Susanne Sperrevik¹, Paul J. Valle¹, John G. Gjelberg²

(1) University of Bergen, Bergen, Norway
(2) Norsk Hydro, Bergen, Norway

ABSTRACT: The Use of 3D Structural Reconstruction in Studying the Interaction between Surface Topography and Deep Marine Channel Deposits in The Lower Congo Basin, Offshore Angola

We have performed a 3D structural restoration of the post rift sequence in The Lower Congo Basin, offshore Angola. The Lower Congo Basin is strongly influenced by salt tectonics, and both diapirs and growth faults affect the post-salt sequence. The salt movement mainly took place from the Late Eocene to the present, and was contemporary with the deposition of the reservoir sands, which are turbidite channel deposits. The 3D seismic reflection data in the study area are of extraordinary quality, allowing us to map channel systems in detail. The channels were mainly depositional, and we expect that both the location and the direction of the channels were dependent on the surface topography at the time of deposition.

Assumtions for reconstruction: 1) Thermal cooling related to post-rift subsidence was finished before the Eocene. 2) The deformation of the crust, by loading, can be modelled using Airy isostasy. 3) The salt diapirs mainly forms by downbuilding. 4) The salt acts as a detatchement zone, implying that salt related deformation only affects the salt itself and the sequence above the salt.

The restoration shows that both the palaeobathymetry and the regional seafloor dip were fairly constant during the studied time interval. By comparing the orientation and location of channels with the structurally restored seafloor topography, the method used in this study has proved to give geologically valid results. The restoration has been used for improving prediction of the distribution of reservoir sands, and as input for secondary migration modelling.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado