Publication: Conodontos ordovícicos del noroeste de España. Aplicación al modelo de sedimentación de la región limítrofe entre las zonas Asturoccidental-Leonesa y Centroibérica durante el Ordovícico Superior
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1999
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Sociedad Geológica de España
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Abstract
Se presentan las asociaciones de conodontos ordovícicos registradas en las "calizas del Trigal" de la Formación Casaio, en la Formación La Aquiana y en los cantos calcáreos englobados en la Fomración Rozadais, pertenecientes a afloramientos del sinclinorio de Truchas (norte de la Zona Centroibérica) y del sinclinal del Caurel-Peñalba (sur de la Zona Asturoccidental-leonesa). Las formas identificadas son Scabbardella altipes (Henningsmoen), Panderodus gracilis (Branson y Mehl), Amorphognathus ordovicicus Branson y Mehl, Amorphognatus sp., Sagittodontina robusta Knüpfer, Sagittodontina? sp, Icriodella sp. y Hamarodus europaeus (Serpagli), que corresponden a la Biozona de Amorphognathus ordovicicus del Ashgill y se describen e ilustran en el apartado sistemático. En función de estos datos y sus circunstancias estratigráficas, se propone una correlación general de las unidades del Ordovícico Superior de la región, presentándose un nuevo modelo que armoniza el marco geotectónico local con los eventos globales del Ashgill comunes a la región nord-gondwaniense. En este sentido, se considera un influjo glaciomarino para la Formación Rozadais (Hirnantiense), cuyo depósito no sería coetáneo con las unidades calcáreas pre-Hirnantienses (Trigal y La Aquiana)
New palaeontological data from Upper Ordovician formations of NW Spain (Caurel-Peñalba and Truchas synclines) are documented. The "Trigal limestones" of the Casaio Formation, the La Aquiana Formation and calcareous pebbles of the Rozadais Formation have yielded conodont assemblages indicating the Ashgillian Amorphognathus ordovicicus Biozone. Scabbardella altipes (Henningsmoen), Panderodus gracilis (Branson & Mehl), Amorphognathus ordovicicus Branson & Mehl, Amrphognathus sp., Sagittodontina robusta Knüpfer, Sagittodontina? sp., Icriodella sp. and Hamarodus erupaeus (Serpagli) have been identified and described. Stratigraphic correlations between gthe different structural units are discused, as well as the regional context of the Upper Ordovician sedimentation. According to a new model which conciliates the local geotectonic setting with the global paleoclimatic events, the Rozadais Formation underwent a glaciomarine influence during the Hirnantian, and is clearly younger in age that other Ashgill units which consist or include pre-Hirnantian limestones (La Aquiana and Casaio formations).
New palaeontological data from Upper Ordovician formations of NW Spain (Caurel-Peñalba and Truchas synclines) are documented. The "Trigal limestones" of the Casaio Formation, the La Aquiana Formation and calcareous pebbles of the Rozadais Formation have yielded conodont assemblages indicating the Ashgillian Amorphognathus ordovicicus Biozone. Scabbardella altipes (Henningsmoen), Panderodus gracilis (Branson & Mehl), Amorphognathus ordovicicus Branson & Mehl, Amrphognathus sp., Sagittodontina robusta Knüpfer, Sagittodontina? sp., Icriodella sp. and Hamarodus erupaeus (Serpagli) have been identified and described. Stratigraphic correlations between gthe different structural units are discused, as well as the regional context of the Upper Ordovician sedimentation. According to a new model which conciliates the local geotectonic setting with the global paleoclimatic events, the Rozadais Formation underwent a glaciomarine influence during the Hirnantian, and is clearly younger in age that other Ashgill units which consist or include pre-Hirnantian limestones (La Aquiana and Casaio formations).