Reversed polarity episode in the Late Brunhes Epoch as confirmed on parallel sections of Pleistocene deposits in the Kinki district, central Japan.

Abstract

Detailed paleomagnetic studies have been carried out on two sections of the Pleistocene sediments in the Kinki district, central Japan: the Takashima Formation exposed on the northwest coast of Lake Biwa, and the terrace forming deposits distributed in the northern area of Akashi City, about 150km west of Lake Biwa. While these strata are assigned to the late Brunhes normal epoch, reversed polarity zones are observed in both sections. Based on correlation of volcanic ash layers intercalated in the sections, these reversed polarity zones are identified as the records of a reversed polarity episode, the Biwa I ‘event’, which was previously reported from a 200-m-long core sample from Lake Biwa. This result confirms occurrence of a fully reversed geomagnetic field in the late Brunhes Epoch at least in central Japan. The Biwa I episode is possibly correlated to the Jamaica ‘event’ known from several deep-sea cores, and then the episode is suggested to be a global geomagnetic phenomenon in the late Brunhes epoch.