珠江三角洲三水盆地早全新世以来 孢粉分析与古环境重建     

黄康有  何嘉卉  宗永强  郑卓  章桂芳  曹玲珑． 《热带地理》2016,36(3):364-373

为了深入探讨珠江三角洲的沉积古环境和古气候历史,在三水市区获取了2个高取芯率的钻孔岩芯,进行了12个AMS 14C测年,并结合孢粉、硅藻等分析结果探讨三水地区全新世的海平面与河流水动力变化,以及古植被演替过程。结果表明：钻孔所在区域全新世沉积总体从9 000 cal. a B.P.左右开始,呈现河流相―河湾相―河口湾相―潮坪相―河口湾相―河漫滩相的演变过程。三水区的早全新世沉积阶段年代最早为9 000 cal. a B.P.左右,表现为河口湾相的淤泥质粉砂沉积,硅藻以淡水种类为主,最高沉积速率为1.6 cm/a。海侵初始时间为8 700 cal. a B.P.左右,最高海平面时间为7 600 cal. a B.P.左右,此时海岸带发育红树林,丘陵山地发育较茂盛的亚常绿热带常绿阔叶林;中―晚全新世阶段（6 500―2 200 cal. a B.P.）,以泥炭粉砂沉积为主,沉积速率为0.2~0.5 cm/a,河口区高潮线附近及河流弯道低洼滩地在5 000 cal. a B.P.前后形成淡水沼泽、河口三角洲边缘区洼地水松林发育。在晚全新世（2 200 cal. a B.P.左右）以来,陆相黏土质沉积指示河口泥沙快速堆积,三角洲平原迅速扩大,沉积速率高达1.7 cm/a。孢粉结果显示次生的芒箕孢子剧增,陆地植被稀疏,人类活动显著增强。  相似文献   

SN 2009ip and SN 2010mc as dual-shock Quark-Novae     

Rachid Ouyed  Nico Koning  Denis Leahy 《天体物理学报》2013,(12):1463-1470

In recent years a number of double-humped supernovae （SNe） have been discovered. This is a feature predicted by the dual-shock Quark-Nova （QN） model where an SN explosion is followed （a few days to a few weeks later） by a QN explo- sion. SN 2009ip and SN 2010mc are the best observed examples of double-humped SNe. Here, we show that the dual-shock QN model naturally explains their light curves including the late time emission, which we attribute to the interaction between the mixed SN and QN ejecta and the surrounding circumstellar matter. Our model applies to any star （O-stars, luminous blue variables, Wolf-Rayet stars, etc.） provided that the mass involved in the SN explosion is ~ 20 Mo which provides good conditions for forming a QN.  相似文献   

Inter-season and interannual variations in fish and macrocrustacean community structure on a eastern English Channel sandy beach: Influence of environmental factors     

Jonathan Selleslagh  Rachid Amara 《Estuarine, Coastal and Shelf Science》2008,77(4):721-730

The intertidal zone of an exposed sandy beach on the French coast of the English Channel was sampled with a 1.5 m beam-trawl over five years (2000 and 2003–2006) at weekly intervals. The fish and macrocrustacean catches were analysed to determine the inter-season and interannual variation in community structure and relate these variations to changes in the major environmental variables. Only six species (plaice Pleuronectes platessa, common goby Pomatoschistus microps, sprat Sprattus sprattus, sand eel Ammodytes tobianus, brown shrimp Crangon crangon and shore crab Carcinus maenas) from the 27 species captured can be considered as dominant species of the intertidal zone, and they accounted for >90% of total numbers. Most individuals caught were young-of-the-year or juvenile. Analysis of similarities (ANOSIM) and similarities percentage (SIMPER) indicated that inter-season variability of community structure (mean average similarity = 47%) was more pronounced than interannual variability (mean average similarity = 65%). Canonical correspondence analysis (CCA) indicates that a substantial component (32.2%) of the measured inter-season variation in community structure can be explained by environmental factors (mainly water temperature). The main inter-season changes in the abundance and community structure were due to the variation of the six key species and reflect the different times of their recruitment. During the five years of the study, the structure of the fish and macrocrustacean spring community persisted from year to year, with the dominant species reappearing consistently even though their abundances fluctuated from year to year. This interannual variation probably reflects variable recruitment success influenced by physico-chemical conditions. In spite of the considerable interannual variation (40 times) in the spring bloom of the prymnesiophyte alga Phaeocystis globosa we found no effect of this bloom on either fish and macrocrustacean species densities or diversity index.  相似文献   

An 18 000‐year pollen and sedimentary record from the cedar forests of the Middle Atlas,Morocco          下载免费PDF全文

M. NOUR EL BAIT  A. RHOUJJATI  F. EYNAUD  A. BENKADDOUR  L. DEZILEAU  K. WAINER  T. GOSLAR  C. KHATER  J. TABEL  R. CHEDDADI 《第四纪科学杂志》2014,29(5):423-432

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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   

Dispersive Particle Transport: Identification of Macroscale Behavior in Heterogeneous Stratified Subsurface Flows     

Ali Fadili  Rachid Ababou  Roland Lenormand 《Mathematical Geology》1999,31(7):793-840

Dispersive mass transport processes in naturally heterogeneous geological formations (porous media) are investigated based on a particle approach to mass transport and on its numerical implementation using LPT3D, a Lagrangian Particle Tracking 3D code. We are currently using this approach for studying microscale and macroscale space–time behavior (advection, diffusion, dispersion) of tracer plumes, solutes, or miscible fluids, in 1,2,3-dimensional heterogeneous and anisotropic subsurface formations (aquifers, petroleum reservoirs). Our analyses are based on a general advection-diffusion model and numerical scheme where concentrations and fluxes are discretized in terms of particles. The advection-diffusion theory is presented in a probabilistic framework, and in particular, a numerical analysis is developed for the case of advective transport and rotational flows (numerical stability of the explicit Euler scheme). The remainder of the paper is devoted to the behavior of concentration, mass flux density, and statistical moments of the transported tracer plume in the case of heterogeneous steady flow fields, where macroscale dispersion occurs due to geologic heterogeneity and stratification. We focus on the case of perfectly stratified or multilayered media, obtained by generating many horizontal layers with a purely random transverse distribution of permeability and horizontal velocity. In this case, we calculate explicitly the exact mass concentration field C(x, t), mass flux density field f(x, t), and moments. This includes spatial moments and dispersion variance ² _x (t) on a finite domain L, and temporal moments on a finite time scale T, e.g., the mass variance of arrival times ² _T (x). The moments are related to flux concentrations in a way that takes explicitly into account finite space–time scales of analysis (time-dependent tracer mass; spatially variable flow through mass). The multilayered model problem is then used in numerical experiments for testing different ways of recovering information on tracer plume migration, dispersion, concentration and flux fields. Our analyses rely on a probabilistic interpretation that emerges naturally from the particle approach; it is based on spatial moments (particle positions), temporal moments (mass weighted arrival times), and probability densities (both concentrations and fluxes). Finally, as an alternative to direct estimations of the flux and concentration fields, we formulate and study the Moment Inverse Problem. Solving the MIP yields an indirect method for estimating the space–time distribution of flux concentrations based on observed or estimated moments of the plume. The moments may be estimated from field measurements, or numerically computed by particle tracking as we do here.  相似文献   

气象厅的强震波形观测、汇集与服务     

川上徹人 《国际地震动态》1999,(5):29-30

目前,气象厅的数字强震波形观测和汇集业务是采用９５型烈度计实施的。现已在全日本以２０ｋｍ的间隔布设了约６００个采用９５型烈度计的全国性观测网（其中气象厅约１５０个,都市约１３０个,郡约１４０个,海啸地震早期检测网测点约１６０个,机动观测点约２０个）。...  相似文献   

Towards a microzonation of the Greater Beirut area: an instrumental approach combining earthquake and ambient vibration recordings     

Marleine Brax  Pierre-Yves Bard  Anne-Marie Duval  Etienne Bertrand  Muhsin-Elie Rahhal  Rachid Jomaa  Cécile Cornou  Christophe Voisin  Alexandre Sursock 《Bulletin of Earthquake Engineering》2018,16(12):5735-5767

Lebanon is situated on the 1000 km long Levant transform fault that separates the Arabic from the African tectonic plates. In Lebanon, the Levant fault splits up into a set of ramifications that had, in the past, generated major destructive earthquakes causing a lot of destruction and thousands of casualties. The most devastating one was the 551 A.D. offshore earthquake that destroyed Beirut, the capital of Lebanon. This paper presents a site effect study in Beirut, aimed at proposing a framework for future microzonation works in the city. It includes two complementary parts. A 6-month, temporary seismological experiment was first conducted to estimate the site response at 10 sites sampling the main geological units of Beirut on the basis of local and regional earthquake recordings. This spatially sparse information was then complemented by a large number (615) of microtremor measurements covering the Beirut municipality and part of its suburbs with a 400 m dense grid. The recordings were analysed with the standard site-to-reference and horizontal-to-vertical spectral ratio methods for earthquake recordings, and the horizontal-to-vertical ratio for ambient noise recordings. Significant ground motion amplification effects (up to a factor of 8) are found in a few areas corresponding to recent deposits. The consistency between results from earthquake and microtremor recordings allows proposing a map of the resonance frequencies within the city and its suburbs, with frequencies ranging from 0.5 to 5 Hz for the deepest deposits, and 5–10 Hz for shallow areas. Finally, the results are discussed and a way to combine the results obtained from the temporary stations to the great number of recordings coming from the permanent Lebanese network is proposed.  相似文献   

Fish composition and assemblage structure in three Eastern English Channel macrotidal estuaries: A comparison with other French estuaries     

Jonathan Selleslagh  Rachid Amara  Pascal Laffargue  Sandric Lesourd  Mario Lepage  Michel Girardin 《Estuarine, Coastal and Shelf Science》2009

This study has analysed for the first time fish composition and assemblage structures of three small macrotidal estuaries of the Eastern English Channel (EEC) and has explored the influences of 19 biotic and abiotic variables on the fish assemblages. Fish from Canche, Authie and Somme estuaries were collected during spring (June 2006 and May 2007) and autumn (September 2006) along the estuarine gradients using a 1.5 m beam trawl. Using identical sampling protocols, the study also analysed and compared for the first time taxonomic and functional aspects of the fish assemblages in 15 estuaries located along the Atlantic and English Channel coasts. SIMPER analysis showed high similarities in fish assemblages in the three EEC estuaries and during either spring or autumn periods. However, intra-estuary similarities were relatively low, indicating that fish assemblage structures (species richnesses or abundances) were more variable within the estuary (salinity gradient) than between estuaries and/or seasons (spring vs autumn). Although numerous environmental variables were included in the study, only 47% of the variability observed in the fish distribution was explained. Fish spatial variations in the EEC estuaries are mostly driven by abiotic variables as opposed to biological interactions. As indicated by CCA, salinity and muddy sediments were the two most important factors structuring the fish assemblages. The macrobenthos being very abundant in the EEC estuaries (580–1121 ind. m⁻²), the availability of potential prey is probably not a limiting factor in the utilization of estuaries by fish. Contrary to the majority of French estuaries dominated by estuarine species (ES), the fish assemblages of the EEC estuaries are clearly dominated by marine migrant (MM) species (65% on average) with high abundance of juveniles (mostly young-of-the-year). Cluster and SIMPROF's analyses distinguished the functional structure of the 15 estuarine fish assemblages into different clusters. The three EEC estuaries form a similar group with the largest French estuaries (Seine, Loire and Gironde). The latters were characterized by higher MM/ES ratio compared to the other French estuaries. Freshwater flow and tidal range were the main factors associated with this group of estuaries. The results of the present study do not indicate that anthropogenic impacts (chemical contamination) on estuaries affect their ecological functioning as described by the fish ecological guilds. It is suggested that the guild approach may not be useful to provide valuable information on the ecological status of estuaries.  相似文献   

A new species of extinct genus Lycopodites from Lower to Middle Jurassic sediments of Irkutsk coal basin (Eastern Siberia)     

Andrei O. Frolov  Irina M. Mashchuk 《世界地质(英文版)》2014,17(1):1-10

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