Late Ordovician to earliest Silurian is an important geological period marked by large geological
and biological events. However, the strata and fossils of this interval are not complete in many
parts of the world. Based on studies of 43 sites in South China, in particular the continuous sections
on the Yangtze platform, we recognize a complete succession including seven graptolite zones and two
shelly faunas. In ascending order, the graptolite zones are the Dicellograptus complanatus,
Dicellograptus complexus, Paraorthograptus pacificus (including Lower Subzone, Tangyagraptus typicus
Subzone and Diceratograptus mirus Subzone), Normalograptus extraordinarius–Normalograptus
ojsuensis, Normalograptus persculptus, Akidograptus ascensus and Parakidograptus acuminatus zones.
The shelly faunas are the Foliomena–Nankinolithus and Hirnantia faunas, which may be correlated
with D. complanatus Zone and N. extraordinarius–N. ojsuensis to part of N. persculptus zones respectively.
The biozonation through this interval from the Yangtze region can be correlated with that of
other parts of the world such as Dob's Linn in Scotland, Spain and Portugal, Thuringia–Saxonia–Bavaria,
Bohemia, Poland, Kazakhstan, Kolyma, Malaya Peninsula, Yukon, Canadian Arctic Islands,
Nevada, Argentina, Niger and Victoria, Australia. The Hirnantian Substage, which has been proposed
by us recently, includes the N. extraordinarius–N. ojsuensis Zone, Hirnantia fauna and N. persculptus
Zone. The base of the Hirnantian Substage is marked by the First Appearance Data (FADs)
of N. extraordinarius and N. ojsuensis, which have been determined to be synchronous on a global
scale.
