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部野佐群和根室群新的磁性地层资料。将该数据集与俄罗斯远东九州、四国岛和库页岛等地的数据集进行汇编，得到了西北太平洋上白垩统地层的区域内综合对比，可以校准到晚白垩世的地磁极性时间尺度。结合磁地层学和生物地层学对比，将这些带划分为晚白垩世C31r至C33r和白垩纪长正常段的地磁极性带。结合高分辨率菊石生物地层学和放射性年龄测年，在北美西部内陆的上白垩世序列中已经记录了相应的地磁反转。加州大谷层序的生物地层学也是明确的，但只有一个反转的层序可以与极性Chron C33r进行对比。南库页岛最完整的极性反转记录将提供一个综合的参考方案，不仅可用于对比北太平洋不同区域的不同动物群组合，而且有助于对上白垩统阶段界线的全球定义。

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.