ABSTRACT: As the result of a study integrating lithostratigraphy and biostratigraphy of the Upper Paleocene (Thanetian) and Lower Eocene (Sparnacian-Ypresian) of the Paris Basin, a new lithostratigraphic unit, the Mont Bernon Group, can be formally recognized. The group includes four formational units: the Mortemer (Mortemer Limestone), the Vaugirard (Plastic Clay), the Soissonnais (Lignitic Clay of Soissons) and Epernay (Lignitic Clay of Epernay) formations and associated members. An integration of charophyte, dinoflagellate cyst and, to a lesser extent, calcareous nannoplankton biostratigraphy allows us to place the succession in an approximate, integrated biostratigraphic framework. Our introduction of a formal lithostratigraphic framework for the Upper Paleocene-Lower Eocene succession in the Paris Basin contributes to emphasize the distinctiveness of the Sparnacian deposits as an independent stratigraphic unit.