The role of dust source area and pedogenesis in three loess-palaeosol sections from North Bulgaria: A mineral magnetic study

Rock magnetic studies of three loess-palaeosol sections from Bulgaria (Harletz and Orsoja in the NW and Durankulak in the NE at the Black Sea coast) have been carried out. Thermomagnetic analyses of magnetic susceptibility point to magnetite as the major ferrimagnetic carrier in the loess and palaeosol units. Maghemite gives a significant contribution to the total magnetic signal in the recent soils (S₀), while in one of the sections-Orsoja-hematite may also be present. The effective magnetic grain sizes deduced from the hysteresis measurements and the ratios M_rs/M_s and B_cr/B_c fall in the pseudo single domain (PSD) range, but the data distributions in a Day diagram for the three different sections are shifted. This is suggested to be caused by different detrital input (e.g. different dust source areas) and varying degrees of pedogenic modification. The calculated background susceptibilities χ_bg differ significantly as well. The lowest value is obtained for the Durankulak section-χ_bg = 9.95 × 10⁻⁸ m³/kg, which is in accordance with the data from other studies of loess-palaeosol profiles from the Black Sea area. The corresponding background susceptibilities for the other two sections studied-Harletz and Orsoja-are significantly higher (33.1 and 17.75 × 10⁻⁸ m³/kg, respectively). Both parent material and pedogenesis are found to be responsible for the observed differences in the magnetic characteristics.