Sedimentation processes and sedimentary characteristics of tidal bores along the north bank of the Qiantang Estuary
Sedimentation processes and sedimentary characteristics of tidal bores along the north bank of the Qiantang Estuary
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钱塘江口北岸潮汐沉积过程及沉积特征
DOI：
10.1007/s11434-012-4993-6
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发表时间：
2012-02
影响因子：
--
通讯作者：
Gao Lei
中科院分区：
文献类型：
--
作者：
Fan DaiDu;Cai GuoFu;Shang Shuai;Wu YiJing;Zhang YanWei;Gao Lei
涌潮是一种独特的地球表面过程，其特点是具有极强的破坏性，具有可预测的周期和大小，并产生独特的沉积特征。潮汐钻孔和相关的快速洪流是上层流态的高度湍流，其速度超过每秒几米。雷诺数(Re)和弗劳德数(Fr)分别大于104和1.0，与常规潮流明显不同，但与浑浊流相似。到目前为止，由于直接测量潮汐钻孔的难度和危险性，人们对涌潮沉积过程和产品的了解一直受到限制。钱塘井被称为世界上最大的破岩井。2010年5月，在钱塘江河口北岸进行了实地调查，观察了洪峰钻孔的出现情况，包括对主航道的水流、水位和浊度的定期观测。为了研究潮汐钻孔的沉积特征，在潮滩上采集了几个短岩心。水动力和沉积学研究表明，泥沙再悬浮、输移和沉积过程主要受潮汐钻孔和随后的突然加速和减速洪流控制，这些洪流仅占河口每个半日潮周期的十分之一。涌潮沉积物通常分选较差，这是因为在强烈的湍流作用下高度混合悬浮后的快速沉积。这一现象的特点是在Ac-M图上没有牵引力电流沉积分量。与发育的块状层理、渐变层理、基底剥蚀构造、卷曲层理和降水构造伴生。这些沉积特征共同构成了广泛分布于深水环境中的浊积岩指纹。然而，涌潮是由强烈变形的潮波传播到浅水环境中引发的，浅水环境在涌潮水头通过后迅速恢复正常的潮汐流动。涌潮沉积通常以潮间带沉积为界，在顶部和两侧都有典型的潮汐层理。涌潮沉积(TBD)和潮汐砂泥沉积(TSD/TMD)不仅在沉积构造上有明显的区别，而且在粒度组成上也有明显的区别。它们可以在粒度二元曲线图中清楚地区分出来，通常是平均粒度与标准差(或排序)的曲线图。TSD>；TSD>；TMD的平均粒度普遍存在一些趋势变化，TMD>；TSD>；TSD(较大的值表示较差的分选)，以及TSD>；TSD>；TMD的偏态和峰度。这些发现无疑将为我们理解涌潮沉积学、古涌潮沉积相和环境以及相关的油气田勘探提供新的线索。
A tidal bore is a unique Earth surface process, characterized by its highly destructive energy, predictable periodicities and magnitudes, and the production of characteristic sedimentary features. Tidal bores and associated rapid flood flows are highly turbulent flows of the upper-flow regime with a velocity over several meters per second. Reynolds (Re) and Froude (Fr) numbers, respectively, are larger than 104and 1.0, making them significantly different from regular tidal flows but analogous to turbidity currents. Until now, understanding of tidal-bore depositional processes and products has been limited because of the difficulty and hazards involved with gauging tidal bores directly. The Qiantang bore is known as the largest breaking bore in the world. Field surveys were carried out in May 2010, along the north bank of the Qiantang Estuary to observe the occurrence of peak bores, including regular observations of current, water level and turbidity at the main channel. Several short cores were sampled on the intertidal flats to study the characteristic sedimentary features of tidal bores. Hydrodynamic and sedimentological studies show that the processes of sediment resuspension, transport and deposition are controlled primarily by the tidal bores, and the subsequent abruptly accelerated and decelerated flood flows, which only account for one tenth of each semidiurnal tidal cycle in the estuary. Tidal-bore deposits are generally poorly sorted because of rapid sedimentation after highly mixed suspension by intense turbulence. This behavior is characteristic of the absence of tractive-current depositional components in aC-Mdiagram. It also goes along with well-developed massive bedding, graded bedding, basal erosion structures, convolute bedding and dewatering structures. Together, these sedimentary features can constitute fingerprinting of turbidites, widely distributed in the deep-water environment. However, a tidal bore is triggered by intensely deformed tidal waves propagating into a shallow-water environment, which returns to regular tidal flows rapidly after the passage of the bore head. The tidal-bore deposits are usually bounded by the intertidal-flat deposits with typical tidal beddings at the top and on both flanks. The difference between tidal-bore deposits (TBD) and tidal sandy/muddy deposits (TSD/TMD) is evident not only in sedimentary structures, but also in the grain-size composition. They can be clearly distinguished in grain-size bivariate plots, typically the plot of mean grain size vs. standard deviation (or sorting). Some trend variations generally exist in mean grain size with TBD>TSD>TMD, sorting with TMD>TBD>TSD (larger value indicating poorer sorting), and both skewness and kurtosis with TSD>TBD>TMD. These findings will undoubtedly shed new light on our understanding of tidal-bore sedimentology, ancient tidal-bore sedimentary facies and environments, and related oil-and-gas field prospecting.
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DOI：
10.1007/978-94-007-0123-6_9
发表时间：
2012
期刊：
--
影响因子：
--
作者：
Daidu Fan
通讯作者：
Daidu Fan
影响因子：
5.8
作者：
S. Greb;A. W. Archer
通讯作者：
S. Greb;A. W. Archer
影响因子：
5
作者：
Wu Xiu-guang
通讯作者：
Wu Xiu-guang
影响因子：
3.5
作者：
S. Greb;A. W. Archer;Darron G. DeBoer
通讯作者：
S. Greb;A. W. Archer;Darron G. DeBoer
影响因子：
5
作者：
Mao Xian-zhong
通讯作者：
Mao Xian-zhong