Dating methods and geomorphic evidence of palaeoenvironmental changes at the eastern margin of the South Peruvian coastal desert (14°30'S) before and during the Little Ice Age

摘要

The Atacama Desert is known to be one of the driest places on earth. However, in the study area between lea and Nasca, South Peru (75-76°W, 14-15°S), palaeoclimate proxies show several semi-arid phases during the Holocene. A more humid period during the early Holocene favoured an open grass land, which allowed the accumulation of desert loess [Eitel, B., Hecht, S., Machtle, B., Schukraft, G., Kadereit, A., Wagner, G., Kromer, B., Unkel, I., Reindel, M., 2005. Geoarchaeological evidence from desert loess in the Nazca-Palpa Region, Southern Peru: palaeoenvironmental changes and their impact on pre-Columbian cultures. Archaeometry, 47, 137-158.]. The Paracas and Nasca cultures existing in that region between the 9th century BC and 7th century AD had propitious conditions to evolve and to settle close to the rivers fed by the monsoonal precipitation in the Cordillera Occidental. Culminating aridity after 600 AD might have caused the collapse of the Nasca civilization. The onset of semi-arid climate towards the end of the Late Intermediate period (～14th century AD), allowed a reoccupation of the area. Here, we present ~(14)C and OSL data from sediments of river terraces, a debris flow and loess snails (Scutalus sp.), indicating appreciable geomorphic activity between 1390 and 1714cal AD. This phase is isochronous to the Little Ice Age period on the northern hemisphere and to an increase in the ice accumulation on the Quelccaya glacier in the Peruvian Altiplano [Thompson, L.G., Mosley-Thompson, E., Bolzan, J.F., Koci, B.R., 1985. A 1500-year record of tropical precipitation in ice cores from the quelccaya ice cap, Peru. Science, 229, 971-973.].