SAND PETROGRAPHY OF TILLS IN THE ROSS EMBAYMENT, ANTARCTICA SOURCE TERRANES

If Ross Sea tills share compositional similarities to till from their source terranes, distinct compositional differences in the sand fractions between East and West Antarctic tills indicate should be useful to analyze the provenance of last glacial maximum tills in the Ross Sea. Thus, we can help constrain the ice contribution of the East Antarctic and West Antarctic Ice Sheets to the last glacial maximum Ross Ice Sheet and asses the validity of the hypothesis that ice streams played a significant role in the Pleistocene disintegration of the West Antarctic Ice Sheet.

We have examined the 500 – 2000 micron fraction of till samples from cores retrieved beneath the Whillans Ice Stream and Ice Streams C in West Antarctica and samples collected proximal to the Darwin, Beardmore, Hatherton, and Byrd outlet glaciers in East Antarctica. The sand fraction of East Antarctic tills are dominantly composed of; (1) (20-40 %) angular intermediate to mafic lithic fragments containing pyroxenes, feldspars, and micas; (2) (5-10 %) fine-grained, quartz-rich detrital sediments including mudstone and siltstone fragments; (3) (25-35 %) rounded quartz fragments; (4) (<1–60 %) rounded carbonate lithic fragments; (6) (10-15 %) angular pyroxene grains; and (7) (<1 %) rounded feldspar grains.

The sand fraction of West Antarctic tills are composed of; (1) (40-60 %) rounded quartz grains and rounded quartz lithic fragments; (2) (<4 %) rounded feldspars grains; (3) (20-40 %) detrital lithic fragments containing primarily quartz; and (4) (15-25 %) felsic lithic fragments containing primarily quartz and phyllosilicates (biotite and chlorite). Interestingly, West Antarctic till samples lack basaltic lithic fragments. The West Antarctic samples indicate that the basaltic bedrock is covered by sediments derived from felsic rocks.