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Channel Complex Architecture of Fine-Grained Submarine Fans at the Base-of-Slope
Arnold H. Bouma (1), Gwang H. Lee (2), Oscar van Antwerpen (3), Timothy W. Cook (4)
The fan-valley or upper fan channel connects the submarine canyon on the outer shelf-upper slope to the basin proper. It is an erosionally-formed channel that is a conduit for sediment transport to the basin. It gradually aggrades as density currents pass through. The valley may widen where it enters the base-of-slope area. Most of the succeeding density flows/slumps are much smaller than the initial, strongly erosional, flow and therefore will not be able to occupy its entire width. As a result, smaller individual channels will be formed, resulting in a massive fill comprised of amalgamated sandstones. Sand-rich levees and overbank deposits flank each of these channels. Frequent channel switching takes place toward locations with a slightly steeper gradient. These switches are most likely initiated by the irregular flow successions and different flow sizes. Erosion between successive channels is common, removing part of the channel fill and adjacent levee deposits. This results in a disorderly distribution of low-permeability barriers creating local obstruction to connectivity.
A study of the sedimentological architecture of the updip mid-fan channel complex was conducted on cliff sections of the Permian Tanqua Karoo subbasin in South Africa, and in Big Rock Quarry in North Little Rock, Arkansas. Seismic records of the base-of-slope of the Mississippi Fan show a widening pattern, while seismic studies of the Bryant Canyon Fan Complex south of the Sigsbee Escarpment reveal channel complexity in the base-of-slope area.
Integration of seismic data and outcrop observations improves our understanding of the complexity of many good reservoir sands, typically overlain by slope shales. Their architecture differs considerably from that of the overlying upper fan channel fill and that of the basin floor proper.
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