Home Multi-Country Search About Admin Login
Cenozoic
Mesozoic
Late Paleozoic
Early Paleozoic
Neoproterozoic


Information provided by geoscience team at Ahmadu Bello University, Zaria, Nigeria --see About

Search by
Select Region(s) to search
Hold Ctrl (Windows/Linux) or Command (Mac) to select multiple
Zone des Alternances Formation
Click to display on map of the Ancient World at:
Zone des Alternances Fm base reconstruction

Zone des Alternances Fm

Period: 
Ordovician

Age Interval: 
Tremadocian.


Province: 
Ahnet Basin, Mouydir Basin

Type Locality and Naming

SW Algeria. It is present in the GF-3 well (van Dijk et al., 2019).

Synonym:

References: Peron et al., 2019; van Dijk et al., 2019.


Lithology and Thickness

The Zone des Alternances Fm has a maximum thickness of 104m, and it is made up of white to pale grey, fine-grained, silty, quartzitic sandstones with intercalations of black shales which are mainly hard, silty, and micaceous with isometric quartz grains (van Dijk et al., 2019). It is mainly composed of clastic sediments going through fluvial to shallow marine (estuarine to upper shoreface) environments (Peron et al., 2019).


Lithology Pattern: 
Clayey sandstone


Relationships and Distribution

Lower contact

It conformably overlies the Les Gres Des Ajjers Fm.

Upper contact

It is conformably overlain by the Les Argiles d’El Gassi Fm.

Regional extent

SW Algeria. 75,000 Km2


GeoJSON

{"type":"Feature","geometry":{"type":"MultiPolygon","coordinates":[[[[-0.96,26.84],[1.04,27.54],[2.69,28.22],[5,28.22],[5.81,27.21],[5.81,26.5],[5.13,25.47],[4.05,24.96],[3.51,24.55],[2.83,23.98],[2.29,23.89],[1.42,23.98],[0.66,25.06],[0.12,25.88],[-0.96,26.84]]]]}}

Fossils


Age 


Age Span: 

    Beginning stage: 
Tremadocian

    Fraction up in beginning stage: 
0.0

    Beginning date (Ma): 
486.85

    Ending stage: 
Tremadocian

    Fraction up in the ending stage: 
0.3

    Ending date (Ma):  
483.92

Depositional setting

Fluvial to shallow marine (estuarine to upper shoreface) environments (Perron et al., 2019).


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.