Synthesis of magnetostratigraphy of the Cretaceous System in the northwest Pacific: Results from the Nemuro Group and the lower Yezo Group

本研究提供了日本北海道下冶三群和根室群的磁性地层学新资料。将该数据集与来自俄罗斯远东九州、四国和库页岛等地的数据集进行汇编，可以对西北太平洋上白垩纪地层进行全面的区域内对比，从而可以将其校准到晚白垩纪的地磁极性时间尺度。结合磁性地层和生物地层对比，将这些带归属于晚白垩世地磁极性时，包括C31 r至C33 r和白垩纪长正常间隔。相应的地磁反转已被记录从上白垩纪的继承北美西部内陆，结合高分辨率菊石生物地层学和放射性年龄测定。加州大峡谷层序的生物地层也很明确，但只有一个反转层段可与极性年代C33 r相对比。最完整的记录极性反转在南库页岛将提供一个综合的参考方案，不仅可以在北太平洋不同地区的不同动物群组合的相关性，而且有助于全球上白垩纪阶段的边界的定义。

This study provides a new magnetostratigraphic data from the lower Yezo Group and the Nemuro Group in Hokkaido, Japan. Compilation of this data set and those from elsewhere as Kyushu, Shikoku and Sakhalin of Russian Far East leads to a comprehensive, intra-regional correlation of the Upper Cretaceous strata in the Northwest Pacific, which can be calibrated to the geomagnetic polarity time scale in the late Cretaceous. The combined magnetostratigraphic and biostratigraphic correlation has assigned these zones to the Late Cretaceous geomagnetic polarity chrons including C31r through C33r and the Cretaceous long normal interval. Corresponding geomagnetic reversals have been documented from the Upper Cretaceous successions of the Western Interior of North America, in combination with high-resolution ammonite biostratigraphy and radiometric age dates. Biostratigraphy of the Great Valley Sequence in California is also well-defined, but there is only one reversed interval that can be correlated with polarity chron C33r. The most complete record of polarity reversals in South Sakhalin would provide an integrated reference scheme which can be of significant use not only to correlate dissimilar faunal assemblages of disparate regions in the North Pacific, but also to contribute to a global definition of Upper Cretaceous stage boundaries.