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Victoria University Antarctic Research Expedition Science and Logistics Reports 1984-85: VUWAE 29

Abstract

Abstract

CIROS in 1984 drilled one hole near the middle of Ferrar Fjord, western McMurdo Sound, in 211 m of water. A sequence of sand and glacial debris was cored (67% recovery) to basement gneiss at 166 m. A preliminary estimate of the age of the sequence, based on diatoms and the abundance of basaltic debris, has it ranging from Early Pliocene (about 4 m.y.) to the present, and equivalent to the upper 183 m of DVDP 10 and the upper 240 m of DVDP 11 in adjacent Taylor Valley. A good chronology is expected from the paleo-magnetic stratigraphy, diatom assemblages and radiometric dating of basaltic material, including a vitric tuff from 124 m sub-bottom.

The core has been subdivided into 13 lithologic units, representing alternations of "interglacial" and "glacial" conditions. The older interglacial units (13, 11 and 9) are diatomaceous mudstones, but the younger ones (7, 5, 3 and 1) are largely black basaltic sand, like that accumulating on the sea floor today. The oldest 2 glacial units (12 and 10) are basal lodgement tills with internal horizontal shearing and clasts of basalt and basement rocks, some of them striated. The younger glacial units (8, 6, 4 and 2) also contain scattered clasts, some striated, but have stratification features suggesting considerable redeposition and settling through water. Nevertheless, all of these units are considered to represent periods when ice was much more extensive than today. The abundance of basaltic debris in most glacial units suggests that ice flowed into Ferrar Fjord mainly from the east, eroding and transporting debris from the volcanic piles south and east of McMurdo Sound.

The CIROS 2 core should lead to a substantial improvement in both chronology and interpretation of glacial history in western McMurdo Sound over the last 4 m.y.