40 Ar/ 39 Ar dating and palaeoenvironments at the boundary of the early-late Badenian (Langhian-Serravallian) in the northwest margin of the Pannonian basin system

The sedimentary fill of the Danube Basin represents the northwestern part of the Central Paratethys Sea. The middle Miocene opening of the basin was associated with volcanic activity. The altered tuff to tuffite layers from the northwest part of the Danube Basin occurs within the NN5 Zone and are accompanied by volcanic sediments with andesite clasts. The biotite 40 Ar/ 39 Ar age of 13.23 ± 1.95 Ma from the Trakovice-4 (1401–1406 m) tuff to tuffite layer covers a large time span, and this is caused by the fine grain size and alterations to biotite crystals. Nevertheless, the age range thus obtained agrees with biostratigraphic ranking. Fresh amphiboles from the Madunice-3 (1200–1195 m) volcanic sandstone give a more accurate age of 13.83 ± 0.11 Ma, and date the maximum fall in sea level to the beginning of late Badenian (Serravallian). The comparison of age data obtained from sedimentological, biostratigraphic and ecological analyses documents the following: (1) major deposition and subsidence took place in the Blatné depression during the late Badenian (early Serravallian, 13.82–12.6 Ma); (2) although the beginning of late Badenian stage is marked by the Badenian Salinity Crisis, only siliciclastic deposition is recorded within the Danube Basin; (3) during the entire late Badenian stage, upwelling conditions (estuarine circulation) are linked with diversified microfossil associations and dysoxic periods; (4) Moreover, the 40 Ar/ 39 Ar age of 13.83 ± 0.11 Ma supports the employment of Globoturborotalita druryi as an index fossil for the onset of the late Badenian. Thus, the Danube Basin represents a location with a well recognised 13.8 Ma early/late Badenian (Langhian /Serravallian) boundary.