Search

Middle Ordovician formations of the Anti-Atlas ranges of southern Morocco provided a diverse record of trilobites, molluscs, echinoderms, brachiopods, graptolites and micro- and ichnofossils from about 180 fossil localities. These were mainly found during the national geological mapping to the 1:200.000 scale, and most of them remained unreferenced until now. The lithostratigraphic position of all fossil localities is briefly studied showing, in some cases, noteworthy discrepances with previous works. Besides this stratigraphical reappraisal, a review of the fossil record for each formation and locality is done, together with a taxonomical update. From a chronostratigraphical point of view, the whole sucession constituted by the Tachilla Formation and First Bani Group formations are here referred to the Mediterranean regional scale. The Oretanian-Dobrotivian and Dobrotivian-Berounian boundaries are located respectively in the Bou-Zeroual Formation and at the top of the Izegguirene Formation. The transition between the lower and upper Oretanian is provisionally established in the upper third of the Tachilla Formation, and those between the lower and upper Dobrotivian at the base or in the lower part of the Ouine-Inirne Formation. A general correlation with the global standard and British regional scales is also suggested for the Middle Ordovician of the Moroccan Anti-Atlas. The basal limit of the Upper Ordovician series probably lies within the lower part of the Izegguirene Formation. Paleobiogeographical data confirm the interest of this area as an important diversification center for many Mediterranean faunas that underwent remarkable dispersal in northern Gondwanan shelves. [Copyright &y& Elsevier]