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ii ACKNOWLEDGEMENTS I want to start first by thanking my adviser, Dr. Judith Schiebout, for her patience, assistance and the amount of freedom she gave me on choosing my topic. She truly opens her heart to her students and she made me feel like I was family. Next I’d like to thank my committee for their patience and guidance with this research. Dr. Huiming Bao taught me much about isotope geochemistry for which I will forever by thankful. Dr. Barbara Dutrow, a paleontologist in her own right, has helped me shape my work into something I’m proud of. I would like to thank Dr. Suyin Ting. Her phenomenal expertise in preparation of the fossils used in this study and extensive mentoring is much appreciated. I’d also like to thank the Gulf Coastal Association of Geological Societies, the LSU museum of Natural Science and the LSU Department of Geology and Geophysics for financial support towards this research. This certainly would not have been possible without them. Acknowledgement is made to the environmental staff at Fort Polk, especially Jim Grafton, without their assistance, we wouldn’t know much about Fort Polk during the middle Miocene. Scientists at the University of Florida are acknowledged for their assistance; doctors Bruce MacFadden, Jason Curtis and George Kamenov. All of the geochemical analysis was performed at th