Several sections of Lower and Middle Cambrian series have been studied on the Khorbosuonka River. Our analysis of stratigraphic distribution of trilobites and brachiopods permitted refinement of biostratigraphic zonal subdivision of Lower and Middle Cambrian deposits. Intervals corresponding to all regional zones of the Atdabanian Stage have been established in the section for the first time. Because of poor paleontological description, no local biostratigraphic subdivisions corresponding to the Profallotaspis jakutensis and Fallotaspis Zones have been recognized in the intervals of Section 1. We have established local biostratigraphic zones, Pagetiellus anabarus and Judomia mattaiensis–Uktaspis granulata, counterparts of the regional zones Pagetiellus anabarus–Nevadella and Judomia–Uktaspis (Prouktaspis), respectively. The preceding zonal subdivision has been confirmed for the Botomian and Toyonian Stages. We only propose to use the name Protolenus–Nelegeria lata instead of Protolenus borealis for the first local biostratigraphic zone. A local biostratigraphic zone, Triplagnostus gibbus, corresponding to the regional Triplanognostus gibbus Zone, has been recognized in the Amgan Stage, at the bottom of the Kuonamka Formation. Beds with Anomocarioides limbataeformis have been established in the Mayan Stage, in the upper half of the Yunkyulyabit-Yuryakh Formation. Of the paleontological collection of trilobites and brachiopods, several forms have been identified as new taxons.

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