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

Volume 70 no. 5 / October 2019

Volume 70 no. 5 / October 2019

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Articles in this issue

  • Deep gravity data interpretation using seismic reflection and well data: A case study of the West Gharib-Bakr area, Eastern Desert, Egypt

    Authors: AHMAD A. AZAB
    Abstract: A rigorous processing and analysis of the gravity data with seismic reflection and borehole information enabled a general view of the deep-seated regional structures in the West Gharib-Bakr area, Eastern Desert, Egypt. In this context, several interpretational techniques were applied to learn more about the supra-basement structures and intra­basement sources. The interpretation started with a review of the seismic data to clarify the structural elements on top of the Miocene strata, where a number of isochronous reflection maps were constructed and had migrated into depth maps. The Bouguer anomaly map was processed using Fast Fourier Transform filtering based on spectral analysis to separate the gravity anomalies into its components. Gravity stripping was also performed under the seismic isopachs and density controls. The gravity effect of each rock unit was calculated and progressively removed from the original data to obtain a new gravity map on top of the Pre-Miocene. To ensure more reliable results, further filtering and analytical processes were applied to the stripped map. The results of seismic analysis show simple structural configurations at the Miocene level, with a significant increase of evaporite thickness along the Gulf of Suez coast. In contrast, analysis of the stripped gravity map reveals a more intricate structure at the Pre-Miocene level, with increasing numbers/lengths of faults on the basement surface. Lineament analysis shows two major peaks trending N0–20°W and N50–70°E, produced by two main forces in NNW–SSE (compression) and ENE–WSW (tension) directions. The models confirmed a rough and ruptured basement surface, with no evidence of any magmatic intrusions penetrating the sediments. The basement relief map delineates five basins/sub-basins in the area which are separated from each other by ridges/saddles.
  • New 40Ar/39Ar, fission track and sedimentological data on a middle Miocene tuff occurring in the Vienna Basin: Implications for the north-western Central Paratethys region

    Abstract: The Kuchyňa tuff is found on the Eastern margin of the Vienna Basin and was formed by felsic volcanism. The Ar/Ar single grain sanidine method was applied and resulted in an age of 15.23 ± 0.04 Ma, which can be interpreted as the age of the eruption. The obtained numerical age is in accordance with the subtropical climate inferred by the presence of fossil leaves that originated in an evergreen broadleaved forest. Furthermore, the described volcanism was connected with the syn-rift stage of the back-arc Pannonian Basin system. The sedimentological data from the underlying sandy mudstones indicate alluvial environment what confirms terrestrial conditions during deposition. Moreover, the tuff deposition probably occurred shortly before the Badenian transgression of the Central Paratethys Sea.
  • Biostratigraphic constraints for a Lutetian age of the Harrersdorf Unit (Rhenodanubian Zone): Implication for basement structure of the northern Vienna Basin (Austria)

    Abstract: The formations underlying the Neogene infill of the Vienna Basin are still poorly documented. Until now correlation of subsurface lithostratigraphic units with those of the Rhenodanubian nappe system and the Magura nappe system, outcropping at the basin margins, has been based on extrapolations. A recent drilling campaign in the Bernhardsthal oil field of the northern Vienna Basin in Austria reached the pre-Neogene basement and provided cuttings for biostratigraphic and paleoecological analyses. Based on these data, acquired by using detailed micro- and nanno-paleontological analyses, a Lutetian age (middle Eocene) and a bathyal depositional environment for the Flysch of the Harrersdorf Unit was documented. The lithological similarity of the drilling with the Steinberg Flysch Formation of the Greifenstein Nappe and its Lutetian age suggests, that the middle Eocene part of the Harrersdorf Unit represents a continuation of the Greifenstein Nappe of the Rhenodanubian Flysch, rather than a frontal part of the Rača Nappe of the Magura Flysch as previously thought.
  • Geophysical and geological interpretation of the Vienna Basin pre-Neogene basement (Slovak part of the Vienna Basin)

    Abstract: The Vienna Basin is situated at the contact of the Bohemian Massif, Western Carpathians, and Eastern Alps. Deep borehole data and an existing magnetotelluric profile were used in density modelling of the pre-Neogene basement in the Slovak part of the Vienna Basin. Density modelling was carried out along a profile oriented in a NW–SE direction, across the expected contacts of the main geological structures. From bottom to top, four structural floors have been defined. Bohemian Massif crystalline basement with the autochthonous Mesozoic sedimentary cover sequence. The accretionary sedimentary wedge of the Flysch Belt above the Bohemian Massif rocks sequences. The Mesozoic sediments considered to be part of the Carpathian Klippen Belt together with Mesozoic cover nappes of Alpine and Carpathian provenance are thrust over the Flysch Belt creating the third structural floor. The Neogene sediments form the highest structural floor overlying tectonic contacts of the Flysch sediments and Klippen Belt as well as the Klippen Belt and the Alpine/Carpathians nappe structures.
  • Mineralogical and physico–chemical properties of bentonites from the Jastrabá Formation (Kremnické vrchy Mts., Western Carpathians)

    Abstract: In the past years an increasing demand for bentonites resulted in the opening of new bentonite deposits in the Jastrabá Formation. The shortage of information, in particular analytical data, on the bentonites from the newly opened Jastrabá Fm. deposits was the motivation for the current study. Smectite is the predominant mineral in all bulk bentonites from the new deposits. Its amount varied between 43 and 90 wt. %. The bulk bentonites also contain variable amounts (10–57 wt. %) of mineral admixtures such as feldspars, mica, opal-CT, kaolinite, quartz and sometimes goethite. The smectite mineral comprising the studied bentonites was montmorillonite. The octahedral Al in the structure of montmorillonite was partially substituted by Mg, and to a lesser extent by Fe. The interlayer space of montmorillonite is occupied predominantly by divalent exchangeable cations (Ca2+ and Mg2+). The dehydroxylation temperature of smectites (> 600 °C) determined on the DTG curves indicates the presence of the cis-vacant variety of montmorillonites. The mean crystallite thicknesses of smectites (TMEAN) calculated by BWA analyses ranges from 7.2 to 11.5 nm. The shape of the crystallite thickness distributions (CTDs) for smectites is lognormal in all cases. Cation exchange capacity (CEC) and total specific surface area (TSSA) increases with increasing amount of smectite. The CEC of 101 meq/100g and TSSA of 616 m2/g correspond to bulk bentonite from the Stará Kremnička III deposit containing 89 wt. % of smectite.