A review of geophysical studies of the lithosphere in the Carpathian–Pannonian region
Abstract: Here, we revisit the most prominent features of the complete Bouguer anomaly map and their interpretation, along with the current knowledge of the lithospheric thickness in the Carpathian–Pannonian region. The stripped gravity map, i.e., the sediment-stripped complete Bouguer anomaly map, was used to interpret the most prominent highs and lows of the gravity field. The complete Bouguer anomaly data were used in structural density modelling and integrated geophysical modelling to determine or revise the previously known sources of the most pronounced gravity features of the region. The Carpathian gravity low was divided into three sub-lows: the Western, Eastern, and Southern. The Western Carpathian gravity low consists of the clearly distinguishable External and Internal lows, which are due to different causes. The source of the External Western Carpathian gravity low reflects the low-density sediments of the External Western Carpathians (2.49–2.59 g cm–3) and the Foredeep (~2.43 g cm–3), while the Internal Western Carpathian gravity low is explained by the upper crustal deficit mass, which is formed by the rocks of the Alpine Tatric and Veporic units. These tectonic units are built mainly from granites and crystalline schists, of which the average density (~2.70 g cm–3) is lower than the average density of the lower crust of the Internal Western Carpathians (~2.90 g cm–3). The main sources of the Eastern and Southern Carpathian gravity lows are the gravity effects of the crustal roots created by continental collision, the Foredeep, and the surface sediments of the External Carpathians. The Pannonian gravity high is caused by the expressive Moho elevation (24–26 km). Since the Pannonian Basin upper mantle, which is built by high-density peridotites or dunites, is located several kilometres closer to the surface, this rock material represents a great excess mass (high-density anomalous bodies). Based on the calculated stripped gravity map, several local gravity highs (˃ +50 mGal) have been recognised, and they are all located in the Danube Basin, the Transcarpathian Basin, the Békés Basin, as well as the Makó trough. Their sources are high-density crustal bodies (Eo-Alpine metamorphic complexes), whose apical parts reach depths of only 7 to 12 km. Finally, the expressive different depths of the lithosphere-asthenosphere boundary in the Western and Eastern Carpathians were explained by the different Neo-Alpine development of both orogens. The mantle lithospheric root (~240 km) in the Eastern Carpathians is results from the sinking of the upper part of the broken slab during the frontal continental collision. On the contrary, no thickening of the mantle lithosphere was observed in the junction zone of the Western Carpathians and the Bohemian Massif. The typical thickness of the continental lithosphere (~100 km) in this zone was explained by the oblique continental collision. The Pannonian Basin system is characterised by one of the thinnest continental crusts (~25 km) and lithospheres (~75 km) in the world.
Geochronology, geochemistry, and geodynamic evolution of Tatric granites from crystallization to exhumation (Tatra Mountains, Western Carpathians)
Abstract: The Western and High Tatra Mountains (northern Slovakia, southern Poland) contain the best-exposed rocks record within the Carpathian orogenic belt. Petrological, geochemical, and geochronological data from granitic assemblages across the Western (n = 1) and High Tatra Mountains (n = 19) were used to understand how they responded to an extended tectonic and magmatic history. Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) zircon dating shows a dominant Early Carboniferous (Tournaisian, TuffZirc age = 349.3 + 2.9 / −1.5 Ma at 95 % confidence, n = 119 spots), but Paleoproterozoic/Neoarchean (2544 ± 33 Ma, ±1σ) to Late Carboniferous (Kasimovian, 305.8 ± 6.2 Ma) dates were also found. The age pattern is consistent with granitic assemblages within the European Variscan belt and suggests an affinity with Armorican terranes derived from a northern Gondwanan Cadomian arc. The final stages of Variscan orogenic collapse are timed at ca. 315 Ma based on the youngest zircon age population. Monazite dated in thin section are also Tournaisian, but the youngest age is Permian (Th–Pb, 270.0 ± 9.1 Ma, ±1σ), consistent with timing of large-scale Pangean Permian extension. High Tatra granite K-feldspar 40Ar/39Ar ages indicate slow post-magmatic cooling after granite crystallization. The oldest 40Ar/39Ar ages from two samples near Lomnický štít (LS) suggest a thermal event in the Late Triassic (~220 Ma), but others from the sub-Tatra fault and near Gerlachovský štít (GS) are younger (Early Cretaceous, ~120 Ma). The thermal history from K-feldspar at the base of LS shows pulsed exhumation at faster rates between 70–55 Ma (300–200 °C) and 45–35 Ma (200–100 °C). The results document the Paleo-Alpine tectonic imprint of the Western and High Tatra Mountains until the onset of more Neo-Alpine exhumation. The data point to uplift earlier than suggested by models of extrusion tectonics applied to the region. Early uplift is connected with Eocene ALCAPA (ALps–CArpathians–PAnnonia) escape leading later to the development of the Carpathian arc.
Facies analysis of gravity flow deposits of an ancient foreland basin (Magura Nappe, Western Carpathians)
Abstract: Sedimentary logging at outcrops remains a basic method of sediment description in the field. The area of sedimentological study in this work was the Slovak western part of the Magura Nappe, which is the largest tectonic unit of the Outer Western Carpathians. Sediments were deposited by gravity flows in the predominantly deep-sea environment of the foreland Magura Basin. The stratigraphic extent of the studied deposits is Late Cretaceous (Cenomanian) to Oligocene/early Miocene. Up to 113 sedimentological logs have been documented in detail with a total thickness of 2022 m. Simplified logging and interpretation of the depositional environment was additionally developed for 15 of the most interesting logs. Sedimentation by debris-flows, turbidity currents, slides, and slumps in the environment of the distributary channel, levee, inter-channel, and basin plain was also interpreted. An important element of the study was the inclusion of paleocurrent directions in the analysis of logs. The purpose of the study was to record the most important outcrops in the region and thus preserve them and make them accessible to the greater public, as well as supplement the characteristics of lithostratigraphic units and knowledge on the sedimentary evolution of the Magura Basin.
Post-Cretaceous–Paleogene slumping in the Subsilesian Unit of the Outer Western Carpathians: Biostratigraphic, sedimentary and magnetic records from the Bystřice section
Abstract: The Bystřice section, which was previously interpreted as the continuous Cretaceous–Paleogene transition, has been newly studied using biostratigraphy (planktonic foraminifers, calcareous nannofossils), magnetic properties, and geochemistry. Biostratigraphy has confirmed the presence of the upper Maastrichtian (UC20dTP nannozone; Abathomphalus mayaroensis foraminifer zone) and Selandian (NP5–NP7 nannozones; P3b–P4b foraminifer zones). Moreover, the Danian is completely absent. Strong remagnetisation of the rocks did not enable magnetostratigraphy of the section. The magnetic fabric indicates tectonic disturbance of the section. The studied strata consist predominantly of paraconglomerates, which are interpreted as slumps. The slumps contain pebbles and blocks of diverse exotic rocks, intraclasts, and reworked carbonate concretions enclosed within a marly matrix. A few thick paraconglomerate bodies are separated by bedded grey silty marls, sequences of medium-rhythmic sandstone turbidites, and conglomerate. Frequent slump folds indicate synsedimentary deformation. Submarine landslides are manifested by folded and thrusted sandstone beds, breccia of partly-lithified sandstones, and characteristic failure planes. In the lower part of the section, marls and paraconglomerates with Maastrichtian microfossils are interbedded with marls containing Selandian microfossils. It is most likely that the whole of the studied sequence was deposited during the Selandian, and that Maastrichtian marls and paraconglomerates represent submarine mass flows. The deposition took place on the basin slope in the bathyal zone. The geochemical proxy parameters indicate more reducing setting, higher input of terrestrial phytodetrite, as well as higher surface-water temperatures in the Maastrichtian, which is confirmed also by occurrences of low-latitude nannoplankton. The Selandian sediments contain a higher share of aquatic organic matter. The pristane/phytane ratio indicates an oxygenated water column, and carbonate δ13C and δ18O isotopes point to lower surface-water temperatures.
Revisiting brachyuran crabs (Malacostraca: Decapoda) from Oligocene and Miocene fish beds of Europe
Abstract: The fossil records of decapod crustaceans (Malacostraca) from Oligocene and Miocene fish beds (i.e. laminated deposits with exceptional fish preservation and high organic content) of Europe have lacked a uniform taxonomic approach, prohibiting assessments of their diversity and distribution. Therefore, we revisited the systematics of brachyuran crabs from these deposits preserved in the Great Caucasian Basin, the Outer Carpathian Basin, and the Pannonian Basin. The revised material originates from the Lower Oligocene of Hungary (Tard Clay Formation), Poland (Menilite Formation), Romania (Dysodilic Shale Formation), and Ukraine (Menilite Formation); Upper Oligocene of Poland (Menilite Formation); and the Lower Miocene of Azerbaijan (Maikopian Series), the Czech Republic (Ždánice–Hustopeče Formation), and Russia (Maikopian Series). Previously unreported material includes decapod specimens from the Lower Oligocene of Abadzekhskaya, Russia. In total, three crab species were distinguished, including Platymaia lethaea (Smirnov, 1929), Liocarcinus oligocenicus (Paucă, 1929), and Necronectes sp. Among them, L. oligocenicus occurs at all studied localities and is the most widespread taxon. Although earlier records of this species were often recognized as separate taxa, we propose that Portunus musceli Paucă, 1929; Portunus lancetidactylus Smirnov, 1929; Portunus arcuatus var. priscus Smirnov, 1929; Nautilograpsus prior Smirnov, 1929; and Portunus atropatanus Aslanova & Dzhafarova, 1975, are junior subjective synonyms of Liocarcinus oligocenicus. Although decapod specimens preserved in Oligocene and Miocene fish beds are often represented by complete or near-complete articulated bodies, their extreme flattening distorts the outline of exoskeleton elements and obscures diagnostic characters on the dorsal carapaces, such as the development of grooves, regions, and cuticular ornamentation, posing a major problem in taxonomic evaluation of these decapods. Other traits commonly not preserved in the fossil record, such as eyes, antennae, and even gonopods can be observed, although their comparison with modern counterparts is limited.
Metabasic rocks from the Zemplinic crystalline basement (Western Carpathians, Slovakia): Metamorphic evolution and igneous protolith
Abstract: The Zemplinic pre-Alpine crystalline basement occur within a northwest-southeast striking tectonic horst, uplifted from the basement of the Cenozoic fill of the East Slovakian Basin. Its tectonic affiliation has not yet been clearly resolved, therefore, this either represents a continuation of the Western Carpathians crystalline basement units to the east or belongs to another tectonic unit. The Zemplinic metabasic rocks are represented by typical amphibolites, which are dark-coloured with strong to weakly foliated or lineated structures. The results of geothermobarometry and constructed phase diagrams indicate a P–T interval of an amphibolite facies with conditions of 610–730 °C at 0.58–0.76 GPa. Their critical mineral association Hbl + Pl + Cpx corresponds to the climax of the orogenic metamorphism of the Zemplinic crystalline basement. Based on their chemical composition, the protolith of metabasic rocks corresponds to two volcanic groups: the sub-alkali basalt (Nb/Y=0.05–0.31) and the alkali basalt (Nb/Y=0.90–1.85). The NbN/ThN values (=0.04–0.19) exhibit “arc” signatures for the sub-alkali metabasalts. The sub-alkali metabasalt group, which is shown in the incompatible element’s diagrams, indicates that it normalized to N-MORB and E-MORB and inclines to E-MORB basalts, with evidence of Zr–Hf, Ti, Y, and Nb depletion. On the other hand, the group of alkali metabasalts tends to be more transitional to the OIB basalts, with evidence of higher enrichment in LREE and MREE, as well as in Th, U, Nb, Zr, Ti, and Y. The Zemplinic metabasic rocks comprise a variety of enriched basalts, running from intra-oceanic towards within-plate or towards intra-oceanic- and island-arc field accord with the extensional supra-subduction regime of back-arc basins. From the point of view of tectonic development, we consider the Zemplinic Unit to be a continuation of the Inner Western Carpathians.