This work presents the calcareous nannofossils assemblages identified in samples recovered from 5 boreholes, drilled on the western side of the Olt River, in the B��beni area. These boreholes crossed the Lower Oligocene-Lower Miocene sedimentary successions. The identified assemblages were included in the following intervals: (i) upper part of NP21 calcareous nannofossil zone to the lower part of NP23 biozone, corresponding to the early Rupelian, (ii) upper part of NP23 biozone up to NP25 biozone, spanning the late Rupelian-Chattian interval, and (iii) NN1 up to NN3 biozones, covering the Aquitanian and Burdigalian stages. The diversity and abundance of the identified nannofossil assemblages allow paleoenvironmental reconstructions., {"references":["Aubry, M.P. (1992). Late Paleogene calcareous nannoplankton evolution: A tale of climatic deterioration. In: D. R. Prothero, D.R., and W. A. Berggren, W.A. (Eds.), Eocene/Oligocene Climatic and Biotic Evolution, Princeton Univ. 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