New understanding of the Xingfuzhilu Formation in the southern part of the Greater Khingan Mountains and a correlation with the neighboring areas

It is an important period for the tectonic evolution of the eastern segment of the Central Asia Orogenic Belt during the Late Permain to Middle Triassic, which involes the final closure of the Paleo-Asian Ocean and the sharp changes of sedimentary environment. The stratotype of the 1st and 2nd Members of the Xingfuzhilu Formation was reinvestigated by the authors. Based on the sporopollen fossils and isotopic ages, combined with previous studies and field investigation, this paper offers some new understanding on the sedimentary succession of Xingfuzhilu Formation. Late Permian-Early Triassic Xingfuzhilu Formation which uses red-bed features as a divided point, is consisted of sand shale and pyroclastic rocks.The conglomerate which were considered as part of the lower member of xingfuzhilu Formation is actually younger than the middle triassic. In this case, this conglometrate should be not be classified as members of xingfuzhilu formation anymore.The sedimentary environment of the Upper part of Linxi Formation and Xingfuzhilu Formation is contemporaneous heterotopic facies. However, the lacustrine sediments of Linxi Foumation were deposited at the center of the basin while the red-bed of Xingfuzhilu Formation were deposited at the edge of the basin respectively. According to the above results and regional data, the study area is overall upper uplift during the period from Late Permain to Middle Triassic.It leads to the conclusion that the the final closure time of the Paleo-Asian Ocean is after Early Triassic.