Abstract: Architectural Characteristics of Fine-Grained Submarine Fans: A Model Applicable to the Gulf of Mexico

Arnold H. Bouma, Henry DeV Wickens, James H. Coleman

Submarine fan deposits in the Gulf of Mexico, modern and ancient, fall in the category of fine-grained, low overall sand/shale ratio basin-floor fans. Models published over the years that have been applied to both exploration and production are based on sand-rich fans, most of which were deposited in active margin settings. These models should not be used for the Gulf of Mexico or any other deep water system with similar basinal settings. Observations from the excellent outcrops of the Permian Tanqua Karoo in southwestern South Africa, together with information from the modern Mississippi Fan, and the Jackfork turbidites in Arkansas, enable the construction of a model that addresses the architecture of both the macro and meso-scale depositional features of fine-grained turbidite systems.

At the entrance to the basin floor the conduit, carved out across the slope, may start to widen. Most of the density flows moving through do not necessarily occupy the conduit's entire width. The result is a complex of laterally and vertically stacked channel fills and associated levee-overbank deposits with a good degree of connectivity.

The channel fills are mostly massive, whereas the levee deposits are low-contrast, low-resistivity thin-bedded sandstones and shales with high permeability. Such sandstones can be potentially very productive. The channels gradually become smaller and as their influence on directing the heads of turbidity currents decreases, oblong sheet sands are deposited, each having a very large width to thickness ratio and a high sand/shale ratio. The vertical stacking patterns within these sheet sands commonly display lateral offset of individual beds or groups of beds, and therefore form a distinct reservoir type with varying internal fluid-flow characteristics.

AAPG Search and Discovery Article #90955©1995 GCAGS 45th Annual Meeting and Gulf Section SEPM, Baton Rouge, Louisiana