Tari, Gabor1, James Molnar1, David Valasek1
(1) Vanco Energy Company, Houston, TX
ABSTRACT: The Folded Belt of the Marginal Ridge, Deep-Water Cape Three Points, Ghana
The fossil marginal ridge of Cote d'Ivoire and Ghana (CIGMR) is a prominent structural and bathymetric feature on the transform margin of equatorial West Africa. Due to strong academic activity for a number of years, the marginal ridge along the Romanche Fracture Zone became the unofficial “locus typicus” for a transform margin setting.
Reprocessing of the academic seismic data and the acquisition/interpretation of 3,000+ kms of new seismic reflection data in the same area resulted in some new structural observations. Most importantly, the new seismic data clearly images a large landward-verging over-thrust system in the Cape Three Points segment of the CIGMR. The geometry of this “nappe” system is identical to those observed at the leading edge of classical folded belts. Other evidence for compressional deformation is provided by a series of inverted syn-rift half grabens and a small, but very well-developed “foredeep basin” due to the load of the incoming folded belt. Whereas these structures are undoubtedly the result of transpressional deformation along the transform margin, it is the dominating compressional component which is responsible for the presence of a number of plays identical to those found in folded belts.
New exploration plays identified include from south to north: a) subthrust closures and stratigraphic terminations; b) en échelon anticlinal crests; c) closures in inverted syn-rift grabens and d) stratigraphic pinchouts within the foreland basin. The landward verging nappe complex had to form during the Cenomanian when continental crust existed on both sides of the transform margin.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.