8. Site 1101¹

Shipboard Scientific Party²

BACKGROUND AND SCIENTIFIC OBJECTIVES

Site 1101 (Fig. F1) lies on sediment Drift 4 (Rebesco et al., 1996, 1997) approximately midway between proposed sites APSHE-05A and APSHE-06A, alternates of Sites 1096 and 1095, respectively.

The opportunity to drill another site on the continental rise of the Pacific margin of the Antarctic Peninsula arose from the persistently unfavorable sea state encountered on the continental shelf while attempting to drill Site 1100 (vessel heave during drilling in shallow water is restricted to 2 m). Site 1101 was chosen to provide answers to questions raised by drilling at Sites 1095 and 1096. Clearance to drill the new location was received from the Ocean Drilling Program on 14 March 1998.

The questions that motivated drilling at Site 1101 were

1. Is the sedimentary record from the late Miocene to present obtained at Sites 1095 and 1096 representative of the entire Pacific margin of the Antarctic Peninsula? Does the regional correlation between seismic units observed in multichannel seismic (MCS) profiles (Rebesco et al., 1997) reflect actual litho- and biostratigraphic correlation?
2. Is there evidence for the late Pliocene Eltanin meteorite impact (Gersonde et al., 1997)? At Site 1096, sedimentary evidence of the meteorite impact may exist in the form of a coarse and well-sorted massive sand bed in a predominantly fine muddy sedimentary sequence. An additional site on the continental rise would test this possibility by seeking a similar anomalous, coeval event.

Site 1101 lies on seismic profile IT92-114 (Fig. F2; "Appendix," and Fig. AF1, both in the "Leg 178 Summary" chapter), where the uppermost seismic Unit M1 (inferred age: late Pliocene to present) lies within reach of the advanced hydraulic piston corer (APC) at ~200 meters below seafloor (mbsf). It is also within a GLORIA survey of the northeastern part of the upper rise (Tomlinson et al., 1992; Rebesco et al., 1996). The base of Unit M1 lies at ~330 mbsf at proposed site APRIS-05A and ~130 mbsf at APRIS-06A (the two original sites on Drift 4). Site 1101 lies in a water depth of 3280 m, 32.5 km southeast of site APRIS-06A and 52.5 km northwest of site APRIS-05A.

In addition, we considered that if the unfavorable sea state for continental shelf drilling continued, Site 1101 could be deepened to penetrate the Miocene Unit M3, below ~350 mbsf, and possibly even M4 at much greater depth beneath an acoustically anomalous Pliocene M2 unit.

The 3.5-kHz sub-bottom profiler record acquired on approach to Site 1101 (Fig. F3) shows a gently dipping, smooth seafloor, with acoustic penetration of ~50 ms (40 m) through parallel reflectors.