T-0 peat-forming plant assemblage preserved in growth position by volcanic ash-fall: A case study from the Middle Pennsylvanian of the Czech Republic
Abstrakt
A Middle Pennsylvanian tuff bed (the Belka bed) in the roof of the Lower Radnice Coal bears To peat-forming vegetation preserved in growth position. This vegetation has been studied in detail at the 12 hectares large Oval coal deposit in the southern part of the Radnice Basin.
Documentation of the fossil record in six excavations and that previously collected in the former opencast mine allowed for a detailed reconstruction of the local peat-forming lepidodendrid-cordaitalean forest structured into well-developed stories. It consists of about 33 species, which colonized the occasionally flooded planar peat swamp precursor of the Lower Radnice Coal.
The canopy story of this vegetation was dominated by Lepidodendron (Paralycopodites) simile, L lycopodioides, Lepidophloios acerosus and Cordaites borassifolius. They formed a relatively dense canopy, locally interrupted with significant gaps allowing development of a rich groundcover that together with liana-like plants represents the most diverse part of the forest.
A less diverse understory composed of calamites, medullosan pteridosperms and Psaronius tree ferns displays a patchy distribution pattern presumably related to density of the canopy. The minimal area that sufficiently represents the pattern of this forest phytocoenosis is estimated to be about 200 m(2), although lower stories are well represented even within much smaller areas of about 60 m(2).
Slight heterogeneity in the population density of dominant taxa (Cordaites vs. lepidodendrid lycopsids) was documented across the Oval coal deposit. The fossil record of the Balka tuff bed also indicates that the coal-forest colonizing the peat swamp prior the generation of forest killed by volcanic ash fall, was destroyed, presumably due to long-lasting flooding and thus suggests that catastrophic events were probably a relatively common part of the evolution of peat-forming Pennsylvanian successions.