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An Analysis of the Formation of the Japan and Chishima Basins by a Paleomagnetic Study of South Sakhalin.

通过南萨哈林岛的古地磁研究分析日本和千岛盆地的形成。

基本信息

批准号：
02041062
负责人：
KODAMA Kazuto
金额：
$ 4.48万
依托单位：
Kochi University
依托单位国家：
日本
项目类别：
Grant-in-Aid for international Scientific Research
财政年份：
1990
资助国家：
日本
起止时间：
1990 至无数据
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-02041062/
关键词：
Sakhalin Upper Cretaceous Paleomagnetism Naiba River テクトニクス

项目摘要

The study area was the region near Bykov City, about 50 km north of Yuzhno-Sakhalinsk City in South Sakhalin, USSR. The area, 20 X 10 km in areal extent, is underlain by Cretaceous through Neogene deposits, with well-exposed Upper Cretaceous sections along the Naiba River and its branches. We spent there 30 days for geological survey and rock sample collection. One week was taken for field surveys of Tertiary sections near Yuzhno-Sakhalinsk, Kholmsk and Kolsakov Cities.An intensive geological mapping was conducted for the Naiba River sections which have long been known as a type locality of the Upper Cretaceous of Northwest Pacific. The ammonite biostraitgraphy established by this study has revealed that the age of the Cretaceous strata ranges Aptian to Maastrichtian. The Cretaceous system is overlain unconformably by coal-rich Paleogene and Neogene formations.Samples for paleomagnetism were collected, using portable rock drill, at 118 different levels of the Cretaceous sections in the Naiba area and at 68 horizons of the Tertiary sections in the Naiba and the other regions. A total of 1224 core samples were drilled in place, from which 2160 specimens were prepared for paleomagnetic measurements. About one fourth of the Tertiary specimens have been measured so far with a cryogenic magnetometer, after progressive alternating field or thermal demagnetization. Intensities of natural remanent magnetization were fairy week, ranging 10^<-4>to 10^<-3> A/m. Only one third of the specimens possessed stable magnetization component. Unfolded directions of the Paleogene specimens deflected eastward by 30^ﾟ to 60^ﾟ in declination, while those of the Neogene did not. The systematic change in declination with time is consistent with that reported for the Tertiary deposits in Hokkaido. It seems therefore that both South Sakhalin and Hokkaido suffered a clockwise rotation in the Tertiary.

研究区域位于苏联南萨哈林州尤日诺-萨哈林斯克市以北约50 km处的比科夫市附近。该区域面积为20 X 10 km，其下为白垩纪至新近纪沉积物，沿着奈巴河及其支流有出露良好的上白垩纪剖面。我们在那里呆了30天，进行地质调查和岩石样品收集。对尤日诺-萨哈林斯克、霍尔姆斯克和科尔萨科夫市附近的第三系剖面进行了为期一周的野外调查，并对长期以来被认为是西北太平洋上白垩统模式产地的奈巴河剖面进行了深入的地质填图。通过研究建立的菊石生物地层学揭示了白垩纪地层的时代范围为Aptian至Maastrichtian。利用便携式凿岩机在奈巴地区白垩系剖面的118个不同层位和奈巴等地区第三系剖面的68个层位采集了古地磁样品。共钻探了1224个岩心样品，从中制备了2160个样品用于古地磁测量。大约四分之一的第三纪标本已被测量到目前为止，与低温磁力计，渐进交变场或热退磁后。自然磁化强度为10 ~ <-4>10^<-3>A/m，为弱磁化。只有三分之一的样品具有稳定的磁化分量。古近纪样品的展开方向在10年间向东偏转了30 ~ 60^m，而新近纪样品的展开方向没有偏转。系统性的变化随时间的递减是一致的，在北海道的第三纪沉积物的报告。因此，似乎南库页岛和北海道在第三纪都经历了顺时针旋转。