Preprints
https://doi.org/10.5194/egusphere-2025-432
https://doi.org/10.5194/egusphere-2025-432
13 Feb 2025
 | 13 Feb 2025

Broken 206Pb/238U carbonate chronometers and 207Pb/235U fixes

Pieter Vermeesch, Noah McLean, Anton Vaks, Tzahi Golan, Sebastian F. M. Breitenbach, and Randall Parris

Abstract. Carbonate U–Pb dating has become a key tool for Quaternary palaeoclimatology and palaeoanthropology beyond the ∼800 ka age limit of Th–U disequilibrium dating. U–Pb geochronology is based on the paired radioactive decay of 238U to 206Pb and of 235U to 207Pb. Current carbonate U–Pb data processing algorithms rely mostly on the 206Pb/238U clock and attach little weight to the 207Pb/235U data. A key weakness of this approach is the need to correct the 206Pb/238U data for initial 234U/238U disequilibrium, which may cause an excess (or deficit) in radiogenic 206Pb compared to secular equilibrium. We introduce a new disequilibrium correction algorithm, using matrix exponentials. This algorithm can be used to undo the effects of U-series disequilibrium using either an assumed initial composition, or a measured set of modern 234U/238U (and optionally 230Th/238U) activity ratios. Using a deterministic Bayesian inversion algorithm, we show that disequilibrium corrections work well for relatively young samples but become unreliable beyond 1.5 Ma and impossible beyond 2 Ma. Using theoretical models and real world examples from Siberia, South Africa and Israel, we show that the uncertainty of the disequilibrium correction of such old samples exceeds the correction itself. Previous ‘Monte Carlo’ error propagation methods underestimate these uncertainties by up to an order of magnitude. We advocate the use of the 207Pb/235U isochron method as a more accurate and precise alternative to 206Pb/238U geochronology for >2 Ma carbonates that are suspected to have experienced significant levels of initial 234U/238U disequilibrium.

Competing interests: Pieter Vermeesch and Noah McLean are associate editors of Geochronology.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.
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Journal article(s) based on this preprint

10 Oct 2025
Carbonate 206Pb ∕ 238U problems and potential 207Pb ∕ 235U fixes
Pieter Vermeesch, Noah McLean, Anton Vaks, Tzahi Golan, Sebastian F. M. Breitenbach, and Randall Parrish
Geochronology, 7, 459–473, https://doi.org/10.5194/gchron-7-459-2025,https://doi.org/10.5194/gchron-7-459-2025, 2025
Short summary
Pieter Vermeesch, Noah McLean, Anton Vaks, Tzahi Golan, Sebastian F. M. Breitenbach, and Randall Parris

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2025-432', Perach Nuriel, 13 Mar 2025
    • AC1: 'Reply on RC1', Pieter Vermeesch, 13 May 2025
  • CC1: 'Comment on egusphere-2025-432', Timothy Pollard, 07 May 2025
    • AC2: 'Reply on CC1', Pieter Vermeesch, 13 May 2025
  • RC2: 'Comment on egusphere-2025-432', Robyn Pickering, 13 May 2025
    • AC3: 'Reply on RC2', Pieter Vermeesch, 29 May 2025

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2025-432', Perach Nuriel, 13 Mar 2025
    • AC1: 'Reply on RC1', Pieter Vermeesch, 13 May 2025
  • CC1: 'Comment on egusphere-2025-432', Timothy Pollard, 07 May 2025
    • AC2: 'Reply on CC1', Pieter Vermeesch, 13 May 2025
  • RC2: 'Comment on egusphere-2025-432', Robyn Pickering, 13 May 2025
    • AC3: 'Reply on RC2', Pieter Vermeesch, 29 May 2025

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload
ED: Publish subject to revisions (further review by editor and referees) (07 Jun 2025) by Axel Schmitt
AR by Pieter Vermeesch on behalf of the Authors (02 Jul 2025)  Author's response   Author's tracked changes   Manuscript 
ED: Publish subject to technical corrections (05 Jul 2025) by Axel Schmitt
ED: Publish subject to technical corrections (05 Jul 2025) by Klaus Mezger (Editor)
AR by Pieter Vermeesch on behalf of the Authors (21 Jul 2025)  Author's response   Manuscript 

Post-review adjustments

AA: Author's adjustment | EA: Editor approval
AA by Pieter Vermeesch on behalf of the Authors (07 Oct 2025)   Author's adjustment   Manuscript
EA: Adjustments approved (07 Oct 2025) by Axel Schmitt

Journal article(s) based on this preprint

10 Oct 2025
Carbonate 206Pb ∕ 238U problems and potential 207Pb ∕ 235U fixes
Pieter Vermeesch, Noah McLean, Anton Vaks, Tzahi Golan, Sebastian F. M. Breitenbach, and Randall Parrish
Geochronology, 7, 459–473, https://doi.org/10.5194/gchron-7-459-2025,https://doi.org/10.5194/gchron-7-459-2025, 2025
Short summary
Pieter Vermeesch, Noah McLean, Anton Vaks, Tzahi Golan, Sebastian F. M. Breitenbach, and Randall Parris

Data sets

Data files and R code for testing Pieter Vermeesch https://github.com/pvermees/supplements

Pieter Vermeesch, Noah McLean, Anton Vaks, Tzahi Golan, Sebastian F. M. Breitenbach, and Randall Parris

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Latest update: 10 Oct 2025
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Short summary
U-Pb dating of cave sediments has provided important new time constraints on the evolution of cave-dwelling organisms (including early humans), and of Earth's climate during the past 5 million years. This paper shows that the most common type of U-Pb dating, which uses 238U and 206Pb, can be inaccurate beyond 2 million years ago. It proposes an alternative type of U-Pb dating, using 235U and 207Pb, as a more accurate alternative.
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