Volume 70, Nº 6 (2025)

The dependence of the isotopic composition of Ne on the partial pressure of Ne, N₂ and the ratio of N₂ /Ne is analyzed for the first time. The scale of the influence of groundwater on the content and isotopic composition of noble gases in CO₂, N₂ and CH₄ gas reservoirs is also estimated. It is shown that the partial pressure of Ne in gas accumulations increases in the range: CO₂ – CH₄ – N₂. The CO₂ gas accumulations are characterized by the mantle isotopic composition of neon, and the N₂ gas accumulations are dominated by a mixture of atmospheric and crustal neon (²⁰Ne/²²Ne is in the range of 8.9–10.2; ²¹Ne/²²Ne 0.040–0.083). The initial concentrations and isotopic composition of Ne and, obviously, other noble gases depend on the conditions of formation of the gas phase that enters the reservoir. Subsequently, the partial pressure of Ne in the CO₂ and CH₄ gas accumulations increases, and the partial pressure of Ne in the N₂ gas accumulations decreases, presumably due to gas exchange with groundwater. A model of gas exchange between gas accumulations and groundwater is proposed, which makes it possible to estimate the distribution of noble gases between them: (1) CO₂ enters reservoirs with negligibly low (~0.008 Pa) partial pressures of mantle Ne. Therefore, the admixture of Ne from groundwater can reach 90 % in them; (2) On the contrary, N₂ deposits have an atmospheric isotopic composition of Ne with the addition of a nucleogenic (crustal) component and a partial pressure higher than in the atmosphere. The ancient Cl–Ca brines at the reservoir pressure below 300 bar are the most likely source of this N₂ gas phase; (3) The isotopic composition of Ne in CH₄ accumulations corresponds to the microbial methane which is formed in near–surface conditions (the environment enriched in atmospheric gases), while thermogenic methane is formed at greater depths. Probably, major part of the Ne and N₂ in the thermogenic CH₄ accumulations are the result of the gas exchange with Cl–Ca brines. In general, the isotopic composition of Ne in CH₄ accumulations reflect the mixing of microbial and thermogenic CH₄ on migration routes to the surface.

A group of Talaya lakes (Gryazevoe, Schuch’e, Goluboe, Nalimnoe are located in the east of the Maimandzhinsky Mountains (Kolyma Highlands). The lakes are of glacial origin. They were formed during the Late Neopleistocene-Early Holocene. Geochemical characteristics of lake sediments, tephra, deluvial deposits, and bedrock were obtained. Based on the analysis of the distribution of major elements, SiO₂/TiO₂, Fe₂O₃/TiO₂, Fe₂O₃/MnO, SiO₂/Al₂О₃, SiO₂/MgO, SiO₂/Fe₂O₃ ratios, ICV, CIA indices, and principal component analysis data, geochemical zones reflecting various sedimentation conditions have been established in sediments. The intervals of biogenic, terrigenous and chemogenic (autigenic) accumulation were revealed. Autigenic iron–containing minerals are represented by sulfides (pyrite, pyrrhotite). Clastic minerals are titanomagnetites, magnetites, and ilmenites. The dependence of the ratios of elements and indices on the graine size of granulometric fractions of deluvium has been studied, the relationship between the geochemical characteristics of lake sediments and deluvial deposits has been established. The main stages of lake development have been reconstructed. A comprehensive characterization of the sediments of the transition interval from the Late Neopleistocene to the Holocene was obtained.