Poubogou Fm

This unit is confined to the escarpment outcrops of the Bombouaka Gr and (in the west) the Kwahu Gr. In the northwestern outcrop the unit pinches out southwards, towards Larabanga. Lower-middle formation of the Bombouaka Gr.

References: Annan-Yorke, 1971; Blay, 1983; Ayite et al., 2008

[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.]

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

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

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

Consist of green-grey, micaceous mudstones and siltstones, commonly with a ‘papery’ fissility. The thin intercalations of siltstone and fine-grained sandstone are typically planar bedded, with sharp top-surfaces and undulatory, slightly channelized bases which in places show spectacular ball-and-pillow load structures (Ayite et al., 2008). The formation grades upwards into the Panabako Formation by increase in the proportion of sandstone relative to argillaceous beds. Within this transition, sandstones are typically grey-green and flaggy, with micaceous laminae, mudstone partings and intraformational mudclast breccia layers. This facies may correlate with the about 55m thick ‘Lower Nakpanduri Sandstone’ of Ayite et al. (2008), which includes quartzitic sandstones showing cross-bedding, flute casts and slump structures.

Acritarchs

Coeval with basal Damongo Fm (suggested by schematic table/diagram in Carney et al., 2010)? If so, then brief interval in mid-Early Tonian.

The formation is largely defined by fluviatile and flood plain depositional environments of shales and sandy shales.