MICROBIALITES IN A HIGH-ALTITUDE ANDEAN LAKE: MULTIPLE CONTROLS ON CARBONATE PRECIPITATION AND LAMINA ACCRETION

GOMEZ, F.J.; KAH, L.C.; BARTLEY, J.K.; ASTINI R.A.

PALAIOS

SEPM-SOC SEDIMENTARY GEOLOGY

Año: 2014 vol. 29 p. 233 - 249

0883-1351

ABSTRACT: Microbialites comprise the mineralized record of early life on Earth and preserve a spectrum of fabrics that reflectcomplex physical, chemical, and biological interactions. The relatively rarity of microbialites in modern environments, however,challenges our interpretation of ancient structures. Here we report the occurrence of microbial mats, mineral precipitates, andoncoids in the Laguna Negra, a high-altitude hypersaline Andean lake in Catamarca Province, Argentina. Laguna Negra is aCa-Na-Cl brine where abundant carbonate precipitation takes place. Extreme environmental conditions, including high UVradiation, elevated salinity, and temperature extremes, restrict multicellular life so that mineralization reflects a combination oflocal hydrologic conditions, lake geochemistry, and microbial activity. The resulting carbonates consist of micritic laminae,botryoidal cement fans, and isopachous cement laminae that are strikingly similar to those observed in Proterozoicstromatolites, providing insight into mechanisms of mineralization. Here, increased saturation with respect to carbonateminerals reflects mixing of spring-fed inlets and lake waters, favoring microbialite formation and preservation. This highlightsthe importance of hydrological mixing zones in microbialite 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 LagunaNegra to provide critical insight into biosignature preservation in both terrestrial and extraterrestrial settings.