LITHOSTRATIGRAPHIC CLASSIFICATION OF SUBSURFACE IN A TYPICAL SEDIMENTARY TERRAIN, SOUTHERN NIGERIA: A CASE STUDY OF UJEMEN – EKPOMA

Abstract

Electrical resistivity imaging was conducted in a sedimentary terrain, Ujemen, Ekpoma, Nigeria to classify the subsurface lithology as well to use the information from the resistivity model to give a general litho-geoelectric section of the area under study. Two dimensional (2-D) electrical resistivity lines were obtained along six profiles using the Wenner-Schlumberger array. 2-D resistivity data in profiles 1, 2, 3 were obtained along 200 m each oriented in the N-S azimuth; while profiles 4, 5, 6 were obtained along 150 m each oriented in the W-S azimuth. RES2DINV software was used to invert the apparent resistivity values into actual resistivity values of the subsurface structure. The 2-D resistivity results showed that the subsurface is classified into two distinct geoelectric layers – the upper poorly bedded lateritic sandstone containing several sedimentary structures; sole structures, extra formational
cast of ironstone, extra formational cast of Kaolin, flute casts mixed together to form the upper regolith and the bedded sequence at the base of the interbeds of different strata - kaolin rich sandstones, clayey sandstone, coarse to grained sandstone, poorly sorted sandstone, and ironstone.