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Precise zircon and monazite ID-TIMS U–Pb dating of three Lower Ordovician altered ash-fall tuff beds (K-bentonites) in the Cantabrian Zone of NW Iberia yielded coeval ages together with an equivalent previously studied sample (477.5 ± 1 (Gutierrez-Alonso et al., 2007)), of 477 ± 1.3 Ma, 477.2 ± 1.1 Ma and 477.3 ± 1 Ma, with a pooled concordia age (all analyses in the four samples) of 477.2 ± 0.74 Ma. A conservative estimation of the volume and mass of the studied K-bentonite beds (using exclusively the CZ data) yields a volume for the preserved deposits of ca. 37.5 km 3 (Volcanic Explosivity Index — VEI = 6, Colossal). When considering other putative equivalent beds in Iberia and neighboring realms (i.e. Armorica, Sardinia) the volume of ejecta associated to this event would make it reach the Supervolcanic–Apocalyptic status (VEI = 8, > 1000 km 3 ). At variance with most known cases of this kind of gigantic eruption events, geological observations indicate that the studied magmatic event was related to continental margin extension and thinning and not to plate convergence. We speculate that a geochronologically equivalent large caldera event recognized in the geological record of NW Iberia could be ground zero of this super-eruption. [ABSTRACT FROM AUTHOR]

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]