【作者】 唐秋华；

【导师】 刘保华；

【作者基本信息】 中国海洋大学 ， 海洋地质， 2009， 博士

【摘要】 东海陆架以宽平的地形、充分的陆源沉积物供应、快速沉降和强动力场为特征,东海中外陆架广泛分布着脊槽相间的海底底形,有研究称之为冰消期海侵以来的潮流沙脊。国内外研究人员对东海陆架脊槽相间的海底底形进行了深入广泛研究,取得了大量有意义的研究成果,但其研究区域主要集中在东海中南部海域。本研究选定的区域位于东海北部外陆架靠近济州岛西南海域,是黄海槽向冲绳海槽延伸的部分,属于黑潮分支黄海暖流的通道入口,对其海底底形形态、沉积物分布及其成因机制的分析研究,有助于全面了解该通道的地形地貌特征及其形成演变规律。本研究基于东海北部外陆架海域获取的高精度多波束声纳数据、地质取样数据、浅地层数据以及水文数据,结合前人的研究成果,利用现代数据处理技术、定量化分析方法以及潮流动力地貌理论,详细系统地分析了海底波状冲刷洼地(Rippled Scour Depressions,RSDs)、海底沙脊三维形态结构及其海底沉积物分布特征,探讨了较强水动力条件下东海北部外陆架海域脊槽相间底形形成原因、演变过程。围绕这个主题,主要论述了下面几个方面:基于研究区获取的高精度多波束声纳数据,构建高精度的海底数字地形模型及声纳影像镶嵌图,生成高分辨率的海底三维形态图、坡度坡向图、特殊地形剖面图以及表层纹理图,准确获取海底RSDs及沙脊的高度、宽度、长度及走向等特征参数。分析发现,研究区东北角存有一个深达153.2m的海底沟壑,其相对高差最大达32m,海底地形变化剧烈,属强侵蚀洼地地形;研究区分布十余条规模较大的直脊型海底RSDs及沙脊,长度从几公里,十几公里到最长40公里左右,脊、槽之间高差一般5m左右,最大达到10m左右,总体走向NW-SE。基于前人的研究成果及在该区域获取的海底地质取样数据,详细分析了37个表层沉积物粒度特征,将研究区沉积物分为细砂(FS)、粉砂质砂(TS)、粘土质砂(YS)、砂-粉砂-粘土(STY)、粘土质粉砂(YT)和粉砂质粘土(TY)等六种类型,结合沉积物厚度分布状况,阐述了研究区沉积物分布规律。同时,基于多波束反向散射强度数据,结合19组海底地质取样数据,建立研究区海底反向散射强度与沉积物粒度特征之间的统计关系模型,并以自组织特征映射神经网络方法以及改进的学习向量量化神经网络方法,实现对海底粉砂质砂、粘土质砂以及砂-粉砂-粘土等三种底质类型的快速自动识别。基于POM(Princeton Ocean Model)海洋数值计算模式,获得研究区M2分潮的流速、流向以及其他相关的数据;通过收集整理日本海洋数据中心的实测海流资料,计算获取研究区的海流流速、流向等数据;应用数据分析方法揭示海洋动力环境要素与RSDs及沙脊形成分布之间的关联,进而详细探讨现代较强水动力与这一区域RSDs以及沙脊之间的作用关系。研究发现,该区潮流方向基本为NW-SE,这一方向基本上与海底底形走向一致,但是其底层流速很小,一般只有30cm/s左右,这一流速很难起动粉砂质或更小粒径的海底沉积物,现代潮流对该区域的海底底形影响已经很小。研究还发现,该区域实测底层最大海流流速达到69cm/s左右,这一流速有能力起动、搬运细砂或粉砂质砂等海底沉积物,对海底底形形态产生一定的动力作用,可能会形成一定程度的侵蚀和堆积地貌,现代水动力仍然改造和维持冰消期海侵以来形成的海底RSDs及沙脊。基于前人的研究成果,获取研究区冰消期海侵以来各时期M2分潮潮流场演变过程,同时结合前人对东海潮流沙脊的相关研究成果,深入细致地研究古代水动力环境与这一区域RSDs及沙脊底形形成、分布及演变的关系。研究得出,冰消期海侵以来,海水由济州岛两侧进入黄海,东海北部外陆架海底受到强烈的水流侵蚀冲刷作用,海底砂质或粉砂质沉积物被较强潮流起动、搬运,在海平面上升停顿期,在较强往复潮流作用下,形成与古潮流NW-SE方向一致的海底RSDs侵蚀地貌及侵蚀-堆积潮流沙脊地貌。更多还原

【Abstract】 The East China Sea shelf has three characteristics as follows: a wide and flat terrain; a variety of land-based sources for sediment; a rapid subsidence and strong power causes. On the outer shelf of the East China Sea undersea ridges and troughs are widely distributed consecutively, the study referred to as tidal sand ridges shaped by the postglacial transgression process. A lot of researches on the submarine bedforms of the East China Sea continental shelf ridges have been done by both domestic and foreign scholars, and a large number of meaningful results have been obtained. But the study area mainly concentrated in the southern part of the East China Sea. The selected area in this paper is located in the outer shelf of the north of the East China Sea near Cheju Island. It’s an extension part of the Yellow Sea Trough turns towards the Okinawa Trough. It’s in the pathway of the Yellow Warm Current which is one of the branches of the Kuroshio Warm Current. The analysis about the seabed morphology, sediment distribution and formation mechanism will contribute to an overall understanding of the formation, evolution and the characteristics of the pathway.Around the study region high-precision multibeam sonar data, geological sampling data, shallow stratigraphic data and hydrological data are all collected, applied with modern data processing technology,quantitative analysis methods and tidal power geomorphologic theory, a detailed report including Rippled Scour Depressions (RSDs), three-dimensional morphology of the seabed sand ridges and distribution of seafloor sediment is characterized. Under such a strong hydrodynamic condition, the formation cause and evolution process of the ridge-trough submarine bedforms in this area are analyzed. On this theme, following aspects are mainly discussed:Based on the high-precision multibeam sonar data on the study area, a high-precision seabed Digital Terrain Model (DTM) and sonar mosaic image are built to generate high-resolution three-dimensional seabed morphologic maps, as well as slope and aspect maps, special terrain profiles and other surface texture maps. Among those maps accurate seabed RSDs and sand ridges’height, width, length, direction and other characteristic parameters can be measured. A deep submarine gully with the depth of 153.2 meters is found in the northeast corner of the study area. The relative height difference is up to 32 meters indicates strong erosion with dramatic changes in seabed topography. There are more than ten large-scale straight ridge RSDs and sand ridges in the study area. They are all NW-SE direction, in length from a few kilometers to 40 kilometers, between ridge and trough the general elevation difference is about 5 meters, the maximum reach up to10 meters.According to previous research and seabed geological sampling data from the seabed, a detailed analysis of granularity characteristic belonged to thirty seven surface sediment is conducted, the sediment can be divided into six categories: Fine Sand (FS), Silty Sand (TS), Clayey Sand (YS), Sand - Silt - Clay (STY), Clayey Silt (YT) and Silty Clay (TY), combined with the distribution of sediment thickness on the study area the distribution discipline is revealed. Based on multibeam backscatter intensity data and 19 geological seafloor sediment sample data, a statistical model which presents the relationship between seabed backscatter signal and sediment type is set up. Using Self-Organizing Feature Map (SOFM) and improved Learning Vector Quantization (LVQ) neural network methods, a fast and accurate automatic identification for three seabed sediment types (TS, YS, STY) implementation is feasible.Applied with the Princeton Ocean Model, the M2 tidal current velocity, direction and other relevant data in the study region are calculated. And the surveying ocean current information is collected from Japan Oceanographic Data Center (JODC). Advanced data analysis methods are applied to explore the relationship between marine dynamic environment and the submarine bedforms formation. The relationship between modern hydrodynamic and RSDs is the further study. The study found that the basic tidal current direction NW-SE is consist to the seabed shape. But the bottom tidal current rate is generally about 30cm/s, too weak to transport sandy or smaller particle of seabed sediments. The impact of the modern hydrodynamic to the submarine beforms in this region has been quite debilitated. In the other hand, the largest ocean current velocity in the seabed could reach to about 69cm/ s, so it’s possible to stir-up and move marine sediments such as fine sand or silty sand. That might lead to a certain erosional and depositional morphology. So, the modern hydrodynamic still have the power to transform and maintain the seabed RSDs and sand ridges.Based on the previous research results, the evolution processes of the M2 tidal current fields can be obtained since the postglacial transgression. Combined with the previous tidal sand ridges research in the East China Sea, a thorough research is conducted to find out how the ancient hydrodynamic environment shapes the formation, distribution and evolution of the RSDs and sand ridges bedforms. It comes to a conclusion that shows submarine beforms on the outer shelf of the north of the East China Sea has been strongly eroded since the postglacial transgression, the seabed material like sandy or silty sediments are started and transported. The seabed erode RSDs and erode-deposit tidal sand ridges morphologies which have the same NW-SE direction coincided with the ancient tidal current are shaped by a strong reciprocating tidal current during the standstill period of the sea level ascending.更多还原