Structure and sediment thickness mapping of eastern dahomey (Benin) basin, southwest Nigeria.
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Date
2022
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Department of Geology, Faculty of Science. Obafemi Awolowo University.
Abstract
This study acquired, processed and interpreted satellite gravity and aeromagnetic data over the Eastern Dahomey Basin, Southwest Nigeria, for lineaments and sediment thicknesses and validated the results with existing well information and results. This was with a view to providing information on the basin’s structural setting, geometry and geotectonics required for the development of its natural resources. Free-air and Bouguer anomaly data of the study area were downloaded from International Centre for Global Earth Models website. High resolution airborne magnetic data covering nineteen magnetic sheets were acquired from the Nigerian Geological Survey Agency, Abuja. The Bouguer anomaly data were separated into Regional Bouguer Anomaly (RGBA) and Residual Bouguer Anomaly (RSBA) data by upward continuation. The Total Magnetic Intensity (TMI) map was corrected for diurnal variation and offset and Reduced to the Equator (RTE). The RTE map was separated into Regional Magnetic Anomaly (RGMA) and Residual Magnetic Anomaly (RSMA) maps. Both the RSBA and RSMA maps were subjected to Total Horizontal Derivative, Analytical Signal and Euler Deconvolution filters and interpreted for lineaments. Sediment thicknesses were generated from Spectral Analysis of RSBA and RSMA data, constrained by existing well data. The gravity and magnetic lineaments and sediment thicknesses were integrated into composite lineament and sediment thickness maps. The composite maps were used to assess prospects for hydrocarbon, geothermal and groundwater resource development within the basin.
Fifty deep seated (1,000-6,500 m) steeply to gently dipping lineaments (suspected to be faults) with lengths varying from 9,400 – 111,500 m and primary orientations in the NS, NE-SW, NW-SE directions with subsidiary E-W direction, were delineated. Composed sediment thicknesses ranged from 20-9,000 m with thicknesses of 20-300 m in the northern flank (Zone A); 500-3,100 m in the central region (Zone B) and 2,500-9,000 m in the southern flank (Zone C). Sediment thickness variations delineated series of basement structures including the earlier mapped Afowo Graben, Ojo Platform, Orimedu Graben, a newly identified horst structure, the Ise Graben and the Okitipupa Ridge, in that order, with onshore and lateral extensions and sediment thicknesses respectively of 20,000-25,000, 48,000 and 3,500-6,600 m; 8,700-11,600, 30,800 and 3,100-5,000 m; 8,800-11,200, 37,500 and 3,800-7,200 m; 3,800-6,700, 28,000 and 2,000-3,500 m; 6,300-12,100, 42,100 and 4,200-7,400 m; 35,900, over 44,500-57,000 and 1,100-3,100 m. The Ondo Basin (western flank of Niger Delta Basin and eastern flank of Zone C) had sediment thicknesses of between 3,500-9,000 m. The identified structures (graben, horst and ridge) had their edges defined by E-W and N-S bounding lineaments with some cross cutting the structures including several delineated subbasins and basement depressions, typical of a rift-like basin. Sediment thicknesses are well over the threshold of 4000 m for crude oil prospection in the southern flank (ZoneC) and over the threshold of 1,500 m for geothermal prospection in parts of the central region (Zone B) and the southern flank (Zone C) with large storativity and transmissivity for hydrocarbon, geothermal water and groundwater.
The study concluded that the Eastern Dahomey Basin has the requisite structural setting and sediment thicknesses for prospective hydrocarbon, geothermal and groundwater development.
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xxii,255p.
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Citation
OKUNUBI, M.O.. (2022)Structure and sediment thickness mapping of eastern dahomey (benin) basin, southwest Nigeria. Department of Geology, Faculty of Science. Obafemi Awolowo University.