Constraints on the early Cambrian radiation and correlation of the Tommotian and Nemakit-Daldynian regional stages of eastern Siberia

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Abstract
Acritarchs of early Cambrian age occur in strata attributed to the Middle Tommotian in northeastern Siberia. A diagnostic assemblage from a part of the Tyusersk Formation referred to the Dokidocyathus regularis Zone (Middle Tommotian) at Chekurovka, and a much poorer assemblage from Ulakhan-Aldyarkhay, indicate time-equivalence with the Heliosphaeridium dissimilare–Skiagia ciliosa acritarch Zone and the correlative Holmia kjerulfi trilobite Zone in Baltica. The bulk of the species turnover which is part of the Cambrian explosion, including archaeocyathans, small shelly fossils, trilobites and acritarchs, is inferred to occur in the Skiagia ornate–Fimbriaglomerella membra-nacea (= Schmidtiellus/Rusophycus faunal zone) and H. dissimilare–S. ciliosa (= Holmia kjerulfi trilobite Zone) acritarch zones.