Carpathian Accretionary Wedge Research Articles

Depositional systems and paleogeography of Upper Cretaceous-Paleogene deep-sea flysch deposits of the Magura Basin (Western Carpathians)

The Outer Western Carpathians are part of the Alpine-Himalayan orogenic belt, and they are formed mostly by the Upper Cretaceous and Paleogene deep-sea “flysch” sequences. Orava region (northern Slovakia), situated in the central part of the Magura Nappe, has an important position for the solution of the geological structure and development of the Magura Nappe. At the beginning of the research, determination of the sedimentary sequences of the Magura Nappe and the fundamental lithotypes and lithofacies was required. A total of 1164 paleocurrent measurements were measured and assigned to lithotypes and lithostratigraphic units obtained during the detailed sedimentological study. The main purpose of the research was the interpretation of the filling history and tectonic activity of the Magura Basin. The results of the detailed sedimentological study were integrated with published data from surrounding regions. Presented palinspastic maps propose a reconstruction of the filling history and tectonic activity in chronological order during the Upper Cretaceous to Oligocene. Maps focus in detail on the western part of the Magura Basin, but they display its surroundings as well. The sedimentary record reflects the activity and gradual shifting of the Western Carpathian accretionary wedge to the north, the uplift of source areas, and the changes in the sea level of the Magura Basin. The paleocurrent analyses joined with the sedimentological and petrographic research allowed to reconstruct the paleogeographic properties of the northern sources of detritic material (Hostýn, Fore-Magura and Silesian Ridges), of the southern source of the material (Western Carpathians accretionary wedge) and of intrabasinal sources as well (Szczawina and Southern-Magura Ridges). We propose a discussion about the character of filling history, defining and position of the source areas and about Hostýn Ridge defined here.

The Stebnyk Formation (Miocene) in the Boryslav-Pokuttya and Sambir nappes of the Ukrainian Carpathians: a record of environmental change in the Carpathian Foredeep

The late Early–Middle Miocene Stebnyk Formation is a ~600–2000 m thick unit of the Boryslav-Pokuttya and Sambir nappes, which contains a molasse succession of the Carpathian Foredeep incorporated within the marginal part of the Outer Eastern Carpathian accretionary wedge. In the valley of thePrutRiver, between Deliatyn and Lanchyn, the Stebnyk Formation covers the alluvial fan deposits of the Sloboda Conglomerate and the deltaic deposits of the Dobrotiv Formation in the south, and the lagoonal salty clays of the Vorotyscha Formation in the north. The Stebnyk Formation is built of mainly rose, greenish and grey calcareous mudstones intercalated with several variable sandstone beds, including thick-bedded packages. The occurrence of tetrapod footprints and raindrop imprints, as well as the overall red-be character prove prevailing continental conditions during deposition of the formation, which is interpreted as sediments of a delta plain with distributary channels filled by the thick sandstone beds and associated by intercalations of thinner beds referred to channel levees and crevasse splays. The upper part of the Stebnyk Formation contains marine microfossils of the NN4 Zone, and locally to the NN5 Zone, corresponding to the early Badenian transgression in the region. In the regional scale, the Stebnyk Formation shows a polarity of facies, with a high contribution of conglomerates and thick-bedded sandstones in the lower part in the north west and fining to the south east, with transportation from the west and north west. The sediments accumulated in an elongated subsiding zone between the rising Carpathian orogen and the forebulge elevation of the foreland, in a warm and semi-dry climatic conditions corresponding roughly to the Mid-Miocene Climatic Optimum. The accumulation was balanced by a subsidence caused by sinking of the platform slab and by sedimentary load.

Geological structure and evolution of the Pieniny Klippen Belt to the east of the Dunajec River – a new approach (Western Outer Carpathians, Poland)

The area studied, known as the Male (Little) Pieniny Mts., belongs to the Pieniny Klippen Belt (PKB), a suture zone that separates the Central Carpathians from the Outer Carpathian accretionary wedge. Along its northern boundary the PKB is separated from the Paleogene to Early Miocene flysch deposits of the Magura Nappe by a narrow, strongly deformed belt belonging to the Grajcarek tectonic Unit. This unit is composed of Jurassic, Cretaceous and Paleocene pelagic and flysch deposits. The Klippen units of the PKB are represented by Jurassic–Lower Cretaceous carbonate deposits overlain by Upper Cretaceous variegated marls and flysch deposits. We describe geological and biostratigraphic evidence concerning the palaeogeographic, stratigraphic and structural relationships between the Pieniny Klippen Belt and the Magura Nappe, that significantly modify previously held views on the evolution of the Male Pieniny Mts. and the Polish sector of the PKB.

The Dobrotiv Formation (Miocene) in the Boryslav-Pokuttya and Sambir nappes of the Ukrainian Carpathians: a record of sedimentary environmental change in the development of the Carpathian Foredeep basin

The late Early Miocene Dobrotiv Formation, a 700–800-m-thick unit, was deposited in a subsiding platform margin, which become involved in the marginal part of the Outer Eastern Carpathian accretionary wedge. The sedimentary succession from the Sloboda Conglomerate up to the Dobrotiv Formation records a transition from alluvial fan through fan-delta to deltaic deposits, followed by the fluvial plain-channel facies of the Stebnyk Formation. The deltaic deposits are mud-dominated, with poorly developed thickening-up packets of beds. Efficient sediment accumulation was balanced by subsidence caused by subsurface loading. Emerged parts of the deltaic sedimentary system include tetrapod footprints and raindrop imprints. The general absence of mudcracks in the Dobrotiv Formation suggests a humid climate. Deposits of the Sloboda, Dobrotiv and Stebnyk formations form fining- and thinning-upwards clastic wedge successions along the Ukrainian Carpathians

Architecture and orogenic evolution of the northeastern Outer Carpathians from cross-section balancing and forward modeling

New balanced and restored cross-sections and a 2D kinematic model illustrate the present geometry of the northeastern Outer Carpathians and quantify their orogenic evolution between the late Eocene and the late Miocene (~35.3 to ~11.0Ma). The balanced cross-section is built on extensive surface and subsurface data and depicts an imbricate fan internally stacked along high-displacement out-of-sequence thrusts. Section restoration yielded 507km of minimum orogenic shortening — at least ~230km more than proposed in previous studies. Our shortening estimate relies on accurate thicknesses of lithostratigraphic units, in most cases thinner than applied before. The average convergence rate between ~35.3 and ~11.0Ma is estimated at 20.8km/My. The forward model, constrained by lower and upper ages of syn-orogenic deposits, traces the advance of the Outer Carpathian accretionary wedge and proves kinematic admissibility of the balanced and restored cross-sections. Progradation rates of the foreland basin depositional sequences, evolving from 9–11km/My between ~41.5 and ~21.1Ma to 22–39km/My between ~21.1 and ~11.0Ma, suggest a two-phase dynamics of the orogenic system. The acceleration of foreland migration at ~21.1Ma likely reflects the onset of northward subduction retreat, linked to the rollback of the European lower plate that gave rise to coeval back-arc extension in the Pannonian Basin.

Stages of development in the Polish Carpathian Foredeep basin

AbstractIn southern Poland, Miocene deposits have been recognised both in the Outer Carpathians and the Carpathian Foredeep (PCF). In the Outer Carpathians, the Early Miocene deposits represent the youngest part of the flysch sequence, while in the Polish Carpathian Foredeep they are developed on the basement platform. The inner foredeep (beneath the Carpathians) is composed of Early to Middle Miocene deposits, while the outer foredeep is filled up with the Middle Miocene (Badenian and Sarmatian) strata, up to 3,000mthick. The Early Miocene strata are mainly terrestrial in origin, whereas the Badenian and Sarmatian strata are marine. The Carpathian Foredeep developed as a peripheral foreland basin related to the moving Carpathian front. The main episodes of intensive subsidence in the PCF correspond to the period of progressive emplacement of the Western Carpathians onto the foreland plate. The important driving force of tectonic subsidence was the emplacement of the nappe load related to subduction roll-back. During that time the loading effect of the thickening of the Carpathian accretionary wedge on the foreland plate increased and was followed by progressive acceleration of total subsidence. The mean rate of the Carpathian overthrusting, and north to north-east migration of the axes of depocentres reached 12 mm/yr at that time. During the Late Badenian-Sarmatian, the rate of advance of the Carpathian accretionary wedge was lower than that of pinch-out migration and, as a result, the basin widened. The Miocene convergence of the Carpathian wedge resulted in the migration of depocentres and onlap of successively younger deposits onto the foreland plate.

Dynamics of the Polish and Eastern Slovakian parts of the Carpathian accretionary wedge: insights from palaeostress analyses

Abstract The arcuate Outer Carpathian accretionary wedge formed in front of the East Alpine-Carpathian-Pannonian (ALCAPA) megablock during the Eocene-Sarmatian. The wedge accreted sediments of the subducting remnants of the Carpathian Flysch Basin, a large oceanic tract left in front of the Alpine orogen. The palaeostress data for the orogenic hinterland (particularly the data related to the Early Miocene extension that was expanding towards the NE), combined with coeval subduction-related volcanism that was expanding towards the NE, indicate that the uneven roll-back of the subduction zone was the main mechanism controlling the development of the northern West Carpathian arc. The palaeostress data for the Tertiary accretionary wedge from the same time period are characterized by outward-fanning σ 1 trajectories that changed gradually during the wedge development. In contrast, the palaeostress data for the hinterland are characterized by preferred-directional stress events that changed abruptly during the wedge development. These palaeostress results are in accordance with the behaviour of the wedge and the hinterland, as the wedge behaved as a weak continuum and the hinterland behaved as a block mosaic with weak boundaries. The fault traces of the northern West Carpathian arc converge to both ends of the arc and suggest that the pre-existing basin was the factor that controlled the arc location. These fault trace patterns are asymmetric, indicating a slightly oblique overall convergence in a NE-SW direction. In accordance with this convergence, the palaeostress data for the accretionary wedge indicate that the western part of the wedge, which is characterized by NW-SE-oriented maximum principal compressional stress σ 1 , was undergoing sinistral transpression. Meanwhile, the eastern part, which is characterized by NE-SW-oriented σ 1 , was undergoing compression. Apparently, the dynamics of the accretionary wedge was further influenced by the shape of an elongated NE-SW-trending ALCAPA megablock, which was located behind the wedge and advanced in the direction of the general Early Miocene convergence during the most pronounced stages of the wedge development. This megablock served as the local indenter, as its strength surpassed that of the accretionary wedge located to its front. Further dynamic complexities were added because of the complex shape of the Magura Unit, which was located in the most proximal portion of the wedge and was stronger than the units in front of it. Wedge outcrops indicate that the large-scale shortening, which is characterized by the development of detachments and ramps, was preceded by an initial layer-parallel shortening. This is indicated by scaly fabrics and minor reverse faults that rotated into locked positions during the later accretion. Several outcrops with a wedge detachment fault indicate that there was a relatively low amount of friction during its development. The décollement zone is several hundred metres thick and shows evidence of transient fluid flow that was driven by pressure gradients. This is documented by frequent hydrofracturing, sandstone dykes and fibrous veins that opened against the weight of the whole wedge, all of which indicate cycles of higher pore fluid pressures that lowered the basal friction.

Fluid inclusion evidence for deep burial of the Tertiary accretionary wedge of the Carpathians

AbstractHydrothermal quartz from mineralized joints of the Carpathian accretionary wedge contains immiscible aqueous, oil‐condensate, methane and carbon dioxide‐rich fluid inclusions. Distribution patterns of the inclusion trapping PT parameters point to a crack‐seal mechanism during upward and lateral migration of hot methane‐rich fluids from overpressured sediments at the base of the accretionary wedge. A simple equation is proposed to calculate depths from densities and trapping pressures of the buoyant inclusion fluids. In the Carpathian accretionary wedge, the paleofluid pressures of 52–306 MPa correspond to a 5‐ to 11‐km‐thick overburden. Prior to exhumation, thickness of the wedge must have attained 10–25 km, of which only c. 50% was preserved until recently. Anomalously high methane densities (up to 0.43 g cm−3) recorded in the lowermost nappe sheets are provisionally interpreted as a result of supralithostatic overpressure due to thermal cracking of oil and kerogen to methane and pyrobitumen at temperatures above 200 °C.

Reconstruction of Cretaceous rifts incorporated in the Outer West Carpathian wedge by balancing

Two balanced cross-sections were constructed through the Outer Carpathians of Poland in order to restore the Early Cretaceous rifts. The rift fill is incorporated into the Tertiary Carpathian accretionary wedge. The data compiled for this study confirm that the Early Cretaceous rifting in the Silesian Basin area was followed by Late Cretaceous–Paleocene basin inversion, Eocene pelagic deposition, and Oligocene syn-orogenic deposition. The original width of the Silesian Basin is about 130–138 km. The overall wedge shortening ranges between 31 and 58% with 57 and 58% in the Silesian Nappe. The rifting commenced at the Jurassic/Cretaceous boundary and formed the horst and graben structures defined by NW–SE striking normal faults. Portions of the horsts become emergent at various times during rifting stages. Sedimentation rates in the grabens varied around 4.7, 2.1 and 1.3 cm/ka during three rifting stages, while sedimentation rates on their slopes varied around 0, 0–1.26 and 0 cm/ka. The altitude difference between horst tops and graben floors did not exceed 2 km. The reconstructed widths of the horsts range between 17.5 and 18.3 km. The reconstructed widths of several grabens in both cross-sections have values 14.5, 45.7, 57.7 and 79.3 km. The rifting-related extension, calculated from fault-striae data, was NE–SW directed. Sometimes, the very low ( σ 2– σ 3)/( σ 1– σ 3) stress ratio of the driving stress configuration resulted in polydirectional extension when the value decreased below 0.1.

Summary of paleomagnetic data from the Central West Carpathians of Poland and Slovakia: Evidence for the late cretaceous-early tertiary transpression

The paper reviews paleomagnetic data from the Central West Carpathians (CWC) of Poland and Slovakia. The CWC constitute an orogen deformed by pre-Tertiary and Tertiary events, situated on the internal side of the Pieniny Klippen Belt and the Tertiary Outer West Carpathian accretionary wedge. The CWC are regarded as the eastern prolongation of the Austroalpine series. There are paleomagnetic evidences for a counterclockwise rotation of the CWC after Oligocene. Having subtracted the effect of this rotation, Middle Cretaceous paleomagnetic poles from the CWC are brought into agreement with preGosau paleopoles from the Upper Austroalpine units of the Northern Calcareous Alps (NCA). It is inferred that a common clockwise rotation of the CWC and NCA had taken place between 90-60 Ma (Middle — Late Cretaceous) during the oblique convergence of the Austroalpine/Central Carpathian realm with the Penninic continental basement.

Structure of the West Carpathian accretionary wedge: Insights from cross section construction and sandbox validation

The restoration of structures along balanced cross sections through the West Carpathian accretionary wedge and pseudo-3D restoration in the Smilno Tectonic Window area shows that various defined units contain sediments from Magura and Silesian depositional areas. The shortened Magura succession was detached at the Upper Cretaceous stratigraphic level. The shortened Silesian sedimentary package was detached at the Lower Cretaceous stratigraphic level. The Magura succession was the southwestern neighbor of the Silesian succession in a large depositional system. Both sedimentary packages were shortened during the Paleogene and the Magura succession was later thrust over the Silesian succession as an out-of sequence oblique thrust during the Neogene. The general shortening mode is piggy-back. Thrust geometries are created by both fault-bend and fault-propagation folding. The common out-of-sequence thrusting is caused by the involvement of the basement in the shortening and by interplay of friction and erosion. The influence of basal friction on thrust sheet length is validated by sand-box models. Variations in friction along the basal thrust include low friction, documented by subhorizontal veins with vertically grown fibers and long thrust sheets, medium friction, indicated by duplexing and high friction, indicated by antiformal stacks and back thrusting.

Tertiary subduction and slab break-off model of the Carpathian–Pannonian region

This paper illustrates the application of multidisciplinary data analysis to the Carpathian–Pannonian region and presents a new Tertiary development model that incorporates all multidisciplinary parameters. During the Late Cretaceous–Eocene, the future Carpathian orogen was part of the larger Alpine–Carpathian orogen formed by the southeastward subduction (135–55 Ma) of the Penninic Ocean and the ultimate collision (55–40 Ma) of the European and Adriatic continents. The subduction in the Alpine region ended by the slab break-off of the subducting oceanic lithosphere from the continental one and by the related magmatism (43–24 Ma). While the Eocene Alps were under continental collision, the Eocene remnant Carpathian Flysch Basin (rCFB) was still subducting. The Carpathians and eastern parts of the Alps started to occupy the region of the present Carpathians during the Early Miocene. The oceanic plate underlying the rCFB subducted southwestwards, later westwards, while the northeastward and eastward migration velocity of the accreting plate boundary decreased through time. The slower subduction rate caused: a steeper dip of the subducting slab; the beginning of the Eggenburgian (22–19 Ma) and following duration of extension in the orogenic hinterland accompanied by the asthenosphere upwelling; the onset of the crustally derived volcanism above the risen asthenosphere and the younger mantle-derived volcanism, progressively less contaminated by the crustal material, all contemporaneous with a shortening in the Carpathian accretionary wedge. The subduction of the rCFB finally led, at the end of the Early Miocene, to a collision with the continental margin along the westernmost part of the present Carpathian Arc. The subduction roll-back of the subducting slab of the rCFB under the advancing Inner Carpathians, the oblique closure of the basin, the progressive change of the subduction to collision from the west to the east along the Carpathian Arc drove a scissors-like break-off of the subducting oceanic slab along the West Carpathians. The break-off in the East Carpathians was driven by the weight of a subducting oceanic slab and buoyancy of the attached continental slab. The break-off started in the west of the Carpathian Arc in the Early Miocene, ran along the arc to its present position in the bend area between the East and South Carpathians and separated the oceanic slab, that subducted passively under its own weight, from the European continental margin. The lateral propagation rate of the slab tear decreased with time. The break-off-related volcanism was synchronous with the final stages of the collision.

Abstract: Structure and Hydrocarbon Potential of the Ukrainian Carpathian Accretionary Wedge

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Late Tertiary paleogeographic evolution of the Western Carpathians

The evolution of the Tertiary basins in the Western Carpathians was closely connected with the evolution of the Carpathian orogenic belt. During the Oligocene, the sea of the Outer Carpathian flysch troughs became for the first time part of the Paratethys regime due to isolation from the Mediterranean Tethys. Oblique collision between the North European Platform and the overriding West Carpathian Plate during the Early Miocene led to the development of the outer accretionary wedge, built up mainly from flysch nappes, and the formation of a foredeep. Intramontane basins developed in transpressional regime along the northern margin of the Early Alpine consolidated Central Carpathians, from where the sea also invaded the hinterland of the orogenic mountain chain. Progradation of the Alpine nappes gradually closed the Early Miocene (stage Eggenburgian) seaway in front of the Alps which led again to the isolation of the basins inside the West Carpathian segment. The marine connection with the Mediterranean started to open again through the West Carpathian hinterland at the end of the Early Miocene (stage Karpatian). In the Middle Miocene, the Outer Carpathian accretionary wedge obtained its present position, followed by the eastward migration of foredeep depocentres. Inside the orogenic belt large transtensional basins opened. The final closure of the marine connections (stage Badenian) led to a gradual decrease of salinity during the Late Miocene. The sedimentation in the Vienna, Danube (Little Hungarian plain) and East Slovakian (Transcarpathian) basins during the Late Miocene and Pliocene was influenced mainly by the thermal subsidence of the Pannonian domain.