Pub Date : 2022-03-11DOI: 10.5194/gchron-4-121-2022
Lauren J. Davies, B. Jensen, D. Kaufman
Abstract. Multiple chronometers can be employed for dating Holocene palaeoenvironmental records, each with its own inherent strengths and weaknesses. Radiocarbon dating is one of the most widely used techniques for producing chronologies, but its application at high-latitude sites can sometimes be problematic. Here, cryptotephra were identified in a core from Cascade Lake, Arctic Alaska, and used to identify and resolve an age bias in Late Holocene radiocarbon dates from the top 1.42 m of the sediment sequence. Identifiable geochemical populations of cryptotephra are shown to be present in detectable concentrations in sediment from the north flank of the Brooks Range for the first time. Major-element glass geochemical correlations are demonstrated between ultra-distal cryptotephra and reference samples from the Late Holocene caldera-forming eruption of Opala, Kamchatka, as well as three eruptions in North America: the White River Ash (northern lobe), Ruppert tephra and the Late Holocene caldera-forming eruption of Aniakchak. The correlated ages of these cryptotephra provide evidence for an old-carbon effect and support preliminary palaeomagnetic secular variation (PSV) correlated ages reported for Cascade Lake. Chronological data from Cascade Lake were then combined using a Bayesian approach to generate an age–depth model that extends back through the Late Holocene and provisionally to 15 000 cal yr BP.
{"title":"Late Holocene cryptotephra and a provisional 15 000-year Bayesian age model for Cascade Lake, Alaska","authors":"Lauren J. Davies, B. Jensen, D. Kaufman","doi":"10.5194/gchron-4-121-2022","DOIUrl":"https://doi.org/10.5194/gchron-4-121-2022","url":null,"abstract":"Abstract. Multiple chronometers can be employed for dating Holocene\u0000palaeoenvironmental records, each with its own inherent strengths and\u0000weaknesses. Radiocarbon dating is one of the most widely used techniques for\u0000producing chronologies, but its application at high-latitude sites can\u0000sometimes be problematic. Here, cryptotephra were identified in a core from\u0000Cascade Lake, Arctic Alaska, and used to identify and resolve an age bias in\u0000Late Holocene radiocarbon dates from the top 1.42 m of the sediment\u0000sequence. Identifiable geochemical populations of cryptotephra are shown to\u0000be present in detectable concentrations in sediment from the north flank of\u0000the Brooks Range for the first time. Major-element glass geochemical\u0000correlations are demonstrated between ultra-distal cryptotephra and\u0000reference samples from the Late Holocene caldera-forming eruption of Opala,\u0000Kamchatka, as well as three eruptions in North America: the White River Ash\u0000(northern lobe), Ruppert tephra and the Late Holocene caldera-forming\u0000eruption of Aniakchak. The correlated ages of these cryptotephra provide\u0000evidence for an old-carbon effect and support preliminary palaeomagnetic\u0000secular variation (PSV) correlated ages reported for Cascade Lake.\u0000Chronological data from Cascade Lake were then combined using a Bayesian\u0000approach to generate an age–depth model that extends back through the Late\u0000Holocene and provisionally to 15 000 cal yr BP.\u0000","PeriodicalId":12723,"journal":{"name":"Geochronology","volume":"29 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-03-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84482507","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-02-23DOI: 10.5194/gchron-4-109-2022
Carol B. Aslanian, R. Jonckheere, B. Wauschkuhn, L. Ratschbacher
Abstract. The tools for interpreting fission-track data are evolving apace, but, even so, the outcomes cannot be better than the data. Recent studies showed that track etching and observation affect confined-track length measurements. We investigated the effects of grain orientation, polishing, etching and observation on fission-track counts in apatite. Our findings throw light on the phenomena that affect the track counts and hence the sample ages, whilst raising the question: what counts as an etched surface track? This is pertinent to manual and automatic track counts and to designing training strategies for neural networks. Counting prism faces and using the ζ calibration for age calculation are assumed to deal with most etching- and counting-related factors. However, prism faces are not unproblematic for counting, and other surface orientations are not unusable. Our results suggest that a reinvestigation of the etching properties of different apatite faces could increase the range useful for dating and lift a significant restriction for provenance studies.
{"title":"Short communication: Experimental factors affecting fission-track counts in apatite","authors":"Carol B. Aslanian, R. Jonckheere, B. Wauschkuhn, L. Ratschbacher","doi":"10.5194/gchron-4-109-2022","DOIUrl":"https://doi.org/10.5194/gchron-4-109-2022","url":null,"abstract":"Abstract. The tools for interpreting fission-track data are evolving apace, but, even\u0000so, the outcomes cannot be better than the data. Recent studies showed that\u0000track etching and observation affect confined-track length measurements. We\u0000investigated the effects of grain orientation, polishing, etching and\u0000observation on fission-track counts in apatite. Our findings throw light on\u0000the phenomena that affect the track counts and hence the sample ages,\u0000whilst raising the question: what counts as an etched surface track? This is\u0000pertinent to manual and automatic track counts and to designing training\u0000strategies for neural networks. Counting prism faces and using the ζ calibration for age calculation are assumed to deal with most etching- and counting-related factors. However, prism faces are not unproblematic for counting, and other surface orientations are not unusable. Our results suggest that a reinvestigation of the etching properties of different apatite faces could increase the range useful for dating and lift a significant restriction for provenance studies.\u0000","PeriodicalId":12723,"journal":{"name":"Geochronology","volume":"369 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-02-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77851592","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract. Chemical weathering alters the chemical composition of mineral grains. As a result, trapped-charge dating signals of primary silicates may be progressively modified. In this study, we artificially weathered three feldspar specimens to understand the effect of proton- and ligand-promoted dissolution on their luminescence properties. We conducted kinetic experiments over 720 h using two solutions: (1) oxalic acid (pH 3, 20 °C), an organic acid with chelating abilities, and (2) aqua regia (pH < 1, 40 °C), a mixture of strong acids creating aggressive acid hydrolysis conditions. These two solutions were chosen to approach over laboratory timescales some of the changes that may occur over geological time scales as minerals weather in nature. The effect of the extracting solutions on mineral dissolution was investigated by following the concentration of elements accumulating in solution, while changes in feldspar surface morphology was assessed by scanning electron microscopy (SEM). Subsequent changes in feldspar luminescence in the near-UV (~340 nm) and blue (~410 nm) thermoluminescence (TL) and infrared stimulated luminescence (IRSL) emission bands were assessed at the multi- and/or single-grain levels to gain insight into the emission spectra, dose response, saturation, and anomalous fading characteristics of the feldspars. In all experiments, only minor feldspar dissolution was observed after 720 h with < 5 % of total Al, Si, Na, and Ca appearing in the aqueous phase, while 5–8 % of the total Mn and Fe were extracted. In general, aqua regia, the more chemically-aggressive solution, had a larger effect on feldspar dissolution compared to that of oxalic acid. Additionally, our results showed that although the TL and IRSL intensities changed slightly with increasing artificial weathering time, the feldspar luminescence properties were otherwise unmodified. This suggests that chemical alteration of feldspar surfaces may not affect luminescence dating signals obtained from natural samples.
{"title":"Potential impacts of chemical weathering on feldspar luminescence dating properties","authors":"M. Bartz, J. Peña, S. Grand, G. King","doi":"10.5194/gchron-2022-3","DOIUrl":"https://doi.org/10.5194/gchron-2022-3","url":null,"abstract":"Abstract. Chemical weathering alters the chemical composition of mineral grains. As a result, trapped-charge dating signals of primary silicates may be progressively modified. In this study, we artificially weathered three feldspar specimens to understand the effect of proton- and ligand-promoted dissolution on their luminescence properties. We conducted kinetic experiments over 720 h using two solutions: (1) oxalic acid (pH 3, 20 °C), an organic acid with chelating abilities, and (2) aqua regia (pH < 1, 40 °C), a mixture of strong acids creating aggressive acid hydrolysis conditions. These two solutions were chosen to approach over laboratory timescales some of the changes that may occur over geological time scales as minerals weather in nature. The effect of the extracting solutions on mineral dissolution was investigated by following the concentration of elements accumulating in solution, while changes in feldspar surface morphology was assessed by scanning electron microscopy (SEM). Subsequent changes in feldspar luminescence in the near-UV (~340 nm) and blue (~410 nm) thermoluminescence (TL) and infrared stimulated luminescence (IRSL) emission bands were assessed at the multi- and/or single-grain levels to gain insight into the emission spectra, dose response, saturation, and anomalous fading characteristics of the feldspars. In all experiments, only minor feldspar dissolution was observed after 720 h with < 5 % of total Al, Si, Na, and Ca appearing in the aqueous phase, while 5–8 % of the total Mn and Fe were extracted. In general, aqua regia, the more chemically-aggressive solution, had a larger effect on feldspar dissolution compared to that of oxalic acid. Additionally, our results showed that although the TL and IRSL intensities changed slightly with increasing artificial weathering time, the feldspar luminescence properties were otherwise unmodified. This suggests that chemical alteration of feldspar surfaces may not affect luminescence dating signals obtained from natural samples.\u0000","PeriodicalId":12723,"journal":{"name":"Geochronology","volume":"82 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-02-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73051242","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Natacha Gribenski, M. Tremblay, P. Valla, G. Balco, B. Guralnik, D. Shuster
Abstract. Diffusion properties of cosmogenic 3He in quartz at Earth’s surface temperatures offer the potential to reconstruct the evolution of past in-situ temperatures directly from formerly glaciated areas, information important for improving our understanding of glacier-climate interactions. In this study, we apply cosmogenic 3He paleothermometry on rock surfaces gradually exposed since the Last Glacial Maximum (LGM) to the Holocene period along two deglaciation profiles in the European Alps (Mont Blanc and Aar massifs). Laboratory experiments conducted on one representative sample per site indicate significant variability in 3He diffusion kinetics between the two sites, with quasi linear Arrhenius behavior observed in quartz from the Mont Blanc site and complex Arrhenius behavior observed from the Aar site, which we interpret to indicate the presence of multiple diffusion domains (MDD). Assuming that same diffusion kinetics apply to all quartz samples along each profile, predictive simulations indicate that 3He abundance in all the investigated samples should be at equilibrium with present-day temperature conditions. However, measured natural 3He concentrations in samples exposed since before the Holocene indicate an apparent 3He thermal signal significantly colder than today. This observed 3He thermal signal cannot be explained with a realistic post-LGM mean annual temperature evolution in the European Alps at the study sites. One hypothesis is that the diffusion kinetics and MDD model applied may not provide sufficiently accurate, quantitative paleo-temperature estimates in these samples; thus, whereas pre-Holocene 3He thermal signal is indeed preserved in the quartz, the helium diffusivity would be lower at Alpine surface temperatures than our diffusion models predict. Alternatively, if the modeled helium diffusion kinetics is accurate, the observed 3He abundances may reflect complex geomorphic/paleoclimatic evolution with much more recent ground temperature changes associated with the degradation of alpine permafrost.
{"title":"Cosmogenic 3He paleothermometry on post-LGM glacial bedrock within the central European Alps","authors":"Natacha Gribenski, M. Tremblay, P. Valla, G. Balco, B. Guralnik, D. Shuster","doi":"10.5194/gchron-2022-1","DOIUrl":"https://doi.org/10.5194/gchron-2022-1","url":null,"abstract":"Abstract. Diffusion properties of cosmogenic 3He in quartz at Earth’s surface temperatures offer the potential to reconstruct the evolution of past in-situ temperatures directly from formerly glaciated areas, information important for improving our understanding of glacier-climate interactions. In this study, we apply cosmogenic 3He paleothermometry on rock surfaces gradually exposed since the Last Glacial Maximum (LGM) to the Holocene period along two deglaciation profiles in the European Alps (Mont Blanc and Aar massifs). Laboratory experiments conducted on one representative sample per site indicate significant variability in 3He diffusion kinetics between the two sites, with quasi linear Arrhenius behavior observed in quartz from the Mont Blanc site and complex Arrhenius behavior observed from the Aar site, which we interpret to indicate the presence of multiple diffusion domains (MDD). Assuming that same diffusion kinetics apply to all quartz samples along each profile, predictive simulations indicate that 3He abundance in all the investigated samples should be at equilibrium with present-day temperature conditions. However, measured natural 3He concentrations in samples exposed since before the Holocene indicate an apparent 3He thermal signal significantly colder than today. This observed 3He thermal signal cannot be explained with a realistic post-LGM mean annual temperature evolution in the European Alps at the study sites. One hypothesis is that the diffusion kinetics and MDD model applied may not provide sufficiently accurate, quantitative paleo-temperature estimates in these samples; thus, whereas pre-Holocene 3He thermal signal is indeed preserved in the quartz, the helium diffusivity would be lower at Alpine surface temperatures than our diffusion models predict. Alternatively, if the modeled helium diffusion kinetics is accurate, the observed 3He abundances may reflect complex geomorphic/paleoclimatic evolution with much more recent ground temperature changes associated with the degradation of alpine permafrost.\u0000","PeriodicalId":12723,"journal":{"name":"Geochronology","volume":"48 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-02-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76252011","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-01-25DOI: 10.5194/gchron-4-55-2022
M. Richter, S. Tsukamoto
Abstract. In this study, we examined the residual doses of the quartz electron spin resonance (ESR) signals from eight young fluvial sediments with known luminescence ages from the Lower Rhine terraces. The single aliquot regenerative (SAR) protocol was applied to obtain the residual doses for both the aluminium (Al) and titanium (Ti) impurity centres. We show that all of the fluvial samples carry a significant amount of residual dose with a mean value of 1270 ± 120 Gy for the Al centre (including the unbleachable signal component), 591 ± 53 Gy for the lithium-compensated Ti centre (Ti-Li), 170 ± 21 Gy for the hydrogen-compensated Ti centre (Ti-H) and 453 ± 42 Gy for the signal that originated from both the Ti-Li and Ti-H centres (termed Ti-mix). To test the accuracy of the ESR SAR protocol, a dose recovery test was conducted and this confirmed the validity of the Ti-Li and Ti-mix signal results. The Al centre shows a dose recovery ratio of 1.75 ± 0.18, whereas the Ti-H signal shows a ratio of 0.55 ± 0.17, suggesting that the rate of signal production per unit dose changed for these signals after the thermal annealing. Nevertheless, all fluvial sediments investigated in this study carry a significant residual dose. Our result suggests that more direct comparisons between luminescence and ESR equivalent doses should be carried out, and, if necessary, the subtraction of residual dose obtained from the difference is essential to obtain reliable ESR ages.
{"title":"Investigation of quartz electron spin resonance residual signals in the last glacial and early Holocene fluvial deposits from the Lower Rhine","authors":"M. Richter, S. Tsukamoto","doi":"10.5194/gchron-4-55-2022","DOIUrl":"https://doi.org/10.5194/gchron-4-55-2022","url":null,"abstract":"Abstract. In this study, we examined the residual doses of the quartz electron spin resonance (ESR) signals from eight young fluvial sediments with known luminescence ages from the Lower Rhine terraces. The single aliquot regenerative (SAR) protocol was applied to obtain the residual doses for both the aluminium (Al) and titanium (Ti) impurity centres. We show that all of the fluvial samples carry a significant amount of residual dose with a mean value of 1270 ± 120 Gy for the Al centre (including the unbleachable signal component), 591 ± 53 Gy for the lithium-compensated Ti centre (Ti-Li), 170 ± 21 Gy for the hydrogen-compensated Ti centre (Ti-H) and 453 ± 42 Gy for the signal that originated from both the Ti-Li and Ti-H centres (termed Ti-mix). To test the accuracy of the ESR SAR protocol, a dose recovery test was conducted and this confirmed the validity of the Ti-Li and Ti-mix signal results. The Al centre shows a dose recovery ratio of 1.75 ± 0.18, whereas the Ti-H signal shows a ratio of 0.55 ± 0.17, suggesting that the rate of signal production per unit dose changed for these signals after the thermal annealing. Nevertheless, all fluvial sediments investigated in this study carry a significant residual dose. Our result suggests that more direct comparisons between luminescence and ESR equivalent doses should be carried out, and, if necessary, the subtraction of residual dose obtained from the difference is essential to obtain reliable ESR ages.\u0000","PeriodicalId":12723,"journal":{"name":"Geochronology","volume":"34 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-01-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91209782","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-01-25DOI: 10.5194/gchron-4-65-2022
T. Dunai, S. Binnie, A. Gerdes
Abstract. Analysis of cosmogenic nuclides produced in surface rocks and sediments is a valuable tool for assessing the rates of processes and the timing of events that shaped the Earth surface. The various nuclides that are used have specific advantages and limitations that depend on the time range over which they are useful, the type of material they are produced in and not least the feasibility of the analytical effort. Anticipating novel applications in Earth surface sciences, we develop in situ-produced terrestrial cosmogenic krypton (Krit) as a new tool, the motivation being the availability of six stable and one radioactive isotope (81Kr, half-life 229 kyr) and of an extremely weathering-resistant target mineral (zircon). We provide proof of principle that terrestrial Krit can be quantified and used to unravel Earth surface processes.
{"title":"In situ-produced cosmogenic krypton in zircon and its potential for Earth surface applications","authors":"T. Dunai, S. Binnie, A. Gerdes","doi":"10.5194/gchron-4-65-2022","DOIUrl":"https://doi.org/10.5194/gchron-4-65-2022","url":null,"abstract":"Abstract. Analysis of cosmogenic nuclides produced in surface rocks and sediments is a\u0000valuable tool for assessing the rates of processes and the timing of events that\u0000shaped the Earth surface. The various nuclides that are used have specific\u0000advantages and limitations that depend on the time range over which they are\u0000useful, the type of material they are produced in and not least the\u0000feasibility of the analytical effort. Anticipating novel applications in\u0000Earth surface sciences, we develop in situ-produced terrestrial cosmogenic\u0000krypton (Krit) as a new tool, the motivation being the availability of\u0000six stable and one radioactive isotope (81Kr, half-life 229 kyr) and of\u0000an extremely weathering-resistant target mineral (zircon). We provide proof\u0000of principle that terrestrial Krit can be quantified and used to\u0000unravel Earth surface processes.\u0000","PeriodicalId":12723,"journal":{"name":"Geochronology","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-01-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77273872","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-01-17DOI: 10.5194/gchron-4-33-2022
A. Mason, A. Vaks, S. Breitenbach, J. Hooker, G. Henderson
Abstract. We describe a new method for the measurement of U/Pb ratios by isotope dilution multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) for the dating of geologically young clean carbonates, particularly speleothems. The method is intended for materials containing little or no initial 232Th. We illustrate and validate the method with four examples ranging from 0.57 to 20 Ma. The new method is capable of applying the 235U–207Pb and 238U–234U–206Pb chronometers, common Pb and quantifiable residual 234U/238U disequilibrium permitting. These provide an alternative to the more widely used 238U–206Pb chronometer, which can be highly inaccurate for samples that are < ca. 20 million years old, owing to uncertainties in the excess initial 234U (hence, excess radiogenic 206Pb) commonly observed in speleothems.
{"title":"A simplified isotope dilution approach for the U–Pb dating of speleogenic and other low-232Th carbonates by multi-collector ICP-MS","authors":"A. Mason, A. Vaks, S. Breitenbach, J. Hooker, G. Henderson","doi":"10.5194/gchron-4-33-2022","DOIUrl":"https://doi.org/10.5194/gchron-4-33-2022","url":null,"abstract":"Abstract. We describe a new method for the measurement of U/Pb\u0000ratios by isotope dilution multi-collector inductively coupled plasma mass\u0000spectrometry (MC-ICP-MS) for the dating of geologically young clean\u0000carbonates, particularly speleothems. The method is intended for materials\u0000containing little or no initial 232Th. We illustrate and validate the\u0000method with four examples ranging from 0.57 to 20 Ma. The new method\u0000is capable of applying the 235U–207Pb and\u0000238U–234U–206Pb chronometers, common Pb and quantifiable\u0000residual 234U/238U disequilibrium permitting. These provide an\u0000alternative to the more widely used 238U–206Pb chronometer, which\u0000can be highly inaccurate for samples that are < ca. 20 million years old,\u0000owing to uncertainties in the excess initial 234U (hence, excess\u0000radiogenic 206Pb) commonly observed in speleothems.\u0000","PeriodicalId":12723,"journal":{"name":"Geochronology","volume":"16 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-01-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89627141","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-01-11DOI: 10.5194/gchron-2021-42-supplement
S. E. Cox, Hayden Miller, F. Hofmann, K. Farley
Abstract. A pervasive challenge in noble gas geochemistry is to ensure that analytical techniques do not modify the composition of the noble gases in the samples. Noble gases are present in the atmosphere and are used in a number of manufacturing procedures and by laboratory equipment. Of particular concern is the introduction of atmospheric or laboratory noble gases to samples during preparation before samples are placed in a vacuum chamber for analysis. Recent work has shown the potential for contamination of crushed samples with air-derived He that is not released by placing the samples under vacuum at low temperature. Using pure He gas as a tracer, we show that the act of crushing samples to a fine powder itself can introduce He contamination, but that this is easily avoided by crushing under liquid or in an inert atmosphere. Because the He is trapped during crushing, the same concern does not extend to samples that are naturally fine-grained when collected. The degree of He contamination even from crushing samples to sizes smaller than typically used for geochronology is insignificant for samples at least 1 Ma and with more than 1 ppm U when the guidelines outlined here are followed.
{"title":"Supplementary material to \"Short Communication: Mechanism and Prevention of Irreversible Trapping of Atmospheric He During Mineral Crushing\"","authors":"S. E. Cox, Hayden Miller, F. Hofmann, K. Farley","doi":"10.5194/gchron-2021-42-supplement","DOIUrl":"https://doi.org/10.5194/gchron-2021-42-supplement","url":null,"abstract":"Abstract. A pervasive challenge in noble gas geochemistry is to ensure that analytical techniques do not modify the composition of the noble gases in the samples. Noble gases are present in the atmosphere and are used in a number of manufacturing procedures and by laboratory equipment. Of particular concern is the introduction of atmospheric or laboratory noble gases to samples during preparation before samples are placed in a vacuum chamber for analysis. Recent work has shown the potential for contamination of crushed samples with air-derived He that is not released by placing the samples under vacuum at low temperature. Using pure He gas as a tracer, we show that the act of crushing samples to a fine powder itself can introduce He contamination, but that this is easily avoided by crushing under liquid or in an inert atmosphere. Because the He is trapped during crushing, the same concern does not extend to samples that are naturally fine-grained when collected. The degree of He contamination even from crushing samples to sizes smaller than typically used for geochronology is insignificant for samples at least 1 Ma and with more than 1 ppm U when the guidelines outlined here are followed.\u0000","PeriodicalId":12723,"journal":{"name":"Geochronology","volume":"15 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-01-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74110252","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Thomas Kolb, K. Tudyka, A. Kadereit, J. Lomax, G. Poręba, A. Zander, L. Zipf, M. Fuchs
Abstract. The μDose system is a recently developed analytical instrument applying a combined α- and β-sensitive scintillation technique for determining the radioactivity arising from the decay chains of 235U, 238U and 232Th as well as from the decay of 40K. The device was designed to meet the particular requirements of trapped charge dating methods and allows the assessment of environmental (i.e. low) levels of natural radionuclides. The μDose system was developed as a piece of low-cost laboratory equipment, but a systematic test of its performance is still pending. For the first time, we present results from a comprehensive performance test based on an inter-laboratory comparison. We compare the results obtained with μDose measurements with those from thick source alpha counting (TSAC), inductively coupled plasma optical emission spectrometry (ICP-OES) and low-level high-resolution gamma spectrometry (HRGS) applied in five participating laboratories. In addition, the reproducibility and accuracy of μDose measurements were tested on certified reference materials distributed by the International Atomic Energy Agency (IAEA; RGU-1, RGTh-1 and RGK-1) and on two loess standards (Nussy and Volkegem) frequently used in trapped charge dating studies. We compare μDose-based results for a total of 47 sediment samples with results previously obtained for these materials by well-established methods of dose rate determination. The investigated natural samples cover a great variety of environments, including fluvial, aeolian, littoral, colluvial and (geo-)archaeological sites originating from high and low mountain regions as well as from lowlands in tropical areas, drylands and mid-latitude zones of Europe, Africa, Australia, Central Asia and the Americas. Our results suggest the μDose system's capability of assessing low-level radionuclide contents with very good accuracy and precision comparable to well-established dosimetry methods. Based on the results of our comparative study and with respect to the practical experiences gained so far, the μDose system appears to be a promising tool for trapped charge dating studies.
{"title":"The μDose system: determination of environmental dose rates by combined alpha and beta counting – performance tests and practical experiences","authors":"Thomas Kolb, K. Tudyka, A. Kadereit, J. Lomax, G. Poręba, A. Zander, L. Zipf, M. Fuchs","doi":"10.5194/gchron-4-1-2022","DOIUrl":"https://doi.org/10.5194/gchron-4-1-2022","url":null,"abstract":"Abstract. The μDose system is a recently developed analytical instrument applying a combined α- and β-sensitive scintillation technique for determining the radioactivity arising from the decay chains of 235U, 238U and 232Th as well as from the decay of 40K. The device was designed to meet the particular requirements of trapped charge dating methods and allows the assessment of environmental (i.e. low) levels of natural radionuclides. The μDose system was developed as a piece of low-cost laboratory equipment, but a systematic test of its performance is still pending. For the first time, we present results from a comprehensive performance test based on an inter-laboratory comparison. We compare the results obtained with μDose measurements with those from thick source alpha counting (TSAC), inductively coupled plasma optical emission spectrometry (ICP-OES) and low-level high-resolution gamma spectrometry (HRGS) applied in five participating laboratories. In addition, the reproducibility and accuracy of μDose measurements were tested on certified reference materials distributed by the International Atomic Energy Agency (IAEA; RGU-1, RGTh-1 and RGK-1) and on two loess standards (Nussy and Volkegem) frequently used in trapped charge dating studies. We compare μDose-based results for a total of 47 sediment samples with results previously obtained for these materials by well-established methods of dose rate determination. The investigated natural samples cover a great variety of environments, including fluvial, aeolian, littoral, colluvial and (geo-)archaeological sites originating from high and low mountain regions as well as from lowlands in tropical areas, drylands and mid-latitude zones of Europe, Africa, Australia, Central Asia and the Americas. Our results suggest the μDose system's capability of assessing low-level radionuclide contents with very good accuracy and precision comparable to well-established dosimetry methods. Based on the results of our comparative study and with respect to the practical experiences gained so far, the μDose system appears to be a promising tool for trapped charge dating studies.\u0000","PeriodicalId":12723,"journal":{"name":"Geochronology","volume":"45 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-01-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89640624","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-12-21DOI: 10.5194/gchron-3-561-2021
P. Jensen, K. Hansen
Abstract. To enable the separation of pre- and postdepositional components of the length distribution of (partially annealed) horizontal confined fission tracks, the length distribution is corrected by deconvolution. Probabilistic least-squares inversion corrects natural track length histograms for observational biases, considering the variance in data, modelization, and prior information. The corrected histogram is validated by its variance–covariance matrix. It is considered that horizontal track data can exist with or without measurements of angles to the c axis. In the latter case, 3D histograms are introduced as an alternative to histograms of c-axis-projected track lengths. Thermal history modelling of samples is not necessary for the calculation of track age distributions of corrected tracks. In an example, the age equations are applied to apatites with predepositional (inherited) tracks in order to extract the postdepositional track length histogram. Fission tracks generated before deposition in detrital apatite crystals are mixed with post-depositional tracks. This complicates the calculation of the post-sedimentary thermal history, as the grains have experienced different thermal histories prior to deposition. Thereafter, the grains share a common thermal history. Thus, the extracted post-depositional histogram without inherited tracks may be used for thermal history calculation.
{"title":"Deconvolution of fission-track length distributions and its application to dating and separating pre- and post-depositional components","authors":"P. Jensen, K. Hansen","doi":"10.5194/gchron-3-561-2021","DOIUrl":"https://doi.org/10.5194/gchron-3-561-2021","url":null,"abstract":"Abstract. To enable the separation of pre- and postdepositional components of the length distribution of (partially annealed) horizontal confined fission tracks, the length distribution is corrected by deconvolution. Probabilistic least-squares inversion corrects natural track length histograms for observational biases, considering the variance in data, modelization, and prior information. The corrected histogram is validated by its variance–covariance matrix. It is considered that horizontal track data can exist with or without measurements of angles to the c axis. In the latter case, 3D histograms are introduced as an alternative to histograms of c-axis-projected track lengths. Thermal history modelling of samples is not necessary for the calculation of track age distributions of corrected tracks. In an example, the age equations are applied to apatites with predepositional (inherited) tracks in order to extract the postdepositional track length histogram. Fission tracks generated before deposition in detrital apatite crystals are mixed with post-depositional tracks. This complicates the calculation of the post-sedimentary thermal history, as the grains have experienced different thermal histories prior to deposition. Thereafter, the grains share a common thermal history. Thus, the extracted post-depositional histogram without inherited tracks may be used for thermal history calculation.\u0000","PeriodicalId":12723,"journal":{"name":"Geochronology","volume":"471 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-12-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83039716","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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