Abstract
Ijebu-Ode and its environs in southwestern Nigeria is located on a geological transition zone from the Precambrian migmatite gneiss rocks and Cretaceous sedimentary rock units of Abeokuta Group. Unique geological structures, complex coexistence of different rock types and poorly defined basal/lateral contacts between the basement and sedimentary rocks typify tectonic events that accompany crustal thinning and downwarping at the basement/sedimentary-basin edge. This posed serious geological decision challenges especially since it is difficult to characterize the area either as sedimentary or crystalline. Aeromagnetic data were collected, the data were filtered, inverted and enhanced using appropriate software packages and subsequently employed to generate model of the subsurface basement topography.
The magnetic intensity distribution in the field ranged from −120 to +80 nT and was found to depend on the size, depth of burial and the thickness of low susceptibility superficial material overlying the magnetite rich crystalline rocks. High magnetic intensity characterized the basement rocks while lower values distinguished the metasediments rocks and sedimentary terrain. The average radial power analysis delineated shallow and relatively deep sources as the two distinct types of magnetic anomalies. Euler deconvolution results referenced to the Minna, Nigeria datum indicate depth range from −80 to +30 m for sources located below and above the mean ground level, respectively. Euler result also revealed that the depth to magnetic sources is heterogeneous and highly erratic around the transition zone, ranging between −25 and +12 m.
This study identified rugged and undulating basement topography around the contact zone; it also delineated the lateral and basal contacts between the two coexisting rock types. Aeromagnetic mapping of basement sedimentary transition zone around Ijebu-Ode has proved very efficient in providing relevant information about the nature of the basement topography which provided vital information requisite for drilling and some engineering constructions decisions.
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Osinowo, O.O., Olayinka, A.I. Aeromagnetic mapping of basement topography around the Ijebu-Ode geological transition zone, Southwestern Nigeria. Acta Geod Geophys 48, 451–470 (2013). https://doi.org/10.1007/s40328-013-0032-6
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DOI: https://doi.org/10.1007/s40328-013-0032-6