Pore-water evolution and solute-transport mechanisms in Opalinus Clay at Mont Terri and Mont Russelin (Canton Jura, Switzerland)

Mazurek, Martin; Haller, Antoine De

doi:10.1007/s00015-016-0249-9

Cited by 23 publications

(11 citation statements)

References 39 publications

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“…The interplay of these mechanisms suggest a lowrate, progressive deformation of gouge. Our microstructural interpretations of deformation mechanisms are in concert 15 with recent geochemical solute-transport studies [Clauer et al, 2017;Mazurek and De Haller, 2017].…”

Section: Resultssupporting

confidence: 67%

“…Therein, the µm-thin shear zones have been interpreted to have acted as temporary fluid conduits with non-porous, impermeable side walls. This assumption is supported by differing geochemical signatures ( 87 Sr/ 86 Sr) of veins to surrounding protolith and by water from borehole-inflow showing a 87 Sr/ 86 Sr similarity to veins and a dissimilarity to the protolith [Techer et al, n.d.;Clauer et al, 2017;Mazurek and De Haller, 2017].…”

Section: Stage 1 -Development Of Scaly Claymentioning

confidence: 99%

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Deformation mechanisms and evolution of the microstructure of gouge in the Main Fault in Opalinus Clay in the Mont Terri rock laboratory (CH)

Laurich¹,

Urai²,

Vollmer³

et al. 2017

Preprint

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Abstract. We studied gouge from an upper-crustal, low offset reverse fault in slightly overconsolidated claystone in the Mont Terri rock laboratory (CH). The laboratory is designed to evaluate the suitability of the Opalinus Clay formation (OPA) to host a repository for radioactive waste. The macroscopically dark gouge displays a matrix-based, P-foliated microfabric bordered and truncated by μm-thin shear zones consisting of aligned clay grains, as shown by BIB-SEM and optical microscopy. TEM-SAED shows evidence for randomly oriented nm-sized clay particles in the gouge matrix, surrounding larger elongated phyllosilicates with a strict P-foliation. For the first time in OPA, we report the occurrence of amorphous SiO2 grains within the gouge. Gouge has lower SEM-visible porosity and almost no calcite grains, compared to undeformed OPA. We present two hypotheses to explain the origin of gouge in the Main Fault: (i) "authigenic generation": fluid-mediated removal of calcite from deforming OPA during shearing, (ii) and "clay smear": mechanical smearing of calcite-poor (yet to be identified) source layers into the fault zone. Based on our data we prefer the first or a combination of both, but more work is needed to resolve this. Microstructures indicate a range of deformation mechanisms including solution-precipitation processes and a gouge which is weaker than OPA because of the lower fraction of hard grains. We infer that the long-term rheology of gouge is more strongly rate-dependent than suggested from laboratory experiments.

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Section: Resultssupporting

confidence: 67%

Section: Stage 1 -Development Of Scaly Claymentioning

confidence: 99%

Deformation mechanisms and evolution of the microstructure of gouge in the Main Fault in Opalinus Clay in the Mont Terri rock laboratory (CH)

Laurich¹,

Urai²,

Vollmer³

et al. 2017

Preprint

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show abstract

“…When modelling these profiles taking into account the local erosion pattern, it was assumed that the upper aquifer in the Passwang formation was activated first, followed by the lower aquifer in the Staffelegg formation. The best interpretation, which includes this concentration pattern, is the process of molecular diffusion whereby solutes in the Opalinus Clay have diffused into the bounding aquifers (Mazurek and de Haller 2017). Also migration experiments with artificial non-to low-sorbing radionuclides in the Mont Terri rock laboratory confirm solute transport by molecular diffusion, The table is ordered into petrophysical (orange), hydraulic (blue), rock-mechanical (grey), thermal (red), and geochemical parameters (yellow, green).…”

Section: Other Key Properties Of Opalinus Claymentioning

confidence: 99%

“…The age of this marine pore-water in the region of the Mont Terri anticline is much younger than the sedimentation age of Opalinus Clay (174 Ma). Researchers applied two approaches to date pore-waters: Clauer et al (2017) interpreted strontium isotope ratios of calcite from the matrix, veins, and fault gouges of the Opalinus Clay to yield an upper Eocene age of 38-36 Ma; Mazurek and de Haller (2017) analysed data on the geochemical evolution of pore-waters in and around Mont Terri giving a slightly younger age, close to the Oligocene/Miocene boundary at ca. 23 Ma.…”

Section: Other Key Properties Of Opalinus Claymentioning

confidence: 99%

Mont Terri rock laboratory, 20 years of research: introduction, site characteristics and overview of experiments

Bossart¹,

et al. 2017

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Geologic repositories for radioactive waste are designed as multi-barrier disposal systems that perform a number of functions including the long-term isolation and containment of waste from the human environment, and the attenuation of radionuclides released to the subsurface. The rock laboratory at Mont Terri (canton Jura, Switzerland) in the Opalinus Clay plays an important role in the development of such repositories. The experimental results gained in the last 20 years are used to study the possible evolution of a repository and investigate processes closely related to the safety functions of a repository hosted in a clay rock. At the same time, these experiments have increased our general knowledge of the complex behaviour of argillaceous formations in response to coupled hydrological, mechanical, thermal, chemical, and biological processes. After presenting the geological setting in and around the Mont Terri rock laboratory and an overview of the mineralogy and key properties of the Opalinus Clay, we give a brief overview of the key experiments that are described in more detail in the following research papers to this Special Issue of the Swiss Journal of Geosciences. These experiments aim to characterise the Opalinus Clay and estimate safetyrelevant parameters, test procedures, and technologies for repository construction and waste emplacement. Other aspects covered are: bentonite buffer emplacement, highpH concrete-clay interaction experiments, anaerobic steel corrosion with hydrogen formation, depletion of hydrogen by microbial activity, and finally, release of radionuclides Geosci (2017) 110:3-22 DOI 10.1007 into the bentonite buffer and the Opalinus Clay barrier. In the case of a spent fuel/high-level waste repository, the time considered in performance assessment for repository evolution is generally 1 million years, starting with a transient phase over the first 10,000 years and followed by an equilibrium phase. Experiments dealing with initial conditions, construction, and waste emplacement do not require the extrapolation of their results over such long timescales. However, experiments like radionuclide transport in the clay barrier have to rely on understanding longterm mechanistic processes together with estimating safety-relevant parameters. The research at Mont Terri carried out in the last 20 years provides valuable information on repository evolution and strong arguments for a sound safety case for a repository in argillaceous formations.

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“…4.8; Pearson et al 2003). The most thorough attempt to reconcile all available hydrogeochemical and isotopic data of the Opalinus Clay in the Mont Terri/Mont Russelin area is provided by Mazurek and De Haller (2017) by unravelling the complex palaeohydrogeological evolution in great detail. It is shown that Opalinus Clay porewaters are not simple binary mixtures of seawater and meteoric water, but their chloride and stable water isotope signatures can potentially be explained by the addition of a component of partially evaporated seawater, followed by mixing with meteoric water.…”

Section: Origin Of Opalinus Clay Porewatersmentioning

confidence: 99%

Safety-relevant hydrogeological properties of the claystone barrier of a Swiss radioactive waste repository: An evaluation using multiple lines of evidence

Gautschi

2017

Grundwasser

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In Switzerland, the Opalinus Clay -a Jurassic (Aalenian) claystone formation -has been proposed as the first-priority host rock for a deep geological repository for both low-and intermediate-level and high-level radioactive wastes. An extensive site and host rock investigation programme has been carried out during the past 30 years in Northern Switzerland, comprising extensive 2D and 3D seismic surveys, a series of deep boreholes within and around potential geological siting regions, experiments in the international Mont Terri Rock Laboratory, compilations of data from Opalinus Clay in railway and motorway tunnels and comparisons with similar rocks.The hydrogeological properties of the Opalinus Clay that are relevant from the viewpoint of long-term safety are described and illustrated. The main conclusions are supported by multiple lines of evidence, demonstrating consistency of conclusions based on hydraulic properties, porewater chemistry, distribution of natural tracers across the Opalinus Clay as well as small-and large-scale diffusion models and the derived conceptual understanding of solute transport.

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Pore-water evolution and solute-transport mechanisms in Opalinus Clay at Mont Terri and Mont Russelin (Canton Jura, Switzerland)

Cited by 23 publications

References 39 publications

Deformation mechanisms and evolution of the microstructure of gouge in the Main Fault in Opalinus Clay in the Mont Terri rock laboratory (CH)

Deformation mechanisms and evolution of the microstructure of gouge in the Main Fault in Opalinus Clay in the Mont Terri rock laboratory (CH)

Mont Terri rock laboratory, 20 years of research: introduction, site characteristics and overview of experiments

Safety-relevant hydrogeological properties of the claystone barrier of a Swiss radioactive waste repository: An evaluation using multiple lines of evidence

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