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Haas J.,Geophysical and Space Science Research Group | Lukoczki G.,Geophysical and Space Science Research Group | Lukoczki G.,University of Alberta | Budai T.,Geological and Geophysical Institute of Hungary | Demeny A.,Hungarian Academy of Sciences
Facies | Year: 2015

In the Late Triassic, a 2–3-km-thick platform carbonate succession formed along the passive margin of the Tethys Ocean. Certain parts of the succession were affected by pervasive dolomitization whereas other parts are only partially dolomitized or non-dolomitized. In the Transdanubian Range, Hungary, the Upper Triassic platform carbonates are extensively distributed and numerous data are available for the space and time relations of the dolomitized and non-dolomitized units. This geological setting provides a unique opportunity for the study of paleogeographical and diagenetic controls of dolomitization of the whole platform complex. This paper presents the characteristic features of the dolomite types of the dolomite-bearing formations and lithofacies types, with a view to interpret the dolomite-forming processes and to determine the main controlling factors of the dolomite genesis. Petrographic features and stable isotope characteristics of the studied successions suggest the predominance of penecontemporaneous and early diagenetic dolomite genesis. Study of the transitional interval between the pervasively dolomitized and the non-dolomitized sequences revealed the general presence of microcrystalline dolomite in the peritidal microbial deposits and the characteristics of partial dolomitization both in the peritidal and subtidal facies. In the peritidal facies, microbially induced Ca–Mg carbonate precipitation is inferred, which was probably complemented by penecontemporaneous mimetic dolomitization of precursor carbonates due to evaporative pumping or seepage influx. Dolomitization of the subtidal facies took place via reflux of slightly evaporated seawater. Dolomitization of the previously deposited carbonate mud commenced during subsequent subaerial exposure but the process of early diagenetic dolomitization may have continued during later exposure events. Recurring subaerial exposure is one of the factors that determine the areal extent of the early dolomitization of the platform carbonates. However, climatic conditions were also crucial. Although the sea-level-controlled, unconformity-bound cyclic facies pattern did not change significantly in the internal platform belt during the nearly 20-My-long time range, a drier climate favored dolomite formation while increasing humidity led to a gradual decreasing intensity of early dolomitization. © 2015, Springer-Verlag Berlin Heidelberg.

Botfalvai G.,Eötvös Loránd University | Botfalvai G.,MTA ELTE Lendulet Dinosaur Research Group | Haas J.,Geophysical and Space Science Research Group | Bodor E.R.,Geological and Geophysical Institute of Hungary | And 4 more authors.
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2016

The Csehbánya Formation (Santonian), exposed in the Iharkút open-pit, Bakony Mountains, Hungary, is made up of a cyclic alternation of conglomerate, sandstone, and variegated siltstone and clay deposited in a fluviolacustrine environment. As a result of continuous excavation since 2002 it has yielded rich and diverse continental vertebrate and plant assemblages. A facies and architectural analysis of the Csehbánya Formation at this location identified four main lithofacies associations with eight subtypes consisting of (1) lenticular sandstones representing river channels, (2) conglomerates with sandstone (coarse grained likewise representing channel deposits), (3) heterolithic-channel fill (high density flash flow deposits) (4) splay sandstones produced by crevasse splays, (5) dark sandy siltstone (small-scale stagnant pool deposits with high organic content), (6) greenish-grey claystone (deposits of shallow lakes and ponds), (7) reddish (moderately drained) paleosols, and (8) yellowish, mottled (hydromorphic) paleosols.The sedimentological investigations revealed that the terrestrial deposits exposed by the Iharkút open-pit were formed in an anastomosing fluvial system because: (i) the alluvial architecture is characterized by large proportion of overbank deposits encasing the channel sandstone bodies, (ii) the ribbon shaped sandstone bodies are dominant, (iii) cross-bedding and lateral accretion are almost completely absent in the channel fill deposits and (iv) the sandstone bodies are clearly isolated from each other, embedded in floodplain sediments, suggesting multiple co-existing channels.The most important vertebrate fossil site (SZ-6) was examined in special detail because it shows peculiar lithological features. The layers richest in fossils (Unit 1) of SZ-6 site are interpreted as a lag deposit formed during an episodic high density flash flood event representing a relatively short time interval, i.e., probably within a single rainy season. © 2015 Elsevier B.V.

Hips K.,Geophysical and Space Science Research Group | Haas J.,Geophysical and Space Science Research Group | Gyori O.,Geophysical and Space Science Research Group
International Journal of Earth Sciences | Year: 2015

Dolomitization of relatively thick carbonate successions occurs via an effective fluid circulation mechanism, since the replacement process requires a large amount of Mg-rich fluid interacting with the CaCO3 precursor. In the western end of the Neotethys, fault-controlled extensional basins developed during the Late Triassic spreading stage. In the Buda Hills and Danube-East blocks, distinct parts of silica and organic matter-rich slope and basinal deposits are dolomitized. Petrographic, geochemical, and fluid inclusion data distinguished two dolomite types: (1) finely to medium crystalline and (2) medium to coarsely crystalline. They commonly co-occur and show a gradual transition. Both exhibit breccia fabric under microscope. Dolomite texture reveals that the breccia fabric is not inherited from the precursor carbonates but was formed during the dolomitization process and under the influence of repeated seismic shocks. Dolomitization within the slope and basinal succession as well as within the breccia zones of the underlying basement block is interpreted as being related to fluid originated from the detachment zone and channelled along synsedimentary normal faults. The proposed conceptual model of dolomitization suggests that pervasive dolomitization occurred not only within and near the fault zones. Permeable beds have channelled the fluid towards the basin centre where the fluid was capable of partial dolomitization. The fluid inclusion data, compared with vitrinite reflectance and maturation data of organic matter, suggest that the ascending fluid was likely hydrothermal which cooled down via mixing with marine-derived pore fluid. Thermal gradient is considered as a potential driving force for fluid flow. © 2015 Springer-Verlag Berlin Heidelberg

Szanyi G.,MTA CSFK GGI | Suranyi G.,Geophysical and Space Science Research Group | Leel-ossy S.,Eötvös Loránd University
Quaternary Geochronology | Year: 2012

Several thermal karstic caves are known in the Rózsadomb area of Budapest, Hungary. On a small, 5-6 km2 territory more than 50 km of cave passages were mapped and documented to host significant cave raft deposits. Cave rafts precipitate at the surface of karst water lakes, and are potential indicators of former karst water levels.Thirty-two samples of cave rafts collected from different elevations in Pál-völgy Cave and five from Szemlo{doubleacute}-hegy Cave were dated by U-series methods using single-collector ICP-MS. Nine samples were older than 450 ka, the upper limit of U-series age determination. Uplift of the area and the associated history of karst paleo-water levels was assessed using the age and present-day elevation above sea level of the cave rafts.A two-phase uplift history was revealed. A slow emergence of the area was succeeded by more rapid uplift. Its beginning varies from cave to cave, suggesting differential movements of 0.15-0.32 mm/y. © 2012 Elsevier B.V.

Economically important black shale-hosted manganese carbonate deposits occur in certain parts of the Transdanubian Range in Hungary. These ore deposits were formed in a short interval coinciding with the Early Toarcian global anoxic and mass extinction event that was associated with drastic perturbations of the oceanographic conditions. During the Early Jurassic the Transdanubian Range Unit was located between two ocean basins. Simultaneous opening of these two basins created an extensional regime resulting in a complex topography with tectonically-controlled small scale basins above an attenuated continental lithosphere. Sluggish circulation led to the development of layered water masses in certain parts of these basins, with oxygenated upper and oxygen-depleted lower reservoirs. This paleogeographic and paleoenvironmental setting favoured the microbially-mediated accumulation of manganese and iron. © 2011 Elsevier B.V..

Kiss G.,Eötvös Loránd University | Molnar F.,Eötvös Loránd University | Palinkas L.A.,University of Zagreb | Kovacs S.,Geophysical and Space Science Research Group | Horvatovic H.,Geological Survey of Bosnia and Herzegovina
International Journal of Earth Sciences | Year: 2012

Comparative volcanological, mineralogical, petrological, and geochemical studies of blocks of Triassic submarine basalt occurrences hosted by the Jurassic mélange have been carried out. The studied localities are located in displaced parts of the Dinarides in NE-Hungary (Darnó Unit), in the Dinarides (Kalnik Mts., Croatia and Vareš-Smreka, Bosnia and Herzegovina), and in the Hellenides (Stragopetra, Greece). The common characteristic of the studied occurrences is the well observable result of the lava-water-saturated sediment mingling, i. e., the presence of the so-called carbonate peperitic facies. Mixing of the basaltic lava with pelagic lime mud (representing the unconsolidated stage of the red, micritic limestone), as well as fluid inclusion and chlorite thermometry data support that the carbonate peperite was formed above CCD and at the Bosnian locality, a shallower water, about 1.4 km depth is proven. The igneous rocks show mainly within-plate basalt geochemical characteristics; MORB signatures are not common. Low temperature (<200°C) hydrothermal alteration is characteristic to the pillow basalt blocks with peperitic facies. The similarities in the volcanological, geochemical, and textural characteristics observed at the different localities support a strong genetic connection among them. The results of this study suggest to the advanced rifting stage origin of the Triassic basaltic suits and their distinction from the true oceanic basalt pillow units of the Dinarides can be based on the occurrences of the peperite facies. © 2011 Springer-Verlag.

Hips K.,Geophysical and Space Science Research Group | Haas J.,Eötvös Loránd University | Poros Z.,Geophysical and Space Science Research Group | Poros Z.,ConocoPhillips | And 2 more authors.
Sedimentary Geology | Year: 2015

Dolomite most commonly forms via replacement of precursor carbonate minerals. For this reason, diagnosing primarily precipitated organogenic dolomite in microbial mat deposits from the rock record is not straightforward, even though the deposits exhibit microbial fabric. Single and multiple dolomite crusts exhibiting microbial fabric occur in a pervasively dolomitized Middle Triassic platform succession. Two sections were studied in the Transdanubian Range. In both sections, two fabric types occur in the upper part of the metre-scale cycles. One of that is microbial boundstone (fabric type 1)-characterised by clusters of dolomite microcrystals which display diagnostic microbial features, such as calcimicrobes, clotted-spherular aggregates and globules. The other one is different in the two sections. In Section 1, it is micritic dolomite (fabric type 2) that is characterised by predominantly fine crystals and contains obscured microbial components. In Section 2, it is bioclastic dolomite (fabric type 3) that is rich in reworked dasycladalean alga fragments and consists of dolomite crystals of wide size-range from fine to coarse. The precipitation of the microcrystalline dolomite phase is interpreted as being facilitated by mats and biofilms favouring/tolerating an increasing frequency of subaerial conditions in the upper intertidal setting. Petrographic analyses revealed that organogenic calcite was also precipitated, especially in mat deposits rich in bioclasts. Synsedimentary dolomitization, resulting in fine crystals, was coupled with aragonite dissolution and it postdated the organogenic precipitation. It took place only in the peritidal caps of the shallowing-upward depositional units. Petrographic analyses provide circumstantial evidence constraining that microcrystalline dolomite did not form via mimetic replacement. Accordingly the microcrystalline dolomite, which shows microbial microfabrics in the studied samples, is interpreted as an organogenic primary precipitate. Both peritidal processes, dolomite precipitation and replacement, were likely controlled by the environmental factors in a semi-arid climate. Those components of the platform succession that were not dolomitized in the peritidal environment were replaced and cemented by medium and coarsely crystalline dolomite during further burial at elevated temperature, as shown by fluid inclusion homogenisation temperature (62 to 83. °C) and negative stable oxygen isotope values. Thus, the majority of the studied formation consists of fabric-destructive dolomite (fabric type 4). © 2014 Elsevier B.V.

Ozsvart P.,MTA MTM ELTE Research Group for Paleontology | Kocsis L.,University of Lausanne | Nyerges A.,MTA MTM ELTE Research Group for Paleontology | Gyori O.,Geophysical and Space Science Research Group | And 2 more authors.
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2016

We studied two boreholes (Cserépváralja-1 and Kiscell-1) with continuous sedimentary records across the Eocene-Oligocene climate transition from the Central Paratethyan area. Assemblages of benthic foraminifera display a shift in dominance by epifaunal taxa in the late Eocene to shallow and deep infaunal taxa in the early Oligocene. Using the benthic foraminiferal oxygen index (BFOI), a decreasing trend of bottom-water oxygen levels is established across the Eocene-Oligocene transition (EOT), leading to the development of dysoxic conditions later in the early Oligocene. Trends in δ18O and δ13C values measured on tests of selected benthic and planktic foraminifera roughly parallel those of the global record of stepped EOT δ18O increase and deviate only later in the early Oligocene, related to the isolation of the Paratethys. The overall similarity of the isotope curves and the presence of a planktic-benthic ecological offset suggest that the original isotope trends are preserved, despite the systematically more negative δ18O values. Of different scenarios, a quasi-uniform diagenetic overprint by fluids with low δ18O values, during burial or uplift, appears best supported. We conclude that the globally established isotopic expression of Antarctic ice sheet growth across the EOT may be recognizable in the Paratethys. Deviations from the global trends after the EOT were caused by regional paleoceanographic changes induced by the progressing Alpine orogeny and sea-level change, which led to a restricted connection with the open ocean, freshwater influx from increased precipitation, and gradual development of bottom-water oxygen depletion. © 2016 Elsevier B.V.

Leel-Ossy S.,Eötvös Loránd University | Szanyi G.,HAS Geodetic and Geophysical Research Institute | Suranyi G.,Geophysical and Space Science Research Group
International Journal of Speleology | Year: 2011

With the discovery of the József-hegy Cave, a cave of hydrothermal origin with an abundance of minerals unknown so far in Hungary came to light. Diversity and the frequency of the occurrence of crystals make this cave similar to the Lechuguilla Cave, even if the dimensions of the mineral precipitations and the passages do not compare in scale. The variety and mass of carbonates and sulphates are surprising. This paper describes the minerals and speleothems of the József-hegy Cave, their occurrence and genesis, including determined ages. The 41 U/Th measurements suggest that speleothems begun to develop in the upper level of the cave more than 350 ka ago. Some of these dated old speleothems were developing in dry passages, thus the uppermost passages of the József-hegy Cave have been dry at least for 350 ka. The karst water level was still at the main passage 200 ka ago and dropped to 120 m asl by the time of ~100 ka before present.

Horvath B.,Eötvös Loránd University | Hips K.,Geophysical and Space Science Research Group
Austrian Journal of Earth Sciences | Year: 2015

Microfacies types presented here are based on thin section analysis of more than 1.500 samples from drilling cores, surface sections and several outcrops from Middle and Upper Triassic slope and basin carbonates in the Aggtelek‒Rudabánya Hills (Hungary). The observed compositional and textural types were grouped into five microfacies associations which are characteristic for slope and basin environments. The clotted micrite “boundstone” typically contains bioclasts, peloids and stromatactis structures. The inhomogeneous clotted micrite-rich groundmass suggests that the sediment originated from mats or mounds enriched in organic matter. Bioclastic wackestone with radiolarians, pelagic bivalve shells and signs of bioturbation was likely deposited in deep-water basinal environment. Bioclastic grainstone‒packstone and bivalve‒crinoid packstone deposited from turbidity currents which often occurred along the slope. The mudstones can be found after events of sudden deepening, mostly related to the drowning of the Steinalm platform. Data based on comparison of stratigraphical logs show that the Middle Triassic was characterised by rapid deepening followed by the formation and expansion of a carbonate slope. During the Late Triassic, the breakup of the Wetterstein platform had an effect on slope environment as well. © 2015, Austrian Geological Society. All rights reserved.

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