Further Sea Ice Drilling The Ciros Project

From 1977 on, the SCAR Working Group on Geology, under the chairmanship of Cam Craddock, provided a useful forum for discussion and planning further drilling in McMurdo Sound in an attempt to provide records from the Antarctic margin to resolve the chronology of early icesheet formation and its subsequent evolution. Meetings with its companion group on geophysics were also important for discussions on marine geophysical surveys being planned for the Antarctic margin. The survey by S.P. Lee was particularly useful for future drilling in providing the first multichannel section of the western margin of the Victoria Land Basin (Cooper and Davey, 1985; Cooper et al., 1987) and showing a thick seaward-dipping sequence that extended close enough to the coast to be drilled from the fast ice.

Discussions at the SCAR meeting in Queenstown (Barrett and Webb, 1981) led to a proposal for Cenozoic investigations in the western Ross Sea (CIROS) to drill four holes in two successive seasons from the sea ice off New Harbour and off Granite Harbour (Barrett, 1982), based on the seismic surveys of Wong and Christoffel (1981) and Cooper et al. (1987). The project logistics were managed by the NZ Antarctic Programme with significant US support and scientific participation, and the drill rig and camp were set up in late 1984, 12km off Marble Point (Fig. 3.3), for the first drill hole (CIROS-1). However, concerns grew about the poor state of the sea ice and just prior to drilling, it was decided to shift the camp and rig 20 km inshore to the CIROS-2 site in Ferrar Fiord. After a number of set-backs, CIROS-2 was successfully drilled 165 m below the sea floor to a granitoid basement, recovering several cycles of Quaternary black sand and diamict and Pliocene mudstone and diamictite. The sequence recorded a number of cycles of glacial advance from the inland ice in the Pliocene followed by cycles in which a Ross Sea ice sheet flowed westward into the Fiord (Barrett and Hambrey, 1992). The core had in fact verified the findings from DVDP-11 in 1973, the drilling system had worked and valuable experience had been gained.

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