Polygonal terrain (or simply, polygons) is a common geomorphological feature in arid regions. Polygons with diverse shapes and different sizes ranging from several meters to more than one hundred meters are widespread in playas. Here, we report a new geometric type of polygons in the playas in the western Qaidam Basin on the northern Tibetan Plateau. These polygons are characterized by raised rims that are interlocked with each other, forming irregular boundaries resembling jigsaw puzzle piece-shapes. The average size of these polygons is around 80 m, which is larger than most of the reported polygons in playas elsewhere. While most polygonal terrain in playa environments is bounded by cracks generated by desiccation or thermal contraction, these unusual features are delimited by raised rims likely caused by a chemical weathering process. Thenardite, a dense anhydrous sodium sulfate mineral originally formed in a saline playa, has been weathered and hydrated to form widespread gypsum. As gypsum leads to a larger volume than thenardite during precipitation, we propose that the volume expansion develops the raised rims of polygons as pressure ridges.

多边形地形（或简称为多边形）是干旱地区的常见地貌特征。形状多样，大小从几米到一百多米不等的多边形在海滩中很普遍。在这里，我们报告了位于青藏高原北部的柴达木盆地西部的普拉亚斯地区一种新的几何类型的多边形。这些多边形的特征是彼此互锁的凸起边缘，形成类似于拼图块形状的不规则边界。这些多边形的平均大小约为80 m，这比其他地方的普拉亚斯报告的大多数多边形都大。尽管海滩环境中的大多数多边形地形都受到干燥或热收缩产生的裂缝的限制，但这些不寻常的特征却是由化学风化过程可能引起的凸起边缘所界定的。芒硝是一种最初在盐滩中形成的致密无水硫酸钠矿物，已风化并水合以形成广泛的石膏。由于在降水过程中石膏导致的体积比芒硝更大，因此我们建议体积膨胀将多边形的凸起边缘发展为压力脊。