Abstract

Sand-sized sediments apparently are rare in outer neritic, bathyal, and abyssal depositional environments, existing either in channels or as blanket turbidite deposits. The forming of suitable potential reservoir objectives in such environments requires mechanisms that can concentrate the available coarse sediment. These occur in submarine canyons, deep sea fan channels, and deep ocean channels that form parts of an essentially continuous transport system extending from the shelf to the abyssal plain.

Many investigators have reported sand-size sediments in these deeper marine channels. Bottom sampling and coring by the Deep Sea Drilling Project have recovered gravel- and sand-sized clastics; bathymetric surveys and reflection seismic profiling have mapped the morphology and subbottom structures of these canyons and channels; and submarine current measurements, photographs, and observations by divers and from submersibles document water movement, erosion, sediment transport and deposition in these channels.

Processes within submarine canyons and channels, such as turbidity currents, sand falls and slumps, and water currents capable of transporting sediment, result in a variety of erosional and constructional features. In general, the channels have the same morphologic characteristics as subaerial ones, including natural levees, meanders, and branching channels. Also, submarine channels migrate like subaerial ones, and the old sites are eventually buried by fine-grained interchannel deposits or pelagic debris.

Structural deformation in sediments of modern depocenters includes slumping, whether initiated by a catastrophic event or by instability resulting from excessive local sedimentation; growth faulting, usually subparallel to the bathymetric contours; and shale or evaporite diapirism. Such tectonism, particularly growth faulting and diapirism, can disrupt or offset these channels and form updip seals.

Petroleum industry operations in progressively deeper water require understanding of the depositional mechanisms, history, and sub-sequent deformation in these coarser clastic units. Gas, condensate, and oil are produced from Cenozoic reservoirs genetically related to such environments of deposition.