Jj. Alvaro et al., Evaporitic constraints on the southward drifting of the western Gondwana margin during Early Cambrian times, PALAEOGEO P, 160(1-2), 2000, pp. 105-122
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.