CONICET | Buscador de Institutos y Recursos Humanos

The shells of bivalves and gastropods found in Holocene marine sediments of the south of Buenos Aires Province show bioerosion traces. Ten sites from three areas were analyzed: Colorado River delta (CRD) (39º15´S/ 39º55´S) (6.9 ? 2.1 ka); Bahia Anegada (BA) (39º55´S/40º31´S) (5.9 - 3.6 ka) and Bahia San Blas (BSB) (40º31´S/40º37´S) (7.5 ? 2.1 ka). These sites are reported (N=2.640 valves). Twelve ichnogenera were identified: Entobia, Iramena, Pinaceocladichnus, Pennatichnus, Maeandropolydora, Caulostrepsis, Gastrochaenolites (Domichnia); Finichnus and Centrichnus (Fixichnia); Gnathichnus and Radulichnus (Pascichnia) and Oichnus (Praedichnia), as well as eight ichnospecies: P. onubensis, F. peristroma, C. eccentricus, G. pentax, R. inopinatus, O. simplex, O. paraboloides, and O. smiley. The highest percentages of bioerosion traces were found in the deposits of BSB with 18.21 %, followed by CRD with 4.30 and BA with 3.70 %. The dominant ichnogenera in CRD are Pennatichnus, Pinaceocladichnus, and Iramena, which reveal the existence of ctenostomate bryozoans suggesting water currents and large availability of phyto- and zooplankton in the environment. The most represented ichnogenera in BA are Entobia and Iramena, which indicate a high temperature range with a sublittoral environment of low sedimentation rate, water currents, high availability of suspension particles and high oxygenation of the water. While those of BSB are Entobia, Maeandropolydora and Oichnus, which suggest long periods of exposition, low energy enviroment, and sandy bottoms with polychaete annelids and carnivorous gastropods. Bioerosion is among the most relevant taphonomic features when interpreting specific environmental characteristics that suggest palaeoecological and palaeoenvironmental conditions during the Late Quaternary.

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