Revisiting marine redox conditions during the Ediacaran Shuram carbon isotope excursion.

Autor: Gong Z; Department of Earth and Planetary Sciences, Yale University, New Haven, Connecticut, USA., Wei GY; Department of Earth and Planetary Sciences, Yale University, New Haven, Connecticut, USA.; School of Earth Sciences and Engineering, Nanjing University, Nanjing, China., Fakhraee M; Department of Earth and Planetary Sciences, Yale University, New Haven, Connecticut, USA., Alcott LJ; Department of Earth and Planetary Sciences, Yale University, New Haven, Connecticut, USA., Jiang L; Department of Earth and Planetary Sciences, Yale University, New Haven, Connecticut, USA.; Key Laboratory of Petroleum Resources Research, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China., Zhao M; Department of Earth and Planetary Sciences, Yale University, New Haven, Connecticut, USA.; Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China., Planavsky NJ; Department of Earth and Planetary Sciences, Yale University, New Haven, Connecticut, USA.
Jazyk: angličtina
Zdroj: Geobiology [Geobiology] 2023 Jul; Vol. 21 (4), pp. 407-420. Date of Electronic Publication: 2023 Feb 08.
DOI: 10.1111/gbi.12547
Abstrakt: The Neoproterozoic carbonate record contains multiple carbon isotope anomalies, which are the subject of intense debate. The largest of these anomalies, the Shuram excursion (SE), occurred in the mid-Ediacaran (~574-567 Ma). Accurately reconstructing marine redox landscape is a clear path toward making sense of the mechanism that drives this δ 13 C anomaly. Here, we report new uranium isotopic data from the shallow-marine carbonates of the Wonoka Formation, Flinders Ranges, South Australia, where the SE is well preserved. Our data indicate that the δ 238 U trend during the SE is highly reproducible across globally disparate sections from different depositional settings. Previously, it was proposed that the positive shift of δ 238 U values during the SE suggests an extensive, near-modern level of marine oxygenation. However, recent publications suggest that the fractionation of uranium isotopes in ferruginous and anoxic conditions is comparable, opening up the possibility of non-unique interpretations of the carbonate uranium isotopic record. Here, we build on this idea by investigating the SE in conjunction with additional geochemical proxies. Using a revised uranium isotope mass balance model and an inverse stochastic carbon cycle model, we reevaluate models for δ 13 C and δ 238 U trends during the SE. We suggest that global seawater δ 238 U values during the SE could be explained by an expansion of ferruginous conditions and do not require a near-modern level of oxygenation during the mid-Ediacaran.
(© 2023 John Wiley & Sons Ltd.)
Databáze: MEDLINE
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