TERRESTRIAL ANALOGS FOR MARS EVAPORITES: MICROBIAL FOSSILIZATION IN MONO LAKE, CALIFORNIA, A NONMARINE EVAPORITE LAKE

Mono Lake is an alkaline, nonmarine hypersaline lake located in eastern California on the western margin of the Great Basin. The lake is 2100 m in elevation, has an average pH of 10, but varies in salinity from 51.3 g/l to 99.4 g/l. A Phillips XL30 environmental electron microscope (ESEM) and a JEOL 6340F field emission scanning electron microscope (FE-SEM) equipped with an IXRF energy dispersive X-ray spectrometer (EDS) are used to analyze benthic, microbial remains from evaporite waters less than 2 meters in depth.

Sand, clay, and silt sized detrital and evaporite minerals were found to contain poorly fossilized filaments, cocci, rod-shaped organisms and biofilms. Filaments, varying in with from 1.7 to 7 microns and lengths extending to 50 microns, are the most common while rods and cocci are less common. Cocci, range from 503 nm to 5 microns, and primarily occur in clumps associated with thin, but sparse biofilm deposits. Thicker, more extensive biofilms occur in association with putative fossilized cocci. The fossilized cocci are approximately the same size as those found in clumps and unfossilized. Rods appear to be rare and are approximately 5 microns in length.

Anions and cations from the collecting sites, listed in descending order are: sulfate, chloride, fluoride and sodium, potassium, magnesium or calcium. The ion concentration shows minimal variation between sites, with the exception of calcium, which ranged from less than .1 mg/l to 53 mg/l.

In comparing our initial investigations with our data from the Dead Sea, it appears the biofilm development is limited and microbial fossilization is uncommon in both sites. These investigations are important baseline studies for potential microbial signatures in Mars rocks.