SEDIMENTOLOGY AND STRATIGRAPHIC ARCHITECTURE OF QUATERNARY PALEOCHANNEL FILL SUCCESSIONS ALONG THE INNER SHELF OF SOUTH CAROLINA, USA

Throughout the Quaternary, numerous high frequency, high amplitude glacioeustatic sea level cycles have left behind a complex network of paleochannels and paleovalleys across the inner continental shelf off the coast of South Carolina. These isolated paleotopographic lows were carved into a substrate of pre-Quaternary rocks and Pleistocene deposits by coastal plain and Piedmont-draining rivers and provided rare accommodation in an overall low-accommodation setting. The distribution, age, composition, and stratigraphic architecture of these sedimentary successions offer insight into both the allogenic and autogenic forces that influenced depositional processes at the time of formation.

As part of a 2015 regional sand resource assessment, a dense grid of high resolution subbottom (Chirp) data was acquired off the coast of Folly Beach, South Carolina by the Bureau of Ocean Energy Management (BOEM). These data provide the spatial resolution required to reconstruct paleochannel connectivity and define the internal stratigraphic architecture of paleochannel and paleovalley successions. Paleochannel fills exhibits concentric, asymmetrical, or horizontal geometries reflect varying degrees of erosion, aggradation, and accretion. Paleovalleys exhibit vertical relief of up to 10 meters and apparent widths of up to 3 kilometers. Within paleovalleys, individual channels are arranged in both multistory and multilateral configurations that are the result of changes in localized autogenic processes as well as regional allogenic controls that influenced accommodation.

In addition to geophysical data, 52 meters of sediment core recovered from 9 locations provide the control necessary to reconstruct depositional processes associated with this architecture. Detailed physical descriptions including sediment composition, lithology, and physical structures; geochemical analysis; ¹⁴C dating; and AAR age estimates of cored intervals reveal channel fill that was deposited during the mid-Holocene and was dominated by tidally-influenced processes in low to mixed energy, estuarine and backbarrier settings.