Evaluating the scatter of Detrital Remanent Magnetizations and its effects on relative paleointensity estimates.

评估碎屑剩磁的分散性及其对相对古强度估计的影响。

• 批准号: 1447035
• 负责人: Dario Bilardello
• 金额: $ 10万
• 依托单位: University of Minnesota-Twin Cities
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-06-15 至 2019-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1447035&HistoricalAwards=false
• 关键词: Evaluating; scatter; Detrital; Remanent; Magnetizations

Records of the geomagnetic field are derived from both igneous and sedimentary rocks, together with certain archeological artifacts. Sedimentary rock sequences are continuous through time, and provide a better picture of the magnetic field's evolution, but bear the limiting disadvantage of only providing relative, rather than absoltute, geomagnetic intensity records. Additionally, sediments are subject to biases, which affect the final distributions of the magnetic particles and the recorded magnetization. While valid correction techniques exist to obviate for notable sediment magnetic-recording biases, to date these are not used to further correct the relative paleointensity records. Conducting a series of deposition experiments in laboratory-controlled magnetic fields, and correcting for the known biases has the potential of improving estimates of relative paleointensity. These improvements would significantly contribute to our understanding of the evolution of the geomagnetic field, and therefore the history of the geodynamo and the formation of the earths interior.Despite the vast amount of research, detrital remanent magnetization (DRM) probably remains the most poorly understood type of magnetic remanence. The importance of sedimentary records in paleomagnetism warrants a sustained effort in fully understanding how sediments acquire their magnetization and how accurately they record the geomagnetic field. The efficiency of DRM is limiting in providing records of magnetic field intensity: the variable scatter of individual magnetic particle directions results in a mean vector that maintains the average orientation of the ambient field but often not its inclination; importantly, the resultant vector length is dependent on the scatter, greatly affecting relative paleointensity (RPI) estimates. Magnetic anisotropy provides a useful measurement of the scatter of particle distributions: through measurements of magnetic anisotropy obtained from deposition experiments conducted in controlled magnetic fields, the effect of the ambient field direction and intensity on particle scatter will be evaluated. Magnetic anisotropy will be used to correct for misalignment biases by restoring the distribution of directions and inclinations. In turn, this allows restoring the intensity of magnetization, permitting a novel approach of investigating RPI. Two approaches are proposed: the first utilizes the anisotropy-corrected magnetizations to provide RPI estimates, while the second will instead utilize the corrected mean resultant vector of each group of experiments as a proxy for the magnetization intensity. The expectation is that the corrected magnetizations and resultant vectors yield more consistent RPI estimates, owing to the field-strength and field-inclination dependence on the inclination error. The resultant vector approach, if successful, would provide a simplified, more applicable means of providing RPI estimates.

地磁场的记录来源于火成岩和沉积岩，以及某些考古文物。沉积岩序列在时间上是连续的，提供了磁场演化的更好图景，但有限的缺点是只提供相对的、而不是绝对的地磁强度记录。此外，沉积物容易受到偏置的影响，这会影响磁性颗粒的最终分布和记录的磁化强度。虽然存在有效的校正技术来消除显著的沉积物磁记录偏差，但到目前为止，这些校正技术还没有被用来进一步校正相对古强度记录。在实验室控制的磁场中进行一系列沉积实验，并对已知的偏差进行校正，有可能提高相对古强度的估计。这些改进将大大有助于我们了解地磁场的演化，从而了解地球发电机的历史和地球内部的形成。尽管有大量的研究，碎屑剩磁(DRM)可能仍然是最鲜为人知的剩磁类型。沉积记录在古地磁中的重要性，需要持续努力，以充分了解沉积物如何获得其磁化作用，以及它们记录地磁场的精确度。DRM在提供磁场强度记录方面的效率是有限的：单个磁粒子方向的可变散射导致平均矢量保持环境磁场的平均取向，但通常不保持其倾角；重要的是，所产生的矢量长度取决于散射，这极大地影响了相对古强度(RPI)的估计。磁各向异性提供了一种有用的颗粒分布散布测量方法：通过测量在受控磁场中进行的沉积实验获得的磁各向异性，将评估环境磁场方向和强度对颗粒散射的影响。磁各向异性将被用来通过恢复方向和倾角的分布来校正未对准偏差。反过来，这允许恢复磁化强度，允许一种新的方法来研究RPI。提出了两种方法：第一种方法利用各向异性校正的磁化来提供RPI估计，而第二种方法则使用每组实验的校正的平均合成矢量作为磁化强度的替代。由于磁场强度和磁场倾角依赖于倾斜误差，因此期望修正的磁化强度和合成矢量产生更一致的RPI估计。如果成功，所产生的向量法将提供一种简化的、更适用的提供RPI估计数的手段。