Geographic and Geological settings

Geographic and geological aspects

The Atlas system extends over some 2000 km between the Moroccan Atlantic margin in the West and Tunisia in the East. This system is bound by major lineaments, called South and North Atlas Faults, with adjacent subatlasic depressions and, is subdivided within Morocco in Middle and High Atlas (figure 1).
The Atlas Mountains represent an intracratonic belt and consist of Mesozoic and Cenozoic formations that accumulated in the foreland of the Tell-Rif Thrust Belt during the Alpine/Atlasic Orogeny.
The Middle Atlas is limited to the North by the Saïs plain and the Rif front-thrust, to the NE by the Guercif Basin, to the E and the SE by the Moulouya depressions, and to the W by the Paleozoic massif of Central Morocco (belonging to the Western Moroccan Meseta). It is composed of the juxtaposition of two structural units: the tabular (or the ”Middle Atlas Causse” ; Termier, 1936) and the folded Middle Atlas. These two units are separated by the North-Middle Atlas Fault as a major lineament. The tabular Middle Atlas is a sub-horizontal structure, composed mainly of neritic carbonates of the lower and middle Liassic. It is organized into a tiered plateau reflecting tilted block structures and consists of two sections (northern and southern), separated by the Tizi n’Tretten Fault. The folded Middle Atlas, oriented NE-SW, is composed of large syncline depressions delimited by narrow anticlinal ridges. the syncline depressions are occupied, essentially, by Toarcian and Dogger material. The Cretaceous and the Paleogene are confined to depressions situated to the W of the Boulemane meridian, while Neogene outcrops occur largely to the NE. Anticline ridges form. The hinge of narrow anticlines, generally represented by Liassic carbonates, is often affected by faults and injected with Triassic - Liassic shale and/or intruded by Jurassic/Cretaceous magmatites (Fedan & El Hassani, 2018).

Geological description

Reading the geological map of Sefrou 1: 100.000th(Charrière 1989 : figure 2) and relative documents (i.e. Termier & Dubar, 1940 ; Martin 1981 ; Benshili, 1987 ; Cirac, 1987 ; Charrière, 1984 and 1992 ; Fedan, 1988; Ahmamou 1987) allows us to subdivide the stratigraphic series of this part of the tabular Middle Atlas into four groups (figure 3):
A Paleozoic basement, with Ordovician to the Carboniferous series, in particular a complete Devonian sequences of conglomerates, limestones, reef limestones and carbonate marls (see Aboussalam et al., 2020).
Post-Paleozoic cover were sedimentation generally starts with the upper Triassic clay-evaporite series (gypsiferous argillites and mixed basalts);
After a major unconformity, above the Jurassic series, outcrop north of Sefrou (in the Sais plain and its borders) marly formations that filling the basin (fig. 3) that shows from base to top:
The stratigraphic series close, after an unconformity, by lacustrine limestones of the Sais (middle to upper Pliocene) and finally the Quaternary Formations (travertines, crusts, alluviums, glacis and terraces).