A COMPARISON OF MICROBIAL FOSSILIZATION PROCESSES FROM THREE TERRESTRIAL EVAPORITE SITES

An understanding of terrestrial evaporite microbial biota, their markers and fossilization processes is important for identifying present or past life signatures from terrestrial and extraterrestrial sources such as Mars meteorites and Mars sample return. The three sites, Storrs Lake, San Salvador Island, Bahamas, Mono Lake, California and the Dead Sea, Israel represent marine and nonmarine sites for comparative investigative studies. Variations between the sites can be attributed to salinity, pH, water chemistry, and seasonal temperature changes, all of which can affect microbial abundance, fossilization, mineral formation and ultimately the bulk chemistry of a geological formation. The three sites have varying types of microbial deposits. Storr's Lake, located at sea level, pH 8, salinity averaging 70 g/l. has extensive stromatolitic structures composed of biofilm, rods, filaments, cocci and diatoms. The fossilized organic remains are generally composed of magnesium enriched calcium carbonate. Mono Lake is 2100 meters above sea level, pH and salinity are similar to Storr's Lake, and has well developed tufa structures varying in height from less than 1 meter to over 4 meters. Algae, cyanobacteria, diatoms, and other microbial forms are present and contribute to the formation of tufas and other evaporite deposits. The Dead Sea is 400 m below sea level, pH 6.3 in the upper water mass, salinity averaging 229.9 g/l, and possesses extensive salt deposits with scant evidence of microbial fossilization as large microbially produced carbonate structures such as tufas and stromatolites are absent. Modern investigative tools can identify microbes from all of these environments, but burial and lithification alter the evidence for life. Confirming the presence of fossilized microbes and their signatures from ancient environments as well as future Mars sample return will be difficult The goal of this study is to identify these biomarkers, and test their suitability for identifying extraterrestrial microbial remains.