Lochkovian (earliest Devonian) transgressions and regressions along the “Tethyan” margin of Gondwana: A review of lithostratigraphical data     

Dmitry A. Ruban 《Gondwana Research》2011,20(4):739-744

Global sea-level rise and consequent regional transgressions are hypothesized at the beginning of the Devonian. A brief review of lithostratigraphical data available from three regions of the “Tethyan” margin of Gondwana, namely Northern Africa, Arabia, and the Tethys Himalaya, suggests that all of them were characterized by a regressive setting in the Lochkovian. In contrast, data from some terranes of the Greater Galatian Superterrane provide evidence of early Lochkovian transgression. The regressive setting documented on the 'Tethyan' margin of Gondwana differs from the transgressive–regressive cycles of Euramerica and the norm of global sea-level rise followed by a highstand. Only regional tectonic processes including those linked with dynamic topography could explain these differences. These processes may have been associated with syn-rift uplift preceding the opening of the Palaeo-Tethys Ocean, mantle uplift at the supercontinent margin, or the Eo-Variscan orogenic phase.  相似文献   

Mode enslavement in a two-layer stellar dynamo     

David Moss  Dmitry Sokoloff 《Monthly notices of the Royal Astronomical Society》2007,377(4):1597-1604

We consider a conventional stellar  α²ω  -dynamo with dynamo generators localized in two spherical shells separated by a passive layer. The signs of the α-effect as well as rotational shear in the dynamo active layers can be chosen to give dynamo waves that propagate in opposite directions (poleward and equatorward) if the layers are considered separately in the framework of the Parker migratory dynamo. In a sequence of numerical experiments we show that the variety of dynamo-generated magnetic configurations in the system under discussion is quite rich. We identify the possibility of almost independent dynamo waves existing in the two layers as well as enslavement of one layer by the other, and of activity waves generated by a joint action of the two layers. We suggest some qualitative explanations of the behaviour and discuss also the limited nature of these explanations. This variety of phenomena suggests previously underexploited freedoms to understand how predictions of dynamo theory may accommodate the observed solar and stellar activity phenomenology.  相似文献   

Solar Activity Record from Archeomagnetic Data     

Dmitry Volobuev 《Solar physics》2004,224(1-2):387-392

Each of the available solar activity (SA) proxy data (historical notes, radio nuclides ¹⁴C and ¹⁰Be production) are contaminated by their specific noise factors. So, any additional proxy with its independent noise factors will essentially increase the accuracy of composite SA restorations. It is proposed here that archaeomagnetic measurements 95% confidence interval (α₉₅) may serve as new proxy for the SA estimation in the past. This proxy is compared with other available proxies during the years 1500–2000.  相似文献   

Correction to: Accelerated reproduction of 2-D periodic waves     

Chalikov  Dmitry 《Ocean Dynamics》2021,71(4):491-491

Ocean Dynamics - A Correction to this paper has been published: https://doi.org/ https://doi.org/10.1007/s10236-021-01450-3  相似文献   

Were Late Cretaceous extinctions of gastropods selective by generic longevity?     

Dmitry A.Ruban 《地学前缘(英文版)》2013,4(1):87-93

Many gastropod taxa went extinct during the Late Cretaceous.The stratigraphic ranges of 268 genera permit to establish the longevity of extinction victims for each stage of this epoch."Young" taxa (originated within 3 epochs before the extinction) prevailed among victims of the extinctions in all stages.The proportion of "old" taxa(originated before the Cretaceous) that went extinct was the highest in the Cenomanian,and it was the lowest in the Coniacian and the Maastrichtian.It appears that the end-Cretaceous mass extinction affected chiefly "young" taxa.However,the comparison with the earlier time intervals suggests that this pattern of selectivity by generic longevity was not specific for the noted catastrophe,but,in contrast,it was typical for the entire Late Cretaceous.The latest Cenomanian environmental perturbation(OAE2) caused a stronger extinction of "old" taxa,and thus,this biotic crisis was less selective by generic longevity.This hypothesis,however,is not proven by the statistical test.  相似文献   

Integrated geological risk mapping: a qualitative methodology applied in St. Petersburg, Russia     

Johannes Klein  Jaana Jarva  Dmitry Frank-Kamenetsky  Igor Bogatyrev 《Environmental Earth Sciences》2013,70(4):1629-1645

The current active development of the city of St. Petersburg in Russia has led to high growth rates in both industrial and housing areas, causing an increased load on geological media. Taking into account the rather unfavourable geological conditions of the city area, such a development can entail to an intensification of environmental risks. Sustainable and cost-effective land-use planning requires information on geological conditions. Stakeholders need general geological information on the area of St. Petersburg, hydrogeological information on groundwater and information on geological risks. Geological risk maps help to identify whether an area under consideration requires special measures for geological risk management. This paper describes a first attempt to analyze potential geological risks in the city of St. Petersburg, Russia. The approach is to introduce a methodology for multi-risk assessment to be used in land-use planning. The core of the methodology is a matrix that assigns a certain level of geological risk depending on the combination of land use stipulated by the master plan of St. Petersburg and geological characteristics. Based on the matrix, a map presenting potential integrated geological risk can be created. At the same time, the combination of the integrated geological risk map, single geological risk maps and the matrix allows the retracement of which geological characteristics and which land use types contribute to the resulting risk. Users of the methodology in St. Petersburg were trained and an end-user manual was prepared by the authors. The methodology was introduced to professionals who utilize geological information and assess potential risks related to geology.  相似文献   

Power-Law Testing for Fault Attributes Distributions   总被引：2，自引：0，他引：2  

Dmitry Kolyukhin  Anita Torabi 《Pure and Applied Geophysics》2013,170(12):2173-2183

This paper is devoted to statistical analysis of faults’ attributes. The distributions of lengths, widths of damage zones, displacements and thicknesses of fault cores are studied. Truncated power-law (TPL) is considered in comparison with commonly used simple power-law (PL) (or Pareto) distribution. The maximal likelihood and the confidence interval of the exponent for both PL and TPL are estimated by appropriate statistical methods. The Kolmogorov–Smirnov (KS) test and the likelihood ratio test with alternative non-nested hypothesis for exponential distribution are used to verify the statistical approximation. Furthermore, the advantage of TPL is proved by Bayesian information criterion. Our results suggest that a TPL is more suitable for describing fault attributes, and that its condition is satisfied for a wide range of fault scales. We propose that using truncated power laws in general might eliminate or relax the bias related to sampling strategy and the resolution of measurements (such as censoring, truncation, and cut effect) and; therefore, the most reliable range of data can be considered for the statistical approximation of fault attributes.  相似文献   

Non-local effects in the mean-field disc dynamo: II – numerical and asymptotic solutions     

Ashley P. Willis  Anvar Shukurov  Andrew M. Soward  Dmitry Sokoloff 《地球物理与天体物理流体动力学》2013,107(4):345-363

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Non-axisymmetric α2Ω-dynamo waves in thin stellar shells     

Andrew P. Bassom ¶  Kirill M. Kuzanyan  Dmitry Sokoloff 《地球物理与天体物理流体动力学》2013,107(4):309-336

Linear α²Ω-dynamo waves are investigated in a thin turbulent, differentially rotating convective stellar shell. A simplified one-dimensional model is considered and an asymptotic solution constructed based on the small aspect ratio of the shell. In a previous paper Griffiths et al. (Griffiths, G.L., Bassom, A.P., Soward, A.M. and Kuzanyan, K.M., Nonlinear α²Ω-dynamo waves in stellar shells, Geophys. Astrophys. Fluid Dynam., 2001, 94, 85–133) considered the modulation of dynamo waves, linked to a latitudinal-dependent local α-effect and radial gradient of the zonal shear flow. These effects are measured at latitude θ by the magnetic Reynolds numbers R _α f(θ) and R _Ω g(θ). The modulated Parker wave, which propagates towards the equator, is localised at some mid-latitude θ_p under a Gaussian envelope. In this article, we include the influence of a latitudinal-dependent zonal flow possessing angular velocity Ω_*(θ) and consider the possibility of non-axisymmetric dynamo waves with azimuthal wave number m. We find that the critical dynamo number D _c?=?R _α R _Ω is minimised by axisymmetric modes in the αΩ-limit (Rα→0). On the other hand, when Rα?≠?0 there may exist a band of wave numbers 0?m?m ^? for which the non-axisymmetric modes have a smaller D _c than in the axisymmetric case. Here m ^? is regarded as a continuous function of R _α with the property m?→0 as R _α→0 and the band is only non-empty when m??>1, which happens for sufficiently large R _α. The preference for non-axisymmetric modes is possible because the wind-up of the non-axisymmetric structures can be compensated by phase mixing inherent to the α²Ω-dynamo. For parameter values resembling solar conditions, the Parker wave of maximum dynamo activity at latitude θ_p not only propagates equatorwards but also westwards relative to the local angular velocity Ω_*(θ _p ). Since the critical dynamo number D _c?=?R _α R _Ω is O (1) for small R _α, the condition m ^??>?1 for non-axisymmetric mode preference imposes an upper limit on the size of |dΩ_*/dθ|.  相似文献   

The State of knowledge about wetlands and their future under aspects of global climate change: the situation in Russia     

Richard D. Robarts  Alexander V. Zhulidov  Dmitry F. Pavlov 《Aquatic Sciences - Research Across Boundaries》2013,75(1):27-38

About two-thirds of Russia’s land area are flat lands, which contributes to the development of conditions favouring wetland formation. Wetlands cover vast areas, especially in the north. Wetlands in the former Soviet Union were not recognized as separate or distinct ecosystems and this is still the situation in Russia today. Bogs are one of the most abundant and typical wetlands and were treated as worthless wastelands. Beginning in the 17th century and continuing under the Soviet government there was an enforced policy to drain wetlands and reclaim the land, mainly for farming. After the collapse of the USSR, this practice was discontinued along with the Soviet model of agriculture and an end to the forced and unnecessary use of pesticides and fertilizers with the result that the toxic load on Russian aquatic systems decreased drastically. Industrial production was also greatly curtailed. While it is now recovering, many of these are turning to environmentally-friendly technologies. The intensity of land-use related impacts upon Russian wetlands is negligible compared to that in more densely populated countries and therefore the environmental conservation of wetlands in Russia may not currently be an urgent problem. There is currently no consensus on what the overall direct and indirect impacts of climate change on the number of Russian wetlands will be—in some areas they may increase but decrease in others. In Russia, the most urgent issue is not the preservation of wetlands but the development of proper wetland management practices. For effective plans, data and information on wetland status, trends and characteristics are required that are not currently available.  相似文献