Investigation of superstructures in mullite by high resolution electron microscopy and electron diffraction

Superstructures in synthetic mullite, Al_4+2x Si_2?2x O_10?x , prepared using the zone melting technique, are studied by high resolution electron microscopy (HREM), electron diffraction, and in situ energy dispersive X-ray spectroscopy. For x=0.40 composition HREM images indicate only short-range order. Near x=0.5 composition mullite has an antiphase domain structure with antiphase boundaries (APB's) oriented parallel to (100). For higher Al-content the APB's run in non-rational orientations which are slightly inclined against the {601}-planes. We propose models for the superstructures in which oxygen vacancies are arranged in channels parallel to the crystal b-axis. The models are supported by a one-to-one match between observed and computer-simulated images. An Al-rich limit of x=2/3 for mullite is deduced on the basis of stereochemical considerations. Different ordering schemes for the tetrahedral cations are believed to result in the orientation change of the APB's near x=0.5 composition.     

Fast-changing processes in a medium subject to loading as detected by resistivity measurements

Making measurements of electric resistivity at 16 s intervals, the authors noticed fast changes of this parameter prior to the occurrence of the main fracture. The changes are superposed on bay pulsations of increasing amplitude and decreasing period. This finding opens prospects for a wider use of an electric resistivity method and proves the high quality of automatic instruments, in particular their high resolution. It also gives evidence for the occurrence of short-period precursors in the fracture zone while the main fracture is being formed.     

A volcanic-carbonate association in the Góry Kaczawskie,Western Sudetes

Amidst metavolcanic rocks and phyllites of the Góry Kaczawskie region occur isolated carbonate bodies known as the Wojcieszów limestones. The bodies enclosed in the metavolcanites show primary (sedimentary) contacts, while those in the phyllites do not have such contacts. The Wojcieszów limestones and metavolcanic rocks form sequences displaying mutual spatial and genetical relations. Submarine volcanic elevations were covered with chemical and biochemical carbonate precipitation, the intensity of which was stimulated and controlled by the volcanic activity.

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Zusammenfassung Inmitten der metavulkanischen Gesteine und Phyllite von Góry Kaczawskie erscheinen isolierte Karbonatgesteinskörper, die als Wojcieszów-Kalke bekannt sind. Die Karbonatgesteine innerhalb der Metavulkanite zeigen sedimentäre Kontakte, während die in den Phylliten eher tektonisch begrenzt sind. So kann man den Wojcieszów-Kalken und den Metavulkaniten eine räumliche und genetische Beziehung zusprechen. Submarine Erhebungen aus Vulkangesteinen waren mit chemischen und biochemisch gefällten Karbonatserien bedeckt, wobei die vulkanische Aktivität die Karbonatbildung unmittelbar beeinflu\te.

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Résumé Parmi les métavolcanites et les phyllites de la région du Góry Kaczawskie, il existe des corps carbonatés isolés connus sous le nom de »calcaires de Wojcieszów«. Ceux qui sont inclus dans les métavolcanites présentent des contacts sédimentaires, contrairement à ceux qui sont inclus dans les phyllites, dont les contacts sont tectoniques. Entre les calcaires de Wojcieszów et les roches métavolcaniques, il est donc possible d'établir des relations spatiales et génétiques. Des reliefs volcaniques sous-marins ont été le siège d'une précipitation carbonatée chimique et biochimique dont l'intensité dépendait de l'activité volcanique.

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Motion of salt water and associated fronts in tideless estuaries

The hydrodynamics of saline water in Polish estuaries are addressed in this paper. The phenomena are described on the basis of field data from several types of estuaries along the Polish Baltic Coast. Field measurements were made to reveal and to characterize the physical processes in these estuaries; this information was then used for analytic testing and verification of mathematical models. The results demonstrate the unsteady and changeable nature of both the flow conditions and the motion of salt water in tideless estuaries. The magnitudes and directions of the barotropic and baroclinic horizontal pressure gradients have a marked influence on the flow characteristics and motion of salt water in these tideless estuaries.     

RC J0311+0507: A candidate for superpowerful radio galaxies in the early universe at redshift z = 4.514

A strong emission line at 6703 Å has been detected in the optical spectrum for the host galaxy (R = 23.1) of the radio source RC J0311+0507 (4C+04.11). This radio galaxy, with a spectral index of 1.31 in the frequency range 365–4850 MHz, is one of the ultrasteep-spectrum objects from the deep survey of a sky strip conducted with RATAN-600 in 1980–1981. We present arguments in favor of the identification of this line with Lyα at redshift z = 4.514. In this case, the object belongs to the group of extremely distant radio galaxies of ultrahigh radio luminosity (P ₁₄₀₀ = 1.3 × 10²⁹ W Hz^?1). Such power can be provided only by a fairly massive black hole (～10⁹ M⊙) that formed in a time less than the age of the Universe at the observed z (1.3 Gyr) or had a primordial origin.     

Tectonic analysis of mine tremor mechanisms from the Upper Silesian Coal Basin

Fault network of the Upper Silesian Coal Basin (USCB) is built of sets of strike-slip, oblique-slip and dip-slip faults. It is a typical product of force couple which acts evenly with the parallel of latitude, causing horizontal and anti-clockwise movement of rock-mass. Earlier research of focal mechanisms of mine tremors, using a standard fault plane solution, has shown that some events are related to tectonic directions in main structural units of the USCB. An attempt was undertaken to analyze the records of mine tremors from the period 1992–1994 in the selected coal fields. The digital records of about 200 mine tremors with energy larger than 1×10⁴ J (M _L >1.23) were analyzed with SMT software for seismic moment tensor inversion. The decomposition of seismic moment tensor of mine tremors was segmented into isotropic (I) part, compensated linear vector dipole (CLVD) part and double-couple (DC) part. The DC part is prevalent (up to 70%) in the majority of quakes from the central region of the USCB. A group of mine tremors with large I element (up to 50%) can also be observed. The spatial orientation of the fault and auxiliary planes were obtained from the computations for the seismic moment DC part. Study of the DC part of the seismic moment tensor made it possible for us to separate the group of events which might be acknowledged to have their origin in unstable energy release on surfaces of faults forming a regional structural pattern. The possible influence of the Cainozoic tectonic history of the USCB on the recent shape of stress field is discussed.     

Types of sedimentary environment in alluvial sediments distinguished on the basis of its chemical constitution: the example of the lower course of the Obra river (Western Poland)

Research concerning chemical constitution of alluvial sediments was done in the lower course of the Obra river (Western Poland). The fragment of vertical profile, which consisted of various alluvial sediments (fine sands, peats, and sandy silts) was chosen for detailed analysis. The main research problem was to determine if lithology and chemical constitution of alluvial deposits are interconnected in a distinct way within studied section of the Obra river valley, and, if changes of chemical elements’ concentration could be used to illustrate depositional processes, which take place in riverbed and floodplain. Concentrations of Fe, Mn, Cu, Zn, Ca, Mg, and K were determined in collected sediment samples. Next, geochemical groups of alluvial sediments were distinguished using cluster analysis. Investigated changes of chemical elements’ concentration show that there is a distinct border between the environment of organic sediments, which marks the place of former functioning of the Obra riverbed, and sandy silts, which were deposited within floodplain during floods. Besides, floodplain sediments, riverbed sediments, and reductive environment within peat deposits were singled out on the basis of the analysis.     

A reconstruction of the palaeohydrological conditions of a flood‐plain: a multi‐proxy study from the Grabia River valley mire,central Poland

This study investigated the Grabia River valley mire in central Poland to reconstruct its palaeoenvironmental conditions from the Younger Dryas to the present. We analysed sedimentological, biological and geochemical data from the palaeo‐oxbow lake and valley mire to identify the principal hydrological trends, especially episodes of high water level. During the Lateglacial and Holocene, the Grabia River had a meandering channel, and its hydraulic parameters and the channel dimensions changed in response to climatic oscillations and vegetation development. We identified phases of high flood intensity and high groundwater level that correlate with regional and supraregional climatic events. The frequency and timing of palaeohydroclimatic oscillations show strong similarities to records from other sites in Poland and the rest of Europe. We show that various analytical methods, namely, pollen, plant macrofossils, Cladocera, Chironomidae, sedimentological, geochemical and radiocarbon data, can be effective tools for reconstructing past hydroclimatic changes in palaeo‐oxbow lakes and investigating the effects of past climate changes on river environments. The high sensitivity of the biota, especially Cladocera, to changes in water level permits the reconstruction of palaeoecological changes, especially flood episodes that occurred in the river valley. In particular, the increase in the proportion of sediment‐associated Cladocera and pelagic taxa was closely correlated with floods. Through comparisons with the palaeobiological data, geochemical data allowed the identification of humid phases within the fen associated with a rising groundwater table, direct fluvial activity (floods) and alluvial deposition. We also discuss the limitations of palaeohydrological reconstructions based on these proxies, especially on fossil aquatic invertebrates.