ON THE NATURE OF ROCKY OUTCROPS ON THE CONTINENTAL MARGIN EAST OF CHARLESTON, SOUTH CAROLINA: PAVEMENTS, MEANDER SCARS, AND LINEAR TRENDS AS DOCUMENTED THROUGH DIRECT OBSERVATION AND REMOTE GEOPHYSICAL METHODS

The lack of sediment availability on the Continental Shelf in the South Atlantic Bight (SAB) combined with a shallow Tertiary geological framework creates a mosaic of intermittently to consistently exposed rocky features that range from very low-relief pavements to linear ridges of rocky exposures two to three meters high and several kilometers long. This paper focuses on the geophysical data results of three educational cruises conducted as part of the NSF-funded educational-focused Transects Program at the College of Charleston and highlights both geological mapping in the offshore as well as geologic mapping training and analysis of field data.

As part of the SAB and with a significant amount of unmapped critical benthic habitat, the study area along a transect extending from Charleston, South Carolina to the shelf edge contains three distinctly different bottom types ranging from 7-m to 50-m water depth. Sidescan sonar mosaics, chirp subbottom profiling, ROV-video transects, bottom grabs, and shallow sediment cores were collected to characterize and document the nature of the materials along various transect sites. The inner most, shallow site consists of primarily an extensive, intermittently exposed pavement of exposed shales and limestones. The intermediate depth site at approximately 18-m depth includes a series of entrenched tidal creek or river channel meanders that incise a rocky platform, creating areas of varied relief. The deeper offshore site at approximately 50-m depth includes a series of boulders along an extensive high-relief ridge.

Each bottom character and the potential for critical habitat in these regions is directly related to the nature of the nearsurface geological materials and stratigraphic architecture, sea level changes and fluctuations since the last glacial maximum, minimal sediment input from other than local sourcing from eroding rock, and the nature of the relief and subsequent burial and exposure due to modern shelf processes. We do not submit here a new classification for hardground and habitat types offshore, but rather provide the reader with a sense of the differences across this portion of the shelf. As these studies continue, we will further investigate the nature of the seafloor with respect to hardground distribution and type, changes in these types through time, and suitability for habitat for each type.