Changes in whole conodont faunas and ?13C values are combined to achieve highresolution
correlations of Upper Silurian successions in many areas (primarily
Gotland, Sk?ne, Lithuania, Bohemia, Austria, Sardinia and Queensland); other areas
are correlated with lower precision. Four of the widely recognised subzones average
considerably less than 0.1 Ma and a fifth interval less than 0.01 Ma. The main
constraints on resolution and precision now achievable are the amount of, and the precision
in, new or previously published data from each local section; centimetric scale
collecting would be worthwhile in many sections. Some stratal characters are more
widespread during certain intervals than might have been expected, for example, the
presence of oncolites and algal coatings in the Icriodontid Zone and the lower part
of the O. snajdri Zone. Similarly, the Dayia navicula bloom in the Upper P. siluricus
Subzone was widespread. So also were muddy-sandy sediments followed by oolite
low in the O. snajdri Zone; crinoids flourished widely when the lower part of the
Lower Icriodontid Subzone was formed. Closely spaced samples show that, in some
intervals, the now well-known ?13C spike was modified considerably by fluctuations;
that is, it is not a smooth plateau. The best-documented fluctuations (19 analyses) are
2.5 smooth cycles with up to 2.7? in amplitude during ca 12,000 years or less in the
base of the O. snajdri Zone. An enigma is the depletion of the spike in some sections,
especially in the best Bohemian section.
