1. College of Earth Science and Resources; Chang'an University; Xi'an 710054 China
2. State Key Laboratory of Palaeobiology and Stratigraphy; Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences; Nanjing 210008 China
3. Key Laboratory of Economic Stratigraphy and Palaeogeography; Chinese Academy of Sciences (Nanjing Institute of Geology and Palaeontology); Nanjing 210008 China