STRUCTURAL CHARACTERIZATION OF THE NIGERIAN SECTOR OF THE DAHOMEY BASIN USING GEOPOTENTIAL FIELD ATTRIBUTES

Abstract

The structural dispositions of the Nigerian sector of the Dahomey Basin have been investigated using attributes of geomagnetic and gravimetric fields. Aeromagnetic anomalies were reduced to the equator to improve the correspondence of the anomalies with the causative bodies. The residual, upward continued, Analytic signal, tilt and horizontal derivatives, and pseudogravity transformation of geopotential attributes and forward models of both geomagnetic and gravimetric anomalies were computed to accentuate geological features including regional faults and fracture network, basement block pattern and depth to magnetic basement. The results show that the basement of the Dahomey Basin ranges from continental to oceanic crust. Some shallow and deep structural lineaments show significant degree of correlation suggesting that some deep lineaments propagate to the surface. Sinistral and dextral faults were mapped. The dominant trends of structures are the NE-SW, NW-SE, N-S and E-W trends. Basement architecture is essentially of horst and grab en architecture with Lagos and Badagry grabens-which straddle the coastline- showing high petroleum prospectivity in that they host significantly thick sediments. Two NE-SW deep seated regional fracture zones extending from the Atlantic Ocean demarcate the western and eastern boundary of the basin. Possible release of stress along these regional fractures may trigger trembling in the subsurface. The implication is that this region may not be totally immune to earthquakes. The geometry of the coastline; Lekki and Lagos Lagoons were suspected to have been influenced by reactivation of Pan African weak zones. Major surface features are deduced to be structurally controlled. Maximum depth to magnetic basement in parts of the grab en is interpreted to be 6387 m. This study has shown the capabilities of geopotential filed attributes in imaging the structural plumbing of sedimentary basins. This knowledge will aid the understanding of the geology of the basin and its resources.