Chemostratigraphy, geomechanical characteristics, and petroleum indicators from southern Bida Basin outcrops, Nigeria

Abstract

The Bida Basin represents one of Nigeria’s most promising yet underexplored sedimentary sequences, with outcropping formations in the southern sector pro viding unique opportunities for integrated petroleum system analysis. This study presents a comprehensive evaluation combining chemostratigraphic characterization, geomechanical property assessment, and petroleum indicator analysis of Cretaceous to Tertiary outcrops across a 450 km2 area in the southern Bida Basin. Sixty-eight samples were systematically collected from five measured sections spanning the Lokoja, Patti, and Agbaja Formations. X-ray fluorescence analysis reveals distinct chemostratigraphic signatures with Ti/Al ratios ranging from 0.042 to 0.078, enabling correlation across 15 km of strike length. Rare earth element patterns indicate mixed provenance from both felsic basement and recycled sedimentary sources. Geomechanical testing demonstrates significant lithological control on rock strength properties, with uniaxial compressive strengths varying from 28.4 MPa in poorly cemented sandstones to 165.7 MPa in ironstone horizons. Young’s modulus values (12.8–89.3 GPa) correlate strongly with quartz content and degree of silicification. Organic geochemical analysis identifies three distinct zones of petroleum potential, with total organic carbon contents reaching 2.8 wt% in organic-rich shales. Rock Eval pyrolysis indicates predominantly Type II/III kerogen with hydrogen indices of 89–234 mg HC/g TOC. Vitrinite reflectance measurements (0.52–0.89% Ro) suggest early to peak oil generation windows across the study area. Surface geochemical anomalies, including elevated C2-C4 hydrocarbon concentrations and distinctive isotopic signatures, provide evidence for active petroleum migration. Integration of these multidisciplinary datasets establishes a robust framework for regional correlation and petroleum system understanding, with implications for both conventional and unconventional resource assessment in Nigeria’s frontier basins.