Tadrart Fm
Type Locality and Naming
First described by Burollet (1960). A type section was designated by Klitzsch from the Tadrart Mountains (Jebel Tadrart) in Takarkhouri, about 35 km South of Ghat and at the eastern edge of Wadi Wan Kasa in Libya (Fig. 7-115, Fig. 7-116, Fig. 7-117).
References: Plauchut & Faure, 1959; Burollet, 1960; Jacqué, 1963; Freulon, 1964; Klitzsch, 1969; Lababidi et al., 1985; Mergl et al., 2000, 2001; Tawadros, 2011; Shalbak, 2015; Hallett, 2002, 2016.
Synonym: Freulon (1964, p. 107)'s old "Séries du Djado" is synonymous with the combined formations of Tadrat and Wan Kasa.
Lithology and Thickness
At the Type Locality (Fig. 1), it comprises massive continental to marginally marine sandstones, ferruginous, cross-bedded, with plant remains in the lower part and trace fossils in the upper part. In Niger, the Tadrart Formation shows the typical facies of cross-bedded or cross-laminated sands, coarse sandstones and granular to conglomeratic sandstones. Thinly bedded siltstones in the middle of the section display ripple-marks. Thickness is 140 m at the Type Locality.
[Figure 1. Stratigraphic column of the Tadrart Fm at the Type Locality (Source: Shalbak, 2015).]
Relationships and Distribution
Lower contact
A strong erosional disconformity occurs between the Silurian (Akakus Fm) and Devonian. On the eastern side of the Murzuq Basin and the northwest side of the Tibesti high, the formation rests unconformably on Cambrian-Ordovician sediments. The Silurian is absent probably by non-deposition.
Upper contact
The top of the Tadrat Formation is placed between the highest cross-bedded sandstones and the first quartzitic sandstones of the Wan Kasa Fm (Jacqué, 1963).
Regional extent
[Figure 2. Outcrop and subsurface extents of the Tadrart Formation in the Murzuq basin of Libya and into the Djado Basin of Niger (Source: Shalbak, 2015).]
[Figure 3. Devonian outcrops in the Djado of Niger, Libya and Algeria (Freulon, 1964). The map shows the Tadrat Fm and what would later be named the Wan Kasa and Awaynat Wanin formations.]
GeoJSON
Fossils
Leiotriletes payius Allen, Retusotriletes cf. ocellatus MacGregor, Ancyrochitina langei Sommer and van Boekel, Ancyrochitina fragilis var. brevis Taug. and Jekh., etc. In Niger: Frequent plant fragments (psilophyte taxa Arthrostigma and Aneurophyton) and rare trace fossils (Fraena, Palaeophycus, Skolithos, diverse bilobate fucoids, and rare Spirophyton).
Age
Depositional setting
Ranges from subtidal to intertidal and continental at the Type Locality and fluvio-continental in the Djado. The two Lower Devonian formations of Tadrart Fm and Wan Kasa Fm make up a single megacycle of the Lochkovian, Pragian and Emsian ages.
Additional Information