Abstract—

This work presents the results of the mineralogical, crystallochemical, and geochronological study of globular phyllosilicates (GPS) of glauconite–illite series from the Bakeevo Formation. This formation is the basal member of the Vendian Asha Group in the Southern Urals. The monomineral GPS fractions representing the globules varying in size and density are composed of Al-glauconite and illite. The Rb–Sr dating of the GPS of the Bakeevo Formation in combination with the modeling of cation distribution in their structure and comparison of the model data with Mössbauer and IR spectroscopy data was performed for the first time. The Rb–Sr age of the Bakeevo glauconite is 642 ± 9 Ma. The mineralogical and geochemical characteristics in combination with model calculations show that the stratigraphic significance of this age is quite reasonable. The initial ⁸⁷Sr/⁸⁶Sr ratio in the glauconitization environment is 0.7080 ± 0.0009 and is consistent within the experimental error with this ratio in the Vendian seawater. Thus, the lower boundary of the Vendian in the Southern Urals has an age of about 640 Ma.

中文翻译：

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Bakeevo组青灰岩的Rb-Sr年龄证明南乌拉尔文迪纳下界

摘要—

这项工作介绍了来自Bakeevo组的辉绿岩-伊利石系列球状层状硅酸盐（GPS）的矿物学，晶体化学和地质年代学研究的结果。该组织是乌拉尔南部南部Vendian Asha集团的基础成员。代表小球尺寸和密度变化的单矿物GPS组分由铝青石和伊利石组成。首次进行了Bakeevo组GPS的Rb-Sr测年，结合结构中阳离子分布的建模以及模型数据与Mössbauer和IR光谱数据的比较。Bakeevo青绿石的Rb–Sr年龄为642±9 Ma。矿物学和地球化学特征与模型计算相结合表明，该年龄的地层意义是相当合理的。青光岩化环境中的⁸⁷ Sr / ⁸⁶ Sr比值为0.7080±0.0009，在Vendian海水中，该比值在实验误差范围内是一致的。因此，乌拉尔山脉南部的文迪安的下界年龄约为640 Ma。