Stratigraphie et paleogeographie de l'Ordovicien de l'Anti-Atlas (Maroc): un essai de synthese

Abstract

The Ordovician formations on the south flank of the Anti-Atlas mountains of Morocco extend from the edge of the Guir hamada near Taouz 850 kilometers southwestward to a hamada in the Tarfaya area. The strike, although parallel to that of the axis of the mountains, contrasts with the southeastward strike of tectonic elements of the Sahara shield to the east. The lithology and paleontology of the Ordovician formations indicate an epicontinental sea with a sinking bottom receiving sandy detritus from the shield area. Distribution of facies indicates the presence of two ridges (moles) extending from the northern part of the adjacent sole.

A wave‐dominated, tide‐modulated model for the Lower Ordovician of the Anti‐Atlas, Morocco

“…2C) (Choubert, 1942), which is composed of the Lower Ordovician Fezouata and Zini formations and of the early Middle Ordovician Tachilla Formation. Destombes (1962) was the first to describe the stratigraphic units of the Ordovician series in the central Anti-Atlas. The lower part of the Fezouata Formation (Tremadocian in age; Figs 2C and 3) consists of quartz-rich siltstones.…”

Age calibration of the Lower Ordovician Fezouata Lagerstätte, Morocco

“…In the absence of index fossils, the upper part of the Fezouata Shale and the Zini Sandstone were initially interpreted as Floian, mainly because of their stratigraphical position below the Tachilla Shale (yielding typical Darriwilian faunas), and their coarse lithology suggesting a possible equivalence with the Armorican Sandstones of western France and Spain (Choubert 1951(Choubert , 1952. A Floian age for this part of the succession was later confirmed by the discovery of relatively diverse graptolite assemblages (Destombes 1962(Destombes , 1970(Destombes , 1971Destombes et al 1985). Their biostratigraphical distribution in the Zagora area was finally published by Destombes (2006b), based on preliminary identifications made by S. Willefert.…”

“…As with graptolites, the occurrence of a relatively diverse assemblage of trilobites in the upper part of the Fezouata Shale of the Central Anti-Atlas is known since the early 1960s (Destombes 1962(Destombes , 1967(Destombes , 1970(Destombes , 1971(Destombes , 1972Destombes et al 1985). Vidal (1998aVidal ( , 1998b Toletanaspis borni and Bathycheilus gallicus, originally defined in the Landeyran Formation, were also recorded by Destombes (1972) at his Moroccan locality 983.…”

“…In the eastern part of the Anti-Atlas, the Lower and Upper Fezouata Shale formations are separated by a thin glauconitic and ferruginous horizon (Destombes 1970;Destombes et al 1985). However, in the central part of the Anti-Atlas (Agdz-Zagora area), this marker bed is absent (Destombes et al 1985), and these two formations are thus frequently grouped into a single unit: the Fezouata Shale (Destombes 1962;Martin et al 2016a).…”

“…1;Vidal 1998b;Vaucher et al 2016Vaucher et al , 2017. A Floian age is traditionally assigned to the upper part of the Fezouata Shale, based on its trilobite and graptolite assemblages (Destombes 1962(Destombes , 1967(Destombes , 1971Destombes et al 1985;Vidal 1998a,b). The detailed analysis of chitinozoan assemblages in the Zagora area (Elaouad-Debbaj 1984) suggested a probable late Floian age (Eremochitina brevis Zone) for the uppermost part of the Fezouata Shale and the Zini Formation.…”