Micromorphology of zheltozems on hard sedimentary rocks and products of their decomposition: Pedogenic and lithogenic features (with the Sochi arboretum as an example)

The analysis of the microfabric of soils developing from calcareous argillites (with sandstone interlayers) and their derivatives revealed the mechanisms of the transformation of the initial lithogenic features into pedogenic features. They include the release of primary carbonates and their segregation in secondary forms, the redistribution of iron oxides, and changes in the shape of the rock fragments and in the optical properties of the fine material in the lithomarge zone. The subsoil—the metamorphic BM horizon—is characterized by a high content of clay composed of chlorite-vermiculite and mica-smectite minerals along with kaolinite. The BM horizon is compact and has a massive microstructure with clay pseudomorphs over skeleton grains and with nonsegregational forms of iron oxide pedofeatures. The diagnostic properties of this horizon are clearly revealed in the soils on both hard rocks and loose colluvium deposits; in the latter case, they are supplemented with a stagnic marble-like pattern. The integrity of these features corresponds to the elementary pedogenic process of the metamorphism of the mineral mass in humid subtropics. In terms of micromorphology, this is a good example of pedoplasmation. The features testifying to the contribution of biota in the topsoils are few; dark compact nodules are common there. Zheltozems developed from hard rocks may be correlated with Cambisols in the WRB system; zheltozems developed from clayey colluvium display the features of clay illuviation; together with some physicochemical characteristics of these soils, they allow us to qualify such soils as Acrisols. There are also eluvial-gley variants of zheltozems with stagnic features.