Microbial carbonates in high-altitude Andean lakes of Catamarca (Argentina): multiple controls in carbonate precipitation and lamina accretion

Microbialites comprise the mineralized record of early life on Earth and preserve a spectrum of fabrics that reflect complex physical, chemical, and biological interactions. The relatively rarity of microbialites in modern environments, however, challenges our interpretation of ancient structures. In this talk I report the occurrence of microbial mats, mineral precipitates, and oncoids in the Laguna Negra, a high-altitude hypersaline Andean lake in Catamarca Province, Argentina. Laguna Negra is a Ca-Na-Cl brine where abundant carbonate precipitation takes place. Extreme environmental conditions, including high UV-radiation, salinity, and temperature extremes, restrict multicellular life so that mineralization reflects a combination of local hydrologic conditions, lake geochemistry, and microbial activity. Stable isotope data (C-O-S) also suggest the combined effect of biological and physical-chemical processes in the recorded isotopic signature. The resulting carbonate consist of micritic laminae, botryoidal cement fans and isopachous cement laminae that are strikingly similar to those observed in Proterozoic stromatolites, providing insight into potential mechanisms of mineralization. Here, increased saturation with respect to carbonate minerals reflects mixing of spring-fed inlets and lake waters favors microbialite formation and preservation. This highlights the importance of hydrological mixing zones in microbialites formation and as taphonomic windows to record microbial activity. Recent discoveries of minerals related to evaporating playa-lake systems on Mars further highlights the potential of Laguna Negra to provide critical insight into biosignature preservation in both terrestrial and extraterrestrial settings.