Cenozoic

Cretaceous

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Benin Formation

Benin Fm

Period:

Neogene, Quaternary

Age Interval:

Miocene - Recent

Province:
Niger Delta - Offshore, Niger Delta - Outcrop, Dahomey Basin

Type Locality and Naming

The Cenozoic section of the Niger Delta is divided into three formations, representing prograding depositional facies that are distinguished mostly on the basis of sand-shale ratios. The Benin Fm is typified by the sands around Benin City where it is estimated to be 3050 m thick. Reynment (1965) reinstated the name Benin Formation (Parkinson, 1907) for the outcropping yellow and white sands and clays which occur in the coastal Nigeria especially in Western and Mid-Western Nigeria. The type area is around Benin (Nwajide, 2013). Short and Stauble (1967) designated the type section as the Elele-1well located about 40 km northeast of Port Harcourt in the southeastern parts of the offshore Niger Delta.

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

The Benin Formation consists of an alternations\of sands and clays, with only a 30m thick lignite interval, the sand intervals range from 1.4 – 14m thick with a total of 33.9m, the clay horizons range from 1.8 – 8.7m thickness (Nwajide, 2013). Characterized by high sand percentage (70–100%) and friable and consists of white, fine to coarse and pebbly, poorly sorted sands. Lignite occurs as thin streaks or as finely dispersed fragments. Within the formation are thin grayish brown shale bands containing plant fragments.

Lithology Pattern:

Sandstone

Relationships and Distribution

Lower contact

Overlies the Agbada Fm (Niger offshore), or unconformably overlies the Illaro Fm or the Ogwash-Asaba Fm (Dahomey Basin)

Upper contact

Conformable with overlying younger sediments of either recent Alluvial deposits or younger Quaternary sediments. The nature of this contact is typically conformable, reflecting a continuous sedimentation process from the formation's onset to the present day.

Regional extent

Niger Delta offshore and onshore and Dahomey Basin. Offshore, the Benin Formation extends from the ocean bottom with a thickness of about 914 m. It retains its characteristics as a deposit consisting of fine to coarse grained, pebbly, poorly sorted, feldspathic and hematitic quartz sand, interbedded with shales, and occasional lignite streaks.

GeoJSON

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Fossils

Fossil spores, foraminifera, ostracods, mollusc fragments, corals, and fish remains.

Age

Miocene – Recent (transgressive); Oligocene to Recent (diachronous onset); with base put here for display purposes as base-Tortonian (mid-Late Miocene) using the base-Messinian mid-point of the delta-facies transect of Fig.7 in USGS report; but adjusting for the onshore and Dahomey basin ranges.

Age Span:

Beginning stage:

Tortonian

Fraction up in beginning stage:

0.0

Beginning date (Ma):

11.63

Ending stage:

Holocene

Fraction up in the ending stage:

1.0

Ending date (Ma):

0.00

Depositional setting

A continental shallow massive sand sequence. The formation is considered to be completely continental, specifically fluvial (Nwajide, 2013). The Benin Formation is reconstructed as the upper and lower flood (delta) plain setting. Also involved are deltaic, estuarine, lagoonal, and fluvio-lacustrine subenvironments. Although some marine shale breaks have been identified within the formation, the bulk of the sediments were deposited in the upper delta plain as freshwater, backswamp, and meander belt facies

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.