Biostratigraphic refinement and new datings for some emersive surfaces in the Kimmeridgian-Tithonian in the southern French Jura and their consequences for sequence stratigraphic interpretations

In various recent studies the area of Saint-Germain-de-Joux (Ain Department , France) has been used as a reference to define a new major sequence bound ary that was added to the Exxon cycle chart and assigned to the Kimmeridgia n-Tithonian boundary. Within the reef complex of SaintGermain-de-Joux the n ew sequence boundary SE 140 is believed to be represented by the horizon ov erlain by a black-pebble conglomerate. A comprehensive survey of the biostr atigraphical data already published proves the age of the discontinuity to be in fact late Kimmeridgian, Beckeri Zone. Following recent refinement of the vertical range of the species of the genus Gravesia, the Kimmeridgian-T ithonian boundary is now placed within the Gravesia beds in the lower part of the bioturbated limestone ("Calcaires a tubulures") of the Couches du Ch ailley Fm.