1. School of Earth Sciences, University of Bristol, 24 Tyndall Avenue, Bristol BS8 1TQ, UK
2. Department of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3AN, UK
3. Department of Earth Sciences, University College London, Gower Street, London WC1E 6BT, UK
4. Statoil ASA, 4035 Stavanger, Norway
5. Department of Earth Sciences, Memorial University of Newfoundland, 300 Prince Philip Drive, St John's, NL, A1B 3X5, Canada