engleski

Clay mineralogy in soils formed on Miocene marls and Plio-Quarternary sediments in temperate climate

Four soil profiles developed on Miocene marls and two soil profiles developed on Plio-Quarternary (PlQ) molasse-type proluvial and fluvial-lacustrine sediments have been investigated at the foothills of Mt. Med- vednica (Croatia). Soils that formed from both sediments were found to be genetically young, consisting only of the topsoil and the transitional horizon overlying the parent material (A-AC-C profile). The aim was to study clay mineral composition of the soils developed on different parent materials and to establish the major processes determining clay minerals occurrence within the soils. Clay minerals were determined by XRD (<2 mm and <2 μm fractions) and FTIR (<2 μm fraction). Fraction <0.2 μm was additionally separated from the PlQ profiles to analyze its clay minerals composition in more detail and to measure the layer charge of swelling clays using O-D method proposed by Kuligiewicz et al. (2015). It was determined that the clay mineralogy of marls consists of mixed-layered smectite-rich illite- smectite, illite, kaolinite, vermiculite, and trace of chlorite, while the one of PlQ sediments consists of smectite, vermiculite, kaolinite, and illite. The observed changes in clay mineralogy within soil horizons (compared to the underlying parent material) include a) the appearance of mixed-layered chlorite-vermiculite in soils on marls and b) the appearance of HIMs and the increased content of vermiculite in soils on PlQ sediments. Layer charge easurements show and increasing trend towards topsoil in PlQ profiles (from 0.61 and 0.50 p.f.u. measured for the parent material to 0.66 and 0.59 p.f.u. in topsoil, respectively), confirmingthat the high-charge swelling clay minerals are more abundant in the soil than in the parent material. The results show that the main process responsible for the clay mineralogy of the analyzed soils is inheritance. However, indication of early stages of clay minerals (trans)formation processes is reflected in the occurrence of mixed-layered chlorite-vermiculite in soils developed on marls, and hydroxyl-interlayered phases, as well as increased content of vermiculite in soils developed on PlQ sediments.

soil clay mineralogy, clay mineral transformations, temperate climate

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