PALEOPHYTOSOCIOLOGICAL ASPECT OF SUBSTANTIATION OF INTERREGIONAL CORRELATION OF THE UPPER CARBONIFEROUS DEPOSITS OF THE DONETS BASIN

Abstract

The paper presents the results of a paleophytosociological substantiation of the interregional correlation of the Kasimovian and Gzhelian deposits of the Donets Basin in connection with consideration of the question of a difference in stratigraphic volumes of the Sphenopteris mathetii (= Alethopteris zeilleri) and Sphenophyllum angustifolium Zones in the Donets Basin and the Sabero Coalfield of Spain due to a diachronicity of the lower boundary of the Sphenophyllum angustifolium Zone. Paleophytosociological data about a composition and spatio-temporal dynamic of ancient plant communities give an understanding of the process of a flora development, which is recorded in the phytostratigraphic scale, and make it possible to carry out the substantiation of the correlation of phytozonal units taking into account ecological-cenotic features of vegetation cover. Based on the analysis of the literary paleoclimate and lithological-facial data and own paleophytosociological studies, it was concluded that during the early Gzhelian time, corresponding to more or less stable glacio-climatic conditions of the middle part of the interglacial interval of the Late Paleozoic glacial period, the diachronicity of the floristic changes in the basins with different types of tectonical and sedimentation processes within a single paleophytochoria may be due to the differences in ecological-landscape conditions that determined the composition and spatial differentiation of vegetation cover. The paleophytosociological studies have shown that the marking taxa of the Sphenophyllum angustifolium Zone, defining its lower boundary by the limestone O5 at the base of the Gzhelian Stage in the Donets Basin, are the diagnostic species of the paleophytocenoses, which dominated in the vegetation cover of the Donets Basin during the early Gzhelian time. The base of the Sphenophyllum angustifolium Zone in the Donets Basin corresponds to the temporal level of an appearance of these new paleophytocenoses, which were spread within coastal lowlands and delta plains. At the beginning of the Gzhelian time, these dominant plant communities of lowlands in the Donets Basin occupied less humid and waterlogged environments than the existing environments at the same time in the Sabero Coalfield of Spain where the marking fern and pteridosperm species of the Alethopteris zeilleri Zone continued to grow. The lower boundary of the Sphenophyllum angustifolium Zone in the Sabero Coalfield, which according to radiometric dating corresponds to the level located close to the limestone Р2 in the Donets Basin, is consistent with the base of the upper Odontopteris schlotheimii Subzone of the Sphenophyllum angustifolium Zone. The lower boundary of the Odontopteris schlotheimii Subzone in the Donets Basin records the temporal level reflecting а change of distribution areas of the paleophytocenosis, i.e. а change of the dominant paleophytocenosis, namely, a reduction of the plant communities on coastal lowlands and a wider distribution of the plant communities within delta plains.