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 costai Zone) age. There are two taxonomic groups of globorotaliids in the studied material: 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 Polish 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 assemblage (alias upper lagenide zone) in regional biostratigraphic scale. The event is recorded by J. transsylvanica Acme, matching with circa 1‰VPDB δ 18 O positive excursion. The event must have resulted in a considerable sea level drop – a trigger of the Moravian ecosystem demolition in the Paratethys environment.