Bima Fm

The Bima Sandstone in the type section could be traced along the river channel south of the bridge, 200 m before the village of Bambam. Similar shales also occur within units of the Bima Sandstone that outcrop extensively on the Lamurde anticline (2 km to the town of Lafiya, on the Gombe – Numan road). The Bima Sandstone is subdivided into a Lower, Middle and Upper Bima (Carter et al., 1963). Good exposure outcrop of the Bima Sandstone can be studied at Biliri, Filiya and Shani, but without the so-called Middle Bima (Obaje, 2009). In Bornu sub-basin below Chad Basin, the Bima Fm includes the interval that is the Yolde Fm further south.

Synonym: Bima Sandstone Fm, Bima Group

References: Reyment, 1965; Adeleye, 1975; Kogbe, 1976; Dessauvagie, 1975; Petters, 1978; Offodile, 1980; Whiteman, 1982; Benkhelil, 1989; Okosun, 1992; Guiraud, 1993; Akandeet al., 1998; Zaborskiet al., 1998; Jauroet al., 2007; Obaje, 2009; Nwajide, 2013

[Fig 1. Stratigraphic successions in the Benue Trough and the Nigerian sector of the Chad Basin]

Continental depositional environment, which evolved from the weathering of the basement rocks. This comprises all sediments derived from the Basement Complex between the Permian and Albian times in response to uplift and weathering. The lithology is made up of poorly sorted, coarse- to medium-grained, thick-bedded to massive sandstones, intercalated with carbonaceous clays, shales, siltstones and mudstones; has variable colors from brown, reddish brown, grey to white (Nwajide, 2013). The Lower Bima Sandstone ranges from 0-1500m. At the base of the Lower Bima Member, there was syndepositional basalt volcanism and this subunit is interpreted as a proto-rift tectono-stratigraphic succession and is about 20m thick at the base of the Lower Bima Member (Zaborski et al., 1997; Nwajide, 2013). Although the Middle Bima lithology is reported to be shaly (dark and carbonaceous), having limestone intercalations in some parts and assumed to be deposited under a more aqueous anoxic condition (lacustrine, brief marine). The Middle Bima Sandstone ranges from 100-500m thick. The Upper Bima has an average of 500m thickness (with a maximum of 1200m in the Lamurde anticline).