蒙古古生代地层研究的新进展   总被引：1，自引：0，他引：1  

王成源  Weddige Karsten  Minjin Chuluun 《吉林大学学报(地球科学版)》2006,36(5):723-735

蒙古国古生代地层的研究以往主要侧重底栖大化石的研究, 很多地层的时代划分、归属问题不能得到很好的解决,底栖化石的地方性很强,不能与国际直接对比。 牙形刺是古生代地层的主导化石, 很多古生代地层问题都可以用牙形刺解决并进行可靠的洲际间对比。2001年笔者在蒙古南戈壁采集了158个样品, 经分析发现了大量牙形刺标本, 解决了很多蒙古的重大地层问题。Arynshand组应当归入下石炭统, 泥盆-石炭系界线在Arynshand组之下, 而不是在此组的内部。Mushgai地区Bayan-Khoshuu Ruins剖面的Mandalovoo组Gavuu 段的上部应属早泥盆世早期, 而不是以前所确定的早志留世, 称为奥咯诺伍德组（Olonovoot Formation）;Gavuu段的下部仍归早志留世。Mandalovoo组应提升为Mandalovoo群;Gavuu段应提升为Gavuu组。南戈壁Shine Jinst地区Tsakhir剖面Tsagaanbulag组的时代是早泥盆世洛霍考夫期, 而不是中晚志留世,Ulaan-Shand剖面Tsagaanbulag组的时代也是早泥盆世洛霍考夫期。Chuluun组的时代为早泥盆世晚埃姆斯期。Tsagaankhaalga组的时代为早艾菲尔期。Indert组为早石炭世。蒙古古生代海相地层大部分是浅水相地层, 并可能存在5个间断：志留系的文洛克统和罗德洛统的下部,下泥盆统布拉格阶的一部分,中泥盆统艾菲尔阶上部,泥盆-石炭系界线地层。蒙古国南部和中部很可能缺失上二叠统的海相沉积。  相似文献   

Improving modelling and inversion in refraction seismics with a first-order Eikonal solver   总被引：1，自引：0，他引：1  

Isabelle Lecomte  Håvar Gjøystdal  ers Dahle  & Ole Christian Pedersen 《Geophysical Prospecting》2000,48(3):437-454

A first-order Eikonal solver is applied to modelling and inversion in refraction seismics. The method calculates the traveltime of the fastest wave at any point of a regular grid, including head waves as used in refraction. The efficiency, robustness and flexibility of the method give a very powerful modelling tool to find both traveltimes and raypaths. Comparisons with finite-difference data show the validity of the results. Any arbitrarily complex model can be studied, including the exact topography of the surface, thus avoiding static corrections. Later arrivals are also obtained by applying high-slowness masks over the high-velocity zones. Such an efficient modelling tool may be used interactively to invert for the model, but a better method is to apply the refractor-imaging principle of Hagedoorn to obtain the refractors from the picked traveltime curves. The application of this principle has already been tried successfully by previous authors, but they used a less well-adapted Eikonal solver. Some of their traveltimes were not correct in the presence of strong velocity variations, and the refractor-imaging principle was restricted to receiver lines along a plane surface. With the first-order Eikonal solver chosen, any topography of the receiving surface can be considered and there is no restriction on the velocity contrast. Based on synthetic examples, the Hagedoorn principle appears to be robust even in the case of first arrivals associated with waves diving under the refractor. The velocities below the refractor can also be easily estimated, parallel to the imaging process. In this way, the model can be built up successively layer by layer, the refractor-imaging and velocity-mapping processes being performed for each identified refractor at a time. The inverted model could then be used in tomographic inversions because the calculated traveltimes are very close to the observed traveltimes and the raypaths are available.  相似文献   

Subterranean microorganisms and radioactive waste disposal in Sweden   总被引：2，自引：0，他引：2  

Karsten Pedersen   《Engineering Geology》1999,52(3-4):163-176

In 1987, microbiology became a part of the Swedish scientific program for the safe disposal of high level nuclear waste (HLW). The goal of the microbiology program is to understand how subterranean microorganisms will interact with the performance of a future HLW repository. The Swedish research program on subterranean microbiology has mainly been performed at two sites in granitic rock aquifers at depths ranging from 70 m down to 1240 m, the Stripa research mine in the middle of Sweden and the Äspö Hard Rock Laboratory (HRL) situated on the south eastern coast of Sweden. Some work has also been performed in cooperation with other national or international research groups in Sweden, Canada and at the natural analogue sites Oklo in Gabon and Maqarin in Jordan. The following conclusions are drawn. There is a very high probability of the existence of a deep subterranean biosphere in granitic rock. The documented presence of a deep biosphere implies that relevant microbial reactions should be included in the performance assessment for a HLW repository. A HLW repository will be situated in a subterranean biosphere that is independent of solar energy and photosynthetically produced organic carbon. The ultimate limitation for an active microbial life will be the availability of hydrogen as energy source over time, and hydrogen has indeed been found in most deep groundwaters. Sulphide producing microorganisms are active in environments typical for a Swedish HLW repository, and the potential for microbial corrosion of the copper canisters must be considered. The bentonite buffer around the copper canisters will be a hostile environment for most microbes due to the combination of radiation, heat and low water availability. Discrete microbial species can cope with each of these constraints, and it is theoretically possible that sulphide producing microbes may be active inside a buffer, although the experiments conducted thus far have shown the opposite. Microorganisms have the capability to enzymatically recombine radiolysis oxidants formed by radiation of water. It has earlier been concluded that the migration of radionuclides due to sorption on microorganisms can be neglected. The influence of microbially produced complexing agents remains to be studied at realistic conditions in deep groundwater. Microorganisms have been found in natural alkaline groundwaters, but it could not be conclusively demonstrated that they were in situ viable and growing, rather than just transported there from neutral groundwater. A possible hypothesis based on the obtained results from investigations of natural alkaline groundwaters is that fresh concrete may be a bit too extreme for active life even for the most adaptable microbe – but this remains to be demonstrated.  相似文献   

Estimation of new production in the North Sea: consequences for temporal and spatial variability of phytoplankton   总被引：2，自引：0，他引：2  

Richardson  Katherine; Pedersen  Flemming Bo 《ICES Journal of Marine Science》1998,55(4):574-580

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Measurements of the vertical correlation in turbulence under broken waves     

Claus Pedersen  Rolf Deigaard  James Sutherland 《Coastal Engineering》1998,35(4):231-249

Turbulence measurements have been carried out in the surf zone of a wave flume. The purpose of the measurements is to determine the length scale of the turbulence generated by the wave breaking. The length scale of the turbulence is estimated on basis of the correlation between simultaneous measurements of the vertical turbulent fluctuations, taken at different levels above the bed.  相似文献   

Recent behavior and possible future evolution of the glacieret in the cirque Golemiya Kazan in the Pirin Mountains under conditions of climate warming     

Peter NOJAROV  Emil GACHEV  Karsten GRUNEWALD 《山地科学学报》2019,(1)

This research reveals relationships between climate variables and inter-annual dynamics in the area of the glacieret located in the cirque Golemiya Kazan in the Pirin Mountains. The study period is 1993–2017. The correlations are identified using statistical methods. Also, a statistical model is constructed, including some climate variables as predictors. Despite the evident decrease of the glacieret's size in the period from the 1950 s onwards, the long-term trends for the last decades have been insignificant. The main climatic factors influencing the inter-annual dynamics in the area of the glacieret are air temperature, precipitation, zonal and meridional winds and relative humidity. With respect to the dynamics in the area of the glacieret, the important trends in the different climate variables are those of the warm period air temperatures and zonal(u) wind. They also determine to a great extent its future development by acting in two opposite directions – rising temperatures in the warm period will lead to a rapid decrease of its area by the end of the melting season, while the change of wind directionfrom west to east in the warm period will increase its area. The influence of the zonal wind in the warm period is explained mainly by the location of the glacieret in the cirque. Generally, the glacieret is tilted downwards from west to east. Thus, westerly winds facilitate blowing away the snow from the surface of the glacieret, assisting its melting in the warm period. Easterly winds do not have such an effect. The combination of the opposite effects of these two most important climate variables leads to the most likely scenario for the future development of the glacieret, according to which by the middle of this century it is expected to turn into a semi-permanent snow patch, which disappears after some summers, and by the end of the century to completely melt every year before the end of the melting season.  相似文献   

The potential of an electrostatically clean geostationary satellite and its use in plasma diagnostics     

K. Knott  P.M.E. Decreau  A. Korth  A. Pedersen  G.L. Wrenn 《Planetary and Space Science》1984,32(2):227-237

Electrostatic charging has given rise to problems on several geostationary spacecraft. This has led to a rigorous electrostatic cleanliness approach in the case of the scientific geostationary satellite GEOS in order to secure correct electric field and low energy plasma measurements. The present paper outlines the relevant charging mechanism, describes a new method for the determination of the equilibrium potential, and reports on actual potential measurements. The potentials observed are very closely related to the actual plasma conditions at the geostationary orbit. It is generally possible to use the potential measurements to characterize the particle population encountered by the spacecraft.Measurements carried out over a period of 4 years are presented by way of examples. A careful analysis shows that the chosen examples are representative and reflect the conditions observed on all other days of the mission. The results lead to the overall conclusion that the equilibrium potential of GEOS in sunlight is always moderately positive and only rarely exceeds + 10 V with respect to ambient space. At no instance in the sunlit portion of the orbit does the spacecraft assume a negative potential. We find that the observed moderate positive equilibrium potential generally is a function of cold plasma density. During the night and early morning part of the orbit we can, however, identify periods where the high energy particle population dictates the equilibrium potential. The electrostatic cleanliness design of GEOS avoids negative charging also under these conditions. In eclipse, a negative potential cannot be avoided but here the electrostatic cleanliness approach chosen for GEOS prevents any differential charging and avoids potentials of several thousand volts which have appeared on other satellites. The cost, in time and effort, of the precautions employed has clearly been justified. The specially developed techniques have since been used on other satellites and the lessons learned have also been applied successfully to operational spacecraft such as METEOSAT 2.  相似文献   

The development of a non-linear autoregressive model with exogenous input (NARX) to model climate-water clarity relationships: reconstructing a historical water clarity index for the coastal waters of the southeastern USA     

Lee  Cameron C.  Sheridan  Scott C.  Barnes  Brian B.  Hu  Chuanmin  Pirhalla  Douglas E.  Ransibrahmanakul  Varis  Shein  Karsten 《Theoretical and Applied Climatology》2017,130(1-2):557-569

Theoretical and Applied Climatology - The coastal waters of the southeastern USA contain important protected habitats and natural resources that are vulnerable to climate variability and singular...  相似文献   

Electrical anisotropy and conductivity distribution functions of fractal random networks and of the crust: the scale effect of connectivity     

Karsten Bahr 《Geophysical Journal International》1997,130(3):649-660

All explanations of the high-conductivity layers (HCL) found by magnetotellurics in the middle or lower crust incorporate a mixture of a low-conductivity rock matrix and a highly conductive phase, for example graphite or saline fluids. In most cases the bulk conductivity of the mixture does not depend on the conductivity of the rock matrix but rather (1) on the amount of high-conductivity material and, in particular, (2) on its geometry. The latter is quantitatively described by the parameter 'electrical connectivity'. Decomposition of the observed bulk conductivity of the mixture into these two parameters results in an ill-posed problem. Even if anisotropy occurs in the HCL, three output parameters (highly conductive phase fraction, connectivity with respect to the X direction, connectivity with respect to the Y direction) have to be estimated from the two bulk conductivities of the anisotropic HCL. The additional information required for solving this problem is provided if instead of single-site data the conductivities from many field sites are evaluated: a sample distribution of the conductivity can then be obtained. Ensembles of random networks are used to create theoretical distribution functions which match the empirical distribution functions to some extent. The use of random resistor networks is discussed in the context of other established techniques for the treatment of two-phase systems, such as percolation theory and the renormalization group approach. Models of embedded networks explain the discrepancy between 'small' anisotropy (2-3) on the laboratory scale and large anisotropy (10-100) found in electromagnetic field surveys encompassing volumes of several cubic kilometres. Strong anisotropy can indicate low electrical connectivity, and a possible explanation is that a network stays close to the percolation threshold.  相似文献   

Three-dimensional image of the Moho undulations beneath the Gulf of Bothnia using wide-angle seismic data     

M. Ali Riahi  C.-E. Lund  Laust B. Pedersen 《Geophysical Journal International》1997,129(2):461-471

The BABEL marine seismic experiment has been carried out to investigate the lithospheric structure and antecedent tectonic signatures of the Baltic Shield, including the Archaean-Proterozoic collisional structure in the northern part of the Gulf of Bothnia.
Lithospheric seismic-reflection streamer data and simultaneously recorded wide-angle reflection and refraction data collected in the Gulf of Bothnia as part of the BABEL project have been used for 3-D modelling. The distribution of land stations around the Gulf provides a good 3-D ray coverage of the PMP reflection data recorded at the eight stations in the area and allows an estimation of strikes and dips of the Moho boundary in the area. The traveltimes of reflected phases are calculated using a method that utilizes the finite-difference solution of the eikonal equation. The Moho wide-angle-reflection (PMP) traveltimes are modelled using an inversion method. A 2-D model from the Gulf of Bothnia extended into the third dimension is used as an initial model. During the inversion the velocity is kept constant and only the Moho boundary is allowed to vary. To estimate the strike of the Moho boundary and the stability of the inversion, two initial models with different strikes are examined.
The results indicate that the Moho depth in the Gulf of Bothnia undulates and has a maximum depth of 55 km in the south, rising to 42 km in the north. The Moho depth variations seem to be step-like. This change in the Moho depth coincides with the location of the presumed fossil subduction zone in the area. The crustal-thickness variations seem to be well approximated by a nearly 2-D structure striking parallel to a postulated subduction zone immediately to the south of the Skellefte area. The presence of the step at the crust/mantle boundary can be interpreted as a result of a plate-collision event at about 2 Ga.  相似文献