Integrated Geophysical and GIS-Remote Sensing Investigations For Geological and Groundwater Mapping in the North- Eastern part of Osun State,Nigeria.
Date
2017
Authors
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Journal ISSN
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Publisher
Obafemi Awolowo University
Abstract
This study mapped the surface and subsurface lineaments associated with the study area,determined their orientations, also determined the geoelectriclayers and their parameters, estimated the overburden thicknesses and evaluated the groundwater potential of the study area. This was with a view to characterize the geological complexities associated with groundwater distribution in the study area.
Geological map, Total Aeromagnetic Intensity (TMI) data and satellite imageries comprising Landsat 8 and Shuttle Radar Topography Mission of the study area, covering about 57 × 47 km2 (bounded by Longitudes 4o32’33” - 5o03’28” E and Latitudes 7o39’58” - 8o05’43” N), were acquired from the United States Geological Survey and Nigeria Geological Survey Agency. 1-D Vertical Electrical Sounding (VES) data using the Schlumberger array configurationwere acquired from various sources. The imageries were spatially filtered for extraction of surface lineaments and verified for their hydrogeological significance. The Total Magnetic Intensity (TMI) data was processed to accentuate anomalies of interest using reduction-to-equator and regional–residual anomaly separation filters. Thereafter, subsurface lineaments were extracted and their depths estimated.The VES data were interpreted quantitatively by partial curve matching technique and 1-D computer assisted forward modeling. The results were used to identify aquifers, determine geoelectric parameters, overburden thickness and electrical coefficient of anisotropy for each of the VES. The lineament density, lineament intersection density, lithology, slope, coefficient of anisotropy and bedrock elevation maps were integrated in ArcGIS to produce the groundwater potential map of the study area.
The aeromagnetic map revealed various relatively short and long wavelengths elongated anomalies diagnostic of relatively shallow and deep two-dimensional (2D) magnetic bodies respectively. The lineament orientation analysis showed that the study area is dissected by several surface and subsurface linear structures, among which the ENE-WSW, WNW-ESE, NNE-SSW, and NNW-SSE trends dominated. The depth of occurrence of the subsurface lineaments ranged from < 50 to 200 m. The lineament density map revealed five (5) lineament cluster zones in the range of 0.00 – 0.90, 0.90 – 2.00, 2.00 – 3.26, 3.26 – 4.45 and 4.45 – 5.68 / km2. Five (5) subsurface geologic layers which included the topsoil, lateritic layer, weathered layer, partly weathered / fractured basement (PWFB) and the fresh bedrock were identified. The weathered layer and PWFB constituted the aquifer units. The overburden thicknesses ranged from 0.40 to 129.00 m. Relatively low overburden thicknesses were observed at regions underlain mostly by porphyritic granite, granite gneiss and banded gneiss lithologies. Relatively high overburden thicknesses were observed at regions underlain mostly by undifferentiatedschist and quartz schist lithologies. The overburden coefficient of anisotropy ranged from 1.0 to 3.04. The synthesis of the lineament density, lineament intersection density, lithology, slope, coefficient of anisotropy and bedrock elevation maps in a GIS environment enabled the characterization of the study area into five different groundwater potential zones of very low, low, moderate, high and very high.
The study concluded that although low groundwater potential dominated the study area, there were zones with moderate and high groundwater potential
Description
xviii,146
Keywords
Geophysical, GIS-Remote sensing, Geological Mapping, Groundwater Mapping, North Eastern Part, Osun State, Nigeria