Carbon isotope variability across the Ediacaran Yangtze platform in South China: Implications for a large surface-to-deep ocean δ¹³C gradient

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• 作者：Ganqing Jiang ; Alan J. Kaufman ; Nicholas Christie-Blick ; Shihong Zhang ; Huaichun Wu
• 关键词：Neoproterozoic ; Ediacaran ; carbon isotopes ; Doushantuo Formation ; Dengying Formation ; Yangtze platform ; South China
• 刊名：Earth and Planetary Science Letters
• 出版年：2007
• 出版时间：15 September 2007
• 年：2007
• 卷：261
• 期：1-2
• 页码：303-320
• 全文大小：3019 K

文摘

New isotope data obtained from relatively conformable, carbonate-rich strata of the Ediacaran Yangtze platform in South China reveal substantial δ¹³C variability. In platform sections, four negative δ¹³C anomalies with a nadir down to ≤− 8‰ (PDB) are present in the interval between the cap carbonate level ( 635 Ma) and the Precambrian/Cambrian boundary ( 542 Ma), while in slope and basinal sections, δ¹³C values are negative through the entire Doushantuo Formation ( 635–551 Ma). If these δ¹³C values are close to their primary seawater signature, they imply a strong (≥ 10‰) surface-to-deep ocean δ¹³C gradient that is consistent with long-term deep ocean anoxia and the presence of a large dissolved organic carbon (DOC) reservoir. The two prominent negative δ¹³C excursions within the Doushantuo Formation above the cap carbonate level are associated with shoaling and local exposure of the platform. The anomalies may thus record remineralization of a large oceanic DOC pool via sulfate reduction that transferred ¹³C-depleted carbon from the oceanic DOC reservoir to the surface ocean during regression. Inconsistencies in Ediacaran δ¹³C profiles globally and variations in South China in particular highlight the need for further evaluation of local departures in δ¹³C from an inferred average seawater signature.