K. J. Licht, Institute of Arctic Alpine Research and Department of Geological Sciences, University
of Colorado, Boulder, Colorado 80309
N. W. Dunbar, New Mexico Geochronology Research Lab, New Mexico Tech, Socorro, New
Mexico 87801
J. T. Andrews, A. E. Jennings, Institute of Arctic Alpine Research and Department of Geological
Sciences, University of Colorado, Boulder, Colorado 80309

ABSTRACT

Analyses of lithology, stratigraphy, and tephra from marine sediment cores collected from the western
Ross Sea during cruises Eltanin 32 and 52 and Deep Freeze 80 and 87 indicate that subglacial till
does not extend to the continental shelf edge. Subglacial till occurs as the lowest unit in most cores
landward (south) of approximately 74°S, while seaward of approximately 74°S, the lowest diamicton
units are glacial marine diamictons. Glacial marine diamictons are distinguished from subglacial tills by
the presence of higher and more variable total organic carbon content downcore, distinct tephra
layers, stratification, higher diatom and foraminifera abundances, higher sand content, and
radiocarbon dates in chronological order downcore. Sand-sized tephra layers from two cores on the
outer continental shelf are interpreted as single eruptive events, one likely to have been derived from
the Mount Melbourne volcano and the other from the Pleiades volcano. Radiocarbon dates from
sediment above and below the tephra layer in one of these cores (Df87-32) show that deposition
indicative of open-water conditions occurred between 22 and 26 ka in the western Ross Sea