EOLIAN SEDIMENTS AND PALEOWIND BEHAVIOR IN THE SOUTHEASTERN UNITED STATES DURING THE LAST GLACIAL MAXIMUM

Under modern conditions, the southeastern U.S. is not a region of prominent eolian sediment mobilization because of a relatively humid climate and surface wind velocities generally <3 m/sec. However, recent research has documented evidence of widespread eolian activity in the southeastern U.S. during the last glacial maximum (LGM). The evidence includes eolian sand dated by optically stimulated luminescence methods in the Carolina Sandhills of South Carolina, around Carolina Bays, and in river valleys throughout the coastal plain. The Carolina Sandhills region, which is located west of the Orangeburg Scarp, is characterized by eolian sand sheets and dunes (mean grain size: 0.35–0.59 mm) derived from underlying Cretaceous sand. The predominance of sand sheets is attributed to coarse grain size and the presence of some vegetation when the sand was mobilized. Dune morphologies and cross-bedding are consistent with winds from the west and (or) northwest. These inferred wind directions are most consistent with modern January wind directions and inferred LGM January wind directions, suggesting that sand mobilization may have occurred preferentially during the winter. The relatively coarse grain size would have required wind velocities of at least 4–6 m/sec, after taking into account the effects of colder air temperatures on eolian sand transport. The Carolina Bays, which are more abundant east of the Orangeburg Scarp, are low-relief elliptical depressions oriented NW-SE with raised sand rims on the eastern sides of many depressions. Most geologists give an eolian interpretation for the orientation of the bays and the origin of many sand rims. River valleys throughout the coastal plain contain vegetated parabolic dunes (mean grain size: 0.25-0.50 mm) on the east side of the modern river channels. The sand is thought to be derived from the river channels, and the parabolic morphology suggests that some vegetation was present to anchor the dune tails. Dune orientations indicate that winds that mobilized the sand blew from the west in Georgia, shifted gradually across the Carolinas to blow from the southwest in North Carolina, and blew from the northwest in Maryland and Delaware. These widespread eolian sediments in the southeastern U.S. suggest stronger winds and relatively arid conditions during the LGM.