ABSTRACT: Ninety-four carbonate samples were analyzed for carbon isotope (d13Ccarb) stratigraphy from the Niagara River Power Project S-1 core, Lewiston, NewYork. Samples were taken from Clinton and Lockport Group rocks in the type area of the Niagaran Provincial Series in order to constrain more precisely the age and correlation of middle Silurian strata of the Appalachian Basin. The well known, Ireviken (Sheinwoodian), positive carbon isotope excursion is present in the sampled section, and indicates that the Irondequoit, Rochester, Decew, Gasport, and Goat Island Formations are all Sheinwoodian in age. This fact has implications for both stratigraphic correlation of Silurian strata throughout North America as well as the interpretation of the stratigraphic record with respect to positive carbon isotope excursions. Here, we discuss the Appalachian Basin sequence in the context of an oceanographicmodel that links changes in global oceanography with alternations between cold and warm climate states.