Gabor C. Tari
Examples of Salt Tectonics from the West African Passive Margins: Exploration in a Major Emerging Petroleum Province
The application of salt structure concepts developed in specific salt basins of the world to salt basins along the West African margin must be used with caution. To conduct a comparative structural analysis, regional reflection seismic transects were constructed across the salt basins of Morocco, Senegal, Guinea Bissau, Equatorial Guinea, Gabon and Angola.
In the post-rift salt basins of Equatorial Guinea, Gabon and Angola updip extension is represented by a broad rafted domain. The extension is balanced by downdip contraction in form of salt tongues, sheets, canopies and the progressive inflation of a massive salt domain at the basinward edge of the salt basin, The efficiency of this gravity spreading across the whole margin is due to the more or less uniform original distribution of Aptian salt in the post-rift succession forining a continuous detachment level.
In contrast, the uneven original distribution of the Upper Triassic and Lower Jurassic syn-rift salt in Morocco, Senegal, and Guinea Bissau is due to the basement highs separating rift halfgrabens creating a different structural pattern. Individual salt structures such as tongues, sheets and canopies originated from isolated patches of the autochthonous salt. In the case of syn-rift salt, updip extension may not be the ultimate driving force for the contractional salt deformation downdip.
In addition to the direct comparison of cross-sectional geometries, the map-view expression of salt tectonics were compared in Morocco and Angola representing salt basin “prototypes” with syn-rift and post-rift salt sedimentation, respectively. Local salt geometries in relation to possible hydrocarbon trap types were also comparatively analyzed within these basins. The similarities and differences have important exploration implications.
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