BODY SIZE AS EVIDENCE FOR STASIS WITHIN THE LATE MAASTRICHTIAN OWL CREEK TYPE SECTION, GULF COASTAL PLAIN

During the last 300 ky of the Maastrichtian, global temperatures experienced a ~2℃ warming excursion attributed to Deccan volcanism, as one of a series of eruptions forming a Large Igneous Province in present day India. The Owl Creek Formation, Mississippi records the last 400ky of the Late Maastrichtian prior to the Cretaceous-Paleogene extinction event, 66 Mya. The timing of global climate change and Owl Creek stratigraphic duration allows us to test the hypotheses that 1.the Owl Creek Formation will record a Late Maastrichtian warming event and 2.the temperature increase will be associated with a decrease in shallow marine invertebrate diversity and a reduction in body volume, based on the impacts of other Large Igneous Province eruptions in the fossil record.

In order to test this hypothesis, bulk samples (0.5L) were collected at 0.5m resolution through 8 meters of Late Maastrichtian section exposed at the Owl Creek Type Section. Fossils were uncovered, identified to species level, assigned ecological life modes, and linear dimensions were measured. The original mineralogy of fossil material provided samples for clumped isotope paleothermometry at the same resolution or higher. Body volume was calculated as an ellipse using linear shell dimensions. A time series evolutionary model was applied to size data to test for directional trends. Metabolic energy of each fossil assemblage was calculated from body volume scaled by family or order-level coefficient applied to standard metabolism.

A diverse mollusk fauna dominated by facultatively mobile, suspension feeding bivalves, gastropods, and scaphopods and nektonic, carnivorous cephalopods is preserved in the Owl Creek Formation. No directional change in temperature was observed nor were directional shifts in diversity, functional ecology composition, or metabolic rate. Stasis of bivalve body volume is supported by time series model and individual bivalve families do not show directional size trends. We interpret these results to suggest that 1. Deccan traps induced warming is not recorded in deposits of the Owl Creek Type Section, 2. The shallow marine environment was buffered from temperature change observed in other marine and terrestrial environments, 3. The warm climate of the Gulf Coastal Plain embayment in Late Cretaceous overprints the global climate signal.