Evolución paleoambiental de la transición glacial - postglacial en la Formación Agua Colorada (Carbonífero, Sierra de Narváez, Noroeste Argentino).

LIMARINO, C.O.; SPALLETTI, L.A. & COLOMBO PIÑOL, F.

Andean Geology

Servicio Nacional de Geología y Minería

Lugar: Santiago; Año: 2010 vol. 37 p. 121 - 143

0718-7092

ABSTRACT The Carboniferous sequences outcroping in the central part of the Sierra de Narváez, Las Angostura area, are described in this paper. From the regional point of view two major Carboniferous sequences have been identified. Firstly, diamictites, conglomerates, sandstones, carbonaceous mudstones and thin coal beds that were included in the Agua Colorada Formation. A second group comprises monotonous sequences of shales and interstratified mudstones and sandstones which were excluded from the Agua Colorada Formation and identified with the informal name of “Marine Late Paleozoic rocks”. Sedimentological characteristics of the Agua Colorada Formation allow recognizing eight facies associations in the Angostura area: 1. monomictic diamictites, 2. polimictic diamictites and conglomerates, 3. coarsening upward shale-sandstone cycles, 4. dark shales, 5. greenish monomictic conglomerates, 6. channalized polimictic conglomerates, 7 coarse grained sandstones, shales and thin coal beds and 8. mudstones and fine grained sandstones. Facies associations 1 and 2, including both massive and resedimented diamictites, are interpreted as related to the well known  Namurian gondwanic glacial event in western basins of Argentina. Facies associations 3, 4 and 5 record the evolution of a fjord environment formed as a consequence of a postglacial transgression (the so-called Namurian postglacial transgression) that flooded glacial valleys in the major part of the Paganzo Basin. Fjord environment was sharply replaced by fluvial sedimentation (facies associations 6 and 7). The base of facies association 6 is marked by a regional incision surface that represents a regional relative sea level fall. Facies association 8 corresponds to the reestablishment of marginal marine conditions towards the uppermost stratigraphic leves.                  Finally, a regional correlation model based on key stratigraphic surfaces and particular types of deposits is proposed among the Sistema del Famatina, Precordillera and Sierras Pampeanas.