Abiotic and Biotic Processes of Mineral Weathering in Tundra Soils on Ultramafic and Mafic Rocks of the Polar Urals, Russia

Abstract

The weathering of mafic and ultramafic rocks in soil environment was investigated in weakly developed soil profiles in order to determine the origin of phyllosilicate association in the soils formed in humid cold climate of the mountainous tundra of the Polar Urals. The objects of the study are represented by soils formed (i) on and underlain by the ultramafic rock and (ii) on the moraine composed of the mafic rock with an admixture of the ultramafic rock fragments. The minerals found in the clay fraction (<1 μm) of the profiles are the same, characterized by the presence of smectite (saponite), which is absent in both mafic and ultramafic rocks; serpentine and talc identified in ultramafic rock; and chlorite. Chlorite was found in both types of rocks. It was shown that the appearance of smectite (saponite) in the weakly developed soil is not related to pedogenesis. But these soil profiles illustrate the possibility of soil formation on “mature” fine earth formed from a high-sensitive ultramafic rock due to chemical weathering. In cold soil environment the more weatherable ultramafic material plays the more important role as a prerequisite for the weathering trends and soil formation than a mafic rock. The admixture of ultramafic materials mitigates the development of Entic Podzols which were earlier found in the Polar Urals on the pure mafic materials. So, the presence of ultramafic materials either predominating or even in admixture results in the “extreme lithological environment” for a pedogenesis and in the formation of weakly developed soils—Regosols and Leptosols.