Comparing the Paleoecology of Molluscan Assemblages from the Plio-Pleistocene Nashua Formation of Northern Florida

The Plio-Pleistocene marine molluscan extinctions in the Western Atlantic are not widely understood. Timing and contributing factors may vary based on latitude, and previous work has focused primarily on assemblages from southern Florida and the Caribbean representative of the Gulf Province and other biogeographic faunal provinces to the south. Here we examine the Nashua Formation from northern Florida near the end of the Carolinian Province. Samples analyzed in this study were collected from spoil piles across three different sites at the East Coast Aggregates quarry near Hastings, FL. One sample from each site was analyzed in 2018 by students in a paleontology course at Georgia State University. Three additional samples were studied in 2021 and 2022. Samples were sieved, shells >5mm retained, and identifiable shells with a visible umbo (bivalves) or apex (gastropods) were picked and then separated as “whole” (>85% of the shell intact) vs. fragmented individuals.

Samples processed in 2018 included an analysis of 1,912 molluscan individuals (S1 = 1081, S2 = 466.5, S3 = 364.5). Site 1 had 22 bivalve genera from 923.5 individuals and 14 gastropod genera from 157 individuals. Site 2 had 32 bivalve genera from 352.5 individuals and 20 gastropod genera from 114 individuals. Site 3 had 28 bivalve genera from 327.5 individuals and 11 gastropod genera from 37 individuals. Samples processed in the last year included an additional analysis of 1,321 bivalve individuals (S1 = 754.5, S2 = 304.5, S3 = 262) and 306 gastropod individuals (S1 = 114, S2 = 156, S3 = 36). Site 1 had 14 bivalve genera and 13 gastropod genera. Site 2 had 19 bivalve genera and 15 gastropod genera. Site 3 had 19 bivalve genera and 9 gastropod genera. The most abundant bivalve in all samples was Mulinia in both 2018 (S1 =  60.9%, S2 = 37.08%, S3 = 46.5%) and samples processed in this last year (S1 = 74.2%, S2 = 37%, S3 = 61%). Data analysis is ongoing and further comparisons are expected to include the study of diversity, abundance, ecology, and drilling from predation across samples and years.