Biotic and Abiotic Signatures in Sulfate- and Carbonate-Rich Hypersaline Lakes as Analogs for Mars

Abstract

Lacustrine sulfate- and carbonate-rich deposits have been detected at Jezero and Gale craters on Mars. The preservation of potential biosignatures in these sites may depend on the nature of precipitated salts and the early diagenetic history of in situ minerals. In this study, we explore a collection of Mars analog hypersaline depositional environments in British Columbia. Magnesium salts and other sulfate and carbonate salts precipitate from the variable water chemistry of Atlin Playa and a suite of lakes on the Cariboo Plateau. Authigenic and detrital grains were distinguished on the basis of their microscale morphology revealed by scanning electron microscopy. Authigenic minerals display distinct textures such as globular or prismatic clumps or delicately preserved cement that envelops angular, detrital grains. However, microscale authigenic textures become rare below the sediment–water interface due to early diagenetic dissolution and reprecipitation of salts during wet–dry cycles in the lakes. Such early diagenetic overprinting of salts could pose problems for identifying primary environments and any potential biosignatures they might have preserved in 3–4 billion-year-old rocks on Mars. The δ¹³C of organic matter and δ³⁴S of sulfate salts are reflective of source materials instead of diagenesis. Total organic carbon content is a function of the abundance of salt minerals, with a well-defined maximum in organic carbon content at an optimum salt content. Our findings demonstrate hypersaline lakes as key preservers of organic carbon and salts as a high-priority mineral target for finding organic carbon on Mars.