Vienna Basin Research Articles

Natural long-term annealing of the zircon fission-track system in Vienna Basin deep borehole samples: constraints upon the partial annealing zone and closure temperature

Fission-track (FT) analysis of zircon from Cretaceous and Tertiary sandstone samples in Vienna Basin boreholes has provided constraints for the thermal stability of the zircon FT system over a geological timescale. Confined track lengths and ages were measured for samples from depths of ∼ 1.5-7.5 km, the deepest with a present environmental temperature of ∼ 200°C. Mean track lengths range from 10.3 to 10.8 μm, indistinguishable within error from the unannealed reference length of 10.7 ± 0.1 μm (± 1 standard error), thus showing no sign of systematic downhole reduction. Central zircon ages are consistently older than stratigraphic ages of parent rocks, with no single-grain ages significantly younger than their respective stratigraphic ages. Such FT age and length evidence strongly suggests that the tracks have not been significantly annealed since sediment deposition. Because the present geothermal regime as well as sample burial depths have been near-constant for at least the past 5 m.y. the lower temperature limit of the zircon FT partial annealing zone is > 200°C for a heating duration of the order of 5–10 m.y. Such evidence from long-term natural annealing is compatible with a zircon FT partial annealing zone cf ∼ 200–350°C derived by the extrapolation of laboratory annealing results based on o̧nfined track length measurements, but cannot alone discriminate between different annealing models. For the zircon FT closure temperature, a perhaps over-simplified concept, these results are consistent with the oft-quoted temperature of ∼ 250°C for cooling rates of ∼ 10–100°C/m.y.

Quantitative subsidence analysis and forward modelling of the Vienna and Danube basins: thin-skinned versus thick-skinned extension

We present the results of a quantitative study of the tectonic evolution of the Vienna and Danube basins by comparing tectonic subsidence histories derived from backstripping of more than 90 wells from Slovakia, Hungary and Austria, with the predictions from forward tectonic modelling. Subsidence analysis and forward modelling, using a modified, non-uniform, extension model address the tectonic relations between different depocentres and the nature of tectonic subsidence. We derived stretching values for the Vienna basin between 1.04 and 1.30 for the crustal extension (δ) and between 1.00 (in the northern part) and 1.60 (southern part) for the lithospheric extension (β). The Danube basin is characterized by crustal extension values (δ) between 1.09 and 1.30 and lithospheric extension values (β) between 1.00 (northern part) and 1.60 (southern part). The Vienna basin shows a trend from thin-skinned extension in the northwestern part to whole lithospheric extension in the central-southern part. The subsidence history of the northwestern part of the Danube basin also reflects a thin-skinned extensional basin formation mechanism. The central and southern parts of the Danube basin show an important component of lithospheric extension. The basin evolution is strongly influenced by the rotating stress field through Miocene times, expressed in different phases of fault reactivation that are observed in the subsidence history.

Seismogeological pattern of a transition area between the Eastern Alps and the Western Carpathians

All available seismological data (earthquake epicentres, macroseismic observations) and the available structural-tectonical, geomorphological and geodetic data for the transition area of two fundamental orogenetic units of Central Europe -the Eastern Alps and the Western Carpathians -are analyzed, with the aim to find seismogenic zones of this area and to assess their possible earthquake activity. The relationship of small local geological structures to the fundamental European tectonic blocks is discussed from the viewpoint of seismotectonic processes expected for the transition area, especially in the Vienna Basin and in the Little Carpathians. The special attention is paid to the densely inhabited area of the city of Bratislava which is situated in the territory under study. Some results could contribute to its further urban planning. On several faults or boundaries in the Western Carpathians relatively intense horizontal displacements have been observed. Fundamental movements on faults of NS to NE-SW directions have mostly sinistral character while on some faults of ENE-WSW direction they are dextral. In the southern parts of the investigated area, dextral movements on local faults of NW-SE direction have been found. A neotectonic model of the broader surroundings of the city of Bratislava is presented.

Illite/Smectite Diagenesis and Its Variable Correlation with Vitrinite Reflectance in the Pannonian Basin

AbstractThe correlation between illite/smectite (I/S) diagenesis and mean vitrinite reflectance (Ro) data is examined in mudrocks from a hydrocarbon exploration well (geothermal gradient 35°C km−1) from the Great Hungarian Plain of the Pannonian Basin System. The expandability of I/S decreases with depth and there is a change from random to ordered mixed-layering at about 2500 m depth. At this depth Ro is about 0.6%. Comparison of the correlation of expandability and Ro from this study to published data for the Vienna Basin and the Transcarpathian Basin, sub-basins of the Pannonian Basin System, shows that the correlation is systematically different for each sub-basin, according to their thermal histories. In the Vienna Basin (geothermal gradient 25°C km−1), for any given value of Ro, the expandability of I/S is less than in the Transcarpathian Basin (geothermal gradient 55°C km−1) and the sediments are older and more deeply buried. Data from the present study are intermediate. This variation is believed to be due to the effect of time on the smectite-to-illite reaction. Results of an optimization procedure to calculate the kinetics of the smectite-to-illite reaction, using as input the expandability depth profiles, and thermal histories constrained by comparison of observed and calculated Ro data, showed that I/S diagenesis in the Pannonian Basin System can be modelled by a single first order rate equation: −dS/dt=elog(A)−E/RT⋅S where S = fraction of smectite layers in I/S, t = time (Ma), e = exponential function, log(A) = frequency factor = 7.5 (Ma−1), E = activation energy = 31.0 kJ mol−1, R = universal gas constant, and T is temperature in Kelvin. This result also suggests an important role for time. By combining the kinetics of the smectite-to-illite reaction with a kinetic model of vitrinite maturation it is possible to define a domain within which all ‘normal’ (burial diagenesis) correlations between Ro and I/S diagenesis should lie. Such diagrams can be used to identify different thermal histories related to different geotectonic settings and ‘anomalous’ data such as that affected by igneous intrusions.

From transpression to transtension: Oligocene-Miocene structural evolution of the Vienna basin and the East Alpine-Western Carpathian junction

Palaeostress analysis in the easternmost Alps and westernmost Carpathians revealed the existence of four different stress fields during Oligocene-Miocene times. The generalized Oligocene-late Middle Miocene maximal horizontal stress axis changes gradually from WNW-ESE to ENE-WSW and the Late Miocene axis trends to NNE-SSW. Except for the late Middle Miocene (late Sarmatian, 11 Ma) weak, transient stress field, the others reflect important deformations and are connected to the formation of the Vienna basin. The integration of microtectonic and stress-field data with other structural observations and sedimentological data resulted in a complete structural analysis. It suggests a four-stage evolution of the Vienna basin and its surroundings. The Late Oligocene and Early Miocene deformations were connected to progressively developed, NE-SW-trending sinistral strike-slip zones. During the earliest Miocene (Eggenburgian, 21-18.5 Ma), the deformations were characterized by transpression. At the end of the Early Miocene (17-16 Ma), the Vienna basin became a pull-apart structure for a short period. Middle and Late Miocene evolution (16-5.4 Ma) was characterized by a combination of extensional and strike-slip faulting (transtension) rather than a pure strike-slip or pure tensional regime.A combination of palaeomagnetic and tectonic data demonstrates that the stress field did not change during the Oligocene and Early Miocene. The compressional axis was oriented originally N-S, and than turned to the actual WNW-ESE or NNW-SSE orientation. The gradual counterclockwise rotation of the structures took place simultaneously with the development of the Late Oligocene-Early Miocene sinistral shear zones. These rotations affected mainly small crustal blocks between strike-slip faults. This mechanism permitted the transfer of sinistral slip toward the northeast through the entire junction area. All these deformations explain the mechanism of the tectonic escape of the whole East Alpine-North Pannonian block.

Petroleum geology of the Carpathian Foredeep and overthrust zones in the Czech Republic

The area is situated at the contact of two regional megastructures -the Bohemian Massif and the Western Carpathians. The eastern slope of the Bohemian Massif dips under the Carpathian Foredeep and thick Flysch nappes and is covered by Variscan and Neoidic autochthonous Palaeozoic, Mesozoic and Palaeogene sediments. In the southeast, the Vienna basin's Neogene fill overlies the units of the Magura Flysch and a part of the Zdanice unit. The area can be divided into three parts. The south is characterized by a thick Jurassic sedimentary complex that overlies the crystalline basement. The basal elastics of this Jurassic complex are very prospective and in the central part of the area the oil field Uhrice II is situated in these strata. In this central part two deep depressions - the Vranovice and Nesvacilka grabens - are the most important buried geomorphological elements. Both are filled with Palaeogene strata. The north of the area is characterized by uplifted crystalline basement with thin autochthonous sediments, mostly with Miocene strata of the foredeep and with the flysh nappes. Thick Palaeogene and Upper Jurassic pelites are supposed to be the main source rocks. The cap rocks are pelitic sequences of variable thicknesses including Jurassic marls, Palaeogene and Miocene claystones and basal claystones of flysch units. Traps are delimited by faults, lithology changes and unconformities.

Helium and neon isotope systematics in carbon dioxide-rich and hydrocarbon-rich gas reservoirs

The isotopic compositions and elemental abundances of helium and neon were measured in three natural gas reservoirs in the Pannonian sedimentary basin of Hungary. Kismarja (a CO 2-rich reservoir) and Szeghalom-South and Szeghalom-North (both CH 4-dominated reservoirs) are located on topographic basement highs close to the Derecske Sub-Basin in eastern Hungary. Mantle-derived neon has been identified in mixed CH 4-CO 2 reservoirs in the Vienna Basin, Austria. This study establishes that mantle-derived neon and helium are a characteristic feature of gas reservoirs throughout the Neogene extensional basins of Hungary and Austria regardless of the dominant active gas composition. 3He 4He ratios within these samples are attributable to a two-component mixing between mantlederived and crustal-radiogenic helium. The percent contribution of mantle-derived 4He varies from 2.3 to 17%. In contrast, neon isotopic ratios indicate that the gases contain a significant component of atmosphere-derived neon in addition to the mantle- and crustal-derived components. 20Ne, 21Ne and 22Ne abundances can be corrected for this atmospheric contribution. Calculated contributions of mantle- and crustal-derived 21Ne are between 3.6–21% and 1–37%, respectively. 20Ne 22Ne c and 21Ne 22Ne c ratios derived for these atmosphere-corrected components correlate with measured R/Ra values and plot along a single two-component mixing line between crustal and mantle isotopic endmembers. This is consistent with a model in which simple mixing occurs between crustal and mantle endmembers with fixed He/Ne ratios. The mixing line is defined by a hyperbolic constant K (where K = ( 4He 22Ne ) rad/( 4 He 22Ne ) mntl) with a mean value of 67.3 ± 11.8. Based on estimated values of 0.47 for 21Ne 22Ne rad and (1.62 ± 0.03)× 10 7 for ( 4He 21Ne ) rad (Kennedy et al., 1990), values of 7.61 × 10 6 for ( He 22Ne ) rad and 11.3 × 10 4 for ( 4He 22Ne ) mntl can be calculated for the Pannonian Basin gases. This ( 4He 22Ne ) mntl value is indistinguishable within error from the value of 8.04 × 10 4 calculated for rare gases in natural gases from the Vienna Basin. These results clearly establish that the continental expression of mantle-derived rare gases in continental extensional systems in Austria and Hungary is distinct and consistently different from that of gases discharging at the spreading ridges where best estimates of ( 4He 22Ne ) mntl are 8.1–11.3 times higher (9.10 × 10 5; Staudacher et al., 1989). Given the remarkable agreement in the continental expression of mantle-derived gases throughout the Pannonian and Vienna Basins, it is difficult to attribute the observed neon enrichment/helium depletion with respect to MORB gases to fractionation related to lithospheric transport processes. Kinetic fraction ation processes involved in transport through the crust might be expected to produce a much wider variation in the observed He/Ne elemental ratios. The consistent, order-of-magnitude neon enrichment observed throughout these gas fields instead implies that mantle-derived fluids in these continental extensional systems may be sourced in a region of the mantle distinct from that supplying the mid-ocean spreading ridges.

Basin Modeling in Overthrust Areas: Outer Carpathian Nappes (NW Vienna Basin): ABSTRACT

Basin Modeling in Overthrust Areas: Outer Carpathian Nappes (NW Vienna Basin): ABSTRACT

Some molluscs from the Badenian (Middle Miocene) west of Pleven (Central Northern Bulgaria). I. Gastropoda: orders Archaeogastropoda and Mesogastropoda

Thirteen taxa of the species group undescribed up to now in Bulgaria are described in this paper. They belong to 9 genera and 9 families of Archaeogastropoda and Mesogastropoda orders. The species were found in outcrops exposed along the right bank of Vit River to the west of the town of Pleven between the villages of Târnene and Bivolare. Only Late Moravian (foraminiferal zone Orbulina suturalis) and Wielichkian (foraminiferal zone Uvigerina) sediments of the Badenian regional stage are exposed in this area. Despite its diversity and facial characteristics, the gastropoda fauna is not stratigraphically tied and therefore does not appear as an indication for the Early Badenian age of these deposits. The similarity of most taxa with those from the Vienna Basin is an evidence of parallelism of their development.

New coral-bivalve association (Actinastrea-Lithophaga) from the Eocene of Florida

The endolithic mytilid bivalve, Lithophaga palmerae n. sp., from the Upper Eocene Ocala Limestone of north-central Florida, sheds new light on the evolution of lithophagids with its unspecialized morphology and highly specialized mode of life. Lithophaga palmerae n. sp. inhabited dead and living coral as indicated by orientation evidence. In living coral, the anterior end of the borehole was sealed off with thick, continuous, “false floors” of CaCO3, as the posterior end was extended to keep pace with coral growth. To date, this new species of lithophagid has been found associated with only one host coral, Actinastrea cf. A. incrustans (Duncan). Association with living coral is found today in L. bisulcata (d'Orbigny) and L. dixonae Scott from the Caribbean and in several Red Sea and Indo-Pacific lithophagids. In the fossil record, live-coral boring has been reported from the Miocene of the Vienna Basin of Austria and from the Pleistocene of Grand Cayman Island in the Caribbean. Lithophaga palmerae n. sp. provides a valuable ancestral link in the evolution of Lithophaga by extending the range of live-coral boring back to the Eocene of Florida.

Geomorphological interpretation of apatite fission-track data — results from the Steinwald region, NE-Bavaria

All available seismological data (earthquake epicentres, macroseismic observations) and the available structural-tectonical, geomorphological and geodetic data for the transition area of two fundamental orogenetic units of Central Europe -the Eastern Alps and the Western Carpathians -are analyzed, with the aim to find seismogenic zones of this area and to assess their possible earthquake activity. The relationship of small local geological structures to the fundamental European tectonic blocks is discussed from the viewpoint of seismotectonic processes expected for the transition area, especially in the Vienna Basin and in the Little Carpathians.The special attention is paid to the densely inhabited area of the city of Bratislava which is situated in the territory under study. Some results could contribute to its further urban planning. On several faults or boundaries in the Western Carpathians relatively intense horizontal displacements have been observed. Fundamental movements on faults of NS to NE-SW directions have mostly sinistral character while on some faults of ENE-WSW direction they are dextral. In the southern parts of the investigated area, dextral movements on local faults of NW-SE direction have been found. A neotectonic model of the broader surroundings of the city of Bratislava is presented.

An Experimentally Derived Kinetic Model for Smectite-to-Illite Conversion and Its Use as a Geothermometer

AbstractThe smectite-to-illite conversion during shale diagenesis has recently been used to constrain the estimate of a basin's thermal history. We have systematically investigated the kinetics for the conversion of a Na-saturated montmorillonite (SWy-1) to a mixed-layer smectite/illite as a function of KCl concentration (from 0.1 to 3 moles/liter) over a temperature range of 250° to 325°C at 500 bars in cold-seal pressure vessels using gold capsules. The results show that the conversion rate can be described by a simple empirical rate equation-dS/dt = A · exp(-Ea/RT) · [K+] · S2where S = fraction of smectite layers in the I/S, t = time in seconds, A = frequency factor = 8.08 × 10-4 sec-1, exp = exponential function, Ea = activation Energy = 28 kcal/mole, R = gas constant, 1.987 cal/deg-mole, T = temperature (degree Kelvin), [K+] = K+ concentration in molarity (M) in the fluid.The results also show that Ca2+ in solutions barely affects the illitization rate, whereas Mg2+ significantly retards the rate. The retardation, however, is not as severe as previously reported. Na+ ion can significantly retard the rate only if the concentration is high.We found that by assuming a range 0.0026-0.0052 moles/liter (100-200 ppm) of K+, concentrations similar to the value typically reported in oil field brines, the present kinetic model can reasonably predict the extent of the smectite-to-illite conversion for a number of basins from various depths and age. This narrow range of potassium concentrations, therefore, is used to model the smectite-to-illite conversion in shale when the actual chemical information of pore fluid is not available.The kinetic equation has been tested using field data from a large variety of geologic settings worldwide (i.e., the Gulf of Mexico, Vienna Basin, Salton Trough Geothermal Area, East Taiwan Basin, Huasna Basin, etc). The results show that the equation reasonably predicts the extent of the reaction within our knowledge of the variables involved, such as burial history, thermal gradients, and potassium concentration.

The use of natural He, Ne and Ar isotopes as constraints on hydrocarbon transport

Hydrocarbon accumulations contain rare gases derived from the atmosphere, the crust and, in some cases, the mantle. The distinctive isotopic structure of these different rare gas components allows them to be resolved. The relative abundances of the He, Ne and Ar in the crustal-, mantle- and atmosphere-derived components provides information on the physical processes which have operated in the sub-surface. When combined with mass balance considerations, the rare gases provide powerful constraints on fluid provenance and transport. The results of case studies from the Pannonian Basin in Hungary, and the Vienna Basin, Austria are reviewed. Natural gas reservoirs in the Pannonian and Vienna basins provide samples from depths between 0.5 and 5.5 km. The atmosphere- and crustal-derived rare gas components show systematic patterns of He/Ar and Ne/Ar fractionation which are in the sense predicted by rare gas partitioning between liquid, such as oil and water, and a gas phase. This could occur either during transport or upon emplacement into the reservoir. The role of diffusive processes in fractionation of rare gases cannot be resolved and is assumed to play only a minor role in hydrocarbon transport in the accumulations investigated. The rare gases also convey information on the extent of interaction between groundwater and hydrocarbons. The relationship between major species, such as CH 4 and rare gas tracers, provides estimates for the minimum volume of groundwater that has interacted with the hydrocarbon phase. In the case of the Pannonian Basin, the results are consistent with a model in which the natural gas has been transported in a CH 4 -saturated water phase, from which the gas has separated upon cooling and/or decompression. The mass balance demonstrates that the interaction between the hydrocarbon gas and groundwater has been on a scale much greater than often envisaged in models of hydrocarbon formation and migration.

Ecological basic research with potential application for groundwater management: D. L. Danielopol & P. Pospisil, in: Hydrological basis of ecologically sound management of soil and groundwater. Proc. symposium, Vienna, 1991, ed H.P. Nachtnebel & K. Kovar, (IAHS; Publication, 202), 1991, pp 215–228

Ecological basic research with potential application for groundwater management D. L. DANIELOPOL Limnologisches Institut, Osterreichische Akademie der Wissenschaften, Gaisberg 116, A-5310 Mondsee, Austria P. POSPISIL, Zoologisches Institut, Universitat Wien, AlthanstraBe 14, A-1090 Wien, Austria J. DREHER, BreitenfurterstraBe 458, A-1236 Wien, Austria ABSTRACT Ecological researches on aquifers can be approached in a hierarchical way. We consider three level of investigation. On a macroscale level the aquifer can be viewed as an ecosystem. The aquifer of the lower terrace of the Danube in the Vienna Basin is such an example. The interest of this approach for groundwater monitoring and management is emphasized. At a lower level of generality groundwater habitats are studied. Several sampling strategies used by groundwater ecologists in order to describe the subsurface environment are presented. The third level is represented by the ecology of groundwater organisms. It is emphasized that more basic research on groundwater biota and new monitoring methods using the biological activity of organisms are urgently needed. INTRODUCTION - THE RISE OF GROUNDWATER ECOLOGY In many countries the management of the groundwater reserves has become a difficult task because of steady increase of conflicting demands on the usage of water resources and a rise in the magnitude and frequency of the environmental degradation of these resources. For a long period of time the quantitative and qualitative evaluation of the groundwater reserves was one of the tasks of hydrologists. They were helped by hydrochemists and bacteriologists (mainly hygienists). The ecological study of the subsurface habitats and organisms was dealt with mainly by scientists trained in various fields of biology e.g. zoology, ecology, microbiology, genetics. We assisted a fast development of groundwater ecology in the last years . This is the scientific branch which deals with the interactions between the subterranean organisms and their subsurface environment (Husmann, 1971). 215

Seismological observations in the eastern Alps

The Institute of Meteorology and Geophysics of the University of Vienna and the Department of Geophysics of the Central Institute of Meteorology and Geodynamics are maintaining a number of seismic stations in Austria. All stations have been established to investigate different research tasks, such as the extent of the lithosphere beneath the Alps and the seismic behaviour of the most prominent active seismic areas in Austria. One of the results was reflected in the negative travel-time residuals derived from the observation of remote earthquakes. These residuals can be explained by a steeply inclined lower boundary of the lithosphere penetrating the asthenosphere down to a depth of approximately 200 km. A simple rigid block model explains the most active seismic zones of the region and the genesis of the Vienna Basin. Seismicity and associated deformations are consistent with the regional N-S compression. Focal depths of the Mur-Mürz (MM) earthquakes must be in the upper crust (less than 8 km deep) as a result of the stress measurements and focal mechanisms. A sinistral strike-slip occurs along numerous short segments of the MM fault.

The nature of mantle neon contributions to Vienna Basin hydrocarbon reservoirs

The abundances and isotopic compositions of He and Ne have been determined in various hydrocarbon gas reservoirs within the Vienna Basin, Austria. These continental gases are the first in which mantle-derived Ne has been resolved. They allow a comparison of the estimated mantle He/Ne ratio with that observed in basalts at mid-ocean ridges. Between 1.9% and 28% of the 4He within these samples is mantle derived, the remainder is crustal-radiogenic. The contribution of mantle-derived 21Ne to the total 21Ne content ranges from < 3% to 34%, the contribution of 21Ne produced nucleogenically in the crust ranges from 0% to 40%. The remaining Ne is atmospheric in origin. 21Ne/ 22Ne and 20Ne/ 22Ne ratios, corrected for atmosphere-derived contributions, correlate with the measured R/R a values. Analyses define a single hyperbolic mixing line between mantle and crustal-radiogenic isotopic end members. This line is defined by the constant [ 4He/ 22Ne] rad/[ 4He/ 22Ne] mn1l = 94.7 ± 9.4. For a crustal [ 4He/ 22Ne] rad ratio of 7.61 × 10 6 [1] the ratio [ 4He/ 22Ne] mn1l = 8.04 × 10 4 for the Vienna Basin gases. This is a factor of 11.3 times lower than the best estimate of the mantle value [ 4He/ 22Ne] mn1l = 9.10 × 10 5, measured in mid-ocean ridge basalts [2]. The magnitude of the mantle Ne enrichment in the Vienna Basin gases cannot be accounted for either by melt formation or degassing and must reflect either the transport of the mantle volatiles through the continental lithosphere or a mantle source relatively enriched in Ne over He.

Borehole-breakouts as geological indications of crustal tensions in the Vienna basin : Marsch, F; Wessely, G; Sackmaier, W Proc International Conference on Mechanics of Jointed and Faulted Rock, Vienna, 18–20 April 1990P113–120. Publ Rotterdam: A A Balkema, 1990

Borehole-breakouts as geological indications of crustal tensions in the Vienna basin : Marsch, F; Wessely, G; Sackmaier, W Proc International Conference on Mechanics of Jointed and Faulted Rock, Vienna, 18–20 April 1990P113–120. Publ Rotterdam: A A Balkema, 1990

Finite element models of stress in eastern Austria during the early Miocene

The transition zone between the Alps and the Carpathian mountains in eastern Austria is characterized by a change of strike of the tectonic units from E-W to SW-NE, resulting in the formation of the Alpine-Carpathian arc. This study investigates the effect that a depression of the eastern edge of the Bohemian Massif, filled with Mesozoic and Tertiary sediments, may have had on the advancing Alpine nappes in the early Miocene. Two-dimensional linear-elastic plane stress finite element models were used to simulate the patterns of stress, faults and seismicity resulting from such a situation. Three different materials were used in the reconstruction of the geological-tectonic setting during the early Miocene: a limestone unit striking east-west, a molasse unit, and a crystalline unit. Whereas the northward movement of the limestone unit in the west is restricted by the crystalline unit, which acts as a buttress, in the east the movement is only slightly retarded by the molasse unit. Calculations show that following such a situation in the early Miocene, pre-existing zones of weakness in the crystalline unit can be reactivated. East of the point where northward movement of the limestone material is no longer restricted, in the area of the present Vienna Basin, the development of a pull-apart type basin is suggested. The main faults for this process are probably reactivated basement faults. A similar basin is predicted 200 km to the east in the region of the West Danube Basin. The results also predict the establishment of a zone of seismic activity, which seems to be reflected by the pattern of seismicity observed in eastern Austria today. Overall, the models show that the present seismic and tectonic patterns can be traced back to the events in the early Miocene, when Alpine nappes draped around the Bohemian Massif.

Migration and retention phenomena of radionuclides in clay-barrier systems

Within the scope of projecting a waste deposit for low- and medium radioactive materials we have investigated the migration behaviour of the nuclides cesium (Cs-137), strontium (Sr-90), cobalt (Co-60) and zinc (Zn-65) in the Badener Tegel, a Miocene clay of the Vienna Basin (Lower Austria). Two fundamental retention processes could be derived from batch tests for the nuclides mentioned above: Sorption processes, in general cation exchange processes on clay minerals (cesium and strontium) and precipitation reactions (zinc and cobalt) which are included by exceeding the solubility product in the changed equilibrium solution with the clay. The migration behaviour of the nuclides was investigated with the help of columns with undisturbed and orientated clay samples under advective conditions. The influences of the hydraulic gradient, fabric and solution composition on the migration behaviour of nuclides can be derived form breakthrough curves and retention coefficients. The grade of fixation of nuclides in the clay can be determined by desorption tests with water of different composition. A more realistic case of contaminant extension in low permeable clays is simulated by diffusion tests in undisturbed samples. For the Badener Tegel, diffusion coefficients and breakthrough times have been determined from which the diffusive nuclide extension can be derived. Again precipitation reactions (especially with zinc) lead to a drastic reduction of the nuclide amounts passing through.

Broadside shooting in the Alpine overthrust - a case study

In the deeper parts of the Vienna Basin, the autochthonous Mesozoic formations, containing source and reservoir rocks, have been exploited for 20 years. Fifteen kilometres northwest of Vienna, in the Alpine overthrust, these target horizons were found beneath the flysch nappes at a depth of about 3 km in the Höftein Field (Schimunek and StröbI1985).