New data are reported on occurrences of calcareous algae and other concurrent groups of fossils in the transient Vendian-Cambrian deposits of the western Altai-Sayan Folded Area (East Sayans, Gornaya Shoria, Kuznetsk Alatau, and Gorny Altai). There are two successive algal complexes: lower — with Korilophyton, Gemma, Razumovskia, Girvanella, Proaulopora, and Renalcis; upper — the same, supplemented with abundant species of the genus Epiphyton and with the genera Batinevia, Tubophyllum, and Subtifloria. These complexes are compared with the Nemakit-Daldyn (Upper Vendian) and Tommotian (Lower Cambrian) associations of algae of the Siberian Platform. A conclusion is made that the lower boundary of the Cambrian in the Altai-Sayan Folded Area can be tentatively drawn where the lower complex is replaced by the upper one. These inferences receive support from rare findings of small shelly fossils.

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