Comparison of Ediacaran platform and slope δ238U records in South China: Implications for global-ocean oxygenation and the origin of the Shuram Excursion
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Comparison of Ediacaran platform and slope δ238U records in South China : Implications for global-ocean oxygenation and the origin of the Shuram Excursion. / Cao, Mengchun; Daines, Stuart J.; Lenton, Timothy M.; Cui, Huan; Algeo, Thomas J.; Dahl, Tais W.; Shi, Wei; Chen, Zhong Qiang; Anbar, Ariel; Zhou, Yao Qi.
In: Geochimica et Cosmochimica Acta, Vol. 287, 2020, p. 111-124.Research output: Contribution to journal › Journal article › Research › peer-review
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TY - JOUR
T1 - Comparison of Ediacaran platform and slope δ238U records in South China
T2 - Implications for global-ocean oxygenation and the origin of the Shuram Excursion
AU - Cao, Mengchun
AU - Daines, Stuart J.
AU - Lenton, Timothy M.
AU - Cui, Huan
AU - Algeo, Thomas J.
AU - Dahl, Tais W.
AU - Shi, Wei
AU - Chen, Zhong Qiang
AU - Anbar, Ariel
AU - Zhou, Yao Qi
PY - 2020
Y1 - 2020
N2 - The Ediacaran Shuram negative carbon isotope excursion (SE) records major paleoceanographic changes during the late Neoproterozoic, possibly linked to a global oceanic oxygenation event, yet its cause(s) remain uncertain. Earlier studies of the upper Ediacaran Doushantuo Formation in South China based on local redox proxies have documented strong spatial redox heterogeneity along shelf-to-basin transects, but variations of δ238U (a global redox proxy) have not yet been examined in deep-water SE carbonates. In this study, we examined δ238U variations through the SE in the upper slope Siduping section. Similar to platform SE sections, Siduping exhibits a shift toward higher δ238U values correlative with the peak of the SE (i.e., maximum negative δ13Ccarb), confirming inferences of global ocean oxygenation during the SE. This raises an apparent paradox, because a global negative carbon isotope excursion implies net oxidant consumption, requiring an ocean-based oxygenation mechanism. We hypothesize that an increase in the efficiency of phosphorus burial due to a plankton-driven shift from dominantly dissolved organic matter (DOM) cycling to greater particulate organic matter (POM) export depleted the ocean of nutrient phosphorus. By producing a steep redox gradient close to the sediment-water interface, we suggest that ocean oxygenation also triggered a globally simultaneous diagenetic event in which isotopically light δ13Ccarb was precipitated in authigenic carbonate minerals. This scenario can account for δ238U differences between shallow-water and deep-water carbonates, which reflect precipitation of relatively larger amounts of authigenic carbonate minerals in shallow-water settings, generating both a larger negative δ13Ccarb shift and a larger early diagenetic δ238U offset.
AB - The Ediacaran Shuram negative carbon isotope excursion (SE) records major paleoceanographic changes during the late Neoproterozoic, possibly linked to a global oceanic oxygenation event, yet its cause(s) remain uncertain. Earlier studies of the upper Ediacaran Doushantuo Formation in South China based on local redox proxies have documented strong spatial redox heterogeneity along shelf-to-basin transects, but variations of δ238U (a global redox proxy) have not yet been examined in deep-water SE carbonates. In this study, we examined δ238U variations through the SE in the upper slope Siduping section. Similar to platform SE sections, Siduping exhibits a shift toward higher δ238U values correlative with the peak of the SE (i.e., maximum negative δ13Ccarb), confirming inferences of global ocean oxygenation during the SE. This raises an apparent paradox, because a global negative carbon isotope excursion implies net oxidant consumption, requiring an ocean-based oxygenation mechanism. We hypothesize that an increase in the efficiency of phosphorus burial due to a plankton-driven shift from dominantly dissolved organic matter (DOM) cycling to greater particulate organic matter (POM) export depleted the ocean of nutrient phosphorus. By producing a steep redox gradient close to the sediment-water interface, we suggest that ocean oxygenation also triggered a globally simultaneous diagenetic event in which isotopically light δ13Ccarb was precipitated in authigenic carbonate minerals. This scenario can account for δ238U differences between shallow-water and deep-water carbonates, which reflect precipitation of relatively larger amounts of authigenic carbonate minerals in shallow-water settings, generating both a larger negative δ13Ccarb shift and a larger early diagenetic δ238U offset.
KW - Carbon isotopes
KW - CIE
KW - Doushantuo
KW - Neoproterozoic
KW - Ocean redox
KW - Uranium isotopes
U2 - 10.1016/j.gca.2020.04.035
DO - 10.1016/j.gca.2020.04.035
M3 - Journal article
AN - SCOPUS:85085296386
VL - 287
SP - 111
EP - 124
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
SN - 0016-7037
ER -
ID: 242288226