T0 peat-forming plant assemblage preserved in growth position by volcanic ash-fall: A case study from the Middle Pennsylvanian of the Czech Republic

Abstract

A Middle Pennsylvanian tuff bed (the Bělka bed) in the roof of the Lower Radnice Coal bears T 0 peat-forming vegetation preserved in growth position. This vegetation has been studied in detail at the 12 hectares large Ovčín 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 Ovčín coal deposit. The fossil record of the Bělka 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.• Key words: Pennsylvanian, T 0 plant assemblage, coal forests, volcanic ash beds, Radnice Basin.

 The late Paleozoic ecological–evolutionary laboratory, and land-plant fossil record perspective

“…In practice, however, a collection of plant fossils is usually analytically time averaged by sampling (Behrensmeyer et al 2000). This happens mostly because of the difficulty of tracing a "T 0 " time horizon (Johnson 2007) laterally for any distance unless it is tied to an "event" of determinable short-term duration, say an ash fall (Wing et al 1993;Opluštil et al 2014). Parautochthonous and some allochthonous assemblages generally represent either members of the same community or plants that lived in close proximity to the depositional environment, in time and space.…”

Lepidophloios acerosus Lindley and Hutton 1831 in the Carboniferous Cucuiova Formation, “Iron Gates” Natural Park (Banat, Romania)

“…A similar species to Lepidophloios acerosus is L. laricinus Sternberg 1825, but the latter has much broader than long leaf cushions, a central position of the leaf scar and a less prominent keel. Oplustil et al (2014) consider Lepidophloios acerosus a canopy taxon, recording it within the lower part of the Radnice Member of the Kladno Formation, in Ovcin, Czech Republic. There, Lepidophloios acerosus is recorded as Bolsovian (Westphalian C) in age.…”

Revision of Dendraena pinnatilobata Němejc from the Pennsylvanian of the Czech Republic

“…Němejc's (1934) (respectively Feismantel's) specimens show more or less large parts of plant remains while our new examination of the locality section provided only several millimetres large plant detritus concentrated to thin discrete zones. Thin discrete zones with common plant detritus rarely accompanied by larger parts of plants are known from the upper re-deposited whetstone part of the Whetstone Horizon in the Radnice Basin (Opluštil et al 2014). These authors stated that plant remains preserved in this upper whetstone part of Whetstone Horizon originally grew probably at valley margins or adjacent hill slopes and subsequently, where they were buried by volcanic ash and subsequently drifted as unconsolidated volcanic ash was washed by rains down the valley.…”