Louisiana State University LSU Digital Commons LSU Master's Theses Graduate School 2010 Taphonomy and sedimentology of two Miocene vertebrate fossil sites on Fort Polk, Louisiana Julie Lynn Hill Louisiana State University and Agricultural and Mechanical College, [email protected] Follow this and additional works at: https://digitalcommons.lsu.edu/gradschool_theses Part of the Earth Sciences Commons Recommended Citation Hill, Julie Lynn, "Taphonomy and sedimentology of two Miocene vertebrate fossil sites on Fort Polk, Louisiana" (2010). LSU Master's Theses. 3336. https://digitalcommons.lsu.edu/gradschool_theses/3336 This Thesis is brought to you for free and open access by the Graduate School at LSU Digital Commons. It has been accepted for inclusion in LSU Master's Theses by an authorized graduate school editor of LSU Digital Commons. For more information, please contact [email protected]. TAPHONOMY AND SEDIMENTOLOGY OF TWO MIOCENE VERTEBRATE FOSSIL SITES ON FORT POLK, LOUISIANA A Thesis Submitted to the Graduate Faculty of the Louisiana State University and Agricultural and Mechanical College in partial fulfillment of the requirements for the degree of Master of Science In The Department of Geology and Geophysics by Julie Lynn Hill B.S., University of Wisconsin – Madison, 2002 August 2010 ACKNOWLEDGEMENTS Special thanks to my major advisor, Dr. Judith Schiebout, for providing conversation and guidance on life, the universe, and everything – from paleontology and academia to cats and good literature. Many thanks to committee members Drs. Laurie Anderson and Brooks Ellwood for stepping in when they were needed and offering new insight and encouragement that helped to shape this thesis. Thank you also to late committee member Dr. John Wrenn, a tough man who asked some tough – and necessary - questions. Thank you to Drs. Ray Ferrell, Wanda LeBlanc, Rick Young, Harry Roberts, and Floyd DeMers for their assistance in the processing of my cores and sediment samples; to Dr. Michael Blum for his willingness to share equipment and lab space; to Mary Lee Eggert, for much- needed assistance with images; and to Clint Edrington and Sidney Agnew for being great field assistants and getting the Geoprobe to go where it had no business being. Thank you to Drs. James Roche, Jonathan Tomkin, Ajoy Baksi, and Huiming Bao for being understanding professors to a harried T.A. The fossil sites on Fort Polk would be undiscovered and unstudied without the initial contact from and continued cooperation and enthusiasm of the historians and scientists at Fort Polk. The support of Director of Public Works, LTC, EN, E. Mazion, Jr., and the environmental staff including Jim Grafton, Bob Hays, Ellen Ibert, and Danny Guillory in particular made this thesis possible. In addition, the previous work of faculty and graduate students at LSU provided the basis upon which this research is based. My appreciation is due also to Drs. Suyin Ting, Barun Sen Gupta, Ray Wilhite, and Wolf Gose (of the University of Texas at Austin); fellow graduate students Mike Williams, Travis Atwood, Grant Boardman, Paul White, and Rebecca Tedford; and to many others for their contributions to our knowledge of the Fort Polk sites. ii EnCana Oil & Gas, ConocoPhillips, and the American Federation of Mineralogical Societies provided much-appreciated financial support for this thesis. I am grateful to my friends from Madison to Baton Rouge, from Boston to Seattle (and the random Aussie and Irishman for variety) for providing support in my endeavors both academic and less intelligent. From old friends (Tara, Margaret, Mandy, and Maitri, I mean you four) that took long phone calls and incoherent e-mails in stride, to new grad school friends that shared beers, talked science, and played video games - you made the long haul bearable. Thanks for being there, whether in person or at the other end of a phone line. I had a blast. Thank you to my sisters for being friends. I hope the ―Golden Girls‖ theme song is stuck in your head now, because as the youngest, it is my job to irritate you. Even from 1000 miles away. Thank you, Mom and Dad, for everything. For smiling and nodding and then eventually just telling me to let you know when I was going to finish. I finished. I’m just slow. You’d never tell that from how I drive, though. iii TABLE OF CONTENTS Acknowledgements……………………………………………………………………….……… ii Abstract……………………………………………………………………………………........... v Introduction…………………………………………………………………………………….... 1 Study Area…………………………………………………………………………..…… 4 Geologic Background…………………………………………………..…………...…… 4 Paleontological Background…………………………………………………...…….…... 9 Materials and Methods…………………………………………………………………………. 16 Sediment Core Collection…………………………………………………….………… 16 Core Processing…………………………………………………………………...……. 16 Mineralogical Analysis…………………………………………………………………. 18 Magnetic Susceptibility……………………………………………………………….... 18 Taphonomy…………………………………………………………………………...… 20 Results……………………………………………………………………………………...…… 22 Core Data………………………………………………………………………….……. 22 Mineralogical Analysis…………………………………………………………………. 24 Magnetic Susceptibility………………………………………………………………… 25 Taphonomy………………………………………………………………………..……. 34 Discussion…………………………………………………………………………………..….. 43 Local Paleoenvironments……………………………………………………….……… 43 Taphonomy and Paleontology…………………………………………………..……… 46 The Age of the Fort Polk Sites………………………………………………….……… 48 Regional Geology, Paleontology, and Implications……………………………...…….. 51 Conclusion……………………………………………………………………………………… 55 References…………………………………………………………………………………….… 57 Appendix: Core Photographs and Descriptions………………………………………………… 63 Vita……………………………………………………………………………………………… 69 iv ABSTRACT The discovery of a terrestrial mammalian fauna in the Miocene deposits on Fort Polk, Louisiana, fills a geographic gap in the Gulf Coast paleontological framework, but the provenance of the fossils, nature of the depositional environments, and relationships between the sites is still debated. This is especially true for the TVOR site cluster. TVOR SE has a mixture of marine and terrestrial vertebrates in association with a partly dissolved, in situ bed of articulated oyster shells, which stands in contrast to the fully terrestrial and freshwater assemblage at TVOR, and the indeterminate site TVOR S. Although limited outcrop may bias the observed fossil assemblages, it is thought that the differing characteristics of the sites are related to changing depositional environments. Taphonomic and geologic data were integrated to create a more complete picture of the paleoenvironmental factors contributing to the formation of the fossil sites. One core each was collected at TVOR S and TVOR SE, and these were studied along with a core previously collected at TVOR site. Magnetic susceptibility (MS) work on the cores suggested correlation between the TVOR S and TVOR SE sites, and possible correlation between TVOR S and TVOR. MS data indicated marine influence at all three sites, including TVOR, which previously had been considered fully terrestrial. Heavy mineral analysis was unfruitful regarding the provenance of the sites. Identified, curated fossils from the sites were assigned to bone dispersal groups to assess the degree of sorting in the fossil assemblages, and it was discovered that the vast majority of both macro- and micro-vertebrate fossils fall into Groups I and II, indicating that the fossil assemblages are the result of transport into the sites rather than attrition of local biota. The geological, geophysical, and paleontological records of the sites give a picture of a quiet, v distal, setting just beginning to reflect environmental changes spurred by local and global geologic processes. vi INTRODUCTION Since the 1993 discovery of a terrestrial mammalian fauna in the Miocene deposits of Louisiana (Schiebout 1994), it has been clear that the fossil sites at Fort Polk, LA, are important both as sources of paleontological data (Schiebout 1997, Schiebout and Ting 2000, Schiebout et al. 2001, 2004) where there had previously been a geographic gap in the Gulf Coast record (Tedford et al. 2004), and as windows on the evolution of Gulf Coast fluvial systems and sedimentary environments (Hinds 1999). Biological and geological histories of the Earth are frequently studied as separate entities; however, the two fields are interrelated and the simultaneous consideration of paleontological and sedimentological data allows for a better understanding of an area’s geologic and biotic history and evolution. The role of depositional and preservational processes in creating the observed fossil record has been recognized for quite some time; the science dealing with these processes was first named ―taphonomy‖ by Efremov (1940). It was Behrensmeyer and Kidwell’s 1985 paper on the subject that pushed taphonomic studies into the forefront of paleontological thought (Martin 1999). It is now well accepted that an understanding of fossil assemblages is incomplete without consideration of the myriad biological, chemical, physical, and geological forces that have acted on them from the time of the organisms’ deaths to the time of collection, curation, and beyond. Fossils are the product of more than just the life of the organism, and their story is that of the life that generated them as well as the environments that contain them. While some work has been done on the depositional and taphonomic histories of the Fort Polk sites (Hinds 1999, Schiebout 1997, Schiebout and Ting 2000, Schiebout et al. 2001, 2004), much remains to be explored