1. Bureau of Economic Geology, John A. and Katherine G. Jackson School of Geosciences, The University of Texas at Austin, University Station, Box X, Austin, TX 78713-8924, USA
2. State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Fuxue Road 18th, Beijing 102200, People’s Republic of China
3. Grant Institute, The King’s Buildings, West Mains Road, University of Edinburgh, Edinburgh EH9 3JW, UK