Middle Atlantic Continental Slope of United States: Deposition and Erosion

Abstract Continuous seismic reflection profiles across outer continental terrace (outer continental shelf and slope) show that directly off Cape Hatteras reflection interfaces (sedimentary strata) with low seaward inclination (≤= 1°) underlie the continental shelf and terminate at the continental slope, which inclines about 9°. On traverses about 200 km north of Cape Hatteras, reflection interfaces (sedimentary strata) do not terminate but incline about 3°, nearly parallel with the continental slope. On the continental slope about 100 km north of Cape Hatteras both relationships are present. The stratal terminations were produced primarily by erosional processes, on scales ranging from erosion of individual strata (< 100 m thick) at the shelf break to rotational slumping of the entire stratigraphic section beneath the continental slope (1.5 km thick). The thickening mantle of sedimentary strata on the continental slope north of Cape Hatteras may have been derived from adjacent fluviatile sources as a result of former discharge regimens. Deposition of the sedimentary mantle on the continental slope may be controlled by the Western Boundary Undercurrent, which flows over the continental slope and the adjacent continental rise. The association of erosional and depositional features is consistent with a model of continental terrace development in which strata accumulate on the continental shelf by upbuilding and on the continental slope by outbuilding while basement subsides during seaward tilting. At the continental slope, strata are terminated primarily by erosional processes. Periodically, rotational slumping at the continental slope occurs, causing strata from the slope and outer shelf to shift to the continental rise and exposing shelf strata at the edge of the continental terrace.