Fossil mega- and microflora from the Březno Beds s.s. (Bohemian Cretaceous Basin, Coniacian)
Introduction
The present paper is the fourth from a series dealing with Coniacian vegetation of the emerged palaeohighs within the Central European Archipelago in the seaway between the Tethys and the northern ocean (Fig. 1A). The systematic description of the flora from the East Sudetic Island (Idzików beds) was given in a monograph by Halamski and Kvaček (2015), the palaeoecological analysis and palaeoclimatological inferences being published separately (Kvaček et al., 2015). The flora from the West Sudetic Island (Chlomek or Chloumek beds, i.e. psammitic facies of the Březno Formation) was described by Halamski and Kvaček (2016). The present paper is devoted to fossil plant remains from the West Sudetic Island and the Bohemian Massif Island (= Mid-European Island) preserved in the mudstone-dominated facies (Březno Beds s.s.) of the Březno Formation. It is a revision of the material described by Bayer (1893), incorporating results of previous studies by Hluštík, 1974, Hluštík, 1979, Hluštík, 1990 on Frenelopsis and by Kunzmann (2007) on Araucaria and related foliage.
Section snippets
Geologic setting
The material studied comes from the Březno Formation (mid-lower Coniacian to lowermost Santonian; Svobodová et al., 2014), a lithostratigraphic unit of the Bohemian Cretaceous Basin (Voigt et al., 2008). More precisely, the present paper deals with plant fossils from the mudstone-dominated (pelitic) facies of the Březno Formation s.l., formerly referred to as the Březno Beds s.s. (vrstvy březenské, Priesener Schichten; Bayer, 1893, Frič, 1893, Frič, 1894, Halamski and Kvaček, 2016). This facies
Megafossils
All plant megafossils studied are preserved as leaf impressions in mudstones. Like in the “Chlomek Beds”, plant material is darker than the surrounding matrix, probably as a result of bacteria-mediated iron oxide deposition (see also Halamski, 2013). In some cases fine details of venation could be observed; overall the preservation state of the flora studied here is better than that of the “Chlomek Beds” flora. However, contrary to initial expectations, no extractable cuticles could be found.
Systematic palaeontology (megaflora)
Division Filicophyta Boureau
Class Leptosporangiatae K.I.Goebel
Fossil-genus Nathorstia Heer
Type: Nathorstia angustifolia Heer (Heer, 1880, p. 7; pl. 1, figs. 1–7).
Type locality and stratum: Patorfik, Greenland; Cretaceous.
cf. Nathorstia sp.
Plate I, 3
Material: Podlesí: pinnule fragment NMP F4659.
Description: Preserved fragment subparallel-sided, 7–9 mm wide and over 3 cm long. Margin entire. Venation consisting of a relatively stout midvein and thin anastomosing veinlets.
Remarks: Nathorstia fascia
Dinoflagellate cysts, spores, and pollen from the Březno beds
Plant microfossil assemblage consists of prevailing dinoflagellate cysts (58%), less numerous angiosperm pollen of the Normapolles group (26%), gymnosperm pollen (9%), and bryophyte and pteridophyte spores (7%). Palynomorphs are illustrated on Plate V. The state of preservation varies from good to poor. Some of the pollen and spores (mainly thick-walled forms) are quite well preserved but most of the dinoflagellate cysts are commonly fragmented or otherwise degraded. Relatively large quantities
Palaeoecology
The very first general observation on the available fossil plant material from the Březno Beds s.s. is that, out of 16 taxa present, most (9 or 56%) are represented by single specimens, four taxa (25%) by two specimens, and only three (Frenelopsis cf. alata, Geinitzia reichenbachii, and Sphenolepis lepidota) by more than two specimens (Table 1). The original vegetation is thus reflected in the assemblage studied in a very distorted way.
The studied assemblage is dominated by conifers in terms of
Conclusions
- 1.
The Březno Beds s.s. (mudstone-dominated facies of the Březno Formation s.l., as opposed to the sandstone-dominated facies forming the Chlomek Beds) cropping out in central part of the Bohemian Cretaceous Basin contain a moderately diverse plant assemblage (megaflora: 16 fossil-taxa; microflora: 26 terrestrial and 16 marine taxa). The terrestrial plants are Coniacian in age and have originated from the West Sudetic and Bohemian Massif Islands belonging to the European Archipelago.
- 2.
The megafossil
Acknowledgements
Photographs are by Lenka Váchová. Jaromír Váňa made the drawing and helped with collection work. The stay of ATH in Prague was financed by the European Union Seventh Framework Programme (FP7/2007–2013) under grant agreement No. 226506 (SYNTHESYS). JK was financially supported by the Ministry of Culture, Czech Republic (DKRVO 2018/04, National Museum, 00023272). Funding for the palynological study by MS was through the research plan RVO67985831 of the Institute of Geology of the Czech Academy of
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