<div>Strontium isotopes (87Sr/86Sr) are useful in the earth sciences (e.g. recognising geological provinces, studying geological processes) as well in archaeological (e.g. informing on past human migrations), palaeontological/ecological (e.g. investigating extinct and extant taxa’s dietary range and migrations) and forensic (e.g. validating the origin of drinks and foodstuffs) sciences. Recently, Geoscience Australia and the University of Wollongong have teamed up to determine 87Sr/86Sr ratios in fluvial sediments selected mostly from the low-density National Geochemical Survey of Australia (www.ga.gov.au/ngsa), with a few additional Northern Australia Geochemical Survey infill samples. The present study targeted the northern parts of Western Australia, the Northern Territory and Queensland in Australia, north of 21.5 °S. The samples were taken mostly from a depth of ~60-80 cm depth in floodplain deposits at or near the outlet of large catchments (drainage basins). A coarse grain-size fraction (&lt;2 mm) was air-dried, sieved, milled then digested (hydrofluoric acid + nitric acid followed by aqua regia) to release total strontium. Preliminary results demonstrate a wide range of strontium isotopic values (0.7048 &lt; 87Sr/86Sr &lt; 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 (&gt;100 km) patterns that appears to be consistent, in many places, with surface geology, regolith/soil type and/or nearby outcropping bedrock. For instance, the extensive black clay soils of the Barkly Tableland define a &gt;500 km-long northwest-southeast-trending low anomaly (87Sr/86Sr &lt; 0.7182). Where carbonate or mafic igneous rocks dominate, a low to moderate strontium isotope signature is observed. In proximity to the outcropping Proterozoic metamorphic provinces of the Tennant, McArthur, Murphy and Mount Isa geological regions, conversely, high 87Sr/86Sr values (&gt; 0.7655) are observed. A potential link 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 strontium 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 strontium isoscape and model derived therefrom can also be utilised in archaeological, paleontological and ecological studies that aim to investigate past and modern animal (including humans) dietary habits and migrations. &nbsp;The new spatial dataset is publicly available through the Geoscience Australia portal https://portal.ga.gov.au/.</div>

<div>Strontium isotopes (87Sr/86Sr) are useful in the earth sciences (e.g. recognising geological provinces, studying geological processes) as well in archaeological (e.g. informing on past human migrations), palaeontological/ecological (e.g. investigating extinct and extant taxa’s dietary range and migrations) and forensic (e.g. validating the origin of drinks and foodstuffs) sciences. Recently, Geoscience Australia and the University of Wollongong have teamed up to determine 87Sr/86Sr ratios in fluvial sediments selected mostly from the low-density National Geochemical Survey of Australia (NGSA; www.ga.gov.au/ngsa). The present study targeted the Yilgarn geological region in southwestern Australia. The samples were mostly taken from a depth of ~60-80 cm (Bottom Outlet Sediments, BOS) in floodplain deposits at or near the outlet of large catchments (drainage basins). A small number of surface (0-10 cm) samples (Top Outlet Sediments, TOS) were also included in the study. For all, a coarse grain-size fraction (<2 mm) was air-dried, sieved, milled then digested (hydrofluoric acid + nitric acid followed by aqua regia) to release total strontium. Overall, 107 NGSA BOS < 2 mm and 13 NGSA TOS < 2 mm were analysed for Sr isotopes. Given that there are ~10 % field duplicates in the NGSA, all those samples originate from within 97 NGSA catchments, which together cover 533 000 km2 of southwestern Australia. Preliminary results for the BOS samples demonstrate a wide range of strontium isotopic values (0.7152 < 87Sr/86Sr < 1.0909) 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 consistent, in many places, with surface geology, regolith/soil type and/or nearby outcropping bedrock. For instance, catchments in the western and central Yilgarn dominated by felsic intrusive basement geology have radiogenic 87Sr/86Sr signatures in the floodplain sediments consistent with published whole-rock data. Similarly, unradiogenic signatures in sediments in the eastern Yilgarn are in agreement with published whole-rock data. Our results to-date indicate that incorporating soil/regolith strontium 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 strontium isoscape and model derived therefrom can also be utilised in archaeological, paleontological and ecological studies that aim to investigate past and modern animal (including humans) dietary habits and migrations.&nbsp; The new spatial dataset is publicly available through the Geoscience Australia portal https://portal.ga.gov.au/.</div>

<div>Strontium isotopes (87Sr/86Sr) are useful in the earth sciences (e.g. recognising geological provinces, studying geological processes) as well as in archaeological (e.g. informing on past human migrations), palaeontological/ecological (e.g. investigating extinct and extant taxa’s dietary range and migrations) and forensic (e.g. validating the origin of drinks and foodstuffs) sciences. Recently, Geoscience Australia and the University of Wollongong have teamed up to determine 87Sr/86Sr ratios in fluvial sediments selected mostly from the low-density National Geochemical Survey of Australia (NGSA; www.ga.gov.au/ngsa). Three regional projects were focussed on: inland southeastern, northern, and southwestern Australia, together covering over 2.5 million km2 of catchment area. Whilst results on <em>total</em> Sr isotopic analyses have been reported previously (Caritat et al. 2022, 2023, 2024), a pilot study targeting the isotopic composition of <em>bioavailable</em> (or labile) Sr was conducted in parallel and this dataset is released here. In contrast to the total Sr isotope analyses, which were conducted mostly on NGSA Bottom Outlet Sediments (BOS; taken on average from ~60-80 cm depth), the bioavailable Sr work used Top Outlet Sediments (TOS; taken from 0-10 cm depth) to make the results more relevant to soil-, plant- and animal-focused applications. Approximately 1 g of air-dried, coarse-sieved (<2 mm) soil sample was reacted with 2.5 M ammonium acetate (buffered to pH 7) for 24 hr on a mixing table, to extract operationally defined plant-available cations (after Stewart et al. 1998). The solution was filtered at 0.45 µm and dried down to incipient dryness. The residue was re-dissolved in 2M nitric acid. The Sr was separated by chromatography and its 87Sr/86Sr ratio determined by multicollector-inductively coupled plasma-mass spectrometry. Results for 278 samples across all three regions demonstrate a wide range of bioavailable Sr isotopic values (0.7050 to 0.7812, median 0.7191) across Australia, reflecting a large diversity of source rock lithologies, geological, pedogenic and biogeochemical processes, and, ultimately, bedrock ages. Modelling and interpretation of this dataset will be presented elsewhere. The resulting bioavailable Sr isoscape for Australia, although sparse at the moment, and models to be derived therefrom, may have applications in archaeological, paleontological and ecological studies that aim to investigate past and modern animal (including humans) dietary habits and migrations.&nbsp;The new spatial dataset is publicly available through the Geoscience Australia portal (https://portal.ga.gov.au/).</div><div><br></div><div>References cited</div><div>Caritat, P. de, Dosseto, A., Dux, F., 2022. A strontium isoscape of inland southeastern Australia, Earth System Science Data, 14, 4271–4286, https://doi.org/10.5194/essd-14-4271-2022 </div><div>Caritat, P. de, Dosseto, A., Dux, F., 2023. A strontium isoscape of northern Australia, Earth System Science Data, 15, 1655–1673, https://doi.org/10.5194/essd-15-1655-2023 </div><div>Caritat, P. de, Dosseto, A., Dux, F., 2024. A strontium isoscape of southwestern Australia and progress toward a national strontium isoscape, Earth System Science Data Discussion [non peer-reviewed preprint], https://doi.org/10.5194/essd-2024-352 </div><div>Stewart, B. W., Capo, R. C., Chadwick, O. A., 1998. Quantitative strontium isotope models for weathering, pedogenesis and biogeochemical cycling, Geoderma, 82, 173–195, https://doi.org/10.1016/S0016-7061(97)00101-8 </div>