PCBs in Central Vietnam coastal lagoons: levels and trends in dynamic environments     

Giuliani S  Piazza R  Bellucci LG  Cu NH  Vecchiato M  Romano S  Mugnai C  Nhon DH  Frignani M 《Marine pollution bulletin》2011,62(5):1013-1024

PCBs were analysed in surficial sediments and selected sediment cores collected between 2002 and 2008 in Central Vietnam coastal lagoons. The aim was to determine contamination levels and trends, and to evaluate the effects of anthropogenic pressures and natural events. Samples were mostly fine-grained with low total PCB concentrations (0.367-44.7 μg kg⁻¹). Atmospheric transport and post depositional processes modify to some degree the fingerprint of PCB inputs to the environment favouring the predominance of 3, 4 and 5 chlorinated congeners. The similarity of congener distributions in contemporary surficial samples also suggests the presence of a unique source over the entire study area, probably connected to mobilisation and long range transports from land-based stocks. The removal of consistent sediment layers is hypothesised based on repeated samplings of the same area. Natural meteorological events (such as typhoons) are suspected to be responsible for these sediment losses.  相似文献   

越南西北部大象山超高温变质岩的发现及其区域构造意义   总被引：1，自引：1，他引：0  

吴虎峻  刘俊来  TRAN MyDung  NGUYEN QuangLuat  PHAM Binh  吴文彬  陈文  张招崇 《岩石学报》2011,27(9):2809-2820

越南西北部大象山群孔兹岩系中发育一套含刚玉+尖晶石+石榴石+夕线石组合的富铝岩石块体,它们呈透镜状包体形式赋存于孔兹岩系内。岩石中刚玉+尖晶石+石榴石+夕线石组合的发育指示岩石经历了超高温变质作用的改造。其中尖晶石和石英的共生组合表明了变质温度高于900℃,而利用岩石退变质矿物组合中的黑云母-石榴石温度计,黑云母-斜长石-石榴石-石英组合温度-压力计估算的变质温度压力条件分别为879~917℃、0.90~0.94GPa。岩石中的早期刚玉+夕线石的组合的存在说明岩石变质作用已经从高角闪岩相进入到了麻粒岩相;而峰期变质矿物组合尖晶石+石英的出现,指示了变质温度高于900℃的超高温变质作用。另一方面,退变质过程中钛铁矿的发育表明岩石经历了快速抬升降压的过程。变质作用的P-T轨迹分析揭示出岩石经历了早期同步升温增压后的快速增温达到峰期条件,后经历快速等温减压过程。这种温压条件的变化与板块会聚过程中由于俯冲板片的断离而使软流圈上涌造成热异常的温压条件变化基本一致。通过对超高温变质岩石进行锆石SIMS U-Pb测年获得的结果大于58Ma,推测这次超高温变质与喜马拉雅运动中印度与欧亚大陆的初期会聚-碰撞作用相关。  相似文献   

东南亚中南半岛与中国西南邻区地层分区及沉积演化历史   总被引：3，自引：1，他引：2       下载免费PDF全文

施美凤林方成  李兴振凌小明 石洪召 《中国地质》2011,38(5):1244-1256

本文通过对东南亚中南半岛的缅甸、泰国、柬埔寨、老挝、越南五国及毗邻的中国西南地区地层的对比研究,依据研究区构造演化、沉积岩石组合和古生物群特征将整个区域划分为5个地层分区:冈瓦纳型的印度地层区、过渡型亲冈瓦纳的滇缅马地层区、过渡型亲华南的印支地层区、属劳亚大陆的扬子地层区和华夏地层区。论述了地层区的基本特征,并进一步对各地层区间做了沉积演化对比,进而阐明了区域的重要构造事件与洋盆沉积演化历史。  相似文献   

Searching for (un)sustainabilty in pangasius aquaculture: A political economy of quality in European retail     

Simon R. Bush  Marjolein Duijf 《Geoforum》2011,42(2):185-196

Drawing on a political economy of food quality, this paper investigates the main sources of uncertainty over the environmental sustainability of Vietnamese pangasius catfish in European markets and how retailers subsequently respond to these uncertainties. Based on media survey and interviews with supermarket retailers across Europe between 2008 and 2010, the analysis focuses on the claims and counterclaims over the sustainability of pangasius aquaculture, how retailers have dealt with the uncertainty these claims have engendered about the fish, and what effect this uncertainty has had on the potential of marketing ‘sustainable pangasius’ in European supermarkets. The paper concludes that successful claims around new food qualities like sustainability by retailers are dependent on the ability of regulatory networks to overcome any perceived illegitimacy of imported products in the face of continuing uncertainty and the wider politics of market protectionism.  相似文献   

The social relations of catfish production in Vietnam     

Ben Belton  David C. Little 《Geoforum》2011,42(5):567-577

The growth of intensive export-oriented Pangasius catfish production in Vietnam’s Mekong Delta is unparalleled in terms of rapidity and scale by any other agricultural sector, with production climbing from a low base to more than 1 million tons in a single decade. This paper examines the effects of this remarkable change on the rural class structure in locations where catfish farming has boomed, and analyses the role of local state-society relations in mediating outcomes resulting from the integration of local actors into the global value chain. We conclude that private economic activity is deeply embedded in informal relations with the state bureaucracy in Vietnam, with the result that the expansion of catfish aquaculture has generally acted to reproduce and entrench existing class relations rather leading to a radical reconfiguration of the rural class structure.  相似文献   

Stress state in the Cuu Long and Nam Con Son basins, offshore Vietnam     

Nguyen Thi Thanh Binh  Tomochika TokunagaNeil R. Goulty  Hoang Phuoc SonMai Van Binh 《Marine and Petroleum Geology》2011,28(5):973-979

The results presented in this paper are the first published estimates of the complete stress tensor in the Cuu Long and Nam Con Son basins, offshore Vietnam. We analysed in situ stress and pore pressure fields in the sedimentary formations using data from petroleum exploration and production wells to evaluate the stress state in these basins. The data were obtained from the seafloor to 4300 m burial depth and include both hydrostatic and overpressured sections. Minimum horizontal stresses were obtained from extended leak-off tests and mini-fracture tests. Maximum horizontal stresses were estimated from drilling-induced fracture parameters and borehole breakout widths in twelve wells using rock properties measured in the laboratory or estimated empirically from wireline logs. Seven data points are located in sediments, and seventeen data points in igneous basement rocks at depths greater than 3000 m.The estimated magnitudes of σ_H are 70-110% of the σ_v magnitudes. Considering the errors in the stress magnitude estimates, their relative magnitudes suggest that a borderline normal/strike-slip stress regime presently exists in normally pressured sequences of the Nam Con Son and Cuu Long basins. Of the twenty-four data points, twenty have effective stress ratios at a critical stress state for faulting on the assumption that there are faults present that are optimally oriented for failure with friction coefficients of ∼0.5. The results suggest that the stress state in these basins is generally critical.  相似文献   

中国—东盟自贸区边境效应实证分析——以滇桂对越进出口为例     

李红  方冬莉 《世界地理研究》2011,(3):27-33,94

本文将边境效应划分为狭义与广义两类,认为广义边境效应包括正负两层效应且随贸易自由化进程动态演进。通过边境省区占相邻两国贸易的比重这一反映边境效应的指数,并对自由贸易进程中的中越边境云南（滇）与广西（桂）两省区2004～2009年对越进出口月度时间序列计量分析,发现边境效应的演进在省际间具有稳定的互动关系,包括力度不同的相互促进与竞争等关联,文章同时探讨边境效应的内外成因,提出以区域合作及协调发展提升边境正效应的沿边开放策略。  相似文献   

东南亚缅泰老越柬五国与中国邻区成矿带划分及成矿特征   总被引：3，自引：0，他引：3       下载免费PDF全文

施美凤  林方成  刘朝基  李兴振  王宏 《沉积与特提斯地质》2013,33(2):103-112

东南亚缅泰老越柬五国与中国西南邻区在大地构造上位于特提斯构造域东段与西太平洋构造域相交接地带,复杂的地质构造演化造就了该区丰富的矿产资源.通过近年来对东南亚中南半岛及中国邻区的地层、构造、岩浆及矿产研究,在大地构造单元划分基础上,本文将研究区划分为两个一级成矿域(特提斯成矿域、环太平洋成矿域)、3个二级成矿省(滇缅马成矿省、印支成矿省、扬子-华夏成矿省)和17个三级成矿带.并对各成矿带的地质及成矿特征进行了简单阐述.  相似文献