Tectonic and astronomical influences on climate and deposition revealed by a Bayesian age-depth model of the Early Eocene Green River Formation, Wyoming

Benjamin Bruck

Abstract: The Wilkins Peak Member (WPM) of the Green River Formation in Wyoming comprises alternating lacustrine and alluvial strata that preserve a detailed record of terrestrial climate during the Early Eocene Climatic Optimum (EECO). We use a Bayesian framework to develop age-depth models for three sites, based on newly determined ⁴⁰Ar/³⁹Ar sanidine and ²⁰⁶Pb/²³⁸U zircon ages from seven silicic tephras. The new models provide two- to ten-fold increases in temporal resolution compared to previous radioisotopic age models, permitting direct comparison of WPM facies to astronomical solutions for insolation. Starting at ~51 Ma, basinwide flooding surfaces atop 6 successive alluvial intervals coincide closely in time with short eccentricity maxima, which has been linked with marine isotopic evidence for hyperthermal events. We infer that warmer conditions caused increased precipitation and lake expansion. Strata deposited ~30% more rapidly prior to ~51 Ma do not exhibit the same relationship however, suggesting that the sensitivity to astronomical forcing was tempered by tectonically induced subsidence of the basin, and that more radioisotopic time control is necessary to account for potential rapid changes in sedimentation rate.

Time: April 21st (14:00)

Advisor: Brad Singer

Co-Authors: Brad S. Singer, Mark D. Schmitz, Alan R. Carroll, Brian R. Jicha, Stephen Meyers, Andrew Walters

Stream: Zoom

Email: bbruck@wisc.edu