Institution: | aDepartment of Geosciences, Faculty of Science, Osaka City University, Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan bCentre for Earth Science Studies, 7250 Akkulam, Thuruvikkal P.O., Trivandrum 695 031, India cDepartment of Geology, Peradeniya University, Kandy, Sri Lanka |