Mars is considered one of the most likely extraterrestrial planets to harbor  or to have once harbored life. The widespread presence of clay minerals on the Martian surface plays a crucial role in the long-term preservation of microorganisms and microorganism-related biosignatures due to their strong adsorption and protective capabilities. Recent discoveries suggest the possible existence of transient or localized brines on Mars, which may alter the mineralogical composition of sedimentary rocks. However, it remains unclear whether such brine-induced changes affect the ability of clay minerals to preserve organic-walled microfossils. In this study, we simulated six typical Martian brine environments to investigate how different brine compositions influence the preservation of organic-walled microfossils within clay minerals. The results show that while brines do not directly degrade the microfossils, they can significantly accelerate the exposure and potential degradation of organic matter by promoting clay mineral dissolution. Notably, brines rich in ferric sulfate exhibited the strongest dissolution effects, and acidic conditions further enhanced the rate of clay mineral breakdown. This study clarifies the differential impact of various brine chemistries on the preservation potential of microbial fossils on Mars, providing critical theoretical guidance for selecting optimal sampling sites in future Martian exploration and life-detection missions.

Mars; Clay mineral; Brines; Dissolution; Microfossils