Gravity-Induced Transfer Faults on the Lower Congo Basin Slope, Offshore Angola (West Africa): Implications for Deep-Marine Hydrocarbon Exploration on Passive Continental Margins

Dengliang Gao and Jeff Milliken
Marathon Oil Corporation, P.O. Box 3128, Houston, Texas 77056

Three-dimensional (3D) seismic structure imaging and mapping along with Bouguer satellite gravity and bathymetry indicate a series of intra-slope lineaments that extend over tens of kilometers across the regional, northwest-trending fold-and-thrust belt on the Lower Congo Basin slope, offshore Angola (West Africa). Geometric relationships and distribution patterns of folds and faults indicate that the cross-regional lineaments have a dominant strike-slip component that is kinematically linked to the contraction along the regional fold-and-thrust belt. Although the oceanic crustal fracture zones might have affected the paleo-topography and sediment thickness that could influence the orientation and location of the intra-slope lineaments in the sedimentary cover, we interpret that these cross-regional strike-slip faults were primarily induced by gravitational sliding as transfer faults to accommodate the differential downslope movement of the Tertiary slope-forming sediments. Allochthonous salt bodies aligned along the transfer faults suggest that the faults have spatially and temporally controlled the dynamic salt evacuation. Gas hydrate deposits and hydrocarbon discoveries along the transfer faults suggest that the faults are spatially and temporally linked to a dynamic hydrocarbon system. These findings and the resulting conceptual model proposed for the Lower Congo Basin slope could be used as an analog for the Gulf of Mexico and other basin slopes where regional gravitational sliding has played an important role in active salt evacuation and focused hydrocarbon accumulation. In particular, the structural play concept derived in this study might have a general applicability to delineating play fairways and assessing hydrocarbon potential in the Gulf of Mexico and other petroliferous sedimentary basins around the world.

AAPG Search and Discover Article #90069©2007 GCAGS 57th Annual Convention, Corpus Christi, Texas