Izégouande Fm

Basal arkosic formation of the Izégouandane Gr of the Tim Mersoï Sub-Basin. [See Figure, and those in the Group entry.]

References: Fabre et al., 1983; Kogbe, 1991; Fabre, 2005; Alfidja et al., 2021.

Synonym: Izegouande Fm. Some authors misspell the name as “Izégouandane Fm”. [NOTE: Izégouande is the proper spelling of the formation, while Izégouandane is the appropriate spelling of the Group.].

[Figure. Top: NW-SE cross-section through the town of Somaïr. Center: N-S cross-section going through Arlit. Bottom: West-East cross-section north of Somaïr (Alfidja et al., 2021).]

In the south, the lithology of the Izégouande formation is made up of feldspathic sandstone (arkose) with carbonate cement, sometimes including lenses of mudstone. In the north, it is mainly made up of very coarse sandstones to conglomerate sandstones (Alfidja et al., 2021). [See details and stratigraphic section in Izégouandane Gr ]. The Izégouande deposits are characterized by important thickness variations related to the synsedimentary activation of the N-S (Arlit Fault-Flexure), N30° (Madaouela fault) and N70° (Tin Adrar fault system) fault systems. The maximum thicknesses of the Izégouande Fm decreases from 70 to 30 m, particularly near the Autruche Fault. The lowest thicknesses were ob­served towards the contact zone with the Arlit fault-flexure (less than 20 m). In the Western compartment, the thickness of the Izégouande is beyond 100 m. (Alfidja et al., 2021). Fabre (2005) reports a maximum thickness of 130 m.

Some silicified wood (Dadoxylon rollei)

Fluvial