Near - surface characterization of sediments of the Sokoto group exposed around Wamakko area, Northwestern Nigeria: an integrated approach

Abstract

An integrated approach involving sedimentological and geophysical studies was carried out to characterize the surface and subsurface geology of part of the southwestern Iullemmeden basin (Sokoto Basin, North-western Nigeria). The Kalambaina Formation (limestone) of the Sokoto Group is being investigated. The general objective of this study was to optimize lateral and vertical resolution amidst the subsurface lithological heterogeneity and that informed the choice of integrating sedimentology and geophysics (involving Vertical Electrical Sounding – VES and Electrical Resistivity Tomography – ERT). Surface geological mapping complemented by geophysical (4 VES and 2 ERT) surveys were carried out. Data integration involved geological (outcrop stratigraphic data), geophysics and data from down-hole core descriptions within the area of investigation. Results of 1D resistivity (VES) yielded QH and QHQ curve types with OH being predominant. Based on their contrasting resistivities, four-layer geoelectric sections was erected using VES data (ironstone topsoil, limestone, shale and clay/sandy clay layers). From the ERT modelling, four lithologic sections were also identified. These lithologic discriminations correlated well with few borehole data within the study area. With integration of geophysics with stratigraphic data , a subsurface facies distribution model (fence diagram) was developed having a high vertical and lateral resolution. This study revealed that during reconnaissance mapping, with integrated approach using resistivity and sedimentological data, accurate subsurface imaging could be achieved, at a reduced exploration cost, even in areas of abrupt facies changes (lithological heterogeneities).

Keywords

• sokoto basin
• electrical resistivity tomography
• lithological heterogeneities
• facies
• resistivity