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Vienna, Austria

Reitner J.M.,Geologische Bundesanstalt | Gruber W.,HOT Engineering | Romer A.,Geologische Bundesanstalt | Morawetz R.,Joanneum Research
Swiss Journal of Geosciences | Year: 2010

We present a study of the inneralpine basin of Hopfgarten focused on the analysis of basin fill in order to reveal its formation in relation to paleo-ice flow and tectonics. The study is based on geological mapping as well as seismic (reflection and refraction) and geoelectrical surveys. The oldest sequence in the basin, identified by seismic stratigraphy at 400 m below surface, consists of coarse grained sediments of supposedly Oligocene to Miocene age, which subsided along faults linked to the Inn fault. Three superimposed sequences, each displaying baselaps in contact with a subglacially formed unconformity and sigmoid foresets, show pleniglacial conditions followed by a glaciolacustrine environment. The uppermost of these three sequences lies on top of last glacial maximum till (LGM; Würmian Pleniglacial; MIS 2) and represents Termination I. The middle sequence is classified as Termination II following the Rissian Pleniglacial (MIS 6). The oldest glacial sequence cannot be constrained chronostratigraphically but might correlate with Termination V following the major glaciation of MIS 12. Limited glacial erosion during the LGM occurred only during the ice build-up phase. Further overdeepening was impeded due to topographic barrier and mutual blockades of glaciers within this highly dissected landscape. The occurrence and relative timing of the impediment was controlled by the onset of transfluences and thus by the altitude of coles. The higher amount of overdeepening during older glacial periods is explained by longer phases of free ice advance in the ice build up phase due to higher transfluences routes at that time. Thus, the preservation of older Pleistocene sequences within the basin may be the result of the lowering of watersheds from one glaciation to the next. Our model of an inverse relationship between glacial shaping of the surface and the subsurface may apply to similar Alpine landscapes as well. © 2010 Swiss Geological Society. Source

Merchel S.,Aix - Marseille University | Merchel S.,Helmholtz Center Dresden | Braucher R.,Aix - Marseille University | Alfimov V.,ETH Zurich | And 3 more authors.
Quaternary Geochronology | Year: 2013

Samples from three medieval rock avalanches from the French (Le Claps, Mont Granier) and Austrian Alps (Dobratsch) and a man-made structure, i.e. the Stephansdom in Vienna, have been analysed for in-situ produced 36Cl by accelerator mass spectrometry (AMS). All four sampling sites of independently known exposure duration turned out to be not appropriate as calibration sites for the determination of the 36Cl-production rate from Ca. Indeed, the determination of short exposure ages for dating rock avalanches and man-made structures by 36Cl is hindered dramatically by inheritance, especially for samples characterized by high natCl-concentrations. Generally, there are hints that the theoretical calculation of 36Cl-production from epithermal and thermal neutron-capture on 35Cl is highly underestimated in all existing models, thus, asking for particular precaution if working on high-Cl samples for any project. Hence, this work evidences that potential high inheritance, even for samples reasonably shielded before exhumation, has to be considered especially when dealing with recently exposed surfaces such as glacially polished rocks, alluvial terraces, fault scarps etc. © 2013 Elsevier B.V. Source

Merchel S.,Aix - Marseille University | Merchel S.,Helmholtz Center Dresden | Mrak I.,University of Ljubljana | Braucher R.,Aix - Marseille University | And 4 more authors.
Quaternary Geochronology | Year: 2014

Over 30 samples from bedrock and boulders from the Veliki vrh rock avalanche have been collected for surface exposure dating. The limestone rocks have been radiochemically treated to isolate and determine long-lived 36Cl by accelerator mass spectrometry. It could be shown that the Veliki vrh rock avalanche from the Košuta Mountain (Slovenia) event can be very likely linked to one of the major historical earthquakes in Europe happening on the 25th of January 1348. Taken into account independently determined denudation rates, inherited 36Cl originating from pre-exposure at shallow depths (20-55m) could be calculated. The high amount of inherited 36Cl, i.e. 17-46% of the total 36Cl, makes this site not suitable for a precise determination of the 36Cl production rate as it was originally anticipated. Veliki vrh is a "classic" rock avalanche of high velocity. The slope failed in the upper part with a translational slide predominantly along the bedding planes, whereas dynamic fragmentation is the cause for further crushing of the material and the long runout. © 2014 Elsevier B.V. Source

Gebhardt H.,Geologische Bundesanstalt | Friedrich O.,UK National Oceanography Center | Friedrich O.,Goethe University Frankfurt | Schenk B.,University of Vienna | And 3 more authors.
Marine Micropaleontology | Year: 2010

The late Cenomanian-early Turonian Oceanic Anoxic Event (OAE-2) represents major paleoceanographic and faunal perturbations. Samples from the northern Tethyan margin (Rehkogelgraben, Eastern Alps) were investigated in order to trace the paleoceanographic processes. Paleoecologic conditions were reconstructed by combining the results of assemblage counts of indicative microfossil groups (foraminifera, and radiolaria). Assemblages, size distributions and abundances show a tripartite subdivision for surface and bottom waters: 1) Oligotrophic surface conditions and oxic bottom waters with a reasonably high food supply for the late Cenomanian interval. 2) An OAE period with black shales characterized by very low numbers but high diversities and a lack of high-productivity indicators among planktic foraminifera. Low abundances of small sized benthic foraminifera indicate low oxic-dysoxic conditions at the seafloor. 3) Post-OAE assemblages are characterized by mesotrophic planktic species and benthic foraminifera suggest oxic bottom waters. It took about 300. ky to re-establish a pelagic carbonate-producing regime. The semi-enclosed basin situation of the Penninic Ocean is thought to be responsible for differences between the high productivity in the world ocean during the OAE-2 and the overall absence of high-productivity indicators and high foraminiferal diversities at Rehkogelgraben. The Penninic Ocean may have even served as a refuge during the environmental crisis. © 2010 Elsevier B.V. Source

Preusser F.,University of Bern | Reitner J.M.,Geologische Bundesanstalt | Schluchter C.,University of Bern
Swiss Journal of Geosciences | Year: 2010

Overdeepened valleys and basins are commonly found below the present landscape surface in areas that were affected by Quaternary glaciations. Overdeepened troughs and their sedimentary fillings are important in applied geology, for example, for geotechnics of deep foundations and tunnelling, groundwater resource management, and radioactive waste disposal. This publication is an overview of the areal distribution and the geometry of overdeepened troughs in the Alps and their foreland, and summarises the present knowledge of the age and potential processes that may have caused deep erosion. It is shown that overdeepened features within the Alps concur mainly with tectonic structures and/or weak lithologies as well as with Pleistocene ice confluence and partly also diffluence situations. In the foreland, overdeepening is found as elongated buried valleys, mainly oriented in the direction of former ice flow, and glacially scoured basins in the ablation area of glaciers. Some buried deeply incised valleys were generated by fluvial down-cutting during the Messinian crisis but this mechanism of formation applies only for the southern side of the Alps. Lithostratigraphic records and dating evidence reveal that overdeepened valleys were repeatedly occupied and excavated by glaciers during past glaciations. However, the age of the original formation of (non-Messinian) overdeepened structures remains unknown. The mechanisms causing overdeepening also remain unidentified and it can only be speculated that pressurised meltwater played an important role in this context. © 2010 Swiss Geological Society. Source

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