Oscillating Geomagnetic Field with a Recurring Reversal Discovered from Lake Biwa
Oscillating Geomagnetic Field with a Recurring Reversal Discovered from Lake Biwa
复制标题
从琵琶湖发现反复反转的振荡地磁场
DOI：
10.2183/pjab1945.48.186
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发表时间：
1972
期刊：
影响因子：
--
通讯作者：
S. Horie
中科院分区：
文献类型：
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作者：
N. Kawai;K. Yaskawa;T. Nakajima;M. Torii;S. Horie
其中一位作者早就提出了一个从琵琶湖下面获取钻孔芯柱的项目。只是最近才令人满意地实现了这一目标。去年秋天，在湖底197米深处，终于挖出了柱状物的最低部分，现在有了一个由绿色粘土颗粒组成的长芯。自第三纪开始，湖泊开始存在，大量的粘土颗粒已经从她广阔的流域收集。它们都不停地落入水中，在水底形成了一层厚厚的淤泥。随着软泥在不断增加的载荷下逐渐固结，上覆颗粒不断增加，一个没有沉积间隙的原状盆地开始缓慢发展，直到其厚度超过1000 m。在显微镜下观察时，地核中含有细小的球形铁磁颗粒，与从海底收集的宇宙尘埃非常相似。在磁力计下进一步观察，发现整个柱体具有微弱但稳定的永久磁性。每个球体在水中下降时都会产生阻尼振荡，直到它的极性与地磁场的极性平行，然后在粘土基质中被磁化。因此，人们可以通过从地核的最高部分到最低部分连续测量磁性来追溯地磁场的时间。图1显示了地磁倾角如何随深度的增加而变化。在上述测量中，选择了40个取样层位，使它们可以均匀地分布在整个柱体上，间距几乎相等，为5 m。然后，从每个层位沿芯轴连续沿着切下三个试样，并在
A project to acquire a boring core column from below Lake Biwa had long been proposed by one of the authors. It is only recently that it was realized satisfactorily. The lowermost portion of the column was finally dug out last autumn from the depth 197 m below the lake bottom, and a long core composed of green clay particles became available now. Since the beginning of the Tertiary period in which the lake started to exist, an enormous amount of clay particles has been gathered from her vast drainage basin. They all were falling ceaselessly in water to form a thick ooze near the bottom. As the ooze became gradually consolidated under increasing load with increasing over-lying particles, an undisturbed basin with no gap of deposition began slowly to develop till its thickness exceeded over more than 1000 m. The core, when examined under the microscope, contains fine spherical ferromagnetic particles resembling conspicuously to the cosmic dust collected from ocean bottom. On further observation under the magnetometer, the whole column was found to possess a weak but stable permanent magnetism. Each sphere made a damped oscillation, whilst it was descending in water, till its polarity became parallel to that of the geomagnetic field and subsequently fossilized within the clay matrix. Consequently, one could trace the geomagnetic field backward in time by measuring the magnetism from the uppermost part of the core to the lowermost successively. In Fig. 1 is shown how the geomagnetic inclination changes with increasing depth. In the above measurements 40 sampling horizons were so chosen that they may spread over the entire column uniformly with a nearly equal separation of 5 m. Then, from each horizon three specimens were cut off successively along the core axis, and measured after the