A specimen of the scaphitid ammonite Acanthoscaphites tridens was collected in situ from the lower part of the Vijlen Member, southwest of Gulpen. This species has been widely quoted as an index for the lowest ammonite zone of the Maastrichtian Stage, but its precise age was poorly known. Associated nannofossils show the Gulpen specimen to come from nannofossil zone CC 24. A calibration of nannofossil and belemnite zones indicates it to be no older than the Belemnella occidentalis Zone, which is well above the base of the Maastrichtian Stage. The Gulpen specimen is thus younger than the type occurrence in the Ukraine which is in nannofossil subzone CC 23B, equivalent to the upper part of the Belemnella lanceolata Zone. -from Authors
