Etude structurale du Léman par sismique réflexion continue

The French-Swiss group for the study of the geological environment of "Lake Geneva", GEOLEM, has completed 1,500 km of seismic profiling by continuous reflection. The results of this survey are the object of the following note. Slip faults observed in the Jura mountains such as the great Pontarlier fault, and the slip planes between wedges of the subalpine molasse, could be followed into the lake and they constitute the most important structural features. The trough of the lake is cut into the molassic formations and at its deepest point is 300 m below sea level. Lake Geneva was formed by subsequent glacial action. The base of the sedimentary sequence filling this trough is a moraine with a maximum thickness of 175 m. This moraine is overlain by glacial-lacustrine and lacustrine sediments varying in thickness from 10 to 20 m. In the delta of the Rhône these sediments reach a maximum thickness of 350 m. Sediments from talus slides and turbidity currents have also been identified