THE THUOUX AND SAVOURNON SECTIONS (SOUTHEASTERN BASIN, FRANCE) AND THE CALLOVIAN-OXFORDIAN BOUNDARY TYPE SECTION

Sedimentary deposits at the Dogger - Malm boundary in the South-East F rance Basin are thick and continuous (Terres Noires facies). This is e xceptional in Western Europe. The ammonite faunal succession exhibits a biochronological resolution that is equal to the ammonite horizon, i .e. approximately 150 000 years. The Dogger - Malm boundary is clearly visible in the Thuoux and Savournon sections (Diois area) which are r eference for the Callovian-Oxfordian boundary. Ammonite fauna are abun dant and detailed analysis of the various lineages enables us to ident ify a very precise demarcation line in both sections on the basis of B oreal ammonites, known only on the North-West European platform, and m ore widespread Tethyan ammonites. This ''mixed zonation'' means the Ca llovian-Oxfordian boundary is recognizable at the global scale. Variat ions in the quantitative distributions of faunas enhance the subdivisi ons obtained by synevolutionary analysis of the various ammonite linea ges. This paper describes and portrays index species by recognized bio stratigraphic units.