PRELIMINARY GROUND PENETRATING RADAR AND GEOMORPHOLOGIC INVESTIGATION OF THE HIGHLY INCISED MAPPSVILLE ESCARPMENT OF NORTHERN ACCOMACK COUNTY (WALLOPS ISLAND NATIONAL WILDLIFE REFUGE), EASTERN SHORE, VIRGINIA

The Pleistocene stratigraphic record of the Eastern Shore, Virginia (just south of the MD-VA line) is the focus of this study. Rising sea levels and recent erosion have exposed bluffs on the shore of Chincoteague Bay (SW of Greenbackville, VA). These strata were mapped as the post-Pliocene Accomack Member of the Omar Formation, and overlying Joynes Neck Sand by Mixon (1985). Even though these strata have been documented through core and some limited upland exposures, their age, geologic origin, and significance relative to glacial-interglacial chronologies remains poorly resolved. We have identified at least five distinctive depositional units in these exposures suggesting complex environmental histories. These are not yet well-aligned with core descriptions of Mixon who interprets the unit as a transgressive barrier island sequence. In contrast, Groot and others (1990) suggested the Omar represented multiple transgressive/regressive cycles. Our studies concur based on both GPR and field evidence.

Lidar mapping of the eroding bluffs shows these geomorphic features align with and are located immediately adjacent to a NE-SW-oriented geomorphic feature mapped as the Metomkin Scarp further south (Mixon, 1985). However, several distinctive scarps merge northward and are likely composited or stacked in northern Accomack County. So herein, this scarp is referred to informally as the “Mappsville” scarp (not to be confused with the Mappsburg scarp further south) until regional relationships can be established. The scarp forms the western boundary of modern coastal bay marshes in the northern Mid-Atlantic Bight. This pilot study reports on the first Ground Penetrating Radar (GPR) investigation of the scarp at Wallops Island National Wildlife Refuge. Although work is ongoing, the newly obtained GPR datasets are being investigated in tandem with sediment data from Powell’s Creek bluff and from Swan’s Gut/Sinnickson bluff. The presence of a newly recognized paleosol (here named the Powell’s Creek) and overlying lagoon deposit both located above modern sea-level suggest an MIS 5e age (or possibly older). Although further investigation is needed, this work is already providing additional insights necessary to resolving the record of environmental change on the Eastern Shore prior to the onset of the Holocene rise.