Middle Miocene calcareous nannofossil and isotope fluctuations in the Central Paratethyan Realm (Eastern Carpathians)

Abstract

This work presents the fluctuation pattern related to the modifications in the calcareous nannofossil diversity and abundance and shift in δ13C and δ18O isotopes identified in a succession situated in the Outer Moldavide nappe system of the Eastern Carpathians. The studied section is mainly made by clays and marls and includes a cm-thick volcanic ash layer dated as 13.32 ± 0.07 Ma (de Leeuw et al., 2018). We have pointed out the biotical response to the environmental changes that took place as a consequence of the “Badenian Evaporitic Crisis” of the Central Paratethyan Realm. Based on the biostratigraphy of the calcareous nannofossils, we identified the Badenian NN5 biozone, argued by the co-occurrence of Sphenolithus heteromorphus, Coronocyclus nitescens and Cyclicargolithus floridanus. The semiqualitative analysis point out the abundant presence of Helicosphaera spp. (mainly H. carteri), which together with Sphenolithus spp., Cyclicargolithus floridanus, Reticulofenestra pseudoumbilicus and Braarudosphaera bigelowii accounted up to 50% calcareous nannofossil assemblages. Most of the found specimens of Braarudosphaera bigelowii are “rounded” morphotypes, as previously identified in several Central Paratethyan Miocene successions (Melinte-Dobrinescu & Stoica, 2013; Peryt et al., 2021), whereas the “classical” specimens with sharp edges and trapezoidal segments are extremely rare. In the studied interval, the values of δ13C and δ18O isotopes show wide ranges, with a significant negative shift of δ13C isotope values towards the top of the studied succession.ReferencesDe Leeuw, A., Tulbure, M., Kuiper, K.F., Melinte-Dobrinescu, M.C., Stoica, M., Krijgsman, W., 2018. New 40Ar/39Ar, magnetostratigraphic and biostratigraphic constraints on the termination of the Badenian Salinity Crisis: Indications for tectonic improvement of basin interconnectivity in Southern Europe. Global and Planetary Change, 169, 1-15.Melinte-Dobrinescu, M.C., Stoica, M., 2013. Badenian Calcareous Nannofossil Fluctuation in the Eastern Carpathians: Palaeoenvironmental significance. Acta Palaeontologica Romaniae, 9(2), 47-56.Peryt, D., Garecka, M., Peryt, T.M., 2021. Foraminiferal and calcareous nannoplankton biostratigraphy of the upper Badenian–lower Sarmatian strata in the SE Polish Carpathian Foredeep. Geological Quarterly, 65(18), 1-22.