Abstract

On the basis of the analysis of literature and cartographic materials, our field observations, results of U–Pb isotope dating of zircons, and examination of paleobotanical collections, it was established that the “Mesophytic” Buor-Kemus fern–gymnosperm flora existed in Eastern Chukotka in the Late Cretaceous longer than in other regions. The volcanics of the Nyrvakinot sequence are partly facially replaced by the sedimentary deposits of the Olkhovaya Formation. Both units contain plant remains of the Buor-Kemus flora. The Amgen volcanogenic sequence lies conformably and without any hiatus on the Nyrvakinot sequence and contains “Cenophytic” plant assemblages with a significant amount of angiosperms, ascribed to the Turonian–Coniacian. These three units were previously considered as the three major constituents of the Etelkuyum Formation. The U–Pb isotope ages of zircons from volcanogenic and tuffaceous sedimentary rocks of the Nyrvakinot sequence show that they accumulated in the Late Сretaceous in the age range of 93–87 Ma (Turonian–Coniacian). Taking into account all data available, it is evident that the Buor-Kemus flora (at least within the Eastern Chukotka segment of the Okhotsk–Chukotka Volcanogenic Belt) existed in the Albian, Cenomanian, Turonian, and, probably, in the early Coniacian.

中文翻译：

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基于楚科奇东部东部海相白垩纪资料的东北亚Buer-Kemus植物区系年龄

摘要

根据对文献和制图资料的分析，我们的野外观察，锆石的U–Pb同位素定年结果以及古植物学的收集，可以确定东部东部存在“中生”的Buor-Kemus蕨类-精子植物区系。白垩纪晚期的楚科奇（Chukotka）比其他地区更长。Nyrvakinot层序的火山在部分表面上被Olkhovaya组的沉积物所取代。两个单位都包含Buor-Kemus植物区系的植物残骸。Amgen火山成因序列位于Nyrvakinot序列上，序列一致，没有任何裂隙，并且包含具有大量被子植物的“ Cenophytic”植物组合，归因于Turonian-Coniacian。这三个单元以前被认为是Etelkuyum组的三个主要组成部分。Nyrvakinot序列的火山成因和凝灰质沉积岩中锆石的U–Pb同位素年龄表明，它们在晚白垩世堆积，年龄范围为93–87 Ma（突尼斯－哥尼亚）。考虑到所有可用数据，很明显，Buor-Kemus菌群（至少在鄂霍次克–楚科奇火山火山带的东部楚科奇片段内）存在于阿尔比亚，切诺曼尼亚，土伦，甚至可能在科尼西亚早期。