Conodont Biostratigraphy Of Late Devonian In Lali,Yizhou,Guangxi

The late Devonian sedimentary sequence is well developed in Guangxi,which contains abundant microfossils such as conodonts,ostracods and foraminifera.Therefore,it is an ideal area to study the Late Devonian biostratigraphy.The study area of this thesis is located in the Lali of Yizhou,where outcrops a good stratigraphic sequence of Late Devonian.This work focuses on the conodont biostratigraphy of Late Devonian in the Niu Jiao Chong section of Yizhou,the lithostratigraphic units of which include in ascendingWuzhishan?D₃w?,Lijiang?D₃l?and Donggangling?D₂d?formations.104 samples were collected and processed,and a large number of well-preserved conodont fossils were obtained from those samples.Based on the study of conodont fossils,53 species of 23 genera were identified and 6 conodont zones were recognized from the study area,which,from bottom to top,include:Polygnathus asymmetricus zone,Ancyrognathus triangularis zone,Palmatolepis jamicae-P.rhenane zone,Palmatolepis linguiformis zone,Palmatolepis triangularis zone and Palmatolepis crepida zone.It is concluded that the age of the Wuzhishan Formation should belong to Famenian,while the Liujiang Formation and the Donggangling Formation belong to Frasnian.Because the first occurrence of the Palmatolepis triangularis is located at 20m from the bottom of the Bed 13 in the study section,which should mark the Fransnian/Famennian?F/F?boundary.