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  3. Identifying temporally and spatially changing boundary conditions at an aquifer – aquitard interface using helium in porewater
 

Identifying temporally and spatially changing boundary conditions at an aquifer – aquitard interface using helium in porewater

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BORIS DOI
10.7892/boris.122299
Date of Publication
June 7, 2018
Publication Type
Article
Division/Institute

Institut für Geologie...

Author
Rufer, Danielorcid-logo
Institut für Geologie
Waber, Niklausorcid-logo
Institut für Geologie
Gimmi, Thomasorcid-logo
Institut für Geologie
Subject(s)

500 - Science::550 - ...

Series
Applied geochemistry
ISSN or ISBN (if monograph)
0883-2927
Publisher
Elsevier
Language
English
Publisher DOI
10.1016/j.apgeochem.2018.05.022
Description
Helium concentrations and 3He/4He isotope ratios of porewater, groundwater and rock were measured on samples collected from a Jurassic sediment sequence at the Mont Terri underground rock laboratory (Northern Switzerland). Porewater He data of rock samples collected from borehole BDB-1 at high spatial resolution across a karstic limestone unit (Passwang Formation) into the underlying claystone sequence (Opalinus Clay, Staffelegg Formation) describe a continuous profile from the water-conducting zone in the limestone
into the clay-rich rocks of low permeability. Concentrations of 4He, 3He and their parent nuclides in the rock allow calculating insitu production and accumulation terms. Since the time of sedimentation, 90%–97% of the in-situ produced 4He has been released to the porewater. Today only 2.5% of the maximum possible accumulated 4He is still retained in the porewater while the major part of in-situ produced 4He was removed from the system presumably by porewater–groundwater exchange. The porewater 4He concentrations show a diffusion profile from the aquitard towards the aquifer, reflecting a) a transient state between 4He in-situ production and porewater–groundwater exchange, b) a transient state from previously higher 4He concentrations in the porewater, and c) a spatially variable boundary in the karstic limestone unit. Evolutionary models of porewater 4He concentration profiles in combination with constraints from independent chemical and isotopic tracers allow deciphering a complex palaeo-hydrogeological history of the system over about the last 30 ka. A local excursion from the general profile towards higher 4He concentrations and 3He/4He ratio in a limestone layer in the Opalinus Clay cannot be further constrained in time based on the present sample frequency, but appears to represent a hydrogeological signal.
Handle
https://boris-portal.unibe.ch/handle/20.500.12422/200304
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FileFile TypeFormatSizeLicensePublisher/Copright statementContent
Rufer et al 2018 (AppGeochem) - Changing boundary conditions [accepted ms].pdftextAdobe PDF5.63 MBAttribution-NonCommercial-NoDerivatives (CC BY-NC-ND 4.0)acceptedOpen
Rufer, Waber, Gimmi 2018 (AppGeochem).pdftextAdobe PDF2.72 MBpublisherpublished restricted
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