Katian (Upper Ordovician) δ13C chemostratigraphy and sequence stratigraphy in the United States and Baltoscandia: A regional comparison

δ13C values of numerous limestone samples from Katian (Upper Ordovician) successions in Oklahoma and the Upper Mississippi Valley document the presence of at least three of the four positive excursions that have been recognized in the lower–middle Katian interval in the Cincinnati region in Ohio, Kentucky, and Indiana. A comparison with Estonia reveals that five out of the six positive excursions now recorded through the Katian succession in the Cincinnati region are present in the coeval stratigraphic intervals in Estonia, which suggests that these represent global perturbations in the carbon cycle. A study of the relations between flooding events and δ13C excursions shows that only some of the excursions occur in transgressive intervals whereas other excursions are in regressive strata and hence, this is in conflict with the idea that positive carbon isotope excursions are forced by rises in sea level. Part of a previously published attempt to use Upper Ordovician sequence stratigraphy for trans-Atlantic correlation is shown to be seriously out of phase with the biostratigraphy and chemostratigraphy. Several of the sequences recognized in the Cincinnati region do not appear to have counterparts in Estonia, which suggests that they do not reflect eustatic, but local, conditions.