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Budapest, Hungary

Bada G.,ELTE Geofizikai es Urtudomanyi Tanszek | Szafian P.,ELTE Geofizikai es Urtudomanyi Tanszek | Vincze O.,Mol Nyrt | Toth T.,Geomega Kft | And 3 more authors.
Foldtani Kozlony | Year: 2010

High-resolution reflection seismic data acquired from Lake Balaton (mainly east of the Tihany Peninsula), provide a solid basis for a detailed analysis of the neotectonic habitat in the region. Two types of seismic profiling - imaging the subsurface with different resolutions and penetration - were utilised to carry out a structural investigation. Singlechannel seismic sections show the uppermost 20 to 30 metres with an unparalleled (decimetre scale) resolution. A closely-spaced seismic grid allowed a 3D structural interpretation to be performed, as well a lateral correlation of the tectonic features. Multi-channel seismic data have a lower (i.e. on the metre scale) resolution which is compensated by deeper penetration down to 150-200 m. The joint interpretation of the two data sets enabled (1) the kinematic interpretation and detailed mapping of neotectonic structural elements, (2) the analysis of the relationship between older (Miocene) and younger (neotectonic) structures, and (3) the reactivation potential of the reconstructed faults. Several shear zones were identified under Balaton; these were oriented mainly parallel to the lake axis. Areas of localised deformation contain numerous smaller scale faults arranged primarily in an en-echelon manner. Geometric and kinematic considerations suggest the presence of relatively wide, sinistral strike-slip fault zones, with most first-order faults being rooted in the basement. Their repeated reactivation is demonstrated in the Miocene as well as post-Miocene (neotectonic). Tectonic activity at the Berhida seismic zone east of Lake Balaton suggests that some of these faults could still be active. Besides faulting, gentle folding of the Upper Miocene (Pannonian s.l.) sediments is also notable. 3D mapping of key horizons and unconformities within the Pannonian strata allowed the identification of a well-defined system of anticlines and synclines of neotectonic origin. However, interpretation of fold axis distribution is not straightforward because features of a secondary deformation appear near the strike-slip fault zones; this has resulted in a complex, often en-echelon folding geometry. The neotectonic habitat at Lake Balaton was put in a more regional context by integrating the reconstructed structural pattern into a neotectonic model of South Transdanubia. Special attention was paid to the age of deformation, and the kinematics and morphological expression of fault geometries; this also referred to the present-day stress field and, particularly, the recent geodynamics of the Pannonian Basin System.

Gabor C.,MAFI | Orsolya S.,ELTE Altalanos es Torteneti Foldtani Tanszek | Imrees M.,Mol Rt | Zoltan H.,Geomega Kft
Foldtani Kozlony | Year: 2010

Gravel, pebbly sand, clean quartz-sand and sandstone - all formed in Lake Pannon - crop out in the vicinity of the Keszthely Hills, Tapolca and Kál Basins; as a geological unit, this is referred to as the Kálla Formation. Up until now its stratigraphic position, its relation to underand overlying formations, as well as to the similar, but virtually older Kisbér Gravel have not been determined with any degree of certainty. Based on descriptions of old wells and sedimentological and stratigraphic data with respect to outcrops, geoelectric measurements were carried out and geological cross-sections were compiled in order to ascertain its stratigraphic relations. Deposits underlying the Kálla Gravel consist of Triassic carbonates, mid-Miocene limestones, pebbly limestones and the Congeria czjzeki-bearing Szák Claymarl. The Kálla Formation is unconformably overlain by silts and sands of the Somló Formation and in some wells by the Tihany Formation (which contains coaly clay beds). The Late Miocene depositional history of the Tapolca Basin can be reconstructed as follows. At about 11-10 Ma, when the lower part of the Szák Claymarl was formed, the area of the present Transdanubian Range was a large peninsula in Lake Pannon. At its southern rim a small, tectonically preformed embayment was created. Around about 10 Ma ago the lake transgressed northwards due to a relative lake-level rise and on the newly-flooded areas small coarse-grained deltas (Kálla Formation) began to form due to small rivers draining the Transdanubian Peninsula. Along the rim of the peninsula several distinct, but coeval gravelly shoreface deposits (Kisbér Gravel) may have been formed. Near to the entry points of rivers (at the deltas) the sedimentation rate compensated and even exceeded the rate of lake-level rise; thus the gravelly-sandy deltaic bodies prograded over the clays, which formerly were deposited below the wave-base. In front of the coarse-grained deltas, the deposition of silts and clays continued. Therefore the Kálla and Szák Formations are partly coeval in the Tapolca Basin. Approximately 9.5-9 ma ago a significant change occurred. Earlier, the sediments were derived from minor local sources (i.e. from the Transdanubian Peninsula); later, following the filling up of the Danube Basin, sediments were derived from the Alps and the Western Carpathians. The major north-western drainage system entered Lake Pannnon as extended deltaic lobes, represented by the silty-sandy beds of the Somló Formation (prodelta and deltafront regions). Parallel with progradation, 9-8 Ma ago the deltaplain corresponding to the Tihany Formation appeared. The overlying alluvial deposits were removed by the Quaternary uplift of the area. With respect to the lithostratigraphic units, it can be concluded that the Szák Claymarl, Kálla and Kisbér Gravels were formed during the same transgressive event. The stratigraphic position of the gravelly formations is different only because of the local variations in sediment input rates. Whereas their source area was the same and their petrographic composition is almost identical. Within the frame of biostratigraphic resolution they are coeval at about 10 Ma and both were formed on the margin of the Transdanubian Peninsula. It is impossible to differentiate the two deposits by geological mapping - therefore their integration as the Kálla Formation is suggested. The Szák Formation, however, is not only a local deposit but can be seen as part of a large clayey lithosome in the fill of Lake Pannon, corresponding to the Endro{double acute}d and Algyo{double acute} Formations. Therefore its timespan over the whole of the Pannonian Basin equals the Late Miocene.

Olah P.,Eotvos Lorand University | Fodor L.,MTA ELTE Geologiai | Toth T.,Geomega Kft | Deak A.,University of Warsaw | And 2 more authors.
Foldtani Kozlony | Year: 2014

Despite previous exploration projects and geological, geophysical maps, knowledge about the structural conditions of the region of the Visegrád and Börzsöny Mountains and the and the east side of the Danube region is uncertain. In recent years several seismic surveys were carried out by the geophysicists of the Eötvös University, Geomega Ltd. and the Technological University of Delft on that section of the River Danube between Budapest and Esztergom. Multi-channel seismic surveys were carried out in both branches of the river around the Szentendre Island, and in two selected areas of the main Danube branch; single-channel data acquisition was performed over a dense network. This led to a good correlation of the data and tectonic features and, furthermore proper projection of well-data became available in the vicinity of the river. On the two test areas, a pseudo-3D interpretation was performed. Integrated interpretation shows that the Triassic basement is unconformably overlain by Oligocene strata (Hárshegy Sandstone, Kiscell Clay, Törökbálint Sandstone Formations) to the north of Budapest. In front of the Börzsöny Mountains, Middle Miocene volcanic rocks, are situated just bellow the fluvial sediments, while in the Pilismarót Basin Middle Miocene marls are present. These formations were deformed by well-identifiable faults, which generally have a NW-SE strike direction. According to our interpretation, most of them were activated in the stress field of the late Early to Middle Miocene (ca. 15–18 Ma), due to NW–SE extension. E–W trending dextral strike-slip faults belong to this phase, while the stress field was, locally, of a strike-slip type, with the same NE–SW extensional axis. Neotectonic reactivation of some faults is possible although this can not be proved unequivocally. The interpretation of the present study suggests a higher level of deformation in the region than previously thought, indicating that the subsurface of the Szentendre Island is densely faulted. The water seismic measurements offer a more detailed image about the structure of the area than the surface observations. © 2015 Hungarian Geological Society.

Uhrin A.,Magyar Allami Foldtani Intezet | Sztano O.,Eotvos Lorand University | Csillag G.,Magyar Allami Foldtani Intezet | Hamori Z.,Geomega Kft
Foldtani Kozlony | Year: 2011

During Late Miocene to Pliocene times, following the gradual infill of Lake Pannon, a widespread alluvial plain was formed throughout the Pannonian Basin, depositing a thick alluvial succession over large areas. The outcrops of these deposits, however, can only be seen at a few locations, chiefly along the rims of the recent mountainous areas. In this paper, the Late Miocene to Pliocene fluvial sedimentary environments are reconstructed on the basis of field observations taken in several outcrops in the south-eastern foreland of the Vértes Hills, a part of Transdanubian Range. Due to poor outcrop conditions, the field observations were supplemented with borehole data and electrical resistivity ground imaging; the latter is a geophysical method recently introduced for applications in fluvial sedimentology. Besides some silt and mud, it is mainly trough, cross-stratified sand that has been deposited in the ancient fluvial channels which appear in the outcrops. Boreholes and geoelectric profiles, however, prove that the bulk of the alluvial deposits consists of floodplain silt and mud that surrounds isolated channel sandbodies. In most of the reconstructed channels, the sedimentary accretions are mainly vertical, demonstrating the lateral stability of the channel paths. Signs of point bar formation (lateral accretion) were recognized at only one location. This palaeoenvironment is very similar to the facies model of anastomosing rivers, although the presence of coexisting interconnected channels cannot be proven in the case considered here. From one of the studied outcrops, a large-scale planar cross-bedded sand is described, and this has been interpreted as the sediment of a braided channel. The measured palaeocurrents and the orientation of a channel sandbody mapped in 3D from geoelectric profiles indicate that the Latest Miocene to Pliocene rivers of the study area flowed chiefly from north-west to south-east, across an alluvial plain with a very gentle slope. The very flat palaeotopography is suggested by the presence of laterally stable channels with low sinuousity. However, structural activity could have resulted in significant alternations of flow direction and river form in certain locations, even creating a braided channel in the vicinity of a presumed synsedimentary fault. The maximum depth of the ancient channels was probably 4 to 7 m, on the basis of the size of bedforms visible in the outcrops. This supports the assumption that the Late Miocene to Pliocene alluvial sediments of the Vértes foreland were deposited by rivers significantly smaller than the recent Danube. Palaeoflow directions and magnitudes of the channels suggest that these rivers drained only the Western Carpathians, located 150-250 km west and north of the study area.

Toth Z.,University of Bremen | Toth T.,Geomega Kft | Szafian P.,TXM Olaj es Gazkutato Kft. | Horvath A.,TXM Olaj es Gazkutato Kft. | And 6 more authors.
Foldtani Kozlony | Year: 2010

The research efforts that took place after the outstanding Balaton project (1891-1918) of Lajos LÓCZY never led to any consensus on the origin and evolution of the lake. However, the application of modern palaeontological and geochemical methods in the framework of the Balaton investigations of the Hungarian Geological Institute (1981-2004) have settled a few critical issues and the first seismic survey of the lake was also performed in 1987. In the period of 1993 to 2007 the Geophysical Department of the Eötvös Loránd University (Budapest) regularly carried out seismic profiling on the lake in association with the summer fieldwork of the university's students. In 1993 Italian and in 2005 German experts took part in the surveys using their marine seismic acquisition technology. The most frequently applied instrument during the university research programmes has been a special Canadian device (IKB-Seistec™). This can generate a seismic signal in the 1 to 10 kHz frequency range and thus offers shallow penetration (20-40 m) and ultra-high resolution (10-20 cm). After a summary of the main results of earlier research, this paper outlines the basic principles and techniques of the seismic method. Then a compilation of the applied instrumentation and data processing is given to assist in understanding the interpretation of the seismic sections of Lake Balaton in the following set of papers in this volume.

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