Submarine channels controlled by salt tectonics: Examples from 3D seismic data offshore Angola

The interaction between salt tectonics and sedimentation, offshore Angola has created a complex slope geometry of submarine channels, intra-slope basins and diapiric salt structures. There are a wide range of slope channel styles in close stratigraphic and geographic proximity, although the controls on these changes are not fully understood. Channels often follow complicated routes downslope, and have developed highly variable channel geometries, with narrow, erosional confined systems, and aggradational, broader systems as end members. Many channels are organised into stacked channel complexes. Rapid transitions in channel geometry are observed where channel systems pass through constrictions in salt wall structures or encounter decreases in slope gradients, for example within intra-slope depressions. Decreases in gradient and the exit points of incised channels mark the transition from narrow, well-defined linear or sinuous channels to broad, weakly confined channels. Important seismic facies changes are also observed where channels approach salt structures that created positive features on the seafloor. Results presented here show that linear, high gradient channels exhibit distinctive geometry changes around salt structures, often forming discreet depositional forms in planview. Lateral changes in sedimentary architecture within depositional lows record salt movement, as facies migrate relative to growing salt structures.