Finely interbedded rock formations are common within the argillaceous soft rock spectrum, yet they are often treated as homogeneous materials in rock engineering and underground construction. This assumption can lead to widely scattered and inaccurate geomechanical parameters, such as strength or stiffness. This study investigates the statistical distribution of marlstone sublayers in the argillaceous Unterangerberg Formation (Tyrol, Austria) and its correlation with geotechnical properties derived from laboratory tests. We analyze uniaxial compressive strength, splitting tensile strength, elasticity modulus, as well as cohesion and friction angle. The testing program encompasses multistage uniaxial and triaxial compression tests, as well as splitting tensile tests. A comprehensive dataset from core logging and rock mechanical laboratory testing is analyzed to assess whether variations in sublayer thickness contribute to the observed dispersion in these geomechanical properties. We also examine how alternative statistical summaries influence the perceived variability of parameters. The results show that the finely interbedded calcareous marlstone layers within the lithology exhibit distinctive geotechnical characteristics, with clay-rich layers generally showing tendencies towards lower strength. Variability in sublayer thickness influences the spread of laboratory test results, and layered specimens tend to yield smeared responses that reflect both constituents. These findings suggest that lithological heterogeneity plays an essential role in soft rock behavior. These results show the need to account for small-scale sedimentary layering and its statistical distribution when predicting the geomechanical behavior of argillaceous soft rock and interpreting laboratory test results for rock engineering applications. Incorporating probabilistic characterization of sublayer heterogeneity can improve predictive reliability and inform design decisions.
Jaggl is a mountain in the Upper Vinschgau, built up of Mesozoic sedimentary rocks and surrounded by crystalline basement rocks of the & Ouml;tztal Nappe. The Jaggl sedimentary rocks were originally interpreted as a remnant of the sedimentary cover of the & Ouml;tztal basement ("cover hypothesis"). Later, a different interpretation became prevalent, according to which the sedimentary rocks and a portion of the adjoining basement rocks represent a tectonic window into a deeper unit underlying the & Ouml;tztal Nappe ("window hypothesis"). A key role is played by the steeply southeast-dipping Arlui Fault along which the Jaggl Mesozoic rocks to the Southeast are in contact with & Ouml;tztal basement rocks to the Northwest. In the "window hypothesis", the displacement along the Arlui Fault should be southeast-side-up, whereas in the "cover hypothesis", it should be southeast-side-down. Our study of ductile (greenschist facies) to brittle fault rocks along the Arlui Fault yielded exclusively evidence for southeast-side-down, i.e. normal faulting. In addition, we identified the prolongation of the Arlui Fault towards northeast, represented by a top-southeast, greenschist-facies mylonite zone within the amphibolite-facies & Ouml;tztal basement. The Arlui Normal Fault belongs to the system of normal faults that overprinted the Austroalpine nappe stack during the Late Cretaceous, the Jaggl rocks are a downthrown part of the cover of the & Ouml;tztal Nappe, and the Jaggl Window does not exist.
Investigating the thermal evolution of continental rifts is essential for understanding how lithospheric extension, surface uplift, and exhumation are recorded in the shallow crust. However, interpreting low-temperature thermochronological data in rift settings remains challenging, particularly where exhumation magnitudes are small and geothermal gradients are elevated and spatially heterogeneous. In such environments, cooling ages may reflect a combination of regional tectonic processes and localized thermal overprints, complicating the reconstruction of rift-related exhumation histories. Here, we present new apatite (U-Th)/He ages from the Black Forest and Vosges Mountains, integrated with published apatite fission-track data, to reconstruct the Cenozoic thermal evolution of the Upper Rhine Graben rift flanks. Sampling along multiple transects perpendicular to the rift axis provides the spatial resolution required to distinguish regional cooling trends from localized thermal perturbations. The data and time-temperature modeling indicate that maximum temperatures were reached during the Late Cretaceous to Paleocene, approaching but generally not exceeding the apatite partial retention and annealing zones (PRZ/PAZ). Cooling occurred in three main phases during the Late Cretaceous, Eocene, and Oligocene, resulting in pronounced single-grain apatite (U-Th)/He age dispersion. A regionally pervasive Miocene reheating event is not required to explain the observed age patterns. Instead, the data are best explained by a combination of incomplete resetting, radiation damage effects, and localized hydrothermal influences in the vicinity of normal faults. These results highlight the importance of integrating multiple low-temperature thermochronometers with high spatial sampling density to disentangle tectonically driven cooling from localized thermal overprinting in intracontinental rift systems.
The central theme of the UNESCO Global Geopark "Ore of the Alps" in Salzburg's Pongau region is prehistoric and historic copper mining in the Eastern Alpine Greywacke Zone. Much is known about the history and geology of the ore deposits. However, to date the effects of mining on groundwater quality is not investigated yet. From January to July 2024, monthly samples were taken from mine water outlets and analysed for field parameters, main and trace elements as well as sulphate isotopes. The quality of mine water was compared with reference stations sampled at the same time. The measurements show that the pH values of the mine water are in the slightly alkaline range, meaning that the heavy metal concentration is mostly harmless, although the mine water has significantly higher concentration than the reference water. The sulphate levels in the mine waters are significantly higher than those of the reference waters. Isotope analyses indicate that the increased sulphate levels are due to sulphide oxidation and thus to mining. Although systematic discharge measurements were not possible observations in one of the mines indicate a positive correlation between discharge and mineralisation. The study shows that historical mining continues to affect water composition. However, as the main ore is chalcopyrite and the mineralisation of the ore veins is bound to carbonates, the effects of sulphide weathering in the aquifer are buffered. The mine water remains pH-neutral to slightly alkaline, so it has only a low potential to dissolve harmful heavy metals. The study provides an overview of the current groundwater situation in the 'Ore of the Alps' UNESCO Global Geopark and confirms that there is no groundwater contamination risk from historic mining facilities. It thus contributes to a holistic understanding of this specific geo-heritage.
In the eastern European Alps, lenses of eclogite occur within a serpentinite body at Hochgrosen in northern Styria, Austria. These rocks belong to the Speik Complex, a subducted meta-ophiolite in the Lower Central Austroalpine basement, and show geochemical characteristics (relative abundances of Ti, V, Sr, Sc, and Si) of MORB magmatites with a backarc basin affinity. Three samples of partly retrogressed eclogites were studied using Lu-Hf geochronology on whole rock and garnet separates. One sample yields a well-defined four-point Lu-Hf isochron at 437.9 +/- 0.8 Ma (Early Silurian). Although partly retrogressed to amphibolite facies, prior equilibration in the eclogite facies is confirmed by the occurrence of omphacite (33.2% jadeite component) inclusions in garnet. Garnet shows a bell-shaped Lu concentration profile, indicating that the Lu-Hf age is related to garnet growth, i.e. eclogite-facies metamorphism. The two other samples were more strongly retrogressed and did not yield isochrons, probably because of Variscan metamorphic overprint. With this new age, the Hochgrosen eclogite is now the oldest eclogite dated so far in the Austroalpine nappes and reflects subduction at the northern margin of Gondwana during the Early Silurian.
