Significant change of extratropical natural variability and potential predictability associated with the El Niño/Southern Oscillation     

WILBUR Y. CHEN  HUUG M. VAN DEN DOOL 《地球，A辑:动力气象学与海洋学》1999,51(5):790-802

  相似文献   

Pleistocene sandur deposits represent braidplains, not alluvial fans     

TOMASZ ZIELINSKI  ANTONIUS J. VAN  LOON 《Boreas: An International Journal of Quaternary Research》2003,32(4):590-611

Weichselian sandar in NE Poland show characteristics that are inconsistent with the commonly accepted alluvial-fan-like model for outwash deposition and sandur formation. Analysis of the lithofacies and their vertical and lateral transitions indicates that the Polish sandar developed as braidplains, not as alluvial fans. Analysis of the geomorphic conditions under which modern sandar form, indicates that these conditions (which are characterized by deposition in a narrow belt between ice-covered mountain ranges and the sea) cannot be considered representative of those that prevailed in the geological past when sandar developed as braidplains in confined valleys, to end up in a lowland area where the deposits could spread out further in lateral directions. The latter conditions have been found consistently for all Polish Weichselian sandar that were investigated in much sedimentological detail. This raises the question whether sandar are alluvial fans or not. Because the development of the sandar in NE Poland seems to be much more representative for outwash deposition than the present-day sandar in Iceland and elsewhere, the current alluvial-fan-like sandur model - based on the fairly exceptional present-day situation with deposition in a narrow belt - should therefore be replaced by the braidplain-like sandur model - based on deposition in a valley and in a wider lowland area in front - that has been established for the Polish examples.  相似文献   

THE LATERAL INFLOW INTO SUBMERGED DRAINS     

A. VAN DER BEKEN  F. DE TROCH  M. DE SOMER  F. C. ZUIDEMA 《水文科学杂志》2013,58(3):273-289

ABSTRACT

An attempt is made to explain the field measurements of piezometric height and discharge rate in a submerged drain system. The lateral inflow into the drain pipe is not necessarily uniformly distributed as is usually assumed. Hence, in analysing the hydrological performance of the drain pipe in the field, this fact must be considered. A general formula (equation (11)) is presented for calculating the actual distribution of the lateral inflow and a practical application is discussed.  相似文献   

Five short pollen diagrams of soils from Jan Mayen, Norway: a testimony of a dynamic landscape   总被引：1，自引：0，他引：1  

W. O. VAN DER KNAAP 《Polar research》1987,5(2):193-206

Five soil cores varying in length from 30 to 42 cm and seven surface samples were analysed for pollen and spores. The soil layers of four cores were probably formed through redeposition of other eroded soils. Only in the Batvika core is the organic fraction of probable local origin, and here a chronology could be established. A total long-distance pollen influx of 14-22.5 grains/cm²/year was calculated. Nearly 2, 000 long-distance pollen grains were counted; the ratios of the dominant pollen types were calculated. Around Batvika the past environment was relatively stable; only one major shift in sedimentation environment is apparent from the diagram. In another diagram, expansion of Taraxacum species could be correlated with anthropogenic soil disturbance. The former presence of Lycopodium alpinum and Selaginella selaginoides on Jan Mayen is indicated by frequent spore finds; the latter species has not been found on the island before. Two unknown spore types are discussed.  相似文献   

Anatomy of a modern open-ocean carbonate slope: northern Little Bahama Bank   总被引：1，自引：0，他引：1  

HENRY T. MULLINS  KATHRYN C. HEATH†  H. MARK VAN  BUREN† CATHRYN R. NEWTON 《Sedimentology》1984,31(2):141-168

The open-ocean carbonate slope north of Little Bahama Bank consists of a relatively steep (4°) upper slope between water depths of 200 and 900 m, and a more gentle (1–2°) lower slope between depths of 900 and 1300+ m. The upper slope is dissected by numerous, small, submarine canyons (50–150 m in relief) that act as a line source for the downslope transport of coarse-grained carbonate debris. The lower slope is devoid of any well-defined canyons but does contain numerous, small (1–5 m) hummocks of uncertain origin and numerous, larger (5–40 m), patchily distributed, ahermatypic coral mounds. Sediments along the upper slope have prograded seaward during the Cenozoic as a slope-front-fill seismic facies of fine-grained peri-platform ooze. Surface sediments show lateral gradation of both grain size and carbonate mineralogy, with the fine fraction derived largely from the adjacent shallow-water platform. Near-surface sedimentary facies along the upper slope display a gradual downslope decrease in the degree of submarine cementation from well-lithified hardgrounds to patchily cemented nodular ooze to unlithified peri-platform ooze, controlled by lateral variations in diagenetic potential and/or winnowing by bottom currents. Submarine cementation stabilizes the upper part of the slope, allowing upbuilding of the platform margin, and controls the distribution of submarine slides, as well as the headward extent of submarine canyons. Where unlithified, sediments are heavily bioturbated and are locally undergoing dolomitization. Upper slope sediments are also ‘conditioned’eustatically, resulting in vertical, cyclic sequences of diagenetically unstable (aragonite and magnesian calcite-rich) and stable (calcite-rich) carbonates that may explain the well-bedded nature of ancient peri-platform ooze sequences. Lower slope sediments have prograded seaward during the Cenozoic as a chaotic-fill seismic facies of coarse-grained carbonate turbidites and debris flow deposits with subordinate amounts of peri-platform ooze. Coarse clasts are ‘internally’derived from fine-grained upper slope sediments via incipient cementation, submarine sliding and the generation of sediment gravity flows. Gravity flows bypass the upper slope via a multitude of canyons and are deposited along the lower slope as a wedge-shaped apron of debris, parallel to the adjacent shelf edge, consisting of a complex spatial arrangement of localized turbidites and debris flow deposits. A proximal apron facies of thick, mud-supported debris flow deposits plus thick, coarse-grained, Ta turbidites, grades seaward into a distal apron facies of thinner, grain-supported debris flow deposits and thinner, finer grained Ta-b turbidites with increasing proportions of peri-platform ooze. Both the geomorphology and sedimentary facies relationships of the carbonate apron north of Little Bahama Bank differ significantly from the classic submarine fan model. As such, a carbonate apron model offers an alternative to the fan model for palaeoenvironmental analysis of ancient, open-ocean carbonate slope sequences.  相似文献   

Accurate Determination of Gallium in South African Primary and Secondary Reference Samples by Ion Exchange Chromatography and Atomic Absorption Spectrometry     

T.N. VAN DER WALT  F.W.E. STRELOW 《Geostandards and Geoanalytical Research》1984,8(2):163-167

Results are presented for gallium in six South African primary rock standards (NIMROCS) and in twelve secondary rock standards (SAROCS). A selective ion exchange procedure is used to separate gallium completely from all other elements, except remaining traces of thorium. It is followed by a determination of gallium with flame atomic absorption spectrometry using the nitrous oxide-acetylene flame, after the addition of 2000 ppm lanthanum as ionization suppressor.  相似文献   

The hydraulic interpretation of turbidites from their grain sizes and sedimentary structures     

JAY VAN  TASSELL 《Sedimentology》1986,33(3):437-438

  相似文献   

Bedform migration and bed-load transport in some rivers and tidal environments     

JAN H. VAN DEN  BERG 《Sedimentology》1987,34(4):681-698

Reliable field data obtained by directly measuring bed-load transport of fine- to coarse-grained bed material are extremely scarce, mainly because of the difficulty of sampling accurately. Therefore, the verification of bed-load transport formulae is largely based on flume experiments, which refer to unrealistic shallow-water conditions. In this study, some bed-load transport formulae were tested against data from natural environments. As an alternative to ascertaining the bed-load transport rate by sampling the bed-load, the transport rate was deduced from data on bedform height and bedform celerity. For this purpose, 43 sets of data from rivers, representing a wide range of bed material, bedform dimensions and hydraulic conditions were collected as were some sets of data from tidal settings. Two formulae were used for the prediction of the bed-load transport: the formula of Van Rijn (1981) and the Kalinske (1947) formula as approximated by Elzerman & Frijlink (1951) (and, in the present study, slightly modified for application to tidal waters). Both the bed-load function of Van Rijn and the modified formula of Kalinske-Frijlink require data which are easily obtained and that can be measured accurately. At those stages of the flow when bed-load transport was high the Van Rijn function tended to overestimate that transport. For flow stages when bed-load transport was low the opposite was true. The modified Kalinske-Frijlink function gave consistently good results: 86% of the transport rates predicted using the river data were within 0·5–2·0 times the values actually measured.  相似文献   

Dynamic analysis of column-supported hyperboloidal shells     

Phillip L. Gould  Subir K. Sen  Herman Suryoutomo 《地震工程与结构动力学》1973,2(3):269-280

The dynamic response of hyperboloidal shells on discrete column supports is studied using a curved rotational shell finite element. In this finite element formulation, the displacement field over each element domain is approximated by polynomial functions in which the coefficients of the linear terms correspond to the nodal values of the displacements and the higher order terms vanish at the nodal circles. The stiffness and mass matrices associated with the equations of motion are derived from Hamilton's variational principle and include the effects of transverse shearing deformation and rotatory inertia. Since the formulation, as such, involves a great many degrees of freedom because of the use of higher order displacement functions, the kinematic condensation technique is employed to reduce the order of the dynamic problem The dynamic analysis indicates the importance of realistically modelling the base region of the shell. Studies on a prototype tower indicates that the base flexibility reduces the natural frequencies of the shell and increases the displacements near the base. The magnitude of this reduction, which could be significant, depends primarily on the tangential stiffnesses of the supporting columns and is hardly affected by the thickened ring beam at the base.  相似文献   

THERMAL NEAR-SURFACE EXPRESSION OF SHALLOW GEOLOGICAL FEATURES*     

J. PH. POLEY  J. VAN STEVENINCK 《Geophysical Prospecting》1971,19(4):695-697

It has been customary in geothermal studies to assume the surface to be an isothermal plane, though difficulties existed to explain the magnitude of thermal anomalies observed in the field under this assumption. Detailed investigations of temperatures at depths between 5 cm and 230 cm show that—after removal of the strong diurnal variations—sizeable anomalies persist right to the surface. Thus, the effective heat transfer (coefficient) at the surface might be lower than commonly assumed.  相似文献