Sedimentología y evolución del campo de dunas de Médanos Grandes (provincia de San Juan, Argentina)

médanos grandes dunefield, which is located near vallecito city at the southeast of san juan province (argentina), is one of the largest eolian depositional systems in argentina. it is formed by draas together with transversal and longitudinal dunes and large blowouts. alluvial plain deposits related to san juan and bermejo rivers, and the pie de palo and valle fértil hills sourround the eolian system (fig. 1). previous works are very scarce (groeber, 1937; rodríguez, 1966), being regairaz et al. (1987) the ones who described the dunefield as made up of complex dunes. the present study can be divided in three steps. firstly, remote sensing images analysis were carried out to define and describe geomorphic units. secondly, granulometric and compositional studies allowed characterizing the deposits that formed the eolian bedforms. finally, a tentative model of the eolian system evolution is also proposed. the positive relief is formed by two mountain belts, the pie de palo range to the north and the valle fertil one to the east. the former is composed of precambrian-early paleozoic anfibolites, maffic and ultramaffic rocks, migmatites and gneisses (pie de palo complex) and the latter (valle fértil complex) by crystalline rocks as well together with sedimentary rocks of cretaceous and triassic ages. low areas are covered by pleistocene to recent alluvial fan, alluvial plain and eolian sediments (fig. 1). the eolian deposits include sandsheets and dunefields with several kinds of bedforms that predominate at the southwest of the valley. médanos grandes dunefield shows several patterns of dunes and draas of different types, size, spacing and alignment. based on these configurations five geomorphic units have been defined and mapped (figs. 3 and 4). geomorphic unit 1 (ug1), which formed the north part of the dunefield is considered to be the oldest. it is made up of 55-meter tall and up to 2000-meter spacing, transversal draas with superimposed dunes (fig. 5). the draas o