23-6 Correlation of Molluscan Diversity With Climate Change in the Plio-Pleistocene Record of Virginia and North Carolina

Session: Paleontology of North America (Posters)

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Abstract:

The mid-Piacenzian Warm Period (MPWP) was an interval of climate change that occurred 3.3-3 Ma and affected marine fossil diversity along the southeastern coast of the United States. This warming period increased global ocean surface temperatures by 3ºC, which is 2ºC warmer than today's oceans. We can use the MPWP as a proxy for modern climate change to predict how it will affect molluscan diversity today. It can also help predict how economically significant species like oysters, hard clams, and scallops will respond to warming climates. 

In southeastern Virginia and northeastern North Carolina, this interval of time is represented by the Yorktown and Chowan River Formations. These sedimentary units are composed of sand, silt, and clay beds recording mid Pliocene to early Pleistocene conditions on the shallow marine shelf. The molluscan fauna of these units is exceptionally abundant, well-preserved, and well-sampled, making it ideal for examining how biotas respond to past environmental change. Previous work in the region suggests that the diversity and richness of molluscan species increased at the same time as temperature, despite an increase in ocean acidification during this interval. Although the MPWP is a short-term event, molluscan species composition and community structure did not return to previous levels immediately following the warming period. 

In this study, we hypothesize that the cooler temperatures recorded in the Chowan River Formation correlate with a decrease in molluscan diversity, species richness, and abundance of warm-water taxa.

Five total bulk samples from the Chowan River Formation were studied. Four were borrowed from the Virginia Museum of Natural History and one was field-collected. Both were sieved to ≥4mm. We identified mollusks to the species level using published monographs and online resources. Abundance was counted to the minimum number of individuals per species. Data analyses were performed using PAST and R to quantify richness (via rarefaction), diversity (Shannon-Wiener), and community structure. 

Preliminary results show that at both the genus and species levels, richness and diversity of Chowan River mollusks are comparable to that of the Rushmere Member, which was deposited during the MPWP. Contrary to expectations, molluscan diversity did not decrease in concert with decreasing temperatures.

Geological Society of America Abstracts with Programs. Vol. 58, No. 1, 2026

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