The Ordovician-Silurian boundary: new data, new concerns

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Abstract
Despite International Union of the Geological Sciences (IUGS) ratification of the International Commission on Stratigraphy recommendation that the base of the Parakidograptus acuminatus zone be the base of the Silurian and that the boundary stratotype be at Dob''s Linn, Scotland [UK], numerous concerns continue to be expressed over the timing of the selections as well as the boundary and its stratotype. The richness of both graptolite and non-graptolite biostratigraphic data in numerous stratigraphic sections from many areas in China published at about the same time that the boundary and stratotype were approved formally and shortly after approval suggest the possibility that boundary designation may have been somewhat premature. The new data from China document clearly the major extinction of characteristic Late Ordovician taxa significantly below the presently accepted System boundary. The new data indicate that the re-radiation of graptolites after the extinction took place in the Glyptograptus persculptus zone, the graptolite zone subjacent to the P. acuminatus zone. New geochemical data from Dob''s Linn reveal a change in chemistry in strata subjacent to the base of the G. persculptus zone that could be used as an aid in correlation. The new data suggest the possibility that the base of the G. persculptus zone, the relatively traditional base of the Silurian, could be as appropriate a System boundary as the base of the P. acuminatus zone.

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