Abstract: Tectono-Stratigraphic Influences on Pre-salt Petroleum Systems of Rio Muni, Equatorial Guinea

Lawrence, Steve - Exploration Consulting Limited, UK

The development of the Rio Muni Basin is defined in 3 tectono-stratigraphic phases: "rift" (Neocomian-Aptian); "transitional" (Aptian-Cenomanian) and "post-rift" (Turonian-P.D.). A broad swathe of rifted (stretched) continental crust is recognized in southern Rio Muni as part of the North Gabon terrain containing the Eastern Sub-basin. Rift trends are normal to the recognized transform zones but oblique to the continental margin. By extrapolation rifting probably occurred in 3 main phases (Berriasian to Hauterivian, Hauterivian to late Barremian and late Barremian to late Aptian). Over most of the offshore margin structure is dominated by gravity-slide tectonics. We postulate that this tectonic activity took place in the Santonian-Coniacian in response to uplift resulting from transpressional reactivation of transform fault-zones. This corresponds with a tectonic phase recognized in large parts of West Africa e.g. Abakalaki foldbelt of Nigeria and basin inversion in North Gabon. The petroleum system of Rio Muni is centered around syn-rift lacustrine (extrapolated from North Gabon) and transitional shallow marine/lagoonal source rocks. In the absence of containing data (e.g. AFTA/VR), a complex thermal/burial history has been rationalized according to the tectono-stratigraphic scheme. Basin modeling shows possible maturity/expulsion/migration models for the petroleum system.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil