Dunkro Fm

Synonym: Dunkro Sandstone Fm

[Fig. 1. Geological map of the Volta Basin and surroundings, after Sougy (1970) and Affaton et al. (1980).]

[Fig. 2. Schematic lithostratigraphic sections showing principal lithologies and inferred correlations between Kwahu and Bombouaka group units across the Volta Basin.]

[Table 1. Published stratigraphic data available for Voltaian deposits]

[Table 2. Proposed lithostratigraphic scheme (left-hand column) compared with previous nomenclature.]

[Fig. 3. Synthetic lithologic section of the Volta Basin sedimentary infilling]

References: Carney et al., 2008

It consists of pink, medium- to coarse-grained, feldspar-lithic arenites with maroon mud flakes and mud-flake-conglomerates and having internal structures such as lateral accretion surfaces and cross-stratification. Cross-beds are locally over steepened, and some bedding is chaotic. Massive sandstones occur in units several meters thick, some containing ‘floating’ pebbles, cobbles and boulders of basement rocks, including mesocratic gneiss. Cobble conglomerates in lenticular beds up to 2m thick are poorly sorted, massive and matrix-supported; bed bases are commonly strongly erosive. Clasts are subangular to well-rounded and include: green chert, various granitoid and foliated metamorphic lithologies and dark green-grey porphyritic volcanic rock. Sandstone is weathered red-brown, medium to coarse-grained and very thickly bedded to locally massive. Some thinner intervals show cross-bedding, which is locally oversteepened. Compositionally, these sandstones are rich in feldspars and lithic grains, and thus are highly immature. The bedding is locally chaotic, with slump sand lenses of bouldery, matrix-rich conglomerate. Paleocurrents are towards the SW and W (Carney et al., 2008). Red-purple sandstone; highly immature composition indicated by abundant feldspar and lithic grains. Medium- to coarse-grained, with sporadic 'floating' pebbles and pebble lags. Pebbles include pink porphyritic, microgranite and foliated and metasedimentary lithologies. Pebble lags seem to be associated with scour troughs.