Jesenice—A new meteorite fall from Slovenia

Abstract– On April 9, 2009, at 3:00 CEST, a very bright fireball appeared over Carinthia and the Karavanke Mountains. The meteoroid entered the atmosphere at a very steep angle and disintegrated into a large number of objects. Two main objects were seen as separate fireballs up to an altitude of approximately 5 km, and witnesses reported loud explosions. Three stones were found with a total weight of approximately 3.611 kg. The measured activity of short‐lived cosmogenic radionuclides clearly indicates that two specimens result from a very recent meteorite fall. All cosmogenic radionuclide concentrations suggest a rather small preatmospheric radius of <20 cm; a nominal cosmic‐ray exposure age based on ²¹Ne is approximately 4 Ma, but the noble gas and radionuclide results in combination indicate a complex irradiation. Jesenice is a highly recrystallized rock with only a few relic chondrules visible in hand specimen and thin section. The texture, the large grain size of plagioclase, and the homogeneous compositions of olivines and pyroxenes clearly indicate that Jesenice is a L6 chondrite. The bulk composition of Jesenice is very close to the published average element concentration for L ordinary chondrites. The chondrite is weakly shocked (S3) as indicated by the undulatory extinction in olivine and plagioclase and the presence of planar fractures in olivine. Being weakly shocked and with gas retention ages of >1.7 Ga (⁴He) and approximately 4.3 Ga (⁴⁰Ar), Jesenice seems not to have been strongly affected by the catastrophic disruption of the L‐chondrite parent body approximately 500 Ma ago.     

Determination of actual limit angles to the surface and their comparison with the empirical values in the Upper Silesian Basin (Czech Republic)

This study deals with the determination of the actual limit angles in the long-term formed subsidence basin in the Czech part of the Upper Silesian Basin (the remaining part lays in Poland). Here there was the most extensive underground exploitation of black coal in the north-east of the Czech Republic. A limit angle is absolutely decisive in the determination of deep mining influences in relation to the current and future utilisation of this territory. The two CSM and Paskov mine localities on the edge of the subsidence basin were selected for this study, since they could not have been affected by mining in neighbouring mines. On the grounds of the long-term levelling monitoring of points on the surface which started prior to mining, the horizontal distance between the mined out area and the undisturbed ground surface was identified. The impact of limit angle on the surface was calculated by means of the horizontal distance and the established mining depth. Such identified actual limit angles reached the values of 36° at the CSM Mine and 25° for the Paskov Mine. The calculated values are significantly lower when compared with the currently applied empirical values of 57° for the CSM Mine and 56° for the Paskov Mine. This means that the extent of the undermining effects is unambiguously wider by 611 m at the CSM Mine and by 883 m at the Paskov Mine. This study thus establishes the existence of a significantly vaster area influenced by coal deep mining than previously expected. The identified facts lead to the conclusion that regular revisions and follow-up updates of the empirically determined parameters are recommended.     

Crystal settling and convection in the Shiant Isles Main Sill

The 168 m-thick Shiant Isles Main Sill is a composite body, dominated by an early, 24 m-thick, picrite sill formed by the intrusion of a highly olivine-phyric magma, and a later 135 m-thick intrusion of olivine-phyric magma that split the earlier picrite into a 22 m-thick lower part and a 2 m-thick upper part, forming the picrodolerite/crinanite unit (PCU). The high crystal load in the early picrite prevented effective settling of the olivine crystals, which retain their initial stratigraphic distribution. In contrast, the position of the most evolved rocks of the PCU at a level ~80% of its total height point to significant accumulation of crystals on the floor, as evident by the high olivine mode at the base of the PCU. Crystal accumulation on the PCU floor occurred in two stages. During the first, most of the crystal load settled to the floor to form a modally and size-sorted accumulation dominated by olivine, leaving only the very smallest olivine grains still in suspension. The second stage is recorded by the coarsening-upwards of individual olivine grains in the picrodolerite, and their amalgamation into clusters which become both larger and better sintered with increasing stratigraphic height. Large clusters of olivine are present at the roof, forming a foreshortened mirror image of the coarsening-upwards component of the floor accumulation. The coarsening-upwards sequence records the growth of olivine crystals while in suspension in a convecting magma, and their aggregation into clusters, followed by settling over a prolonged period (with limited trapping at the roof). As olivine was progressively lost from the convecting magma, crystal accumulation on the (contemporaneous) floor of the PCU was increasingly dominated by plagioclase, most likely forming clusters and aggregates with augite and olivine, both of which form large poikilitic grains in the crinanite. While the PCU is unusual in being underlain by an earlier, still hot, intrusion that would have enhanced any driving force for convection, we conclude from comparison with microstructures in other sills that convection is likely in tabular bodies >100 m thickness.     

Summary findings of the fourth international radiocarbon intercomparison (FIRI)(1998–2001)

Interlaboratory comparisons have been widely used in applied radiocarbon science. These are an important part of ongoing quality assurance (QA) programmes, which are vital to the appropriate interpretation of the evidence provided by the ¹⁴C record in Quaternary applications (including climate change and environmental reconstruction). International comparisons of laboratory performance are an essential component of the quality assurance process in radiocarbon dating. If the user community is to have confidence in radiocarbon results, it needs to be assured that laboratories world wide are producing measurements that are reliable and in accordance with ‘good practice’. The findings from the most recent (completed in 2001) and extensive (more than 90 participating laboratories) radiocarbon intercomparison (FIRI) are reported here. This study was designed (i) to assess comparability, or otherwise, of the results from different laboratories and (ii) to quantify the extent and possible causes of any interlaboratory variation. The results demonstrate that there are no significant differences amongst the main measurement techniques (gas proportional counting, liquid scintillation counting and accelerator mass spectrometry (AMS)) but there is evidence of small laboratory offsets relative to known age samples for some laboratories. There is also evidence in some cases of underestimation of measurement precision. Approximately 10% of all results were classified as extreme (outliers) and these results were generated by 14% of the laboratories. Overall, the evidence supports the fact that radiocarbon laboratories are generally accurate and precise but that, notwithstanding internal QA procedures, some problems still occur, which can best be detected by participation in independent intercomparisons such as FIRI, where the results allow individual laboratories to assess their performance and to take remedial measures where necessary. The results from FIRI are significant in that they show a broad measure of agreement between measurements made in different laboratories on a wide range of materials and they also demonstrate no statistically significant difference between measurements made by radiometric or AMS techniques. Copyright © 2002 John Wiley & Sons, Ltd.     

DTSGUI: A Python Program to Process and Visualize Fiber-Optic Distributed Temperature Sensing Data

Fiber-optic distributed temperature sensing (FO-DTS) has proven to be a transformative technology for the hydrologic sciences, with application to diverse problems including hyporheic exchange, groundwater/surface-water interaction, fractured-rock characterization, and cold regions hydrology. FO-DTS produces large, complex, and information-rich datasets. Despite the potential of FO-DTS, adoption of the technology has been impeded by lack of tools for data processing, analysis, and visualization. New tools are needed to efficiently and fully capitalize on the information content of FO-DTS datasets. To this end, we present DTSGUI, a public-domain Python-based software package for editing, parsing, processing, statistical analysis, georeferencing, and visualization of FO-DTS data.     

Oscillations in the 45 – 5000 MHz Radio Spectrum of the 18 April 2014 Flare

Using a new type of oscillation map, made from the radio spectra by the wavelet technique, we study the 18 April 2014 M7.3 flare (SOL2014-04-18T13:03:00L245C017). We find a quasi-periodic character of this flare with periods in the range 65?–?115 seconds. At the very beginning of this flare, in connection with the drifting pulsation structure (plasmoid ejection), we find that the 65?–?115 s oscillation phase slowly drifts towards lower frequencies, which indicates an upward propagating wave initiated at the start of the magnetic reconnection. Many periods (1?–?200 seconds) are found in the drifting pulsation structure, which documents multi-scale and multi-periodic processes. On this drifting structure, fiber bursts with a characteristic period of about one second are superimposed, whose frequency drift is similar to that of the drifting 65?–?115 s oscillation phase. We also checked periods found in this flare by the EUV Imaging Spectrometer (EIS)/Hinode and Interface Region Imaging Spectrograph (IRIS) observations. We recognize the type III bursts (electron beams) as proposed, but their time coincidence with the EIS and IRIS peaks is not very good. The reason probably is that the radio spectrum is a whole-disk record consisting of all bursts from any location, while the EIS and IRIS peaks are emitted only from locations of slits in the EIS and IRIS observations.     

NARROWBAND dm-SPIKES OBSERVED DURING THE 15 JUNE 1991 FLARE

We performed a statistical analysis of the dm-spikes that were present for an exceptionally long period (more than 10 min) during the 15 June 1991 flare. We realized that the polarization degree, the duration and the mutual delay of the R- and L-components were nearly the same for both CW and ACW cases. CW (ACW) means the clockwise (anti-clockwise) sense of the loop in the R–L versus L+R plots, when the data of a single spike are considered according to the time sequence. The presence of such a loop is determined by the delay of the weaker (stronger) polarimetric component in respect to the other one. The increase of the polarization percentage started first at 610, then at 408 and afterwards at 327 MHz. It was found that the duration of spikes was almost completely independent from the polarization degree. The mean duration of spikes at different frequencies corresponds to that computed using the formula of Güdel and Benz. Like the mean duration, also the mean delay decreased with increasing frequency. The CW/ACW ratio varied simultaneously for the frequencies we recorded during an interval of about three minutes. Spikes were considered as the radio manifestation of superthermal electrons accelerated in the MHD cascading waves. The evolution of spikes and their parameters were qualitatively interpreted within the flare reconnection model with turbulent plasma outflows.     

Bosumtwi impact structure,Ghana: Evidence for fluidized emplacement of the ejecta

The about 10.5 km diameter Bosumtwi impact crater is one of the youngest large impact structures on Earth. The crater rim is readily noticed on topographic maps or in satellite imagery. It defines a circular basin filled by water (Lake Bosumtwi) and lacustrine sediments. The morphology of this impact structure is also characterized by a circular plateau extending beyond the rim and up to 9–10 km from the center of the crater (about 2 crater radii). This feature comprises a shallow ring depression, also described as an annular moat, and a subdued circular ridge at its outer edge. The origin of this outermost feature could so far not be elucidated based on remote sensing data only. Our approach combines detailed topographic analysis, including roughness mapping, with airborne radiometric surveys (mapping near‐surface K, Th, U concentrations) and field observations. This provides evidence that the moat and outer ring are features inherited from the impact event and represent the partially eroded ejecta layer of the Bosumtwi impact structure. The characteristics of the outer ridge indicate that ejecta emplacement was not purely ballistic but requires ejecta fluidization and surface flow. The setting of Bosumtwi ejecta can therefore be considered as a terrestrial analog for rampart craters, which are common on Mars and Venus, and also found on icy bodies of the outer solar system (e.g., Ganymede, Europa, Dione, Tethys, and Charon). Future studies at Bosumtwi may therefore help to elucidate the mechanism of formation of rampart craters.     

Fluid-assisted retrogression of garnet and P–T history of metapelites from HP/UHP metamorphic terrane (Pohorje Mountains, Eastern Alps)

Fluid inclusions in garnet combined with element X-ray mapping, phase equilibrium modelling and conventional thermobarometry have been used to constrain the metamorphic evolution of metapelitic gneiss from the HP/UHP metamorphic terrane of Pohorje Mountains in the Eastern Alps, Slovenia. Retrograde P–T trajectory from ~2.75 GPa and 780°C is constrained by the composition of matrix phengite (6.66 apfu Si) coexisting with garnet cores, kyanite and quartz. The intersection of the X _Prp = 0.25 isopleth for the garnet with the upper stability boundary for K-feldspar in the matrix indicates near-isothermal decompression to ~0.9 GPa at 720°C. Temperatures over 650°C during this stage are corroborated by the high degree of ordering of graphite inclusions associated with Zn, Mg-rich staurolite and phlogopite in the Mg-rich (X _Prp = 0.22–0.25) garnet cores. Majority of garnet porphyroblasts are depleted in Mg (down to X _Prp = 0.09) and enriched in Mn (up to X _Sps = 0.12) along cracks and at their margins. The associated retrograde mineral assemblage comprises Zn, Mg-poor staurolite, muscovite, biotite–siderophyllite, sillimanite and quartz. The onset of the retrogression and the compositional modification of the garnet porphyroblasts were accompanied by the addition of fluid-deposited graphite around older graphite inclusions, probably due to removal of water from a graphite-buffered COH fluid by dissolution in partial silicic melt. Instantaneous expulsion of water near the melt solidus (640°C, max. 0.45 GPa) caused dissolution of the graphite at redox conditions corresponding to 0.25–1.25 logfO₂ units below the QFM buffer, giving rise to a H₂O–CO₂–CH₄ fluid trapped in primary inclusions in Mn-rich, Mg-poor, almandine garnet that reprecipitated within the retrogressed domains. The absence of re-equilibration textures and consistent densities of the fluid inclusions reflect a near-isochoric cooling postdating the near-isothermal decompression. Bulk water content in the metapelite attained 2 wt% during this stage. The low-degree partial melting and extensive hydration due to the release of the internally derived, low-pressure aqueous fluids led to the reset of peak-pressure mineral assemblage.