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A three-dimensional study of a modern flood-tidal delta in South Carolina was conducted using historical charts and photographs, geomorphic and sedimentologic process measurements, and shallow seismic profiling. Results suggest that the flood-tidal delta developed in response to shoreline erosion of the Santee River delta since the river was dammed and diverted in the first half of this century. The Santee flood-tidal delta complex consists of a transgressive sequence topped with tidal delta deposits 1 to 1.5 m thick. The clean, coarse to medium-grained sand of the flood-tidal delta is underlain by tidal flat, tidal channel fill, and bay-fill sediments. Beneath that lies estuarine-lower delta plain deposits.
The relationship of peak ebb and flood currents to the depth of flow and the degree of shielding by topographic highs exerts control over bed-form orientation and distribution. Ebb-oriented bed forms dominate the tidal delta surface, but preferential preservation favors flood-oriented bed forms owing to higher hydraulic energy on the ebb shield and flood ramp, and by protection from ebb currents provided in the lee of the ebb shield. Textural and mineralogic evidence indicates that littoral-derived sediments are being deposited in the North Santee channel. Seismic and stratigraphic data indicate the maximum volume of clean sand in the flood-tidal delta is between 387,000 and 500,000 m3.
Surface mapping suggests that the North Santee flood-tidal delta will continue to transgress the adjacent tidal flat, weld onto nearby Cane Island, and be capped by salt marsh if undisturbed by rediversion of the Santee. The flood-tidal delta would apper in
the stratigraphic column as a thin sheet sand with local variation in internal physical and biogenic sedimentary structures. Overall bed-form orientation would be slightly flood dominant, and the flood-tidal delta sands would be sealed on top and bottom with fine-grained, organic-rich sediments. Modern flood-tidal deltas are excellent sources for beach nourishment projects and, given sufficient burial, ancient flood-tidal deltas could make good petroleum reservoirs.
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