Continental weathering as the source of iron in Jurassic iron oolites from Switzerland
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Published:2023-05-24
Issue:1
Volume:116
Page:
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ISSN:1661-8726
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Container-title:Swiss Journal of Geosciences
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language:en
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Short-container-title:Swiss J Geosci
Author:
Schunck StefanORCID, Rickli JörgORCID, Wohlwend Stephan, Weissert Helmut, Vance DerekORCID
Abstract
AbstractIron is extremely insoluble in oxic seawater. The lack of a large aqueous reservoir means that sediments rich in authigenic iron are rare in the modern ocean. In the Middle Jurassic, however, condensed iron-rich sedimentary rocks are widely distributed. Their formation coincides with increased volcanic activity and continental weathering related to the breakup of Pangea, suggesting iron supply through one of these processes. We studied three Swiss shallow-marine iron oolites from Herznach, Windgällen and Erzegg, all from condensed sedimentary sequences of Middle to early Late Jurassic age, to constrain the source of iron to these rocks, combining radiogenic neodymium, strontium and stable iron isotope analyses. Leached authigenic neodymium isotope compositions, which appear to preserve the primary signature, serve as a tracer for the potential involvement of hydrothermal fluids in the formation of the iron oolites. The three iron oolite successions yield crustal Nd isotope compositions (εNd between − 9 and − 7), providing no evidence for the involvement of such fluids. It is, thus, more likely that iron in the sediments derived from detrital fluvial inputs. Strontium isotope compositions, which could potentially support these findings, point to metamorphic overprinting associated with Alpine thrusting. The light iron isotope signatures associated with Middle to early Late Jurassic condensed sequences, δ56Fe between − 1.49 and − 0.57‰, suggest that microbially-mediated iron reduction was also involved in generating these sediments.
Funder
Swiss Federal Institute of Technology Zurich
Publisher
Springer Science and Business Media LLC
Reference141 articles.
1. Baioumy, H., Omran, M., & Fabritius, T. (2017). Mineralogy, geochemistry and the origin of high-phosphorus oolitic iron ores of Aswan, Egypt. Ore Geology Reviews, 80, 185–199. https://doi.org/10.1016/j.oregeorev.2016.06.030 2. Baker, D.W. (1964). The Windgällen Fold: A restudy of a classical Alpine structure. Zurich, Switzerland, ETH Zurich, Diploma Thesis, unpublished, 79pp. 3. Beard, B. L., Johnson, C. M., Cox, L., Sun, H., Nealson, K. H., & Aguilar, C. (1999). Iron isotope biosignatures. Science, 285(5435), 1889–1892. https://doi.org/10.1126/science.285.5435.1889 4. Beard, B. L., Johnson, C. M., Skulan, J. L., Nealson, K. H., Cox, L., & Sun, H. (2003). Application of Fe isotopes to tracing the geochemical and biological cycling of Fe. Chemical Geology, 195(1–4), 87–117. https://doi.org/10.1016/S0009-2541(02)00390-X 5. Berger, A., Wehrens, P., Lanari, P., Zwingmann, H., & Herwegh, M. (2017). Microstructures, mineral chemistry and geochronology of white micas along a retrograde evolution: An example from the Aar massif (Central Alps, Switzerland). Tectonophysics, 721, 179–195. https://doi.org/10.1016/j.tecto.2017.09.019
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