Ostracods from the Albian/Cenomanian boundary in the Achterhoek area (eastern part of The Netherlands)

The only outcrop of the Cenomanian in The Netherlands is found in the eastern part of the country, near the town of Winterswijk. Here, in the bed of a brook, the Oossinkbeek, white chalks are exposed. Not far from this locality, just a few hundred metres to the NE, the only exposure of the Albian in The Netherlands is found as well, represented here mainly by greensands and greyish siltstones. Samples from both localities were examined for their microfaunal content (ostracods and foraminifera). In addition, samples from a few wells in the surrounding area were included in the study. The recovered ostracod faunas are described in this paper. They prove that, with the exception of the top layers exposed in the Oossinkbeek, the chalks of Kotten are primarily of Early Cenomanian age rather than of Middle Cenomanian age, as was generally accepted until now. One of the wells is believed to contain, at a depth of 10 m, the Albian/Cenomanian boundary; the formal boundary between Early and Late Cretaceous. To provide a basis for comparison, samples from the Middle Cenomanian chalk of the nearby Schenking Quarry (Wettringen, Germany) were also examined for their ostracod content, and are included in this study.