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Loess/Palaeosol Section in Šarengrad, Srijem, Croatia

The Pleistocene loess and Holocene alluvial sediments are dominant lithological members of Eastern Slavonia. The Upper Pleistocene loess/palaeosol section “Šarengrad”, representing the oldest loess deposits in the region, was investigated using field and laboratory research methods.. Investigated section is located on the south bank of the Danube River near Šarengrad in the easternmost part of Croatia. The section was investigated on the several vertical profiles with a total length of 16.20 m. . The section is characterised by four palaeosol levels. The oldest, hydromorphic palaeosol is covered by laminated alluvial sediment and the loess. The second palaeosol is well developed dark brown soil, about 2 m thick. The other two soils are less developed brownish palaeosols.. The age determination of the loess sediments between the palaeosols by IRSL provides a more reliable base for the identification of soil forming periods. Geochemical (content of major and trace elements, and REE, TOC, pH, CaCO3 content) and sedimentological (grain size, lamination, microscopic characteristic of carbonate concretions), characteristics of investigated palaeosols explained the main characteristics and degree of pedogenesis, while differences in composition of heavy and light mineral fraction emphasized differences in source material for the sediments under investigation. Presence of erosional discontinuities and infilling of crotovinas with soil material indicate that some of palaeosols are eroded and so an incomplete record.. Two samples were taken from the Šarengrad section. The stratigraphically oldest sample was taken from loess above a strong palaeosol and yielded an IRSL age estimate of 86.6±8.6 ka. The upper sample also collected from loess gave an IRSL age estimate of 55.3±5.5 ka, indicating that most of the middle pleniglacial, pleniglacial and late glacial records are missing at the Šarengrad section. Results of MS indicate process of rubification in the third best developed palaeosol and limonitization in hydromorphic palaeosol.. The mineralogical composition was obtained by X-ray diffraction using Philips diffractometer with CuKα radiation on ten randomly oriented powdered bulk samples of loess and different palaeosols, as well as on their clay fraction (< 2μm) that is separated by sedimentation. The bulk mineral composition of all the samples is typical of loess/palaeosol sequences. Major phases are quartz, mica, feldspars and chlorite, as well as carbonates (calcite and dolomite). The carbonates occur in very small amounts and in some samples lack in two older palaeosol. Minor phases are amphiboles. Other heavy minerals as opâque minerals, chlorite, biotite, epidote-zoisite, amphibole, pyroxene, garnet, kyanite, staurolite, tourmaline, zircon, rutile, titanite, apatite and chromite are proved only by microscopic investigations. The clay fractions are composed mainly of illitic material, chlorite and smectite. Kaolinite, proved by DMSO, is present in negligible amount, and lacks in third palaeosol. Small amount of interstratified mineral with smectitic and illitic layers as well as chloritic and vermiculitc layers are also present.. The main grain size fraction is represented by silt. Higher content of clay fraction is present in palaeosol horizons, especially in second, well developed soil where pedogenic process was intensive. The carbonate content is highest in lower part, except in the oldest noncarbonated hydromorphyc palaeosol. The modal analyses show strongly abraded typical aeolian spherical grains characterised by pitted well-rounded surface. Palaeosol horizons could be clearly extracted based on weathering coefficients, Ba/Sr, and (CaO+Na2O+MgO+K2O)/Al2O3. The content of REE, as well as trace elements, is higher in palaeosol then in loess horizons.

loess; palaeosol; Šarengrad; Srijem; Croatia

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