Chemical chronology of the Southern Coalsack     

S. D. Rodgers  S. B. Charnley  R. G. Smith  H. M. Butner 《Monthly notices of the Royal Astronomical Society》2007,379(2):807-815

  相似文献   

About time: An integrative approach to effective environmental policy     

David J. Hardisty  Ben Orlove  David H. Krantz  Arthur A. Small  Kerry F. Milch  Daniel E. Osgood 《Global Environmental Change》2012,22(3):684-694

Intertemporal trade-offs are ubiquitous in environmental decision-making and policy, yet comprehensive, practical guides are lacking. This paper introduces an adaptive, iterative approach to environmental policy, combining the insights of economics, psychology, and anthropology. We first summarize the major paradigms of each discipline, including models, concepts of time preference, strengths, and blind spots. Subsequently, we illustrate the integrative approach through four real-world environmental examples: a shopper purchasing a light bulb, an organization doing building renovations, a community considering a new source of renewable energy, and international organizations developing index insurance for farmers in the Horn of Africa. One-dimensional approaches are ill-suited to real-world challenges such as these, because each discipline only tackles one facet of the issue. In contrast, with each discipline informing the others, the integrative approach is more than the sum of its parts. This paper provides a concise guide for applied researchers and policy makers alike.  相似文献   

Preliminary laboratory investigations into the attenuation of compressional and shear waves on near-surface marine sediments     

Arthur Ayres  Friedrich Theilen 《Geophysical Prospecting》2001,49(1):120-127

The attenuation of compressional and shear waves ( Q _p and Q _s) has been studied by several authors but most of these investigations were performed on deep buried reservoir sandstones in order to distinguish between gas and condensate reservoirs and water-saturated sandstones. We present a preliminary investigation into the use of seismic wave attenuation as a measure of the geotechnical parameters of the near-surface marine sediments, a little-studied geological setting. A 6.9 m-long gravity core was taken from the continental slope of the Barents Sea at a water depth of 2227 m. The core was primarily composed of brown to olive-grey clayey mud, having a high content of foraminifers and being locally bioturbated. The values of Q _p and Q _s were determined using the rise-time method at 19 and 18 different points of the core, respectively, and they were correlated with geotechnical parameters such as wet bulk density, porosity, water content, shear strength and C/P ratio (the ratio of shear strength to overburden pressure). The calculated correlation coefficients for all correlations ranged from −0.39 to 0.41, suggesting that the attenuation characteristics of seismic waves could not be used to derive geotechnical parameters of marine sediments. However, with such a small data set it is difficult to determine clearly whether attenuation is primarily a frequency-dependent parameter and consequently not related to sediment properties, or whether the limited number of data points is the main factor responsible for the low correlation coefficients observed. Moreover, several different methods are available for the computation of the quality factor Q , and the rise-time method may not be the most appropriate means of determining the attenuation on near-surface marine sediments.  相似文献   

跨越太平洋的合作--美日预防地震损失策略     

蔡泽尔 《国际地震动态》1999,(5):26-28

在日本神户和美国加州北岭破坏性地震发生后,美国和日本加强了在地震政策方面的合作.1996年4月,"减轻自然灾害活动"成为两个面临全球严峻挑战的国家之间正在进行的美日全球远景规划合作计划(the United States-Japan Common Agenda for Cooperation in the Global Perspective)的一部分.  相似文献   

A basalt-trachyte-phonolite series from Ua Pu,Marquesas Islands,Pacific Ocean     

Arthur Clive Bishop  Alan Robert Woolley 《Contributions to Mineralogy and Petrology》1973,39(4):309-326

The paper describes a suite of volcanic and intrusive rocks from Ua Pu, one of the Marquesas Islands, situated in the central Pacific Ocean. The rocks comprise alkali olivine basalts, hawaiites, mugearites, trachytes, and phonolites. Their petrographic characters are briefly described and 24 new chemical analyses presented. The rocks fall into a sodic and a potassic series, since some rocks are richer in K₂O than Na₂O, whilst the phonolites have exceptionally high total alkali contents.The differentiation of the series is discussed and special attention is paid to the phonolites in which icositetrahedral pseudomorphs occur. It is concluded that these pseudomorphs are probably after analcime rather than leucite.  相似文献   

Low-background gamma counting: applications for210Pb dating of sediments   总被引：1，自引：0，他引：1  

Claire L. Schelske  Arthur Peplow  Mark Brenner  Craig N. Spencer 《Journal of Paleolimnology》1994,10(2):115-128

Sediment cores from three lakes were dated with²¹⁰Pb using a constant rate of supply (CRS) model. We used low-background gamma counting to measure naturally occurring levels of²¹⁰Pb,²²⁶Ra, and¹³⁷Cs in sediment samples because sample preparation is simple and non-destructive,²²⁶Ra activity provides a direct measure of supported²¹⁰Pb activity for each sample analyzed, and¹³⁷Cs activity may provide an independent age marker for the 1962–1963 peak in atmospheric fallout of this radionuclide. In one core supported²¹⁰Pb activity was estimated equally well from²²⁶Ra activity of each sampling interval or from the mean total²¹⁰Pb activity of constant activity samples at depth. Supported²¹⁰Pb activity was constant with depth in this core. In a short freeze core, determining²²⁶Ra activity of every sample proved advantageous in estimating supported²¹⁰Pb activity because supported²¹⁰Pb activity could be estimated from²¹⁰Pb measurements only at the deepest sampling interval. Supported²¹⁰Pb activity estimated from²²⁶Ra activity also yielded more precise estimates of highly variable sedimentation rates. In the third core²²⁶Ra activity exceeded²¹⁰Pb activity at the top of the core and varied 20 fold with depth. This high input of²²⁶Ra in disequilibrium with²¹⁰Pb is attributed to recent erosion of radium-bearing materials in the drainage basin. These data invalidate the assumption that supported²¹⁰Pb activity is constant in sediment cores and can be estimated from the mean total²¹⁰Pb activity at depths where²¹⁰Pb activity is constant. We recommend using gamma counting or another independent assay of²²⁶Ra to validate the assumption of constant supported²¹⁰Pb activity in sediment cores if there is reason to expect that²²⁶Ra activity varies with depth.This is the fourth of a series of papers to be published by this journal following the 20 ^th anniversary of the first application of²¹⁰Pb dating of lake sediments. Dr. P.G. Appleby is guest editing this series.  相似文献   

The effect of manganese on olivine-quartz-orthopyroxene stability     

Steven R. Bohlen  Arthur L. Boettcher  Wayne A. Dollase  Eric J. Essene 《Earth and Planetary Science Letters》1980,47(1):11-20

The effect of manganese on the stability of ferrosilite relative to fayalite + quartz has been experimentally determined to assess its importance to orthopyroxene barometry. Reaction reversals in a piston-cylinder apparatus were obtained to within 0.1-kbar intervals indicating instability of Fs₉₅Rh₅ below 10.3, 10.9, 11.4, 12.2, 12.9, 13.7 kbar and Fs₉₀Rh₁₀ below 9.8, 10.4, 10.9, 11.6, 12.4 and 13.2 kbar at 750, 800, 850, 900, 950 and 1000°C, respectively. Each mole % MnSiO₃ extends the pyroxene stability by approximately 0.12 kbar relative to FeSiO₃. Electron microprobe analyses of run products indicate a small preference of Mn for pyroxene over olivine withK_DMn-Fe^opx-oliv = 1.2?1.5, similar to values observed for natural pairs. Mössbauer spectra are consistent with a random distribution of Mn between the M1 and M2 sites in the orthopyroxene. These experimental data allow downward revision of pressure estimates based on the orthopyroxene barometer in areas where Mn is a significant component in orthopyroxene.  相似文献   

Zur Frage der Beziehungen zwischen Tektonik und Landformung     

Prof. Dr. Arthur Winkler-Hermaden 《International Journal of Earth Sciences》1960,50(1):273-290

Zusammenfassung Das Problem der Beziehungen zwischen Tektonik und Landformung beinhaltet die zeitliche und die genetische Verknüpfung der tektonischen Zyklen in der Erdgeschichte mit dem Ablauf des geomorphologischen Geschehens, Fragestellungen, welche besonders in Europa von verschiedenen Forschungsrichtungen (Geologie, physische Geographie) behandelt werden und welche einen Vergleich der erzielten Ergebnisse sehr nahelegen. Die Großformen der Erdrinde werden in erster Linie durch die endogenen, tektonischen Kräfte geschaffen. Die Landformung erscheint aber außerdem durch das Wirken der jeweiligen klimatischen Faktoren (Büdel, J., 1948) und durch den Stand des Meeresspiegels, des letzteren als der maßgeblichen, zeitlich wechselnden Erosionsbasis, beeinflußt; Umstände, auf welche, der Zielsetzung entsprechend, in diesem Aufsatz nicht näher eingegangen werden soll. Die morphologischen und die tektonischen Entwicklungen spiegeln sich in den Sedimentationen der jeweiligen Zeiträume der jüngeren geologischen Vergangenheit, unter Berücksichtigung der durch eine Filterwirkung bedingten Unterdrückung der Abbildung sekundärer Vorgänge (E.Wegmann, 1948), in großen Zügen wider, so daß auch diese zur Klärung der Erscheinungen heranzuziehen sind.Im folgenden sollen die einschlägigen Fragestellungen, hauptsächlich an Hand der jüngsttertiären Entwicklungsgeschichte der Alpen und ihrer weiteren Umrahmung, einschließlich der östlichen Randbecken, geprüft werden, wobei insbesondere eine Stellungnahme zu strittigen tektonischen Problemstellungen erfolgen muß, welch letztere für den Ablauf der Landformung von grundsätzlicher und maßgeblichster Bedeutung erscheinen.  相似文献   

Subduction, back-arc spreading and global mantle flow     

Bradford H. Hager  Richard J. O'Connell  Arthur Raefsky 《Tectonophysics》1983,99(2-4)

The shapes and orientations of Benioff zones beneath island arcs, interpreted as marking the location of subducted lithosphere, provide the best presently available constraints on the global convective flow pattern associated with plate motions. This global flow influences the dynamics of subduction. Subduction zone phenomena therefore provide powerful tests for models of mantle flow. We compute global flow models which, while simple, include those features which are best constrained, namely the observed plate velocities, applied as boundary conditions, and the density contrasts given by thermal models of the lithosphere and subducted slabs. Two viscosity structures are used; for one, flow is confined to the upper mantle, while for the other, flow extends throughout the mantle.Instantaneous flow velocity vectors match observed Benioff zone dips and shapes for the model which allows mantle-wide flow but not for the upper mantle model, which has a highly contorted flow pattern. The effect of trench migration on particle trajectories is calculated; it is not important if subduction velocities are greater than migration rates. Two-dimensional finite element models show that including a coherent high viscosity slab does not change these conclusions. A coherent high viscosity slab extending deep into the upper mantle would significantly slow subduction if flow were confined to the upper mantle. The maximum earthquake magnitude, M_w, for island arcs correlates well with the age of the subducted slab and pressure gradient between the trench and back-arc region for the whole mantle, but not the upper mantle, flow model. The correlations with orientations of Benioff zones and seismic coupling strongly suggest that the global return flow associated with plate motions extends below 700 km. For both models, regions of back-arc spreading have asthenospheric shear pulling the back-arc toward the trench; regions without back-arc spreading have the opposite sense of shear, suggesting global flow strongly influences back-arc spreading.  相似文献   

A GIS-Based Ground Water Contamination Risk Assessment Tool for Pesticides   总被引：4，自引：0，他引：4  

Michael G. Sinkevich Jr  .  M. Todd Walter  Arthur J. Lembo Jr  .  Brian K. Richards  Natalia Peranginangin  Sunnie A. Aburime  Tammo S. Steenhuis 《Ground Water Monitoring & Remediation》2005,25(4):82-91

  相似文献