4. Site 1095¹

Shipboard Scientific Party²

BACKGROUND AND SCIENTIFIC OBJECTIVES

Site 1095 (Fig. F1) is the more distal of two sites on a hemipelagic sediment drift on the continental rise off the northwestern Pacific margin of the Antarctic Peninsula. Site 1095 lies in a water depth of 3840 m on the northwestern termination of the drift and was selected to obtain the deeper part of the stratigraphic section, where the overlying sediments are thinner than at the drift crest (Site 1096).

The site was chosen on the upper part of the northwest flank of the drift, bordering the deep-sea channel system that separates sediment Drifts 7 and 6 on the continental rise (Figs. F1A, F2). The sedimentary cover, more than 1200 m thick, rests on a dissected oceanic basement dated at ~42.7 Ma by magnetic anomalies (Barker, 1982; see also "Site 1096" chapter, and Barker and Camerlenghi, Chap. 2, this volume). A short 3.5-kHz sub-bottom profile crossing the slope (Fig. F3) shows layering parallel to the seafloor for 25 ms (~20 m). Multichannel seismic (MCS) profiles across the site (I95-137 and I95-135A [Fig. F1B; also see "Appendix," and Fig. AF1, both in the "Leg 178 Summary" chapter]) indicate that the upper part of the section (~100 ms) rests unconformably on a highly reflective unit, whose base was correlated with the base of Unit M2 (onset of "Drift Maintenance" stage) of Rebesco et al. (1997). The total thickness of Units M1 and M2 here is 300 ms, compared with the 740 ms at the proximal drift site (Site 1096; about 75 km closer to the margin). The deeper Units M3 and M4 ("Drift Growth" stage of Rebesco et al., 1997) are therefore more accessible to drilling than at Site 1096.

Drilling at Site 1095 was intended to examine the earlier stages of drift development and glacial evolution (see Barker and Camerlenghi, Chap. 2, this volume) and to answer specific questions related to the state of glaciation of the adjacent continent.

1. Is the present depositional system, documented from work on piston cores (Camerlenghi et al., 1997b; Pudsey and Camerlenghi, 1998), a plausible analogue for the older depositional environment reflected within the cored section?
2. Was deposition cyclic within the lower part of the drift section? If so, what are the cycle frequencies? And what does this cyclicity represent?
3. Can the onset of the present stage of continental glaciation (involving regular ice-sheet excursions to the shelf edge) be recognized in the drift sediments? Is there a relationship between drift development and continental glacial history?
4. Can the terrigenous fraction be used to examine the erosional (uplift?) history of the Antarctic Peninsula?

The answers to many of these questions will come only after detailed and extensive work onshore, but it will be possible here to assess the potential of the recovered cores and point toward some of the work required.