Stratigraphy of the upper cretaceous and lower tertiary strata in the Tethyan Himalayas of Tibet (Tingri area,China)   总被引：26，自引：0，他引：26  

H. Willems  Z. Zhou  B. Zhang  K. -U. Gräfe 《International Journal of Earth Sciences》1996,85(4):723-754

The 1500-m-thick marine strata of the Tethys Himalaya of the Zhepure Mountain (Tingri, Tibet) comprise the Upper Albian to Eocene and represent the sedimentary development of the passive northern continental margin of the Indian plate. Investigations of foraminifera have led to a detailed biozonation which is compared with the west Tethyan record. Five stratigraphic units can be distinguished: The Gamba group (Upper Albian - Lower Santonian) represents the development from a basin and slope to an outer-shelf environment. In the following Zhepure Shanbei formation (Lower Santonian - Middle Maastrichtian), outer-shelf deposits continue. Pebbles in the top layers point to beginning redeposition on a continental slope. Intensified redeposition continues within the Zhepure Shanpo formation (Middle Maastrichtian - Lower Paleocene). The series is capped by sandstones of the Jidula formation (Danian) deposited from a seaward prograding delta plain. The overall succession of these units represents a sea-level high at the Cenomanian/Turonian boundary followed, from the Turonian to Danian, by an overall shallowing-upward megasequence. This is followed by a final transgression — regression cycle during the Paleocene and Eocene, documented in the Zhepure Shan formation (?Upper Danian - Lutetian) and by Upper Eocene continental deposits. The section represents the narrowing and closure of the Tethys as a result of the convergence between northward-drifting India and Eurasia. The plate collision started in the Lower Maastrichtian and caused rapid changes in sedimentation patterns affected by tectonic subsidence and uplift. Stronger subsidence and deposition took place from the Middle Maastrichtian to the Lower Paleocene. The final closure of remnant Tethys in the Tingri area took place in the Lutetian.  相似文献   

The Silurian of Gotland (Sweden): facies interpretation based on stable isotopes in brachiopod shells     

Chr Samtleben  A. Munnecke  T. Bickert  J. Pätzold 《International Journal of Earth Sciences》1996,85(2):278-292

The Silurian of Gotland, Sweden, consists of 440 m of carbonate deposits. Repeatedly, uniform sequences of micritic limestones and marls are interrupted by complex-structured reefs and by adjacent platform sediments. Generally, the alteration of facies is interpreted as the result of sea-level fluctuations caused by a gradual regression with superimposed minor transgressive pulses. The purpose of this study is a facies interpretation based on both field observations and stable isotope measurements of brachiopod shells. Approximately 700 samples from stratigraphically arranged localities in different facies areas have been investigated. The carbon and oxygen isotopes show principally parallel curves and a close relationship to the stratigraphic sequence. Lower values occur in periods dominated by deposition of marly sequences. Higher values are observed in periods dominated by reefs and extended carbonate platforms. The oxygen isotope ratios are interpreted to reflect paleosalinity changes due to varying freshwater input, rather than to paleotemperature. Carbon isotope ratios are believed to have been connected to global changes in the burial of organic carbon in black shales during periods of euxinic deep water conditions. Consequently, the facies succession on Gotland results from global paleoclimatic conditions. Changes in terrigenous input due to different rates of weathering and freshwater runoff, rather than sea-level fluctuations, control the carbonate formation of the Silurian on Gotland.  相似文献   

Accretion and exhumation at a Variscan active margin, recorded in the Saxothuringian flysch     

J. Schäfer  H. Neuroth  H. Ahrendt  W. Dörr  W. Franke 《International Journal of Earth Sciences》1997,86(3):599-611

The Saxothuringian flysch basin, on the north flank of the Central European Variscides, was fed and eventually overthrust by the northwestern, active margin of the Tepla-Barrandian terrane. Clast spectra, mineral composition and isotopic ages of detrital mica and zircon have been analyzed in order to constrain accretion and exhumation of rocks in the orogenic wedge. The earliest clastic sediments preserved are of early Famennian age (ca. 370?Ma). They are exposed immediately to the NW of the suture, and belong to the par-autochthon of the foreland. Besides ultramafic (?ophiolite) material, these rocks contain clasts derived from Early Paleozoic continental slope sediments, originally deposited at the NW margin of the Saxothuringian basin. These findings, together with the paleogeographic position of the Famennian clastics debris on the northwestern passive margin, indicate that the Saxothuringian narrow ocean had been closed by that time. Microprobe analyses of detrital hornblendes suggest derivation from the “Randamphibolit” unit, now present in the middle part of the Saxothuringian allochthon (Münchberg nappes). Detrital zircons of metamorphic rocks formed a little earlier (ca. 380?Ma) indicate rapid recycling at the tectonic front. The middle part of the flysch sequence (ca. early to middle Viséan), both in the par-autochthon and in the allochthon, contains abundant clasts of Paleozoic rocks derived from the northwestern slope and rise, together with debris of Cadomian basement, 500-Ma granitoids and 380?Ma (early Variscan) crystalline rocks. All of these source rocks were still available in the youngest part of the flysch (c. middle to late Viséan), but some clasts record, in addition, accretion of the northwestern shelf. Our findings permit deduction of minimum rates of tectonic shortening well in excess of 10–30?mm per year, and rates of exhumation of ca. 3?mm/a, and possibly more.  相似文献   

Comparison of Cu and Zn cycling in eutrophic lakes with oxic and anoxic hypolimnion     

HanBin Xue  René Gächter  Laura Sigg 《Aquatic Sciences - Research Across Boundaries》1997,59(2):176-189

Data on the cycling of Cu and Zn in two eutrophic lakes are presented: Lake Greifen that becomes seasonally anoxic in its hypolimnion and Lake Sempach that is aerated during winter and oxygenated during summer. They suggest that hypolimnetic oxygenation 1) enhances the release of copper from the sediment but 2) also accelerates the entrapment and deposition of Cu and Zn by freshly formed Mn- and Fe-oxides.  相似文献   

A reexamination of the valley wind system in the Alpine Inn Valley with numerical simulations   总被引：2，自引：0，他引：2  

G. Zängl 《Meteorology and Atmospheric Physics》2004,87(4):241-256

Summary This paper presents idealized numerical simulations of the valley wind circulation in the Alpine Inn Valley, which are compared with existing data and are used to improve our dynamical understanding of the valley wind. The simulations have been performed with the Penn State/NCAR mesoscale model MM5. They use a high-resolution realistic topography but idealized large-scale conditions without any synoptic forcing to focus on the thermally induced valley wind system. The comparison with the available observations shows that this simplified set-up is sufficient to reproduce the essential features of the valley wind.The results show that the tributaries of the Inn Valley have a considerable impact on the along-valley mass fluxes associated with the valley wind circulation. The upvalley mass flux is found to increase where tributaries enter the Inn Valley from the north, that is, from the direction where the Alpine foreland is located. On the other hand, the upvalley mass flux is reduced at the junctions with southern tributaries because part of the upvalley flow is deflected into these tributaries. For the downvalley flow, the situation is essentially reversed, but the influence of the valley geometry on the flow structure is larger than for the upvalley flow. The most important feature is a lateral valley contraction near the valley exit into the Alpine foreland. It reduces the downvalley mass flux at low levels, so that the wind maximum in the interior of the valley is shifted to a fairly large distance from the ground. North of the valley contraction, however, the downvalley flow strongly accelerates and forms a pronounced low-level jet. A dynamical analysis indicates that this acceleration can be interpreted as a transition from subcritical to supercritical hydraulic flow. Another interesting feature is that the low-level jet maintains its structure for several tenths of kilometres into the Alpine foreland. This appears to be related to the fact that the lateral wind shear on the flanks of the jet is associated with a strong dipole of potential vorticity (PV). Due to the conservation properties of the PV, the downstream advection of the PV dipole leads to the formation of a band-like feature that decays fairly slowly.  相似文献   

Climate and Water: From Climate Models to Water Resources Management and Vice Versa   总被引：4，自引：0，他引：4  

Olli Varis  Tommi Kajander  Risto Lemmelä 《Climatic change》2004,66(3):321-344

This article reviews the recent developments in the functional chain from climate models to climate scenarios, through hydrology all the way to water resources management, design and policy making. Although climate models, such as Global Circulation Models (GCMs) continue to evolve, their outputs remain crude and often even inappropriate to watershed-scale hydrological analyses. The bridging techniques are evolving, though. Many families of regionalization technologies are under progress in parallel. Perhaps the most important advances are in the field of regional weather patterns, such as ENSO (El Niño-Southern Oscillation), NAO (North Atlantic Oscillation) and many more. The gap from hydrology to water resources development is by far not that wide. The traditional and contemporary practices are well in place. In climate change studies, the bottleneck is not in this link itself but in the climatic input. The tendency seems to be towards integrated water resources assessments, where climate is only one among many changes that are expected to occur, such as demography, land cover and land use, economy, technologies, and so forth. In such a pragmatic setting a risk–analytic interpretation of those scenarios is often called for. The above-outlined continuum from climate to water is a topic where the physically based modelers, the empiricists and the pragmatists should not get restricted to their own way of thinking. The issues should develop hand in hand. Perhaps the greatest challenge is to incorporate and respect the pragmatic policy-related component to the two other branches. For this purpose, it is helpful to reverse the direction of thinking from time to time to start—instead of climate models—from practical needs and think how the climate scenarios and models help really in the difficult task of designing better water structures, outline better policies and formulate better operational rules in the water field.  相似文献   

Revising macroseismic data in Switzerland: The December 20, 1720 earthquake in the region of Lake Constance     

Monika Gisler  Donat Fäh  Reto Schibler 《Journal of Seismology》2004,8(2):179-192

Upgrading the Earthquake Catalog of Switzerland (ECOS) included revising the earthquake of 1720. This change has major importance for history and seismology.Although that quake has been the subject of several publications, none was based on critical methods. This re-evaluation of the event is built upon a new and more reliable database established after investigating archives and libraries. Using data from such historical sources, we assigned new site intensities, adopting the criteria established by the European macroseismic scale EMS 98 (Grünthal, 1998).We discovered that the event had been assigned an overestimated intensity, due to interpretation errors in former earthquake catalogs and compilations. We recommend reducing the intensity from I₀= VIII to I₀= VI (EMS 98). The moment magnitude is given as M_W= 4.6. Since the event had been considered the largest for its respective area, downgrading it now will influence the seismic hazard assessment for this region.  相似文献   

Silica depleted melting of pelites. Petrogenetic grid and application to the Susqueda Aureole, Spain   总被引：2，自引：0，他引：2  

M. Riesco  K. Stüwe  J. Reche  F. J. Martinez 《Journal of Metamorphic Geology》2004,22(5):475-494

Metapelitic rocks in the low pressure contact metamorphic aureole around the Susqueda igneous complex, Spain show a number of features that make them an ideal testing ground for the modelling of silica‐undersaturated melting. Rocks in the aureole experienced localized depletion in silica by the segregation of quartz veins during a pre‐anatectic, regional cordierite‐andalusite grade metamorphic event. These rocks were then intruded by gabbroic to dioritic rocks of the Susqueda igneous complex that formed a migmatitic contact metamorphic aureole in the country rocks. This migmatisation event caused quartz‐saturated hornfels and restite formation in rocks that had experienced no quartz vein segregation in the previous regional metamorphic event, but silica‐undersaturated melting in those rocks that were previously depleted in silica. Silica‐undersaturated melting is investigated using a new petrogenetic P–T projection and equilibrium pseudosections calculated in the KFMASH and NCKFMASH systems, respectively. The grid considers quartz absent equilibria and a range of phases that form typically in silica‐undersaturated bulk compositions, for example corundum. It is shown that the quartz‐rich precursors in the Susqueda contact aureole produced about 10% melt during contact metamorphism. However, most of this melt was extracted leaving behind rocks with restitic bulk compositions and minor leucosome segregation. It is suggested that the melt mixed with the host igneous rocks causing an apparent magmatic zoning from diorite in the centre of the complex to tonalite at the margins. In contrast, the quartz‐poor precursors (from which the quartz veins segregated) melted in the silica‐undersaturated field producing a range of assemblages including peritectic corundum and spinel. Melting of the silica‐undersaturated rocks produced only negligible melt and no subsequent melt loss.  相似文献   

Effet du vieillissement des céramiques poreuses sur leur capacité à évaluer la concentration de pesticide en solution     

Nicolas Domange  Caroline Grégoire  Véronique Gouy  Michèle Tremolières 《Comptes Rendus Geoscience》2004,336(1):49-58

The soil solution sampling by ceramic cups allows pesticide transfer monitoring in the soil during long times. The ageing of material involves a bias in the sampling results. In laboratory, the comparison of two types of ceramic suction cups, new and installed in situ during four years, shows a modification of the hydrodynamic properties and a possible evolution of the adsorption capacity of the matrix. The passage rate, as well qualitative as quantitative, is better for the old material. Recommendations about site management are finally exposed. To cite this article: N. Domange et al., C. R. Geoscience 336 (2004).  相似文献   

Compositional variations (major and trace elements) of clinopyroxene and Ti-andradite from pyroxenite, ijolite and nepheline syenite, Alnö Island, Sweden     

Jaana Hode Vuorinen  Ulf H  lenius  Martin J. Whitehouse  Joakim Mansfeld  Alasdair D.L. Skelton 《Lithos》2005,81(1-4):55-77

Clinopyroxenes from pyroxenite, ijolite and nepheline syenite from the main intrusion of the Alnö complex define two sub-parallel compositional trends with respect to Na, Ca and Fe_TOT plotted against alkali-pyroxene fractionation index (Na–Mg). Both trends define a smooth fractionation of increasing Na and Fe_TOT and decreasing Ca with increasing Na–Mg, but one set of samples contain clinopyroxenes that constantly plot at higher Na and lower Fe_TOT and Ca (at similar Na–Mg) than the rest of the samples. Clinopyroxenes with higher Ca and Fe_TOT and lower Na (trend 1) co-exist with substantial amounts of Ti-andradite (up to 70 vol.%), while the sample set defining the more Na-rich trend (trend 2) lack co-existing Ti-andradite. Clinopyroxenes from both trends show fractionated REE patterns with a distinct difference in HREE content, reflecting the content of co-existing Ti-andradite. The rocks of the first Ti-andradite-bearing trend crystallized slightly prior to the rocks of the second trend, probably from a primitive, Ca- and Ti-rich nephelinitic magma. Crystallisation of pyroxenite and melteigite occurred under low aSiO₂ and high aCaO and aTiO₂ as evidenced by the presence of perovskite and sometimes substantial amounts of magnetite. Subsequent increase in aSiO₂ is evidenced in the overgrowth of perovskite by titanite, which in turn is overgrown by Ti-andradite. Nepheline syenitic residuals crystallized under higher aSiO₂ and aNa₂O and lower aCaO and aTiO₂, which reduced Ti-andradite into an accessory phase and produced more Si- and Na-rich clinopyroxenes. Some of these residuals probably also mixed with new primitive magma producing a hybrid magma that crystallised the more Na-rich and Ca- and Fe_TOT-poor clinopyroxenes of trend 2. The complete lack of Ti-andradite in these rocks indicates different crystallisation conditions and also a different magma composition.  相似文献