Floras of clastic and peat-forming Pennsylvanian wetlands: are they different? A case study from the Upper Radnice Coal (late Duckmantian), Kladno Coalfield, Czech Republic
Abstrakt
Floras of two ecologically and taphonomically different fossiliferous horrizons associated with the late Duckmantian Upper Radnice Coal in the Kladno Coalfield are compared. These fossiliferous horizons include the Velká Opuka that is a 10 or more cm thick volcaniclastic parting embedded in the coal and the Mydlák, which is a laminated mustone in the roaf of the same seam.
Observations made in coal mines suggest that the Velká opuka bears autochtonous in situ preserved peat-forming vegetation, whereas the Mydlák is a lacistrine sediment, that contains mostly clastic wetlands. Material from museum collections and our own field data show that floras of both fossiliferous horizons consist of representatives of the same families and genera but differ in their proportions and to a large part in species composition.
This is demonstrated by only 40 % overlap of 89 plant species identified in both horizons. Flora of the Velká opuka is dominated by lycopsids, either by arborescent lepidodendrids or by the sub-arborescent genus Omphalophloios.
Co-dominant are sphenopsids and locally common are ferns and cordaitaleans. The Mydlák flora is more diverse and dominated by pteridosperms, whereas the proportion of lycopsids is lower and their composition partly different.
Taxa abundant in the Velká opuka and nearly absent in the Mydlák include Omphalophloisos feistmantelii, Lepidodendron longifolium and L. ophiurus. Abundant in the Mydlák and mostly missing in the Velká opuka are Laveineopteris tenuifolia, L. bohemica, Sphenopteris spiniformis, Eusphenopteris mummularia, Lepidodendron aculeatum and L. mannebachense.
Prevalence of pteridosperms in clastic wetland floras of the Mydlák is in agreement with existing observations.