TIME-SERIES ISOTOPIC AND ELEMENTAL COMPOSITIONS OF MINERALIZED MICROBIALITES WITHIN A HIGH-ALTITUDE ANDEAN LAKE (LAGUNA NEGRA, CATAMARCA PROVINCE, NW ARGENTINA)
Mineralized microbial mats and oncolites within Laguna Negra, a high-altitude (4100 m) hypersaline, closed basin Andean lake in Argentina, preserve a complex alternation of distinct carbonate fabrics—including microbially precipitated micrite, botryoidal features, and distinctly isopachous cement phases—that are interpreted to reflect a combination of physical and biological influence on carbonate nucleation and growth. Detailed preservation of successive, potentially seasonal, laminae, within these microbialites permit the unique opportunity to reconstruct a time-series for both inorganic and organic carbonate phases.
Here we present preliminary findings of our study. Geochemical evolution of Laguna Negra is reconstructed via analysis of oxygen isotopes and trace elemental compositions, and paired isotopic analysis of inorganic and organic carbon is then used to infer the relative effects of evaporation and biotic activity in the evolution of Laguna Negra. Initial data suggests that environmental parameters (derived from C-O isotope covariance and trace element concentration) vary with geographic position within the lake, and that C-isotopes provide a sensitive record of fluctuating environmental conditions. We are currently exploring the potential correlation between geochemical parameters and the discrete microfabrics that may reflect a spectrum of microbial associations. Ultimately, understanding of the relative effects of environmental and biotic parameters on the evolution of lacustrine deposits will enhance out understanding of both paleoenvironmental change and its potential relationship to microbialite mineralization.