Constraints on Miocene oceanography and climate in the Western and Central Paratethys: O-, Sr-, and Nd-isotope compositions of marine fish and mammal remains

The Paratethys evolved as a marginal sea during the Alpine–Himalayan orogeny in the Oligo-Miocene. Sediments from the northern Alpine Molasse Basin, the Vienna, and the Pannonian Basins located in the western and central part of the Paratethys thus provide unique information on regional changes in climate and oceanography during a period of active Alpine uplift. Oxygen isotope compositions of well-preserved phosphatic fossils recovered from the sediments support deposition under sub-tropical to warm-temperate climate with water temperatures of 14 to 28 °C for the Miocene. δ¹⁸O values of fossil shark teeth are similar to those reported for other Miocene marine sections and, using the best available estimates of their biostratigraphic age, show a variation until the end of the Badenian similar to that reported for composite global record. The ⁸⁷Sr/⁸⁶Sr isotope ratios of the fossils follow the global Miocene seawater trend, albeit with a much larger scatter. The deviations of ⁸⁷Sr/⁸⁶Sr in the samples from the well-constrained seawater curve are interpreted as due to local input of terrestrially-derived Sr. Contribution of local sources is also reflected in the ε_Nd values, consistent with input from ancient crystalline rocks (e.g., Bohemian Massif) and/or Mesozoic sediments with ε_Nd < ? 9. On the other hand, there is evidence for input from areas with Neogene volcanism as suggested by samples with elevated ε_Nd values > ? 7. Excluding samples showing local influence on the water column, an average ε_Nd value of ? 7.9 ± 0.5 may be inferred for the Miocene Paratethys. This value is indistinguishable from the ε_Nd value of the contemporaneous Indian Ocean, supporting a dominant role of this ocean in the Western and Central Paratethys.