1. CAS Key Laboratory of Economic Stratigraphy and Palaeogeography, Nanjing Institute of Geology and Palaeontology, and Center for Excellence in Life and Palaeoenvironment, Chinese Academy of Sciences, Nanjing 210008, China
2. Department of Earth and Planetary Sciences, University of California at Davis, Davis, California 95616-8605, USA
3. Department of Geosciences, Virginia Tech, Blacksburg, Virginia 24061, USA