OXYGENATION DYNAMICS AND ECOLOGICAL RESILIENCE ACROSS OCEANIC ANOXIC EVENT 2 IN THE NORTH AMERICAN WESTERN INTERIOR SEAWAY (Invited Presentation)

Oceanic Anoxic Events (OAEs) represent extreme periods where large expanses of the Earth’s oceans were depleted of dissolved oxygen, serving as potential analogues to ongoing warming-driven deoxygenation. Substantial portions of the oceans were anoxic/euxinic during OAE 2 at the Cenomanian-Turonian boundary (∼94 Ma), whereas the Western Interior Seaway (WIS) records oxygenated conditions during that time. Here we employ combined organic geochemical, trace metal, and palynological data from Cenomanian–Turonian age sediments from five sites in the WIS to decipher changing redox and ecological conditions across a paleoenvironmental and >30^° paleolatitudinal transect. Heterogeneity across the sites is apparent, but we identify the following key relationships and trends among oceanographic variables: 1) increasing total organic carbon (TOC) and CaCO₃ percentages denote the onset of a sea-level maximum towards the end of OAE2; 2) the C₂₈ sterane is shown to be a useful marker for prasinophyte abundance, and concurrent increases in this marker and overall sterane abundance indicate prasinophyte-driven increase in algal productivity in a stratified water column; and 3) sterane ratios may be a more robust geochemical proxy than trace metal redox proxies (e.g., molybdenum and vanadium) for assessing the Benthic Oxic Zone. Moreover, our biomarker and trace metal redox data are inconsistent with some previously reported trends for the WIS overall, particularly for proximal settings. We therefore deduce that local controls, such as nutrient-driven expansion and intensification of the oxygen minimum zone, and/or anoxia directly below the sediment-water interface driven by deposition of organic-rich sediments, have overprinted regional trends. This study highlights the important relationship between local and global controls on chemostratigraphic records and combined organic-inorganic multi-proxy approaches that can help us recognize and see through local overprints toward broad expressions of ocean-scale trends.