Early Neogene base-of-slope sediment at site 397, DSDP Leg 47a: sequential evolution of gravitative mass transport processes and redeposition along the northwest African passive margin.

Site 397 revealed a 1300m thick Neogene sediment wedge directly overlying strata on the upper continental rise off Cape Bojador. A major erosional event stripped sediment from the rise and slope, probably during Oligocene time and produced a hiatus of c.100 my. Slumping of slope sediment and cutting of submarine canyons commenced in M. Miocene. A thick sequence (554 m) of slump units, debris flow units, intercalated mud turbidites, and turbiditic sands accumulated on the upper continental rise. Slope gradients gradually decreased, and during early-late to M. Miocene c.200m of slumped hemipelagic marls and turbiditic sands intercalated with undisturbed hemipelagic marls were deposited. By early-late Miocene time, redeposition of sediment had ceased. -from Authors