Geologie karbonskeho reliktu mezi Liskem a Hyskovem v kontextu paleobotaniky a palynologie (westphal, duckmant)

Carboniferous sediments extend in SW-NE direction in the area between the municipalities of Lísek and Hýskov. They belong to outliers of Permo-Carboniferous continental basins in Central and Western Bohemia. This small area near the town of Beroun is very well known due to historical coal mining. It was studied, particularly in the time when coal was still extracted, and samples of flora were collected (they are deposited in "Geologisches Bundesanastalt" in Vienna and National Museum in Prague). The thickness of this Carboniferous outlier is about 60-80 m. Lithology of the outlier is variable. Very coarse clastic deposits occur in the lower part of the outlier fill (near Hýskov) consisting mostly of coarse-grained conglomerates, often with a clast-supported structure, and interpreted as debris flows (Šiftancová 2005) of proximal alluvial fans. Other abundant facies occuring at these localities include fine- up to medium-grained sandstones and arkoses with ripple marks, parallel stratification, and also low angle cross-bedding, lamination that originated in fluvial paleoenvironment by changing transporting power of the streams. The deposits originated in an environment with predominantly high energy transporting power of the streams. Transported clasts of conglomerates had a size of 5-14 cm. Preserved flora from this lower part of the outlier (the so-called Stradonice flora) is found only within the so-called Whetstone Horizon, which is mainly composed of acid fine-grained volcaniclastics. These sediments are likely to have been deposited in a shallow depression with episodic streams. In general, the prevailing paleoenvironment in this area was not favourable for peat-forming as follows from ecology and identified floral assemblage of this stratigraphic level. The flora does not represent a typical wetland assemblage like at some other sites of the Whetstone Horizon in the Central and Western Bohemian basins. The assemblage is composed of progymnosperms (Rhacopteris elegans), endemic pteridosperms [Havlenaea (Odontopteris) stradonicensis, Havlenaea (Mixoneura) praeovata, "Mixoneura" muensterifolia, "Triphyllopteris" rhomboidea, etc.] and cordaitaleans - Cordaites borassifolius. Lycopsids and sphenopsids are rare. The upper part of the strata sequence in the studied outlier (close to Lísek) consists mainly of fine-grained clastic and organogenic sediments like coal seams, grey and black claystones, siltstones and fine- grained sandstones. Coarse-grained arkoses and sandstones, and conglomerates lie at the base of the section. The lithology of the entire upper part of the strata sequence reflect the changing transportation power of streams and ending up with prevailing sedimentation from suspension and peat forming. This assumption was confirmed by a study of flora collected at waste rock dump near an abandoned coal mine. This Duckmantian flora represents a wetland assemblage where lycopsids (Lepidodendron acutum, Lepidofloyos laricinus), sphenopsids (Sphenophyllum myriophyllum, Calamites sp.), and lyginopterid pteridosperm (e.g. Sphenopteris nummularia and S. obtusiloba) are most abundant. Such assemblage indicates a steady climate with little or no seasonal changes.
Megaspores and miospores were studied from Lísek, Stradonice and Zdejcina. Lycospora and Microspinosporites prevail in coal and carbonaceous shales. Lycophyte spores dominate (Lycospora) and megaspores Cystosporites or Microspinosisporites and megaspore Lagenoisporites , which are common in some samples, were isolated from Lepidostrobus and Flemingites cones. Sub-arborescent lycophytes (Spencerites and Polysporia) and herb lycophyte (Selaginella) were identified using spores.