Shallow Cenozoic seismic stratigraphy and structure: South Carolina lower coastal plain and continental shelf

摘要

Single-channel high-resolution seismic reflection data from the South Carolina lower Coastal Plain and continental shelf delineate no substantial deformation that could possibly be associated with the seismicity of the Charleston area. Correlation of the seismic data with available wells reveals seaward-dipping Paleocene through Quaternary depositional sequences representing carbonate and terrigenous sediments that were deposited in shallow to outer shelf paleoenvironments. Only middle Eocene and younger units are delineated on the lower Coastal Plain due to limited acoustic penetration. The seismic profiles also reveal thick Miocene and Pliocene progradational sediments within a broad north-northwest–south-southeast–trending depositional basin in the middle to outer shelf region. The variations in the thicknesses of the depocenters are attributed to an interrelationship of subaerial and marine processes, which are in turn governed by the shifting of the Gulf Stream, the Suwannee Channel, and sea level. The Cenozoic section in the study area indicates a stable structural framework except offshore Charleston where the Paleocene through Miocene reflectors are displaced by a northeast-southwest–trending monoclinal flexure downthrown to the southeast. The amount of displacement decreases from 20 m on the Paleocene surface to 10 m on the shallowest Miocene reflector seen 10 m below the sea floor. This flexure probably originated by reactivation of the deeply seated pre-Cretaceous Helena Banks fault revealed in multichannel profiles reported elsewhere.