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Acta Geologica Hungarica
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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The Mesozoic complex of Darnó Hill area in NE Hungary, according to well core documentation, is made up of two units. The upper unit, the Darnó Unit s.s., consists predominantly of blocks of ophiolitic rocks (pillow and massive basalt, gabbro) and subordinate abyssal sediments (red radiolarite and red pelagic mudstone of either Ladinian-Carnian or Bathonian-Callovian age, as well as bluish-grey, sometimes blackish siliceous shale of the latter age). The basalt is geochemically of MOR type, based on earlier evaluations. However, it comes in two types: reddish or greenish amygdaloidal pillow basalts with peperitic facies containing reddish micritic limestone inclusions, and green basalts without any sedimentary carbonate inclusion. The former type is probably Middle- Triassic, advanced rifting stage-related basalt, whereas the latter is probably of Jurassic age, corresponding to the Szarvaskõ-type basalt of the western Bükk Mountains. Pre-Miocene presence of an ultramafic sheet above the complex is indicated by serpentinite pebbles in the Lower Miocene Darnó Conglomerate.

The lower unit, corresponding to the Mónosbél Unit of the western Bükk Mountains, consists of lower slope and toe-of-slope type sediments: dark grey shale and bluish-grey siliceous shale of Jurassic age, both showing distal turbiditic character, with frequently interbedded carbonate turbidites and debris flow deposits containing cm- to dm-sized limestone and micaceous sandstone clasts. One to ten m-sized slide blocks of reddish, siliceous Triassic Bódvalenke-type limestone associated with the above-mentioned reddish, amygdaloidal basalt also occur. In one of the studied cores a block comprising evaporitic siliciclastics akin to those of the Middle Permian Szentlélek Formation and black, fossiliferous limestone similar to the Upper Permian Nagyvisnyó Limestone Formation of the Bükk Mountains, was also encountered.

A preliminary comparison with similar Triassic advanced rifting-type basalt and limestone/radiolarite of the western ophiolite zone of the Balkan Peninsula is presented (Fig. 1): the Zagorje region of NW Croatia, the Zlatibor-Zlatar Mountains of SW Serbia, and the North Pindos and Othrys Mountains, as well as Euboea Island, of Northern Greece. We propose the terms “Loggitsi Basalt” for such Triassic basalt containing peperitic facies, after the village of Loggitsion located in the central part of the Othrys Mts, and “Bódvalenke Limestone” for the transitional facies between Hallstatt Limestone and Triassic red radiolarite, after the village of Bódvalenke located in the Rudabánya Hills. The northwesternmost occurrence of both of these typical Neotethyan formations can be found in NE Hungary (Darnó Hill and Bódva Unit of Rudabánya Hills, respectively).

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