Carpathian Orogen Research Articles

Crustal and upper mantle 3-D Vs structure of the Pannonian region from joint earthquake and ambient noise Rayleigh wave tomography

SUMMARY The Pannonian Basin, situated in Central Europe, is surrounded by the Alpine, Carpathian and Dinaric orogens. To understand its tectonic characteristics and evolution, we determine a shear wave velocity model of its crust, mantle lithosphere and asthenosphere consistently by jointly inverting Rayleigh wave phase velocities measured consistently from earthquake (EQ) and ambient noise (AN) data. For the AN data, continuous waveform data were collected from 1254 stations, covering an area within 9° from the centre of the Pannonian Basin during the time period from 2006 to 2018. This data set enabled the extraction of over 164 464 interstation Rayleigh phase-velocity curves, after applying a strict quality control workflow. For the EQ data set more than 2000 seismic events and about 1350 seismic stations were used in the broader Central and Eastern European region between the time-span of 1990 to 2015, allowing us to extract 139 987 quality controlled Rayleigh wave phase-velocity curve. Using the combined data set, a small period- and distance-dependent bias between ambient noise and earthquake measurements, mostly below 1 per cent but becoming larger towards longer periods has been found. After applying a period and distance dependent correction, we generated phase-velocity maps, spanning periods from 5 to 250 s. 33 981 local dispersion curves were extracted and a new approach is introduced to link their period-dependent roughness to the standard deviation. Using a non-linear stochastic particle swarm optimization, a consistent 3-D shear wave velocity model (PanREA2023) encompassing the crust and upper mantle down to 300 km depth was obtained with a lateral resolution reaching about 50 km at the centre of the study area for shorter periods. The crust beneath the Carpathian orogen exhibits a distinct low-velocity anomaly extending down to the Moho. It is referred to as Peri-Carpathian anomaly. Similar anomalies were observed in the Northern Apennines, while the Eastern Alps and Dinarides, as collisional orogens, generally demonstrate higher velocities in the upper crust. High crustal shear wave velocities are also evident in the Bohemian Massif and the East European Craton. The brittle upper crust of the Pannonian Basin is characterized by alternating NE–SW trending high- and low-velocity anomalies: the western and central Pannonian low-velocity anomalies and the Transdanubian and Apuseni high-velocity anomalies related to Miocene sedimentary basins and intervening intervening interbasinal highs exposing Pre-Cenozoic rocks including crystalline basement rocks. Beneath the Southeastern Carpathians, a NE-dipping slab was identified, extending to depths of at least 200 km, while a slab gap is evident beneath the Western Carpathians. A short south-dipping Eurasian slab was imaged beneath the Eastern Alps down to only 150–200 km depth. The Adriatic lithosphere is subducting near-vertically dipping beneath the Northern Apennines, and a slab gap was observed beneath the Central Apennines. In the Northern Dinarides, a short slab was evident, reaching depths of around 150 km. The Southern Dinarides featured a thinned but possibly incompletely detached slab.

From nappe stacking to strike-slip deformation: Alpine structural overprints refined by cave and karst geology in the Danubian thin-skinned units (Southern Carpathians, Romania)

Caves are ideal environments for preserving quantifiable deformational indicators in orogenic areas, as they are conditioned by regional tectonics. The caves and karst of Isverna, developed in the Barremian-Aptian limestones of the Danubian sedimentary nappes (Southern Carpathians, SW Romania), expose formerly undetected evidence of compressional tectonics, overlapping older structures related to décollement and deformation of the underlying Turonian-Senonian tectonic mélange. The Danubian domain (the distal part of the Moesian Platform) was incorporated into the Carpathian Orogen during the Late Cretaceous subduction of the Ceahlău–Severin Ocean and collision with the continental Dacia mega-unit. Subsequent Eocene–Oligocene orogen–parallel extension led to the development of a metamorphic core complex and detachment faults, constructing a complicated arcuate fault system around the Moesian Platform during the Late Miocene strike-slip deformation. The integrated analysis of structural, kinematic, and geomorphological data indicates a connection between the strike-slip deformation and the subsequent shortening, exhumation and surface exposure of Cerna Nappe within the Isverna shear zone. Four main evolutionary stages of the Danubian thin-skinned units in the central Mehedinți Mountains were distinguished from cave and karst geology, and illustrated in a detailed 3D model: i) Initial décollement and mélange deformation during the Alpine nappe stacking; ii) Extensional décollement toward SE; iii) Dextral shearing and WNW-ESE contraction; iv) Karstification and cave development. Most structural and kinematic markers recorded within the limestones of the Cerna Nappe date from stage (iii), whereas older structures were better preserved in the tectonic mélange of the Lainici Nappe. The resulting model could be further integrated into the polyphase tectonic evolution of the Southern Carpathians and their relation with the Moesian Platform. This study demonstrates the utility of caves and karst for constraining the chronology of tectonic deformations in complex structural systems and for reconstructing more refined conceptual 3D models.

Upper Cenozoic conglomeratic formations as a rock record of the turning points in the evolution of the Carpathian orogen and its foreland

Upper Cenozoic conglomeratic formations as a rock record of the turning points in the evolution of the Carpathian orogen and its foreland

STRUCTURAL POSITION AND DISTRIBUTION OF THE LOWER CRETACEOUS BLACK SHALE DEPOSITS WITHIN THE SILESIAN NAPPE OF THE UKRAINIAN CARPATHIANS

The article presents the results of studying the structural position and distribution of potentially oil-generating, organic-enriched Lower Cretaceous black shale deposits of the Shypot Formation, developed within the Silesian Nappe, using the methods of geological mapping and structural analysis. We concluded, that these deposits, which are exposed in the Vicha River basin near the town of Volovets among a continuous field of Oligocene flysch, are the part of the stratigraphic succession of the Silesian Nappe, and they are not a large olistolith or an allochthonous tectonic remnant of another, more internal nappe. Shypot Formation fills a large (1 × 3 km) subvertical tectonic lens. The rocks of the Shypot Formation are represented here by medium-rhythmic flysch: sandstone beds alternating with dark gray and black foliated mudstone (black shale) layers. They are lithified products of both medium-density turbidite flows and hemipelagic deposition of clayey material with a significant amount of organic matter. In the contact zone of the tectonic lens with the surrounding rocks, the deposits are intensively deformed, almost isoclinal folds with subvetrical hinges are observed, which suggest the strike-slip movements. A tectonic mélange is recorded here, which is represented by small blocks (clastolites) of brittle sandstones, sometimes similar to Shypot sandstones, placed in a silt-pelitic ductile matrix. Foliation of the mélange matrix is also subvertical and close to the meridional and/or subcarpathian direction. The structural studies carried out show that in the zone of this contact there were compressive stresses perpendicular to the Carpathian orogen, and stress fields that caused strike-slip movements, most likely right-lateral along the Carpathian thrusts. The tectonic lens is located within the broad Latorytsa-Stryi shear zone, and probably extruded out from deep horizons by transpressive movements (compression and strike-slip) and forms a “positive flower structure”. The vertical foliation in the mélange suggests that small blocks of Shypot sandstones were extruded up together with the ductile mélange matrix during diapirism. Similar processes probably led to the rise of a large lens of Shypot sandstones as the positive flower structure. The studies suggests that the black shale deposits of the Shypot Formation, enriched with organic matter, are widespread at some depth within the Silesian Nappe, and in some places are pushed up to the level of the Oligocene flysch. As a result, the Shypot Formation and Oligocene flysch are now in direct contact along faults/mélange zones. The presence of Lower Cretaceous potentially oil- and gas-generating black shale deposits within the Silesian Nappe significantly increases the prospects for oil and gas exploration in this area.

Characteristics structures of the mélange zones in the Ukrainian Carpathians

Mélange is characterized by the block-in-matrix fabric in which rigid blocks of different sizes, lithologies, and ages are distributed in a ductile matrix. Though mélange is a significant component of orogenic belts, in the Ukrainian Carpathians, mélanges of tectonic origin have not been reported. We have described the mélange zones widespread in the Pieniny Klippen Belt, Marmarosh Klippen Zone, and the inner nappes of the Outer Ukrainian Carpathians, as well as the typical deformation structures developed within them.
 The mélange matrix is characterized by a scaly fabric formed by cleavage surfaces and somewhere arranged in S-C structures. Lenticular clasts within the matrix show their long axis aligned to the tectonic foliation. Rotation of the boudins occurs against the shear direction following the formation of the S-C structures. The rigid clasts somewhere demonstrate sigma-type rotation structures. Some blocks within the mélange are highly fractured up to tectonic breccias.
 The study of tectonic slicken-sides and other deformation structures within the Pieniny belt demonstrates the presence of regular stress fields correlated with the geodynamics of the Carpatho-Pannonian region. The main stress field indicates the SW-NE regional compression related to the formation of Carpathian nappes and S-N — trending dextral strike-slip faults. Our study in the Priborzhava quarries records the Oash right-lateral strike-slip fault zone. In the Pieniny Klippen Belt some oblique normal faults of the Carpathian direction are related to the Transcarpathian Depression formation. The study showed that the mélange zones in the inner part of the Ukrainian Carpathians were formed largely due to strike-slip movements. In contrast, in the outer part of the Carpathian orogen, they formed mainly due to thrusting.

Deformation pattern of the Lower Triassic sedimentary formations of the Silica Nappe: Evidence for dynamics of the Western Carpathian orogen

Deformation pattern of the Lower Triassic sedimentary formations of the Silica Nappe: Evidence for dynamics of the Western Carpathian orogen

A petrochronological study of Fe[sbnd]Ti oxides in rodingites of the Western Carpathians, Slovakia

Rodingitization is the metasomatic transformation of mafic lithologies into rodingite, a Ca-rich and Si-poor rock associated with serpentinized ultramafic bodies. Serpentinization and rodingitization occur simultaneously but it remains challenging to obtain absolute ages on these events in order to identify the geodynamic setting of their formation. In this study, we investigate rodingites from an occurrence in the Western Carpathians with the aim to define the timing of rodingite formation during the tectono-metamorphic evolution of the Carpathian Orogen. The rodingites consist mainly of vesuvianite, diopside, garnet and chlorite. They are noticeably characterized by the presence of FeTi rich aggregates composed of ilmenite, rutile, titanite and calcite. Textural relationships and chemical compositions of the investigated FeTi minerals document their hydrothermal-metamorphic origin. These minerals are characterized by considerable rare earth element (REE) concentrations with prevailing positive Eu anomaly, which presumably derives from the plagioclase-rich protolith of the investigated rodingites. Moreover, the similarity of REE patterns between the analysed phases suggests that the REE concentrations in FeTi minerals are controlled by the immobility and availability of these elements in the system. A particular lamellae texture composed of rutile and calcite originated from titanite destabilization. The titanite destabilization was triggered by cooling, silica leaching and influx of CO2-rich fluids. In situ UPb dating of rutile, which have formed by retrograde breakdown of titanite during rodingitization, yields a crystallization age of 102.6 ± 19.9 Ma. This age is in good agreement with Cretaceous ages of the regional alpine metamorphic evolution reported in the literature and suggests that the rodingitization and serpentinization processes took place during the exhumation and cooling of the accretionary wedge resulting from the closure of the Meliata Ocean.

Volcanic debris avalanche deposits and their significance in the architecture and evolution of the Miocene-Quaternary Călimani-Gurghiu-Harghita volcanic range (Eastern Transylvania, Romania)

The Călimani-Gurghiu-Harghita volcanic range (CGH) represents the surface manifestation of the post-collisional magmatism that followed the docking of its basement, the Dacia Mega Unit, onto the East European margin. Between ca. 11 and 0.3 Ma, detachment of subducted slab, magma generation, and volcanic activity in CGH propagated south-southeastward, sub-parallel with the collisional Eastern Carpathian Orogen, resulting in the construction of a series of mostly composite volcanoes dominated by calc-alkaline lavas and pyroclastic products. The generally well-preserved axial row of the CGH volcanic edifices is accompanied by voluminous volcaniclastic deposits of which sources and emplacement history persist as a matter of debate. In the standard view reflected in regional scale geologic maps, these deposits represent products of complete erosion of hypothetical earlier volcanoes. Other interpretation, however, suggest that they are at least partially constituted by voluminous volcanic debris avalanche deposits (VDADs).By combining evidence from field observation and GIS analysis with published and new data from petrography, bulk-rock geochemistry, and K/Ar geochronology, here we demonstrate that VDADs vastly dominate these volcanoclastic deposits. In addition to two previously identified VDADs (Western Călimani and Vârghiş), we show that further six VDADs (Eastern Călimani, Fâncel-Lăpuşna, Ostoroş, Ivo-Cocoizaş, Luci, and Pilişca) were generated due to the sector failure of a series of CGH volcanoes, most of which still preserve well-distinguishable collapse scars. Based on our estimates, debris avalanches with volumes between <1 km3 and > 100 km3 displaced 0.4–39% of the source edifices, transferring nearly a third of their cumulated volcanic output to the observed volcaniclastic deposits.K/Ar age constraints suggest VDAD formation closely followed in space and time the migrating volcanic activity between ca. 7.8 and 1.5 Ma. Relying on this age pattern, collapse scar orientations, and VDAD runout directions, we propose that regional scale deformation of the Dacia lithosphere imposed by progressive detachment of the underlying subducted slab, manifested on the surface as a transient subsidence–uplift couple traveling along CGH as well as opening of intramountain basins at the eastern flank of the range, was responsible for basement tilting and faulting that destabilised the CGH volcanic edifices. Seismic activity associated with slab detachment and shallow crustal fault system as well as explosive volcanic eruptions may have triggered the collapse of these edifices, leading to the generation of the VDADs.

Evaluation of the Possibilities Validation of Interval Velocity Models Using Non-Seismic Data and Its Impact on Geological Interpretation of PreSDM Results

The paper presents the problem of generation and validation of Velocity Interval Depth (VID) models with the application of non-seismic geophysical and geological data. The study area is a part of the Carpathian Foredeep located close to its contact with the Carpathian Overthrust. In this area of complicated geological structure, hydrocarbon deposits have been successfully explored for decades with seismic methods and drilling. The research applied the Simultaneous Joint Inversion (SJI) of independent geophysical data, which is a modern methodology of geophysical data processing, that is still under development. Such an attempt was necessary due to the lack of a sufficiently dense grid of wells in the study area, in which seismic velocities would be correctly recorded. Such data would be then applied for the generation of relevant VID models, which in turn, could be used to perform the Prestack Depth Migration (PreSDM) procedures. The application of procedures taking advantage of independent geophysical and geological data enabled researchers to control the generation process of the spatial VID model in the areas without wells. The analyses aimed to verify the correctness of VID model evaluation and its influence on the quality of seismic imaging in the area of the Carpathian Overthrust. Precisely, the influence was tested of such non-standard generation procedure of seismic velocity fields, not only on the PreSDM results but also on the geological interpretation of both the Rączyna and the Jodłówka gas deposits. The latter aspect of the presented results seems to be crucial to the effectiveness of petroleum exploration in the transition zone between the Carpathian Orogen and the Carpathian Foredeep.

Shallow seismic structure around the Vrancea Seismic Zone from joint inversion of ambient noise H/V ratios and surface wave dispersion

The South-East Carpathians in Romania host the Vrancea Seismic Zone (VSZ), an intraplate seismic nest of frequent high magnitude earthquakes that cause unusually high damage over extended areas. Estimating the amplification of seismic signals strongly depends on the depth to the geophysical bedrock and the complex near surface geological structures. To improve seismic hazard estimates and ultimately mitigate seismic risk, we determine the frequency of resonance at 81 broadband seismic stations in southeast Romania using the horizontal-to-vertical spectral ratio (HVSR) of ambient seismic noise. We jointly invert HVSR functions with Rayleigh wave phase velocity dispersion curves using a Markov-chain Monte Carlo algorithm under the assumption of a diffuse field. Our results show excellent correlation between the fundamental frequency of resonance and local surface geology: stations located on foreland sedimentary basins show HVSR peaks in the range 0–1 Hz, while those located in orogenic nappes reach values as high as 10 Hz. Seismic bedrock topography mirrors the crystalline bedrock depth inferred from gravity modeling, but is consistently ∼2000 m shallower, corresponding to the interface between Paleozoic-Triassic to Jurassic-Cretaceous sedimentary levels on the Moesian Platform constrained by borehole data. The near surface seismic model shows anomalously low velocities in the Focsani forearc basin, adjacent to the VSZ, consistent with extremely low resonance frequencies and deep sedimentary layer successions (>5 km). In the back-arc of the Carpathian Orogen, at the contact with the Transylvanian Basin, average resonance frequencies are <2 Hz and inferred seismic bedrock depths vary laterally, likely affected by buried volcanic structures and diapiric salt domes. Our study presents the largest endeavor to study anomalous intensity patterns and local site effects in and around the VSZ and has fundamental implications for seismic risk evaluation and future civil engineering design planning.

The seismic attenuation signature of collisional orogens and sedimentary basins within the Carpathian Orogen

The seismic attenuation signature of collisional orogens and sedimentary basins within the Carpathian Orogen

Three-layer structure of the Carpathian sedimentary prism from the results of seismic migration on the PANCAKE and RomUkrSeis WARR profiles

The method of finite-difference migration of reflected/refracted waves, applied to the PANCAKE and RomUkrSeis WARR seismic profiles, made it possible to form wave images of sedimentary layer and crystalline basement under the Carpathian orogen to a depth of 25 km. The study area belongs to Ukrainian Carpathians, which consist of Outer Carpathians — the Cretaceous-Neogene accretionary prism and Inner Carpathians —fragments of Alkapa and Tissia-Dakia microplates. The Carpathian belt is thrusted over the Neogene Carpathian Foredeep, which was laid on the basement of the Eastern/West European platforms. We used a technique specially developed for WARR study to generate a wave image of basement and deep sedimentary basin. The wave images obtained for two profiles show the presence of deep troughs (accretionary prism) under the Carpathian orogen and reveal their similarities and differences due to the peculiarities of the tectonic development in the junction zone of East- and West European platforms. The sedimentary prism reaches a depth of 20 km and consists of three nested troughs distinguished well in the wave field and characterized by different velocities on velocity models. The upper two layers up to ~15 km belong to the allochthon of the Ukrainian Carpathians and the underlying sequence. Whereas the lower one (15—21 km) could represent the older complexes of the basement, up to the Neoproterozoic age (Ediacaran), associated with accretion of young plates from the west to the East European platform and formation of the Trans-European suture zone. The deep trough along the RomUkrSeis profile is significantly narrower than along the PANCAKE one, which indicates a stronger shortening of the sedimentary basin (and possibly the upper crust) in the southeastern part of Ukrainian Carpathians. The sedimentary prism on both profiles is bounded from both sides by steeply dipping faults — from the east by the Forecarpathian fault, and from the west by the Transcarpathian fault along PANCAKE profile and by the Dragos Voda fault on RomUkrSeis profile, which may indicate active strike-slip tectonics.

The relationship of the oil and gas fields of the Forecarpathian region with the regional faults system and deep structure

The oil and gas fields of Forecarpathian oil and gas region are compared with the structure of earth’s crust and regional faults. Most of the oil and gas condensate fields are localized in Borislav-Pokutia nappe over Precarpathian Fault zone. The majority of gas fields are located in under thrusting zone of the Sambir fault, which is a gently dipping detachment connected with the Forecarpathian fault and other faults of autochthonous basement. The regional gravity low of Carpathian Foredeep is also limited from northeast by the Sambir fault and from the southwest by the Uzhok fault. The Forecarpathian fault tends to the central part of gravity low. Transverse Tyachev-Nadvorna fault displaces the gravity low and delimits the oil and gas condensate fields. Velocity model along the wide-angle reflection and refraction PANCAKE profile shows a deep (25 km) sedimentary trough under the Carpathian Orogen. The Forecarpathian fault coincides with a jump of the Moho under the trough. Along the RomUkrSeis profile under Carpathian Orogen there were revealed a sedimentary trough as deep as 15 km and a low-velocity domain under the trough. From northeast, the trough is limited by the Forecarpathian fault, which goes up to the keel structure of the Moho discontinuity. Structure of the trough under Carpathian Orogen reflects development of East European Platform margin. The earliest stage of the formation of Baltica paleocontinent passive margin is seen in the structure of the trough’s lower part. Autochthonous basement under Borislav-Pokutsky and Skiba nappes includes a Riphean Massif limited by the Krakovets, Forecarpathian and Uzhok faults. The oil and gas condensate fields are located above the Riphean Massif.&#x0D; The purpose of this article is to analyze the fault system and the structure of the earth’s crust in the Forecarpathian oil and gas region, as well as their relationship with the distribution of oil and gas deposits, taking into account new WARR profiles and other geological and geophysical data.

ГЕОДИНАМІКА

The purpose of the work is the analysis and geological-tectonic interpretation of the anomalous gravity field of the Ukrainian Carpathians and adjacent territories, as well as the construction of a density model of the Earth's crust and upper mantle according to the international PANCAKE seismic profile. The need to build a density model along the PANCAKE profile is due to the significant interest of a number of geologists and geophysicists in the results of seismic research along this profile. It is also caused by certain discrepancies in the seismological models of different authors. The gravity modeling technique, used in the work, includes the analysis of geological-geophysical maps and models. They are related to the geological-tectonic structure of the research region, to the creation of the initial structural part of the model and to the determination of the densities of strata and blocks of the model. The geometry and densities of the model are refined by the selection method, which is based on the interactive solution of the direct problem of gravimetric and the analysis of the reasons for the inconsistency of the calculated gravity field and Bouguer anomalies. A qualitative correspondence of the density model to the tectonic interpretation of the seismic section along the PANCAKE profile was achieved by using the methods of gravity modeling. The modelling results confirm the four-layer structure of the Earth's crust: the sedimentary cover, the upper, middle, and lower parts of the crust, which differ significantly in density. There is also evidence of the difference of the ALCAPA lithospheric plate, Flysch Carpathians and Precambrian Craton in Earth's crust and upper mantle structure. The ALCAPA plate is characterized by a small thickness (up to 29 km) and a low density of the Earth's crust. The density of the ALCAPA upper mantle is lower (3.20-3.21×103 kg/m3) compared to the upper mantle under the Ukrainian Carpathians and the East European Craton (3.28-3.30×103 kg/m3). This may be related to a change of a mantle composition and increased heat flow under ALCAPA. The Ukrainian fragment of the East European craton in the PANCAKE profile zone is characterized by a typical thickness of the crust (~41-45 km). The upper part of the crystalline crust, in contrast to the middle (2.86-2.90×103 kg/m3) and the lower part (2.98-3.10×103 kg/m3), is characterized by a lower density and greater differentiation in horizontal direction and with depth (from 2.66×103 kg/m3 to 2.86×103 kg/m3). The complex transition zone (subduction zone, Carpathian Orogen) between the ALCAPA microplate and the East European Craton causes an intense negative Bouguer anomaly – the Carpathian gravity minimum, which reaches -90×10-5 m/s2. It has a complex nature: Neogene and Paleogene-Cretaceous flysch rocks low density (≤2.50×103 kg/m3) of the Boryslav-Pokuttia cover, the main huge Precarpathian sub-vertical fault (&gt;4 km) on the extreme southwestern slope of the platform (relatively local factors) and significant deepening of the MOHO surface under the Carpathian structure (regional factor). According to our density model, the depth of the MOHO under the front of the Carpathian thrust reaches 56 km.

RHAETIAN FORAMINIFERS FROM THE WESTERN BLACK SEA SHELF: NEW EVIDENCE FOR HETEROZOAN CARBONATE FACTORIES IN THE PALAEOTETHYS

The North Dobrogean Orogen (NDO) is a NW-SE trending fold-and-thrust belt in the eastern foreland of the Alpine Carpathian Orogen, palaeogeographically representing the westernmost segment of the Palaeotethys-issued Cimmeride Orogenic System. Eastwards, the NDO structurally extends into the Romanian sector of the western Black Sea continental shelf. The Triassic development of North Dobrogea is well known for its Tethyan-type facies and richness in various groups of fossils, but little attention has been paid to microfacies and fossil content of the offshore Triassic. The drill hole 817 LV of the Lebada Vest oilfield, offshore Romania, ends in the Rhaetian (Upper Triassic) limestone olistolith, from which a rich association of foraminifers and ostracods was recovered. The limestone also contains sponge spicules, mollusc fragments, echinoderm ossicles, bryozoans, and brachiopods. Foraminiferal assemblage from the residue consists of agglutinated species only. Tolypamminids, Gaudryinopsis triadica (Kristan-Tollmann), G. triassica (Trifonova), G. kelleri (Tappan), Ammobaculites tzankovi (Trifonova), A. zlambachensis Kristan-Tollmann, Verneuilinoides racema (Trifonova), and Trochammina spp. predominate. Non-agglutinated species, determined from thin sections include Ophthalmidium spp., and rare involutinids Trocholina ex gr. intermedia/umbo and “Involutina turgida” (Involutina ex gr. liassica). The rich ostracod assemblage is dominated by Bairdiidae. Species of the Paracyprididae and Sigilliidae families are rather common. The conodont Norigondolella steinbergensis (Mosher) was also found. The deposition is suggested to take place in a relatively deep setting (outer shelf) offshore heterozoan-dominated platform in relatively cool waters.

Assessment of the influence of the overthrusting Carpathian orogen on the course of petroleum processes in its basement formations in the Rzeszów region

The article presents the concept of petroleum systems modeling in the area with complex fold-thrust belt structure. The aim of the study was to verify the views on the influence of the overtrusting Carpathian orogen on the course of petroleum processes in the basement (Meso-Palaeozoic) formations. The project was implemented in the marginal zone of the Skole Unit (Outer Carpathians) overlapping various structural and tectonic units of the basement. The area of Rzeszów city was selected as it presents adequate complexity of the geological structure to meet assumed methodological objectives of the project and, at the same time, provides relatively vast amount of geological data available which creates a conditions for a comprehensive approach. The study was carried out using the Dynel 2D and PetroMod 2D software. The course of the structural and tectonic evolution of the area was reconstructed in 5 stages, the results of which were subsequently applied in a dynamic modeling of the petroleum systems. The modeling results made it possible to recreate and analyze the course of a complex geological processes, the effects of which are manifested, among others, by the time and amounts of generated hydrocarbons as well as the dynamics of expulsion, migration and accumulation processes. The results show the course of petroleum processes in each stage of the petroleum basin evolution, revealing a special role of thrust tectonic of Outer Carpathians on basement formations. For the adopted assumptions of the structural and tectonic evolution, the generation of hydrocarbons by Lower Palaeozoic source rocks was initiated with the overthrusting of the Carpathians. This increases the chances of their accumulation in reservoir intervals sealed by an overthrusting orogen. This is a positive premise in the context of petroleum exploration in the area.

Geological control of young orogenic mountain morphology: From geomorphological analysis to reinterpretation of geology of the Outer Western Carpathians

The paper presents a new concept of geological control of the Outer Western Carpathians (OWC) morphology. The establishment of the Carpathians' morphology dates back to the stage of evolution of sedimentary basin, when huge blocks of solidified rock massifs were gravitationally displaced into the foreland sedimentary basins, forming finally isolated hills. The altitudinal difference between the Beskidy Mts. and the Carpathian foothills is caused by the structural positions of these two segments of rock massifs within the orogenic megastructure during the compressional stage. Indeed, the tectonic elements that formed during the earliest stage of compression took (and still take) the highest structural and altitudinal position, whereas the elements incorporated into the orogen as the last have taken a lower topographic position, forming a belt of foothills. Therefore, this difference in topography is not related to rock resistance only, as was previously thought. The rotation of the Carpathian blocks during the orogenic thrusting and the formation of strike-slip fault zones parallel to the Carpathian tectonic thrusts formed a flower structure, which has played a significant role in morphology (insular character of). During the stage of secondary tectonic deformation – including the rotation of the Carpathian tectonic segments, strike-slip faulting and the radial extension and large extensional collapse of the Carpathian massifs – the principal features of the Carpathian relief as well as the main river valleys were formed. Gravitational collapse resulted in back-thrusting and the tectonic exhumation of the Carpathian massifs, which helps to explain the problem of seemingly large denudation of the Carpathian overburden of a thickness estimated at several kilometres. Chaotic complexes (synsedimentary and syntectonic mélanges), which frequently occur in the Carpathians, are very important for the Carpathian morphology and river valley development (controlled not only by faults) as well as the formation of isolated hills. Analysis of the Carpathian morphology supported by the Bouguer's gravity anomalies map, and geological data allow us to present a new hypothesis that the Carpathians were formed as a huge regional flower structure, without the participation of subduction, which has formerly been considered to play the crucial role in the formation of the Carpathian orogen.

Foreland migration of orogenic exhumation during nappe stacking: Inferences from a high-resolution thermochronological profile over the Southeast Carpathians

The exhumation mechanism of orogens showing one structural vergence, or single-sided orogens, is still not fully understood due to their common transition from periods of high convergence to slab retreat. The overprinting of inherited nappe stacks by subsequent back-arc extension makes it difficult to assess the low amounts of contractional exhumation observed, which are furthermore difficult to interpret due to long residence times in partial retention zones of typical low-temperature thermochronology markers. This is the case in many orogens worldwide and is often observed in the Mediterranean area as well. One notable exception is the Romanian segment of the Carpathian Mountains, where the back-arc extension took place far from the location where the nappe stack formed. To understand the mechanics of contractional exhumation in this single-sided orogen, we generated a new high-resolution low-temperature (apatite fission-track and U-Th/He) thermochronological transect across the Southeast Carpathian nappe stack and its foreland. This new dataset and its correlation with previous exhumation and kinematic studies demonstrate that the gradual accretion of sediments and crustal material was associated with an exhumation that migrated progressively towards the foreland throughout the entire contractional history. The exhumation style changed when the thin-skinned deformation was interrupted by periods of crustal accretion, associated either with the late Eocene onset of continental collision or with the late Miocene locking of the subduction system. The generally accepted moments of onset and termination of slab retreat are not directly visible in available exhumation data of the Southeast Carpathians. Our results are in agreement with modelling studies, which inferred that the formation of single-sided collisional wedges is primarily controlled by the pre-existing rheology of continental plates and is associated with large amounts of continental subduction. • Formation of the Southeast Carpathian orogen is associated with a pattern of migration of exhumation towards the foreland; • The initial exhumation pattern is modified by the onset of continental collision and locking of the subduction system; • The formation of such orogens is primarily controlled by plates rheology and prolonged periods of continental subduction.

The missing craton edge: Crustal structure of the East European Craton beneath the Carpathian Orogen revealed by double-difference tomography

The Trans-European Suture Zone (TESZ) is the most important and extensive continental suture in Europe, marking the edge of the East European Craton (EEC), from the North Sea to the Black Sea. It corresponds to significant changes in surface geology and deep crustal structure, evident in seismic, gravitational and magnetic studies. However, the TESZ disappears beneath the Eastern Carpathians accretionary nappes and Neotethys ophiolites, thrusted over the subducted EEC passive margin in Romania that may have experienced progressive southward break-off generating post-collisional volcanism and anomalous seismicity in the Vrancea region of the South-East Carpathians. To illuminate the missing TESZ section and investigate the change in crustal properties from the Precambrian EEC across the collisional orogen and the impact of related volcanism, we determined a 3D seismic model of P and S wave velocities of the Eastern Carpathians in Romania. With the advent of new permanent broadband and short-period seismic stations of the Romanian Seismic Network, we were able to lower the earthquake magnitude detection threshold to 0.5 ML, largely expanding the earthquake database and create seismic images of the crust across the Carpathians. Using double-difference tomography and waveform cross-correlation differential times, we relocated local crustal earthquakes between 2010 and 2017 and jointly inverted for the 3D P and S -wave velocity structure down to the Moho discontinuity. Our study provides the highest resolution 3D crustal seismic model of this area to date and emphasizes the manifestation of surface tectonic boundaries at lower crustal depths. The TESZ is highlighted at mid-to lower-crustal depths beneath the Carpathian nappes, east of the post-collisional volcanic belt, as a gently-dipping transition from high Vp in the eastern footwall, the dipping Precambrian basement, to low Vp beneath the Carpathian Orogen to the west and a downward decrease in Vp/Vs. In parts of the volcanic region, Vp/Vs ratios increase suggesting the presence of fluids, mafic material and partial melts that may have altered the seismic structure of the TESZ. Relocated hypocenters are vertically distributed in the velocity transition zone from low to high especially beneath the youngest volcanoes in the south, consistent with a hypothetically active magmatic plumbing system. In the northern segment, where volcanoes are older, relatively high velocities are estimated and seismicity tends to cluster in the top 10 km, likely connected to a recently reactivated fault system. Seismicity in the foreland of the East Carpathians aligns along the NW-SE trending major crustal faults and continues beneath the thrust belt, suggesting the East European Craton basement extends beneath the orogen as far as the volcanic belt.

RomUkrSeis: Seismic model of the crust and upper mantle across the Eastern Carpathians – From the Apuseni Mountains to the Ukrainian Shield

RomUkrSeis is a controlled source wide-angle reflection and refraction (WARR) profile acquired in August 2014. It is 675 km long, running roughly SW-NE from the Apuseni Mountains in Romania and the Transylvanian Basin, crossing the arc of the Eastern Carpathian orogen and terminating in the East European Craton (EEC) in SW Ukraine. Well-constrained 2-D ray-tracing P- and partly S-wave velocity models have been constructed along the profile from 348 single-component seismic recorders and eleven shot points. The Eastern Carpathian arc formed in the Cenozoic and have obscured the pre-existing Teisseyre-Tornquist Zone (TTZ), which is a transition zone between the Precambrian EEC and continental terranes accreted to it from the southwest in the Palaeozoic. The TTZ is characterised by low-velocity through its entire crust (6.0–6.3 km/s) and a considerable width (~140 km). It is interpreted as EEC crust stretched during rifting and continental margin formation in the Neoproterozoic and early Palaeozoic. The crust of the TTZ has a “trough in trough” structure wherein an upper body of ~40 km width comprising Outer Carpathian (Vp 4.9 km/s) and Late Palaeozoic-Mesozoic (Vp 5.4 km/s) units to 15 km depth lies above a wider, deeper one of inferred Neoproterozoic-early Palaeozoic strata. The crust of the Transylvanian Basin and Apuseni Mountains is relatively thin (~32 km). A high-velocity body at 4–12 km depth in this area is interpreted as a rootless fragment of an ophiolite complex exposed at the surface in this area. The lower crust beneath the Transylvanian Basin displays higher velocities than adjacent segments. Moho topography is strongly differentiated along the profile, varying from 32 to 50 km. The Moho shape, especially in the area between the Inner and Outer Carpathians, suggests a NE dip and, hence, thrusting of the Tisza-Dacia lowermost crustal and upper mantle units under the TTZ domain which, in turn, could be thrust under the cratonic (EEC) block.