Magnetostratigraphic Study for Quaternary in Japan

在本项目中，我们打算建立日本第四纪的精确磁地层。年龄越小，地磁场的波动幅度越小。在历史和考古年龄方面，通过对考古资料的回顾，结合最近获得的考古证据，得到了日本古代和中世纪地磁方向的精确的长期变化。火山岩、湖泊沉积物和石笋的古地磁研究表明，全新世的长期变化具有较好的一致性。通过对陆地和湖底沉积物的古地磁测量，获得了中晚更新世不同的详细磁地层剖面。特别是在宫城县北部出土了许多旧石器时代早期石器的研究，给出了一个几乎完整的布鲁内斯正极性时代的磁地层序列。在这个序列中发现了10次大的地磁波动，如倒转和偏移。Brunhes/Matuyama边界也出现在序列的最底层。这一结果表明，在日本诸岛居住并制造石器的人类历史，最早可追溯到60年前。同时对布伦什正极性期的磁地层年龄定年也有重要贡献。

In this project, we intended to establish the precise magnetostratigraphic of the Quaternary in Japan. The younger the ages are, the smaller the amplitude of the fluctuation of the geomagnetic field becomes.As for the historical and archeological age, precise secular variations of the geomagnetic field direction of the Japanese ancient and medieval age are obtained by reviewing archeomagnetic data with the recently obtained archeological evidence. Secular variations of the Holocene obtained from the paleomagnetic studies of volcanic rocks, lake sediments and stalagmites show a good agreement with each other.By the paleomagnetic measurements on sediments of both on land and lake bottom, it is obtained vary detailed magnetostratigraphic sections of the middle and late Pleistocene. Especially, the studies carried out in the northern part of the Miyagi Prefecture where many stone implements of the early paleolithic age were excavated gave an almost complete magnetostratigraphic sequence of the Brunhes Normal Polarity Epoch. Ten big geomagnetic fluctuations such as reversals and excursions are found in the sequence. Brunhes/Matuyama Boundfary is also found in the lowermost horizon of the sequence. This result revealed that the history of the human beings who dwelled and made stone implements in the Japanese Islands, trace back to 60 ka at the oldest. And also it will highly contribute on the magnetostratigraphic age dating in the Brunhes Normal Polarity Epoch.