A depositional model for a wave‐dominated open‐coast tidal flat,based on analyses of the Cambrian–Ordovician Lagarto and Palmares formations,north‐eastern Brazil

Open‐coast tidal flats are hybrid depositional systems resulting from the interaction of waves and tides. Modern examples have been recognized, but few cases have been described in ancient rock successions. An example of an ancient open‐coast tidal flat, the depositional architecture of the Lagarto and Palmares formations (Cambrian–Ordovician of the Sergipano Belt, north‐eastern Brazil) is presented here. Detailed field analyses of outcrops allowed the development of a conceptual architectural model for a coastal depositional environment that is substantially different from classical wave‐dominated or tide‐dominated coastal models. This architectural model is dominated by storm wave, low orbital velocity wave and tidal current beds, which vary in their characteristics and distribution. In a landward direction, the storm deposits decrease in abundance, dimension (thickness and spacing) and grain size, and vary from accretionary through scour and drape to anisotropic hummocky cross‐stratification beds. Low orbital wave deposits are more common in the medium and upper portion of the tidal flat. Tidal deposits, which are characterized by mudstone interbedded with sandstone strata, are dominant in the landward portion of the tidal flat. Hummocky cross‐stratification beds in the rock record are believed, in general, to represent storm deposits in palaeoenvironments below the fair‐weather wave base. However, in this model of an open‐coast tidal flat, hummocky cross‐stratification beds were found in very shallow waters above the fair‐weather wave base. Indeed, this depositional environment was characterized by: (i) fair‐weather waves and tides that lacked sufficient energy to rework the storm deposits; (ii) an absence of biological communities that could disrupt the storm deposits; and (iii) high aggradation rates linked to an active foreland basin, which contributed definitively to the rapid burial and preservation of these hummocky cross‐stratification deposits.     

Coastline configuration and geomorphologic development mode of arc-shaped coast in South China

1IntroductionArc-shaped bays are quite common on exposed sediment coast in South China, where the crenulate-bay beaches occur with the presence of two consecutive headlands and a predominant wave approach oblique to the alignment of the upcoast and downcoast headlands (Yasso, 1965). Oblique persistent swell striking a shoreline transports sediment alongshore and sculptures a coast into arc-shaped beaches. The shoreline of beach appearance mainly consists of straight segment and shadow segment…     

Simulation of wind-induced near-inertial oscillations in a mixed layer near the east coast of Korea in the East/Japan Sea

Using a simple damped slab model,it was possible to show that a local wind induced 88%(15 of 17)of the near-inertial oscillations(NIO)observed in the mixed layer near the east coast of Korea from 1999 to 2004.The model,however,overestimated the energy level in about two-thirds of the simulated cases,because the slab model was forced with winds whose characteristic period was shorter than the damping time scale of the model at 1.5 d.At the observation site,due to typhoons and orographic effects,high-frequency wind forcing is quite common,as is the overestimation of the energy level in the slab model results.In short,a simple slab model with a damping time-scale of about 1.5 d would be enough to show that the local wind was the main energy source of the near-inertial energy in this area,but the model could not be used to accurately estimate the amount of the work done by the wind to the mixed layer.     

海阳砂质海岸岸滩演化

基于海阳近岸海域的水深地形、表层沉积物粒度以及遥感影像等资料,利用泥沙起动流速和沿岸输沙数理公式以及岸滩演化数学模型,探讨了海阳近岸海域岸滩演化特征及主要控制因素。研究结果表明,研究区总体处于动态平衡状态,潮流很难使泥沙发生直接起动,波浪造成的沿岸输沙总体向ENE方向运移。影响研究区冲淤变化的因素主要有河流来沙、波浪以及人工构筑物。河流径流量减小,导致研究区泥沙来源减少,加剧了局部海岸侵蚀;近岸人工构筑物的建设,改变了泥沙输运趋势,并导致局部冲淤环境发生变化;波浪是控制研究区泥沙运移、沉降的关键因素,控制着研究区冲淤演化的整体格局。     

福建南部沿海的江豚

在闽南厦门至漳浦沿海获22只江豚,根据背部棘状小结节的数量与分布,可明显分为两个亚种,即指名亚种(N.P.Phocaenoides,81%)和北方亚种(N.P.Sunameri,19%),表明本海域是几个亚种的混栖地带,分析了这些江豚的外部形态和种群结构,测定了脂肪层及各内脏的重量.     

海岸沿岸流垂向分布实验研究

进行海岸沿岸流模型实验,利用ADV(acoustic doppler velocimeter)测量了沿岸流流速沿垂直岸线方向多个断面的垂向分布。采用Faria等的方法对实验结果进行了分析,将沿岸流沿水深分为上层和下层两部分:下层采用对数分布来表达沿岸流的垂向分布;上层考虑了波浪引起的自由表面的波动,流速分布为修正的对数分布。最后对沿岸流垂向分布特征做了分析,并与Visser和Hamilton的实验结果做了对比。     

Circulation and dispersion in a cancellate coast: The rivers,bays and estuaries of central Maine

The glacially carved central coast of Maine is incised by river systems with interconnecting channels, offshore-trending submarine ridges, and narrow passages between nearshore islands and headlands. The tidal range exceeds 3 m, leading to complex and vigorous circulation patterns with strong flows in narrow channels, near river mouths, and between islands. The spongiform coastal morphology allows enhanced exchange between offshore waters, estuaries and internecine bays, resulting in rapid dispersal of nutrients, larvae and contaminants throughout the region. A fine-grid numerical circulation model has been used to examine the influences of the tides, river flows and winds on the dispersion of lobster larvae and pollutants in the nearshore and riverine environment. This paper describes the model application, presents a few salient features of the circulation patterns, and examines some implications for the coastal environment. For example, under realistic tides and variable southwest summer winds, about 80% of neutral near-surface particles introduced near the offshore islands (a proxy for stage IV lobster larvae from offshore sources) remain within a few km of the islands over a two-week period. On the other hand, a persistent, periodic sea breeze can remove more than two-thirds of the particles from the domain over the same period. Tidal mixing disperses pollutants entering the upper Kennebec River to the offshore and through internecine passages in about one week.     

城市设计在青岛海岸规划中的应用

在分析青岛海岸工程的特点及遍海岸工程对城市风貌影响影响的基础上,应用城市设计学对青岛的海岸规划与布局提出构想,并以沙子口海岸整治为例,提出滨海城市设计中适宜的岸线和海岸整治工程。     

Rheological Properties and Incipient Motion of Cohesive Sediment in the Haihe Estuary of China

The Haihe cohesive sediment, which is typical in China, is studied systematically for its basic physical and incipientmotion properties. Following the requirements of dredging works in the Haihe Estuary, cohesive sediment samples weretaken from three locations. Laboratory experiments were conducted to determine the rheological properties of these sam-ples and to examine the incipient motion of the cohesive sediment. It is found that the cohesive sediment has an obviousyield stress τb, which increases with the mud density in a manner of an exponential function, and so does the viscosityparameter η. The cohesive sediment behaves like a Bingham fluid when its density is below 1.38 ～ 1.40 g/cm3, andwhen denser than these values, it may become a power-law fluid. The incipient motion experiment also revealed that theincipient velocity of the cohesive sediment increases with the density in an exponential manner. Therefore, the incipientmotion is primarily related to the density, which is different from the case for non-cohesive sediment in which the incipi-ent motion is correlated with the diameter of sand particles instead. The incipient motion occurs in two different ways de-pending on the concentration of mud in the bottom. For sufficiently fine particles and a concentration lower than1.20 g/cm3, the cohesive sediment appears as fluidized mud, and the incipient motion is in the form of instability of aninternal wave. For a higher concentration, the cohesive sediment appears as general quasi-solid-mud, and the incipientmotion can be described by a series of extended Shields curves each with a different porosity for newly deposited alluvial mud.     

江苏沿海互花米草盐沼动态变化及影响因素研究

收集了1988-2001年12个时相的江苏盐城幅卫星影像,提取了双洋河口至梁垛：河闸之间的互花米草盐沼;统计了不同时期的分布信息。分析表明：①互花米草盐沼在江苏扩张非常迅速,到2001年7月互花米草盐沼分布面积达129．28km^2,从射阳河口至梁垛河闸之间的潮问中上带泥滩大部分已被互花米草盐沼所覆盖;②由于生态位的影响,互花米草盐沼沿平行于海岸线方向的扩张速度快于垂直于海岸线方向的扩张速度;③依据野外调查和卫星影像分析,互花米草盐沼扩张可分为3个阶段：立地阶段、快速扩张期及成熟期。此外,还对互花米草盐的影响因素进行了探讨。