The Amery Ice Shelf-Lambert Glacier ice drainage system drains ~22% of the East Antarctic Ice Sheet (EAIS); therefore, Lambert Glacier responds to fluctuations in the EAIS. During Cenozoic glacial episodes, the Lambert Glacier advanced to various points on the shelf, sometimes to the shelf edge, prograding the shelf (see Figs. F1 and F2 in the "Leg Summary" chapter; Fig. F1). A major change in Prydz Bay shelf progradation took place in late Neogene time when a fast-flowing ice stream developed and excavated a channel (Prydz Channel) across the shelf on the western side of Prydz Bay (see Fig. F3 in the "Leg Summary" chapter). The erosion surface marking this change can be mapped from the shelf to the continental rise (Surface PP12; Surface A of Mitzukoshi et al., 1986). Since then, basal debris carried to the shelf edge by the ice stream has been deposited in a trough mouth fan on the upper slope, similar to fans deposited on other high-latitude margins (Boulton, 1990; Larter and Cunningham, 1993). This change may reflect the earliest growth of thick ice on the Ingrid Christensen Coast, deflecting the Lambert Glacier when it advanced (O'Brien and Harris, 1996).
Grounding zone wedges formed by Lambert Glacier in the Prydz Channel are only ~80 km seaward of the current Amery Ice Shelf edge (O'Brien et al., 1999). Domack et al. (1998) used 14C accelerated mass spectrometry dating of cores from the wedge crests and Prydz Channel to demonstrate that these wedges are last glacial maximum (LGM) grounding zone deposits, indicating that Lambert Glacier did not ground at the shelf edge during the LGM. This raises questions as to which glacial episodes throughout late Neogene time produced a major advance and what paleoenvironmental conditions existed when the major advance occurred. The best location to find answers to these questions is in the trough mouth fan, which received siliciclastic sediment from the ice front when the shelf eroded during major ice advances and deposited hemipelagic material during interglacials and smaller glaciations.
Site 1167 was located in the middle of the Prydz Channel Fan with the intent of drilling through a section that was reasonably complete without being so close to the shelf edge that it would have been affected by large-scale slumping (Fig. F2). Models of trough mouth fan sedimentation (e.g., Boulton, 1990) suggest that thick siliciclastic units should correspond to peaks in Antarctic ice volume, whereas periods of reduced ice volume should be represented by hemipelagic sediments.