The rudist-bearing carbonate platform succession of Marsia, in the northern Simbruini Mts. (Central Apennines), is described for the first time through the analysis of two stratigraphic sections, and better characterized by the study of three single significant outcrops located outside the sections. The identification of the rudist assemblages, related facies and micropaleontological analyses of the collected samples allowed to determine the age of this Upper Cretaceous succession, and the definition of a biostratigraphic frame for the of the entire study area. The Marsia composite stratigraphic section encompasses the late Turonian-early/middle Campanian interval, and records the evolution from inner platform-low hydrodynamic setting in the late Turonian, to an open platform setting characterized by high hydrodynamism in the late Santonian-early/middle Campanian. This succession has been compared to the already described Trevi, Santa Maria dei Bisognosi and Subiaco carbonate platform successions, and to regional bioevent schemes, in order to constrain the evolution of these carbonate facies in a wider sedimentological and stratigraphic context. Since the late Turonian, a spreading of rudist facies occurred throughout the central-southern Apennines, representing the first Upper Cretaceous rudist bioevent. In the Simbruini area inner platform environments, characterized by soft fine-grained sediment, are widespread. The successions of Marsia and Trevi, which are marked by upper Turonian inner platform facies with a thriving oligospecific rradiolitid association characterized by semi-infaunal lifestyle, record this bioevent. During the Santonian and the early Campanian a gradual increase in hydrodynamic conditions is recorded by rudist assemblages with hippuritids and robust radiolitids, associated with rare corals and echinoids which mark the second and third Upper Cretaceous rudist bievent, recorded at Marsia, Trevi and Santa Maria dei Bisognosi. The middle Campanian-Maastrichtian bioevents are only represented at Santa Maria dei Bisognosi and Subiaco, where high energy bioclastic facies, dominated by the peculiar radiolitid Sabinia sp., occur
