Magnetostratigraphic Study for Quaternary in Japan

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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.