右江盆地富宁地区石炮组化石及顶部凝灰岩年代学特征及意义OA北大核心CSTPCD

Through field geological investigation,the author collected fossils of Early Triassic bivalves and ammonites about 100 m below the interface between Banna Formation of Middle Triassic and Shipao Formation of Lower Triassic in Funing area of Youjiang Basin,and found a tuff layer with a thickness of about 5 m between T1/T2 interface,which was dated by LA-ICP-MS U-Pb isotope.The isotopic ages of(249.0±1.9)Ma,(247.9±3.4)Ma and(245.5±1.6)Ma were obtained from bottom to top,which were consistent within the error range.The upper boundary age of the Shipao Formation was obtained for the first time in the Lower Triassic.The newly discovered tuff beds and fossils can be used as Early-Middle Triassic isochronous stratigraphic markers for regional comparison,which enriches the distribution range of Early Triassic volcanic rocks in Youjiang Basin.It is considered that it is reasonable to use this set of tuff as a marker for the division of T1/T2 in southeastern Yunnan of Youjiang Basin.Based on the previous data,this set of tuffs and fossils provides important chronological and paleontological evidence for the demarcation of T1/T2 boundary in South China block,and it is considered that the age of the Anniian/Olynikian boundary should be set at 245.5 Ma,which may be more reasonable.