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Abstract

The paper presents a study of a Lower Carboniferous (Visean) clastic sequence commonly called Bobrikovsky Formation, deposited in the Volga-Ural Petroleum Province, Orenburg Region. Our investigation included sedimentological description of core samples from hydrocarbon wells and well log correlations. Facies were identified by well log patterns and calibrated by core sedimentology. The Bobrikovsky Formation is proposed to be interpreted as an overall transgressive-regressive succession in a nearshore-tidal environment. Transgressive lagoon-estuary and barrier island facies became regressional lagoon fill-type settings.

Open access

Abstract

The Algyő High (AH) is an elevated crystalline block in southeastern Hungary covered by thick Neogene sediments. Although productive hydrocarbon reservoirs are found in these Neogene sequences, numerous fractured reservoirs also occur in the pre-Neogene basement of the Pannonian Basin. Based on these analogies, the rock body of the AH might also play a key role in fluid storage and migration; however, its structure and therefore the reservoir potential is little known. Based on a comprehensive petrologic study in conjunction with analysis of the spatial position of the major lithologies, the AH is considered to have been assembled from blocks with different petrographic features and metamorphic history. The most common lithologies of garnet-kyanite gneiss and mica schist associated with garnetiferous amphibolite are dominant in the northwestern and southeastern parts of the AH. The first regional amphibolite facies metamorphism of the gneiss and mica schist was overprinted by a contact metamorphic (metasomatic) event during decompression in the stability field of kyanite. Garnet-bearing amphibolite experienced amphibolite facies peak conditions comparable with the host gneiss. Regarding the similarities in petrologic features, the northwestern and southeastern parts of the area represent disaggregated blocks of the same rock body. The central part of the AH area is characterized by an epidote gneiss-dominated block metamorphosed along with a greenschist-facies retrograde pathway as well as a chlorite schist-dominated block formed by greenschist-facies progressive metamorphism. The independent evolution of these two blocks is further confirmed by the presence of a propylitic overprint in the chlorite schists. The different metamorphic blocks of the northwestern, southeastern and central parts of the AH probably became juxtaposed along post-metamorphic normal faults developed due to extensional processes. The supposed brittle structural boundaries between the blocks could have provided hydrocarbon migration pathways from the adjacent over-pressured sub-basins, or could even represent suitable reservoirs.

Open access

Abstract

Three distinct paragenetic and compositional types of tourmaline were described from the Velence Granite and the surrounding contact slate. Rare, pitch-black, disseminated tourmaline I (intragranitic tourmaline) occurs in granite, pegmatite, and aplite; very rare, black to greenish-gray, euhedral tourmaline II (miarolitic tourmaline) occurs in miarolitic cavities of the pegmatites; abundant, black to gray, brown to yellow or even colorless, acicular tourmaline III (metasomatic tourmaline) occurs in the contact slate and its quartz-tourmaline veins. Tourmaline from a variety of environments exhibits considerable variation in composition, which is controlled by the nature of the host rock and the formation processes. However, in similar geologic situations, the composition of tourmaline can be rather uniform, even between relatively distant localities. Tourmaline I is represented by an Al-deficient, Fe3+-bearing schorl, which crystallized in a closed melt-aqueous fluid system. Tourmaline II is a schorl-elbaite mixed crystal, which precipitated from Li- and F-enriched solutions in the cavities of pegmatites. Tourmaline III shows an oscillatory zoning; its composition corresponds to schorl, dravite, and foitite species. It formed from metasomatizing fluids derived from the granite. This is the most abundant tourmaline type, which can be found in the contact slate around the granite.

Open access

Abstract

Due to the global oil price crisis in 2014, one of the MOL's preventive/reactive measures was to identify geologically or commercially risky elements within their portfolio. This involved reevaluation of all geologic data from Field A in the Volga-Urals Basin. In re-evaluating Field A, several unexpected challenges, problems and pitfalls were faced by the interdisciplinary team performing the task of building a new database, quality checking, and interpreting data dating back to 1947. To overcome these challenges related to this mature field, new approaches and fit-for-purpose methods were required in order to achieve the overall goal of obtaining a reliable estimation of remaining hydrocarbon potential. In the first phase a first-pass 3D geologic model was constructed, along with wrangling, cleaning and interpreting 70 years of subsurface data. This paper focuses on the main challenges involved in evaluating or reevaluating reservoir aspects of a mature field.

The primary challenges were related to the estimation of remaining in-place hydrocarbon volumes, the optimization of infill well placement, the identification of primary and secondary well targets, the identification of critical data gaps, and the planning of new data acquisitions. The hands-on experience gained during the development of the geologic model provided invaluable information for the next steps needed in the redevelopment of the field.

Open access
Central European Geology
Authors: Elemér Pál-Molnár, Luca Kiri, Réka Lukács, István Dunkl, Anikó Batki, Máté Szemerédi, Enikő Eszter Almási, Edina Sogrik, and Szabolcs Harangi

Abstract

The timing of Triassic magmatism of the Ditrău Alkaline Massif (Eastern Carpathians, Romania) is important for constraining the tectonic framework and emplacement context of this igneous suite during the closure of Paleotethys and coeval continental rifting, as well as formation of back-arc basins.

Our latest geochronological data refine the previously reported ages ranging between 237.4 ± 9.1 and 81.3 ± 3.1 Ma. New K/Ar and U–Pb age data combined with all recently (post-1990) published ages indicate a relatively short magmatic span (between 238.6 ± 8.9 Ma and 225.3 ± 2.7 Ma; adding that the most relevant U–Pb ages scatter around ∼230 Ma) of the Ditrău Alkaline Massif. The age data complemented by corresponding palinspastic reconstructions shed light on the paleogeographic environment wherein the investigated igneous suite was formed.

The magmatism of the Ditrău Alkaline Massif could be associated with an intra-plate, rift-related extensional tectonic setting at the southwestern margin of the East European Craton during the Middle–Late Triassic (Ladinian–Norian) period.

Open access
Central European Geology
Authors: Máté Zsigmond Leskó, Richárd Zoltán Papp, Ferenc Kristály, József Pálfy, and Norbert Zajzon

Abstract

Although the Mesozoic rocks of the Transdanubian Range have been the subject of a multitude of different studies, mineralogical research is largely underrepresented. The clay mineralogy of Lower Jurassic (especially the Pliensbachian and Toarcian) strata was broadly investigated earlier; however, systematic high-resolution clay mineralogical studies remain scarce. Here we present a mineralogical study focusing on the Upper Pliensbachian strata of the Lókút-Hosszúárok section, located near the Eplény Manganese Ore Field. We identified dioctahedral smectite, randomly interstratified illite/smectite, illite as 10 Å phyllosilicate, quartz and cristobalite. Based on our new results we propose that the smectite was formed by aging of Mg or Fe hydroxide-silica precipitates. The smectite and cristobalite were presumably formed from the siliceous tests of radiolarians, whose abundance was controlled by a local upwelling system. The occurrence of Pliensbachian smectite in the Lókút outcrop shows similarities with the Úrkút smectites known from both Pliensbachian and Toarcian strata, which implies that similar processes controlled the sedimentation during the Pliensbachian as well as during the black (gray) shale-hosted ore accumulation in the Eplény and Úrkút basins.

Open access

Abstract

In this paper we review five cancellariid assemblages from the Hungarian part of the Pannonian Basin (Börzsöny, Bakony, and Mecsek Mts regions) which yielded 26 species. Ten species are recorded for the first time in Hungary. One species, Scalptia nemethi n. sp. is described as new. A revision of the Hungarian museum collections and historical Hungarian literature is also provided. Sveltia salbriacensis Peyrot 1928 is considered a junior subjective synonym of Petitina inermis (Pusch 1837).

Open access

Abstract

The laboratory micro X-ray diffraction (μ-XRD) technique is a suitable method to study minerals in-situ in whole-rock specimens without any sample preparation or in polished thin sections, and even in small amounts in powdered form. The micro X-ray diffraction method uses the conventional, closed-tube X-ray generator, but modifications were needed in the diffraction column, sample holder and detector in order to achieve μ-XRD capability.

In this paper, we present a case study of the capillary method used in µ-XRD on hydrothermal clay mineral assemblages that formed in the Velence Mts (Hungary). The capillary method in µ-XRD has many advantages in the investigation of small amounts of clay minerals: (1) easy and rapid preparation of randomly oriented, powdered samples; (2) rapid measurements; (3) accurate diffraction patterns. By using the capillary method, the formation of preferred orientation can be eliminated; thus the (hkl) reflection of the clay minerals can be precisely measured. Illite polytype quantification and the investigation of (060) reflection of clay minerals can be used satisfactorily in µ-XRD.

Hydrothermal clay mineral assemblages are indicative of temperature and pH. Their examination can determine the physicochemical parameters of the hydrothermal fluids that interacted with the host granite in the Velence Mts. The analyzed hydrothermal clay minerals from the western part of the mountains suggest lower temperatures (150–200 °C) and intermediate pH conditions. In contrast, the clay mineral assemblages' characteristics for the eastern part of the mountains indicate more intense argillization and higher temperatures (∼220 °C) and intermediate pH conditions.

Open access

Abstract

Permian felsic volcanic rocks were encountered in petroleum exploration boreholes in SE Hungary (eastern Pannonian Basin, Tisza Mega-unit, Békés–Codru Unit) during the second half of the 20th century. They were considered to be predominantly lavas (the so-called “Battonya quartz-porphyry”) and were genetically connected to the underlying “Battonya granite.” New petrographic observations, however, showed that the presumed lavas are crystal-poor (8–20 vol%) rhyolitic ignimbrites near Battonya and resedimented pyroclastic or volcanogenic sedimentary rocks in the Tótkomlós and the Biharugra areas, respectively. The studied ignimbrites are usually massive, matrix-supported, fiamme-bearing lapilli tuffs with eutaxitic texture as a result of welding processes. Some samples lack vitroclastic matrix and show low crystal breakage, but consist of oriented, devitrified fiammes as well. Textural features suggest that the latter are high-grade rheomorphic ignimbrites.

Felsic volcanic rocks in SE Hungary belong to the Permian volcanic system of the Tisza Mega-unit; however, they show remarkable petrographic differences as compared to the other Permian felsic volcanic rocks of the mega-unit. In contrast to the crystal-poor rhyolitic ignimbrites of SE Hungary with rare biotite, the predominantly rhyodacitic–dacitic pyroclastic rocks of the Tisza Mega-unit are crystal-rich (40–45 vol%) and often contain biotite, pyroxene, and garnet. Additionally, some geochemical and geochronological differences between them were also observed by previous studies. Therefore, the Permian felsic volcanic rocks in SE Hungary might represent the most evolved, crystal-poor rhyolitic melt of a large-volume felsic (rhyodacitic–dacitic) volcanic system.

The Permian volcanic rocks of the studied area do not show any evident correlations with either the Permian felsic ignimbrites in the Finiş Nappe (Apuseni Mts, Romania), as was supposed so far, or the similar rocks in any nappe of the Codru Nappe System. Moreover, no relevant plutonic–volcanic connection was found between the studied samples and the underlying “Battonya granite.”

Open access

Abstract

The fuzzy clustering technique is one of the ways of organizing data that presents special patterns using algorithms and based on the similarity level of data. In this study, in order to cluster the resulting data from the Babakoohi Anticline joints, located north of Shiraz, K-means and genetic algorithms are applied. The K-means algorithm is one of the clustering algorithms easily implemented and of fast performance; however, sometimes this algorithm is located in the local optimal trap and cannot respond with an optimal answer, due to the sensitivity of this algorithm to the centers of the primary cluster. In addition, it has some basic disadvantages, such as its inappropriateness for complicated forms and also the dependency of the final result upon the primary cluster. Therefore, in order to perform the study more accurately and to obtain more reliable results, the genetic algorithm is used for categorizing the data of joints of the studied area. Applying this algorithm for leaving the local optimal points is an effective way. The results of clustering of the aforementioned data using the two above techniques represent two clusters in the Babakoohi Anticline. Furthermore, for validity and surveying of the results of the suggested techniques, various mathematical and statistical techniques, including ICC, Vw, VMPC, and VPMBF, are applied, which supports the similarity of the obtained results and the data clustering process in two algorithms.

Open access