Integrated Chitinozoan Biostratigraphy, Chemostratigraphy and Geochronology Strengthen the North American Upper Ordovician Reference Standard (cincinnati Area, U.s.a.)

The Cincinnati area, located in the American Midwest, is the North America Upper Ordovician reference standard, with a biostratigraphical framework based on conodonts and graptolites. Despite its lofty title, the application and reproducibility of this framework across North America are complicated by several factors including provincialism, facies dependence, the lack of biostratigraphical resolution for conodonts, and the absence of graptolites from many sections. The integration of chitinozoan biostratigraphy, chemostratigraphy, and geochemistry has led to the development of a chronostratigraphic model that is applicable across North America and will clarify intercontinental correlations. As a first step, chitinozoan taxonomic studies were conducted in several sections in the Cincinnati area, spanning the Chatfieldian, Edenian, Maysvillian, and Richmondian regional stages. Many of the 71 chitinozoan species identified are also present in biostratigraphic reference sections from other parts of the Laurentian (Quebec and Anticosti Island, Canada, and Oklahoma, USA) and Avalonia (England and Wales) paleocontinents. Based on the lowest local occurrences of selected species, ten chitinozoan biozones were defined and their stratigraphical patterns are shown to be reproducible across several states of the U.S. midcontinent. The redefinition of the primary lower boundary criteria for the Edenian, Maysvillian, and Richmondian regional stages is proposed, linking them to biozone boundaries and introducing new basal stratotypes: the base of the Plectochitina spongiosa chitinozoan Biozone as the basal boundary of the Edenian Stage (Point Pleasant Formation, MY-14-01 core, Kentucky); the base of the Clathrochitina manglechitinozoan Biozone as the basal boundary of the Maysvillian Stage (Kope Formation, MY-14-01 core, Kentucky); and the base of the Amorphognathus ordovicicus conodont Biozone as the basal boundary of the Richmondian Stage (Arnheim Formation, Southgate Hill section, Indiana). New carbon isotope chemostratigraphy data strengthen these chronostratigraphic interpretations. A K-bentonite containing zircons from the northwestern margin of the Cincinnati area yields a weighted mean 206Pb/238U age (CA-ID-TIMS method) of 448.82 ± 0.34/0.39/0.62 Ma, anchoring the early Maysvillian Stage and the Hyalochitina hyalophrys? subzone of the Tanuchitina hooksae Biozone to near the middle of the Katian Global Stage. This new chronostratigraphic framework integrates chitinozoan, graptolite, and conodont biostratigraphy with high-resolution carbon isotope chemostratigraphy and U-Pb geochronology. Based on multiple sections, our study identifies and corrects miscorrelations of units from shallow to deep marine settings across the Cincinnati reference area, with significant implications for regional tectonism associated with the later phases of the Taconic orogeny. This framework furthers characterization of temporal signatures throughout the Upper Ordovician and into the basal Silurian, and creates a strong baseline for advancing regional and global chronostratigraphic models.