Terminal Ediacaran Stratigraphy and Macrofossils in Northern Qaidam Block and Northwestern North China Block

The terminal Ediacaran strata developed in northern Qaidam Block and western and southwestern North China Block are composed of a lower diamictite unit and an upper finer-grained siliciclastic unit. The combination of two units is represented by the Hongtiegou and Zhoujieshan formations in northern Qaidam Block, the Zhengmuguan and Tuerkeng formations in western North China Block, and the Luoquan and Dongpo formations in southwestern North China Block. Abundant macrofossils have been reported from the upper finer-grained siliciclastic unit in recent years, including Ediacara-type fossil Charnia, tubular fossil Shaanxilithes, palaeopascichnids, macroalgae, and other taxa. The occurrence of the terminal Ediacaran candidate index fossil Shaanxilithes in Zhoujieshan, Tuerkeng, and Dongpo formations constrains the depositional age of these post-glacial siliciclastic units to be ~550–539 Ma. Together with the co-occurrence of Charnia in the Zhoujieshan Formation and palaeopascichnids in the Dongpo Formation, it suggests that those conformably underlying diamictite units, which show a gradual transition to the upper siliciclastic units, are also late Ediacaran glacial depositions, probably later than the Gaskiers glaciation. Overall, combined paleontological, stratigraphic, and geochronological data reveal a large unconformity between the terminal Ediacaran strata and underlying Paleo-Mesoproterozoic strata, and also supports that the Qaidam Block had a close paleogeographic affinity to the North China Block during the late Ediacaran. The widespread occurrences of late Ediacaran glacial deposits around these two blocks may suggest that the Qaidam Block and North China Block were situated in middle to high latitudes, rather than equatorial region as suggested in many previous reconstructions, during the late Proterozoic.