NO FUNCTIONAL CHANGE IN ECOLOGY AND BODY SIZE IN RESPONSE TO GLOBAL CLIMATE EVENTS IN THE LATE MAASTRICHTIAN OWL CREEK FORMATION

The Owl Creek type section, Mississippi, records some portion of the last 400 ka of the Maastrichtian stage concluding with the end-Cretaceous extinction event, 66 Mya. During the last 300 ka of the Maastrichtian, global temperatures increased and then decreased, likely caused by a major pulse of Deccan volcanism. Due to these global climate changes, we expect the Owl Creek type section to record a temperature increase, a decrease in diversity and body volume of marine invertebrates and an increase in abundance of low activity-level invertebrate fauna, similar to the ecological effects of other large igneous provinces in the geologic record.

The Owl Creek type section has been included in decades of taxonomic, biostratigraphic, and functional ecological research on the Maastrichtian. This study represents the first series of systematic samples at a 0.5 m resolution throughout 9 m of exposure. Bulk samples were collected to reduce temporal and paleontological biases. Macrofossils larger than 2 mm were extracted from these samples and identified to the species level whenever possible. Ecological guild classifications, motility, tiering, and diet, were assigned to specimens using current literature. Complete specimens were measured along primary axes to collect body size data.

The Owl Creek Fm contains a diverse mollusk fauna dominated by suspension feeding, facultatively mobile bivalves, gastropods, scaphopods and nektonic, carnivorous cephalopods similar to previous studies of Maastrichtian shallow marine deposits from the Gulf Coastal Plain. Preliminary results indicate a decrease in species richness and diversity throughout the section, no significant change in shell volume in the most abundant mollusk families, and no directional changes in functional ecology. D47-based paleotemperature reconstructions from benthic bivalves and nektobenthic ammonites indicate benthic seawater temperatures at this site averaged ~23°C varying little throughout the stratigraphic section while foraminifera derived planktic temperatures averaged ~33°C. The lack of temperature, taxonomic and ecological change in the Owl Creek Fm suggests either that Deccan warming was not recorded in these strata or that the Mississippi Embayment shallow marine shelf environment was buffered against global-scale climate change.