Abstract: Detailed petrographic studies on marbles are rare in the Hungarian geological literature. Determination of the mineral phases and their grain size, examination of the grain boundaries as well as deformation microstructures, however, can provide a comprehensive information about the metamorphic evolution and the deformation history of a marble unit.
The metamorphic basement block near the village of Dorozsma contains a few-meter-thick marble zone within the Békés–Codru Zone. A petrographic study of archive thin sections representing this marble zone was carried out from the boreholes Dorozsma–4, Dorozsma–7 and Dorozsma–54.
The fine-grained marble samples show heteroblastic texture with a composition of carbonate + quartz + muscovite + Mg-chlorite ± talc. The carbonate crystal boundaries are dominantly sutured, embayed and rarely curved. All the morpho logical types of deformation twins appear in the samples, but dominantly twin types II and IV are present. The characteristic features of the samples are small dissolution cavities filled with fine crystalline carbonate, blocky quartz and, in some cases, with saddle dolomite. In the samples from the borehole Dorozsma–4 small inclusion free carbonate grains substitute the deformation twins of the large carbonate crystals. In addition, small carbonate neoblasts and Mgchlorite flakes can be found among the large carbonate crystals. Characteristic microstructures of the samples from the well Dorozsma–7 are large sigmoid carbonate clasts in a very fine-grained matrix. The deformation twins of the car - bonate clasts can be easily identified and show the signs of recrystallization. These samples beside the carbonate clasts also contain irregularly shaped polycrystalline quartz grains with dissolved edges, undulose extinction and signs of incipient dynamic recrystallization.
The microstructures presented above suggest a polyphase deformation. The D1 deformation event took place above 250 °C based on the relict microstructures. The subsequent D2 ductile deformation event was a low-temperature dynamic recrystallization with a simple shear component, which could be the result of a hydrolitic weakening effect of hydro - thermal fluids during deformation of the Dorozsma marble.
Keywords: Dorozsma, marble, petrography, ductile deformation, metasomatism
Abstract: In this study rocks samples of Gyűrűfű Rhyolite Formation were observed from deep drillings at northern foreland of the Villány Mts. Remained cores and thin sections from Bisse–1, Peterd–1, Szava–1, Vókány–2, Egerág–7 and Szalánta–3 drillings were available in varying — but generally restricted — number for the petrographic reambulation. Based on the new petrographic descriptions and the previous reports, 2 main lithological groups were distinguished in the area: lava rocks and pyroclastites. Based on the mineralogical composition and texture the following rock types are distinguishable: (1) pyroclastites with rhyolitic composition (Peterd–1; Vókány–2, upper section; Egerág–7, upper section; Szalánta–3, upper section and presumably Bisse–1, upper section); (2) lava rocks with rhyolitic composition (Bisse–1, lower section; Szava–1; Vókány–2, lower section); (3) lava rocks with dacitic composition (Egerág–7, lower section); (4) lava rocks with rhyodacitic–dacitic composition (Szalánta–3, lower section).
At northern foreland of the Villány Mts, the magmatic activity started with lava flows (creating a rhyolitic lava dome/lava flow in the area of Szava and Bisse–Vókány and rhyodacitic–dacitic lava rocks in the area of Egerág–Szalánta) and was followed by explosive eruptions, covering the area with thick ignimbrite sheets.
Pyroclastites explored by drillings have rhyolitic composition at present but their crystal-rich character may refer to dacitic initial melt composition; resembling to the so-called crystal-rich monotoneous intermediates. These products are connected to reactivated crystal mush from middle–upper crustal magma reservoirs. Considering that pyroclastites were affected by a posterior K-metasomatic process (e.g. adularization of feldspars in rocks of Peterd–1), the modification of their chemical composition cannot be excluded. Further studies of the garnet crystals observed in the pyroclastites of Egerág–7 and Szalánta–3 deep drillings could help to refine the nature of Permian volcanism in the area.
Our new results suggest that at northern foreland of the Villány Mts — similarly to analogous regions of European Variscides (e.g. Intra-Sudetic Basin, Southern Permian Basin, Munt˛ii Apuseni) — a chemically complex, possibly long lasting volcanic system worked and produced the rock materials that were formerly handled as one separate stratigraphical marker formation. For further investigation of this system, radiometric age dating of each borehole (U-Pb, zircon) and whole rock (major and trace elements) geochemical analyses are planned.
Keywords: Villány Mountains, Gyűrűfű Rhyolite, Permian, pyroclastite, lava rock, garnet, K-metasomatism
Abstract: Echinoids are characteristic fossils of the Central Paratethyan Miocene marine sediments, particularly in the Badenian (Middle Miocene), which is coeval with the Langhian and the early Serravallian. The Leitha Limestone Formation of normal-salinity, shallow-marine facies can be traced from Slovenia to Bulgaria and from Austria to Ukraine including the southern part of Poland. In Hungary the Leitha Limestone Formation contains several layers which yielded a high diversity of echinoids.
In Budapest and in its immediate vicinity only the upper Badenian part of the Leitha Limestone Formation occurs, which has been assigned to the Rákos Member.
In Budapest the predominant part of fossil echinoderms indicates late Badenian age. The previously found echinoids came from several localities, for example from road cuts; however, most of the specimens were found in excavation pits from the 1960’s to the 1980’s, e.g. in the course of the canalization works of Gyakorló utca and Kerepesi út and the construction of the Sugár Mall in Örs vezér tér in the Eastern part of the city. The main collectors were Péter SOLT, Pál MÜLLER and Sándor MIHÁLY; the latter established an echinoderm collection in the Hungarian Geological Institute. In this collection more than 500 echinoids from Budapest are preserved. MIHÁLY himself also studied these specimens but — despite the large collection — he published only few papers due to his regrettable early death.
Badenian strata exposed later, during the construction of a new shopping mall (Árkád 1) in 2001–2002, contained echinoids, as well. Newly collected material recovered from the biogenic sands of the Leitha Limestone Formation outcropping within the city of Budapest provides novel data on the Upper Badenian echinoid fauna of Hungary.
The collected material (except the holotype which is located in the Hungarian Mining and Geological Survey of Hungary) belongs to Mihály DUNAI’s private collection. The specimens initially were covered by calcareous biogenic sand which required preparation by root and wire brush. We made comparative studies in the collection of the Natural History Museum Vienna. This material contains most of the Austrian Badenian Brissus abeli fossils including the paratype of Brissus abeli (REIDL, 1941). Based on this research and the study of images in the literature, it can be stated that — compared to other fossil Brissus forms — the new Hungarian Brissus material has outstandingly good preservation. The following morphological characters have been measured: length, width and height of the test, distance from the apical disc from anterior margin, maximal width of plastron, and horizontal width of subanal fasciole.
Here we record, for the first time, members of the genus Brissus from the Middle Miocene of Hungary. The material is attributed to two different taxa, namely B. abeli (REIDL, 1941), also known from contemporary deposits of Austria and the Western Ukraine, and a new species of Brissus, i.e. Brissus mihalyi n. sp. The latter can be clearly distinguished from previously described species of the genus Brissus by its very anterior apical disc and wide angle between its anterior paired petals.
The novel material provides new insight into the taxonomy, distribution and evolution of the genus Brissus and the Badenian echinoid fauna of the Central Paratethys.
Keywords: Echinodermata, Central Paratethys, upper Badenian, Leitha Limestone, taxonomy
Abstract: Fluid inclusions trapped in drill cores and cuttings may provide essential information about the ancient fluid system. Information can be obtained about the chemical composition and the vertical dimensions of the fluid system as well as the palaeo-fluid contacts by analysing the gas and volatile compounds of those trapped fluid remnants. Logging the extracted gas and volatile compounds over drill section we can represent the profile of hydrocarbon, non-hydrocarbon and further derived parameters. A gas-analyser was built at the Department of Mineralogy, Geochemistry and Petrology, University of Szeged for analysing fluid inclusions by mechanical decrepitation in a low-pressure and high-temperature crushing chamber. The released compounds are analysed by a quadrupole mass spectrometer connected directly to the crushing chambers.
There are indispensable conditions to examine drill cuttings, such as the sample preparation and the crushing pro - cedure for decrepitating the fluid inclusions at high efficiency. For the reproducible, representative and optimal meas - urement protocol we performed crushing tests on pre-sieved quartz sand and cleaning tests on pre-contaminated quartz sand. According to the results of crushing tests the amount of sample, hits rate and squeezing time, all modify the crushing efficiency but at different ways. Based on our experiments, in order to mechanically decrepitate fluid inclusions at the highest efficiency 0.5–1.0 g amount of sample, at least 50 hits and 1 sec squeezing time must be applied.
Comparing the efficiencies of different cleaning procedures it was verified that cleaning of the highly-contaminated drill cuttings with detergent is necessary to get representative analytical results. However, this cleaning procedure sig ni - ficantly rises the duration of sample preparation and hence the measuring time of the individual samples.
Based on the results of tests performed we have developed a measurement protocol for gas analysis of drill cores and cuttings, furthermore have marked out directions of the potential developments.
Keywords: gas-analyser, cuttings cleaning procedures, crushing tests, fluid-inclusion stratigraphy
Abstract: Since the beginning of the 1960th two new events have revolutionized the evolution of geological thought. One of them, the plate tectonics, which is well known to the public, the other one is the recognition of mantle-derived rocks and the new results related to the investigation of the latter samples. Even if these results have also revolutionized the earth sciences, the real significance of this issue is known to a narrower group of specialists only. The present paper discusses the history of recognition of mantle samples and tries to demonstrate the immense progress of our knowledge due to the detailed investigations of these rock samples.
Keywords: history of science, mantle, peridotite