INTERNATIONAL CORRELATION OF MAGNETO-BIOSTRATIGAPHY OF JAPANESE CRETACEOUS

在日本北海道和俄罗斯萨哈林岛南部的上白垩统沉积地层中发现了一系列正极性和反极性带。结合磁性地层学和生物地层学的对比，我们将这些带划分为晚白垩世的极性层，包括白垩纪的超年代。日本西南部泉群的极性层序由极性反转的最低层和厚层的正极性层以及两个极性反转的中间层组成。根据以前的生物地层年龄的限制，这些极性区的模式相匹配的极性变化，从Chrons 33r通过31r在早期Campanian最早的马斯特里赫特阶段。在北海道中部的上埃佐群和萨哈林岛南部的比科夫群中，发现了正常极性的厚层序列。Ezo群的正极性层被一个短的反极性层覆盖，它们产出了丰富的Cenomanian至Campanian时代的化石。因此，最有可能的是，正常极性可以被指定为白垩纪的正常极性超时C34 n和上覆的反转带被指定为随后的Chron 33 r在早期Campanian。萨哈林岛南部厚层的正极性层上至少覆盖着三个反极性层带，其中包括Campanian早期的Chrons 33r和Maastrichtian的Chrons 32r和31r，这些反极性层带均为西北太平洋白垩系首次记录。极性反转的连续记录及其与日本和远东其他地区常见的动物群组合的相关性提供了一个综合参考，该参考对于连接北太平洋的当地生物地层带具有价值，并作为另一个校准基础，以寻求建立上白垩纪阶段边界的全球定义。

A series of normal and reversed polarity zones have been found from [he Upper Cretaceous sedimentary strata in Hokkaido of Japan and south Sakhalin of Russia. Combined magnetostratigraphic and biostratigraphic correlation has enabled us to assign these zones to the Late Cretaceous polarity chrons including the Cretaceous superchron.A polarity sequence in the Izumi Group in southwest Japan consists of the lowermost horizon of reversed polarity and a thick succession of normal polarity with two intervening horizons of reversed polarity. Based upon previous biostratigraphic age constraints, the Pattern of these polarity zones matches a polarity change from Chrons 33r through 31r during the early Campanian to the earliest Maastrichtian stages. Thick successions of normal polarity were recognized in the Upper Ezo Group in central Hokkaido and the Bykov Group in south Sakhalin. The normal polarity horizon of the Ezo Group is overlain by a short reversed horizon, and they yield abundant fossils of Cenomanian to Campanian age. It is thus most likely that the normal polarity can be assigned to the Cretaceous normal polarity superchron C34n and the overlying reversed zone assigned to subsequent Chron 33r in the early Campanian. The thick horizon of normal polarity in south Sakhalin is overlain by at least three zones of reversed polarity, including Chrons 33r in the early Campanian and Chrons 32r and 31r in Maastrichtian.All these reversed polarity chrons have been documented for the first time from the Cretaceous systems of the Northwest Pacific. The successive record of polarity reversals and their correlation to faunal assemblages that commonly occur in Japan and other areas in the Far East provide an integrated reference that should be of value for linking local biostratigraphic zonations in the North Pacific and serve as another basis for calibration in the quest to establish a global definition of Upper Cretaceous stage boundaries.