Quantifying Inclination Shallowing and Representing Flattening Uncertainty in Sedimentary Paleomagnetic Poles
Quantifying Inclination Shallowing and Representing Flattening Uncertainty in Sedimentary Paleomagnetic Poles
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DOI：
10.1029/2022gc010682
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发表时间：
2022-10
期刊：
影响因子：
3.7
通讯作者：
J. Pierce;Yiming Zhang;E. Hodgin;N. Swanson‐Hysell
中科院分区：
文献类型：
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作者：
J. Pierce;Yiming Zhang;E. Hodgin;N. Swanson‐Hysell
倾角是磁化矢量与水平面的角度。碎屑沉积岩经常经历倾角变浅，由此同沉积过程导致相对于局部地磁场倾角平坦的碎屑剩磁。记录的倾向与真实值的偏差给重建古纬度带来了挑战。估计平坦因子 (f) 的一种广泛使用的方法是将磁化矢量集合的形状与古世变模型（伸长/倾斜 [E/I] 方法）导出的形状进行比较。很少有研究将这种统计方法的结果与凭经验确定的平坦因子进行比较，而且在元古代还没有研究。在这项研究中，我们评估了 Cut Face Creek 砂岩 11 亿年前含赤铁矿红层内的倾角变浅情况，该红层以已知倾角的熔岩流为界。以火山岩的这种倾向作为预期方向，我们发现碎屑赤铁矿剩磁变得平坦，f=0.650.560.75 $f=0.6{5}_{0.56}^{0.75}$，而颜料赤铁矿磁化强度与火山岩具有共同的平均值。使用颜料赤铁矿方向作为预期倾角，结果为 f=0.610.550.67 $f=0.6{1}_{0.55}^{0.67}$ 。这些平坦因子与通过 E/I 方法 f=0.640.510.85 $\left(f=0.6{4}_{0.51}^{0.85}\right)$ 估计的一致，支持其在深度时间的应用。然而，所有方法都具有与确定平坦因子相关的显着不确定性。这种不确定性可以被纳入古地磁极，所得的椭圆近似于肯特分布。不应寻求寻找“平坦因子”或假设单一值，而应认识到平坦因子固有的不确定性并将其纳入古地磁综合中。
Inclination is the angle of a magnetization vector from horizontal. Clastic sedimentary rocks often experience inclination shallowing whereby syn‐ to post‐depositional processes result in flattened detrital remanent magnetizations relative to local geomagnetic field inclinations. The deviation of recorded inclinations from true values presents challenges for reconstructing paleolatitudes. A widespread approach for estimating flattening factors (f) compares the shape of an assemblage of magnetization vectors to that derived from a paleosecular variation model (the elongation/inclination [E/I] method). Few studies exist that compare the results of this statistical approach with empirically determined flattening factors and none in the Proterozoic Eon. In this study, we evaluate inclination shallowing within 1.1 billion‐year‐old, hematite‐bearing red beds of the Cut Face Creek Sandstone that is bounded by lava flows of known inclination. Taking this inclination from the volcanics as the expected direction, we found that detrital hematite remanence is flattened with f=0.650.560.75 $f=0.6{5}_{0.56}^{0.75}$ whereas the pigmentary hematite magnetization shares a common mean with the volcanics. Using the pigmentary hematite direction as the expected inclination results in f=0.610.550.67 $f=0.6{1}_{0.55}^{0.67}$ . These flattening factors are consistent with those estimated through the E/I method f=0.640.510.85 $\left(f=0.6{4}_{0.51}^{0.85}\right)$ supporting its application in deep time. However, all methods have significant uncertainty associated with determining the flattening factor. This uncertainty can be incorporated into paleomagnetic poles with the resulting ellipse approximated with a Kent distribution. Rather than seeking to find “the flattening factor,” or assuming a single value, the inherent uncertainty in flattening factors should be recognized and incorporated into paleomagnetic syntheses.