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5 now at Shell Exploration & Production International B.V., Netherlands (Michael.Faulkner@shell.com) Abstract Marine geophysical data from the deep sea adjacent to the Ross Sea, Antarctica suggest that �70 km of extension occurred between East and West Antarctica from 46 to 2� Ma. The Northern and V ictoria Land Basins in the western Ross Sea adjacent to the Transantarctic Mountains accommodated 95 km of this extension. Several kilometers of Oligocene sediments are found in the Central Trough and Eastern Basin in the eastern Ross Sea. Subsidence modeling accounts for these accumulations with about 40 km of extension in each basin centered on 35 Ma; therefore Ross Sea-wide Tertiary extension was comparable to extension in the deep-sea system. The early Tertiary geometry was of one oceanic rift that branched into at least three rifts in the continental lithosphere. This pattern is likely due to the contrast of physical properties and thermal state between the two different lithospheres at the continent-ocean boundary. Citation: Decesari, R.C., D.S. Wilson, B.P. Luyendyk, and M. Faulkner (2007), Cretaceous and Tertiary extension throughout the Ross Sea, Antarctica, in Antarctica: A Keystone in a Changing World - Online Proceedings of the �0th ISAES, edited by A.K. Cooper and C.R. Raymond et al., USGS Open-File Report 2007-1047, Short Research Paper 098, 6 p.; doi:�0.3�33/of2007-1047.srp098

Seismic-reflection data from the easternmost Ross Sea image buried scour-and-fill troughs and flat-topped ridges interpreted as having formed by glacial erosion and deposition during the Oligo-cene. The NNW-SSE orientation of the troughs and lack of similar Oligocene glacial features within the central Ross Sea suggests that the ice issued from the highlands of Marie Byrd Land located 100 km away and that portions of the West Antarctic Ice Sheet formed earlier than previously accepted. Existing global climate models (GCMs) do not produce West Antarctic ice caps for the Oligocene, in part due to low elevations modeled for that time. Evidence for Oligocene ice beyond the paleocoast suggests a higher elevation for the early Cenozoic Marie Byrd Land and Ross Embayment than at present.