胡安·德富卡洋中脊富锌烟囱体流体通道演化特征     

董从芳  周怀阳  彭晓彤  袁远  姚会强 《海洋学报》2012,34(4):99-108

对采自Faulty Towers(47°57.447'N,129°6.568'W)硫化物烟囱群一个不再活动的烟囱体硫化物开展了详细的矿物学和地球化学研究。样品从外壁往内壁方向可划分为4个矿物组合带,分别为重晶石-无定形硅-铁氧羟化物带;白铁矿-黄铁矿-无定形硅-重晶石带;白铁矿-黄铁矿-闪锌矿-纤锌矿带;纤锌矿-黄铜矿-白铁矿带。从底部到顶部,样品通道形态主要有3种:不规则、不连续的多通道;椭圆形单通道;封闭的通道。矿物学研究证实,烟囱体以低温矿物组合白铁矿、纤锌矿为主,高温矿物黄铜矿少见,仅局限分布在流体通道附近。210Pb定年结果表明,烟囱壁形成经历较短时间(约3 a),而通道的闭合则经历了相对长的过程(约17 a)。结合矿物学研究,最终恢复了整个尖塔结构的生长历史。  相似文献   

^210Pb Chronology and Trace Metal Geochemistry in the Intertidal Sediment of Qinjiang River Estuary, China^210Pb Chronology and Trace Metal Geochemistry in the Intertidal Sediment of Qinjiang River Estuary, China     

XIA Peng  MENG Xianwei  FENG Aiping  YIN Ping  WANG Xiangqin  ZHANG Jun 《青岛海洋大学学报(英文版)》2012,(2):165-173

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137Cs and 210Pbex as soil erosion tracers in the hilly Sichuan Basin and the Three Gorges area of China     

Zhonglin Shi  Anbang Wen  Xinbao Zhang  Xiubin He  Hao Li  Dongchun Yan 《山地科学学报》2012,9(1):27-33

Accelerated soil erosion and land degradation represent major environmental problems for agricultural lands.Reliable information on the rates of soil loss is urgently needed.The traditional techniques for documenting rates of soil loss may meet this need,but face many limitations.The fallout radionuclides,especially 137 Cs and 210 Pb ex,are increasingly used as effective tracers to quantify soil erosion rates,and they represent a valuable complement to the existing classical methods.This paper aims to introduce the basis for assessing soil erosion rates on cultivated and uncultivated slopes by using 137 Cs and 210 Pb ex measurements,to compare the 137 Cs and 210 Pb ex reference inventories,and to report several case studies undertaken in the hilly area of Sichuan Basin and the Three Gorges area of China.  相似文献   

Establishing Holocene sediment core chronologies for northern Ungava lakes, Canada, using humic acids (AMS C) and Pb     

milie Saulnier-Talbot  Reinhard Pienitz  Thomas W. Stafford Jr. 《Quaternary Geochronology》2009,4(4):278-287

The absence of datable macrofossils in six sediment cores recovered from northern Ungava (Canada) lakes constituted a major challenge for the establishment of reliable lacustrine chronologies for the Holocene. Consequently, AMS radiocarbon dating of humic acids was used to assess age–depth in the cores. The reliability of the radiocarbon results near some of the core tops was evaluated through ²¹⁰Pb dating. The offset of sediment radiocarbon ages with their most probable time of formation and deposition in the lakes was found to be in the order of about 1000 years for recently deposited sediments. However, the basal dates in one core covering the entire postglacial period yielded a remarkable fit with previously established dates performed on marine shells at the maximum marine limit. Hence, the aim of this study was to describe how the two dating methods can be combined to address some of the problems paleolimnologists face when trying to assign ages to high-latitude lake sediment records. Suggestions are made for improving the quality of age–depth models developed in future studies for northernmost Québec and other comparable regions where paleolimnologists must deal with the combined challenges of very slow sediment accumulation rates in lakes, an extreme paucity of datable material and the sequestration of old carbon in the watersheds.  相似文献   

Mercury contamination history of an estuarine floodplain reconstructed from a Pb-dated sediment core (Berg River, South Africa)     

T.J. Kading  R.P. Mason  J.J. Leaner 《Marine pollution bulletin》2009,59(4-7):116

Mercury deposition histories have been scarcely documented in the southern hemisphere. A sediment core was collected from the ecologically important estuarine floodplain of the Berg River (South Africa). We establish the concentration of Hg in this ²¹⁰Pb-dated sediment core at <50 ng g⁻¹ Hg_T throughout the core, but with 1.3 ng g⁻¹ methylmercury in surface sediments. The ²¹⁰Pb dating of the core provides a first record of mercury deposition to the site and reveals the onset of enhanced mercury deposition in 1970. The ratio of methylmercury to total mercury is relatively high in these sediments when compared to other wetlands.  相似文献   

Floodplain development in an engineered setting     

Michael Bliss Singer  Rolf Aalto 《地球表面变化过程与地形》2009,34(2):291-304

Engineered flood bypasses, or simplified conveyance floodplains, are natural laboratories in which to observe floodplain development and therefore present an opportunity to assess delivery to and sedimentation within a specific class of floodplain. The effects of floods in the Sacramento River basin were investigated by analyzing hydrograph characteristics, estimating event‐based sediment discharges and reach erosion/deposition through its bypass system and observing sedimentation patterns with field data. Sediment routing for a large, iconic flood suggests high rates of sedimentation in major bypasses, which is corroborated by data for one bypass area from sedimentation pads, floodplain cores and sediment removal reporting from a government agency. These indicate a consistent spatial pattern of high sediment accumulation both upstream and downstream of lateral flow diversions and negligible sedimentation in a ‘hydraulic shadow’ directly downstream of a diversion weir. The pads located downstream of the shadow recorded several centimeters of deposition during a moderate flood in 2006, increasing downstream to a peak of ～10 cm thick and thinning rapidly thereafter. Flood deposits in the sediment cores agree with this spatial pattern, containing discrete sedimentation layers (from preceding floods) that increase in thickness with distance downstream of the bypass entrance to several decimeters thick at the peak and then thin downstream. These patterns suggest that a quasi‐natural physical process of levee construction by advective overbank transport and deposition of sediment is operating. The results improve understanding of the evolution of bypass flood control structures, the transport and deposition of sediment within these environments and the evolution of one class of natural levee systems. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

黄海和渤海沉积物 210Pb活度的分布特征   总被引：3，自引：1，他引：2  

齐君  李凤业  宋金明 《地球化学》2005,34(4):47-52

利用α多道能谱仪测定了黄海和渤海海域 58个表层沉积物样品的 210Pb活度,探讨了黄海和渤海表层沉积物中 210Pb活度的空间分布特征.渤海中部、北黄海中部泥质沉积区和南黄海中部泥质沉积区是 210Pb活度的高值区.渤海湾内、莱州湾内及北黄海西南部沿岸海域则是 210Pb活度的低值区.黄海和渤海海区 210Pb的富集、分布特征受到研究海区水动力条件和沉积物粒级的制约.根据位于黄海和渤海泥质沉积区的 3个岩芯 210Pb活度的垂直分布资料,并结合 2个站位所取岩芯的 210Pb活度的垂直分布资料,探讨了 210Pb活度的垂直分布与沉积环境之间的关系.黄海和渤海 210Pb活度呈现高值的泥质沉积区,其 210Pb活度随岩芯深度衰减的垂直分布很有规律且沉积速率较低,由此可以反映泥质沉积区稳定的沉积环境.  相似文献   

南极普里兹湾海域的近现代沉积速率     

于培松  扈传昱  刘小涯  潘建明  张海生 《沉积学报》2009,27(6):1172-1177

沉积速率主要受上层海洋生物生产的影响,而在湾口浅滩区沉积速率则主要受底栖生物的影响。此外,水流、水体稳定度、冰封期长短和海底地形等条件也对沉积速率产生一定的利用中国第21次南极科学考察获得的普里兹湾海域的沉积物样品,运用沉积地层同位素210Pb测年技术,探讨了该海域沉积物的近现代沉积速率及其影响因素。研究结果表明,南极普里兹湾海域的近现代沉积速率变化范围在0.47～1.88 mm/a之间,平均值为1.06 mm/a,高于南极罗斯海而低于威德尔海,总体上与南、北极多个海区的沉积速率相当。在湾内和冰架边缘区影响,沉积速率的分布是多种因素共同控制的结果。在生物量较高、水体条件较为稳定的湾内中心区域,沉积速率较高,而冰架边缘区的沉积速率则较低  相似文献   

Sedimentation and chronology of heavy metal pollution in Oslo harbor, Norway   总被引：2，自引：0，他引：2  

Aivo Lepland  Thorbjørn J. Andersen  Hans Peter H. Arp  Gijs D. Breedveld  Anders Rindby 《Marine pollution bulletin》2010,60(9):1512-1522

Stratigraphic profiles of Cu, Cd and Hg in ten sediment cores from the Oslo harbor, Norway, combined with results of radiometric dating demonstrate that pollution by these metals peaked between 1940 and 1970. Dating results indicate that Hg discharges peaked between 1940 and 1950, Cd reached maximum ca. 1955-1960, and Cu has the highest concentration in sediment interval corresponding to ca. 1970. Geochemical profiles and maxima of Cu, Cd and Hg concentrations can be used as chronostratigraphic markers for sediment cores from the Oslo harbor. Acoustic backscatter and sediment core data indicate that propeller wash affects the seabed in the Oslo harbor. The propeller-induced turbulence causes erosion, and in places exposes and remobilizes contaminated sediments that accumulated in the harbor during previous decades. Such re-exposure of contaminated sediments could be detrimental to local ecosystems and offset remediation efforts, warranting further impact studies and potential mitigation strategies to prevent redistribution.  相似文献   

利用~(210)Pb、~(137)Cs和~(241)Am计年法测算云南抚仙湖现代沉积速率   总被引：2，自引：0，他引：2  

王小雷  杨浩  赵其国  魏荣菲 《湖泊科学》2010,22(1)

通过对云南抚仙湖沉积物柱芯样品的~(210)Pb、~(137)Cs和~(241)Am测试表明,柱芯剖面上有明显的1963年和1986年~(137)Cs蓄积峰,验证了1975年次级蓄积峰存在的可能性,这些峰形完好的蓄积峰对抚仙湖的现代沉积环境有明显的时标意义。利用~(137)Cs计年法得到抚仙湖沉积物自1963年、1975年及1986年以来到2007年的平均沉积速率分别为0.063g/(cm~2·a)、0.052g/(cm~2·a)和0.039g/(cm~2·a),说明了过去近五十年抚仙湖沉积速率整体上经历了一个由快到慢的过程。借助于~(241)Am的1963年蓄积峰可以提高~(137)Cs计年的准确性。根据~(210)Pb CRS计年模式,计算出每个样品深度所对应的年代,与~(137)Cs计年法比较存在一定的偏差,分析了两种计年方法存在差异性的原因。通过质量深度和年代分析,抚仙湖的沉积速率变化幅度比较大,表明抚仙湖近129年来的沉积环境不稳定,可能与相应历史时期的人类活动有密切的关系。  相似文献