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Banded iron travertines at the Ilia Hot Spring (Greece); an interplay of biotic and abiotic factors leading to a modern banded iron formation analogue?

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doi: 10.1002/dep2.55
Authors:Kanellopoulos, Christos; Thomas, Camille; Xirokostas, Nikolaos; Ariztegui, Daniel
Author Affiliations:Primary:
National and Kapodistrian University of Athens, Department of Geology and Geoenvironment, Athens, Greece
University of Geneva, Switzerland
Institute of Geology and Mineral Exploration, Greece
Volume Title:Depositional Record
Source:The Depositional Record, 5(1), p.109-130. Publisher: Wiley, Hoboken, NJ, United States. ISSN: 2055-4877
Publication Date:2019
Note:In English. 90 refs.; illus., incl. 3 tables, sketch map
Summary:A hot spring at Ilia in the Greek Island of Euboea precipitates iron-rich travertine at an ore-grade concentration (up to 35.3 wt% Fe). This hydrothermal chemical sediment system deposits bands of iron oxyhydroxides (ferrihydrite), millimetres to centimetres thick, alternating with calcium carbonate-dominated layers, creating "Banded Iron Travertine" (BIT). The ferrihydrite laminae display a dendritic texture formed of spherical nodules often covering filaments identified as bacterial stalks of Zetaproteobacteria. These microaerophilic iron-oxidizing bacteria were identified by their 16S rRNA gene sequences in ferrihydrite-enriched samples from areas under high water flow. They were missing in the aragonite/calcite-dominated samples exhibiting features of aerial exposure and cyanobacteria instead. These characteristics, and the relative depletion in Fe-rich layers of redox-sensitive elements like Mn and Ce, as well as the presence of halite in Ca-rich layers, suggest that the bands form by successive changes in hydrothermal flow. This allowed microaerophilic iron oxidation to form Fe-rich layers, while Ca-rich bands precipitated when the hydrothermal water had time to equilibrate with the atmosphere. This sea water-dominated hydrothermal system is enriched in reduced iron and rapidly precipitating carbonates and ferrihydrite in the form of bands, having similarities to "Banded Iron Formation" (BIF). BIF represents archives of Earth's primitive biogeochemistry although the combined abiotic and biotic processes that have likely led to their formation are not fully resolved. Diagenesis and metamorphism have a strong imprint on BIF. Thus, continuous efforts are pursued to identify modern analogues that could help unravel their formation. Although carbonate is not a common feature of BIFs, Ilia system provides an interesting analogue for their depositional processes and potential microbial-mineral associations they may have hosted. It also presents pre-diagenesis facies association and mineralogy that could bring new clues for unravelling BIF modes of formation and the salient biogeochemical conditions characteristic of their original depositional environment. Abstract Copyright (2019), John Wiley & Sons, Ltd.
Subjects:Banded iron formations; Calcium carbonate; Carbonate rocks; Chemically precipitated rocks; Depositional environment; Diagenesis; Eh; Ferrihydrite; Ferruginous composition; Ground water; Hot springs; Hydrothermal conditions; Iron formations; Metals; Microorganisms; Modern analogs; Nucleic acids; Oxides; Precambrian; Precipitation; Rare earths; RNA; Sedimentary rocks; Springs; Textures; Thermal waters; Trace elements; Travertine; X-ray diffraction data; Euboea; Europe; Greece; Southern Europe; Bacteria; Cyanobacteria; Ilia Hot Springs; Zetaproteobacteria
Coordinates:N375500 N390000 E0244000 E0225000
Record ID:848628-6
Copyright Information:GeoRef, Copyright 2021 American Geosciences Institute. Reference includes data from John Wiley & Sons, Chichester, United Kingdom
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