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- ItemDetailed Fluid Inclusion and Stable Isotope Analysis on Deep Carbonates from the North Alpine Foreland Basin to Constrain Paleofluid Evolution(London : Hindawi, 2019) Mraz, Elena; Wolfgramm, Markus; Moeck, Inga; Thuro, KuroschThe recent interest on environmentally friendly energy resources has increased the economic interest on the Upper Jurassic carbonate rocks in the North Alpine Foreland Basin, which serves as a hydrogeothermal reservoir. An economic reservoir use by geothermal fluid extraction and injection requires a decent understanding of porosity–permeability evolution of the deep laying Upper Jurassic strata at depths greater than 2000 m. The analysis of paleofluids caught in cements of the rock mass helps to determine the postdepositional reservoir evolution and fluid migration. Therefore, the high- and low-permeability areas of the Upper Jurassic in the North Alpine Foreland Basin referred to as Molasse Basin were analyzed by means of encountered postdepositional cements to determine the reservoir evolution. The cements were sampled at different hydrocarbon and geothermal wells, as well as at outcrops in the Franconian and Swabian Alb. To determine the composition and temperature of the paleofluids, fluid inclusions and cements of the Upper Jurassic carbonate rocks were analyzed by microthermometry and stable isotope measurements. Since drill cuttings are a rather available sample material compared to drill cores, a new microthermometry measurement method was achieved for the around 1 mm drill cuttings. Salinity and formation temperature of paleofluids in fluid inclusions and isotope data are consistent with previous studies and reveal a 5-stage evolution: the main cementation phases are composed of (I) the early diagenesis in limestones (200-400 m, 40-50°C), (II) early diagenetic dolomitization, and (III) burial dolomitization (1-2 km, II: 40-90°C; III: 70-100°C; 40 g/L NaCl equiv.), and (IV) late burial calcification (IIIa: 110-140°C, IIIb: 140-200°C) linked to tectonic features in the Molasse Basin. In the outcrop samples, a subsequent (V) cementation phase was determined controlled by karstification. In the southwest, an increase in salinity of the fluid inclusions in vein calcites, above the salinity of the Jurassic seawater, highlights the influence of basin fluids (diagenetic, evaporitic). In the other eastern wells, vein calcites have precipitated from a low saline fluid of around 10-20 g/L NaCl equiv. The low salinity and the isotope values support the theory of a continuous influence of descending meteoric fluids. Consequently, the Upper Jurassic seawater has been diluted by a meteoric fluid to a low saline fluid (<1 g/L), especially in areas with high permeability. Here, we show how a better understanding of cementation trajectory at depth can help to generate a better understanding of geothermal usability in deep carbonate reservoirs.
- ItemInitiation and development of normal faults within the German alpine foreland basin: The inconspicuous role of basement structures(Hoboken, NJ : Wiley, 2016) Hartmann, Hartwig von; Tanner, David C.; Schumacher, SandraIn a large seismic cube within the German Alpine Molasse Basin, we recognize large normal faults with lateral alternating dips that displace the Molasse sediments. They are disconnected but strike parallel to fault lineaments of the underlying carbonate platform. This raises the question how such faults could independently develop. Structural analysis suggests that the faults grew both upward and downward from the middle of the Molasse package, i.e., they newly initiated within the Molasse sediments and were not caused by reactivation of the faults in the carbonate platform and/or crystalline basement. Numerical modeling of the basin proves that temporarily and spatially confined extensional stresses existed within the Molasse sediments but not in the carbonate platform and basement during lithospheric bending. The workflow shown here gives a new and as yet undocumented insight in the tectonic and structural processes within a foreland basin that was affected by buckling and bending in front of the orogen.
- ItemInsolation-paced sea level and sediment flux during the early Pleistocene in Southeast Asia([London] : Macmillan Publishers Limited, part of Springer Nature, 2021) Vaucher, Romain; Dashtgard, Shahin E.; Horng, Chorng-Shern; Zeeden, Christian; Dillinger, Antoine; Pan, Yu-Yen; Setiaji, Romy A.; Chi, Wen-Rong; Löwemark, LudvigGlobal marine archives from the early Pleistocene indicate that glacial-interglacial cycles, and their corresponding sea-level cycles, have predominantly a periodicity of ~ 41 kyrs driven by Earth’s obliquity. Here, we present a clastic shallow-marine record from the early Pleistocene in Southeast Asia (Cholan Formation, Taiwan). The studied strata comprise stacked cyclic successions deposited in offshore to nearshore environments in the paleo-Taiwan Strait. The stratigraphy was compared to both a δ18O isotope record of benthic foraminifera and orbital parameters driving insolation at the time of deposition. Analyses indicate a strong correlation between depositional cycles and Northern Hemisphere summer insolation, which is precession-dominated with an obliquity component. Our results represent geological evidence of precession-dominated sea-level fluctuations during the early Pleistocene, independent of a global ice-volume proxy. Preservation of this signal is possible due to the high-accommodation creation and high-sedimentation rate in the basin enhancing the completeness of the stratigraphic record.