The Belemnella stratigraphy of the Campanian– Maastrichtian boundary; a new methodological and taxonomic approach

Abstract

The taxonomy and stratigraphy of the Upper Campanian and Lower Maastrichtian belemnites from the Vistula (central Poland) and Kronsmoor (northern Germany) sections are revised on the basis of new collections from the Vistula section as well as a reinvestigation of the classic collection of Schulz from the Kronsmoor section. For the taxonomic description a new biometric procedure is proposed, which can be applied to both the genera Belemnella and Belemnitella. For the species-level taxa recognition the Artificial Neural Networks method, the self-organizing Kohonen algorithm, was implemented. This new taxonomic and methodological approach enabled the recognition of nine species of the genus Belemnella. Five of them can be assigned to the existing species B. lanceolata, B. longissima , B. inflata, B. obtusa and B. vistulensis. However, the species concept differs from that applied by Schulz (1979). As a consequence, the stratigraphic ranges of these species are modified. Four species are left in open nomenclature and represent possibly new species. Future studies may reveal that they might be assigned to East European forms from Ukraine or Russia.The species of Belemnella recognized are placed into the stratigraphic framework based on the standard ammonite and inoceramid bivalve zonations, especially those recognized in the Vistula section. The newly proposed belemnite zonation for the Vistula and Kronsmoor sections is correlated via inoceramids with the standard GSSP at Tercis, France, in order to identify the base of the Maastrichtian Stage. The Campanian–Maastrichtian boundary as defined in Tercis is placed here at the base of the newly defined B. obtusa and B. vistulensis Zones [“obtusa/vistulensis”] – thus it is markedly higher than the traditional boundary based on the FAD of representatives of the genus Belemnella. This new boundary coincides well with a distinct turnover of belemnite guard morphology and represents one of the most important points in the early evolutionary history of Belemnella.Three belemnite zones defined by their lower boundaries are recognized in the Campanian–Maastrichtian interval, in addition to three subzones recognized within the B. obtusa Superzone. The B. lanceolata and B. inflata zones as understood here are referred to the Upper Campanian [Tercis definition]. The B. obtusa Zone is subdivided into three subzones, viz.: Belemenlla vistulensis, Belemnella sp. G and Belemnella sp. F, which are referred to the Lower Maastrichtian [Tercis definition].The fast evolving species of Belemnella enable the proposal of a biostratigraphic scheme with a resolution that is higher than those based on inoceramid bivalves and ammonites – the longevity of a belemnite zone could be as low as 200Ky.