Shallow marine carbonates of the Anisian H & aacute;mor Dolomite Formation in the B & uuml;kk 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 H & aacute;mor Formation. The coarse crystalline dolomite cement in the fractures and pores was precipitated from relatively high temperature (cc. 170 degrees 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.

The initiation of continental rifting from the latest Early Triassic was reconstructed by correlation of sedimentary formations deposited in the western end of Neotethys (in the Dinaric–Alpine oceanic branch). The shallow-marine and basinal strata of the Silica Nappes and the Bódvarákó Series from the Torna Nappe (located in the southern part of the Inner Western Carpathians) were studied and compared to sedimentary successions described from the Alps, the Carpathians and the Dinarides. The depositional zonation, developed on the shelf during the Late Permian‒Early Triassic transgression, was dissected and rearranged from the latest Early Triassic. The facies pattern and the differential sedimentary evolution of the shelf domains suggest that the accelerated subsidence began in the latest Early Triassic, and was connected to the onset of continental rifting. Three stages are reconstructed in the studied time-frame. (1) Dark grey carbonates, very poor in fossils, were deposited in restricted and hypersaline intraplatform basins in many shelf domains. In the external domains, shallow-marine carbonates, depositional gaps and terrestrial deposits are typical (formations in the Southern Alps, the External Dinarides and the Serbian–Macedonian Massif). From the latest Early Triassic, this latter shelf segment formed a threshold that restricted water circulation from the intraplatform basins. (2) Shallowing-up carbonate successions mark the next stage that implies a period of tectonic quiescence on the shelf from the late Early Anisian to late Middle Anisian. A peculiar change in biota occurring in previously restricted domains was coeval in shallow-marine and deep-marine settings. The biotic change is revealed by observations that dark grey carbonates, which are very poor in fossils, are overlain by carbonate successions rich in fossils typical for normal-marine water. The biota and environmental changes indicate the opening of a passage which allowed the circulation of well-oxygenated and normal-salinity marine water towards the previously restricted depositional areas. The geodynamic setting switching from continental rifting to spreading in the southern sector of the Dinaric–Alpine oceanic branch (Hellenides and Albanides), triggered the opening of the gateway between the future continental margins, i.e., between the External Dinaridic domain (Adria) and Serbian–Macedonian Massif (Eurasia). (3) Following the biotic event in the northern sector of the shelf, subsidence accelerated and additional intraplatform basins opened from the latest Pelsonian.

In the Transdanubian Range (Hungary), a wide spectrum of Triassic dolomites is known. Mechanism of dolomitization of the platform carbonate successions was subject of a number of studies but the study of dolomitization of basinal carbonates is very limited. Petrographical and isotope–geochemical characteristics of the Upper Triassic dolomitized carbonate deposits, formed in a fault-controlled intraplatform basin, and interpretation of the dolomite-forming processes are presented in the current paper. From the latest Carnian to Middle Norian under semi-arid climatic conditions density-driven flux of seawater derived mesohaline fluids was the dominant mechanism of the near-surface pervasive dolomitization of the thick platform carbonate succession. In the late Middle Norian incipient rifting of the Alpine Tethys led to establishment of an extensional structural regime and onset of the formation of the Kössen Basin. In the study area, above the dolomitized platform carbonate succession, platform-derived carbonate sediments were accumulated in a fault-bounded, semi-restricted sub-basin of the Kössen Basin, whereas talus breccias and debrites were deposited near a basin-bounding master fault. The basin deposits (lower and upper members of the Rezi Dolomite Formation) were subject of early diagenetic dolomitization in shallow burial setting. Enhanced salinity seawater was the dolomitizing fluid; the synsedimentary fracturing may have promoted the fluid flow and thereby the dolomitization. Thick-bedded carbonates (middle member of the Rezi Dolomite Formation) representing a progradational tongue of the ambient platform are intercalated between the basin deposits. The dolomitization of this unit can be explained by the reflux model.

Distinct stages of deformation and fluid flow-related diagenetic alterations are recorded in Lower Miocene sandstone and conglomerate of the Pannonian Basin, Central Europe. Multiple generations of structural elements (deformation bands, calcite dominoes and veins) as well as host rocks were investigated using petrographical, elemental and stable isotope geochemical methods together with fluid inclusion petrography and microthermometry. The integration of acquired structural and diagenetic data into a subsidence model constrains the spatial and temporal evolution of deformation mechanisms and diagenetic processes. The six investigated sites represent central and marginal areas during both the pre-rift and syn-rift phases of basin evolution. The elements of pre-rift phases were preserved at the eastern margin, where eogenetic calcite precipitated in the host rocks and in the early types of deformation bands. Their δ18OPDB isotope values from −4.3‰ to −1.9‰ paired with δ13CPDB isotope values from −3.8‰ to 1.8‰ refer to precipitation from connate marine and mixed marine and meteoric pore water. The syn-rift phases are represented by eogenetic calcite and start of shallow mesogenetic diagenetic alterations in marginal position as well as in the basin centre. The δ18OPDB and δ13CPDB isotope ratios in these calcites yielded values from −15.2‰ to −5.7‰ and from to −18.5‰ to -–1.6‰, respectively. The gradual depletion in heavy isotopes shows positive covariance as the deformation progressed in time. This trend is attributed to an increasing proportion of deeply circulating meteoric fluid. The sporadic fluid inclusion data confirm meteoric fluid contribution to certain carbonate cement phases. The distinguished calcite generations in pre-rift and syn-rift structural elements and host rocks were mainly related to the phases of intense subsidence that, together with the increased rift-related heat flow, warmed up the circulating fluids. The isotope values deviating from the general trend allow the recognition of local source of light carbon contribution to basin-wide fluid-flow evolution, and cannot be tied to the switch in tectonic settings from pre-rift compression to syn-rift extension.

Calcification of microbial mats adds significant amounts of calcium carbonate to primary coral reef structures that stabilizes and binds reef frameworks. Previous studies have shown that the distribution and thicknesses of late Quaternary microbial crusts have responded to changes in environmental parameters such as seawater pH, carbonate saturation state, and sediment and nutrient fluxes. However, these studies are few and limited in their spatio-temporal coverage. In this study, we used 3D and 2D examination techniques to investigate the spatiotemporal distribution of microbial crusts and their responses to environmental changes in Integrated Ocean Drilling Program (IODP) Expedition 325 (Great Barrier Reef Environmental Changes) fossil reef cores that span 30 to 10 ka at two locations on the GBR reef margin. Our GBR microbialite record was then combined with a meta-analysis of 17 other reef records to assess global scale changes in microbialite development (i.e., presence/absence, thickness) over the same period. The 3D results were compared with 2D surface area measurements to assess the accuracy of 2D methodology. The 2D technique represents an efficient and accurate proxy for the 3D volume of reef framework components within the bounds of uncertainty (average: 9.45 +/- 4.5%). We found that deep water reef frameworks were most suitable for abundant microbial crust development. Consistent with a previous Exp. 325 study (Braga et al., 2019), we also found that crust ages were broadly coeval with coralgal communities in both shallow water and fore-reef settings. However, in some shallow water settings they also occur as the last reef framework binding stage, hundreds of years after the demise of coralgal communities. Lastly, comparisons of crust thickness with changes in environmental conditions between 30 and 10 ka, show a temporal correlation with variations in partial pressure of CO2 (pCO(2)), calcite saturation state (Omega(calcite)), and pH of seawater, particularly during the past similar to 15 kyr, indicating that these environmental factors likely played a major role in microbialite crust development in the GBR. This supports the view that microbialite crust development can be used as an indicator of ocean acidification.

The Lower Triassic succession of the Transdanubian Range in Hungary comprises limestones, dolomite, marl, sandstones and siltstones, deposited in tidal flat, lagoon and ooid shoal environments on the marginal ramp of the western Neotethys. Seven cores were chosen for petrographic and stable isotope investigations aiming to reconstruct the paragenetic sequence with special regard to the dolomitization and hydrothermal events. Five lithotypes were differentiated: (i) dolomite, (ii) sandy, silty, clayey dolomite, and dolomarl, (iii), dolomitic siltstone and sandstone, (iv) dolomitic limestone, and (v) limestone. In these lithotypes, three types of dolomites are present: non-ferroan replacive, ferroan replacive, and ferroan cement. Fabric retentive and fabric destructive non-ferroan replacive dolomitization are interpreted to have occurred by seepage reflux. Supporting evidence includes the presence gypsum and anhydrite in the Lower Triassic beds. Stable isotope values of the ferroan dolomite (δ18O of −10.7 to −4.2‰ and δ13C of −4.8 to 4.7‰) suggest dolomitization by fluids of relatively high temperature. The similar stable isotope values (δ18O of −9.3 to −5.8‰ and δ13C of −1.9 to 2.5‰) of the non-ferroan dolomite phase suggest that the reflux dolomite was overprinted by this second dolomitization event. Traces of exotic minerals, such as barite, chalcopyrite, galena and sulphosalts were found as fillings of vugs and fractures in the dolomite-cemented sandstone. The metals could have been sourced from the underlying Permian red sandstone beds. The heterogeneous sediment composition had profound impact on the diagenesis of these sedimentary successions.

A dolomit első leirasa ota eltelt tobb mint ket evszazad alatt e fontos karbonatos kőzetfajta kepződesenek korulmenyeit illetően igen lenyeges tudomanyos eredmenyek szulettek, es ezek alapjan tudomanyosan megalapozott kepződesi modellek valtak ismertte. Hosszu vitakat kovetően altalanosan elfogadott lett, hogy a kiterjedt dolomit kőzettestek meszuledekekből vagy meszkovekből asvanyhelyettesitessel jottek letre, tovabba az, hogy a dolomitasvany a kőzetek porusaiban cementkent is kivalik. A cikk rovid attekintest ad a dolomitkutatas tortenetenek legfontosabb allomasairol bemutatva a kepződesi viszonyok tisztazasanak nehezsegeit, problemait es azt is, hogy milyen koncepciok merultek fel a megfigyelt jelensegek magyarazatara, tovabba, hogy egy-egy uj felismeres, megfigyeles nyoman milyen kepződesi modelleket javasoltak. A cikk bemutatja a dolomit kőzetfajtak alapvető litologiai, petrografiai es geokemiai jellegeit es az azok megfigyelesere, meresere leggyakrabban alkalmazott vizsgalati modszereket. Attekintest ad a dolomitkepződes altalanos felteteleiről, legfontosabb folyamatairol a jelenlegi ismeretek szerint, es vazolja a kulonboző szedimentacios (tavi es tengeri) kornyezetekben es diagenetikus (sekely-, koztes es melybetemetődesi) tartomanyokban vegbemenő dolomitkepződesi folyamatokat. A cikk masodik resze attekinti a hazankban előfordulo dolomit kőzetfajtakat, es tomoren ismertet nehany esettanulmanyt is a dolomit kőzetfajtakban igen gazdag Dunantuli-kozephegyseg, valamint a Tiszai-főegyseg teruleteről. Az esettanulmanyok azt is demonstraljak, hogy minden dolomitosodott kőzettest mas es mas sajatsagokat mutat, amelyek gyakran tobb stadiumu folyamatsor eredmenyekent jottek letre. Ezeket elsősorban a befogado kepződmeny jellegei, a dolomitosodasi folyamatok egymasutanisaga, valamint lokalis tektonikai es regionalis geodinamikai tenyezők hatarozzak meg.

Deeply buried Pannonian (Upper Miocene) siliciclastic deposits show evidence of secondary porosity development via dissolution processes at a late stage of diagenesis. This is demonstrated by detailed petrographic (optical, cathodoluminescence, fluorescence, and scanning electron microscopy) as well as elemental and stable isotope geochemical investigations of lacustrine deposits from the Makó Trough, the deepest depression within the extensional Pannonian back-arc basin. The analyses were carried out on core samples from six wells located in various positions from centre to margins of the trough. The paragenetic sequence of three formations was reconstructed with special emphasis on sandstone beds in a depth interval between ca 2700 and 5500 m. The three formations consist, from bottom to top, of (1) open-water marls of the Endrőd Formation, which is a hydrocarbon source rock with locally derived coarse clastics and (2) a confined and (3) an unconfined turbidite system (respectively, the Szolnok and the Algyő Formation). In the sandstones, detrital grains consist of quartz, feldspar, and mica, as well as sedimentary and metamorphic rock fragments. The quartz content is high in the upper, unconfined turbidite formation (Algyő), whereas feldspars and rock fragments are more widespread in the lower formations (Szolnok and Endrőd). Eogenetic minerals are framboidal pyrite, calcite, and clay minerals. Mesogenetic minerals are ankerite, ferroan calcite, albite, quartz, illite, chlorite, and solid bituminous organic matter. Eogenetic finely crystalline calcite yielded δ13CV−PDB values from 1.4 to 0.7‰ and δ18OV−PDB values from –6.0 to –7.4‰, respectively. Mesogenetic ferroan calcite yielded δ13CV−PDB values from 2.6 to –1.2‰ and δ18OV−PDB values from –8.3 to –14.0‰, respectively. In the upper part of the turbidite systems, remnants of the migrated organic matter are preserved along pressure dissolution surfaces. All these features indicate that compaction and mineral precipitations resulted in tightly cemented sandstones prior to hydrocarbon migration. Interconnected, secondary, open porosity is associated with pyrite, kaolinite/dickite, and postdates of the late-stage calcite cement. This indicates that dissolution processes took place in the deep burial realm in an extraformational fluid-dominated diagenetic system. The findings of this study add a unique insight to the previously proposed hydrological model of the Pannonian Basin and describe the complex interactions between the basinal deposits and the basement blocks.

Microbialite is a type of organosedimentary desposits where the presence of organic matrix of a microbial biofilm plays predominant role in petrogenesis. This study reviews previous researches on microbial-induced carbonate deposits, microbe–mineral interaction in carbonate precipitation, and sedimentary and petrographic features of these deposits. It also presents modern deposits and some case studies from Hungary. The activity of the bacterial biofilm communities has a significant effect on their environment and can initiate crystal nucleation and growth. The mineral precipation can be both biologically induced and influenced wise, in contrast with biologically-controlled biominealisation that is common in organisms with internal or external calcareous skeletons. The mineralization in the biofilms is related to the increasing alkalinity and the released Ca2+ ions, which elevates the carbonate saturation level of the pore water, or to increasing pH level. Previous studies showed that mineral precipation takes places in several stages. Firstly, there is an increase in local alkalinity in the extracellular polymetric substance (EPS) that favors the formation of amorphous CaCO3 gel. Secondly, nanospheres appear in the matrix that provide substrates for mineral nucleation. Carbonate minerals that form in the realm of diagenesis have a specific petrogaphic features. Clotted micrite as well as the presence of calcimicrobes and fenestral pores are the microscopic components that define the microbialite. In addition to the microscopic fabric, microbialites also have various macroscopic fabric and structures that place them into four categories: laminated stromatolite, blothcy thrombolite, bush-like dendrolite, and structureless leiolite. Biofilm originated crusts can form in cavities of reef frameworks that also belong to the term of microbialite. Microbialites can compose microbial reefs or layered, stratiform sheets that are defined by the shape of the deposits and facies connections.

A dolomit első leírása óta eltelt több mint két évszázad alatt e fontos karbonátos kőzetfajta képződésének körülményeit illetően igen lényeges tudományos eredmények születettek, és ezek alapján tudományosan megalapozott képződési modellek váltak ismertté. Hosszú vitákat követően általánosan elfogadott lett, hogy a kiterjedt dolomit kőzettestek mészüledékekből vagy mészkövekből ásványhelyettesítéssel jöttek létre, továbbá az, hogy a dolomit ásvány a kőzetek pórusaiban cementként is kiválik. A cikk rövid áttekintést ad a dolomitkutatás történetének legfontosabb állomásairól bemutatva a képződési viszonyok tisztázásának nehézségeit, problémáit és azt is, hogy milyen koncepciók merültek fel a megfigyelt jelenségek magyarázatára, továbbá, hogy egy-egy új felismerés, megfigyelés nyomán milyen képződési modelleket javasoltak. A cikk bemutatja a dolomit kőzetfajták alapvető litológiai, petrográfiai és geokémiai jellegeit és az azok megfigyelésére, mérésére leggyakrabban alkalmazott vizsgálati módszereket. Áttekintést ad a dolomitképződés általános feltételeiről, legfontosabb folyamatairól a jelenlegi ismeretek szerint és vázolja a különböző szedimentációs (tavi és tengeri) környezetekben és diagenetikus (sekély-, köztes és mélybetemetődési) tartományokban végbemenő dolomitképződési folyamatokat. A cikk második része áttekinti a hazánkban előforduló dolomit kőzetfajtákat és tömören ismertet néhány esettanulmányt is a dolomit kőzetfajtákban igen gazdag Dunántúli-középhegység, valamint a Tiszai főegység területéről. Az esettanulmányok azt is demonstrálják, hogy minden dolomitosodott kőzettest más és más sajátságokat mutat, amelyek gyakran több stádiumú folyamatsor eredményeként jöttek létre. Ezeket elsősorban a befogadó képződmény jellegei, a dolomitosodási folyamatok egymásutánisága, valamint lokális tektonikai és regionális geodinamikai tényezők határozzák meg.

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.

In the Transdanubian Range (Hungary), dolostone and dolomitic limestone appear in a number of sedimentary successions formed from the Late Permian to the Late Triassic in various depositional settings and under various diagenetic conditions, whereas only a negligible amount of dolomite was detected in the post-Triassic formations. Seven dolomite-bearing units representing ramp, small and large carbonate platforms, and intraplatform basin settings are presented in this synopsis. In most cases, multi-stage and polygenetic dolomitization was inferred. The main mass of the dolostones was formed via near-surface diagenetic processes, which were commonly preceded by the formation of synsedimentary dolomite. Accordingly, surficial conditions that prevailed during sediment deposition controlled the dolomite-forming processes and thus the lateral extension and the time span of dolomitization. The area of episodic subaerial exposure was a critical controlling factor of the lateral extension of the near-surface dolomite genesis, whereas its temporal extension was mostly governed by climate. Burial diagenesis usually resulted in only moderate dolomitization, either in connection with compactional fluid flow or via thermal convection. The Triassic fault zones provided conduits for fluid flow that led to both replacive dolomitization and dolomite cement precipitation. In the Late Triassic extensional basins, synsedimentary fault-controlled dolomitization of basinal deposits was reconstructed.

Az eggenburgi koru, sekelytengeri kornyezetben kepződott Petervasarai Homokkő Formaciot, mint ismert rezervoar kőzet felszini analogjat vizsgaltuk. A szemcseosszetetel, a diagenezistortenet es a porozitasfejlődes rekonstrukciojahoz terepi vizsgalatokat es petrografiai megfigyeleseket vegeztunk, melyeket geokemiai meresek egeszitettek ki. A vizsgalt, apro-durvaszemcses, kőzettormelekes homokkőben a komponensek mennyisegi aranya alapjan negy litofacies kulon - boztethető meg; ezek a porozus (LF1), matrixgazdag (LF2), cementgazdag (LF3), es matrix- es cementgazdag (LF4) homokkőtipusok. A diagenezis soran, az eogenezis tartomanyaban kepződott autigen asvanyok a glaukonit, a fram - boidalis pirit, sziderit, kalifoldpat tovabbnovekedesi cement, kaolinit es a feltetelezhetően nagyon kis mennyisegű kalcit - cement. A legalabb 80 °C-os hőmersekletet elerve, a mezogenezis tartomanyaban megjelent a kvarc tovabb novekedesi cement, kevert szerkezetű illit/szmektit es albit keletkezett. Igy a fokozatosan betemetődott homokkőben a porozitas folyamatosan csokkent a kompakcio es a megjelenő uj asvanyfazisok miatt. A legnagyobb mennyisegben megjelenő,egyik legkesőbbi autigen asvanyfazis a kalcit. Ez főleg asvanyhelyettesiteskent, kisebb reszben pedig cementkent,elszigetelt lencsekben van jelen. A rendelkezesre allo geokemiai adatok alapjan, figyelembe veve a terulet foldtani felepiteset, a kalcit eredete tobb genetikai modellel is magyarazhato. Ezek szerint kepződhetett egyreszt a mezogenezis tartomanyaban, az uledekkel betemetődott modosult tengeri eredetű porusfluidumbol, masreszt keletkezhetett toresek menten a kőzettestbe aramlott egzotikus fluidumbol. Ez utobbi esetben is ket valtozat lehetseges, vagy egy magas hőmersekletű formacios fluidumbol valt ki, vagy egy melyre cirkulalt es felmelegedett meteorikus eredetű fluidumbol. A homokkő jelentős porozitassal rendelkezik, főleg a kalcitot nem tartalmazo reszeken. Ez a porozitas a kiemelkedes soran, a felszin kozeleben alakulhatott ki a beszivargo meteorikus vizek oldo hatasa reven. A feltarasban megjelenő kulonleges mallasi formak kialakulasaban a homokkő diagenezistortenetenek jelentős szerepe volt. For this paper, the Eggenburgian Petervasara Sandstone — a shallow marine siliciclastic formation — was studied as a surface analogue for known reservoir rocks. Field observation in the area of Kishartyan, detailed petrography (including SEM, CL) and geochemical analysis (XRD, SEM-EDS, stable isotope analysis) were applied to find out more about the diagenetic processes, the burial history, the porosity evolution, and their relationship with the weathering forms. The composition of the fine to very coarse-grained sandstones varies between subarenite and litharenite. The most common detrital grains are mono- and polycrystalline quartz and sedimentary rock fragments (cherts, dolomites and metamorphic rock fragments). Ductile grains are represented by micas and altered volcanoclastic rock fragments. Based on the proportion of components, four lithofacies were distinguished: porous sandstone (LF1), matrix-rich sandstone (LF2),cement-rich sandstone (LF3), and matrix and cement rich sandstone (LF4). The eogenetic minerals are: glauconite,framboidal pyrite, flattened rhombohedral siderite crystals, K-feldspar overgrowth cement, kaolinite, and (supposedly)small amounts of calcite. The maximum burial temperature was likely reached at around 80 °C; this is indicated by the presence of quartz overgrowth cement, mixed layer illite/smectite, and replacive and cementing albite. These minerals were formed in the mesogenetic realm. During eogenesis and mesogenesis, the porosity of the sandstone progressively decreased due to compaction and the precipitation of authigenic minerals. Calcite is one of the latest diagenetic minerals and occurs both as a replacive phase and as cement. The distribution of calcite within the studied sandstone is heterogeneous. Calcite is present in elongated lenses where the sandstone has a very low porosity. Considering the geochemical data and the geological setting, the origin of the calcite can be explained by several genetic models. According to these models, the formation of the calcite may have taken place either in the mesogenetic realm from modified marine pore waters (buried together with the sediment), or from an exotic fluid channelled along fault zones. In the second scenario, there are two possibilities regarding the origin of the parent fluid: namely, (a) a formational fluid or (b) a deeply circulated, warmed-up meteoric fluid. The high porosity of the sandstone is the result of dissolution by meteoric water during uplift. Diagenetic evolution of the sandstone had a crucial role in the formation of the weathering morphology.

Microfacies types presented here are based on thin section analysis of more than 1.500 samples from drilling cores, surface sections and several outcrops from Middle and Upper Triassic slope and basin carbonates in the Aggtelek‒Rudabanya Hills (Hungary). The observed compositional and textural types were grouped into five microfacies associations which are characteristic for slope and basin environments. The clotted micrite “boundstone” typically contains bioclasts, peloids and stromatactis structures. The inhomogeneous clotted micrite-rich groundmass suggests that the sediment originated from mats or mounds enriched in organic matter. Bioclastic wackestone with radiolarians, pelagic bivalve shells and signs of bioturbation was likely deposited in deep-water basinal environment. Bioclastic grainstone‒packstone and bivalve‒crinoid packstone deposited from turbidity currents which often occurred along the slope. The mudstones can be found after events of sudden deepening, mostly related to the drowning of the Steinalm platform. Data based on comparison of stratigraphical logs show that the Middle Triassic was characterised by rapid deepening followed by the formation and expansion of a carbonate slope. During the Late Triassic, the breakup of the Wetterstein platform had an effect on slope environment as well. Die hier prasentierten Mikrofazies-Typen basieren auf der Analyse von mehr als 1500 Proben der Region Aggtelek-Rudabanya (Ungarn). Die Proben entstammen entweder aus Bohrungen oder Oberflachenaufschlussen, z.T. kunstlicher Natur. Die beobachteten Mikrofazies-Typen wurden in funf verschiedene Mikrofaziesassoziationen untergliedert, die typisch fur Abhang- bzw. Beckenablagerungen sind. Der „clotted micritic boundstone“ fuhrt Bioklasten, Peloide und Stromatactis-Strukturen. Der nicht homogene „clotted micrite“ erlaubt eine Interpretation, dass das Sediment von Matten bzw. Mounds, die reich an organischer Substanz sind, herzuleiten ist. Bioklastische Wackestones mit Radiolarien, offen marinen Muschelschalen und Bioturbation werden einem Tiefwasserablagerungsraum zugeordnet. Bioklastische Grainstones bzw. Packstones und Krinoiden-Muschel Packstones werden als turbiditische Ablagerungen interpretiert, wie das haufig an Abhangen zu beobachten ist. Die Mudstones treten nach Ereignissen mit abrupter Vertiefung auf und sind meist mit dem Ertrinken der Steinalm Karbonatrampe in Verbindung stehend. Basierend auf den Vergleichen verschiedener Profile kann konstatiert werden, dass die Mittel-Trias charakterisiert war durch ein rasches Vertiefen des Ablagerungsraumes,gefolgt von der Entstehung und folgender Ausdehnung von karbonatischen Abhangen. Wahrend der Spaten Trias zeigt auch das Zerbrechen der Wetterstein-Karbonatplattform einen Einfluss auf die Hangsedimentation.

Dolomite most commonly forms via replacement of precursor carbonate minerals. For this reason, diagnosing primarily precipitated organogenic dolomite in microbial mat deposits from the rock record is not straightforward, even though the deposits exhibit microbial fabric. Single and multiple dolomite crusts exhibiting microbial fabric occur in a pervasively dolomitized Middle Triassic platform succession. Two sections were studied in the Transdanubian Range. In both sections, two fabric types occur in the upper part of the metre-scale cycles. One of that is microbial boundstone (fabric type 1)—characterised by clusters of dolomite microcrystals which display diagnostic microbial features, such as calcimicrobes, clotted–spherular aggregates and globules. The other one is different in the two sections. In Section 1, it is micritic dolomite (fabric type 2) that is characterised by predominantly fine crystals and contains obscured microbial components. In Section 2, it is bioclastic dolomite (fabric type 3) that is rich in reworked dasycladalean alga fragments and consists of dolomite crystals of wide size-range from fine to coarse. The precipitation of the microcrystalline dolomite phase is interpreted as being facilitated by mats and biofilms favouring/tolerating an increasing frequency of subaerial conditions in the upper intertidal setting. Petrographic analyses revealed that organogenic calcite was also precipitated, especially in mat deposits rich in bioclasts. Synsedimentary dolomitization, resulting in fine crystals, was coupled with aragonite dissolution and it postdated the organogenic precipitation. It took place only in the peritidal caps of the shallowing-upward depositional units. Petrographic analyses provide circumstantial evidence constraining that microcrystalline dolomite did not form via mimetic replacement. Accordingly the microcrystalline dolomite, which shows microbial microfabrics in the studied samples, is interpreted as an organogenic primary precipitate. Both peritidal processes, dolomite precipitation and replacement, were likely controlled by the environmental factors in a semi-arid climate. Those components of the platform succession that were not dolomitized in the peritidal environment were replaced and cemented by medium and coarsely crystalline dolomite during further burial at elevated temperature, as shown by fluid inclusion homogenisation temperature (62 to 83 °C) and negative stable oxygen isotope values. Thus, the majority of the studied formation consists of fabric-destructive dolomite (fabric type 4).

Climate warming during the late Permian is associated with the most severe mass extinction event of the Phanerozoic, and the expansion of hypoxic and anoxic conditions in shallow shelf settings. It has been hypothesised that wave aeration provided a 'habitable zone' in the shallowest environments that allowed the survival and rapid recovery of benthic invertebrates during the Early Triassic. We test this hypothesis by studying the rock and fossil records of the Aggtelek Karst, Hungary. Nearshore settings recorded in the Bódvaszilas Sandstone Formation and units A and D of the Szin Marl Formation are characterised by taxonomically homogenous fossil assemblages of low diversity and low evenness. Ecological and taxonomic recovery in this environmental setting was hampered by persistent environmental stress. This stress is attributed to increased runoff related to climate warming during the Early Triassic that resulted in large salinity fluctuations, increased sedimentation rates and eutrophication that led to seasonal hypoxia and an environment only favourable for opportunistic taxa. In contrast, shoal and mid-ramp settings further offshore are characterised by high diversity faunas with a greater functional complexity. Prior to the late Spathian Tirolites carniolicus Zone, the shelly fossils and trace fossils are limited to settings aerated by wave activity, which supports the habitable zone hypothesis. In the Tirolites carniolicus Zone, however, the oxygen minimum zone retreats offshore and the habitable deeper shelf settings are rapidly colonised by shallow water taxa, evidenced by the highest levels of diversity and bioturbation recorded in the study. Locally, full recovery of marine ecosystems is not recorded until the Illyrian, with the establishment of a sponge reef complex.

Dolomitization of relatively thick carbonate successions occurs via an effective fluid circulation mechanism, since the replacement process requires a large amount of Mg-rich fluid interacting with the CaCO3 precursor. In the western end of the Neotethys, fault-controlled extensional basins developed during the Late Triassic spreading stage. In the Buda Hills and Danube-East blocks, distinct parts of silica and organic matter-rich slope and basinal deposits are dolomitized. Petrographic, geochemical, and fluid inclusion data distinguished two dolomite types: (1) finely to medium crystalline and (2) medium to coarsely crystalline. They commonly co-occur and show a gradual transition. Both exhibit breccia fabric under microscope. Dolomite texture reveals that the breccia fabric is not inherited from the precursor carbonates but was formed during the dolomitization process and under the influence of repeated seismic shocks. Dolomitization within the slope and basinal succession as well as within the breccia zones of the underlying basement block is interpreted as being related to fluid originated from the detachment zone and channelled along synsedimentary normal faults. The proposed conceptual model of dolomitization suggests that pervasive dolomitization occurred not only within and near the fault zones. Permeable beds have channelled the fluid towards the basin centre where the fluid was capable of partial dolomitization. The fluid inclusion data, compared with vitrinite reflectance and maturation data of organic matter, suggest that the ascending fluid was likely hydrothermal which cooled down via mixing with marine-derived pore fluid. Thermal gradient is considered as a potential driving force for fluid flow.

One of the most complete Permian-Triassic boundary sections located in the Bukk 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 Balvany North section with the Meishan 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 Balvany North section exhibits the lowest extinction rate of all PTB sections studied for ostracods analysis associated with a high level of endemism.