A model of cyclic recurrence (~0. 6 -1.2 myr) of three fusulinid assemblages in the Middle Pennsylvanian siliciclastic-carbonate succession of the Donets Basin is proposed. Each cycle records progressive turnover of assemblages in shallow marine environments in response to sea-level and regional climate change. A Hemifusulina-assemblage (A), adapted to cooler and reduced salinity seawater records the onset of sea level rise accompanied by humid climatic conditions. Sea level high stand is captured by the Beedeina-Neostaffella-OzawainellaTaitzehoella (or Beedeina-dominated) assemblage (B), characteristic of relatively deeper-water environments. The B assemblage is successively replaced by the most diverse population of the warm-water Fusulinella-dominated assemblage (C). This assemblage, which occurs in the upper limestones of each fusulinid cycle records the onset of sea level fall accompanied by a shift to drier conditions and likely increased seawater salinity.The proposed model permits robust interbasinal correlation of the Pennsylvanian successions of the Tethyan realm. Fusulinids of the A and C 2 assemblages are the most provincial and therefore the most useful for paleogeographic reconstructions. Specifically, they delineate originally contiguous regions that subsequently were dispersed hundreds to thousands of kilometers, whereas fusulinids of the B assemblage hold the highest potential for global correlation. Extinction at the Moscovian -Kasimovian transition of fusulinid genera of the A and B assemblages, which inhabited predominately cooler and normal salinity (perhaps hyposaline) waters, can be explained by the onset of global warming in the earliest Late Pennsylvanian. Fusulinid assemblages define various types of distribution patterns that differ by tectonic setting of the studied basins suggesting that fusulinid assemblage patterns hold potential for reconstructing the paleogeography and tectonic evolution of Pennsylvanian basins of eastern Laurasia.
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, andFusulinella?kumpani, are proposed in the interval from the top of Limestone M10to 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 gurkovensisn. sp.,Beedeina innaeformisn. sp., andFusulina sosninaen. 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. AHemifusulina-association indicates the beginning of transgression; the late transgression–high sea level stand is designated by theBeedeina–Neostaffella–Ozawainella–Taitzehoellaassemblage which is successively replaced by the most diverseFusulinella-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.
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