Cluster Observations of the Magnetospheric Low-Latitude Boundary Layer and Cusp during Extreme Solar Wind and Interplanetary Magnetic Field Conditions: I. 10 November 2004 ICME     

Y. V. Bogdanova  C. J. Owen  G. Siscoe  A. N. Fazakerley  I. Dandouras  O. Marghitu  Z. Kaymaz  H. Rème  E. A. Lucek 《Solar physics》2007,244(1-2):201-232

We present a study of the magnetospheric cusp response to extreme external parameters during passage of the ICME over the Earth on 10 November 2004, based on Cluster observations of the plasma properties inside the low-latitude boundary layer (LLBL)/cusp regions. Two separate events are observed while Cluster is in the dawn sector, 07 – 08 h magnetic local time (MLT). First, a LLBL/cusp crossing occurs during a period of strong southward IMF. During this time, the LLBL/cusp is very small, ∼0.8 – 1° invariant latitude (ILAT) and moves equatorward, down to 67° ILAT. This can be explained by the occurrence of significant magnetopause erosion due to enhanced dayside sub-solar reconnection. The energy of the plasma inside this region is higher than normal, and the low-energy cut-off often observed in the ion data is also unusually high. This might be explained by the suggestion that the local magnetosheath Alfvén velocity and deHoffmann – Teller velocity are also both extremely high. However, the plasma convection and parallel velocity inside this region are not very high. The second event discussed in this paper is a LLBL/cusp crossing during strong equatorial IMF (mostly due to the dominant dawn – dusk component). Under these conditions, occurring at the same time as pulses of solar wind dynamic pressure, the observations are very complicated. However, we suggest that in the polar region of the southern hemisphere, Cluster cross two LLBLs/cusps, spatially separated by polar cap plasma. The first LLBL/cusp is formed by anti-parallel reconnection in the dusk sector of the southern hemisphere and the second is formed by anti-parallel reconnection in the dawn sector of the northern hemisphere. The second LLBL/cusp is located at extremely low latitude, less than ∼66.3° ILAT. During all LLBL/cusp crossings, strong ionospheric O⁺ ion outflow is detected in the form of a narrow beam with limited pitch-angle range.  相似文献   

How global are the Jurassic–Cretaceous unconformities?     

Svetlana O. Zorina  Oksana S. Dzyuba  Boris N. Shurygin  Dmitry A. Ruban 《地学学报》2008,20(5):341-346

The reality of the global‐scale sedimentation breaks remains controversial. A compilation of data on the Jurassic–Cretaceous unconformities in a number of regions with different tectonic settings and character of sedimentation, where new or updated stratigraphic frameworks are established, permits their correlation. Unconformities from three large reference regions, including North America, the Gulf of Mexico, and Western Europe, were also considered. The unconformities, which encompass the Jurassic‐Cretaceous, the Lower–Upper Cretaceous and the Cretaceous–Palaeogene transitions are of global extent. Other remarkable unconformities traced within many regions at the base of the Jurassic and at the Santonian–Campanian transition are not known from reference regions. A correlation of the Jurassic–Cretaceous global‐scale sedimentation breaks and eustatic curves is quite uncertain. Therefore, definition of global sequences will not be possible until eustatic changes are clarified. Activity of mantle plumes is among the likely causes of the documented unconformities.  相似文献   

Effects of resuspension on benthic fluxes of oxygen,nutrients, dissolved inorganic carbon,iron and manganese in the Gulf of Finland,Baltic Sea     

Elin Almroth  Anders Tengberg  Johan H. Andersson  Svetlana Pakhomova  Per O.J. Hall 《Continental Shelf Research》2009,29(5-6):807-818

The effect of resuspension on benthic fluxes of oxygen (O₂), ammonium (NH₄⁺), nitrate (NO₃^?), phosphate (PO₄^3?), silicate (Si(OH)₄), dissolved inorganic carbon (DIC), total dissolved iron (Fe) and total dissolved manganese (Mn) was studied at three different stations in the Gulf of Finland (GoF), Baltic Sea during three cruises in June–July 2003, September 2004 and May 2005. The stations were situated on different bottom types in the western, central and eastern part, respectively, of the open GoF. The fluxes were measured in-situ using the autonomous Göteborg benthic lander. To simulate resuspension events, the stirring speed was increased in two of the four chambers of the lander after approximately half of the incubation time. The other two chambers were used as control chambers. Clear effects of resuspension were observed on the oxygen fluxes where an increase of the consumption was observed in 88% of the cases and on average with 59% (stdev=53). The NH₄⁺ fluxes were affected in 50% of the cases (4 out of 8 incubations) at stations with low bottom water oxygen concentrations, but in no cases where the bottom water was oxygenated (0 out of 9 incubations). The NH₄⁺ fluxes decreased by 26±27% in 2005 and by 114±19% in 2003. There was no clear effect of resuspension on the fluxes of any of the other solutes in this study. Thus, resuspension events did not play a significant role in release/uptake of NO₃^?, PO₄^3?, Si(OH)₄, DIC, Fe and Mn in GoF sediments. However, increased oxygen consumption as a result of resuspension may lead to spreading of anoxic/suboxic bottom water conditions, and thus indirectly to increased benthic release of phosphate, ammonium and iron.  相似文献   

Effects of and methods for determination of induced magnetic anisotropy of igneous and metamorphosed rocks     

Vladimir S. Vetchfinskii  Igor Túnyi  Peter Vajda  Svetlana. S. Solov’eva 《Studia Geophysica et Geodaetica》2013,57(1):118-137

The phenomena of the magnetic memory of rocks associated with paleointensity, paleotemperature, and paleostress are reviewed and discussed here. The methods for the determination of the paleointensity and the paleoconditions are described and discussed in terms of their sensitivity and applicability. The determination of paleoconditions (stress and temperature) is essential for understanding rock mineral formation and rock history. Such knowledge is applicable also in ore deposit geology and geophysics. The phenomena of the magnetic memory manifest themselves through the constriction and asymmetry in the hysteresis loops, as well as through a nonlinear pattern in the anhysteretic magnetization curve, both being due to the induced magnetic anisotropy. The pros and cons of some applied methods are reviewed. The superposition of several paleotemperatures (re-heatings of the rock) and/or paleostresses is studied also. Under certain conditions, a rock can remember information on several paleotemperatures (paleo-heating events), as well as the respective intensities of the geomagnetic field of the past.  相似文献   

Phyllosilicate minerals in the hydrothermal mafic–ultramafic-hosted massive-sulfide deposit of Ivanovka (southern Urals): comparison with modern ocean seafloor analogues     

Paolo?NimisEmail author  Svetlana?G.?Tesalina  Paolo?Omenetto  Paola?Tartarotti  Catherine?Lerouge 《Contributions to Mineralogy and Petrology》2004,147(3):363-383

We have studied textural relationships and compositions of phyllosilicate minerals in the mafic–ultramafic-hosted massive-sulfide deposit of Ivanovka (Main Uralian Fault Zone, southern Urals). The main hydrothermal phyllosilicate minerals are Mg-rich chlorite, variably ferroan talc, (Mg, Si)-rich and (Ca, Na, K)-poor saponite (stevensite), and serpentine. These minerals occur both as alteration products after mafic volcanics and ultramafic protoliths and, except serpentine, as hydrothermal vein and seafloor mound-like precipitates associated with variable amounts of (Ca, Mg, Fe)-carbonates, quartz and Fe and Cu (Co, Ni) sulfides. Brecciated mafic lithologies underwent pervasive chloritization, while interlayered gabbro sills underwent partial alteration to chlorite + illite ± actinolite ± saponite ± talc-bearing assemblages and later localized deeper alteration to chlorite ± saponite. Ultramafic and mixed ultramafic–mafic breccias were altered to talc-rich rocks with variable amounts of chlorite, carbonate and quartz. Chloritization, locally accompanied by formation of disseminated sulfides, required a high contribution of Mg-rich seawater to the hydrothermal fluid, which could be achieved in a highly permeable, breccia-dominated seafloor. More evolved hydrothermal fluids produced addition of silica, carbonates and further sulfides, and led to local development of saponite after chlorite and widespread replacement of serpentine by talc. The Ivanovka deposit shows many similarities with active and fossil hydrothermal sites on some modern oceanic spreading centers characterized by highly permeable upflow zones. However, given the arc signature of the ore host rocks, the most probable setting for the observed alteration–mineralization patterns is in an early-arc or forearc seafloor–subseafloor environment, characterized by the presence of abundant mafic–ultramafic breccias of tectonic and/or sedimentary origin.Editorial responsibility: J. Hoefs  相似文献   

Some information on testate amoebae of Iceland     

Vera Opravilová  Svetlana Zahrádková 《Limnologica》2003,33(2):131-137

In samples of mosses collected during an expedition in the year 1987 along the southern border of Iceland, in seven habitats on the slopes of Skerhöll Hill, south of the glacier Svínafellsjökull, 80 taxa of testate amoebae have been recorded. From these taxa 24 species are new to Iceland. Up to now, including our own data, on the basis of available sources 174 taxa have been reported for Iceland. In the mosses Racomitrium heterostichum and Racomitrium fasciculare an Assulina muscorum — Centropyxis globulosa-association has been recorded.  相似文献   

Berriasian Stage of the Crimean Mountains: Zonal subdivisions and correlation   总被引：1，自引：1，他引：0  

V. V. Arkad’ev  T. N. Bogdanova  S. V. Lobacheva  E. D. Kalacheva  I. I. Sey 《Stratigraphy and Geological Correlation》2008,16(4):400-422

Biostratigraphy of the Berriasian Stage in the Crimean Mountains is specified and substantiated. Fragments of all the standard stage zones (jacobi, occitanica, and boissieri) are distinguished based on the found index species, and position of the Jurassic-Cretaceous boundary is targeted. According to verified distribution of ammonites, the jacobi Zone is divided into the jacobi and grandis subzones crowned by the Malbosiceras chaperi Beds. The Tirnovella occitanica-Retowskiceras retowskyi Beds and overlying Dalmasiceras tauricum Subzone are recognized in deposits of the occitanica Zone. The upward succession of biostratigraphic units established in the boissieri Zone includes the Euthymiceras-Neocosmoceras Beds, Riasanites crassicostatus Subzone, Symphythyris arguinensis and Jabronella sf. paquieri-Berriasella callisto Beds. The last biostratigraphic unit is suggested in this work instead the former Zeillerina baksanensis Beds. Except for the jacobi Zone, the substantiated ammonoid zonation is practically identical to the Berriasian biostratigraphic scale of the northern Caucasus, although the Berriasian-Valanginian boundary has not been defined in the Crimean Mountains based on ammonites. Several marker levels of bivalve mollusks and four biostratigraphic subdivisions of brachiopod scale are distinguishable here. As for the latter, these are (from the base upward) the Tonasirhynchia janini, Belbekella airgulensis-Sellithyris uniplicata, Symphythyris arguinensis, and Zeillerina baksanensis beds.  相似文献   

New data on the early Archean age of granitoids in the Volga-Ural segment of the East European Craton     

E. V. Bibikova  S. V. Bogdanova  A. N. Larionov  A. A. Fedotova  A. V. Postnikov  L. P. Popova  T. I. Kirnozova  M. M. Fugzan 《Doklady Earth Sciences》2008,419(2):243-247

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Petrology and geochemistry of back-arc basin basalts from Lau Basin spreading ridges at 15°, 18° and 19°S   总被引：1，自引：0，他引：1  

Dr. T. J. Falloon  Dr. A. Malahoff  Dr. L. P. Zonenshaina  Dr. Y. Bogdanova 《Mineralogy and Petrology》1992,47(1):1-35

Summary Fresh back-arc basin lavas were recovered during five dives of the submersible Mir during the 1990 cruise of the research vessel Akademik Mstislav Keldysh to the Lau Basin. Three dives were conducted on the central spreading center of the King's Triple Junction (KTJ) in the northeastern part of the Lau Basin east of Niuafo'ou Island at approximately 15°S. The lavas from the KTJ can be divided into types I and II based on their similarities to N-MORB and the BABB magma type ofSinton andFryer (1987) respectively. One dive each was made on the Central Lau Spreading Center (CLSC) at 18°S and the Eastern Lau Spreading Center (ELSC) at 19°S. Lavas sampled on the CLSC were associated with active hydrothermal sulphide chimneys occurring at the base of a collapsed caldera structure on the central volcanic axial high. Sampled lavas from both the CLSC and ELSC are all of type I geochemistry.The results of the Keldysh 90 cruise are integrated with previous work to evaluate the geochemical characteristics of the Lau Basin crust as a whole and geochemical zonation models for back-arc basin development. An important part of this review of Lau Basin basalt geochemistry is the recognition of boninites and rocks of boninitic affinity which occur at off-ridge locations throughout the Lau Basin. These are suggested to erupt during the initial stages of development of new spreading ridges associated with episodes of ridge jump or the propagation of back-arc spreading ridges into arc crust.Hf-Th-Ta systematics of the Lau Basin lavas are used to identify unmodified mantle source compositions and possible subduction-related enriched components. Unmodified mantle source compositions range from D-, N-, and E-MORB to OIB. All Lau Basin lavas show some evidence of enrichment by a H₂O ± LILE ± LREE-enriched component, a slab derived hydrous fluid. The slab-derived fluid is not homogeneous in composition perhaps reflecting the presence or absence of a subducted sediment component.The sampled lavas from the KTJ confirm the uniqueness of the BABB magma type ofSinton andFryer (1987).

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Zusammenfassung Dieser Artikel berichtet über erste Ergebnisse einer Forschungsexpedition in das Lau Basin, ausgeführt mit dem Forschungsschiff Akademiker Mstislav Keldysh und dem Mini-U-Boot Mir. Drei Tauchfahrten führten zur zentralen Achse der King's triple junction (KTJ) im nordöstlichen Teil des Lau Basins östlich der Insel Niuafo'ou (15°S). Die dort beprobten Laven werden auf der Basis ihrer chemischen Zusammensetzung eingeteilt in die Typen I und II, entsprechend der Klassifikation vonSinton andFryer (1987) in N-MORB und BABB. Eine vierte Tauchfahrt zum zentralen Lau Spreading Center (CLSC, 18°N) erbrachte Fragmente von Sulphidschloten eines aktiven Black Smoker innerhalb einer kollabierten Calderastructur. Eine fünfte Tauchfahrt zum östlichen Lau Spreading Center (ELSC, 19°N) erbrachte Laven vom Typus I (entsprechend N-MORB).Unter Berücksichtigung früherer Arbeiten gestatten die Ergebnisse der Keldysh 90 Expedition eine geochemische Charakterisierung des Lau Basins, sowie eine Bewertung bestehender Zonierungsmodelle fur die Entstehung und Evolution von Backarc Basins. Entlang der gesamten Achse im Lau Basin, aber abseits des eigentlichen aktiven Spreading Centers, werden Boninite und Laven boninitischer Affinität beobachtet. Diese Boninite können als integraler Teil des Frühstadiums eines Backarc Spreading Centers gedeutet werden, und entstehen möglicherweise dort, wo Spreading Centers in die Kruste eines Inselbogens vordringen oder dann, wenn es zu einer abrupten Positionsänderung der Achse kommt.Die Hf-Th-Ta Konzentrationen und Verhältnisse in Lau Basin Laven gestatten die Identifikation mehrerer Mantel-Endglieder (entsprechend D-MORB, N-MORB, E-MORB, und OIB), sowie einer an H₂O und LILE-LREE angereicherten Komponente, die mit Subduktionstätigkeit und anschließender Mantelmetasomatose in Zusammenhang gebracht wird. Die angereicherte Komponente war vermutlich inhomogen aufgrund variabler Anteile subduzierter Sedimente. Die Laven des Lau Basins bestätigen die vonSinton andFryer (1987) vorgeschlagene geochemische Sonderstellung von BABB Magmentypen.

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With 8 Figures  相似文献   

Manganese carbonates in the upper quaternary sediments of the Deryugin basin (Sea of Okhotsk)     

A. S. Astakhov  R. Tiedemann  I. O. Murdmaa  O. Yu. Bogdanova  A. V. Mozherovsky  N. A. Sereda 《Oceanology》2006,46(5):716-729

The mineral and chemical compositions of authigenic carbonates are studied by several methods in a sediment core obtained from the axial zone of the Deryugin riftogenic basin. Manganese carbonates (kutnahorite, rhodochrosite) associated with manganiferous calcite, manganiferous pyrite, and nontronite are first identified in the Sea of Okhotsk. Manganese carbonates in the Holocene diatomaceous ooze were presumably formed due to diagenetic transformation of sedimentary manganese hydroxides, organic matter, and biogenic silica, while those found in the underlying turbidites precipitated owing to the intermittent influx of endogenic fluids migrating along sand interbeds.  相似文献