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Eperkés Hill is a thoroughly studied classic exposure, yet its facies interpretation is still debated. The issue is whether Upper Triassic - lowermost Jurassic carbonates are regular beds or blocks embedded within the Kimmeridgian-Berriasian limestone. The answer to this question is important for the interpretation of the structural evolution and paleogeography of the Transdanubian Range area at the Jurassic-Cretaceous boundary; we decided therefore to contribute to the solution by applying paleomagnetism to the problem.  We tested several regular beds and suspected olistoliths from two artificial exposures. In order to check the consistency of the paleomagnetic signal on site level, we drilled three or more cores from each, and subjected them to standard paleomagnetic laboratory processing and evaluation.  We found that magnetic parameters were distinctly different for "regular" beds and for suspected olistoliths, but that the paleomagnetic signal was consistent within every site. However, between-site consistency was extremely high for regular beds, but was non-existent for the "megabreccia" horizon. Thus, our results confirm that older limestone was moved and re-deposited during the Late Jurassic-Early Cretaceous, indicating geodynamic conditions similar to those in the Northern Calcareous Alps.

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Partial and pervasive dolomitization of foreslope and toe-of-slope deposits of an early Carnian carbonate platform was investigated to understand the process and mechanism of dolomitization. Based on petrographic observations and C and O isotope data, the dolomitization took place in a near-surface to shallow burial setting; seawater of slightly elevated salinity was likely the dolomitizing fluid. The circulation system was maintained by reflux of evaporated sea water and geothermal heating of cold seawater derived from the surrounding deeper basin. The dolomitization was mostly controlled by the permeability of the platform-derived calcareous sediments.

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Abstract

For comparative studies of Upper Triassic cyclic platform carbonates, the Transdanubian Range (Hungary) and the Pelagonian Zone (Greece) were chosen. Paleogeographically they represent two distant segments of the passive margin of the Neotethys Ocean. During the Late Triassic, on this wide margin a very extensive tropical carbonate platform domain was developed, referred to as the Dachstein-type carbonate platform system. The Transdanubian Range (TR) represents a segment of a continent-encroaching platform system, whereas the Pelagonian-Subpelagonian Zone (PG) may have been a large isolated platform, surrounded by deep-water basins. The discussed Upper Triassic thick platform carbonates (Fődolomit/Hauptdolomit Formation and Dachstein Limestone in the TR, and Pantokrator Formation in the PG) are made up of cyclically arranged facies deposited under similar environmental conditions in the interior zones of carbonate platforms. Three characteristic major facies types can be distinguished: shallow subtidal-lagoonal, intertidal and supratidal-pedogenic, which correspond to the three typical lithofacies (members C, B and A) of Fischer's (1964) Lofer-cycle. The cycles are usually bounded by discontinuity surfaces related to subaerial exposure and pedogenic alteration. The meter-scale (Lofer) cyclicity is predominant throughout the successions. However, various stacking patterns including symmetric complete, truncated, incomplete, and condensed cycles or even alternating peritidal and subtidal facies without any disconformity are recognized in both areas studied. Pervasive or partial early diagenetic dolomitization affected some parts of the cyclic successions in both areas. However, age-dependence of the early dolomitization was clearly demonstrated only in the TR, where the older part of the platform carbonate succession was subject to pervasive dolomitization, whereas the younger part is non-dolomitized and there is a transitional unit between them. This trend is attributed to the climate changing from semiarid to more humid. The Upper Triassic platform carbonates of the TR and PG show strikingly similar features concerning the litho- and biofacies, the stacking pattern and the thickness of the elementary cycles, despite their distant and different paleogeographic setting within the western Neotethys realm. This suggests a eustatic signal, i.e. the cyclic deposition was essentially controlled by orbitally-forced eustatic sea-level changes, although the contribution of autocyclic mechanisms cannot be excluded either. Definite signatures of subaerial exposure (karstic features and vadose meteoric diagenesis) at and below the cycle boundaries also support allocyclic control. In the northeastern part of the TR the carbonate platform was drowned at the Triassic-Jurassic boundary, whereas platform conditions persisted until the end of the Hettangian in the southwestern part. However, the Hettangian part of the succession is characterized by non-cyclic subtidal limestone, implying an upward-deepening trend. In contrast, in the PG the platform conditions continued until early to middle Liassic, and the Liassic succession is typified by well-developed pedogenic features, suggesting long-lasting subaerial exposure intervals, i.e. an upward-shallowing trend.

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The Middle Triassic Wetterstein Limestone was investigated on the Feuerkogel, in the eastern Höllengebirge area, Austria. Cephalopod-bearing coquina interbeds consisting predominantly of orthocone cephalopods were found within the dasycladacean inner platform lagoon facies. Based on sedimentological studies the coquina beds are interpreted as storm accumulations. Dasycladacean biostratigraphic data permit assigning the studied succession to the Late Anisian-Early Ladinian interval. Ammonites of age-diagnostic value found in the coquina horizon suggest the Avisianum Subzone of the Reitzi Zone that corresponds to the upper part of the Anisian.

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Abstract

In the Middle Anisian, extensional tectonic movements led to the development of isolated carbonate platforms in the area of the southwestern part of the Transdanubian Range. The platforms are made up of meter-scale peritidal–lagoonal cycles bounded by subaerial exposure surfaces. One of the platform successions (Tagyon Platform) consists predominantly of limestone that contains partially and completely dolomitized intervals, whereas the other one (Kádárta Platform) is completely dolomitized. Drowning of the platforms took place in the latest Pelsonian to the early Illyrian interval when submarine highs came into existence and then condensed pelagic carbonate successions with volcanic tuff interbeds were deposited on the top of the drowned platforms from the late Illyrian up to the late Ladinian. The comparative study of dolomitization of the coeval platforms, affected by different diagenetic histories, is discussed in the current paper. Traces of probably microbially-mediated early dolomitization were preserved in the slightly dolomitized successions of the Tagyon Platform. This might also have been present in the successions of the Kádárta Platform, but was overprinted by geothermal dolomitization along the basinward platform margin and by pervasive reflux dolomitization in the internal parts of the platform. The Carnian evolution of the two submarine highs was different, and this may have significantly influenced the grade of the shallow to deeper burial dolomitization.

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Abstract

The Mid-Hungarian (or Zagreb-Zemplin) Line of WSW-ENE strike divides the Pannonian basement into two mega-units, the Tisia Composite Terrane in the SE and the ALCAPA Composite Terrane in the NW. They became juxtaposed no earlier than the Middle Miocene (Karpathian). Their present adjacent zones show very different Variscan and Alpine evolution and relationships, which are briefly reviewed here and confronted in the light of detailed correlational work published during the last decade. The present contribution summarizes Variscan and Alpine evolution of units/terranes juxtaposed along the Mid-Hungarian Line, the major terrane boundary in the pre-Neogene basement of the Pannonian Basin, as can be seen on the Circum-Pannonian terrane maps.

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Abstract

In the Pilis Range, NW of Budapest, contemporaneous Upper Triassic platform and basin facies occur. The paper presents the extent and basic characteristics of these facies with interpretation of their depositional conditions, and summarizes the available biostratigraphic data. Based on previous and recent studies a general depositional model is displayed and the history of the basin evolution is outlined. Within the Dachstein Platform an extensional intraplatform basin (Feketehegy Basin) came into existence during the middle part of the Norian. An asymmetric basin was formed, bounded by steep and gentle slopes, respectively. The platform progradation that may have resulted in the termination of the basin began at the gentle margin probably in the latest Norian-earliest Rhaetian.

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Acta Geologica Hungarica
Authors:
János Haas
,
Ágnes Görög
,
Sándor Kovács
,
Péter Ozsvárt
,
Ilona Matyók
, and
Pál Pelikán

The basement of the Pannonian Basin is made up of tectonostratigraphic terranes of varying origin. They gradually amalgamated to form the large Alcapa and Tisza-Dacia composite terranes that were juxtaposed during the Tertiary. In North Hungary, in the basement of the Tertiary volcanic complex of the Mátra Mts and in the western part of the Bükk Mts, remnants of a Jurassic accretionary wedge were encountered. Ore exploration boreholes encountered several hundred-meter thick carbonate and siliceous shale-radiolarite successions in the basement of the Mátra Mts (Darnó Complex). Based on detailed studies of Core Recsk-109, the carbonate succession consists predominantly of grainstone with packstone-wackestone intercalations. Peloidal bioclastic grainstone is the most common texture type but sand-sized intraclasts and oncoid and ooid grains also occur locally. The most spectacular feature is the large amount of coarse to medium sand-sized fragments of calcified cyanobacteria ("Porostromata"). Platform-derived foraminifera and fragments of crinoids are also common. Gravity flows transported the carbonate detritus to the site of deposition at the lower foreslope and proximal toe-of-slope. Based on foraminifera the succession is Aalenian? or Early Bajocian in age.  In the southern part of the Bükk Mts fine-grained, graded oolitic, peloidal grainstone with shale and radiolarite interlayers occur in surface exposures and cores (Bükkzsérc Limestone Formation). These deposits were formed via turbidity currents in a basin relatively far from the carbonate producing platforms. Based on foraminifera the age of the formation is Early Bajocian-Bathonian. Radiolarian faunas suggesting Late Bajocian-Early Bathonian and Early Bathonian-Early Callovian age respectively, were found in a silicified carbonate and radiolarite succession that occurs below the Bükkzsérc Limestone with a tectonic contact. In the wider region Middle to Late Jurassic carbonate platforms and reef facies are known only in the Dinarides, in the area of the Adriatic (Dinaridic) Carbonate Platform. Coeval platform-derived redeposited carbonates and intercalated pelagic basin deposits were reported from the slopes of the Adriatic platform and the periplatform basins of the Slovenian Trough and the Bosnian Flysch Zone. These data confirm the previously suggested paleogeographic connections between the Dinaridic units and the Darnó and Bükk units during the Jurassic

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Acta Geologica Hungarica
Authors:
János Haas
,
Kinga Hips
,
Pál Pelikán
,
Norbert Zajzon
,
Annette E. Götz
, and
Edit Tardi-Filácz

The Permian/Triassic boundary was recognized in continuous marine successions in several outcrops in the Bükk Mts, North Hungary and in a few core sections in the northeastern part of the Transdanubian Range. In the Bükk Mts, of four studied boundary sections only two proved to be complete. They represent an outer ramp setting. In these sections the topmost Permian is made up of dark gray limestone, rich in fragments of crinoids, calcareous algae, mollusks, brachiopods, ostracods, and foraminifera. There is a dramatic decrease in the amount of the bioclasts in the last two limestone layers, which are overlain by a 1 m-thick shale bed. The lower two-thirds of this bed still contain Permian fauna but its upper part is almost free of bioclasts. The overlying platy limestone contains a pauperized fossil assemblage indicating stress conditions. The two core sections studied in the Transdanubian Range represent an inner ramp setting. The uppermost Permian is made up of lagoonal-sabkha cycles. It is overlain by subtidal packstone-grainstone, rich in Late Permian fossils. Oolitic facies characterizes the boundary interval. Onset of ooid formation was probably the consequence of biotic decline leading to cessation of skeletal carbonate production. Along with oolite beds, stromatolites, micrite with "microspheres" and fine siliciclastic microlayers characterize the basal Triassic succession, reflecting overall stress conditions and the changing energy of the depositional environment.

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Central European Geology
Authors:
János Haas
,
Tamás Budai
,
István Dunkl
,
Éva Farics
,
Sándor Józsa
,
Szilvia Kövér
,
Annette E. Götz
,
Olga Piros
, and
Péter Szeitz

The 1,200-m-deep Budaörs-1 borehole provided important data for our understanding of the stratigraphy and tectonic setting of the southern part of the Buda Hills. Although previous reports contained valid observations and interpretations, a number of open questions remained. The importance of this borehole and the unsolved problems motivated us to revisit the archived core. The new studies confirmed the existing stratigraphic assignment for the upper dolomite unit (Budaörs Dolomite Formation) as the dasycladalean alga flora proved its late Anisian to Ladinian age assignment. An andesite dike was intersected within the Budaörs Dolomite. U–Pb age determination performed on zircon crystals revealed a Carnian age (~233 Ma), and settled the long-lasting dispute on the age of this dike, proving the existence of a Carnian volcanic activity in this area after the deposition of the Budaörs Dolomite. Palynostratigraphic studies provided evidence for a late Carnian to early Norian age of the upper part of the lower unit (Mátyáshegy Formation). This result verified an earlier assumption and reinforced the significance of the tectonic contact between the upper unit (Budaörs Formation) and the lower unit (Mátyáshegy Formation). Based on structural observations and construction of cross sections, two alternative models are presented for the structural style and kinematics of the contact zone between the Budaörs and Mátyáshegy Formations. Model A suggests a Cretaceous age for the juxtaposition, along an E–W striking sinistral transpressional fault. In contrast, model B postulates dextral transpression and an Eocene age for the deformation. The latter one is better supported by the scattered dip data; however, both scenarios are considered in this paper as possible models.

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