Water circulation control on carbonate-δ18O records in a low permeability clay formation and surrounding limestones: The Upper Dogger–Oxfordian sequence from the eastern Paris basin, France

摘要: Abstract Upper Dogger to Oxfordian Formations in the eastern part of Paris basin (France) are currently being investigated by French nuclear waste management agency (Andra), testing feasibility long-term deep disposal Callovo-Oxfordian claystones. Characterising hydrogeological behaviour claystones is, therefore, essential evaluating its potential as a geological barrier. In order evaluate and quantify water/rock interactions experienced over time these Formations, bulk carbonate δ 13 C 18 O were measured calculations water–rock ratios used explain carbonate-δ changes. Meteoric porewater maximum temperature reached about 40 °C considered. The Jurassic marine was preserved overlying limestones (−0.28‰ 3.39‰/PDB), while values lower 0–5‰ (−6.25‰ −1.32‰/PDB). Calculations show that Limestone data: (i) have random-like distribution through theoretical O-W/R curves (ii) suggest (0.08–0.4) needed changes higher factor 2–20 compared present-day ratio. These features indicate advection both aquifers. According history basin, this could been effective since Jurassic/Cretaceous transition times. Inversely, content trends observed for data controlled post-depositional fluid–rock interaction with ratio (0.02–0.15) similar porewater/rock 130 m thick claystone appears remarkably homogenous regarding properties. This study suggests an initial replacement meteoric water only after porosity reduced present value, thus demonstrating clay has mainly isolated from advective circulation. Only upper 20 m Formation underwent heterogeneous exchange (W/R 0.01 0.3), probably result mineralogical heterogeneity proximity aquifer. confirms barrier properties it natural hydrological earliest times diagenesis.