Structural features of Nigeria's coastal margin: an assessment based on age data from wells

Abstract

Geological age data from 127 wells drilled for petroleum exploration and production purposes in both the onshore and offshore sections of the Nigerian coastal margin have been examined and correlated from well to well across the margin. By examining the variations in depth to selected key geological marker horizons, the positions of faults and fractures have been inferred between wells and along designated cross-sections. These faults extend across the margin from land to sea, and most of them trend northeast-southwest and north-south. Graben and horst structures dominate the western part of the Nigerian margin. The most prominent of these features on the western part of the margin is the Okitipupa structure, a basement ridge that separates the sediments of the Tertiary Niger Delta to the east from those of the Cretaceous Dahomey Embayment to the west. The Niger Delta basin and the major faults bounding it are the other important tectonic features on the Nigerian coastal margin. It appears that major fractures and transcurrent faults influenced sedimentation rates in different parts of the margin throughout the Tertiary period. A landward prolongation of two main oceanic fracture zones (Chain and Charcot) appears to merge well with some of the inferred faults, especially in the case of the Chain Fracture Zone. It is a well known fact that seismic activities are associated with oceanic fracture zones. The delineation of the extensions of these faults and fractures in the Nigerian continental interior can be regarded as an important basic step towards the assessment of the seismicity of the country's coastal margin. The next logical step would be to determine, through the deployment of a seismograph network, the level of activities associated with these faults.