Abstract

The C–O–Sr isotope composition of carbonates and the S–Sr isotope composition of gypsum were studied in the Ordovician section and the Upper Cambrian–Lower Silurian boundary horizons of the Vilyui structural-facies zone located in the central Siberian Platform. The upsection decrease of the ⁸⁷Sr/⁸⁶Sr ratio within 0.70920‒0.70795 and the value of δ³⁴S ~ 25‒28‰, typical for the reference sections of this stratigraphic interval, indicates a good connection between the basin and the World Ocean in the Ordovician and Early Silurian, but its isolation in the Late Cambrian (Kholomolokh Formation) when the ⁸⁷Sr/⁸⁶Sr ratio (0.7085) was lower than the oceanic one. The sharp ⁸⁷Sr/⁸⁶Sr ratio decrease from ~0.7087 to 0.7080 in the Khar’yalakh Formation (~45 m thick) can be correlated with the interval from the upper Darriwilian-to-upper Sandbian stages of the ICC (Middle Ordovician Volgian horizon–Upper Ordovician Baksanian or Dolborian horizon of the Russian GSS). Based on this benchmark and lithological features of the section, we discuss the causes of wide variations in δ¹³С (‒7.2 to 1.6‰) and δ¹⁸О (16.9‒29.8‰) in the carbonates, as well as a possible correlation of carbon isotope excursions in the Vilyui section with the global carbon isotope events.

中文翻译：

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西伯利亚台地维柳伊构造相带奥陶系矿床С-О-Sr-S同位素地球化学及化学地层对比

摘要

在西伯利亚地台中部维留伊构造相带的奥陶纪剖面和上寒武统—下志留统边界层进行了碳酸盐的C-O-Sr同位素组成和石膏的S-Sr同位素组成研究。⁸⁷ Sr/ ⁸⁶ Sr 比值在 0.70920-0.70795 范围内上升，δ 34 ^S ~ 25-28‰ 是该地层层段参考剖面的典型特征，表明该盆地与世界海洋之间存在良好的联系。奥陶纪和早志留世，但在晚寒武世（Kholomolokh 组）时⁸⁷ Sr/ ⁸⁶ Sr 比值（0.7085）低于海洋。锐利的⁸⁷ Sr/⁸⁶ Sr 比率在 Khar'yalakh 组（约 45 m 厚）中从 ~0.7087 下降到 0.7080 可能与 ICC 上 Darriwilian 到上 Sandbian 阶段的间隔相关（中奥陶统伏尔加地层 - 上奥陶统 Baksanian 或俄罗斯 GSS 的 Dolborian 地平线）。基于该基准和剖面岩性特征，我们讨论了碳酸盐中δ ¹³ С（-7.2 至1.6‰）和δ ¹⁸ О（16.9-29.8‰）变化较大的原因，以及可能的相关性。 Vilyui 剖面的碳同位素偏移与全球碳同位素事件。