A critical evaluation of carbon isotope stratigraphy and biostratigraphic implications for Late Cretaceous global correlation

The combination of chemostratigraphy with biostratigraphy and magnetostratigraphy substantially increases the precision and temporal resolution of inter-regional correlations and helps overcome problems that arise from differences in biostratigraphic schemes, facies or provincialism of key fossils. By using an iterative approach to stepwise increase precision of the correlations, isochroneity of first and last occurrences of marker species versus chemostratigraphy is tested, which helps to improve biostratigraphic zonations, to assess zonal boundary ages and to identify useful criteria for defining Late Cretaceous stage boundaries, many of which are still not formally defined. The presented correlations indicate a consistent position for most planktic foraminifer zonal boundaries relative to corresponding isotope shifts during the mid-Cretaceous sea-level high, whereas diachroneity appears to be more pronounced during the Late Campanian and Maastrichtian global sea-level fall. A similar pattern is observed for trans-continental consistency in the δ13C shifts. Graphic correlation of isotopic shifts, magnetostratigraphic and biostratigraphic events among the compared sections is used to detect hiatuses or relative changes sediment accumulation rates and visualizes consistency or offsets of individual biostratigraphic markers relative to chemo- and magnetostratigraphy. Finally, an attempt of a global average δ13C stack is presented for the Turonian through Maastrichtian.