Slight carbon-isotope perturbation at the J/K boundary (base of the Calpionella Zone) – A proxy tool for correlation? A brief summary

Stable isotope (δ13C, δ18O) data from bulk rock in the Jurassic–Cretaceous transition are characterised by stability of values in many Tethyan carbonate sections, predominantly those laid down under deeper-water marine conditions. The generally straight trend in the δ13Ccarb curve at the J/K boundary interval does not show any significant value expressions that are useful for interregional correlation. However, in several bio- and magnetostratigraphically well-calibrated sections that have been studied, especially in the Carpathian–Alpine terrain (and some additional sections elsewhere in Tethys), a very slight carbon isotopic negative excursion directly at the J/K boundary (sensu base of the Calpionella Zone/Alpina Subzone) shows an almost identical trend. We assume it represents a rather weak geochemical marker at the Tithonian/Berriasian boundary which, nevertheless, may be identified as a useful tool for stratigraphic correlation.