Distinction and grain-size characteristics of intertidal heterolithic deposits in the middle Qiantang Estuary (East China Sea)
Distinction and grain-size characteristics of intertidal heterolithic deposits in the middle Qiantang Estuary (East China Sea)
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DOI：
10.1007/s00367-015-0398-2
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发表时间：
2015-03
影响因子：
2.1
通讯作者：
D. Fan;Shuai Shang;Guofu Cai;Junbiao Tu
中科院分区：
文献类型：
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作者：
D. Fan;Shuai Shang;Guofu Cai;Junbiao Tu
对潮间带杂岩沉积物进行粒度分析的常规取样程序极有可能无意中混合两个或更多不同的沉积单元，从而使数据解释复杂化。传统上，沉积学家不太注意泥层，由于缺乏内部结构，虽然这样的层的粒度种群应编码更多的信息细泥絮凝过程比桑迪层。本文对钱塘江口中段大尖山潮滩9个短柱样的泥质和桑迪层进行了粒度分析。在黄家岩从较低的河口，不受涌潮影响的核心，作为比较。采用曲线拟合的方法将每个粒度分布分解为两个高斯分布。累积图表明，潮间带沉积物大多分散为间歇性和均匀的悬浮载荷，牵引载荷不存在或非常从属。可以想象，这与涌潮搅动的水流以及细砂和粗粉砂颗粒的高度动态性质有关。选择性搬运和沉积作用产生了三种不同的沉积单元，即涌潮沉积、潮桑迪沉积和潮泥沉积。这些也可以区分任何两个纹理参数的二元图。潮汐流的向岸衰减反映在桑迪层逐渐变细和变薄，从较低的平坦块状砂，通过中平坦混合沉积（块状砂和潮汐韵律层的交替），到较高的平坦潮汐韵律层。这种梯度也很好地表示在稍微减少（增加）排序和减少（增加）比例的较粗（较细）的水力种群在泥层。虽然在桑迪层的水力种群中没有可辨别的相应趋势，但可以根据特征性沉积结构加以区分。泥质（桑迪）层的絮凝极限为8~10 μm（16 μm），平均为41.73%（26.41%）。最合理的解释是，絮凝物的限制敏感地响应悬浮泥沙成分和环境水力和水化学设置的微妙变化。相比之下，黄家岩岩芯的层理不明显，细泥和絮状物含量较高，这与河口下游潮坪上部能量较弱，既无涌潮，也无大浪发生相一致。
The routine sampling procedure for grain-size analysis of intertidal heterolithic deposits runs a high risk of inadvertent mixing of two or more different sedimentation units, which would consequently complicate data interpretation. Traditionally, sedimentologists pay less attention to muddy layers due to a lack of internal structures, although the grain-size populations of such layers should encode more information on fine-mud flocculation processes than sandy layers. In this paper, individual muddy and sandy layers of nine short cores from the Da-Jian-Shan tidal flats of the middle Qiantang Estuary in the East China Sea, which experiences tidal bores, were sampled separately for grain-size analysis. A core taken at Huang-Jia-Yan from the lower estuary, not affected by tidal bores, served for comparison. A curve-fitting method was employed to decompose each grain-size distribution into two Gaussian populations. Cumulative plots indicate that intertidal sediments are mostly dispersed as intermittent and uniform suspension loads, traction loads being absent or very subordinate. This is conceivably linked to flows agitated by tidal bores, and to the highly dynamic nature of fine sand and coarse silt particles. Selective transport and deposition have produced three distinct sedimentation units, namely, tidal-bore deposits, tidal sandy deposits, and tidal muddy deposits. These can also be discriminated on bivariate plots of any two textural parameters. Shoreward attenuation of tidal flows is reflected in the gradual fining and thinning of sandy layers from lower-flat massive sands, through middle-flat hybrid deposits (alternations of massive sands and tidal rhythmites), to upper-flat tidal rhythmites. This gradient is also well represented in slightly decreasing (increasing) sorting and decreasing (increasing) proportions of the coarser (finer) hydraulic populations in the muddy layers. Although no corresponding trends are discernible in the hydraulic populations of the sandy layers, these can be distinguished on the basis of characteristic sedimentary structures. The floc limit and floc volume fraction, estimated from the modes and proportions of the finer hydraulic populations, are 8~10 μm (16 μm) and on average 41.73% (26.41%) for muddy (sandy) layers, respectively. The most plausible explanation is that the floc limit sensitively responds to subtle changes in the suspended sediment composition and the ambient hydraulic and hydrochemical settings. In comparison, the Huang-Jia-Yan core features blurred bedding and higher contents of fine mud and flocs, these being consistent with the weaker energy on the upper tidal flat of the lower estuary where neither tidal bores nor bigger waves occur.