Ground Magnetic and Electrical Resistivity Mapping for Basement Structurs over Charnokitic Terrain in Ado-Ekiti Area, Southwestern Nigeria

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Author(s) Okwoli E. | Onoja, O.S. | Udoeyop, U.E.
Pages 683-689
Volume 3
Issue 10
Date October, 2014
Keywords Profiles, geomagnetic section, magnetic intensity, geoelectric section
Abstract

A combined Magnetic and Vertical Electrical Sounding (VES) geophysical methods was carried out in parts of Ado-Ekiti in order to map the area for basement structures. The survey was designed to determine the overburden thickness, the relief and structural disposition of the bedrock within the study area. A total of fifteen traverses were established in the study area, and probed by the magnetic method using the GSM 8 Proton Precession Magnetometer (PPM) with station intervals of 10m. Also, six (6) VES data were obtained using Ohmega resistivity meter. The Schlumberger array was employed. The magnetic and VES data were qualitatively and quantitatively interpreted. The geomagnetic sections reveal an overburden thickness ranging from 5 m to 30 m. Also varying geologic (basement) structures (relief/configuration) such as ridges, depressions (some of which were interpreted as basement structural zones) were also identified. From the geoelectric section, four geologic layers were delineated, these are; the topsoil, the lateritic clay layer, the weathered basement and the fresh basement. The resistivity value in this area showed that the layers are dominated by clay materials with a little proportion of laterite. It could be deduced from the study (magnetics and electrical resistivity) that the basement is very close to the surface (usually less than 15 m overburden thickness), except in some areas on the magnetic sections and VES 3 with an overburden thickness of about 16 m, this VES point may be a structural zone and good for groundwater development.

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