Magnetostratigraphy of Mesozoic and Paleozoic Systems in Japan

1. 2.古地磁测量设备：1987年安装了一台自动超导岩石磁力仪（2G 760 R），使测量沉积岩极弱的剩余磁化成为可能。北海道的第三系：对北海道中部第三纪沉积物的古地磁研究表明，北海道中部在晚白垩世和早第三纪之间经历了一次绕垂直轴逆时针（CCW）旋转90 ^O的构造运动，之后在中新世中期又经历了一次顺时针（CW）旋转60 ^O的构造运动.九州南部第三系：对九州南部种子岛和日南地区中新世沉积物的古地磁研究表明，在过去5 Ma期间，九州南部发生了约30 ^O的逆时针旋转。这表明南九州是一个独立的构造单元，不属于西南日本地块.北海道白垩系：在北海道中部白垩系江佐群的最上部层序中发现了一个反极性带，其年代为早坎帕尼亚世的33 r。下部层序均表现为正极性，可归属于白垩纪正极性超时。偏角向西偏转，表明该地区存在CCW旋转。日本西南部的白垩系：四国和淡路岛上白垩纪泉群的磁性地层学研究确定了三个反向极性带，分别位于松山市西部、峨山山脉东部和淡路岛南部。它们分别可归属于晚白垩世33 r、32 r和32.1r亚时。据估计，泉群的沉积速率非常高，高达0.7至1厘米/年。

1. Equipment for paleomagnetic measurement : An automated superconducting rock-magnetometer (2G760R) was installed in 1987, which made it possible to measure extremely weak remnant magnetization of sedimentary rocks.2. Tertiary System in Hokkaido : A paleomagnetic study of the Tertiary deposits in central Hokkaido demonstrated that central Hokkaido had experienced a counter-clockwise (CCW) tectonic rotation by 90^O about the vertical axis during the period between late Cretaceous and early Tertiary and, afterwards, suffered a clockwise (CW) rotation by 60^O during the middle Miocene.3. Tertiary System in south Kyushu : Paleomagnetic studies of the Miocene deposits in Tanegashima Island and Nichinan district in south Kyushu indicated that a CCW rotation by about 30^O had taken place in south Kyushu during the last 5 Ma. This suggests that south Kyushu is an independent tectonic unit which does not belong to the Southwest Japan block.4. Cretaceous System in Hokkaido : A reversed polarity zone, correlatable to chron 33r in the early Campanian, was found from the uppermost successions of the Cretaceous Ezo Group in central Hokkaido. All the lower successions showed normal polarity which can be assigned to the Cretaceous normal polarity superchron. Declinations were deflected westward, suggesting a CCW rotation for the area.5. Cretaceous System in southwest Japan : Magnetostratigraphic studies of the Upper Cretaceous Izumi Group in Shikoku and Awaji Islands identified three reversed polarity zones from the west of Matsuyama City, eastern Asan Mountains, and southern Awaji Island. They are correlatable to chrons 33r, 32r, and subchron 32.1r in the latest Cretaceous, respectively. The estimated sedimentation rate of the Izumi Group is extremely high, as much as 0.7 to 1 cm/yr.