Rb and Sr Geochemical Characterization of the Chinese Loess Stratigraphy and Its Implications for Palaeomonsoon Climate   总被引：1，自引：0，他引：1  

CHEN JunDepartment of Earth Sciences  Nanjing University  Nanjing WANG Yongjin  Department of Geography  Nanjing Normal University  Nanjing CHEN Yang  LIU Lianwen  JI Junfeng Department of Earth Sciences  Nanjing University  Nanjing  LU Huayu Xi ''an State Key Laboratory of Loess  Quaternary Geology  Chinese Academy of Sciences  Xi ''an 《《地质学报》英文版》2000,74(2):279-288

Concentrations and distributions of Rb and Sr in loess and palaeosol samples from the Luochuan profile have been studied, in grain-size fractions and chemical forms. Results show that Rb is quite rich in the fraction of less than 2μm, and exits only in the residual phase, while Sr is distributed in sand and silt fractions, occurring in the residual and carbonate phases. Therefore, variations of the concentrations of Rb and Sr in loess and palaeosols are closely related not only to dustfall compositions depending on winter monsoon wind strength but also to summer monsoon-induced pedogenic intensity. This indicates that variations of Rb/Sr ratio in Chinese loess sequences represent cyclic alternations of East Asian summer and winter monsoon climates on the orbital time-scale. Variations in Sr concentrations along the sequence bear a high similarity to the oxygen isotope record of the deep sea sediments over the past 2.5 Ma, whereas variations in Rb concentrations are in good agreement with the record of  相似文献   

Characterization of landscape pattern based on land economic niche change: A case study in Ganzhou,Gansu Province,China     

Hua Li Tong  Pei Ji Shi  Xue Bin Zhang  Zai Yan Li 《寒旱区科学》2018,10(3):261-270

Land use change has a profound impact on biodiversity and ecological processes, and is closely related to changes in landscape patterns. This paper introduces the theory and method of land economic niche into landscape ecology, which provides a new method for spatial characterization of urban and rural spatial landscape patterns. Based on this theory, this paper analyzes the landscape pattern of Ganzhou District by using Landsat images as data source in 1995, 2000, 2005,2010 and 2015. We calculated the land economic niche by applying the niche potential theory. Combined with the theory of landscape ecology, we explored the effects of the land economic niche change on the landscape pattern at a county scale.The results show that economic niche of construction land, watershed and farmland increased during 1995–2015, and grassland declined significantly. The economic niche of farmland, construction land, watershed and grassland show a negative correlation with the number of patches(NP), fragmentation index(FN) and the fractal dimension index(FD), and had a positive correlation with the aggregation index(AI). There was no significant correlation between the forest land economic niche and landscape metrics. The change of land economic niche has a driving effect on the landscape pattern of the county, which can represent the economic development direction of Ganzhou District. The land economic niche is closely related to the landscape type which can directly obtain an economic benefit.  相似文献   

Applying energy theory to understand the relationship between the Yangtze River and Poyang Lake   总被引：1，自引：1，他引：0  

Mofei Chen  Jinyun Deng  Shaoying Fan  Yitian Li 《地理学报(英文版)》2018,28(8):1059-1071

The complex relationship between the Yangtze River and Poyang Lake controls the exchange of water and sediment between the two, and exerts effects on water resources, flooding, shipping, and the ecological environment. The theory of energy is applied in this paper to investigate the physical mechanisms that determine the nature of the contact between the Yangtze River and Poyang Lake and to establish an energy difference (F_e) index to quantify the interactions between the two systems. Data show that F_e values for this interaction have increased since the 1950s, indicating a weakening in the river effect while the lake effect has been enhanced. Enclosure of the Three Gorges Reservoir (TGR) has also significantly influenced the relationship between the river and the lake by further reducing the impacts of the Yangtze River. The river effect also increases slightly during the dry season, and decreases significantly at the end of the flooding period, while interactions between the two to some extent influence the development of droughts and floods within the lake area. Data show that when the flow of the five rivers within this area is significant and a blocking effect due to the Yangtze River is also clearly apparent, floods occur easily; in contrast, when the opposite is true and the flow of the five rivers is small, and the Yangtze River can accommodate the flow, droughts occur frequently. Construction and enclosure of the TGR also means that the lake area is prone to droughts during September and October.  相似文献   

Kernel Principal Component Analysis for Efficient,Differentiable Parameterization of Multipoint Geostatistics   总被引：6，自引：5，他引：1  

Pallav Sarma  Louis J. Durlofsky  Khalid Aziz 《Mathematical Geosciences》2008,40(1):3-32

This paper describes a novel approach for creating an efficient, general, and differentiable parameterization of large-scale non-Gaussian, non-stationary random fields (represented by multipoint geostatistics) that is capable of reproducing complex geological structures such as channels. Such parameterizations are appropriate for use with gradient-based algorithms applied to, for example, history-matching or uncertainty propagation. It is known that the standard Karhunen–Loeve (K–L) expansion, also called linear principal component analysis or PCA, can be used as a differentiable parameterization of input random fields defining the geological model. The standard K–L model is, however, limited in two respects. It requires an eigen-decomposition of the covariance matrix of the random field, which is prohibitively expensive for large models. In addition, it preserves only the two-point statistics of a random field, which is insufficient for reproducing complex structures. In this work, kernel PCA is applied to address the limitations associated with the standard K–L expansion. Although widely used in machine learning applications, it does not appear to have found any application for geological model parameterization. With kernel PCA, an eigen-decomposition of a small matrix called the kernel matrix is performed instead of the full covariance matrix. The method is much more efficient than the standard K–L procedure. Through use of higher order polynomial kernels, which implicitly define a high-dimensionality feature space, kernel PCA further enables the preservation of high-order statistics of the random field, instead of just two-point statistics as in the K–L method. The kernel PCA eigen-decomposition proceeds using a set of realizations created by geostatistical simulation (honoring two-point or multipoint statistics) rather than the analytical covariance function. We demonstrate that kernel PCA is capable of generating differentiable parameterizations that reproduce the essential features of complex geological structures represented by multipoint geostatistics. The kernel PCA representation is then applied to history match a water flooding problem. This example demonstrates that kernel PCA can be used with gradient-based history matching to provide models that match production history while maintaining multipoint geostatistics consistent with the underlying training image.  相似文献   

Site characterization for CO<Subscript>2</Subscript> geologic storage and vice versa: the Frio brine pilot,Texas, USA as a case study     

Christine Doughty  Barry M. Freifeld  Robert C. Trautz 《Environmental Geology》2008,54(8):1635-1656

Careful site characterization is critical for successful geologic storage of carbon dioxide (CO₂) because of the many physical and chemical processes impacting CO₂ movement and containment under field conditions. Traditional site characterization techniques such as geological mapping, geophysical imaging, well logging, core analyses, and hydraulic well testing provide the basis for judging whether or not a site is suitable for CO₂ storage. However, only through the injection and monitoring of CO₂ itself can the coupling between buoyancy flow, geologic heterogeneity, and history-dependent multi-phase flow effects be observed and quantified. CO₂ injection and monitoring can therefore provide a valuable addition to the site-characterization process. Additionally, careful monitoring and verification of CO₂ plume development during the early stages of commercial operation should be performed to assess storage potential and demonstrate permanence. The Frio brine pilot, a research project located in Dayton, Texas (USA) is used as a case study to illustrate the concept of an iterative sequence in which traditional site characterization is used to prepare for CO₂ injection and then CO₂ injection itself is used to further site-characterization efforts, constrain geologic storage potential, and validate understanding of geochemical and hydrological processes. At the Frio brine pilot, in addition to traditional site-characterization techniques, CO₂ movement in the subsurface is monitored by sampling fluid at an observation well, running CO₂-saturation-sensitive well logs periodically in both injection and observation wells, imaging with crosswell seismic in the plane between the injection and observation wells, and obtaining vertical seismic profiles to monitor the CO₂ plume as it migrates beyond the immediate vicinity of the wells. Numerical modeling plays a central role in integrating geological, geophysical, and hydrological field observations.  相似文献   

Multi-Scale and Multi-Resolution Stochastic Modeling of Subsurface Heterogeneity by Tree-Indexed Markov Chains     

Michel Dekking  Amro Elfeki  Cor Kraaikamp  Johannes Bruining 《Computational Geosciences》2001,5(1):47-60

  相似文献   

Enzymological classification of salt lakes in Romania     

Vasile Muntean  Radu Crisan  Daniela Paşca  Stefan Kiss  Mihail Drăgan-Bularda 《International Journal of Salt Lake Research》1996,5(1):35-44

Sediments of 56 salt lakes from Romania were studied enzymologically. The following 7 enzymatic and nonenzymatic catalytic activities have been measured: phosphatase, H₂O₂-splitting in nonautoclaved (catalase) and autoclaved samples, TTC reduction in nonautoclaved (dehydrogenase) and autoclaved samples, without or with glucose addition. A formula is proposed for the evaluation of the enzymatic potential of salt lake sediments or other habitats. A hierarchy of the studied lakes has been established on the basis of the enzymatic potential of their sediments expressed as enzymatic indicator.  相似文献   

滇西高黎贡变质岩带南段淡色花岗岩脉年代学特征及构造意义   总被引：2，自引：0，他引：2  

唐渊  王冬兵  廖世勇  王保弟  尹福光  王立全 《岩石学报》2016,32(8):2347-2366

高黎贡构造带作为藏东三江地区大地构造上的一条重要构造带,在印度-欧亚板块碰撞过程中起着重要的调节作用,并被认为是该地区发生"大陆逃逸"与地块旋转的西边界。本文以高黎贡构造带中的深变质岩为研究对象,通过对高黎贡变质岩带南段进行详细地构造解析,发现其内部广泛发育一系列或顺岩石面理、或切割面理分布的淡色花岗岩脉;并选取了5个淡色花岗岩脉样品进行锆石U-Pb测年,这5个样品的锆石~(206)Pb/~(238)U年龄值主要分布于二个区间:68~40Ma和24~21Ma,并在45Ma左右形成一个巨大的峰值。基于锆石的晶形、晶内结构和微量元素组成特征等方面进行锆石成因学分析,认为本文所测试的5个淡色花岗岩脉样品的锆石为深熔作用过程中形成的锆石;从而推测高黎贡变质岩带南段发生深熔作用并形成淡色花岗岩脉的时代主要集中于68~40Ma和24~21Ma。  相似文献   

酶解褐藻胶寡糖的HPCE分析方法研究     

孙燕  吕志华  王远红  张真庆 《中国海洋大学学报(自然科学版)》2005,35(6):984-986

采用高效毛细管电泳法（HPCE）对酶解褐藻胶寡糖进行了分离分析,考察了缓冲液浓度、pH、电压及温度等参数对寡糖分离的影响.实验结果表明在pH=2.5,100mmol/L 磷酸盐缓冲液中,运行电压20kV,电泳由负极到正极,温度30℃,235nm紫外检测条件下,酶解褐藻胶寡糖获得了高效分离.  相似文献   

Pore pressure assessment from well data and overpressure mechanism: Case study in Eastern Tunisia basins     

Samah Adouani  Riadh Ahmadi  Mahmoud Khlifi  Dhaou Akrout  Eric Mercier  Mabrouk Montacer 《Marine Georesources & Geotechnology》2020,38(7):830-843

Abstract

Independent and complementary methods were used for pore pressure assessment in the eastern Tunisian basins. Drilling data and surveys allow settling the pore pressure profile in these basins. The main used parameters are mud weights, formation pressure surveys, drilling parameters, well logs, fluids exchange with formation and borehole issues. In the eastern Tunisia platform, the pore pressure profiles show changes in overpressure magnitude in all the three dimensions of the basin (location and depth/stratigraphy). We highlighted two overpressure intervals form bottom to top: The late Cretaceous in the North-eastern part, and the Tertiary overpressure interval hosted in the Palaeocene to Miocene series. The structural analysis of overpressure location shows that the Tertiary interval is likely to have originated in a disequilibrium compaction in Cenozoic grabens. Pore pressure cross sections and maps confirm the link between active normal faults that segmented the basin to grabens and highs and pore pressure anomalous area. In the Senonian interval, we noted mature source-rocks that can explain the overpressure in the late Cretaceous interval. In addition, the recent to active compressive tectonics may have contributed to both pore pressure anomaly generations. The fluid overpressures characterization in the eastern Tunisian sedimentary basins helps in hydrocarbons exploration. Indeed, the overpressure interval in the reservoir levels stimulates and improves the production in the oilfields and contributes to hydrocarbon trapping. Moreover, the adequate prediction of pore pressure profile contributes to reduce drilling cost and enhance the drilling operations safety.  相似文献