New occurrences of the Early Ordovician Fezouata ...

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Jul 13, 2018 - Ordovician Konservat-lagerstätte yielding abundant and diverse, fully marine assemblages, comparable in preservation to the numerous ones ...
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5 International Paleontological Congress – Paris, 9 -13 July 2018

New occurrences of the Early Ordovician Fezouata Biota (Morocco): predicted and found 1

Bertrand Lefebvre* , Bernard Pittet 1, Farid Saleh 1, Pierre Sansjofre 2, Muriel Vidal 2, Khadija El Hariri 3 1 Laboratoire de Géologie de Lyon - Terre, Planètes, Environnement (LGL-TPE) – Université Claude Bernard Lyon 1 : UMR5276 – 2, rue Raphaël Dubois, 69622 Villeurbanne Cedex, France 2 Laboratoire Géosciences Océan (LGO) – Université de Brest : UMR6538 – Institut Universitaire Européen de la Mer, rue Dumont d’Urville, 29280 PLOUZANE´, France 3 Département des Sciences de la Terre – Faculté des Sciences et Techniques, Université Cadi-Ayyad, BP 549, 40000 Marrakech, Morocco

The Early Ordovician Fezouata Shale, in the Central Anti-Atlas of Morocco, is the only known Ordovician Konservat-lagerstätte yielding abundant and diverse, fully marine assemblages, comparable in preservation to the numerous ones occurring in Cambrian Series 2 and 3. The Fezouata Biota represents a unique mixture of post-Cambrian organisms (e.g. asterozoans, cirripeds, crinoids, eurypterids, graptolites, ostracods), along with soft-bodied to lightly sclerotised taxa, typical of the Cambrian Explosion (e.g. anomalocaridids, demosponges, lobopodians, marrellomorphs, naraoiids, palaeoscolecids). It thus illustrates a key evolutionary transition during the onset of the Great Ordovician Biodiversification Event. In recent years, both the biostratigraphic distribution and the palaeoenvironmental context of the Fezouata Lagerstätte have been clarified. In the Ternata plain (N. of Zagora), exceptional preservation appears to be restricted to two stratigraphic intervals (i.e. within the late Tremadocian A. murrayi Biozone and the middle Floian ?B. jacksoni Biozone), and also to a narrow range of palaeoenvironmental conditions (i.e. distalmost, storm-influenced zone of the lower shoreface). Based on the northward prograding trend evidenced for Lower Ordovician deposits in the Zagora area, investigations for new occurrences of the Fezouata Biota were carried out recently. As expected, new levels with exceptional preservation were found both in slightly older deposits (late Tremadocian) occurring in a palaeogeographically more proximal setting (about 20 km southward), and in younger deposits (late Floian) in a more distal context (about 70 km northward). These preliminary results confirm the close link between exceptional preservation and associated environmental conditions, and the predictive role that the recognition of sedimentary constraints can play for new paleontological discoveries. In the Central Anti-Atlas, the occurrence of diachronous Lagerstätten offers an unique opportunity to describe several successive exceptionally preserved assemblages spanning the late Tremadocian–late Floian time interval.

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