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1.
Magnetic fabric study of the SE Rhenohercynian Zone (Bohemian Massif): Implications for dynamics of the Paleozoic accretionary wedge 总被引：2，自引：0，他引：2
The progressive deformation recorded in the magnetic fabric of sedimentary rocks was studied in the SE Rhenohercynian Zone (RHZ), eastern margin of the Bohemian Massif, Czech Republic. Almost 800 oriented samples of the Lower Carboniferous mudstones and graywackes were collected from the SSE part of the Czech RHZ, so-called the Drahany Upland. The anisotropy of magnetic susceptibility (AMS) is predominantly controlled by the preferred orientation of paramagnetic phyllosilicates, mainly iron-bearing chlorites. A regional distribution of the magnetic fabric within the Drahany Upland revealed an increasing deformation from the SSE to the NNW. In the SE, the magnetic fabric is bedding-parallel with magnetic lineation scattered in the bedding plane or trending N–S to NNE–SSW. Further to the NW, the magnetic foliation rotates from the bedding-parallel orientation to the orientation parallel to the evolving cleavage. This rotation is accompanied by a decrease of the anisotropy degree and the prolate nature of the anisotropy ellipsoids. The magnetic lineation is parallel to the strike of the bedding, bedding/cleavage intersection, pencil structure or the fold axes on a regional scale. In the NW part of the Drahany Upland, the magnetic foliation becomes parallel to the cleavage accompanied by an increase of the anisotropy degree and the oblate nature of the anisotropy ellipsoids. The increasing trend of deformation corresponds to the SSE–NNW increase in the degree of anchimetamorphism; both trends being oblique to the main lithostratigraphic formations as typically observed in the sedimentary rocks of the accretionary wedges. The SSE–NNW increase in deformation and anchimetamorphism continues to the Nízký Jeseník Mts., representing the northern part of the same accretionary wedge. The kinematics of deformation could not be unambiguously assessed. The observed magnetic fabric may reflect either lateral shortening or horizontal simple shear or a combination of both mechanisms. Regarding the subduction process, it seems that the sedimentary sequences of the Drahany Upland were subducted, partly offscraped and accreted frontally or partly underplated as opposed to the Nízký Jeseník Mts. where some return flow must have occurred. 相似文献
2.
Here, we address the sediment dynamics in the Black Sea based on analysis of remote sensing data from the Medium Resolution
Imaging Spectrometer and numerical simulations with Nucleus for European Modelling of the Ocean model. Boundary conditions
consist of realistic meteorological forcing, including significant wave height generated by wave prediction model. A number
of sensitivity runs was analysed with the aim to find the most suitable parameters governing sediment fluxes. The comparison
between numerical simulations and remote sensing data gives credibility to the quality of simulations. The combined effect
of wind waves and currents in the bed layer controls the sediment resuspension that appears to be the major basin-wide source
of sediment. Sensitivity experiments included or excluded different forcing terms, e.g. sediment flux from rivers enable to
determine the spatial extensions of different point sources. It is concluded that wind-wave forcing is manifested in the sediment
dynamics through episodic high energy events contributing to the increase of horizontal sediment fluxes over the northwestern
shelf. Both satellite images and numerical model simulations demonstrated that the penetration of suspended sediment into
the basin interior was governed by the dynamics of coastal and open-ocean eddies. While fine sediment at sea surface could
cross the continental slope propagating into the open ocean, coarser fractions follow the bottom and their penetration into
the open ocean is limited. The conclusion is thus that the deposition patterns correlate with the specific shape of Black
Sea topography, and the largest depositions are observed in the area of continental slope. 相似文献
3.
Pavel Koten Pavel Spurný Ji&#x;í Borovi
ka Stephen Evans Andrew Elliott Hans Betlem Rostislav &#x;tork Klaas Jobse 《Meteoritics & planetary science》2006,41(9):1305-1320
Abstract— In this paper, we provide an overview of meteors with high beginning height. During the recent Leonid meteor storms, as well as within the regular double station video observations of other meteor showers, we recorded 164 meteors with a beginning height above 130 km. We found that beginning heights between 130 and 150 km are quite usual, especially for the Leonid meteor shower. Conversely, meteors with beginning heights above 160 km are very rare even among Leonids. From the meteor light curves, we are able to distinguish two different processes that govern radiation of the meteors at different altitudes. Light curves vary greatly above 130 km and exhibit sudden changes in meteor brightness. Sputtering from the meteoroid surface is the dominating process during this phase of the meteor luminous trajectory. Around 130 km, the process switches to ablation and the light curves become similar to the light curves of standard meteors. The sputtering model was successfully applied to explain the difference in the beginning heights of high‐altitude Leonid and Perseid meteors. We show also that this process in connection with high altitude fragmentation could explain the anomalously high beginning heights of several relatively faint meteors. 相似文献
4.
Jiří Borovička Pavel Koten Pavel Spurný Rostislav Štork 《Earth, Moon, and Planets》2008,102(1-4):485-493
We present an analysis of sporadic meteor number 07406018, observed by image intensified video cameras at two stations, which
showed a pronounced deceleration along its trajectory. We have applied the erosion model to analyze simultaneously the deceleration
and light curve. We have found that the meteoroid had a low density of about 500 kg m−3, consistent with its cometary orbit. The meteoroid structure was, nevertheless, markedly different from the Draconid meteoroids,
studied recently with the same model. The size of the constituent grains was larger and the erosion energy was higher than
in Draconids. The meteor spectrum was also different from Draconid spectra and showed very bright Na lines. The meteoroid
composition was probably different from normal cometary composition. 相似文献
5.
Environmental risks associated with aeration of a freshwater sediment exposed to mine drainage water 总被引：1，自引：0，他引：1
The study examined freshwater sediments from a pond receiving waters from an open-pit lignite quarry located in Europe's Black Triangle in the northern part of the Czech Republic. Sediments were studied with respect to chemical changes upon aeration to assess the risks associated with their acidification and release of toxic metals. Three types of sediments were sampled: orange precipitates of ferric oxides, underlying black anoxic material and brown clayey material from the original bottom of the pond. The experiment revealed that only black anoxic sediment presents environmental concerns upon aeration. Its redox potential rose steeply from -124 up to +412 mV within the first 50 h of aeration, afterwards, it increased only slowly and reached a finale value of +663 mV after 362 h of aeration. The redox changes were accompanied by sulphate production. Up to 97,037.8 mg of sulphate was released into the solution from 1 kg of the sediment. Consequently, the pH values dropped from 6.7 down to 3.3 within the first 50 h of aeration and reached a value of 2.7 at the end of the experiment. The decrease of pH values was followed by increased zinc and manganese mobility. Iron solubilisation was not continuous. An initial drop in iron mobility was followed by an increase, after which the mobility decreased again. This fluctuation reflected the changes in iron solubility depending on the oxidation state and pH changes in the sediment suspension. 相似文献
6.
Measurements of temperature and velocity microstructure near and downstream of a shallow seamount are used to compare fossil turbulence versus non-fossil turbulence models for the evolution of turbulence microstructure patches in the stratified ocean. According to non-fossil oceanic turbulence models, all overturn length scales LT of the microstructure grow and collapse in constant proportion to each other and to the turbulence energy (Oboukov) scale LO and the inertial buoyancy (Ozmidov) scale
of the patches; that is, with LTrms ≈1.2LR and viscous dissipation rate ≈ 0*. According to the Gibson fossil turbulence model, all microstructure originates from completely active turbulence with 0 ≈ 3LT2N3(≈ 280*) and LT/√6 ≈ LTrms, but this rapidly decays into a more persistent active-fossil state with 0F ≈ 30vN2, where N is the buoyancy frequency and v is the kinematic viscosity and, without further energy supply, finally reaches a completely fossil turbulence hydrodynamic state of internal wave motions, with F. The last turbulence eddies, with ≈ F, vanish at a buoyant-inertial-viscous (fossil Kolmogorov) scale LKF that is much smaller than the remnant overturn scales LT for large 0/F ratios. These density, temperature, and salinity overturns with LT ≈ 0.6 LR0 0.6 LR persist as turbulence fossils (by retaining the memory of o) and collapse very slowly. In the near wake below the summit depth of Ampere seamount, a much larger proportion of completely active turbulence patches was found than is usually found in the ocean interior away from sources. Dissipation rates and turbulence activity coefficients
of microstructure patches were found to decrease downstream, suggesting that the active turbulence indicated by the patches with AT 1 was caused by the presence of the seamount as a turbulence source. Therefore, the turbulence and mixing processes of ocean layers far away from turbulence sources probably have been undersampled by microstructure data sets lacking any AT 1 patches. This is because large fractions of the mixing and viscous dissipation of the patches occur in short-lived active turbulence regimes that are too brief to be detected. Consequently, large underestimates of the true space-time average turbulence fluxes and turbulence and scalar dissipation rates may result if non-fossil turbulence models are assumed in ocean microstructure data interpretation. 相似文献
7.
J. Kalvoda O. Babek O. Fatka J. Leichmann R. Melichar S. Nehyba P. Spacek 《International Journal of Earth Sciences》2008,97(3):497-518
The Brunovistulian terrane represents a microcontinent of enigmatic Proterozoic provenance that was located at the southern
margin of Baltica in the early Paleozoic. During the Variscan orogeny, it represented the lower plate at the southern margin
of Laurussia, involved in the collision with the Armorican terrane assemblage. In this respect, it resembles the Avalonian
terrane in the west and the Istanbul Zone in the east. There is a growing evidence about the presence of a Devonian back-arc
at the margin of the Brunovistulian terrane. The early Variscan phase was characterized by the formation of Devonian extensional
basins with the within-plate volcanic activity and formation of narrow segments of oceanic crust. The oldest Viséan flysch
of the Rheic/Rhenohercynian remnant basin (Protivanov, Andelska Hora and Horní Benesov formations) forms the highest allochthonous
units and contains, together with slices of Silurian Bohemian facies, clastic micas from early Paleozoic crystalline rocks
that are presumably derived from terranes of Armorican affinity although provenance from an active Brunovistulian margin cannot
be fully excluded either. The development of the Moravo–Silesian late Paleozoic basin was terminated by coal-bearing paralic
and limnic sediments. The progressive Carboniferous stacking of nappes and their impingement on the Laurussian foreland led
to crustal thickening and shortening and a number of distinct deformational and folding events. The postorogenic extension
led to the formation of the terminal Carboniferous-early Permian Boskovice Graben located in the eastern part of the Brunovistulian
terrane, in front of the crystalline nappes. The highest, allochthonous westernmost flysch units, locally with the basal slices
of the Devonian and Silurian rocks thrusted over the Silesicum in the NW part of the Brunovistulian terrane, may share a similar
tectonic position with the Giessen–Harz nappes. The Silesicum represents the outermost margin of the Brunovistulian terrane
with many features in common with the Northern Phyllite Zone at the Avalonia–Armorica interface in Germany. 相似文献
8.
Paleogeography of the Early Badenian connection between the Vienna Basin and the Carpathian Foredeep
The paleogeographic reconstruction for an early Badenian connection of the Vienna Basin and the Carpathian Foredeep in the Mikulov area (Mikulov Gate) based on paleontological (otoliths) and geological (regional geology, tectonics) data has been provided. The ecologically homogenous deep water associations of otoliths in the most NW tip of the Vienna Basin (Sedlec HJ-2 Borehole) links up bathymetrically with nearly adequate otolith assemblages in the southernmost Moravian part of the foredeep. Ten meso- and bathypelagic teleost species have been identified in the Vienna Basin for the first time. Geological analyses proved inversion processes of recurrent nature along old faults of the NW-SE direction in the Dyje (Thaya) Depression. In the early Badenian the Mikulov Gate resulted from the sagging block of the Waschberg Zone. This marine channel was relatively deep (> 200m, as indicated by otoliths) and in all probability flooded an entire front of the nappes in this area. 相似文献
9.
The sequential extraction procedure was proposed and used to study of mercury speciation in real samples of soil. Samples
of soil profiles together with bedrock and coal were taken from sampling spots in the vicinity of surficial coal beds in an
area with natural coal outcrops. The proposed sequential extraction procedure involves the following fractionation: organic
mercury compounds, extractable mercury in an acidic medium, mercury bound to humic substances, elemental Hg and mercury bound
to complexes, HgS and residual mercury. The significant distribution of mercury between the two portions—mercury bound to
humic substance and HgS was determined in the majority of samples. The mercury bound to humic substances created a significant
contribution, especially to the top layer of soil. On the other hand, HgS was the dominant form in the samples from lower
layers of the soil profile. The mercury content in the samples did not show a distinct mobility. The influence of soil parameters
on the mercury distribution in the studied samples was investigated and discussed. 相似文献
10.
The dependence of stream depletion by seasonal pumping on various hydraulic characteristics and engineering factors 总被引：3，自引：2，他引：1
Compensation pumping is used to alleviate deficiencies in streamflow discharge during dry seasons. Short-term groundwater pumping can use aquifer storage instead of catchment-zone water until the drawdown reaches the edge of the stream. The capacitance is a complex, dimensionless parameter of an aquifer system that defines the delayed effect on streamflow when there is groundwater pumping. This parameter is a function of aquifer hydraulic characteristics, pumping time, and distance between the well and stream edge; the latter can involve stream leakance and vertical leakance of an associated aquitard. Three typical hydraulic cases of combined water systems (major catchment-zone wells close to the stream and compensation pumping wells) were classified depending on their capacitance structure (i.e. the relationship between surface water and groundwater): (1) perfect hydraulic connection between the stream and aquifer; (2) imperfect hydraulic connection between the stream and aquifer; and (3) essentially imperfect hydraulic connection between the stream and the underlying confined aquifer. The impact of various hydraulic characteristics and engineering factors on stream depletion was examined by conceptual and numerical modeling. To predict the suitability and efficiency of a combined water system application, regression tests were undertaken on unit stream depletion and capacitance, and power dependencies were defined. 相似文献