Beyond Route 66: Some observations on US geography at AAG 100     

Herman van der Wusten 《GeoJournal》2004,59(1):47-50

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Decoupling of As and Fe release to Bangladesh groundwater under reducing conditions. Part I: Evidence from sediment profiles     

A. Horneman  A. van Geen  P.E. Mathe  R.K. Dhar  M.A. Hoque  M. Shamsudduha  K.M. Ahmed 《Geochimica et cosmochimica acta》2004,68(17):3459-3473

This study reexamines the notion that extensive As mobilization in anoxic groundwater of Bangladesh is intimately linked to the dissolution of Fe oxyhydroxides on the basis of analyses performed on a suite of freshly collected samples of aquifer material. Detailed sediment profiles extending to 40 to 70 m depth below the surface were obtained at six sites where local groundwater As concentrations were known to span a wide range. The sediment properties that were measured include (1) the proportion of Fe(II) in the Fe fraction leached in hot 1.2 N HCl, (2) diffuse spectral reflectance, and (3) magnetic susceptibility.In parallel with local concentrations of dissolved As ranging from <5 to 600 μg/L, Fe(II)/Fe ratios in shallow (gray) Holocene sands tended to gradually increase with depth from values of 0.3 to 0.5 to up to 0.9. In deeper (orange) aquifers of presumed Pleistocene age that were separated from shallow sands by a clay layer and contained <5 μg/L dissolved As, leachable Fe(II)/Fe ratios averaged ∼0.2. There was no consistent relation between sediment Fe(II)/Fe and dissolved Fe concentrations in groundwater in nearby wells. The reflectance measurements indicate a systematic linear relation (R² of 0.66; n = 151) between the first derivative transform of the reflectance at 520 nm and Fe(II)/Fe. The magnetic susceptibility of the shallow aquifer sands ranged from 200 to 3600 (x 10⁻⁹ m³/kg SI) and was linearly related (R² of 0.75; n = 29) to the concentrations of minerals that could be magnetically separated (0.03 to 0.79% dry weight). No systematic depth trends in magnetic susceptibility were observed within the shallow sands, although the susceptibility of deeper low-As aquifers was low (up to ∼200 × 10⁻⁹ m³/kg SI).This set of observations, complemented by incubation results described in a companion paper by van Geen et al. (this volume), suggests that the release of As is linked to the transformation of predominantly Fe (III) oxyhydroxide coatings on sand particles to Fe(II) or mixed Fe(II/III) solid phases with a flatter reflectance spectrum such as siderite, vivianite, or magnetite, without necessarily resulting in the release of Fe to groundwater. The very low As/Fe ratio of magnetically separated minerals compared to the As/Fe of bulk acid leachate (2 vs. 40 10⁻⁶, respectively) suggests that such a transformation could be accompanied by a significant redistribution of As to a mobilizable phase on the surface of aquifer particles.  相似文献   

Holocene climate variability   总被引：17，自引：0，他引：17  

Paul A. Mayewski  Eelco E. Rohling  J. Curt Stager  Wibjrn Karln  Kirk A. Maasch  L. David Meeker  Eric A. Meyerson  Francoise Gasse  Shirley van Kreveld  Karin Holmgren  Julia Lee-Thorp  Gunhild Rosqvist  Frank Rack  Michael Staubwasser  Ralph R. Schneider  Eric J. Steig 《Quaternary Research》2004,62(3):243-255

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Placing man in the New West: Masculinities of The Last Picture Show     

Grayson Holmes  Leo Zonn  Altha J. Cravey 《GeoJournal》2004,59(4):277-288

The Last Picture Show does not fall within the genre of the Western, yet the cinematic narrative mourns the loss of the iconic Westerner — a man — and the passing of his home places that constitute the Old West. This paper is concerned with the ways in which this man and his places are transformed along with the embryonic but inexorable emergence of the New West — and its attendant demand for recognition of hitherto unheard voices (e.g., women, Latinos) — that accompanied significant social, cultural and political shifts that were beginning to emerge within the country as a whole in the represented early 1950s. His represented sites of contestation are found within the frame of the small west Texas town of Anarene, created by Larry McMurtry's novel of the same name as the film, both of which reflect contexts of the era in which they were constructed — the mid 1960s to early 1970s. We suggest that the film shows a great sensitivity to the ways in which particular masculinities are constituted in specific places, to the tensions that arise from the changing nature and definitions of masculinity as they are linked to these places, and with his sense of nostalgia and loss that accompanies his inevitable decline. But there is no clear and empowered place for women in these new places, only a recontextualized form of a patriarchal order which is not relational and which still maintains essentialist assumptions of gender. The Old West has taken new shape, much to the chagrin of man, but it is hardly a New West, with its emerging and representative voices. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Crustal thickening in an extensional regime: application to the mid-Norwegian Vøring margin     

J.W. van Wijk  R. van der Meer  S.A.P.L. Cloetingh 《Tectonophysics》2004,387(1-4):217-228

The structure of the mid-Norwegian volcanic Vøring margin at the onset of the Maastrichtian–Paleocene extension phase reflects the cumulative effect of earlier consecutive rifting events. Lateral structural differences present on the margin at that time are a consequence of migration of the location of maximum extension in time between Norway and Greenland. The most important imprints (Moho depth, thermal structure) of these events on the lithosphere are incorporated in a numerical simulation of the final extension phase. We focus on a possible mechanism of formation of the Vøring Marginal High and address the relationship between spatial and temporal evolution of crustal thinning and thickening, uplift of the surface and strength of the lithosphere.It is found that the Vøring Basin formed the strongest part of the margin which explains why the Maastrichtian–Paleocene rift axis was not located here but instead jumped westward with respect to the earlier rift axes locations. The modeling study predicts that local crustal thickening during extension can be expected when large lateral thermal variations are present in the lithosphere at the onset of extension. Negative buoyancy induced by lateral temperature differences increases downwelling adjacent to the rifting zone; convergence of material at the particular part of the margin is mainly taken up by the lower crust. The model shows that during the final phase of extension, the crust in the Vøring Marginal High area was thickened and the surface uplifted. It is likely that this dynamic process and the effects of magmatic intrusions both acted in concert to form the Marginal High.  相似文献   

Online submission     

Marjolein van Breemen 《Journal of Arid Environments》2004,57(4):409

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(Trans)national Bodies, (Trans)national Languages and the Transformation of Local Urban Space     

Francis Leo Collins 《New Zealand geographer》2004,60(1):52-59

This paper discusses some of the ways that international students, particularly those from East Asia, are involved in the transformation of urban space in Auckland City. Using existing economic reports, local media accounts and the author's initial observations, the paper identifies how the embodied and linguistic practices of international students are involved in the changing landscapes of Auckland's inner city. This cursory reading serves to identify a research agenda and to reflect upon some key theoretical textxs. The insights of Arjun Appadurai, Michael Peter Smith and Ulrich Beck are used to suggest that the changes in Auckland, whilst certainly local, are also influenced fry factors that emerge from beyond the borders of international students' origin communities, cities and nations.  相似文献   

The influence of particle composition on thorium scavenging in the NE Atlantic ocean (POMME experiment)     

M. Roy-Barman  C. Jeandel  M. Souhaut  M. Rutgers van der Loeff  I. Voege  N. Leblond  R. Freydier 《Earth and Planetary Science Letters》2005,240(3-4):681-693

²³⁰Th, ²³²Th and ²³⁴Th were analyzed in sinking particles collected by moored and drifting sediment traps in the NE Atlantic Ocean (POMME experiment) in order to constrain the phase(s) carrying Th isotopes in the water column. It reveals a contrasted behaviour between ²³⁴Th and ²³⁰Th. ²³⁴Th is correlated to the particulate organic carbon suggesting that it is primarily scavenged by organic compounds in the surface waters. ²³⁰Th_xs is correlated with Mn, Ba and the lithogenic fraction that are enriched in small suspended particles and incorporated in the sinking particulate flux throughout the water column. The lack of correlation between ²³⁰Th_xs and CaCO₃ or biogenic silica (bSi) indicates that CaCO₃ and bSi are not responsible for ²³⁰Th scavenging in the deep waters of this oceanic region. ²³⁰Th is generally correlated with the lithogenic content of the trapped material but this correlation disappears in winter during strong atmospheric dust inputs suggesting that lithogenic matter is not directly responsible for ²³⁰Th scavenging in the deep waters or that sufficient time is required to achieve particle–solution equilibration. MnO₂ could be the prevalent ²³⁰Th_xs-bearing phase. The narrow range of K_{d_MnO2}^Th obtained for very contrasted oceanic environments supports a global control of ²³⁰Th_xs scavenging by MnO₂ and raises the possibility that the ²³⁰Th–²³¹Pa fractionation is controlled by the amount of colloidal MnO₂ in seawater.  相似文献   

A magnetoclimatological investigation of Pampean loess, Argentina   总被引：3，自引：0，他引：3  

J. C. Bidegain  M. E. Evans  A. J. van Velzen 《Geophysical Journal International》2005,160(1):55-62

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Seismic velocities of granulite-facies xenoliths from Central Ireland: Implications for lower crustal composition and anisotropy     

Riana van den Berg  J. Stephen Daly  Matthew H. Salisbury   《Tectonophysics》2005,407(1-2):81-99

V_p and V_s values have been measured experimentally and calculated for granulite-facies lower crustal xenoliths from central Ireland close to the Caledonian Iapetus suture zone. The xenoliths are predominantly foliated and lineated metapelitic (garnet–sillimanite–K-feldspar) granulites. Their metapelitic composition is unusual compared with the mostly mafic composition of lower crustal xenoliths world-wide. Based on thermobarometry, the metapelitic xenoliths were entrained from depths of c. 20–25 ± 3.5 km and rare mafic granulites from depths of 31–33 ± 3.4 km. The xenoliths were emplaced during Lower Carboniferous volcanism and are considered to represent samples of the present day lower crust.V_p values for the metapelitic granulites range between 6.26 and 7.99 km s^{− 1} with a mean value of 7.09 ± 0.4 km s^{− 1}. Psammite and granitic orthogneiss samples have calculated V_p values of 6.51 and 6.23 km s^{− 1}, respectively. V_s values for the metapelites are between 3.86 and 4.34 km s^{− 1}, with a mean value of 4.1 ± 0.15 km s^{− 1}. The psammite and orthogneiss have calculated V_s values of 3.95 and 3.97 km s^{− 1}, respectively.The measured seismic velocities correlate with density and with modal mineralogy, especially the high content of sillimanite and garnet. V_p anisotropy is between 0.15% and 13.97%, and a clear compositional control is evident, mainly in relation to sillimanite abundance. Overall V_s anisotropy ranges from 1% to 11%. Poisson's ratio (σ) lies between 0.25 and 0.35 for the metapelitic granulites, mainly reflecting a high V_p value due to abundant sillimanite in the sample with the highest σ. Anisotropy is probably a function of deformation associated with the closure of the Iapetus ocean in the Silurian as well as later extension in the Devonian. The orientation of the bulk strain ellipsoid in the lower crust is difficult to constrain, but lineation is likely to be NE–SW, given the strike-slip nature of the late Caledonian and subsequent Acadian deformation.When corrected for present-day lower crustal temperature, the experimentally determined V_p values correspond well with velocities from the ICSSP, COOLE I and VARNET seismic refraction lines. Near the xenolith localities, the COOLE I line displays two lower crustal layers with in situ V_p values of 6.85–6.9 and 6.9–8.0 km s^{− 1}, respectively. The upper (lower velocity) layer corresponds well with the metapelitic granulite xenoliths while the lower (higher velocity) layer matches that of the basic granulite xenoliths, though their metamorphic pressures suggest derivation from depths corresponding to the present-day upper mantle.  相似文献