Abstract
Geomorphological studies have been carried out in rapidly evolving salt caves related to small watersheds in the San Pedro de Atacama area, Chile. Radiocarbon ages of bones and wood from cave deposits, combined with the presence of large salt caves, geomorphological and sedimentological observations, and the results of micrometer measurements outside and in some of the caves, suggest a period of speleogenesis in the Cordillera de la Sal during the onset of the Holocene, during which the large halite cave systems developed, followed by an early Holocene hyperarid period. Most smaller caves (i.e. Lechuza del Campanario) most probably formed at the start of the wetter mid-Holocene period (5–4.4 ka), when precipitation was never intense enough to entrain large amounts of sediments, but enough to trigger cave development. A diamicton in Lechuza del Campanario Cave radiocarbon dated at ca. 4.4 ka shows that at least one high intensity rainfall event occurred in this recharge basin during the mid-Holocene wet interval. A wet period with lower intensity rainfall events followed between 4.0 and 2.5 ka, causing the 4.4 kyrs old diamicton in Lechuza del Campanario Cave to be entrenched, and the alluvial fan at the downstream end of Palacio del Sal Cave to be covered with windborne sediments dated by OSL at around 3.6 ka. At ca. 2 ka there was a high-intensity rainfall event documented by the age of a twig stuck in the ceiling of the Palacio del Sal Cave, followed by a period with lower intensity rain events until ca. 1.3 ka, when another intense flood produced a mudflow that deposited a second diamicton in Lechuza del Campanario Cave. From then on clustering of radiocarbon ages for wood and bone recovered from caves indicates increased rainfall intensity in the period ca. 0.9–0.5 ka, followed by no registered events until a minor flood at ca. 0.13 ka. The four-centuries long wetter time interval (0.9–0.5 ka), corresponding to the Medieval Climate Anomaly, has been an archeologically important period in the Atacama Desert (Tiwanaku culture).The observations and a detailed review of paleoclimate literature from this key area have allowed the development of a landscape evolution model related to changing climate conditions during the Late Holocene.
Highlights
The Atacama Desert, and especially the area around the Salar de Atacama (23°S, 68°10′ W, ca. 2500 m asl, Chile) is among the driest places on Earth, with mean annual rainfall below 25 mm (Houston and Hartley, 2003; De Waele and Forti, 2010)
We explored the effects of different climate regimes on landscape evolution, as recorded by the salt cave systems of the Cordillera de la Sal during the Holocene
Bones and twigs brought into the caves by flood events in Cueva Lechuza del Campanario and in the Palacio del Sal, Chulacao, and fossil Chulacao caves were photographed, their locations noted, and cemented samples were extracted using a hammer
Summary
The Atacama Desert, and especially the area around the Salar de Atacama (23°S, 68°10′ W, ca. 2500 m asl, Chile) is among the driest places on Earth, with mean annual rainfall below 25 mm (Houston and Hartley, 2003; De Waele and Forti, 2010). The marked aridity started well before the onset of the Quaternary This aridity was interrupted by wetter periods (Placzek et al, 2010), mostly during cooler intervals of the Quaternary for the Altiplano (Jungers et al, 2013), but hyperaridity appears to have been dominant during the last 3 Myr (Hartley and Chong, 2002). The presence of the Rutland cell in the western Pacific, which brings cold water close to the coast (Humboldt Current) creating a temperature inversion that inhibits the transport of Pacific moisture eastward over the continent, and 3) the rain shadow effect of the Andes mountain chains. Three factors are considered responsible for the arid climate (Houston, 2006; Garreaud et al, 2009): 1) the latitude, where permanent subtropical highs prevail such as the SE-Pacific anticyclone; 2)
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