DISCOVERY OF THE CONODONT LINEAGE FROM Idiognathodus swadei TO I.turbatus IN SOUTH CHINA AND ITS IMPLICATIONS

The current base of the global Kasimovian Stage is raised to approximately the base of the Khamovnikian Substage.This level is approximately one substage higher than the traditional base of the Kasimovian at the base of the Krevyakinian Substage in the Moscow Basin of Russia,but it facilitates global correlation.Either Idiognathodus sagittalis Kozitskaya,1978 or Idiognathodus turbatus Rosscoe Barrick,2009a is the potential biostratigraphic marker by which the level of the base of the Kasimovian Stage can be selected and correlated globally.I.sagittalis is based on material from the Donets Basin(Ukraine).A possible ancestor-descendent lineage from I.nikitini n.sp.to I.sagittalis may be present in the Moscow Region.I.turbatus is based on material from Midcontinent North America.A lineage from Idiognathodus swadei Rosscoe Barrick,2008 to I.turbatus has been described from Midcontinent North America.Both lineages and the first appearance datums(FADs) of I.sagittalis and I.turbatus need further investigation in all regions for identification of potential GSSP candidates.Very abundant conodonts are found from the big collections of the Moscovian-Kasimovian boundary interval in the Naqing section,among which many transitional morphotypes(similar to I.sagittalis) with rapid morphological transformation from I.swadei to I.turbatus are found.Therefore,the important conodont evolutionary lineage from I.swadei to I.turbatus is confirmed in the Moscovian-Kasimovian boundary interval in South China.In addition to North America and South China,I.turbatus has been recognized also in the Moscow Region,the southern Urals,and the Donets Basin:thus,it is easily correlated globally.The lineage from I.swadei to I.turbatus is confirmed from North America and South China.Accordingly,the FAD of I.turbatus is the most potential boundary marker for the base of the global Kasimovian Stage.The Naqing section is an apparently conformable,condensed section of deep-water marine carbonates,which meets the criteria for the establishment of a GSSP,thus,this section deserves further investigation.