CONCENTRIC SAND RIMS DOCUMENT THE EVOLUTION OF A CAROLINA BAY IN THE MIDDLE COASTAL PLAIN OF SOUTH CAROLINA

New optically stimulated luminescence ages yield an account of the long-term evolution of a Carolina bay, indicating alternating periods of activity and stabilization over the last 36,000 years. Big Bay is a Carolina bay located about 10 km west of the confluence of the Wateree and Congaree Rivers in South Carolina on Shaw Air Force Base’s Poinsett Electronic Combat Range. The bay is roughly 5 x 3 km in area, is infilled with organic material, and supports a thick cover of hydric vegetation. The western edge of the bay was covered by a sand sheet, dated previously by optical dating to ~74,000 years, with surface reworking that produced parabolic dunes between around 30,000 and 33,000 years ago. The southern and eastern edges of the bay are marked by a series of a dozen or more concentric sand rims. In places, the inner- and outer-most rims are separated by nearly 700 m. Luminescence dating samples indicate that the sand rims are progressively younger toward the center of the bay. Four rims selected for dating have ages of 35,660±2600; 25,210±1900; 11,160±900; and 2,150±300 years ago. All errors quoted are the standard error of the mean of 12 to 20 sensitivity-corrected, single aliquot regeneration (SAR) individual paleodose determinations per sample. The consistency of the SAR paleodoses and consequent low standard errors reflect rapid stabilization of the sand rim with little, if any, influence of bioturbation on the luminescence characteristics of sediment at 60-75 cm depth. The trend of younger sand rims toward the bay center indicates that the bay has shrunk in area over the last 36,000 years, reducing the distance measured SW-NE across the bay from rim to rim, from 3.3 km to 2.3 km. An additional date of 20,390±1600 years documents eolian reworking of sediment associated with an adjacent bay to the southwest. Another new luminescence date from the Carolina bay rim bordering Arabia Bay in southern Georgia shows the rim was active 12,630±1000 years ago. These dates indicate bay rims were periodically active well after the maximum advance of the Wisconsin ice sheet.