MINERALOGY AND GEOCHEMISTRY OF HOT SPRING DEPOSITS IN YELLOWSTONE NATIONAL PARK

It is well established that lithotrophic microbes and the communities that they support contribute significantly to the chemistry of the biosphere. Chemotrophic metabolism, specifically energy production from inorganic chemicals such as hydrogen, reduced iron, and reduced sulfur compounds, is phylogenetically widely distributed among Bacteria and Archaea, and these metabolisms predominate in high-temperature hydrothermal environments where siliceous sinter is deposited while phototrophic metabolism dominate in lower temperature hydrothermal environments. How these microbiological communities contribute to precipitation of siliceous sinter deposits, and how biological signals are preserved remain open questions. To explore possible connections between silica sinter precipitation, biosignature preservation, and microbiological processes, samples of surface and subsurface hydrothermal deposits as well as contextual volcanic bedrock were collected from Yellowstone National Park. Samples were collected from predominantly circum-neutral to alkaline sites in the Lower Geyser Basin, and from predominantly low pH sites in the Norris Geyser Basin. Samples were analyzed by powder X-ray diffraction, X-ray fluorescence spectroscopy, Raman spectroscopy plus thin section and scanning electron microscopy. Maghemite ferric oxide occurs in many of the hot spring samples. Samples from Steep Cone are particularly high in sodium and chlorine, suggestive of accumulation through evaporation of hydrothermal water. Volcanic outcrop sample from the ~ 150 Ka Nez Perce Creek flow of the Central Plateau Member was relatively rich in iron and potassium, as was a surface sample of subsurface hydrothermal deposits exposed as ejecta by a hydrothermal eruption crater near the Fairy Falls trailhead in the Lower Geyser Basin. Raman data show a high kerogen content in siliceous sinter from an extinct hot spring sample, along with clear images of microbial organisms. The diverse biogeochemical profiles along the ‘Bison Pool’ outflow channel (a circum-neutral, boiling hot spring in the Lower Geyser Basin) typify possible extreme conditions on extraterrestrial bodies, and more specifically, may mirror environments present during the deposition of silica at the Home Plate site in Gusev Crater on Mars.