A number of ecological and geochemical transformations occurred during late Ediacaran and early Cambrian time, the effects of which are difficult to overestimate. However, the strong linkage of biostratigraphic and chemostratigraphic methods with lithofacies makes the localization of the Precambrian–Cambrian boundary and its correlation with lithologically contrasting sections highly debatable. We analyse the taxonomy and stratigraphic distribution of small skeletal fossils and trace fossils, the carbonate carbon and oxygen isotope composition, and U–Pb detrital zircon age in the Ediacaran–Cambrian transitional interval of the Irkutsk Cis–Sayans Uplift (southwestern Siberian Platform). This interval (Moty Group) comprises a transgressive succession with red-coloured alluvial to deltaic siliciclastic deposits (Shaman Formation) and overlying shallow-marine carbonates (Irkut Formation). The lower Irkut Formation hosts sporadic and poorly preserved tubular Cambrotubulus fossils, which are known from both the terminal Ediacaran Period (c. 550–541 Ma) and the Terreneuvian Epoch (541–521 Ma), and typical Fortunian trace fossils, including an index ichnotaxon of the Cambrian boundary Treptichnus pedum. The biostratigraphic and carbonate carbon isotope data and U–Pb concordia ages of 531.1 ± 5.2 Ma (mean weighted, 530.6 ± 5.3 Ma) of the five youngest zircon grains from the lower Irkut Formation indicate that at least the shallow-marine carbonates of the upper Moty Group correspond to the Cambrian Stage 2 (c. 529–521 Ma). In the Irkutsk Cis–Sayans Uplift, the Cambrian Period tentatively began before or during the accumulation of the alluvial to deltaic siliciclastic Khuzhir and Shaman formations, and this crucial divide remained unmarked in the palaeontological and isotopic records.

中文翻译：

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西伯利亚台地西南部伊尔库茨克-萨彦隆隆起埃迪卡拉-寒武纪过渡层的碎屑锆石年龄和生物地层和化学地层限制

埃迪卡拉纪晚期和寒武纪早期发生了许多生态和地球化学变化，其影响难以高估。然而，生物地层学和化学地层学方法与岩相的紧密联系使得前寒武纪-寒武纪边界的定位及其与岩性对比剖面的相关性备受争议。我们分析了伊尔库茨克独联体-萨彦斯隆起（西伯利亚西南部）埃迪卡拉纪-寒武纪过渡段的小型骨骼化石和微量化石的分类学和地层分布、碳酸盐碳和氧同位素组成以及 U-Pb 碎屑锆石年龄。该层段（Moty 组）包括一个海侵层系，带有红色冲积层至三角洲硅质碎屑沉积物（Shaman 组）和上覆的浅海相碳酸盐岩（Irkut 组）。下伊尔库特组有零星且保存不良的管状剑管从埃迪卡拉纪末期已知的化石（C。550–541 Ma) 和 Terreneuvian 纪 (541–521 Ma)，以及典型的 Fortunian 痕迹化石，包括寒武纪边界的索引 ichnotaxon香菇. 来自 Irkut 组下部的五个最年轻的锆石颗粒的生物地层和碳酸盐碳同位素数据和 U-Pb concordia 年龄为 531.1 ± 5.2 Ma（平均加权，530.6 ± 5.3 Ma）表明，至少上部的浅海相碳酸盐Moty Group对应寒武纪第二阶段（C。529-521 马）。在伊尔库茨克独联体-萨彦隆隆起，寒武纪暂时开始于冲积层至三角洲硅质碎屑 Khuzhir 和萨满地层的堆积之前或期间，而这一关键分界在古生物学和同位素记录中仍未标记。