Stratigraphy of the upper Vijlen Member (Gulpen Formation; Maastrichtian) in northeast Belgium, the southeast Netherlands and the Aachen area (Germany), with special reference to belemnitellid cephalopods

摘要

Recent studies have demonstrated the complex depositional history of the Vijlen Member (Gulpen Formation) in the Maastricht-Aachen-Liege area, on which synsedimentary tectonics had a profound impact, in conjunction with regressive and transgressive episodes, the oldest portion of this member being preserved only locally, within channel-like structures. Our reinterpretation of the Vijlen Member, here presented, is at variance with current belemnite stratigraphy. To account for incongruities, reworking of belemnites is here proposed as a typical feature during Vijlen Member deposition. A renewed study of belemnites on the basis of these new data suggests that intervals 4-6 of the Vijlen Member are of late Maastrichtian age. With respect to the mean values of populations of Belemnitella junior Nowak and Belemnitella lwowensis Naidin, Vijlen Member intervals 4-5 are coeval with the Spyridoceramus tegulatus/Belemnitella junior Zone (sensu germanico), whereas at least the upper portion of interval 6 is correlatable with the basal Tenuipteria argentea/Belemnitella junior Zone (sensu germanico). Although reworking of belemnites appears to have been a common feature, this cannot be properly substantiated without additional geochemical analyses of individual guards. For this reason, we refrain from proposing a biostratigraphic zonation of the Vijlen Member based on belemnites. Alternatively, scaphitid ammonites might be used to subdivide this member, because species such as Acanthoscaphites (Acanthoscaphites) tridens (Kner), A. (Euroscaphites) varians blaszkiewiczi Jagt, Kennedy & Machalski, Hoploscaphites constrictus (J. Sowerby), H. tenuistriatus (Kner) and Hoploscaphites sp. have been recorded. The last-named taxon represents an interspecies hybrid between the North American Jeletzkytes dorfi Landman & Waage and an unidentified subspecies of the endemic European lineage of H. constrictus, allowing correlation of the lower portion of Vijlen Member interval 6 with the Hoploscaphites birkelundae Zone of the United States Western Interior