Geochemical methods for identifying the genesis of underground ice in Central Yamal

The reduction of permafrost top and the increase in ground temperature lead to the risk of gas manifestations from thawing permafrost. Gas-saturated epigenetic marine permafrost deposits, as well as certain types of ground ice in Yamal, pose a potential danger of greenhouse gas emissions into the atmosphere. A study of the genesis of ground ice in the Vaskiny Dachi geocryological research station was conducted from 2019 to 2021. Four types of ground ice were studied in the sediments of the III plain in Central Yamal – relict ice, pseudomorphs, lens ice and massive ice. The work aims to investigate the genesis of ground ice and its relationship with host deposits in the context of climate change. Based on data on the patterns of ice occurrence in natural outcrops, the lithological composition of the host deposits, and the petrological characteristics of the ice in thin sections, the authors propose to identify geochemical markers indicating the genesis of the ice. The cryolithological structure was established, the lithological composition of the deposits was determined using a laser granulator, and the ionic composition of the ice and deposits was defined using ionometric titration, titrimetry, atomic absorption, atomic emission, turbidimetry, and ionometry methods. The structure and texture of the ice, as well as its ionic and elemental composition, were studied using inductively coupled plasma mass spectrometry. A relationship was established between the chemical composition, texture, and structure of relict, lens-shaped, massive ice, and host deposits. In the upper part of the section at the boundary of the lake sediment layer, continental salinization was identified, whereas in the lower part, the chemical composition indicates coastal-marine conditions. The ionic composition confirms the coastal-marine genesis of the massive ice; a saline pseudomorph was distinguished, differing in structure and texture of the ice and chemical composition from relict ice. The distribution of rare earth elements allowed for the determination of the conditions of ice formation. Lens-shaped ice and pseudomorphs exhibit negative cerium and positive europium anomalies, unlike relict ice. It was established that freezing occurs in water-saturated conditions for massive, lens-shaped ice, and pseudomorphs. The applicability of geochemical markers for clarifying the conditions of ground ice formation and the genesis of deposits, taking into account the cryolithological structure of the sections, was justified.