1. Centre for Integrated Petroleum Research, University of Bergen Allegt. 41, N-5007 Bergen, Norway john.howell@geo.uib.no
2. Department of Earth Sciences, University of Ottawa 140 Louis Pasteur Pvt, Ottawa, Canada K1N 6N5
3. Centro de Investigaciones Geológicas, Universidad Nacionald de La Plata-CONICET Calle 1 No. 644, B11900TAC, La Plata, Argentina