Statistical analysis of the Late Miocene sequences on the southeastern Danube Basin margin based on borehole data

The strata of lacustrine, deltaic and alluvial sequences of the southeastern Danube Basin (se DB) deposited during the Pannonian were reached by numerous boreholes. Even though the large amount of available data there are inconsistencies in recent knowledge, concerning distribution of different formations in the basin fill as well as the interpretation of their surficial occurrences. The purpose of this study is to utilize the full strength of available borehole data to characterize the spatial distribution and internal architecture of each penetrated sedimentary formation defined by Kováč et al. (2011). The used database contains more than 700 boreholes reaching average depth of 300 m, which lithological logs were digitalized according to main grain size in each described stratum and considering the origin of the layer. The resulting database comprises up to 16 000 documented layers. For purposes of the statistical analysis were created (1) pie charts of percentual share of each described lithotype (clays, fine sands, sands, gravels) for individual stratigraphic unit; (2) histograms of the percentual content of coarse (sandy and gravely) layers in a lithological column for each strat. unit; (3) histograms of single unit/stratum thickness for each lithotype in each strat. unit; and (4) interpolated maps of spatial distribution of coarse layers (percentual content) in each strat. unit. Area of the se DB, bordering with the Transdanubian Range Mts. (TR), represented before the regression of the Lake Pannon a submerged basement high. Specific depositional conditions occurred, because main input of sediment from the Western Carpathians on the northeast and from the paleo-Danube delta on the northwest fell into the offshore depocenter in the central depression of the DB. Lacustrine strata of the Ivanka Fm. deposited there mainly in a sublittoral zone contain therefore highly bioturbated clays and silts, while sand or coarser sediment is almost absent. This succession described only from core material and well-logs of deep boreholes is comparable to the Szák Fm. described in the Hungarian part of the basin. Subsequent regression of the Lake Pannon took place through mentioned deltaic systems prograding from the North. The shelf slope prograded to studied area across the offshore environment of the central depression before ca. 9.0 Ma. The deltaic sequence, considered as the Beladice Fm., is widely documented by studied boreholes. It is typical with alternating occurrence of brackish and freshwater to terrestrial mollusk fauna and common layers of lignite. Lithological composition of the sequence is highly fine grained: 88% clays, 6% silts/very fine sands, 6% sands. Layers coarser than clays form usually 3-18% of a lithological column. Majority of very fine sands and sands form units 1-9 m thick with peak thickness in 2-6 m. A single rhythm of lithological change, which could be assumed as parasequence according to Sztanó & Magyar (2007), reaches thickness 10-35 m with most frequent value of ca. 25 m. Based on observed situation we can expect, that mouth bars, beach ridges and channels representing the thickest sandy bodies form a minor part of the volume, while the main part of upward coarsening cycles were formed by filling of interdistributary bays and lagoons on the delta plain. On the basis of used data was identified a distinct sedimentary unit, which underlies the deltaic Beladice Fm. in the transitional zone between the se DB and the TR, named the complex of shelfal sands. The strata consist of sublittoral Congeria czjzeki mollusk alternated with littoral fauna. Average lithology of the complex consists of 57% clays, 16% fine sands, 22% sands and 5% gravels. However, the complex is laterally variable and single borehole may consist up to 90% of sandy and gravely layers. The thickness of individual sandy unit is unclear due to amalgamation. Described lithology is interpreted as a result of sedimentary trap formed between deltaic lobes on the North and partially subaerial exposed islands of the TR on the South. While the deltaic Beladice Fm. consists almost no gravely layers, the gravel described in the complex was probably derived from the TR. Distinguishing of the alluvial Volkovce Fm. from the underlying deltaic Beladice Fm. could be concluded by absence of the brackish mollusk fauna, but it is difficult to exclude the possibility of missing information. The alluvial sequence consists of significantly lower portion of coal layers. Clays form 79%, fine sands 6.5%, sands 14%, 0.5% gravels. Individual well profile consists usually of 5-30% coarse layers. Sandy bodies reach thickness 3-15 m with peak thickness in 5-11 m, fine sands form bodies 1-8 m thick. We can assume that the main portion of the sandy deposits in studied alluvial sequence is bound to meandering channel belts ca. 8 m thick, which are occasionally amalgamated. The few meters thick sandy and fine sandy units represent levees and crevasse splays. Alluvial facial associations with described parameters were documented also on outcrops. Spatial correlation indicates prevailing orientation of sandy bodies in NW-SE direction, while paleocurrent analysis from field denotes direction from N and NW. The majority of documented sandy bodies are located in the western part of the studied area. The boundary between deltaic and alluvial sequences is despite the wealth of data not easy to correlate. The similarity of depositional processes and resulting geological setting of both sequences lead to conclusion that interpreting an outcrop assignment to formation based on lithofacies without precise paleontological analysis and control by boreholes, could be groundless

40Ar/39Ar geochronology of Burdigalian paleobotanical localities in the central Paratethys (south Slovakia)

The Lipovany and Mučín paleobotanical localities contain important floral associations within the tuff horizons, which were used for determination of subtropical to tropical climatic conditions during the Early Miocene. Based on the combination of results from plagioclase and biotite 40Ar/39Ar dating, the age of the tuff deposition is around 17.3Ma. For the Lipovany locality, single-grain 40Ar/39Ar convergent ages of 17.49±0.54Ma and 17.28±0.06Ma, for plagioclase and biotite were obtained, respectively. The Mučín locality only provide an imprecise convergent age of 16.5±1.4Ma due to the small size of the analyzed plagioclase crystals. The results thus allowed to include the fossil subtropical flora of the studied localities in the late Ottnangian regional stage (upper part of the Burdigalian). Additionally, these age data indicate that deposition of the overlaying Salgótarján Formation starts much later than originally thought (during Ottnangian-Karpatian boundary)

Evolution of the lower Badenian depositional system in the East Slovakian Basin: Implications for reservoir rock potential

The Transcarpathian Basin, consisting of the Predov and Trebisov sub-basins, is situated at the border of the Western and Eastern Carpathians. Hydrocarbon exploration in this basin has been ongoing for more than 60 years and reserves of economic importance are located in the E to NE part of the basin. The Trebisov sub-basin was analysed to characterize and predict lower Badenian (Langhian) reservoir rocks. To achieve this aim, new sedimentary facies, seismic facies, petrographic and paleontological analyses were performed, combined with original total porosity and permeability measurements. Based on the planktic foraminifera and calcareous nannoplankton zonation, the lower Badenian sequence in the Trebisov sub-basin was divided into a lower and an upper interval. The presence of very well sorted sandstone layers, glauconite grains, albitization, selective alteration of tuffs into zeolites as well as the fossil assemblages reinforce the volcanic influenced marine environments. Documented sedimentary structures indicate subaqueous density flows preceded by the newly observed fluvial and deltaic facies. The total sandstone porosity measurements indicate a gradual porosity decrease with depth marked by a value of 13.21 % at the surface decreasing down to 6.41 % at similar to 3 km below the surface. These numbers correspond to reservoirs with low to reduced porosity. Diagenetic products such as illite, chlorite and feldspar cement together with compaction effects, and variations in the crystallinity in siliceous cement led to the modification of initial porosity. The potential lower Badenian reservoir sandstones are frequently deformed by strike-slip faults responsible for the large pull-apart basin complex (seen as horsetail structures on reflection seismic sections) forming various fault-bounded structural traps. The lower Badenian sandstones present at the top of two anti-clinal structures in the central part of the basin, display very strong reflection amplitudes on newly merged 3D reflection seismic data underlining the additional exploration potential in the basin.Web of Science73435231

Evolution of depositional systems and sedimentary cycles in Želiezovce Depression of the Danube Basin

Five deep wells (Pozba4, Pozba3, Dubnik1, Nová Vieska1, Modrany1), drilled in the Želiezovce depression of the south-east Danube Basin penetrate the Cenozoic sedimentary record in overall thickness ranging from 1000 m up to 3000 m, the total thickness gradually increases from South to the North. This area is well known for the complex geological structure related to the Central Western Carpathians and Transdanubian Range junction along the Hurbanovo – Diösjenö line. Many authors have studied this area in the past,  nevertheless Depositional systems, sedimentary cycles and the development of sedimentary facies were never understood in detail. The Re-evaluation of biostratigraphy, paleoecology, sedimentology and the Re-interpretation of e-logs ware all incorporated into well correlations, what resulted in definition of four main sedimentary cycles: (1) The Lowermost Oligocene cycle, consisting of mudstones with occasional sandstone intercalations, associated with slope to offshore marine environment what is supported by the presence of the NP 22 calcareous nannoplankton zone. (2) The transgressive Langhian (Lower Badenian) deposits, composed of mudstones with epiclastic volcanic material and tuffite beds ware associated with shelfall to offshore environement the age is supported by the NN4 - NN5 calcareous nannoplankton zone. (3) The Serravallian (Upper Badenian - Sarmatian) cycle is composed mainly by mudstones with abundant Lithothamnium fragments associated with brackish coastal pain environment, supported by the NN6 calcareous nannoplankton zone and by the mass occurrence of fish scales and  Ervilia dissita (Eichwald) bivalves. (4) The overlying strata are represent the Tortonian-Pliocene (Pannonian-Pliocene) cycle, consists mostly from claystone which are overlain by sandstone and siltstones layers is associated with lake, deltaic and alluvial plain environment. 

Cummingtonite-bearing volcanic rocks: first evidence in the Central Slovak Volcanic Field

Within the framework of reinterpretation of the depositional evolution of the Komjatice depression, presence of cummingtonite in weakly lithified sediment has been detected. The sediment is formed by volcanic lithoclasts and phenocrysts with a small admixture of non-volcanic grains. The different mineral composition and various degrees of alteration of volcanic lithoclasts, together with structural features point to epiclastic origin. Therefore, the studied samples can be described as volcanic paraconglomerate and sandstone. The cummingtonite is found in rusty coloured volcanic lithoclasts and in the heavy fraction. Cummingtonite-bearing volcanic rocks have not been described so far from the Slovak Neogene volcanic fields. Therefore its presence in the studied samples represents the first indication of such volcanic rock in Slovakia. The aim of the article is to invoke interest for finding these volcanic rocks in situ

First evidence for Permian-Triassic boundary volcanism in the Northern Gemericum: geochemistry and U-Pb zircon geochronology

Several magmatic events based on U-Pb zircon geochronology were recognized in the Permian sedimentary succession of the Northern Gemeric Unit (NGU). The Kungurian magmatic event is dominant. The later magmatism stage was documented at the Permian-Triassic boundary. The detrital zircon assemblages from surrounding sediments documented the Sakmarian magmatic age. The post-orogenic extensional/transtensional faulting controlled the magma ascent and its emplacement. The magmatic products are represented by the calc-alkaline volcanic rocks, ranging from basaltic metaandesite to metarhyolite, associated with subordinate metabasalt. The whole group of the studied NGU Permian metavolcanics has values for the Nb/La ratio at (0.44–0.27) and for the Nb/U ratio at (9.55–4.18), which suggests that they represent mainly crustal melts. Magma derivation from continental crust or underplated crust is also indicated by high values of Y/Nb ratios, ranging from 1.63 to 4.01. The new 206U–238Pb zircon ages (concordia age at 269 ± 7 Ma) confirm the dominant Kungurian volcanic event in the NGU Permian sedimentary basin. Simultaneously, the Permian-Triassic boundary volcanism at 251 ± 4 Ma has been found for the first time. The NGU Permian volcanic activity was related to a polyphase extensional tectonic regime. Based on the new and previous U-Pb zircon ages, the bulk of the NGU Permian magmatic activity occurred during the Sakmarian and Kungurian. It was linked to the post-orogenic transpression/transtension tectonic movements that reflected the consolidation of the Variscan orogenic belt. The Permian-Triassic boundary magmatism was accompanied by extension, connected with the beginning of the Alpine Wilson cycle

Provenance of Permian Malužiná Formation sandstones (Hronicum, Western Carpathians): evidence from monazite geochronology

The Permian Malužiná Formation and the Pennsylvanian Nižná Boca Formation are Upper Paleozoic volcano- sedimentary complexes in the Hronicum nappe system. Sandstones, shales and conglomerates are the dominant lithological members of the Malužiná Formation sequence. Detrital monazites were analysed by electron microprobe, to obtain Th-U-Pb ages of the source areas. The majority of detrital monazites showed Devonian-Mississippian ages, ranging from 330 to 380 Ma with a weighted average of 351 ± 3.3 (2σ), that correspond well with the main phase of arcrelated magmatic activity in the Western Carpathians. Only a small portion of detrital monazites displayed Permian ages in the range of 250-280 Ma, with a significant maximum around 255 Ma. The weighted average corresponds to 255 ± 6.2 Ma. These monazites may have been partially derived from the synsedimentary acid volcanism that was situated on the margins of the original depositional basin. However, some of the Triassic ages (230-240 Ma), reflect, most likely, the genetic relationship with the overheating connected with Permian and subsequent Triassic extensional regime. Detrital monazite ages document the Variscan age of the source area and also reflect a gradual development of the Hronicum terrestrial rift, accompanied by the heterogeneous cooling of the lithosphere

Late Permian volcanic dykes in the crystalline basement of the Považský Inovec Mts. (Western Carpathians): U–Th–Pb zircon SHRIMP and monazite chemical dating

This paper presents geochronological data for the volcanic dykes located in the northern Považský Inovec Mts. The dykes are up to 5 m thick and tens to hundreds of metres long. They comprise variously inclined and oriented lenses, composed of strongly altered grey-green alkali basalts. Their age was variously interpreted and discussed in the past. Dykes were emplaced into the Tatricum metamorphic rocks, mostly consisting of mica schists and gneisses of the Variscan (early Carboniferous) age. Two different methods, zircon SHRIMP and monazite chemical dating, were applied to determine the age of these dykes. U-Pb SHRIMP dating of magmatic zircons yielded the concordia age of 260.2 ± 1.4 Ma. The Th-U-Pb monazite dating of the same dyke gave the CHIME age of 259 ± 3Ma. Both ages confirm the magmatic crystallization at the boundary of the latest Middle Permian to the Late Permian. Dyke emplacement was coeval with development of the Late Paleozoic sedimentary basin known in the northern Považský Inovec Mts. and could be correlated with other pre-Mesozoic Tethyan regions especially in the Southern Alps