A method to determine warm and cool steppe biomes from pollen data; application to the Mediterranean and Kazakhstan regions     

Pavel E. Tarasov  Rachid Cheddadi  Joel Guiot  Sytze Bottema  Odile Peyron  Jordina Belmonte  Vittoria Ruiz-Sanchez  Fatima Saadi  Simon Brewer 《第四纪科学杂志》1998,13(4):335-344

An objective method for the assignment of pollen spectra to appropriate biomes has been published recently. The aim of this paper is to improve the distinction between warm and cool steppes, thus refining vegetation and climate reconstruction, particularly during the Last Glacial Maximum. A set of modern pollen spectra from the Mediterranean and Kazakhstan regions, dominated today by open vegetation types, has been analysed statistically in order to relate pollen taxa abundances to warm and cool grass/shrub plant functional types (PFTs). A statistical test using modern pollen data shows that the method is able to distinguish between cool and warm steppe biomes with a high degree of confidence. The method has been applied to two fossil pollen records. The results of this exercise showed that cool steppe dominated in central Greece between 18 000 and 13 000 yr BP, while in western Iran the vegetation was at the boundary between cool and warm steppes. These vegetation types were replaced by warm mixed forest in Greece and warm steppe in Iran after that time span. © 1998 John Wiley & Sons, Ltd.  相似文献   

日本掀起对活断层定义和地震预报的热烈讨论   总被引：1，自引：1，他引：0  

中川和之 《国际地震动态》1999,(5):32-33

１９９７年１１月由日本地震学会宣传委员会发起的英文简称为ｎｆｍｌ的活动至１９９８年２月初已２个多月了。截至１９９８年２月５日,已有１４５名参与者。他们就地震、防灾、科学教育和媒体的作用进行了内容广泛的讨论。参与者中不仅有地震学专家,还有宣传、教育、行...  相似文献   

Effect of phosphatation and calcination on the environmental behaviour of sediments     

Moussa Dia  Rachid Zentar  Nor-edine Abriak  Ange Nzihou  Guy Depelsenaire  Alain Germeau 《国际泥沙研究》2019,34(5):486-495

Dredging operations produce considerable quantities of materials, to be managed and this opens an opportunity for valorization in civil engineering. However, the contamination of the dredged sediments has become a major problem to solve. The major contaminants are heavy metals and organic compounds. This study focuses on the use of phosphoric acid (H3PO4) to stabilize heavy metals from sediments and destroy organic matter by calcination at 650 °C with a goal of using sediments in roadworks. Several studies have been conducted in this eld. The stabilized materials obtained have been used in civil engineering. The main purpose of this work is to discuss the environmental behavior of marine sediment treated by phosphatation and calcination. Two types of phosphoric acids were used. The pH dependence leaching test has been used as the basic characterization to evaluate the effect of the type of phosphoric acid on the metals behavior in a valorization scenario. The standard leaching test and the Toxicity Characteristic Leaching Procedure (TCLP) were conducted as compliance tests. In regards of the obtained results, the environmental assessment has also shown a reduction in the availability of targeted heavy metals in alkaline environment whatever the type of acid used for treatment. This opens opportunities for co-valorization.  相似文献   

Environmental factors structuring fish composition and assemblages in a small macrotidal estuary (eastern English Channel)   总被引：4，自引：1，他引：3  

Jonathan Selleslagh  Rachid Amara 《Estuarine, Coastal and Shelf Science》2008,79(3):507-517

The fish assemblage structure was analyzed along an estuarine gradient of a small macrotidal estuary (the Canche, France). Fishes were collected every two months between May 2006 and July 2007 from 12 sampling stations using a 1.5-m beam trawl with a 5 mm mesh size in the cod end. To complement this information, sampling was also performed using 15-m fyke nets (8 mm mesh size in the cod end). For each sample, abiotic (temperature, salinity, pH, oxygen, turbidity, river flow, wind speed and depth) and biotic (macro crustacean species abundances) were recorded. Throughout the study, 28 fish species belonging to 20 families were collected. Fish catches were dominated by juveniles, especially Young-Of-the-Year (YOY) for the majority of the species. According to the Index of Relative Importance (IRI), common goby Pomatoschistus microps, flounder Platichtys flesus, sprat Sprattus sprattus, sea-bass Dicentrarchus labrax and plaice Pleuronectes platessa were the most abundant species, together accounting for 99.2% of the total IRI. Estuarine residents (ER = 66.2%) and marine juvenile migrants species (MJ = 31.4%) were the most important ecological guilds. The structure of the fish assemblage and its relationship to environmental variables was examined using multivariate techniques. Cluster and non-metric multidimensional scaling (nMDS) analysis defined six distinct groups in the Canche estuary, which are discriminated by specific species (SIMPER). Spatio-temporal variations in fish assemblage structure reflect the density peaks of the most abundant species. Spearman rank correlations and canonical correspondence analysis (CCA) showed that among the ten environmental variables examined, temperature, salinity and Crangon crangon (a potential predator for YOY fish or prey for older ones) are the three most important factors influencing fish species richness and abundances. Our observations reinforce the idea that certain fish species may have different life history styles in different geographic areas. The present study highlights the necessity of a better knowledge of the connectivity between estuaries and adjacent marine areas. The Canche constitutes an important ecosystem for fishes and as it is subject to little anthropogenic disturbance; its ichthyofauna can be viewed as a reference or normal assemblage for small temperate macrotidal estuaries.  相似文献   

On paleoecology of carnivorous dinosaurs ( Tyrannosauridae，Dromaeosauridae) from Late Cretaceous fossil deposits of Amur region，Russian Far East          下载免费PDF全文

Ivan U． Bolotsky 《世界地质(英文版)》2011,14(1):1-14

Present article is on Russian Far East carnivorous dinosaur paleoecology． Described summary is based on detailed study and comparison of isolated shed teeth morphology．  相似文献   

Improvement of the JRC Calculation Using Different Parameters Obtained Through a New Survey Method Applied to Rock Discontinuities     

Pedro Alameda-Hernández  Jorge Jiménez-Perálvarez  José A. Palenzuela  Rachid El Hamdouni  Clemente Irigaray  Miguel A. Cabrerizo  José Chacón 《Rock Mechanics and Rock Engineering》2014,47(6):2047-2060

This paper presents a new, fast and economical method for digitizing a rock surface profile to determine its joint roughness coefficient (JRC) value (Barton and Choubey, Rock Mech Rock Eng 10:1–54, 1977) using a set of existing parameters, the appropriateness of which has been tested. The new procedure was applied to four rock road cuts in the Alpujarra area of Granada province (Andalusia, Spain), supported by 117 digitized profiles. The method avoids any personal subjectivity bias. The usual subjectivity in the visualization and assessment of the JRC value is estimated here by a survey test answered by 90 trained users. The survey test consisted of a set of JRC visual comparisons of 12 roughness profiles, selected from the 117 profiles surveyed during the field research in the Alpujarra region, with the Barton typical profiles. The results of the survey clearly show systematic inaccuracies in the traditional procedure that are reduced if the advice presented in the conclusions of this paper is taken in account when performing the visual estimation.  相似文献   

An XPEEM study of structural cation distribution in swelling clays. I. Synthetic trioctahedral smectites     

Delphine Vantelon  Rachid Belkhou  Isabelle Bihannic  Laurent J. Michot  Emmanuelle Montargès-Pelletier  Jean-Louis Robert 《Physics and Chemistry of Minerals》2009,36(10):593-602

X-PEEM images and XPS were collected on isolated layers of three synthetic swelling clays, one hectorite and two saponites with various charge, recording the Si(2p), Al(2p) and Mg(2p) core level spectra from the clay sheets. Spectra were fitted to determine the different components of the core levels. Due to their large full width at half maximum, Si XPS spectra were fitted using two to three doublets. It appears that, for a given clay mineral, Si, Al and Mg binding energies (BE) were constant, for all the observed layers. However, variations of the Si BE were observed depending on the nature of the mineral investigated. The various components obtained from the fit of Si spectra could be assigned to different substitution rates; binding energy shifting to lower values with substitution increase in the layer. Furthermore, variations in Si BE according to charge location were assigned to the influence of exchangeable cation.  相似文献   

SWAT manual calibration and parameters sensitivity analysis in a semi-arid watershed in North-western Morocco     

Youssef Brouziyne  Aziz Abouabdillah  Rachid Bouabid  Lahcen Benaabidate  Ons Oueslati 《Arabian Journal of Geosciences》2017,10(19):427

Being a laborious approach, manual calibration of hydrologic model in a semi-arid context requires in-depth knowledge of the watershed and as much as possible field input data to obtain reliable simulations. In this study, manual calibration and relative sensitivity analysis approaches of the SWAT model (Soil and Water Assessment Tool) were applied for water balance in a 1993 km² watershed (on the R’dom river) located in North-western Morocco. The watershed is located in a semi-arid area dominated by agro-forestry activities. The objectives of this study were (i) to perform a local sensitivity analysis of the SWAT model taking into consideration the watershed characteristics and (ii) to implement a detailed methodology of manual calibration and validation of the model in a semi-arid context. Sensitivity analysis has been carried out on 12 different SWAT input parameters, and has revealed that 4 input parameters only were the most influential ones on flow components of the R’dom watershed. Model manual calibration was conducted along 2006 and 2007 by comparing measured and predicted monthly and daily discharges and taking Nash-Sutcliffe coefficient (NSE), determination coefficient (R ²), and percent bias (PBIAS) as goodness-of-fit indicators. Validation has been performed by the same approach through 2008 and 2009 period. All final NSE values were above 0.5, R ² values exceeded 0.7, and PBIAS lower than 25% demonstrating satisfactory model performances over the study watershed conditions. The SWAT model set-up with measured input data, manually calibrated and validated, reflects well the real hydrologic processes occurring in the R’dom watershed and can be used to assess current and future conditions and to evaluate alternative management practices.  相似文献   

Première caractérisation palynologique du Trias moyen dans le Haut Atlas ; implications pour l'initiation du rifting téthysien au Maroc     

El Hassane El Arabi  José Bienvenido Diez  Jean Broutin  Rachid Essamoud 《Comptes Rendus Geoscience》2006,338(9):641-649

The Middle Anisian has been palynologically characterized for the first time, at the whole Moroccan scale, in the High Atlas of Marrakech. The stratigraphic, tectonic and paleogeographic implications of this discovery are analysed. To cite this article: E.H. El Arabi et al., C. R. Geoscience 338 (2006).  相似文献   

Gold–palladium mineralization at Bleïda Far West, Bou Azzer–El Graara Inlier, Anti-Atlas, Morocco     

Mustapha El Ghorfi  Thomas Oberthür  Frank Melcher  Volker Lüders  Abdelmajid El Boukhari  Lhou Maacha  Rachid Ziadi  Hssain Baoutoul 《Mineralium Deposita》2006,41(6):549-564

The structurally controlled Au–Pd mineralization at Bleïda Far West occurs in a volcano-sedimentary rock sequence in altered amphibolites and chlorite schists of the Neoproterozoic Bou Azzer–El Graara inlier. The Au–Pd mineralization is virtually sulfide-free; instead, gold is associated with hematite, barite, quartz, and calcite. The gold grains are silver- and palladium-bearing (up to 19 wt% Ag and 6.3 wt% Pd) and are intergrown with a distinct suite of mainly Pd-dominated platinum group minerals, namely mertieite-I/isomertieite, merenskyite, keithconnite, kotulskite, palladseite, and sperrylite, defining a Au–Pd–As–Sb–Se–Te chemical signature. Stable isotope and fluid inclusion studies indicate a wide range of fluid compositions with a prominent saline component. In conjunction with the mineral association, oxidizing fluids are indicated, and Au and PGE transport and deposition likely took place by chloride complexes in the epithermal range, at elevated f O₂ and/or low pH. It is still speculative whether the mineralization is late Pan-African (～600–550 Ma) in age, or connected with the Variscan orogeny (～330–300 Ma), or related to some other hydrothermal event. Common to all Au–Pd mineralizations worldwide (Brazil, Australia, UK), including Bleïda Far West, is their formation in the epithermal (<300°C) range; deposition mainly in brittle structures; sulfide-poor mineral assemblages comprising hematite, sulfate minerals, and selenides; and metal transport by, and deposition from, oxidized, chloride-rich fluids. These deposits are further characterized by noble metal abundances in the order Au>Pd>Pt and the chemical signature Au–Pd–Se–Te (±As, Sb, Bi). As such, the Au–Pd association represents a discrete style of gold mineralization distinct from other classes of gold deposits.  相似文献