Seismic profiling in the Western Ross Sea

1. The main objective of the Ross Oceanographic Seismic Survey was to collect further information (Northey & Sissons, 1974) on the structure and thickness of sediment in McMurdo Sound.

   The results serve the dual purpose of indicating the best sites for the Dry Valley Drilling Project to drill, as well as providing a means of tracing stratigraphic horizons away from the drill sites using the seismic reflection profiles. Seismic velocities in the top sedimentary layers can be found from the refraction results.

2. Good profiling weather (low wind speeds, open sea water further west and south than usual) and few major equipment faults allowed us to carry out a very thorough profiling programme both in Terra Nova Bay and McMurdo Sound; a contributing factor to the almost continuous profiling was having two independent but parallel sets of equipment which could be interfaced at any stage.
3. Preliminary investigation of the results in Terra Nova Bay appear to show two major glaciations to have shaved the sediment cover off to about 450 m and 650 m below present sea level, possibly caused by extended grounding of the Ross Ice shelf. There was later deposition of over 300 m of glacial moraine in places. An unusually deep area was found in Terra Nova Bay (1300 m); total sediment thickness here exceeds 1 km.
4. In McMurdo Sound there are many infilled valleys with sediment thicknesses up to 500 m. These layers are seen to dip at between 1/2° and 2° to the west in the northern part of the Sound, whereas in the southern part acoustic bedrock (basalt?) has little sedimentary cover and a rugged topography. Hence on first appraisal it seems that better results from drilling would be obtained as far north as winter ice conditions permit.