Evaporitic constraints on the southward drifting of the western Gondwana margin during Early Cambrian times

Lower Cambrian evaporites and carbonates are reported from nearly all the p latforms of the western Gondwana margin, which comprises the Souss, Ossa-Mo rena, Cantabro-Iberian, Armorican and Montagne Noire-Sardinian Basins. Both lithologies were deposited in climatically restricted belts and their chan ging palaeogeographic distributions, according to recent biostratigraphic c orrelations, are used to infer the latitudinal motion of this margin. As a result, the time span involved in the Cordubian-Ovetian-Marianian interval (8-10 m.y,) requires a relative high rate of drifting, which supports the h igh apparent polar wander path rates (defined by palaeomagnetic data) propo sed for Early Palaeozoic times. The varied and abundant relies of primary t o early dia genetic evaporites (gypsum, anhydrite and halite) demonstrate t hat extensive evaporitic conditions were associated with carbonate and mixe d platform systems in an Early Cambrian arid subtropical belt, Evaporites w ere originally more abundant than suggested by the reported remains because the deposits have undergone a multistep diagenesis that erased most of the former morphologies, Some petrographic criteria are proposed for recognizi ng silica pseudomorphs after evaporites, such as the development of 'chicke n-wire' and enterolithic structures, and the presence of lenticular to loze nge-shaped crystals of gypsum and anhydrite relies. (C) 2000 Elsevier Scien ce B.V. All rights reserved.