| Summary: | The results studying the distribution of uranium and thorium in groundwaters of the oil-gas-bearing deposits of the Arctic regions of West Siberia are presented for the first data. The studied water is very diverse in chemical composition and TDS (from ultrafresh to weak brines). The concentration of radionuclides in waters are (mg/l): 238U (4.90•10-7 - 5.14•10-3), 232Th (1.90•10-6-8.93•10-3). The ratio of 232Th/238U is 0.07-93.1 and the maximum value is reached in waters of the valanginian aquifer. For waterproof horizons, the ratio of 232Th/238U is 1.82-5.23 with an average value of 3.56. The rocks of Bazhenov Formation, the nature of the radioactivity of which is associated with uranium, is characterized by the lowest values of 232Th/238U=0.07-1.71. The formation of the radionuclide composition of waters with high 232Th/238U ratios occurred in a reducing environment with the wide development of elisional processes, where thorium is capable of migration.
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