Biosignature preservation in stromatolites from the Carri Laufquen Lakes System, Patagonia: implications for Martian palaeolacustrine environments

The Carri Laufquen Lakes System is a highly alkaline, basalt-hosted lacustrine environment in northern Patagonia, Argentina. Diverse morphologies of Late Pleistocene sub-fossil stromatolites occur along the lakeshores. Using detailed optical and electron microscopy, spectroscopy and organic geochemical analyses, this study shows that stromatolite growth and early diagenetic processes were strongly influenced by microbially controlled organomineralisation. Mineralisation of extracellular polymeric substances and cyanobacterial sheaths promoted early lithification and exceptional preservation of stromatolite fabrics and biosignatures. Organic matter is closely associated with Al–bearing silicate minerals at the micro–nanoscale, enhancing fossilisation potential and preserving biogeochemical signatures. The resulting mineral assemblage in the Carri Laufquen stromatolites, dominated by Mg-carbonate with minor Al-silicates and carbonaceous material, resembles the geochemistry of ancient lacustrine deposits around the margins of Jezero crater, highlighting the propensity of such deposits for biosignature preservation, and providing a framework for detailed characterisation of such materials following Mars Sample Return.