Slope Tectonic Influences on Submarine Channel Location, Geometry and Evolution: Examples from the Shallow Sub-Seafloor, Offshore Angola

Emmanuel Eseroghene Adiotomre, Martin Gee, Rob Gawthorpe, and Duncan Irving
University of Manchester, Manchester, United Kingdom

Case studies from 3D seismic surveys from the Angolan margin, West Africa allow the seafloor and shallow subsurface structure of the slope, and the response of channel systems to slope deformation to be determined. In the study area, slope topography is dominated by NW-SE-trending growth faults and salt-cored folds at a high angle to the regional dip of the slope. Growth faults evolve by lateral propagation and linkage of segments to form major fault zones, c. 50 km long, that give the shallow section a tilted fault-block topography. Salt-cored folds have similar along-strike dimensions to the linked fault zones and are flanked by growth synclines. Evolution of both folds and faults significantly changes the dip and dip direction of the seafloor which strongly controls channel location and development. Important transitions in channel geometry are observed where channel systems approach or pass through constrictions in salt walls, 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 channels to broad, weakly confined channels and sheet complexes. Single channels commonly divert around growing topographic highs leading to discreet J- or S-shaped planforms. Alternatively, where multiple channels become focused in a particular area of the slope they commonly follow the regional slope gradient and incise through the local growth fold and/or fault.

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