Structural evolution of the deepwater West Niger Delta passive margin

A detailed investigation of the structural evolution of the deepwater west Niger Delta was undertaken from the combination of industry 2D and 3D seismic reflection datasets. The study has been focused on three themes: crustal architecture, thrusting in oceanic crust and the role of multiple detachments in developing the structural style in the area. Detailed analysis and mapping of the basement structures, crustal thickness and distribution, identification and analysis of thrust-fault pattern and its relationships to detachment levels have provided a completely new understanding of the structural evolution of the deepwater west Niger Delta. The study shows that the area is underlain by oceanic crust that is characterised by a thickness of 5-7 km and by internal reflectivity consisting of both dipping and sub-horizontal reflectors. Inclined reflections can be traced up to the top of the crust where they offset it across a series of minor to major SW-NE striking basement thrusts in the SE of the study. The crust is thinnest around a major transform structure, the Chain Fracture Zone possibly related to the local geometry of the spreading fabrics with no significant variation the crustal thickness across the transform zone. Detachments are located within the 'Dahomey unit', and the transition between the Agbada and Akata Formations (Top Akata). Quantitative measurements of fault displacements show that the utilisation of different detachments results in contrasting styles of thrust propagation and fold growth. Two geographical zones are defined. In zone A, (NW sector of the study area), the stratigraphically shallowest Dahomey detachment is dominant and is associated with thrust truncated folds while in zone B, (SE sector of the study area) a stratigraphically lower detachment approximately at the Agbada-Akata Formation boundary is associated with thrust propagation folds