Print this pageArchitecture and Reservoir Characterization of Fine-Grained Submarine Fans
BOUMA, ARNOLD H.
Fine-grained submarine fans differ significantly from coarser-grained, sand-rich fans. Fine-grained ones prograde directly and then switch laterally to compensate for seafloor topography. However, an entire complex of several of these fans will prograde incrementally.
Based on studies on modem and ancient fan deposits in the Gulf of Mexico, Arkansas, Venezuela, and South Africa, a depositional model has been developed that emphasizes three major depositional end members.
Initiated by a relative sea-level lowering, a large slide/slump will start on the outer shelf-upper slope area. A large "channel" will be formed across the slope that will become a conduit for all sediment used to construct that particular fan. Initial deposition of most density flows takes place at the base-of-slope with the formation of a complex of wide, rather thin channel fills, locally separated by shales. Vertical connectivity will be rather good.
Once on the basin plain the depositional mode will change to channel-levee-overbank units, each one normally bifurcating in the downslope part of the middle fan. Channels will switch laterally for compensation purposes. Channel fills consist of amalgamated sandstones. The levees are low-contrast, low-resistivity, thin-medium bedded sandstones, alternating with silty shales. The overbank deposits become finer farther away from the channel.
The distributary channels gradually shoal, will not be able to control the heads of density currents, and overflowing will result. Sheet sands form that will be partially amalgamated and partially separated by thin shales.