Early Glacial Late Eocene

In Prydz Bay, ODP Sites 739, 742 and 1166 recovered sediments deposited immediately before major glaciation (Barron et al., 1991; Cooper and O'Brien, 2004). The lithologies vary from dark siltstones to poorly sorted sands and bedded mudstone with lonestones. Seismic sections show that the sands overlie an undulating erosion surface, suggesting a period of erosion, possibly related to a relative low stand of sea-level (Erohina et al., 2004, Fig. PB-3). The sand unit fines up-section into the mudstone, which contains lonestones, marine diatoms and dynocysts (Shipboard Scientific Party, 2001a). Strand et al. (2003) interpret the sand unit as a fluvial to delta plain channel deposit. They found sand-grain surface textures that suggest erosion and breakage by glaciers, implying the presence of at least valley glaciers in the hinterland of Prydz Bay. The overlying mudstone with lonestones suggests a marine transgression, with floating ice as a feature of the resulting shallow embayment.

Macphail and Truswell (2004) report palynomorphs in the fine-grained units that indicate a late Eocene age (middle Nothofagites asperus zone), representing an age range from 33.9 to 39.1 Ma. This age overlaps with the age suggested by diatoms in the transgressive mudstones (33-37 Ma, Shipboard Scientific Party, 2001a). Macphail and Truswell (2004) also propose that the palynological assemblage was derived from a flora similar to stunted Nothofagus rainforest scrub, and consisted of ground-hugging plants and canopy trees about 1 m high. Today, such floras occur outside of Antarctica at higher altitudes, where cool temperatures limit tree growth. Therefore, the Prydz Bay flora reflects a cool to cold environment at sea-level. More precise temperature estimates are not possible because the plants present were tolerant of a wide range of conditions (Macphail and Truswell, 2004).

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