Estimating the Thickness of Sedimentation within Lower Benue Basin and Upper Anambra Basin, Nigeria, Using Both Spectral Depth Determination and Source Parameter Imaging

The Total Aeromagnetic Data covering the study area was subjected to First Vertical Derivative, Spectral Depth Analysis, and Source Parameter Imaging (SPI). The result from the First Vertical Derivative shows that the Northern part of the area is covered by the young biotite granite of Precambrian origin, and the western edge is covered by the old granite, gneisses, and migmatite of Western Nigeria, while the remaining area is covered by the cretaceous sedimentary deposits. The entire area was divided into forty-eight sections. Spectral Depth Analysis was run for each of these forty-eight sections; the result shows that a maximum depth above 7？km was obtained within the cretaceous sediments of Idah, Ankpa, and below Udegi at the middle of the study area. Minimum depth estimates between 188.0 and 452 meters were observed around the basement regions. Results from Source Parameter Imaging show a minimum depth of 76.983 meters and a maximum thickness of sedimentation of 9.847？km, which also occur within Idah, Ankpa, and Udegi axis. The disparity observed in depth obtained by each method is discussed based on the merit and demerit of each method, and the depths obtained were compared with results from previous researchers. Geophysical implication of the result to oil and gas exploration in the area is briefly discussed. 1. Introduction Of all the magnetic minerals that occur in nature, magnetite is the most abundant. Aeromagnetic surveys reflect almost exclusively the distribution of magnetite and pyrrhotite in rocks. On a global basis, the others can probably be ignored [1, 2]. Thus aeromagnetic surveys, in particular terms, map the magnetite in the rocks below the aircraft. While aeromagnetic surveys are extensively used as reconnaissance tools, there has been an increasing recognition of their value for evaluating prospective areas by virtue of the unique information they provide. Outline of the roles of aeromagnetic survey is as follows [3].(i)Delineation of volcano-sedimentary belts under sand or other recent cover, or in strongly metamorphosed terrains when recent lithologies are otherwise unrecognizable. (ii)Recognition and interpretation of faulting, shearing, and fracturing not only as potential hosts for a variety of minerals, but also an indirect guide to epigenetic, stress related mineralization in the surrounding rocks. (iii)Identification and delineation of post-tectonic intrusive. Typical of such targets are zoned syenite or carbonatite complexes, kinerlites, tin-bearing granites, and mafic intrusions. (iv)Direct detection of deposits of