Soil development on basic and ultrabasic rocks in cold environments of Russia traced by mineralogical composition and pore space characteristics

摘要

Recent soils from basic (amphibolite and meta-gabbro amphibolite) and ultrabasic (serpentinous dunite) rocks formed in cold and humid climates of Northern Eurasia (Russia) were studied to detail the characterization of soils and rocks with special attention to the interdependence of porosity system and rock mineralogy. The study plots were located in taiga and tundra zones of East Fennoscandia and the Polar Ural Mountains. A variety of methods was used including optical microscopy, X-ray diffraction and Rietveld analysis, and three supplemental methods for the determination of pore space characteristics in rocks: (i) mercury intrusion porosimetry, (ii) a modification of this method using the intrusion of a molten alloy (Wood's metal), and (iii) scanning atomic-force microscopy. The results illustrate that the specification of the porosity system is a significant factor in tracing the clay mineralogy in soils formed from hard rocks. Ultrabasic rock is the most sensitive to weathering, as determined by (i) the high value of small pores, especially those with a radius of 10 nm, (ii) the elongated form of the pores and surface roughness, and (iii) zones with an accumulation of phyllosilicates in regions with higher porosity causing the formation of soil enriched by clay minerals.