Contens of Volume 59     

Henry F. Diaz  Jon K. Eischeid  Chris Duncan  Raymond S. Bradley 《Climatic change》2003,59(3):417-418

  相似文献   

The Cretaceous and younger thermal history of the KTB site (Germany): apatite fission-track data from the Vorbohrung     

D. A. Coyle  G. A. Wagner  E. Hejl  R. Brown  P. Van den Haute 《International Journal of Earth Sciences》1997,86(1):203-209

A detailed fission-track analysis was carried out on 41 apatite samples from the 4001-m-deep pilot hole of the German Continental Deep Drilling Program (KTB). The investigations include dating by the population method and length measurements of horizontal confined tracks. Age and length information indicate that all samples above the present-day partial annealing zone cooled from temperatures above 120?°C in the Cretaceous. The top two kilometres of the profile show less variation of age with depth than was expected. Modelling of the profile indicates that the distribution of fission track ages with depth requires that the profile was disturbed during or after cooling through the partial annealing zone. Modelling of individual samples reveals that at least the upper 2?km experienced reverse faulting, effectively thickening the upper part of the rock column by up to 1000?m in the Tertiary. A present-day partial annealing zone for apatite was observed between 2000 and 4000?m (～60–110?°C). This confirms earlier in situ observations of the position of the partial annealing zone.  相似文献   

Beyond the impasse: the power of political ecology in Third World environmental research   总被引：3，自引：0，他引：3  

Raymond L Bryant 《Area》1997,29(1):5-19

Summary In the context of a deepening impasse in Third World environmental research, this paper suggests that researchers should adopt a political ecology perspective to ensure that research addresses the political and economic issues that underlie the Third World's environmental problems. Since an understanding of unequal power relations is central to political ecology, the paper considers how questions of power influence human-environmental interaction, before assessing briefly how research of this kind might contribute to a resolution of the Third World's environmental problems.  相似文献   

Politics, Geography, and 'Political Geography By Joe Painter. Arnold Press, London, 1995     

Michael Brown 《New Zealand geographer》1997,53(2):67-68

  相似文献   

Invariants in toroidal and tangentially geostrophic frozen-flux velocity fields     

Andrew Jackson  Raymond Hide 《Geophysical Journal International》1996,125(3):925-927

We derive two new types of invariant that must be obeyed by the radial magnetic field at the core-mantle boundary if the hypothesis of frozen flux is valid and the fluid motion is either toroidal or tangentially geostrophic there. These general invariants incorporate specific invariants that are already known and can, in principle, be tested using magnetic data that cover an interval of time.  相似文献   

Measurement of natural stresses in a Provence mine (Southern France)     

Patrick Gaviglio  Pascal Bigarre  Hafid Baroudi  Jack-Pierre Piguet  Raymond Monteau 《Engineering Geology》1996,44(1-4):77-92

Stress measurements were carried out in the Arc syncline using drifs in a lignite mine. Eleven sites were investigated using the flat jack and hydraulic fracturing (or stimulating) methods. Two stress states were found to coexist, one isotropic, the other highly anisotropic. The orientations of the principal stresses are not homogeneous and an orientation ranging from E-W to NE-SW predominates locally. This does not accord with the regional stress field. The vertical stresses are systematically underestimated.  相似文献   

The making of Stars 'R' Us!     

Serena Viti  Wendy Brown  Martin McCoustra  Helen Fraser  Nigel Mason  Robert Massey 《Astronomy& Geophysics》2004,45(6):6.22-6.24

The team behind a successful project to broaden the understanding of astrochemistry – Serena Viti, Wendy Brown, Martin McCoustra, Helen Fraser, Nigel Mason and Robert Massey – recount how they went about it and what benefits resulted.  相似文献   

The geomorphic dynamics and environmental history of an upper deltaic floodplain tract in the Sacramento–San Joaquin Delta,California, USA     

K. J. Brown  G. B. Pasternack 《地球表面变化过程与地形》2004,29(10):1235-1258

A multi‐proxy approach was used to examine the geomorphic dynamics and environmental history of an upper deltaic ?oodplain tract in the Sacramento–San Joaquin Delta, California. Three long cores were collected from the McCormack–Williamson Tract (MWT) and these cores were analyzed for bulk density, loss‐on‐ignition, ?ne (clay and silt) content, Al concentration, magnetic susceptibility, pollen, and charcoal. Radiocarbon dates obtained for the cores were converted into calendar years and an age–depth model was constructed. Long‐term vertical accretion and sedimentation rates were estimated from the age–depth model. Cross‐core relations show that coarse sediment generally accumulates more rapidly and has greater magnetic susceptibility compared to ?ne sediment. Percentage ?ne and LOI data show a strong linear relationship that indicates ?ooding is the primary mechanism for the deposition of particular organic matter on the ?oodplain and that landscape wash load has contributed a highly consistent fraction of persistent organic matter averaging 5·5 per cent to the site. Down‐core grain size pro?les show two hydrological domains in the cores, namely millennial ?ne–coarse ?uctuations superimposed on general up‐core ?ning. Coarse sediment is viewed as channel or near‐channel overbank deposits, whereas ?ne deposits are considered to be distal overbank ?ood deposits. The coarse–?ne ?uctuations are indicative of changing depositional settings as channels migrated laterally across MWT, whereas the upward ?ning trend re?ects a combination of self‐limiting overbank deposition as ?oodplain elevation increased and decreasing competence as sea‐level rise reduced ?ood‐pulse energy slopes. MWT has been cross‐cut and incised numerous times in the past, only to have the channels abandoned and subsequently ?lled by ?ne sediment. The channels around MWT attained their modern con?guration about 4000 years ago. MWT likely came under tidal in?uence at about 2500 cal BP. Wetlands have recently developed on MWT, but they are inorganic sediment dominated. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Soft X-ray spectroscopic studies of the reaction of fractured pyrite surfaces with Cr(VI)-containing aqueous solutions     

Colin S. Doyle  Tom Kendelewicz  Gordon E. Brown Jr 《Geochimica et cosmochimica acta》2004,68(21):4287-4299

We have used synchrotron-based soft X-ray core-level photoemission and adsorption spectroscopies to study the reaction of aqueous sodium chromate solutions with freshly fractured pyrite surfaces. Pyrite surfaces were reacted with 50 μM sodium chromate solution at pH 7 for reaction times between 1 min and 37 hr. Additional experiments were performed at pH 2 and pH 4 with 50 μM sodium chromate solutions and at pH 7 with 5 mM solutions. At chromate concentrations of 50 μM, all chromium present on the pyrite surface was in the form of Cr(III), while at 5 mM, both Cr(III) and Cr(VI) were present at the pyrite surface. Minor quantities of oxidized sulfur species (sulfate, sulfite, and zero-valent sulfur) were identified as reaction products on the pyrite surface. The amount of oxidized sulfur species observed on the surface was greater when pyrite was reacted with 5 mM Cr(VI) solutions because the rate of chromium deposition exceeded the rate of dissolution of pyrite oxidation products, effectively trapping Cr(VI) and oxidized sulfur species in an overlayer of iron(III)-containing Cr(III)-hydroxide. This work shows that pyrite, an extremely cheap and readily available waste material, may be suitable for the removal of hexavalent chromium from acidic to circumneutral waste streams. The reduced chromium ultimately forms a coating on the pyrite surface, which passivates the pyrite surface towards further oxidation.  相似文献   

Beryllium-10 in Australasian tektites: Constraints on the location of the source crater     

P. Ma  K. Aggrey  C. Tonzola  C. Schnabel  P. de Nicola  J.T. Wasson  L. Brown  R. Middleton 《Geochimica et cosmochimica acta》2004,68(19):3883-3896

By using accelerator mass spectrometry we have measured the ¹⁰Be concentrations of 86 Australasian tektites. Corrected to the time of tektite production ∼0.8 My ago, the ¹⁰Be concentrations (10⁶ atom/g) range from 59 for a layered tektite from Huai Sai, Thailand, to 280 for an australite from New South Wales, Australia. The average value is 143 ± 50. When tektites are sorted by country, their average measured ¹⁰Be concentrations increase slowly with increasing distance from Southeast Asia, the probable location of the tektite producing event, from 59 ± 9 for 6 layered tektites from Laos to 136 ± 20 for 20 splash-form tektites from Australia. The lowest ¹⁰Be concentrations for tektites fall on or within a contour centered off the shore of Vietnam, south of the Gulf of Tonkin (107°E; 17°N), but also encompassing two other locations in the area of northeastern Thailand previously proposed for the site of a single tektite-producing impact. The ¹⁰Be concentrations of layered tektites show only a weak anticorrelation (R ∼ −0.3) with the numbers of relict crystalline inclusions.Loosely consolidated, fine-grained terrestrial sediments or recently consolidated sedimentary rocks are the most likely precursor materials. Dilution of sediments with other kinds of rock raises problems in mixing and is not supported by petrographic data. Sedimentary columns that have the right range of ¹⁰Be concentrations occur off the coasts of places where sedimentation rates are high relative to those in the deep sea. A single impact into such a region, 15 to 300 m thick, could have propelled near-surface, high-¹⁰Be material farthest—to Australia—while keeping the deeper-lying, low-¹⁰Be layers closer to home. We do not rule out, however, other proposed mechanisms for tektite formation.  相似文献