Self-potential anomalies in the lateritic cover of the Nsimi watershed in southern Cameroon: origin and influence of electrical and granulometric parameters

This study evaluates the use of the geoelectric self-potential (SP) method on a typically thick lateritic cover in the tropical rain forest of the Nsimi watershed of South Cameroon. In this respect, we have deployed SP and Wenner resistivity profiling along 10 tracks, which has enabled us to produce an SP map and a Wenner resistivity profile of the watershed. Because the application of the SP method is not ideal, the interpretation of our profiles is based on correlations between SP, elevation, electrical resistivity and well-constrained granulometric parameters in the watershed. The absence of a correlation between Sp and electrical resistivity suggests that these natural potentials would not be the result of a simple circulating current by Ohm's law through the medium, but would be associated with electromotive forces, either electrokinetic or electrochemical potential. The positive correlation observed between SP and elevation enables us to discard an electrokinetic origin for the Nsimi watershed SP and to propose an electrochemical one instead. This is confirmed by a clear linear correlation between SP and the percentage of clay material in the lateritic covers. This further enables us to define loose clay-rich horizons in the laterites. (C) 2003 Elsevier B.V All rights reserved.