The formation of gypsum ridges in the endorheic Qaidam Basin and implications for irregular polygonal ridges on Mars

Gypsum ridges, positive-relief landforms composed of nearly pure (~96%) gypsum megacrysts, are uniquely found in the Qaidam Basin on the northern Tibetan Plateau, a recognized terrestrial analog of Martian basins. Here, we investigate the distribution, morphology, and mineralogy of these ridges in the basin, and find that their formation involves gypsum deposition along interior fractures of salt domes, followed by exhumation into ridge forms through wind erosion. We propose that the deposition of gypsum resulted from the mixing of oxidized, surface fluids rich in SO 4 2− and subsurface brines enriched in Ca 2+ through a deep biogeochemical sulfate removal process. Comparison of these terrestrial ridges with irregular polygonal ridges on Mars (e.g., in Nili Fossae) reveals notable morphological similarities in their longitudinal and cross-sectional profiles. Our findings highlight the role of subsurface fluids in ridge formation and suggest that these ridge systems are high-priority targets for exploring subsurface fluids and their potential indication of the deep biosphere on Mars. • Qaidam gypsum ridges are morphologically analogous to Martian irregular polygonal ridges. • Ridges are formed from gypsum infilling of the pre-existing fractures. • Gypsum ridges deposit due to the mixing of the SO 4 2− -rich surface brine and Ca 2+ -rich subsurface brine. • Wind erosion subsequently exhumes gypsum-filled fractures into ridges. • Martian irregular polygonal ridges maybe an indication of astrobiologically significant subsurface brine reservoir.