Biostratigrafická a paleoenvironmentální interpretace mikrofosilií ze souvrství „Schneckengraben“ ve spodní skupině gosauské křídy v okolí Wörschach-Liezenu v Severních Vápencových Alpách

0568535 - GLÚ 2023 RIV CZ cze J - Článek v odborném periodiku
Lobitzer, H. - Svobodová, Marcela - Hradecká, L. - Švábenická, L.
Biostratigrafická a paleoenvironmentální interpretace mikrofosilií ze souvrství „Schneckengraben“ ve spodní skupině gosauské křídy v okolí Wörschach-Liezenu v Severních Vápencových Alpách.
[Microfossil record of the “Schneckengraben Formation” (Lower Gosau Subgroup of the Wörschach-Liezen, Northern Calcareous Alps) and its biostratigraphic and paleoenvironmental interpretation.]
Zprávy o geologických výzkumech = Geoscience Research Reports. Roč. 52, č. 2 (2019), s. 111-116. ISSN 0514-8057
Institucionální podpora: RVO:67985831
Klíčová slova: Northern Calcareous Alps * Lower Gosau Subgroup * Coniacian * foraminifers * palynomorphs * nannofossils
Obor OECD: Paleontology
Způsob publikování: Open access
https://app.geology.cz/img/zpravyvyzkum/fulltext/04_Lobitzer_190616.pdf

Mikrofosilie ve vzorcich WW1 až WW5 dokládaji mělké pobřežní vody s kolísáním salinity. Rozvoj zelených řas a absence marinních prvků ve vzorku WW4 dokonce upozorňují na sladké vody. Celkově lze prostředí interpretovat jako mořskou transgresi, která v oblasti Wörschach-Liezen nastala ve středním coniaku. Druh Micula staurophora, jehož první výskyt je korelován s bází zóny UC10, dokládá geologické stáří od středního coniaku výše. Nálezy sladkovodních řas Chomotriletes spolu s dinocystami rodu Chatangiella (WW4), vyskytujícími se v mělkovodním mořském prostředí, a s pylovými zrny Classopollis classoides, charakterizující maršové sedimenty, indikují mělkomořské příbřežní prostředí.

In the framework of cooperation between the Austrian Geological Survey which has financially supported field works, 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 brackish 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. WilleJanoschek 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 and Spirillina 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. If present, both foraminifers and calcareous nannofossils prove the Coniacian. Palynomorphs from WW1 and WW2 samples correspond to the Coniacian age, while those from WW3 and WW4 samples point to a wider stratigraphic range – the Senonian. The occurrence of Micula staurophora (Fig. 4-1, 2) indicates the nannoplankton zone UC10, the base of which is corellated with the Middle Coniacian (Burnett 1998). The presence of microfossils implies a shallow sea of common salinity near the land. Benthicforaminifers and nannofossils, and the absence of palynomorphs in WW5 sample show a deeper marine environment. An exception represents sample WW4 where only sporomorphs were found. Green algae Chomotriletes minor (Fig. 3-3) emphasize here fresh waters and swamps. Based on these data, the paleoenvironment can be interpreted as a shallow water near the land with fluctuating salinity and/or a gradual sea water level rising (Fig. 5). The presence of freshwater algae Chomotriletes together with dinocysts of genus Chatangiella occurring in shallow marine environment, and pollen grains Classopollis classoides characterizing the marshes deposits support the coastal waters. The above interpretations point to a marine transgression. Stratigraphic age: Middle Coniacian with possible extension to the Santonian.
Trvalý link: https://hdl.handle.net/11104/0341653