STRATIGRAPHY OF A STRANDED MID-PLEISTOCENE CHESAPEAKE BAY SHORELINE COMPLEX, DORCHESTER COUNTY, MARYLAND, USA

Three mid Pleistocene highstand deposits within a subtle ridge (~ 5 meters relief) of the Parsonsburg Sand and adjacent flat-lying Kent Island Formation, were identified by O’Neal et al. (2001) at the landward edge of a low (MSL to ~ + 10 m MSL), broad (~ 40 km) platform on the eastern margin of the Chesapeake Bay, in Dorchester County, Maryland. Together, these highstand units cut into the underlying Miocene Pensauken Formation, and form a stranded estuarine shoreline complex, likely emplaced during climate-driven sea level cycles of + 12 m (min.), + 11 m (min.), and + 14 m MSL, during oxygen isotope stage 11 age (O’Neal et al., 2002). In the current investigation we present additional data to support, clarify, and modify these findings.

Two ground penetrating radar (GPR) surveys totaling ~ 1750 meters, 15 hand augered boreholes, and seven vibracored lithologic sections were collected parallel to the radar profile of O’Neal et al. (2001, 2002), and perpendicular to the linear trend of the Parsonsburg Sand deposit near Rhodesdale, Maryland, to confirm the lateral extent of the suspected paleoshoreline complex. Transgressive ravinement surfaces, gravel lag deposits, and paleosols within these data reveal a fourth highstand deposit of ~ + 8 m MSL (min.) within the complex, and establish four parallel to sub-parallel paleoshoreline and/or shoreline incision trends. GPR and lithologic data collected across the Parsonsburg linear high reveal a low dune and overwash field associated with the shoreline of the youngest highstand unit, and establish a revised sea level of ~ + 13 m for this event. These results confirm the Parsonsburg Sand and Kent Island Formation at this location, as a stranded shoreline complex of the Chesapeake Bay, and strengthen the regional correlation of these deposits as mid Pleistocene in age (O’Neal and McGeary, 2002).