Integrated stratigraphy of the Kronsmoor section (northern Germany), a reference point for the base of the Maastrichtian in the Boreal Realm

Abstract

Results of detailed multistratigraphic analyses of the campanian–Maastrichtian boundary section at Kronsmoor in northern Germany are summarised and calibrated with the Gssp at Tercis les Bains, southwest France. Additionalmarkers for the definition of the boundary in the Boreal Realm are proposed, and a detailed carbon isotope curve around the campanian–Maastrichtian boundary in the chalk facies of the Boreal epicontinental sea is presented. The c isotopic GSSP marker for global correlation is the markedly abrupt decrease of c. 0.7 ‰ δ13c directly at the campanian–Maastrichtian boundary as dated by ammonites. In electronic borehole measurements the Kronsmoor section covers the SP peaks 53 to 64 and the base of the Maastrichtian being situated just below SP peak 60. The first occurrence (FO) of the ammonite Pachydiscus neubergicus, which corresponds to biohorizon 1 at Tercis, falls in the upper part of nannofossil Zone UC15, at both localities. Biohorizon 3 is the FO of the ammonite Diplomoceras cylindraceum, which first appears in the upper campanian of Tercis and at Kronsmoor enters significantly above the Fo of Belemnella lanceolata, the conventional Boreal belemnite marker for the base of the Maastrichtian stage. Based on ammonite evidence, the internationally accepted base of the Maastrichtian at Kronsmoor is located between the Fos of Diplomoceras cylindraceum (Upper Campanian) and Pachydiscus neubergicus (Lower Maastrichtian) c. 11 m above flint layer F 600, at which the first representatives of the belemnite genus Belemnella, in particular Bn. lanceolata occur. The latter thus is a Late Campanian species, appearing c. 450 ky prior to the ammonite-based boundary. The FOs of Belemnella pseudobtusa (sensu Schulz) resp. Belemnella obtusa (sensu Remin) directly at the boundary can be use as the coleoid proxy for the definition of the base of the Maastrichtian in the Boreal Realm. To define the boundary by benthic foraminifera the last occurrence (LO) of Neoflabellina praereticulata is suitable. Biohorizon 12, as defined at Tercis, involves the nannofossil Uniplanarius trifidus, however, at Kronsmoor this species is rare, occurs only sporadically and also significantly lower in comparison to Tercis. It is possible though to compare and correlate nannofossil events between Kronsmoor and Tercis using cosmopolitan taxa such as Broinsonia parca constricta and Eiffellithus eximius. The LO of the latter appears to be situated just above the boundary in both sections; it follows from this that the top of nannofossil Zone UC 15 is of early Maastrichtian age.