MACROFOSSIL, PLANKTONIC FORAMINIFERAL AND NANNOFOSSIL ZONATION AT THE CAMPANIAN MAASTRICHTIAN BOUNDARY

Recent compilations and correlations of macrofossil, microfossil and nannofossil zonation across the Campanian/Maastrichtian boundary commonly correlate the base of a Belemnella lanceolata belemnite Zone, Acanthoscaphites tridens and Pachydiscus neubergicus ammonite Zones, the top of a Globotruncanita calcarata planktonic foraminiferal Zone and the base of a Quadrum trifidum nannofossil Zone. These horizons do not coincide. Of the various markers proposed for this boundary, the first occurrence of Belemnella (Belemnella) lanceolata (SCHLOTHEIM) is older than, progressively, the first occurrences of Hoploscaphites constrictus (J. SOWERBY), Pachydiscus (P.) neubergicus (HAUER) and Acanthoscaphites tridens (KNER), and the last occurrence of Quadrum trifidum (STRADNER) PRINS & PERCH-NIELSEN, and younger than the progressively older last and first occurrence of Nostoceras (N.) hyatti STEPHENSON, last occurrence of Globotruncanita calcarata (CUSHMAN), and first occurrence of Globotruncana falsostuarti SIGAL and Quadrum trifidum (STRADNER) PRINS & PERCH-NIELSEN. Rather than corresponding, as in published schemes, the base of the Belemnella lanceolata Zone lies in the upper part of the Globotruncana falsostuarti or G. aegyptiaca planktonic foraminiferal Zone of authors, and within the Tranolithus phacelosus (= T. orionatus) nannofossil Zone (CC23). What is regarded as Upper Campanian in macrofossil terms is regarded as Lower Maastrichtian in microfossil and nannofossil terms, even though the boundary defined by these groups is widely taken as synchronous by geochronologists, sequence stratigraphers and others.