Displaced South Alpine and Dinaridic elements in the Mid-Hungarian Zone

Abstract The Mid-Hungarian Zone is a WSW–ENE trending composite structural unit in the basement of the Pannonian Basin that is made up of displaced crustal fragments (terranes) of South Alpine and Dinaridic origin. In the early stage of the Alpine evolution these fragments were located in various sectors of the NW Neotethys region, representing different paleogeographic settings from passive margin through continental slope to oceanic basement. Middle to Late Jurassic closure of the Neotethys led to the development of a suture zone made up of subduction-related complexes that can be followed all along the strike of the Dinarides. During the Cretaceous compressional stages, nappe stacks were formed from the accretionary complex and the fragments of the previously disrupted passive margin. Eastward extrusion (escape) of the ALCAPA Mega-unit during the Oligocene to Early Miocene led to large-scale displacement of fragments of this nappe stack, transporting them to their present-day position, and resulted in dispersal of the northwestern segment of the suture zone. The paper summarizes the basic characteristics of the dislocated blocks, evaluates their relationships and determines their original setting

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

Partial dolomitization of foreslope and toe-of-slope facies of a Carnian carbonate platform, Transdanubian Range, Hungary

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