Microbial Silicification in Sinters from Two Terrestrial Hot Springs in the Uzon Caldera,Kamchatka, Russia

Silicification of microbial communities is the most pervasive form of mineralization in two terrestrial hot springs in the Uzon Caldera. X-ray diffraction and electron microscopy reveal a diverse sinter mineral assemblage dominated by opal-A with accessory sulfur, sulfides, alunite group minerals, oxides, and oxyhydroxides. Aluminum laminations (reported for the first time) noted in one deposit may slow opal-A transformational rates enabling mineralized microbial remnants to exist longer in the rock record. Although preservation of microbial forms decreases over time, the collective mineral assemblage and patterning suggests that they are the most persistent lines of evidence of life in the geologic record.