Knickpoints and crescentic bedform interactions in submarine channels
Knickpoints and crescentic bedform interactions in submarine channels
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DOI：
10.1111/sed.12886
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发表时间：
2021-06-01
期刊：
影响因子：
3.5
通讯作者：
Vendettuoli, Daniela
中科院分区：
文献类型：
--
作者：
Chen, Ye;Parsons, Daniel R.;Vendettuoli, Daniela
海底峡谷将全球范围内数量可观的沉积物、营养物质、污染物和有机碳输送到深海。裂点是在众多海底峡谷中发现的重要地形特征，它们很可能在峡谷演化以及流经其中的含泥沙海底水流（浊流）的行为中起着重要作用。尽管先前的研究已将超临界浊流与裂点和较小的新月形底形的形成联系起来，但在实地尺度上，水流与这些海底特征的动力学之间的关系仍然受到很大限制。本研究调查了不列颠哥伦比亚省比特湾44公里长的海底峡谷系统中裂点和新月形底形的分布、变化和相互作用。对一系列重复的测深调查进行的小波分析表明，海底峡谷的底部由一系列裂点组成，这些裂点上叠加有更高频率的新月形底形。单个裂点之间相隔数百米到数千米，较小的叠加新月形底形在整个峡谷系统中的波长从约16米到约128米不等。裂点迁移是由频繁的浊流通过所驱动的，并起到重新分布和重新组织新月形底形的作用。对浊流的直接测量表明，裂点迁移引起的海底重新组织可以改变流场，进而控制新月形底形的位置和形态。在一个裂点处获取的一组沉积岩芯剖面显示，在裂点下游区域的沉积物有砂 - 泥层理，堆积速率较高。此处记录的水流、裂点和底形之间的相互作用很重要，因为它们可能主导着保存下来的海底峡谷 - 河床沉积物的特征。
Submarine channels deliver globally important volumes of sediments, nutrients, contaminants and organic carbon into the deep sea. Knickpoints are significant topographic features found within numerous submarine channels, which most likely play an important role in channel evolution and the behaviour of the submarine sediment-laden flows (turbidity currents) that traverse them. Although prior research has linked supercritical turbidity currents to the formation of both knickpoints and smaller crescentic bedforms, the relationship between flows and the dynamics of these seafloor features remains poorly constrained at field-scale. This study investigates the distribution, variation and interaction of knickpoints and crescentic bedforms along the 44 km long submarine channel system in Bute Inlet, British Columbia. Wavelet analyses on a series of repeated bathymetric surveys reveal that the floor of the submarine channel is composed of a series of knickpoints that have superimposed, higher-frequency, crescentic bedforms. Individual knickpoints are separated by hundreds to thousands of metres, with the smaller superimposed crescentic bedforms varying in wavelengths from ca 16 m to ca 128 m through the channel system. Knickpoint migration is driven by the passage of frequent turbidity currents, and acts to redistribute and reorganize the crescentic bedforms. Direct measurements of turbidity currents indicate the seafloor reorganization caused by knickpoint migration can modify the flow field and, in turn, control the location and morphometry of crescentic bedforms. A transect of sediment cores obtained across one of the knickpoints show sand-mud laminations of deposits with higher aggradation rates in regions just downstream of the knickpoint. The interactions between flows, knickpoints and bedforms that are documented here are important because they likely dominate the character of preserved submarine channel-bed deposits.