广西六景泥盆纪吉维阶-弗拉斯阶界线层牙形石生物地层

Conodont Biostratigraphy across the Givetian-Frasnian Boundary (Devonian) of Liujing,Guangxi

广西六景泥盆系剖面是我国泥盆系标准剖面之一 ,通过对其吉维阶 -弗拉斯阶界线上下地层进行详细的牙形石生物地层研究 ,自上而下识别出 12个牙形石带 :Palmatolepis jamieae带、Palmatolepis hassi带、Palmatolepispunctata带、Palmatolepistransitans带、上 Mesotaxisfalsiovalis带、下 Mesotaxisfalsiovalis带、Klapperina dispar-ilis带、上 Schmidtognathus hermanni- Polygnathus cristatus带、下 Schmidtognathus hermanni- Polygnathus cristatus带、上 Polygnathus varcus带、中 Polygnathus varcus带、下 Polygnathus varcus带。吉维阶 -弗拉斯阶界线 (即中 -上泥盆统界线 )由 Ancyrodella binodosa→ Ancyrodella rotundiloba early form→ Ancyrodella rotundiloba late form这一演化线系中的 Ancyrodella rotundiloba early form的首次出现确定 ,处于下 Mesotaxis falsiovalis带下部 ,在谷闭组底界之上 1.80 m处。

Liujing Section (Guangxi, South China) is one of the standard sections of Devonian age in China. The conodont biostratigraphy of the upper part of the Givetian to the lower part of the Frasnian is studied in detail in this paper, and twelve conodont zones are recognized in descending order: Palmatolepis jamieae Zone, Palmatolepis hassi Zone, Palmatolepis punctata Zone, Palmatolepis transitans Zone, Upper Mesotaxis falsiovalis Zone, Lower Mesotaxis falsiovalis Zone, Klapperina disparilis Zone, Upper Schmidtognathus hermanni Polygnathus cristatus Zone, Lower Schmidtognathus hermanni Polygnathus cristatus Zone, Upper Polygnathus varcus Zone, Middle Polygnathus varcus Zone, Lower Polygnathus varcus Zone. According to the correlation with the GSSP for the Middle Upper Devonian Boundary, the Givetian Frasnian boundary (i.e.Middle Upper Devonian boundary) at Liujing is defined by the first occurrence of Ancyrodella rotundiloba early form, which is in the evolutionary line from Ancyrodella binodosa to Ancyrodella rotundiloba early form, then to Ancyrodella rotundiloba late form. This boundary is within the Lower Mesotaxis falsiovalis Zone, 1.80m above the base of Gubi Formation.