Sedimentology (2013) 60, 1733–1754 doi: 10.1111/sed.12051 Microbiological processes in banded iron formation deposition NICOLE R. POSTH*1 , KURT O. KONHAUSER† and ANDREAS KAPPLER* *Center for Applied Geosciences, University of Tuebingen, 72076, Tuebingen, Germany (E-mail:
[email protected]) †Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2E3 ABSTRACT Banded iron formations have been studied for decades, particularly regard- ing their potential as archives of the Precambrian environment. In spite of this effort, the mechanism of their deposition and, specifically, the role that microbes played in the precipitation of banded iron formation minerals, remains unresolved. Evidence of an anoxic Earth with only localized oxic areas until the Great Oxidation Event ca 2Á45 to 2Á32 Ga makes the investi- gation of O2-independent mechanisms for banded iron formation deposition relevant. Recent studies have explored the long-standing proposition that Archean banded iron formations may have been formed, and diagenetically modified, by anaerobic microbial metabolisms. These efforts encompass a wide array of approaches including isotope, ecophysiological and phylog- eny studies, molecular and mineral marker analysis, and sedimentological reconstructions. Herein, the current theories of microbial processes in banded iron formation mineral deposition with particular regard to the mechanisms of chemical sedimentation and post-depositional alteration are described. The main findings of recent years are summarized and compared here, and suggestions are made regarding cross-disciplinary information still required to constrain the role of the biosphere in banded iron forma- tion deposition. Keywords Aerobic and anaerobic Fe(II) oxidation, anoxygenic phototrophs, atmospheric evolution, banded iron formations, cell-mineral aggregates, mineral diagenesis.