Dynamics and behaviour of suspended sediment in macrotidal estuaries along the south coast of the English Channel     

Jacques Avoine  Claude Larsonneur 《Continental Shelf Research》1987,7(11-12)

A review is given of suspended sediment dynamics in macrotidal regimes using examples of estuaries situated along the French coast of the English Channel. Characteristic features of estuarine turbidity maxima are described over a range of time-scales, which includes semidiurnal and neap-spring tidal cycles, and seasonal fluctuations of river discharge. The present behaviour of the fluvial sediment influx within these systems is described, taking into account the geological history of estuarine infilling.  相似文献   

Book review     

Peter Molnar  John D. Weeks  Claude J. Allegre  Yehuda Bock  Stephen K. Dobos  Leszek Czechowski  Kacper R. Rybicki  Krzysztof Haman 《Pure and Applied Geophysics》1987,125(4):679-698

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The kinetics of nucleation and crystal growth and scaling laws for magmatic crystallization     

Genevieve Brandeis  Claude Jaupart 《Contributions to Mineralogy and Petrology》1987,96(1):24-34

Magmatic crystallization depends on the kinetics of nucleation and crystal growth. It occurs over a region of finite thickness called the crystallization interval, which moves into uncrystallized magma. We present a dimensional analysis which allows a simple understanding of the crystallization characteristics. We use scales for the rates of nucleation and crystal growth, denoted by I _m and Y _m respectively. The crystallization time-scale _c and length-scale d _c are given by (Y _m ³ /I _m )^–1/4 and (·) _m ^1/2 respectively, where is thermal diffusivity. The thickness of the crystallization interval is proportional to this length-scale. The scale for crystal sizes is given by (Y _m /I _m )^1/4. We use numerical calculations to derive dimensionless relationships between all the parameters of interest: position of the crystallization front versus time, thickness of the crystallization interval versus time, crystal size versus distance to the margin, temperature versus time. We assess the sensitivity of the results to the form of the kinetic functions. The form of the growth function has little influence on the crystallization behaviour, contrary to that of the nucleation function. This shows that nucleation is the critical process. In natural cases, magmatic crystallization proceeds in continously evolving conditions. Local scaling laws apply, with time and size given by =(Y ³/I)^–1/4 and R=(Y/I)^1/4, where Y and I are the rates at which crystal are grown and nucleated locally. is the time to achieve crystallization and R the mean crystal size. We use these laws together with petrological observations to infer the in-situ values of the rates of nucleation and growth. Two crystallization regimes are defined. In the highly transient conditions prevailing at the margins of basaltic intrusions, undercoolings are high and the peak nucleation and growth rates must be close to 1cm^–3· ^–1 and 10^–7cm/s, in good agreement with laboratory measurements. In quasi-equilibrium conditions prevailing in the interior of large intrusions, undercoolings are small. We find ranges of 10^–7 to 10^–3 cm^–3 s^–1 and of 10^–10 to 10^–8cm/s for the local rates of nucleation and growth respectively.  相似文献   

An observational study of radiative and turbulent cooling in the nocturnal boundary layer (ECLATS experiment)     

Claude Estournel  Raoul Vehil  Daniel Guedalia 《Boundary-Layer Meteorology》1986,34(1-2):55-62

The contribution of radiative and turbulent processes to nocturnal atmospheric cooling has been studied using the experimental data of the ECLATS experiment which took place in the African Sahel; the radiative and turbulent fluxes were determined taking thermal advection into account. The turbulent cooling rate is predominant; it decreases strongly with altitude at the beginning of the night, which is the main cause of inversion formation.  相似文献   

Climate and desertification — Editorial     

Jean Pascal van Ypersele  Michel M. Verstraete 《Climatic change》1986,9(1-2):1-4

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U(Th)Pb systematics and ages of Himalayan leucogranites, South Tibet   总被引：5，自引：0，他引：5  

Urs Schrer  Rong-Hua Xu  Claude J. Allgre 《Earth and Planetary Science Letters》1986,77(1)

The age and origin of five leucogranites from the High and Tethys Himalaya, and two country-rock gneisses were investigated by UPb dating of zircon fractions and single grains, and fractions of monazite. Additionally, ThU concentrations in whole rock powders and isotopic compositions of Pb in leached K-feldspars were determined. Monazites yield ages of 16.8 ± 0.6 m.y. for the Nialam migmatite-granite, 15.1 ± 0.5 m.y. for the Lhagoi Kangri granite, 14.3 ± 0.6 m.y. for a granite from Mt. Everest, and 9.8 ± 0.7 m.y. and 9.2 ± 0.9 m.y. for two varieties of the Maja granite. These data, together with monazite ages of 21.9 ± 0.2 and 24.0 ± 0.4 m.y., determined earlier on the Makalu granite [1], substantiate a period of intracontinental granite emplacements from 24 to 9 m.y. ago, i.e. from uppermost Oligocene to late Miocene times. Such a period of plutonic activity is consistent with the view that all these granites result from intracrustal melting following the collision of India with Eurasia. Furthermore, the individual ages, together with structural relationships between granites and country rocks suggest that granite formation and tectono-metamorphism occurred as alternating and strongly related processes with a periodicity of 7 to 9 m.y. Inherited lead components, present in all granite zircons point to large proportions of Precambrian material in the magma source regions, up to 2200 m.y. old.ThU systematics between monazite and country rocks indicate that U has been leached from most of the granites after crystallisation of monazite.Zircon dating of the Kangmar granite gneiss, which occurs in a window through the Tethys Himalayan sediments, shows that this pluton, transformed to a gneiss during the Alpine orogeny, crystallised in lowermost Palaeozoic times 562 ± 4 m.y. ago.  相似文献   

Book reviews     

A. Barrie Pittock  Sherry D. Oaks  Michel M. Verstraete 《Climatic change》1985,7(2):253-259

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Source terms and source strengths of the carbonaceous aerosol in the tropics     

Hélène Cachier  Patrick Buat-Menard  Michel Fontugne  Jacques Rancher 《Journal of Atmospheric Chemistry》1985,3(4):469-489

Atmospheric aerosol samples were collected in the Ivory Coast, primarily at Lamto (6°N, 5°W) between 1979 and 1981. The samples were analysed for total particulate carbon concentration and isotopic composition (¹³C/¹²C) by mass spectrometry. Observed concentrations were found high compared to values reported for temperate regions. Fine particulate carbon in the submicrometersize range accounted for 50 to 80% of the reported concentrations. At Lamto, both particulate carbon concentrations and isotopic ratios exhibit a large temporal variability which is shown to reflect the diversity of sources and their seasonal evolution. Natural emissions from the equatorial forest during the wet season, and biomass burning during the dry season, appear to be the major sources. The latter, though active during only a third of the year, is, on an annual basis, the most important source. Based on the data obtained at Lamto, an attempt has been made to estimate the flux of fine particulate carbon emitted from the tropical regions into the global troposphere. This flux, which is of the order of 20×10¹² g C/yr, appears to be equivalent to the flux of fine particulate carbon emitted from industrial sources. These results suggest that the tropospheric burden of fine particulate carbon in lowlatitude regions is dominated by the long-range transport of carbonaceous aerosols originating from the Tropics.  相似文献   

Carbon dioxide in cave atmospheres. New results in belgium and comparison with some other countries     

Camille Ek  Michel Gewelt 《地球表面变化过程与地形》1985,10(2):173-187

More than 600 measurements of the carbon dioxide content of cave air in Belgium lead up to the conclusion that the main factors of its distribution are: (1) a flow originating from the biomass and diffusing in the soil and the voids of bedrock; (2) a trend, discernible in very still air only, to go down by density; (3) in some caves, draughts caused, for instance, by a swift underground stream. Results in Belgium are compared with published and unpublished data from other countries, showing that CO₂ is often less abundant in cold climate caves and in caves of semi-arid regions (influence of the biomass). Special attention is paid to human contamination during analyses: the influence of people passing through the cave nearby the operator, but also the influence of the operator himself are discussed, and the use of special precautions (including a CO₂-absorbing mask) in defined critical situations is stressed.  相似文献   

Programs and means developed by C.E.A. for clay characterization     

Rosemarie Atabek  Michel Jorda  R. Andre-jehan 《Engineering Geology》1985,21(3-4):209-213

This paper is devoted to the program and means implemented within the Atomic Energy Commission (C.E.A.), with the collaboration of the National Agency for Radioactive Wastes (A.N.D.R.A.), to assess the properties of argillous materials, coming from French deposits. These are good candidates as constituent elements of engineered barriers for the disposal of weakly and highly harmful wastes (such as radioactive wastes).  相似文献