Mikrosonden- und Röntgenbeugungs-Untersuchungen an Tonbelägen von lessivierten Böden aus Löß

Microprobe and x-ray diffraction studies of clay coatings in leached soils derived from loess Point analyses of Si, Al, K, Mg, Ca, Fe, Mn, as well as of Zn and Pb of clay coatings in soil thin sections from illuvial horizons of four leached soils were carried out using an electron microprobe (EMA). The K, Mg, Si, and Al content, the Si/Al-molar ratio of coatings and XRD-analyses indicate that the clay coatings consist mainly of illitic clay minerals. This suggests either a mineral-specific displacement of illite or the formation of illitic clay coatings from migrated smectite or expanded illite (“illitization”) through subsequent K uptake. The clay coatings show, with the exception of Fe, Mn, Zn and Pb, only little variation in their chemical composition within the same horizon. Between the horizons of the investigated soils, however, distinct differences in the total element content, especially in the K content may occur. The strong vertical variation of the K content in clay coatings in some horizons is probably due to acidic conditions and lateral infiltration which lead to an increased weathering of illite and the depletion of K. The EMA results show that Pb is predominantly bound in Fe-Mn-Oxide coatings on the surface of clay minerals or in Fe-Mn-Oxide precipitates within clay coatings. Microanalyses of K depleted clay coatings indicate on the other hand an increased fixation of Zn in expanded illites.