A strontium isoscape of northern Australia

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 (www.ga.gov.au/ngsa; last access: 15 December 2022). The present study targeted the northern parts of Western Australia, the Northern Territory and Queensland, north of 21.5&deg; S. The samples were taken mostly from a depth of ~60&ndash;80 cm in floodplain deposits at or near the outlet of large catchments (drainage basins). A coarse (&lt; 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 (&gt; 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 &gt; 500 km-long northwest-southeast-trending unradiogenic anomaly (87Sr / 86Sr &lt; 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 (&gt; 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; https://dx.doi.org/10.26186/147473; last access: 15 December 2022).</p

Age and weathering rate of sediments in small catchments:The role of hillslope erosion

Uranium-series (U-series) isotopes in river material can be used to determine quantitative time constraints on the transfer of erosion products from source to sink. In this study, we investigate the U-series isotope composition of river-borne material in small catchments of Puerto Rico and southeastern Australia in order to improve our understanding of (i) the controls on the U-series isotope composition of river-borne material and (ii) how erosion products acquire their geochemical characteristics. In both regions, thorium isotopes track the origin of sediment and dissolved loads. Stream solutes are mainly derived from the deepest part of the weathering profile, whereas stream sediments originate from much shallower horizons, even in landslide-dominated Puerto Rican catchments. This suggests that in environments where thick weathering profiles have developed, solutes and sediments have distinct origins. The U-series isotope composition of stream sediments was modelled to infer a weathering age, i.e. the average time elapsed since the sediment\u27s minerals have started weathering. In southeastern Australia, the weathering age of stream sediments ranges between 346 ± 12 kyr and 1.78 ± 0.16 Myr, similar to values inferred from weathering profiles in the same catchment. Old weathering ages likely reflect the shallow origin of sediments mobilised via near-surface soil transport, the main mechanism of erosion in this catchment. Contrastingly, in Puerto Rico weathering ages are much younger, ranging from 5.1 ± 0.1 to 19.4 ± 0.4 kyr, reflecting that sediments are derived from less weathered, deeper saprolite, mobilised by landslides. Weathering ages of stream sediments are used to infer catchment-wide, mineral-specific weathering rates that are one to two orders of magnitude faster for Puerto Rico than for southeastern Australia. Thus, the type of erosion (near-surface soil transport vs. landslide) also affects the weathering rate of river sediments, because their weathering ages determine the potential for further weathering during sediment transport and storage in alluvial plains

Rapid regolith formation over volcanic bedrock and implications for landscape evolution

The ability to quantify how fast weathering profiles develop is crucial to assessing soil resource depletion and quantifying how landscapes evolve over millennia. Uranium-series isotopes can be used to determine the age of the weathering front throughout a profile and to infer estimates of regolith production rates, because the abundance of U-series isotopes in a weathering profile is a function of chemical weathering and time. This technique is applied to a weathering profile in Puerto Rico developed over a volcaniclastic bedrock. U-series isotope compositions are modelled, revealing that it takes 40-60. kyr to develop an 18. m-thick profile. This is used to estimate an average regolith production rate of 334±46. mm/kyr. This value is higher by a factor of up to 30 when compared to production rates estimated for weathering profiles developed over granitic or shale lithologies. This quantitatively underpins the lithological control on rates of regolith production (in a neighbouring watershed but over a granitic bedrock, production rates are only ~30-40. mm/kyr). Moreover, by comparing these results to a compilation of soil erosion rates, it is clear that landscapes are controlled by the balance (or imbalance) between regolith production and erosion: soil-mantled landscapes are the result of a relative balance between production and erosion, whereas in cratonic areas, thicker weathering profiles are generated because erosion fails to match regolith production rates.9 page(s

Technical note: Optimizing the utility of combined GPR, OSL, and Lidar (GOaL) to extract paleoenvironmental records and decipher shoreline evolution

Records of past sea levels, storms, and their impacts on coastlines are crucial for forecasting and managing future changes resulting from anthropogenic global warming. Coastal barriers that have prograded over the Holocene preserve within their accreting sands a history of storm erosion and changes in sea level. High-resolution geophysics, geochronology, and remote sensing techniques offer an optimal way to extract these records and decipher shoreline evolution. These methods include light detection and ranging (lidar) to image the lateral extent of relict shoreline dune morphology in 3-D, ground-penetrating radar (GPR) to record paleo-dune, beach, and nearshore stratigraphy, and optically stimulated luminescence (OSL) to date the deposition of sand grains along these shorelines. Utilization of these technological advances has recently become more prevalent in coastal research. The resolution and sensitivity of these methods offer unique insights on coastal environments and their relationship to past climate change. However, discrepancies in the analysis and presentation of the data can result in erroneous interpretations. When utilized correctly on prograded barriers these methods (independently or in various combinations) have produced storm records, constructed sea-level curves, quantified sediment budgets, and deciphered coastal evolution. Therefore, combining the application of GPR, OSL, and Lidar (GOaL) on one prograded barrier has the potential to generate three detailed records of (1) storms, (2) sea level, and (3) sediment supply for that coastline. Obtaining all three for one barrier (a GOaL hat-trick) can provide valuable insights into how these factors influenced past and future barrier evolution. Here we argue that systematically achieving GOaL hat-tricks on some of the 300+ prograded barriers worldwide would allow us to disentangle local patterns of sediment supply from the regional effects of storms or global changes in sea level, providing for a direct comparison to climate proxy records. Fully realizing this aim requires standardization of methods to optimize results. The impetus for this initiative is to establish a framework for consistent data collection and analysis that maximizes the potential of GOaL to contribute to climate change research that can assist coastal communities in mitigating future impacts of global warming

Considerations for U-series dating of sediments: insights from the Flinders Ranges, South Australia

Uranium isotope ratios have been determined for the fine-grained detrital fraction of Pleistocene Wilkawillina valley-fill sediments, four local Proterozoic bedrock samples and fine-grained aeolian material from a sand dune deposit of the Flinders Ranges, South Australia. The aim was to quantify the comminution age, i.e. the time elapsed since physical weathering of the bedrock, and residence time of the valley-fill sediments and to place tighter constraints on input parameters for the comminution age calculation. Despite using two independent approaches for determination of the recoil lost fraction of 234U from the sediment (weighted geometric and surface area estimates), samples fail to produce realistic comminution ages and hence, residence times. The issues involved in the ability to determine sediment comminution ages are discussed. The (234U/238U) activity ratio of the local bedrock is not in secular equilibrium, despite the bedrock being much older than 1Ma, i.e. the timeframe for 234U and 238U to reach secular equilibrium in a closed system. Using the average Flinders Ranges bedrock (234U/238U) ratio instead of an assumed (234U/238U) activity ratio of unity for the source would significantly reduce calculated residence times. This result warrants concern for future studies using the comminution approach for which a secular equilibrium source (234U/238U) activity ratio is assumed. Significant input of aeolian material may modify the measured (234U/238U) activity ratios. Such input may be more tightly constrained in future studies using rare earth element and radiogenic isotopic data. Future comminution studies would benefit from further consideration of the importance of 1) leaching lost 234U from source rock and bulk sediment samples, 2) wind deposition of fine-grained material and 3) the appropriateness and robustness of sample pre-treatment procedures

Assessment of metal concentrations in the SOD1\u3csup\u3eG93A\u3c/sup\u3e mouse model of amyotrophic lateral sclerosis and its potential role in muscular denervation, with particular focus on muscle tissue

Background: Amyotrophic lateral sclerosis (ALS) is among the most common of the motor neuron diseases, and arguably the most devastating. During the course of this fatal neurodegenerative disorder, motor neurons undergo progressive degeneration. The currently best-understood animal models of ALS are based on the over-expression of mutant isoforms of Cu/Zn superoxide dismutase 1 (SOD1); these indicate that there is a perturbation in metal homeostasis with disease progression. Copper metabolism in particular is affected in the central nervous system (CNS) and muscle tissue. Methods: This present study assessed previously published and newly gathered concentrations of transition metals (Cu, Zn, Fe and Se) in CNS (brain and spinal cord) and non-CNS (liver, intestine, heart and muscle) tissues from transgenic mice over-expressing the G93A mutant SOD1 isoform (SOD1 G93A), transgenic mice over-expressing wildtype SOD1 (SOD1WT) and non-transgenic controls. Results: Cu accumulates in non-CNS tissues at pre-symptomatic stages in SOD1G93A tissues. This accumulation represents a potentially pathological feature that cannot solely be explained by the over-expression of mSOD1. As a result of the lack of Cu uptake into the CNS there may be a deficiency of Cu for the over-expressed mutant SOD1 in these tissues. Elevated Cu concentrations in muscle tissue also preceded the onset of symptoms and were found to be pathological and not be the result of SOD1 over-expression. Conclusions: It is hypothesized that the observed Cu accumulations may represent a pathologic feature of ALS, which may actively contribute to axonal retraction leading to muscular denervation, and possibly significantly contributing to disease pathology. Therefore, it is proposed that the toxic-gain-of-function and dying-back hypotheses to explain the molecular drivers of ALS may not be separate, individual processes; rather our data suggests that they are parallel processes

The delicate balance between soil production and erosion, and its role on landscape evolution

The diversity in landscapes at the Earth’s surface is the result, amongst other things, of the balance (or imbalance) between soil production and erosion. While erosion rates are well constrained, it is only recently that we have been able to quantify rates of soil production. Uranium-series isotopes have been useful to provide such estimates independently of erosion rates. In this study, new U-series isotope are presented data from weathering profiles developed over andesitic parent rock in Puerto Rico, and granitic bedrock in southeastern Australia. The site in Australia is located on a highland plateau, neighbouring a retreating escarpment where soil production rates between 10 and 50 mm/kyr have been determined. The results show that production rates are invariant in these two regions of Australia with values between 15 and 25 mm/kyr for the new site. Andesitic soils show much faster rates, about 200 mm/ kyr. Overall, soil production rates determined with U-series isotopes range between 10 and 200 mm/ kyr. This is comparable to erosion rates in soil-mantled landscapes, but faster than erosion in cratonic areas and slower than in alpine regions and cultivated areas. This suggests that soil-mantled landscapes maintain soil because they can: there is a balance between production and erosion. Similarly, thick weathering profiles develop in cratonic areas because, despite slow erosion rates, soil production is still significant. Bare landscapes in Alpine regions are probably the result of the inability of soil production to catch up with fast erosion rates, although this needs testing by U-series isotope studies of these regions. Finally, the range of production rates is up to several orders of magnitude lower than erosion rates in cultivated areas, demonstrating quantitatively the fast depletion of soil resources with common agricultural practices

Last interglacial (MIS 5e) sea-level determined from a tectonically stable, far-field location, Eyre Peninsula, southern Australia

The last interglacial maximum (Marine Isotope Substage 5e [MIS 5e], 128¿116 ka) is a distinctive event in recent Earth history. Shoreline successions of this age are important for calibrating climate models and defining the overall behaviour of the crust¿mantle system to fluctuating ice and ocean-water volumes. In a global context, the recently intensified interest in last interglacial shoreline successions has revealed considerable variability in the magnitude of sea-level rise during this time interval and highlighted the need to examine paleosea-level evidence from tectonically stable, far-field settings. Situated in the far-field of continental ice sheets and on the tectonically stable Gawler Craton, the 300 km coastal sector of western Eyre Peninsula between Fowlers Bay and Lake Newland in southern Australia represents an important region for defining the glacio-eustatic (ice-equivalent) sea-level attained during the last interglacial maximum based on the relative sea-level observations from this region. Low-energy, shoaling upward, peritidal bioclastic carbonate successions of the last interglacial (locally termed Glanville Formation) formed within back-barrier, estuarine¿lagoonal environments in the lee of eolianite barrier complexes (locally termed Bridgewater Formation) along this coastline. The well-preserved shelly successions (coquinas) contain diverse molluscan fossil assemblages including species no longer living in the coastal waters of South Australia (e.g. the Sydney cockle Anadara trapezia and the benthic foraminifer Marginopora vertebralis). The extent of amino acid racemisation (a measure of fossil age based on increasing d/l value) in a range of species, and in particular A. trapezia and Katelysia sp., confirms the time equivalence of the isolated embayment-fill successions, correlated with the informal type section of the Glanville Formation at Dry Creek, north of Adelaide. Preliminary U-series analyses on A. trapezia also suggest a correlation with the last interglacial maximum, but further highlight the complexity in dating fossil molluscs by the U-series method in view of their open-system behaviour. The shelly successions of the Glanville Formation occur at elevations higher than attained by sea-level in the current, Holocene interglacial. A higher sea-level of between 2.1 ± 0.5 and 4 ± 0.5 m above present sea-level is inferred for the last interglacial maximum (MIS 5e) along this coastline based on the elevation of sedimentary successions host to the shallow subtidal¿intertidal fossil molluscs Katelysia sp., and Anadara trapezia. The paleosea-level observations place a lower limit on the sea-level attained during the last interglacial maximum and suggest that caution be exercised in the definition of the upper limit of sea-level during this interglacial

Sediment residence time reveals Holocene shift from climatic to vegetation control on catchment erosion in the Balkans

Understanding the evolution of soil systems on geological time scales has become fundamentally important to predict future landscape development in light of rapid global warming and intensifying anthropogenic impact. Here, we use an innovative uranium isotope-based technique combined with organic carbon isotopes and elemental ratios of sediments from Lake Ohrid (North Macedonia/Albania) to reconstruct soil system evolution in the lake's catchment during the last ~16,000 cal yr BP. Uranium isotopes are used to estimated the paleo-sediment residence time, defined as the time elapsed between formation of silt and clay sized detrital matter and final deposition. The chronology is based on new cryptotephra layers identified in the sediment sequence. The isotope and elemental data are compared to sedimentary properties and pollen from the same sample material to provide a better understanding of past catchment erosion and landscape evolution in the light of climate forcing, vegetation development, and anthropogenic land use. During the Late Glacial and the Early Holocene, when wide parts of the catchment were covered by open vegetation, wetter climates promoted the mobilisation of detrital matter with a short paleo-sediment residence time. This is explained by erosion of deeper parts of the weathering horizon from thin soils. Detrital matter with a longer paleo-sediment residence time, illustrating shallow erosion of thicker soils is deposited in drier climates. The coupling between climatic variations and soil erosion terminates at the Early to Mid-Holocene transition as evidenced by a pronounced shift in uranium isotope ratios indicating that catchment erosion is dominated by shallow erosion of thick soils only. This shift suggests a threshold is crossed in hillslope erosion, possibly as a result of a major change in vegetation cover preventing deep erosion of thin soils at higher elevation. The threshold in catchment erosion is not mirrored by soil development over time, which gradually increases in response to Late Glacial to Holocene warming until human land use during the Late Holocene promotes reduced soil development and soil degradation. Overall, we observe that soil system evolution is progressively controlled by climatic, vegetation, and eventually by human land use over the last ~16,000 years