Outcrop scale evidesnce of late-fluid flows and secondary sulfate minerals on exhumed surfaces – Earth versus Mars comparison

Secondary sulfate minerals are abundant in Gale crater on Mars and in some cases exhibit distinctive morphological features on the exhumed surfaces of sedimentary formations. These are bright-toned sulfate-rich halos and salt accumulations on the eroded bedding planes, but their origin and aqueous processes are still not well understood. To address this knowledge gap, we investigated similar features of sulfate-rich deposits in the Rio Puerco watershed, New Mexico to better understand their formation processes. During five individual months between 2012 and 2024, the studied halo-like features, bedding planes, and pseudo-layers were enriched in various Ca-Mg-Na sulfate minerals such as gypsum, thenardite, bloedite and hexahydrite. These sulfate-rich accumulations were common at the outcrop scale on the exhumed surfaces of sedimentary rocks but in some years, they were also visible on aerial images. Comparisons between the individual wet and dry months suggest that their formation is directly controlled by episodic (ephemeral) water activity related to the semi-arid climate. Episodic flows and infiltration of meteoric water and repeated cycles of redissolution of the already existing sulfate-rich secondary minerals on and near the surface lead to their reprecipitation and distinctive accumulations in halo-like features, bedding planes, and pseudo-layers. We hypothesize that sulfate-rich halos and bedding planes observed in Gale crater on Mars might have been related to the late-stage fluid flows on or within the exhumed surfaces induced by past meteoric water activity under dry conditions.