TY - JOUR

T1 - The distribution of uranium and thorium in groundwaters of the West Siberian artesian basin

AU - Novikov, D. A.

AU - Vakulenko, L. G.

AU - Yan, P. A.

AU - Dultsev, F. F.

AU - Chernykh, A. V.

N1 - The work on chemistry of waters the northern areas was supported by the Ministry of Science and Higher Education of the Russian Federation (Projects FSWW-0022-0014) and by the Russian Science Foundation and government of Novosibirsk Oblast (Project 22-17-20029) for the southern areas.

PY - 2025/11

Y1 - 2025/11

N2 - The data on the distribution of uranium and thorium in groundwaters and fluid-impermeable layers of the Mesozoic sediments in the northern regions of the West Siberian basin are presented. The studied waters are diverse in major-ion chemistry and total salinity (from 2 to 5 up to 63,3 g/L). The concentrations of natural radionuclides vary within broad ranges (mg/L): U (4,90∙10-7 – 5,14∙10–3), Th (1,90∙10-6 – 8,93∙10–3). The Th/U ratio varies from 0,07 to 93,1, and its maximal value is characteristic of the waters from the Valanginian aquifers. The Th/U ratio detected for fluid-impermeable rocks is within rather narrow range, 1,82–5,24, 3,56 on average. Against this background, the lowest values Th/U = 0,07–1,71 are characteristic of the rocks of Bazhenov formation, known for its natural radioactivity to be related to uranium. The radionuclide composition of groundwaters of the oil and gas bearing sediments with high Th/U ratios was formed under strongly reductive conditions, when thorium is more mobile than uranium. The evolution of the sedimentary basin led to widespread water expulsion processes and redistribution of U and Th in the water – rock system. Under the oxidative geochemical settings of the upper hydrodynamic zone, U is much better soluble than Th, though it also can be adsorbed on the surface of minerals and get bound into secondary mineral phases. No increase in U and Th concentrations with an increase in the age of water-bearing sediments was detected in the reductive geochemical settings. The results obtained provide for the first time the confirmation of thorium-based nature of radioactivity of the groundwaters in one of the world's largest West Siberian artesian basin.

AB - The data on the distribution of uranium and thorium in groundwaters and fluid-impermeable layers of the Mesozoic sediments in the northern regions of the West Siberian basin are presented. The studied waters are diverse in major-ion chemistry and total salinity (from 2 to 5 up to 63,3 g/L). The concentrations of natural radionuclides vary within broad ranges (mg/L): U (4,90∙10-7 – 5,14∙10–3), Th (1,90∙10-6 – 8,93∙10–3). The Th/U ratio varies from 0,07 to 93,1, and its maximal value is characteristic of the waters from the Valanginian aquifers. The Th/U ratio detected for fluid-impermeable rocks is within rather narrow range, 1,82–5,24, 3,56 on average. Against this background, the lowest values Th/U = 0,07–1,71 are characteristic of the rocks of Bazhenov formation, known for its natural radioactivity to be related to uranium. The radionuclide composition of groundwaters of the oil and gas bearing sediments with high Th/U ratios was formed under strongly reductive conditions, when thorium is more mobile than uranium. The evolution of the sedimentary basin led to widespread water expulsion processes and redistribution of U and Th in the water – rock system. Under the oxidative geochemical settings of the upper hydrodynamic zone, U is much better soluble than Th, though it also can be adsorbed on the surface of minerals and get bound into secondary mineral phases. No increase in U and Th concentrations with an increase in the age of water-bearing sediments was detected in the reductive geochemical settings. The results obtained provide for the first time the confirmation of thorium-based nature of radioactivity of the groundwaters in one of the world's largest West Siberian artesian basin.

KW - Rock-water interactions

KW - Thorium

KW - Uranium

KW - West Siberia

UR - https://www.scopus.com/pages/publications/105015415231

UR - https://www.mendeley.com/catalogue/2b9751a0-b7f5-3525-9df0-c4168db3ebce/

U2 - 10.1016/j.apgeochem.2025.106563

DO - 10.1016/j.apgeochem.2025.106563

M3 - Article

VL - 193

JO - Applied Geochemistry

JF - Applied Geochemistry

SN - 0883-2927

M1 - 106563

ER -