Structure and Miocene evolution of the Gdów tectonic "embayment" (Polish Carpathian Foredeep) : a new model based on reinterpreted seismic data

Analysis of previously available stratigraphic data coupled with the re-interpretation of seismic profiles calibrated by boreholes has allowed the construction of a new tectonic model of evolution of the Gdów "embayment" - a tectonic re-entrant located along the Carpathian front east of Kraków (southern Poland). This model shows that the main phase of localized fault-controlled subsidence took place in the Early Badenian and was associated with deposition of the locally overthickened Skawina Formation. Also, deposition of evaporites of the Wieliczka Formation seems to have been tectonically controlled by local basement faulting. Supra-evaporitic siliciclastic deposits have developed as a result of overall north-directed sediment progradation from the eroded Carpathian belt towards the Carpathian Foredeep. During the final stages of development of the Carpathian fold-and-thrust wedge the previously subsiding Gdów "embayment" area was uplifted and basement faults were reactivated either as reverse faults or as low angle thrust faults. Along the leading edge of this inverted structure a triangle zone developed, with backthrusting along the evaporitic level. As a result, overthickened evaporites, formed in local tectonically-controlled depressions within the area of the Gdów "embayment" area have been strongly folded and internally deformed

Deep seismic reflection profiles in SE Poland reveal a Variscan thin-skinned fold-and-thrust belt encroaching the East European Craton

20th EGU General Assembly, EGU2018, Proceedings from the conference held 4-13 April, 2018 in Vienna, AustriaRecent years have brought a significant progress in understanding of the external Variscides in Poland. Combined POLCRUST-01 and PolandSPAN deep seismic surveys imaged for the first time a Variscan thin-skinned fold-and-thrust belt that encroaches onto a little deformed basement slope of the East European Craton (EEC) much farther eastward than the previously postulated position of the Variscan deformation front. This deformed belt consists of several tectonic units, to a various degree overprinted by Variscan shortening and inversion (Fragment tekstu)

The shape of the Variscan Belt in Central Europe : strike-slip tectonics versus oroclinal bending

"The European Variscan belt sharply changes its trend in easternmost Germany and western Poland, where the ENE- to NE-striking structures are replaced by the ESE- to SE-trending ones. The structures of still another, NNE-SSW strike, take the lead, however, along the SE margin of the Bohemian Massif. The Variscan belt seems, thus, to make nearly a U-turn, encircling the Bohemian Massif from the north. This has been explained for almost a century by assuming a 180° oroclinal loop, in which the Rhenohercynian and Saxothuringian tectonostratigraphic zones inarm the core of the Bohemian Massif. According to this classical view, the outermost tectonostratigraphic zone of the Variscan belt, the Rhenohercynian Zone, continues eastward in the deep substratum of the Permian-Mesozoic basin and reappears at the surface along the eastern rim of the Bohemian Massif." (fragm.

Late Palaeozoic strike-slip tectonics versus oroclinal bending at the SW outskirts of Baltica: case of the Variscan belt’s eastern end in Poland

Geophysical and geological data from the eastern sector of the Central European Variscan belt are presented and reviewed in the regional tectonic context. Matched filtering of isostatic gravity, guided by results of spectral analysis, along with other derivatives of gravity and magnetic fields reveal a dominant WNW–ESE-trending pre-Permian structural grain in the external zones of the Variscan belt in Poland. This trend is confirmed by regional distribution of dips in Carboniferous and Devonian strata that were penetrated by boreholes beneath Permian-Mesozoic sediments. Based on these data, two alternative concepts explaining the connection of the Variscan belt and its NE foreland, those of strike-slip tectonics versus oroclinal bending, are discussed. The WNW–ESE structural trend in the Variscan foreland is parallel to a set of major strike-slip fault zones in the area, including those of Upper Elbe, Intra-Sudetic, Odra, Dolsk and Kraków-Lubliniec. These faults are considered to convey a significant dextral displacement between Laurussia and Gondwana. The revised position of the Variscan deformation front shows a similar, uninterrupted, generally WNW–ESE trend, up to the SE border of Poland, which indicates an initial continuation of the Variscan belt into the area of the present-day Western Carpathians. The geometry of the Variscan deformation front along with the pattern of the Variscan structural grain are inconsistent with the idea of an oroclinal loop affecting the external, non-metamorphic Variscan belt. However, the data presented do not entirely rule out an oroclinal loop within the Variscan internides. The still possible options are (1) a semi-oroclinal model postulating ~ 90° bending of the Variscan tectonostratigraphic zones into parallelism with the WNW–ESE strike-slip faults or (2) an orocline limited only to the belt linking the Wolsztyn High and Moravo-Silesian non- to weakly-metamorphic fold-and-thrust belt. Regardless of the kinematic model preferred, our data indicate that structural evolution of the Polish Variscides was concluded with the end-Carboniferous NNE–SSW shortening that resulted in the present-day extent of the Variscan deformation front

Tertiary development of the Polish and eastern Slovak parts of the Carpathian accretionary wedge : insights from balanced cross-sections

During Eocene-Sarmatian, a Polish-eastern Slovak portion of the Outer West Carpathian accretionary wedge was deformed in front of the ALCAPA terrane. This portion advanced into the area of the subducting remnant Carpathian Flysch Basin, a large oceanic tract left in front of the Alpine orogen. Western parts of the wedge were characterized by a noticeable lack of involvement of thick-skin thrusting and by a predominant development of fault-propagation folds. Eastern parts of the wedge were characterized by the involvement of thick-skin thrusting, triangle zones and back-thrusts. The frontal portion of the wedge was characterized by a décollement formed along the shale and gypsum formations of the Badenian molasse sediments, which resulted in the increased width of the thrust sheets. Forelandward thinning of foreland basin sediments indicates that the portion of the European Platform attached to the subducting oceanic lithosphere flexed underneath the advancing Carpathians as early as the Eocene. Oligocene sediments record syn-depositional thrusting by abrupt thickness changes over short distances. Younger periods of the thrusting are documented by the Eggenburgian-Karpatian piggy-back basin carried by thrust sheets in the frontal portion of the ALCAPA terrane, the Early Miocene age of the youngest sediments in the central portion of the wedge and involvement of the middle Badenian molasse sediments in the frontal portion of the wedge. The end of the shortening is documented by the lower Sarmatian end of the strike-slip fault activity behind the wedge, by the middle Sarmatian transgression over the deformed wedge in the Orava-Nowy Targ Basin, which is located in the rear portion of the wedge, and by the Sarmatian undeformed sediments sealing the wedge front. The existence of the forebulge in front of the advancing Carpathians is documented by local Eocene, Oligocene and Lower Miocene unconformities in the frontal portion of the wedge

On the nature of the Teisseyre-Tornquist Zone

The authors interpret the structure of the Central Carpathian-North European plates suture zone in Poland, where three main Carpathian tectonic units: the Central Carpathian, Pieniny Klippen Belt (PKB) and Outer Carpathian are present. In general, the PKB follows this zone. Several deep bore-holes were drilled in this region and the seismic lines were tied to bore-hole data and geological maps. The Polish PKB belongs to the complex geological structure stretching from Vienna in Austria to Romania. The rocks included in the PKB tectonic components were deposited within the paleogeographic realm known as the Alpine Tethys, mainly during the Jurassic-Early Cretaceous times. Both strike-slip and thrust components occur within the Polish section of the PKB. The strongly tectonized, few kilometer wide PKB zone is limited by a flower structure marked by two major faults, linked to the strike-slip zone. These faults reach the North European Platform (part of the North European Plate). The flysch sequences, arranged into a series of north-vergent thrust-sheets, constitute the main component of the PKB in the survey zone. They contain olistoliths, which are mainly Jurassic-Early Cretaceous in age. The PKB tectonic components of different age, strike-slip, thrust as well as toe-thrusts and olistostromes are mixed together, giving the present-day mélange character of this belt, where individual units are hard to distinguish. Two olistostrome belts (mélange units) exist within the PKB structure. The seismic lines show the Central Carpathian Paleogene rocks covering the Paleozoic Central Carpathian Basement south of the PKB. The Subtatric covers the High-Tatric autochthonic and allochthone rocks. The Central Carpathian Plate is thrust over the North European Platform in the Podhale region. The allochthonous Outer Carpathians consist of several nappes (thrust-sheets) verging northward. They are thrust over each other and over the North European Platform which dips gently southward

Late Palaeozoic strike‑slip tectonics versus oroclinal bending at the SW outskirts of Baltica: case of the Variscan belt’s eastern end in Poland

Geophysical and geological data from the eastern sector of the Central European Variscan belt are presented and reviewed in the regional tectonic context. Matched filtering of isostatic gravity, guided by results of spectral analysis, along with other derivatives of gravity and magnetic fields reveal a dominant WNW–ESE-trending pre-Permian structural grain in the external zones of the Variscan belt in Poland. This trend is confirmed by regional distribution of dips in Carboniferous and Devonian strata that were penetrated by boreholes beneath Permian-Mesozoic sediments. Based on these data, two alternative concepts explaining the connection of the Variscan belt and its NE foreland, those of strike-slip tectonics versus oroclinal bending, are discussed. The WNW–ESE structural trend in the Variscan foreland is parallel to a set of major strike-slip fault zones in the area, including those of Upper Elbe, Intra-Sudetic, Odra, Dolsk and Kraków-Lubliniec. These faults are considered to convey a significant dextral displacement between Laurussia and Gondwana. The revised position of the Variscan deformation front shows a similar, uninterrupted, generally WNW–ESE trend, up to the SE border of Poland, which indicates an initial continuation of the Variscan belt into the area of the present-day Western Carpathians. The geometry of the Variscan deformation front along with the pattern of the Variscan structural grain are inconsistent with the idea of an oroclinal loop affecting the external, non-metamorphic Variscan belt. However, the data presented do not entirely rule out an oroclinal loop within the Variscan internides. The still possible options are (1) a semi-oroclinal model postulating ~ 90° bending of the Variscan tectonostratigraphic zones into parallelism with the WNW–ESE strike-slip faults or (2) an orocline limited only to the belt linking the Wolsztyn High and Moravo-Silesian non- to weakly-metamorphic fold-and-thrust belt. Regardless of the kinematic model preferred, our data indicate that structural evolution of the Polish Variscides was concluded with the end-Carboniferous NNE–SSW shortening that resulted in the present-day extent of the Variscan deformation front

Salt tectonics in front of the Outer Carpathian thrust wedge in the Wieliczka area (S Poland) and its exposure in the underground salt mine

Salt deposits in the Wieliczka area (Wieliczka Salt Deposit – WSD) in southern Poland comprise salt-rich strata belonging to an evaporite succession that originated in the Carpathian Foredeep basin in the Middle Miocene Badenian (Serravallian) times, ca 13.81–13.45 Ma. Although they have been mined since the 13th century and decades of investigations provided abundant data on their origin and structure, some aspects of their geological evolution are still not fully understood. This study presents current concepts on the lithostratigraphy and tectonics of the WSD. The salt-bearing facies developed near to the southern basin margin, delineated by the Carpathian orogenic front. Such a location triggered the redeposition of sediments and gravity-driven deformation followed by tectonic deformation related to the forelandward advancement of the Carpathian thrusts. As a result, the WSD consists of folds and slices composed of two main salt members: (1) the stratified salt member, with intercalating salt, sulphates and siliciclastics, and (2) the boulder salt member, built of clays with large, isolated blocks of salt. The stratified member contains abundant meso-scale tectonic structures recording the soft-sediment deformation and deformation related to the northward tectonic push exerted by the advancing Carpathian thrust wedge. The boulder member originated due to the syntectonic erosion of evaporites along the basin margins and their redeposition during progressive northward migration of the Carpathian front. Recent interpretations of seismic data imply that the WSD constitutes the core of a triangle zone developed at the contact of the Carpathian orogenic wedge with the backthrust-displaced foredeep sedimentary fill. Meso-scale examples of sedimentary and tectonic structures in the salt-bearing succession exposed in the underground Wieliczka Salt Mine are described and their formation modes discussed

Evolution of the Miocene deposits of the Carpathian Foredeep in the vicinity of Rzeszów (the Sokołów-Smolarzyny 3D seismic survey area)

The Miocene Carpathian foredeep basin in Poland (CFB) developed in front of the Outer Carpathian fold-and-thrust belt, at the junction of the East European craton and the Palaeozoic platform. 3D seismic data, cores and well logs from Sokołów area (vicinity of Rzeszów) were used in order to construct new depositional model of the Miocene succession of the Carpathian foredeep. The gas-bearing Miocene infill of the CFB is characterized by a shallowing-upward trend of sedimentation and consists of hemipelagic, turbiditic and deltaic and nearshore-to-estuarine facies associations. Lowermost part of the Miocene infill seems to has been deposited from the North. Such direction of sediment supply was related to influence of existing relief of the pre-Miocene basement, where very deep (up to 1,5 km) erosional valleys cut into the pre-Miocene (Precambrian) basement due to inversion and uplift of the SE segment of theMid-Polish Trough are located. Upper part of theMiocene infill reflects sediment progradation from the South, from the Carpathian area into the foredeep basin. In the Rzeszów area existence of the so-called anhydrite-less island, i.e. relatively large area devoid of the Badenian evaporitic cover caused by the post-Badenian uplift and widespread erosion of evaporites,has been postulated for many years. Interpretation of 3D seismic data showed that such model should be abandoned. In the studied part of the CFB, Late Badenian evaporitic sedimentation was restricted to the axial parts of deep paleovalleys. Evaporites deposited in these valleys have been rarely encountered by exploration wells as such wells were almost exclusively located above basement highs separating erosional paleovalleys, hence giving incorrect assumption regarding regional lack of evaporitic cover. It is possible that in axial parts of these valleys important gas accumulations might exist, charged from the South and sealed by the Badenian evaporites