Cryogenic Features in Meadow Podbels of the Middle Amur Lowland as Revealed by Micromorphological Analysis

Meadow podbels (dark-humus gleyic and gleyed podbels in the Russian soil classification system) in the west of their range experience deep and prolonged freezing manifested in cryogenic deformations of horizons and in their microstructures. Microfeatures of soils on permafrost are well known, and the objective of this study was to identify them in three profiles of meadow podbels taking into account particular features of their cryological and moisture regimes. Unlike northern permafrost-affected soils, meadow podbels have dark-humus horizons with weakly expressed cryogenic features; in eluvial horizons, these are platy microstructures and numerous humus-iron nodules of different size. In the textural horizons, there are specific microstructures: rounded or ellipsoidal aggregates with humus-iron nodules in the center and ooidal aggregates with iron impregnation in the center and optically oriented clay along the periphery. Typical microfeatures of gley in the lower clayey horizons are combined with partially deformed illuviation clay coatings. Unlike soils with permafrost, the separation of micromass and skeleton grains is weak, as well as their ring-shaped orientation.