BIOMARKER ANALYSES OF WYOMING’S MOWRY SHALE: ASSESSING DYNAMIC ENVIRONMENTAL CONDITIONS DURING A RESTRICTED ANOXIC EVENT

The Mowry Shale is a siliceous formation deposited during an early transgression of the Western Interior Seaway (WIS) around 99 Ma. Generally, organic-rich black shale deposits are attributed to suboxic to anoxic bottom water conditions at the time of deposition (Wignall, 2005), which promotes organic matter preservation by limiting aerobic respiration. Multiple ocean anoxic events (OAEs) are documented in sediments from the WIS (Boudinot 2021; Tessin et al., 2018), but the factors that lead to both global (e.g., OAE2) and parochial (e.g., the Mowry Shale) OAEs are still enigmatic (Rickman 2014; Robinson et al., 2023). Research detailing the processes that influenced the development of WIS anoxia and resulting organic production and/or preservation throughout the Mowry formation utilizing diverse biomarkers has the potential to yield unique insights on OAEs, including changes in carbon cycling and redox conditions (French et al., 2022). Here we present new data on the Mowry Shale Formation, using thermally immature core material sourced from the northwest area of Wyoming’s Powder River Basin (PRB). This work characterizes bulk d¹³C_organic and compares trends in these data to abundances and distribution of terrestrial plant wax and archaeal membrane-spanning lipids isoGDGTs. In particular, we test if compound-specific carbon isotope analyses on crenarchaeol is feasible in Mowry Shale materials (Elling et al., 2019). This work seeks to understand how the environmental conditions represented in lower to middle Mowry compare to those of the upper Mowry, and how these relate to ocean anoxia and perturbations to the carbon cycle.