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Zone de Passage Formation
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Zone de Passage Fm base reconstruction

Zone de Passage Fm

Period: 
Silurian

Age Interval: 
Gorstian-Pridoli


Province: 
Ahnet Basin, Mouydir Basin

Type Locality and Naming

SW Algeria. Passage between clays below and sands above

Synonym: Transition Beds Fm

Reference:


Lithology and Thickness

The upper part of the “Hot Shales Fm” or ‘Argiles à Graptolites’ is called, in subsurface terminology, the Zone de Passage Fm. This Fm shows a progressive upward enrichment in sandy material (an intercalation of thin sandstone and clay beds), forming coarsening-upward sequences.


Lithology Pattern: 
Clayey sandstone


Relationships and Distribution

Lower contact

Transition downward into the Hot Shales Fm

Upper contact

Truncated at its top by an unconformity (upper Pridoli absent) to the Oued Samene Fm

Regional extent

SW Algeria. 75,000 Km2


GeoJSON

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Fossils


Age 

Gorstian-Pridoli (used here). But in the Ahnet Basin, a regression produced an unconformity with a hiatus that also omitted the middle Pridoli portion.

Age Span: 

    Beginning stage: 
Gorstian

    Fraction up in beginning stage: 
0.0

    Beginning date (Ma): 
426.74

    Ending stage: 
Pridoli

    Fraction up in the ending stage: 
0.5

    Ending date (Ma):  
420.87

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.