Achegour Fm

Fachi is an oasis surrounded by the Ténéré desert and the dunes of the Erg of Bilma in eastern Niger. Renault, 1953; From the same name area.

References: Renault, 1953; Boureau, 1955; Faure et al., 1956; Furon, 1964; Faure, 1966; Fabre et al., 1983; Meister et al., 1994;

Synonym: Grès d’Achegour; Equivalents: Fachi Fm; Tiffa Fm; Dibella Fm. Analogous in some respects to the sandstone cycles of the Tégama group.

Monotonous sandstone formation that rests on the basement. They were observed from the north of Ezerza to Fazeï, passing through Achegour (all near Fachi). Sandstone of light colors, coarse or fine-grained, with oblique and cross-bedded stratification in large banks; generally tender, these sandstones are often strongly silicified near the faults which break up the outcrops. Traces of plants are scarce. 0 to 700 m thickness. From top to bottom (Faure (1966)):

• 30 m of fine sandstone with ferruginous intercalations.
• 150 m of fine or medium sandstone with cross-bedded stratification compris­ing a level with traces of Vegetation.
• 20 m of coarse or conglomeratic heterogeneous sand, with cross-bedded strati­fication.
• Rubefied unconformity surface with almost no rolled debris of quartz.
• Precambrian basement: slightly metamorphic arkoses and conglomerates.

Traces of plants (Podocarpites saharianum Boureau and imprints of leaves of Dicotyledonous Angiosperms (Laurophyllum and Cinnamomoides)). Abundant fauna of vertebrae (dinosaurs and crocodiles).

Continental

Represents the base of the surface formations in the Bilma basin. It corresponds to the upper part of the "Continental Intercalaire" and makes up the Tégama group in the region.