COUPLED PETROGRAPHIC OBSERVATIONS AND RAMAN ANALYSIS OF MICROFOSSILS AND ORGANIC COMPOUNDS FROM ACID-SALINE EVAPORITES: PRELIMINARY RESULTS

Ephemeral acid saline lakes of Western Australia and northern Chile are rare on Earth and have complex chemical processes and products. These two distinctly different geologic settings host similar acid brines and chemical sediments. Recent work on neutral to alkaline halite has identified specific and viable prokaryotes and algae within primary fluid inclusions. Could halite and gypsum precipitated from acid brines also entrap microorganisms? Our preliminary petrographic observations suggest prokaryotes, eukaryotes and organic compounds in fluid and solid inclusions in Lake Magic halite from Western Australia and Salar Gorbea gypsum from Chile.

In January of 2006, chevron and cumulate halite was collected from shallow lake waters of pH 1.7 – 1.9 and salinity as high as 32% TDS at Lake Magic in Western Australia. This halite exhibits at least two types of suspect microorganisms preserved in fluid and solid inclusions along growth bands. Cocci and rod shapes of 1-3 micron diameter are considered suspect prokaryotes. Larger 4-6 micron in diameter yellow spherules are suspected to be eukaryotic microorganisms, such as algae. Yellow eukaryotic suspects exhibit a thin gel layer, indicating possible halophilic and/or acidophilic adaptive traits. Preliminary laser Raman spectroscopic analysis has identified the presence of beta-carotene. We interpret these suspect prokaryotes and eukaryotes as native to the acid brine lake waters.

Bottom-growth gypsum was collected at Salar Gorbea in northern Chile in March of 2007, from shallow lake waters of pH 1.8 – 3.3 and up to 28% TDS. This gypsum contains pennate diatoms as solid inclusions, as well as suspect prokaryotes and algae within fluid inclusions.

This work shows that detailed optical investigations of evaporites can yield important data about microbial communities. While these acid brine lakes are not abundant on Earth, the recognition of extremophiles and the understanding of their fossilization within fluid inclusions have significant implications for life on early Earth and on Mars.