10. SEDIMENTARY AND STRUCTURAL CHARACTERISTICS OF THE CRETACEOUS ALONG THE CÔTE D’IVOIRE-GHANA TRANSFORM MARGIN AND IN THE BENUE TROUGH: A COMPARISON1Jean Benkhelil,2 Jean Mascle,3 and Michel Guiraud4 |
The Côte d’Ivoire-Ghana Marginal Ridge (CIGMR) and the Benue Trough were formed during the Early Cretaceous under similar tectonic conditions and continental sedimentary environments. Early stages of sedimentary infilling are characterized by the deposition of subaerial, lacustrine, deltaic, and transitional marine sediments, successively, from the Late Jurassic to the Albian. Intracontinental transcurrent faulting, occurring in the Aptian–Albian, was superimposed on earlier rifting structures, resulting in pull-apart sub-basins. The extensional-transtensional tectonics caused unstable conditions during the sedimentation, resulting in syn-sedimentary deformations such as water-escape structures, listric normal faults, slumps, and intraformational conglomerates. From the Albian to the end of the Cretaceous, the two domains were under marine conditions, and there was deposition of shallow-water carbonates of fine terrigenous sediments. Compressional movements occurred in the late Albian–Cenomanian along the CIGMR and during the Santonian in the Lower Benue Trough resulting in intense deformations in both domains, with folding, cleavage, and shearing. Thermal events, partly related to the compressional phase, were recorded in the sediments of the two basins, including hydrothermal activity and low-grade metamorphic crystallizations. After the compressional event, the two basins have different evolutions; the CIGMR became a passive margin, with open marine sedimentation, while the Benue Trough was almost completely uplifted when a second compressional phase occurred in the Upper Benue Trough at the Cretaceous/Tertiary boundary. |
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