Sofia N. Lessovaia

Mineralogical composition of shallow soils on basic and ultrabasic rocks of East Fennoscandia and of the Ural Mountains, Russia.

The influence of epigenetic (pre-pedogenetic) alteration of basic and ultrabasic rocks leading to the formation of phyllosilicate mineral associations is not well known. The purpose of this study was to gain further understanding of the processes involved by investigating the mineral associations of shallow soils underlain by amphibolites and metamorphosed gabbro-diabases (East Fennoscandia) and by serpentinous dunites (olivinite) and metagabbro amphibolites (the Ural Mountains). Where phyllosilicates were absent from the bedrock, they were also absent from the sola. The pedogenic alteration of the initial mineral soil matrix was very weak and did not result in a significant accumulation of phyllosilicates in the soils (East Fennoscandia). Pedogenesis enhanced the transformation of phyllosilicates, a process initiated by epigenic rock alteration.Phyllosilicates in the sola from basic and ultrabasic rocks of the Polar Urals were largely inherited according to their origin. The inherited phyllosilicate association of the sola from ultrabasic rocks included talc, serpentine, and chlorite. Saponite resulted from pedogenesis; its distribution in various thin soils dependingon the processes of neoformation and decomposition, the latter probably taking place under the influence of lichens and moss.Chlorite and illite and products of their transformation, including vermiculite, comprise the phyllosilicate association of a solum from basic rock, and traces of talc were found. The distribution of vermiculite and randomly interstratified chlorite-vermiculite (C-V) depended on the processes of chlorite vermiculitization and vermiculite decomposition.

TRAPROCK TRANSFORMATION INTO CLAYEY MATERIALS IN SOIL ENVIRONMENTS OF THE CENTRAL SIBERIAN PLATEAU, RUSSIA

The study of hard rock conversion into fine earths and clayey materials in the pedosphere is important in understanding the relative proportions of recent soil features to features that were inherited from ancient epochs. Cold environments are widely thought to be areas of physical weathering, but the coexistence of physical and chemical processes have also been shown. To further examine mafic rock (dolerite) weathering in soil environments and the conversion into clayey materials, Entic Podzols formed in the cold continental climate were studied. The key study was located in the central part of the flood basalt complex, or traps (traprocks), of the Central Siberian Plateau (Russia). The qualitative mineralogy was studied using X-ray diffraction and the quantitative mineral composition was determined using X-ray diffraction and subsequent Rietveld analysis. The micromorphological characteristics of the soils were studied in thin sections. Dolerite fragments and fine earths were sampled from soil profiles underlain by dolerite. XRD analyses indicated that pyroxene and especially plagioclase contents in the dolerite fragments and fine earths decreased from the bottom to the top soil horizons mostly in the mature soil profiles that were affected by chemical weathering of dolerite. The dioctahedral and trioctahedral smectites in the soils were inherited from a dolerite previously subjected to chemical weathering. The smectite was conserved in the inherited aggregates and protected against dissolution even in acidic soil horizons. Recent pedogenesis processes fractured individual fragments, converted it into soil micromass, and slightly decreased the total smectite content of the <1 µm soil fraction. However, in soil samples collected from the bottom to the top horizons of a mature soil profile, trioctahedral smectite contents decreased as dioctahedral smectite contents increased. This suggests that dioctahedral smectites formed by pedogenic alteration of inherited trioctahedral smectites.

Clay Minerals in the Loose Substrate of Quarries Affected by Vegetation in the Cold Environment (Siberia, Russia)

Pioneer plant communities play an important role in the process of parent substrate colonization by biota and a successful restoration of ecosystem as well, especially in the first stages of recovery successions. The aim of the present research is to study the influence of plant communities of the initial stages of primary succession on the mineral composition of substrates from sandy quarries situated in the forest-tundra zone to understand the specificity of substrate transformation initiated by vegetation, Western Siberia close to the town of Labytnangi. Sandy substrate was quarried here in former open woodlands, in communities with spruce, larch, and birch in the overstory and dwarf shrubs, mosses, and lichens in the ground layer. The time of vegetation development in quarries varies from 15 to 40 years. In substrates, pH values decrease simultaneously with the rise of moistening as well as plant canopy closure, which also influences the moistening. Clay size fraction of all samples is characterized by the same mineral association, as follows: highly smectitic clay, minerals of the mica group, chlorite, and kaolinite. In addition, traces of quartz were also identified. According to our findings, the changes in substrate mineralogy affected by the plant community decrease from mosses (reduced proportion of highly smectitic clay and transformation of chlorite into random mixed-layer chlorite-smectite), lichens (reduced proportion of highly smectitic clay), and vascular plants (absence of changes).

Biogenic Weathering of Mineral Substrates (Review)

A biological impact on weathering was recognized already at the beginning of the twentieth century, when biochemical influence of the lichen growth on rocks was convincingly demonstrated. Later it was shown that the progress of solid rock weathering initiated by biological colonization was affected by the initial porosity system and sensitivity of mineral association. In the meantime a considerable amount of diverse scientific data confirm the importance of biological rock colonizers (lichens and free-living rock biofilms) in mineral material dynamics as they occur at the atmosphere-exposed rock surfaces on local as well as global scale. Subaerial rock biofilms—microbial ecosystem including free-living heterotrophic and phototrophic settlers of bare rock surfaces—are characteristic for the first stage of primary succession of terrestrial ecosystems on mineral substrates. These cultivable and free-living communities are dominated by fungi and set the stage for the later development of a lichen cover, but in comparison to lichens also represent a new tool for laboratory experimentation and thus open a new stage of work in geomicrobiology. The minerals sensitivity to microbially induced biological weathering can be demonstrated by studies of natural samples as well as by the laboratory mesocosm experiments.

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

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.