Iron isotopes and the redox evolution of Ediacaran sediments

IF 2 4区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY Comptes Rendus Geoscience Pub Date : 2021-01-27 DOI:10.5802/CRGEOS.44
F. Moynier, D. Fike, Gabrielle Menard, W. Fischer, J. Grotzinger, A. Agranier
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Abstract

The Ediacaran age (ca. 570 Ma) Shuram excursion, a ca. 12h depletion in δCcarb, 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 (δFecarb) reveals an anomalous 56Fe-depletion (down to −1.05h) in strata containing the Shuram excursion, while the underlying and overlying strata have crustal δFecarb values. These depleted δ Fecarb 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
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铁同位素与埃迪卡拉纪沉积物氧化还原演化
埃迪卡拉纪(约570 Ma)的舒拉姆(Shuram)漂移(δ碳水化合物约12小时的消耗)可能记录了海洋沉积物的剧烈氧化,这与大型后生动物出现之前地球碳循环的重组有关。然而,一些地球化学指标表明,它可能记录了影响沉积物的次生过程,如沉积后蚀变。碳酸盐中铁的稳定同位素组成(δFecarb)表明,在含有Shuram偏移的地层中存在异常的56fe损耗(低至- 1.05h),而下伏和上覆地层具有地壳δFecarb值。这些在Shuram偏移期间耗尽的δ Fecarb数据反映了铁氧化物的不完全还原,受低环境有机碳含量的限制。沉积氧化铁的脉冲升高将消耗有限的有机碳池的大部分,因此在氧化铁向沉积物的碎屑输送增强期间,将产生非常低的净有机碳埋藏。这些结果暗示了舒拉姆漂移的同沉积起源,它代表了地球沉积壳的氧化还原成分向更氧化的条件的转变,可能消除了大气中长期存在的缓冲
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来源期刊
Comptes Rendus Geoscience
Comptes Rendus Geoscience 地学-地球科学综合
CiteScore
2.80
自引率
14.30%
发文量
68
审稿时长
5.9 weeks
期刊介绍: Created in 1835 by physicist François Arago, then Permanent Secretary, the journal Comptes Rendus de l''Académie des sciences allows researchers to quickly make their work known to the international scientific community. It is divided into seven titles covering the range of scientific research fields: Mathematics, Mechanics, Chemistry, Biology, Geoscience, Physics and Palevol. Each series is led by an editor-in-chief assisted by an editorial committee. Submitted articles are reviewed by two scientists with recognized competence in the field concerned. They can be notes, announcing significant new results, as well as review articles, allowing for a fine-tuning, or even proceedings of symposia and other thematic issues, under the direction of invited editors, French or foreign.
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