Examples of deep water salt tectonics from West Africa: are they analogs to the deep water salt-cored foldbelts of the northern Gulf of Mexico?

Tari, G. C., P. R. Ashton, K. L. Coterill, J. S. Molnar, M. C. Sorgenfrei, P.W.A. Thompson, D. W. Valasek, Vanco Energy Company, Houston, Texas; and J. R. Fox, Argonauta Energy Company, Houston, TX

Abstract

A critical exploration issue concerns the applicability of salt structure concepts developed in mature salt basins such as the Gulf of Mexico (GOM) to frontier salt basins of Africa. To conduct a comparative analysis, regional transects were constructed across the salt basins of Morocco, Senegal/Gambia, Equatorial Guinea, Gabon and Angola. These then are compared to published regional cross-sections from the GOM. In addition to the direct comparison of cross-sectional geometries, the map-view expression of salt tectonics were also analyzed in the GOM and Morocco versus Angola, representing basin types with synrift and post-rift salt sedimentation, respectively.

Regional scale similarities of the salt basins include the progressive complication of salt-related structures basinward, the change from an extensional domain in the shelf to a compressional domain in the slope and the presence of a toe-thrust front at the oceanward edge of the basins. Additional factors which influence the salt-deformational styles include the underlying basement structure, the original thickness and map-view distribution of salt, regional basinward tilt, and the proximity to major sediment entry points into the basin.

Regional scale differences are partly attributed to the relative stratigraphic position of the salt in relation to the rifting of the margin. The Triassic/Jurassic salt in Morocco and the Jurassic salt in the GOM are located in the synrift sequence as opposed to the Aptian salt of Gabon/Congo/Angola which was deposited in the post-rift succession. In synrift salt settings, updip extension may not be the ultimate driving force for the contractional salt deformation downdip due to the lack of a basin-wide detachment efficiently linking all the salt structures together. This difference appears to impact significantly the basin-wide distribution of salt-related structural traps.