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Copyright by Christopher K. Hendrix 2016 Copyright by Christopher K. Hendrix 2016 The Thesis Committee for Christopher K. Hendrix Certifies that this is the approved version of the following thesis: Chemolithofacies of the Upper Cretaceous Buda Formation and Austin Chalk Group, South-Central Texas: A Product of Integration of Lithologic and Chemical Data APPROVED BY SUPERVISING COMMITTEE: Supervisor: Robert G. Loucks Co-Supervisor: Harold D. Rowe Charles Kerans William Fisher Chemolithofacies of the Upper Cretaceous Buda Formation and Austin Chalk Group, South-Central Texas: A Product of Integration of Lithologic and Chemical Data by Christopher K. Hendrix, B.S. Thesis Presented to the Faculty of the Graduate School of The University of Texas at Austin in Partial Fulfillment of the Requirements for the Degree of Master of Science in Geological Sciences The University of Texas at Austin December, 2016 Dedication To my wife, Jourdin, for providing endless encouragement and support. To my parents, for inspiring my curiosity about the natural world. Acknowledgements I would like to thank my co-advisors, Bob Loucks and Harry Rowe, for the time and effort they spent teaching me and guiding my research. I would also like to thank my committee members, Charlie Kerans and Bill Fisher, for the many hours spent in the classroom and field, in addition to their review of my thesis. Thank you to Nestor Phillips for sharing insights on the Cretaceous of Texas, and helping me explore it with geochemical techniques. I would also like to thank my colleagues Michael Nieto, Lauren Redmond, and Katherine Fry, for their collaboration with and discussions about this research. Many thanks go to Evan Sivil for maintaining a pragmatic disposition and answering several questions about the geochemical laboratory. I would also like to thank Rob Nikirk, Krystal Heibel, and Zain Abdi for taking the time to teach me numerous lab procedures. Lastly, I would like to express my extreme gratitude to my colleagues at the Core Research Center and the Bureau of Economic Geology: James Donnelly, Nate Ivicic, Brandon Williamson, Bill Molthen, Joseph Smitherman, and Kenneth Edwards. You all were instrumental in making this work possible. This work was supported by the State of Texas Advanced Oil and Gas Resource Recovery program (STARR), led by William A. Ambrose (STARR-30), at the Bureau of Economic Geology. This work also received financial support from the American Association of Petroleum Geologists, the Gulf Coast Association of Geological Societies, and the Jackson School of Geosciences at the University of Texas at Austin. v Abstract Chemolithofacies of the Upper Cretaceous Buda Formation and Austin Chalk Group, South-Central Texas: A Product of Integration of Lithologic and Chemical Data Christopher K. Hendrix, M.S. Geo. Sci. The University of Texas at Austin, 2016 Supervisor: Robert G. Loucks Co-Supervisor: Harold D. Rowe The Upper Cretaceous Cenomanian Buda Formation and Coniacian-Campanian Austin Chalk Group of Texas and northern Mexico are calcareous mudrock (chalk) successions deposited on the drowned lower Cretaceous Comanche platform. Investigations covering depositional systems, lithofacies, and diagenesis have been completed over the years, but no up-to-date chemostratigraphic studies have been conducted on either the Buda or Austin Chalk units. This investigation has supplemented sedimentological analysis with high-resolution X-ray-fluorescence (XRF) geochemical data. Two methods were employed to define chemofacies from an XRF dataset to test whether geochemical data can enhance description of the lithofacies and add insight to the lithostratigraphic analysis. vi Buda and Austin units are composed of four lithofacies in the subsurface of south- central Texas: (1) calcisphere globigerinid wackestone, (2) calcisphere globigerinid mud- dominated packstone, (3) calcareous mudstone, and (4) argillaceous calcareous mudstone. Observations of elemental curves plotted versus depth identified the alternation of calcite-rich chemofacies with dolomite-, clay-, and pyrite-rich chemofacies. Multiple iterations of hierarchical cluster analysis applied to the XRF dataset revealed seven chemofacies: (1) Ca-enriched, (2) Mg-enriched, (3) Al-enriched, (4) S-enriched, (5) P-enriched, (6) Zn-enriched, and (7) Ni-enriched. Neither chemofacies method is capable of defining lithofacies, but each can be used to substantiate mineralogical variability at the sub-lithofacies scale. The XRF-curve-based chemofacies identified large-scale oscillations in mineralogical composition while the HCA chemofacies identified mineralogical variability at the resolution of XRF sampling. Chemolithofacies are defined as lithofacies that are additionally characterized by chemofacies data. Delineation of the chemolithofacies is achieved by applying geochemical (and in this case mineralogical) descriptors to the lithofacies units based on the geochemical data. Ca-enriched calcisphere globigerinid wackestones and packstones are the dominant chemolithofacies of the Buda Formation and Austin Chalk Group. Calcisphere globigerinid wackestones, calcisphere globigerinid mud-dominated packstones, calcareous mudstones, and argillaceous calcareous mudstones enriched in dolomite, clays, and pyrite make up the other chemolithofacies. Variability in the chemolithofacies is attributed to rock units of more mixed mineralogy as a result of intermittent, sustained periods of increased extrabasinal sediment delivery to the shelf. vii Table of Contents List of Tables ...........................................................................................................x List of Figures ........................................................................................................ xi INTRODUCTION ...................................................................................................1 DATA AND METHODS ........................................................................................7 Core Description Techniques ........................................................................12 X-Ray Diffraction .........................................................................................13 Energy-Dispersive X-Ray Fluorescence (XRF) ...........................................14 Hierarchical Cluster Analysis (HCA) ...........................................................17 Rock-Eval Pyrolysis......................................................................................19 GEOLOGIC SETTING .........................................................................................20 The Drowned Upper Cretaceous South Texas Shelf in the Ancestral Gulf of Mexico .................................................................................................21 Stratal Architecture .......................................................................................22 LITHOFACIES ......................................................................................................24 Calcisphere Globigerinid Wackestone Lithofacies .......................................25 Calcisphere Globigerinid Mud-Dominated Packstone Lithofacies ..............29 Calcareous Mudstone Lithofacies .................................................................32 Argillaceous Calcareous Mudstone Lithofacies ...........................................35 Associated Diagenetic Features ....................................................................38 CHEMOFACIES ...................................................................................................43 Elemental Proxies from XRF Data and their Relationships .........................44 Chemofacies Delineation from XRF versus Depth ......................................49 XRF-Curve-Based Chemofacies of the Buda Formation ....................50 No. 1H Willerson Buda Formation .............................................51 No. 1 Valcher Buda Formation ...................................................54 No. 1 Hendershot, C.J. Buda Formation .....................................57 No. 1 Marburger Buda Formation ..............................................60 viii XRF-Curve-Based Chemofacies of the Austin Chalk Group ..............63 No. 1 Valcher Austin Chalk Group.............................................64 No. 1 Hendershot, C.J. Austin Chalk Group...............................67 No. 1 Marburger Austin Chalk Group ........................................70 Chemofacies from Hierarchical Cluster Analysis.........................................73 Ca-enriched HCA Chemofacies ...........................................................75 Mg-enriched HCA Chemofacies..........................................................77 Al-enriched HCA Chemofacies ...........................................................79 S-enriched HCA Chemofacies .............................................................81 P-enriched HCA Chemofacies .............................................................83 Zn-enriched HCA Chemofacies ...........................................................85 Ni-enriched HCA Chemofacies ...........................................................87 DISCUSSION ........................................................................................................89 Advantages and Limitations of the Chemofacies Methods ..........................90 Distribution and Integration of Lithofacies and Chemofacies in the Buda Formation .............................................................................................93 Distribution and Integration of
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