It is important to understand the past responses of earth's terrestrial geochemical reservoirs to atmospheric perturbations in order to predict future impacts on the existing environment. The "initial Eocene thermal maximum" (IETM, ca. 55 Ma) was a short-lived (~100 - 200 kyr) global warming event driven by a sudden increase in greenhouse gases similar in temporal scale to present-day anthropogenic influxes. This influx was postulated to have been due to a massive release of methane from marine gas hydrates. The subsequent increased levels of atmospheric greenhouse gases [carbon dioxide (CO2) and methane (CH4)] had a worldwide impact on the earth's surficial processes and functional partitioning of biogeochemical cycles. Marine records of the IETM clearly document the isotopic and mineralogic shifts triggered by this perturbation, while the response on subaerially exposed landmasses is not as well understood. Of particular interest is the transient character of this climatic overshoot, which reflects the presence of negative feedbacks (accelerated weathering reactions) that stabilized climate by reducing atmospheric levels of greenhouse gases. We propose to study the influence of this climatic warming on sedimentation patterns and weathering rates within the remarkably fine-textured sedimentary members of the Williston Basin (WB) in western North Dakota. These units contain well preserved, multi-proxy information (i.e., palynomorph/ macrofloral fossils, authigenic minerals and paleopedogenic features, well-preserved organic materials) that lends itself well to temporal and spatial cross-correlation. This study poses the hypothesis that the fine resolution stratigraphic package in the WB records a sympathetic terrestrial signal/response to the release of isotopically-light marine methane hydrate and subsequent global warming. To investigate this hypothesis, we will use 1) whole sediment composition, 2) semi-quantitative clay mineralogy, and 3) stable isotope geochemistry to ascertain alterations and rates in sedimentary process and sub-aerial weathering intensity in response to the warmer global climate hypothesized to have prevailed during the IETM. Our preliminary investigations provide evidence indicating that a record of the IETM is preserved within the WB and that there is a definitive shift in sediment geochemistry across this boundary. This integrated record can be tied to well-documented IETM records in neighboring contemporaneous interior basins (e.g., Bighorn Basin of Wyoming) and will augment our understanding of mid-latitude sub-continental response to rapid climate change. Broader Impacts: It is important to compare the reality of a well-preserved multi-proxy stratigraphic record to thermodynamic models of biogeochemical fluxes and estimated physical reconstructions from an interdisciplinary aspect. The linkage of our records to those preserved in the Big Horn Basin will build a stronger understanding of sub-continental land mass responses to rapid global warming. The principle investigators will utilize the information to strengthen fledgling research programs in paleoenvironmental reconstruction and paleopedology. This study will be a mechanism for graduate/ undergraduate students to develop research projects. Once investigative work has yielded a comprehensive data set, a colloquium field trip class will be conducted, with participants conducting weekly discussions in preparation for a two-week field excursion through the Western Interior Basin (WIB) province (Williston, Powder River, Bighorn, Wasatch, and Green River Basins). This will provide students an opportunity to view and synthesize sub-continental scale information. Manuscripts from this project will be published in recognized interdisciplinary earth science journals and a linked website devoted to the WIB with specific focus on the work encompassed by this study will be constructed for access by the academic community. Finally, results of this proposed research will be incorporated into a public outreach program at the University of Wisconsin Geology Museum.
