Abstract The Ediacaran-Cambrian Bambui Group in Brazil records an anomalously positive excursion in carbonate carbon isotopes (δ13Ccarb) with a sustained plateau of ca. +15‰ (aka the Middle Bambui positive Excursion–MIBE). Considering that the δ13Ccarb signals in Ediacaran-Cambrian seawaters do not typically exceed +6‰, the MIBE therefore represents a profound carbon cycle anomaly in Earth’s history. Although intensive studies have been done on the Bambui Group, origins of the MIBE remain enigmatic. In order to better constrain the biogeochemical carbon and sulfur cycles during the MIBE, high-resolution chemostratigraphic analysis was conducted for both the plateau (i.e., Lagoa do Jacare Formation) and the recovering part (i.e., lower Serra da Saudade Formation) of the MIBE. Chemostratigraphic profiles reveal remarkably different values in δ13Ccarb, δ13Corg, δ18Ocarb, and δ34Spyrite between these two studied MIBE intervals. The new data show that the plateau of the MIBE is characterized by coupled higher δ13Ccarb, higher δ13Corg, and higher δ34Spyrite signals compared with the recovering part of the MIBE. Based on multiple lines of sedimentological, geochemical, and modelling evidence, we propose that the possibilities of enhanced organic carbon burial and porewater methanogenesis are insufficient to explain the MIBE. Instead, local controlling factors, including water-column methanogenesis, low-sulfate conditions, and enhanced carbonate recycling in a restricted basin may have played a role, independently or in unison, in generating this profound positive δ13Ccarb excursion. Therefore, the MIBE may reflect a local or regional event, instead of a global carbon cycle anomaly. We caution against the use of the MIBE in chemostratigraphic correlations on a global scale or any other attempt to infer global carbon cycling at that time. The biogeochemical landscape of the late Ediacaran-Cambrian basins and ocean margins may be more heterogeneous than previously thought.

中文翻译：

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全球还是本地？限制巴西中班布伊碳循环异常的起源

摘要 巴西埃迪卡拉纪-寒武纪 Bambui 群记录了碳酸盐碳同位素 (δ13Ccarb) 的异常正偏移，持续稳定期约为 +15‰（又名中班布正游览-MIBE）。考虑到埃迪卡拉纪-寒武纪海水中的 δ13Ccarb 信号通常不超过 +6‰，因此 MIBE 代表了地球历史上一个深刻的碳循环异常。尽管对 Bambui 集团进行了深入研究，但 MIBE 的起源仍然是个谜。为了更好地约束 MIBE 期间的生物地球化学碳和硫循环，对 MIBE 的高原（即 Lagoa do Jacare 组）和恢复部分（即较低的 Serra da Saudade 组）进行了高分辨率化学地层分析. 化学地层剖面揭示了这两个研究的 MIBE 区间之间 δ13Ccarb、δ13Corg、δ18Ocarb 和 δ34Spyrite 的显着不同值。新数据表明，与 MIBE 的恢复部分相比，MIBE 高原的特征是耦合更高的 δ13Ccarb、更高的 δ13Corg 和更高的 δ34Spyrite 信号。基于沉积学、地球化学和建模证据的多条线，我们提出增强有机碳埋藏和孔隙水产甲烷的可能性不足以解释 MIBE。相反，局部控制因素，包括水柱产甲烷、低硫酸盐条件和受限盆地中增强的碳酸盐循环，可能在产生这种深刻的 δ13Ccarb 正向偏移方面发挥了独立或协同作用。所以，MIBE 可能反映局部或区域事件，而不是全球碳循环异常。我们告诫不要在全球范围内使用 MIBE 进行化学地层相关性或任何其他推断当时全球碳循环的尝试。晚埃迪卡拉纪-寒武纪盆地和海洋边缘的生物地球化学景观可能比以前认为的更加异质。