Carpathian Thrust Belt Research Articles

Source rock potential of the Miocene sedimentary rocks in the Carpathian Foredeep of the Czech Republic

We determine the organic matter content, its thermal maturity, genetic type, and source rock potential of the Miocene sedimentary rocks in the Czech Carpathian Foredeep. In the Czech Republic the Carpathian Foredeep represents a peripheral foreland basin formed due to the tectonic emplacement and loading of the Alpine-Carpathian Thrust Wedge onto the passive margin of the Bohemian Massif. Random vitrinite/huminite reflectance measurements and maceral analyses were performed on 25 samples from the Carpathian Foredeep succession. Additionally, results of 135 TOC content measurements, 141 Rock-Eval pyrolysis analyses and 27 vitrinite reflectance measurements were used to evaluate the regional distribution and depth trends for the entire Carpathian Foredeep. The thermal maturity of organic matter is between the immature part and peak of the oil window (Tmax = 413–448°C). Beneath the Western Carpathian Thrust Belt, the thermal maturity reaches higher values (Rr = 0.43–0.58%, Tmax = 429–448°C). The hydrocarbon generation potential is poor or fair, even if the total organic carbon values indicate good or even very good source rock potential. This is mainly due to the prevailing gas-prone Type III kerogen. The best source rocks were observed in the Miocene strata of the southern and central segments of the area discussed.

Selected aspects of modern seismic imaging and near-surface velocity model building in the area of Carpathian fold and thrust belt

Despite the increasing technological level of the reflection seismic method, the imaging of fold and thrust belts remains a demanding task, and usually leaves some questions regarding the dips, the shape of the subthrust structures or the most correct approach to velocity model building. There is no straightforward method that can provide structural representation of the near-surface geological boundaries and their velocities. The in-terpretation of refracted waves frequently remains the only available technique that may be used for this purpose, although one must be aware of its limitations which appear in the complex geological settings. In the presented study, the analysis of velocity values obtained in the shallow part of Carpathian orogenic wedge by means of various geophysical methods was carried out. It revealed the lack of consistency between the results of 3D refraction tomography and both the sonic log and uphole velocities. For that reason, instead of the indus-try-standard utilization of tomography, a novel, geologically-consistent method of velocity model building is pro-posed. In the near-surface part, the uphole velocities are assigned to the formations, documented by the surface geologic map. Interpreted time-domain horizons, supplemented by main thrusts, are used to make the velocity field fully-compatible with the litho-stratigraphic units of the Carpathians. The author demonstrates a retrospective overview of seismic data imaging in the area of the Polish Carpathian orogenic wedge and discusses the most recent global innovations in seismic methodology which are the key to successful hydrocarbon exploration in fold and thrust regions.

Application of fluorescent light microscopy to enhanced lithofacies analysis of Jurassic carbonate rocks, SE Bohemian Massif

Upper Jurassic limestones and dolomites of the Vranovice Formation occur on the southeastern slopes of the Bohemian Massif below the Western Carpathian thrust belt. They represent a special type of reservoir rocks in the potential geothermal systems and exhibit highly variable porosity, permeability, and flow mechanisms due to different type of diagenesis and pervasive dolomitization. Fluorescence and translucent light microscopy was used for more detailed petrographic analysis of Vranovice limestones and dolomites. Isopachous, syntaxial and dolomitic cements were distinguished along with fossils recrystallization. Two generations of dolomite were identified – replacement dolomite and zonal cementation dolomite, what suggests a number of changes in the formation water chemistry during the dolomitization process. Extent of the observed dolomitization is inversely related to the porosity of the Jurassic rocks. Postdiagenetic generation of fissures cutting the strata due to tectonic deformation is documented by bright fluorescent color. In the studied samples of Vranovice limestones and dolomites the fissures represent the most important migration pathways, more than pore throats themselves. Further genetic information on petoleum migration is interpreted from intercrystalline porosity filled with precipitated solid bitumen. Present results provide basis for further investigations in pore-water-rock interactions and changes in chemical conditions during diagenesis.

Where is There Chance to Find Deep Prospects Below the Outer Western Carpathian Thrust Belt?

In the period of 80 and 90th, the intensive deep drilling and seismic profiling program in the Outer Western Carpathian belt has been realized for confirming the idea about the existence and opening of new promising plays beneath some of these thin-skinned belts. Many trans-Carpathian 2D seismic transects opened discussion on the understanding of the complex structure of thrust belts and its basement. The recent development of exploration, based on the new modern play concepts, has brought new light on this problem. The new 3D and the reprocessed 2D seismic sections from Czech and Slovak part of the Western Carpathian Flysch Belt disclosed several potentially new prospects, combined with the cover of the foreland of European plate. New significant reserves of hydrocarbons may occur in subthrust autochthonous and parautochthonous series buried below the frontal zones of thin-skinned thrust belts. The study of the deepest parts of the Carpathian Flysch belt has been based on the complex geochemical, structural analyses and geophysical Data reprocessing, supplied by verification along the chosen balanced sections. Four examples of 2D seismic transects, with registration up to 9-12 seconds, that present different tectonic style of structures of Flysch Belt and its platform basement, influenced by older large-scale faults, is presented from the western, northern and eastern parts of the Outer Western Carpathians. From point of view of hydrocarbon prospection, the most important features of the seismic profiles are the anticline structures of the North European Platform (NEP) below the thrust stack of the Flysch Belt. From the west to east the Týnec-Cunín, Drietoma, Orava and Zbudza elevations can be distinguished, created by a passive margin of the European plate, in the second and third structures probably by parautochthonous blocks of the same plate.

Burial history, thermal history and hydrocarbon generation modelling of the Jurassic source rocks in the basement of the Polish Carpathian Foredeep and Outer Carpathians (SE Poland)

Burial history, thermal history and hydrocarbon generation modelling of the Jurassic source rocks in the basement of the Polish Carpathian Foredeep and Outer Carpathians (SE Poland)Burial history, thermal maturity, and timing of hydrocarbon generation were modelled for the Jurassic source rocks in the basement of the Carpathian Foredeep and marginal part of the Outer Carpathians. The area of investigation was bounded to the west by Kraków, to the east by Rzeszów. The modelling was carried out in profiles of wells: Będzienica 2, Dębica 10K, Góra Ropczycka 1K, Goleszów 5, Nawsie 1, Pławowice E1 and Pilzno 40. The organic matter, containing gas-prone Type III kerogen with an admixture of Type II kerogen, is immature or at most, early mature to 0.7 % in the vitrinite reflectance scale. The highest thermal maturity is recorded in the south-eastern part of the study area, where the Jurassic strata are buried deeper. The thermal modelling showed that the obtained organic matter maturity in the initial phase of the "oil window" is connected with the stage of the Carpathian overthrusting. The numerical modelling indicated that the onset of hydrocarbon generation from the Middle Jurassic source rocks was also connected with the Carpathian thrust belt. The peak of hydrocarbon generation took place in the orogenic stage of the overthrusting. The amount of generated hydrocarbons is generally small, which is a consequence of the low maturity and low transformation degree of kerogen. The generated hydrocarbons were not expelled from their source rock. An analysis of maturity distribution and transformation degree of the Jurassic organic matter shows that the best conditions for hydrocarbon generation occurred most probably in areas deeply buried under the Outer Carpathians. It is most probable that the "generation kitchen" should be searched for there.

Sedimentary Records of Paleogene (Eocene to Lowermost Miocene) Deformations near the Contact between the Carpathian Thrust Belt and Moesia

The kinematic models proposed for the Tertiary evolution of the Romanian Carpathians explain its arcuate shape by the progressive displacement of the upper plate (Tisza-Dacia block) around the western margin and then along the northern margin of Moesia, the latter representing the stable foreland autochthon. The main tectonic events took place in the Eocene when a former nappe pile, formed by the end of the Cretaceous and representing the actual Southern Carpathians, underwent extension. This episode was followed by dextral wrenching that was accompanied by the opening of the Getic Depression as a pull-apart basin along the northern Moesian margin, at the current location of the Southern Carpathian foothills. This deformation operated from Oligocene to Lower Miocene times. Although from the Lower Miocene onwards the progressive eastwards motion of the Tisza-Dacia block accounted for well-defined accommodating structures in both the frontal (Eastern Carpathians) and lateral (Getic Depression) sides of the accretionary wedge, the Eocene to Lower Miocene tectonics left apparently no imprint upon the outer thin-skinned belt.We have looked for the sedimentary records of these tectonic events by building and integrating several detailed sedimentary logs near the contact between the Outer Carpathians and Moesia. Two main facies associations were defined in terms of basin energy, i.e. proximal high-energy prograding associations, represented by coarser sedimentary units and distal variable-energy aggrading associations. Based on the wide incision observed at the base of the high-energy units and on the clast provenance, we assume a tectonic origin for the vertical changes observed in the dipping attitude of the beds, which account for angular unconformities. Importantly, the regional correlation of the Eocene-Lowermost Miocene formations points to a progressive migration in time and space of the high-energy sedimentary units, which get younger eastwards, consistent with the direction of the tectonic transport of the Carpathian allochthon.

Oil reservoirs in foreland basins charged by thrustbelt source rocks: insights from numerical stress modelling and geometric balancing in the West Carpathians

Abstract The West Carpathian thrustbelt advanced northeastwards over the European Platform. Its thrust sheets comprise sediments of the Early Cretaceous rifts that evolved on a passive margin of the European Platform, the Late Cretaceous-Paleocene basins formed by rift inversion, and the Eocene-Oligocene flexural basin. Geochemical analyses established a clear link between pooled oils in the foreland and the Oligocene Menilite Formation inside the thrustbelt. In order to understand the driving forces for this oil migration scenario, finite-element models of fault-propagation and fold-bend folds are used to study the mean stress distribution in the thrust sheets and the foreland. Mean stress has a profound control on the pore fluid pressure through the relationship affected by sediment porosity, and sediment skeleton and fluid compressibilities. Modelling results suggest that only fault-propagation folds are capable of generating foreland-directed mean stress gradients as they are characterized by a large foreland area of decreased mean stress, by coupled increased/decreased mean stress areas on advancing/receding sides of the ramp tip, and an overall mean stress decrease inside the thrust sheet in the direction towards the foreland. This interpretation is in accordance with the dominant fold-and-thrust style in the Western Carpathians inferred from balanced cross-section restoration. It shows that frontal fault-propagation folding was active during the late Oligocene-Early Miocene, providing an effective tectonic driving force for hydrocarbon migration from source rocks inside the thrustbelt towards reservoirs in the foreland.

Biomarker oil-to-source rock correlation in the Western Carpathians and their foreland, Czech Republic

Biomarker analyses indicate that at least two petroleum systems operate in the Vienna basin, Carpathian thrust belt and the European foreland plate in Moravia--one associated with Jurassic and the other with Palaeogene organic-rich rocks. Four oils from the sub-Carpathian foreland plate and one sample from the Vienna basin were analysed and geochemically compared to extracts from Jurassic and Palaeogene source rocks. Two oils from the subthrust foreland plate Lubna-18 and Dolni Lomna-1) are genetically related based on similar geochemical compositions. These oils show high oleanane and 24-nordiacholestane ratios, age-related biomarker ratios that are consistent with an origin from Palaeogene organic-rich rocks. These rocks are inferred to be either the Menilitic shales of the Carpathian thrust belt or autochthonous Palaeogene deposits buried below the thrust belt. Two other oils from the subthrust plate (Zdanice-7 and Damborice-16 correlate geochemically with extracts from Jurassic source rocks in the Sedlec-1 and Nemcicky-1 wells. Like the oil extracts, these oils lack oleanane and show low 24-nordiacholestane ratios, supporting an origin from Jurassic organic-rich marls. The oil sample from the Vienna basin (Tynec-34) appears to be a mixture of the two oil groups.

Possibilities of Hydrocarbon Exploration Beneath and Within the Northern Carpathian Thrust Belt :ABSTRACT

Possibilities of Hydrocarbon Exploration Beneath and Within the Northern Carpathian Thrust Belt :ABSTRACT

Exploring for Hydrocarbons Under Thrust Belts--A Challenging New Frontier in the Carpathians and Elsewhere

New significant reserves of hydrocarbons may occur in subthrust autochthonous and parautochthonous series buried below the frontal zones of thin-skinned thrust belts. The subthrust plays have been tested in several orogenic belts of the world, the Carpathians being one of the best examples. The arcuate thin-skinned Carpathian orogenic belt, which evolved during the Mesozoic and Cenozoic, is thrust tens of kilometers over its Neogene foredeeps and the underlying European plate. Various structural and stratigraphic settings and potential hydrocarbon plays have been recognized within the buried margins of the European plate, including a late Paleozoic Hercynian compressional system, Mesozoic rifted margins of the Tethys, and a Cenozoic synorogenic foreland-type fault system. Possibly, deeper parautochthonous structures, documented on examples from the southern Apennines, may also be present below the thin-skinned frontal zone of the Carpathian thrust belt. In addition to these structural settings, large Paleogene valleys/submarine canyons have been found within the margins f the European plate. These structural and morphologic features, if combined with source rocks, reservoirs, and proper burial history, represent potential hydrocarbon plays. Generation of hydrocarbons from sources within the subthrust plate was greatly enhanced by emplacement of the wedge-shaped thrust belt, which may also provide a regional seal; therefore, the combination of the long and complex geological history of the European plate with the impact of the Alpine thrusting and foreland deformation created unique conditions for generation, entrapment, and preservation of hydrocarbons in subthrust settings.

Exploration for Hydrocarbons Under Thrust Belts: A Challenging New Frontier in the Carpathians

The Carpathian thrust belt has been explored with mixed results. Large reserves of oil and gas have been found in Romania and the western Ukraine, while exploration in other areas has been disappointing. Deep drilling and seismic profiling, as well as better understanding of structure, however, has contributed to the opening of promising new plays beneath the allochthonous belt. The thin-skinned Carpathian thrust belt is characterized by a long-range tectonic transport over the Neogene foredeep and the underlying European platform. The complex structure of the platform involves Caledonian and Variscan compressional deformation, Mesozoic extension, related to the development of the northern Tethyan margins, and Cenozoic normal faulting and wrenching associated with the Alpine Orogeny. Elements of the platform were also detached and incorporated into the thrust belt proper. In addition to numerous structural plays, significant morphologic features, such as large Paleogene and neogene buried valleys, have been found within the platform margins. Both the valley fill and the associated subsea fans and channels represent promising plays. Generation of hydrocarbons from various source rocks within the platform was greatly enhanced by emplacement of the wedge-shaped Carpathian thrust belt. The low heat flow, typical for the subthrust setting, enabled generation and preservationmore » of hydrocarbons at great depths. Although several oil and gas fields have been found in shallower parts of the platform, the deeper structures (below 5 km) remain mostly unexplored. The complexity and diversity of subthrust geology offers a big challenge to exploration, but also provides an opportunity for finding significant oil and gas accumulations not only in the Carpathians, but elsewhere under thin-skinned thrust belts.« less

Structural Style Analysis as a Hydrocarbon Exploration Basis for the Carpathian Thrust Belt of Romania

As a result of a Cretaceous-Tertiary sedimentary wedge movement over a basal detachment surface, the present structure of the Carpathian Thrust Belt was successively completed by the Miocene compressional stages of the Alpine Orogenesis. The major basal detachment overpassed the platform, ending at different stratigraphic levels as a [open quotes]blind[close quotes] thrust. The inner thrust sheets were formed by a fault bend folding mechanism, while the outer sheets were formed, primarily, by a propagation fold. The vertical play of the platform blocks created a complex ramp geometry which represents the main control for the deep structural style. The platform thresholds retained the displacement of the thrust sheets, generating duplex systems. In order to illustrate the main structural features, several regional cross sections have been analyzed and balanced. Selected examples point out how the depositional and structural history of parts of the Thrust Belt and their associated hydrocarbon accumulations can be interpreted and evaluated to reduce the exploration risk. Considering the intense exploration of the shallow and medium depths of the Carpathian Thrust Belt petroliferous basins, indentification of new targets relies upon understanding the original distribution of the source and reservoir rocks and the tectonic transport mechanisms which placed them inmore » an allochthonous position over the platform. Therefore, some restored sections have been used to map the initial location of the hydrocarbon prospective facies. Local structural styles of deep levels have also been examined in an attempt to discover new duplex systems.« less

Tectonic Setting and Hydrocarbon Habitat of External Carpathian Basins in Romania

During the Alpine evolution of Romania, two distinct depositional areas evolved in the external zones of the Carpathians: the Paleogene flysch and Neogene Molasse basin of the eastern Carpathians, and the Paleogene and Neogene Molasse basin of the southern Carpathians. Both basins were compressionally deformed during the Neogene, giving rise to the development of a succession of nappes and thrust sheets. The internal elements of the external Carpathians corresponding to the Tarcau and marginal folds nappes and the external elements forming the sub-carpathian nappe and foredeep were thrusted over significant distances onto the European platform. Intense exploration of the external Carpathian thrustbelt has led to the discovery of more than 100 oil and gas pools. Reservoirs are provided by Oligocene, Burdigalian, Sarmatian, and Pliocene clastic rocks. A prolific hydrocarbon charge is derived from regionally distributed Oligocene oil source rocks. Traps are mainly of the structural type and involve faulted anticlines, [open quotes]scale folds,[close quotes] and compressional structures modified by salt; stratigraphic pinch-out and unconformity related traps play a secondary role. On the basis of selected examples, the development and distribution of hydrocarbon pools will be discussed in terms of thrust kinematics and the structure of different platform blocks. The philosophymore » of past exploration activities will be reviewed, and both success cases and failures will be discussed. Remaining oil and gas plays, aimed at shallow as well as at deep objectives, will be highlighted.« less

Paleogene Canyons of Tethyan Margin and Their Hydrocarbon Potential, Czechoslovakia

Two Paleogene canyons buried below the Neogene foredeep and the Carpathian thrust belt in Southern Moravia have been outlined by drilling and seismic profiling. The features, as much as 12 km wide and over 1000 m deep, have been traced for 40 km. They are cut into Mesozoic and Paleozoic carbonate and clastic deposits and underlying Precambrian crystalline rocks. The sedimentary fill is made of late Eocene and early oligocene marine deposits, predominantly silty mudstones and siltstones. Sandstones and conglomerates are distributed mainly in the lower axial part of the valleys. Proximal and distal turbidites, grain-flow and debris-flow deposits have been identified in the fill. The common occurrence of slump folds, pebbly mudstones, and chaotic slump deposits indicate that mass movement played a significant role in sediment transport inside the canyons. The canyons are interpreted as being cut by rivers, then submerged and further developed by submarine processes. The organic rich mudstones of the canyon fill are significant source rocks (1-10% TOC). They reached the generative stage only after being tectonically buried below the Carpathian thrust belt in middle Miocene time. Channelized sandstones and proximal turbidities provide reservoirs of limited extent, although more substantial accumulations of sands are possible furthermore » downslope at the mouth of these canyons. Several oil fields have been discovered both within the canyon fill and the surrounding rocks. Similar Paleogene valleys may be present elsewhere along the ancient Tethyan margins buried below the Neogene foredeeps and frontal zones of the Alps and Carpathians. Their recognition could prove fruitful in the search for hydrocarbons.« less

Evolution of the Pannonian Basin System: 1. Tectonics

The Carpathian arc formed during Cretaceous to Miocene time by continental collision between Europe and smaller continental fragments following southward and westward subduction of ocean floor. During the last stages of thrusting in the outer Carpathians, a set of discrete basins formed behind the Carpathian loop. These basins are regions of middle to late Miocene extension and are connected to each other and to areas of coeval shortening in the outer Carpathian thrust belt by a system of strike‐slip faults. Sinistral northeast trending and dextral northwest trending sets of conjugate shears reflect overall east‐west extension of the intra‐Carpathian region during middle to late Miocene time. Palinspastic reconstruction of the basins indicates about 100 (±50) km of east‐west extension across the intra‐Carpathian region during this time. We interpret the Vienna basin, which is superimposed partly on the flysch nappes of the outer West Carpathians, as the result of thin‐skinned extensional tectonics above a shallow detachment surface within the crust. Extension of upper crustal rocks above this detachment was probably accomodated by thrusting of the outermost nappes of the West Carpathians over the European platform. Extension of basins farther inside the Carpathian loop probably involved rocks at deeper crustal levels and within the upper mantle. The most internally situated basins formed by extensional processes that involved the entire lithosphere. Thus the depth to which extension occurred seems to be closely related to the proximity of each basin to the active thrust front in the Carpathians. This can be related to the geometry of the subduction zone. Extension within the intra‐Carpathian basins began first in the northernmost basins and migrated southward and eastward over a ten million year period. Palinspastic reconstruction of the basins at three different times during the Miocene (17.5, 16.5 and 13.0 Ma) predicts eastward migration of the zone of thrusting and shortening within the Carpathian mountains to accomodate the synchronous eastward and southward migration of areas of extension. From these reconstructions, about 120 (±60) km of east‐west shortening is predicted across the outer East Carpathians from about 17.5 Ma until present. Both predictions are in good agreement with the timing and magnitude of shortening in the Carpathian thrust belt as determined directly from rocks within the belt. From this we infer a close relationship for middle to late Miocene extension of the intra‐Carpathian region and middle to late Miocene crustal shortening within the outer Carpathians. During middle and late Miocene time, deformation of the Pannonian fragment was dominated by extensional and wrench tectonics, except along a narrow zone in the outer Carpathian thrust belt. Middle and late Miocene thrusting in the Carpathians is interpreted as the result of simple shear caused by relative motion between Europe and the overriding Pannonian fragment at the subduction boundary, rather than of regional compression of lithospheric rocks at depth. The initiation of extensional tectonics within the intra‐Carpathian region in middle Miocene time can be related to reorganization of major fragment boundaries of the Eastern European Alpine system.

Carpathian Foreland Fold and Thrust Belt and Its Relation to Pannonian and Other Basins

The foreland fold and thrust belt of the Carpathians can be traced from Austria through the western and eastern Carpathians to the south Carpathian bend in Romania where most of its structural units plunge beneath younger Pliocene-Pleistocene cover. Folds in the youngest rocks at the south Carpathian bend continue westward, until all surface expression disappears before reaching the Danube River. The fold and thrust belt is flanked by elements of the European, Russian, and Moesian cratonal areas which are overlain by a variable width and thickness of foredeep deposits that are partly involved within the external fold and thrust belt. Internal to the fold and thrust belt are older parts of the Carpathian orogene formed mainly on continental crust. These older structures have significant differences in evolution between the western and eastern Carpathians. The foreland fold and thrust belt consists predominantly of flysch in its inner parts and molasse in its outer parts. These sedimentary rocks are cut into a series of thrust sheets that have moved relatively toward the craton. Oldest flysch units are Late Jurassic and the youngest units are Miocene. Some of the flysch units of the inner part of the belt may have been underlain by oceanic crust, whereas the younger, more external molasse units were underlain by continental crust. Timing of thrusting is only well-constrained locally, but suggests that deformation in the western Carpathians developed during Oligocene to Miocene time. In the eastern Carpathians, structural activity continued into the Pliocene, and deep earthquake activity at Vrancea suggests subduction. Deformation is sti l locally active. A volcanic arc of Miocene to Holocene age lies internal to the fold and thrust belt. Magmatic activity appears to have migrated externally and eastward in time. Contemporaneous with thrusting was the development of Neogene basins in the intra-Carpathian region. These basins exhibit a two-phase subsidence history (except for the Pannonian and Transylvanian basins)--fast initial subsidence, followed by a period of slower linear subsidence. The Pannonian basin shows only a reasonably fast linear subsidence. Structural and thermal models indicate the basins were formed by about 100% stretching. The convex east loop of the Carpathian foreland fold and thrust belt is a result of the collision of continental fragments against a recess in the combined European-Moesian plate. In this region, subduction or downbending of the subducted slab results in an extensional stress field, suggesting that thrusting and apparent compression along the mountain belt are only thin-skinned, superficial effects due to the inability to subduct light upper crustal material and detachment of the crust from the underlying lithosphere. The dominant forces seem to be those acting on the downgoing slab, which produce shortening along the plate boundary, and plate geometry that inhibits rigid plate convergence.