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doi:10.2204/iodp.sp.318.2008

Drilling strategy

To obtain the most complete record of the history of Antarctic glaciation, the drilling strategy is to sample sediments from this margin in a shelf-rise-abyssal plain transect. The continental shelf strata (Fig. F7) contain the direct (i.e., presence or no presence of ice), albeit low, resolution record of glaciation. The corresponding continental rise and abyssal plain strata (Figs. F9, F12) contain the distal (i.e., cooler versus warmer) but more continuous and easier to date record of glaciation. The Wilkes Land margin has the advantage in that the unconformity presumably reflecting the "onset" of glaciation (Unconformity WL-U3) can be traced from the shelf to the abyssal plain, allowing the links between the proximal and the distal records to be established.

Our plan is to conduct coring and wireline logging operations at five sites: one on inner shelf continental shelf deep basins (proposed Site ADEL-1B or alternates), two on the continental shelf (proposed Sites WLSHE-09B and WLSHE-08A or alternates), one on the continental rise (proposed Site WlRIS-04A-or alternate), and one on the abyssal plain (proposed Site WLRIS-02A or alternate) (Fig. F5).

Timing and nature of the onset of glaciation

The timing and nature of the onset of glaciation in this segment of the eastern Wilkes Land margin is targeted in two depositional environments: (1) the continental shelf and (2) the abyssal plain.

Continental shelf proposed Sites WLSHE-09A, WLSHE-09B, WLSHE-07A, WLSHE-07B, WLSHE-10A, and WLSHE-11A (Figs. F7 and "Appendix figures") are designed to obtain a low-resolution but direct record allowing the reconstruction of the timing and nature of first glacial strata preserved at the Wilkes Land margin. Our first priority site is proposed Site WLSHE-09B, where we can sample preglacial and glacial strata separated by a regional unconformity (WL-U3) at relatively shallow depth (165 m). Additionally, we have five alternate sites (proposed Sites WLSHE-09A, WLSHE-07A, WLSHE-07B, WLSHE-10A, and WLSHE-11A) designed as contingency sites for unfavorable ice conditions and/or to account for the possibility that our interpretations are wrong (i.e., strata below and above Unconformity WL-U3 are of glacial origin or they are preglacial, respectively). These alternate sites will allow us to either target older strata by drilling deeper at proposed Site WLSHE-09B or younger strata at alternate sites (proposed Sites WLSHE-09A, WLSHE-07A, WLSHE-07B, WLSHE-10A, and WLSHE-11A) in order to accomplish our main objective, which is to date the onset of glaciation in this segment of the East Antarctic margin.

Abyssal plain proposed Site WLRIS-02A (Fig. F12 and "Appendix figures") is designed to provide the more continuous but distal (cooler versus warmer) record of the timing and nature of the onset of glaciation. Because the onset of glaciation unconformity (WL-U3) can be traced from the continental shelf to the abyssal plain we expect for the first time to be able to link the response of the margin sedimentation and biota to the first arrival of the ice to the shelf.

Fluctuations and transition of glacier regimes

Drilling at proposed Sites WLSHE-08A or alternate Sites WLSHE-08B, WLSHE-10A, and WLSHE-11A (Fig. F7 and "Appendix figures") is designed to sample strata below and above the regional erosional Unconformity WL-U8, which marks an important change in the geometry of the progradational wedge. The transition across this unconformity from low-dipping to steeply dipping foreset strata is inferred to correspond with large fluctuations in the glacial regime during the late Miocene and possibly to reflect the transition from a wet-based dynamic to a cold-based persistent ice sheet glacier regime.

Distal record of climate variability

Proposed Site WLRIS-04A (Fig. F13) or alternate proposed Site WLRIS-03A (Fig. F14) are designed to sample the mixed turbidite-contourite continental rise ridges (Figs. F9, F13). These ridges are expected to contain a high-resolution section of inferred late Neogene to Quaternary age and to provide a history of climate and paleoceanographic variability from the middle Miocene to the Quaternary. The record from this site should be similar to that obtained from drilling similar depositional environments during ODP Leg 178 in the Antarctic Peninsula (Barker, Camerlenghi, Acton, et al., 1999) and ODP Leg 188 in Prydz Bay (O'Brien, Cooper, Richter, et al., 2001).

Ultrahigh resolution Holocene record

Proposed Site ADEL-01B and alternate proposed Site ADEL-01C (Figs. F8, F15, F16, F17) are designed to sample the 200–230 m of relatively transparent Holocene sedimentary drape (the drift unit) overlying a hard reflector that is interpreted as a glacial diamict.

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