Mid‐Holocene vegetation dynamics in the Tejo River estuary based on palaeobotanical records from Ponta da Passadeira (Barreiro–Setúbal,Portugal)     

Luis Gómez‐Orellana  Pablo Ramil‐Rego  Ernestina Badal  Yolanda Carrión Marco  Castor Muñoz Sobrino 《Boreas: An International Journal of Quaternary Research》2014,43(4):792-806

This paper presents the results of pollen and charcoal analyses carried out in the sedimentary formation of Ponta da Passadeira, south of the Tejo River estuary, Portugal. The data provide information regarding the evolution of the coastline and ecosystem of the estuary during the mid and late Holocene. The study focuses on a group of upright woody fossilized tree remains that, together with those identified earlier by García‐Amorena et al. (2007), form part of the fossil forest of Ponta da Passadeira. Eight remains were identified as Pinus pinaster, four as Pinus pinea and one as Pinus sp. Two specimens of these species were dated to 6523 and 5805 cal. a BP. Pollen analysis was undertaken in a clay layer located at the same point as the fossil forest, which is currently below sea level; the base of the clay layer was dated to 4906 cal. a BP. The pollen spectra reflect the dynamics of the vegetation that grew on this deposit, whereas the sporopollinic input masks the contribution of the regional vegetation. Wood charcoal remains recovered at an adjacent Final Neolithic settlement were also analysed, and a Pinus sp. specimen was radiocarbon dated to 5050 cal. a BP. The correlation amongst the three records provides key ecological markers for the understanding of the evolution of coastline ecosystems, and helps to clarify and understand the Holocene sea rise on the Atlantic seaboard of Iberia. The geographical location of Ponta da Passadeira is strategic because it enables a more clear definition of the configuration of landscapes that show an inflection point in this area of central Portugal.  相似文献   

Dynamic response of road pavement resting on a layered poroelastic half‐space to a moving traffic load     

Xue‐Qian Fang  Shao‐Pu Yang  Jin‐Xi Liu  Xiao‐Song Zhang 《国际地质力学数值与分析法杂志》2014,38(2):189-201

This paper is dedicated to study the dynamic response of a thin‐plate resting on a layered poroelastic half‐space under a moving traffic load. Based on the dynamic poroelastic theory of Biot, the general solutions of the homogeneous poroelastic foundation are obtained by Fourier translation. By using the transmission and reflection matrices method in the frequency domain, the equivalent stiffness of the layered poroelastic half‐space is presented. Kirchhoff's hypotheses are applied to obtain the vertical displacement of the thin plate. By using the inverse Fourier transform, the time domain solution is obtained. As an example of three layers, the influences of the load velocity, the material properties of poroelastic layers, and the flexural rigidity of the plate on the response of the pavement system are examined. Analyses show that a soft intermediate layer results in the significant increase of vertical displacement of road pavement. Comparison with the existing work validates the present model. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Analytical solution for transient groundwater flow during slug test in vertical cutoff walls     

Jeehee Lim  Dongseop Lee  Hyun‐Jun Choi  Hangseok Choi 《国际地质力学数值与分析法杂志》2014,38(17):1855-1870

An analysis method for transient groundwater flow during slug tests performed in vertical cutoff walls is presented. The analytical solution for evaluating hydraulic conductivity of vertical cutoff walls is derived by applying the method of images to the previously developed analytical solution that is exclusively applicable to an infinite aquifer. Two distinct boundary conditions are considered to account for the configuration of the vertical cutoff wall: the wall‐soil formation interfaces with or without the existence of filter cakes, that is, constant‐head boundary and no‐flux boundary conditions. A series of type curves is constructed from the analytical solution and compared with those of a partially penetrated well within an aquifer. The constant‐head boundary condition provides faster hydraulic head recovery than the aquifer case. On the other hand, the no‐flux boundary condition leads to a delayed hydraulic head recovery. The greater the shape factor and well offset from the center of the cutoff wall, and the smaller the width of the cutoff wall, the greater the effect of the boundary condition observed in the type curves. This result shows the significance of considering proper boundary conditions at the vertical cutoff wall in analyzing slug tests. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Raman spectroscopy of olivine in dunite experimentally shocked to pressures between 5 and 59 GPa     

S. Farrell‐Turner  W. U. Reimold  M. Nieuwoudt  R. M. Erasmus 《Meteoritics & planetary science》2005,40(9-10):1311-1327

Abstract— Previous Raman investigations on experimentally shocked ingle‐crystal olivine indicated that the olivine Raman bands seemingly shift to a higher wave number with increasing shock pressure. If this effect could be confirmed, Raman analysis of natural shock‐metamorphosed minerals could potentially provide an important shock barometric tool. We carried out a Raman spectroscopic study on olivine in a series of natural dunite samples experimentally shocked to pressures between 5 and 59 GPa. In addition, we analyzed olivine grains in a sample of the Cold Bokkeveld C1 meteorite. We studied samples of several dunites with olivine of 90.64–92.00 mole% Fo to determine Raman effects in the region from 200 to 900 cm^?1. Several olivine grains per sample/shock pressure stage were analyzed. Raman analysis, however, showed little or no shift with increasing shock pressure. The shifts to higher or lower frequencies observed were not specific for a given pressure stage, with some grains within a sample showing more shift than others. This finding is unrelated to the crystallographic orientation of analyzed grains and cannot be related systematically to the different degrees of optically determined shock metamorphism of the analyzed grains. We identified an increase in full width at half maximum (FWHM) for the 824 cm^?1 band with increased shock pressure in the shocked Åheim samples above 45 GPa and, to a lesser extent, for the 856 cm^?1 band. Evaluation of band broadening of olivine in the Cold Bokkeveld meteorite showed FWHM values that were much greater (9–20 cm^?1) than those of olivine in the shocked dunite samples (7–12 cm^?1). We concluded that these differences in FWHM are due to differences in chemical composition between the meteoritic and the experimentally shocked olivine. Therefore, using Raman spectroscopy to detect small shifts in wave numbers to higher frequencies with increased shock pressure does not yield consistent effects for polycrystalline dunite. An extra band at 650 cm^?1 was identified in the Raman spectra of the unshocked Mooihoek dunite and the Åheim dunite samples shocked to 5, 29.3, and 59 GPa, as well as another at 696 cm^?1 in all the spectra of the 59 GPa Åheim sample. The cause of these extra bands is not known. Comparison of these results with Raman spectra of olivine from the Cold Bokkeveld C1 meteorite did not allow us to determine shock pressures for the meteoritic olivine.  相似文献   

Sulfide mineralogy and redox conditions in some shergottites     

Jean‐Pierre LORAND  Vincent CHEVRIER  Violaine SAUTTER 《Meteoritics & planetary science》2005,40(8):1257-1272

Abstract— Magmatic sulfide mineralogy has been studied in 2 olivine‐phyric shergottites (DaG 476 and SaU 005) and 4 basaltic shergottites (Zagami, Shergotty, Los Angeles, and NWA 480). Modal abundances of magmatic sulfides, as estimated by image analysis on thin section, are high (0.16 to 0.53 area percent) and correlate positively with abundances of Fe‐Ti oxides. Sulfides are mesostasis minerals, being mostly interstitial grains or locally enclosed in post‐cumulus melt inclusions (e.g., SaU 005) in olivine. Sulfides in shergottites are composed of major pyrrhotite containing pentlandite exsolutions associated with minor amounts of Cu sulfides (chalcopyrite and/or cubanite). Hot desert finds (e.g., DaG 476) show abundant fracture‐filling iron (oxy)hydroxides of probable terrestrial origin. Unaltered sulfides show metal‐rich hexagonal pyrrhotite compositions with metal/sulfur (M/S) ratio ranging between 0.936 ± 0.005 and 0.962 ± 0.01. This compositional range corresponds to the two‐phase structural domain 2C + nC of the Fe‐S system; however, the high‐temperature disordered hexagonal 1C pyrrhotite structure would be in better agreement with magnetic properties of shergottites. Ni contents in pyrrhotite increase from Los Angeles (<0.05 at%) to Shergotty, Zagami, and NWA 480 (0.2–0.5 at%), and DaG 476 and SaU 005 (up to 3 at%). The higher Ni values of pyrrhotite in olivine‐phyric shergottites correlate with the abundance of pentlandite exsolutions, both reflecting more primitive Ni‐rich sulfide liquids where abundant olivine crystallized. This result and the strong correlation between sulfide abundances and Fe‐Ti oxides argue for a primary magmatic origin of these sulfides. Although they reproduce the trend of magmatic oxygen fugacity conditions determined from Fe‐Ti oxide pairs, observed pyrrhotite compositions are systematically more metal‐deficient compared to those calculated from the Fe‐S‐O system. This suggests post‐magmatic oxidation during cooling on Mars, followed by terrestrial weathering for hot desert finds.  相似文献   

Weathering of meteorites from Oman: Correlation of chemical and mineralogical weathering proxies with 14C terrestrial ages and the influence of soil chemistry     

A. Al‐KATHIRI  B. A. HOFMANN  A. J. T. JULL  E. GNOS 《Meteoritics & planetary science》2005,40(8):1215-1239

Abstract— Fifty‐four fragments of ordinary chondrites from 50 finds representing all searched areas in central Oman and all weathering stages were selected to compare the physical, chemical, and mineralogical effect of terrestrial weathering with ¹⁴C terrestrial ages. ¹⁴C ages range from 2.0 to >49 kyr with a median value of 17.9 kyr. The peak of the age range, which is between 10–20 kyr, falls in an arid climate period. A comparison of the chemical composition of Omani chondrites with literature data for unweathered H and L chondrites demonstrates a strong enrichment in Sr and Ba, and depletion in S during weathering. Water contents in H chondrites increase with terrestrial age, whereas L chondrites show a rapid initial increase followed by nearly constant water content. Correlating Sr, Ba, and H₂O with age indicates two absorption trends: i) an initial alteration within the first 20 kyr dominated by H₂O uptake, mainly reflecting Fe‐Ni metal alteration, and ii) a second Ba‐and Sr‐dominated stage correlated with slower and less systematic weathering of troilite that starts after H₂O reaches ?2 wt%. Sulfur released from troilite partly combines with Ba and Sr to form sulfate minerals. Other parameters correlated with ¹⁴C age are degree of weathering, color of powdered meteorites, and the Ni/Fe ratio. Chemical analyses of 145 soils show a high degree of homogeneity over the entire interior Oman Desert, indicating large‐scale mixing by wind. Soil samples collected from beneath meteorite finds typically are enriched in Ni and Co, confirming mobilization from the meteorites. High Cr and Ni concentrations in reference soil samples, which decrease from NE to SW, are due to detrital material from ultramafic rocks of the Oman Mountains.  相似文献   

Dark energy and dark matter haloes     

Michael Kuhlen  Louis E. Strigari  rew R. Zentner  James S. Bullock †  Joel R. Primack 《Monthly notices of the Royal Astronomical Society》2005,357(1):387-400

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Interaction of trace metals with natural particle surfaces: Comparison between adsorption experiments and field measurements     

Beat Müller  Laura Sigg 《Aquatic Sciences - Research Across Boundaries》1990,52(1):75-92

The distribution of the metal ions Zn and Pb between particulate and dissolved phase in river Glatt was studied by field measurements and compared with calculated simulations, using parameters obtained by adsorption experiments with natural suspended particulate material. Differences in distribution coefficients obtained from field data are observed in function of the sampling locations and of the composition of the particulate matter.Experiments in which metal ion solutions are titrated with a suspension of natural particles and analyzed by anodic stripping voltammetry, are interpreted in terms of binding capacities and conditional stability constants of Zn and Pb with the surface sites. Binding constants of a particular metal ion varied very little for all samples. We obtained mean values for the conditional average complex formation constants at pH 8 of: log^cond K _Pb = 9.44 ± 0.18 and log^cond K _Zn = 8.17 ± 0.20. At this pH, binding capacities of 5 10^–3 – 1.7 10^–2 mol/kg of particles were obtained for samples collected at different locations and times; organic material, iron and manganese oxides are considered to be the main components that control the adsorption to the particles.Distribution coefficients are calculated from the experimentally obtained binding capacities and conditional stability constants. Calculated distribution coefficients for Zn agree with those obtained from the field data and are not very sensitive to changes in the composition of the solution. Good agreement was obtained for lead as well; for some samples it was important to take two types of sites with different affinity into consideration.  相似文献   

Kernel Principal Component Analysis for Efficient,Differentiable Parameterization of Multipoint Geostatistics   总被引：6，自引：5，他引：1  

Pallav Sarma  Louis J. Durlofsky  Khalid Aziz 《Mathematical Geosciences》2008,40(1):3-32

This paper describes a novel approach for creating an efficient, general, and differentiable parameterization of large-scale non-Gaussian, non-stationary random fields (represented by multipoint geostatistics) that is capable of reproducing complex geological structures such as channels. Such parameterizations are appropriate for use with gradient-based algorithms applied to, for example, history-matching or uncertainty propagation. It is known that the standard Karhunen–Loeve (K–L) expansion, also called linear principal component analysis or PCA, can be used as a differentiable parameterization of input random fields defining the geological model. The standard K–L model is, however, limited in two respects. It requires an eigen-decomposition of the covariance matrix of the random field, which is prohibitively expensive for large models. In addition, it preserves only the two-point statistics of a random field, which is insufficient for reproducing complex structures. In this work, kernel PCA is applied to address the limitations associated with the standard K–L expansion. Although widely used in machine learning applications, it does not appear to have found any application for geological model parameterization. With kernel PCA, an eigen-decomposition of a small matrix called the kernel matrix is performed instead of the full covariance matrix. The method is much more efficient than the standard K–L procedure. Through use of higher order polynomial kernels, which implicitly define a high-dimensionality feature space, kernel PCA further enables the preservation of high-order statistics of the random field, instead of just two-point statistics as in the K–L method. The kernel PCA eigen-decomposition proceeds using a set of realizations created by geostatistical simulation (honoring two-point or multipoint statistics) rather than the analytical covariance function. We demonstrate that kernel PCA is capable of generating differentiable parameterizations that reproduce the essential features of complex geological structures represented by multipoint geostatistics. The kernel PCA representation is then applied to history match a water flooding problem. This example demonstrates that kernel PCA can be used with gradient-based history matching to provide models that match production history while maintaining multipoint geostatistics consistent with the underlying training image.  相似文献   

gLucifer: next generation visualization framework for high-performance computational geodynamics     

Dave R. Stegman  Louis Moresi  Robert Turnbull  Julian Giordani  Patrick Sunter  Alan Lo  Steve Quenette 《Visual Geosciences》2008,13(1):71-84

High-performance computing provides unprecedented capabilities to produce higher resolution 4-D models in a fraction of time. Thus, the need exists for a new generation of visualization systems able to maintain parity with the enormous volume of data generated. In attempting to write this much data to disk, each computational step introduces a significant performance bottleneck, yet most existing visualization software packages inherently rely on reading data in from a dump file. Available packages make this assumption of postprocessing at quite a fundamental level and are not very well suited for plotting very large numbers of specialized particles. This necessitates the creation of a new visualization system that meets the needs of large-scale geodynamic modeling. We have developed such a system, gLucifer, using a software framework approach that allows efficient reuse of our efforts in other areas of research. gLucifer is capable of producing movies of a 4-D data set “on the fly” (simultaneously with running the parallel scientific application) without creating a performance bottleneck. By eliminating most of the human efforts involved in visualizing results through postprocessing, gLucifer reconnects the scientist to the numerical experiment as it unfolds. Data sets that were previously very difficult to even manage may be efficiently explored and interrogated without writing to disk, and because this approach is based entirely on memory distributed across as many processors as are being utilized by the scientific application, the visualization solution is scalable into terabytes of data being rendered in real time.  相似文献