A Comparison of Upper Cretaceous Deepwater Depositional Systems in the Deep Ivorian Basin. Influences of a Rift Dominated Versus Shear Dominated Margin

Recent exploration offshore Ghana and Cote D’Ivoire has focused on Upper Cretaceous channel-levee complexes deposited on the mid to upper slope of the Deep Ivorian Basin. This has resulted in several major oil and gas discoveries such as Jubilee, Tweneboa, Enyenra, Odum, Akasa, Paradise and Dzata in reservoirs that range in age from U. Albian to Campanian.

The Deep Ivorian Basin stretches from Cape Three Points in western Ghana in the east to the Cote D’Ivoire-Liberia border in the west. It is situated between the St. Paul Fracture Zone to the northwest and the Romanche Fracture Zone to the southeast. The early opening history of the Atlantic along this margin was, to a large extent, controlled by the interplay of shear movement along these WSW-ENE trending transform faults and NW-SE trending rift related faults. The basin can, therefore, be divided in to a westerly shear dominated sector and an easterly rift dominated sector. Early rifting was also influenced by pre-existing Pan African lineaments resulting in a complex rift topography.

The easterly, rift dominated zone is underlain by attenuated continental crust whereas, in the west, the transition from continental to oceanic crust is much more abrupt. The earliest oceanic crust developed during mid to late Albian times and subsequent thermal subsidence created the sink for sediment entering the Deep Ivorian Basin from the north and northeast. Sediment transport distances from shelf to basin floor are significantly longer in the rift dominated sector compared to the shear dominated sector implying significant differences in paleoslope and the development of accommodation space.

The acquisition of large 3-D seismic surveys has demonstrated that the characteristics and morphology of the Upper Cretaceous deepwater deposystems varies along the margin and reflect, among other things, these differences in paleoslope, sediment transport distance and the influence of the underlying basin floor topography, as developed during the early rifting phase.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California