The pre-Mesozoic basement of the SW Paris basin (France) revisited - Focus on the structural evolution of the Late Carboniferous-Early Permian sedimentary basins under their post depositional sedimentary cover
Résumé
Late Carboniferous to Early Permian basins are found in several rather small places in and around the present-day French Variscan basement. They are mostly considered as intramontane post-orogenic (Variscan) basins, developed in close relationships with crustal to lithospheric geological events. On the other hand, little is known about their subsurface occurrences under their post depositional sedimentary covers. This is for instance the case in the Paris basin, where only few regional studies aimed to find their location under the Mesozoic sedimentary cover. Our approach is based on the interpretation of newly reprocessed seismic lines (about 1480 km length) acquired by the oil industry in the 80'. For the first time (1) we get a comprehensive view of the geometry of these basins (well data compilation, interpretation of geological surfaces and internal geometries, specific facies); (2) we are able to identify several families of faults according to their period of activity; (3) we propose a detailed structural pattern of the area, whose faults were active during the filling of the basins and discuss the mode of extension; (4) we calculate thickness maps both in TWT and in m, allowing a pseudo-3D view of the three identified basins (Arpheuilles, Contres and Brécy basins; thicknesses up to 3000 m); (5) finally we illustrate and estimate the pre-Triassic uplift recorded by these sedimentary basins (of about 1500 m). As exemplified here, these geological objects still have much to teach us about the transition from the Palaeozoic Variscan cycle to the Mesozoic sedimentary cycle, not to mention their industrial applications.