Abstract

The study of mollusk fauna from the Vendian–Cambrian sections of the Western Mongolia revealed common species of mollusks between the Bayangol Formation of Mongolia and the Nemakit-Daldynian and Tommotian stages of the Siberian Platform. We show that the Cambrian lower boundary (in terms of the General Stratigraphic Chart of Russia) in the Zavkhan structural-facies zone of the Western Mongolia can be recognized in the sections by the first appearance of the following Tommotian species of mollusks, i.e. Watsonella crosbyi Grabau, Bemella jacutica (Missarzhevsky), Aldanella sibirica Parkhaev et Karlova, Merismoconcha tommotica (Zhegallo), Asiapatella undulata (Yu), Pseudoscenella taishirica (Zhegallo), Purella tenuis Zhegallo, and Protoconus orolgainicus (Zhegallo). These species compose the faunal assemblage of the Watsonella crosbyi–Merismoconcha tommotica Zone, which is traced in the middle and upper parts of the Bayangol Formation. Thus, in contrast to previous studies that placed the base of the Cambrian near the base of the Bayangol Formation, we significantly raised the lower boundary of the Cambrian system up to the level of the middle to upper part of the Bayangol Formation.

中文翻译：

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根据软体动物学资料，蒙古西部地段前寒武纪-寒武纪边界的位置

摘要

对蒙古西部文迪安-寒武纪地段的软体动物群的研究揭示了蒙古巴彦高勒组与西伯利亚地台内马吉特-达尔丁阶和托莫特阶之间常见的软体动物种类。我们表明，蒙古西部扎夫汗构造相带的寒武纪下界（根据俄罗斯地层总图）可以通过下列软体动物Tommotian种的首次出现在剖面中识别出来，即Watsonella crosbyi Grabau、Bemella jacutica (Missarzhevsky)、Aldanella sibirica Parkhaev et Karlova、Merismoconcha tommotica (Zhegallo)、Asiapatella undulata (Yu)、Pseudoscenella taishirica (Zhegallo)、Purella tenuis Zhegallo 和Protoconus orolgainicus (Zhegallo)。这些物种构成了Watsonella crosbyi-Merismoconcha tommotica区的动物群，该区位于巴彦高勒组的中上部。因此，与以往将寒武系底部置于巴彦郭勒组底部附近的研究不同，我们将寒武系下界显着抬高至巴彦郭勒组中上部水平。