Abstract

The association of organic-walled microfossils of the Kaltasy Formation, which includes morphologically complex large forms, is considered on the basis of previous and new materials. In general, the Kaltasy microbiota is similar to many associations of the Neoproterozoic (Late Riphean and Vendian) microfossils and, originally, was erroneously interpreted as Late Riphean, in spite of missing Late Riphean index taxa and geological evidence of its Early Riphean age. The Early Riphean age of the formation was supported by results of Re–Os, U–Pb, and other modern methods of isotope geochronology, whereas the low ⁸⁷Sr/⁸⁶Sr ratios and almost invariant δ¹³C values of its rocks are comparable with isotopic characteristics of the Mesoproterozoic sequences of >1300 Ma. The application of geochemical methods using high-reagent Fe (FeHR) and C and S isotopes has showed that relatively deep rocks of the Arlan Subformation of the Kaltasy Formation accumulated under aerobic oxidation conditions (ratio FeHR/FeT < 0.38). This contradicts a common concept of the presence of an anoxic ocean in the Mezoproterozoic, but explains the presence of morphologically complex large eukaryotic forms of microbiota, which were abundant in Neoproterozoic oxygenic basins.

中文翻译：

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伏尔加河-乌拉利亚地区下里phean Kaltasy组微生物群落的年龄边界和地层学重要性

摘要

在以前的和新的材料的基础上，考虑了卡尔塔斯组有机壁微化石的结合，其中包括形态复杂的大形式。通常，卡尔塔斯微生物群与新元古代（晚里菲安和文迪安）微化石的许多相似，并且最初被错误地解释为晚里菲安，尽管缺少了晚里菲安索引类群和早期里菲安时代的地质证据。形成的早期年龄里菲用的Re-Os，U-Pb和同位素年代学的其他现代方法的结果，支持而低⁸⁷ SR / ⁸⁶ Sr比值和几乎不变的δ ¹³其岩石的C值与> 1300 Ma的中元古代序列的同位素特征相当。使用高反应性铁（FeHR）以及C和S同位素的地球化学方法的应用表明，在有氧氧化条件下，相对较深的Kaltasy地层Arlan亚型岩石堆积（FeHR / FeT比<0.38）。这与中元古代存在缺氧海洋的一般概念相矛盾，但是解释了形态复杂的大型真核微生物群的存在，这种形态在新元古代含氧盆地中含量很高。