The Late Pennsylvanian vegetation of the Donets Basin, Ukraine: Syntaxonomy of plant communities

Abstract

A reconstruction and classification of Kasimovian and Gzhelian plant communities of the Donets Basin that constituted the Late Pennsylvanian vegetation cover of the region is proposed. Reconstructions of palaeophytocoenoses are based on the identification of the floristic сomposition of fossil assemblages and the lithological-facial features of plant-bearing strata from 69 phytooryctocoenoses that were found in more than 30 plant fossil localities and 20 boreholes within the Bahmut and Kalmius–Torets depressions. The plant remains were studed from lacustrine, swamp, deltaic, floodplain and lagoonal deposits that indicate biotopes corresponding to coastal lowlands, deltaic plains, floodplains and river valley slopes. The morphological and quantitative characteristics of plant fossils indicate that these palaeophytocoenoses in different time intervals of the Late Pennsylvanian belonged to four vegetation types, namely to coastal semi-aquatic vegetation, wetland forests, wetland woodlands and seasonally dry woodlands. The classification of plant communities was conducted using the ecological and floristic approach for vegetation classification by the Braun-Blanquet method. The identification of plant community types (syntaxa) from the lowest rank (association) to the higher ranks (alliance, order, and class) was made as a result of an analysis of the floristic composition and ecological conditions of palaeophytocoenoses. The major criteria for determining the syntaxa are the diagnostic species including characteristic and differential species, which are considered as indicators of environmental conditions. The newly compiled prodromus of Kasimovian and Gzhelian plant communities consists of 11 classes, 16 orders, 21 alliances and 21 associations. The prodromus reveals the syntaxonomic composition of the Late Pennsylvanianvegetation cover of the Donets Basin and provides an understanding of past vegetation dynamics. The syntaxonomic changes of vegetation are traced in the four time intervals that are correspond to regional stratigraphic units, namely Toretskian (Kasimovian), Kalynovian (early Gzhelian), Luganskian (middle Gzhelian), and Vyskrivskian (late Gzhelian), and are characterised by the plant associations of certain classes and orders.