The evolution of tidal creek networks,mary river,northern Australia     

A. David Knighton  Colin D. Woodroffe  Kevin Mills 《地球表面变化过程与地形》1992,17(2):167-190

Tidal creek networks have in 50 years extended over 30 km inland across the coastal plains of the Mary River in northern Australia, invading freshwater wetlands and destroying the associated vegetation. The networks have grown at an exponential rate through a combination of main channel extension and tributary development, with concomitant widening of the creeks. A large tidal range, very small elevational differences over the plains, and the availability of preexisting channel lines (notably in the form of palaeochannels) have been major factors contributing to the rapid rate of expansion. Close parallels exist between these networks and terrestrial networks as regards modes of growth and planimetric properties. A channel is initiated when the diffuse flow of a seepage zone becomes concentrated through localized scour. Subsequent development is characterized by the rapid extension of long first-order channels, with most tributary addition occurring later. Model tests suggest that branching was more likely on exterior links in the early stages but that exterior and interior link branching became more equally likely through time. Although the headward limits of the main creeks seem to have been reached, tributary infilling will continue to progress upstream. Only in the most downstream parts is a stable drainage density being approached. The networks not only satisfy the laws of drainage network composition and the basic postulates of the random model but also depart from topologic randomness in similar ways to terrestrial networks. Both topologic and length properties have changed during evolution but largely at the link rather than network scale. The close correspondence with terrestrial networks may be due to the low relief and the relatively unconstrained nature of growth in which availability of space was the main determining factor.  相似文献   

PREM-ZSCHAU滞弹地球模型对表面负荷的脉冲响应   总被引：3，自引：0，他引：3       下载免费PDF全文

肖强  许厚泽 《地球物理学报》1990,33(3):319-328

利用PREM模型及ZSCHAU的地球内部粘滞性模型,解算了地球对表面负荷的脉冲响应问题,包括频率域和时间域的解.得到的复勒夫数及复格林函数表明,在ω>10~(-8)/s的频段内,地球的响应可视为基本上是弹性的,只有像冰后调整、地幔对流这样长期的运动,粘滞性才起重要作用;在ω<10~(-13)/s的频段,地球响应呈流体状态.  相似文献   

重力场的潮汐变化观测及其研究   总被引：6，自引：1，他引：6  

孙和平  许厚泽  徐建桥  柳林涛 《地球科学进展》2000,15(1):53-57

基于我国武汉超导重力仪长周期序列潮汐观测数据,研究了重力场潮汐变化特征,精密确定了地球潮汐常数,讨论了重力观测中的海潮负荷和大气效应问题;根据地球自由核章动在周日重力潮汐观测中的共振效应确定了自由核章动的复本征周期和品质因子Q值,研究了极移重力效应;并对进一步利用重力潮汐观测研究地球物理问题进行了讨论。  相似文献   

Transitional environments of the lower Maastrichtian South-Pyrenean Basin (Catalonia,Spain): The Fumanya Member tidal flat     

《Cretaceous Research》2016

Sedimentological, palaeontological and geochemical data provide detailed evidence of a marine-to-lagoon environmental succession around the Campanian-Maastrichtian boundary in the Ibero-Armorican domain. This regression is recorded by the succession of several environments of the south-central Pyrenees basin: open marine mixed shelf, marine restricted mixed shelf (both rudist-rich), tidal flat, lagoon and fluvial dominated. The tidal flat setting belongs to the Fumanya Member here described, which is the base of the Posa and Massana formations (Tremp Group). The Fumanya Member is 5 m thick, is built up of marly limestones and was an elongated tidal mudflat (100 km long, 25 km wide) developed in a foreland trough and was separated from the Atlantic Ocean by an island-barrier system. In the lagoon environment, marginal marine waters and continental fresh waters alternated as documented by geochemistry and fossil molluscs. The Fumanya Member is a dinosaur megatracksite, reporting the roaming activity only of sauropods in tidal flats, a likely secure area against predators. Feeding activity of these herbivores took place in the lagoonal-lacustrine environments of the Posa Formation above the Fumanya Member.  相似文献   

Depositional environment and hydrocarbon potential of marginal marine sediments of Eocene from western India: A palynofacies perspective     

《Marine and Petroleum Geology》2016

Palynofacies and palynological data from Eocene sediments documents a comprehensive picture of the nature (degraded, structured, non-structured, amorphous etc.) of organic matter, their distribution, and depositional setting for Matasukh lignite mines of Nagaur Basin in western India. Four Sporomorph Eco Groups (SEG) are defined based on the palynological data viz., Upland SEG, Lowland SEG, Coastal SEG and Tidally influenced SEG. Principal component analysis was used to categorize the organic matter into two palynofacies. Palynofacies-A is dominated by brown Phytoclasts (in particular cuticles) and Palynofacies-B is dominated by amorphous organic matter, mainly derived from terrestrially degraded material. In Palynofacies-B there is a reduced frequency of cuticles and high frequency of non-biostructured amorphous phytoclasts in comparison to Palynofacies-A. Further the Integration of Tidal limit index and Phytoclast preservation index suggest that the sediments were deposited in a proximal setting and were regularly influenced by brackish-marine water. The sand bed with current bedding in which the troughs are draped with lignitic clay indicate the tidal wave action. Tyson's ternary diagram indicates the deposition of these sediments in a sub-oxic to dysoxic condition, rich in Kerogen Type-II/III. Thermal alteration index (TAI) shows that the sediments of Matasukh lignite mine have attained maturation (the characteristic value reached by hydrocarbon generating sediments) to generate dry gas as majority of the organic matter is of Type-III Kerogen with few samples yielding Type-II. These sediments were deposited in deltaic plain, in particular, fluvial dominated marginal marine environment.  相似文献   

潮汐混合对大西洋经圈翻转环流(AMOC)模拟影响的数值模拟研究   总被引：1，自引：1，他引：0  

于子棚  刘海龙  林鹏飞 《大气科学》2017,41(5):1087-1100

海洋中的潮汐混合对大西洋经圈翻转环流AMOC(Atlantic Meridional Overturning Circulation)模拟的影响是海洋环流模式研究的热点问题之一。本文采用IAP/LASG发展的气候系统海洋模式LICOM(LASG/IAP Climate system Ocean Model)及与海冰耦合模式进行了有无潮汐混合方案的试验,重点探讨了潮汐混合对AMOC强度模拟的影响。结果显示,引入潮汐混合后模拟的AMOC强度极大值比对照试验增加约1倍,更接近RAPID(Rapid Climate Change Programme)观测。而且,潮汐混合试验中模拟的AMOC上层环流深度(3200 m)比对照试验加深1000 m左右,同样更接近RAPID观测。海洋底部的垂直混合增强,使海洋层结变得更加不稳定,加强了北大西洋高纬地区,特别是拉布拉多海等地区的深对流,这是AMOC加强的直接原因。同时,潮汐混合试验中上层海洋环流也加强,增加了中低纬副热带高盐海水向高纬输送,使表层增密,海洋层结更加不稳定,也可以进一步增强AMOC。  相似文献   

短滨螺Littorina brevicula排卵及运动潮汐节律性的研究     

薛钦昭 《海洋科学》1991,(4)

本文在室内无潮汐因子作用条件下对采集于青岛太平湾基岩海岸潮间带的短滨螺进行观察,发现其具有和潮汐同步的排卵和运动节律性。30d后,仍能观察到排卵的潮汐节律性。1a后,短滨螺不呈现排卵的潮汐节律性。  相似文献   

湄洲湾的潮流和余流特征     

黄荣祥  陈冠惠 《海洋科学》1994,18(1):67-70

湄洲湾是福建省中部沿海的港湾，湾内三面为大陆所环抱，湾口朝向东南进入台湾海峡。该湾呈西北向深入内陆约１８ｎｍｉｌｅ，湾口有湄洲岛作为屏障和标志，使整个湾口分成文甲口门（北口宽约０．６５ｎｍｉｌｅ）和剑屿－鹅尾山口门（南口，宽约５．６１ｎｍｉｌｅ）两个口门，距湾口约５ｎｍｉｌｅ的盘屿、大竹等岛屿及距湾口约１２ｎｍｉｌｅ的屿、横屿等岛屿为湾内两道屏障，再往内为内沃。屿和横屿间水面宽约０．５１ｎｍｉｌｅ，水深约２０ｍ，它和北端肖厝－秀屿及南端峰尾－西亭深槽相连接，是该湾的主航道（图１）。该湾航道宽阔水…  相似文献   

西涌湾及邻近海域物理自净能力研究   总被引：1，自引：0，他引：1  

王学昌  娄安刚  郑丙辉  富国  孟伟 《海洋科学》2002,26(11):34-37

利用不规则三角形网格和分步杂交方法建立了西涌湾及邻近海域的二维变边界潮流数值模型，并在此基础上建立了相应海域的拉格朗日余流模型，对拟建排污口标识质点的运移轨迹进行跟踪，通过计算公式，给出了西涌湾及邻近海域的水交换活跃区和滞缓区，并为拟设排污口进行了优化选择。  相似文献   

Tidal Mixing in the Kuril Straits and Its Impact on Ventilation in the North Pacific Ocean     

Tomohiro Nakamura  Takahiro Toyoda  Yoichi Ishikawa  Toshiyuki Awaji 《Journal of Oceanography》2004,60(2):411-423

A numerical study using a 3-D nonhydrostatic model has been applied to baroclinic processes generated by the K ₁ tidal flow in and around the Kuril Straits. The result shows that large-amplitude unsteady lee waves are generated and cause intense diapycnal mixing all along the Kuril Island Chain to levels of a maximum diapycnal diffusivity exceeding 10³ cm²s⁻¹. Significant water transformation by the vigorous mixing in shallow regions produces the distinct density and potential vorticity (PV) fronts along the Island Chain. The pinched-off eddies that arise and move away from the fronts have the ability to transport a large amount of mixed water (∼14 Sv) to the offshore regions, roughly half being directed to the North Pacific. These features are consistent with recent satellite imagery and in-situ observations, suggesting that diapycnal mixing within the vicinity of the Kuril Islands has a greater impact than was previously supposed on the Okhotsk Sea and the North Pacific. To examine this influence of tidal processes at the Kurils on circulations in the neighboring two basins, another numerical experiment was conducted using an ocean general circulation model with inclusion of tidal mixing along the islands, which gives a better representation of the Okhotsk Sea Mode Water than in the case without the tidal mixing. This is mainly attributed to the added effect of a significant upward salt flux into the surface layer due to tidal mixing in the Kuril Straits, which is subsequently transported to the interior region of the Okhotsk Sea. With a saline flux into the surface layer, cooling in winter in the northern part of the Okhotsk Sea can produce heavier water and thus enhance subduction, which is capable of reproducing a realistic Okhotsk Sea Mode Water. The associated low PV flux from the Kuril Straits to the open North Pacific excites the 2nd baroclinic-mode Kelvin and Rossby waves in addition to the 1st mode. Interestingly, the meridional overturning in the North Pacific is strengthened as a result of the dynamical adjustment caused by these waves, leading to a more realistic reproduction of the North Pacific Intermediate Water (NPIW) than in the case without tidal mixing. Accordingly, the joint effect of tidally-induced transport and transformation dominating in the Kuril Straits and subsequent eddy-transport is considered to play an important role in the ventilation of both the Okhotsk Sea and the North Pacific Ocean. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献