Bioerosion on Late Pleistocene (MIS 7 and MIS 5e) marine molluscs A palaeoclimatological and palaeoecological comparison with modern beaches (Río Negro, Argentina)

CHARO MELISA; ACEÑOLAZA, GUILLERMO; CAVALLOTTO, JOSE LUIS; GISELA CHARO

Acta Geologica Sinica (English version)

Geological Society of China

Año: 2022

The Late Pleistocene littoral ridges of southern South America, especially those of the north of the Argentinean Patagonia, contain remains of mollusc shells with bioerosion traces. Eleven sites (two from MIS 7, four from MIS 5e and five from modern beaches) with 37 taxa were analyzed, in the area between west of Baliza San Matías and Las Grutas (41°S, Río Negro Province). Eight ichnogenera were reported: Entobia, Meandropolydora, Pinaceocladichnus, Iramena, Caulostrepsis, Gastrochaenolites and Rogerella (Domichnia) and Oichnus (Praedichnia) and three ichnospecies were found: O. simplex, O. paraboloides and G. torpedo. The most frequent ichnogenera are Entobia and Oichnus, which appear in the two periods. According to the presence and abundance of biogenic traces, the MIS7 sites are characterized by infralittoral environments with waters of moderate energy and abundance of rocky substrate; MIS 5 sites represent environments of intermediate stability, deeper water of low sedimentation and sandy substrate; in turn, modern beaches have clear waters of low energy and both sandy and rocky substrate. We concluded that the environment of the northern coast of Río Negro was dynamic and heterogeneous during the late Quaternary.