Diagenesis studies of both siliciclastic and carbonate rock units face the challenge of constraining the temperature and age of the successive episodes of mineral crystallization. The first objective of this PhD work was to test the potential of two recently developed isotopic tools (the "clumped isotopes" Δ47 geothermometer and the laser ablation U-Pb geochronometer) to integrate conventional carbonate diagenesis studies. The second objective was to reconstruct the diagenetic, thermal and hydrogeological histories of the Middle Jurassic carbonate reservoirs of the Paris Basin. To achieve these goals, we studied sedimentary and diagenetic carbonates mostly collected from the basin subsurface (i.e. exploration cores). The good sedimentological and petrographic characterization of the samples, together with the analysis of fluid inclusions and Δ47 thermometry, allowed us to determine the temperature and the chemical/isotopic compositions of the mineralizing fluids, to finally reach several first-order information. First, we show that the Δ47 allows to simultaneously and precisely reconstruct the formation temperature of diagenetic carbonates in the range 60-100 °C (with an accuracy of ~ 3-5 °C) and the oxygen isotopic composition of the parent fluids (δ18Owater) with a precision of ~ 1 ‰. Secondly, this work improves our knowledge on the thermal history and past fluid-flows having occurred at the basin scale. In particular, the coupling of the Δ47 thermometer with the U-Pb chronometer permitted, for the first time, to set absolute thermo-chronological constraints on each of the fluid-flow episodes investigated. More broadly, this unprecedented Δ47 /(U-Pb) coupling reveals a wide spectrum of applications in the low-temperature thermochronology domain (10-100 °C). We anticipate that this thermo-chronological approach will stimulate future applications in the analysis of sedimentary basins via carbonate diagenesis studies.
Keywords: carbonate diagenesis; Δ47 thermometry; U-Pb chronometry; fluid inclusions; Paris basin; thermal history; Δ47 /(U-Pb) thermo-chronology