Timescales of regional circulation of saline fluids in continental crystalline rock aquifers (Armorican Massif, western France)
In recent decades, saline fluids have been sampled worldwide at great depths in continental basements. Although some of them have been attributed to marine transgressions, the mechanisms allowing their circulation are not understood. In this paper, we describe the horizontal and vertical distributio...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2015-03-01
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| Series: | Hydrology and Earth System Sciences |
| Online Access: | http://www.hydrol-earth-syst-sci.net/19/1413/2015/hess-19-1413-2015.pdf |
| Summary: | In recent decades, saline fluids have been sampled worldwide at great depths
in continental basements. Although some of them have been attributed to
marine transgressions, the mechanisms allowing their circulation are not
understood. In this paper, we describe the horizontal and vertical
distributions of moderately saline fluids (60 to 1400 mg L<sup>−1</sup>) sampled
at depths ranging from 41 to 200 m in crystalline rock aquifers on the
regional scale of the Armorican Massif (northwestern France). The horizontal
and vertical distributions of high chloride concentrations are in good
agreement with both the altitudinal and vertical limits and the succession of
the three major transgressions between the Mio-Pliocene and Pleistocene ages.
The mean chloride concentration for each transgression area is exponentially
related to the time spanned until the present. It defines the potential laws
of leaching (displacement) of marine waters by fresh meteoric waters. The
results of the Armorican aquifers provide the first observed constraints for
the timescales of seawater circulation in the continental crystalline
basement and the subsequent leaching by fresh meteoric waters. The general
trend of increasing chloride concentration with depth and the time frame for
the flushing process provide useful information to develop conceptual models
of the paleo-functioning of Armorican aquifers. |
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| ISSN: | 1027-5606 1607-7938 |