Бюллетень Почвенного института им. В.В. Докучаева (May 2018)
The diversity of calcareous inclusions and the specificities of their transformation within the soils of thermal Pym-Va-Shor area
Abstract
The calcareous inclusions in soils of Pym-Va-Shor (Nenets Autonomous District) are interesting due to the possibility of observation of ancient and present impact of thermal waters on the soil cover. The water mineralization 1.48 g/l, the content of hydrocarbonate-ion 0.15-0.16 g/l, pH 8.0-8.5, SAR 4.9-10.1 which allows them to form the travertines of calcareous composition (with the rate of 0.037-0.090 mm/year). The two types of calcareous inclusions are classified according to the macrostructure: first are the dense calcitic rocks from the early Devonian and Carbonic periods; the second are the porous travertines. The comparative analysis of microspecificities allowed us to observe the prevalation of grains of the cryptocrystallic and micritic calcite with specifically dense package. The solution specificities are marked precisely from the outer sides of pieces. There are always inclusions of foraminifera in rocks and there are no ferric and clay films specific for travertines of soil horizons. Travertines also show traces of mollusks shells and prevailing of sites with different size and density of calcite packing. Loose packed zones with crypto-grains (35 mm). The specificities of travertines microcomposition stipulate about the active microbial participation during their forming, along with participation of vegetation, and low expense of water with temperature about 30°C. We determined the microspecificities of travertines, reflecting the processes of their transformation in denudations and the soil profile: increase of calcite crystals (the process of recrystallization is specific for sustainable denudation conditions); forming of high internal fine porosity (the leaching process is specific for travertins decomposition in soils near modern thermal springs); cracky pores between minerals (the process of physical decomposition of inclusions in soils outside thermal springs). All of the studied soils, except the podzolized podbur, include the travertines similar in microstructure at the depth of 90 cm, which is a feature of the existance of the previous “older” and more powerful hydrothermal system.
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