Submarine Channel Geometry and Salt Tectonics Revealed by 3-D Seismic and Visualization, Offshore West Africa

Martin Gee and Rob Gawthorpe
University of Manchester, Manchester, United Kingdom

Deep water turbidite channels are an important element of many continental margins and can form significant hydrocarbon reservoirs. Where continental margins are affected by salt tectonics, channels display a wide range of geometries, often changing significantly over a few kilometres within a single system. However, the controls on these changes are not fully understood. On the Angola margin, interaction between salt tectonics and sedimentation has created a complex slope topography of intra-slope basins and diapiric salt structures. Channels often follow complicated routes through this topography, and may develop highly variable channel sequences with narrow, erosional confined systems, or aggradational, broader systems as end members. Important transitions in channel geometry are observed where channel systems pass through constrictions in salt wall structures or within intra-slope basins where slope gradients decrease. Decreases in gradient and the exit points of incised channel valleys mark the transition from narrow, well-defined linear or sinuous to broad, weakly confined channels. These transitions are observed where channels approach depositional lows surrounding upstanding salt structures, and are associated with important facies changes. Results indicate that linear, high gradient channels exhibit significant geometry changes around salt structures. Sedimentary bodies often deposit within depositional lows as discreet J or S-shaped structures in planview. Lateral variations in sedimentary architecture within depositional lows records salt movement, as facies migrate relative to salt structures. Results improve our ability to predict subsurface channel geometries and recognise key evolutionary trends.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005