Implications of Foraminiferal Assemblages and Geochemical Proxies in the Numanha Formation, Northern Benue Trough, Nigeria

Abstract

The Numanha Formation within the Yola Arm of the Northern Benue Trough represents an important Upper Cretaceous stratigraphic interval that records significant paleoenvironmental and depositional changes associated with the evolution of the West African intracontinental rift system. Despite its stratigraphic importance, detailed multiproxy investigations integrating micropaleontology and geochemistry remains limited. This study presents a comprehensive analysis of benthonic foraminiferal assemblages and major–trace element geochemistry from twelve shale samples collected from the Numanha stream section within the period of 7th -14th of May,2025 in order to reconstruct depositional environment, oxygenation conditions, sediment provenance, and basin dynamics during the Coniacian. Quantitative foraminiferal analysis reveals assemblages dominated by arenaceous benthonic taxa, particularly Haplophragmoides ssp (55.59%) and Ammobaculites ssp (35.90%), with minor occurrences of Ammotium spp, Miliammina spp, Reophax spp, and Trochammina ssp, while planktonic foraminifera are completely absent. Geochemical analyses done using the VANTA Portable XRF machine reveal elevated concentrations with mean values such as Si>128, 862, Al>57, 004, Fe>52, 125, Ti>5, 090, K>4, 995, Zr>332 and indicating a moderate to strong influx of terrigenous material. In contrast, the enrichment of Ni>94.4, V>76.77, and Mo>3.62 suggests intermittent dysoxic to suboxic bottom water conditions. When integrated with micropaleontological evidence, these geochemical proxies suggest that deposition occurred within an inner-neritic to marginal marine shelf environment. This setting was likely characterized by high sediment supply, restricted water circulation, and episodic marine transgressions. The combined dataset supports a depositional model involving a proximal mud-dominated shelf developed during the Coniacian transgressive–regressive cycle within the Northern Benue Trough. These findings contribute to improved paleoenvironmental reconstruction, sequence stratigraphic interpretation, and evaluation of source-rock potential in the Upper Cretaceous succession of the Yola Arm.