Institute of Geology and Paleontology, Graduate School of Science, Tohoku University, Aobayama, Sendai 980-8578, Japan

Department of Earth Sciences, Faculty of Science, Kumamoto University, Kurokami 2-39-1, Kumamoto 860-8555, Japan

Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology (JAMSTEC). Monobe-otsu 200, Nangoku, Kochi 783-8502, Japan

Institute of Earth Sciences (Geology and Palaeontology), University of Graz, Heinrichstrasse 26, 8010 Graz, Austria

John A. and Katherine G. Jackson School of Geosciences, Department of Geological Sciences, The University of Texas at Austin, 1 University Station C1100, Austin, Texas 78712-0254, USA

Institut für Geowissenschaften, Universität Potsdam-Postfach 60 15 53, 14415 Potsdam, Germany