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NON-MARINE BIVALVES FROM THE MOSPYNE FORMATION (UPPER BASHKIRIAN) OF THE DONETS BASIN: TAXONOMY, PALEOECOLOGY, AND STRATIGRAPHIC SIGNIFICANCE

Remains of non-marine bivalves are widespread in the Carboniferous of the Donets Basin (Eastern Ukraine). The studies of this group of fauna are important for stratigraphy, paleoecology and paleobiogeography. The remains of non-marine bivalves were found in sediments of the Mospyne Formation; Carbonicola obtusa (Hind) and Naiadites sp. were found in the roof shale of the g2 coal bed; Curvirimula trapeziforma (Dewar) and C. tesselata (Jones) were identified in the roof shale of the g12 coal bed, and Carbonicola rectilinearis Trueman et Weir and C. limax Wright were found in the siltstone below G12 limestone layer. The upper part of the lower half of the Mospyne Formation is attributed to the Carbonicola rectilinearis Member, which probably corresponds to the upper part of the lenisulcata Zone (Langsettian) of Western Europe. The lower limit of this member is in the floor of a thick sandstone bed 43 m below G12 limestone layer. The upper boundary of Carbonicola rectilinearis Member is situated at the g12 coal layer. The Carbonicola pseudorobusta Zone, previously identified by M.T. Sergeeva as member with fauna, is distinguished between the roof shale of the g12 coal bed and h61 coal bed. This zone corresponds to the communis Zone in Western Europe. Bivalves from the roof shale of the g12 coal layer and roof shale of the g2 coal layer lived in shallow-water eutrophic freshwater or brackish lakes in the coastal accumulation lowland. These basins were characterized by significantly reduced aquatic organism assemblage and hydrogen sulfide contamination of silts and, possibly, the bottom layer of the water column. Representatives of the genera Curvirimula and Naiadites were found in the sediments of these lakes. These genera apparently led a pseudoplanktonic lifestyle, attaching themselves to various bottom objects with byssus. The bivalves from the siltstones below the G12 limestone layer (Carbonicola) lived in a shallow-water, refreshed lagoon. 
 