Cenozoic

Cretaceous

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Abakaliki Formation

Abakaliki Fm

Period:

Cretaceous

Age Interval:

Lower Cretaceous

Province:
Benue Trough South

Type Locality and Naming

The Asu River Gr in the Southern Benue Trough comprises the upward succession of the Ogoja Sandstone Fm, Awi Fm, Mamfe Fm, Abakaliki Fm (Abakaliki Shale Fm), and Mfamosing Limestone Fm. This unit was described by Reynment (1965) as having it type locality in the Abakaliki Town. The type area of the Abakaliki Fm is exposed in the gently undulating terrain in the general area lying between Ezambgo and Abakaliki township. The formation was described as the Abakaliki Shale in the type area (Reyment, 1965). The type locality is at Mgbo village, about 7km north of Ezamgbo and 16km west of Abakaliki town. Ebonyi Formation Type area.

Synonym: Abakaliki Shale Fm

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

Lithology and Thickness

Abakaliki Fm, which has an average thickness of about 500 m, is dominantly shale, dark grey in color, blocky, and non-micaceous in most locations. It is calcareous (calcite-cemented) and deeply weathered to brownish clay. The top is sometimes identified in boreholes with the commencement of rapidly alternating beds of shale and mudstone which characterize the latter unit. The formation is estimated at 2500m thick based on the covariance of illite abundance with depth of burial (Dunnoyer de Seconzac et al., 1967; Agumanu, 1986). The formation underlies a gently undulating terrain in the Ntezi-Ezamgbo area and southwards to Amagu-Agba.

Lithology Pattern:

Claystone

Relationships and Distribution

Lower contact

Lies on the Awi Fm

Upper contact

Conformably underlies the Mfamosing Limestone Fm

Regional extent

Southern Benue Trough

GeoJSON

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Fossils

Ammonites (Diploceras quadratum, Hysteroceras binum, Elobiceras lobitoense, Gyaloceras ibo, Mortoniceras ishiaguense, Acanthocerass p., Acompoceras sp.), gastropods, pelecypods (Anatinaagassizi, Panopea cf. gurgitis), foraminifera, brachiopods, crinoids, algae (Cayeuxia, Pianella – Reijers and Petters, 1997), plant remains, Thalassinoides and Planolites

Age

The entire Asu River Gr spans the Aptian through Cenomanian according to strat-chart used by Obaje (2013). Other than the Mfamosing Limestone Fm, which spans the Cenomanian, the other 4 formations are given sub-equal duration in the Aptian-Albian interval.

Age Span:

Beginning stage:

Albian

Fraction up in beginning stage:

0.5

Beginning date (Ma):

106.85

Ending stage:

Albian

Fraction up in the ending stage:

1.0

Ending date (Ma):

100.50

Depositional setting

Alluvial – marine depositional environment which marked a crucial juncture in the geological history of the Lower Benue Trough, marking the beginning of significant sedimentation associated with the rifting and marine transgression during the Early Cretaceous period

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.