Dating of sedimentary rock intervals using visual comparison of carbon isotope records: a comment on the recent paper by Bergström et al. concerning the age of the Winneshiek Shale

The recently published Lethaia paper by Bergstrom et al. (https://doi.org/10.1111/let.12269) on the age of the Ordovician Winneshiek Shale (Iowa, USA), and the impact that formed the Decorah crater which hosts this rock unit, is an interesting scientific contribution, although there are a number of problems with the interpretations and data presentation that merit comment. Due mainly to a lack of adequate critical assessment of δ13C data and biostratigraphical control, we contend that the conclusions of Bergstrom et al. are poorly founded and should not be cursorily accepted and propagated in future scientific literature.