GROUND-PENETRATING RADAR (GPR) AND OPTICALLY STIMULATED LUMINESCENCE (OSL) DATA FROM QUATERNARY SANDS IN THE CAROLINA SANDHILLS, CHESTERFIELD COUNTY, SOUTH CAROLINA

The Carolina Sandhills region extends from western Georgia to central North Carolina along the updip portion of the U.S. Atlantic Coastal Plain province. In Chesterfield County, South Carolina, the Sandhills region forms a relatively high plateau comprised of Cretaceous sand to poorly lithified sandstone (Middendorf Formation) overlain by Quaternary sand (Pinehurst Formation). This plateau is dissected by incised valleys with streams and terraces. Most of the uplands and terraces are covered by Quaternary sand, except the lowest terrace (6 m above Juniper Creek). Soil types range from deeply weathered plinthitic ultisols to argillic ultisols to sandy entisols. Imagery derived from LiDAR point cloud data reveals that the Quaternary sand forms subdued hills of up to 6 m of relief, with steeper sides on the southeast. Outcrops of the Quaternary sand do not display primary sedimentary structures, although paleosols are present in some outcrops. Ground-penetrating radar (GPR) data indicate: (1) the unconformity between the Cretaceous sand and the overlying Quaternary sand shows at least 5 m of relief locally; (2) the Quaternary sand that forms the hills is up to 6 m thick; and (3) the uppermost 2 m of many of the sand hills do not display sedimentary structures, but 2- to 5-m thick sets of southeast-dipping cross-bedding are visible at depths below 2 m. Optically stimulated luminescence (OSL) data from the Quaternary sand have yielded ages ranging from ca. 46 to 9 thousand years (ka).

These observations suggest the following interpretations: (1) considerable dissection occurred after deposition of the Cretaceous sand and before deposition of the Quaternary sand; (2) the Quaternary sand was derived from the underlying Cretaceous sand, and consists of degraded eolian bedforms that migrated from the northwest; (3) the paleosols within the Quaternary sand attest to multiple episodes of sand mobilization and stabilization; (4) the OSL ages indicate that episodes of Quaternary sand mobilization occurred prior to, during, and after the Last Glacial Maximum; (5) the absence of cross-bedding in the upper 2 m of the Quaternary sand is attributed to bioturbation by vegetation that stabilized the bedforms; and (6) the terrace that lacks the cover of Quaternary sand formed after the last episode of eolian sand mobilization.