The "Formation gréso-glauconieuse" (Ultrahelvetic Prealps, Haute-Savoie, France) was previously attributed to the Aptian - Albian on the basis of rare nannofossils and cephalopod fragments. However, in this study, several samples yielded residual assemblages containing spinose globigerinids that suggest a middle Eocene age (P9-P12 planktonic foraminiferal zones) for this formation. Sedimentological analysis revealed the occurrence of slump and bottom-current deposits within the "Formation gréso-glauconieuse". Our results provide new insight into the palaeogeography and the palaeoceanography of the northern Alpine margin during the Palaeogene and emphasize the importance of reworking processes in fine-grained sedimentation.