PALEOCLIMATE OF THE CRETACEOUS–PALEOGENE GULF COASTAL PLAIN AND ITS RELATIONSHIP TO EXTINCTION PATTERNS

The Gulf Coastal Plain (GCP) has long been a target for studies of faunal extinction patterns across the Cretaceous–Paleogene (KPg) boundary due to its abundance of well-preserved invertebrate faunas. Previous work has focused on the KPg extinction event itself and environmental change directly caused by the Chicxulub impact. However, marine environments preceding and following the impact need better characterization to interpret taxonomic and ecological changes. With this new information, we can determine which marine environments supported survivorship, extinction, and evolution of species and their communities before, during, and after the impact. Temperature and salinity have been shown to have a first-order control on survivorship and distribution change in modern shallow shelf invertebrate species, thus, here we present clumped isotope data from 6+ KPg boundary sites from four states across the GCP (Arkansas, Alabama, Mississippi, and Georgia) that document Δ47 (a proxy for temperature) and δ¹⁸O_water values (a proxy for salinity) over the region before and after the KPg boundary. Seawater temperatures in the region were reconstructed to be 22-27°C and show very little change across the boundary. We show that δ¹⁸O_water values across the GCP were similar to the enriched δ¹⁸O_water values of the modern Gulf of Mexico, which is much higher than the typically-assumed ice-free end member. This difference between assumed and actual δ¹⁸O_water values renders previous δ¹⁸O_carb temperature estimates too high and indicates that the end-Cretaceous GCP may have been environmentally similar to the modern Gulf. We observe a slight increase in δ¹⁸O_water into the Paleogene at multiple sites, possibly due to the restriction of the Western Interior Seaway and increase in local salinity. This sizable dataset supports that there was little change in marine environmental conditions on either side of the KPg boundary, suggesting that the short-term change associated with the bolide impact controlled patterns of species and community turnover. The dataset also demonstrates resilience of this shallow shelf environment over time regardless of the existence of short, high-magnitude, perturbation.