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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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