A Study On The Late Devonian Conodont And Its Biostratigraphy Of Late Devonian In Baoshan, West Yunnan

The Devonian is well developed in the Baoshan Block. The Devonian conodont samples in the present study were collected from two drillings(ZK8-13 and DZK39-4) in the Xiyi and Dongshan areas of the Baoshan region. More than 500 conodont specimens were obtainedand some important species were deccribed herein.In the collection of the drilling ZK8-13 from Xiyi area, more than 140 conodont elements were obtained from the Member1 of the Xiangshan Formation and Heyuanzhai Formation.They contain 12 species, including 1 conformis species and 3 indeterminate species which were assinged into 5 genera, including Ancyrodella curvata, Ancyrodella spp., A. nodosa, Ancyrognathus triangularis, Icriodus alternatus alternatus, Icriodus sp., Palmatolepis hassi, Pa. simpla, Polygnathus webbi, Po. elegantulus, Polygnathus cf. tenellus and Polygnathus sp. A. More than 360 conodont elements were obtained from the samples of the Member 1 of the Xiangshan Formation and Heyuanzhai Formation of the drilling core DZK39-4 of the Dongshan area in Shidian. Twenty-one species, including 2 conformis species and 4 indeterminate species, assinged into 4 genera, this assemblage were similar to the counterpart from Xiyi, include Ancyrodella curvata, A. iodes, A. nodosa, I. a. alternatus, I. expansus, I. symmetricus, Icriodus sp. A, Palmatolepis hassi, Pa. jamieae, Pa. simpla, Pa. transitans, Palmatolepis sp. A, Palmatolepis cf. rhenana rhenana, Palmatolelis sp., Polygnathus aequalis, Po. elegantulus, Po. linguiformis linguiformis, Po. webbi, Po. xylus xylus, Polygnathus cf. tenellus and Polygnathus sp. B.Sixteen species and 5 genera, including 2 conformis species and 3 indeterminate species were described and discussed. Four condont zones were recognized, namely the Icriodus expansus Zone, the Palmatolepis transitans Zone, the Ancyrodella curvata zone and Icriodus alternatus alternatus—Palmatolepis hassi zone. These biostratigraphic scheme can be correlated with the contemporaneous successionsin Guangxi Province of China, Morocco of North Africa and Western Thailand of Southeastern Asia. The conodont faunas were assigned to the Early Givetian to Late Fransian. The conodont assemblage from the Member1 of the Xiangshan Formation indicates an age of the Late Devonian rather than the previously assigned Early Carboniferous. This study supply some new conodont-based biostratigraphic information for the Devonian successions of the Baoshan Block.