Constraining porewater chemistry in a 250m thick argillaceous rock sequence

Wersin, Paul; Mazurek, Martin; Mäder, Urs; Gimmi, Thomas; Rufer, Daniel; Lerouge, Catherine; Traber, Daniel (2016). Constraining porewater chemistry in a 250m thick argillaceous rock sequence. Chemical geology, 434, pp. 43-61. Elsevier 10.1016/j.chemgeo.2016.04.006

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The geochemistry of an argillaceous rock sequence from a deep borehole in NE-Switzerland was investigated. The focus was to constrain the porewater chemistry in low permeability Jurassic rocks comprising the Liassic, the Opalinus Clay formation, the 'Brown Dogger' unit and the Effingen Member (Malm). A multi-method approach including mineralogical analysis, aqueous and Ni-ethylenediamine extraction, squeezing tests and pCO(2) measurements as well as geochemical modelling was applied for this purpose. A consistent dataset was obtained with regard to the main solutes in the porewaters. A fairly constant anion-accessible porosity of similar to 50% of the total porosity was deduced for all analysed samples which displayed variable clay-mineral contents. Sulphate concentrations were shown to be constrained by a sulphate-bearing phase, presumably by celestite or a Sr-Ba sulphate. Application of a simple equilibrium model, including cation exchange reactions, calcite and celestite equilibrium showed good agreement with squeezing data, indicating the suitability of the modelling approach to simulate porewater chemistry in the studied argillaceous rocks. The modelling highlighted the importance of correct determination of the exchangeable cation population. The analysis corroborates that squeezing of the studied rocks is a viable and efficient way to sample porewater.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Institute of Geological Sciences
08 Faculty of Science > Institute of Geological Sciences > Rock-Water Interaction

UniBE Contributor:

Wersin, Paul; Mazurek, Martin; Mäder, Urs; Gimmi, Thomas and Rufer, Daniel

Subjects:

500 Science > 550 Earth sciences & geology

ISSN:

0009-2541

Publisher:

Elsevier

Language:

English

Submitter:

Daniel Rufer

Date Deposited:

08 Jul 2016 16:29

Last Modified:

08 Jul 2016 16:29

Publisher DOI:

10.1016/j.chemgeo.2016.04.006

Web of Science ID:

000376458900004

BORIS DOI:

10.7892/boris.84366

URI:

https://boris.unibe.ch/id/eprint/84366

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