Updated Stratigraphic Mapping Reveals Insights Into the Late Pleistocene Evolutionary History of the Virginia Eastern Shore, US Mid-Atlantic Coast

Contradictory interpretations of upper Pleistocene (120–40 ka) sedimentary deposits along the US Mid-Atlantic Coast have hindered the development of a reliable regional sea-level curve for the last glacial cycle. This study presents new and compiled sediment cores, ground-penetrating radar, topographic data, aerial imagery, and limited geochronology from geologic units emplaced along the ocean-facing side of the Virginia Eastern Shore during mid- and late-Pleistocene periods of higher-than-present relative sea level: the Accomack Member (Omar Formation), the Butlers Bluff Member (Nassawadox Formation), the Joynes Neck Sand, and the Wachapreague Formation. Minor lithologic and morphologic updates are presented for the MIS 5e/5c Butlers Bluff Member, which is interpreted as a southward-prograding spit emplaced atop penecontemporaneous shoreface sediments or older transgressive sediments which fill the Exmore Paleochannel. The Joynes Neck Sand is reinterpreted as a coastal lag deposit, correlated with the Ironshire Formation in Maryland and Delaware, likely emplaced during MIS 5c. The Wachapreague Formation is determined to be a composite unit composed of two newly mapped members—the Locustville and Upshur Neck—which differ in lithology, internal architecture, and surficial morphology. The older and western Locustville Member (MIS 5a) is characterized by progradational beach and foredune ridges built atop transgressive shoreface and backbarrier deposits, and is correlated with the Sinepuxent Formation in Maryland and Delaware. The younger and eastern Upshur Neck Member of the Wachapreague Formation (late MIS 5a) is distinguished by surficial recurved ridges and preserved washover, dune, and channel-fill structures associated with spit growth atop shoreface deposits. These findings indicate that the Wachapreague Formation was constructed during two sequential highstands: an initial phase of sea-level rise and then fall allowed for deposition of the Locustville Member as a transgressive-highstand-regressive barrier system; and, following a period of lower-than-present sea level, a later highstand resulted in partial erosion of the easternmost Locustville and growth of the Upshur Neck Member. Finally, we update earlier descriptions of an aeolian sand sheet, likely deposited during MIS 3c, that discontinuously overlies most of the east-central Virginia Eastern Shore. Together, these findings update interpretations of the depositional history of the southern Delmarva Peninsula, and allow for future refinement of the sea-level history of the last interglacial-to-glacial period along the mid-field US Mid-Atlantic coast.