Organic-walled phytoplankton biostratigraphy of the Eocene-Oligocene transition in the Kallo borehole and the Rupelian stratotype area (northwestern Belgium)

A detailed study of the assemblages of organic-walled phytoplankton in the Eocene-Oligocene transition beds in the Kallo borehole and its comparison with the assemblages around the same transition in boreholes at Niel, Hingene-Wintham and Terhagen (the Rupelian stratotype area), reveals a hiatus between the Wintham Silt Member and the Ruisbroek Sand Member (sensu Steurbaut, 1986, 1992) in the stratotype area. In the Kallo section the sedimentation history from the latest Eocene into the Early Oligocene is more completely represented than in the stratotype area of the Rupelian.