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Abstract: Structural Styles and Basin Development Within the Submarine Gulf of Guinea Foldbelt : Deepwater Niger Deltaic Headland

Edward A. Duncan, Phil J. Townsend

Interpretation of regional seismic lines across the Niger deltaic headland from the present coastline to basin plain identifies an extensive belt of compressional structures. These structures are believed to be genetically tied to the extensional fault regime of the onshore and near offshore. The linked extensional and compressional structures grow throughout the development of the delta Large scale imbricate thrust stacks, isolated simple ramp anticlines and tip folds exist and play an important role in basin development at a local and regional level.

The thrust and foldbelt evolved as a completely submarine province generally, though not always, exhibiting a normal sequence of thrusting. Thrust top basins evolved from troughs between growing tip folds to fully cannibalised "piggybacks" as thrust propagation continued. Given the turbiditic nature of the main basin filling depositional systems, the structural evolution and basin shape are precisely recorded by seismic stratigraphic onlap patterns.

The interplay between an actively deforming depositional surface and prevailing deepwater depositional systems created a range of basin fill geometries. These vary from highly "ponded", onlapping turbidite and debris flow units, to concordant, concentrically folded, pelagic and hemipelagic drape. Local, significant unconformities develop but should not be confused with true sequence boundaries, just as interpreted condensed sections need not relate to transgression of the delta. The quality and volume of data over the Gulf of Guinea foldbelt provides a rare opportunity to study a range of complex structural and stratigraphic relationships generally not easily observed in mountainbelts.

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France