Micropalaeontology of a Moroccan Ordovician deposit yielding soft-bodied organisms showing Ediacara-like preservation

A newly discovered locality of an hitherto unknown age, but now estimated t o the Late Ordovician, in south-eastern Morocco has yielded numerous specim ens of problematic soft-bodied metazoans preserved in coarse sandstones. Th e excellent preservation of the recovered specimens permits an improved und erstanding of both the palaeobiology of these Ordovician metazoans and the taphonomic processes associated with them. This style of soft-tissue preser vation is closely comparable to that of the late Neoproterozoic problematic Ediacaran organisms, and is virtually absent in the Phanerozoic. Palynolog ical analysis (chitinozoans and acritarchs) of shaly intercalations in an o phiuroid-bearing sandstone slab facilitates accurate identification of the site as belonging to the Upper Ktaoua Formation and thus a relative dating of the associated fossils. The chitinozoan assemblage is relatively well pr eserved, moderately diverse and closely comparable to the previously descri bed chitinozoan fauna from the Upper Ktaoua Formation (Rawtheyan, late midd le Ashgill age). Acritarchs are abundant but mostly ill-preserved; nonethel ess they clearly indicate an undifferentiated Ashgill age, consistent with the chitinozoan chronostratigraphic result. These datings prove that the ne wly discovered Moroccan metazoan assemblage contains one of the oldest know n paropsonemids, and possibly some of the youngest protolyelloids and aglas pidids. The new finds also show that Ediacara-like coarse-elastic preservat ion did not completely vanish with the onset of the Phanerozoic. (C) Etditi ons scientifiques et medicales Elsevier SAS.