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Use of 87Sr/86Sr ratios in groundwater to assess inter-aquifer connectivity

Created 17/10/2025

Updated 17/10/2025

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The Keep River area in the East Kimberley, northern Australia, is underlain by aquifers hosted in both unconsolidated Cenozoic sediments, and Permo-Carboniferous sandstone bedrock. The Permo-Carboniferous sandstone aquifer is in places overlain by the Cenozoic aquifer, and in other areas is exposed at surface, with hydraulic gradients between the aquifers indicating vertical flow from the Permo-Carboniferous sandstone into the Cenozoic. Connectivity between these two aquifers is important to proposals to increase development of irrigated agriculture. Water quality in both aquifers appears to be controlled by the same processes, with extremely fresh (TDS < 100 mg/L) water occurring close to recharge areas, and saline (TDS > 30,000 mg/L) water in both aquifers close to the coast. This makes the identification of connectivity from major ion chemistry difficult. We present new groundwater chemistry and monitoring data for the Keep River area, and describe the use of 87Sr/86Sr ratios in groundwater to identify areas of possible inter-aquifer connectivity. Strontium isotope ratios (87Sr/86Sr) provide an additional method of characterising groundwater. Production of 87Sr occurs through radioactive decay of 87Rb which has a half-life of ~ 4.7 Ga. On the timescales typical of groundwater residence times, 87Sr/86Sr of aquifer material can be treated as constant. The 87Sr/86Sr ratio of groundwater changes over time as a result of equilibration between groundwater and the aquifer matrix. In sedimentary rocks and sediments 87Sr/86Sr will be controlled by the provenance of sediments and is usually dominated by feldspars in siliciclastic lithologies. Highly evolved groundwater samples, identified by elevated Si in solution, show distinctly different 87Sr/86Sr ratios between the Cenozoic and Permo-Carboniferous aquifers, which may indicate limited vertical flow between the aquifers. Further work will focus on the spatial distribution of variations in 87Sr/86Sr ratios. Presented at the 2019 Australasian Groundwater Conference (AGC 2019)

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Field Value
Title Use of 87Sr/86Sr ratios in groundwater to assess inter-aquifer connectivity
Language eng
Licence Not Specified
Landing Page https://data.gov.au/data/en/dataset/1108168a-8411-4dcb-89db-b7a921f008ad
Contact Point
Geoscience Australia Data
clientservices@ga.gov.au
Reference Period 23/09/2025
Geospatial Coverage
Map data © OpenStreetMap contributors
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Data Portal Geoscience Australia

Data Source

This dataset was originally found on Geoscience Australia "Use of 87Sr/86Sr ratios in groundwater to assess inter-aquifer connectivity". Please visit the source to access the original metadata of the dataset:
https://ecat.ga.gov.au/geonetwork/srv/eng/csw/dataset/use-of-87sr-86sr-ratios-in-groundwater-to-assess-inter-aquifer-connectivity