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Geologické výzkumy na Moravě a ve Slezsku / Geological research in Moravia and Silesia
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  This is an Open Access Journal Open Access journal
ISSN (Online) 2336-4378
Published by Masaryk University Homepage  [11 journals]
  • Coarse gravel deposits at the Dyje–Pulkau watershed south of Znojmo
           (Czechia–Austria): new knowledge confronted with current stratigraphy

    • Authors: Pavel Roštínský, Jaroslav Šmerda, Eva Nováková
      Abstract: More gravel occurrences are preserved on largely flat summits in the upland area at the Dyje–Pulkau watershed (Carpathian Foredeep nearby distinct southeastern margin of the Bohemian Massif developed along the Waitzendorf fault system) than marked in geological maps. As to stratigraphy, their western sites were hitherto considered to be marine deposits of Lower Badenian (Middle Miocene age). New knowledge about distribution, geomorphological setting, clast size and basic petrography of the gravel compared with some of the same type data on numerous coarse grained Neogene or Quaternary sediments of various genesis preserved in the surroundings (in total 17 basic gravel categories with subhorizontal surfaces distinguished) indicate presumable younger (Late) Miocene or Pliocene age of the deposits, the latter recently proposed for a few eastern gravel sites in Austria. The watershed gravel is distributed in two WNW–ESE trending subparallel belts of different petrology: southern one > 7 km long dominantly composed of quartz-rich rocks (redeposited from sequences of the foredeep basin, mostly Ottnangian) and northern one > 13 km long with high content of Dyje Massif granitoid rocks (lower mineral maturity; primary origin within the margin of the Bohemian Massif, but likely redeposited from younger Lower Badenian sediments) extended across transverse boundary between much finer Karpathian and Lower Badenian sequences in the current Carpathian Foredeep (lower stratigraphic constraint). The analogous petrographic differences also occur between two groups of rare depositional sites within near steep marginal slope of the Bohemian Massif; however, the slope category rich in crystalline clasts includes there double quantity of granitoid rocks and minimum quarzite compared with the northern watershed belt in the foredeep basin. The direction and age of material transport into both watershed gravel belts (from WNW) could be similar to that supplying about 5 other quartz-rich gravel categories in the north or south (supposedly driven by streams from WNW or NW), some containing redeposited moldavites originated about 15 Ma. The presumable (Late) Pliocene onset of the Dyje river downcutting in its present-day deep valley section subparallel to the very outer limit of the Bohemian Massif (higher stratigraphic constraint) could be related to young complex movement activity of the Waitzendorf fault system resulting in current block-type topography and disturbing the older dominant WNW–ESE to NW–SE directed regional transport of clastic material.
      PubDate: 2022-10-26
      Issue No: Vol. 29, No. 1-2 (2022)
       
  • Odhad detekční schopnosti stanice VRAC s ohledem na seismické jevy
           registrované v letech 2011 až 2021

    • Authors: Josef Havíř
      Abstract: Širokopásmová seismická stanice VRAC (Vranov u Brna), provozovaná Ústavem fyziky Země (Masarykova univerzita), je zapojena do různých projektů zaměřených na monitorování seismických jevů. Zásadní je zejména její zapojení do globální sítě Mezinárodního monitorovacího systému CTBTO (Comprehensive Nuclear-Test_ban Treaty Organization). Dále je stanice VRAC také jednou z permanentních širokopásmových stanic České regionální seismické sítě. Data stanice VRAC jsou tak rutinně zpracovávána s ohledem na detekci seismických jevů, jejichž zdroje se nachází v různých epicentrálních vzdálenostech, od lokálních, přes regionální až po teleseismické. Cílem tohoto článku je stručně předvést jednoduchý odhad detekční schopnosti stanice VRAC s ohledem na seismické jevy z různých epicentrálních vzdáleností. Tento jednoduchý odhad detekční schopnosti byl založen na studiu magnitudo-četnostních vztahů. K tomuto účelu byl využit soubor seismických jevů registrovaných stanicí VRAC v letech 2011 až 2021. Zmíněný soubor zahrnuje 52246 seismických jevů, z toho 33161 regionálních jevů, jejichž zdroje se nacházely v regionálních vzdálenostech. tj. do 2000 km, od stanice VRAC. V rámci magnitudo-četnostní analýzy byly pro každou dílčí sadu, obsahující vždy jevy z dané epicentrální vzdálenosti, zjišťovány dva parametry, a to: hodnota nejčetnějšího magnituda Ma a hodnota magnituda Mm v minimu derivace funkce závislosti nelogaritmované četnosti jevů na magnitudu. Hodnota Mm dobře odpovídá tomu místu na klasickém magnitudo-četnostním grafu, kde dochází k tzv. roll-off efektu. Grafy obou sledovaných parametrů (Ma i Mm) ukazují strmý nárůst hodnot v regionálních vzdálenostech, následovaný plochou částí křivky v epicentrálních vzdálenostech 20°až 80°. Velmi zřetelně se projevuje snížená detekční schopnost v zónách seismického stínu, a to jak v zóně spjaté se zónou snížených rychlostí v hlubších partiích zemského nitra (vnější jádro), tak i se zóno snížených rychlostí odpovídající astenosféře. Dosažené výsledky umožňují odhadnout detekční práh stanice VRAC pro jevy v epicentrálních vzdálenostech 20° až 80° na hodnotu v rozmezí od 4,5 do 4,9.
      PubDate: 2022-10-26
      Issue No: Vol. 29, No. 1-2 (2022)
       
  • Podzemní vody hluboké struktury regionálního rozsahu:
           Pasohlávky–Laa an der Thaya

    • Authors: Kateřina Chroustová, Adam Říčka, Bibiána Pasternáková, Tomáš Kuchovský, Vladimír Opletal, Slavomír Nehyba, Magdalena Bottig
      Abstract: The regions of South Moravia in Czech Republic and Lower Austria are well-known for their use of thermal mineral waters for balneological purposes. Mineral waters are exploited from a Jurassic aquifer by two about 1.5 km deep wells MUS-3G (Pasohlavky, Czech Republic) and Laa TH Nord 1 (Laa an der Thaya, Austria). This Jurassic aquifer buried below the Neogene foredeep overlies a crystalline basement of Bohemian Massif and continues to the southeast below the Western Carpathians. Jurassic sediments which are mainly composed of autochthonous carbonates increase their thickness in this direction due to the decline of the crystalline basement. Because of this decline, there are two developments of Jurassic sediments, the shallower on the northwest and the deeper on the southeast. The zone between these two developments is known as the Mušov transition zone. For sustainable mineral water resources development, a groundwater flow pattern and recharge are evaluated. This evaluation includes both the hydrogeologic structure of Jurassic carbonates and hydraulically continuous underlying and overlying rocks. Because of the considerable depth of this hydrogeologic structure, which ranges from 100 to 3 000 metres below sea level, this study was based mostly on archive reports related to deep wells at the study area. The extent of studied units was identified on well-log data and geophysical survey interpretation. The resulting groundwater level contour map is based on the spatial distribution of hydraulic heads ranging approx. from 180 to 220 metres above sea level (masl) that were derived from pressure and water density conditions at the Jurassic aquifer. The general direction of groundwater flow is from northwest and southeast to the drainage zone (hydraulic head approx. 170–190 masl) identified in the middle of the studied area, which is identical to a course of the Mušov transition zone and parallel to the course of Dyje river (water table 170–180 masl). The northwestern part of the studied hydrogeological structure also differs from the southeastern part in a lower total mineralization which indicates active inflow of fresh water. The study was also enhanced by a spatial distribution of hydraulic parameters of all modelled units. These parameters were derived from hydrodynamic tests. The hydraulic conductivity values for the major Jurassic aquifer range from 6,0×10-4 to 1,3×10-9 m/s. The occurrence of the higher hydraulic conductivity near the drainage zone indicates the presence of a well-developed drainage network.
      PubDate: 2022-10-26
      Issue No: Vol. 29, No. 1-2 (2022)
       
  • Chemické složení amfibolů v polétavém prachu z vybraných lokalit
           Brněnska

    • Authors: David Buriánek, Jiří Svatuška
      Abstract: This study aimed to characterise the morphological and chemical properties of amphiboles from airborne dust in three localities studied in Brno and its surroundings. We analysed approximately 2 g of airborne dust particles from each sample. The mineralogical and morphological characteristics of the dust particles were examined by polarised-light microscopy and electron microprobe analysis (SEM–WDX). All studied airborne dust inorganic particles with length ≥5 μm show ratio ≤3: 1 or diameter ˃3 μm and therefore does not be potentially dangerous to human health. We compared the chemical analyses of airborne dust particles (tremolite-actinolite, magnesiohornblende, pargasite) with existing chemical composition amphiboles from possible source areas. The airborne dust from the locality in the centre of the Brno town is completely dominated by amphiboles derived from basic and ultrabasic rocks of the Central Basic Belt of the Brno Massif. The granitoids of the Brno massif was also a significant source of dust particles. Anthropogenic activity can explain a substantial proportion of amphibole from a relatively small body of amphibolites in the Central Basic Belt of the Brno Massif because these rocks are widely used as sanding material in the entire Brno agglomeration. The second locality of Rosice (west of Brno) is dominated by amphiboles from the west and northwest metamorphic units (Moravian and Moldanubicum). Amphiboles from the rocks of the Brno massif situated to the southeast are also presented. Amphiboles in the airborne dust from the Rajhradice (locality situated SE from Brno) predominantly originated from the rocks of the Central Basic Belt of the Brno Massif (including amphibolites). Calcareous microfossils suggest that an essential component of the dust is also the material transported from the southeast, where dominated sediments of the Carpathian Flysch units and their foreland. Our results validate amphiboles as valuable minerals for identifying source areas from which dust has been derived and confirm dominant wind flows in the SE and NW directions.
      PubDate: 2022-10-26
      Issue No: Vol. 29, No. 1-2 (2022)
       
 
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