--> ABSTRACT: Geophysical Basin Structure of the Cotonou (Dahomey/Benin) Basin, West African Gulf of Guinea, by Olufemi O. Babalola; #91003 (1990).

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ABSTRACT: Geophysical Basin Structure of the Cotonou (Dahomey/Benin) Basin, West African Gulf of Guinea

Olufemi O. Babalola

The frontier Cotonou basin (or Dahomey/Benin embayment), situated west of the prolific Niger Delta basin, appears from seismic, gravity, and aeromagnetic interpretation, as a series of grabens and troughs confined on the west and east by the Romanche and the Chain fracture zones, respectively. The Keta trough of the western basin rim was formed by a 2700-m southeasterly downthrow of the Adina fault. This trough is separated by a north-northeasterly fault from the Lome-Anecho gravity high. Eastward, the arcuate Allada-Adjohon trough is abutted on its southern flank by the northwest-trending Nokue-Afowo trough and separated from the northwesterly Ikorodu trough by the 50-km-wide, aeromagnetically inferred Ilaro-Otta ridge. The Ikorodu trough is adjoined on the northwest by he Aiyetoro trough and on the southeast by the Yemoja offshore graben trending east-northeast as the Seme oil-field structural trend.

North of the regional northeasterly axial, gravity positive, structural divide (the continental precursor of the Charcot fracture zone), a series of half-grabens (notably the Aplahoue, Bohicon, and Ketou troughs), normal faulted eastward and downthrown in the west, dominate the landward western rim of the Cotonou basin. Graben-bounding faults control the upper valleys of the basin drainage, converge toward the regional intrabasin structural trend and continue into the Fenyi-Yakoe fault and the Charcot fracture zone. These faults resulted from brittle dextral shear of continental crust oblique to local, preexisting north-northeast structural trends. In the eastern basin rim, preexisting north-northwest structural trends influenced the shearing stress regime to generate small, shallow, tructurally bounded, east-northeast- and north-northwest-trending grabens.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990