Crustal structure of the deepwater west Niger Delta passive margin from the interpretation of seismic reflection data

Abstract

The interpretation of 2D and 3D seismic reflection data complemented with gravity data allows the crustal architecture of the deepwater west Niger Delta passive margin to be defined. The data show 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. Some of the dipping reflections can be traced up to the top of the basement where they offset it across a series of minor to major thrust faults. Other internal reflections are attributed to extensional shear zones and possibly due to intrusions in the lower crust. The Moho can be correlated as a discrete reflection over >70% of the study area. It is generally smooth, but localised relief of up to 1 km is observed. The southeastern part of the study area is dominated by a zone of SW–NE striking basement thrusts. The crustal thickness in the study area is below the global average for a typical oceanic crust. Generally the crust is thinnest around a major transform structure, the Chain Fracture Zone, possibly related to the local geometry of the spreading fabrics. There is no significant variation in the thickness of the crust across this ocean–ocean transform in the area. The recognition of oceanic crust has profound implications for heat flow and thermal maturation of hydrocarbons in the Niger Delta petroleum province.