1. University of Leeds, School of Earth Sciences, Leeds LS2 9JT, United Kingdom.
2. Shell International Exploration and Production B. V., Research and Technical Services, EPT-GA, Volmerlaan, P.O. Box 60, 2280 AB Rijswijk, The Netherlands.
3. GETECH, c/o University of Leeds, School of Earth Sciences, Leeds LS2 9JT, United Kingdom. Emails: