THE STRUCTURAL CHARACTERISTICS OF A TRANSFORM MARGINAL BASIN: TAKING THE BENIN BASIN OF WEST AFRICA AS AN EXAMPLE

The Benin Basin is a well-developed rift basin under drifting stage without salt rock deposition. With reference to the formation and evolution of the Atlantic, this study divided the tectonic evolutionary stages, defined the boundry of the rift basin and structural styles, and analyzed the structural characteristics of the Benin Basin. Under the constraints of stress pattern in the rifting stage of early Cretaceous, the basin was composed of the eastern extensional tectonic region and the west strike-slip tectonic region, that made the rift basin wide in east and narrow in west. The eastern extensional tectonic region has a well developed E-W fault system, consisting of listric normal faults, whereas the west strike-slip tectonic region a NE-SW strike-slip fault system, consisting of steep strike slip faults. By the joint control of the stress field in early Cretaceous, the tectonic inversion in late Cretaceous and the gravitational detachment in Cenozoic, the Benin Basin has well developed in the structural types caused by stretching, transtensional, compressional, and gravitational detachment. All the four types of structural types provide favorable conditions for the formation of various structural traps in the basin.