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

Volume 71 no. 5 / October 2020

Volume 71 no. 5 / October 2020

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Articles in this issue

  • Early Carboniferous successive I/S granite magmatism recorded in the Malá Fatra Mountains by LA-ICP-MS zircon dating (Western Carpathians)

    Abstract: In situ U–Pb zircon dating by the ICP-MS technique from tonalite located in the southern margin of the Kriváňska Malá Fatra granite massif records a Concordant age of 353 ± 3 Ma for zircon cores, 342 ± 3 Ma for their rims but the zircons from granodiorite on the northern margin of the massif show only coeval Concordant age of 342 ± 3 Ma from both cores and rims. The obtained ages establish successive Tournaisian and Visean magmatic events in the Variscan Malá Fatra crystalline basement and an intimate relationships between two Lower Carboniferous intrusions. The Th/U ratio from zircon cores of Tournaisian tonalite shows a magmatic value of 1.0, whereas the ratio with value of 0.2 from zircon rims most likely represent the thermal imprint from emanated hydrothermal fluids from identified Visean granodiorite intrusion with similar Th/U zircon ratio of 0.4. The short time span of about 11 Ma for the origin of these two granitoid intrusive phases in the Malá Fatra Mountains advocates a relatively rapid Variscan convergence from a probably terminated Tournaisian arc magmatic regime to Visean collisional setting.
  • Source rock potential of the Oligocene Menilite Formation in the Czech sector of the Subsilesian Unit (Flysch Carpathians)

    Abstract: The Oligocene Menilite Formation represents the most important hydrocarbon source rock in the Flysch Carpathians. The formation is laterally uniform across long distances but shows strong vertical heterogeneity reflecting changes in depositional environments, which control the source rock potential. In the Czech Republic, the Menilite Formation is subdivided into the Subchert Member (nannofossil zone NP22), Chert Member (upper NP22 to lower NP23), Dynów Marlstone (NP23) and Šitbořice Member (upper NP23 to lower NP25). The present study describes in detail the Bystřice nad Olší section in the Subsilesian Unit where all four members are exposed including the uppermost part of the underlying Frýdlant Formation (Sheshory Marls). The present Frýdlant Formation has a negligible source rock potential compared to the Menilite Formation. The Menilite Formation in the Bystřice nad Olší section has mostly “good” source rock potential, although the TOC indicates “very good” potential. The Subchert Member (average TOC: 3.6 wt. %; HI up to 505 mg HC/g TOC) and the Chert Member (average TOC: 2.2 wt. %; HI up to 790 mg HC/g TOC) are the most prolific units. Based on organic petrography and HI, the kerogen is classified as type II and I. Indications of admixtures of type III kerogen are limited to samples with low TOC contents (
  • Three-dimensional distribution of glass and vesicles in metasomatized xenoliths: A micro-CT case study from Nógrád–Gömör Volcanic Field (Northern Pannonian Basin)

    Abstract: In this study, three clinopyroxene-enriched upper mantle xenoliths, petrographically classified as wehrlite, were investigated from the Nógrád–Gömör Volcanic Field with the use of X-ray microtomography. Our main goal was to quantify the volume of the glass phase and the vesicles to reveal their three-dimensional distribution. Among the studied wehrlite xenoliths, one is weakly and two are strongly metasomatized. The two latter wehrlite xenoliths are characterized by higher modal amount of glass and vesicles, which suggests a genetic connection between glass and concomitant vesicles, and the metasomatic agent. The glass, which was a melt at mantle conditions, forms an interconnected network. This may explain the presence of the electromagnetic anomaly with high electrical conductivity beneath the study area. Our study contributes to the better understanding of melt migration and its metasomatic effect in the lithospheric mantle beneath monogenetic volcanic fields.
  • Hydrocarbon source rock potential and paleoenvironment of lower Miocene diatomites in the Eastern Carpathians Bend Zone (Sibiciu de Sus, Romania)

    Abstract: Diatomites are prolific hydrocarbon source rocks in many basins worldwide. In the broader Carpathians, diagenetically altered diatomites are called menilites, and menilitic shale successions are regarded as the most prolific hydrocarbon source rocks in the region. The abandoned Sibiciu de Sus quarry, located in the Eastern Carpathian Bend Zone of Romania, provides large exposures of the upper part of the Lower Miocene Upper Menilites, composed of various diatomite lithologies, cherts, menilitic shales and quartz-rich sandstone. The sediments are highly deformed due to soft-sediment deformation and subsequent Miocene to Pliocene contractional tectonics. Twenty-two diatom-bearing samples were examined in order (a) to determine the hydrocarbon source rock potential, (b) to document the diatom assemblages and (c) to interpret the depositional environment. The hydrocarbon potential of the studied rocks is considered good to very good, with an average TOC of 3.77 wt. % (max. 9.57 wt. % TOC) and type II–III kerogen (avg. HI: 384 mg HC/g TOC). Tmax does not exceed 424 °C suggesting that the organic matter is thermally immature. Despite that, the Production Index is high (0.1–0.3), which proves the presence of migrated hydrocarbons. The source potential index (SPI) indicates that the exposed section, if mature, could generate about 1.3 t HC/m2. As the diatom preservation does not enable chemical extraction of individual valves, this study describes only genus-level findings. The diatom assemblages are dominated by Aulacoseira and Actinocyclus, whereas Ellerbeckia, Paralia and Rhaphoneis are rarely observed. The diatom assemblages indicate a nearshore, brackish-water depositional setting.
  • Early middle Miocene paleoenvironmental evolution in southwest Transylvania (Romania): Interpretation based on foraminifera

    Abstract: The paleoenvironmental changes produced during the early middle Miocene have been restored based on foraminiferal assemblages collected from the Hațeg Basin in the southwestern part of Transylvania. The identified planktonics suggest a late early Badenian age (Orbulina suturalis: mid-late Langhian) and relatively warm water temperature (high percentages of Trilobatus trilobus together with Trilobatus quadrilobatus, Globigerinella regularis, and Orbulina suturalis). Composition, abundance, diversity, and distribution of the benthic assemblages indicate fluctuations in the paleoecological parameters and nutrient supply in shelf settings. Separating the assemblages based on the preferred life habitat and feeding strategies along with analysis of species distribution using univariate (Fisher Alpha, Shannon, Simpson, Pielou, Hurlbert) and multivariate statistical indices (Bray Curtis distance matrix) aided in interpreting the paleoenvironmental changes along the succession (food content, oxygenation, changes in the hydrodynamics). The results suggest a relatively shallow and well-oxygenated depositional environment with few intervals of increased nutrient supply and decreased oxygen content, warm surface waters as well as a deepening upward trend along the section.
  • Geochemistry and Sr–Nd–Pb isotope characteristics of Miocene basalt–trachyte rock association in transitional zone between the Outer Western Carpathians and Bohemian Massif

    Abstract: Representative samples covering all petrographic types of the Miocene subvolcanic (dykes and sills) basalt–trachyte rock association from the Uherský Brod area (UB, Moravia) in the Czech Republic were studied. The UB area is associated with the Klippen Zone in the neighbourhood of the contact of the Carpathian–Pannonian Block with the Bohemian Massif. The petrographic and geochemical features of the subvolcanic rocks from the UB area only partly resemble those of the calc-alkaline rocks in a similar structural position in the coeval Pieniny area in Poland as well as of the transitional calc-alkaline rocks from the Central Slovakian volcanic field. The Miocene subvolcanic rocks were generated by melting of the variably metasomatised sub-lithospheric source and subsequent fractional crystallisation of the primary basaltic magma. The compositional characteristics of this rock series straddle the alkaline and subalkaline volcanic rock fields, while the rocks from the Pieniny area and from the Central Slovakian volcanic field are predominantly calc-alkaline andesites. The distribution of incompatible elements such as U, Th, REE, Nb, Ta, Sr, Ba as well as LaN/YbN ratios and Sr–Nd–Pb isotope composition of the rocks from the UB and Pieniny areas differ substantially, whereas the geochemical patterns of the UB rocks are slightly similar to those of the transitional rocks from the Central Slovakian volcanic field. The modest contents of incompatible trace elements in the andesitic rocks from the Pieniny area share several characteristics of the prevalent calc-alkaline andesitic rocks from the Carpathian–Pannonian region. Basaltic–trachytic series from the UB area are characterised by higher ɛNd (~2.5) and lower 87Sr/86Sr (~0.704) and 207Pb/204Pb (~15.65) initial values in comparison with the calc-alkaline rocks from the Carpathian–Pannonian region including the Pieniny area. Nevertheless, the basaltic–trachytic rocks from the UB, richer in some of the incompatible trace elements (e.g., U, Th, REE, Sr and Ba) partly resemble (including Sr–Nd–Pb isotopes) the Na-alkaline Miocene volcanic rock series of the NE shoulder of the Cheb–Domažlice Graben in the Bohemian Massif.