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Les Gres Des Ajjers Formation
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Les Gres Des Ajjers Fm base reconstruction

Les Gres Des Ajjers Fm

Period: 
Cambrian

Age Interval: 
Paibian – Cambrian Stage 10


Province: 
Reggane Basin, Ahnet Basin, Mouydir Basin

Type Locality and Naming

SW Algeria.

Synonym: Les Grès des Ajjers Fm; Azzel Matti Fm (portions of Ahnet Basin), Amguid Fm (portions of Mouydir Basin). Also known as Unit II (Peron et al., 2018).

References: Peron et al., 2018, 2019

[Figure 1: Map showing the six assessment units (AUs) in the Reggane Basin Province, Algeria (USGS, 2018).]

[Figure 2: Paleozoic litho-stratigraphic, sequence stratigraphy, and tectonic framework of the north peri-Hoggar basins (North African Saharan Platform) (Perron et al., 2020).]

[Figure 3: Geodynamic synthesis and lithostratigraphy of the Central Sahara and the Ouagarta Chain with major tectonic events (Kracha, 2011).]

[Figure 4: Geographical map of the basins of North Africa – showing the Reggane Basin (Carte SONATRACH, Division Exploration, in Akkouche, 2007).]


Lithology and Thickness

It is made up of fluvial sandstones facies, which is equivalent to the unit II in subsurface, but thickness has not been certainly established (Peron et al., 2018, 2019). It is about 43m thick, and it is made up of altered quartzites, sometimes slightly metamorphosed, red to brown, and sometimes greenish colored, medium- to coarse-grained and up to conglomeratic (in some cases), ferruginous and pyritic with glauconitic inclusions, and showing interlayering with grey black, micaceous, silty, and sometimes foliated shales (van Dijk et al., 2019).


Lithology Pattern: 
Sandstone


Relationships and Distribution

Lower contact

Reggane Basin -- non-conformably (?) overlies the Precambrian Basement Complex. Ahnet Basin – unconformable on Les Series Ouallen. Mouydir Basin – unconformable on Les Series Pourpree.

Upper contact

It is conformably overlain by the Les Gres Fm in Reggane Basin, and conformably by the Zone des Alternances Fm in the Ahnet Basin and Mouydir Basin.

Regional extent

SW Algeria. 75,000 Km2


GeoJSON

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Fossils


Age 

Onset is transgressive, and as old as Guzhangian in parts of the basins. Base Paibian used here as average. Top extends to lowermost Tremadocian in Reggane Basin.

Age Span: 

    Beginning stage: 
Paibian

    Fraction up in beginning stage: 
0.0

    Beginning date (Ma): 
497.00

    Ending stage: 
Tremadocian

    Fraction up in the ending stage: 
0.0

    Ending date (Ma):  
486.85

Depositional setting


Depositional pattern:  


Additional Information


Compiler:  

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

Wendt J., Kaufmann B., Belka Z., Korn D (2008): Carboniferous Stratigraphy and Depositional Environments in the Ahnet Mouydir Area (Algerian Sahara). In: Facies. DOI 10.1007/s10347-008-0176-y

Wendt J., Kaufmann B., Belka Z., Klug C. & Lubeseder S. (2006): Sedimentary evolution of a Palaeozoic basin and ridge system: the Middle and Upper Devonian of the Ahnet and Mouydir (Algerian Sahara). Geol. Mag. 143 (3) pp. 269–299. doi:10.1017/S0016756806001737

Derder M, E.M., Henry B., Amenna M., Bayou B., Djellit H., Guemache M. A., Hemmi A. (2009): New structural implications for the central Sahara (Algeria), from the revisited Upper Carboniferous “Hassi Bachir” Formation: Paleomagnetic constraints. Tectonophysics, 463: pp.69–76.

Perron P., Guiraud M., Vennin E., Moretti I., Portier E., L. Le Pourhiet, M. Konaté (2018): Influence of basement heterogeneity on the architecture of low subsidence rate Paleozoic intracratonic basins (Reggane, Ahnet, Mouydir and Illizi basins, Hoggar Massif). Solid Earth, 9: pp.1239-1275.