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1.
Through a detailed study of sequence boundaries, it is concluded that sequence stratigraphy is an independent regional and transitional stratigraphic system between local lithostratigraphy and global chronostratigraphy. Therefore, a new tripartite stratigraphic classification scheme has been proposed. By combining organically the concept of sequence boundaries with the GSSP, it is suggested that the GSSP should be chosen in a conformale portion of a related sequence boundary, and the boundary established in light of this concept is defined as the Best Natural Boundary (BNB). The definition of the BNB points out the working area and stratigraphic level for the GSSP. By referring to a case study of the Permian Guadalupian/Lopingian boundary, the concept of the BNB has been elaborated in detail, and it is proposed that the BNB of the Guadalupian and the Lopingian lies between the Mesogondolella granti Zone and the Ctarkina postbitteri Zone, which is also the sequence chronostratigraphic boundary between th  相似文献   

2.
Analysis of the four cases of the sequence boundary (SB)-transgressive surface (TS) relation in nature shows that applying transgressive surfaces as sequence boundaries has the following merits: it improves the methodology of stratigraphic subdivision; the position of transgressive surface in a sea level curve is relatively fixed; the transgressive surface is a transforming surface of the stratal structure; in platforms or ramps, the transgressive surface is the only choice for determining the sequence boundary; the transgressive surface is a readily recognized physical surface reflected by seismic records in seismostratigraphy. The paper reaches a conclusion that to delineate a SB in terms of the TS is theoretically and practically better than to delineate it between highstand and lowstand sediments as has been done traditionally.  相似文献   

3.
It is well known that in pyroxene structure,there are two metal sites,M1 and M2.Generally speaking,Ferrous iron in each of these sites would normally be expected to give rise to a doublet,However,anomalies have been found in the relative areas of the peaks in the room temperature spectra of some clinopyroxene(CPX)when the above assignment is followed.According to the calculation of Next Nearest Neighbor configurations of divalent cations in M1,we found that the four configurations of M1 can be divided into two groups.One group is 3Ca configuration that increases with the content of Ca(p.f.u);the other group is made up of three No-3Ca configurations that decrease with the content of Ca.The two groups contribute to the spectrum structure of M1.so in this study we fit two doublets for ferrous iron in M1.Though there were several reports on Fe^3 in tetrahedral site previously,it was not sure that Fe^3 occupies the T site is a universal fact in CPX,despite of the content of Al.We found that the Fe^3 in the T site fitted by Moessbauer spectroscopy is negatively correlated to the Si content in the T site and positively correlated to the Fe^3 in the T site estimated on the supposition that Fe^3 and Al occupy the T site randomly.If it is true.it is important in the modeling of ion exchange geobarometries and geothermomeries.  相似文献   

4.
《《幕》》2008,31(3):290-290
Ten years ago, the IUGS fecognized the need to introduce changes in order to reflect the new circumstances that were evolving in the world. That vision resulted in a Strategic Action Plan which was approved in the year 2000, and slightly modified in 2004 by a document entitled Vision ＆ Road Map towards 2011, the year that the Union will celebrate its 50th anniversary. With these two documents in our hands and a series of actions being carried out, it seems that we are just walking on the right path and that it is only necessary to follow it. However, a series of actions still need to be considered and implemented.  相似文献   

5.
On the basis of previous studies and by means of field geological, remote sensing, petrographical,mineralogical, petrochemical and geochemical investigations, the authors studied the temporal-spatial distribu-tion of the regional structures, volcanic structures and products of volcanic activity in the coastal area ofsoutheastern Zhejiang. On the basis and through a systematic comparison of the products of magmatism in thearea, it is considered that there exists a compsite volcanic structural belt composed of linear and circular struc-tures and it has been demonstrated that there exist volcanic intrusive complexes--"trinity" composed of vol-canic, subvolcanic and plutonic rocks. It is suggested that the volcanic intrusive complexes in the area belong tothe typical syntexis series and that its materials were derived from a mixed source of crust and mantle.  相似文献   

6.
The Jinman copper deposit,which is situated on the northern margin of the Lanping-Simao back-arc basin,western Yunnan Province,is a silver-bearing,high-grade vein-type copper deposit.Comprehensive element geochemical studies of the host rocks and hydrothermal minerals revealed the regularities in the distribution,mobilization and transport of elements from the host rocks to hydrothermal minerals.In conjunction with the fluid inclusion and isotope data,it is suggested that the ore-forming fluid was derived mainly from a deep source characterized by CO2 enrichment and reduction in nature.It is also suggested that the oreforming materials come largely from a deep source.although the contribution of the country rocks should not be ruled out.It is also found that some hydrothermal minerals are possessed of MREE-enrichment patterns.It is deduced that the REEs in the deep-source ore fluid were transported in the form of CO3^2- complexes and were deposited in a continental basin(or a hot-spring basin).  相似文献   

7.
Sulfates are a main constituent of aerosols, which sulfate aerosols, it is necessary to determine what can cause various environmental problems sulfate ions are contained in these aerosols In the evaluation of the influence of In this study, sulfur K-edge XANES was used to determine sulfate species present in size-fractionated aerosol particles based on the post-edge structure after the main absorption peak in the XANES region. Aerosol samples were collected as part of the Japan-China joint project, ＂Asian Dust Experiment on Climate Impact＂ using a low-volume Andersen-type air sampler. XANES was measured at Beamline BL-9A at Photon Factory, Japan. A comparison of the XANES spectra of reference sulfate materials and aerosol samples collected in Tsukuba in Japan clearly showed that （NH4）2SO4 was the main sulfur species in particles with a smaller diameter and gypsum was the main sulfur species in particles with a larger diameter. A simulation of the XANES spectra by reference materials allows us to obtain the quantitative mixing ratios of the different sulfate species present in the aerosol samples. The presence of minor sulfur species other than （NH4）2SO4 and gypsum at the surface of mineral aerosols is suggested in our simulations and by a surface-sensitive conversion electron/He-ion yield XANES. In the absence of a contribution from a large dust event, the mole concentration of gypsum in the mineral aerosol fraction determined by XANES is similar to that of Ca which is determined independently using ion chromatography. This shows that the Ca and sulfate in the mineral aerosols are present only as gypsum. Considering that calcite is the main Ca mineral in the original material arising from an arid and semi-arid area in China, it is strongly suggested that gypsum is formed in aerosol during its long-range transportation by a reaction between calcite and sulfate ions.  相似文献   

8.
Molar-tooth carbonate refers to a sort of rock that has ptygmatical folded structure comparable to the ivory. This kind of carbonate exists in a special time range (from Middle to Neoproterozoic). Its origin and the possibility to use it in stratigraphic correlation of the paleocontinent is the key task of the IGCP447, a project on Proterozoic molar tooth carbonates and the evolution of the earth (2001-2005). The importance lies in that the molar-tooth structure is the key to solving problems related to Precambrian biological and global geochemical events. The molar-tooth structure is associated with microorganisms. Development and recession of such carbonates have relations with the evolution process of early lives and abrupt changes in sea carbonate geochemistry. In recent years, based on researches on petrology, geochemistry and Sr isotope of molar-tooth carbonate in the Jilin-Liaoning and Xuzhou-Huaiyang area, the authors hold that it can be used as a marker for stratigraphic sequence and sedimentary  相似文献   

9.
Fossil cytoplasm is a new research topic of interest in paleobotany. Atomic force microscope （AFM） is a new technology applied widely in physics and biology; however, it is rarely used in paleontology. Here we applied AFM for the first time to study fossil cytoplasm. The results indicate that the fossil cytoplasm is heterogeneous and full of ultrastructures, just like extant cytoplasm, and that the application of AFM, especially in combination with other techniques, can reveal the subcellular details of fossil plants with more confidence.  相似文献   

10.
Defining the Jurassic-Cretaceous boundary is a controversy in stratigraphic study of the world. It has been widely accepted that this boundary can be defined at the bottom of Berriasian in Tethys, with the appearance of the ammonite Berriasella jacobi dating to ca. 145 Ma. However, it is difficult for the widespread terrestrial deposits in China to correlate with the international standard of marine facies. The Somanakamura Group in Japan is represented by a succession of marine-continental transitional strata. It provides a bridge of marine and nonmarine stratigraphic correlation. The ammonite and radiolarian fossils preserved in this group suggest an age from Bajocian to early Valanginian. The J-K boundary was defined in or atop the Tomizawa Formation of the group according to the ammonite data. The present authors study the fossil spores and pollen newly found from the Tomizawa and Koyamada formations. Three assemblages have been recognized. They are Assemblage 1 (Cyathidites-Classopollis) from the upper part of the Tomizawa Formation, Assemblage 2 (Cyathidites-Jiaohepollis) from the lower part of the Koyamada Formation, and Assemblage 3 (Cyathidites-Spheripollenites-Ephedripites) from the middle to upper part of the Koyamada Formation. With the reference of ammonite evidence, the J-K boundary can be defined between Assemblage 1 and Assemblage 2. This palynological J-K boundary can be correlated with that of terrestrial sequence in China. However, local biostratigraphy imply that the continental J-K boundary in China is of 135 or 137 Ma age. It has a considerable discrepancy from the marine standard. Biogeographically, the distribution pattern of spores and pollen in southern China is in accordance with that in the Somanakamura Group, which parallels the Tuchengzi Formation in northeastern China. By the palynological correlation between the Somanakamura Group and the strata in southern China, and then with the sequence in northeastern China, it is suggested that the continental J-K boundary is located in the Tuchengzi Formation.  相似文献   

11.
A quantitative analysis of the distortion of octahedral and tetrahedral coordination polyhedra with respect to perfect symmetry in crystal structures is presented. The distortion of a polyhedron is defined by all the fourfold and threefold pseudo-symmetries. Tests on the significance of the pseudo-symmetries are presented. In forsterite the results are compared to ones previously proposed, based on the pseudo-symmetry of fourth order expansion of the crystal field, and also compared to the pseudo-symmetries of the environment of Mn2+ and Gd3+ that were determined by electron paramagnetic resonance (EPR) measurements. Agreements and differences between these results are given.  相似文献   

12.
Clinopyroxenes of the solid solution series hedenbergite (CaFeSi2O6)–petedunnite (CaZnSi2O6) were synthesized at temperatures of 825–1200°C and pressures of 0.5–2.5 GPa. Compositions were determined by electron microprobe analysis. Selected crystals were investigated by means of single crystal diffraction and structure refinement and the structural distortion was studied depending on the substitution of iron by zinc on the octahedral M1 site. It is shown that the coordination of the M1 site has the most significant effect on M–O bond lengths, with changes on the other sites accommodating this distortion. The mean quadratic elongation and the octahedral angle variance as quantitative measures of the distortion of the coordination polyhedron were correlated with former results of 57Fe Mössbauer spectroscopy at 298 K. The results presented now complete an earlier work on synthetic, crystalline powders of the same material and deliver exact structural data that were not possible to obtain by Rietveld refinements on powder data.  相似文献   

13.
Chromium L3,2 energy loss near-edge structures (ELNES) of nine chromium compounds were measured in a transmission electron microscope to study the effect of valence state and site geometry of chromium on spectral features. The compounds studied represent a set of standards with given valence state and coordination. The chromium coordination is either octahedral or tetrahedral with different degree of distortion. The distortion of polyhedra results in a loss of the fine detail of spectral features in Cr L3,2 ELNES spectra. The effect of valence state manifests in a systematic chemical shift of the ELNES spectra by about 2 eV per oxidation state for octahedrally coordinated Cr and 0.4–1.4 eV per oxidation state for tetrahedrally coordinated Cr. On the basis of collected Cr L3,2 ELNES spectra we propose a simple quantification technique for the determination of chromium oxidation state in oxidic compounds which is independent of the coordination.  相似文献   

14.
章礼明  方磐 《矿物学报》1991,11(3):209-213
本文碳硅钙石产于安徽濉溪邹楼铁矿床中。对该矿物进行了某些矿物学研究,修正了前人的碳硅钙石X射线粉晶衍射指标中的错误和不足。根据晶体结构测定结果,作者应用键价模型讨论了碳硅钙石结构中配位多面体的结构畸变等晶体化学问题。  相似文献   

15.
The electric field gradient (EFG) tensors of 7Li and 23Na in a zektzerite, NaLiZrSi6O15 single crystal have been determined by the nuclear magnetic resonance technique. The quadrupole coupling constants, e2qQ/h and the asymmetry parameters, η, for 7Li are 119 ± 5 kHz, 0.05 and for 23Na 2.42 ± 0.15 MHz, 0.86 respectively. In both cases, the EFG tensors show the two-fold site-symmetries at the Li- and Na-sites. For 7Li, the magnitude of the quadrupole coupling constant and the principal axis of the EFG tensor reflect the large angular distortion of the [LiO4] tetrahedron. The large quadrupole coupling constant of 23Na indicates a high degree of distortion of the Na coordination polyhedron.  相似文献   

16.
X-ray absorption spectroscopy at the Mg K-edge is used to obtain information on magnesium environment in minerals, silicate and alumino-silicate glasses. First-principles XANES calculations are performed for minerals using a plane-wave density functional formalism with core-hole effects treated in a supercell approach. The good agreement obtained between experimental and theoretical spectra provides useful information to interpret the spectral features. With the help of calculation, the position of the first peak of XANES spectra is related to both coordination and polyhedron distortion changes. In alumino-silicate glasses, magnesium is found to be mainly 5-fold coordinated to oxygen whatever the aluminum saturation index value. In silicate glasses, magnesium coordination increases from 4 in Cs-, Rb- and K-bearing glasses to 5 in Na- and Li-bearing glasses but remains equal as the polymerization degree of the glass varies. The variation of the C feature (position and intensity) is strongly related to the alkali type providing information on the medium range order.
Stéphanie RossanoEmail:
  相似文献   

17.
It is shown the possibility to determine the coordination of paramagnetic ions in disordered solid structures, e.g., in barium borate glasses. For this purpose the electron paramagnetic resonance (EPR) method was used to study α-and β-BaB2O4 crystals and glasses of 45·BaO × 55·B2O3 and 40·BaO × 60·B2O3 (mol%) composition activated by Ag+ and Pb2+ ions. After the samples were exposed to X-rays at 77 K, different EPR centers were observed in them. In α-and β-BaB2O4 crystals and glasses the EPR centers Ag2+, Ag0, Pb+, Pb3+, and hole centers of O− type were studied. The EPR parameters of these centers and their arrangement in crystal structure were determined. It is shown that Pb3+ ions in β-BaB2O4 crystals occupy Ba2+ position in an irregular polyhedron from the eight oxygen, whereas in α-BaB2O4 crystals they occupy Bа2 position in a sixfold coordination. Pb+ ions in α-BaB2O4 crystals occupy Bа1 position in a ninefold coordination from oxygen. In barium borate glasses, Pb3+ ions were studied in coordination polyhedron from six oxygen atoms and in a polyhedron from nine to ten oxygen atoms. It is assumed that the established difference in the structural position of Pb3+ ions in glasses is due to their previous incorporation in associative cation–anion complexes (AC) and “free” structure-forming cations (FC). Computer simulations have been performed to analyze the stability of specific associative complexes and to compare their bond lengths with experimental data.  相似文献   

18.
如何分析区域资源环境与社会经济之间的协调匹配程度,是促进区域经济可持续发展首先需要厘清的问题。基于资源环境承载协调理论,构建了基于双曲距离协调度的资源-经济系统的协调分析模型方法。根据该模型对全国依赖地下水资源且开发程度较高的514个县的地下水资源和经济数据进行了协调关系分析,评价了各县地下水资源禀赋与其承载的经济体之间的协调关系水平,结果显示2个系统之间的协调匹配程度及空间上具有较大差异性。东北和西北大部分地区处于地下水资源与经济协调的正向区间,区域经济发展仍具有一定潜力,华北及南方大部分地区处于负向协调区间,经济的发展超越了地下水资源的承载能力。  相似文献   

19.
孕育光催化活性的天然含钒金红石矿物学特征   总被引：4，自引：7，他引：4       下载免费PDF全文
天然含钒金红石平均含V2O5可达1．22％，Fe2O30．39％，ZnO0．35％，CuO0．22％，这些金属离子可替代八面体中Ti^4 。V以5价形式存在，配位多面体呈三方双锥，其在晶格内部对Ti的替代导致晶格畸变，打破了配位多面体原有的八面体对称而呈四方双锥的几何形态，并产生结构微应力。透射电镜研究表明，该天然金红石结构内部存在位错、晶界等缺陷，可以成为光催化活性位。对其进行受力、受热以及微波辐射等改性作用后，晶胞发生不同程度的膨胀，可能导致晶格畸变及应变能增加，进一步促进光催化活性。研究结果表明，该天然含钒金红石孕育有良好的光催化活性。  相似文献   

20.
叶玲  张敬阳  吴季怀 《矿物学报》2007,27(2):121-126
利用蒙脱石的层间活性,用过渡金属离子与配位体生成的配合物改性蒙脱石,通过测定改性蒙脱石对直接大红染料的脱色性及XRD图,研究配合物的中心离子种类、配位体种类、制备方法等对蒙脱石层间结构及吸附较大分子化合物性能的影响。结果表明,带正电的配合物离子能够有效进入蒙脱石层间、增大层间距;4或6配位数的配合物改性蒙脱石能明显提高对染料的吸附性;采用金属离子为先驱体,先插入蒙脱石层间,再原位生成配合物的两步法效果较好。  相似文献   

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