安徽淮南群四顶山组燧石Sm-Nd年龄测定   总被引：1，自引：0，他引：1  

杨杰东郑文武  陶仙聪王宗哲 《地质论评》2004,50(4):413-417

在对苏皖北部的上前寒武系进行了矿物学研究基础上,选择安徽北部淮南群四顶山组燧石作为测定对象,系统测试Rb-Sr和Sm-Nd同位素,应用Sm-Nd等时线方法进行了定年。本次研究表明,安徽淮南群四顶山组燧石可能是在海洋环境中形成,主要反映了陆源物质特征,其形成时代约为800Ma。这为苏皖北部地区上前寒武系是位于华北区青白口系和扬子区震旦系之间的一套地层提供了一个新的证据,也进一步印证了淮南生物群属于先伊迪卡拉期的学术观点。  相似文献   

煤成甲烷碳同位素分馏的动力学模拟   总被引：10，自引：6，他引：4  

熊永强  耿安松  刘金钟 《地球化学》2004,33(6):545-550

主要目的是通过动力学模拟实验与GC-IRMS技术建立煤成甲烷碳同位素分馏的动力学模拟.热解产物中甲烷碳同位素的测定结果表明,同时假定生气过程中同位素分馏系数(α)固定不变和所有产甲烷母质具有相同的初始碳同位素组成(δ13Co)对于解释煤化过程中的碳同位素分馏是不可行的.在本研究中,为了解决陆源有机质的非均质性,应用了两个方法:一是假定对于煤中所有产甲烷前身物具有一个相同的初始碳同位素组成(δ13Co),通过调整各个平行反应的△Ea,i(Ea,i13C-Ea,i12C)来拟合实测甲烷同位素组成的变化;另一个是假定在整个生气过程中同位素分馏系数(α)不变,即△Ea,i为常数,通过改变fi13C来实现与实测甲烷同位素的拟合.动力学计算结果表明,在2℃/Ma的地质升温速率下两种方法具有相似的结果.  相似文献   

SWAT-based runoff and sediment simulation in a small watershed,the loessial hilly-gullied region of China:capabilities and challenges   总被引：2，自引：0，他引：2  

Lin-jing QIU  Fen-li ZHENG  Run-sheng YIN 《国际泥沙研究》2012,27(2):226-234

Model calibration and validation are necessary before applying it for scenario assessment and watershed management.This study presented the methodology of evaluating Soil and Water Assessment Tool(SWAT) and tested the feasibility of SWAT on runoff and sediment load simulation in the Zhifanggou watershed located in hilly-gullied region of China.Daily runoff and sediment event data from 1998-2008 were used in this study;data from 1998-2003 were used for calibration and 2004-2008 for validation.The evaluation statistics for the daily runoff simulation showed that the model results were acceptable,but the model underestimated the runoff for high-flow events.For sediment load simulation,the SWAT performed well in capturing the trend of sediment load,while the model tended to underestimate sediment load during both the calibration and validation periods. The disparity between observed and simulated data most likely resulted from limitations of the existing SCS-CN and MUSLE methods in the model.This study indicated that the modification of SWAT components is needed to take rainfall intensity and its duration into account to enhance the model performance on peak flow and sediment load simulation during heavy rainfall season.  相似文献   

An analytical study on turbulence with mixed-flow model and two-phase model     

Dan-xun LI  Marian MUSTE  Qiang ZHONG  Xing-kui WANG 《国际泥沙研究》2012,27(2):235-239

Suspended sediment is carried by turbulent water flows in rivers.Traditional sediment-laden flow analysis treats the suspension as a mixed liquid,and recent two-phase flow model enables separate velocity measurement of the two coupling phases.A simplified theoretical analysis was presented to discuss the differences between the two models in reporting turbulence intensity in experimental research.The turbulence intensity of the mixture is lower than the weighted average of those of the two phases in mixed-flow experiments.The mixture’s turbulence intensity becomes higher than the average of the two phases in two-phase experiments due to the presence of velocity lag.The same set of data may lead to either an underestimation or an overestimation of actual turbulence levels when different models are used.  相似文献   

Seasonal timing of stratospheric final warming associated with the intensity of stratospheric sudden warming in preceding winter   总被引：1，自引：0，他引：1  

HU JingGao  REN RongCai  XU HaiMing  YANG ShuangYan 《中国科学:地球科学(英文版)》2015,(4):615-627

The association of seasonal timing of stratospheric final warming events(SFWs) in spring and the occurrence of major and minor stratospheric sudden warming events(SSWs) in midwinter were investigated through statistical analysis, parallel comparison, and composite analysis, based on the NCEP-NCAR reanalysis dataset covering 1958–2012. It was found that the intensity and occurrence of winter SSW events can largely affect the timing of spring SFWs. Specifically, the SFW onset dates tend to be later(earlier) after the occurrence(absence) of winter major SSWs. However, the occurrence or absence of minor SSWs does not change the frequency of early and late SFWs. A parallel comparison of the temporal evolution of the anomalous circulation and planetary-waves between major SSW and minor SSW winters indicates that the stratospheric polar vortex(polar jet) will keep being anomalously stronger 30 days after major SSW onset. And the associated significant negative Eliassen-Palm(EP) flux anomalies can persist for as long as 45 days after major SSW events. In contrast, the circulation anomalies around the occurrence of minor SSW events can last only a few days. To further verify the possible influence of the occurrence of major SSWs on the seasonal timing of SFWs, composite analysis was performed respectively for the 21 major-SSW years, 15 minor-SSW years, and the 15 non-SSW years. Generally, planetary-wave activity in the extratropical stratosphere tends to be stronger(weaker) and the westerly polar jet is anomalously weaker(stronger) in major-SSW(non-SSW) winters. But in the following spring, the planetary-wave activity is weaker(stronger) accompanied with an anomalously stronger(weaker) stratospheric polar vortex. In spring after minor-SSW years, however, the stratospheric polar vortex and the westerly polar jet exhibit a state close to climatology with relatively gentle variations.  相似文献   

Comparisons of GCM cloud cover parameterizations with cloud-resolving model explicit simulations     

WANG XiaoCong  LIU YiMin  BAO Qing  WU GuoXiong 《中国科学:地球科学(英文版)》2015,(4):604-614

Three kinds of the widely-used cloudiness parameterizations are compared with data produced from the cloud-resolving model(CRM) simulations of the tropical cloud system. The investigated schemes include those based on relative humidity(RH), the semi-empirical scheme using cloud condensate as a predictor, and the statistical scheme based on probability distribution functions(PDFs). Results show that all three schemes are successful in reproducing the timing of cloud generation, except for the RH-based scheme, in which low-level clouds are artificially simulated during cloudless days. In contrast, the low-level clouds are well simulated in the semi-empirical and PDF-based statistical schemes, both of which are close to the CRM explicit simulations. In addition to the Gaussian PDF, two alternative PDFs are also explored to investigate the impact of different PDFs on cloud parameterizations. All the PDF-based parameterizations are found to be inaccurate for high cloud simulations, in either the magnitude or the structure. The primary reason is that the investigated PDFs are symmetrically assumed, yet the skewness factors in deep convective cloud regimes are highly significant, indicating the symmetrical assumption is not well satisfied in those regimes. Results imply the need to seek a skewed PDF in statistical schemes so that it can yield better performance in high cloud simulations.  相似文献   

激光雷达测量技术在地学中的若干应用   总被引：3，自引：0，他引：3  

马洪超 《地球科学》2011,36(2):347-354

对激光雷达测量技术在全球冰川监测、局部断裂带提取、滑坡监测和稳定性评价以及海岸线提取和海岸侵蚀等方面的应用做了较为全面的综述.作为一种新型的对地观测手段,激光雷达(含星载、机载、车载和地面)的应用已经从传统的测绘扩大到包括文物保护在内的诸多其他应用领域.所综述的激光雷达技术在地学研究中的4个应用方面,是传统地学研究中与全球变化和人居环境最为密切的方向.分析表明,激光雷达技术在这些研究方向中的应用大有作为.   相似文献   

基于二维经验模态分解的重磁异常分离     

陈建国  肖凡  常韬 《地球科学》2011,36(2):327-335

由于地质过程的复杂性及成矿过程的多期次叠加性,原始重磁异常往往是多种地质因素的混合信息,既包含区域背景异常信息,也包含与矿床(体)、矿化蚀变带以及隐伏岩体等与找矿密切相关的地质要素所引起的局部重磁异常.如何从复杂的叠加重磁异常中分离出具有找矿意义的局部异常,是当前矿产勘查和资源潜力评价工作中面临的难题之一.采用经验模态分解(EMD)方法来分解重磁异常,为提高分解的稳健性提出了用双调和样条插值(BSI)进行包罗面插值的新方法,并以云南个旧地区重磁数据为例,对其进行非线性多尺度分解,实现对区域异常与局部重磁异常的分离,揭示了深层次找矿信息并拓宽了经验模态分解方法的应用领域.   相似文献   

基于整数小波变换的空间矢量数据压缩方法     

余先川  张君兰  张立保 《地球科学》2011,36(2):381-385

针对空间曲线矢量数据相邻坐标点间坐标值大小差别不大的特点,提出一种新的矢量数据压缩方法:首先将空间坐标点间的差值转换为整型的偏移量,使用偏移量表示矢量数据的坐标点;然后利用整数小波变换(IWT)处理偏移量序列,最后对变换后的小波系数进行无损熵编码.使用此方法对中国数字地理地图数据的SHP文件进行压缩,实验结果显示, 压缩比超过11,高于其他类似方法,表明本压缩方法能够实现较高压缩比的空间矢量数据无损压缩.   相似文献   

Pattern and timing of late Cenozoic rapid exhumation and uplift of the Helan Mountain,China   总被引：2，自引：0，他引：2  

LIU JianHui  ZHANG PeiZhen  ZHENG DeWen  WAN JinLin  WANG WeiTao  DU Peng & LEI QiYun State Key Laboratory of Earthquake Dynamics 《中国科学:地球科学(英文版)》2010,(3)

The Helan Mountain, an intraplate deformation belt in the North China Craton, is located in the northern portion of the China North-South seismic belt, and at the northwestern margin of the Ordos Block. The Cenozoic deformation history of the Helan Mountain is characterized by extension along the eastern Helan Mountain fault (EHSF), resulting in the exhumation and uplift of the Helan Mountain, relative to the rifting of the adjacent Yinchuan Basin. Here we present new apatite fission track (AFT) data from several transects adjacent to the EHSF in the central and northern Helan Mountain. AFT ages from the northern Helan Mountain (Dawukou and Zhengyiguan transects) range from 10 Ma to 89 Ma, whereas AFT ages from the southern Helan Mountain (Suyukou transect) are greater than 71 Ma. The AFT data analysis reveals initiation of rapid uplift and exhumation of the Helan Mountain at 10–12 Ma. Additionally, a plot of the AFT ages versus their mean track length shows a distinctive "boomerang" pattern indicating that the Helan Mountain experienced a discrete phase of accelerated exhumation beginning at 10-12 Ma. Spatially, AFT samples systematically increase in age away from the EHSF and are consistent with late Cenozoic exhumation that was slow in the southwestern Helan Mountain and rapid in the northeastern Helan Mountain, as well more rapid adjacent to the EHSF and slower away from the EHSF. Obviously, the spatial distribution of late Cenozoic exhumation indicates that normal faulting of the EHSF is related to southwestward tilting and rapid exhumation of the Helan Mountain beginning at 10–12 Ma. The uplift and exhumation of the Helan Mountain was a response to the intensive extension of the northwestern margin of the Ordos Block in the late Cenozoic; this occurred under a regional extensional stress field oriented NW-SE along the Yinchuan-Jilantai-Hetao and the Weihe-Shanxi graben systems adjacent to the Ordos Block.  相似文献