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

• Published in: Lethaia
• Main Authors: Terfelt F., Stouge S., BAGNOLI, GABRIELLA
• Other Authors: Terfelt, F., Bagnoli, Gabriella, Stouge, S.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2012
• Subjects: Canada; Cow Head; Green Point; Newfoundland
• Online Access: http://hdl.handle.net/11568/152484; https://doi.org/10.1111/j.1502-3931.2011.00275.x

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