Stable isotope paleohydrology of pedogenic carbonates in the Wayan Formation (Albian) from the wedge-top depozone in the North American Cretaceous Western Interior Basin By Jeffrey Bryce Ross Submitted to the graduate degree program in Geology and the Graduate Faculty of the University of Kansas in partial fulfillment of the requirements for the degree of Master of Science. ________________________________ Chairperson Gregory Ludvigson ________________________________ Andreas Möller ________________________________ Luis González ________________________________ J. Douglas Walker Date Defended: August 23, 2016 The Thesis Committee for Jeffrey Ross certifies that this is the approved version of the following thesis: Stable isotope paleohydrology of pedogenic carbonates in the Wayan Formation (Albian) from the wedge-top depozone in the North American Cretaceous Western Interior Basin ________________________________ Chairperson Gregory Ludvigson Date approved: August 23, 2016 ii Abstract Determining the presence and effects of orogenic rain shadows on paleoclimate is challenging, but critical to understanding overall moisture and heat transport. This thesis presents new data and interpretation for the climate system of the Cretaceous greenhouse world, which is a major keystone in Earth system science. Stable isotopic paleohydrologic data on mid-Cretaceous paleosols spanning from paleoequatorial sites in Colombia to paleoarctic latitudes in Alaska have been used to constrain the oxygen isotope mass balance of the Albian hydrologic cycle. At mid-latitudes (40-50°N paleolatitude), sideritic paleosols predominate, indicating paleoenvironments with positive precipitation – evaporation (P-E) balances, local exceptions with negative P-E balances occur on the immediate leeward side of the Sevier Orogen, where calcic paleosols in the wedge-top depozone record paleoenvironments with negative P-E balances in the orographic rain shadow. Stratigraphic sections in the Wayan Formation of Idaho (WF) were sampled from the wedge-top depozone. The units consist of stacked m-scale mudstone paleosols separated by m-scale sandstone-siltstone beds. Sections were sampled for organic carbon isotope profiles, and B-horizons from 6 well-developed paleosols were sampled for detrital zircons to determine maximum depositional ages. The first of these from the WF has produced a U-Pb concordia age of 101.0 ± 1.1 Ma, placing it in the uppermost Albian. This same WF section has produced a stratigraphic trend of upwardly decreasing δ13C values ranging from -24 upwards to -27‰ VPDB, suggesting correlation to the late Albian C15 C- isotope segment. Pedogenic carbonates from the WF principally consist of micritic calcite, with carbon-oxygen isotope values that array along meteoric calcite lines (MCLs) with δ18O values that range between -9.47 up to -8.39‰ VPDB. At approximately 42°N paleolatitude, these MCL values produce calculated paleoprecipitation values of -8.12 to -7.04‰ VSMOW, a range that is consistent with the estimates produced from other proxies at the same paleolatitudes across North America. These results indicate that despite the orographic rain shadow effect, the processes of meridional iii atmospheric moisture transport in this locale were similar to those in more humid mid-latitude paleoenvironments elsewhere in the continent. iv Acknowledgements I would like to thank my field assistant, Stephan Oborny, for his help trenching and collecting samples, Luke Miller for his assistance processing samples. I would also like to thank Ted Dyman for walking me through a section of the Blackleaf Formation, and L. J. Krumenaker and Dave Varricchio of Montana State University for assistance in locating suitable Wayan Formation outcrops. And thanks to: Adrienne Duarte, Tony Layzell, Josh Feldman, Ty Tenpenny, and Maggie Graham for the training they provided to help me process samples. I would like to personally thank my advisor, Greg Ludvigson for the support he provided when work was not proceeding as planned. Many thanks to my committee members, Dr. González, Dr. Möller, and Dr. Walker for the help they provided in data interpretations. And I would like to say thank you to the entire Geology Department at The University of Kansas and the Alumni who offer grants and scholarships to help graduate students fund their research, specifically: Joseph M. Patterson Scholarship, Encana Energy Scholarship, Devon Energy Scholarship, Roy and Freda Lehman Scholarship, Gerhard Student Prize for Field Research in Geology, and AWG Osage Chapter for their generous donations. v Table of Contents Abstract .................................................................................................................................................iii Acknowledgements ................................................................................................................................ v Chapter 1: Preface .................................................................................................................................. 1 Original Scope of Project and Condensed Thesis .............................................................................. 1 Chapter 2: Submitted Manuscript for Publication ................................................................................. 3 Introduction ........................................................................................................................................ 3 Methods .............................................................................................................................................. 5 Wayan Formation Outcrop ............................................................................................................. 5 Pedogenic Carbonate Nodules ........................................................................................................ 5 Organic Carbon Isotopes ................................................................................................................ 6 U-Pb geochronology of zircon ....................................................................................................... 7 Results ................................................................................................................................................ 8 Petrography and Stable Isotope Data for Pedogenic Carbonates ................................................... 8 Organic Carbon Isotope Chemostratigraphy ................................................................................ 10 U-Pb geochronology of zircon from sample WN1.5 .................................................................... 11 Discussion ........................................................................................................................................ 12 Conclusions ...................................................................................................................................... 15 Chapter 3: Future Work ....................................................................................................................... 17 Continuation of Thesis Research...................................................................................................... 17 Wayan Formation ......................................................................................................................... 17 Blackleaf Formation ..................................................................................................................... 17 Future Plans for Publication ............................................................................................................. 18 References ............................................................................................................................................ 19 Figures.................................................................................................................................................. 24 Appendix A: Zircon Analyses ............................................................................................................. 31 13 Appendix B: δ Corg Analyses.............................................................................................................. 41 Appendix C: δ13C and δ18O Analyses .................................................................................................. 42 vi Chapter 1: Preface Original Scope of Project and Condensed Thesis The original thesis project was planned as an investigation of δ13C and δ18O of pedogenic 13 carbonates and δ Corg of 50 meters of measured section of the Blackleaf Formation in the Lima Peaks region of Beaverhead County of southwestern Montana and the Wayan Formation in the Caribou Basin of Bonneville County of eastern Idaho. Detrital zircon sampling was also planned to aid in obtaining maximum depositional ages (MDA) of paleosol horizons, which contained pedogenic carbonate nodules. A total of 38 meters was trenched and sampled from 4 locations in the Blackleaf Formation and a total of 50 meters was trenched and sampled from 3 transects of the Wayan Formation. Research from a continuous 27 meter measured section of the Wayan Formation was presented at the International Geoscience Programme (IGCP) 609 at Nanjing University, China in September, 2015. After presenting, I was asked to contribute a manuscript to an IGCP609 special issue to be published in Science China Earth Sciences (Springer). After discussion with my advisor, it was decided to condense the scope