Giant polygonal anhydrite ridges in the Southern Permian Basin

Giant polygonal anhydrite ridges with diameters of 2−4 km have been identified in the NE margin of the Southern Permian Basin in Poland. The primary ridges reach heights of 80−120 m, and secondary ridges, <40 m in height, subdivide them into smaller cells ∼1 km in diameter. The ridges were up to ∼40% higher before the alteration of gypsum to anhydrite. Both seismic and gravity surveys indicate the presence of similar structures over an area of thousands of square kilometers. Two alternative hypotheses, gypsum diapirism and free water convection, are proposed to explain their formation.