HOW TO IDENTIFY BIOGENICITY OF SEDIMENARTY STRUCTURES ON TERRESTRIAL PLANETS – EXAMPLES FROM > 3.7 GA SANDSTONES ON MARS

On Earth, microbial mats on clastic aquatic deposits are very common. Such microbenthos exists since at least 3.48 Ga and constitutes some of the oldest fossils in the rock record. This high age of such fossil life suggests to search for similar structures in equivalent old rocks on other terrestrial planets such as Mars. The Martian > 3.7 Ga Gillespie Lake deposits display centimeter- to meter-scale structures that resemble in macroscopic morphology microbial structures including ‘erosional remnants and pockets,’ ‘mat chips,’ ‘roll-ups,’ ‘desiccation cracks,’ and ‘gas domes.’ The sedimentary-like structures are not distributed at random, but are arranged in spatial associations and temporal successions like microbial mat – related sedimentary structures on Earth. With these observations in hand, follow-up investigations on microfabrics in thin-sections, geochemical analyses on mineral content and the comparison with similar, but abiotic sedimentary structures are suggested. Such investigations, however, require returned samples and a better understanding of the physico-chemical conditions of this Martian environment more than 3.7 Ga ago. Proposed here is a strategy for detecting, identifying, confirming, and differentiating possible microbial mat structures in siliciclastic deposits in future missions to Mars and other planets.