View of Field Site of the Meeteetse Formation at Elk Basin, Wyoming 4
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UNIVERSITY OF CINCINNATI Date:___________________ I, _________________________________________________________, hereby submit this work as part of the requirements for the degree of: in: It is entitled: This work and its defense approved by: Chair: _______________________________ _______________________________ _______________________________ _______________________________ _______________________________ Taxonomic Diversity, Faunal Analysis and Paleoecology of a microvertebrate site in the Late Cretaceous Meeteetse Formation, Northern Wyoming A thesis submitted to the Division of Research and Advanced Studies of the University of Cincinnati in partial fulfillment of the Requirements of the degree of MASTER OF SCIENCE In the Department of Geology Of the College of Arts and Sciences 2005 by Ji-Yeon Shin B.S., Ewha Women’s University, 2002 Committee Chair: Dr. Glenn W. Storrs ABSTRACT A microvertebrate study of a fossil locality in the Late Cretaceous Meeteetse Formation, northern Wyoming, has resulted in the discovery of more than one thousand specimens and at least fifteen vertebrate taxa. The Meeteetse vertebrate fauna is highly aquatic. Dominance of fresh water fish, such as Myledaphus and Lepisosteus, soft-shelled turtles and crocodiles is indicative. A small theropod tooth belongs to Saurornitholestes. Hadrosaurs and ceratopsians are present. A rare multituberculate molar and an incisor were also recovered and referred to Mesodma. Analysis of sedimentology and ecology of the vertebrates and invertebrates indicate that the Elk Basin site in the Meeteetse Formation was deposited in a broad flood plain associated with ponds and small lakes in humid climate conditions in the early Maastrichtian. ii ACKNOWLEDGMENTS This study was carried out under the guidance of my committee chair, Dr. Glenn W. Storrs, to whom I am especially grateful for suggesting this study, valuable advice, deep interest and support of the project. I would like to thank my other committee members, Dr. Carlton E. Brett and Dr. David L. Meyer for contributing many critical suggestions and valuable discussion. Dr. Carlton E. Brett especially gave constant encouragement, for which I am very grateful. I would like to thank Dr. Warren Huff for giving valuable comments on dating and generously helping me with photographing small specimens using his facility. I am also grateful to Dr. David L. Meyer for helping with initial photography. Mason Jane Milam gave help and advice on photography at Cincinnati Museum Center. I am especially grateful for Bill Garcia and Dale Gnidovec who spent so many hours to help collect samples and screen in the hot weather. Their help was indispensable. I am also thankful to volunteers at Cincinnati Museum Center who helped me with detailed screening. I would like to thank Dr. Donald B. Brinkman for providing a detailed illustrated guide to identify microvertebrate specimens, for which I am most grateful. iii I must thank Ana Londono for helping with screening and sorting at Cincinnati Museum Center and for constant support in the office. She has been a source of knowledge and advice in geology, and provided constant friendship throughout this study. Finally, special thanks to my family at home for their endless support, for cheering me up in the low times and encouraging me to pursue my dreams. Financial support for this research was provided by Cincinnati Museum Center and the University of Cincinnati Department of Geology. iv TABLE OF CONTENTS ABSTRACT…………………………………………………...…………………………….ii ACKNOWLEDGMENTS ...…………...………...……….…...…...……………….……….. iii TABLE OF CONTENTS …………………………………………………………………….v LIST OF FIGURES ...………………………………………………………...………………vii LIST OF TABLES ..........................................................................................................ix CHAPTER 1 INTRODUCTION ……………………………………………………………………...……. 1 BACKGROUND …………………………………………………………………….…...…... 7 General stratigraphy and sedimentology…………………………………...……. 7 Depositional history during the Late Cretaceous in Wyoming...…………...…. 13 Stratigraphy and sedimentology of the field site in Elk Basin ......................... 15 METHODS ………………………………………………………………………………….. 22 CHAPTER 2 FAUNAL LIST OF VERTEBRATES.............................................................................. 25 SYSTEMATIC PALEONTOLOGY …………………………………………………...…..... 28 INVERTEBRATE FAUNA ........................................................................................... 56 ANALYSIS OF MEETEETSE VERTEBRATE FAUNA ……………………………….... 57 PALEOECOLOGICAL ANALYSIS ……………………………………………………...... 60 Paleoenvironment of the Meeteetse Formation based on sedimentology .........61 Paleoecology of the Meeteetse Formation based on vertebrates ………….…..61 v CONCLUSIONS …………………………………………………………………….……... 65 REFERENCES …………………………………………………………………….………. 67 vi LIST OF FIGURES Figure No. Page No. 1. Map of Wyoming showing location of the field site at Elk Basin and adjacent basins 2 2. Geographic location of field site of the Meeteetse Formation at Elk Basin, Wyoming 3 3. Overview of field site of the Meeteetse Formation at Elk Basin, Wyoming 4 4. Latest Cretaceous (Maastrichtian) paleogeographic map of western North America 8 5. Stratigraphic position of exposures in Big Horn Basin and adjacent regions in Wyoming 10 6. General stratigraphy of the Elk Basin section 11 7. Overview of the field site at Elk Bain 16 8. Closer view of the field site 17 9. Stratigraphic position of the Meeteetse Formation at field site at Elk Basin 18 10. A thirty cm deep trench at field site for describing micro-stratigraphic section 19 11. Columnar section of the field site of the Meeteetse Formation at Elk Basin 21 12. Buckets used to collect sediments from field 23 13. Wood screens before matrix distribution 23 14. Screens in water before processing 24 15. Wet screening device at Cincinnati Museum Center 24 vii 16. Lonchidion selachos 29 17. Myledaphus bipartitus 31 18. A dentition of extant Raja sp. 32 19. Acipenser sp. 33 20. Kindleia fragosa 36 21. Lepisosteus sp. 38 22. Teleost 40 23. Plesiobaena sp. 43 24. Basilemys sp. 44 25. Adocus sp. 44 26. Aspideretes sp. 45 27. Borealosuchus sp. 47 28. Saurornitholestes langstoni 49 29. Hadrosaur 50 30. Ceratopsian 52 31. Ornithischian ossified tendons 53 32. Mesodma sp. 54 33. Relative abundance of vertebrates based on groups 58 viii LIST OF TABLES TABLE NO. PAGE NO. 1. Micro-stratigraphic description of the Meeteetse Formation at field site 20 2. Relative abundance of Meeteetse Fauna 57 3. Relative abundance of vertebrates based on groups 58 4. Environmental preferences of selachian taxa in the Meeteetse Formation 62 ix Introduction Vertebrate microfossil studies provide an important source of paleoecological information. Microvertebrate localities are those where small skeletal remains, such as small bones and teeth of various vertebrates, have become concentrated. Materials can be obtained through surface collecting and wet screening. Earlier microvertebrate studies of the Late Cretaceous showed that paleoenvironmental interpretations can be made based on faunal and sedimentological analyses. These studies have provided an understanding of the changes in paleocommunity structure during the Late Cretaceous (Estes, 1964; Estes and Berberian, 1970; Sahni, 1972; Dodson, 1983; Lehman, 1987; Brinkman, 1990). In this study, non-marine vertebrate microfossils from the Late Cretaceous Meeteetse Formation were analyzed and paleoecology was assessed based on taxonomic diversity and sedimentology. The Meeteetse Formation was first described by Hewett (1914) from exposures near the town of Meeteetse in the southwestern part of the Big Horn Basin (Fig. 1) in south-central Montana and northern Wyoming. The Meeteetse Formation is a predominantly terrestrial unit, ranging from Campanian to early Maastrichtian in age. The field site is located near an oil well pad at Elk Basin, northeast of Powell, Wyoming (Fig. 2 and Fig. 3). Exact field site details are on file at Cincinnati Museum Center (CMC). 1 Figure 1: Map of Wyoming showing location of the field site of the Meeteetse Formation at Elk Basin and adjacent basins. Modified from Hicks (1993) 2 Figure 2: Geographic location of field site of the Meeteetse Formation at Elk Basin, Wyoming 3 Figure 3: Overview of field site of the Meeteetse Formation at Elk Basin, Wyoming, scale in meter. 4 The Meeteetse Formation has yielded relatively few vertebrate fossils until now. The discovery of a new microvertebrate site in Elk Basin, Wyoming has given the Meeteetse Formation new potential. Preliminary finds include isolated dinosaur teeth and bone fragments (Ornithischia and Theropoda), portions of turtle shells, gar scales (Lepisosteus) and freshwater skate teeth (Myledaphus) (Hicks, 1993). In addition, the Elk Basin locality appears highly fossiliferous, and holds the potential for further discovery of rare squamates and mammalian taxa, as indicated by the discovery of multituberculate teeth during this study. This project examined the taxonomic diversity and paleoecology of the Elk Basin locality. A detailed collection of microvertebrates from the new locality recovered over one thousand of specimens. A complete faunal analysis of bulk samples, including species identification and relative abundances, was conducted. The paleoenvironmental condition of the site was assessed on the basis of the fauna, taphonomy of the samples, sedimentology, and regional stratigraphy. Estes, (1964) classic work on the Lance Formation (late Maastrichtian) resulted in the