The sedimentary environment and boundary of Permian-Triassic strata in the southern Da Hinggan Mountains, Inner Mongolia

The continental Permian-Triassic boundary is one of the most important problems in the study of the global PermianTriassic boundary. Based on collecting and analyzing tuff samples,the authors conducted LA-ICP-MS U-Pb dating of zircon and obtained an age of (255.5±1.1)Ma in the stratotype section of the middle part of Xingfuzhilu Formation. A total of 20 species of 17 genera sporopollen fossils were discovered on the top of the tuff in the stratotype section. The age of Xingfuzhilu Formation is late Late Permian-early Early Triassic according to the sporopollen fossils. It is considered that the middle part of Xingfuzhilu Formation should be late Late Permian whereas the upper part belongs to early Early Triassic. The boundary of Permian and Triassic strata in Da Hinggan Mountains is actually located inside Xingfuzhilu Formation. Moreover,the Late Permian-Early Triassic strata are of continuous deposition in Da Hinggan Mountains. With red-red features as a dividing point,Xingfuzhilu Formation totally reflects the thermal,arid and strong oxidation climate. It can be dated back to late Late Permian-early Early Triassic. The red beds came into existence from the late Late Permian in Da Hinggan Mountains. In addition,the climate changed from warm and rainless to arid and thermal,which is in accord with features of neighbouring North China and Junggar basin in Xinjiang. These data prove that the thermal,arid and strong oxidation climate did exert an profound influence on Da Hinggan Mountains.