Palaeomagnetism of a Core from Lake Biwa (I)

Abstract

A core 197.2m long was taken from the central region of Lake Biwa. About 10000 serial specimens were prepared from the axis of the core to study palaeomagnetism. They have remanent magnetization stable enough to allow us to decipher the geomagnetic field of the past. The palaeomagnetic results are shown in detail down to 30m from the top of the core. The age of this depth is estimated at about 60000yr B. P. Smoothed curves of magnetic inclination and intensity as functions of depth are obtained by a seven-point moving average, reflecting the variation of the past geomagnetic field.

A geomagnetic reversal in the latest Brunhes epoch discovered at Shibutami, Japan.

“…In Japan, an excursion at 18,000 years B.P. found in the sediment core from the Lake Biwa was reported by NAKAJIMA et al (1973) andYASKAWA et al . (1973).…”

Site 488

“…The upper magnetozone correlates with the Brunhes normal polarity epoch and three short reversed polarity intervals with short events, established in Lake Biwa sediments (B, H, and I; K and L of Yaskawa et al, 1973). K and L of Yaskawa et al (1973) correlates with the Blake Event; the middle magnetozone can be correlated with the later part of the Matuyama reversed polarity epoch.…”

Paleomagnetism of a core from Osaka Bay.

“…In Japan, such investigations started with lacustrine deposits in Lake Biwa (YASKAWA et al, 1973) and were followed by work in Lake Kizaki (HORIE et ad., 1980). Although the main purpose of these works is to observe a secular variation of the past geomagnetic field, there is still few explanations on recording process of the geomagnetic field in sediments.…”