海南岛万泉河口沉积物有机碳、 氮同位素的特征及其环境意义^*   总被引：4，自引：0，他引：4  

葛晨东  王颖  T.F.Pedersen  O.Slaymaker 《第四纪研究》2007,27(5):845-852

对海南岛万泉河口沙美内海柱样K3和K4沉积物进行生物地球化学指标总有机碳(TOC)、总氮(TN)、有机碳同位素(δ¹³ C)、氮同位素(δ¹⁵ N)的分析,以及²¹⁰ Pb定年了解其近代变化特征,追踪沉积物有机质来源的变化,提取沉积环境演变及人类活动的信息。K3中TOC的变化介于0.51 ％ ~1.12 ％ ,K4变化介于0.43 ％ ~1.49 ％ ,而其随时间的变化反映了流域内人类活动的历史。17世纪TOC含量明显增加记录了明末清初开始流域内广泛种植农作物的活动,19世纪以来TOC含量逐渐增加,至现代达最高值,对应了工业革命以来人类活动的增强。K3和K4的δ¹³ C值变化分别在-24.38 ‰ ~-21.02 ‰ 之间和-24.74 ‰ ~-20.17 ‰ 之间,δ¹⁵ N值变化分别在2.20 ‰ ~4.62 ‰ 之间和2.39 ‰ ~5.02 ‰ 之间,映证了本区沉积物有机质是陆源物质和海洋物质混合的特点。明末清初开始流域内广泛种植玉米等农作物造成δ¹³ C值增加和δ¹⁵ N值减少; 自19世纪以来至现在,该区的经济活动增加,人口的持续增长,尤其是近50年来化肥农药的大量使用,造成陆源输入的有机碳含量大幅增加,使δ¹³ C值减少和δ¹⁵ N比值增加。 δ¹³ C值自19世纪以来就逐渐变轻,说明陆源和海洋有机碳的比例发生了变化,较轻的陆源有机碳比例相对增加,较重的海洋有机碳比例相对减少,反映了玉带滩沙坝的增长、沙美内海封闭、海水交换作用减少的状况。C/N比值分别从底部的16.19和17.36到顶部减小为11左右,自19世纪以来呈明显减小的趋势也反映了沙美内海泻湖自生的藻类有机质供应越来越多,也说明了其逐渐封闭、水动力条件越来越弱,与外海的交换作用逐渐减少的状况。  相似文献   

Pull-apart formation and strike-slip partitioning in an obliquely divergent setting, Leka Ophiolite, Norway   总被引：1，自引：0，他引：1  

S. J. Titus  H. Fossen  R. B. Pedersen  J. L. Vigneresse  B. Tikoff 《Tectonophysics》2002,354(1-2)

The Leka Ophiolite Complex (LOC) is located on the island of Leka, Norway, and belongs to the Uppermost Allochthon of the Scandinavian Caledonides. The rocks of the adjacent mainland and most of the surrounding islands are basement gneisses and supracrustal rocks not related to the ophiolite complex. Paleostress analysis, gravity inversion, and regional geology support a fault-bounded rhombochasm geometry for the LOC. The paleostress inversions revealed two types of tensors, interpreted as small strains: (1) horizontal extension, generally E–W to NE–SW, and (2) horizontal extension in the same direction with an added component of perpendicular horizontal contraction. A strong positive gravity anomaly (25 mGal) is centered on Leka, and gravity inversion indicates that the LOC lies directly below its surface exposures with steep-sided walls and a flat bottom located at 7 km depth. The faults bounding the LOC probably initiated during postorogenic extension in the Scandinavian Caledonides. The faults are regional in scale and are parallel to other NE–SW trending en echelon faults along the Norwegian coastline and on the adjacent mainland.A pull-apart structure explains the down-dropping and subsequent preservation of the LOC, as it is surrounded by rocks from lower structural positions within the nappe stack. The paleostress directions from Leka support a sinistral component of shear along these faults. The gravity inversion is consistent with a fault-bounded geometry. This pull-apart structure, as uniquely recorded by the dense ophiolitic rocks, suggests that strike-slip partitioning was active in an obliquely divergent setting.  相似文献   

Fronts in the Kattegat: The hydrodynamic regulating factor for biology     

Flemming Bo Pedersen 《Estuaries and Coasts》1993,16(1):104-112

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Channelling contribution to tipper vectors: a magnetic equivalent to electrical distortion   总被引：2，自引：0，他引：2  

Ping Zhang  Laust B. Pedersen  Marianne Mareschal  Michel Chouteau 《Geophysical Journal International》1993,113(3):693-700

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A palynological and sedimentological study of Cretaceous floodplain deposits of the Atane Formation at Skansen and Igdlunguaq, Disko, West Greenland     

Eva Bundgaard Koppelhus  Gunver Krarup Pedersen 《Cretaceous Research》1993,14(6)

A palynological and sedimentological study has been carried out on the Cretaceous fluvial and deltaic Atane Formation of West Greenland. Two localities, Skansen and Igdlunguaq on the southern coast of Disko island, have been studied. The sediments are divided into two genetic facies associations interpreted as representing deposition in fluvial channels and on a floodplain. The facies indicate that most of the sediments on the floodplain accumulated in swamps or shallow lakes, whereas abundant spores and pollen indicate the presence of vegetated land nearby. The palynomorph assemblages recovered consist of 72 species of spores and pollen grains of bryophytes, pteridophytes, gymnosperms and angiosperms. The palynomorphs from Skansen and most of those from Igdlunguaq indicate a maximum age-range from late Albian to Cenomanian for the successions sampled, although a mid Cenomanian age seems most likely. The highest horizon examined at Igdlunguaq may, however, be late Cenomanian or Turonian in age. The assemblages compare well with palynofloras from North America and Northwest Europe.  相似文献   

Conductivity structure of crust in the Tangshan seismic area and the possibility of exploring potential seismic sources by magnetotelluric method   总被引：1，自引：0，他引：1  

Xinling Qin  L. B. Pedersen  Yulin Zhao  Ping Zhang  Fuye Qian  Wei Qian  Zhengnan Li  Jingxian Du 《地震学报(英文版)》1992,5(2):355-365

It is shown by the result of digital magnetotelluric soundings in the Tangshan seismic area and its surrounding regions that the crust under the surface conductive sediments is divided into two layers,i. e., the resistive upper crust and the conductive lower crust. The upper crust wherein the Tangshan main shock and most of the aftershocks occurred is a convex lens-like body which is cut by faults at the east, south and west sides. The focus of the mainshock was located at the position of maximum thickness of the resistive upper crust while the spatial variation of Curie point isothermal surface and the deepest limit of the depths of aftershocks coincide with the downward depression of the bottom of the resistive upper crust. Thus, the Tangshan main shock and most of its aftershocks were related closely to the resistive upper crust from the view points of either vertical layering or lateral variations. And there were only a very few aftershocks in the conductive lower crust. The mechanical property of the rocks transforms from being brittle in the upper crust into ductile in the lower crust mainly due to the combination of different factors, e.g., increase of confining pressure, change in minerals, rise in temperature as well as stabilization of slips by high pore—pressure. A small amount of water and a rise in temperature may lead to a decrease of the electric resistivity within the rock while a change in the static pressure and mineral content within the rock causes very little change in the electric resistivity. Thus it is deduced that a resistive upper crust and a more conductive lower crust from the view points of either vertical or lateral variations are related to the brittle and ductile properties respectively. Hence it is possible that there is a relationship between the electric structure of the crust and zones of potential seismic hazard. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 354–363, 1991. The project is supported by the Chinese Joint Seismological Science Foundation, and the Swedish International Development Authority.  相似文献   

An airborne tensor VLF system. From concept to realization1     

Laust B. Pedersen  Wei Qian  Lars Dynesius  Ping Zhang 《Geophysical Prospecting》1994,42(8):863-883

Radio signals from very low frequency (VLF) transmitters distributed world-wide have been used for several decades to study the lateral variations of the electrical conductivity in the upper few hundred metres of the earth's crust. Traditionally, in airborne applications, the total magnetic fields from one or two transmitters are measured to form the basis for construction of maps that primarily show those conductive structures that are parallel or subparallel to the direction to the transmitters. The tensor VLF technique described in this paper makes use of all signals available in a predefined frequency band to construct transfer functions relating the vertical magnetic field and the two horizontal magnetic field components. These transfer functions are uniquely determined for a particular measuring site and contain information about the lateral conductivity variations in all directions. First experiences with real field data, acquired during a test survey in Sweden, show that maps of the so-called peaker, the spatial divergence of the transfer functions, give an image of the conducting structures. Most of the structures can be correlated to small valleys filled with conducting sediments or valleys underlain by conductive fracture zones in the crystalline rocks.  相似文献   

Fluid flow in sedimentary basins: model of pore water flow in a vertical fracture   总被引：2，自引：0，他引：2  

TOM Pedersen  KNUT Bjørlykke 《Basin Research》1994,6(1):1-16

Open fractures provide high-permeability pathways for fluid flow in sedimentary basins. The potential for flow along permeable or open fractures and faults depends on the continuity of flow all the way to the surface except in the case of convective flow. Upward flowing fluid cools and may cause cementation due to the prograde solubility of quartz, but in the case of carbonates such flow may cause dissolution. The rate and duration of these processes depend on the mechanisms for sustaining fluid flow into the fracture, the geometries of fracture and sedimentary beds intersected, permeability, pressure and temperature gradients. Heat loss to the adjacent sediments causes sloping isotherms which can induce non-Rayleigh convection. To analyse these problems we have used a simple model in which a single fracture acts as a pathway for vertically moving fluid and there is no fluid transport across the walls of the fracture except near its inlet and outlet. Four mechanisms for fluid flow into the lower part of the fracture are considered: decompression of pore water; compaction of intersected overpressared sediments; focusing of compaction water derived from sediments beneath the fracture; and finally focusing of pore water moving through an aquifer. Water derived from the basement is not considered here. We find that sustained flow is unlikely to have velocities much higher than 1–100 m/yr, and the flow is laminar. The temperature of the fluid expelled at the top of the fracture increases by less than 1% and the vertical temperature gradient in the fracture remains close to the geothermal gradient. Where hot water is introduced from basement fractures (hydrothermal water) during tectonic deformation, much higher velocities may be sustained in the overlying sediments, but here also this depends on the permeability near the surface. Most of the cooling of water with (ore) mineral precipitation will then occur near the surface. In most cases, pore water decompression and sediment compaction will yield only very limited pore water flux with no significant potential for cementation or heating of the sediments adjacent to the fracture. Focusing of compaction water from sediments beneath the fracture or from an intersected aquifer can yield fluxes high enough to cement an open fracture significantly but the flow must be sustained for a very long time. For velocities of 1–100 m/yr, it takes typically 0.3–30 Myr to cement a fracture by 50%. The highest velocities may be obtained when a fracture extends all the way to the surface or sea floor. When a fracture does not reach the sediment surface, the flow velocity is reduced by the displacement of water in the sediments near the top of the fracture. The flow into the fracture from the sediments may often be rate limiting rather than the flow on the fracture. Sedimentary rocks only a few metres from the fracture will receive a much lower flux than the fracture. The fracture will therefore close due to cementation before significant amounts of silica can be introduced into adjacent sandstones. The isotherm slope in the adjacent sediments will in most cases be less than 10–20°. Non-Rayleigh convection velocities in the sediments adjacent to the fracture are too small to cause any significant diagenetic reactions such as quartz cementation. These quantifications of fluid flow in fractures in sedimentary basins are important in terms of constraining models for diagenesis, heat transport and formation of ore minerals in a compaction-driven system.  相似文献   

Oxygen deficient Ti oxides (natural magnéli phases) from mudstone xenoliths with native iron from Disko,central West Greenland     

A. K. Pedersen  J. G. Rønsbo 《Contributions to Mineralogy and Petrology》1987,96(1):35-46

Mudstone xenoliths in a strongly reduced andesitic subaquatic breccia with native iron from the Asuk Member on Disko contain Ti oxides which are oxygen deficient relative to rutile. Ore microscopy reveals that the mudstone xenoliths contain former clastic oxide grains which have equilibrated to blue Ti oxides and grey aluminous Ti oxides. They also contain still immature coal fragments in a glassy matrix with native iron.The blue oxides are compositionally similar to magnéli phases Ti_nO_2n–1 within the range n=4 to 7, and several grains contain more than one natural magnéli phase. Two other phases found are 1) pale orange blebs in magnéli phases with a composition approaching Al₁Ti ₁ ³⁺ Ti ₂ ⁴⁺ O₇ (AlTi phase B) and 2) grey oxide rims on magnéli phases or independent grains of the compositional series Al_2–x(Ti _0.5 ⁴⁺ (Mg,Fe)_0.5)_xTi _n–2 ⁴⁺ O_2n–1 with n mostly between 7 and 10 (AlTi phase A). The natural magnéli phases equilibrated at oxygen fugacities 4 to 5 log units below the Fe-W oxygen buffer at igneous temperatures and represent the most reduced high-temperature environment yet recorded among native iron bearing rocks from Disko. The extremely reducing conditions were met in rocks where coal fragments were still in a state of degassing hydrocarbon components at the time of quenching. Field geology and carbon barometry indicate equilibration at pressures of less than 10 bars.  相似文献   

One dimensional diffusion of radiogenic 87Sr and fluid transport of volatile elements across the margin of a metamorphosed Archaean basic dyke from Saglek,Labrador     

N. Springer  S. Pedersen  D. Bridgwater  W. E. Glassley 《Contributions to Mineralogy and Petrology》1983,82(1):26-33

An example of diffusion in a natural solid rock is described using ⁸⁷Sr as a tracer. The distribution of excess radiogenic ⁸⁷Sr across the contact of a metamorphosed basic dyke in a granodioritic gneiss is shown to fit closely to a mathematically modelled theoretical diffusion curve. It is suggested that the excess radiogenic Sr was generated by the breakdown of older Rb-rich biotite in the country rock to form chlorite during a late-stage greenschist facies metamorphism, and then taken up into a fluid phase migrating along the country rock — dyke interface. This fluid introduced silica, alkalies, light REE, H₂O, CO₂, N and Cl into the marginal zone of the dyke, probably during fluid migration along grain boundaries. The present irregular distribution of the volatile constituents across the contact and in the dyke excludes a diffusion controlled distribution. The distribution of volatiles probably reflects the influence of the existing mineralogy on the geochemical anomaly actually recorded from a post magmatic process. Evidence is presented that the diffusivity of radiogenic Sr was enhanced by the presence of a volatile phase.  相似文献