Abstract
Research activities close to the south western edge of the coastal line has shown inland extension of deep oceanic features identified as regional fault zones. This research work focused on mapping of inland extension of Chain Fault zones into the south-western part of Nigeria using both satellite images and aeromagnetic intensity map over a 55 km by 55 km Ifon Basement-Sedimentary area. The area is a transition zone between the south-western basement complex and sedimentary basin of the south-western Nigeria. Interpretations of magnetic field over the area revealed intra-sedimentary features identified as fault zone which form an alignment and inland extension pattern with the offshore Chain fault zone. On the account of the qualitative and quantitative interpretation of the acquired aeromagnetic data, the Landsat-ETM+ multi-spectral bands and Digital Elevation Model (DEM) of the topography of the area, the evidence of inter-sedimentary tectonic events are recorded in the geomorphic characteristics of the study area’s terrain in relation to the underlying influence of geology and structural trends revealed by extracted lineaments. From geophysical and geomorphologic interpretations, the observed geomorphic characteristics show three physiographical areas: the northern uplifted block (connection of a series of hills cut by deep-sided valleys), the central SW-NE trending subsided block (or graben) and the southern uplifted block. This geomorphic pattern of a series of flat and highly undulating terrain broken by a series of deep valleys and hills is believed to be related to rifting arising from the influence of the transform fault zones, which subdivide the area into smaller units. The rift valleys in the area are long, deep valleys bounded by parallel faults, or fractures. In addition, the predominant SW/NE, SE/NW and E-W trending linear structures mapped as fracture/faults cut the basement and penetrated the overlying Cretaceous and Tertiary sediments in the study area. Key word: Chain Fault zones, transform faults, rifting, inter-sedimentary tectonics, south-western Nigeria Embayment.
Highlights
Detailed analyses of the aeromagnetic total intensity field and Landsat-enhanced thematic (ETM)+ multi-spectral satellite images over Ifon Basement-Sedimentary area of the transition zone of the south-western Nigeria Embayment were carried out in order to study the morphology and structural geologic features underlying the area and possible link with the deep ocean transform fault zones
The geophysical investigation was complemented by photo-lineament interpretation using topographic and geologic maps, satellite imagery and Digital Elevation Model of the study area
The transform fracture zone is responsible for the strike-slip deformations resulting into the graben-horst patterns which influence deposition of sediments from major rivers draining the area from the north to the southern basin margins
Summary
Detailed analyses of the aeromagnetic total intensity field and Landsat-ETM+ multi-spectral satellite images over Ifon Basement-Sedimentary area of the transition zone of the south-western Nigeria Embayment were carried out in order to study the morphology and structural geologic features underlying the area and possible link with the deep ocean transform fault zones. Evidence about the intra-sedimentary features relationship with the influence of basin margin is yet to be fully established. In this paper both spectra and Euler Deconvolution were used to analyze total magnetic field data of acquired by the Geological Survey of Nigeria through the airborne survey carried out in 1965 and complied and compiled by Earth Science Limited in 1975.
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