Abstract The Pleistocene Fuji–Einstein system in the northeastern Gulf of Mexico consists of a shelf-edge delta that is directly linked to and coeval with two submarine channel–levee systems, Fuji and Einstein. There is a continuous transition between the channel fills and the delta clinoforms, and the seismic reflections of the prodelta are continuous with the levee deposits. Five smaller delta lobes within the Fuji–Einstein delta formed through autocyclic lobe switching that was superimposed on a single falling-to-rising sea-level cycle. The corresponding stratigraphic complexity is difficult to interpret in single downdip seismic sections, especially where elongated mudbelts are attached to some of the delta lobes. The two slope channel systems, Fuji and Einstein, deeply incise the shelf-edge delta. However, late-stage delta progradation was coeval with slope-channel development, and, as a result, there is no easily mappable, single erosional surface separating channel deposits from deltaic sediments. During early delta-lobe development, a gully field forms on the upper slope, directly downdip from the delta lobe. As the delta progrades, one of the larger gullies in the middle of the field captures most of the denser flows and gradually evolves into a sinuous channel. The larger delta-related slope channels source 2–4 km-wide submarine aprons where they encounter areas with lower gradients. If the slope gully or channel remains active for a long enough time, its corresponding submarine apron smooths out the slope and becomes incised by the later bypassing flows. The well-preserved and mappable 3D shelf-edge architecture provides a rare opportunity to understand relationships between deltaic and slope depositional systems.

Abstract The morphology of a 1250 km 2 portion of the middle slope off the western Niger Delta shows that gradients on the Pleistocene slope vary both spatially and at different stratigraphic levels. In the deeper section, three lower-gradient steps are connected by three higher-gradient ramps, generating a stepped-slope morphology. Through time, preferential accumulation of slope aprons, composed of mass-transport deposits, compensationally stacked lobes, and overbank deposits (wedge-shaped outer levees), helped fill slope accommodation, smoothing over the gradient change across ramps and steps, and vice versa. Consequently at the local scale, the stepped slope evolved into a smoother slope that is nearly graded at the modern seafloor. As in other studies, preferential accumulation of sediment on the slope is believed to reflect in part the deceleration of sediment gravity flows (both turbidity currents and debris flows) as they encountered lower-gradient steps. Down-slope changes in slope morphology also caused variations in the amount, and presumably rate, of erosion along the axes of canyons in the study area—with increased incision depth where knickpoints cut through positive-relief bathymetric structures in an attempt to establish a graded profile. Along the Benin-major Canyon there is an inverse linear relationship between the thickness of deposits that accumulate on the slope adjacent to the canyon and the amount of vertical erosion along its axis. The thickest outer levee deposits coincide with canyon segments that have the shallowest incision, in turn corresponding to slope segments showing a sharp decrease in pre-incision gradient. This implies that the increase in sediment flux to outer levees on some parts of the stepped slope results from a combination of increased overspill from flows passing through shallower canyon reaches, and increased sedimentation caused as mud-dominated flows decelerated on lower-gradient slope segments immediately adjacent to the canyon. Thus there appears to be an intimate relationship between slope morphology, canyon incision depth, and the thickness of overbank deposits adjacent to canyons.

Abstract Field and simulation studies indicate that channel architecture and the presence of channel-base drapes (CBDs) can have a significant impact on oil recovery and represent key uncertainties in the understanding of a turbidite channel reservoir. Accordingly, understanding the frequency and distribution of CBDs provides valuable insights into reservoir performance. Core and dipmeter data contain information that can be used to recognize channel-base disconformities and associated CBDs. By comparing the observed number of channel-base disconformities to the observed number of disconformities overlain by mudstone, a statistical assessment of their frequency and distribution can be made. In a spatial sense, the fraction observed in the wells represents the average percentage of the channel elements within the reservoir that are overlain by a drape.