Paleomagnetic Study of Antarctic Deep-Sea Cores
Paleomagnetic Study of Antarctic Deep-Sea Cores
复制标题
南极深海岩心的古地磁研究
DOI：
10.1126/science.154.3747.349
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发表时间：
1966
期刊：
影响因子：
56.9
通讯作者：
John H. Foster
中科院分区：
文献类型：
--
作者：
N. Opdyke;Billy P. Glass;J. D. Hays;John H. Foster
用旋转磁力仪测量了南极7个深海岩心的约650个样品的磁倾角和磁倾角。这一系列测量提供了一种磁性地层学，其基础是每个岩心的正极或反极化样的区域，然后与Cox等人的磁性地层学相关联。(1)。其中一个岩芯(V16-134)给出了大约350万年前的古地磁场的连续记录。当选定的样品经受交变磁场退磁时，大多数被发现具有被150个奥斯特的磁场去除的不稳定成分；来自两个岩心的所有样品在150奥斯特的磁场中部分退磁。这两个核心的平均倾斜度与核心位置纬度的环境磁场的平均倾斜度非常一致。还发现样品的强度在反转点降低；如果像发电机理论所假设的那样，偶极场的强度降到零并以相反的极性重新建立，这一发现是可以预料的。我们认为岩心的磁化作用是碎屑磁铁矿存在的结果，尽管也可能存在其他磁性矿物。根据放射虫的向上顺序消失，在这些南极岩心中识别出四个动物群带(、X、和)。动物群的边界和逆转彼此之间具有相同的关系，这表明它们都是依赖于时间的现象。利用先前确定的反转时间，人们可以在岩芯中确定以下事件的年代：1)放射虫动物群边界：-X，200万年；-，X-，70万年；-，40万至50万年。这些日期与之前从无线电度量日期推断的年龄很好地吻合。2)大约200万年前，南极硅藻开始渗流沉积。3)首次发现冰筏碎屑，大约在250万年前。人们还可以计算沉积速率，在所研究的岩心中，每1000年从1.1毫米到大约8.0毫米不等。印度洋岩心的沉积速率高于别林豪森海岩心。岩心的动物群变化和逆转的近乎一致表明了一种因果关系，但并没有证明这一点。从这项研究中我们得出结论，古地磁地层学是对深海岩心进行对比和定年的唯一方法，未来对这些岩心的研究可能会提供超过400万年的地球磁场历史的完整或几乎完整的记录。
The magnetic inclinations and inten sities of about 650 samples from seven deepsea cores taken in the Antarctic were measured on a spinner magnetometer. This series of measurements provided a magnetic stratigraphy, based on zones of normally or reversally polar ized specimens for each core, which was then correlated with the magnetic stra tigraphy of Cox et al. (1). One core (V16-134) gave a continuous record of the paleomagnetic field back to about 3.5 million years. When selected samples were subject ed to alternatingfield demagnetization, most were found to have an unstable component that was removed by fields of 150 oersteds; all samples from two cores were partially demagnetized in a field of 150 oersteds. The average inclination in these two cores was then in good agreement with the average inclination of the ambient field for the latitude of the core site. It was also found that the intensities of the samples decreased at the points of reversal; this finding is to be expected if, as has been postulated by the dynamo theory, the intensity of the dipole field decreases to zero and builds again with opposite polarity. We believe that the magnetiza tion of the cores results from the pres ence of detrital magnetite, although other magnetic minerals also may be present. Four faunal zones (, X, , and ) have been recognized in these Antarctic cores on the basis of upward sequential disappearance of Radiolaria. The faunal boundaries and reversals consistently have the same relations to one another, indicating that they are both timedependent phenomena. Using previously determined times of reversal, one may date the following events in the cores: 1) Radiolarian faunal boundaries:-X, 2 million years; X-, 0.7 million years; -, 0.4 to 0.5 million years. These dates are in good agreement with ages previously extrapolated from radio metric dates. 2) Initiation of Antarctic diatom ooze deposition, approximately 2.0 mil-lion years ago. 3) First occurrence of ice- rafted detritus, approximately 2.5 million years ago. One can also calculate rates of sedi mentation, which vary in the cores studied from 1.1 to about 8.0 millimeters per 1000 years. Sedimentation rates for the Indian Ocean cores are higher than for the Bellingshausen Sea cores. The near coincidence of faunal changes and reversals in the cores suggests but does not prove a causal relation. We conclude from this study that paleomagnetic stratigraphy is a unique method for correlating and dating deep sea cores, and that future work with such cores may provide a complete or nearly complete record of the history of the earth's magnetic field beyond 4 million years.