Determination of depth to buried magnetic rocks under the lower Sokoto Basin, Nigeria, using aeromagnetic data.

Abstract

Statistical spectral analysis of the residual magnetic field values is employed in this research to determine the depth to the magnetic basement rocks under the lower Sokoto Basin. The area of study lies between longitude 4 to 5 E and latitude 1030\' to 1130\' N. For this analysis the study area is divided into 49 sections allowing spectral depth determination at every 15km by 15km interval of the field. The spectral analysis reveals two prominent magnetic layers. The first layer depth varies from 0.22km to 0.96km with an average value of 0.457km; while the second layer depth varies from 0.46km to 1.96km with an average value of 1.45km. The first magnetic layer is attributed to lateritic ironstone, ferruginous sandstone and effect of surrounding basement rocks while the second layer is attributed to magnetic rocks intruded onto the basement surface, lateral discontinuities in basement susceptibilities and interbasement features like faults and fractures. The second layer depth thus represents the depth to basement in the area and this depth has an average value of 1.44km. This represents the average thickness of the sedimentary formation overlying the Basement Complex within the lower flange of the Sokoto Basin. The generalized depth to basement map produced reveals that the basin is generally shallow with a maximum depth of 1.93km. This depth estimates reduces the possibility of hydrocarbon accumulation. The magnetic depth estimates and the surface plot of the second layer depth reveal an irregular basement floor resulting from gentle folding of the basement rock.

Keywords: Spectral depth, buried magnetic rocks and aeromagnetic data

Nigerian Journal of Physics Vol. 19 (2) 2007: pp. 275-284