Environmental perturbations around the Badenian/Sarmatian (Middle Miocene) boundary in the Central Paratethys: Micropalaeontological and organic geochemical records

Abstract

The boundary between the two regional Middle Miocene stages (the Badenian and Sarmatian) of the Central Paratethys is associated with the largest faunal turnover event in the Paratethys realm. A recent study performed in the northern Polish Carpathian Foredeep revealed that the Badenian/Sarmatian boundary is coeval with a major change in benthic and planktonic foraminiferal assemblages that occurs a few metres below the beginning of the Anomalinoides dividens Interval Zone in our section. The lowermost Sarmatian biozone is the Elphidium angulatum Partial Range Zone, and its lower boundary corresponds to the disappearance of almost all Badenian foraminiferal species. Detailed analysis of a fully cored borehole in southern Poland using micropalaeontological tools (foraminifera and palynology) and a range of (inorganic and organic) geochemical methods indicated that during the late Badenian and almost the entire profile of Anomalinoides dividens Zone, oxic or suboxic sedimentary conditions prevailed. In the Elphidium angulatum Zone and the lowest part of the subsequent Anomalinoides dividens Zone, suboxic and anoxic conditions dominated the sea bottom. This research indicated that the sudden disappearance of marine Badenian species in the Polish Carpathian Foredeep was caused by a rapid change in basin chemistry although not necessarily it implies open marine conditions changing to brackish water environments.