THE DEVONIAN SYSTEM OF THE DONG UJIMQIN BANNER,NEI MONGGOL

Devonian strata are well developed and well exposed in the Dong Ujim- qin Banner,Nei Monggol.They have a relatively complete sequence and contain an abundance of fossils.So this area is a favourable area for studying the Devonian System of northern China.Through regional surveys on a scale of 1.200000,a section has been constructed.The Devonian is divided into the upper,middle and lower series,and six formations have been newly established.The six formations are descrided from the base upward as follows: （1）The Baruntehua Formation（D~1b）of the lower Devonian,consisting mainly of tuffaceous siltstone,argillaceous siltstone and argillite and contain- ing relatively abundant brachiopods and coral fossils,1119m thick. （2）The Aobaotinghundi Formation（D~1a）of the lower Devonian,consist- ing mainly of argillaceous siltstone and tuffaceous siltstone and containing abundant brachiopod fossils,499m thick. （3）The Wendur Aobaote Formation（D~2w）of the middle Devonian, consisting mainly of tuff and siltstone and containing an abundance of bra- chiopod and coral fossils,1228m thick. （4）The Tarbagt Formation（D₂t）of the middle Devonian,consisting mainly of siliceous siltstone,argillaceous siltstone and slate and containing brachiopod and coral fossils,1501m thick. （5）The Cailunguoshao Formtion（D₃c）of tge upper Devonian,consisting mainly of medium-to fine-grained grawacke arkose in the upper part and argillaceous siltstone in the lower part,containing an abundance of brachiopod fossils,564m thick. （6）The Angel Yinwula Formation（D₃α）of the upper Devonian,consist- ing mainly of silty sandstone and slate and containing small quantities of plant fossils and spores and spollen,4496m thick. The above-mentioned results of regional surveys provide reliable infor- mation for a further study of the Devonian strata of China,particularly the Devonian of northern China,and are of certain significance for the study of the development history of the geological structures of northern China.