PALEOBIOLOGY OF THERMOPHILIC MICROBIAL COMMUNITIES PRESERVED IN OPALINE SILICEOUS HYDROTHERMAL SINTER DEPOSITS

This study aims to determine whether evidence of the paleoenvironment of thermal spring ecosystems are preserved in the sinter deposits of Mickey Hot Springs located in southeastern Oregon. The biofabrics and microfossils of sinter deposits at extinct vents were compared to the microbial mats and microorganisms found in active thermal springs. Research at other geothermal fields have shown that the combination of hydrothermal fluids supersaturated with silica and thermophilic microbial communities in the hot springs result in the preservation of biofabrics and microbes as morphological and carbonaceous microfossils. These biosignatures can be seen in the optical light microscope (OLM), transmission electron microscope (TEM), and scanning electron microscope (SEM). The biosignatures can be used to determine the paleoenvironment of an old sinter horizon when there is a correlation between distinct microbial communities (biofacies) and the microbially influenced sinter deposits (lithofacies). The different thermophilic microbial communities are usually dominated by a single taxa whose distribution is constrained to a specific temperature range, making it possible to identify the approximate water temperature of the spring in any one biofacies zone. Furthermore, the morphology of the mats of the microbial community may reflect the relative hydrodynamics of the water (i.e. stationary or flowing), which results in the production of distinct sinter lithofacies if the mat biofabrics are silicified.

Sinter and biological samples were collected, fixed in 2.5% gluteraldehyde in filtered spring water, and prepared in the laboratory for analysis with various microscopy and diffraction techniques. The results of X-ray diffraction (XRD) analyses indicate the primary mineralogy of the deposit is opaline silica. OLM and SEM analyses indicate the presence of microfossils in the recent sinters. Such techniques have also revealed how distinct biofabrics form as a result of similarly orientated silicified filaments. The results of the initial field and laboratory investigation revealed that there are distinct lithofacies around each of the extinct vents. These and additional findings will be compiled and used to reconstruct the paleoenvironment of the extinct vent sites studied.