Abstract Paleoproterozoic sedimentary successions are important archives of the redox evolution of Earth’s atmosphere and oceans. Efforts to unravel the dynamics of our planet’s early oxygenation from this archive rely on various geochemical proxies, including stable carbon and sulfur isotopes. However, ancient metasedimentary rocks often experienced early- and late-stage (bio)geochemical processes making it difficult to discern primary environmental signals from bulk-rock δ13Corg and δ34S values. Such complexity in carbon and sulfur isotope systematics contributes to uncertainty about the redox structure of Paleoproterozoic oceans. A currently popular idea is that, following the Great Oxidation Event, global changes led to low-oxygen environments and temporally fluctuating ocean redox conditions that lasted until the Neoproterozoic. The volcano-sedimentary rocks of the Onega Basin have figured prominently in this concept, particularly the exceptionally organic-rich rocks of the 1.98 Ga Zaonega Formation. However, a growing body of evidence shows that local depositional processes acted to form the δ13Corg and pyrite δ34S records of the Zaonega Formation, thus calling for careful assessment of the global significance of these isotope records. Placing new and existing organic carbon and sulfur isotope data from the Zaonega Formation into the context of basin history and by comparing those results with key Paleoproterozoic successions of the Francevillian Basin (Gabon), the Pechenga Greenstone Belt (NW Russia) and the Animikie Basin (Canada), we show that the stratigraphic δ13Corg and pyrite δ34S trends can be explained by local perturbations in biogeochemical carbon and sulfur cycling without requiring global drivers. Despite their temporal disparity, we also demonstrate that individual successions share certain geological traits (e.g. magmatic and/or tectonic activity, hydrocarbon generation, basin restriction) suggesting that their pyrite δ34S and δ13Corg trends were governed by common underlying mechanisms (e.g. similar basinal evolution and biogeochemical feedbacks) and are not necessarily unique to certain time intervals. We further show that pyrites in these successions that are most likely to capture ambient seawater sulfate isotopic composition have consistent δ34S values of 15–18‰, which hints at remarkable stability in the marine sulfur cycle over most of the Paleoproterozoic Era.

中文翻译：

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识别古元古代有机碳和硫同位素记录的全球与盆地控制

摘要 古元古代沉积序列是地球大气和海洋氧化还原演化的重要档案。从这个档案中解开我们星球早期氧化动力学的努力依赖于各种地球化学代理，包括稳定的碳和硫同位素。然而，古老的变质沉积岩经常经历早期和晚期（生物）地球化学过程，因此很难从大块岩石 δ13Corg 和 δ34S 值中辨别主要环境信号。碳硫同位素系统学的这种复杂性导致了古元古代海洋氧化还原结构的不确定性。目前流行的观点是，在大氧化事件之后，全球变化导致低氧环境和持续到新元古代的海洋氧化还原条件的时间波动。Onega 盆地的火山沉积岩在这一概念中占有突出地位，尤其是 1.98 Ga Zaonega 组的富含有机物的岩石。然而，越来越多的证据表明，局部沉积过程形成了 Zaonega 组的 δ13Corg 和黄铁矿 δ34S 记录，因此需要仔细评估这些同位素记录的全球意义。将来自 Zaonega 组的新的和现有的有机碳和硫同位素数据置于盆地历史背景中，并将这些结果与 Francevillian 盆地（加蓬）、Pechenga 绿岩带（俄罗斯西北部）和 Animikie 盆地的关键古元古代序列进行比较（加拿大），我们表明，地层 δ13Corg 和黄铁矿 δ34S 趋势可以通过生物地球化学碳和硫循环中的局部扰动来解释，而无需全球驱动。尽管它们在时间上存在差异，但我们还证明，单个序列具有某些地质特征（例如岩浆和/或构造活动、生烃、盆地限制），表明它们的黄铁矿 δ34S 和 δ13Corg 趋势受共同的潜在机制（例如相似的盆地演化和生物地球化学反馈）并且对于某些时间间隔不一定是唯一的。我们进一步表明，这些序列中最有可能捕获环境海水硫酸盐同位素组成的黄铁矿具有一致的 δ34S 值，为 15–18‰，