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

Two shallow high-resolution seismic reflection profiles acquired across part of the western Molasse Basin near Geneva have been processed and interpreted. Three seismic facies have been identified in the Chattian Lower Freshwater Molasse. They are associated with depositional environments in a sand-bed meandering river setting. A distal floodplain environment, characterized by alternations of thick shales and thin sandstones and by palustrine-lacustrine limestones, is represented by a poorly reflective seismic facies with discontinuous reflections. Thick sand-filled channels generate a highly reflective facies with continuous reflections. Highly re-flective and continuous reflections characterize the third facies, which is generated by shales and thick proximal clastic deposits, indicative of a proximal floodplain environment. This scientific approach leads to applications in subsurface lithological predictions associated with geotechnical and environmental assessments in the densely populated Swiss Plateau where Molasse sediments form a large part of the substrate.