Fakultät für Geowissenschaften - Digitale Hochschulschriften der LMU

The present work combines palaeomagnetic and rock magnetic methods with clay mineralogy, isotope geochemistry of clay minerals and trace element geochemistry of Fe-oxide leachates to study remagnetised sedimentary rocks from Palaeozoic outcrops in Middle and Eastern Europe. Three areas were selected (NE Rhenish Massif, Barrandian and Holy Cross Mountains), where the causes of Late Palaeozoic remagnetisations are yet unclear. The results yield important implications for the processes and mechanisms responsible for the remagnetisations in the areas studied.

NE Rhenish Massif: A Late Carboniferous remagnetisation (component B) is identified in Late Palaeozoic carbonate and clastic rocks from the NE Rhenish Massif. Three individual incremental regional fold tests across the area show a unique and distinctive variation in timing of remagnetisation relative to the age of folding. The remagnetisation is postfolding in the South and of synfolding origin in the North of the area. Consequently, the timing and the duration of the remagnetisation event is constrained by the age of folding, which varies throughout the area and reflects a northward migration of the deformation front during 325 Ma to 300 Ma. Comparison of the resulting palaeolatitude of the NE Rhenish Massif with the palaeolatitudinal drift history for the region yields an estimate for the age of remagnetisation of ca. 315 - 300 Ma, which is in good agreement with the age of deformation. The concordance of the magnetic palaeoinclinations obtained from the entire area indicates that the rocks were remagnetised during a relatively short period of only a few My. The thermal stability of the remanence up to 550°C the comparably low palaeotemperatures in the studied region and the short duration of the remagnetisation event favour a chemical remagnetisation process.

Rock magnetic experiments reveal a complex magnetomineralogy of the remagnetised Palaeozoic sediments from the NE Rhenish Massif. The dominant carrier of the Carboniferous magnetisation component is magnetite, but pyrrhotite and hematite accompany magnetite as carrier of the NRM in some grey carbonates and red sandstones or red nodular limestones, respectively. The hysteresis ratios, magnetic viscosity and low temperature behaviour of the carbonate rocks give strong evidence for the presence of very fine grained (superparamagnetic) magnetic minerals. This material is also thought to be responsible for similar rock magnetic properties of siliciclastic rocks. This interpretation, however, is not unique for the siliciclastic rocks, due to the predominance of detrital MD magnetite and the high amount of paramagnetic material. The hysteresis ratios from medium to coarse grained rocks and reef carbonates fall in or close to the fields of MD magnetite and remagnetised carbonates, respectively. The fine grained clastic rocks (siltstones) and limestone turbidites have intermediate hysteresis properties. This implies the presence of very fine grained magnetic material in all lithologies of the NE Rhenish Massif, which is indicative for authigenic growth of magnetic minerals and formation of a CRM. However, the magnetic fingerprint of SP grains gets increasingly disguised with increasing amount of detrital MD magnetite in clastic rocks.

K-Ar dating of <0.2µm clay fractions indicates two diagenetic events in the NE Rhenish Massif. The observation of K-Ar isochrons rules out contamination from detrital sources and preferential loss of radiogenic ^40Ar from authigenic illites. Middle Devonian clastic rocks are characterised by an illitisation event at 336 +/- 6.2 Ma, which is probably connected to a major magmatic event at ca. 340 - 330 Ma in the Mid-German Crystalline Rise. The second period of illite formation at 312 +/- 10 Ma is coeval to the northward migration of deformation through the Rhenish Massif and is only recorded by Upper Devonian and Lower Carboniferous rocks. This indicates that the metamorphic conditions were n

The Earth's magnetic field is generated by the motion of liquid iron-rich material in the outer core. One of the most drastic manifestations of the dynamics in the outer core are polarity reversals of the magnetic field. The processes controlling geomagnetic reversals, however, are still poorly understood. The mathematical formulation of the dynamics of the liquid outer core show such a degree of complexity that a universal numerical model still remains elusive. Given that the last reversal occurred about 780,000 years ago, direct observations of a reversal have never been possible. Thus we are left with records of ancient reversals recorded in sequences of sedimentary and igneous rocks. Documenting any systematics in reversal processes will provide substantial information about the outer core and core mantle boundary conditions. However, despite the advances in deciphering the behaviour of the field during polarity transitions, reversal records yield controversial results and thus answers to several key questions are still enigmatic.

Detailed studies of palaeodirectional and absolute palaeointensity patterns of geomagnetic reversals are scarce and are restricted to the Cenozoic so far. In order to verify or reject concepts developed on the basis of this dataset, reversal records which occurred in the more distant geological past of the Earth are needed. This work presents the results obtained from the Siberian Trap Basalts (Russia) which are coeval with the Permo-Triassic boundary (250 Ma). The sequence yields the by far oldest hitherto studied detailed record of a geomagnetic transition from reversed to normal polarity and provides new insights in transitional field behaviour.

Three sections (Talnakh, Listvjanka and Abagalakh) comprising a total of 86 lava flows have been sampled in the Noril'sk region, located at the northwestern rim of the Siberian Trap Basalt province. They provide a complete coverage of the lava pile outcropping in the area. The samples have been subjected to palaeomagnetic direction analysis and to Thellier-type palaeointensity experiments. Extensive rockmagnetic investigations and microscopical studies have been carried out to asses the reliability of the palaeomagnetic information recorded by the lava flows.

Magnetite and Ti-poor titanomagnetites were identified to be the carriers of the characteristic remanent magnetisation. The reversibility of the thermomagnetic curves and the observation of exsolution lamellae by ore microscopy give clear evidence for a primary high-temperature oxidation of the titanomagnetite. It can thus be inferred that the measured palaeodirectional and intensity information obtained from these flows was acquired shortly after extrusion of each flow.

The demagnetisation of the natural remanence reveals only one direction of magnetisation for most samples. Thermal and alternating field demagnetisation methods are equally effective in isolating the characteristic remanent magnetisation. Occasional overprints have maximum unblocking temperatures of 350°C or remanence coercivities less than 20 mT. Reliable palaeointensity estimates were obtained for approx. 50% of the samples. The relatively high success rate can be attributed to the enhanced magnetic and thermal stability of high-temperature oxidised titanomagnetites.

In the lower part of the sequence reversed polarity of the Earth's magnetic field is identified. The associated palaeointensities yield values around 10 µT. The subsequent flows recorded transitional configurations. A tight cluster of virtual geomagnetic poles (VGPs) in mid northerly latitudes, comprising the results of 15 flows, is observed during the transition. Within the cluster the record shows a pronounced and well defined increase in intensity from around 6 to 13 µT. A doubling of local field intensity infers that large scale dynamic processes in the outer core are responsible for this feature, making a strong case for a reasonable temporal stability (se

A 3D refraction and reflection seismic travel time tomography was developed on the basis of the widespread Local Earthquake Tomography (LET) method SIMULPS. To include crustal scale refraction seismic observations in the inversion the accuracy of this method was adjusted for long ray paths and high resolution. Floating or discontinuous reflectors are modelled on separate grids by bi-cubic splines, and an appropriate reflection ray tracer was developed using the Approximate Ray Tracing/Pseudo Bending (ART/PB) method. Accuracy was adjusted by several means: arcuate ART trajectories are roughly adjusted to the velocity field before bending, multiple ART travel time minima are perturbed and step length along the ray path for distant observations is reduced by iterative resegmentation. The resulting ray tracer also finds head waves as long as interface geometry is not too complex. The extensions have been tested with some simple synthetic models focusing on problems connected with discontinuities and low velocity zones.

The inversion algorithm was then applied to a wide-angle data set from the Eastern Alps recorded by seismological three-component stations during the TRANSALP campaign. From Vibroseis records a high resolved model for the upper crust was derived, which was extended to depth with low resolution using distant observations from dynamite shots. The resulting model correlates well with known geologic structures in the upper crust. The middle and lower crust shows distinct velocity functions for the European and the Adriatic part of the profile. The European Moho is resolved from the Northern Calcareous Alps in 40 km depth to the Alpine root in ca. 55 km depth, where it seems to lose its reflective character. Only few reflections from the Adriatic Moho were recorded yielding a depth of ca. 40 km. Lower crustal structure is interpreted as a result of southward subduction of Penninic oceanic crust before collision.

Long-term threats to groundwater quality arising at regional scale from the exploitation of deep groundwaters, and some ways to tackle with them have been revealed by Seiler (1983, 1987, 2001), Seiler & Lindner (1995). They have shown that, once the passive recharge zone of a groundwater system is penetrated by pumping wells and the duration and/or rate at which these are operated exceeds a certain threshold, the natural hydrogeologic barrier between the passive and the active recharge zone gets disrupted, and deep water turnover rates get visibly accelerated; alongside with them, the migration of near-subsurface pollutants towards greater aquifer depths is enhanced in such a way that (a) it remains unnoticeable to standard water quality monitoring for a good number of years, and (b) by the time it is perceived by standard monitoring instruments, it has already affected depths and areas so large that it has turned into a major, irreversible degradation of water quality at regional scale. The deep water abstraction rate beyond which such negative effects occur lies far below the bulk recharge rate estimation; moreover, the actual 'feeding streamlines' of a deep pumping well stretch laterally far upstream the well, so that the usual protection zones concentric around the well itself will not really protect it (Seiler 1987, 2001).

Here, the possibility of an early-warning system regarding deep aquifer contamination, and of a process-oriented control of deep groundwater abstractions is examined anew: first explained in terms of a time scale contrast between the transport of 'polluting' and of 'monitoring' species, it is then investigated numerically for two hydrogeologic situations, one with a mild and one with a marked permeability change over depth. The progressive contamination of the deep aquifer is simulated assuming a simplified, yet realistic scenario of shallow aquifer pollution; and the environmental radioisotope response to deep water abstractions is predicted as a function of pumping rate, duration and depth, and of aquifer heterogeneity.

The readjustment time of environmental radioisotope repartitions under given hydraulic stress lies somewhere between the (relatively short) pressure adjustment time (determined by hydraulic diffusivities, or T/S) and the (depth-dependent) groundwater age value. The time scope of radioisotope response to hydraulic stress will thus increase with depth, however in competition with radioactive decay which makes isotope concentrations decrease with depth and become irrelevant below a so-called 'nil-line' defined by the detection limit of the respective isotope (the latter may advance toward greater depths, as detection techniques improve).

The possibility of an EARLY-WARNING system resides in the time-scale contrast between the ('slow') migration of polluting species and the ('rapid') spatial readjustment of monitoring species. The time scope of a PROCESS-ORIENTED control is confined to the interval in which the response of monitoring species correlates monotonously with the magnitude of the applied stress (pumping rate). For deep porous aquifers of the (Bavarian) Upper Freshwater Molasse with an average porosity over 10%, the time scope of a process-oriented control, before the environmental radioisotope responses under different pumping regimes approach a common plateau, comprises at least 4-5 decades.

Besides hydraulics and solute transport, an interest arose for dealing with transient groundwater ages, during or following hydraulic stress. Groundwater age, or 'flow-time', or residence time repartitions are often invoked as a 'microscopic' foundation of lumped-parameter models for (conservative) solute transport in groundwater. How stable are these repartitions against hydraulic perturbations? can their hydraulically-induced shift with time be related consistently and unequivocally to variations in the lumped-parameter values used by black-box models to assess system change? Part of

Ziel der Arbeit ist die Untersuchung der geometrischen und zeitlichen Abfolge der Bewegungen an der Salzachstörung und der Achentaler Schubmasse. Die Untersuchungen stützen sich vorwiegend auf Paäostressuntersuchungen, Untersuchungen von fluiden Einschlüssen und seismischen Daten.

U-Pb-SHRIMP dating of zircons, zircon morphology, geochemistry and isotopic data of metamagmatites from the Bayerischer Wald (Germany) reveal a complex evolution of this section of the Moldanubian Zone exposed in the western Bohemian Massif of the central European Variscan belt. In the south-western part of the Bayerischer Wald Upper Vendian magmatism is constrained by SHRIMP ages of 555 ± 12, 549 ± 7 and 549 ± 6 Ma from metarhyolites and a metabasite. Inherited zircon cores were not observed. Zircon overgrowths yielding pooled ages of 316 ± 10 and 319 ± 5 Ma provide evidence for Variscan metamorphic zircon growth; cathodoluminescence imaging reveals a two-stage metamorphic overprint.

In contrast, Lower Ordovician magmatism and anatexis are documented in the north-eastern parts of the Bayerischer Wald by metagranitoids (480 ± 6, 486 ± 7 Ma) and a leucosome (491 to 457 Ma). Inherited zircon cores are found in Lower Ordovician metamagmatites indicating a Palaeoproterozoic-Archaean (2.70, 2.02 Ga) source region, presumably of Gondwana affinity (West African craton), and documenting Cadomian magmatism (>615 to 560 Ma).

Upper Vendian magmatism is assumed at an active continental margin with ensialic back-arc development (εNd(t) –4.58 to +1.22). An active continental margin setting, possibly with some lateral variation (accretion/collision) is envisaged for the Lower Ordovician producing granitoids, rhyolites, leucosomes (εNd(t) -0.5 to -6.27) and andesites.

A tentative palaeogeographic reconstruction puts the "Bayerischer Wald" in a close relationship with the Habach terrane (proto-Alps), as the "eastern" extension of terranes of the northern Gondwana margin.

The aim of this study is to obtain a better understanding of the hydrological and geochemical contexts of the heavy metal transport in watersaturated porous aquifer sediments, where both copper (Cu) and antimony (Sb) are the main focus. The background of investigation is based on questions within the scope of the redevelopement of past industrial waste deposits areas and groundwater protection.

The functional and experimental part of this study was initially comprised of planning, conception and set-up of a column arrangement which served as a model of the sediment-/groundwater system as well as the development of appropriate preparation and sampling techniques. The experimental set-up run was suitable for simulation of groundwater flow with velocities between centimetre and metre per day. In order to differentiate results concerning the migration behaviour of the heavy metals copper and antimony, laboratory experiments were conduced in three water aquifer systems Quaternary Gravel, Tertiary Sand and Dogger-Sand of southern Germany. Between the systems carbonate, clay, or iron contents vary. Quartz-Sand was served as the reference material.

Copper was injected as the cationic form of copper nitrate (Cu(NO3)2) and antimony as anionic potassium antimonat (K[Sb(OH)6]). The investigations included short-term (Dirac-impulse) and long-term (Pulse-injection) experiments. A calcareous water served as an eluent for sediments with high buffer capacity and a rainwater-mimic modelwater as an eluent for the sediment with lower buffer capacity.

Determination of distribution coefficients (batch-experiments) and thermodynamic modelling of solubility in different experimental waters led to maximum values in the calcareous water for copper as well as antimony, where the solubility of copper was 30 % lower than for antimony. Due to the additional complexes found in the DOC-water of the Dachauer Moos copper has a significantly higher mobility. The effect is even more significant by applying EDTA-water.

Mass balance of the column experiments show that copper is fundamentally less mobile (recovery 0-18 %) in contrast to antimony (recovery 85-99 %). Differences in the sorption behaviour were reflected in the retardation values, which subsequently distinguished almost three orders for both elements. Cumulatively, these results show that the sorption capacities for copper can not be achieved even after a total input of 201 mg Cu (Quaternary Gravel) by injection pulses over two years. However, sorption capacities can be attained with antimony after only 10.4 days (Tertiary Sand), after 11.4 days (Dogger-Sand) and after 1.5 years (Quaternary Gravel), respectively. Qualitatively, the results of copper can be described with a fast irreversible sorption kinetic, and antimony with a slow reversible one.

Three mathematical models were applied to simulate the experimental data set. The observed Sb-breakthrough curves modelled quite well with the one-dimensional linear reaction model of CAMERON & KLUTE (1977) and the determination of corresponding dynamic reaction parameters. However, a satisfying fit could not be found for copper with this model in a buffered system for the two following reasons: 1.) The precipitation processes and 2.) the complex surface-active processes which were assumed next to the predominant sorption reactions. Therefore non-linear model approaches were employed for the fit. Initially, the observed Sb-curves were fitted using two-site Langmuir-isotherm first order kinetics, allowing for quantification of sorption capacities, -affinities and –rates. Applying three-site Langmuir-isotherm first order kinetics also includes precipitation processes. With all models, a satisfying fit of the desorption processes in the declining curve part emerged. However the sorption processes could still not be satisfactorily described.

Experiments investigating the influence of both complexing agents, DOC and EDTA, on the migration behaviour of co