Pre IceSheet Pre Late Eocene

The Lambert Graben and Prydz Bay basin formed during the Carboniferous or Permian (Arne, 1994; Lisker et al., 2005) and were depocentres in pre-ice-sheet times. Seismic data from the Prydz Bay shelf show pre-ice-sheet sequences of parallel, moderately continuous reflectors (Figs. PB-2 and PB-3). ODP Sites 740, 741 and 1166 penetrated pre-ice-sheet sediments that were deposited in fluvial to fluvio-deltaic environments. ODP Site 740 intersected interbedded sandstone, siltstone and mudstone with reddish coloration (Shipboard Scientific Party, 1989), interpreted as fluvial flood plain deposits (Turner, 1991). The red coloration suggests a seasonal fluctuating rainfall regime but the age of this unit remains unknown (Truswell, 1991). It could be as old as Triassic, based on the presence of Triassic sediments in the northern Prince Charles Mountains (Leitchenkov, 1991; McLoughlin and Drinnan, 1997a, b). However Leitchenkov (1991) identified a thick (up to 5 km), faulted and high-velocity (up to 5.2km/s) unit on multichannel data underlying these red beds. This sequence predates the main phase of breakup-related crustal extension, leading him to correlate the deep unit with Permian-Triassic sediments of the northern Prince Charles Mountains (Leitchenkov, 1991). If so, then the red beds in ODP Site 740 are likely Early Cretaceous or Late Jurassic in age.

ODP Sites 741 and 1166 intersected Cretaceous sediments beneath the Cenozoic section. The Cretaceous comprises interbedded dark siltstone and

Figure PB-2: Diagramatic section across Prydz Bay shelf and slope based on Russian seismic lines SAE 32002 and RAE 4005. K1 are Cretaceous sediments. Location shown in Fig. PB-1.

Sile 1166 Site 742 ne

3500 3000 3500 Sh«poim i(no 4500 4S00 5?00

Sile 1166 Site 742 ne

3500 3000 3500 Sh«poim i(no 4500 4S00 5?00

Figure PB-3: Seismic section between ODP sites 742 and 1166. Sequence PS2A2 comprises fluvio-deltaic sands of late Eocene age. Sequence PS2A1 overlies an erosion surface and comprises late Eocene marine muds with lonestones. Location shown in Fig. PB-1 (modified from Erohina et al., 2004).

sandstone with minor coal of probable delta plain to lagoonal origin. The ODP Site 1166 section is Turonian-Santonian(?), whereas ODP Site 741 recovered an older section of middle Aptian sediment (Fig. PB-3). Macphail and Truswell (2004) describe the palynomorphs from ODP Site 1166, and interpret the assemblage as indicating a conifer-dominated woodland vegetation, consistent with a cool, humid climate.

The continental rise seaward of Prydz Bay contains up to 5 km of post-rift sediments (Figs. PB-2, Foldouts PB-1 and PB-2; Mizukoshi et al., 1986, Stagg et al., 2004a, b). The lowermost seismic stratigraphic unit has parallel, mostly continuous reflectors typical of deep-ocean deposition that probably occurred during pre-ice-sheet times (Mizukoshi et al., 1986; Kuvaas and Leitchenkov, 1992; Kuvaas et al., 2005).

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