Oxygen cycle of the Martian atmosphere-regolith system: Delta O-17 of secondary phases in Nakhla and Lafayette

Oxygen isotope fractionations among silicates, carbonates, and sulfate from Nakhla and Lafayette can be used to resolve how multiple oxygen isotope re servoirs formed and evolved on Mars and to gain insight into the environmen t and processes that led to the formation of the SNC carbonates and other s econdary minerals. Carbonates and sulfate from Nakhla and Lafayette carry a n imprint of atmospheric chemistry analogous to that documented on Earth bu t reflect an inhospitable environment where ozone, hydrogen peroxide, and o dd oxygen compounds transferred their signature of atmospheric oxygen isoto pe fractionations to water, ice, and minerals that formed in the regolith a t low temperature. Such an environment would not be conducive to the preser vation of easily oxidized organic compounds. Its existence provides an abio tic, isotopic benchmark. Biotic processes should produce isotopic fractiona tions that lie on a coherent mass fractionation line and not the mass-indep endent fractionation relationships observed in the present study.