Ordovician δ13C chemostratigraphy: A global review of major excursions and their ties to graptolite and conodont biostratigraphy

Abstract Recent studies on δ13C chemostratigraphy have produced a wealth of new information of major importance for clarification of local and global stratigraphic relationships. Currently, approximately 15 named positive and negative isotopic excursions have been identified in the Ordovician System. Some of these are significant and geographically widespread, whereas others are poorly developed and regional, thus hindering unambiguous usage. Because isotopic age data useful for precise excursion dating are rarely available in the Ordovician, biostratigraphic information from geographically widespread fossil groups such a graptolites and conodonts are of critical importance for correct identification of isotopic excursions. This study is a global review of the relations between Ordovician δ13C excursions and graptolite and conodont biostratigraphic units with special emphasis on Baltoscandia, North America, and Argentina, three large regions that have been centers of Ordovician chemostratigraphic research. In this report we review for each excursion its proper nomenclatural designation, relations to biostratigraphic units, its known geographic range, and key study localities.