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Shallow marine carbonates of the Anisian Hámor Dolomite Formation in the Bükk Mountains, NE Hungary were studied to determine the mechanism and controlling factors of the dolomitization. Petrographic features, along with C and O stable isotope properties of the investigated rocks, indicate near-surface/shallow burial dolomitization of the shallow, subtidal-peritidal carbonate succession. This occurred via long-term circulation of relatively low-temperature fluid of sea-water origin. Geothermal convection may have been the driving force of this circulation. For application of this model, we need to assume that segmentation of a previously-established shallow ramp had already initiated in the Western Neotethys earlier in the middle Anisian. Unfortunately, we have only indirect evidence of this in the studied area. Still, the structural evolution and the related paleogeographic setting may have been the basic controlling factors of the pervasive early diagenetic near-surface/shallow burial dolomitization of the Hámor Formation. The coarse crystalline dolomite cement in the fractures and pores was precipitated from relatively high temperature (cc. 170 °C) water. Comparing the stable isotope values of the bulk rock and the fracture-occluding dolomite cement phase suggests a host-rock buffered fluid flow probably in the Late Cretaceous deformation phase. [ABSTRACT FROM AUTHOR]

The paper focuses on the reservoir heterogeneity of a sandstone formation in which the main issue is the evaluation of diagenetic features. Integrated data from field observations as well as petrographic and geochemical analyses from surface and core sections from different structural settings were applied. In the shallow marine Pétervására Sandstone, eogenetic minerals are comprised of calcite, pyrite and siderite; mesogenetic minerals are albite, ankerite, calcite, quartz, mixed layer clays and kaolinite. Dissolution occurred during mesogenetic and telogenetic phases. Ankerite is only present in the core setting, where the sandstone is at ca. 900 m depth and diagenetic calcite predates quartz cementation. Based on stable isotopic values (δ13 CV-PDB −18.3 to −11.4 ‰ and δ18 OV-PDB −9.5 to −7.2 ‰), diagenetic calcite is of mesogenetic origin and was precipitated from fluids migrated along fault zones from the underlying, organic matter-rich formation. In outcrop setting, on the other hand, calcite is present in a larger quantity and postdates quartz cementation. Carbon isotope data (δ13 CV-PDB = −9.9 to −5.1 ‰) indicate less contribution of light isotope, whereas more negative oxygen isotopic values (OV-PDB = −13.1 to −9.9 ‰) likely imply higher temperature of mesogenetic fluids.However, carbon–oxygen isotope covariation can indicate precipitation from meteoric fluid. In this case, further analyses are required to delineate the final model.

One of the most complete Permian-Triassic boundary sections located in the Bükk Mountains (Hungary) was sampled for ostracod study. Seventy-six species are recognized, belonging to twenty genera. Fifteen new species are described and figured: Acratia? jeanvannieri Forel sp. nov., Acratia nagyvisnyoensis Forel sp. nov., Bairdia anisongae Forel sp. nov., Bairdia davehornei Forel sp. nov., Callicythere? balvanyseptentrioensis Forel sp. nov., Cytherellina? magyarorszagensis Forel sp. nov., Eumiraculum desmaresae Forel sp. nov., Hollinella fengqinglaii Crasquin sp. nov., Hungarella gerennavarensis Crasquin sp. nov., Langdaia bullabalvanyensis Crasquin sp. nov., Liuzhinia venninae Forel sp. nov., Liuzhinia bankutensis Forel sp. nov., Microcheilinella egerensis Forel sp. nov., Reviya praecurukensis Forel sp. nov., Shemonaella? olempskaella Forel sp. nov. One species is renamed: Bairdia baudini Crasquin nom. nov. Comparison of the Bálvány North section with theMeishan section (Zhejiang Province, South China), Global Boundary Stratotype Section and Point (GSSP) of the Permian-Triassic Boundary (PTB), reveals discrepancies linked to the environmental setting and particularly to bathymetry. The stratigraphical distribution of all the species is given and diversity variations are discussed. The BálványNorth section exhibits the lowest extinction rate of all PTB sections studied for ostracods analysis associated with a high level of endemism. [ABSTRACT FROM AUTHOR]