PLEISTOCENE ENCROACHMENT OF THE WATEREE RIVER SAND SHEET INTO BIG BAY ON THE MIDDLE COASTAL PLAIN OF SOUTH CAROLINA

SREL Reprint #2568 PLEISTOCENE ENCROACHMENT OF THE WATEREE RIVER SAND SHEET INTO BIG BAY ON THE MIDDLE COASTAL PLAIN OF SOUTH CAROLINA MARK J. BROOKS Savannah River Archaeological Research Program South Carolina Institute of Archaeology and Anthropology University of South Carolina PO. Box 400 New Ellenton, SC 29809 BARBARA E. TAYLOR Savannah River Ecology Laboratory University of Georgia Drawer E Aiken, SC 29802 PETER A. STONE South Carolina Department of Health and Environmental Control Ground Water Protection Division Columbia, SC 29201 LEONARD R. GARDNER Department of Geological Sciences University of South Carolina Columbia, SC 29208 ABSTRACT In Sumter County, South Carolina, an inland sand sheet east of the floodplain of the Wateree River has encroached into Big Bay and may have buried other Carolina bays completely. The encroachment provides an opportunity to study relationships between the development of dunes and Carolina bays, oriented oval depressions that are common on the south Atlantic Coastal Plain. The sand sheet was derived from the Wateree River floodplain, probably when it was much more sparsely vegetated than at present. A drill hole at the leading edge of the sand sheet, where it encroaches into the western side of Big Bay, revealed clays of the Duplin Formation overlain by 4.5 m of organically enriched bay-fill sediments (>48,000 radiocarbon yr B.P.) and 4.5 m of eolian sand. Pollen assemblages from the lower part of the bay fill indicate that the adjacent terrestrial vegetation was open and dominated by grasses. Oak and hickory suggest warm conditions, perhaps Oxygen Isotope Stage 5 (134-75 ka B.P.), an interval that spans the Sangamon interglacial to the early Wisconsinan, or early Oxygen Isotope Stage 3 (6532 ka B.P.), during the Wisconsinan. Pollen assemblages from the middle of the bay rill indicate an open, pine-dominated terrestrial community, plausibly associated with cool climate, perhaps Oxygen Isotope Stage 4 (75-65 ka B.P.), a period of early Wisconsinan glacial advance. Buried soil horizons in the upper half of the bay fill suggest that encroachment of the sand sheet was episodic, with a major episode occurring before 48,000 radiocarbon yr B.P. Conifer macrofossils suggest relatively dry conditions in the basin at that time; dry climate is also requisite for massive transport of sand. This major episode may thus have occurred under cool, dry climate in Oxygen Isotope Stage 4 or under warm, dry climate early in Oxygen Isotope Stage 3. Archaeological evidence indicates that redistribution of sediment on the sand sheet continued at least intermittently into the Holocene, although activity may have slowed after 4000-3000 yr B.P. SREL Reprint #2568 Brooks, M. J., B. E. Taylor, P. A. Stone, and L. R. Gardner. 2001. Pleistocene encroachment of the Wateree River sand sheet into Big Bay on the Middle Coastal Plain of South Carolina. Southeastern Geology 40:241-257. To request a reprint