Clay minerals in the stream floodplain soils in undisturbed landscapes of the Southern Taiga (with the soil of the state central forest nature and biosphere reserve as an example)

An X-ray diffraction technique was used to study the composition of clay material from floodplain soddy- and mucky gley soils formed in the valleys of small streams in the reserve. The content of nonexpandable minerals was higher and the labile mineral content was lower in the fine fractions of the floodplain soils than in similar fractions of upland soils found in adjacent positions. Two types of disordered mixed-layered not found in upland soils-namely, illite-chlorites and chlorite-vermiculites with a variable proportion of individual layeres-were detected in the clay material. Both types of mixed-layer minerals are supposed to originate from stony fragments containing phyllosilicates of supergenic or post-magmatic origin.