Oligocene/Miocene Depositional System, Volta Fan Fold Belt, Ghana
K. A. Nibbelink, J. D. Huggard, 2002. "Oligocene/Miocene Depositional System, Volta Fan Fold Belt, Ghana", Sequence Stratigraphic Models for Exploration and Production: Evolving Methodology, Emerging Models and Application Histories, John M. Armentrout, Norman C. Rosen
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Inversion structures of the Volta Fan Fold Belt, Ghana developed during the Upper Cretaceous in response to right lateral strike slip movement along a restraining bend in the Romanche fault zone across the Keta Arch. The depositional architecture of the Oligocene to Miocene deep water sandstone reservoirs was controlled by topography created by the inversion structures and subsequent erosion during the Upper Oligocene, 30 my lowstand of sea level. Erosion at the 30 my sequence boundary cut 15 to 20 canyons across the shelf. These canyons were cut 200 to 500 meters deep, 1 to 2 km wide and provided a critical part of the sediment delivery system from the Volta River, across the shelf to the deep water.
Amplitude patterns from 3-D seismic define the deepwater sequences that systematically fill the topographic relief created by the Upper Cretaceous structural and Oligocene erosional events. Upper Oligocene to Lower Miocene sedimentation consists of 1) base of shelf fans at the mouth of the shelf canyons, 2) ponded fans behind the inversion structures, and 3) basin floor fans in front of these structures. Middle Miocene fan systems are deposited in a back stepping succession with the larger fans on the flanks of the Keta Arch. During the Upper Miocene, a major progradation of the shelf occurs and the deep water topography is filled, which allows fan sedimentation across the entire arch. These Oligocene to Miocene deep water sandstones as well as the deeper Upper Cretaceous sandstones should provide excellent reservoirs for the developing hydrocarbon system in the Volta Fan Fold Belt.