Hydrothermal Fossilization of Microorganisms at the Earth's Surface in Iceland

The fossilization of biota and formation of low- and high-temperature hydrothermally altered rocks were studied in solfataric fields, artificial hot lakes, at natural hot springs, and on heated beach within the present-day rift zone at the Reykjanes, Nesjavellir, Geysir, Landmannalaugar, Namafjall, and Oxarfjodur geothermal areas. The hydrothermally altered rocks can be divided into the following mineral types: (1) smectite assemblage with iron oxides and hydroxides; (2) smectite assemblage with sulfides (pyrite); (3) kaolinite-metahalloysite assemblage with sulfates, anatase, and boehmite; and (4) siliceous assemblage. The detailed study of the hydrothermally altered rocks allowed us to elucidate some environmental features of modern fossilization and replacement of organic matter with clay minerals, iron oxyhydroxides, and silica. The fossilized microstructures have been described in rocks of the smectite and siliceous assemblages. It has been shown that the pseudobiomorphic (actually, abiogenic) micro- and nannostructures are formed in the moving water of silica deposition zone.