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

1Pierrick Roperch, 2Jérôme Gattacceca, 3Millarca Valenzuela, 2Bertrand Devouard, 4Jean-Pierre Lorand, 5Cesar Arriagada, 2Pierre Rochette,6,7Claudio Latorre, 8Pierre Beck
Earth and Planetary Science Letters 469, 15-26 Link to Article [http://doi.org/10.1016/j.epsl.2017.04.009]
1Géosciences Rennes, CNRS–INSU, Université de Rennes 1, Rennes, France
2CNRS, Aix Marseille Univ., IRD, Coll France, CEREGE, Aix-en-Provence, France
3Instituto de Astrofísica, P. Universidad Católica de Chile, Av. Vicuña Mackenna 4860, Santiago, Chile
4Laboratoire de Planétologie et Géodynamique, CNRS UMR 6112, Université de Nantes, 2 Rue la Houssinière, 44322, Nantes, France
5Departamento de Geología, Facultad de Ciencas Físicas y Matemáticas, Universidad de Chile, Plaza Ercilla 803, Santiago, Chile
6Centro UC del Desierto de Atacama and Departamento de Ecología, Pontificia Universidad Católica de Chile, Alameda 340, Santiago, Chile
7Institute of Ecology & Biodiversity (IEB), Santiago, Chile
8Institut de Planétologie et d’Astrophysique de Grenoble (IPAG), 414, Rue de la Piscine, Domaine Universitaire, 38400 St-Martin d’Hères, France
Copyright Elsevier

We 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.

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