Abstract

Approximately 6,100 km of 3.5-kHz echo-sounding profiles was correlated with a GLORIA side-scan sonar image of the mid-Atlantic United States (34°N, 70°W) lower slope-upper continental rise. The image allows us to map the major erosional and depositional features and to identify major processes that have shaped the area.

The GLORIA imagery shows three approximately triangular-shaped sediment-gather areas that cover the upper-rise and slope transition areas near Wilmington, Baltimore, and Norfolk Canyons. The gather areas, which are interspersed with hemipelagic drape areas, are composed of dendritic networks of channels that extend from the base of the slope toward major channel systems on the middle rise, such as Wilmington Valley. Seaward of Cape Hatteras, a tongue-shaped area of mottled high back scatter on the GLORIA imagery denotes the Albemarle-Currituck mass-movement complex, a large (60 km wide by >190 km long) area of the sea floor that is marked by the disruption of upper-rise sedimentary strata and by mass-flow deposits.

Interpretation of GLORIA imagery and echo-sounding profiles indicates that mass movement is the predominant process affecting sediment on the United States east coast mid-Atlantic slope and upper rise and that isobath-parallel sediment movement by geostrophic currents is restricted mainly to the lower continental rise. The mass-movement processes evident on the rise probably were most active during the Pleistocene, when sea level was lower and sediment input more active.

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