共查询到18条相似文献，搜索用时 187 毫秒
1.
砾石钙膜作为一种反映环境变化的沉积物标志 ,记录了比较完整的环境和气候信息 ,其实物的直接表现形式就是沉积了明暗相间的纹层 ,而形成明暗纹层的主要原因是受沉积时碳酸盐的纯度和结晶物的粒度以及杂质等的影响。作者用普通的扫描仪获取钙膜纹层明暗度图像 ,通过计算机自动识别获取明暗度变化的特征曲线 ,并将其与深海氧同位素曲线、黄土 -古土壤序列、黄土粒度曲线、磁化率曲线等进行对比分析 ,从而达到确定砾石钙膜所代表的地貌面年龄的目的 ,同时分析其气候效应。初步研究表明 ,这种方法是可行的 ,它不仅提高了定年的精度和时间跨度 ,同时也拓宽了沉积物年代学方法在古环境及古气候研究中的应用 相似文献
2.
3.
阿尔金山东段山前砾石钙膜累积速率及其在估算断层活动年代方面的应用 总被引：3，自引：0，他引：3
干旱－半干旱地区冲洪积物顶面土壤中发育的砾石钙膜含有明显的年龄信息,其工及由统计计算得到的累积速率可用来估算所在冲洪积物或土壤的形成年代。 相似文献
4.
5.
6.
青藏高原北部砾石粒径变化对气候和构造演化的响应 总被引：2，自引：0，他引：2
青藏高原周边广泛分布的晚新生代砾岩是高原强烈隆升的产物, 但也可能仅仅是气候变化造成. 通过对青藏高原北部代表性砾岩, 酒西盆地老君庙剖面上部酒泉砾石层和戈壁砾石层进行详细的砾石粒径变化研究, 发现约0.8 Ma以来酒泉、戈壁砾石层砾石粒径不仅具有明显的变粗趋势, 而且还发育了9个显著的粗细变化旋回, 并且可与黄土-古土壤和深海氧同位素气候旋回进行良好对比, 粗、细砾石层分别对应于季风气候的暖湿和干冷时期, 具有显著的大约10万年和4.1万年周期. 由于我国西北第四纪晚期的气候是持续变干, 因此, 初步认为酒泉-戈壁砾石层中砾石粒径的持续变粗反映了高原第四纪晚期持续强烈的构造隆升, 而其中的旋回是对第四纪冰期-间冰期气候旋回变化的响应, 后者叠加于前者之上, 从而为高原周边砾岩层主要是高原强烈隆升的产物提供了重要的证据. 相似文献
7.
西昆仑山南红山湖沉积反映的过去150年湖区环境变化 总被引：23，自引：0，他引：23
采用～２１０Ｐｂ和～１３７Ｃｓ方法对西昆仑山南红山湖 ２号孔（长 １．０７ ｍ）湖泊岩芯进行了定年和沉积速率研究，获得了分辨率达１．４年的过去约１５０年（１８５０～１９９７年）连续湖泊沉积环境序列．该沉积柱子的总有机碳、总氮、元素地球化学、碳酸钙、粒度、介形虫丰度等变化表明，这些环境代用指标具有很好的一致性，反映了湖区环境具有１９世纪下半叶的冷湿、１９世纪末期到２０世纪２０年代的暖湿和２０年代开始的暖干变化背景．２０年代以来又具有次一级的冷暖／干湿波动，可以划分为１９２２～１９６０年间的冷干／暖湿波动、１９６０年以来的强烈暖干化以及出现于７０年代中期到８０年代末期的短暂冷湿过程．其中，７０年代中期至末期的湿润时期和８０年代中期开始的干旱环境在邻近地区的器测气象记录中得到证实，粒度数据与器测降水记录具有较好的相关性．与同一地区的古里雅冰芯记录对比，该孔指示环境冷暖的代用指标（ＴＯＣ）与冰芯中代表温度变化的δ～１８Ｏ变化具有很好的对应关系，但指示干湿程度的指标与冰芯中代表降水大小的冰川积累量变化关系较差．该孔湖泊沉积记录表明，选取的代用指标具有明确的环境意义，湖芯序列能够反映高分辨率的气候环境变化． 相似文献
8.
云南鹤庆盆地15万年以来的介形类及环境变迁 总被引：13，自引：3，他引：10
云南鹤庆盆地HQ钻孔剖面分析出介形类13属．32种．根据介形类丰度、分异度及百分含量的变化情况,结合孢粉、总有机碳含量(TOC)、碳氮比(C／N)、碳酸盐含量等的分布,将鹤庆盆地近15万年以来的古气候、古环境变化初步划分为5个阶段,同时又划分出若干亚阶段．总的气候特征为冷期偏湿、暖期偏干,在冷湿和暖干的宏观波动背景上存在次级波动,反映出其气候变化的区域特性．同时．各气候阶段基本可与深海氧同位素V28-38钻孔、黄土／古土壤序列邙山剖面反映的气候阶段相对比,又显示出其气候变化的协同性．在构造与气候的双重作用下．在11790aBP左右湖盆被彻底切开． 相似文献
9.
选取江苏及邻区地电台网13个台站地电场观测分钟值,采用泰勒多项式和曲面样条函数模型建立地电日变化模型,使用模型曲线描述不同年份、同农历日期、同等磁情天气的实测地电日变化,结果表明:使用分钟值曲线建立的地电日变化模型,更能清晰反映日变化特点,并可反映一天当中台站观测环境、测量系统等变化引起的地电变化;使用同一区域地电台网中若干台站同方向测道的样本曲线,建立各测道电场变化模型,可反映其自身特征及共性特征。 相似文献
10.
青藏高原现代湖泊变化与考察初步报告 总被引：18，自引：5，他引：13
青藏高原广布的湖泊敏感地记录着气候与环境变化过程的信息．因它在地球中、低纬度地区最少受人类活动干扰,环境的演化变迁忠实地反映了纯自然过程,因此继南、北极之后,青藏高原正在成为研究全球变化的新的热点地区．青藏高原上的湖泊绝大部分为封闭湖盆,湖泊水位的变化直接记录着流域内的水量平衡变化过程．可敏感反映气候的变化．湖泊水化学性质记录了湖泊自身的演化历史,湖泊沉积物则包含着丰富的湖泊物理、化学、生物的沉积过程信息,这些过程与气候、环境演变又有着密切的关系．为了探讨湖泊沉积物和湖泊水体中的物理、化学、生物… 相似文献
11.
12.
原地宇宙成因核素测年方法在地质及地理研究领域应用广泛,测年对象众多。石英因其致密的晶体结构不易被大气成因10Be污染,以及较低的27Al含量的特点而成为宇宙成因核素测年方法中一种理想的测年物质。在分离石英样品10Be和26Al的实验流程中,石英的提纯是其中的一个关键环节。原始的HCl/H2O2和HF/HNO3蚀刻分离提纯石英方法应用广泛、安全可靠,但处理样品周期长、效率较低。因此,在原始流程的基础上,设计了3组实验流程与原始流程进行对比。结果显示,在样品石英纯度较高的基础上,可以通过减少超声波使用时间、增加蚀刻溶液浓度及每步样品处理量的方法,提高样品的处理效率,同时可以用加热磁力搅拌器替代超声波清洗器进行石英样品的HF/HNO3蚀刻提纯 相似文献
13.
There are many examples of exposed or buried rock surfaces whose age is of interest to geologists and archaeologists. Luminescence dating is a well-established method of absolute chronology which has been successfully applied to a wide range of fine-grained sediments from hundreds of years to several hundred thousand years. Optical stimulated luminescence (OSL) has been recently proposed as a new method to date these rock surfaces (Laskariset al., 2011; Sohbatiet al., 2012a; Chapotet al., 2012; Pedersonet al., 2014; Sohbatiet al., 2015; Freieslebenet al., 2015). The basic principle is that luminescence signal of rock surface will soon decay when the rock is exposed to sunlight. When the rock surface is turned to be buried side, the OSL signal begins to accumulate again. With the variation of residual luminescence with depth, it is possible to estimate exposure and burial history of the rock. This article describes briefly the different luminescence dating methods for rock surfaces, its progress, application examples and present problems. For instance, Sohbatiet al. (2011) studied the depth dependence of the bleaching of the IRSL signal from granitic rocks, Laskaris and Liritzis (2011) proposed a mathematical function to describe the attenuation of daylight into rock surfaces, Sohbatiet al. (2012a) developed their model to include the environmental dose rate, Sohbatiet al. (2012b) overcame the problem of parameter estimation by using a known-age road-cut sample for calibration, Sohbatiet al. (2012c) further developed the OSL surface exposure dating model by including the simultaneous effect of daylight bleaching and environmental dose rate, and so on. These studies indicate that OSL dating method for rock surface can be applied widely to studies of geological and geomorphological evolution, archeology and Quaternary tectonic activity. 相似文献
14.
Apatite (U-Th)/He dating has gained popularity since its rejuvenation as geochronometry and thermochronometry applied in the deduction of the geological processes of the upper-three-km crust.However,this irreplaceable method,which has the lowest known closure temperature (~70℃),sometimes is suffering from large dispersion and deviation because of its dating theory,its analytical method,and its diffusion process.In this paper,we summarized ten factors impacting the accuracy of (U-Th)/He dating.They are grain size,fluid and mineral inclusions,α-particle ejection,α-particle implantation,U-Th zonation,radiation damage,chemical composition,samarium concentration,multiple thermal events,and U-series disequilibrium.We discussed how these ten factors would affect the (U-Th)/He ages and how to reduce and/or avoid the deviation caused by them.The factors of grain size (different size,different diffusion domain) and inclusions (parentless 4He) can be suppressed in the procedure of grain selection under binocular.It is the precise measurement of a homogenous crystal that endows the (U-Th)/He dating method credible due to the correction of α-particle ejection based on the dimension of crystals.The possible implantation of α-particles can be evaluated by the negative correlation of age and eU (eU=[U]+0.235[Th]).U-Th zonation,a heterogeneous distribution of parent nuclides,makes the correction of α-particle ejection inaccurate;besides,this factor also amplifies the side effects of radiation damage and grain size.LA-ICP-MS can detect this phenomenon.Radiation damage outstands when the samples experience reheating or long residence time in partial retention zone (40~70℃),indicated by the positive correlation between age and eU/[4He].Apatite (U-Th)/He age can be entangled by higher Cl content,with which the crystal accumulates more radiation damage,leading to a larger age,meanwhile this factor needs more investigation.Having larger half-life than U-series nuclides,the 147Sm is not a big problem in the dating of a large timescale,while more precise event needs the data of 147Sm in the age calculation.The multiple thermal events should be evaluated to exclude thermal perturbation,when applying the (U-Th)/He geo/thermochronology to the deduction of a particular thermal event.U-series disequilibrium has an impact on the ages smaller than 1Ma,making the age results larger than the true one.U-series disequilibrium method and mineral couples can solve this problem.Inclusion,α-particle ejection and implantation,and U-Th zonation are at the mercy of analytical methods.The factors stemming from helium diffusion in the crystals are grain size,radiation damage,Cl content,multiple thermal events.The dating theory of (U-Th)/He method renders U-series disequilibrium and 147Sm outstand as side effects in some specific conditions.It would be our pleasure if this paper could provide some useful information for the works relevant to this dating method. 相似文献
15.
CHRONOLOGY OF YICHANG GRAVEL LAYER BASED ON QUARTZ TI-LI CENTER ESR DATING AND ITS IMPLICATIONS FOR THE INCISION TIMING OF THE THREE GORGES VALLEY 
下载免费PDF全文
下载免费PDF全文 WEI Chuan-yi LIU Chun-ru LI Chang-an YIN Gong-ming HAN Fei ZHANG Dai LI Ya-wei ZHANG Yu-fen 《地震地质》1979,42(1):65-78
Uplift of Tibet Plateau and formation of Asian Monsoon greatly affect East Asian geomorphological evolution, climate change and environment systems. Thus, those phenomena also control the origin, size and direction of river systems. The Yangtze River, as the most important linkage between Tibet Plateau and the East Asian marginal seas, delivers large volumes of water, sediment, and associated chemicals from its headwater regions and tributaries to the East China Sea, significantly influencing sedimentary system evolution in its drainage basin. Therefore, the formation of the modern Yangtze River and its geological-time evolution history have been paid more and more attention to since the beginning of the last century. After debated for more than a century, the First Bend in Shigu area and the Three Gorges have been known as the key capture point of the Yangtze River's evolution history. In particularly, the Three Gorges incision period remains greatly controversial, which mainly focuses on Cretaceous period-Neogene period, early Pleistocene period, and late Quaternary period.
The Yichang Gravel, just located downstream and outlet of the Three Gorges with an inverted triangle shape, is mainly distributed in western Jianghan Basin with over 1 000km2. Because of its wide distribution and key geographical location, many typical profiles of Yichang Gravel have been the critical materials for studies on stratigraphic division, geomorphic evolution, and paleoenvironment change in middle Yangtze River Basin, especially on the Three Gorges incision history. Based on the previous field investigation, the Yichang gravel unconformably overlies the Cretaceous bedrocks and underlies the mid-Pleistocene vermicular red earth. In addition, studies on heavy mineral assemblages, Pb isotopic compositions of detrital K-feldspar grains, magnetic characteristics as well as pollen assemblage characteristics have showed that sediments in Yichang Gravel are mainly derived from upper Yangtze River Basin, such as Jinshangjiang drainage, Minjiang drainage, Jialingjiang drainage and Wujiang drainage. Based on the above comprehensive analysis, researchers demonstrated that the depositing time of Yichang Gravel can best constrain the Three Gorges incising time.
The absolute altitude of Yichang Gravel exceeds 110m, and many thick sand lens are developed from top to bottom of the profiles. In this study, we applied the quartz Ti-Li center ESR dating method in Yichang Gravel to determine its absolute formation age, and then to constrain the minimum cutting-through time of Three Gorges. Eight samples(SXY-1, SXY-2, YC-1-4, LJY-1, LJY-2)were collected from the sand lens at depths of 4m, 19m, 40m, 51m, 63m, 75m, 83m and 99m respectively from the top of the profile. At the same time, in order to evaluate the residual dose of Ti-Li center after sunlight bleaching, we also sampled four modern surface Yangtze River sediments near Yichang Gravel for ESR measurement.
The result shows that the quartz Ti-Li center ESR signal intensity of the 4 modern fluvial sediments samples are zero, which implies that the Ti-Li center ESR signal intensity of quartz in Yichang Gravel sand lens could be bleached to zero before the last burial. Thus, the above results indicate that the ESR dating results of this paper are reliable. The ESR absolute age from top to bottom of the profile is 0.73Ma BP,0.87Ma BP,0.98Ma BP,1.04Ma BP,1.05Ma BP,1.10Ma BP, 1.11Ma BP, 1.12Ma BP, respectively. The ESR dating results show that the Yichang Gravel began to deposit at about 1. 12Ma BP until 0. 73Ma BP, and the Ti-Li center ESR age indicates that the Yangtze River cut through Three Gorges area no later than 1.12Ma BP. 相似文献
16.
17.
18.
活动构造研究、近现代火山研究、古地磁研究等要求K-Ar和Ar-Ar年代学方法不断向越来越小的年龄尺度和越来越精细的方向发展。文中以腾冲等火山地区的K-Ar和Ar-Ar年代学研究结果及实验方法研究结果为根据,对K-Ar和Ar-Ar方法的精细测年及其检验进行阐述。说明K-Ar和Ar-Ar年代测定结果是单个样品的单次测量结果,其影响因素包括样品因素和实验因素。为了提高测年结果的准确度和精确度,必须有严格而合理的野外采样和实验过程,并且在具体的地质样品年代测量之外,还应经常利用一系列可能的方法对实验结果进行检验 相似文献