Subaqueous volcaniclastic successions in the Middle Triassic of Western Hungary

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Triász platform- és medencefáciesek kapcsolata a Pilis vonulatban = Relationship between Triassic platform and basin facies of the Pilis Range

A Pilis Dachsteini Mészkő kifejlődését peritidális és sekély szubtidális rétegtagokból felépülő, ciklusos rétegsor jellemzi, amely a biosztratigráfiai vizsgálatok szerint a nori emeletbe tartozik. A Dachsteini-platform pereméhez közeli lejtőfáciest lito- és bioklasztokból, valamint bekérgezett szemcsékből álló durvaszemcsés üledék alkotja, amely alatt a platformlagúnára és a medencére jellemző kagylók viharok által átülepített kokvinái együtt fordulnak elő. A Dachsteini Mészkővel részben heteropikus Feketehegyi Mészkő rétegsorát disztális tempesztit- és medencefáciesű rétegek váltakozása építi fel. A Feketehegyi Mészkőben található átülepített zöldalga-töredékek nori korú flórát jeleznek az egyidős Dachsteini platformon. A Pilis Dachsteini Mészkő rétegsora a Tethys selfjén kialakult sekélytengeri platform háttérlagúnájában képződött a nori során. A nori közepén aktivizálódott extenziós tektonika hatására jött létre a platformon belül a félárok-jellegű Feketehegyi-medence, amelynek lankás oldalán egyenlejtes rámpa jött létre, sekélytengeri kagyló-kolóniákkal és viharüledékekkel. A kiemelt helyzetben maradt blokkok peremét foltzátonyokkal tarkított ooid-homokdombok alkották, bekérgező szervezetekkel. A medence mélyebb régiójában ugyanakkor disztális turbiditek és medenceüledékek rakódtak le. A késő-nori legnagyobb elöntés idején a Feketehegyi-medence nyitottabbá vált, majd az ezt követő magas vízállás idején a platformlejtő előrenyomult a medence irányába a nori–rhaeti határán. | The Pilis Hills are made up predominantly of the Dachstein Limestone of Norian age. It is characterised by alternation of peritidal and shallow subtidal Lofer cycles. However, coeval basin facies with distal tempestite interlayers (Feketehegy Limestone) also occur in the Pilis. Redeposited fragments of Norian green-algae constrain the synchrony of the platform and basin facies. Proximal tempestite beds with mollusc coquina indicate the upper part of low-angle slopes between the basin and the platform. In the northern part of the Pilis, the mollusc coquina beds are overlain by thick limestone of forereef slope facies. The Dachstein Limestone of the Pilis was formed in the internal platform domain of the Dachstein platform system which developed along the margin of the Neotethys during the Late Triassic. As a result of extensional tectonic movements activated in the mid-Norian the half-graben type Feketehegy Basin came into existence. On the low-angle side of this basin a homoclynal ramp was developed where bivalve coquinas and proximal storm deposites were accumulated. Oolitic mounds with patch reefs were developed along the margin of the elevated blocks. Basinal carbonates and distal tempestites were deposited in the deepest part of the basin. At the time of the Late Norian maximum flooding the Feketehegy Basin became more open; it was probably followed by progradation of the ambient platform during the subsequent latest Norian – earliest Rhaetian highstand period

A Dunántúli-középhegység középső-triász földtörténete: medencefejlődés és vulkanizmus = Middle Triassic history of the Transdanubian Range: basin evolution and volcanism

A Dunántúli-középhegység DNy-i részén szigetplatformokkal tagolt tengermedencék jöttek létre a középső-triász során, amelyek kialakulásában jelentős szerepet játszott a szinszediment tektonika. Ezzel szemben a Kelet-Bakonytól ÉK-re lévő területet karbonátplatformok uralták, amelyek között egy kisebb méretű medence léte igazolható a Budai-hegység Ny-i előterében. A platformok épülését (a "karbonátgyár működését") alapvetően a tengerszint relatív változásai határozták meg, ezek között a globális (eusztatikus) hatások elkülöníthetőek a lokális vagy regionális (elsősorban tektonikus, illetve vulkanotektonikus) hatásoktól. A Dunántúli-középhegység középső-triász medencéinek és platformjainak fejlődésében a vulkáni működés nem játszott lényeges szerepet, szemben a Déli-Alpokkal. A késő-anisusi savanyú vulkanizmus üledékei átülepítettek, mállási termékeik azonban jelentősen hozzájárulhattak a tengervíz tápanyag-utánpótlásához. A kelet-bakonyi sekély ladin medencébe egy közeli vulkáni szárazulatról lepusztuló törmelék ugyanakkor nem mutatható ki a Déli-Bakony mélyebb nyílttengeri medencéiben, ami arra utal, hogy a két medence közötti üledékszállítást kiemelt terület gátolta. | In the southwestern part of the Transdanubian Range isolated platforms and basins were formed during the Middle Triassic, controlled by synsedimentary tectonics. The area located northeast of the Eastern Bakony Mts was dominated by carbonate platforms, only a small intraplatform basin can be reconstructed in the western foreland of the Buda Mts. The evolution of the platforms (productivity of the carbonate factory) was basically controlled by relative sea-level changes, which were provoked by global and regional or local (e.g. tectonic or volcanotectonic) influences. Contrary to the Southern Alps, volcanic activity didn't play a decisive role in the evolution of the Middle Triassic basins and platforms of the Transdanubian Range. However, the weathering material of the Late Anisian redeposited acidic volcanic sediments might have significantly supported the nutrient supply of the sea water. Eroded clasts derived from a near volcanic island into the shallow Eastern Bakony ladinian basin can?t be detected in the deeper pelagic basins of the Southern Bakony. This can be explained by the existence of an uplifted area hindering the sediment transport between the two basins

Középső-triász platformkarbonátok és vulkanitok vizsgálata a Latemar környékén (Dolomitok, Olaszország) [Middle Triassic platform carbonates and volcanites in the Latemar area (Dolomites, Italy)]

Sponsored by the T043341 project of the Hungarian Research Found (OTKA) we have investigated the buildup of the Middle Triassic Latemar platform (Western Dolomites), its volcanic stuctures and also basinal successions of the surrounding area. Our leader on the field trip was Nereo Preto from the Padova University. The relatively small isolated Middle Triassic carbonate platform of the Latemar is one of the most famous Triassic platform of the Dolomites. It is surrounded by pelagic sediments of coeval interplatform basins. The main part of the platform is built up by cyclic peritidal to subtidal lagoon facies. Within this succession more than 600 shallowing upward basic cycles were reconstructed and several higher cyclostratigraphic units were defined. These cycles have been interpreted as orbitally forced Milankovič cycles. Based on their concept therefore 14 My were estimated for the duration of the deposition of the whole carbonate sequence. However, on the basis of new biostratigraphic and radiometric data that yielded a duration only between 2 and 4,7 My a group of researchers questioned this interpretation. The Sciliar (Schlern) Formation has been only slightly dolomitized on the Latemar, this causes unique preservation of the fossils. Dasycladacean algae and ammonoids occure together in the platform succession. Correlation of algae and ammonoid zonation can give a chance to use a more accurate and detailed chronostratigraphic chart within the Middle Triassic platforms not only in the Dolomites but in the whole area of the Western Tethys. Ammonite bearing limestone lying above the "lower edifice" belongs to the Avisianum Subzone of the Reitzi Zone (sensu VÖRÖS 1998). Based on our field observations this facies can be interpreted as infilling of a channel which connected the platform-lagoon with the pelagic basin. Within the overlying platform carbonate succession the Crassus and Serpianensis Subzone (sensu MIETTO, MANFRIN 1995) can be detected while in the uppermost part of the section the basal Curionii Zone was also indicated. Preliminary investigations of algae-assemblage show (Fig. 5) that the last occurence of Diplopora annulatissima can be correlated with the base of Secedensis (Nevadites) Zone, while the first occurence of Teutloporella herculea fits to the base of Curionii Zone. The later change in the flora may give the opportunity to fix the newly difined Anisian/Ladinian boundary within thick platform carbonate successions, as well. Being calibrated with ammonite zones the Dasycladacean zonation of the Latemar provides useful tool for chronostratigraphic subdivision of the Budaörs Dolomite (lithostratigraphic counterpart of the Schlern Formation) and for reconstruction of the evolution of Middle Triassic platforms in the Transdanubian Range. A series of dyke swarm cross cuts the carbonate platform of the Latemar. The individual dykes are mafic, aphanitic to microholocrystalline, and they vary in thickness between dm to tens of metres. The dyke margins are generally straight, however, long wavelength and small amplitude undulations have been recognized in case of thick dykes. The dykes have chilled margin up to 10 cm in width. Quench crystals of plagioclase are common in mm-size range and their size increases toward the centre of the dykes. The dykes are more weathered than the surrounding carbonate material, and therefore their location is represented by sharp irregularities in the otherwise flat top of the platform. Along the dyke strikes in the centre of the Latemar three pyroclastic breccia zone have been identified. The southernmost is a complex association of tilted limestone beds that are surrounded by a coarse-grained pyroclastic breccia. They form funnel shape disturbed zone in the carbonate platform with an average width of 150 m. In the pyroclastic breccia, angular shape basaltoid lapilli are common. Basaltoid lapilli are abundant in lherzolite nodules with angular shape and few cm in diameter. Similar, but larger nodules form cumulate zones in the basal region of the exposed volcaniclastic succession. The volcanic clasts are generally altered, but their shape is still angular, and closely resembling their non-abraded, primary origin due to fragmentation of the magma by an explosive volcanic eruption. The volcanic clasts, as well as the intruded irregularly shaped dykes in the lower part of the volcanic pipe are chilled indicating sudden cooling by magma-water interaction as an inferred fragmentation process. In the pyroclastic breccia hosts there are large angular shape blocks of debris that have been derived from the surrounding carbonate platform units. These clasts range cm to few m size in diameter and they are always angular, indicating that they must have been consolidated and hard by the time they have been disrupted by an eruption. In the upper part of the volcanic breccia pipe mega-blocks up to few tens of metres across have been identified. They are tilted, rotated, and form a chaotic zone in the pyroclastic breccia host all indicates that they have been derived from a former conduit/crater wall. The general architecture of the volcanic breccia pipe is inferred to be a diatreme that is an exposed and exhumed volcanic conduit of a former phreatomagmatic volcano. North of the above described diatreme two other pyroclastic breccia body forms a few tens of metres wide semicircular zone. Each of them is rich in angular limestone fragments, gravels, and bedded red lapilli tuff fragments. Carbonate clasts often form trains of clasts indicative of some sort of movement through the pyroclastic breccia zone inferred to be a result of a fluidization through the volcanic pipe. Each pyroclastic breccia pipe shows angularity, chilled margins, microlite-free textural features on the juvenile clasts that are indicative for fragmentation by sudden cooling of magma by magma/water interaction. The identified three pyroclastic breccia pipes are inferred to be diatremes, root zones of former small to medium volume, mafic, phreatomagmatic volcanoes. K/Ar dating of the sample from the diatreme gave an age of 204±7.8 My (Balogh Kadosa pers. comm.). Near to the Latemar on the Dos Capel, a thick succession of pelagic basin fcies (Livinallongo Formation, partly heteropic with the Sciliar Formation) crops out which is interbedded with several dm thick pyroclastic beds of typical "pietra verde". The grading, sorting, lower and upper bed contacts indicate that these beds were predominantly deposited by ash turbidites that carried volcanic material into the basin. Thin layers of fall beds also exist. Near the top of the Dos Capel sequence a well-exposed thickly to thinly bedded, accidental lithic-rich, cross-bedded or stratified, occasionally dune-bedded lapilli tuff and tuff succession crops out. These beds are rich in angular limestone clasts that occasionally form shallow impact sags on the underlying bed surface. The juvenile clasts are angular, chilled, and low in vesicularity, characteristic for juvenile fragments fragmented by phreatomagmatic explosive interaction of melt and water. The large volume of the accidental lithic clasts in the pyroclastic rock units indicates that the magma fragmentation must have occurred in subsurface environment and/or the volcanic conduit was partially closed. On the basis of the preliminary field study and comparison of different volcanic facies in and around the Latemar highlight the possible facies relationships between diatremes that cut through the platform and their eruption fed tephra falls deposited in the pelagic basin and/or produced pyroclastic density currents that may initiated volcaniclastic turbidites transported pyroclasts deep into the basin around the platforms. It is also inferred that in a shallow water environment pyroclastic mounds and associated tuff cones may have produced volcanic islands on top of platforms and an entire lateral facies transition could be expected to be identified in the near future via systematic mapping and interpretation of the pyroclastic successions in the region

Late Triassic platform, slope and basin deposits in the Pilis Mountains, Transdanubian Range, Hungary

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

A triász zátonyok fejlődése a Tethys északi peremén = Evolution of the Triassic Reefs on the Northern Part of the Tethys

Elkészítettük az Aggteleki platform 10 000-es térképét. Két zátonyt különítettünk el. Leírtuk faunájukat és flórájukat, összesen 98 fajt. Egy új fajt (Aggtecella hungarica) és egy új ásványt (nonstrandit) írtunk le. Rekonstruáltuk a platform fejlődését az anisusi-ladin-ban. Egész pontosan meghatároztuk a zátony kialakulás korát: Trinodosus subzona. Az első zátony a Trinososus subzóna kezdetétől a Curionii subzónáig létezett, majd a zátony ÉK-re progradált. Bebizonyítottuk, hogy a Neotethys riftesedése és az Aggteleki zátony kialakulása között ok-okozati összefüggés van. Kimutattuk, hogy minden neptúni telér három időszakban keletkezett: Binodosus-, Trinodosus-, Avisianum subzone. | We finished the 1:10 000 map about the Aggtelek platform. We distinguished two reefs, described their fauna and flora, all together 98 species. We described a new species (Aggtecella hungarica) and a new mineral (nonstrandit). We reconstructed the evolution of the platform during the Anisian-Ladinian. We determined the exact age of the reef forming: Trinodosus subzone. The first reef existed from the beginning of the Trinososus subzone until the Curionii subzone, than the reef prograded to the NE. We proved, that there is a causal relation between the rifting of the Neotethys and the forming of the Aggtelek reef. We justified, that every neptunian dykes originated during three interval: Binodosus-, Trinodosus-, Avisianum subzone

The Budaörs-1 well revisited: contributions to the Triassic stratigraphy, sedimentology, and magmatism of the southwestern part of the Buda Hills

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

Change from shallow to deep-water environment on an isolated carbonate platform in the Middle Triassic of the Transdanubian Range (Hungary)

The stratigraphic and paleoecologic investigations of the Middle Triassic Kádárta section of the western part of the Transdanubian Range (Hungary) let an insight to the drowning of an isolated carbonate platform and the deposition of the following pelagic successions in deep neritic and bathyal environment. The biostratigraphic and radiometric ages revealed the presence of a gap between the Pelsonian (Middle Anisian) shallow-marine carbonates and the overlying deep-water succession, since the onset of pelagic sedimentation was dated as late Illyrian (latest Anisian). This suggests that the study area was located on a relatively high paleotopographic position after the break-up of the Neotethys in the late Pelsonian. Correlation with other localities of the western Neotethys indicates that some sections were located either on rapidly subsiding blocks (e.g., Klisura – Dinarides, Schreierkogel – Northern Calcareous Alps, Baradla Cave – Aggtelek-Rudabánya Unit) or on more emerged highs (Rid – Dinarides). The integrated ammonoid and conodont biostratigraphy accompanied by Usingle bondPb ages provided a good opportunity for correlations with Ladinian key sections (Bagolino, Monte San Giorgio, Rio Nigra) from the Southern Alps