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Michael Waitzinger and Fritz Finger

Abstract

Complexly zoned microcrystals of uraninite were encountered in orthogneiss from the central Tauern Window in Austria (K1 gneiss, Felbertal scheelite mine) and analysed in-situ for U, Th and Pb with state-of-the-art FE-SEM/EDX techniques. A three times finer spatial resolution was achieved using an acceleration voltage of 8 kV, compared to the classic 15–20 kV set-up of U–Th–total Pb electron microprobe dating. The lower voltage allows a spheroid of material with a diameter of only 0.3 µm to be selectively analysed. Careful tests on three uraninite reference materials show that the low-voltage method yields sufficient precision and accuracy for U–Th–total Pb uraninite dating, with errors on individual spot ages in the order of 10–30 Ma. By means of this innovative analysis technique, small-scale age zoning patterns could be resolved and dated in the uraninite microcrystals from the orthogneiss. Based on microstructures observed in backscattered electron images we interpret that an older uraninite generation in the rock, with a late Permian formation age (~260 Ma), was recycled two times through a coupled dissolution–reprecipitation process at ~210 Ma and at ~30 Ma. The younger dissolution–reprecipitation phase at ~30 Ma coincides with the Alpine regional metamorphism (lower amphibolite facies). The two older ages (~210 Ma and ~260 Ma) have been previously recognized in rocks from the Tauern Window by uraninite dating, but it is the first time here that both are recorded in the same rock and even the same uraninite grain. The present study shows that recrystallized accessory uraninite can provide a sensitive geological “hard disk” where several discrete thermal events of an area are stored. In addition, our work attests that the mineral uraninite has an unexpected geochronological robustness, even on the microcrystal scale.

Open access

Zbigniew Kordalski and Andrzej Sadurski

Abstract

During the last nine years, the 133 main groundwater reservoirs in Poland (MGR) have been documented; these were published last year. Some of these are situated in the coastal zone of the southern Baltic Sea. MGR numbers 111 and 112 are in the Gdańsk area and are discussed in the present paper. The study area is situated on the border region of the moraine plateau of the Cashubian Lakeland, the western part of the Vistula River delta plain and the Bay of Gdańsk. The area of the main groundwater reservoir in no. 112 is developed in Quaternary strata and referred to as Żuławy Gdańskie; it comprises predominantly the city of Gdańsk and slightly exceeds 100 km2. There is also a Cretaceous aquifer, rich in groundwater resources, which is named MGR no. 111, beneath the Quaternary reservoir mentioned above. The area studied and modelled totalled 364 km2, on account of the hydraulic connection between these aquifers. Methods of hydrogeological research, groundwater flow simulations, resources calculation are outlined in the present paper.

Open access

Ryszard Hoc, Andrzej Sadurski and Zenon Wiśniowski

Abstract

During the construction of mathematical models for mapping hydrogeological conditions it is necessary to apply simplifications, both in the geological structure and in hydrogeological parameters used. The present note discusses problems surrounding the mapping of glaciotectonic disturbances that occur in the northern part of Wolin Island (northwest Poland). For this part of the island, a direct outflow of groundwater towards the Baltic Sea basin has been determined on the basis of geophysical survey results. An important feature in the hydrogeological conditions here is the isolation of groundwater from both the Baltic Sea and Szczecin Lagoon by clay with a Cretaceous xenolith. Such a geological structure explains the presence of perched water at considerable heights in zones close to the cliffs, without any significant hydraulic connection with surrounding reservoirs. Hydrogeological conditions of Wolin Island have been modelled using the Visual MODFLOW package v.4.2. In the vertical section, these conditions can be simplified to one aquifer (Pleistocene-Holocene), in which two aquifers can be distinguished. In a large part of the island, these remain in mutual hydraulic contact: layer I – upper, with an unconfined aquifer, and layer II – lower, with a confined aquifer, locally an unconfined one. The schematisation of hydrogeological conditions adopted here has allowed to reproduce present groundwater dynamics in the study area.

Open access

Marta Dendys, Andrzej Szczepański and Barbara Tomaszewska

Abstract

The Miechów Trough and the central part of the Carpathian Foredeep in southern Poland have a highly complex geological structure and numerous fault zones. These features play a significant role in hydrogeological conditions of the area. In this area drinking water, medicinal groundwater or thermal groundwater occur, so recognition of their circulations is basic for reasonable groundwater management. In this note, a hydrogeological conceptual model, created for the purpose of regional scale mathematical modelling, is presented. This conceptual model illustrates the geology of the hydrogeological system modelled, as well as hydrogeological conditions and characteristics of groundwater circulation, as determined by tectonics. Typical of the research area is the wide diversity of geological and hydrogeological conditions. The Busko-Zdrój area, a region with a long history of exploitation of medicinal groundwater, presents the best example.

Open access

Diethard Sanders, Hannah Pomella and Charlotte Gild

Abstract

In intramontane landscapes shaped by glacial-interglacial cycles, the most rapid changes during the proglacial/paraglacial phases may be amplified by catastrophic mass-wasting. Herein, we describe the Last Glacial Maximum (LGM) to Holocene development of a catchment in the Northern Calcareous Alps wherein intense proglacial/paraglacial sedimentation and descend of a rock avalanche persistently modified drainage and sediment dispersal.

During buildup of the LGM, the pre-last glacial Strassberg valley – the trunk valley of this study – was filled with a proglacial fluvio-lacustrine succession. Thereafter, the area became largely buried under the Inn ice stream. During deglacial ice melt, copious sediment was shed from glacially-conditioned mountain flanks. Alluvial fans cut off from their former supply area, and perched in isolated position, result from presumed sediment dispersal across dead ice. Shortly after deglaciation, a ~11 Mm3 rock avalanche detached from a high cliff, overran an opposing mountain ridge, and spread over a lower-positioned plateau. The rock avalanche blocked the Strassberg valley and set the base-level to an intramontane basin that persists until present. A quartz OSL age from a loess drape above the rock-avalanche deposit dates mass wasting prior to 18.77 ± 1.55 ka; so far, this is the oldest age-bracketed post-LGM catastrophic mass-wasting of the Eastern Alps.

After mass wasting, the valley was barred by the rock-avalanche deposit. This, in turn, triggered a westward switch of drainage thalweg and stream incision. The present Strassberg valley is an epigenetic bedrock gorge 1.5 km in length and down to 100 m in depth. A 234U/230Th calcite disequilibrium age of 9 ± 1 ka from cemented talus indicates that most incision took place during the late-glacial to early Holocene. Aside of the large-scale morphology (valleys, ranges) the drainage, the smaller-scale morphology, and the sediment volumes of the study area are mainly coined by proglacial/paraglacial processes and by rock avalanching. Holocene landscape changes are modest and chiefly comprise aggradation of high-positioned scree slopes, colluvial/alluvial redeposition and stream incision, and slope stabilization by reforestation. Our results underscore that intramontane sceneries are mosaics with respect to the age of landforms and that large parts of the landscape still are off geomorphic equilibrium with interglacial conditions.

Open access

Georg H. Erharter and Markus Palzer-Khomenko

Open access

Lenka Šamajová, Jozef Hók, Miroslav Bielik and Ondrej Pelech

Abstract

Density modelling was carried out along five profiles oriented across the expected deep contact between the Bohemian Massif and the Internal Western Carpathians in western Slovakia. The density models reveal the continuation of the Bohemian Massif beneath the External and Internal Western Carpathians tectonic units. The eastern margin of the Bohemian Massif is situated at depth south-east of the surface outcrops of the Pieniny Klippen Belt and changes its position in the surveyed area. The contact of the Internal Western Carpathians with the Bohemian Massif and External Western Carpathians is subvertical. This sharp contact is manifested as the transtension to extension zone towards the surface.

Open access

Kamil Juśko, Jacek Motyka, Kajetan d’Obyrn and Zbigniew Adamczyk

Abstract

Areas of intense mine drainage that are subjected to numerical modelling require the construction of a complex model structure that will properly reflect actual conditions. This paper presents the process and results of constructing such a structure for the Olkusz Zinc and Lead Ore Mining Area, an area situated in a cone of depression the extent of which reaches 500 km2. This size range calls for a selection of appropriate external boundaries, properly separated from these of the mine drainage area. The complex geological structure of the Olkusz area, associated with considerable variation in the thickness of rock formations, discontinuities of rock levels and occurrence of numerous faults, must be schematised so that calculation layers can be identified. The faults in the study area have to be reflected in the regional model structure, although only those faults that actually affect groundwater flows should be selected. The model structure needs to include detailed recognition and reflection of hydraulic contacts between aquifer levels, together with a selection of hydrogeological parameters that are different for particular formations. Only a complex structure built in such a manner may be the foundation of further model studies.

Open access

Józef Górski, Krzysztof Dragon and Roksana Kruć

Abstract

In the paper, a comparison of the efficiency of riverbank treatments is outlined for the Krajkowo well field, where different methods of water abstraction are used. The water is extracted from 29 vertical wells that are located at a distance of 60–80 m from the channel of the River Warta and from a horizontal well with radial drains located 5 m below the bottom of the river. The results of a two-year water-quality investigation indicate that the water quality in both types of abstraction system is influenced by the quality of river water. The water quality observed in the horizontal well is closely similar to that of the river water, with similar concentrations of sulphates, nitrates and micropollutants, but a reduction in bacteriological contamination and plankton is clearly seen. The reduction in contaminants is mainly the result of physical processes, such as mechanical entrapment of suspended material and colloids as well as bacteria and plankton. In the vertical wells, the influence of contamination from river water is also visible, but the reduction in contamination is more significant, especially in cases of bacteria, plankton, micropollutants and nitrates, and is determined by both physical and chemical processes, such as sorption, dissolution, red-ox processes and denitrification. The present research shows that river water treatment is more effective in the case of vertical wells. The most favourable distance of a well from the channel of the river, from the perspective of water quality, is 150–200 m, which corresponds to a residence time of about six months.