Research Prospects on Marine Ladinian-Carnian Boundary in Guizhou Province

The Global Boundary Stratotype Section and Point (GSSP) for Ladinian-Carnian Boundary (LCB) was defined at Prati Di Stuores/Stuores Wiesen Section in Italy at a level coinciding with the lowest occurrence of the ammonoid Daxatina canadensis. This GSSP level is commonly considered to near the lowest occurrence of the conodonts Quadralella polygnathiformis or Budurovignathus diebeli. However, the placement of the LCB within sections of South China is controversial, because the primary ammonoid marker for LCB (D. canadensis) hasn't been reported in South China. The working placement of LCB based on ammonoid biostratigraphy (e.g., Trachyceras) is considerably higher than the levels where the conodont biostratigraphy would suggest its position. For example, ammonoids in the southwest Guizhou region with the best marine record in South China suggest the LCB should be assigned near the top of Zhuganpo Formation, whereas conodont biostratigraphy suggests that the LCB should be at the base of Zhuganpo Fm.. The Dapingzi Section in Zhenfeng County of Guizhou Province, yielded elements of the conodonts Quadralella polygnathiformis and Budurovignathus sp. from the transitional bed near the top of Yangliujing Formation, which suggests an assignment to the lowermost Carnian (the "Cordevolian" substage, as used by some authors). Therefore, this conodont assemblage would imply that the LCB in the Dapingzi Section should be placed within the upper part of Yangliujing Formation, below the base of the Zhuganpo Formation. However, to accurately assign the LCB within the marine deposits of South China requires integrating the ammonoid and conodont biostratigraphy with additional stratigraphic correlation methods, such as magnetostratigraphy and U/Pb ages.