CONTROLS ON ORGANIC CARBON BURIAL IN THE LATE CENOMANIAN WESTERN INTERIOR SEAWAY (Invited Presentation)

The Cenomanian-Turonian Ocean Anoxic Event 2 represents one of the most significant episodes of organic carbon burial in Earth history. Presumably triggered by massive addition of volcanic CO₂ to the atmosphere and peak greenhouse warming, it is also characterized by a brief interval of cooling, the Plenus Cold Event (PCE), interpreted from patterns in biogeographic data and paleotemperature proxies. In this study, we present evidence that this cooling event was absent or muted within the Western Interior Seaway (WIS) and argue that analysis of the event leads to a deeper understanding of the controls on organic matter burial during OAE’s. Clumped isotope data from the basin suggest persistent extreme warmth during the Late Cenomanian, macroinvertebrate fossil assemblages do not record a decrease in temperature, and changes in other paleoceanographic proxies do not correlate temporally with PCE signals from other locales. Using proxy data to guide construction of GCM model simulations, we explore possible hypotheses to explain these observations. The results suggest that the paleogeographic configuration of the basin and its gateways to adjoining oceans, which evolved in association with changing pCO₂ and sea level, influenced winter sea ice formation at the northern aperture of the seaway, water mass circulation, salinity, temperature, and water column stratification. We hypothesize that northward advection of warm Tethyan water muted expression of Plenus cooling in the seaway, and increased salinity sufficiently to reduce density stratification, which led to ventilation of the seafloor in the mid-latitude part of the seaway, especially during the first half of OAE2. This work demonstrates how integrated analysis of the Western Interior’s unique paleogeographic and paleoceanographic conditions helps explain why organic carbon burial was reduced rather than enhanced during one of the largest ocean anoxic events in Earth history.