Compactional behavior of fine-grained sediments — examples from Deep Sea Drilling Project cores     

Ulf Bayer  Andreas Wetzel 《International Journal of Earth Sciences》1989,78(3):807-819

Laboratory experiments, statistical analysis of field data and theoretical models are combined in the attempt to derive standard compaction curves for various deep-sea sediments which are in compaction equilibrium with the overburden. A revised and generalized version of Athy's law together with laboratory experiments allows the classification of sediments in terms of the amount of porewater structurally bound to the particles' surfaces. Especially suction pressure experiments are useful in quantifying the forces that bind water on the particle surfaces. The sediments analyzed almost range from systems of »suspended grains« to nearly perfect »colloidal systems«. The methods and equations required to derive the relevant parameters are given for both, downhole porosity/density measurements and laboratory experiments.

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Zusammenfassung Die Synthese experimenteller Labordaten, statistischer Analysen von Messungen an Kernen und theoretischer Modellierung der Kompaktion im Gleichgewicht mit der Auflast ermöglicht die Definition von Typ-Kurven für das Kompaktionsverhalten von verschiedenen Tiefsee-Sedimenten. Eine erweiterte und verbesserte Form der Athy'schen Gleichung erlaubt zusammen mit Laborexperimenten, Sedimente entsprechend des Anteils an strukturell gebundenem Porenwasser zu klassifizieren. Anhand von Saugspannungsexperimenten können die Bindungskräfte zwischen Wasser und Partikeloberflächen abgeschätzt werden. Die untersuchten Sedimente reichen von »suspendierten Körnern« bis zu einem »kolloidalen System«. Die notwendigen Methoden und Gleichungen zur Bestimmung der relevanten Parameter aus Bohrlochdaten und Laborexperimenten werden diskutiert.

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Résumé A partir d'une synthèse de résultats d'expériences de laboratoires, d'analyses statistiques de données de terrain et d'une modélisation théorique, il est possible d'établir des courbes standard du processus de compaction pour divers types de sédiments de mer profonde, pour lesquels la compaction est en équilibre avec la charge. Une version revue et généralisée de la loi d'Athy permet, en accord avec les résultats expérimentaux, de classer les sédiments selon la quantité d'eau intersticielle liée structuralement à la surface des particules. Les sédiments analysés correspondent à des systèmes qui vont du type à «grains suspendus» à des colloïdes presque parfaits. Les auteurs présentent une discussion détaillée des méthodes et des équations néssaires à l'obtention des paramètres significatifs tant à partir des expériences de laboratoire qu'à partir des mesures de porosité/densité effectuées dans les forages.

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Turbulent characteristics of a shallow convective internal boundary layer     

Ann-Sofi Smedman  Ulf Högström 《Boundary-Layer Meteorology》1983,25(3):271-287

Turbulent characteristics of a 50 to 100 m deep convective internal boundary layer (I.B.L.) have been studied. The data were gathered at a flat coastal site (Näsudden on the island of Gotland, Sweden) during three consecutive days in May 1980 which were characterized by a steady, very stable stratified marine approach flow. The site is situated on a flat area ca. 1500 m from the shoreline. Only daytime runs have been analysed in the present paper. The sensible heat flux at the ground was typically 200 W m^-2 and was found to decrease more or less linearly with height throughout the I.B.L., being slightly negative at greater heights. The momentum flux was also found to decrease with height, but nevertheless shear production of turbulent kinetic energy was found to be large throughout the entire I.B.L. The analysis shows that the turbulent regime has a mixed character. Certain characteristics, such as the rate of growth of the I.B.L., appear to be almost entirely controlled by mechanical turbulence, while others, notably temperature variance and the spectrum of vertical velocity, scale remarkably well with w _* and z _i, in accordance with the results found in fully convective conditions during the experiments at Minnesota and Aschurch. Other turbulent characteristics, such as spectra of the horizontal wind components measured near the top of the I.B.L. tend to adhere to mixed-layer scaling in the high frequency range, exhibiting much increased energy in the lower (reduced) frequency range. Spectra of the velocity components from 10 m are shown to be in general agreement with findings from ‘ideal’, homogeneous sites (Kansas) when properly normalized, although the low frequency part of u- and v-spectra are slightly reduced compared to the case with deep convection.  相似文献   

Antagonistic structures in border areas: Local milieux and local politics in the Polish-German twin city Gubin/Guben     

Ulf Matthiesen  Hans-Joachim Bürkner 《GeoJournal》2001,54(1):43-50

Cross-border communication and co-operation at the Eastern fringe of the European Union seems so far to have been a matter of political initiative and a lot of good will at the levels of national, regional and local governance. This article maintains that everyday culture must be given more notice when cross-border activities are regarded at the local level, especially in twin cities. The case of the German-Polish twin city Guben/Gubin reveals a strong tendency towards a new divergence of thought and action between formal and informal levels of action, namely the level of local politics and governance and the level of local everyday milieux. While the politics of Euroregions, local administrations and local governments is very often directed towards establishing symbolic gestures of border-crossing and mutual understanding, social milieux at the ‘base’ of local societies are rather driven by a paradoxical mixture of hope, anxiety, resentments and prejudice, thus producing contradictions and even conflict with official political initiative. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Stoßwellenmetamorphose des Anorthosits vom Manicouagan Krater,Québec,Canada     

Dr. Ulf Dworak 《Contributions to Mineralogy and Petrology》1969,24(4):306-347

The central anorthosite peak of the Maniconagan crater displays characteristic shock deformation and transition phenomena in plagioclase feldspars, scapolithe, apatite and other maphitic minerals. The optical orientation of plagioclases is determined. With increasing shock, a trend to a highly disordered structure of the plagioclase lattice can be observed. Rock fracturing occurs at low pressures. At higher pressures different kinds of isotropisation features and planar deformation structures in plagioclase, scapolithe and apatite can be distinguished. These planar elements can be interpreted as glide planes of low crystallographic indices, set in motion during shock compression by plastic deformation. Their optical orientation is measured. At very high pressures a completely isotropic phase, the s. c. diaplectic glass is formed. The physical properties of diaplectic plagioclase crystals and diaplectic glass are determined which are different from those of an unshocked crystal and its molten plagioclase glass of the same chemical composition. The diaplectic plagioclase phases are apparently mixed phases of molten glass and normal crystal. This can be proved by x-ray and infrared absorption studies. These results are correlated to shock recovery experiments and hugoniot states of plagioclase. All shock effects of plagioclases are classified into three groups according to the low pressure regime, mixed phase regime and high pressure regime. The low pressure regime is characterised by strong fracturing, the mixed phase regime by the development of planar elements, which were transformed during shock compression into the high pressure plagioclase phase with hollandite structure. The latter is converted into diaplectic glass after pressure release. The high pressure regime is characterised by complete transformation of plagioclase into the high pressure phase, which is unstable and reverts completely to the amorphous phase (diaplectic glass or maskelynite) at zero pressure density.

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Meinem verehrten Lehrer, Herrn Prof. Dr. W. v. Engelhardt, danke ich für die Unterstützung bei der Bearbeitung des Themas. Herrn Dr. D. Stöffler danke ich für klärende Diskussionen und Ratschläge. Dem Ministère des Richesses Naturelles, Québec, Canada, sowie Herrn M.S. J. Murtaugh sei für die großzügige Unterstützung bei den Geländearbeiten im Manicouagan-Krater gedankt. Die Deutsche Forschungsgemeinschaft hat die Arbeit finanziell unterstützt.  相似文献   

Carbon isotopic fractionation during a mesocosm bloom experiment dominated by Emiliania huxleyi: Effects of CO₂ concentration and primary production     

Albert Benthien  Ingrid Zondervan  Jens Hefter  Ulf Riebesell 《Geochimica et cosmochimica acta》2007,71(6):1528-1541

We investigated the effect of CO₂ and primary production on the carbon isotopic fractionation of alkenones and particulate organic matter (POC) during a natural phytoplankton bloom dominated by the coccolithophore Emiliania huxleyi. In nine semi-closed mesocosms (∼11 m³ each), three different CO₂ partial pressures (pCO₂) in triplicate represented glacial (∼180 ppmv CO₂), present (∼380 ppmv CO₂), and year 2100 (∼710 ppmv CO₂) CO₂ conditions. The largest shift in alkenone isotopic composition (4-5‰) occurred during the exponential growth phase, regardless of the CO₂ concentration in the respective treatment. Despite the difference of ∼500 ppmv, the influence of pCO₂ on isotopic fractionation was marginal (1-2‰). During the stationary phase, E. huxleyi continued to produce alkenones, accumulating cellular concentrations almost four times higher than those of exponentially dividing cells. Our isotope data indicate that, while alkenone production was maintained, the interaction of carbon source and cellular uptake dynamics by E. huxleyi reached a steady state. During stationary phase, we further observed a remarkable increase in the difference between δ¹³C of bulk organic matter and of alkenones spanning 7-12‰. We suggest that this phenomenon is caused mainly by a combination of extracellular release of ¹³C-enriched polysaccharides and subsequent particle aggregation induced by the production of transparent exopolymer particles (TEP).  相似文献   

Calcium isotope fractionation in coccoliths of cultured Calcidiscus leptoporus, Helicosphaera carteri, Syracosphaera pulchra and Umbilicosphaera foliosa     

Nikolaus Gussone  Gerald Langer  Markus Geisen  Blair A. Steel  Ulf Riebesell 《Earth and Planetary Science Letters》2007,260(3-4):505-515

Four species of marine calcifying algae, the coccolithophores Calcidiscus leptoporus, Helicosphaera carteri, Syracosphaera pulchra and Umbilicosphaera foliosa were grown in laboratory cultures under temperatures varying between 14 and 23 °C, and one species, C. leptoporus, under varying [CO₃²⁻], ranging from 105 to 219 μmol/kg. Calcium isotope compositions of the coccoliths resemble in both absolute fractionation and temperature sensitivity previous calibrations of marine calcifying species e.g. Emiliania huxleyi (coccolithophores) and Orbulina universa (planktonic foraminifera) as well as inorganically precipitated CaCO₃, but also reveal small species specific differences. In contrast to inorganically precipitated calcite, but similar to E. huxleyi and O. universa, the carbonate ion concentration of the medium has no statistically significant influence on the Ca isotope fractionation of C. leptoporus coccoliths; however, combined data of E. huxleyi and C. leptoporus indicate that the observed trends might be related to changes of the calcite saturation state of the medium. Since coccoliths constitute a significant portion of the global oceanic CaCO₃ export production, the Ca isotope fractionation in these biogenic structures is important for defining the isotopic composition of the Ca sink of the ocean, one of the key parameters for modelling changes to the marine Ca budget over time. For the present ocean our results are in general agreement with the previously postulated and applied mean value of the oceanic Ca sink (Δ_sed) of about − 1.3‰, but the observed inter- and intra-species differences point to possible changes in Δ_sed through earth history, due to changing physico-chemical conditions of the ocean and shifts in floral and faunal assemblages.  相似文献   

Pétrographie des „Permoskyth“ der Jaggl-Plawen-Einheit (Südtirol) und Diskussion der Detritusherkunft mit Hilfe von Kathoden-Lumineszenz-Untersuchungen     

Dr. Detlev K. Richter  Dipl.-Geol. Ulf Zinkernagel 《International Journal of Earth Sciences》1975,64(1):783-807

The Permo-Scythian deposits E of Lake Reschen (North-Italy) are composed of a sequence of terrestrial sediments in Verrucanofacies and of a series of detrital carbonate and lagoonal-evaporitic rocks (“Wechselschichten”) overlaid by Anisian fossiliferous dolomites. Examinations by cathodo-luminescence give reference to the source area of the detrius and to the diagenesis of the sediments. Further statements can be made by X-ray (triclinity of K-feldspars; inclusions in authigenic minerals) and chemical examinations (composition of dolomites). The detritus of the slightly metamorphic rocks, indicated by the crystallinity of illite, does not originate from the underlying “Plawenkristallin” and from the adjacent “ötztalkristallin”, respectively, but by 70% from a porphyritic source area that is supposed to be located in the region of Lugano.  相似文献   

A new key pole for the East European Craton at 1452 Ma: Palaeomagnetic and geochronological constraints from mafic rocks in the Lake Ladoga region (Russian Karelia)     

Natalia V. Lubnina  Satu Mertanen  Ulf Söderlund  Svetlana Bogdanova  Tatiana I. Vasilieva  Dmitry Frank-Kamenetsky 《Precambrian Research》2010

Palaeomagnetic and geochronological studies on mafic rocks in the Lake Ladoga region in South Russian Karelia provide a new, reliably dated Mesoproterozoic key paleopole for the East European Craton (Baltica). U–Pb dating on baddeleyite gives a crystallisation age of 1452 ± 12 Ma for one of the studied dolerite dykes. A mean palaeomagnetic pole for the Mesoproterozoic dolerite dykes, Valaam sill and Salmi basalts yields a paleopole at 15.2°N, 177.1°E, A₉₅ = 5.5°. Positive baked contact test for the dolerite dykes and positive reversal test for the Salmi basalts and for the dykes confirm the primary nature of the magnetisation. Comparison of this Baltica palaeopole with coeval paleomagnetic data for Laurentia and Siberia provides a revised palaeoposition of these cratons. The results verify that the East European Craton, Laurentia and Siberia were part of the supercontinent Columbia from the Late Palaeoproterozoic to the Middle Neoproterozoic.  相似文献   

The provenance of northern Kalahari Basin sediments and growth history of the southern Congo Craton reconstructed by U–Pb ages of zircons from recent river sands     

Andreas Gärtner  Ulf Linnemann  Mandy Hofmann 《International Journal of Earth Sciences》2014,103(2):579-595

The southern Congo Craton is widely overlain by Meso- to Cenozoic sediments of the northern Kalahari Basin, which hamper any correlation of basement units. The latter are represented by the Archaean Angola and Kasai Blocks, while the southern cratonic margin is framed by several Meso- to Neoproterozoic orogenic belts. For provenance analysis of the sedimentary cover and reconstruction of the main zircon-forming events, we studied zircons from recent sediments of the largest rivers at the southern margin of the Congo Craton. U–Pb zircon ages suggest a major amount of the sediments to originate from E Lufilian and Kibaran Belts, while input from the S Damara Belt seems to increase to the W. Ages related to the Angola Block were only noticed in the westernmost parts of the working area, which is not in accordance with the SE-trending drainage pattern, proposed to have been onset during the Cretaceous. Thus, it is assumed that the Meso- to Cenozoic sedimentary cover extended further west than today prior to the Mesozoic to Neogene uplift of the Angola Block and that subsequent erosion exhumed the basement stepwise from west to east. A recurrent destabilisation of the southern margin of the Congo Craton at ~2.7, 1.9, 1.0 and 0.6 Ga is supposed to be represented by major peaks in the age distribution pattern of the total amount of concordant zircons. This is in accordance with similar studies in adjacent areas. Additionally, the obtained data fit well to several hypothesised major events during the supercontinent cycle.  相似文献   

Magnetohydrodynamic instabilities and turbulence in accretion disks     

Georg P. Schramkowski  Ulf Torkelsson 《Astronomy and Astrophysics Review》1996,7(1):55-96

In this paper we review the possibilities for magnetohydrodynamic processes to handle the angular momentum transport in accretion disks. Traditionally the angular momentum transport has been considered to be the result of turbulent viscosity in the disk, although the Keplerian flow in accretion disks is linearly stable towards hydrodynamic perturbations. It is on the other hand linearly unstable to some magnetohydrodynamic (MHD) instabilities. The most important instabilities are the Parker and Balbus-Hawley instabilities that are related to the magnetic buoyancy and the shear flow, respectively. We discuss these instabilities not only in the traditional MHD framework, but also in the context of slender flux tubes, that reduce the complexity of the problem while keeping most of the stability properties of the complete problem. In the non-linear regime the instabilities produce turbulence. Recent numerical simulations describe the generation of magnetic fields by a dynamo in the resulting turbulent flow. Eventually such a dynamo may generate a global magnetic field in the disk. The relation of the MHD-turbulence to observations of accretion disks is still obscure. It is commonly believed that magnetic fields can be highly efficient in transporting the angular momentum, but emission lines, short-time scale variability and non-thermal radiation, which a stellar astronomer would take as signs of magnetic variability, are more commonly observed during periods of low accretion rates. Received October 12, 1995 / Accepted November 16, 1995  相似文献