Barium-isotopic constraints on the origin of post-Marinoan barites

Peter W. Crockford, Boswell A. Wing, Adina Paytan, Malcolm S.W. Hodgskiss, Kimberley K. Mayfield, Justin A. Hayles, Julia E. Middleton, Anne Sofie C. Ahm, David T. Johnston, Fabricio Caxito, Gabriel Uhlein, Galen P. Halverson, Benjamin Eickmann, Marta Torres, Tristan J. Horner

Research output: Contribution to journalArticlepeer-review

75 Scopus citations

Abstract

Measurements of triple oxygen isotope ratios in barite horizons within post-Marinoan cap carbonates have provided some of the most compelling evidence that the Marinoan glaciation was a Snowball Earth event. However, the origin of these barite horizons remains unresolved. To constrain the Ba sources, and thus formation mechanisms of these horizons, we analyzed the Ba isotope composition of post-Marinoan barite deposits from Northwest Canada, Northern Norway, Brazil and South China. We augment these analyses with a Ba isotope survey of almost 100 modern and ancient additional barite measurements, including samples from pelagic (or ‘marine’), hydrothermal, terrestrial, Proterozoic stratiform and cold seep environments. Unlike modern cold seep or terrestrial barites, we find that globally-distributed post-Marinoan barites exhibit a relatively narrow isotopic range, suggesting a well-mixed, effectively limitless Ba source. Moreover, post-Marinoan deposits exhibit a similar mean Ba isotope composition to modern marine barites, which we interpret as evidence of a marine Ba source. Considered alongside existing geochemical, geological, and new Ba isotope survey data, we conclude that Ba in barite horizons was sourced from a well-mixed, Ba-replete but SO4-poor reservoir that accumulated during the Marinoan Snowball Earth interval. This deep Ba reservoir was then transported upward—either by ocean circulation or dolomitization of underlying cap carbonates—and was brought into contact with continental weathering-derived sulfate in a post-glacial meltwater surface layer. Thus, in addition to providing a plausible mechanism for generating globally-synchronous deposition of post-Marinoan barite horizons that reconciles all existing geochemical and geological data, our results demonstrate the utility of Ba isotopes to interrogate the origin of enigmatic barite deposits throughout the sedimentary record.

Original languageEnglish
Pages (from-to)234-244
Number of pages11
JournalEarth and Planetary Science Letters
Volume519
DOIs
StatePublished - 1 Aug 2019
Externally publishedYes

Keywords

  • barite
  • barium cycle
  • barium isotopes
  • cryogenian
  • Marinoan
  • Snowball Earth

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science

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