Department of Mineralogy ; University of Geneva
Paläontologisches Institut und Museum ; Universität Zürich
Institute of Geology ; University of Lausanne
Work supported by the Swiss NSF project 200021-103335, by the Swiss NSF project 200020-105090/1, by a Rhône-Alpes-Eurodoc grant, and by the Association Franco-chinoise pour la Recherche Scientifique et Technique (PRA T99-01).