The Oligocene of the SW portion of the Swiss Molasse Basin consists mainly of lenticular, detritic sediments deposited in deltaic environments in which fossils are reported to be rare. The systematic search for fossils carried out during the years from 1967 to 1973 furnished foraminifera, molluscs, ostracods, remains of vertebrates and plants. However, the only fossils which proved to be of age significance are the mammals, in particular rodents, whose teeth only can be used for specific determinations. On the basis of assemblages of mammal teeth it was possible to determine the presence of the vertebrate zones of Antoingt, Cournon and Coderet, which correspond to the upper part of the Middle Oligocene and the Upper Oligocene. The other fossils proved stratigraphically inconclusive but helpful in the determination of the environmental conditions of the Oligocene deposits.

The sediment, whose main constituants are sand, clay and limestone, were analysed lithologically using a triangular diagram, which was subdivised in 12 lithologie classes each defining a particular type of lithofacies. The distribution and frequencies of theses lithofacies types permitted the recognition of 3 lithologic units which are also characterised by distinct paleoecologic criteria.

No general sedimentologic theory can be presented for this part of the Molasse Basin using the distribution and frequencies of the thickness of the beds, the predominant colors, and the method of transition matrices. For the subdivision of these deltaic deposits, the classic stratigraphic methods supported by objective lithologic data, are better suited than the statistical approach.