Abstract. We introduce a set of methods for analyzing cosmogenic-nuclide depth profiles that formally integrates surface erosion and muogenic production, while retaining the advantages of the linear inversion. For surfaces with erosion, we present solutions for both erosion rate and total eroded thickness, each with their own advantages. For practical applications, erosion must be constrained from external information, such as soil-profile analysis. By combining linear inversion with Monte Carlo simulation of error propagation, our method jointly assesses uncertainty arising from measurement error and erosion constraints. Using example depth profile data sets from the Beida River, northwest China and Lees Ferry, Arizona, we show that our methods robustly produce comparable ages for surfaces with different erosion rates and inheritance. Through hypothetical examples, we further show that both the erosion rate and eroded-thickness approaches produce reasonable age estimates so long as the total erosion less than twice the nucleon attenuation length. Overall, lack of precise constraints for erosion rate tends to be the largest contributor of age uncertainty, compared to the error from omitting muogenic production or radioactive decay.
{"title":"Combined linear regression and Monte Carlo approach to modelling exposure age depth profiles","authors":"Yiran Wang, M. Oskin","doi":"10.5194/gchron-2021-34","DOIUrl":"https://doi.org/10.5194/gchron-2021-34","url":null,"abstract":"Abstract. We introduce a set of methods for analyzing cosmogenic-nuclide depth profiles that formally integrates surface erosion and muogenic production, while retaining the advantages of the linear inversion. For surfaces with erosion, we present solutions for both erosion rate and total eroded thickness, each with their own advantages. For practical applications, erosion must be constrained from external information, such as soil-profile analysis. By combining linear inversion with Monte Carlo simulation of error propagation, our method jointly assesses uncertainty arising from measurement error and erosion constraints. Using example depth profile data sets from the Beida River, northwest China and Lees Ferry, Arizona, we show that our methods robustly produce comparable ages for surfaces with different erosion rates and inheritance. Through hypothetical examples, we further show that both the erosion rate and eroded-thickness approaches produce reasonable age estimates so long as the total erosion less than twice the nucleon attenuation length. Overall, lack of precise constraints for erosion rate tends to be the largest contributor of age uncertainty, compared to the error from omitting muogenic production or radioactive decay.\u0000","PeriodicalId":12723,"journal":{"name":"Geochronology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77353746","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. Dosimetric dating techniques rely on accurate and precise determination of environmental radioactivity. Gamma spectrometry is the method of choice for determining the activity of 238U, 232Th and 40K. With the aim to standardise gamma-spectrometric procedures for the purpose of determining accurate parent nuclide activities in natural samples, we outline here basics of gamma spectrometry and practical laboratory procedures. This includes gamma radiation and instrumentation, sample preparation, finding the suitable measurement geometry and sample size for a given detector and using the most suitable energy peaks in a gamma spectrum. The issue of correct efficiency calibration is highlighted. The procedures outlined are required for estimating contemporary parent nuclide activity. For estimating changing activities during burial specific data analyses are required and these are also highlighted.
{"title":"Technical note: Quantifying Uranium-series disequilibrium in natural samples for dosimetric dating – Part 1: gamma spectrometry","authors":"B. Mauz, P. Nolan, P. Appleby","doi":"10.5194/gchron-2021-32","DOIUrl":"https://doi.org/10.5194/gchron-2021-32","url":null,"abstract":"Abstract. Dosimetric dating techniques rely on accurate and precise determination of environmental radioactivity. Gamma spectrometry is the method of choice for determining the activity of 238U, 232Th and 40K. With the aim to standardise gamma-spectrometric procedures for the purpose of determining accurate parent nuclide activities in natural samples, we outline here basics of gamma spectrometry and practical laboratory procedures. This includes gamma radiation and instrumentation, sample preparation, finding the suitable measurement geometry and sample size for a given detector and using the most suitable energy peaks in a gamma spectrum. The issue of correct efficiency calibration is highlighted. The procedures outlined are required for estimating contemporary parent nuclide activity. For estimating changing activities during burial specific data analyses are required and these are also highlighted.\u0000","PeriodicalId":12723,"journal":{"name":"Geochronology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-11-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73264943","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 : 2021-10-29DOI: 10.5194/gchron-3-525-2021
R. Smedley, D. Small, Richard S. Jones, S. Brough, J. Bradley, Geraint T. H. Jenkins
Abstract. A new luminescence erosion meter has huge potential for inferring erosion rates on sub-millennial scales for both steady and transient states of erosion, which is not currently possible with any existing techniques capable of measuring erosion. This study applies new rock luminescence techniques to a well-constrained scenario provided by the Beinn Alligin rock avalanche, NW Scotland. Boulders in this deposit are lithologically consistent and have known cosmogenic nuclide ages and independently derived Holocene erosion rates. We find that luminescence-derived exposure ages for the Beinn Alligin rock avalanche were an order of magnitude younger than existing cosmogenic nuclide exposure ages, suggestive of high erosion rates (as supported by field evidence of quartz grain protrusions on the rock surfaces). Erosion rates determined by luminescence were consistent with independently derived rates measured from boulder edge roundness. Inversion modelling indicates a transient state of erosion reflecting the stochastic nature of erosional processes over the last ∼4.5 kyr in the wet, temperate climate of NW Scotland. Erosion was likely modulated by known fluctuations in moisture availability and to a lesser extent temperature, which controlled the extent of chemical weathering of these highly lithified rocks prior to erosion. The use of a multi-elevated temperature, post-infra-red, infra-red stimulated luminescence (MET-pIRIR) protocol (50, 150 and 225 ∘C) was advantageous as it identified samples with complexities that would not have been observed using only the standard infra-red stimulated luminescence (IRSL) signal measured at 50 ∘C, such as that introduced by within-sample variability (e.g. surficial coatings). This study demonstrates that the luminescence erosion meter can infer accurate erosion rates on sub-millennial scales and identify transient states of erosion (i.e. stochastic processes) in agreement with independently derived erosion rates for the same deposit.
{"title":"Erosion rates in a wet, temperate climate derived from rock luminescence techniques","authors":"R. Smedley, D. Small, Richard S. Jones, S. Brough, J. Bradley, Geraint T. H. Jenkins","doi":"10.5194/gchron-3-525-2021","DOIUrl":"https://doi.org/10.5194/gchron-3-525-2021","url":null,"abstract":"Abstract. A new luminescence erosion meter has huge potential for inferring erosion rates on sub-millennial scales for both steady and transient states of erosion, which is not currently possible with any existing techniques capable of measuring erosion. This study applies new rock luminescence techniques to a well-constrained scenario provided by the Beinn Alligin rock avalanche, NW Scotland. Boulders in this deposit are lithologically consistent and have known cosmogenic nuclide ages and independently derived Holocene erosion rates. We find that luminescence-derived exposure ages for the Beinn Alligin rock avalanche were an order of magnitude younger than existing cosmogenic nuclide exposure ages, suggestive of high erosion rates (as supported by field evidence of quartz grain protrusions on the rock surfaces). Erosion rates determined by luminescence were consistent with independently derived rates measured from boulder edge roundness. Inversion modelling indicates a transient state of erosion reflecting the stochastic nature of erosional processes over the last ∼4.5 kyr in the wet, temperate climate of NW Scotland. Erosion was likely modulated by known fluctuations in moisture availability and to a lesser extent temperature, which controlled the extent of chemical weathering of these highly lithified rocks prior to erosion. The use of a multi-elevated temperature, post-infra-red, infra-red stimulated luminescence (MET-pIRIR) protocol (50, 150 and 225 ∘C) was advantageous as it identified samples with complexities that would not have been observed using only the standard infra-red stimulated luminescence (IRSL) signal measured at 50 ∘C, such as that introduced by within-sample variability (e.g. surficial coatings). This study demonstrates that the luminescence erosion meter can infer accurate erosion rates on sub-millennial scales and identify transient states of erosion (i.e. stochastic processes) in agreement with independently derived erosion rates for the same deposit.","PeriodicalId":12723,"journal":{"name":"Geochronology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-10-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78260379","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 : 2021-10-19DOI: 10.5194/gchron-3-505-2021
A. Christ, P. Bierman, J. Lamp, J. Schaefer, G. Winckler
Abstract. The preservation of cosmogenic nuclides that accumulated during periods of prior exposure but were not subsequently removed by erosion or radioactive decay complicates interpretation of exposure, erosion, and burial ages used for a variety of geomorphological applications. In glacial settings, cold-based, non-erosive glacier ice may fail to remove inventories of inherited nuclides in glacially transported material. As a result, individual exposure ages can vary widely across a single landform (e.g., moraine) and exceed the expected or true depositional age. The surface processes that contribute to inheritance remain poorly understood, thus limiting interpretations of cosmogenic nuclide datasets in glacial environments. Here, we present a compilation of new and previously published exposure ages of multiple lithologies in local Last Glacial Maximum (LGM) and older Pleistocene glacial sediments in the McMurdo Sound region of Antarctica. Unlike most Antarctic exposure chronologies, we are able to compare exposure ages of local LGM sediments directly against an independent radiocarbon chronology of fossil algae from the same sedimentary unit that brackets the age of the local LGM between 12.3 and 19.6 ka. Cosmogenic exposure ages vary by lithology, suggesting that bedrock source and surface processes prior to, during, and after glacial entrainment explain scatter. 10Be exposure ages of quartz in granite, sourced from the base of the stratigraphic section in the Transantarctic Mountains, are scattered but young, suggesting that clasts entrained by sub-glacial plucking can generate reasonable apparent exposure ages. 3He exposure ages of pyroxene in Ferrar Dolerite, which crops out above outlet glaciers in the Transantarctic Mountains, are older, which suggests that clasts initially exposed on cliff faces and glacially entrained by rock fall carry inherited nuclides. 3He exposure ages of olivine in basalt from local volcanic bedrock in the McMurdo Sound region contain many excessively old ages but also have a bimodal distribution with peak probabilities that slightly pre-date and post-date the local LGM; this suggests that glacial clasts from local bedrock record local landscape exposure. With the magnitude and geological processes contributing to age scatter in mind, we examine exposure ages of older glacial sediments deposited by the most extensive ice sheet to inundate McMurdo Sound during the Pleistocene. These results underscore how surface processes operating in the Transantarctic Mountains are expressed in the cosmogenic nuclide inventories held in Antarctic glacial sediments.
{"title":"Cosmogenic nuclide exposure age scatter records glacial history and processes in McMurdo Sound, Antarctica","authors":"A. Christ, P. Bierman, J. Lamp, J. Schaefer, G. Winckler","doi":"10.5194/gchron-3-505-2021","DOIUrl":"https://doi.org/10.5194/gchron-3-505-2021","url":null,"abstract":"Abstract. The preservation of cosmogenic nuclides that accumulated during periods of prior exposure but were not subsequently removed by erosion or\u0000radioactive decay complicates interpretation of exposure, erosion, and burial ages used for a variety of geomorphological applications. In glacial\u0000settings, cold-based, non-erosive glacier ice may fail to remove inventories of inherited nuclides in glacially transported material. As a result,\u0000individual exposure ages can vary widely across a single landform (e.g., moraine) and exceed the expected or true depositional age. The surface\u0000processes that contribute to inheritance remain poorly understood, thus limiting interpretations of cosmogenic nuclide datasets in glacial\u0000environments. Here, we present a compilation of new and previously published exposure ages of multiple lithologies in local Last Glacial Maximum\u0000(LGM) and older Pleistocene glacial sediments in the McMurdo Sound region of Antarctica. Unlike most Antarctic exposure chronologies, we are able to\u0000compare exposure ages of local LGM sediments directly against an independent radiocarbon chronology of fossil algae from the same sedimentary unit\u0000that brackets the age of the local LGM between 12.3 and 19.6 ka. Cosmogenic exposure ages vary by lithology, suggesting that bedrock source\u0000and surface processes prior to, during, and after glacial entrainment explain scatter. 10Be exposure ages of quartz in granite, sourced\u0000from the base of the stratigraphic section in the Transantarctic Mountains, are scattered but young, suggesting that clasts entrained by sub-glacial\u0000plucking can generate reasonable apparent exposure ages. 3He exposure ages of pyroxene in Ferrar Dolerite, which crops out above outlet\u0000glaciers in the Transantarctic Mountains, are older, which suggests that clasts initially exposed on cliff faces and glacially entrained by rock\u0000fall carry inherited nuclides. 3He exposure ages of olivine in basalt from local volcanic bedrock in the McMurdo Sound region contain many\u0000excessively old ages but also have a bimodal distribution with peak probabilities that slightly pre-date and post-date the local LGM; this suggests\u0000that glacial clasts from local bedrock record local landscape exposure. With the magnitude and geological processes contributing to age scatter in\u0000mind, we examine exposure ages of older glacial sediments deposited by the most extensive ice sheet to inundate McMurdo Sound during the\u0000Pleistocene. These results underscore how surface processes operating in the Transantarctic Mountains are expressed in the cosmogenic nuclide\u0000inventories held in Antarctic glacial sediments.\u0000","PeriodicalId":12723,"journal":{"name":"Geochronology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-10-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87388658","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 : 2021-09-23DOI: 10.5194/gchron-3-465-2021
J. Hopkins, Janine E. Bidmead, D. Lowe, R. Wysoczanski, B. Pillans, L. Ashworth, A. Rees, F. Tuckett
Abstract. Although analyses of tephra-derived glass shards have been undertaken in New Zealand for nearly four decades (pioneered by Paul Froggatt), our study is the first to systematically develop a formal, comprehensive, open-access reference dataset of glass-shard compositions for New Zealand tephras. These data will provide an important reference tool for future studies to identify and correlate tephra deposits and for associated petrological and magma-related studies within New Zealand and beyond. Here we present the foundation dataset for TephraNZ, an open-access reference dataset for selected tephra deposits in New Zealand. Prominent, rhyolitic, tephra deposits from the Quaternary were identified, with sample collection targeting original type sites or reference locations where the tephra's identification is unequivocally known based on independent dating and/or mineralogical techniques. Glass shards were extracted from the tephra deposits, and major- and trace-element geochemical compositions were determined. We discuss in detail the data reduction process used to obtain the results and propose that future studies follow a similar protocol in order to gain comparable data. The dataset contains analyses of glass shards from 23 proximal and 27 distal tephra samples characterising 45 eruptive episodes ranging from Kaharoa (636 ± 12 cal yr BP) to the Hikuroa Pumice member (2.0 ± 0.6 Ma) from six or more caldera sources, most from the central Taupō Volcanic Zone. We report 1385 major-element analyses obtained by electron microprobe (EMPA), and 590 trace-element analyses obtained by laser ablation (LA)-ICP-MS, on individual glass shards. Using principal component analysis (PCA), Euclidean similarity coefficients, and geochemical investigation, we show that chemical compositions of glass shards from individual eruptions are commonly distinguished by major elements, especially CaO, TiO2, K2O, and FeOtt (Na2O+K2O and SiO2/K2O), but not always. For those tephras with similar glass major-element signatures, some can be distinguished using trace elements (e.g. HFSEs: Zr, Hf, Nb; LILE: Ba, Rb; REE: Eu, Tm, Dy, Y, Tb, Gd, Er, Ho, Yb, Sm) and trace-element ratios (e.g. LILE/HFSE: Ba/Th, Ba/Zr, Rb/Zr; HFSE/HREE: Zr/Y, Zr/Yb, Hf/Y; LREE/HREE: La/Yb, Ce/Yb). Geochemistry alone cannot be used to distinguish between glass shards from the following tephra groups: Taupō (Unit Y in the post-Ōruanui eruption sequence of Taupō volcano) and Waimihia (Unit S); Poronui (Unit C) and Karapiti (Unit B); Rotorua and Rerewhakaaitu; and Kawakawa/Ōruanui, and Okaia. Other characteristics, including stratigraphic relationships and age, can be used to separate and distinguish all of these otherwise-similar tephra deposits except Poronui and Karapiti. Bimodality caused by K2O variability is newly identified in Poihipi and Tahuna tephras. Using glass-shard compositions, tephra sourced from Taupō Volcanic Centre (TVC) and Mangakino Volcanic Centre (MgVC) can be separated using
{"title":"TephraNZ: a major- and trace-element reference dataset for glass-shard analyses from prominent Quaternary rhyolitic tephras in New Zealand and implications for correlation","authors":"J. Hopkins, Janine E. Bidmead, D. Lowe, R. Wysoczanski, B. Pillans, L. Ashworth, A. Rees, F. Tuckett","doi":"10.5194/gchron-3-465-2021","DOIUrl":"https://doi.org/10.5194/gchron-3-465-2021","url":null,"abstract":"Abstract. Although analyses of tephra-derived glass shards have been undertaken in New\u0000Zealand for nearly four decades (pioneered by Paul Froggatt), our study is\u0000the first to systematically develop a formal, comprehensive, open-access\u0000reference dataset of glass-shard compositions for New Zealand tephras. These\u0000data will provide an important reference tool for future studies to identify\u0000and correlate tephra deposits and for associated petrological and\u0000magma-related studies within New Zealand and beyond. Here we present the\u0000foundation dataset for TephraNZ, an open-access reference dataset for\u0000selected tephra deposits in New Zealand. Prominent, rhyolitic, tephra deposits from the Quaternary were identified,\u0000with sample collection targeting original type sites or reference locations\u0000where the tephra's identification is unequivocally known based on\u0000independent dating and/or mineralogical techniques. Glass shards were\u0000extracted from the tephra deposits, and major- and trace-element geochemical\u0000compositions were determined. We discuss in detail the data reduction\u0000process used to obtain the results and propose that future studies follow a\u0000similar protocol in order to gain comparable data. The dataset contains\u0000analyses of glass shards from 23 proximal and 27 distal\u0000tephra samples characterising 45 eruptive episodes ranging from Kaharoa (636 ± 12 cal yr BP) to the Hikuroa Pumice member (2.0 ± 0.6 Ma)\u0000from six or more caldera sources, most from the central Taupō Volcanic\u0000Zone. We report 1385 major-element analyses obtained by electron microprobe\u0000(EMPA), and 590 trace-element analyses obtained by laser ablation\u0000(LA)-ICP-MS, on individual glass shards. Using principal component analysis (PCA), Euclidean similarity coefficients, and geochemical investigation,\u0000we show that chemical compositions of glass shards from individual eruptions\u0000are commonly distinguished by major elements, especially CaO, TiO2,\u0000K2O, and FeOtt (Na2O+K2O and SiO2/K2O), but not\u0000always. For those tephras with similar glass major-element signatures, some\u0000can be distinguished using trace elements (e.g. HFSEs: Zr, Hf, Nb; LILE: Ba,\u0000Rb; REE: Eu, Tm, Dy, Y, Tb, Gd, Er, Ho, Yb, Sm) and trace-element ratios\u0000(e.g. LILE/HFSE: Ba/Th, Ba/Zr, Rb/Zr; HFSE/HREE: Zr/Y, Zr/Yb, Hf/Y;\u0000LREE/HREE: La/Yb, Ce/Yb). Geochemistry alone cannot be used to distinguish between glass shards from\u0000the following tephra groups: Taupō (Unit Y in the post-Ōruanui\u0000eruption sequence of Taupō volcano) and Waimihia (Unit S); Poronui (Unit\u0000C) and Karapiti (Unit B); Rotorua and Rerewhakaaitu; and\u0000Kawakawa/Ōruanui, and Okaia. Other characteristics, including\u0000stratigraphic relationships and age, can be used to separate and distinguish\u0000all of these otherwise-similar tephra deposits except Poronui and Karapiti.\u0000Bimodality caused by K2O variability is newly identified in Poihipi and\u0000Tahuna tephras. Using glass-shard compositions, tephra sourced from\u0000Taupō Volcanic Centre (TVC) and Mangakino Volcanic Centre (MgVC) can be\u0000separated using ","PeriodicalId":12723,"journal":{"name":"Geochronology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-09-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73640381","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 : 2021-08-19DOI: 10.5194/GCHRON-3-421-2021
B. Ritter, A. Vogt, T. Dunai
Abstract. We established a new laboratory for noble gas mass spectrometry that is dedicated for the development and application to cosmogenic nuclides at the University of Cologne (Germany). At the core of the laboratory are a state-of-the-art high mass resolution multicollector Helix MCPlus (Thermo-Fisher) noble gas mass spectrometer and a novel custom-designed automated extraction line. The Mass-spectrometer is equipped with five combined Faraday Multiplier collectors, with 1012 Ω and 1013 Ω pre-amplifiers for faraday collectors. We describe the extraction line and the automized operation procedure for cosmogenic neon and the current performance of the experimental setup. Performance tests were conducted using gas of atmospheric isotopic composition (our primary standard gas); as well as CREU-1 intercomparison material, containing a mixture of neon of atmospheric and cosmogenic composition. We use the results from repeated analysis of CREU-1 to assess the performance of the current experimental setup at Cologne. The precision in determining the abundance of cosmogenic 21Ne is equal or better than those reported for other laboratories. The absolute value we obtain for the concentration of cosmogenic 21Ne in CREU is indistinguishable from the published value.
{"title":"Technical Note: Noble gas extraction procedure and performance of the Cologne Helix MC Plus multi-collector noble gas mass spectrometer for cosmogenic neon isotope analysis","authors":"B. Ritter, A. Vogt, T. Dunai","doi":"10.5194/GCHRON-3-421-2021","DOIUrl":"https://doi.org/10.5194/GCHRON-3-421-2021","url":null,"abstract":"Abstract. We established a new laboratory for noble gas mass spectrometry that is dedicated for the development and application to cosmogenic nuclides at the University of Cologne (Germany). At the core of the laboratory are a state-of-the-art high mass resolution multicollector Helix MCPlus (Thermo-Fisher) noble gas mass spectrometer and a novel custom-designed automated extraction line. The Mass-spectrometer is equipped with five combined Faraday Multiplier collectors, with 1012 Ω and 1013 Ω pre-amplifiers for faraday collectors. We describe the extraction line and the automized operation procedure for cosmogenic neon and the current performance of the experimental setup. Performance tests were conducted using gas of atmospheric isotopic composition (our primary standard gas); as well as CREU-1 intercomparison material, containing a mixture of neon of atmospheric and cosmogenic composition. We use the results from repeated analysis of CREU-1 to assess the performance of the current experimental setup at Cologne. The precision in determining the abundance of cosmogenic 21Ne is equal or better than those reported for other laboratories. The absolute value we obtain for the concentration of cosmogenic 21Ne in CREU is indistinguishable from the published value.\u0000","PeriodicalId":12723,"journal":{"name":"Geochronology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-08-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83749167","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 : 2021-08-02DOI: 10.5194/GCHRON-3-415-2021
Yang Li, P. Vermeesch
Abstract. Conventional Re–Os isochrons are based on mass spectrometric estimates of 187Re/188Os and 187Os/188Os, which often exhibit strong error correlations that may obscure potentially important geological complexity. Using an approach that is widely accepted in 40Ar/39Ar and U–Pb geochronology, we here show that these error correlations are greatly reduced by applying a simple change of variables, using 187Os as a common denominator. Plotting 188Os/187Os vs. 187Re/187Os produces an “inverse isochron”, defining a binary mixing line between an inherited Os component whose 188Os/187Os ratio is given by the vertical intercept, and the radiogenic 187Re/187Os ratio, which corresponds to the horizontal intercept. Inverse isochrons facilitate the identification of outliers and other sources of data dispersion. They can also be applied to other geochronometers such as the K–Ca method and (with less dramatic results) the Rb–Sr, Sm–Nd and Lu–Hf methods. Conventional and inverse isochron ages are similar for precise datasets but may significantly diverge for imprecise ones. A semi-synthetic data simulation indicates that, in the latter case, the inverse isochron age is more accurate. The generalised inverse isochron method has been added to the IsoplotR toolbox for geochronology, which automatically converts conventional isochron ratios into inverse ratios, and vice versa.
{"title":"Short communication: Inverse isochron regression for Re–Os, K–Ca and other chronometers","authors":"Yang Li, P. Vermeesch","doi":"10.5194/GCHRON-3-415-2021","DOIUrl":"https://doi.org/10.5194/GCHRON-3-415-2021","url":null,"abstract":"Abstract. Conventional Re–Os isochrons are based on mass spectrometric estimates of 187Re/188Os and 187Os/188Os, which often exhibit\u0000strong error correlations that may obscure potentially important geological complexity. Using an approach that is widely accepted in 40Ar/39Ar and U–Pb geochronology, we here show that these error correlations are greatly reduced by applying a simple change of variables, using 187Os as a common denominator. Plotting\u0000188Os/187Os vs. 187Re/187Os produces an\u0000“inverse isochron”, defining a binary mixing line between an inherited\u0000Os component whose 188Os/187Os ratio is given by the\u0000vertical intercept, and the radiogenic 187Re/187Os ratio, which corresponds to the horizontal intercept. Inverse isochrons facilitate\u0000the identification of outliers and other sources of data dispersion.\u0000They can also be applied to other geochronometers such as the K–Ca\u0000method and (with less dramatic results) the Rb–Sr, Sm–Nd and Lu–Hf\u0000methods. Conventional and inverse isochron ages are similar for\u0000precise datasets but may significantly diverge for imprecise ones. A\u0000semi-synthetic data simulation indicates that, in the latter case, the\u0000inverse isochron age is more accurate. The generalised inverse\u0000isochron method has been added to the IsoplotR toolbox for\u0000geochronology, which automatically converts conventional isochron\u0000ratios into inverse ratios, and vice versa.\u0000","PeriodicalId":12723,"journal":{"name":"Geochronology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-08-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80906189","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 : 2021-06-30DOI: 10.5194/gchron-3-383-2021
Simon Nachtergaele, J. De Grave
Abstract. A new method for automatic counting of etched fission tracks in minerals is described and presented in this article. Artificial intelligence techniques such as deep neural networks and computer vision were trained to detect fission surface semi-tracks on images. The deep neural networks can be used in an open-source computer program for semi-automated fission track dating called “AI-Track-tive”. Our custom-trained deep neural networks use the YOLOv3 object detection algorithm, which is currently one of the most powerful and fastest object recognition algorithms. The developed program successfully finds most of the fission tracks in the microscope images; however, the user still needs to supervise the automatic counting. The presented deep neural networks have high precision for apatite (97 %) and mica (98 %). Recall values are lower for apatite (86 %) than for mica (91 %). The application can be used online at https://ai-track-tive.ugent.be (last access: 29 June 2021), or it can be downloaded as an offline application for Windows.
{"title":"AI-Track-tive: open-source software for automated recognition and counting of surface semi-tracks using computer vision (artificial intelligence)","authors":"Simon Nachtergaele, J. De Grave","doi":"10.5194/gchron-3-383-2021","DOIUrl":"https://doi.org/10.5194/gchron-3-383-2021","url":null,"abstract":"Abstract. A new method for automatic counting of etched fission tracks in minerals is\u0000described and presented in this article. Artificial intelligence techniques\u0000such as deep neural networks and computer vision were trained to detect\u0000fission surface semi-tracks on images. The deep neural networks can be used\u0000in an open-source computer program for semi-automated fission track dating\u0000called “AI-Track-tive”. Our custom-trained deep neural networks use the YOLOv3\u0000object detection algorithm, which is currently one of the most powerful and\u0000fastest object recognition algorithms. The developed program successfully\u0000finds most of the fission tracks in the microscope images; however, the user\u0000still needs to supervise the automatic counting. The presented deep neural\u0000networks have high precision for apatite (97 %) and mica (98 %). Recall\u0000values are lower for apatite (86 %) than for mica (91 %). The\u0000application can be used online at https://ai-track-tive.ugent.be (last access: 29 June 2021), or it can be downloaded as an offline application\u0000for Windows.\u0000","PeriodicalId":12723,"journal":{"name":"Geochronology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-06-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77557047","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 : 2021-06-23DOI: 10.5194/GCHRON-3-371-2021
B. Mauz, Loïc A. Martin, M. Discher, C. Tribolo, S. Kreutzer, Chiara Bahl, A. Lang, N. Mercier
Abstract. The dose rate of the 90Sr / 90Y beta source used in most luminescence readers is a laboratory key parameter. There is a well-established body of knowledge about parameters controlling accuracy and precision of the calibration value but some hard-to-explain inconsistencies still exist. Here, we have investigated the impact of grain size, aliquot size and irradiation geometry on the resulting calibration value through experiments and simulations. The resulting data indicate that the dose rate of an individual beta source results from the interplay of a number of parameters, most of which are well established by previous studies. Our study provides evidence for the impact of aliquot size on the absorbed dose in particular for grain sizes of 50–200 µm. For this grain-size fraction, the absorbed dose is enhanced by ∼ 10 %–20 % as aliquot size decreases due to the radial increase of dose rate towards the centre of the aliquot. The enhancement is most variable for 50–100 µm grains mounted as aliquots of < 8 mm size. The enhancement is reversed when large grains are mounted as small aliquots due to the edge effect by which the dose induced by backscattered electrons is reduced. While the build-up of charge dictates the increase of absorbed dose with the increase of grain size, this principle becomes more variable with changing irradiation geometry. We conclude that future calibration samples should consist of subsamples composed of small, medium, large and very large quartz grains, each obtaining several gamma doses. The calibration value measured with small, medium and large aliquots is then obtained from the inverse slope of the fitted line, not from a single data point. In this way, all possible irradiation geometries of an individual beta source are covered, and the precision of the calibration is improved.
{"title":"Technical note: On the reliability of laboratory beta-source calibration for luminescence dating","authors":"B. Mauz, Loïc A. Martin, M. Discher, C. Tribolo, S. Kreutzer, Chiara Bahl, A. Lang, N. Mercier","doi":"10.5194/GCHRON-3-371-2021","DOIUrl":"https://doi.org/10.5194/GCHRON-3-371-2021","url":null,"abstract":"Abstract. The dose rate of the 90Sr / 90Y beta source used in most\u0000luminescence readers is a laboratory key parameter. There is a\u0000well-established body of knowledge about parameters controlling accuracy and\u0000precision of the calibration value but some hard-to-explain inconsistencies\u0000still exist. Here, we have investigated the impact of grain size, aliquot\u0000size and irradiation geometry on the resulting calibration value through\u0000experiments and simulations. The resulting data indicate that the dose rate\u0000of an individual beta source results from the interplay of a number of\u0000parameters, most of which are well established by previous studies. Our\u0000study provides evidence for the impact of aliquot size on the absorbed dose\u0000in particular for grain sizes of 50–200 µm. For this grain-size\u0000fraction, the absorbed dose is enhanced by ∼ 10 %–20 % as\u0000aliquot size decreases due to the radial increase of dose rate towards\u0000the centre of the aliquot. The enhancement is most variable for 50–100 µm\u0000grains mounted as aliquots of < 8 mm size. The enhancement is\u0000reversed when large grains are mounted as small aliquots due to the edge\u0000effect by which the dose induced by backscattered electrons is reduced.\u0000While the build-up of charge dictates the increase of absorbed dose with the\u0000increase of grain size, this principle becomes more variable with changing\u0000irradiation geometry. We conclude that future calibration samples should\u0000consist of subsamples composed of small, medium, large and very large quartz\u0000grains, each obtaining several gamma doses. The calibration value measured\u0000with small, medium and large aliquots is then obtained from the inverse\u0000slope of the fitted line, not from a single data point. In this way, all\u0000possible irradiation geometries of an individual beta source are covered,\u0000and the precision of the calibration is improved.\u0000","PeriodicalId":12723,"journal":{"name":"Geochronology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80714673","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}
S. Scheidt, M. Lenz, R. Egli, D. Brill, M. Klug, K. Fabian, M. M. Lenz, R. Gromig, J. Rethemeyer, B. Wagner, Grigory Federov, M. Melles
Abstract. This work represents the first palaeomagnetic study carried out on the sedimentary record of lake Levinson-Lessing, which is the deepest lake in northern Central Siberia. Palaeomagnetic analyses were carried out on 730 discrete samples from the upper 38 m of the 46 m-long core Co1401, which was recovered from the central part of the lake. Alternating field demagnetisation experiments were carried out to obtain the characteristic remanent magnetisation. The relative palaeointensity is determined using the magnetic susceptibility, the anhysteretic remanent magnetization and the isothermal remanent magnetization for normalization of the partial natural remanent magnetization. The chronology of Co1401 derives from accelerated mass spectrometer radiocarbon ages, optically stimulated luminescence dating, and correlation of the relative palaeointensity of 642 discrete samples with the GLOPIS-75 reference curve. This study focuses on the part >10 ka but although includes preliminary results for the upper part of the core. The record includes the geomagnetic excursions Laschamps and Mono Lake, and resolves sufficient geomagnetic features to establish a chronology that continuously covers ~62 ka. The results reveal continuous sedimentation and high sedimentation rate between 45 and 95 cm ka−1. High lock-in depths are suggested from the low variability of the magnetic record compared to data sets of reference records with lower sedimentation rate. Although the horizontal component of the characteristic remanent magnetization can only be used with caution because Co1401 was cored without core segment overlap, the magnetic record of Co1401 is the only high-resolution record of relative palaeointensity and palaeosecular variations from the Arctic tangent cylinder going back to ~62 ka.
摘要这项工作是对西伯利亚北部最深的湖泊列文森-莱辛湖的沉积记录进行的第一次古地磁研究。对从湖中部回收的Co1401号46 m长岩心上38 m处的730个离散样品进行了古地磁分析。进行了交变磁场退磁实验，得到了特征剩磁。利用磁化率、非滞后剩磁和等温剩磁对部分自然剩磁进行归一化，确定了相对古强度。Co1401的年代学来自加速质谱仪放射性碳年龄、光学激发发光定年以及642个离散样品的相对古强度与GLOPIS-75参考曲线的相关性。这项研究主要集中在bbb10ka部分，但也包括了岩心上部的初步结果。该记录包括Laschamps和Mono湖的地磁漂移，并解析了足够的地磁特征，以建立一个连续覆盖~62 ka的年代学。结果表明，该区在45 ~ 95 cm ka−1范围内具有连续沉降和高沉降速率。与沉积速率较低的参考记录数据集相比，磁记录的低变异性表明了高锁深。虽然Co1401的特征剩余磁化强度的水平分量只能谨慎使用，因为Co1401是在没有岩心段重叠的情况下取芯的，但Co1401的磁记录是北极切线柱上~62 ka以来相对古强度和古长期变化的唯一高分辨率记录。
{"title":"A 62-ka geomagnetic palaeointensity record from the Taymyr Peninsula, Russian Arctic","authors":"S. Scheidt, M. Lenz, R. Egli, D. Brill, M. Klug, K. Fabian, M. M. Lenz, R. Gromig, J. Rethemeyer, B. Wagner, Grigory Federov, M. Melles","doi":"10.5194/gchron-2021-12","DOIUrl":"https://doi.org/10.5194/gchron-2021-12","url":null,"abstract":"Abstract. This work represents the first palaeomagnetic study carried out on the sedimentary record of lake Levinson-Lessing, which is the deepest lake in northern Central Siberia. Palaeomagnetic analyses were carried out on 730 discrete samples from the upper 38 m of the 46 m-long core Co1401, which was recovered from the central part of the lake. Alternating field demagnetisation experiments were carried out to obtain the characteristic remanent magnetisation. The relative palaeointensity is determined using the magnetic susceptibility, the anhysteretic remanent magnetization and the isothermal remanent magnetization for normalization of the partial natural remanent magnetization. The chronology of Co1401 derives from accelerated mass spectrometer radiocarbon ages, optically stimulated luminescence dating, and correlation of the relative palaeointensity of 642 discrete samples with the GLOPIS-75 reference curve. This study focuses on the part >10 ka but although includes preliminary results for the upper part of the core. The record includes the geomagnetic excursions Laschamps and Mono Lake, and resolves sufficient geomagnetic features to establish a chronology that continuously covers ~62 ka. The results reveal continuous sedimentation and high sedimentation rate between 45 and 95 cm ka−1. High lock-in depths are suggested from the low variability of the magnetic record compared to data sets of reference records with lower sedimentation rate. Although the horizontal component of the characteristic remanent magnetization can only be used with caution because Co1401 was cored without core segment overlap, the magnetic record of Co1401 is the only high-resolution record of relative palaeointensity and palaeosecular variations from the Arctic tangent cylinder going back to ~62 ka.\u0000","PeriodicalId":12723,"journal":{"name":"Geochronology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-06-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88645538","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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