Article Dans Une Revue Applied Geochemistry Année : 1994

Stable isotope conservation and origin of saline waters from the Middle Jurassic aquifer of the Paris Basin, France

Résumé

Seventy-nine samples of formation water from geothermal boreholes, oilfield and groundwater wells, tapping the Dogger (Middle Jurassic) limestone reservoir of the Paris Basin, have been analyzed for their 2H, 180, TDS, bromide and chloride contents. Geostatistical mapping of 2 H and of la O contents and their variations with chloride content indicate that both isotopes have a common origin and a similar behaviour within the aquifer. The 62H and t~180 values increase progressively from the outcrops toward a zone where temperature, Cl-and TDS values are high. The ~H and 6180 values are very uniform in this zone and do not show any relation with formation temperature, in contrast to what is generally observed in other sedimentary basins. A discussion of isotope exchange with the carbonate matrix for oxygen, and with H2S for deuterium, shows that such processes are not controlling the heavy isotope contents of ~roundwaters. This is attributed to the relatively short residence time of groundwaters in the aquifer. Both H and 180 contents of groundwater may thus be considered as conservative tracers in the Dogger aquifer of the Paris Basin and their initial contents are modified only by fluid mixings. Complex mixing processes account for stable isotope composition, TDS, CI-and Br-values of the Dogger fluids. All mixtures include a brine component. Meteoric water percolated and dissolved halite in the Triassic aquifer (secondary brine). This saline solution mixed with some residual primary brine, then migrated via vertical faults into the Dogger aquifer. Such migration is found to be in agreement with data from fluid inclusions in late carbonate cements from the Liassic and Dogger strata. The requirement that these units were exposed implies that meteoric invasion could not have occurred before the Tertiary. Successive mixings of the brine with several types of meteoric waters depleted in heavy isotopes account for the present isotope and chemical compositions of the Dogger fluids.

Dates et versions

irsn-03881939 , version 1 (02-12-2022)

Identifiants

Citer

Jean-Michel Matray, M Lambert, Jean-Charles Fontes. Stable isotope conservation and origin of saline waters from the Middle Jurassic aquifer of the Paris Basin, France. Applied Geochemistry, 1994, ⟨10.1016/0883-2927(94)90040-X⟩. ⟨irsn-03881939⟩
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