Advances in the Lower Ordovician of the western Iberian Chain, NE Spain

The western Iberian Chain of NE Spain represents a lateral prolongation of the West Asturian-Leonese Zone. As other proximal sectors fringing NW Gondwana, the chain comprises a con -formable and continuous Furongian-Tremadocian transition, comprising a thick (3600-4500 m) Lower Ordovician sedimentary succession, exclusively composed of siliciclastic strata and deposited in mid-latitude (temperate) waters. Although the shelly fossil record is not abun - dant, some key trilobites and brachiopods allow the identification of distinct biogeographic links with the Argentinian margin of West Gondwana, Oaxaca (Mexico), and the neighbouring Montagne Noire (France), with which a common biostratigraphic biozonation can be en vis - aged. Two phosphoritic interbeds rich in linguliformean brachiopods punctuate the Valconchan and Borrachon formations, and represent event beds related to condensation processes and sedimentation of explosive ignimbritic tuffs, respectively.