Abstract Late Neoproterozoic cap carbonates formed following the Cryogenian glaciations may record information about the significant climate change and ocean chemistry evolution immediately after the Snowball Earth events. Large negative carbon isotope anomalies and enigmatic sedimentary structures have been identified from the post-Marinoan cap carbonates across the globe, but their formation mechanism remains debatable due to difficulties of distinguishing overlapped chemical signatures and diagenetic alterations. In this study, we present I/(Ca+Mg) profiles of four sections from a shallow-to-deep water transect of the basal Doushantuo cap carbonates, one of the most extensively studied Ediacaran units in South China. Most samples have I/(Ca+Mg) values lower than 1 μmol/mol with a few exceptions in the shelf sections up to ∼2.5 μmol/mol. All calcite samples with extremely low δ13C have iodine signal below detection limit, suggesting carbonate precipitation from anoxic seawater or diagenetic fluids. Among the four sections, the slope section has the lowest I/(Ca+Mg) values, suggesting that it may have experienced more extensive fluid-buffered diagenesis and more severe loss of IO3–. In combination with available major, trace, rare earth element and isotope data, the temporal I/(Ca+Mg) variations support freshwater mixing and deep-water upwelling in proximal sites and transient oxidation during deposition of the Doushantuo cap carbonates.

中文翻译：

---

华南扬子地块埃迪卡拉纪陡山沱盖碳酸盐的碘记录

摘要 低温冰期形成的晚新元古代盖层碳酸盐可能记录了雪球地球事件后立即发生的显着气候变化和海洋化学演化的信息。已经从全球各地的后马里诺盖层碳酸盐中识别出大型负碳同位素异常和神秘的沉积结构，但由于难以区分重叠的化学特征和成岩改变，它们的形成机制仍然存在争议。在这项研究中，我们展示了基础陡山沱盖碳酸盐岩（华南埃迪卡拉纪单元之一）浅至深水断面的四个剖面的 I/(Ca+Mg) 剖面。大多数样品的 I/(Ca+Mg) 值低于 1 μmol/mol，只有少数样品在架子部分的值高达 ~2.5 μmol/mol。所有具有极低 δ13C 的方解石样品都具有低于检测限的碘信号，表明来自缺氧海水或成岩流体的碳酸盐沉淀。四个剖面中，斜坡剖面的 I/(Ca+Mg) 值最低，表明其可能经历了更广泛的流体缓冲成岩作用和更严重的 IO3-损失。结合现有的主要、痕量、稀土元素和同位素数据，I/(Ca+Mg)的时间变化支持近端的淡水混合和深水上升流以及陡山沱盖碳酸盐沉积过程中的瞬时氧化。表明它可能经历了更广泛的流体缓冲成岩作用和更严重的 IO3-损失。结合现有的主要、痕量、稀土元素和同位素数据，I/(Ca+Mg)的时间变化支持近端的淡水混合和深水上升流以及陡山沱盖碳酸盐沉积过程中的瞬时氧化。表明它可能经历了更广泛的流体缓冲成岩作用和更严重的 IO3-损失。结合现有的主要、痕量、稀土元素和同位素数据，I/(Ca+Mg)的时间变化支持近端的淡水混合和深水上升流以及陡山沱盖碳酸盐沉积过程中的瞬时氧化。