Magnetic study of Late Pleistocene loess/palaeosol sections from Siberia: palaeoenvironmental implications

Rock-magnetic properties, including anisotropy of magnetic susceptibility, were investigated in detail for two loess/palaeosol sections in south-western Siberia (Bachat and Kurtak). The results obtained agree with the 'Alaskan' type of susceptibility variations for the Kurtak section, showing maximum susceptibility values in loess horizons and minima in palaeosols. For the Bachat section the palaeoenvironmental record, expressed through susceptibility, is not clear, in spite of the geographical proximity of the two sections. Instead, frequency-dependent magnetic susceptibility (FD%) discriminates well between loess and palaeosol units, showing maxima in pedocomplexes and minima in loess units. This suggests certain pedogenic formation of fine ferrimagnetic grains in soils. Studies of anisotropy of magnetic susceptibility (AMS) reveal a well-defined sedimentary magnetic fabric for both sections. Different origins of loess deposition, pure aeolian at Bachat and aeolian affected by secondary processes at Kurtak are reflected in the AMS patterns. The two sections also show different high-temperature behaviour of magnetic susceptibility. While for the Bachat section only one type of thermomagnetic curve was found, the Kurtak section shows different behaviour for loess and palaeosol units. Magnetic properties of samples from the two sections are discussed in terms of palaeoclimatic and depositional conditions.