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Submarine Sediment Routing Systems on the Western Niger Delta Slope: Autogenic and Allogenic Signal Propagation and Preservation


High-resolution seismic reflection, bathymetry, and core data demonstrate the recent activity and evolution of submarine sediment routing systems on the western Niger Delta slope. Two submarine channels ~ 15 km apart conveyed sediment downslope during the late Quaternary, constructing channel-belt deposits and intraslope submarine fans. The southern channel has two segments, an upslope anastomosing segment and a downslope entrenched, sinuous segment. The northern channel terminates into an intraslope submarine fan with a bypass channel that forms a tributary to the southern channel. The upslope northern and southern channels are of similar dimensions and sediment flux was likely similar in both channels; however, local channel curvature and topographic effects result in variable deposition rates, with very rapid deposition (3 meters/kiloyear) in some locales. Both submarine channels were actively conveying sand downslope during Marine Isotope Stage (MIS) 3. The southern channel was abandoned at 19 ka during the last glacial maximum (LGM), suggesting an autogenic rather than an allogenic mechanism for the cessation of sand. Abandonment is progressive in the southern channel, with the cessation of sand deposition younging up-system over a ~ 4 ka period, with the most updip locations being fully abandoned at ~ 15 ka. The northern channel was abruptly abandoned at 14 ka, suggesting an allogenic mechanism such as rapid sea level rise during Melt-Water Pulse 1-A. An increase in the mud deposition rate during the Holocene is attributed to increased Niger River discharge at the onset of the West African Monsoon at 14 ka. This study indicates that there are complex interactions between autogenic and allogenic signals in submarine sediment routing systems. These signals can coincide in time and space, and the propagation and preservation of these signals is highly dependent on local conditions. Interpreting autogenic and allogenic signals in the preserved stratigraphic record can be perilous without the regional context and high-resolution geomorphic record that studies such as these provide.