The Whetstone Horizon (Bolsovian) with in situ preserved flora in the locality Kamenný Újezd near Nýřany (Pilsen Basin)
Abstract
In the Nýřany coalfield in southern part of the Pilsen Basin coals of the Nýřany (Asturian) and Radnice (Bolsovian) members crop near the surface between the villages Pankrác and Blatnice. The roof of the Lower Radnice Coal consists of a layer of kaolinised vitrocrystalic tuff bed called the „bělka“ and is followed by redeposited volcaniclastics forming together the Whetsone Horizon.
The tuff bed preserves fossils of coal-forming vegetation buried in situ by volcanic ash fall. Historical collections from the area show that the volcanic ash bed contains morphologically and anatomically well preserved plant fossils.
As the coal mining declined, however, these important paleontological localities in the Pilsen Basin became inaccessible and their potential for palaeoecological investigation remained unexplored. Based on the new geological survey of the area, the pit was dig at the margin of the former mining field Karel near the village Kamenný Újezd in 2012.
This exploratory pit reached 0,15 m thick fossiliferous bělka bed in the depth of 6,2 m. The bělka provided seven plant species within an exposed area of 1 m2.
Some samples were preserved not only morphologically, but also anatomically. Plant assemblage was dominated by herbaceous sphenopsid with co-dominant ferns having sphenopteroid and pecopteroid type of foliage and lepidodendrid leafy shoots.
This assemblage corresponds to that collected previously in surrounding coal mines or on their dumps. Among these previous findings remains of arborescent lycopsid Lepidodendron (=Paralycopodites) simile prevail.
The findings from tuff bed exposed by the probe show that the undergrowth consisted of Sphenophyllum cf. myriophyllum and phylophoral fern Rhodea sp. growing in otherwise lepidodendrid forest. More complex and detailed research is planned at this new locality in close future.