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91.
沼泽发育过程中堆积的各类沉积物真实地记录了区域环境演变与沼泽发育过程。以霍林河下游漫流区--向海沼泽湿地为研究对象,由137Cs、210Pb法定年实现沉积层深度坐标向年代坐标的转换,对其典型沉积剖面特征元素比值进行了综合剖析。结果表明:稳定元素对比值Ti/Al是判断不同沉积物来源是否一致的较好指标。剖面上下Ti/Al比值在一定层序的波动变化表明物源的波动性,洪水成因可能性较大。综合比较,V/(V+Ni)比值用于沼泽湿地缺氧沉积环境的判别标准可靠性较好。贫氧环境是向海沼泽湿地主要特征之一,其次是缺氧或含氧环境,各环境之间频繁振荡,体现了内流河下游半干旱区沼泽地表水周期和干湿环境转换频繁的特征。 相似文献
92.
Cs. Sajg 《Organic Geochemistry》2000,31(12)
Biological marker maturity parameters were used to estimate the minimum HC generation temperatures of crude oils from Eastern Hungary. More than 50 oils and oil shows were analysed. Molecular- and homologous-ratios of biological marker compounds (triterpanes, steranes, mono- and triaromatic steroid hydrocarbons) were used as maturation parameters. The oils have at least five maturity stages, i.e. they have been generated under different thermal conditions. The highest reservoir temperature in each group was chosen as the best estimate of the groups' temperature just below the generation temperature, i.e. reservoirs of the group might be expected to be at shallower depths (lower temperatures) than those of the generation zone due to vertical migration into pools. For each maturation level, a threshold temperature range for genesis was inferred from reservoir temperatures; they are from 130–135°C for the least mature oils to 210–215°C for the most mature oils. In the least mature oils cracking was not observed, hence carbon–carbon cracking reactions had not taken place during their genesis. The most mature oils are intensively cracked oils; they are almost condensates. Two major genetic groups (families) of oils were found in the area. Both are present in each maturation level. The effects of migration were checked, and no influence on maturation was found. A number of the oils are in overpressured reservoirs within, or just above, the zone of the present-day active oil generation, hence the present-day temperatures of the pools must have been maximum temperatures. Contrary to the traditionally accepted temperature range for petroleum generation–maturation reactions (50–150°C), there is strong evidence from this study that the onset of oil generation requires temperatures higher than 130°C and is still proceeding above 215°C. 相似文献
93.
Surendra P. Verma 《Journal of Earth System Science》2000,109(1):79-88
This paper presents error propagation equations for modeling of radiogenic isotopes during mixing of two components or end-members.
These equations can be used to estimate errors on an isotopic ratio in the mixture of two components, as a function of the
analytical errors or the total errors of geological field sampling and analytical errors. Two typical cases (“Small errors”
and “Large errors”) are illustrated for mixing of Sr isotopes. Similar examples can be formulated for the other radiogenic
isotopic ratios. Actual isotopic data for sediment and basalt samples from the Cocos plate are also included to further illustrate
the use of these equations. The isotopic compositions of the predicted mixtures can be used to constrain the origin of magmas
in the central part of the Mexican Volcanic Belt. These examples show the need of high quality experimental data for them
to be useful in geochemical modeling of magmatic processes. 相似文献
94.
Der-Wen Chang J. M. Roesset Chan-Hua Wen 《Soil Dynamics and Earthquake Engineering》2000,19(8):157-558
This paper introduces the mathematics and procedures used in developing a time-dependent damping model for integration analyses of structural response. To establish the time-dependent viscous damping model, frequency-dependent damping ratios of the structure under a series of steady-state unit impulses corresponding to actual loads are first calculated. For simplicity, the ratios can be incorporated with the static stiffness of the structure to model approximately the impulse induced damping spectrum. According to the nature of the problem, these ratios can be calculated from the theoretical impedance functions and experimental observations. With the computed damping spectrum, the damping coefficient in the time domain can be obtained with the Fourier transform technique. Adopting the impulse–response method, the damping can be modeled rationally through integration with changing loads. Numerical examples are presented to show the feasibility of this model while the transform criterion is satisfied. 相似文献
95.
96.
97.
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
98.
从矿山生产经营的主要指标分析入手,建立以效益为目标函数的经济分析模型,全面进行矿产经济评价,探讨生产成本、出矿品位、贫化率、矿石产量等对矿山经营效果的影响,从而找出影响矿山经济效益的主要因素,进行指导矿山生产。 相似文献
99.
G. A. Valui E. Yu. Moskalenko A. A. Strizhkova G. R. Sayadyan 《Russian Journal of Pacific Geology》2008,2(2):150-157
The Cretaceous-Paleogene granites of the Eastern Sikhote Alin volcanic belt (ESAVB) and Late Cretaceous granitoids of the Tatibin Series (Central Sikhote Alin) are subdivided into three groups according to their oxygen isotope composition: group I with δ18O from +5.5 to +6.5‰, group II with δ18O from +7.6 to +10.2‰, and group III with less than +4.5‰. Group I rocks are similar in oxygen isotope composition to that of oceanic basalts and can be derived by melting of basaltic crust. Group II (rocks of the Tatibin Series) have higher δ18O, which suggests that their parental melts were contaminated by sedimentary material. The low 18O composition of group III rocks can be explained by their derivation from 18O-depleted rocks or by subsolidus isotopic exchange with low-18O fluid or meteoric waters. The relatively low δ18O and 87Sr/86Sr in the granitoids of Primorye suggest their derivation from rocks with a short-lived crustal history and can result from the following: (1) melting of sedimentary rocks enriched in young volcanic material that was accumulated in the trench along the transform continental margin (granites of the Tatibin Series) and (2) melting of a mixture of abyssal sediments, ocean floor basalts, and upper mantle in the lithospheric plate that subsided beneath the continent in the subduction zone (granites of the ESAVB). 相似文献
100.
孟加拉湾由于陆源物质大量输入产生稀释效应,使碳酸盐含量表现为冰期时减小、间冰期时增大的“大西洋型”旋回。通过对该区四支活塞岩芯的有孔虫溶解指数、浮游有孔虫沉积通量、CaCO3 沉积通量和 >16 0 μm粗组分沉积通量的分析发现,研究区碳酸盐溶解作用强烈,表现出冰期减弱而间冰期增强的总趋势,且溶解作用滞后于浮游有孔虫壳的氧同位素旋回,尤以氧同位素 4、5期的高溶解度情况与印度洋和太平洋氧同位素 5期晚期至 4期为CaCO3溶解高峰一致。因此,孟加拉湾地区的CaCO3 旋回是大西洋型稀释作用与太平洋型溶解作用两者叠加的产物. 相似文献