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

沉积物提供了地磁场行为的详细和连续的记录。除其他外，这些时间序列提供了对过去相对场强变化的估计，这些估计被用来校准源自高层大气中核素产生的气候代用指标。在从沉积物中提取和比较地磁场信息时，一个压倒一切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颗粒上的外部场的扭矩获得的，这被称为沉积（碎屑）或沉积后的剩磁磁化。然而，成岩过程可以在沉积期间或之后沉淀铁磁性铁氧化物和/或硫化物，从而产生二次化学剩余磁化。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，但后者的识别仍然具有挑战性的现有方法，因此它的潜在影响往往被忽视-特别是关于相对古强度记录。从再沉积实验的初步结果，我们表明，各向异性的非滞后reheticrehetic磁化参数随相对paleointensity，这意味着我们可能已经找到了一种方法，以减少分散在paleointensity估计的基础上磁各向异性。另一方面，化学剩磁具有与沉积剩磁大不相同的各向异性特征。我们展示了一个例子，沉积物从百慕大隆起（ODP网站1063），其中包含的化学沉淀物云英岩的视野。不同工作组对该场地的先前研究得出结论，碎屑磁铁矿是唯一的剩磁载体。利用无磁滞回线磁化技术，通过实验鉴定了云英岩。我们想使用基于无滞后反射磁化的实验，以更好地了解化学和沉积过程之间的古强度记录过程的差异，以及它们何时同时起作用，最终目标是产生更强大的相对古强度记录。

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.