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TRANSFORMATION OF MAFIC AND ULTRAMAFIC ROCKS INTO SOIL CLAYEY MATERIALS IN THE CRITICAL ZONE OF COLD ENVIRONMENTS
Lessovaia, Sofia N.
- Conference Paper
Rights / licenseIn Copyright - Non-Commercial Use Permitted
Studies of creating fine earth materials from hard rocks and following transformation into clayey material in soil environments are very important to understand the processes that are active in the critical zone of high latitudes and polar zones. These zones are widely thought to be areas of physical weathering only. The aim of the present research was to study (i) the conversion of highly weathering mafic and particularly ultramafic rocks into clayey materials and (ii) the characteristics in clay mineralogy including clay minerals distribution in the soils profiles in the cold environments. The study plots were located on the Polar Urals and the Central Siberian Plateau (Russia). The objects were mature profiles of Haplic Cryosol (Reductaquic) and Entic Podzol derived from and underlain by ultramafic and mafic rocks, correspondently. Haplic Cryosol (Reductaquic) was located on mountainous tundra of the Rai-Iz massif, the Polar Urals, which are the part of the Ural Mountains in the area of the Arctic Circle. Entic Podzol was located in the central part of the flood basalt complex, or traps (traprocks) of the Central Siberian Plateau. The traprocks, which are mafic rocks, were represented by dolerite in the study plot. Mineral association in rock fragments sampled from lithic contact of soil profiles were studied in thin sections using optical microscopy. Quantitative mineralogical compositions of rocks and soils (the fine size <1 μm fractions) were determined on randomly oriented powder specimens using XRD followed by Rietveld analysis. Despite the fact that the investigated soils have been forming from the different types of rocks, high proportions of smectite were identified in the bottom horizons. Smectite was not identified in the ultramafic rock itself, which are dominated by olivine, serpentine, talc, chlorite, and sometimes amphiboles. Appearance of smectite in the soil from ultramafic rock was due to chemical weathering in the fine earth formation from hard rock. In contrast, both di- and trioctahedral smectites were found in mafic rock previously subjected to chemical weathering. An inherited nature of smectite in the soil on mafic rock was revealed. Based on XRD patterns of oriented samples, smectite was predominant in the bottom horizons of the soils. The amorphous content significantly increased in the fine size fractions particularly in the middle and upper soil horizons of both soil types in comparison with that in the rocks, which was additionally indicated by the increase of proportions of extractable Fe, Al, and Si. These observations would illustrate intensive chemical weathering during pedogenesis. A smectite transformation into an amorphous phase could be concluded due to (i) acidification in the soil on mafic rock and (ii) acidification only in the rhizosphere in soil on ultramafic rock characterized by neutral to alkaline pH-values. However, the quantitative analysis of the XRD patterns from the randomly oriented powder of these specimens revealed that the smectite was still present and proportions of amorphous materials did not significantly increase in the upper horizons. In the soil profile on ultramafic rock the proportions of predominant dioctahedral smectite and trioctahedral smectite were approximately the same in the upper and bottom horizons, whereas in the soil profile on mafic rock the proportion changes from the bottom to the upper horizons with a decrease of trioctahedral and an increase of dioctahedral smectite. Thus, this study revealed that smectite is a more stable mineral in the critical zone of cold environments than previously thought , correlating data  of predominance of non-crystalline or poorly ordered materials in the weathering crust and soils of cold climates Show more
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López Galindo, Alberto
Book titleScientific Research Abstracts
PublisherDigilabs - Bari, Italy
Organisational unit08669 - Gruppe ClayLab
02607 - Institut für Geotechnik (IGT) / Institute for Geotechnical Engineering (IGT)
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