A GEOPHYSICAL, STRATIGRAPHIC AND PALYNOLOGICAL INVESTIGATION OF THE CENTRAL DEPRESSION ON ST. CATHERINES ISLAND, GEORGIA

St. Catherines Island, Georgia, is a barrier island consisting of a high-standing Late Pleistocene core surrounded by low-standing Holocene salt marsh, channel margin, and ridge and swale deposits. A linear topographic low, the Central Depression (CD) trends NE-SW, and parallels the long axis of the island within the Pleistocene core. The CD hosts fresh water marshes and ponds, and historic accounts indicate the former presence of “crystal springs”. A 100 MHz Ground Penetrating Radar (GPR) profile across the northern portion of the CD reveals a trough-like subsurface structure coincident with the CD. Possible origins for this feature include a buried channel, a solution collapse depression, or a small graben. To investigate the origin of the structure, nine vibracores were obtained in a transect across the CD providing shallow stratigraphy, samples for sedimentological and palynological study and ground-truth for a higher resolution 250 MHz GPR profile. The palynological investigation of the CD should constrain the nature and duration of the local wetland. Initial investigation of cores recovered from the CD reveal a significant amount of fossil palynomorphs. Samples from 25-35 cm in Core 1 indicate a Myrica-dominated wetland. Samples from 70-75 cm indicated a different plant community with an Ericaceae-dominated shrub swamp. Integration of palynological data from the cores into a stratigraphic and geophysical profile across the CD may provide some indirect information on island hydrology and constrain the origin of the CD and the hydrologic system that supported ancient wetlands in the CD.