Abstract: Back-Barrier Sedimentation on Tide-Dominated Coastline of South Carolina

Pulak K. Ray

The study of surface sediments of St. Phillips Island, South Carolina, and flow dynamics of its back-barrier tidal creeks connecting two estuaries, St. Helena Sound on the north and Port Royal Sound on the south, indicates that the sedimentation pattern is controlled primarily by channel morphology and slope wash from the ridges. The back-barrier sediment sequence which forms during rising sea level represents channel, tidal-flat, low-marsh, and high-marsh environments. The sequence is capped with slope-wash sand. Characteristic lithology, flora, and fauna allow easy delineation of the sediments. On the basis of flow characteristics and the resulting sedimentation pattern the tidal creek can be divided into three zones, two of which are straight sections near the mouth and the midsection ("nodal zone"). In these two zones the maximum flood and ebb velocities are close to high tide, whereas at the nodal zone they are near low tide. The salinity is related inversely to temperature near the mouths but, as a result of excess evaporation, it is directly proportional to temperature at the nodal zone. The maximum suspended sediment concentrations correspond to the peak ebb and flood flows. Tide-velocity curves involve temporal asymmetry in the three zones resulting in a unidirectional flow of short duration, prolonged stagnation, and extensive sedimentation during flood tide at the n dal zone. A large contribution of organic matter from the marshes and sediments from slumping during ebb tide results in a net-negative sediment budget even in areas of active sedimentation. Data from the study will be helpful in barrier-island planning and management programs.

AAPG Search and Discovery Article #90961©1978 AAPG Annual Convention and Exhibition, Oklahoma City, Oklahoma