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51.
The Limón back‐arc basin belongs to the southern Central American arc‐trench system and is situated at the east coast of Costa Rica. The basin‐fill consists of Late Cretaceous to Pleistocene sedimentary rocks. A northern and a southern sub‐basin can be defined, separated by the E–W‐trending Trans Isthmic Fault System. The North Limón Basin is nearly undeformed, whereas the South Limón Basin is characterized by a fold‐and‐thrust belt. Both sub‐basins have a very similar sedimentary fill and can act as a natural laboratory for reconstructing controlling factors of arc‐related sedimentary basins as well as the influence of deformation on a basin system. Modelling focused on burial history and temperature evolution. Two‐dimensional simulations were carried out with the software PetroMod®. The geohistory curve of the North Limón Basin is overall linear, indicating continuous subsidence. The South Limón Basin is also characterized by continuous subsidence, but rates strongly increased at the beginning of the Neogene. Despite a rapid Plio‐Pleistocene deformation of the fold‐and‐thrust belt, the present‐day temperature field is not disturbed in that area. The modelling results indicate a mean heat flow of 60 mW m?2 for the North Limón Basin and 41 mW m?2 for the South Limón Basin. These values are low compared with other back‐arc basins. The lower values are attributed to the following effects: (1) underlying basaltic crust, (2) the lack of an initial rift phase, (3) the low extension rates, (4) absence of volcanic activity and (5) insulation effects of a thick sediment pile. The reasons for the locally lower heat flow in the southern sub‐basin can be found in the low‐angle subduction of the Cocos Ridge. Owing to the low subduction angle, the cool fore‐arc mantle‐wedge below the island‐arc is pushed backwards increasing the cooled area. 相似文献
52.
Soft-sediment deformation structures in NW Germany caused by Late Pleistocene seismicity 总被引：1，自引：0，他引：1
New data on seismically triggered soft-sediment deformation structures in Pleniglacial to Late Glacial alluvial fan and aeolian sand-sheet deposits of the upper Senne area link this soft-sediment deformation directly to earthquakes generated along the Osning Thrust, which is one of the major fault systems in Central Europe. Soft-sediment deformation structures include a complex fault and fold pattern, clastic dikes, sand volcanoes, sills, irregular intrusive sedimentary bodies, flame structures, and ball-and-pillow structures. The style of soft-sediment deformation will be discussed with respect to brittle failure, liquefaction and fluidization processes, and was controlled by (1) the magnitude of the earthquake and (2) the permeability, tensile strength and flexural resistance of the alluvial and aeolian sediments. It is the first time in northern Germany that fluidization and liquefaction features can be directly related to a fault. The occurrence of seismicity in the Late Pleistocene and in the seventeenth century indicates ongoing crustal movements along the Osning Thrust and sheds new light on the seismic activity of northern Germany. The Late Pleistocene earthquake probably occurred between 15.9 ± 1.6 and 13.1 ± 1.5 ka; the association of soft-sediment deformation structures implies that it had a magnitude of at least 5.5. 相似文献
53.
Ocean Dynamics - Die 7. Sitzung der Kommission für nachhaltige Entwicklung (Commission on Sustainable Development, CSD) der Vereinten Nationen fand vom 19. bis 30. April 1999 im... 相似文献
54.
Jutta Jahnel Christian Zwiener Thomas J. Gremm Gudrun Abbt‐Braun Fritz H. Frimmel Carola Kussatz Dieter Schudoma Werner Rocker 《洁净——土壤、空气、水》2001,29(4):246-253
Quality Targets for Pesticides and Other Pollutants in Surface Waters Surface waters are not only adversely affected by industrial and municipal wastewaters but also by diffuse sources. For the control of the ecological water quality, so‐called quality targets are set. The quality targets are threshold concentrations for hazardous substances related to the protected goods like water ecosystems, drinking water supply, sediments, or fishing. In this paper, quality targets for the protection of aquatic life in surface waters were derived on the basis of a concept developed by the International Commission for the Protection of the Rhine (Internationale Kommission zum Schutze des Rheins – IKSR). The quality targets for the selected hazardous substances, which mainly belong to the chemical class of pesticides, were calculated using ecotoxicological results for species of bacteria, algae, fish, and small crustaceans, as the four trophic standards of the water ecosystem. In cooperation with the Federal Environmental Agency (Umweltbundesamt – UBA) the effect data were taken from ecotoxicological data bases. According to the concept of the IKSR, the lowest test result for the most sensitive species was multiplied by an assessment factor. This proceeding concerns the difficulty in describing the complex interactions in water ecosystems with toxicity data of single laboratory experiments for a few organisms. For seven pesticides quality targets below 0.1 μg/L were proposed. These results show that the ecotoxicologically based quality targets might be even lower than the limit values for pesticides in drinking water of 0.1 μg/L. But for most of the substances the determined values are significantly higher. The great concentration range of quality targets demonstrates distinctly that one standard concentration for all pesticides could not be given with regard to the different effects on aquatic organisms. 相似文献