Contribution of the geoelectric method to the identification of geological formations in the Ngaoundal locality (Adamawa, Cameroon)

Abstract

• The apparent iso-resistivity maps show low, medium and high resistivity ranges. • Ten major types of sounding curves were identified in the study area. • A dominance of lateritic soils on the surface, sandy-clay soils in the middle. • Electrical anomalies reflect the loose weathered, fracture and healthy formations. • Three classes zones of low, medium and high thickness. This study highlights the contribution of geo-electricity to the characterization of geological formations in the Ngaoundal area. Electrical mapping using the Schlumberger device was carried out over 29.9 km², with fifty-one vertical electrical soundings (VES) conducted at 700 m intervals across a zone entirely covered by soils developed on a granitic bedrock. Apparent resistivity maps, for depths ranging from AB/2 = 1.5 to 100 m, reveal low, medium, and high resistivity ranges. Ten main types of VES curves (Q, HK, KH, H, KQ, QH, HKH, K, KQH, and QHK) were identified, classified according to depth and resistivity. Integrated analysis of resistivity maps and VES curves shows lateritic soils dominating the surface, sandy-clay soils at intermediate depth, and fractured or sound bedrock at greater depth. Four pseudo-resistivity sections highlight weak ( ρ < 350 Ω·m), medium (350 ≤ ρ ≤ 1800 Ω·m), and strong ( ρ ≥ 1800 Ω·m) anomalies, corresponding respectively to loose weathered formations (weathered granite, gravelly soils), fractured granites, and sound granites forming the bedrock. The lateritic layer thickness map identifies three classes: low (1.33–2.58 m), medium (2.59–2.84 m), and high (2.85–8.94 m). Comparison with existing water borehole data confirms the consistency of geophysical models. This complementarity between geophysical methods and direct borehole observations reinforces the reliability of the approach and provides a robust framework for geological and hydrogeological interpretation of the subsurface in the Ngaoundal region.