The palaeoclimatic significance of Cenozoic marine macrofossil assemblages from Cape Roberts Project drillholes, McMurdo Sound, Victoria Land Basin, East Antarctica

Abstract The Cape Roberts Project (CRP) drilled three sedimentary cores at 77.00°S and 163.7°E, about 12–14 km east of Cape Roberts, McMurdo Sound in the Ross Sea, East Antarctica. The total CRP recovery consists of about 1500 m of Cenozoic strata and 100 m of Paleozoic-age Beacon Supergroup rocks. As many as 594 horizons produced macrofossils that prove to be significant to understand past Ross Sea depositional environments and contribute new information about Antarctic climate. In particular, the Cape Roberts Project opened important windows on the paleoclimatic history of East Antarctica during the Early Pleistocene, Early Miocene and Oligocene. The Early Pleistocene carbonate unit in CRP-1 holds a truly polar macrofauna but also documents a peculiar (interglacial?) climatic event with strongly reduced seasonal sea-ice formation in the Ross Sea. The Early Miocene (CRP-1 and CRP-2/2A) and Late Oligocene macrofossil assemblages (CRP-2/2A and CRP-3) are consistent with cold-water environments and may be interpreted to indicate sub-polar conditions. The Early Oligocene assemblages contain modiolid mussels that are definitely not truly polar and suggest significantly warmer-than-present seawater conditions, although definitely colder than during the Middle–Upper Eocene known in James Ross Basin and McMurdo erratics. Finally, the suggestion that CRP reached Upper Eocene strata is considered possible on the base of an undescribed modiolid mussel found at the bottom of pre-Beacon sediments in the CRP-3 drill core.