Description de deux nouvelles Cyclotelles (Bacillariophyceae) de milieux alcalins et eutrophes:Cyclotella costei nov. sp. etCyclotella wuethrichiana nov. sp.     

Jean Claude Druart  François Straub 《Aquatic Sciences - Research Across Boundaries》1988,50(2):182-188

Two new species of the genus Cyclotella are presented which have been discovered during ecological and paleoecological research studies in the littoral zone of two small alkaline eutrophic lakes in France (Lake Paladru) and in Switzerland (Lake Le Loclat). These new species are namedCyclotella costei nov. sp. andCyclotella wuethrichiana nov. sp.  相似文献   

Effects of F,B2O3 and P2O5 on the solubility of water in haplogranite melts compared to natural silicate melts     

François Holtz  Donald B. Dingwell  Harald Behrens 《Contributions to Mineralogy and Petrology》1993,113(4):492-501

The effects of F, B₂O₃ and P₂O₅ on the H₂O solubility in a haplogranite liquid (36 wt. % SiO₂, 39 wt. % NaAlSi₃O₈, 25 wt. % KAlSi₃O₈) have been determined at 0.5, 1, 2, and 3 kb and 800, 850, and 900°C. The H₂O solubility increases with increasing F and B content of the melt. The H₂O solubility increase in more important at high pressure (2 and 3 kb) than at low pressure (0.5 kb). At 2 kb and 800°C, the H₂O solubility increases from 5.94 to 8.22 wt. % H₂O with increasing F content in the melt from 0 to 4.55 wt. %, corresponding to a linear H₂O solubility increase of 0.53 mol H₂O/mol F. With addition of 4.35 wt. % B₂O₃, the H₂O solubility increases up to 6.86 wt. % H₂O at 2 kb and 800°C, corresponding to a linear increase of 1.05 mol H₂O/mol B₂O₃. The results allow to define the individual effects of fluorine and boron on H₂O solubility in haplogranitic melts with compositions close to that of H₂O-saturated thermal minima (at 0.5–3 kb). Although P has a dramatic effect on the phase relations in the haplogranite system, its effect on the H₂O solubility was found to be negligible in natural melt compositions. The concominant increase in H₂O solubility and F can not be interpreted on the basis of the available spectroscopic data (existence of hydrated aluminofluoride complexes or not). In contrast, hydrated borates or more probably boroxol complexes have been demonstrated in B-bearing hydrous melts.  相似文献   

The Barents Sea Ice Sheet — A model of its growth and decay during the last ice maximum     

Anders Elverhi  Willy Fjeldskaar  Anders Solheim  Mona Nyland-Berg  Lars Russwurm 《Quaternary Science Reviews》1993,12(10)

On the basis of geomorphological and sedimentological data, we believe that the entire Barents Sea was covered by grounded ice during the last glacial maximum. ¹⁴C dates on shells embedded in tills suggest marine conditions in the Barents Sea as late as 22 ka BP; and models of the deglaciation history based on uplift data from the northern Norwegian coast suggest that significant parts of the Barents Sea Ice Sheet calved off as early as 15 ka BP. The growth of the ice sheet is related to glacioeustatic fall and the exposure of shallow banks in the central Barents Sea, where ice caps may develop and expand to finally coalesce with the expanding ice masses from Svalbard and Fennoscandia.The outlined model for growth and decay of the Barents Sea Ice Sheet suggests a system which developed and existed under periods of maximum climatic deterioration, and where its growth and decay were strongly related to the fall and rise of sea level.  相似文献   

The photoelectron spectra of some Tl-Sb sulphosalts     

Ivan Gržetić  Tonći Balić Žunic 《Physics and Chemistry of Minerals》1993,20(4):285-296

The results of X-ray induced photoelectron spectroscopy (XPS) experiments on several phases of the ternary system Tl-Sb-S are reported. The binding energies of the inner S, Sb and Tl electrons increase with increasing quantities of Sb and decreasing amounts of Tl in these compounds. This is explained by the influences of the proportions of the bonded metals on the effective electron affinity of S. The higher proportions of the more electronegative element bonded to S cause the increase of its effective electron affinity. The results for Tl₂S (carlinite), Tl₃SbS₃, TlSbS₂ (weissbergite), TlAsS₂ (lorandite) and Sb₂S₃ (antimonite) can be interpreted in this way. The results for Tl₄S₃ suggest a predominantly covalent character of bonding for both Tl(III) and Tl(I), which are present in this sulfide. From comparison with Tl₃SbS₄ it could be supposed that Tl(III)-S bond has a more covalent character than Sb(V)-S bond. The results for Tl₃SbS₄ are in agreement with crystal structure data and the results of Moessbauer spectroscopy. For AsS (realgar) the binding energies of the inner electrons of As and S significantly increase, showing that the electrons in molecular orbitals are less strongly bonded to individual atoms, as compared to pure elements. The results for the amorphous TlSb₅S₈ (corresponding in composition to parapierrotite) suggest that in amorphous compound the Tl-S bonding is stronger and the coordination of Tl more regular than in a crystalline one.  相似文献   

Comment on “monitoring well placement using conditional simulation of hydraulic head” by Dale H. Easley,Leon E. Borgman and Denis Weber     

Zekâi Sen 《Mathematical Geosciences》1993,25(2):241-243

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Intercrystalline cation partitioning between minerals of the triplite-zwieselite-magniotriplite and the triphylite-lithiophilite series in granitic pegmatites     

Paul Keller  François Fontan  André-Mathicu Fransolet 《Contributions to Mineralogy and Petrology》1994,118(3):239-248

Minerals of the triphylite-lithiophilite, Li(Fe, Mn)PO₄, and the triplite-zwieselite-magniotriplite series, (Mn, Fe, Mg)₂PO₄F, occur in the late stage period of pegmatite evolution. Unfortunately, neither are the genetic relationships between these phosphates fully understood nor are thermodynamic data known. Consequently, phosphate associations and assemblages from 8 granitic pegmatites — Clementine II, Rubicon II and III, and Tsaobismund (Namibia); Hagendorf-Süd and Rabenstein (Germany); Valmy (France); Viitaniemi (Finland) — have been tested for compositional zoning and intercrystalline partitioning of main elements by electron microprobe techniques. Although the selected pegmatites display varying degrees of fractionation, and the intergrowth textures indicate different genetic relationships between the phosphates, the plots of mole fractions X _Fe=Fe/(Fe+Mn+Mg+Ca), X _Mn=Mn/(Fe+Mn+Mg+Ca), and X _Mg=Mg/(Fe+Mn+Mg+Ca) can be fitted relatively well with smooth curves in Roozeboom diagrams. Their deviations from symmetrical distribution curves are mainly dependent upon X _Mg or X _Ca, and upon non-ideal solutions. Surprisingly small differences between the partition coefficients were detected for intergrowths of different origin. However, the partitioning of shared components among coexisting phases is clearly dependent upon the conditions of formation. Compositional zoning is observed only when both Fe–Mn phosphates are intergrown mutually or with other Fe–Mn–Mg mineral solid-solutios. Thus, the zoning does not seem to be due to continuous crystallization, but to later diffusion processes. The triplite structure has preference for Mn, Mg, and Ca, while Fe prefers minerals of the triphylite series. A quantification of main element fractionation between minerals of the triphylite and the triplite series is possible in the cases where diffusion can be excluded. For the Fe/(Fe+Mn) ratios of core compositions an equation with a high correlation coefficient (R=0.988) was determined: Fe/(Fe+Mn)_Tr=[Fe/(Fe+Mn)_Li]/{2.737-(1.737)[Fe/(Fe+Mn)_Li]} (Tr=triplite series, Li=triphylite series). Consequently, the Fe/(Fe+Mn) ratio of the triplite series can now also be used in the interpretation of pegmatite evolution, just like that of the triphylite series which has been successfully applied in the past.  相似文献   

The origin of the high-K latites from Camp Creek,Arizona: constraints from experiments with variable fO2 and a_{{\text{H}}_{\text{2}} {\text{O}}}     

Sonia Esperança  John R. Holloway 《Contributions to Mineralogy and Petrology》1986,93(4):504-512

Near-liquidus melting experiments were performed on a high-K latite at fO₂'s ranging from iron-wustite-graphite (IWG) to nickel-nickel oxide (NNO) in the presence of a C-O-H fluid phase. Clinopyroxene is a liquidus phase under all conditions. At IWG , the liquidus at 10 kb is about 1,150° C but is depressed to 1,025° C at NNO and . Phlogopite and apatite are near-liquidus phases, with apatite crystallizing first at pressures below 10 kb. Phlogopite is a liquidus phase only at NNO and high . Under all conditions the high-K latites show a large crystallization interval with phlogopite becoming the dominant crystalline phase with decreasing temperature. Increasing fO₂ affects phlogopite crystallization but the liquidus temperature is essentially a function of . The chemical compositions of the near-liquidus phases support formation of the high-K latites under oxidizing conditions (NNO or higher) and high . It is concluded from the temperature of the H₂O-saturated liquidus at 10 kb, the groundmass: crystal ratio and presence of chilled latite margins around some xenoliths that the Camp Creek high-K latite magma passed thru the lower crust at temperatures of 1,000° C or more.  相似文献   

Determination of Aquifer Parameters by the Slope-Matching Method     

Zekâi Sen 《Ground water》1986,24(2):217-223

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Multispectral remote sensing of biomass burning in West Africa     

J. Ricardo  A. De França  J. -M. Brustet  J. Fontan 《Journal of Atmospheric Chemistry》1995,22(1-2):81-110

Remote sensing measurements provide a vauable means of determining the extent of burning areas and of estimating the overall distribution of pollutant sources (identified from experimental studies) in time and space. This distribution has to be taken into account in the boundary conditions of chemistry atmospheric models.Recent methods developed for the remote sensing of active fires in tropical or temperated forest zones, have been found to be completely inadequate for fire detection on West African savannas. In order to accurately estimate the active fire distribution in the function of different sorts of West African savannas (Sahelian, Sudanian and Guinean) and forests, a multispectral methodology has been developed based on NOAA/11-AVHRR satellite data, with the purpose of eliminating as much as possible the problems related to large surface heterogeneity, confusion and bias, produced by clouds, smoke, haze, background emissivities, etc.Unlike other methods, the results show that the multispectral method, in spite of its selectivity, provides realistic results, and does not under- or over-estimate the number of fires that can be sensed by the satellite. Consequently, this methodology is more appropriate than the simplest ones for a systematic sensing of this phenomenon.  相似文献   

The stratospheric quasi-biennial oscillation observed in the semidiurnal ground pressure data     

Hector Teitelbaum  François Vial  Pierre Bauer 《Annales Geophysicae》1995,13(7):740-744

Ground pressure observations made at Macao (22^○N, 113^○E) from 1953 to 1991 are analyzed and compared with the stratospheric quasi-biennial oscillation (QBO) data obtained during the same interval. The periods of the two phenomena and their time evolution are found to be close to each other. Furthermore, the time series of the stratospheric winds and the S2(p) QBO signature are highly correlated, thus confirming earlier analysis. On this basis, pressure measurements obtained at Batavia (now Djakarta: 6^○S, 107^○E) from 1870 to 1944 are used to trace back the QBO phenomenon before the advent of systematic stratospheric balloon measurements. The inferred period, which varies between 25 and 32 months, suggests that the QBO has been present in the atmosphere at least since 1870.  相似文献