Ameki Gr

Cenozoic

Cretaceous

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Ameki Gr

Period:

Paleogene

Age Interval:

Eocene

Province:
Niger Delta - Outcrop

Type Locality and Naming

The Ameki Group was given early attention by the Geological Survey of Nigeria but then affirmed by Nwajide (1979, 1980) and eventually nominating three component members that are laterally equivalent. It is an upward succession of the Ameki Fm, the Nanka Fm, and the Nsugbe Fm. The facies of the Ameki Group conformably overlie the Imo Fm and they pinch out eastwards and westwards (Nwajide, 2013). The Ameki Fm is well exposed along the railway cutting in the Ameki Villlage north of Umuahia (Reyment, 1965). The Nanka Fm name is derived from the Nanka town, an extensive area of which has been so deeply gullied as to expose the bedrock which is elsewhere covered by thick lateritic soil development (Nwajide, 2013). Nsugbe Fm was separated from the Nanka Fm and considered its lateral equivalent because it has a lithological succession that is different from the Nanka Fm, its textural characteristics set it apart, it has a degree of induration unknown to the Nanka Fm, and covers a substantial area of over 1000km² (Nwajide, 2013). Its type locality is around Nsugbe, a town some 10km north of northeast Onitsha (Nwajide, 2013).

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; Jauro et al., 2007; Zaborski et al., 1998; Obaje,2009; Nwajide, 2013

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

Lithology and Thickness

Nsugbe Fm, the upper unit, consists of two upward coarsening cycles. The lower cycle consists of flat-bedded, occasionally wave ripple-laminated, and burrowed, clayey, medium grained sandstone. The cycle is capped off by an oligomictic, sharp-based, thick conglomerate composed of well-rounded quartz pebbles set in a matrix of coarse and poorly sorted ferruginous sandstone (Nwajide, 2013).

Nanka Fm, the middle unit, has a lithology of overwhelmingly loose, flaser-bedded, and fine to medium sand, with a few mudrock breaks (Nwajide, 2013). The thickness of the formation is estimated to be about 305m

Ameki Fm, the lowest unit, consists of grey-green sandy clays, sandy claystones and sandstones at its type locality in Eastern Nigeria. Two main lithological divisions have been recognized: a lower with fine to coarse grained sandstones with intercalations of calcareous shale and thin shelly limestone, limestone nodules; and an upper with coarse cross bedded sandstones, bands of fine grey-green sandstones and sandy clay (Whiteman, 1982). The maximum thickness estimate for the formation ranges from 1200-1500m (Nwajide, 2013). Lutetian – Early Bartonian (Whiteman, 1982).

Lithology Pattern:

Clayey sandstone

Relationships and Distribution

Lower contact

The Ameki Gr unconformably overlies the Imo Shale Fm (Imo Fm)

Upper contact

Overlain unconformably by the Ogwashi-Asaba Fm

Regional extent

Niger Delta outcrop to Anambra Basin

GeoJSON

null

Fossils

Whale remains (Pappocetus lugardi), Nautiloid (Deltoidnautilus nwajidei), gastropods (Siphonochelus nigeriensis, Turritella sp.)

Age

Eocene. The basal Ameki Fm begins in the Lutetian (Whiteman, 1982).

Age Span:

Beginning stage:

Lutetian

Fraction up in beginning stage:

0.0

Beginning date (Ma):

48.07

Ending stage:

Priabonian

Fraction up in the ending stage:

1.0

Ending date (Ma):

33.90

Depositional setting

The Ameki Fm was deposited in deltaic to shallow marine environment (Whiteman, 1982). The Nanka Fm has a Continental/coastal plain deposit to a shoreface setting and the Nsugbe Fm is characterized by a beach depositional setting (Nwajide, 2013)

Depositional pattern:

Additional Information

Compiler:

Enam O. Obiosio, Solomon Joshua Avong and Henry Nasir Suleiman (2024)- Stratigraphic Lexicon compiled from the following books:

Nigeria: Its Petroleum Geology, Resources and Potential, by Arthur Whiteman, 1982; (Volume 1) Published by Graham and Trotman Ltd.

A review of the Cretaceous System in Nigeria by P. M. Zaborski (1998) In Africa Geoscience Review, Vol.5, No.4, pp385-483

Geology and Mineral Resources of Nigeria by Nuhu George Obaje, Published by Springer-Verlag Berlin Heidelberg 2009; http://www.springer.com/series/772

Geology of Nigeria Sedimentary Basins, Nwajide C. S., 2013; Published by CSS Bookshops Limited, Lagos Nigeria.