Tectofacies ordovícicas y evolución de la cuenca eopaleozoica de la precordillera Argentina

Abstract

After a typical passive margin setting during the Cambrian, two basically different tectofacies evolved simultaneously and mostly independently during the Ordovician in the Argentinean Precordillera basin. The eastern domain characterizes epicontinental depositional systems developed on a stable margin, while the western domain is composed of deep-sea turbiditic systems which developed on a high subsidence «cuasioceanic» substratum. The two domains were set aside during the Ocloyic movements and later tectonic phases of the Caledonic cycle. A regional unconformity developed by upwarping of the former platform (eastern domain) conforms the downlaping surface of the Late Ordovician and Silurian siliciclastic shallow marine sequences. This regional doming is interpreted as a peripheral bulge in an incipient foreland basin caused by a type A subduction to the present west. This hypothesis is quite different from former ones and solves most of the stratigraphic and architectural problems during the Ordovician and Silurian Silurian and Devonian depocenters are mainly localized on the eastern domain and conform a succession of shallow marine sequences, which commonly characterize forelands. The different unconformities affecting the Silurian and Devonian deposits are interpreted as basin relaxation periods and as global sea-level oscillations. The Late Devonian Chanic diastrophysm involved an important shortening (definitive annexation of the two domains) and caused the main paleogeographic rearrangement, supported by the regional angular unconformity which separates the Lower Palaeozoic from the Upper Palaeozoic continental deposits.