U-PB DETRITAL ZIRCON GEOCHRONOLOGY OF THE LATE PALEOCENE EARLY EOCENE WILCOX GROUP, EAST-CENTRAL TEXAS A Thesis by PRESTON JAMES WAHL Submitted to the Office of Graduate and Professional Studies of Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Chair of Committee, Thomas E. Yancey Co-Chair of Committee, Mike Pope Committee Members, Brent V. Miller Walter Ayers Head of Department, Rick Giardino August 2015 Major Subject: Geology Copyright 2015 Preston James Wahl ABSTRACT Sediment delivery to Texas and the northwestern Gulf of Mexico during the Early Paleogene represents an initial cycle of tectonic-influenced deposition that corresponds with the timing of late Laramide uplift. Sediments shed from Laramide uplifts to east- central Texas and the northwestern Gulf of Mexico during this time are preserved in strata of the Wilcox Group and lower Claiborne Group. U-Pb dating of detrital zircons from closely spaced stratigraphic units within these groups and the underlying Midway Group by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) reveals the relative arrival time of late Laramide-age detrital zircons to east-central Texas and distinct detrital zircon age assemblages. Comparison of zircon age assemblages from this study with data from potential source regions and additional Wilcox and Claiborne Group samples along the Texas and Louisiana Gulf Coastal Plain provides insight into paleodrainage during the Early Paleogene. The relative arrival time of late Laramide-age detrital zircons to east-central Texas corresponds with deposition of the Hooper Formation of the Wilcox Group, although the presence of these detrital zircons fluctuates within younger samples. Comparison of composite detrital zircon age spectra from sediment source regions and from locations along the Texas and Louisiana Gulf Coastal Plain shows that source regions contain unique distributions of ages, with age components that are similar to Gulf Coastal Plain data. Detrital zircon age data may support relatively similar sediment sources or a similar paleodrainage area for the majority of observed ages within the Midway Group, Wilcox ii Group, and Carrizo Formation in east-central Texas. Louisiana Wilcox Group and east- central Texas (Tehuacana Member through Carrizo Formation) data are similar and contrast with data of the south Texas Wilcox Group. This may support similar paleodrainage for Louisiana and east-central Texas and a different paleodrainage to the south Texas area. Data may also support the introduction of a new sediment source or a greater contribution of detrital zircons from an already existing source by the time of Queen City Formation (lower Claiborne Group) deposition in east-central Texas. Comparison of Louisiana Claiborne Group data with east-central Texas Queen City Formation data indicates that this source was also available during deposition of younger Claiborne Group strata in Louisiana. iii DEDICATION This thesis is dedicated to my parents, Dwayne and Sharon Wahl, and my brothers, Billy and Michael. Sharon, thank you for seeing the geologist in me at an early age and never giving up on me. Thank you for all the music lessons and trips to the bookstore, for teaching me to play chess, and for letting me dig through rock piles outside the grocery store in Bismarck. Dwayne, thank you for passing on to me a work ethic that knows no end, and for teaching me that dedication and passion for your work truly pays off. iv ACKNOWLEDGEMENTS I would like to thank my committee chairs, Drs. Thomas Yancey and Mike Pope, and my committee members, Drs. Brent Miller and Walt Ayers, for their support during my time at Texas A&M University. Thanks are also due to Dr. Ray Guillemette for assistance with cathodoluminescence and backscatter electron imaging, and to Luz Romero for her help during the data collection and processing stages of this study. I also would like to extend my gratitude to ConocoPhillips, Marathon Oil, and the South Texas Geological Society for providing fellowship support for my education and research. v TABLE OF CONTENTS Page CHAPTER I INTRODUCTION ...................................................................................1 CHAPTER II GEOLOGIC BACKGROUND ................................................................6 CHAPTER III METHODS .........................................................................................10 CHAPTER IV DETRITAL ZIRCON GEOCHRONOLOGY ........................................ 18 Fractionation and Secondary Zircon Standards .......................................... 18 East-Central Texas Data .............................................................................21 East-Central Texas Results and Discussion ............................................... 29 Kolmogorov-Smirnov Test ..........................................................................35 CHAPTER V SOURCE REGIONS AND GULF COASTAL PLAIN LOCATIONS ...... 39 CHAPTER VI CONCLUSIONS ................................................................................53 Recommendations for Future Study ............................................................54 REFERENCES CITED .............................................................................................55 APPENDIX A ...........................................................................................................78 APPENDIX B .........................................................................................................117 APPENDIX C .........................................................................................................126 APPENDIX D .........................................................................................................139 APPENDIX E .........................................................................................................185 APPENDIX F .........................................................................................................198 APPENDIX G .........................................................................................................213 APPENDIX H .........................................................................................................215 vi LIST OF FIGURES FIGURE Page 1 Generalized stratigraphic column for east-central Texas showing stratigraphic levels of sampling .....................................................................4 2 Location of samples collected between the Trinity and Colorado Rivers in east-central Texas..........................................................................5 3 Stylized average thickness column for lithostratigraphic units in east-central Texas between the Trinity and Colorado Rivers ........................ 9 4 Arrangement of detrital zircon samples, primary standards, secondary standards, and NIST glass standards in an epoxy puck ............ 12 5 Detrital zircon grain map example ...............................................................14 6 Fractionation factor and secondary zircon standard 206Pb/238U ages ........... 18 7 Normalized probability density plots and associated histograms for east-central Texas detrital zircon samples ............................................. 23 8 GTS (2012) timescale overlain on normalized probability density plots for east-central Texas detrital zircon samples ..................................... 24 9 Normalized probability density plots and associated histograms for east-central Texas detrital zircon samples with ages younger than 300 Ma .......................................................................................................25 10 GTS (2012) timescale overlain on normalized probability density Plots for east-central Texas detrital zircon samples with ages younger than 300 Ma ..................................................................................26 11 Normalized composite probability density plot for QC detrital zircon ages, positioned above a similar style plot and associated histogram for east-central Texas (Teh-CZ) samples .................................................... 28 12 Composite probability density plot for east-central Texas samples with ages younger than 300 Ma ..................................................................28 13 Composite probability density plot with age groups and age labels for detrital zircon ages in east-central Texas ............................................... 30 vii FIGURE Page 14 Normalized probability density plots for each sample with age groups and age labels.................................................................................31 15 Composite probability density plot with associated histograms, age groups, and age labels for all samples in east-central Texas with ages younger than 300 Ma .........................................................................33 16 Normalized probability density plots for each sample with age groups and age labels for ages younger than 300 Ma................................. 34 17 One-sigma absolute error vs. age for all detrital zircon ages within 10% discordance. ......................................................................................38 18 North American basement terranes ............................................................39 19 Paleogeographic reconstructions with inferred paleodrainage pathways during the Late Paleocene and Early Eocene ............................ 41 20 Locations of compiled studies for source regions and Texas and Louisiana Gulf