Cenozoic

Cretaceous

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Illo Formation

Illo Fm

Period:

Cretaceous

Age Interval:

Upper Cretaceous pre-Maastrichtian

Province:
Sokoto Basin (S. Iullemmeden Basin)

Type Locality and Naming

This Continental Intercalaire Gr of continental sediments consists the Illo Fm and Gundumi Fm in the Sokoto sub-basin. The Illo Formation is a lateral equivalent of the Gundumi Fm. The type section of the Illo Fm is on the hill east of Gore village about 3.5 km north of Giro 42m of the succession is exposed (Nwajide, 2013).

Reference section: Reyment,1965; Adeleye,1975; Kogbe,1976; Dessauvagie, 1975; Petters, 1978; Offodile, 1980; Whiteman, 1982; Benkhelil,1989; Okosun, 1992; Guiraud, 1993; Akandeet al., 1998; Zaborski et al., 1998; Jauroet al., 2007; Obaje,2009; Nwajide, 2013

[Fig. 1. Stratigraphic successions in the Nigerian sector of the lullummeden Basin (Sokoto Basin)]

Lithology and Thickness

Illo Fm is the lateral equivalent of the Gundumi Fm and includes interbedded clays and grits, with an intermediate pisolitic and nodular clay member, and attains over 240 m. The deposits are continental, fluviatile to fluvio-lacustrine in origin.

Lithology Pattern:

Sandy claystone

Relationships and Distribution

Lower contact

Non-conformably overlies the Basement Complex. Like the Gundumi Fm sediments, the Illo Formation unconformably overlies the basement.

Upper contact

Unconformably underlies the Rima Gr (Taloka Fm). Deposition was terminated by the Maastrichtian transgression.

Regional extent

Iullemmeden Basin

GeoJSON

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Fossils

Group contains Plant fossils, freshwater invertebrates, such as mollusks

Age

Late Cretaceous (only indicated as “Pre-Maastrichtian”; with Turonian-Campanian span implied by the Geology and Mineral Resources of Nigeria, for graphic purposes, Gundumi Fm arbitrarily placed here as spanning the Turonian-Santonian with the coeval Illu Fm as Campanian)

Age Span:

Beginning stage:

Campanian

Fraction up in beginning stage:

0.0

Beginning date (Ma):

83.65

Ending stage:

Campanian

Fraction up in the ending stage:

1.0

Ending date (Ma):

72.17

Depositional setting

The Illu Fm deposits are continental, fluviatile to fluvio-lacustrine in origin. Continental – Alluvial to lacustrine (Nwajide, 2013). The “Continental Intercalaire” is important in Africa, it can facilitate the unity of facies, flora and fauna, which showed a uniform climate over large parts of Africa, and the change from the Jurassic to Cretaceous. The Karoo Series (Karoo Gr) of South Africa can be correlated with the upper beds of the lower portion of the “Continental Intercalaire” (Furon, 1960). The “Continental Intercalaire” corresponds to the upper part of the Nubian Sandstone, which, in the Arabo-Nubian shield, is a generalized term that begins at the base of the Paleozoic.

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.