The Cryogenian Sturtian and Marinoan glaciations stand as the most extreme climate events in Earth history. Intriguingly, large-scale Mn carbonates characterize the nonglacial interlude of this period in South China. The formation mechanism of Mn carbonates and the potential correlation underlying this temporal association remain elusive. Here, we present an integrated petrographic and geochemical study of drill core materials intercepting the Mn-bearing Datangpo Formation. Rare earth element patterns of these Mn carbonates exhibit positive Ce anomalies and a lack of Y anomalies, which differ from those of modern seawater but resemble marine Mn-Fe oxides. These features, combined with negative carbonate carbon isotope compositions (δC as light as −9.9 ‰ VPDB), indicate the presence of oxide precursors and the incorporation of light carbon during Mn-carbonate precipitation. Phosphate oxygen isotope ratios (δO) of HCl-extractable apatite reveal a ∼4 ‰ difference in the average δO between Mn-rich and Mn-poor rocks. We propose that the more positive δO of Mn-rich samples may result from the dominance of phosphate released by reductive dissolution of metal oxides or a heavier oxygen isotope signal of surrounding waters with which isotopic equilibrium has been reached. We further illustrate how marine invasions into coastal anoxic basins could have triggered the formation of Mn oxides and highlight the role of glaciation–deglaciation in the development of giant Mn deposits.

中文翻译：

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斯图尔蒂安冰川作用后的水文动力学和锰矿化


成冰纪斯图尔蒂安冰川和马里诺冰川是地球历史上最极端的气候事件。有趣的是，大规模的锰碳酸盐是华南这一时期非冰期间期的特征。碳酸锰的形成机制以及这种时间关联背后的潜在相关性仍然难以捉摸。在这里，我们对截取含锰大塘坡组的钻芯材料进行了综合岩石学和地球化学研究。这些碳酸锰的稀土元素模式表现出正 Ce 异常和缺乏 Y 异常，这与现代海水的稀土元素模式不同，但类似于海洋锰铁氧化物。这些特征与负碳酸盐碳同位素组成（δ13C 轻至-9.9% VPDB）相结合，表明氧化物前体的存在以及锰碳酸盐沉淀过程中轻碳的结合。可提取 HCl 的磷灰石的磷酸盐氧同位素比 (δ18O) 显示，富锰岩石和贫锰岩石之间的平均 δ18O 差异约为 4 ‰。我们认为，富锰样品的 δ18O 值更正可能是由于金属氧化物还原溶解释放的磷酸盐占主导地位，或者是周围水域已达到同位素平衡的氧同位素信号较重。我们进一步说明了海洋入侵沿海缺氧盆地如何引发锰氧化物的形成，并强调了冰川作用-消冰川作用在巨型锰矿床发育中的作用。