Evidence for multiple Plio-Pleistocene lake episodes in the hyperarid Atacama Desert

Abstract

20Cosmogenic nuclide exposure dating of ancient shoreline terraces of the Quillagua-Llamara 21 Soledad Lake in the central Atacama Desert of northern Chile provides new insights in the 22 paleohydrology of the driest desert on Earth. The lake developed in a paleo-endorheic drainage 23 system in the Central Depression prior to draining into the Pacific due to incision of the Río Loa 24 canyon. The durations of lake stages were sufficiently long to form wave-erosion induced 25 shoreline terraces on the wind-exposed slopes of former islands. Successively younger shoreline 26 levels are preserved over an elevation range of 250 m due to progressive uplift of the islands 27 coeval with the lake stages. Cosmogenic 10 Be-and 21 Ne-derived exposure ages of the shorelines 28 reveals that the hyperarid conditions in the Rio Loa catchment were interspersed by several 29 pluvial stages during the Pliocene and Pleistocene, which generated a large and persistent lake in 30 the Quillagua-Llamara basin. The exposure ages of the final lake stage provide the maximum age 31 for the incision of the Río Loa canyon (274±74 ka) and the subsequent breaching of the Coastal 32 Cordillera. 33 34 35 36 37 38 39 40 41

Neogene fluvial landscape evolution in the hyperarid core of the Atacama Desert

“…3C ), indicates that the incision of the paleo-channel terminated prior to the incision of the Río Loa (Fig. 5E ) in the Middle/Upper-Pleistocene (post MIS 10) 54 , 55 .…”

The formation of NeH+ in static vacuum mass spectrometers and re-determination of 21Ne/20Ne of air

“…Typically, the measured Ne signal from minerals and rocks is significantly less than the amount of air-Ne used for mass discrimination and sensitivity determinations (e.g. Ritter et al, 2018). A 10-fold decrease in Ne abundance significantly affects the NeH + correction, resulting in an increased 21 Ne/ 20 Ne of up to 0.7% at 70 eV, and 0.15% for 110 eV ( Figure 3B) (see differences in correction techniques outlined in Table 4).…”

“…The improved precision of isotope ratio determinations combined with the lower uncertainty of air 21 Ne/ 20 Ne has implications for studies that require the calculation of the absolute amount of non-atmospheric 21 Ne ( 21 Ne * ), such as cosmogenic exposure dating (Codilean et al, 2008;Ritter et al, 2018) and (U-Th)/Ne geochronology (Gautheron et al, 2006).…”

Historical assembly of Zygophyllaceae in the Atacama Desert

“…Recent evidence suggests that the age of aridity can be dated back to the Miocene or even Oligocene (Dunai et al 2005). However, we still lack a detailed knowledge of the process, since an understanding of the timing of the onset of aridity remains elusive (Ritter et al 2018), and only few studies have addressed the timing of diversifications of Atacama Desert plant groups (e.g., Luebert and Wen 2008, Dillon et al 2009, Heibl and Renner 2012, Böhnert et al 2019.…”