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ABSTRACT Miocene Paleoenvironments and Paleosol ABSTRACT Miocene Paleoenvironments and Paleosol pH Proxies William E. Lukens, Ph.D. Mentor: Steven G. Driese, Ph.D. Paleoenvironmental analysis is an interdisciplinary endeavor that draws on sedimentology, stratigraphy, geochemistry, and geostatistics. This dissertation includes two paleoenvironmental case studies and the development of a new suite of proxies for soil pH. The first case study was performed at Coffee Ranch, the site of a late Miocene (6.6 Ma) bonebed in the Texas Panhandle. Using sedimentology, stratigraphy, and paleopedology, the depositional environments at Coffee Ranch were reconstructed as a fluvial system with seasonally-variable discharge, alluvial paleosols with seasonal water deficit, and intermittent eolian deposits. Climate state was constrained using a combination of paleosol morphological properties, micromorphological associations, pedotransfer functions for climate variables, and elemental mass-balance trends, all of which were consistent with a mean annual precipitation (MAP) nearly double modern values and a much warmer and less seasonally variable mean annual temperature (MAT) than modern conditions. An early Miocene (ca. 17.5 Ma) fossil site located at Ngira, western Kenya, was also analyzed using fluvial geomorphologic and paleopedologic techniques. The Ngira fossil locality preserves a large number of vertebrate fossils, but has a conspicuous lack of primate remains, unlike nearby contemporaneous fossil sites that contain some of the world’s best preserved early Miocene fossil apes. Using pedotransfer functions for climate variables, as well as elemental mass-balance and paleosol morphological indices, the site was reconstructed as having a strongly seasonal, dry subhumid climate. Stable carbon isotopes from pedogenic carbonates are consistent with a surprisingly large amount of C4 biomass, which was used in conjunction with the presence of microcharcoal grains and rodent community paleoecology to interpret an open-canopy habitat for the site. Finally, a soil database was analyzed, with the goal of producing predictive models for soil pH using elemental oxides as input variables. It was found that large-scale vegetation and climate patterns correlate with soil pH; however, elemental ratios traditionally used to predict MAP and MAT were shown to more closely predict pH than climate. Three new pH pedotransfer functions were applied on succession of middle and late Triassic paleosols from western Pangea, and the results indicate that a paleosols became progressively more alkaline as the megamonsoon climate system gradually diminished. Miocene Paleoenvironments and Paleosol pH Proxies by William Ellis Lukens, B.S., M.S. A Dissertation Approved by the Department of Geosciences Stacy C. Atchley, Ph.D., Chairperson Submitted to the Graduate Faculty of Baylor University in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy Approved by the Dissertation Committee Steven G. Driese, Ph.D., Chairperson Lee C. Nordt, Ph.D. Daniel J. Peppe, Ph.D. Stephen I. Dworkin, Ph.D. Joseph D. White, Ph.D. Accepted by the Graduate School December 2017 J. Larry Lyon, Ph.D., Dean Page bearing signatures is kept on file in the Graduate School. Copyright © 2017 by William E. Lukens All rights reserved TABLE OF CONTENTS LIST OF FIGURES .......................................................................................................... vii LIST OF TABLES ............................................................................................................. ix ACKNOWLEDGMENTS ................................................................................................. xi CHAPTER ONE ................................................................................................................. 1 Introduction ..................................................................................................................... 1 CHAPTER TWO ................................................................................................................ 3 Sedimentology, Stratigraphy, and Paleoclimate at the Late Miocene Coffee Ranch Fossil Site in the Texas Panhandle ................................................................................. 3 Abstract ....................................................................................................................... 3 Introduction ................................................................................................................. 4 Methods..................................................................................................................... 10 Results ....................................................................................................................... 17 Discussion ................................................................................................................. 34 Conclusions ............................................................................................................... 44 Acknowledgments..................................................................................................... 45 CHAPTER THREE .......................................................................................................... 46 The Early Miocene Critical Zone at Karungu, Western Kenya: An Equatorial, Open Habitat with Few Primate Remains .............................................................................. 46 Abstract ..................................................................................................................... 46 Introduction ............................................................................................................... 47 Methods..................................................................................................................... 53 Results ....................................................................................................................... 60 Discussion ................................................................................................................. 76 Conclusions ............................................................................................................... 92 Acknowledgments..................................................................................................... 94 CHAPTER FOUR ............................................................................................................. 95 Reconstructing pH of Paleosols Using Geochemical Proxies ...................................... 95 Abstract ..................................................................................................................... 95 Introduction ............................................................................................................... 96 Methods................................................................................................................... 100 Principal Components Analysis Results ................................................................. 105 Regression Analysis ................................................................................................ 118 Discussion ............................................................................................................... 126 v Application .............................................................................................................. 128 Conclusions ............................................................................................................. 132 Acknowledgments................................................................................................... 132 BIBLIOGRAPHY ........................................................................................................... 154 vi LIST OF FIGURES Figure 1.1. Location of Coffee Ranch and Mendota Ranch study sites in the Texas Panhandle .......................................................................................................................5 Figure 1.2. Stratigraphic sections for Coffee Ranch and Mendota Ranch ...........................8 Figure 1.3. Outcrop photographs from Coffee and Mendota Ranch .................................18 Figure 1.4. Fluvial channel facies and flow-indicating structures .....................................19 Figure 1.5. Photomicrographs of selected lithofacies features ..........................................22 Figure 1.6. Field photographs of paleosol features ............................................................26 Figure 1.7. Photomicrographs of selected pedogenic features ..........................................27 Figure 1.8. Mass-balance geochemical analysis results .....................................................31 Figure 1.9. Paleoclimate results for selected pedofacies ...................................................32 Figure 1.10. Oxygen stable isotopic values of pedogenic, tufa and fracture-fill carbonates ....................................................................................................................33 Figure 1.11. Equal-area plot of characteristic paleomagnetic directions ...........................35 Figure 1.12. Cross-plot of Ca translocation vs. strain ........................................................38 Figure 2.1. Location of the Ngira study site ......................................................................51 Figure 2.2. Stratigraphic section at Ngira ..........................................................................52 Figure 2.3. Profiles
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