The oxic degradation of sedimentary organic matter 1400 Ma constrains atmospheric oxygen levels

Zhang, Shuichang; Wang, Xiaomei; Hammarlund, Emma U.; Jin, Sheng; Wang, Yu; Canfield, Donald E.

doi:10.5194/bg-14-2133-2017

Cited by 47 publications

(46 citation statements)

References 70 publications

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“…The results of Diamond et al (2018) (2017), Zhang et al (2017 and Zhang, Wang et al (2015) [ FePy/FeHR are much higher than in Xiahuayuan, and are consistent with euxinic depositional conditions (Diamond et al, 2018). In Xiahuayuan, by contrast, the data are more consistent with a ferruginous depositional environment .…”

Section: Comparison Of Resultssupporting

confidence: 67%

“…The C to S ratios in unit 1 are generally lower than those from "normal marine" sediments. The organic-rich sediments from unit 1 are heavily enriched in reactive Fe, providing more iron for sulfidization, and many of them deposited under euxinic conditions Zhang et al, 2017). Indeed, the trends between C and S in unit 1 are similar to those in modern euxinic settings that accumulate high proportions of reactive Fe and where pyrite formation is not sulfide limited (Raiswell & Berner, 1985).…”

Section: Sulfur To Carbon Relationshipsmentioning

confidence: 88%

“…However, we have also generated a new data set on the δ 98 Mo of Xiamaling Formation rocks. These data were obtained from previously described core and outcrop samples collected in the Xiahuayuan region of the North China Craton ( Figure 1) Zhang, Wang et al, 2015;Zhang et al, 2017). Our analyzed samples range through units 1, 2, 3, and 4 of the Xiamaling Formation as described below.…”

Section: Me Thodsmentioning

confidence: 99%

“…The transition between unit 2 and unit 1 is gradual, and the boundary between these units has been taken as the first appearance of organic-poor, trace-metal-poor green shales that are infrequent at first, but become more frequent moving up stratigraphy Zhang et al, 2017). The green shales and black shales of unit 1 represented two different geochemical environments, and the geochemical indicators are consistent with the green shales having deposited in oxygenated waters and the black shales having deposited in anoxic waters, a mix between ferruginous and euxinic conditions Zhang et al, 2017). The transition between the green and black shale units may also have been climate controlled (Zhang, Wang et al, 2015).…”

Section: Connections Between the Xiamaling Formation And The Open Oceanmentioning

confidence: 99%

“…It seems unlikely that these fluctuations in δ 34 S were associated with frequent opening and closing of the Xiamaling basin to the global ocean. Instead, these δ 34 S variations have been explained by bottom-water fluctuating between oxic and anoxic conditions as possibly driven by climate change and subsequent changes in basin circulation Zhang, Wang et al, 2015;Zhang et al, , 2017. The 34 S-enriched pyrites were formed in the water column of euxinic waters, where sulfate reduction was incomplete allowing pyrites to capture the isotope fractionation associated with sulfate reduction .…”

Section: Sulfur Isotopesmentioning

confidence: 99%

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Paleoenvironmental proxies and what the Xiamaling Formation tells us about the mid‐Proterozoic ocean

et al. 2019

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The Mesoproterozoic Era (1,600–1,000 million years ago, Ma) geochemical record is sparse, but, nevertheless, critical in untangling relationships between the evolution of eukaryotic ecosystems and the evolution of Earth‐surface chemistry. The ca. 1,400 Ma Xiamaling Formation has experienced only very low‐grade thermal maturity and has emerged as a promising geochemical archive informing on the interplay between climate, ecosystem organization, and the chemistry of the atmosphere and oceans. Indeed, the geochemical record of portions of the Xiamaling Formation has been used to place minimum constraints on concentrations of atmospheric oxygen as well as possible influences of climate and climate change on water chemistry and sedimentation dynamics. A recent study has argued, however, that some portions of the Xiamaling Formation deposited in a highly restricted environment with only limited value as a geochemical archive. In this contribution, we fully explore these arguments as well as the underlying assumptions surrounding the use of many proxies used for paleo‐environmental reconstructions. In doing so, we pay particular attention to deep‐water oxygen‐minimum zone environments and show that these generate unique geochemical signals that have been underappreciated. These signals, however, are compatible with the geochemical record of those parts of the Xiamaling Formation interpreted as most restricted. Overall, we conclude that the Xiamaling Formation was most likely open to the global ocean throughout its depositional history. More broadly, we show that proper paleo‐environmental reconstructions require an understanding of the biogeochemical signals generated in all relevant modern analogue depositional environments. We also evaluate new data on the δ98Mo of Xiamaling Formation shales, revealing possible unknown pathways of molybdenum sequestration into sediments and concluding, finally, that seawater at that time likely had a δ98Mo value of about 1.1‰.

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