Abstract
The facies analysis of the syn-rift sequences Bima I Formation in the Gongola Sub-basin of the Northern Benue Trough displayed assemblages of trough crossbedded sandstones facies, planar crossbedded sandstone facies, massive bedded sandstone facies, ripple laminated sandstone facies, parallel bedded sandstone facies and mudstones facies. These arrays of facies form two suites of facies association that consist of the lacustrine-delta complex depicting coarsening upward cycles and fluvial complexes showcasing fining upwards cycle the former accounts for a scenario where the incremental accommodation is lower than the sediment discharge, whereas the latter is reflective of a case where improved subsidence rate induces high accommodation rate that outruns sediment supply. The stratigraphic architecture of the syn-rift Bima I Formation indicated that the lacustrine-delta are restricted to the lower stratigraphic horizons whereas the fluvial complexes essentially defines the upper stratigraphic zones of this formation.
Highlights
The intracratonic Benue Trough located in Nigeria is part of the chain of basins in the West and Central African Rift System, falling in between the Chad and Niger/Delta Basins
Its evolution and basin architecture is quite defined with horst and graben system, typical of rift basin (Shettima, 2016). The opening of this trough is accompanied with Aptian – Albian marine transgression that terminated in the Central Benue Trough, leaving continental depositional processes to dominate the Northern Benue Trough, thereby depositing the syn and Shettima Bukar, Mohammed Bukar, and Fatima Dupe Adams post – rift sequences of the continental Bima Formation (Guiraud, 1990).This depositional regime is synonymous to the Bornu Basin in Nigeria (Avbovbo et al, 1986) and contemporaneously represents the basal sedimentary sequences of the Doba, Deseo, Salamat, Grein, Kafra, Termit, Tenere and Mugland Basins of the West and Central African Rift System (Genik, 1992)
The structural configuration of the Gongola Sub-basin built of half graben system provided the template for the evolution of the facies assemblages in the syn-rift Bima I Formation which indicated the development of lacustrine, deltaic and fluvial depositional environment in the non-marine rift complex (Fig.6)
Summary
The intracratonic Benue Trough located in Nigeria is part of the chain of basins in the West and Central African Rift System, falling in between the Chad and Niger/Delta Basins It stretches for over 1000 km in length and varies in width between 50 – 150km (Fig.1), and host more than 6000m of Cretaceous – Tertiary sediments associated with volcanics (Fig.). Stratigraphic architectures of rift systems are commonly disposed with alluvial fan, lacustrine and fluvial packages (Schlische and Olsen, 1990) but owing to varying sedimentation and tectonics, several depositional packages may evolve (Smooth, 1991) These varying packages have strong implication on the petroleum system of these basins, the need to re-evaluate the Bima Formation in this perspective. This present research aims to examine in detail the facies association and clay mineralogy of the entire Cretaceous Bima Formation of the Gongola Sub – basin, with an objective of establishing depositional styles and paleoenvironments
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