Ranges of 79 conodont species are used to effect a graphic correlation of upper Llandoverian-Pridolian (Silurian) rocks in 30 stratigraphic sections in Europe and North America. A Silurian Composite Standard Section (CSS) developed by this method provides the total stratigraphic ranges for all species for which there is information in the system. These ranges are stated in terms of the sequence of Silurian rocks at Cellon, Austria, which is the Standard Reference Section (SRS).
The Llandoverian/Wenlockian and Ludlovian/Pridolian boundaries are recognized based on the position of the "golden spike" in the boundary stratotypes, the Leasows (Hughley Brook) and Pozary sections, which form parts of the CSS. Range-data for graptolite species in ten of the stratigraphic sections are used to approximate positions of all other boundaries between Silurian series and stages that have been designated in boundary-stratotypes that are not parts of the Composite Standard Section. The Pridolian is shown to have had a longer duration than either the Ludlovian or Wenlockian, and the Llandoverian possibly approximated the Pridolian in duration. The CSS is divisible into ≃48 Standard Time Units (STU's) of conceptually equal length; hence the chrono-stratigraphy based on it resolves at a level two to four times higher than any previously proposed for the Silurian. The CSS is also divided into a succession of conodont chronozones that are based on zones proposed by Walliser (1964), Aldridge (1972), and Barrick and Klapper (1976). Conodont chronozones can be recognized with confidence only in sections that are parts of the CSS framework.