Cenozoic

Cretaceous

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Awi Formation

Awi 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. Its type section is exposed at a road cut some 9km south of the Awi Village – which is actually located on the basement complex (Nwajide, 2013).

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

Awi Fm: In some locations, it is the basal non-calcareous, sandy, conglomeratic unit of the Asu River Group also directly overlying the Basement Complex but to the north of Calabar. The conglomeratic beds are typically succeeded by the coarse to very coarse pebbly sandstones, grading upwards into medium to fine sandstone, siltstone/claystone and black carbonaceous shale. It has two horizons of thin black, carbonaceous, lignitic and pyritic shale markers that contain poorly preserved shallow marine foraminifera.

Lithology Pattern:

Coarse-grained sandstone

Relationships and Distribution

Lower contact

Lies on the Mamfe Fm. In some regions, the Awi Fm also forms part of the basal unit of the Asu-River Group and directly overlies the Basement Complex in the North of Calabar.

Upper contact

Conformably underlies the Abakaliki 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:

0.0

Beginning date (Ma):

113.20

Ending stage:

Albian

Fraction up in the ending stage:

0.5

Ending date (Ma):

106.85

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

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.