The youngest Maastrichtian ammonite faunas from Poland and their dating by scaphitids

Abstract

The youngest Maastrichtian ammonite faunas from Poland are discussed in terms of their taxonomic composition, dating and significance for the end-Cretaceous extinction debate. The fauna from the top of the classic Upper Maastrichtian succession at Nasiłów comprises Baculites spp. (including B. anceps), Hoploscaphites constrictus subsp. A, Menuites terminus, Pachydiscus jacquoti and Sphenodiscus binckhorsti. The commonest components of this fauna, i.e. Baculites spp. and H. constrictus subsp. A, occur also at the top of the Maastrichtian at Bochotnica, Prawiedniki, Mętów and Klimusin. A distinctive fauna, identified for the first time in Poland, is present at the top of the Upper Maastrichtian at Mełgiew. It is composed of H. constrictus subsp. B and Baculites sp. In the standard Upper Maastrichtian Boreal succession at Stevns Klint, Denmark, H. constrictus subsp. A is present in the white chalk and is replaced by H. constrictus subsp. B in the overlying Grey Chalk. Details of the evolutionary succession of H. constrictus as recorded at Stevns Klint allow for relative dating of the ammonite occurrences in Poland. The youngest ammonite faunas from Nasiłów, Bochotnica, Prawiedniki, Mętów and Klimusin, which include H. constrictus subsp. A are considered to be older than the ammonite fauna from the Grey Chalk in Denmark. In contrast, the topmost Maastrichtian fauna from Mełgiew, with H. constrictus subsp. B, is thought to be coeval with that from the top of the Grey Chalk. The abundant occurrence of ammonite specimens at the top of the Maastrichtian successions at Stevns Klint and Mełgiew supports some earlier views that the Boreal ammonites did not suffer any perturbations immediately prior to the end of the Cretaceous.