ANSTO :: Browsing by Author "Codilean, AT"

Browsing by Author "Codilean, AT"

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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.
Constraining the age of Aboriginal rock art using cosmogenic Be-10 and Al-26 dating of rock shelter collapse in the Kimberley region, Australia
(Australian National University, 2019-09-09) Cazes, G; Fink, D; Fülöp, RH; Codilean, AT
The Kimberley region, northwest Australia, possesses an extensive and diverse collection of aboriginal rock art that potentially dates to more than 40,000 years ago. However, dating of such art using conventional techniques remains problematic. Here, we develop a new approach which makes use of the difference in production rates of in-situ 10Be and 26Al between intact rock walls and exposed surfaces of detached slabs from rock art shelters to constrain the age of Aboriginal rock-art. In the prevailing sandstone lithology of the Kimberley region, open cave-like rock shelters with cantilevered overhangs evolve by the collapse of unstable, partially rectangular, blocks weakened typically along joint-lines and fractures. On release, those slabs which extend outside the rock face perimeter will experience a higher production rate of cosmogenic 10Be and 26Al than the adjacent rock which remains intact within the shelter. The dating of these freshly exposed slabs can help reconstruct rock-shelter formation and provide either maximum or minimum ages for the rock art within the shelter. At each site, both the upper-face of the newly exposed fallen slab and the counterpart intact rock surface on the ceiling need to be sampled at their exact matching-point to ensure that the initial pre-release cosmogenic nuclide concentration on slab and ceiling are identical. The calculation of the timing of the event of slab release is strongly dependent on the local production rate, the new shielding of the slab surface and the post-production that continues on the ceiling sample at the matching point. The horizon, ceiling and slab shielding are estimated by modelling the distribution of neutron and muon trajectories in the irregular shaped rock-shelter and slab using 3D photogrammetric reconstruction from drone flights and a MATLAB code (modified from G. Balco, 2014) to estimate attenuation distances and model the production rate at each sample. Five rock-art sites have been dated and results range from 9.8±1.9 ka to 180.8±22.3 ka. While the date obtained for the youngest site can be interpreted as both a maximum and minimum age for the art due to its positioning over different walls of this specific shelter, all the other sites give maximum art ages which are significantly older than presumed human occupation in Australia. However, within the context of regional landscape geomorphology, these relatively young ages give new insights into the contrasting modes of landscape evolution in the Kimberley, and the importance of episodic escarpment retreat overprinted by passive basin-wide denudation which from numerous previous measurements are as low as 1-5 mm/ka (i.e. averaging timescales of ~400 kyr). A large number of similar sites in the region have been mapped and are potential candidates for this new approach which can constrain the controversial relative chronology of the various aboriginal rock art styles.
Determining the origin and changing shape of landscape-scale rock formations with three-dimensional modelling: the Borologa rock shelters, Kimberley region, Australia
(Wiley, 2021-05-02) Genuite, K; Delannoy, JJ; David, B; Unghango, A; Balanggarra Aboriginal Corporation; Cazes, G; Fulop, R; Fink, D; Codilean, AT; Ouzman, S; Veth, P; Harper, S; Green, H; Finch, D; Urwin, C
Archaeologists often wonder how and when rock shelters formed, yet their origins and antiquity are almost never systematically investigated. Here we present a new method to determine how and when individual boulders and rock shelters came to lie in their present landscape settings. We do so through 3D laser (LiDAR) mapping, illustrating the method by example of the Borologa Aboriginal site complex in the Kimberley region of northwestern Australia. Through a combination of geomorphological study and high-resolution 3D modelling, individual blocks of rock are refitted and repositioned t680their originating cliff-line. Preliminary cosmogenic nuclide ages on exposed vertical cliff faces and associated detached boulders above the Borologa archaeological sites signal very slow detachment rates for the mass movements of large blocks down the Drysdale Valley slopes, suggesting relative landscape stability over hundreds of thousands of years (predating the arrival of people). These findings offer hitherto unknown details of the pace of regional landscape evolution and move us toward a better understanding of patterns of human occupation in a context of relatively stable rock outcrops both within the sites and across the region. © 1999-2021 John Wiley & Sons, Inc
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.
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.
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
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.
Late Neogene climatic features recorded by isotope records in the Issyk Kul basin, Kyrgyzstan
(Copernicus GmbH, 2021-04-19) Kudriavtseva, A; Sobel, E; Codilean, AT; Roud, S; Wack, M; Gilder, S; Hoke, G; Mulch, A; Mikolaichuk, A; Fink, D; Fülöp, RH; Wilcken, KM
We present two carbonate oxygen and carbon isotope records from late Miocene – early Pleistocene stratigraphic sections from the southern flank of the Issyk Kul basin, Kyrgyz Tien Shan. The two sections are 700 and 500 m thick and composed of fluvial and lacustrine sediments. They were dated using magnetostratigraphy (Roud et al., G-Cubed, in review) and 26Al/10Be isochron burial dating (presented here). Carbonate stable isotope data is useful for reconstruction of climate in Asia over the Cenozoic. Oxygen isotopes are commonly used to detect moisture sources and their interaction with topography. Pedogenic carbon isotopes are used to reconstruct past atmospheric CO2 levels or the spread of C4 vegetation. The environment of Central Asia is primarily affected by the northern mid-latitude westerlies − winds transporting moisture eastward across Eurasia. Issyk Kul basin is situated on the windward side of the northern Tien Shan. Published data suggest that the Tien Shan mountain ranges interacted with the westerlies since late Oligocene and reorganized Central Asian climate during Neogene (Caves et al., 2017; Charreau et al., 2012; Macaulay et al., 2016; Wang, et al., 2020). The amount of existing published paleoclimate data from northern Central Asia is scarce compared to interior China, and therefore the influence of the Tien Shan uplift on climate in Asia during the Cenozoic is poorly reconstructed. Our data provide new insight into the role of the range and its interaction with the westerlies in forming climate on the windward side of the northern Tien Shan in the late Neogene. We combine our data with published stratigraphically-older sections nearby (Macaulay et al., 2016) to complete the Neogene stable isotope record of the Issyk Kul basin and study how the evolution of the basin influenced regional climate. Our d18O and d13C values show slightly positive trends, unlike stratigraphically-older data from the Issyk Kul basin. The preliminary interpretation suggests that the circulation pattern within the range was changed in late Miocene possibly reflecting active tectonic uplift northward of the basin and an increase in aridification.
Long-term waterfall dynamics in monsoonal Australia based on cosmogenic Be-10
(AMS-13 The Thirteenth International Conference on Accelerator Mass Spectrometry, 2014-08-24) Fujioka, T; May, JH; Fink, D; Nanson, GC; Jansen, JD; Codilean, AT
Extensive plateaus, arrays of escarpments and a variety of waterfalls are iconic to northern Australia. How old and stable are these features ? Tectonically, northern Australia has been quiescent during the Quaternary. Rainfall is highly seasonal and dominated by the summer monsoon. In this setting, regional landscape dynamics should be strongly afected by uctuations in monsoon and the associated uvial processes. Here, we examine timescales and processes of waterfall evolution in northern Australia. Situated in the Kimberley sandstone plateau, Durack Falls comprise a series of 1-3 m falls, while Bindoola Fall is a large 15 m fall. Surprise Creek, 100 km south of Darwin, has three 3-5 m waterfalls with deep plunge pools developed at the edge of a quartzite plateau. Over 30 samples were collected from bedrock straths up- and downstream of the waterfalls and on their headwall. Their 10Be exposure ages (assuming zero erosion) reveal contrasting results. While two waterfalls in the Kimberley show relatively young, variable ages (15-110 ka for Durack and 11-57 ka for Bindoola), Surprise Creek indicates old, but uniform ages (94-160 ka). Out-of-channel,undisturbed bedrock exhibits consistently high 10Be equivalent to steady-state erosion rates of 2-5 mm/ka, in agreement with typical bedrock erosion rates observed across Australia. Based on these data, we here present a model to evaluate process and rates of waterfalls formation, and discuss the controlling factors.
Lowland river responses to intraplate tectonism and climate forcing quantified with luminescence and cosmogenic 10Be
(Elesevier Science BV, 2013-03-15) Jansen, JD; Nanson, GC; Cohen, TJ; Fujioka, T; Fabel, D; Larsen, JR; Codilean, AT; Price, DM; Bowman, HH; May, JH; Gliganic, LA
Intraplate tectonism has produced large-scale folding that steers regional drainage systems, such as the 1600 km-long Cooper Ck, en route to Australia's continental depocentre at Lake Eyre. We apply cosmogenic Be-10 exposure dating in bedrock, and luminescence dating in sediment, to quantify the erosional and depositional response of Cooper Ck where it incises the rising Innamincka Dome. The detachment of bedrock joint-blocks during extreme floods governs the minimum rate of incision (17.4 +/- 6.5 mm/ky) estimated using a numerical model of episodic erosion calibrated with our 10Be measurements. The last big-flood phase occurred no earlier than similar to 112-121 ka. Upstream of the Innamincka Dome long-term rates of alluvial deposition, partly reflecting synclinal-basin subsidence, are estimated from 47 luminescence dates in sediments accumulated since similar to 270 ka. Sequestration of sediment in subsiding basins such as these may account for the lack of Quaternary accumulation in Lake Eyre, and moreover suggests that notions of a single primary depocentre at base-level may poorly represent lowland, arid-zone rivers. Over the period similar to 75-55 ka Cooper Ck changed from a bedload-dominant, laterally-active meandering river to a muddy anabranching channel network up to 60 km wide. We propose that this shift in river pattern was a product of base-level rise linked with the slowly deforming syncline-anticline structure, coupled with a climate-forced reduction in discharge. The uniform valley slope along this subsiding alluvial and rising bedrock system represents an adjustment between the relative rates of deformation and the ability of greatly enhanced flows at times during the Quaternary to incise the rising anticline. Hence, tectonic and climate controls are balanced in the long term. © 2013, Elsevier Ltd.
Million-year lag times in a post-orogenic sediment conveyor
(American Association for the Advancement of Science, 2020-06-19) Fülöp, RH; Codilean, AT; Wilcken, KM; Cohen, TJ; Fink, D; Smith, AM; Yang, B; Levchenko, VA; Wacker, L; Marx, SK; Stomsoe, N; Fujioka, T; Dunai, TJ
Understanding how sediment transport and storage will delay, attenuate, and even erase the erosional signal of tectonic and climatic forcings has bearing on our ability to read and interpret the geologic record effectively. Here, we estimate sediment transit times in Australia’s largest river system, the Murray-Darling basin, by measuring downstream changes in cosmogenic 26Al/10Be/14C ratios in modern river sediment. Results show that the sediments have experienced multiple episodes of burial and reexposure, with cumulative lag times exceeding 1 Ma in the downstream reaches of the Murray and Darling rivers. Combined with low sediment supply rates and old sediment blanketing the landscape, we posit that sediment recycling in the Murray-Darling is an important and ongoing process that will substantially delay and alter signals of external environmental forcing transmitted from the sediment’s hinterland. Copyright © 2020 The Authors
Quantifying soil loss with in-situ cosmogenic 10Be and 14C depth-profiles
(Elsevier, 2015-04-01) Fülöp, RH; Bishop, P; Fabel, D; Cook, GT; Everest, J; Schnabel, C; Codilean, AT; Xu, S
Conventional methods for the determination of past soil erosion provide only average rates of erosion of the sediment's source areas and are unable to determine the rate of at-a-site soil loss. In this study,we report insitu produced cosmogenic 10Be, and 14C measurements from erratic boulders and two depth-profiles from Younger Dryas moraines in Scotland, and assess the extent to which these data allow the quantification of the amount and timing of site-specific Holocene soil erosion at these sites. The study focuses on two sites located on end moraines of the Loch Lomond Readvance LLR):Wester Cameron and Inchie Farm, both near Glasgow. The site nearWesterCameron does not showany visible signs of soil disturbance andwas selected in order to test (i) whether a cosmogenic nuclide depth profile in a sediment body of Holocene age can be reconstructed, and (ii) whether in situ 10Be and 14C yield concordant results. Field evidence suggests that the site at Inchie Farm has undergone soil erosion and this site was selected to explore whether the technique can be applied to determine the broad timing of soil loss. The results of the cosmogenic 10Be and 14C analyses atWester Cameron confirm that the cosmogenic nuclide depth-profile to be expected from a sediment body of Holocene age can be reconstructed. Moreover, the agreement between the total cosmogenic 10Be inventories in the erratics and the Wester Cameron soil/till samples indicate that there has been no erosion at the sample site since the deposition of the till/moraine. Further, the Wester Cameron depth profiles show minimal signs of homogenisation, as a result of bioturbation, and minimal cosmogenic nuclide inheritance from previous exposure periods. The results of the cosmogenic 10Be and 14C analyses at Inchie Farm show a clear departure from the zero-erosion cosmogenic nuclide depth profiles, suggesting that the soil/till at this site has undergone erosion since its stabilisation. The LLR moraine at the Inchie Farm site is characterised by the presence of a sharp break in slope, suggesting that the missing soilmaterialwas removed instantaneously by an erosion event rather than slowly by continuous erosion. The results of numerical simulations carried out to constrain the magnitude and timing of this erosion event suggest that the eventwas relatively recent and relatively shallow, resulting in the removal of circa 20e50 cm of soil at a maximum of ~2000 years BP. Our analyses also show that the predicted magnitude and timing of the Inchie Farm erosion event are highly sensitive to the assumptions that are made about the background rate of continuous soil erosion at the site, the stabilisation age of the till, and the density of the sedimentary deposit. All three parameters can be independently determined a priori and so do not impede future applications to other localities. The results of the sensitivity analyses further show that the predicted erosion event magnitude and timing is very sensitive to the 14C production rate used and to assumptions about the contribution of muons to the total production rate of this nuclide. Thus, advances in this regard need to be made for the method presented in this study to be applicablewith confidence to scenarios similar to the one presented here. © 2015, Elsevier B.V.
Recycling of Pleistocene valley fills dominates 125 ka of sediment flux, upper Indus River
(European Geophysical Union, 2016-01-01) Munack, H; Blöthe, JH; Fülöp, RH; Codilean, AT; Fink, D; Korup, O
Rivers draining the semiarid Transhimalayan Ranges along the western Tibetan Plateau margin underwent alternating phases of massive valley infill and incision in Pleistocene times. The imprints of these cut-and-fill cycles on long-term sediment fluxes have remained largely elusive. We investigate the timing and geomorphic consequences of headward incision of the Zanskar River, which taps the vast More Plains valley fill that currently impedes drainage of the endorheic high-altitude basins of Tso Kar and Tso Moriri. In situ 10Be exposure dating and topographic analyses indicate that a phase of valley infill gave way to net dissection of the >250-m thick sedimentary stacks ∼125 ka ago, i.e. during the last interglacial (MIS 5e). Rivers eroded >14.7 km3 of sediment from the Zanskar headwaters since then, fashioning specific sediment yields that surpass 10Be-derived denudation rates from neighbouring catchments by factors of two to ten. We conclude that recycling of Pleistocene valley fills has provided Transhimalayan headwater rivers with more sediment than bedrock denudation, at least since the beginning of the last glacial cycle. This protracted liberation of sediment stored in thick valley fills could bias rate estimates of current sediment loads and long-term bedrock denudation. © Author(s)
Refinement to the extraction of in-situ cosmogenic C-14
(Australian and New Zealand Institutes of Physics, 2021-11-17) Fülöp, RH; Smith, AM; Yang, B; White, DA; Codilean, AT
In situ C-14 is an important addition to the cosmogenic nuclide toolkit. Its relatively short half-life - 5730 years - as compared to the longer-lived cosmogenic nuclides, means that it is substantially more sensitive to short term variations in process rates or more suitable at investigating recent exposure events. In-situ C-14 used in combination with Al-26 and Be-10 is also particularly well suited to studying the relatively short timescales that characterize fluvial sediment transfer and storage. Despite the above, the extraction of in-situ C-14 from geological samples is still problematic, with recent laboratory intercomparison studies showing considerable overdispersion in both intra and inter laboratory comparisons of standard materials. The discrepancies between laboratories have been attributed to several factors, including the quality of some intercomparison materials, however, clear consensus on the matter is yet to be reached. Here we present results of in-situ cosmogenic C-14 analyses in the Cronus-A and Cronus-R laboratory intercomparison materials and various samples obtained using the ANSTO/UOW in-situ C-14 extraction system, that suggest the presence of carbon containing minerals within these materials. Our results indicate that quartz separates need a different purity measurement that what would normally be acceptable for cosmogenic Be-10 and Al-26 analyses. Further, we do not observe a bias in results on those samples that underwent froth-floatation to remove feldspars, however applying a final 50% HF etch will result in removal of unwanted minerals. Based on analyses on fluid inclusions we adopted cycled in-vacuo 600oC pre-cleaning for samples and observe improvements in reproducibility for material in the 212-500 micron grainsize range.
Repeated megafloods from glacial Lake Vitim, Siberia, to the Arctic Ocean over the past 60,000 years
(Elsevier, 2018-05-01) Margold, M; Jansen, JD; Codilean, AT; Preusser, F; Gurinov, AL; Fujioka, T; Fink, D
Cataclysmic outburst floods transformed landscapes and caused abrupt climate change during the last deglaciation. Whether such events have also characterized previous deglaciations is not known. Arctic marine cores hint at megafloods prior to Oxygen Isotope Stage (OIS) 2, but the overprint of successive glaciations means that geomorphological traces of ancient floods remain scarce in Eurasia and North America. Here we present the first well-constrained terrestrial megaflood record to be linked with Arctic archives. Based on cosmogenic-nuclide exposure dating and optically stimulated luminescence dating applied to glacial-lake sediments, a 300-m deep bedrock spillway, and giant eddy-bars > 200-m high, we reconstruct a history of cataclysmic outburst floods from glacial Lake Vitim, Siberia, to the Arctic Ocean over the past 60,000-years. Three megafloods have reflected the rhythm of Eurasian glaciations, leaving traces that stretch more than 3500 km to the Lena Delta. The first flood was coincident with deglaciation from OIS-4 and the largest meltwater spike in Arctic marine-cores within the past 100,000 years (isotope-event 3.31 at 55.5 ka). The second flood marked the lead up to the local Last Glacial Maximum, and the third flood occurred during the last deglaciation. This final 3000 km3 megaflood stands as one of the largest freshwater floods ever documented, with peak discharge of 4.0–6.5 million m3s−1, mean flow depths of 120–150 m, and average flow velocities up to 21 m s−1. © 2018 Elsevier Ltd.
Sediment transport dynamics in central Australian low-gradient landscapes quantified with cosmogenic nuclides
(Science Council of Japan, 2015-07-26) Struck, M; Jansen, JD; Codilean, AT; Fujioka, T; Fink, D; Kotevski, S
Erosion and sediment routing are key to understanding landscape evolution. In this regard, low-gradient landscapes have remained effectively unstudied in spite of their vast global extent, whereas steep mountain regions have been the focus of most research efforts. Sediment transport and storage is widely thought to occur on much longer timescales in regions of low relief relative to their steep counterparts. Here we apply in situ-produced cosmogenic nuclides to examine the sediment transport and storage history of a low-gradient catchment (Peake River) in arid central Australia. The catchment covers 27,300 km2 with a total relief of 394 m and a mean slope of 32 ± 29 m/km (mean ± 1σ, calculated from 1 arc-sec SRTM). Previous studies in central Australia have focused mainly upon local measurements of landscape lowering and bedrock erosion; however, to better understand the processes shaping these landscapes, we adopt a source-to-sink approach coupling bedrock and hillslope colluvium measurements of cosmogenic nuclides with basin-wide measurements in fluvial sediment. Variation in concentrations and ratios of 10Be and 26Al in sediment provides insights to residence times and burial history as grains are transmitted through the bedrock-hillslope-stream sediment conveyor. Our preliminary results reveal basin-wide erosion rates ranging from 0.2 to 5.8 m/Myr (weighted mean = 0.41 ± 0.03 m/Myr), which are among the lowest rates ever measured. We discuss the sediment dynamics of flat landscapes, emphasizing the contrast with steeper settings. Copyright © 2015, XIX INQUA Congress LOC
Short duration glacial advances: implications for cosmogenic dating chronologies
(Australian Nuclear Science and Technology Organisation, 2021-11-17) White, DA; Fülöp, RH; Fink, D; Fujioka, T; Blaxell, M; Jeromson, MR; Codilean, AT
Cosmogenic nuclides are now the mainstay technique for constraining past ice advances in terrestrial environments. However, limited erosion of bedrock and recycling of older glacial sediments complicates the interpretation of dated records. Where younger deposits or striated bedrock surfaces contain nuclides inherited from previous periods of exposure, cosmogenic dates overestimate deglaciation by tens to hundreds of thousands of years. This is especially problematic in Antarctica, where low erosion rates and cold-based glaciation produce widespread inheritance in erratics or bedrock surfaces. Studies using long-lived nuclides such as Be-10 have identified sites where <5% of erratics are inheritance-free, making it logistically difficult to measure ice sheet retreat. To address this issue, the short-lived nuclide in-situ C -14 is being applied in Antarctic deglaciation studies. The relatively recent deglaciation across most parts of Antarctica mean inheritance in erratics can be detected by discordant Be-10 and C-14 ages. Bedrock may also be dateable using C-14 if the inherited nuclides decay below measurement uncertainties while ice cover is present. However, both these approaches, particularly direct bedrock dating, make assumptions of the duration of the glacial advance. To test these approaches we measured C-14 in bedrock surfaces from sites across East Antarctica between Enderby Land (48oE) and Vincennies Bay (107oE). At each site, the true deglaciation age was well established via Be-10 ages on erratics, and in some cases, coincident with the onset of biogenic sedimentation in lake and marine basins. We find that the assumption of a long-duration Last Glacial Maximum (LGM) is not widely met. The two inland sites appear to have been buried long enough to re-set the C-14 signal. However, at least four sites along the East Antarctic coastline displayed bedrock surfaces that were saturated with C-14, despite clearly having been covered by ice during the early Holocene. These results mean that in-situ C-14 ages must be carefully interpreted, especially when used on bedrock. Bedrock surfaces that provide discrete ages can be used to indicate that deglaciation has occurred since the global Last Glacial Maximum. However, those with saturated surfaces provide equivocal results unless supporting evidence can support the expected duration of the LGM. © The Authors
SIRIUS Performance: 10Be, 26A1 and 36C1 measurements at ANSTO
(Elsevier, 2019-09-15) Wilcken, KM; Fujioka, T; Fink, D; Fülöp, RH; Codilean, AT; Simon, KJ; Mifsud, C; Kotevski, S
SIRIUS – a 6 MV pelletron accelerator at ANSTO was delivered and installed in 2014–2015. After initial testing and commissioning phase we have now moved into routine operations. Quality assurance data from the past 2 years demonstrates the excellent performance and SIRIUS is now our preferred instrument for 10Be, 26A1 and 36C1 analyses. © 2019 Elsevier B.V.
Soil production and transport on postorogenic desert hillslopes quantified with 10Be and 26Al
(GeoScienceWorld, 2018-01-02) Struck, M; Jansen, JD; Fujioka, T; Codilean, AT; Fink, D; Egholm, DL; Fülöp, RH; Wilcken, KM; Kotevski, S
Hillslopes stand at the top of the geomorphic conveyor belt that produces and transports mass throughout landscapes. Quantification of the tempo of hillslope evolution is key to identifying primary sediment production and understanding how surface processes shape topography. We measured cosmogenic 10Be and 26Al on three desert hillslopes in postorogenic central Australia and quantified their soil dynamics and evolution. We found that hillslope morphology is governed by lithological factors, and differing nuclide abundances reflect the main sediment transport processes. Slope wash is widespread, and shrink-swell soil processes drive downslope creep and upward migration of gravels detached from underlying bedrock. We applied Monte Carlo–based inversion modeling to reconstruct soil production and the exhumation histories of stony mantle gravels. Underlying silty soils derive from eolian dust inputs dating to at least 0.2 Ma and possibly more than 1 Ma, in line with intensified aridity. Exposed bedrock erodes at ∼0.2–7 m/m.y., and under soil, it erodes at maximum rates of <0.1 m/m.y. up to 10 m/m.y. Accordingly, particles spend 2–6 m.y. or more in the upper 0.6 m of the bedrock column and an additional ∼0.2–2 m.y. or more within hillslope soils. Such long periods near the surface result in surface particles acquiring inherently low 26Al/10Be ratios. Bedrock erodibility underpins regional variations in erosion rate, and the slow tempo of hillslope evolution is largely independent of base level. This suggests a distinctive top-down evolution among postorogenic hillslopes set by authigenic rates of sediment production, rather than by fluvial incision as in tectonically active settings. © 2021 Geological Society of America
Spatial pattern of denudation in a lithologically controlled sub-tropical flat landscape: insights from the Kimberley region, NW Australia
(European Geophysical Union, 2016-01-01) Cazes, G; Fink, D; Codilean, AT; Fülöp, RH
The Kimberley region, northwest Australia, is well known for its expansive and diverse collection of prehistorical aboriginal rock art that potentially dates back to 40,000 years ago. The region is characterized by a tropical, semiarid climate with a monsoonal rainfall distribution and a flat landscape interrupted by massive sandstone mesas and deeply incised bedrock river gorges. In order to constrain the chronology of the rock art it is necessary to quantify the spatial and temporal dimensions of landscape evolution. We report cosmogenic 10Be and 26Al concentrations in modern fluvial sediment collected from 27 catchments with areas spanning several orders of magnitude (13.6 – 13,900 km2 ). All catchments are characterized by a very low topographic gradient (average basin slopes < 3◦ ) and subdued local relief of at most 200m. Assuming negligible sediment storage times and rapid sediment transport driven by the annual monsoonal washout, we calculate 10Be based catchment-wide denudation rates ranging between 1.87 ± 0.23 and 9.48 ± 1.05 m.Myr−1 . These low rates are among the slowest recorded in the world, despite the strong climatic seasonality of the region. Our measured denudation rates exhibit a strong correlation with topographic gradient, which in the overall flat landscapes of the Kimberley, is controlled by the prevailing sandstone bedrock lithology and the presence of numerous escarpments adjacent to the river channels. We present a modelling approach that makes use of the 26Al/10Be ratio in the fluvial sediments as a source tracer (ie escarpment cliffs, river channels, plateau bedrocks), and use this to explore the control and retreat rate of the eroding escarpment cliffs in order to provide information on the spatial distribution of denudation in the landscape. © Author(s) 2016. CC Attribution 3.0 License.

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