PALEOECOLOGY OF THE PLIO-PLEISTOCENE NASHUA FORMATION IN NORTHERN FLORIDA: MOLLUSCAN ASSEMBLAGES FROM THE UPPER 2A SAMPLE AT BUCK HAMMOCK MATERIALS

Examining Plio-Pleistocene marine assemblages and causal factors of the extinction pulses that affected them is important for studying the current sixth mass extinction, as understanding the variability and response of ecosystems to natural disturbances prior to human impacts is needed. Changes in western Atlantic marine communities were widespread, but limited research has been done on assemblages near the biogeographic boundary between the Carolinian and Gulf Provinces in northern Florida. This study analyzes molluscan assemblages from the Nashua Formation as collected in situ from Buck Hammock Materials near Deer Park, Florida. Multiple samples were obtained from the lower and upper parts of the quarry wall in September 2022. This study focuses on sample Upper 2A (~2 gallons) that was processed by students in a paleontology class at Georgia State University in Fall 2023. Methodologies included shell sieving (>5 mm retained), genera classification for shells with umbos (bivalves) and apices (gastropods), followed by analyses of diversity, abundance, life modes, predation, bioerosion, shell size, and taphonomy. The majority of specimens have been sorted and identified; fragmented and smaller shells are still being processed. Bivalves dominated the sample, constituting 89.28% of all specimens, while gastropods accounted for 10.72%. So far, 1449 bivalve and 174 gastropod individuals have been processed (=2844 shells). Only six bivalve and six gastropod genera each have been identified to date, indicating lower richness compared to other samples from this quarry. Dominant genera included Mulinia, Donax, and Crepidula. Shell sizes averaged 20-30 mm; Tagelus is the largest genus while Pleuromeris represented the smallest specimens. Many of the shells processed so far have been “whole” (>85% of the shell intact) and are well preserved, although some shells exhibited dark staining and/or signs of bioerosion from polychaetes. Predatory drill holes from gastropods were also observed. The presence of small shells as well as fragmented shells with sharp edges suggest limited transport from where these taxa lived. Ultimately, additional samples from this quarry and other locations need to be analyzed and compared to understand more about changes in these communities during the Plio-Pleistocene.