Geology of salars in Northern Chile

Abstract

Northern Chile, which includes the extremely arid Atacama Desert and the semiarid Andean Highlands, has more than 100 basins with interior drainage; most contain salars (salt-encrusted playas). The area of interior drainage totals more than 38,000 square miles, within which salars and clay playas extend over a total area of about 2,800 square miles. In addition, hills and valleys in the Atacama Desert are extensively covered either with a thin hard saline crust, chiefly salt-cemented soil, or with a powdery soil that has a high content of saline material, chiefly anhydrite and gypsum.The region has an exceptional variety of types of hard saline crusts that are generally rare in other deserts, and many morphological and structural salt features, some of which may be unique. Soft saline crusts and clay playas, more characteristic of arid regions elsewhere, are also present. Hard salar crusts have formed by deposition of saline material in open water or by capillary migration and evaporation of near-surface ground water. Such crusts generally range from a few inches to several feet in thickness. Locally, crusts may attain thicknesses of several tens of feet, and one salar, Salar Grande, is a basin filled with highpurity rock salt to a local depth of at least 560 feet.Six general types of hard salar crusts are distinguished: (1) layered massive rock salt with a rugged surface, (2) slabby or nodular silty rock salt, (3) rugged gypsum or anhydrite, (4) massive coarsely crystalline rock salt, (5) smooth rock salt, and (6) silty nitrate-bearing saline crust. Soft surfaces or crusts include moist gypsum-bearing crusts, which commonly contain nodules and layers of ulexite in Andean salars, and moist to dry puffy soils and crusts that contain gypsum, thenardite and mirabilite as the principal saline constituents. An unusual chemical feature of the salars and the desert soils of northern Chile is the general paucity of carbonate minerals (for example, trona, calcite, and aragonite) which are widespread in other desert regions.Among the many morphological and s• tructural features that can be recognized in and near salars of northern Chile, the most unusual occur in hard rock-salt crusts, which in themselves are scarce in other arid regions. Included are features due to corrosion of rock-salt crusts by windblown water or free-flowing surface water, such as: ( 1) salt cusps and crenulate margins of salars, (2) salt channels, (3) salt pseudobarchans, and ( 4) salt tubes. Constructional features• in the salars include: ( 1) gypsum buttresses at borders of saline ponds, (2) salt veins, (3) salt stalactites, and (4) salt cones. In some salars, new fresh-water springs have formed steep-walled brine pools in thick rock-salt crusts. Prominent salt cascades and constructional salt terraces have been built up in one Andean valley by springs that are fed by brine from a nearby salar ( Salar de Pedernales).Sag basins and prominent scarps occur along faults that cut through the salt mass of Salar Grande.Of . the 67 closed basins in the An...

Sedimentology and climatic environment of alluvial fans in the martian Saheki crater and a comparison with terrestrial fans in the Atacama Desert

“…Solute-cemented playa deposits are common in the southwestern United States and in the salars of the Atacama Desert. In the Atacama and similar desert settings elsewhere, the segregation of mineral precipitates within the sediments often results in volumetric expansion and small-scale deformation of the surface sediments, resulting in chaotic surface topography at meter to decameter scales (e.g., the ''Devil's Golf Course'' in Death Valley National Park (Hunt et al, 1966;Smoot and Castens-Seidel, 1995) and similar forms in Atacama salars (Stoertz and Ericksen, 1974). The roughness of the Saheki bench surfaces may thus be a combination of chemical cementation, small-scale deformation associated with playa sedimentation, and disturbance by impact gardening.…”

Geology and resources of Salars in the central Andes

“…Most of these features have been described by Stoertz and Ericksen (1974) Recent fault movement has initiated spring activity within several salars, of which one manifestation is formation of "brine pools" in halite crusts.…”

“…(Stoertz and Ericksen, 1974). The largest lakes existed in the Bolivian Altiplano during late Pleistocene (Fig.…”

“…General features of salars in northern Chile were described by Ericksen (1963), Stoertz and Ericksen (1974), Vila (1974), and Chong (1984. Moraga and others (1974) made a detailed study of Salar de Atacama, the largest salar in northern Chile, to evaluate the lithium resources.…”

“…Basins have been tilted, causing migration of lakes and salars towards the depressed sides of the basins (Stoertz and Ericksen, 1974). Such salars tend to show an asymmetrical zoning in which the halite crust is crowded against the depressed side and the sulfate zone towards the upraised side (Fig.…”