SPECTRAL DEPTH ESTIMATION AND UPWARD CONTINUATION ANALYSIS OF PARTS OF BORNO BASIN, NIGERIA USING AEROMAGNETIC DATA

Abstract

In this study, spectral depth and upward continuation analysis of the residual magnetic field values covering parts of Borno Basin have been used to study the subsurface structure in parts of Borno Basin with a view to determining the hydrocarbon of the area. The study area extends from the latitude 12o 00’ to 13o 50’ North and longitude 12o 00’ to 13o 50’ East and is covered by eight (8) aeromagnetic maps. The maps were digitized on a 19 by 19 grid layout and recorded on coding sheets which were merged to generate a composite dataset and of which a composite map of the area was produced. The Polynomial method of filtering was applied to obtain a regional-residual separation. The filtered residual map was Fourier transformed after dividing the whole area into sixteen (16) overlapping blocks. The resultant logarithm of spectral energy and frequency were plotted graphically and the depths to the magnetic source were estimated. The first layer depth varies in thickness from 0.18 km minimum to 0.37 km maximum. The second layer (h2) depth varies from a thickness of 1.79 km minimum to 5.34 km maximum. 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 inter-basement features like faults and fractures. The second layer thus represents the depth to basement in the area and this depth has a maximum thickness of 5.34 km. The second layer (h2) depth contour map and 10 km upward continuation map of the total magnetic intensity of the study area show that the northeast between latitude