Abstract Recent studies suggest that the massive Precambrian dolomite successions were likely the products of specific seawater conditions known as “dolomite seas”. However, whether these so-called “dolomite seas” existed in the terminal Ediacaran ocean has not yet been constrained. The widespread botryoidal dolomite with well-preserved sedimentary fabrics from the Upper Ediacaran Dengying Formation (ca. 551 to 545 Ma), South China can be potentially an ideal target to constrain this issue. Results showed that within the botryoidal dolomite, fibrous dolomite cements are the dominant constituent part, and either grew upward from microbialite layers or occurred in sheet cracks within the microbialites, implying a syn-sedimentary diagenesis. Two different types of fibrous cements are newly redefined: fascicular and radial slow dolomite. Well-preserved chemical and cathodoluminescent zonations and length-slow optical characters are direct evidence for syn-sedimentary primary dolomite precipitation, different with the previous alternative interpretations of mimetic dolomitization of aragonite or high-Mg calcite precursors. In contrast, microbialite matrix consists of finely crystalline dolomicrite and preserved microbial fabrics, reveling an early mimetic dolomitization of aragonitic precursors. The dolomite precipitation and mimetic dolomitization likely occurred in coeval seawater or seawater-type fluids as indicated by comparable δ13C and 87Sr/86Sr data with global changes. In particular, the presence of primary dolomite cement precipitates within botryoidal dolomite can reflect that the specific “dolomite seas”, associated with anoxic or even euxinic shallow water conditions (inferred by redox-sensitive trace elements and REEs) and increased microbial activity, also prevailed in the terminal Ediacaran ocean. However, the occurrence of “dolomite seas” was not one occasional event, but common even if not persistent in the early to terminal Neoproterozoic oceans. This study helps to improve the understanding of “dolomite problem” and ubiquitous distribution of Precambrian dolomite worldwide.

中文翻译：

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华南扬子克拉通灯影组葡萄状白云岩岩石地球化学特征：对埃迪卡拉纪末期“白云岩海”的制约

摘要 最近的研究表明，大规模的前寒武纪白云岩序列很可能是被称为“白云岩海”的特定海水条件的产物。然而，这些所谓的“白云岩海”是否存在于埃迪卡拉纪末期海洋中，尚未受到约束。来自华南上埃迪卡拉纪灯影组（约 551 至 545 Ma）的广泛分布的葡萄状白云岩具有保存完好的沉积结构，可能是限制这一问题的理想目标。结果表明，在葡萄状白云岩内，纤维状白云岩胶结物是主要组成部分，它们要么从微生物岩层向上生长，要么出现在微生物岩内部的片状裂缝中，表明是同沉积成岩作用。新定义了两种不同类型的纤维胶结物：束状和放射状慢白云岩。保存完好的化学和阴极发光带以及长慢光学特征是同沉积原生白云石沉淀的直接证据，与之前对文石或高镁方解石前驱体的模拟白云石化的替代解释不同。相比之下，微生物岩基质由细晶白云石和保存完好的微生物织物组成，揭示了文石前体的早期模拟白云石化。具有全球变化的可比 δ13C 和 87Sr/86Sr 数据表明，白云岩沉淀和模拟白云石化可能发生在同时期的海水或海水型流体中。特别是葡萄状白云岩中原生白云岩胶结物沉淀的存在，可以反映出特定的“白云岩海”，与缺氧甚至富氧浅水条件（由氧化还原敏感的微量元素和稀土元素推断）和微生物活动增加有关，也在埃迪卡拉纪末期海洋中盛行。然而，“白云岩海”的出现并不是偶然事件，而是在早期至新元古代末期海洋中即使不持续存在也很常见。该研究有助于提高对“白云岩问题”和世界范围内前寒武纪白云岩普遍分布的认识。