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A REVISION OF THE DARRIWILIAN BIOSTRATIGRAPHIC CONODONT ZONATION IN TANGSHAN,HEBEI PROVINCE BASED ON NEW CONODONT COLLECTIONS

2014; Paleontological Society of China; Linguagem: Inglês

0001-6616

Wang Zhi-ha,

Hydrocarbon exploration and reservoir analysis

The present study is based on samples from the Beianzhuang and Machiakou formations at Zhaogezhuang,Tangshan in Hebei.The rich conodont faunas of these units were previously studied by An et al.(1983).Our samples were very productive and yielded numerous specimens of not only the same endemic species as reported by An et al.(1983)such as Aurilobodus leptosomatus,Loxodus dissectus, Tangshanodus tangshanensis, Rhipidognathus maggolensis, R. laiwuensis, Triangulodus changshanensis,and Erraticodon tangshanensis,but also more widely distributed species,such as Histiodella holodentata,Eoplacognathus pseudoplanus and Eoplacognathus suecicus.An et al.(1983)subdivided the Ordovician Lower Machiakou Formation(= Beianzhuang Formation of this paper)into the Aurilobodus leptosomatus-Loxodus dissectus Zone and the Tangshanodus tangshanensis Zone,and the Upper Machiakou Formation(=Machiakou Formation of this paper) into the Eoplacognathus suecicus-Acontiodus? linxiensis Zone and the Plectodina onychodonta Zone.They correlated the Lower and Upper Machiakou formations with the Dawan Formation(Dapingian)and Kuniutan Formation(Darriwilian)of South China,respectively.Until now this conodont biostratigraphy and associated correlations have been generally used by Chinese geologists.The first occurrences and ranges of Aurilobodus leptosomatus,Loxodus dissectus,Tangshanodus tangshanensis,and Histiodella holodentata(=Histiodella infrequensa An in the paper of An et al.,1983)are nearly the same in our study section(Text-fig.1)and as shown by An et al.(1983,text-fig.7).However,it is impossible tosubdivide the Beianzhuang Formation into the Aurilobodus leptosomatus-Loxodus dissectus Zone and the Tangshanodus tangshanensis Zone based on the first occurrences and ranges of zonal species. Also,it is very difficult to correlate these zones with those of other areas because of the striking provincial faunal differences.Based on the present restudy of our conodonts collected from these formations combined with a detailed analysis of the conodont species ranges shown by An et al.(1983,text-fig.7),the present authors propose a revision of the previous conodont zonation.Hence, the Aurilobodus leptosomatus-Loxodus dissectus Zone and the Tangshanodus tangshanensis Zone of An et al.(1983)in the Beianzhuang Formation are proposed to be replaced by the Histiodella holodentata-Tangshanodus tangshanensis Zone,and the Eoplacognathus suecicus-Acontiodus?linxiensis Zone and the Plectodina onychodonta Zone of An et al.(1983)in the Machiakou Formation are proposed to be replaced by the the Eoplacognathus suecicus Zone.All of these zones are referred to the Darriwilian of the Middle Ordovician and can be correlated with the contemporary faunas of South China,the Tarim Basin of Xinjiang,BaltoScandia and North American Midcontinent.The currently revised the Histiodella holodentata-Tangshanodus tangshanensis Zone is not as the same as the Tangshanodus tangshanensis Zone of An et al.(1983).It includes the Aurilobodus leptosomatus-Loxodus dissectus Zone and the Tangshanodus tangshanensis Zone of An et al.(1983),but has been subdivided into the Rhipidognathus laiwuensis and the R.maggolensis subzones.The Eoplacognathus suecicus Zone can also be subdivided into the Acontiodus?linxiensis and the Plectodina onychodonta subzones.