The present publication deals with recent palynological results of a relatively small interval of Muschelkalk and exposures of the overlying clay deposits in the Winterswijk quarries. For the first time the Lower Muschelkalk Member in the Netherlands could be independently dated as Bithynian (Anisian, Middle Triassic). Contrary to widely accepted opinions the overlying almost black clay deposit is not Liassic but Rhaetian in age and it is assigned to the Sleen Shale Formation. This marginal marine clay which pinches out to the south, is in turn overlain by a light gray, full-marine Lower-Oligocene clay of the Rupel Formation. An anomalous occurrence of Liassic clay is now attributed to subrosion of Röt salt followed by collapse of the overlying Muschelkalk, Rhaetian and Lias strata.
