Paleogene karst bauxites in the northeastern Transdanubian Range and their cover sequences provide valuable sedimentary archives, despite their weathered nature and vague paleontological records. ...U–Pb detrital zircon geochronology combined with heavy mineral analysis indicates ‘local’ Alpine aeolian and fluvial sources and ‘distant’ aeolian sources connected to the Bohemian Massif. Records of episodic Paleogene volcanic eruptions related to igneous complexes of the Adamello and probably also the Bergell, Recsk and Balkan Peninsula, are reflected by euhedral zircon crystals. Their U–Pb geochronology supplies age constraints for the phases of subaerial exposure of the karstic surface and the accumulation of bauxitic protoliths and helps to improve the existing stratigraphic records and to define stages of denudation in the northeastern Transdanubian Range. Distinct phases of subaerial exposure and accumulation of the bauxite's protoliths are identified as ca. 42, 35 and 31 Ma; alternating with episodes of subsidence, represented by siliciclastic and carbonatic sequences at ca. 38, 32 and 31 Ma. Besides Paleogene volcanism, zircon dating also revealed contributions from the Middle Triassic tuffs of the Transdanubian Range. Garnet, epidote, kyanite, staurolite, and xenotime/monazite crystals suggest fluvial drainage of diverse metamorphic units of the Austroalpine basement from the Eastern- and Southern Alps, which also supplied most of the pre-Mesozoic zircons. However, the unexpectedly high proportion of Variscan ages in the bauxites most likely relate to igneous rocks of the Bohemian Massif, thus suggesting additional long-distance aeolian sources. The new data allow for detailed reconstructions of the Paleogene evolution and palaeogeography of the northeastern Transdanubian range.
The occurrence, shape, structure and eruption style of monogenetic volcanoes, such as maars, tuff rings, tuff cones and scoria cones, are generally governed by several internal (composition of the ...magma, magmatic flux, ascent rate, viscosity, volatile contents) and external conditions (regional and local tectonics, topography, and the presence of surfacial, ground and meteoric water). These controlling factors are together responsible for the eruption style, distribution pattern, volcanic facies architecture and morphology of the monogenetic volcanic landforms.
The Late Miocene to Pleistocene Bakony–Balaton Highland Volcanic Field (BBHVF) in western Hungary is a typical small sized (<
50 eruption centres), basaltic, intraplate “monogenetic” volcanic field. Generally, initial eruptions of the BBHVF were phreatomagmatic (n
=
~
28); however, a lesser number (n
=
~
14) of predominantly scoria cone forming eruptions are also inferred. The temporal distribution of the Strombolian style scoria cones was concentrated mostly between 3 and 2.5
Ma. A detailed study of the changes in eruption styles recorded in the pyroclastic sequences suggested a change from a conventional phreatomagmatic to a magmatic fragmentation style during the activity of the volcanic field. A clear correlation has been identified between the long-term environmental changes of the region that resulted in a gradual shift from a more phreatomagmatic eruption style to a more magmatic eruption style. Detailed examination of the temporal distribution of K–Ar and Ar–Ar radiometric data, Digital Elevation Model and Dense Rock Equivalent-based volume calculations of eruptive products and origin of pyroclastic rocks (e.g. phreatomagmatic or magmatic) preserved in variously eroded monogenetic volcanoes were utilized to integrate available volcanological and climatological data to identify potential links between external and internal controlling parameters that responsible for long-term eruption style changes.
At least 6 volcanic cycles have been identified by cluster analysis. Time gap between the cycles were vary from 1.66 up to 0.06
Ma, while the average eruption recurrence rate was ~
0.1078
Ma/event. The time-volume diagram of the volcanism of BBHVF have shown time-predictive behavior combined with low magma-flux (total preserved volume ~
2.867
km
3) and output rates (0.53
km
3/Ma for the entire volcanic field and 0.90
km
3/Ma for the last 5
cycles), suggesting that volcanism was largely tectonically-controlled and not magmatically-controlled.
Furthermore, the topographic differences between the northern (“elevated”) and southern (“basin-like”) parts of the volcanic field, are also important in local differences in dominant fragmentation style, because the elevated part of the field was prone to host large, more magmatically-evolved volcanoes, than on the lower, water-saturated, unconsolidated sediments, which favored to the magma/water interaction driven phreatomagmatic fragmentation.
The third controlling parameter, which seems to play an important role in controlling the eruptive style of monogenetic volcanism at BBHVF, was the paleoclimate fluctuation, especially during the time interval of 3.0 to 2.5
Ma. Thus, mainly the long-term environmental changes (e.g. aridification) have been response the shifting fragmentation style from phreatomagmatic to more magmatic ones.
► Environmental changes can influence the fragmentation style of monogenetic volcanoes. ► Volcanism of BBHVF was most likely to control by tectonic forces. ► Eruption activity of BBHVF was characterized by time-predictive behaviour. ► The drier periods are favoured to the formation of scoria cones.
The formation and deformation history of back-arc basins play a critical role in understanding the tectonics of plate interactions. Furthermore, opening of extensional back-arc basins during the ...overall convergence between Africa and Europe is a fundamental process in the overall tectonic evolution of the Mediterranean and adjacent areas. In this frame, Miocene tectonic evolution of the western Pannonian Basin of Central Europe and its connection to inherited Cretaceous structures of the Eastern Alpine nappes are presented.
Revision of published and addition of new structural and thermochronological data, as well as seismic profiles from the western Pannonian Basin is complemented by high-resolution thermo-mechanical numerical modeling in order to propose a new physically consistent tectono-sedimentary model for the basin evolution. The onset of extension is dated as ~25–23 Ma, and higher rates are inferred between 19 and 15 Ma at the south-western part of the area (Pohorje, Kozjak Domes, Murska Sobota Ridge, and Mura-Zala Basin). Rift initiation involved the exhumation of the middle part of the Austroalpine nappe pile along low-angle detachment faults and mylonite zones. The Miocene low-angle shear zones could reactivate major Cretaceous thrust boundaries, the exhumation channel of ultra-high-pressure rocks of the Pohorje Dome, or Late Cretaceous extensional structures. Miocene extension was associated with granodiorite and dacite intrusions between 18.64 and 15 Ma. The Pohorje pluton intruded at variable depth from ~4 to 16–18 km and experienced ductile stretching, westward tilting, and asymmetric exhumation of its eastern side. Terrestrial early Miocene (Ottnangian to Karpatian, 19–17.25 Ma) syn-rift depositional environment in supradetachment basins evolved to near-shore and bathyal one by the middle Miocene (Badenian, 15.97–12.8 Ma). Deformation subsequently migrated eastwards to the western part of the Transdanubian Range (Keszthely Hills) and to newly formed grabens. In this formerly emerged terrestrial area active faulting started at 15–14.5 Ma and continued through the late Miocene almost continuously up to ~8 Ma but basically terminated in the Mura-Zala Basin by ~15 Ma (early Badenian). These observations suggest a ~200 km shift of active faulting, basin formation, and related syn-tectonic sedimentation from the SW (Pohorje and Mura-Zala Basin) toward the Pannonian Basin center. Building on the above described observational and modeling data makes the Pannonian Basin an ideal natural laboratory for understanding the coupling between deep Earth and surface processes.
•Variable extensional structures characterize the western Pannonian Basin.•Exhumation of deeper crustal rocks along detachments occurred in the Miocene.•Depocenters and faulting shifted from basin margin toward basin center.•Thermomechanical modelling predicts depocenter migration within 12 Ma.•Miocene extensional structures reactivated and were bounded to inherited weakness zones.
Gravelly tsunami event beds are well known from some contemporary shores, but they are far less known from the pre-Quaternary depositional record. Lacustrine examples are particularly exceptional. ...Here we present multidisciplinary evidence for a lacustrine cobble to boulder gravel deposited as an onshore paleo-tsunamiite and discuss features that help to identify the depositional setting. The deposit was formed on the rocky shore of a large peninsula within the late Miocene Lake Pannon (Hungary). The lake was several hundred meters deep, and near to the study area it was about 50–80 km wide. The inferred paleo-tsunami deposit includes subangular clasts that are exclusively derived from the underlying Cretaceous sandstone. Imbrication of the bouldery gravel points to landward transport of the clasts, however, a 15-cm-thick lens of cross-bedded sand records an opposing flow direction. The clayey sand matrix contains fossils, i.e. fragmented and articulated mollusc shells, as well as ostracods, that lived on the nearby sandy shoreface and offshore. The facies of the gravel indicates a short-distance transport of clasts typical for an extreme wave event. None of the depositional features e.g. various degree of clast roundness, seaward dipping imbrication, bidirectional transport indicators, clast-supported fabric, large thickness of beds, and lack of grading is either unique to tsunami deposits or excludes storm wave origin. An extreme storm wave origin, however, is discarded in this case, when paleogeography and climate are considered. The combination of matrix-supported fabric, presence of a mixed clayey-sandy matrix in the clast-supported parts, and preservation of articulated mollusc shells, as well as mixture of clasts and fossils from different zones of the shore, identify these beds as paleo-tsunami deposits. As coeval volcanism is not known, a hypothetic tsunami could have been related either to an earthquake along nearby normal faults or to large-scale sliding events on the closely located shelf slope due to rapid deposition or seismic shocks. The recognition of these event beds reinforces structural observations on the syn-depositional character of nearby faults, active after the middle Miocene climax of synrift tectonics in the Pannonian Basin. Thick, boulder-sized onshore paleo-tsunamiites are useful indicators of a paleogeographic situation in which tsunami waves were amplified to produce noticeable beds in the rock record.
Display omitted
•Imbricated cobble to boulder gravel formed as an onshore lacustrine paleo-tsunamiite.•Clay, sand, gravel and articulated shells from different coastal zones were mixed.•Storm origin is discarded due to consideration of paleogeography and climate.•Paleo-seismic events and localized synsedimentary fault activity are indicated.•Major slope failure events and amplifying paleogeography are also indicated.
In the Transdanubian Range, Pannonian Basin, Hungary, karstic sinkholes on a planation surface of Triassic carbonates are filled by grey clayey–silty kaolin deposits. The provenance and accumulation ...age of these strongly altered terrestrial karst-filling sediments are constrained by X-ray powder diffraction, heavy mineral analysis and zircon U–Pb dating. The heavy minerals of the Southern Bakony Mountains samples are dominated by the ultra-stable zircon–rutile–tourmaline association. Zircon U–Pb data indicate accumulation between 20 and 16 Ma. Furthermore, Archaean to Palaeogene grains were also determined, reflecting the principally fluvial recycling of Eocene bauxites and their cover sequences. In contrast, the sample from the Keszthely Hills consists almost exclusively of airborne material including zircons of 18–14 Ma, reflecting a dominant contribution from the Carpathian–Pannonian Neogene volcanism. The shift in the Miocene age components is inferred to have been caused by the landscape evolution and burial history of the planation surface remnants controlled by local block tectonics.
Combined sedimentological and structural analysis was carried out in the field and on 2D seismic reflection profiles to recognize pre-orogenic structures in a Cretaceous fold-and-thrust belt. ...Detailed field observations were made in the Keszthely Hills, Western Hungary, while 2D seismic interpretation was carried out in the neighbouring Zala Basin. As a result, a fault-controlled intraplatform basin system was identified by a detailed analysis of bounding faults, and related outcrop-scale structures. The Norian–Rhaetian (227–201.3 Ma) synsedimentary faulting was associated with talus breccia formation, small-scale faulting, and dyke formation, in addition to slumping and other soft-sediment deformations. Based on the distribution of talus breccia, WNW–ESE-trending map-scale normal faults were identified in the Keszthely Hills, which is in agreement with the directly observed outcrop-scale synsedimentary faults. On seismic sections, similar WNW- or NW-trending Late Triassic normal faults were identified based on thickness variations of the syn-rift sediments and the presence of wedge-shaped bodies of talus breccia. Normal faulting occurred already in the Norian, and extensional tectonics was active through the Early and Middle Jurassic. The Late Triassic grabens of the western Transdanubian Range could be correlated with those in western part of the Southern Alps, and the Bajuvaric nappe system of the Northern Calcareous Alps. These grabens were situated on the proximal Adriatic margin, and they represent the first sign of the Alpine Tethys rifting. The locus of extension was laterally migrated westward, towards the distal Adriatic margin during Early and Middle Jurassic.
Large rivers can act as important ecological barriers for small mammals, but their exact role is debated. Here we examine the effect of the river Danube on populations of the European ground ...squirrel, an important representative of steppe communities, by studying the Quaternary history both of ground squirrels and of the Danube in the Pannonian Basin, in Hungary. The Danube experienced considerable channel changes during the Quaternary, with >100 km westward shift of its middle reach, interrupted by temporary eastward movements. Besides autogenic river processes, tectonically induced avulsions have played a role in re-routing channels. Three of the four Spermophilus species certainly extended their ranges on both sides of the Danube, referring to repeated river crossings during the Quaternary. Hydrological events, most importantly rapid river course changes (avulsions) but also meander cut-offs are viable mechanisms to enable ground squirrel populations to cross large rivers. On longer timescales, oscillating river course changes can maintain gene exchange across the river.
Mega-yardangs are known to form under extremely arid, warm or in some instances moderate climates. Here we report on the mega-yardang field of the Pannonian Basin (Hungary), which was uniquely formed ...under periglacial, probably semi-arid conditions, and discuss its implications on factors controlling yardang formation in general.
The yardang field is composed of advanced, streamlined forms and of less aerodynamic ridges separated by well-developed corridors. The length of the largest features exceeds 60
km, their height varies around 150
m. Together with ventifacts, deflation hollows and wind-blown sand areas, the yardang field is part of an integrated eolian feature system driven by northerly to northwesterly winds. Dating of ventifact surfaces with in situ produced cosmogenic nuclides places the onset of significant wind erosion to the Early Pleistocene (1.5
Ma). OSL-dated young loess, from which well-developed yardangs were sculpted, and wind-blown sands show that eolian action continued until the early Holocene. The long temporal range of wind erosion compared to average yardang formation rates and the rarity of advanced yardang forms indicate intermittent and relatively short, most probably millennial-scale deflation periods. Since the Early Holocene the system has been inactive, and demonstrates that yardangs can persist in a recognizable form for several millennia even under less arid conditions.
The main control on yardang formation appears to be the existence of strong unidirectional winds, in the Pannonian Basin facilitated mainly by the channeling effect of topographic lows in the surrounding mountain chains. Yardangs can form even under semi-arid climates; however, the rarity of these occurrences suggests that this requires a special association of environmental conditions. Yardang formation is facilitated by homogeneous lithology, namely by widespread weakly consolidated, sandy sediments. The distribution of yardang fields is controlled by vertical neotectonic movements, which provided uplifted areas to be sculptured and topographic obstacles that sheltered downwind sediments. Faulting can be excluded as a controlling factor in mega-yardang formation, nor is the role of jointing supported.
► In the Pannonian Basin we identified the northernmost mega-yardang field. ► It was formed under periglacial conditions in the Pleistocene. ► Yardangs can form in cold climates and under semi-arid conditions. ► The main control on yardang formation appears to be strong unidirectional winds.
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