Morphological Typology and Petrography of Plio-Quaternary Continental Carbonates of Aït Chaïb, Skoura Basin, Middle Atlas, Morocco

Abstract

The Plio-Quaternary Ait Chaib basin occupies the northwestern part of the Skoura Syncline, which is part of the northern Middle Atlas Folded Zone. This intracontinental basin was formed probably in the Pliocene after the Tortono-Messinian regression sea. The Plio-Quaternary deposits are bound by fluvial conglomerates and continental carbonates. They consist of barrage travertines; travertine limestones and oncholitic travertine silts and sands of the upstream and downstream deposits. These travertines laterally pass to lacustrine limestones at the bottom of the basin. The genesis of these continental carbonates, correlative to phases of karstification, has affected the Meso-Cenozoic carbonate deposits of the folded Middle Atlas, and is linked to favorable paleo-environmental conditions of geological, geomorphological, hydrogeological, hydrological and bioclimatic order. The petrographic study of these lacustrine limestones shows laminar structure allowing to assimilate into continental stromatolites. They were formed by cyanobacterial mats in a shallow lacustrine environment in which water were was non-turbid and supersaturated in limestone solution, coming from karstic springs staking out the Middle Atlasic North Accident. The important diagenesis evolution is linked to the surface water table contain, which has as a floor gypsiferous lagoonal marl of the Upper Miocene age.