Jezero crater, an ancient lake basin that is the landing site of the Mars 2020 Perseverance rover, contains a carbonate-bearing rock unit termed the margin fractured unit. Some of the carbonates in these rocks may have formed in a fluviolacustrine environment and therefore could preserve biosignatures of paleolake-inhabiting lifeforms. Here we evaluate whether these margin fractured unit carbonates formed as authigenic precipitates in a fluviolacustrine environment or via alteration of primary minerals by groundwater. We integrate thermal inertia measurements from the Thermal Emission Imaging System (THEMIS), spectral analyses from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), examination of stratigraphic relationships in Jezero crater using High Resolution Science Experiment (HiRISE) and Context Camera (CTX) images and digital elevation models. We also compare the Jezero crater results to observations from the Curiosity rover in Gale crater. We find that margin fractured bedrock with the deepest visible-to-near-infrared carbonate absorptions also has exceptionally high thermal inertia and thickness relative to other carbonate-bearing units in Jezero crater, consistent with enhanced cementation and crystallization by groundwater. Our results indicate that it is equally likely that carbonates in Jezero crater formed via alteration of primary minerals by alkaline groundwater rather than as authigenic precipitates in a fluviolacustrine environment. Jezero crater may have hosted ancient subsurface habitable environments related to these groundwaters, where life-sustaining redox energy was generated by water-rock interactions. The Mars 2020 Perseverance rover could encounter biosignatures preserved from this carbonate-forming environment, whether it was fluviolacustrine or in the subsurface.

Previous studies have shown that Mt. Sharp has stratigraphic variation in mineralogy that may record a global transition from a climate more conducive to clay mineral formation to one marked by increased sulfate production. To better understand how small-scale observations along the traverse path of NASA’s Curiosity rover might be linked to such large-scale processes, it is necessary to understand the extent to which mineral signatures observed from orbit vary laterally and vertically. This study uses newly processed visible-near infrared CRISM data and corresponding visible images to re-examine the mineralogy of lower Mt. Sharp, map mineral distribution, and evaluate stratigraphic relationships. We demonstrate the presence of darker-toned strata that appears to be throughgoing with spectral signatures of monohydrated sulfate. Strata above and below this zone are lighter-toned and contain polyhydrated sulfate and variable distribution of Fe/Mg clay minerals. Clay minerals are observed at multiple stratigraphic positions; unlike the kieserite zone these units cannot be traced laterally across Mt. Sharp. The kieserite zone appears to be stratigraphically confined, but in most locations the orbital data do not provide sufficient detail to determine whether mineral signatures conform to or cut across stratigraphic boundaries, leaving open the question as to whether the clays and sulfates occur as detrital, primary chemical precipitates, and/or diagenetic phases. Future observations along Curiosity’s traverse will help distinguish between these possibilities. Rover observations of clay-bearing strata in northwest Mt. Sharp may be more reflective of local conditions that could be distinct from those associated with other clay-bearing strata.