Sedimentary Facies Relationships and Depositional Environments of the Maastrichtian Enagi Formation, Northern Bida Basin, Nigeria

The sedimentary facies of the Maastrichtian Enagi Formation exposed across the Agbona ridge at Share and Shonga areas was investigated for the first time to characterize their depositional facies and interpret the depositional environments. Well exposed vertical profiles of the sediments were studied along road cuts, erosional channels and cliff drops with special attention focused on their internal physical and biogenic attributes. The facies and facies associations in the lithostratigraphic units mapped include conglomerate, sandstone and claystone. The conglomerate facies is moderately sorted; grain supported and mature, showing evidence of reworking and recycling. Association of this facies with herringbone cross stratified sandstone beds probably indicates tidal channel lag origin. The sandstone facies are commonly compositionally mature, bioturbated and contain clasts of reworked clays and clay drapes and these suggest high energy tidal channels and shoreface. The associated unidirectional cross bedded sandstones subfacies and kaolinitic claystones are interpreted as braided fluvial channels and floodplain deposits. The gross sedimentation pattern and characteristics suggest predominance of trangressive shallow marine processes occasionally incised by fluvial channels. The clay deposit associated with the floodplains may offer economic resource potential in the area.