Linking the redox cycles of Fe oxides and Fe-rich clay minerals: an example from a palaeosol of the Upper Freshwater Molasse

Authors: Stanjek, H.; Marchel, C.

Source: Clay Minerals, Volume 43, Number 1, March 2008 , pp. 69-82(14)

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Abstract:

A profile within the Upper Freshwater Molasse (OSM) of eastern Switzerland was sampled. Particle-size analyses, bulk chemical analyses, cation exchange capacities and Fe fractions (oxalate- and dithionite-citrate-bicarbonate-soluble Fe, total Fe) were measured. The mineralogical composition was determined by X-ray diffraction and quantified with Rietveld analysis. The layer charge of selected fine-clay samples was determined with the alkylammonium method using chain n_c = 12. The profile could be divided into a lower sequence (I) and an upper sequence (II) by a hiatus. Chemical data, particle-size distributions and calcite contents indicated that soil formation was essentially restricted to wetting-drying cycles associated with redox cycles evident from Fe_o/Fe_d and Fe_d/Fe_t ratios. A significant correlation between the d₀₆₀ values of the dioctahedral smectite-illite mixed-layer phases and Fe_o/Fe_d was interpreted as the influence of microbial Fe³⁺ reduction, which affected both the Fe oxides and Fe-rich clay minerals. This is the first evidence that the Fe dynamics of both mineral groups may be linked. The amount of illitization also correlated with Fe_o/Fe_d, but only in the upper part of the profile. This indicates that wetting-drying cycles were necessary for the illitization process.

Keywords: PALAEOSOL; REDOX DYNAMICS; BACTERIAL FE REDUCTION; FE-RICH SMECTITE/ILLITE; ILLITIZATION

Document Type: Research article

DOI: http://dx.doi.org/10.1180/claymin.2008.043.1.05

Publication date: 2008-03-01

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