Mid-Holocene serpulid build-ups in an estuarine environment (Buenos Aires Province, Argentina)
Abstract A bed with several serpulid build-ups is described from a Holocene outcrop at Quequen Grande River, Argentina. The tubes were dated at 6360 ± 80 years BP. The morphology and size parameters of the serpulids were compared to different species of serpulids from the literature and tubes of Ficopomatus enigmaticus , Hydroides dianthus and Hydroides plateni from Argentinean waters. In spite of the fact that today only F. enigmaticus constructs build-ups in Argentine brackish environments, the fossil tubes could not be assigned to this species, but instead, they show close similarities to those of the two species of Hydroides . The sequence is interpreted as having originated from a brackish environment. At present, neither the endemic H. plateni nor any other species of Hydroides construct build-ups in brackish waters of southern South America. This suggests, that suitable environments to construct aggregates were more widespread than today or that the invasion of F. enigmaticus replaced Hydroides ; alternatively various causes may have acted jointly.