Geo-electrostratigraphic investigation of Gulak and surrounding areas, northeastern Nigeria

This study presents a quantitative geo-electrostratigraphic investigation of Gulak and its environs in northeastern Nigeria to evaluate subsurface lithology and groundwater potential within a basement complex terrain. Detailed geological field mapping guided the establishment of ten (10) Vertical Electrical Sounding (VES) stations distributed across the study area. Data were acquired using an ABEM SAS 1000 Terrameter with the Schlumberger array configuration, achieving a maximum current electrode spacing (AB/2) suitable for deep subsurface penetration. Sounding data were interpreted using INTERPEX inversion software to generate geoelectric layer models and electrostratigraphic sections. The results revealed three to four geoelectric layers across the VES locations, with resistivity values ranging from 2.02 to 73,900 Ωm and layer thicknesses varying between 0.019 m and 155.6 m, reflecting significant lithological heterogeneity. Identified curve types include HK (70%), QK, HQ, and AH, indicating alternating conductive and resistive subsurface sequences typical of weathered and fractured basement aquifers. Three geoelectric cross-sections (Profiles A–A′, B–B′, and C–C′) delineated variations in overburden thickness and basement depth, which range from shallow weathered zones to deeper fractured bedrock horizons. Aquiferous layers were characterized by moderate resistivity values (typically 50–800 Ωm) and appreciable thickness, suggesting favorable groundwater storage conditions. Based on these parameters, seven VES points (1, 2, 3, 6, 7, 8, and 9) were classified as high groundwater potential zones, two points (5 and 10) as moderate, and one point (4) as low potential due to its high resistivity and thin weathered layer. The integration of resistivity data with geological mapping provides a reliable framework for groundwater targeting, borehole siting, and sustainable water resource development in the Gulak area.