International Journal of Science and Research (IJSR) ISSN: 2319-7064 ResearchGate Impact Factor (2018): 0.28 | SJIF (2018): 7.426 Volume 8 Issue 6, June 2019 www.ijsr.net Licensed Under Creative Commons Attribution CC BY Evaluation of Lateritic Soil from Field Resistivity Data at Okada, South-South, Nigeria Arekumo Thank God 1 , Lawrence O. Oghale 2 1, 2 Department of Physics Federal University Otuoke, Bayesa State, Nigeria Abstract: The electrical properties of laterites was a useful tool for electrical resistivity investigations to evaluate depth and area extent of laterite top soil in Okada South-South, Nigeria. On the field electrical resistivity tomography survey was conducted along four profile using Schlumberger –Wenner configuration. Acquired resistivity data were interpreted based on least square method, the resultant apparent resistivity sections were interpreted with constrain from known lithostratigraphy of the area to infer the true resistivity variation of the different litho units. The litho log from a section of a road cut outcrop on which line 1 electrical survey was done, serves as a reference for correlation between apparent resistive values and actual lithology. A tie of laterite to apparent resistivity for the study area shows a resistivity values of 600 -1000 Ωm are laterites, 300 – 600 Ωm lateritic soil with varying degree of laterization, while 100 Ωm and bellow are clay related, these references agrees with standard references for these lithologies. The electrical resistivity tomography method was effective in delineating clay units from lateritic areas. In terms of exploration, Line 1 and 2 showed extensive concentration of laterite which toward line 2 and 3 decreased with increased patch occurrence of clays. Keywords: Laterite, Electrical Resistivity Tomography, Okada 1. Introduction Rusty-red iron oxides soils commonly called laterites, are soils developed near the earth's surface by intensive weathering of the underlying parent materials. The mechanism of weathering (laterization) involves a prolonged acid dissolving the host mineral, followed by hydrolysis and precipitation of insoluble oxides and sulfates of iron, aluminum and silica. Imprints of these processes were globalized during the mid-Tertiary to mid- Quaternary periods as observed in many parts of Nigeria and Sub-Sahara Africa, aided by tropical conditions which prevent the erosion of top soil while leaching progresses. Laterites vary significantly according to the parent rock mineralogy and geomorphology of the area (Sudha, 2009). The evaluation of the mineral potential and geological mapping of laterite deposits is imperative due to its verse economic important for ore mineral, construction, water treatment, agriculture etc. which has not been or is under exploited in this region when compared to others. Evaluation of laterites deposits has evolved from pit dug litho-logs and sampling method, were lateral differentiations are based on interpolations between rather distant pits and the three- dimensional (3-D) geometry is poorly understood Robain, H. et. al., 1996. To reduce erroneous interpretation the need for lateral continuity as much as vertical variation with depth is greatly emphasised. Recent works has shown that the application of relatively low frequencies (i.e. <100 kHz), electrical resistivity measurements is an effective tool characterizing soils with compositional gradient (Robain, H. et. al., 1996; Anicet B. et. al., 2006). Resistivity is a material property and does not depend on the media geometry. In soil systems, bulk resistivity of the soil is measured, which represents the composite resistivities of the pore fluid, degree of saturation, composition of the solids etc (Sebastian, 2005; Thevanayagam, 1993 and Ward, 1990). For laterite studies, the Electrical Resistivity Tomography (ERT) method is preferred. The ERT method provides a more quantitative and rigorous spatial imaging of the geophysical electrical resistance data which improves on other (DC) electrical resistivity method (Daily et. al., 2005). Also in geological complex terrains most DC methods are inadequate especially where it becomes necessary to have a continuous 2D coverage (Akinlabi and Adeyemi, 2014). I. In general, ERT soundings in such laterite setting show a basic three-layer geoelectrical succession with a low resistive clay-rich saprolite layer sandwiched between much more resistive materials corresponding to the iron crust and basement (Ritz et. al., 1999). The aim of this work is to investigate conduct nature of laterite deposits, delineate the width and depth using Electrical Resistivity Tomography (ERT) in Okada South-south Nigeria. 2. Geology of the Study Area The study area is located in Okada town, about 28km from Benin City, South-Western Nigeria (fig. 1), within latitude 6 o 40’ – 6 o 45’ N and longitudes 5 o 20’ – 5 o 25’ E. The area lies within the rain forest region of Nigeria with rainy season occurring from April to October. The mean annual rainfall values range from 1500mm to 1830mm. Rainfall within the area are usually characterized by high surface runoff due to its generally low infiltration rates and high canopy trees. The laterite unit in the area is part of the Benin Formation outcrop that is the topmost unit of the Niger Delta Basin consists of about 90% sand and a few shale intercalations. Shale content increases downwards while sand and sandstones are coarse to fine grained, poorly sorted, mostly unconsolidated and commonly subangular to well rounded in texture. The Benin Formation was deposited in continental-fluviatile environment with varying thickness of 0 to 10000 ft, the age ranges from Oligocene to Recent (Whiteman, 1982). The Benin Formation outcrops at Okada as Okada sand. Paper ID: ART20198933 10.21275/ART20198933 2188