Stratigraphy and depositional palaeogeography of the Early Cretaceous basins in Da Hinggan Mountains-Mongolia orogenic belt and its neighboring areas

Based on a review of the Early Cretaceous stratigraphy and depositional palaeogeography in the Da Hinggan Mountains-Mongolian orogenic belt(DMOB)(i.e., the southern margin of the Central Asian Orogenic Belt) in combination of previous results and regional geological survey, this paper attempts to discuss the Early Cretaceous sedimentary basins in term of stratigraphy and sedimentology. Overlying the early coarse grained deposits of the late Jurassic-early Cretaceous period, there exists a huge NE-trending volcanic and sedimentary rock belt consisting of thick acidic-intermediate lavas, volcaniclastic rocks and fluvial-lacustrine sedimentary rocks, which is well correlatable with the Zhangjiakou Formation and the younger strata(Dabeigou,Formation, Yixian Formation etc.). Studies show that rifting basins were unique in the east of the DMOB in the Early Cretaceous period, and high terrain, fluvial and lacustrine environments were co-existent as well, which provided a favorable paleoecology and an ideal setting for emerging of the Jehol Biota at that time. Moreover, as a result of intense NE-trending crust extension in the Early Cretaceous period, the basins extended farther. At the same time, sedimentary basins and the Jehol Biota correspondently extended further, reaching such regions as northern Hebei, western Liaoning, southern Inner Mongolia, Far East and East Asia. Studies show that the Da Hinggan volcanic rocks belt was likely generated by partial melting of newly underplated basaltic lower crust as a result of asthenosphere upwelling, but with no well-grounded evidence showing the relation with the subduction of the Izanagi plate, which preluded more large-scale regional crust stretch of eastern China in the mid-late Early Cretaceous. In addition, eastern China in the late Early Cretaceous was totally in a back-arc tectonic setting of the subduction of the Izanagi plate towards the Eurasia.