Bioerosion on marine molluscs of MIS 5e in Faro Segunda Barranca, South of Buenos Aires Province, Argentina

Faro Segunda Barranca is located in the south of Buenos Aires Province (40º46´S/62º16´W), where Late Pleistocene marine deposits (108 – 102 Ka correlated with MIS 5e) have been identified, as well as the modern beach. In a sample of 158 mollusc shells, nine ichnogenera and four ichnospecies were found in two sites. Seven ichnogenera were found in the Late Pleistocene (Site 1), while nine ichnogenera and four microbioerosion morphotypes were found in the modern beach (Site 2). Both sites yielded Iramena, Maeandropolydora, Entobia, Caulostrepsis and Pinaceocladichnus (Domichnia), Finichnia (Fixichnia) and Oichnus (Praedicnia); Trypanites and Gastrochaenolites (Domichnia) were present only in Site 2. The most abundant Late Pleistocene ichnogenera are Iramena and Pinaceocladichnus, suggesting an environment of low sedimentation, with moderate water current and availability of suspension particles. Whereas in the modern beach, Maeandropolydora is dominant, suggesting a sublitoral environment and sandy bottom; the record of Trypanites and Gastrochaenolites indicates hard substrate and shallow environment. The identified ichnogenera suggest changes in the environmental features between the MIS 5e and the modern beach at Faro Segunda Barranca