High-resolution Seismic Facies of Alluvial Depositional Systems in the Lower Freshwater Molasse (Oligocene-early Miocene, Western Swiss Molasse Basin)

Book excerpt: This PhD research showed the contribution of the high-resolution seismic reflection method to the seismic stratigraphic analysis of variable-scale, alluvial depositional systems in the Lower Freshwater Mollasse of the western Swiss Molasse Basin. Seismic data acquired offshore with an airgun source imaged alluvial architectural elements. Metre-thick, channel-fill complexes and flood plain deposits were clearly distinguished. On land, two types of data were recorded, each with a different source : in-hole shotgun and explosives. Data acquired with the former source imaged sandstone-filled multistory channels, but the resolution was not high enough to define their internal structure. The frequency content of the data recorded with explosives did not surely permit the distinction between sandstone- and shale-dominated bodies. More generally, the results demonstrated the potential of the method for predicting subsurface lithologies in cemented fluvial deposits, in association with outcrop and borehole studies.