Thermal history and timing of fluid flow at the Ardèche palaeomargin, France

Abstract

Abstract The fluid evolution, the timing of fluid flow and the thermal history of the faulted Ardèche passive palaeomargin, France, were reconstructed using detailed mineralogical, petrological, geochemical and geophysical studies applied on core material from Triassic sandstone and Liassic carbonate units of the BA1 and MM1 boreholes. It could be shown that an early cementation significantly reduced the porosity of the rocks. Application of various geothermometers and chronothermometers showed that the outcropping Jurassic units underwent a degree of diagenetic evolution corresponding to the onset of the oil window. In the Triassic sandstone, temperatures reached 130–145°C as recorded by the dolomitic cements. Fluids in thermal disequilibrium with their host rock were found, implying supply of fluids from deeper levels. The decrease of temperature below 120 ± 10°C during the Eocene is explained by the erosion of 1900 m of mainly Cretaceous sediments. A fault system was active at different periods, especially at 190 Ma and during the post-Cretaceous uplift.