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Djebilet Gr
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Djebilet Gr base reconstruction

Djebilet Gr

Period: 
Devonian

Age Interval: 
Lochkovian - Pragian


Province: 
Tindouf Basin

Type Locality and Naming

Djebilet-Yetti subbasin (exposed on northwest margin of Tindouf Basin)

Synonym:

References: Guerrak, 1989;

[Fig. 1: Geological map of the Tindouf Basin region. (from Guerrak, 1989).]

[Fig. 2: Location of the Tindouf Basin Province, North Africa, and the six assessment units (AUs) (USGS, 2019).]

[Fig. 3: Stratigraphic column of the Tindouf Basin region (Guerrak, 1989).]

[Fig. 4: Stratigraphic correlation of the northern and southern flanks of the Tindouf Basin (Guerrak, 1989).]

[Fig. 5: Stratigraphic column of the study area (redrawn after Guerrak, 1988a).]


Lithology and Thickness

The Djebilet Gr has an estimated thickness of 50-100m, and is made up of siltstones and sandstones with oolitic ironstone capping the entire group (Guerrak, 1989). The Group is made up of two formations: the Upper Djebilet and Lower Djebilet (both are summarized here in this lexicon to avoid linking confusion with "Djebilet").

The Lower Djebilet Fm is characterized by crinoidal limestones at the base, mudstones with fine-grained sandstone layers (0.5 to 1 cm thickness) in the midsection, and lenticular calcareous sandstones with oolitic fragments in the top section (Guerrak, 1983; Ciampalini et al., 2012).

The Upper Djebilet Fm is characterized at the base by alternating mudstones, siltstones and fine-grained sandstones (tabular-planar cross-bedded) that transitions into argillaceous sandstones. The top is characterized by thick oolitic ironstone with wave-form ripple marks that starts at the base with non-magnetic hematitic chamositic ore, magnetic hematitic-chamositic ore in the middle, and non-magnetic hematitic-chamositic ooids with siderite inclusions (Guerrek, 1989).


Lithology Pattern: 
Sandy claystone


Relationships and Distribution

Lower contact

Overlies the Sebkha Mabbes Fm

Upper contact

Overlain by the Oued Talha Gr

Regional extent

Extends throughout southern flanks of the Tindouf Basin, and Djebilet-Yetti subbasin (exposed on northwest margin of Tindouf Basin)


GeoJSON

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Fossils

Lower Djebilet has Crinoids, ostracods, orthoceratidae, and lamellibranchs ; Upper Djebilet has Brachiopods, trace fossils (Skolithos).


Age 

Lochkovian – Pragian (Lower Djebilet as Lochovian; Upper Djebilet as Pragian)

Age Span: 

    Beginning stage: 
Lochkovian

    Fraction up in beginning stage: 
0.00

    Beginning date (Ma): 
419.00

    Ending stage: 
Pragian

    Fraction up in the ending stage: 
1.0

    Ending date (Ma):  
410.51

Depositional setting

Lowe Djebilet is Offshore shelf - wave base – shoreface; Upper Djebilet is Offshore shelf – foreshore – lagoonal depositional environments (Guerrak, 1989)


Depositional pattern:  


Additional Information


Compiler:  

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

Andrea Ciampalini, Francesca Garfagnoli, Benedetta Antonielli, Chiara Del Ventisette & Sandro Moretti (2012) Photo-lithological map of the southern flank of the Tindouf Basin (Western Sahara), Journal of Maps, 8:4, 453-464, DOI: 10.1080/17445647.2012.746947

Guerrak S. (1989): Time and space distribution of Palaeozoic oolitic ironstones in the Tindouf Basin, Algerian Sahara. In: Young, T. P. & Taylor, W. E. G. (eds), 1989: Phanerozoic Ironstones

Geological Society Special Publication 46, pp. 197-212

Guerrak S. (1988a): Geology of the Early Devonian oolitic iron ore of the Gara Djebilet field. Saharan Platform, Algeria. Ore Geology Reviews, (In Press).