PALEOTHERMOMETRY, ECOLOGICAL METRICS, AND METABOLIC RATES SHED LIGHT ON SHALLOW MARINE ECOSYSTEM RESPONSES TO THE K-PG BOUNDARY EVENTS IN THE U.S. GULF COASTAL PLAIN

The stratigraphic record of the shallow marine habitat from the latest Maastrichtian and Cretaceous-Paleogene boundary (KPB) sections in the U.S. Gulf Coastal Plain (GCP) provides the potential to capture both the ecological effects of Deccan warming and the lasting consequences of the environmental change following the end-Cretaceous bolide impact. Previous work in the GCP has produced conflicting interpretations of the ecological strategy of shelf macrofauna in the immediate extinction aftermath, perhaps due to location on the shelf or regional habitats. We evaluate field-based collections from five KPB sections that span the latest Maastrichitian (last 400ky of the Cretaceous) and the early Danian (first 1 to 2 My). We apply D47 clumped isotope paleothermometry, quantitative diversity, size, and metabolism metrics paired with functional ecology to interpret extirpation/extinction selectivity, survival, and re-establishment of shallow marine ecosystems.

We expect that body size will be reduced to accommodate metabolic stress from Deccan warming but will increase in the Danian, due to selection against small body size at mass extinctions. Loss of primary productivity should result in lower assemblage motility as an energy conservation strategy. While taxa with higher metabolic rates may able to accommodate the metabolic stress from Deccan warming we anticipate reduced assemblage metabolic energy in the Danian in response to shutdown of export productivity to the shelf.

We detect no directional trend in shallow shelf temperature or mollusk-dominated assemblage diversity, ecological guild occupation, or shell size through the Late Maastrichtian. It’s possible the Deccan warming signal is either not recorded in the time range of the studied sections or does not substantially change the already warm temperatures of the Mississippi embayment. In the Danian, oysters, turritellids, and bryozoans are common constituents of shallow shelves while oysters and nuculanid bivalves dominate the nearshore. Lower motility and suspension feeding are the predominant life modes in the initial community restructuring. Across the KPB, mollusks experience the loss of the smallest size classes and overall increase in average and maximum size within families with continuous records, in support of selection against small size.