The international working group on the Cambrian-Ordovician boundary: report of progress

The Working Group has the responsibility of recommeizdirzg a specific level within a suitable stratigraphic section to serve as the global stratotype for the Cambrian-Ordovician boundary. Commencing in 1974, comprehensive studies culminated in a plenary session held in Calgary in 1985 and resulted in decisions on the "golden-spike" principle of selecting the boundary at a horizon just below the first influx ofplanktic (nematophorous) graptolites. Conodonts are to be used as the primary guide for the selection of the specijic horizon and the global stratotype section must have potential for studies using paleomagnetism, geochemistry, and other nonbiological correlation tools. The spec$ic horizon will correspond approximately to the base of the Tremadoc Series of Wales and will be slightly higher than the base of the Canadian Series as used in western North America.