A paleoecological study of cored wells located both in the lagoon and on the periphery of the atoll documents the major stages of build-up the Plio-Quaternary reef. Acquisition of atoll morphology has occurred by progressive differentiation between sheltered internal zones, where biodetrital sedimentation is dominant, and seaward edge characterized by organic construction. On its seaward edge, the atoll is composed of a prograding system of fringing reefs, each edified during a period of sea-level rise. Thus, atoll genesis does not result simply from progressive subsidence, nor from preferential dissolution of the central zone of a carbonate platform.