Biostratigraficka a paleoenvironmentalni interpretace mikrofosilii ze souvrstvi „Schneckengraben“ ve spodni skupine gosauske kridy v okoli Wörschach-Liezenu v Severnich Vapencovych Alpach

In the framework of cooperation between the Austrian Geological Survey, Czech Geological Survey and the Institute of Geology of the Czech Academy of Sciences, v. v. i., a multidisciplinary research of Mesozoic deposits has been carried out by authors of this paper over the last thirty years in the Northern Calcareous Alps including the Gosau Group. Although the biostratigraphy is here based on macrofauna, the microfossils helped to clarify both relative age of deposits and their paleoenvironment.
The “Gosau of Wörschach-Liezen“ is situated in the mountain ranges north of the Enns valley (Fig. 1) between the village of Wörschach and the district town Liezen in Styria (Steiermark). This area of the Northern Calcareous Alps is tectonically strongly disturbed and only isolated outcrops of Gosau Group sediments of the Coniacian to Paleogene age overlay the Triassic carbonate rocks (Fig. 2). The lower part of the Gosau Group sequence is represented by several hundreds of meters thick conglomerates of the Kreuzgraben Formation with isolated intercalations of bedded sandstones and grey sandy marls, which Pober (1984) called the “Schneckengraben Formation“. Sediments locally show a rich but poorly preserved brakish and/or marine macrofauna, that provides only insufficient stratigraphic data. Janoschek (1968) and Pober (1984) report finds of the ammonite Protexanites bourgeoisi (De Grossouvre), which confirm the Upper Coniacian age. Wille-Janoschek in Janoschek (1968) mentioned in the washed material indeterminable Robuli, miliolids, ostracods, small gastropods, bivalves, echinoderms, fish teeth and coal particles. However, Pober (l.c.) did not investigate any microfossils.
Detailed studies of microfauna, palynomorphs and calcareous nannofossils provided further stratigraphic and paleoenvironmental data. Samples WW1-WW5 taken at the classic locality „Schneckengraben“ and its surrounding outcrops are represented mostly by green-grey sandy claystones and grey marlstones.
Samples WW2, WW3 and WW5 provided tests of foraminifers. Relatively rich benthic foraminifers with Gaudryina pyramidata, G. rugosa Tritaxia tricarinata, Lenticulina sp., Stensioeina exsculpta, Quadrimorphina allomorphinoides, and Dorothia conula were observed only in sample WW5. Sample WW3 contains scarce foraminifers of genera Quinqueloculina a Spirilina that tolerate possible changes in water salinity.
Minor and poorly preserved calcareous nannofossils of an amount of 1-3 fragments per 10 fields of view of the microscope were found in samples WW1, WW2 and WW5. Species Micula staurophora, zone UC10 indicates the Middle Coniacian age. Presence of nannofossils confirms the marine environment.
The majority of collected sediments (samples WW1-WW4) included numerous well- preserved phytoclasts of yellow, brown and black color shades, palynomorphs with the predominance of angiosperm pollen of the Normapolles group, small reticulate tricolpates, fern spores, conifer pollen, fragments of dinoflagellate cysts, and acritarchs. Some palynomorphs were filled with pyrite crystals that resulted in their corrosion. Genus Oculopollis (Fig. 3-1) proves the Coniacian-Maastrichtian age. Palynomorphs were not found in sample WW5.

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