Sedimentological interpretation of high-resolution seismic facies in the Lower Freshwater Molasse (Chattian, western Switzerland)

Two shallow high-resolution seismic reflection profiles acquired across par t of the western Molasse Basin near Geneva have been processed and interpre ted. Three seismic facies have been identified in the Chattian Lower Freshw ater Molasse, They are associated with depositional environments in a sand- bed meandering river setting. A distal floodplain environment, characterize d by alternations of thick shales and thin sandstones and by palustrine-lac ustrine limestones, is represented by a poorly reflective seismic facies wi th discontinuous reflections. Thick sand-filled channels generate a highly reflective facies with continuous reflections. Highly reflective and contin uous reflections characterize the third facies, which is generated by shale s and thick proximal elastic deposits, indicative of a proximal floodplain environment. This scientific approach leads to applications in subsurface l ithological predictions associated with geotechnical and environmental asse ssments in the densely populated Swiss Plateau where Molasse sediments form a large part of the substrate.