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Quaternary geochronology
Elsevier
Quaternary geochronology

Elsevier

1871-1014

Quaternary geochronology/Journal Quaternary geochronologyAHCIISTPSCI
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    The SPICE project: Calibrated cosmogenic Al-26 production rates and cross-calibrated Al-26 /Be-10, Al-26/C-14, and 26Al/21Ne ratios in quartz from the SP basalt flow, AZ, USA

    Fenton, Cassandra R.Binnie, Steven A.Dunai, TiborNiedermann, Samuel...
    15页
    查看更多>>摘要：The formally named SP lava flow is a quartz-, olivine- and pyroxene-bearing basalt flow that is preserved in the desert climate of northern Arizona, USA. The flow is independently dated with an 40Ar/39Ar age of 72 +/- 4 ka (20) and has undergone negligible erosion and/or burial, making its surface an ideal site for direct calibration of cosmogenic nuclide production rates. Production rates for cosmogenic 26Al have been determined from SP flow quartz in this study and are combined with production rates for 10Be, 14C, and 21Ne (Fenton et al., 2019) to yield a suite of production rate ratios. The error-weighted mean, sea-level, high latitude (SLHL) total reference production rate of 26Al is 25.8 +/- 2.5 at/g/yr (25x; standard error) using time-independent Lal (1991)/Stone (2000) (St) scaling factors. The St scaled spallogenic 26Al rate is 25.0 +/- 2.4 at/g/yr integrated over the past 72 ka. This rate overlaps within 20 uncertainty with other St-scaled production rates in the literature. SLHL spallogenic 26Al production rates in SPICE quartz (SP Flow Production-Rate Inter-Calibration Site for Cosmogenic-Nuclide Evaluations) are nominally lower if time-dependent Sf, Sa, and Lm scaling factors are used, yielding values of 22.9 +/- 2.2 at/g/yr, 22.6 +/- 2.2 at/g/yr, and 24.1 +/- 2.2 at/g/yr (25x), respectively. All 26Al production rates in SP flow quartz overlap within 20 uncertainty, regardless of time independent or time dependent scaling. Production rate ratios for cosmogenic 26Al/10Be, 26Al/14C, and 26Al/21Ne are based on the total, local production rates of each cosmogenic nuclide, independent of scaling models, and have error-weighted means (+/- 25x; standard error) of 6.7 +/- 0.6, 2.23 +/- 0.20, and 1.51 +/- 0.13, respectively. This study suggests that, similar to cosmogenic 21Ne and 10Be production rates in SP flow quartz, production rates of cosmogenic 26Al in quartz do not significantly increase when integrated over 72 ka, a time span which includes the period of decreased magnetic strength from 20 to 50 ka.
      原文链接:
    • NSTL
    • Elsevier

    Testing a new combined (U,Th)-He and U/Th dating approach on Plio-Pleistocene calcite speleothems

    Makhubela, Tebogo, VKramers, Jan D.
    18页
    查看更多>>摘要：The geochronology of cave deposits in the Cradle of Humankind UNESCO World Heritage Site in South Africa provides a timeframe essential for the interpretation of its fossils. The uranium-lead (U-Pb) and uranium-thorium disequilibrium (U/Th) dating of speleothems, mostly flowstones that underlie and blanket the fossil-bearing sediments, have been effective in this sense, but U-Pb is limited by the requirement of similar to 1 ppm U concentrations and low common Pb contents, and U/Th has a c. 500 ka limit of applicability. Here we report age results for calcite-aragonite speleothems obtained using a new combined uranium-thorium-helium ((U,Th)-He) and U/Th dating routine. We reproduced within analytical uncertainty, the published U-Pb or U/Th ages for (a) flowstone in three drill core samples in the range 2000-3000 ka, (b) a flowstone hand sample taken at surface with an age of 1800 ka, and (c) five underground flowstone samples in the range 100-800 ka. Calcite retentivity for He under cave conditions is thus demonstrated. In the few cases where helium loss was observed in speleothems, only some of the subsamples were affected, and to varying degrees, suggesting loss by lattice damage not related to diagenetic processes, rather than volume diffusion. In the 100 to 800 ka range, the combined U/Th disequilibrium and (U,Th)-He method also yielded reliable values for initial (Th-230/U-238) and (U-234/U-238) activity ratios. Importantly, most subsamples had high initial (Th-230/U-238) values, ranging from 1.0 to 19.7, although having low Th/U ratios. This is probably due to incorporation of Fe-Mn oxides-hydroxides dust, on which Th-230 was previously adsorbed. Such samples are mostly not dateable by U/Th without the additional input from the He analysis. If not detected and corrected for, such high initial (Th-230/U-238) values can lead to inaccurate U/Th and U-Pb ages. Our study shows that the incorporation of He analysis in U/Th dating has broad potential application, with four methods for calculating the ages, in carbonates from different environments where U-Pb or U/Th dating would not work.
      原文链接:
    • NSTL
    • Elsevier

    Improved age estimates for Holocene Ko-g and Ma-f-j tephras in northern Japan using Bayesian statistical modelling

    Chen, Xuan-YuBlockley, Simon P. E.Staff, Richard A.Xu, Yi-Gang...
    8页
    查看更多>>摘要：The Ko-g and Ma-f-j tephras are two key isochronous marker layers in northern Japan, which are from the largest Plinian eruptions of Komagatake volcano (VEI = 5) and Mashu caldera (VEI = 6), respectively. Despite extensive radiocarbon studies associated with the two tephras, individual calibrated results show considerable variations and thus accurate ages of these important eruptions remain controversial. Bayesian statistical approaches to calibrating radiocarbon determinations have proven successful in increasing accuracy and sometimes precision for dating tephras, which is achieved through the incorporation of additional stratigraphic information and the combination of evidence from multiple records. Here we use Bayesian approaches to analyse the proximal and distal information associated with the two tephra markers. Through establishing phase and deposition models, we have taken into account all of the currently available stratigraphic and chronological information. The cross-referencing of phase models with the deposition model allows the refinement of eruption ages and the deposition model itself. Using this we are able to provide the most robust current age estimates for the two tephra layers. The Ko-g and Ma-f-j tephras are hereby dated to 6657-6505 (95.4%; 6586 +/- 40, l +/- cy) cal yr BP, and 7670-7395 (95.4%; 7532 +/- 72, l +/- cy) cal yr BP, respectively. These updated age determinations underpin the reported East Asian Holocene tephrostratigraphic framework, and allow sites where the tephra layers are present to be dated more precisely and accurately. Our results encourage further applications of Bayesian modelling techniques in the volcanically active East Asian region.
      原文链接:
    • NSTL
    • Elsevier

    UThwigl - An R package for closed- and open-system uranium-thorium dating

    Dosseto, AnthonyMarwick, Ben
    13页
    查看更多>>摘要：For several decades, uranium-thorium (U-Th) dating has allowed geochronologists to precisely date geological materials, providing invaluable geochronological constraints on Quaternary processes. Open-system dating of bones and teeth has also provided ages of human and faunal remains of archaeological significance. To facilitate access to closed-and open-system U-Th dating to the broad scientific community, here we provide an R package, named UThwigl. Description of input and output parameters is given, as well as a guide for running the model. The package can be used three different ways: (i) as a web application, (ii) through a web browser with an internet connection, or (iii) in R (most efficiently with RStudio). Examples of application of the model are also provided, showing that it yields ages within error of previously published values.
      原文链接:
    • NSTL
    • Elsevier

    The build-up of the laboratory-generated dose-response curve and underestimation of equivalent dose for quartz OSL in the high dose region: A critical modelling study

    Peng, JunWang, XulongAdamiec, Grzegorz
    17页
    查看更多>>摘要：The application of a regeneration procedure for optically stimulated luminescence (OSL) dating requires that the dose-response curve (DRC) of a natural sample is the same as that of a laboratory-generated one. However, the build-up of the laboratory-generated DRCs of quartz has been widely reported in the literature, i.e., the laboratory-generated DRCs are significantly higher than the natural counterparts in the high dose region (above 150 or 200 Gy). This results in severe underestimation of equivalent dose (D-e) for quartz OSL in the high dose region during the application of a single-aliquot regenerative-dose (SAR) protocol. However, the potential mechanism governing the build-up of the laboratory-generated DRC is still unclear. In this study, we performed a comprehensive investigation of the natural and laboratory-generated OSL signals and DRCs using a kinetic model for quartz. We compared the differences in charge concentrations between natural and laboratory-irradiated aliquots following irradiation and monitored the competition for holes and electrons during preheat and stimulation, for the natural, regenerative, and test dose cycles. In the course of the modelling, we could see the buildup of laboratory-generated DRCs, the underestimation of D-e, and a double exponential saturation characteristic of the DRCs. We demonstrated a discrepancy in competition for electrons in the deep electron trap and recombination centres during stimulation between the natural, regenerative, and test dose cycles. The simulation results are directly relevant to quartz OSL D-e determination using the SAR protocol and reveal the mechanisms responsible for the experimentally observed different behaviours between natural and laboratory-generated DRCs.
      原文链接:
    • NSTL
    • Elsevier

    Luminescence dating of quartz from ironstones of the Xingu River, Eastern Amazonia

    Niyonzima, P.Sawakuchi, A. O.Bertassoli Jr, D. J.Pupim, F. N....
    13页
    查看更多>>摘要：This study reports on the first investigation into the potential of quartz luminescence dating to establish for-mation ages of ferruginous duricrust deposits (ironstones) of the Xingu River in Eastern Amazonia, Brazil. The studied ironstones comprise sand and gravel cemented by goethite (FeO(OH)), occurring as sandstones and conglomerates in the riverbed of the Xingu River, a major tributary of the Amazon River. The Xingu ironstones have a cavernous morphology and give origin to particular habitat for benthic biota in an area that hosts the largest rapids in Amazonia. So far, the Xingu ironstones have uncertain formation ages and their sedimentary origin is still poorly understood. In this way, seven samples of ironstones distributed along the lower Xingu River were collected for optically stimulated luminescence (OSL) dating of their detrital quartz sand grains. Addi-tionally, the organic content of some samples was dated by radiocarbon (C-14) for comparison with quartz OSL ages. The luminescence ages of the sand-sized quartz grains extracted from the ironstones were obtained from medium (100-300 grains) and small (10-20 grains) aliquots using the single aliquot regenerative-dose (SAR) protocol. Equivalent doses (D-e) distributions have varied overdispersion (OD) both for medium size aliquots (OD = 19-58 %) and small size aliquots (OD = 29-76 %). No significant trend was observed between D-e and aliquot size. The studied ironstones grow over the riverbed, but stay below or above water throughout the year due to the seasonal water level variation of the Xingu River. However, the effect of water saturation in dose rates is reduced due to relatively low porosity of ironstones. Water saturated dose rates (dry sample dose rates) range from 2.70 +/- 0.21 (2.79 +/- 0.22) Gy/ka to 12.34 +/- 0.97 (13.26 +/- 1.12) Gy/ka, which are relatively high when compared to values reported for Brazilian sandy sediments elsewhere (similar to 1 Gy/ka). Samples with high over-dispersion (>40 %) are mainly attributed to mixing of grains trapped in different time periods by goethite cementation. The obtained OSL ages for water saturated (dry) samples range from 3.4 +/- 0.3 (3.3 +/- 0.4) ka to 59.6 +/- 6.0 (58.1 +/- 6.4) ka, using D-e determined from medium size aliquots and dose response curves fitted by an exponential plus linear function. Radiocarbon ages of the bulk organic matter extracted from selected ironstone varied from ca. 4 cal ka BP to ca. 23 cal ka BP. Significant differences were observed between OSL and radio-carbon ages, suggesting asynchronous trapping of organic matter and detrital quartz within the ironstone matrix. These late Pleistocene to Holocene ages indicate that ironstones of the Xingu River result from an active surface geochemical system able to precipitate goethite and cement detrital sediments under transport. The obtained ages and differences between OSL and radiocarbon ages point out that the ironstones have multiphase and spatially heterogeneous growth across the Xingu riverbed. Our results also expand the application of lumines-cence dating to different sedimentary deposits.
      原文链接:
    • NSTL
    • Elsevier

    Investigating the applicability of a standardised growth curve approach on Middle Pleistocene sediments from northern Switzerland

    Mueller, DanielaPreusser, Frank
    12页
    查看更多>>摘要：The introduction of the Single Aliquot Regenerative Dose (SAR) protocol established luminescence dating as an indispensable tool in Quaternary research. A major impediment of this technique is the time required for measurements, since the protocol is repeated for various aliquots of each sample to establish a sound statistical basis. To reduce the demand on machine time, Standardised Growth Curve (SGC) approaches have been developed and successfully applied for samples from some regions. However, differences in luminescence properties require careful testing of this techniques when applied to samples with other geological background. In this study, the application of the SGC approach of Li et al. (2016) is successfully verified for multi-grain aliquots of coarse-grained quartz and feldspar samples from three sites in northern Switzerland. In-depth quality control measures ensure the reproducibility of equivalent dose (De) values obtained by the common SAR protocol and sample-specific SGCs. For both minerals little sensitivity was found to the re-normalisation dose and the sample-specific SGCs performed well. In contrast to other studies, no different types of dose response curve shape were observed for quartz. A minimum number of full SAR measurements of eight and six aliquots per sample has been found appropriate for quartz and feldspar, respectively. For the fading corrected feldspar signals, site-specific SGC worked well and De values of up to 800 Gy were consistently replicated. In summary, sample-specific SGCs for samples from northern Switzerland perform well and their application reduces measurement times by up to 70%. The construction of a regional SGC may well be beneficial, however, caution regarding the choice of given doses and curve fitting is recommended and a thorough verification of SGC results is needed before the technique is widely applied.
      原文链接:
    • NSTL
    • Elsevier

    Rapid in situ assessment of luminescence-bleaching depths for deriving burial and exposure chronologies of rock surfaces

    Sellwood, E. L.Kook, M.Jain, M.
    13页
    查看更多>>摘要：Recent developments in luminescence dating offer new ways to date exposure and burial durations of rocks. The new rock surface dating methods ideally require high-resolution data, faster sample preparation and measurement times, and field screening methods to select samples with appropriate luminescence characteristics and bleaching histories. Presented here is a demonstration of an EMCCD (electron multiplying charge coupled device) based system capable of imaging high-resolution infrared stimulated luminescence (IRSL) and infraredphotoluminescence (IRPL) from rock samples. The IRPL can be detected at both 880 nm and 955 nm. Using this instrument, the entire luminescence-depth profile can be reconstructed by imaging a single surface cut perpendicular to the exposed rock face. We demonstrate the possibility of reconstructing luminescence-depth profiles suitable for rock surface dating from large (cm-scale) rock samples, without using a regeneration dose for normalisation of the natural luminescence signals. Based on the different bleaching characteristics of the IRSL and IRPL emissions at 880 nm and 955 nm, we show that it is possible to gain reliable estimates of bleaching depths from measurement of as few as two images of the IRPL signal (one for each emission), or from measurement of the IRSL decay curve. We thus by-pass laborious sample preparations and the need for a gamma source to estimate the bleaching depth, thereby extending the 2D luminescence-depth profile imaging technique to other laboratories that lack access to ionising radiation facilities. This study also makes a significant progression towards development of a field instrument for in situ relative exposure dating, and sample screening for rock surface burial dating.
      原文链接:
    • NSTL
    • Elsevier

    A high-resolution Lateglacial-Early Holocene tephrostratigraphy from southernmost Sweden with comments on the Borrobol-Penifiler tephra complex

    Larsson, Simon A.Wastegard, Stefan
    12页
    查看更多>>摘要：We present results from a cryptotephra investigation performed at a high resolution (0.5 cm) on sediments from Ko center dot rsla center dot ttamossen in southernmost Sweden. Six peak concentration levels were detected and extracted for geochemical analysis by electron probe microanalyser. Five of these levels were successfully analysed and we propose correlations to the Ha center dot sseldalen Tephra, the Vedde Ash, and the Laacher See Tephra (adding new analysis results for the first geochemically confirmed finding of the latter in Sweden), as well as an undetermined Borrobol-type tephra. The tephra identifications were combined with radiocarbon dated macrofossils in order to create an age model for the sampled sediments based on Bayesian methods. Stratigraphical and chronological results were found to concur with a previous study of the site and our results form the basis for discussion concerning the issues surrounding Lateglacial Borrobol-type tephras, of which we suggest further review in order to unlock these tephras' full potential for Quaternary studies.
      原文链接:
    • NSTL
    • Elsevier

    An (U-Th)/He age for the small Monturaqui impact structure, Chile

    Ukstins, Ingrid A.Wartho, Jo-AnneCabrol, Nathalie A.Grin, Edmond A....
    11页
    查看更多>>摘要：Single-crystal (U-Th)/He dating of 32 apatite and zircon crystals from an impact breccia yielded a weighted mean age of 663 +/- 28 ka (n = 3; 4.2 % 2s uncertainties) for the Monturaqui impact structure, Chile. This similar to 350 m diameter simple crater preserves a small volume of impactite consisting of polymict breccias that are dominated by reworked target rock clasts. The small size, young age and limited availability of melt material for traditional geochronological techniques made Monturaqui a good test to define the lower limits of the (U-Th)/He system to successfully date impact events. Numerical modeling of He-4 loss in apatite and zircon crystals shows that, for even small craters such as Monturaqui, the short-lived compressional stage and shock metamorphic stage can account for the observed partial to full resetting of (U-Th)/He ages in accessory minerals. Despite the distinctly different He-4 diffusion parameters of apatite and zircon, the 2s-overlapping youngest ages are recorded in both populations of minerals, which supports the inference that the weighted mean of the youngest (U-Th)/He population is the age of formation of this impact structure.
      原文链接:
    • NSTL
    • Elsevier