Main Article Content
Observations and comments on the classification schemes proposed for the Voltaian Basin sediments on the West African craton by various Geologists
Abstract
Subsurface data indicate over 6000 metres thick of sedimentary infill in the Voltaian Basin on the West African craton made up of three major lithofacies (groups) separated by distinct unconformities. These are: Lower Voltaian Group composed of over 2000 metres thick of indurated
quartzitic sandstones with subordinate shales at the base, overlain by dense, greenish, poorly sorted and graded bedded sandstones and siltstones with subordinate shales of about 2000 metres thick; Middle Voltaian Group consisting of the triad: conglomerate – dolomitic limestone – bedded chert with intercalations of sandstone, siltstone, mudstone and shales of over 700 metres thick, and overlain by about 550 metres thick of greenish, flysch-type sediments. The Upper Voltaian Group is composed of distinctly continental facies (molasses) of reddish brown, chocolatebrown,
brown coloured, poorly sorted sandstones, conglomerates, siltstone and mudstones of about 400 metres thick, and a sequence of thinly bedded, micaceous sandstones with clay galls of about 120 metres thick capped by massive cross-bedded arkosic sandstone of about 300 metres
thick. Reviews of the classification schemes proposed by various geologists are basically similar. However, general discrepancies, inconsistencies and contradictions in the stratigraphic positions of some of the rock units have been observed, as well as terminologies to describe rock units
which are inconsistent with stratigraphic concepts and principles.
quartzitic sandstones with subordinate shales at the base, overlain by dense, greenish, poorly sorted and graded bedded sandstones and siltstones with subordinate shales of about 2000 metres thick; Middle Voltaian Group consisting of the triad: conglomerate – dolomitic limestone – bedded chert with intercalations of sandstone, siltstone, mudstone and shales of over 700 metres thick, and overlain by about 550 metres thick of greenish, flysch-type sediments. The Upper Voltaian Group is composed of distinctly continental facies (molasses) of reddish brown, chocolatebrown,
brown coloured, poorly sorted sandstones, conglomerates, siltstone and mudstones of about 400 metres thick, and a sequence of thinly bedded, micaceous sandstones with clay galls of about 120 metres thick capped by massive cross-bedded arkosic sandstone of about 300 metres
thick. Reviews of the classification schemes proposed by various geologists are basically similar. However, general discrepancies, inconsistencies and contradictions in the stratigraphic positions of some of the rock units have been observed, as well as terminologies to describe rock units
which are inconsistent with stratigraphic concepts and principles.
