Groundwater dating in the Great Artesian Basin (GAB) using radioactive noblegas isotopes (Kr-85, Ar-39, Kr-81)

R. Purtschert, A.J. Love, Z-T. Lu, W. Jiang, P. Mueller, G-M. Yang, P. Shand, D. Wohling, S. Fulton, W. Aeschbach-Hertig, L. Broder

In the proceedings of: GeoMontréal 2013: 66th Canadian Geotechnical Conference; 11th joint with IAH-CNC

Session: Isotope Tracing I

ABSTRACT: The Great Artesian Basin (GAB) of Australia is one of the largest groundwater basins in the world and contains the largest storage of potable groundwater in the Australian continent. Our study area is focused on the western margin of the GAB between the Finke River system in the Northern Territory and the iconic Dalhousie springs in South Australia. This represents the direction of groundwater flow from recharge to discharge through the Dalhousie spring complex. For the first time we have provided a comprehensive suite of analyses not only of Cl-36, He-4, C-14, Ar-39, stable isotopes of the water molecule and noble gases but also, Kr-85 and Kr-81. Our results indicate a spectrum of fitracer groundwater agesfl ranging from modern as indicated by C-14 (T1/2: 5730 yr) and Ar-39 (T1/2: 269 yr) up to hundreds of thousands of years as indicated by Kr-81 (T1/2: 229 kyr), Cl-36 (T1/2:5730 yr) and He-4. Kr-81 ages are used for an assessment of factors that may influence the interpretation of He-4 and Cl-36 concentrations in terms of groundwater residence times. Our comprehensive data set including three radioactive noblegas isotopes provides the basis for a deeper understanding of environmental tracer systematics in order to obtain a greater knowledge of regional groundwater flow systems

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