Victoriano Pujalte (a), Juan Ignacio Baceta (a) & Birger Schmitz (b)
(a) Department of Stratigraphy and Paleontology, Faculty of Science and Technology, University of the Basque Country UPV/EHU, Ap. 644, 48080 Bilbao, Spain. E- mail: victoriano.pujalte@ehu.es
(b) Division of Nuclear Physics, Department of Physics, University of Lund, P.O. Box 118, SE-221 00 Lund, Sweden.