THE TIMING OF CAROLINA BAY AND INLAND DUNE ACTIVITY ON THE ATLANTIC COASTAL PLAIN OF GEORGIA AND SOUTH CAROLINA

Carolina bays (oriented, elliptical, depressional wetlands of the Atlantic Coastal Plain) act as specialized indicators of paleoenvironments and past hydrologic regimes because each responds to local, rather than regional, environmental changes. At the same time, the population of all bays, widespread throughout the Atlantic Coastal Plain, holds in aggregate a broader-scale picture of regional changes. In addition, Carolina bays have been preferred locations for pre-historic human activity, especially during the late Pleistocene/early Holocene, and therefore can be used to examine human-environmental relationships.

Luminescence and radiocarbon dating of inland dunes and Carolina bay rims indicate activity during multiple phases over the past 100,000 years. Some bays have evolved through phases of activity and inactivity over tens of thousands of years, as evidenced both by multiple rims along a single bay and by multiple ages within single rims. Bay rims, the sandy ridges typically bordering the southern and eastern sides of bays, are composed of both shoreface and eolian deposits. The shoreface deposits represent open-water phases with high-energy shoreline conditions. The eolian component of the rims represents periods of lower or fluctuating water levels that would have exposed the shoreface to winds.

The large degree of correspondence between bay and dune activity is consistent with the theory that both dunes and the eolian component of bay rims were shaped during times of strong and persistent westerly to southwesterly winds with dry or seasonally dry conditions. Both dunes and bays were active during the Wisconsin glaciation, with ages tending to fall between 15,000 and 40,000 years BP, and near the isotope stage 5/stage 4 boundary 70,000 to 80,000 years BP.

Dune and bay activity does not correspond precisely, however, as some bay rims appear to have been active during periods of relatively higher water levels that allowed open-water, ponded conditions in the bays. Multiple episodes of rim formation at Big Bay, South Carolina, for example, indicate that the bay was an open-water lake with active margins well into the Holocene, during which time only minor dune reworking, rather than full-scale dune formation and migration, has been documented.