Within the central part of the Soviet Arctic a set of sections exposing successive strata from the Lower Cambrian to the Ordovician has been studied in detail. On the basis of rock composition and fossils, detailed lithostratigraphic and biostratigraphic subdivisions have been established.

From the Yenesey River on the west to the right bank of the Lena on the east, lateral and vertical heterogeneity of facies is found in Cambrian deposits. However, regularities in the evolution of trilobites and distinctive changes in their assemblages with time permit subdivisions of the Cambrian into stages, zones, and horizons.

Middle Cambrian strata are underlain conformably by rocks of the Lenian Stage containing three faunal zones in the Siberian north. The boundary between the series is determined by the disappearance of the Protolenidae and the appearance of numerous Oryctocephalidae and Agnostidae. The Middle Cambrian, according to the accepted stratigraphic code of the USSR, is divided into the Amganian and Maiyanian Stages. The Amganian deposits, in spite of their facies complexity, are characterized by similar trilobite assemblages and may be subdivided into 3 zones.

The boundary between the Amganian and Maiyanian Stages is distinguished by the disappearance of characteristic Amganian species and the appearance of representatives of Anomocarioides, Metanonocare, Anopolenus, and Dorypyge. The Maiyanian beds are lithologically uniform and richly fossiliferous; this stage also includes 3 zones.

Throughout the area there was continuous sedimentation across the Middle-Upper Cambrian boundary. This boundary is based on the disappearance of Lejopyge, Anomocarina, and Bonneterrina and the appearance of species of Homagnostus, Agnostus, Damesella, Buttsia, Proceratopyge, and other genera.

Upper Cambrian deposits in the central Siberian north contain several facies each with different trilobite assemblages but, due to the presence of many common species, their contemporaneity may be established easily. Upper Cambrian trilobites are grouped into 3 large assemblages, the duration of each corresponding to a stage. Within each assemblage, fossils are grouped by species and genera into a total of 6 zones.

It is difficult to determine the Upper Cambrian boundary in continuous sections because of monotonous rocks and the undifferentiated nature of the faunas.

Middle and Upper Cambrian deposits of the Siberian north are well correlated with contemporaneous formations both within the USSR and beyond its boundaries. The mutual occurrence of forms typical of different paleozoogeographical provinces within these deposits suggests that these correlations are valid.

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