Tectono-stratigraphic evolution and architecture of the Miocene Rio del Rey basin (Cameroon margin, Gulf of Guinea)
The Rio Del Rey basin located in the Gulf of Guinea is one of the two basins lining the Cameroonian coast. It evolved since the Cenozoic in a tectono-magmatic and seismic complex setting. During the Miocene, this evolution was controlled by tectonics, relative sea level changes, basin filling and mantle dynamics. Two deposit megasequences of second order, MS1 and MS2, were pointed out. MS1 (lower Miocene), aggradational and corresponding to the Isongo turbidites deposited during a period of relative sea level drop registered two sequences of third order differentiated by the degree of channel incision: S1a (Aquitanian–Burdigalian), hardly incised and S1b (Serravallian), moderately incised. A double extension along N–S (Burdigalian) and NE–SW (Serravallian) directions responsible for a set of horsts and grabens, high subsidence and depocentres trending NW–SE affected these sequences. MS2 (middle to upper Miocene), progradational and corresponding to deltaic alternations deposited during a period of creation of available space were controlled by the tilting, wrenching, a second stretching phase and low sedimentary filling. MS2 recorded three cycles of 3rd order: S2a (lower Tortonian), S2b (upper Tortonian) and S2c (Messinian) differentiated by their morphology in ramp for S2a and S2b and slope for S2c. The formation of grabens and horsts and the tilting of the margin coincide with the high activity of the Cameroon volcanic line interpreted as a result of deep mantle dynamics affecting the inner Congo craton lithosphere. This architecture, which differs from those of the other basins of the Gulf of Guinea, partly explains the low oil production of this basin.