Shape difference of mud clasts depending on depositional facies: application of newly modified elliptic Fourier analysis to hybrid event beds
Shape difference of mud clasts depending on depositional facies: application of newly modified elliptic Fourier analysis to hybrid event beds
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DOI：
10.2110/jsr.2020.67
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发表时间：
2020-10
影响因子：
2
通讯作者：
S. Fukuda;H. Naruse
中科院分区：
文献类型：
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作者：
S. Fukuda;H. Naruse
混合事件层是沉积物重力流的沉积物，通过其通道改变其流变行为，夹带泥质沉积物并阻尼湍流。杂化事件层的泥质相常伴有丰富的泥质碎屑，其大小和形状各异。混合事件层中碎屑产状的变化有望保存海底密度流中泥质沉积物夹带和搬运过程的信息。然而，以往对混合事件层的分析侧重于描述碎屑的整体产状，而不是统计大小和形状分析，因为传统的形状参数无法表征泥屑的复杂形状。本文对泥质碎屑进行了一种新的定量颗粒形状分析，并对碎屑大小和形状的空间变化进行了可视化，这表明了夹带泥质碎屑的来源和搬运系统的多样性。该方法修正了传统的椭圆傅里叶分析方法，用傅里叶功率谱代替了传统的椭圆傅里叶描述子，克服了镜面形状问题。此外，主成分分析比传统的形状参数更有效地捕获重要的形状属性。将该方法应用于日本中部下更新世大台组沉积重力流沉积中的泥屑。结果表明，泥质碎屑的形状和大小差异与沉积相密切相关，而与离源距离无关。杂化事件层中碎屑层段的角度高于其他相。砂质无构造相的碎屑具有不同于层状相的以伸长和凹凸为基础的形状特征。不同形状分析方法之间的比较表明，没有一种传统方法能够像本文所提出的方法那样有效地可视化这些趋势。这些结果突出了泥沙颗粒定量形状分析的重要性和基于fps的椭圆傅里叶分析的有效性。
Hybrid event beds are the deposits from sediment gravity flows that change their rheological behavior through their passage, entraining muddy sediments and damping turbulence. Muddy facies of hybrid event beds are often associated with abundant mud clasts which show a wide variety of size and shape. The variation of clast occurrence in hybrid event beds is expected to preserve the information of entrainment and transport processes of muddy sediments in submarine density currents. However, previous analyses of hybrid event beds have focused on describing the overall clast occurrence rather than the statistical size and shape analyses because traditional shape parameters are incapable of characterizing the complex shape of mud clasts. Here, a new quantitative grain-shape analysis of mud clasts is conducted and allows visualization of the spatial variation of clast size and shape, which suggests the wide variety of origin and transport systems of entrained mud clasts. This new method revises the traditional elliptic Fourier analysis, substituting Fourier power spectra (FPS) for traditional elliptic Fourier descriptors to overcome the mirror-wise shape problem. Further, principal-component analysis is shown to capture significant shape attributes more effectively than traditional shape parameters. The proposed method is applied to mud clasts in sediment-gravity-flow deposits in the lower Pleistocene Otadai Formation, central Japan. Results imply that there are distinctive shape and size differences of mud clasts that are strongly associated with depositional facies rather than the distance from the source. The clasts have a higher angularity than other facies in the debrite intervals in hybrid event beds. It is also shown that clasts in sandy, structureless facies have different characteristics in shapes based on elongation and convexity compared to laminated facies. Comparison between different shape-analysis methods demonstrates that none of the traditional methods are able to visualize these trends as effectively as the method presented herein. These results highlight the importance of the quantitative shape analysis of sediment grains and the effectiveness of FPS-based elliptic Fourier analysis.