Tari, Gabor¹, Eva Moldovanyi¹, James Molnar¹, Gary Walters¹
(1) Vanco Energy Company, Houston, TX

ABSTRACT: An Exceptionally Large Detached Fault Block: San Pedro Ridge, Offshore Côte d’Ivoire, West Africa

Most of the structures drilled so far along the transform margin of Côte d’Ivoire, Ghana, Togo and Benin are either transpressional anticlines or basement involved normal fault blocks. A very notable exception is the large (~30x5 km strike and dip dimensions, respectively) San Pedro Ridge structure in western Côte d’Ivoire. Recently acquired 2D and 3D seismic data provided the basis for the structural analysis of this gravity-driven feature. As opposed to the mostly Albian syn-transform structures, the San Pedro structure formed during the Cenomanian. The continuing thickening of the sedimentary cover and repeated fault activity in the underlying basement resulted in a large-scale failure of this part of the margin sliding into the deep-water. To accommodate this gravity-driven movement, the updip extension was compensated by a compressional anticline downdip. The megaslide block is clearly detached above the crystalline basement. Cenomanian clastics were ponded behind the megaslide in the newly created accommodation space, in a narrow trough. There is no expression of the underlying structure on the modern seafloor. Despite the basinward tilt of the megaslide block since its formation due to the regional thermal subsidence of the margin, it has still very significant structural closure on its updip extensional segment. The San Pedro structure is considered as a gravity-driven and therefore very unusual feature for this segment of the West African margin with significant exploration implications.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.