1. Institute of Geology, Tallinn University of Technology, 19086 Tallinn, Estonia;
2. Department of Earth Science and Astronomy, The University of Tokyo, Komaba 153-8902, Japan; ,
3. Department of Earth Sciences, Programme for Palaeobiology, Uppsala University, Uppsala 75236, Sweden;
4. Department of Geology and Mineralogy, Kyoto University, Kyoto 606-8502, Japan;