Distinguishing detrital versus chemical remanent magnetization in sediments: Toward a better understanding of relative paleointensity records

区分沉积物中的碎屑与化学剩磁：更好地理解相对古强度记录

• 批准号: 389869201
• 负责人: Professor Dr. Stuart Alan Gilder
• 金额: --
• 依托单位: Sektion Geophysik
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2017
• 资助国家: 德国
• 起止时间: 2016-12-31 至 2020-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/389869201?language=en
• 关键词: Distinguishing; detrital; versus; chemical; remanent

Sediments provide detailed and continuous records of geomagnetic field behavior. Amongst other things, these time series provide estimates for relative field intensity variations in the past, which are used and to calibrate climate proxies stemming from nuclide production in the upper atmosphere. An overriding assumption when extracting and comparing geomagnetic field information from sediments is that the recording mechanism remained constant. The common hypothesis is that magnetic remanence is acquired via torque from the external field acting on a magnetic particle, which is termed a depositional (detrital) or post-depositional remanent magnetization. However, diagenetic processes can precipitate ferrimagnetic iron oxides and/or sulphides during or after deposition, thereby producing a secondary, chemical remanent magnetization. The physics behind the recording mechanisms between depositional and chemical remanences are fundamentally different, yet the identification of the latter remains challenging with existing methods, and thus it's potential influence is often ignored--especially concerning relative paleointensity records. With preliminary results from redeposition experiments we show that anisotropy of anhysteretic remanent magnetization parameters vary with relative paleointensity, which means we may have found a means to reduce the scatter in paleointensity estimates based on magnetic anisotropy. On the other hand, a chemical remanent magnetization has a much different anisotropy signature than a depositional remanence. We show an example of sediments from the Bermuda Rise (ODP site 1063) that contains horizons of the chemical precipitate greigite. Previous studies from different working groups on this site conclude detrital magnetite is the sole remanence carrier. The identification of greigite was made possible through experiments using anhysteretic remanent magnetization techniques. We would like to use anhysteretic remanent magnetization-based experiments to better understand how the paleointensity recording process differs between chemical and depositional processes, as well as when they act simultaneously, with the ultimate goal of producing more robust relative paleointensity records.

沉积物提供了地磁场行为的详细且连续的记录。除其他外，这些时间序列提供了过去相对场强变化的估计，这些变化可用于校准高层大气中核素产生产生的气候代理。从沉积物中提取和比较地磁场信息时，最重要的假设是记录机制保持不变。常见的假设是，剩磁是通过作用在磁性粒子上的外部场的扭矩获得的，这被称为沉积（碎屑）或沉积后剩磁。然而，成岩过程可以在沉积期间或之后沉淀亚铁磁性铁氧化物和/或硫化物，从而产生二次化学剩磁。沉积和化学剩磁之间的记录机制背后的物理原理是根本不同的，但后者的识别对现有方法仍然具有挑战性，因此它的潜在影响经常被忽视——特别是在相对古强度记录方面。通过再沉积实验的初步结果，我们表明非滞留剩磁参数的各向异性随相对古强度的变化而变化，这意味着我们可能找到了一种减少基于磁各向异性的古强度估计中的分散性的方法。另一方面，化学剩磁具有与沉积剩磁截然不同的各向异性特征。我们展示了百慕大隆起（ODP 站点 1063）的沉积物示例，其中包含化学沉淀灰岩层。该地点不同工作组之前的研究得出结论，碎屑磁铁矿是唯一的剩磁载体。通过使用非磁滞剩磁技术的实验，使绿镁石的鉴定成为可能。我们希望使用基于非磁滞剩磁的实验来更好地了解化学过程和沉积过程之间的古强度记录过程有何不同，以及它们何时同时作用，最终目标是产生更可靠的相对古强度记录。

项目成果

Relative paleointensity estimates from magnetic anisotropy: Proof of concept

根据磁各向异性估计相对古强度：概念证明

• DOI: 10.1016/j.epsl.2019.05.003
• 发表时间: 2019
• 期刊: Earth and Planetary Science Letters
• 影响因子: 5.3
• 作者: Gilder;K. Wack;Ježek
• 通讯作者: Ježek

A Multi‐Proxy Approach to Unravel Late Pleistocene Sediment Flux and Bottom Water Conditions in the Western South Atlantic Ocean

• DOI: 10.1029/2020pa004058
• 发表时间: 2021-02
• 期刊: Paleoceanography and Paleoclimatology
• 影响因子: 3.5
• 作者: G. L. Mathias;S. Roud;C. Chiessi;M. C. Campos;B. Dias;T. Santos;A. Albuquerque;F. Toledo;K. B. Costa;B. Maher