CONICET | Buscador de Institutos y Recursos Humanos

The South American Arid Diagonal extends in Argentina from Puna to Patagonia regions. Several dune fields are scattered between the Andes and Pampas ranges, covering plains and plateaus. One of the northernmost dune fields is occupying the tectonic valley known as Bolsón de Fiambalá. White transverse dunes extend from west to east, climbing to the Fiambalá Range. Some outcrops from the surrounding area are useful to understand the evolution of this dune field. At the Chaschuil valley, a profile composed of 4 m of stratified sands and gravels were sampled at Las Lozas. Epiphytes and benthic diatom assemblages suggest a shallow lake located at 3700 m altitude. Many of these brackish/freshwater aerophilous taxa tolerate desiccation periods and salt concentration. The assemblages were dominated by Nitzschia frustulum, Nitzschia linearis, Achnanthes thermalis var. rumrichorum, Epithemia adnata, Pinnularia viridis y Nitzschia capitellata. Limestones from this outcrop gave ages of 32,000±520 and 29,380±410 radiocarbon years BP (Garleff et al. 1993), suggesting the Marine Isotopic Stage 3. The Holocene Interglacial is recorded either at the Chaschuil and Abaucán rivers valleys. Lake deposits at 3000 m altitude gave ages between 6175±70 and 2990±70 radiocarbon years BP (Garleff et al. 1993). The sand of this dune field at the northern part of the Bolsón was supplied by the fanglomerates located to the west, at Medanitos. There is also a significant supply of pumicite, derived from the Cerro Blanco volcanic dome. Aridity increase is recorded from archaeological evidences and confirmed by the discharge records of the Abaucán River during the 1919-1957 interval. Although these sand dunes with a high content in volcanic glass clearly derived from the Andes, other sand dunes from central Argentina derived from the deactivation of the Desaguadero-Curacó system.