The Styrian Basin: A key to the Middle Miocene (Badenian/Langhian) Central Paratethys transgressions

In the Styrian Basin, early Miocene marine sedimentation of the Karpatian (upper Burdigalian) ended with basin shallowing, marked regression and tectonic movements. The Karpatian sedimentation cycle corresponds to the global 3 rd order cycle TB 2.2, followed by the Bur5/Lan1 sea-level fall. This regression was combined with tectonic movements (the Styrian Tectonic Phase), seen in the Styrian Unconformity by an angular discordance at the Wagna and Katzengraben outcrops and also in deep wells. Sediments of the first middle Miocene (Badenian/Langhian) transgression are commonly eroded or reduced in thickness at the basin borders. In the basin center, the bathyal environment continues from the Karpatian to the Badenian. Sediments of the first Badenian transgression have been dated by calcareous nannoplankton as NN4 and correlated by the occurrence of Praeorbulina sicana with the basal Langhian. The 3 rd order sequence corresponds to TB 2.3. The erosional phase of the sea-level fall Lan2/Ser1 can only be observed in near-shore facies, followed by transgressive beds within Zone NN5, which represents the second, main Badenian transgression in the Central Paratethys and corresponds to the long global cycle TB 2. The highstand system tract of this cycle is expressed in carbonate build-ups of the Weissenegg Formation. According to the global 3 rd order sequences, the youngest sediments of the Retznei section (< 14.39 Ma) overlying the carbonate buildups belong to the falling-stage system tract of TB2, but did not record regression, but instead continuous deepening of the Styrian Basin, indicating strong subsidence during the early middle Miocene.