Late Quaternary molluscan assemblages from the coastal area of Bahيa Bustamante (Patagonia, Argentina): Paleoecology and paleoenvironments

Variations in the composition, distribution, and diversity of molluscan assemblages from Patagonian marine terraces (MT) formed during the late Quaternary sea-level highstands and neotectonic events—between the late Pleistocene, mid-Holocene, and present—are discussed. Molluscs and associated macrofauna (balanids, brachiopods, polychaetes, bryozoans) from nine fossiliferous localities and three modern sites suggest paleoecological, paleobiogeographical, and paleoenvironmental implications for paleoclimatic interpretations of the coastal area of Bahia Bustamante–Caleta Malaspina (∼44.9 and 45.3°S) since marine oxygen isotope stage (MOIS) 7. Crepidula protea, Buccinanops paytensis, and Brachidontes rodriguezi are first recorded for the late Pleistocene MTIV (MOIS5-7); Nacella (Patinigera) deaurata, Epitonium magellanicum, B. paytensis, Aequipecten tehuelchus, and Clausinella gayi are recorded for the mid-Holocene MTVI (MOIS1) in the area. These molluscs currently live in the SW Atlantic, but Venericardia procera represents a northward migration and Tegula atra a faunal extinction in response to climate change. Overall, they indicate hard substrates, shallow waters, and truly marine conditions, similar to the modern littoral. With respect to temperature, the qualitative, quantitative, morphological, and distributional variations suggest slightly higher SST during the mid-Holocene (MTVI, MOIS1, hypsithermal), colder for MTV (MOIS5c?, 5a?), and warmer or similar for MTIV (MOIS5e, 7?).