Geochemistry of Mars and Implications for Organic Carbon Preservation - Observations from Rover Data and Terrestrial Analogs

Curiosity and Perseverance rovers have been exploring ancient river and lake deposits in Gale Crater and Jezero Crater, Mars since 2012 and 2021, respectively. Understanding the geochemistry of these environments at small scales is key to assembling a thorough picture of the habitability of Mars through time. In Chapter 2, I proposed that the formation of certain sulfate minerals in Gale Crater is the result of pyrite oxidation as opposed to evaporation of lake water. This has significant implications for the ancient environment of Gale Crater since these deposits do not represent eras of the ancient lake drying out but rather extended continuity and stability of the aqueous system, which shows greater promise for habitability. Chapters 3-5 studied terrestrial analog sites for geochemical and textural characteristics of rock packages in Jezero crater in order to assess their biosignature preservation potential in the form of organic carbon. In the hyper arid river deposits of the Amargosa River in Death Valley, California, organic carbon persisted in fluvial deposits at low abundance despite oxidizing conditions and saturated sediments, and suggested that ancient river deposits on Mars may retain traces of organics in fine‐grained deposits if they are present during deposition. Comparing concretions found in the lake deposits of Jezero Crater to terrestrial concretions of similar mineralogy and formation mechanism, all three sites of terrestrial concretions contained significant concentrations of organic carbon (up to ~2 wt.%), which suggested that concretions at Jezero Crater reflect local sites of enhanced biosignature preservation potential. In the hypersaline sulfate and carbonate rich deposits of lakes in British Columbia, Canada, organic carbon is correlated with abundance of salt minerals specifically. The samples with the highest organic C content (up to ~23 wt. %) also have high salt content (up to ~75 wt. %). This designates hypersaline lakes as key preservers of organic carbon and salts as the highest priority mineral target for finding organic carbon on Mars. In summary, this PhD demonstrates that detailed analysis of the mineral deposits on Mars at the centimeter to micrometer scale reveal early Mars to be a highly habitable planet.