Pre IceSheet Pre LateOligocene Time

This period includes seismic sequence RSS-1 between the acoustic basement and unconformity RSU-6 (Fig. RS-3, Foldouts RS-1 and RS-2) and, in the Victoria Land basin, acoustic units V4 and V5 (Cooper et al., 1987).

Acoustic basement rocks have been sampled at two sites, and are Palaeozoic Beacon Formation rocks at the CRP-3 site adjacent to the coast (Cape Roberts Science Team, 2000) and are inferred palaeozoic and Cretaceous igneous and metamorphic rocks at DSDP Site 270 in the centre of the Ross Sea (Hayes and Frakes, 1975). The basins are believed to hold sedimentary rocks of Cretaceous and younger age (Hinz and Block, 1984; Cooper et al., 1991c), but Sedimentary rocks older than late Eocene have not been cored by drilling. Upper Eocene sediments have been cored in the CIROS-1 drillhole in McMurdo Sound (Coccioni and Galeotti, 1997; Fielding et al., 1997; Hannah et al., 1997; Monechi and Reale, 1997). The presence of ubiquitous lonestones (Barrett, 1989) testifies that glaciers (but not necessarily continent-size ice sheets) were calving at sea-level then.

Eocene erratic rocks are found in coastal areas (Levy et al., 1995), and have flora indicating cool, but not glacial, climates in the McMurdo area (Stillwell and Feldmann, 2000). Offshore basin analysis, mainly from MCS

reflection data, suggests that in Cenozoic pre-ice-sheet times, the Ross Sea was dissected by high-standing subaerial ridges, now seen as the buried Coulman high and Central high (De Santis et al., 1995). Prior outcropping of these ridges is suggested by the presence of regoliths above the basement at DSDP Site 270 (Hayes and Frakes, 1975).

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