Surface vitrification caused by natural fires in Late Pleistocene wetlands of the Atacama Desert

International audienceWe describe extended occurrences of unusual silicate glass surface layers from the Atacama Desert (Chile). These glasses, found near the town of Pica at four localities separated by up to 70 km, are neither fulgurites, nor volcanic glasses, nor metallurgical slags related to anthropic activity, but show close similarities to other glasses that have been previously attributed to large airbursts created by meteoroids entering the Earth's atmosphere. The glasses are restricted to specific Late Pleistocene terrains: paleo-wetlands and soils rich in organic matter with SiO2-rich plant remains, salts and carbonates. 14C dating and paleomagnetic data indicate that the glasses were formed during at least two distinct periods. This rules out the hypothesis of a single large airburst as the cause of surface melting. Instead, burning of organic-rich soils in dried-out grassy wetlands during climate oscillations between wet and dry periods can account for the formation of the Pica glasses. Large oases did indeed form in the hyperarid Atacama Desert due to elevated groundwater tables and increased surface discharge during the Central Andean Pluvial Event (roughly coeval with the Mystery interval and Younger Dryas). Finally, we discuss the implications of our results for the other surface glasses previously attributed to extraterrestrial events