科研之友
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摘要
A new protocol using the viscous remanent magnetization (VRM) of boulders to date cataclysmic geological events such as tsunamis, glacial floods, and landslides is presented and its performance is assessed against two jokulhlaups (glacial floods) of known age in Iceland. High-intensity jokulhlaups have the ability to break off large boulders from bedrock and emplace and rotate them. These rocks originally carried a remanent magnetization parallel to the geomagnetic field during their formation. After being rotated by the flood, they acquire a VRM parallel with Earth's magnetic field. In continuous thermal demagnetization experiments the unblocking temperature of the VRM can be determined, and subsequent rock magnetic VRM acquisition experiments can be used to establish a relationship between the unblocking temperature and the acquisition time, from which the time since the flood can be determined. The protocol was tested on 44 boulders from 2 historical jokulhlaups in Iceland and found to yield good order-of-magnitude estimates: 72 yr (confidence limits 11-360 yr) versus known 155 yr at the Solheimajokull jokulhlaup and 290 yr (confidence limits 80-2300 yr) versus known 288 yr for the Kotarjokull jokulhlaup. The method can therefore be a valuable tool for future dating of cataclysmic events.
- 出版日期2017-4
