CHARACTERIZATION OF A SUBMARINE CHANNEL-LOBE TRANSITION ZONE, WESTERN NIGER DELTA

Near-seafloor core and seismic-reflection data from the western Niger Delta continental slope document the facies, architecture, and evolution of a submarine channel-to-lobe transition zone. At an abrupt decrease in slope, a submarine channel transitions into an 8 km long x 8 km wide intraslope submarine fan. This fan’s surface is not channelized, but core data indicates sand deposition at all locations on the fan. Core and radiocarbon age data indicate that sand beds progressively stack to the south during the late Pleistocene, resulting in the compensation of at least two lobe elements. The distal edge of the intraslope fan has multiple knickpoints that coalesce into an exit channel, indicating partial flow bypass.

The seafloor expression of this submarine channel-lobe transition zone is particularly interesting. The right-hand levee extends onto the intraslope submarine fan as a ridge, which contains two large (> 1000 m long) scours. This ridge directed flows from the channel onto the southern half of the intraslope fan during the late Pleistocene. Sediment-wave formation at the channel mouth suggests deposition from alternating segments of supercritical and subcritical flow with hydraulic jumps in between. Core data provide lithologic calibration of the transition zone and inputs for numerical modeling of the seafloor surface. This unique dataset provides a detailed view of a transition zone common in submarine environments and establishes linkages between surface geomorphology, depositional processes, and the stratigraphic record.