Stratigraphically important ammonites from the Campanian–Maastrichtian boundary interval of the Middle Vistula River section, central Poland

ABSTRACT Machalski, M. 2012. Stratigraphically important ammonites from the Campanian-Maastrichtian boundary interval of the Middle Vistula River section, central Poland. Acta Geologica Polonica, 62 (1), 91-116. Warszawa. The formal definition of the Global Stratotype Section and Point (GSSP) for the base of the Maastrichtian Stage at Tercis, southwest France, is based on the first or last occurrences of twelve taxa, including three species of ammonites, Pachydiscus (Pachydiscus) neubergicus, Diplomoceras cylindraceum, and Nostoceras (Nostoceras ) hyatti. The taxonomy and stratigraphical distribution of these, and allied forms, are studied, on the basis of material from the opoka succession across the upper Campanian-lowermost Maastrichtian boundary in the Middle Vistula River section, central Poland. In view of the imprecise location of two ammonite GSSP markers in that section, a direct ammonite-based correlation with the GSSP at Tercis is impossible. However, data available indicate that in the Middle Vistula River section the first occurrence of Pachydiscus (P.) neubergicus and the last occurrence of Nostoceras (N.) hyatti are situated significantly higher than the first occurrence of Belemnellalanceolata, the traditional belemnite marker for the base of the Maastrichtian Stage in the Boreal Realm, and that Diplomoceras cylindraceum appears significantly below this level. There are no unequivocal records of Pachydiscus (P.) neubergicus from the Belemnella lanceolata Zone s.l. in the Middle Vistula River section.