Changes in whole conodont faunas and δ13C values are combined to achieve highresolution correlations of Upper Silurian successions in many areas (primarily Gotland, Skåne, 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 δ13C 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.
Late Ludfordian correlations and the Lau Event
CORRADINI, CARLO;
2012-01-01
Abstract
Changes in whole conodont faunas and δ13C values are combined to achieve highresolution correlations of Upper Silurian successions in many areas (primarily Gotland, Skåne, 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 δ13C 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.
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