Fossilised Pioneer Microbialite Communities on Basaltic Substrates at Lake Ashenge (Tigray, Ethiopia): A Model for Ecosystems in Noachian–Hesperian Martian Lakes?

Abstract

Microbial communities are strongly controlled by local nutrient availability, frequently resulting from mineral weathering and erosion. On Earth, basaltic rocks in habitable alkaline lacustrine environments are often initially colonised by ‘pioneer’ communities that induce the precipitation of fine‐scale microbial carbonate ‘coatings’; on Mars, if a biosphere ever emerged in Noachian–Hesperian alkaline lakes, similar microbial carbonate coating precipitates may be expected to develop over mafic volcanic sequences. Identifying and characterising such phenomena in terrestrial settings thus provides critical guidance for distinguishing potential microorganism–basalt interactions in ancient Martian lakeshore sedimentary successions. Herein, we report the micromorphology and geochemistry of post‐Palaeogene pioneer microbial communities preserved within carbonate coatings on basaltic substrates at Lake Ashenge, Tigray, Ethiopia. We show that morphological traces of the pioneer microbial community are primarily associated with microscale dissolution of feldspar and volcanic glass, which presumably released essential elemental nutrients to the community. We propose an astrobiological model for the potential widespread formation and preservation of such carbonate coatings in lacustrine settings on early Mars, highlighting that carbonated mafic igneous rock sequences have already been sampled by the Mars 2020 Perseverance rover, and may be biosignature‐bearing. We emphasise, however, that detecting such subtle microbial biosignatures within these carbonates likely lies beyond the capabilities of rover instrumentation and necessitates advanced analysis in terrestrial laboratories following Mars Sample Return.