Viséan flora from the Moscow Coal Basin (Baltic Plate; European Russia): Local evolution in the context of global tendencies

Global-scale palaeoenvironmental perturbations during the Viséan Stage affected all regional plant communities within the Equatorial Belt. The Moscow Coal Basin, which occupies the central part of the present-day Russian Platform, provides an exceptional palaeobotanical record permitting to document the patterns of floral responses to the noted perturbations. A careful study of macroplant remains allowed to identify 28 species and to establish their stratigraphic ranges. Five types of plant communities evolved on the southern margin of the basin, namely flood-plain peat bogs with lycopods, semi-aquatic sphenopsids, mesophilic communities of river valleys with fern-like plants, lepidophytic communities of flood-plain clastic swamps, and coastal communities of lycopods. These communities developed on the western basin margin: peat bogs of freshwater lakeshores and flood-plains dominated by lycopsids and gymnosperms with Cordaites sp. leaves, flood-plain clastic swamps with lepidophytes, semi-aquatic sphenopsids, mesophilic communities of river valley and lake depression sides formed by plants with fern-like leaves, and coastal communities of lycopods. Two Viséan palaeophytogeographic units such as the Southern Moscow District and the Western Moscow District can be distinguished. Each belonged to the particular palaeo-river valley. In the local stratigraphic record, the Gryzlovia meyenii Assemblage Zone (Bobrikian–lower Tulian) and the Sublepidodendron shvetzovii Assemblage Zone (upper Tulian–Venevian) are delineated. A boundary between them correlates with vegetation changes traced through the entire Equatorial Belt. Thus, this boundary corresponds to a major floristic turnover. The Viséan climate does not provide an unambiguous explanation of the latter. Dynamics of the shorelines linked to the eustatic fluctuations was able, however, to affect the local plant communities. Specific “stigmarian limestones” were formed in regressive conditions, when plant colonized rapidly the coastal carbonate mud. The plate tectonics was a very important factor of plant migrations within Euramerican Floristic Realm. Pre-existed separation of the Hunic terranes and the Laurussian margin might have been responsible for differences between the Northern and Southern European palaeophytogeographic provinces.