Ordovician on the move: geology and paleontology of the “Túnel Ordovícico del Fabar” (Cantabrian free highway A–8, N Spain)

• Juan Carlos Gutiérrez Marco ^[1] ; Enrique Bernárdez ^[1] ; Isabel Rábano ^[2] ; Graciela N. Sarmiento ^[1] ; María C. Sendino ^[1] ; Roberto Albani ^[3] ; Grabriella Bagnoli ^[3]
  1. [1] Universidad Complutense de Madrid

     Universidad Complutense de Madrid

     Madrid, España

     
  2. [2] Instituto Geológico y Minero de España

     Instituto Geológico y Minero de España

     Madrid, España

     
  3. [3] University of Pisa

     University of Pisa

     Pisa, Italia

     

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• Localización: Serie correlación geológica, ISSN-e 1666-9479, ISSN 1514-4186, Vol. 17, Nº. 1, 2003
• Idioma: inglés
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• Resumen

  • The Ordovician succession of the Cantabrian Zone (northwestern Spain) is very incomplete and sparsely fossiliferous, especially in comparison with to other areas in the Hesperian (or Iberian) Massif. Lower to lower Middle Ordovician rocks overlie the Cambrian succession in apparent conformity, but with a probable basal gap. In most areas of the Cantabrian Zone, younger Ordovician rocks do not exist and Arenigian sandstones (Armorican Quartzite facies of the Barrios Formation) are paraconformably overlain by Silurian, Upper Devonian or Lower Carboniferous rocks. The only record of post–Arenigian sediments eastwards of the Asturian Central Coal Basin is at the Laviana nappe, where upper Oretanian to lower Dobrotivian fossiliferous shales have been recently reviewed by Gutiérrez–Marco et al., (1996, 1999). However, detailed knowledge of the Ordovician biostratigraphy of this area is severely limited by the absence of continuous sections, resulting from the softer rocks being differentially eroded and almost invariably covered.

    The recent construction of a superhighway along the Asturian coast (Autovía del Cantábrico, A–8) opened a temporary window that provided the opportunity to study these usually unexposed shale units and interbeds, which comprise the Cambrian–Ordovician successions of the Laviana and Rioseco nappes. The excavation of El Fabar tunnel near Berbes provided complete, continuous, fresh exposure of the stratigraphy in the tunnel walls and also in the talus along the highway south of Torre before it was subjected to hydrosowing (Figure 1). These continuous and remarkably fossiliferous Ordovician sections provided substantial stratigraphic and paleontological data that previously unavailable. Study of the tunnel section followed the daily rhythm of excavation. The important scientific discoveries and the model of collaboration between Science and Industry, i.e., between the construction engineers and crews and the scientists, has been the subject of several recent articles in newspapers and magazines and of radio broadcasts. As a result of this publicity and scientific importance, the tunnel was officially renamed "Túnel Ordovícico del Fabar" (Ordovician tunnel of El Fabar), and an exhibition of fossils of Asturian tunnel is being prepared with financial support from the Spanish Government. FCC Construcción S.A., the company that built the tunnel and adjacent highway segments between 1998 and 2002, published a book that describes this unique and initially quixotic experience and the scientific discoveries in the tunnel.