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

Abstract

Košťák et al. (Cretaceous Research, Volume 151, November 2023, 105,617) reported a negative shift of δ13C values in several sections near the Tithonian/Berriasian boundary, and emphasized its correlation potential. Although there is no agreement on the biostratigraphic location of this stage boundary at Tré Maroua, i.e., at the dismissed candidate for the Berriasian GSSP, it does not really affect our negative conclusion on the authors' potential proxy. Besides the biostratigraphic context, not much consideration was given to the structural and sedimentologic contexts, which undermines their line of argument. In conclusion, on the basis of published information as well as new observations, it is shown that their coeval “perturbation” on the δ13C curve is uncertain and questionable.