A preliminary study of some Sandbian (Upper Ordovician) grapholites from Venezuela
The Lower Sandbian Nemagraptus gracilis Zone comprises one of the most widespread, and easily recognizable graptolite faunas in the Ordovician System. The base of the N. gracilis Zone also marks the base of the Upper Ordovician Series, and is internationally defined by the FAD of the eponymous speci...
| Autores: | , , , |
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| Tipo de recurso: | otro |
| Fecha de publicación: | 2011 |
| País: | España |
| Institución: | Consejo Superior de Investigaciones Científicas (CSIC) |
| Repositorio: | DIGITAL.CSIC. Repositorio Institucional del CSIC |
| OAI Identifier: | oai:digital.csic.es:10261/60947 |
| Acceso en línea: | http://hdl.handle.net/10261/60947 |
| Access Level: | acceso abierto |
| Palabra clave: | Graptolites Ordovician Sandbian South America Venezuela Biogeograph |
| Sumario: | The Lower Sandbian Nemagraptus gracilis Zone comprises one of the most widespread, and easily recognizable graptolite faunas in the Ordovician System. The base of the N. gracilis Zone also marks the base of the Upper Ordovician Series, and is internationally defined by the FAD of the eponymous species, with the Global Stratotype Section and Point (GSSP) located at Fågelsång in Scania, southern Sweden (Bergström et al., 2000, 2009). Finney and Bergström (1986) provide a general account of the widespread record of this biozone in Europe, America, Australasia and China. In South America, graptolites of the N. gracilis are best known from the Argentine Precordillera (Cuyania Terrane), within the Portezuelo del Tontal, Las Aguaditas, Los Azules and Sierra de la Invernada formations in the central Precordillera, in the Yerba Loca Formation of the western Precordillera, and in the La Cantera Formation of the eastern Precordillera (see for example Borrello and Gareca, 1951; Blasco and Ramos, 1976; Brussa, 1996, 1997; Peralta, 1998; Ortega and Albanesi, 1998; Ortega et al., 2008 and references therein). Nemagraptus gracilis Zone faunas are rare in the Central Andean Basin, where single occurrences of only N. gracilis itself have been reported from three localities in Bolivia and Peru (Laubacher, 1974; Brussa et al., 2007). In northern South America, the single known occurrence of Sandbian age graptolites, including possible specimens of Nemagraptus is restricted to the Caparo Formation, which crops out in the southern Mérida Andes of Venezuela, close to its tectonic boundary with the Barinas-Apure basin (Leith, 1938; Pierce et al., 1961; Shell and Creole, 1964). Recent new collecting by some of the authors (JCGM, JR, JG) has provided additional material that confirms the identification of a Sandbian graptolite fauna in the region that can be assigned to the N.gracilis Biozone, a fauna that is described and illustrated for the first time in this part of South America. |
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