CONICET | Buscador de Institutos y Recursos Humanos

The Tres Cruces basin presents an excellent record of deposits linked to the evolution of the foreland in the context of the Andean orogeny in the Eastern Cordillera, Central Andes. The Cenozoic synorogenic deposits are represented by Casa Grande, Río Grande, and Pisungo formations with thicknesses up to 5000 m. The detailed sedimentological and paleoenvironmental analysis on the north-central sector of the Tres Cruces basin allowed the recognition of an unconformity over post-rift Salta Group, marked by the progradation of an ephemeral fluvial system (Casa Grande Formation) over the Lumbrera Formation during the middle Eocene. The establishment of a meandering fluvial system with flow directions to the east, and an increase of lithic content versus quartz content, support the idea of a distal orogenic front uplifting to the west. During the late Oligocene, an erosive unconformity and the change to a braided fluvial system characterize the Río Grande Formation, where the coarsening-upwards arrangement, paleocurrents with a distributary pattern, and the increase of volcanic fonts are related to the approach of the orogenic front. From the late Miocene, Pisungo Formation deposits are restricted to local syncline depressions, characterized by diffuse geometries and boulder clast size with a rotation of the paleocurrent directions, indicating the development of local highs and the low capacity of river systems. Our analyses suggest an environmental progradation from meandering to braided and later to an alluvial fan fluvial system linked with a change from distal to proximal foreland between Casa Grande and Río Grande formations, to an intermontane system in Pisungo Formation. These results provide an adequate temporal framework for the study of environmental and landscape evolution of Eastern Cordillera and have direct implications for the local and regional development of the Andean orogenesis.