From Greenhouse to Icehouse – The Eocene/Oligocene - UMass ...

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Author's personal copy Figure 8.4: Cartoon depicting the Victoria Land coast in Early/Late Oligocene time, with glacier- and river-influenced coast, and vegetated mountainsides and lowlands. This scenario is based on a combination of sedimentological evidence and floral data from CIROS-1 and Cape Roberts cores (from Hambrey et al., 2002). Reproduced with permission of The Geological Society Publishing House, Bath, UK. polythermal glaciers. The cold frigid regime of today only began at the end of Pliocene time. The Early Oligocene landscape was characterized by temperate glaciers flowing from the early East Antarctic Ice Sheet, some terminating in the sea, and others on braided outwash plains (Fig. 8.4). 8.2.5. The Prydz Bay Region From Greenhouse to Icehouse – The Eocene/Oligocene in Antarctica 321 Drilling in Prydz Bay was undertaken by two ship-borne legs of the ODP (Fig. 8.5). In contrast to the western Ross Sea cores, core-recovery rates here were much less satisfactory; hence interpreting depositional processes is more questionable. Nevertheless, plausible scenarios have been derived, albeit lacking precise constraints owing to core loss. Prydz Bay represents the continuation of the Lambert Graben, which contains the Lambert Glacier–Amery Ice Shelf System, an ice drainage basin covering approximately 1 M km 2 , draining 13% of the East Antarctic Ice Sheet by surface
322 J. E. Francis et al. Author's personal copy Figure 8.5: Location of drill sites in Prydz Bay, East Antarctica, from ODP legs 119 and 188. Continental shelf sites 742 and 1166 include strata the cross the E/O transition. From shipboard Scientific Party (2001a). Reproduced with permission of the Ocean Drilling Program, College Station, Texas. area. Thus, the record in Prydz Bay provides a signal of the ice sheet as a whole since its inception, and complements the Oligocene (?) to Pliocene uplifted glaciomarine record in the Prince Charles Mountains (see Haywood et al., 2008; Chapter 10). Prydz Bay itself is dominated by a trough-mouth fan that prograded during phases of glacier advance to the shelf break. Like the western Ross Sea, large data-sets are available covering all aspects of core analysis from ODP Legs 119 and 188 (Barron, Larsen, & Shipboard Scientific Party, 1991; Cooper and O’Brien, 2004; Cooper et al., 2004) and a convenient summary has been provided by Whitehead et al. (2006). ODP Leg 119 obtained two cores, 739 (480 m) and 742 (316 m), the lower parts of which were loosely dated as Middle Eocene to Early Oligocene. The dominant facies recovered was massive diamictite, with minor stratified diamictite and sand (Hambrey et al., 1991, 1992). Poorly consolidated finegrained facies may well have been washed away during the drilling, however, since core-recovery rates were less than 50%. A few broken shell fragments are present, but there is a dearth of material suitable for precise dating. The base of
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