ABSTRACT: Upper Cenomanian through lower Coniacian calcareous nannofossil biostratigraphy is integrated with macrofossil and lithostratigraphic correlations at the reference section for the Mancos Shale in Mesa Verde National Park, CO. Interpretations of key biostratigraphic events and 13C values from bulk-rock carbonate fit well with the placement of stage boundaries by Leckie et al. (1997) and observations of nannofossil biostratigraphy in equivalent successions in the Western Interior. Tethyan nannofossil zone CC10b brackets the Cenomanian-Turonian boundary between 22.7–27.6m. Anannofossil zonal boundary between CC13 and CC14 is placed at 200.4-201m supporting the existence of an unconformity in the basal Smoky Hill Member suggested by Leckie et al. (1997). Lithraphitdites eccentricumWatkins is elevated to species status, the highest occurrence ofwhich may provide an additional datum in the upperCenomanian. Eprolithus octopetalusVarol is proposed as a lower Turonian marker,with a lowest occurrence as a potential alternative to Quadrum gartneri Prins and Perch-Nielsen for indicating the Cenomanian-Turonian boundary.