The impact of Outer Western Carpathian nappe tectonics on the recent stress-strain state in the Upper Silesian Coal Basin (Moravosilesian Zone, Bohemian Massif)
Abstract: The Upper Silesian Coal Basin (USCB) represents a typical foreland basin developed during the Variscan orogenic phase of the Late Carboniferous. Later, during the Alpine orogeny the Outer Western Carpathian nappes were thrust over the post-Variscan foreland, to which the USCB belongs. Due to this complex tectonic history, redistribution of stress fields occurred in the post-Variscan basement. Furthermore, post-Variscan denudation processes probably also contributed to recent stress regimes. Nevertheless, the impact of the West Carpathian orogeny can be regarded as the most significant influence. The in-situ measurement of recent stress fields in deposits of the Karvina Formation of the USCB and structural analysis of the Czech part of the USCB, has focused on verification of the structure and stress interference of the Carpathian nappes and post-Variscan foreland basement. In the southernmost part of the Karvina Subbasin, the easternmost domain of the USCB, situated in the apical zone of the Variscan accretionary wedge, hydrofracturing and overcoring stress measurements have been recorded in coal seams from selected coal mines. The data have been supplemented by interpretation of focal mechanism solutions of mine induced seismic events. Measurements of recent in-situ stress regimes in the Karvina Formation of the USCB indicate a dominant generally NW–SE orientation of the maximum horizontal compression stress. The results demonstrate that the stress-strain regime in the Karvina Formation in the Variscan Upper Carboniferous basement is significantly influenced by the stress field along the Outer Western Carpathian nappes front. Besides improving our understanding of recent regional stress fields within an area of mutual structural-tectonic interference by both the Variscan and Alpine orogenies, the measured data may contribute to more optimal and safer mining activities in the coal basin.
Structural pattern and emplacement mechanisms of the Krizna cover nappe (Central Western Carpathians)
Abstract: The Central Western Carpathians are characterized by both the thick- and thin-skinned thrust tectonics that originated during the Cretaceous. The Krizna Unit (Fatric Superunit) with a thickness of only a few km is the most widespread cover nappe system that completely overthrusts the Tatric basement/cover superunit over an area of about 12 thousands square km. In searching for a reliable model of its origin and emplacement, we have collected structural data throughout the nappe body from its hinterland backstop (Veporic Superunit) to its frontal parts. Fluid inclusion (FI) data from carbonate cataclastic rocks occurring at the nappe sole provided useful information about the p-T conditions during the nappe transport. The crucial phenomena considered for formulation of our evolutionary model are: (1) the nappe was derived from a broad rifted basinal area bounded by elevated domains; (2) the nappe body is composed of alternating, rheologically very variable sedimentary rock complexes, hence creating a mechanically stratified multilayer; (3) presence of soft strata serving as decollement horizons; (4) stress and strain gradients increasing towards the backstop; (5) progressive internal deformation at very low-grade conditions partitioned into several deformation stages reflecting varying external constraints for the nappe movement; (6) a very weak nappe sole formed by cataclasites indicating fluid-assisted nappe transport during all stages; (7) injection of hot overpressured fluids from external sources (deformed basement units) facilitating frontal ramp overthrusting under supralithostatic conditions. It was found that no simple mechanical model can be applied, but that all known principal emplacement mechanisms and driving forces temporarily participated in progressive structural evolution of the nappe. The rear compression operated during the early stages, when the sedimentary succession was detached, shortened and transported over the frontal ramp. Subsequently, gravity spreading and gliding governed the final nappe emplacement over the unconstrained basinal foreland.
An Upper Jurassic–Lower Cretaceous carbonate platform from the Valcan Mountains (Southern Carpathians, Romania): paleoenvironmental interpretation
Abstract: The results of a biostratigraphic and sedimentological study of the Upper Jurassic–Lower Cretaceous limestones cropping out in the southern sector of the Vâlcan Mountains in Romania are presented, including the definition of microfacies types, fossil assemblages and environmental interpretation. Six microfacies types (MFT 1–MFT 6) have been identified, each of them pointing to a specific depositional environment. The deposits are characteristic of a shallow carbonate platform. They contain normal marine or restricted marine facies deposited in low or high energy environments from the inner, middle and outer platform. The age attribution of these deposits (Late Jurassic to Berriasian–Valanginian–?Hauterivian, and Barremian) is based on foraminiferal and calcareous algae associations. The micropaleontological assemblage is exceptionally rich in the Vâlcan Mountains and brings new arguments for dating the Upper Jurassic–Lower Cretaceous limestones in this area.
Oligocene dinoflagellate cysts from the North Alpine Foreland Basin: new data from the Eggerding Formation (Austria)
Abstract: In spite of detailed geological and geophysical investigations, information available on palynostratigraphy for the successions deposited in the Austrian part of the North Alpine Foreland Basin (NAFB) is scanty. For the first time, relatively diverse and well preserved Oligocene dinocyst assemblages, comprising 53 genera and 138 species, are presented from the organic-rich sediments of the Eggerding Formation. These assemblages contribute to the biostratigraphy of the Oligocene deposits within the NAFB. Dinocysts such as Chiropteridium lobospinosum, Membranophoridium aspinatum, Cordosphaeridium spp., Enneadocysta spp., Deflandrea spp., Spiniferites/Achomosphaera group, Hystrichokolpoma spp., Apteodinium spp., Glaphyrocysta/Areoligera complex and Wetzeliella spp. represent the main palynological elements. The occurrence of Chiropteridium spp., Tuberculodinium vancampoae, Distatodinium biffii and Wetzeliella gochtii is of particular importance for regional correlations within the Lower Oligocene sediments. A comparison with age-controlled assemblages from the North Sea Basin, Carpathian and circum-Mediterranean regions substantiate the attribution to the Rupelian. Lack or sporadic occurrence of the oceanic taxa (e.g. Nematosphaeropsis and Impagidinium) and dominance of Glaphyrocysta/Areoligera indicate an inner-neritic marine setting during the deposition of the studied intervals. Although, it is difficult to reconstruct precisely the climatic conditions based on the recorded dinocysts, warm? sea surface water is suggested. A variation in salinities is interpreted based on the abundances of Homotryblium spp. The abundance of Peridiniaceae taxa (e.g. Lejeunecysta, Wetzeliella, and Deflandrea) indicates nutrient-rich surface water.
Sapphires related to alkali basalts from the Cerova Highlands, Western Carpathians (southern Slovakia): composition and origin
Abstract: Blue, grey-pink and pink sapphires from the Cerova Highlands, Western Carpathians (southern Slovakia) have been studied using CL, LA-ICP-MS, EMPA, and oxygen isotope methods. The sapphire occurs as (1) clastic heavy mineral in the secondary sandy filling of a Pliocene alkali basaltic maar at Hajnacka, and (2) crystals in a pyroxene-bearing syenite/anorthoclasite xenolith of Pleistocene alkali basalt near Gortva. Critical evaluation of compositional diagrams (Fe, Ti, Cr, Ga, Mg contents, Fe/Ti, Cr/Ga, Ga/Mg ratios) suggests a magmatic origin for clastic blue sapphires with lower Cr and Mg, but higher Fe and Ti concentrations in comparison to the grey-pink and pink varietes, as well as similar compositional trends with blue sapphire from the Gortva magmatic xenolith. Moreover, blue sapphires show similar δ18O values: 5.1 ‰ in the Gortva xenolith, 3.8 and 5.85 ‰ in the Hajnacka placer, closely comparable to mantle to lower crustal magmatic rocks. On the contrary, pink and grey-pink sapphires show higher Cr and Mg, but lower Fe and Ti contents and their composition points to a metamorphic (metasomatic) origin.
Late Pleistocene voles (Arvicolinae, Rodentia) from the Baranica Cave (Serbia)
Abstract: Baranica is a cave system situated in the south-eastern part of Serbia, four kilometers south to Knjazevac, on the right bank of the Trgoviski Timok. The investigations in Baranica were conducted from 1994 to 1997 by the Faculty of Philosophy from Belgrade and the National Museum of Knjazevac. Four geological layers of Quaternary age were recovered. The abundance of remains of both large and small mammals was noticed in the early phase of the research. In this paper, the remains of eight vole species are described: Arvicola terrestris (Linnaeus, 1758), Chionomys nivalis (Martins, 1842), Microtus (Microtus) arvalis (Pallas, 1778) and Microtus (Microtus) agrestis (Linnaeus, 1761), Microtus (Stenocranius) gregalis (Pallas, 1779), Microtus (Terricola) subterraneus (de Selys-Longchamps, 1836), Clethrionomys glareolus (Schreber, 1780) and Lagurus lagurus (Pallas, 1773). Among them, steppe and open area inhabitants prevail. Based on the evolutionary level and dimensions of the Arvicola terrestris molars, as well as the overall characteristics of the fauna, it was concluded that the deposits were formed in the last glacial period of the Late Pleistocene. These conclusions are rather consistent with the absolute dating of large mammal bones (23.520±110 B.P. for Layer 2 and 35.780±320 B.P. for Layer 4).