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

Volume 58 no. 4 / August 2007

Volume 58 no. 4 / August 2007

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Articles in this issue

  • Oxfordian and Callovian radiolarians from the Bucegi Massif and Piatra Craiului Mountains (Southern Carpathians, Romania)

    Abstract: This paper regards the description and the first dating of the radiolarian assemblages of the Jurassic siliceous successions in the Bucegi and Piatra Craiului Mts (Southern Carpathians, Romania). The most representative Jurassic outcrops for this area have been sampled: La Poliţie, Strunga, Strunguliţa, Rătei Valley and Sfânta Ana Olistolith (Bucegi Massif), and Sirnea, Umeri and Vladusca (Piatra Craiului Mts). The investigated successions are formed by a great variety of sediments, most of them characterized by a large amount of siliciclastic admixture. The sampled layers are constituted by well stratified siliceous limestone or chert, and their thickness usually ranges between 0.5 and 1 m. The Sfânta Ana sample comes from a Jurassic olistolith included in a Lower Cretaceous flysch. The Nassellaria/Spumellaria and sponge spicules/radiolarians ratios provided information about the depositional environments. In well-preserved samples the N/S ratio varies from 1.7 to 2.8, and the spicules/radiolarians ratio is around 0.6: this means that the siliceous sediments were deposited in distal or relatively deep waters. The biostratigraphical analysis has been carried out by applying two radiolarian zonations based on the Unitary Associations method: most samples are referred to the middle-late Oxfordian. The only exception is represented by the Rătei sample that is assigned to the Callovian. The Romanian successions are easily comparable with other Tethyan sections where the Oxfordian levels are generally the richest in radiolarians. Even in environments with siliciclastic supply (Southern Carpathians) the sedimentation drastically changed during the Oxfordian and became siliceous.
  • The Upper Oligocene–Lower Miocene Krosno lithofacies in the Carpathian Flysch Belt (Czech Republic): sedimentology, provenance and magnetic fabrics

    Abstract: The Krosno lithofacies is the Upper Oligocene–Lower Miocene synorogenic sequence that terminates the flysch sedimentation in the orogenic system of the Western Carpathians. Its deposition replaced the hypoxic sedimentation of the underlying Oligocene Menilite Formation. This change in deposition was connected with the Helvetian Neoalpine orogeny which iniciated the fundamental rearangement in the orogenic belt, gradual isolation of foreland basins and creation of the “Protoparatethys”. The differences in deformation between the Krosno lithofacies and the underlying Upper Cretaceous to Eocene strata are recorded in all tectonofacial units of the Outer (Menilite-Krosno) Group of thrust sheets. Moreover, a trend towards increase of ductile deformation from the outer to the inner margin of the Flysch Belt is evident. The investigation of translucent heavy minerals produced evidence of different spectra between the Krosno lithofacies and underlying strata of individual tectonofacial units. The spatial distribution of the Krosno lithofacies and the transport of clastic material from the SE indicate the deposition of a submarine fan that prograded to the NW.
  • Lower Badenian biostratigraphy and paleoecology: a case study from the Carpathian Foredeep (Czech Republic)

    Abstract: The biostratigraphy and paleoecology of the Middle Miocene, Lower Badenian deposits were studied in two boreholes (Ivan-1 and Vranovice-1) situated in the southern part of the Carpathian Foredeep, Czech Republic. Planktonic foraminifers document the M5b Zone of Berggren et al. (1995). Presence of Uvigerina macrocarinata Papp et Turnovsky and Praeorbulina glomerosa circularis (Blow) indicates “Lower Lagenid Zone” sensu Grill (1941). Calcareous nannofossils with Helicosphaera waltrans, H. walbersdorfensis and Sphenolithus heteromorphus give evidence for the NN5 Zone of calcareous nanoplankton (Martini 1971). Quickly changeable paleoenvironment, especially sea-level fluctuation and non-stable conditions are documented by five types of microfauna: 1. shallow-water foraminifers accompanied by fragments of molluscs and bryozoans — shallow sublittoral (infralittoral), 2. joint occurrence of agglutinated and calcareous benthic foraminifers — circalittoral to upper bathyal, 3. euryoxybiont foraminifers indicate low oxygen content in bottom water of the deeper sublittoral (circalittoral), 4. dominance of planktonic foraminifers with pyritized tests — low oxygen sea, circalittoral to upper bathyal, 5. mixed assemblages of shallow- and deep-water foraminifers document slumps. Generally, relatively shallow epicontinental sea of normal salinity with nutrient supply is supported by coastal nannoflora with higher numbers of Reticulofenestra minuta, Coccolithus pelagicus, and helicosphers. Low abundances of sphenoliths and scarce occurrence of discoasters may imply cooler surface waters. High numbers of reworked nannofossils reflect transgression.
  • Late Miocene sequence stratigraphy of the Pannonian Basin fill (Kiskunhalas–Melykut region, Hungary): how core, electric log and seismic data fit together?

    Abstract: In the area of the Danube–Tisza Interfluve, Pannonian Basin, Hungary, sedimentological, paleontological and well log interpretations of fully cored boreholes made it possible to establish the sequence stratigraphic subdivision of the Upper Miocene lacustrine and fluvial sections of boreholes Kaskantyu Kas-2, Janoshalma J-1 and Bacsalmas Ba-1, of which Kas-2 is paleomagnetically dated. 8 sequences were determined in borehole Kas-2 and 6–6 ones in the boreholes J-1 and Ba-1 respectively. The correlation of the sequences was made along two independent composite seismic lines with the help of cross seismic profiles and well logs of 29 boreholes. 11 sequences were marked out in the Upper Miocene basin fill. The areal distribution of the sequences reflects the NW–SE direction of the sediment transport. By the time of maximum flooding surface (MFS) 2, the area was almost completely flooded. The oldest 4 sequences were identified in a seismically observable thickness in the NE Kiskunhalas depression. Their condensed layers are present in the well Ba-1 in the SE part of the area, revealed by dinoflagellates. Sequences 5 to 11 are present in well-observable thickness in the study area. The thickest part of the successive sequences is shifting towards the SE. Sequences 8 and 10 are developed only in the eastern part of the area. The basin evolution had two major phases: from 10.2 Ma to approximately 7.6 Ma the sequences 1–4 were characterized by local sediment accumulation despite their complete water cover, while between 7.6 and 6.6 Ma (sequences 5–10) regional sedimentation occurred.
  • Late Miocene vegetation and climate of the Balkan region: palynology of the Beli Breg Coal Basin sediments

    Abstract: The results of palynological studies of Neogene freshwater deposits of the Beli Breg Graben (West Bulgaria) are presented. We analysed pollen and spores with the aim of obtaining data about the composition and structure of fossil vegetation and climate conditions. The main vegetation paleocommunities, which existed during the fossilization process, are characterized as mixed mesophytic and swamp forests, communities of aquatic plants, and herbaceous paleocoenoses. The climate data reconstructed by the Coexistence Approach indicate a warm temperate climate with mean annual temperatures around 16 ºC and with mean temperature of at least 4 ºC during the coldest month. With annual precipitation rates commonly above 1000 mm climatic conditions were overall humid, although partly seasonally drier conditions are evident from the data.
  • Clay mineral distribution patterns in the southeastern Mediterranean Sea during the late Quaternary

    Abstract: The clay mineral distribution patterns in three stratigraphically well-defined piston cores containing the uppermost five sapropel sequences (70,000 years BP to the present) in the southeastern Mediterranean Sea have been studied. The temporal variations and spatial distribution of the sum of smectite plus kaolinite, the dominant clay minerals of the Nile River, can be closely related to enhanced suspended sediment transport by the Nile that occurred mostly during the transition phases from an arid to a moist paleoclimatic episode. The most pronounced input of Nilotic provenance clay occurs within and between the sapropel layers S-5 and S-4. Between circa 70,000 and 45,000 years BP this time interval marks the transition phase from the cold-arid early Würmian period to the very wet middle Würmian phase that affected the Nile drainage system and probably caused the activation of numerous wadi systems. The other most intense similar phase occurred after 12,500 years BP as manifested by the concomitant increase of hemipelagic sedimentation, due to the extensive Nile flooding and the resulting dramatic increase in suspensite delivery, leading to a pronounced increase of the Nile clay assemblages within the S-1. Major sea-level fluctuations, such as the regression at 18,000 years BP, had a pronounced effect on clay mineralogy leading to a marked increase in the deposition of illite micas plus mixed layered clays reflecting intensification of shelf erosion.
  • Seismic activity of the Alpine-Carpathian-Bohemian Massif region with regard to geological and potential field data

    Abstract: The seismicity of the geological complexes of the northern part of the Eastern Alps, the Western Carpathians and the Bohemian Massif is investigated by means of new seismic stations and a review of earthquake catalogues available. Eleven earthquake catalogues are evaluated and checked for multiple entries, fake earthquakes and mistakes. The final data set of earthquakes covers the time span from 1267 to 2004 and comprises 1968 earthquakes in total. The resulting epicentral map provides a very detailed idea of the seismicity of this region. An attempt at a seismo-tectonic interpretation of earthquakes based on the geological overview of the region is presented. Gravity and airborne magnetometry data in addition to seismic events are collected and cross-border maps are compiled and analysed in order to determine the spatial extent of these geological structures. The Linsser filtering technique is used to trace faults at two depth horizons — 4 and 8 km. Correlation between the epicentres of earthquakes and lineaments derived from gravity data is discussed for major historical earthquakes such as Neulengbach (1590) or Scheibbs (1867). This data set enables us to determine seismically active fault structures and to get an insight into the fault system interaction. The ability to assess the potentially seismically active vertical and horizontal extent of fault structures enables improved hazard assessments in future. The magnetometric map shows a belt of positive anomalies which reflects the presence of magnetized rocks between the Bohemian Massif and the Alpine-Carpathian zone.