Geological and geophysical investigations in the area around the southern Ryukyu islands - Report on RN02 cruise by T/S Nagasaki Maru -

摘要

As a part of the educational cruise (RN02 Cruise) for students of Faculty of Science, University of the Ryukyus, by T/S Nagasaki Maru, the scientific survey was carried out during May 27 to June 6, 2002. Geomagnetic survey was carried out in the Okinawa Trough and south of Ryukyu arc to investigate geomagnetic structure around the Nansei Islands. Several magnetic dipole anomalies were recognized at the Ishigaki knoll and west of the Ishigaki knoll in south Okinawa Trough. Two sites were sampled using a Niino-type dredger, and 13 sites were sampled using an Okean-type grab sampler. Surface sediments were successfully recovered from an island shelf through an adjacent slope off the west coast of Miyako Island. A large number of live large foraminifera, Cycloclepeu8 sp. were collected at a 94 m-deep island shelf site. Mediumgrained. sandstones containing fossil shell fragments were recovered at the seafloor between Yonaguni and Iriomote Islands and the west slope of Miyako Saddle. These rocks were considered to be recovered directly from the rocky bottom. We dredged seafloor samples at the northern shelf off Ishigaki-jima and Iriomote-jima to confirm the location of "Iriomote Submarine volcano" which erupted in 1924. No volcanic rocks were recovered from the shelf.