Carbonate Soil Cryogenesis in South Yakutia (Russia)

Abstract

The present study investigates changes occurring in the material composition and properties of the South Yakutian carbonate soils during cryogenesis. The nature of the transformations of certain limestone varieties composing the surfaces of rock massifs was determined using scanning electron microscopy, 3D X-ray tomography, as well as lithological–mineralogical and optical–petrographic studies, over a 10-year period. The areas in carbonate rock massifs with increased clay content, pyritisation, dolomitisation, and baritisation, as well as zones of calcite and dolomite junction, were found to be least resistant to the effects of processes associated with water phase transitions, i.e., freezing and thawing. The mineral proportion of limestone on the surface of soil massifs chemically processed over a 10-year period reached 5–7% of the volume of the weathered rocks. In the process of transformation, not only the composition of the rocks changed, but also the nature of the structural bonds that significantly influence their mechanical strength properties. The number of cracks for weathered soil samples increased by 9–16%; their opening increased by 13–18%. For rocks initially having uniaxial compression strength in the range of 33–46 MPa, this strength was reduced by 19–27%. Laboratory experiments on 1000-fold cyclic freezing and thawing of carbonate rock samples (which corresponds to an 8–10-year period of weathering on the surface of a mountain outcrop under the natural conditions of South Yakutia) demonstrate the similarity of these changes with those observed in samples taken from the sides of open pits 10 years ago. In general, soils are influenced by a wide range of environmental factors under natural conditions. The significant influence of alternating temperatures on the changes in the composition and structure of limestones in South Yakutia is characterised in detail.

Cryogenesis of granites and gneisses in South Yakutia

“…The sharp decrease in the number of fractures is observed only in the range from 46 to 116 μm (Figure 18, Table 4). It is remarkable that, within this range, an abrupt change in the fracturing is inherent in the limestones of South Yakutsk district; however, for the latter, the result is directly opposite (increase in the number of fractures) (A. Melnikov et al, 2021).…”

“…Some description of structural and material transformations of dolomites and limestones is available in A. Melnikov et al (2021). Thus, rocky soil cryogenesis at the regional level has been insufficiently studied.…”

“…While this work combines diverse systematic diagrams for describing the alterations proceeding in the sandstones of this region occurring under the influence of cryogenesis, this is limited to assessing the stability of coal quarry benches. Some description of structural and material transformations of dolomites and limestones is available in A. Melnikov et al (2021). Thus, rocky soil cryogenesis at the regional level has been insufficiently studied.…”