Western Washington University Western CEDAR WWU Graduate School Collection WWU Graduate and Undergraduate Scholarship Summer 2019 Increased Hydrologic Variability Near the Paleocene-Eocene Boundary (Piceance Creek Basin, Colorado, U.S.A.)) Anna Lesko Western Washington University, [email protected] Follow this and additional works at: https://cedar.wwu.edu/wwuet Part of the Geology Commons Recommended Citation Lesko, Anna, "Increased Hydrologic Variability Near the Paleocene-Eocene Boundary (Piceance Creek Basin, Colorado, U.S.A.))" (2019). WWU Graduate School Collection. 889. https://cedar.wwu.edu/wwuet/889 This Masters Thesis is brought to you for free and open access by the WWU Graduate and Undergraduate Scholarship at Western CEDAR. It has been accepted for inclusion in WWU Graduate School Collection by an authorized administrator of Western CEDAR. For more information, please contact [email protected]. INCREASED HYDROLOGIC VARIABILITY NEAR THE PALEOCENE-EOCENE BOUNDARY (PICEANCE CREEK BASIN, COLORADO, U.S.A.) By Anna Lesko Accepted in Partial Completion of the Requirements for the Degree Master of Science ADVISORY COMMITTEE Chair, Dr. Brady Foreman Dr. Robyn Dahl Dr. Kirsten Fristad Kathleen L. Kitto, Acting Dean MASTER’S THESIS In presenting this thesis in partial fulfillment of the requirements for a master’s degree at Western Washington University, I grant to Western Washington University the non-exclusive royalty-free right to archive, reproduce, distribute, and display the thesis in any and all forms, including electronic format, via any digital library mechanisms maintained by WWU. I represent and warrant this is my original work, and does not infringe or violate any rights of others. I warrant that I have obtained written permissions from the owner of any third party copyrighted material included in these files. I acknowledge that I retain ownership rights to the copyright of this work, including but not limited to the right to use all or part of this work in future works, such as articles or books. Library users are granted permission for individual, research and non-commercial reproduction of this work for educational purposes only. Any further digital posting of this document requires specific permission from the author. Any copying or publication of this thesis for commercial purposes, or for financial gain, is not allowed without my written permission. Anna Lesko 1 June 2019 INCREASED HYDROLOGIC VARIABILITY NEAR THE PALEOCENE-EOCENE BOUNDARY (PICEANCE CREEK BASIN, COLORADO, U.S.A.) A Thesis Presented to The Faculty of Western Washington University In Partial Fulfillment of the Requirements for the Degree Master of Science By Anna Lesko 1 June 2019 ABSTRACT The Paleocene Eocene Thermal Maximum (PETM) was a rapid global warming event that occurred approximately 56 million years ago and represents the largest and most abrupt warming event of the Cenozoic Era. The PETM caused mean annual temperatures to increase at least 5°C globally above the already warm, greenhouse climate state of the early Paleogene. The warming and associated perturbation of the carbon cycle had numerous consequences for paleoenvironments and paleobiologic systems. This study investigates the hydrologic response to the PETM within the interior of North America and presents a new d13C bulk organic record. This study generates reconstructions of floodplain drainage and paleo-precipitation in the Piceance Creek Basin of northwest Colorado (U.S.A.). A semi-quantitative soil morphology index was used to characterize floodplain drainage and whole-rock geochemistry in order to estimate mean annual precipitation from a 124-meter stratigraphic section in the western portion of the Piceance Creek Basin. The section can be roughly litho- and bio-stratigraphically correlated to isotopically, well- constrained PETM stratigraphic intervals. The new bulk organic d13C record exhibits a range of values with an average of -22.3‰ ± 0.9 (1s). Variability in d13C values does not appear to be related to the amount of carbon nor lithology sample. Up-section there is a 40-meter thick interval over which d13C values shift ~2‰ to lower values and then return to baseline values. This interval corresponds to the lateral equivalent of the lower portion of the Molina Member, which is known to correlate with PETM. This study suggests the new isotopic record documents the PETM, but additional isotopic and biostratigraphic work needs to be performed to confirm. Within the hypothesized PETM interval soil morphology indices double in the upper portion of the structured isotopic shift, which indicates transiently better drainage in the floodplain. Mean annual precipitation (MAP) estimates from soil geochemistry are ~1500 mm/year before and after the iv isotopic excursion, and values as low as ~500 mm/year associated with the upper portion of the isotopic shift. This represents a 40% to 60% decrease in MAP in the basin. These results document greater drying in the Piceance Creek Basin as compared to the well-studied Bighorn Basin in northwest Wyoming wherein previous studies documented an increase in the soil morphology by 80% and decrease in MAP by 30-40% using identical methodologies as well as paleofloral records. When combined with other regional proxy datasets the results are consistent with general circulation model outputs that indicate widespread drying within the continental interior of North America as well as increased variability within the hydrologic cycle during the PETM. Moreover, this study supports the hypothesis that an enhanced hydrologic cycle is a robust response by the climate system to elevated atmospheric pCO2 levels, whether the carbon is ultimately sourced from anthropogenic sources or otherwise. v ACKNOWLEDGEMENTS I would like to recognize my advisor, Dr. Brady Foreman, for being a wonderful mentor as well as encouraging and pushing me to succeed. I am incredibly grateful for the opportunities you have provided, and I will carry with me the experiences and knowledge you have given me. I would like to thank my committee members, Dr. Robyn Dahl and Dr. Kirsten Fristad for their generous support and guidance with regards to my research. I would also like to recognize Katie Snell and her lab group for hosting and helping me process my samples. Thank you to Ben Paulson for help within the lab. This manuscript would have not been completed without the lab assistance from WWU undergraduates Lindsey Gibson, Jeffrey Wegener, and graduate student Masoud Miraezi. Funding for this project was provided by National Geographic Society, Research and Exploration Grant (#9867-16). vi Table of Contents ABSTRACT ......................................................................................................................................... iv ACKNOWLEDGEMENTS .................................................................................................................. vi LIST OF FIGURES AND TABLES ................................................................................................. viii INTRODUCTION ................................................................................................................................ 1 GEOLOGIC SETTING ......................................................................................................................... 5 Piceance Creek Basin .................................................................................................................................... 5 Wasatch Formation ....................................................................................................................................... 6 METHODS ......................................................................................................................................... 10 Field Techniques......................................................................................................................................... 11 Stable Isotope Geochemistry ...................................................................................................................... 11 Whole-Rock Geochemistry ......................................................................................................................... 15 RESULTS............................................................................................................................................ 18 Carbon Isotope Record ............................................................................................................................... 18 Floodplain Drainage .................................................................................................................................. 19 Mean Annual Precipitation ....................................................................................................................... 20 DISCUSSION ...................................................................................................................................... 21 Interpretation of Carbon Isotope Record ................................................................................................. 21 Hydrologic Changes ................................................................................................................................... 25 CONCLUSIONS .................................................................................................................................. 29 REFERENCES CITED ......................................................................................................................