Basin scale thermal and fluid-flow histories revealed by carbonate clumped isotopes (Δ47) – Middle Jurassic carbonates of the Paris Basin depocentre

The reconstruction of past diagenetic conditions in sedimentary basinsis often under-constrained. This results from both the analytical challenge of performing the required analyses on the minute sample amounts available from diagenetic mineral phases and the lack of tracers for some of the diagenetic parameters. The carbonate clumped isotopes thermometry (Δ47) opens new perspectives for unravelling the temperatures of diagenetic phases together with the source of their parent fluids, two parameters that are otherwise impossible to constrain in the absence of exploitable fluid inclusions. Here is reported the study of a large number of sedimentary and diagenetic carbonate phases (from Middle Jurassic reservoirs of the Paris Basin depocentre) by combining detailed petrographic observations with a large number of Δ47 data (n > 45) on a well-documented paragenetic sequence, including calcite and dolomite burial cements. The data reveal carbonate crystallization at temperatures between 29°C and 98°C from fluids with δ18Owater values between -7‰ and +2‰, in response to the progressive burial and uplift of the Paris Basin, throughout 165 Myr of basin evolution. Coupled to the time-temperature evolution previously estimated from thermal maturity modelling, these temperatures allow determining the timing of four successive cementation episodes. The overall dataset indicates a history of complex water mixing with a significant contribution of hypersaline waters from the Triassic aquifers migrated upward along faults during the Cretaceous subsidence of the basin. Subsequent large-scale infiltrations of meteoric watersinduced a dilution of these pre-existing brines in response to the Paris Basin uplift in the Tertiary. Overall, the data presented here allow proposing an integrated approach to characterize the cementation events affecting the studied carbonate reservoir units, based on temperature, oxygen isotope composition and salinity of the parent fluids as well as on petrographic grounds. This article is protected by copyright. All rights reserved.