ABSTRACT
The inference of Palaeogene ice masses of considerable extent in West Antarctica conflicts with interpretations of palaeoenvironmental conditions and a consideration of glacio-marine processes responsible for any ice-rafting into the southeast Pacific Ocean.
The earliest ice-rafted sediments recovered by the Deep Sea Drilling Project off Antarctica are from the Ross Sea and include pebbles mainly of metasedimentary lithology. Barrett suggested a provenance in sub-ice Marie Byrd Land, and from this Hayes and Frakes argued for the formation of an extensive ice sheet in West Antarctica in the Oligocene. Radio echo sounding along the front of the southern Transantarctic Mountains, oxygen-isotope and sedimentological studies suggest that DSDP results are better explained by development of vigorously calving tidewater valley and outlet glaciers, possibly located in the Whitmore-Thiel-Transantarctic Mountains area during the Oligocene rather than establishment of a large ice sheet – ice shelf environment in Marie Byrd Land.
Conditions suitable for the growth of a marine ice sheet in West Antarctica did not obtain until Late Miocene times (4–5 MY BP) when a further severe cooling of Antarctic waters occurred. The first unequivocal evidence for the presence of grounded West Antarctic ice is provided by a marked unconformity in Ross Sea stratigraphy at this time. That an ice mass discharging from Marie Byrd Land extended to the continental break-of-slope is demonstrated by the regional extent of the unconformity, terrestrial geologic evidence of expanded conditions and δ180 determinations which impute ice volumes greater than today.
