Can the He-4 clock be calibrated by Cl-36 for groundwater dating?

The ratio of dissolved excess He-4 concentration to the He-4 accumulation rate is equivalent to the residence time of groundwater if He-4 is accumulated at a constant rate. Groundwater contains Cl-36 from cosmogenic and subsurface production sources. The He-4 clock can be applied by using the correlation between cosmogenic Cl-36 decay or the subsurface Cl-36 production and the excess He-4 increase. We calibrated the He-4 clock in the Great Artesian Basin (GAB), Australia, considering dissolution of chloride from the rock matrix. Cosmogenic Cl-36 is dominant over Cl-36 produced in the subsurface in the Coonarrible Embayment of the GAB, because the quartzose sandstone aquifers have a low density of thermal neutrons. The He-4 accumulation rate was estimated to be 9.6 x 10(-11) ccSTP/g(H2O) (.) y(-1) in the GAB. We then applied this method to estimation of the groundwater residence time in the Tokachi Basin, Japan, where both cosmogenic and subsurface Cl-36 are present in the groundwater. The longest estimated residence time was 2.3 million years, based on a He-4 accumulation rate of (1.2 - 2.1) x 10(-12) ccSTP/cm(H2O)(3) (.) y(-1), assuming that ion filtration occurred as pore water was squeezed by the deeply subsiding sedimentary strata in the basin. (c) 2007 Elsevier B.V. All rights reserved.