Browsing by Author "Fujioka, T"

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    26Al/10Be ratios reveal the source of river sediments in the Kimberley, NW Australia
    (Wiley, 2020-02-07) Cazes, G; Fink, D; Codilean, AT; Fülöp, RH; Fujioka, T; Wilcken, KM
    We use cosmogenic 10Be and 26Al in both bedrock and fluvial sediments to investigate controls on erosion rates and sediment supply to river basins at the regional scale in the Kimberley, NW Australia. The area is characterised by lithologically controlled morphologies such as cuestas, isolated mesas and extensive plateaus made of slightly dipping, extensively jointed sandstones. All sampled bedrock surfaces at plateau tops, ridgelines, and in the broader floodplain of major rivers over the region show similar slow lowering rates between 0.17 and 4.88 m.Myr-1, with a mean value of 1.0 ± 0.6 m.Myr-1 (n=15), whilst two bedrock samples collected directly within river-beds record rates that are one to two orders of magnitude higher (14.4 ± 1.5 and 20.9 ± 2.5 m.Myr-1, respectively). Bedrock 26Al/10Be ratios are all compatible with simple, continuous sub-aerial exposure histories. Modern river sediment yield lower 10Be and 26Al concentrations, apparent 10Be basin-wide denudation rates ranging between 1.8 and 7.7 m.Myr-1, with a median value of 2.6 m.Myr-1, more than double the magnitude of bedrock erosion rates. 26Al/10Be ratios of the sediment samples are lower than those obtained for bedrock samples. We propose that these depleted 26Al/10Be ratios can largely be explained by the supply of sediment to river basins from the slab fragmentation and chemical weathering of channel gorge walls and plateau escarpments that result in diluting the cosmogenic nuclide concentration in river sediments measured at the basin outlets. The results of a mass-balance model suggest that ~60–90% of river sediment in the Kimberley results from the breakdown and chemical weathering of retreating vertical sandstone rock-walls in contrast to sediment generated by bedrock weathering and erosion on the plateau tops. This study emphasises the value of analysing two or more isotopes in basin-scale studies using cosmogenic nuclides, especially in slowly eroding post-orogenic settings. © 2019 John Wiley & Sons, Ltd.
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    Antiphase dynamics between cold-based glaciers in the Dry Valleys region and ice extent in the Ross Sea, Antarctica during MIS 5
    (Australian Nuclear Science and Technology Organisation, 2021-11-17) Anderson, JTH; Fink, D; Fujioka, T; Wilson, GS; Wilcken, KM; Abramov, A; Demidov, N
    During interglacial conditions in Marine Isotope Stage (MIS) 5, outlet and alpine glaciers in the Dry Valleys region, Antarctica, appear to have advanced in response to increased open ocean in the Ross Sea. However, the timing and extent of antiphase behaviour between these glaciers and ice in the Ross Sea is poorly resolved. Here, we report the antiphase behaviour through retreat of a peripheral lobe of Taylor Glacier in Pearse Valley, an area that was glaciated during MIS 5. First, we measured cosmogenic ¹⁰ Be and ²⁶ Al in 3 granite cobbles from thin, patchy drift (Taylor 2 Drift) in Pearse Valley to constrain the timing of retreat of Taylor Glacier. Assuming simple continuous exposure, our exposure ages suggest Taylor Glacier had partially retreated from Pearse Valley no later than 71 ka. Timing of retreat after 71 ka, until the Last Glacial Maximum (LGM), when Taylor Glacier was at a minimum position, remains unresolved. Second, we measured paired ¹⁰ Be and ²⁶ Al depth profiles to ~3 metres in permafrost in proximity to the cobble sampling sites at Pearse Valley and neighbouring Lower Wright Valley. The ¹⁰ Be and ²⁶ Al depth profiles from both sites show no clear exponential attenuation trend which suggest that both deposits are too young for the most recent exposure (≥71 ka for Pearse Valley and LGM – early Holocene for Lower Wright Valley) to alter the profile, and measured nuclide concentrations are essentially dominated by inheritance. Using ¹⁰ Be depth profile data from Pearse Valley we calculate a maximum age of ~100 ka for surface layer permafrost formation. The cobble exposure-ages and depth profile constrain surface permafrost formation in Pearse Valley to between ~71 – 102 ka, following the retreat of the Taylor Glacier from Pearse Valley. These new data are consistent with geochronology from central Taylor Valley, and suggest changes in moisture delivery over Taylor Dome during MIS 5c and 5a appear to be associated with the extent of the Ross Ice Shelf and sea ice in the Ross Sea. Our ²⁶ Al/¹⁰ Be concentration ratios for all depth profile samples also exhibit relatively constant and suppressed ratios of 4.3 and 5.2 for Pearse and Wright valleys, respectively, indicating that prior to surface permafrost formation, these sediments experienced a significant complex prior exposure history. Assuming a simple burial scenario, the observed ²⁶ Al/¹⁰ Be ratios are equivalent to a total exposure-burial history of ~1.2 Ma, somewhat consistent with the Packard dune field in Victoria Valley. Our new data corroborate antiphase behaviour between outlet and alpine glaciers in the Dry Valleys region and ice extent in the Ross Sea, and imply a causal mechanism with cold-based glacier advance and retreat being controlled by moisture availability and drying, respectively due to ice retreat and expansion in the Ross Sea. © The Authors
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    Asynchronous glaciations in arid continental climate
    (Elsevier, 2018-02-15) Batbaatar, J; Gillespie, AR; Fink, D; Matmon, A; Fujioka, T
    Mountain glaciers at ∼26–19 ka, during the global Last Glacial Maximum near the end of the last 105 yr glacial cycle, are commonly considered on the basis of dating and field mapping in several well-studied areas to have been the largest of the late Quaternary and to have advanced synchronously from region to region. However, a numerical sensitivity model (Rupper and Roe, 2008) predicts that the fraction of ablation due to melting varies across Central Asia in proportion to the annual precipitation. The equilibrium-line altitude of glaciers across this region likely varies accordingly: in high altitude, cold and arid regions sublimation can ablate most of the ice, whereas glaciers fed by high precipitation cannot ablate completely due to sublimation alone, but extend downhill until higher temperatures there cause them to melt. We have conducted field studies and 10Be dating at five glaciated sites along a precipitation gradient in Mongolia to test the Rupper/Roe model. The sites are located in nearby 1.875 × 1.875° cells of the Rupper/Roe model, each with a different melt fraction, in this little-studied region. The modern environment of the sites ranges from dry subhumid in the north (47.7° N) to arid in the south (45° N). Our findings show that the maximum local advances in the dry subhumid conditions predated the global Last Glacial Maximum and were likely from MIS 3. However, we also found that at ∼8–7 ka a cirque glacier in one mountain range of the arid Gobi desert grew to a magnitude comparable to that of the local maximum extent. This Holocene maximum occurred during a regional pluvial period thousands of years after the retreat of the Pleistocene glaciers globally. This asynchronous behavior is not predicted by the prevailing and generally correct presumption that glacier advances are dominantly driven by temperature, although precipitation also plays a role. Our findings are consistent with and support the Rupper/Roe model, which calls for glaciation in arid conditions only at high altitudes of sub-freezing temperatures, where the melt fraction in ablation is low. We expect a heterogeneous pattern of glacial responses to a changing modern climate in cold arid regions; an individual glacier advance should not be necessarily interpreted as evidence of cooling climate.© 2017 Elsevier Ltd.
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    Beryllium isotope signatures of ice shelves and sub-ice shelf circulation
    (Elsevier, 2019-01-01) White, DA; Fink, D; Post, AL; Simon, KJ; Galton-Fenzi, BK; Foster, S; Fujioka, T; Jeromson, MR; Blaxell, M; Yokoyama, Y
    Be isotopes are a useful tracer of sediment source and transport pathways but have not been widely tested in glacio-marine environments. We measured Be isotopes in a range of depositional environments from open marine, sub-ice shelf and subglacial settings throughout Prydz Bay, one of Antarctica's largest ice drainage systems. We find that strong sub-ice shelf and bottom current circulations can advect 10Be-rich open marine sediments into an ice shelf cavity, and 10Be-poor terrestrial sediments onto the continental shelf at the ice shelf outflow, meaning that 10Be concentrations reflect sub-ice shelf circulation patterns rather than depositional environment. However, HCl-extractable 10Be/9Be ratios can provide a more robust discrimination of sediment deposited in open marine and sub-ice shelf settings. Thus, Be isotopes are a useful tracer of both environmental setting and sub-ice shelf circulation strength in both modern and paleo-ice sheet margins. Crown Copyright © 2018 Published by Elsevier B.V.
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    Buried, but not forgotten — reconciling climate dynamics with catchment evolution in the East Kimberley using 10Be & 26Al
    (Australian Geosciences Council, 2012-08-05) Swander, ZJ; Dosseto, A; Fink, D; Mifsud, C; Fujioka, T
    In the well entrenched bedrock rivers of northwest Australia, fluvial geomorphic processes rely both on intense energy pulses input to the hydrologic system, and the negation of bedrock choke points or “gates”. Established Quaternary paleoclimate records identify warm and wet interglacial conditions associated with catastrophic flood episodes along the inland Ord River during the Upper Pleistocene. Today, the “neo-Ord” cuts a jagged 600km mixed bed course through the semi-arid landscape of the East Kimberley, when seasonally inundated by monsoon. Beneath the Ivanhoe Plain near Kununnura, up to 30m of pre-Holocene aggraded valley fill obscure the river’s paleo-path to the Joseph Bonaparte Gulf, over 100km from present day mouth. By exploring the links between fluvial activity and monsoon variability, this project aims to constrain the chronology of bedrock channel migration in the transition from older to younger bedrock gates, and any associated incision. This was accomplished by quantifying 16 in situ bedrock minimum exposure ages from 5 study sites across varied lithologies. Terrestrial Cosmogenic Radionuclides (TCN), 10Be and 26Al, are the result of incoming cosmic radiation sparking spallation reactions penetrating ∼50cm of the the bedrock surface. Our results will test the hypothesis that multiple early interglacial intensifications of the regional monsoon, dating back to MIS 11, would provide the catalyst for trunk channel migration and a general disruption of the steady-state. Base level readjustment should manifest most clearly by rapid bedrock incision within gorges, and at back-cutting knickpoint retreats along unconstrained rock bars.
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    The Centre for Accelerator Science at ANSTO
    (International Atomic Energy Agency, 2014-01-14) Hotchkis, MAC; Child, DP; Cohen, DD; Dodson, JR; Fink, D; Fujioka, T; Garton, D; Hua, Q; Ionescu, M; Jacobsen, GE; Levchenko, VA; Mifsud, C; Pastuovic, Z; Siegele, R; Smith, AM; Wilcken, KM; Williams, AG
    In 2009, the Federal government provided funding of $25m to ANSTO through the Education Investment Fund, to build state-of-the-art applied accelerator science facilities, with the primary aim of providing world-leading accelerator mass spectrometry (AMS) and ion beam analysis (IBA) facilities. New buildings are now under construction and Building plans are now well advanced, and two new accelerators are on order with National Electrostatics Corporation, USA. The 1MV AMS accelerator system is designed with the capability to perform high efficiency, high precision AMS analysis across the full mass range. Large beam-optical acceptance will ensure high quality and high throughput radiocarbon measurements. High mass resolution analyzers, at low and high energy, coupled to a novel fast isotope switching system, will enable high quality analysis of actinide radioisotopes. The 6MV tandem accelerator will be instrumented with a wide range of AMS, IBA and ion irradiation facilities. The three ion sources include hydrogen and helium sources, and a MCSNICS sputter source for solid materials. The AMS facility has end stations for (i) a gasabsorber detector for 10Be analysis, (ii) a time-of-flight detector, (iii) a gas-filled magnet and(iv) a general use ionization detector suited to 36Cl and other analyses. Initially, there will be four IBA beamlines, including a new ion beam microprobe currently on order with Oxford Microbeams. The other beamlines will include an on-line ion implanter, nuclear reaction analysis and elastic recoil detection analysis facilities. The beam hall layout allows for future expansion, including the possibility of porting the beam to the existing ANTARES beam hall for simultaneous irradiation experiments.Two buildings are currently under construction, one for the new accelerators and the other for new chemistry laboratories for AMS and mass spectrometry facilities. The AMS chemistry labs are planned in two stages, with the new radiocarbon labs to come in the second phase of work.
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    Challenging intraplate orogens: from geomorphology to lithospheric dynamic. The French Massif Central case study
    (Copernicus GmbH, 2020-05-04) Malcles, O; Vernant, P; Ritz, JF; Fink, D; Cazes, G; Fujioka, T; Braucher, R; Camps, P
    In the 60’s, the formulation of the plate tectonic theory changed our understanding of the Earth dynamics. Aiming at explaining the earth first order kinematics, this primary theory of plate tectonic assumed rigid plates, a necessity to efficiently transfer stress from one boundary to another. If successful to explain, at first order, the plate-boundary evolutions, this theory fails when compared to the unpredicted but identified deformation located inside the plate-domains: the intraplate orogens. Indeed, the intraplate regions are thought to be slowly, if at all, deforming. Therefore, it is expected that intraplate regions do not show important finite deformation, that is to say, no mountains. Some intraplate regions, however, have important relief: the Snowy Mountains (Australia), the Ural Mountains (Russia) or the Massif Central (France) for examples. Traditionally, such regions are interpreted as old structures that are slowly eroded, interpretations that are most of the time weakly constrained. Our study is aiming at providing stronger constraints and then a better understanding of such challenging area that are the intraplate orogen domains. Because direct measurements of deformations (e.g. GNSS: Global Navigation Satellite System or InSAR: Interferometric Synthetic Aperture Radar) are most of the time below the precision level, it is necessary to derive this information from the landscape evolution. To do so, terrestrial cosmogenic nuclide (TCN) technics are a key method, allowing to constraint the temporal landscape evolution. Classically, two TCN-based approaches are used to quantify the landscape evolution rate: burial ages and watershed-wide denudation rates, based on measurement in quartz sediment of 10Be and 26Al concentrations, two radioactive cosmogenic isotopes. Using the Massif Central (France) as study area, we show that this region is currently deforming. From new geochronological constraints and a geomorphometric study, we propose that the region undergoes an active uplift encompassing the last c.a. 4 Ma. It can be explained by the combination of at least two phenomena: the first one is the uplift triggering event, that has yet to be clearly identified, and the second one: the erosional isostatic adjustment enhancing the first one and possibly continuing after the end of the first one.
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    Controls on 10Be dilution in catchments affected by coseismic landsliding: a 2016 Kaikōura earthquake case-study
    (Australian Nuclear Science and Technology Organisation, 2021-11-17) Wilkinson, C; Stahl, T; Jones, K; Fujioka, T; Fink, D; Norton, KP
    The 2016 Mw 7.8 Kaikōura earthquake triggered tens of thousands of landslides across the northern Canterbury and southern Marlborough regions in the South Island of Aotearoa New Zealand. The influence of landslides generated by this earthquake on sediment generation, transport and deposition in stream networks has varied across the region and through time — some catchments show significant and near-immediate responses while others show little to no change despite the extensive landsliding. We measured 10Be concentrations in detrital quartz sands over a two-year period in the Conway River catchment, which has a total area of ~475 km2 and had ~13 M m3 of new landslide material liberated from hillslopes during the 2016 Kaikōura earthquake. Samples for 10Be analysis were collected at the rangefront of the Seaward Kaikōura Mountains and near the catchment outlet on three sampling campaigns between 2017-2018. We also carried out a similar sampling regime in the nearby Hurunui catchment, which was unaffected by the 2016 Kaikōura earthquake. Measured 10Be concentrations were converted to basin wide mean denudation rates using accepted GIS-based elevation and shielding programs. Our results indicate that apparent catchment-wide erosion rates in the Conway River (i) did not change through time, (ii) have remained similar to basin mean erosion rates for the Hurunui, (iii) overlap with the range of values for exhumation rates of the region (from previously published low-temperature thermochronology data), and (iv) are influenced in part by selection of grain size. We also compared our 10Be concentrations for the Conway catchment to values derived by modelling mean landslide 10Be concentrations constrained by local production rates, detailed mapping of all landslides across the catchment, area-volume scaling, and landslide-channel connectivity estimates. Our modelling estimates show that the mean 10Be concentrations derived from landslide sediment would have been sufficient to dilute pre-earthquake catchment-wide 10Be values by up to a factor of 3. We explore various landscape and landslide parameters that may explain the mismatch between measured and modelled 10Be and ascertain that the combination of storage, site specific channel connectivity, and landslide geometries/failure mechanisms likely exert first-order controls on in-situ 10Be concentrations following such a large catchment-wide disturbance event. We conclude that using fluvial quartz grains to characterise catchment response to landsliding and the mass balance of earthquakes, is subject to a number of factors that are highly site-specific. © The Authors
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    Cosmogenic evidence for limited local LGM glacial expansion, Denton Hills, Antarctica
    (Elsevier, 2017-12-15) Joy, K; Fink, D; Storey, BC; De Pascale, GP; Quigley, M; Fujioka, T
    The geomorphology of the Denton Hills provides insight into the timing and magnitude of glacial retreats in a region of Antarctica isolated from the influence of the East Antarctic ice sheet. We present 26 Beryllium-10 surface exposure ages from a variety of glacial and lacustrine features in the Garwood and Miers valleys to document the glacial history of the area from 10 to 286 ka. Our data show that the cold-based Miers, Joyce and Garwood glaciers retreated little since their maximum positions at 37.2 ± 6.9 (1σ n = 4), 35.1 ± 1.5 (1σ, n = 3) and 35.6 ± 10.1 (1σ, n = 6) ka respectively. The similar timing of advance of all three glaciers and the lack of a significant glacial expansion during the global LGM suggests a local LGM for the Denton Hills between ca. 26 and 51 ka, with a mean age of 36.0 ± 7.5 (1σ, n = 13) ka. A second cohort of exposure ages provides constraints to the behaviour of Glacial Lake Trowbridge that formerly occupied Miers Valley in the late Pleistocene. These data show active modification of the landscape from ∼20 ka until the withdrawal of ice from the valley mouths, and deposition of Ross Sea Drift, at 10–14 ka. © 2017 Elsevier Ltd.
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    Cosmogenic radionuclides as signatures of past Solar storm events
    (Australian National University, 2019-09-09) Smith, AM; Wilcken, KM; Simon, KJ; Dee, MW; Kuitems, M; Scifo, A; Moy, A; Curran, MAJ; Wallner, A; Fink, D; Fujioka, T
    This collaborative project examines the relationship between the ‘Carrington Event’ (CE), the largest solar storm of modern times, and two recently discovered cosmic radiation events of greater magnitude, the ‘Miyake Events’ (ME). The intention is to construct cosmogenic isotope (14C, 10Be and 36Cl) profiles across the CE, so they can be compared with similar data that have already been obtained for the ME. We will use ice cores from Law Dome, East Antarctica, collected under Australian Antarctic Science awards, for the 10Be and 36Cl analyses. The large diameter DSS0506 ice core will permit high-resolution measurements at ANSTO of 10Be and 36Cl across the CE. Furthermore, we also intend to measure 10Be and 36Cl in the main DSS ice core across the ME. These measurements will complement existing data as both isotopes will be measured in the same ice core for each event for the first time and at high temporal resolution. New tree rings spanning the CE and ME, sourced from the Oxford Dendrochronology Laboratory, have been measured for 14C at the University of Groningen at mostly annual resolution. The ultimate goal of this study is to determine whether or not all three events are manifestations of the same phenomena. A secondary goal is to provide a check on the independent DSS-main ice core chronology. The CE of 1859 is known from geomagnetic data and contemporary records of the aurorae, which were observed as far south as the tropics. The event predated ground-based neutron detectors and routine cosmogenic isotope measurement, so the intensity of the incident particle radiation is still a matter of conjecture. Indeed, this question has been thrown into sharp focus recently by new discoveries in palaeoastronomy. Analyses of natural archives (tree-rings and ice-cores) have revealed that production of the cosmogenic isotopes 14C, 10Be and 36Cl spiked dramatically in the years 774-775 AD and 993-994 AD. Such anomalies could only have been generated by sudden bursts of cosmic radiation. Several sources were initially proposed for the radiation, however, the consensus now is that they were driven by solar activity. Here we discuss progress with the measurement of the cosmogenic radioisotopes and consider how the relative production rates of the cosmogenic radioisotopes may be used to substantiate a solar cause for the historical radiation events and to infer the spectral hardness of the initiating solar protons. © The Authors.
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    Deciphering the role of terrigenous sediment supply for headwater channels in the Pilbara, WA
    (Australasian Quaternary Association Inc., 2022-12-06) Flatley, AJ; May, JH; Fujioka, T; Fink, D
    Using a multi cosmogenic nuclide approach (10Be and 26Al) we investigate terrigenous sediment supply in catchments to provide much needed baseline denudation rates in the Pilbara region. Detailed analysis of catchment morphometric properties and lithology have been combined with cosmogenic nuclide measurements to improve our understanding of sediment pathways, residence times and storage in headwater catchments. Our results suggest that this region has some of the lowest erosion rates in the world, between 0.94-4.04 mMyr-1, a range similar to previously measured channel bedrock rates in the region, but somewhat higher than results from outcrops on mesa summits previously measured using 53Mn (0.8 ± 0.6 mMyr-1). This apparent offset in erosion rates between horizontal bedrock surfaces and basin wide averages infers that the vast areas of iron-rich rock surfaces within the region are unlikely a major contributor of sediment to the system. Instead, vertical faces in the catchments have a role as a dominant sediment source and there is a complex erosional history of in-channel sediments within the headwater streams. Our results show 26Al/10Be ratios lower than the nominal production ratio, suggesting that the channel sediments are provided from either (or combination of) long-term, shallow buried regolith, or non-horizontal surfaces in the landscape (e.g., gorges and exposed cliffs). Erosion at the margins of the river channels is hence a key source of sediment supply and broadly the hillslope-headwater channel sediment conveyer is a minor contributor. Base-level stability and highly resistant nature of the prevailing lithology in the region results in these extremely low erosion rates in a high slope environment. Within these headwater catchments, sediment contributions are compounded by topographic inversion, increased albeit episodic fluvial activity and highly erosion resistant Banded Iron Formation. The study demonstrates that a multi cosmogenic nuclide approach is useful, not only to evaluate denudation rates, but also to decipher the complex history of sediment production and transport.
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    Development of a multi-method chronology spanning the last glacial interval from Orakei maar lake, Auckland, New Zealand
    (European Geosciences Union, 2020-12-15) Peti, L; Fitzsimmons, KE; Hopkins, JL; Nilsson, A; Fujioka, T; Fink, D; Mifsud, C; Christl, M; Muscheler, R; Augustinus, PC
    Northern New Zealand is an important location for understanding Last Glacial Interval (LGI) palaeoclimate dynamics, since it is influenced by both tropical and polar climate systems which have varied in relative strength and timing. Sediments from the Auckland Volcanic Field maar lakes preserve records of such large-scale climatic influences on regional palaeo-environment changes, as well as past volcanic eruptions. The sediment sequence infilling Orakei maar lake is continuous, laminated, and rapidly deposited, and it provides a high-resolution (sedimentation rate above ∼ 1 m kyr−1) archive from which to investigate the dynamic nature of the northern New Zealand climate system over the LGI. Here we present the chronological framework for the Orakei maar sediment sequence. Our chronology was developed using Bayesian age modelling of combined radiocarbon ages, tephrochronology of known-age rhyolitic tephra marker layers, 40Ar∕39Ar-dated eruption age of a local basaltic volcano, luminescence dating (using post-infrared–infrared stimulated luminescence, or pIR-IRSL), and the timing of the Laschamp palaeomagnetic excursion. We have integrated our absolute chronology with tuning of the relative palaeo-intensity record of the Earth's magnetic field to a global reference curve (PISO-1500). The maar-forming phreatomagmatic eruption of the Orakei maar is now dated to > 132 305 years (95 % confidence range: 131 430 to 133 180 years). Our new chronology facilitates high-resolution palaeo-environmental reconstruction for northern New Zealand spanning the last ca. 130 000 years for the first time as most NZ records that span all or parts of the LGI are fragmentary, low-resolution, and poorly dated. Providing this chronological framework for LGI climate events inferred from the Orakei sequence is of paramount importance in the context of identification of leads and lags in different components of the Southern Hemisphere climate system as well as identification of Northern Hemisphere climate signals. © Author(s) 2020 This work is distributed under the Creative Commons Attribution 4.0 Licence.
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    Discordant 26Al/10Be ratios as an indicator of bedrock plucking: case studies from northern Australia
    (Australian Nuclear Science and Technology Organisation, 2021-11-17) Fujioka, T; May, JH; Fink, D; Nanson, GC
    With the number of multi cosmogenic nuclide data from detrital samples increased, it becomes apparent that discordant ²⁶ Al/¹⁰ Be ratios are not exception but common. Traditionally, depressed ²⁶ Al/¹⁰ Be ratios, below the nominal production ratio of 6.8, have been interpreted as prior burial. However, in northern Australia, such scenario is highly unlikely as the region is subject to intensive annual floods and therefore river channels normally lack long-term sediment storage. Another possible interpretation for lower ²⁶ Al/¹⁰ Be ratios is non-steady state erosion, such as stochastic bedrock plucking. Such interpretation has an important implication to the sediment source and production mechanism, and therefore to the basin-wide erosion rate approach that assumes a steady-state erosion at sediment source. In this study, we measured ¹⁰ Be and ²⁶ Al concentrations from three different waterfall sites in northern Australia with contrasting lithological and physical characteristics, in an attempt to capture depleted ²⁶ Al/¹⁰ Be ratios. Our results indicate that ²⁶ Al/¹⁰ Be ratios from two sandstone-dominated sites show consistently lower values (4.3-6.1), consistent with non-steady erosion interpretation, whereas data from a quartzite-dominated site (5.9-6.9) are indistinguishable from steady-state interpretation. Detrital samples collected downstream at each site indicate the similar trend as respective bedrock sites, implying that sediments are largely derived from the waterfall bedrock surfaces. In this paper, we discuss the results in the context of lithological difference and physical erosion mechanism between the sites. © The Authors
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    The distribution and fractionation of beryllium isotopes in various reactive phases of Antarctic marine sediments
    (Australian Nuclear Science and Technology Organisation, 2021-11) Jeromson, MR; Fujioka, T; Fink, D; Post, A; Simon, KJ; Sánchez-Palacios, JT; Blaxell, M; Enge, TG; Wilcken, KM; White, DA
    Beryllium isotopes, ¹⁰ Be and ⁹ Be, in Antarctic marine sediments are increasingly being applied as paleoenvironmental proxies and indicators of past ice shelf extent. The evidence base for interpreting meteoric-¹⁰ Be concentrations and ¹⁰ Be/⁹ Be ratios has largely been derived from examining their spatial distribution in modern depositional environments, or by correlation with other proxies in paleo-records, such as diatom abundance. Meteoric-¹⁰ Be is geochemically adsorbed onto sediment grains in the reactive phase during transport from the atmosphere to deposition on the seafloor. Unlike meteoric-¹⁰ Be, ⁹ Be is both available within the reactive phase after crustal weathering and native within mineral lattice in significant quantities. The complexity in fixing and preserving the Be isotopes onto grain surfaces leads to uncertainties in selecting the chemistry methods to consistently extract the reactive phases of ¹⁰ Be and ⁹ Be in different sediments. This gap in understanding the physical behaviour and geochemical forms of reactive Be in Antarctic sediments limits their utility in reconstruction of paleoenvironmental conditions. We conducted a sequential leach procedure on three homogenised sediment grab samples from the front of the Amery Ice Shelf that span a range of water masses. Using different chemical reagents, from very weak to very strong, five phases of Be isotope signatures were extracted sequentially, including : i) water soluble, ii) amorphous oxides leached by 0.5M HCl, iii) crystalline oxides leached by 1M NH₂ OH-HCl in 1M HCl, iv) organic leached by 0.01M HNO₃ and H₂ O₂ , and v) mineral/residual phase dissolved by HF– with the water through to organic leach making the reactive phase. We found that the amorphous and crystalline oxide phases contained the largest fraction of ¹⁰ Be, about 90% of total ¹⁰ Be, with the remaining 10% being in the mineral/residual phase. For ⁹ Be, the oxide phases contained only 10-30%, the majority of ⁹ Be being in the residual phase. The water-soluble and organic chemical treatments were inefficient in extracting any significant reactive Be. This distribution has been observed in other deep marine and continental riverine sediments. However, the proportional distribution of the two isotopes between the amorphous and crystalline oxides differed for our Antarctic sediments compared to those other studies. While reactive ⁹ Be was close to equally split across the two oxide phases, 80% of reactive ¹⁰ Be was located within the amorphous phase, with the remainder within the crystalline oxide phase. The difference in fractionation provides evidence for different sources of each isotope and different processes affecting their deposition. ⁹ Be is sourced primarily from the Earth’s crust and is likely segregated into the different fractions during the process of subglacial chemical weathering. Open water ¹⁰ Be is processed in the water column, where interaction with biogeochemical processes likely segregates it into the more labile phases. These findings inform decisions regarding the selection of procedures for efficient and reproducible extraction of meteoric-¹⁰ Be, and for understanding the processes that drive the source and distribution of different isotopes around ice shelf systems. © The Authors
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    Erosion and the sediment conveyor in central Australia
    (Geological Society of Australia, 2016-02-29) Jansen, JD; Chappell, J; Struck, M; Eccleshall, SV; Fujioka, T; Codilean, AT; Fülöp, RH; Fink, D; Cohen, TJ; Nanson, GC
    Why are the Neogene sedimentary fills across central Australia generally thin and discontinuous? One long-standing explanation is that sluggish tectonism and intensified aridity have combined to suppress rates of erosion and sediment production yielding a landscape crowded with inherited, preMiocene forms. Quantifying rates of sediment production, residence time and transport is possible with numerous methods, but the recent growth of cosmogenic nuclide (CN) analysis has provided unprecedented quantitative insights to rates of landscape evolution. Measurements of in situ produced cosmogenic 10Be and 26Al integrate rates of surface processes over million-year timescales—the last part of the Neogene in which aridity has strengthened across the continental interior. We present a compilation of ~600 published and unpublished 10Be and 26Al measurements from central Australia with a focus on the Neogene Eyre Basin and its periphery. Outlying and inlying bedrock uplands serve as engines of sediment production via erosion of bedrock. Surrounding the bedrock outcrops are vast sediment conveyors of varying efficiency and tempo: hillslopes, pediments, and alluvial fans are interim storage/burial zones for sediment in transit to the network of low-gradient rivers, dunes, and playas towards base level. Interactions between fluvial and aeolian processes are especially pertinent to sediment flux in the Eyre Basin. Major rivers such as the Cooper and Finke traverse dunefields in their lower reaches where quantities of alluvia are recirculated into dunes and vice versa. Tracking the trajectories of sediment from source-to-sink (including aeolian recirculation) remains a major challenge, but is central to unravelling the sedimentary dynamics of central Australia's Neogene basins. Based on the CN compilation we estimate 1) spatially averaged erosion rates at the scale of a hillslope or river catchment; 2) pointbased erosion rates on bedrock surfaces; 3) residence time of sediment in hillslope regolith and alluvial fans; and 4) cumulative burial history of sediments in transit. Catchment-scale erosion rates (n~100) are consistently low (<10 m/Myr) and include some of the lowest rates ever measured (~0.3 m/Myr); however, a small group of catchments in the Flinders Ras yield higher erosion rates (~30–60 m/Myr). Bedrock hillslopes (n~200) tend to erode even slower (<5 m/Myr), with a subset of Flinders Ras sites again being the exception (~10–30 m/Myr) and suggesting the influence of recent tectonism. Several CN depth-profiles measured on hillslopes and alluvial fans indicate sediment residence times >0.5 Myr, and high-resolution sampling along three hillslopes with differing morphology (linear, convex, and concave) reveals major variations in sediment production and transport rates that hint at the long-term evolution. In the rivers, fluvial sediments show a weak tendency to increase cumulative burial history downstream (1–2 Myr), consistent with the expanding accommodation space for storage and burial. Dune sediments sampled in the Simpson and Tirari dunefields (n~16) contain cumulative burial histories (up to 1.5 Myr) similar to that of the intersecting rivers. This points to an intimate mix of fluvial and aeolian processes in areas approaching base level. Curiously, these sediments occur in the lowest part of the continent and contain the longest histories of cumulative burial, yet do not form part of the thickest sedimentary fills in the Eyre Basin.
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    Evolution of sandstone peak-forest landscapes – insights from quantifying erosional processes with cosmogenic nuclides
    (Wiley, 2017-10-16) May, JH; Huang, HQ; Fujioka, T; Fink, D; Codilean, AT; Yu, GA; Ma, Y; Wulf, G; Gu, J
    The sandstone peak-forest landscape in Zhangjiajie UNESCO Global Geopark of Hunan Province, China, is characterized by >3000 vertical pillars and peak walls of up to 350 m height, representing a spectacular example of sandstone landform variety. Few studies have addressed the mechanisms and timescales of the longer-term evolution of this landscape, and have focused on fluvial incision. We use in situ cosmogenic nuclides combined with GIS analysis to investigate the erosional processes contributing to the formation of pillars and peak-forests, and discuss their relative roles in the formation and decay of the landscape. Model maximum-limiting bedrock erosion rates are the highest along the narrow fluvial channels and valleys at the base of the sandstone pillars (~83–122 mm kyr−1), and lowest on the peak wall tops (~2.5 mm kyr−1). Erosion rates are highly variable and intermediate along vertical sandstone peak walls and pillars (~30 to 84 mm kyr−1). Catchment-wide denudation rates from river sediment vary between ~26 and 96 mm kyr−1 and are generally consistent with vertical wall retreat rates. This highlights the importance of wall retreat for overall erosion in the sandstone peak-forest. In combination with GIS-derived erosional volumes, our results suggest that the peak-forest formation in Zhangjiajie commenced in the Pliocene, and that the general evolution of the landscape followed our sequential refined model: (i) slow lowering rates following initial uplift; (ii) fast plateau dissection by headward knickpoint propagation along joints and faults followed by; (iii) increasing contribution of wall retreat in the well-developed pillars and peak-forests and a gradual decrease in overall denudation rates, leading to; (iv) the final consumption of pillars and peak-forests. Our study provides an approach for quantifying the complex interplay between multiple geomorphic processes as required to assess the evolutionary pathways of other sandstone peak-forest landscapes across the globe. Copyright © 2017 John Wiley & Sons, Ltd.
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    Exploring sediment dynamics from source to sink in the Murray-Darling basin using cosmogenic 14C, 10Be, and 26Al
    (Australasian Quaternary Association Inc., 2018-12-10) Fülöp, RH; Codilean, AT; Marx, SK; Cohen, TJ; Fink, D; Yang, B; Smith, AM; Wilcken, KM; Fujioka, T; Wacker, L; Dunai, TJ
    The relatively short half-life of 14C, namely, 5730 years, means that, compared to the other cosmogenic nuclides, it is substantially more sensitive to short term variations in process rates. Both the erosion of steep mountains and the dynamics of sediment transport, storage and recycling occur over timescales that are too short to be detectable by the cosmogenic nuclides that are currently used routinely, namely 10Be and 26Al. In situ 14C on the other hand is ideally suited for these short timescales, and used in combination with 26Al and 10Be, it will allow for rapid fluctuations in process rates and/or the relatively short timescales that characterise sediment transfer and storage to be measured accurately. The above make in situ 14C an important addition to the cosmogenic radionuclide toolkit. We present results of in situ cosmogenic 14C system blank and calibration sample measurements obtained with the recently established ANSTO/UOW in situ 14C extraction system. The 14C extraction scheme follows the design of the University of Cologne, which exploits the phase transformation of quartz to crystobalite to quantitatively extract the carbon as CO2. Offline high-temperature furnace extraction allows a relative rapid sample throughput and can accommodate samples ranging between 0.5 to 4 grams of clean quartz. Following extraction and isolation, the CO2gas is graphitised using a micro-furnace and then measured using AMS similarly to routine small radiocarbon samples. We also present results of 14C, 26Al, and 10Be analyses from sediment samples collected from Australia’s largest river system, the Murray-Darling basin. We use the downstream changes in the ratios of the three radionuclides in samples collected at key locations along the rivers to quantify sediment mixing and sediment storage times in the river basin. Substantial 26Al/10Be ‘burial’ signal is observed in downstream Murray and Darling samples, while in situ 14C suggests complex burial-exposure histories in these samples. This could have implication of interpreting geochemical proxies at the outlet of Murray-Darling Basin for identification of paleoclimate driven sediment sources (i.e. Monsoon vs. Westerlies). © The Authors
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    Extracting 10Be and 9Be from Antarctic marine sediments – a comparison of different extraction techniques
    (Australian Nuclear Science and Technology Organisation, 2021-11-17) Jeromson, MR; Fujioka, T; Fink, D; Post, AL; Simon, KJ; Sánchez-Palacios, JT; Blaxell, M; Enge, TG; Wilcken, KM; White, DA
    Application of meteoric-¹⁰ Be (M¹⁰ Be) in sediments and soils from diverse geomorphic settings has been active for many decades. In some cases, M¹⁰ Be is normalized by the reactive ⁹ Be from the same sediment sample. Given the complexities in geochemical pathways that M¹⁰ Be is incorporated in the reactive mineral phase of such sediments, very different Be isotope chemistry extraction techniques have been developed. Measurement of M¹⁰ Be and the reactive phase of ⁹ Be in coastal Antarctic marine sediments has increasingly become promising as a paleo-proxy for the presence (or absence) of past ice shelves, and/or subglacial meltwater discharge from grounded outlet glaciers draining the ice sheet. However, published works select different methods to chemically leach Be isotopes from the reactive phase of Antarctic marine sediment and few studies have quantitively compared the efficacy of different leaching recipes. This is problematic because comparisons of ¹⁰ Be/⁹ Be ratios across different Antarctic sites assumes the same chemical fractionation of Be isotopes regardless of the leaching method. We examined three large-volume sediment grabs from near the Amery Ice Shelf front in East Antarctica that represent a range of grainsize and environmental conditions. For Be extraction, homogenised materials from each of the three samples were treated with four different leaching procedures, 1–3 targeting the reactive phase: 1) 6M HCl; 2) 0.5M HCl followed by 1M hydroxylamine hydrochloride in 1M HCl; 3) 0.04M hydroxylamine hydrochloride in 25% acetic acid solution 4) a total extraction dissolving in HF, HNO₃ , and HClO₄ . We also selected one grab to assess the effect of grainsize within the following fractions: <38 um, 38–63 um, 63–90 um, 90–125 um, and >125 um. Each fraction was leached with 6M HCl for 24 hours at room temperature. We found that both the 6M HCl and the 1M hydroxylamine procedures leached the same amount of ¹⁰ Be as the total extraction, while the 0.04M hydroxylamine treatment leached only two thirds. Interestingly, the 6M HCl and the 0.04M hydroxylamine procedures leached the same relative proportion of ⁹ Be to ¹⁰ Be, and thus gave the same ¹⁰ Be/⁹ Be ratio, while the 1M hydroxylamine procedure leached relatively more ⁹ Be in relation to ¹⁰ Be, resulting in a lower ¹⁰ Be/⁹ Be than the other two methods. As shown in previous studies, our results indicate that Be-isotope concentrations varied inversely with grainsize, in our case increasing 4- fold from coarsest to finest fractions, critically showing that the ¹⁰ Be/⁹ Be ratio remained constant across all grainsizes. Hence, grainsize can be normalised by applying the reactive ¹⁰ Be/⁹ Be ratio. We conclude that differences in leaching procedures, can lead to significant variations in efficiencies in extracting Be isotopes from the reactive phase of sediment, whereas the ¹⁰ Be/⁹ Be ratio appears to remain the same. This study highlights the importance of careful method selection and its consistent application to allow for comparison between studies and more robust interpretation.
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    Extraction and purification of quartz in rock using hot-phosphoric acid for in situ cosmogenic exposure dating
    (Elsevier Science BV, 2013-01-01) Mifsud, C; Fujioka, T; Fink, D
    Quartz extraction and purification is essential for the successful measurement of Be-10 and Al-26 by AMS for exposure dating. The common procedure involves repetitive etching by ultrasonic heating and agitation in a dilute aqueous HF solution (2% w/w), which has proven adequate for quartz rich rock (i.e., granite, quartzite). We have developed an alternative method using hot phosphoric acid (250 degrees C), which preferentially dissolves silicates but not quartz. This method is particularly effective on samples with very low quartz abundance or with cryptocrystalline silica (i.e., greywacke, silcrete, chert) to enhance quartz recovery. We describe the method in detail and present data that compares the efficiency and the benefits of the two methods. © 2013, Elsevier Ltd.
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    Extraction and purification of quartz using phosphoric acid
    (12th International Conference on Accelerator Mass Spectrometry (AMS-12), 2011-03-24) Mifsud, C; Fujioka, T; Fink, D
    Quartz extraction and purification from rocks, sediment, soil and dust samples is essential for the successful measurement of 10Be and 26Al by Accelerator Mass Spectrometry (AMS). The common procedure used involves initial water washing to remove fines then Aqua Regia treatment followed by density separation using lithium silicon tungstate then magnetic separation and finally selective etching of powder samples by ultrasonic heating and agitation in a dilute aqueous (~2% w/w) hydrofluoric acid solution (HF). This technique has proven adequate for quartz rich rock types ( ie granite, quartzite). The etching method alone typically involves 4-5 cycles of HF 2% etchings and the result is ~10-30% mass loss. However for fine grained and or low quartz (non-felsic) bearing samples such as flint, silcrete, andesite, diorite) density and magnetic separation are inefficient. Furthermore, HF etching will readily dissolve fine quartz grains and thus severely affects yields. We have developed an alternative method using hot phosphoric acid (~250°C), which preferentially dissolves silicates and many other minerals but not quartz. Differentiation of quartz from other minerals (e.g., feldspars, plagioclase) is excellent, density and magnetic separation is not required and usually fewer cycles are required than with conventional HF etching. Hence the hot phosphoric acid method is particularly effective on rocks containing fine grain quartz, e.g., greywacke, silcrete and chert, to enhance quartz recovery. As a bonus this method will bulk extract zircons if required. The technique is far more cost effective by using cheap commercial grade reagents and reduced risk compared to handling highly hazardous HF solutions. We present semi-quantitative data that compares the efficiency and the benefits of the two methods. Copyright (c) 2011 AMS12