Tectono-stratigraphic evolution of the offshore western Niger Delta from the Cretaceous to present: Implications of delta dynamics and paleo-topography on gravity-driven deformation

The interaction between sedimentary wedge dynamics and paleo-fracture zones is investigated offshore western Niger Delta lobe (WNDL) to reconstruct the evolution of the delta from the Cretaceous to present. This was achieved through detailed regional seismic interpretation, calibrated with well data. Our results suggest that high sedimentation rates in the WNDL since the Serravallian-Tortonian triggered the migration of the 'Oligocene-Tortonian extensional zone' and gravity spreading seawards (from a present-day onshore to a present-day offshore position), with extensional, translational and contractional deformation. An additional increase in sedimentation rate since the early Pliocene, further accelerated gravity spreading and the development of the present-day contractional front. A five-stage tectono-stratigraphic evolution of the offshore WNDL from the late Cretaceous to present is proposed. Paleo-topographies formed by the Charcot and Chain Fracture Zones exerted depositional control on the stratigraphic architecture of the offshore WNDL from the Cretaceous to Serravallian. Differential subsidence on both sides of the relict Charcot and Chain transform faults is responsible for the segmentation of gravity-driven deformation of the eastern and western Niger Delta lobes. In addition, a comparison of the stratigraphic architecture of the eastern Niger Delta lobe (ENDL) and WNDL demonstrates a similar overall progradation and sediment bypass to the deep basin during the Pliocene. During the Pleistocene, the two lobes show a distinct evolution and architecture: the ENDL shows an overall retrogradation and sediment sequestration on the shelf, whereas the WNDL displays an overall progradation and sediment bypass. This study documents long-term and large-scale control of delta dynamics and paleo-topography on gravity-driven deformation of the offshore eastern and western Niger Delta lobes, and similar analysis could be applied in the reconstruction of other passive margin basins.