Abstract—

This paper presents new age estimates and results obtained by the chemostratigraphic study of dolostones of the Billyakh Group, which consists of the Kotuikan and the Yusmastakh formations. The Billyakh Group forms the upper part of the Riphean section of the Anabar uplift in northern Siberia. The stepwise dissolution technique was used for the first time to determine the ⁸⁷Sr/⁸⁶Sr, ²⁰⁶Pb/²⁰⁴Pb, and ²⁰⁷Pb/²⁰⁴Pb isotopic ratios in dolostones. The Rb‒Sr systematics was studied by the chemical removal of about a third of the crushed sample (fraction L1) by the preliminary acid leaching in 0.2 N CH₃COOH and the subsequent partial dissolution (fraction L2) of the remaining part of the sample in CH₃COOH with the same concentration. The Pb‒Pb isotope systematics of dolostones was studied by the six-step dissolution of crushed samples in 0.5 N HBr. These procedures led to the removal of secondary carbonate material and greatly improved the quality of Sr chemostratigraphic and geochronological information. The initial ⁸⁷Sr/⁸⁶Sr ratios of the least altered carbonate material (fraction L2) of the Billyakh Group dolostones are 0.70502 ± 0.00029 in the Kotuikan Formation, 0.70519 ± 0.00026 in the lower subformation of the Yusmastakh Formation, and 0.70511 ± 0.00018 in the upper subformation of the Yusmastakh Formation. The Pb‒Pb age of early diagenesis of Kotuikan and Yusmastakh dolostones (1519 ± 18 Ma at MSWD = 1.8) was calculated from the results obtained for carbonate fractions L3–L6. Secondary carbonate fractions L1‒L2 are characterized by a Pb‒Pb age of 1466 ± 54 Ma at MSWD = 0.6. The δ¹³C values vary from ‒1 to ‒0.4‰ in dolostones of the Kotuikan Formation and from ‒0.4 to +0.8‰ in those of the Yusmastakh Formation (from ‒0.1 to +0.4‰ in the lower subformation and from ‒0.4 to +0.8‰ in the upper subformation). Comparison of these variations, as well as variations in the initial ⁸⁷Sr/⁸⁶Sr ratios in dolostones of the Kotuikan Formation and the Lower and Upper Yusmastakh subformations (0.70460‒0.70499, 0.70450‒0.70525, and 0.70462‒0.70523, respectively), does not make it possible to distinguish these units on the basis of chemostratigraphic characteristics.

中文翻译：

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Anabar 隆起下 Riphean Billyakh 群白云岩中的 Sr 和 Pb 同位素组成：化学地层学和年代学中的阶梯浸出技术

摘要——

本文介绍了通过对由 Kotuikan 组和 Yusmastakh 组组成的 Billyakh 组白云岩的化学地层学研究获得的新年龄估计和结果。Billyakh 群形成了西伯利亚北部 Anabar 隆起 Riphean 段的上部。首次采用逐步溶解技术测定白云岩中⁸⁷ Sr/ ⁸⁶ Sr、²⁰⁶ Pb/ ²⁰⁴ Pb 和²⁰⁷ Pb/ ²⁰⁴ Pb 同位素比值。_{通过在 0.2 N CH 3}中进行初步酸浸，化学去除约三分之一的粉碎样品（馏分 L1）来研究 Rb-Sr 系统学。COOH 以及随后样品剩余部分在相同浓度的 CH _{3 COOH 中的部分溶解（部分 L2）。}通过粉碎样品在 0.5 N HBr 中的六步溶解研究了白云岩的 Pb-Pb 同位素系统学。这些程序导致次生碳酸盐物质的去除，并大大提高了 Sr 化学地层学和地质年代学信息的质量。最初的⁸⁷ Sr/ ⁸⁶Billyakh 组白云岩中蚀变最小的碳酸盐物质（组分 L2）的 Sr 比在 Kotuikan 组中为 0.70502 ± 0.00029，在 Yusmastakh 组下亚组中为 0.70519 ± 0.00026，在 Yusmastakh 组上亚组中为 0.70511 ± 0.00018 . Kotuikan 和 Yusmastakh 白云岩早期成岩的 Pb-Pb 年龄（MSWD = 1.8 时为 1519 ± 18 Ma）是根据碳酸盐组分 L3-L6 获得的结果计算的。次生碳酸盐组分 L1-L2 的特征是在 MSWD = 0.6 时 Pb-Pb 年龄为 1466 ± 54 Ma。δ ¹³C 值在 Kotuikan 组白云岩中从 -1 到 -0.4‰ 不等，在 Yusmastakh 组中从 -0.4 到 +0.8‰ 变化（下部亚地层从 -0.1 到 +0.4‰ 和 -0.4 到 +0.8‰在上部子地层中）。这些变化的比较，以及Kotuikan 组和下和上 Yusmastakh 亚组白云岩中初始⁸⁷ Sr/ ⁸⁶ Sr 比率的变化（分别为 0.70460-0.70499、0.70450-0.70525 和 0.70462-0.70523）没有使根据化学地层特征区分这些单位成为可能。