Comment on paper by Ritter et al. (2018), Evidence for multiple Plio-Pleistocene lake episodes in the hyperarid Atacama Desert, published in Quaternary Geochronology: v. 44, p. 1–12. DOI: 10.1016/j.quageo.2017.11.002

Abstract

Abstract Ritter et al. (2018) analyzed the Quaternary history of a purported paleo-lake in the Atacama Desert of northern Chile. They provide a much more thorough analysis than previous publications of the field relationships where there are landform benches surrounding a bedrock knob, Cerro Soledad. They conclude that the benches formed due to shoreline erosion by a paleo-lake while Cerro Soledad rose in elevation due to tectonic activity. Ritter et al. (2018) also used terrestrial cosmogenic nuclide (Neon, Beryllium, and Aluminum) data to determine a history of the landforms, and thus what they conclude is a history of former lake levels and uplift rate. This Comment examines the distribution of mapped geological units, especially Pliocene lake deposits, relative to the locations sampled and described by Ritter et al. (2018). We find that some of the benches sampled for cosmogenic nuclide dating occur on Miocene and Pliocene lacustrine strata, which opens the possibility that clasts were recycled from Miocene-Pliocene lake deposits into the Pleistocene bench clast population. We reach the alternative interpretation that differential resistance to erosion by hillslope processes created most benched forms on the flanks of Cerro Soledad, rather than generation of the benches by shoreline processes. An alternative exhumation scenario which utilizes the cosmogenic exposure ages better explains many of the landforms. In this scenario, the cosmogenic nuclide exposure dates reveal valley-scale denudation in response to tectonic uplift of Cerro Soledad, reduction of valley floor elevation by dissolution of evaporite units, and capture of the valley by the Loa River, rather than shoreline erosion. Irrespective of the alternative interpretation, the exposure history chronological information provided by Ritter et al. (2018) provides new opportunities to examine environmental fluctuations in the central Atacama Desert.