A stage subdivision of the Cambrian System is proposed. In the lower series four stages are distinguished (the Tommotian, Atdabanian, Botomian, Tojohnian); in the middle series, two (the Amga and Maya stages); in the upper series, three (the Ayusakkanian, Sakian, and Aksayan stages). The stratotypes of the stages of the lower and middle series are located on the Siberian Platform, while the stratotypes of the stages of the upper series are found in Kazakhstan (the Maly Karatau). The lower boundary of the Cambrian is drawn along the bottom of the Al. sunnaginicus Zone, the lower boundary of the middle series along the Schistocephalus Zone, and that of the upper series along the Cormagnostus simplex Zone. The Cambrian–Ordovician boundary is not quite clear yet, but it is most likely to be drawn along the bottom of the C. proavus Zone.

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