Miocene high elevation in the Central Alps

Reconstructing Oligocene–Miocene paleoelevation contributes to our understanding of the evolutionary history of the European Alps and sheds light on geodynamic and Earth surface processes involved in the development of Alpine topography. Despite being one of the most intensively explored mountain ranges worldwide, constraints on the elevation history of the European Alps remain scarce. Here we present stable and clumped isotope measurements to provide a new paleoelevation estimate for the mid-Miocene (∼14.5 Ma) European Central Alps. We apply stable isotope δ–δ paleoaltimetry to near-sea-level pedogenic carbonate oxygen isotope (δ18O) records from the Northern Alpine Foreland Basin (Swiss Molasse Basin) and high-Alpine phyllosilicate hydrogen isotope (δD) records from the Simplon Fault Zone (Swiss Alps). We further explore Miocene paleoclimate and paleoenvironmental conditions in the Swiss Molasse Basin through carbonate stable (δ18O, δ13C) and clumped (Δ47) isotope data from three foreland basin sections in different alluvial megafan settings (proximal, mid-fan, and distal). Combined pedogenic carbonate δ18O values and Δ47 temperatures (30±5 ∘C) yield a near-sea-level precipitation δ18Ow value of -5.8±1.2 ‰ and, in conjunction with the high-Alpine phyllosilicate δD value of -14.6±0.3 ‰, suggest that the region surrounding the Simplon Fault Zone attained surface elevations of >4000 m no later than the mid-Miocene. Our near-sea-level δ18Ow estimate is supported by paleoclimate (iGCM ECHAM5-wiso) modeled δ18O values, which vary between −4.2 ‰ and −7.6 ‰ for the Northern Alpine Foreland Basin.

The interplay of Malm carbonate permeability, gravity-driven groundwater flow, and paleoclimate – implications for the geothermal field and potential in the Molasse Basin (southern Germany), a foreland-basin play

The Molasse Basin in Southern Germany is part of the North Alpine Foreland Basin and hosts the largest accumulation of deep geothermal production fields in Central Europe. Despite the vast development of geothermal energy utilization projects especially in the Munich metropolitan region, the evolution of and control factors on the natural geothermal field, more specifically the time-varying recharge and discharge governing groundwater and heat flow, are still debated. Within the Upper Jurassic (Malm) carbonate aquifer as the main geothermal reservoir in the Molasse Basin, temperature anomalies such as the Wasserburg Trough anomaly to the east of Munich and their underlying fluid and heat transport processes are yet poorly understood. We delineate the two end members of thermal–hydraulic regimes in the Molasse Basin by calculating two contrasting permeability scenarios of the heterogeneously karstified Malm carbonate aquifer along a model section through the Wasserburg Trough anomaly by means of two-dimensional numerical thermal-hydraulic modelling. We test the sensitivity of the thermal-hydraulic regime with regard to paleoclimate by computing the two Malm permeability scenarios both with a constant surface temperature of 9 °C and with the impact of paleo-temperature changes during the last 130 ka including the Würm Glaciation. Accordingly, we consider the hydraulic and thermal effects of periglacial conditions like permafrost formation and the impact of the numerous glacial advances onto the Molasse Basin. Thermal-hydraulic modelling reveals the effect of recurrent glacial periods on the subsurface targets of geothermal interest, which is minor compared to the effect of permeability-related, continuous gravity-driven groundwater flow as a major heat transport mechanism.

New insights on the Early Cretaceous (Hauterivian–Barremian) Urgonian lithostratigraphic units in the Jura Mountains (France and Switzerland): the Gorges de l’Orbe and the Rocher des Hirondelles formations

The Hauterivian–Barremian series of the Jura Mountains were measured over more than 60 sections along a 200 km long transect between Aix-les-Bains (Savoie Department, France) and Bienne (Bern Canton, Switzerland), which prompted the need for a revision and improvement of the current lithostratigraphic scheme for this stratigraphic interval. A new formation, the Rocher des Hirondelles Formation, is proposed in replacement of the unsuitable Vallorbe Formation, while the Gorges de l'Orbe Formation is formally described. The Gorges de l'Orbe Formation, equivalent to the well-known “Urgonien jaune” facies, consists of two members, namely Montcherand Member and Bôle Member. The Rocher des Hirondelles Formation, equivalent to the “Urgonien blanc” facies, consists of three members, i.e. Fort de l'Écluse Member, Rivière Member and Vallorbe Member. The marly Rivière and Bôle members appear to present time-equivalent lithostratigraphic units, recording a major sedimentological event affecting contemporarily both formations. This study proposes a new sedimentary model opening a new point of view on the long-living controversies about the age of the Urgonian series from the Jura Mountains. The data point to strong diachronic ages of lithostratigraphic units with a late Hauterivian to early Barremian occurrence of the “Urgonian blanc” facies in the Meridional Jura area versus a latest Barremian age in the Central Jura area, reflecting a general progradation of the Urgonian shallow-water carbonate platform from the present-day Meridional Jura area toward external deeper-water shelf environments of the present-day Central Jura area and Molasse basin.

Miocene high elevation and high relief in the Central Alps

Reconstructing Oligocene-Miocene paleoelevation contributes to our understanding of the evolutionary history of the European Alps and sheds light on geodynamic and Earth’s surface processes involved in the development of Alpine topography. Despite being one of the most intensively explored mountain ranges worldwide, constraints on the elevation history of the European Alps, however, remain scarce. Here we present stable and clumped isotope geochemistry measurements to provide a new paleoelevation estimate for the mid-Miocene (~14.5 Ma) European Central Alps. We apply stable isotope δ-δ paleoaltimetry on near sea level pedogenic carbonate oxygen isotope (δ18O) records from the Northern Alpine Foreland Basin (Swiss Molasse Basin) and high-Alpine phyllosilicate hydrogen isotope (δD) records from the Simplon Fault Zone (Swiss Alps). We further explore Miocene paleoclimate and paleoenvironmental conditions in the Swiss Molasse Basin through carbonate stable (δ18O, δ13C) and clumped (Δ47) isotope data from three foreland basin sections in different alluvial megafan settings (proximal, mid-fan, and distal). Combined pedogenic carbonate δ18O values and Δ47 temperatures (30 ± 5 °C) yield a near sea level precipitation δ18Ow value of −5.8 ± 0.2 ‰ and in conjunction with the high-Alpine phyllosilicate δD record suggest that the region surrounding the SFZ attained surface elevations of > 4000 m no later than the mid-Miocene. Our near sea level δ18Ow estimate is supported by paleoclimate (iGCM Echam5-wiso) modeled δ18O values, which vary between −4.2 and −7.6 ‰ for the Northern Alpine Foreland Basin.

Hydrochemical Zoning and Chemical Evolution of the Deep Upper Jurassic Thermal Groundwater Reservoir Using Water Chemical and Environmental Isotope Data

A comprehensive hydrogeological understanding of the deep Upper Jurassic carbonate aquifer, which represents an important geothermal reservoir in the South German Molasse Basin (SGMB), is crucial for improved and sustainable groundwater resource management. Water chemical data and environmental isotope analyses of D, 18O and 87Sr/86Sr were obtained from groundwater of 24 deep Upper Jurassic geothermal wells and coupled with a few analyses of noble gases (3He/4He, 40Ar/36Ar) and noble gas infiltration temperatures. Hierarchical cluster analysis revealed three major water types and allowed a hydrochemical zoning of the SGMB, while exploratory factor analyses identified the hydrogeological processes affecting the water chemical composition of the thermal water. Water types 1 and 2 are of Na-[Ca]-HCO3-Cl type, lowly mineralised and have been recharged under meteoric cold climate conditions. Both water types show 87Sr/86Sr signatures, stable water isotopes values and calculated apparent mean residence times, which suggest minor water-rock interaction within a hydraulically active flow system of the Northeastern and Southeastern Central Molasse Basin. This thermal groundwater have been most likely subglacially recharged in the south of the SGMB in close proximity to the Bavarian Alps with a delineated northwards flow direction. Highly mineralised groundwater of water type 3 (Na-Cl-HCO3 and Na-Cl) occurs in the Eastern Central Molasse Basin. In contrast to water types 1 and 2, this water type shows substantial water-rock interaction with terrestrial sediments and increasing 40Ar/36Ar ratios, which may also imply a hydraulic exchange with fossil formation waters of overlying Tertiary sediments.

The interplay of Malm carbonate permeability, gravity-driven groundwater flow, and paleoclimate – implications for the geothermal field and potential in the Molasse Basin (Southern Germany), a foreland-basin play

The Molasse Basin in Southern Germany is part of the North Alpine Foreland Basin and hosts the largest accumulation of deep geothermal production fields in Central Europe. Despite the vast development of geothermal energy utilization projects especially in the Munich metropolitan region, the evolution of and control factors on the natural geothermal field are still debated. Especially seismic and deep well data from extensive oil and gas exploration in the Molasse Basin led to conceptual hydrogeological and thermal-hydraulic models. Corrected borehole-temperature data helped to constrain subsurface temperatures by geostatistical interpolation and facilitated the set-up of 3D temperature models. However, within the geothermally used Upper Jurassic (Malm) carbonate aquifer, temperature anomalies such as the Wasserburg Trough anomaly to the east of Munich and their underlying physical processes are yet poorly understood. From other foreland basins like the Alberta Basin in Western Canada, it is known that climate during the last ice age has a considerable effect even on subsurface temperatures up to two kilometres depth. Therefore, we study the impact of paleoclimatic changes on the Molasse Basin during the last 130 ka including the Würm glaciation. We consider the hydraulic and thermal effects of periglacial conditions like permafrost formation and the impact of the numerous glacial advances onto the Molasse Basin. The major difference between the thermal-hydraulic regime in the western and eastern parts of the Southern German Molasse Basin are delineated by calculating two contrasting permeability scenarios of the heterogeneously karstified Malm carbonate aquifer. Thermal-hydraulic modelling reveals the effect of recurrent glacial periods on the geothermally drillable subsurface, which is minor compared to the effect of permeability-related, continuous gravity-driven groundwater flow as a major heat transport mechanism. Practically, the results might help to reduce the exploration risk for geothermal energy projects in the Molasse Basin. More importantly, this study serves as a reference for the comparison and understanding of the interplay of high permeability aquifers, gravity-driven groundwater flow and paleoclimate in other orogenic foreland basins worldwide.

Porosity estimation and characterization of a geothermal carbonate reservoir in the South German Molasse Basin based on seismic inversion and attribute analysis

<p>The Molasse Basin is one of the most promising areas for deep geothermal exploration in Germany and a very ambitious project in this region is to power the entire district heating system of the city of Munich with renewable energies by 2040; a major part of this will consist of geothermal energy. As part of a joint project (financed by the German Federal Ministry For Economic Affairs And Energy; FKZ 0324332B) the Leibniz Institute for Applied Geophysics (LIAG) works together with the Munich City Utilities (Stadtwerke München), to improve reservoir characterization and sustainable reservoir exploration within the German Molasse Basin. The target horizon for hydrothermal exploration is the aquifer in the Upper Jurassic carbonates. A major problem is the strong heterogeneity of the carbonates. Compared to quantity and quality of the structural data of the reservoir, the database of reservoir properties such as density, porosity and permeability, which describe the geothermal potential, is insufficient. Therefore, it is necessary to generate such data in order to improve the value of the structural information. A 3D seismic survey cannot only provide structural information, but also important reservoir properties such as elastic parameters and seismic attributes. One of the most important attributes is the acoustic impedance, which can be determined with a seismic inversion and used to estimate a porosity volume.</p><p>The data basis for this study was the 170km² GRAME-3D seismic survey measured in Munich, a structural geological model, and drilling and logging data from the geothermal site “Schäftlarnstraße”.</p><p>The inversion results show low impedance values at the top of the reservoir, but also at the middle part. Spatially, the intermediate block of the Munich fault shows low values but also the eastern part of the hanging wall block and the western part of the footwall block. Based on a well correlation a relationship between acoustic impedance and porosity could be determined and a 3D porosity volume was calculated. In the upper part but also in the middle part of the reservoir areas with increased porosity (>10%) are shown, which might indicate a high geothermal potential.</p><p>For a better classification, an attribute analysis was performed. The intermediate block and the eastern part of the hanging wall block show strongly fractured rocks. In contrast, there are hardly any conspicuous features in the western part of the footwall block, although high porosities are also expected here. This suggests that the presence of faults is not the only factor favoring high porosities in carbonates. More likely is a combination with karstification processes, which is why even areas that do not show enhanced tectonic deformation have high porosities.</p>