The late Middle Pleistocene non-marine molluscan fauna of borehole Noorderhoeve-19E117 (province of Noord-Holland, the Netherlands)

In borehole Noorderhoeve-19E117, molluscan assemblages from the lower portion of the marine Eemian deposits as well as from underlying fluvial deposits of Middle Pleistocene age, have been studied; separating these deposits is boulder clay of Saalian age. The pre-Saalian fluvial assemblages are predominated by Corbicula fluminalis (Müller) s. lat, and show the presence of Borysthenia naticina (Menke) and Pisidium clessini Neumayr. Based upon amino-acid racemization (AAR) analysis, these assemblages are assigned to the Oostermeer Interglacial, i.e. the last interglacial of the Middle Pleistocene. This means that the currently assumed Holsteinian age of this part of the Urk Formation is incorrect and that the local extinction of B. naticina and P. clessini occurred two interglacials later than hitherto thought.