Stratigraphic sections in the high Precambrianlow Cambrian of Siberia are described. They have yielded the variety of fossils—archaeocyathids, gastropods, hyolithids, hyolithelminthids, poriferids, tommotiids and others—that characterize the Tommotian, Atdabanian and Lenian Stages. Some shelly fossils are found high in the Precambrian (Yudomian). The Tommotian Stage is regarded here as the lowest Cambrian unit. Trilobites first appear at the base of the Atdabanian Stage. A selection of fossils is illustrated and briefly described. Faunas from equivalent levels in Sweden (Tommotian Stage) and England (Nuneaton: Tommotian Stage; Comley: Atdabanian Stage) are cited. Comments are offered on ranges and on distribution (it is already apparent that certain Atdabanian Stage fossils are not restricted to the “provinces” identified for trilobites). The problems of recognizing primary shell-structure, the existence of symmetry-pairings, the manner of coiling of shells and the occurrence of perforations of shells (some seemingly due to boring by predators) are also discussed.

Carbon isotopic oscillations are useful to elucidate the stratigraphy and biogeochemical events around the Precambrian–Cambrian transition. New isotopic data from the Manykaj and Emyaksin formations of the eastern Anabar Uplift (Siberia) help to correlate the Lower Cambrian and Neoproterozoic–Cambrian transitional beds across the Siberian Platform. The similarity of trends and amplitudes of the carbon isotopic curves, together with biostratigraphic and sequence-stratigraphic markers from the Anabar Uplift, provide a precise correlation with the southern part of the Siberian Platform. Diagenesis of argillaceous limestones of the Emyaksin Formation has apparently not affected the primary isotopic variations. The resulting curve is nearly identical in sections about 100 km apart in the Tommotian–Atdabanian portion of the formation. Relatively frequent and pronounced isotopic oscillations in the lower beds of the Emyaksin Formation fit between features I and II of the southern Siberian isotopic reference scale but are undetected therein owing to the depositional hiatus at the base of the Tommotian Stage in its type section. This confirms the transgressive onlap from the north suggested by previous studies, and makes the appearance of the Cambrian skeletal fossils on the Siberian Platform less abrupt. The hiatus in the south appears to embrace at least two biostratigraphic zones as recognized in the north. The case is strengthened for a pre-Tommotian Cambrian Stage in Siberia, the biostratigraphic framework for which has been elaborated earlier.

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The enigmatic fossil Tumulduria incomperta Missanhevsky 1969 from the basal Tommotian Stage at ‘Dvortsy’ on the Aldan River, Siberian Platform, is reinvestigated in light of the report (Fedorov et al. 1979, Dokl. AN SSSR 249) of trilobite remains from the same beds. Comparisons of these supposed trilobites with old and new collections from ‘Dvortsy’ leave no doubt that they are identical to Tumulduria incomperta. Tumulduria is represented by phosphatic plates with a crude bilateral symmetry, consisting of a central longitudinal rounded ridge flanked by flat lateral portions. They are built of growth lamellae overlapping each other along the axis of symmetry. The surface carries prominent transverse folds and lamellar terminations. There is considerable morphological variation, and the similarity of some specimens to trilobites is only superficial. Tumulduria is interpreted as a bilaterally symmetrical metazoan with a dorsal protective plate; it probably represents a short‐lived group that left no descendants.

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