Abstract Stress variations in the Earth's crust need to be understood in both the spatial and temporal domains to address a number of pressing societal issues. In this paper, precise three-dimensional records of fault kinematic behaviour obtained by mechanical extensometers are used to investigate changes in stress states along major faults in the Eastern Alps. The monitored faults are fractures with evident Upper Quaternary displacement and are directly attributed to their master tectonic structures. The results demonstrate that activity at the submillimetric scale is highly episodic; periods of repose are punctuated by conspicuous reactivation events affecting one or more of the displacement components. An original approach named the SMB2018 method is used to define the stress state associated with each fault reactivation event. The outputs evidence significant short-term changes in the local stress regime. The directions of the principal normal stresses calculated from these reactivation events present generally similar patterns for both compressional and extensional stress states. Consequently, submillimetric fault activity cannot be controlled by a rotating stress field; such shifts can only be caused by a change in the magnitude of the individual principal normal stresses so that the maximum compression changes to the minimum and vice versa.

Abstract During the current trend of the energy transition, many stratigraphic intervals that previously were thought as uneconomical from an oil and gas business perspective are being re-evaluated for low-carbon energy resource potential such as geothermal. This study presents a case study from the Vienna Basin, Austria, where the Early Badenian Rothneusiedl Formation has been targeted for a re-evaluation, utilizing existing sparse subsurface datasets of vintage quality. The historical cores were subjected to diverse analytical techniques covering sedimentological, petrophysical and thermophysical aspects. These analysis techniques provided the fundamental lithological characteristics and led to the creation of a synthetic conceptual sedimentological log, resultant selection of samples for further analyses, as well as the creation of gross depositional environment maps. The reservoir and thermal properties guided by the core-based lithofacies were required for evaluating the feasibility of the target strata. Overall, the limited and historical cores provided significant and robust data that proved crucial for assessing uncertainties and identifying sub-areas of the Vienna Basin for harnessing geothermal energy. This study demonstrates an important case example of the utilization of historical cores to their maximum potential and reiterates the value of core-derived data amongst digital technologies of the twenty-first century.

Abstract: There is no consensus about the rate and style of clay mineral diagenesis in progressively buried sandstones v. interbedded mudstones. The diagenetic evolution of interbedded Miocene sandstones and mudstones from the Vienna Basin (Austria) has therefore been compared using core-based studies, petrography, X-ray diffraction and X-ray fluorescence. There was a common provenance for the coarse- and fine-grained sediments, and the primary depositional environment of the host sediment had no direct effect on illitization. The sandstones are mostly lithic arkoses dominated by framework grains of quartz, altered feldspars and carbonate rock fragments. Sandstone porosity has been reduced by quartz overgrowths and calcite cement; their pore-filling authigenic clay minerals consist of mixed-layer illite–smectite, illite, kaolinite and chlorite. In sandstones, smectite illitization progresses with depth; at 2150 m there is a transition from randomly interstratified to regular interstratified illite–smectite. The overall mineralogy of mudstones is surprisingly similar to the sandstones. However, for a given depth, feldspars are more altered to kaolinite, and smectite illitization is more advanced in sandstones than in mudstones. The higher permeability of sandstones allowed faster movement of material and pore fluid necessary for illitization and feldspar alteration than in mudstones. The significance of this work is that it has shown that open-system diagenesis is important for some clay mineral diagenetic reactions in sandstones, while closed-system diagenesis seems to operate for clay mineral diagenesis in mudstones.

Abstract Shale gas is produced from fine-grained siliciclastic sediments that are typically rich in organic carbon. Nearly all shales contain thermal gas generated in situ at mature to overmature levels of thermal alteration, although gas of biogenic origin is also produced from some shales. While shale gas production in the USA began in 1821, it is only in the last few years that it has become widely significant (currently about 8% of the domestic gas). In contrast, European shale gas exploration is still in its infancy. In general, European sedimentary basins offer the best potential for shale gas occurrence because thick, organic matter-rich sediments occur in nearly all Phanerozoic strata. Even so, there is little knowledge about the factors controlling shale gas generation and, more importantly, shale gas production in European basins. These factors are not necessarily the same as those that control commercial shale gas production in the USA. Palaeozoic sediments of Cambrian to Ordovician age are currently being tested for their shale gas potential and productivity in Sweden, as are those of Silurian age in Poland. Moreover, Lower and Upper Carboniferous sedimentary successions from England in the west to Poland in the east probably contain shale gas, but their depth, thickness and thermal maturity may be limiting factors for exploration in continental regions. Lower Carboniferous black shales in the Dniepr–Donets Basin of the Ukraine may also hold a significant potential. Moreover, organic-rich sediments of Oligocene/Miocene age in the Paratethyan Basin may offer shale gas potential, for example in the Pannonian Basin. At present, Upper Jurassic black shales are currently being tested for their shale gas potential in the Vienna Basin. European analogues of known biogenic shale gas systems may occur locally in organic-rich Lower Cretaceous sediments in the North German Basin with gas generation being related to Pleistocene glaciation/deglaciation cycles.