Sedimentary records of reversal transitions ‐ Magnetization smoothing artefact or geomagnetic field behaviour?
Sedimentary records of reversal transitions ‐ Magnetization smoothing artefact or geomagnetic field behaviour?
复制标题
反转转变的沉积记录 - 磁化平滑人工制品或地磁场行为？
DOI：
10.1029/92gl02140
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发表时间：
1992
影响因子：
5.2
通讯作者：
E. Herrero
中科院分区：
文献类型：
--
作者：
R. Weeks;M. Fuller;C. Laj;A. Mazaud;E. Herrero
在过去的1200万年的沉积记录反转显示出他们的VGP路径的优先选择。这一观测结果可能与长期的核幔动力学有关。然而，有人认为，沉积VGP路径可能是一个假象，由于平滑混合非对映前和后过渡方向。我们在这里表明，平滑不切实际的长时间尺度需要产生中间磁化方向，这是纯粹的混合物的前和后过渡方向的沉积物中，其剩磁主要是沉积（DRM）或沉积后剩磁（PDRM）。沉积记录的过渡显示VGP的路径局限于立即前和后过渡VGP的平面，但是已经观察到。这可以用非反转场中的非轴对称偏置来解释[Gubbins和Bloxham，1987; Constable，1992]，它在反转中起作用。因此，只要磁化方向被适当地清洁以给出单分量方向，则反向VGP路径的优先偏移将归因于场行为而不是磁化过程的伪影。然而，如果测量在岩石形成时获得的初级磁化和稍后获得的次级磁化的混合，则将产生伪影。
Sedimentary records of reversals for the past 12 million years exhibit preferred longitudes of their VGP paths. This observation may be related to long term aspects of core-mantle dynamics. However, it has been suggested that sedimentary VGP paths could be an artefact due to smoothing which mixes non antipodal pre- and post-transitional directions. We show here that smoothing over unrealistically long time scales is required to generate intermediate directions of magnetization which are purely mixtures of pre- and post-transitionals directions in sediments whose remanence is primarily depositional (DRM) or post-depositional remanence (PDRM). Sedimentary records of transitions showing VGP paths confined to the planes of immediately pre- and post-transitional VGPs have however been observed. These can be explained by non-axisymmetric bias in the non-reversing field [Gubbins and Bloxham, 1987; Constable, 1992], which plays a role in reversals. Therefore, provided that magnetization directions are properly cleaned to give single component directions, the preferential longitudes of reversal VGP paths will be due to field behaviour and not to an artefact of the magnetization process. If, however, mixtures of primary magnetization acquired at the time of the formation of the rock and secondary magnetization acquired later are measured, then artefacts will be generated.