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Char Gr

Char Gr

Period: 
Calymmian

Age Interval: 
Late Calymmian


Province: 
Taoudeni Basin

Type Locality and Naming

This formation is mainly in the western portion (e.g., Adrar and Hohd sub-basins) of the Taoudeni Basin, which a vast intracratonic sedimentary basin spanning parts of Mauritania, Mali, Algeria, Burkina Faso and Guinea. The Char Group sediments, only exposed in the northwestern margin of the basin, are mostly developed over the Archaean basement of the Reguibat Shield (Martin-Monge et al. 2016).

Synonym: This group is equivalent to the lower portion of the Souroukoto Gr in the Hodh-Afolle Subbasin.

References: Martin-Monge et al., 2016

[Fig. 1: Location of the Taoudeni Basin Province and the four assessment units defined in the study by Brownfield et al. (2015)]

[Fig. 2: The Taoudeni Basin (Taupin et al., 2017)]

[Fig. 3: Abolag-1 well, R well and Atar Group type section stratigraphy, facies description and correlation in the Taoudeni Basin, and organic richness profile in the Abolag-1 well (Claue,1981; Rooney et al.2009; Trompette,1973; Albert-Villanueva et al. 2016).]

[Fig. 4: Generalized stratigraphy of the Taoudeni Basin in Mauritania. Lithostratigraphic name equivalences are provided for the Adrar, Hank and Hodh depocentres. The major discontinuities are numbered and reference to global glacial and tectonic events is provided. (From Martin-Monge et al. (2016) as modified after Lahondere et al., 2003, 2005]


Lithology and Thickness

The Char Group represents the first of three major fining upwards transgressive cycles. The basal Agueni Formation consists predominantly of coarse to fine grained, thick to very thick bedded (0.8 to 4.0 m), quartz arenites and local accumulations of arkosic sandstones (Taylor and Giles, 2013). The conformably overlying Azougui Formation consists of interbedded mudstone, siltstone, sandstone, and dolostone. The contact is generally identified at the base of the first purple-red mudstone or dolomitic sandstone above the quartzitic sandstones of the Agueni Formation (Taylor and Giles, 2013).


Lithology Pattern: 
Sandstone


Relationships and Distribution

Lower contact

Upper contact

Regional extent

This group is mainly in the western portion (e.g., Adrar-Hohd sub-basin) of the Taoudeni Basin


GeoJSON

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Fossils


Age 

See Hohd Super Gr entry for discussion of age assignments to Neoproterozoic units. The legend to the USGS regional map (Bradley et al., 2015) indicates that the onset of the lowest units begins shortly after 1600 Ma. Temporarily, the onset is arbitrarily set here as 1500 Ma (mid-Calymmian); with its lower Char Gr plus Foum Chor Fm (and regional equivalents) arbitrarily placed as upper Calymmian through lower Ectasian (1500 to 1300 Ma), then the major regional "D2" regional unconformity.

Age Span: 

    Beginning stage: 
Calymmian

    Fraction up in beginning stage: 
0.5

    Beginning date (Ma): 
1,500.00

    Ending stage: 
Calymmian

    Fraction up in the ending stage: 
1.0

    Ending date (Ma):  
1,400.00

Depositional setting

Deposition occur in a shallow-marine environment (Martin-Monge et al., 2016). The Char Group is interpreted as a passive continental margin sequence deposited during a period of rifting of the western margin of the West African Craton (Taylor and Giles, 2013).


Depositional pattern:  


Additional Information


Compiler:  

Enam O. Obiosio, Solomon Joshua Avong and Henry Nasir Suleiman (2024) - Stratigraphic Lexicon compiled from the following publications:

Wenzhe, G. (2009): Hydrocarbon generation conditions and exploration potential of the Taoudeni Basin, Mauritania. Pet. Sci., 6: pp.29-37

Taylor, C. D. and Giles, S. A. (2013): Mineral Potential for Sediment-Hosted Copper Deposits in the Islamic Republic of Mauritania: Phase V, Deliverable 75. U.S. Geological Survey, Reston, Virginia

Martin-Monge, A., Baudino, R., Gairifo-Ferreira, L. M., Tocco, R., Badali, M., Ochoa, M., Haryono, S., Soriano, S., El Hafiz, N., Mez, J. H., Chacon, B., Brisson, I., Grammatico, G., Varade, R., and Abdallah, H. (2016): An unusual Proterozoic petroleum play in Western Africa: the Atar Group carbonates (Taoudeni Basin, Mauritania). In: Sabato Ceraldi, T., Hodgkinson, R. A. & Backe, G. (eds) Petroleum Geoscience of the West Africa Margin. Geological Society, London, Special Publications, 438, http://doi.org/10.1144/SP438.5

Bradley, D. C., Motts, H. A., Horton, J. D., Giles, Stuart, and Taylor, C. D. (2015): Geologic Map of Mauritania (Phase V, Deliverables 51a, 51b, and 51c), Chap. A1 of Taylor, C. D., ed., Second Projet de Renforcement Institutionnel du Sector Minier de la Republique Islamique de Mauritanie (PRISM-II): U.S. Geological Survey Open-File Report 2013-1280-A1, 3 pl., http://dx.doi.org/10.3133/ofr20131280