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 conformable 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 abundant, 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 enviaged. Two phosphoritic interbeds rich in linguliformean brachiopods punctuate the Valconchán and Borrachón formations, and represent event beds related to condensation processes and sedimentation of explosive ignimbritic tuffs, respectively.
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Álvaro, J. J., Ezzouhairi, H., Ribeiro, M. L., Ramos, J. F. and Solá, T. 2008. Early Ordovician volcanism in the Iberian Chains (NE Spain) and its influence on the preservation of shell concentrations. Bulletin de la Société Géologique de France, 179(6), 569–581.
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Álvaro, J. J., Casas, J. M. and Quesada, C. 2021. Reconstructing the pre-Variscan puzzle of Cambro‒Ordovician basement rocks in the southwestern European margin of Gondwana. In Pannotia to Pangaea: Neoproterozoic and Paleozoic Orogenic Cycles in the Circum-Atlantic Region (Murphy, J. B., Strachan, R. A. and Quesada, C., eds). Geological Society, London, Special Publications, 503, 531‒562.
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Havlíček, V. and Josopait, V. 1972. Articulate brachiopods from the Iberian Chains, northern Spain (Middle Cambrian–Upper Cambrian–Tremadoc). Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen, 140, 328–353.
Josopait, V. 1972. Das Kambrium und das Tremadoc von Ateca (Westliche Iberische Ketten, NE Spanien) (The Cambrian and Tremadocian of Ateca (western Iberian Chains, NE Spain)). Münstersche Forschungen zur Geologie und Palaeontologie, 23, 1–123 (in German).
Kolb, S. and Wolf, R. 1979. Distribution of Cruziana in the Lower Ordovician sequence of Celtiberia (NE Spain) with a revision of the Cruziana rugosa-group. Neues Jahrbuch für Geologie und Paläontologie, Monatshefte, 1979(8), 457–474.
Robison, R. A. and Pantoja-Alor, J. 1968. Tremadocian trilobites from the Nochixtlan Region, Oaxaca, Mexico. Journal of Paleontology, 42(3), 767–800.
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Schmitz, U. 1971. Stratigraphie und Sedimentologie im Kambrium und Tremadoc der Westlichen Iberischen Ketten nördlich Ateca (Zaragoza), NE Spanien (Stratigraphy and sedimentology in the Cambrian and Tremadocian of the western Iberian Chains north of Ateca (Zaragoza), NE Spain). Münstersche Forschungen zur Geologie und Paläontologie, 22, 1–123 (in German).
Shergold, J. H. and Sdzuy, K. 1991. Late Cambrian trilobites from the Iberian Mountains. Zaragoza Province. Spain. Beringeria, 4, 193–235.
Tortello, M. F. 2003. Biostratigraphic significance of the latest Cambrian–earliest Ordovician agnostoid trilobites from Northwestern Argentina. Geologica Acta, 1, 61–72.
Vizcaïno, D. and Álvaro, J. J. 2003. Adequacy of the Early Ordovician trilobite record in the southern Montagne Noire (France): biases for biodiversity documentation. Transactions of the Royal Society of Edinburgh: Earth Sciences, 93, 393–401.
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Zamora, S., Álvaro, J. J. and Vizcaïno, D. 2009. Pelmatozoan echinoderms from the Cambrian–Ordovician transition of the Iberian Chains (NE Spain): early diversification of anchoring strategies. Swiss Journal of Geosciences, 102, 43–55.
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