Abstract We demonstrate how lithological and mechanical stratification of Ediacaran–Carboniferous sedimentary package governs strain partitioning in the Lublin Basin (LB) which was incorporated in the marginal portion of the Variscan fold-and-thrust belt. Based on the geometry of seismic reflectors, the pre-Permian–Mesozoic sedimentary sequence was subdivided into two structural complexes differing in structural style. The lower one reveals forelandward-vergent imbrication, while the upper one comprises fold train, second-order deformations, and multiple local detachments. Lithological composition of the upper structural complex controlled geometry, kinematics, and position of compressional deformations in stratigraphic profile. System of foreland-vergent thrusts which links lower and upper detachment developed due to efficiency of simple shear operating in heterogeneous clastic-carbonate-evaporitic strata of the Lower–Upper Devonian age. Internal homogeneity promoted the formation of conjugate sets of thrusts in Silurian shales and Upper Devonian limestones. Structural seismic interpretation combined with sequential restoration revealed localised thickening of Devonian strata and up to 5% difference in length of Devonian horizons. This mismatch is interpreted as a manifestation of distributed shortening, including layer-parallel shortening (LPS), which operated before or synchronously to the initiation of folding. The amount of distributed strain is comparable with numbers obtained in external parts of other fold-and-thrust belts. The outcomes derived from this study may act as a benchmark for studying variability in a structural style of multilayered sequences which were incorporated in the external portion of other fold-and-thrust belts.
Abstract The southern Baltic Sea is a peculiar area, where the Sorgenfrei‐Tornquist Zone (STZ), stretching from Bornholm into the North Sea, connects to the Teisseyre‐Tornquist Zone (TTZ) that continues SE up to the Black Sea. In this study, we show the structure and evolution of this controversially debated area, both on crustal and basin scale, by using three seismic reflection profiles combined with 2‐D potential field data. The results demonstrate that the southern Baltic Sea is underlain by a thick crust of the East European Craton with a Moho depth in the range of 38–42 km. The overall crustal architecture is shaped by three phases of localized stretching in the early Paleozoic, Devonian‐Carboniferous, and Permian‐Mesozoic. The most spectacular feature of the southern Baltic Sea is a zone of thick‐skinned compressional deformation produced by Late Cretaceous‐early Paleogene inversion, including a system of thrusts and back thrusts penetrating the entire crust in an 80–90 km wide inversion zone. ENE‐vergent thrusts are traced from the top of the Cretaceous down to the Moho and they are accompanied by back thrusts of opposite vergence, also reaching the Moho. Inversion tectonics resulted in the uplift of a block of cratonic crust as a pop‐up structure, bounded by thrusts and back thrusts, and the displacement of the Moho within the STZ and TTZ. The similar mechanism of intra‐cratonic inversion was recognized for the Donbas Foldbelt in eastern Ukraine, and it may be characteristic of rigid cratons, where deformation is localized in a few preexisting zones of weakness.
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 Trailing edge of the Carpathian fold-and-thrust belt between Kraków and Tarnów has been subjected to intense studies because of its control over rich deposits of rock salt (Wieliczka and Bochnia salt mines) and hydrocarbon accumulations. In vicinity of Gdów, Carpathian orogenic front in the area south-east of Kraków recedes to the south, forming a "bay" or "embayment" filled with the Miocene deposits of the Carpathian foredeep basin. Over decades, numerous tectonic models of the Gdów "embayment" have been published. Originally, sedimentary infill of the "embayment" was identified as the Lower Badenian sub-evaporitic (Skawina Beds), with remnants of the Upper Badenian foredeep evaporites only locally preserved at the surface or shallow subsurface. Later, although without sufficiently presented micropalaeontological evidences, new models have been proposed that assumed dominance of the supra-evaporitic Machów Formation (Chodenice and Grabowiec Beds). Analysis of available stratigraphic data coupled with interpretation of good quality seismic profiles calibrated by deep wells allowed for construction of a new tectonic model of evolution of the Gdów "embayment". Under this model, main phase of localized fault-controlled subsidence took place in Early Badenian and was associated with deposition of locally overthickened Skawina Formation. Also deposition of evaporites of the Wieliczka Formation was locally tectonically controlled, similarly to earlier models by Garlicki (1971). Supra-evaporitic siliciclastics have developed as a result of an overall north-directed sediment progradation from the eroded Carpathian belt towards the Carpathian foredeep. During final stages of development of the Carpathian fold-and-thrust wedge previously subsiding Gdów "embayment" area was uplifted, basement faults have been reactivated either as a reverse or low angle thrust faults. Along the leading edge of such inverted structure a triangle zone developed, with backthrust formed along the evaporitic level. As a result, overthickened evaporites, formed in local, tectonically-controlled depressions present within the Gdów "embayment" areahave been strongly folded and internally deformed. 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
Abstract. The evolution of orogenic wedges can be determined through stratigraphic and thermochronological analysis. We used apatite fission-track (AFT) and apatite and zircon (U-Th-Sm)/He (AHe and ZHe) low-temperature thermochronology to assess the thermal evolution of the Ukrainian Carpathians, a prime example of an orogenic wedge forming in a retreating subduction zone setting. Whereas most of our AHe ages are reset by burial heating, eight out of ten of our AFT ages are partially reset, and all ZHe ages are non-reset. We inverse-modelled our thermochronology data to determine the time-temperature paths of six out of the 8 nappes composing the wedge. The models were integrated with burial diagrams derived from the stratigraphy of the individual nappes, which allowed us to distinguish sedimentary from tectonic burial. This analysis reveals that accretion of successive nappes and their subsequent exhumation mostly occurred sequentially, with an apparent exhumation rate increase towards the external nappes. Following a phase of tectonic burial, the nappes were generally exhumed when a new nappe was accreted, whereas, in one case, duplexing resulted in prolonged burial. An early orogenic wedge formed with the accretion of the innermost nappe at 34 Ma, leading to an increase in sediment supply to the remnant basin. Most of the other nappes were accreted between 28–18 Ma. Modelled exhumation of the outermost nappe started at 12 Ma, and was accompanied by out-of-sequence thrusting. The latter was linked to emplacement of the wedge onto the European platform and consequent slab detachment. The distribution of thermochronological ages across the wedge, showing non-reset ages in both the inner and outer part of the belt, suggests that the wedge was unable to reach dynamic equilibrium for a period long enough to fully reset all thermochronometers. Non-reset ZHe ages indicate that sediments in the inner part of the Carpathian embayment were mostly supplied by the Inner Carpathians, while sediments in the outer part of the basin were derived mostly from the Trans-European suture zone or the European margin. Our results suggest that during the accretionary phase, few sediments were recycled from the wedge to the foredeep. Most of the sediments exhumed from the Ukrainian Carpathian wedge were likely transported directly to the present pro- and retro- foreland basins.
Celem prowadzonych prac bylo określenie budowy geologicznej czapy anhydrytowej oraz nadkladu wysadu solnego „Damaslawek”. Podstawowym narzedziem badawczym byly wysokorozdzielcze dane sejsmiki refleksyjnej. Dodatkowo wykonano pomiary i interpretacje danych geoelektrycznych, oraz reinterpretacje archiwalnych danych grawimetrycznych i geofizyki otworowej. Uzyskane dane sejsmiczne charakteryzowaly sie wysoką jakością. Zintegrowana interpretacja geofizyczno-geologiczna pozwolila na bardzo precyzyjne określenie glownych i podrzednych deformacji tektonicznych, rozwinietych w obrebie czapy oraz w jej nadkladzie. Zidentyfikowano wiele reaktywowanych uskokow inwersyjnych, ktore najprawdopodobniej przynajmniej cześciowo byly związane z ruchami przesuwczymi. Analiza sejsmostratygraficzno-tektoniczna pokazala, iz niektore strefy uskokowe byly aktywne rowniez w czwartorzedzie.
GEOPHYSICAL-GEOLOGICAL STUDY OF CAPROCK AND OVERBURDEN OF THE DAMASŁAWEK SALT DOME (CENTRAL POLAND)
Summary
The goal of completed research project was to establish reliable geological model of cap rock and overburden of the Damaslawek salt dome. High-resolution reflection seismic profiling was main research method used for this project. Additionally, geoelectrical profilingand interpretation as we l! as reinterpretation of available gravity and well log data was completed. Acquired seismic data were ofvery high quality. Integrated geophysical-geological interpretation allowed the major and subordinate tectonic deformations present within cap rock and salt domes overburden to be precisely distinguished. Numerous inversion faults possibly at least partly related to strike-slip movements were identified. Seismostratigraphic-tectonic analysis showed that some of identified fault zones were active also during the Quaternary.
We performed reinterpretation of the DEKORP-BASIN’96 offshore deep reflection seismic profiles PQ-002 and PQ-004-005 running ENE-WSW in the South Baltic area through the transition zone between the East European Craton (EEC) in the NE and the Palaeozoic Platform in the SW. These profiles intersect the Teisseyre-Tornquist Zone (TTZ) and the Sorgenfrei-Tornquist Zone (STZ) to the south and north of the Bornholm Island, respectively. While the STZ is considered to be an intra-cratonic structure within the EEC, the TTZ is often believed to represent the actual edge of the Precambrian craton. Regardless of their origin and tectonic position, both zones are characterized by intense compressional deformations associated with the Alpine inversion of the Permian-Mesozoic basins at the transition from the Cretaceous to Paleogene.Our research aimed to explain the structure of the transition zone between the EEC and the Palaeozoic Platform and check whether its structure differs north and south of Bornholm. We also aimed at documenting the nature of the Late Cretaceous deformations and their relationship to the STZ and TTZ, as well as the marginal zone of the EEC.Both PQ profiles show a continuation of the EEC crust toward the WSW beyond the STZ and TTZ. The cratonic crust has a considerable thickness and is characterized by a deep Moho position along the entire length of the profiles. The depth of Moho is in our interpretation much greater than that postulated in previous interpretations. Consequently, numerous reflections once interpreted as upper mantle reflections occur within the lower crust in our opinion.The most spectacular feature of both PQ profiles is related to the zones of thick-skinned compressional deformation associated with the Alpine inversion along the STZ and TTZ. Crustal-scale, ENE-vergent thrusts have been traced from the top of the Cretaceous down to the Moho in terms of the detachment faults through the entire crust. They are accompanied by back thrusts with vergence toward the WSW, which also reach the Moho. The Late Cretaceous deformation resulted in the uplift of a block of cratonic crust as a pop-up structure, bounded by thrusts and back thrusts, and displacement of the Moho within the STZ and TTZ. It also led to the formation of the Late Cretaceous syn-inversion troughs on both sides of the uplifted wedge providing evidence for the age of deformation.The STZ and TTZ, imaged by the PQ profiles, appear as zones of the localised Late Cretaceous thick-skinned deformation that is superimposed on the EEC crust and its sedimentary cover. Within these zones, the Moho is faulted in several places and a large block of the basement is uplifted as a crustal-scale pop-up structure. A similar crustal architecture characterises the Dnieper-Dontes Paleorift, which was also inverted in the Late Cretaceous. A special position is occupied by the island of Bornholm, located in the middle of the pop-up structure, which owes its formation to the Late Cretaceous inversion of the sedimentary basin in this place.This study was funded by the Polish National Science Centre grant no UMO-2017/27/B/ST10/02316.
CHARACTERISTICS OF THE MIOCENE SUBDUCTION ZONE OF THE POLISH CARPATHIANS: RESULTS OF FLEXURAL MODELLING
Summary
Flexural modelling technique was applied in order to characterise Miocene subduction zone of the Polish Carpathians. This technique relies on assumption that continental collision zone and related subduction of lower lithospheric plate can be adequately approximated by flexure of thin, elastic plate of uniform thickness (lithosphere) floating on the fluid half-space of zero viscosity (asthenosphere). Flexure of the lithosphere can be due to two types of loads: topographic loads related to the weight of the orogenic belt and sediments of the foredeep basin, and subsurface loads acting on the end of subducted lithospheric. Obtained results showed that along the Carpathians elastic properties of the lower (foreland) lithospheric plate change significantly. Effective elastic thickness EET was estimated to be in range of 8-16 km in the western Polish Carpathians, and 20-25 km in their eastern part. This can be attributed to the fact that in the western Polis h Carpathians foreland plate belongs to the Western European Platform (younger age of consolidation and lower flexural rigidity) while in the eastern segment of the thrust belt to the Teisseyre-Tornquist zone and Eastern European Platform (older age of consolidation and higher flexural rigidity). AIso, it was proved that for all the profiles subsurface loads were most important for the observed present-day flexure ofthe foreland lithospheric plate. This fact, combined with other features of the Carpathians, Carpathian Foredeep Basin and Pannonian Basin can serve as a proof that the Carpathian Miocene collision zone developed in relation to retreating subduction zone. Slab-pull mechanism can be postulated as the main subduction-driving mechanism for the Miocene evolution of the Polish Carpathians. This mechanism can possibly be caused by negative buoyancy of the subducted oceanic or thinned continental crust. It can also be concluded that development of the Carpathian Foredeep basin was mainly controlled by deep tectonic processes active within the subduction zone that also controlled thrusting of the Outer Carpathian flysch nappes.
