Subsurface Geological Mapping Using Schlumberger VES in Taraba State

This study applies Schlumberger vertical electrical sounding to produce subsurface geological maps in selected areas of Taraba State, North East Nigeria. Taraba State's geological diversity, encompassing basement complex, Benue Trough sedimentary sequences, and volcanic intrusions, creates variable groundwater conditions that have not been systematically mapped at local government level. This study acquires VES data at 28 stations in Bali, Kurmi, and Gashaka local government areas, including both basement complex and sedimentary terrain, with maximum AB/2 extending to 400 metres. Standard IPI2WIN inversion generates layer resistivity and thickness models at each station. Geostatistical kriging interpolates layer parameters spatially to produce resistivity cross-sections and isopach maps. Geological interpretation integrates available 1:250,000 geological maps from NGSA. Findings reveal a west to east transition from basement complex-dominated terrain with typical three to four layer models (resistive surface, weathered zone, fresh basement) to sedimentary terrain showing laterally persistent medium-resistivity (30 to 80 ohm-metres) sandy formations indicative of potential aquifer zones in the Benue Trough. Weathered basement depths average 24 metres in the western sector, with depths to fresh basement ranging from 18 to 65 metres. The sedimentary sector shows a productive sand horizon at 45 to 90 metres depth with interpreted hydraulic conductivity of 3 to 12 metres per day. The study provides the first quantitative subsurface geological framework for the surveyed areas and recommends follow-up hydrogeological drilling to confirm the interpreted aquifer potential in the sedimentary terrain.

Keywords: Schlumberger VES, subsurface mapping, basement complex, Taraba State, hydrogeology.