Eze-Aku Gr

Eze-Aku Group was introduced by Murat (1972) and maintained by Nwajide (2013). The type locality is in the area of Eze-Aku, Awgu Division (Geological Survey of Nigeria and Shell D’Arcy, in International Stratigraphic Lexicon 1956). In the Benue Trough South, the Group consists of the upward succession of Igumale Fm,), Nkalagu Limestone Fm and. Eze-Aku Shales Fm (Eze-Aku Fm). For the Eze-Aku Fm, the locality is at Eze-Aku, Awgu Division (Geological Survey of Nigeria and Shell D’Arcy, in International Stratigraphic Lexicon 1956). For Benue Trough Central, Nwajide (2013) had also used a Eze-Aku Group for the upward succession of the Keana Fm, Zurak Fm, Makurdi Fm, and the Wukari Fm at the top of the sequence, as members of the group; but in this Lexicon, those formations are not combined in a group.

Synonym: Ezeaku Fm, Eze-Aku Fm, Ezeaku Gr, Eze-Aku Shale Group (Murat, 1972), Cross River Group for Benue Trough South (Ekwueme, 1987; Elueze et al., 1999; Obaje et al., 2000; Ehinola et al., 2000).

References: Reyment, 1965; Adeleye, 1975; Kogbe, 1976; Dessauvagie, 1975; 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

The Eze-Aku Gr is generally estimated to be about 1000m thick (Reynment, 1965; International Stratigraphic Lexicon, 1956).

SUCCESSION in Benue Trough SOUTH:

Eze-Aku Fm (Eze-Aku Shales Fm): Upper unit of Eze-Aku Gr consists of hard, flaggy, calcareous shales and siltstones which are grey or black in color and have yielded many impressions of Inoceramus. In the Southern Benue Trough, the Eze-Aku Shale is said to be about 2000ft thick by Cratchley and Jones (965). The type locality is at Eze-Aku town.

Nkalagu Fm (Nkalagu Limestone Fm): Middle unit of Eze-Aku Gr in this region is limestone typically fossiliferous and micritic, and interbedded are shale layers, which are typically dark grey to black. Having thickness that can range from 100 to 300 meters.

Igumale Fm: Lower unit of Eze-Aku Gr in this region is primarily of sandstones (fine to coarse-grained), shales (dark grey to black, suggesting deposition in low-energy environments), and limestones.