EVIDENCE FOR BIOMINERALIZATION AND PRESERVATION OF MICROORGANISMS IN SILICEOUS SINTER DEPOSITS FROM THE UZON CALDERA, KAMCHATKA, RUSSIA

Siliceous sinter deposits collected from two high temperature terrestrial hot springs contain evidence of biomineralization and preservation of microorganisms. Bulk geochemical conditions for two fluids vents (designated vents 1 and 2) were characterized with temperatures of 80° and 85° C, pH’s of 5.5, Eh’s –200 to -240 mV and 240 mV, alkalinities of 220 ppm and 160 ppm, sulfide’s of < 0.1 ppm, sulfate’s of 220 ppm and 210 to 350 ppm, phosphate’s of 1.53 ppm and 0.45 to 2.06 ppm, total iron’s 0.01 to 0.09 ppm and 0.03ppm, dissolved silica’s 126 ppm and 139 ppm, and dissolved oxygen of 0.3 ppm and 0.6 to 2.7 ppm, respectively for vents 1 and 2. CO2 gases released from vents 1 and 2 are 28% and 49%, and CH4 is 11% and 25%, respectively. The ratio of CO2/CH4 is 2.5 for vent 1 and 2.0 for vent 2.

Sinter deposits collected contained thin microbial mats, which were preserved in 2% glultaraldhyde to enable scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analysis of mineral-microbe relationships. SEM and EDS studies have revealed silicified segmented and nonsegmented tubes, broken iron oxide shells, and corroded pyrite surfaces. Thin filamentous and rod shaped microbes and diatoms are the dominant organisms. The sinter deposits are dominantly opal-A and elemental sulfur. Thermogravimetric analysis (TGA) reveals elemental sulfur comprises < 3% of the bulk mineralogy. Other mineral phases present include quartz, opal-CT, kaolinite, gypsum, pyrite, and minor calcite. Texturally, the sinter deposits are finely laminated and occasionally display a stromatolitic morphology, which is typical of sinter deposits found worldwide.

Springs with siliceous sinters that appear most geochemically similar to those studied here include those from New Zealand geothermic regions. Major differences however include K, Na, and Si values that are lower than those measured in New Zealand, and Li, Mg, and Mn values that are greater. When compared to Loburu hot springs in the Kenya Rift Valley, Li, SO4, Mg, and Ca concentrations are again greater in the two Uzon springs, along with dissolved Si, which is also greater.

Sinters formed offer an ideal place to study microbial preservation since the first microbes on Earth may have formed in similar high temperature reducing environments.