A fusulinoidean taxonomic study of the Gurkovo and Kalinovo sections allows us to refine the biostratigraphy of the poorly studied Myachkovian (upper Moscovian) strata of the “N” Formation in the Donets Basin. Three fusulinid biozones, Hemifusulina graciosa–Fusiella spatiosa, Fusulina cylindrica–Fusulinella pseudobocki, and Fusulinella ? kumpani, are proposed in the interval from the top of Limestone M10 to the base of N3, and they are correlated with coeval strata in the historical type area of the Moscow Basin. A total of 33 fusulinid species and subspecies belonging to eight genera are described, including three new species: Hemifusulina gurkovensis n. sp., Beedeina innaeformis n. sp., and Fusulina sosninae n. sp. The main evolutionary trend in fusulinoidean morphology in the late Moscovian is the appearance of massive secondary deposits in the limestone of the “N” Formation.
Specific temporal and distributional patterns of the Middle Pennsylvanian fusulinoidean assemblages indicate variations in sea level stand. Variations are cyclic, with periods ∼600,000–1,000,000 years. A Hemifusulina-association indicates the beginning of transgression; the late transgression–high sea level stand is designated by the Beedeina–Neostaffella–Ozawainella–Taitzehoella assemblage which is successively replaced by the most diverse Fusulinella-dominant association, which occupied a progressively shallowing sea.
The similarity of fusulinoidean assemblages in the Moscow and Donets Basins and their cognate evolution trends reveal a connection between both regions at least during Podolskian–Myachkovian time.