Distinguishing subglacial till and glacial marine diamictons in the western Ross Sea, Antarctica: Implications for a last glacial maximum grounding line

Analyses of lithology, stratigraphy, and tephra from marine sediment cores collected from the western Ross Sea during cruises Eltanin 32 and 52 and De ep Freeze 80 and 87 indicate that subglacial till does not extend to the co ntinental shelf edge. Subglacial till occurs as the lowest unit in most cor es landward (south) of approximately 74 degrees S, while seaward of approxi mately 74 degrees S, the lowest diamicton units are glacial marine diamicto ns, Glacial marine diamictons are distinguished from subglacial tills by th e presence of higher and more variable total organic carbon content downcor e, distinct tephra layers, stratification, higher diatom and foraminifera a bundances, higher sand content, and radiocarbon dates in chronological orde r downcore. Sand-sized tephra layers from two cores on the outer continenta l shelf are interpreted as single eruptive events, one likely to have been derived from the Mount Melbourne volcano and the other from the Pleiades vo lcano, Radiocarbon dates from sediment above and below the tephra layer in one of these cores (D f87-32) show that deposition indicative of open-water conditions occurred between 22 and 26 ha in the western Ross Sea.