Maps Showing the Stratigraphic Framework of South Carolina's Long Bay from Little River to Winyah Bay

South Carolina's Grand Strand is a heavily populated coastal region that
supports a large tourism industry. Like most densely developed coastal
communities, the potential for property damage and lost revenues associated
with coastal erosion and vulnerability to severe storms is of great concern. In
response to these concerns, the U.S. Geological Survey (USGS) and the South
Carolina Sea Grant Consortium have chosen to focus upon the Grand Strand (the
arcuate strand of beaches between the North Carolina Border and Winyah Bay, SC)
and adjacent Long Bay as a portion of Phase II of the South Carolina/Georgia
Coastal Erosion Study (SC/GCES).

Phase I of the SC/GCES (1994 - 1999) focused upon critical areas of erosion
along the central portion of the South Carolina coastline. Research conducted
during Phase I began to identify how physical processes, inlet-beach
interaction, framework geology and shoreline geometry combine to control
patterns of erosion along the central South Carolina coast. Phase II of SC/GCES
(1999 - present) was designed to gain a further understanding of the factors
affecting shoreline change within northern South Carolina and Georgia. Specific
goals of the Phase II study include: 1) quantifying historic shoreline change
and identifying erosional hotspots; 2) mapping geologic framework and
determining its role in the area's coastal evolution; and 3) calculating a
sediment budget and identifying transport mechanisms within the study area.

In November 1999, to address the second goal of Phase II of the SC/GCES, the
USGS, Coastal Carolina University (CCU) and Scripps Institution of Oceanography
(SIO) began a program to systematically map the geologic framework within the
South Carolina segment of Long Bay. Data sources used to produce these maps
include high-resolution sidescan-sonar, interferometric sonar swath bathymetry
and sub-bottom profiling. Surface sediment samples, vibracores and video data
provide groundtruth for the geophysical data. The goals of the program include
determining regional-scale sand-resource availability (needed for ongoing beach
nourishment projects) and investigating the role that inner-shelf morphology
and geologic framework play in the evolution of this portion of coastal South
Carolina.

This report presents preliminary maps generated through integrated
interpretation of geophysical data, which detail the geometries of Cretaceous
and Tertiary continental shelf deposits, show the location and extent of
paleochannel incisions, and define a regional transgressive unconformity and
overlying bodies of reworked sediment. Defining the shallow sub-surface
geologic framework will provide a base for future process-oriented studies and
provide insight into coastal evolution.

[Summary provided by the USGS.]