The Central Paratethys during Oligocene as an ancient counterpart of the present-day Black Sea: Unique records from the coccolith limestones

摘要: Abstract Four isochronous Oligocene coccolith limestone horizons from the Carpathians were examined in order to reconstruct paleoceanographic conditions Central Paratethys. The dominance of small and size-uniform pyrite framboids, occurrence low-diversity dinoflagellate cysts coccolithophorids presence biomarker molecule 28,30-dinorhopane indicate that water column was stratified with upper being relatively well‑oxygenated, but bottom anoxic. latter is confirmed by fine consistent horizontal laminations various parts basin, scarcity benthic organisms their trace fossils. limestones exhibit typical marine δ13C values, are significantly depleted 18O enriched 87Sr relative contemporaneous ocean water. These isotopic compositions result a decreased salinity surface waters caused an increased riverine input. This lack or impoverishment planktonic foraminifers, abundance goniodomid massive nannoplankton assemblages, which indicates salinities as low 17‰ high productivity column. observations formed during periods when connection Paratethys global limited, impeded exchange causing development low-salinity bottom-water anoxia. During deposition oldest Tylawa horizon, primary enhanced chemocline positioned exceptionally Moreover, values both carbonates organic matter this horizon suggest widespread methane venting took place basin NP23. All these data show experienced similar those current Black Sea, can be used modern analogue, especially for horizon. Therefore, perceived potential effect future post-depositional processes marls analogous having been deposited Sea 2.7 kyr.