International Geological Journal - Official Journal of the Carpathian-Balkan Geological Association

Volume 71 no. 1 / February 2020

Volume 71 no. 1 / February 2020

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Articles in this issue

  • Physical properties of Hradište border fault (Turiec Basin, Western Carpathians, Slovakia) inferred by multidisciplinary geophysical approach

    Abstract: The Hradište border fault zone has played an important role in the development of the tectonic contact of the Cenozoic sediments of the Turiec Basin with the Malá Fatra Mountains crystalline basement. Seismic, geoelectric, radiometric, gravimetric, magnetometric and ground penetrating radar measurements were used to study the physical properties and determine the exact position and inclination of this fault zone down to a depth of up to 40 m. The Hradište border fault zone represents an almost vertical physical boundary characterized by decreasing seismic velocity (from 3.0 km.s−1 to 2.2 km.s−1) and decreasing electrical resistivity (500 to 150 Ω.m) when passing from the basement west of the fault to sediments to its east. It corresponds also to a compact segment of the lowest volume activity of radon 222Rn values in soil air (8 kBq.m−3 on average) and maximum horizontal gravity gradient (−0.0076 mGal.m−1). The discovery of this anomalous zone also helps us to distinguish two different anomalous blocks. The block west of the fault represents the orthogneisses of the Tatric crystalline complex belonging to the Malá Fatra Mountains. The eastern block is built-up by the Bystrička Member Pliocene sediments of the Turiec Basin. Our study serves as a case study for geophysical research on faults in different tectonic units of the Western Carpathians and other similar orogens.
  • Geoelectrically distinct zones in the crust of the Western Carpathians: A consequence of Neogene strike-slip tectonics

    Abstract: Seismic reflection profile 2T is one of the best known geophysical profiles in the Carpathian region. It is very interesting from the geological point of view, because it cross-cuts all the basic tectonic units of the Western Carpathians. This profile was only interpreted by seismic methods and has never been modelled by the magnetotelluric method or compared with results of other geophysical methods. This missing study is the main objective of our paper and results in the new interpretation of the Western Carpathian crustal structure. The 2T profile can be divided into four main independent tectonic zones from an electrical conductivity viewpoint, and this is also supported by information from seismic, gravimetric and partly geothermic results. The first zone from the north is the segment of the Outer Western Carpathians with conductive sedimentary sequences of the Flysch belt overriding the non-conductive European platform. The following zone is represented by resistive migmatitic complexes of the Tatric Unit. The next zone to the south is composed from much more conductive metamorphic complexes of the Veporic Unit. The southernmost zone is characterized by very conductive structures in the whole crust. The boundaries of the zones in the geophysical cross-sections are manifested by subvertical Neogene (Neoalpine) strike-slip zones. The 2-D zones visible in the cross-sections and on the maps are the projections of the separate independent crustal segments. Older tectonic structures (mainly the Paleo-alpine and Hercynian overthrusts) are preserved inside these crustal segments.
  • Fixing a J/K boundary: A comparative account of key Tithonian–Berriasian profiles in the departments of Drôme and Hautes-Alpes, France

    Abstract: This work summarises the results of ten years of study of the palaeomagnetism and biostratigraphy of Tithonian–Berriasian profiles in the middle Vocontian Basin: at Le Chouet, Le Ravin de Font de Saint Bertrand, Charens, Belvedere (Haute Beaume) and Tré Maroua. This study has thus focussed on the “Calcaires Blancs vocontiens”, a predominantly micritic formation developed locally in microfacies categories SMF 2, SMF 3 and SMF 4. Facies zones FZ 3 and FZ 4 indicate deposition in upper to mid slope environments. We record key biotic markers across the J/K boundary, notably the primary marker Calpionella alpina, and supporting secondary datums founded on calpionellid, calcareous nannofossil, calcareous dinoflagellate and ammonite occurrences. All this is keyed to the Global Polarity Time Scale. Here we recognise the Tithonian/Berriasian boundary as coincident with the base of the Alpina Subzone (Calpionella Zone). Geographically, this is the most widespread correlatable datum in the traditional boundary interval, and it can be calibrated with other widespread fossil markers in magnetozone M19n.
  • Delineating the subsurface geological features of the Southern Abu Gharadig Basin, North Western Desert, Egypt, based on gravity and magnetic data

    Abstract: The gravity and magnetic data in the area south of the Qattara Depression has been investigated to define the structural framework of that area. Several techniques were applied to these data such as separation of regional and residual components, lineament analysis, tilt angle derivative, spectral analysis, and 2.5D gravity and magnetic modelling. The regional-residual separation was carried out using the Fast Fourier Transform to assess the sedimentary basins and the uplifted blocks. Lineament analysis was carried out to explain the main tectonic trends. The spectral analysis technique was applied to magnetic data to determine the depth to the basement surface along 21 profiles. 2.5D gravity and magnetic modelling along four profiles indicates that the area is formed from uplifted and down-faulted blocks of granitic and basaltic rocks. A tentative structural relief map was constructed to outline the main basins and uplifts. The results of this study show a thick sedimentary cover within the Abu Gharadig Basin exceeds 3000 m in most parts of the area under consideration. This sedimentary cover is thin in the south-western part within Faghur Basin. The structural pattern indicates that the area was affected mainly by: NE (Tibesti), ENE (Syrian Arc), N–S (East African), and NW (Suez) tectonic trends. The geothermal gradient was determined for six square areas. It has an average value of about 20.23 °C/km that can generate hydrocarbons within the outlined sedimentary basins. Because of the presence of thick clastic to carbonate rocks that were subjected to faulting and sufficient geothermal gradient to mature source rock; the Southern Faghur and Abu Gharadig basins can be considered as a promising region for further hydrocarbon exploration.
  • Uranium isotopic ratios and their implication for uranium–uranium dating and groundwater circulation studies: A case study from speleothems of the Demänová caves, Nízke Tatry Mts., Slovakia

    Abstract: Detailed analyses of speleothems collected in caves of the Demänová Valley, Nízke Tatry, Slovakia, have found significant variability in uranium concentrations and initial 234U/238U activity ratios, plus correlation between these variables. They are related to the ages of samples and their differing locations in the caves. Strong variability of initial 234U/238U activity ratios is the reason for serious limitations in applying the 234U/238U Regional Uranium Best Estimate method as an age estimator for speleothems older than the range of the 230Th/234U method (500 ka). The strong variability of uranium contents in speleothems, rocks and waters and their isotopic compositions allowed us to distinguish distinct periods with changes in water circulation paths or distribution/weathering degrees of deposits in surface alimentation areas or in the epikarst zone, that result from the more ready leaching of the 234U isotope from sediments. Periods characterised with higher initial 234U/238U activity ratios are most likely associated with the deposition of “fresh” colluvial deposits and/or soil development (potential uranium source) in the alimentation area. Gradual decrease of initial 234U/238U activity values indicate prolonged stable weathering and uranium leaching conditions. The Demänová results indicate periods of intensive erosion and “fresh” sediment deposition in the alimentation areas at ~120 ka, ~80–70 ka, and during the Holocene.
  • Monazite U–Th–total Pb age constraints on an early Permian volcanic event in the South Carpathians, Romania

    Abstract: The sequence of Permian volcanic and volcaniclastic rocks (up to 2 km thick) in the Sirinia Basin (Svinița-Svinecea Mare sedimentary zone) of the Upper Danubian Units, South Carpathians, is considered to be the product of subaqueous volcanism passing into a subaerial volcanism and subsequent deposition by debris flow. The investigated volcano-sedimentary rocks are composed of a rhyolitic clastic framework embedded within a fine-grained matrix. The electron probe microanalyses of monazites in the rhyolite clasts and in the volcaniclastic matrix yielded a U–Th–total Pb mean age of 296±3.2 Ma. This result is the first to constrain the age of the volcanic activity event recorded in the volcaniclastic rocks of the Sirinia Basin. The monazite age also estimates the maximum depositional age of the volcano-sedimentary rocks as not older than early Permian (middle Asselian).