长江口泥质区的季节性沉积效应

1IntroductionThe continental shelf of the East China Sea (ECS) is one of the widest shelves in the world. There are several mud areas distributing like patches on a background of widespread coarser ambient sediments of silt and sand on the continental shelf of the ECS. The coastal mud area can be divided into two parts, namely, the Changjiang Estuary mud area (CEMA) in the north and Zhejiang coastal mud area in the south. Between these two parts there is a silt area (Figure 1). The CE…     

NUMERICAL MODELING OF THE SEABED MORPHOLOGY OF THE SUBAQUEOUS YELLOW RIVER DELTA

1 wrsoorCnoxThe Yenow mver delta is ereated by the river transponing sediment bom the Loess Plateau to the shallOWBOhai Gulf during the paSt l45 years. lh recent years, the water discharge and sediment load enedg thesea have bein ched dramacaily The river end chann shital northeastWed hom QingshulgOuN to qngshulgou-Chah chaDnel in 1996, resulting in a new regfor of sedimenboon and erosion ofthe subaqucous delta.,A nUInerial model for river sediInen dispersion and seabed mOrPhofogy of t…     

GRAIN SIZE DISTRIBUTION OF SEDIMENT IN THE NORTHERN EAST CHINA SEA AND THE RELATIONSHIP WITH THE SEA CURRENTS

1 INTRODUCTION The East China Sea, one of the largest continental marginal seas in the world, receives large amount of suspended sediment from the land annually (Milliman and Meade, 1983; Shen, 1999). Since late Pleistocene, the deposition of the suspended sediment over the relict sandy sediment induces the complicated distribution of surface sediment (Fig. 1). Many studies have been done on the surface sediment distribution, sedimentation rate, concentration and dispersion of suspen…     

Significance of carbon isotopes in carbonate sequence stratigraphy

Based on the research on sequence stratigraphy of the Permian in Southwest China, in conjunction with the carbon isotope data from the typical sections at Ganluo, Sichuan and Tianlin and Mashan, Guangxi, the authors suggest that the genetic framework and internal architicture of different sequences possess quite different carbon isotopic characteristics. Therefore, the following problems can be solved in terms of carbon isotopic values, evolutionary curve patterns and structures of carbonate sequences: (1) to determe the nature of sequence boundary surface and related geological events; (2) to recognize various kinds of sedimentary system tracts; (3) to discuss the internal architicture and genetic framework of the sequences and their evolution; (4) to subdivide and correlate sedimentary sequences on a regional or global scale; and (5) to enhance the resolution of sequence stratigraphic analysis. Stable carbon isotopes have proved themselves to be valid in sequence stratigraphic studies of carbonate rocks, as demonstrated by our results presented in this paper.     

Tide‐modulated hyperpycnal flows off the Huanghe (Yellow River) mouth,China

Few hyperpycnal flows have ever been observed in marine environments although they are believed to play a critical role in sediment dispersal within estuarine and deltaic depositional systems. The paper describes hyperpycnal flows observed in situ off the Huanghe (Yellow River) mouth, their relationship to tidal cycles, and the mechanisms that drive them. Simultaneous observations at six mooring stations during a cruise off the Huanghe mouth in the flood season of 1995 suggest that hyperpycnal flows observed at the river mouth are initiated by high concentrations of sediment input from river and modulated by tides. Hyperpycnal flows started near the end of ebb tides, when near‐bottom suspended sediment concentration (SSC) increased rapidly and salinity decreased drastically (an inverse salt wedge). The median grain size of suspended particles within the hyperpycnal layer increased, causing strong stratification of the suspended sediments in the water column. Towards the end of flood tides, the hyperpycnal flow attenuated due to frictions at the upper and lower boundaries of the flow and tidal mixing, which collapsed the stratification of the water column. Both sediment concentration and median grain size of suspended particles within the bottom layer significantly decreased. The coarser sediment particles were deposited and the hyperpycnal flows stopped. The intra‐tidal behaviors of hyperpycnal flows are closely associated with the variations of SSC, salinity, and stratification of the water column. As nearly 90% of riverine sediment is delivered to the sea during the flood seasons when hyperpycnal flows are active, hyperpycnal flows at the Huanghe mouth and the river's high sediment loads have caused rapid accretion of the Huanghe delta. Copyright © 2010 John Wiley & Sons, Ltd.     

Sustained growth of the largest uninhabited alluvial island in the Changjiang Estuary under the drastic reduction of river discharged sediment

The evolution of the Changjiang Delta is obviously affected by current rapidly rising sea level and drastically declining river discharge, and it is also vital for the sustainable development of Shanghai and the Changjiang River Economic Belt, which represent China's economic development leader and major national strategic area, respectively. In this paper, the growth pattern of Jiuduansha Island, the largest uninhabited alluvial island in the Changjiang Estuary, is studied in terms of the change in elevation, position and area over the past 50 years through using satellite-derived instantaneous shoreline positions and high/low tide exposure areas based on 497 satellite images from 1974 to 2020; and the influencing factors and future development patterns are further discussed by comparison with other alluvial islands or sandbars in the estuary. The results show that Jiuduansha Island has maintained a rapid or even accelerated area growth rate, although the sediment discharge of the Changjiang River has sharply decreased in recent decades. This sustained growth is mainly attributed to the existence of the estuarine turbidity maximum zone, coarsening fluvial sediment, onshore sediment replenishment by tide, cone-like geomorphology of Jiuduansha Island, and siltation promotion effect of vegetation. The growth rate of the low tide exposure area of Jiuduansha Island increased from 1.9 km~2 a~(-1) in 1974–1990 to 3.0 km~2 a~(-1) in 1990–2020, and the growth rate of the high tide exposure area reached as high as 3.7 km~2 a~(-1) in 1994–2020. The implementation of the Deep-Water Channel Project has significantly affected the evolution of Jiuduansha Island, including shifting the heads of Shangsha and Zhongxiasha from severe retreat to rapid accretion, and promoting tidal flat progradation seaward of the Jiangyanansha and Zhongxiasha, but restricting the growth of the low tide exposure area of Jiuduansha Island.     

灰色关联度概念在地质判别分析中的应用

将灰色系统理论中关联度的概念应用于地质判别分析，得到一种新的判别分析方法──灰色判别分析。该方法的基本思想是通过计算未知样品与多组已知样品间的关联度大小来实现样品的分类。经地质学的实例计算表明，该方法切实可行。     

利用MAPX实现空间数据库与属性数据库的挂接

数据库是 GIS的基础 ,而空间数据库与属性数据库的挂接则是 GIS的要点。本文以渤海区域地质信息管理系统数据为例 ,阐述了基于 GIS的海洋地学管理信息系统中数据库的组织方法 ,包括空间数据库与属性数据库数据分类、分层方案 ,命名及编码规则。在此基础上 ,重点讨论了在 VisualBasic环境下运用 MAPX实现空间数据库与属性数据库的挂接方法。     

深基坑支护设计的弹性抗力有限元法

采用弹性抗力有限元方法讨论多支撑锚桩的深坑支护设计问题。该方法与传统的静力平衡法相比有其优越性,能够计算出不同开挖阶段的桩顶位移,桩身弯距随深度的变化,模拟开挖过程,最大限度地协调支护结构与土体的变形关系,并能确定出最小的桩身弯距设计值及各层锚杆的锚固力。并以实例运用该方法对青岛某基坑工程的支护进行了设计,取得了满意效果     

Longitudinal residual circulation in the South Passage of Yangtze Estuary:Combined influences from runoff,tide and bathymetry

Classical estuary circulation theory states that in the longitudinal direction of an estuary there exists a single circulation with landward,near-bottom,and sea...