Publication Date:
2022-05-25
Description:
© The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Earth-Science Reviews 172 (2017): 140-177, doi:10.1016/j.earscirev.2017.06.012.
Description:
Iron formations (IF) represent an iron-rich rock type that typifies many Archaean and Proterozoic
supracrustal successions and are chemical archives of Precambrian seawater chemistry and postdepositional
iron cycling. Given that IF accumulated on the seafloor for over two billion years of
Earth’s early history, changes in their chemical, mineralogical, and isotopic compositions offer a
unique glimpse into environmental changes that took place on the evolving Earth. Perhaps one of
the most significant events was the transition from an anoxic planet to one where oxygen was
persistently present within the marine water column and atmosphere. Linked to this progressive
global oxygenation was the evolution of aerobic microbial metabolisms that fundamentally
influenced continental weathering processes, the supply of nutrients to the oceans, and, ultimately,
diversification of the biosphere and complex life forms. Many of the key recent innovations in
understanding IF genesis are linked to geobiology, since biologically assisted Fe(II) oxidation,
either directly through photoferrotrophy, or indirectly through oxygenic photosynthesis, provides a
process for IF deposition from mineral precursors. The abundance and isotope composition of
Fe(II)-bearing minerals in IF additionally suggests microbial Fe(III) reduction, a metabolism that is
deeply rooted in the Archaea and Bacteria. Linkages among geobiology, hydrothermal systems, and
deposition of IF have been traditionally overlooked, but now form a coherent model for this unique
rock type. This paper reviews the defining features of IF and their distribution through the
Neoarchaean and Palaeoproterozoic. This paper is an update of previous reviews by Bekker et al.
(2010, 2014) that will improve the quantitative framework we use to interpret IF deposition. In this
work, we also discuss how recent discoveries have provided new insights into the processes
underpinning the global rise in atmospheric oxygen and the geochemical evolution of the oceans.
Description:
KOK, TJW, RH, CAP and AB would like to thank the Natural Sciences and Engineering Research
Council of Canada (NSERC) for its financial support. LJR gratefully acknowledges the support of a
Vanier Canada Graduate Scholarship. CMJ, DSH, NJP and TWL acknowledge support from the
NASA Astrobiology Institute. SVL acknowledges support from the European Institute for Marine
Studies (LabexMER, ANR-10-LABX-19). HT and PBHO thank ASSMANG Ltd for providing research funding.
Repository Name:
Woods Hole Open Access Server
Type:
Preprint
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