MAGNETIC-SUSCEPTIBILITY OF CONCRETIONS IN SOILS OF THE SOUTHERN TAIGAZONE

The soil concretions in the southern part of the taiga zone are charac terized by a low magnetic susceptibility, except for concretions of mo derate magnetic susceptibility that are found in soils on varved clay. Magnetic susceptibility values in soil concretions are almost indepen dent elf soil hydromorphism development. The low-magnetic iron oxides- ferroxyhyte, goethite, and ferrihydrite-predominate in these concretio ns. Unlike thermodynamically stable goethite, which may be chemogenica l, thermodynamically unstable hydroxides (feroxyhyte and ferrihydrite) are formed in concretions by iron-oxidizing microorganisms. This proc ess is facilitated by a low content of bivalent iron and humus, which is typical for nongleyed soils.