Petrology and microstructure of distal impact ejecta from the Flinders Ranges,Australia

Abstract— The Acraman impact ejecta from Bunyeroo Gorge in the central Flinders Ranges consist of clast-bearing and sandy sublayers set in a shale host rock. A calculated transient crater diameter for the Acraman impact of at least 34 km was obtained from average thicknesses and estimated distances of the ejecta from the impact in the Gawler Ranges. The ejecta contain numerous grains of quartz and zircon that display impact-produced features, including one or more sets of decorated planar deformation features. There is also much unshocked material incorporated in the ejecta layer. The coarse-grained ejecta layer embedded within fine-grained sediments allowed easy passage for diagenetic fluids that produced a porous honeycomb structure in the clays and enhanced the content of elements such as Cu, Pb, Zn, and U. The clay fraction of the ejecta layers consists of vermiculite and kaolinite, probably formed from alteration and weathering of glassy components. It appears that quartz and zircon grains are the only remnants unaltered by diagenetic processes.     

High-frequency X-ray variability as a mass estimator of stellar and supermassive black holes

There is increasing evidence that supermassive black holes in active galactic nuclei (AGN) are scaled-up versions of Galactic black holes. We show that the amplitude of high-frequency X-ray variability in the hard spectral state is inversely proportional to the black hole mass over eight orders of magnitude. We have analysed all available hard-state data from RXTE of seven Galactic black holes. Their power density spectra change dramatically from observation to observation, except for the high-frequency (≳10 Hz) tail, which seems to have a universal shape, roughly represented by a power law of index −2. The amplitude of the tail,   C _M   (extrapolated to 1 Hz), remains approximately constant for a given source, regardless of the luminosity, unlike the break or quasi-periodic oscillation frequencies, which are usually strongly correlated with luminosity. Comparison with a moderate-luminosity sample of AGN shows that the amplitude of the tail is a simple function of black hole mass,   C _M = C / M   , where   C ≈ 1.25 M_⊙ Hz⁻¹  . This makes   C _M   a robust estimator of the black hole mass which is easy to apply to low- to moderate-luminosity supermassive black holes. The high-frequency tail with its universal shape is an invariant feature of a black hole and, possibly, an imprint of the last stable orbit.     

Seismic wave velocities in the sedimentary cover of Poland: Borehole data compilation

A knowledge of seismic wave velocities in the sedimentary cover is of great importance for interpreting reflection and refraction seismic data, deep seismic soundings and regional and global seismic tomography. This is particularly true for regions characterized by significant thicknesses and a complex sedimentary cover structure. This paper presents the results of an analysis of seismic P-wave velocities in the sedimentary cover of Poland, a complex area of juxtaposition of major tectonic units: the Precambrian East European Craton, the Palaeozoic Platform of Central and Western Europe, and the Alpine orogen represented by the Carpathian Mountains. Based on vertical seismic profiling data from 1188 boreholes, the dependence of velocity versus depth was determined for regional geological units and for successions from the Tertiary and Quaternary to the Cambrian. The data have been approximated by polynomials, and velocity-depth formulas are given down to 6000 m depth. The velocities in the sedimentary cover have been compared with those from other areas in Europe.     

Influence of the atmospheric conditions on PM<Subscript>10</Subscript> concentrations in Poznań, Poland

This study investigates atmospheric conditions’ influence on the mean and extreme characteristics of PM₁₀ concentrations in Poznań during the period 2006–2013. A correlation analysis was carried out to identify the most important meteorological variables influencing the seasonal dynamics of PM₁₀ concentrations. The highest absolute correlation values were obtained for planetary boundary layer height (r = ?0.57), thermal (daily minimum air temperature: r = ?0.51), anemological (average daily wind speed: r = ?0.37), and pluvial (precipitation occurrence: r = ?0.36) conditions, however the highest correlations were observed for temporal autocorrelations (1 day lag: r = 0.70). As regulated by law, extreme events were identified on the basis of daily threshold value i.e. 50 μg m^?3. On average, annually there are approximately 71.3 days anywhere in the city when the threshold value is exceeded, 46.6 % of those occur in winter. Additionally, 83.7 % of these cases have been found to be continuous episodes of a few days, with the longest one persisting for 22 days. The analysis of the macro-scale circulation patterns led to the identification of an easy-to-perceive seasonal relations between atmospheric fields that favour the occurrence of high PM₁₀ concentration, as well as synoptic situations contributing to the rapid air quality improvement. The highest PM₁₀ concentrations are a clear reaction to a decrease in air temperature by over 3 °C, with simultaneous lowering of PBL height, mean wind speed (by around 1 m s^?1) and changing dominant wind directions from western to eastern sectors. In most cases, such a situation is related to the expansion of a high pressure system over eastern Europe and weakening of the Icelandic Low. Usually, air quality conditions improve along with an intensification of westerlies associated with the occurrence of low pressure systems over western and central Europe. Opposite relations are distinguishable in summer, when air quality deterioration is related to the inflow of tropical air masses originating over the Sahara desert.     

Cosmogenic chlorine-36 production rates in terrestrial rocks

Chlorine-36 is produced in rocks exposed to cosmic rays at the earth surface through thermal neutron activation of ³⁵Cl, spallation of ³⁹K and ⁴⁰Ca, and slow negative moun capture by ⁴⁰Ca. We have measured the ³⁶Cl content of ¹⁴C-dated glacial boulders from the White Mountains in eastern California and in a ¹⁴C-dated basalt flow from Utah. Effective, time-intergrated production parameters were calculated by simultaneous solution of the ³⁶Cl production equations. The production rates due to spallation are 4160 ± 310 and 3050 ± 210 atoms ³⁶Cl yr⁻¹ mol⁻¹³⁹K and ⁴⁰Ca, respectively. The thermal neutron capture rate was calculated to be (3.07 ± 0.24) × 10⁵ neutrons (kg of rock)⁻¹ yr⁻¹. The reported values are normalized to sea level and high geomagnetic latitudes. Production of ³⁶Cl at different altitudes and latitudes can be estimated by appropriate scaling of the sea level rates. Chlorine-36 dating was performed on carbonate ejecta from Meteor Crater, Arizona, and late Pleistocene morainal boulders from the Sierra Nevada, California. Calculated ³⁶Cl ages are in good agreement with previously reported ages obtained using independent methods.     

A comparison of the flood precipitation episode in August 2002 with historic extreme precipitation events on the Czech territory

The hydro-meteorological characteristics of the flood from August 2002, which affected a great part of the Czech territory, particularly the Vltava and Labe river basin, were compared with corresponding conditions during similar flood events in the summer seasons of 1997, 1890, 1897 and 1903. The comparison shows analogies in synoptic conditions and causal precipitation heights. The heaviest precipitation fell in the area of a considerable horizontal pressure gradient on the rearward side of the cyclone which advanced very slowly to the north-east across Central Europe and created conditions for the transport of moist air as well as for an organized long-term updraft enhanced in orographically exposed regions. The varying features of the individual events were based on the spatial–temporal distribution of causal precipitation and also on the very different saturation of the catchments. It was chiefly the extraordinary time concentration of precipitation together with the highest catchment saturation that made the flood in 2002 the most extreme.The extremeness of meteorological fields during two episodes in July 1997 was compared with two episodes in August 2002 with the aid of the reanalysis data from ECMWF. The first episode in 1997 and the second episode in 2002 were the most similar and more extreme in terms of the large-scale fields of basic meteorological quantities. The similar features of these episodes are specifically an intensive influx of moisture into Central Europe and intensive upward motions in the precipitation area. The extremeness of upper- and low-level potential vorticity fields was evaluated to diagnose the behavior of the cyclone and frontal precipitation bands accompanying it. The suitable spatial configuration of positive upper- and low-level potential vorticity anomalies induced an additional amplification of upward motions in the precipitation area that apparently contributed to triggering the heavy precipitation over Central Europe. On the whole, quantities reached more extreme values during the second episode in 2002.