HOLOCENE SHELL ACCUMULATIONS FROM CABO FRIO COASTAL PLAIN, SOUTHEASTERN BRAZIL: TAXONOMY, TAPHONOMY, GEOCHRONOLOGY AND PALEOENVIRONMENTAL IMPLICATIONS -- Preprint doi:10.5710/AMGH.27.07.2017.2979

Aline Meneguci Da Cunha, Joao Wagner De Alencar Castro, Marcelo De Araújo Carvalho

Abstract


The shell accumulations produced during the Holocene transgression are recorded in the entire coastal zone of South America, and allow for the correlation of different areas. In order to obtain information about taxonomy, taphonomic process and paleoecology, mollusk faunas from six sites in the coastal plain of Cabo Frio area, southeastern Brazil, were analyzed. These analyses were integrated with sea level and paleoenvironmental changes in the area. Taxonomic analysis identified 42 mollusk species, 25 of which 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. Radiocarbon dating of shells revealed ages between 6260 and 5819 cal. yr BP. Cluster analysis showed four faunal associations: Anomalocardia brasiliana, Tivela mactroides, Neritina virginea and Pitar fulminatus. The integration of mollusk associations and taphonomic signatures allowed to distinguish two paleoenvironments: 1) a marine restricted one (6260-5950 cal. yrs 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. yrs BP) dominated by Tivela mactroides, Neritina virginea and Pitar fulminatus associations, with a high degree of fragmentation and disarticulation, denoting a high wave energy environment and marine currents.

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