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Abstract
Siderite (FeCO 3 ) is often assumed to precipitate from dissimilatory reduction of Fe-(oxyhydr)oxides, but geochemical and mineralogical analyses from ferruginous (anoxic, Fe-rich) Canyon Lake, USA, suggest Fe-carbonate represents a direct early precipitate unrelated to substantial oxide burial.X-ray absorption near edge structure (XANES) spectroscopy of sediment trap materials and an anoxic sediment core indicated a mixture of Fe(II) and Fe(III) in water column particulates and ferruginous surface sediments, while all Mn phases were reduced.About 60 cm below the sediment-water interface, Fe-Mn carbonates were detected by X-ray diffraction and XANES, while Fe extended X-ray absorption fine structure (EXAFS) spectra were best fit with combinations of a biogenic Fe-oxyhydroxide ("Bio Fe"), greigite, and siderite.Sediment Fe speciation indicates a large pool of reduced Fe with a minor component of oxides.Although we found no evidence of significant carbonate phases above or below the 60 cm horizon, equilibrium modelling indicates siderite supersaturation throughout surface sediment porewater, with pH as the primary control on supersaturation.We conclude that delivery of wildfire ash to sediments increased pH, initiating siderite precipitation from ferruginous porewater.
Department
Earth Sciences
Publication Date
4-30-2024
Journal Title
Geochemical Perspectives Letters
Publisher
European Association of Geochemistry
Digital Object Identifier (DOI)
Document Type
Article
Recommended Citation
Grengs, A., Ledesma, G., Xiong, Y., Katsev, S., Poulton, S.W., Swanner, E.D., Wittkop, C. (2024) Direct precipitation of siderite in ferruginous environments. Geochem. Persp. Let. 30, 1–6. https://doi.org/10.7185/geochemlet.2414
Rights
© 2024 The Authors
Comments
This is an open access article published by European Association of Geochemistry in Geochemical Perspectives Letters in 2024, available online: https://dx.doi.org/10.7185/geochemlet.2414