1. Department of Geosciences, University of Oslo, PO Box 1047 Blindern, NO-0316 Oslo, Norway (e-mail: o.a.blaich@geo.uio.no)
2. Eni E&P, EASS, Via Emilia 1, I-20097 San Donato Milanese, Italy (present address)
3. Global Exploration, Statoil, Forusbeen 50, N-4035 Stavanger, Norway
4. Géosciences-Rennes, 35042 Rennes Cedex, France