Re‐evaluation of the conodont Iapetognathus and implications for the base of the Ordovician System GSSP

摘要: In 2000, the International Union of Geological Sciences (IUGS) ratified decision from Working Group on Cambrian–Ordovician Boundary (COBWG) to place Global boundary Stratotype Section and Point (GSSP) for base Ordovician System in Green section, Newfoundland, Canada, at a point coinciding with first appearance conodont Iapetognathus fluctivagus. However, restudy successions shows that this species is not present interval, as consequence section does fulfil biostratigraphical requirements GSSP. The GSSP horizon now defined based level part-way through range I. preaengensis – lower datum (FAD). true FAD fluctivagus above planktonic graptolites well preaengensis. As these problems, other sections Cow Head necessary. A redefinition suggested. following four alternative horizons have potential new level: Cordylodus intermedius; andresi; Eoconodontus notchpeakensis; agnostoid Lotagnostus americanus. (Less)