The shell accumulations produced during the Holocene transgression are recorded along the entire coastal zone of South America and allow for the correlation of different areas. In order to obtain information about taxonomy, taphonomic processes and paleoecology, the mollusk faunas from six sites on the coastal plain of the Cabo Frio area, southeastern Brazil, were analyzed. These analyses were integrated with the sea level and paleoenvironmental changes in the area. The taxonomic analysis identified 42 mollusk species, of which 25 were bivalves, 15 gastropods and two scaphopods. The taphonomic analysis showed two types of assemblages, an autochthonous one, formed in anoxic hypersaline conditions, and an allochthonous one, characterized by a shallow marine environment. The radiocarbon dating of the shells revealed ages between 6260 and 5819 cal. years BP. The cluster analysis showed four faunal associations: Anomalocardia brasiliana, Tivela mactroides, Neritina virginea and Pitar fulminatus. The integration of mollusk associations and taphonomic signatures allowed the authors to distinguish two paleoenvironments: 1) a marine restricted one (6260–5950 cal. yearss BP) dominated by the Anomalocardia brasiliana association, with a low degree of abrasion and fragmentation suggesting a low-energy environment; and 2) a nearshore paleoenvironment (5950–5819 cal. years BP) dominated by the Tivela mactroides, the Neritina virginea/Olivella and the Pitar fulminatus associations, with a high degree of fragmentation and disarticulation denoting a high wave energy environment and marine currents.