长江口北支倒灌影响区盐度预测经验模型   总被引：1，自引：0，他引：1       下载免费PDF全文

孙昭华  严鑫  谢翠松  李奇 《水科学进展》2017,28(2):213-222

为预测不同径流过程影响下的盐水入侵强度,以长江口南支上段为研究对象,采用实测资料和理论分析相结合,建立了以大通流量和农历日期快速估算氯度值的经验模型。首先,以徐六泾实测潮位资料结合调和分析理论,在考虑11个主要分潮情况下证明日均潮差为半月周期函数,提出了用农历日期估算日均潮差的方法;其次,采用东风西沙实测氯度资料,选用不同函数形式,分析了以支汊盐水倒灌为主的情况下日均氯度对径流、潮差的量化响应关系;最后,提出了指数函数形式的氯度预测经验模型,模型计算值与实测值之间的决定系数在0.8以上。提出的经验模型可由大通流量快速估算特定位置的盐度,为相关的工程和规划研究提供了便捷途径。  相似文献   

Experimental floods in the River Spöl,Swiss National Park: Framework,objectives and design     

Thomas?ScheurerEmail author  Peter?Molinari 《Aquatic Sciences - Research Across Boundaries》2003,65(3):183-190

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Climatic change recorded by stable isotopes and trace elements in a British Holocene tufa   总被引：1，自引：0，他引：1  

E. R. Garnett  J. E. Andrews  R. C. Preece  P. F. Dennis 《第四纪科学杂志》2004,19(3):251-262

Combined stable isotope (δ¹⁸O and δ¹³C) and trace element (Mg, Sr) geochemistry from bulk tufa calcite and ostracod shell calcite from an early Holocene British tufa reveal clear records of Holocene palaeoclimatic change. Variation in δ¹⁸O is caused principally by change in the isotopic composition of Holocene rainfall (recharge), itself caused mainly by change in air temperature. The δ¹³C variability through much of the deposit reflects increasing influence of soil‐zone CO₂, owing to progressive woodland soil development. Bulk tufa Mg/Ca and Sr/Ca are controlled by their concentrations in the spring water. Importantly, Mg/Ca ratios are not related to δ¹⁸O values and thus show no temperature dependence. First‐order sympathetic relationships between δ¹³C values and Mg/Ca and Sr/Ca are controlled by aquifer processes (residence times, CO₂ degassing and calcite dissolution/reprecipitation) and probably record intensity of palaeorainfall (recharge) effects. Stable isotope records from ostracod shells show evidence of vital effects relative to bulk tufa data. The ostracod isotopic records are markedly ‘spiky’ because the ostracods record ‘snapshots’ of relatively short duration (years), whereas the bulk tufa samples record averages of longer time periods, probably decades. The δ¹⁸O record appears to show early Holocene warming, a thermal maximum at ca. 8900 cal. yr BP and the global 8200 yr BP cold event. Combined δ¹³C, Mg/Ca and Sr/Ca data suggest that early Holocene warming was accompanied by decreasing rainfall intensity. The Mg/Ca data suggest that the 8200 yr BP cold event was also dry. Warmer and wetter conditions were re‐established after the 8200 yr BP cold event until the top of the preserved tufa sequence at ca. 7100 cal. yr BP. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

桂林甑皮岩洞穴遗址钙华板14C年代学研究   总被引：2，自引：3，他引：2       下载免费PDF全文

王华  张会领  涂林玲  覃嘉铭  冯玉梅 《地球学报》2005,26(4):333-336

甑皮岩遗址是新石器时代保存较完整的一个人类洞穴遗址，距今有8．0～12．0ka的历史。本文通过对洞穴遗址钙华板^14C年代的测定，并对比了遗址内贝壳和木炭的^14C年代。初步论证了钙华板^14C年代的可靠性，并探讨甑皮岩古人类活动及穴居的最后年代为6．6ka BP。通过对钙华板^14C年代研究为遗址洞穴地层的划分提供了新的年代依据。  相似文献   

C and O stable isotope variability in recent freshwater carbonates (River Krka, Croatia)     

S. Lojen  T. Dolenec†‡  B. Vokal‡  N. Cukrov§  G. Mihel&#;i&#;§  W. Papesch¶ 《Sedimentology》2004,51(2):361-375

Three types of recent carbonate precipitates from the River Krka, Croatia, were analysed: (1) bulk tufa from four main cascades in a 34 km long section of the river flow through the Krka National Park; (2) a laminar stromatolite‐like incrustation formed in the tunnel of a hydroelectric power plant close to the lowest cascade; and (3) recent precipitates collected on artificial substrates during winter, spring and summer periods. Stable isotope compositions of carbon (δ¹³C) and oxygen (δ¹⁸O) in the carbonate and organic carbon (δ¹³C_org) were determined and compared with δ¹⁸O of water and δ¹³C of dissolved inorganic carbon (DIC). The source of DIC, which provides C for tufa precipitation, was determined from the slope of the line ([DIC]/[DIC₀]?1) vs. (δ¹³C‐DIC × ([DIC]/[DIC₀])) ( Sayles & Curry, 1988 ). The δ¹³C value of added DIC was ?13·6‰, corresponding to the dissolution of CO₂ with δ¹³C between ?19·5 and ?23·0‰ Vienna Pee Dee Belemnite (VPDB). The observed difference between the measured and calculated equilibrium temperature of precipitation of bulk tufa barriers indicates that the higher the water temperature, the larger the error in the estimated temperature of precipitation. This implies that the climatic signals may be valid only in tufas precipitated at lower and relatively stable temperatures. The laminar crust comprising a continuous record of the last 40 years of precipitation shows a consistent trend of increasing δ¹³C and decreasing δ¹⁸O. The lack of covariation between δ¹³C and δ¹⁸O indicates that precipitation of calcite was not kinetically controlled for either of the elements. δ¹³C and δ¹⁸O of precipitates collected on different artificial substrates show that surface characteristics both of substrates and colonizing biota play an important role in C and O isotope fractionation during carbonate precipitation.  相似文献   

Petrographic and trace element analysis of uranium-rich tufa calcite, middle Miocene Barstow Formation, California, USA     

Jennifer M. Cole  E. Troy Rasbury†  Isabel P. Montañez‡  Vicki A. Pedone§  Antonio Lanzirotti¶  Gilbert N. Hanson† 《Sedimentology》2004,51(3):433-453

An integrated petrographic and spectroscopic (X‐ray diffraction, phosphor imaging and synchrotron X‐ray absorption spectroscopy) study of tufas from the Miocene Barstow Formation, California, relates sample morphology, mineralogy and geochemical composition. The tufas, composed mainly of calcite that formed at the interface between an ancient alkaline lake and ground or spring waters, have textures similar to those of microbially mediated terrestrial stromatolites and travertines. The tufas have elevated concentrations of a number of trace elements including Mn, Fe, Sr and U. Synchrotron X‐ray fluorescence analyses show that U concentrations can exceed 500 p.p.m. X‐ray absorption spectroscopy indicates that the U in these samples is incorporated as U(IV). It is suggested here that alkaline lake waters had a high U/Ca ratio and tufa calcite formed where groundwater or (possibly epithermal) springs brought in Ca and trace elements such as Sr. The rapid, and possibly microbially mediated, precipitation of calcite allowed for incorporation of high concentrations of trace metals as either structural substitutes or extremely fine‐scale inclusions.  相似文献   

The formation and environmental significance of calcite rafts in tropical tufa-depositing rivers of northern Australia     

M. P. Taylor  R. N. Drysdale†  K. D Carthew 《Sedimentology》2004,51(5):1089-1101

Spring‐fed rivers of the Barkly karst in tropical northern Australia form an array of tufa and related freshwater carbonate deposits. One of these deposits, calcite rafts, is precipitated at the water–air interface principally as a consequence of CO₂ degassing and evaporation. Calcite rafts have been reported in cave environments but have not been described in detail from fluvial systems. Observations using scanning electron microscopy coupled with water chemistry data reveal that they form by a combination of physical, chemical and biological processes. They grow downwards into the water column and form a dentate lower surface, while a flat upper surface occurs at the water–air interface. The rafts are readily inhabited by microorganisms, particularly diatoms, which frequently become entombed by calcite as the rafts develop. The decay of the biological material leaves voids, creating a pock‐marked texture. The rafts are subject to secondary calcite growth along the crystal edges. Once they become submerged in the water column after disturbance of the water surface, they may become completely covered by this overgrowth, creating a homogeneous veneer. The rafts form in quiescent settings, principally behind tufa dams in large, lake‐like water bodies along each river. Therefore, they can be used in conjunction with adjacent exposures of other tufa facies to decipher palaeohydrological conditions. Although the rafts are extremely thin and fragile, they are readily preserved within fossil waterhole facies, and their occurrence has been identified in rocks from the Quaternary to the Tertiary.  相似文献   

Stable Carbon Isotope Geochemical and Hydrochemical Features in the System of Carbonate-H_2O-CO_2 and Their Implications—Evidence from Several Typical Karst Areas of China   总被引：6，自引：0，他引：6  

Liu Zaihu  Yuan Daoxian  He Shiyi Institute of Karst Geology  Qixing Rd.  Guilin  Guangxi 《《地质学报》英文版》1997,71(4):446-454

On the basis of hydrochemical observation and experimental calculation, the features of stable carbon isotope geochemistry in the karst dynamic systems of the Guilin Karst Experimental Site, Huanglong Ravine and Wujiangdu Dam Site are summarized in this study. Furthermore, an attempt has been made to solve several geochemical problems, such as the origin of CO2 in the system, kinetic fractionation of carbon isotopes during calcite deposition, hydrochemistry and formation of tufa, and carbon-14 dating of tufa of hydrothermal origin. The results show that three kinds of karst dynamic system can be distinguished: (1) the shallow system, such as the Guilin Karst Experimental Site, in which soil CO2 provides the an active agent for karst processes; (2) the geothermal system, such as the Huanglong Ravine, in which metamorphic or/ and juvenile CO, is the source of activity for karst; (3) the anthropogenic system, such as the Wujiangdu Dam Site, in which the stable carbon isotope geochemical and hydrochemical f  相似文献   

美国西尔斯盐湖钙华研究综述     

李瑞琴  刘成林  LOWENSTEIN T K 《岩石矿物学杂志》2021,40(5):965-976

钙华具有重要的科研价值。美国加利福尼亚州西尔斯湖内北部、中部和西南部广泛发育钙华丘,丘状体的高度从几厘米至45 m不等,通常高度为5～12 m。钙华丘内存在4种沉积相,分别为多孔海绵状钙华沉积相、结壳状钙华沉积相、柱状钙华沉积相和薄层结壳状钙华沉积相。从时空分布来讲,钙华呈两种沉积层序,分别为多孔海绵状钙华沉积相-结壳状钙华沉积相-薄层结壳状钙华沉积相-多孔海绵状钙华沉积相和多孔海绵状钙华沉积相-柱状钙华沉积相-薄层结壳状钙华沉积相-多孔海绵状钙华沉积相。这些钙华主要由方解石和文石组成,从微观尺度来讲,主要由纳米球晶体和棒状晶体组成,被解释为是微生物作用活动的结果。钙华沉积相中δ~(13)C的测定结果均为正值,表明西尔斯湖钙华属于热成因钙华。对西尔斯湖钙华主要沉积类型及沉积成因的讨论,可以为我国钙华研究提供对比参考资料。  相似文献   

长春城市土地生态区的生态建设   总被引：5，自引：1，他引：4  

刘惠清  许嘉巍  卜兆君 《地理研究》1999,18(3):267-272

城市是以土地为基础,以人为中心的自然社会经济复合系统,根据物流、能流与信息流联系的强弱,把长春市划分为48个土地生态元,以土地生态元组合的相似性为依据将其合并为8个各具特色的土地生态区。根据各土地生态区存在的问题,在仿自然原型的基础上,对其进行人与自然共同创造的设计,将长春市建成既符合人类利益又不违背生物圈组织原则的理想城市。  相似文献