A new Permian bivalve zonal scale of northeastern Asia. Article 1: Zonal subdivision

Extensive new data obtained during the recent decade on several Permian reference sections in the northern, western, and southern Verkhoyansk region; the Balygychan block; the Omolon massif; and some adjacent regions provided grounds for substantial refining of the Permian bivalve zonal scale of northeastern Asia. The modified version of this scale includes 24 biostratigraphic units ranked as zones, subzones, and faunal beds. Zonal assemblages of bivalve mollusks were refined and supplemented, and the age of the zones was specified and substantiated. The stratigraphic distribution of the defined bivalve taxa is illustrated by a special detailed table.