Volume 113 (2020): Issue 1 (January 2020)

A first consistent and homogenized polygon-based inventory of rock glaciers of the Austrian Alps is presented. Compiling previous inventories and updating them by using digital elevation models (1 m grid resolution) derived from airborne laser scanning yield a dataset of 5769 rock glaciers in a ca. 48400 km² large area. A consistent methodological approach for assigning attributes, stored in a detailed attribute table, was developed and applied here to improve comparability and reproducibility. The majority (60 %) of the studied landforms is considered to be relict (no permafrost); the remaining 40 % may still contain permafrost ice and are thus classified as intact. Rock glaciers range in elevation from 476 to 3312 m a.s.l. and cover a total area of 303 km². The distribution of rock glaciers is mainly related to the topography of the Austrian Alps and related effects such as past glaciation history.

In addition, a comprehensive analysis of the hydrological catchment areas of all individual rock glaciers was carried out. A hydrological catchment analysis in rock glacier areas is of great interest for sustainable water management issues in alpine catchments as these landforms represent shallow aquifer systems with a relatively high storage and thus buffer capability, especially in crystalline bedrock areas. A total area of almost 1280 km² is drained through rock glaciers.

The presented rock glacier and rock glacier catchment inventories provide an important basis for further research, particularly for a better understanding of the hydrogeology and geomorphology of alpine catchments and their potential alteration in the light of climate change, but also in terms of paleoglaciation and deglaciation in the Alpine Lateglacial to Holocene period. As such, the inventories are seen as an important base to stimulate further research.

Diatomaceous sediments are often prolific hydrocarbon source rocks. In the Paratethys area, diatomaceous rocks are widespread in the Oligo-Miocene strata. Diatomites from three locations, Szurdokpüspöki (Hungary) and Limberg and Parisdorf (Austria), were selected for this study, together with core materials from rocks underlying diatomites in the Limberg area. Bulk geochemical parameters (total organic carbon [TOC], carbonate and sulphur contents and hydrogen index [HI]) were determined for a total of 44 samples in order to study their petroleum potential. Additionally, 24 samples were prepared to investigate diatom assemblages.

The middle Miocene diatomite from Szurdokpüspöki (Pannonian Basin) formed in a restricted basin near a volcanic silica source. The diatom-rich succession is separated by a rhyolitic tuff into a lower non-marine and an upper marine layer. An approximately 12-m thick interval in the lower part has been investigated. It contains carbonate-rich diatomaceous rocks with a fair to good oil potential (average TOC: 1.28% wt.; HI: 178 to 723 mg HC/g TOC) in its lower part and carbonate-free sediments without oil potential in its upper part (average TOC: 0.14% wt.). The composition of the well-preserved diatom flora supports a near-shore brackish environment. The studied succession is thermally immature. If mature, the carbonate-rich part of the succession may generate about 0.25 tons of hydrocarbons per square meter. The diatomaceous Limberg Member of the lower Miocene Zellerndorf Formation reflects upwelling along the northern margin of the Alpine-Carpathian Foreland. TOC contents are very low (average TOC: 0.13% wt.) and demonstrate that the Limberg Member is a very poor source rock. The same is true for the underlying and over-lying rocks of the Zellerndorf Formation (average TOC: 0.78% wt.). Diatom preservation was found to differ considerably between the study sites. The Szurdokpüspöki section is characterised by excellent diatom preservation, while the diatom valves from Parisdorf/Limberg are highly broken. One reason for this contrast could be the different depositional environments. Volcanic input is also likely to have contributed to the excellent diatom preservation in Szurdokpüspöki. In contrast, high-energy upwelling currents and wave action may have contributed to the poor diatom preservation in Parisdorf. The hydrocarbon potential of diatomaceous rocks of Oligocene (Chert Member; Western Carpathians) and Miocene ages (Groisenbach Member, Aflenz Basin; Kozakhurian sediments, Kaliakra canyon of the western Black Sea) has been studied previously. The comparison shows that diatomaceous rocks deposited in similar depositional settings may hold largely varying petroleum potential and that the petroleum potential is mainly controlled by local factors. For example, both the Kozakhurian sediments and the Limberg Member accumulated in upwelling environments but differ greatly in source rock potential. Moreover, the petroleum potential of the Szurdokpüspöki diatomite, the Chert Member and the Groisenbach Member differs greatly, although all units are deposited in silled basins.

Aftershock identification plays an important role in the assessment and characterization of large earthquakes. Especially, the length of the aftershock sequence is an important aspect of declustering earthquake catalogues and therefore impacts the frequency of earthquakes in a certain region, which is important for future seismic hazard assessment. However, in intraplate regions with low deformation rates and low to moderate seismicity, it is still questionable if aftershocks after a major event may continue for much longer time. In this study, we use one of the earliest instrumentally recorded earthquakes, the 1906 Dobrá Voda earthquake (Ms/I_max=5.7/VIII-IX), to compare different approaches of aftershock determination and their suitability for understanding the recorded earthquake sequence. The Dobrá Voda segment of the Vienna Basin Transfer Fault System is one of the seismically most active zones in Slovakia with the 1906 earthquake as the strongest recorded earthquake. We first assess the epicentral intensity of the earthquake according to the Environmental Intensity Scale (ESI2007) using contemporary descriptions of earthquake effects. This additional information leads to constrain the maximal intensity to IESI2007=IX. This result agrees well with first the assessment of Imax in 1907 and indicates the reliability of this intensity data. In the second step, earthquake data are plotted for two spatial windows extending 13 km and 26 km from the epicenter of the mainshock, respectively. Despite uncertainties regarding the completeness of data due to war times and lack of nearby seismic stations, the overall temporal evolution of seismicity can apparently not be described as an Omori-type aftershock sequence following the event in 1906. Instead, earthquake occurrence within 13 km of the mainshock shows elevated earthquake activity right after the 1906 event that only decays to a lower level of activity within decades after the mainshock. The decline of seismicity therefore occurs over time scales which are much longer than those predicted by the Omori relation. We conclude that today’s seismic activity may still be affected by the 1906 earthquake.

One of the major issues in Neoproterozoic geology is the extent to which glaciations in the Cryogenian and Ediacaran periods were global in extent and synchronous or regional in extent and diachronous. A similarly outstanding concern is determining whether deposits are truly glacial, as opposed to gravitationally initiated mass flow deposits in the context of a rifting Rodinia supercontinent. In this paper, we present 115 publically available, quality-filtered chronostratigraphic constraints on the age and duration of Neoproterozoic glacial successions, and compare their palaeocontinental distribution. Depositional ages from North America (Laurentia) clearly support the idea of a substantial glacial epoch between about 720-660 Ma on this palaeocontinent but paradoxically, the majority of Australian glacial strata plot outside the previously proposed global time band for the eponymous Sturtian glaciation, with new dates from China also plotting in a time window previously thought to be an interglacial. For the early Cryogenian, the data permit either a short, sharp 2.4 Ma long global glaciation, or diachronous shifting of ice centres across the Rodinia palaeocontinent, implying regional rather than global ice covers and asynchronous glacial cycles. Thus, based on careful consideration of age constraints, we suggest that strata deposited in the ca. 720-660 Ma window in North America are better described as belonging to a Laurentian Neoproterozoic Glacial Interval (LNGI), given that use of the term Sturtian for a major Neoproterozoic glacial epoch can clearly no longer be justified. This finding is of fundamental importance for reconstructing the Neoproterozoic climate system because chronological constraints do not support the concept of a synchronous panglacial Snowball Earth. Diachroneity of the glacial record reflects underlying palaeotectonic and palaeogeographic controls on the timing of glaciation resulting from the progressive breakup of the Rodinian supercontinent.

Fast moving palaeo-ice masses within the European Alpine Ice Cap (EAIC) during the Last Glacial Maximum within the large valleys of the European Alps are likely comparable in terms of their subglacial conditions to ice streams that drained the larger Quaternary Ice Sheets in Europe and North America. Unlike these continental-style ice sheets, the ice inundating the European Alps, like the Cordilleran Ice Sheet in North America, flowed through confined bedrock valleys that, at close to the glacial maximum, acted in a similar manner to ice streams. Little mention exists as to the extent of soft sediment basal deformation in these deep valleys although increasingly such conditions are known from several parts of the EAIC. The Drau (Drava) ice stream during the Alpine Last Glacial Maximum (= Würmian Pleniglacial, ~ 29 – ~20 ka) as well as small tributary glacier during the early Lateglacial phase of ice decay (~20 – 19 ka) appears as a temperate, fast-moving ice mass that would likely be underlain by soft deforming sediment. It is the underlying microsedimentology of parts of the Drau Valley catchment in the Lienz area of Austria that is the focus of this paper. The tills in the Isel Valley at Ainet reveal a detailed depiction of soft sediment deformation processes throughout the basal zones of this ice stream illustrative of temperate basal ice conditions and comparable to those tills of northern Austria under the Inn Ice Stream. The tills exhibit the characteristics of ongoing active soft-sediment deformation. The evidence from Ainet supports the contention that most likely subglacial processes beneath ice streams in the palaeo-EAIC were comparable to those today in Antarctica and in the Quaternary ice streams of the Cordilleran, Laurentide and North European Ice Sheets.

This paper presents a revised sequence stratigraphy for the lower, middle and upper Badenian depositional systems of the Austrian Vienna Basin based on the integration of 3D seismic surveys and well data. The study area in the central and northern part of the Austrian Vienna Basin is covered with 3D seismic data. According to a new sequence stratigraphic framework established in the southern part of the Vienna Basin, the Badenian is subdivided into three 3^rd order depositional sequences. For each sequence, paleogeographic maps are created, representing coeval depositional systems within a chronostrati-graphic interval. Lower Badenian sediments of the 1^st sequence (Ba1) represent fillings of the pre-Badenian sub-basins with a major change of sediment transport direction. The early stage of the 1^st sequence is dominated by subaerial braided river deposits which use two pronounced canyon systems (Mistelbach Canyon and Reinthal Canyon) on the northwestern margin of the Vienna Basin as a bypass zone towards the marine depositional system of the North Alpine-Carpathian Foredeep. The late stage of the 1^st sequence reflects the change from subaerial to marine depositional environments with main sediment influx from the west, creating two major eastwards prograding delta systems (Zistersdorf Delta and Mühlberg Delta). Depositional systems of the middle Badenian 2^nd sequence (Ba2) reflect the interplay between ongoing extensional fault tectonics and major sea-level changes. Lower Badenian paleo-highs in the northern part are drowned during the 3^rd sequence (Ba3), thus the Mühlberg Delta and the Zistersdorf Delta merge into one delta system. During the Ba3 the drowning of the Spannberg Ridge initiates a clockwise rotation of the Zistersdorf Delta. Thus, the former Zistersdorf Delta transforms into the Matzen Delta covering the Spannberg Ridge. Together with the Mühlberg Delta, they represent the last full marine depositional system of the eastward prograding paleo-Danube Delta in the Austrian Vienna Basin.

This study reports new data on the occurrence of elk remains in the western, mountainous part of Austria and also provides a compilation of all currently known 107 elk finds of the upper Pleistocene to upper Holocene in this country. The altitudinal distribution reveals two maxima for Austria: a lower one at about 400 m a.s.l., which comprises the alpine foreland, and a second one at about 1600-1800 m a.s.l., reflecting the abundance of vertical caves in the Northern Calcareous Alps at this elevation (animal traps). Vorderkarhöhle in Tyrol is the highest known elk find in Austria (1860 m a.s.l.), interestingly located above the tree line. Although only 11% of all elk sites in Austria have been radiocarbon-dated, stratigraphic and archaeo-logical constraints allow to assign 90% of those sites that lack radiometric dating to either the upper Pleistocene (18%) or the Holocene (72%). Among the latter, upper Holocene sites dominate (78%), followed by middle (16%) and lower Holocene (6%) sites. The youngest radiocarbon-dated elk find in Austria is from Gaflein Valley (Tyrol, 1285-1359 cal BP), in agreement with data from the Swiss Alps, showing that the elk survived beyond Roman times in the Alps and became extinct before the onset of the Middle Ages.

Recent studies established the lithological and chemical sediment evolution in the Lower Austrian Molasse Basin (LAMB), a part of the North Alpine foreland basin, during the Early Miocene. In this study, we aim to integrate the clay mineralogy of seven wells across the LAMB with a newly proposed lithostratigraphy, and to infer implications for provenance, palaeo-geography and palaeoclimate. The results of our qualitative and quantitative evaluation of the clay-sized fraction with x-ray diffractometry largely support the stratigraphic model. The early stage of foreland basin formation (Egerian/Eggenburgian?) is represented by kaolinite contents up to 93 % in the clay sized fraction. This indicates an orogen-external source, i.e. the Bohemian Massif, and erosion of intensively chemical weathered products during this early Molasse basin stage. The over-lying marine Robulus Schlier (lower/middle Ottnangian) is characterized by a distinctly reduced kaolinite content and overall increased illite content compared to the other formations. Illite was predominantly provided from denudation of the rising Eastern Alps, i.e. characterizing the orogen-internal provenance. The pelites of the overlying carbonate poor Traisen Formation (upper Ottnangian) show again a higher kaolinite and smectite content. In the largely coeval basinal Wildendürnbach Formation, smectite reaches up to 70 % in the clay sized fraction. Peak smectite values may be linked to volcanic ash input from the nearby Carpathian volcanic arc. Generally rising smectite versus illite ratios during the Ottnangian-Karpatian could point to a warming and intensified chemical weathering of the rising Alpine orogen.