Abstract

The evolution of temperature and fluid circulations through time in the Ardeche passive margin is studied from several geometrical reconstitutions, using a numerical thermo-convective model taking into account the evolution of the physical parameters during the burial. The results of this study show that, until the late Triassic stage, fluid circulations occur in the Permo-Carboniferous and Triassic layers, as well as in the basement to the west of the basin. Starting with Jurassic stage, a dissymmetry appears on each side of the Uzer fault, to the east, the thermal regime is conductive whilst to the west, the thermal regime is convective, implying circulations between the Triassic layer and the basement, which will disappear at the Cretaceous stage. During the Cretaceous stage, only a maximum cover of 2000 m associated with a regional heat flow of 80+ or -5 mW.m (super -2) can explain the palaeo-temperatures measured in the sediments. The thermal regime of the margin is then totally conductive. On the present time geometry, the Uzer fault separates two different hydrological domains. To the east, the layers are impervious, associated with a purely conductive thermal regime, while to the west, fluid circulations occur in sedimentary formations.

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