Abstract Polygonal grounds are landscape features commonly associated with periglacial environments originating from freeze-thawing cycles or frost-related processes. However, such a genesis is unlikely for polygonal grounds on alluvial surfaces in the warm and hyper-arid Atacama Desert due to the lack of enduring sub-zero temperatures and limited water availability, whereas a cracking mechanism based on thermal contraction and/or desiccation is more plausible. To differentiate between those mechanisms, we performed a quantitative morphometric terrain characterization in combination with a geochemical and sedimentological analysis on three polygonal networks located in the Yungay area of the Atacama Desert, Chile. Our data show that these sand wedge polygons differ from other polygonal features in the Yungay area such as salt polygons and mud crack polygons from playa environments in regard to composition, morphometry and topographical setting. The investigated polygonal soils are composed of siliciclastic sediment that is mainly cemented by sulfates (gypsum & anhydrite) in the shallow ground (~0–50 cm) and by nitrates and chlorides in the deeper ground (~50–100 cm) while being separated by about 1 m deep, salt-poor and V-shaped sand wedges. The low clay content (~2 wt%) makes an exclusive desiccation origin less relevant whereas the high salt content (63 wt%) and the high surface temperature variations make thermal contraction origin more likely. Morphometric data indicate a link between topography and polygon geometry, as the flat-centered polygons (mean size 3.9 to 4.7 m) are aligned either in slope direction or perpendicular to it, while being more elongated on steeper slopes, which is common to thermal contraction polygons. Although we cannot exclude that desiccation cracking plays a minor role for the formation of the here described polygons, we conclude that their genesis is dominated by thermal contraction.

中文翻译：

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超干旱阿塔卡马沙漠盐固结土壤中的新型沙楔多边形

摘要 多边形地面是通常与源自冻融循环或霜冻相关过程的冰​​缘环境相关的景观特征。然而，由于缺乏持久的零以下温度和有限的水供应，温暖和极度干旱的阿塔卡马沙漠冲积表面上的多边形地面不太可能发生这种成因，而基于热收缩和/或干燥的开裂机制是更合理。为了区分这些机制，我们结合地球化学和沉积学分析对位于智利阿塔卡马沙漠 Yungay 地区的三个多边形网络进行了定量形态测量地形表征。我们的数据显示，这些沙楔多边形在组成、形态测量和地形设置方面不同于 Yungay 地区的其他多边形特征，例如来自 playa 环境的盐多边形和泥裂多边形。所研究的多边形土壤由硅质碎屑沉积物组成，主要由浅层（~0-50 cm）中的硫酸盐（石膏和硬石膏）胶结，深层地层（~50-100 cm）中主要由硝酸盐和氯化物胶结，同时分离约 1 m 深、贫盐和 V 形沙楔。低粘土含量 (~2 wt%) 使唯一的干燥起源不太相关，而高盐含量 (63 wt%) 和高表面温度变化使热收缩起源更有可能。形态测量数据表明地形和多边形几何之间的联系，因为平心多边形（平均尺寸为 3.9 到 4.7 m）在坡度方向或垂直于坡度方向对齐，而在更陡峭的坡度上更细长，这在热收缩多边形中很常见。虽然我们不能排除干燥开裂对这里描述的多边形的形成起次要作用，但我们得出结论，它们的起源主要是热收缩。