Geochemical time-series analysis and reconstruction of environmental fluctuations from mineralized microbialites of a high-altitude, hypersaline Andean lake (Laguna Negra, Catamarca Province, NW Argentina)

BUONGIORNO, JOY; KAH, L.C.; GOMEZ, F.J.

Bergen

Congreso; Biosignatures Across Time and Space; 2014

Nordic Network of Astrobiology and the Centre of Geobiology at the University of Bergen

Geochemical time-series analysis and reconstruction of environmental fluctuations from mineralized microbialites of a high-altitude, hypersaline Andean lake (Laguna Negra, Catamarca Province, NW Argentina) Buongiorno, Joy1, Kah, Linda C.1 and Gomez, Fernando J.2 1University of Tennessee, Knoxville, United States 2LAC-Laboratorio de Analisis de Cuencas, CICTERRA-Centro de Investigaciones en Ciencias de la Tierra, FFEFyN, Universidad Nacional de Cordoba, Cordoba, Argentina Environmental fluctuations, including those related to climate, hydrological balance, and biological productivity, are preserved, in part, by carbonate deposits within lacustrine systems. With the recent discovery of putative ancient lacustrine environments on Mars [1], efforts continue to understand both habitability of extreme environments as well as the potential preservation of physical and chemical biosignatures. To adequately distinguish between biogenic and abiogenic signatures, however, and to understand the roles of biotic and abiotic parameters in biosignature preservation necessitates examination of terrestrial analogues sensitive to changes across the biogenic/abiogenic spectrum. Hydrologically closed-basin lakes are amongst the most sensitive systems, exhibiting dramatic responses to shifts in both abiotic and biotic parameters. Therefore, the sediments within these terminal lacustrine systems have great potential for permitting detailed reconstruction of environmental conditions via geochemical and isotopic proxy data. Mineralized microbial mats and microbialites within Laguna Negra, a high-altitude (4100 m a.s.l.) hypersaline, closed-basin Andean lake in Argentina, preserve a complex alternation of distinct carbonate fabrics, including biogenic micrite, botryoidal textures, and distinct isopachous abiotic cement phases, the combination of which reflect complex physical and biological influences on carbonate nucleation and growth as related to fabric evolution [2]. Detailed preservation of successive--potentially seasonal--laminae within these microbialites affords the unique opportunity for paleoenvironmental reconstruction of fluctuations through time-wise analysis of both inorganic and organic phases. Here, we present the findings of our on-going study. Geochemical evolution of Laguna Negra is reconstructed through multi-proxy analysis, including oxygen isotopes and trace elemental compositions. Paired isotopic analysis of inorganic and organic carbon is used to infer relative effects of evaporation and biotic activity throughout the evolution of Laguna Negra. Carbon and oxygen isotope covariance and trace element concentrations suggest that environmental parameters responsible for geochemical signals show spatial variability within the lake. A reliable record of changing hydrological conditions is provided by carbon isotopes, with extreme 13C enrichment up to > 18 ? (vs. VPDB), which may be the heaviest naturally-occurring isotopic composition within the published carbonate record. We are currently exploring the potential correlation between discrete microfabrics and their associated geochemical signatures to understand the spectrum of microbial influence on textures. Ultimately, elucidation of the relative effects of environmental and biotic parameters on the evolution of lacustrine deposits will enhance our understanding and interpretive ability of the viability of harsh extraterrestrial environments.