Glacial Geology of Cape Bird, Ross Island, Antarctica.

Located on the northwest coast of Ross Island in McMurdo Sound, Cape Bird features virtually unweathered surface drift with erratics from the Transantarctic Mountains (TAM) and with enclosed marine shell fragments. This Cape Bird drift is cut by Holocene beaches. The chronology of drift deposition and beach formation comes from AMS radiocarbon dates of associated marine shells, and of penguin bones and skin. The results indicate that a grounded ice sheet with a surface elevation in excess of 590 m deposited Cape Bird drift after 26,860 14C yr BP. The enclosed erratics, shells, and foraminifers indicate that a component of the ice within this sheet flowed through the TAM, grounded on the Ross Sea floor, and ultimately advanced landward onto the lower slopes of Mount Bird. On the basis of similar physical weathering characteristics, far-traveled erratics, radiocarbon chronology, and geomorphic setting, Cape Bird drift is correlated with Ross Sea drift elsewhere in the McMurdo Sound region. Reconstructed surface contours for the grounded ice sheet are based on the areal distribution and upper limit of Cape Bird/Ross Sea drift on ice-free areas alongside McMurdo Sound. The ice surface sloped down to the west from the Ross Embayment toward the TAM. A major flowline within this sheet passed westward around northern Ross Island, southward over Capes Bird and Royds, and then again westward across the sound. This ice-flow direction is required because of the paucity of kenyte erratics in Cape Bird drift. Kenyte, a distinctive bedrock lithology, is common on the west coast of Ross Island, south of Cape Bird. Therefore, the lack of widespread kenyte erratics in Cape Bird drift precludes northward flow of grounded glacier ice during the last glacial maximum (LGM). Wave-washed sediment and beach ridges at Cape Bird extend to 7.6 m above mean high tide (MHT). A set of five low-elevation beaches, all less than 4.0 m above MHT, is parallel with the modern coastline. A higher... [ABSTRACT FROM AUTHOR]