142-1 Comparing marine molluscan communities of the Nashua and Anastasia Formations across the Plio-Pleistocene of Florida

Session: Undergraduate and Graduate Geoscience Student Lightning Talk Showcase (Posters)

Poster Booth No.: 17

Presenting Author:

Shannon Horvath

Authors:

Horvath, Shannon M.¹, Weinstein, Sofia R. Y.², Acosta, Kaitlyn A.³, Boardman, Eliza J.⁴, Nguyen, Kiet V.⁵, Hira, Kayla N.⁶, Visaggi, Christy C.⁷, Portell, Roger W.⁸

(1) Georgia State University, Atlanta, GA, USA, (2) Georgia State University, Atlanta, GA, USA, (3) Georgia State University, Atlanta, GA, USA, (4) The New School, Atlanta, GA, USA, (5) Georgia State University, Atlanta, GA, USA, (6) Georgia State University, Atlanta, GA, USA, (7) Georgia State University, Atlanta, GA, USA, (8) Florida Museum of Natural History, Gainesville, FL, USA,

Abstract:

Understanding marine molluscan extinctions across Plio-Pleistocene units in Georgia and north-central Florida is key to understanding community changes in the Western Atlantic. Previous research has focused on assemblages from the Carolinas and south Florida, but this study examines a biogeographic gap in data for Georgia and north-central Florida. Six samples of the Plio-Pleistocene Nashua Formation were retrieved from spoil piles at different sites within a quarry at East Coast Aggregates (ECA) in Hastings, FL. Multiple in situ samples of the Nashua Formation from the lower and upper sections of the quarry wall were processed from Buck Hammock Materials (BH) near Deer Park, FL. Additional Pleistocene samples from the Anastasia Formation at World Golf Village (WGV) in St. Augustine, FL, were made available through the Florida Museum of Natural History. Laboratory methods involved sieving samples and picking, sorting, and identifying shells, including separating whole from fragmented specimens. Analytical methods included an examination of diversity, abundance, ecology, and drilling predation. Preliminary results indicate differences in the diversity of faunas between lower and upper BH samples, and in comparison to rich ECA assemblages, as well as the younger WGV samples of the Anastasia Formation. Across all three localities (>34,000 shells), bivalves were dominant at all sites, accounting for over 95% of individuals. Ecologically, actively mobile, infaunal, suspension-feeding bivalves were most common. Predatory carnivores generally dominated gastropod feeding types except in lower BH samples. One notable pattern is the contrast in richness and Shannon H diversity between the ECA samples and the BH and WGV localities. Drilling frequencies were higher for ECA samples compared to the other sites. Sample processing is still ongoing for small, rare, and poorly preserved specimens. Next steps in this research include contributing new data from additional Nashua localities in Florida and examining understudied formations in Georgia to see how paleocommunities change in adjacent and/or younger units. Other work in progress is to clarify comparisons across localities by doing strontium isotope stratigraphy. This comparative study helps better understand how molluscan communities responded to past environmental changes at a biogeographic boundary between the Carolinian and Gulf provinces. Examining how marine communities respond to natural disruptions in the ecosystem has conservation implications for studying human impacts and addressing the sixth extinction in modern habitats.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

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