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Iron isotopes and the redox evolution of Ediacaran sediments

Moynier, Frederic and Fike, David A. and Menard, Gabrielle and Fischer, Woodward W. and Grotzinger, John P. and Agranier, Arnaud (2021) Iron isotopes and the redox evolution of Ediacaran sediments. Comptes Rendus. Géoscience, 352 (8). pp. 579-588. ISSN 1778-7025. doi:10.5802/crgeos.44.

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The Ediacaran age (ca. 570 Ma) Shuram excursion, a ca. 12‰ depletion in δ¹³C_(carb), may record a dramatic oxidation of marine sediments associated with a reorganization of Earth’s carbon cycle closely preceding the rise of large metazoans. However, several geochemical indicators suggest it may instead record secondary processes affecting the sediments such as post-depositional alteration. The stable isotopic composition of iron incorporated within carbonates (δ⁵⁶Fe_(carb)) reveals an anomalous ⁵⁶Fe-depletion (down to -1.05‰) in strata containing the Shuram excursion, while the underlying and overlying strata have crustal ⁵⁶Fe-δ⁵⁶Fe_(carb) values. These depleted δ⁵⁶Fe_(carb) data during the Shuram excursion reflect incomplete reduction of iron oxides, limited by low ambient organic carbon contents. This elevated pulse of sedimentary iron oxides would consume the majority of the limited pool of organic carbon and therefore would give rise to very low net organic carbon burial during a time of enhanced detrital delivery of oxidized iron to the sediments. These results imply a syndepositional origin for the Shuram excursion, which represents a shift in the redox composition of Earth’s sedimentary shell toward more oxidizing conditions, perhaps removing a long-lived buffer on atmospheric oxygen.

Item Type:Article
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URLURL TypeDescription
Moynier, Frederic0000-0003-4321-5581
Fike, David A.0000-0003-2848-0328
Fischer, Woodward W.0000-0002-8836-3054
Grotzinger, John P.0000-0001-9324-1257
Additional Information:© 2021 Centre Mersenne, l'Académie des sciences, and the authors. This article is licensed under the Creative Commons Attribution 4.0 International License. Manuscript received 18th September 2020, revised 15th December 2020, accepted 18th December 2020. FM thanks the Academie des Sciences et l’Institut de France for the PrixMme VictorNoury and to have the possibility to submit this paper. We deeply appreciate constructive comments from two anonymous reviewers and from the editor Francois Chabaux, which greatly improved this manuscript. FM acknowledges funding from the European Research Council under the H2020 framework program/ERC grant agreement (#637503-PRISTINE) and financial support of the UnivEarthS Labex program at Sorbonne Paris Cité (#ANR-10-LABX-0023 and #ANR-11-IDEX-0005-02), and the ANR through a chaire dexcellence Sorbonne Paris Cité. Parts of this work were supported by IPGP multidisciplinary program PARI, and by Region île-de-France SESAME Grant (no. 12015908). We thank the Oman Ministry of Oil and Gas for permission to publish this paper. This research was supported by Petroleum Development Oman (PDO) and a grant from the Agouron Institute to D.A.F. and W.W.F. We would like to thank PDO for access to samples and logistical support.
Funding AgencyGrant Number
Academie des Sciences et l’Institut de FranceUNSPECIFIED
European Research Council (ERC)637503
Agence Nationale pour la Recherche (ANR)ANR-10-LABX-0023
Agence Nationale pour la Recherche (ANR)ANR-11-IDEX-0005-02
Sorbonne Paris CitéUNSPECIFIED
Institut de Physique du Globe de Paris (IPGP)UNSPECIFIED
Region île-de-France12015908
Petroleum Development OmanUNSPECIFIED
Agouron InstituteUNSPECIFIED
Subject Keywords:Geochemistry, Ediacara, Shuram excursion, Fe isotopes, Oxygenation, Redox change, Ocean
Issue or Number:8
Record Number:CaltechAUTHORS:20210219-120046813
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:108125
Deposited By: George Porter
Deposited On:22 Feb 2021 16:03
Last Modified:16 Nov 2021 19:09

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