安徽巢湖平顶山西坡剖面印度阶与奥伦尼克阶界线层高分辨率牙形石生物地层

High-Resolution Conodont Biostratigraphy in the Induan-Olenekian Boundary Strata at West Pingdingshan Section, Chaohu, Anhui Province

下三叠统印度阶与奥伦尼克阶全球候选层型剖面之一的中国安徽省巢湖市平顶山西坡剖面界线层,经连续不间断采样获得大量牙形石化石并进行详细的分带工作,建立了该界线层牙形石生物地层.由下往上划分为:1.Neospathodus dieneri带;2.N.waageni带.前者依次分为3个亚带:N.dieneri Morphotype1亚带,N.dieneri Morphotype2亚带和N.dieneri Morphotype3亚带.牙形石带可与该界线层的菊石带进行很好的对比;在详细区分牙形石Neospathodus属内各种特征的基础上,结合地层分布情况,跨越印度阶与奥伦尼克阶界线,演化谱系十分明显,牙形石N.dieneri Morphotype3在奥伦尼克阶之底即Smithian初期演化为:N.dieneri Morphotype3→N.waageni→N.pingdingshanensis、Neos-pathodus dieneri Morphotype3→N.waageni(细齿直立型)→N.n.sp.R和Neospathodus dieneri Morphotype3→N.pakistanensis.从谱系演化的观点出发认为:N.waageni的首现点作为奥伦尼克阶底界是合理的,并在该剖面确定了印度阶与奥伦尼克阶界线位于第24-16层,距剖面大隆组与殷坑组界线40.49m处.

Repeated （more than ten times） conodont analyses have recovered thousands of conodont specimens which are especially rich in the Induan-Olenekian boundary strata, at the West Pingdingshan Section located in Chaohu City, Anhui Province, a candidate GSSP of the Induan-Olenekian boundary. The most distinctive forms are the conodonts of the Neospathodus dieneri group and N. waageni group, as well as some new elements. Based on the general characteristics of the Neospathodus species and their biogeographic distribution, an evolutionary lineage of the species is proposed： N. dieneri Morphotype 3→N. waageni→N, pingdingshanensis,Neospathodusdieneri Morphotype 3→N. waageni（upright denticles）→N. n. sp. R and Neospathodusdieneri Morphotype 3→N. pakistanensis. The first occurrence of N. waageni, which is regarded as the indicator of the Induan-Olenekian boundary, is situated at 40. 49 m above the boundary between the Dalong and Yinkeng formations. The recognition of this evolutionary lineage of Neospathodus is of great importance for a better understanding and definition of the Lower Triassic conodont zonation.