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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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