Biological Origin of Precambrian Banded Iron Formations

• Applicant: Professor Dr. Andreas Kappler
• Subject Area: Palaeontology
• Term: from 2006 to 2012
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 34732933

Banded Iron Formations (BIFs) are Precambrian sedimentary deposits that consist of alternating layers of silica and iron minerals and represent one of the most enigmatic features in the geologic record. Cyanobacterial oxygen is suggested to have caused a chemical oxidation of iron(II) to iron(III), which is followed by the precipitation and deposition of iron minerals. The mechanism responsible for the formation of the earliest BIFs, which were likely precipitated in the absence of molecular oxygen (O2), however, is still unclear. Anoxygenic phototrophic bacteria able to oxidize iron(II) to iron(III) with light as energy source (“photoferrotrophs”) have recently been discovered. The main goal of this project is to evaluate the potential role of these phototrophic iron(II)-oxidizing bacteria in the deposition of Precambrian BIFs by ecophysiological studies with modern bacteria. In the first funding period the rates of phototrophic Fe(II) oxidation were determined under different eco-physiological conditions, the cell-mineral aggregates formed were characterized and the primary mineral precipitates formed by these bacteria were identified leading to the conclusion that these organisms could have been responsible for BIF deposition. Additionally, we suggested ocean water temperature fluctuations as the key trigger responsible for the alternating layering of Si and Fe minerals in BIFs. In the second funding period we intend to determine the dependence of these organisms on biologically important trace metals (Co, Mo, V). From comparison to trace metal dependence in oxygenic photosynthetic microbes (cyanobacteria) and Archean seawater trace metal concentrations (inferred from concentrations in BIFs) we would like to constrain the presence of photoferrotrophs vs cyanobacteria and better understand the potential competition or dominance of one of these organisms vs. the other.

• DFG Programme: Research Grants
• International Connection: Canada
• Participating Person: Professor Dr. Kurt O. Konhauser