A DETAILED δ13C CURVE THROUGH THE CINCINNATIAN SERIES (UPPER ORDOVICIAN) IN ITS TYPE AREA: SIGNIFICANCE FOR REGIONAL CHEMOSTRATIGRAPHIC CORRELATIONS

Over 130 samples from the approximately 250 m thick Cincinnatian Series in its type area (near Cincinnati, Ohio) have provided the most detailed δ¹³C curve through this interval known anywhere in the world. Among coeval successions in the world, the type Cincinnatian Series is unique in being relatively thick, developed in a predominantly richly fossiliferous limestone facies, and having not been subjected to notable post-depositional thermal alteration, hence it is an ideal succession for δ¹³C analyses. The entire Edenian and most of the Maysvillian Stage was sampled from the Minerva drill core, which was drilled in Kentucky near the reference sections of these stages. Samples from the upper Maysvillian and Richmondian Stages were taken from the Elkhorn drill core, whose drill-site in westernmost Ohio is in the type region of the Richmondian Stage. The uppermost Cincinnatian (Hirnantian Stage) is missing in the type Cincinnatian region, as shown by the detailed biostratigraphy and now δ¹³C chemostratigraphy. However, a composite δ¹³C curve from these type Cincinnatian drill cores and Hirnantian δ¹³C curves from Nevada and Anticosti Island, Quebec provides the first, stratigraphically virtually complete, curve through the entire North American Upper Ordovician. Preliminary comparisons with stratigraphically less complete δ¹³C curves from Oklahoma and Nevada show striking coeval δ¹³C fluctuations (+1 to +2‰) indicating that our new Cincinnatian Series δ¹³C curve will prove to be highly significant for local and global correlation. This curve is particularly important because it is tightly tied to a detailed biostratigraphy based on conodonts, graptolites, chitinozoans, and megafossils.