Panabako Fm

Upper formation of the Bombouaka Gr. The Panabako Formation of northern Ghana and its extensions in the francophone terrains are equivalent to the Anyaboni Fm and Abetifi Fm of the southeastern fringe of the Basin (Carney et al. 2010). Roadside exposures 4.6km west of Langbinsi and west of Gambaga Town is identified for this formation.

Synonym: Panabako Sandstone Fm

References: Annan-Yorke, 1971; Blay, 1983; Viljoen et al., 2008; Jordan et al., 2009; Carney et al. 2010; Coueffe et al., 2011; Abu, 2018

[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]

This unit mainly consists of quartz-arenites, which are the probable lateral equivalents of sandstones in the Mpraeso Fm, Abetifi Fm and Obocha Fm of the Kwahu Gr. It overlies the Poubogou Fm with defined clastic sediments of Aeolian environment largely with quartzitic and feldspathic sandstones. The formation has paleosol features of pseudokarren structures marking its contact with the overlying Kodjari Formation of the Oti/Pendjari Gr. Remote imagery suggest that the 150-200m thickness of the unit includes two sandstone sequences, the upper of which forms eroded ‘sugarloaf’ cappings above the lower sandstone. This upper sandstone may have been partially eroded prior to deposition of the Oti-Pendjari Gr, since the base of the latter rests unconformably on the gentle, southwards dip-slope of the lowermost Panabako sandstone package (Jordan et al., 2009). Roadside exposures 4.6km west of Langbinsi, comprises fine- to medium-grained sparsely feldspathic quartz-arenites that commonly have broad, shallow, swaley or trough-like structures, with unidirectional cross-stratification. A similar distance west of Gambaga, quartz-arenites are moderately feldspathic, with some fine- and coarse-grained, locally gritty layers in tabular cross-stratified beds that locally show isoclinal, syn-sedimentary folding. Plane laminated beds commonly intervene between the cross-stratified sets. Poorly developed herringbone crossbedding and reactivation surfaces have been described from the formation by Viljoen et al. (2008). Current directions show a similar range to the Kwahu Group, although NW and SE sets are more common. Viljoen et al. (2008) recorded a predominance of NNE over NW and E directions in other exposures.

Acritarchs

Early Tonian. Base may be coeval with the basal sands of the Mpraeso Fm (hence mid-Early Tonian)

Characterized by clastic sediments of Aeolian depositional environment and the presence of well-defined algal mats in the Sakogu areas (northern Ghana). Paleocurrent directions show NW and SE common sets and recorded a predominance of NNE over NW and E directions in some exposures. The Formation has paleosol features of pseudokarren structures marking its contact with the overlying Kodjari Formation of the Oti/Pendjari Group (Abu 2018).