Introduction to papers on the Cambrian–Ordovician Boundary

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Abstract
The Working Group has the responsibility of recommending 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 in Calgary in 1985 resulting in decisions on the ‘golden-spike’ principle of selecting the boundary at a horizon just below the first influx of nematophorous graptolites. Conodonts are to be used as the primary guide for the selection of the specific horizon and the global stratotype section must have potential for studies using paleomagnetism, geochemistry and other non-biological correlation tools. The specific horizon will correspond approximately to the base of the Tremadoc Series of Wales and slightly higher than the base of Canadian Series as used in western North America.The Calgary meeting considered the Broom Point and Green Point sections in Newfoundland, Canada, and the Xiaoyangqiao section at Dayangcha, China, as prime candidates to serve as the global stratotype. A delegation from the Working Group inspected the Dayangcha sections in 1986. For this visit, comprehensive documentation and description of the sequence were prepared and published and are briefly summarized in the present issue.Specific uncertainties remain to be resolved for the Dayangcha and Newfoundland stratigraphic sections before the Working Group will be ready to recommend selection of a global stratotype.