Effects of pre-salt structures onpost-salt structural development investigated by analogue sand box experiments

Abstract

The Angola margin displays a broad range of salt-related structures such as, normalfaults, rollovers, salt diapirs, folds and reverse faults, developed by gravity sliding which is the major mode of deformation of post-salt sediments. Laboratory experimentson brittle-ductile models are used to study deformation above the salt and further compare the structures with those seen on seismic data from the Kwanza basin. Four experiments were carried out using sand and silicone putty to represent sediments and salt, respectively. The silicone layer was given a double wedged shape to simulate more precisely the initial geometry of the Aptian salt basin in the Angolan margin. Different barriers, both in their position and orientation in the model, were used to investigate the effects and impacts on sediment deformation. The results show three main domains: anextensional domain in the upslope area, where the arrangement of extensional structuresis believed to be directly resulting from variations in mechanical coupling between sediments and salt layers, developing growth faults and rollovers; a diapir domain in the transition, developing extensional diapirs and at later stage squeezed diapirs; and a compressional domain in the downslope area, where the contraction is accommodated by the upslope extension, developing folds and reverse faults, and at the late stage compressional diapirs. It is also noticed that when the basement barrier is located between the sealed tilted blocks and the diapir area, the model shows more diapirs andless extension in the upslope area than when the basement barrier is in the central area.