The role of summer monsoon-typhoons in the formation of nearshore coarse-grained ripples, depression, and sand-ridge systems along the Shimizu coast, Suruga Bay facing the Pacific Ocean, Japan
The role of summer monsoon-typhoons in the formation of nearshore coarse-grained ripples, depression, and sand-ridge systems along the Shimizu coast, Suruga Bay facing the Pacific Ocean, Japan
复制标题
夏季季风-台风对日本骏河湾清水沿岸近岸粗粒波纹、洼地和沙脊系统形成的作用
DOI：
10.1016/j.margeo.2014.03.018
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发表时间：
2014
期刊：
影响因子：
2.9
通讯作者：
K. Nemoto
中科院分区：
文献类型：
--
作者：
S. Yoshikawa;K. Nemoto
粗粒波纹（cgr）在日本中部骏河湾西北部面向太平洋的清水海岸的海底洼地-沙脊系统中形成。本文通过对2005 - 2007年高分辨率测深、水下摄像机海底观测、高分辨率地震测量和浅层海底挖沟等资料的分析，详细描述了该系统的地貌和沉积特征，并探讨了该系统的形成过程和维持过程。在水深5-30 m的海底洼地，cgr发生在比周围砂质海底深约40-70 cm的海底洼地。在许多情况下，波纹在相对狭窄的陆架上主要由细沙（< 70厘米高，100-400米长）组成的海岸正常砂脊之间的洼地中发展。砂脊岸线宽度为10 ~ 100 m，坳陷岸线宽度为10 ~ 150 m。cgr（波长< 3.5 m，高度< 30 cm）的波峰几乎与海岸平行，形状对称或略不对称，表明波浪产生振荡流。大波纹的波峰由砾石组成（最大长轴：5-8厘米），波谷由细到极细的沙子组成。夏秋两季台风经过时，cgr -洼地-沙脊系统广泛发展。在较窄的陆架上，表层细粒沉积物和表层及地下粗粒沉积物分别形成砂脊和cgr，在台风相关风暴中被反复侵蚀和再沉积。相比之下，活性沉积物目前仅限于较宽陆架区域的表面细沉积物。构成cgr的沉积物似乎既来自现代海滩沉积物，也来自残留沉积物。我们假设cgr -洼地-砂脊系统似乎主要受风暴期间海底侵蚀和海上定向沉积物输运的控制，这些过程可能取决于陆架宽度。事实上，砂脊（覆盖cgr）仅在较窄的陆架上发育，这意味着显著的海上导向运输。地表覆盖砂质沉积物（如砂脊）的厚度和分布限制了cgr的分布和海底表达。这代表了对活动边缘陆架上海底洼地中cgr分布的一种新的解释，该陆架接受大量的砂质和含砾的河流沉积物供应，与被动边缘缺乏沉积物的陆架上看到的过程不同。
Coarse-grained ripples (CGRs) develop within the seafloor depression–sand ridge systems along the Shimizu coast, in the northwestern part of Suruga Bay facing the Pacific Ocean, central Japan. In this paper, we analyze data from high-resolution bathymetry, seafloor observation by an underwater video camera, and high-resolution seismic surveys and seafloor trenching of shallow strata, obtained between 2005 and 2007, to describe their geomorphological and sedimentological characteristics in detail, and to examine the formative processes and maintenance of the systems.In water depths of 5–30 m, CGRs occur in seafloor depressions that are approximately 40–70 cm deeper than the surrounding sandy seafloor. In many cases, the ripples develop in depressions between shore-normal sand ridges composed mainly of fine sand (< 70 cm high, 100–400 m long) on a relatively narrow shelf. The alongshore width of the sand ridges is 10–100 m, and that of the depressions is 10–150 m. The CGRs (wavelength < 3.5 m, height < 30 cm) have almost shore-parallel crests with a symmetrical or slightly asymmetrical shape, suggesting wave-generated oscillating flows. The crests of the lager ripples are composed of gravel (maximum long axis: 5–8 cm) and the troughs consist of fine to very fine sand. The CGR–depression–sand ridge systems develop widely during the passage of typhoons in the summer–autumn seasons. At the narrower shelf, the surface fine-grained sediments and the surface and subsurface coarse-grained sediments, which form the sand ridges and the CGRs respectively, are repeatedly eroded and redeposited during typhoon-related storms. In contrast, active sediments are currently limited to the surface fine deposits on the wider shelf areas. The sediments that make up the CGRs appear to be derived from both modern beach sediments and relict sediments. We postulate that the CGR–depression–sand ridge system appears to be controlled mainly by both seafloor erosion and offshore-directed sediment transport during storms, and these processes may depend on the shelf width. In fact, the sand ridges (covering the CGRs) that imply significant offshore-directed transport only develop on the narrower shelf. The distribution and seabed expression of the CGRs is constrained by the thickness and distribution of surface-covering sandy sediments, such as the sand ridges. This represents a new interpretation of the distribution of CGRs within seafloor depressions on the shelf of an active margin that receives a large supply of sandy and gravelly fluvial sediments, and differs from the processes seen on the sediment-starved shelves of passive margins.