Facies analysis and paleoenvironments of the upper cretaceous sediments in share – Lafiagi areas, northern Bida basin, Nigeria

The Bida Basin is located in central Nigeria and it is perpendicular to the main axis of the Benue Trough. Due to its large areal extent and facies variation, the basin is often geographically divided into northern and southern Bida Basins. Whereas, aspects of the mineral resource and sedimentation history of the sediments in NW and SE extremes have been consistently studied, the present study area (Share-Lafiagi-Shonga areas) remains either unknown or under-reported. In the study area, fifteen vertical profiles of the Campanian-Maastrichtian sediments were studied along road cuts, erosional channels and Cliff sides with special attention focused on their internal physical and biogenic attributes. The sedimentological analysis permitted recognition of five distinct depositional facies; alluvial fan, braided channel, floodplain, tidal channel and shoreface in the lithostratigraphic units mapped. In Unit I, the proximal alluvial fan facies were preserved as conglomeratic facies which overly nonconformably, the Pre-Cambrian weathered schists and granites. Both the matrix and grain supported subfacies are indicative of gravity induced alluvial processes. The braided channel facies comprising of conglomeratic sandstone, medium-coarse grained sandstone subfacies are wide spread and their fluvial origin is supported by unidirectional flow pattern and absence of marine biogenic features. The sequence grades into claystone facies which probably formed in localized non marine floodplains. The younger Unit II comprises of conglomerate, sandstone and claystone facies. The conglomerate facies is moderately sorted and mature showing evidence of reworking and recycling. Association of this facies with herringbone cross stratifified beds probably indicates tidal channel lag origin. The sandstone facies are commonly compositionally mature, bioturbated and contain clasts of reworked clays and clay drapes suggesting high energy tidal channels and shoreface subenvironments. The depositional model for the Upper Cretaceous sediments in the study area is strongly dominated by alluvial processes which in places evolved into shallow marine processes and frequently incised by fluvial channels. The clay deposits of the floodplain may offer economic resource potential in the area.