Constraining oceanic oxygenation during the Shuram excursion in South China using thallium isotopes

Haifeng Fan, Sune G. Nielsen, Jeremy D. Owens, Maureen Auro, Yunchao Shu, Dalton S. Hardisty, Tristan J. Horner, Chelsie N. Bowman, Seth A. Young, Hanjie Wen

Research output: Contribution to journalArticlepeer-review

18 Citations (Scopus)

Abstract

Ediacaran sediments record an unusual global carbon cycle perturbation that has been linked to widespread oceanic oxygenation, the Shuram negative C isotope excursion (NCIE). However, proxy-based estimates of global ocean redox conditions during this event have been limited largely due to proxy specificity (e.g., euxinic sediments for Mo and U isotopes). Modern global seawater documents a homogenous Tl isotope composition (ε205Tl = −6.0) due to significant manganese oxide burial, which is recorded in modern euxinic sediments. Here, we provide new data documenting that sediments deposited beneath reducing but a non-sulfidic water column from the Santa Barbara Basin (ε205Tl = −5.6 ± 0.1) also faithfully capture global seawater Tl isotope values. Thus, the proxy utilization of Tl isotopes can extend beyond strictly euxinic settings. Second, to better constrain the global redox conditions during the Shuram NCIE, we measured Tl isotopes of locally euxinic and ferruginous shales of the upper Doushantuo Formation, South China. The ε205Tl values of these shales exhibit a decreasing trend from ≈−3 to ≈−8, broadly coinciding with the onset of Shuram NCIE. There are ε205Tl values (−5.1 to −7.8) during the main Shuram NCIE interval that approach values more negative than modern global seawater. These results suggest that manganese oxide burial was near or even greater than modern burial fluxes, which is likely linked to an expansion of oxic conditions. This ocean oxygenation may have been an important trigger for the Shuram NCIE and evolution of Ediacaran-type biota. Subsequently, Tl isotopes show an increasing trend from the modern ocean value to values near the modern global inputs or even heavier (ε205Tl ≈ −2.5 ~ 0.4), occurring prior to recovery from the NCIE. These records may suggest that there was a decrease in the extent of oxygenated conditions in the global oceans during the late stage of the Shuram NCIE.

Original languageEnglish
Pages (from-to)348-365
Number of pages18
JournalGeobiology
Volume18
Issue number3
DOIs
Publication statusPublished - May 1 2020
Externally publishedYes

Keywords

  • Doushantuo Formation
  • ocean oxygenation
  • Shuram NCIE
  • thallium isotopes

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Environmental Science(all)
  • Earth and Planetary Sciences(all)

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