Cenozoic

Cretaceous

Information provided by geoscience team at Ahmadu Bello University, Zaria, Nigeria --see About

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Keana Formation

Keana Fm

Period:

Cretaceous

Age Interval:

Cenomanian-Turonian

Province:
Benue Trough Central

Type Locality and Naming

The Keana Fm has its type locality at the Keana Anticline across the River Benue from Makurdi (Offodile, 1976).

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

Lithology and Thickness

Keana Fm: The Keana Fm resulted from the Cenomanian regression which deposited fluvio-deltaic sediments. The formation consists of cross-bedded, coarse-grained feldsparthic sandstones, occasional conglomerates, and bands of shales and limestones towards the top. It has no certain established thickness estimate, but Nwajide (2013) estimated the thickness to be about 700m.

Lithology Pattern:

Coarse-grained sandstone

Relationships and Distribution

Lower contact

The Keana Fm has a gradational and unconformable contact onto the underlying Awe Fm (Zaborski, 1998; Offodile, 1976, 1984; Reynment and Offodile, 1977). Although also reported as Unconformably overlies the Asu River Gr (of which Awe Fm is the upper unit)

Upper contact

Underlies the Zurak Fm

Regional extent

Benue Trough Central . It is the equivalent of the Yolde Fm and Pindiga Fm in the Upper Benue Trough.

GeoJSON

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Fossils

Ammonites (Euomphaloceras septemseriatum, Hoplitoides ingens), Foraminifera, bivalves (Costagyraolis iponensis), Gastropods

Age

Middle Cretaceous. The four formations indicated in the Cenomanian through mid-Turonian interval are given quasi-equal durations here (Keana Fm = Early Cenomanian, Zurak Fm = Middle Cenomanian, Makurdi Fm = Late Cenomanian, and the Wukari Fm = lower Turonian)

Age Span:

Beginning stage:

Cenomanian

Fraction up in beginning stage:

0.0

Beginning date (Ma):

100.50

Ending stage:

Cenomanian

Fraction up in the ending stage:

0.3

Ending date (Ma):

98.52

Depositional setting

Marine depositional environment, specifically a shallow to moderately deep marine setting. The presence of organic-rich shales suggests periods of low oxygen levels, likely associated with restricted circulation or high productivity.

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.