Chad Fm

Based on exploratory wells studied by Moumouniet al. (2007), the Fika / Chad formations boundary is fixed at about1,500 m depth except in Kasade – 1 where it is estimated to be at about 700 m.

Reference section: Carteret al., 1963; Reyment,1965; Adeleye,1975; Kogbe,1976; Dessauvagie, 1975; Petters, 1978; Offodile, 1980; Whiteman, 1982; Wright et al., 1985: 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]

[Fig. 2 Sedimentary Basins of Nigeria (Obaje, 2009)]

This is the uppermost Pliocene–Pleistocene formation consisting of fluviatile and lacustrine thick bodies of clay, separating three major sand bodies, with lenses of diatomite up to a few meters thick (Wright, 1985). The three sand bodies correspond to the upper, middle and lower aquifers defined by Barber and Jones (1965). The sand is uncemented with angular and subangular quartz grains. The clay is massive and locally gritty in texture. Both the sand and the clay are of variable colors ranging from brown, yellow, and white to grey. The three sand bodies correspond to the upper, middle and lower aquifers defined by Barber and Jones (1965). The lower member is made of sands and sandy clays while the middle and the upper consist of sandy clays with diatomite and clays and sands, respectively. Near Maiduguri, the formation is more than 1800ft thick. The sandy sediments are often poorly sorted and particles of all grades from clay to gravel may occur in the same sample. Sandy lenses often occur and are believed to be fan-shaped deposits along the margins of the ancient Lake Chad, the impersistent sands are believed to have been deposited in times of flood by rivers.

Uppermost Pliocene – Pleistocene