PALEOECOLOGY OF MOLLUSCAN COMMUNITIES IN THE PLIO-PLEISTOCENE NASHUA FORMATION: PRELIMINARY RESULTS OF SAMPLE UPPER 3C FROM BUCK HAMMOCK MATERIALS IN DEER PARK, FLORIDA

Western Atlantic molluscan assemblages of the Plio-Pleistocene have been studied primarily from the Carolinas, south Florida, and in the Caribbean. Differences in recovery after extinction episodes have been noted between the Carolinas and south Florida, but a gap in data exists near the biogeographic province boundary in north Florida along the U.S. East Coast. This research focuses on contributing new paleoecological data on mollusks from the understudied Nashua Formation, in part to see how communities may have responded to extinction episodes near this biogeographic boundary between the Carolinian and Gulf Province. Bulk samples of fossils were collected in situ from Buck Hammock Materials near Deer Park, FL. Nine samples each were retrieved from lower and upper sections of the quarry wall in fall 2022. Preliminary results for sample Upper 3C are presented here as part of work done by students in a paleontology class at Georgia State University in fall 2023. The bulk sample (~2 gallons) was sieved and shells greater than 5mm with umbos or apexes were retained. Specimens were then sorted by genus and either categorized as whole (if >85% of the shell was intact) or fragmented. Shells were studied for the presence of predatory drill holes and other forms of bioerosion or post-mortem damage, and data on size were recorded for common genera. The majority of the sample has been processed but sorting through finer fragmented individuals is ongoing. So far, the sample consists of 17 bivalve genera (3,251 shells/1625.5 individuals) and 6 gastropod genera (301 individuals). Like other samples studied from the upper section of the quarry wall, results for Upper 3C show that the most abundant genera were suspension feeders as dominated by Mulinia and Donax (infaunal bivalves) and Crepidula (epifaunal gastropod). Other commonly noted bivalve genera included Abra, Anadara, Nucula, and Spisula. The majority of gastropod genera observed to date are represented by carnivores. Most of the shells are small (5mm-20mm) and fairly well-preserved with minimal bioerosion. Fragmented specimens are more angular indicating limited transport. More work is needed to finalize sample processing before correlating results to other quarry samples and for comparing broader biogeographic variation of these assemblages during the Plio-Pleistocene.