A review of shear wave splitting in the crack-critical crust   总被引：7，自引：0，他引：7  

Stuart Crampin  Sebastien Chastin 《Geophysical Journal International》2003,155(1):221-240

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Numerical modelling of depositional sequences in half-graben rift basins   总被引：1，自引：0，他引：1  

Rob L. Gawthorpe  Stuart Hardy  Bryan Ritchie 《Sedimentology》2003,50(1):169-185

ABSTRACT A three‐dimensional numerical model of sediment transport and deposition in coarse‐grained deltas is used to investigate the controls on depositional sequence variability in marine half‐graben extensional basins subject to eustatic sea‐level change. Using rates of sea‐level change, sediment supply and fault slip reported from active rift basins, the evolution of deltas located in three contrasting structural settings is documented: (1) footwall‐sourced deltas in high‐subsidence locations near the centre of a fault segment; (2) deltas fed by large drainage catchments at fault tips; and (3) deltas sourced from drainage catchments on the hangingwall dip slope. Differences in the three‐dimensional form and internal stratigraphy of the deltas result from variations in tilting of the hangingwall and the impact of border fault slip rates on accommodation development. Because subsidence rates near the centre of fault segments are greater than all but the fastest eustatic falls, footwall‐sourced deltas lack sequence boundaries and are characterized by stacked highstand systems tracts. High subsidence and steep bathymetry adjacent to the fault result in limited progradation. In contrast, the lower subsidence rate settings of the fault‐tip and hangingwall dip‐slope deltas mean that they are subject to relative sea‐level fall and associated fluvial incision and forced regression. Low gradients and tectonic tilting of the hangingwall influence the geometry of these deltas, with fault‐tip deltas preferentially prograding axially along the fault, creating elongate delta lobes. In contrast, broad, sheet‐like delta lobes characterize the hangingwall dip‐slope deltas. The model results suggest that different systems tracts may be coeval over length scales of several kilometres and that key stratal surfaces defining and subdividing depositional sequences may only be of local extent. Furthermore, the results highlight pitfalls in sequence‐stratigraphic interpretation and problems in interpreting controlling processes from the preserved stratigraphic product.  相似文献   

Sulphide inclusions in diamonds from the Koffiefontein kimberlite, S Africa: constraints on diamond ages and mantle Re–Os systematics     

D.G. Pearson  S.B. Shirey  J.W. Harris  R.W. Carlson 《Earth and Planetary Science Letters》1998,160(3-4):311-326

Re–Os isotope compositions of syngenetic sulphide inclusions in both eclogite suite (E-type) and peridotite suite (P-type) parageneses in diamonds from the Koffiefontein mine, South Africa have been analysed using a technique capable of analysing single inclusion grains, or, in some cases multiple inclusions from the same diamonds. Sulphide inclusion Ni contents broadly correlate with Os abundances in that low-Ni (6.8–8.7% Ni), E-type sulphides have 4.7 to 189 ppb Os whereas the two high-Ni (25%), P-type sulphides have 5986 and 6097 ppb Os. Two P-type sulphides from the same diamond define the first mineral isochron obtained for a single diamond which has an age of 69±30 Ma with chondritic initial ¹⁸⁷Os/¹⁸⁸Os. This indicates that the sulphides, and hence the host diamond, crystallised close to the time of kimberlite emplacement (90 Ma), in the Mesozoic. This is supported by Pb isotopic measurements of a fragment from one of the sulphides, together with the absence of significant Type IaB nitrogen aggregation in the host diamond lattice. E-type sulphide inclusions have radiogenic Os isotopic compositions, ¹⁸⁷Os/¹⁸⁸Os 0.346 to 2.28, and Re–Os model ages from 1.1 to 2.9 Ga. They define an array on a Re–Os isochron diagram that may be interpreted as defining a single period of E-type sulphide growth at 1.05±0.12 Ga, with an elevated initial ¹⁸⁷Os/¹⁸⁸Os. Alternatively, two episodes of sulphide crystallisation, from a chondritic reservoir, may be invoked in the Archaean and in the Proterozoic. The results for both P- and E-type diamonds point to a spectrum of diamond crystallisation ages. High contents of both Re and Os, and the similarity of Re/Os ratios of sulphide inclusions in diamonds to whole rock eclogite and peridotite xenoliths indicate that small amounts of sulphides can dominate the mantle budget of both these elements during melting. Recent addition to the lithospheric mantle of high-Os material similar to that from which the P-type sulphides crystallised may explain the variable, sometimes young Os model ages seen in whole rock xenolith Re–Os data.  相似文献   

EURD: First Year Results     

Carmen Morales  José F. Gómez  Joaquín Trapero  Stuart Bowyer  Jerry Edelstein  Eric Korpela 《Astrophysics and Space Science》1998,263(1-4):393-396

EURD (Espectrógrafo Ultravioleta extremo de Radiación Difusa), one of the instruments onboard the Spanish satellite MINISAT-01, is a spectrograph specially designed to detect diffuse radiation, covering the wavelength range of 350-1100 Å, with a spectral resolution of 6-8 Å. Its main scientific objectives are the detection of the emission line spectrum from the hot phase of the interstellar medium and the spectrum of the upper atmospheric airglow. In order to reduce geocoronal noise, EURD always observes in the anti-sun direction and only when the satellite is in orbital eclipse. After more than one year of observation we have obtained the best spectrum of the upper atmospheric nightglow in this wavelength range, the spectrum of 15 OB stars and the spectrum of the full Moon throughout the year. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Satellite-derived vegetation index and cover type maps for estimating carbon dioxide flux for arctic tundra regions     

Douglas Stow  Allen Hope  William Boynton  Stuart Phinn  Donald Walker  Nancy Auerbach 《Geomorphology》1998,21(3-4)

The spatial variability and co-variability of two different types of remote sensing derivatives that portray vegetation and geomorphic patterns are analyzed in the context of estimating regional-scale CO₂ flux from land surfaces in the arctic tundra. For a study area encompassing the Kuparuk River watershed of the North Slope of Alaska, we compare satellite-derived maps of the normalized difference vegetation index (NDVI) generated at two different spatial resolutions to a map of vegetation types derived by image classification of data from the Landsat multispectral scanner (MSS). Mean values of NDVI for each cover type stratum are unique (with the exception of moist acidic tundra and shrubland types). Based on analysis of semi-variograms generated for SPOT-NDVI data, most of the vegetation cover and landform features of this arctic tundra landscape have spatial dimensions of less than 1 km. Thaw lakes on the coastal plain and glacial depositional landforms, such as moraines in the foothills, seem to be the largest features, with vegetation units having dimensions no larger than 700 m. Frequency distributions of NDVI and vegetation types extracted for sampling transects flown by an aircraft sensing CO₂ flux, relative to distributions for the entire Kuparuk River watershed, suggest a slight sampling bias towards greater cover of mesic wet sedge tundra and thaw lakes and associated lower NDVI values. The regional pattern of NDVI for the North Slope of Alaska corresponds primarily to differences between the two major physiographic provinces of this region.  相似文献   

Successful Evaluation of EPA's New Screening Model     

Stuart Cohen 《Ground Water Monitoring & Remediation》1998,18(4):55-57

"A successful test of such a conservative screening tool would predict concentrations of pesticides that are in the upper 95 to 99% confidence interval of appropriate monitoring results."  相似文献   

Dispersion Moments of Fumigating Plumes – Lidar Estimates and Pdf Model Simulations     

Ashok K. Luhar  Stuart A. Young 《Boundary-Layer Meteorology》2002,104(3):411-444

Near-instantaneous vertical scans ofpower plant plumes, sampled by a lidar over three days as part ofthe 1995 Kwinana Coastal Fumigation Study, are analysed to obtainhourly-averaged total dispersion moments up to fourth order, andalso the relative and meander spreads. Two distinct fumigationcases, termed as neutral and stable cases, are observed dependingon whether the plume transport prior to fumigation takes place ina neutral atmosphere, or in a stable region above the neutralatmosphere. Plumes in the stable case are observed to undergoslower fumigation. The mean spreads display contrasting behavioursfor the two fumigating cases, while the vertical skewness shows anegative peak value of about -1 for the neutral case and -2for the stable case in the fumigation zone. The lateral skewnessis positive with a peak value of about unity for both cases, andis attributed to wind directional shear within the thermalinternal boundary layer. The vertical kurtosis is greater than theGaussian value of 3 in the fumigation zone, while the lateralkurtosis is scattered about this value. A recently-developedskewed probability density function model with wind shear isapplied to describe the fumigation data. Overall, the modelsimulates the observed vertical and lateral statistics well up tothe fourth order, except for the lateral skewness and kurtosisvalues in the stable case, which is probably due to the lidar'srange and sensitivity constraints and an inadequate sample size.Although the lateral turbulent diffusion in the model is Gaussian(i.e., zero skewness), the inclusion of wind shear in the model ismanifested in the predicted lateral skewness being greater thanzero in the fumigation zone, and of similar magnitude to the lidardata in the neutral case.  相似文献   

Through-Water Close Range Digital Photogrammetry in Flume and Field Environments   总被引：4，自引：0，他引：4  

Justin Butler  Stuart Lane  Jim Chandler  & Ekaterini Porfiri 《The Photogrammetric Record》2002,17(99):419-439

Measurement of the structure of gravel-bed river surfaces is crucial for understanding both bed roughness and the sediment entrainment process. This paper describes the use of close range digital photogrammetry to measure and monitor change occurring in submerged river gravel-beds in both flume and field environments. High-resolution digital elevation models (DEMs) were obtained and two-media (through air and water) techniques were used to correct for the e.ects of refraction at the air/water interface. Although suitable refractive models have been developed, the use of proprietary software to generate DEMs automatically introduces the problem of how to re-establish collinearity. A simple refraction correction algorithm based upon analytical geometry was developed and is described. This algorithm was designed for use after initial DEM acquisition and allows any photogrammetric software package to be used for data acquisition. Application of this algorithm led to improvements in DEM accuracy by reducing the systematic, depth-dependent bias caused by refraction
Research carried out in a flume environment allowed the algorithm to be tested by measuring a flooded and drained bed surface. Non-systematic differences between the "dry" and "wet" DEMs arose from reductions in stereomatching success in the two-media case. This effect was thought to be due to light attenuation and the introduction of residual parallax. Results suggest that close range digital photogrammetry can be used to extract high quality DEMs of submerged topography in both flume and field fluvial environments, which represents a particularly exciting development for fluvial geomorphologists  相似文献   

Functional assessment of a reference wetland set as a tool for science, management and restoration   总被引：1，自引：0，他引：1  

Stuart E. G. Findlay  Erik Kiviat  W. Charles Nieder  Elizabeth A. Blair 《Aquatic Sciences - Research Across Boundaries》2002,64(2):107-117

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Large N-S convergence at the northern edge of the Tibetan plateau? New Early Cretaceous paleomagnetic data from Hexi Corridor, NW China   总被引：1，自引：0，他引：1  

Yan Chen  Hanning WuVincent Courtillot  Stuart Gilder 《Earth and Planetary Science Letters》2002,201(2):293-307

Nine Early Cretaceous paleomagnetic sites have been collected in the Yumen area of the Hexi Corridor (NW China). Magnetic directions isolated at lower temperatures fail the fold test, and lie close to the geocentric axial dipole field direction before tilt correction. High temperature components are carried by magnetite and/or hematite, all with normal polarity, and pass the fold test. The average paleomagnetic pole from the nine sites is at λ=75.5°N, φ=169.9°E (A₉₅=7.7°). These results are consistent with those from other areas of the North China block (NCB), but significantly different from those from the Qaidam Basin on the southern side of the Qilian Mountains. They suggest that: (1) the Yumen region behaved as a rigid part of the NCB since at least the Early Cretaceous; (2) 740±500 km of north-south directed convergence has taken place between the NCB and Qaidam, within the Qilian Mountains and (3) extrusion of Qaidam was accompanied by a 23±5° relative rotation with respect to North China. This is larger than implied by the maximum left lateral slip on the Altyn Tagh fault system. The same data imply some 1000±800 km of Cenozoic motion between the Tarim and NCB blocks, which were so far believed to have formed a rigid entity since at least the Jurassic. One interpretation could be that all Tarim and Qaidam Cretaceous paleomagnetic samples from red beds, but not those from Yumen and the NCB, suffered significant inclination shallowing, as observed in Cenozoic red beds from Central Asia. So far, we do not find support for this possibility. Possible tectonic interpretations include: (1) the existence of a large, as yet uncharted, tectonic discontinuity between Tarim and the NCB in the vicinity of the desert corridor near 95-100°E longitude; (2) the occurrence of significant deformation within southwestern Tarim, to the north of Yingjisha where paleomagnetic sites were obtained, or (3) persistent clockwise rotation of Tarim with respect to the NCB, for at least 20 Ma, at the rate found for current block kinematics.  相似文献