海洋地质与环境重点实验室知识库

        海底沙波是一种常见的海底地貌，其形成和演化与海底沉积物的性质、区域地形地貌特征和水动力环境等密切相关。因此对海底沙波的研究有助于我们了解研究区的沉积环境演变、海平面变化和水动力环境的演变等，具有十分重要的理论意义。快速运动的沙波往往会威胁海底管道和海底电缆的安全，而海底砂矿又蕴藏着丰富的金属元素和矿物。因此，对海底沙波的研究不仅具有理论意义，还有十分重要的工程意义和经济价值。
        在中国南海北部的陆架坡折附近，广泛分布着各种类型的海底沙波。这些沙波的存在和移动为海底人工设施带来了潜在的风险，例如：番禺油气田的部分输气管道位于沙波分布区内，存在因沙波活动而导致的悬跨现象。有学者曾对该地区的沙波进行过研究，但是由于缺少高精度的水深数据等多方面的数据，现有的研究对南海北部沙波的形成时代、是否运动和运动的动力来源等问题存在诸多争议。有的研究者认为沙波为残留沙波且不会发生运动，有的学者认为沙波是现代形成的，可在潮流作用下活动，也有研究者认为其在风暴潮的作用下运动。
        本文对在南海北部陆架坡折附近获取的表层沉积物样品进行粒度测试和年代测试，并分析了区域沉积物的类型和分布特征及输运趋势。利用多年的多波束测深数据，提取了沙波的形态特征参数，通过剖面对比获得了沙波的迁移方向和距离。通过分析底流数据等探讨了沙波形成演化的动力机制。
        研究结果表明，表层沉积物主要由砂质和砾石成分组成，粉砂和黏土成分含量相对较少。研究区的沙波为现代沙波，沉积物由冰期物质、冰消期物质和全新世的物质混合而成，年代跨度范围广，呈现出新老混杂的特点。研究区的沉积物基本沿着陆架坡折向海和向陆两个主要方向输运，同时也存在少量的沿陆架坡折和跨陆架坡折输运现象。
        根据沙波的分布范围、形态特征参数和迁移规律，研究区的沙波存在五个主要的分布区，总体上可以分为两种类型。第一类沙波主要分布在水深大于145 m的深水区，并且所处海底坡度大于0.3°。沙波的脊线和所处海域的等深线平行，沙波倾向于SE的深水方向，且向SE方向迁移。沙波的波长和波高具有很强的指数关系，即H1=0.0597λ^0.92（R=0.67），关系式位于Flemming全球平均线的上方。第二类沙波分布于水深小于145 m浅水区，并且沙波分布的海底的坡度一般小于0.5°。沙波的脊线与等深线呈一定的夹角，沙波倾向NW的浅水区方向，向NW方向的上坡移动。沙波的波长和波高的指数关系式处于Flemming全球平均线的下方，为H2=0.0677λ^1.34（R=0.83）。研究区有两个子区域的沙波则具有这两类沙波的混合特征，是沙波的混合分布区。
        南海北部陆架坡折附近的内孤立波源于吕宋海峡，或者由南海北部的潮地激发作用产生。起源于吕宋海峡的内孤立波跨越南海海盆，向南海北部陆架和陆坡浅化，与东沙群岛发生碰撞分成两部分，而后又在东沙群岛后面相交。内孤立波在浅化过程中会造成海底的强流，只有内波导致的强流才能造成研究区沙波的迁移运动。在浅化过程中，内孤立波在南海北部陆架坡折区域会发生极性转化，即由下凹型内孤立波转换为上凸型内孤立波。下凹型的内孤立波主要分布在陆架坡折下部的深水区，其在海底产生的强流与其传播方向相反，流向深水区且流速较大，下凹型内孤立波的影响区域与第一类沙波的分布区域相对应。上凸型的内孤立波主要分布在陆架坡折上部相对较浅的区域，其在海底产生的强流与其传播方向相同，流向浅水区且流速较小，上凸型内孤立波影响的区域与第二类沙波的分布区域相一致。因此内波是南海北部陆架坡折附近海底沙波差异化分布和迁移运动的主要原因。
      本研究表明内波是深水沙波形成和演化的主要动力因素，丰富了沙波形成和演化的理论，对今后深水沙波的研究具有重要的指导意义。 

Submarine sand waves are a common seabed landform, the formation and evolution of sand waves are closely related to the nature of seabed sediments, regional topography and hydrodynamic environment. Therefore, the study of seabed sand waves is helpful for us to understand the evolution of sedimentary environment, the changes of sea level and the evolution of hydrodynamic environment in the study area, which is of great theoretical significance. Rapidly moving sand waves often threaten the safety of submarine pipelines and submarine cables. In addition, submarine sand deposits generally contain many metallic elements and minerals. Therefore, the study of submarine sand waves not only has theoretical significance, but also has very important engineering significance and economic value.

Various types of submarine sand waves are widely distributed near the shelf break of northern South China Sea. The existence and movement of these sand waves pose potential risks for submarine artificial facilities. For example, some gas pipelines of PanYu oil and gas fields are in the sand wave distribution area, and there are suspension phenomena caused by sand wave activities. Some researchers have done some studies on sand waves near the shelf break of northern South China Sea. May be due to lacking of high-precision bathymetric data and other data, researchers have a lot of debate about the age of formation of sand waves and whether the sand waves can move or not, and where the power source of motion comes from. Some researchers believe that the sand waves are residual bedforms and will not move. Some researchers believe that sand waves are formed and migrating under modern tidal current. Some researchers believe that sand waves are moving under the influence of storm surge.

In this paper, the surface sediments obtained near the shelf break of northern South China Sea were used to grain size measurement and AMS¹⁴C dating. The distribution characteristics and transport path of surface sediments are also analyzed. The morphological parameters of sand waves are extracted basing on the multi-beam bathymetry data collected for many years. The migrating distance and direction are obtained by cross-section comparison in different years. The mechanism of the formation and evolution of sand waves is discussed by analyzing the bottom current data.

The results show that the surface sediments are mainly composed of sandy gravel components, while the silt and clay components are relatively small. The sand waves in the study area are modern sand waves. The sediments are mixed with glacial materials, ice-eliminating materials and Holocene materials. The ages of most sediment span a wide range showing a character of mixing old and modern sediments. The sediment in the study area are basically transported to the sea and the land. At the same time, there are also a small amount of transportation along the shelf break and across the shelf break.

According to the distribution range, morphological parameters and migration of sand waves, there are five main distribution areas of sand waves in the study area. The sand waves in study area can be divided into two classes. Class 1 sand waves are distributed in deep water areas with a water depth of more than 145 m. And the slope of the seabed where sand waves are distributed is greater than 0.3°. The crest lines of sand waves are parallel to the isobath of the study area. All the class 1 sand waves incline to deep water of the SE direction and migrates to SE direction. There is a strong exponential relationship between the wavelength and the wave height of sand waves, H₁=0.0597λ^0.92 (R=0.67), which is above the mean Flemming line. Class 2 sand waves are distributed in shallow waters with a water depth of less than 145 m, and the slope of the seabed is less than 0.5°. The crest lines of sand waves are intersect with the isobath, and the sand wave incline to shallow water of the NW direction and migrate to the upstream. The exponential relationship between the wavelength and wave height of sand waves is below the Flemming line, which is H₂=0.0677λ^1.34 (R=0.83). The sand waves in two sub-regions of the study area have the mixed characteristics of these two classes of sand waves, which are the mixed distribution areas of sand waves.

The internal solitary wave near the shelf break of northern South China Sea originates from the Luzon Strait, or is generated by the internal tidal excitation of the northern South China Sea. The internal solitary waves originating from the Luzon Strait transport across the South China Sea basin and shallow to the continental shelf and continental slope of northern South China Sea. They collide with the Dongsha Islands and are divided into two parts, and then intersect behind the Dongsha Islands. The internal solitary wave will cause a strong bottom current during the shoaling process, and only the strong current can move the sand waves in the study area. During the shoaling process, the internal solitary wave will undergo polarity conversion near the shelf break of northern South China Sea. It means the internal solitary wave will be transformed from the depression internal solitary wave to the elevation internal solitary wave. The depression internal solitary waves are mainly distributed in the deep waters of the continental slope, which cause the strong current on the seabed opposing to its propagation direction, flowing to the downstream, and the velocity is relatively large. The influence area of the depression internal solitary wave corresponds to the distribution area of class 1 sand waves. The elevation internal solitary waves are mainly distributed in the relatively shallow area of the shelf, which cause strong current on the seabed in keeping with its propagation direction, flowing to upstream, and the velocity is small. The affected region by the elevation internal solitary wave is consistent with the distribution region of class 2 sand waves. Therefore, internal waves are the main reason for the differential distribution and migration of submarine sand waves near the shelf break of the northern South China Sea.

This study shows that internal waves are the main driving force for the formation and evolution of deep-water sand waves, which enriches the theory of sand wave formation and evolution, and has important guiding significance for the study of deep-water sand waves in the future.

第1章 引言... 1

1.1 研究背景及意义... 1

1.2 研究现状... 2

1.2.1 沙波的分类... 3

1.2.2 沙波的形态特征... 4

1.2.3 沙波的迁移... 8

1.2.4 沙波的内部层理和结构... 10

1.2.5 沙波的形成和演化的控制因素... 11

1.2.5.1 水动力环境因素... 11

1.2.5.2 沉积物的性质... 15

1.2.5.3 影响沙波形成和发育的其他因素... 16

1.3 南海北部沙波的研究现状... 16

1.4 本文主要的研究内容... 18

第2章 区域背景... 21

2.1 研究区的位置... 21

2.2 区域地质情况... 21

2.2.1 地形地貌特点... 21

2.2.2 构造特点... 22

2.3 研究区的水文特征... 25

2.3.1 南海北部水动力条件... 25

2.3.2 南海北部的内波... 26

第3章 资料来源和方法... 29

3.1 数据资料来源... 29

3.1.1 沉积物资料... 29

3.1.2 多波束水深资料... 30

3.1.3 浅部地层数据和侧扫声呐数据... 30

3.1.4 水动力数据... 31

3.2 数据资料处理方法... 31

3.2.1 表层沉积物样品处理... 31

3.2.2 多波束数据的处理和误差分析与校正... 34

第4章 表层沉积物的粒度和特征... 37

4.1 表层沉积物的粒级组分特征... 37

4.2 沉积物的类型和分布... 38

4.3 表层沉积物的粒度参数分布特征和空间差异... 39

4.4 沉积物的起动流速... 40

4.5 沉积物的测年结果... 44

4.6 沉积环境分区... 45

4.7 表层沉积物的输运趋势... 49

4.8 本章小结... 51

第5章 沙波的形态特征和分布规律... 53

5.1 沙波的分布规律... 53

5.2 沙波的形态特征... 59

5.3 沙波的内部结构和底界面... 63

5.4 本章小结... 64

第6章 沙波的迁移过程及特征... 67

6.1 沙波的迁移特征... 67

6.2 沙波迁移距离的计算... 72

6.3 沙波的体积变化及区域差异... 76

6.4 本章小结... 80

第7章 内波影响下的水动力环境... 81

7.1 研究区的实测水动力特征... 81

7.1.1 底流基本特征... 82

7.1.2 底流的内波特征... 84

7. 2 潜标数据分析和内孤立波的传播... 88

7.3 本章小结... 92

第8章 沙波的形成演化和迁移动力机制... 93

8.1 常规水动力条件对海底沙波的影响... 93

8.2 极端海况对海底沙波的影响... 94

8.3 南海的内波生成传播及近底的动力过程... 96

8.3.1 内孤立波的浅化和极性转换... 96

8.3.2 内波对沉积物搬运的影响... 98

8.4内波控制下海底沙波的形成演化和迁移机制... 99

第9章 结论和下一步工作建议... 101

9.1 结论... 101

9.2 下一步工作建议... 102

参考文献... 103

附 录... 119

致 谢... 121

作者简历及攻读学位期间发表的学术论文与研究成果 123