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1.
<正>湖泊是陆地水圈的重要组成部分,受大气圈、水圈、岩石圈和生物圈共同影响,是各个圈层相互作用的连接点。湖泊接纳了来自地表丰富的侵蚀物质,是陆地环境变化的天然档案馆,形成了较为完整的湖泊沉积物。湖泊沉积物不同赋存形态Rb/Sr比值可以反演流域搬运与化学风化作用:非残渣态Rb/Sr比值反映流域化学风化作  相似文献   

2.
湖泊沉积物Rb/Sr比值在古气候/古环境研究中的应用与展望   总被引:4,自引:1,他引:3  
Rb和Sr在赋存矿物和表生地球化学行为等方面存在显著差异,因而各种记录体中的Rb/Sr比值被广泛应用于古气候/古环境研究。湖泊沉积物中的Rb、Sr主要包括2部分来源:一是流域物理侵蚀直接带来的陆源碎屑组分,在沉积物中多以残渣态(碎屑矿物)形式存在;二是流域化学风化带来的溶解态物质,在湖泊水体中通过物理吸附、化学沉淀和生...  相似文献   

3.
利用湖泊沉积物中Rb/Sr值来反映受古气候制约的流域陆地化学风化率的变化,并恢复了岱海近400a以来以小冰期为特征的、具有100a准周期(经谱分析)的气候波动历史。通过磁化率、粘土矿物含量和种类的综合分析,确证了湖泊沉积物Rb/Sr值的变化可以用来重建流域内化学风化率与其相应的古气候演化过程,是湖泊沉积记录中具有比磁化率更明显气候意义的有效代用指标。  相似文献   

4.
喀斯特地区的生态环境具有先天脆弱性,对气候变化响应敏感,是研究气候变化-生态环境变化耦合关系的理想场所.选取我国典型喀斯特地区湖泊白鹇湖为研究对象,系统分析了沉积物柱芯有机质C/N比值、Sr/Rb比值和孢粉的剖面变化.研究结果表明,白鹇湖地区3.6~2.2kaB.P.气候持续向干旱化方向发展,导致流域陆地植被显著退化,草本植物减少,蕨类植物增加,湖泊陆源有机质输入减少,沉积物有机质C/N比值降低.该干旱事件还导致流域化学风化作用减弱,Sr/Rb比值增大.白鹇湖过去5000年的气候与生态环境变化历史表明自然气候变化对喀斯特生态环境可产生重大影响,为喀斯特生态环境先天脆弱性提供了历史性证据.  相似文献   

5.
黄旗海湖泊柱状沉积物的全样、77~20 μm、<20 μm粒级的钛(Ti)、锰(Mn)、锶(Sr)、銣(Rb)、钡(Ba)、锆(Zr)等元素含量分析表明,元素在湖泊沉积物各粒级组分的丰度存在较大差异:Ti、Zr倾向于在粗颗粒中富集,Mn、Sr、Rb倾向于在细颗粒中富集,Ba的富集粒级不明显。Ti、Zr与Mn、Rb的颗粒粒级富集倾向可能是其硅酸盐矿物颗粒碎化过程的结果,而Sr则与湖泊自生碳酸盐有关。元素比值Zrc/(Rbc+Bac)、Zrc/Rbc与Ti、Zr的粒度效应Tic/Tif、Zrc/Zrf指示了沉积物重、轻矿物的相对比率,是流域侵蚀强度与湖泊涨缩的信息指示;Ba、Rb与Sr在细粒级的含量之比Baf/Srf、Rbf/Srf指示了硅酸盐与碳酸盐矿物的相对含量,是流域风化、侵蚀搬运强度与湖泊过程(包括物理/化学/生物)等混合信息指示,没有明确的环境指向性。  相似文献   

6.
流域生物、化学风化对小冰期气候变化的响应   总被引:2,自引:3,他引:2  
岱海近500年沉积物的孢粉,介形类和地球化学记录表现了流域生物,化学风化对全球性小冰期气候波动明显而快速的响应,孢粉量的下降,化学风化强度的减弱(高Rb/Sr比值)以及意外湖花介(Limnocythere inopinata)的繁盛反映了小冰期最盛期岱海地区以干旱为特征的气候环境及其造成的高矿化度湖水,其中,介形类丰度及种类对环境变化的反应最迅速,植被生长的调节则要缓慢一些,内陆湖泊流域植被的衰弱与干旱环境下化学风化强度的减弱以及风尘作用的加强是相辅相成的。  相似文献   

7.
对采自青藏高原中部错鄂湖泊钻孔近200m以上深处、形成于2.8Ma以来的沉积岩岩芯中Sr,Rb,Zr含量变化及Rb/Sr,Zr/Rb比进行了研究,并结合其岩性、粒度、粘土矿物组成,分析了该地区2.8Ma来化学风化的相对强度和古环境演化过程。研究表明,2.8Ma来青藏高原中部的环境经历了3个演化阶段:在深约197-170m(2.8-2.5Ma)岩性段,低Sr含量,高Rb/Sr和Zr/Rb比揭示的是较弱的化学风化过程,反映了与当时强烈的高原隆升运动有关;在约170-38.5m(约2.5-0.8Ma)段,高Sr含量,低Rb/Sr和Zr/Rb比记录的是该流域较强的化学风化阶段,与高原在稳定期中部总体处于温湿或凉湿的环境下的结论吻合;在38.5-0m(约0.8-0Ma)段,总体Sr含量处于相对低值,Rb/Sr比相对较高,化学风化相对较弱,表明高原中部处于较寒冷的环境之中,高原整体已隆升到4000m以上。  相似文献   

8.
青海湖近千年来气候环境变化的湖泊沉积记录   总被引:56,自引:15,他引:56       下载免费PDF全文
本文根据青海湖沉积岩芯(QH00A)碳酸盐含量、TOC和Rb/Sr等环境指标的综合分析,探讨了该地区近千年来的气候变化过程和化学风化史。结果表明:青海湖地区近千年来经历了5次冷湿期和5次暖干期,气候组合类型为冷湿与暖干交替。中世纪暖期、小冰期以及20世纪以来的升温在该沉积岩芯中得到良好的记录。沉积岩芯Rb/Sr较好地记录了湖泊流域化学风化的历史,并揭示流域化学风化的主要控制因素为气温变化。  相似文献   

9.
粒度分组:提取古环境变化信息的一种有效方法   总被引:3,自引:0,他引:3  
对南京老虎山黄土-古土壤剖面全样和三个粒级组分(《2 μm、2~45μm和》45 μm)的Rb/Sr比值进行了系统研究.结果表明,Rb/Sr比值是衡量黄土和古土壤化学风化强度的良好地球化学指标;粒度分组是利用Rb/Sr比值研究古环境变化的有效方法.通过粒度分组,可以排除不同粒度组分之间由于Rb/Sr初始比值不同造成的互相干扰.《2 μm粒级的(Rb/Sr)-Sr反相关图的R2值最大(达0.97),说明该粒级指示化学风化作用的灵敏度最高,研究Rb/Sr比值这一地球化学指标最理想.  相似文献   

10.
内蒙古黄旗海H3剖面中发育黄旗海全新世高湖面时形成的湖相粉砂质沉积。对全样、77~20μm粒级、小于20,μm粒级沉积物的Rb、Sr含量,以及小于20,μm粒级样品中碳酸盐矿物种类及含量的测试结果表明,全新世早、中期形成的湖泊沉积物中,自生富锶文石是Sr在沉积物中含量较高的主要原因。各粒级沉积物中Rb、Sr含量与沉积物粒度组成的关系表明:Sr倾向富集于黏粒(4,μm)中,可能与湖泊自生碳酸盐以泥晶为主有关,而Rb倾向富集于4~28,μm颗粒粒级中,可能与其硅酸盐矿物碎化过程的特点有关;Sr与Rb存在粒度效应,且二者粒度效应明显不同。Rb/Sr与湖泊、流域的诸多过程及沉积物粒度效应有关,在不同湖泊演化阶段,其具体的环境含义不同,这是湖泊沉积与风化壳的不同之处。  相似文献   

11.
The Rb/Sr ratios of lake sediments have been suggested as indicators of weathering intensity by increasing work. However, the geochemistry of Rb/Sr ratios of lake sediments is variable between different lakes. In this study, we investigated the spatial and temporal patterns of Rb/Sr ratios, as well as those of other major elements in surface sediments of Lake Qinghai. We find that the spatial pattern of Rb/Sr ratios of the bulk sediments correlates well with that of the mass accumulation rate, and those of the terrigenous fractions, e.g., SiO2, Ti, and Fe. The temporal variations of Rb/Sr ratios also synchronize with those of SiO2, Ti, and Fe of each individual core. These suggest that Rb/Sr ratios of the surface sediments are closely related to terrigenous input from the catchment. Two out of eight cores show similar trends between Rb/Sr ratios and precipitation indices on decadal scales; however, the other cores do not show such relationship. The result of this study suggests that physical weathering and chemical weathering in Lake Qinghai catchment have opposite influence on Rb/Sr ratios of the bulk sediments, and they compete in dominating the Rb/Sr ratios of lake sediments on different spatial and temporal scales. Therefore, it is necessary to study the geochemistry of Rb/Sr ratio of lake sediments (especially that on short term timescales) particularly before it is used as an indicator of weathering intensity of the catchment.  相似文献   

12.
柴达木察尔汗贝壳堤剖面Sr同位素及其环境意义   总被引:6,自引:0,他引:6  
根据对柴达木盆地察尔汗古湖贝壳堤剖面酸不溶组分和酸溶组分的提取及其87Sr/86Sr的测定,结合沉积物中Rb/Sr的变化,指出Sr同位素组成特征可有效指示源区化学风化和沉积区古环境变化;依据酸溶组分中盐度指标Sr/Ca, Sr/Ba值与Sr同位素组成曲线的对比分析,揭示酸溶组分Sr同位素可以较好的指示水体形成时的盐度。通过分析贝壳堤剖面化学风化和部分盐度变化过程,探讨了研究区晚更新世39.6~ 17.1 ka BP(未经校正的AMS 14C测年结果,全文同)湖泊高湖面的演化历史。  相似文献   

13.
A series of faulted inland basins were developed in the central Qinghai-Tibet Plateau, among which the Co Ngoin Basin containing thick lacustrine sediments is located in the peripheral area of the Indian monsoon. In this paper, we present the weathering history and paleoclimatic changes in the last 2.8 Ma based on studies of high-resolution temporal distributions of Sr, Rb and Zr concentrations, Rb/Sr and Zr/Rb ratios and δ ^13C and TOC for the Co Ngoin sediments, in combination with the sediment properties, grain size distribution and clay mineralogy. The sedimentary records indicate three environmental stages in the last 2.8Ma. At the core depth of 197-170m (about 2.8-2.5Ma), low-intensity chemical weathering in the Co Ngoin catchment was experienced under warm-dry to cool-wet climate conditions with relatively low Sr concentration and high Rb/Sr and Zr/Rb ratios. The sudden occurrence of both subalpine coniferous forest and coarses and and gravel sediments in the Co Ngoin core reflects a strong tectonic uplift. The high Sr concentrations and low Rb/Sr and Zr/Rb ratios reflect a relatively strong chemical weathering between 2.5Ma and 0.8Ma (at the core depth of 170-38.5m) under a temperate/cool and wet climate, characterized by mud and silt with fine sand, probably indicating a stable process of denudation and planation of the plateau. Above the depth of 38.5m (about 0.8-0Ma), the coarsening of sediments indicates a strong tectonic uplift and a relatively low intensity of chemical weathering as supported by the record of sediments having relatively low Sr concentrations and high Rb/Sr and Zr/Rb ratios. Since then, the plateau has taken the shape of the modern topographic pattern above 4000m a.s.l.  相似文献   

14.
The lightness (L*) and concentrations of Rb, Sr and organic carbon (Corg) have been measured in the age-constrained lake sediment cores recovered from Co Ngoin in the central Tibetan Plateau. Dissolved Sr flux is a dominant control on the variation of Rb/Sr ratios in the sediments. Variations in color and geochemical proxies of Co Ngoin sediments display a continuous history of late glacial to mid-Holocene chemical versus physical weathering intensity in response to past climatic changes between approximately 13,500 and 4500 cal yr B.P. A lower chemical weathering under a late glacial climate was followed by a higher weathering during the Holocene Optimum. Weathering intensity in the central Tibetan Plateau catchment also responds to well-known climatic events, such as the Younger Dryas (YD), and possibly the Holocene Event 5 (HE-5). Although there are differences in time or duration of the climatic events, many of the well-known late glacial to mid-Holocene events occurred in high-elevation Co Ngoin where atmospheric circulation might play a hemispherical role in climatic forcing. The sediment hiatus since c. 4200 14C yr B.P. in the Co Ngoin indicates a period of desiccation that was probably associated with a sharp decrease in summer monsoon strength. Our lascustrine results not only imply catchment weathering variations in response to late glacial to mid-Holocene climatic conditions in the central plateau, but also provide further evidence for global connections between regional climates.  相似文献   

15.
The Medieval Warm Period and Little Ice Age in the Daihai Area, North China   总被引:1,自引:0,他引:1  
Rb/Sr ratio, CaCO3 content, organic carbon (Corg) concentration, magnetic suscep-tibility and clay mineralogy of 4.0 m sediments samples recovered from Daihai Lake, northern China, are presented in the paper. Weathering and paleoclimatic change history during the last 2300 years is reconstructed in terms of the variations of Rb/Sr ratios in the sediment sequence, including the Little Ice Age and Medieval Warm Period. Our results suggest that the evolution processes of weathering and paleoclimate can be rebuilt in terms of the variations of Rb/Sr ratios in the lake sediment sequence, in combination with magnetic susceptibility, Corg, CaCO3 contents and clay mineralogy.  相似文献   

16.
Jin, Z. D., Bickle, M. J., Chapman, H. J., Yu, J., An, Z., Wang, S. & Greaves, M. J. 2010: Ostracod Mg/Sr/Ca and 87Sr/86Sr geochemistry from Tibetan lake sediments: Implications for early to mid‐Pleistocene Indian monsoon and catchment weathering. Boreas, 10.1111/j.1502‐3885.2010.00184.x. ISSN 0300‐9483 Lacustrine sediment serves as a valuable archive for tracing catchment weathering processes associated with past climatic and/or tectonic changes. High‐resolution records of fossil ostracod Mg/Ca, Sr/Ca and 87Sr/86Sr ratios from a lake sediment core from the central Tibetan Plateau reveal a temporal link between lake‐water chemistry and catchment weathering and distinct monsoonal oscillations over the early to mid‐Pleistocene. Between 2.01 and 0.95 Ma, lake‐water chemistry was dominated by a high proportion of carbonate weathering related to variations in the Indian monsoon, resulting in relatively low and constant ostracod 87Sr/86Sr but obvious fluctuations in Mg/Ca, Sr/Ca and δ18O. Across the mid‐Pleistocene transition (MPT), a significant increase in 87Sr/86Sr and frequently fluctuating ratios of ostracod Mg/Ca, Sr/Ca and δ18O are coincident with increases in both Chinese loess grain size and Arabian Sea lithogenic flux. This correlation indicates an increased glaciation and a strong monsoon seasonal contrast over the plateau. The increase in lake‐water 87Sr/86Sr across the MPT highlights a change in catchment weathering patterns, rather than one in climate‐enhanced weathering intensity, with an increased weathering of 87Sr‐rich minerals potentially induced by marked extensive glaciation and strong seasonality in the central plateau.  相似文献   

17.
Uncertainties in paleoenvironmental interpretations for traditional chemical analysis of bulk samples result from different grain-size sub-populations of sediments containing variable distributions of elements and minerals. Therefore, it is important to understand the elemental and mineral distribution in different grain sizes in determining the quantitative relationship between chemical weathering and climatic change. We sieved a series of Xiashu loess samples into three sub-populations of different grain sizes (<2, 2–45 and >45 μm, respectively), and then analyzed each population for rubidium (Rb), strontium (Sr), rare earth elements and magnetic susceptibility. In comparison with elemental concentrations of bulk samples, clay mineralogy and illitic crystallinity, our results show that distinct elemental distributions and magnetic susceptibilities for different grain-size sub-populations are controlled by sorting and/or chemical weathering, although we also suggest that the Xiashu loess may have the same provenance as the Central Chinese Loess. Maximum concentrations of Rb and fine-grained magnetic minerals in the less than 2 μm sub-population, coupled with our finding of maximum Sr in the larger than 45 μm fraction, indicate that Sr was lost during chemical weathering. Grain-size sub-population analysis is, therefore, an effective method for extracting paleoenvironmental information, because individual sub-populations show minimal variations in initial Rb/Sr ratios compared to bulk analysis of all sizes together. Furthermore, a negative correlation between Rb/Sr ratios and Sr concentrations for the <2 μm fraction (R2 = 0.97) may indicate that clay is a sensitive indicator of intensity of chemical weathering and is an ideal sub-population for determining Rb/Sr ratios, but not for magnetic susceptibility.  相似文献   

18.
早全新世降温事件的湖泊沉积证据   总被引:12,自引:1,他引:12  
我国华北干旱-半干旱区封闭湖泊流域化学风化历史记录了全新世以来次级的气候环境波动过程。高精度的沉积物地球化学、物理及生物参数变化表明,在全新世早-中期过渡阶段存在一次强降温气候事件,具体表现为流域化学风化减弱(高Rb/Sr比)、湖泊产生力减弱(低有机碳)以及湖泊水位下降。虽然该事件的寒冷程度比Younger Dryas弱,但是其与来自湖沼(包括北极、非洲、北美、西欧、青藏高原、祁连山等)、海洋(比北大西洋、地中海、加勒比海等)、欧-美大陆生物组合、极地冰芯等在内的环境记录的冷事件发生时间基本一致,集中发生于8.0-8.5ka B.P.之间。  相似文献   

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