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

Abstract

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.

Keywords:

• silicification
• bacteria
• Kamchatka
• Uzon
• hot springs

ACKNOWLEDGMENTS

We thank Doug Crowe, Chris Romanek, Andy Neal, and Sherry Cady for their comments. John Shield and Don Roberts assisted with SEM analysis. We would again like to thank Doug Crowe and Gennadii Karpov for permission to use their map in Figure 1. This work was funded by a grant from the National Science Foundation Microbial Observatory Program (NSF MO 0238407) and the University of Georgia, Department of Geology Wheeler-Watts Fund. We thank Kronostky Preserve for permission to work in the Uzon Caldera.

Notes

*Values measured in situ n.d. = not determined.

^†Determined through EDS analysis.

*Determined through XRD analysis.

^† Determined through EDS analysis.

*Determined through XRD analysis.