Abstract
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.
Highlights
The Bida Basin is a linear NW – SE trending embayment and is oriented perpendicular to the main axis of the Benue Trough and the Niger Delta basin of Nigeria (Figure 1)
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
Some authors have addressed some of the components of the petroleum potential of the Bida Basin as part of the on-going studies of the petroleum potential assessments of the Nigerian Inland basins (Idowu & Enu, 1992; Braide, 1992b; Ojo, 1992; Obaje et al, 2004; Akande et al, 2005)
Summary
The Bida Basin is a linear NW – SE trending embayment and is oriented perpendicular to the main axis of the Benue Trough and the Niger Delta basin of Nigeria (Figure 1). The rocks in this region basically are lateral equivalents of those in the northern parts, their distribution, geological developments and depositional history are worth studying and, the documentation will help to further understand the geology of the entire basin. It should be pointed out here that all the work on the northern Bida basin cited above are obviously restricted to areas north of river Niger and did not cover the present area where huge sediments are preserved. From our experience in the southern Bida Basin (Ojo & Akande, 2006, 2009), the depositional model of Braide (1992b) which forecloses influence of marine processes in that basin needs to be re-examined
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