EOLIAN DUNES OF LATE QUATERNARY AGE ON THE FLOODPLAIN OF THE SAVANNAH RIVER, JASPER COUNTY, SOUTH CAROLINA

In Jasper County, South Carolina, approximately 50–70 km from the coast, a cluster of vegetated sand hills is present in the flood plain of the Savannah River, between the modern river channel and the east bank of the flood plain. These sand hills rest on an unconformity above post-Miocene sand, muddy sand, and mud. The sand hills cover an area that is approximately 15–20 km long and 1–4 km wide, and they form degraded parabolic shapes with tails pointing west. The maximum thickness of the sand is approximately 7 m, and the sand cover is relatively continuous except in some of the western and southern portions of the sand hills. The hills consist of yellowish-orange medium to fine sand, overlain by a 0.1–0.6-m thick veneer of brown medium to fine sand. Both the yellowish-orange sand and the brown sand are composed primarily of very well sorted, well rounded to very well rounded quartz. Within the sands, there is no visible evidence of sedimentary structures, unconformities, or paleosols (other than pervasive bioturbation by vegetation). Five Optically Stimulated Luminescence dates from the yellowish-orange sand have yielded ages ranging from 32–17 ka.

The sand hills are interpreted as remnants of an eolian dune field that was active just before and during the Last Glacial Maximum (LGM). It is not clear whether the dunes were mobile during all of this time, or whether there were discrete intervals of eolian sediment mobilization separated by intervals of eolian sediment stabilization. Nevertheless, it appears that just prior to and during the LGM the climate became relatively arid and (or) the wind strength increased, causing fluvial sediments of the Savannah River to be reworked into parabolic eolian dunes. During this time, some vegetation may have been present to stabilize the tails of the dunes. The dunes migrated to the east away from the Savannah River, but did not reach the east bank of the flood plain before the climate became less arid and (or) wind strength decreased, resulting in stabilization of the dunes by vegetation. Since the LGM, changes in aridity and wind strength have not exceeded thresholds for eolian remobilization of the dunes, the dunes have remained stabilized, the dune morphology has been degraded, and pedogenic processes have imparted a brown color to the uppermost 0.1–0.6 m of the dunes.