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The role of purple sulphur bacteria in carbonate precipitation of modern and possibly Early Precambrian stromatolites

Type of publication Peer-reviewed
Publikationsform Original article (peer-reviewed)
Publication date 2011
Author Warthmann R. Vasconcelos C. Bittermann A.G. and McKenzie J.A.,
Project Using New Geochemical and Nanotechnological Approach to Study Biomineralization in Microbiolites
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Original article (peer-reviewed)

Journal Lecture Notes in Earth Sciences
Volume (Issue) 131
Page(s) 141 - 149
Title of proceedings Lecture Notes in Earth Sciences
DOI DOI 10.1007/978-3-642-10415-2_9

Abstract

Carbonate mineral formation in stromatolites and laminated microbial mats is still a subject of debate. Laminated structures found in sedimentary rocks of the Warrawoona Group, Western Australia (3.5 Ga) provide evidence of very early microbially-mediated carbonate layers. However, the microbial impact on the formation can rarely be proven since fossilized organisms and geochemical traces are missing. Recent studies performed in an environmental setting considered to be an analogue for the Archean could supply new evidence of participation of specific microorganisms, regarded as “living fossils”. Anoxygenic photosynthetic sulfur bacteria are considered to be one of the oldest forms of life and are abundantly present today in microbial mats from the hypersaline lagoon Lagoa Vermelha, Brazil. Studies on recent living and calcifying stromatolites, artificial anaerobic microbial mats and pure culture experiments show that purple sulfur bacteria may play an important role in the calcification process. By their assimilation of CO2, these microbes oxidize H2S to elemental sulfur, which was probably one of the earliest anoxygenic phototrophic reactions. The associated pH gradients formed in the biofilm can lead to carbonate precipitation as observed experimentally in artificial stromatolites. Today modern proteobacteria do the same reactions as their ancestors in the Precambrian, producing carbonate layers as a fossil. In summary, even before the evolution of oxygenic photosynthesis, anaerobic sulfur bacteria may have contributed to the formation of biologically-mediated carbonates resulting in the well-known carbonate laminae found in fossil microbial mats and stromatolites.
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