Mineralogical and Micromorphological Diagnostics of Pedogenesis on Intermediate and Mafic Rocks in the Northern Taiga of the Timan Range

Resumo

Mineralogical, micromorphological, and physicochemical characteristics of soils developed on the outcrops of intermediate and mafic rocks in the central part of the Timan Range under northern taiga vegetation are discussed. These soils have been classified within the order or iron-metamorphic soils of the new Russian soil classification system and as Hyperskeletic Leptosols (Humic) in the WRB system. The in situ accumulation of nonsilicate iron compounds (ferrugination) controlled by the specific features of iron-rich parent rocks is the major process in these soils. In dependence on the composition of parent material, the direction of its modern weathering, the character of plant litter, the degree of its biological transformation, and the presence of features attesting to the mobility of silicate plasmic material, these soils are subdivided into two types: rzhavozems on colluvium of mafic rocks with some admixture of siliceous morainic fine earth and organic rzhavozems on the eluvium of mafic rocks with a predominance of specific polycrystalline aggregates of iddingsite and bowlingite (saponite) representing supergene postmagmatic pseudomorphs after pyroxenes and olivine with the initially different iron contents.