The direct precipitation model of Mn‑carbonate formation, based on investigation of the modern sedimentary record and simulation experiments, is commonly used to explain the genesis of both modern and ancient Mn‑carbonate deposits. This process is considered to be primarily influenced by physicochemical conditions and lacks microbial mediation. Despite the established role of microbes in global Mn cycling and biomineralization, the specific contribution of microbial processes to Mn‑carbonate formation remains understudied. In this study, Ediacaran Mn‑carbonates from South China with well-preserved micro-stromatolites offer a novel insight into understanding the microbes involved in the formation of Mn-deposits. Petrological observations reveal that the laminated Mn-ores mainly consist of alternating layers of dark Mn‑carbonate and light-colored dolomite laminae. Mn‑carbonate minerals, dominantly rod-like rhodochrosite crystals, exhibit a close spatial relationship with micro-stromatolites, suggesting a possible link to microbial activity. Geochemical results display that these Mn‑carbonates document high δ13C values (average = −1.65 ‰) compared to typical diagenetic Mn‑carbonate indicating the seawater likely contributed to the carbon source. Combined with alabandite deposition, small-sized pyrite framboids, and positive Eu anomalies, the Ediacaran Mn‑carbonates may have formed by microbially-mediated direct precipitation in Mn-rich anoxic seawater. The Mn‑carbonate and micro-stromatolite laminae accumulated during a period of enhanced bacterial activity, driven by episodic inputs of hydrothermal Mn2+ and bioessential elements. The present study highlights the microbially-mediated significant role in the primary precipitation pathway of Mn‑carbonate. Direct precipitation of Mn‑carbonate deposits, controlled by ocean conditions as well as enhanced by microbial processes, may account for the formation of other ancient economic manganiferous sedimentary deposits.

中文翻译：

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微生物强迫碳酸盐锰直接沉淀在华南埃迪卡拉纪微叠层石中


基于对现代沉积记录的调查和模拟实验，锰碳酸盐岩形成的直接沉淀模型通常用于解释现代和古代锰碳酸盐矿床的成因。这个过程被认为主要受物理化学条件的影响，缺乏微生物介导。尽管微生物在全球 Mn 循环和生物矿化中的作用已确立，但微生物过程对 Mn-carbonate 形成的具体贡献仍未得到充分研究。在这项研究中，来自华南地区的埃迪卡拉纪 Mn 碳酸盐和保存完好的微叠层石为了解参与 Mn 矿床形成的微生物提供了新的见解。岩石学观察表明，层状 Mn-矿石主要由深色 Mn-carbonate 和浅色白云岩层交替层组成。碳酸盐锰矿物，主要是棒状菱锰矿晶体，与微叠层石表现出密切的空间关系，表明可能与微生物活动有关。地球化学结果表明，与典型的成岩 Mn 碳酸盐相比，这些 Mn-carbonates 的 δ13C 值较高（平均值 = -1.65 ‰），表明海水可能为碳源做出了贡献。结合阿拉班岩沉积、小尺寸黄铁矿碎屑和阳性 Eu 异常，埃迪卡拉纪 Mn-carbonates 可能是由微生物介导的在富含 Mn 的缺氧海水中的直接沉淀形成的。Mn-carbonate 和微叠层石层在热液 Mn2+ 和生物必需元素的偶发输入驱动下，在细菌活性增强期间积累。本研究强调了微生物介导的 Mn-carbonate 初级沉淀途径中的重要作用。 碳酸盐锰矿床的直接沉淀，受海洋条件控制并受到微生物过程的增强，可能是其他古老的经济芒甘尼沉积矿床形成的原因。