首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 421 毫秒
1.
Acta Geologica Sinica (hereinafter referred to as the Acta) starting publication in 1922, is a quaterly academia periodical sponsored by the Geological Society of China (GSC). It has been one of the science and technology periodicals in China with the longest history.  相似文献   

2.
Systematic determination of and adsorption experiment on fluorine in the carbonate rock-soil-water system in the karst region studied in Guzhou Province,in conjunction with the mineral surface and soil chemistry data,have revealed the geochemical characteristics of F and the mechanisms of its transport and entrichment in the rock-soil-water-system of the karst region central guizhou province,Deep-seated underground waters(-100m or lower)and soil layers in the karst region of central Guizhou are characterized by high-F anomalies whereas shallow-level underground and surface waters by low contents of F(mostly lower than 05mg/L).Fluorine in soil and water in the region studied comes largely from Triassic marine strata dominated by gypsum-bearing carbonate rocks.The special adsorption and desorption of F on the surface of geothite in soil layers are the important mechanisms of its transport and enrichment in the rock-soil-water system of the karst region studied.  相似文献   

3.
In this paper. it is demonstrated that there exist marine horizons in the upper part of the lower subcycleand the upper subeycle of the Kizilsu Group in Xinjiang. based on new evidence of authigenic glauconite.boron content. carbon and oxygen stablc isotopic analyses. and lithological and sedimentary features. The up-per part of the lower subeycle is the lowermost marine horizon of the Cretaceous in the western Tarim Basin,which is inferred to be of Barremian age.  相似文献   

4.
There is a zone of blastomylonites containing hornblende gneisses of Lewisian Inliertype in the northeast-east of Yell,Shetland.This zone with a north—northwesterlytrend consists of blastomylonised hornblende-banded gneiss,hornblende-feldspar gneissand mica-felsie-gneiss with lenses of hornblende gneiss.It is indicated that theblastomylonite zone is actually a ductile shear zone and the sense of shear is dextral.This contributes to understanding the details of tectonic evolution in this area,and thiszone is probably a part of tectonic system of the British Caledonides.  相似文献   

5.
  相似文献   

6.
In the eastern part of Chian there had occurred large-scale gold mineralization during the Mesozoic,resulting in a large number of inprotant gold ore-concentrated areas.In this paper we have selected some isotope data(including four gold deposits previously studied and two gold deposis in this work)of Au-bearing quartz veins of the representative gold deposits in six impor-tant gold ore-concentrated areas in the periphery of the North China Platform and calculated their metallogenic ages using the method of Ludwig(2.90 version).The results show that the repre-sentative gold deposits in the six gold ore-concentrated areas were formed during the Mesozoic.  相似文献   

7.
Spectrogram analysis of seven natural gamma-ray logging of Member 1 of the Qingshankou Formation (K2qn1) and Member 1 and 2 of the Nenjiang Formation (K2n1-2) of Late Cretaceous age in the Songliao Basin reveals sedimentary cyclicities controlled by Milankovitch climate periodicities. The recognition of Milankovitch cycles allows estimation of an average accumulation rate of ~7.55–8.62 cm/ka for the K2qn1 sections, and ~6.69–10.16 cm/ka for the K2n1-2 sections. Two marine transgression events occurred during the deposition of K2qn1 and K2n1-2 and their ages are at ~0.74–1.10 Ma and ~2.38–4.84 Ma, respectively. Identification of Milankovitch cycles from fine-grained deep lake sedimentary rocks in the Songliao Basin may provide great potential for high-resolution stratigraphic subdivisions and correlations.  相似文献   

8.
The Campanian-Maastrichtian phosphatic deposits in Egypt,called the Duwi Forma-tion,comprise a part of the extensive Middle East to North African phosphogenic province of Late Cretaceous to Paleogene age.The province holds the greatest accumulation of phosphorites in the geological history,possibly in excess of 70 billion metric tons.The phosphate resources in Egypt alone exceed 3 billion metric tons.Two-third of these three billions occur only in the Abu-Tartur area.Among the phosphorite deposits in Egypt,the phosphorites of the Abu-Tartur area are characterized by high contents of iron ranging from 3% to 7% with an average of 5%.The detailed mineralogical and geochemical studies on the Abu-Tartur phosphorites revealed that iron is found in the form of pyrite,ankerite,clay minerals,microinclusions,and iron oxide.Pyrite,which is the major fraction,occurs as filling cement and partial to complete teplacement of phosphatic grains and confined to the fresh phosphorites while iron oxide occurs as cryp-tocrystalline aggregates of red to brown particles and is confined to the weathered outcrops.Ex-clusive relations between pyrite in the fresh phosphorite samples inside the Abu-Tartur mine and iron oxide in the equivalent horizon of the weathered exposure indicated that iron oxide was formed by the oxidation of pyrite as a result of weathering.All of these forms harm the quality of ore,manufacturing processes,and the produced phosphoric acid and fertilizers.  相似文献   

9.
Awan Yath Yath 《GeoJournal》1995,36(1):93-101
The magnitude of housing demand and the inadequacy of public housing in most cities of the Third World have led to the emergence of types of housing which, while having different names, are classified as squatter settlements. In Khartoum, the expansion of squatter settlements has mainly been due to political processes that resulted in dramatic urban needs generated by uneven development, widespread migration, demographic growth and income inequalities. In the recent years, however, rural recession, civil war, drought, floods and famine combined to turn the Sudanese capital city into a reception centre for a considerable number of displaced people from areas affected. Here the bulk of the displaced persons found accommodation in huts that they built themselves. The government responded to such a situation by embarking on a large scale deportation programme. Attempts to bargain, resist, or to cope with the political system, on the part of the displaced people, proved to be in vain. Available estimates suggest that at least two thirds of the two or more million migrants who moved to Khartoum during the last sixteen years, have now been forcibly driven back to rural areas.  相似文献   

10.
The UK is a country with limited direct experience of natural disasters. Whilst landslide losses are not negligible and fatalities are rare, accounts are under-reported. Financial losses from landslides are poorly understood but likely to be considerably in excess of £10 million per year. As a result, a strategic management framework has evolved based upon small, low-impact events punctuated by occasional larger events or larger landslides affecting urban areas. We present an overview of the different landslide management mechanisms in the UK and discuss them in context of cases studies to explore their effectiveness. We conclude with three issues that may have implications for landslide management in the UK and other ‘low-risk’ countries. Firstly, the evidence base by which landslide hazards and risks are measured is insufficient and limitations in existing information need to be better understood. Secondly, existing guidance on strategic and responsive management needs to be assessed for its fitness for purpose. Thirdly, we encourage debate about the importance of near misses.  相似文献   

11.
The 2008-05-12 Wenchuan mud-volcano-earthquake was accompanied with eruption of a huge volume of gas and stone, revealing that earthquakes generally result from instant reverse phase explosion of supercritical water (SCW) at the supercritical point. In the deep parts of the crust and mantle there still exists a large amount of supercritical water equivalent in order of magnitude to that of the Earth’s hydrosphere. Soft fluids which exist in the MOHO at the top of the upper mantle are the so-called deep supercritical fluids (SCWD). Supercritical water (SCW) has n×103 times strong capability to dissolve gas. Its viscosity is extremely low and its diffusivity is extremely strong. Therefore, it can naturally migrate toward a region with relatively negative pressure. In the steep break zone of the MOHO at the 57–65 km depth beneath the earthquake belt, due to mutation of overburden pressure, SCWD can automatically separate out CaSiO3 and other inorganic salts, evolving into the SCW (H2O-CO2-CH4O system. In going upwards to the 10–20-km depth of the crust SCW will be accumulated as an earthquake-pregnant reservoir in the broken terrain. The phase-transition heat of SCW is estimated at 606.62 kJ/kg and the reverse phasing kinetic energy is 2350.8 kJ/kg. When automatic exhaust at the time of decompression reaches the critical pressure (Pc), the instant explosion reverse phase will be normal-state air water. It will release a huge volume of energy and high-kinetic-energy gas which has been expanded by a factor of 1000, leading to the breaking of the country rocks overlying the earthquake-pregnant reservoir, thus giving rise to a Ms 8.0 earthquake. As a result, there were formed eruptive and air-driven (pneumatic) debris flows whose volumatric flow rate reaches n×1014 m3/s, and their force greatly exceeds the power of INT explosive of the same equivalent value.  相似文献   

12.
Cenozoic basalt in eastern China contains abundant ultramafic xenoliths which are specimens of pyrolitesreleased during basaltic magma eruption. A total of 405 P-T data of pyroxene in the ultramafic rocks have beencollected, which present a more precise pyroxene geotherm. The average geothermal gradient in the upper man-tle represented by the pyroxene geotherm is about 3.3℃ / km, which is much less than that derived from theconductive thermal model (≈14℃ / km), implying the great significance of convective heat transfer. The calcu-lation shows that the contributions of convective and conductive heat transfers are 79% and 21%, respectively.The perturbation in the thermal structure of the upper mantle is an important manifestation of thetectonothermal event of Cenozoic continental rifting and intense basaltic volcanism in eastern China. Based onthe pyroxene geotherm and its comparison with the current geothermal field derived from the measurements ofthe surface heat flows, it is suggested that the Moho may be a secondary thermal boundary. The currentgeothermal field and the thermal structure of the lithosphere in eastern China may mainly reflect the result ofthe tectonothermal disturbance in the Neogene-Quaternary, in other words, the lithosphere has just begun toCool.  相似文献   

13.
Railway alignments through the Canadian Cordillera are constantly exposed to slope instabilities. Proactive mitigation strategies have been in place for a few decades now, and instability record keeping has been recognized as an important aspect of them. Such a proactive strategy has enhanced the industry’s capacity to manage slope risks, and some sections have been recognized as critical due to the frequency of instabilities. At these locations, quantification of the risks becomes necessary. Risk analysis requires knowledge of some variables for which statistical data are scarce or not available, and elicitation of subjective probabilities is needed. A limitation of such approaches lies in the uncertainty associated to those elicited probabilities. In this paper, a quantitative risk analysis is presented for a section of railway across the Canadian Cordillera. The analysis focused on the risk to life of the freight train crews working along this section. Upper and lower bounds were elicited to cope with the uncertainties associated with this approach. A Monte Carlo simulation technique was then applied to obtain the probability distribution of the estimated risks. The risk probability distribution suggests that the risk to life of the crews is below previously published evaluation criteria and within acceptable levels. The risk assessment approach proposed focuses on providing a measure of the uncertainty associated with the estimated risk and is capable of handling distributions that cover more than two orders of magnitude.  相似文献   

14.
Comparative planetology is an interdisciplinary science between Earth sciences and astronomy. It studies physical, chemical and dynamical properties of planets and satellites and their surface characteristics, interior structures and chemistry, magnetic field, climate and possible existence of life. Although the study of comparative planetary science is at its infancy stage in China, it is very encouraging to see that 25 papers were received by the session, which is much more than what we expected. It indicates that more and more scientists are interested in this research field. These papers can be classified into three categories: solar planets, extra-solar planets, and moon explorations. Scientists from both China and oversea reported their recent results.  相似文献   

15.
The geology of New South Wales is diverse, spanning Paleoproterozoic to modern materials and their various associated landforms and soils. In recognition of the intrinsic geological value of the State, around 150 geological sites were nominated to the now defunct Register of the National Estate, with the objective of geoconservation. However, these sites did not encompass the full range of geology of New South Wales; neither did they offer registered sites any protection. Analysis shows that the types of sites nominated were biased towards sedimentary and igneous rocks, and fossils, with under representation of metamorphic rocks, site-restricted soils, geomorphology and hydrogeology. To test the utility of the Brocx and Semeniuk ‘Geoheritage Toolkit’, a subset of the Register listings was re-examined, focusing on the Sydney Basin. Within the Sydney Basin, 59 nominated sites were reassessed using various geoheritage categories and the hierarchical framework of scale of the Toolkit. Four sites within the Sydney Basin were found to have features of international to national significance, and to have national historical value. These sites will need to be renominated for State and National listing. Clearly, to ensure that University teaching sites, as well as stratigraphic and lithologic type sections and reference sites, reflecting the geodiversity of New South Wales are conserved for future generations, a greater number of sites need to be put forward for heritage listing.  相似文献   

16.
The Carboniferous prototype sedimentary basin in the Tazhong (Central Tarimbasin) area is recognized as a compressive intracratonic depressional one. Three type Ⅰ sequenceboundaries and three type Ⅱ sequence boundaries can be identified in the CarboniferousSystem, which can accordingly be divided into five sedimentary sequences. These sequencespossess stratigraphic characters of the standard sequence and correspond to the depositionalstratigraphic unit of a third-order eustatic cycle. They can be regionally or globally correlatedwith each other. The framework of sequence stratigraphy of the intracratonict basin in thestudy area distinctly differs from that of the passive continental-margin basin in the lack ofdepositional systems of early-middle lowstand, poor development of the deeply incised valleyand condensed section of the maximum sea-flood, good development of type Ⅱ sequenceboundaries and coastal plain depositional systems coexisting with shelf-type fan deltas underwet climatic conditions, Which consequently led to the formation of a paralic lithofacies frame-work.  相似文献   

17.
The topic of this paper is the retrieval of hidden or secondary information on complex spatial variables from geophysical data. Typical situations of obscured geological or geophysical information are the following: (1) Noise may disturb the signal for a variable for which measurements have been collected. (2) The variable of interest may be obscured by other geophysical processes. (3) The information of interest may formally be captured in a secondary variable, whereas data may have been collected for a primary variable only, that is related to the geophysical process of interest. Examples discussed here include mapping of marine-geologic provinces from bathymetric data, identification of sea-ice properties from snow-depth data, analysis of snow surface data in an Alpine environment and association of deformation types in fast-moving glaciers from airborne video material or satellite imagery. Data types include geophysical profile or trackline data, image data, grid or matrix-type data, and more generally, any two-dimensional or three-dimensional discrete or discretizable data sets. The framework for a solution is geostatistical characterization and classification, which typically involves the following steps: (1) calculation of vario functions (which may be of higher order or residual type, or combinations of both), (2) derivation of classification parameters from vario functions, and (3) characterization, classification or segmentation, depending on the applied problem. In some situations, spatial surface roughness is utilized as an auxiliary variable, for instance, roughness of the seafloor may be derived from bathymetric data and be indicative of geological provinces. The objective of this paper is to present components of the geostatistical classification method in a summarizing and synoptical manner, motivated by applied examples and integrating principal and generalized concepts, such as hyperparameters and parameters that relate to the same physical processes and work for data in oversampled and undersampled situations, parameters that facilitate comparison among different data types, data sets and across scales, variograms and vario functions of higher order, and deterministic and connectionist classification algorithms.  相似文献   

18.
A new computer simulation of the development of grain shape and crystallographic preferred orientations in dynamically recrystallizing aggregates is presented. This model is based on a uniform array of points, each of which represents a small area of crystal. This model combines homogeneous strains, simplified versions of the lattice rotations predicted by Taylor-Bishop-Hill theory, mobile grain boundaries and the nucleation of subgrains. It allows the progressive development of the fabrics and microstructures to be followed. The limitations of the simplifying assumptions used in this model are discussed.  相似文献   

19.
Detailed lithological study of tills was carried out at exposures along the Adz’va, Bol’shaya Rogovaya, and Seida rivers—northern tributaries of the Usa River—in the northeasternmost area of the Timan-Pechora-Vychegoda region. The results of grain size, mineralogical, and petrographic analyses coupled with measurements of orientation of elongated clasts in tills made it possible to substantiate the presence of three moraine horizons. Lithological features of the Pechora (Dnieper) and Polyarny (Ostashkovo) horizons of tills testify to the input of terrigenous material from Novaya Zemlya. The upper (middle Pleistocene) till, which is also as defined as the Vychegoda (or Moscovian) till, represents clastic material derived from the Polar and Subpolar Urals. Lithological properties have been defined for the stratification and correlation of tills. A chart of lithological criteria has been compiled for the subdivision and correlation of middle and upper Pleistocene tills in the Far Northeast of European Russia.  相似文献   

20.
In recent years, voices in Jordan became lauder to exploit the fresh to brackish deep groundwater overlain by fresh groundwater bodies. In this article the implications of such a policy on the existing fresh water bodies are worked out through studying the sources of salinity in the different aquifer systems and the potentials of salinity mobilization by artificial changes in the hydrodynamic regimes. It is concluded that extracting the groundwater of deep aquifers overlain by fresh water bodies, whether the deep groundwater is fresh to brackish, brackish or salty, is equivalent to extracting groundwater from the overlying fresh groundwater bodies because of the hydraulic connections of the deep and the shallow aquifers’ groundwaters. The consequences are even more complicated and severe because exploiting the deep groundwater containing brackish or salty water will lead to refilling by fresh groundwater leaking from the overlying aquifers. The leaking water becomes salinized as soon as it enters the pore spaces of the emptied deep aquifer matrix and by mixing with the deep aquifer brackish or saline groundwater. Therefore, the move to exploit the deep groundwater is misleading and damaging the aquifers and is unjust to future generation's rights in the natural wealth of Jordan or any other country with similar aquifers’ set-up. In addition, desalination produces brines with high salinity which cannot easily be discharged in the highlands of Jordan (with only very limited access to the open sea) because they will on the long term percolate down into fresh water aquifers.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号