Revision of the Ordovician Luohe Formation in Hanbeibudunzhao area of Altan Hil, Inner Mongolia

During the 1∶50000 regional geological survey in Altan Hil area of Dong Ujimqin Banner，Inner Mongolia, near the border between China and Mongolia, the Ordovician Luohe Formation in Hanbeibudunzhao was redefined on the basis of such factors as rock association, paleontological characteristics and stratigraphic correlation. The revised Luohe Formation can be divided into three lithologic members. The strata are characterized by shore - shallow sea sedimentation according to grain size analysis. Fossils, regional stratigraphic correlation and analysis of sediment source all indicate that Luohe Formation was formed in Late Ordovician. These results not only provide basic data for Ordovician study and correlation of the Hinggan stratigraphic region but also possess important theoretical and practical significance for the study of the Early Paleozoic tectonic evolution on the southern margin of the Siberia plate.