Preservation of bacterial microfossils of Fe-oxidizing bacteria during diagenesis of sedimentary deposits, i.e. banded iron formations
Final Report Abstract
Precambrian banded iron formations (BIF) represent the largest iron deposits on the planet. While Fe(II)-oxidizing bacteria (FeOB) have been potentially involved in the formation of banded iron formations, no microfossils related to Fe(II) oxidation have been found so far in the rock record to confirm this hypothesis. The main goal of this project was to evaluate the preservation potential of different types of FeOB under the diagenetic conditions that have occurred in the largest BIF found in South Africa or in Western Australia. As these sedimentary deposits started forming before major chemical changes occurred in the oceans and atmosphere, e.g. before oxygen started to accumulate in the atmosphere, we studied two types of bacteria that would be relevant for BIF formation. The bacterium Acidovorax sp. BoFeNl oxidizes Fe(II) under anoxic conditions, while the bacterium Gallionella oxidizes Fe(II) under microoxic conditions. We studied, as a function of temperature (T) and pressure (P), BoFeNl cells encrusted in Fe minerals and of organo-mineral structures - so-called twisted stalks - produced by Gallionella-like microorganisms. We characterized the evolution of morphology, mineralogy and organic matter content using microscopy and spectroscopy. Our results show that both microbial systems have the potential to be preserved in rocks with a diagenetic history. In particular we defined the temperature-pressure range within which microbial remains can be expected to be preserved, we evaluated the role of Fe in the preservation of the morphology and the organic content of cells or extracellular structures and we determined if Si (at a concentration similar to the Archean ocean) improved the preservation of Fe-encrusted microbial remains. Moreover, we provide spectroscopic signatures that could help to identify such fossils in the rock record.
Publications
- (2015) Experimental diagenesis of organo-mineral structures formed by microaerophilic Fe(II)-oxidizing bacteria. Nature Communications, 6:6277
Picard, A., Kappler, A., Schmid, G., Quaroni, L., Obst, M.
(See online at https://doi.org/10.1038/ncomms7277) - Limited influence of Si on the preservation of Fe mineral‐encrusted microbial cells during experimental diagenesis. Geobiology, Volume14, Issue3, May 2016, Pages 276-292. First publ. 2015
Picard, A., Obst, M. Schmid, G., Zeitvogel, F., Kappler, A.
(See online at https://doi.org/10.1111/gbi.12171)
