Anhydrite-dissolution Porosity in the Upper Muschelkalk Carbonate Aquifer, NE-Switzerland: Implications for Geothermal Energy and Geological Storage of Gas

Aschwanden, Lukas; Diamond, Larryn W.; Adams, Arthur; Mazurek, Martin

doi:10.1016/j.proeps.2017.01.011

Cited by 3 publications

(2 citation statements)

References 6 publications

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“…Today the northern margin of the Trigonodus Dolomit within Switzerland is an aquifer, in which infiltrating low-salinity waters (<10 g kg À1 NaCl-eq.) have dissolved anhydrite nodules and mixed with the original dolomitizing hypersaline brine (Aschwanden et al, 2017). The low-salinity fluid has extremely high 87 Sr/ 86 Sr ratios up to 0Á717, as recorded by secondary calcite in crosscutting fractures, and so potentially it could have imposed the observed depth trends during the Neogene via recrystallization.…”

Section: Strontium Isotope Compositionsmentioning

confidence: 99%

Dolomitization by hypersaline reflux into dense groundwaters as revealed by vertical trends in strontium and oxygen isotopes: Upper Muschelkalk, Switzerland

2018

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The Trigonodus Dolomit is the dolomitized portion of the homoclinal ramp sediments of the Middle Triassic Upper Muschelkalk in the south‐east Central European Basin. Various dolomitizing mechanisms, followed by recrystallization, have been previously invoked to explain the low δ18O, high 87Sr/86Sr, extensive spatial distribution and early nature of the replacive matrix dolomites. This study re‐evaluates the origin, timing and characteristics of the dolomitizing fluids by examining petrographic and isotopic trends in the Trigonodus Dolomit at 11 boreholes in northern Switzerland. In each borehole the ca 30 m thick unit displays the same vertical trends with increasing depth: crystal size increase, change from anhedral to euhedral textures, ultraviolet‐fluorescence decrease, δ18OVPDB decrease from −1·0‰ at the top to −6·7‰ at the base and an 87Sr/86Sr increase from 0·7080 at the top to 0·7117 at the base. Thus, dolomites at the top of the unit record isotopic values similar to Middle Triassic seawater (δ18OVSMOW = 0‰; 87Sr/86Sr = 0·70775) while dolomites at the base record values similar to meteoric groundwaters from the nearby Vindelician High (δ18OVSMOW = −4·0‰; 87Sr/86Sr = >0·712). According to water–rock interaction modelling, a single dolomitizing or recrystallizing fluid cannot have produced the observed isotopic trends. Instead, the combined isotopic, geochemical and petrographic data can be explained by dolomitization via seepage‐reflux of hypersaline brines into dense, horizontally‐advecting groundwaters that already had negative δ18O and high 87Sr/86Sr values. Evidence for the early groundwaters is found in meteoric calcite cements that preceded dolomitization and in fully recrystallized dolomites with isotopic characteristics identical to the groundwaters following matrix dolomitization. This study demonstrates that early groundwaters can play a decisive role in the formation and recrystallization of massive dolomites and that the isotopic and textural signatures of pre‐existing groundwaters can be preserved during seepage‐reflux dolomitization in low‐angle carbonate ramps.

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Section: Strontium Isotope Compositionsmentioning

confidence: 99%

Dolomitization by hypersaline reflux into dense groundwaters as revealed by vertical trends in strontium and oxygen isotopes: Upper Muschelkalk, Switzerland

2018

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“…New geological, geophysical, hydraulic, and hydrochemical results are provided in Grimm et al (2005), Jodocy and Stober (2009a, b), Stober and Jodocy (2011), Geyer and Gwinner (2011), Stober et al (2013), Stober (2013), and LGRB (2005, 2015. Information on the deep Muschelkalk aquifer in northern Switzerland can be found in Nagra (2013Nagra ( , 2014, Aschwanden et al (2014), Heuberger and Morgenthaler (2023).…”

Section: Introductionmentioning

confidence: 99%

The Muschelkalk aquifer of the Molasse basin in SW-Germany: implications on the origin and development of highly saline lithium-rich brines in calcareous hydrothermal reservoirs

Stober,

Grimmer,

Kraml

2023

Geotherm Energy

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Highly saline lithium-rich hydrothermal fluids (measured chloride concentration up to 44 g kg−1, lithium concentration up to 162 mg kg−1) occur in the deep calcareous Muschelkalk aquifer beneath the northern Alpine foreland (Molasse) basin. We have combined geologic, hydraulic, hydrochemical, and stress field data of the Triassic Muschelkalk aquifer beneath younger sediments of Triassic–Jurassic successions and the Cenozoic Molasse basin of SW-Germany for a synthesis to constrain the origin and development of these brines. In contrast to the regional southeast plunge of Jurassic and Cenozoic strata, low-gradient groundwater flow in the Upper Muschelkalk aquifer is to the north, induced by regional recharge from west, south, and east. The investigated area is seismically active and north trending maximum horizontal stress likely fosters development of necessary fracture permeability for northward flow in the competent carbonates of the Upper Muschelkalk aquifer. The highest lithium concentrations and total dissolved solids (TDS) can be found in the southern parts of the Muschelkalk aquifer. Here, the Muschelkalk Group overlays directly a crystalline basement swell separating two ENE-trending Permocarboniferous troughs. We argue that the highly saline lithium-rich fluids originate from fluid–rock interaction of meteoric water with Variscan crystalline basement rocks and entered the Muschelkalk aquifer on top of the basement swell by permeable faults and fractures. The marginal calcareous sand-rich facies of the Muschelkalk enables the inflow of brines from crystalline basement faults and fractures into the aquifer. We thus argue for an external origin of these brines into the aquifer and further intra-reservoir development by dilution with meteoric water.

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Experimental analysis of dynamic and static mechanical properties of deep thick anhydrite cap rocks under high-stress conditions

Yin

Xie

2018

Carbonates Evaporites

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Anhydrite-dissolution Porosity in the Upper Muschelkalk Carbonate Aquifer, NE-Switzerland: Implications for Geothermal Energy and Geological Storage of Gas

Cited by 3 publications

References 6 publications

Dolomitization by hypersaline reflux into dense groundwaters as revealed by vertical trends in strontium and oxygen isotopes: Upper Muschelkalk, Switzerland

Dolomitization by hypersaline reflux into dense groundwaters as revealed by vertical trends in strontium and oxygen isotopes: Upper Muschelkalk, Switzerland

The Muschelkalk aquifer of the Molasse basin in SW-Germany: implications on the origin and development of highly saline lithium-rich brines in calcareous hydrothermal reservoirs

Experimental analysis of dynamic and static mechanical properties of deep thick anhydrite cap rocks under high-stress conditions

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