Guzhangian (mid Cambrian) trilobites from siliceous concretions of the Valtorres Formation, Iberian Chains, NE Spain

In the carbonate-siliciclastic strata of West Gondwana (e. g. in the Montagne Noire, France), the aftermath of the mid Languedocian (mid Cambrian) regression is characterized by a late Languedocian major turnover of trilobite families and a Furongian-early Tremadocian radiation related to the stepwise immigration of trilobite invaders from East Gondwana under persistent transgressive conditions. The scarcity of upper Languedocian fossil accumulations in clayey substrates has inspired the sampling of the palaeogeographically most distal parts of the Iberian Chains (Spain), where diagenetic dissolution of ubiquitous hexactinellid sponge spicules has favoured the formation of siliceous concretions. These have yielded the trilobites Peronopsis cf. insignis, Oidalagnostus trispinifer, Proampyx difformis (= Proampyx aculeatus), Bailiaspis? glabrata (= Holocephalina agrauloides, by ontogeny), Holasaphus cf. centropyge and a paradoxidid gen. et sp. indet. Despite preservation and sampling biases, the identification of this taphonomic window in offshore clayey substrates of West Gondwana allows the recognition of a strong biogeographical link with Baltica, and the correlation of the global Guzhangian Stage and the Solenopleura? brachymetopa Zone of Scandinavia with part of the Mediterranean upper Languedocian Substage.