THE QUATERNARY STRATIGRAPHIC ARCHITECTURE OF A LOW-ACCOMMODATION, PASSIVE-MARGIN SHELF (SANTEE DELTA, SOUTH CAROLINA, USA)

Paleo-incisions, regional and local stratigraphic bounding surfaces, as well as aggradational and progradational lithosomes are key components of an integrated stratigraphic framework for the coastal plain and inner shelf of the Santee Delta region along the SE Atlantic margin of the United States. The Piedmont-draining Santee River of South Carolina forms the only river-fed delta along the US east coast and has been a major sediment source for the region throughout recent geologic history. In addition to the modern incised valley, offshore and onshore mapping incorporating a range of geophysical and geological datasets confirms the location of a separate precursor Santee paleovalley south of the modern Santee Delta. Offshore, a complex network of paleochannels can be projected onshore where they align with these ancient river valleys. Pre-Quaternary rocks across the inner continental shelf are covered by a patchwork of Pleistocene and Holocene marine and paralic deposits. Seismic facies analysis coupled with sediment core data indicate that these units were deposited in range environments including tide-influenced backbarrier lagoons/estuaries, wave- and river-dominated delta fronts, transgressive sand sheets and shoals, as well as shelf sand ridges throughout the Pleistocene and Holocene. The depositional architecture and preservation potential of these units is strongly influenced by the low-gradient nature of the continental shelf in this region. Increased rates of progradation, extent of subaerial exposure, and the high degree of transgressive reworking are all driven, in part, by local and regional accommodation.