ANSTO :: Browsing by Author "Mifsud, C"

Browsing by Author "Mifsud, C"

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ANSTO AMS facility sample processing and target preparation: an update
(20th International Radiocarbon Conference, 2009-06-01) Jacobsen, GE; Barry, LA; Bertuch, F; Hua, Q; Mifsud, C; Pratap, P; Reilly, N; Varley, S; Williams, AG
The ANSTO AMS Facility has been operating for the past 17 years, and comprises two accelerators complemented with a suite of chemistry laboratories dedicated to the processing of samples for carbon, beryllium, aluminium, iodine, and actinide analyses. The facility performs and supports a wide range of research in the areas of paleoclimate change, water resource sustainability, archaeology, geomorphology, and nuclear safeguards. As a result, the chemistry laboratories are called upon to process a large variety of sample types and increasing numbers of samples. The radiocarbon laboratories process charcoal, wood, sediments, pollen, carbonates, waters, textiles, and bone though the pretreatment stages, combustion or hydrolysis, and graphitization. Over the years, we have continually worked to improve pretreatment methods, reduce sample size, and reduce background. Construction of a dedicated low-background combustion and graphitization system is underway. The cosmogenic laboratories process quartz-bearing rocks and sediments through cleaning, dissolution, separation, and purification of Be and Al and preparation of targets as oxides. In this poster, we will summarize the current methods and developments in the radiocarbon and cosmogenic chemistry laboratories.
The ANTARES AMS facility at ANSTO
(Elsevier, 2004-08) Fink, D; Hotchkis, MAC; Hua, Q; Jacobsen, GE; Smith, AM; Zoppi, U; Child, DP; Mifsud, C; van der Gaast, H; Williams, A; Williams, M
This paper presents an overview of ANTARES operations, describing (1) technical upgrades that now allow routine 0.3–0.4% 14C precision for 1 mg carbon samples and 1% precision for 100 micrograms, (2) proficiency at 236U measurements in environmental samples, (3) new developments in AMS of platinum group elements and (4), some major application projects undertaken over the period of the past three years. Importantly, the facility is poised to enter into a new phase of expansion with the recent delivery of a 2 MV 14C tandem accelerator system from High Voltage Engineering (HVE) and a stable isotope ratio mass spectrometer from Micromass Inc. for combustion of organic samples and isotopic analysis. © 2004 Elsevier B.V.
Beryllium-10 in forams and marine sediments; a new chemo-stratigraphic tracer for the late quaternary
(Eleventh International Conference on Accelerator Mass Spectrometry, 2008-09) Levchenko, VA; Opdyke, BN; Fink, D; Mifsud, C; Williams, AA
The production rate of cosmogenic isotopes 10Be and 14C is influenced by varitions in the primary cosmic ray flux and by charges of the Earth's magnetic field, which has experienced a number of significant perturbations during the late Quaternary (e.g. Lashamp Mono Lake excursion, circa 41 ka BP). Understanding these changes and synchronising variations in palaeomagnetic intensity derived from various marine sediment cores can often help constrain the quality of 14C dating, particularly in the interval between 20 and 50 ka ago, and establish reliable chronologies for ocean sedimentation rate changes. A common proxy for these palaeomagnetic changes is atmospheric fallout of 10Be in bulk sediments. However terrigenous and recycled sediments also deliver high 10Be concentrations thus strongly complicating the process required to isolate direct atmospheric from continental derived 10Be. As an alternative to geochemical speciation, grain size or leaching procedures in sediments we suggest that changes in 10Be concentrations in planktonic foraminifera can be used as a global stratigraphic marker. We are investigating planktonic foraminifera collected from Core MD - 982167, which was recovered from the Scott Plateau in the Eastern Indian Ocean at latitude of 13° S. The MD- 982167 already has an established stable isotope stratigraphy and a high sedimentation rate of 10 to 20 cm per ka. Initial results of paired 14C and 10Be determinations in foraminifera and fine fraction of the core sediments as a function of core depth have been obtained and subsequently will be compared to palaeomagnetic measurements currently in progress. An improved chronology for this high resolution core that has recorded brief, less than one thousand year duration, climatic events during the studied time interval will allow much better correlation between marine sedimentary records and the detailed chronologies established from the ice cores.
A bright future for accelerator science at ANSTO
(Australian Institute of Nuclear Science and Engineering (AINSE), 2009-11-25) Hotchkis, MAC; Child, DP; Cohen, DD; Dodson, JR; Fink, D; Garton, DB; Hua, Q; Ionescu, M; Jacobsen, GE; Levchenko, VA; Mifsud, C; Siegele, R; Smith, AM; Williams, AG; Winkler, S
In the May 2009 budget, the Federal Government announced funding of $25m to ANSTO through the Education Investment Fund, to build state-of-the-art applied accelerator science facilities, by upgrading and replacing existing facilities and laboratories at ANSTO. Currently, ANSTO's researchers, jointly with researchers from all 37 Australian universities, plus other agencies such as CSIRO, government departments and local government bodies, and overseas collaborators and customers, use ANSTO's accelerator facilities for analysis of a wide range of materials, predominantly by Accelerator Mass Spectrometry (AMS) and Ion Beam Analysis (IBA). There are >100 external users of those facilities every year. © 2009 AINSE
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.
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, DB; 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.
Cosmogenic radionuclide chronology of pre-last glacial cycle moraines in the Western Arthur range, Southwest Tasmania
(Elsevier, 2010-11) Kiernan, K; Fink, D; Greig, D; Mifsud, C
Cosmogenic 10Be and 26Al exposure ages of 12 boulders from two moraine complexes in the Western Arthur Range of southwest Tasmania, which previously were considered to have been deposited during the Last Glacial Maximum, predate the Last Glacial Cycle. Zero-erosion minimum exposure ages range from 95 ka to 232 ka based on weighted mean 10Be and 26Al ages per boulder. For a reasonable choice of erosion rates, 10Be boulder ages range from 105 to 326 ka, respectively. Although a direct association of moraine construction to a specific marine isotope stage (MIS) glaciation is not definitive, erosion-corrected exposure ages indicate glacial advances commensurate with MIS-6 and -10, although the latter advance may be attributable to MIS-8 if the erosion rate correction is an over-estimate. Given the relatively close proximity of the dated moraines to their source cirques, this new cosmogenic glacial chronology implies a very limited extent for any younger glacial advances that occurred in the Western Arthur Range during the Last Glacial Cycle (post MIS-5) including the global LGM. © 2010, Elsevier Ltd.
Defining past volume of grounded ice in the Ross Sea
(Geological Society of New Zealand, 2009-11-26) Lilly, K; Wilson, GS; Fink, D; Levy, R; Mifsud, C
A large portion of global sea-level increase over the last glacial cycle is believed to originate from reduction in the volume of West Antarctic ice including ice grounded across the Ross Sea. The evidence for this comes from observation of glacigene sediments in the Ross Embayment, both onshore and offshore, indicating a much greater ice extent in the past. However, much of this evidence is not dated directly. Marine geophysical surveys show that the Antarctic Ice Sheet did in many locations ground out to the continental shelf edge, but it is not clear whether this happened at the Last Glacial Maximum. On land, our understanding of former ice extent in the Ross Sea region comes primarily from a glacial sedimentary deposit known as the Ross Sea Drift. The limit of these sediments has been used to define the volume of grounded ice in the Ross Sea and by further inference in the adjacent West Antarctic, representing an ice volume of some 9 million km3, or 14 m sea level equivalent. However, the Ross Sea Drift is defined by common processes and facies rather than as a time restricted unit and conflicting interpretations from different locations suggest different timing and different ice configurations. The geographic area of the southern McMurdo Ice Shelf (between Black Island, Minna Bluff and Mount Discovery) is identified as a location where the reconstructions are in greatest conflict. We present new constraints on the age of formation of these moraines from the application of cosmogenic exposure dating on 16 sandstone erratics collected from moraines on the flanks of Minna Bluff and Mount Discovery. These ice shelf marginal moraines have traditionally been included in the Ross Sea Drift. The sandstone erratics themselves are ideal targets for exposure dating as they include large blocks (> 1 m) that sit proud of the surrounding drift, they are quartz rich and are from an Eocene formation for which there is no known outcrop. While the origin of the erratics is not confirmed, each of the available reconstructions infers them to have been exhumed by advancing ice grounded in the Ross Sea. Thus we can assume that their exposure age relates to glacial erosion and deposition.
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.
The early rise and late demise of New Zealand’s last glacial maximum
(Proceedings of the National Academy of Sciences of the United States of America, 2014-06-13) Rother, H; Fink, D; Shulmeister, J; Mifsud, C; Evans, M; Pugh, J
Recent debate on records of southern midlatitude glaciation has focused on reconstructing glacier dynamics during the last glacial termination, with different results supporting both in-phase and out-of-phase correlations with Northern Hemisphere glacial signals. A continuing major weakness in this debate is the lack of robust data, particularly from the early and maximum phase of southern midlatitude glaciation (∼30–20 ka), to verify the competing models. Here we present a suite of 58 cosmogenic exposure ages from 17 last-glacial ice limits in the Rangitata Valley of New Zealand, capturing an extensive record of glacial oscillations between 28–16 ka. The sequence shows that the local last glacial maximum in this region occurred shortly before 28 ka, followed by several successively less extensive ice readvances between 26–19 ka. The onset of Termination 1 and the ensuing glacial retreat is preserved in exceptional detail through numerous recessional moraines, indicating that ice retreat between 19–16 ka was very gradual. Extensive valley glaciers survived in the Rangitata catchment until at least 15.8 ka. These findings preclude the previously inferred rapid climate-driven ice retreat in the Southern Alps after the onset of Termination 1. Our record documents an early last glacial maximum, an overall trend of diminishing ice volume in New Zealand between 28–20 ka, and gradual deglaciation until at least 15 ka. © 2014, National Academy of Sciences of the United States of America.
Extensive glaciation in Transbaikalia, Siberia, at the Last Glacial Maximum
(Elsevier, 2016-01-15) Margold, M; Jansen, JD; Gurinov, AL; Codilean, AT; Fink, D; Preusser, F; Reznichenko, NV; Mifsud, C
Successively smaller glacial extents have been proposed for continental Eurasia during the stadials of the last glacial period leading up to the Last Glacial Maximum (LGM). At the same time the large mountainous region east of Lake Baikal, Transbaikalia, has remained unexplored in terms of glacial chronology despite clear geomorphological evidence of substantial past glaciations. We have applied cosmogenic 10Be exposure dating and optically stimulated luminescence to establish the first quantitative glacial chronology for this region. Based on eighteen exposure ages from five moraine complexes, we propose that large mountain ice fields existed in the Kodar and Udokan mountains during Oxygen Isotope Stage 2, commensurate with the global LGM. These ice fields fed valley glaciers (>100 km in length) reaching down to the Chara Depression between the Kodar and Udokan mountains and to the valley of the Vitim River northwest of the Kodar Mountains. Two of the investigated moraines date to the Late Glacial, but indications of incomplete exposure among some of the sampled boulders obscure the specific details of the post-LGM glacial history. In addition to the LGM ice fields in the highest mountains of Transbaikalia, we report geomorphological evidence of a much more extensive, ice-cap type glaciation at a time that is yet to be firmly resolved. © 2015 Elsevier Ltd.
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.
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
Flood-flipped boulders: in-situ cosmogenic nuclide modeling of flood deposits in the monsoon tropics of Australia
(Geological Society of America, 2014-12-04) Fujioka, T; Fink, D; Nanson, GC; Mifsud, C; Wende, R
During the Quaternary, extreme floods along the Durack River, in the Kimberley, northern Australia, dislodged, transported, and stacked massive meter-sized boulders from the underlying bedrock channel floor. Field evidence identified a population of the boulders to have been overturned after detachment. We measured in situ cosmogenic 10Be and 26Al concentrations in six imbricated boulders to constrain the timing of flood events. We present a simple numerical model that simultaneously solves the expressions for the predicted nuclide concentrations from the exposed and hidden surfaces of a flipped boulder to calculate the time since it was overturned. The ability of the model to unequivocally discern whether a boulder was overturned depends on boulder thickness and the site-specific steady-state erosion rate. Of the six boulders sampled, our model successfully determined four finite flip ages, whereas the other two boulders indicated steady state and were either not flipped or flipped sufficiently long ago for the nuclide profile to have returned to steady state. While the two older model ages (ca. 150 ka and ca. 260 ka) are strongly sensitive to assumptions made for the local erosion rate correction, the two younger flip ages, 5.6 ± 1.0 ka and 10.3 ± 1.9 ka, are robust against such corrections. Early to mid-Holocene major floods have been recorded in other parts of northern Australia. We suggest that similar Holocene floods occurred in the Kimberley and that such extreme events may have been widespread in northern Australia in the late Quaternary. Our boulder-flip model can be applicable to similar deposits associated with other extreme events such as paleo-tsunamis. © 2014, Geological Society of America.
An improved radiocarbon chronology and calibration over the Laschamp event: 14C – 10Be cross synchronisation
(Geological Society of Australia, 2010-07-04) Levchenko, VA; Opdyke, BN; Fink, D; Mifsud, C; Williams, AG; Klootwijk, C
The production rate of cosmogenic isotopes 10Be and 14C is influenced by variations in the primary cosmic ray flux and by changes of the Earth’s magnetic field, which has experienced a number of significant perturbations during the late Quaternary (e.g. Lashamp/Mono Lake excursion, circa 41 ka BP). Understanding these changes and synchronising variations in palaeomagnetic intensity derived from various marine sediment cores can often help constrain the quality of 14C dating, particularly in the interval between 20 and 50 ka ago, and establish reliable chronologies for ocean sedimentation rate changes. A common often used proxy for these palaeomagnetic changes is atmospheric fallout of 10Be in marine sediments. We are investigating the Core MD – 982167, which was recovered from the Scott Plateau in the Eastern Indian Ocean at latitude of 13°S. The MD‐982167 already has an established stable isotope stratigraphy and a high sedimentation rate of 10 to 20 cm per ka. A series of 14C and 10Be determinations in foramifera and fine fraction of the core sediments as a function of core depth have been obtained. Palaeomagnetic measurements with the aim to determine the position of geomagnetic disturbances like Laschamp and Mono Lake as recorded in the ocean sediments were also done on the samples from the same core. Synchronisation of palaeomagnetic, 10Be and radiocarbon records together with the application of 10Be pulse as a global chronostratigrafic marker is discussed. An improved chronology for this high resolution core that has recorded brief, less than one thousand year duration, climatic events during the studied time interval will allow much better correlation between marine sedimentary records and the detailed chronologies established from the ice cores.
An improved radiocarbon chronology for MD-982167, eastern Indian Ocean: synchronizing paleomagnetic intensity and 10Be across the Laschamp event
(20th International Radiocarbon Conference, 2009-06-02) Levchenko, VA; Fink, D; Opdyke, BN; Mifsud, C; Williams, AG; Klootwijk, C
The production rate of cosmogenic isotopes 10Be and 14C is influenced by variations in the primary cosmic-ray flux and by changes of the Earth’s magnetic field, which has experienced a number of significant perturbations during the late Quaternary (e.g. Laschamp excursion, ca. 41 kyr BP). Understanding these changes and synchronizing variations in paleomagnetic intensity derived from various marine sediment cores can often help constrain the quality of 14C dating, particularly for times beyond IntCal04 between 30 and 50 kyr ago, leading to improved overall core chronologies and determination of ocean sedimentation rates. An often used proxy for these paleomagnetic changes is the concentration of atmospheric fallout of 10Be in marine sediments. The ocean core MD-982167 recovered from the Scott Plateau in the eastern Indian Ocean (13°09′S, 121°35′E; depth of 1981m) has an established δ18O stable isotope stratigraphy and a high sedimentation rate of 10 to 20 cm/kyr based on a preliminary chronology tied to ice-core records. This in turn makes MD-982167 amenable to high-resolution 10Be assay across the Laschamp period. We have completed measurements of 10Be and 14C (in both foraminifera and fine sediments) and paleomagnetic intensity in core MD-982167. We are able to correlate variations in 10Be with paleomagnetic intensity recorded in these ocean sediments based on our detailed radiocarbon age-depth profile and confirm a strong presence of the Laschamp excursion at 39.9 ± 1.3 kyr BP. Comparing the variations of atmospheric-derived 10Be in MD-982167 tied to our improved radiocarbon chronology with 10Be established from the ice cores and will allow much better correlation between marine sedimentary and ice-core records across recent stadial and interstadial climatic events.
Improving the accuracy of aluminium assay in purified quartz for in situ cosmogenic exposure dating
(GNS Science, 2011-03-24) Fujioka, T; Fink, D; Mifsud, C
Precise and accurate measurement of the natural aluminium content in purified quartz powder, [Al], extracted from surface bedrock and/or sediment samples for in situ cosmogenic nuclide dating is critical for reliable 26Al exposure ages and 26Al/10Be ratios for burial dating. Numerous articles have cited issues regarding reliability of 26Al ages paired to 10Be ages, not only due to poor statistical error, but also due to uncertainty in [Al]. Loss of Al during aliquot preparation for ICPOES from bulk HF solutions of dissolved quartz or inaccurate assay via ICP (or AA) will result in reduced 26Al concentrations. In turn this will, depending on magnitude of the loss with respect to typical age errors, lead to lower-than-expected 26Al ages when compared to corresponding 10Be ages. If the loss is excessive, this may result in depressed 26Al/10Be ratios and thus a false burial signal. Over the past 4 years we have performed repetitive Al assays from a parent HF solution prepared from ~25 g of a low-iron glass sand (NIST-165a; ~320 ppm [Al]) using identical methods as for all quartz samples. The solution was used as an in-house laboratory standard for [Al] and shows a limiting 1σ of ±5% (n ~50) via ICP-OES at a commercial laboratory. The spread in paired NIST-165a duplicates measured per batch is better than ±1%. To determine the accuracy of our procedures, we prepared sets of solutions (1–10 ppm Al) from 3 different quartz powders using the standard addition method. Initial results indicate a 3-7% offset between [Al] based on the standard addition method and that based on the conventional calibration curve. Copyright (c) 2011 AMS12.
Integrated age modelling of numerical, correlative and relative dating of a long lake sediment sequence from Orakei maar palaeolake, Auckland, New Zealand
(Copernicus GmbH, 2019-04-11) Peti, L; Augustinus, PC; Fujioka, T; Mifsud, C; Nilsson, A; Muscheler, R; Fitzsimmons, KE; Hopkins, JL
Accurate and precise chronologies are fundamental for successful Quaternary palaeo-climate/environment reconstruction and correlation with global climatic events. Aside from varved lake sequences, chronologies for sediment archives typically depend on age models developed from a limited number of dated horizons, often with large associated errors, age reversals, or minimum/maximum age constraints. Whilst the approach to generating chronologies for sediment cores has moved on from linear interpolation to considering age uncertainties and developing more nuanced accumulation models, these age models rarely reach the resolution and precision desired for millennial-scale palaeo-climatic correlations, particularly beyond the limits of the more precise radiocarbon method. Bayesian modelling offers the opportunity to optimise age models by combining all available information on the depositional history of the basin. Here we address this issue for the Orakei maar palaeolake sequence from Auckland, New Zealand. The Orakei maar sequence offers a high-resolution and continuous record of climatic variations spanning much of the last glacial cycle and is one of the few from the southern hemisphere mid-latitudes. The Orakei sequence spans ca. 120 to 10 ky; our chronology is derived from tephrochronology, radiocarbon dating, post-IR IRSL luminescence dating, relative palaeomagnetic intensity changes and meteoric Beryllium-10 flux. Prior to 40 ka, our age model relies on comparison with the global PISO-1500 palaeointensity stack and 10Be-flux. We generate our age model for the time interval ca. 50 to 10 ky using Bacon (rBacon in R), using non-normal error distribution of un-calibrated ages when necessary, facies-dependent variable mean accumulation rates and accounting for thick horizons of instantaneous deposition (i.e. tephra and mass movement deposits). This approach allows us to generate a high-resolution age model suitable for correlation of millennial-scale oscillations in our record, based on environmental magnetism and meteoric 10Be flux, with global records of past climate such as polar ice core, tropical lake and speleothem archives. © Author(s) 2018. CC Attribution 4.0 license.
Late quaternary fluvial incision and aggradation in the Lesser Himalaya, India
(Elsevier, 2018-10-01) Dosseto, A; May, JH; Choi, JH; Swander, ZJ; Fink, D; Korup, O; Hesse, PP; Singh, T; Mifsud, C; Srivastava, P
Reconstructing how rivers respond to changes in runoff or sediment supply by incising or aggrading has been pivotal in gauging the role of the Indian Summer Monsoon (ISM) as a geomorphic driver in the Himalayas. Here we present new chronological data for fluvial aggradation and incision from the Donga alluvial fan and the upper Alaknanda River, as well as a compilation of previous work. In addition to conventional OSL-SAR (Single-Aliquot Regenerative-Dose) dating method, we have tested and applied pulsed OSL (POSL) dating for quartz samples that include K-rich feldspar inclusions, which is expected to improve the applicability and validity of OSL ages in the Lesser Himalaya. For previously dated deposits, our OSL ages are shown to be systematically older than previously reported ages. These results suggest periods of aggradation in the Alaknanda and Dehradun Valleys mainly between ∼25 and 35 ka. This most likely reflects decreased stream power during periods of weakened monsoon. In addition, in-situ cosmogenic beryllium-10 was used to infer bedrock surface exposure ages, which are interpreted as episodes of active fluvial erosion. Resulting exposure ages span from 3 to 6 ka, suggesting that strath terraces were exposed relatively recently, and incision was dominant through most of the Holocene. In combination, our results support precipitation-driven fluvial dynamics, which regulates the balance between stream power and sediment supply. On a larger spatial scale, however, fluvial dynamics are probably not spatially homogeneous as aggradation could have been taking place in adjacent catchments while incision dominated in the study area. © 2018 Elsevier Ltd.
Multi-method age model of a long lake sediment sequence from Orakei maar palaeolake, Auckland, New Zealand
(International Union for Quaternary Research (INQUA), 2019-07-30) Peti, L; Fink, D; Fujioka, T; Mifsud, C; Nilsson, A; Muscheler, R; Fitzsimmons, KE; Hopkins, JL; Augustinus, PC
Meaningful reconstructions of Quaternary palaeo-climate and -environmental reconstruction rely heavily on accurate and precise chronologies. Long and continuous lake sediment sequences are outstanding archives of past climatic change but, unless varved, depend on the development of detailed age models. Such models estimate the age-depth-relationship of the sequence from a limited number of dated horizons, which often carry large associated errors, age reversals, or minimum/maximum age constraints. Approaches to chronology development for sediment sequences have seen major improvements such as more nuanced Bayesian accumulation models but still rarely reach the resolution and precision desired for the study objectives in the context of high-resolution palaeo-climatic correlations of global events. This is particularly true beyond the limits of the well-established and more precise radiocarbon dating method. Sediment archives older than 50 ka have often not been used to its full potential for the lack of chronology estimates. In such cases, alternative methods including correlative and relative dating methods may need to be employed. Currently, a standardised method of integrating absolute dating with wiggle-matched curves of comparable proxies between the unknown and a dated sequence is lacking. Here we address this problem in the context of the Orakei maar palaeolake sequence from Auckland, New Zealand. This sediment record is a high-quality example of one of the rare high-resolution and continuous lacustrine archives of climatic variations in the southern hemisphere mid-latitudes over much of the last glacial cycle. Based on previous estimates, the Orakei sequence spans the interval ca. 126 cal ka BP to 9 cal ka BP. The presented Orakei chronology is based on absolute ages from tephrochronology, radiocarbon dating and post-IR IRSL luminescence dating. Prior to 40 ka, tuning of relative palaeomagnetic intensity changes and meteoric Beryllium-10 flux to the global PISO-1500 palaeointensity stack between absolute age markers allows to establish a novel accumulation model for the Orakei sequence. This approach allows us to generate a high-resolution age model suitable for correlation of millennial-scale oscillations from the SW Pacific to global records of past climate such as polar ice core, tropical lake and speleothem archives. © The Authors.

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