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Iridets Formation
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Iridets Fm base reconstruction

Iridets Fm

Period: 
Carboniferous

Age Interval: 
Tournaisian.


Province: 
Ahnet Basin, Mouydir Basin

Type Locality and Naming

It is exposed west of Gara Azel Matti. Its Type Localities are Iridet et Tahtania and Iridet el Fourkania, and its Tyle Section is located in Anou Tirechchoumine where its maximum thickness is 170m (Wendt et al., 2009). Conrad (1973) coined the term Dalle (=bed) des Iridet for an excellent calcareous marker bed between the underlying Tibaradine Fm and the overlying Gres de Kreb ed Douro Fm or the Argilles de Tirechoumine Fm.

Synonym: Formation des Iridet

References: Conrad, 1973; Wendt et al., 2009


Lithology and Thickness

Formation des Iridet Fm is represented by a 170-m-thick sequence of dark shales with several intercalated, 0.2–1 m thick, limestone levels. In Jebel Mouima, Iridet Fm is reduced to a single 1-m-thick layer of skeletal limestone, with maximum thickness of 170m (Wendt et al., 2009).


Lithology Pattern: 
Shallow-marine marl


Relationships and Distribution

Lower contact

It conformably overlies the Tibaradine Fm.

Upper contact

It is conformably overlain by the Argilles de Tirechoumine Fm.

Regional extent

75,000 Km2


GeoJSON

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Fossils

ammonoids, orthoconic (up to 0.5 m long) and coiled nautiloids, gastropods, brachiopods, bryozoans, solitary rugose corals, tabulates (Michelinia and others), crinoid stems and foraminifers (Wendt et al., 2009).


Age 


Age Span: 

    Beginning stage: 
Tournaisian

    Fraction up in beginning stage: 
0.9

    Beginning date (Ma): 
347.99

    Ending stage: 
Tournaisian

    Fraction up in the ending stage: 
1.0

    Ending date (Ma):  
346.73

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.