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Revista de la Asociación Argentina de Sedimentología
versión impresa ISSN 1853-6360
Resumen
MANASSERO, Marcelo; CINGOLANI, Carlos; CUERDA, Alfredo y ABRE, Paulina. Sedimentología, paleoambiente y procedencia de la Formación Pavón (Ordovícico) del Bloque de San Rafael, Mendoza. Rev. Asoc. Argent. Sedimentol. [online]. 1999, vol.6, n.1-2, pp.75-90. ISSN 1853-6360.
The San Rafael Block lies in west-central Mendoza, and has SSE-NNW structural trends in the southern continuation of the Precordillera (Fig. 1a). To the North and South it is bounded by the Cuyo and Neuquén oil-rich basins, respectively. To the East, the San Rafael Block passes into the Pampean Plains vanishing under the back arc volcanics and modern sedimentary cover; to the West, the boundary is defined by the Frontal Cordillera. Previous studies on the Pavón Formation with respect to regional stratigraphy and structure were carried out recently by the research group (Cuerda & Cingolani, 1998; Cuerda, Cingolani & Manassero, 1998, 1999). The study area comprises the eastern sector of the Cerro Bola close to the main locality of San Rafael within the Mendoza Province (Figs.1b and 1c). This paper gives a bed-by-bed description of the siliciclastic sandy facies of the Pavón Formation (Fig. 1b) with a total thickness of 700 m. It crops out in the central region of the San Rafael Block, and is intruded by rhyolites of the Gondwanic Magmatic Association of Permian-Triassic age (Fig. 2). It also shows a rich graptolite fauna within the black shales and siltstones. The age of the Pavón Formation is Early Caradoc based on the presence of the Climacograptus bicornis Biozone. The following sedimentological features have been recognized within the Pavón Formation: good sorting, sand dominated facies, regular tabular bedding with sharp contacts and abundant graptolites in fine sediments; on the other hand, there are scarce flow and load casts at the base of the beds, and also scarce channels and syndepositional deformation structures (Figs. 3, 4, 5 and 7). All these sedimentological features suggest gravity flows in a relatively deep marine sedimentary environment. Petrographical and geochemical analysis of sandstones (Figs. 9, 10 and 11), and paleocurrent data point to a recycled orogen and/or continental block as a source area to the east of the study region. The development of cleavage, siliceous recrystallization and illite cristallinity data suggest deep burial diagenetic conditions. The proposed depositional model for this unit is that of a turbidite sand-rich ramp (Fig. 12) with the source area located in the region of Ponon Trehue (Fig. 1b). This source area is interpreted to be a relative narrow shelf between an ocean and a granitoid basement quite close to the coast, where substancial volumes of sand were produced.
Palabras clave : Ordovician; San Rafael Block; Sandy gravity flows; Cortical provenance; Anchimetamorfism.