Fine particle deposition to initially starved,stationary, planar beds     

NATHAN T. HAMM  W. BRIAN DADE  CARL E. RENSHAW 《Sedimentology》2009,56(7):1976-1991

Reported here are results from new flume experiments examining deposition and entrainment of inert, silt‐sized particles (with spherical diameters in the range from 20 to 60 μm) to and from planar, impermeable and initially starved beds underlying channel flows. Bed surfaces comprised smooth or fixed sand‐size granular roughness and provided hydraulically smooth to transitionally rough boundaries. Results of these experiments were analysed with a simple model that describes the evolution of vertically averaged concentration of suspended sediment and accommodates the simultaneous delivery to and entrainment of grains from the bed. The rate of particle arrival to a bed diminishes linearly, and the rate of particle entrainment increases by the 5/2 power, as the value of the dimensionless Saffman parameter S = u_*³/g’ν approaches a threshold value of order unity, where u is the conventional friction velocity of the turbulent channel flow, g’ is the acceleration due to gravity adjusted for the submerged buoyancy of individual particles and ν is the kinematic viscosity of the transporting fluid. This transport behaviour is consistent with the notion that non‐cohesive, silt‐sized particles can neither reach nor remain on an impermeable bed under flow conditions where mean lift imposed on stationary particles in the viscous sublayer equals or exceeds the submerged weight of individual particles. Within the size range of particles used in these experiments, particle size and the characteristic size of granular roughness, up to that of medium sand, did not affect rates of dimensionless arrival or entrainment to a significant degree. Instead, a new but consistent picture of fine‐particle transport is emerging. Silt‐sized material, at least, is subject to potentially significant interaction with the bed during intermittent suspension transport at intermediate flow speeds greater than the value required for initiation of transport (ca 20 cm sec^?1) but less than the value (ca 50 cm sec^?1) required by the Saffman criterion ensuring transport in fully passive suspension or, equivalently, ‘wash‐load’.  相似文献   

Stage boundaries of the Triassic in Northeast Asia     

A. G. Konstantinov  T. V. Klets 《Stratigraphy and Geological Correlation》2009,17(2):173-191

The International Union of Geological Science approved the stage boundaries suggested by the international working groups for the Tethyan Triassic. In this work we estimate the possibility of their establishment and correlation in the Boreal sections of Northeast Asia, based on the analyzed distribution of ammonoids and conodonts. As the conodonts of the Induan Stage have not been identified for sure in the region under study, the lower boundary of the Triassic System is defined here at the base of the Otoceras concavum Zone of the ammonoid scale. In addition to the ammonoids Hedenstroemia hedenstroemi (Keyserling), the first occurrence of the conodonts Pseudogondolella nepalensis (Kozur et Mostler) is suggested to be the biomarker of the Olenekian Stage base. The lower boundaries of the Anisian and Ladinian stages, defined respectively at the basal levels of the Paracrochordiceras-Japonites Beds in Northern Dobrogea and the Eoprotrachyceras curionii Zone in the Brescian Prealps are recognizable, though with some reservations, at the base of the Grambergia taimyrensis and Eonathorstites oleshkoi zones in Northeast Asia. According to the priority principle and similarity between the ammonoid faunas of the Daxatina cf. canadensis Subzone and Frankites regoledanus Zone, the lower boundary of the Carnian Stage is defined at the base of the Alpine Trachyceras aon Zone. In Northeast Asia, this boundary is established at the base of the “Protrachyceras” omkutchanicum Zone, as we take into account the fact that the Daxatina and Stolleyites ammonoid genera occur in sections of British Columbia below the stratigraphic level of the Trachyceras forms. The lower boundary of the Norian Stage is concurrent with the base of the Guembelites jandianus Zone in the Alps and equivalent Stikinoceras kerri Zone in North America and Striatosirenites kinasovi Zone in Northeast Asia. The conodont species Norigondolella navicula (Huckriede) that is most important for the Boreal-Tethyan correlation cannot be used as a biomarker of the Norian lower boundary because of its problematic diagnosis and rare occurrence in the Boreal sections. The Rhaetian Stage base is defined at the appearance level of the Misikella conodont genus in the Hallstatt region, Austria, that is simultaneously the disappearance level of the characteristic Norian bivalves (Monotis) and ammonoids (Metasibirites). In Northeast Asia, this boundary is established at the top of the Monotis ochotica Zone. The correlation between the biostratigraphic units of the Middle-Upper Triassic conodont scale established in Northeast Asia and standard ammonoid zonation is verified.  相似文献   

地下水对基坑开挖的影响以及防治措施的研究     

范加冬  张令刚 《岩土工程技术》2009,23(3):135-138

基于地下水的不同类别及其特性,分析了包气带水、潜水以及承压水的影响及其预防措施。分析表明,对于包气带水和潜水其影响主要是引起基坑渗流,通过打隔水桩截断之即可收到很好的效果;对于承压水其影响主要是引起基坑突涌,分析了传统降水法（明沟排水、深井排水等）的效果及其存在的弊端。在新方法的研究中,基于球形颗粒理想化最松散堆积模型,研究了弹性条件下饱和土的力学特性。研究表明,基坑的破坏主要有两种方式,弯矩破坏和剪力破坏。利用材料力学原理分别计算出其最小隔水厚度hmin^s、hmin^w,理论分析表明,只要通过增设压板改变最大弯矩的值可以使hmin^s、hmin^w降到hmin。  相似文献   

Formation Mechanism of "Drag Depressions" and Irregular Boundaries in Intraplate Deformation     

DENG Jun  HUANG Dinghu  WANG Qingfei  HOU Zengqian  LU Qingtian  YAOLingqing  XIN Hongbo  ZHANG Qiang  WEI YanguangKey Laboratory of Lithospheric Tectonics  Exploration  China University of Geosciences  Beijing  Ministry of Education  Beijing  China University of Geosciences  Wuhan  Hubei Institute of Mineral Resources  Chinese Academy of Geological Sciences  Beijing 《《地质学报》英文版》2004,78(1):267-272

Almost all intraplate caprocks experienced strong deformation during the convergence of microplates, and then disintegrated into many secondary geologic units with the special characters, such as irregular boundaries and particular structural assemblages. In order to understand the formation mechanism of these special phenomena, a rheological experiment on the structural scenery of the Tongling area is carried out. The result shows that the primary regular and uniform boundaries of the Tongling area becomes irregular because of the enclosing and confinement of surrounding geological units in the process of "compression-shearing-rotation-drag"; simultaneously, two specific "drag depressions" developed at two opposite corners of the block. The former and the later phenomena can be regarded as a typical regional-scale rheological effect and necessary outcome of intraplate deformation respectively.  相似文献   

大陆架在国家可管辖海域划界问题研究   总被引：3，自引：0，他引：3  

张耀光  王圣云  宋欣茹  耿雅冬 《地理与地理信息科学》2004,20(3):52-55,108

大陆架是地质地理学研究的内容,随着人类对海洋的开发,大陆架已成为国家在海洋权益维护方面重要的内容。该文阐述了大陆架制度的形成以及在可管辖海域划界中的作用,并对我国专属经济区和大陆架制度以及大陆架在我国可管辖海域划界中所面临的问题进行了分析。  相似文献   

Tilt梯度及其水平导数提取重磁源边界位置   总被引：7，自引：6，他引：1  

王想  李桐林 《地球物理学进展》2004,19(3):625-630

探讨了用于探测异常源边界和形状的Tilt梯度及其水平导数的方法及其性质．通过模型试算,论证了Tilt梯度及其水平导数的有效性,并从理论上给予了证明．Tilt梯度及其水平导数的方法及其性质可广泛用于区域重磁异常的构造解释之中。  相似文献   

BOOK REVIEWS     

《The Professional geographer》1987,39(1):94-129

Book Reviewed in this article: The Rice Economy of Asia . Randolph Barker and Robert W. Herdt with Beth Rose. Using Microcomputers: A Guidebook for Writers, Teachers, and Researchers in the Social Sciences . Blaine A. Erie—the Lake that Survived . Noel M. Burns. Geology and Society . Donald R. Coates. Caves and Karst of Kentucky . Percy H. Dougherty, ed. Altered Harvest: Agriculture, Genetics, and the Fate of the World's Food Supply . Jack Doyle. The Middle East and North Africa, A Political Geography . Alasdair Drysdale and Gerald H. Blake. Clamor at the Gates. The New American Immigration . Nathan Glazer, ed. Development and the Landowner: An analysis of the British experience . Robin Goodchild and Richard Munton. Discovering Landscape in England and Wales . Andrew Goudie and Rita Gardner. The Modern Plantation in the Third World . Edgar Graham and Ingrid Floering. Social Relations and Spatial Structures . Derek Gregory and John Urry, eds. The World Food Problem 1950–1980 . David Grigg. Costa Rica: A Geographical Interpretation in Historical Perspective . Carolyn Hall. The Urbanization of Capital: Studies in the History and Theory of Capitalist Urbanization . David Harvey Consciousness and the Urban Experience: Studies in the History and Theory of Capitalist Urbanization . David Harvey. Reviving Main Street . Deryck Holdsworth, ed. Rural Roads and Poverty Alleviation . John Howe and Peter Richards, eds. Uneven Development in Southern Europe: Studies of Accumulation, Class, Migration and the State . Ray Hudson and Jim Lewis, eds. Karst Geomorphology . J. N. Jennings. The Geomorphology of North-west England . R. H. Johnson, ed. Climate Impact Assessment: Studies of the Interaction of Climate and Society . Robert Kates, Jesse Ausubel, Mimi Berberian, eds. Public Service Provision and Urban Development . Andrew Kirby, Paul Knox, and Steven Pinch, ed. State and Market: The Politics of the Public and the Private . Jan-Erik Lane, ed. Living Cities . Twentieth Century Fund Task Force on Urban Preservation Policies. World Climatic Systems . John G. Lockwood. Urban Ethnicity in the United States. New Immigrants and Old Minorities . Lionel Maldonaldo and Joan Moore, eds. Culture and Conservation: The Human Dimension in Environmental Planning . Jeffrey A. McNeely and David Pitt, eds. The Andean Past. Land, Societies, and Conflicts . Magnus Mörner. Gaia: An Atlas of Planet Management . Norman Myers, ed. Progress in Industrial Geography . Michael Pacione, ed. Progress in Political Geography . Michael Pacione, ed. Rivers and Landscape . Geoff Petts and Ian Foster. Urbanization and Planning in the 3rd World: Spatial Perceptions and Public Participation . Robert B. Potter. One Island, Two Nations? A Political Geographical Analysis of the National Conflict in Ireland . D. G. Pringle. Circulation in Third World Countries . R. Mansell Prothero and Murray Chapman. The Ozarks Outdoors: A Guide for Fishermen, Hunters, and Tourists . Milton D. Rafferty. Suburban Burglary: A Time and a Place for Everything . George Rengert and John Wasilchick. Geomorphology and Soils . K.S. Richards, R.R. Arnett, and S. Ellis, eds. The Homes and Homeless of Post-War Britain . Frederick Shaw. Indochinese Refugees in America . Paul J. Strand and Woodrow Jones, Jr. Wild Horses and Sacred Cows . Richard Symanski. Forever Wild: Environmental Aesthetics and the Adirondack Forest Preserve . Philip G. Terrie. The Regional Economic Impact of Technological Change . A.T. Thwaites and R.P. Oakey, eds. The Good Life . Yi-Fu Tuan.  相似文献   

Changes in strain trajectories in three different types of plate tectonic boundary deduced from earthquake focal mechanisms     

J. L. Giner-Robles  J. M. Gonzlez-Casado  P. Gumiel  C. García-Cuevas 《Tectonophysics》2003,372(3-4):179-191

Principal strain orientations (minimum horizontal compression—ex and maximum horizontal compression—ey) were established at three different types of plate tectonic boundary: two transform faults, an oceanic ridge located on the Southeast Indian Ridge and a trench located close to the South Sandwich Archipelago. To establish the strain patterns in each zone, 104 earthquake focal mechanisms (centroid-moment tensor solutions for earthquakes with mb≥4; Harvard seismology data, CMT) were examined by fault population analysis. Despite the existence of only one tectonic process that controlled deformation in these zones (divergence, convergence or passive displacement), and only one main strain tensor, several coeval strain ellipsoids were found. These differed from the main strain tensor in the location of the principal strains. In general, permutations were observed between the principal strains, i.e., interchanges between the location of the principal strain axes maintaining the strain ellipsoids in the same 3D orientation. Only in some cases were changes in the ellipsoid orientation associated with major structures.  相似文献   

The composite magnetic anomaly map of the East Antarctic     

A. V. Golynsky  S. V. Alyavdin  V. N. Masolov  A. S. Tscherinov  V. S. Volnukhin 《Tectonophysics》2002,347(1-3)

Airborne and marine magnetic observations in East Antarctica and adjacent seas of the Indian Ocean were compiled for a magnetic anomaly map of the Antarctic. For East Antarctica, over 260,000 line km of Russian reconnaissance magnetic data were used that had been collected since 1955 mainly at line spacings of about 5, 20 and 50 km. For the offshore areas, magnetic data from American, Australian, German, Japanese, and Russian marine expeditions were incorporated. Digitally recorded data and data digitized from published and unpublished maps and profiles were included in the compilation. Local grids of these data were developed and merged into a regional grid at an interval of 5 km. The prime product of this compilation is a shaded-relief map that shows the most complete and coherent perspective to date of the region's magnetic character. In combination with other types of data, the compilation provides new insight on the tectonic features and history of this largely inaccessible region of the world. It maps out approximately 4300 km of the Antarctic Continental Margin Magnetic Anomaly (ACMMA) related to Gondwana breakup, new cratons and mobile belts, and large submarine igneous provinces.  相似文献   

Geophysical Evidence for Terrane Boundaries in South-Central Argentina   总被引：1，自引：0，他引：1  

Carlos J. Chernicoff  Eduardo O. Zappettini   《Gondwana Research》2004,7(4):1105-1116

The geological interpretation of high-resolution aeromagnetic data over the La Pampa province, in central Argentina, in addition to lower resolution magnetic information from the region of the Neuquén and Colorado basins, leads to the definition of the precise boundaries of the Chilenia, Cuyania, Pampia and Patagonia terranes, as well as that of the Río de la Plata Craton, within the study region. The high-resolution aeromagnetic survey data are compared and studied in conjunction with all the available geological information, to produce a map of the solid geology of this region, which is largely covered by Quaternary sediments. A number of structures of different magnitudes, as well as their relative chronology, are also recognized, i.e., regional faults, sub-regional faults, fractures and shear zones, as well as the most conspicuous magnetic fabric of the basement that reflects its main planar structures. Three different basements are distinguished on the basis of their contrasting magnetic character, and are interpreted to represent the Cuyania and Pampia terranes and the Río de la Plata Craton, separated from each other by large-scale discontinuities. In the western part of the study region an additional major discontinuity separates the Chilenia and Cuyania terranes. In the southernmost area studied, WNW-trending structures are predominant, particularly a major NNE-vergent thrust that indicates the truncation of the Cuyania-Pampia suture and is regarded to be related to the possible collision of the Patagonia terrane. An E–W – trending magnetic and gravity anomaly traversing the full extra-Andean Argentine territory, located immediately to the south of 39°S, represents a major structure. The activation of this structure during the Mesozoic gave rise to the Huincul Ridge and marks the interruption of the distinct N-S structures of the Chilenia, Cuyania and Pampia terranes, as well as those of the Río de la Plata Craton, to the north. This E–W represents the suture zone of the Patagonia terrane.  相似文献