古第三紀花崗岩の古地磁気(I)

Granitic rocks dated at 36 to 64 million years were collected from eight localities in San-in distnct, and the magnetrc polality versus their ages was determined by paleomagnetic methods. Samples dated at 57±3 and 63 million years have shown the normal polarity after stability tests and those dated at 46 and 50±6 million years the reversed polarity. The direction of the natural remanent magnetization of samples taken from Ningyo-toge, Sangenya and Otani deviated slightly from the present geomagnetic field direction. It rs likely to be due to change in directron of the geomagnetic field such as a field reversal or secular variation.