Articles | Volume 7, issue 1
https://doi.org/10.5194/gchron-7-83-2025
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/gchron-7-83-2025
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Research article
| 
19 Mar 2025
Research article |
| 19 Mar 2025
| 19 Mar 2025
Measuring varve thickness using micro-computed tomography (µCT): a comparison with thin section
Marie-Eugénie Meusseunan Pascale Jamba
CORRESPONDING AUTHOR
Centre Eau Terre Environnement, Institut National de la Recherche Scientifique, Québec, Canada
GEOTOP Montréal, Quebec, H2X 3Y7, Canada
Pierre Francus
Centre Eau Terre Environnement, Institut National de la Recherche Scientifique, Québec, Canada
GEOTOP Montréal, Quebec, H2X 3Y7, Canada
Antoine Gagnon-Poiré
Centre Eau Terre Environnement, Institut National de la Recherche Scientifique, Québec, Canada
GEOTOP Montréal, Quebec, H2X 3Y7, Canada
currently at: Ministère de l'environnement, de la lutte contre les changements climatiques, de la faune et des parcs, Québec, Canada
Guillaume St-Onge
GEOTOP Montréal, Quebec, H2X 3Y7, Canada
Institut des sciences de la mer (ISMER), Université du Québec à Rimouski (UQAR) and Canada Research Chair in Marine Geology, Rimouski, QC G5L 3A1, Canada
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Antoine Lachance, Matthew Peros, Jeannine-Marie St-Jacques, Pierre Francus, and Nicole K. Sanderson
EGUsphere, https://doi.org/10.5194/egusphere-2025-400, https://doi.org/10.5194/egusphere-2025-400, 2025
This preprint is open for discussion and under review for Climate of the Past (CP).
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This study explores storm patterns in eastern Canada's Magdalen Islands over 4000 years, using coastal peatlands to understand past storm activity. Our findings reveal key storm periods, including during the Little Ice Age, linked to broader climatic shifts like the Atlantic Multidecadal Variability. By comparing our results with other North American records, we show how peat data can complement marine storm archives and improve our understanding of past storms.
François Lapointe, Antoine Gagnon-Poiré, Pierre Francus, Patrick Lajeunesse, and Clarence Gagnon
EGUsphere, https://doi.org/10.5194/egusphere-2025-97, https://doi.org/10.5194/egusphere-2025-97, 2025
This preprint is open for discussion and under review for Climate of the Past (CP).
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A new 1500-year-long sediment record entirely made of annual laminations (varves) from a deep lake in Labrador was analyzed to perform a reconstruction of past hydroclimatic conditions. The varve thickness was linked to regional snow and rain precipitations. Our record indicates more precipitations during the 1050–1225 CE period, that is corresponding to the Medieval Climate Anomaly, whereas the 15th–19th centuries, related to the Little Ice Age, shows a drier climate.
Antoine Gagnon-Poiré, Pierre Brigode, Pierre Francus, David Fortin, Patrick Lajeunesse, Hugues Dorion, and Annie-Pier Trottier
Clim. Past, 17, 653–673, https://doi.org/10.5194/cp-17-653-2021, https://doi.org/10.5194/cp-17-653-2021, 2021
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A very high quality 160-year-long annually laminated (varved) sediment sequence of fluvial origin was recently discovered in an especially deep lake in Labrador. Each varve represents 1 hydrological year. A significant relation between varves' physical parameters (i.e., thickness and grain size extracted from each annual lamination) and river discharge instrumental observations provided the opportunity to develop regional discharge reconstructions beyond the instrumental period.
Chris S. M. Turney, Helen V. McGregor, Pierre Francus, Nerilie Abram, Michael N. Evans, Hugues Goosse, Lucien von Gunten, Darrell Kaufman, Hans Linderholm, Marie-France Loutre, and Raphael Neukom
Clim. Past, 15, 611–615, https://doi.org/10.5194/cp-15-611-2019, https://doi.org/10.5194/cp-15-611-2019, 2019
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This PAGES (Past Global Changes) 2k (climate of the past 2000 years working group) special issue of Climate of the Past brings together the latest understanding of regional change and impacts from PAGES 2k groups across a range of proxies and regions. The special issue has emerged from a need to determine the magnitude and rate of change of regional and global climate beyond the timescales accessible within the observational record.
Eleanor Georgiadis, Jacques Giraudeau, Philippe Martinez, Patrick Lajeunesse, Guillaume St-Onge, Sabine Schmidt, and Guillaume Massé
Clim. Past, 14, 1991–2010, https://doi.org/10.5194/cp-14-1991-2018, https://doi.org/10.5194/cp-14-1991-2018, 2018
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We present our results from a radiocarbon-dated core collected in central Nares Strait, NW Greenland. Sedimentological and geochemical data reveal that marine sedimentation began ca. 9.0 cal ka BP with the complete opening of the strait occurring at 8.3 cal ka BP. The collapse of the glacial buttress in central Nares Strait led to accelerated glacial fluxes of the bordering ice sheets between 8.3 and 7.5 cal ka BP, while the Humboldt Glacier retreated in eastern Kane Basin ca. 8.1 cal ka BP.
Johannes P. Werner, Dmitry V. Divine, Fredrik Charpentier Ljungqvist, Tine Nilsen, and Pierre Francus
Clim. Past, 14, 527–557, https://doi.org/10.5194/cp-14-527-2018, https://doi.org/10.5194/cp-14-527-2018, 2018
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We present a new gridded Arctic summer temperature reconstruction back to the first millennium CE. Our method respects the age uncertainties of the data, which results in a more precise reconstruction.
The spatial average shows a millennium-scale cooling trend which is reversed in the mid-19th century. While temperatures in the 10th century were probably as warm as in the 20th century, the spatial coherence of the recent warm episodes seems unprecedented.
The spatial average shows a millennium-scale cooling trend which is reversed in the mid-19th century. While temperatures in the 10th century were probably as warm as in the 20th century, the spatial coherence of the recent warm episodes seems unprecedented.
Hans W. Linderholm, Marie Nicolle, Pierre Francus, Konrad Gajewski, Samuli Helama, Atte Korhola, Olga Solomina, Zicheng Yu, Peng Zhang, William J. D'Andrea, Maxime Debret, Dmitry V. Divine, Björn E. Gunnarson, Neil J. Loader, Nicolas Massei, Kristina Seftigen, Elizabeth K. Thomas, Johannes Werner, Sofia Andersson, Annika Berntsson, Tomi P. Luoto, Liisa Nevalainen, Saija Saarni, and Minna Väliranta
Clim. Past, 14, 473–514, https://doi.org/10.5194/cp-14-473-2018, https://doi.org/10.5194/cp-14-473-2018, 2018
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This paper reviews the current knowledge of Arctic hydroclimate variability during the past 2000 years. We discuss the current state, look into the future, and describe various archives and proxies used to infer past hydroclimate variability. We also provide regional overviews and discuss the potential of furthering our understanding of Arctic hydroclimate in the past. This paper summarises the hydroclimate-related activities of the Arctic 2k group.
Roger D. Flood, Roberto A. Violante, Thomas Gorgas, Ernesto Schwarz, Jens Grützner, Gabriele Uenzelmann-Neben, F. Javier Hernández-Molina, Jennifer Biddle, Guillaume St-Onge, and APVCM workshop participants
Sci. Dril., 22, 49–61, https://doi.org/10.5194/sd-22-49-2017, https://doi.org/10.5194/sd-22-49-2017, 2017
François Lapointe, Pierre Francus, Scott F. Lamoureux, Mathias Vuille, Jean-Philippe Jenny, Raymond S. Bradley, and Charly Massa
Clim. Past, 13, 411–420, https://doi.org/10.5194/cp-13-411-2017, https://doi.org/10.5194/cp-13-411-2017, 2017
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Using a unique annually-laminated record (varve) from the western Canadian High Arctic, we found a significant relationship between our varve record and instrumental and reconstructed Pacific Decadal Oscillations (PDOs). The negative (positive) PDO (North Pacific Index) phases increase precipitation as low sea-ice extent, warmer temperature and winds reach our region more efficiently. Our results imply that future negative PDO phases will likely impact the already rapidly warming Arctic.
Odile Crabeck, Ryan Galley, Bruno Delille, Brent Else, Nicolas-Xavier Geilfus, Marcos Lemes, Mathieu Des Roches, Pierre Francus, Jean-Louis Tison, and Søren Rysgaard
The Cryosphere, 10, 1125–1145, https://doi.org/10.5194/tc-10-1125-2016, https://doi.org/10.5194/tc-10-1125-2016, 2016
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We present a new non-destructive X-ray-computed tomography technique to quantify the air volume fraction and produce separate 3-D images of air-volume inclusions in sea ice. While the internal layers showed air-volume fractions < 2 %, the ice–air interface (top 2 cm) showed values up to 5 %. As a result of the presence of large bubbles and higher air volume fraction measurements in sea ice, we introduce new perspectives on processes regulating gas exchange at the ice–atmosphere interface.
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Chetan Nathwani, Dawid Szymanowski, Lorenzo Tavazzani, Sava Markovic, Adrianna L. Virmond, and Cyril Chelle-Michou
Geochronology, 7, 15–33, https://doi.org/10.5194/gchron-7-15-2025, https://doi.org/10.5194/gchron-7-15-2025, 2025
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We performed a statistical analysis of high-precision U–Pb zircon age distributions. This reveals that volcanic and porphyry zircon age distributions are skewed to younger ages, whereas plutonic age distributions are skewed to older ages. We show that this is caused by truncation of zircon crystallisation by magma evacuation rather than differences in magmatic flux. Our contribution has key implications for modelling of magma dynamics and eruption ages using zircon age distributions.
Christoph Glotzbach and Todd A. Ehlers
Geochronology, 6, 697–717, https://doi.org/10.5194/gchron-6-697-2024, https://doi.org/10.5194/gchron-6-697-2024, 2024
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The (U–Th–Sm) / He dating method helps understand the cooling history of rocks. Synthetic modelling experiments were conducted to explore factors affecting in situ vs. whole-grain (U–Th) / He dates. In situ dates are often 30 % older than whole-grain dates, whereas very rapid cooling makes helium loss negligible, resulting in similar whole-grain and in situ dates. In addition, in situ data can reveal cooling histories even from a single grain by measuring helium distributions.
Steven Denyszyn, Donald W. Davis, and Denis Fougerouse
Geochronology, 6, 607–619, https://doi.org/10.5194/gchron-6-607-2024, https://doi.org/10.5194/gchron-6-607-2024, 2024
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Decay of U to Pb in baddeleyite is used for dating mafic rocks, but some daughter Pb atoms can be ejected out of the crystal, resulting in ages that seem too young. Atom probe tomography was used to map U and Pb atoms in 3D within baddeleyite crystals and estimate the average distance that Pb atoms are displaced by recoil. This allows us to test the relationship between crystal size and apparent age. There is also evidence for clustering of U atoms, inviting more work on how this may occur.
Jesús Muñoz-Montecinos, Andrea Giuliani, Senan Oesch, Silvia Volante, Bradley Peters, and Whitney Behr
Geochronology, 6, 585–605, https://doi.org/10.5194/gchron-6-585-2024, https://doi.org/10.5194/gchron-6-585-2024, 2024
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Dating the roots of plate boundaries is essential for understanding geologic processes, but geochemical limitations, particularly in young mafic rocks, make this challenging. Advancements in mass spectrometry now enable high-resolution analysis of micro-domains. We assess these limitations by dating rocks from Syros. Multi-phase mineral analysis improves age uncertainty 6-fold. We emphasize the importance of the local geologic context and propose strategies to mitigate uncertainties.
Andrew L. Gorin, Joshua M. Gorin, Marie Bergelin, and David L. Shuster
Geochronology, 6, 521–540, https://doi.org/10.5194/gchron-6-521-2024, https://doi.org/10.5194/gchron-6-521-2024, 2024
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The multiple-diffusion domain (MDD) model quantifies the temperature dependence of noble gas diffusivity in minerals. However, current methods for tuning MDD parameters can yield biased results, leading to underestimates of sample temperatures through geologic time. Our "MDD Tool Kit" software optimizes all MDD parameters simultaneously, overcoming these biases. We then apply this software to a previously published 40Ar/39Ar dataset (Wong, 2023) to showcase its efficacy.
Allison W. Jacobel, Kassandra M. Costa, Lily M. Applebaum, and Serena Conde
EGUsphere, https://doi.org/10.5194/egusphere-2024-2775, https://doi.org/10.5194/egusphere-2024-2775, 2024
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The equatorial Pacific is an important region that helps determine Earth's climate. This work presents new age models for two sediment core sites located in that region, spanning the last 280 ka. Our age models are based on new radiocarbon dates and oxygen isotope measurements. We also use the oxygen isotope data to infer changes in sea surface salinity patterns, finding evidence for a change in the position of the Intertropical Convergence Zone (ITCZ) on glacial/interglacial timescales.
Marcel Guillong, Elias Samankassou, Inigo A. Müller, Dawid Szymanowski, Nathan Looser, Lorenzo Tavazzani, Óscar Merino-Tomé, Juan R. Bahamonde, Yannick Buret, and Maria Ovtcharova
Geochronology, 6, 465–474, https://doi.org/10.5194/gchron-6-465-2024, https://doi.org/10.5194/gchron-6-465-2024, 2024
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RA138 is a new reference material for U–Pb dating of carbonate samples via laser ablation inductively coupled plasma mass spectrometry. RA138 exhibits variable U–Pb ratios and consistent U content, resulting in a precise isochron with low uncertainty. Isotope dilution thermal ionization mass spectrometry analyses fix a reference age of 321.99 ± 0.65 Ma. This research advances our ability to date carbonate samples accurately, providing insights into geological processes and historical timelines.
Nil Irvalı, Ulysses S. Ninnemann, Are Olsen, Neil L. Rose, David J. R. Thornalley, Tor L. Mjell, and François Counillon
Geochronology, 6, 449–463, https://doi.org/10.5194/gchron-6-449-2024, https://doi.org/10.5194/gchron-6-449-2024, 2024
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Marine sediments are excellent archives for reconstructing past changes in climate and ocean circulation. Yet, dating uncertainties, particularly during the 20th century, pose major challenges. Here we propose a novel chronostratigraphic approach that uses anthropogenic signals, such as the oceanic 13C Suess effect and spheroidal carbonaceous fly-ash particles, to reduce age model uncertainties in high-resolution marine archives over the 20th century.
Birk Härtel and Eva Enkelmann
Geochronology, 6, 429–448, https://doi.org/10.5194/gchron-6-429-2024, https://doi.org/10.5194/gchron-6-429-2024, 2024
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We present a new data analysis workflow for thermochronological data based on plots of radiogenic daughter vs. radioactive parent concentration. The daughter–parent relationship helps to identify the sources of age variation. Our workflow classifies the daughter–parent relationship and provides further suggestions, e.g., if a dataset can be described by a sample age and which type of sample age to report. We also introduce Incaplot, which is software for creating daughter–parent plots.
Pieter Vermeesch
Geochronology, 6, 397–407, https://doi.org/10.5194/gchron-6-397-2024, https://doi.org/10.5194/gchron-6-397-2024, 2024
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The age of some geological materials can be estimated from the ratio of certain radiogenic "daughter" isotopes to their radioactive "parent". However, in many cases, the age estimation process is complicated by the presence of an inherited component of non-radiogenic daughter isotopes. This paper presents an improved algorithm to estimate the radiogenic and non-radiogenic components, either separately or jointly.
André Navin Paul, Anders Lindskog, and Urs Schaltegger
Geochronology, 6, 325–335, https://doi.org/10.5194/gchron-6-325-2024, https://doi.org/10.5194/gchron-6-325-2024, 2024
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The “Likhall” bed helps to constrain the timing of increased meteorite bombardment of the Earth during the Ordovician period. It is important to understand the timing of this meteorite bombardment when attempting to correlate it with biodiversity changes during the Ordovician period. Calibrating a good age for the “Likhall” bed is, however, challenging and benefited in this study from advances in sample preparation.
Megan A. Mueller, Alexis Licht, Andreas Möller, Cailey B. Condit, Julie C. Fosdick, Faruk Ocakoğlu, and Clay Campbell
Geochronology, 6, 265–290, https://doi.org/10.5194/gchron-6-265-2024, https://doi.org/10.5194/gchron-6-265-2024, 2024
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Sedimentary provenance refers to the study of the origin of sedimentary rocks, tracing where sediment particles originated. Common sedimentary provenance techniques struggle to track mafic igneous and metamorphic rock sources and rutile forms in these rock types. We use rutile form ancient sedimentary rocks in Türkiye to present new recommendations and workflows for integrating rutile U–Pb ages and chemical composition into an accurate sedimentary provenance reconstruction.
Ruohong Jiao, Shengze Cai, and Jean Braun
Geochronology, 6, 227–245, https://doi.org/10.5194/gchron-6-227-2024, https://doi.org/10.5194/gchron-6-227-2024, 2024
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We demonstrate a machine learning method to estimate the temperature changes in the Earth's crust over time. The method respects physical laws and conditions imposed by users. By using observed rock cooling ages as constraints, the method can be used to estimate the tectonic and landscape evolution of the Earth. We show the applications of the method using a synthetic rock uplift model in 1D and an evolution model of a real mountain range in 3D.
Erin E. Donaghy, Michael P. Eddy, Federico Moreno, and Mauricio Ibañez-Mejia
Geochronology, 6, 89–106, https://doi.org/10.5194/gchron-6-89-2024, https://doi.org/10.5194/gchron-6-89-2024, 2024
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Chemical abrasion (CA) is a technique that reduces or eliminates the effects of Pb loss in zircon U–Pb geochronology. However, CA has yet to be applied to large-n detrital zircon (DZ) analyses. We show that CA does not negatively impact or systematically bias U–Pb dates, improves the resolution of age populations defined by 206Pb/238U dates, and increases the percentage of concordant analyses in age populations defined by 207Pb/206Pb dates.
Glenn R. Sharman and Matthew A. Malkowski
Geochronology, 6, 37–51, https://doi.org/10.5194/gchron-6-37-2024, https://doi.org/10.5194/gchron-6-37-2024, 2024
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The mineral zircon is widely used to determine the age of rocks based on the radioactive decay of U to Pb, but the measured U–Pb date can be too young if the zircon loses Pb. We present a method for estimating the distribution of apparent Pb loss by mathematical convolution. Applying this approach to 10 samples illustrates contrasting patterns of apparent Pb loss. This study highlights the importance of quantifying Pb loss to better understand its potential effects on zircon U–Pb dates.
Stijn Glorie, Sarah E. Gilbert, Martin Hand, and Jarred C. Lloyd
Geochronology, 6, 21–36, https://doi.org/10.5194/gchron-6-21-2024, https://doi.org/10.5194/gchron-6-21-2024, 2024
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Radiometric dating methods, involving laser ablation as the sample introduction, require robust calibrations to reference materials with similar ablation properties to the analysed samples. In the case of the rubidium–strontium dating method, calibrations are often conducted to nano powder with different ablation characteristics than the crystalline minerals. We describe the limitations of this approach and recommend an alternative calibration method involving natural minerals.
Alex Lipp and Pieter Vermeesch
Geochronology, 5, 263–270, https://doi.org/10.5194/gchron-5-263-2023, https://doi.org/10.5194/gchron-5-263-2023, 2023
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We propose using the Wasserstein-2 distance (W2) as an alternative to the widely used Kolmogorov–Smirnov (KS) statistic for analysing distributional data in geochronology. W2 measures the horizontal distance between observations, while KS measures vertical differences in cumulative distributions. Using case studies, we find that W2 is preferable in scenarios where the absolute age differences in observations provide important geological information. W2 has been added to the R package IsoplotR.
W. Marijn van der Meij, Arnaud J. A. M. Temme, Steven A. Binnie, and Tony Reimann
Geochronology, 5, 241–261, https://doi.org/10.5194/gchron-5-241-2023, https://doi.org/10.5194/gchron-5-241-2023, 2023
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We present our model ChronoLorica. We coupled the original Lorica model, which simulates soil and landscape evolution, with a geochronological module that traces cosmogenic nuclide inventories and particle ages through simulations. These properties are often measured in the field to determine rates of landscape change. The coupling enables calibration of the model and the study of how soil, landscapes and geochronometers change under complex boundary conditions such as intensive land management.
Michael C. Sitar and Ryan J. Leary
Geochronology, 5, 109–126, https://doi.org/10.5194/gchron-5-109-2023, https://doi.org/10.5194/gchron-5-109-2023, 2023
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We developed code to automatically and semi-automatically measure dimensions of detrital mineral grains in reflected-light images saved at laser ablation–inductively coupled plasma–mass spectrometry facilities that use Chromium targeting software. Our code uses trained deep learning models to segment grain images with greater accuracy than is achievable using other segmentation techniques. We implement our code in Jupyter notebooks which can also be run online via Google Colab.
Peter E. Martin, James R. Metcalf, and Rebecca M. Flowers
Geochronology, 5, 91–107, https://doi.org/10.5194/gchron-5-91-2023, https://doi.org/10.5194/gchron-5-91-2023, 2023
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There is currently no standardized method of performing uncertainty propagation in the (U–Th) / He system, causing data interpretation difficulties. We present two methods of uncertainty propagation and describe free, open-source software (HeCalc) to apply them. Compilation of real data using only analytical uncertainty as well as 2 % and 5 % uncertainties in FT yields respective median relative date uncertainties of 2.9 %, 3.3 %, and 5.0 % for apatites and 1.7 %, 3.3 %, and 5.0 % for zircons.
Stella Birlo, Wojciech Tylmann, and Bernd Zolitschka
Geochronology, 5, 65–90, https://doi.org/10.5194/gchron-5-65-2023, https://doi.org/10.5194/gchron-5-65-2023, 2023
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Sediment cores from the volcanic lake Holzmaar provide a very precise chronology based on tree-ring-like annual laminations or varves. We statistically combine this varve chronology with radiometric dating and tested three different methods to upgrade the age–depth model. However, only one of the three methods tested improved the dating accuracy considerably. With this work, an overview of different age integration methods is discussed and made available for increased future demands.
Peter van der Beek and Taylor F. Schildgen
Geochronology, 5, 35–49, https://doi.org/10.5194/gchron-5-35-2023, https://doi.org/10.5194/gchron-5-35-2023, 2023
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Thermochronometric data can provide unique insights into the patterns of rock exhumation and the driving mechanisms of landscape evolution. Several well-established thermal models allow for a detailed exploration of how cooling rates evolved in a limited area or along a transect, but more regional analyses have been challenging. We present age2exhume, a thermal model that can be used to rapidly provide a synoptic overview of exhumation rates from large regional thermochronologic datasets.
Marianna Corre, Arnaud Agranier, Martine Lanson, Cécile Gautheron, Fabrice Brunet, and Stéphane Schwartz
Geochronology, 4, 665–681, https://doi.org/10.5194/gchron-4-665-2022, https://doi.org/10.5194/gchron-4-665-2022, 2022
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This study is focused on the accurate measurement of U and Th by wet chemistry and laser ablation methods to improve (U–Th)/He dating of magnetite and spinel. The low U–Th content and the lack of specific U–Th standards significantly limit the accuracy of (U–Th)/He dating. Obtained U–Th results on natural and synthetic magnetite and aluminous spinel samples analyzed by wet chemistry methods and LA-ICP-MS sampling have important implications for the (U–Th)/He method and dates interpretation.
Aratz Beranoaguirre, Iuliana Vasiliev, and Axel Gerdes
Geochronology, 4, 601–616, https://doi.org/10.5194/gchron-4-601-2022, https://doi.org/10.5194/gchron-4-601-2022, 2022
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U–Pb dating by the in situ laser ablation mass spectrometry (LA-ICPMS) technique requires reference materials of the same nature as the samples to be analysed. Here, we have explored the suitability of using carbonate materials as a reference for sulfates, since there is no sulfate reference material. The results we obtained are satisfactory, and thus, from now on, the sulfates can also be analysed.
Pieter Vermeesch
Geochronology, 4, 561–576, https://doi.org/10.5194/gchron-4-561-2022, https://doi.org/10.5194/gchron-4-561-2022, 2022
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Secondary ion mass spectrometry (SIMS) is the oldest and most sensitive analytical technique for in situ U–Pb geochronology. This paper introduces a new algorithm for SIMS data reduction that treats data as
compositional data, which means that the relative abundances of 204Pb, 206Pb, 207Pb, and 238Pb are processed within a tetrahedral data space or
simplex. The new method is implemented in an eponymous computer programme that is compatible with the two dominant types of SIMS instruments.
Emily H. G. Cooperdock, Florian Hofmann, Ryley M. C. Tibbetts, Anahi Carrera, Aya Takase, and Aaron J. Celestian
Geochronology, 4, 501–515, https://doi.org/10.5194/gchron-4-501-2022, https://doi.org/10.5194/gchron-4-501-2022, 2022
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Apatite and zircon are the most widely used minerals for dating rocks, but they can be difficult to identify in some crushed rock samples. Incorrect mineral identification results in wasted analytical resources and inaccurate data. We show how X-ray computed tomography can be used to efficiently and accurately distinguish apatite from zircon based on density variations, and provide non-destructive 3D grain-specific size, shape, and inclusion information for improved data quality.
Dale R. Issler, Kalin T. McDannell, Paul B. O'Sullivan, and Larry S. Lane
Geochronology, 4, 373–397, https://doi.org/10.5194/gchron-4-373-2022, https://doi.org/10.5194/gchron-4-373-2022, 2022
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Phanerozoic sedimentary rocks of northern Canada have compositionally heterogeneous detrital apatite with high age dispersion caused by differential thermal annealing. Discrete apatite fission track kinetic populations with variable annealing temperatures are defined using elemental data but are poorly resolved using conventional parameters. Inverse thermal modelling of samples from northern Yukon reveals a record of multiple heating–cooling cycles consistent with geological constraints.
Michael Dietze, Sebastian Kreutzer, Margret C. Fuchs, and Sascha Meszner
Geochronology, 4, 323–338, https://doi.org/10.5194/gchron-4-323-2022, https://doi.org/10.5194/gchron-4-323-2022, 2022
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The R package sandbox is a collection of functions that allow the creation, sampling and analysis of fully virtual sediment sections, like having a virtual twin of real-world deposits. This article introduces the concept, features, and workflows required to use sandbox. It shows how a real-world sediment section can be mapped into the model and subsequently addresses a series of theoretical and practical questions, exploiting the flexibility of the model framework.
Gregor Pfalz, Bernhard Diekmann, Johann-Christoph Freytag, Liudmila Syrykh, Dmitry A. Subetto, and Boris K. Biskaborn
Geochronology, 4, 269–295, https://doi.org/10.5194/gchron-4-269-2022, https://doi.org/10.5194/gchron-4-269-2022, 2022
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We use age–depth modeling systems to understand the relationship between age and depth in lake sediment cores. However, depending on which modeling system we use, the model results may vary. We provide a tool to link different modeling systems in an interactive computational environment and make their results comparable. We demonstrate the power of our tool by highlighting three case studies in which we test our application for single-sediment cores and a collection of multiple sediment cores.
Andrea Madella, Christoph Glotzbach, and Todd A. Ehlers
Geochronology, 4, 177–190, https://doi.org/10.5194/gchron-4-177-2022, https://doi.org/10.5194/gchron-4-177-2022, 2022
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Cooling ages date the time at which minerals cross a certain isotherm on the way up to Earth's surface. Such ages can be measured from bedrock material and river sand. If spatial variations in bedrock ages are known in a river catchment, the spatial distribution of erosion can be inferred from the distribution of the ages measured from the river sand grains. Here we develop a new tool to help such analyses, with particular emphasis on quantifying uncertainties due to sample size.
Yang Li and Pieter Vermeesch
Geochronology, 3, 415–420, https://doi.org/10.5194/gchron-3-415-2021, https://doi.org/10.5194/gchron-3-415-2021, 2021
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A conventional isochron is a straight-line fit to two sets of isotopic ratios, D/d and P/d, where P is the radioactive parent, D is the radiogenic daughter, and d is a second isotope of the daughter element. The slope of this line is proportional to the age of the system. An inverse isochron is a linear fit through d/D and P/D. The horizontal intercept of this line is inversely proportional to the age. The latter approach is preferred when d<D, which is the case in Re–Os and K–Ca geochronology.
Cécile Gautheron, Rosella Pinna-Jamme, Alexis Derycke, Floriane Ahadi, Caroline Sanchez, Frédéric Haurine, Gael Monvoisin, Damien Barbosa, Guillaume Delpech, Joseph Maltese, Philippe Sarda, and Laurent Tassan-Got
Geochronology, 3, 351–370, https://doi.org/10.5194/gchron-3-351-2021, https://doi.org/10.5194/gchron-3-351-2021, 2021
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Apatite and zircon (U–Th) / He thermochronology is now a mainstream tool to reconstruct Earth's evolution through the history of cooling and exhumation over the first dozen kilometers. The geological implications of these data rely on the precision of measurements of He, U, Th, and Sm contents in crystals. This technical note documents the methods for He thermochronology developed at the GEOPS laboratory, Paris-Saclay University, that allow (U–Th) / He data to be obtained with precision.
Kalin T. McDannell and Dale R. Issler
Geochronology, 3, 321–335, https://doi.org/10.5194/gchron-3-321-2021, https://doi.org/10.5194/gchron-3-321-2021, 2021
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We generated a synthetic dataset applying published kinetic models and distinct annealing kinetics for the apatite fission track and (U–Th)/He methods using a predetermined thermal history. We then tested how well the true thermal history could be recovered under different data interpretation schemes and geologic constraint assumptions using the Bayesian QTQt software. Our results demonstrate that multikinetic data increase time–temperature resolution and can constrain complex thermal histories.
Birk Härtel, Raymond Jonckheere, Bastian Wauschkuhn, and Lothar Ratschbacher
Geochronology, 3, 259–272, https://doi.org/10.5194/gchron-3-259-2021, https://doi.org/10.5194/gchron-3-259-2021, 2021
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We carried out thermal annealing experiments between 500 and 1000 °C to determine the closure temperature of radiation-damage annealing in zircon (ZrSiO4). Our results show that the different Raman bands of zircon respond differently to annealing. The repair is highest for the external rotation Raman band near 356.6 cm−1. The closure temperature estimates range from 250 to 370 °C for different bands. The differences in closure temperatures offer the prospect of multi-T zircon Raman dating.
Pieter Vermeesch
Geochronology, 3, 247–257, https://doi.org/10.5194/gchron-3-247-2021, https://doi.org/10.5194/gchron-3-247-2021, 2021
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This paper shows that the current practice of filtering discordant U–Pb data based on the relative difference between the 206Pb/238U and 207Pb/206Pb ages is just one of several possible approaches to the problem and demonstrably not the best one. An alternative approach is to define discordance in terms of isotopic composition, as a log ratio distance between the measurement and the concordia line. Application to real data indicates that this reduces the positive bias of filtered age spectra.
Blair Schoene, Michael P. Eddy, C. Brenhin Keller, and Kyle M. Samperton
Geochronology, 3, 181–198, https://doi.org/10.5194/gchron-3-181-2021, https://doi.org/10.5194/gchron-3-181-2021, 2021
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We compare two published U–Pb and 40Ar / 39Ar geochronologic datasets to produce eruption rate models for the Deccan Traps large igneous province. Applying the same approach to each dataset, the resulting models agree well, but the higher-precision U–Pb dataset results in a more detailed eruption model than the lower-precision 40Ar / 39Ar data. We explore sources of geologic uncertainty and reiterate the importance of systematic uncertainties in comparing U–Pb and 40Ar / 39Ar datasets.
Nicholas P. McKay, Julien Emile-Geay, and Deborah Khider
Geochronology, 3, 149–169, https://doi.org/10.5194/gchron-3-149-2021, https://doi.org/10.5194/gchron-3-149-2021, 2021
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This paper describes geoChronR, an R package that streamlines the process of quantifying age uncertainties, propagating uncertainties through several common analyses, and visualizing the results. In addition to describing the structure and underlying theory of the package, we present five real-world use cases that illustrate common workflows in geoChronR. geoChronR is built on the Linked PaleoData framework, is open and extensible, and we welcome feedback and contributions from the community.
Leonie Peti, Kathryn E. Fitzsimmons, Jenni L. Hopkins, Andreas Nilsson, Toshiyuki Fujioka, David Fink, Charles Mifsud, Marcus Christl, Raimund Muscheler, and Paul C. Augustinus
Geochronology, 2, 367–410, https://doi.org/10.5194/gchron-2-367-2020, https://doi.org/10.5194/gchron-2-367-2020, 2020
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Orakei Basin – a former maar lake in Auckland, New Zealand – provides an outstanding sediment record over the last ca. 130 000 years, but an age model is required to allow the reconstruction of climate change and volcanic eruptions contained in the sequence. To construct a relationship between depth in the sediment core and age of deposition, we combined tephrochronology, radiocarbon dating, luminescence dating, and the relative intensity of the paleomagnetic field in a Bayesian age–depth model.
Roger Powell, Eleanor C. R. Green, Estephany Marillo Sialer, and Jon Woodhead
Geochronology, 2, 325–342, https://doi.org/10.5194/gchron-2-325-2020, https://doi.org/10.5194/gchron-2-325-2020, 2020
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The standard approach to isochron calculation assumes that the distribution of uncertainties on the data arising from isotopic analysis is strictly Gaussian. This excludes datasets that have more scatter, even though many appear to have age significance. Our new approach requires only that the central part of the uncertainty distribution of the data defines a "spine" in the trend of the data. A robust statistics approach is used to locate the spine, and an implementation in Python is given.
Simon J. E. Large, Jörn-Frederik Wotzlaw, Marcel Guillong, Albrecht von Quadt, and Christoph A. Heinrich
Geochronology, 2, 209–230, https://doi.org/10.5194/gchron-2-209-2020, https://doi.org/10.5194/gchron-2-209-2020, 2020
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The integration of zircon geochemistry and U–Pb geochronology (petrochronology) allows us to improve our understanding of magmatic processes. Here we could reconstruct the ~300 kyr evolution of the magma reservoir that sourced the magmas, fluids and metals to form the Batu Hijau porphyry Cu–Au deposit. The application of in situ LA-ICP-MS and high-precision CA–ID–TIMS geochronology to the same zircons further allowed an assessment of the strengths and limitations of the different techniques.
Julia Kalanke, Jens Mingram, Stefan Lauterbach, Ryskul Usubaliev, Rik Tjallingii, and Achim Brauer
Geochronology, 2, 133–154, https://doi.org/10.5194/gchron-2-133-2020, https://doi.org/10.5194/gchron-2-133-2020, 2020
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Our study presents the first seasonally laminated (varved) sediment record covering almost the entire Holocene in high mountainous arid Central Asia. The established floating varve chronology is confirmed by two terrestrial radiocarbon dates, whereby aquatic radiocarbon dates reveal decreasing reservoir ages up core. Changes in seasonal deposition characteristics are attributed to changes in runoff and precipitation and/or to evaporative summer conditions.
Pieter Vermeesch
Geochronology, 2, 119–131, https://doi.org/10.5194/gchron-2-119-2020, https://doi.org/10.5194/gchron-2-119-2020, 2020
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The U–Pb method is one of the most powerful and versatile methods in the geochronological toolbox. With two isotopes of uranium decaying to two different isotopes of lead, the U–Pb method offers an internal quality control that is absent from most other geochronological techniques. U-bearing minerals often contain significant amounts of Th, which decays to a third Pb isotope. This paper presents an algorithm to jointly process all three chronometers at once.
Jon Woodhead and Joseph Petrus
Geochronology, 1, 69–84, https://doi.org/10.5194/gchron-1-69-2019, https://doi.org/10.5194/gchron-1-69-2019, 2019
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Recently developed methods for in situ U–Pb age determination in carbonates have found widespread application, but the benefits and limitations of the method over bulk analysis approaches have yet to be fully explored. Here we use speleothems – cave carbonates such as stalagmites and flowstones – to investigate the utility of these in situ dating methodologies for challenging matrices with low U and Pb contents and predominantly late Cenozoic ages.
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Short summary
This article presents a non-destructive method for studying laminated sediments with X-ray micro-computed tomography (μCT). It aims to study the possibility of using μCT as an analytical tool to analyse varved sediments in the context of paleoclimatic studies. As a result, µCT offers the possibility of doing fast analysis and constitutes a powerful tool to improve the quality of results through the access of a 3D view, allowing for choosing the most representative part of a varved record.
This article presents a non-destructive method for studying laminated sediments with X-ray...
