Eolian erosion of polygons in the Atacama Desert as a proxy for hyper-arid environments on Earth and beyond

Abstract

Polygonal networks occur on various terrestrial and extraterrestrial surfaces holding valuable information on the pedological and climatological conditions under which they develop. However, unlike periglacial polygons that are commonly used as an environmental proxy, the information that polygons in the hyper-arid Atacama Desert can provide is little understood. To promote their use as a proxy, we investigated a polygonal network within an inactive channel that exhibits uncommonly diverse surface morphologies and mineral compositions, using geochemical and remote sensing techniques. Our findings show that the polygons belong to a continuous network of the same genetic origin. Their differences result from post-formational differential eolian erosion up to 50 cm depth, exposing indurated subsurface horizons rich in sulfate or nitrate and chloride. Their location in an ancient channel could lead to the misinterpretation of fluvial polygon erosion, however, we find no such signs but evidence for aqueous resurfacing of microtopography by fog and minimal rainwater infiltration. Our findings extend the use of polygons as proxies in the Atacama Desert, indicating saline soils and hyper-arid conditions. We conclude that this example of polygon erosion can guide future polygon research, especially regarding the use of erosional surfaces on Earth and beyond to gain valuable subsurface insights.

Salt Constructs in Paleo-Lake Basins as High-Priority Astrobiology Targets

“…It is notable that differences between the characteristics of intra-salar and extra-salar topographic constructs were commonly observed. The difference in polygonal morphology inside versus outside many salt deposits belies some difference either in the mechanisms of their formation or in erosional processes [79]. Terrestrial ice-related landforms bear resemblance to martian "brain terrain" and the features observed in this study; for example, the "vermicular ridge features" of the Canadian Arctic described by Hibbard et al [80] that form via paraglacial ice ablation.…”

Habitability of Polygonal Soils in the Hyper‐Arid Atacama Desert After a Simulated Rain Experiment

“…In contrast, polygonal networks are a characteristic landscape-scale feature on alluvial surfaces in the Yungay region and display a particular form of more local soil heterogeneities. These fracture networks are characterized by saltpoor sand wedges outlining salt-rich polygons of several meters in diameter, forming extensive hexagonal and orthogonal patterns that have been proposed as environmental proxies for saline soils and hyper-arid conditions (Sager et al, 2021(Sager et al, , 2022. In general, the upper meters of alluvial soils in the Yungay region are classified into locally termed soil horizons that can vary in depth, degree, and type of salt cementation (Ericksen, 1981): The uppermost horizon is the chusca, a non-indurated gypsic horizon, underlain by the costra, an indurated gypsic horizon.…”