Geological Magazine

Original Articles

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

J. JAVIER ÁLVAROa1 c1, SAMUEL ZAMORAa2, DANIEL VIZCAÏNOa3 and PER AHLBERGa4

a1 Centre of Astrobiology (CSIC/INTA), Ctra. de Torrejón a Ajalvir km 4, 28850 Torrejón de Ardoz, Spain

a2 Department of Palaeontology, The Natural History Museum, Cromwell Road, London SW7 5BD, UK

a3 7 Jean-Baptiste Chardin, Maquens, 11090 Carcassonne, France

a4 Division of Geology, Department of Earth and Ecosystem Sciences, Lund University, Sölvegatan 12, 223 62 Lund, Sweden

Abstract

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.

(Received June 28 2011)

(Accepted May 23 2012)

(Online publication July 19 2012)

Keywords:

  • taphonomy;
  • biogeography;
  • Languedocian;
  • Baltica;
  • Gondwana

Correspondence:

c1 Author for correspondence: alvarobjj@cab.inta-csic.es

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