Globorotaliid intervals of the sub-evaporite badenian (Middle Miocene) in the upper silesia basin (Central Paratethys, Poland)

Abstract

Globorotaliids of the Skawina Formation (Badenian) come from deposits representing CPN 7 {Orbulina suturalis Zone) and CPN 8 sub-evaporite Wielician (Globigerina druryi-G. decoraperta Zone alias Uvigerina costaiZone) age. There are two taxonomic groups of globorotaliids in the studied mate rial: globoconellids (Globoconella bykovae and G. minoritesta) and jenkinsellids (Jenkinsella mayeri and J. transsylvanica). There are five stratigraphically-rank intervals of these foraminifers prior to the Middle Badenian salinity crisis in Central Paratethys. The investigated Badenian begins with G. bykovae-J. mayeri association followed by the first occurence (FO) of J. transsylvanica. The closing member of the CPN 7 biozone is the G. bykovae-J. transsylvanica assemblage. The jenkinsellids disappear during CPN 7: J. mayeri first and J. transsylvanica after. Since the base of CPN 8 in situ jenkinsellids have not been noted in the Badenian deposits. The CPN 8 begins with a stratigraphic interval barren of globorotaliids (biozone IIC in the Pollsh Paratethys). It is followed by episodic appearances of globoconellids (G. bykovae and G. minoritesta) in the sub-evaporite Wielician (IID biozone in Poland). G. minoritesta has been found in only one case so far. The globorotaliid stratigraphic units are distinct and well-correlated with changes in climate and the circulation of water masses in Paratethys. This study provides additional data on Mi3 in Paratethys. It documents a cryptic cooling event in the late Orbulina suturalis Zone (mid CPN 7) located at the late IIA-B as-semblage (alias upper lagenide zone) in regional biostratigraphic scale. The event is recorded by J. transsylvanica Acme, matching with circa 1%oVPDB δ18O positive excursion. The event must have resulted in a considerable sea level drop - a trigger of the Moravian ecosystem demolition in the Paratethys environment.