3-DIMENSIONAL EVOLUTION OF THE KEUPER OF THE PARIS BASIN BASED ON DETAILED ISOPACH MAPS OF THE STRATIGRAPHIC CYCLES - TECTONIC INFLUENCES

Detailed isopach maps of the stratigraphic cycles of the Keuper of the Paris basin are used to reconstruct the 3D evolution of the basin cyc le by cycle and to investigate the influence of tectonic movements. Th e major base-level cycles record variations in the rate of subsidence in time and space. The area of greatest subsidence, which was confined to the east of the basin during the Scythian-Carnian cycle, shifted n orthwestwards during the Carnian-Liassic cycle. Within the ''Marnes ir isees inferieures'', the E-W faults abruptly limited the extent of sal t deposits to the north and south by forming a ''corridor'' where subs idence was greater. The westward shift of areas of subsidence induced by the migration of fault activity enhanced the migration of salt seri es which was bounded by the Saint-Martin-de-Bossenay fault. The cessat ion of fault activity in the eastern part of the basin marked the end of halite sedimentation. From the ''Gres a roseaux'' formation, a gene ral northwestward tilt of the basin with corresponding depocentre migr ation induced a truncation within the ''Marnes irisees superieures''. The depocentres were located in the west which was the site of most fa ult activity which influenced the fluvial deposits by creating tilted blocks where sediment could accumulate.