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HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

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Abstract:Investigations of the Lower Miocene of the Transylvanian Basin reveal particularly high abundances ( > 90 % of total foraminifera) of small sized biserial foraminifera (Bolivina/Streptochilus). This biotic event has not been noticed in the Transylvanian Basin so far probably owing to the facies misinterpretation and the small size of the specimens. SEM investigations allow more precise identification of biserial planktonic taxa and more accurate taxonomic interpretations. The high abundance of Bolivina/Streptochilus assemblages provide evidence for paleogeographic connections to the IndoPacific area and support new paleoenvironmental interpretations at the transition from the Early to Middle Miocene in relation to the paleoceanographic events. Both planktonic foraminifera and calcareous nannoplankton suggest a late Burdigalian age. A new Bolivina/Streptochilus Abundance Biozone is proposed just below the Early/Middle Miocene boundary.

ver sity, De part ment of Ge ol ogy and Re search Cen ter for In te grated Geo log i cal Stud ies,