CONICET | Buscador de Institutos y Recursos Humanos

The Permian red beds of the De La Cuesta Formation in the Sierra de Narváez (northwestern Argentina) are essentially made up of sandstones associated with mudstones and subordinated conglomerates. Facies distributions and stacking patterns indicate that these sediments result from the interaction between aeolian and ephemeral fluvial systems, represented by aeolian dune, dry aeolian interdune aeolian sand sheet, mudflat, wet aeolian interdune, and fluvial deposits. The De La Cuesta Formation is characterised by aeolian (erg) sequences alternating with non-aeolian (terminal alluvial fan mudflat) sequences. Each erg sequence is limited at the base by a regionally extensive deflationary supersurface and at the top by an extinction surface. A number of architectural elements, such as aeolian dunes limited by interdunes, grouped crescent aeolian dunes, longitudinal dunes, and draa with superimposition of crescent dunes are recognised in the erg sequences. The sand sea developed during phases of increasing aridity, while nonaeolian deposition occurred during more humid phases. Thus, the aeolianfluvial interaction systems are ascribed to cyclical climatic changes. Within the drier hemicycles, the rhythmic alternance between draa deposits, and aeolian dune and interdune deposits indicates higher frequency cycles that could be attributed to subtle climatic oscillations and/or changes in sand supply and availability. The development of the Permian sand sea in the Mediterranean Paganzo Basin seems to be related to the growth of a volcanic chain to the west. This topographic barrier, which was characterised by shallow marine carbonate sedimentation separated the Paganzo Basin from the Chilean Basin, along the western margin of Gondwana. The correlation between the Permian erg and the shallow marine carbonates suggests a regional cooling period during the Middle Permian in western Gondwana.