Analytic Signal and Spectral Centroid Methods for Interpretation of Magnetic Anomalies: Applicability to the entire Sokoto Basin, Nigeria
Shehu,A. T.1, Nwankwo, L. I.2 and Salako, K. A.3
1Physics Unit, Centre for Preliminary and Extra-Mural Studies, Federal University of Technology Minna, Niger State, Nigeria
2Department of Physics, University of Ilorin, Kwara State, Nigeria
3Department of Physics, Federal University of Technology, Minna, Niger State, Nigeria
E-mail: atshehu2006@gmail.com, linwankwo@unilorin.edu.ng, kasalako2012@gmail.com
ABSTRACT
Sokoto Basin in northwestern Nigeria is bounded by latitudes 10.00oN and14.00oN and longitudes 3.50 oN and 7.00 oE and has a total surface area of about 111,925 km2. This study is in line with the Federal Government of Nigeria’s effort on hydrocarbon exploration in inland basins beyond Niger Delta region of Nigeria for a sustainable economic development in Nigeria. The digital residual data acquired from NGSA covered the entire Sokoto Basin was divided into twenty two (22) overlapping blocks and each block analyzed using spectral (Fourier) centroid method to obtain Regional estimation of depths to top of anomalous magnetic bodies. These depths indicate clearly the magnitude of variations in depth of both the basement topography and other intrusive in the area, these depths information were subsequently used to generate the contour and the 3D map of the area.An analytic signal method was then used to generate a map on which the amplitude of displayed function is directly and simply related to a physical property of the subsurface rocks. The depths to top of magnetic sources in the study area regarded as sedimentary thickness was found to range between 0.59 and 2.11 km with an average of 1.22 km. The 2D analytic signal map of the study area revealed occurrence of faults and magnetic minerals, mostly trending in the north-west direction and being dominant in the area in terms of distribution due to broader central African rift system. Those anomalies whose amplitude varies between 0.043 and 0.130 m and(pink and red) are observed to be well distributed in the study area. Another major observed anomalies ranging between 0.0018 and 0.0042 m (blue colour) are observed in the southeastern parts of the area. Observed at the north central, and northwestern part of the area are amplitude ranging between 0.0113 and 0.0173 m (yellow colour) correspond to areas with thick sedimentary cover while Blue and pink areas correspond to areas with thin sedimentary cover. However, the minimum thickness of sediment required for hydrocarbon generation is 2.3 km if other conditions are favorable. Therefore, hydrocarbon exploration may not be feasible in the basin, the area is therefore recommended for detail mineral and geothermal investigation.
Keywords: Residual anomaly, Spectral centroid, Analytic signal, Sedimentary thickness, and Basement topography
