Thick carbonate-dominated successions in northwestern Siberia document secular variations in the C-isotopic composition of seawater through Mesoproterozoic and early Neoproterozoic (Early to early Late Riphean) time. Mesoproterozoic dolomites of the Billyakh Group, Anabar Massif, have delta 13C values that fall between 0 and -1.9 permil versus PDB, with values in the upper part of the succession (Yusmastakh Formation) consistently higher than those of the lower (Ust'-Il'ya and Kotuikan formations). Consistent with available biostratigraphic and radiometric data, delta 13C values for Billyakh carbonates compare closely with those characterizing early Mesoproterozoic carbonates (about 1600-1200 Ma) worldwide. In contrast, late Mesoproterozoic to early Neoproterozoic limestones and dolomites in the Turukhansk Uplift exhibit moderate levels of secular variation. Only the lowermost carbonates in the Turukhansk succession (Linok Formation) have delta 13C values that approximate Billyakh values. Higher in the Turukhansk succession, delta 13C values vary from -2.7 to +4.6 permil (with outliers as low as -5.0 permil interpreted as diagentically altered). Again, consistent with paleontological and radiometric data, these values compare well with isotopic values from 1200 to 850 Ma successions elsewhere. Five sections measured in different parts of the Turukhansk basin show nearly identical patterns of variation, confirming that carbonate delta 13C correlates primarily with time and not facies. The Siberian sections illustrate the potential of integrated biostratigraphic and chemostratigraphic data in the intra- and interbasinal correlation of Mesoproterozoic and early Neoproterozoic rocks.

中文翻译：

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元古代碳酸盐的碳同位素组成；西伯利亚西北部的 Riphean 层序（阿纳巴尔地块、图鲁汉斯克隆起）

西伯利亚西北部的以碳酸盐为主的厚层序列记录了中元古代和新元古代早期（早到晚五世早期）海水 C 同位素组成的长期变化。Anabar Massif 的 Billyakh 群中元古代白云岩的 delta 13C 值与 PDB 相比介于 0 到 -1.9 permil 之间，层序上部（Yusmastakh 组）的值始终高于下部（Ust'-Il） 'ya 和 Kotuikan 编队）。与现有的生物地层学和辐射测量数据一致，比利亚克碳酸盐岩的 delta 13C 值与世界范围内早期中元古代碳酸盐岩（约 1600-1200 Ma）的特征值非常接近。相比之下，Turukhansk 隆起中晚中元古代至早新元古代灰岩和白云岩表现出中等程度的长期变化。只有 Turukhansk 层序（Linok 组）中最底层的碳酸盐岩具有与 Billyakh 值近似的 delta 13C 值。在Turukhansk 序列中较高的delta 13C 值在-2.7 到+4.6 permil 之间变化（异常值低至-5.0 permil 被解释为diagentically 改变）。同样，与古生物学和辐射测量数据一致，这些值与其他地方 1200 至 850 Ma 序列的同位素值比较良好。在图鲁汉斯克盆地不同部分测量的五个剖面显示出几乎相同的变化模式，证实碳酸盐三角洲 13C 主要与时间相关，而不是与相相关。