Palaeomagnetism of the loess/palaeosol sequence in Viatovo (NE Bulgaria) in the Danube basin   总被引：1，自引：0，他引：1  

Diana Jordanova  Jozef Hus  Jordan Evlogiev  Raoul Geeraerts 《Physics of the Earth and Planetary Interiors》2008,167(1-2):71-83

The results of a palaeomagnetic investigation of a 27 m thick loess/palaeosol sequence in Viatovo (NE Bulgaria) are presented in this paper. The sequence consists of topsoil S₀, seven loess horizons (L₁–L₇) and six interbedded palaeosols (S₁–S₆) overlying a red clay (terra rossa) complex. Magnetic viscosity experiments, IRM acquisition, AMS analysis and NRM stepwise alternating and thermal demagnetisation experiments of pilot samples were implemented for precise determination of the characteristic remanence and construction of a reliable magnetostratigraphical scheme. Analysis of IRM acquisition curves using the expectation – maximization algorithm of Heslop et al. [Heslop, D., Dekkers, M., Kruiver, P., van Oorschot, H., 2002. Analysis of isothermal remanent magnetization acquisition curves using the expectation – maximization algorithm. Geophys. J. Int., 148, 58–64] suggests that the best fitting is obtained by three coercivity components. Component 1 corresponds to SD maghemite/magnetite, while component 2 is probably related to the presence of oxidised detrital magnetites. The third component shows varying coercivities depending on the degree of pedogenic alteration of the samples and probably reflects the presence of detrital magnetite grains oxidised at different degree.

The relevance of the Viatovo section as a key representative sequence for the loess cover in the Danube basin is confirmed by the presence of geomagnetic polarity changes in the lower part of the sequence. The youngest one recorded in the seventh loess unit L₇ can be identified as corresponding to the Matuyama/Brunhes palaeomagnetic polarity transition. Two normal magnetozones were found in the red clay complex, probably corresponding to the Jaramillo and Olduvai subchronozones of the Matuyama chron.  相似文献   

Orbital dispersion of comet Encke's meteoroids     

Jozef Klačka  Eduard M. Pittich 《Earth, Moon, and Planets》1995,68(1-3):369-379

The orbital evolution of model meteoroids ejected from the comet Encke has been investigated. The particles abandon the mother body with velocities 20 and 40 ms^-1 perihelion within the interval of the past 10,000 years. Their 10,000 years old osculating orbits were numerically integrated forward, using a dynamical model of the solar system consisting of all planets. Forces from solar electromagnetic and corpuscular radiation effecting the particles are considered, too. Orbital dispersions of the model meteoroids are presented. The importance of nongravitational forces for a long-term orbital evolution of meteoroid streams is shown.  相似文献   

Chemical and physical properties of Žďár nad Sázavou L chondrite and porosity differentiation using computed tomography     

Dominika Kalasov  Tom&#x; Zikmund  Pavel Spurný  Jakub Haloda  Ji&#x;í Borovi ka  Jozef Kaiser 《Meteoritics & planetary science》2020,55(5):1073-1081

A very bright and long bolide was observed over the eastern part of the Czech Republic during late local evening on December 9, 2014. This bolide was recorded by professional instruments in the Czech part of the European Fireball Network. Three meteorites weighing in total 87 g were found in the predicted area and were named ??ár nad Sázavou. The complete material composition of the meteorite was obtained from one cut‐off piece using petrography, mineralogy, and scanning electron microscopy (together with X‐ray energy dispersive spectroscopy and wavelength dispersive spectroscopy). X‐ray computed tomography (CT) was applied on all pieces for the determination of their grain and bulk density, digitization of shape, and examination of the structural homogeneity. CT has proved its important role for nondestructive exploration of brecciated meteorites formed by distinct lithologies or petrological types. In this article, we discuss its limits in terms of structural and material resolution based on the correlation of state‐of‐the‐art CT data and SEM images. Furthermore, we introduce a new way of air cavity quantification, which distinguishes the natural porosity of meteorite and cracks related to erosion processes. This helps to discuss the presence of weathering products based on comparison of the meteorite pieces found at different times after impact.  相似文献   

Cosmogenic radionuclides and mineralogical properties of the Chelyabinsk (LL5) meteorite: What do we learn about the meteoroid?          下载免费PDF全文

Pavel P. Povinec  Matthias Laubenstein  A. J. Timothy Jull  Ludovic Ferrière  Franz Brandstätter  Ivan Sýkora  Jozef Masarik  Juraj Beňo  Andrej Kováčik  Dan Topa  Christian Koeberl 《Meteoritics & planetary science》2015,50(2):273-286

On February 15, 2013, after the observation of a brilliant fireball and a spectacular airburst over the southern Ural region (Russia), thousands of stones fell and were rapidly recovered, bringing some extremely fresh material for scientific investigations. We undertook a multidisciplinary study of a dozen stones of the Chelyabinsk meteorite, including petrographic and microprobe investigations to unravel intrinsic characteristics of this meteorite. We also study the short and long‐lived cosmogenic radionuclides to characterize the initial meteoroid size and exposure age. Petrographic observations, as well as the mineral compositions obtained by electron microprobe analyses, allow us to confirm the classification of the Chelyabinsk meteorite as an LL5 chondrite. The fragments studied, a few of which are impact melt rocks, contain abundant shock melt veins and melt pockets. It is likely that the catastrophic explosion and fragmentation of the Chelyabinsk meteoroid into thousands of stones was in part determined by the initial state of the meteoroid. The radionuclide results obtained show a wide range of concentrations of ¹⁴C, ²²Na, ²⁶Al, ⁵⁴Mn, ⁵⁷Co, ⁵⁸Co, and ⁶⁰Co, which indicate that the pre‐atmospheric object had a radius >5 m, consistent with other size estimates based on the magnitude of the airburst caused by the atmospheric entry and breakup of the Chelyabinsk meteoroid. Considering the observed ²⁶Al activities of the investigated samples, Monte Carlo simulations, and taking into account the ²⁶Al half‐life (0.717 Myr), the cosmic‐ray exposure age of the Chelyabinsk meteorite is estimated to be 1.2 ± 0.2 Myr. In contrast to the other radionuclides, ¹⁴C showed a very large range only consistent with most samples having been exposed to anthropogenic sources of ¹⁴C, which we associate with radioactive contamination of the Chelyabinsk region by past nuclear accidents and waste disposal, which has also been confirmed by elevated levels of anthropogenic ¹³⁷Cs and primordial ⁴⁰K in some of the Chelyabinsk fragments.  相似文献   

Erratum to “Mineral waters in Slovakia — Evaluation of chemical composition stability using both historical records and the most recent data” [J. Geochem. Explor. 107 (2010) 382–390]     

Dušan Bodiš  Jozef Kordik  Igor Slaninka  Peter Malík  Pavel Liščák  Daniel Panák  Jarmila Božíková  Daniel Marcin 《Journal of Geochemical Exploration》2011,108(3):233

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Mineral and geothermal waters of Slovakia     

Jozef Kriš  Jozef Marton  Ivona Skultétyová 《GeoJournal》1995,35(4):431-442

From 1955 to 1985 an intensive hydrogeological survey has been carried out in Slovakia, in order to ascertain the conditions of forming mineral and geothermal waters in various geological structures and to find new sources of the afore-mentioned waters. The survey helped to clarify the laws of their distribution and evaluate the quantitative and qualitative properties of water developing on the basis of geologic-tectonic conditions and physical-geographic terms of the given territory. The Slovakian territory belongs to the Carpathian geological system. Five separate geological units having a different hydrologic characteristic, quality and water yield of reserves and resources form this geological system. A great number of mineral and thermal springs in Slovakia displaying different quantities and quality, provide numerous possibilities of their practical utilization.  相似文献   

Problem of the Rotating Magnetoconvection in Variously Stratified Fluid Layer Revisited     

Šimkanin  Ján  Brestenský  Jozef  Ševčík  Sebastián 《Studia Geophysica et Geodaetica》2003,47(4):827-845

The linear magnetoconvection in the rotating uniformly as well as non-uniformly stratified horizontal layer with azimuthal magnetic field is investigated for the various mechanical and electrical boundary conditions and especially, for various values of Roberts number. The developed diffusive perturbations (modes) are strongly influenced not only by the mentioned properties of boundaries but also by complicated coupling of viscous, thermal and magnetic diffusive processes. The mean electromotive force produced by developed hydromagnetic instabilities is also investigated to determine the hydromagnetic processes which are appropriate for -effect. The presented paper is an unification of hitherto published results of the authors and gives a short survey of many developments of corresponding model by Soward (1979).  相似文献   

Alternating field-impressed AMS in rocks     

Bernard Henry  Diana Jordanova  Neli Jordanova  Jozef Hus  Jérôme Bascou  Minoru Funaki  Dimo Dimov 《Geophysical Journal International》2007,168(2):533-540

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Palaeoclimatic implications of the magnetic record from loess/palaeosol sequence Viatovo (NE Bulgaria)   总被引：1，自引：0，他引：1  

Diana Jordanova  Jozef Hus  Raoul Geeraerts 《Geophysical Journal International》2007,171(3):1036-1047

Loess-palaeosol deposits in the lower Danube area represent the southeastern edge of the loess cover in Europe. Detailed rock magnetic investigations of the loess/palaeosol sequence in Viatovo in NE Bulgaria reveal that magnetite and maghemite of very fine superparamagnetic grain size are responsible for the magnetic enhancement of palaeosol units. A detailed palaeoclimatic record is obtained through high-resolution measurements of magnetic susceptibility, frequency dependent magnetic susceptibility and CaCO₃ content. Magnetic proxies indicate a more warm and humid climate during the development of the older palaeosol units (S₄–S₆).  相似文献   

Spatial variability of phytoplankton, nutrients and new production estimates in the waters around Svalbard   总被引：3，自引：0，他引：3  

Georgina Owrid  Giorgio Socal  Giuseppe Civitarese  Anna Luchetta  Jozef Wiktor  Eva-Maria Nöthig  Inger Andreassen  Ursula Schauer  Volker Strass 《Polar research》2000,19(2):155-171

Phytoplankton dynamics and carbon input into Arctic and sub-Arctic ecosystems were investigated around Svalbard, in summer 1991. Phytoplankton biomass, species composition and dissolved nutrient concentrations were analysed from water samples collected along seven transects. Phytoplankton biomass was low especially to the north (Chlorophyll-a mean 0.3 pg 1- '), where flagellates dominated the communities and only ice-diatoms were present. To the west, the phytoplankton composition was representative of a summer Atlantic community, in a post-bloom state. Zooplankton grazing, mainly by copepods, appeared to be the main control on biomass to the west and north of Svalbard.
In the Barents Sea (east of Svalbard), an ice edge bloom was observed (Chlorophyll-a max. 6.8 pgl-') and the ice edge receded at a rate of approximately 1 1 km day-'. The phytoplankton community was represented by marginal ice species, especially Phaeocystis poucherii and Chaeroceros socialis. South of the ice edge, Deep Chlorophyll Maxima (DCM) were observed, as surface waters became progressively nutrient-depleted. In these surface waters, the phytoplankton were predominantly auto- and heterotrophic flagellates.
Carbon production measurements revealed high net production (new and regenerated) to the north of the Barents Sea Polar Front (BSPF); it was especially high at the receding ice edge (reaching 1.44gC m-'day-'). To the south, a low level of production was maintained, mainly through regenerative processes.  相似文献