INTERNATIONAL CORRELATION OF MAGNETO-BIOSTRATIGAPHY OF JAPANESE CRETACEOUS

在日本北海道和俄罗斯库页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。结合磁地层学和生物地层学对比，我们可以将这些带划分为晚白垩世的极性克伦，包括白垩纪的超时代。日本西南部出泉群的一个极性序列由最低的反极性层位和一系列厚实的正极性层序组成，中间有两个反极性层位。根据以前的生物地层年龄限制，这些极性带的模式符合从坎帕尼亚早期的克莱恩斯33R到31R到最早的马斯特里赫特阶段的极性变化。在北海道中部的上Ezo群和库页岛南部的Bykov群中发现了厚厚的正极性序列。埃佐群的正极性层位被一个短的反转层位覆盖，它们产生了丰富的塞诺莫尼亚到坎帕尼亚时代的化石。因此，很可能将正极性归属于早寒武世白垩纪正极性超时C34n，并将上覆的反转带归属于随后的Chron 33r。库页岛南部厚厚的正常极性层被至少三个反极性带覆盖，包括坎帕尼亚早期的克莱恩斯33R和马斯特里赫蒂安的克莱恩斯32R和31R。所有这些反极性克莱恩斯在西北太平洋的白垩纪系统中首次被记录下来。日本和远东其他地区经常出现的极性反转及其与动物群组合的相互关系的连续记录提供了一个综合参考，对于连接北太平洋当地的生物地层分带具有价值，并作为寻求建立上白垩统阶段界线的全球定义的另一个校准依据。

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.