Paleoambiental and paleogeographic evolution of the cambrian basin of the Argentine Precordillera

Abstract

The Cambrian rocks of the Argentine Precordillera are analyzed in space and time to arrive at new interpretation of the precordilleran continental margin. The lithostratigraphy and biostratigraphy are incorporated into a nonpalinspastic paleogeographic model that accords with the structural distribution of the Precambrian basement, now exposed in the western Sierras Pampeanas.The lithofacies and biofacies assemblages recognized in all the precordilleran cambrian basins provide evidence to interpretate a rimmed platform. It is posible to distinguish three large areas corresponding to an inner platform, an outer platform and a mixed zone where both platforms interfinger with a rim and talus. In the later Early Cambrian, a mixed open platform was developed above underlying, localized rifting stage with siliciclastics and evaporites of the intracontinental graben system. A faunistic hiatus near the Lower-Middle Cambrian boundary is present in the all Precordillera wich appears to correlate with the Hawke Bay regressive event in the Appalachian area of North America. In the later Middle Cambrian a rimmed platform with lagoon, inner barriers, terrigenous and coastal sabkha facies developed at the eastern, and shoals or barriers were built at the western margin of the shelf, evolving seaward with an open subtidal platform. During the Late Cambrian, a broad peritidal platform prograded to the west, bounded by sand barriers mainly in the southern areas, meantime the northern areas remaining less restricted. Around the Cambrian-Ordovician boundary interval, a new rimmed platform was established but the platform margin retreated to the east as part of a flooding event. A distensive tectonic collapse of the carbonate platform began in the latest Cambrian in the southern areas.