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https://doi.org/10.5194/se-2017-113
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
02 Nov 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Solid Earth (SE).
Sedimentary mechanisms of a modern banded iron formation on Milos Island, Greece
Ernest Chi Fru1,2, Stephanos Kilias3, Magnus Ivarsson4, Jayne E. Rattray1, Katerina Gkika3, Iain McDonald2, Qian He5, and Curt Broman1 1Department of Geological Sciences, 10691, Stockholm University, Stockholm, Sweden
2School of Earth and Ocean Sciences, Cardiff University, Park Place, CF10 3AT, Cardiff, UK
3Department of Economic Geology and Geochemistry, Faculty of Geology and Geoenvironment, National and Kapodistrian University of Athens, Panepistimiopolis, Zographou, 15784, Athens, Greece
4Department of Palaeobiology, Swedish Museum of Natural History, Box 50007, Stockholm, Sweden
5School of Chemistry, Cardiff University, Park Place, CF10 3AT, Cardiff, UK
Abstract. An Early Quaternary shallow submarine hydrothermal iron formation (IF) in the Cape Vani sedimentary basin (CVSB) on Milos Island, Greece, displays banded rhythmicity similar to Precambrian banded iron formation (BIF). Sedimentary, stratigraphic reconstruction, biogeochemical analysis and micro-nanoscale mineralogical characterization confirms the Milos rocks as modern Precambrian BIF analogues. Spatial coverage of the BIF-type rocks in relation to the economic grade Mn ore that brought prominence to the CVSB implicates tectonic activity and changing redox in the deposition of the BIF-type rocks. Field-wide stratigraphic and biogeochemical reconstruction demonstrates two temporal and spatially isolated iron deposits in the CVSB with distinct sedimentological character. Petrographic screening suggest the previously described photoferrotrophic-like microfossil-rich IF (MFIF), accumulated on basement andesite in a ~ 150 m wide basin, in the SW margin of the basin. A strongly banded non-fossiliferous IF (NFIF) caps the Mn-rich sandstones at the transition to the renowned Mn-rich formation. Geochemical evidence relates the origin of the NFIF to periodic submarine volcanism and water column oxidation of released Fe(II) in conditions apparently predominated by anoxia, similar to the MFIF. This is manifested in the lack of shale-normalized Ce anomalies. Raman spectroscopy pairs hematite-rich grains in the NFIF with relics of a carbonaceous material carrying an average δ13Corg signature of ~ −25 ‰. However, a similar δ13Corg signature in the MFIF is not directly coupled to hematite by mineralogy. The NFIF, which post dates large-scale Mn deposition in the CVSB, is composed primarily of amorphous Si (opal-SiO2 · nH2O) while crystalline quartz (SiO2) predominates the MFIF. An intricate interaction between tectonic processes, changing redox, biological activity and abiotic Si precipitation, formed the unmetamorphosed BIF-type deposits.

Citation: Chi Fru, E., Kilias, S., Ivarsson, M., Rattray, J. E., Gkika, K., McDonald, I., He, Q., and Broman, C.: Sedimentary mechanisms of a modern banded iron formation on Milos Island, Greece, Solid Earth Discuss., https://doi.org/10.5194/se-2017-113, in review, 2017.
Ernest Chi Fru et al.
Ernest Chi Fru et al.
Ernest Chi Fru et al.

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Short summary
Milos Island hosts young banded iron formations, which are chemical sediments last seen in the marine sedimentary record ca. 600 million years ago. Major deposition, 3800–1800 million years ago, is believe to reflect an ocean-atmosphere system radically different from today. The Milos analogue sediments demonstrate that special environmental conditions of oxygen, submarine hydrothermal activity and microbial processes are required for these types of rocks to form in the modern marine biosphere.
Milos Island hosts young banded iron formations, which are chemical sediments last seen in the...
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