Over the past 200,000 years, Earth has experienced massive fluctuations in ice volume that have resulted in changes in global sea level by 150 m or more. In comparison to regions to the south and north, the mid-Atlantic region of the United States is currently experiencing the greatest rate of sea-level rise along the East Coast. This reflects compounding effects of glacial isostatic adjustment and melting ice sheets. Reconstructing the history behind these sea-level fluctuations has significant importance for interpreting paleoenvironments and the evolution of coastal and shallow-marine systems, as well as for predicting possible future magnitudes of sea-level rise. Here, we seek to refine estimates of past sea-level change by reconstructing the evolution of the Wachapreague Formation on the Eastern Shore of Virginia during the Sangamonian interglacial period. We do so through field mapping and collection and analysis of stratigraphic data, including direct-push sediment cores to depths of >20 m below modern sea level. This is supplemented with geochronology provided by infrared stimulated luminescence. Together, these data reveal a complex history of sea-level change during the middle to late Sangamonian interglacial, including evidence of sequential sea-level highstands at 68 and 53 ka. These resulted in the formation of two separate geologic units, the Wachapreague and Upshur Neck Formations, which in the past had been assumed to have formed during a single phase of transgression and regression. As these periods correspond with relatively low global sea level, our findings indicate that isostatic land adjustment due to changing ice volumes is delayed by as much as 10,000 years. This results in relative sea-level fluctuations which are mismatched with global sea level and reflect the complexity of future response of local sea level to accelerating eustatic sea-level rise.
Clarke, Cameron, "Unraveling the History of Pleistocene Sea-Level Change in Virginia: Insights from the Wachapreague Formation, Virginia Eastern Shore" (2022). Geology Senior Theses. William & Mary. Paper 33.