M. Ritz et al., Electrical imaging of lateritic weathering mantles over granitic and metamorphic basement of eastern Senegal, West Africa, J APP GEOPH, 41(4), 1999, pp. 335-344
The electrical properties of several tens of metres of lateritic weathering
mantle were investigated by using electrical resistivity tomography (ERT)
in two basement areas of eastern Senegal. The field survey was conducted al
ong two profiles providing continuous coverage. Colour-modulated pseudosect
ions of apparent resistivity vs. pseudo-depth were plotted for all survey L
ines, giving an approximate image of the subsurface structure. In the area
underlain by granitic basement, the pseudosection suggests a very inhomogen
eous weathered layer in which the apparent resistivity changes more rapidly
than thickness. In the second area, underlain by schists, the lateral chan
ges in electrical properties are less pronounced than those of the granitic
area. Interpretation of 2D Wenner resistivity data yielded considerable de
tail about the regolith, even without pit information. In both areas, the n
ear-surface topsoil comprising undersaturated lateritic material is highly
resistive. The intermediate layer with low resistivities (e.g., 20-100 Ohm
m) contains clays including small quantities of water. The third, highly re
sistive layer reflects the granitic basement. Comparison of ERT survey resu
lts with pit information shows general agreement and suggests that ERT can
be used as a fast and efficient exploration tool to map the thick lateritic
weathering mantle in tropical basement areas with hard rock geology. (C) 1
999 Elsevier Science B.V. All rights reserved.