Salt tectonics on the Angolan margin, synsedimentary deformation processes

Seismic data from the Angolan margin and laboratory experiments on brittle-ductile models are used to study thin-skinned deformation above the salt at margin scale, which is characterized by extension upslope and contraction downslope. The initial geometry of the salt basin was wedging out, both landward and seaward, and the salt was entirely covered by sediments at the onset of gravity-driven deformation. Downslope contraction is accommodated by upslope extension. The upslope extensional domain is subdivided into three subdomains with (1) sealed tilted blocks, (2) growth fault and rollover systems, and (3) extensional diapirs. We interpret this particular arrangement of extensional structures as directly resulting from variations in mechanical coupling between brittle (sediments) and ductile (salt) layers. The downslope contractional domain is subdivided into three subdomains with (1) diapirs squeezed at late stage, (2) polyharmonic folds and thrust faults developed at early stage, and (3) folds and thrusts developed at late stage. This structural zoning results from the initiation of contraction at a distance from the salt toe and further migration of contraction immediately downslope and upslope.