Time filter

Source Type

Zuschin M.,University of Vienna | Harzhauser M.,Natural History Museum Vienna | Hengst B.,University of Vienna | Mandic O.,Natural History Museum Vienna | Roetzel R.,Geological Survey of Austria
Geology | Year: 2014

The question of ecosystem stability is central to ecology and paleoecology and is of particular importance for estuaries, which are environmentally highly variable, considered as geologically short lived, and among the most degraded modern ecosystems of our planet. Understanding their ecological dynamics over geological time scales requires paleontological data in a sequence stratigraphic framework, which allows evaluation of paleocommunity dynamics in an environmental context. A 445-m-thick estuarine succession in a satellite basin of the Vienna Basin (Austria) shows continuous sedimentation over 700 k.y. and can be divided into two transgressive systems tracts and a highstand systems tract. In contrast to expectations, no major physical disturbances of the ecosystem involving abrupt changes in diversity and biofacies composition occurred at fl ooding surfaces and at the sequence boundary. Accommodation space remained remarkably constant over the depositional history of the basin, and all changes between depositional environments were therefore more or less gradational. Biotic change along the studied succession can be described as a gradual faunal replacement in response to habitat tracking, a process also reported for some normal marine shelf environments. Benthic assemblages in the estuarine succession were strongly dominated by a few taxa and developed along two indirect gradients, water depth and hydrodynamic energy. These gradients show subtle long-term trends, corresponding to the sequence stratigraphic architecture. Tectonics affected the sequence architecture in this particular marginal marine setting: it controlled accommodation space and sedimentary input, and provided stable boundary conditions over hundreds of thousands of years. Our study demonstrates for the fi rst time that estuaries, which are under great environmental pressure today, are resilient to natural environmental perturbations and can persist over geological time scales. © 2013 Geological Society of America. Source

Baron I.,Geological Survey of Austria | Baron I.,Brno University of Technology | Beckovsky D.,Brno University of Technology | Mica L.,Brno University of Technology
Landslides | Year: 2014

We present a new approach for mapping open cracks and tension fractures within rock slope instabilities and rock cliffs, which resides in high-resolution ground-based and airborne infrared thermography (IRT). The method is restricted to cold seasons, and its utility is demonstrated through three examples from the Flysch Belt of the Outer West Carpathians (rockslides at Kopce Hill and Mt. Kněhyně) and from the Northern Calcareous Alps (deep-seated gravitational slope deformations in Gschliefgraben/Mt. Traunstein). The approach is based on a contrast between temperatures deep within the rock mass, which at a depth of few meters represent local mean annual values, and winter-time temperatures of the ground surface. In winter, warmer, buoyant air from depth rises to the ground surface through open cracks and joints, and the temperature contrast can be detected by IRT. Our test survey was conducted in the beginning of February 2012, in order to achieve the best contrast between temperatures around open tension cracks and the adjacent ground. For temperature sensing, we used a FLIR B360 thermal camera; for airborne surveys in the ambient air, temperatures at the time of our surveys ranged from approximately -19 to -7 °C. IRT results conclusively revealed the presence of open cracks, loosened rock zones, and pseudo-karst caves over a distance sometimes greater than 1 km. The IRT approach proved useful for rapidly assessing the distribution of open cracks and tension fractures, key information required for assessing rockfall and rockslide hazard. © 2012 Springer-Verlag Berlin Heidelberg. Source

Rogl F.,Museum of Natural History | Egger H.,Geological Survey of Austria
Geology | Year: 2010

The initial appearance of the planktonic foraminiferal genus Hantkenina has been used for about fifty years to recognize the base of the Lutetian and middle Eocene. However, probably as a result of incomplete stratigraphic records, discrepant ranges of Hantkenina have been reported by various investigators at many Eocene sections. Here we report the first complete evolutionary transition from Clavigerinella to Hantkenina, from the northwestern Tethyan deep-water section at Holzhäusl (Salzburg, Austria). A newly discovered species, Hantkenina nov. sp., is the link between Clavigerinella caucasica and Hantkenina mexicana. This finding unequivocally heralds the initial entry of Hantkenina, which is correlated to the upper part of calcareous nannoplankton Subzone NP15b (Sullivania gigas Subzone), to be defined. This indicates a mismatch of ∼4.5 m.y. between the base of the Lutetian at the type locality, which has been placed within Sub-zone NP14b, and the first appearance datum of Hantkenina. Consequently, the first occurrence of Hantkenina can no longer be used as a marker for the base of the middle Eocene. © 2010 Geological Society of America. Source

Starnberger R.,University of Innsbruck | Drescher-Schneider R.,University of Graz | Reitner J.M.,Geological Survey of Austria | Rodnight H.,University of Innsbruck | And 2 more authors.
Quaternary Science Reviews | Year: 2013

Drill cores from the inner-alpine valley terrace of Unterangerberg, located in the Eastern Alps of Austria, offer first insights into a Pleistocene sedimentary record that was not accessible so far. The succession comprises diamict, gravel, sand, lignite and thick, fine grained sediments. Additionally, cataclastic deposits originating from two paleo-landslide events are present. Multi-proxy analyses including sedimentological and palynological investigations as well as radiocarbon and luminescence data record the onset of the last glacial period (Würmian) at Unterangerberg at ~120-110 ka. This first time period, correlated to the MIS 5d, was characterised by strong fluvial aggradation under cold climatic conditions, with only sparse vegetation cover. Furthermore, two large and quasi-synchronous landslide events occurred during this time interval. No record of the first Early Würmian interstadial (MIS 5c) is preserved. During the second Early Würmian interstadial (MIS 5a), the local vegetation was characterised by a boreal forest dominated by Picea, with few thermophilous elements. The subsequent collapse of the vegetation is recorded by sediments dated to ~70-60 ka (i.e. MIS 4), with very low pollen concentrations and the potential presence of permafrost. Climatic conditions improved again between ~55 and 45 ka (MIS 3) and cold-adapted trees re-appeared during interstadials, forming an open forest vegetation. MIS 3 stadials were shorter and less severe than the MIS 4 at Unterangerberg, and vegetation during these cold phases was mainly composed of shrubs, herbs and grasses, similar to what is known from today's alpine timberline. The Unterangerberg record ended at ~45 ka and/or was truncated by ice during the Last Glacial Maximum. © 2013 Elsevier Ltd. Source

Kim J.-H.,Korea Institute of Geoscience and Mineral Resources | Supper R.,Geological Survey of Austria | Tsourlos P.,Aristotle University of Thessaloniki | Yi M.-J.,Korea Institute of Geoscience and Mineral Resources
Geophysical Journal International | Year: 2013

A new 4-D inversion algorithm is developed so that any data misfits and model roughness in the space and time domains can be selectively minimized, in terms of either the L1 norm or the L2 norm. This study is motivated by the experience that a 4-D inversion adopting full L2 norm minimization may sometimes result in a model that is too smoothly varying with time. It is further encouraged by the realization that a particular criterion of either L1 or L2 norm cannot be universally optimal for accurately reconstructing the subsurface condition. In addition, we try to overcome difficulties of jointly choosing two optimal regularization parameters in space and time domains. To achieve this, we devise automatic determination methods, not only of the Lagrangian multipliers for the space-domain smoothness constraint, but also of the regularization parameter for penalizing the model roughness along the time axis. Both kinds of regularization parameters are actively updated at each iteration, according to variations in data misfit and model roughness. We conducted inversion experiments using synthetic and field monitoring data to test the proposed algorithms, and further to compare the performance of L1 and L2 norm minimizations. Both the synthetic and field data experiments demonstrated that the proposed automatic determination method produced ground changes that were more similar to the true changes than those of approaches using pre-determined parameter values. Inversion experiments showed that L1 normminimization of the time-domain roughness could reduce the problem of overly smooth model changes when the subsurface changes are locally confined, but that the L2 norm approach would be more reasonable when the changes are expected to be widespread. © The Authors 2013. Published by Oxford University Press on behalf of The Royal Astronomical Society. Source

Discover hidden collaborations