1. a ORSTOM , 70 route d'Aulnay, 93140 Bondy, France and Université Paris IV
2. b Université Paris VI, Dpt de Geotectonique , 4 Place Jussieu, 75252 Paris Cedex 05, France
3. c Norsk Polaristitutt , Postboks 158, 1330 Oslo lufthavn, Norway
4. d Thames Polytechnic, School of Earth Sciences , Walburgh House Bigland Street, London, El 2NG, U.K.