Les monticules micritiques sinemuriens sur la transversale de Midelt-Errachidia (Haut Atlas Central, Maroc)

Abstract

In the central High Atlas of Morocco, the Liassic series present different mud-moundtype carbonate buildups, well developed in the Midelt area, towards the boundary between the Lower and the Upper Sinemurian. Near Foum Tillicht, these structures show a real evolution within the Upper Sinemunan interval, from simple small-scale bodies at the base, up to big and complex forms at the top. Their sedimentological and palaeontological features indicate microbolites and sponge buildings developed in deep and open marine conditions, within the subphotic zone, at the lower part of the storm wave interval. These buildups are closely linked to tectonic processes as they grow on the normal synsedimentary faults which affected the central atlasic area during the Lower Liassic period, leading to the breakup of the Early Sinemurian carbonate platform and the induced installation of the Upper Sinemurian subsiding basin. Silting by hemipelagic sediments led to death of buildings. Similar palaeogeographic changes and geodynamic evolution have been recently described from different structures in North Africa, Western Europe and North America.