An analysis of shear waves observed in VSP data from the superdeep well at Kola, Russia   总被引：1，自引：0，他引：1  

Per Digranes  Yngve Kristoffersen  Nazim Karajev 《Geophysical Journal International》1996,126(2):545-554

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Micas of the muscovite-lepidolite series from the fregeneda pegmatites (Salamanca,Spain)   总被引：1，自引：0，他引：1  

Roda Robles  E.  Pesquera Peréz  A.  Velasco Roldán  F. 《Mineralogy and Petrology》1995,55(1-3):145-157

Summary In the Fregeneda area different types of pegmatites can be recognized by their mineralogy, morphology, internal structure and field relationships. The most common type corresponds to a simple pegmatite with homogeneous internal structure, but zoned Li-bearing pegmatites also are relatively widespread. Cassiterite-bearing pegmatites are subordinate. The pegmatites are spatially associated to the Lumbrales granite. This is a parautochthonous, fine- to medium-grained, two-mica granite, one of the syntectonic massifs which were deformed during the third phase of Hercynian deformation. Representative micas selected from the different groups of pegmatites were studied to determine wether the pegmatites can be related by a common fractionation path, and how different pegmatite types are related to the spatially associated Lumbrales granite. Compositional variations in the micas depend on the pegmatite type. Muscovite coexisting with Li-micas in the Li-bearing pegmatites is one of the richest in Al₂O₃ (35.4–37.7 wt%) and the poorest in FeO (0.2–1.5 wt%) and MgO (0–0.3 wt%), whereas muscovite of the simple discordant pegmatites shows the highest FeO (2.2–3.3 wt%) and that from the Lumbrales granite is the richest in MgO (0.5–0.7 wt%) and TiO₂ (0.6–1.1 wt%). On the other hand, Sn (70–1168 ppm), Li (< 5–22253 ppm), F (880–21470 ppm), Cs (< 5–1696 ppm), Rb (800–9181 ppm) and other trace elements seem to increase with distance from the Lumbrales granite, and K/Rb decreases. According to this ratio, the exterior Li-bearing pegmatites are the more evolved, whereas the interior pegmatites are less evolved, and are richer in Cs, Li and Zn than other pegmatite types.

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Glimmerminerale der Muscovit-Lepidolith-Serie aus den Pegmatiten von Fregeneda, Salamanca, Spanien

Zusammenfassung Im Gebiet von Fregeneda sind auf Grund ihrer Mineralogie, Morphologie, Internstruktur und Geländebeziehungen verschiedene Pegmatittypen zu unterscheiden. Am häufigsten sind einfache homogen aufgebaute Pegmatite. Zonar gebaute Li-Pegmatite sind ebenfalls weit verbreitet, Zinnstein-führende Pegmatite treten hingegen zurück, Die Pegmatite sind räumlich mit dem Lumbrales Granit, einem paraautochtonen, fein- bis mittelkörnigen Zwei-Glimmergranit, assoziiert, Dieser gehört einem der syntektonischen Massive, die während der dritten Phase der hercynischen Deformation deformiert wurden, an. Repräsentative, aus den verschiedenen Pegmatittypen separierte Glimmerminerale wurden untersucht, um zu klären, inwieweit die Pegmatite über einen direkten Fraktionierungspfad zu verbinden sind und in welcher Beziehung sie zu dem Lumbrales Granit stehen. Die Variation der Zusammensetzung der Glimmer hängt vom Pegmatittyp ab. Muscovite, die mit Li-Glimmern koexistieren, sind die relativ Al₂O₃-reichsten (32–37.7 Gew.%) und Fe- (0.2–1.5 Gew.%.) und Mg-ärmsten (0–0.3 Gew.%). Jene aus dem Lumbrales Granit sind die reich an MgO (0.5–0.7) und TiO₂ (0.6–1.1 Gew.%). Die Gehalte von Sn (70–1168 ppm), Li (< 5–22253 ppm). F (880-21470 ppm), Cs (< 5–1696 ppm), Rb (800–9181 ppm) und anderer Spurenelemente nehmen mit der Entfernung vom Lumbrales Granit zu, während K/Rb abnimmt. Auf Grund dieses Verhältnisses sind die externen Li-führenden Pegmatite höher, die internen Pegmatite hingegen geringfügiger entwickelt. Erstere sind daher auch reicher an Cs, Li und Zn.

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With 4 Figures  相似文献   

Pre-Cambrian atmosphere:evidence from the Pre-Cambrian of Sweden     

Per Geijer 《Geochimica et cosmochimica acta》1956,10(5-6):304-308

Sedimentary haematite ores of central Sweden give evidence of the existence of an oxidizing atmosphere about 2000 × 10⁶ years ago. This is not consistent with Rankama's conclusions from the unoxidized condition of a diorite conglomerate in Finland. Therefore a (later) Pre-Cambrian conglomerate in northern Sweden has been examined for comparison. Where it is made up of dioritic material no proofs of oxidation can be found, but where the material is mainly iron-ore pebbles, magnetite ore is found to have been completely oxidized to haematite (martite) before being embedded as pebbles in the conglomerate.  相似文献   

Using the pseudospectral technique on curved grids for 2D acoustic forward modelling1     

Per Nielsen  Flemming If  Per Berg  Ove Skovgaard 《Geophysical Prospecting》1994,42(4):321-341

The Fourier pseudospectral method has been widely accepted for seismic forward modelling because of its high accuracy compared to other numerical techniques. Conventionally, the modelling is performed on Cartesian grids. This means that curved interfaces are represented in a ‘staircase fashion‘causing spurious diffractions. It is the aim of this work to eliminate these non-physical diffractions by using curved grids that generally follow the interfaces. A further advantage of using curved grids is that the local grid density can be adjusted according to the velocity of the individual layers, i.e. the overall grid density is not restricted by the lowest velocity in the subsurface. This means that considerable savings in computer storage can be obtained and thus larger computational models can be handled. One of the major problems in using the curved grid approach has been the generation of a suitable grid that fits all the interfaces. However, as a new approach, we adopt techniques originally developed for computational fluid dynamics (CFD) applications. This allows us to put the curved grid technique into a general framework, enabling the grid to follow all interfaces. In principle, a separate grid is generated for each geological layer, patching the grid lines across the interfaces to obtain a globally continuous grid (the so-called multiblock strategy). The curved grid is taken to constitute a generalised curvilinear coordinate system, where each grid line corresponds to a constant value of one of the curvilinear coordinates. That means that the forward modelling equations have to be written in curvilinear coordinates, resulting in additional terms in the equations. However, the subsurface geometry is much simpler in the curvilinear space. The advantages of the curved grid technique are demonstrated for the 2D acoustic wave equation. This includes a verification of the method against an analytic reference solution for wedge diffraction and a comparison with the pseudospectral method on Cartesian grids. The results demonstrate that high accuracies are obtained with few grid points and without extra computational costs as compared with Cartesian methods.  相似文献   

Land degradation,natural resources and local knowledge in the sahel zone of Burkina Faso   总被引：4，自引：0，他引：4  

Per Lindskog  Anna Tengberg 《GeoJournal》1994,33(4):365-375

This paper proposes a conceptual model that integrates physical and ecological aspects with human aspects of land degradation through a multidisciplinary approach. The model was applied at the local level in a case study in northern Burkina Faso. Assessments of the degradation of the vegetation cover from aerial photographs and a satellite image were analysed in the framework of the model. Another input to the model was results from interviews and field visits with peasants living in the area.The local knowledge of the physical symptoms of land degradation and of the physical variables, eg rainfall and wind, is very close to the scientific logic. However, people do not generally see the links between these variables and the symptoms. Likewise, they do not perceive land degradation to be influenced in any way by human actions. Instead, the cause of land degradation is attributed to God, Allah. Thus, an important field of intervention for governments and development agencies should be to make people aware of their role in land management.  相似文献   

Acidic compounds in biodegraded petroleum     

Tanja Barth  Sylvi Hiland  Per Fotland  Kjell Magne Askvik  Bent Skaare Pedersen  Anna Elisabet Borgund 《Organic Geochemistry》2004,35(11-12):1513

Twelve oil samples have been characterised by titration, FT-IR and chromatographic analysis to determine the differences between the organic acid composition of biodegraded and non-biodegraded oils. The biodegraded oils have higher total acid and total base contents, both by titration and extraction. The molecular weight ranges of the extracted acids are lowest in the biodegraded oils, and the equivalent weight calculations indicate a dominance of multi-functional molecules. Gel permeation chromatography gives a molecular weight range with most of the molecules between 300 and 500 g/mol. FT-IR shows that the extracted acids from biodegraded oils are more carboxylic and aliphatic while the non-degraded oils are more phenolic. Molecular analysis of the derivatised extracts give UCM envelopes for biodegraded oils, and no molecular identification. The results indicate that the acidic constituents in biodegraded oils are a product of the biodegradation, as the composition is very different from the non-biodegraded oils.  相似文献   

Early Holocene history of the Baltic Sea, as reflected in coastal sediments in Blekinge, southeastern Sweden   总被引：4，自引：0，他引：4  

Bjrn E. Berglund  Per Sandgren  Lena Barnekow  Gina Hannon  Hui Jiang  Gran Skog  Shi-Yong Yu 《Quaternary International》2005,130(1):111

Integrated palaeoecological studies of two fiord sediment sequences in the province of Blekinge, SE Sweden, covering the time span 11,000–5000 cal BP, reveal the timing and the environment for the Ancylus Lake/Littorina Sea transition 9800–8500 cal BP. The first ingression of saline water into the Baltic Sea through the Danish Straits occurred earlier than formerly assumed. New evidence, particularly mineral magnetic and palaeobotanical analyses, demonstrate that on the general trend of the eustatically caused Littorina transgression several minor fluctuations of the water level can be identified between 8500 and 5000 cal years BP. A distinct regression phase around 8100 cal BP is correlated with the Greenland ice-core cold event dated to 8200 ice-core years BP. This is described as a regional climatic catastrophe for the Baltic Sea region. The coastal stratigraphy is compared with the offshore stratigraphy earlier studied. A tentative shore displacement curve for Early and Middle Holocene is presented.  相似文献   

Thallium isotope composition of the upper continental crust and rivers—An investigation of the continental sources of dissolved marine thallium     

Sune G. Nielsen  Mark Rehkämper  Per Andersson  Peter W. Swarzenski  Detlef Günther 《Geochimica et cosmochimica acta》2005,69(8):2007-2019

The thallium (Tl) concentrations and isotope compositions of various river and estuarine waters, suspended riverine particulates and loess have been determined. These data are used to evaluate whether weathering reactions are associated with significant Tl isotope fractionation and to estimate the average Tl isotope composition of the upper continental crust as well as the mean Tl concentration and isotope composition of river water. Such parameters provide key constraints on the dissolved Tl fluxes to the oceans from rivers and mineral aerosols.The Tl isotope data for loess and suspended riverine detritus are relatively uniform with a mean of ε²⁰⁵Tl = −2.0 ± 0.3 (ε²⁰⁵Tl represents the deviation of the ²⁰⁵Tl/²⁰³Tl isotope ratio of a sample from NIST SRM 997 Tl in parts per 10⁴). For waters from four major and eight smaller rivers, the majority were found to have Tl concentrations between 1 and 7 ng/kg. Most have Tl isotope compositions very similar (within ±1.5 ε²⁰⁵Tl) to that deduced for the upper continental crust, which indicates that no significant Tl isotope fractionation occurs during weathering. Based on these results, it is estimated that rivers have a mean natural Tl concentration and isotope composition of 6 ± 4 ng/kg and ε²⁰⁵Tl = −2.5 ± 1.0, respectively.In the Amazon estuary, both additions and losses of Tl were observed, and these correlate with variations in Fe and Mn contents. The changes in Tl concentrations have much lower amplitudes, however, and are not associated with significant Tl isotope effects. In the Kalix estuary, the Tl concentrations and isotope compositions can be explained by two-component mixing between river water and a high-salinity end member that is enriched in Tl relative to seawater. These results indicate that Tl can display variable behavior in estuarine systems but large additions and losses of Tl were not observed in the present study.  相似文献   

Fourier-transform Infrared Spectroscopy (FTIRS), a New Method to Infer Past Changes in Tree-line Position and TOC using Lake Sediment     

Peter Rosén  Per Persson 《Journal of Paleolimnology》2006,35(4):913-923

This study tests the hypothesis that Fourier-transform infrared spectroscopy (FTIRS) of lake sediments can be used to infer past changes in tree-line position and total organic carbon (TOC) content of lake water. A training set of 100 lakes from northern Sweden spanning a broad altitudinal and TOC gradient from 0.7 to 14.9 mg/l was used to assess whether vegetation zones and TOC can be modelled from FTIR spectra of surface sediments (0–1 cm) using principal component analysis (PCA) and partial least squares (PLS) regression. Preliminary results show that FTIRS of lake sediments can be used to reconstruct past changes in tree line and the TOC content of lake water, which is hardly surprising since FTIRS registers the properties of organic and minerogenic material derived from the water mass and the drainage area. The FTIRS model for TOC gives a root mean squared error (RMSECV) of calibration of 1.4 mg/l (10% of the gradient) assessed by internal cross-validation (CV) yielding an R_cv² of 0.64. This should be compared with a near-infrared spectroscopy (NIRS) and diatom transfer function for TOC from the same set of lakes, which have a R_cv² of 0.61 and 0.31, and RMSECV of 1.6 and 2.3 mg/l, respectively. The FTIRS-TOC model was applied to a Holocene sediment core from a tree-line lake and the results show similar trends as inferences from NIRS and pollen from the same core. Overall, the results indicate that changes in FTIR spectra from lake sediments reflect differences in catchment vegetation and TOC, and that FTIRS-models based on surface-sediment samples can be applied to sediment cores for retrospective analysis.  相似文献   

Performance of the In Situ Microcosm Technique for Measuring the Degradation of Organic Chemicals in Aquifers     

Per H. Nielsen  Thomas H. Christensen  Hans-Jørgen Albrechtsen  Robert W. Gillham 《Ground Water Monitoring & Remediation》1996,16(1):130-140

An in situ microcosm (ISM) consists of a stainless steel cylinder isolating about 2 L of the aquifer and is equipped with valves allowing for loading and sampling from the ground surface. During the last five years, this technique has been used frequently to study the degradation of organic chemicals in polluted and pristine aquifers representing different redox environments. The ISM technique has great potential for providing field-relevant degradation potentials and rate constants, but care must be taken in using the equipment and interpreting the results. This paper provides details concerning the installation and operation of an ISM and presents experiences concerning data interpretation and monitoring of redox conditions.  相似文献