16 Jan 2023
16 Jan 2023
Status: this preprint is currently under review for the journal ESSD.

A strontium isoscape of northern Australia

Patrice de Caritat1, Anthony Dosseto2, and Florian Dux2 Patrice de Caritat et al.
  • 1Geoscience Australia, GPO Box 378, Canberra ACT 2601, Australia
  • 2Wollongong Isotope Geochronology Laboratory, School of Earth, Atmospheric and Life Sciences, University of Wollongong, Wollongong NSW 2522, Australia

Abstract. Strontium isotopes (87Sr / 86Sr) are useful in the Earth sciences as well as in forensic, archaeological, palaeontological, and ecological sciences. As very few large-scale Sr isoscapes exist in Australia, we have identified an opportunity to determine 87Sr / 86Sr ratios on archive fluvial sediment samples from the low-density National Geochemical Survey of Australia (; last access: 15 December 2022). The present study targeted the northern parts of Western Australia, the Northern Territory and Queensland, north of 21.5° S. The samples were taken mostly from a depth of ~60–80 cm in floodplain deposits at or near the outlet of large catchments (drainage basins). A coarse (< 2 mm) grain-size fraction was air-dried, sieved, milled then digested (hydrofluoric acid + nitric acid followed by aqua regia) to release total Sr. The Sr was then separated by chromatography and the 87Sr / 86Sr ratio determined by multicollector-inductively coupled plasma mass spectrometry. Preliminary results demonstrate a wide range of Sr isotopic values (0.7048 to 1.0330) over the survey area, reflecting a large diversity of source rock lithologies, geological processes and bedrock ages. Spatial distribution of 87Sr / 86Sr shows coherent (multi-point anomalies and smooth gradients), large-scale (> 100 km) patterns that appear to be broadly consistent with surface geology, regolith/soil type, and/or nearby outcropping bedrock. For instance, the extensive black clay soils of the Barkly Tableland define a > 500 km-long northwest-southeast-trending unradiogenic anomaly (87Sr / 86Sr < 0.7182). Where carbonate or mafic igneous rocks dominate, a low to moderate Sr isotope signature is observed. In proximity to the outcropping Proterozoic metamorphic basement of the Tennant, McArthur, Murphy and Mount Isa geological regions, conversely, radiogenic 87Sr / 86Sr values (> 0.7655) are observed. A potential correlation between mineralisation and elevated 87Sr / 86Sr values in these regions needs to be investigated in greater detail. Our results to-date indicate that incorporating soil/regolith Sr isotopes in regional, exploratory geoscience investigations can help identify basement rock types under (shallow) cover, constrain surface processes (e.g. weathering, dispersion), and, potentially, recognise components of mineral systems. Furthermore, the resulting Sr isoscape and future models derived therefrom can also be utilised in forensic, archaeological, paleontological and ecological studies that aim to investigate, e.g., past and modern animal (including humans) dietary habits and migrations. The new spatial Sr isotope dataset for the northern Australia region is publicly available (de Caritat et al., 2022a;; last access: 15 December 2022).

Patrice de Caritat et al.

Status: open (until 13 Mar 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on essd-2022-446', Ian Moffat, 31 Jan 2023 reply
  • RC1: 'Comment on essd-2022-446', Ian Moffat, 31 Jan 2023 reply
  • RC2: 'Comment on essd-2022-446', Malte Willmes, 31 Jan 2023 reply

Patrice de Caritat et al.

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A strontium isoscape of northern Australia de Caritat, P., Dosseto, A., and Dux, F.

Patrice de Caritat et al.


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Short summary
This new, extensive dataset from northern Australia contributes considerable new data and knowledge to Australia’s strontium isotope coverage. The data are discussed in terms of the lithology and age of the source lithologies. This dataset will reduce northern-hemisphere bias in future global strontium isotope models. Other potential applications of the new data include mineralisation, hydrology, food tracing, dust provenancing, and historic migrations of people and animals.