Calcareous nannofossil events around the Eocene-Oligocene boundary in the Umbrian Apennines (Italy)

Six pelagic sections from the Umbrian area have been investigated to provide a detailed biostratigraphy and magnetostratigraphy at the Eocene-Oligocene boundary. Data from calcareous nannofossils, benthonic and planktonic foraminifera show that no catastrophic extinctions occurred at the boundary, but that the latter is characterized by sequential events. The last occurrences of Discoaster barbadiensis and D. saipanensis are found at an older level than the extinction of Hantkenina, which marks the Eocene-Oligocene boundary. Variations in abundance of several calcareous nannofossil species have been observed close to the boundary. An increase of Isthmolithus recurvus, a cold water indicator, just below the Eocene-Oligocene boundary, seems to be a peculiar event well recognizable also in Spain and in some DSDP sites from the South Atlantic.