MAIN STAGES OF DEVELOPMENT OF THE LATE CARBONIFEROUS FLORA AND VEGETATION IN THE DONETS BASIN AS THE BASIS OF JUSTIFICATION OF REGIONAL STRATIGRAPHIC UNITS AT THE PALAEOECOSYSTEM LEVEL

Four stages of development of the late Carboniferous vegetation cover have been established that correspond to the time intervals of four regional subdivisions of the Donets Basin − the Toretsian and Kalynovian Regional Stages, the Luganskian and Vyskrivskian Horizons of the Myronivskian Regional Stage. The analysis of phytostratigraphic and paleophytocenological data showed that the stages of vegetation development are characterized by the dominant plant communities in rank of orders of widespread landscapes. Сhanges from one stage to another are considered as the paleophytocenotic events, which are expressed by the changes of dominant communities of certain landscape types. The levels of paleophytocenotic events coincid with the bases of regional subdivisions The bases of the Toretsian and Kalynovian correspond to the levels of paleophytocenotic events, which were manifested by the formation of new communities types as a result of the evolutionary renewal of composition of wetland calamitean-fern and fern-pteridosperm forests of coastal lowlands as well as lycopsid and calamitean-fern forests of deltaic plains. The base of the Myronivskian (Luganskian Horizon) corresponds to the level of the paleophytocenotic event that was expressed by, firstly, the appearance of new communities types of seasonally dry pteridosperm woodlands of river valleys as a result of the evolutionary renewal of their composition, secondly, the appearance of new communities types of wetland calamitean-fern woodlands of coastal lowlands and calamitean-fern and pteridosperm woodlands of deltaic plains, the formation of which were due to the reduction of species compositions and the changes of dominants. The lower boundary of the Vyskrivskian Horizon corresponds to the level of the paleophytocenotic event that was expressed by the appearance of new communities types of wetland calamitean-fern and fern-pteridosperm woodlands of coastal lowlands and seasonally dry fern-pteridosperm woodlands of lacustrine-lagoon plains, the formation of which were associated with plant migrations and the appearance of new dominants. The considered paleophytocenotic events are manifestations of phytocoenogenetic processes, which led to paleophytocenotic changes, and mark main palaeoecosystem transformations in view of vegetation development stages.