Geochronology最新文献

{"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":null,"pages":null},"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}

{"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":null,"pages":null},"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}

{"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":null,"pages":null},"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}

{"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":null,"pages":null},"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}

{"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":null,"pages":null},"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}

{"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":null,"pages":null},"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}

{"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":null,"pages":null},"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}

{"title":"Deformation recorded in polyhalite from evaporite detachments revealed by 40Ar ∕ 39Ar dating","authors":"L. Richards, F. Jourdan, A. Collins, R. King","doi":"10.5194/gchron-3-545-2021","DOIUrl":"https://doi.org/10.5194/gchron-3-545-2021","url":null,"abstract":"Abstract. The Salt Range Formation is an extensive evaporite sequence in northern\u0000Pakistan that has acted as the primary detachment accommodating Himalayan\u0000orogenic deformation from the north. This rheologically weak formation forms\u0000a mylonite in the Khewra Mine, where it accommodates approximately 40 km\u0000displacement and is comprised of intercalated halite and potash salts and\u0000gypsiferous marls. Polyhalite [K2Ca2Mg(SO4)4⚫2H2O] grains taken from potash marl and crystalline halite samples are used as geochronometers to date the formation and identify the closure temperature of the mineral polyhalite using the 40Ar/39Ar step-heating laser and furnace methods. The diffusion characteristics measured for two samples of polyhalite are diffusivity (D0), activation energy (Ea), and %39Ar. These values correspond to a closure temperature of\u0000ca. 254 and 277 ∘C for a cooling rate of 10 ∘C Myr−1.\u000040Ar/39Ar age results for both samples did not return any reliable\u0000crystallisation age. This is not unexpected as polyhalite is prone to\u000040Ar* diffusion loss and the evaporites have experienced numerous phases of deformation resetting the closed K/Ar system. An oldest minimum heating step age of ∼514 Ma from sample 06-3.1 corresponds relatively well to the established early Cambrian age of the formation. Samples 05-P2 and 05-W2 have measured step ages and represent a deformation event that partially reset the K/Ar system based on oldest significant ages between ca. 381 and 415 Ma. We interpret the youngest measured step ages, between ca. 286 and 292 Ma, to represent the maximum age of deformation-induced recrystallisation. Both the youngest and oldest measured step ages for samples 05-P2 and 05-W2 occur within the time of a major unconformity in the area. These dates may reflect partial resetting of the K/Ar system from meteoric water infiltration and recrystallisation during this non-depositional time. Otherwise, they may result from mixing of Ar derived by radiogenic decay after Cambrian precipitation with partially reset Ar from pervasive Cenozoic deformation and physical recrystallisation.\u0000","PeriodicalId":12723,"journal":{"name":"Geochronology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-12-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80485089","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}

{"title":"Supplementary material to \"Reconciling the Apparent Absence of a Last Glacial Maximum Alpine Glacial Advance, Yukon Territory, Canada, through Cosmogenic Beryllium-10 and Carbon-14 Measurements\"","authors":"B. Goehring, B. Menounos, Gerald Osbron, Adam C. Hawkins, B. Ward","doi":"10.5194/gchron-2021-43-supplement","DOIUrl":"https://doi.org/10.5194/gchron-2021-43-supplement","url":null,"abstract":"Abstract. We present a new in situ produced cosmogenic beryllium-10 and carbon-14 nuclide chronology from two sets (outer and inner) of alpine glacier moraines from the Grey Hunter massif of southern Yukon Territory, Canada. The chronology potential of moraines deposited by alpine glaciers outside the limits of the Last Glacial Maximum (LGM) ice sheets potentially provide a less-ambiguous archive of mass balance, and hence climate than can be inferred from the extents of ice sheets themselves. Results for both nuclides are inconclusive for the outer moraines, with evidence for pre-LGM deposition (beryllium-10) and Holocene deposition (carbon-14). Beryllium-10 results from the inner moraine are suggestive of canonical LGM deposition, but with relatively high scatter. Conversely, in situ carbon-14 results from the inner moraines are tightly clustered and suggestive of terminal Younger Dryas deposition. We explore plausible scenarios leading to the observed differences between nuclides and find that the most parsimonious explanation for the outer moraines is that of pre-LGM deposition, but many of the sampled boulder surfaces were not exhumed from within the moraine until the Holocene. Our results thus imply that the inner and outer moraines sampled pre- and post-date the canonical LGM and that moraines dating to the LGM are lacking likely due to overriding by the subsequent Late Glacial/earliest Holocene advance.\u0000","PeriodicalId":12723,"journal":{"name":"Geochronology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-12-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84456028","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}

{"title":"sandbox – Creating and Analysing Synthetic Sediment Sections with R","authors":"M. Dietze, S. Kreutzer, M. Fuchs, Sascha Meszner","doi":"10.5194/gchron-2021-39","DOIUrl":"https://doi.org/10.5194/gchron-2021-39","url":null,"abstract":"Abstract. The majority of palaeoenvironmental information is inferred from proxy data contained in accretionary sediments, called geo-archives. The validity of proxy data and analysis workflows are usually assumed implicitly, with systematic tests and uncertainty estimates restricted to modern analogue studies or reduced-complexity case studies. However, a more generic and consistent approach to exploring the validity and variability of proxy functions would be to translate a given geo-archive into a model scenario: a \"virtual twin\". Here, we introduce a conceptual framework and numerical toolset that allows the definition and analysis of synthetic sediment sections. The R package sandbox describes arbitrary stratigraphically consistent deposits by depth-dependent rules and grain-specific parameters, allowing full scalability and flexibility. Virtual samples can be taken, resulting in discrete grain-mixtures with well-defined parameters. These samples can then be virtually prepared and analysed, for example to test hypotheses. We illustrate the concept of sandbox, explain how a sediment section can be mapped into the model and, by focusing on an exemplary field of application, we explore universal geochronological research questions related to the effects of sample geometry and grain-size specific age inheritance. We summarise further application scenarios of the model framework, relevant for but not restricted to the broader geochronological community.\u0000","PeriodicalId":12723,"journal":{"name":"Geochronology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-12-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86158624","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}