The key role of bedrock composition in the formation of carbonates on Mars

Abstract

Martian carbonates are fundamental minerals for understanding the geochemical and climatic evolution of the planet and the search for potential life, representing one of the key objectives for the Perseverance rover at Jezero Crater. However, the scarcity of carbonate reservoirs on the surface compared to the extent of terrestrial carbonates questions whether these carbonates are indicators of past surface conditions or products from deeper processes unrelated to martian climate. We investigate the formation of carbonates by surface weathering under a CO₂ atmosphere in a suite of individual minerals and martian simulants based on the early Mars crust composition. We identify the formation of magnesium carbonates in olivine-bearing samples, but not in the early martian crust simulants. These findings are consistent with the association of carbonates with olivine-rich substrate detected on Mars and highlight the role of the substratum composition in the distribution of carbonates formed by surface processes. Hence, we conclude that the limited surface reservoirs of carbonate are reconcilable with the existence of a CO₂-rich atmosphere on early Mars.