科研之友
微信
新浪微博
Facebook
分享链接
摘要
The iron-bearing compounds in manganese deep sea sediments (nodules and crusts) are studied by Mossbauer spectroscopy at 77, 4.2 and 0.3 K. The Mossbauer parameters and the concentration of the two main components alpha-FeOOH (goethite) and Fe5HO8 center dot 4H(2)O (ferrihydrite), are measured in 1 mm sampling steps. The mineral goethite exhibits defect crystal structure. It shows a Mossbauer sextet with broad and asymmetric lines at 77 K and at room temperature partially a doublet due to superparamagnetic state. Ferrihydrite has a very low blocking temperature (%26lt; 20 K) and in our measurements at 0.3 K, shows a Mossbauer sextet with broad lines. X-ray topography images of Fe-Mn nodules and crusts reveal a specific layer structure related to two long-period variations-1.9 million years (Ma) of the eccentricity e and 1.2 Ma of the obliquity epsilon of Earth%26apos;s axis, respectively. According to the Milankovitch astronomical theory they can enforce drastic changes of climate. The hydrogenous Fe-Mn nodules and crusts have a very low growth rate of 2-10 mm/Ma, while the diagenetic nodules grow faster, 10-50 mm/Ma. So time intervals up to 20 Ma could be covered. Some global geological events such as the rise of the Isthmus of Panama and the beginning of the modern bottom water circulation (about 6.4 Ma before present) have changed the crusts structure and have been discussed. Some specific boundaries in the layer structure of nodules are easily identified. This allows a quick initial self-dating of the nodules without the use of expensive isotopic radiometric methods of dating.
- 出版日期2013-7
