Nkporo Gr

Synonym: Upper Grits and Sandstones (Falconer, 1911)

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

Lafia Fm: is the northern extension of the Nkporo Group facies (Offodile, 1976a). The maximum thickness of 1,500m has been assigned but it wedges out in the east and southeast where it thinly overlies the Awgu Formation of the Southern Benue Trough (Nwajide, 2013). It is made up of white to grey, cross-bedded, fine to coarse, poorly sorted, feldspathic sandstone, succeeded by white to brown clay, and bright red, friable ferruginous sandstone, capped by laterite. Ehinola et al. (2000) characterize the formation as consisting of rhythmic successions of shale, limestone, siltstone and sandstone, with coal interbeds. The type locality and naming of the Lafia Formation is the Lafia Town, Nasarawa State (Nwajide, 2013) and the characterization was done by Offodile (1976) by logging a 25m section on the bank of River Amba in Lafia Town.

Enugu Fm: The Enugu Shales are about 3,000ft thick (Reyment, 1965) and consists of shales and occasional sandstones. The shales are grey blue or dark and contain occasional white sandstones and striped sandy shale beds. The bands of impure coal occur in nodules and lenticles of clay and ironstones are common towards the top of the formation. The Enugu Formation has two distinguishable sandstone bodies – the Otobi and Okpaya Sandstones (Nwajide, 2013) and located near Enugu Municipality (Grove, 1951). Otobi Sandstone Member: it is a relatively small body and overlies the Awgu Shale and laterally interfingers with the shaly facies of the Enugu Formation (Nwajide, 2013). Okpaya Member: it is made up of alternation of siltstone and fine sandstones and becomes more shaly upwards. (Nwajide, 2013). Foraminifera recorded within this unit (Haplophragmoides excavate, Hap. hausa, Ammobaculitessp., Ammoastutasp.) – Nwajide (2013) and Petters (1995), Ammonite (Lybicocerasangolense), Gastropods (Turritella), Palynomorphs (Faveotriletesmargaritae, Cingulatisporitesornatus, Syncolporitessyriatratus) – Mebradu (1990).

Owelli Fm: consists of massive, hard ferruginous sandstones. They are prominently cross-bedded in places and are generally medium to coarse-grained and contain pebble bands. Occasionally thin silty or argillaceous bands are present (Whiteman, 1982). The Owelli Sandstone is in general about 1,500ft thick (Simpson, 1954). There are also interbeds of marine, dark grey, micaceous, pyritic, calcareous, and occasionally glauconitic shales (Nwajide, 2013). Located near the village of Owelli on the old road from Enugu to Awgu (Reyment, 1965; Nwajide, 2013).

Nkporo Shale Fm: Consists chiefly of blue or dark grey shales with occasional thin beds of sandy shale and sandstone. Reyment (1965) gave a thickness of 3280ft to the Nkporo Shale but varies with location (Whiteman, 1982). The formation consists of dark grey to black, fissile, friable and soft shales and mudstones with occasional thin beds of sandy shale, fine sandstone and marl with coatings of sulphur. Located near Nkporo Village in Abia State. The Nkporo shale contain the following; Ammonites (Lybicocerasafikpoense, Innoceramussp., Sphenodiscus, Bostrychoceras, Pachydiscus, Cirroceras), Foraminifera (Afrobolivina, Gabonella, Bolivinaexplicata, Bulimina fang, B.prolixa), Skolithos, Thalassinoides, Ophiomorpha, Palynomorphs. The Leru Section of the Nkporo Shale has dolerite boulders occupying the first 2m of the section at the base and said to be of hypabyssal bodies emplacement mode.

Afikpo Fm: consists of sandstones and shales (Akaa, 1995). Thickness of about 120m (Okoro, 2009). The lower third of the formation is made up of black to grey shales intruded and partly baked by dolerite sill. The mid - section is an alternation of siltstones, trough cross-bedded fine to medium grained sandstones and thin shales. Both sandstones are pebbly and bioturbation is intense with Ophiomorpha in the upper parts (Nwajide, 2013). The uppermost part consists of carbonaceous shale and siltstones interbedding with a thin coal seam occurring midway. Located near Afikpo Town (Akaa, 1995)