1. Key Laboratory of Shale Gas and Geoengineering, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China, wangyibo@mail.iggcas.ac.cn
2. Also at Institutions of Earth Science, Chinese Academy of Sciences, Beijing 100029, China; and University of Chinese Academy of Sciences, Beijing 100049, China.
3. Also at Institutions of Earth Science, Chinese Academy of Sciences, Beijing 100029, China.