Post-depositional remanent magnetization lock-in depth in precisely dated varved sediments assessed by archaeomagnetic field models
Post-depositional remanent magnetization lock-in depth in precisely dated varved sediments assessed by archaeomagnetic field models
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DOI：
10.1016/j.epsl.2014.11.016
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发表时间：
2015-01
影响因子：
5.3
通讯作者：
Anette Mellström;A. Nilsson;T. Stanton;R. Muscheler;I. Snowball;N. Suttie
中科院分区：
文献类型：
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作者：
Anette Mellström;A. Nilsson;T. Stanton;R. Muscheler;I. Snowball;N. Suttie
要评价沉积后剩磁锁锁作用的存在及其对沉积古地磁记录的影响，需要精确的年代学。在此，我们利用基于古磁数据的模型预测，介绍了来自瑞典变湖泊沉积物（Kälksjön和Gyltigesjön湖）的两个古地磁记录的锁定模拟结果。利用14c摆动匹配定年技术提高了3000 ~ 2000 cal BP期间Kälksjön阀年表的精度，该时期具有明显的古地磁长期变化特征。该方法使我们能够推断出不确定性为±20年的年龄模型（概率范围为95.4%）。此外，我们将Kälksjön与Gyltigesjön的古地磁记录进行了比较，发现Gyltigesjön具有相应的14c摆动匹配年代学。由摆动匹配年代学得到的古地磁特征的年龄比古地磁模型预测的年龄要早。采用不同的滤波函数进行锁定建模，以解释湖泊沉积物古地磁数据的时间偏移和振幅。分析表明，线性锁相函数的锁相深度（在锁相深度以下没有自然剩磁）范围在Kälksjön的30至80厘米和Gyltigesjön的50至160厘米之间最适合解释这些数据。没有生物扰动“混合带”的沉积物相对较深的锁定深度可归因于湖泊沉积物相对较高的有机含量和较低的密度，这有助于形成沉积物序列较厚的松散上部带，在该区域可以发生磁颗粒的重新排列。
Accurate and precise chronologies are needed to evaluate the existence and effect of a post-depositional remanent magnetization lock-in process on sedimentary palaeomagnetic records. Here we present lock-in modelling results of two palaeomagnetic records from varved lake sediments (lakes Kälksjön and Gyltigesjön) in Sweden by using model predictions based on archaeomagnetic data. We used the14C wiggle-match dating technique to improve the precision of the Kälksjön varve chronology in the period between 3000 and 2000 cal BP, which is characterized by pronounced palaeomagnetic secular variation. This method allowed us to infer an age model with uncertainties of ±20 years (95.4% probability range). Furthermore, we compared the palaeomagnetic record of Kälksjön to Gyltigesjön, which has a corresponding14C wiggle-matched chronology. The ages of palaeomagnetic features derived from the wiggle-matched varve chronologies are older than those predicted by the archaeomagnetic models. Lock-in modelling was performed with different filter functions to explain the temporal offset and the amplitude of the lake sediment palaeomagnetic data. The analyses suggest that a linear lock-in function with lock-in depths (the depth below which no more natural magnetic remanence is acquired) that range between 30 and 80 cm in Kälksjön and 50 and 160 cm in Gyltigesjön are most appropriate to explain the data. These relatively deep lock-in depths in sediments without a bioturbated ‘mixed-zone’ can be attributed to the relatively high organic contents and low density of the lake sediments, which contribute to a thick unconsolidated upper zone of the sediment sequence in which re-alignment of magnetic particles can take place.