The infill history of a salt withdrawal mini-basin in the contractional domain of the gravity-driven salt system on the Angolan passive margin has been reconstructed using a high resolution three-dimensional seismic data-set. Well-constrained biostratigraphy has allowed calculation of the growth rate of the basin-bounding structures. Within the interval of stratigraphy investigated, the depositional style of sediments preserved in the basin has changed in response to changes in the rate of growth of the coeval, adjacent salt structures.
During the early part of the basin history, sedimentation in the slope system was dominated by a series of erosional channel complex systems, which are 1-3 km wide and contain a preserved infill 100-200 m thick. The creation of sea floor topography by contemporaneous salt movement and the development of salt-cored anticlines caused the channels to be deflected, diverted, off-set, or incised deeply as they interacted with the developing slope topography.
Subsequent salt movement, and a concomitant increase in the growth rate of the basin-bounding anticlines, led to more elevated topography and the development of extensive slumping of sediment into the basin centers, forming large mass transport deposits. As salt movement continued, the basin became largely enclosed; bound by a well-developed salt wall to the west and a series of complex salt structures to the east, where salt-cored anticlines developed laterally into salt diapirs. These complex structures controlled the flow pathways of sediment both into and out of the basin. The growth rate of the structures constraining the western margin of the basin slowed at this time, and as a result, sediment transported from the east by feeder channels formed ponded fan systems comprised of sheets of sand each formed by multiple small channels.
Understanding the impact that active growth structures can have on sediment distribution and facies development is invaluable in the exploration and production of oil and gas. In this area, the association of the channels with the structure has formed reservoir-trap combinations for four major oil fields, Plutao, Saturno, Marte and Venus, being combined together as the PSVM development. In each field, the specific interaction of the channels with the growing topography has controlled the channel architecture and facies development; this has meant that different development plans, risks and uncertainties are required for each field.