²³⁴U/²³⁸U variation of deep groundwater in low permeable formation

Abstract

As a potential isotopic tracer for groundwater hydrological research, isotopic variation of ²³⁴U/²³⁸U ratios was precisely determined by mass spectrometry. Isotopic variation of ²³⁴U/²³⁸U activity ratios was analyzed from a deep groundwater in low permeable aquifer in Horonobe area in Hokkaido. As the result, ²³⁴U/²³⁸U activity ratios showed disequilibrium conditions, and varied with their sampling depth. Moreover, the formation ages of the carbonate samples precipitated in the aquifer were estimated to evaluate long-time lithological stability in this area. The calculated ages for the carbonate precipitations were almost under the secular equilibrium condition, and they formed at least less than about one million years ago.