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31.
Jiayu Rong Michael Melchin S. Henry Williams Tatyana N. Koren Jacques Verniers 《《幕》》2008,31(3):315-318
The Global Stratotype Section and Point (GSSP) for the base of the Silurian System was defined in 1985. Since that time, a number of researchers have suggested that this section has serious deficiencies for use as a GSSP. As a result, in 2000, the Subcommission on Silurian Stratigraphy (SSS) proposed undertaking a formal restu@ of this GSSP, which was subsequently approved by the International Commission of Stratigraphy (ICS). The result of this restudy was the formal proposal that the current GSSP, at 1.6 m above the base of the Birkhill Shale, at Dob's Linn, Scotland, should be maintained as the same locality and stratigraphic level, but the bios- tratigraphical definition of the boundary should be revised. The previously defined, basal Silurian grapto- lite zone, the Parakidograptus acuminatus Zone, should be subdivided into a lower Akidograptus ascensus Zone and a higher E acuminatus Zone. The base of the A. ascensus Zone, marked by the first appearance of A. ascensus, should be regarded as the biostratigraphic mark for the base of the Silurian. This proposal has now been formally approved by the SSS and ICS, and ratified by International Union of Geological Sciences. This is the first GSSP to undergo formal restudy and redefini- tion, and the proposal also included a recommended procedure for restudy of GSSPs. 相似文献
32.
An analysis of the reasons for the displacements of long-term embankments maintained on permafrost soils indicates that they mainly occur due to plastic deformations in the layer of seasonal freezing and thawing; therefore, the reconstruction of permafrost is not effective in this case. It is proposed to strengthen these embankments with the help of using jet technology for cementation of the top layer of the roadbed. This approach is considered through the example of the deforming embankment on 6,278 km of the Turinskaya-Karymskaya section of the Trans-Siberian Railway. 相似文献
33.
Vladimir POPOVICHEV Oleg EREMIN Natalya RODIONOVA Tatyana TSARINA Nikolai BOBKO 《《地质学报》英文版》2014,88(Z1):96-97
正1 Introduction It is known that more than 300 lakes and lagoons are present in the Crimean Peninsula,which are divided depending on position to 7 groups:Perekop,Tarkhankut,Evpatoriyskaya,Khersonesskaya,lake on the mountainpastures,Kerch and Genicheskaya.Almost the all lakes,with the exception of the small freshwater lakes,which situated on mountain pastures of the Main ridge of 相似文献
34.
Hirotsugu Minami Akihiro Hachikubo Hirotoshi Sakagami Satoshi Yamashita Yusuke Soramoto Tsuyoshi Kotake Nobuo Takahashi Hitoshi Shoji Tatyana Pogodaeva Oleg Khlystov Andrey Khabuev Lieven Naudts Marc De Batist 《Geo-Marine Letters》2014,34(2-3):241-251
The isotopic and ionic composition of pure gas hydrate (GH) water was examined for GHs recovered in three gravity cores (165–193 cm length) from the Kukuy K-9 mud volcano (MV) in Lake Baikal. A massive GH sample from core St6GC4 (143–165 cm core depth interval) was dissociated progressively over 6 h in a closed glass chamber, and 11 sequentially collected fractions of dissociated GH water analyzed. Their hydrogen and oxygen isotopic compositions, and the concentrations of Cl– and HCO3 – remained essentially constant over time, except that the fraction collected during the first 50 minutes deviated partly from this pattern. Fraction #1 had a substantially higher Cl– concentration, similar to that of pore water sampled immediately above (135–142 cm core depth) the main GH-bearing interval in that core. Like the subsequent fractions, however, the HCO3 – concentration was markedly lower than that of pore water. For the GH water fractions #2 to #11, an essentially constant HCO3 –/Cl– ratio of 305 differed markedly from downcore pore water HCO3 –/Cl– ratios of 63–99. Evidently, contamination of the extracted GH water by ambient pore water probably adhered to the massive GH sample was satisfactorily restricted to the initial phase of GH dissociation. The hydrogen and oxygen isotopic composition of hydrate-forming water was estimated using the measured isotopic composition of extracted GH water combined with known isotopic fractionation factors between GH and GH-forming water. Estimated δD of ?126 to ?133‰ and δ18O of ?15.7 to ?16.7‰ differed partly from the corresponding signatures of ambient pore water (δD of ?123‰, δ18O of ?15.6‰) and of lake bottom water (δD of ?121‰, δ18O of ?15.8‰) at the St6GC4 coring site, suggesting that the GH was not formed from those waters. Observations of breccias in that core point to a possible deep-rooted water source, consistent with published thermal measurements for the neighboring Kukuy K-2 MV. By contrast, the pore waters of core St6GC4 and also of the neighboring cores GC2 and GC3 from the Kukuy K-9 MV show neither isotopic nor ionic evidence of such a source (e.g., elevated sulfate concentration). These findings constrain GH formation to earlier times, but a deep-rooted source of hydrate-forming water remains ambiguous. A possible long-term dampening of key deep-water source signatures deserves further attention, notably in terms of diffusion and/or advection, as well as anaerobic oxidation of methane. 相似文献
35.
Physics of seasonally ice-covered lakes: a review 总被引:2,自引:0,他引:2
36.
Tatyana M. Pak Christoph A. Hauzenberger Lukas P. Baumgartner 《Chemical Geology》2003,200(3-4):377-393
The solubility of the high grade pelite assemblage albite+K-feldspar+andalusite+quartz at 650 °C and 2 kbar was determined in aqueous solutions over a total chloride range of 0.01–3 mCltot using rapid-quench hydrothermal technique. The concentration of Na, K, Si, and Al was determined in the fluid phase after quench. The K/Na ratio was determined by approaching the equilibrium from below and above. It is 0.34 at low chloride concentrations and decreases slightly to 0.31 with increasing total chloride. Silica and aluminum concentrations were determined only from undersaturation. The silica solubility is found to be independent of chloride concentration and is 0.13 molal. Aluminum is nearly independent of chloride concentration decreasing only slightly from 0.0015 to 0.0007 molal. Comparison of the experimental data with thermodynamic model calculations demonstrates that the silica concentrations are well predicted, while significant differences exist between individual databases for Al speciation and its total concentration. Al concentrations are underestimated by up to 10 to 15 orders of magnitude using the SUPCRT92 database. Predicted K/Na ratios are underestimated by up to 30%. The best predictions achieved for this simplified high-grade pelite assemblage are those using the SUPCRT92 database with revised thermodynamic data for feldspars and K- and Na-species (J. Phys. Chem. Ref. Data 24 (1995) 1401) and additional Al-species (Am. J. Sci. 295 (1995) 1255; Geochim. Cosmochim. Acta 61 (1997) 2175). The use of ideal mixing for neutral complexes in combination with the extended Debye–Hückel activity model for the charged species yields the most compatible speciation model. 相似文献
37.
Sub-surface precipitation of salts in supercritical seawater 总被引:2,自引:0,他引:2
Martin Hovland Tatyana Kuznetsova† Håkon Rueslåtten‡ Bjørn Kvamme† Hans Konrad Johnsen¶ Gunnar E. Fladmark§ Andreas Hebach† 《Basin Research》2006,18(2):221-230
Extremely low solubility of typical seawater salts within certain supercritical sections of their pressure–temperature composition space is a proven experimental fact. Its consequences are often referred to as either 'shock crystallization' or 'out-salting'. Our alternative model for the formation of salt deposits hypothesizes that high temperatures and pressures characteristic for the high heat-flow zones of tectonically active basins may bring submarine brines into the out-salting regions and result in the accumulation of geological-scale salt depositions.
To confirm the laboratory observations, molecular-scale simulations (molecular dynamics) have been employed to study structural changes in a model seawater system where temperature increased from ambient to near-critical and supercritical. Fluid properties and phase transition regions extracted from the simulations were then used as input parameters for a reservoir simulator program to model out-salting in a simple hydrothermal geological system. Both numerical simulations and laboratory experiments confirm that supercritical out-salting is a viable process of geological significance for the formation and accumulation of evaporites. We suggest two regions where hydrothermally associated salts may be depositing today: Atlantis II Deep, in the Red Sea, and Lake Asale, Ethiopia. 相似文献
To confirm the laboratory observations, molecular-scale simulations (molecular dynamics) have been employed to study structural changes in a model seawater system where temperature increased from ambient to near-critical and supercritical. Fluid properties and phase transition regions extracted from the simulations were then used as input parameters for a reservoir simulator program to model out-salting in a simple hydrothermal geological system. Both numerical simulations and laboratory experiments confirm that supercritical out-salting is a viable process of geological significance for the formation and accumulation of evaporites. We suggest two regions where hydrothermally associated salts may be depositing today: Atlantis II Deep, in the Red Sea, and Lake Asale, Ethiopia. 相似文献
38.
Wilson JG Komakhidze A Osadchaya T Alyomov S Romanov A Tediashvili M 《Marine pollution bulletin》2008,57(1-5):202-207
Anthropogenic pressures have resulted in measurable impacts on the coastal ecosystems of the northern (Sevastopol Bay, Ukraine) and eastern (Batumi aquatoria, Georgia) Black Sea. Indices suggest that major impacts are relatively localized and are comparable to similar situations in the northern Atlantic. In contrast, biodiversity was appreciably lower than from comparable north Atlantic waters. The number of macrobenthic species was typically round 50, less than half the number that might be expected from similar exercises in US or European waters. Site-specific indices likewise indicated a somewhat lower diversity within communities, yielding metrics which would indicate a measure of stress in N. Atlantic situations. Microbial status was generally good, although regions close to urbanisation did not comply with standards laid down in the current EC Bathing Water Directive (76/EC/160). Likewise viruses were more commonly, although not exclusively, associated with urban locations, as were phages. Microbial investigation of the sediments confirmed the presence of heterotrophic and oil-oxidising bacteria. Abundance of the latter was closely correlated to the degree of oil contamination of the sediments, and to temperature, although for both, the results showed that the increase in bacterial abundance did level off beyond a certain point. Numbers of oil-oxidising bacteria in the water column displayed a classical response to temperature, with abundance doubling over a 10-degree C rise in temperature. Overall the results suggest that while indices in current use are useful in evaluating coastal quality in the Black Sea, some adjustments would be necessary especially in the establishment of baseline or reference values. 相似文献
39.
Igor Bashmachnikov Tatyana Belonenko Pavel Kuibin Denis Volkov Victor Foux 《Ocean Dynamics》2018,68(12):1711-1725
Mean radial distributions of various dynamic characteristics of the permanently existing anticyclonic Lofoten vortex (LV) in the Norwegian Sea are obtained from an eddy-permitting regional hydrodynamic MIT general circulation model. It is shown that the model adequately reproduces the observed 3D thermohaline and dynamic structure of the vortex. The obtained radial distribution of the mean vertical velocity is found to form a complex structure: with the upward fluxes along the axis in and above the anticyclonically rotating LV core, compensated by the downward fluxes in the vortex skirt. These vertical motions maintain the vortex potential energy anomaly against dissipation. This secondary circulation is generated by the centrifugal force and, to a lesser extent, by the horizontal dispersion of the vortex energy, both intensified towards the sea surface. Below the vortex core, the maximum downward vertical velocity converges towards the vortex axis with depth. At these depth levels, the secondary circulation is forced by Ekman divergence in the bottom mixed layer. The theory of columnar vortices with helical structure, applied to the LV, relate the radial profiles of the vertical velocity with those of the horizontal circulation. The theoretically predicted the radial patterns of the mean vertical velocity in the LV were close to those, obtained from the primitive equation ocean model, when approximating the radial patterns of the azimuthal velocity with the Rayleigh profile. 相似文献
40.
Siberian larch (Larix sibirica Ledeb.) forests cover the largest areas in the Eurasian boreal zone, but there are insufficient data on its root system including the structure and functional traits of ectomycorrhizas (EM). The aim of this research is to find out if the morphological parameters of Larix sibirica EMs responded to the changes in elevation and main ecological factors (soil humidity, soil richness, soil acidity and habitat illumination). Using light microscopy, we studied EM diameter, root diameter, mantle width, and mantle volume share, share of tannin cells layers, EM density and EM length of Larix sibirica in two main types of plant communities along the elevation gradient at the Northern and Subpolar Urals. Differences in the environment were traced using phytoindication approach and the Ellenberg ecological scales. All the studied traits depend on the elevation and studied ecological factors. The diversity of fungal mantles is low, and the proportion of unstructured and pseudoparenchymatous mantles is high in response to the deterioration of the humidity, soil nitrogen content and acidity at higher-altitude habitats. Results of EM quantitative parameters measurements confirmed this pattern. We found a decline in the EM linear dimensions accompanied by a compensatory growth of the EM density with the raised elevation and the deterioration of environmental conditions. 相似文献