Experimental study of chemical evolution and isotope fractionation of Cl and Br in pore water expelled during strong clay compaction

Strydom, Jessica; Sterpenich, Jérôme; Grgic, Dragan; Richard, Antonin; Eggenkamp, Hans G.M.; Agrinier, Pierre; Louvat, Pascale; Mosser-Ruck, Régine; Gaire, Patrick; Gaucher, Eric C. (2022). Experimental study of chemical evolution and isotope fractionation of Cl and Br in pore water expelled during strong clay compaction. Applied geochemistry, 140, p. 105274. Elsevier 10.1016/j.apgeochem.2022.105274

[img] Text
Strydom_2022.pdf - Published Version
Restricted to registered users only
Available under License Publisher holds Copyright.

Download (4MB) | Request a copy
[img] Text
Strydom_2022_pre-proof.pdf - Accepted Version
Restricted to registered users only until 1 June 2023.
Available under License Publisher holds Copyright.

Download (1MB) | Request a copy

In sedimentary basins, clay compaction by burial can lead to fluid overpressure and is suspected to also generate fresh waters, but few geochemical tracers are available to assess this process both qualitatively and quantitatively. Our objective was to carry out experiments on the chemical - and halogen (Cl, Br) isotope evolutions of pore water expelled during clay compaction. For this, the smectite-rich bentonite MX80 and an illite-rich marl (Sainte-Suzanne) were equilibrated with ocean water. During two compaction experiments under high fluid pressure (45 MPa), mechanical stress (up to 150 MPa) and temperature (up to 150 °C), it was found that the chemistry and isotope behavior is considerably different between the swelling clay and the non-swelling clay. We saw a general decrease of the cat- and anion concentrations in the expelled water, for swelling clay while its concentration slightly increases in the remaining pore fluid. This was not the case for non-swelling clay. More freshening of the expelled water occurred during the compaction at higher temperature. We also observed a larger range of isotopic variation for Br (δ81Br from 0.9‰ up to 1.5‰) than for Cl (δ37Cl from −0.5‰ to −0.1‰) in the compaction experiments. During the compaction of illite-rich marl, no significant variation of Cl isotope (δ37Cl close to 0‰) was observed while the δ81Br value of the expelled water showed the same general increase (from 0.9‰ up to 1.5‰) as during the compaction of smectite-rich bentonite. We observed limited mineralogical transformations in terms of dissolution/precipitation processes. Therefore the surface chemistry of the clay in combination with decreasing porosity, in part, drive the anion and isotope evolution. We propose that significant retention of Cl and Br in the pore water of the compacted smectite-rich bentonite is indicative of ultrafiltration and that Cl and Br isotopes are promising tracers to consider when tracking the origin of low-salinity formation waters in sedimentary basins.

Item Type:

Journal Article (Original Article)

Division/Institute:

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

UniBE Contributor:

Gaucher, Eric Claude Marie

Subjects:

500 Science > 550 Earth sciences & geology

ISSN:

0883-2927

Publisher:

Elsevier

Language:

English

Submitter:

Dr Eric Claude Marie Gaucher

Date Deposited:

05 May 2022 15:12

Last Modified:

08 May 2022 02:05

Publisher DOI:

10.1016/j.apgeochem.2022.105274

BORIS DOI:

10.48350/169756

URI:

https://boris.unibe.ch/id/eprint/169756

Actions (login required)

Edit item Edit item
Provide Feedback