THE LATE PLIOCENE AND PLEISTOCENE MARINE STRATIGRAPHIES OF SOUTH CAROLINA AND SOUTHEASTERN VIRGINIA

A working stratigraphy for the Pleistocene marine section at the surface has been developed for 1:24,000 scale quadrangle mapping in South Carolina. This was refined on the basis of use in the field and is based on stratigraphy by Shattuck, Sloan, Cooke, Colquhoun, McCartan and others, Weems, and Doar and Willoughby. The units from oldest to youngest are: Wicomico, Penholoway, Ladson, Ten Mile Hill beds, Pamlico, Princess Anne, and Silver Bluff. Erosional scarps mark the boundaries between these units. Scarp toe elevations are used to determine maximum relative sea level for the seaward deposits.

The scarp toe elevations in South Carolina are:

Wicomico Fm – +90 ft (27.5m) Surry scarp

Penholoway Fm – +70ft (21.4m) Dorchester scarp

Ladson Fm - +57ft (17.4m) Macbeth scarp

Ten Mile Hill beds - +35 ft (10.7m) Bethera scarp

Pamlico Fm - +22ft (6.7m) Suffolk scarp

Princess Anne Fm - +17 ft (5.2m) Awendaw scarp

Silver Bluff Fm - +10ft (3m) Mt Pleasant scarp

Recent work in South Carolina and in North Carolina is challenging some of the age assignments, and possibly the names, for some units and geomorphic features. However, the stratigraphy used here is presented in a format to allow correlation to other Southeastern States with minimal effort.

In Virginia, the morphology of erosional scarps and paleo offshore features generally follows similar elevations as here shown for South Carolina. Scarp toe elevation may not exactly represent paleoshorelines, but the values are close. As the mapped lithologies typically correlate highly with morphology and are bounded by unconformities, our current guidelines for Cenozoic allostratigraphy are as follows:

Alloformation Scarp toe elevation, feet (SE Va)

Windsor 95 ( ~102 in Richmond area)

Charles City 76

Chuckatuck 57

Shirley 48

Tabb, Sedgefield 28

Tabb, Lynnhaven 18

Tabb, Poquoson 7

The elevations of earliest Pleistocene and older sediments likely have been affected by regional tilting and faulting in the Fall Zone. The results of man's activities (400 years) and surface processes such as colluviation commonly obscure consistent morphologic relationships.