ustralian Geological Survey Organization, Canberra, Australia

A magnetic anomaly map and a free air anomaly map of Prydz Bay, of the adjacent slope and over the continental rise area (63°S-69.5°S, 69°E-81°E) were compiled using Russian, Australian, Japanese and other available data (more than 20 000 km in total length). Adjustment of different data sets was performed before gridding and making contour maps. Crossover differences of the magnetic data were significantly reduced by removing data segments with short-period time variations, by applying time variation corrections of Mawson Station to Australian and Japanese data, and by giving a constant bias to each trackline. Crossover differences of the gravity data were also substantially reduced by applying a constant bias to each cruise/leg. According to the compiled gravity data, in the western part of Prydz Bay the continent ocean boundary is inferred to be situated around the shelf edge at the seaward end of Prydz Channel, while it is in the continental rise in the eastern part. The gravity data also suggest the presence of sediments in the Prydz Bay basin reaching a thickness of about 8 km and overlying a "granitic" layer; the Moho beneath the basin is located at a depth of about 22 km. According to the magnetic data, highly-magnetized rocks occur at shallow depths northwest of the Prydz Bay basin and other parts of Prydz Bay.

The Antarctic region has profoundly affected the global climates of the past 50 million years, influencing sea levels, atmospheric composition and dynamics, and ocean circulation. A greater understanding of this region and the Antarctic cryosphere is crucial to a broader understanding of the global climates and palaeoceanography at all scales. Much of the information obtained during the last two decades derives from studies of sedimentary sequences drilled in and around Antarctica. Eight Ocean Drilling Program (ODP) legs have contributed significantly to the understanding of this evolution. These legs include Leg 113 in the Weddell Sea (Barker et al., 1988, 1990), Leg 114 in the Subantarctic South Atlantic (Ciesielski et al., 1988, 1991), Leg 119 in Prydz Bay and on Kerguelen Plateau (Barron et al., 1989, 1991), Leg 120 on Kerguelen Plateau (Schlich et al., 1989; Wise et al., 1992), Leg 177 in the southeast Atlantic sector of the Southern Ocean (Gersonde et al., 1999), Leg 178 on the Antarctic Peninsula (Barker et al., 2002), Leg 188 in Prydz Bay (O’Brien et al., 2001), and Leg 189 in the Tasmanian region (Exon et al., 2001). More recently, a series of three holes were drilled in McMurdo Sound, Ross Sea, as part of the Cape Roberts Project (CRP; Cape Roberts Science Team, 1998 1999, 2000; Hambrey et al., 1998; Barrett et al., 2000, 2001). In spite of these efforts, which have significantly advanced our understanding of the Cenozoic tectonics and palaeoenvironments of the Antarctic region, important questions and problems remain unresolved. Chief amongst these are the timing of the onset of the East Antarctic Ice Sheet (EAIS), the causes of the cooling events at around 24 and 14 Ma, and the warming events of the mid-Pliocene and Marine Isotope Stages 31 (1.07 Ma) and 11 (0.36 Ma) (Shackleton et al., 1995).