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951.
Lian-Jun Feng Xue-Lei Chu Jing Huang Qi-Rui Zhang Hua-Jin Chang 《Gondwana Research》2010,18(4):632-637
In South China, the Datangpo black shales (663 Ma–654.5 Ma) were deposited during the Cryognian interglacial time between the Sturtian and Marinoan glaciations. Multi-geochemical proxies, including different iron speciation and relevant ratios (FeHR/FeT, FeP/FeHR and FeT/Al ratios) and molybdenum concentrations, were used to reconstruct the paleo-depositional environment of this black shale horizon. The ratios of different iron species (FeHR/FeT > 0.38 and FeP/FeHR < 0.80) suggest an overall anoxic conditions (ferruginous) over the deposition of the black shales, although intermittent euxinic (FeHR/FeT > 0.38 and FeP/FeHR ≈ 0.80) and oxic (FeHR/FeT < 0.38) intervals could have occurred. Furthermore, FeT/Al ratios (FeT/Al ≤ 0.51) confirm that water column may not be persistent euxinia during the deposition of the Datangpo black shales. Meanwhile, molybdenum concentrations show a decreasing trend towards the top of the black shales, reconciling the gradual oxygenating trend during this period as stated above. Compared to δ34SPy values in the Mesoproterozoic deep ocean, more positive δ34SPy values of this study may result from a small size of sulfate reservoir. The small-size sulfate reservoir and concurrent enrichment of molybdenum indicate that the ocean chemistry in the Cryogenian Period is similar to that in the Archean Eon. 相似文献
952.
Yusheng Wan Dunyi Liu Simon A. Wilde Jianjin Cao Bin Chen Chunyan Dong Biao Song Lilin Du 《Journal of Asian Earth Sciences》2010,37(2):140-153
The Yunkai Terrane is one of the most important pre-Devonian areas of metamorphosed supracrustal and granitic basement rocks in the Cathaysia Block of South China. The supracrustal rocks are mainly schist, slate and phyllite, with local paragneiss, granulite, amphibolite and marble, with metamorphic grades ranging from greenschist to granulite facies. Largely on the basis of metamorphic grade, they were previously divided into the Palaeo- to Mesoproterozoic Gaozhou Complex, the early Neoproterozoic Yunkai ‘Group’ and early Palaeozoic sediments. Granitic rocks were considered to be Meso- and Neoproterozoic, or early Palaeozoic in age. In this study, four meta-sedimentary rock samples, two each from the Yunkai ‘Group’ and Gaozhou Complex, together with three granite samples, record metamorphic and magmatic zircon ages of 443–430 Ma (Silurian), with many inherited and detrital zircons with the ages mainly ranging from 1.1 to 0.8 Ga, although zircons with Archaean and Palaeoproterozoic ages have also been identified in several of the samples. A high-grade sillimanite–garnet–cordierite gneiss contains 242 Ma metamorphic zircons, as well as 440 Ma ones. Three of the meta-sedimentary rocks show large variations in major element compositions, but have similar REE patterns, and have tDM model ages of 2.17–1.91 Ga and εNd (440 Ma) values of −13.4 to −10.0. Granites range in composition from monzogranite to syenogranite and record tDM model ages of 2.13–1.42 Ga and εNd (440 Ma) values of −8.4 to −1.2. It is concluded that the Yunkai ‘Group’ and Gaozhou Complex formed coevally in the late Neoproterozoic to early Palaeozoic, probably at the same time as weakly to un-metamorphosed early Palaeozoic sediments in the area. Based on the detrital zircon population, the source area contained Meso- to Neoproterozoic rocks, with some Archaean material. Palaeozoic tectonothermal events and zircon growth in the Yunkai Terrane can be correlated with events of similar age and character known throughout the Cathaysia Block. The lack of evidence for Palaeo- and Mesoproterozoic rocks at Yunkai, as stated in earlier publications, means that revision of the basement geology of Cathaysia is necessary. 相似文献
953.
2008年初上海冰雪天气与冷空气路径的相关性研究 总被引:3,自引:1,他引:2
2008年1月10日至2月2日,中国南方地区出现了自1951a以来最为严重的连续低温冰雪灾害天气。研究表明,冰雪天气是北方强冷空气与南方暖湿气流共同作用的结果。进一步研究得到,低空冰点以下温度是下雪的基本条件,但上海冬季降水性质还与冷空气路径有关,当冷高压中心位于蒙古东部,冷空气从中路偏东南下时,上海受到东北海风的暖海面调节,近地面气温升高,使雪花在降落过程中融为雨水,上海以雨为主偶有小雪;当冷高压中心位于蒙古西部,冷空气从中路南下,上海吹西北来陆风时,脱离了冬季暖海面调节,雪花保持固态着地,上海同内陆地区一样下雪。 相似文献
954.
Dong‐Chan Koh Ho‐Wan Chang Kwang‐Sik Lee Kyung‐Seok Ko Yongje Kim Won‐Bae Park 《水文研究》2005,19(11):2225-2245
Ground water from springs and public supply wells was investigated for hydrochemistry and environmental isotopes of 3H, 18O and D in Jeju volcanic island, Korea. The wells are completed in a basaltic aquifer and the upper part of hydrovolcanic sedimentary formation. Nitrate contamination is conspicuous in the coastal area where most of the samples have nitrate concentrations well above 1 mg NO3 N/l. Agricultural land use seems to have a strong influence on the distribution of nitrate in ground water. Comparison of stable isotopic compositions of precipitation and ground water show that ground water mostly originates from rainy season precipitation without significant secondary modification and that local recharge is dominant. 3H concentration of ground water ranged from nearly zero to 5 TU and is poorly correlated with vertical location of well screens. The occurrence of the 3H‐free, old ground water is due to the presence of low permeability layers near the boundary of the basaltic aquifer and the hydrovolcanic sedimentary formation, which significantly limits ground water flow from the upper basaltic aquifer. The old ground water exhibited background‐level nitrate concentrations despite high nitrate loadings, whereas young ground water had considerably higher nitrate concentrations. This correlation of 3H and nitrate concentration may be ascribed to the history of fertilizer use that has increased dramatically since the early 1960s in the island. This suggests that 3H can be used as a qualitative indicator for aquifer vulnerability to nitrate contamination. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
955.
Many civil infrastructures are located near the confluence of two streams, where they may be subject to inundation by high flows from either stream or both. These infrastructures, such as highway bridges, are designed to meet specified performance objectives for floods of a specified return period (e.g. the 100 year flood). Because the flooding of structures on one stream can be affected by high flows on the other stream, it is important to know the relationship between the coincident exceedence probabilities on the confluent stream pair in many hydrological engineering practices. Currently, the National Flood Frequency Program (NFF), which was developed by the US Geological Survey (USGS) and based on regional analysis, is probably the most popular model for ungauged site flood estimation and could be employed to estimate flood probabilities at the confluence points. The need for improved infrastructure design at such sites has motivated a renewed interest in the development of more rigorous joint probability distributions of the coincident flows. To accomplish this, a practical procedure is needed to determine the crucial bivariate distributions of design flows at stream confluences. In the past, the copula method provided a way to construct multivariate distribution functions. This paper aims to develop the Copula‐based Flood Frequency (COFF) method at the confluence points with any type of marginal distributions via the use of Archimedean copulas and dependent parameters. The practical implementation was assessed and tested against the standard NFF approach by a case study in Iowa's Des Moines River. Monte Carlo simulations proved the success of the generalized copula‐based joint distribution algorithm. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
956.
The governing equations for one‐dimensional consolidation of layered structured soils under time‐dependent loading are established. Using simplified k‐σ′ and mv‐σ′ models, n‐layered structured soils are transformed into (n + 1) or (n + 2)‐layered soils in which the thickness of upper and lower layers are gradually changing. The approximate solutions for the governing equations are then obtained under two types of boundary conditions, and the computer program is developed. Based on the solutions and computer program, the consolidation behavior of layered structured soils with soft interlayer is studied. It is shown that the permeability and compressibility of the soft interlayer have the greatest influences on the rate of settlement and rate of the dissipation of excess pore water pressure. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
957.
An understanding of groundwater flow and chemistry is important to operate underground storage caverns. Groundwater flow is mainly affected by cavern operating conditions. Groundwater chemistry is modified by disinfection activities for removing possible biological clogging and by mixing with cement pore water. It is important to discern these two effects, because wells affected by the disinfection activities may have hydrological connections with water curtains used to inject the disinfectant. However, it is difficult to separate these two effects using graphical methods because of their similar chemical characteristics. Instead, multivariate statistical analysis, such as principal component analysis (PCA) and factor analysis (FA), can be used. Groundwater samples for chemical analysis were obtained from four surveys in 1999–2000. Based on the results from PCA and FA, it appears that there were temporal variations of seepage water into the propane area when the cavern operation fluctuated, but we could not observe such variation in the butane area. These changes may occur mainly at depth, where water flow is slow and water renewal in the cavern surrounding is limited. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
958.
建立在统计信号处理理论基础上的相关检测器和匹配滤波器取得了广泛的应用,但两种模型都是建立在对实际通信信道线性化近似基础上的,在适应信道的非线性变化方面有所不足.利用神经网络自适应、非线性和高速并行运算的特点,在此提出了一种结构简单有效的神经网络接收机,并可推广到其他确知信号. 相似文献
959.
鞍山东山风景区3.8—2.5Ga古老岩带的同位素地质年代学和地球化学 总被引:18,自引:0,他引:18
鞍山东山风景区古老岩带呈巨型包体存在于立山奥长花岗岩(3.1Ga)中,其主体为条带状片麻岩(3.8Ga)。此外还有金云母透闪石岩、(含)黑云斜长角闪岩、闪长质片麻岩、变石英闪长质岩石、细粒奥长花岗岩、二长花岗岩、伟晶岩脉等。测定了部分岩石的锆石年龄,其中变石英闪长质岩石(A9604)为3.65Ga(Wan et al.,1999),闪长质片麻岩(A9317)为3.5Ga、二长花岗岩(类型I,A9605)为3.1Ga,黑云斜长角闪岩(A0019)为3.3Ga、细粒奥长花岗岩(A0017)为3.2Ga、二长花岗岩(类型Ⅱ,A0020),为2.6Ga,有关岩石的地球化学组成特征在文中地进行了简要介绍,在此基础上,提出了该古老岩带的地质同位素年代演化序列,认为鞍山地区不同时代、不同成因地质体空间上共存是该芡长期地质演化的结果,而不是后期构造作用把它们拼合到一起的,鞍山地区很可能存在>3.8Ga的古老地壳岩石。 相似文献
960.