspars and spherulites are com mon features. 91 92 (Scholle, 1979). Rock fragments are generally abundant in the sandstones. They are mostly volcanic, of acidic composition, and comprise from approximately 2 to 94% of the clast abundance in the samples examined optically. The volcanic rock fragments are composed of microlites of plagioclase feldspar, or felted masses of very small lath-like plagioclase crystals, set in a dark glassy matrix. The glassy matrix is mostly potassium feldspar. Larger euhedral feldspar grains and anhedral or straight edged and embayed quartz crystals are also common. The plagioclase crystals show well-developed twinning and sometimes growth composition lines. Sanidine is also present. Plutonic rock fragments are rare and composed of large quartz, orthoclase and twinned plagioclase feldspar grains. Metamorphic rock fragments are also low in abundance and occur only in the sandstones near the top of the formation. They consist of stretched quartz and feldspar grains with crenulated contacts. Volcanic glass, showing various amounts of devitrification, is common in the sandstones. It's abundance was included in the estimated percentages determined for rock fragment abundance since i t may also be altered and unaltered volcanic rock fragments lacking microlites or phenocrysts. The glass is composed of potassium feldspar. Spherulites, a common devitrification feature, occur in all the samples of sandstone studied by thin section. 93 Accessory minerals include detrital biotite, muscovite, chlorite and rutile grains. Most of the mica flakes are oriented parallel to bedding. Micrite rip-up clasts and peloids are rare, but can make up as much as an estimated 5% of the volume of some sandstones. The sandstones with carbonate allochems are found directly above carbonate strata. Micro-crystalline epidote occurs within the matrix of some of the sandstones. The sandstones are lightly to heavily stained by limonite or hematite and sometimes a combination of both. This staining accounts for the shades of yellow, orange and brown in the fresh and weathered rock. The white and gray sandstones show the least amount of staining. The green sandstones have micro-crystalline epidote in their matrices and also chlorite flakes as an accessory mineral. Seams of fine-grained, often microcrystalline material, are a typical feature in some of the sandstones. Some of the seams are fille d with chalcedony, but most contain a combination of micrite, clay and probably micro-crystalline epidote. The seams are more deeply stained by limonite or hematite, and sometimes both, than the surrounding sandstone. Interpretation The sandstones probably were deposited as sheet-flood material in the distal facies of the alluvial fans bordering the ancient 94 Copper Canyon lake. This interpretation is suggested by the grain size, the laterally continuous or lenticular nature of the beds and the massive and sometimes planar-stratification (Bull, 1972). The absence of any lamination within most of the sandstone beds m ay be due to very rapid deposition from suspension (Blatt, et a l . , 1980) as might be expected for sheet-flood type sedimentation. Sheet floods are common on alluvial fans where rainstorms result in down-slope sheet runoff (Cooke and Warren, 1973). The grading of clasts in some of the sandstone beds is similar to other sheet flood deposits where the graded bedding is produced through waning flow (Tucker and Burchette, 1977). Micrite rip-up clasts and peloids were incorporated into the sandy sediment during a flooding event when the distal facies of the alluvial fans prograded onto the carbonate sediments in the center of the basin. The seams of fine-grained material may result from the concentration of insoluble particles and dissolved minerals by fluid movement (Scholle, 1979). The origin of the chalcedony probably results from the dissolution of volcanic glass and detrital silicate clasts followed by precipitation of the dissolved silica as chalcedony. 95 Si 1tstone Three basic types of siltstone exist in the Copper Canyon Formation. The distinction is based on differences in mineralogy. The fir s t type is dolomite siltstone and is similar to the dolomitic carbonate rocks in the evaporite facies, except that the percentage of terrigenous clastic material is sufficient to classify the rock as a siltstone (Fig. 25). The rock occurs in the evaporite facies bedded with dolomitic mudstones, wackestones and packstones (Plates 1 and 2). Vertebrate tracks and parting lineations occur on some of the surfaces of the siltstone strata. The siltstone is composed of approximately 70% terrigenous clastic grains and approximately 30% matrix material. Clast composition includes an estimated 85% quartz and 5% feldspar grains, 5% volcanic glass fragments and 5% micrite intraclasts. The quartz grains are angular to sub-angular, show straight extinction and sometimes have straight sides and rounded edges typical of volcanic quartz. The grains are also mostly water-clear, only rarely containing inclusions. Both plagioclase and potassium feldspar grains are present and are also angular to sub-angular. Both the quartz and feldspar clasts are roughly elongate in shape and usually oriented parallel to stra tific atio n . The volcanic glass present shows a salt and pepper type extinction pattern commonly associated with d e vitrification. The roughly round-shaped intraclasts range from .25 m m to 6 m m in length. The matrix consists primarily of dolomitic micrite with small patches 96 Fig. 25. Photomicrograph of a dolomitic siltstone with calcite cement. 97 of sparry dolomite or calcite occurring within the matrix. A small amount of clay appears to be dispersed within the micrite matrix. The second type of siltstone is similar in color, mineralogy and sedimentary structure to the sandstones. I t is usually poorly indurated, slope forming and occurs throughout the evaporite and bioclastic carbonate facies. It is generally sandy with rare occurrences of pebble-sized material and is sometimes shaley. It forms both laterally continuous and long lenticular beds in the carbonate member. Planar or cross-stratification is absent. The third type of siltstone exists in only one known place in the formation (Appendix B-Detailed Section 3). It forms a bed 23 cm thick which is moderately indurated and cliff-form ing. The bottom 8 cm of the siltstone bed is red in color (light red 5R 6/6, pale red 5RP 6/2) while the upper 15 cm of the bed is green (moderate greenish yellow 10Y 7/4). No planar or cross stratification is evident. The siltstone consists of approximately 75% to 90% angular to sub-angular grains, predominantly twinned plagioclase feldspar and small amounts of monocrystalline quartz grains (Fig. 26). Volcanic rock fragments and glass have an estimated abundance of 5%. The green color in the top part of the bed results from high concentration of microcrystalline epidote, comprising between approximately 10% and 25% of the green siltstone. The red siltstone gets its color from about the same percentage of aggregates of small spherical bodies of jarosite. Much of the jarosite occurs in heavy concentration in and along veins in the rock. 99 Fig. 26. Photomicrograph of jarosite-rich siltstone. Note that many of the clastic grains appear corroded. This may be due to hydrothermal activity which m ay also be responsible for the high concentration of jarosite. 100 Interpretati on The dolomitic siltstone was deposited in a playa-lake mudflat environment. This interpretation is suggested by its similarity to the dolomitic carbonates in mineralogy, outcrop characteristics and occurrence within the evaporite facies. The presence of micrite intraclasts in the siltstone is also strong evidence for a play-lake origin of the siltstone. Flooding of the playa would have eroded dry, cracked or incompletely consolidated sediment from the playa surface and incorporated the erosional fragments into the siltstone. Silt-sized sediment carried in the floodwater may also have aided the formation of micrite intraclasts. Parting lineations in the siltstone resulted from the orientation of non-equidimensional grains by current action (Picard and High, 1973). The lineation is formed in the upper flow regime and has been observed in other siltstones (Picard and Hulen, 1969). Apparently, floodwaters coming from the alluvial fans were of sufficient velocity to orient the s ilt grains parallel to flow. Higher velocity flow would probably occur over playa surfaces near the toes of the alluvial fans. Since the playa-lake surface was nearly fla t, floodwater would rapidly lose its velocity as it approached the center of the playa. Thus, the lineations may be indicative of playa-lake margins. The higher percentage of terrigenous clasts in the siltstone than in the similar dolomitic carbonates may also result from the dropping of floodwater clastic 102 load near the margins of the playa as flow velocity decreased. Terrigenous clastic content in playa rocks would probably decrease from siltstones with dolomitic micrite matrix near the playa margins to almost pure dolomitic micrite towards the center of the pi aya-1 ake. The second type of siltstone, similar in mineralogy and color to the sandstones, probably originated from sheet flood deposits on the distal fan facies near the margins of the playa-lake. This is suggested by the laterally continuous and sometimes lenticular nature of the siltstone strata, the fine-grain size and the absence of internal stratification (Reineck and Singh, 1980). The occurrence of this type of siltstone within both facies of the carbonate member of the formation indicates that the alluvial fans occasionally prograded out onto the finer-grained clastic and carbonate lake sediments in the center of the basin. The origin of the jarosite and epidote in the siltstone bed is uncertain. The presence of jarosite may indicate that the bed was originally rich in volcanic ash. Jarosite is known to be an alteration product of volcanic glass, but how it forms is unknown (Kerr, 1977). The presence of high concentrations of jarosite in and along veins in the siltstone suggests that fluid activity was important in concentrating the mineral in the rock and m ay also have been involved in alteration of some component of the siltstone into jarosite. 103 Claystone Claystone is the least com mon lithology in the Copper Canyon Formation. I t occurs in beds from 10 to 18 centimeters thick in the center of the bioclastic carbonate facies interbedded with shaley siltstones (Plate 2). The claystone beds grade laterally into bioclastic carbonate and sandy siltstone beds towards the southeast and northwest edges of the bioclastic carbonate facies. Planar and cross-stratification is lacking both in thin section and in outcrop. The rock is moderately indurated and slope-forming. The claystone is very pale orange (10YR 8/2) and grayish orange (10YR 7/4) fresh, weathering to pale yellowish orange (10YR 8/6). Thin seams of dusky yellowish brown (10YR 2/2), organic rich material occur in the claystone. The seams are parallel to bedding. Organic carbon analysis for an average sample of the rock yielded 1 % total carbon content. The claystone is approximately 92% clay-sized material with 4% very fine to fine sand-sized, angular to sub-rounded clasts of plagioclase feldspar and quartz. Mud peloids, 88 to 177 microns in diameter, form an estimated 2% of the claystone. Accessory minerals, including microcrystalline epidote, biotite, chlorite and muscovite flakes, account for approximately 1% total abundance. The rock is moderately stained by limonite and, to a lesser extent, hematite. The clay mineral or minerals in the rock were unidentifiable by X-ray diffraction analysis. A strong, broad peak with several 104 smaller peaks occurred between 20° and 22° (2eCu) on the diffractogram, but could not be ascribed to any clay mineral or zeolite. Interpretation The claystone probably originated as deposits in the central, or deepest part of the ancient freshwater Copper Canyon lake. This interpretation is suggested by the fine-grain size, the occurrence of the claystone in the center of the bioclastic carbonate facies and the lateral grading of the claystone into bioclastic carbonate or sandy siltstone strata. In an idealized picture for the distribution of sediment in lakes (Twenhofel, 1932), m ud would be expected to occur in the center of a lake where hydraulic energy is the lowest. Sandy siltstones would laterally surround and interfinger with the central, finer-grained m ud facies. The interbedding of the claystone with sandy siltstone beds indicates that floods coming off the alluvial fans were, at times, intense enough to carry silt-sized sediment into the center of the lake. Once flooding ceased, m ud settled out of suspension. The occurrence of claystone strata in the center of the bioclastic carbonate facies may have resulted from concentration of m ud in the center of the lake by these flood currents. The lateral association of some of the claystone beds with bioclastic carbonate strata probably resulted from less intense flooding of the basin, with only clay-sized material washed into and concentrated in the 105 center of the lake. The presence of m ud peloids in the claystone indicates that bioturbating organisms were present. The seams of organic-rich material, however, indicate that only partial reworking of the sediment by the organisms occurred. This probably was the result of rapid deposition of the interbedded clay and s ilt strata removing them from further bioturbation. The clay-sized material probably resulted from the weathering of the volcaniclastic debris in the alluvial fans. Volcanic rock, especially i f glass-rich, typically alters to clay minerals or zeolites (Pettijohn, 1975). The absence of any peaks on the diffractogram that could be ascribed to a clay mineral is probably due to poor crystal 1inity of the clays. Part of the broad peak between 20° and 22° (20Cu) may result from the quartz and feldspar grains in the claystone and possibly some d iffic u lt to identify zeolite mineral. 106 IGNEOUS ROCKS V itric Tuff V itric tu ff occurs solely in the bioclastic carbonate facies of the formation (Plate 2). I t forms laminae from approximately 5 millimeters thick to beds up to 15 centimeters in thickness. No stratificatio n or other sedimentary structures are apparent. The tu ff is commonly found interbedded with bioclastic carbonate in units laterally continuous across the center of the bioclastic carbonate facies. The beds thin and die out towards the margins of the facies with no tu ff beds occurring where the bioclastic carbonate interfingers with the conglomerate member of the formation. Tuff beds are also found interbedded with fine-grained sandstone units within the center of the bioclastic carbonate facies and also appear to die out laterally towards the margins of the facies. The v itric tu ff is grayish-brown (5Y 3/2) fresh, grayish orange (10YR 7/4) weathered, poorly indurated and usually slope-forming. The tu ff is composed of an estimated 95% fine sand-sized glass shards with a curved, spicule-like morphology. It is rhyolitic in composition, composed predominantly of feldspar and, to a lesser extent, quartz. The tu ff is grain-supported, usually highly porous with only approximately 5% matrix material present. The matrix mineral is mostly radially fibrous chalcedony. The base of some bioclastic carbonate beds overlying tu ff strata show mixing of carbonate with ash grains. 107 Interpretation The v itric tu ff originated from the deposition of air-borne volcanic ash in the ancient Copper Canyon freshwater lake. The wel1-preserved shard morphology typical of air-borne ash from explosive volcanic events (Pettijohn, 1975) and the close association of the tu ff with the bioclastic carbonate beds supports this interpretation. The lack of stratification and the well-preserved morphology indicate absence of reworking of the ash and deposition in a quiet, standing body of water. The occurrence of most of the tu ff beds in the center of the bioclastic carbonate facies may have resulted from removal of the ash from the lake margins and its concentration into the center of the lake by floodwaters coming down from the alluvial fans. The v itric tu ff found interbedded with fine sandstone beds was also probably deposited subaqeously over the toes of the alluvial fans which prograded into the lake. Most of the ash that fe ll onto the alluvial fans, however, was probably eroded away and incorporated into other clastic and carbonate sediments in the basin. Since the source area for the alluvial fans consisted of glassy volcanic rocks, it is d iffic u lt to distinguish the importance of the contribution of ash to the rest of the lithologies in the basin. The distinction is complicated by the fragile nature of the glass shards which is easily destroyed by transport and the unstable nature of glass which readily devitrifies to further obscure origin (Pettijohn, 1975). 108 The brown color of the tu ff results from hematite staining and is also an optical effect caused by refraction and internal reflection of light such that blue rays are absorbed and red-orange light transmitted (Pettijohn, 1975). The matrix material probably results from the release of silica from the glass shards and precipitation of the dissolved silica in the form of chalcedony. 109 Basalt The last basalt unit in the Copper Canyon Formation, which served as the strati graphic lower lim it for detailed study of the formation (see geologic map, Appendix B), is the thickest exposed in the formation (Plates 1 and 2). I t is approximately 320 meters thick in the center of the evaporite facies thinning appreciably towards the margins of the facies and entering laterally into the conglomerate member of the formation. The basalt unit has a strongly concave upward or lens shape, with the central part of the lens being both underlain and overlain by dolomitic carbonate strata. The northern part of the lens is enclosed by thick sections of pebble to cobble conglomerate that thin towards the center of the lens. The southern part of the lens is enclosed in dolomitic carbonate with only the very end of the basalt unit entering into the conglomerate member. The dolomitic carbonate and pebble to cobble conglomerate beds in contact with the base of the basalt lens show signs of baking. The contact between the top of the basalt unit and the overlying pebble to cobble conglomerate is erosional, with clasts of basalt occurring in the conglomerate. The top of the basalt unit overlain by dolomitic carbonate appears to be scoriaceous. The basalt is well-indurated, generally cliff-forming and usually vesicular, although solid, non-vesicular rock is also common. The basalt is brownish black (5YR 2/1) and dark gray (N3) 110 fresh, weathering to olive gray (5Y 3/2) and grayish olive (10Y 4/2). The basalt has a porphyritic, ophitic to intergranular and felty texture. The rock is composed of an estimated 53% plagioclase feldspar, 28% ferromagnesian minerals, 10% in te rs titia l glass, 6% phenocrysts and xenocrysts, and 3% of some amygdlaloidal fillin g mineral. Plagioclase phenocrysts and xenocrysts and strongly embayed quartz xenocrysts are most common. Olivine phenocrysts also occur. The phenocrysts and xenocrysts are as long as 2 m m set in a groundmass of plagioclase microlites 0.1 to 0.2 m m long, granular ferromagnesian minerals, in te rs titia l glass and finer plagioclase feldspar laths. The plagioclase commonly displays oscillatory or normal zoning and sometimes contains inclusions. The in te rs titia l glass is largely altered to an orange material that is probably the mineraloid palagonite. Small amygdules fille d with a greenish mineral exhibiting a crude, radially fibrous structure, occur in the basalt (Fig. 27). The green mineral may be some type of zeolite. The plagioclase groundmass has an An content of 55.3% and the plagioclase xenocrysts an An content of between 50 and 60% (Drewes, 1963). The Si02 content of the basalt is 51.3% (Drewes, 1963). Interpretati on Drewes (1963) originally classified the rock as a porphyritic andesite recognizing that its composition fe ll close to the basalt-andesite classification boundary. Based on the Si02 and 111 Fig. 27. Photomicrograph of basalt showing z e o lite -fille d amygdule and plagioclase laths. The plagioclase laths show no signs of alteration due to weathering. K-Ar age dating of this sample yielded a date of 7.5+.5 m.y. (see section entitled "Age"). 112 ferromagnesian mineral content, the rock m ay be reclassified as a porphyritic leuco-basalt (classification of Streckeisen, 1979). The porphyritic leuco-basalt was extruded onto the playa-lake and alluvial fan sediments in the ancient Copper Canyon basin. This interpretation is suggested by the occurrence of a baked zone beneath the basalt unit, the occurrence of basalt clasts in the conglomerate beds above the basalt and the scoriaceous tops of the basalt lens in contact with dolomitic carbonate strata. The concave-upward shape of the flow resulted from the original configuration of the sediments in the basin, where the alluvial fans fringing the nearly fla t playa-lake surface formed a concave upward depositional surface for the basalt. The concave upward shape was further accentuated by synclinal folding following deposition of the basalt and erosion of the flow material from the limbs of the syncline so that the greatest thickness of the basalt was preserved in the low, central part of the fold (Otton, 1977). The alteration of the in te rs titia l glass to palagonite m ay be due to weathering or extrusion of the basalt onto a wet surface. Palagonite forms when basic glass is hydrated by contact with water vapor, as occurs in palagonite-rich basaltic tuffs extruded below glacial ice in Greenland (Williams, et a l., 1954). 114 PROVENANCE The angularity and size of the rock clasts in the conglomerate member indicates an uplifted, nearby source terrane for the terrigenous clastic beds in the Copper Canyon Formation. As previously mentioned, the clasts in the conglomerate consist primarily of volcanic rocks of acidic composition. These clasts were derived from the older volcanic terrain surrounding the ancient Copper Canyon basin, as suggested by their similarity in petrology to Drewes' (1963) "older volcanics." Plutonic rock fragments, primarily monzonite, occur less frequently and are most common in the upper parts of the formation. The monzonite clasts were most likely derived from lower Tertiary intrusive rocks lying unconformably beneath the "older volcanics" (Drewes, 1963). Clasts of limestone, dolomite and quartzite are rare and also occur in the upper part of the formation. These clasts were most likely derived from the Paleozoic Noonday and Pogonip Formations which overlie metamorphic basement rock. Metamorphic rock fragments are rare in the terrigenous clastic strata and were found in only one sandstone bed near the top of the formation. The conglomerates of the Mormon Point Formation, which overlie the Copper Canyon Formation, however, contain metamorphic rock fragments. The clast types in the Copper Canyon Formation record the rapid stripping of the central Black Mountains during u p lift in Tertiary time (Otton, 1977). The "older volcanics" provided the most debris to the alluvial fans bordering the basin. As erosion 115 proceeded through the cover of rocks surrounding the basin, the plutonic monzonitic rocks beneath the "older volcanics" began contributing to the alluvial fan material. Stripping continued until Paleozoic limestones, dolomites and quartzites were reached at which time they contributed clasts to the upper parts of the formation. The appearance of metamorphic rock fragments in sandstone beds near the top of the formation represents the beginning of erosion of basement rock and contribution of metamorphic debris into the basin. The conglomerates of the Mormon Point Formation are distinguished from those of the Copper Canyon Formation principally by the occurrence of metamorphic clasts. The leuco-basalt lenses also contributed material to the alluvial fans in the Copper Canyon Formation as intra-basinal erosional fragments. The presence of v itric tu ff strata in the bioclastic carbonate facies of the formation suggests that pyroclastic a ir -fa ll material also contributed clastic grains to the basin's sediments. The quiet, freshwater lake environment represented by the bioclastic carbonates allowed for good preservation of the v itric tu ff. Pyroclastic material may also have contributed debris to the sediments in the evaporite facies, but was not preserved in bedded form because of flood activity and increased probability of reworking and incorporation of the ash into other clastic and carbonate sediments. The importance of the contribution of pyroclastic debris to the basin's sediments is d iffic u lt to 116 determine mainly because the older volcanics also contributed glassy material to the lithologies in the formation. Since shard- morphology is rarely preserved in transported or reworked sediments due to its fragile nature, and since glass readily alters to other minerals, the pyroclastic glass fragments cannot easily be distinguished from the glass contributed by the "older volcanics." 117 GEOLOGIC AND DEPOSITIONS HISTORY During late Tertiary to Recent time in Death Valley, a series of geologic events related to severe northwesterly crustal extension and strike-slip faulting began to reshape the older Paleozoic sedimentary and Mesozoic metamorphic terrain that had been eroded away in early Cenozoic time to a rolling landscape of low re lie f (Otton, 1977; Hildreth, 1976). Beginning about 10 to 12 million years ago, the deeply buried crystalline terrane was intruded by a series of granitic to monzonitic dikes and plutons. Concommitant with these intrusions was extension accompanied by normal faulting in the upper crust (Wright and Troxel, 1973). As extension proceeded, the central Black Mountains underwent great u p lift and erosion so that most of the 20,000 feet of Paleozoic rock cover was subsequently eroded away (Otton, 1977). At the same time as u p lift, and after most of the Paleozoic cover was removed, extrusion of the "older volcanics" occurred (Otton, 1977). After deposition of the older volcanics ceased, the Black Mountains fault block was further uplifted and broken many times by normal faults (Drewes, 1963). The Copper Canyon Formation was deposited in a structural basin formed as a result of this normal faulting and through synclinal folding occurring during deposition. Four generalized sections measured from the base to the top of the Copper Canyon Formation, and associated detailed sections taken 118 above the last basalt flow, allow determination of the geologic and depositional history of the formation. Plate 1 shows the generalized sections for the bottom half of the formation, Plate 2 for the top half. Appendix B contains the detailed sections and a geologic m ap of the formation adapted from Drewes (1963) which gives the locations of both the generalized and detailed sections. The generalized sections and geologic m ap show the relationship of the conglomerate and carbonate members of the formation. Section 1 was measured within the thickest exposures of the conglomerate member in the southern part of the formation. The pebble to cobble conglomerate of the conglomerate member is the dominant lithology in the formation, accounting for approximately 70% of the lithologies present. Sections 2 and 4 were measured along the laterally interfingering boundaries between the carbonate and conglomerate members. Section 3 parallels the axis of the syncline that runs through the center of the carbonate member. Lithologies present in the carbonate member make up the remaining 30% of the formation. The carbonate member reaches its maximum thickness along the axis of the syncline. With tectonic development of the basin and subsequent erosion of its uplifted margins, flooding carried eroded debris from the older volcanic terrain to form large alluvial fans at both the north and south sides of the basin which, at fir s t , met in the center. Later, and probably as a result of less intense fan deposition and development of a standing body of water, 119 fine-grained carbonate and gypsum were precipitated in the center of the basin. The thick sections of dolomitic carbonate in the evaporite facies resulted from numerous flooding, evaporation and evaporite precipitation events in a playa-lake environment. The evaporite facies includes the lower, middle and most of the upper parts of the carbonate member of the formation. It reaches a maximum thickness of 1500 m along the axis of the syncline. It thins appreciably towards the northeast and southwest edges of the carbonate member, as represented by generalized sections 2 and 4. The playa-lake environment suggested for the evaporite facies requires an arid or sub-arid climate and deposition in an enclosed basin. Paleobotanical data for late Tertiary times in the Death Valley area indicates a sub-arid climate with warm, year-round temperatures and annual rainfall of 15 inches (Axelrod, 1957). The 15 inches of annual rainfall would have allowed for frequent flooding of the basin and the warm temperatures enabled the formation of the playa-lake through high evaporative rates. The enclosure of the basin may have been fa cilitate d through up lift at its margins and blockage of possible outlets by alluvial fan deposits and basalt flows. Generalized sections 2, 3 and 4 show the relationship of the gypsum and dolomitic carbonate beds. The thickest gypsum deposits occur above the thickest section of the last basalt lens. The gypsum strata grade laterally into dolomitic carbonate beds towards 120 both the northern and southern edges of the evaporite facies. In plan view this would represent a central salt pan surrounded by wide carbonate m ud fla ts . This relationship reflects the order of precipitation of carbonate minerals and gypsum from evaporating lake water. After flooding of the playa ceased, evaporation concentrated solute load with carbonate minerals precipitating during most of the evaporative phase. Only after most of the lake water had evaporated would the more highly soluble mineral, gypsum, be precipitated and accumulate in the center of the basin. Two basalt lenses occur in the lower evaporite facies separated from each other by a thick section of playa-lake deposits. The lenses were deposited as flows on top of a concave upward surface formed by alluvial fans of high re lie f fringing a fla t or nearly fla t playa-lake surface. The concave-upward shape of the basalt units was derived from this original depositional surface and also from synclinal folding of the lenses following deposition. As folding progressed, the parts of the lenses on the arms of the syncline were uplifted and eroded with the thickest sections of basalt then preserved along the axis of the syncline (Otton, 1977). The axis of the syncline was also the axis and lowest area of the basin. This is suggested by the thick accumulation of fine-grained playa sediments along the synclinal axis and the occurrence of gypsum strata above the thickest section of the basalt lens which most likely accumulated in the central or lowest areas of the basin. Dolomitic carbonate strata also tend to 121 be thicker along the axis of the syncline, thinning towards the margins of the evaporite facies. Generalized section 1, although predominantly conglomerate, contains isolated playa-lake deposits typical of the evaporite facies (Fig. 28). Apparently, small, enclosed basins developed within the alluvial fan deposits allowing floodwater to collect and playa-lake deposition to occur. These small basins were also formed structurally through folding of the formation as deposition occurred. The basalt lens in generalized section 1 was coevally deposited with the last basalt flow in the evaporite facies (generalized sections 2 and 3). It is also synclinally folded, and is separated from the basalt lense in the evaporite facies by a small anticline. The two flows were, at one time, most likely connected but through post-depositional folding the basalt on the anticline was eroded away leaving the unit discontinuous across the basi n. Detailed sections 1 and 2 (Appendix B) were taken along generalized section 3 in the evaporite facies of the formation. Detailed section 1 was measured across the thickest gypsum deposits along outcrops in Copper Canyon wash above the last basalt flow in the formation. The thickest package of gypsum units is about 8 meters thick, with most of these strata separated by paper thin mudstone laminae. Thinner packages of bedded gypsum units and individual gypsum beds are interbedded with mostly dolomitic 122 Fig. 28. Photograph showing an isolated playa-lake deposit within the conglomerate member in the southern part of the formation. Gypsum units (bright white) are interbedded with dolomitic carbonate strata (tan). The length of the area pictured in the photograph is 5/10 of a kilometer. 123 124 carbonate and rarely siltstone strata. The gypsum was deposited in the salt pan in the hydrologic lowest point in the basin, surrounded by wide dolomitic carbonate m ud fla ts . The interbedding with dolomitic carbonate strata suggests that the salt pan moved laterally in response to changing position of the lowest areas of the basin. This most likely was due to normal faulting at the edges of the basin and folding while deposition was occurring. The siltstone beds were deposited during intense flooding of the playa, with the fine-grained distal facies of the alluvial fans prograding out onto the central evaporite fla ts . Detailed section 2 (Appendix B) was measured across dolomitic carbonate strata typical of the evaporite facies. The dolomitic carbonate strata were formed through precipitation of evaporating playa-lake water, leaving behind m ud flats that were subaerially exposed as the shoreline receded. The presence of in-place fossil reeds, numerous vertebrate tracks, ripple marks, mudcracks and burrows indicates a shoreline environment. The occurrence of dolomitic siltstones indicates that clastic material carried onto the carbonate m ud flats was incorporated into the muds during flooding events. Granule-pebble conglomerate, sandstone and siltstone beds record the progradation of the distal facies of the alluvial fans onto the m ud fla ts . The presence of coarser terrigenous clastic beds in the mudflat environment than in the salt pan is due to its proximity to the main portions of the alluvial fans. 125 Detailed section 3 (Appendix 8) was measured along generalized section 4 at the northern edge of the evaporite facies. This section represents the margins of the playa-lake where strong interfingering of alluvial fan and playa-lake sediments occurs. The alluvial fan rocks are coarse conglomerates deposited as debris flows and finer-grained conglomerates and sandstones deposited from sheet floods in the lower medial or distal fan facies. These deposits interfinger with lacustrine dolomitic carbonates which were away from major clastic sedimentation areas of the alluvial fans. In the upper part of the evaporite facies, along generalized section 3 above Copper Canyon wash, bedded bioclastic carbonates in units up to several meters in thickness begin to appear. These units are separated by thick sections of dolomitic carbonate. The bioclastic carbonates were deposited in a quiet, shallow, freshwater lake environment. Detailed sections 4 and 5 (Appendix B) were measured in the upper evaporite facies lateral to generalized section 3. Detailed section 4 shows bioclastic carbonate units with a maximum thickness of 3 meters separated by thicker units of dolomitic carbonate. Matrix-supported granule-pebble conglomerate occurs in this section, although i t is usually the formation and occurring mostly in the upper evaporite and bioclastic carbonate facies. Detailed section 5 shows an approximately 3 meter thick unit of bioclastic carbonate separating thick sections of dolomitic carbonate both above and 126 below. Both these detailed sections represent the beginning of change from almost entirely playa-lake deposition of the lower and middle evaporite facies to almost entirely freshwater lake carbonate deposition of the bioclastic carbonate facies. The bioclastic carbonate beds represent the beginning of change towards increased ra in fa ll, the development of an outlet in the basin and possibly connection with other freshwater lakes, or possibly cooler annual temperatures which would reduce evaporation rates and allow development of a more permanent body of water. The increased occurrence of beds of terrigenous clastic material associated with the beginning of freshwater lake carbonate deposition, and originating from alluvial fan sedimentation, suggest an increase in the frequency of flooding events in the basin in comparison to the lower and middle evaporite facies where terrigenous clastic beds are of less abundance. The occurrence of matrix-supported debris flows may also substantiate this interpretation. Increased rainfall would have allowed for faster weathering of the volcanic clasts in the alluvial fans providing for a high mud-matrix content in the debris flow deposits. The bioclastic carbonate facies occurs at the top of the carbonate member reaching a maximum thickness of 157 m along the top of generalized section 3 in the axis of the basin. I t thins to 35 m near the southern edge of the carbonate member and to possibly 127 an equal thickness at the northern edge, although most of this section is covered. Detailed sections 6, 7 and 8 (Appendix 8) were measured within the bioclastic carbonate facies along generalized section 3 and lateral to i t . These detailed sections were measured along the thickest part of the bioclastic carbonate facies. The bioclastic carbonate facies represents a relatively stable time of freshwater lake carbonate deposition. The higher abundance of alluvial fan clastic deposits within this facies in comparison with the evaporite facies is an indication of more frequent and intense flooding of the basin. Tuff beds originating from a ir -fa ll ash deposits are preserved in the center of this facies and indicate quiet, standing water conditions. Claystone beds within this facies represent deeper water sedimentation in the center of the freshwater lake. One dolomitic carbonate bed near the top of the bioclastic carbonate facies (detailed Section 7, Appendix B represents a return to playa-lake conditions before the close of deposition of the formation. Detailed section 9 (Appendix B) was measured along generalized section 2, at the top of the formation. The top of this section shows interfingering of pebble to cobble conglomerate with lacustrine rocks of the bioclastic carbonate facies. Sandstone beds occur between the fingers of conglomerate and sometimes exist between bioclastic carbonate strata. The sandstone beds were most 128 likely deposited as sheet flood material from the alluvial fans during flooding of the basin. W hen followed laterally towards the conglomerate member of the formation, the bioclastic carbonate beds end abruptly in depositional contact with conglomerate. Apparently, once alluvial fan sedimentation ceased after flooding, carbonate deposition resumed and overlaped onto fan deposits. The base of detailed section 9 shows the upper part of the evaporite facies as represented by dolomitic carbonate beds. A schematic block diagram of the depositional environment envisaged for a play-lake complex (Figure 29, modified from Eugster and Hardie, 1975) may be used to summarize the facies relationships in the Copper Canyon Formation. The lacustrine and fluvial deposits reflect syntectonic deposition related to u p lift along the margins of the basin and contemporaneous folding. Large alluvial fans flanked the uplifted margins of the basin and were laterally transitional into lacustrine sediments. Playa-lake deposition dominated most of the history of lacustrine sedimentation in the basin. Cycles of basin flooding, evaporation and evaporite mineral precipitation formed wide, usually exposed mudflats surrounding and grading laterally into gypsum deposits that accumulated in the central salt pan of the playa-lake. Towards the end of Copper Canyon times, playa-lake deposition was replaced by freshwater lake bioclastic carbonate deposition. The carbonate member of the formation shows an increase in occurrence of terrigenous clastic strata from the lower and middle 129 Fig. 29. Schematic block diagram of a playa-lake complex, modified from Eugster and Hardie (1975). This model is envisaged for the environment of deposition of the evaporite facies of the Copper Canyon Formation. 130 Prevailing Weather / Exposed Mudflats Shallow la k p / Gypsum Deposits Carbonate Playa Muds evaporite facies where they are rare, to the upper evaporite and bioclastic carbonate facies where they become more abundant. This fining to coarsening upward stratigraphic sequence is similar to an idealized lacustrine sequence (Picard and High, 1972). The fining to coarsening upwards stratigraphy resembles regressive marine sequences where fine-grained rocks deposited below wave base grade upward into coarser shore and fluvial deposits (Visher, 1965). For a lake, this sequence results from progressive f illin g of a basin fir s t by predominantly fine-grained subaqeously deposited or precipitated sediments then coarser terrigenous elastics as the basin shallows out from f illin g and fluvial processes become more important (Picard and High, J r., 1981). 132 AG E The Copper Canyon Formation was firs t assigned a middle Pliocene age based on the size of horse tracks and "other diagnostic features" of the ichnofauna (Curry, 1941). This age determination was probably based on a knowledge of equid skeletal hoof structure from Hemphillian skeletal fossil localities in southern California which were thought to be middle Pliocene in age at the time Curry published his abstract on the Copper Canyon ichnofauna. With the widespread use of potassium-argon dating since the late 1950's, the Hemphillian land mammal age has been reassigned to the late Miocene to middle Pliocene, or approximately 10.2 to 3.9 m.y.b.p. (time scale of Berggren and Van Couvering, 1974). This would change Curry's epoch designation from middle Pliocene to late Miocene. The use of horse hoof-print size to determine the age of the formation is, at best, tenuous. Both large and small horses existed side by side in southern California from early Miocene to Pleistocene times (Downs, 1968). This is also true for the camel ids (Downs, 1968). The mastodon tracks, however, may be used to establish a lower age lim it for the formation. The fir s t occurrence of mastodons in North America is late middle Miocene, but they persisted well into the Pleistocene (Downs, 1968, with new epoch designations from Berggren and Van Couvering, 1974). The mastodon tracks, then, place the age of the formation somewhere between late middle Miocene and Pleistocene times. 133 Further evidence for the age of the formation comes from the "older volcanics" which outcrop throughout the Black Mountains and underlie the Copper Canyon Formation (Drewes, 1963). Seven K-Ar age determinations of the "older volcanics" have been made (Fleck, 1970). Three of the samples, taken from outcrops four miles north of Copper Canyon near Dantes' View, gave ages of 6.32 ± .13 my, 6.34 ± .13 m y and 6.49 _ + .13 my. The remaining four dates were established for samples taken nine miles southeast of Copper Canyon near Hidden Springs and yielded ages of 7.60 _ + .30 my, 7.77 _ + .15 my, 8.02 + _ .16 m y and 8.20 _ + .16 my. These dates place the age of the Copper Canyon Formation as being no older than middle late Miocene (time scale of Berggren and Van Couvering, 1974). The 6-8.2 million year age range for the older volcanics, however, implies on extended period of volcanic deposition which m ay possibly have begun prior to the 8.2 million year lower age determination. An extended period of formation of the "older volcanics" is also suggested from the 5,000 foot thickness of the unit and interbedding of the volcanics with fanglomerate and playa-lake deposits (Drewes 1963; Fleck, 1970). Two K-Ar age determinations of basalt flows within the Copper Canyon Formation gave conflicting ages. One done for this study yielded a date of 7.5 + _ .5 m y for the last basalt flow in the formation. This places the formation in the middle to upper late Miocene, using the time scale of Berggren and Van Couvering (1974). Another age date taken from a basalt flow approximately 490 meters 134 below the last flow in the formation gave an age date of 4.9 million years (Otton, 1977). This corresponds to an early Pliocene age (Berggren and Van Couvering, 1974). The reason for the discrepancy between these two dates is unknown. The basalt sample taken for age determination for this study was thin-sectioned and examined optically for any signs of alteration of the plagioclase feldspars used in the dating process, but none were found. Although the 4.9 m y date appears reasonable, a 7.0 to 7.5 million year date for the formation may be feasible i f the older volcanics underlying the formation are approximately 8 million years old or older. In the tectonically active Tertiary Copper Canyon basin, depositional rates may have been very high and could account for the slight difference in K-Ar dates between the oldest date for the "older volcanics" and the last basalt flow in the Copper Canyon Formation. The Furnace Creek Formation, also in the Black Mountains, was deposited between 6.3 and 5.4 million years ago and had a minimum depositional rate of 127 cm/1000 years as determined from establishing the lower and upper age limits of the formation using K-Ar dates (Fleck, 1970). The Furnace Creek Formation was deposited in an environment similar to that of the evaporite facies of the Copper Canyon Formation (Drewes, 1963). I f this depositional rate can be applied to the evaporite facies of the Copper Canyon Formation, the approximately 525 meters of sedimentary rock between the older volcanics and the last basalt 135 flow would require less than half a million years to be deposited. This would be well within the oldest age date of 8.2 m y for the older volcanics underlying the formation and the 7.5 m y date obtained for the last basalt flow in the section. The only solutions to the conflict in K-Ar dates would be further dating of a statistical number of basalt samples, dating of the older volcanics directly beneath the formation, or fission track dating of the v itric tu ff in the biocalstic carbonate facies of the formation. Even though the K-Ar dates are in conflict, they both place the Copper Canyon Formation within the limits of the Hemphillian land mammal age. 136 I I . VERTEBRATE ICHNOLOGY O F THE COPPER CANYON FORMATION 137 INTRODUCTION The presence of vertebrate ichnofossils in the Copper Canyon Formation was fir s t mentioned by Curry (1941). Included in the collection he listed were tracks of artiodactyls, carnivores, horses, a proboscidean and both web-footed and small and large wading birds. The environmental setting of these tracks was interpreted to be a Pliocene playa-lake. In a popular account of the geology of the Death Valley area, Curry stated that "in the valley there are more m amm al tracks than in all the rest of the world" (1941), even though other localities had been documented previously. Since the early 1940's, however, many other occurrences, and sometimes large numbers, of mammalian and avian tracks in Cenozoic deposits around the world have been reported in the literature. Much of this literature only mentions the presence of vertebrate tracks, but sometimes offers more descriptive information on the morphology and size of the footprints as well. Some workers, however, give a more detailed analysis of the tracks and the rocks they occur in. Valuable information contained in these papers sometimes includes comparison of the tracks with skeletal fossils, the factors affecting track preservation and the environment of deposition of the lithologies that the tracks were found in. Table 1 is a survey of some of the available literature, including papers that only briefly mention the presence of vertebrate tracks as part 138 Table 1: Annotated References from Cenozolc Vertebrate Track Literature. Reference Anonymous (i9605 A lf (1959) A lf (1966) A lf (p e r. comm.) Ammanlyazov, 1C., et a l . (19797 ~ Behrensmeyer and Laporte (1981) Bel 1 and Oe Merlo (1969) Brain (1954) B jo rk , et a l . (1976) C aste ret (1948) Geogr. Loc. and Form. Environ, of Track Form. H t h . of Impress, (unless otherwise noted)_________ volcanic ash Age Eocene Track V a rie tie s " p rim itiv e horse* northeastern Utah casts southern C a lif . Barstow Form. southern C a lif . Barstow Form. southern C a l if . Barstow Form Turkmenistan, USSR Akchagll beds flo o d p la ln (w a te rh o le ) la c u s trin e la c u s trin e s h o re l1ne, epico n tin e n ta l sea claysto ne, sand stone mudstone, t u f - faceous sandstone quartzose, f e l d - spathlc limestone medium grained 1Imestones Upper T e r tia r y Miocene (15-16my) M1ocene (15+my) P le is to cene (2.5«ny) a r tlo d a c ty 1 (camel, antelop e), carn ivore (c a t, bear-dog) a rtfo d a c ty 1 (camel, a n telo p e), c arnivo re (c a t, bea r-d o g ), birds proboscidean a rtio d a c ty ls (camels, g a ze lle s , sheep), carnivore ( c a t ) , web-footed bl rds northern ICenya, ICoobl Fora Form. Austral 1 a s h o re l1ne la c u s trin e coastal dune sandy mud "aeol1an1te" - "consolidated dune limestone" P le is to cene ( 1 .5 - 1.6my) Upper P le is to cene human, hippo, bovlds, birds b1 rd Goldau, S w itzer land Molasse Form. South Dakota, Brule Form. G rotto of A1dene, Gulf o f Lions, France d e lt a ic mud f la t s s h a l1ow, ephemeral pool s cave m arls, very f in e grained sandstones claystone clay Miocene 011gocene p e rrls o d a c ty ls (rh in o s , t a p ir s ) , a r t io d a c t y ls , b ird s , t u r t l e a rtlo d a c ty ! (cam el), carnivore (can1d) Hoiocene bear tracks and (1 5 ,0 0 0 - claw marks on cave 20,0 00 y rs ) w a lls , bear fu r Impressions, hyena, human 1 3 9 Table 1: Annotated References from Cenozolc Vertebrate Track Literature (Cont.). R eference FhifTir jm r r Curry (1939) Curry (1 94 1 ) Curry (1957) de R aa f, et a l . (1 96 5 ) Duges (1894) E rickso n (1967) Moussa (1968) Gardner (1940) Geogr. Loc. and Form. E n v i-o n . of Track Form. L 1 th . of Im press, (un less oth erw ise n o te d ) shaley cla y sto n e Age Upper O lig o - cene-Mi ocene PI e ls to c e n e Mi ddle P Ii ocene Track V a r ie t ie s W y omlng, Whi te R iv e r s e rie s S a lt Creek H i l l s Death V a lle y , CA w a te rh o le , f lo o d p la ln Death V a lle y , CA playa lake Copper Canyon beds p e 'i s s o d a c ty 1s ( b r o n to th e r e s , rh i n o s), a r t io d a c t y ls (e n te lo d o n ts , cam els) cam el, horse, wading b ir d s , probosci dean c arn i v o re s , horses, cam elids and otn er a r t i o d a c t y ls , b ir d s , probosc- 1 dean southwestern la c u s t r in e “im pure" d o lo m i- Eocene webbed and non- U in ta B as in , m u dflats t i c , shaley webbed foo ted U tah , Green lim estones b i r ds, p r im it i v e R iv e r Form. per 1s so d a c ty 1 ( t a p i r ? ) , small r e p t i l e , inver te b r a te s n o rth ern Spain co a s ta l shore lin e calcareo us s h a le s , s i l t - stones and sandstones Lower 0 1 i gocene w eb-fo oted bi rds San Juan Lagos, Mexi co a r g i 11aceous lim eston e Late P11ocene- P le i stocene b ir d , cat U tah , Green R iv e r s h o re lin e Form ation la c u s tr in e d o lo m itic Eocene p e ris s o d a c ty 1 carbo nate mud- ( t a p ir ? , h o rs e ), stone w eb -fo oted b ir d , 1n v e rte b r a te A rizo na f in e - g r a in e d red sandstone P le i stocene a r t io d a c t y l (c a m e l), bear o r g ia n t s lo th 1 4 0 Table 1: Annotated References from Cenozoic Vertebrate Track Literature (Cont.). R eference Johnston (1937) Lamb (1968) L ap o rte and Behrensmeyer (1980) Leaky and Hay (1979) Link (1982) Lucas (1928) L e s s e r ti sseur (1 94 8 ) Mangin (1962) Mossman and S a rje a n t (1 98 3 ) Geogr. Loc, and Fo:-m. west Texas E n v iro n , of Track Form, " f l u v i a l---------- L i t h . of Im press, (un less o th erw ise noted) f in e v o lc a n ic ash Mi ddle P11ocene Track V a r i e t ie s c a n id s , f e l i d s , prob oscideans, a r t i o d a c t y ls (c a m e ls ), e q u id s , bird s New M exico, Ancha Form, of Santa Fe group Kenya, Koobi Fora Form. Tanzani a , L a e t o l i l Beds f lo o d p la in ( ? ) v o lc a n ic ash P le is to c e n e camel f lo o d p la in , lake margin savanna ( f lo o d p la i n ) mudstones, f i n e - P l1 o - ungulates grained sandstones P le is to c e n e (h ip p o s, a n te lo p e s ), t u f f s P Iio c e n e b ir d s , hominid homi ni d, p rim a te s , hares, c a rn i v ores , h o rs e s , prob oscidean s, rh in o s , c h a lic o - t h e r e s , p ig s , gi »-af f e s , bovi ds southern C a l i f . , Ridge B as in , P iru Gorge Sandstone member o f Ridge Route Form. l a c u s t r i n e , s hallow fre s h w a te r s h a le s , f i n e grain ed sand stones Upper Mi ocene mammal p ris o n y a r d , Carson C it y , Nev. w a te rh o le Q uaternary s lo t h , mammoth, d e e r, w o lf Pyrenees M t s ., N a v a rra , Spain and France d e lt a lc mudf1ats A rg e n tin a , Rio Negro Form. Paleogene bird s P11ocene (3.5rny) ground s lo th 1 4 1 Table 1: Annotated References from Cenozoic Vertebrate Track Literature (Cont.). R eference Geogr. Loc. and Form. E n v iro n , of Track Form. MounTaTn (T95fT) Nahoon P o in t, South A fric a L 1 th . o f Im press, (u n less oth erw ise n o te d )__________ w e )1- s o r t e d , c a lc a re o u s , f in e to medium grained sandstone a p h a n itic lim e stones "red and green beds" Age P le i stocene Track Vari e t i es human, b ir d s , Ni nni nger (1 9 4 1 ), Mahard (1 9 4 9 ), Brady and S e ff (1 9 5 9 ), anonymous (1960) Panin (1961) A riz o n a , Verde Form ati on c onfluence of P utn ei and Zabala R iv e rs , Romani a c o a s ta ld u n e p ia y a -1 a k e (3 0 ,0 0 0 y rs ) cat Late T e r t ia r y or E a rly P le i stocene Mi ddle Mi ocene (H e !v e ti a n ) p rob oscid ean , c a ts , b ears, t a p i r , vario us a r t i o d a c t y ls ( in c lu d in g c am e ls ) bi r d s , a r t i odacty 1 s Panin and Avram (1962) Ci s c a rp a th la n M tn s ., Romania Mi ocene b i r d, c a r n i vores, p ro b o s c i dean Panin and S tefan esco (1968) P l a z ia t (1964) Richardson and Rupport (1941 ), Brown (1 9 4 7 ), B ice (1 97 9 ) Rich (1979) Robertson and S te rn b e rg (1 94 2 ) Romania, Molasse Format i on Fra n c e , Molasse D ep osits Lake Managua Ni caragua Tasmani a Kansas s h o r e li ne, marine mud flo w d e p o sits around Lake Managua w a te rh o le "red and green beds" g r i t t y marls v o lc a n ic mud stone c la y s to n e reworked C retaceous chalk (c h a lk y m a r l) Mi ocene Eocene ( L u t e t i e n ) Holocene (6 ,5 0 0 y r s ) M id - T e r t i a r y P Ii ocene a r t l o d a c t y 1s, p e ri sso dactyl ( r h i n o ) bi rds human, d e e r, o t t e r , peccary, b is o n , b ird s , 1iz a r d s b ir d (dromorni t h i d s ) a r t l o d a c t y 1 (c a m e l) , c a r n i vore (c an ids or f e l i d s ) , rh in o s , mastodon R uthe fo rd and Russel (1914) A lb e r t a , Paskapoo Beds sandstone Upper Paleocene t r 1 d a c t y l c a r n i vore (Creodont o r c o n d y la rth ) 1 4 2 Table 1: Annotated References f-om Cenozoic Vertebrate Track Literature (Cont.). R eference_______ Simpson (1941) Smith (1982) S qu ires and Advocate (1982) V ia lo v (1960) Weidmann and R eichel (1979) Wetmore (1956) L 1 th . o f Im press. Geogr. Loc. E n v iro n , o f (un less o th erw ise and form .____________Track Form.____________noted 1_________ . A9e_______ Craighead C averns, Cave r e d c la y mixed f’ le : stocene Tennessee w ith f in e sand to p r e h is t o r i c Southern C a l i f . , Ridge B asin , O s ito Canyon and Cereza Peak S h a le Members of Peace V a lle y Form ation Southern C a l i f . , D ili g e n c ia Form. la c u s t r ln e , shallo w fre s h w a te r shorel1ne la c u s t r in e c la y sto n e Miocene very f in e to f in e g rained sandstone Lower Mi ocene C is c a rp a th ia n M tn s . , U .S .S .R ., S teb ni tsky d e p o sits F ra n c e , Molasse Form ation s h o r e l1ne la c u s t r in e s h o r e lin e of lagoon and f re s h w a te r 1 ake a rg 1 1laceous s ilt s t o n e a rg 1 1laceous si lts to n e Miocene 0 1 1 gocene- Miocene Loui si ana Lowe- Miocene Track V a r i e t ie s la rg e ja g u a - t r a c k s , claw marks on cave wal 1 s mammal p o s s ib le b ird tra c k s b ird bi rds bi rd 1 4 3 of a larger study to papers to tally concerned about tracks themselves. The table includes, when available, the geographic location, geologic formation, environment of deposition, lithology of track impression, age and the types of tracked reported in each of the references. One of the most valuable pieces of information obtained from the literature in Table 1 is the environments of deposition of the rocks in which the tracks occur. Four major environments conducive to track preservation have been recognized. The most common is the shoreline environment, including mainly those of shallow freshwater and playa lakes, but also the shorelines of large, epicontinental seas, lagoons and in deltaic mudflat environments. Dessication cracks, ripple marks and raindrop impressions are the sedimentary structures commonly mentioned as being associated with track-impressed surfaces in these environments. Fluvial environments are the next most common. These include floodplain or savannah-type settings, waterholes and possibly the banks of ephemeral streams. Although none of the literature specifically cites the occurrence of tracks in the ancient bank deposits of ephemeral streams, they do occur in similar modern environments (Picard and High, Jr. 1973). Aeolian and cave environments are the two least frequently cited environments of track preservation. The aeolian environments cited are principally sand dunes adjacent to coastal marine environments. Vertebrate tracks in caves occur on the floors and 144 walls of passageways. All four of these major environments apparently attracted vertebrates looking for food, water and sometimes shelter. These environments also serve as sites for the accumulation of fine-grained sediments necessary for vertebrate track preservation. The track impressions documented in Table 1 occur exclusively in fine-grained clastic and carbonate rocks. No Cenozoic vertebrate track impressions have been documented in any lithology coarser than medium-grained sandstones. Cenozoic vertebrate track literature published since the mid-1960's has increasingly focused more on the preservation of the footprints and their environmental and paleoecological significance. Most noteworthy is a paper by Laporte and Behrensmeyer (1980) on vertebrate tracks and bioturbation in PIio-Pleistocene si 1icic la s tic rocks and Recent sediments in Kenya. This paper is important in that it not only describes the occurrence and stratigraphic context of the tracks, but also examines the variables affecting track preservation. The variables examined include the rate of trampling, rate of burial, sediment texture and the water content of the sediment at the time of impression. The interrelationship of these variables determines the potential for track preservation and the quality of the tracks themselves, in terms of how accurately a hoof or foot is molded. Laporte and Behrensmeyer (1980) also emphasize the importance of substrate reworking by terrestrial vertebrates, showing that its 145 significance is comparable to bioturbation caused by benthic invertebrates in marine sediments where primary grain fabric and sedimentary structues are often disturbed. The effect of sediment water content on track morphology at the time of impression has also been studies by Weidmann and Riechel (1979) through examining Miocene bird tracks and to some extent by Vialov (1966) through studying a wide variety of mammalian and avian tracks. The tracks of artiodactyls, perissodacty1s, carnivores and birds are the most commonly mentioned ichnofossils in the lite ra tu re . Documented occurrences of the tracks of proboscideans, edentates (sloths) and hominids are rarer. Identification of these ancient vertebrate tracks has been accomplished principally through comparing them to tracks of living vertebrates. In Table 1, for example, many ancient tracks have been identified as being those of antelopes, camels, wolves, pigs, etc. These identifications are based on sim ilarity in form between ancient and modern tracks and should not always be taken to imply that the tracks were necessarily made by a closely related ancestor of any of these animals themselves. The tracks le ft by different orders of vertebrates such as artiodactyls, perissodactyls, carnivores and birds are significantly different such that ancient footprints can be assigned to one of them. Within the orders, however, so much sim ilarity can exist between the footprints le ft by different taxa that correlation of a track with one specific trackmaker may be 146 d iffic u lt, i f not impossible. A survey of the literature in Table 1 indicates that significant track differences exist down to the superfamily level for artiodactyls, family level for carnivores and perissodactyls, birds possibly down to order level and proboscideans down to sub-order level such that assignment of a trackmaker to a given track can be reliably made. The correlation of extinct vertebrates with time-equivalent footprints has, however, been made down to the genus and even species level. This has been fa cilitate d by the close association of vertebrate tracks with skeletal fossils either in the same formation or in nearby, time equivalent formations. Examples of this include the correlation of mammal tracks and skeletal fossils in the Brule Formation of South Dakota (Bjork, 1976), near a Pliocene water hole in west Texas (Johnston, 1937), in the Oligocene White River series (Chaffee, 1943), in the Avawatz Formation in southern California (Alf, 1959), between tracks and skeletons of the Dromornithidae, an extinct family of large ground birds found in Australia (Rich, 1979) and between jaguar bones and footprints in a cave in Tennessee (Simpson, 1941). There are problems, however, with the correlation of skeletal fossils and tracks. The preservation of vertebrate body fossils is rare in any environment. Thus, there may not be a representative skeleton for each animal that frequented an environment conducive to track preservation. Indeed, many extinct species of vertebrates 147 are known only from their footprints (Mossman and Sarjeant, 1983). Even i f a representative body fossil for each species of track-producing animal existed, the variability in track morphology resulting from hoof differences caused by ontogeny, sex differences and natural variability within the population may make correlation d iffic u lt. Significant differences in the manus and pes of a single camel may also exist (e.g. Murie, 1974). There may also be no accurate way of reconstructing the soft tissues that form a good part of the hooves and feet of most vertebrates from skeletal fossils alone. These complications usually make the typical correlations which involve comparing only sizes of digits and track lengths an approximation, at best. The only truly accurate method of correlation between skeletal fossils and ancient footprints would be to find a vertebrate “dead in his tracks." A track classification scheme designed to be independent from, but also similar to, classifications based on living vertebrates and body fossils has been proposed by Vialov (1966). Although other vertebrate trace fossil classification schemes have been devised by other workers (see Sarjeant, 1975), most of them are concerned only with reptilian traces. Vialov's classification, although unused in western vertebrate trace fossil literature, has been widely used in ichnological literature from eastern Europe and the Soviet Union. I t is hitherto the most complete vertebrate trace fossil classification scheme available, encompassing not only reptilian traces, but those of birds and mammals as well. 148 In the Vialov classification, vertebrate tracks are classified under Vertebratichnia, which is subdivided into several groups including the Mammalipedia and Avipedia. The subdivision Mammalipedia consists of three major orders, the Carnivoripedida, Perissodactipedida, and the Artiodactipedida. Each of these orders may be further divided into suborders, as the Pecoripedoidel which is included under the Artiodactipedida. Vialov (1966) also proposed genera based on morphological sim ilarity of ancient tracks to those le ft by modern vertebrates. For instance, all two-toed cloven-hoof tracks are classified under the genus Pecoripeda which may be further divided into sub-generic groups such as Gazel1ipeda, Ovipeda and Cervipeda based on the morphological comparability of the ancient tracks with those le ft by modern gazelles, sheep and deer. This does not imply, however, that these traces were necessarily formed by an ancestor or even a close relative of any of these modern animals. The Vialov (1966) classification also allows for species designations due to morphological variability with the genera or sub-genera themselves. The study of vertebrate tracks can contribute much to the fields of paleontology, paleoecology and sedimentology. Since many extinct species of vertebrates are known only from their tracks, a study of these traces can f i l l part of the void in knowledge of Cenozoic vertebrate diversity le ft by poor preservation of body fossils. The tracks may also extend the geologic range of some 149 vertebrates and aid evolutionary studies. Since tracks are preserved where they were formed, they have much to offer in the study of vertebrate paleoecology, especially in the environments they lived and frequented and their paleogeographic range. In terms of sedimentology, the terrestrial bioturbation caused by the trampling of vertebrates m ay have had significant impact on the preservation of primary sedimentary structures and original grain fabric. This may be an important consideration in the study of ancient terrestrial environments. The restriction of vertebrate tracks to only a few environments and the mode of occurrence of these tracks may also aid in elucidating terrestrial environments of deposition. A large variety and number of vertebrate tracks occur in the evaporite facies of the Copper Canyon Formation. Artiodactyl tracks are, by far, the most common; those of birds, equids, felids and proboscideans are much less abundant. In the sections that follow, wel1-preserved tracks of these animals have been identified using the ichnological classification scheme of Vialov (1966) and have been related to recent vertebrate hoof and foot structures. The preservation of the tracks and the environmental factors which affected it are examined. These environmental factors include the grain size and water content of the sediment at the time of impression, the rate of vertebrate trampling and rate of burial of the tracks. The playa-lake environment of the Copper Canyon 150 Formation, as represented by the evaporite facies, is discussed in relation to its ab ility to preserve vertebrate tracks and compared to other similar ancient and modern environments, as well. Finally, the paleoecology of the vertebrates who le ft the tracks is interpreted in relationship to the ancient playa-lake environment. 151 SYSTEMATIC ICHNOLOGY - MAMMALIPEDIA Order Artiodactipedida Suborder Pecoripedoidei Pecori peda (Ovipeda) sp. A (Figures 30 and 31) Dimensions: 7.5 cm to 26.5 cm long, 5.5 cm to 21.0 cm wide, average width: 9.3 cm. Total number of tracks measured: 98 Abundance: Most com mon artiodactyl track type. Description: Oval-shaped tracks generally longer than they are wide. The outer margins of the pads are rounded, both pads being of equal, or nearly equal, size and shape. The pads are widest near the center of the track, tapering to the toes and somewhat to the heel. Toe outlines are sharp, the toes pointing straight forward. The interdigital septum, or ridge, is straight and narrow, connecting the space between the toes with a small indentation between the two pads in the heel region. 2* Pecori peda (Ovi peda) sp. B (Figures 32, 33 and 34) Dimensions: 6.0 cm to 12.0 cm long, 5.5 cm to 11.5 cm wide, average length: 9.4 cm, average width: 9.1 cm. Total number of tracks measured: 15 Abundance: Second to Ovipeda sp. A as most common artiodactyl track type. 152 Fig. 30. Photograph showing impressions of Pecori peda (Ovipeda) sp. A. The ruler at the bottom of the photograph is 30.5 cm long. 153 1 5 4 Fig. 31. Photograph showing casts of Pecoripeda (Qvipeda) S £ . A. 155 Fig. 32. Photograph showing impression of Pecoripeda (Ovipeda) sp. B. The lens cap is 5 cm in di ameter. 157 1 5 8 Fig. 33. Photograph showing cast of Pecoripeda (Ovipeda) sp. B. Casts of raindrop imprints occur around the track. 159 Fig, 34, Photograph showing casts of Pecori peda (Qvipeda) sp. B and Pecoripeda sp. C. Pecoripeda TOvipeda) sp. B (B), has nails at the tips of the toes. The track cast at (C) is also probably Pecori peda (Ovipeda) sp. B. The large track at the far right (D) is probably Pecori peda (Ovi peda) sp. B, and the far le ft track (A) Pecoripeda sp. C, may be the manus and pes of a single camel. The cast of Pecoripeda sp. C (A) shows slight outward curvature of the toes. Note the thin mudcrack casts. The square is 2.5 cm across. 161 1 6 2 Description: Similar to species A, except tracks are more strongly oval shaped, being almost as wide as they are long. The outside boundaries of the pads are also considerably rounder. The toes are sharp and point straight forward. One well-preserved cast shows the presence of nails at the tips of the toes (Fig. 34). The impression of the interdigital septum is straight and narrow. An indentation between the pads in the heel region exists and is connected to the interdigital septum. 3* Pecoripeda sp. C (Figures 34 and 35) Dimensions: 9.2 cm to 13.1 cm long, 9.0 cm to 13.0 cm wide. Total number of tracks measured: 3 Abundance: Rare Description: Oval-shaped tracks, as wide or nearly as wide as they are long. Equal-sized pads, very bulbous at the heel, tapering towards the toes. The points of the toes curve away from the longitudinal axes of the tracks. The impression of the interdigital septum is straight, connecting the space between the toes with a strong indentation between the pads in the heel region. 4- Pecoripeda sp. D (Figures 36 and 37) Dimensions: 13.0 cm to 17.5 cm long, 6.5 to 7.0 cm wide. Total number of tracks measured: 4 Abundance: Rare 163 Fig. 35. Photograph showing impression of Pecoripeda sp. C. 164 1 6 5 Fig. 36. Photograph showing cast of Pecoripeda sp. D. 166 1 6 7 Fig. 37. Photograph showing cast of Pecori peda s£. D. The ruler is 15 cm long. 168 Description: Rectangular shaped tracks, longer than they are wide. Pads equal in size, only slightly bulbous at heel or not at a ll. Outside boundaries of pads straight to very slightly curved. Toes usually pointed straight forward or uncommonly pointed slightly inward. The interdigital septum is straight and narrow and almost always extends from heel to toe and is generally deep in wel1-preserved casts. Pi scussion The hoof structure of artiodactyls is accurately reflected in these well-preserved tracks. The artiodactyl hoof has two developed digits, each digit consisting of three phalanges (Romer, 1966). Information on the tissues surrounding the digits comes from studies of modern camel feet (Arnautovic and Abdalla, 1969). In modern camels, each digit is covered by an elastic structure comprised of three cushions which laterally surround and are connected to each d ig it. The three cushions consist of a large central one and two comparatively smaller ones on each side which extend antero-posteriorly all along the foot. A thick padding of elastic tissue, called the yellow bed, is situated on the posterior part of the foot. I t completely surrounds the posterior part of the central cushion and forms the heel of the foot. A tissue covering exists at the base of each pad on the foot. An interdigital septum exists between the digits, giving fixation to the coverings of the foot and also separates the digits from each 170 other. These tissues are probably similar in form, at least in a gross sense, to those of ancient artiodactyls as is indicated by the sim ilarity in track morphologies between Upper Tertiary forms and most living genera (e.g. Murie, 1974). Modern asiatic and african camels, however, have developed a common covering over both digits and their cushions (Young, 1950). This common covering consists of a nail and a single large pad on each foot. The development of this common covering has been interpreted as a recent adaptation that enables these animals to walk on soft or sandy ground (Young, 1950). The digits of the forefeet are longer and thicker than the hindfeet in artiodactyls. Consequently, the pads, heel and associated coverings surrounding the digits are also larger in size. The larger size of the feet of the forelimbs m ay be that the center of gravity of the animal is closer to the anterior rather than the posterior part of the body. Although a complete artiodactyl trackway is not exposed, Fig. 34 may show a manus and pes of a single camel. The pes is about one-third smaller in size. The artiodactyl tracks preserved in the Copper Canyon Formation are similar in morphology to those observed in modern tracks (e.g. Murie, 1974). Studies of recent artiodactyl tracks help to illuminate some of the problems associated with the study of ancient ones. Even though modern artiodactyls leave tracks that 171 are distinctive as a group, within the group there are confusing sim ila rities . Modern tracks show wide diversity in the dimensions and shapes of the pads, toes and heels, and in the shape of the interdigital septum between species and even within a single species. The sim ilarities in these features between different species can also make distinguishing their tracks nearly impossible. To further complicate matters, all the morphological elements of the hoof can change during ontogeny with some young artiodactyls leaving distinctly different tracks than older animals (e.g. Murie, 1954). Differences between the hooves of male and female animals can also exist, with this difference also reflected in the morphologies of the tracks they produce. Even the manus and pes impressions of a single animal can be significantly different to be classified as different ichnotaxa. For example, Fig. 34 shows the manus and pes of one artiodactyl, both of which have been classified under different sub-genera. Although i t is d iffic u lt to discern changes in hoof morphology with age in ancient footprints, changes in recent artiodactyls have been documented. The curvature of toes away from the longitudinal axis of llamas occurs in older individuals (Chaffee, 1943). This change with age has also been used to explain the curvature of toes in larger ancient camel tracks associated with smaller tracks with straight toes (Chaffee, 1943). This may also account for the curvatures of the toes in the large track of Figure 34. 172 Order Perissodactipedida Family Hippipedidae Hippipeda sp. A (Fig. 38) Dimension: 8.0 to 9.3 cm long, 5.3 to 5.7 cm wide. Total number of tracks measured: 10 Abundance: Rare Description: Rectangular-shaped tracks with single, rounded toe and perfectly parallel and long sides. The inside area of the tracks tend to be concave downward. A subtle v-mark exists at the posterior end of some of the tracks. 2. Hippipeda sp. B (Fig. 39) Dimensions: 7.4 to 7.6 cm long, 7.3 to 7.6 cm wide. Total number of tracks measured: 6 Abundance: Rare Description: Like species A, except tracks are more oval shaped, so that they are wider and have shorter sides. The inside area of the tracks also tends to be concave downward, but no v-mark exists at the posterior end of the tracks. 3* Hippipeda sp. C (Fig. 40) Dimensions: 8.0 cm long, 6.8 cm wide. Total number of tracks measured: 6 Abundance: Rare 173 Fig. 38. Photograph showing impressions of Hippipeda sp. A. Faintly visible in some of the tracks is the v-shaped frog mark at the back of the hoof (arrow). The ruler is 15 cm long. 174 Fig. 39. Photograph showing impressions of Hippipeda sp. B. The ruler is 15 cm long. 176 1 7 7 Fig. 40. Photograph showing impressions The ruler is 15 cm long. Hippipeda sp. C. 178 Description: Oval-shaped tracks consisting of a single toe with sides more strongly curved outward from the center of the track. The posterior sides of the toe impression curve inward towards the longitudinal axes of the tracks. Pi scussion The only recognized perissodactyl (odd-toed ungulate) tracks in the Copper Canyon Formation are those of horses. The evolution of equid hoof structure has been from five complete digits on each hoof in Miocene forms to reduction in the number of digits t i l l only one toe remains, as in modern horses (Romer, 1966). Reduction of the lateral digits had progressed sufficiently by the Late Miocene that some genera had only one effective digit (Romer, 1966). The ancient tracks described here are similar to modern horse tracks which are produced by single round or oval hooves (Murie, 1974). Absent in most of the Copper Canyon tracks, however, is the v-mark of the frog near the back of the hoof. In Hippipeda sp. B, however, the v-mark is present although very subtly expressed. 180 Order Carnivoripedida Family Carnivoripedae Subfamily Felipedinae 1. Bestiopeda (Felipeda) sp. A (Fig. 41) Dimensions: Main pad, maximum width 4.8 cm, maximum length 7.2 cm, toes, maximum width 2.5 cm, maximum length 2.4 m . Total number of tracks measured: 1 Abundance: Rare Description: Large, equilateral triangle-shaped main pad with four toes arranged in a curved row at the anterior end of the main pad. The points of the triangular shaped pad are flattened. The posterior end of the main pad is slightly concave inward. The main pad shows the deepest impression with the toe impressions much shallower. No claw marks are present. 2. Bestiopeda (Felipeda) sp. B (Fig. 42) Dimensions: Main pad, maximum width 8.0 cm, maximum length 7.6 cm, toes, maximum width 2.6 cm, maximum length 3.0 cm. Total number of tracks measured: 1 Abundance: Rare Description: Like species A, except central pad is more triangular in shape, lacking flattened points. One side of the pad is slightly larger than the other two. The posterior 181 Fig. 41. Photograph showing cast of Bestiopeda (Felipeda) sp. A. 182 1 8 3 Fig, 42. Photograph showing cast of Bestiopeda (Felipeda) sp. B. 184 end of the main pad is marked by an indentation. The main pad is the deepest impressed, with the toe impression much shallower. No claw marks are present. Discussi on Both cat and dog feet consist of a large posterior pad or heel with four padded toes arranged in a row at the anterior end of the foot. Both cats and dogs have claws associated with their toes. Cats normally keep their claws retracted, whereas those of dogs are permanently extended. Because of this, dog footprints almost always show claw marks whereas cat tracks rarely do (Murie, 1974). Since the carnivore footprints in the Copper Canyon Formation are analogous to the morphology of modern cat tracks, they have been included under the subgenus Felipeda, which was proposed as an addition to an earlier carnivore track classification scheme of Vialov (1961), by Panin and Avram (1962). The main pad impression is deeper than the toes because the main pad supports most of the weight of the animal (Young, 1950). 186 Order Proboscipedida 1. Proboscipeda sp. (Fig. 43) Dimensions: Circumference - 42 to 52 cm, depth of impressions - 6-20 cm. Total number of tracks measured: 6 Abundance: Only one trackway in formation. Description: Deep circular depressions with no internal morphology preserved. Discussion The only sub-ungulate tracks represented in the Copper Canyon Formation are those of proboscideans. Proboscideans have five digits in each foot united by a web to make a firm basis and having small, fla t nails at the tips (Young, 1950). The digits form a semi-circular pattern presumably enclosed, in fossil forms as in living elephants, in a thick pad (Young, 1950). These tracks are similar to others also described as those of proboscideans in the late Tertiary or early Pleistocene Verde Formation in Arizona (Brady and Seff, 1959) and in Miocene deposits of the Ciscarpathean Mountains in Romania (Panin and Avram, 1962). Better preserved tracks showing five digits surrounding a large central pad in the Pliocene of west Texas have been identified as those of mastodons (Johnston, 1937). 187 Fig. 43. Photograph showing proboscidean trackway. 188 1 8 9 The Copper Canyon trackway is bipedal in appearance, probably as a result of the proboscidean placing both the front and hind feet in the same track, which is the typical gait of a proboscidean. 190 SYSTEMATIC ICHNOLOGY - AVIPEDIA 1. Avipeda sp. A (Fig. 44) Dimensions: 5.0 to 9.0 cm long, 6.5 to 8.0 cm wide. Total number of tracks measured: 3 Abundance: Rare Description: Large tracks with long, straight central claw with two shorter, anteriorly curved claws on each side. No indication of webbing or hind toe present. 2. Avipeda sp. B (Fig. 45) Dimensions: 2.0 to 2.2 cm long, 2.3 to 2.8 cm wide. Total number of tracks measured: 10 Abundance: Rare Description: Small tracks consisting of three claws of roughly equal length. Side claws are straight and at an approximately 30° to 45° angle from the central claw. No indication of webbing on hind toe present. 3. Avipeda sp. C (Fig. 46) Dimensions: 2.0 cm long, 3.0 cm wide. Total number of tracks measured: 6 Abundance: Rare Description: Small tracks consisting of three claws of roughly equal length. Two side claws at 90° angle from central claw and curved toward anterior part of foot. No indication of webbing or hind toe present. ______________________________________131 Fig. 44. Photograph showing cast of Avipeda sp. A. The lens cap is 5 cm in diameter. 192 1 9 3 Fig. 45. Photograph showing impressions of Avipeda sp. B. The lens cap is 5 cm in diameter. 194 Fig. 46. Photograph showing casts of Avipeda sp. C. 196 4. Avipeda sp. D (Fig. 47) Dimensions: 7.6 cm long, 8.4 cm wide Total number of tracks measured: 5 Abundance: Rare Description: Tracks consisting of three claws of equal length with webbing present between claws. Possible presence of short hind toe. 5. Avipeda sp. E (Fig* 48) Dimensions: 1.7 cm long, 2.3 cm wide Total number of tracks measured: 3t Abundance: Rare Description: Small, three clawed tracks with claws of equal length and presence of a hind toe. The two side claws are at 90° from central claw. No indication of webbing present. 6. Avipeda sp. F (Figs. 49 and 50) Dimension: 7.5 to 11.0 cm long, 5.5 to 12 cm wide Total number of tracks measured: 5 Abundance: Rare Description: Long central toe with two shorter toes at each side. Angle between central and adjacent toes varies from 30° to 50°. One toe is curved probably due to imperfect impression of the foot. 198 Fig. 47. Photograph showing impressions of Avipeda sp. D. All the impressions, except the one showing distinct webbing (arrow), were formed in gooey mud. The bird track showing distinct webbing was formed in near-moist sediment conditions where the foot could sink deeply enough to allow impression of the webbing, but not too deep to cause distortion of the impression upon extraction of the foot. The quarter is 2.2 cm across. 199 Fig. 48. Photograph showing casts of Avipeda sp. E. Note the small keels at the posterior ends of the footprints. The ruler is 15 cm long. 201 Fig. 49. Photograph showing impression of Avipeda sp. F. 203 Fig. 50. Photograph showing impressions of Avipeda sp. F. The ruler is 15 cm long. 205 2 0 6 Discussi on Bird feet consist of three digits or claws that extend anteriorly from the base of the foot. The angles between the middle and lateral claws may vary between different taxa. Webbing between the anterior digits may also be present. Studies of recent tracks have shown that many impressions do not show every toe (Murie, 1954) and webbed feet can produce imprints without leaving impressions from the webbing (Mountain, 1966). Species A is similar to tracks described by Weidmann and Reichel (1979) except that webbing is present between the digits in the tracks they describe. Similar tracks are also described by Panin and Avram (1962) as webbed and which are similar to tracks made by birds in the Order Anseriformes. This order includes heron-type wading birds such as ducks, geese and swans (Romer, 1966). Species A tracks were also probably made by similar birds, with the webbing absent in the impressions. Species B, C, and D may also have been made by anseriform birds. Species E tracks are similar to those formed by birds in the Order Charadriiformes. This order includes many types of shore birds that are typically web-footed such as plovers and sandpipers (Romer, 1962). Species F is similar in morphology, but smaller in size, to ancient tracks identified as being made by birds in the Order Ralliformes (Panin and Avram, 1962). Typical members of this order include marsh birds, waders and heavy flie rs (Romer, 1966). 207 STRATIGRAPHY AND LITHOLOGIC SETTING O F TRACKS The vertebrate tracks occur only in the evaporite facies of the formation. Both casts and impressions are most commonly found on 30° to 60° dipping slopes on bedding planes exposed by erosion along washes. Isolated or small groups of tracks are most common. Rarely, however, bedding surfaces several meters square are covered with vertebrate impressions. The occurrence of the footprints within the evaporite facies depends primarily on good bedding plane exposure. Some species and even orders of mammal tracks, such as the Proboscidean footprints, occur only once in exposures of the formation. Most of the different orders of mammal tracks, and the bird tracks, however, occur throughout the evaporite facies and no distinct change, even to the species level, was observed in traverses from the base to the top of this facies. Track casts and impressions are found almost solely in dolomitic carbonate mudstones, wackestones, packstones and dolomitic siltstones. The carbonates typically contain between an estimated 1 to 12% fine to coarse s ilt-sized terrigenous clastic grains, mostly angular to sub-angular quartz. Some of the carbonates may contain as much as an estimated 37% terrigenous clastic grains. Tracks are also found in subarkosic sandy siltstones with approximately 70% clasts and 30% dolomitic micrite matrix. Although no vertebrate track impressions are directly observable in sandstone strata, the presence of dolomitic carbonate 208 casts above deeply eroded sandstone strata is evidence of the existence of the impressions. The poor induration of many of the sandstone strata prevents good fie ld exposure of bedding surfaces to view impressions directly. These sandstone strata are similar in outcrop characteristics and mineralogy to other sandstones in the formation studied in thin section which contain between approximately 10 and 40% dolomitic carbonate m ud matrix. Petrographic data obtained from studying thin sections of lithologies containing track impressions are tabulated in Appendix A. The track impressions occur in laminae that are only paper thin to beds as thick as 20 cm. One artiodactyl hoof impression in a dolomitic carbonate bed just over 1 cm thick was thin sectioned. Planar laminations in the bed were deformed and paralleled the outlines of the track. The laminations near the surface of the impression are most strongly deformed, those near the base of the bed are less deformed and follow track outlines more broadly. The most common casting lithology is dolomitic carbonate. Rarely, granule-pebble conglomerate (Fig. 51) and gypsum (Fig. 52) are the casting lithologies. In both these cases the medium of impression was dolomitic carbonate. The track impressions fille d with conglomerate show good morphological detail with few signs of abrasion. The single gypsum cast was found out of place in Copper Canyon wash. The bottom of the cast contained some dolomitic carbonate indicating that i t was the medium of impression. 209 Fig, 51. Photograph showing artiodactyl hoofprint (probably Pecoripeda (Ovipeda) sp. A) p a rtia lly fille d by granule-pebble con glomerate. No signs of scouring are evident. The knife is 9 cm long. 210 2 1 1 Fig. 52. Photograph of gypsum cast of artiodactyl hoofprint (Pecoripeda sp.). The quarter is 2.2 cm across. 212 ENVIRONMENTAL FACTORS AFFECTING TRACK PRESERVATION Grain size and sediment water content are the two most important variables affecting vertebrate track preservation (see discussion in Introduction). In the Copper Canyon Formation most track impressions occur in carbonate rocks which were either formed from pure carbonate m ud or had a high carbonate m ud content. Siltstone strata containing track impressions also have a high carbonate m ud content. The presence of mud in the sediments preserving track impressions is important for several reasons. Its fine-grain size allows for accurate molding of the vertebrate hoof or foot, its cohesiveness allows for preservation of morphology once the hoof or foot is withdrawn from the sediment and i t also indurates upon drying. The fine grain size of muddy sediment makes the accurate modeling of the vertebrate hoof or foot possible. Even subtle morphological detail may be preserved by muddy sediment. For instance, Cheirotherium footprints in Triassic marls in England show not only sharp track outlines and claw marks but also show detailed skin patterns (Figs. 14, 15 from Frey, 1975; Beasley, 1904). In the Copper Canyon Formation, wel1-preserved artiodactyl tracks often show chisel-sharp outlines and sometimes even small nails at the tips of the toes (Fig. 34). Even traces of invertebrates of considerably less body weight available to deform muddy sediment into an impression exist in the geologic record. 214 For example, arthropod tracks formed in muds deposited in freshwater peri glacial lakes in the late Carboniferous or early Permian of northern Natal show a si nous series of tel son marks with associated small grooves representing setae or plantulae marks (Savage, 1971). In lacustrine mudstones of the Green River Formation in Utah, wavelike and irregular-1ine tra ils interpreted as having been made by nematodes and insect larvae are preserved in good detail (Moussa, 1970). In the Copper Canyon Formation, several varieties of small tracks, probably also of invertebrate origin, occur in well-preserved condition (Fig. 53). These examples of tracks and tra ils of both vertebrate and invertebrates indicate the ab ility of muddy sediment to preserve the activities of these organisms with high resolution. Fine and medium-grained sands may also preserve morphological d e tail, especially i f some m ud is present. In coarse-grained sand and coarser clastic sediments, however, morphological resolution of subtle features may suffer especially when the size of the grains in the sediment is larger than the morphological details they are attempting to mold. The extreme case of this situation is in conglomerates where large clasts make the preservation of even large scale morphology impossible. As sediments involved in track impression coarsen, they also become less plastic and thus less deformable into an impression. The absence of any tracks in lithologies coarser than fine sandstone in the Copper Canyon Formation and a review of the literature available on Cenozoic vertebrate tracks (Table 1) supports this interpretation. 215 Fig. 53. Photograph showing trackways (ichnogenus unknown) probably of invertebrate origin, in dolomitic carbonate mudstone. The dime is 1.5 cm across. 216 2 1 7 Another important quality of mud that enables good track preservation is its cohesive properties. Given that the sediment water content is right for good track preservation, the cohesiveness of mud allows an impression to maintain its morphological integrity from the time the hoof or foot is lifte d from the sediment until i t dries. Coarser grained sediment, such as clean sand, loosens as it dries to obscure morphology making the track more susceptible to damage by renewed flooding or wind a c tiv ity . In the Copper Canyon Formation, sandstone strata were formed from sediments deposited at the toes or distal facies of alluvial fans. The higher velocity of floodwater occurring in this environment and the less cohesive property of sands deposited there would have made this a less likely environment for good track preservation than in the finer grained muds deposited or precipitated in the lower-energy lacustrine environment. Even though a good track impression may be formed in moist sand, its preservation potential is low because of the lack of cohesion of sand upon drying and the relatively high energy of environments in which i t is deposited. I t is also the lack of cohesive properties of sand that makes the potential preservation of tracks in sand possible over a narrower range of sediment water content than in mud (Fig. 54, from Laporte and Behrensmeyer, 1980). Sand becomes too loose to preserve an impression when either dry or saturated with water. Track preservation in sand, especially i f it lacks or has a low m ud content, is heavily dependent on gentle f il lin g of 218 Fig, 54. Schematic diagram showing the relationship of grain size and sediment water content to vertebrate track preservation, from Laporte and Behrensmeyer (1980). 219 WATER CONTENT co Potential co Tracks SEDIMENT TEXTURE 2 2 0 the track impression by sediment while the sand is s t ill moist. This shortens the length of time in which a potential track may be preserved in sand, as opposed to mud. As mud content increases, the preservation potential of tracks probably increases. For Triassic dinosaur footprints in sandstone beds from South Wales, Tucker and Burchette (1977) determined that the presence of about 20% m ud in the sediment was important in the footprint preservation since its cohesiveness was increased, imparting better molding characteristics and also allowing for a more indurated surface that would resist erosion upon drying. The sandstone strata inferred to contain track impressions in the Copper Canyon Formation are similar to other sandstones in the evaporite facies examined in thin section which contained carbonate m ud ranging from an estimated 10% to 40% total composition. The cohesive property of mud that enables an impression to harden as it dries is important since i t provides resistance to erosion by wind and succeeding floods. Even those tracks fille d with conglomerate show few signs of erosion (Fig. 51). The time interval betwen the formation of the footprints and th eir burial also affects preservation potential. I f the impression has not had adequate time to dry, i t may be susceptible to scour by floods. The footprints form irregularities or defects in the beds which may lead to changes in flow pattern that cause scouring to occur. Although scour marks definitely resulting from 221 footprints have not been observed in the formation, scour marks in track-rich beds have been documented in Triassic strata in South Wales (Tucker and Burchette, 1977). These scour marks were interpreted as having resulted from floods removing footprints formed on playa mudflats. Hardening of the impressions prior to renewed flooding would most likely increase the chances of preservation of vertebrate tracks. Track impressions le ft subaerially exposed for too great a time may also have decreased preservation potential. Wind and further animal activity may damage or destroy the impressions. There may also be some point at which further drying of a track impressed surface becomes a destructive process. The development of mudcracks in track beds may disrupt the tracks and cause even more irregularities to allow succeeding floods to scour the tracks away. In the Copper Canyon Formation, strata containing tracks only rarely show signs of mudcracking. Where i t does occur, it is only shallowly expressed. This indicates that m ud surfaces may only have to be partially dry to allow optimum preservation potential of vertebrate impressions. Slight dessication during subaerial exposure may be all that is needed to make the surface firm and scour-resistant (Tucker and Burchette, 1977). The good preservation of many of the tracks in the formation, the general absence of mudcracks, and few signs of erosion due to contemporaneous surface processes, indicates that there was a 222 relatively short time between the creation of the footprints and th eir burial. The presence of carbonate rocks as casts in most of the impressions implies that the impressions were covered with water for a time during f il lin g with precipitated carbonate mud. Even partial drying of the tracks must have prevented them from fallin g apart while submerged. This is most likely due to the cohesive properties of the mud. Also, the carbonate its e lf may have increased the durability of the impressions by acting much like quick drying cement. I f carbonate m ud does behave in this way when subaerially exposed, it might also be another explanation for the absence of strongly developed mudcracks and scouring in the track-bearing strata. Although grain size is in trin sic ally important in track preservation, water content of the sediment at the time of impression most strongly controls track morphology. For clay and s ilt-r ic h sediment, a variety of track morphologies exist for any given trackmaker due to water content of the sediment at the time of impression. Figure 54, a schematic diagram from Laporte and Behrensmeyer (1980), interrelates the effects that grain size and sediment water content have on track preservation. In mud, the best quality tracks are produced with a sediment water content termed "moist." This optimum sediment water content has also been termed 223 "slightly damp" (Tucker and Burchette, 1977). When the sediment is either saturated or dry, good track preservation is impossible. Between these two extremes, however, a variety of morphologies for any given type of track can exist reflecting the water content of the sediment at the time of impression. Artiodactyl hoof impressions exhibit the greatest changes in morphology with different sediment water content. The best track impressions accurately record the structure of the hoof and are formed in "moist" or "slightly damp" mud. Examples of well-preserved artiodoctyl tracks are shown in Figures 30-37. Elements of track morphology indicative of impression in moist m ud are sharp hoof outlines, including good resolution of the toes and heel, and structures internal to the edges of the track including resolution of the two pads and the interdigital ridge. The presence of a ridge separating the two pads is present on wel1-preserved tracks generally less than 2 cm deep (e.g. Figs. 31-33). Deeper, wel1-preserved tracks in the formation lack these internal ridges even though the rest of the hoof morphology is accurately molded (Fig. 55). The absence of interdigital ridges in deeper impressions may be due to compaction of m ud into the septum such that i t remains there rather than in the impression. Figure 56 shows two recent, deep artiodactyl impressions formed in moist mud. Both of the impressions have interdigital ridges, but in one track i t is only subtly expressed. I t may also be that deep impressions with 224 Fig. 55. Photograph of deep (greater than 2 cm in depth), wel1-preserved, artiodactyl hoof impression (Pecoripeda (Ovipeda) sp. B) formed in moist sediment. Note the absence of the interdigital ridge common to shallower impressions formed in moist sediment. 225 Fig. 56. Photograph showing two deep (approximately 2 cm) artiodactyl tracks (Pecoripeda sp.) formed in recent mud around Crater Lake in the Maroon Wilderness, Colorado. Part of the in terdig ital ridge in the right impression appears as though i t was pulled up with the artiodactyl hoof after impression. The quarter is 2.2 cm across. 227 interdigital ridges are formed until mud f i l l s the interdigital septum leaving i t unavailable for molding in future tracks. For shallow impressions, compaction of m ud into the septum may be less of a problem, with the mud not sufficiently compacted into the space to remain there. Continuous, raised rims occur at the margin of many impressions (Fig. 57). In many cases, these rims help to better define track outlines. Raised rims are formed when mud is pushed from under the hoof and out and along its sides, displacing mud at the margins of the hoof into a raised edge. Well-preserved deep impressions lack raised edges (Fig. 55). This is probably due to the water content of "moist mud" and the thickness of the deformed stratum. Water content must be sufficiently low that the plug of mud pushed down beneath the hoof can be compacted into the surrounding stratum without causing deformation at the surface. This requires that the thickness of the stratum be generally greater than the depth of impression. This is true for many of the deep well-preserved impressions. There are some, however, in which the hoof sank completely to an undeformable surface beneath. In these cases, a slight arching upward of the surface surrounding the track is present (Figs. 58 and 59). Tracks impressed in thin strata, where the hoof contacts an undeformable surface below, commonly develop raised rims. Whether a slight arching upward of the stratum surface or a raised rim develops is most likely 229 Fig. 57. Photograph of surface of dolomitic carbonate bed showing an artiodactyl track (Pecoripeda sp.) with a continuous raised rim around its edges (upper rig h t). The two carnivore tracks at the le ft of the photograph appear to have been impressed under near-moist sediment conditions (arrows). Note the wel1-developed raindrop impressions on the bedding surface. The knife is 9 cm long. 230 r* ^ J .*** I s f V Fig. 58. Photograph of two artiodactyl hoof impressions (Pecoripeda sp.) surrounded by bedding surface which has been arched slightly upward. The ruler is 15 cm long. 232 2 3 3 Fig. 59. Photograph of an artiodactyl hoof impression (Pecoripeda sp.) surrounded by bedding surface which has been arched strongly upward. The ruler is 15 cm long. 234 dependent on the amount of space into which the plug of m ud pushed below the hoof can be accommodated. Raised rims w ill be formed in thin strata (generally less than 2 cm thick) when the hoof penetrates to an undeformable surface below. In progress!vely thicker strata deformation around the perimeter of the hoof broadens out because there is more space for the displaced m ud to be compacted beneath the hoof rather than be restricted solely to displacement at its sides. This results in an arching upward of the sediment surface around the track, rather than the development of a raised rim. Sediment with a high water content, termed "gooey" by Laporte and Behrensmeyer (1980), produces distinctive morphologies for artiodactyl tracks. In thick strata, where the animal's hoof can sink several centimeters into very wet, muddy sediment, the dominant track morphology is ovate depressions (Fig. 60). These tracks typically show no internal structure such as toe outlines, pads or interdigital ridges. This is probably due to flowage of mud back into the impression once the hoof is lifte d from the sediment to obscure detail. This interpretation is suggested by the concave upward shape of the impressions, which is deepest near the center and shallows upward towards the margins of the depression. The edges of these tracks are often raised and most likely result from the incompressibi1ity of the water in the m ud with displaced sediment squeezing up and around the hoof. The in fillin g of m ud into the impression is probably fa c ilita te d by 236 M g . 60. Photograph showing close-up of a squelch mark. The dime is 1.5 cm across. 237 2 3 8 these raised rims. Ovate depressions with raised edges that were probably formed by animals traveling in wet, muddy sediment have been termed "squelch marks" (Tucker and Burchette, 1977). A track-congested surface in the formation, consisting mostly of squelch marks, shows good examples of this morphology (Fig. 61). Some raised edges around ovate depressions appear as though m ud stuck to the hoof as i t was withdrawn from the sediment leaving unusually steep sides around part of the track (Fig. 62). This may have resulted from m ud with a stickier consistency due to less sediment water content than in the gooey muds responsible for squelch marks. Squelch marks may be formed while the sediment is s t i l l covered by a thin film of water with the m ud developing a stickier consistency once the sediment becomes subaerially exposed. As sediment water content decreases from its gooey state, hoof impressions begin to show better morphological detail. For example, Figure 63 shows a track with raised edges with faint toe impressions, but no indications of having two pads. This track was most likely formed in m ud with a water content slightly less than in saturated conditons. With further drying of the sediment, toe and pad structures develop. The interdigital ridge, although subtly expressed, begins to appear in shallow impressions (Fig. 64, the two large impressions of Fig. 65). The subdued expression of the interdigital ridge may be due to the in ability of the mud to preserve a high-relief internal ridge because of the s t i l l high water content. The depth of impression may also be a factor in 239 Fig. 61. Photograph of a track-congested dolomitic carbonate surface consisting mostly of squelch marks. The ruler is 15 cm long. 240 Fig. 62. Photograph of dolomitic carbonate surface containing artiodactyl impressions (probably Pecoripeda (Qvipeda) sp. A) formed in gooey to sticky sediment (A) and near-moist sediment (B). The ruler is 15 cm long. 242 Fig. 63. Photograph showing artiodactyl hoof impression (Pecoripeda sp. ) formed somewhere between gooey and sticky sediment conditions. The knife is 9 cm long. 244 2 4 5 Fig. 64. Photograph showing presence of subtle interdigital ridge in artiodactyl hoof impression (probably Pecoripeda (Qvipeda) sp. B). The quarter is 2.2 cm long. 246 Fig. 65. Photograph showing presence of interdigital ridge in shallow artiodactyl hoof impressions. Tracks A and C are probably Pecoripeda (Ovipeda) sp. B. Track B is probably Pecoripeda (Ovipeda) sp. A. The ruler at the top of the photo is 15 cm long. 248 2 4 9 preserving the interdigital ridge in m ud with high water content. The interdigital ridge in shallow impressions in thin strata may have higher preservation potential than deeper tracks in thick strata due to less internal re lie f and thus less flowing of m ud back into the impression. The rims around the tracks pictured in Figures 64 and 65 are s t i l l strongly expressed and indicate a s t ill high sediment water content. With further drying of the sediment, toe, pad and interdigital structures gain better expression. The raised rims also become less obvious. Figure 66 shows such a track, but pad detail has been somewhat obscured by m ud flowing into the track after impression. At some point between gooey and moist sediment conditions, the mud develops a sticky consistency. Tracks which show all the elements of well-preserved ones formed in moist m ud can also be formed in sticky mud. These impressions, however, show distorted morphology due to parts of the impression sticking to the hoof and pulled p artially upward with it upon extraction from the sediment. Although small parts of the impression might remain stuck to the hoof, most remain in the track after detaching from the hoof. The cohesiveness of the sticky mud makes this possible. Figure 67 shows an artiodactyl track with the interdigital ridge disconnected from the toes, raised slightly above the impression and extending into one of the pads. This track was most likely formed by part of the interdigital ridge sticking to the hoof, which was than carried upward while s t ill attached at its distal end to the heel of the 250 Fig. 66. Photograph showing artiodactyl hoof impression (Pecoripeda sp.) formed in sediment with a water content between gooey and sticky conditions. The track is 12 cm long. 251 2 5 2 Fig. 67. Photograph showing an artiodactyl track impression (Pecoripeda sp.) formed in sticky m ud (upper right impression). The arrow shows the displaced in terdig ital ridge. The ruler is 15 cm long. 253 2 5 4 impression. At some point, detachment occurred with the proximal part of the ridge fa lling into the pad impression. The difference in width between the two pads and their distorted appearance probably resulted from different amounts of m ud flowing from the sides of the impression. Some tracks formed in thin (less than 2 cm thick) strata show hollow interdigital ridges with parts of the base of some pad impressions raised from the stratum beneath (Fig. 68, two bottom center tracks). These structures also indicate a sticky consistency for the m ud at the time of impression. With a decrease in sediment water content in sticky mud, the moist sediment condition ideal for track preservation is reached. As the sediment water content decreases from its moist condition, depth of impression decreases and morphological detail looses resolution. Figure 69 shows a track impression made in hardening sediment. Raised edges are absent, pad resolution is low and the heel outline is nearly absent. Some tracks in hardening sediment have crinkled edges usually along just one side of the impression (Fig. 70). The crinkled edges consist of closely-spaced, irregular ridges and are most likely the result of compression of slightly plastic m ud along the edge of the hoof formed during impression. A carbonate surface in the evaporite facies shows several hoofprints formed from the time when sediment water content was 255 Fig. 68. Photograph of dolomitic carbonate surface showing artiodactyl impressions (probably Pecoripeda (Ovipeda) sp. A) formed in sticky (A, B), moist (C) and hardening (D), sediment conditions. The hollow interdigital ridge (E), and the pad impressions raised from the stratum below (F), are morphological features indicating sticky sediment conditions at the time of impression. The quarter is 2.2 cm across. 256 2 5 7 Fig. 69. Photograph of artiodactyl impression (Pecoripeda sp.) formed in hardening sediment. 258 Fig. 70. Photograph of artiodactyl impression (probably Pecoripeda (Qvipeda) sp. B) formed in hardening sediment with crinkled edges on one side. The dime is 1.5 cm across. 260 2 6 1 slightly higher than in moist conditions to when drier conditions arose (Fig. 68). As previously discussed, the two tracks in the bottom center of the figure were formed while the m ud had a sticky consistency. The track in the upper right hand corner of Figure 68 was formed under moist conditons and shows good morphological detail at least at the front of the impression. The interdigital ridge, however, is absent from the center and heel areas of the impression. This may be due either to the absence of space between the pads at the back of the hoof or may reflect a spatial difference in sediment water content at the time of impression. The center and heel areas of the track may have been impressed into drier sediment than the front of the impression. The two impressions to the far le ft of Figure 68 were formed when the sediment was slightly drier than in moist conditions. Depth of impression is shallower and toe and heel resolution have lost detai1. Next to artiodactyl tracks, bird tracks in the Copper Canyon Formation exhibit the greatest changes in morphology with changes in sediment water content. Morphologies indicative of impression in gooey, sticky and moist m ud exist. Morphologies representative of impression in hardening sediment are absent in the ichnofauna. This may be due to the low body weight of birds and their resulting in a b ility to deform hardening sediment. Tracks formed in moist m ud show sharp claw impressions. Raised rims are absent in 262 well-preserved tracks probably due to only slight displacement of mud beneath the bird's feet because of low body weight. Figures 44 and 45 show wel1-preserved bird tracks formed in moist mud. Bird tracks indicative of impression in gooey m ud are usually highly contorted. This probably resulted from the bird's foot sinking several centimeters into gooey mud and then twisting of the toes as the foot was extracted from the sediment (Fig. 71). Part of the distortion also results from mud flowing into the track after extraction of the foot. Figure 47 shows the presence of webbing between the claws on a few of the tracks. The webbed track in the lower right hand corner is shallower than the tracks above i t , and foot morphology is better preserved. Since this track is part of a long trackway, its better preservation most likely resulted from spatial changes in sediment water content with the better preserved track impressed into mud with a firmer consistency then in gooey mud. Webbing may only be preserved in tracks formed in m ud with a higher water content than in moist mud. Slightly wetter sediment than that in moist m ud probably allows the bird's foot to sink a l i t t l e deeper into the sediment enabling impression of the webbing to occur. The tracks in gooey m ud may have been formed while the m ud was s t ill covered by water while the better formed track was impressed in drier, subaerially exposed mud. With a decrease in sediment water content from gooey mud, sediment with a firmer, although stickier, consistency develops. 263 Fig. 71. Photograph of bird tracks (Avipeda sp. D) formed in sticky mud. Sediment actually stuck to, and was pulled up with, the foot at the time of impression. The ruler is 15 cm long. 264 Figure 72 shows a bird trackway impressed into sticky mud. A sticky consistency at the time of impression is indicated by plugs of m ud pulled up above the bedding surface. The plugs occur where the three claws join at the base of the foot impression. Some of the claw outlines are obscured or absent probably due to m ud flowing in the impression once the foot was extracted from the sediment. The morphologies of cat tracks in the Copper Canyon Formation are suggestive of impression in both slightly gooey and moist sediment conditions. Tracks formed in gooey m ud lack poor resolution of main pad and toe structures. The impressions are concave upward indicating that mud flowed back into the track once the foot was lifte d from the sediment. Mud flowage obscures the detailed morphology, especially of the main pad impression, and broadens track outlines (Fig. 73). Carnivore tracks formed in moist sediment show both sharp detail in the main pad impressions and the four toes are separate and easy to distinguish from one another (Figs. 44 and 42). Almost all the carnivore tracks have raised rims around the main pad and toe impressions. The raised rims are usually only subtly expressed and represent slightly higher sediment water content than would be expected for perfectly moist m ud conditions. Horse tracks in the formation show only minor morphological va ria b ility with changes in sediment water content. This may be due to the simple morphology of the tracks, most of which contain no morphology within the impression outlines even when they appear 266 Fig. 72. Photograph of bird tracks (Avipeda sp.) formed in sticky mud. Note the occurrence of plugs of carbonate at the base of the claws in some of the track impressions. 267 Fig. 73. Photograph of dolomitic carbonate surface containing artiodactyl impressions (Pecoripeda sp .) and two carnivore impressions (Bestiopeda (Felipeda) sp.) (at arrow) formed in gooey mud. The ruler is 15 cm 1 ong. 269 k it y 2 7 0 to have been formed in moist sediment. One exception to this is Hippipeda sp. A tracks, where the v-mark of the frog of the horse's hoof is subtly expressed. Examples of preservation in moist m ud show sharp toe outlines and are generally shallowly impressed (Figs. 38-40). Figure 74 shows two tracks, the one at the right probably formed in sticky mud, and the le ft track formed while the mud was moist or just beginning to harden. The track formed in sticky m ud has a greater depth of impression and some slumping of mud along the outlines of the track is evident. As sediment water content decreases from moist conditions, track impression becomes shallower and the hoof outline loses resolution (Fig. 75, far left impression). The proboscidean trackway (Fig. 43) in the formation was probably impressed in sticky mud. This interpretation is indicated by the presence of only slight indications that mud flowed into the impressions after removal of the feet and the deepness of the impressions. The great depth of the impressions is due to the weight of the animal. The walls of the impressions are mostly vertical. I f the trackway was formed in gooey sediment, there most likely would have been considerably more fTowage of m ud back into the impression and broadening of track outlines. The walls and bottoms of the tracks have hummocky surfaces which also indicate a sticky consistency at the time of impression. The presence of raised edges along the perimeters of some of the tracks also 271 Fig. 74. Photograph showing horse tracks (probably Hippipeda sp. B) formed under sticky (le ft impressi on) and moist or hardening (right impression) sediment conditions. The lens cap is 5 cm in diameter. 272 Fig. 75. Photograph showing horse tracks (probably Hippipeda sp. B) formed under moist (A) and hardening (B) sediment conditions. The ruler is 15 cm long. 274 2 7 5 indicates that the sediment water content was higher than under moist sediment conditions. The absence of toe impressions in the tracks may be due to low preservation potential of these features in sticky m ud resulting from the possible lack of strong definition of the toes in the proboscidean foot. Another possibility is that both the front and hind feet were placed in the same track, thereby obscuring subtle morphological detail. In summary, the vertebrate tracks of the Copper Canyon Formation are preserved because of the fine-grain size of the carbonate sediment they were impressed in and the resulting cohesiveness and induration of the sediment upon drying which directly results from the fine-grain size. The sediment water content at the time of impression has a strong influence on vertebrate track morphology. Tracks formed in water-saturated sediment, or gooey mud, lack strong morphological detail. Once the vertebrate hoof or foot is lifte d from the gooey sediment, m ud flows back into the impression to obscure track detail. Generally, only the broadened outline of the track is preserved. Rims around the tracks are also common, resulting from the incompressibility of water and the displacement of m ud from underneath the hoof or foot and out and around their sides. As sediment water content decreases, tracks show better morphological detail. This results from less flowage of m ud back into the impression and from increased cohesivenss which allows retention of track outlines and preservation of structures with re lie f. As sediment water content decreases from its gooey state, i t 276 develops a sticky consistency. Morphologies indicative of sticky sediment include distorted impressions resulting from parts of the impression sticking to the hoof or foot and pulled partially upward with i t and the development of rims around the track outlines. With further drying of the sediment, moist conditions are reached. Track detail is well-preserved, no in fillin g of m ud into the impression from its sides is evident and rims around the tracks are only subtly expressed, i f at a ll . With further drying of the sediment, impressions become shallower and morphological detail looses expression due to the loss of plasticity of the sediment. Several variables act with changing sediment water content to affect track morhology. The depth of impression is one of the most important of these. Tracks less than 2cm deep are better preserved than deeper tracks where the sediment water content is higher than in moist conditions. This is due principally to less flowage of m ud back into shallower impressions because of less re lie f along the sides of the impressions. The body weight of the vertebrates making the impressions is also important. Heavy animals, such as artiodactyls, carnivores, perissodactyls and proboscideans, can form deep tracks which, under moist sediment conditions, accurately record the morphology of the feet or hooves. Animals of considerably less body weight, such as birds, leave tracks which do not always completely record foot morphology. Webbing is a good example of this and may be best preserved in tracks formed in sediment with a higher water content than that present in moist mud. 277 RATE O F TRAMPLING AND RATE O F BURIAL The amount of time between track formation and burial and the activity of the animals during this time interval affect the preservation and spatial relationship of tracks (Fig. 76, from Laporte and Behrensmeyer, 1980). Well-preserved tracks occur where rates of trampling and burial are both moderate. I f established tra ils are used by the animals, the tra ils are most likely to be preserved under moderate burial rates. As burial rates increase, but trampling remains moderate, isolated tracks tend to occur. With high rates of trampling and low rates of burial, the sediment becomes to tally reworked and good quality track impressions become rare. Poor preservation of tracks also results when rates of burial and trampling are low. Tracks in the Copper Canyon Formation occur in small, isolated groups and on bedding surfaces highly bioturbated by the animal's ac tivity. The spatial relationships of these tracks is indicative of both isolated and to tally reworked conditions (Fig. 76). Isolated tracks are the rnost common in the formation. The term "isolated tracks" is interpreted to mean that individual tracks or small groups of tracks do not appear to be part of a game t r a i l . Game tra ils may be recognized by stacking of tracks on top of one another in section. This is not observed in the evaporite facies, even where tracks are relatively abundant. In most cases, 278 Fig. 76. Schematic diagram showing relationship between rate of trampling and rate of burial and their effects on vertebrate track preservation, from Laporte and Behrensmeyer (1980). 279 RATE O F TRAMPLING t Totally « Reworked Well Preserved * • • Poorly *. .•** Isolated Preserved Tracks RATE OF BURIAL 2 8 0 vertebrate bioturbation of the carbonates was low as sedimentary structures such as low-angle crossbedding and planar laminations are wel1-preserved within the same strata adjacent to the tracks and in strata both above and below them. The isolated tracks suggest high rates of burial and low rates of trampling (Fig. 76). They might also be due, however, to spatial differences in sediment water content on the playa mudflats. Animals traversing the mudflats perpendicular to the shoreline would only leave footprints on the narrow and concentric band of wet sediment surrounding the shoreline its e lf. Once dry sediment was reached, no record of the animal's activity would be preserved. The absence of game tra ils in the formation was most likely due to a combination of high rates of burial and low rates of trampling due to the absence of a permanent body of fresh water. High rates of burial resulted from numerous flooding and carbonate precipitation events that created the thick section of carbonate rock in the evaporite facies. Low rates of trampling of the carbonate surfaces were most likely due to the character of the lake water its e lf, possibly becoming too saline as evaporation concentrated solute load. Vertebrates, then, might only have been attracted to the playa-lake when other more palatable sources of water were unavailable. Game tra ils are probably only formed where a permanent, freshwater lake exists with a population of vertebrates that frequent the environment. The presence of tracks 231 stacked on top of each other in section have been observed in Quaternary sediments in Kenya and have been interpreted as game tra ils where animals repeatedly crossed delta mudflats, going back and forth from land to a permanent, freshwater lake (Laporte and Behrensmeyer, 1980). The absence of game tra ils in the formation suggests that vertebrates only occasionally visited the ancient Copper Canyon playa-lake. Carbonate surfaces highly bioturbated by vertebrates also exist in the formation (Fig. 61). Track outlines overlap on the impression-congested surfaces. The hummocky surface also suggests that the beds were highly reworked. The strata both above and below these surfaces are not bioturbated, indicating that a game t r a il did not exist. The schematic diagram from Laporte and Behrensmeyer (1980), Fig. 76, implies that this reworked surface was exposed for a long period of time before burial. This may, however, reflect locally intense activity of the animals for only a short period of time prior to drying and burial. 282 ENVIRONMENTS O F TRACK PRESERVATION The abundance of well-preserved tracks indicates that the evaporite facies of the Copper Canyon Formation, of playa-lake origin, provided an excellent environment for the preservation of vertebrate footprints. The sedimentological factors of the ancient Copper Canyon playa-lake environment which contributed to good footprint preservation include the nature of the sediments that accumulated in the playa, the relationship of the shoreline to the sediment surfaces involved in track impression, the opportunities for sub-aerial exposure and subsequent drying of track impressed surfaces and the presence of sediment accumulation rates sufficiently high to insure quick burial of the impressions. The presence of fine-grained sediments is one of the most important factors for good track preservation. The playa-lake environment serves as a sink for evaporite precipitation and for accumulation of fine-grained clastic sediments washed down from alluvial fans. For the evaporite facies of the Copper Canyon Formation, most of the fine-grained sediments were precipitated carbonate muds formed after flooding of the playa ceased and while evaporation was concentrating solute load of the lake water. The presence of the carbonate its e lf may have increased the preservation potential of the tracks by acting as a cement and forming a well-indurated surface that would resist erosion, upon drying. 283 The length of time during which the playa sediments were sub-aerially exposed yet sufficiently wet to record track impressions was also important. As the playa-lake evaporated after a flooding event, a narrow and concentric band of wet sediment in the exposed mudflats would have surrounded and followed the receding shoreline. The narrow band of wet sediment would have contained thinner bands of gooey m ud along the edge of the shoreline (and probably sediment s t ill covered by a thin film of water) with sticky mud, moist m ud and hardening sediment lying successively away from the shoreline. This spatial difference in sediment water content is seen in vertebrate tracks and trackways where changes in morphology occur over short distances due to variations in m ud consistency. The migrating wet band of playa m ud would have allowed for an extended period of time for any one depositional event to receive track impressions. The cyclic events of playa flooding, evaporation, carbonate precipitation and subaerial exposure also would have provided fresh surfaces for vertebrates to trample. The association of the tracks with raindrop impressions, ripple marks, runzel marks, mudcracks and sometimes in-place fossil reeds substantiates the importance of shoreline environments for good track preservation. The presence of bird tracks attributed to the skeletal fossil order charadriformes, which consists predominantly of shore birds, is further evidence for preservation of the vertebrate tracks in a shoreline environment. 284 As the band of wet sediment moved with the receding shoreline, i t le ft behind a drying, sometimes track impressed surface. At least partial drying of the track impressions was crucial to their preservation. The climatic conditions under which a playa-lake forms, namely where the rate of evaporation exceeds rainfall (Cooke and Warren, 1973), is conducive to quick exposure and drying of the mudflats surrounding the retreating shoreline. Quick burial of the tracks, before they could suffer disintegration from wind and further vertebrate trampling over the dry surface, would also be important to their preservation. The evaporite facies of the Copper Canyon Formation most likely had a high rate of sedimentation which fa c ilita te d quick burial of the tracks in precipitated carbonate mud. The abundance and well-preserved condition of many of the tracks may, in themselves, be indicative of high rates of sedimentation. One of the tracks was preserved as a gypsum cast (Fig. 52). The original impression was most likely formed on the playa-lake mudflat near the central gypsum salt pan. F illin g of the impression with gypsum most likely occurred after a successive flooding of the playa resulted in progradation of the central salt pan over the track-impressed mudflat. This type of preservation of tracks is rare, due to the solubility of gypsum. No occurrences of gypsum casts or imprints of vertebrates have been previously documented. 285 Although the ancient Copper Canyon playa-lake served as an excellent environment for preservation of vertebrate tracks, this may not be true of all playas. The rates of sedimentation, types of fine-grained deposits, and the abundance of vertebrates in the area can vary for different playa-lake settings. As previously mentioned, playas can form where evaporation is considerably greater than annual rainfall (Cooke and Warren, 1973). The highest rates of sedimentation occur where both annual precipitation and evaporation are high. Late Miocene paleobotanical data from California and Nevada indicates that the Copper Canyon playa lake formed in a warm climate with approximate annual rainfall between 15 and 20 inches (Axelrod, 1957, with new epoch designations from Beggren and Van Couvering, 1974). The existence of the playa-lake its e lf indicates that the temperatures were high enough to allow for evaporation of the annual ra in fa ll. The high rainfall and warm temperatures enabled the development of the thick sequence of carbonate rock in the evaporite facies. The climatic conditions during Copper Canyon time were also conducive to the development of savannah-type grasslands that allowed for the existence of a wide variety and large number of vertebrates (Axelrod, 1981; Savage, et al_., 1954). These conditions, taken together, provided for the creation and preservation of the vertebrate tracks in the formation. Playas existing where annual precipitation is low are less likely to be good environments for vertebrate track preservation. 286 This is mainly due to low rates of sedimentation caused by low annual ra in fa ll. Tracks impressed on the playa mudflats would have a greater chance of being destroyed due to extended sub-aerial exposure. Low annual rainfall may also prohibit the development of a sufficiently extensive and varied fauna that could support populations of vertebrates. This is the case for playa lakes in the southwestern United States where annual precipitation rates in the areas where they occur rarely exceed three or four inches and both diversity and abundance of vertebrates are low. The rates of sedimentation are also low. For example, the m ud intervals in Searles Lake have an accumulation rate of 25 cm/1000 years (Smith, 1979). Although a quantitative estimate of the rate of sedimentation of the Copper Canyon Formation doesn't exist, inferential evidence indicates that the rate may have been high. Sedimentological evidence from the evaporite facies supporting this includes the presence of mostly smooth surfaces on the dolomitic carbonate strata, the common occurrence of slump structures and the abundant, well-preserved vertebrate ichnofauna (see sections entitled "Dolomitic Carbonates-Interpretation" and "Rate of Trampling and Rate of Burial"). The Late Miocene Furnace Creek Formation, also in the Black Mountains, was deposited in an environment similar to that of the evaporite facies of the Copper Canyon Formation (Drewes, 1963). It had a minimum depositional rate of 127 cm/1000 years (Fleck, 1970). Set in a tectonically 287 active basin (Drewes, 1963) with an annual rate of precipitation of between 15 and 20 inches (Axelrod, 1957), the Copper Canyon Formation may have had a similarly high rate of deposition. The type of sediments that can accumulate in playa basins is also variable. For the ancient Copper Canyon playa, the mudflats consisted of precipitated carbonate m ud surrounding a small central gypsum salt pan. Other playas, both ancient and recent, may have similar deposits, predominantly clay-rich sediments, a wide variety of salts or a combination of all these types in a variety of proportions. Playa-lakes with large carbonate, s ilt and clay mudflats would serve as good candidates for preservation of vertebrate footprints. Playas consisting of more extensive salt deposits, such as Saline and Deep Springs Lakes (Hardie, et a l., 1978; Jones, 1965) have less extensive mudflats available for track impression and the salt its e lf would also discourage vertebrates from coming to drink. Other Cenozoic playa-lake environments similar to the evaporite facies of the Copper Canyon Formation were also sites for preservation of vertebrate tracks. The Upper Tertiary or Early Pleistocene Verde Formation in Arizona contains aphanitic limestones deposited in a playa-lake environment (Mahard, 1949). Proboscideans, cats, bears, artiodactyls and tapirs visited this environment as suggested by the occurrence of their tracks in this formation (Brady and Seff, 1959; Nininger, 1942). The absence of 288 extensive salt deposits associated with the carbonates and the presence of gastropods (Mahard, 1949) indicates that the playa-lake usually contained water suitable to draw a vertebrate population to drink. The dolomitic carbonates of the Eocene Green River Formation were also formed in a playa-lake environment and served to record vertebrate track impressions (Curry, 1957). The only other sedimentary environment in the Copper Canyon Formation to preserve vertebrate footprints is the distal facies of the alluvial fans surrounding and interfingering laterally with the precipitated carbonate deposited in the ancient playa lake. The rarity of tracks found in this facies, preserved only as casts in carbonate strata above sandstone beds, indicates that the distal fan facies was less conducive to preservation of tracks as compared to the playa-lake environment. This is due to the coarse-grained nature of the sediments deposited on the fans and higher flood water velocities which can scour away tracks in the fan's sandy deposits. From a survey of available vertebrate track litera tu re, the preservation of tracks on alluvial fans also seems rare. One well documented occurrence for dinosaur tracks from South Wales exists (Tucker and Burchette, 1977). The tracks occur on the surfaces of thin-bedded, fine to medium-grained sandstones which were deposited by sheet floods on an alluvial fan. Indeed, most Triassic examples of dinosaur footprints are preserved in environments similar to those of Cenozoic mammals and birds. Although details of the 289 lithologies of impression are rarely given in older descriptions of dinosaur tracks, "most Triassic examples appear to have formed on emergent mudflats in marginal lacustrine, playa or floodplain situations" (Tucker and Burchette, 1977). The absence of vertebrate tracks in the bioclastic carbonates, even those which contain evidence of subaerial exposure, warrants an explanation. This, in part, m ay be due to the fewer number of outcropping bioclastic carbonate surfaces as opposed to those of the dolomitic carbonates. The absence of tracks, however, may also be attributed to the nature of shorelines in freshwater lake environments. Factors affecting vertebrate track preservation in freshwater lake shoreline environments include the relative permanency of the shoreline in both time and space as compared to those of playa-lakes and the amount of vertebrate bioturbation around lake margins. More stable shoreline environments, typical of freshwater lakes, may be less conducive to track preservation than those of playa-lakes. Whereas in playa-lakes the shoreline constantly changes because of evaporating lake water, freshwater lake shorelines are more permanent. This results in less total surface area exposed over time to receive track impressions. The absence of a quickly receding shoreline also lessens chances for drying of the footprints, thus decreasing their preservation potential. 290 Freshwater lakes are also more likely to draw large populations of vertebrates to their shorelines. Intense vertebrate activity along a permanent shoreline is less likely to be conducive for track preservation than temporary shorelines exposed to minimal vertebrate tr a ff ic . This is due to intense bioturbation which would leave homogenized sediment devoid of sedimentary structures without any obvious tracks preserved (Laporte and Behrensmeyer, 1980). 291 PALEOECOLOGY Examination of track abundances indicates that artiodactyls most commonly frequented the ancient Copper Canyon playa-lake; birds, equids, felids and proboscideans were less common. The absence of distinct game tra ils and the haphazard arrangement of tracks implies that the animals were more than just in transit. The existence of the temporary lake may have been what attracted the animals to this spot, congregating in a similar fashion to modern mammals around water holes. During dry periods, the playa-lake may have served as an important source of palatable water drawing a large variety of vertebrates to trample across the mudflats. This may have been particularly true after thunderstorms, the playa serving as a storage area for runoff water. I f the K-Ar basalt date done for this study is accurate, the playa-lake may, at times, have been a desirable source of water for the local or migrating vertebrate populations since the Late Miocene was the driest time in the Tertiary (Axelrod, 1957, with new epoch designation from Berggren and Van Couvering, 1974). Food sources m ay also have drawn the animals to the margins of the playa-lake. The herbivorous animals, including the artiodacty1s, equids, proboscideans and possibly some of the birds, may have feed on plants growing around the margins of the playa. The presence of in-place fossil reeds and a transported palm trunk 292 indicate that vegetation was present. Green algal scums, which often form on the surfaces of temporary lakes and ponds, may also have provided a food source for the herbivores (eg. Picard and High, 1973). The presence of herbivores drinking and grazing was probably what drew carnivores to the area. Carnivore tracks in the formation are always found in association with those of artiodactyls, which may have been their target of prey. The presence of single tracks or trackways of carnivores in strata with artiodactyl tracks may suggest that the carnivores were solitary while the artiodactyls were gregarious, probably traveling in small groups. The presence of invertebrate tra ils and burrows also suggests the existence of food sources commonly used by birds. The tracks in the Copper Canyon Formation reflect part of the wide diversity of vertebrates present in southern California during the Hemphillian. Several varieties of grazing camels and horses flourished during this age (Downs, 1968). The progressive decline in annual precipitation beginning in early Tertiary times and continuing to the start of the Pleistocene promoted the development of extensive grasslands and steppe-vegetation which was conducive to the evolution and radiation of these grazing animals (Axelrod, 1981). An environment similar to that of the area surrounding the 293 ancient Copper Canyon lake exists today. The Serengeti plains of east Africa consist of grasslands dominated by large herding, grazing and mixed grazing - browsing ungulates and their predators (Van Couvering, 1980). This fauna, like that of the Late Miocene North American one, evolved in response to the development of extensive grasslands (Van Couvering, 1980), but escaped periods of major Quaternary extinction because of its equitorial position (Axelrod, 1967). The ancient Copper Canyon lake drew animals from surrounding grasslands to trample across its mudflats, much like waterholes and lakes draw animals from the Serengeti grasslands seeking food and water. 294 SUM M ARY AND CONCLUSIONS A study of the vertebrate footprints from the Copper Canyon Formation, and a survey of the available literature, has shown that marginal lacustrine environments are one of the best for preservation of tracks. Environmental factors of the ancient Copper Canyon playa lake which contributed to good footprint preservation include: 1) periods of flooding and intense evaporation which resulted in receding shorelines that presented wet, fine-grained sediment surfaces for impression and subsequent subaerial exposure and 2) high sediment accumulation rates which insured quick burial of the tracks. The major sedimentological factors that influence track morphology are grain size and sediment water content. The best impressions are formed in moist, muddy sediment. Variations in the morphology of any given type of track occur with changes in sediment water content at the time of impression. Morphologies indicative of track impression in sediment with water contents from saturated to nearly dry exist. The depth of impression and the thickness of the stratum of impression act in conjunction with sediment water content to control track morphology. The rate of trampling can also have a strong influence on preserved morphologies. High rates of trampling leave the sediment highly bioturbated with only obscured morphology preserved. Low and moderate rates of trampling allow for the most distinct 295 morphologies to be preserved. Future work could consist of neoichnological experiments which would test the effects of grain size and sediment water content on track morphology. This might be facilitated through the use of models of vertebrate hooves or feet, impressing them into m ud of different consistencies around modern playa-lake margins and observing the resulting morphologies. The qualitative terms for sediment consistency, as gooey, sticky, moist and hardening could also be quantitatively defined by actually measuring sediment water contents associated with the different types of morphologies. Detailed studies of vertebrate tracks, in conjunction with a determination of the environments of deposition of the lithologies they occur in, may add substantially to knowledge of the distributions and paleoecology of ancient vertebrates. This m ay especially be true in parts of the world where lacustrine rocks are common, as in the western U.S. (Picard and High, 1972). Further work is needed in locating track lo calities, classifying the vertebrate footprints and determining their age to realize important contributions to vertebrate paleoecology from a consideration of footprints. 296 REFERENCES Alf, Raymond M., 1959. Mammal footprints from the Avawatz Formation, California. Bulletin, Southern California Academy of Sciences, 58(1):1— 7. A lf, Raymond M., 1966. Mammal trackways from the Barstow Formation, California. Bulletin, Southern California Academy of Sciences, 65(4):258-264. Amanniyazov, K., Nigarov, A., and Uzakov, 0 ., 1979. Petrified traces of animals in the paleodesert. Problemy Osvoeniia Pustyn, 5:80-82. Anonymous, 1960. The "Strawberry Slab". Geotimes, 5(3):34. Arnautovic, I. and Abdalla, 0 ., 1969. Elastic structures of the foot of the camel. Acta Anatomica, 72:411-428. Axelrod, Daniel I . , 1967. Quaternary Extinctions of Large Mammals. University of California Publications in Geological Sciences, v. 74, 42 pp. Axelrod, Daniel I . , 1957. Late Tertiary floras and the Sierra Nevada u p lift. Bulletin, Geological Society of America, 68:19-46. Axelrod, Daniel I . , 1973. History of the Mediterranean ecosystem in California. In: diCastri, F. and Monney, H. A. (eds.), Ecological studies: Analysis and Synthesis (Mediterranean Type Ecosystems - Origin and Structure), vol. 7. Springer- Verlag, New York p. 225-276. Axelrod, Daniel I . , 1981. Role of volcanism in climate and evolution. Geological Society of America, Special Paper 185, 59 pp. Beasley, H. C., 1904. Report on footprints from the Trias, Part 1. Report, British Association for the Advancement of Science, (Southport, 1903):219-230. Behrensmeyer, Anna K. and Laporte, Leo F., 1981. Footprints of a Pleistocene hominid in northern Kenya. Nature, 289:167-169. Bell, K. N. and DeMerlo, J. A., 1969. Some fossil bird tracks. Victorian Naturalist, 86:134-135. 297 Berggren, W . A. and Van Couvering, J. A., 1974. The late Neogene: Biostratigraphy, geochronology and paleoclimatology of the last 15 million years in marine and continental sequences. Palaeogeography, Palaeoclimatology, Palaeoecology, 16 (1/2): 1-216. Bice, D. C., 1979. Tephra correlation and the age of human footprints near Managua, Nicaragua. Abstracts, Geological Society of America, vol. 11, no. 7, p. 388. Bjork, Philip R., 1976. Mammalian tracks from the Brule Formation of South Dakota. Proceedings, South Dakota Academy of Science, 55:154-158. B latt, Harvey, Middleton, Gerard and Murray, Raymond, 1980. Origin of Sedimentary Rocks. Prentice-Hal1, New Jersey, 782 pp. Brady, L. F. and Seff, Philip, 1959. "Elephant H ill" . Plateau, 31:80-82. Bram, Heinrich, 1954. Fahrten von wirbeltieren aus der subalpinen Molasse des Bergsturz gebietes von Goldau. Ecologae, Geologae Helvetiae, 47:406-417. Brinton, D. G., 1887. On an ancient human footprint from Nicaragua. Proceedings, American Philosophical Society, 24:437-444. Brown, Roland W., 1947. Fossil plants and human footprints in Nicaragua. Journal of Paleontology, 21(l):38-40. Bull, William B., 1972. Recognition of alluvial-fan deposits in the stratigraphic record. In: Rigby, J. Keith and Hamblin, Kenneth Wm., Recognition of Ancient Sedimentary Environments. Society of Economic Paleontologists and Mineralogists, Special Publication No. 16, p. 63-83. Casteret, Norbert, 1948. The footprints of prehistoric man: Vivid new evidence of our ancestors of fifteen thousand years ago. The Illustrated London News, October 9, p. 408-410. Chaffee, Robert G., 1943. Mammal footprints from the White River Oligocene. Notulae Naturae, 116:1-13. Cooke, Ronald V. and Warren, Andrew, 1973. Geomorphology in Deserts. Anchor Press, London, 374 pp. Curry, Donald H., 1939. Tertiary and Pleistocene mammal and bird tracks in Death Valley. Abstracts, Geological Society of America, 50:1971-72. 298 Curry, Donald H., 1941. Mammalian and avian ichnites in Death Valley. Abstracts, Geological Society of America, 52:1979. Curry, D. H., 1941. Two billion years in Death Valley. Saturday Evening Post, June 13, p. 16-17, 102, 105. Curry, H. D., 1957. Fossil tracks of Eocene vertebrates, south western Uinta Basin, Utah. In: Intermountain Association of Petroleum Geologists, Eighth Annual Field Conference, p. 42- 47. deRaaf, Dr. J. F. M., Beets, Dr. C., and van der Sluigs, Kortenbout, G., 1965. Lower Oligocene bird-tracks from northern Spain. Nature, 207:146-148. Downs, Theodore, 1968. Fossil Vertebrates of Southern California. University of California Press, Berkeley and Los Angeles, 61 pp. Drewes, Harold, 1963. Geology of the Funeral Peak quadrangle, California, on the east flank of Death Valley. United States Geological Survey Professional Paper 413, 78 pp. Duges, Alfredo, 1894. Felis fosil de San Juan de los Lagos. La Naturaleza, 2(8):421-423. Dunham, R. J., 1962. Classification of carbonate rocks according to depositional texture. In: Ham, W . E., Classification of Carbonate Rocks. American Association of Petroleum Geologists, Memoir 1, p. 108-121. Erickson, Bruce R., 1967. Fossil bird tracks from Utah. Museum Observer, 5:1-6. Eugster , Hans P. and Hardie, Lawrence A., 1975. Sedimentation in an ancient playa-lake complex: The Wilkins Peak Member of the Green River Formation of Wyoming. Bulletin Geological Society of America, 86(3):319-334. Eugster, H. P. and Hardie, L. A., 1978. Saline lakes. In: Lerman, Abraham (ed.), Lakes-Chemistry, Geology, Physics. Springer-Verlag, New York, p. 237-293. Fleck, R. J., 1970. Age and tectonic significance of volcanic rocks, Death Valley area, California. Bulletin, Geological Society of America, 81(9):2807-2816. Folk, R. L., 1962. Spectral subdivision of limestone types. In: Ham, W . E. (ed.), Classification of Carbonate Rocks. American Association of Petroleum Geologists, Memoir 1, p. 62-84. 299 Folk, R. L., 1974. Petrology of Sedimentary Rocks. Hemphill's Book Store, Austin, Texas, 182 pp. Gardner, William A., 1940. Place of the gods. Natural History, January, p. 41-54. Gloppen, Tor G. and Steel, Ron J., 1981. The deposits, internal structure and geometry in six alluvial fan-fan delta bodies (Devonian-Norway) - A study in the significance of bedding sequence in conglomerates. In: Ethridge, Frank G. and Flores, Romeo, M., Recent and Ancient Nonmarine Depositional Environments: Models for Exploration. Society of Economic Paleontologists and Mineralogists, Special Publication no. 31, p. 49-69. Hardie, Lawrence A., Smoot, Joseph P., and Eugster, Hans P., 1978. Saline lakes and their deposits: a sedimentological approach. In: Matter, Albert and Tucker, Maurice E. (eds.), Modern and Ancient Lake Sediments. Special Publication Number 2, International Association of Sedimentologists, Oxford, p. 7-41. Hawley, J. E. and Hart, R. C., 1934. Cylindrical structures in sandstones. Bulletin, Geological Society of America, 45: 1017-1034. Hildreth, Wes, 1976. Death Valley Geology. Death Valley Natural History Association, Death Valley, 72 pp. Hooke, R., 1967. Processes on arid-region alluvial fans. Journal of Geology, 75:438-460. Johnston, C. Stuart, 1937. Tracks from the Pliocene of west Texas. American Midland Naturalist, 18(1):147-152. Jones, Blair F., 1965. The hydrology and mineralogy of Deep Springs Lake, Inyo County, California. Unitd States Geological Survey Professional Paper, 502-A, 56 pp. Kelts, K. and Hsu, K. H., 1978. Freshwater carbonate sedimenta tion. In: Lerman, Abraham (ed.). Lakes-Chemistry, Geology, Physics. Springer-Veriag, New York, p. 295-323. Kerr, Paul F., 1977. Optical Mineralogy. McGraw-Hill, New York, 492 pp. Lamb, Samuel H., 1968. Trail to oblivion. New Mexico W ildlife, November-December, p. 21. 300 Laporte, Leo F. and Behrensmeyer, Anna K., 1980. Tracks and subtrate reworking by terrestrial vertebrates in Quaternary sediments of Kenya. Journal of Sedimentary Petrology, 50(4): 1337-1346. Leakey, M. D. and Hay, R. L., 1979. Pliocene footprints in the Laetolil Beds at Laetoli, northern Tanzania. Nature, 278: 317-323. Lessertisseur, Jacques, 1955. Traces fossiles d'activite* animale. Memoires de la Societe' Geologique de France, no. 74, 148 pp. Link, Martin H., 1982. Sedimentology of the Upper Miocene Piru Gorge Sandstone Member of the Ridge Route Formation, Ridge Basin, Southern California. In: Crowell, J. C. and Link, M. H., (eds), Geologic History of Ridge Basin, Southern California. Pacific Section, Society of Economic Paleon tologists and Mineralogists, p. 127-134. Lucas, Frederick A., 1928. Fossil footprints. Evolution, November, p. 5. Mahard, Richard H., 1949. Late Cenozoic chronology of the upper Verde Valley, Arizona. Journal of the Scientific Laboratories, Denison University 41:97-127. Mangin, Jean Philippe, 1962. Traces de pattes d'oiseaux et flute - casts associes dans un "facies flysch" du Tertiaire Pyreneen. Sedimentology 1:163-166. McGowen, H. and Groat, G. G., 1971. Van Horn Sandstone, west Texas: An alluvial fan model for mineral exploration. Bureau of Economic Geology, University of Texas, Austin, Investiga tion 72, 57 pp. Mossman, David J. and Sarjeant, William, A. S., 1983. The foot prints of extinct animals. Scientific American, 248(1): 74-85. Motts, Ward S., 1970. Some hydrologic and geologic processes influencing playa development in the western parts of the Basin and Range Province, United States. In: Motts, Ward S. (ed.), Geology and Hydrology of Selected Playas in Western United States. Geology Department, University of Massachusetts, Amherst, Mass., p. 237-286. Mountain, Edgar D., 1966. Footprints in calcareous sandstone at Nahoon Point. South African Journal of Science, 62:103-111. 301 Moussa, Mounir T., 1968. Fossil tracks from the Green River Formation (Eocene) near Soldier Summit, Utah. Journal of Paleontology, 42(b):1433-1438. Moussa, Mounir T., 1970. Nematode Fossil tra ils from the Green River Formation (Eocene) in the Vinta Basin, Utah. Journal of Paleontology, 44(2):304-307. Muller, G., Irion, G. and Forstner, U., 1972. Formation and diagenesis of inorganic carbonates in the lacustrine environment. Natur wissenschaften, 59:158-164. Murie, Olaus J ., 1974. A Field Guide to Animal Tracks. Peterson Field Guide Series, No. 9, Houghton M ifflin , Boston, 375 pp. Nininger, H. H., 1941. Hunting prehistoric lion tracks in Arizona. Plateau, 14(2):21-27. Otten, James K., 1977. Geology of the Central Black Mountains, Death Valley, California: The Turtleback Terrane. Unpub lished Dissertation, Pennsylvania State University, 155 pp. Panin, N., 1961. Asupra unor urme organice si mecanice din Miocenul de la confluenta Putnei Cu Zabala. Studii si Cercetari Geologie, 6:63-73. Panin, N. and Avram, E., 1962. Noi urme de vertebrate in Miocenul Subcar patilar Rominesti. Studii si Cercetari Geologie, 7(3-4):455-484. Panin, N. and Stefaneseu, M., 1968. Un nou punct ihno-fosi1ife r in Molasa Mincena din Carpatii o rien tali. Studii si Cercetarie Geologie, Geof., Geogr., Seria Geologie, 13(2):521-528. Pettijohn, F. J ., 1975. Sedimentary Rocks. Harper and Row, San Francisco. 628 pp. Picard, M. Dane and Hulen, J. B., 1969. Parting lineation in siltstone. Bulletin, Geological Society of America, 80(12): 2631-2636. Picard, M. D. and High, L. R., 1972. C riteria for recognizing lacustrine rocks. In: Rigby, J. Keith and Hamblin, Kenneth Wm., Recognition of Ancient Sedimentary Environments. Society of Economic Paleontologists and Mineralogists, Special Publication No. 16, p. 108-145. Picard, Dane M. and High J r., Lee R., 1973. Sedimentary Structures of Ephemeral Streams (Developments in Sedimentology, 17). Elsevier Scientific Publishing Company, New York, 223 pp. 302 Picard, M. Dane and High J r., Lee R., 1981. Physical stratigraphy of ancient lacustrine deposits. In: Ethridge, Frank G. and Flores, Romeo, M., Recent and Ancient Nonmarine Depositional Environments: Models for Exploration. Society of Economic Paleontologists and Mineralogists, Special Publication no. 31, p. 233-259. Plaziat, Jean-Claude, 1964. Pistes d1 oiseaux et remaniements synsedimentaires dans le lu tetier du detroit de Carcassorne (Aude). Bull. Soc. Geol. de France, 7 (6): 289-293. Reineck, H. E., 1969. Die entstehung von runzelmarken. Sencken- bergiana Marit, 1:165-168. Reineck, H. E. and Singh, I. B., 1980. Depositional Sedimentary Environments. Springer-Veriag, New York, 549 pp. Rich, Pat Vickers, 1979. The Dromornithidae, an extinct family of large ground birds endemic to Australia. Australia Bureau of Mineral Resources, Geology and Geophysics, Bulletin 184, 195 pp. Richardson, F. B. and Ruppert, K., 1941. Nicaragua. Yearbook, Carnegie Instituion of Washington, 41 (269-271). Robertson, George M. and Sternberg, George F., 1942. Fossil mam m al tracks in Graham County, Kansas. Transactions, Kansas Academy of Science, 45:258-261. Romer, Alfred Sherwood, 1966. Vertebrate Paleontology. University of Chicago Press, Chicago, 111., 468 pp. Rutherford, Ralph L. and Russell, Loris S., 1914. Mammal tracks from the Paskapoo Beds of Alberta. Bulletin, Geological Society of America, 25:262-264. Sanders, J. E., 1965. Primary sedimentary structures formed by turbidity currents and related resedimentation mechanisms. In: Middleton, G. V. (ed)., Primary Sedimentary Structures and their Hydrodynamic Interpretation. Society of Economic Paleontologists and Mineralogists, Special Publication 12, p. 192-219. Sarjeant, William Antony S., 1975. Fossil tracks and impressions of vertebrates. In: Frey, Robert W . (ed.). The Study of Trace Fossils. Springer-Verlag, New York, p. 283-324. 303 Savage, Donald E., Downs, Theodore, and Poe, Owen J ., 1954. Cenozoic land lif e of southern California, In: Jahns, Richard H. (ed.), Geology of Southern California: Historical Geology. California Division of Mines, Bulleton 170, chapter 3, p. 43- 58. Savage, Norman, M., 1971. A varvite ichnocoenosis from the Dwyka Series of Natal. Lethaia, 4:217-233. Scholle, Peter A., 1978. Carbonate rock constituents, textures, cements, and porosities. American Association of Petroleum Geologists, Memoir 27, 241 pp. Scholle, Peter A., 1979. Constituents, textures, cements, and porosities of sandstones and associated rocks. American Association of Petroleum Geologists, Memoir 28, 201 pp. Simpson, Gaylord George, 1941. Discovery of Jaguar bones and footprints in a cave in Tennessee. Novitates, American Museum of Natural History, no. 1131, p. 1-12. Smith, George I . , 1979. Subsurface stratigraphy and geochemistry of late Quaternary evaporites, Searles Lake, California. United States Geological Survey Profesional Paper 1043, 130 pp. Smith, Paul R., 1982. Sedimentology and diagenesis of the Miocene Peace Valley Formation, Ridge Basin, southern California. In: Crowell, J. C., and Link, M. H. (eds.), Geologic History of Ridge Basin, Southern California. Pacific Section Society of Economic Paleontologists and Mineralogists, p. 151-158. Squires, Richard L. and Advocate, David M., 1982. Sedimentary facies of the non marine Lower Miocene Diligencia Formation, Canyon Springs area, Orocopia Mountains, Southern California. In: Ingersoll, R. V. and Woodburne, M. 0. (eds.), Cenozoic Non-Marine Deposits of California and Arizona. Pacific Section, Society of Economic Paleontologists and Mineralogists, p. 101-106. Streckeisen, Albert, 1979. Classification and nomenclature of volcanic rocks, lamprophyres, carbonitites and melitic rocks: Recommendations and suggestions of the I.U.G.S. subcommission on the systematics of igneous rocks. Geology, 7 (7):331— 335. Tucker, Maurice E. and Burchette, Trevor, P., 1977. Triassic dinosaur footprints from south Wales: Their context and preservation. Palaeogeography, Palaeoclimatology, Palaeoecology, 22(3):195-208. 304 Twenhofel, W . H. (ed.)* 1932. Treatise On Sedimentation. Williams and Wilkins Co., Baltimore, 926 pp. Van Couvering, Judith, A. H., 1980. Community evolution in east Africa during the late Cenozoic. In: Behrensmeyer, Anna K., and H ill, Andrew P. (eds.), Fossils in the Making, University of Chicago Press, Chicago, p. 272-298. Van Houten, F. B., 1973. Origin of red beds, a review: 1961-1972. Annual Review of Earth and Planetary Sciences, (1):39-61. Vialov, 0. S., 1960. New fossil footprints of a bird in the Miocene of Ciscarpathia. Doklady Akademii Nauk SSSR, 135(5): 1237-1239. Vialov, 0. S., 1961. Paleogenovoy flish svernogo sklona karpat. AN, USSR, Investigations. Vialov, 0. S., 1966. Sledy Zhiznedeyatel-nosti Qrganizmow i Ikh Paleontologiches-koe Znachenie. (The Traces of the Vital Activity of Organisms and their Paleontological Significance). Akad. Nauk. Ukraine, S.S.R., 219 pp. Visher, G. S., 1965. Use of vertical profile in environmental reconstruction. Bulletin, American Association of Petroleum Geologists 49:41-61. Walker, T. R., 1967. Formation of red beds in modern and ancient deserts. Bulletin, Geological Society of America, 78(3): 353-368. Weidmann, Marc and Reichel, Manfred, 1979. Traces de pattes d'oiseaux dans la Molasse suisse. Ecologae, Geologae Helvetiae, 72(3):953-971. Wetmore, Alexander, 1956. Footprint of a bird from the Miocene of Louisiana. Condor, 58:389-390. Williamson, Charles R. and Picard, Dane M., 1974. Petrology of carbonate rocks of the Green River Formation (Eocene). Journal of Sedimentary Petrology, 44(3):738-759. Williams, Howel, Turner, Francis J. and Gilbert, Charles M., 1954. Petrography - An Introduction to the Study of Rocks in Thin Section. W . A. Freeman and Company, San Francisco, 406 pp. 305 Wright, L. A. and Troxel, B. W., 1973. Shal1ow-fault interpreta tion of Basin and Range Structure, southwestern Great Basin. In: de Jong, K. A. and Scholten, Robert (eds.), Gravity and Tectonics. John Wiley and Sons, New York, p. 397-407. Young, J. Z., 1950. The Life of Vertebrates. Clarendon Press, Oxford, 767 pp. 3 0 6 APPENDIX A Summary of Thin Section Data From Major Lithologles In the Carbonate Member 3 0 7 DOLOMITIC CARBONATES Thi n S ectio n Allochems 0-thochems U I D S C T e rrigen ou s Q F VRF AM T e x tu ra l C la s s . (Dunham, 1962) 2 - 80 20 - 90 10 3 61 36 <1 d o lo m itic carbonate mudstone 11a 12 78 10 100 100 - 70 28 - 2 d o lo m itic wackestone l i b 3 60 37 1 2 100 80 20 - <1 d o lo m itic carbonate mudstone 12 60 35 5 100 100 58 37 5 <1 d o lo m itic packstone S it e A S it e B S it e C S it e E V e rte b r a te Im p re s sio n -B e arin g L ith o lo g le s 1. <1 97 3 _ 100 100 _ 65 35 * • d o lo m itic carbo nate mudstone 1 . - 73 27 - - 100 - - 60 34 - 6 d o lo m itic carbonate mudstone 2. _ 97 3 _ • 100 ” 8 2 • 90 d o lo m itic carbonate mudstone 1. 3 72 25 100 - 100 - - 79 17 1 3 d o lo m itic carbonate mudstone 1. 2 95 3 100 - 100 - - 6 1 93 d o lo m itic carbonate mudstone 2 . 40 57 3 100 - 100 - - 58 40 - 2 d o lo m itic packstone 3. - 91 9 " _ 100 - - 45 53 1 1 d o lo m itic carbonate mudstone 4 . 35 61 4 100 - 100 - - 70 28 1 1 d o lo m itic wackestone 5. 22 70 8 98 2 98 2 - 80 20 « 1 <1 d o lo m itic wackestone 6 . 70 25 5 100 - 100 - - 70 30 - « 1 d o lo m itic packstone 7 . 4 29 67 100 90 10 90 10 « 1 Coarse S ilt s t o n e : d o lo m itic v o lc a n ic subarkose (F o lk , 1974 1. - 95 5 - - 100 - - 78 21 - 1 d o lo m itic carbonate mudstone 2. 35 50 15 95 5 100 - - 90 8 - 2 d o lo m itic wackestone 0 - orthochems T - te rrig e n o u s e la s t ic s u . . .... .. . 1 D S • y C i I J y C llU U d LfdMIL.3 - u n id e n t if ie d allochem - i n t r a c la s t s - d o lo m itic m lc r it e - sparry c a l c it e Q - qu artz F - fe ld s p a r - v o lc a n ic rock fragments VRF AM accessory m in erals * S it e lo c a tio n s shown on map on fo llo w in g page. 3 0 8 EXPLANATION OF SYMBOLS C Aluvkm C M o r m o n Point Fo rm a txx Copper Canyon Formation C o n g lo m e ra te M e m b e r 0 Carbonate M e m b e r 6 Basalt C Older Volcanos # P recam bria n M etam orph ic Basement N o rm a l Fault Contacts S y n c B n e Generalized Sections 1—4 Detailed Sections 1 ~ £ Collection Site of Basalt for Radiometric Dating m m . 3 1 0 BIO CLASTIC CARBONATES Thi n S ec tio n A 0 AT 1ochems OS AG G Oo O-thochems T e x tu ra l A Com positional Names 4 95 4 1 19 79 <1 - 2 <1 98 - 2 Packed I n t r a c l a s t i c Pel 1e t i ferous o s tracod b io m ic M te Packstone 6 84 15 1 83 17 - - - - 100 - - Packed o s tra c o d - bea~1ng p e lm ic r it e Packstone 9a 79 20 1 85 15 - - - - 100 - - Packed o s tra c o d - b e a rin g p e lm ic r it e Packstone 9b 69 30 1 80 19 - 1 - - 90 - 10 Packed o s t-a c o d - b ea rln g p e lm ic r it e Packstone 2' 30 67 3 5 94 - 1 - - 97 3 - Sparse p e l l e t l - ferous ost-acod biomi c r i t e Wackestone 6' 69 30 1 75 25 - - - - 99 <1 1 Packed ostracod biopelm i c r i t e Packstone 7 ' 80 20 - 99 1 - - 100 Chalcedony cemented packed p e lo id a l carbonate rock Packstone 12' 75 25 <1 20 80 - - - - 98 - 2 Packed p e ll e t l f e r o u s ostracod b io m lc r ite Packstone 14' 78 20 2 85 15 - - - - - - - Packed o s t-a c o d - b ea rln g p e lm ic r it e Packstone B' 30 70 <1 80 20 - 79 21 Chalcedonic sparse o s tra c o d -b e a ri ng p e lm lc ri te Wackestone C ' 60 40 <1 5 90 5 - - - 88 12 - Packed a lg a l p e lo id a l ostracod bi omi c ri t e Packstone 3" 65 35 <1 98 2 - - - - 89 - 12 Chalcedonic f o s s l l - ife r o u s p e lm ic r it e Packstone 4" 45 35 20 55 11 - - 34 - 43 57 - P oo rly washed i n t r a c l a s t i c sandy p e ls p a r it e dolom1t1c Packstone 0 - orthochems T - te rrig e n o u s e la s t ic s P - p e lo id s AG - algae G - gastropods I - In t r a c la s t s M - c a l d t l c m ic r it e S - sparry c a l c it e C - chalcedony 3 1 1 5t£ S A N D S T O N E S Thin Section T 0 A Q Terrigenous F R A M Rock Fragments VRF GRF MRF A ll I . M atrix M S c Grain Size Range * Mode Compositional Name (Folk, 1974) 1 80 20 - 1 91 5 3 100 - - 100 - - 1.5-4.0 2.5 volcanic arkose 3 90 10 - 5 60 35 <1 99 1 - 100 - - 1.5-4.0 2.0 volcanic H t h lc arkose 5 80 20 - 1 79 20 <1 100 - - 100 - - 1.5-3.5 2.5 volcanic 11th1c arkose 7 75 25 - 4 6 90 <1 100 - - 100 - - -0 .5 -3 .5 2.5 volcanic H th a r e n lte 8 79 20 1 3 27 70 <1 99 1 100 100 - - -1 .5 -4 .0 2.0 volcanic feldspathlc 11tharen1te 10 69 30 1 1 3 94 2 99 1 100 100 - - 0.0-4.0 1.75 volcanic I1tharen1te 13 68 30 2 <1 68 30 2 99 1 100 100 - - -.7 5 -.2 5 .75 volcanic l l t h l c arkose 5* 85 15 - 1 44 35 <1 100 - - 100 - - 1.5-3.5 2.5 volcanic l l t h l c arkose 5" 59 40 1 10 30 60 <1 100 - 100 - 100 <1 1.5-4.0 2.5 feldspathlc volcanic a re n lte 2" 90 10 - 28 69 2 1 10 90 - 100 - - -.5 -3.5 1.5 volcanic arkose T - terrigenous elastics 0 - orthochems A - allochems Q - quartz F - feldspar R - rock fragments A M - accessory minerals V R F - volcanic rock fragments M R F - metamorphlc rock fragments 1 - Intracla sts M - m lcrlte S - sparry c a lclte C - chalcedony APPENDIX B Geologic M ap D etailed S tratig rap h ic Sections 3 1 3 EXPLANATION OF SYMBOLS C Aluvkm # M orm on Point Form ation Copper Canyon Formation # Conglom erate M em ber 0 Carbonate M em ber % Basalt % O W er Vokanics # Precam brian Metam orphic Basement Norm al Fauft Contacts Sync lin e Generalized Sections 1—4 Detailed Sections 1 -9 Collection Site of Basalt . for Radiometric Dating ^ 314 315 m W f i I /Z M i l e C .I.V 40' LITH O LO G Y Dolomitic Carbonate Gypsum Bioclastic Carbonate Pebble—Cobble Conglomerate Granule—Pebble Conglomerate Sandstone SUtstono W E A TH E R E D PROFILE TH IN SEC TIO N # Claystooe V itn c T utt Basalt S s a iS S S e S S Para 1 1 * 1 Laminations Cross Stratification Flat Bedding Gratod BaMtoa Dosoieatioo Cracks TRACE F0S3A.S CamivoripodWa Avipodia Rato Trank Gastropods BASAL CONTACTS Abrupt Erosienal Explanation of Symbols Used for For Detailed Sections and Generalized Sections (Plates 1 & 2). 3 1 6 I Meter 86 80 m Covered BaTilKv n . \ UItLTD B l M i i Detailed Section 1 3 1 7 30- 2 5 - TOn\u)n\unTfi ' ' 1 " , I U ff"' "lu O jp.'VVti.M \ n liM i'; % ' 1 V < ■'• '"■y,»' f/l.' M V u! v , ij-l ji'iY.'. r w mu '! mi'UUMUmi v^rnAi tm'!(a 117 ' t 1 *!M <!'(i 1U 11 ’U ! iM'llU' ju,i V / m '1 m'1 '^ 20 _ 15 - 7 V ~ T T 7 r / r r / / 7T7 T Z n 3 1 8 r , L .IL U iw m w w uni 'MRv cun w.ithimmiitKv nliui ii U \H m i nif\n UtliMll'Jmlii KHVffMl!t!llllVi~ I Meter ic > e > c > $ - < 5 -s“ o OOoOOOoo1 o o o o o o o 0) OOOOOQOqo} 1 0 - D e t a i l e d S e c t i o n 2 3 2 0 0 la lb 3 2 1 I Meter 2 0 5— 1 0 - 5 - *o°oV)°&3s<& o o « > Q O o H 00 6 o ^ c o ^ l r^ c o \-Jo o t> 0 o o o ° o o O ' —^ o o O o Df<n e x 00 O o & 3 2 ® £ > oo ° ^ O S ? 9 p ; ° oQgo° Q a C3? i 1 r. <D®oC P l § ' ^ C j o ~ '*' ■ '" ' O O _ f s o f s G S * ^ > o r \ ® 6 r \ 2*2, CO O S o £ > o S Q SS£)S?£>^ O S ^ O o e C S o Q o ^ O S o c o C ^.oo r" QC> Q .— ) o O V ' Q z l ' / r h l o S Q j S Q 0 ^ oo O 0° O C < —> r> O j e^a. tot>Q CZ3 • & Oc>CXyr* o° S ~J O O ^ S 2 OtJ Q o p £ T C 9 & < & -Jarositic Siitstone D e t a ile d S e c t i o n 3 3 2 2 I Meter 5 0 - J V 45 v . 'jJ il/j 4 0 - 3 /. /. /.'7\ i ' r ~ l 7 » ‘ i ‘/ J / V 3 V ) i J r ~ 3 / , > 1 T rrT r T r v 2 0 - r r n 4 H 5 m Covered N / / / , / /'7 « .•■ •• •••i ••• )• .« •• > • , V X 5" Detailed Section 4 323 1 5 1 0 - 5 - 0. o oooo ooo. Oo oo o O oo OOOO&OC’ OI o o o o o o © © c a o 0 o o o o oo o o ©006 b„o C C J 0 6 0 OOOO OOO' 3 7*7— / " / —T .2 1 7 7 7 / — 7 r i L i. j. z lzj \ m r i I r r T tth x i n " " f O O 0_ f> O ■ o j O l 0 0 ^ 0 0 0 0 D © O 0 OOO 6 uo o o o o o ^ n i x in I I I I I • I J 7~T~7 D O 7 7 7 1 1 1 1 S ] tf z P ^ = L i 7 iT — 7 7 X X J 0 ^ 6 0 0 cy3-^p_^gQo. z : / , y , : z ;iz \i 7 1 7 = S z z: E g TJ. Z~ T ~Z o o C o"o o b g-.QX P j2 r r z r z z z f z r 3 z / "7 7 r . L Z i 3 2 4 I Meter 6^ 4 - 3 - jfnj J i '/ ’/ *! -r% ~ r P 7 T P F i V / V / 7 ^ 7 1 l l l l i 1 i r l ° r r ~ n L J _ 1 -J 5 i l l r r I f * T 1 j ~ r ~ D ~ i~ i i ' r S i l l (oo o o o o p c j ----------- o o o / Z Z .Z 7 7 ZZ/ 7 Z.Z I2 ‘ 0 Carbonate Mounds C ? Undisturbed Carbonate Stratum D e t a i l e d S e c tio n 5 325 VO < N C O 0 0 0 o- -o O o O 0 0 0- c. 0 7 4 “ > Q ) 2 CO o a» CO o JL a w V 0 D 0 Pi 2H3 ir o a ro o o ■ < o 0 ) o r 0 o L r R ^ £ d I l 1 1 t r T I . I ■ I ' P F 3 2 8 I Meter 36 31- 2 6 _ 5 _ ti Q b 'l^'n n:!i n D C cp)»r?K Q ?°) /^ooor^°"or V / 7 7 7 C K f Q o * w o U .» ~ 1 *5 i" , ■* ■> 1 — p w* '— 1 I * 1 S 3 Z ; . co * o i ' i i ^ ° Q ° ' 3 “°oC )S q^^ p o Q °o o V > o g fi S’ O O Q Q O l Q g g Q S S r a S ^ Covered 16 O o o °^P c ? O ^0 0-0 o O_o tft. 0 .9 Q t& ..s .. P ^ w T " ^ ft® Detailed Section 7 I Meter Detailed 50- 4 5 - 4 0 - 35— % * o *, '' i . i . i ' . i p v *' T ' - r n ~ T - " l i l t f * & i p A Q rD $ \ Q g O f f i i . » > > D 5 G H Section 8 3 3 0 30 _ 20 - 1 5 - 4 M & c 3 '& e 3 OO O OO o oo Q o O OQQo^ Q0 O^O^O O C 14' 3 3 1 1 0 - e o ooooooj o o o o o o o o O 0 o o t o O o O o o o Cl DO OC» t c oj o o o o o o 5 - p p p t . O ° o o o © o o o a o o o © O O © D o o o e > c ? c* o o o o o c y o ,.r o o o © o o o o o o C » O o o o © o c > 3 3 2 40 - 3 5 - 3 0 - 25 I Meter O v8cQ O i s o o O Z o Q . s s d a Q & Q Z O o °o o o oo °% o y £ } Q p & £ > £ O % % V 0 O 0 -6 o"o ca < e » c ? O o o % * _ . Q Q ^ O ° ^ c ? O % % 0 ° v o £ D £ > P o ° c O ° o g < •* •' --- :■ .. *.w : Detailed Section 9 2" 333 20 1 5 - 1 0 - zzzzz 5 - 3 3 4 5 0 0 M oSQ o o SO o O o L1TH0FACIES Conglomerate Member Evaporite Facies Bioclastic Carbonate Facies Basalt Carbonate Member Plate 1 Generalized Sections Lower P a r t Copper Canyon Fro. N 5 0 0 M 0 Mormon Point F m. e>°o°oL3 8 S C O ° o ° o 8 J ° C ( S o ° O O Cl g O o °0 - D i l i 0 ) 0 0 C S o o z z z z z :i “O O C 5 Q Q tz n j—L fj. E SESa E E 7— r Q Q 7 y I covered o > ° ° f < — O p V "Older Volcanics" Mormon Point F m. O V r z z z r t 'rr'm 3 =SS? 3 = 3 T o U ZS . 7~ n ~ L T J / f l r z T z r o ^cnao„oZ 6 covered / •* / znznzx a covered covered VVrV^ i i i Z T .c n . / r r n F y W Plate 2 Generalized Sections Mormon Point F m. ,A_A A j A A A j ^A/ o o SeSSOS^S '2 Ogg > o o Q i r .. L o o„s^JL' £ ? _ q SSE S Q M Q II . Q . §§. Q i 0 c . sa O O |0|V D |g .< | o o r s o o < S o .2 Q _So^_Q PjSAa r 1 —? o o A o O o f < ^ Q O Q _ V v l0 9 j: O O C~l->0o0 0 o o o o O vj c Cd o g C ? g g C £ ° o ° Oo ° o ° » S2 l r_z ’ 1 r _ r Z T 2 T Z Z Z Z Z Z Z IT T 1 1 1 11 O o r—> to o C N ° ^ v - P o q C -jJ o (— p O O O p O O C -O o o < -r^J O © O o t~ v — > o o C ^ ) 0 OO O o d o C~~Z o O T ~ > o o f i=J_o o JZ Jlo.sT t SnLUAi o o O^P ° o 5 TSO Q C 'O O o s — r o £ ? ,oo o o ( o o r'V'-? o o O o j O OZjT. O o _ O a CO o o r \ o o c i b - L q i T o q A o o n o o ~ e.p q 2-5 = ' / O o r~ S O O s ~ \o O O S X O O S / o ,0 ^ 0 0 o°o( o o O O O CVo o C 3 gS&Sgcl 9.9 .crx-0 Q-£^xg, CbSSQSSC P P . . Q \P Q jQ .?a ’" ° £ 2 S L d Mormon Point F m. o°C? D°o°o ° 8 G n ° ° oo C3S° C CJoS O o o o n ° ° r o o O X / O 0 S xx o o -Ms o o °0 s s o s s c Q Z 0 ° s 0 i oO O oo Q p CJ oo S 03 ° 0 o o ^ o °o 0 M O O O O o U osa°o°o[ a s s D oo£?o 0 O !Ps o O ('~ ? O o f O O < 1 Oo H o o x O?o° OSS 0 2 S g Q 4 ‘ S 9 -.( r b ° ° ^ o o OoCZ o o C2v°° I S O o s s e?oSC?g 0 O 5^,0°f O O L^/OOl r v v ^ o o $rs°°r O O U - v / O O ^ o t z o ; ? g o O S S oo (— O o L , o o C^7°o[ O O C— J D O V O o o O o ) 0 o Z Q ° ° o \ o n O O O O / 5 U g g U o ^ s s r \ s ; O ’ SS ’ O 00^ 0 l_ _ 1 o o Oo O 6 O O S S Q K Q re ? s g o ^ B ° o ; s s G S S O ! p P /— \ op o O Q OSSC3SSC, r \ o f r^ .° . £>°sossc g f ? S S O S ’ c c ossc M u fk z I Z S O S S C o.tsO' m a z e O D 0 ° 00 ? O C k o 6 C O 6 r2 i.p . . ° rrs ^ V , o o r s o o c ^ v , 9’ 9..VO Qo T.< 0 >%%€D%tC o o ra>6 ° o c O O S 3 O O S > 0 T v e r 0 o0 o C P S S 0 .1 o o o r o o o r Qpga ~ T o --- Q ° o £ O Q 0=s o / - - - - -s Upper P a r t Copper Canyon Fm.

Linked assets

University of Southern California Dissertations and Theses

Conceptually similar

PDF

Paleoenvironmental analysis of the Upper Cretaceous (Santonian/Campanian) Forbes Formation, Sacramento Valley, California

PDF

Depositional systems of the mid-Tertiary Gene Canyon and Copper Basin Formations, eastern Whipple Mountains, California

PDF

Stratigraphy and sedimentology of the Drummond Mine Limestone, Starhope Creek, Idaho

PDF

Depositional environments of the Neogene Hungry Valley Formation: Sedimentary response to the initiation of the San Andreas Fault, Ridge Basin, Southern California

PDF

Pliocene lacustrine stromatolites of the Furnace Creek formation, Death Valley, California

PDF

Paleoenvironmental analysis of Upper Cretaceous Pleasants Sandstone Member (Williams Formation), Santa Ana Mountains, Southern California

PDF

Facies and depositional environments of Guadalupian strata (Brushy Canyon and Cherry Canyon Formations), northwestern Delaware Basin, west Texas

PDF

Stratigraphy and sedimentation patterns Upper Miocene Puente formation (Mohnian-Delmontian) northwestern Puente Hills, Los Angeles County, California

PDF

Sedimentology of the northern half of the Laguna Salada, Baja California

PDF

Geology of a part of the Funeral Mountains, Death Valley National Monument, California

PDF

Neogene evolution of the Garlock-Death Valley fault junction, southeastern California

PDF

Stratigraphy and sedimentary petrology of the Moss Back Member of the Late Triassic Chinle Formation, north Temple Wash - San Rafael Desert area, Emery County, Utah

PDF

Utilization of paired cores in sedimentological studies of the Mozambique Channel in the southwest Indian Ocean.

PDF

Stratigraphy and paleontology of the Monte Cristo Limestone, Goodsprings Quadrangle, Nevada

PDF

Sedimentology of the Beck Spring Dolomite, eastern Mojave Desert, California

PDF

Petrology and diagenesis of the early Miocene Skooner Gulch and Gallaway Formations, Point Arena, California

PDF

Vertical sequence analysis of late Pliocene pico formation sediments in Adams Canyon, Ventura County, California.

PDF

Paleoenvironmental analysis of late Cretaceous continental slope deposits (Holz Shale Member, Ladd Formation), Black Star Canyon (Santa Ana Mountains), Southern California

PDF

Fourier grain-shape analysis of quartz sand from the eastern and central Santa Barbara littoral cell, Southern California

PDF

Oligocene - Miocene Sedimentology of the Tecolote Tunnel section of Southern California

Asset Metadata

Creator Scrivner, Paul Joseph (author)

Core Title Stratigraphy, sedimentology and vertebrate ichnology of the Copper Canyon Formation (Neogene), Death Valley National Monument

Degree Master of Science

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag OAI-PMH Harvest,Sedimentary Geology

Language English

Contributor Digitized by ProQuest (provenance)

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c30-122645

Unique identifier UC11225312

Identifier usctheses-c30-122645 (legacy record id)

Legacy Identifier EP58739.pdf

Dmrecord 122645

Document Type Thesis

Rights Scrivner, Paul Joseph

Type texts

Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Access Conditions The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the au...

Repository Name University of Southern California Digital Library

Repository Location USC Digital Library, University of Southern California, University Park Campus, Los Angeles, California 90089, USA