Sedimentological analysis and radioisotopic age of the Las Cañas Formation in Dulce river outcrops, Río Hondo, Santiago del Estero (Northwestern Argentina)

Abstract

In northwestern Argentina (NWA), particularly at ~27° S, the best known Neogene depocenters are intermountain tectonic valleys located in the Sierras Pampeanas geological province. Conversely, basins located to the east from the Aconquija and Ambato ranges, toward the Chaco-Pampean Plain, have been scarcely studied due to the extensive vegetal coverage. In the last decade, despite some contributions were focused in these areas and reported valuable data concerning tectonic and lithological interpretations, chronostratigraphic data are scarce, even absent so far. Herein we present a sedimentological analysis and an 40Ar/39Ar age of the Dulce River outcrops related to the Neogene Guasayán Range deposits, at the transition between NW Sierras Pampeanas and Chaco-Pampean Plain basin (~27° S). The study area includes Neogene fossiliferous sediments of the Las Cañas Formation; particularly, we focused in a section located between Cañada de la Costa and Sotelo localities (Río Hondo Department, Santiago del Estero Province). The chronostratigraphic study allowed us to assign an early Pliocene age to the studied section of the unit; the first absolute dating obtained for this formation is 3.73 ± 0.07 Ma. The measured stratigraphic logs are ~540 m thick of relatively well-preserved light to reddish-brown clastic deposits. The paleoenvironmental analysis of partial stratigraphic sections suggests the presence of a braided sandy river with well-developed muddy floodplains. We identified two fossiliferous beds below the dated tuff bed, separated by a tuffaceous-sandstone deposit. The new chronostratigraphic datum indicates that the Guasayán Range began to rise during the late Pliocene. Based on the stratigraphy, absolute age, and geographical location of the studied area, a correlation among the Las Cañas Formation, India Muerta Formation (NW Sierras Pampeanas), and the Pozo del Tigre Member, Chaco Formation (Chaco-Pampean Plain) is suggested. This study represents a significant contribution in the context of the scarcely, isolated, and fossiliferous Neogene outcrops of the Tucumán Basin.