Badenian–Sarmatian chronostratigraphy in the Polish Carpathian Foredeep

Abstract

The Miocene of the northern part of the Polish Carpathian Foredeep contains a record of events particularly important in the evolution of the Central Paratethys Basin. There, the Paratethyan Badenian Salinity Crisis resulted in the deposition of evaporite gypsum deposits of the Krzyżanowice Formation. The ensuing post-evaporite marine Badenian deposition is recorded by the marly Pecten Beds. The transition to the overlying clays of the Syndesmya Beds represents the initial deterioration of normal marine conditions within the basin, and is associated with the disappearance of typical stenohaline faunal components during the Badenian–Sarmatian Extinction Event, and the subsequent appearance of endemic Sarmatian taxa. The history of these Paratethyan events has hitherto been only poorly dated. New 40Ar/39Ar dating of biotite and volcanic glass from a rhyolite tuff within the Pecten Beds (Babczyn-2 core) constrains its depositional age to 13.06±0.11Ma. This age suggests that the faunal extinction presumably took place after 13.06±0.11Ma, and that the salinity crisis ended before then. This result is consistent with other reliable radiometric age constraints that collectively suggest that the crisis began shortly after 13.81±0.08Ma (de Leeuw et al., 2010), and that evaporite deposition took place ca. 13.60±0.07Ma (de Leeuw et al., 2010). Both the Badenian evaporites and the Pecten Beds in Carpathian Foredeep are thus Serravallian in age and represent the lower part of Neogene Nannoplankton Zone 6 (NN 6).