Conodont Biostratigraphy Across The Devonian-Carboniferous Boundary Interval At The Naqing And Madao Sections In Guizhou Of South China

The Global Standard Stratotype Section and Point(GSSP)for the base of the Carboniferous System,the Mississippian Subsystem,the Lower Mississippian Series,and the Tournaisian Stage was set up in the La Serre section,Montagne Noire,southern France.The current Devonian-Carboniferous boundary(DCB)is based on the First Appearance Datum(FAD)of the conodont Siphonodella sulcata in the evolutionary lineage Si.praesulcata-Si.sulcaa.However,further work on the GSSP have revealed several problems,and thus,both the criterion and section of Devonian-Carboniferous Boundary was expected to be re-built soon.Also,Late Devonian through Early Mississippian is a critical period marked by greenhouse-icehouse transition.Research on the conodont biostratigraphy in this period can also contribute to the correlation of global events.In this dissertation,2 sections in South China were studied for solving the problems mentioned above.Conodont materials from the Naqing section in Luodian and the Madao section in Dushan of Guizhou have been studied.Nine conodont zones were recognized in the DCB interval in the Naqing section.They are,in ascending order:the Palmatolepis marginifera marginifera Zone,the Palmatolepis rugosa trachytera Zone,the Polygnathus styriacus Zone,the Palmatolepis gracilis manca Zone,the Palmatolepis gracilis expansa Zone,the Siphonodella isosticha Zone,the Gnathoduspunctatus Zone,the Gnathodus typicus-Gnathodus cuneiformis Zone and the Gnathodus typicus-Protognathodus cordiformis Zone.Several key conodont biozones across the DCB interval elsewhere in the world have not been found yet in the Naqing section mainly because of the facies control,where a barren interval(84-92.5 m)is composed of clastic rocks.Thus,the DCB in the Naqing section is tentatively put in the clastic rocks,between the Palmatolepis gracilis expansa Zone and the Siphonodella isosticha Zone.Three conodont zones were recognized in the DCB interval in the Madao section.They are,in ascending order:the Bispathodus ultimus Zone,the Siphonodella isosticha Zone and the Polygnathus communis carina Zone.The DCB in the Madao section was tentatively put at the base of the dolomite in the Rongxian Formation.Furthermore,correlations of these conodont zones with those from other regions in the world,and ranges of some key conodont species were discussed;all the conodont species found from the two sections were described,among them,Pseudopolygnathus micropunctatus Morphotype 1 and Morphotype 3 were first reported in South China.The above results will lay a good foundation for both the restudy of the DCB and the research on bio-and environmental events during the Late Devonian through the Early Mississippian critical greenhouse-icehouse climate transition in South China.