REVISION OF THE PLEISTOCENE DORCHESTER AND SUMMERVILLE SCARPS, THE INLAND LIMITS OF THE PENHOLOWAY TERRACE, CENTRAL SOUTH CAROLINA

Geomorphic boundaries of marine Pleistocene terraces (toes of scarps) in South Carolina were examined on 1:24,000 topographic maps, aerial photographs, and new 1:24,000 STATEMAP geologic maps. Did the Dorchester Scarp at its type location face a Pleistocene estuary or the Pleistocene Atlantic Ocean? Colquhoun (1962) interpreted the Dorchester Scarp as formed by a marine Pleistocene highstand at 75 ft elevation and as the boundary between the Wicomico and Penholoway terraces. Colquhoun (1962) also interpreted the Summerville Scarp as formed by a marine Pleistocene highstand at approximately 75 ft elevation and as the boundary between the Penholoway and Talbot terraces. Relationships show: 1) that the Dorchester Scarp at Four Hole Swamp is the boundary between older barrier-island deposits beneath the Wicomico terrace and younger estuarine deposits of the Penholoway terrace; 2) that the Summerville Scarp at Lincolnville is the boundary between older beach deposits beneath the Wicomico terrace and the younger beach deposits beneath the Penholoway terrace; and 3) that a barrier island core separated the two scarps formed during the same Pleistocene highstand. A modern analog is Hilton Head Island. It contains two Pleistocene barrier-island cores separated by successively lower scarps formed during successively lower highstands. The mainland behind the island has two estuarine shoreline scarps in the back-barrier system. Both barrier-island and estuarine scarps were formed during the same highstands, with successive reoccupation of the back-barrier estuarine systems.