**Acknowledgements**

This research was funded by the Science and Technology Research and Development Program of China Petroleum and Chemical Corporation (No. P06088), Nonprofit Special Research Program (No. 200811015), Land Resource Survey Project of the Ministry of Land and Natural Resources, China (No. 1212010782003), Major State Research Development Program of China (No. 2016YFC0600202) and the China Geological Survey (CGS, No. DD20160183).
