Relative contributions of silicate and carbonate rocks to riverine Sr fluxes in the headwaters of the Ganges   总被引：1，自引：0，他引：1  

Mike J. Bickle  Hazel J. Chapman  Nigel B.W. Harris  Talat Ahmad 《Geochimica et cosmochimica acta》2005,69(9):2221-2240

Exhumation of the Himalayan-Tibetan orogen is implicated in the marked rise in seawater ⁸⁷Sr/⁸⁶Sr ratios since 40 Ma. However both silicate and carbonate rocks in the Himalaya have elevated ⁸⁷Sr/⁸⁶Sr ratios and there is disagreement as to how much of the ⁸⁷Sr flux is derived from silicate weathering. Most previous studies have used element ratios from bedrock to constrain the proportions of silicate- and carbonate-derived Sr in river waters. Here we use arrays of water compositions sampled from the head waters of the Ganges in the Indian and Nepalese Himalaya to constrain the end-member element ratios. The compositions of tributaries draining catchments restricted to a limited range of geological units can be described by two-component mixing of silicate and carbonate-derived components and lie on a plane in multicomponent composition space. Key elemental ratios of the carbonate and silicate components are determined by the intersection of the tributary mixing plane with the planes Na = 0 for carbonate and constant Ca/Na for silicate. The fractions of Sr derived from silicate and carbonate sources are then calculated by mass-balance in Sr-Ca-Mg-Na composition space. Comparison of end-member compositions with bedrock implies that secondary calcite deposition may be important in some catchments and that dissolution of low-Mg trace calcite in silicate rocks may explain discrepancies in Sr-Ca-Na-Mg covariation. Alternatively, composition-dependent precipitation or incongruent dissolution reactions may rotate mixing trends on cation-ratio diagrams. However the calculations are not sensitive to transformations of the compositions by incongruent dissolution or precipitation processes provided that the transformed silicate and carbonate component vectors are constrained. Silicates are calculated to provide ∼50% of the dissolved Sr flux from the head waters of the Ganges assuming that discrepancies between Ca-Mg-Na covariation and the silicate rock compositions arise from addition of trace calcite. If the Ca-Mg-Na mixing plane is rotated by composition-dependent secondary calcite deposition, this estimate would be increased. Moreover, when ⁸⁷Sr/⁸⁶Sr ratios of the Sr inputs are considered, silicate Sr is responsible for 70 ± 16% (1σ) of the ⁸⁷Sr flux forcing changes in seawater Sr-isotopic composition. Since earlier studies predict that silicate weathering generates as little as 20% of the total Sr flux in Himalayan river systems, this study demonstrates that the significance of silicate weathering can be greatly underestimated if the processes that decouple the water cation ratios from those of the source rocks are not properly evaluated.  相似文献   

Pore water testing and analysis: the good,the bad,and the ugly   总被引：8，自引：0，他引：8  

Chapman PM  Wang F  Germano JD  Batley G 《Marine pollution bulletin》2002,44(5):359-366

The increasingly common practice of collecting and assessing sediment pore water as a primary measure of sediment quality is reviewed. Good features of this practice include: pore water is a key exposure route for some organisms associated with sediments; pore water testing eliminates particle size effects; pore water analyses and tests can provide useful information regarding contamination and pollution. Bad features include: pore water is not the only exposure route; pore water tests lack chemical or biological realism: their "sensitivity" relative to other tests may be meaningless due to manipulation and laboratory artifacts; many sediment and surface dwelling organisms are not directly influenced by pore water. Bad features can become ugly if: other exposure pathways are not considered (for toxicity or bioaccumulation); manipulation techniques are not appropriate; pore water tests are inappropriately linked to population-level effects. Pore water testing and analyses can be effective tools provided their limitations are well understood by researchers and managers.  相似文献   

Velocity sensitivity in transversely isotropic media1     

C.H. Chapman  D.E. Miller 《Geophysical Prospecting》1996,44(3):525-549

We consider the problem of determining and predicting how the wave speeds in particular directions for a transversely isotropic (TI) medium depend on particular combinations of the density-normalized moduli A_ij. The expressions for the q^P and q^SV velocities are known to depend on four moduli. Normally, we can only determine three independent parameters from q^P data, or two from q^SZ data, as the others have much lower sensitivity. The resolvable parameters are conveniently described by axial and off-axis parameters: for q^P rays, P_0°= A₁₁, P_90°= A₃₃ and P_45°=(A₁₁+ A₃₃)/4 + (A₁₃+2A₅₅)/2; and for q^SV rays, S_0°= S_90°=A₅₅ and S 45°= (A₁₁+ A ₃₃)/4- A₁₃/2. These parameters control the magnitude of the squared-velocities on the axes and at approximately 45°. For an arbitrary TI medium, if the medium is perturbed in a way that preserves a particular parameter, then slowness points in the associated direction and mode witl be approximately preserved in the new medium. we refer to these parameters as ‘push-pins’, i.e. if a parameter is fixed, the associated part of the slowness surface is pinned in place. Because, these five push-pins only contain four independent moduli, we can only fix at most three push-pins. Perturbing one of the other parameters inevitably perturbs the other. Numerical results illustrating the linkage between two push-pins, when three are fixed, are presented. So-called anomalous TI media occur when the roles of the q^P and q^SV waves are reversed: in some directions the faster ray has transverse polarization. That, in turn, requires anomalous velocities at the push-pins, i.e. S_0° > P_0°, S_45° > P_45° and/or S_90° > P_90° (equivalent to the usual anomalous conditions A₁₁ < A₅₅, < 0 and/or A₃₃ < A⁵⁵). In the Appendix, we confirm that anomalous sensitivities of the velocities at the five push-pins only occur in such media, although the push-pins still apply if interpreted appropriately. Truly anomalous sensitivities, in which push-pins play no role, only occur in media near the boundary between normal and anomalous.  相似文献   

Digital photogrammetry based automatic measurement of sandstone roof of a mine     

Rajendra Singh  D P Chapman  K B Atkinson 《Journal of the Indian Society of Remote Sensing》1997,25(1):47-59

Automatic close range photogrammetric measurements are of immense importance for a hazardous industry like mining. Unfortunately, available stereomatching techniques fail for high resolution close range images due to the large variation of object depth. In this paper a diffraction grating based laser dot-matrix projector along with a CCD camera is used for automatic close range measurement of a textureless and featureless object like massive sand stone strata. Targeting of object’s surface with large number of laser dots simultaneously solved two major problems: identification of conjugate points and precise image co-ordinate measurement. Least squares based template matching is used for centroid location of images of laser dots which provided 0.03 (mean) pixels accuracy. Using analytical techniques, camera model of the projector was developed by placing it rigidly on the teleseope of a geodimeter Bundle adjustment procedure is adopted for accurate estimation of interior orientation parameters of the projector which resulted precise co-ordinates of the object space during a test scan by the developed system.  相似文献   

High-latitude HF Doppler observations of ULF waves. 1. Waves with large spatial scale sizes     

D. M. Wright  T. K. Yeoman  P. J. Chapman 《Annales Geophysicae》1997,15(12):1548-1556

A quantitative study of observations of the ionospheric signatures of magnetospheric ultra low frequency (ULF) waves by a high-latitude (geographic: 69.6°N 19.2°E) high-frequency Doppler sounder has been undertaken. The signatures, which are clearly correlated with pulsations in ground magnetometer data, exhibit periods in the range 100–400 s and have azimuthal wave numbers in the range 3–8. They are interpreted here as local field line resonances. Phase information provided by O- and X-mode Doppler data support the view that these are associated with field line resonances having large azimuthal scale sizes. The relative phases and amplitudes of the signatures in the Doppler and ground magnetometer data are compared with a model for the generation of Doppler signatures from incident ULF waves. The outcome suggests that the dominant mechanism involved in producing the Doppler signature is the vertical component of an E × B bulk motion of the local plasma caused by the electric field perturbation of the ULF wave.  相似文献   

Late-glacial paleoenvironment of Lake Algonquin sediments near Clarksburg,Ontario     

P. F. Karrow  T. W. Anderson  L. D. Delorme  B. B. Miller  L. J. Chapman 《Journal of Paleolimnology》1995,14(3):297-309

Excavation below the Lake Algonquin gravel beach bar near Clarksburg, Ontario, exposed mollusc-bearing clay over a lens of plant debris. This is the northernmost and most deeply buried Lake Algonquin fossil site found thus far in Ontario. It is the first site to provide dates from directly below the Algonquin beach bar. Two radiocarbon dates of about 11 200 years confirm the age of isostatically transgressing Lake Algonquin. Plant macrofossils (21 taxa), pollen (39 taxa), molluscs (12 taxa), and ostracodes (18 taxa) indicate that the climate was colder than present by several degrees and the forest-tundra ecotone was nearby initially but retreated northward rather quickly. Upward increases in abundances and diversity of molluscs and ostracodes suggest it was a time of rapid migration and colonization of species.Deceased, 1 November 1994This is the 7th in a series of papers published in this special AMQUA issue. These papers were presented at the 1994 meeting of the American Quaternary Association held 19–22 June, 1994, at the University of Minnesota, Minneapolis, Minnesota, USA. Dr Linda C. K. Shane served as guest editor for these papers.  相似文献   

Population movement studied at microscale: Experience and extrapolation     

Chapman M 《GeoJournal》1987,15(4):347-365

The context for this paper is the nature of generalization deriving from the study of particular cases of human behaviour. With specific reference to field research on population movement conducted amongst individuals, households, small groups, and village communities in third world societies, it challenges the convention that both generalization and extrapolation are based inevitably and exclusively on the number of cases or events subject to examination. An evaluation is made of the methodological aspects of four different studies of population mobility at microscale, undertaken between 1965 and 1977 in the Solomon Islands and northwest Thailand. On this basis, integrated field designs that incorporate a range of intersecting instruments are favoured for their technical flexibility and logical strength. With case studies of third world villages, market centres, and urban neighbourhoods, generalization and extrapolation is based on depth of understanding and the power of theoretical connections.  相似文献   

Exsolution intergrowths of titanian ferrocolumbite and niobian rutile from the Weinebene Spodumene Pegmatites,Carinthia, Austria     

Dr. P. Černý  Dr. R. Chapman  R. Göd  Dr. G. Niedermayr  Dr. M. A. Wise 《Mineralogy and Petrology》1989,40(3):197-206

Summary Titanian ferrocolumbite is a rare accessory mineral in the spodumene-bearing pegmatites at Weinebene, Carinthia, Austria. It contains abundant exsolved niobian rutile and scarce inclusions of cassiterite that may be primary. The titanian ferrocolumbite is relatively homogeneous with Mn/(Mn + Fe) 0.24–0.33, Ta/(Ta + Nb) 0.09–0.13 (atomic ratios) and 0.47–0.88 Ti per 12 cations (2.7–5.0 wt.% TiO₂). Natural specimens are considerably disordered but become more ordered on heating. Niobian rutile has Mn/(Mn + Fe) 0.00–0.04 and Ta/(Ta + Nb) 0.26–0.38; it concentrates Fe, Ta, Ti and Sn relative to the Mn- and Nb-enriched ferrocolumbite. The overall scarcity of Nb, Ta-oxide minerals in the spodumene-bearing pegmatites of southern Ostalpen conforms to their general features ranking them with the albite-spodumene type of rare-element pegmatites.With 4 Figures  相似文献   

Burying response of an intertidal gastropod to freshwater and copper contamination     

H.F. Chapman  J.M. Hughes  R.L. Kitching 《Marine pollution bulletin》1985,16(11):442-445

The effects of sublethal concentrations of freshwater and copper on the burying responses of the intertidal marine gastropod, Polinices incei, are presented. Such responses are inhibited by both pollutants and the two also act additively. Behavioural responses obtained in a 30 min assay were found to be good predictors of the results of 96 h lethal assays. The results are discussed in light of previous work.  相似文献   

Acute toxicity of mine tailings to four marine species     

D.G. Mitchell  J.D. Morgan  G.A. Vigers  P.M. Chapman 《Marine pollution bulletin》1985,16(11):450-455

Acute toxicity bioassays were conducted on mine tailings produced by pilot plant testing for the proposed Quartz Hill molybdenum mine, which will be situated near Ketchikan, Alaska. Tailings bioassays were conducted in seawater with juvenile coho salmon (Oncorhynchus kisutch), mussel larvae (Mytilus edulis), infaunal amphipods (Rhepoxynius abronius), and euphausiids (Euphausia pacifica). The same general range of mine tailings concentrations was acutely toxic to all four test species with acute effects observed between 61 000 to 277 000 mg l^?1 (wet wt) tailings solids (range of 95% confidence limits for LC₅₀ and EC₅₀ values). Chemical analyses of bioassay test solutions and leaching test solutions were conducted for metals (including Cd, Cu, Pb, Zn, Mn and Mo), EPA Priority Pollutant base/neutral organics, and more general parameters such as sulphate, nitrate/nitrite, cyanides, phosphate and ammonia. Parameters possibly contributing to the observed toxicity were complex contaminant mixtures including total suspended solids and heavy metals. The present study provides information related to the marine disposal of mine tailings and shows that these mine tailings present a relatively low level of acutely toxic effects.  相似文献