A precise worldwide correlation of early Ordovician graptolite sequences

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Abstract
Fourteen early Ordovician (Tremadoc-Llandeilo) graptolite sequences from around the world are precisely (infrazonally) correlated, based on the stratigraphic ranges of 130 species and species groups. The composite standard sequence (CSS) of graptolites has been determined from the six best regional sequences by a nonparametric graphic correlation. Two data sets were selected: one comprised first appearance events of 103 taxa, the other, first and last appearance events of 45 taxa. The results of the two runs accord well and reveal respectively 66 and 73 successive bioevents in early Ordovician time. Event spacing averages 0.7–0.8 Ma and enables fine subdivision, correlation and homotaxial testing for diachroneity. The strong correlation between each of the six regional sequences and the CSS indicates the high level of accordance among graptolite successions around the world.

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