THE PORTEZUELO DEL TONTAL FORMATION: A WIDESPREAD STORM-DOMINATED SILICICLASTIC SHELF OF THE LOWER CARADOCIAN, WESTERN PRECORDILLERA, SAN JUAN PROVINCE, ARGENTINA.

BASILICI, GIORGIO; PERALTA, SILVIO H; FINNEY, STANLEY C.

Belem do Pará

Congreso; 3rd Latinoamerican Congress of Sedimentology; 2003

Asociación Brasilera de Sedimentología

The Portezuelo del Tontal Formation (PTF), about 2000 m thick, is a succession composed of medium-fine grain-sized sandstone, and rare fine conglomerate, alternating with very fine grain-sized sandstone and rare silty argillite. Spalletti et al. (1989) interpreted the PTF as a canyon-fed deep-water fan, recognising channel, channel-lobe and lobe architectural elements. The PTF is part of the Western Precordillera, which belongs to the Cuyana Terrane. This microplate, according to a more recent vision (see Astini, 1998), rifted from the Laurentian Plate in the Early Cambrian and during the Early Ordovician it collided against Western Gondwana margin. In agree with this model the PTF (see synthesis in Bordonaro, 1999) constitutes the external part of the Cuyana passive margin, representing deep-water depositional systems at the distal slope (rise) of the continental margin. In this work the sedimentological, palaeogeographic and geotectonic interpretations of the PTF are revised, producing a new vision on the depositional and geological regional context. We analysed the depositional mechanisms and the architecture of the PTF in two areas: a) at the east of the spring of the Arroyo de la Quebrada de Dom Polo (at the Antena area) and b) at the Portezuelo del Tontal Pass. We used new biostratigraphic and geochronological data to link this unit with the general geotectonic contest. In this work the sedimentological, palaeogeographic and geotectonic interpretations of the PTF are revised, producing a new vision on the depositional and geological regional context. We analysed the depositional mechanisms and the architecture of the PTF in two areas: a) at the east of the spring of the Arroyo de la Quebrada de Dom Polo (at the Antena area) and b) at the Portezuelo del Tontal Pass. We used new biostratigraphic and geochronological data to link this unit with the general geotectonic contest. et al. (1989) interpreted the PTF as a canyon-fed deep-water fan, recognising channel, channel-lobe and lobe architectural elements. The PTF is part of the Western Precordillera, which belongs to the Cuyana Terrane. This microplate, according to a more recent vision (see Astini, 1998), rifted from the Laurentian Plate in the Early Cambrian and during the Early Ordovician it collided against Western Gondwana margin. In agree with this model the PTF (see synthesis in Bordonaro, 1999) constitutes the external part of the Cuyana passive margin, representing deep-water depositional systems at the distal slope (rise) of the continental margin. In this work the sedimentological, palaeogeographic and geotectonic interpretations of the PTF are revised, producing a new vision on the depositional and geological regional context. We analysed the depositional mechanisms and the architecture of the PTF in two areas: a) at the east of the spring of the Arroyo de la Quebrada de Dom Polo (at the Antena area) and b) at the Portezuelo del Tontal Pass. We used new biostratigraphic and geochronological data to link this unit with the general geotectonic contest.