PRESERVATION OF BIOSIGNATURES IN HALITE AND GYPSUM FROM MARS-ANALOG ACID BRINE LAKES AND ASSOCIATED EOLIAN SEDIMENTS (Invited Presentation)

Numerous recent studies have documented hydrated sulfates and chlorides, commonly in close association with clay minerals, iron oxides, and the acid minerals jarosite and alunite, on Mars. Similar mineral suites on Earth are found in modern acid saline lake systems in Western Australia and in the high Andes of Chile. In addition, ancient acid saline deposits are known from red beds and evaporite strata in the Permo-Triassic and Proterozoic. What can these terrestrial acid saline lake and associated eolian systems teach us about the possibility of life on Mars and the likelihood of preservation of biosignatures in the martian rock record? Plenty, as the rapid growth halite and gypsum from surface brines make them particularly good repositories for bacteria, archaea, and algae, as well as liquids and gases from the environment. Desiccation of lakes and physical reworking of lake sediments by wind leads to eolian grains sourced from lakes that entomb lake biosignatures.

Here, we describe some preliminary results of our ongoing investigation of preservation of biological materials from extreme acid brine environments. Drawing upon transmitted light petrography, UV-vis petrography, laser Raman spectrometry, lipid biomarkers, and metagenomic and metatranscriptomic analyses, we: (1) describe a preliminary inventory of microorganisms and organic compounds in acid saline lake waters, groundwaters, and sediments from Western Australia; (2) present evidence from modern acid halite and gypsum from Western Australia and Chile that microorganisms and organic compounds can be trapped as solid inclusions and within fluid inclusions; and (3) suggest that the preservation of biosignatures in acid halite and gypsum over ancient timescales is possible.

Transmitted light and UV-vis petrography, along with laser Raman spectroscopy, are an important first step in detecting biosignatures in saline minerals. Organic compounds in both halite and gypsum can be identified by their laser Raman signatures. Despite the host gypsum’s strong Raman peaks, high-resolution targeting of micron-scale individual phases within fluid inclusions can identify some organic signatures within Mars-analog saline sediments and sedimentary rocks. These techniques can be used in situ to provide evidence for the presence of biosignatures on Mars.