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1.
Existing methods of cosmogenic nuclide burial dating perform well provided that sediment sources undergo steady rates of erosion and the samples experience continuous exposure to cosmic rays. These premises exert important limitations on the applicability of the methods. And yet, high mountain sediment sources are rife with transient processes, such as non-steady erosion by glacial quarrying and/or landsliding, or temporary cosmic-ray shielding beneath glaciers and/or sediment. As well as breaching the premises of existing burial dating methods, such processes yield samples with low nuclide abundances and variable 26Al/10Be ratios that may foil both isochron and simple burial-age solutions. P–PINI (Particle-Pathway Inversion of Nuclide Inventories) is a new dating tool designed for dating the burial of sediments sourced from landscapes characterized by abrupt, non-steady erosion, discontinuous exposure, and catchments with elevation-dependent 26Al/10Be production ratios. P–PINI merges a Monte Carlo simulator with established cosmogenic nuclide production equations to simulate millions of samples (10Be–26Al inventories). The simulated samples are compared statistically with 10Be–26Al measured in field samples to define the most probable burial age. Here, we target three published 10Be–26Al datasets to demonstrate the versatility of the P–PINI model for dating fluvial and glacial sediments. (1) The first case serves as a robust validation of P–PINI. For the Pulu fluvial gravels (China), we obtain a burial age of 1.27 ± 0.10 Ma (1σ), which accords with the isochron burial age and two independent chronometers reported in Zhao et al. (2016) Quaternary Geochronology 34, 75–80. The second and third cases, however, reveal marked divergence between P–PINI and isochron-derived ages. (2) For the fluvial Nenana Gravel (USA), we obtain a minimum-limiting burial age of 4.5 ± 0.7 Ma (1σ), which is compatible with unroofing of the Alaska Range starting ∼ 6 Ma, while calling into question the Early Pleistocene isochron burial age presented in Sortor et al. (2021) Geology 49, 1473–1477. (3) For the Bünten Till (Switzerland), we obtain a limiting burial age of <204 ka (95th percentile range), which conforms with the classical notion of the most extensive glaciation in the northern Alpine Foreland assigned to the Riss glaciation (sensu marine isotope stage 6) contrary to the isochron burial age presented in Dieleman et al. (2022) Geosciences, 12, 39. Discrepancies between P–PINI and the isochron ages are rooted in the challenges posed by the diverse pre-burial 26Al/10Be ratios produced under conditions characteristic of high mountain landscapes; i.e., non-steady erosion, discontinuous cosmic-ray exposure, and elevation-dependent 26Al/10Be production ratios in the source region, which are incompatible with the isochron method, but easily accommodated by the stochastic design of P–PINI. 相似文献
2.
Paul Muzikar 《地球表面变化过程与地形》2011,36(7):946-952
The 26Al–10Be burial dating method has been applied to a range of problems in geochronology. This technique allows us to determine the burial age of quartz‐containing sediments, by measuring the concentration of cosmogenic 10Be and 26Al in the quartz. In its most basic form, the method assumes a simple history (single exposure episode followed by burial) for the quartz clasts. Balco and Rovey have recently developed an innovative isochron version of this method, which can take into account a more complicated exposure history for the quartz, and used it to date a series of glacial tills. There can be constraints on the slope and intercept of the isochron, depending on how we model the geology of the Balco–Rovey approach. We show how to take these constraints into account when fitting the slope and intercept; we apply a Bayesian approach, in which there is a straightforward way to implement constraints. We discuss the important issues that arise; a variety of choices must be made in choosing the prior, both in what geological insights to include and in how to include them. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
3.
T.V. Makhubela J.D. Kramers D. Scherler H. Wittmann P.H.G.M. Dirks S.R. Winkler 《地球表面变化过程与地形》2019,44(15):2968-2981
In situ cosmogenic nuclides are an important tool for quantifying landscape evolution and dating fossil-bearing deposits in the Cradle of Humankind (CoH), South Africa. This technique mainly employs cosmogenic 10-Beryllium (10Be) in river sediments to estimate denudation rates and the ratio of 26-Aluminium (26Al) to 10Be (26Al/10Be), to constrain ages of sediment burial. Here, we use 10Be and 26Al concentrations in bedrock and soil above the Rising Star Cave (the discovery site of Homo naledi) to constrain the denudation rate and the exposure history of soil on the surface. Apparent 10Be-derived denudation rates obtained from pebble- to cobble-sized clasts and coarse-sand in soil (on average 3.59 ± 0.27 m/Ma and 3.05 ± 0.25 m/Ma, respectively) are 2-3 times lower than the bedrock denudation rates (on average 9.46 ± 0.68 m/Ma). In addition, soil samples yield an average 26Al/10Be ratio (5.12 ± 0.27) that is significantly lower than the surface production ratio of 6.75, which suggests complex exposure histories. These results are consistent with prolonged surface residence of up to 1.5 Ma in vertically mixed soils that are up to 3 m thick. We conclude that the 10Be concentrations accumulated in soils during the long near-surface residence times can potentially cause underestimation of single-nuclide (10Be) catchment-wide denudation rates in the CoH. Further, burial ages of cave sediment samples that consist of an amalgamation of sand-size quartz grains could be overestimated if a pre-burial 26Al/10Be ratio calculated from the surface production is assumed. © 2019 John Wiley & Sons, Ltd. 相似文献
4.
Duanne White Réka-Hajnalka Fülöp Paul Bishop Andrew Mackintosh Gordon Cook 《Quaternary Geochronology》2011,6(3-4):289-294
Cosmogenic nuclide exposure dating of glacial clasts is becoming a common and robust method for reconstructing the history of glaciers and ice sheets. In Antarctica, however, many samples exhibit cosmogenic nuclide ‘inheritance’ as a result of sediment recycling and exposure to cosmic radiation during previous ice free periods. In-situ cosmogenic 14C, in combination with longer lived nuclides such as 10Be, can be used to detect inheritance because the relatively short half-life of 14C means that in-situ 14C acquired in exposure during previous interglacials decays away while the sample locality is covered by ice during the subsequent glacial. Measurements of in-situ 14C in clasts from the last deglaciation of the Framnes Mountains in East Antarctica provide deglaciation ages that are concordant with existing 26Al and 10Be ages, suggesting that in this area, the younger population of erratics contain limited inheritance. 相似文献
5.
We applied both single-sample and isochron methods of cosmogenic-nuclide burial dating to determine the age of the sedimentary fill in Unaweep Canyon, western Colorado, USA. This stratigraphic sequence is of interest because it documents capture and diversion of the ancestral Gunnison River by the Colorado River during late Cenozoic incision of the Colorado Plateau. Seven 26Al–10Be burial ages from sedimentary infill penetrated by a borehole in central Unaweep Canyon, as well as a 26Al–10Be burial isochron age formed by multiple clasts and grain-size separates in a sample from the stratigraphically lower Gateway gravels, indicate that canyon blockage, initiation of lacustrine sediment accumulation, and presumed river capture, took place 1.41 ± 0.19 Ma. Lacustrine sedimentation ceased 1.34 ± 0.13 Ma. 相似文献
6.
7.
Ari Matmon Onn Crouvi Yehouda Enzel Paul Bierman Jennifer Larsen Naomi Porat Rivka Amit Marc Caffee 《地球表面变化过程与地形》2003,28(5):493-506
Activities of 26Al and 10Be in five chert clasts sampled from two beach ridges of late Pleistocene Lake Lisan, precursor of the Dead Sea in southern Israel, indicate low rates of chert bedrock erosion and complex exposure, burial, and by inference, transport histories. The chert clasts were derived from the Senonian Mishash Formation, a chert‐bearing chalk, which is widely exposed in the Nahal Zin drainage basin, the drainage system that supplied most of the material to the beach ridges. Simple exposure ages, assuming only exposure at the beach ridge sampling sites, range from 35 to 354 ky; using the ratio 26Al/10Be, total clast histories range from 0·46 to 4·3 My, unrelated to the clasts' current position and exposure period on the late Pleistocene beach ridges, 160–177 m below sea level. Optically stimulated luminescence dating of fine sediments from the same and nearby beach ridges yielded ages of 20·0 ± 1·4 ka and 36·1 ± 3·3 ka. These ages are supported by the degree of soil development on the beach ridges and correspond well with previously determined ages of Lake Lisan, which suggest that the lake reached its highest stand around 27 000 cal. years BP . If the clasts were exposed only once and than buried beyond the range of significant cosmogenic nuclide production, then the minimum initial exposure and the total burial times before delivery to the beach ridge are in the ranges 50–1300 ky and 390–3130 ky respectively. Alternatively, the initial cosmogenic dosing could have occurred during steady erosion of the source bedrock. Back calculating such rates of rock erosion suggests values between 0·4 and 12 m My?1. The relatively long burial periods indicate extended sediment storage as colluvium on slopes and/or as alluvial deposits in river terraces. Some clasts may have been stored for long periods in abandoned Pliocene and early Pleistocene routes of Nahal Zin to the Mediterranean before being transported again back into the Nahal Zin drainage system and washed on to the shores of Lake Lisan during the late Pleistocene. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
8.
Cosmogenic nuclide depth-profiles are used to calculate the age of landforms, the rates at which erosion has affected them since their formation and, in case of deposits, the paleo-erosion rate in the source area. However, two difficulties are typically encountered: 1) old deposits or strongly affected by cosmogenic nuclide inheritance often appear to be saturated, and 2) a full propagation of uncertainties often yields poorly constrained ages. Here we show how to combine surface-exposure-dating and burial-dating techniques in the same profile to get more accurate age results and to constrain the extent of pre-depositional burial periods. A 10Be–26Al depth-profile measured in an alluvial fan of SE Iberia is presented as a natural example. 相似文献
9.
Based on cosmogenic 10Be and 26Al analyses in 15 individual detrital quartz pebbles (16–21 mm) and cosmogenic 10Be in amalgamated medium sand (0.25–0.50 mm), all collected from the outlet of the upper Gaub River catchment in Namibia, quartz pebbles yield a substantially lower average denudation rate than those yielded by the amalgamated sand sample. 10Be and 26Al concentrations in the 15 individual pebbles span nearly two orders of magnitude (0.22 ± 0.01 to 20.74 ± 0.52 × 106 10Be atoms g−1 and 1.35 ± 0.09 to 72.76 ± 2.04 × 106 26Al atoms g−1, respectively) and yield average denudation rates of ∼0.7 m Myr−1 (10Be) and ∼0.9 m Myr−1 (26Al). In contrast, the amalgamated sand yields an average 10Be concentration of 0.77 ± 0.03 × 106 atoms g−1, and an associated mean denudation rate of 9.6 ± 1.1 m Myr−1, an order of magnitude greater than the rates obtained for the amalgamated pebbles. The inconsistency between the 10Be and 26Al in the pebbles and the 10Be in the amalgamated sand is likely due to the combined effect of differential sediment sourcing and longer sediment transport times for the pebbles compared to the sand-sized grains. The amalgamated sands leaving the catchment are an aggregate of grains originating from all quartz-bearing rocks in all parts of the catchment. Thus, the cosmogenic nuclide inventories of these sands record the overall average lowering rate of the landscape. The pebbles originate from quartz vein outcrops throughout the catchment, and the episodic erosion of the latter means that the pebbles will have higher nuclide inventories than the surrounding bedrock and soil, and therefore also higher than the amalgamated sand grains. The order-of-magnitude grain size bias observed in the Gaub has important implications for using cosmogenic nuclide abundances in depositional surfaces because in arid environments, akin to our study catchment, pebble-sized clasts yield substantially underestimated palaeo-denudation rates. Our results highlight the importance of carefully considering geomorphology and grain size when interpreting cosmogenic nuclide data in depositional surfaces. 相似文献
10.
Degradation of glacial deposits quantified with cosmogenic nuclides,Quartermain Mountains,Antarctica
Many glacial deposits in the Quartermain Mountains, Antarctica present two apparent contradictions regarding the degradation of unconsolidated deposits. The glacial deposits are up to millions of years old, yet they have maintained their meter‐scale morphology despite the fact that bedrock and regolith erosion rates in the Quartermain Mountains have been measured at 0·1–4·0 m Ma?1. Additionally, ground ice persists in some Miocene‐aged soils in the Quartermain Mountains even though modeled and measured sublimation rates of ice in Antarctic soils suggest that without any recharge mechanisms ground ice should sublimate in the upper few meters of soil on the order of 103 to 105 years. This paper presents results from using the concentration of cosmogenic nuclides beryllium‐10 (10Be) and aluminum‐26 (26Al) in bulk sediment samples from depth profiles of three glacial deposits in the Quartermain Mountains. The measured nuclide concentrations are lower than expected for the known ages of the deposits, erosion alone does not always explain these concentrations, and deflation of the tills by the sublimation of ice coupled with erosion of the overlying till can explain some of the nuclide concentration profiles. The degradation rates that best match the data range 0·7–12 m Ma?1 for sublimation of ice with initial debris concentrations ranging 12–45% and erosion of the overlying till at rates of 0·4–1·2 m Ma?1. Overturning of the tills by cryoturbation, vertical mixing, or soil creep is not indicated by the cosmogenic nuclide profiles, and degradation appears to be limited to within a few centimeters of the surface. Erosion of these tills without vertical mixing may partially explain how some glacial deposits in the Quartermain Mountains maintain their morphology and contain ground ice close to the surface for millions of years. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
11.
We present a Bayesian isochron approach to interpret measurements of multiple cosmogenic nuclides from glacially modified bedrock surfaces with complex exposure histories. An isochron approach explicitly incorporating glacial erosion is ideally suited for this problem; such erosion must be accounted for but has traditionally been ignored. Previous methods required treating each sample individually (to account for glacial erosion) and subsequently averaging results for the entire dataset. Geological considerations, however, suggest a more robust approach is to treat samples in the dataset here (and samples from other conceivable datasets) simultaneously. The Bayesian isochron method is applied to a previously published set of in situ 14C and 10Be measurements from a set of samples spanning the forefield of the Rhone Glacier, Switzerland. Results indicate 6.4 ± 0.5 kyr of integrated exposure and 4.7 ± 0.5 kyr of cumulative burial, similar to previous estimates, but with much smaller uncertainties. The reduced uncertainties result from fitting the exposure and burial duration to the entire dataset, while explicitly accounting for glacial erosion. The method presented here should be applicable with minor modifications in a number of geologic settings, and further demonstrates the utility of paired in situ 10Be and 14C measurements for unraveling complex exposure histories over during the Holocene and late Pleistocene. 相似文献
12.
Kristina Hippe Tiemen Gordijn Vincenzo Picotti Irka Hajdas John D. Jansen Marcus Christl Christof Vockenhuber Colin Maden Naki Akçar Susan Ivy-Ochs 《地球表面变化过程与地形》2019,44(3):766-780
Determining sediment transfer times is key to understanding source-to-sink dynamics and the transmission of environmental signals through the fluvial system. Previous work on the Bolivian Altiplano applied the in situ cosmogenic 14C-10Be-chronometer to river sands and proposed sediment storage times of ~10–20 kyr in four catchments southeast of Lake Titicaca. However, the fidelity of those results hinges upon isotopic steady-state within sediment supplied from the source area. With the aim of independently quantifying sediment storage times and testing the 14C-10Be steady-state assumption, we dated sediment storage units within one of the previously investigated catchments using radiocarbon dating, cosmogenic 10Be-26Al isochron burial dating, and 10Be-26Al depth-profile dating. Palaeosurfaces appear to preserve remnants of a former fluvial system, which has undergone drainage reversal, reduction in catchment area, and local isostatic uplift since ~2.8 Ma. From alluvium mantling the palaeosurfaces we gained a deposition age of ~580 ka, while lower down fluvial terraces yielded ≤34 ka, and floodplains ~3–1 ka. Owing to restricted channel connectivity with the terraces and palaeosurfaces, the main source of channel sediment is via reworking of the late Holocene floodplain. Yet modelling a set of feasible scenarios reveals that floodplain storage and burial depth are incompatible with the 14C-10Be disequilibrium measured in the channel. Instead we propose that the 14C-10Be offset results from: (i) non-uniform erosion whereby deep gullies supply hillslope-derived debris; and/or (ii) holocene landscape transience associated with climate or human impact. The reliability of the 14C-10Be chronometer vitally depends upon careful evaluation of sources of isotopic disequilibrium in a wide range of depositional and erosional landforms in the landscape. © 2018 John Wiley & Sons, Ltd. 相似文献
13.
Charlotte Prud'homme Riccardo Vassallo Christian Crouzet Julien Carcaillet Jean-Louis Mugnier Joaquin Cortés-Aranda 《地球表面变化过程与地形》2020,45(5):1168-1180
Cosmogenic nuclide dating of glacial landforms may lead to ambiguous results for ice retreat histories. The persistence of significant cosmogenic concentrations inherited from previous exposure may increase the apparent exposure ages for polished bedrocks affected by limited erosion under ice and for erratic boulders transported by glaciers and previously exposed in high-altitude rock walls. In contrast, transient burying by moraines, sediments and snow decreases the apparent exposure age. We propose a new sampling strategy, applied to four sites distributed in the Arc and Arve valleys in the Western Alps, to better constrain the factors that can bias exposure ages associated with glacial processes. We used the terrestrial cosmogenic nuclide 10Be (TCN) to estimate the exposure time from paired sampling of depth profiles in polished bedrock and on overlying erratic boulders. For a given sampling site, the exposure ages for both the polished bedrock and boulder are expected to be the same. However, in six cases out of seven, boulders had significantly higher 10Be surface concentrations than those of the associated polished surfaces. In present and past glacial processes, the 10Be distribution with depth for boulders and bedrocks implies the presence of an inheritance concentration of 10Be. Our study suggests that 10Be concentrations in erratic boulders and in polished bedrocks provide maximum and minimum exposure ages of the glacial retreat, respectively. © 2019 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd 相似文献
14.
Andreas Dehnert Oliver Kracht Frank Preusser Naki Akçar Hans Axel Kemna Peter W. Kubik Christian Schlüchter 《Quaternary Geochronology》2011,6(3-4):313-325
Cosmogenic isotope burial dating, using 10Be and 26Al, was applied to Plio–Pleistocene fluvial successions from the Lower Rhine Embayment, Germany. The approach consists of three principal steps: (1) measurement of cosmogenic nuclides in depth profiles, (2) modelling of hypothetical nuclide concentrations based on a first-order conceptualisation of the geological context and the principal succession of depositions and subsequent erosional and burial phases, and (3) using parameter estimation to identify values for the a priori unknown model parameters (burial age, initial nuclide concentrations, terrace erosion rates) that result in minimal disagreement between hypothetical and measured nuclide concentrations.The Late Pliocene Kieseloolite Formation was dated to 3650 ± 1490 ka and the Early Pleistocene Waalre Formation to 900 ± 280 ka. The unconformably overlying Upper Terrace Formation revealed ages of 740 ± 210 ka and 750 ± 250 ka for the two different sites. These findings are in good agreement with independent age control derived by bio-, magneto-, and litho-stratigraphy. Furthermore, identifiability and uncertainty analysis reveal a relationship between burial depth and sensitivity of isotope concentrations to burial age and erosion rate. Our results indicate that using shallower buried samples would enable a considerably more robust estimation of the burial age and the terrace erosion rate. Uncertainties arose mainly from nuclide measurements, and not from the uncertainties derived from modelling or insufficient knowledge of nuclide production and decay properties. 相似文献
15.
Isochron burial dating with cosmogenic nuclides is used in Quaternary geochronology for dating sediments in caves, terraces, basins, and other depositional environments. However, the method has seldom been rigorously tested against an independent chronology. Here, we report a direct comparison of isochron burial dating with K-Ar and 40Ar/39Ar bracketing ages on volcanic flows that sandwich a fluvial gravel layer in the Xinjiang province of northwestern China. The ages agree to within analytical uncertainty, validating the assumptions and physical constants used in the isochron burial dating method. 相似文献
16.
Some areas within ice sheet boundaries retain pre-existing landforms and thus either remained as ice free islands (nunataks) during glaciation, or were preserved under ice. Differentiating between these alternatives has significant implications for paleoenvironment, ice sheet surface elevation, and ice volume reconstructions. In the northern Swedish mountains, in situ cosmogenic 10Be and 26Al concentrations from glacial erratics on relict surfaces as well as glacially eroded bedrock adjacent to these surfaces, provide consistent last deglaciation exposure ages (∼8-13 kyr), confirming ice sheet overriding as opposed to ice free conditions. However, these ages contrast with exposure ages of 34-61 kyr on bedrock surfaces in these same relict areas, demonstrating that relict areas were preserved with little erosion through multiple glacial cycles. Based on the difference in radioactive decay between 26Al and 10Be, the measured nuclide concentration in one of these bedrock surfaces suggests that it remained largely unmodified for a minimum period of 845−418+461 kyr. These results indicate that relict areas need to be accounted for as frozen bed patches in basal boundary conditions for ice sheet models, and in landscape development models. Subglacial preservation also implies that source areas for glacial sediments in ocean cores are considerably smaller than the total area covered by ice sheets. These relict areas also have significance as potential long-term subglacial biologic refugia. 相似文献
17.
R. Braucher P. Del Castillo L. Siame A.J. Hidy D.L. Bourlés 《Quaternary Geochronology》2009,4(1):56-67
Measurements of radioactive in situ-produced cosmogenic nuclide concentrations in surficial material exposed to cosmic rays allow either determining the long-term denudation rate assuming that the surface studied has reached steady-state (where production and losses by denudation and radioactive decay are in equilibrium) (infinite exposure time), or dating the initiation of exposure to cosmic rays, assuming that the denudation and post-depositional processes are negligible. Criteria for determining whether a surface is eroding or undergoing burial as well as quantitative information on denudation or burial rates may be obtained from cosmogenic nuclide depth profiles. With the refinement of the physical parameters involved in the production of in situ-produced cosmogenic nuclides, a unique well-constrained depth profile now permits determination of both the exposure time and the denudation rate affecting a surface. In this paper, we first mathematically demonstrate that the exponential decrease of the in situ-produced 10Be concentrations observed along a depth profile constrains a unique exposure time and denudation rate when considering both neutrons and muons. In the second part, an improved chi-square inversion model is described and tested in the third part with actual measured profiles. 相似文献
18.
F. Kober S. Ivy‐Ochs G. Zeilinger F. Schlunegger P. W. Kubik H. Baur R. Wieler 《地球表面变化过程与地形》2009,34(3):398-412
Terrestrial cosmogenic nuclide (TCN) concentrations measured in river sediments can be used to estimate catchment‐wide denudation rates. By investigating multiple TCN the steadiness of sediment generation, transport and depositional processes can be tested. Measurements of 10Be, 21Ne and 26Al from the hyper‐ to semi‐arid Rio Lluta catchment, northern Chile, yield average single denudation rates ranging from 12 to 75 m Myr–1 throughout the catchment. Paired nuclide analysis reveals complex exposure histories for most of the samples and thus the single nuclide estimates do not exclusively represent catchment‐wide denudation rates. The lower range of single nuclide denudation rates (12–17 m Myr–1), established with the noble gas 21Ne, is in accordance with palaeodenudation rates derived from 21Ne/10Be and 26Al/10Be ratio analysis. Since this denudation rate range is measured throughout the system, it is suggested that a headwater signal is transported downstream but modulated by a complex admixture of sediment that has been stored and buried at proximal hillslope or terrace deposits, which are released during high discharge events. That is best evidenced by the stable nuclide 21Ne, which preserves the nuclide concentration even during storage intervals. The catchment‐wide single 21Ne denudation rates and the palaeodenuation rates contrast with previous TCN‐derived erosion rates from bedrock exposures at hillslope interfluves by being at least one order of magnitude higher, especially in the lower river course. These results support earlier studies that identified a coupling of erosional processes in the Western Cordillera contrasting with decoupled processes in the Western Escarpment and in the Coastal Cordillera. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
19.
Role of in situ cosmogenic nuclides 10be and 26al in the study of diverse geomorphic processes 总被引：1，自引：0，他引：1
K. Nishiizumi C. P. Kohl J. R. Arnold R. Dorn I. Klein D. Fink R. Middleton D. Lal 《地球表面变化过程与地形》1993,18(5):407-425
The central premises of applications of the in situ cosmogenic dating method for studying specific problems in geomorphology are outlined for simple and complex exposure settings. In the light of these general models, we discuss the information that can be derived about geomorphic processes, utilizing concentrations of in situ produced cosmogenic radionuclides 10Be (half-life=1·5 ma) and 26A1 (half-life=0·7 ma) in a variety of geomorphic contexts: glacial polish and tills; meteorite impact craters; alluvial fans; paleo-beach ridges; marine terraces; sand dunes; and bedrock slopes. We also compare 10Be-26Al data with results obtained by other dating methods. We conclude that the technique of measuring in situ cosmic ray produced nuclides holds promise for quantitative studies of processes and time-scales in a wide range of geomorphological problems. 相似文献
20.
The Qinghai-Tibetan Plateau is an important area for the study of Quaternary glaciation. Optically stimulated luminescence (OSL) dating has the potential to contribute to the chronology of glaciation in this region, but it is important to assess the accuracy of OSL dating of these glacial sediments. In this study, single grain quartz OSL signals are examined for five glacial samples collected from the moraines outside the Baiyu Valley, southeastern Tibet. The quartz grains exhibit poor luminescence characteristics, with a small proportion of grains passing the screening criteria. Grains which pass the screening criteria have relatively low signal intensity, leading to De values with large uncertainties. MAM and CAM were used to determine De values for these samples. The OSL ages are consistent with the sequence of events derived from the geomorphological relationship of the samples, and also with previous published radiocarbon ages. However, it is more difficult to reconcile the OSL ages and the terrestrial cosmogenic nuclide (TCN) 10Be ages. Analysis of both single grain quartz OSL data and TCN 10Be data is complex in this area. Further work is required to increase confidence in the OSL ages generated for the glacial sediments from this region. 相似文献