Iguéllala Mountains Fm

The Type Section was taken on the two northern buttes of the Iguéllala Hills (5°50' to 6°45'). Greigert, 1966a.

References: Furon, 1933; Greigert, 1966a; Greigert & Pougnet, 1967; Fabre et al., 1983; Dikouma, 1990; Meister et al., 1992; Alzouma, 1994; Mathey et al., 1995; Moumouni et al., 2019.

Synonym: Iguellala Mountains Fm, *Iguéllala Mounts Fm; "Série des Monts Iguéllala". Equivalent(s): Béréré Fm of Damergou; Zoo Baba Fm and Arentigué Fm of Eastern Niger Basin (Figure)

A calcareous and siliciclastic succession that consists of thinly bedded, gray to yellow, fine to medium, often carbonaceous sandstones, intercalated with gypsiferous gray shales and yellow marly limestones. 25-m thick. A lithological summary of the Type Section is:

• at the top, the Nigericeras limestone;
• micaceous sandstones;
• alternating sands and sandy marls;
• limestones with molluscs, including weathered ammonites;
• sandstones, marls;
• marl and gypsum; at the base, teeth of Coelodus; at the top, Nigericeras, Vascoceras, Paravascoceras, gastropods;
• sandstone with ammonites;
• clays and sandstones ;
• sandstone with ammonites (the same genera as above), sea urchins (Hemiaster, Micropedina);
• sandstone with clastic quartz and calcareous cement, with abundant molluscs with Neolobites vibreyanus;
• clayey salty marls;
• fine sandstone with Exogyra, sandy gray marls with Exogyra and nautiloids.

[Figure. Lithology of the Iguéllala Mountains Fm (central Iullemmeden Basin) and its lithological correlation with the Béréré Fm of the Damergou area (eastern Iullemmeden Basin) and the Zoo Baba Fm of the Eastern Niger Rift basin (Source: Mathey et al., 1995).]

Lamellibranchs, Ammonites (Neolobites, Nigericeras, Acantboceras, Vascoceras, Paravascoceras), echinoids (Hemiaster, Heterodiadema, Cidaris), bivalves (Exogyra olisiponensis) and gastropods.

Marine; T1 & T2 transgressions