INSUGEO   12554
INSTITUTO SUPERIOR DE CORRELACION GEOLOGICA
Unidad Ejecutora - UE
libros
Título:
Ordovician of the World
Autor/es:
SÁ, A.; GUTIÉRREZ.-MARCO, J.C; PICARRA, J.M.; GARCÍA BELLIDO, D.; VAZ, N., ; ACEÑOLAZA, G.F.
Editorial:
Instituto Geominero de España
Referencias:
Lugar: Madrid; Año: 2011 p. 675
ISSN:
978-84-7840-857-3
Resumen:
The Armorican Quartzite is one of the most characteristic units of the Paleozoic of SW Europe, beingrepresented in the Lower Ordovician succession of Brittany and Normandy (western France), and also overmost of the Hesperian and Iberian massifs of the Iberian Peninsula (in the clarified sense of San José,2006), with the exception of the Ossa-Morena and South-Portuguese zones (Gutiérrez-Marco et al., 2002;Vera, 2004; Ribeiro, 2006). In Portugal and from north to south, the Armorican Quartzite facies isequivalent to the Marão Formation of Trás-os-Montes (Sá et al., 2005), the Santa Justa Formation of theTabagón-Valongo-Tamames domain (Romano and Diggens, 1974), the Armorican Quartzite Formation ofthe Buçaco and Amêndoa-Mação areas (Young, 1988; Romão, 2000a) and the Serra do Brejo Formationin the Dornes area (Cooper, 1980). In spite of the generalized absence of biostratigraphical ties forcorrelation other than ichnofossils and a few chitinozoan or graptolite data, the latter generally comingfrom the overlying shales, the Armorican Quartzite in Portugal have been considered as involving adiachronism in sedimentation from Arenig to Llandeilo, becoming younger from west to east (Ribeiro,1974) according to regional data from the Valongo to Trás-os-Montes areas. These data have beencompiled in some syntheses (Hammann et al., 1982; Romano, 1982; Oliveira et al., 1992). However, thesingle paleontological argument in support of such diachronism, a Llandeilian trilobite found in the middlepart of the Marão Formation at Moncorvo (Teixeira and Rebelo, 1976) was later reviewed by Gutiérrez-Marco et al. (1995), and Sá et al. (2003, 2009), who demonstrated that the supposed trilobite was inreality the trace fossil Rusophycus carleyi (James), also recorded in other Gondwanan areas within theArenigian succession (Seilacher, 1970; Gibb et al., 2010). No other authors were able to demonstrate theclaimed diachronism in the sedimentation of the Armorican Quartzite, whose deposit took place entirely inthe Eremochitina brevis chitinozoan biozone (Paris, 1981, 1990; Paris et al., 1982, 2007), regarded asA.A. Sá, J.C. Gutiérrez-Marco, J.M. Piçarra, D.C. García-Bellido, N. Vaz and G.F. Aceñolaza484“early-mid Arenigian” or as late Floian according to the global scale (Paris et al., 2007; Videt et al., 2010).Romão et al. (2010) recently questioned the current age of the Armorican Quartzite in the southernCentral Iberian Zone, and supported a local late Cambrian age for this formation in the Amêndoa-Carvoeiro synform based in a couple of ichnological data, a single U-Pb dating, and some highlyspeculative tectonostratigraphic inferences which in our opinion are far from being demonstrated. Alsowith reference to this area, Romão et al. (2010) envisaged the Armorican Quartzite as a highly diachroniclate Cambrian to Early Ordovician unit for the Iberian Peninsula. This statement is refuted here with thepresentation of new ichnologic evidence that supports the